Lowest-threshold solar laser operation under cloudy sky condition

Abstract

Classical solar-pumped lasers often demand a significant amount of concentrated solar power for laser emission, which is only attainable under clear sky condition, limiting their applicability. In this research, we report the first solar laser emission at very low threshold solar power under cloudy sky condition by end-side-pumping a 2.5 mm diameter, 25 mm length Ce:Nd:YAG rod at the focus of a parabolic mirror concentrator. The Ce:Nd:YAG solar laser performance was also evaluated under clear sky condition for comparison. Low threshold pump power of 32.4 W for continuous-wave solar-pumped laser was obtained under clear sky condition, being two times lower than the previous record. However, the cloud-filtered infrared sunlight enabled notable improvements in the solar laser performance by lessening the thermal lensing effects in the laser medium. The threshold pump power was further reduced to 29.2 W and maximum solar laser output of 14 W was successfully measured. This nearly doubled the focal slope efficiency from 4.03% during clear weather to 7.71% under a cloudy sky. The solar-to-laser conversion efficiency of 6.32% was nearly tripled compared to the 2.32% on a clear sky, while the solar laser conversion efficiency of 21.47 W/m2 was nearly twice the value of 12.62 W/m2 obtained on a clear day. This demonstrates that a cloudy environment could be an asset for solar laser research.