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-mu m radiation is demonstrated. The Ho3+-doped silica fiber laser produced a maximum output power of 1.5 W at a slope efficiency of similar to 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 mu m at a slope efficiency of similar to 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 mu m. An output power of 0.31 W was produced at a slope efficiency of 10%. The energy transfer up-conversion 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 I-5(6) 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 similar to 2.1-mu m laser transition.