Comparison of thermal management techniques for semiconductor disk lasers

Semiconductor Disk Lasers (SDLs) are compact lasers suitable for watt to multi-watt direct generation in the 6702350nm waveband and frequency-doubled operation in the ultraviolet and visible regions. This is, however, critically dependent on the thermal management strategy used as, in this type of laser, the pump is absorbed over micrometer lengths and the gain and loss are temperature sensitive. In this paper, we compare the two heat dissipation techniques that have been successfully deployed to-date: the “thin device” approach where the semiconductor active mirror is bonded onto a heatsink and its substrate subsequently removed, and the “heatspreader” technique where a high thermal conductivity platelet is directly bonded onto the active part of the unprocessed epilayer. We show that for SDLs emitting at 1060nm with pump spots of ~80μm diameter, the heatspreader approach outperforms the thin-device alternative, with the best results being obtained with a diamond heatspreader. Indeed, the thermal resistances are measured to be 4.9, 10.4 and 13.0 K/W for diamond-bonded, SiC-bonded and flip-chip devices respectively. It is also observed, as expected, that the thermal management strategy indirectly affects the optimum output coupling and thus the overall performance of these lasers.