High-efficiency kW-class QCW 88x-nm diode semiconductor laser bars with passive cooling

We present our recent efforts to improve power rating, efficiency, reliability, and cost of diode laser bars in the 88x nm wavelength band. QCW kW-class diode laser bars are grown by metal-organic chemical vapor deposition (MOCVD), and are cleaved, passivated, coated, and die bonded onto either standard copper CS-style heat sinks using indium solder, or onto expansion matched CuW CS heat sinks using AuSn solder. In an effort to realize high power operation, the high efficiency 880-nm epitaxial design has been optimized. Bars of varying fill factors, cavity lengths, and facet coating reflectivities are explored to improve the rated electrical to optical (E-O) efficiency up to approximately 70% under low duty cycle QCW operations. The enhanced E-O efficiency makes possible not only the passive cooling of the devices, but also reliable operation in the kW power range. We demonstrate that the semiconductor laser bars can survive over 100 million laser shots working in QCW mode. It is expected that the development of these passively cooled, highly efficient and highly reliable QCW kW-class diode laser bars will enable commercial applications.