@article{RoosHoqueKlimešovaetal.2023, author = {Roos, Andreas Hult and Hoque, Ziaul and Klimešov{\´a}, Eva and Ben Ltaief, Ltaief and Medina, Cristian and Jurkovič, Matej and Albrecht, Martin and Finke, Ondřej and Hort, Ondřej and Nejdl, Jaroslav and Mudrich, Marcel and Andreasson, Jakob and Krikunova, Maria}, title = {Electron correlation dynamics in atomic Kr excited by XUV pulses and controlled by NIR laser pulses of variable intensity}, series = {New Journal of Physics}, volume = {25}, journal = {New Journal of Physics}, publisher = {Institute of Physics Publishing (IOP)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-16987}, year = {2023}, abstract = {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.}, language = {en} } @article{JurkovičovaBenLtaiefRoosetal.2024, author = {Jurkovičov{\´a}, Lucie and Ben Ltaief, Ltaief and Roos, Andreas Hult and Hort, Ondřej and Finke, Ondřej and Albrecht, Martin and Hoque, Ziaul and Klimešov{\´a}, Eva and Sundaralingam, Akgash and Antipenkov, Roman and Grenfell, Annika and Špaček, Alexandr and Szuba, Wojciech and Krikunova, Maria and Mudrich, Marcel and Nejdl, Jaroslav and Andreasson, Jakob}, title = {Bright continuously tunable vacuum ultraviolet source for ultrafast spectroscopy}, series = {Communications Physics}, volume = {7}, journal = {Communications Physics}, publisher = {Nature Publishing Group}, issn = {2399-3650}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-18462}, year = {2024}, abstract = {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.}, language = {en} } @article{MedinaLagdsmandBenLtaiefetal.2023, author = {Medina, Cristian and L{\ae}gdsmand, Asbj{\o}rn {\O}rnemark and Ben Ltaief, Ltaief and Hoque, Ziaul and Roos, Andreas Hult and Jurkovičov{\´a}, Lucie and Hort, Ondřej and Finke, Ondřej and Albrecht, Martin and Nejdl, Jaroslav and Stienkemeier, Frank and Andreasson, Jakob and Klimešov{\´a}, Eva and Krikunova, Maria and Heidenreich, Andreas and Mudrich, Marcel}, title = {Long-lasting XUV activation of helium nanodroplets for avalanche ionization}, series = {New Journal of Physics}, volume = {25}, journal = {New Journal of Physics}, publisher = {Institute of Physics (IOP)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-17701}, year = {2023}, abstract = {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.}, language = {en} } @article{KlimesovaRoosHoqueetal.2024, author = {Klimesov{\´a}, Eva and Roos, Andreas Hult and Hoque, Ziaul and Smijesh, N. and Squibb, R.J. and Coudert-Alteirac, H. and Feifel, R. and Andreasson, Jakob and Krikunova, Maria}, title = {Update on MAC End-Station at ELI Beamlines Facility}, series = {Acta Physica Polonica A}, volume = {145}, journal = {Acta Physica Polonica A}, number = {2}, publisher = {Institute of Physics (IOP) and Polish Physical Society}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-18840}, pages = {118 -- 122}, year = {2024}, abstract = {The MAC end-station at the ELI Beamlines facility is a multipurpose user's station for atomic, molecular, and optical sciences and coherent diffractive imaging. The technical design of the station, the available instruments, and an overview of the whole beamline have been published in Eur. Phys. J. Spec. Top. 230, 4183 (2021). Here, we address ongoing upgrades of the MAC end-station that will provide users with advanced capabilities for beam manipulation and electron/ion detection. The upgrades include (i) the installation of a beam preparation chamber in front of the MAC chamber, (ii) a magnetic bottle electron spectrometer with high collection and detection efficiency and high energy resolution, and (iii) an event-driven TPX3CAM detector for velocity map imaging spectrometer, which provides both spatial and temporal information for each pixel. We present results from the first commissioning measurements with these instruments, confirming their performance for state-of-the-art experiments in atomic, molecular, and optical sciences.