arXiv subjects

J. Degallaix

Publications and source records attributed to J. Degallaix.

17 recordsLinked to original sources

arXiv2026

Mirror Surface Evaluation for the Einstein Telescope Using Virtual Mirror Maps

The performance of mirrors in optical interferometers is critically influenced by their surface quality. Accurate metrology enables mirror surfaces to be characterized through phase maps describing their three-dimensional structure after coating. In this work, we combine Zernike polynomial decomposition and spatial frequency (PSD) analysis with numerical optical simulations to quantify the impact of surface distortions on the reflected optical field. The method is validated using metrology data from mirrors currently installed in the Advanced Virgo gravitational-wave detector. Building on this validation, we introduce a framework for generating realistic virtual mirror maps that reproduce both low order aberrations and high spatial frequency content of measured surfaces. These virtual maps are used in optical simulations to systematically explore and compare candidate surface quality specifications for future detectors, with particular focus on the Einstein Telescope. Our results show that metrology-informed virtual mirrors provide a practical design tool to assess the impact of different surface specifications on optical performance, and to relate future requirements to the performance of existing interferometers.

physics.optics↗

arXiv2025

Development of ion-beam sputtered silicon nitride thin films for low-noise mirror coatings of gravitational-wave detectors

Brownian thermal noise of thin-film coatings is a fundamental limit for high-precision experiments based on optical resonators such as gravitational-wave interferometers. Here we present the results of a research activity aiming to develop lower-noise ion-beam sputtered silicon nitride thin films compliant with the very stringent requirements on optical loss of gravitational-wave interferometers. In order to test the hypothesis of a correlation between the synthesis conditions of the films and their elemental composition and optical and mechanical properties, we varied the voltage, current intensity and composition of the sputtering ion beam, and we performed a broad campaign of characterizations. While the refractive index was found to monotonically depend on the beam voltage and linearly vary with the N/Si ratio, the optical absorption appeared to be strongly sensitive to other factors, as yet unidentified. However, by systematically varying the deposition parameters, an optimal working point was found. Thus we show that the loss angle and extinction coefficient of our thin films can be as low as $(1.0 \pm 0.1) \times 10^{-4}$ rad at $\sim$2.8 kHz and $(6.4 \pm 0.2) \times 10^{-6}$ at 1064 nm, respectively, after thermal treatment at 900 $^{\circ}$C. To the best of our knowledge, such loss angle value is the lowest ever measured on this class of thin films. We then used our silicon nitride thin films to design and produce a multi-material mirror coating showing a thermal noise amplitude of $(10.3 \pm 0.2) \times 10^{-18}$ m Hz$^{-1/2}$ at 100 Hz, which is 25\% lower than in current mirror coatings of the Advanced LIGO and Advanced Virgo interferometers, and an optical absorption as low as $(1.6 \pm 0.5)$ parts per million at 1064 nm.

physics.ins-det↗

arXiv2021

Exploration of co-sputtered Ta$_2$O$_5$-ZrO$_2$ thin films for gravitational-wave detectors

We report on the development and extensive characterization of co-sputtered tantala-zirconia thin films, with the goal to decrease coating Brownian noise in present and future gravitational-wave detectors. We tested a variety of sputtering processes of different energies and deposition rates, and we considered the effect of different values of cation ratio $η=$ Zr/(Zr+Ta) and of post-deposition heat treatment temperature $T_a$ on the optical and mechanical properties of the films. Co-sputtered zirconia proved to be an efficient way to frustrate crystallization in tantala thin films, allowing for a substantial increase of the maximum annealing temperature and hence for a decrease of coating mechanical loss. The lowest average coating loss was observed for an ion-beam sputtered sample with $η= 0.485 \pm 0.004$ annealed at 800 $^{\circ}$C, yielding $\overlineφ = 1.8 \times 10^{-4}$. All coating samples showed cracks after annealing. Although in principle our measurements are sensitive to such defects, we found no evidence that our results were affected. The issue could be solved, at least for ion-beam sputtered coatings, by decreasing heating and cooling rates down to 7 $^{\circ}$C/h. While we observed as little optical absorption as in the coatings of current gravitational-wave interferometers (0.5 parts per million), further development will be needed to decrease light scattering and avoid the formation of defects upon annealing.

physics.ins-det↗

arXiv2021

Optical and mechanical properties of ion-beam-sputtered Nb$_2$O$_5$ and TiO$_2$-Nb$_2$O$_5$ thin films for gravitational-wave interferometers

Brownian thermal noise associated with highly-reflective mirror coatings is a fundamental limit for several precision experiments, including gravitational-wave detectors. Recently, there has been a worldwide effort to find mirror coatings with improved thermal noise properties that also fulfill strict optical requirements such as low absorption and scatter. We report on the optical and mechanical properties of ion-beam-sputtered niobia and titania-niobia thin films, and we discuss application of such coatings in current and future gravitational-wave detectors. We also report an updated direct coating thermal noise measurement of the HR coatings used in Advanced LIGO and Advanced Virgo.

