High-pulse-energy 3.9-μm lasers in Ho:BYF

Experimental results describing pulsed lasers operating near 3.9 mum on the Ho3+ (I-5(5)-I-5(6)) transition in highly-doped ( > 10 at.%) barium yttrium fluoride (BaY2F8 or BYF) will be presented. The I-5(5) manifolds in Ho:BYF were pumped using a flashlamp excited, free-running Cr:LiSAF laser tuned to the Ho3+ absorption peak near 89 nm. Ho3+ concentrations of 10%, 20%, 30% and 40% in BYF were lased in a simple end-pumped resonator. Some similar data was also obtained in 10% and 20% Ho:YLF. The highest 3.9 mum pulse energy obtained in the comparative study was 55 mJ (at similar to10% optical-to-optical efficiency) using the 30% Ho:BYF crystal. A dual end-pumped laser in 30% Ho:BYF was also demonstrated, providing a pulse energy of 90 mJ in a near diffraction limited beam (M-2 similar to 1.2). Emission decay data was taken to shed light on the observed dependence of laser efficiency on holmium concentration and excitation density. The lifetimes of both lasing levels (I-5(5) and I-5(6)) deviate rather significantly from their low-concentration values. Plausible energy transfer processes that may be responsible for the observed trends in the laser and emission data will also be discussed.