Anharmonic interactions of nonequilibrium phonons in LiYF4:Pr3+

We have investigated the decay of nonequilibrium phonons in LiYF4:Pr3+ (1 at. %) at a temperature of 9.5 K. Nonequilibrium phonon populations at 51.9, 66.0, and 113 cm-1 are generated monochromatically with a high-power pulsed far-infrared laser via defect-induced one-phonon absorption, and their temporal and spectral evolution detected using anti-Stokes absorption. We observe the broadband distribution that results from the anharmonic decay of the initial monochromatic phonon population. The experimental data are modeled using a Monte Carlo simulation based on spontaneous three phonon processes. The simulation is in good agreement with the experimental data.