"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

Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: two-level models

A theoretical study of the resonance optical response of assemblies of oriented short (as compared to an optical wavelength) linear Frenkel chains is carried out using a two-level model. We show that both transmittivity and reflectivity of the film may behave in a bistable fashion and analyze how the effects found depend on the film thickness and on the inhomogeneous width of the exciton optical transition.Comment: 26 pages, 9 figure

Generation of ultra-short light pulses by a rapidly ionizing thin foil

A thin and dense plasma layer is created when a sufficiently strong laser pulse impinges on a solid target. The nonlinearity introduced by the time-dependent electron density leads to the generation of harmonics. The pulse duration of the harmonic radiation is related to the risetime of the electron density and thus can be affected by the shape of the incident pulse and its peak field strength. Results are presented from numerical particle-in-cell-simulations of an intense laser pulse interacting with a thin foil target. An analytical model which shows how the harmonics are created is introduced. The proposed scheme might be a promising way towards the generation of attosecond pulses. PACS number(s): 52.40.Nk, 52.50.Jm, 52.65.RrComment: Second Revised Version, 13 pages (REVTeX), 3 figures in ps-format, submitted for publication to Physical Review E, WWW: http://www.physik.tu-darmstadt.de/tqe

Simulations of radiation pressure ion acceleration with the VEGA Petawatt laser

The Spanish Pulsed Laser Centre (CLPU) is a new high-power laser facility for users. Its main system,VEGA, is a CPA Ti:Sapphire laser which, in itsfinal phase, will be able to reach Petawatt peak powers inpulses of 30 fs with a pulse contrast of 1:1010at 1 ps. The extremely low level of pre-pulse intensitymakes this system ideally suited for studying the laser interaction with ultrathin targets. We have usedthe particle-in-cell (PIC) code OSIRIS to carry out 2D simulations of the acceleration of ions from ultrathinsolid targets under the unique conditions provided by VEGA, with laser intensities up to 1022Wcm 2impinging normally on 20–60 nm thick overdense plasmas, with different polarizations and pre-plasmascale lengths. We show how signatures of the radiation pressure-dominated regime, such as layercompression and bunch formation, are only present with circular polarization. By passively shaping thedensity gradient of the plasma, we demonstrate an enhancement in peak energy up to tens of MeV andmonoenergetic features. On the contrary linear polarization at the same intensity level causes the targetto blow up, resulting in much lower energies and broader spectra. One limiting factor of RadiationPressure Acceleration is the development of Rayleigh–Taylor like instabilities at the interface of theplasma and photonfluid. This results in the formation of bubbles in the spatial profile of laser-acceleratedproton beams. These structures were previously evidenced both experimentally and theoretically. Wehave performed 2D simulations to characterize this bubble-like structure and report on the dependencyon laser and target parametersWe thank the OSIRIS consortium (UCLA/IST) for the use ofOSIRIS and IST for the use of the their clusters for the production ofthe simulation data. We also thank Prof Paul McKenna and hisgroup of the University of Strathclyde for the fruitful discussions.We acknowledge the EU-funded LA3NET consortium under grantnumber GA-ITN-2011-289191. E.C.J. acknowledges the supportfrom MINECO (FIS2013-44174-P) and from Junta de Castilla y Leon(Project no. SA116U13