LISA optical bench development

experimental investigation of differential-wavefront sensing for a spaceborne gravitational wave detector

verfasst von: Alvise Pizzella
betreut von: Gerhard Heinzel
Abstract: The Laser Interferometer Space Antenna (LISA) is a satellite mission led by the European Space Agency (ESA) scheduled to be launched in 2035. It will be the first space-based gravitational wave (GW) observatory, aiming to detect GWs in the 10^−4 − 10^−1 Hz band. Heterodyne laser interferometry is used to measure changes in distance between two test masses (TMs) shielded by two spacecraft and separated by millions of kilometers. The ambitious sensitivity of pm/ √Hz presents many technical challenges, such as the weak-light condition and the coupling of the angular jitter of the spacecraft and TMs to the interferometrically-measured longitudinal displacement, or tilt-to-length (TTL). Addressing this weak-light condition requires careful optimization of the heterodyne detection system, mainly of the quadrant photoreceivers (QPRs) and the phasemeter (PM) electronics. The angular motion of the spacecraft and especially the jitter of the moving optical subassemblies (MOSAs) introduce additional phase noise that is one of the main contributors to the total displacement noise. To mitigate these effects, differential wavefront-sensing (DWS) is employed. DWS serves both in flight for the active control of the position and rotation of the TMs, MOSAs and spacecraft, and on ground, for calibration and subtraction of residual TTL in post-processing. The sensitivity of the DWS technique under weak-light conditions and in the presence of tilts remains uncharacterized. This gap represents a major focus of the current work, aiming to evaluate DWS performance in conditions that closely simulate those expected in LISA during flight. During this thesis, such performance was demonstrated for the first time using TDOBS, a testbed representative of LISA’s optical bench (OB). This is an ultrastable interferometer testbed that has been developed to validate critical interferometric techniques for the LISA mission. The testbed features a pair of steering mirrors that can induce synthetic tilts between the beams to simulate spacecraft or TM motion. This experiment, which already successfully demonstrated optical reduction of TTL by means of imaging systems (ISs) using kHz beat notes, was upgraded to beat notes in the 5-25 MHz band, becoming fully LISA representative. Furthermore, TDOBS features low-noise QPRs comparable to those of LISA. The first part of the thesis focuses on understanding the DWS signals, modelling their dependence on the geometrical properties of the optical setup, and their calibration. This section is essential for connecting the measurements performed in TDOBS to their analogue in LISA, and for estimating how to test LISA’s requirements on the ground. The second part focuses on the experimental setup. The DWS noise performance is characterized and broken down into individual noise contributors. Experimental investigations are presented, including first-time measurements of DWS noise under weak-light conditions and in the presence of beam tilts. The working principle of a novel architecture of tracking beat notes from a quadrant photodiode (QPD) is demonstrated for the first time using optically generated beat notes. To conclude, the future improvements and projects of TDOBS together with the takeaways for LISA are discussed.
Organisationseinheit(en): PhoenixD: Simulation, Fabrikation und Anwendung optischer Systeme
QUEST Leibniz Forschungsschule
Typ: Dissertation
Anzahl der Seiten: 227
Publikationsdatum: 03.02.2025
Publikationsstatus: Veröffentlicht
Elektronische Version(en): https://doi.org/10.15488/18487 (Zugang: Unbekannt)
: Details im Forschungsportal „Research@Leibniz University“

BibTeX

@phdthesis{4ad6b1aeeae346ed8d5b5f5783fa9548,
title = "LISA optical bench development: experimental investigation of differential-wavefront sensing for a spaceborne gravitational wave detector",
abstract = "The Laser Interferometer Space Antenna (LISA) is a satellite mission led by the European Space Agency (ESA) scheduled to be launched in 2035. It will be the first space-based gravitational wave (GW) observatory, aiming to detect GWs in the 10^−4 − 10^−1 Hz band. Heterodyne laser interferometry is used to measure changes in distance between two test masses (TMs) shielded by two spacecraft and separated by millions of kilometers. The ambitious sensitivity of pm/ √Hz presents many technical challenges, such as the weak-light condition and the coupling of the angular jitter of the spacecraft and TMs to the interferometrically-measured longitudinal displacement, or tilt-to-length (TTL). Addressing this weak-light condition requires careful optimization of the heterodyne detection system, mainly of the quadrant photoreceivers (QPRs) and the phasemeter (PM) electronics. The angular motion of the spacecraft and especially the jitter of the moving optical subassemblies (MOSAs) introduce additional phase noise that is one of the main contributors to the total displacement noise. To mitigate these effects, differential wavefront-sensing (DWS) is employed. DWS serves both in flight for the active control of the position and rotation of the TMs, MOSAs and spacecraft, and on ground, for calibration and subtraction of residual TTL in post-processing. The sensitivity of the DWS technique under weak-light conditions and in the presence of tilts remains uncharacterized. This gap represents a major focus of the current work, aiming to evaluate DWS performance in conditions that closely simulate those expected in LISA during flight. During this thesis, such performance was demonstrated for the first time using TDOBS, a testbed representative of LISA{\textquoteright}s optical bench (OB). This is an ultrastable interferometer testbed that has been developed to validate critical interferometric techniques for the LISA mission. The testbed features a pair of steering mirrors that can induce synthetic tilts between the beams to simulate spacecraft or TM motion. This experiment, which already successfully demonstrated optical reduction of TTL by means of imaging systems (ISs) using kHz beat notes, was upgraded to beat notes in the 5-25 MHz band, becoming fully LISA representative. Furthermore, TDOBS features low-noise QPRs comparable to those of LISA. The first part of the thesis focuses on understanding the DWS signals, modelling their dependence on the geometrical properties of the optical setup, and their calibration. This section is essential for connecting the measurements performed in TDOBS to their analogue in LISA, and for estimating how to test LISA{\textquoteright}s requirements on the ground. The second part focuses on the experimental setup. The DWS noise performance is characterized and broken down into individual noise contributors. Experimental investigations are presented, including first-time measurements of DWS noise under weak-light conditions and in the presence of beam tilts. The working principle of a novel architecture of tracking beat notes from a quadrant photodiode (QPD) is demonstrated for the first time using optically generated beat notes. To conclude, the future improvements and projects of TDOBS together with the takeaways for LISA are discussed.",
author = "Alvise Pizzella",
year = "2025",
month = feb,
day = "3",
doi = "10.15488/18487",
language = "English",
publisher = "Leibniz Universit{\"a}t Hannover",
school = "Leibniz University Hannover",
}