Holmium YLF amplifier performance and the prospects for multi-Joule energies using diode-laser pumping

Laser studies that examined the amplifier characteristics of holmium-doped yttrium lithium fluoride (YLF) at 300 K are discussed. An inversion ratio n⁵I₇/n _Ho of 0.37 was reached, resulting in a measured small-signal gain coefficient of 0.50 cm^-1. In a flashlamp pumping experiment, an output energy of 240 mJ was achieved for 38.5 mJ of input energy, resulting in a large gain of 6.2. An amplifier model developed for diode laser pumping was adapted to consider this flashlamp-pumped case. The agreement between the theory and the experiment is good. Multipass amplifier calculations using the model suggest that the Ho:Tm:YLF laser crystal can support a 12% electrical to optical efficiency at 300 K, even in the presence of upconversion