Abstract

Defect-induced one-phonon absorption¹ of far-infrared radiation is used to generate monochromatic nonequilibrium phonon populations in LaF₃:Pr³⁺ at a range of frequencies throughout the acoustic band. The pump source for this generation mechanism is a transversely excited atmospheric-pressure CO₂-laser-pumped superradiant cell. Phonon occupation numbers of order 10 are generated. Phonons are optically detected in a time-resolved frequency-selective manner by using the anti-Stokes absorption sideband of the ³P₀ state of Pr³⁺. The lifetime of these phonons is determined and is found to obey the ω^-5 dependence as predicted by the isotropic dispersionless model for anharmonic decay of acoustic phonons.² The spectral dynamics associated with the decay of these phonons is also investigated and is compared with a rate-equation analysis that includes backfeeding of the decay products. The production of double-frequency phonons by a three-phonon confluence process is also demonstrated.

© 1990 Optical Society of America