1,043 research outputs found
Features of ion acceleration by circularly polarized laser pulses
The characteristics of a MeV ion source driven by superintense, ultrashort
laser pulses with circular polarization are studied by means of
particle-in-cell simulations. Predicted features include high efficiency, large
ion density, low divergence and the possibility of femtosecond duration. A
comparison with the case of linearly polarized pulses is made.Comment: 4 pages, 4 figure
Efficiency of radiation friction losses in laser-driven "hole boring" of dense targets
In the interaction of laser pulses of extreme intensity () with high-density, thick plasma targets, simulations show
significant radiation friction losses, in contrast to thin targets for which
such losses are negligible. We present an analytical calculation, based on
classical radiation friction modeling, of the conversion efficiency of the
laser energy into incoherent radiation in the case when a circularly polarized
pulse interacts with a thick plasma slab of overcritical initial density. By
accounting for three effects including the influence of radiation losses on the
single electron trajectory, the global `hole boring' motion of the laser-plasma
interaction region under the action of radiation pressure, and the
inhomogeneity of the laser field in both longitudinal and transverse direction,
we find a good agreement with the results of three-dimensional particle-in-cell
simulations. Overall, the collective effects greatly reduce radiation losses
with respect to electrons driven by the same laser pulse in vacuum, which also
shift the reliability of classical calculations up to higher intensities.Comment: 15 pages, 3 figure
Quantum effects on radiation friction driven magnetic field generation
Radiation losses in the interaction of superintense circularly polarized
laser pulses with high-density plasmas can lead to the generation of strong
quasistatic magnetic fields via absorption of the photon angular momentum (so
called inverse Faraday effect). To achieve the magnetic field strength of
several Giga Gauss laser intensities W/cm are required
which brings the interaction to the border between the classical and the
quantum regimes. We improve the classical modeling of the laser interaction
with overcritical plasma in the "hole boring" regime by using a modified
radiation friction force accounting for quantum recoil and spectral cut-off at
high energies. The results of analytical calculations and three-dimensional
particle-in-cell simulations show that, in foreseeable scenarios, the quantum
effects may lead to a decrease of the conversion rate of laser radiation into
high-energy photons by a factor 2-3. The magnetic field amplitude is suppressed
accordingly, and the magnetic field energy - by more than one order in
magnitude. This quantum suppression is shown to reach a maximum at a certain
value of intensity, and does not grow with the further increase of intensities.
The non monotonic behavior of the quantum suppression factor results from the
joint effect of the longitudinal plasma acceleration and the radiation reaction
force. The predicted features could serve as a suitable diagnostic for
radiation friction theories.Comment: 10 pages, 3 figure
Radiation Reaction Effects on Electron Nonlinear Dynamics and Ion Acceleration in Laser-solid Interaction
Radiation Reaction (RR) effects in the interaction of an ultra-intense laser
pulse with a thin plasma foil are investigated analytically and by
two-dimensional (2D3P) Particle-In-Cell (PIC) simulations. It is found that the
radiation reaction force leads to a significant electron cooling and to an
increased spatial bunching of both electrons and ions. A fully relativistic
kinetic equation including RR effects is discussed and it is shown that RR
leads to a contraction of the available phase space volume. The results of our
PIC simulations are in qualitative agreement with the predictions of the
kinetic theory
Ion dynamics and coherent structure formation following laser pulse self-channeling
The propagation of a superintense laser pulse in an underdense, inhomogeneous
plasma has been studied numerically by two-dimensional particle-in-cell
simulations on a time scale extending up to several picoseconds. The effects of
the ion dynamics following the charge-displacement self-channeling of the laser
pulse have been addressed. Radial ion acceleration leads to the ``breaking'' of
the plasma channel walls, causing an inversion of the radial space-charge field
and the filamentation of the laser pulse. At later times a number of
long-lived, quasi-periodic field structures are observed and their dynamics is
characterized with high resolution. Inside the plasma channel, a pattern of
electric and magnetic fields resembling both soliton- and vortex-like
structures is observed.Comment: 10 pages, 5 figures (visit http://www.df.unipi.it/~macchi to download
a high-resolution version), to appear in Plasma Physics and Controlled Fusion
(Dec. 2007), special issue containing invited papers from the 34th EPS
Conference on Plasma Physics (Warsaw, July 2007
Highlights from particle-in-cell simulations of superintense laser-plasma interactions
A selection of results from particle-in-cell simulation of laser-plasma interactions in two and three spatial dimensions are presented. The generation of coherent, long-living electromagnetic structures and the 3D dynamics of selfchanneling have been studied in low-density plasmas. The acceleration of ions driven by radiation pressure in high-density, thin targets is also investigated
Surface Oscillations in Overdense Plasmas Irradiated by Ultrashort Laser Pulses
The generation of electron surface oscillations in overdense plasmas
irradiated at normal incidence by an intense laser pulse is investigated.
Two-dimensional (2D) particle-in-cell simulations show a transition from a
planar, electrostatic oscillation at , with the laser
frequency, to a 2D electromagnetic oscillation at frequency and
wavevector . A new electron parametric instability, involving the
decay of a 1D electrostatic oscillation into two surface waves, is introduced
to explain the basic features of the 2D oscillations. This effect leads to the
rippling of the plasma surface within a few laser cycles, and is likely to have
a strong impact on laser interaction with solid targets.Comment: 9 pages (LaTeX, Revtex4), 4 GIF color figures, accepted for
publication in Phys. Rev. Let
Catnip as an olfactory enrichment: effects on behavioural and endocrine parameters in captive tigers
Widening use of dexamethasone implant for the treatment of macular edema
Sustained-release intravitreal 0.7 mg dexamethasone (DEX) implant is approved in Europe for the treatment of macular edema related to diabetic retinopathy, branch retinal vein occlusion, central retinal vein occlusion, and non-infectious uveitis. The implant is formulated in a biodegradable copolymer to release the active ingredient within the vitreous chamber for up to 6 months after an intravitreal injection, allowing a prolonged interval of efficacy between injections with a good safety profile. Various other ocular pathologies with inflammatory etioÂpathogeneses associated with macular edema have been treated by DEX implant, including neovascular age-related macular degeneration, Irvine–Gass syndrome, vasoproliferative retinal tumors, retinal telangiectasia, Coats’ disease, radiation maculopathy, retinitis pigmentosa, and macular edema secondary to scleral buckling and pars plana vitrectomy. We undertook a review to provide a comprehensive collection of all of the diseases that benefit from the use of the sustained-release DEX implant, alone or in combination with concomitant therapies. A MEDLINE search revealed lack of randomized controlled trials related to these indications. Therefore we included and analyzed all available studies (retrospective and prospective, comÂparative and non-comparative, randomized and nonrandomized, single center and multicenter, and case report). There are reports in the literature of the use of DEX implant across a range of macular edema-related pathologies, with their clinical experience supporting the use of DEX implant on a case-by-case basis with the aim of improving patient outcomes in many macular pathologies. As many of the reported macular pathologies are difficult to treat, a new treatÂment option that has a beneficial influence on the clinical course of the disease may be useful in clinical practice
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