What is the nature of neutron stars? Where are r-process elements formed in the
Universe? Multimessenger observations of neutron star mergers might provide us
with the key to answer these and other important open questions in theoretical
astrophysics. In this talk, I will review our current theoretical understanding
of how neutron star mergers proceed and of how the dynamics is imprinted...
I will give a broad overview of the scientific targets of the Einstein Telescope in astrophysics, cosmology, and fundamental physics.
Primordial black holes form in the early universe and can give rise to mergers at high redshift. This distinctive feature can be exploited by 3G detectors to distinguish primordial binaries from the ones generated by other astrophysical formation channels. By considering a primordial black hole population compatible with current gravitational wave data, we show that 3G detectors such as the...
Gravitational wave measurements of the tidal deformability
in neutron-star binary coalescences are golden sources to infer properties of the still unknown equation of state (EoS) of dense matter above
the nuclear saturation density. In this talk I will show how, using a
Bayesian-ranking test we can quantify the ability of current and future gravitational-wave observations to discriminate...
The first direct detection of gravitational waves by the LIGO and VIRGO collaborations has opened up new avenues to explore the Universe. Currently operating and planned gravitational wave detectors mostly focus on the range below 10 kHz, where signatures from known astrophysical sources are expected to be discovered. However, based on what happens with the electromagnetic spectrum, there...
The Einstein Telescope design and R&D activities are gaining momentum and a project organisational structure is being developed and put in place. This presentation gives a brief update on the status, highlights current and future activities and opportunities for participation.
Joshua Smith and the Cosmic Explorer Team
We present an overview of the status of and plans for Cosmic Explorer (CE), the U.S. contribution to the third-generation gravitational-wave detector network. CE will observe gravitational-wave sources across the history of the universe. Sources that are barely detectable by today’s instruments will be resolved with incredible precision....
DECIGO is a future gravitational wave antenna for direct observation of primordial gravitational waves from the early universe. It will be formed by three spacecraft separated by 1,000km from each other. B-DECIGO is its precursor mission with 1/10 scale. It is still very sensitive at 0.1Hz frequency band to observe compact binaries, intermediate-mass BBHs, and GW foregrounds. In this...
The TianQin project was initiated in 2014. The goal is to launch the space-based gravitational-wave observatory around 2035 and to detect GWs in the frequency range 10-4~1 Hz. TianQin consists of three satellites on nearly identical geocentric orbits with radii of the order 105 km, forming a normal triangle constellation. In order to achieve the scientific goals, the nongravitational...
Abstract:
GW170817 was a golden event for multi-messenger astronomy made possible by gravitational wave detection. This this event allowed us to gleam an insight into short gamma-ray bursts, neutron star mergers, jet formation and topology, r-process nucleosynthesis but information about the merger and post-merger phases of the system are still unbeknown to us. A gravitational wave detector...
Upgrades in instrumentation and technology over the next five to ten years will enable the LIGO and Virgo detectors to explore gravitational-wave sources with higher fidelity and the potential to make phenomenal new discoveries. To realize its full potential gravitational-wave astronomy would require the construction of new facilities that can host increasingly improved instrumentation for a...
The Laser Interferometer Space Antenna (LISA) mission is a space-based gravitational wave detector, that consists of three spacecrafts in a triangular formation with 2.5-million-kilometer sides. The displacement sensitivity goal is approximately 10 pm/√Hz for each arm-link to detect gravitational waves in the frequency band, 100 $\mu$Hz to 1 Hz.
The proposed research introduces a novel...
The LSC has formed a working group to study scenarios for upgrading the LIGO detectors in the 2025-2035 timeframe. While the work of this group has not yet started in earnest, I will introduce the subject and make an invitation for people to give input on this topic at this workshop.
During last spring the Virgo Collaboration began an effort to define the scientific program in the decade ~ 2026-2036, which corresponds to the period between the end of the O5 data taking and a possible first Einstein Telescope data taking. This work encompasses two axes, developed in parallel: identifying the major science questions to which Virgo - in the framework of the LVK network - can...
The R&D activities on the A+ coatings are close to end. The coating recipe has to be confirmed in about 2 months and then it will be the time to optimize the coating deposition on full scale substrates. The legacy of this R&D period is full of new insights about the origin of thermal noise in coatings, less numerous are the insights on the origin of absorption in amorphous materials, but,...
Crystalline mirror coatings of epitaxially-grown GaAs/AlGaAs are a most promising option for LIGO’s Post-O5 upgrade. With extremely low optical losses and a coating thermal noise that is more than 5x lower that Advanced LIGO coatings, these crystalline coatings represent the most significant improvement in coatings research in the past 20 years. The change from amorphous to crystalline...
