K. H. Kim et al. [13] studied thermal effects on cavity stability of chromium- and neodymium-doped gadolinium scandium gallium garnet laser under solar simulator pumping. Only at low solar simulator beam intensities of up to 1500 solar constants (203 W/cm2) was the laser operation lasting longer than 10 min achieved. For higher pump beam intensities of up to 2500 solar constants (338 W/cm2), a quasi-cw-laser operation was obtained with continuously chopped pumping, with a duty cycle of 0.5 and a repetition rate of 13 Hz. The experimental results were compared with a calculated stability condition of the laser resonator for various pump powers and showed that the thermal focusing of the Cr:Nd:GSGG is 8-15 times greater than that of the neodymium-doped yttrium aluminium garnet (Nd:YAG) laser for the pump beam intensities from 1000 to 3000 solar constants.
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