Postprocessing of tilt-to-length noise with coefficient drifts in TianQin using a null time-delay interferometry channel

TL;DR

This paper presents a method to estimate and remove tilt-to-length noise in TianQin's interferometric data by using null TDI channels and accounting for coefficient drifts, improving noise suppression accuracy.

Contribution

It introduces a novel approach to estimate TTL coupling coefficients with linear drifts using null TDI channels, enhancing postprocessing noise removal in TianQin.

Findings

Estimated TTL coefficients with 10 μm/rad accuracy in simulations.

Highlighting the importance of estimating drift coefficients to keep residual noise below 0.3 pm.

Identified the impact of jitter measurement correlation on estimation accuracy.

Abstract

Tilt-to-length (TTL) coupling is expected to be one of the major noise sources in the interferometric phase readouts in TianQin mission. Arising from the angular motion of spacecraft (SC) and the onboard movable optical subassemblies (MOSAs), TTL noise needs to be removed in postprocessing after suppressing the laser phase noise with time-delay interferometry (TDI) technique. In this article, we show that we can estimate the TTL coupling coefficients using the null TDI channel {\zeta} and remove the TTL noise in the commonly used Michelson variables with the estimated coefficients. We introduce the theoretical model of TTL noise in TDI and consider linear drifts in the linear TTL coefficients for noise estimation and subtraction. The TTL coefficients with drifts are estimated successfully with an accuracy of 10 {\mu}m/rad in our numerical simulation. We discuss the impact of point-ahead angle compensation error and wavefront error, and find it necessary to estimate linear drift coefficients and quadratic TTL coefficients to keep TTL noise residuals below the 0.3 pm noise reference curve. However, the estimation accuracy suffers greatly from the correlation between yaw jitter measurements that contain the same SC jitter. Assuming all angular jitters induced by MOSAs are independent, choosing a frequency range with relatively higher MOSA yaw jitter noise levels is beneficial to the TTL coefficient estimation.