Publication

of Prof. Uwe D. Zeitner

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Highlighted authors are members of the University of Jena.

  3. Long-lived hot and dense plasma from relativistic laser–nanowire array interaction

    Year of publicationPublished in:Matter and Radiation at Extremes E. Eftekhari-Zadeh, M. Gyrdymov, P. Tavana, R. Loetzsch, I. Uschmann, T. Siefke, T. Käsebier, U. Zeitner, A. Szeghalmi, A. Pukhov, D. Serebryakov, E. Nerush, I. Kostyukov, O. Rosmej, C. Spielmann, D. Kartashov
    Long-lived hot and dense plasmas generated by ultra-intense laser beams are of critical importance for laser-driven nuclear physics, bright hard X-ray sources, and laboratory astrophysics. We report the experimental observation of plasmas with nanosecond-scale lifetimes, near-solid density, and keV-level temperatures, produced by irradiating periodic arrays of composite nanowires with ultra-high-contrast relativistically intense femtosecond laser pulses. Jet-like plasma structures extending up to 1 mm from the nanowire surface were observed, emitting K-shell radiation from He-like Ti ²⁰⁺ ions. High-resolution X-ray spectra have been analyzed using 3D particle-in-cell (PIC) simulations of the laser–plasma interaction combined with collisional–radiative modeling (FLYCHK). The results indicate that the jets consist of plasma with densities of 10 ²⁰ –10 ²² cm −³ and keV-scale temperatures, persisting for several nanoseconds. We attribute the formation of these jets to the generation of kilotesla-scale global magnetic fields during the laser interaction, as predicted by PIC simulations. These fields may drive long-timescale current instabilities that sustain magnetic fields of several hundred tesla, sufficient to confine hot, dense plasma over nanosecond durations.
    University Bibliography Jena:
    fsu_mods_00034666External link

  4. Scalable plasmonic metasurfaces with features down to 2 nm: advancing nanofabrication for enhancing nonlinear optical effects

    Year of publication J. Gour
    This thesis focuses on the development of a scalable nanofabrication approach for plasmonic metasurfaces and on their linear and nonlinear optical characterization, supporting both localized and collective resonances. First, by combining high-throughput electron-beam writing techniques such as variable shaped beam and character projection strategies with standard metal lift-off processes, large-area plasmonic nanobar metasurfaces were realized on a 100 mm fused silica wafer. These nanobar arrays exhibit resonant lattice plasmon conditions at the excitation and emission wavelengths, leading to enhanced second- and third-harmonic generation. To push the limits of field confinement, a wafer-scale fabrication approach was developed to achieve plasmonic metasurfaces with sub-5 nm gap features. Through a wafer-scale nanofabrication process, independently shaped bow-tie antennas with gap widths down to 2 nm were achieved. Measurements and simulations confirm gap-plasmon modes and collective resonances, while deviations between experiment and theory indicate nonlocal effects. The 2 nm-gap metasurfaces achieve 2–3 orders of magnitude higher second-harmonic efficiency compared to larger-gap structures, and their angular nonlinear response correlates strongly with linear lattice resonance features. Overall, this work demonstrates reliable and scalable fabrication of plasmonic metasurfaces with controllable gap sizes approaching the sub-nanometer regime. The results highlight the need for advanced theoretical models that account for nonlocal response in sub-5 nm nanostructures and open pathways for metasurface-based applications in molecular sensing, nanoscale trapping, and petahertz optoelectronic devices.
    University Bibliography Jena:
    fsu_mods_00029210External link

  5. Ultra shallow silicon EUV gratings fabricated via ion irradiation

    Year of publicationPublished in:EUV and X-Ray Optics: Synergy between Laboratory and Space IX: 7-8 April 2025, Prague, Czech Republic J. Kaufmann, R. Ciesielski, K. Freiberg, M. Walther, A. Fernández Herrero, S. Lippmann, V. Soltwisch, T. Siefke, U. Zeitner
    University Bibliography Jena:
    fsu_mods_00026647External link

  6. Fabrication of ultra-shallow EUV gratings in silicon via ion irradiation

    Year of publicationPublished in:Advances in X-ray/EUV sources, optics, and components XX J. Kaufmann, R. Ciesielski, K. Freiberg, M. Walther, A. Herrero, S. Lippmann, V. Soltwisch, T. Siefke, U. Zeitner
    University Bibliography Jena:
    fsu_mods_00029436External link

