Both sides cooled packages for high-power diode laser bars

The packaging of high power diode laser bars requires a high cooling efficiency and long-term stability. Due to the increasing output power of the diode laser bars the cooling performance of the packaging becomes more important. Nowadays micro-channel heat sinks seem to be the most efficient cooling concept with regard to high power applications. The active area of the p-side down mounted laser bar is located directly above the micro-channels. Conductively cooled heat sinks are also used in conjunction with the bars mounted on copper CS mount, WCu submount or other high performance materials. All these the above mentioned packaging ideas use wire bonds or thin copper sheets as a n-contacts. The thermal advantage of these contacts can be neglected. Active n-contact cooling is typically used to achieve new records of optical output power in the labs. This work analyzes the properties of an additional n-contact cooling. The cooling performance of a package cooled on both sides can be improved by more than 20% when compared with typical wire bonds or metal sheets. Different packaging styles with metal sheets, heat spreaders (expansion matched) and active n-side cooling are investigated. Also the effectiveness of n-side cooling with regards to the fill-factor and cavity length is analyzed. The first part of the paper approaches the topic theoretically. Simulations are carried out and show the advantages and differences of different package styles in comparison to bar geometries variations. The second part of the work characterizes and analyses fabricated samples made out of copper in view of cooling performance, handling, and induced stress. The results of different bar geometries and packaging styles are compared and guidelines for n-side cooling are developed.