Laser and Particle Beams


SPECIAL ISSUE: ECLIM '98 Papers

X-ray emission produced by hot electrons from fs-laser produced plasma— diagnostic and application


I.  USCHMANN a1, P.  GIBBON a1, D.  KLÖPFEL a1, T.  FEURER a1, E.  FÖRSTER a1, P.  AUDEBERT a2, J.-P.  GEINDRE a2, J.-C.  GAUTHIER a2, A.  ROUSSE a3 and C.  RISCHEL a3
a1 Friedrich-Schiller-Universität Jena, Institut für Optik und Quantenelektronik, Abteilung Röntgenoptik, Max-Wien-Platz 1, D-07743 Jena, Germany
a2 Laboratoire pour l'Utilisation des Lasers Intenses, CNRS UMR7605, Ecole Polytechnique, 91128 Palaiseau, France
a3 Laboratoire d'Optique Appliquée—ENSTA, CNRS UMR 7639, INSERM U451, Ecole Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France

Abstract

High intensity fs-laser pulses can deliver focused intensities in the region of 1016–1019 W/cm2. If the laser pulse is focused onto a solid or gaseous material, a plasma is created. The electrons, as well as the ions are accelerated in the strong laser field up to energies in the range of keV to several MeV. The interaction of the high energy particles with cold material, that is, the solid target yield of intense X-ray emission, K-shell—as well as bremsstrahlung-radiation. The K-shell emission from layered targets is a useful indicator of the production efficiency, energy distribution, and transport of hot electrons produced in fs-laser plasmas. For the diagnosis of laser plasma interaction and its application as an intense X-ray source, the spatial, temporal and spectral distribution of K-shell X rays is of fundamental importance. Focusing crystal spectrographs can be used to obtain a single shot X-ray spectra of laser plasmas produced by table top fs-lasers. With a spatial- and spectral-focusing spectrograph based on a toroidally bent crystal, the emission region of the hot plasma and K[alpha]-radiation can be determined. Recording the spectra online by a frontside illuminated charge-coupled device (CCD) allows alignment of the crystal spectrograph, as well as the laser beam focusing leading to different X-ray source sizes. Using a controlled fs-prepulse, an increase in K[alpha] radiation could be observed with the diagnostic.

Measurements of calibrated high resolution spectra are compared with particle-in-cell (PIC) calculations of the laser absorption and hot electron production postprocessed by a Monte–Carlo (MC) transport model of electron stopping and K[alpha] X-ray generation.

(Received January 14 1999)
(Accepted January 14 1999)



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