Next generation of cooling approaches for diode laser bars

Abstract

The field of applications for diode laser bars is growing continuously. The reasons for this are the growing width of available wavelengths and the increasing optical output power. In parallel to this the requirements for packaging for the high power diode laser bars increase and are more manifold. Expansion matched, non corrosive, non erosive, low thermal resistance and high thermal conductivity are some of the keywords for the packaging in the near future. Depending on the thermal power density, two different types of heat sinks are used: active and passive. The active heat sinks can further be subdivided in micro- or macro-channel heat sinks. The development of macro-channel heat sinks was necessary because of the limited lifetime of the common micro-channel heatsink. The bigger channels reduce especially erosion and corrosion effects. By taking the increasing resonator length of the laser bars into account the cooling performance of the macro-channel heatsink will be sufficient for many applications. In cases of high thermal power densities there are still no alternatives to micro-channel heat sinks. New material combinations shall minimize the erosion and corrosion effects. New raw materials such as diamond composite materials with a higher thermal conductivity than copper and matched thermal expansion will find their working field at first in the passively cooling of laser bars. The next generation of active heat sinks will also be partly made out of the high performance materials. The point of time for this improvement depends on machining behavior, availability and price of the raw material.