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Triply positive charged ions of the isotope Th-229 (Th³⁺) are of particular interest as the basis for a high-precision optical clock. As the isotope is radioactive, it is only available in very small quantities and conventional methods for realising an ion source (for example by vaporisation) are not applicable in this case. PTB has now developed an apparatus for generating, cooling and storing Th³⁺ as recoil ions from the radioactive decay of U-233. A thin film of U-233 emits the desired ions into the vacuum, but with a high initial energy of more than 80 keV. By decelerating in high-purity helium gas, it is possible to collect the ions and transfer them to an ion trap. There they are stored together with Sr⁺ ions, which are cooled to a temperature in the millikelvin range using laser light. The coupling with the Sr ions also reduces the energy of the Th³⁺ to a value that is about 11 orders of magnitude below the starting energy after the U-233 decay. The stored Th³⁺ ions are now available at low energy for precision measurements of their resonance frequencies. This provides a basis for studying the properties and structure of this unusual isotope.

Optical properties of atmospheric aerosols, such as aerosol optical depth (AOD), are determined from solar radiation measurements using filter radiometers, known in such measurement applications as sun photometers. Here we present calibration of filter radiometers from the European branches of aerosol monitoring networks AERONET, GAW-PFR, and SKYNET with respect to their spectral irradiance responsivities. The calibrations were carried out at PTB within the framework of the EMPIR project 19ENV04 MAPP “Metrology for aerosol optical properties” using the tunable laser-based setup, TUable Lasers In Photometry (TULIP). The realization of the spectral responsivity measurements of the filter radiometers at the TULIP setup, results, uncertainty contributions and implications are discussed in this conference paper.

A new EURAMET Traceability Project “Traceability of the GAW-PFR reference Precision Filter Radiometers to the SI” was started in collaboration between PTB, Working Group 4.11 “Spectroradiometry” and PMOD/WRC. PMOD/WRC is designated by the World Meteorological Organisation (WMO) to operate the World aerosol Optical depth Research and Calibration Center (WORCC). WORCC is responsible for hosting the world reference for Aerosol Optical Depth (AOD), formed as a set of Precision Filter Radiometers (PFR). Furthermore, it operates the AOD monitoring network established within the frame of the Global Atmospheric Watch (GAW) program (GAW-PFR network). The WORCC mandate also encompasses to provide AOD traceability from its GAWPFR reference to other global and regional AOD monitoring networks. This is achieved through the Filter Radiometer comparison campaign held a PMOD/WRC every five years, and by collocating PFR travel standards at other network calibration sites (e.g. ACTRIS CARS). The collaboration between PTB and PMOD/WRC with respect to the SI-traceability of spectral solar irradiance of the PFR started in 2019 and continued in the framework of the EMPIR project 19ENV04 MAPP, “Metrology for aerosol optical properties”. The proposed project aims at providing SI-traceability to the global AOD monitoring community through comparisons with the GAWPFR reference, which is made up of a set of PFR instruments, of which one or more instruments will be annually calibrated at PTB.

Die Arbeitsgruppe 4.53 Solarmodule beteiligt sich im Rahmen eines DFG-Forschungsprojekts an der Untersuchung, wie die flächendeckende Installation von Photovoltaik (PV)-Anlagen das städtische Mikroklima im Freien und in Innenräumen hinsichtlich der thermischen Behaglichkeit der Einwohner und der Luftqualität beeinflusst. Projektleiter ist die Leibniz Universität Hannover und weiterer Projektpartner die Technische Universität Dresden.

Die Arbeitsgruppe 4.53 Solarmodule beteiligt sich seit Dezember 2023 an einem europäischen Vorhaben zur Entwicklung von Standardisierungsmethoden für das Ökodesign und die Energieverbrauchskennzeichnung von Photovoltaikprodukten.

Die Arbeitsgruppe 4.53 Solarmodule hat im Rahmen eines BMWK-Forschungsprojekts den bestehenden LED-Sonnensimulator grundlegend überarbeitet und an die Anforderungen moderner Solarmodule angepasst.

A working group of the Consultative Committee for Time and Frequency (CCTF), with the participation of PTB, has drawn up a plan for a future redefinition of the second based on the progress made with optical atomic clocks. The progress achieved and the improvements still required are being discussed in order to secure in the long term and to improve the quality of frequency measurements and time scales established today with cesium atomic clocks. A possible date for a redefinition is 2030.

PTB and NIST performed a comparison for high accuracy continuous wave optical power measurements in the kilowatt regime. The NIST carried out measurements with a power meter relying on photon momentum, while PTB performed the measurements with a modified off-the-shelf thermal power meter. The non-absorbing photon momentum measurement approach permits the two power meters to measure the same laser beam optical path simultaneously, resulting in a direct comparison of the meters supported by an optical system to accommodate differences in instrument settling times. The results show agreement within the expanded uncertainties for each instrument. NIST and PTB illustrate a degree of equivalence of 0.49% with an expanded uncertainty of 1.37% (k = 2) for an average result across all power levels.

Single photon emitters in hexagonal boron nitride have gathered a lot of attention due
to their favourable emission properties and the manifold of possible applications. Despite
extensive scientic effort, the exact atomic origin of these emitters has remained unkown
thus far. Recently, several studies have tied the emission in the yellow spectral region
to carbon-related defects, but the exact atomic structure of the defects remains elusive.
In this study, photoluminescence emission and excitation spectroscopy is performed on a
large number of emitters within this region. By comparison of the experimental data with
theoretical predictions, the origin of yellow single photon emission in hexagonal boron nitride is determined. Knowledge of this atomic structure and its optical properties is crucial for the reliable implementation of these emitters in quantum technologies.

Mithilfe von kurzwelliger und energiereicher UVC-Strahlung werden schon seit Jahrzehnten Oberflächen, Trinkwasser oder Raumluft desinfiziert. Dabei nutzt man aus, dass diese Strahlung Zellen schädigen kann – insbesondere diejenigen von Viren, Bakterien oder anderen Mikroorganismen. Allerdings kann sie auch Zellen in menschlichen Organen wie Haut und Auge schädigen. Die radiometrische Kalibrierung im Bereich der UV-Strahlung bei hohen Bestrahlungsstärken ist eine der Aufgaben im Fachbereich Photometrie und Spektroradiometrie der Physikalisch-Technischen Bundesanstalt (PTB). Das Hauptaugenmerk richtet sich dabei immer mehr auf sehr kurzwellige UVC-Strahlung. Verstärkt durch die Corona-Epidemie wird aktuell diskutiert, ob sogenannte Fern-UVC-Strahlung zwischen 200 nm und 240 nm, die nahezu nicht in Haut und Auge eindringt, auch offen strahlend und im öffentlichen Raum eingesetzt werden könnte. Allerdings lässt sich das Risiko für die Allgemeinbevölkerung noch nicht ausreichend abschätzen. Peter Sperfeld, Mitarbeiter der Arbeitsgruppe Spektroradiometrie in der PTB, hat als UV-Experte an einer Empfehlung der Strahlenschutzkommission der Bundesregierung mitgewirkt und unterstützt die Feststellung, dass die bisherigen Erkenntnisse noch nicht ausreichen, um einen Einsatz von Fern-UVC-Strahlung zur Desinfektion in Anwesenheit von Menschen zu befürworten.