Photon avalanche laser

Laser output at 4.9 ..mu..m has been obtained from a Pr doped LaCl/sub 3/ crystal. Pump laser energy at 529 nm is coupled into the crystal via the photon avalanche process. This process involves metastable state ion absorption of a pump photon and subsequent ion-ion energy transfer. The latter step generates two metastable state ions (self-induced absorption). This highly nonlinear process is characterized by a sharp onset with pump intensity and, at higher intensities, depopulation of the ionic ground state. Experimental results will be compared with predictions from an existing rate equation model.