339 research outputs found
Numerical simulation of drop impact and rebound phenomena on smooth and micro-structured hydrophobic surfaces
Numerical and experimental analysis of local flow phenomena in laminar Taylor flow in a square mini-channel
Coherent Manipulation of Quantum Delta-kicked Dynamics: Faster-than-classical Anomalous Diffusion
Large transporting regular islands are found in the classical phase space of
a modified kicked rotor system in which the kicking potential is reversed after
every two kicks. The corresponding quantum system, for a variety of system
parameters and over long time scales, is shown to display energy absorption
that is significantly faster than that associated with the underlying classical
anomalous diffusion. The results are of interest to both areas of quantum chaos
and quantum control.Comment: 6 pages, 4 figures, to appear in Physical Review
Optical properties of (AlxGa1−x)0.52In0.48P at the crossover from a direct-gap to an indirect-gap semiconductor
The optical properties and the dynamics of excitons and the electron-hole plasma have been studied in disordered (AlxGa1−x)0.52In0.48P near to the direct-to-indirect band gap crossover. In particular we have investigated three epitaxial layers grown by solid-source molecular beam epitaxy with varying Al content x. Two of them have compositions in the immediate vicinity of the crossover point, the other is assigned to the indirect-gap regime. Both direct and indirect recombination processes contribute to the photon emission from the material. Since the relative importance of the different recombination processes depends strongly on temperature, excitation intensity, and excitation pulse duration, the processes can be identified by changing these parameters. As a result, we can determine the relative alignment of the conduction band minima and the distribution of the electrons among them. At high excitation levels the two crossover samples show stimulated emission at a photon energy of ∼2.29 eV, i.e., in the green spectral range. Using the variable stripe length method, we find an optical gain of up to ∼600 cm−1 at excitation levels of ∼350 kW/cm2.Stimulated emission involves direct recombination. This conclusion is reached from the experiments and from line-shape modeling, including a self-consistent treatment of populations and renormalization of the conduction band minima
Real-time dynamics of the formation of hydrated electrons upon irradiation of water clusters with extreme ultraviolet light
Free electrons in a polar liquid can form a bound state via interaction with the molecular environment. This so-called hydrated electron state in water is of fundamental importance e.g.~in cellular biology or radiation chemistry. Hydrated electrons are highly reactive radicals that can either directly interact with DNA or enzymes, or form highly excited hydrogen (H∗) after being captured by protons. Here, we investigate the formation of the hydrated electron in real-time employing XUV femtosecond pulses from a free electron laser, in this way observing the initial steps of the hydration process. Using time-resolved photoelectron spectroscopy we find formation timescales in the low picosecond range and resolve the prominent dynamics of forming excited hydrogen states
Control of Dynamical Localization
Control over the quantum dynamics of chaotic kicked rotor systems is
demonstrated. Specifically, control over a number of quantum coherent phenomena
is achieved by a simple modification of the kicking field. These include the
enhancement of the dynamical localization length, the introduction of classical
anomalous diffusion assisted control for systems far from the semiclassical
regime, and the observation of a variety of strongly nonexponential lineshapes
for dynamical localization. The results provide excellent examples of
controlled quantum dynamics in a system that is classically chaotic and offer
new opportunities to explore quantum fluctuations and correlations in quantum
chaos.Comment: 9 pages, 7 figures, to appear in Physical Review
Reconstruction of attosecond pulses in the presence of interfering dressing fields using a 100 kHz laser system at ELI-ALPS
Intensity dependence of multiple orbital contributions and shape resonance in high-order harmonic generation of aligned N molecules}
We report measurements and theoretical simulations of high-order harmonic
generation (HHG) in aligned N molecules using a 1200-nm intense laser field
when the generating pulse is perpendicular to the aligning one. With increasing
laser intensity, the minimum in the HHG spectra first shifts its position and
then disappears. Theoretical simulations including the macroscopic propagation
effects in the medium reproduce these observations and the disappearance of the
minimum is attributed to the additional contribution of HHG from inner
orbitals. We also predict that the well-known shape resonance in the
photoionization spectra of N should exist in the HHG spectra. It is most
clearly seen when the generating laser is parallel to the aligning one, and
disappears gradually as the angle between the two lasers increases. No clear
evidence of this shape resonance has been reported so far when using lasers
with different wavelengths. Further experimentation is needed to draw
conclusions.Comment: 8 pages, 4 figure
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