Evaluations of electric field in laser-generated pulsed plasma

Abstract

Evaluations of the electric field developed in non-equilibrium laser-generated plasma were obtained from laser ablation experiments at INFN-LNS of Catania and PALS of Prague at the regime of 1010 W/cm2 and 1016 W/cm2 intensity, respectively. Evaluations are based on the measurements of ion energy distributions from Ta plasma in vacuum obtained through an electrostatic ion energy analyser (IEA) used in both laboratories. IEA gives the energy-to-charge ratio from ion detection with time-of-flight technique. Ion energy distributions can be fitted by Coulomb-Boltzmann-shifted function which depends on the equivalent plasma temperature, plasma expansion process and Coulomb interactions. The energetic shift of the experimental distributions increases with the charge state, indicating that an equivalent voltage able to accelerate ions is developed inside the plasma. Assuming near Local Thermal Equilibrium (LTE) conditions, the voltage can be supposed developed on distances comparable with the Debye legth. Thus, from evaluations and measurements of the plasma temperature and density, it was possible to calculate the shielding length in the plasma and consequently the electrical field. Results indicate that high electric fields, of the order of tens of MV/cm or higher, can be produced inside the laser-generated plasma in the two regimes of laser intensity.