2 μm eye-safe solar-pumped laser

Solar-pumped laser using solar radiation as pumping source converts sunlight to laser directly. It has the following advantages over other solid-state lasers: sufficient energy resource, clean and pollution-free, long service life, and low manufacturing costs. Up to now, researches on solar-pumped laser have been limited to the 1 μm band with Nd3+ doped gain medium. By analyzing the absorption spectrum of the existing solid-state materials, we have found that Tm3+ doped materials have strong absorption in visible light band where the solar radiation is strong. 2 μm eye-safe laser has a greater application prospect in the fields of remote sensing, LiDAR, medical treatment, and space optical communication. In this paper, the absorption spectrum and spectral overlap of two common laser crystals, Tm:YAG and Tm:YAP, with the solar radiation have been analyzed and calculated. The threshold pump power density of these two crystals were calculated as 1.14 Kw/cm3, 1.434Kw/cm3 respectively. Tm:YAG crystal with lower threshold pump power density was selected as the gain medium and a two-stage pumping model was built. A Fresnel lens was used as the primary solar light concentrator. The secondary concentrator was a conic cavity with a defused high reflection surface. The laser rod with grooved side wall was installed in the conical cavity. Tracepro was used to optimize the whole setup. The work in this paper made a theoretical preparation for experimental research of 2 μm solar-pumped laser.