  Brillouin microscopy has recently emerged as powerful technique to
characterize the mechanical properties of biological tissue, cell and
biomaterials. However, the potential of Brillouin microscopy is currently
limited to transparent samples, because Brillouin spectrometers do not have
sufficient spectral extinction to reject the predominant non-Brillouin
scattered light of turbid media. To overcome this issue, we developed a
spectrometer composed of a two VIPA stages and a multi-pass Fabry-Perot
interferometer. The Fabry-Perot etalon acts as an ultra-narrow band-pass filter
for Brillouin light with high spectral extinction and low loss. We report
background-free Brillouin spectra from Intralipid solutions and up to 100
microns deep within chicken muscle tissue.
