# Thermal modulation for suppression of parametric instability in advanced gravitational wave detectors

## TL;DR

This study investigates thermal modulation as a method to suppress three-mode parametric instability in advanced gravitational wave detectors, demonstrating effective stabilization through finite element analysis and thermal control techniques.

## Contribution

The paper provides a detailed finite element analysis showing thermal modulation can suppress parametric instability without degrading optical performance in gravitational wave detectors.

## Key findings

- Thermal modulation with a 1 Watt, 0.01 Hz CO2 laser stabilizes acoustic modes.
- Suppression factor is linearly proportional to peak modulation power.
- Rear surface heating compensates for surface deformation effects.

## Abstract

Three-mode parametric instability is a threat to attaining design power levels in Advanced gravitational wave detectors. The first observation of three-mode parametric instability in a long optical cavity revealed that instabilities could be suppressed by time variation of the mirror radius of curvature. In this paper, we present three dimensional finite element analysis of this thermo-acousto-optics system to determine whether thermal modulation could provide sufficient instability's suppression without degrading time averaged optical performance. It is shown that deformations due to the time averaged heating profile on the mirror surface can be compensated by rear surface heating of the test mass. Results show that a $CO_2$ laser heating beam with a modulation amplitude of $1$ Watt at 0.01 Hz is sufficient to stabilize acoustic mode with parametric gain up to 3. The parametric gain suppression factor is linearly proportional to the peak modulation power.