One of the keys of interferometric gravitational wave detector projects is to make improvement plan for future. In KAGRA collaborations, we discuss the plan of KAGRA+, which is the next step. The white paper was released on August 2019, just after the previous GWADW. I explain the history and conclusion of this white paper briefly.
The observation of gravitational waves is highly influenced by the detectors sensitivity, that is limited at low frequencies (10 -100 Hz) by the thermal noise. For this reason, the monolithic suspensions are one of the most important upgrades of the interferometric detectors including Advanced Ligo (aLigo) and Advanced Virgo (AdV). The target sensitivity for the new updates of Advanced Virgo...
The target sensitivity of Advanced Virgo for O4 is about 90-120 Mpc for the BNS range. To achieve this, several hardware upgrades are under process. One of the most relevant concerns the installation of the Signal Recycling Mirror. I will describe the procedure followed for locking the Dual Recycled Michelson Interferometer along with the tuning of CO_2 central heating, which assists the lock...
In this talk I will give an overview of the currently ongoing seismic characterisation of the Sos Enattos area, the proposed first corner site for ET in Sardinia. In 2019 we started an extensive measurement campaign proving the low environmental noise features of the area. Several measurement stations are installed at surface and at the different depths along the former mine tunnels. New...
The Sar-Grav Laboratory is a seed of the third generation of gravitational wave interferometer: Einstein Telescope. The infrastructure is located beside the Sos Enattos mine in Lula (Nuoro, Sardinia). The region is characterized by a very low seismic and anthropogenic noise therefore, Sar-Grav aims to host underground experiments like low seismic noise experiments, cryogenic payloads, low...
The LIGO Voyager upgrade is designed to maximize the reach of the existing observatory facilities, with radiatively-cooled silicon optics and coatings that enable high-power cryogenic interferometry. I will discuss the ongoing project to realize this design at the 40 m Lab.
Using the optical coating facility at the ANU we will concentrate towards low-loss optical coatings for large scale optics used in gravitational wave detectors. The work is focused on the near-term needs and long-term requirements, either for 1 um or 2 um optical wavelengths. Also work on 2 um optical squeezing generation and its control is underway. A low-frequency gravitational-force sensor...
Next generation surface-based gravitational wave detectors will have increased arm-length of up to 40 km. Due to the earth’s curvature 30 m deep trenches or tunnels are required for a straight laser beam to reach the end-stations. Locations with minimal soil digging and filling could help reduce the construction cost. We use digital elevation data to find such optimal locations, in the USA,...
In this talk we present the plans in Glasgow to upgrade or 10m interferometer into a cryogenic facility. The facility will utilise a single 10m reference cavity based on suspended fused silica optics, and a pair of Leidon cryocoolers for a short cryogenic reference cavity. The facility is aimed to be a fast turnaround system with studies focussing on ice growth on optics, monitoring cryogenic...
An overall feasibility study is carried out in Sardinia as one of potential site for the construction of the Einstein Telescope (ET), a third-generation gravitational wave underground observatory.
In order to optimize the location of the corner points of the tunnels hosting the interferometer a technical feasibility study is performed, also including cost-benefit analyses.
A 3D modeling of...
The SAR-GRAV underground laboratory is located in SOS-ENATTOS mine area (Lula Mining District, Sardinia) and was designed to host small-to-medium-sized experiments, intended as individual experiments of fundamental physics and geophysics, and prototypes of equipment for larger experiments, such as future gravitational wave detectors. The laboratory, which will host the ARCHIMEDE experiment...
To realize the design sensitivity of Advanced LIGO+, about a factor of two in coating thermal noise reduction is required. For ET-HF and the initial Cosmic Explorer design very similar coating thermal noise levels are assumed. Another requirement on the highly-reflective mirror coatings is low optical absorption of <1ppm which is challenging to meet.
Multimaterial designs allow for a...
In this talk we present a summary of the mitigation strategies followed up in the current LIGO/Virgo experimental setups, together with the related studies carried out to determine the residual noise budget, potentially affecting the GW signals. We conclude with some indications of potential improvements in preparation for 3rd generation experiments.
A cryogenic mechanical loss measurement setup built at Stanford University can operate from room temperature down to at least 12K. The experimental method described is based on actuation of a Si oscillator and measurement of its quality factor (Q-factor). The film’s mechanical loss can be obtained using the Q-factors of coated and uncoated resonators. Experimental results obtained for several...
We here discuss our preliminary findings regarding laser microsctructuring and high-absorption coatings as a potential choice for surface treatments in gravitational wave telescopes for scattered light reduction.
SiN has emerged as one of the most promising materials for the next-generation optical coatings in the mirrors of GW detectors. Optical absorption is currently one of the most critical parameters affecting the performances of SiN films, as a very low absorption is required for GW applications; optical absorption may arise from a variety of causes, including non-ideal stoichiometry and...
