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

摘要

Experimental results describing pulsed lasers operating near 3.9 μm on the Ho~(3+) (~5I_5-~5I_6) transition in highly-doped (> 10 at. %) barium yttrium fluoride (BaY_2F_8 or BYF) will be presented. The ~5I_5 manifolds in Ho:BYF were pumped using a flashlamp excited, free-running Cr:LiSAF laser tuned to the Ho~(3+) absorption peak near 889nm. Ho~(3+) 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 μm pulse energy obtained in the comparative study was 55 mJ (at ～10% 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 ～ 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 (~5I_5 and ~5I_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.