HOLMIUM YLF AMPLIFIER PERFORMANCE AND THE PROSPECTS FOR MULTI-JOULE ENERGIES USING DIODE-LASER PUMPING

Laser studies were performed that examined the amplifier characteristics of holmium-doped yttrium lithium fluoride (YLF) at 300 K. An inversion ratio nI-5(7)/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 was developed for diode laser pumping and adapted to consider this flashlamp-pumped case. There is good agreement between the theory and experiment. 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.