Simple design for fiber coupled 9xx nm kW- QCW pump module with high duty cycle based on customized chips and lateral heat removal

W. Pittroffa , B. Eppicha, G. Erberta, R. Platza, D. Tyrallab, G. Tränklea

Published in:

Proc. SPIE, vol. 8965, Photonics West, San Francisco, USA, Feb. 1-6, 896515 (2014).

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Abstract:

High power 9xxnm QCW- pump modules are very interesting for high- and ultra-high-energy laser systems. Main relevant issues beside price and power conversion efficiency are long term stability of the mounting scheme and stable fiber coupling. We present a design based on diode laser stacks with lateral heat removal. A single stack element consists of a diode laser, which is soldered on both sides to CuW carriers using AuSn. Life test over 1000 h showed no degradation. DCB coolers are subsequently soldered onto both outer sides of the stack. The thermal resistance of a single stack element is about 1.7 K/W. For >3 J pulse energy the stack contains 28 elements. ≥60% power conversion efficiency of the used 940 nm diode laser chips at 120 W output power allows ≥20% duty cycle without substantial heating (maximum measured output power >200 W). The light is collimated in vertical direction for each stack element. We choose a size for the FAC which allows staggering the beams of two stacks. The diode laser chips have an aperture width of 1.2 mm and a lateral divergence <14° (95% power) at 120 W. Fiber coupling is performed by cylindrical lenses in both directions. For 6 J pump energy two stacks are used, coupled into 1.9 mm diameter fiber with a high optical coupling efficiency of >90%. The principle design is very flexible to match other demands in fiber size and output power.

a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
b Technische Hochschule Wildau, Bahnhofstraße, 15745 Wildau, Germany

Keywords:

High power diode lasers, QCW lasers, fiber coupling, diode laser bonding.