Logo PTB

Latest scientific news and
News from the Annual Report (in German only)

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.

[ more ]

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.

[ more ]

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.

[ more ]

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.

[ more ]

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.

[ more ]

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.

[ more ]

Die AG 4.51 Reflexion und Transmission (https://www.ptb.de/cms/ptb/fachabteilungen/abt4/fb-45/ag-451.html) des Fachbereichs 4.5 Angewandte Radiometrie der PTB Braunschweig betreibt im Arbeitsbereich der gerichteten Reflexions- und Transmissionsmessungen eine Referenzapparatur, die einen nominellen Wellenlängenbereich von 200 nm bis maximal 20 m abdeckt. Zur Erzeugung der Messtrahlung oberhalb von ca. 3,5 m stehen breitbandige thermische Strahler sowie in relativ weiten spektralen Bereichen durchstimmbare Bleisalzdiodenlaser zur Verfügung. Letztere besitzen im Vergleich zu den thermischen Strahlungsquellen mit einigen mW eine höhere spektrale Ausgangsleistung, sind allerdings in der Handhabung sehr komplex. So müssen die Laserdioden mittels eines evakuierten Stirling-Kühlsystems bei Temperaturen von einigen 10K betrieben werden. Die Wellenlängenselektion erfolgt dann über die Variation von Diodenstrom und Arbeitstemperatur.

[ more ]

Diffuse reflectance measurements in sphere geometries are usually performed using a single photodetector. However measurements of graininess require also spatial resolution, thus they are performed using a radiometric camera attached to the integrating sphere. The usually applied measurement geometry is d:0°. When performing such measurements on glossy samples, the phenomenon of gloss exclusion can directly be observed: a dark area corresponding to the specular excluded solid angle. METAS and PTB have performed a systematic study on a set of samples having different values of gloss, lightness, and colour, using two different measurement setups. It was found that the size of the dark area could be calculated using geometric relations of the measurement setup. Furthermore, the reflectance factor of the dark area, compared to its surround can be correlated with the gloss value of the sample: the higher the gloss of the sample, the greater the difference between the dark area and its surround.

[ more ]

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.

[ more ]

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).

[ more ]