US Patent 7286587 Holmium doped 2.1 micron crystal laser

A Ho:YAG crystal laser is disclosed which is doped with less than 2% holmium to reduce the lasing threshold and up-conversion, thereby increasing the operating efficiency of the laser. The laser does not need sensitizer ions so energy mismatches introduced by the sensitizer ions ale eliminated to the thereby increase the efficiency of the laser while minimizing detrimental thermal loading in the laser caused by up-conversion loss processes. The Ho:YAG crystal laser is directly pumped by a Thulium fiber laser at 1.9 μm at the holmium 5I7 to 5I8 transition to produce an output at 2.1 μm yielding a very low quantum defect. The laser is embodied as a thulium fiber laser pumped oscillator or an amplifier.