Optics

For observation of aerosol properties, such as the essential climate variable aerosol optical depth (AOD), several measurement networks, such as AERONET, GAW-PFR and SKYNET, are established. The temperature coefficients of sun photometers from AERONET (AErosol Robotic NETwork) network are required to correct for varying ambient temperatures within the framework of the EMPIR project 19ENV04 MAPP “Metrology for aerosol optical properties”. Spectrally resolved measurement of the temperature dependency of the photometers were performed and are presented in this paper.

Here we present a compact LED-based source designed within the framework of the EMPIR project 19 ENV04 MAPP “Metrology for aerosol optical properties” for monitoring responsivities of the AERONET Europe radiometers. The aim of the task was to design an LED source flangeable to an integrating sphere that would allow to track responsivity changes of the network instruments. For this purpose the spectral flux of the source must cover the bands of the Cimel sun photometers used in this network and be stable and reproducible at a level of ~0,1%. The design includes 9 LEDs in surface-mount device (SMD) package, one for each band of the sun photometer, soldered on a printed circuit board (PCB). The temperature of the LEDs is accurately controlled by a Peltier device attached to the other side of the PCB. The LEDs are connected in series and operated in stabilized current (CC) mode. Several such LED boards have been built. The devices have been...

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...