GWADW2023 - Gravitational-Wave Advanced Detector Workshop

21 May 2023, 16:00 → 27 May 2023, 08:00 Europe/Rome

Hotel Hermitage, La Biodola, Isola d'Elba

Francesco Fidecaro (University of Pisa and INFN)

Since the end of the third observation run O3 by the km size interferometers, an intense work of upgrade and preparation for O4 has been performed to achieve a better sensitivitiy, with the expectation of a large increase of merger events, and possibly the observation of new gw sources.

In parallel, the preparation work for third generation interferometers Einsten Telescope and Cosmic Explorer is in full swing, with many R&D activities going on, dedicated laboratories being set up, and long term concepts being elaborated.

The community is growing in size, contributing to the preliminary design and assessing the qualities of the sites candidate to host the instruments. This workshop is the main opportunity worldwide to present the work on detectors leaving, as is tradition, ample space for informal discussions.

Sessions begin on Monday, May 22nd, in the morning and finish on Friday, May 26th, in the afternoon.

Sunday, 21 May

19:00 Welcome drink

Welcome drink at the Fuoco di Bosco restaurant

Monday, 22 May

Welcome

1 Welcome

Speaker: Francesco Fidecaro (University of Pisa and INFN)

welcome.pdf

Science from O4 to Post O5

Conveners: Matteo Barsuglia, Marica Branchesi (Istituto Nazionale di Fisica Nucleare), Barbara Patricelli (Istituto Nazionale di Fisica Nucleare)

2 Populations of binary compact objects: exciting prospects with gravitational-wave astronomy

Advanced LIGO and Advanced Virgo have so far detected a total of 90 compact binary coalescences. These observations provided crucial information on neutron star and black hole populations, and already changed our understanding of the formation of compact binary systems. In this talk I will focus on some of the outstanding open questions raised by gravitational-wave observations, including the formation channels of binary black holes and the origin of intermediate-mass black holes. I will then discuss how observations with current and next-generation detectors will contribute to compact object population studies.

Speaker: Irina Dvorkin (Institut d'Astrophysique de Paris, Sorbonne Université)

gwadw-2023-idvorkin.pdf

3 Perspectives for cosmology with current detectors and next generation detectors

The LIGO, Virgo and KAGRA collaboration (LVK) are already proposing upgrades and observing plans for the decade between the 5th observing run (~2027) and the advent of third generation detectors in 2035. In this talk I will discuss the prospects, with the planned Post-O5 upgrades and beyond, of observing compact binary coalescences at cosmological scales. Given the current observations, I will discuss the expected rate of detections and low-latency localization prospects. Finally, I will focus on the prospects of measuring the Hubble constant with GW sources accompanied (and not) by an electromagnetic counterpart. I will show that with just one year of Post-O5 observation we could be able to constrain the expansion rate of the Universe today at a sub-percent level precision.

Speaker: Simone Mastrogiovanni (INFN - Roma 1)

post_O5_GWADW.pdf

4 Perspectives for fundamental physics and exotic compact objects with current detectors and next generation detectors

Perspectives for fundamental physics and exotic compact objects with current detectors and next generation detectors

Speaker: Massimo Vaglio

GWADW2023-MassimoVaglio.pdf

5 Forecasting the Detection and Parameter Estimation Capabilities for different ET Designs

Einstein Telescope (ET) is an European project for a third generation gravitational wave detector. The reference design is based on a triangular shape of three nested detectors of 10 km arms, where each arm consists of a ‘xylophone’ configuration made of one interferometer tuned towards high frequencies and the other one, cryogenic, towards low frequencies. The talk will overview the science perspectives of ET reference design and considering: different shapes (triangle versus 2L), different choices of arm length, the use of only high-frequency instruments. A broad class of scientific output is examined, ranging from compact binary coalescences to multi-messenger astronomy and cosmology.

Speaker: Ulyana Dupletsa (Istituto Nazionale di Fisica Nucleare)

Dupletsa_GWADW2023.pdf

10:30 Coffee break

Science for the large observatories

Conveners: Matteo Barsuglia, Marica Branchesi (Istituto Nazionale di Fisica Nucleare), Barbara Patricelli (Istituto Nazionale di Fisica Nucleare)

6 Loud and Bright: challenges and needs of MM astronomy

The near and long term future of multi-messenger astronomy is strictly bound to the evolution of detectors for GW and of major ground/space-based electromagnetic facilities. Also our knowledge of the current MM sources is expected to evolve in the next few years with refinements of the current scenarios and possible new classes of EM counterparts. I will discuss the main challenges and needs that future EM facilities will face and should fulfil to fully exploit the scientific content of forthcoming joint GW-EM discoveries.

Speaker: Giancarlo Ghirlanda (Istituto Nazionale di Astrofisica - Osservatorio di Brera & INFN sezione di Milano Bicocca)

Ghirlanda_Elba_2023.pdf

7 PTA data analysis

PTA data analysis

Speaker: Golam Shaifullah

Shaifullah_Pulsar Timing Arrays @ GWADW2023.pdf

8 PTA science perspectives

PTA science perspectives

Speaker: Delphine Perrodin

PTAscience.pdf

9 Panel: Scientific objectives of different GW projects, the R&D needed, difficulties and opportunities

Scientific objectives of different GW projects, the R&D needed to reach the goals, the potential difficulties and opportunities

Speakers: Bram Slagmolen (The Australian National University), Harald Lueck, Prof. Kentaro Somiya (Tokyo Institute of Technology), Lisa Barsotti (LIGO-MIT), Rana Adhikari (Caltech), Stefan Ballmer (Syracuse University), Viviana Fafone (Istituto Nazionale di Fisica Nucleare)

230522_Fafone_GWADW_VnEXT_v2.pdf

A#_GWADW_Panel.pdf

Barsuglia panel_monday.pdf

EinsteinTelescope.pdf

GWADW_CE_panel.pdf

KAGRA, KAGRA+ and beyond ver4.pdf

NEMO-Sparkler-GWADW2023.pdf

12:30 Lunch break

Third generation Infrastructures

Convener: Kevin Kuns

10 Parametric Instabilty challenges next-Generation detectors would need to consider

In the run-up to LIGO's O4 commencement, some new Parametric Instability (PI) challenges have cropped up. Whilst LIGO has infrastructure to deal with PI, the best method still proves to be thermally tuning these instabilities out, with active damping being a risky endeavor. Despite the chances of facing compounding PI problems on the path to O5 being high at LIGO, the issue is still expected to be manageable. Proposals for many future detectors and upgrades hope to leverage larger test masses, test masses with materials with higher mechanical Q factors, larger beam spots, longer arm lengths, and of course higher laser power. These changes are fantastic for the prospect of increasing interferometer sensitivity but are simultaneously increasing the magnitude of PI gain as well as the probability of encountering PI. Design of upgrades would benefit from appreciating that PI could lead to inoperability of the detector at the desired specifications.

Speaker: Vladimir Bossilkov (LIGO Livingston)

BossilkovV.pdf

diff_RH_change.mp4

11 Cosmic Explorer input optics designs

Optomechanical designs for third-generation gravitational-wave detectors are currently under development. The input optics for 3G detectors will be a major consideration for the infrastructure and facilities costs. In this talk we will discuss the requirements for input optics for Cosmic Explorer, and consider some optical designs which satisfy those requirements with minimal facilities costs.

Speaker: Craig Cahillane (Syracuse University)

Cosmic Explorer input optics designs

12 New Generation Superattenuators (NGSA) for Einstein Telescope

The 3rd generation instrument era is approaching, and the Einstein Telescope giant Laboratory is becoming a reality with the possibility to install a detector for Gravitational Waves observations in an underground site where seismic noise is 100 times smaller than on the surface. Moreover, new available technologies and the experience acquired in operating advanced detectors are crucial points to further extend the detection bandwidth down to 2-3 Hz with the possibility to suspend a cryogenic payload. NGSA is an R&D project based on the improvement of the vibration isolation performance for the 3rd generation detectors starting from the present mechanical system of the Advanced VIRGO interferometer (2nd generation instrument) which is considered compliant with the future generation. Following two experimental lines, we studied the possibility of improving the attenuation performance of a multistage pendulum chain equipped with compact magnetic anti-springs that is hung to a double Inverted Pendulum in nested configuration (NIP). The final goal of our experimental activity is the construction and test of a NIP prototype to be installed in ‘Laboratorio di Fisica Sperimentale della Gravitazione’ at Naples. In this talk, we present the status of the NGSA project.

Speaker: Lucia Trozzo (Istituto Nazionale di Fisica Nucleare)

Trozzo_GWADW23.pdf

13 Crystalline AlGaAs coatings for future gravitational wave detectors

The sensitivity of current gravitational wave detector (GWD) such as advanced LIGO is partially limited by thermal noise arising from amorphous silica and titania-doped tantala coatings at their most sensitive frequency band. Future GWDs are planned to employ low thermal noise coatings so that one can explore further into the Universe with improved sensitivity. Crystalline AlGaAs coatings are promising coating candidates for such future upgrades because of their low coating thermal noise. However, the lock acquisition used in current detectors cannot be used due to the narrow band gap of AlGaAs coatings; thus, alternative schemes must be developed. To solve this problem, we propose a new lock-acquisition scheme using a wavelength-doubled laser. We have produced dichroic AlGaAs mirrors to enable this new lock acquisition scheme and are characterizing their performance. In addition, we have investigated the mechanical loss of AlGaAs coatings at cryogenic temperature using a cryogenic gentle nodal suspension system. We will present the results of cryogenic AlGaAs mechanical loss measurements and the current status of the development of dichroic AlGaAs coatings toward future GWDs.

Speaker: Satoshi Tanioka

AlGaAs_GWADW.pdf

14 Voyager

update on the Voyager upgrade of LIGO

Speaker: Rana Adhikari (Caltech)

Voyager GWADW 2023.pdf

15 First study of scattered light in the main arms of the Einstein Telescope gravitational wave detector

As part of the design of the Einstein Telescope (ET) gravitational wave detector, a thorough study of the scattered light and its impact in the sensitivity must be performed to ensure that is not going to compromise the experiment. We present the first estimation of the sources of scattered light inside the main arms of ET for both high- and low-frequency interferometers and propose a baffle configuration and vacuum pipes radii as a recommendation during the design phase. The estimations of noise are done using both analytic and numerical tools and the results point out that the scattered light noise can be sub-dominant at all frequencies as long as the recommendations described are followed.

Speaker: Marc Andrés Carcasona (IFAE)

AndresCarcasona_GWADW2023.pdf

17:30 Coffee break

O4 commissioning, O5 and postO5 plans

Conveners: Yoichi Aso (National Astronomical Observatory of Japan), Jenne Driggers (Caltech), Viviana Fafone (Istituto Nazionale di Fisica Nucleare), Daniel Sigg (LIGO Hanford Observatory)

16 Advanced LIGO Detector Commissioning for O4

Both the LIGO Livingston and LIGO Hanford Observatories have made significant progress in upgrading detector sensitivity in preparation for the fourth observing run. This talk will summarize the various equipment upgrades and detector commissioning efforts performed to achieve the new sensitivity.

Speaker: Elenna Marie Capote

GWADW2023.pptx

17 LIGO Frequency Dependent Squeezing for O4

A quick overview of O4 LIGO frequency dependent squeezing (on behalf of O4 LIGO squeezer team).

Speaker: Nutsinee Kijbunchoo (University of Adelaide)

SQZoverviewGWADW_2023_draft6.pptx

18 Prospects for 1 MW arm cavity powers in O5

LIGO Hanford has achieved 430 kilowatts of resonating laser power prior to observing run four, the highest in any long-baseline interferometer in the world. Achieving this level of power required major upgrades and advanced commissioning techniques. In this presentation we will review the A+ upgrades between O3 and O4, overview the measured resonating power at LIGO Hanford, and discuss the path forward to achieving even higher power in O5 and beyond.

Speaker: Craig Cahillane (Syracuse University)

Prospects for achieving 1 MW arm cavity powers in O5

19 LIGO A♯: Post-O5 plans for LIGO

The LSC plans on upgrading the current LIGO detectors to a detector known as A♯ after the conclusion of the fifth observing run. A♯ includes an increase of the test mass mass to 100 kg, 10 dB of frequency dependent squeezing, an increase in the arm power to 1.5 MW, redesigned suspensions, a reduction in the coating Brownian noise by a factor of two, improved seismic isolation, and suppression of Newtonian noise from Rayleigh waves. All of the upgrades planned for A♯ are required R&D efforts for Cosmic Explorer.

Speaker: Kevin Kuns

Asharp.pdf

20 Status of Advanced Virgo+

The forth Observing Run (O4) of the Advanced gravitational wave detectors will start on May 25th. This talk aims to present the current status of the Virgo detector performance in terms of sensitivity and duty cycle. Then an overview of the challenges that the commissioning has faced as a consequence of the upgrades of the detector will be given. Finally, a description of the main actions to be performed on the detector to reach the target sensitivity will be described.

Speaker: Julia Casanueva Diaz (EGO)

Status of Advanced Virgo+_v3.pdf

21 Lesson learned from AdvancedVirgo+ ISC Commissioning

In this work I’ll present the main issues that have been discovered during the phase of Commissioning of the AdvancedVirgo+ detector. Indeed, the control of the interferometer become more complex in presence of marginally stable cavities as it is strongly affected by optical defects. Starting from the installation of the new Auxiliary Laser System, I will discuss how we tried to improve the robustness of the lock acquisition and the technical solutions we implemented to optimize the steady state control.

Speaker: Dr Piernicola Spinicelli (EGO)

VIR-0402A-23.pdf

22 Quantum noise reduction for AdV+

The detection of gravitational waves is limited by quantum noise from vacuum field fluctuations. To overcome this limitation, squeezed vacuum states can reshape the shot and radiation pressure noise contributions by manipulating the quadrature amplitude distribution. While injecting a frequency-independent squeezed (FIS) vacuum state allowed for sub-shot noise limited sensitivity in the last observation run, it enhanced the quantum radiation pressure noise and limited low-frequency sensitivity. To address this, a frequency-dependent squeezed (FDS) vacuum field can be injected into the detection port, minimizing total quantum noise at each frequency for maximum noise reduction across the full detector bandwidth. In this talk, we show the status of the commissioning of the AdV+ FDS source, which is generated by a phase rotation of a state through a 285 m long, high-finesse, near-detuned optical resonator. In particular, we present a detailed analysis of the correlations between detuning frequency drift and temperature, which were crucial for optimizing the performance of the FDS source. We will also discuss the long-term stability measurements and we will showcase the first injection of the FIS source inside the interferometer, which shows promising results for the reduction of quantum noise and for the injection of the FDS.

Speaker: Luis Diego Bonavena (Istituto Nazionale di Fisica Nucleare)

GWADW_2023_bonavena.pdf

23 Squeezing in the post-O5 era and synergies with third generation detectors.

Detectors of the post-O5 era, as Virgo_nEXT and third generation detectors, as Einstein Telescope aim to achieve squeezing levels of the order of 10 dB. This implies a drastic reduction in optical losses, down to a level of a few percent. In this presentation, we will describe the study to reach these squeezing levels in the context of the Virgo_nEXT concept study, and the possible synergies with third-generation detectors, which aim at the same goals. In particular, we will illustrate possible avenues to reduce input and output losses, phase noise losses, filter cavity losses and interferometer losses.

Speaker: Eleonora Capocasa (APC)

SQZ_VnEXT_Capocasa.pdf

24 KAGRA commissioning experience

KAGRA, the interferometric gravitational-wave telescope in Japan, will
join the upcoming O4 with the better sensitivity than O3GK. Since the
spring of 2020, we have performed overhauling of the interferometer to
improve the sensitivity and stability. In this talk, we will report on
our integration and commissioning works until today, and show some plans
for the future.

