Reflective coatings on mirror bodies are key elements of gravitational wave detectors and are a topic of intense research in the community. Two classes of coatings are currently studied namely a broad range of amorphous compounds and a few crystalline materials. The latter group consists of AlGaAs / GaAs and AlGaP / GaP.
In this presentation, the potential of crystalline oxides coatings is...
Substrate-transferred crystalline coatings made from aluminum gallium arsenide (AlGaAs) have lower thermal noise than the ion beam sputtered amorphous oxides currently used in ground based gravitational wave detectors. AlGaAs coatings also exhibit excellent optical properties and both thermal noise and optical performance has been successfully utilized in other precision optics applications. ...
In the current development of optical coatings for high precision instruments like GW interferometers thermal Brownian noise currently pose a limiting factor on the performances obtainable. In particular in the VIRGO experiment, in the 50-300 Hz region, thermal brownian noise act as the dominant contribution.
Since the Brownian noise is commonly attributed to the existence of many local...
Mechanical loss and thermal noise from both the test mass substrates and their coatings are important factors in the sensitivity of current gravitational wave detectors The next generation of gravitational wave detector are proposed to operate at low temperatures, requiring a change in test mass material and coatings designed to work at higher wavelengths. Silicon has been proposed as an...
Cooling mirrors to cryogenic temperatures has been proposed as a strategy to improve the sensitivity of gravitational waves detectors (GWD). The effects of low temperatures on the optical response of mirrors have to be evaluated; additionally, important issues - such as the formation of an ice layer on the surface of mirrors - must be carefully studied to assess their impact on the GWD...
In this talk I will review the physical mechanisms that can lead to continuous gravitational wave emission, focusing mainly on the role of neutron stars. I will discuss which physical scenarios can be explored with continuous waves, and review recent searches by the LIGO, Virgo, KAGRA collaboration. I will show, in particular, that the sensitivity of the searches has now reached the point...
We present a multiple test for the targeted search of continuous gravitational waves from an ensemble of known pulsars, combining multidetector single pulsar statistics defined through the 5n-vector method. In order to maximize the detection probability, we describe a rank truncation method to select the most promising sources within the ensemble, based on the p-values computed for single...
The current catalog of gravitational waves (GWs) from binary black hole (BBH) mergers allows to conduct refined tests to probe the validity of the general relativity (GR) theory against alternative predictions. It has been proposed that black holes (BHs) may have exotic characteristics making them different from GR BH, such as exotic compact objects (ECOs): they would produce repeated GW...
Being arguably the most massive binary black hole merger event observed to date, GW190521 deserves special attention. The exceptionally loud ringdown of this merger makes it an ideal candidate to search for gravitational wave echoes, a proposed smoking gun for the quantum structure of black hole horizons. We perform an unprecedented multi-pronged search for echoes via two well-established and...
When it comes to gravitational wave signals, both waveform reconstruction and sky localization benefit from as broad a detector network as possible. And yet, in several instances the contribution of the Virgo detector has not been fully exploited, because the advantages are offset by the overall increase of background noise.
This is especially concerning for multi-messenger events, and it...
While the current sensitivity of the interferometers makes the detection of overlapping signals between two different gravitational waves (GWs) very unlikely, this will be quite common for the next generation of detectors: indeed, the detection rate will be high enough so that the probability to have two or more events at the same time is expected to be very high.
We present the results of...
The LIGO-Virgo-KAGRA O4 observing run will bring the amount of gravitational wave (GW) detections to an unprecedented level. The full exploitation of this opportunity will be possible if we provide innovative tools for quick data analysis using intuitive grafical user interface. In particular this approach is important in the electromagnetic follow-up decision process, as the time spent on...
KAGRA is the first Gravitational Wave (GW) detector which is located in an underground facility and operates the test masses at cryogenic temperatures. For these two major differences with respect to Advanced LIGO and Advanced Virgo, KAGRA is usually addressed as 2.5G detector and its experience will help to bridge the gap between 2G (aLIGO and AdV) and 3G detectors such as Einstein Telescope,...
Motivated by capturing putative quantum effects at the horizon scale, we model the black hole horizon as a membrane with fluctuations following a Gaussian profile. By extending the membrane paradigm at the semiclassical level, we show that the quantum nature of the black hole horizon implies partially reflective boundary conditions and a frequency-dependent reflectivity. This generically...
Since the first detection of gravitational waves (GW) in 2015 by the LIGO and VI
RGO collaborations, the scientific community has been pushing for improving GW detectors as well as the analysis methods and models for noise control. The new generation of GW detectors, LISA and Einstein Telescope (ET), is expected to be orders of magnitude more sensitive than the previous ones, especially in...
Light scattering issues specific to high performance optical components have received considerable attention over the last decade for several reasons.
Firstly, the manufacturing processes of interference filters have benefited from technological breakthroughs which today allows the routine manufacture of stacks with several hundreds of thin films on substrates with extreme polishes. Such...
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 frequencies. Modulations due to the back-scattered light appear both in phase and amplitude quadratures of the output light. It is proposed to use dual-homodyne detection to measure both quadratures and to discriminate between GW...
