Accurate and Efficient Modeling of the Transverse Mode Instability in High Energy Laser Amplifiers

TL;DR

This paper models the transverse mode instability (TMI) in high energy laser amplifiers as a three-wave mixing process, showing that a phase-matched model can efficiently predict TMI behavior in typical application limits.

Contribution

It introduces a phase-matched three-wave mixing model for TMI that offers computational advantages over traditional coupled mode methods.

Findings

TMI is a stimulated thermal Rayleigh scattering process in the typical application limit.

The phase-matched model significantly reduces computational complexity.

The model accurately captures the TMI dynamics in high energy laser amplifiers.

Abstract

We study the transverse mode instability (TMI) in the limit where a single higher-order mode (HOM) is present. We demonstrate that when the beat length between the fundamental mode and the HOM is small compared to the length scales on which the pump amplitude and the optical mode amplitudes vary, TMI is a three-wave mixing process in which the two optical modes beat with the phase-matched component of the index of refraction that is induced by the thermal grating. This limit is the usual limit in applications, and in this limit TMI is identified as a stimulated thermal Rayleigh scattering (STRS) process. We demonstrate that a phase-matched model that is based on the three-wave mixing equations can have a large computational advantage over current coupled mode methods that must use longitudinal step sizes that are small compared to the beat length.