The problem of back-scattered light is a major issue at low frequencies and must be tackled to make ET sensitive down to 2 Hz. Back-scatter arises as DC light, either by well-defined light paths due to the design of the optics, by diffraction of the tails of these light paths or imperfect surfaces of the test masses. Diverted out of the main modes and scattered back by modulated surfaces, it...
Silicon nitride (SiNx) is a well-known coating material, with a relatively high refractive index and very low mechanical loss. In this talk, we will present the development history of ion-beam sputtered amorphous SiNx coatings for gravitational-wave detectors at the Laboratoire des Matériaux Avancés (LMA-IP2I). As this research and development activity is still ongoing to date, we will present...
Brownian noise in the current second generator detectors is limited by the internal mechanical energy dissipation of the high index material composing the dielectric reflector stack. One promising alternative to the currently used titania-doped tantala is a mixture of titania and germania. We report here the status of the research on this new material, estimates of the achievable improvements...
Surface roughness of optics and dust contamination are two main sources of stray light in advanced GW detectors: stray light can not only contribute extra noise if it recouples to the main beam when reflected by vibrating surfaces, but can also spoil the control signals of the interferometer.
Given the extremely low roughness of the optics employed, dust contamination is critical as it can...
Cosmic Explorer requires an unprecedented level of isolation from the ground and from thermal noise. If we want to reach the design sensitivity of $10\rm^{-23} Hz^{-1/2}$ down to 5Hz, scaling up the LIGO A+ technology might not be enough, and new designs, as well as new technologies, need to be investigated.
One possibility is Cosmic Explorer 2, or CE2, which either uses a $\rm 1\mu m$ laser...
Third generation gravitational-wave observatories extend their detection bands down to several Hertz. Enhancing sensitivity in this frequency regime will uncover higher mass black hole binaries, and provide earlier identification of multi-messenger astronomy events. Reaching astronomically relevant sensitivities, at these frequencies, requires overcoming technical and fundamental noise...
Radiative cooling is a contact-free cooling technique that allows cooling of 100kg scale mirrors to cryogenic temperatures. However, future optomechanical applications require lightweight mirrors, for which radiative cooling is inefficient. In this talk, I will present optical refrigeration as a low-vibration cooling method for a phase-sensitive optomechanical amplifier, proposed to improve...
Torsion-bar antenna (TOBA) is a ground-based gravity gradiometer proposed for measurement of gravity gradient fluctuations such as gravitational waves and gravity gradient noise. TOBA consists of two perpendicular torsion pendulum, and the low mechanical resonant frequency of torsion pendulums enables us to measure gravity gradient of frequencies around 0.1 Hz. TOBA aims to achieve the...
We present our theoretical calculations of the effective emissivity for the LIGO Voyager test masses. Once Si at 123 K is a semi-transparent material, the emissivity depends on the mean thickness and the absorption, both calculation is also shown in this presentation. Finally, we present our recent resuts using internal reflexions for the mean thickness calculations.
A laser strainmeter measures deformation of the ground by sensing distance between two separated points based on the optical interferometer with reference to wavelength of light. To monitor accurate ground deformations and broadband ground motions, a long-baseline laser strainmeter (geophysics interferometer, GIF) was constructed in the KAGRA tunnel and it has been in operation since then.
We review the current effort for driving the design of the Cryoneic and vacuum system foer the Einstein Telescope Project.
With the need to move to 3rd generation cryogenically cooled detectors, work is ongoing at Glasgow to investigate design, bonding and characterisation of silicon suspensions operating at cryogenic temperatures. Here we present an update on these activities, including details of initial cooling experiments conducted on a silicon ribbon suspending a 1kg mass.
The scientific target of cooling-down test mass payloads of ET without affecting the capability of reaching very high sensitivity in the low frequency range is often assessed as achievable. Indeed, relevant developments have still to be pursued with the perspective of a reasonable technical design. Moreover, the overall design of cryostats and its technical facets are interlaced with several...
The low-frequency interferometer in the Einstein Telescope (ET-LF) shall be operated at test mass temperatures of 10 K to 20 K. Motivated by the potential of using superfluid helium (He-II) for cooling the test masses, we derive a general cooling concept for the ET-LF cryostats. This concept is based on a helium refrigerator at each ET corner station, providing cooling ...
The second-generation gravitational wave detectors are starting to be limited by quantum noise in the entire detection bandwidth. With the use of frequency independent squeezing, aLIGO and Advanced Virgo achieved a quantum noise reduction at high frequency while increasing it at low frequency. To avoid this issue, we can inject into the interferometer a squeezed state which rotates as a...