physics.ins-det↗

arXiv2019

A standard siren measurement of the Hubble constant from GW170817 without the electromagnetic counterpart

We perform a statistical standard siren analysis of GW170817. Our analysis does not utilize knowledge of NGC 4993 as the unique host galaxy of the optical counterpart to GW170817. Instead, we consider each galaxy within the GW170817 localization region as a potential host; combining the redshift from each galaxy with the distance estimate from GW170817 provides an estimate of the Hubble constant, $H_0$. We then combine the $H_0$ values from all the galaxies to provide a final measurement of $H_0$. We explore the dependence of our results on the thresholds by which galaxies are included in our sample, as well as the impact of weighting the galaxies by stellar mass and star-formation rate. Considering all galaxies brighter than $0.01 L^\star_B$ as equally likely to host a BNS merger, we find $H_0= 76^{+48}_{-23}$ km s$^{-1}$ Mpc$^{-1}$ (maximum a posteriori and 68.3% highest density posterior interval; assuming a flat $H_0$ prior in the range $\left[ 10, 220 \right]$ km s$^{-1}$ Mpc$^{-1}$). Restricting only to galaxies brighter than $0.626 L^\star_B$ tightens the measurement to $H_0= 77^{+37}_{-18}$ km s$^{-1}$ Mpc$^{-1}$. We show that weighting the host galaxies by stellar mass or star-formation rate provides entirely consistent results with potentially tighter constraints. While these statistical estimates are inferior to the value from the counterpart standard siren measurement utilizing NGC 4993 as the unique host, $H_0=76^{+19}_{-13}$ km s$^{-1}$ Mpc$^{-1}$ (determined from the same publicly available data), our analysis is a proof-of-principle demonstration of the statistical approach first proposed by Bernard Schutz over 30 years ago.

astro-ph.CO↗

arXiv2018

Calibration of Advanced Virgo and Reconstruction of the Gravitational Wave Signal h(t) during the Observing Run O2

In August 2017, Advanced Virgo joined Advanced LIGO for the end of the O2 run, leading to the first gravitational waves detections with the three-detector network. This paper describes the Advanced Virgo calibration and the gravitational wave strain h(t) reconstruction during O2. The methods are the same as the ones developed for the initial Virgo detector and have already been described in previous publications, this paper summarizes the differences and emphasis is put on estimating systematic uncertainties. Three versions of the h(t) signal have been computed for the Virgo O2 run, an online version and two post-run reprocessed versions with improved detector calibration and reconstruction algorithm. A photon calibrator has been used to establish the sign of h(t) and to make an independent partial cross-check of the systematic uncertainties. The uncertainties reached for the latest h(t) version are 5.1% in amplitude, 40 mrad in phase and 20 microseconds in timing.

gr-qc↗

arXiv2018

Infrared spectroscopy of silicon for applications in astronomy

This work focuses on the characterization of various bulk silicon (Si) samples using Fourier Transform InfraRed (FTIR) and grating spectrometers in order to get them suitable for applications in astronomy. Different samples at different impurity concentrations were characterized by measuring their transmittance in the infrared region. Various lines due to residual impurity absorption were identifed and temperature dependence of impurity absorption is presented. Concentrations of doped samples (rho ~ 0.2 - 25000 Ohm cm) were determined from impurity absorption at low temperatures and from Drude free carrier absorption at 300K.

cond-mat.mtrl-sci↗

arXiv2017

Host galaxy identification for binary black hole mergers with long baseline gravitational wave detectors

The detection of three black hole binary coalescence events by Advanced LIGO allows the science benefits of future detectors to be evaluated. In this paper we report the science benefits of one or two 8km arm length detectors based on the doubling of key parameters in an advanced LIGO type detector, combined with realisable enhancements. It is shown that the total detection rate for sources similar to those already detected, would increase to $\sim$ 10$^{3}$--10$^{5}$ per year. Within 0.4Gpc we find that around 10 of these events would be localizable to within $\sim 10^{-1}$ deg$^2$. This is sufficient to make unique associations or to rule out a direct association with the brightest galaxies in optical surveys (at r-band magnitudes of 17 or above) or for deeper limits (down to r-band magnitudes of 20) yield statistically significant associations. The combination of angular resolution and event rate would benefit precision testing of formation models, cosmic evolution and cosmological studies.

astro-ph.HE↗

arXiv2016

GEO 600 and the GEO-HF upgrade program: successes and challenges

The German-British laser-interferometric gravitational wave detector GEO 600 is in its 14th year of operation since its first lock in 2001. After GEO 600 participated in science runs with other first-generation detectors, a program known as GEO-HF began in 2009. The goal was to improve the detector sensitivity at high frequencies, around 1 kHz and above, with technologically advanced yet minimally invasive upgrades. Simultaneously, the detector would record science quality data in between commissioning activities. As of early 2014, all of the planned upgrades have been carried out and sensitivity improvements of up to a factor of four at the high-frequency end of the observation band have been achieved. Besides science data collection, an experimental program is ongoing with the goal to further improve the sensitivity and evaluate future detector technologies. We summarize the results of the GEO-HF program to date and discuss its successes and challenges.

