Investigation of n-side cooling in regards to bar geometry and packaging style of diode laser

Abstract

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 in regard to high power applications. The active area of the p-side down mounted laser bar is located directly above the micro channels. In other applications where conductive cooled heat sinks are used the bars are mounted on copper CS mount, CuW submount or high performance materials. All these packaging ideas use wire bonds or thin copper sheets as a n-contacts. The thermal advantage of these contacts can be neglected. N-contact cooling is typically used to achieve new records of optical output power in the labs. These studies analyze 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. The effect of n-side cooling with regards to the fill-factor and cavity length is analyzed also. The first part of this 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 studies 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.