Highly-efficient multi-watt Yb:CaLnAlO_4 microchip lasers

摘要

Tetragonal rare-earth calcium aluminates, CaLnAlO_4 where Ln = Gd or Y (CALGO and CALYO, respectively), are attractive laser crystal hosts due to their locally disordered structure and high thermal conductivity. In the present work, we report on highly-efficient power-scalable microchip lasers based on 8 at.% Yb:CALGO and 3 at.% Yb:CALYO crystals grown by the Czochralski method. Pumped by an InGaAs laser diode at 978 nm, the 6 mm-long Yb:CALGO microchip laser generated 7.79 W at 1057-1065 nm with a slope efficiency of η = 84% (with respect to the absorbed pump power) and an optical-to-optical efficiency of η_(opt) = 49%. The 3 mm-long Yb:CALYO microchip laser generated 5.06 W at 1048-1056 nm corresponding to η = 91% and η_(opt) = 32%. Both lasers produced linearly polarized output (σ-polarization) with an almost circular beam profile and beam quality factors M_(x.y)~2 <1.1. The output performance of the developed lasers was modeled yielding a loss coefficient as low as 0.004-0.007 cm~(-1). The results indicate that the Yb~(3+)-doped calcium aluminates are very promising candidates for high-peak-power passively Q-switched microchip lasers.