physics.ins-det↗

arXiv2015

Cost-benefit analysis for commissioning decisions in GEO600

Gravitational wave interferometers are complex instruments, requiring years of commissioning to achieve the required sensitivities for the detection of gravitational waves, of order 10^-21 in dimensionless detector strain, in the tens of Hz to several kHz frequency band. Investigations carried out by the GEO600 detector characterisation group have shown that detector characterisation techniques are useful when planning for commissioning work. At the time of writing, GEO600 is the only large scale laser interferometer currently in operation running with a high duty factor, 70%, limited chiefly by the time spent commissioning the detector. The number of observable gravitational wave sources scales as the product of the volume of space to which the detector is sensitive and the observation time, so the goal of commissioning is to improve the detector sensitivity with the least possible detector down time. We demonstrate a method for increasing the number of sources observable by such a detector, by assessing the severity of non-astrophysical noise contaminations to efficiently guide commissioning. This method will be particularly useful in the early stages and during the initial science runs of the aLIGO and adVirgo detectors, as they are brought up to design performance.

gr-qc↗

arXiv2014

Advanced Virgo: a 2nd generation interferometric gravitational wave detector

Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network with the two Advanced LIGO detectors in the US and GEO HF in Germany, with the goal of contributing to the early detections of gravitational waves and to opening a new observation window on the universe. In this paper we describe the main features of the Advanced Virgo detector and outline the status of the construction.

gr-qc↗

arXiv2014

Reconstruction of the gravitational wave signal $h(t)$ during the Virgo science runs and independent validation with a photon calibrator

The Virgo detector is a kilometer-scale interferometer for gravitational wave detection located near Pisa (Italy). About 13 months of data were accumulated during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and September 2011, with increasing sensitivity. In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the gravitational wave strain time series $h(t)$ from the detector signals is described. The standard consistency checks of the reconstruction are discussed and used to estimate the systematic uncertainties of the $h(t)$ signal as a function of frequency. Finally, an independent setup, the photon calibrator, is described and used to validate the reconstructed $h(t)$ signal and the associated uncertainties. The uncertainties of the $h(t)$ time series are estimated to be 8% in amplitude. The uncertainty of the phase of $h(t)$ is 50 mrad at 10 Hz with a frequency dependence following a delay of 8 $μ$s at high frequency. A bias lower than $4\,\mathrm{μs}$ and depending on the sky direction of the GW is also present.

gr-qc↗

arXiv2008

DC-readout of a signal-recycled gravitational wave detector

All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme was implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal-recycling are considered.

gr-qc↗

arXiv2008

Beating the spin-down limit on gravitational wave emission from the Crab pulsar

We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first nine months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms.

astro-ph↗

arXiv2008

Using the etalon effect for in-situ balancing of the Advanced Virgo arm cavities

Several large-scale interferometric gravitational-wave detectors use resonant arm cavities to enhance the light power in the interferometer arms. These cavities are based on different optical designs: One design uses wedged input mirrors to create additional optical pick-off ports for deriving control signals. The second design employs input mirrors without wedge and thus offers the possibility to use the etalon effect inside the input mirrors for tuning the finesse of the arm cavities. In this article we introduce a concept of maximized flexibility that combines both of these options, by featuring wedges at the input mirrors and using the etalon effect instead in the end mirrors. We present a design for the arm cavities of Advanced Virgo. We have used numerical simulations to derive requirements for the manufacturing accuracy of an end mirror etalon for Advanced Virgo. Furthermore, we give analytical approximations for the achievable tuning range of the etalon in dependence on the reflectance, the curvature and the orientation of the etalon back surface.

gr-qc↗

arXiv2006

Compensation of Strong Thermal Lensing in High Optical Power Cavities

In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors such as Advanced LIGO, we show that strong thermal lenses form in accordance with predictions and that they can be compensated using an intra-cavity compensation plate heated on its cylindrical surface. We show that high finesse ~1400 can be achieved in cavities with internal compensation plates, and that the cavity mode structure can be maintained by thermal compensation. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.

gr-qc↗

arXiv2005

Parametric instabilities and their control in advanced interferometer GW detectors

A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite acoustic modes in the test masses in the frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO optical cavity parameters with fused silica test masses, parametric instability excites 7 acoustic modes in each test mass, with parametric gain R up to 7. For the alternative sapphire test masses only 1 acoustic mode is excited in each test mass with R ~ 2. Fine tuning of the test mass radii of curvature cause the instabilities to sweep through various modes with R as high as ~2000. Sapphire test mass cavities can be tuned to completely eliminate instabilities using thermal g-factor tuning with negligible degradation of the noise performance. In the case of fused silica test mass, instabilities can be minimized but not eliminated.

gr-qc↗