GWADW2022 - Approaching
the low-frequency design
sensitivity of ground-based
detectors
Monday 23 May 2022 - Saturday 28 May 2022
GatherTown and ZOOMBook of Abstracts

Contents
He-II filled marionette suspension for the cryogenic payload of the ET-LF interferometer 7

1

Characterisation of bonded silicon components towards assemblies for 3rd generation detectors 67 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Sapphire suspension in KAGRA –Current design and perspective- 60 . . . . . . . . . . .

1

Sapphire technology for cryogenic detectors: new results from Lyon 64 . . . . . . . . . .

2A new approach for suspending cryogenic mirrors 10 . . . . . . . . . . . . . . . . . . . .

2

Silicon suspensions: thermal noise and mechanical properties 49 . . . . . . . . . . . . . .

3

Thermal and mechanical simulation of the cryo-payload: status and preliminary results. 14

3AdV+ low frequency noises challenges and plans 59 . . . . . . . . . . . . . . . . . . . . .

3

Approaches to low frequency noise in LIGO 28 . . . . . . . . . . . . . . . . . . . . . . . .

4

Multi-messenger observations of gravitational-wave transients 6 . . . . . . . . . . . . . .

4

Observing black holes throughout the Universe 5 . . . . . . . . . . . . . . . . . . . . . . .

4Introduction of the meeting 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

Low-frequency, high-resolution, optical inertial sensors 77 . . . . . . . . . . . . . . . . .

5Filter cavity longitudinal control for frequency dependent squeezing 65 . . . . . . . . . .

5Enhanced Baffles for future Gravitational wave Interferometers 75 . . . . . . . . . . . . .

6

Superconducting inertial sensor with low-noise actuators for gravitational-wave observatories 73 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Optical simulations of stray light on instrumented baffles surrounding Virgo end mirrors
during O5 52 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Tunable coherence for straylight suppression in high precision interferometers 41 . . . .

7Angled beam expander telescopes for the Michelson beams in third generation Gravitational Wave Observatories 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Optimization of design parameters for Gravitational Wave detector DECIGO including fundamental noises 24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Probing dipole radiation with the low-frequency gravitational-wave observatories 15 . .
iii

8Electromagnetic Follow-up of Binary Neutron Star Mergers with Early Warnings from Decihertz Gravitational-wave Observatories 11 . . . . . . . . . . . . . . . . . . . . . . . 9
Prospects for Detecting Exoplanets around Double White Dwarfs with LISA and Taiji 129Realistic Detection and Early Warning of Binary Neutron Stars with Decihertz Gravitationalwave Observatories 18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Space gravitational wave antenna DECIGO 25 . . . . . . . . . . . . . . . . . . . . . . . . 10
Space GW Antenna B-DECIGO 46 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Localization of gravitational waves using machine learning 56 . . . . . . . . . . . . . . . 11
Practical quantum noise estimate of optical-spring quantum locking for space gravitational
wave detector DECIGO 66 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
The Sar-Grav Laboratory at the Sos Enattos site, one of the quietest site in the 2-10 Hz
frequency range 72 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Gravitational wave sources in the low frequency region and their distances 62 . . . . . . 12
The Current Status of TOrsion-Bar Antenna (TOBA) Experiment 58 . . . . . . . . . . . . 12
Displacement-noise-free neutron interferometer for gravitational wave detection at low
frequencies 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Current Status of Quantum Locking Experiment for Space Gravitational Wave Antenna
DECIGO 26 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Cool-down studies of the low-frequency interferometer in the Einstein Telescope 36 . . . 14
Design and Alignment of Compact Optical Heads for Test Mass Readout with Deep-Frequency
Modulation 38 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Silicon as a detector suspension material 61 . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Precision limits and a readout algorithm for DFM Interferometry 37 . . . . . . . . . . . . 15
Tonga’s volcano eruption signals measured by the evironmental monitoring systems of
KAGRA Observatory 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Broadband quantum noise reduction for AdV+ 43 . . . . . . . . . . . . . . . . . . . . . . 16
Compensating decoherence of squeezed light in cavity-enhanced quantum metrology 27

16

Juggled interferometer for gravitational wave detection 32 . . . . . . . . . . . . . . . . . 16
SpicyPy: a common python tool for signal processing and control systems 39 . . . . . . . 17
Substrate transferred aluminum gallium arsenide (AlGaAs) crystalline coatings 2 . . . . . 17
Optical absorption of TiO2 doped SiO2 as a replacement high index coating material 47 .

18

TiO2 :SiO2 coating thermal noise and optical studies 48 . . . . . . . . . . . . . . . . . . . 18
Angular Signal Amplification with a Coupled Cavity for Torsion-Bar Antenna 13 . . . . . 19

Estimating the Newtonian noise of groundwater at the KAGRA 44 . . . . . . . . . . . . . 19
Control of Dual-Pass Fabry-Perot Cavity for space gravitational wave antennas : DECIGO
and B-DECIGO 45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
CO2 mode cleaner for Thermal Compensation System of Advanced Virgo+ 71 . . . . . . 20
Vibration analysis of ETpathfinder cryogenic heat-links 63 . . . . . . . . . . . . . . . . . 20
Measuring thermal noise in gram-scale Si flexures at 123 K 31 . . . . . . . . . . . . . . . . 21
Vibration Analysis of KAGRA Cryostat at Cryogenic Temperature 17 . . . . . . . . . . . 21
Review of LIGO’s LF workshop 29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
BRDF revisited 55 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Stray Light Measurements With an Instrumented Baffle in the Advanced Virgo Input Mode
Cleaner Cavity 53 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Scattered light measurement and active mitigation for Advanced Virgo Plus 23 . . . . . . 23
Fast Scattering transient noise at LIGO Livingston 68 . . . . . . . . . . . . . . . . . . . . 23
GWADW2023 21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Panel discussions 20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
ET at 3 Hz - can we break the ’controls noise’ wall? 74 . . . . . . . . . . . . . . . . . . . . 24
Closing remark 22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Cosmic Explorer at low frequency 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
The latest development in ALFRA, the UWA low-frequency rotational accelerometer 4 . . 24
E-TEST: A Compact Isolation Concept for Future Einstein Telescope 76 . . . . . . . . . . 25
New Generation Superattenuators for Einstein Telescope 34 . . . . . . . . . . . . . . . . . 25
Update on sensing seismic platform relative motion using Digital Interferometry 33 . . . 26
Introduction 69 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Newtonian Noise in the Einstein Telescope 57 . . . . . . . . . . . . . . . . . . . . . . . . 26
Tunnel configurations and seismic isolation optimization in underground gravitational wave
detectors 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Astigmatic mode mismatch sensing for the next gravitational wave detectors. 54 . . . . . 27
Birefringence characterisation of KAGRA ITMs and simulation with FINESSE 51 . . . . . 28
Low-frequency magnetic noise in terrestrial GW detectors: the case study of AdV+ Faraday
isolator 42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Demonstrating Interferometric Sensors to Improve Local Control of Suspended Optics 40 29

Low-Frequency control noise - Modelling ASC loops with Finesse 35 . . . . . . . . . . . . 29

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Cryogenics for LF / 7

He-II filled marionette suspension for the cryogenic payload of
the ET-LF interferometer
Authors: Xhesika Koroveshi1 ; Steffen Grohmann1
1

KIT

Abstract. The low-frequency interferometer in the Einstein Telescope (ET-LF) shall be operated attest mass temperatures of 10 K to 20 K. Motivated by the potential of using superfluid helium (HeII) for cooling the test masses due to its exceptional heat transport properties and presumably low
dissipative behaviour, we present the concept of integrating a double-walled He-II filled marionette
suspension in the payload design. During the cool-down process, supercritical helium (He-I) at
adjustable temperature flows in counter-flow through the double-walled suspension in order to cool
the marionette. In steady-state operation, the suspension is filled with liquid He-II at rest, providing
ultra-low noise cooling at 2 K via steady-state heat conduction. Considering the crucial role of the
payload suspensions on the ET-LF sensitivity, we present the results of a thermal and mechanicalfeasibility analysis with particularfocus on suspension thermal noise.

Cryogenics for LF / 67

Characterisation of bonded silicon components towards assemblies for 3rd generation detectors
Author: Gregoire Lacaille1
1

Glasgow

Corresponding Author:

A crucial milestone was recently completed in the IGR in the form of thefirst silicon suspension hanging on Hydroxide catalysis bonds andsurviving cooling to cryogenics temperatures. Although the prototype
allowed to validate multiple engineering concepts, it is expected that
HCB won’t meet the thermal noise requirements for the 3rd generation ofgravitational waves detectors. For this reason, the focus is now placedon improving the bonding technique, and particularly on investigating
direct bonding. A range of surface activation processes is studied withthe help of a brand-new surface profiler to correlate surface property
and bond quality. Bonded samples are prepared for strength andmechanical loss measurements. The testing processes have had to bere-thought to fit the new geometry used, and preliminary results on theeffect of pre and post-processing are obtained.

Cryogenics for LF / 60

Sapphire suspension in KAGRA –Current design and perspectiveAuthor: Takafumi Ushiba1
1

ICRR

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Corresponding Author: ushiba@icrr.u-tokyo.ac.jp

Cooling mirrors and their suspensions are promising way to reduce thermal noise. To maximize
the benefits of cooling, utilizing low mechanical loss material at cryogenic temperature is essential;
therefore, KAGRA mirrors and their suspension fibers are made of sapphire. To achieve good cryogenic suspension, there are several technical difficulties because the suspension needs not only low
mechanical loss for thermal noise reduction but also high thermal conductivity for keeping mirror
temperature low. In this talk, we present a review of the current KAGRA sapphire suspension andits perspective.