Speaker: Tomotada Akutsu (National Astronomical Observatory of Japan)

GWADW_akutsu_20230522s.pdf

Tuesday, 23 May

CTN: Coating thermal noise

Conveners: Elisabetta Cesarini (Istituto Nazionale di Fisica Nucleare), Jessica Steinlechner

25 A structural study of the properties of amorphous silica coatings for low internal friction optics

Speaker: Laura Silenzi

A structural study of the properties of amorphous silica coatings for low internal friction optics

26 TiO2:SiO2 /SiO2 HR coatings for future detector upgrades

Speaker: Graeme Mcghee

TiO2:SiO2 /SiO2 HR coatings for future detector upgrades

27 Advancements in Atomic Structure Research for Amorphous Coatings

Speaker: Kiran Prasai

Advancements in Atomic Structure Research for Amorphous Coatings

28 AlGaAs coating: Status, challenges, and the prospects for A#

Speaker: Steven Penn (LSC - Hobart & William Smith Colleges, Syracuse University)

AlGaAs coating: Status, challenges, and the prospects for A#

29 Cryogenic temperature characterisation of mechanical losses in low-refractive index coating material AlF3

Speaker: Federica Fabrizi (Istituto Nazionale di Fisica Nucleare)

Cryogenic temperature characterisation of mechanical losses in low-refractive index coating material AlF3

30 Hydrogen-induced ultra-low optical absorption and mechanical loss in amorphous silicon for gravitational-wave detectors

Speaker: Frances Hellman

Hydrogen-induced ultra-low optical absorption and mechanical loss in amorphous silicon for gravitational-wave detectors

10:30 Coffee break

Low Frequency Noise, Control and Sensing 1

Conveners: Katherine Dooley (Cardiff University), Maddalena Mantovani (EGO), Dr Conor Mow-Lowry (Vrije Universiteit Amsterdam and Nikhef), Dr Paola Puppo (INFN - ROMA)

31 Development of a highly sensitive, multi-channel suspension point interferometer

Inter-platform motion in the seismic frequency range presents a challenge for both current and future generation detectors. Reduction of this movement requires displacement sensing over 3 degrees-of-freedom between each pair of isolation platforms, and the stabilisation outcome is dependent on the sensor performance.

At ANU, we are prototyping a multi-channel, optical displacement sensor. Using a simple Mach-Zehnder interferometer configuration, we unlock the highest potential for optical sensitivity. The multiplexing is provided by Digital Interferometry (DI), distinguishing channels via their optical time-of-flight. This technique requires no additional optical hardware and maximises the simplicity of the setup.
In this talk, we present the latest characterisation of our prototype sensor. We also discuss the challenges in moving towards sub-picometer displacement sensitivity at sub-Hz frequencies, as well as the technical and deployment readiness of our sensor.

Speaker: Bram Slagmolen (The Australian National University)

SPI_using_DI_YaZ_GWADW2023.pdf

32 Progress towards a 6 DoF inertial sensor: commisioning and application in semi-classical gravity measurements

We present further progress on our six-degree-of-freedom (6D) inertial sensor. Our purpose is to improve on the low-frequency seismic noise sensing of the current aLIGO detectors with a device that is capable of simultaneously reading out all six degrees of freedom and decoupling the troublesome cross couplings, such as tilt-longitude that affect commercial seismometers. We have reached the final phase of testing for the metal prototype and are ready to begin commissioning of the more compact fused silica version (C-6D), which has been designed with direct LIGO application in mind. Aside from the usual content on the functionality of 6D, we would like to highlight our recent investigation into the semi-classical gravity model of the Schroedinger-Newton equation, as this application is less familiar to the low-frequency community, and showcases the 6D device’s performance in an experimental role. We couple our sensor with a high-finesse (300,000) optical cavity to enhance the quantum interaction. We present a three-part summary of our progress: (a) the final results of the metal 6D testing, (b) results of a novel application of the 6D sensor towards fundamental physics research – testing the Schroedinger-Newton equation, (c) commissioning update on C-6D.

Speaker: Jiri Smetana (University of Birmingham)

J Smetana GWADW 2023.pdf

33 Back-scattered light from the Output Faraday Isolator at LIGO-Hanford

Back-scattered light from the Output Faraday Isolator at LIGO-Hanford

Speaker: Eleonora Polini (MIT)

OFI scattering LHO GWADW.pdf

34 A novel concept for seismic attenuation systems in gravitational wave detectors

F. Fidecaro, M. Razzano, A. Allocca, L. Bellizzi, S. Bianchi, V. Boschi, E. Calloni, M. Carpinelli, P. Chessa, D. D'Urso, R. De Rosa, L. Di Fiore, F. Fabrizi, I. Ferrante, A. Fiori, A. Gennai, A. Longo, L. Massaro, L. Papalini, M. Palaia, M. Montani, D. Rozza, P. Ruggi, L. Trozzo, M. Vacatello, A. Viceré

Third generation ground-based gravitational wave detectors will expand our view of the Universe. The Einstein Telescope will be an order of magnitude more sensitive than Advanced Virgo and LIGO and expand its frequency range down to 3 Hz. This low-frequency sensitivity will be crucial in addressing important scientific questions, including the formation and evolution of high-mass black holes and the physics of neutron stars. We present a new concept for suppressing seismic noise in the next generation of ground-based detectors. The model is based on the approach of the passive attenuation system achieved with the Virgo Superattenuator and aims at lowering the height of the ET mirror suspensions, 17-m high in the current design. Construction and operation complexity as well as civil engineering works would be significantly reduced. The concept has been developed within the project “Black Holes for ET in SArdinia” (BHETSA) gaining from the long experience gained in the design, simulation and construction of the Advanced Virgo seismic isolation system.

Speaker: Francesco Fidecaro (University of Pisa and INFN)

20230523 GWADW.pdf

35 Heavy suspension designs for LIGO A#

LIGO A# is an upgrade path for the LIGO facilities which has recently been recommended (LIGO-T2200287). This upgrade is suggested after the completion of O5. A major part of the upgrade is to replace the optics with 100 kg mirrors on new suspensions. The new suspensions are based on the design history of the Advanced LIGO and GEO suspensions, and incorporate lessons learned from the operation of Advanced LIGO. In this talk I will describe the design of the upgraded Suspensions and discuss the opportunities and challenges we see with these new, heavy suspension. With heavier optics, higher stress fibers, and upgraded suspensions we anticipate that A# will be able to reach fundamental noise sources down to 10 Hz.

Speaker: Brian Lantz (Stanford Univ.)

Lantz-A#_sus_talk_GWADW_G2301049.pdf

12:30 Lunch break

Squeezing, Topology, Quantum Information: Ideas for beyond 3G Part 1

Conveners: Shtefan Danilishin (University of Glasgow), Yanbei Chen

36 Straylight suppression with tunable coherence in high precision interferometers

As straylight is a dominating limitation for the sensitivity of gravitational wave detectors, we investigate new laser operation concepts and interferometer topologies for a more straylight-resilient detector configuration.
Our main focus is the use of tunable coherence realized by phase modulation following a pseudo-random-sequence on the interferometer laser.
While this breaks the coherence of the delayed straylight and thereby reduces its intrusive impact, it effectively realizes a pseudo white-light interferometer with tunable coherence length which we investigate in more complex topologies.
We already simulated this concept in a Michelson-interferometer and present now recent findings on the response of cavities to the PRN modulation from our numerical simulations. At the same time we are progressing with experimental studies and give an overview of the current status.

Speaker: Mr Daniel Voigt (Universität Hamburg)

2023_GWADW_May.pdf

37 A phase-insensitive table-top quantum filter

We present the results of ongoing experimental work on a table-top prototype for a stable optomechanical phase-insensitive quantum filter. Recent studies have shown that such filters can increase the bandwidth-sensitivity product of both kilometre-scale GW detectors and table-top systems. Our prototype, the Birmingham quantum amplifier, is based on the optomechanical interaction between a high-Q silicon nitride membrane and a system of two coupled optical cavities with a total length of 6 m. This system will operate in the resolved sideband regime and is expected to enhance the sensitivity of the interferometer in the frequency range of $1-20$ kHz.

Our current objective is to perform a proof-of-principle classical demonstration of the signal amplification provided by this setup, as well as showcase its inherent stability without the need for an external controller. Our recent results, which we will discuss in detail, include the successful installation and frequency stabilisation of a two-metre-long quantum filter cavity, whose eigenmode is coupled to the motion of a commercial silicon nitride membrane with a resonant frequency of 229 kHz.

We also discuss the phase-insensitive sensitivity enhancement potential in future GW detectors, including its robustness to optical loss and complementary use with methods based on squeezed light.

Speaker: Artemii Dmitriev (University of Birmingham)

qamp_GWADWMay2023_talk.pdf

38 Digital Discovery of interferometric Gravitational Wave detectors

Conventional design processes for complex (quantum) optics experiments and devices, such as gravitational wave detectors, rely heavily on the expertise and intuition of human researchers. However, given the vast and often counterintuitive search space of potential experimental configurations, alternative approaches may prove beneficial. The advent of powerful computational algorithms and artificial intelligence (AI) provides an opportunity to augment human creativity and uncover innovative, unconventional solutions.

In this presentation, we showcase a comprehensive, large-scale exploration of the search space for potential gravitational wave detectors using advanced computational algorithms. By defining a quasi-universal interferometer with hundreds of continuous parameters, we employ efficient discovery algorithms to navigate the vast search space. This space encompasses numerous human-designed systems from the past and may reveal previously undiscovered and innovative solutions. Our findings demonstrate new, superior solutions across several physically relevant frequency ranges.

This presentation aims not only to share our results but also to engage the scientific community for feedback on the physics of the digitally discovered solutions and stimulate discussions on computational simulators such as Finesse.

Speaker: Mario Krenn

Krenn_GWADW.pdf

39 Fundamental quantum limit achieved by internal squeezing in cavity-enhanced interferometric measurements

Squeezed light has achieved remarkable success in enhancing the sensitivity of GW detectors, with up to 6dB improvements in GEO600 and frequency-dependent squeezing in other detectors. However, this demands extremely high quality for optical systems, as even minimal loss significantly reduces quantum enhancement. This is particularly relevant for next-generation detectors with other operational wavelengths (e.g. around 2 μm), which may not permit flawless photodetection.

We propose a novel approach to compensate for quantum decoherence. Our method employs an optimally tuned quantum squeezer within the signal-extraction cavity, which either restores externally injected squeezing or amplifies the signal, depending on loss levels. This approach allows to achieve the ultimate sensitivity limit, which is defined only by the internal loss in the interferometer.

We present the first experimental enhancement of the detector sensitivity using a combination of externally injected and internally generated squeezing. We demonstrate for the first time quantum sensitivity enhancement independent on the detection loss. This is achieved by tuning the internal squeeze strength in an optimal way, as prescribed by the new decoherence-induced quantum limit.

This study, with its experimental evidence and new quantum limit, paves the way for new approaches to next-generation interferometer designs with enhanced sensitivity and high loss tolerance.

Speaker: Mikhail Korobko (University of Hamburg)

GWADW23_decoherence_Korobko.pdf

40 Twin michelson interferometers with Einstein–Podolsky–Rosen squeezing

A theoretical two-carrier heterodyne detection scheme, which agrees with the sensitivity performance of homodyne readout for a gravitational wave detector, has been recently proposed. This scheme, with careful choice of readout/heterodyne frequency, is predicted to avoid low frequency noises which generally plague audio band squeezing experiments such as scattered light, control noise or experimental control signals around the local oscillator.

In this work we experimentally investigate the quantum enhancement, via Einstein–Podolsky–Rosen (EPR) squeezed states, of the proposed two-carrier heterodyne detection scheme using a table-top twin Michelson sensor experiment with balanced heterodyne readout. Each sensor receives one of the entangled EPR pairs such that the signals encoded onto the optical carrier of each sensor can be detected together against an engineered, low noise, quantum state. We will present the latest results.

Speaker: Daniel Gould

Einstein-Podolsky-Rosen Entangled Interferometers - Daniel Gould.pdf

17:30 Cheese and wine

Tuesday Poster session

41 Predicting the motion of a high-Q pendulum subject to seismic perturbations using machine learning

The seismically excited motion of high-Q pendula in gravitational-wave observatories sets a sensitivity limit to sub-audio gravitational-wave frequencies. Here, we report on the use of machine learning to successfully predict the motion of a high-Q pendulum with a resonance frequency of 1.4 Hz that is driven by natural seismic activity. We achieve a reduction of the displacement power spectral density of 40 dB at the resonant frequency 1.4 Hz and 6 dB at 11 Hz. Our result suggests that machine learning is able to significantly reduce seismically induced test mass motion in gravitational-wave detectors in combination with corrective feed-forward techniques.

Speaker: Daniel Hartwig (Universität Hamburg)

poster_GWADW23.pdf

42 Laser Welding the 100 g Mirrors for the AEI 10 m Prototype Suspensions with Micrometer Precision

The $10\,\mathrm{m}$-Prototype Interferometer of the Albert-Einstein-Institute Hannover will test new techniques to surpass the Standard Quantum Limit. The required displacement sensitivity of the Fabry-Perot Michelson interferometer is below $10^{-19}\,\mathrm{m / \sqrt{Hz}}$ at $200\,\mathrm{Hz}$. The $100\,\mathrm{g}$ test mass mirrors are designed as triple suspensions, where the last pendulum stage is quasi-monolithic. Four $20\,\mathrm{\mu m}$ thin glass fibers are laser welded to each of the mirrors. This welding procedure needs to be done with micrometer precision to ensure the suspended mirrors to be straight within a differential pitch angle of $10\,\mathrm{mrad}$. In cooperation with the Fraunhofer Institute for Applied Optics and Precision Engineering in Jena, a semi-automated fiber welding machine was designed. The setup is equipped with a $120\,\mathrm{W}$ $\text{CO}_2$ laser to cleave and weld the glass fibers with micrometer precision. A piezo-driven fiber gripper with 12 degrees of freedom is used to hold and align the fiber. With an autocollimator telescope, we measure the differential pitch angle, which can be corrected through repeated welding steps. In the future, this technique will also be applicable to other mirror suspensions of similar dimensions.

Speaker: Juliane von Wrangel (Albert Einstein Institute Hannover)

43 Instrumented baffles for Advanced Virgo +

As part of the upgrade program towards Advanced Virgo+ that started after the end of O3, instrumented baffles are being installed in the detector. These baffles are equipped with photosensors in order to monitor the distribution of scattered light in the cavities in real time and help with beam alignment. A first instrumented baffle was installed in the input mode cleaner (IMC) cavity in 2021 and is currently operational. Between O4 and O5, new, larger instrumented baffles will be installed around the end mirrors in the main arms. In this contribution we report results from the two years of operation of the IMC instrumented baffle, and present results from scattered light simulations used for the design of the new baffles, including their expected functionalities, progress in the construction and first tests of sensors.

Speaker: Adrian Macquet

44 A direct mode mismatch sensing scheme between the recycling cavities and arms.

Precise optical mode matching is of critical importance to future gravitational wave detectors. Mode mismatching will lead to excess losses, degrading squeezing. Automatic spatial-mode matching schemes have the potential to reduce losses and improve temporal loss stability. We propose a mode-sensing scheme with error signals directly proportional to the mismatch between the recycling cavities and arms.

The scheme uses RF interference between an auxiliary test field and the carrier field and produces error signals for both waist size & waist position mismatch. In this talk, I provide a summary of the scheme, as applied to a simplified ET-LF. I will then discuss proof-of-principal work carried out at LLO. This work will facilitate the routine use of extremely high levels of squeezing in current and future gravitational-wave detectors.

Speaker: Dr Aaron Goodwin-Jones (University of Western Australia)

2023_05_15-GWADW_CC-v2.pdf

45 Vibration attenuation system for a cryogenic Coating Thermal Noise measurement setup

Currently, the sensitivity of the second generation Gravitational-Wave (GW) detectors is limited in the low and mid frequency range by Thermal Noise (TN) and Seismic Noise (SN).
Major improvements in GW instrumentation science are expected from the Thermal Noise (TN) reduction in the mid-frequency range of the detectors, achievable also by cooling down the mirrors to $10$ K.
In order to select the coating material that are intended to be used in the 3-rd generation of detectors, the TN of new coatings should be directly measured using an interferometric method in a cryogenic environment.
A setup enabling this kind of characterization is under development.
In this poster, an overview of the experiment is shown focusing on the isolation system I am developing in order to reduce the ground vibration that can affect the measurement.
By design, a double-stage attenuator consisting of an inverted pendulum pre-isolator and a pendulum stage are expected to provide nearly four orders of magnitude noise reduction at $30$ Hz, corresponding to a residual displacement around $10^{-13}$ m/√Hz for the optical setup. These figures also take into account the effect of the heat conduction link between the suspended optical table and the cold finger of the cryocooler.

Speaker: Enrico Porcelli (Nikhef/University of Maastricht)

PosterGWADW-CTN.pdf

46 Astigmatic mode mismatch sensing for the next gravitational wave detectors

Quantum Noise Reduction in Gravitational Wave detectors is mainly limited by the optical losses generated by the mismatch between the vacuum squeezed beam and the resonant cavities of the interferometer. These aberrations must be measured and corrected. For this reason, different efforts have been made to develop wave-front sensing techniques to measure the mismatch between optical cavities.
However, the current technologies based on spherical Gaussian beams are not enough for the next generation of Gravitational Wave Detectors. In fact, the higher requirement on the optical losses imposes to compensate also the mode-matching generated by astigmatic aberrations, so a new generation of wavefront sensor technique is needed.
Here we will present an upgrade of the Mode Conversion technique that extends the mismatch measurement from the only symmetric aberrations to a complete characterisation of the mismatch between an astigmatic Gaussian beam and a resonance cavity. This extension uses four additional Quadrants Photodiodes sensors to detect the beat note between the Sidebands of the TEM00 and the second-order Hermite-Gauss mode TEM11 of the carrier. In particular, we will describe the method and present the first experimental results of this technique.

