High-frequency nonequilibrium phonons in laser materials

Nonequilibrium phonon generation and detection are demonstrated in both YLF:Pr{dollar}sp{lcub}3+{rcub}{dollar} and YAG:Pr{dollar}sp{lcub}3+{rcub}{dollar}. The investigation of the spectral, temporal and spatial dynamics associated with the relaxation of monochromatic high-frequency phonons in these laser materials is presented in this dissertation.; In the case of YLF:Pr{dollar}sp{lcub}3+{rcub}{dollar}, anharmonic interactions dominate the phonon relaxation resulting in a broad-band spectral distribution. The initial decay products that evolve directly from the monochromatic distribution have been experimentally observed for the first time.; In the case of YAG:Pr{dollar}sp{lcub}3+{rcub}{dollar}, inelastic phonon scattering from electronic transitions of Pr{dollar}sp{lcub}3+{rcub}{dollar} ions at highly distorted sites has been observed. These processes lead to a highly peaked phonon spectrum. Additionally, the effects of a background thermal distribution on the phonon relaxation processes in YAG:Pr{dollar}sp{lcub}3+{rcub}{dollar} have been investigated over the temperature range 9-25 K.; High-frequency phonon propagation has also been studied in YAG:Pr{dollar}sp{lcub}3+{rcub}{dollar} in the single crystal fiber geometry. Phonon propagation in the fiber geometry can be interpreted in terms of the distance dependence of an effective one-dimensional diffusion constant. The temporal and spectral regimes in which quasi-diffusive and purely diffusive phonon transport occur are determined.