GSA and ESA dual-wavelength pumped 2.3 μm Tm:YLF laser on the 3H4→3H5 transition

The population trapping effect of the ${{}^3\mathrm{F}}_4$ level is an important factor limiting the power scaling of the 2.3 μm thulium (Tm) laser on the ${{}^3\mathrm{H}}_4\to {{}^3\mathrm{H}}_5$ transition. In this Letter, we demonstrate a novel scheme of ground state absorption (GSA) (${{}^3\mathrm{H}}_6\to {{}^3\mathrm{H}}_4$) and excited state absorption (ESA) (${{}^3\mathrm{F}}_4\to {{}^3\mathrm{H}}_4$) dual-wavelength pumped 2.3 μm Tm lasers. Introducing an ESA pumping process can accurately excite the ${\mathrm{Tm}}^3$ ions accumulated in the ${{}^3\mathrm{F}}_4$ level to the ${{}^3\mathrm{H}}_4$ level, constructing a double populating mechanism for the upper laser level ${{}^3\mathrm{H}}_4$. A proof-of-principle experimental demonstration of the GSA (785 nm) and ESA (1470 nm) dual-wavelength pumped 2.3 μm $\mathrm{Tm}:{\mathrm{LiYF}}_4$ (Tm:YLF) laser was realized. A maximum continuous-wave output power of 1.84 W at 2308 nm was achieved under 785 and 1470 nm dual-wavelength pumping, increased by 60% compared with the case of 785 nm single-wavelength pumping under the same resonator condition. Our work provides an efficient way to achieve higher output power from 2.3 μm Tm-doped lasers on the ${{}^3\mathrm{H}}_4\to {{}^3\mathrm{H}}_5$ transition.