Packaging of High-Power Bars for Optical Pumping and Direct Applications

Continuous cost reduction, improved reliability and modular platform guide the design of our next generation heatsink and packaging process. Power scaling from a single device effectively lowers the cost, while electrical insulation of the heatsink, low junction temperature and hard solder enable high reliability. We report on the latest results for scaling the output power of bars for optical pumping and materials processing. The epitaxial design and geometric structures are specific for the application, while packaging with minimum thermal impedance, low stress and low smile are generic features. The isolated heatsink shows a thermal impedance of 0.2 K/W and the maximum output power is limited by the requirement of a junction temperature of less than 68 degrees C for high reliability. Low contact impedance are addressed for drive currents of 300 A. For pumping applications, bars with a fill factor of 60% are deployed emitting more than 300 W of output power with an efficiency of about 55% and 8 bars are arranged in a compact pump module emitting 2 kW of collimated power suitable for pumping disk lasers. For direct applications we target coupling kilowatts of output powers into fibers of 100 mu m diameter with 0.1 NA based on dense wavelength multiplexing. Low fill factor bars with large optical waveguide and specialized coating also emit 300 W.