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.
Spontaneous Brillouin scattering is an inelastic scattering process arising from inherent thermal density fluctuations, or acoustic phonons, propagating in a medium. Over the last few years, Brillouin spectroscopy has shown great potential to become a reliable non-invasive diagnostic tool due to its unique capability of retrieving viscoelastic properties of materials such as strain and stiffness. The detection of the weak scattered light, in addition to the resolution of the Brillouin peaks (typically shifted by few GHz from the central peak) represent one of the greatest challenges in Brillouin. The recent development of high sensitivity CCD cameras has brought Brillouin spectroscopy from a point sampling technique to a new imaging modality. Furthermore, the application of Virtually Imaged Phased Array (VIPA) etalons has dramatically reduced insertion loss simultaneously allowing fast (<1s) collection of the entire spectrum. Hitherto Brillouin microscopy has been shown the ability to provide unique stiffness maps of biological samples, such as the human lens, in a non-destructive manner. In this work, we present results obtained using our Brillouin microscope to map the stiffness variations in the walls of blood vessels in particular when atherosclerotic plaques are formed. The stiffness of the membrane that covers the plaques is critical in developing acute myocardial infarction yet it is not currently possible to credibly assess its stiffness due to lack of suitable methods.