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

Abstract

Employing a commercially available off-axis parabolic mirror of ⌀50.8 or ⌀76. 2 mm caliber and ⌀1 or 1 × 1 × 10 mm Cr3+, Nd3+-co-doped YAG ceramic micro laser medium (LM), our compact solar-pumped lasers (μSPL) 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 ηpower have not exceeded so far 1%. Numerical assessments of μSPL performance using a fundamental expression of laser oscillation based on experimentally obtained parameters were performed. Dependences of ηpower on transmittance of an output coupler, mode-matching efficiency ηmode, 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 ηmode between 0.3 and 0.5 coming from the present confocal resonator roughly reproduced ηpower around 1%. Based on the assessments, possible approaches for further improvement of μSPL performance were evaluated including employment of composite LM to increase ηmode.