Direct solar illumination was used to pump a 1/4" x 3" Nd:Cr:GSGG rod and achieved quasi CW laser action at average powers of 20 watt. The solar radiation was chopped at a duty cycle of 20% to avoid crystal fracture. Peak power outputs were as high as 100 watt on a clear day. Slope efficiencies, relative to the solar power reaching the crystal, were close to 10%. Near field and far field beam patterns were recorded by a TV system in order to study the thermal behavior of the crystal. At maximum irradiation levels, the output from a 25 cm long flat concave cavity, had a beam divergence on the order of 30 mrad. Details of the experimental system and the calibration procedures are given.
"Solar Pumped Nd:Cr:GSGG Laser", Proc. SPIE 1038, 6th Mtg in Israel on Optical Engineering, (5 July 1989); doi: 10.1117/12.951089; https://doi.org/10.1117/12.951089