Cryogenics for LF / 64

Sapphire technology for cryogenic detectors: new results from
Lyon
Author: Teo Aventin1
1

iLM

Corresponding Author:

The institutes iLM and iP2i in Lyon are involved on a significant effort to develop the sapphire
technology for the future cryogenic detectors. iLM is taking care of the crystalline growth of ultralow level of optical absorption and mechanical losses of mirror substrates and last stage suspensions.
iP2i through the platform LMA develops the ultra-low level of total optical losses of mirrors, working
on aberration, scattering and absorption. The collaboration is finalising the development of a largeoven able to grow 500kg sapphire ingots for the production of 450mm diameter mirrors. In parallel
the investigation on the growth of ultra-low absorption sapphire is ongoing and the details on themost recent result of 10ppm/cm sapphire will be presented. The impact that this new advancement
will have on the ET suspensions will be given too.

Cryogenics for LF / 10

A new approach for suspending cryogenic mirrors
Authors: Francesca Badaracco1 ; Kazuhiro Agatsuma2 ; Alessandro Bertolini3 ; Andrea Chincarini4 ; Joris van
Heijningen1 ; Luca Naticchioni5 ; Paolo Ruggi6 ; Stefano Selleri7 ; Riccardo DeSalvo8
1

UCLouvain

2

University of Birmingham

3

NIKHEF

4

INFN Genova

5

INFN Roma

6

EGO

7

Università di Firenze

8

University of Utah

Corresponding Author: francesca.badaracco@uclouvain.be

The Einstein Telescope will increase the sensitivity to gravitational wave detections with respect tothe current detectors, especially in the low-frequency band (down to 2 Hz). Reaching such sensitivities at low frequencies implies great technology challenges: in order to reduce the seismic and thethermal noise very soft suspensions and cryogenic temperatures are needed. A big challenge arises
here: to bring and to keep a test mass at temperatures around 10 K we need to extract heat from it.
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The only way to do this is via thermal conductivity of the test mass suspension elements. However,soft suspensions are non-compatible with the need of extracting heat which would require short suspensions with a large cross section. We propose here a new suspension morphology in order to allow
a good heat extraction without spoiling the softness of the suspensions. This should provide a goodsolution to one of the biggest technological problems of building the Einstein Telescope.

Cryogenics for LF / 49

Silicon suspensions: thermal noise and mechanical properties
Author: Flavio Travasso1
1

University of Camerino - INFN Perugia

Corresponding Author: flavio.travasso@pg.infn.it

The design of cryogenic suspensions for mass tests for future generation GW detectors is based on
the balancing of several factors: mechanical properties, thermal conductivity, resonance frequencies,
thermo-mechanical stress and generally any parameter that aims to reduce thermal noise of test
masses. The talk will present the state of the art of studying the mechanical and thermal propertiesof silicon as a function of the orientation of the axes and how these can influence the design of amonolithic suspension. Furthermore, the measurements of the limit load on fibers produced at the
maximum of the current technique will be described and compared with the expected limit load,
trying to understand the limiting factors. Finally, we will describe the tests done so far to measure
the mechanical dissipations of the mono-crystalline silicon fibers and the limits found.

Cryogenics for LF / 14

Thermal and mechanical simulation of the cryo-payload: status
and preliminary results.
Author: Paola Puppo1
1

INFN RomaCorresponding Author: paola.puppo@roma1.infn.it

In the design of the cryogenic payload, thermal and mechanical FEA models are used for optimizing
the system both for its structural and thermal behavior. The thermal study is important to have thetemperature distribution along the suspension wires and the thermal resistances of to the various
interconnections between the parts of the suspension. The mechanical study gives the estimationof the losses present in the system. We will present the status of this combined method to have an
estimation of the suspension thermal noise with the Levin method.

Plenary / 59

AdV+ low frequency noises challenges and plans
Author: Michal Was1
1

LAPP/CNRS

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Corresponding Author: was@lapp.in2p3.fr

Advanced Virgo Plus is a two step plan for improving the sensitivityof Advanced Virgo for the O4 and O5 observing runs. After discussing
the low frequency noises that have limited AdV in O3, we will present
the planned AdV+ upgrades and adjustments that aim at reducing the low
frequency fundamental and technical noises for O4 and O5.

Plenary / 28

Approaches to low frequency noise in LIGO
Author: Lee McCuller1
1

CaltechCorresponding Author: mcculler@caltech.edu

This talk will overview the current views of low frequency noise contributions in LIGO. This overview
provides context to discuss potential upgrade options either to reduce direct noise contributions or
to address underlying causes of complex bilinear noises.

Plenary / 6

Multi-messenger observations of gravitational-wave transients
Author: Alessandra Corsi1
1

Texas Tech University

Corresponding Author: alessandra.corsi@ttu.edu

Starting from the example of GW170817, I will discuss prospects for multi-messenger gravitationalwave astronomy, highlighting opportunities to clarify currently open questions in the field, while
expanding multi-messenger studies beyond the realm of compact binary mergers.

Plenary / 5

Observing black holes throughout the Universe
Author: Colpi Monica1
1

University of Milano Bicocca

Corresponding Author: monica.colpi@unimib.it

I will overview how extending detector sensitivities at low gravitational wave frequencies will let
us observe the first merging stellar black holes forming at cosmic dawn, and unveil the still elusive
population of intermediate-mass black holes, which provides clues on the yet unknown origins of
the massive black holes lurking at the centres of today’s galaxies.

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Plenary / 3

Introduction of the meeting
Author: Kentaro Somiya1
1

Tokyo Institute of Technology

Corresponding Author: somiya@icrr.u-tokyo.ac.jp

Poster session I / 77

Low-frequency, high-resolution, optical inertial sensors
Author: Anthony Amorosi1
1

U Liege

Large-scale, high-end, scientific instruments see their performances significantly impaired by residual ground motion at low frequencies. Namely, recent development of gravitational wave detectors
aims to detect gravitational waves whose strain is as low as 10-20 Hz-1/2 in the sub-Hz frequency
range, while seismic noise can be 10 times larger in this frequency range. High performance active
isolation strategy and seismic sensors are required to address this issue.
The Precision Mechatronics Laboratory, based in ULiège and ULB, Belgium, has a large experience indeveloping high-resolution optical inertial sensors intended to be used in active control. The latest
inertial sensors, HINS and VINS, are based on an Long-range, Michelson-type, optical readout witha sensitivity of 2∙10-13 m/√Hz at 1 Hz. They have a resolution of 2∙10-12 m/√Hz at 1 Hz, 1∙10-13m/√Hz at 10 Hz and 3∙10-14 m/√Hz at 100 Hz.
A new, compact, design of the sensors is being developed. The sensor is designed to fit a 10 x 10 x
10 cm box, reducing the original design of VINS by a factor of 8. The mechanics also features fusedsilica joints for and reduced low-frequency thermal noise. Ringdown tests demonstrate a Q-factorof 2800 in open-air.

Poster session I / 65

Filter cavity longitudinal control for frequency dependent squeezing
Author: Barbara Garaventa1
Co-author: on behalf of the AdV+ QNR team
1

INFN and Genova University

Broadband mitigation of quantum noise in interferometric gravitational-waves detectors can beachieved via frequency dependent squeezing (FDS) of the vacuum field at the dark port of the interferometer. This allows to reduce the vacuum field phase fluctuations at high frequency, where
quantum shot noise dominates, and the amplitude fluctuation at low frequency, where the contribution of quantum radiation pressure noise is higher.
Advanced Virgo and Advanced LIGO will implement FDS during the O4 science run, by coupling afrequency-independent squeezed vacuum to an optical filter cavity (FC) with an optical pole in theaudio domain. In such scheme, the crossover frequency where amplitude squeezing is converted
into phase squeezing depends on the detuning between the FC resonance and the carrier field in theinterferometer.
Coarse longitudinal control of the filter cavity can be easily achieved by means of an auxiliary fieldat the second harmonic of the IR carrier. However, the lock point accuracy is generally limited. An
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accurate longitudinal control with an IR field is achieved with either a bright, subcarrier field or withthe weak RF sidebands used for the coherent control of the squeezing ellipse angle. We propose analternative solution overcoming some drawbacks of such schemes.

Poster session I / 75

Enhanced Baffles for future Gravitational wave Interferometers
Authors: Stefano SelleriNone ; Riccardo DeSalvo1
1

University of Utah

The problem of mitigating scattered light noise within interferometer arm
tubes has been addressed via the insertion of baffles that intercept thestray rays which after interacting with the tube walls may be reinjected in
the Fabry-Perot resonator, carrying the vibrational noise of the walls.
Such a problem has been dealt with conical, serrated, baffles that may
still be source of noise due to diffraction at their edges. Recently,
helical baffles have been proposed, showing that diffraction is reduced andmechanical construction easier, not needing serration.

Poster session I / 73

Superconducting inertial sensor with low-noise actuators for gravitationalwave observatories
Author: E.C. Ferreira11
Co-authors: F. Bocchese ; F. Badaracco 2 ; A. Gatti ; J. van Heijningen 2 ; S. Lucas ; A. Perali ; F. Tavernier
1

UC Louvain

2

UCLouvain

The cryogenic environment of gravitational-wave detectors, such as Einstein Telescope (ET), can beused in combination with superconducting materials to open up pathways to low-loss actuators andsensor mechanics.
We are developing a Cryogenic Superconducting Inertial Sensor (CSIS) with a displacement sensitivity of several fm/√Hz at 0.5 Hz. Such highly sensitive device can monitor the effects of low-vibration
cryocoolers applied to the penultimate stage of ET as well as possibly assist in the suspension control.
In CSIS, superconducting thin film spiral coils use the Meissner effect to form actuators as part of aforce feedback sensing scheme. This actuator reduces losses of the sensor mechanics by not using
magnets in the actuator, which greatly reduces viscous eddy current damping. We investigate properties as magnetic field and current density distribution of the coil by finite element analysis using
COMSOL. The magnetic field and force applied by the actuators have also been simulated analytically and the results agree with COMSOL ones.
We also present results from the thin film fabrication process to produce 1 cm diameter coils. Superconducting thin films deposited on silicon substrate are being cryogenically tested.

