Selection rules for cavity-enhanced Brillouin light scattering from magnetostatic modes

Brillouin light scattering (BLS) is a useful tool for studying magnons, the elementary excitations of magnetic order. However, this process is typically quite weak. In order to enhance BLS, optical cavity modes, such as the whispering gallery modes in a sphere of transparent magnetic material, can be exploited. Here, the authors study cavity-enhanced BLS from magnons in a range of different magnetostatic modes. The selection rules that govern the process are identified and understood based on recent theoretical predictions (Phys. Rev. B 96, 094412 (2017)). Additional enhancement of BLS can be achieved through the better spatial overlap of higher-order magnetic modes with the optical modes.