Advanced Laser Diode Cooling Concepts
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1076-K07-06
Advanced Laser Diode Cooling Concepts Ryan Feeler1, Jeremy Junghans1, Edward Stephens1, Greg Kemner1, Fred Barlow2, Jared Wood2, and Aicha Elshabini2 1 Cutting Edge Optronics, 20 Point West Boulevard, St. Charles, MO, 63301 2 Electrical Engineering, University of Idaho, Buchanan Engineering, Room 213, PO Box 441023, Moscow, ID, 83844-1023 ABSTRACT A new, patent-pending method of cooling high-power laser diode arrays has been developed which leverages advances in several areas of materials science and manufacturing. This method utilizes multi-layer ceramic microchannel coolers with small (100’s of microns) integral water channels to cool the laser diode bar. This approach is similar to the current stateof-the-art method of cooling laser diode bars with copper microchannel coolers. However, the multi-layer ceramic coolers offer many advantages over the copper coolers, including reliability and manufacturing flexibility. The ceramic coolers do not require the use of deionized water as is mandatory of high-thermal-performance copper coolers. Experimental and modeled data is presented that demonstrates thermal performance equal to or better than copper microchannel coolers that are commercially available. Results of longterm, high-flow tests are also presented to demonstrate the resistance of the ceramic coolers to erosion. The materials selected for these coolers allow for the laser diode bars to be mounted using eutectic AuSn solder. This approach allows for maximum solder bond integrity over the life of the part. INTRODUCTION Recent advances in semiconductor technology have led to the creation of laser diode bars capable of producing hundreds of watts of CW output power. These devices typically operate with electrical-to-optical efficiencies in the range of 50-75%. As a result a tremendous amount of waste heat is generated, with heat fluxes on the order of 1 kW/cm2 common in the industry today. As device technology continues to improve and optical output powers continue to increase, additional waste heat will need to be removed by laser diode packages. The most common method of removing large amounts of waste heat in a laser diode package is by using microchannel-cooled packaging technologies. This method allows for cooling fluid to pass very near to the laser diode bar, with typical distances from the laser diode bar to the cooling fluid of approximately 200 µm. Most commercially-available microchannel coolers are made by diffusion bonding multiple layers of copper, each of which is typically 200400 µm thick. The laser diode bar is often soldered directly to the copper cooler with indium solder. It is also common to solder the bar to a CTE-matched heatsink, and then solder the resulting subassembly to a copper MCC. This configuration allows hard solder to be more easily used. While this approach provides excellent thermal performance, there are several drawbacks. The use of metallic microchannel coolers causes the electrical path to come in direct
contact with the coolant. This requires the use of deio
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