Coherent Cancellation of Photothermal Noise in GaAs/Al$_{0.92}$Ga$_{0.08}$As Bragg Mirrors

TL;DR

This paper demonstrates the fabrication and optimization of AlGaAs crystalline coatings on fused silica substrates to coherently cancel thermoelastic and thermorefractive noise, significantly reducing photothermal noise in high-precision optical experiments.

Contribution

It introduces a novel layer structure for AlGaAs coatings that achieves coherent cancellation of thermo-optic noise, advancing low-noise optical mirror technology.

Findings

Evidence of successful thermo-optic noise reduction

Optimized layer structure induces coherent cancellation

Photothermal transfer function measurements confirm noise suppression

Abstract

Thermal noise is a limiting factor in many high-precision optical experiments. A search is underway for novel optical materials with reduced thermal noise. One such pair of materials, gallium arsenide and aluminum-alloyed gallium arsenide (collectively referred to as AlGaAs), shows promise for its low Brownian noise when compared to conventional materials such as silica and tantala. However, AlGaAs has the potential to produce a high level of thermo-optic noise. We have fabricated a set of AlGaAs crystalline coatings, transferred to fused silica substrates, whose layer structure has been optimized to reduce thermo-optic noise by inducing coherent cancellation of the thermoelastic and thermorefractive effects. By measuring the photothermal transfer function of these mirrors, we find evidence that this optimization has been successful.