Classification of power-degrading mechanisms in an optically pumped four-level laser: an analytical approach

Abstract

In this paper, coupled power-gain equations were derived and solved to investigate the role of different power-degradation mechanisms on the continuous-wave power performance of a laser in the absence of thermal effects. Nine different power-degradation cases were considered, including a low-gain ideal four-level operation, ground-state reabsorption, pump excited-state absorption with and without storage, laser excited-state absorption with and without storage, intermediate storage, and Auger-type energy transfer upconversion with and without storage. There were three distinct types of laser performance identified, in terms of how the output power varies as a function of the pump power. Explicit analytical expressions were derived for the threshold pump power P-th, slope efficiency eta, and the product P-th eta/T as a function of output coupler transmission T and other physical parameters that describe the power degradation mechanism. The analytical approach developed here provides valuable insight about the role of major power degradation mechanisms in lasers, and it should be applicable to the analysis of a wide range of low-power, optically pumped laser media, including solid-state, fiber, and ceramic lasers.