Critical experimental facts pertaining to models and associated universalities for low-frequency Raman scattering in inorganic glass formers

Specific information extracted from low-frequency Raman data, for a widely varied in chemical nature class of inorganic glass formers, are presented showing the weakness of the basis on which relevant current models and phenomenological correlations rely. The three pertinent issues of the field, namely, relaxation to vibration contribution, the frequency dependence of the depolarization ratio, and the low-frequency behavior of photon-phonon coupling coefficient are discussed in light of nontrivial data for strong, fragile, and intermediate glasses. It is shown that putative well-known universalities, e.g., the correlation of the strong or fragile character of a supercooled liquid with the strength of the fast dynamics and the frequency independence of the depolarization ratio in the low-frequency Raman region are not well established, due to the limited consideration of experimental data.