Dark-field Brillouin microscopy.

Brillouin microscopy is a non-contact and label-free technique for mapping fundamental micro-mechanical properties in the volume of biological systems. Specular reflections and elastic scattering easily overwhelm the weak Brillouin spectra due to the limited extinction of virtually imaged phased array spectrometers, thereby affecting the image acquisition. In this Letter, a dark-field method was demonstrated to reject the elastic background light using an annular illumination and a confocal detection. To validate the method, images of polystyrene and liquid samples were obtained using both a confocal and the dark-field system. An extinction ratio of 30 dB was readily achieved.