Poster session I / 52
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Optical simulations of stray light on instrumented baffles surrounding Virgo end mirrors during O5
Author: Marc Andrés Carcasona1
Co-author: Adrian Macquet 11

IFAE

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 monitoring of the stray light around the mirrors. We present optical simulations of the light distribution in
the detector’s main cavities to assess the ability of the sensors to effectively monitor misalignmentand defects on the mirrors’ surface and to play a role in the pre-alignment of the interferometer.
The effect of the backscattered light from the baffles is also computed and projected over the O5
sensitivity curve, to evaluate possible effects of the presence of instrumented baffles on the ultimate
sensitivity of the detector.

Poster session I / 41

Tunable coherence for straylight suppression in high precisioninterferometers
Authors: Daniel Voigt1 ; Oliver Gerberding2
1

University Hamburg

2

Universität Hamburg

As straylight is a dominating limitation for the sensitivity of gravitational wave detectors, weinvestigate the use of tunable coherence in the form of phase modulation following a pseudo-randomsequence 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-lightinterferometer with tunable coherence length. While this has been proven to work with digital demodulation for multiplexing in digital interferometry, we now study optical demodulation at thesignal ports of a Michelson-interferometer with higher modulation speeds to reduce the remaining
coherence length. As a first step, we present results and estimated suppression factors from a numerical simulation in preparation of the experimental studies in a tabletop interferometer.

Poster session I / 9

Angled beam expander telescopes for the Michelson beams inthird generation Gravitational Wave Observatories
Authors: Riccardo DeSalvo1 ; Blow Jeremy2 ; Bosque Claudio Pineda 3 ; Stefano Selleri4
1

University of Utah

2

Incera Solutions LLC

3

California State University

4

Università di Firenze

Third generation of Gravitational Wave detectors like the Einstein Telescope or theCosmic Explorer will be Michelson interferometers with Fabry-Perot cavities in the arms,
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using mirror test masses with diameter at the limit of technical feasibility. Unlike otherdetectors, the Einstein Telescope will have a 60° angle between the arms. Because of its
larger incidence angle, at any given beam size, it would require beam splitters almost doublein size and much heavier than the 90° case. It is proposed here to install beam expander
telescopes with angled mirrors located inside the Michelson interferometer between the
Fabry-Perot cavities and the beam splitter. Beyond reducing the beam sizes and thebeam splitter to manageable sizes, the proposed solution allows to bring the optimal
recombination angle to 90°. The proposed geometry offers a natural way to separate thebeam splitters of different detectors into individual, smaller and more stable caverns, thus
improving observatory observation-time efficiency, to provide needed beam diagnostic
points and convenient degrees of freedom for beam alignment into both the Fabry-Perotcavities and the beam splitter, as well as to provide a method for maintaining optimal mode
matching of the two arms onto the beam splitter without thermal compensation plates.

Poster session I / 24

Optimization of design parameters for Gravitational Wave detector DECIGO including fundamental noises
Author: Yuki Kawasaki1
Co-authors: Seiji Kawamura 1 ; Koji Nagano 2 ; Shuichiro Yokoyama 3 ; Bin Wu 1 ; Tomohiro Ishikawa 1 ; Shoki
Iwaguchi 1 ; Ryuma Shimizu 1 ; Izumi Watanabe
1Department of Physics, Nagoya University

2

Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency

3

The Kobayashi-Masukawa Institute for the Origin of Particles and the Universe, Nagoya University

The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational
wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial
GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement of the target sensitivity of DECIGO is required. In the previous studies,
DECIGO’s parameters were optimized to maximize the signal-to-noise ratio (SNR) of the PGW toquantum noise including the effect of diffraction loss. To simulate the SNR more realistically, we
optimize DECIGO’s parameters considering the GWs from double white dwarfs (DWDs) and thethermal noise of test masses. We consider two cases of the cutoff frequency of GWs from DWDs.
In addition, we consider two kinds of thermal noise: thermal noise in a residual gas and internal
thermal noise. To investigate how the mirror geometry affects the sensitivity, we calculate it bychanging the mirror mass and thickness. As a result, we obtained the optimums for the parametersthat maximize the SNR that depends on the mirror radius. This result shows that a thick mirror witha large radius gives a good SNR and enables us to optimize the design of DECIGO.

Poster session I / 15

Probing dipole radiation with the low-frequency gravitationalwave observatories
Authors: Junjie Zhao1 ; Lijing ShaoNone ; Yong GaoNone ; Chang LiuNone ; Zhoujian CaoNone ; Bo-Qiang MaNone

1

Beijing Normal University

Atom-interferometer gravitational-wave (GW) observatory, as a new design of ground-based GW detector for the near future, is sensitive at a relatively low frequency for GW observations. Taking the
proposed atom interferometer Zhaoshan Long-baseline Atom Interferometer Gravitation Antenna
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/ Book of Abstracts(ZAIGA), and its illustrative upgrade (Z+) as examples, we investigate how the atom interferometer will complement ground-based laser interferometers in testing the gravitational dipole radiationfrom binary neutron star (BNS) mergers. A test of such kind is important for a better understandingof the strong equivalence principle laying at the heart of Einstein’s general relativity. To obtain a statistically sound result, we sample BNS systems according to their merger rate and population, fromwhich we study the expected bounds on the parameterized dipole radiation parameter B. Extracting
BNS parameters and the dipole radiation from the combination of ground-based laser interferometers and the atom-interferometer ZAIGA/Z+, we are entitled to obtain tighter bounds on B by a
few times to a few orders of magnitude, compared to ground-based laser interferometers alone, ultimately reaching the levels of |B| < 10−9 (with ZAIGA) and |B| < 10−10 (with Z+).

Poster session I / 11

Electromagnetic Follow-up of Binary Neutron Star Mergers with
Early Warnings from Decihertz Gravitational-wave Observatories
Authors: Yacheng Kang1 ; Chang Liu1 ; Lijing Shao1
1

Peking University

We investigate the prospects of electromagnetic follow-up for binary neutron star (BNS) mergers,
with the help of early warnings from decihertz gravitational-wave (GW) observatories, B-DECIGO
and DO-Optimal. Extending Liu et al. (2022), we not only give quick assessments of joint short
γ-ray burst (sGRB) detection rates for different γ-ray satellites and BNS population models, but alsoelaborate on the analyses and results on multi-band kilonova detections for survey telescopes withdifferent limiting magnitudes. During an assumed 4-year mission time for decihertz GW observatories, we find that DO-Optimal performs better than B-DECIGO as a whole on the detection rate, andhas a larger detectable distance for joint sGRB/kilonova searches. Taking the log-normal population
model for BNS mergers and a one-day early-warning time as an example, we discuss the accuracy inlocalization and timing, as well as the redshift distributions for various synergy observations withelectromagnetic facilities and decihertz GW detectors. Based on our analyses, we propose a feasible“wait-for” pattern as a novel detecting mode for future multi-messenger astrophysics.

Poster session I / 12

Prospects for Detecting Exoplanets around Double White Dwarfs
with LISA and Taiji
Authors: Yacheng Kang1 ; Chang Liu1 ; Lijing Shao1
1

Peking University

Recently, Tamanini & Danielski discussed the possibility of detecting circumbinary exoplanets (CBPs)
orbiting double white dwarfs (DWDs) with the Laser Interferometer Space Antenna (LISA). Extending their methods and criteria, we discuss the prospects for detecting exoplanets around DWDs not
only by LISA, but also by Taiji, a Chinese space-borne gravitational-wave (GW) mission. We first
explore how different binary masses and mass ratios affect the abilities of LISA and Taiji to detect
CBPs. Second, for certain known detached DWDs with high signal-to-noise ratios, we quantify thepossibility of CBP detections around them. Third, based on the DWD population obtained from
the Mock LISA Data Challenge, we present basic assessments of the CBP detections in our Galaxy
during a 4 yr mission time for LISA and Taiji. We discuss the constraints on the detectable zone ofeach system. With the DWD population, we further inject two different planet distributions with an
occurrence rate of 50% and constrain the total detection rates. We briefly discuss the prospects for
detecting habitable CBPs around DWDs with a simplified model. These results can provide helpful
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inputs for upcoming exoplanetary projects and help analyze planetary systems after the common
envelope phase.

Poster session I / 18

Realistic Detection and Early Warning of Binary Neutron Stars
with Decihertz Gravitational-wave Observatories
Authors: Chang Liu1 ; Yacheng Kang1 ; Lijing Shao1
1

Peking University

We investigated the detection and localization of binary neutron star (BNS) populations with decihertz gravitational-wave observatories in a realistic detecting strategy, including real-time observations and early warnings. Assuming 4 years’ operation of B-DECIGO, we found that the detected
BNSs can be divided into three categories: (a) sources that merge within 1 year, which could be
localized with an uncertainty of ∆Ω ∼ 100 deg2 ; (b) sources that merge in 1-4 years, which take up
three quarters of the total events and yield the most precise angular resolution with ∆Ω ∼ 10−2 deg2
and time-of-merger accuracy with ∆tc ∼ 10−1 s; and (c) sources that do not merge during the 4-yr
mission window, which enable possible early warnings, with ∆Ω ∼ 10−1 deg2 and ∆tc ∼ 100 s. Furthermore, we compared the pros and cons of B-DECIGO with the Einstein Telescope, and exploredthe prospects of detections using 3 other decihertz observatories and 4 BNS population models. In
realistic observing scenarios, we found that decihertz detectors could even provide early-warning
alerts to a source decades before its merger while their localizations are still more accurate thanground-based facilities.

