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Near-field holography (NFH) combined with electron beam lithography (EBL)-written phase masks is a promising method for the rapid realization of diffraction gratings with high resolution and high accuracy in line density distribution. We demonstrate a dynamic exposure method in which the grating substrate is shifted during pattern transfer. This reduces the effects of stitching errors, resulting in the decreased intensity of the optical stray light (i.e., Rowland ghosts). We demonstrate the intensity suppression of ghosts by 60%. This illustrates the potential for dynamic NFH to suppress undesirable periodic patterns from phase masks and alleviate the stitching errors induced by EBL.

In this study, we investigate analytically and experimentally the roles of quasi-linearly polarized (LP), hybrid, plasmonic and photonic modes in optical detection and excitation with aperture tips in scanning near-field optical microscopy. Aperture tips are tapered and metal-coated optical fibers where small circular apertures are made at the apex. In aperture tips, there exist plasmonic modes that are bound at the interface of the metal cladding to the inner dielectric fiber and photonic modes that are guided in the area of the increased index in the dielectric fiber core. The fundamental photonic mode, although excited by the free-space Gaussian beam, experiences cutoff and turns into an evanescent mode. The photonic mode also becomes lossier than the plasmonic mode toward the tip aperture, and its power decay due to absorption and reflection is expected to be at least 10 -9 . In contrast, the fundamental plasmonic mode has no cutoff and thus reaches all the way to the tip aperture. Due to the non-adiabaticity of both modes' propagations through the taper below a core radius of 600 nm, there occurs coupling between the modes. The transmission efficiency of the plasmonic mode, including the coupling efficiency and the propagation loss, is expected to be about 10 -6 that is at least 3 orders of magnitude larger than that of the photonic mode. Toward the tip aperture, the longitudinal field of the photonic mode becomes stronger than the transverse ones while the transverse fields always dominate for the plasmonic mode. Experimentally, we obtain polarization resolved images of the near-field at the tip aperture and compare with the x- and y-components of the fundamental quasi-LP plasmonic and photonic modes. The results show that not only the pattern but also the intensity ratios of the x- and y-components of the aperture near-field match with that of the fundamental plasmonic mode. Consequently, we conclude that only the plasmonic mode reaches the tip aperture and thus governs the near-field interaction outside the tip aperture. Our conclusion remains valid for all aperture tips regardless of the cladding metal type that mainly influences the total transmission efficiency of the aperture tip.

We report the fabrication of periodic structures with a critical dimension of 90 nm on a fused silica substrate by i-line (𝜆=365 nm) proximity mask-aligner lithography. This realization results from the combination of the improvements of the optical system in the mask aligner (known as MO exposure optics), short-period phase-mask optimization, and the implementation of self-aligned double patterning (SADP). A 350 nm period grating is transferred into a sacrificial polymer layer and coated with an aluminum layer. The removal of the metal initially present on the horizontal surfaces and on top of the polymer grating leaves a 175 nm period grating on the wafer, which can be used as a wire grid polarizer. A computation of the efficiency is performed from the measured profile and confirms the deep-blue visible to infra-red operation range.

A reactive ion etching technique for the preparation of statistical ""Black Germanium"" antireflection surfaces, relying on self-organization in a Cl2 etch chemistry, is presented. The morphology of the fabricated Black Germanium surfaces is the result of a random lateral distribution of pyramidal etch pits with heights around (1450 ± 150) nm and sidewall angles between 80° and 85°. The pyramids' base edges are oriented along the crystal directions of Germanium, indicating a crystal anisotropy of the etching process. In the Vis-NIR, the tapered Black Germanium surface structure suppresses interface reflection to

A new route to prepare nanoporous SiO2 films by mixing atomic-layer-deposited alumina and silica in an angstrom-scale is presented. The selective removal of Al2O3 from the composites using wet chemical etching with phosphoric acid resulted in nanoporous thin SiO2 layers. A diffusion-controlled dissolution mechanism is identified whereby an interesting reorganization of the residual SiO2 is observed. The atomic scale oxide mixing is decisive in attaining and tailoring the film porosity. The porosity and the refractive index of nanoporous silica films were tailored from 9% to 69% and from 1.40 to 1.13, respectively. The nanoporous silica was successfully employed as antireflection coatings and as diffusion membranes to encapsulate nanostructures.

