Midinfrared holmium fiber lasers

The use of the high-power Tm³⁺-doped silica fiber laser as a pump source for Ho³⁺-doped silica and Ho³⁺-doped fluoride fiber lasers for the generation of 2.1-μm radiation is demonstrated. The Ho³⁺-doped silica fiber laser produced a maximum output power of 1.5 W at a slope efficiency of ∼82%; one of the highest slope efficiencies measured for a fiber laser. In a nonoptimized but similar fiber laser arrangement, a Ho³⁺-doped fluoride fiber laser produced an output power of 0.38 W at 2.08 μm at a slope efficiency of ∼50%. A Raman fiber laser operating at 1160 nm was also used to pump a Ho³⁺-doped fluoride fiber laser operating at a wavelength of 2.86 μm. An output power of 0.31W was produced at a slope efficiency of 10%. The energy transfer upconversion process that depopulates the lower laser level in this case operates at a higher efficiency when the pump wavelength is closer to the absorption peak of the ⁵I₆ energy level, however, this energy transfer process does not impede to a great extent the performance of the Ho³⁺-doped fluoride fiber laser based on the ∼2.1μm laser transition.