defined polarization state is a key requirement in numerous photonic applications. For example, linear optical polarizers are frequently utilized in lithography, [7,8] industrial vision, [9] microscopy, ellipsometry [10] or astronomic remote sensing systems. [11] All these applications substantially benefit from efficient nano-optical wire grid polarizers.A wire grid polarizer (WGP) is a grating type metasurface (see Figure 1). The typical operation principle for such elements requires the transmittance of TM polarized light T TM (TM transversal magneticelectrical field orthogonal to the ridges) to be much larger than that of TE polarized light T TE (transversal electric-electrical field parallel to the ridges) to achieve a significant anisotropic filter functionality. Here, the extinction ratio E r = T TM /T TE is used to express the suppression of TE polarized light. [12] WGPs are highly beneficial because of large achievable element sizes (wafer size), compactness (wafer thickness), and large acceptance angles. [13] Furthermore, their nano-optical nature allows an easy integration into other (nano-)optical elements, such as litho graphy masks, [14] enabling local polarization control. Currently, applications advance toward shorter wavelengths in order to benefit from smaller foci and characteristic electronic transitions, which can be utilized for material analysis. While WGPs are well established in the VIS and IR, suitable ones were not available in the deep ultraviolet (DUV) spectral range until very recently. [12,15,16] The lack of applicable DUV WGPs originates from challenging requirements on both structure and material properties.A structural period of the polarizer has to fulfilling the zero order conditionto avoid propagation of diffraction orders greater than the zeroth one.[17] For a normal incidence of light (ϕ = 0°) with a wavelength λ in the DUV and a fused silica substrate with a refractive index n sub a period p in the order of 100 nm is necessary. Additionally, an aspect ratio (see Figure 1: ratio of height and ridge width) larger than five is typically required. [12] The simultaneous realization of large aspect ratio and small periods is technologically extremely challenging. Fortunately however, advances in nanotechnology do allow the fabrication of such structures. [18] Pelletier et al. [15] demonstrated aluminum WGPsWire grid polarizers (WGPs), periodic nano-optical metasurfaces, are convenient polarizing elements for many optical applications. However, they are still inadequate in the deep ultraviolet spectral range. It is shown that to achieve high performance ultraviolet WGPs a material with large absolute value of the complex permittivity and extinction coefficient at the wavelength of interest has to be utilized. This requirement is compared to refractive index models considering intraband and interband absorption processes. It is elucidated why the extinction ratio of metallic WGPs intrinsically humble in the deep ultraviolet, whereas wide bandgap semiconductors are superior materia...

We report a coherent mid-infrared (MIR) source with a combination of broad spectral coverage (6-18 μm), high repetition rate (50 MHz), and high average power (0.5 W). The waveform-stable pulses emerge via intrapulse differencefrequency generation (IPDFG) in a GaSe crystal, driven by a 30-W-average-power train of 32-fs pulses spectrally centered at 2 μm, delivered by a fiber-laser system. Electro-optic sampling (EOS) of the waveform-stable MIR waveforms reveals their single-cycle nature, confirming the excellent phase matching both of IPDFG and of EOS with 2-μm pulses in GaSe.

We report on experimental results in a new regime of a relativistic light-matter interaction employing mid-infrared (3.9 m wavelength) high intensity femtosecond laser pulses. In the laser generated plasma, the electrons reach relativistic energies already at rather low intensities due to the fortunate  2 -scaling of the kinetic energy with the laser wavelength. The lower intensity suppresses optical field ionization and creation of the pre-plasma at the rising edge of the laser pulse efficiently, enabling an enhanced efficient vacuum heating of the plasma. The lower critical plasma density for long-wavelength radiation can be surmounted by using nanowires instead of flat targets. In our experiments 80% of the incident laser energy has been absorbed resulting in a long living, keV-temperature, high-charge state plasma with a density of more than three orders of magnitude above the critical value. Our results pave the way to laser-driven experiments on laboratory astrophysics and nuclear physics at a high repetition rate.[ ] . The generated plasmas have solid density, corresponding to an unprecedented >10 3 n cr of the driving laser pulses. II. Experimental setupThe experiments were carried out at the high energy OPCPA laser system delivering 90 fs laser pulses at the 3.9 µm idler wavelength with the energy on the target up to 25 mJ at a 20 Hz repetition rate [11,12]. The beam was focused by an off-axis parabolic mirror onto a

The spatial and compositional complexity of 3D structures employed in today's nanotechnologies has developed to a level at which the requirements for process development and control can no longer fully be met by existing metrology techniques. For instance, buried parts in stratified nanostructures, which are often crucial for device functionality, can only be probed in a destructive manner in few locations as many existing nondestructive techniques only probe the objects surfaces. Here, it is demonstrated that grazing exit X‐ray fluorescence can simultaneously characterize an ensemble of regularly ordered nanostructures simultaneously with respect to their dimensional properties and their elemental composition. This technique is nondestructive and compatible to typically sized test fields, allowing the same array of structures to be studied by other techniques. For crucial parameters, the technique provides sub‐nm discrimination capabilities and it does not require access‐limited large‐scale research facilities as it is compatible to laboratory‐scale instrumentation.

A double-patterning process for scalable, efficient, and deterministic nanoring array fabrication is presented. It enables gaps and features below a size of 20nm. A writing time of 3min/cm2 makes this process extremely appealing for scientific and industrial applications. Numerical simulations are in agreement with experimentally measured optical spectra. Therefore, a platform and a design tool for upcoming next generation plasmonic devices like hybrid plasmonic quantum systems are delivered

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Substantial discrepancies are commonly observed when comparing the predicted and measured optical performance of deep-ultraviolet tungsten wire grid polarizers. Particularly, the extinction ratio is strongly impaired. Therefore, we investigate major differences between assumed and actual achieved properties regarding geometry and material of the grating structure as the origin of theses discrepancies. We find an improvement potential for the extinction ratio of one order of magnitude by improving the material and a factor of four by improving the geometry. Our results allow for a purposeful revision of fabrication processes and will therefore significantly contribute to the improvement of deep-ultraviolet wire grid polarizers.

Metasurfaces offer promising possibilities for emerging photonic applications like see‐through, near‐eye displays. Vistec Electron Beam lithography systems with variable shaped beam (VSB) and cell projection (CP) technology provide a flexible solution to generate repetitive structures on large substrates. Excellent pattern fidelity is achieved in a feasible write‐time, enabling prototyping or the manufacturing of replication masters.