Brillouin light scattering by magnetic quasi-vortices in cavity optomagnonics

TL;DR

This paper explores how orbital angular momentum exchange between optical vortices and magnetic quasi-vortices in a ferromagnetic sphere affects Brillouin light scattering, revealing nonreciprocal behaviors with potential applications in chiral optics and opto-spintronics.

Contribution

It experimentally demonstrates the conservation of orbital angular momentum in cavity optomagnonics and its impact on nonreciprocal Brillouin scattering behaviors.

Findings

Orbital angular momentum exchange influences scattering directionality.

Nonreciprocal behaviors depend on vortex angular momentum states.

Potential for new chiral optical and spintronic devices.

Abstract

A ferromagnetic sphere can support \textit{optical vortices} in forms of whispering gallery modes and \textit{magnetic quasi-vortices} in forms of magnetostatic modes with non-trivial spin textures. These vortices can be characterized by their orbital angular momenta. We experimentally investigate Brillouin scattering of photons in the whispering gallery modes by magnons in the magnetostatic modes, zeroing in on the exchange of the orbital angular momenta between the optical vortices and the magnetic quasi-vortices. We find that the conservation of the orbital angular momentum results in different nonreciprocal behaviors in the Brillouin light scattering. New avenues for chiral optics and opto-spintronics can be opened up by taking the orbital angular momenta as a new degree of freedom for cavity optomagnonics.