# Thermal distortions of non-Gaussian beams in Fabry-Perot cavities

## TL;DR

This paper models thermal distortions in wide, flat-topped mesa beams within Fabry-Perot cavities, assessing their impact on optical mode profiles and thermal noise, and proposes correction methods relevant for gravitational wave detectors.

## Contribution

It introduces a detailed modeling approach for thermal effects on mesa beam cavities and compares these effects with Gaussian beam systems, providing insights for detector upgrades.

## Key findings

- Thermal distortions significantly alter mesa beam profiles.
- Thermal noise increases due to mirror deformations.
- Proposed correction methods can mitigate thermal effects.

## Abstract

Thermal effects are already important in currently operating interferometric gravitational wave detectors. Planned upgrades of these detectors involve increasing optical power to combat quantum shot noise. We consider the ramifications of this increased power for one particular class of laser beams--wide, flat-topped, mesa beams. In particular we model a single mesa beam Fabry-Perot cavity having thermoelastically deformed mirrors. We calculate the intensity profile of the fundamental cavity eigenmode in the presence of thermal perturbations, and the associated changes in thermal noise. We also outline an idealized method of correcting for such effects. At each stage we contrast our results with those of a comparable Gaussian beam cavity. Although we focus on mesa beams the techniques described are applicable to any azimuthally symmetric system.