Abstract
The interest in measuring acoustic and optic vibrations of glasses at terahertz frequencies is explained. Techniques used for Brillouin spectroscopy at scattering vectors Q⩾1 nm−1 are briefly described and compared. Experimental results, for example on vitreous silicas or glassy selenium, show that plane-wave acoustic excitations exhibit a crossover from propagation to strong scattering as Q is increased. Optical excitations at similar frequencies form a ‘boson peak’. These fairly local excitations can obey ‘molecular-like’ selection rules. The findings reveal a somewhat unexpected strong elastic inhomogeneity in the structure of glasses at the extended length scale of ∼5 nm, about which so little is known otherwise.
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More From: Comptes Rendus de l'Academie des Sciences Series IV Physics
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