title: Spatial characteristics of Kalpha x-ray emission from relativistic femtosecond laser plasmas.
abstract: The spatial structure of the Kalpha emission from Ti targets irradiated with a high intensity femtosecond laser has been studied using a two-dimensional monochromatic imaging technique. For laser intensities I<5 x 10(17) W/cm(2), the observed spatial structure of the Kalpha emission can be explained by the scattering of the hot electrons inside the solid with the help of a hybrid particle-in-cell/Monte Carlo model. By contrast, at the maximum laser intensity I=7 x 10(18) W/cm(2) the half-width of the Kalpha emission was 70 microm compared to a laser-focus half-width of 3 microm. Moreover, the main Kalpha peak was surrounded by a halo of weak Kalpha emission with a diameter of 400 microm and the Kalpha intensity at the source center did not increase with increasing laser intensity. These three features point to the existence of strong self-induced fields, which redirect the hot electrons over the target surface.
authors.affiliation: Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany.
authors.forename: Ch
authors.initials: Ch
authors.lastname: Reich
authors.forename: I
authors.initials: I
authors.lastname: Uschmann
authors.forename: F
authors.initials: F
authors.lastname: Ewald
authors.forename: S
authors.initials: S
authors.lastname: Düsterer
authors.forename: A
authors.initials: A
authors.lastname: Lübcke
authors.forename: H
authors.initials: H
authors.lastname: Schwoerer
authors.forename: R
authors.initials: R
authors.lastname: Sauerbrey
authors.forename: E
authors.initials: E
authors.lastname: Förster
authors.forename: P
authors.initials: P
authors.lastname: Gibbon