Subpicosecond dynamics of intense laser-cluster interaction: keV x rays and highly charged ion production

We have performed studies of keV X-ray production from (Ar)n , (Kr)n and (Xe)n rare gas clusters (with n between 104 and 106 atoms/cluster) submitted to intense (~10^18 W/cm2) infrared (800 nm) laser pulses. Up to 10^6 3 keV photons per pulse at a moderate (~10^15/cm3) atomic density have been observed. High resolution spectroscopy studies in the case of (Ar)n clusters have also been performed, giving unambiguous evidence of highly charged (up to heliumlike) ions with K vacancies production. We have determined the photon energies and the absolute photon emission yields as a function of several physical parameters governing the interaction : size and atomic number of the clusters, peak intensity of the laser. Unexpectedly low laser intensity thresholds (~10^15Wcm-2) have been measured. The results obtained indicate nevertheless that X-rays may be emitted before cluster explosion on a subpicosecond time scale, and that several mechanisms must be involved in the first stage of the production of the hot nanoplasma induced from each cluster.