Theoretical comparison of Er³⁺-doped crystal lasers

The theoretical results are presented from a model that has been developed to simulate the 3 μm laser transition in Er³⁺ -doped laser crystals. The rate equations for the seven lowest energy levels of Er:YAG, Er:YSGG, Er:YLF and Er:BAYF have been solved numerically for both continuous wave (cw) and pulsed (Q-switched and gain switched) laser operation with direct optical pumping into the ⁴I_11.2 energy level. The dependence of slope efficiency on the Er³⁺ * concentration for each laser crystal was investigated for cw operation and the relative performance of Er(15%):YLF, Er(15%):BAYF, Er(50%):YAG and Er(50%):YSGG was compared for each mode of operation. The change in the slope efficiency of Er: YLF at high Er³⁺ concentration, due to additional multi-ion processes, was calculated for a wide range of rate coefficients. It was determined that the slope efficiency could be reduced by as much as 12% by these processes and thus could explain the reduction in the slope efficiency as determined experimentally for lasers using highly doped fluoride crystals as the gain medium.