Adaptive thermal compensation of test masses in advanced LIGO

TL;DR

This paper presents a method for active thermal compensation in LIGO's test masses to correct wavefront distortions caused by laser power absorption, improving gravitational wave detector sensitivity.

Contribution

It introduces a thermal correction technique using direct heating and laser scanning to mitigate wavefront distortions in interferometric gravitational wave detectors.

Findings

Proof-of-principle experiment conducted at MIT

Thermal correction effectively reduces wavefront distortions

Method improves interferometer sensitivity by compensating thermal effects

Abstract

As the first generation of laser interferometric gravitational wave detectors near operation, research and development has begun on increasing the instrument's sensitivity while utilizing the existing infrastructure. In the Laser Interferometer Gravitational Wave Observatory (LIGO), significant improvements are being planned for installation in ~2007, increasing strain sensitivity through improved suspensions and test mass substrates, active seismic isolation, and higher input laser power. Even with the highest quality optics available today, however, finite absorption of laser power within transmissive optics, coupled with the tremendous amount of optical power circulating in various parts of the interferometer, result in critical wavefront deformations which would cripple the performance of the instrument. Discussed is a method of active wavefront correction via direct thermal actuation on optical elements of the interferometer. A simple nichrome heating element suspended off the face of an affected optic will, through radiative heating, remove the gross axisymmetric part of the original thermal distortion. A scanning heating laser will then be used to remove any remaining non-axisymmetric wavefront distortion, generated by inhomogeneities in the substrate's absorption, thermal conductivity, etc. A proof-of-principle experiment has been constructed at MIT, selected data of which are presented.