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Planar plasmonic lenses have attracted a great deal of interest over the last few years for their super-resolution focusing capabilites. These highly compact structures with dimensions of only a few micrometres allow for the focusing of light to sub-wavelength-sized spots with focal lengths reaching into the far-field. This offers opportunities for new methods in nanometrology; for example, applications in microscopic Mueller matrix ellipsometry setups. However, the conventional plasmonic lens is challenging to fabricate. We developed a new design for plasmonic lenses, which is called the inverted plasmonic lens, to accommodate the lithographic fabrication process. We used numerical simulations based on the finite element method in combination with particle swarm optimization to determine ideal parameter ranges and tolerances for the design of inverted plasmonic lenses for different wavelengths in the visible and near-infrared domain and focal lengths between 5 μm and 1 mm.

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Photonic integrated circuits (PICs) are revolutionizing nanotechnology, with far-reaching applications in telecommunications, molecular sensing, and quantum information. PIC designs rely on mature nanofabrication processes and readily available and optimised photonic components (gratings, splitters, couplers). Hybrid plasmonic elements can enhance PIC functionality (e.g., wavelength-scale polarization rotation, nanoscale optical volumes, and enhanced nonlinearities), but most PIC-compatible designs use single plasmonic elements, with more complex circuits typically requiring ab initio designs. Here we demonstrate a modular approach to post-processes off-the-shelf silicon-on-insulator (SOI) waveguides into hybrid plasmonic integrated circuits. These consist of a plasmonic rotator and a nanofocusser, which generate the second harmonic frequency of the incoming light. We characterize each component’s performance on the SOI waveguide, experimentally demonstrating intensity enhancements of more than 200 in an inferred mode area of 100 nm2, at a pump wavelength of 1320 nm. This modular approach to plasmonic circuitry makes the applications of this technology more practical.

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A round robin comparison of freeform form measurements was carried out by the project partners and stakeholders of a European metrology research project. Altogether six measuring instruments were considered: five different (pointwise and areal) optical devices and one tactile device. Three optical freeform surfaces were used for the comparison measurements, where two specimens were measured by five instruments and one specimen by four instruments. In this paper, the evaluation methods and results of this round robin are presented for the three freeform surfaces made from a temperature-stable material, Super Invar ®. The freeforms had diameters of 40 mm, 50 mm and 100 mm and best-fit radii of 39.75 mm (convex), 40.9 mm (convex) and 423.5 mm (concave). For comparison, the bilateral pointwise differences between the available measurements were calculated. The root-mean-square values of these differences ranged from 15 nm to 110 nm (neglecting spherical contributions) and provided an insight into the status of typical freeform measurement capabilities for optical surfaces.

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The paper presents the effect of mechanical mounting of optical reference elements on their surface shape. Optical reference surfaces are key elements when traceable, highly accurate and precise optical surface measurements are required. In order to calibrate measuring instruments and compare the metrological capabilities of different metrology institutes, universities and other stakeholders, the reference artefacts were developed. Different measurement instruments require a different way of mounting and the reference artefacts are supposed to be useful for reliable and repeatable calibration of a great majority of the instruments worldwide. However, not only their shape was critical, but also the way of mounting was crucial. FEM analyses followed by experiments have revealed an unacceptable surface shape error in the order of hundreds of nanometres in the case of the commonly used screw mount, even for low applied torques. Other mounting options, such as the collet chuck or the Morse taper, are examined by means of FEM analysis and verified by interferometric measurements. It is shown that only the Morse taper can fulfil the strict criterion of less than 30 nm for surface shape deviation due to mounting, which is required in optical surface shape metrology.

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Die Mikrowellensynthese ist ein essentieller Bestandteil der Fontänenuhren. Mit ihr werden die für die Zustandspräparation und die Anregung des Uhrenübergangs benötigten Mikrowellensignale erzeugt. Unsicherheiten in diesem Teilsystem wirken sich direkt auf die Gesamtunsicherheit der Fontänenuhren aus. Durch Anpassungen im Synthesizer-Design wurden die Unsicherheitsbeiträge der Mikrowellensynthese auf ein vernachlässigbares Niveau reduziert und im Rahmen einer neuen Evaluation verifiziert.

