Efficient High-Power Laser Diodes

High-power broad-area diode lasers are the most efficient light sources, with 90-μm stripe GaAs-based 940-980 nm single emitters delivering > 10 W optical output at a power conversion efficiency ηE(10 W) > 65%. A review of efforts to increase ηEis presented here and we show that for well-optimized structures, the residual losses are dominated by thep-side waveguide and nonideal internal quantum efficiency ηi. The challenge in measuring efficiency to sufficient precision is also discussed. We show that ηEcan most directly be improved using low heat sink temperature THSwith ηE(10 W) reaching > 70% atTHS= -50 °C. In contrast, increases in ηEat THS= 25 °C require improvements in both material quality and design, with growth studies targeting increased ηiand reduced threshold current and design studies seeking to mitigate the impact of thep-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reducep-side losses, at the penalty of increased threshold current. The benefit of EDAS designs is shown here using diode lasers with 30-μm stripes, (in development as high beam quality sources for material processing). Efficiency increases of ~ 10% relative to conventional designs are demonstrated at high powers.