Efficient single-axial-mode operation of a Ho:YAG ring laser pumped by a Tm-doped silica fiber laser

Efficient single-frequency operation of a Ho:YAG ring laser at room temperature with a traveling-wave TeO2 acousto-optic modulator to enforce unidirectional operation is reported. By use of a 2-at. % Ho3+-doped 10-mm-long Ho:YAG rod, end pumped by a cladding-pumped tunable Tm-doped silica fiber operating at 1.9 microm, the Ho:YAG ring laser yielded 3.7 W of single-frequency output at 2.1 microm in a diffraction-limited TEM00 beam with M2 < 1.1 for an incident pump power of 8.8 W. The rf power required for unidirectional operation was 0.3 W and corresponded to an increase in cavity loss for the lasing direction (due to diffraction) of only 0.5%. The prospects for further improvement in efficiency are discussed.