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• High Power Laser Science and Engineering
• Vol. 4, Issue 1, 010000e3 (2016)
Ren′e Platz, Bernd Eppich, Juliane Rieprich, Wolfgang Pittroff, G¨otz Erbert, and Paul Crump
Author Affiliations
• Ferdinand-Braun-Institut, Leibniz-Institut f¨ur H¨ochstfrequenztechnik, Gustav-Kirchhoff-Stra?e 4, 12489 Berlin, Germany
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Abstract

Tailored diode laser single emitters with long (6 mm) resonators and wide (1.2 mm) emission apertures that operate with 940 nm emission wavelength were assembled in novel edge-cooled vertically stacked arrays, and used to construct a compact and highly efficient fiber coupled pump source for Yb:YAG pulsed high-energy class solid-state lasers. The novel configuration is shown to allow repetition rates of 200 Hz at 1 ms pulse duration, at an output power of 130 W per single emitter. The emission of two stacked arrays was then optically combined to realize pump modules that deliver 6 kW peak power (pulse energy 6 J) from a 1.9 mm core diameter fiber, with wall plug efficiency of 50%. This represents a significant improvement in terms of duty cycle and electro-optical efficiency over conventional sources. The pump module has been successfully tested at the Max Born Institute, Berlin during trials for pumping of disk lasers.This work was funded in part via the European Regional Development Fund (ERDF) under contract number 20072013 2/42.

1 Introduction

High-energy class diode pumped solid-state lasers (HEC-DPSSLs) with pulse energies ${>}$1 J (ns- to fs-pulses) and average powers of several hundred watts are increasingly required in industry, science and basic research[1, 2]. Fields of applications include laser shock peening, material analytics, attosecond spectroscopy or particle acceleration. However, the achievable performance of such a system is limited by the characteristics of the diode laser pump sources. The diode lasers are operated in quasi-continuous wave (QCW) mode, with pulse widths matched to the upper state lifetime of the crystal in use. Commercially available multi-kW QCW diode pump sources are based on low-cost vertical stacked diode laser bars with inefficient rear side cooling. Typically, they operate at maximum pulse width ${\it\tau}=1$ ms and maximum repetition rate $f=10$ Hz, corresponding to a duty cycle $dc=1\%$ (see for example Refs. [2, 3]). However, repetition rates of several hundred Hz are required to boost average power from the DPSSL and to increase the shot frequency[4]. Although very high-power continuous wave diode laser pump sources are commercially available and can be used for power scaling, they are typically not preferred as they can lead to overheating of the YAG crystal[5]. Since the lifetime of the diode laser stacks is a complex function of QCW pulse conditions and stack construction[6], careful mechanical design is needed to ensure reliability under the required operational conditions. In all cases, high-power conversion efficiency and a compact, low-cost mechanical design are important.

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Ren′e Platz, Bernd Eppich, Juliane Rieprich, Wolfgang Pittroff, G¨otz Erbert, Paul Crump. High duty cycle, highly efficient fiber coupled 940-nm pump module for high-energy solid-state lasers[J]. High Power Laser Science and Engineering, 2016, 4(1): 010000e3