The injection of phase-squeezed vacuum states, in ground based gravitational wave detectors, already demonstrated its efficiency during the last observative run by reducing quantum noise of about 3 dB, above 100 Hz. At this stage, the consequent increase of quantum noise below this frequency, due to the anti-squeezed amplitude quadrature, did not affect the detector sensitivity, being this...
For broadband quantum noise reduction of gravitational-wave detectors, frequency-dependent squeezed vacuum states realized using a filter cavity is a mature technique and will be implemented in Advanced LIGO and Advanced Virgo from the fourth observing run. To obtain the benefit of frequency-dependent squeezing, length and alignment of the filter cavity with respect to squeezed vacuum states...
The fundamental requirement for the angular sensing and control (ASC) scheme is to suppress the angular mirror motion at low frequencies, to overcome radiation pressure induced angular instabilities, without reintroducing noise in the GW signal. In the process of controlling test masses' angular motion at low frequencies, high-frequency noise is introduced in the observation band originating...
Squeezed light is critical in gravitational-wave detection for reaching sensitivities below the standard quantum limit. The success of future detectors will rely on achieving far greater squeezing levels, with an ultimate goal of 10 dB of quantum noise reduction. Even as squeezer technology matures, the internal losses of current detectors remain too large to support such high levels of...
The alignment control systems of gravitational wave interferometers extensively rely on heterodyne imaging techniques to sense various length & misalignment degrees of freedom. This is achieved via demodulating the beat of various radio-frequency sidebands measured on single and quadrant element photo-diodes. Such a technique offers very high bandwidth sensing but is limited to resolutions of...
LISA is a constellation of three spacecraft exchanging laser beams on a 2.5 Mkm triangle. The GW measurement exploits heterodyne interferometric phase measurements of the distance between distant optical benches, with additional interferometers measuring the test mass to optical bench movement, and the optical phase difference of the two lasers onboard the same spacecraft. Stray light (SL) can...
The Gentle Nodal Suspension (GeNS) has become the most common technique for measuring coating mechanical dissipation, showing an unprecedented result repeatability on disk shaped substrates. GeNS gives the possibilities to perform measurement so accurate that it is possible to follow even tiny changes in the sample mechanical behavior. The high level of sensitivity makes some new systematic...
In this talk, we will introduce several aspects of stray-light control in the KAGRA interferometer. The stray light to be controlled include ghost beams and scattered light produced at optics and mechanical structures in the interferometer and recombined somehow back into the main beam path. These unwanted lights could become critical noise in the end. Although the stray-light noise can be...
The high reflective mirrors of the gravitational waves detector LIGO & Virgo present in the coating many micrometer size defects that scattered the light in the interferometer. This scattered light induces a loss of the laser power of the order of a few tens of parts per million (ppm) and a phase noise because of the recombination with the main beam after reflection on the tube walls. This...
The observational horizon of interferometric gravitational wave (GW) detectors is limited by thermal noise in the coating at mid-range frequency, where first GW signals have been detected and many others are expected. The main responsible are the intrinsic dissipations, intimately linked to the inelastic behaviour of the amorphous coating materials. This behaviour is generally explained by the...
Noise from laser backscattering and spurious beam couplings has been an important limitation in first and second generation detectors. In this talk we discuss the on-going design and experimental work for Cosmic Explorer, focusing on the modeling of light scattered by the mirror surface roughness, point defects and noise due to light scattered and diffracted/clipped by the arm cavity baffles.
GW detector highly reflective coatings are obtained by alternate layers of material with different refractive indexes. Brownian thermal noise associated with the coating stack, limits the mid-frequency region of the GW detector designed sensitivity. Thermal noise reduction can be achieved minimizing the overall thickness of the stack, increasing the refractive index contrast . Fluoride’s...
For the O5 run of LIGO, it is planned to make a change to the detection scheme, operating with balanced homodyne detection. This involves the introduction of a local oscillator beam derived from the power recycling cavity, to be re-combined with the signal beam from the interferometer in the detection chamber. The layout of the detection chamber has been re-designed to accommodate dual output...
The structure of ternary coatings featuring minimum thermal (Brownian) noise under prescribed transmittance and absorbance constraints is investigated and found to consist of a few tapered quasi-Bragg triplets on top of an almost fixed-thickness stack of wuasi Bragg doublets using the highest contrast material pair.
The noise reduction of coatings based on aSi, TiO2::Ta2O5 and SiO2 as well as...
Substrate-transferred crystalline coatings have demonstrated low thermal noise and excellent optical properties in multiple precision optics applications. The primary challenge in implementing these single-crystal gallium arsenide / aluminum gallium arsenide multilayers in terrestrial interferometric gravitational-wave detectors is the necessity to scale the size of the coatings to ≥ 30 cm in...
