Development of 2.94 μm room temperature CW Er:YAG laser technology

In this paper, we report a simple structure, room-temperature operation, LD end-pumped 2.94 μm Er:YAG continuous wave laser. The laser uses double-ended bonded YAG end caps to reduce the end-surface temperature of the crystal. The pump source uses a small core diameter output fiber and an aspheric mirror coupling system, which reduces the dispersion rate of small pump spots in the crystal and therefore improves pumping uniformity. When the pump light wavelength is 969.7 nm, the absorption of pump light in the front section of Er:YAG crystal is weak, accordingly the thermal aggregation effect of the front end of the laser gain medium is mitigated. We observed and compared the temperature of the end faces of bonded and non-bonded Er:YAG crystals with a thermal imaging camera, simulated the thermal distribution using COMSOL software, and proved the effectiveness of the above measures in reducing the thermal effect of highly doped Er:YAG crystal. We finally succeeded in achieving a continuous laser output of 2.94 μm at 155 mW. We also observed the output wavelength’s red-shift phenomenon with the pump power increase and explained it theoretically at the energy transfer level.