Dissertation/Thesis Abstract

Einfluss von Geometrie und magnetischem Feld auf die Effizienz supraleitender Nanodraht-Einzelphotonendetektoren
by Lusche, Robert, Ph.D., Technische Universitaet Berlin (Germany), 2015, 137; 10717659
Abstract (Summary)

The aim of this thesis is to a gain deeper understanding of the single photon detection process in superconducting nanowire single-photon detectors (SNSPDs). A detailed knowledge of the physical principles and mechanisms which the detection process is based on helps to improve specific detector parameters and hence the suitability of such detectors for various applications. Several theoretical models of the detection process have been compared to the results of measurements of photon and dark count rates in meander-type TaN- and NbN-SNSPDs with different wire-widths in a broad range of wavelengths, transport currents and magnetic fields . In the first part of the thesis, measurements of the photon and dark count rates of TaN- and NbN-SNSPDs with varying wire width are described. For each meander spectra of the intrinsic detection efficiency (IDE) were derived. The IDE represents the probability that the SNSPD generates a measurable voltage pulse upon absorption of a photon. The recorded IDE spectra have shown a characteristic cut-off wavelength up to which photons were detected with a probability of 100 per cent. Furthermore it was found that the cut-off wavelengths increases linearly with the increase in the inverse wire width. This observation is best explained by the refined hot spot model. The second part of the thesis describes the influence of magnetic field on the photon and dark count rates of NbN-SNSPDs. In order to apply magnetic fields to the meanders a continuous-flow inset for mobile 4He storage dewars was constructed. It was shown for the first time, that the photon count rate exhibits a magnetic field dependence. Furthermore it could be shown that the measured dependence of the photon and dark count rate on the magnetic field is in good agreement with the theoretical model of vortex-assisted photon detection in narrow superconducting lines. Hence, within this thesis it could be confirmed that magnetic vortices are involved in the single photon detection mechanism for wavelengths larger than the cut-off wavelength. Quantitative comparison of this model with the experimentally derived dependencies of photon and dark count rates on the magnetic field have shown that dark counts predominantly occur in the bends while photon counts may occur in both bends and straight portions of the meander. The straight portions contribute to the photon count rate either at large applied currents or at large photon energies.

Indexing (document details)
Advisor: Dähne, Mario
Commitee: Hübers, Heinz-Wilhelm, Meyer, Hans-Georg
School: Technische Universitaet Berlin (Germany)
School Location: Germany
Source: DAI-C 81/1(E), Dissertation Abstracts International
Subjects: Electrical engineering, Nanotechnology, Electromagnetics
Keywords: Wire width, Magnetic field , Superconducting nanowire, Single-photon detectors
Publication Number: 10717659
ISBN: 9781392546574
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