1,039 research outputs found
"Single-cycle" ionization effects in laser-matter interaction
We investigate numerically effects related to ``single-cycle'' ionization of
dense matter by an ultra-short laser pulse. The strongly non-adiabatic response
of electrons leads to generation of a megagauss steady magnetic field in
laser-solid interaction. By using two-beam interference, it is possible to
create periodic density structures able to trap light and to generate
relativistic ionization frontsComment: 12 pages, 6 figures, to be published in Laser and Particle Beam
Fast magnetic reconnection in laser-produced plasma bubbles
Recent experiments have observed magnetic reconnection in
high-energy-density, laser-produced plasma bubbles, with reconnection rates
observed to be much higher than can be explained by classical theory. Based on
fully kinetic particle simulations we find that fast reconnection in these
strongly driven systems can be explained by magnetic flux pile-up at the
shoulder of the current sheet and subsequent fast reconnection via two-fluid,
collisionless mechanisms. In the strong drive regime with two-fluid effects, we
find that the ultimate reconnection time is insensitive to the nominal system
Alfven time.Comment: 5 pages, 4 figures, accepted by Phys. Rev. Let
Primordial helium recombination II: two-photon processes
Interpretation of precision measurements of the cosmic microwave background
(CMB) will require a detailed understanding of the recombination era, which
determines such quantities as the acoustic oscillation scale and the Silk
damping scale. This paper is the second in a series devoted to the subject of
helium recombination, with a focus on two-photon processes in He I. The
standard treatment of these processes includes only the spontaneous two-photon
decay from the 2^1S level. We extend this treatment by including five
additional effects, some of which have been suggested in recent papers but
whose impact on He I recombination has not been fully quantified. These are:
(i) stimulated two-photon decays; (ii) two-photon absorption of redshifted HeI
line radiation; (iii) two-photon decays from highly excited levels in HeI (n^1S
and n^1D, with n>=3); (iv) Raman scattering; and (v) the finite width of the
2^1P^o resonance. We find that effect (iii) is highly suppressed when one takes
into account destructive interference between different intermediate states
contributing to the two-photon decay amplitude. Overall, these effects are
found to be insignificant: they modify the recombination history at the level
of several parts in 10^4.Comment: 19 pages, 11 figures, to be submitted to PR
Three-dimensional Gross-Pitaevskii solitary waves in optical lattices: stabilization using the artificial quartic kinetic energy induced by lattice shaking
In this Letter, we show that a three-dimensional Bose-Einstein solitary wave
can become stable if the dispersion law is changed from quadratic to quartic.
We suggest a way to realize the quartic dispersion, using shaken optical
lattices. Estimates show that the resulting solitary waves can occupy as little
as -th of the Brillouin zone in each of the three directions and
contain as many as atoms, thus representing a \textit{fully
mobile} macroscopic three-dimensional object.Comment: 8 pages, 1 figure, accepted in Phys. Lett.
Focusing of Intense Subpicosecond Laser Pulses in Wedge Targets
Two dimensional particle-in-cell simulations characterizing the interaction
of ultraintense short pulse lasers in the range 10^{18} \leq I \leq 10^{20}
W/cm^{2} with converging target geometries are presented. Seeking to examine
intensity amplification in high-power laser systems, where focal spots are
typically non-diffraction limited, we describe key dynamical features as the
injected laser intensity and convergence angle of the target are systematically
varied. We find that laser pulses are focused down to a wavelength with the
peak intensity amplified by an order of magnitude beyond its vacuum value, and
develop a simple model for how the peak location moves back towards the
injection plane over time. This performance is sustained over hundreds of
femtoseconds and scales to laser intensities beyond 10^{20} W/cm^{2} at 1 \mu m
wavelength.Comment: 5 pages, 6 figures, accepted for publication in Physics of Plasma
Collimated electron jets by intense laser beam-plasma surface interaction under oblique incidence
Oblique incidence of a p-polarized laser beam on a fully ionized plasma with a low density plasma corona is investigated numerically by Particle-In-Cell and Vlasov simulations in two dimensions. Energetic electrons which propagate into the plasma corona in front of the target are observed. The fast electrons are collimated by quasi-steady magnetic fields. The magnetic fields enhance the penetration depth of the electrons into the corona. A scaling law for the angle of the ejected electrons with incident laser intensity is given
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