An IR-emitting holmium-doped fluoride glass fiber laser developed by researchers at the Institut d'Optique Graduate School (Palaiseau, France) and the University of Sydney (Sydney, Australia) has high slope efficiency and also provides strong visible upconversion fluorescence at many wavelengths in the visible region, showing a high fluorescence-to-pump-energy ratio. The device could lead to other useful shortwave-IR lasers, both pulsed and continuous-wave, in the 2.1 μm spectral region.
The laser, which emits at 2.08 μm, is resonantly pumped at 2.051 μm with a cladding-pumped, tamarium-doped silica glass fiber laser. Because the holmium-doped-fiber portion of the setup has a base material of ZBLAN fluoride, rather than silicate, the laser is suitable for 2.94 μm and visible emission. A 1.1 m long version of the laser produces 6.66 W of power at 2.08 μm with a slope efficiency of 72%. Fluorescence emission was observed for pump levels as low as a few milliwatts, and occurred at 910, 656, 544, and 491 nm. The researchers believe that reducing the proportion of holmium in the fiber could lead to emission at 2.94 μm, and that writing a grating in the core to produce distributed feedback could produce narrow-linewidth operation. Contact Stuart Jackson at[email protected].