Tuning the Thermal Expansion Properties of Optical Reference Cavities with Fused Silica Mirrors

TL;DR

This study explores how attaching LTE rings to fused silica mirrors in optical cavities can effectively tune the zero crossing temperature of the cavity's thermal expansion, enhancing stability for precision applications.

Contribution

It introduces a novel method of tuning the zero crossing temperature of optical cavities using LTE rings attached to Fused Silica mirrors, supported by simulations and measurements.

Findings

Attaching LTE rings shifts the zero crossing temperature by up to 30 K.

Deformation due to differential thermal expansion impacts cavity stability.

Finite element simulations align with experimental measurements.

Abstract

We investigate the thermal expansion of low thermal noise Fabry-Perot cavities made of Low Thermal Expansion (LTE) glass spacers and Fused Silica (FS) mirrors. The different thermal expansion of mirror and spacer deforms the mirror. This deformation strongly contributes to the cavity's effective Coefficient of Thermal Expansion (CTE), decreasing the zero crossing temperature by about 20 K compared to an all-LTE glass cavity. Finite element simulations and CTE measurements show that LTE rings optically contacted to the back surface of the FS mirrors allow to tune the zero crossing temperature over a range of 30 K.