Next-generation active and passive heatsink design for diode lasers

ABSTRACT Successful thermal and stress management of edge-emitting GaAs-based diode la sers is key to their performance and reliability in high-power operation. Complementary to advanced epitaxial structures and die-fabrication processes, next-generation heatsink designs are required to meet the requirements of emerging applications. In this paper, we detail the development of both active and passive heatsinks designed to match the coefficient of thermal expansion (CTE) of the laser die. These CTE-matched heatsinks also offer low thermal resistance, compatibility with AuSn bonding and improved manufacturability. Early data representing the performance of high-power devices on the new heatsinks are included in the presentation. Among the designs are a water-cooled, mini-channel heatsink with a CTE of 6.8 ppm/qC (near to the nominal 6.5 ppm/ qC CTE of GaAs) and a thermal resistance of 0.43 qC/W (assuming a 27%-fill-factor diode-laser bar with a cavity length of 2 mm). The water flow in the heatsink is isolated from the electrical potential, eliminating the possibility of electrolytic corrosion. An additional feat ure of the integrated design is the reduction in required assembly steps. Our next-generation, passive, CTE-matched heatsink employs a novel design to achieve a reduction of 16% in thermal resistance (compared to the predecessor commercial product). CTE’s can be engineered to fall in the range of 6.2-7.2 ppm/ qC on the bar mounting surface. Comparisons between simulated performance and experimental data (both in CW and long-pulse operation) will be pr esented for several new heat-sink designs. Keywords: GaAs diode laser bar, mini-channel heatsink, CTE match, AuSn