Optical EngineeringEmission quantum efficiency and heating effects in YAG:Nd3+ lasers
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The intrinsic limitations of emission quantum efficiency of Nd3+ in YAG that lead to heating of active element are analyzed. The main factors characteristic of the system of active ions that lead to heat are the quantum defect and the emission quenching due to energy transfer by cross-relaxation and multisite structure (especially for laser or diode pumping). It is shown that for concentrations of interest for lasers, the reduction of emission quantum efficiency by energy transfer is due to two types of interactions between active ions. The high-resolution data are used to explain the global behavior of metastable level emission kinetics and the concentration reduction of quantum efficiency. An analytic expression for the fractional thermal load is obtained, imposing a lower limit at each concentration. The estimated values of emission quantum efficiency and fractional load are in agreement with reported measured values.