Accumulated charge on vacuum mirrors can cause degradation of the signal-to-noise ratio in opto-mechanical measurements due to electrostatic coupling of the surface charge to the environment. A conductive film with minimal optical absorption and scattering can dissipate the charge without altering the optical performance of high reflectivity mirrors. We present Aluminum doped ZnO coatings...
The event rate of current observatories is partially limited by noise arising from temperature-driven position fluctuations of the test mass mirror surfaces used for probing space time dynamics.
Future gravitational-wave observatories address this limitation by using cryogenically cooled test masses;
current approaches for continuously removing heat (resulting from absorbed laser light) rely...
Nowadays, sensors' resolution limits their performance at low frequency which reduces their operating range. Sensors with a good resolution at low frequency are required to improve the performance of gravitational wave detectors in the sub-Hz frequency range. We are currently developing an inertial sensor with a sufficient resolution at low frequency from 10 mHz to 100 Hz. We are focusing on...
Ground based gravitational wave detectors are limited at low frequencies by seismic noise and other related technical noise sources.
In order to overcome these limitations, we study the use of interferometry based, local displacement sensors as part of the active seismic noise mitigation at the pendulum-suspensions of these detectors.
Our idea is to use so called “Deep-Frequency-modulated”...
The Laser Interferometer Space Antenna (LISA) will be the first space-based gravitational wave observatory. LISA is a high precision interferometer in space with an arm length of 2.5 million km. The optical benches are made by bonding silicate glass components to an ultra-low-expansion glass ceramic which does not allow rearrangements of the optical components. Since the development,...
Thermal noise of the test masses is one of the limiting noise sources in Advanced detectors. It is expected to remain a limiting noise source in future detectors, despite radical changes to the design including cryogenic operations, new materials and the use of longer laser wavelengths. We will discuss progress towards verifying higher-order Hermite-Gauss laser modes as possible alternative or...
GW170817 opened a new era of the observation of the Universe through the multi-messenger astronomy. The full exploitation of this new era will pass through the realisation of innovative tools, possibly compliant with the FAIR principles, allowing the efficient exchange of essential information between the different partners in a multi-messenger observation. Present and future gravitational...
For ground-based GW detectors, seismic vibration is the dominating source of noise in low frequency region (0.1 to 10 Hz), limiting both sensitivity and duty cycle. Thanks to high performant suspension systems, like the Virgo Superattenuator, the presently operational 2nd generation advanced GW antennas have extended their detection band down to 10 Hz. The plan for future 3rd generation...
Massive halo compact astrophysical objects (MACHOs) are a potential candidate of dark matter, the presence of which in the interstellar medium can cause deflection of gravitational waves (GWs), a phenomenon called gravitational lensing. If we do not find any lensing signature in the LIGO-Virgo data of gravitational waves, we can put an upper cut-off on their abundance in the mass range of...
Improving the sensitivity of existing and future ground-based gravitational-wave detectors will enable us to detect more astronomical sources with higher precision. As the gravitational-wave signals are strong and present for a longer time in the low-frequency regime, it would be beneficial to extend the current sensitivities to lower frequencies (< 10Hz). However, seismic noise coupling into...
The Laboratory of Space Systems and Optomechanics (LASSO) at Texas A&M University is working to create novel, highly sensitive inertial sensors by combining our fused-silica optomechanical resonators with compact, high-precision interferometers. Our resonators have high mechanical quality factors and low thermal acceleration noise. Q’s of 2.45 x 10^5 were previously achieved at mTorr...
TOBA (TOrsion-Bar Antenna) is a ground-based gravitational wave detector using a torsion pendulum. The resonant frequency of torsional motion is ~1 mHz, therefore TOBA has good design sensitivity of $10^{-19}$ /√Hz at 0.1 Hz in low frequencies (0.1 Hz – 10 Hz). TOBA can detect intermediate mass black hole binary mergers and so on. A prototype detector Phase-III TOBA with a 35 cm-scale pendulum...
To detect gravitational waves at frequencies below 30Hz the low-frequency sensitivity of the current observatories must be improved and, in the case of LIGO, this is caused by control noise from a mixture of sources. To facilitate this improvement in sensitivity, new seismic and suspension sensors are required. This poster outlines the development of these new sensors that can be applied to...
Tilt coupling is one of the limiting factors for the low-frequency sensitivity of gravitational-wave detectors. Implementing inertial seismic isolation of the suspension platform in all 6 DoF makes it quiet in all degrees of freedom simultaneously and minimises coupling of all DoF to interferometer length. In this poster, we discuss the potential improvement in the sensitivity of GW detectors...
A dual-pass differential Fabry–Perot interferometer (DPDFPI) is one candidate of the interferometer configurations utilized in future Fabry–Perot type space gravitational wave antennas, such as Deci-hertz Interferometer Gravitational wave Observatory (DECIGO) and B-DECIGO. In this poster, the working principle of the DPDFPI has been investigated and necessity to adjust the absolute length of...
