Inelastic neutron and low-frequency Raman scattering in niobium-phosphate glasses: the role of spatially fluctuating elastic and elasto-optic constants

We investigate the low-frequency enhancement of vibrational excitations (\u27boson peak\u27) in niobium-phosphate glasses through the combination of inelastic neutron and polarization-resolved Raman scattering. The spectra of these glasses reveal an enhancement of the vibrational density of states and of the cross section for spontaneous Raman scattering in the frequency range below 150 cm(-1). A recent theoretical model that is based on fluctuating elastic and elasto-optic (Pockels) constants provides a unified description of the measured neutron and Raman spectra, including the depolarization ratio