Towards optomechanical parametric instabilities prediction in ground-based gravitational wave detectors

TL;DR

This paper develops a detailed predictive model for optomechanical parametric instabilities in gravitational wave detectors, incorporating optical and mechanical mode interactions, and assesses effects like mirror size and thermal deformations.

Contribution

It introduces a high-precision modeling approach for optical and mechanical modes, enhancing prediction accuracy of parametric instabilities in advanced gravitational wave detectors.

Findings

Mechanical mode losses quantified with combined measurements and finite element analysis.

Mirror size and thermal effects significantly influence higher-order optical modes.

Model can predict parametric instability thresholds for the Advanced Virgo detector.

Abstract

Increasing the laser power is essential to improve the sensitivity of interferometric gravitational wave detectors. However, optomechanical parametric instabilities can set a limit to that power. It is of major importance to understand and characterize the many parameters and effects that influence these instabilities. Here, we model with a high degree of precision the optical and mechanical modes that are involved in these parametric instabilities, such that our model can become predictive. As an example, we perform simulations for the Advanced Virgo interferometer (O3 configuration). In particular we compute mechanical modes losses by combining both on-site measurements and finite element analysis with unprecedented level of detail and accuracy. We also study the influence on optical modes and parametric gains of mirror finite size effects, and mirror deformations due to thermal absorption. We show that these effects play an important role if transverse optical modes of order higher than four are involved in the instability process.