For further development in beam quality of high power diode laser systems a new type of diode laser bars has been realized recently. Compared to commercially available broad area diode laser bars the lateral design of tapered diode laser bars consists of a ridge waveguide and a tapered section, where the tapered structure determines high output power and the high brightness is provided by the ridge waveguide structure. Unfortunately the different lateral structure leads to astigmatism effects which are also thermally affected in continuous wave operation. Hence in terms of diode laser systems with essentially fast- and slow-axis collimation micro-optics the full characterization of tapered diode laser bars is necessary. Where the wavelengths and divergences of tapered diode bars are relatively easy to measure, the beam profile with its apparently inside the tapered structure located lateral source is not. With a telecentric optics the caustic of the individual emitters of the bars are detected by the use of a fiber sensor with a resolution of 10 μm in fast- and slow-axis direction. Subsequently with beam analysis software the astigmatism can be calculated. As a result of several measurements of tapered bars of different wavelengths we detected good homogeneity over the bar concerning the amount of astigmatism but a slight current dependency. So particularly with regard to beam shaping micro-optics the application to high power diode laser systems seems to be sophisticated so far.
Beam quality and output power of mostly 2-dimensional stacked diode laser systems are insufficient for the demands of materials processing. To increase the output power at almost constant beam-quality, superimposition of diode laser bars of different wavelengths as well as polarization-multiplexing of s- and p-polarized laser beams is possible. Different techniques for wavelength-multiplexing have been developed. The so-called multi-filter concept of a spanned coated etalon with edge-filters has turned out best. The concept features a modular design, simple adjustment and easy add-on of more wavelengths. Concerning the polarization-multiplexing we take advantage of the almost linear polarized diode laser bars. Ordinary used beam splitter cubes with a cemented structure are less qualified for high radiance. Hence the beam combination is achieved with beam displacers made of a birefringent crystal (YVO<SUB>4</SUB>) which provide high transmittance and convenient adaptation. Finally an experimental set-up with 8 diode laser bars of 4 different wavelengths, i.e. 8-times beam superimposition, is realized. The set-up called multiplexer obtains a radiance of about 4 x 10<SUP>6</SUP> W cm<SUP>-2</SUP> sr<SUP>-1</SUP> and outnumbers all other comparable high power diode laser systems.