Competition between green and infrared emission in Er:YLiF4 upconversion lasers

The competition between two laser transitions in Er:YLiF4 (4S3/2 → 4I15/2 at 551 nm and 4S3/2 → 4I13/2 at 850 nm) is studied using a model based on rate equations. The laser emission is pumped by upconversion at 795 nm; for comparison, we also discuss upconversion pumping by another mechanism, at 970 nm. The conditions that favor laser emission in various regimes on these two transitions are found.