Gravitational-wave interferometric detectors have many internal seismic platforms to support the various suspended optics. For future detectors, the relative motion of these seismic platforms, via coupling to the auxiliary length controls of the suspended optics, are predicted to be the limiting noise source at low frequencies below 1 Hz. By measuring, then stabilizing the relative motion...
Multi-fringe capable, compact laser interferomters are studied as sensors for displacement sensing of suspended test masses and inertial sensors in future ground-based detectors to improve their low-frequency noise. We are investigating such a sensor, or optical head, design that uses a quasi-monolithic component and deep-frequency modulation interferometry to enable sub-picometer level...
The Einstein Telescope will have Michelson interferometers with Fabry-Perot cavities in the two arms. They will need the widest possible stored beams to reduce thermal noise, using mirror test masses with diameter at the limit of technical feasibility. Recombining those wide beams into the beam splitter would be challenging in any case. Unlike other detectors, the Einstein Telescope will...
The Glasgow Cryogenic Interferometer Facility will be a double cavity cryogenic interferometer prototype with suspended silicon optics which will allow the testing of future technologies required for 3rd generation detectors. This poster discusses the modelling of one of the room temperature steering suspensions which will be used at this facility.
There are many astrophysical scenarios where extreme mass ratio inspiral (EMRI) binaries can be surrounded by matter (esp. dark matter) distribution. The mass distribution can affect the dynamical properties (e.g. orbital frequency, orbital velocity, etc.) and the rate of energy radiation from the EMRI. We assume a power law dependency of mass distribution density on the radial distance from...
LIGO and Virgo have detected more than 70 signals from black hole and/or neutron star mergers. All measured signals come in-band at around 30 Hz as suspension control noise, fueled by many cross couplings between angular and translational degrees of freedom, is dominant below 30 Hz. It is impossible to know, but exciting to imagine what signals are lurking there once we can access this...
Cosmic Explorer (CE) is the US concept for a next-generation ground-based gravitational-wave observatory. CE will have the ability to determine the nature of the densest matter in the universe, reveal binary black hole (BH) populations throughout cosmic time, probe the history of the expanding universe, and explore Einstein’s relativity with unprecedented precision. Sources that are barely...
Ground-based interferometric gravitational wave detectors at LIGO are complex instruments that need to be in light resonance or 'locked' in order to take data and make astronomical observations. The 'lock' is maintained by a series of control loops which can be disturbed by systematic or environmental factors. Multiple detectors need to be simultaneously in lock to triangulate the sky location...
The science goals of ET rely on achieving astrophysically interesting sensitivity below 5Hz. This presents an enormous technical challenge, and it was a major focus of the recent ET Instrument Science Board workshop. The question is broken down into several parts: we looked at the key noise-drivers in current detectors and attempt to identify strategies to mitigate them by design in ET. This...
Condensation on the surface of the main mirror and the viewport for oplev of the radiation shield is a serious problem at the cryogenic gravitational wave telescopes, KAGRA. In order to find a way to cool the main mirror down to the required temperature (~20 K) while preventing condensation, cryo-group of KAGRA conducted a cooling experiment of the main mirror using the a KAGRA cryostat.
In...
The cryogenic mirror is a direct way to reduce thermal noise. To cool the mirror at cryogenic temperature, the conductive cooling with heat links is necessary, however, they become a new path of vibration transfer simultaneously. We have newly developed a vibration isolation system for heat links and successfully reduced vibration transfer. Details of design and performance tests will be reported.
On April 6 & 7, 2021, the LSC held a workshop focused on the low frequency (<30 Hz) performance of the Advanced LIGO detectors, the sources of the excess noise, and various approaches to improve the noise. In this talk, I will review a few key points which were presented and then discuss the recommendations which were made in the Workshop Report, L2100055.
In the future cryogenic gravitational-wave detectors such as the ET and LIGO Voyager, a molecular layer formed on the cryogenic mirror surface can become one of the problems due to its optical loss. We theoretically estimated the optical loss induced by the molecular layer and revealed that the optical absorption induced by the molecular layer. In addition, we developed 10 K folded optical...
The third generation GW detectors has to provide an unprecedented sensitivity, this requires a careful study on all the intereferometer defects that could spoil its performance. For this reason in order to face this challenge, one of the starting points is to establish the RMS requirements that will allow reaching the target sensitivity. This work is focused on the requirements referring to...
One of the key enabling technologies in the third generation laser-interferometer GW detectors is the cryogenic system required for cooling the main optics to 10 – 20K. Accounting for the extreme sensitivity that is targeted, it is of paramount importance that the cryogenic cooling under continuous operation is essentially vibration free. Joule-Thomson cryocoolers using sorption compressors...
