Investigation of diode-pumped 2.8-mu m Er:LiYF4 lasers with various doping levels

We report on efficient lasers emission of Er:LiYF4 at 2.8 mu m. 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 similar to 15%. At this Er3+ 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 mu m, which is of interest for several applications based on the strong water absorption in this wavelength range.