Polychromatic x-ray production in helium from a femtosecond high-intensity laser system

Abstract : Polychromatic x-ray radiation has been produced during the relativistic interaction of a 50-TW femtosecond laser with a helium gas jet. We have characterized the spectrum and the angular distribution of the x-ray emission as well as its dependency on the laser polarization and on the plasma electronic density. We have observed a broad continuous spectrum peaking at 0.15 keV with a significant tail up to 2 keV. The radiation was fairly collimated.