Photon avalanche effect in LaCl 3 : Pr 3 +

The phenomenon of photon avalanche, which involves both an excited state absorption process from a metastable level and a cross relaxation energy transfer process responsible for the large increases in population of this metastable level, has been investigated in LaCl ₃:Pr ³⁺. 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 of coupled rate equations combined with the propagation of a Gaussian beam. We develop a model with only one adjustable parameter, the excited state absorption cross section, which provides a good description of all of our experimental data. We have estimated values of the excited state absorption cross section for the various ³H ₅→ ³P ₀ pumping transitions at different temperatures.