Confocal Brillouin microscopy for three-dimensional mechanical imaging

Acoustically induced inelastic light scattering, first reported in 1922 by Brillouin(1), allows non-contact, direct readout of the viscoelastic properties of a material and has widely been investigated for material characterization 2, structural monitoring 3 and environmental sensing'. Extending the Brillouin technique from point sampling spectroscopy to imaging modality(5) would open up new possibilities for mechanical imaging, but has been challenging because rapid spectrum acquisition is required. Here, we demonstrate a confocal Brillouin microscope based on a fully parallel spectrometer-a virtually imaged phased array-that improves the detection efficiency by nearly 100-fold over previous approaches. Using the system, we show the first cross-sectional Brillouin imaging based on elastic properties as the contrast mechanism and monitor fast dynamic changes in elastic modulus during polymer crosslinking. Furthermore, we report the first in situ biomechanical measurement of the crystalline lens in a mouse eye. These results suggest multiple applications of Brillouin microscopy in biomedical and biomaterial science.