The HR GHHG Gas beamline is currently providing XUV APTs on target with up to >100 pJ/shot in the 25-70 eV photon energy range at 100 kHz repetition rate [1,2]. The schematic optical layout is given in the section Main Experimental Geometries. The beamline is equipped with an electron time-of-flight (TOF) spectrometer, which serves as the primary tool for temporally characterising the XUV pulses via RABBITT [1,2], positioned in the first target area of the beamline. The beamline is designed with a second target area for an experimental end-station, provided either by ELI ALPS or by the user. For flux and spectral characterisation of the XUV, a photodiode and a flat-field spectrometer are continuously available. The beamline is in continuous upgrade and optimisation to extend the available parameter range .
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 Gas beamline is primarily designed to study dynamical effects on the femtosecond to attosecond timescale in gas phase targets, primarily being the subject of research in atomic-, molecular- and optical (AMO) physics. These involve control of atomic states , measuring photoionisation time delays , or imaging atomic- or molecular systems . The HR GHHG Gas beamline is also a great tool for attosecond chemistry .
Representative parameters of the HR GHHG Gas beamline are given below:
|Available now (HR-1 short pulse mode, Ar gas, AI filter)*|
|Repetition rate||100 KHz|
|Energy stability||13% RMS, (±35% peak-to-peak)|
|Strehl ratio||not available|
|Temporal quality||not available|
|Pulse duration||<400 as (in <12 fs attosecond pulse train)|
|Average power||up to ~60 µW|
|Pulse energy (max)||600 pJ (110 pJ on target)|
|Pulse energy (min-max range)||6 - 600 pJ (10-110 pJ on target)|
|Central wavelength||25 nm (50 eV)|
|Spectral bandwidth||17 nm - 50 nm (25 eV - 70 eV)|
|Pointing stability||not available|
|Temporal contrast (ns)||not available|
|Temporal contrast (ps)||not available|
|Polarisation||linear (p or s) (planned upgrade for circular/elliptical polarisation)|
|CEP stabilisation||not applicable|
|Near field intensity distribution||Gaussian|
|Beam size||~130 µm (intensity FWHM, focused, based on measurement with VMI in spatial mode)|
*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 the availability of other specifications.
The schematic layout of the HR GHHG Gas beamline can be seen in the figure below.
Recombination of the XUV and IR beams is available separately for “Target area 1” and “Target area 2” in sections “Recombination #1” and “Recombination #2”, respectively. Due to geometrical limitations the two target areas are not available simultaneously.
Figure 1: The schematic layout of the HR GHHG Gas beamline can be seen in the figure
Permanent target system (“Target area 1” in “Main experimental geometries”):
Electron time-of-flight (TOF) spectrometer (Stefan Kaesdorf ETF-11)
(Potentially available for other smaller target systems provided by user)
Exchangeable target system (“Target area 2” in “Main experimental geometries”):
One of ELI ALPS’ end stations (e.g. VMI ES or ReMi ES have been used in combination with the HR GHHG Gas beamline)
The following diagnostics are available as diagnostics tools and metrology in a permanent manner in the HR GHHG Gas 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