The interferometric detection of tiny ripples in the fabric of spacetime called gravitational waves require extreme noise sensitive operating conditions for detectors such LIGO, Virgo, KAGRA, as well as the future planned LISA and ET. One such instrument noise source is scattered light from optical components, that can induce phase noise in the output signal by recombining with the main...
A peculiar kind of stray light that can affect the performance of a squeezing-enhanced gravitational-wave interferometer is the light that travels backwards along the squeezed light injection path. After being amplified by the nonlinear process inside the optical parametric oscillator (OPO), the backscattered light eventually reaches the readout photodiode of the interferometer with a random...
In addition to the fundamental noises (quantum noise, thermal noise, and seismic noise) affecting the sensitivity of ground-based gravitational-wave interferometers, the technical noises often limit some frequency bands. A substantial part of the detector commissioning is devoted to the study and the mitigation of technical noises. Scattered light is among these noises. In this presentation,...
The LIGO Scientific, Virgo and KAGRA Collaborations recently released the third gravitational-wave transient catalog or GWTC-3, significantly expanding the number of gravitational wave (GW) signals. There are various models proposed to describe the underlying mass distribution of these compact objects using computational extensive Bayesian hierarchical models and use them to predict the...
Wavefront sensing allows for probing mode mismatch, higher order modes and thermal effects in gravitational-wave interferometers, all of which need to be well controlled as they impact the interferometer’s stability and sensitivity. The phase cameras installed at Advanced Virgo (AdV) are capable of generating amplitude and phase images of the laser beam wavefront at any beat frequency of...
The increase of the optical power expected for the new observing run (O4) will lead to an improvement of the interferometer (ITF) sensitivity with a consequently increase of the detection volume and the number of candidate sources. At this condition, the thermal distortions, induced by absorption inside the optics, degrade the ITF performance reducing the quality of the control signals and the...
On 14 September 2015, a century after the birth of General Relativity, all the scientific and technological efforts for the experimental detection of gravitational waves (GWs) found a reward. The instruments that allowed the first direct detection are second-generation GW interferometers, such as LIGO and Virgo. At present, after the conclusion of the scientific observing run O3, about 90 GW...
As straylight is a dominating limitation for the sensitivity of gravitational wave detectors, we investigate the use of tunable coherence in the form of phase modulation following a pseudo-random-sequence on the interferometer laser to break the coherence of the delayed straylight. Thereby, we aim to reduce its intrusive impact on the measurement by effectively realizing a pseudo white-light...
As part of the second phase of Advanced Virgo update program, instrumented baffles are being constructed to be installed around the end mirrors in the main FP cavities, in continuation of what has been implemented for the input mode cleaner end mirror during phase I. According to the current design, these baffles will be equipped with more than 200 photosensors, allowing for real-time...
Stray light is suspected to be a major culprit for the excess noise measured in present gravitational wave interferometers, and is projected to be even more dangerous for the next generation of instruments which will attempt to further push the sensitivity limits. Stray light originating in different areas of the detectors and through various mechanisms can impact the performance either...
In the past decades the sensitivities of gravitational wave detectors have been improved leading to the detection of more than 90 events. The detection rate should dramatically increase as the sensitivity of the interferometers improves. The LIGO/Virgo/Kagra Scientific Collaboration will increase the range and the sensitivity of gravitational wave interferometers by applying new techniques...
The LISA mission, which has been accepted by ESA as the ESA-L3 Gravitational Wave Mission, aims at measuring gravitational waves in the sub-Hz band using inter-spacecraft interferometry. LISA consists in a constellation of three satellites in triangle formation with 2.5 Gm-long arms following along an Earth-like heliocentric orbit. The target sensitivity of pm/Hz1/2 presents unprecedented...
We investigated the tilt-to-length contribution to the measure of the distance of the LISA satellites at the vertexes of the triangular constellation [1]. The aberrations of the beam wavefront have been introduced using Zernike polynomials. This greatly limited the spatial frequency of the considered aberrations and the study of local defects due to the optics traversed by the measuring beam....
Torsion-Bar Antenna (TOBA) 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 $10^{-19} \, / \sqrt{\mathrm{Hz}}$ at 0.1 Hz in low frequencies (0.1 Hz – 10 Hz). TOBA can detect intermediate mass black hole binary mergers, Newtonian noise, and so on. A prototype detector...
Quantum noise is a fundamental limit in Gravitational Waves (GW) detectors and is made up of shot noise (SN) at high frequencies (above about 100Hz) and radiation pressure noise (RPN) at lower frequencies. To reduce this noise, GW interferometers use a technique called squeezing with which we can improve only one of the contributions, while worsening the other: so far, the choice has been to...
One of the main limits of the Quantum Noise Reduction in Gravitational Wave detectors is the optical losses generated by the mismatch between the vacuum squeezed beam and the resonant cavities of the interferometer. In order to correct those aberrations, we need to be able to measure them. For this reason, different efforts have been made to develop wave-front sensing techniques to measure the...
