Spectral broadening in Brillouin imaging

Brillouin microscopy is an emerging imaging modality that provides fundamental information about mechanical properties of media in a non-contact manner. To date, low numerical aperture (NA) optics have been used, due to noticeable angular broadening of the Brillouin spectrum at higher NAs. In this work, we investigate theoretically and experimentally the dependence of spectral broadening effects in Brillouin imaging on system NA, for both 90 ° and 180 ° scattering geometries. Lineshape deformations and broadening are found to be minimised in a backscattering geometry, hence paving the way for high resolution in-vivo mechanical imaging.