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High power diode lasers can be used for a lot of applications such as pumping of solid state lasers, direct material processing (for example welding, soldering, annealing) and printing. The successful use of high power diode lasers depends on their high efficiency and reliability in combination with a long lifetime. For a further increase in the quality of high power diode lasers the properties of semiconductor laser bars have to be improved as well as the mounting techniques for these bars onto specially designed heat sinks. For most applications the electro-optical properties of the high power diode lasers have to be known exactly. Detailed information on the propagation characteristics and the transverse mode distribution of diode laser beams is necessary for the optimization of the overall performance. In addition the electro-optical characterization is a first test for the quality of high power diode lasers. An automated test set-up developed at the Fraunhofer-Institut fur Lasertechnik will be presented. The electro-optical data such as threshold current, slope efficiency, center wavelength, spectral width, total conversion efficiency and cw-output power can be measured as a function of driving current as well as the beam divergence angles in fast and slow direction of the high power diode lasers. Different methods to determine the exact divergence angles will be discussed. A high power test set-up is developed which allows driving currents up to 360 A. Using diode laser bars developed at the Fraunhofer- Institute fur Angewandte Festkorperphysik a record cw-output power of 267 W could be achieved at 333 A. |