Speaker: Antonio Perreca (Istituto Nazionale di Fisica Nucleare)

47 Torsion-Bar Antenna and its Angular Sensor

Torsion-Bar Antenna (TOBA) is a ground-based gravitational-wave detector using a torsion pendulum. The resonant frequency of torsional motion is $\sim 1\, \mathrm{mHz}$, therefore TOBA has good design sensitivity in low frequency, specifically $10^{-19} \, /\sqrt{\mathrm{Hz}}$ at $0.1\, \mathrm{Hz}$. TOBA can detect intermediate-mass black hole binary mergers, Newtonian noise, and so on. A prototype detector Phase-III TOBA with a 35 cm-scale test mass is under development to demonstrate noise reduction. The target sensitivity is set to $10^{-15} \, /\sqrt{\mathrm{Hz}}$ at $0.1\, \mathrm{Hz}$. To achieve our target sensitivity, we need to measure the pendulum rotation precisely. We propose a wavefront sensor with a coupled cavity (Coupled WFS) as an angular sensor for Phase-III TOBA. In our method, an auxiliary cavity is used to compensate Gouy phase of a main cavity and enhance the first-order TEM modes in the main cavity. The experimental demonstration was successfully performed. Here we show the principle of TOBA and demonstration results of a Coupled WFS.

Speaker: Ms Yuka Oshima (University of Tokyo)

Torsion-Bar_Antenna_YukaOshima.pdf

48 Optical simulations for the aberration control in VnEXT

In VnEXT, the evolution of Virgo beyond the AdV+ project, the sensitivity is expected to improve by a factor of 10 compared to O5. The increasingly high power stored in the interferometer will require high-precision thermal control of the cavity mirrors to cope with the optical aberrations induced by thermal effects resulting from a circulating power up to 1.5 MW.
The Thermal Compensation System (TCS) sensors and actuators, conceived to tackle the aberrations coming from thermally driven effects must be enhanced to cope with a high-power operation of the detector.
The identification of the new requirements and, eventually, the need to change or improve the actuators already adopted is currently under investigation through optical simulations which are fundamental to carefully model the real interferometer behavior and tune its working point.
The outcomes of the modeling study for the case of marginally stable recycling cavities will be presented, focusing on the implementation of an additional ring heater in a symmetric configuration, with the purpose of decoupling the thermo-elastic correction from the associated thermal lens. This device can be beneficial for the TCS actuation independently from the specific optical layout.

Speaker: Matteo Lorenzini (Istituto Nazionale di Fisica Nucleare)

49 LIDA: A Detector for Axions and a Testbed for GW Detectors

We present a laser-interferometric detector for axions (LIDA) which is, on the one hand, a testbed for several effects relevant for gravitational-wave (GW) detectors, and, on the other hand, a proposed future application of the LIGO facilities in the 3G era. Our detector is based on the polarisation-sensitive readout of a high-finesse cavity at up to 200kW of circulating power. We will be able to observe short- and longterm effects of thermal and polarisation origin, and to test advanced coating materials under realistic conditions. Furthermore, the existing LIGO facilities are optimally suited to scale up our tabletop detector after CE and ET become operational. This would boost the sensitivity similar to GW detection, and either significantly improve on the constraints of the photon-axion coupling or even enable the measurement of an axion signal. We have already collected science data and reached 58kW of circulating power, which significantly exceeds the intensities on the LIGO mirrors.

Speaker: Alex Gill (University of Birmingham)

LIDA_GWADW_2023_final.pdf

50 Coating thermal noise mitigation through multi mode readout

Coating thermal noise, arising from random Brownian motions of the mirror coating materials, is the main limitation of precision measurements at frequencies below 10 Hz. We proposed a multi cavity transverse mode readout scheme [1] that realises an equivalent thermal noise level of a mesa flat-top beam, which is well known to be efficient at thermal noise reduction compared to a conventional Gaussian beam by effectively increasing the sampling area, yet has technical difficulties in generation. With optimal weighings of different spacial modes, this novel approach allows us to improve the coating thermal noise by a factor of 2.46 with 25 modes and 1.61 with 3 modes in short cavities. In this talk, I will give an overview of this thermal noise mitigation method via compositional Hermite - Gaussian modes. The design of a reference cavity with high thermal noise and the uptodate experimental progress of the stabilised reference laser will also be presented.

[1] Andrew Wade and Kirk McKenzie. Mirror coating-thermal-noise mitigation using multi-spatial-mode cavity readout. Physical Review A, 106(2):023511, 2022.

Speaker: Jue Zhang (Australian National University)

TN poster final copy.pdf

51 Optical resonator-based precision displacement sensing using GHz phasemeters

Knowledge of changes in distance, known as displacement sensing, is crucial for detecting gravitational waves. In addition to detecting test-mass motion in inertial sensors, we also want to monitor unwanted displacements in suspension systems to increase detector sensitivity.
This poster presents the idea of using optical cavities for displacement sensing, and introduces a heterodyne cavity-tracking scheme in combination with GHz frequency measurements that is capable of reaching noise levels below $10^{-16}\ m/\sqrt{Hz}$ at low frequencies with reasonable cavity and readout configurations. We discuss the main sources of noise and provide a preliminary noise budget. To use this scheme as a displacement sensor, one tracks the heterodyne frequency and retrieves the displacement information. We are currently developing a high-dynamic range frequency tracking system called the 'GHz Phasemeter', and we present our initial results.

Speaker: Mr Shreevathsa Chalathadka Subrahmanya (Universität Hamburg)

SCS_GWADW23_poster.pdf

52 Stabilized laser system at 1550 nm wavelength for the ET-LF interferometers

Proposed future gravitational wave detectors place high demands on their stabilized laser system. Especially the proposed interferometers operating with cryogenically cooled silicon mirrors demand another laser wavelength than current detectors. In addition, some of these detectors are expected to be sensitive to gravitational waves down to a few hertz.
We present a prototype for a pre-stabilized laser system at 1550 nm wavelength with frequency and power stabilizations optimized for the needs of gravitational wave detectors. A power stabilization with shot noise limited performance below a relative power noise of $1\times10^{-8}\textrm{Hz}^{-1/2}$ between 100 Hz to 100 kHz and an active frequency stabilization with a unity-gain frequency above 2 MHz were operated simultaneously. Out-of-loop measurements are performed to characterize the achieved stability and to analyze sensor noise limits.
Further research and development are needed to extend this demonstrated high stability towards the low-frequency band of the Einstein Telescope low-frequency interferometers. We present a specific experiment designed to analyze the fundamental sensing and control limitations at these low frequencies in our laser system.

Speaker: Fabian Meylahn (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))

Stabilized_Laser_System_at_1550nm.pdf

53 Bright Squeezed Light Generation and Quantum Correlation Measurements

State-of-the-art, high-precision metrology experiments like gravitational wave detectors require carefully stabilized laser sources with exceptionally low relative power noise (RPN). The RPN is fundamentally quantum noise limited by the relative shot noise (RSN) for classical states of light. As the RSN scales inversely with the square root of the optical power, it can be reduced by increasing the power, i.e., making the laser "brighter". However, this poses various technical challenges and cannot be scaled indefinitely. Thus, additionally "squeezed" states of light can be applied to reduce the RPN below the classical quantum noise limit. This project investigates methods to generate high-power, sub-relative-shot-noise (or "bright squeezed") light. Also, the quantum correlation measurement technique is investigated as an alternative to traditional power noise sensing by correlating two photodetector signals. As presented, this method is capable of sub-shot noise measurements and could serve as a bright squeezing sensor.

Speaker: Jasper Venneberg (Albert Einstein Institute / Max Planck Institute for Gravitational Physics Hannover)

54 Study and mitigation of the Virgo air conditioning system noise

The heating, ventilation and air conditioning (HVAC) systems for the experimental halls of the Virgo interferometer generate considerable low-frequency noise of seismic, acoustic and electromagnetic nature that could affect detector sensitivity. This was experienced several times in the Virgo detector lifetime and most recently during the third science run. In preparation for the fourth run, we carried out an extensive study to identify critical noise components and noise pathways. We have designed and implemented several interventions to reduce the noise produced by the HVAC plants inside the experimental areas achieving significant improvements.
In this poster, we describe the main solutions adopted, their implementation and the results obtained. Overall, we would like to propose a few technical solutions and rules of good practice that may be useful for the design of future interferometer air conditioning plants.

Speaker: Dr Maria Concetta Tringali (European Gravitational Observatory)

GWADW2023.pdf

55 A Novel Bipolar Passive Charge Management System for Contactless Test Masses Using Slow Photoelectrons

We demonstrate a novel bipolar Passive Charge Management (PCM) technique using slow photoelectrons generated by a single UV-LED of either 275nm or 295nm, directed at gold-coated floating Test Masses (TM). Slow photoelectrons are defined as having kinetic energies <eV(TM)max, where V(TM)max is the maximum allowable potential for the TM. The slow-photoelectron system requires ≅5minutes to converge to zero TM potential from 100mV, with a drift rate of ≅2.0mV/day. For reference, V(TM)max≅80mV for LISA and LISA Pathfinder.
We also validated the dual source PCM method using 255nm UV LEDs, with intensity adjusted through fine-tuning of their excitation currents, and illuminating the TM and its housing. Following an exposure of <30 sec to UV, this PCM system converges from 1V to zero TM potential with a drift rate of ≅1.5mV/day.
PCM systems depend critically on the stability and reproducibility of the photoemission properties. Results for flight and ground data for 255±1nm UV-LEDs confirm that the equilibrium potential of the TM is independent of the UV intensity, reproduceable to ±6mV (±6fC/pF) for six months, and strongly dependent on the geometry of the system.
For instruments with electric fields surrounding the TM and more complex geometries additional adaptations will be required.

Speaker: Saps Buchman (Stanford University)

56 Compact Optical Vault Grade Inertial Sensors.

Vault-grade inertial sensors are essential for isolating test masses in gravitational wave detectors from ground motion. In order to achieve excellent noise performance, these sensors are typically big bulky and not vacuum compatible. These features limit the deployment of such sensors and contribute to control noises, which currently prevent the low-frequency performance of LIGO from reaching design sensitivity. We will present designs of optical inertial sensors that can reach competitive performance to these vault-grade inertial sensors in a compact optic and, further, show results from our prototype sensors. The sensors encode their motion in an oscillating piece one inch in diameter. The oscillators achieve high Q factors of about 300000 to suppress thermal noise to a vault-grade level. We further present a readout scheme for such oscillators, which is sufficiently precise to achieve vault-grade performance. Designs like this will be an essential part of any future ground-based gravitational wave detector's mission to achieve its goals for low-frequency detection.

Speaker: Jonathan Carter (Max Planck Institute for Gravitational Physics)

57 Characterization of heterodyne phase locking for a Newtonian force sensor

Newtonian noise will likely limit the low-frequency sensitivity of future terrestrial gravitational wave detectors. Commissioning of the third-generation Torsion Pendulum Dual Oscillator (TorPeDO), a sensor for direct detection of Newtonian noise is in progress at the Australian National University. This sensor comprises of two freely suspended perpendicular torsion bars and they differentially rotate in response to Newtonian fluctuations. The differential angle is optically measured via length changes of four Fabry-Perot cavities formed around the two torsion bars. The Pound-Drever-Hall technique is used to interrogate each cavity with an individual laser. However, the free-running frequency noise of readout lasers will dominate the sensor readout. To mitigate this, each of the readout lasers is controlled to a common reference laser with a heterodyne phase-locked loop. We will present the implementation and characterization of the four simultaneous heterodyne phase-locked loops and discuss their performance and limits with respect to the scientific readout requirements for the TorPeDO.

Speaker: Avanish Kulur Ramamohan (Australian National University)

Poster_GWADW_TorPeDO_PLL.pdf

58 Squeezed light for the low-frequency interferometers of ET

The generation of strongly squeezed vacuum states is a key technology for future ground-based gravitational wave detectors to reach sensitivities beyond their classical quantum noise limit. Due to increased noise at sub-audio frequencies, the generation and subsequent characterization of such states are particularly challenging in the low-frequency range addressed by the Einstein Telescope low-frequency interferometers (ET-LF). Electronic noise in control loops and readouts, scattered light, as well as rising laser noise towards lower frequencies are the most likely reasons for excess low-frequency noise.
We found various linear and nonlinear noise coupling mechanisms of laser noise to the homodyne readout of the squeezed states. By using different techniques to reduce these couplings and employing a stabilized laser system, we demonstrated for the first time the generation of 11.5 dB squeezed vacuum states down to the lowest frequencies of the detection band of ET-LF at a wavelength of 1550 nm. Furthermore, based on the precise characterization of our setup we were able to derive the photodiodes' quantum efficiency, which is about 1 % worse than seen for 1064 nm. This finding should be considered for detection loss estimations and maybe trigger further investigations of the photodiodes for 1550 nm wavelength.

Speaker: Fabian Meylahn (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))

Squeezed_light_for_the_ET_LF_interferometers.pdf

59 Single frequency thulium fibre lasers between 1900nm and 2050nm

Thulium-doped silica fibre (TDF) lasers have a broad emission band near 2 $\mu$m, making them attractive for use with next-generation cryogenic-silicon gravitational wave detectors. We have demonstrated single-frequency, polarised 2 $\mu$m TDF distributed Bragg reflector (DBR) lasers at wavelengths between 1900 nm and 2050 nm. A high Tm concentration allows the use of a short cavity length, ensuring robust single-frequency operation whilst achieving high efficiency and output powers of up to 80 mW at 2050 nm. These DBR lasers would be suitable for use as a seed laser for further amplification to achieve the application requirements. We also describe a fibre laser mount that provides the thermal and mechanical stability required to achieve low-noise free-running operation.

Speaker: Georgia Bolingbroke (OzGrav - University of Adelaide)

60 Developement of the optical lock-in phase camera

Phase cameras are devices which perform differential wavefront sensing at high spatial resolutions. The intended purpose of these devices is to provide high resolution amplitude & phase maps of the various RF control sidebands for diagnostic purposes during commissioning. The increased spatial resolution allows the sensing of high order modes which may be key to understanding unsolved commissioning problems such as offsets in the RF error signals, precise mode matching & thermal actuator effects.

This work focuses on the continued development of the University of Adelaide design of phase camera, known as the optical lock-in camera. It also provides a general background of phase cameras and recent work on their applications.

Speaker: Mitchell Schiworski (OzGrav, University of Adelaide)

GWADW_2023_poster_SCHIWORSKI.pdf

61 Mechanical and Optical Design of TCS Test Facility

It has become critical to understand and develop effective Thermal Compensation System (TCS) schemes in order to achieve design sensitivity in current and next generation gravitational wave detectors. A full-scale TCS test facility has been proposed and funded for construction at the University of Adelaide. This facility will allow thermal compensation systems to be tested at full scale before they are implemented on the kilometer scale gravitational wave detectors. Design work for this test facility to-date has focused on both the structural and optical design of the facility. Optical design work has focused on selecting large-scale optics for the projecting telescope and evaluating aberrations within the optical system. Structural design has focused on the vacuum chamber and the required feed-throughs to support the optics. Analysis of these features, and the overall design of the facility will be presented.

Speaker: Madison Simmonds

62 Methods for Cryogenic Mechanical Loss Measurements

Even at cryogenic temperature the thermo-elastic effect can hinder mechanical loss measurements of coatings deposited on crystalline substrates by coupling the different contributions, from the substrate and from the coating itself, to the loss angle. We show here that a careful choice of the geometry of the substrate can drastically reduce this effect allowing more accurate measurements of the quality factor of novel coatings for the next generation of gravitational wave detectors. We also show the results of a recent investigation on the mechanical losses of sapphire substrates.

Speaker: Lorenzo Mereni (LMA (CNRS))

63 IBS TiO2:GeO2 single layer and HR stacks coating Q measurements and modelling

Coating thermal noise is one of the dominant noise sources in current gravitational wave detectors and ultimately limits their sensitivity to signals from weaker or more distant astronomical sources.

Here we present investigations into the promising candidate high-n coating material for future detectors: TiO2:GeO2. Specifically a mixture of 44% TiO2 / 56% GeO2, as well as pure SiO2 coatings, deposited via IBS at Colorado State University have been investigated, as both single layers and together in two HR stack configurations.

