Efficient 2-micron Ho lasers based on fluoride crystal hosts

Highly efficient, water cooled, resonantly pumped Ho3+ fluoride lasers have been demonstrated at 2 μm. The laser materials, 0.5 at.% Ho:YLF, 0.5 at.% Ho:BYF, and 0.5 at.% Ho:BaYLuF, were resonantly pumped with an IPG Tm:fiber laser operating at 1940 nm. Laser action occurred on the 5I7 to the 5I8 manifold with center wavelengths of 2062.6 nm, 2074.0 nm, and 2075.2 nm respectively. Continuous wave (CW) operation of 0.5% Ho:BYF achieved a maximum efficiency of approximately 68% with a 50% reflective output coupler. Pulsed operation of this laser system produced 4 mJ pulses at 500 Hz with a slope efficiency of 38%.