Poster session I / 25

Space gravitational wave antenna DECIGO
Authors: Seiji Kawamura1 ; DECIGO-working groupNone
1

Nagoya University

DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese spacegravitational-wave antenna with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at detection ofprimordial gravitational waves, which could have been produced during the inflationary period rightafter the birth of the universe. There are many other scientific objectives of DECIGO, including thedirect measurement of the acceleration of the expansion of the universe, and reliable and accurate
predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO
consists of four clusters of observatories placed in the heliocentric orbit. Each cluster consists ofthree spacecraft, which form three differential Fabry-Perot interferometers with an arm length of
1,000 km. Three clusters of DECIGO will be placed far from each other, and the fourth cluster will
be placed in the same position as one of the three clusters to obtain the correlation signals for thedetection of the primordial gravitational waves. In this presentation, we will explain the aimed
sciences, the mechanical and optical design, and the current status of DECIGO.

Poster session I / 46

Space GW Antenna B-DECIGO
Authors: Masaki Ando1 ; DECIGO groupNone

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University of Tokyo

B-DECIGO is a space gravitational wave antenna mission. While it is a precursor mission of DECIGO,
we can expect fruitful sciences with B-DECIGO. One of the most exciting science cases is detection ofcompact binary system before merger. It will enlarge the possibility of multi-messenger astronomy
with electro-magnetic wave observations at the time of merger. In this presentation , we will review
the science cases and mission concept of B-DECIGO.

Poster session I / 56

Localization of gravitational waves using machine learning
Author: Seiya Sasaoka1
Co-authors: Yilun Hou 1 ; Kentaro Somiya 1 ; Hirotaka Takahashi 2
1

Tokyo Institute of Technology

2

Tokyo City University

An observation of gravitational waves is a trigger of the multi-messenger search of an astronomical event. A combination of the data from two or three gravitational wave detectors indicates thelocation of a source and low-latency data analysis is key to transferring the information to otherdetectors sensitive at different wavelengths. In contrast to the current method, which relies on thematched-filtering technique, we proposed the use of machine learning that is much faster and possibly more accurate than matched filtering.
Our machine-learning method is a combination of the method proposed by Chatterjee et al. and amethod using the temporal convolutional network.
We demonstrate the sky localization of a gravitational-wave source using four detectors: LIGO H1,
LIGO L1, Virgo, and KAGRA, and compare the result in the case without KAGRA to examine thepositive influence of having the fourth detector in the global gravitational-wave network.

Poster session I / 66

Practical quantum noise estimate of optical-spring quantum locking for space gravitational wave detector DECIGO
Author: Ryuma ShimizuNone
Co-authors: Yuki Kawasaki 1 ; Izumi Watanabe 1 ; Tomohiro Ishikawa 1 ; Shoki Iwaguchi ; Bin Wu 1 ; Yutaro
Enomoto 2 ; Shuichiro Yokoyama 3 ; Seiji Kawamura 1
1

Department of Physics, Nagoya University

2

Department of Engineering, University of Tokyo

3

The Kobayashi-Masukawa Institute for the Origin of Particles and the Universe, Nagoya University

The DECi-hertz Interferometer for Gravitational-wave Observatory(DECIGO) aims mainly at thedetection of primordial gravitational waves (PGWs) originating from inflation. Recent observations
by the Planck satellite and others have lowered the upper limit of PGWs. Thus, it is necessary to
improve the target sensitivity of DECIGO. A newly proposed method to reduce the quantum noiseof DECIGO is quantum locking with an optical spring. In this method, a short cavity is added to themain cavity, sharing one mirror of both cavities. The error signal in this auxiliary cavity is obtained
properly in a homodyne detection, and fed back to the shared mirror to cancel the radiation pressure
noise of the main cavity. In our previous study, the optimal sensitivity assuming ideal homodyne
detection without any additional noise was obtained by simulation. In this study, we investigate
a more realistic design, taking into account the mixture of the vacuum fluctuations incident to thehomodyne detection system. In this poster, we explain the latest results of this investigation
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Poster session I / 72

The Sar-Grav Laboratory at the Sos Enattos site, one of the quietest site in the 2-10 Hz frequency range
Author: Domenico D’Urso1
1

University of Sassari and INFN

Einstein Telescope (ET) will be the third generation of gravitational wave interferometer to be built
in Europe. One of the sites candidates to host ET is located in Sardinia (Italy), near the Sos Enattos
mine, where a seismometer’s net already proves the quietness of the site. The Sar-Grav laboratory, aseed of ET, aims to host underground experiments, cryogenic payloads, low frequency and cryogenic
sensor development that need low seismic and anthropogenic noise. On the surface there are ahangar of about 900 square meters, an optical laboratory and a control room; a 20 tons crane andcleaned rooms are planned to be installed. Underground, an area of 250 square meters and small
experimental areas are planned to be built, while different stations at different depths are hosting
sensors like seismometers and magnetometers. A fundamental physics experiment, Archimedes, isunder installation in the surface area and will be moved underground in the future.
The site will host the test of the preliminary seismic isolation system, currently under studies , thatwill be designed to improve seismic attenuation in the low frequency region (0.1-10 Hz) and reduce
the frequency of mechanical resonances.

Poster session I / 62

Gravitational wave sources in the low frequency region and theirdistances
Author: Rosa Poggiani1
1

University of Pisa

Pulsars are expected to be strong sources of low frequency gravitational waves in ground based
interferometers. The knowledge of their distances is a key parameter to estimate the gravitationalemission. The pulsar distances are usually estimated using dispersion measure. The Gaia data releaseprovides information on the distance, kinematic and photometric properties of nearly two billions
astronomical sources, among them some pulsars and accreting neutron star systems.
The Gaia based distances of some systems relevant for gravitational astronomy will be discussed.

Poster session I / 58

The Current Status of TOrsion-Bar Antenna (TOBA) Experiment
Authors: Satoru Takano1 ; Yuka Oshima2 ; Ching Pin Ooi3 ; Yuta Michimura4 ; Masaki Ando3
1

The University of Tokyo

2

University of Tokyo]

3

University of Tokyo

4

CaltechPage 12

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Torsion-bar antenna (TOBA) is a ground-based gravity gradiometer proposed for measurement ofgravity gradient fluctuations such as gravitational waves and gravity gradient noise. TOBA consistsof 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 sensitivity 10ˆ(-19) / √Hz at 0.1 Hz.
For the final sensitivity goal we are developing a prototype Phase-III TOBA in order to investigate
technical issues and establish noise reduction scheme. One of the key topic of Phase-III TOBA iscryogenic suspension system for the reduction of the thermal noise. Another key point is the readout system with monolithic interferometer. We will show the current situation of the developments
and future upgrade plans for further improvement.

Poster session I / 16

Displacement-noise-free neutron interferometer for gravitational
wave detection at low frequencies
Author: Shoki Iwaguchi1
Co-authors: Atsushi Nishizawa 2 ; Yanbei Chen 3 ; Yuki Kawasaki 1 ; Masaaki Kitaguchi 4 ; Taigen Morimoto 1 ;Tomohiro Ishikawa 1 ; Bin Wu 1 ; Izumi Watanabe 1 ; Ryuma Shimizu 1 ; Hirohiko Shimizu 1 ; Yuta Michimura 5 ;Yutaka Yamagata 6 ; Seiji Kawamura 1
1

Department of Physics, Nagoya University

2

Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo

3

Theoretical Astrophysics 350-17, California Institute of Technology

4

The Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University

5

Department of Physics, University of Tokyo

6

RIKEN Center for Advance Photonics, RIKEN

Improvement of the sensitivity of gravitational-waves (GWs) detectors at lower frequencies is stillchallenging on account of displacement noise sources, such as thermal noise, seismic noise, and radiation pressure noise. One of the solutions is the displacement-noise-free interferometer (DFI). At
frequencies lower than 1Hz, however, the DFI has less sensitivity to GWs because the propagation
time of light is much shorter than the period of the GWs. To resolve this problem, DFI with neutrons
instead of laser, which is called a neutron DFI, was proposed. In a neutron DFI with neutrons propagating much more slowly than light, the neutron propagation time can be comparable to the periodof GWs at lower frequencies. This enables us to cancel displacement noise without cancellation of
the GW signals. Also, we proposed a simplification of the detector configuration by taking advantage of the ability to adjust the neutron speeds depending on the configuration. In our poster, we
discuss the principle of the neutron DFI as well as a plan of the demonstration experiment.

Poster session I / 26

Current Status of Quantum Locking Experiment for Space Gravitational Wave Antenna DECIGO
Authors: Tomohiro Ishikawa1 ; Izumi WatanabeNone ; Shoki IwaguchiNone ; Bin Wu1 ; Yuki Kawasaki1 ; Ryuma
Shimizu1 ; Koji Nagano2 ; Yutaro Enomoto3 ; Kentaro Komori2 ; Yuta Michimura4 ; Akira Furusawa3 ; Seiji Kawamura1

1

Department of Physics, Nagoya University

2

Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency

3

Department of Engineering, University of Tokyo

4

Department of Physics, University of Tokyo

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The DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanesespace mission with 1,000 km arm cavities. One of the main objectives of DECIGO is the detectionof primordial gravitational waves (PGWs) produced in the inflation period. We should improve
DECIGO’s target sensitivity, which is limited by quantum noise, to enhance the possibility of thedetection of PGWs.
The standard squeezing techniques to reduce the quantum noise are not effective because of thelarge diffraction loss in DECIGO due to the long arm length. Therefore, we proposed a new method,quantum locking with an optical spring, to reduce the quantum noise in a relatively broad frequency
band. Quantum locking is the technique, in which each mirror of the long arm cavity (main cavity)
is shared by two short-arm cavities (sub-cavities). Then the sub-cavities control the mirrors’ motionof the main cavity. Interferometer signals obtained from the main cavity and the two sub-cavities
can be combined to optimize the sensitivity of DECIGO.
In parallel with the theoretical analysis of the technique, we have been performing the experimentto verify the principle of the theory. In this poster session, we explain the current status of thequantum locking experiment.

