SAMOP 2023 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 11: Precision Measurements: Gravity I

Q 11.1: Talk

Monday, March 6, 2023, 17:00–17:15, E214

a testbed for Tilt-To-Length coupling and Differential-Wavefront-Sensing performance in LISA — •Alvise Pizzella, Miguel Dovale, and Gerhard Heinzel — AEI Hannover, Germany

The LISA mission aims at measuring gravitational waves (GWs) in the sub-Hz band using inter-spacecraft interferometry. It consists in a constellation of three satellites in triangle formation with 2.5 Gm-long arms following an Earth-like heliocentric orbit. The target sensitivity of pm/Hz^1/2 presents unprecedented technical challenges; such as minimal detected power levels, causing shot noise, and the coupling of the angular jitter of the spacecraft and test masses to the interferometrically-measured longitudinal displacement (Tilt-To-Length (TTL) coupling). TTL is forecasted to be the second highest noise entry in LISA. In order to readout from the heterodyne interference beatnote the length and angular signals, necessary for respectively GWs detection and maintaining the interferometer*s alignment, LISA implements Differential-Wavefront-Sensing (DWS), combining the individual phase readouts from the four segments of a Quadrature PhotoDiode (QPD). An ultra stable interferometer testbed representative of the Optical Bench (OB) of a LISA spacecraft has been developed in order to validate the critical interferometric techniques for LISA. The testbed features steering mirrors that can induce synthetic tilts between the beams to simulate spacecraft or test mass motion. This experiment has been used to demonstrate optical reduction of TTL by using imaging. Current work is focusing on developing a new method to readout the DWS and achieving nrad DWS noise levels.