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 η
_E
(10 W) > 65%. A review of efforts to increase η
_E
is presented here and we show that for well-optimized structures, the residual losses are dominated by the
p
-side waveguide and nonideal internal quantum efficiency η
_i
. The challenge in measuring efficiency to sufficient precision is also discussed. We show that η
_E
can most directly be improved using low heat sink temperature T
_HS
with η
_E
(10 W) reaching > 70% at
T
_HS
= -50 °C. In contrast, increases in η
_E
at T
_HS
= 25 °C require improvements in both material quality and design, with growth studies targeting increased η
_i
and reduced threshold current and design studies seeking to mitigate the impact of the
p
-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reduce
p
-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.