1,060 research outputs found
Broadening of hot-spot response spectrum of superconducting NbN nanowire single-photon detector with reduced nitrogen content
The spectral detection efficiency and the dark count rate of superconducting
nanowire single-photon detectors (SNSPD) has been studied systematically on
detectors made from thin NbN films with different chemical compositions.
Reduction of the nitrogen content in the 4 nm thick NbN films results in a more
than two orders of magnitude decrease of the dark count rates and in a red
shift of the cut-off wavelength of the hot-spot SNSPD response. The observed
phenomena are explained by an improvement of uniformity of NbN films that has
been confirmed by a decrease of resistivity and an increase of the ratio of the
measured critical current to the depairing current. The latter factor is
considered as the most crucial for both the cut-off wavelength and the dark
count rates of SNSPD. Based on our results we propose a set of criteria for
material properties to optimize SNSPD in the infrared spectral region.Comment: 15 pages, 6 figure
Transfer ionization and its sensitivity to the ground-state wave function
We present kinematically complete theoretical calculations and experiments
for transfer ionization in HHe collisions at 630 keV/u. Experiment and
theory are compared on the most detailed level of fully differential cross
sections in the momentum space. This allows us to unambiguously identify
contributions from the shake-off and two-step-2 mechanisms of the reaction. It
is shown that the simultaneous electron transfer and ionization is highly
sensitive to the quality of a trial initial-state wave function
Cloud detection and classification based on MAX-DOAS observations
Multi-axis differential optical absorption spectroscopy (MAX-DOAS)
observations of aerosols and trace gases can be strongly influenced by
clouds. Thus, it is important to identify clouds and characterise their
properties. In this study we investigate the effects of clouds on several
quantities which can be derived from MAX-DOAS observations, like radiance, the colour index (radiance ratio at two selected wavelengths), the
absorption of the oxygen dimer O<sub>4</sub> and the fraction of inelastically
scattered light (Ring effect). To identify clouds, these quantities can be
either compared to their corresponding clear-sky reference values, or their
dependencies on time or viewing direction can be analysed. From the
investigation of the temporal variability the influence of clouds can be
identified even for individual measurements. Based on our investigations we
developed a cloud classification scheme, which can be applied in a flexible
way to MAX-DOAS or zenith DOAS observations: in its simplest version, zenith
observations of the colour index are used to identify the presence of clouds
(or high aerosol load). In more sophisticated versions, other
quantities and viewing directions are also considered, which allows
subclassifications like, e.g., thin or thick clouds, or fog. We applied our
cloud classification scheme to MAX-DOAS observations during the
Cabauw intercomparison campaign of Nitrogen Dioxide measuring instruments
(CINDI)
campaign in the Netherlands in summer 2009 and found very good agreement
with sky images taken from the ground and backscatter profiles from a lidar
- …