Accuracy of joint refractive index and phonon velocity estimation using Brillouin light backscattering in the platelet geometry
Résumé
Brillouin light backscattering from isotropic platelet samples involves the contribution of two phase-matched longitudinal acoustic phonons. A primary, stronger, signal is provided by the usual condition of a phonon wavevector collinear to and twice as large as the incident photon wavevector inside the medium. After reflection of incident light on the backside of the platelet, another bulk phonon propagating along the platelet axis contributes a secondary, weaker, signal that is independent of the index of refraction but dependent on the angle of incidence. Combining contributions from both phonons, the refractive index and the acoustic phonon velocity can be estimated jointly and precisely in the backscattering geometry from experimental data. Experiments with poly(methyl methacrylate), fused silica, and soda-lime glass platelets are used to assess the accuracy of the estimation. It is argued that the secondary Brillouin signal dictates the estimation of velocity whereas the primary Brillouin signal dictates the estimation of the index of refraction.
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Cite 10.5281/zenodo.15109270 Jeu de données Ugarak, F., Mosset, A., & Laude, V. (2025). Brillouin backscattering spectra for PMMA, fused silica, and soda lime glass [Data set]. Zenodo. https://doi.org/10.5281/ZENODO.15109270