STIMULATED-EMISSION OF PHONONS IN AN ACOUSTICAL CAVITY

Stimulated emission is studied of phonons resonant with the metastable Zeeman-split (E) over bar((2)E) doublet in ruby. initial population i nversion of this two-level system is prepared by selective pulsed opti cal pumping, and the ensuing stimulated emission of resonant phonons i s observed via an accelerated growth of the luminescence intensity ema nating from the lower level. Under favorable conditions, a periodic re currence of the process of stimulated emission is observed, which poin ts to a phonon cavity formed by the end faces of the crystal in combin ation with a limited interaction length of the resonant phonons. To an alyze these phenomena in detail, use is made of rate equations for the phonon occupation and the level populations with explicit account of their position dependences. With plausible assumptions an analytic sol ution of these equations is achieved, which excellently fits the data. The effect of lattice anharmonicity is shown to depend on the phonon energy in agreement with the theoretical prediction.