EMISSION QUANTUM EFFICIENCY AND HEATING EFFECTS IN YAG-ND3+ LASERS

The intrinsic limitations of emission quantum efficiency of Nd3+ in YA G that lead to heating of active element are analyzed. The main factor s characteristic of the system of active ions that lead to heat are th e quantum defect and the emission quenching due to energy transfer by cross-relaxation and multisite structure (especially for laser or diod e pumping). It is shown that for concentrations of interest for lasers , the reduction of emission quantum efficiency by energy transfer is d ue to two types of interactions between active ions. The high-resoluti on data are used to explain the global behavior of metastable level em ission kinetics and the concentration reduction of quantum efficiency. An analytic expression for the fractional thermal load is obtained, i mposing a lower limit at each concentration. The estimated values of e mission quantum efficiency and fractional load are in agreement with r eported measured values. (C) 1996 Society of Photo-Optical instrumenta tion Engineers.