21nm x-ray laser Thomson scattering of laser-heated exploding foil plasmas

Recent experiments were carried out on the Prague Asterix Laser System (PALS) towards the demonstration of a soft x-ray laser Thomson scattering diagnostic for a laser-produced exploding foil. The Thomson probe utilized the Ne-like zinc x-ray laser which was double-passed to deliver ∼1 mJ of focused energy at 21.2 nm wavelength and lasting ∼100 ps. The plasma under study was heated single-sided using a Gaussian 300-ps pulse of 438-nm light (3ω of the PALS iodine laser) at laser irradiances of 1013-1014 W cm-2. Electron densities of 1020-1022 cm-3 and electron temperatures from 200 to 500 eV were probed at 0.5 or 1 ns after the peak of the heating pulse during the foil plasma expansion. A flat-field 1200 line mm-1 variable-spaced grating spectrometer with a cooled charge-coupled device readout viewed the plasma in the forward direction at 30o with respect to the x-ray laser probe. We show results from plasmas generated from ∼1 (micro)m thick targets of Al and polypropylene (C3H6). Numerical simulations of the Thomson scattering cross-sections will be presented. These simulations show electron peaks in addition to a narrow ion feature due to collective (incoherent) Thomson scattering. The electron features are shifted from the frequency of the scattered radiation approximately by the electron plasma frequency ±ωpe and scale as ne1/2