High power diode lasers (HPDL) have become very attractive as an intelligent tool for direct material processing as well as pump sources for miniaturized solid state lasers and fiber lasers since optical beam transformation systems generate the required beam circularization from the originally highly asymmetric brightness of the output beam. This presentation focuses on reliable microassembling processes to realize micro-optical beam transformation systems for high power diode laser bars and stacks for the efficient coupling of the beam into optical fibers at reasonable costs. The modular semi automatic micro assembly set up realized consists of a six axes alignment system with an accuracy in the submicron range for the three spatial axes as well as microrad for the three rotational axes, a semi-automatic glue dispenser as well as respective grippers and magazines which are necessary for the handling of the micro optical components. The established automation processes for the mounting of the fast axis collimation (FAC) lenses are of particular interest for the assembly of e.g. fiber coupled modules of diode laser stacks whereas more than 20 fast-axis collimations are necessary.

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The assembly of fast-axis collimating lenses (FAC-) with high power laser diode (HPLD) bars and stacks is discussed. FAC-lenses are cylindrical lenses of high numerical aperture (NA.> 0.5) and short focal length (200 .tm..1 mm) for the collimation of the strongly divergent radiation emitted perpendicular to the active region of a high power laser diode bar. These FAC-lenses are necessary for all kind of beam transformation systems using HPLD bars and stacks. The lenses have to be fixed at the heat sink ofthe laser diode bar with an accuracy of < 0.3 im and for special transformation systems with a defmite tilt of 1 ..2°and an accuracy of better than mrad. In most cases an active assembly of the whole beam transformation system is necessary. Here we propose another approach. . A master system is assembled in a traditional way. The diode bar and the fixed FAC-lens are removed from the system.. The intensity distribution behind the FAC-lens in connection with conventional cylindrical lens for slow axis imaging is measured and compared to a theoretical system design. . Stops are fabricated according to the intensity distribution and placed in a defmite distance to the laser diode bar.. FAC lenses are mounted in front of a single diode bar by maximizing the total power passing the stop system. With the help of this approach a first step towards a semi-automated assembly is done for fiber coupling of a laser diode bar into a 200 tm multimode optical fiber ofN.A.= 0.2. The system requires a slightly tilted FAC-lens of very short focal length (300 .tm) and hence a high accuracy of the lens assembly.

A microoptical beam transformation system for coupling of high power laser diode bars into multimode optical fibers is introduced. The key components are a gradient-index (GRiN) cylindrical lens for the collimation of the fast-axis radiation and an array of blazed gratings for beam deflection of the single emitter bundles in the slowaxis. Excellent optical performance and high numerical aperture is required for the cylindrical lens. The lenses are fabricated by Ag/Na ion exchange and exhibit diffraction-limited performance up to NA. 0.5. The array of blazed gratings is produced by e-beam lithography in a variable dose writing mode. The diffraction efficiency into the desired order is higher than 85 % for each element. Using these elements coupling of more than 60 % of the output power of a 19 emitter high power laser diode bar (P0 =20 W) into a 200 tm fiber of NA. 0.2 is achieved. Applications in fiber laser pumping, solid state laser pumping as well as laser soldering and plastic welding are discussed.

A novel technique, the so-called skew ray imaging concept, has been developed for beam transformation of high power diode laser bars. It leads to beam circularization with optimum brightness conservation. This concept uses two key microoptical components : a fast axis collimator microlens (FAC) of high isoplanatism (for example GRIN cylindrical lenses) and a special array ofbeam deflecting elements (redirector), the number ofwhich corresponds to the single emitter number ofthe diode laser. Using this concept of skew ray imaging in a modified form, prototypes of pumping sources for visible fiber lasers have been developed and built up. Several Watts ofoptical power have been focussed into a small spot of25 .tm with a numerical aperture of 0.35. GRIN cylindrical microlenses with 0. 1 mm focal length and diffractive blazed gratings as redirector have been used. The grating periods ofthe redirector sections have been between 8 and 100 pm. They have been produced by e-beam direct writing in resist. After optimization of the fabrication process the diffraction efficiencies of all sections have been beyond 86% with good reproducibility. Special techniques have been used for system integration. The FAC microlenses have been attached to a copper lens holder with a subsequent gluing process ofthe holder to the laser diode heatsink. A UV-curable adhesive with extremely low shrinkage has been selected. The redirector element has been integrated with an additional possibility for lateral adjustment in order to compensate minor residual walk-offeffects ofthe microlens when the laser power is varied from zero to maximum.A very compact pumping source of3" x 1 " x 1 " dimensions has been realized with 5 W optical power in the desired spot. First diode pumped fiber laser operation in the visible has been demonstrated with this sources.