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Single‐photon sources (SPSs) based on quantum emitters hold promise in quantum radiometry as metrology standard for photon fluxes at the low light level. Ideally this requires control over the photon flux in a wide dynamic range, sub‐Poissonian photon statistics, and narrow‐band emission spectrum. In this work, a monochromatic SPS based on an organic dye molecule is presented, whose photon flux is traceably measured to be adjustable between 144 000 and 1320 000 photons per second at a wavelength of (785.6 ± 0.1) nm, corresponding to an optical radiant flux between 36.5 and 334 fW. The high purity of the single‐photon stream is verified, with a second‐order autocorrelation function at zero time delay below 0.1 throughout the whole range. Such molecule‐based SPS is hence used for the calibration of a single‐photon avalanche detector against a low‐noise analog photodiode traceable to the primary standard for optical radiant flux (i.e., the cryogenic radiometer). Due to the narrow bandwidth of the source, corrections to the detector efficiency arising from the spectral power distribution are negligible. With this major advantage, the developed device may finally realize a low‐photon‐flux standard source for quantum radiometry.

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Spectral responsivity (SR) measurements are a powerful technique to measure the opto-electronic properties of photovoltaic devices like solar cells or PV modules. Although the SR determination of solar cells is a common and established technique for many years, much more effort must be taken to determine the SR of PV modules due to their size. Significantly larger and more complex solar simulator must be used, which led to a variety of different measurement techniques, each with its own disadvantages. In this work we present SR and linearity measurements performed with an LED-based solar simulator, which is capable of measuring the SR of a whole PV module within a reasonable amount of time. The principal solar simulator characteristics with its advantages and challenges are presented, including the properties of the emitted spectrum and the homogeneity of the resulting light field. The evaluation of our method, which is performed at conditions close to standard test conditions (STC) and bears characteristics of a differential spectral responsivity (DSR), is presented and demonstrated on different silicon-based and thin film PV modules, respectively. With the ability to tune the spectral irradiance gradually while maintaining an AM1.5g-like spectrum, linearity measurements of the short-circuit current of PV modules have been performed and are presented as well.

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Solar simulators for PV modules often consist of several lamps arranged side by side to provide the irradiance necessary for PV module testing under standard test conditions. Since these simulators are no point sources, the angular distribution of the radiance emitted by the simulators can lead to systematic deviations in measured PV device’s performances. To quantify the opening angle of a solar simulator, pictures of a digital single-lens reflex (DSLR) camera and irradiance measurements of a CCD-array spectroradiometer were combined to derive its approximate spectral radiance distribution. We applied our technique to an LED-based solar simulator, where the radiance of 18 different LED colors could be examined separately and thus an approximation of the spectral radiance emitted by the simulator can be made. An angle of incidence of 15.6° has been observed for this system at the center of a PV module, raising to about 21.5° towards the edge of the test plane.

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Am LENA, in Kooperation mit der TUBS und der PTB, werden nanostrukturierte GMR-Mikrofarbfilter designt, entwickelt und gefertigt. In Kombination mit CCD oder CMOS Bildsensoren sollen damit effiziente spektroskopische Sensoren für Anwendungen in Medizin und Biologie entwickelt werden. Die GMR-Farbfilter basieren auf periodischen Subwellenlängen-Metallgittern in Kombination mit einer dielektrischen Wellenleiterschicht. Die Filterfunktion wird dabei pixel-spezifisch über die Strukturparameter (z.B. Gitterperiode oder Füllfaktor) angepasst.

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We show a novel method to derive best-fitting sample parameters and their uncertainties from measured Mueller matrices.
The nonoptimal treatment of depolarization in current approaches to evaluate Mueller matrix measurements may lead to systematic measurement errors and inadequate uncertainty estimations, particularly for surfaces with substantial depolarization. To overcome these issues, we develop improved analysis methods providing realistic uncertainty estimations and more reliable measurement results.
Commonly used merit functions treat depolarization of Mueller-ellipsometry measurements as a residual error in the optimization process. The best fit solution has the smallest overall depolarization. We propose to use depolarization to derive a weight-factor for each residual contribution to the merit-function.
Exploiting raw data provided by our Sentech SE 850 ellipsometer we include also measurement statistics in the merit function. With it, embedded into a Bayesian approach the best-fit values and their uncertainties are determined much more reliably and realistically.
We demonstrate the advantages of this new method analyzing both virtual and real measurement data.

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