TY - JOUR A1 - Jurkovičová, Lucie A1 - Ben Ltaief, Ltaief A1 - Roos, Andreas Hult A1 - Hort, Ondřej A1 - Finke, Ondřej A1 - Albrecht, Martin A1 - Hoque, Ziaul A1 - Klimešová, Eva A1 - Sundaralingam, Akgash A1 - Antipenkov, Roman A1 - Grenfell, Annika A1 - Špaček, Alexandr A1 - Szuba, Wojciech A1 - Krikunova, Maria A1 - Mudrich, Marcel A1 - Nejdl, Jaroslav A1 - Andreasson, Jakob T1 - Bright continuously tunable vacuum ultraviolet source for ultrafast spectroscopy JF - Communications Physics N2 - Ultrafast electron dynamics drive phenomena such as photochemical reactions, catalysis, and light harvesting. To capture such dynamics in real-time, femtosecond to attosecond light sources are extensively used. However, an exact match between the excitation photon energy and a characteristic resonance is crucial. High-harmonic generation sources are advantageous in terms of pulse duration but limited in spectral tunability in the vacuum ultraviolet range. Here, we present a monochromatic femtosecond source continuously tunable around 21eV photon energy utilizing the second harmonic of an optical parametric chirped pulse amplification laser system to drive high-harmonic generation. The unique tunability of the source is verified in an experiment probing the interatomic Coulombic decay in doped He nanodroplets across the He absorption bands. Moreover, we achieved intensities sufficient for driving collective processes in multiply excited helium nanodroplets, which have been previously observed only at free electron lasers. Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-18462 SN - 2399-3650 VL - 7 PB - Nature Publishing Group ER - TY - JOUR A1 - Medina, Cristian A1 - Lægdsmand, Asbjørn Ørnemark A1 - Ben Ltaief, Ltaief A1 - Hoque, Ziaul A1 - Roos, Andreas Hult A1 - Jurkovičová, Lucie A1 - Hort, Ondřej A1 - Finke, Ondřej A1 - Albrecht, Martin A1 - Nejdl, Jaroslav A1 - Stienkemeier, Frank A1 - Andreasson, Jakob A1 - Klimešová, Eva A1 - Krikunova, Maria A1 - Heidenreich, Andreas A1 - Mudrich, Marcel T1 - Long-lasting XUV activation of helium nanodroplets for avalanche ionization JF - New Journal of Physics N2 - We study the dynamics of avalanche ionization of pure helium nanodroplets activated by a weak extreme-ultraviolet (XUV) pulse and driven by an intense near-infrared (NIR) pulse. In addition to a transient enhancement of ignition of a nanoplasma at short delay times ${\sim}200$ fs, long-term activation of the nanodroplets lasting up to a few nanoseconds is observed. Molecular dynamics simulations suggest that the short-term activation is caused by the injection of seed electrons into the droplets by XUV photoemission. Long-term activation appears due to electrons remaining loosely bound to photoions which form stable 'snowball' structures in the droplets. Thus, we show that XUV irradiation can induce long-lasting changes of the strong-field optical properties of nanoparticles, potentially opening new routes to controlling avalanche-ionization phenomena in nanostructures and condensed-phase systems. KW - nanoplasma KW - helium nanodroplet KW - pump–probe spectroscopy KW - avalanche ionization KW - high-harmonic generation KW - extreme ultraviolet Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17701 VL - 25 PB - Institute of Physics (IOP) ER - TY - JOUR A1 - Roos, Andreas Hult A1 - Hoque, Ziaul A1 - Klimešová, Eva A1 - Ben Ltaief, Ltaief A1 - Medina, Cristian A1 - Jurkovič, Matej A1 - Albrecht, Martin A1 - Finke, Ondřej A1 - Hort, Ondřej A1 - Nejdl, Jaroslav A1 - Mudrich, Marcel A1 - Andreasson, Jakob A1 - Krikunova, Maria T1 - Electron correlation dynamics in atomic Kr excited by XUV pulses and controlled by NIR laser pulses of variable intensity JF - New Journal of Physics N2 - We have investigated the possibility to track and control correlation dynamics of valence electrons in krypton (Kr) initiated by the absorption of one extreme ultraviolet (XUV) photon. In this investigation, pump-probe experiments have been performed where monochromatized single high-harmonics at photon energies 29.6, 32.8, and 35.9 eV have been used as pump to populate different intermediate excited states. A temporally delayed near-infrared (NIR) pulse probes the population of various decay channels via the detection of Kr²⁺ ion yields and its transient profiles. We observe that by varying the NIR pulse intensity within a range from 0.3 x 10¹³ to 2.6 x 10¹³ W cm⁻², the shape of the Kr²+ transient profile changes significantly. We show that by varying the intensity of the NIR pulse, it is possible—(i) to control the ratio between sequential and non-sequential double ionization of Kr; (ii) to selectively probe quantum beating oscillations between Kr+* satellite states that are coherently excited within the bandwidth of the XUV pulse; and (iii) to specifically probe the relaxation dynamics of doubly excited (Kr**) decay channels. Our studies show that the contribution of different ionization and decay channels (i)–(iii) can be altered by the NIR pulse intensity, thus demonstrating an efficient way to control the ionization dynamics in rare gas atoms. KW - electron correlation KW - control ionization dynamics KW - krypton satellite states KW - XUV/NIR pump-probe KW - HHG KW - quantum beating oscillation KW - doubly excited states Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-16987 VL - 25 PB - Institute of Physics Publishing (IOP) ER -