1,957 research outputs found
Attosecond two-photon interferometry for doubly excited states of helium
We show that the correlation dynamics in coherently excited doubly excited
resonances of helium can be followed in real time by two-photon interferometry.
This approach promises to map the evolution of the two-electron wave packet
onto experimentally easily accessible non-coincident single electron spectra.
We analyze the interferometric signal in terms of a semi-analytical model which
is validated by a numerical solution of the time-dependent two-electron
Schr\"odinger equation in its full dimensionality.Comment: 5 pages, 4 figure
Probing Electron Correlation via Attosecond XUV Pulses in the Two-Photon Double Ionization of Helium
Recent experimental developments of high-intensity, short-pulse XUV light
sources are enhancing our ability to study electron-electron correlations. We
perform time-dependent calculations to investigate the so-called "sequential"
regime (photon energy above 54.4 eV) in the two-photon double ionization of
helium. We show that attosecond pulses allow to induce and probe angular and
energy correlations of the emitted electrons. The final momentum distribution
reveals regions dominated by the Wannier ridge break-up scenario and by
post-collision interaction.Comment: 4 pages, 5 figure
Nano-wires with surface disorder: Giant localization lengths and dynamical tunneling in the presence of directed chaos
We investigate electron quantum transport through nano-wires with one-sided
surface roughness in the presence of a perpendicular magnetic field.
Exponentially diverging localization lengths are found in the
quantum-to-classical crossover regime, controlled by tunneling between regular
and chaotic regions of the underlying mixed classical phase space. We show that
each regular mode possesses a well-defined mode-specific localization length.
We present analytic estimates of these mode localization lengths which agree
well with the numerical data. The coupling between regular and chaotic regions
can be determined by varying the length of the wire leading to intricate
structures in the transmission probabilities. We explain these structures
quantitatively by dynamical tunneling in the presence of directed chaos.Comment: 15 pages, 12 figure
Tailored high-contrast attosecond electron pulses for coherent excitation and scattering
Temporally shaping the density of electron beams using light forms the basis for a wide range of established and emerging technologies, including free-electron lasers and attosecond electron microscopy. The modulation depth of compressed electron pulses is a key figure of merit limiting applications. In this work, we present an approach for generating background-free attosecond electron pulse trains by sequential inelastic electron-light scattering. Harnessing quantum interference in the fractional Talbot effect, we suppress unwanted background density in electron compression by several orders of magnitude. Our results will greatly enhance applications of coherent electron-light scattering, such as stimulated cathodoluminescence and streaking
Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation
We present indications of thermalization and cooling of quasi-particles, a
precursor for quantum condensation, in a plasmonic nanoparticle array. We
investigate a periodic array of metallic nanorods covered by a polymer layer
doped with an organic dye at room temperature. Surface lattice resonances of
the array---hybridized plasmonic/photonic modes---couple strongly to excitons
in the dye, and bosonic quasi-particles which we call
plasmon-exciton-polaritons (PEPs) are formed. By increasing the PEP density
through optical pumping, we observe thermalization and cooling of the strongly
coupled PEP band in the light emission dispersion diagram. For increased
pumping, we observe saturation of the strong coupling and emission in a new
weakly coupled band, which again shows signatures of thermalization and
cooling.Comment: 8 pages, 5 figures including supplemental material. The newest
version includes new measurements and corrections to the interpretation of
the result
Nano-wires with surface disorder: Giant localization lengths and quantum-to-classical crossover
We investigate electronic quantum transport through nano-wires with one-sided
surface roughness. A magnetic field perpendicular to the scattering region is
shown to lead to exponentially diverging localization lengths in the
quantum-to-classical crossover regime. This effect can be quantitatively
accounted for by tunneling between the regular and the chaotic components of
the underlying mixed classical phase space.Comment: 4 pages, 3 figures; final version (including added references
Structural dynamics probed by high-coherence electron pulses
Ultrafast measurement technology provides essential contributions to our understanding of the properties and functions of solids and nanostructures. Atomic-scale vistas with ever-growing spatial and temporal resolution are offered by methods based on short pulses of x-rays and electrons. Time-resolved electron diffraction and microscopy are among the most powerful approaches to investigate nonequilibrium structural dynamics. In this article, we discuss recent advances in ultrafast electron imaging enabled by significant improvements in the coherence of pulsed electron beams. Specifically, we review the development and first application of ultrafast low-energy electron diffraction for the study of structural dynamics at surfaces, and discuss novel opportunities for ultrafast transmission electron microscopy facilitated by laser-triggered field-emission sources. These and further developments will render coherent electron beams an essential component in future ultrafast nanoscale imaging
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