Method of analysis of the spectra obtained by microfocused Brillouin light scattering

In microfocused Brillouin light scattering ($\ensuremath{\mu}$-BLS), light focusing accelerates the measurement, but also merges the response of different spin-wave modes into a single spectrum. To disentangle the contribution of each spin wave, this manuscript reports a comprehensive theoretical model that treats the measured signal as the sum of all back-scattered contributions captured by the microscope objective. Applied to a 50-nm CoFeB film, it reveals how optical parameters, spin-wave dispersion, and mode profiles shape the intensity and line shape of $\ensuremath{\mu}$-BLS.