Comparison of thermal management techniques for semiconductor disk lasers

ABSTRACT Semiconductor Disk Lasers (SDLs) are compact lasers suitable for watt to multi-watt direct generation in the 670-2350nm waveband and frequency-doubled operation in the u ltraviolet and visible regions. This is, however, criticallydependent on the thermal management strategy used as, in this type of laser, the pump is absorbed over micrometerlengths and the gain and loss are temperature sensitive. In th is paper, we compare the two heat dissipation techniques thathave been successfully deployed to-date: the “thin device” approach where the semiconductor active mirror is bondedonto a heatsink and its substrate subsequently removed, and the “heatspreader” technique where a high thermalconductivity platelet is directly bonded onto the active part of the unprocessed epilayer. We show that for SDLs emittingat 1060nm with pump spots of ~80µm diameter, the heatspreader approach out performs the thin-device alternative, withthe best results being obtained with a diamond heatspreader. I ndeed, the thermal resistances are measured to be 4.9, 10.4and 13.0 K/W for diamond-bonded, SiC-bonded and flip-chip devi ces respectively. It is also observed, as expected, thatthe thermal management strategy indirectly affects the optimum output coupling and thus the overall performance ofthese lasers.Keywords: Semiconductor disk laser, Vertical external-cavity surface emitting laser, VECSEL, high-power, thermalmanagement