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Several journals
Image: Ira Winkler, IAP (University Jena)

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  1. Linear and Nonlinear Optical Properties of SiO2/TiO2 Heterostructures Grown by Plasma-Enhanced Atomic Layer Deposition

    Authors
    J. Liu, M. Mičulka, R. Rafi, S. Beer, D. Sevriukov, S. Nolte, S. Schröder, A. Tünnermann, I. Staude, A. Szeghalmi
    Year of publication
    Published in:
    Coatings
    Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk crystals under electric dipole approximation. Nonlinear thin films made from bulk crystals are technologically challenging because of complex and high-temperature fabrication processes. In this work, heterostructures made of two distinct amorphous materials, namely SiO ₂ and TiO ₂ , were prepared through plasma-enhanced atomic layer deposition (PEALD) with deposition temperature of 100 °C. By using the uniaxial dispersion model, we characterized the form birefringence of the deposited films, which can play a crucial role for the phase-matching condition in nonlinear waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective bulk second-order susceptibility, (Formula presented.) = 1.30 ± 0.13 pm/V, at a wavelength of 1032 nm. Noteworthy, we observed strong SHG signals from two-component nanolaminates, which are several orders of magnitude larger than those from single layers. The SHG signals from our samples only require the broken inversion symmetry at the interface. Here, optical properties of nanocomposites can be precisely engineered using the promising PEALD technology.
    University Bibliography Jena:
    fsu_mods_00035974External link

  2. Transverse mode characterization in optical fibers using singular value decomposition

    Authors
    Y. Tu, C. Pfleghar, C. Jauregui, J. Limpert
    Year of publication
    Published in:
    Optics Express
    What we believe to be a new scalar and data-driven approach to experimentally characterize the transverse modes of optical fibers is proposed in this paper. It retrieves the orthogonal modal base set of the fiber via singular value decomposition after collecting a large set of data under different coupling conditions. The results show good agreement with the simulated transverse modes. Due to its operating principle, this approach can characterize any fiber, regardless of its length or size, a prominent advantage compared to other experimental approaches.
    University Bibliography Jena:
    fsu_mods_00035538External link

  4. Polarization-maintaining, rod-type, ytterbium-doped, multi-core fiber for high power operation

    Authors
    Y. Khalil, C. Jauregui, A. Klenke, M. Bahri, J. Nold, N. Haarlammert, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Optics Express
    It has been previously observed that each core in a multi-core fiber has its own birefringence properties. Therefore, obtaining a laser output with a well-defined polarization pattern from a multi-core fiber is challenging. In this work, we explain the origin of this core-dependent birefringence and present a polarization-maintaining, 35-core fiber design that is tested in an oscillator setup, delivering over 100W of power with a polarization contrast ratio close to 10dB. This is a significant improvement with respect to a comparable non-polarization-maintaining multi-core fiber.
    University Bibliography Jena:
    fsu_mods_00030211External link

  5. 117-mJ pulse energy, high average power, Q-switched Yb-doped 49-core fiber amplifier

    Authors
    M. Bahri, C. Jauregui, A. Klenke, M. Lenski, J. Nold, N. Haarlammert, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Optics Express
    This work presents the simultaneous scaling of the average power and pulse energy emitted by multicore fiber laser systems. This is achieved through two series of experiments that use a generation of Yb-doped multicore fiber amplifiers with 49 cores, seeded by a Q-switched multicore fiber laser. One of the main results of these experiments is a total pulse energy of up to 117 mJ at a repetition rate of 5 kHz in quasi-continuous pumping operation. In a different experiment with a smaller core size multicore fiber, an average power of 400 W was achieved at a repetition rate of 5 kHz, corresponding to a pulse energy of 80 mJ in continuous pumping. The experimental results match our simulation predictions, providing valuable insights into the further energy scalability of Yb-doped multicore fibers.
    University Bibliography Jena:
    fsu_mods_00030210External link

