Sequentially-Shifted Excitation (SSE) Brillouin spectroscopy for recovering signal contaminated with strong scattering, absorption or fluorescence

Abstract

The presented work shows a novel approach to correct the undesired background in Brillouin spectra. Specifically, we have developed a Brillouin spectroscopy modification suitable for correction of distortions caused by a molecular filter’s absorption, fluorescent background, or ambient room light. Due to the weak intensity of the Brillouin signal, a distortion of the baseline or a partial absorption of Brillouin peak can have strong impact on data analysis. In the worst case, such as investigation of strongly scattering biological material with simultaneous fluorescence measurements, these perturbations can make it impossible to accurately determine the Brillouin shift. A new Sequentially-Shifted Excitation (SSE) Brillouin spectroscopy method has been developed to allow acquisition of quality Brillouin spectra in most challenging of conditions. The idea behind this method is the observation that the Brillouin and elastically scattered light strongly depend on the wavelength of the incident light, and the location of their respective peaks in the final spectrum changes in response to the smallest change in excitation wavelength. On the other hand, the fluorescence background or distortions due to molecular filter absorption remain the same for small, ~1 pm, changes in incident wavelength. SSE Brillouin spectroscopy involves acquiring multiple Brillouin spectra using slightly offset excitation wavelengths, and computationally separating the signal and distortion/background components, thus recovering the Brillouin signal. The application of SSE Brillouin spectroscopy in highly-scattering sample is presented experimentally using sample of cream.