PICOSECOND ACOUSTIC-PHONON DYNAMICS IN LAF3-PR3+

A plasma switching technique is used to generate subnanosecond, far-in frared (FIR) pulses with frequency 113 cm(-1). The generation of subna nosecond FIR pulses enables us to improve the time resolution of phono n spectroscopic measurements from 50 ns to 350 ps. As an application o f this technique, we investigate the subnanosecond dynamics of high-fr equency phonons in 0.5% LaF3:Pr3+. In particular, we report on the gen eration and detection of a subnanosecond nonequilibrium phonon populat ion at 113 cm(-1), and the temporal evolution of the resulting decay p roducts. The frequency dependence of the phonon relaxation rates of ac oustic phonons in this material is found to deviate from the omega(5) frequency dependence predicted by an isotropic model with linear dispe rsion. A more realistic model based on the actual dispersion curves of the material is presented and compared with the data.