Gain and energy storage in holmium YLF

It is demonstrated that Q-switched holmium lasers are capable of high-gain and high-energy operation at 300 K. Small-signal gain coefficients of 0.50 and 0.12 cm/sup -1/ have been measured in YLF and YAG, respectively. Small-signal gains of 0.50 cm/sup -1/ are comparable to those achievable in Nd-YAG and are not typical of low-gain materials. This large gain in the Ho:YLF material is made possible by operating the amplifier in the ground state depletion mode. The amplifier performance data and associated analysis presented demonstrate that efficient energy storage is possible with very high excited state ion densities of the Ho /sup 5/I/sub 7/ upper laser level. This is an important result since upconversion can limit the /sup 5/I/sub 7/ population. Although upconversion was still present in this experiment, it was possible to achieve efficient energy storage, demonstrating that the problem is manageable even at high excitation densities in YLF.<>