GDR Ondes Gravitationnelles: workshop "développement des détecteurs"

mardi 10 juin 2025, 09:30 → 17:15 Europe/Paris

200/1-101 - Salle 101 (IJCLab)

Le groupe de travail "développement des détecteurs" du GdR "Ondes Gravitationnelles" organise un workshop la journée du mardi 10 Juin 2025 qui se déroulera de 10h à 17h. Le but de ce workshop est d'identifier et faire découvrir un large panel des activités R&D autour de la détection des ondes gravitationnelles. 

La matinée sera consacrée à la problématique des simulations optiques tandis que l'après-midi permettra des discussions plus larges sur les activités de R&D dans les différentes collaborations au travers de présentations des participants.

Le repas sera pris à la cantine du CESFO (à côté du laboratoire) au tarif "invité" (~6-7 euros par personnes à payer en espèces). L'inscription est obligatoire pour obtenir l'attestation permettant de bénéficier de ce tarif.

Lien zoom : https://ijclab.zoom.us/j/97593392234?pwd=VdCmNoIVPvb1woabUAQlumcPhsbjOT.1

10:00 → 10:25 Café d'accueil

10:25 → 10:30 Mot d'accueil

Orateur: Valerie CHAMBERT (IJCLAB-in2p3-Universite-Paris-Saclay)

10:30 → 13:00 Outils de simulations optiques (35' + 15' questions)

10:30 Nombres et Lumière : introduction à la propagation numérique de la lumière

Orateur: Jean-Yves Vinet

ConfGDR_OG.pptx

11:20 Zemax simulations for GW detectors : design, optimization, tolerancing and knowledge of instruments

Orateur: Christelle Buy (L2I Toulouse, CNRS/IN2P3, Université de Toulouse)

Zemax-GdROG-2025.pdf

12:10 Simulation optique avec OSCAR : un code FFT sur Matlab

Cette présentation abordera le principe des simulations optiques basés sur la propagation dite par FFT puis, après une présentation de l'outil, sera abordé une introduction à l'utilisation de OSCAR permettant de réaliser ce type de simulation avec différentes sortes d'imperfections.
En particulier, après avoir vu les bonnes pratiques pour l'exploitation d'OSCAR, nous verrons l'exemple d'une simulation d'une cavité résonante considérants différents défauts (profils de surface / désalignement / faisceau désadapté en mode) généralement utile pour spécifier des paramètres clés des détecteurs d'ondes gravitationnelles.

Orateur: Jerome DEGALLAIX (Laboratoire des Matéraux Avancés)

13:00 → 14:00 Repas

14:00 → 17:00 Contributions (15' + 5' de questions)

14:00 Finesse 3 simulation for GW detector: using multi-modal simulation to design and prepare the O5 upgrade on Virgo

Backscattered light is a source of noise in the Virgo interferometer. A fraction of light scattered by elements in optical benches recouples with the main beam, either in the Fabry-Perot cavity for end-arm benches or in the Signal Recycling Cavity for detection benches. During O4, the mirror of the signal recycling cavity (SR) was misaligned to increase the sensitivity.
If it’s possible to directly measure the noise added by the backscattered light, transfer functions are necessary to link this measurement to a fraction of backscattered light by benches. These transfer functions allow linking the movement of the bench to h(t). Previously, these transfer functions were obtained using Optickle, which is not maintained anymore and cannot model mirror misalignment.
In this talk, I will describe how Finesse 3 helped me to update this Optickle model to compute new transfer functions between bench movements and h(t). I will also describe general Finesse 3 capability on transfer function measurement.

Orateur: Augustin DEMAGNY (LAPP)

Présentation.pdf

14:20 Optical simulation methods to study the losses in the stable recycling cavities of Advanced Virgo+

In this talk, we present the methods used to study losses in the stable recycling cavities of the Advanced Virgo+ detector. The analysis is based on FFT simulation tools developed within the LIGO-Virgo collaboration, specifically the OSCAR and SIS codes.

