Abstract

Operation of a high power laser amplifier [1] made of Nd doped silicate and phosphate glasses pumped by an alexandrite laser at 782 nm has shown the existence of significant losses on the stored energy. In agreement with previous works, mostly performed on crystals such as Nd :YAG [2], Nd :LaF₃ and Nd :SrF₂ or glasses such as Nd :ZBLAN, these losses are mainly attributed to excited state absorption (ESA) and up-conversion (UC) energy transfer mechanisms. Simulations of population inversion starting from classical fluorescence decay and absorption measurements made as a function of pump fluence with phosphate and silicate glasses doped by 3% and 3.5% Nd ions such as LG760 and LG680 (Schott), respectively, show that an important part of the energy is lost and converted into heat by U.C. and that a non-negligible part is lost due to ESA. ESA spectra were thus systematically recorded in the pump (300-850 nm) and emission (850-1800 nm) domains of several Nd doped high power laser glasses including the above ones and others (LSG91H and LHG8 glasses from Hoya) to obtain absolute cross section values for all the relevant ESA transitions and to be able to determine the respective contributions of ESA and UC as a function of doping concentration and of pump intensity. Simulations are made by using adequate rate equations in which the ESA and emission cross sections and the overlap integrals of the corresponding spectra which are necessary to determine the energy transfer parameters are derived both experimentally and numerically with the aid of the Judd-Ofelt formalism.

© 1998 IEEE