  6. Single-frame randomized probe imaging in the EUV using a high-order harmonic source

    Authors
    S. Chew, W. Eschen, C. Liu, M. Abdelaal, J. Limpert, J. Rothhardt
    Year of publication
    Published in:
    Optics Express
    We report the demonstration of single-frame randomized probe imaging (RPI) using a 13.5 nm extreme ultraviolet (EUV) beam from a table-top high-harmonic generation (HHG) source. Three types of beams—a smooth, vortex, and speckle beam—were used to investigate the effect of different illuminations on image quality. Single-frame RPI reconstructions were successfully achieved for all beam types, with the highest resolution of 110 nm obtained using the EUV speckle beam. Comparisons with ptychography reconstructions confirm the advantages of structured illuminations over a smooth beam, showing improved convergence and image fidelity. Furthermore, averaging a small number of RPI images reconstructed from individual diffraction patterns significantly improves the resolution to sub-100 nm. These results demonstrate the capability of single-frame RPI to deliver rapid, high-resolution EUV imaging, offering a promising approach for applications limited by acquisition time, such as ultrafast pump-probe studies and real-time feedback.
    University Bibliography Jena:
    fsu_mods_00034896External link

  7. Recent developments in the understanding and passive mitigation of transverse mode instability

    Authors
    C. Jauregui, Y. Tu, S. Kholaif, F. Möller, G. Palma-Vega, N. Haarlammert, T. Walbaum, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Optical Fiber Technology: Materials, Devices, and Systems
    In this article we look at the newest developments in the understanding and mitigation of TMI in single-core fibers. This includes recent quantitative measurements that reveal the dependence of the TMI threshold on the modal content of the seed, systematic measurements on the dependence of the TMI threshold on the fiber core size, as well as the study of TMI in PM fibers including a novel passive mitigation strategy and the static modal energy transfer recently observed in these fibers.
    University Bibliography Jena:
    fsu_mods_00029154External link

  8. Over 400 W average power, sub-two-cycle, carrier-envelope phase-stable fiber laser system

    Authors
    I. Seres, E. Shestaev, M. Tschernajew, P. Jójárt, C. Gaida, N. Walther, T. Bartyik, B. Gilicze, Z. Bengery, D. Hoff, M. Kienel, T. Eidam, J. Limpert, Á. Börzsönyi, K. Varjú, Z. Várallyay
    Year of publication
    Status
    Review pending
    Published in:
    High Power Laser Science and Engineering
    We report on the development of a carrier-envelope phase (CEP)-stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad root mean square. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability and sub-two-cycle pulse durations. Similar to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source, this newly developed system is accessible to the international research community in peer-reviewed open user calls of the Extreme Light Infrastructure European Research Infrastructure Consortium.
    University Bibliography Jena:
    fsu_mods_00035153External link

  9. Dose constraints for high-resolution imaging of biological specimens with extreme ultraviolet and soft X-ray radiation

    Authors
    C. Liu, L. Licht, J. Rothhardt
    Year of publication
    Published in:
    Ultramicroscopy
    We present a theoretical evaluation of radiation dose constraints for extreme ultraviolet (EUV) and soft X-ray microscopy. Our work particularly addresses the long-standing concern regarding strong absorption of EUV radiation in biological specimens. Using an established dose–resolution model, we compare hydrated and dehydrated cellular states and quantify the fluence required for nanoscale imaging. Our analysis identifies a protein window spanning photon energies from ∼70 eV up to the carbon K-edge (284 eV). Towards the upper end of this range, at photon energies above 100 eV, EUV microscopy could in principle achieve sub-10 nm half-pitch resolution in dehydrated samples at doses well below the Henderson limit. In this situation, the radiation dose required for EUV imaging is predicted to be substantially lower than what is required for comparable resolution in water window soft X-ray microscopy. Furthermore, EUV photons with sufficiently high energy exhibit penetration depths of µm-level in dehydrated biomatter, enabling exceptional amplitude and phase contrast through thin cellular regions and small cells. These findings provide quantitative guidelines for photon energy selection and support the EUV protein window as a dose-favorable and physically viable modality for high-resolution, label-free, material-specific imaging of dehydrated biological matter.
    University Bibliography Jena:
    fsu_mods_00034593External link

  10. Predicting the structure of ultra shallow EUV gratings fabricated via ion irradiation

    Authors
    J. Kaufmann, T. Siefke, U. Zeitner
    Year of publication
    Published in:
    Applied Surface Science: a journal devoted to applied physics and chemistry of surfaces and interfaces
    University Bibliography Jena:
    fsu_mods_00030054External link

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

    Authors
    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
    Year of publication
    Published in:
    Matter and Radiation at Extremes
    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
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