We explore three simulation methods. First, we study beam reflection on curved mirrors at non-negligible angles of incidence. This highlights the limitations of the paraxial approximation and demonstrates the importance of accurately modeling mirror interfaces to better estimate aberration-induced losses.

Second, we compare the results produced by OSCAR and SIS regarding optimizing the mirrors’ radius of curvature (RoC) to minimize coupling losses in the stable cavities. The comparison reveals some small discrepancies that will be worth investigating.

Finally, we introduce a new method to simulate vacuum-squeezed state losses in the signal recycling cavity—an analysis that was previously not feasible. This technique provides new insights into critical losses to the squeezing system of Advanced Virgo+.

Orateur: Ward AMAR

GdR Workshop_10062025_Optical simulations methods for low-losses stable recycling cavities-FinalVersion.pptx

14:40 Optical Simulation using python : analysis of tilt-to-length coupling for LISA

Space based gravitational wave detectors are plagued with a parasitic coupling between the jitter of the laser beams relative to one another and the optical path length read out of the interferometer. This noise source was not limiting on ground based GW detectors since the state of the art stabilisation technologies developed for LVK observatories allow to have extremely stable test masses, thus extremely stable interferometric beams.

This will not be the case for space based observatories that will be subjected to many external forces acting on different systems of the instrument and inducing important levels of jitter on all 3 spacecrafts, then being imprinted on the laser beams exiting and incoming onto the spacecraft.

In some case, this coupling can be mitigated by the use of careful design and calibration; but with some sources like wavefront error we won't be able to differentiate between TTL and a true GW signal. For this reason, simulation have to be performed to assess the influence of wavefront error on the TTL coupling in order to be able to properly choose the specification to impose on the quality of the optical system as a whole.

For this contribution, I will give an overview of the current knowledge about TTL coupling, and give a few information about the context of this study.

I will then describe the simulation tool developed for this study and summarize the main results that have been obtained and finally open about the next steps.

Orateur: Maxime VINCENT (AstroParticule et Cosmologie)

PrésentationGDR_DevDet.pptx

15:00 Reduction of flexing-filtering noise in TDI

In early 2024, ESA formally adopted the Laser Interferometer Space Antenna (LISA) space mission -- with the aim of measuring gravitational waves emitted in the millihertz range. The constellation employs three spacecrafts that exchange laser beams to make interferometric measurements over a distance of 2.5 million kms. The measurements will then telemetered down to Earth at a lower sampling frequency. Anti-aliasing filters will be used on board to limit spectral folding of out-of-band laser noise. The primary noise concern in these measurements is laser frequency noise, caused by the variability in the arm-length of the constellation via the disproportionate movement of the spacecrafts and the Doppler effect. Minimization of this noise requires virtual time-shifting of the data using delay operators to build a beam path that simulates equal-arm interferometers. The non-commutativity of these delay operators and on-board filters manifests as a noise (flexing-filtering) that significantly contributes to the noise budget. This non-commutativity is a consequence of the non-flatness of the filter in-band. Attenuation of this noise requires high-order and computationally expensive filters, putting additional demands on the spacecraft.

My presentation will explore an alternative method to reduce this flexing filtering noise via the introduction of a modified delay operator -- accounting for the non-commutativity with the filter in the delay operation itself. This approach allows us to reduce the flexing-filtering noise by over three orders of magnitude whilst reducing the dependency on the flatness of the filter. The work is supplemented by numerical simulations of the data processing chain that compare the results with those of the standard approach

Orateur: Shivani Harer

Harer_GDR _10.06.2025.pdf

15:20 Coffee break

15:40 Recent progress on a noise budget for a lunar GW detector

The Moon offers a unique environment for gravitational wave (GW) detection thanks to its low seismic noise and lack of atmosphere. During the Apollo missions, the Lunar Surface Gravimeter (LSG) was deployed in an early attempt to detect GWs via ground motion, though it ultimately fell short of its objectives. Today, in the context of renewed lunar exploration, new mission concepts such as LGWA and LILA aim to leverage the Moon’s quiet seismic environment to probe the GW spectrum in the deci-Hz band.

