Dependence of the evolution of heat in neodymium-doped yttrium aluminum garnet on the output power

It was found experimentally that the evolution of heat during stimulated emission under continuous pumping conditions was less than in the absence of a resonator (i.e., in the absence of stimulated emission). The difference between the amounts of heat evolved with and without a resonator was a function of the output power of the coherent radiation and of the transmission of the semitransparent mirror in the resonator. Within the limits of the experimental error, this difference was the same for active elements in which the concentration of neodymium differed by a factor of 2. The lower heat evolution during the stimulated emission was attributed to the absorption of the pumping radiation by ions at a metastable level and to nonradiative transitions to lower levels (in crystals with higher concentrations of neodymium). The rate of evolution of heat in low-loss active elements increased by 20–30%, when the stimulated emission stopped and this could damage these elements.