Publication

DOI:

10.1016/j.apsusc.2026.166007External link

University Bibliography Jena:

fsu_mods_00030054External link

DOI:

10.1016/j.vacuum.2025.114781External link

University Bibliography Jena:

fsu_mods_00028385External link

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.

DOI:

10.1063/5.0306455External link

University Bibliography Jena:

fsu_mods_00034666External link

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.

DOI:

10.22032/dbt.68370External link

University Bibliography Jena:

fsu_mods_00029210External link

DOI:

10.1117/12.3055797External link

University Bibliography Jena:

fsu_mods_00026647External link

DOI:

10.1117/12.3061518External link

University Bibliography Jena:

fsu_mods_00029436External link

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.

DOI:

10.1088/1361-6528/adc4ecExternal link

University Bibliography Jena:

fsu_mods_00023928External link

DOI:

10.1109/CLEO/EUROPE-EQEC65582.2025.11111027External link

University Bibliography Jena:

fsu_mods_00027672External link

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.

DOI:

10.1364/OME.540146External link

University Bibliography Jena:

fsu_mods_00020928External link

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.

DOI:

10.1364/OE.531071External link

University Bibliography Jena:

fsu_mods_00015789External link

DOI:

10.1117/12.3022706External link

University Bibliography Jena:

fsu_mods_00016232External link

Data transmission through optical fibers, lithographic production of semiconductor components, and sensors for autonomous driving are just a few examples for optical technologies in modern societies. The usage of diffractive optical elements (DOEs) offers possibilities for almost arbitrary manipulation of light within small available spaces. One popular approach is the use of metamaterials, which can have properties that are impossible for classical materials. Here, mainly effective-index structures of dielectric materials have been considered. Computer-generated holograms (CGHs), a special type of DOEs, can be used to generate almost arbitrary intensity distributions by their diffraction pattern. The simulation of light propagation through DOEs can be quite challenging. A rigorous simulation of the entire element is often too difficult due to the enormous computational requirements. The aim of this work is to overcome the limitations of established algorithms. For this purpose, new methods for the optical simulation of general DOEs have been developed: On the one hand, the use of suitable approximations allows a significant reduction of the computational effort to solve Maxwell's equations. On the other hand, physical simulations can be bypassed by machine learning to predict the optical function. In addition, the application of the new methods to design and optimization tasks is demonstrated. The presented methods can be used to optimize a variety of DOEs, for example metalenses or beamsplitters with high numerical aperture. In particular, the design of pattern generators for three-dimensional measurement of objects, face recognition, or camera calibration are promising application areas.

DOI:

10.22032/dbt.61641External link

University Bibliography Jena:

fsu_mods_00014288External link