In situ substrate birefringence characterization in gravitational wave detectors using a heterodyne polarimetry method

TL;DR

This paper introduces a heterodyne polarimetry technique for in situ measurement of substrate birefringence in gravitational wave detectors, aiding in diagnosing and improving detector sensitivity.

Contribution

The paper presents a novel heterodyne polarimetry method for in situ birefringence characterization of test mass substrates in gravitational wave detectors.

Findings

Successfully demonstrated the method with a tabletop setup.

Discussed the method's applicability to current and future detectors.

Analyzed the detectable birefringence limits.

Abstract

High-quality test mass substrates play essential roles in laser interferometric gravitational wave detectors. Inhomogeneous birefringence distribution in test mass substrates, however, can degrade the sensitivity of the detector by introducing the optical loss and disturbing the interferometer controls. In this paper, we present a heterodyne polarimetry method that enables in situ birefringence characterizations, hence diagnosing the gravitational wave interferometer. We experimentally demonstrate the proposed method with a tabletop setup. We also discuss its applicability to current and future gravitational wave detectors and the detectable limit.