2 May 2014 Generating a high brightness multi-kilowatt laser by dense spectral combination of VBG stabilized single emitter laser diodes
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Generating high power laser radiation with diode lasers is commonly realized by geometrical stacking of diode bars, which results in high output power but poor beam parameter product (BPP). The accessible brightness in this approach is limited by the fill factor, both in slow and fast axis. By using a geometry that accesses the BPP of the individual diodes, generating a multi kilowatt diode laser with a BPP comparable to fiber lasers is possible. We will demonstrate such a modular approach for generating multi kilowatt lasers by combining single emitter diode lasers. Single emitter diodes have advantages over bars, mainly a simplified cooling, better reliability and a higher brightness per emitter. Additionally, because single emitters can be arranged in many different geometries, they allow building laser modules where the brightness of the single emitters is preserved. In order to maintain the high brightness of the single emitter we developed a modular laser design which uses single emitters in a staircase arrangement, then coupling two of those bases with polarization combination which is our basic module. Those modules generate up to 160 W with a BPP better than 7.5 mm*mrad. For further power scaling wavelength stabilization is crucial. The wavelength is stabilized with only one Volume Bragg Grating (VBG) in front of a base providing the very same feedback to all of the laser diodes. This results in a bandwidth of < 0.5 nm and a wavelength stability of better than 250 MHz over one hour. Dense spectral combination with dichroic mirrors and narrow channel spacing allows us to combine multiple wavelength channels, resulting in a 2 kW laser module with a BPP better than 7.5 mm*mrad, which can easily coupled into a 100 μm fiber and 0.15 NA.
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H. Fritsche, H. Fritsche, Ralf Koch, Ralf Koch, B. Krusche, B. Krusche, F. Ferrario, F. Ferrario, Andreas Grohe, Andreas Grohe, S. Pflueger, S. Pflueger, W. Gries, W. Gries, "Generating a high brightness multi-kilowatt laser by dense spectral combination of VBG stabilized single emitter laser diodes", Proc. SPIE 9134, Semiconductor Lasers and Laser Dynamics VI, 91340U (2 May 2014); doi: 10.1117/12.2052582; https://doi.org/10.1117/12.2052582

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