Investigation of diode-pumped 2.8-microm Er:LiYF(4) lasers with various doping levels

We report on efficient lasers emission of Er:LiYF(4) at 2.8 microm. The crystals were pumped by InGaAs semiconductor laser emitting near 970 nm. The laser performance was investigated for different doping levels and yielded an optimum doping level of ~15%. At this Er(3+) concentration we achieved a slope efficiency of 35%, which is identical to the quantum defect. Pumping at high power levels permits a true cw output power of 1.1 W at 2.8 microm, which is of interest for several applications based on the strong water absorption in this wavelength range.