48,861 research outputs found
Control of recollision wave packets for molecular orbital tomography using short laser pulses
The tomographic imaging of arbitrary molecular orbitals via high-order
harmonic generation requires that electrons recollide from one direction only.
Within a semi-classical model, we show that extremely short phase-stabilized
laser pulses offer control over the momentum distribution of the returning
electrons. By adjusting the carrier-envelope phase, recollisions can be forced
to occur from mainly one side, while retaining a broad energy spectrum. The
signatures of the semi-classical distributions are observed in harmonic spectra
obtained by numerical solution of the time-dependent Schr\"{o}dinger equation.Comment: 8 pages, 4 figures; v2: Added some extra clarifications; v3: minor
grammatical change
Konrad-Thaler-Gedächtnispreis der Arachnologischen Gesellschaft
Erstverleihung im Rahmen des Treffens der deutschsprachigen Arachnologen in Halle am 15.09.200
An Efficient Beam Steerable Antenna Array Concept for Airborne Applications
Deployment of a satellite borne, steerable antenna array with higher directivity and gain in Low Earth Orbit makes sense to reduce ground station complexity and cost, while still maintaining a reasonable link budget. The implementation comprises a digitally beam steerable phased array antenna integrated with a complete system, comprising the antenna, hosting platform, ground station, and aircraft based satellite emulator to facilitate convenient aircraft based testing of the antenna array and ground-space communication link. This paper describes the design, development and initial successful interim testing of the various subsystems. A two element prototype used in this increases the signal-to-noise ratio (SNR) by 3 dB which is corresponding to more than 10 times better bit error rate (BER)
Exploring the electron density in plasmas induced by extreme ultraviolet radiation in argon
The new generation of lithography tools use high energy EUV radiation which
ionizes the present background gas due to photoionization. To predict and
understand the long term impact on the highly delicate mirrors It is essential
to characterize these kinds of EUV-induced plasmas. We measured the electron
density evolution in argon gas during and just after irradiation by a short
pulse of EUV light at 13.5 nm by applying microwave cavity resonance
spectroscopy. Dependencies on EUV pulse energy and gas pressure have been
explored over a range relevant for industrial applications.
Our experimental results show that the maximum reached electron density
depends linearly on pulse energy. A quadratic dependence - caused by
photoionization and subsequent electron impact ionization by free electrons -
is found from experiments where the gas pressure is varied. This is
demonstrated by our theoretical estimates presented in this manuscript as well.Comment: submitted to J. Phys. D. 16 pages, 8 figure
Surface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots
On-chip quantum information processing requires controllable quantum light
sources that can be operated on-demand at high-speeds and with the possibility
of in-situ control of the photon emission wavelength and its optical
polarization properties. Here, we report on the dynamic control of the optical
emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio
frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of
a piezoelectric lithium niobate crystal equipped with a SAW delay line onto
which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like
exciton localization centers induced by compositional fluctuations within the
InGaN nanoshell were identified using stroboscopic micro-photoluminescence
(micro-PL) spectroscopy. They exhibit narrow and almost fully linearly
polarized emission lines in the micro-PL spectra and a pronounced anti-bunching
signature of single photon emission in the photon correlation experiments. When
the nanowire is perturbed by the propagating SAW, the embedded QD is
periodically strained and its excitonic transitions are modulated by the
acousto-mechanical coupling, giving rise to a spectral fine-tuning within a
~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be
further combined with spectral detection filtering for temporal control of the
emitted photons. The effect of the SAW piezoelectric field on the QD charge
population and on the optical polarization degree is also observed. The
advantage of the acousto-optoelectric over other control schemes is that it
allows in-situ manipulation of the optical emission properties over a wide
frequency range (up to GHz frequencies).Comment: arXiv admin note: text overlap with arXiv:1902.0791
Time-and-motion tool for the assessment of working time in tuberculosis laboratories: a multicentre study
SETTING: Implementation of novel diagnostic assays in tuberculosis (TB) laboratory diagnosis requires effective management of time and resources. OBJECTIVE: To further develop and assess at multiple centres a time-and-motion (T&M) tool as an objective means for recording the actual time spent on running laboratory assays. DESIGN: Multicentre prospective study conducted in six European Union (EU) reference TB laboratories. RESULTS: A total of 1060 specimens were tested using four laboratory assays. The number of specimens per batch varied from one to 60; a total of 64 recordings were performed. Theoretical hands-on times per specimen (TTPS) in h:min:s for Xpert® MTB/RIF, mycobacterial interspersed repetitive unit-variable number of tandem repeats genotyping, Ziehl-Neelsen staining and manual fluorescence microscopy were respectively 00:33:02 ± 00:12:32, 00:13:34 ± 00:03:11, 00:09:54 ± 00:00:53 and 00:06:23 ± 00:01:36. Variations between laboratories were predominantly linked to the time spent on reporting and administrative procedures. Processing specimens in batches could help save time in highly automated assays (e.g., line-probe) (TTPS 00:14:00 vs. 00:09:45 for batches comprising 7 and 31 specimens, respectively). CONCLUSIONS: The T&M tool can be considered a universal and objective methodology contributing to workload assessment in TB diagnostic laboratories. Comparison of workload between laboratories could help laboratory managers justify their resource and personnel needs for the implementation of novel, time-saving, cost-effective technologies, as well as identify areas for improvement
Weak Localization Thickness Measurements of Si:P Delta-Layers
We report on our results for the characterization of Si:P delta-layers grown
by low temperature molecular beam epitaxy. Our data shows that the effective
thickness of a delta-layer can be obtained through a weak localization analysis
of electrical transport measurements performed in perpendicular and parallel
magnetic fields. An estimate of the diffusivity of phosphorous in silicon is
obtained by applying this method to several samples annealed at 850 Celsius for
intervals of zero to 15 minutes. With further refinements, this may prove to be
the most precise method of measuring delta-layer widths developed to date,
including that of Secondary Ion Mass Spectrometry analysis
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