In this talk, I will present a feasibility study—conducted in collaboration between geophysicists at IPGP and astrophysicists at APC—for a lunar strainmeter designed to detect GWs via surface deformation in the mHz-band. I will first describe the Moon’s response function to gravitational waves, taking into account its internal elastic structure. This allows us to evaluate how a passing GW would couple to measurable surface strain. I will then present a preliminary noise budget for such an instrument, including contributions from quantum noise, mirror thermal noise, laser frequency noise, and deep moonquake noise.

Orateur: Léon Vidal (APC/IPGP)

Recent progress on a noise budget for a lunar GW detector

16:00 Filter Cavities for Squeezing in the Einstein Telescope: Design and Challenges

The Einstein Telescope (ET) is a next-generation observatory for gravitational waves. It will push sensitivity beyond current detectors. One major challenge is quantum noise. This limits the detector at both low and high frequencies. The baseline design uses frequency-dependent squeezing to reduce this noise. It includes two filter cavities (FCs) for the low-frequency interferometers and one for the high-frequency interferometer.

This talk focuses on the filter cavities. I will start with the global timeline of the R&D phase. Then I will explain why FCs are essential in the ET design. The main part of the presentation will cover current design efforts. I will discuss how the cavities can be placed in the ET infrastructure. I will also look at questions around cavity length and type. Two-mirror and three-mirror cavity options will be compared. I will mention ideas like using a single tunable cavity instead of two. I will also briefly touch on alternatives such as EPR entanglement.

Orateur: M. Yuhang Zhao (APC, Université Paris Cité)

slides

16:20 Quantum performances of resonant cavities schemes for frequency-dependent squeezing in future generation gravitational-wave detectors

Gravitational-wave detectors use frequency-dependent quantum squeezing
to reduce the impact of quantum noise on the detector bandwidth. While a
single filter cavity (FC) is enough to achieve the frequency dependence for cur-
rent detectors, future generations such as Einstein Telescope Low-Frequency
(ETLF) will be operated with a detuned signal recycling cavity. This will re-
quire a complex rotation of the squeezing ellipse to achieve optimal quantum
noise reduction. For this complex rotation a single filter cavity is not suffi-
cient, two filter cavities (2FC) or one 3-mirrored coupled filter cavity (CFC)
have to be implemented. In this work, after having derived the equations of
quantum degradation for systems composed of more than one cavity, we com-
pare the feasibility and performances of these two systems (2FC and CFC) with
respect to various kinds of squeezing degradation sources: loss, mismatch and
phase noise. A special focus is also given to the impact of the middle mirror
in the coupled cavity configuration. This work extends previous analysis about
2FC and CFC in terms of squeezing degradation and uses new tools to derive
and compare quantum noise degradations using optimal readout schemes that
generalize homodyne detection.

Orateur: Isander-Louis AHREND

CFC vs 2 FC presentation -1.pdf

16:40 Linear three-mirror cavity for quantum noise reduction: resonant behavior, stability and meter-scale prototype

Fabry-Perot cavities are used in present GW interferometers for the frequency-dependent squeezing technique, which reduces quantum noise across the entire observation frequency range. However, they may not offer sufficient control over the squeezing properties required for next-generation detectors, in particular the Einstein Telescope. To this end, different filtering system configurations are currently being explored. Among these, linear three-mirror cavities are of particular interest due to their unique characteristics, especially resonance peak splitting and their equivalence to two-mirror cavities with variable finesse. I will discuss simulations we conducted to examine how the resonant behavior and stability of these systems vary with different configurations, as well as experimental measurements taken from a meter-scale prototype that demonstrates variable finesse and resonance splitting.

Orateur: M. Paul STEVENS (CNRS / IJCLab)