The photothermal effect in interferometers

TL;DR

This study measures the photothermal effect in a cross-polarized interferometer at audio frequencies, confirming theoretical predictions about mirror heating and length changes due to light absorption.

Contribution

It provides experimental validation of existing theories on photothermal effects in interferometer mirrors using a novel measurement approach.

Findings

Good agreement with theoretical models

Demonstrated photothermal effects at audio frequencies

Validated uncoated mirror behavior

Abstract

We have measured the photothermal effect in a single cross-polarized interferometer at audio frequencies (5 Hz - 4 kHz). In a Fabry-Perot interferometer, light in one polarization is chopped to periodically heat the interferometer mirrors, while light in the orthogonal polarization measures the mirror length changes. Tests of a polished solid metal mirror show good agreement with relevant proposed theories by Braginsky et al. ["Thermodynamical fluctuations and photo-thermal shot noise in gravitational wave antennae," Physics Letters A 264, 1-10 (1999)] and Cerdonio et al. ["Thermoelastic effects at low temperatures and quantum limits in displacement measurements," Physical Review D 63 082003 (2001)] describing uncoated optics.