Poster session III / 36

Cool-down studies of the low-frequency interferometer in the
Einstein Telescope
Authors: Lennard Busch1 ; Steffen Grohmann2
1

Karlsruhe Institute of Technology (KIT)2

KIT

Corresponding Author: lennard.busch@kit.edu

The low-frequency interferometer in the Einstein Telescope (ET-LF) shall be operated at temperatures of 10 K to 20 K. One cooling concept provides ultra-low noise cooling for steady-state detector
operation using a He-II-filled suspension capillary, in which the heat transport takes place by steadystate heat conduction.
During cool-down, the double-walled capillary enables the flow of single-phase helium to a heatexchanger interface that is coupled by forced convection with the cryogenic infrastructure.
We present a first model of this interface, as well as corresponding thermal and fluid-dynamic numerical simulation results for a transient cool-down process.

Poster session III / 38

Design and Alignment of Compact Optical Heads for Test Mass
Readout with Deep-Frequency Modulation
Authors: Meenakshi MaheshNone ; Oliver Gerberding1
1

Universität Hamburg

Improving the low-frequency range (1 - 10 Hz) of ground-based detectors requires compact interferometric sensors with high displacement sensitivity and dynamic. We combine Deep frequency
modulation and compact interferometric techniques to develop a sensor for local test mass readout.
We introduce an optical head design with on-axis beam topology realized in a Quasi-Monolithic
component (QMC) comprised of cube beam splitters, which ensures beam transmission throughperpendicular surfaces to keep angular alignment constant when operated in air or vacuum. This
On-axis beam propagation should enable sub-picometer level displacement sensing and nano-radiantilt sensing with a high displacement range. We implemented and investigated a table-top model ofPage 14

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the QMC achieving high contrast values. The beam propagation and polarization effects in the QMC
are analyzed and we present our current design for an integrated sensor.

Poster session III / 61

Silicon as a detector suspension material
Authors: Graeme Eddolls1 ; Alan Cumming1 ; Giles Hammond1 ; Karen Haughian1 ; Gregoire Lacaille1 ; Iain
Martin1 ; Sheila Rowan1 ; James Hough2 ; Russell Jones1
1

University of Glasgow

2

University of Glasgow

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 the first demonstration of abonded cryogenically cooled silicon suspension.

Poster session III / 37

Precision limits and a readout algorithm for DFM Interferometry
Authors: Tobias Eckhardt1 ; Oliver Gerberding1
1

Universität Hamburg

Current gravitational wave detectors are limited by local sensor noise and other related technicalnoise sources at low frequencies below 10 Hz. We aim to use compact displacement sensors basedon deep-frequency modulation interferometry for the local readout of test-masses to overcome theselimitations.
In this poster I present our work on the readout of such compact displacement sensors. We analysed
the limitations of such sensors by computing the Cramer-Rao lower bound of the phase estimate in
the presence of common noise sources. And we developed a new algorithm to extract the interferometric phase in deep-frequency-modulation interferometry in a fast and non-recursive way.
First results show that our improved sensor can reach a higher precision than the currently ones
used at the LIGO suspension while also having a larger dynamic range.

Poster session III / 30

Tonga’s volcano eruption signals measured by the evironmental
monitoring systems of KAGRA Observatory
Author: Tatsuki Washimi1
1

NAOJ

On January 15, 2022, at 04:14:45 (UTC), the undersea volcano of Hunga Tonga-Funga Ha’apai erupted
and caused global seismic, atmospheric, and electromagnetic waves. They were transmitted to
Kamioka, more than 8000 km away, and were observed by environmental sensors not only on the
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ground but also inside KAGRA’s underground facility. In this talk, these signals measured by KAGRA’s environmental monitors and the transfer functions from the air-pressure wave in the atmosphere to the underground environmental disturbances (e.g., air-pressure, seismic motion) will bereported.

Poster session III / 43

Broadband quantum noise reduction for AdV+
Author: Marco Vardaro1
1

University of Amsterdam

Technical noise limits the low-frequency sensitivity of interferometric gravitational-wave detectors. Consequently, an effort has been made in recent decades to reduce them, which has led tothe emergence of other limiting sources in the overall low-frequency noise budget. Among thesenoise sources there is the radiation pressure noise which, as demonstrated by LIGO and Virgo in thethird observation run„ can deteriorate the low frequency sensitivity when large amounts of FIS is
injected. In the next few years a huge work to improve the low frequency sensitivity of the gravitational wave interferometers is planned, therefore the quantum radiation pressure noise will limit the
low frequency sensitivity even without FIS injection. For this reason, all collaborations are developing a frequency-dependent squeezing sources that should allow to fully benefit from the injectionof squeezed states leading to a reduction of quantum noise in the whole detector bandwidth.
In this talk we present the status of the development and commissioning of the AdV+ frequency dependent squeezing source based on the filter cavity rotation method. Additionally to the reductionof the quantum noise at all frequencies, in the AdV+ FDS setup, a mitigation system for the straylight detrimental effect is also implemented.

Poster session III / 27

Compensating decoherence of squeezed light in cavity-enhanced
quantum metrology
Author: Mikhail Korobko1
Co-authors: Jan Südbeck 2 ; Sebastian Steinlechner 2 ; Roman Schnabel 2
1
2

Institute for Laser Physics, University of Hamburg
University of Hamburg

Quantum states of light are being more commonly used to increase the sensitivity of various sensors.
They allow to reach high sensitivity without using significant light power, and thus find applicationin various fields, from biological sensing to gravitational-wave detection. At the same time, thesestates are very fragile, and even a small amount of decoherence can significantly reduce their benefit.
We propose a new approach that allows to compensate part of quantum decoherence, thus increasing
the sensitivity beyond the previously established decoherence-induced quantum limit. To achievethis, we use an optimally tuned quantum squeezer placed directly inside the detector cavity. Thissqueezer operates to restore the externally injected squeezing or to amplify the signal, depending on
the level of loss. It can be flexibly tuned to the optimal operation. We present the first experimental
combination of intra-cavity and externally injected squeezing used to enhance detector’s sensitivity.
We demonstrate for the first time how optimal tuning allows to compensate quantum decoherence.
Finally, we derive the new decoherence-induced quantum limit. Based on this approach, we develop
the quantum expander for the detection bandwidth of GW detectors, which allows to significantly
increase the sensitivity at high frequencies.

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Poster session III / 32

Juggled interferometer for gravitational wave detection
Authors: Bin Wu1 ; Tomohiro Ishikawa1 ; Shoki IwaguchiNone ; Ryuma Shimizu1 ; Izumi Watanabe1 ; Yuki Kawasaki1; Yuta Michimura2 ; Shuichiro Yokoyama3 ; Ryota Nishimura4 ; Seiji Kawamura1
1

Department of Physics, Nagoya University

2

Department of Physics, University of Tokyo

3

The Kobayashi-Masukawa Institute for the Origin of Particles and the Universe, Nagoya University

4

Nagoya University

Juggled interferometer (JIFO) is a novel type of earthbound gravitational wave detector targetinga frequency band of 0.1–10 Hz. By using repeatedly free-falling test masses, JIFO can in principle
decouple test masses from the seismically noisy environment and avoid suspension thermal noise ina straightforward manner. Since the test masses are in a weightless state, as is the case with spacegravitational wave detectors, JIFO would be a good testbed for technologies of space projects.
Here, the concept of the Michelson-type JIFO is introduced. Then the experiment setup and the data
readout method of a JIFO are discussed. Considering the displacement noise budget of the Einstein
Telescope (ET), we show that the juggled test masses could significantly improve the sensitivity at 0.12.5 Hz even with discontinuous data. The science cases brought with the improved sensitivity would
include detecting quasi-normal modes of black holes with 104-105 Msun, testing Brans-Dicke theory
with black-hole and neutron-star inspirals, and detecting primordial-black-hole-related gravitational
waves.

Poster session III / 39

SpicyPy: a common python tool for signal processing and control
systems
Author: Artem Basalaev1
1

University of Hamburg

Within gravitational wave research community (including but not limited to LIGO-Virgo-KAGRA,
Einstein Telescope and LISA collaborations) a lot of work in understanding and improving the detectors involves signal processing and modelling of control systems. Historically, different softwaretools were used for these purposes. We believe that it is possible to create a single software toolthat can be useful for many different applications in these domains. This would help to facilitate
exchange of knowledge between collaborations, and could be used in teaching.
We aim to develop a python package intended as a general tool with a simple but powerful interface
to facilitate control systems modelling, signal processing, and provide an interface between the two.
It may rely on other well-known and tested packages already used for these applications, but it will
abstract interactions with them with a unified interface. Potential applications include time series
analysis, suspensions modelling, feeding sensor signals through a control system, and more. The
project is a collaborative open-source effort across the groups from the start, and new contributors
are always welcome. We are currently focused on compiling software requirements specification
and are in discussions with researches from different collaborations to understand the most common
potential applications.