In high frequency band, the quantum sensitivity is ultimately limited by the optical losses in signal recycling cavity (SRC). The sensitivity limit is independent of the arm length and the squeezing level, which constraints our ability to detect signals from binary neutron star mergers. By creating a cavity with two ETMs of the arm cavities, we can form a sloshing-Sagnac interferometer. It...
Back-scattered light results in parasitic modulations of the output light of gravitational-wave observatories. It constitutes a major noise source at low audio-band and sub-audio-band frequencies. Whereas gravitational-wave (GW) signals exclusively appear as amplitude modulations of the output light, modulations due to back-scattered light in general also have projections onto the phase...
White light signal enhancement using an optomechanical negative dispersion systems show promise to dramatically increase the sensitivity bandwidth of gravitational wave detectors. At the University of Western Australia three promising mechanical resonators are being designed and investigated. Demonstrated properties of a phononic metamaterial device have been shown in simulation to increase...
Broadband suppression of both shot noise and backaction noise in the GW interferometer can be achieved by adding an auxiliary table-top setup with a room temperature gas cell in magnetic field as the central element [1,2]. The basic idea is the measurement of motion beyond SQL using an atomic spin as a “negative mass oscillator”. The idea has been recently experimentally demonstrated for a...
We propose a new method beyond the standard quantum limit using an optical parametric amplification (OPA) in a signal recycling cavity (SRC) for the next generation gravitational-wave detector. This method has the advantage of improving the detection sensitivity in a high-frequency band. The OPA technique with a nonlinear crystal realizes a stiff optical spring without increasing the...
The levitated-sensor detector aims to look for gravitational waves (GW) in the frequency range from 10 kHz to 300 kHz. Since it is based on a resonant interaction between the GW and the levitated particle, it can have a significantly smaller footprint than the kilometer-scale detectors, inspring the first generation detector to be tabletop! I will explain the latest design modifications that...
Heating elements surrounding the core optics of Gravitational Wave Interferometer are used to correct the radius of curvature of the high reflectivity surface that can deviate from the nominal value because of manufacturing defects and the non-zero absorption of the laser power in the substrate and in the coatings of the test masses. The typical actuation time of these actuators (usually...
The Einstein Telescope (ET) is a third generation gravitational wave observatory, currently in the planning stage in Europe. The ET project involves the construction of a triangular shape underground facility with 10 kilometres long arms buried in ca. 250 m depth. At the corner points, large caverns host the required infrastructure. The border region between the Netherlands, Belgium and...
In the design studies of the next-generation gravitational wave detectors, coating Brownian thermal noise is a major noise contribution at frequencies around 100Hz. One proposed method to mitigate this noise source is to use a higher-order laser mode instead of the currently used fundamental Gaussian mode because their more uniform intensity distributions could average better over the mirror...
Cryogenic gravitational wave detectors are planned to be significantly more sensitive than current room temperature detectors. Cryogenic detection relies on materials that have low mechanical loss and Brownian noise at low temperatures, ruling out the use of the fused silica mirrors currently used. Silicon is proposed as a cryogenic mirror substrate due to its excellent mechanical loss and...
The four sapphire mirrors in KAGRA will be cooled down to 20K to reduce thermal noise. We selected substrates with the lowest thermal absorption for the input mirrors. As for birefringence, we conducted an X-ray analysis to determine the direction of the crystal axis so that the effect of birefringence on to the laser beam is negligible. However, when we operated the interferometer with the...
The Einstein Telescope (ET) is an advanced, third generation gravitational wave observatory, currently in the planning stage in Europe. The ET project involves construction of a triangular shape underground facility with 10 kilometres long arms. The border region between the Netherlands, Belgium and Germany is considered as a potential location and will be further investigated in a feasibility...
The wavelength of 2um is a candidate for the next generation gravitational-wave detectors such as LIGO Voyager and Einstein Telescope. Although the technical leap of the wavelength change impacts almost all the optical components of laser interferometry, only a few investigations have been ongoing. This poster will present the R&D experiments planned in the Gravitational Exploration Institute,...
All gravitational-wave observatories (GWOs) have been using the laser wavelength of 1064 nm. Ultra-stable laser devices are at the sites of GEO 600, Kagra, LIGO and Virgo. Since 2019, not only GEO 600 but also LIGO and Virgo have been using separate devices for squeezing the uncertainty of the light, so-called squeeze lasers. The sensitivities of future GWOs will strongly gain from reducing...
Cryogenic suspensions are subjected to a number of conflicting requirements.
An idea replacing the suspension fibers with massive beams is presented here to suspend the mirrors while attempting to solve these constraints.