}, language = {en} } @article{KlimesovaKulykMartinetal.2025, author = {Klimesova, Eva and Kulyk, Olena and Martin, Lucas Janos and Sch{\"u}tte, Bernd and Fr{\"u}hling, Ulrike and Drescher, Markus and Pan, Rui and Stojanovic, Nikola and Bermudez Macias, Ivette J. and D{\"u}sterer, Stefan and Andreasson, Jakob and Wieland, Marek and Krikunova, Maria}, title = {Electron thermalization and ion acceleration in XUV-produced plasma from nanoparticles in He gas environment}, series = {New Journal of Physics}, volume = {27}, journal = {New Journal of Physics}, publisher = {Institute of Physics Publishing (IOP); Deutsche Physikalische Gesellschaft}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-19818}, year = {2025}, abstract = {We use intense femtosecond extreme ultraviolet (XUV) pulses with a photon energy of 92 eV from the FLASH free electron laser to irradiate substrate-free CsCl nanoparticles surrounded by a He gas with a number density of around 1015 cm-3. By simultaneously detecting electrons and energetic ions from the laser-irradiated micron-size target we study the acceleration mechanism of light ions at the microplasma-vacuum boundary as well as at the layer close to the nanoparticle surface. When the XUV pulse interacts with the gas alone, helium ions are accelerated to energies exceeding 100 eV. In the presence of the nanoparticle, light ions gain additional energy in the electric field around the ionized nanoparticle and their energy spectrum changes considerably. We present an electrostatic model to explain the ion acceleration mechanisms both with and without the nanoparticle and discuss the role of the gas environment in experiments.}, language = {en} } @unpublished{ŠevaevNomerotskiŠvihraetal.2025, author = {Ševaev, Dmitrij and Nomerotski, Andrei and Švihra, Peter and Sishodia, Keshav and Roos, Andreas Hult and Albrecht, Martin and Andreasson, Jakob and Krikunova, Maria and Klimešov{\´a}, Eva}, title = {Studies of ultrafast dynamics in substrate-free nanoparticles at ELI using Timepix3 optical camera}, series = {arXiv.org}, journal = {arXiv.org}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-20875}, year = {2025}, abstract = {We present a novel application of the Timepix3 optical camera (Tpx3Cam) for investigating ultrafast dynamics in substrate-free nanoparticles at the Extreme Light Infrastructure European Research Infrastructure Consortium (ELI ERIC). The camera, integrated into an ion imaging system based on a micro-channel plate (MCP) and a fast P47 scintillator, enables individual time-stamping of incoming ions with nanosecond timing precision and high spatial resolution. The detector successfully captured laser-induced ion events originating from free nanoparticles disintegrated by intense laser pulses. Owing to the broad size distribution of the nanoparticles (10-500 nm) and the variation in laser intensities within the interaction volume, the detected events range in occupancy from near-zero to extremely high, approaching the readout limits of the detector. By combining time-of-flight and velocity map imaging (VMI) techniques, detailed post-processing and analysis were performed. The results presented here focus on the performance of Tpx3Cam under high-occupancy conditions, which are of particular relevance to this study. These conditions approach the limitations imposed by the camera readout capabilities and challenge the effectiveness of standard post-processing algorithms. We investigated these limitations and associated trade-offs, and we present improved methods and algorithms designed to extract the most informative features from the data.}, language = {en} } @article{SishodiaBenLtaiefScheeletal.2026, author = {Sishodia, Keshav and Ben Ltaief, Ltaief and Scheel, Niklas and F{\"o}ldes, Istv{\´a}n B. and Roos, Andreas Hult and Albrecht, Martin and Staněk, Maty{\´a}š and Jurkovičov{\´a}, Lucie and Hort, Ondrej and Nejdl, Jaroslav and Garc{\´i}a-Alfonso, Ernesto and Halberstadt, Nadine and Andreasson, Jakob and Klimešov{\´a}, Eva and Krikunova, Maria and Krishnan, Sivarama and Heidenreich, Andreas and Mudrich, Marcel}, title = {XUV fluorescence as a probe of interatomic coulombic decay of resonantly excited He nanodroplets}, series = {Scientific Reports}, volume = {16}, journal = {Scientific Reports}, number = {1}, publisher = {Springer Nature}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-21050}, year = {2026}, abstract = {Superfluid He nanodroplets resonantly excited by extreme ultraviolet (XUV) pulses can relax via interatomic coulombic decay (ICD), generally considered an ultrafast process. Here, we introduce a novel approach to probe the dynamics of ICD in He nanodroplets over timescales ranging from femtoseconds to nanoseconds. Our method relies on detecting XUV fluorescence emitted from the nanodroplets as they are driven into a nanoplasma by subsequent intense infrared pulses. Nanoplasma ignition is facilitated by tunnel ionization of XUV-excited He∗ atoms attached to the droplets; it thus serves as a sensitive probe of their relaxation dynamics. The observed nanosecond-scale decay is attributed to ICD between pairs of He∗ atoms undergoing roaming motion on the droplet surface, as supported by quantum-mechanical and classical model calculations.}, language = {en} }