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We present a table-top, efficient and power scalable scheme enabling the effective generation of extreme ultraviolet radiation up to 100 eV photon energy. Therefor ultrashort pulses (< 20fs) in the visible spectral range (515 nm) are used to drive high harmonic generation (HHG) in helium. This allows for a significant efficiency boost compared to near-infrared (NIR) drivers, enabled by the favourable scaling of the single-atom response of λ-6 [1]. The experimental realization of a mulitpass cell delivering 15.7 fs pulses with a peak power close to 25 GW at 515 nm and an overall efficiency (IR to compressed green pulse) of >40 %. In conjunction, preliminary HHG results will be presented, paving the way for mW-class HHG sources at 13.5 nm.

With active multicore fibers (MCFs), many parallel amplifying waveguides can be densely assembled into a common glass cladding. A tapered fiber geometry applied to MCFs enhances the power and energy scalability of these systems by increasing the doped waveguide volume and reducing peak irradiance while maintaining low output mode order. Recent high-energy experiments have achieved 37 mJ ns-class pulse energies with Yb-doped tapered MCFs, with potential application to a new generation of compact MCF-based coherently-combined laser systems. In this submission, latest experimental results with tapered MCFs and flexible fabrication of taper profiles as a post-draw processing step will be discussed. Numerical analyses of MCF tapers will be presented, using beam propagation method (BPM) and mode-decomposition techniques to study mode coupling and inter-core crosstalk. These simulations are used to guide the tapering of existing fibers and aid the design of future “taper-ready” MCFs.

We demonstrate 33-fold pulse compression employing a 6-m-long hollow-core fiber and chirped mirrors. 1 mJ, 170 fs pulses at 1030 nm are compressed to 5.1 fs (1.5 optical cycles) with 70% efficiency.