The powerful beams stored in the Fabry Perot cavities of gravitational wave detectors deposit heat on the mirror coatings and cause thermal lensing. We present an experiment that studies the feasibility to balance that excess heat by selectively absorbing the black body heat that at ambient temperature naturally radiates from the test masses. It is shown how the coating heating effect can be...
Gravitational forces that oscillate at audio-band frequencies are measured with masses suspended as pendulums that have resonance frequencies even lower.
If the pendulum is excited by thermal energy or by seismic motion of the environment, the measurement sensitivity is reduced.
Conventionally, this problem is mitigated by seismic isolation and linear damping, potentially combined with...
A factor of two in coating thermal noise reduction is required to achieve the design sensitivity of Advanced LIGO+. For ET-HF and the initial Cosmic Explorer design very similar coating thermal noise levels are assumed. Low optical absorption of the coatings of <1ppm is also required, but challenging to meet.
Multimaterial designs allow for a trade-off between thermal noise and absorption,...
As improvements to the current gravitational wave detector network are implemented, and as new detectors are added to the network, any new mirror coating designs must overcome the twofold challenge of producing sufficiently lower thermal noise perfomance, as well as maintaining a low level of optical absorption. Here we present an update on our research into characterizing the room...
Advanced gravitational waves detectors revealed until now a significant number of signals from the mergers of compact objects with amplitudes of the order of 10^(-21)-10^(-22). The necessity to increase the detection volume and the number of candidate sources requires an improvement of the sensitivity of the interferometers (ITF). For this purpose, an increase of laser power in the ITF and...
Advanced gravitational-wave detectors require low-loss Faraday isolators in the squeezer path, in order to maximize the benefits of the squeezed light injection. The University of Florida and Montclair State University have developed and are currently building two designs of low-loss Faraday isolators for the A+ upgrade, one output Faraday isolator (20 mm clear aperture) and two squeezer...
Gravitational wave detectors impose extremely stringent requirements for the optical and mechanical properties of their mirrors. Research in new coating material focuses on minimizing mechanical losses which directly relate to the coating thermal noise. At the same time, absorption and scattering losses need to be kept at extremely low levels, since they strongly affect the operation and...
While gravitational waves are regularly detected in several gravitational wave detectors globally, the research endeavors to improve the sensitivity of these detectors continues. Low mechanical loss and low optical absorption are key requirements of future coatings. Amorphous silicon has very low loss but relatively high absorption at the relevant wavelengths. Crystalline silicon also has low...
Authors: V. Spagnuolo, S. Gouvalas, I.W. Martin, G. McGhee, P. Murray, S. Tait, C. Clark, S. Hild, and J. Steinlechner
For current gravitational wave interferometers, the limit in sensitivity at their most sensitive frequencies originates from the combination of thermal noise and quantum noise. The main contribution to the thermal noise arises from the Brownian motion of high reflectivity...
Suspension thermal noise is a significant noise source for torsion pendulums. Two ways to reduce it is to utilize cryogenic temperatures and crystalline fibres. We record our progress here in utilising both in tandem to achieve low suspension noise levels, with an eye on achieving high Q for use in TOrsion Bar Antenna (TOBA), a proposed gravitational wave detector aimed at 0.1-10 Hz
Future gravitational wave detectors plan to operate at cryogenic temperatures using crystalline silicon test masses which are transparent at higher wavelengths of light. Here we present measurements of a multi-material coating design that uses layers of ion-plated tantala, silica and amorphous silicon to reduce coating thermal noise and produce low optical absorption at low temperatures. Here...
Thermo-optic noise is one of the possible sources of coating thermal noise that affects precision optical measurements, such as gravitational-wave detectors. A lot of effort is dedicated to identify coatings with low Brownian noise, but also coating thermo-optic noise should be considered as a possible limiting noise source for the next generation of GWDs mirrors. SiNx is one of the most...
A signal-recycling Michaelson interferometer with an optical parametric amplification (OPA) has a large potential for a high-frequency gravitational-wave detection. The OPA using a nonlinear crystal in the signal-recycling cavity amplifies the signal and makes a stiff optical spring. A number of degrees of freedom need to be controlled to stabilize the system. Using a digital signal-processing...
The sensitivity of second-generation gravitational-wave detectors is limited in the low frequency region by Newtonian noise. Noise cancellation using Wiener filters has been shown to mitigate the effects of seismic Newtonian noise. This involves placing an array of seismometers around the test mass to monitor the ground fluctuations. Optimal positioning of the seismometers around the test mass...
In interferometric gravitational wave detectors, thermal noise from the mirrors, originating from mechanical dissipation in the coating films, represents the major limitation to sensitivity. Significant experimental effort has led to improvements during these years and currently the most advanced technology is the one of amorphous coatings. Yet, there is still a lack of understanding of the...
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