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Absolute three-dimensional measurement of refractive index via dual Brillouin spectroscopy (Conference Presentation)
Author(s): Antonio Fiore; Giuliano Scarcelli
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Paper Abstract

Three-dimensional mapping of refractive index can help understanding several biomedical phenomena such as metastatic potential of tumor cells and alteration of crystalline lens, as well as decouple biomechanical measures in Brillouin microscopy from the refractive index of the sample. Current techniques to measure the distribution of refractive index rely on the determination of the optical phase delay induced by the sample. These approaches require knowing, measuring or assuming the geometrical path of the light, as well as accessing the sample from at least two sides, conditions not trivial for many biological samples. To overcome these limitations, we developed a spectroscopy technique that can measure the local refractive index in an absolute manner, without sampling the optical phase delay; to achieve this goal, we probed two co-localized Brillouin scattering geometries. In both configurations, the photons were phase-matched to the same phonon axis; as a result, the index of refraction is the only physical quantity that affects the ratio of the measured Brillouin frequency shifts, allowing a local, absolute measurement of the refractive index. We performed a proof-of-principle experiment of this method and demonstrated a refractive index accuracy of 0.001, with spatial resolution of ~5μm (lateral) by ~40 μm (axial). The confocal configuration ensures three-dimensional mapping with high resolution, and the epi-detection configuration allows access to the sample from the same side. This technique can potentially constitute a new approach in investigating biological phenomena providing both index of refraction and mechanical information with a single measurement.

Paper Details

Date Published: 4 March 2019
PDF
Proc. SPIE 10880, Optical Elastography and Tissue Biomechanics VI, 108800R (4 March 2019); doi: 10.1117/12.2510406
Show Author Affiliations
Antonio Fiore, Univ. of Maryland, College Park (United States)
Giuliano Scarcelli, Univ. of Maryland, College Park (United States)


Published in SPIE Proceedings Vol. 10880:
Optical Elastography and Tissue Biomechanics VI
Kirill V. Larin; Giuliano Scarcelli, Editor(s)

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