Geometric tilt-to-length coupling in precision interferometry: mechanisms and analytical descriptions

TL;DR

This paper analyzes geometric tilt-to-length coupling in precision interferometers, providing analytic descriptions of mechanisms, discussing limitations of geometric models, and suggesting design strategies to reduce TTL noise in systems like LISA.

Contribution

It introduces a detailed categorization and analytic expressions for geometric TTL coupling mechanisms, highlighting their limitations and proposing design approaches for noise mitigation.

Findings

Analytic expressions for geometric TTL mechanisms

Geometric description alone is insufficient for accurate TTL noise prediction

Design strategies can reduce TTL noise in interferometers

Abstract

Tilt-to-length coupling is a technical term for the cross-coupling of angular or lateral jitter into an interferometric phase signal. It is an important noise source in precision interferometers and originates either from changes in the optical path lengths or from wavefront and clipping effects. Within this paper, we focus on geometric TTL coupling and categorize it into a number of different mechanisms for which we give analytic expressions. We then show that this geometric description is not always sufficient to predict the TTL coupling noise within an interferometer. We, therefore, discuss how understanding the geometric effects allows TTL noise reduction already by smart design choices. Additionally, they can be used to counteract the total measured TTL noise in a system. The presented content applies to a large variety of precision interferometers, including space gravitational wave detectors like LISA.