An ultrafast fiber chirped-pulse amplification laser system based on coherent combination of 16 ytterbiumdoped rod-type amplifiers is presented. It generates 10 mJ pulse energy at 1 kW average power and 120 fs pulse duration. A partially helium-protected, twostaged chirped-pulse amplification grating compressor is implemented to maintain the close to diffractionlimited beam quality by avoiding nonlinear absorption in air.

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We demonstrate the reliable generation of 1-mJ, 31-fs pulses with an average power of 1 kW by postcompression of 200-fs pulses from a coherently combined Yb:fiber laser system in an argon-filled Herriotttype multi-pass cell with an overall compression efficiency of 96%. We also analyze the output beam, revealing essentially no spatio-spectral couplings or beam quality loss.

High harmonic generation (HHG) enables coherent extreme-ultraviolet (XUV) radiation with ultra-short pulse duration in a table-top setup. This has already enabled a plethora of applications. Nearly all of these applications would benefit from a high photon flux to increase the signal-to-noise ratio and decrease measurement times. In addition, shortest pulses are desired to investigate fastest dynamics in fields as diverse as physics, biology, chemistry and material sciences. In this work, the up-to-date most powerful table-top XUV source with 12.9 ± 3.9 mW in a single harmonic line at 26.5 eV is demonstrated via HHG of a frequency-doubled and post-compressed fibre laser. At the same time the spectrum supports a Fourier-limited pulse duration of sub-6 fs in the XUV, which allows accessing ultrafast dynamics with an order of magnitude higher photon flux than previously demonstrated. This concept will greatly advance and facilitate applications of XUV radiation in science and technology and enable photon-hungry ultrafast studies.

The pulse-energy scaling technique electro-optically controlled divided-pulse amplification is implemented in a high-power ultrafast fiber laser system based on coherent beam combination. A fiber-integrated front end and a multi-pass cell based back end allow for a small footprint and a modular implementation. Bursts of 8 pulses are amplified parallel in up to 12 ytterbiumdoped large-pitch fiber amplifiers. Subsequent spatiotemporal coherent combination of the 96 total amplified pulse replicas to a single pulse results in a pulse energy of 23 mJ at an average power of 674 W, compressible to a pulse duration of 235 fs. To the best of our knowledge, this is the highest pulse energy ever accomplished with a fiber CPA system.