High-resolution radial Ka spectra obtained from a multi-keV electron distribution in solid-density titanium foils generated by relativistic laserematter interaction

We studied temperature and Ka yield radial profiles of thin titanium foils as a result of femtosecond high-power laser pulse irradiation at several 1019 W/cm2 by high-resolution x-ray spectroscopy. Laseraccelerated electrons heat the cold solid to bulk temperatures of up to w50 eV. The plasma strongly affects the shape of the emitted Ka doublet, which is surveyed by x-ray spectroscopy with both high spectral (E/DE 15,000) and 1D spatial (Dx 13.5 mm) resolutions. Temperature-dependent spectra modeled by line-shape calculations are compared with Abel-inverted experimental spectra and provide a radial temperature distribution. The radially resolved Ka yield shows a depletion of the Ka1-line at the position of the laser focus. The density gradients induced by prepulses are modeled by hydrodynamic simulations, and density-dependent line-shape models are applied. The x-ray yield as function of foil thickness is explained by partial refluxing of a multi-keV electron distribution inside the foil, supported by Monte-Carlo simulations. Finally, we derive parameters to optimize the peak brilliance of such a laserdriven thin foil x-ray source. 2011 Elsevier Ltd. All rights reserved.