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Subject: Extreme ultraviolet pulse ×

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    Compact intense extreme-ultraviolet source
    (Washington, DC : OSA, 2021) Major, Balázs; Ghafur, Omair; Kovács, Katalin; Varjú, Katalin; Tosa, Valer; Vrakking, Marc J. J.; Schütte, B.
    High-intensity laser pulses covering the ultraviolet to terahertz spectral regions are nowadays routinely generated in a large number of laboratories. In contrast, intense extreme-ultraviolet (XUV) pulses have only been demonstrated using a small number of sources including free-electron laser facilities [1-3] and long high-harmonic generation (HHG) beamlines [4-9]. Here we demonstrate a concept for a compact intense XUV source based on HHG that is focused to an intensity of $2 \times 10^{14}$ W/cm$^2$, with a potential increase up to $10^{17}$ W/cm$^2$ in the future. Our approach uses tight focusing of the near-infrared (NIR) driving laser and minimizes the XUV virtual source size by generating harmonics several Rayleigh lengths away from the NIR focus. Accordingly, the XUV pulses can be refocused to a small beam waist radius of 600 nm, enabling the absorption of up to four XUV photons by a single Ar atom in a setup that fits on a modest (2 m) laser table. Our concept represents a straightforward approach for the generation of intense XUV pulses in many laboratories, providing novel opportunities for XUV strong-field and nonlinear optics experiments, for XUV-pump XUV-probe spectroscopy and for the coherent diffractive imaging of nanoscale structures.
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    Imaging plasma formation in isolated nanoparticles with ultrafast resonant scattering
    (Melville, NY : AIP Publishing LLC, 2020) Rupp, Daniela; Flückiger, Leonie; Adolph, Marcus; Colombo, Alessandro; Gorkhover, Tais; Harmand, Marion; Krikunova, Maria; Müller, Jan Philippe; Oelze, Tim; Ovcharenko, Yevheniy; Richter, Maria; Sauppe, Mario; Schorb, Sebastian; Treusch, Rolf; Wolter, David; Bostedt, Christoph; Möller, Thomas
    We have recorded the diffraction patterns from individual xenon clusters irradiated with intense extreme ultraviolet pulses to investigate the influence of light-induced electronic changes on the scattering response. The clusters were irradiated with short wavelength pulses in the wavelength regime of different 4d inner-shell resonances of neutral and ionic xenon, resulting in distinctly different optical properties from areas in the clusters with lower or higher charge states. The data show the emergence of a transient structure with a spatial extension of tens of nanometers within the otherwise homogeneous sample. Simulations indicate that ionization and nanoplasma formation result in a light-induced outer shell in the cluster with a strongly altered refractive index. The presented resonant scattering approach enables imaging of ultrafast electron dynamics on their natural timescale.