Prof Peter Norreys FInstP;

Abstract:

The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied by photoneutron activation in copper. We show that the gamma-ray beam moves from the target normal to the direction of the k(laser) vector as the scale length is increased. Similar behavior is found also in 2D particle-in-cell simulations.

Abstract:

Protons with energies up to 18 MeV have been measured from high density laser-plasma interactions at incident laser intensities of 5×1019W/cm2. Up to 1012 protons with energies greater than 2 MeV were observed to propagate through a 125µm thick aluminum target and measurements of their angular deflection were made. It is likely that the protons originate from the front surface of the target and are bent by large magnetic fields which exist in the target interior. To agree with our measurements these fields would be in excess of 30 MG and would be generated by the beam of fast electrons which is also observed. © 2000 The American Physical Society.

Abstract:

Fast electron generation and propagation were studied in the interaction of a green laser with solids. The experiment, carried out with the LULI TW laser (350 fs, 15 J), used [Formula Presented] emission from buried fluorescent layers to measure electron transport. Results for conductors (Al) and insulators (plastic) are compared with simulations: in plastic, inhibition in the propagation of fast electrons is observed, due to electric fields which become the dominant factor in electron transport. © 2000 The American Physical Society.

Abstract:

We analyze recent experimental results on the increase of fast electron penetration in shock compressed plastic [Phys. Rev. Lett. 81, 1003 (1998)]. It is explained by a combination of stopping power and electric field effects, which appear to be important even at laser intensities as low as [Formula Presented] An important conclusion is that fast electron induced heating must be taken into account, changing the properties of the material in which the fast electrons propagate. In insulators this leads to a rapid insulator to conductor phase transition. © 2000 The American Physical Society.