Highly efficient emerald laser

Abstract

We report highly efficient quasi-cw laser operation in emerald. A crystal of 3 mm in length was pumped longitudinally by a krypton laser at 647.1 nm in a nearly concentric cavity. A64% output slope efficiency was measured with an output coupler of 1.16% transmission at 768 nm. The maximum output power reached 1.65 W with 3.63 W of pump power and was pump power limited. These results are among the highest in efficiency reported in laser-pumped Cr lasers operating in a quasi-cw mode. The calculated round trip laser loss was 0.11% in our sample, corresponding to 0.36%/cm. The laser quantum yield was 76%. A tuning range of 720-842 nm was achieved with a single element birefringent filter. Excitation spectra indicated that the relative fluorescence quantum yield was close to unity in the visible region of the emerald absorption bands. The calculated emission cross section was 3.3 × 10−20cm2 at 750 nm for the c-axis polarization. The excited state absorption was estimated from the laser results to be 20% of the stimulated emission cross section at 768 nm. The pump power threshold of the present laser was at 230 mW with a 60-µm pump beam radius. A scheme for the miniaturization of a tunable emerald laser to accept diode pumping is also discussed.