Study of Ultraintense Laser-Produced Fast-Electron Propagation and Filamentation in Insulator and Metal Foil Targets by Optical Emission Diagnostics

Abstract

The transport of an intense electron beam produced by ultrahigh intensity laser pulses through metals and insulators has been studied by high resolution imaging of the optical emission from the targets. In metals, the emission is mainly due to coherent transition radiation, while in plastic, it is due to the Cerenkov effect and it is orders of magnitude larger. It is also observed that in the case of insulators the fast-electron beam undergoes strong filamentation and the number of filaments increases with the target thickness. This filamented behavior in insulators is due to the instability of the ionization front related to the electric field ionization process. The filamentary structures characteristic growth rate and characteristic transversal scale are in agreement with analytical predictions.

Relativistic High-Current Electron-Beam Stopping-Power Characterization in Solids and Plasmas: Collisional Versus Resistive Effects

“…The REB transports energy from the generation region (with density and temperature in the level of a few g=cm 3 and a few eV, respectively) to the high-density ($ 400 g=cm 3 ) and hightemperature ($ 300 eV) core, where it must deliver a minimum of 20 kJ to heat the fuel to thermonuclear temperatures ($ 5-10 keV) [6]. The energy transport efficiency can be limited by such physical processes as collisional or collective energy loss [7], divergence [8,9], filamentation [10][11][12], etc. The energy losses over the highly inhomogeneous electron transport zone should be accurately predicted for a successful full-scale FI design.…”

Characterisation and Manipulation of Proton Beams Accelerated by Ultra-Short and High-Contrast Laser Pulses

“…It is assumed that a 50 µm path length in this low Z substance has a negligible effect on the energy and main direction of the electrons. Propagating through the foil, the electron beam undergoes filamentation (Manclossi et al, 2006), but nonetheless with unaltered beam directions emerging from the target. To block any light from the laser pulse and its harmonics, a 6 mm Schott BG18 filter and a 3 mm VG8 filter were inserted into the beam path.…”

“…The observed phenomena are attributed to the continuous movement of the proton emission source up to about 20 μm. When electron beam filamentation occurs during electron propagation inside the target, as it is the case for insulators (Manclossi et al, 2006, Fuchs et al, 2003, several proton emission points and, correspondingly, multiple parabolic traces would be measured. The proton spectra from 13 and 20 μm Mylar targets taken at a relatively low laser pulse contrast (∼10 −7 ) indicate many separate proton emission points on the target.…”

Review of Energetic Particle Generation and Electromagnetic Radiation from Intense Laser-Plasma Interactions at the Institute of Physics, Chinese Academy of Sciences

“…When the fast electrons reach the target rear surface, the induced strong electric fields can accelerate ions (preferably protons) by the target normal sheath acceleration (TNSA) mechanism [2]. When the fast electrons pass the rear target surface-vacuum boundary, transition radiation (TR) occurs [25]. Therefore, the characteristics of the proton beam and the optical light emission at the rear surface correlate with fast-electron transport.…”