Low-Q Brillouin scattering from glasses

A general framework for the understanding of Brillouin scattering spectra observed in glasses with light, X-rays, or neutrons is presented. Several sources of acoustic damping are discussed. Crossovers between different damping regimes can occur, depending on the glass and on the temperature. Generally, the damping of sound culminates in the THz frequency range with a Ioffe-Regel limit corresponding to a resonance with the boson peak. This limit should be of direct relevance to BRISP, as the instrument will mostly operate in that region.