C. Fiebig, B. Eppich, W. Pittroff, G. Erbert

Published in:

Proc. SPIE, vol. 6876, no. 68760J (2008).

Abstract:

For the pumping of solid state lasers with high peak power pulses up to the TW range QCW diode laser stacks with pulse lengths between 200µs and 2ms are used. To realize long-term stable pump modules we already presented high power, high brightness 100W QCW diode laser bars [1] having a lateral aperture of 1.7mm only, a length of 4mm and a vertical divergence of 14° FWHM. Based on these we have developed a mounting scheme for stacks with > 1kW output power using these new kind of diode lasers. Due to the geometric dimensions of the chip we successfully realized a stack with a passive cooling scheme on both sides. Furthermore, we only used expansion matched materials such as CuW and Al2O3 ceramics, as well as AuSn solder processes for fixing the parts together. As a result the stack is very insensitive against environmental influences. Due to the small vertical divergence we were able to use fast axis collimators with large focal lengths, which relax the lens adjustment tolerances. At the conference we will present results for diode laser stacks with an output power of more than 1kW at duty-cycles up to 10% and an efficiency of about 50%. The beam parameter product for such diode laser stacks result in < 50mm·mrad for the vertical direction and in < 75mm·mrad for the lateral direction. These beam parameter values enable the coupling of the pump module to an optical fiber having a 1.2mm core diameter and a NA of 0.22. Furthermore, the low vertical fill factor of the stack radiation allows the combination of two stacks by beam deflection mirrors without significantly degrading beam quality, hence doubling the power coupled into the same fiber.

Keywords:

diode laser, second harmonic generation, tapered laser, distributed Bragg reflector, Boyd-Kleinman theory, partial coherence, beam propagation factor, Agrawal’s nonlinear kernel

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