We generate high-order harmonics with a 50 W, Yb femtosecond fiber laser system operating at 100 kHz in a tight focusing configuration. We achieve a high photon flux even with pulses longer than 500 fs. We collect the diverging XUV harmonic beam in a 35 mrad wide solid angle by using a spectrometer designed to handle the high thermal load under vacuum and refocus the XUV beam onto a detector where the beam is characterised or can alternatively be used for experiments. This setup is designed for a 50 eV XUV bandwidth and offers the possibility to perform XUV-IR pump probe experiments with both temporal and spectral resolution. The high-order harmonics were generated and optimized at 100 kHz by using several gas target geometry (a gas jet and a semi-infinite gas cell) and several gases (Argon, Krypton, Xenon) that provide XUV beams with different characteristics. After the spectrometer and for HHG in Xenon, we detect more than 4x10 10 photons per second over 4 harmonics, that is a useful XUV power on target of 0.1 µW. This corresponds to the emission of more than 1µW per harmonic at the source and we achieved similar flux with both the semi-infinite cell and the jet. In addition, we observe a strong spectral selectivity when generating harmonics in a semi-infinite gas cell as few harmonics clearly dominate the neighbouring harmonics. We attribute this spectral selectivity to phase matching effects.
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