Impact of refractive index heterogeneity on stimulated Brillouin scattering microscopy: a quantitative analysis

TL;DR

This paper investigates how refractive index heterogeneity impacts stimulated Brillouin scattering microscopy, revealing that RI mismatches cause focal distortions that reduce measurement accuracy, with implications for quantitative biomechanical imaging.

Contribution

It provides a quantitative analysis of RI heterogeneity effects on SBS microscopy using simulations and experiments, highlighting limitations of fiber-coupling as a proxy for gain.

Findings

RI heterogeneity causes focal field distortion and reduces Brillouin gain.

Focal distortions degrade shift precision at material interfaces.

Fiber-coupling efficiency is not a reliable proxy for Brillouin gain.

Abstract

Stimulated Brillouin scattering (SBS) microscopy enables label-free biomechanical imaging, with Brillouin gain serving as a critical contrast parameter for quantitative analysis. However, the influence of sample-induced refractive index (RI) heterogeneity on gain measurements remains poorly understood. Here, we quantitatively investigate, how RI mismatch affects SBS microscopy using finite element simulations and experiments on a phantom sample comprising polydimethylsiloxane beads embedded in agarose gel. We demonstrate that RI heterogeneity induces focal field distortion that reduce pump-probe beam overlap, resulting in attenuated Brillouin gain and degraded shift precision at material interfaces. Crucially, we establish that fiber-coupling efficiency, commonly used for system alignment, cannot serve as a linear proxy for Brillouin gain due to its heightened sensitivity to focal field distortion.