# Light scattering by magnons in whispering gallery mode cavities

## TL;DR

This paper theoretically investigates how magnons in a magnetic sphere interact with whispering gallery optical modes, revealing asymmetric scattering and reflection properties that depend on magnon angular momentum and magnetization direction.

## Contribution

It introduces a theoretical model of light-magnon interactions in whispering gallery mode cavities, highlighting asymmetric scattering and reflection phenomena linked to magnon properties.

## Key findings

- Low angular momentum magnons cause forward scattering with asymmetry.
- Large angular momentum Damon Eschbach magnons reflect light inelastically.
- Reflection spectra depend on magnetization direction, enabling controllable energy transfer.

## Abstract

Brillouin light scattering is an established technique to study magnons, the elementary excitations of a magnet. Its efficiency can be enhanced by cavities that concentrate the light intensity. Here, we theoretically study inelastic scattering of photons by a magnetic sphere that supports optical whispering gallery modes in a plane normal to the magnetization. Magnons with low angular momenta scatter the light in the forward direction with a pronounced asymmetry in the Stokes and the anti-Stokes scattering strength, consistent with earlier studies. Magnons with large angular momenta constitute Damon Eschbach modes are shown to inelastically reflect light. The reflection spectrum contains either a Stokes or anti-Stokes peak, depending on the direction of the magnetization, a selection rule that can be explained by the chirality of the Damon Eshbach magnons. The controllable energy transfer can be used to manage the thermodynamics of the magnet by light.