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A: Atomphysik
A 17: Hauptvortr
äge: Cluster in starken Laserfeldern
A 17.1: Hauptvortrag
Donnerstag, 16. März 2006, 10:40–11:10, H7
Properties of X-Ray Emission during Laser-Cluster Interaction — •Emily Lamour — Universites Paris 6 et 7, INSP, campus Boucicaut, 40 rue de Lourmel, 75015 Paris
When large rare gas clusters are submitted to intense femtosecond laser pulses, the experimental results show a strong energetic coupling between radiation and matter leading to the observation of atomic ions with up to MeV energies, hot electrons of few keV, as well as X-rays in the keV range. We have measured absolute X-ray yields as a function of physical parameters governing the interaction; namely laser intensity, pulse duration, wavelength or polarization state of the laser light, size and nature of the clusters (Ar, Kr, Xe). The X-ray emission is related to the production of highly stripped ions giving, hence, a direct signature of inner shell vacancies creation on a very short time scale (down to few fs). Indeed, we have studied de-excitation of species from Ar12+ to Ar16+ with K vacancy for Ar clusters and from Xe24+ to Xe34+ with L vacancies for Xe clusters. We have highlighted, for the first time, a laser intensity threshold in the X-ray production very low (for instance ∼ 2.1014 W/cm2 for a pulse duration of 300 fs); well below the laser intensity where the ponderomotive energy of the electrons is sufficient to create inner shell vacancies. This effect may be explained by the role of electron-ion collisions inside the cluster. In addition, to better understand the role of electron heating mechanisms involved, the influence of the pulse duration and of the wavelength (400 nm / 800 nm) has been investigated under well controlled conditions. Finally, a saturation of the X-ray emission probability above a critical cluster size (∼ 5 105 atoms per cluster for Ar) has been found.