Experimental results describing pulsed lasers operating near 3.9 μm on the Ho 3+ ( 5I 5- 5I 6) transition in highly-doped (\u3e 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