We measured the Q factors of uncoated and coated disks to infer the Q of the coatings themselves. This was carried out through several stages of heat treatment. Furthermore, we implement an effective medium model to estimate the Q of the HR stacks from our single layer measurements alone, and then compare these predictions with Q's measured from the real HR stacks. From this, we can observe any discrepancies between measurements and predictions, and infer the nature of any measured excess losses, and their evolution with heat treatment.

Speaker: Graeme Mcghee

GWADW2023_gmcghee_tige_poster_final.pdf

64 Mechanical and Optical Characterization of sputtered amorphois GaN thin film for high reflectivity and low-loss coatings

In present gravitational wave (GW) detectors, the limiting noise at mid-frequency range is due to the Brownian thermal noise in the multilayer reflective coating, in particular the intrinsic dissipation of the high refractive index material. The anelastic behavior of amorphous materials is explained by the presence of metastable states that are separated by an energy barrier. 

To reduce the dissipation in the material a reduction of the total density of metastable state is needed. Amorphous films whose constitutive atoms have a coordination number larger than 3 should be characterized by a low amount of these states. Indeed, the structure is more rigid making structural reorganization more difficult.

Sputtered amorphous GaN has been considered as a possible candidate for the high refractive index material for future GW detector mirrors. After a first optimization of the deposition parameters, an explorative investigation on mechanical and optical properties has been conducted through GeNS and ellipsometry measurements.

Speaker: Diana Lumaca (Università di Roma Tor Vergata e INFN Sezione di Roma Tor Vergata)

Poster_versione6-2.pdf

65 Juggled interferometer for gravitational wave detection

Juggled Interferometer is a Michelson-type interferometer aiming at improving the sensitivity of earthbound GW detectors at 0.1–10 Hz. This improvement can be achieved with repeatedly free-falling test masses (juggling), which decouples test masses from the seismically noisy environment and avoids suspension thermal noise. With this improved sensitivity, a Juggled Interferometer would be capable to detect Quasi-normal modes of massive black holes and some other gravitational wave sources.

We are now building up a prototype to test the basic ideas of a Juggled Interferometer. The whole interferometer is designed to be put inside a vacuum tank and the laser would be injected into it through a fiber. The test masses, together with the vacuum tank, are accelerated by a linear motor. And by adjusting the acceleration, the release and catch of the test masses can be achieved.

In this poster, the concept design and more details about the current status of the experiment will be introduced.

Speaker: Ms Bin Wu (Nagoya University)

66 Test facility for experimental investigations of the He-II based ET-LF payload cooling concept

The Einstein Telescope (ET) is a third generation gravitational wave detector, combining a low-frequency (LF) and a high-frequency (HF) laser interferometer. Cryogenic operation of ET-LF in the temperature range of 10-20 K is essential to suppress the suspension thermal noise (STN), which dominates the detection sensitivity at frequencies below 10 Hz. The minimization of the STN requires suspension materials with high thermal conductivity and low mechanical dissipation at cryogenic temperatures. Motivated by the exceptional heat conductivity of static He-II and a presumably low dissipation, a new marionette suspension design with a He-II filled titanium tube has been proposed and, theoretically, shown to meet the ET-D sensitivity requirements.The concept includes open fundamental questions that can only be addressed by measurements of the mechanical Q-factor, providing crucial insights in the dissipative behaviour of such a system. Hence, an experimental setup for cryogenic Q-factor measurements is being planned.The scope of experiments and a first conceptual design are being presented here. Beside the Q-factor measurements, a main focus of this facility is given to R&D on the integration of the He-II system and the mechanical interface to the payload in view of noise isolation.

Speaker: Xhesika Koroveshi (KIT)

67 Development status of the inner thermal shielding for the ET-LF cryogenic payloads

The Einstein Telescope (ET) is a planned third-generation gravitational-wave detector that includes a low-frequency (LF) and a high-frequency (HF) laser interferometer.
Cryogenic operation of ET-LF is imperative for exploiting the full scientific potential of ET, with mirrors operated at temperatures of $10\,\mathrm{K}$ to $20\,\mathrm{K}$ in order to limit thermal noise.
Thermal shielding is essential to support the cool-down process and to reduce both the particle adsorption and the heat load on the optics.
Additionally in steady-state operation, mechanical vibrations must be kept to an absolute minimum to limit the noise input by scattered light.

We present the development progress of a thermal shield surrounding the cryogenic payloads of ET-LF, which considers rapid cool-down and low vibration in steady-state operation.
During cool-down, cooling tubes enable the flow of supercritical helium, driving the shield temperature decrease by forced convection.
For steady-state operation, the shield cooling mechanism is converted to heat conduction at $2\,\mathrm{K}$ via static He-II in the same tubes.
The conceptual design status is explained by means of analytical and numerical modeling results.

Speaker: Lennard Busch (Karlsruhe Institute of Technology (KIT))

68 Towards a NEMO prototype

Future detectors, such as NEMO, Voyager, & Cosmic Explorer, will likely use Silicon optics, ~2000nm lasers, cryogenic temperatures, active mode control, high-circulating power & AlGaAs coated mirrors. We present progress & plans towards a prototype coupled cavity that combines these technologies. This poster presents an overview of the experimental topology and status updates.

On input optics & suspensions, we show progress in stabilising a 1995nm laser to a 7m ultra-stable, suspended cavity. We present the characterisation of our piezo pre-isolation scheme.

On active mode control, we present a coupled cavity mode sensing scheme and the development of large-diameter, thermally actuated recycling mirrors (TSAMS).

On cryogenics, we show a status update on our cooling scheme and the successful integration of the technologies in the vacuum envelope.

Together, these updates develop the path towards a high-power, 3G prototype facility. This facility is essential in developing the NEMO concept.

Speaker: Dr Aaron Goodwin-Jones (University of Western Australia)

2023_05_15-GWADW_NEMO-v2.pdf

69 The statics of the maraging blades in SuperAttenuators: simulation and tests

In 2027, the Advanced Virgo Plus (AdV+) gravitational-wave detector will enter Phase II, a thermal noise reduction upgrade involving the increase of the terminal mirror masses from 42 kg to 104 kg. Both the terminal SuperAttenuators will thus have their load increased and their parts upgraded in such a way to keep the natural oscillation frequencies unchanged.
This requires a revision of all the vertical oscillators in the terminal SuperAttenuators, based on thin elastic blades of maraging steel.
Triggered by the need for stiffer maraging blades, we present a study of the statics of these parts of the SuperAttenuator and of the ideal loads. Furthermore, a simulation code allowing accurate previsions for realistically shaped blades is presented in comparison with the experimental tests. We show that the code can be also used to characterize the material, by getting an experimental value of the elastic modulus.

Speaker: Piero Chessa (Istituto Nazionale di Fisica Nucleare)

GWDW2023_#100.pdf

70 Observation and interpretation of bichromatic thermal detuning in Virgo filter cavity

Bichromatic control schemes are used to control Fabry-Perot cavities used as filter cavity for frequency dependent squeezing and to acquire the lock of kilometric arm cavities. In the Advanced Virgo+ filter cavity, we observed that the phases of different colors of light are subject to temperature changes in the mirrors. Here we report the evidence of this thermal detuning and its interpretation. The coating thermal properties are used to calculate the detuning and are found to be consistent with the experimental results. The knowledge and effect of this thermal detuning are important to set requirements for the mirrors and their temperature stability anytime bichromatic controls are used but also provide a new method to measure the thermal properties of mirror coatings.

Speaker: Yuhang Zhao

71 A study of suspensions with flexures in compression for cryogenic mirrors

The Einstein Telescope will operate with cryogenic mirrors at 10-20K. This temperature needs to be maintained by extracting heat coming from absorption in the substrate and coating and thermal radiation. We present a study of an alternative to tensile suspensions of the Einstein Telescope mirrors. The mirror suspensions presented here tackle the conflicting requirements of being good heat conductors while remaining soft to preserve low thermal noise vibration isolation. Additionally, using small diameter silicon flexures deals with the low tensile strength of crystalline silicon.
The design consists of large suspension beams, connected to marionette and mirror, by thin, small flexures. The architecture is organised such that the flexure sustains compressive load only. The bending strain due to mirror motion is concentrated in this flexible part, and therefore we expect a low suspension thermal noise. Here, we show the trade-offs induced by this suspension design, focussing on the flexure design, and how it affects the frequency and thermal response of the system.

Speaker: Morgane Zeoli (Université Catholique de Louvain-la-Neuve)

230516 - GWADW - Poster - MORGANE ZEOLI.pdf

72 SPARSE: a high performance scatterometer with imaging ability

For high quality optical surfaces used in gravitational wave detectors, the quantization and reduction of light scattered by localized defects is a challenge. The defects are less than a micron in size, are caused by the manufacturing process (polishing, coating, storage, assembly), and are sparsely distributed (less than one defect per 100 micrometers of diameter). In gravitational wave detectors, they must be accurately evaluated because they become a significant source of scattering and thus a cause of performance degradation.

To address this problem, the CONCEPT group at Institut Fresnel has developed a dedicated instrument called SPARSE (SPatially and Angularly Resolved Scatterometry Equipment). This instrument combines the principles of a scatterometer with an imaging system to provide spatially resolved measurements of BRDF, BTDF, and transmittance. It can resolve up to approximately 400,000 26x26 µm² micro-areas on a one-inch-diameter component. SPARSE can measure scattering levels as low as $10^{-8}sr^{-1}$ and the data processing is designed to distinguish and quantify the weight of localized defects, contamination, scratches and roughness in the scattering budget.

We will provide a detailed description of the experimental setup, the results of its metrological qualification and several examples of measurements on representative samples.

Speaker: Adrien Bolliand (Institut Fresnel)

SPARSE_high_performance_scatterometer_with_imaging_ability.pdf

73 OctoPyus: a package to simulate seismic isolation systems for the third-generation Gravitational Wave detectors

The next generation ground-based gravitational wave detectors will expand our view of the Universe. The Einstein Telescope, expected to be built in Europe in the next decade, will be an order of magnitude more sensitive than Advanced Virgo and LIGO and expand its frequency range down to 3 Hz. This low-frequency sensitivity will allow the detection of high-redshift black hole coalescences and increase the number of expected multimessenger observations of compact binary systems, including binary neutron stars. Higher sensitivity at low frequencies can be achieved with next-generation seismic attenuation systems based on those currently used for Advanced Virgo. We present Octopyus, a simulation software dedicated to the development and study of new solutions for passive seismic isolation for the Einstein Telescope. The aim is to decrease the size of seismic attenuators, which are 17-m high in the current design, and significantly reduce the amount of underground civil works needed. The simulator has been developed within the project “Black Holes for ET in SArdina” (BHETSA) and combines the long experience gained in the simulation and construction of the Advanced Virgo seismic isolation system with an optimized, state-of-the-art simulation engine. Octopyus will allow to explore different seismic attenuation configurations and evaluate their performance, thus contributing to the development of one of the key elements of the whole Einstein Telescope project.

Speaker: Massimiliano Razzano (University of Pisa and INFN-Pisa)

74 The crystallization process in amorphous Ta2O5 thin films.

Amorphous Ta2O5 thin films are at the heart of the mirrors of gravitational wave interferometers. Their mechanical and optical properties determine the noise floor of the whole instrument in its most sensitive frequency range and thus the portion of the observable Universe.
Those optical coatings are deposited in their amorphous form by PVD processes. It is then customary to expose the coatings to specific thermal treatments in order to improve their mechanical and optical properties. In doing so, the structure of the amorphous oxide rearranges itself to reach more stable configurations, leading eventually to the formation of nano-crystalline regions. This phenomenon is generally considered detrimental with respect to the final properties of the coating. Yet, there is a significant lack of knowledge on the detailed physics taking place in this early structural change.
In this poster we report our findings on the structural and optical investigation of this material when it is subjected to thermal treatments inducing the formation of crystalline nano-regions. Their evolution is probed by structural techniques and ab-intio methods. The results are analyzed on the basis of specific structural models. The impact of the nano-crystal on the light scattering properties is also reported as a function of the crystallized fraction in the films.

Speaker: Dr Giulio Favaro

75 Exploring the Mass of Gravitons through Strong Lensing in the Next Generation of Gravitational Wave Detectors

This study investigates the use of strong lensed gravitational waves (GWs) to constrain the mass of the graviton, a crucial parameter in fundamental physics. By simulating lensing by point mass lenses of various masses (400, 4000, and 4000000 solar masses) and a singular isothermal sphere (SIS) model with a mass of 4000000 solar masses, we calculate the strain of GWs and show that the signal-to-noise ratio (SNR) of the lensed signal would be significantly improved, particularly for the next-generation GW detector, the Einstein Telescope (ET). Unlensed signals would also be improved by a magnitude of 250 compared to Advanced LIGO O4 with the next-generation spaced-borne GW detector, the DECi-hertz Interferometer Gravitational wave Observatory (DECIGO). The study suggests that the DECIGO would provide a more significant advantage for improving the SNR of the lensed GW signals as the mass of the lens increases. Furthermore, the study estimates the expected constraint on the mass of the graviton using the next generation of space-based and ground-based GW detectors. These findings highlight the potential of wave effects of lensed GWs for improving the SNR and constraining the mass of the graviton, which has significant implications for fundamental physics research.

Speaker: Shuaibo Geng (National Center for Nuclear Research)

76 Mitigation of non-axisymmetric optical aberrations in Advanced Virgo plus

The absorption of laser power in the core optics of ground-based gravitational wave detectors induces thermoelastic deformations and changes of the optical path length, that add up to mirror manufacturing defects causing deviations from the ideal optical configuration of the interferometer and worsening its performances. To mitigate these distortions a thermal compensation system (TCS) has been implemented in Advanced Virgo. TCS is currently designed to deal with axisymmetric wavefront distortions that represent the main contribution to the aberration budget. However, in view of the input power increase foreseen in the observing run O5 an adaptive control of residual non-axisymmetric optical aberrations is known to be necessary. Deformable Mirrors (DM) have been studied as possible actuators. The main advantage with respect to scanning beam actuators is that the DM correction does not introduce additional frequency-dependent noise. A Modified Gerchberg-Saxton (MoG-S) algorithm based on the measured device influence function matrix has been developed to extract the phase to be applied by the DM to obtain the heating pattern required for a complementary wavefront correction of the non-axisymmetric aberrations. We present the MoG-S simulations of the DM-based system and the results of the experimental tests.

Speaker: Claudia Taranto (Istituto Nazionale di Fisica Nucleare)

77 Detuning the signal recycling cavity in AdV+

The current GW detectors (LIGO, Virgo and KAGRA) are Dual Recycled Fabry Perot Michelson Interferometers which are all controlled to operate in a broadband, Resonant Sideband Extraction (RSE) configuration. By changing the microscopic length of the Signal Recycling mirror, one obtains a Detuned RSE (DRSE) setup. It has been previously shown that a lossless DRSE configuration presents unique physical phenomena such as the presence of an opto-mechanical spring and a reduction of quantum noise below the standard quantum limit without injecting squeezed light.

In this contribution, we study the advantages and difficulties for operating AdV+ in a DRSE configuration. We show that DRSE can reduce some of the problems related to the degeneracy of the signal recycling cavity in Virgo. Furthermore, with the current noise budget of AdV+, DRSE can improve the sensitivity for BNS and BBH detection compared to the current RSE counterpart. We predict the technical challenges and main noise contributions associated with controlling DRSE using the optical simulation tool Finesse3 and propose a commissioning strategy to switch between the RSE and DRSE configurations. We estimate the optimal quantum noise reduction granted by injection of frequency-independent or frequency-dependent squeezed vacuum from the squeezing source currently used in AdV+.

Speaker: Jacques Ding

Poster DRSE GWADW V3.pdf

78 Upgrades of the reference actuator for the calibration of Advanced Virgo+

The gravitational waves detectors of the LIGO, Virgo and Kagra collaborations use a mirror actuator using the radiation pressure of a laser as a reference for the calibration. This actuator is called the photon calibrator (PCal). The displacement of the mirror induced by the PCal is estimated from a measurement of the power of the laser reflected by the mirror. Thus, the calibration of the power sensors of the PCal is needed. This calibration has to be absolute and common with the collaborations LIGO and Kagra.
In this presentation, the design of the PCal installed on the Virgo interferometer will be shown, as well as the method to absolutely calibrate its power sensors. A procedure including the three collaborations and two national institutes of metrology (NIST and PTB) has been established to to inter-calibrate the power measurement standards of the different collaboration. And a setup to inter-calibrate the spheres has been built at LAPP and improved. Thanks to these improvements, the uncertainty on the mirror displacement estimation is expected to be below the 1% level for the O4 run. The plans for the upgrades toward O5 will be also shown.

