The HR GHHG Gas attosecond beamline of ELI-ALPS is driven by the 100 kHz high average-power HR-1 laser system and produces attosecond pulse trains (APTs) for XUV – IR pump-probe measurements on gas-phase targets . Different spectral ranges and fluxes can be provided utilizing different rare gas targets. The beamline is under continuous upgrade and optimization, currently providing up to 50 pJ, ~166 as long XUV APTs on target in the 30-70 eV photon energy range at 100 kHz repetition rate . The schematic optical layout is given in Figure 1. The beamline is equipped with an electron time-of-flight (TOF) spectrometer, which serves as the primary tool for temporally characterizing the XUV pulses via RABBITT, positioned in “Target area 1”. In “Target area 2”, an experimental end-station can be positioned according to the users’ needs. For flux and spectral characterization of the XUV, a photodiode and a flat-field spectrometer are continuously available.
Figure 1. Schematic optical layout of the HR GHHG Gas beamline.
Table 1 shows the measured specifications of the HR-1 laser system and the XUV radiation generated using HHG. After the planned upgrade of the HR-1 laser system in the second half of 2021 and the arrival of the HR-2 laser in the second half of 2022, the specifications of the beamline are expected to substantially improve for experiments planned to be performed during 2022.
Table 1. Measured parameters of the HR-1 laser system (in long pulse mode) and the XUV radiation generated thorugh HHG.
Representative data of the achievable XUV spectrum, XUV flux and XUV APT temporal characteristics are given in Figure 2 and Figure 3.
Figure 2. The measured XUV flux and spectrum.
Figure 3. (a) Measured RABBITT trace, (b) corresponding XUV spectrum and reconstructed phase, (c) reconstructed average pulse shape in the XUV APT. 
 Peng Ye et al., J. Phys. B: At. Mol. Opt. Phys. 53 154004 (2020).
 Peng Ye et al., “High-flux 100-kHz attosecond pulse source driven by a high average power annular laser beam”, submitted to Ultrafast Science, available on arXiv (2021).