The SYLOS laser driven Gas High Harmonic Generation Compact beamline is a gas target based Attosecond XUV beamline of ELI-ALPS. It produces isolated attosecond pulses (IAP) using polarisation gating technique and “high” flux attosecond pulse trains (APTs) for pump-probe measurements with the following wavelength combinations: XUV-IR, XUV-XUV. The beamline provides full laser and attosecond XUV characterisation. There is a dedicated chamber for endstation with a Calibrated XUV photodiode, XUV beamprofiler, XUV wavefront sensor, XUV spectrometer, bipolar Time of Flight (ToF) tube, Ion Microscope. Furthermore, the beamline is designed to accommodate custom made equipment (detectors, spectrometers, endstations etc.). The beamline is well suited for XUV radiation in femtosecond timescale (APTs) and in attosecond timescale (IAPs) due to its loose focusing geometry and the optimisation of generation via quasi phase-matching using multiple gas jets and/or gas cells.
XUV-XUV pump probe experiments in the nonlinear regime. Attosecond metrology. Ionisation dynamics in XUV regime. Time resolved studies.
The GHHG SYLOS Compact beamline can be driven either by the 10 Hz SEA laser or the 1kHz Sylos laser. The strength of the beamline is its variable loose focusing geometries combined with two different harmonic generation sources (gasjets or gascells). This geometry is providing about > 1 uJ (at generation using SEA) XUV pulse energies. Due to the flexibility in the attosecond XUV generation (laser energy, pulse duration, GDD, beam size, target gas pressure, gas sample and length of the target), tailoring the generated radiation for the actual experiment is possible.
The beamline is designed to provide attosecond XUV pulse 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 Diagnostic chamber hosts split multi-layer XUV mirrors along with an off axis toroidal mirror, which allows the following combinations for pump-probe experiments: XUV-IR, XUV-XUV. Therefore, the beamline is well suited for attosecond time resolved atomic and molecular experiments, including studies in the nonlinear regime.
In the Compact beamline’s user arm there is possibility to attach chambers, devices/detectors brought by users. The XUV beam characterised in the diagnostic chamber can be sent to the user arm.
Table 1 shows the measured specifications of the SYLOS and the SEA laser systems.
|Central wavelength||891 nm||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 Compact beamline
BS: Beam steering chamber, also changes the polarisation of the laser from s (vertical) to p (horizontal).
PG1: Polarisation gating chamber with halfwave plate and quarterwave plate to modulate the polarisation of the driving laser field. Figure 1 (a) is the laser beamprofile which is converted to an annular shape from the input gaussian. Another modulation on the laser beam is depicted in Figure 1 (e) which acts as delay stage for IR-XUV pump probe.
Compressor: to compress the laser pulse duration close to its Fourier limited value.
PG2 DM: Hosts the deformable mirror to correct the wavefront of the laser and a polarisation gating setup for IAP’s XUV generation.
f-10, f-6, f-3: are the three focusing chambers containing spherical mirrors of focal length 10 ,6 and 3 m respectively.
HHG chamber: The target area of the XUV generation, containing multiple gasjets (Figure 1 (d)) and/or a gascell.
BM: Beam management chamber to select the arm the XUV is guided to. It also hosts a split silicon plate to introduce wavefront splitting for pump probe experiments Figure 1 (c). Figure 1 (b) is a conical mirror of 2” in diameter to select only XUV to pass through the centre and reflect the annular IR.
CC: The characterisation chamber contains a bipolar electron/ion ToF with a back-focusing split-and-delay option (Figure 1 (f)) for XUV-XUV pump-probe experiments and for attosecond temporal characterisation. Furthermore, an ion microscope (IM) combined with a grazing incidence focusing optic is available. Pulsed gas jet targets are provided for both instruments. It also includes a MCP-Phosphor setup as a XUV beamprofiler and a calibrated XUV photodiode for pulse energy measurement.
ES, AC: A mirrored “user arm” accepts a custom user end station. Optionally (or alternatively), the “direct arm” can be used to avoid spectral constraints and to increase the XUV pulse energy at an end-station target.
Figure 1: Schematic layout of the GHHG SYLOS Compact beamline.
|SEA||XUV radiation (generated in Ar, 200 nm Al filter)|
|Central wavelength||825 nm||25 nm (50 eV)|
|Average power||Up to 425 mW||Up to 4 μW (at generation)|
|Pulse energy||40 mJ||Up to 400 nJ (at generation)|
|Stability of the pulse energy||< 2 % (rms)||<2% (std)|
|Repetition rate||10 Hz||10 Hz|
|Bandwidth||750 -960 nm||17-77 nm (16-70 eV)|
|Pulse durationPulse duration||< 12 fs||TBD|
|Beam diameter 1/e2||60 mm||< 15 mm (at diagnostic chamber)|
|Polarization||p (horizontal)||p (horizontal)|
Table 2: Measured parameters of the SEA laser system and the XUV radiation generated through HHG
XUV and VUV flat-field spectrometers.
Figure 2: Harmonic spectrum generated using SEA laser.
XUV beam profiler
Figure 3: XUV beam profile recorded in multijet combination using SEA laser. (a) Single jet (b) Another Single jet (c) Double jet.
XUV wavefront sensor
Bipolar Time-Of-Flight detector
 S. Kuhn, J. Phys. B: At. Mol. Opt. Phys. 50, 132002 (2017)
 I. Orfanos, Phys. Rev. A 106, 043117 (2022)