Poster session III / 2
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Substrate transferred aluminum gallium arsenide (AlGaAs) crystalline coatings
Authors: Gregory Harry1 ; Steve Penn2 ; Cole Garrett3 ; Andri Gretarsson4
1

American University

2

Hobart and William Smith Colleges

3

Thorlabs

4

Embry-Riddle Aeronautical University

Substrate-transferred crystalline coatings made from aluminum gallium arsenide (AlGaAs) have very
low thermal noise compared to the ion beam deposited amorphous oxides used until now in gravitational wave detectors. AlGaAs coatings also show excellent optical properties and both thermal
noise and optical performance has been demonstrated in other precision optics applications. The
primary challenge to using AlGaAs coatings in future detectors is the coating diameter necessary
and the large mass and thickness of the test mases. We present results on 10 cm diameter AlGaAs
coatings and propose multiple pathways to implement AlGaAs coatings on upgrades to current detectors with up to 40 kg masses and on future detectors with larger masses. We also show scheduleand budget plans that allow AlGaAs to be used in future gravitational wave detectors.

Poster session III / 47

Optical absorption of TiO2 doped SiO2 as a replacement high index coating material
Authors: Simon Tait1 ; Ross Johnston1 ; Iain Martin1 ; Graeme McGhee2 ; Peter Murray2 ; Viola Spagnuolo3 ; Jessica
Steinlechner3 ; Lukas Terkowski4 ; Sheila Rowan1 ; James Hough2
1

University of Glasgow

2

University of Glasgow

3

Maastricht University

4

Universite de Hamburg

The sensitivity of 3rd generation gravitational wave detectors is currently projected to belimited by the level of Brownian coating thermal noise produced from highly reflecting
mirror coatings. In the current detectors layers of Ta2 O5 , a material with higher
refractive index (n = 2.14), has higher levels of optical absorption compared the lower index
layers of SiO2 (n=1.44). To improve detector sensitivity and duty cycle, the optical andmechanical properties of new doped coating materials are being investigated. This work
presents measurements of the optical absorption of SiO2 and SiO2 doped with
TiO2 layers as part of a highly reflecting coating stack. Utilising the photothermal
common-path interferometry technique, we discuss the effects of heat treatment andcrystallisation on the optical performance of the material compared to current aLIGO
coatings.

Poster session III / 48

TiO2 :SiO2 coating thermal noise and optical studies
Authors: Graeme McGheeNone ; Viola Spagnuolo1 ; Simon Tait2 ; Ross Johnston2 ; Lukas Terkowski3 ; Peter Murray4; James Hough4 ; Sheila Rowan2 ; Jessica Steinlechner1 ; Iain Martin2
1

Maastricht University

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University of Glasgow

3

Universite de Hamburg

4

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Current gravitational wave detectors are limited in their most sensitive frequency range by the mirror coating thermal noise which arises from the Brownian motion of the coating materials on theinterferometer test mass optics. For the next generation detector upgrades and beyond, it is imperative to find coating materials/topologies that reduce this mechanical effect, whilst still meeting thedesired optical requirements. Titania-doped silica had been identified as a coating material candidate
which could potentially improve detector sensitivity.
We present here our investigations into the mechanical and optical properties of highly-reflective
coating stacks made of pure SiO2 and TiO2 doped SiO2, deposited via ion beam sputtering (IBS). Two
different concentrations of TiO2 doping in the high-refractive index layers of our coating stacks
were investigated, with mechanical loss and optical absorption being measured through different
steps of heat treatment for each, with the level of coating thermal noise being calculated from theformer.

Poster session III / 13

Angular Signal Amplification with a Coupled Cavity for TorsionBar Antenna
Author: Yuka Oshima1
Co-authors: Satoru Takano 1 ; Ching Pin Ooi 1 ; Masaki Ando 1
1

University of Tokyo

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 / 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 Phase-III
TOBA with a 35 cm-scale pendulum
is under development to demonstrate noise reduction. The tar√
get sensitivity is set to 10−15 / Hz at 0.1 Hz. To achieve our target sensitivity, we need to measure
the pendulum rotation precisely. We propose a coupled wavefront sensor (Coupled WFS) as an angular sensor for Phase-III TOBA. In our method, an auxiliary cavity is used to compensate Gouy
phase of a main cavity and enhance the first-order TEM modes in the main cavity. The experimental
demonstration was successfully performed in 2021. In this workshop, we will show the principle
and demonstration results of a Coupled WFS.

Poster session III / 44

Estimating the Newtonian noise of groundwater at the KAGRA
Author: Takanori Suzuki1
Co-author: Kentaro Somiya 1
1

Tokyo Institute of Technology

Changes due to gravitational waves are very small, so noise is generated due to various factors. KAGRA was built 300 meters underground to reduce ground vibrations. The groundwater generated
underground is discharged through pipes. The gravity gradient generated by the universal gravitation force due to the oscillation of the water surface through the pipe may cause the mirror ofPage 19

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KAGRA to shake and become a noise to the target sensitivity of KAGRA.
Our experiment was conducted using the simulation software Flow-3D in order to know the magnitude of Newtonian noise. The Newtonian noise was evaluated by calculating the waveform of theflowing water.

Poster session III / 45

Control of Dual-Pass Fabry-Perot Cavity for space gravitational
wave antennas : DECIGO and B-DECIGO
Author: Masaya OnoNone
Co-authors: Koji Nagano 1 ; Kentaro Komori 1 ; Yuta Michimura 2 ; Masaki Ando 3
1

Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency

2

Department of Physics, University of Tokyo

3

University of Tokyo

A dual-pass Fabry-Perot cavity will be used for DECIGO (DECi-hertz Interferometer Gravitationalwave observatory) and B-DECIGO. To detect gravitational waves, it is necessary to establish themethod to control the dual-pass Fabry-Perot cavity. We can divide this issue in two parts, “Length
control” and “Alignment control”. For Length control, it is demonstrated that we can control thelength of dual-pass Fabry Perot cavity with Pound-Drever-Hall technique. On the other hand, for
Alignment control, though the method was already proposed (WaveFront Sensor and Beam Pointing
Control), it is not demonstrated yet. Therefore, an experiment is needed for the demonstration.In
this poster, we show the principle to control the dual-pass Fabry-Perot cavity in the direction of theangle and explain the experiment to demonstrate it.

Poster session III / 71

CO2 mode cleaner for Thermal Compensation System of Advanced
Virgo+
Author: P. Giri1
Co-authors: E. Cesarini ; V. Fafone ; M. Lorenzini ; D. Lumaca ; Y. Minenkov ; I. Nardecchia ; A. Rocchi
1

INFN Pisa

As planned for its fifth observation run O5, Advanced Virgo+ will have 80 Watts in main laser. The
absorption of laser power in the interferometer’s core optics leads to thermal effects causing opticalaberrations, ultimately preventing interferometer’s operation. To recover detector’s ideal operation,
Thermal Compensation System (TCS) is needed to correct wavefront distortions. In particular, tocorrect the axisymmetric part of the spurious thermal lens in the power recycling cavity, a heating
pattern is projected on a compensation plate using Double Axicon System (DAS) where a 50 Watts
CO2 laser beam is reshaped using axicons. Due to O5 stringent requirements on the residual of DAS
correction, heating pattern distortions caused by the known amount of higher-order modes (HOM)
in the CO2 beam cannot be tolerated. To remove these HOMs, we are constructing an optical modecleaner which will allow us to retain 95% of the CO2 laser power for compensation with a strong
reduction of HOM related residual correction. To our knowledge, this is the first time a mode cleaner
is designed for a high power CO2 laser. We present here the requirements, motivation and current
status of the work, discussing the issues related to the CO2 wavelength and power.

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Poster session III / 63

Vibration analysis of ETpathfinder cryogenic heat-links
Author: Andrei Utina1
Co-authors: Rogier Elsinga 2 ; Eric Hennes 2 ; Alessandro Bertolini 3 ; Sebastian Steinlechner 4 ; Stefan Hild

5

1

Maastricht University

2

Nikhef3

NIKHEF

4

University of Hamburg

5

Maastricht University, Nikhef

The Einstein Telescope pathfinder (ETpathfinder) is a cryogenic testbed for the next generation ofgravitational-waves antennas. To reach the target temperature of 18 K, ETpathfinder cryogenic
payloads are designed to extract heat from the test masses by integrating low stiffness and highly
conductive heat-links that connect to the cryocoolers. Since the interferometer test masses are very
sensitive to mechanical vibrations, the noise from the cryocoolers through the heat conductor should
be carefully monitored and controlled. This work presents the modeling and experimental measurements of the mechanical vibrations transferred by the heat-links in a dedicated payload setup. To
investigate the stability criterion of the cold-head, seismic noise propagated via the heat-links is thenprojected to the displacement sensitivity of ETpathfinder.

Poster session III / 31

Measuring thermal noise in gram-scale Si flexures at 123 K
Author: Disha Kapasi1
1

Ms

Future terrestrial gravitational wave detectors are limited by fundamental noise sources, one ofwhich is the thermal noise arising in the test masses and suspensions in the frequency band where
ground-based detectors are sensitive. To mitigate this noise, future detectors are envisioned to operate at cryogenic temperatures using silicon optics as test masses and silicon ribbons to suspend
the test masses. Silicon ribbons resemble cantilever topology, and therefore studying the thermal
noise in the flexing of a gram-scale silicon cantilever is analogous to the suspension thermal noise
encountered in these ribbon suspensions. At the Australian National University, I have built an operational cryogenic infrastructure to measure the broadband thermal noise of silicon flexures at 123
K. In this talk, I will present initial results of our cool-down tests, thermal noise measurements fromthe experiment and future plans.

