Disentanglement of Multiple Scattering Contribution in Brillouin Microscopy

Abstract

Due to multiple scattering (MS), Brillouin spectroscopy is currently limited to analyzing transparent materials or the surface of opaque samples. To favor the applications toward in-depth 3D analysis, we provide a new analytic expression and an innovative experimental method to isolate the MS effect. The analytic model, derived from a fundamental description of the interaction process, compares well with a new experimental method, named polarization gated Brillouin spectroscopy, which selects the MS contribution through light polarization. Both experimental and analytic methods are tested against a benchmark material, milk, demonstrating their capability to extract reliable micromechanical parameters even for the in-depth investigation of highly turbid material.

Polarization gated Brillouin spectroscopy: new perspectives for turbid media analysis

“…The first analytic description of the Brillouin spectrum as a sum of two components, the first one related to the ballistic contribution and the second to the MS is described in ref. 24 where an excellent agreement between the experimental data and the analytic model is found. Here we demonstrate how to obtain the pure ballistic contribution using a simple experimental method.…”

“…For further information refer to ref. 24 . The chosen scattering configuration is the back-scattering geometry, where the same microscope objective focuses the light and collects the scattered one.…”

“…As occurs in many optical imaging methods, also for Brillouin spectroscopy the investigation of highly turbid media is extremely challenging 24 . This happens not only for issues related to light extinction or limited penetration depth, but also, and even more importantly, because the presence of local heterogeneities in refractive index -at the origin of the opacity of tissues -induces multiple scattering of light.…”

Principal component analysis in application to Brillouin microscopy data

“…Specifically, we scaled each measured spectrum linearly to lie between the values of 0 and 1 over the frequency range of interest (between 4 and 8 GHz for biological media and between 9 and 13 GHz for plexiglass) by dividing the spectra by respective Brillouin peak maximum. Note that in highly scattering media, low-frequency spectral components associated with multiple scattering phenomenon may present a challenge for normalisation procedure and would need to be removed separately [17].…”

Terahertz Spatiotemporal Wave Synthesis in Random Systems

“…The physics of wave propagation in multiple scattering environments has been of interest in various domains ranging from solid-state physics to optics and seismology, whether in quantum or classical regimes. − The study of the statistical moments of the transmitted wave amplitude resulted in the definition of many physical parameters of scattered fields that enabled the investigations of waves within complex systems, e.g., the mean free path, the diffusion constant, or the dimensionless conductancealso known as the Thouless factor. Empirical manifestations of multiple scattering in diffusive regimes, such as coherent backscattering, long-range correlation, and wave localization, have also been observed for different kinds of waves (e.g., acoustic, plasma). − Unlike other domains, like acoustics, where the number of spatially independent modulation points is relatively small, at optical frequencies, spatial light modulators (SLMs) offer millions of degrees of freedom to control the propagation of coherent light.…”