Experimental observations and simulations on relativistic self-guiding of an ultra-intense laser pulse in underdense plasmas

Abstract

The experimental images of the sidescattered light from a plasma, created by the multiterawatt laser pulse propagating in a hydrogen gas jet, exhibit clear dependence on both gas jet pressure and laser power. Two-and three-dimensional simulations of wave propagation, in presence of the relativistic electron mass increase and the ponderomotive expel of electrons, have been performed to reproduce the Thomson radiation from the plasma electrons. They show electron cavitation induced by the beam focusing, self-focusing, self-guiding, smoothing of the beam nonuniformities and, at larger power, beam filamentation. A bremsstrahlung model with account of the ionization, heating, expansion, and recombination dynamics of the gas, provides the plasma emission background. Both Thomson emission and bremsstrahlung are required to recover the experimental emission patterns. Among the interpretations, a scenario of laser self-guiding over five Rayleigh lengths can be found for 10 TW laser power and 5ϫ10 18 cm Ϫ3 electron density, which surprisingly disappears at larger powers and densities.

Space- and time-resolved observation of extreme laser frequency upshifting during ultrafast-ionization

“…2 (top), it can be explained in terms of pulsation regime of self-guided propagation. 29 In this regime, the scattering efficiency decreases with periodical reduction of the scattering volume and local electron density. It is a typical self-modulation instability.…”

Electron Acceleration by a Laser Wakefield in a Relativistically Self-Guided Channel

“…This effect has been shown to have a power threshold given by P c 16.5n c ͞n e ͓GW͔, where n c is the critical density (when v p v 0 ) [4]. Recent simulations [13] have shown that this effect has different properties, depending on the laser power. At the critical power threshold, only the focal intensity increases.…”

“…This is consistent with the strong blueshifting we observe in the scattered spectra. Even though simulations indicate that the laser focuses to ϳ2 mm [13], the complex dynamics that occur as the laser continually focuses and defocuses in the plasma make it impossible to determine the minimum self-focused beam width from the far field divergence angle.…”

“…In order to reach the high intensity necessary to create the plasma wave, the laser pulses must be focused tightly, and thus the interaction length will be short, limited by diffraction to the Rayleigh range ͑Z R pr 2 0 ͞l͒. Several methods have been proposed or demonstrated to extend the propagation distance beyond the diffraction limit, most notably preformed channels [4,11] and relativistically selfguided channels [12][13][14][15][16]. In this Letter, we report, for the first time, laser wakefield acceleration in a self-guided channel.…”

Channel guiding for laser wakefield accelerators

“…Specifically, a channel with a radially parabolic density profile of the form n(r) = n 0 + ∆nr 2 /r 2 0 can guide a Gaussian laser pulse with a constant spot size r 0 provided the channel depth ∆n satisfies ∆n = ∆n c , where ∆n c = 1/πr e r 2 0 is the critical channel depth [4] and r e = * Work supported by the U.S. . Plasma channels have been created in the laboratory by a variety of methods: (i) Passing a long laser pulse through an optic to create a line focus in a gas, which ionizes and heats the gas, creating a radially expanding hydrodynamic shock [1,[5][6][7][8][9][10][11], (ii) using a slow capillary discharge to control the plasma profile [12], and (iii) using the ponderomotive force of an intense, relativistically self-guided laser pulse in a plasma, which creates a channel in its wake [13][14][15][16][17][18][19][20][21].…”