  7. Fabrication of shallow EUV gratings on silicon by irradiation with helium ions

    Year of publicationPublished in:Nanotechnology J. Kaufmann, R. Ciesielski, K. Freiberg, M. Walther, A. Fernández Herrero, S. Lippmann, V. Soltwisch, T. Siefke, U. Zeitner
    To accurately achieve structure height differences in the range of single digit nanometres is of great importance for the fabrication of diffraction gratings for the extreme ultraviolet range (EUV). Here, structuring of silicon irradiated through a mask by a broad beam of helium ions with an energy of 30 keV was investigated as an alternative to conventional etching, which offers only limited controllability for shallow structures due to the higher rate of material removal. Utilising a broad ion beam allows for quick and cost effective fabrication. Ion fluence of the irradiations was varied in the range of 10¹⁶ ... 10¹⁷ ions · cm⁻². This enabled a fine tuning of structure height in the range of 1.00 ± 0.05 to 20 ± 1 nm, which is suitable for shallow gratings used in EUV applications. According to transmission electron microscopy investigations the observed structure shape is attributed to the formation of point defects and bubbles/cavities within the silicon. Diffraction capabilities of fabricated elements are experimentally shown at the SX700 beamline of BESSY II. Rigorous Maxwell solver simulation based on the finite-element method and rigorous coupled wave analysis are utilised to describe the experimental obtained diffraction pattern.
    University Bibliography Jena:
    fsu_mods_00023928External link

  8. Nonlinear harmonic generation in sub-5 nm plasmonic nanogap metasurfaces

    Year of publicationPublished in:2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) S. Beer, J. Gour, P. Paul, A. Alberucci, A. Szeghalmi, T. Siefke, U. Peschel, U. Zeitner, S. Nolte
    University Bibliography Jena:
    fsu_mods_00027672External link

  9. Fabrication of low-loss lithium niobate on insulator waveguides on the wafer scale [Invited]

    Year of publicationPublished in:Optical Materials Express M. Younesi, T. Kasebier, I. Elmanov, Y. Li, P. Kumar, R. Geiss, T. Siefke, F. Eilenberger, F. Setzpfandt, U. Zeitner, T. Pertsch
    We report on the wafer scale fabrication of single-mode low-loss lithium niobate on insulator waveguides utilizing a chemically amplified resist and an optimized dry etching method. The fabricated single-mode waveguides are free of residuals and re-deposition, with measured losses for straight waveguides around 2 dB/m (0.02 dB/cm). We present a method offering advantages for large-scale production mainly due to its cost-effectiveness and faster writing time. This work holds promise for advancing integrated photonics and optical communication technologies.
    University Bibliography Jena:
    fsu_mods_00020928External link

  10. Nonlinear harmonic generation in sub-5 nm plasmonic nanogap metasurfaces

    Year of publicationStatusReview pendingPublished in:European Quantum Electronics Conference in Proceedings Conference on Lasers and Electro-Optics/Europe, CLEO/Europe 2025 and European Quantum Electronics Conference, EQEC 2025 S. Beer, J. Gour, P. Paul, A. Alberucci, A. Szeghalmi, T. Siefke, U. Peschel, U. Zeitner, S. Nolte
    University Bibliography Jena:
    fsu_mods_00034865External link

  11. Mid-infrared dielectric laser acceleration in a silicon dual pillar structure

    Year of publicationPublished in:Optics Express L. Brückner, T. Chlouba, Y. Morimoto, N. Schönenberger, T. Shibuya, T. Siefke, U. Zeitner, P. Hommelhoff
    Dielectric laser accelerators use near-infrared laser pulses to accelerate electrons at dielectric structures. Driving these devices with mid-infrared light should result in relaxed requirements on the electron beam, easier fabrication, higher damage threshold, and thus higher acceleration gradients. In this paper, we demonstrate dielectric laser acceleration of electrons driven with 10 µm light in a silicon dual pillar structure. We observe the acceleration of 27 keV electrons by 1.4 keV, corresponding to a 93 MeV/m acceleration gradient. The damage threshold of the structures of 3.3 ± 0.6 GV/m peak field is significantly higher than for near-infrared accelerators. The dual pillar acceleration structure itself even survived 5.2 ± 0.9 GV/m, the highest field strength we could achieve with the current system. This together with the larger structure acceptance bodes well for future dielectric laser accelerators driven with mid-infrared light.
    University Bibliography Jena:
    fsu_mods_00015789External link

  12. Miniaturized fluorescence measurement system with novel dichroic beam splitter cubes with 3 by 3 by 3 cubic millimeters and special optical direction-selective filters

    Year of publicationPublished in:Optical Design and Engineering IX R. Müller, T. Siefke, U. Zeitner, K. Neckermann, M. Hintz, B. Ploss, M. Lappschies
    University Bibliography Jena:
    fsu_mods_00016232External link
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