Power coupling losses for misaligned and mode-mismatched higher-order Hermite-Gauss modes

TL;DR

This paper analyzes how misalignment and mode-mismatch affect power coupling losses in higher-order Hermite-Gauss modes, revealing increased susceptibility that challenges their use in advanced gravitational-wave detectors.

Contribution

It provides analytical and numerical insights into how mode order influences coupling losses, highlighting limitations for higher-order modes in precision optical systems.

Findings

Higher-order HG modes are more susceptible to beam perturbations.

Losses scale linearly and quadratically with mode indices.

Mode-mismatch tolerance decreases significantly for higher modes.

Abstract

This paper analytically and numerically investigates misalignment and mode-mismatch induced power coupling coefficients and losses as a function of Hermite Gauss (HG) mode order. We show that higher-order HG modes are more susceptible to beam perturbations when, for example, coupling into optical cavities: the misalignment and mode-mismatch-induced power coupling losses scale linearly and quadratically with respect to the mode indices respectively. As a result, the mode-mismatch tolerance for the $\mathrm{HG}_{3,3}$ mode is reduced to a factor of 0.28 relative to the currently-used $\mathrm{HG}_{0,0}$ mode. This is a potential hurdle to using higher-order modes to reduce thermal noise in future gravitational-wave detectors.