Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Laser-driven MeV proton beams are highly suitable for quantitative diagnosis of density profiles in dense matter by employing them as a particle probe in a point-projection imaging scheme. Via differential scattering and stopping, the technique allows to detect density modulations in dense compressed matter with intrinsic high spatial and temporal resolutions. The technique offers a viable alternative/complementary route to more established radiographic methods. A Monte-Carlo simulation package, MPRM, has been developed in order to quantify the density profile of the probed object from the experimentally obtained proton radiographs. A discussion of recent progress in this area is presented on the basis of analysis of experimental data, which has been supported by MPRM simulation. © 2008 Elsevier B.V. All rights reserved.

Abstract:

Experiments were performed in which intense laser pulses (up to 9×1019 W/cm2) were used to irradiate very thin (submicron) mass-limited aluminum foil targets. Such interactions generated high-order harmonic radiation (greater than the 25th order) which was detected at the rear of the target and which was significantly broadened, modulated, and depolarized because of passage through the dense relativistic plasma. The spectral modifications are shown to be due to the laser absorption into hot electrons and the subsequent sharply increasing relativistic electron component within the dense plasma. © 2008 The American Physical Society.

Abstract:

The generation of quasimonoenergetic electron beams, with energies up to 200 MeV, by a laser-plasma accelerator driven in a hydrogen-filled capillary discharge waveguide is investigated. Injection and acceleration of electrons is found to depend sensitively on the delay between the onset of the discharge current and the arrival of the laser pulse. A comparison of spectroscopic and interferometric measurements suggests that injection is assisted by laser ionization of atoms or ions within the channel.