The SYLOS laser driven Gas High Harmonic Generation Long beamline is a gas target based attosecond XUV beamline of ELI-ALPS. It produces “high” flux attosecond pulse trains (APTs) for pump-probe measurements with the following wavelength combinations: XUV-IR, XUV-XUV, IR-XUV-XUV. The beamline provides full laser and attosecond XUV characterisation. There is a dedicated CAMP chamber for endstation with a supersonic gas-jet and an electron Time of Flight (ToF) tube. Furthermore, the beamline is designed to accommodate custom made equipment (detectors, spectrometers, endstations etc.). The beamline is well suited for attosecond XUV radiation optimisation due to its extra loose focusing and the adjustability of the length of the generating gas cells.
The flexibility of the system (laser energy, pulse duration, GDD, beam size, target gas pressure, type and cell length, focal length, etc.) allows studying the gas HHG process, and optimisation of different phase-matching regimes.
As a high flux attosecond pulse source, and its built-in interferometer allowing the synchronisation of up to 4 pulses (Future development: XUV-XUV-IR-IR) a wide variety of pump-probe studies can be carried out in the ultrashort timescale. Future developments will increase the available wavelengths of ultrashort pulses from THz via visible to the XUV regime.
XUV-XUV pump probe experiments in the nonlinear regime. Attosecond metrology. Ionisation dynamics in XUV regime. Time resolved studies. Atomic, Molecular and Optical studies in the attosecond regime.
The GHHG SYLOS Long beamline can be driven either by the 10 Hz SEA laser or the 1kHz SYLOS laser. The strength of the beamline is its unique ultra loose focusing geometry combined with two different harmonic generation sources. This geometry is providing the > 300 nJ (at generation) XUV beam energies. The focusing is done by a deformable mirror (DM), located in the Monster chamber, see Figure 1, and the focal distances are:
Short 19 m: The laser is focused into the HHG1 chamber. This is a gas cell with variable length between 32-75 cm.
Long 55 m: The laser is focused into the HHG2 cell system which has a total length of 6 m. It consists of 15 independent gas cells and their pressure and gas type can be individually controlled.
Due to the flexibility in the attosecond XUV generation (laser energy, pulse duration, GDD, beam size, target gas pressure, type and cell length) there is space to tailor the generated radiation into the need of the experimental run.
The beamline is designed to provide attosecond XUV beam energy, spatial profile, spectral- and pulse duration characterisation. For this purpose the beamline is equipped with an XUV imaging spectrometer, XUV photodiode, XUV wavefront sensor and an XUV beamprofiler. An electron ToF is used to perform RABBIT measurement to estimate the pulse duration.
The Interferometer chamber hosts a Mach-Zender interferometer. It allows the following combinations for pump-probe experiments: XUV-IR, IR-IR, XUV-XUV. Therefore, the beamline is well suited for attosecond time resolved atomic and molecular experiments.
ELI-ALPS provides a CAMP chamber as the endstation, but there is a possibility to attach chambers, devices/detectors brought by users.
Table 1 shows the measured specifications of the SYLOS 2 and the SEA laser systems.
|Central wavelength||825 nm|
|Average power||Up to 32 W||Up to 425 mW|
|Pulse energy||32 mJ||40 mJ|
|Stability of the pulse energy||< 2 % (rms)||< 2 % (rms)|
|CEP stability||220 mrad||N/A|
|Repetition rate||1 kHz||10 Hz|
|Bandwidth||750-1250 nm||750 -960 nm|
|Pulse duration||< 7 fs||< 12 fs|
|Beam diameter 1/e2||60 mm||60 mm|
|Strehl ratio||> 0.7||0.93|
|Polarization||s (vertical)||s (vertical)|
|Beam pointing stability||< 15% of divergence||< 5% of divergence|
Table 1: Characteristic parameters for the driving laser of the GHHG Sylos Long beamline
Figure 1 shows the schematic layout of the GHHG SYLOS Long beamline. It spans for laboratories and is roughly 70 m long. It includes the:
Compressor chamber: to compress the laser pulse duration close to its Fourier limited value,
Periscope chamber: to raise the laser beam to the right height and provide vertical polarisation,
Monster chamber: to set the beamsize and host the deformable mirror for focusing. Furthermore, laser wavefront, pulse duration, energy is measured next to this chamber.
SYLOS chamber: turns the focused beam backwards into the generation target (HHG1) in case of using the 19 m focusing,
HF chamber: turns the focused beam backwards into the generation target (HHG2) in case of using the 55 m focusing,
HHG1 chamber: a gas cell with variable length between 32 and 75 cm
HHG2 chamber: a series of individual gas cells over 6 m. Each of them allows the adjustment of the gas pressure and gas type individually.
Transport chamber: Hosts a mirror to send the beam either into the Interferometer chamber or into the Diagnostic chamber
Interferometer chamber: Hosts a Mach-Zender interferometer. A holey mirror separates the XUV and the IR into two arms. In the XUV arm, a Split Delay Unit is located to provide XUV-XUV pump-probe experiments. The IR arm can be delayed with respect to the XUV arm, allowing XUV-IR pump-probe experiments.
Diagnostic chamber: characterises the XUV radiation via the XUV imaging spectrometer, XUV wavefront sensor, XUV photodiode and the XUV beamprofiler.
Refocusing chamber: Using a Wolter-type toroidal mirror setup focuses the XUV into the endstation with 1 to 1 imaging.
CAMP chamber: general purpose end station equipped with an Evan-Lavie supersonic gas-jet and an electron TOF.
|SEA||XUV radiation (generated in Ar, after200 nm Al filter)|
|Central wavelength||825 nm||25 nm (50 eV)|
|Average power||Up to 425 mW||TBC|
|Pulse energy||40 mJ||> 300 nJ|
|Stability of the pulse energy||< 2 % (rms)||TBC|
|Repetition rate||10 Hz||10 Hz|
|Bandwidth||750 -960 nm||17-77 nm (16-70 eV)|
|Pulse duration||< 12 fs||TBC|
|Beam diameter 1/e2||60 mm||< 15 mm (at diagnostic chamber)|
|Polarization||s (vertical)||s (vertical)|
|Beam pointing stability||< 5% of divergence||N/A|
Figure 1: Schematic layout of the GHHG SYLOS Long beamline
In the figure below, the end-station and/or characterisation ports of the beamline are shown. The large number of output ports allows the connection of multiple user end-stations to the beamline at the same time which can considerably reduce switching time between consecutive experimental campaigns. Many of the beamline output ports are designed symmetrically, which offers the possibility to characterise the XUV radiation parallel at the symmetric port with the same geometrical conditions. The highest possible flux is available at the straight output arm (P1). A user end-station connected here can get the unconditioned harmonic beam.
Figure 2. Beamline end-station and/or characterisation ports.
XUV and VUV flat-field spectrometers
XUV beam profiler
XUV wavefront sensor
Electron Time-Of-Flight detector
 S.Kuhn, J. Phys. B: At. Mol. Opt. Phys. 50, 132002 (2017)