X-Ray Spectroscopy of Dense Plasmas Produced by Isochoric Heating with Ultrashort Laser Pulses

Abstract

Hot plasma with temperatures up to 500 eV and densities close to solid state have been generated by focusing intense ultrashort laser pulses on flat solid targets. The heating process is attributed to the energetic electrons, which are created during the laser plasma interaction. They propagate deeply into the target and heat it isochorically. The laser was a frequency‐doubled Ti:Sapphire laser with an energy of 60 mJ and a pulse duration of 150 fs. It was focused on layered plane solid targets with an incidence angle of 45° and p‐polarized. The K‐shell spectra emitted from thin Al sample layers embedded in solid carbon show features such as line broadening, line shift and strong satellite emission, which are characteristic of dense plasmas. The typical duration of the x‐ray emission is a few ps. Al targets covered by a diamond layer show that the depth (expressed through areal density) up to which the target is heated is close to 1 mg/cm2, which corresponds to the range of 20 keV electrons. This means that a considerable fraction of 20 to 25% of the incident laser energy is deposited by the hot electrons in the target.