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News from the Annual Report (in German only)

 

Sparkle, as defined by ASTM E284 -17 Standard Terminology of Appearance is "the aspect of the appearance of a material that seems to emit or reveal tiny bright points of light that are strikingly brighter than their immediate surround and are made more apparent when a minimum of one of the contributors (observer, specimen, light source) is moved". Since the measurement of this visual texture is important for automotive, cosmetic or displays industries, a measurement scale need to be developed, so that traceability can be provided by national metrology institutes (NMI) or designated institutes. Some of them (PTB, METAS, CMI and CSIC) have defined the measurands for sparkle and have developed a photometric and image-based methodology to measure them. The specific objective of this research work is to test the existing capabilities of these NMIs to measure sparkle.

 

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The Supplementary Comparison COOMET.PR-S2 was carried out to ensure the correctness and comparability of angle of rotation of plane of polarization measured by the Participants of the comparison within the uncertainties claimed for their measuring facility.
COOMET.PR-S2 was conducted within the Regional Metrology Organization (RMO) "Euro-Asian Cooperation of National Metrological Institutions" known as COOMET and has the RMO project number of 438/RU/08.
The Comparison was piloted by the All-Russian Research Institute for Optical and Physical Measurements (VNIIOFI). Four NMIs from two RMOs (COOMET and EURAMET) participated in the comparison.
This report describes the measurement results of three quartz control plates (QCP) with different value of optical rotations at the wavelength of He-Ne laser (632.8 nm).

 

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Single-photon sources play an important role in several fields of research, e.g. in quantum key distribution and quantum-enhanced measurements. In radiometry, a single-photon source is very favorable, compared to a classical source, as a standard source for the detection efficiency calibration of single-photon detectors. Furthermore, such source is necessary to close the gap between classical and quantum radiometry, i.e. for the direct comparison between classical analogue detectors and single-photon detectors. We present the metrological realization of an absolute single-photon source based on a nitrogen-vacancy (NV-) center in nanodiamond, which is under development at the Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute. This source is traceable to national standards for optical radiant power and spectral power distribution via an unbroken chain in terms of its absolute spectral photon flux per wavelength and absolute spectral radiant flux per wavelength. This investigation includes a full determination of the measurement uncertainty. Besides this, we calculated the angular emission behavior of such a NV-center and compared the results with the measurement of the angle-dependent emission of an NV-center in nanodiamond.

 

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Single-photon sources play an important role in many of the emerging quantum technologies. Beside their implementation in quantum computing and quantum key distribution [1, 2], they are also interesting for the radiometry [1]. Ideally, single-photon sources have neither multi-photon emission nor background emission. Such a source has the potential to become a standard source in radiometry [2]. Moreover, a single-photon source is ideal for calibrating single-photon detectors, because of the omitted influence of the photon statistics on the calibration results [1]. For that reason, a single-photon source was developed at PTB, which photon flux is absolutely known and traceable to primary standards. 

 

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Single-photon sources have a wide field of implementation, e.g. in quantum key distribution, quantum computing, and quantum-enhanced optical measurements. Because of their negligible background and high suppression of multi-photon emission, single-photon sources have the potential to become a standard source in radiometry. Such source is necessary to close the gap between classical and quantum radiometry. The metrological realization of a room temperature absolute single-photon source based on a nitrogen-vacancy (NV-) center in nanodiamond was already carried out by the Physikalisch-Technische Bundesanstalt (PTB) via an unbroken traceability chain to the national standards [Rodiek, 2017].
In order to improve the understanding of the emission characteristics, we investigated the angular emission behavior of NV-centers in nanodiamonds. These NV-centers in nanodiamonds are located in the vicinity of a dielectric structure, namely a microscope cover glass. We will present the development of a model [based on Lukosz,1979] of the angular distribution of the emitted light. The angular dependent emission of NV-centers is measured by back focal plane imaging. Furthermore, the theoretical simulations of the radiation patterns are compared with the measurement of the angle dependent emission. The results will be shown at the symposium.

 

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Das Interesse an genauen und rückgeführten Messungen der Modulationstransferfunktion (MTF) von abbildenden Objektiven ist insbesondere für den Einsatz im Automotive-Bereich stark gestiegen. In einem gemeinsamen Projekt der beteiligten Partner soll die metrologische Basis für rückgeführte MTF-Messungen in der Industrie geschaffen werden. Dazu wurde in der Physikalisch-Technischen Bundesanstalt (PTB) eine Anlage realisiert, welche die MTF von Objektiven mittels Spalt-Spalt-Abtastung oder mit einer Kamera misst. Es wird eine Messunsicherheit von 0,01 (k=2) angestrebt.
Untersuchungen an der Anlage zur Messung der MTF werden vorgestellt, die sich mit der Stabilität der Lichtquelle und der Mechanik, sowie mit den Einflüssen der Objektausrichtung und des Auswerteverfahrens mittels CCD/CMOS-Kamera befassen. Experimentelle Ergebnisse werden Simulationen gegenübergestellt. Zusätzlich wird die Anlage in einem virtuellen Experiment modelliert, welches objektorientierte Programmierung mit optischem Ray Tracing kombiniert. Es berücksichtigt die Eigenschaften der Mechanik und des Prüflings und wird zur Abschätzung der Messunsicherheit und zur Optimierung der Anlage eingesetzt.

