Concentration and power dependencies of level population of 2.8-μm laser transition in YLF:Er crystals under cw laser diode pumping

An influence of inter-ionic cross relaxation processes (up- conversion, self-quenching) on concentration and power dependence's of the inverse population of 4 I 11/2 and 4 I 13/2 laser levels in YLF:Er crystals under CW laser-diode pumping were studied both theoretically and experimentally. Computer simulations were carried out taking into account not only pair interaction but also the multi-ion interaction in the whole system. Optimal Er concentration for 3-micrometers CW lasing was estimated as 10- 15%.