Poster session III / 17

Vibration Analysis of KAGRA Cryostat at Cryogenic Temperature
Author: Rishabh Bajpai1
Co-authors: Takayuki Tomaru 2 ; Nobuhiro Kimura 3 ; Takafumi Ushiba 3 ; Kazuhiro Yamamoto 4 ; Toshikazu
Suzuki 5 ; Tohru Honda 6
1

SOKENDAI

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2

National Astronomical Observatory of Japan

3

The University of Tokyo Institute for Cosmic Ray Research Kamioka Observatory

4

University of Toyama

5

The University of Tokyo Institute for Cosmic Ray Research

6

High Energy Accelerator Research Organisation/ Book of Abstracts

Large-scale Cryogenic Gravitational-Wave Telescope, KAGRA is a second-generation gravitationalwave detector (GWD) located in Japan. The features that distinguish KAGRA from other GWDs are
its underground location and cryogenic operation of the four main mirrors. The underground location provides a quiet site with low seismic noise, while the cryogenic operation cools the mirrors
down to 20 K, reducing the thermal noises. However, cryocooler vibration and structural resonancesof the cryostat can contaminate detector sensitivity as they couple to test mass through the heat-links.
Monitoring and characterization of the vibration inside the cryostat is critical for the optimum noise
performance of KAGRA.
In April, 2020 KAGRA conducted an international observation run, “O3GK” along with GEO600.
During this run several noise sources were identified and a noise budget was prepared. However, as
the mirrors were not cooled the noise transfer via heat-links was estimated based on room temperature, in vacuum vibration measurement performed 2.5 years before O3GK. During the upcoming
observation run the mirrors will be cooled down, so we performed vibration analysis of the cooling system at cryogenic temperature to study its impact on detector sensitivity. In this poster, we
describe the KAGRA cooling system and discuss the results of vibration analysis.

Review of LIGO’s LF workshop / 29

Review of LIGO’s LF workshop
Corresponding Author: pf@ligo.mit.edu

Scatter light for LF / 55

BRDF revisited
Author: Hiroaki Yamamoto1
1

CaltechCorresponding Author: hiroy@caltech.edu

Bidirectional Reflectance Distribution Function (BRDF) of LIGO and Virgo test masses quantifies thereflection of mirrors. It is related to the round trip loss (RTL) of the arm cavity and to various straylights which induce noises in various ways. The available data of BRDF is limited and the RTL cannot
be fully calculated by using existing BRDF data. This talk summarizes existing BRDF data of aLIGO,
AdVirgo and 40m to characterize the overall view of BRDF and its applications to understand thecavity loss and to quantify stray light induced noises.

Scatter light for LF / 53

Stray Light Measurements With an Instrumented Baffle in the
Advanced Virgo Input Mode Cleaner Cavity
Author: Giada Caneva SantoroNone

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In April 2021, a new instrumented baffle was installed surrounding the suspended end mirror of
the Virgo’s Input Mode Cleaner (IMC) cavity, as part of the phase I upgrade of the Advanced Virgointerferometer. The device is equipped with photo sensors that monitor the stray light inside thecavity. It serves as a demonstrator of the technology for the baffles that will monitor the stray lightin the main arms, which will be installed during the phase II upgrade in the near future.
We will give an overview of the status of the instrumented baffle and its integration into the Virgoenvironment and present results on the measured scattered light distribution inside the cavity using
data collected between spring 2021 and spring 2022, with Virgo in commissioning phase. The sensitivity and performance stability of the baffle is discussed and the data is compared to scattered light
simulations.
These results will serve to calibrate the simulations and demonstrate the potential of instrumented
baffles to detect defects in the mirrors and to improve the understanding of the scattered light inside
ground-based gravitational wave experiments like Virgo.

Scatter light for LF / 23

Scattered light measurement and active mitigation for Advanced
Virgo Plus
Author: Eleonora Polini1
1

LAPP - CNRS/IN2P3

Corresponding Author: polini@lapp.in2p3.fr

Scattered light is a source of noise which limits the performance of current gravitational wave detectors.
In order to understand and mitigate this effect it is important to know quantitatively the amount oflight backscattered by all the elements located on optical benches. To this purpose we built at LAPP
an interferometric scattermeter with which the BRDF of the desired elements is measured.
In parallel, in Virgo we are working to mitigate the identified scattered light sources. On the one
hand, we conducted a complete mitigation campaign of secondary beams, i.e. ghost beams, on all
Virgo subsystems. As these unwanted beams propagate, they can produce scattered light that recombines with the interferometer beam. On the other hand, we developed a control loop to actively
correct the stray light noise that was affecting the squeezing system. The principle of this system
can be applied in other circumstances.

Scatter light for LF / 68

Fast Scattering transient noise at LIGO Livingston
Author: Siddharth SoniNone
Corresponding Author: siddsoni@mit.edu

During the third Observing run, Fast Scattering was the mostfrequent source of transient noise at LIGO Livingston. The noise shows up
as arches in time-frequency plane, usually separated by 0.25 sec (4 Hz) or
0.5 sec (2 Hz) from each other. This noise has been found to be correlatedwith elevated levels of ground motion in the anthropogenic and microseismic
band. Depending on the amount of relative motion in these two bands, 2 Hz
or 4 Hz fast scatter shows up. To localize the potential coupling to thedetector, we examined the correlation between ground motion at End andCorner stations with the noise in DARM.

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Summary / 21

GWADW2023

Summary / 20

Panel discussions

Summary / 74

ET at 3 Hz - can we break the ’controls noise’ wall?
Author: Conor Mow-Lowry1
1

NikhefCorresponding Author: c.m.mow-lowry@vu.nl

The Einstein Telescope aims to have astrophysically interesting
sensitivity at 3Hz. The performance goal is a factor of ˜10ˆ6 quieter
than LIGO and Virgo at that frequency. This talk will present a recipe
for addressing controls noise in a systematic manner at the design stage
with supporting evidence from existing instruments.

Summary / 22

Closing remark

Summary / 19

Cosmic Explorer at low frequency
Author: Evan HallNone
Corresponding Author: evanhall@mit.edu

This talk will discuss the problems that must be solved to achieve Cosmic Explorer’s low frequency
sensitivity goals.

Suspensions for LF / 4

The latest development in ALFRA, the UWA low-frequency rotational accelerometer
Authors: Ammar Al-Jodah1 ; Jack Williamson1 ; Li Ju1 ; John Winterflood1

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1

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The University of Western Australia

Corresponding Author: ammar.al-jodah@uwa.edu.au

Ground rotation sensors at low-frequency have a vital role in improving seismic isolation systems
in advanced and 3G gravitational wave detectors. It was found that using seismometers as the solesource of ground motion measurement results in undistinguishable motion detection between horizontal and tilt motion, especially below 100 mHz. Therefore, pure angular motion measurement isnecessary to separate tilt and translation to be applied as feedback in active isolation control. ALFRA is a low-frequency rotational accelerometer developed at the University of Western Australia(UWA) to detect ground tilt motion. It is a compact, inertial reference style rotation sensor thatcan be mounted in three orientations to detect ground tilt around a different axis of interest. A
preliminary study of a prototype showed that ALFRA can achieve high readout sensitivity of few
nrad/√Hz above 20 mHz and 0.1 nrad/√Hz above 50 mHz in measuring ground tilt. In this work, wewill present our latest design for ALFRA and highlight several improvements that will be added toour previous design to enhance several aspects of the sensor and increase its sensitivity, usability,
and convenience of adjustment.

Suspensions for LF / 76

E-TEST: A Compact Isolation Concept for Future Einstein Telescope
Author: AMEER SIDER1
1

Precision Mechatronics Laboratory, Université de Liège, B-4000 Liège, Belgium

Corresponding Author: asider@uliege.beThis study presents a low frequency isolation system in the framework of E-TEST project which is a
research facility for Einstein Telescope. The isolation system combines a passive inverted pendulum
and an active inertial platform. The design of this isolator allows reducing the overall height of
the isolation system. We address the isolation system design, its dynamics and the control strategy
applied. The simulation results show that the seismic noise could successfully be reduced by about
3 orders of magnitude at 1 Hz in horizontal when the control is applied. To avoid spoiling theperformance at high frequency, the inertial platform is designed in such a way that the first flexible
internal mode appears above 300 Hz.

Suspensions for LF / 34

New Generation Superattenuators for Einstein Telescope
Author: Lucia Trozzo1
1

Istituto Nazionale di Fisica Nucleare

Corresponding Author: lucia.trozzo@na.infn.it

Seismic noise and local disturbances are dominant noise below 10 Hz (0.1-10 Hz).With the introduction of high performance seismic isolation systems based on mechanical pendula,the 2nd generation GW antennas have reached the scientific goal of the direct observation of GW signals thanks
to the extension of the frequency band down to 10 Hz. Now,the 3rd generation instrument era isapproaching and the Einstein Telescope giant interferometer is becoming a reality with the possibility to install the detector in an underground site where seismic noise is 100 times smaller then on
surface. Moreover,new available technologies and the experience acquired in operating advanced
detectors are key points to further extend the detection bandwidth down to 2-3 Hz with the possibility to suspend cryogenic payload and then mitigating Thermal Noise too.In this talk, we present the
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preliminary studies devoted to improve seismic attenuation performance of the Advanced VIRGOSuperattenuator in the low frequency region.Following the experimental lines,we analyze the possibility to improve the vertical attenuation performance with a multistage pendulum chain equippedwith magnetic anti-springs that is hung to a double Inverted Pendulum in nested configuration.The
feedback control requirements and the possible strategies to be adopted for this last element, will bepresented.

Suspensions for LF / 33

Update on sensing seismic platform relative motion using Digital
Interferometry
Authors: Sheon Chua1 ; Bram Slagmolen2
1

ANU Centre for Gravitational Astrophysics - OzGrav

2

ANU Centre for Gravitational Astrophysics

Corresponding Author: sheon.chua@anu.edu.au

The relative motion of seismic platforms, via coupling to the auxiliary length controls of the suspended optics, are predicted to be the limiting noise source for future gravitational-wave detectors
at frequencies below 1 Hz. By measuring, then stabilizing this relative motion, the effective control
feedback to the optics will be reduced and hence the noise coupling will be less, and potentially
improve detector noise performance. The measurement of the relative motion with forms of suspension platform interferometry is an ongoing area of interest and research. Digitally-enhanced
Interferometry is a decade-mature technique for sensing relative motion, by providing time-tagged
pseudorandom phase modulation to isolate signals based on time-of-flight delay. The application ofdigitally-enhanced interferometry for suspension sensing is an active area of development within
the Newtonian Noise research program at the Australian National University, and offers another potential method for sensing relative platform motion. We present an update on recent developmentsof digitally-enhanced interferometry towards suspension sensing and measurement.