 

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In Wissenschaft und Technik werden vermehrt große optische Flächen eingesetzt, z. B. für astronomische Teleskopspiegel und in der Optik- und Automobilindustrie. Dabei werden auch zunehmend Asphären und Freiformflächen verwendet. Dies schafft einen Bedarf an einer hochgenauen und rückgeführten Formmessung von großen Optiken.
Wir entwickeln ein Konzept für die optische Formmessung an Flächen bis zu einer Größe von 1,5 m und mit Krümmungsradien größer 10 m. Interferometrische, deflektometrische und Wellenfront-basierte Messköpfe werden auf ihre Eignung untersucht. Während der Messung wird der jeweilige Messkopf verfahren und für stärker gekrümmte Prüflinge mit einer kardanischen Aufhängung bezüglich der Flächennormalen nachgeführt. Bei Stitching-Verfahren werden Messfehler mithilfe der Traceable Multiple Sensor-Methode [1] reduziert. Schnitte werden zu einer 3D-Topographie zusammengeführt. Zur Fehleranalyse wird ein virtuelles Instrument implementiert. Wir erläutern die Messprinzipien und zeigen erste Simulationsergebnisse.

 

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Für eine Vielzahl von optischen Anwendungen, wie z.B. bei adaptiven Optiken in der Astronomie, der optischen Formmessung, der Ophthalmologie oder für sub-Nanometer genaue Längenmessungen ist es notwendig, optische Wellenfronten möglichst genau (besser als ë/50) zu bestimmen. Hierfür wird von der PTB und der Optocraft GmbH innerhalb eines gemeinsamen TransMeT-Projektes eine rückführbare Kalibrierung von Wellenfrontsensoren (WS) entwickelt, welche auf dem Prinzip des Traceable Multisensor (TMS) Verfahrens basiert. Aufbauend auf der im letzten Jahr vorgestellten Charakterisierung mittels ebener Wellenfronten, stellen wir hier ein Verfahren vor, bei dem die Charakterisierung der WS mit gekrümmten Wellenfronten mit einem Radius bis zu ca. 0,5 m durchgeführt wird. Dies ermöglicht eine umfassendere Charakterisierung des WS: Neben der Referenzposition der Spots kann damit auch die Empfindlichkeit, sowie der systematische Sensorfehler in Abhängigkeit vom Wellenfrontgradienten bestimmt werden. Wir stellen den verwendeten Messaufbau vor und zeigen erste Messergebnisse. Anschließend diskutieren wir unterschiedliche Einflussfaktoren auf die Messungen sowie die Justage des Wellenfrontsensors.

 

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The assumption that the reflectance of white diffuse reflectance standards is identical to that of the perfect reflecting diffuser (PRD) allows these standards to be used to characterize reflectance or radiance factors of any surface at any irradiation/collection geometry simply by comparison. However, this assumption is only true within certain limits, and, for some applications, requirements may be out of those limits. PTB and IO-CSIC have studied the variation of the reflectance with respect to the bidirectional geometry for the four most typical white diffuse materials (barium sulfate, opal glass, ceramic and Spectralon), at in- and out-of plane geometries and at spectral range from 380 nm to 1700 nm. We have defined descriptors in order to more clearly quantify the spectral reflectance variation with the bidirectional geometries. The values obtained for these descriptors have been separately presented for the visible and near infrared spectral ranges. In both spectral ranges, deviations of white diffuse reflectance standards with respect to the PRD were found, regarding both Lambertian behaviour and spectral constancy. The observed deviation from the BRDF is in general very large for high incidence and collection angles (reaching in many cases 20%). Therefore, it is not possible to assume Lambertianity in standards at those geometries when calibrating

 

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The uncertainty for photometric responsivity calibrated with the tunable lasers in photometry setup (TULIP) at Physikalisch-Technische Bundesanstalt (PTB) is presented. The measurement and the uncertainty calculation presented were done in preparation for the upcoming new traceability chain for luminous intensity at PTB. Regarding the new traceability a comprehensive uncertainty calculation is needed to take into account all steps of the traceability chain. The components of the measurement model are described and the correction factor for bandwidth and the inclusion of correlations are evaluated in detail. Assumptions that can help accessing unknown spectral correlations are described and their effect on the measurement uncertainty of photometric responsivity is calculated.

 

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