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The future of high power laser techniques

: Poprawe, R.; Loosen, P.; Hoffmann, H.-D.


Schuöcker, D. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.; TU Wien:
XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers 2006 : 4 - 8 September 2006, Gmunden, Austria
Bellingham, WA: SPIE, 2007 (SPIE Proceedings Series 6346)
ISBN: 978-0-8194-6430-9
ISBN: 0-8194-6430-9
Paper 634602 (Pt.1)
International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers <16, 2006, Gmunden>
Fraunhofer ILT ()

High Power Lasers have been used for years in corresponding applications. Constantly new areas and new processes have been demonstrated, developed and transferred to fruitful use in industry. With the advent of diode pumped solid state lasers in the multi-kW-power regime at beam qualities not far away from the diffraction limit, a new area of applicability has opened. In welding applications speeds could be increased and systems could be developed with higher efficiently leading also to new perspectives for increased productivity, e.g. in combined processing. Quality control is increasingly demanded by the applying industries, however applications still are rare. Higher resolution of coaxial process control systems in time and space combined with new strategies in signal processing could give rise to new applications. The general approach described in this paper emphasizes the fact, that laser applications can be developed more efficiently, more precisely and with higher quality, if the laser radiation is tailored properly to the corresponding application. In applying laser sources, the parameter ranges applicable are by far wider and more flexible compared to heat, mechanical or even electrical energy. The time frame ranges from several fs to continuous wave and this spans approximately 15 orders of magnitude. Spacewise, the foci range from several m to cm and the resulting intensities suitable for materials processing span eight orders of magnitude from 103 to 1011 W/cm2. In addition to space (power, intensity) and time (pulse) the wavelength can be chosen as a further parameter of optimization. As a consequence, the resulting new applications are vast and can be utilized in almost every market segment of our global economy (Fig. 1). In the past and only partly today, however, this flexibility of laser technology is not exploited in full in materials processing, basically because in the high power regime the lasers with tailored beam properties are not available and consequently many applications are not developed yet or are not operatable at optimized parameters. Because of their systematic flexibility in the sense layed out above, solid state lasers are the class to be considered in this context, diode pumped solid state lasers as well as high power diode lasers. In the past years the intrinsic beam quality of diode lasers in terms of divergence, smile and stability as well as the lifetime increased significantly. Single bars with beam parameter products around BPP=20 mm*mrad have been demonstrated. Lifetimes of 30.000h (90%) @100W cw operation are available /29/, /30/. Consequently the market increasingly accepts this type of lasers and new application domains like welding and metal deposition are investigated. Also the beam quality of high power diode lasers has been increased at many groups working in the field of coherent coupling or incoherent superposition [1]. Corresponding by the direct application of high power high quality diode lasers increasingly enters the markets. For all concepts the key demand is its applicability in terms of the specification of the process the laser is designed for. The characteristics of the laser with respect to power and energy on the one hand and quality in terms of space (spacial coherence, focussability), time (puls e duration and duty cycle) and wavelength have to match the demands of the specific application. Therefore, we face an intense trend for diversification of lasers in the named characteristics. There may be dominant large markets and niches but on the other hand there will not be a "best" laser or laser concept in the general sense.