Versatile multimodal modality based on Brillouin light scattering and the photoacoustic effect

Abstract

Multimodal optical techniques are useful for the comprehensive characterization of material properties. In this work, we developed a new, to the best of our knowledge, multimodal technology that can simultaneously measure a subset of mechanical, optical, and acoustical properties of the sample and is based on the integration of Brillouin (Br) and photoacoustic (PA) microscopy. The proposed technique can acquire co-registered Br and PA signals from the sample. Importantly, using synergistic measurements of the speed of sound and Brillouin shift, the modality offers a new approach to quantifying the optical refractive index, which is a fundamental property of a material and is not accessible by either technique individually. As a proof of concept, we demonstrated the feasibility of integrating the two modalities and acquired the colocalized Br and time-resolved PA signals in a synthetic phantom made out of kerosene and CuSO4 aqueous solution. In addition, we measured the refractive index values of saline solutions and validated the result. Comparison with previously reported data showed a relative error of 0.3%. This further allowed us to directly quantify the longitudinal modulus of the sample with the colocalized Brillouin shift. While the scope of the current work is limited to introducing the combined Br-PA setup for the first time, we envision that this multimodal modality could open a new path for the multi-parametric analysis of material properties.

Speed of sound measurement and mapping in transparent materials by impulsive stimulated Brillouin microscopy

“…The longitudinal modulus mapping of the sample is determined by measuring the optical frequency shift of the scattered light. Considering the large scattering angle (90 • or 180 • ) of the light received by the conventional Brillouin microscope [3,4], the Brillouin frequency shift can reach GHz. So far, BM has been widely used in biological and biomedical research.…”

“…Using photoacoustic microscopy, the SOS can be obtained by calculating the time of flight of the photoacoustic signal. However, it needs prior knowledge of the physical distance between the detector and the location of the excitation beam [4]. ISBS does not introduce the time-of-flight method, so there is no prior requirement for sample size.…”