Speaker: Paul Lagabbe (LAPP)

poster_GWADW_lagabbe.pdf

79 Jiggled interferometer for ground-based low-frequency gravitational wave detector

Improvement of the sensitivity of gravitational waves (GWs) at lower frequencies is important for 3rd-generation detectors. While space-based detectors, such as DECIGO and LISA, remove seismic noise and suspension thermal noise on account of the free-fall state of mirrors, these noises limit the sensitivity of the ground-based detectors, such as Einstein Telescope and Cosmic Explorer. One of the methods to remove these noise is the juggled interferometer(JIFO). The JIFO is a ground-based gravitational wave detector using repeatedly free-falling test masses. The JIFO can improve the sensitivity at lower frequencies than other ground-based detectors in the absence of these noises. However, the JIFO has some practical problems, for example, the laser source following a free-fall mirror and BS and the mirror tilt during a free-fall trajectory. To resolve this problem, we propose the “jiggled” interferometer as an advanced version of a juggled interferometer. The “jiggled” interferometer is a shorter repeat-cycle time of free-falling than JIFO, for example, 0.01s cycle time (100Hz). The shorter cycle time can resolve the above problems. In this presentation, we discuss the conceptual design of the jiggled interferometer and some data analysis methods.

Speaker: Shoki Iwaguchi (Nagoya University)

80 Mode matching sensing through RF Higher Order Modulation method

In the upcoming Advanced Virgo+ upgrade, the goal is to reduce quantum noise across the detector's entire bandwidth by introducing a frequency-dependence using a 300m long cavity (Filter Cavity). However, there can be a mismatch between the fundamental mode of the squeezed vacuum field and the cavity-supported mode that can lead to optical losses. This mismatch is described in terms of the higher-order mode (HOM) content of the former in the latter's defined base. When the cavity locks onto the fundamental mode, reflected HOMs can reveal information on the origin of the mismatch, such as differences in the dimensions and positions of the waist that will generate the Laguerre-Gaussian mode LG10.
To detect this HOM mismatch, we are developing an innovative method based on RF Higher Order Mode Modulation. This approach involves generating sidebands on the LG10 mode using an electro-optical lens (EOL) which is made up of a lithium niobate crystal with electrodes on top. The shape of the electrodes determines the ability of the object to act as a lens. By sending a sine wave with a frequency twice of the HOM spacing frequency, we can have one of the sideband resonating inside the locked cavity while the other is reflected. In this way we break the sidebands symmetry being possible to sense the beat signal between the carrier LG10 mode and the LG10 sideband on a single-element photodiode.
The I/Q demodulation at the sideband frequency allows for extracting the real and imaginary parts of the LG10 mode, which are proportional to the waist size and waist position mismatch, respectively.

Active correction of mode-mismatch is essential to enhance the performance of the interferometer. The technique presented here allows to implement mode-mismatch sensing with minimal additional hardware (it can use the single-element photodiode usually present for PDH locking).

Speaker: Gabriella Chiarini (Istituto Nazionale di Fisica Nucleare)

gwadw_poster.pdf

81 Mode mismatch impact on squeezed light in ET

Squeezed light is central to the success of future GW detectors, such as Einstein Telescope, but it's also very susceptible to various sources of loss. One of the most important and at the same time less understood sources is mode mismatch between different cavities in the interferometer. Not only it affects the squeezing directly as usual loss, but also couples in anti-squeezing, if the phases between the fundamental and higher-order modes are not matched. Future detectors have multiple cavities, and different processes that impact mode matching between them, and especially the relative phase between the modes. Understanding this process is crucial for planning future detectors. Unfortunately, this issue has not yet received the attention it calls for.

In ET, we are working on this issue, but we require a significant increase in human resource and expertise on the subject. This poster intends to draw attention to the problem and spark discussions on the issue among the participants.

Speaker: Mikhail Korobko (University of Hamburg)

82 Towards birefringence mitigation

To reduce thermal noise, KAGRA and 3G gravitational waves detectors will operate at cryogenic temperature. This requires the use of crystalline test-masses which could be birefringent. This birefringence leads to several issues from characterization to detector performances. We are now developping a quick method to measure and compensate birefringence as well as a new alignment control scheme that should allow to mitigate most of the birefringence issues.

Speaker: Marc Eisenmann (NAOJ)

83 Low energy electrons to neutralize electrostatic charges on cryogenic test mass mirrors.

To preserve the unquestionable improvements deriving by cooling down the mirrors at cryogenic temperature (LT), the methods adopted to mitigate all possible noise sources for gravitational wave detection need to be compliant with cryogenics.
Electrostatic charging is an already known limiting noise source. At room temperature, a mitigation method proposed by the LIGO collaboration has been successfully applied. If this method will be considered to mitigate charging at LT, a significantly thick condensed N2 layer will develop on the mirrors, severely affecting detection. The development of a new technology is then mandatory to preserve the performances envisaged by cryogenics.
Here we present a novel mitigation method compatible with cryogenics. By performing electrostatic measurements on a Si substrate, we show how to neutralize both a positive and negative charge by properly tuning the energy of an electron beam impinging on the sample surface. A study of irradiation parameters is given, highlighting the strict correlation between the surface voltage, monitored during the neutralization process, and the secondary electron emission properties intrinsic of the material. Preliminary XPS and Raman investigations have shown that, within the detectability limit, electron irradiation below few hundreds’ eV does not induce observable structural defects on the substrate.

Speaker: Roberto Cimino (Istituto Nazionale di Fisica Nucleare)

84 The Gravitational Wave Sky Simulator: a new package for fast simulations of gravitational wave sources

Since the first detection of gravitational waves, new data analysis algorithms and methods have emerged. However, to be developed and tested, these new methods require simulated datasets to compensate for the lack of large numbers of real events currently available. Furthermore, upgrades of existing detectors and planning for next-generation instruments, like the Einstein Telescope or Cosmic Explorer, require detailed simulations of observing scenarios.
The Gravitational Wave Sky Simulator (GWSkysim) is a fast simulator of gravitational wave sources. The package, written in Python, offers several types of astrophysical and transient noise sources which can be defined via population parameters and can be embedded in stationary or colored noise.
Both current and future-generation interferometers can be selected in any network configuration. For each of them, a set of default sensitivity curves can be chosen, and the program uses them to reproduce realistic noise in which the simulated signals can be embedded to resemble the most realistic dataset possible.

GWSkysim combines the capability of simulating gravitational wave sources with a customizable and user-friendly interface, with the goal of easily providing simulations for various purposes related to gravitational waves.

Speaker: Lucia Papalini (Istituto Nazionale di Fisica Nucleare)

85 Gravitational Wave Data Manager – A Python package for managing multichannel gravitational wave data

The Gravitational Wave Data Manager (GWdama) is a Python package that aims at providing an easy way to access Gravitational Wave data and output well-organized datasets, that can be then used for various purposes, including the data management of multichannel data coming from different instruments as well as the development of new data analysis methods, such as Machine Learning.

GWdama behaves as a multi-purpose and multi-format data management library for gravitational wave data.

Data is organized into a HDF hierarchical structure consisting of groups and subgroups of data. This approach can be used to store sets of homogeneous data, e.g., multiple chunks of strain data, as well as sets consisting of signals recorded by different instruments in the same time frame.

The typical use case of this package is data acquisition and preparation. GWdama can access data in the most commonly used environment in the field of gravitational waves and can provide basic operations for data manipulation and plotting. Although it is primarily meant for GW data, it is built to be sufficiently generic to handle any data type, including sensors used for the measurements of interest of the Einstein Telescope Site Preparation Board.

Speaker: Maria Antonietta Palaia (Istituto Nazionale di Fisica Nucleare)

86 Sensitivity optimization method for DECIGO: Combination of multiple detector outputs using the square completion method

The DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) project is the future Japanese space mission, which aims at detecting primordial gravitational waves (PGWs) produced in the inflation period. Three arm cavities with 1,000 km compose one cluster of Michelson laser interferometers. We theoretically proposed a quantum locking with optical spring to improve DECIGO’s quantum-noise-limited target sensitivity for the PGWs with the large optical diffraction loss of the cavities.

Quantum locking is a mirror control technique with auxiliary short low-loss cavity. Combining the technique with an optical spring, we successfully improved the target sensitivity by a broader dip in the frequency regime.

In an experiment, we demonstrated a portion of the technique that combines multiple detector outputs from the quantum locking system to optimize the target sensitivity. The combination was obtained by the square completion method. The experiment uses a simplified tabletop optical setup, two identically designed Fabry-Perot cavities sharing each end mirror. The shot noise is simulated by the classical noise directly injected into the signals, while the radiation pressure noise is simulated by shaking mirrors. The frequency dependence of the combination is obtained by the simulation reflecting the experimental setup.

We show the experimental result in this presentation

Speaker: Tomohiro Ishikawa

87 Dark matter Axion search with riNg Cavity Experiment DANCE: Latest optical system and sensitivity

Researches on cosmology and astrophysics have revealed that more than 80% of the matter in the universe consists of an unknown substance, or dark matter. The nature of dark matter is still unknown and many searches have been conducted for various dark matter candidates. Axion-like particles (ALPs) are undiscovered particles that are well-motivated candidates for ultralight dark matter. The interaction between ALPs and photons slightly causes the rotational oscillation of linearly polarized light, and therefore ALP dark matter can be detected by the measurement of the polarization rotation of a laser beam.
Recently, some ALP dark matter search experiments using the laser interferometer have been proposed. The basic idea is to use an optical cavity, which can enhance the effective light path and also the duration of the interaction with the ALP dark matter. With this technique, the polarization rotation can be amplified and high-sensitive ALP dark matter search can be conducted.
In this workshop, I will introduce our interferometric ALP dark matter search experiment: DANCE and will report its latest sensitivity.

Speaker: Hiroki Fujimoto (University of Tokyo)

GWADW2023_fujimoto2.pdf

88 Alignment Sensing and Control of Laser Interferometer for DECIGO and B-DECIGO

DECIGO(DECi-hertz Interferometer Gravitational-wave Observatory)is a space-based gravitational wave detector that has a good sensitivity at low frequencies from 0.1 Hz to 10 Hz. DECIGO can detect gravitational waves from intermediate-mass black hole binary mergers and gravitational wave background. It leads to the verification of the formation scenario of supermassive black holes and inflation theories in the early universe.DECIGO is a triangular-shaped laser interferometer consisting of 3 satellites that are in a precise formation flight. By controlling and measuring the distance between each satellite, the interferometer detects distortion of space caused by gravitational waves. Each side of the triangular laser interferometer is an optical cavity, and its length is designed to be 1000 km for DECIGO and 100 km for B-DECIGO. This cavity is called Dual-Pass Fabry-Perot cavity because the laser beams from satellites on both sides are incident on it. It is necessary to protect the interferometer from disturbances such as solar wind in space, and to control the position and alignment of the mirrors that consist of Dual-Pass Fabry-Perot cavity. In this presentation, we introduce the methods to sense and control these mirrors (WaveFront Sensor and Beam Pointing Control for alignment control), and an experiment for demonstration and verification of them. As the result, we succeeded in a simultaneous control 2 dofs of length and 12dofs of alignment which are all dofs of Dual-Pass Fabry-Perot cavity.

Speaker: Masaya Ono (The University of Tokyo)

89 Current status of experiments to verify the principle of quantum locking for DECIGO

The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. One of the most important DECIGO’s goals is the observation of the primordial GW background (PGW). To increase the possibility of PGW observation, we need to improve the sensitivity of DECIGO, which is limited by quantum noise.

Standard squeezing used in ground-based detectors cannot be used for DECIGO because the effect of diffraction loss is significant in DECIGO’s main cavity with a long arm length of 1000km. Therefore, quantum locking technology has been proposed as a new method for quantum noise reduction. Quantum locking is a technique to improve the sensitivity of DECIGO using signals obtained from the sub-cavity, which shares one mirror with the main cavity.
"Ponderomotive squeezing" and "Homodyne detection" are applied to the sub-cavity. By combining the signals from the main cavity (that contains the GW signals) and sub-cavity, we can achieve sensitivity beyond the limit due to quantum noise in a certain range of frequencies.

Currently, we are conducting experiments to verify this method. In this poster session, we explain the status of the quantum locking experiment.

Speaker: Yuki kawasaki (Department of Physics, Nagoya University)

90 Quantum Noise Reduction in Gravitational Wave Detector DECIGO by Quantum Locking including Cavity Detuning and Homodyne Detection

The DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a gravitational wave antenna, which is designed to have the optimum sensitivity in the low-frequency band for detection of primordial gravitational waves. Detections of primordial gravitational waves are expected to reveal various unsolved problems, such as proof of cosmic inflation. However, the original design of DECIGO cannot achieve the sensitivity that greatly exceeds the upper limit of the energy density of primordial gravitational waves shown by the recent Planck observations. Thus, we considered reducing quantum noise that limits the sensitivity to improve its detectability.

Our method, which uses two additional short sub-cavities, optical-spring, and homodyne detection, called optical-spring quantum locking, is effective in reducing quantum noise. In this method, the subcavities signals are used to control the mirrors of the main cavity, and choosing the appropriate detection axis reduces quantum noise. We investigate the use of homodyne detection and optical spring in the main cavity of the interferometer as a next step to improve sensitivity. In this presentation, we will present current results from simulations, touching on the principles of these techniques and the problems associated with their use.

Speaker: Kenji Tsuji (Nagoya University)

91 An Interferometric Instrument for the Determination of Spectral and Angular Dependence of Back-reflected Light from Smooth Optical Surfaces

Here we present the experimental results obtained for backscattered and retro-reflected light from optical components, including uncoated and anti-reflective coated windows and mirrors, using the BARRITON (BAck-scattering and Retro-Reflection by InterferomeTry with lOw cohereNce) instrument. BARRITON is an interferometric set-up based on the Fourier transform spectrometry technique, where the use of balanced optical detection suppresses the relative intensity noise of the input light source, thus improving the signal-to-noise ratio and allowing the measurement of the angular dependence of the back reflection on the order of 10-10 (10-4 sr-1 in terms of ARS measurement). In addition, the low coherence nature of the broadband light source allows accurate identification of the different optical interfaces and their respective back reflection and back scattering contributions. Finally, we demonstrate the recording of the spectral dependence of the reflection coefficient of anti-reflective coated windows with tunable spectral resolution from 0.2 nm to a few nanometers, with the lowest recorded value for an AR-coated interface between 80 ppb and 1.6 ppm. This work is performed in the context of the Stray Light Working Group of the LISA Consortium.

Speaker: Imran KHAN (Institut Fresnel)

Poster_GWADW_Khan.pdf

92 Treatment of Vacuum Fields in Cavity with Diffraction Loss for Space Gravitational Antenna DECIGO

The DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is an interferometer with a frequency band between 0.1 and 10 Hz. One of the main objectives of
DECIGO is to detect primordial gravitational waves (PGW) originating from inflation. However,
recent observations of cosmic microwave background lowered the upper limits of normalized
gravitational wave energy density for PGW. DECIGO is required to improve its target sensitivity.

Introducing quantum locking, homodyne detection, and optical spring to DECIGO has been considered for improvement of DECIGO’s sensitivity.

Homodyne detection and optical spring were implemented in DECIGO’s sub-cavity. Diffraction
loss occurs in DECIGO’s main cavity because the main cavity length is long, 1000 km. When incorporating an optical spring into the main cavity, vacuum field mixing corresponding to
diffraction loss must be considered.

This poster explains vacuum fields in a cavity with diffraction loss.

Speaker: Kurumi Umemura

93 Technological demonstrators towards the OGSE for the LISA mission

The LISA space interferometer aims at GW detection with ~3x10^-20/√Hz strain sensitivity, resulting in a displacement sensitivity of 11pm/√Hz over a path length of 2.5x10^9 m in the frequency range from 3x10^-5 to 1 Hz.
The LISA France Collaboration is in charge of the ground optical tests of the MOSA (Moving Optical Sub-Assembly), including the Optical Bench, Telescope and Gravitational Reference Sensor. Special check-out equipment is required, such as the Far-Field Optical Ground Support Equipment aiming at measuring the Tilt-To-Length coupling coefficient between angular residual beam jitter and longitudinal path length. The FF-OGSE simulates the incoming jittering beam and measures the associated longitudinal path length change.
We present two prototypes – the Zerodur InterFerOmeter and the TTL-OB - that will demonstrate the optical performance, the functional tests, the limits on sensitivity and the precision of the path length measurements achievable on-ground. These two benches are the first part of the design and specification for the FF-OGSE.
The Stray Light OGSE aims at stray light characterization in the integrated MOSA. It measures and identifies, separately, the different sources of stray light through the measurement of the corresponding fringe patterns while scanning the laser’s optical frequency.

