N. M. Naumova

Interaction of an ultrashort, relativistically strong laser pulse with an overdense plasma

The results of an analytical description and of a particle‐in‐cell simulation of the interaction of an ultrashort, relativistically intense laser pulse, obliquely incident on a nonuniform overdense plasma, are presented and several novel features are identified. The absorption and reflection of the ultraintense electromagnetic laser radiation from a sharp‐boundary plasma, high harmonic generation, and the transformation into low‐frequency radiation are discussed. In the case of weak plasma nonuniformity the excitation of nonlinear Langmuir oscillations in the plasma resonance region and the resulting electron acceleration are investigated. The vacuum heating of the electrons and the self‐intersection of the electron trajectories are also studied. In the case of a sharp‐boundary plasma, part of the energy of the laser pulse is found to be converted into a localized, relativistically strong, nonlinear electromagnetic pulse propagating into the plasma. The expansion of the hot electron cloud into the vacuum ...

Nonlinear electrodynamics of the interaction of ultra-intense laser pulses with a thin foil

An analytical description of the interaction of laser light with a foil, described as a thin slab of overdense plasma, is presented together with the results of multidimensional particle in cell simulations. The matching conditions at the foil result in nonlinear boundary conditions for the wave equation. The conditions for relativistic transparency are given. The interaction with the foil leads to shaping of the laser pulse. In the case of oblique incidence of a relativistically intense pulse, nonlinear coupling modifies the pulse polarization and causes emission of high harmonics and generation of an electric current. Strong focalization of the reflected pulse, in particular in three-dimensional simulations, is observed for normal and oblique incidence due to the induced distortion of the foil surface.

Nonlinear depletion of ultrashort and relativistically strong laser pulses in an underdense plasma

The depletion of a relativistically strong laser pulse in the course of interaction with underdense plasmas is considered. The driving mechanisms of distortion and fast depletion of the pulse due to the nonlinear plasma wake excitation are discussed. The role of the backward stimulated Raman scattering in the process of the leading front steepening is traced. Electron acceleration and heating due to plasma wave breaking are demonstrated. The evidence that the final stage of the pulse depletion can be accompanied by the formation of relativistically strong solitonlike electromagnetic modes is presented.

Low-frequency relativistic electromagnetic solitons in collisionless plasmas

A relativistic electromagnetic soliton solution in the model of a one-dimensional, unbounded, cold, collisionless plasma is obtained without using the envelope approximation. The breaking of solitons with over-critical amplitudes is observed. The stability of undercritical solitons and the breaking of overcritical solitons are demonstrated by a particle-in-cell computer simulation.

Generation of collimated beams of relativistic ions in laser-plasma interactions

A method is proposed for generating collimated beams of fast ions in laser-plasma interactions. Two-dimensional and three-dimensional particle-in-cell simulations show that the ponderomotive force expels electrons from the plasma region irradiated by a laser pulse. The ions with unneutralized electric charge that remain in this region are accelerated by Coulomb repulsive forces. The ions are focused by tailoring the target and also as a result of pinching in the magnetic field produced by the electric current of fast ions.

Polarization, hosing and long time evolution of relativistic laser pulses

The effect of the pulse polarization and of the accelerated fast electrons on the propagation anomalies (“hosing” and “snaking”) of a high-intensity laser pulse in an underdense plasma is investigated with two dimensional particle in cell simulations. The pulse deflection and the type of plasma modes (solitons, vortices) into which the laser pulse energy is eventually deposited, are shown to depend on the pulse polarization.

Ion acceleration by superintense laser pulses in plasmas

Ion acceleration by petawatt laser radiation in underdense and overdense plasmas is studied with 2D3V-PIC (Particle in Cell) numerical simulations. These simulations show that the laser pulse drills a channel through the plasma slab, and electrons and ions expand in vacuum. Fast electrons escape first from the electron-ion cloud. Later, ions gain a high energy on account of the Coulomb explosion of the cloud and the inductive electric field which appears due to fast change of the magnetic field generated by the laser pulse. Similarly, when a superintense laser pulse interacts with a thin slab of overdense plasma, its ponderomotive pressure blows all the electrons away from a finite-diameter spot on the slab. Then, due to the Coulomb explosion, ions gain an energy as high as 1 GeV.

On the design of experiments for the study of relativistic nonlinear optics in the limit of single-cycle pulse duration and single-wavelength spot size

We propose a set of experiments with the aim of studying for the first time relativistic nonlinear optics in the fundamental limits of single-cycle pulse duration and single-wavelength spot size. The laser system that makes this work possible is now operating at the Center for Ultrafast Optical Science at the University of Michigan. Its high repetition rate (1 kHz) will make it possible to perform a detailed investigation of relativistic effects in this novel regime. This study has the potential to make the field of relativistic optics accessible to a wider community and to open the door for real-world applications of relativistic optics, such as electron/ion acceleration and neutron and positron production.

Generation of subcycle relativistic solitons by super intense laser pulses in plasmas

Abstract 2D and 3D particle in cell simulations of the interaction of ultra-short, high-intensity laser pulses with inhomogeneous plasmas show the formation of long-lived electromagnetic solitons. These solitons consist of electron density depressions and intense electromagnetic field concentrations with a bigger amplitude and a lower frequency than those of the laser pulse. A significant portion of the electromagnetic energy is trapped in the form of solitons. Due to the plasma inhomogeneity, the solitons propagate toward the plasma–vacuum interface where they radiate away their energy in the form of bursts of low frequency electromagnetic radiation.

Fixed blueshift of high intensity short pulse lasers propagating in gas chambers

An explanation is given for the fixed blueshift observed of an intense short pulse laser propagating in a gas chamber filled with helium. The observed shift is found to be independent of the laser power and gas pressure above some critical power. The results are explained by the formation of filaments, which occur due to nonlinear gas polarization effects. The blueshift is in qualitative agreement with a one dimensional particle-in-cell simulation including ionization of the gas.