Propagation of phonon pulses in vitreous silica

The arrival of thermal pulses propagating through glass is retarded at high excitation energies, The retardation time is approximately proportional to the excitation energy, suggesting characteristics of nonequilibrium phonon s at high densities in glass. The late time signal decays approximately exp onentially with a decay constant independent of excitation energy. (C) 1999 Elsevier Science B.V. All rights reserved.