Speaker: Dr Marco Nardello (ARTEMIS/OCA)

94 Practical quantum noise estimate of optical-spring quantum locking for space gravitational wave detector DECIGO

The DECi-hertz Interferometer for Gravitational-wave Observatory(DECIGO) aims mainly at the detection of primordial gravitational waves (PGWs) originating from inflation. Recent observations by the Planck satellite and others have lowered the upper limit of PGWs. Thus, it is necessary to improve the target sensitivity of DECIGO. A newly proposed method to reduce the quantum noise of DECIGO is quantum locking with an optical spring. In this method, a short cavity is added to the main cavity, sharing one mirror of both cavities. The error signal in this auxiliary cavity is obtained properly in a homodyne detection, and fed back to the shared mirror to cancel the radiation pressure noise of the main cavity. In our previous study, the optimal sensitivity assuming ideal homodyne detection without any additional noise was obtained by simulation. In this study, we investigate a more realistic design, taking into account the mixture of the vacuum fluctuations incident to the homodyne detection system. In this poster, we explain the latest results of this investigation.

Speaker: Ryuma Shimizu

95 Machine learning for glitches classification in Advanced Virgo O3

Glitches are short-duration, transient noises that can affect data quality and mask astrophysical signals. Therefore, it is extremely important to characterize them to understand their origin and mitigate them. A key step in this process is to characterize the different glitch families, that are thought to be linked to their different production mechanisms.

Glitches can be classified according to their morphology when represented as spectrograms. Convolutional Neural Networks (CNNs) have been proven to be a great tool in classifying 2D data such as spectrograms. In this work, we use CNNs to carry on a systematic study of glitches in Advanced Virgo O3 data.

We trained our deep learning model on ∼170k glitches starting from Advanced LIGO O3a glitches, labeled by the citizen science project GravitySpy, and used this model to label Advanced Virgo O3a data. We then use this data to build a new, custom model to label the remaining Virgo glitches, producing a catalog of families of Virgo glitches in O3, a key step toward a systematic real-time characterization of glitches in Advanced Virgo data.

Speaker: Michele Vacatello (Istituto Nazionale di Fisica Nucleare)

96 Scattered light noise from suspended optics in Virgo and LIGO Hanford

Scattered light that re-couples with the main beam of current gravitational wave detectors is a major limitation of their sensitivity, particularly at low frequencies. The detector noise depends on the amount of produced scattered light and the relative motion between the scattering objects and the interferometer. To address this issue in Virgo, we estimated the amount of scattered light generated by the most critical objects on the suspended benches (i.e. OFI, OMC, photodiodes etc), either measuring it with a back-scatterometer at LAPP or computing it. Then, we derived the scattered light noise projections for all the Virgo suspended benches. The projections were compared to the measurements from O3 and O4 and showed a reduction of scattered light due to the mitigation campaign carried out during the commissioning for O4. Additionally, we measured the scattered light noise coming from the critical elements in LIGO Hanford to estimate the amount of re-coupled light, including the one coming from the squeezing port. The results of this study allow to better understand the current limitations and to take actions for the future upgrades of gravitational waves detectors.

Speaker: Eleonora Polini (MIT)

97 Towards a monolithic suspension for the Einstein Telescope: crystalline silicon welding

Silicon is one of the candidates for the construction of monolithic mirror suspensions of 3rd generation GW detectors. In this context, one of the open challenges is the realization of the interfaces between the suspension fibers and the rest of the system. Having a technology that allows the welding of two crystalline components is therefore a first crucial step. With this aim, we decided to investigate the possibility of welding two silica cladded crystalline silicon rods using a technique developed by Clemson University (Prof. Ursula Gibson). The inserting of a thin gold leaf between the two rods creates a eutectic alloy, which improves the quality of the weld. Through the Virgo silica fiber production machine, which is equipped with fine control of movements and CO2 laser power, soldering is carried out and then followed by recrystallization of the soldered part and migration of the gold residue. The technique will be described in detail and the promising results of the preliminary tests will be presented.

Speaker: Francesco Piergiovanni (Istituto Nazionale di Fisica Nucleare)

GWADW_2023_Poster#111.pdf

98 Balanced Homodyne Readout at the 40m Prototype Interferometer

LIGO Caltech operates a 40-meter prototype interferometer to validate interferometer technologies. The current experimental focus is to conduct testing of the balanced homodyne readout (BHR) scheme before integrating it into aLIGO detectors for O5. With the BHR scheme, the differential arm length signal is obtained by mixing the local oscillator (LO) field and the interferometer output field at the Michelson dark port. The LO field is obtained from the transmission of a folding mirror in the power recycling cavity. This presentation will provide a detailed discussion of the BHR testing at the 40m prototype.

Speaker: Koji Arai (California Institute of Technology)

99 Faraday isolators for future gravitational-wave detectors - Characterization of a commercial isolator at 2052 nm and plans for Voyager.

Faraday isolators are needed in various areas of the gravitational-wave detectors, either requiring very low-loss (in the squeezer area), or high-power operation (in the input area), all while maintaining excellent optical isolation and low-noise performance.

Ultra-low-loss Faraday isolators have been built for the A+ output and squeezer isolators, and have shown excellent performance during the current commissioning runs. At longer wavelengths however, although commercial isolators are available, low-loss designs are not as mature, and fewer options for high-precision optics and lasers for testing are accessible, and more work is needed to develop suitable isolators.

We would like to present the results of our investigations characterizing a commercially available Faraday isolator at 2052 nm wavelength, status and plans for building a pathfinder for the Voyager, and to invite the discussion for options to consider while moving forward. We will also review the current status of available materials for these isolators in a range of wavelengths 1-2 um, of interest for future gravitational-wave detectors.

Speaker: Rodica Martin (Montclair State University)

100 The Low-Frequency frontier. Exploring the impact of low-frequency sensitivity on the detection of transient sources

Third generation ground-based gravitational wave detectors as the Einstein Telescope will expand our view of the Universe. In the meantime, upgrade programs as Virgo_nEXT are planned to boost the sensitivity of existing detectors such as Advanced Virgo in the post-O5 time frame. In this context, improving seismic noise attenuation is particularly promising to enhance the sensitivity at low frequencies. For instance, low-frequency sensitivity will enable the detection of coalescences of massive black holes and increase the number of expected multimessenger observations associated with the merger of neutron stars. We explored the impact of next-generation seismic isolation system on the observational capabilities of gravitational wave detectors, with particular attention to the post-O5 Virgo plans and to the Einstein Telescope. We will report on the observational scenario and localization capabilities that could be achieved by improving sensitivity at low frequencies.

Speaker: Massimiliano Razzano (University of Pisa and INFN-Pisa)

TestAbstract1

101 Cryogenic payload prototype at ARC

A program dedicated to cryogenic payload development is ongoing at the Amaldi Research Center at the Sapienza University in Rome. We plan to use solid conduction to extract the heat from the test mass and to test the main features of a viable payload, designed to be closely sized to ET targets. The test mass will initially be a dummy body, but all the main parts included in the payload will be suitable to test the crucial aspects of the system.

Speaker: Ettore Majorana (Dipartimento di Fisica, Sapienza Università di Roma)

Poster_Payload_Elba_V9 (1).pdf

102 Compact displacement sensors using Deep-Frequency Modulation Interferometry

Compact displacement sensors with sub-picometer level performance between 0.01Hz and 100Hz are a crucial technology for future detectors, detector upgrades and inertial sensors to reduce noise in suspension control and test-mass sensing. We are investigating sensors based on Deep-Frequency Modulation Interferometry (DFMI) for this purpose at the University of Hamburg and we will present our status on all relevant aspects. This includes the development our optical sensing head, which combines on-axis sensing with ghost beam suppression and balanced readout. We also discuss a new readout algorithm that provides optimal phase and absolute ranging estimation with minimal processing delays, enabling us to implement dozens of sensors in the future. We present the current testing and performance results achieved in table-top experiments and discuss the identified limitations and future improvements. We also present our seismic isolation platform that we will use to test the sensors on suspensions in vacuum and its commissioning status. Finally, we discuss our model for the fundamental readout limitations of DFMI-based sensors and how we are working to overcome this limitation to reach sub-femtometer precision in future sensor iterations by using resonant enhancement in combination with DFMI.

Speaker: Oliver Gerberding (Universität Hamburg)

103 First demonstration of neural sensing and control in a kilometer-scale gravitational wave observatory

Suspended optics in gravitational wave (GW) observatories are susceptible to alignment perturbations and, in particular, to slow drifts over time due to variations in temperature and seismic levels. Such misalignments affect the coupling of the incident laser beam into the optical cavities, degrade both circulating power and optomechanical photon squeezing, and thus decrease the astrophysical sensitivity to merging binaries. Traditional alignment techniques involve differential wavefront sensing using multiple quadrant photodiodes, but are often restricted in bandwidth and are limited by the sensing noise. We present the first-ever successful implementation of neural network-based sensing and control at a gravitational wave observatory and demonstrate low-frequency control of the signal recycling mirror at the GEO 600 detector. Alignment information for three critical optics is simultaneously extracted from the interferometric dark port camera images via a CNN-LSTM network architecture and is then used for MIMO control using soft actor-critic-based deep reinforcement learning. Overall sensitivity improvement achieved using our scheme demonstrates deep learning’s capabilities as a viable tool for real-time sensing and control for current and next generation GW interferometers

Speaker: Tomislav Andric (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))

GWADW2023_TAndric_70x100.pdf

104 Experimental validation for low frequency isolation of six degree of freedom systems using inertial sensors

After the first detection of gravitational waves in 2015, a new era in understanding the universe took off. To make such detection, gravitational wave detectors are required to operate in an ultra-stable environment that can be obtained only by isolating them from external disturbances. Active isolation control is a major approach in this context, it was successfully implemented in LIGO's positioning platform [1], where it is possible to obtain amplitude spectral densities lower than $10^{-12}$ $\text{m}/\sqrt{\text{Hz}}$ for vertical and longitudinal seismic isolation at frequencies higher than 1 Hz. Nevertheless, it is still extremely challenging to obtain such good performances at lower frequencies. This talk addresses theoretical approaches and corresponding experimental validations for low-frequency active damping and isolation of a six degree of freedom platform using super high-resolution inertial sensors. The active platform is actively isolated by up to two orders of magnitude for frequencies between 0.1 Hz and 10 Hz.
[1] F. Matichard, B. Abbott, S. Abbott, and D. Coyne, “Advanced ligo two-stage twelve-axis vibration isolation and positioning platform. part 2: Experimental investigation and tests results,” Precision Engineering,vol. 40, 04 2015.

Speaker: Mouhamad Haidar Lakkis

Wednesday, 24 May

Low Frequency Noise, Control and Sensing 2

Suspension modeling, integration with sensing and control, linear control and Neural Networks

Conveners: Dr Conor Mow-Lowry (Vrije Universiteit Amsterdam and Nikhef), Katherine Dooley (Cardiff University), Dr Paola Puppo (INFN - ROMA)

105 Mitigating low-frequency noise: role of tilt, software tools, controller optimization

Tilt-induced noise plays a crucial role in current and planned gravitational-wave (GW) detectors, as well as in smaller seismically-stabilized platforms. We present an example case for seismically-isolated platform "VATIGrav" in our laboratory, discussing tilt measurement setup, modelling of system performance and potential mitigation strategies. In this work we use general-purpose open source simulation toolkit "Spicypy" that we develop in collaboration with other researchers across the GW science community, including LISA, LIGO and Einstein Telescope collaborations. In the example case presented, we model control system dynamics with seismic disturbance propagating through it, taking into account sensor noise and tilt effects. Other capabilities of Spicypy project are briefly discussed, in particular highlighting plans for optimization of the controller and system geometry for the "VATIGrav" platform, and other systems such as suspensions of the Einstein Telescope.

Speaker: Artem Basalaev (Universität Hamburg)

LF_noise_mitigation_A.Basalaev.pdf

106 A Systems Approach to Evaluating the Status of ET-LF Seismic Attenuation Proposals

The Einstein Telescope low-frequency (ET-LF) interferometers will extend the detection band for gravitational-waves down to 3 Hz. Significant design decisions, such as an underground infrastructure, have already been taken. With the instrument proposal due in the mid-2020’s other design decisions are under active deliberation.
Critical to achieving the displacement sensitivity of ET-LF is the seismic attenuation system. Among the design requirements this subsystem needs to satisfy are seismic isolation, and avoiding reinjection of ‘technical noise’. Controls and technical noises limit the low-frequency performance of some current detectors, and no demonstrated design satisfies the ET-LF length displacement requirements.
We compare different seismic attenuation proposals, from a systems perspective, focusing on length control. Implications for ‘technical noises’; alignment control; and payload actuation are calculated, and included. The resulting displacement spectra of the test mass mirrors are contrasted with each other, and the ET-LF design requirements. We address if proposed seismic attenuation systems satisfy the length displacement requirements of the ET-LF design.

Speaker: Nathan Holland (Nikhef/VU Amsterdam)

GWADW2023-NA_Holland-A_Systems_Approach_to_Evaluating_ETLF_SAS_Proposals-v2p00.pdf

107 The “Akìnetos” Large-band Tiltmeter for Virgo ground tilt measurement

Newtonian noise (NN) is one of the limiting noise sources for the low-frequency sensitivity of GW detectors. To measure this contribution, during O3 a tiltmeter was installed in Virgo as part of a NN reduction system. As tiltmeter, we exploited the prototype balance for the Archimedes experiment, devoted to the measurement of the interaction between quantum vacuum energy and gravity. The same prototype was moved to Sos-Enattos in Lula (NU) to measure the ground tilt at the site candidate to host the 3G GW detector ET. The comparison of ground tilt noise at the two sites showed that the latter is about 100 times quieter than the Virgo site. This measurement also demonstrated that the prototype sensitivity reaches values below $10^{(-12)}$ rad⁄√Hz in the region between 1 and 10 Hz, which makes it the most sensitive tiltmeter in the world.
In view of O4, a new tiltmeter was designed, realized, and recently installed close to the Virgo North End tower. Besides the NN reconstruction aims, we will test the coherence of the tiltmeter data with the Virgo interferometer signal and with the environmental data below 10Hz, possibly giving a contribution to the noise reduction already in this phase of Virgo interferometer.

Speaker: Annalisa Allocca (Universita' Federico II di Napoli - INFN Napoli)

GWADW2023 - Status of Tiltmeter.pdf

108 MIMO approach for the longitudinal control of Advanced Virgo plus: interferometer and filter cavity

Gravitational Wave (GW) detectors must use control loops to achieve the desired working point. Typically, these detectors have 4 or 5 main longitudinal Degrees of Freedom (DoFs) for which it is usually possible to extract suitable error signals by design. Therefore, they can be considered as diagonal systems allowing to close all the loops following a typical Single-Input Single-Output (SISO) control design approach. However, when the system is characterized by strong couplings among the different DoFs, this technique no longer holds and an alternative approach should be used: the Multiple-Input Multiple-Output (MIMO) system approach. Two main topics should be further investigated.
At first, a reliable system identification technique should be used to take into account the cross-couplings among the different DoFs.
Secondly, stability margins derived from SISO systems are often overoptimistic, becoming not valid for a MIMO closed loop system, introducing instabilities even for small variations of both gain and phase of the system. Therefore, it is necessary to study the robustness of the system in a different way.
In this work, we present the results obtained using a MIMO approach to describe the longitudinal controls of Advanced Virgo. At first, we describe a model of the control scheme for the 5 degrees of freedom of the interferometer. Then, we present a study made on the Frequency Dependent Squeezing (FDS) system: in particular, we describe the system identification technique and robustness study of a MIMO system composed by two inputs and two outputs: the main laser of the squeezed light source and the filter cavity.

Speaker: Enzo Tapia (Nikhef)

MIMO_sys_identification_GWADW_2023.pdf

10:30 Coffee break

Thermal effects in interferometry and squeezing

Conveners: Daniel Brown (University of Adelaide), Stefan Hild (Maastricht University and Nikhef), Alessio Rocchi (Istituto Nazionale di Fisica Nucleare)

109 A bildungsroman of the TCS in Advanced Virgo

The sensitivity and operability of advanced interferometric gravitational wave detectors are impacted by the distributed budget of optical aberrations due to cold defects and thermal effects enhanced by the high input power. The Thermal Compensation System (TCS) of Advanced Virgo is a complex and versatile environment with the twofold scope of characterizing and correcting the aberration budget. The integration of the TCS is the result of many years of experience in the design of thermal actuators/wavefront sensing and in the implementation of commissioning strategies. Thermal effects are now managed using several configurations of wavefront sensing and many actuators exploiting thermo-elastic and thermo-optic couplings. The Advanced Virgo commissioning phases have been a rich and rewarding build environment to understand the features of thermal effects and the variety of compensation strategies. We report about the evolution of TCS concepts in the framework of Advanced Virgo commissioning efforts.

