Abstract :
Raman and inelastic neutron spectra of vitreous silica were compared in order to derive the Raman light-to-vibration coupling coefficient C(ν) in the spectral interval between 10 and 600 cm−1. C(ν) shows different frequency dependences in different spectral regions: between 30 and 110 cm−1, C(ν)∝ν; between 110 and 450 cm−1, C(ν) is constant; and finally, between 450 and 550 cm−1, C(ν) sharply decreases. The results are discussed in the frame of the existing models for the vibrational excitations in vitreous silica. The crossover frequency of C(ν) at ∼110 cm−1 is interpreted as the onset of phonon localization in the sense of Ioffe-Regel rule.
