A High Intensity Attosecond Light Source in Compact Geometry at ELI ALPS User Facility

TL;DR

This work reports the commissioning of the SYLOS Compact GHHG beamline at the ELI ALPS facility, which delivers high-flux attosecond XUV pulses suitable for nonlinear XUV studies. By combining loose focusing, dual gas-jet quasi-phase matching, polarization gating, and RABBITT diagnostics, the beamline generates attosecond pulse trains at 1 kHz with durations around a few hundred attoseconds and XUV energies up to ~1 μJ (≈308 nJ at generation) across 15–40 eV. The authors demonstrate two-photon double ionization of Ne and Ar using XUV pulses, confirming the beamline's capability for nonlinear attosecond experiments and ultrafast electron dynamics investigations, including the potential for XUV–XUV pump–probe schemes at high repetition rates. These results establish a versatile, open-access platform for exploring higher-order nonlinear XUV processes, correlated electron dynamics, and attosecond science in atomic, molecular, and condensed matter systems, without relying on dressing IR fields.

Abstract

High-order harmonic generation (HHG) has become a standard technique for producing attosecond XUV pulses in the laboratory, yet the high flux necessary for nonlinear XUV photoionization remains accessible to only a few research groups. Here, we introduce the SYLOS Compact high-harmonic beamline at ELI ALPS, specifically designed to provide the flux required for non-linear optics in the XUV. We present a detailed characterization of the beam line demonstrating its capability to generate and utilize both intense attosecond pulse trains and isolated attosecond pulses. We further showcase the two-XUV-photon double ionization of neon (Ne) and argon (Ar), achieved in a user campaign. The results underscore the beamline's capability to support cutting-edge attosecond experiments and investigations of ultrafast electron dynamics on the attosecond scale.

Figures (7)

• Figure 1: A full schematic of the Compact Beamline at ELI ALPS depicting the individual sections of beam propagation, associated diagnostics and results. PG1 chamber for transmissive optics, Compressor chamber with a set of chirped mirrors, 6WC for beam steering, Deformable mirror (DM) positioned at $45^\circ$ in PG2, Focusing section consisting of three chambers LF1-3 with f=10 m, 6 m and 3 m focusing mirrors, and the turning chambers IR-St. XUV-G hosts gas targets in the form of gascell and gasjets. XUV-BS-L, XUV-BM, XUVD are for beam separation, beam management and diagnostics respectively (a) The near field profile of the SEA laser, (b) Measured focal spot after wavefront correction, (c) XUV beamprofile, XUV spectra generated in Xenon with (d) Al filter and (e) Sn filter on the beampath. (f) A typical high harmonic spectra of Neon.
• Figure 2: (a) Radial dependence of the gas density distribution for the expansion of argon into vacuum from an APCV3 nozzle with 500 $\mu m$ orifice diameter, and peak density along the nozzle axis. Assuming a temperature of 300 K, the corresponding peak pressure would reach 0.5 bar for a density of $1 \times 10^{25}\, m^{-3}$. (b) Pressure profile taken at the center of the nozzle, black dotted line on (a). Red curve: Fit of the profile by an exponential decay, yielding a decay length of 240 $\mu$m.
• Figure 3: XUV spectra generated by the SEA laser using the pinhole shaped nozzle gas jet (GJ2) with (a) Neon, (b) Argon and (c) Xenon.
• Figure 4: XUV beam profiles (a) for the GJ1 gas jet, (b) for the GJ2 gas jet and (c) both together. The spot size diameter is about 8 mm and does not change with the number of sources.
• Figure 5: RABBITT trace (a) Evolution of the photoelectron spectra generated in argon as a function of the delay plate angle. (b) Retrieved attosecond pulse duration. The blue one shows reconstructed pulse from the photoelectron spectra, the red curve is the Fourier transform limitted one.