Speaker: Matteo Lorenzini (Università di Roma Tor Vergata e INFN Sezione di Roma Tor Vergata)

GWADW2023_Lorenzini.pptx

110 A direct mode mismatch sensing scheme between the recycling cavities and arms

Speaker: Aaron Goodwin-Jones

2023_07_GWADW.pdf

111 Mitigation of Point Absorbers in the AdV+ core optics: the actuator design

Speaker: Maria Cifaldi (Istituto Nazionale di Fisica Nucleare)

GWADW2023_Cifaldi (1).pdf

112 Mode mismatch challenges at Advanced Virgo and the phase camera

Speaker: Ricardo Cabrita (UCLouvain)

PhaseCameraVirgo_GWADW.pdf

113 General discussion on adaptive optics for future GW detectors

Speakers: Alessio Rocchi (Istituto Nazionale di Fisica Nucleare), Daniel Brown (University of Adelaide)

12:30 Lunch break

Site characterization

Conveners: Kazuhiro Yamamoto, Kevin Kuns

114 Distributed seismic fiber networks and their potential for Newtonian noise cancellation in the Einstein Telescope

The next generation of gravitational wave detectors, such as the Einstein Telescope, face a significant limitation known as Newtonian Noise. This noise source arises from seismic waves that cause gravitational acceleration of the suspended test masses in the detector, interfering with the measurement of gravitational waves. One strategy to eliminate Newtonian Noise requires seismic field measurements using large sensor arrays, the estimation of the test mass acceleration perturbation, and the correction of the gravitational wave data in post-processing. The need for a huge number of seismic sensors leads to practical challenges and high costs. Distributed fiber strain sensors have the potential to overcome these as they provide individual seismic measurement points over the entire length of the fiber. Our research in Hamburg, in collaboration with the WAVE initiative on the research campus Bahrenfeld/DESY, is focused on investigating large seismic sensor networks and the use of fiber sensors. In this talk, we will present results from the WAVE seismic network including measurements in accelerator tunnels (EuXFEL) and discuss the benefits of fiber sensors. Additionally, we will outline our plans to develop improved seismic fiber sensors using digitally enhanced interferometry to meet the demanding requirements of the Einstein Telescope.

Speaker: Katharina-Sophie Isleif

20230523_KSI_GWADW_ET-NNC-DI-Seismic_Sensors-WAVE.pdf

115 A study of deep neural networks for Newtonian noise subtraction

Vincent van Beveren (Nikhef), Maria Bader (Nikhef), Jo van den Brand (Nikhef and Maastricht University), Henk Jan Bulten (Nikhef), Xander Campman (Shell), Soumen Koley (Nikhef, GSSI), Frank Linde (Nikhef)

The Euregio Meuse-Rhine border region of Belgium, Germany and the Netherlands has been identified as a candidate site for hosting Einstein Telescope. Newtonian coupling of ground vibrations to the core optics of the detectors may limit the sensitivity of Einstein Telescope at frequencies below about 10 Hz. The contribution of Newtonian noise is site specific and depends on the ambient seismic field which in turn depends on the site's geology and the distribution of surface and underground seismic-noise sources. We have investigated the application of machine learning in combination with the deployment of seismic sensor networks to predict seismic displacement noise at specific locations on the surface and underground. Moreover we have modeled a deep neural network that allows to subtract Newtonian noise from the strain data measured by Einstein Telescope. The seismic-field model is based on a complete solution of the elastodynamic wave equations for a horizontally-layered soil structure. The geology features soft-soil layers on hard-rock and was shown to be effective in attenuating Newtonian noise from surface waves below the required sensitivity. In addition our model includes a random background of body waves with all possible angles of incidence. We show that a deep neural network is effective in predicting Newtonian noise, whereas an Wiener filter approach is effective when surface boundary conditions dominate the Newtonian-noise contributions.

Speaker: Henk Jan Bulten

GWADW2023_Bulten_NN.pdf

116 Einstein Telescope site characterization in Sardinia

Due to its unique geophysical features and to the low population density of the area, Sos Enattos is a promising candidate site to host the Einstein Telescope (ET), the third-generation Gravitational Wave Observatory. The characterization of the Sos Enattos former mine, close to the first of the possible ET corners, started in 2010 with the deployment of seismic and environmental sensors underground. In particular, since 2019 an extensive array of seismometers, magnetometers and acoustic sensors have been installed in three stations along the underground tunnels, with one additional station at the surface. Moreover, temporary arrays of seismometers and geophones were installed in the surrounding area. For the characterization of the other two corners, named P2 and P3, two boreholes 270 m deep were excavated, determining the good quality of the drilled granite and orthogneiss rocks and the absence of significant thoroughgoing fault zones. The two boreholes are instrumented with broadband seismometers, measuring since 2021 the seismic noise at 252m and 264m of depth, revealing an outstanding low level of vibrational noise in the low-frequency band of ET-LF (2-10Hz), beating the Peterson's low noise model (NLNM) and resulting -along with those installed at Sos Enattos- among the quietest seismic stations in the world in that frequency band. The low seismic background and the reduced number of seismic glitches ensure that just a moderated Newtonian noise subtraction would be needed to achieve the ET target sensitivity at low frequencies. In addition to passive seismic measurements, active seismic campaigns have been carried out at the two corners to reveal the features of the subsoil. Moreover, the electromagnetic noise is monitored with magnetometers deployed close to the boreholes, and acoustic noise sensors will be deployed in the area during this year. Finally, a temporary array of broadband seismometers has been recently deployed along a 15-km long line, stretching from the P2 corner to the closest wind farm, to characterize the attenuation with distance of noise produced by existing wind turbines.

Speaker: Dr Luca Naticchioni (INFN Roma)

GWADW23 SosEnattos LNAT.pdf

117 Ambient noise studies in Sardinia for the Einstein Telescope

One of the design goals of Einstein Telescope (ET) is to extend the observation band of terrestrial gravitational wave detectors from 20 Hz down to 2 Hz. Since the coupling of a detector to its environment becomes stronger at lower frequencies, characterization of environmental disturbances at the ET candidate sites is paramount. In this talk, we present the first long term analysis of the time-variant properties of the seismic field at the Sardinia candidate site connected to natural as well as anthropogenic phenomena. The analysis was carried out using the network of permanent and temporary instruments installed at the Sos Enattos Mine and at the proposed locations of the vertices of the ET triangle. We find that temporal variations of source distributions and of the noise spectra generally follow predictable trends in the form of diurnal, weekly, or seasonal cycles. Specific seismic sources were identified such as road bridges. Moreover, these studies underline the suitability of the Italian candidate site at hosting ET and reveal an exceptionally low level of vibrational noise below 10 Hz and resulting among the quietest seismic stations in the world in that frequency band.

Speaker: Matteo Di Giovanni (Gran Sasso Science Institute)

Presentazione GWADW.pdf

17:30 Coffee break

Moon and Space

Conveners: Kirk McKenzie, Prof. Seiji Kawamura (Nagoya University)

118 LISA Status and Overview

Status and overview of LISA will be presented.

Speaker: Oliver Gerberding (Universität Hamburg, Institut fur Experimentalphysik)

20230524_GWADW_LISA.pptx

119 Space gravitational wave antenna DECIGO and B-DECIGO

DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna. There are many science targets that DECIGO aims at, including the detection of primordial gravitational waves, direct measurement of the acceleration of the Universe, the revelation of the formation of massive black holes, and many others. DECIGO consists of four clusters of spacecraft, and each cluster consists of three spacecraft with three Fabry-Perot Michelson interferometers. As a pathfinder/science mission of DECIGO, we plan to launch B-DECIGO to demonstrate technologies necessary for DECIGO and lead to fruitful multimessenger astronomy. B-DECIGO is a small-scale version of DECIGO with a sensitivity good enough to provide frequent detection of gravitational waves. In this talk, I will explain the aimed sciences, the mechanical and optical design, and the current status of DECIGO and B-DECIGO.

Speaker: Prof. Seiji Kawamura (Nagoya University)

DECIGO_GWADW_20230524.pptx

120 LGWA status

We will present the mission concept and give an update of the payload concept and science-case studies. We present the status of the preparation of new lab facilities for LGWA, payload development, and collaboration activities.

Speaker: Jan Harms (Istituto Nazionale di Fisica Nucleare)

LGWA_GWADW.pptx

121 Developing a toolset for adjustable picometer- stable interferometers for future gravitational wave detectors

Optical benches for low-frequency, picometer-stable laser interferometry, as used
in the space-based gravitational wave detector LISA, are usually made by bond-
ing silicate glass components to an ultra-low-expansion glass ceramic. To pro-
vide ground-support equipment for the mission and for testing parts of the in-
struments we are studying a toolset to realize picometer-stable interferometers
which, in contrast, are adjustable. For this we use an ULE-ceramic baseplate
with thermally compensated optical mounts which are mounted in the bench
using invar insets, screws and clamps. Our toolset will be placed inside a vac-
uum chamber to suppress temperature noise and reach a stability of 1 pm/√Hz
down to 3 mHz. A testbed for adjustable ultra-stable interferometers might have
further applications in other, future gravitational wave detectors on the ground
and in space. We present the current status of our set-up and the concept of
a heterodyne laser locking experiment to verify the stability of our approach
before implementing a larger-scale optical bench.
1

Speaker: Marcel Beck (Universität Hamburg)

Marcel_Beck_GWADW_Elba_2023.pdf

122 Sub-femtoWatt Laser Phase tracking for space-based gravitational wave detection

This talk presents a demonstration of robust phase tracking in the weak-light regime (10 femtoWatts and below). In addition we present modelling, simulation and experimental work that demonstrate, for the first time, phase tracking at the sub-femtowatt level, more than 1,000 times less optical power than what is planned for the Laser Interferometer Space Antenna (LISA). As well as improving on the previous results in the field, this work addresses the gap in our understanding of how these phase tracking behave in the weak-light regime. This technology is mission enabling for missions such as microHertz band space-based gravitational wave detectors and improves relaxes requirements on received optical power for other space-based interferometric missions.

Speaker: Callum Sambridge

Sub-femtoWatt laser phase tracking for LISA and beyond.pptx

19:15 Pre Social Dinner

20:00 Social Dinner

Thursday, 25 May

Prototypes for R&D 1

Prototypes for current interferometers

Conveners: Koji Arai (Caltech), Bram Slagmolen (The Australian National University), Dr Sebastian Steinlechner (Maastricht University & Nikhef)

123 A New Facility for Testing GW Thermal Compensation Systems at Full Scale

Improving the sensitivity of current and next generation gravitational wave detector requires increased circulating power and improved quantum noise suppression from squeezing. To achieve the sensitivity increases requires that the optical surfaces within the interferometer must be controlled to exquisite precision. These surfaces are controlled by the thermal compensation system. Unfortunately, changes to the thermo-optic state of the interferometer have very long-time constants and affect the control signals of multiple interferometer degrees of freedom. This makes the commissioning and improving the thermal compensation systems in-situ and extremely complicated and time-consuming task. Further, commissioning time in the full-scale interferometers is extremely valuable and to date the time needed to completely understand and optimize the thermal compensation systems
We are building a full-scale thermal compensation test facility. This will allow us to characterize the thermal response of LIGO size test masses at full scale and also full characterize new actuation and sensing schemes before they are installed in the LIGO Observatories. In this talk we will describe this new facility.

Speaker: David Ottaway

OttawayTalk.pdf

124 Test Of New Interferometric Sensors In The AEI 10 m Prototype

The Albert-Einstein-Institute (AEI) 10m Prototype in Hannover, Germany serves as a testbed for techniques needed for future gravitational wave detectors. The ongoing work is to build a Fabry-Perot-Michelson interferometer which is limited by quantum noise over a wide range of input powers.
Even before the full interferometer is operational, improvements such as new interferometric sensors and their effect on a complex interferometer can be tested while also gaining practical experience with them. The suspension platform interferometer has recently been moved to a readout which is fully integrated in the CDS to improve robustness and simplify maintenance. Homodyne quadrature interferometers (HoQIs), in collaboration with the VU Amsterdam, were installed at the intermediate mass of the main beam splitter suspension to improve its damping performance.

Speaker: Johannes Lehmann (AEI Hannover)

GWADW2023_JohannesLehmann.pdf

125 Compact isolation of a large mirror at low frequency

The study presents the updates and challenges of compact isolation of a large mirror (100 kg) at low frequency (below 10 Hz). The isolator consists of mounting a passive inverted pendulum platform (IPP) on an active inertial platform (AP) and suspending multiple cascaded pendulums from the IPP. The new approach results in a very low resonance frequency (0.07 Hz) and provides ultra-low frequency seismic isolation. On the other hand, several challenges need to be addressed such as the coupling of IPP with AP.

Speaker: Mr Ameer Sider (PML - Precision Mechatronics Laboratory, Université de Liège, B-4000 Liège, Belgium)

A.Sider (U Liege) - Elba.pptx

126 ETpathfinder status

The third-generation of gravitational wave observatories, such as the Einstein Telescope (ET) and Cosmic Explorer, aim for an improvement in sensitivity of at least a factor of ten over a wide frequency range compared to the current advanced detectors. In order to inform the design of the 3G detectors and to develop and qualify their subsystems, dedicated test facilities are required. The ETpathfinder prototype uses full interferometer configurations and aims to provide a high sensitivity facility in a similar environment as ET. Along with the interferometry at 1550 nm and silicon test masses, ETpathfinder will focus on cryogenic technologies, lasers and optics at 2090 nm and advanced quantum-noise reduction schemes. In my talk, I will present the current status of ETpathfinder and the construction of its subsystems.

Speaker: Sebastian Steinlechner (Maastricht University & Nikhef)

ETpathfinder status.pdf

127 Mariner: The Cryogenic Upgrade of the 40m Prototype Interferometer

"Mariner: The Cryogenic Upgrade of the 40m Prototype Interferometer"

LIGO Caltech operates a 40m prototype interferometer to validate interferometer technologies. Mariner is a prototype project of the 40m interferometer to be a prototype of Voyager, which is the cryogenic version of the LIGO interferometers. The Mariner interferometer employs cryogenic silicon test masses and a 2$\mu$m laser. This presentation will discuss the technical details of the Mariner interferometer.

Speaker: Koji Arai (California Institute of Technology)

Mariner_GWADW2023.pdf

128 High power 2um cryogenic Silicon suspended coupled cavity progress and challenges - HOPF

Silicon with AlGaAs coatings is a promising technology for future gravitational wave detectors. There are several unanswered questions that we aim to probe in experiments at the University of Western Australia and the High Optical Power Facility. In this presentation we present measured results of birefringence in float zone Silicon test-masses and beam-splitters. We present the characterisation plan for 10cm diameter Silicon mirrors with AlGaAs coatings. We explain the design and progress that has been made towards the cryogenic Silicon suspended coupled cavity. And describe some of the major challenges we have faces along the way.

Speaker: Carl Blair (University of Western Australia)

2023_05_24-GWADW.pdf

10:30 Coffee break

High Frequency detection

Conveners: Nancy Aggarwal, Hartmut Grote (Cardiff University), Michael Tobar

129 A Gravitational Wave Detector for Post-Merger Neutron Stars: Beyond the Quantum Loss Limit of Michelson Fabry–P\'erot Interferometer

Advanced gravitational-wave detectors that have made groundbreaking discoveries are Michelson interferometers with resonating optical cavities as their arms. As light travels at a finite speed, these cavities are optimal for enhancing signals at frequencies within the bandwidth, beyond which, however, a small amount of optical loss will significantly impact the high-frequency signals. We find an elegant interferometer configuration with an ``L-resonator" as the core, significantly surpassing the loss-limited sensitivity of dual-recycled Fabry–Perot-Michelson interferometers at high frequencies. Following this concept, we provide a broadband design of a 25km detector with outstanding sensitivity between 2kHz and 4kHz. We have performed Monte-Carlo population studies of binary neutron star mergers, given the most recent merger rate from the GWTC-3 catalog and several representative neutron star equations of state. We find that the new interferometer configuration significantly outperforms other third-generation detectors by a factor of 1.7 to 4 in the signal-to-noise ratio of the post-merger signal. Assuming a detection threshold with signal-to-noise ratio $>5$ and for the cases, we have explored, the new design is the only detector that robustly achieves a detection rate of the neutron star post-merger larger than one per year, with the expected rate between $\mathcal{O}(1)$ and $\mathcal{O}(10)$ events per year.

