Relativistic electron generation in interactions of a 30 TW laser pulse with a thin foil target

Abstract

Energy and angular distributions of the fast outgoing electron beam induced by the interaction of a 1 J, 30 fs, 2 x 10(19) W/cm(2), 10 Hz laser with a thin foil target are characterized by electron energy spectroscopy and photonuclear reactions. We have investigated the effect of the target thickness and the intensity contrast ratio level on the electron production. Using a 6-microm polyethylene target, up to 4 x 10(8) electrons with energies between 5 and 60 MeV were produced per laser pulse and converted to gamma rays by bremsstrahlung in a Ta secondary target. The rates of photofission of U as well as photonuclear reactions in Cu, Au, and C samples have been measured. In optimal focusing conditions, about 0.06% of the laser energy has been converted to outgoing electrons with energies above 5 MeV. Such electrons leave the target in the laser direction with an opening angle of 2.5 degrees.

Fast-electron transport and induced heating in aluminum foils

“…The small size of the 2 0 source at 100 m depth can alone be considered as an experimental evidence of the presence of a highly collimated electron component. Such a component was also detected by independent measurements performed with the same interaction setup, but using a diagnostic based on a nuclear activation technique: 24,25 for 10 m Al foils, a 13°HWHM electron beam divergence was measured from bremsstrahlung ͑␥ ,n͒ reactions in copper samples located Ϸ25 mm behind the target. 26 The supplementary divergence of the relativistic component could be explained by Coulomb effects on the electron beam propagation in vacuum.…”

On the behavior of ultraintense laser produced hot electrons in self-excited fields

“…8,9 However, it is also known that the total energy of hot electrons observed in vacuum is only a few percent or less of the laser energy in experiments. 10 The relation between the high production and the low observed efficiencies has not been fully understood. It is well known that very strong magnetic and electrostatic fields are excited in a vicinity of the target.…”

Laser-Triggered Nuclear Reactions

“…The lower energy limit for this nuclear activation technique is set by the lowest reaction thresholds, which are provided by the fission reactions of 238 U and 232 Th with roughly 6 MeV or 9 Be with 1.7 MeV. Angular distributions of bremsstrahlung may be determined similarly: a number of activation samples, such as pieces of copper, are arranged around the laser focus [2,3,60,61,64]. After irradiation, the activities of these samples are measured.…”

“…Those bremsstrahlung photons, protons, and ions with energies in the typical range of the nuclear giant dipole resonances of about a few to several tens of MeV may then induce nuclear reactions, such as fission, the emission of photoneutrons, or proton-induced emission of nucleons. To induce one of these reactions, a certain energy threshold -the activation energy of the reaction -must be exceeded.Since the first demonstration experiments, nuclear reactions were used for the spectral characterization of laser-accelerated electrons and protons as well as bremsstrahlung [2,3,4,5]. A whole series of classical known nuclear reactions has been shown to be feasible with lasers, such as photo-induced fission [6,7], proton-and ion-induced reactions [5,8,9], or deuterium fusion [10,11,12,13,14].…”