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Direct diode lasers and their advantages for materials processing and other applications

: Fritsche, H.; Ferrario, F.; Koch, R.; Kruschke, B.; Pahl, U.; Pflueger, S.; Grohe, A.; Gries, W.; Eibl, F.; Kohl, S.; Dobler, M.


Dorsch, F. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
High-Power Laser Materials Processing. Lasers, Beam Delivery, Diagnostics, and Applications IV : 10-12 February 2015, San Francisco, California
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9356)
ISBN: 978-1-62841-446-2
Paper 93560I, 6 S.
Conference "High-Power Laser Materials Processing - Lasers, Beam Delivery, Diagnostics, and Applications" <4, 2015, San Francisco/Calif.>
Fraunhofer ILT ()

The brightness of diode lasers is improving continuously and has recently started to approach the level of some solid state lasers. The main technology drivers over the last decade were improvements of the diode laser output power and divergence, enhanced optical stacking techniques and system design, and most recently dense spectral combining Power densities at the work piece exceed 1 MW/cm(2) with commercially available industrial focus optics. These power densities are sufficient for cutting and welding as well as ablation. Single emitter based diode laser systems further offer the advantage of fast current modulation due their lower drive current compared to diode bars. Direct diode lasers may not be able to compete with other technologies as fiber or CO2-lasers in terms of maximum power or beam quality. But diode lasers offer a range of features that are not possible to implement in a classical laser. We present an overview of those features that will make the direct diode laser a very valuable addition in the near future, especially for the materials processing market. As the brightness of diode lasers is constantly improving, BPP of less than 5mm*mrad have been reported with multi-kW output power. Especially single emitter-based diode lasers further offer the advantage of very fast current modulation due to their low drive current and therefore low drive voltage. State of the art diode drivers are already demonstrated with pulse durations of <10 mu s and repetition rates can be adjusted continuously from several kHz up to cw mode while addressing power levels from 0-100%. By combining trigger signals with analog modulations nearly any kind of pulse form can be realized. Diode lasers also offer a wide, adaptable range of wavelengths, and wavelength stabilization. We report a line width of less than 0.1nm while the wavelength stability is in the range of MHz which is comparable to solid state lasers. In terms of applications, especially our (broad) wavelength combining technology for power scaling opens the window to new processes of cutting or welding and process control. Fast power modulation through direct current control allows pulses of several microseconds with hundreds of watts average power. Spot sizes of less than 100 mu m are obtained at the work piece. Such a diode system allows materials processing with a pulse parameter range that is hardly addressed by any other laser system. High productivity material ablation with cost effective lasers is enabled. The wide variety of wavelengths, high brightness, fast power modulation and high efficiency of diode lasers results in a strong pull of existing markets, but also spurs the development of a wide variety of new applications.