Speaker: Teng Zhang

GWADW_TengZhang.pptx

130 Detecting high frequency (10-100KHz) gravitational waves with levitated micro disks

We will present an update on the Levitated Sensor Detector (LSD) project for detection of high frequency (10-100kHz) gravitational waves above the region previously probed by LIGO. Well motivated sources of gravitational waves in this frequency band include superradiance from QCD axion clouds around black holes and PBH mergers. The experiment will make use of optically-levitated micron-scale flat disk-likes with the advantage of reduced photon recoil heating. We discuss experimental trapping results of high aspect ratio NaYF4 hexagonal plates and our recent milestone of increasing the test mass by an order of magnitude. Finally, we examine the progress of the 1-meter prototype that is in construction at Northwestern University.

Speaker: Dr george winstone (northwestern university)

GWADW 2023 twenty minute version (1).pptx

131 Bulk Acoustic Wave cavities for high-frequency gravitational wave antennas

High frequency gravitational wave (GW) detection based on a cryogenic bulk acoustic wave (BAW) cavity has been explored for a several years now at the University of Western Australia. A recent paper reported the observation of rare events of uncertain origin with the first antenna of this kind. In this report we describe the work towards setting up a second site with a high-frequency GW antenna based on BAWs cavities at the University of Milano Bicocca, including preliminary characterization of commercially available BAW devices and plans towards the construction of an array of antennas providing wide-band sensitivity in a range from around 1 MHz to a few 10 MHz.

Speakers: Tommaso Tabarelli De Fatis (Istituto Nazionale di Fisica Nucleare), Tommaso Tabarelli de Fatis (Università di Milano Bicocca and INFN (Milan. Italy))

TabarellideFatis.pdf

TalkLaBiodola_20230525_v1.pdf

132 Superfluid Helium for Detecting Dark Matter & Gravitational Waves

Many cosmological and astrophysical observations point to the existence of ‘dark matter’ - an abundant substance of unknown origin which interacts very weakly with ordinary matter. Surprisingly, despite >$100M of investment and decades of intensive research efforts, dark matter particles have not yet been directly observed. This highlights the urgent need to develop and deploy new experimental approaches in the search for dark matter. One alternative is to use superfluid helium as a target material for dark matter collisions. To enable this capability, we must look to a separate field of research called superfluid cavity optomechanics which focuses on the optical control and measurement of phonons within superfluid helium.

Interestingly, in developing this new experimental platform for dark matter searches, we found it is also sensitive to high frequency gravitational waves. Here, I will outline the experimental configuration and approximate strain sensitivity of our proposed system, with the goal of instigating collaborations to help guide system modifications relevant to gravitational wave detection.

Speaker: Glen Harris (University of Queensland)

DarkMatterTalk_GlenHarris_GWADW.pptx

133 High Frequency detection discussion

Speakers: Hartmut Grote (Cardiff University), Nancy Aggarwal

GWADW2023_HG.pdf

12:30 Lunch break

Thermal effects simulation

Conveners: Daniel Brown (University of Adelaide), Stefan Hild (Maastricht University and Nikhef), Alessio Rocchi (Istituto Nazionale di Fisica Nucleare)

134 Working with marginally-stable dual-recycling cavities: Finesse simulations for commissioning Virgo in O4 and beyond

Speaker: Anna Green (Nikhef, VU)

VIR-0490A-23 GWADW talk 2023.pdf

135 Thermal Distortions in A+ and post-O5: What about them are bad and what is actually required for correction?

Speaker: Aidan Brooks (California Institute of Technology)

ASharp Thermal Modeling.pdf

136 Next generation Integrated package for Gravitational Wave Simulation

Speaker: Hiroaki Yamamoto (LIGO Lab / Caltech)

G2300656-GWADW2023-v7.pdf

137 Discussion on simulation tools for GW interferometers

Speakers: Alessio Rocchi (Istituto Nazionale di Fisica Nucleare), Daniel Brown (University of Adelaide)

17:30 Cheese and wine

Thursday Poster session

Friday, 26 May

Low Frequency Noise Fair

Convener: Gabriele Vajente (Caltech)

Vajente_GWADW_LF.pdf

138 Low Frequency Noise Fair

Speaker: Gabriele Vajente (Caltech)

padlet.png

Vajente_GWADW_LF.pdf

10:30 Coffee break

Squeezing, Topology, Quantum Information: Ideas for beyond 3G Part 2

Ideas for future developments, optical topologies, quantum sensing and processing

Conveners: Yanbei Chen, Shtefan Danilishin (University of Glasgow)

139 Squeezed State Amplification To Mitigate Detection Loss

Future Gravitational wave detectors will be upgraded to silicon optics and suspensions to mitigate thermal noise. Therefore the gravitational wave interferometer will operate at longer wavelengths to reduce optical absorption in silicon. At ANU we are operating a squeezed light system at a wavelength of 1984 nm designed to be suitable for injection into future GW detectors. We produce 11 dB of squeezing however the photodetector quantum efficiency limits the level of measured squeezing to 4 dB below shot noise.

An interesting alternative to high quantum efficiency photodiodes at 1984 nm would be to amplify the signal and vacuum above detector losses to preserve the signal-to-noise ratio. We model the addition of an optical parametric amplifier (OPA) after the squeezer and show realistic gains of 15 that can recover about 98% of the detection losses. The model also indicates this system is relatively insensitive to phase noise as we are looking at the anti-squeezed quadrature. The addition of an OPA at the dark port of a gravitational wave detector may also be compatible with future detector designs. We are currently designing an OPA with a lower threshold and higher nonlinear gain to test the model.

Speaker: Kar Meng Kwan (The Australian National University (Centre for Gravitational Astrophysics))

GWADW Squeezed state amplification to mitigate detection loss.pptx

140 Proof-of-principle experiment for polarization circulation speed meter

In interferometric gravitational wave detectors, quantum radiation pressure noise limits their sensitivity at low frequencies. Speed meters are one of the solutions to reduce the back-action noise. Recently, a new type of design utilizing polarization of light, the polarization circulation speed meter, has been proposed. Since this design requires only a slight modification to the conventional interferometers, it is the latest incarnation of speed meters and could be a design for the future detectors, such as Einstein Telescope. In our presentation, we review the mechanism of the polarization circulation speed meter and show details of the ongoing proof-of-principle experiment, especially how to control the speed meter interferometer.

Speaker: Yohei Nishino (The University of Tokyo)

GWADW2023.pdf

141 All-optical cascaded coherent quantum noise cancellation

Opto-mechanical sensors such as gravitational wave detectors are limited by the standard quantum limit (SQL). One way to surpass the SQL is coherent quantum-noise cancellation (CQNC). In CQNC, the quantum back-action noise from the opto-mechanical system is cancelled by an effective negative-mass oscillator (ENMO). In our approach to realising CQNC, the positive-mass oscillator and the effective negative-mass oscillator are cascaded in series all optically. Both systems can be characterised independently first.
The opto-mechanical cavity is formed by a membrane at the edge (MATE) system. For this meter system, the opto-mechanical coupling strength and other relevant parameters, such as the linewidth can be measured.
The ENMO consists of a particular two-mode squeezer where both polarisations are coupled. In this cavity, a waveplate acts as the coupling element and a type II PPKTP crystal as the down-conversion element. Here, e.g. the coupling strengths and cavity linewidths are of interest.
We present the current status of the two subsystems and give the next steps towards their combination in a CQNC experiment.

Speaker: Dr Jonas Junker (Leibniz Universität Hannover)

Jonas_Junker_GWADW_CQNC.pptx

142 A table-top experiment for implementing EPR conditional squeezing in 2nd and 3rd Generation GW detectors

During the scientific run O4, gravitational-wave detectors will attain broadband Quantum Noise reduction through Frequency-Dependent Squeezing (FDS), by coupling a 300m-long Filter Cavity (FC) to the main interferometer. This required additional infrastructure work and maintenance, and will inevitably add optical losses (~1 ppm/m).
In 3rd generation detectors, km-long FCs will be needed, due to the increased arm length.
We are currently working at the European Gravitational Observatory (EGO) on a table-top optical prototype with the aim to implement an alternative proposal to achieve FDS, without employing a FC. The core working principle of the scheme is based upon the generation of two-mode squeezing. The two beams will be EPR-entangled, and this transfers the rotation of the squeezing ellipse from a detuned idler beam to the signal beam, resonating in a small-scale interferometer. This foresees a future implementation in km-scale real detectors.
An EPR squeezer would constitute a cheaper and more compact setup, and it would allow for more flexibility than the currently used FC scheme.
This talk will illustrate the basics of EPR conditional squeezing, and then the current status of the EPR R&D experiment at EGO will be presented.

Speaker: Francesco De Marco (Sapienza University of Rome & Istituto Nazionale di Fisica Nucleare)

De-Marco_GWADW_EPR.pdf

143 Development of a signal amplification system using nonlinear optical effects for next-generation gravitational wave detectors

Optical squeezing is a well-known technique to reduce quantum noise. This technique has been implemented in actual gravitational wave detectors such as LIGO or Virgo. On the other hand, an opto-mechanical method using an optical spring generated by slightly displacing the signal recycling mirror from its resonant position, i.e. detuning, has also been investigated to increase the sensitivity of gravitational wave detectors. To improve the sensitivity of high-frequency signals, a new method has been proposed in which the optical spring is enhanced by optical parametric amplification: OPA, a kind of nonlinear optical effect, and the resonance of the optical spring amplifies the high-frequency gravitational wave signals.

The optical spring binds the suspended mirror and changes its mechanical behavior. Therefore, the signal amplification method combining OPA and optical spring can be verified by measuring the transfer function of the optical system. For this purpose, we constructed a signal recycling Michelson interferometer: SRMI, composed of a suspended mirror, and stably controlled it with a digital system. We also measured the transfer function of the SRMI and confirmed the generation of the optical spring. In addition, we realized the OPA inside the SRMI by injecting strong pump light into a nonlinear optical crystal installed inside the SRMI and performed coherent control of the OPA. In this presentation, I will report the details of these experiments.

Speaker: Mr Kaido Suzuki (Tokyo Institute of Technology)

gwadw2023kaidosuzuki最新1.pdf

12:30 Lunch break

Cryogenics

Cryogenics for future detectors

Convener: Kazuhiro Yamamoto

144 ET studies on Cryogenics and Vacuum for the Einstein Telescope detector.

We will reassert the scientific reasons for using cryogenics to increase the sensitivity of low-frequency ET, we will focus on studies related to the structure of cryogenic payload and superfluid helium cryostat, in addition to studies on cryo-pumps to be used in ET. We will conclude by presenting a brief review of cryogenic facilities under development at the various laboratories of international collaboration.

Speaker: Steffen Grohmann

230526 GWADW Overview of cryogenics in ET-LF.pdf

145 Design development of the cryogenic pumps for the low frequency interferometer of the Einstein Telescope

The Einstein Telescope (ET) is hosting interferometers to detect both low-frequency (LF) and high-frequency gravitational wave signals.
In order to reduce thermal noise, the main optics will partly be cooled to cryogenic temperatures below 20 K for ET-LF. Here, special measures are needed to mitigate frost formation on the cryogenic mirror, which is critical due to degradations of the optical performance. To allow for a system analysis of the cryogenic vacuum area, a Test Particle Monte Carlo model has been established with the KIT in-house code ProVac3D. It assesses the impinging rate of residual gas on the cryogenic mirror, depending on the particle sources and the pumping performance of the installed cryopumps. These cryopumps are a result of extensive simulations of the system and its gas sources with ProVac3D in order to fulfill the multiple pressure requirements. Besides the vacuum considerations, in a next step the heat loads on the mirror as well as on the cryopumps need to be addressed.
This paper will show a conceptual design of the ET-LF cryopumps that fulfills the requirements on vacuum pressures and monolayer formation times on the mirror. Additionally, first technical design ideas for a modular in-pipe type cryopump will be discussed.

Speaker: Katharina Battes (KIT)

Battes_GWADW2023_v1.1.pptx

146 Vacuum and cryogenic simulations for gravitational-wave interferometry

The advent of future cryogenic wave detectors pose stringent criteria on noise from residual gas. Depending on the mirror temperature, different gas species may sublimate. Furthermore, the residual gas may cause optical path length changes in the arms and cause Brownian motion. The outgassing from gas from different surfaces (cables, thermal shields, vacuum vessels depends on the temperature and history (pump time after venting). To model correctly these aspects (including enhanced Brownian motion from gas trapped between mirror and reaction mass) a simulation package has been developed that tracks thermal radiation and residual gas between all surfaces and evolves the time-dependent coupled equations that describe the local impingement rates, the heat flows and gas flows in the system.

Speaker: Henk Jan Bulten

GWADW2023_Bulten_vac.pdf

147 Radiative modeling and cryogenic design for LIGO Voyager prototype

The proposed LIGO Voyager upgrade would require novel 2-μm interferometric techniques and radiative cooling of 200 kg silicon optics to cryogenic temperatures. Efficient cooldown to 123K is contingent upon strong radiative heat transfer between test masses and cold shielding. The strength of radiative coupling is largely dependent on surface emissivities, which must be high enough to offset heating from a high-power laser and other systematic heat loads. The Mariner upgrade at the Caltech 40m interferometer aims to prototype Voyager technologies. We discuss thermal modeling of 40m silicon core optics, in order to inform optimal coating and shielding design choices for Mariner. We present an emissivity measurement setup to estimate and verify material emissivities within specification tolerances. Samples are cooled in a cryostat to 123K, and robust emissivity estimates are obtained using MCMC multi-parameter estimation. We present a preliminary cryogenic design of an ITM chamber for Mariner Phase I. This work will outline key considerations for radiative cooling of future cryogenic interferometry.

Speaker: Radhika Bhatt (LIGO Laboratory, Caltech)

GWADW_Mariner.pdf

148 Prototyping cryogenics development for ET at the Amaldi Research Center.

Einstein Telescope nominal sensitivity, below 20 Hz, implies innovative technologies associated to cryogenics and revised mechanical design for test mass suspension. It is foreseen to cool the main optics and their suspensions down to 10-20 K. The use of solid thermal conduction and pulse-tube technology appears suitable if properly designed. The reduction of technical noise is demanding and constrains the payload design. Though the performance of the existing techniques must be carefully validated in this context, significant developments must be further carried out. The heat extraction capability of pure and crystalline materials is extremely important, but to exploit it on a 1:1 scale payload, several intermediate steps must be validated and is strongly interlaced with mechanical issues.
A cryostat prototype meant to test the basic features of a full-scale cryogenic payload is under development at the Amaldi Research Center. The test mass in the payload will be dummy, but the main components involved in the heat extraction and last suspension stages will be realistic. A suitable thermal modelling is the key activity to guide the development of the cooling lines, the cryostat and, finally, the payload. FEM is being used to determine the overall design step by step, with the target of providing relevant solutions to be ported to ET-LF.

Speakers: Mr Marco Ricci (Istituto Nazionale di Fisica Nucleare), Valentina Mangano (Istituto Nazionale di Fisica Nucleare)

GWADW2023_Mangano,Ricci.pptx

149 Optical Absorption and Birefringence correlation in KAGRA Sapphire Test Masses

To reduce the impact of thermal noises in the sensitivity of gravitational wave detectors, cryogenic operation is planned for future 3G detectors such as Einstein Telescope and it is already implemented in the 2.5G detector KAGRA. To benefit from cryogenic operations, test masses substrate material needs to be changed from amorphous fused silica to crystalline material. The choice of KAGRA for the substrate of its test masses was sapphire. Crystalline materials have very different optical behavior with respect to glasses and the study and characterization of such properties is crucial to ensure the high performances necessary for gravitational wave detectors.
In this presentation, we are presenting the results on the characterization of KAGRA sapphire test masses in terms of optical absorption and birefringence and present our interpretation of a common source for both optical properties. This study, although performed solely on sapphire, has great impact on the choice and fabrication process of any crystalline material for future detectors which will make use of crystalline test masses.

Speaker: Matteo Leonardi (Università di Trento)

20230522_GWADW_MIR_animated.pdf

17:30 Coffee break

Summaries

150 Summary and discussion

Speakers: Rana Adhikari (Caltech), Marica Branchesi (Istituto Nazionale di Fisica Nucleare), Francesco Fidecaro (University of Pisa and INFN), Prof. Kentaro Somiya (Tokyo Institute of Technology), Gabriele Vajente (Caltech)

close out.pdf

151 Next year candidature

Speakers: Bram Slagmolen (The Australian National University), David McClelland (The Australian National University)

GWADW 2024 Australia bid.pdf

152 Meeting photographs

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19:30 Closeout

Saturday, 27 May

07:00 Bus departure