Single-photon detectors are a pivotal component in photonic quantum technologies. A precise and comprehensive calibration of the inherent detection efficiency is of utmost importance to ensure the proper evaluation of the performance in view of the specific technological application of interest, such as the protection against security breaches in quantum cryptographic solutions. Here we report on a systematic study on and comprehensive analysis of the estimation of the inherent detection efficiency of two commercial single-photon detectors based on single-photon avalanche diodes (SPADs) for various mean photon numbers and at high laser pulse repetition rates using different techniques. We observed an unexpected and significant drop in the inherent detection efficiency at detection rates of 10 % and higher relative to the maximum detection rate. It is demonstrated that for data analysis a statistical model for the detection rate...

Solid immersion lenses (SILs) have the potential to enhance the single-photon emission properties of color centers in diamond, e.g., of germanium-vacancy (GeV-) centers, due to an increase of the photon extraction from the diamond. We present the successful generation of GeV-centers in bulk diamond, the fabrication of hemispherical SILs with GeV-centers using a focused ion beam (FIB) and the metrological characterization of the emission of the GeV-centers in SILs in terms of the spectral distribution, the single-photon purity, the saturation behavior, and the emitter’s excited state lifetime. We could verify a significant increase of the detector count rate for GeV-centers in SILs compared to those without a SIL. The singlephoton purity and detector count rate were measured for different excitation powers and were evaluated in a combined model. This allows the possibility to distinguish between the linear background emission and...

Jan Spichtinger, a PhD student from PTB, won this year’s award for the best young scientist at the 12th High Level Expert Meeting on Asphere Metrology. The “Ultrapräzise Oberflächenbearbeitung” e.V. (Ultraprecise Surface Processing) Competence Center (CC UPOB) held this meeting virtually on 15-16 March 2022. The event was rounded off with the presentation of the Young Scientist Award (YSA) which honors young scientists in the fields of high-precision surface manufacturing and metrology. The meeting’s audience that was made up of experts from these fields selected the PTB doctoral student because of his work on the high-accuracy form measurement of moderately curved optical surfaces. He presented his research under the title of “Stitching interferometry for moderately curved freeform surfaces” and went on to introduce a new measurement method called SCaLA (stitching interferometry with cavity length and angle measurement). This method is...