INTERLEAVED IMMERSION COOLED HIGH BRIGHTNESS LASER DIODES FOR NEXT GENERATION LASER SYSTEMS

Abstract

High-power semiconductor laser diode arrays are increasingly required to deliver higher brightness while maintaining compact size, efficiency, and reliability. Meeting these demands places stringent requirements on thermal management, particularly as optical components such as fast-axis collimating lenses are integrated into interleaved-immersion-cooled (IIC) laser diode architectures, which combine microchannel heat sinks with immersion cooling to enable compact, high brightness operation. Although flow nonuniformity in microchannel cooling has been widely studied, the coupled effects of optical lensing, inlet flow modification, and emitter-resolved thermal and spectral behavior in high-power laser diode bars have not been previously quantified.This work presents a combined experimental and modeling investigation of plenum-fed microchannel cooling for high-power laser diode bars with and without optical lensing. Two inlet geometries, a cutback and a no-cutback configuration, are examined to evaluate tradeoffs between pressure drop, thermal resistance, and wavelength uniformity. Experimental measurements include bulk temperature, pressure drop, emitter-resolved centroid wavelength, and spectral full width at half maximum (FWHM) over a range of coolant flow rates. These data are integrated with a thermal resistance network and a CFD-based porous-media and three-dimensional heat-transfer modeling framework to relate inlet flow structure to both bulk and emitter-level thermal behavior. Results show that adding a lens does not significantly change the overall thermal resistance of the system, with bulk temperature differences typically remaining below 4°C. However, emitter-resolved measurements reveal that lensing modifies local cooling near the bar edges, increasing wavelength nonuniformity at low flow rates (0.175–0.275 kg/min), with a lens-induced increase in peak-to-peak centroid wavelength spread of approximately 0.52–0.91 nm. Modeling indicates that uniform-flow thermal gradients account for approximately half of the measured wavelength spread, while inlet-driven flow redistribution and non-thermal effects, such as packaging-induced stress and electro-thermal current redistribution, contribute to the remaining variation. As flow rate increases, enhanced mixing reduces sensitivity to inlet topology, leading to improved wavelength uniformity. Overall, this study clarifies the relative roles of channel maldistribution, inlet-plenum dynamics, and non-thermal effects in governing emitter-level temperature and spectral behavior in lensed IIC architectures. The results demonstrate that high brightness (>2× SOA) can be maintained in compact, optically integrated microchannel-cooled laser diode bars when both hydraulic constraints and localized inlet effects are properly managed.