Studies of the mechanical loss of silicon flexures in a temperature region from 5 to 300 K are presented, where the flexures have been prepared by different fabrication techniques of interest for the construction of suspension elements of future interferometric gravitational wave detectors. A lowest mechanical loss of 3 × 10(exp -8) was observed for a 130 m thick flexure at around 10 K. While the mechanical loss follows the thermo-elastic predictions down to 50 K, at lower temperatures the observed loss is found to be a function of surface roughness. This surface loss is of interest for all applications using silicon-based oscillators at low temperatures. The extraction of a surface loss parameter using results from our measurements and those of other authors is presented and the relevance for future gravitational wave detector suspensions is discussed. A surface loss parameter alpha (ind s) = 0.5 pm was obtained. This reveals that the surface loss of silicon is significantly lower than the surface loss of fused silica.

In this contribution we review out latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials (MMs) at will. We give three examples of metamateiral design that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numerical simulations. Particular emphasis is put on the significance of such tailored effecitve properties of optical MMs.

Progress in the development of lithographic fabrication technologies and their availability for optical applications has moved their use for the realization of novel gratings into the focus of modern optics. Only lithography opens the flexibility to generate almost arbitrary grating patterns and thus make the full potential of grating functions accessible. In particular, the dedicated use of sub-wavelength patterns opens up novel grating functionalities and applications.

Laminar-type gratings as soft x-ray beam splitters for interferometry are presented. Gold-coated grating beam splitters with 1000 lines/mm are designed for grazing incidence operation at 13: 9 nm. They are routinely fabricated using electron beam lithography and ion etching techniques. The laminar grating is measured to have almost equal absolute efficiencies of about 20% in the zeroth and -1st orders, which enables a fringe visibility up to 0.99 in the interferometer. The discrepancy of the grating profiles between the optimized theoretical and the experimental results is analyzed according to the comparison of the optimized simulation results and the measurement realization of the grating efficiencies. By a precise control of the grating profile, the grating efficiency in the -1st order and the fringe visibility could be improved to 25% and 1, respectively.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1997-2000, In this paper, we report our investigation on the light trapping enhancement of silicon solar cells via the introduction of nanoscale gratings on the back side of solar cells. The grating is designed to diffract long wavelengths, typically from 900 nm to 1100 nm, leading to an enhancement of the photons path length in the solar cell. Therefore, a gain in current and then efficiency can be expected. The optimal grating parameters were first calculated via RCWA simulations, and were found to be a period of 310 nm for a flat front side and 410 nm for a textured front side. Test structures, with flat and textured front and back side and various silicon dioxide thicknesses on the back side, were then fabricated to confirm the simulation results. Reflection measurements performed on these test structures show a decrease of the reflection in that particular wavelength range for a flat front side. However, spectral response measurements of solar cells will be the only characterisation that can assure us that this decrease in reflection is inducing an increase of absorption in the silicon, as expected by simulation and not in the aluminium layer.

We present a comparison of three different technologies for the fabrication of micro-optical elements with arbitrary surfaces. We used direct laser writing in photoresist, binary mask lithography in combination with reactive ion etching in fused silica, and High-Energy- Beam-Sensitive (HEBS) glass graytone lithography in photoresist. We analyzed the efficiencies and the deflection angles of different elements in order to quantify the performance of the different technologies. We found that higher effencies can be achieved with refractive type elements, while precise deflection angles can be obtained more easily with diffractive elements.

We investigate dispersion properties of photonic crystal waveguides in a low-index material system. The modes above the light line, of a waveguide consisting of one row of missing holes (W1), exhibit high losses due to out-of-plane radiation. In contrast, the index-guided modes below the light line show moderate losses and we demonstrate both theoretically and experimentally that high dispersion is possible. Furthermore we investigate wider defect waveguides operated within the photonic band gap, where a mini-stopband with a very large suppression of transmission was found. The dispersion properties of these waveguides are discussed.

The realization of ultra low-loss dielectric reflection gratings with diffraction efficiencies between 7% and 0.02% is presented. By placing the grating beneath the highly reflective layerstack scattering was significantly reduced. This concept allows the all-reflective coupling of high laser radiation to high finesse cavities, thereby circumventing thermal effects caused by absorption in the substrate.