5kW burst-mode femtosecond amplifier system for the European XFEL pump-probe laser development M. Kellert1, M. Pergament1, K. Kruse1, J. Wang1, G. Palmer1, G. Priebe1, L. Wissmann1, U. Wegner1, M. Emons1, J. Morgenweg2, T. Mans2, M. J. Lederer1 1. European X-Ray Free-Electron Laser-Facility GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany 2. Amphos GmbH, Kaiserstr. 100, 52134 Herzogenrath, Germany Corresponding author:
[email protected]
Operating at repetition rates of up to 4.5MHz, the successful implementation of superconducting LINAC technology at the European XFEL will boost the time averaged X-ray power density substantially above current values. This high pulse rate will only occur during 600µs long bursts of 10Hz repetition rate, resulting in up to 27000 pulses per second. Optical femtosecond pump-probe lasers will be needed for more than 50% of all experiments at the facility and will need to match this burst-mode emission pattern. There are currently no “offthe-shelf” commercial femtosecond laser technologies producing this kind of output at close to mJ-level energies per pulse and sub-20fs pulse width. Therefore, at the European XFEL, a development project was launched in order to close this gap in time for the start of commissioning in 2016 [1]. We present the design and performance of a high power burst-mode amplifier system for the sub-ps pump pulses of a non-collinear parametric amplifier (NOPA). The chirped-pulse amplification (CPA) frontend- and pre-amplifiers are based on all-fiber and Yb:YAG InnoSlab technology respectively and are described elsewhere [2-4]. They provide a burst output power of up to 500W at pulse widths ≈800fs after compression and intra-burst repetition rates between 100kHz and 4.5MHz. However, to achieve the desired mJ-level NOPA pulse energies, the output power of the pump amplifier needs upscaling by at least one order of magnitude. We show a booster amplifier, which achieves this in a single stage. The design of the booster also relies on slab geometry. A 25mm wide Yb:YAG crystal is end-pumped by up to 16kW of 940nm QCW laser-diode light, shaped to provide uniform distribution in the slow axis and nearly Gaussian distribution in the fast axis of the slab. The highly elliptical seed beam from the pre-amplifier double-passes the slab to saturate at a burst power level of 5.1kW during a burst length of 1.35ms. Due to the high gain of this amplifier we observe beam shape distortions due to extraction in the uniformly pumped slow axis, leading to non-Gaussian beam propagation after amplification. These effects can be corrected using beam filtering/shaping, leading to a moderate power loss of 10% and a nearly diffraction limited beam quality in both axes (M2
