Complex diagnostic and numerical study of x-ray and particle emissions under relativistic ultra-short laser-solid interaction

Abstract

In this report, we present the experimental results on generation of X-ray emission and particle acceleration using high temporal contrast (~10-9 at picosecond time scale), ultrashort (~\ 30\ fs), relativistic (a_0\approx5) near-IR laser pulses interacting with Ti¬tanium foils. Complex diagnostics, including the energy spectra of accelerated electrons from both front and rear target sides, electron angular distribution and X-ray spectroscopy of the plasma emission were employed. Analysis of the characteristic radiation produced by highly charged Ti+20 ions led to the conclusion that laser-plasma interaction, which leads to the generation of keV hot plasma, occurs at plasma densities 10x higher than relativistic critical electron density. Numerical simulations, including hydrodynamic calculations to model pre-plasma, generated on nanosecond-picosecond time scale under our experimental conditions, and relativistic particle-in-cell simulations for main pulse interaction with the plasma reproduce well electron energy and angular distributions. They show the onset of hole boring effect under near normal incidence that leads to plasma density steepening and enables penetration of high intensity laser radiation into the overcritical plasma to much higher densities (up to 30 n_{cr}), what is in a good agreement with the results of X-ray spectroscopy.