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Aktuelle Forschungsnachrichten und Nachrichten aus dem Jahresbericht

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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Spectroscopic Mueller matrix ellipsometry is a promising tool for the characterization of nanostruc-tured surfaces. Direct optical measurements of samples with geometrical dimensions smaller than the incident wavelength are inherently limited by the classical resolution limit. However, as an indi-rect measurement technique, this limit does not apply to ellipsometry. In this contribution, we in-vestigated the influence of manipulations of the near-field on the off-diagonal Mueller matrix ele-ments. We designed and fabricated individual resist nanostructures on a silicon wafer. The struc-tures possess distinct geometrical features in the range from several nanometers to a few microm-eters and were produced by electron beam lithography. We performed spectroscopic measure-ments with a commercial ellipsometer to determine the Mueller matrices of the samples. In addi-tion, nanosized silicon carbide grating structures were examined. Using a Finite Element software, we compared the measurements to simulations of the Mueller matrices to identify geometrical features.

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The range of possible implementations of single-photon sources in quantum information processing is rapidly growing. In order to achieve high accuracy and metrological traceability, we need reliable methods for their absolute characterization. Furthermore, single-photon emitters could be implemented as a standard source for the detection efficiency calibration of single-photon detectors. The precise measurement of small photon fluxes requires sources with high efficiency, narrow bandwidth and high single-photon purity. A promising candidate, which meets all these criteria, is an InGaAs quantum dot embedded in a deterministic photonic structure. We present measurements of the photon flux, the emission characteristics and the second-order correlation function of the InGaAs/GaAs single-photon source. The spectral filtering of the emission is realized by two bandpass filters, each having a full width at half maximum of 0.5 nm and a transmission of about 90 %. In contrast to the standard filtering method with a monochromator, our method reduces the photon losses, thus resulting in high count rates combined with high single-photon purity.

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Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for the generation of coordinated universal time (UTC). At present, more than 12 timing laboratories around the world use SAtellite Time and Ranging Equipment (SATRE) modems in TWSTFT operations and contribute data for the realization of UTC. The advantages of TWSTFT are its small calibration uncertainty (≤1.0 ns if the link is calibrated with a TWSTFT mobile station) and its long-term link stability. However, the precision of SATRE TWSTFT in the operational networks is degraded by a daily variation pattern (diurnal) in the TWSTFT results. The diurnal with varying amplitude appears virtually in all SATRE TWSTFT links. The observed peak-to-peak variation of the diurnals can reach 2.0 ns in some cases. So far, studies on the sources of the diurnal have not provided conclusive understanding of the diurnal's dominant origin.

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Single-photon sources are set to be a fundamental tool for metrological applications as well as for quantum information related technologies. Because of their upcoming widespread dissemination, the need for their characterization and standardization is becoming of the utmost importance. Here, we illustrate a strategy to provide a quantitative estimate of the multi-photon component of a single-photon source, showing the results achieved in a pilot study for the measurement of the second-order autocorrelation function g(2)(0) of a low-noise CW heralded single photon source prototype (operating at telecom wavelength λ = 1550 nm) realized in INRiM. The results of this pilot study, involving INRiM, NPL and PTB, will help to build a robust and unambiguous procedure for the characterization of the emission of a single-photon source.

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Bericht über den Stand der pränormativen Aktivitäten in CIE JTC 12 "The measurement of sparkle and graininess" und über neuartige definierte Proben zur Charakterisierung von Messapparaturen und -verfahren.

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We present the concept of a new setup, which combines two different sampling methods to measure the modulation transfer function of camera objectives. The development process with the goal of reaching a measurement uncertainty of 0.01 (k=2) is supported by optical ray tracing simulations in addition to the geometrical modeling of the system.

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