Thermal resistance in dependence of diode laser packages

Abstract

High power diode laser bars require packages with a high cooling efficiency and long-term stability. Due to the increasing output power of the diode laser bars the thermal resistance of the packaging becomes even more important. It is the key information about the cooling efficiency of a package and in particular of the heat sink. Besides the heat sink the thermal resistance depends also on the solder interface, packaging process, and bar structure such as fill factor and resonator length. This work presents a thermal comparison of different packaging types and laser bar designs. Different package types are experimentally measured and analyzed by numerical calculations to obtain information about the influence of the different parameters: Conductively cooled and water cooled copper heat sinks as well as a new type of expansion matched micro-channel heat sink made out of Cu-AlN sandwich are investigated. In addition to the different packages, laser bars with different resonator lengths are mounted and analyzed regarding their thermal behavior; the dependency of the thermal resistance on the resonator length is a particular interest of the investigation. In parallel to the experiments thermal simulations of the same packages and laser bar geometries are performed. The boundary conditions chosen in the simulations are comparable to the experimental values and the same parameters are varied. The relations between theoretical and experimental results are presented. The analysis shows the influencing factors, so that the optimum package can be chosen for a specific application.