A testbed for Tilt-To-Length coupling and Differential-Wavefront-Sensing performance in LISA @LISAcommunity

Uploaded July 2022 | Updated September 2026, 14 minutes ago

LISAâ's ambitious sensitivity of pm/Hz1/2 presents many technical challenges; one of the main issues is the coupling of the angular jitter of the spacecraft and test masses to the interferometrically-measured longitudinal displacement (Tilt-To-Length coupling, or TTL). LISA will use the Differential-Wavefront-Sensing (DWS) method to keep the satellites aligned, which combines the individual phase readouts from the four segments of a Quadrature PhotoDiode (QPD). An ultra-stable interferometer testbed representative of a LISA spacecraft's Optical Bench (OB) 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 test mass motion. This experiment has been used to demonstrate optical reduction of TTL by using imaging systems to image the point of rotation of the beams into the detector plane. Current work focuses on reducing optical noise sources down to the target DWS sensitivity at the few nrad/Hz1/2 level in the LISA heterodyne detection band. Finally, the experiment will also serve as an optical testbed for a new method to readout the DWS signals from the QPDs.

Authors: Alvise Pizzella, Miguel Dovale, Gerhard Heinzel
Presenter: Alvise Pizzella

A testbed for Tilt-To-Length coupling and Differential-Wavefront-Sensing performance in LISA

$Evaluating a phenomenological approach to spin precession in current gravitational wave events. Unlike in Newtonian dynamics, if two gravitationally bound objects are individually spinning in general relativity, their spins will interact and their orbit will precess. This spin precession leaves an imprint on the gravitational wave signal. The catalog of gravitational wave events has already been investigated for spin precession, described using the two effective parameters $chi_{rm eff}$ and $chi_{P}$ (focussing on the spin precession of binary black holes). Here, we repeat the investigation but with a geometrical approach. Spin precession is characterised as the spin precession of the orbital plane, split into its azimuthal motion (its precession) and its polar motion (its nutation). Looking for these effects, and understanding what binary parameters influence them, is non-trivial. We use sequential prior conditioning to resolve this. Prior conditioning is performed by combining prior distributions with posterior distributions of the parameters were conditioning our priors on. We find that nutation, given its small expected amplitudes, is difficult to constrain. Precession, on the other hand, is clearly constrained, especially for events with highly unequal masses and relatively high signal to noise ratios. We also construct a synthetic binary that we would expect to have a high nutational amplitude, and show that with the future detector sensitivities of ground based gravitational wave observatories, these events are detectable and their nutation can be constrained to be non-zero. Authors: Daria Gangardt, Davide Gerosa, Michael Kesden, Viola De Renzis, Nathan Steinle Presenter: Daria Gangardt$

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