Assessment of possible performances of compact solar-pumped lasers using transparent Cr3+, Nd3+-co-doped YAG ceramics micro rods

Employing a commercially available off-axis parabolic mirror of 050.8 or 076. 2 mm caliber and 01 or 1 x 1 x 10 mm Cr3+, Nd3+-co-doped YAG ceramic micro laser medium (LM), our compact solar-pumped lasers (mu SPL) could oscillate continuously without any forced air cooling from 11:00 a.m. beyond 5:30 p.m. tracking the sun outdoors. However, their energy conversion efficiencies eta power have not exceeded so far 1%. Numerical assessments of mu SPL performance using a fundamental expression of laser oscillation based on experimentally obtained parameters were performed. Dependences of eta power on transmittance of an output coupler, mode-matching efficiency eta mode, length of LM, distributed loss constant in LM, and Cr content as well as the necessity of the concentration ratio as high as 10,000 were elucidated. The values of eta mode between 0.3 and 0.5 coming from the present confocal resonator roughly reproduced eta power around 1%. Based on the assessments, possible approaches for further improvement of mu SPL performance were evaluated including employment of composite LM to increase eta mode.