Efficient holmium-doped solid-state lasers pumped by a Tm-doped silica fiber laser

We report on efficient operation of Ho:YAG and Ho:YLF lasers in-band pumped by a tunable Tm-doped silica fiber laser. The Tm-doped fiber laser could be tuned over 150 nm from similar to 1860 to 2010 nm with a relatively narrow linewidth (<0.5 nm) at output power levels in excess of 9 W with a high power stability (RMS < 1.5%). Using a simple standing-wave cavity configuration, >6.4 W of TEMinfinity output was obtained from a Ho:YAG laser at 2.1 mum at the maximum incident pump power of 9.6 W at 1907nm from the Tm fiber laser, corresponding to an optical-to-optical efficiency of 67%, and the slope efficiency with respect to incident pump power was 80%. For a similar resonator design, 4.8 W of output at 2.07 mum was generated from a Ho:YLF laser at an incident pump power of 9.4 W, corresponding to an optical conversion efficiency of 51%. The different levels of performance of the Ho: YAG and Ho: YLF are compared and their relative merits discussed. Using a simple ring resonator geometry and an acousto-optic modulator to enforce unidirectional operation, we have obtained 3.7 W of single-longitudinal-mode output from a Ho:YAG laser. The prospects for further improvement in performance and higher output power are discussed.