The photon-avalanche effect: review, model and application

The photon-avalanche effect, which involves both absorption from a metastable intermediate level and cross-relaxation energy transfer, introduces a new trend in the achievement of efficient up-conversion lasers. A review of the observations of the photon-avalanche effect in rare-earth doped crystals is made and illustrated with specific examples. Then, a theoretical model is developed showing clearly the conditions for the avalanche to occur. This model is successfully applied to our recent experimental results and may be used to interpret the avalanche process whatever the material is.