X-ray Spectroscopy, a tool to investigate intense laser - cluster interaction

The interaction between short laser pulses (electric field > 109 V/m) and Van Der Waals clusters induces an intense electronic excitation of the matter. In particular, the energy coupling between the radiation and the matter is much more efficient than for atomic or solid targets. Experimentally, highly charged ions (like Xe40+), energetic electrons (with Ekin > 3keV) and keV x-rays have been observed. Whereas many studies concentrated on ion emission yields [1], we are interested on the x-ray production (E > 1 keV) when large rare gas cluster ((Ar)n, (Kr)n and (Xe)n with n>104 atoms/cluster) are submitted to intense (up to 5 1017 W/cm2) ultra - short (50 fs to 1 ps) laser pulses (IR-800 nm or UV-400 nm). The x-rays observed are emitted by highly charged ions: for example, from Ar11+ to Ar16+ with K vacancies in the case of Ar clusters [2] and from Xeq+ with q " 24 with L vacancies in the case of xenon. Our goal is to understand how electrons initially produced by optical field ionisation can reach enough energy to generate a strong production of ions with inner shell vacancies. Because the heating mechanisms involved remain controversial, we perform studies, under well-controlled conditions, on the evolution of the absolute photon emission yields and the complete charge state distribution with different physical parameters governing the interaction (like intensity, polarization, and wavelength of the laser, size and density of the clusters). A set of experimental data will be presented and discussed. References [1] Ditmire et al., Phys. Rev. A 53 (1996) 3379. [2] Lamour et al., Proc. of SPIE 4504 (2001) 97 and Rozet et al Physica Scripta T92 (2001) 113. [3] Adoui et al NIM B 205 (2003) 341.