Tm-doped fiber amplifiers are good sources for high energy laser, DIRCM, LIDAR, remote sensing and spectroscopy. The reported Tm-doped amplifiers have efficiencies between 55% to 65%. The diode lasers that are commercially available at 793 nm produce about 35% ex-fiber efficiency. Therefore, the power conversion efficiency of Tm-doped amplifiers is only in the range of 20% - 23% which is less than half that of Yb-doped amplifiers. One straightforward way to improve the e-o power conversion efficiency of Tm-doped fiber amplifiers is to boost the efficiency of 793 nm diode pump from 35% to >55%. This will enable >36% efficient Tm-doped fiber amplifiers. With improvement in epitaxial design, we have demonstrated 64% at 15.5 W producing fiber-coupled package with 400 W in 225-μm/0.22 NA and 54% ex-fiber efficiency in packages with <0.63 kg/kW and <0.49 cc/W specific mass and specific volume, respectively. Further improvement is underway and we will update the latest results.
In this paper, we show results of further brightness improvement and power-scaling enabled by both the rise in chip brightness/power and the increase in number of chips coupled into a given numerical aperture. We report a new chip technology using x-REM design providing a record ~340 W output from a 2×12 nLIGHT element® in 105 μm diameter fiber. These diodes will allow next generation of fiber-coupled product capable of >250W output power from 105 μm/0.15 NA beam at 915 nm. There is also an increasing demand for low SWaP fiber-coupled diodes for enabling compact high energy laser systems for defense applications. We have demonstrated 600 watts and 60% efficiency at 15C in 220 μm/0.22 NA fiber resulting in specific mass and volume of 0.44 kg/kW and of 0.5 cm3/W respectively.
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