# Optimal mode matching in cavity optomagnonics

## TL;DR

This paper proposes a theoretical method to significantly enhance optomagnonic coupling in whispering gallery mode cavities by including exchange interactions, potentially enabling better magnon manipulation in YIG spheres.

## Contribution

The study generalizes previous models to include exchange interactions, predicting up to 40-fold increase in coupling to surface magnons in YIG spheres.

## Key findings

- Coupling to surface magnons can be up to 40 times larger than to macrospin modes.
- Enhancement is insufficient for current magnon manipulation but can be improved with nanostructuring or better materials.
- Theoretical prediction guides future experimental efforts in cavity optomagnonics.

## Abstract

Inelastic scattering of photons is a promising technique to manipulate magnons but it suffers from weak intrinsic coupling. We theoretically discuss an idea to increase optomagnonic coupling in optical whispering gallery mode cavities, by generalizing previous analysis to include the exchange interaction. We predict that the optomagnonic coupling constant to surface magnons in yttrium iron garnet (YIG) spheres with radius $300\,\mathrm{\mu}$m can be up to $40$ times larger than that to the macrospin Kittel mode. Whereas this enhancement falls short of the requirements for magnon manipulation in YIG, nanostructuring and/or materials with larger magneto-optical constants can bridge this gap.