Measurements of energetic electrons and protons produced by a petawatt scale laser

Measurement of energetic electrons produced by focusing the Vulcan petawatt pulse onto the edge of a supersonic gas jet is performed. During the experiment, the laser consistently produced 650 fs duration pulses delivering ~ 180 J on target and generating intensities greater than 3 times 10²⁰ Wcm^-2. Electrons are measured up a maximum energy of greater than 350 MeV, the highest energy observed from any laser-plasma interaction to date. It appears from computational modelling of the interaction that the increase in intensity has moved Vulcan from operating in the plasma wave acceleration regime to one where a form of direct laser acceleration is dominant. In addition, ion acceleration from the interaction of the laser pulse with a underdense plasma is studied using a laser power 1000 times the critical power for relativistic self-focusing to occur. In this new regime, we find a strong correlation between maximum ion energy vs. plasma density which is also confirmed by simulations. This study suggests that high plasma density will lead to more efficient ion acceleration and that electrostatic shocks in the plasma may contribute to the acceleration of these energetic ions