Suspensions for LF / 69

Introduction
Corresponding Author: joris.vanheijningen@uclouvain.be

Suspensions for LF / 57

Newtonian Noise in the Einstein Telescope
Authors: Francesca Badaracco1 ; Luca Naticchioni2
1

UCLouvain

2

INFN RomaCorresponding Author: francesca.badaracco@uclouvain.be

Newtonian noise (NN) was predicted to represent the very last sensitivity wall in Earth based gravitational wave detectors already by their first pioneers. Virgo will soon implement the first NN
cancellation system ever and the knowledge we acquired during its development will be an asset inPage 26

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evaluating what we need to reduce as much as possible the NN in the Einstein Telescope.
The problem here will be different given that the Einstein Telescope will be located underground,
this will imply new difficulties that will contribute to spoil the NN cancellation capabilities. In thistalk we will review the key points we must keep in mind to develop the NN cancellation system for
the Einstein Telescope.

Suspensions for LF / 8

Tunnel configurations and seismic isolation optimization in underground gravitational wave detectors
Author: Riccardo DeSalvo1
Co-authors: Andrea Paoli 2 ; Florian Amann 3 ; Francesca Badaracco 4 ; Luca Paoli 2 ; Paolo Ruggi 2 ; Stefano Selleri
51

University of Utah

2

EGO

3

rwth aachen

4

UCLouvain

5

Università di Firenze

Corresponding Author: riccardo.desalvo@gmail.com

Gravitational wave detectors like the Einstein Telescope (ET) will be built a few hundred meters
underground to reduce both seismic and Newtonian noise. Underground facilities must be designed
to take full advantage of the shielding properties of the rock mass to maximize the detector´s performance. A major issue with the ET design are the corner points, where caverns need to be excavatedin stable and low permeability rock. This paper proposes a new topology that moves the top stagesof the seismic attenuation chains and the re-combination of the beams of the Michelson interferometers in separate excavations far from the beam-line and equipment induced noise while the test
mass mirrors remain in the main tunnels. Distributing the seismic attenuation chain components
over multiple tunnel levels allows the use of arbitrarily long seismic attenuation chains that relegate
the seismic noise at frequencies completely outside the low-frequency noise budget, thus keeping
the door open for future Newtonian noise suppression methods. Separating the input-output and recombination optics of different detectors into separate caverns drastically improves the observatory
detection efficiency and allows staged commissioning. The proposed scheme eliminates structuraland instrumentation crowding while the reduced sizes of excavations require fewer support measures.

Technical noise for LF / 54

Astigmatic mode mismatch sensing for the next gravitational wave
detectors.
Authors: Andrea Grimaldi1 ; Antonio Perreca2
1

TIFPA-INFN, University of Trento

2

TIFPA - University of Trento

One of the main limits of the Quantum Noise Reduction in Gravitational Wave detectors is the opticallosses 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 mismatch between optical cavities.
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However, the current technologies based on the spherical Gaussian Beam are not enough for the
next generation of Gravitational Wave Detectors. In fact, the higher requirement on the opticallosses imposes to compensate also the modematching generated by astigmatic aberrations, so a newgeneration of wavefront sensor technique is needed.
Here we will present an upgrade of the Mode Conversion Telescope technique that extends themismatch measurement from the only symmetric aberrations to a complete characterisation of themismatch between an astigmatic Gaussian beam and a resonance cavity. This extension uses four additional Quadrants Photodiodes sensors to detect the beat note between the Sidebands of the TEM00
and the second-order Hermite-Gauss mode TEM11 of the carrier. In particular, we will describe themethod and present the first experimental results of this technique.

Technical noise for LF / 51

Birefringence characterisation of KAGRA ITMs and simulation
with FINESSE
Authors: Haoyu WangNone ; Yoichi Aso1 ; Yutaro EnomotoNone ; Eiichi HiroseNone ; Keiko Kokeyama2 ; Matteo
Leonardi1 ; Kentaro Somiya3 ; Hiroaki Yamamoto4 ; Yuta Michimura4
1

NAOJ

2

Cardiff University

3

Tokyo Institute of Technology

4

CaltechCorresponding Author: h.wang2013@outlook.com

KAGRA is a cryogenic detector using sapphire mirrors as its test masses. The sapphire material waschosen mainly for its high thermal conductivity, low absorption and high transmittance of the 1064
nm laser. However, sapphire has a few disadvantages like birefringence. During the commissioning,
we found out the interferometer had unexplained optical losses and beam distortions due to thebirefringence effect from two input test masses. These issues degrade the detector controllability
and sensitivity to the astronomical gravitational waves. In this talk, we would like to update ourbirefringence characterisation of KAGRA input test masses. We also proposed a method to model theimpact of birefringence effect to the interferometer using the simulation software FINESSE.

Technical noise for LF / 42

Low-frequency magnetic noise in terrestrial GW detectors: thecase study of AdV+ Faraday isolator
Author: Jean-Loup RaymondNone
Co-authors: Alessio Buggiani ; Andrea Chincarini 1 ; Antonino Chiummo ; Beatrice D’Angelo ; Irene Fiori 2 ;Matthieu Gosselin ; Romain Gouaty ; Federico Paoletti ; Paolo Ruggi 3 ; Maria Concetta Tringali
1

INFN Genova

2

European Gravitational Observatory

3

EGO

Corresponding Author: jeanloup.raymond@ego-gw.it

The coupling of environmental magnetic fields is a limiting factor for the lowfrequency sensitivityof future ground-based interferometers. Coupling can occur at various locations, such as actuation
magnets of the mirror and optical benches isolation systems. Eddy currents in conductive parts
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can locally warp magnetic fields and enhance magnetic forces. A major goal for future detectors is
to reduce magnetic fields and coupling with specific interferometer components. A characteristic
example is the optical Faraday isolators, which are used to block reflected light beams by meansof a magneto-optic crystal immersed in an intense static magnetic field. We present the study of apassive magnetic shield for the F I of the suspended detection bench of the AdV+ phase II detector.
We illustrate the design optimization process and highlight critical points we faced and solved. We
propose a procedure to measure the displacement of the bench due to an injected magnetic field
coupling to the Faraday isolator.

Technical noise for LF / 40

Demonstrating Interferometric Sensors to Improve Local Controlof Suspended Optics
Authors: Alexandra Mitchell1 ; Jesse van Dongen2
1

Nikhef/VU Amsterdam

2

NikhefCorresponding Author: a.l.mitchell@vu.nl

Control noise dominates the low frequency spectrum of gravitational wave detectors. Improving
sensors and hence local control will ease requirements for global control and reduce noise reinjected into the detector. Three Homodyne Quadrature Interferometers (HoQIs) were installed at the
middle-mass of the beamsplitter triple suspension at AEI-Hannover’s 10m prototype interferometer.
HoQIs have compact baseplates designed to mount on the ‘lower tablecloth’ of the Big BeamSplitter
Suspension (BBSS) for LIGO’s A+ upgrade. Hollow, gold-coated retroreflectors mounted on the mass
improve robustness to misalignment. The complete optical and electronic signal chain for in-vacuum√
use was tested. Signals were dominated by ground motion, but a level of ˜3 × 10−13 m/ Hz wasseen at a few hundred Hz. The fringe visibility changed by less than 0.05 when we applied the largest
possible vertical misalignment of 180um. The suspension is now ready to be tested in-vacuum. The
benefits of using HoQI to damp resonance peaks in the BBSS have been modelled. We predict an
improvement of factor 8 in peak suppression, and factor 60 lower RMS motion of the optic at 1Hz.
If deployed on multiple suspensions, this can allow a reduction of auxiliary control bandwidths andassociated noise in the 10-20Hz band.

Technical noise for LF / 35

Low-Frequency control noise - Modelling ASC loops with Finesse
Author: Riccardo MaggioreNone
Co-authors: Alexandra Mitchell 1 ; Andreas Freise 1 ; Antonella Bianchi 1 ; Conor Mow-Lowry 1 ; Daniel Brown 2; Jonathan Perry 1 ; Mischa Sallé 1 ; Paolo Ruggi 3
1

Nikhef2

University of Adelaide

3

EGO

Corresponding Author: r.maggiore@nikhef.nl

The Einstein Telescope (ET) is a third-generation gravitational-wave detector, which is expected tobe 1000 times more sensitive than current instruments at low frequencies. In this frequency range,
detectors have been limited by technical noises. Alignment control is at the frontline of the limiting
noises.
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The amount of angular control noise chained to the sensitivity depends upon the bandwidth of thealignment control systems. By using low-bandwith control loops ET can keep the control noise
below ET fundamental noises. We are building a model of such an alignment control scheme, using
Finesse, a python-based interferometer simulation program.
We started with modelling Advanced Virgo’s alignent control system, which incorporates highfinesse optical cavities and the last two stages of the super-attenuator. Control filters in the global
basis have been implemented as used during O3 run and the resulting closed-loop MIMO matrix accounts for cross-coupled degrees of freedom, both in sensing and actuation. We will use this model
to evaluate the alignment controllability of the Virgo opto-mechanical plant for O5 run, design thecontrol strategy and test its noise performance. We will use the experience on validation from Virgo
to design the alignment scheme for ET.

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