Photon avalanche effect in LaCl3 : Pr3+

The phenomenon of photon avalanche, which involves both an excited state ab sorption process from a metastable level and a cross relaxation energy tran sfer process responsible for the large increases in population of this meta stable level, has been investigated in LaCl3:Pr3+. In this paper, we report on the intensity dependence of both the steady-state fluorescence and the temporal evolution of the avalanche signal as a function of temperature (80 K to room temperature). Comparisons are made between experimental results and mathematical models based on a six-level system described by a series o f coupled rate equations combined with the propagation of a Gaussian beam. We develop a model with only one adjustable parameter, the excited state ab sorption cross section, which provides a good description of all of our exp erimental data. We have estimated values of the excited state absorption cr oss section for the various H-3(5) --> P-3(0) pumping transitions at differ ent temperatures.