Propagation issues and fast particle source characterization in laser-plasma interactions at intensities exceeding 1019 W/cm2

A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser-plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 1019 W/cm2. The transmission of laser energy through long scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of propagation at densities above the critical density, possible due to relativistic effects. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-MeV protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out.