The HR GHHG Condensed attosecond, XUV-IR pump-probe beamline incorporates a time-delay compensated (TDC) monochromator to provide users with the possibility of selecting different XUV photon energy regions of the generated high-order harmonic radiation down to the 50 meV spectral bandwidth, while preserving the few (tens of) femtosecond duration of the XUV pulses. Transmission of the total available XUV spectrum (in “broadband” operation) or monochromatic pulses with longer temporal extent, but higher flux (in “high-flux” mode, HFM) is also possible . The beamline is in continuous upgrade and optimisation to extend the available parameter range, the first experiments were carried out in 2022.
Upon achieving the CEP stability of the driver lasers, isolated attosecond pulse production will be available (foreseen by the experimental period of this call).
The HR GHHG Cond beamline is primarily designed to study dynamical effects on the femtosecond to attosecond timescale in solid-state targets, primarily being the subject of research in condensed state physics and chemistry or surface science. These involve studies of phase transitions , the analysis of laser-assisted photoelectric effect , or following electronic correlations and collective excitations, electron transport, transient and unoccupied states [5,6].
Representative parameters of the HR GHHG Cond beamline are given below:
|Available now (HR-1 short pulse mode, Ar gas, Al filter)*|
|Repetition rate||100 kHz|
|Energy stability||±50 %|
|Strehl ratio||not available|
|Temporal quality||not applicable|
|Pulse duration||170 as pulses (in 20 fs attosecond pulse train during broadband operation, down to 15 fs in monochromatic operation)|
|Average power||9.5 µW (3.4 μW on target)|
|Pulse energy (max)||95 pJ (34 pJ on target)|
|Pulse energy (Min-Max range)||3 - 95 pJ (1 - 34 pJ on target)|
|Central wavelength||30 nm (42 eV)|
|Spectral bandwidth||19 - 39 nm (32 - 66 eV)|
|Pointing stability||not available|
|Temporal contrast (ns)||not applicable|
|Temporal contrast (ps)||not applicable|
|Polarization||linear (p or s)|
|CEP stabilization||not applicable|
|Near field intensity distribution||Gaussian|
|Beam size||not available|
*Due to the high flexibility of the beamline, other parameters (spectral range, pulse duration, …) are available. Users are strongly suggested to contact the equipment responsible for availability of other specifications.
The schematic layout of the HR GHHG Cond beamline can be seen in the figure below.
Recombination of the XUV and IR beams is done before “Target area 1” in section “Monochromator stage 2 & Recombination”. This allows for parallel measurements with the electron-TOF detector in “Target area 1” and in the solid-state physics end station NanoESCA. The two stages of the XUV monochromator (“Monochromator stage 1” and “Monochromator stage 2 & Recombination”) are responsible for the spectral tuning and time-compensation of the XUV radiation, thus providing femtosecond duration XUV beam with adjustable spectral parameters.
Figure 1: The schematic layout of the HR GHHG Cond beamline
Permanent target systems:
Electron time-of-flight (TOF) spectrometer (Stefan Kaesdorf ETF-11)
Solid-state physics end station (“NanoESCA”)
(“Target area 1” potentially available for other smaller target systems provided by the user, or alternative setup soon to be available for transmission measurements of thin solid targets.)
The following diagnostics are available as diagnostics tools and metrology in a permanent manner in the HR GHHG Cond beamline:
Electron TOF spectrometer (Stefan Kaesdorf ETF-11) for temporal characterisation of the XUV APTs using the RABBITT method 
XUV photodiode (NIST 40790C) for XUV energy measurements
XUV flat-field spectrometer (home built) for spectral characterisation