Short Intense Laser Pulse Collapse in Near-Critical Plasma

It is observed that the interaction of an intense ultra-short laser pulse with an overdense gas jet results in the pulse collapse and the deposition of a significant part of energy in a small and well localized volume in the rising part of the gas jet, where the electrons are efficiently accelerated and heated. A collisionless plasma expansion over 150 microns at a sub-relativistic velocity (~c/3) has been optically monitored in time and space, and attributed to the quasistatic field ionization of the gas associated to the hot electron current. Numerical simulations in good agreement with the observations suggest the acceleration in the collapse region of relativistic electrons, along with the excitation of a sizeable magnetic dipole that sustains the electron current over several picoseconds. Perspectives of ion beam generation at high repetition rate directly from gas jets are discussed

Scalings for ultra-relativistic laser plasmas and monoenergetic electrons

The similarity theory is derived for ultra-relativistic laser-plasma interactions. First, it is shown that the most fundamental S-similarity is valid for both under- and overdense plasmas. Then, the particular case of tenious plasma is considered in great detail. It is shown that the electron dynamics in this case has two characteristic scales. The fast scale corresponds to relaxation to some attractor solution. The slow dynamics describes an adiabatic evolution of this attractor. This leads to a remarkable wave breaking exclusion rule in the 3D geometry. A similarity theory for the slow dynamics allows obtaining simple ``engineering'' scalings for the maximum electron energies, the number of accelerated electrons, the electron beam density, and for the acceleration distance. These scalings are aimed at design of a high-energy laser-plasma accelerator generating electron beams with superior properties

Towards laser based improved experimental schemes for multiphoton e+ e- pair production from vacuum

Numerical estimates for pair production from vacuum in the presence of strong electromagnetic fields are derived, for two experimental schemes : the First concerns a laser based X-FEL and the other imitates the E144 experiment. The approximation adopted in this work is that of two level multiphoton on resonance. Utilizing achievable values of laser beam parameters, an enhancedproduction efficiency of up to 10^11 and 10^15 pairs can be obtained, for the two schemes respectively.Comment: 6 pages, 4 figure

Excitation of nonlinear two-dimensional wake waves in radially-nonuniform plasma

It is shown that an undesirable curvature of the wave front of two-dimensional nonlinear wake wave excited in uniform plasma by a relativistic charged bunch or laser pulse may be compensated by radial change of the equilibrium plasma density.Comment: 6 pages, 4 figure

Transverse Dynamics and Energy Tuning of Fast Electrons Generated in Sub-Relativistic Intensity Laser Pulse Interaction with Plasmas

The regimes of quasi-mono-energetic electron beam generation were experimentally studied in the sub-relativistic intensity laser plasma interaction. The observed electron acceleration regime is unfolded with two-dimensional-particle-in-cell simulations of laser-wakefield generation in the self-modulation regime.Comment: 10 pages, 5 figure

Temporary Acceleration of Electrons While Inside an Intense Electromagnetic Pulse

A free electron can temporarily gain a very significant amount of energy if it is overrun by an intense electromagnetic wave. In principle, this process would permit large enhancements in the center-of-mass energy of electron-electron, electron-positron and electron-photon interactions if these take place in the presence of an intense laser beam. Practical considerations severely limit the utility of this concept for contemporary lasers incident on relativistic electrons. A more accessible laboratory phenomenon is electron-positron production via an intense laser beam incident on a gas. Intense electromagnetic pulses of astrophysical origin can lead to very energetic photons via bremsstrahlung of temporarily accelerated electrons