263 research outputs found
On the interaction of a single-photon wave packet with an excited atom
The interaction of a single-photon wave packet with an initially excited
two-level atom in free space is studied in semiclassical and quantum
approaches. It is shown that the final state of the field does not contain
doubly occupied modes. The process of the atom's transition to the ground state
may be accelerated, decelerated or even reversed by the incoming photon,
depending on parameters. The spectrum of emitted radiation is close to the sum
of the spectrum of the incoming single-photon wave packet and the natural line
shape, with small and complicated deviations.Comment: 17 pages, 5 figure
Revealing the properties of Chuyurmov-Gerasimenko's shallow sub-surface through CONSERT's measurements at grazing angles
International audienceThe aim of the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) is the characterization of the inner structure and electrical properties of the Chuyurmov-Gerasimenko's nucleus. The instrument will sound the comet's nucleus between the lander Philae at the comet's surface and the Rosetta main spacecraft. A coarse three-dimensional model of the complex dielectric permittivity inside the nucleus will be reconstructed from the whole set of data obtained during the first science phase [3]. The work presented here show how a limited set of data acquired at grazing angles during a single low altitude fly-by can be used to characterize the shallow sub-surface of the nucleus. The study is based on simulated data obtained by two different electromagnetic models: the accurate pseudo spectral time-domain method and a much faster ray-based approximation taking into account material and path-loss
Lyapunov Potential Description for Laser Dynamics
We describe the dynamical behavior of both class A and class B lasers in
terms of a Lyapunov potential. For class A lasers we use the potential to
analyze both deterministic and stochastic dynamics. In the stochastic case it
is found that the phase of the electric field drifts with time in the steady
state. For class B lasers, the potential obtained is valid in the absence of
noise. In this case, a general expression relating the period of the relaxation
oscillations to the potential is found. We have included in this expression the
terms corresponding to the gain saturation and the mean value of the
spontaneously emitted power, which were not considered previously. The validity
of this expression is also discussed and a semi-empirical relation giving the
period of the relaxation oscillations far from the stationary state is proposed
and checked against numerical simulations.Comment: 13 pages (including 7 figures) LaTeX file. To appear in Phys Rev.A
(June 1999
Imaging of THz waves in 2D photonic crystal structures embedded in a slab waveguide
We present space- and time-resolved simulations and measurements of single-cycle terahertz (THz) waves propagating through two-dimensional (2D) photonic crystal structures embedded in a slab waveguide. Specifically, we use a plane wave expansion technique to calculate the band structure and a time-dependent finite-element method to simulate the temporal evolution of the THz waves. Experimentally, we measure the space–time evolution of the THz waves through a coherent time-resolved imaging method. Three different structures are laser machined in LiNbO3 crystal slabs and analyzing the transmitted as well as the reflected THz waveforms allows determination of the bandgaps. Comparing the results with the calculated band diagrams and the time-dependent simulations shows that the experiments are consistent with 3D simulations, which include the slab waveguide geometry, the birefringence of the material, and a careful analysis of the excited modes within the band diagrams.Swiss National Science Foundation (project no. 200020-119934
Analytical Performance Evaluation of New DESI Enhancements for Targeted Drug Quantification in Tissue Sections
Desorption/ionization (DI)-mass spectrometric (MS) methods offer considerable advantages of rapidity and low-sample input for the analysis of solid biological matrices such as tissue sections. The concept of desorption electrospray ionization (DESI) offers the possibility to ionize compounds from solid surfaces at atmospheric pressure, without the addition of organic compounds to initiate desorption. However, severe drawbacks from former DESI hardware stability made the development of assays for drug quantification difficult. In the present study, the potential of new prototype source setups (High Performance DESI Sprayer and Heated Transfer Line) for the development of drug quantification assays in tissue sections was evaluated. It was demonstrated that following dedicated optimization, new DESI XS enhancements present promising options regarding targeted quantitative analyses. As a model compound for these developments, ulixertinib, an inhibitor of extracellular signal-regulated kinase (ERK) 1 and 2 was used
Structural and dynamic disorder, not ionic trapping, controls charge transport in highly doped conducting polymers
Doped organic semiconductors are critical to emerging device applications,
including thermoelectrics, bioelectronics, and neuromorphic computing devices.
It is commonly assumed that low conductivities in these materials result
primarily from charge trapping by the Coulomb potentials of the dopant
counter-ions. Here, we present a combined experimental and theoretical study
rebutting this belief. Using a newly developed doping technique, we find the
conductivity of several classes of high-mobility conjugated polymers to be
strongly correlated with paracrystalline disorder but poorly correlated with
ionic size, suggesting that Coulomb traps do not limit transport. A general
model for interacting electrons in highly doped polymers is proposed and
carefully parameterized against atomistic calculations, enabling the
calculation of electrical conductivity within the framework of transient
localisation theory. Theoretical calculations are in excellent agreement with
experimental data, providing insights into the disordered-limited nature of
charge transport and suggesting new strategies to further improve
conductivities
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