Spontaneous Brillouin scattering is an inelastic scattering process arising from inherent thermal density fluctuations, or acoustic phonons, propagating in a medium. The recent development of high throughput efficiency Virtually Imaged Phased Array (VIPA) etalons and high sensitivity CCD cameras has dramatically reduced the data acquisition time, in turn enabling the extension of Brillouin spectroscopy from a point sampling technique to an imaging modality. Hitherto Brillouin microscopy has shown great capabilities to non-invasively assess the biomechanics in the volume of biological samples, such as the lens cornea, atherosclerotic plaques and cells.
Spectral contrast is key to optically probe biological systems, where the elastic Rayleigh scattering and specular reflection are orders of magnitude greater than the Brillouin signal. In VIPA spectrometers, the elastic background light introduces crosstalk signals that overwhelms the weak Brillouin peaks, thus impeding the acquisition of biomechanical images. One method to increase the contrast is to add more etalons in tandem and crossed with respect to each other. Nevertheless, this comes at the cost of a reduced throughput efficiency and a significantly increase system complexity. Here we demonstrate a method to increase the contrast by more than 30dB respect to standard VIPA spectrometers without the requirement of any additional optical or dispersive components. Our method was demonstrated by acquiring Brillouin images of single cells at a sub-micron spatial resolution, where the biomechanical properties of individual cellular structures were investigated.
Giuseppe Antonacci and Giancarlo Ruocco, "High-contrast Brillouin microscopy for noncontact subcellular biomechanical imaging (Conference Presentation)," Proc. SPIE 10496, Optical Elastography and Tissue Biomechanics V, 104960U (Presented at SPIE BiOS: January 28, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2287376.5752215951001.
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