KEV X-RAY-EMISSION PRODUCED BY A SUBPICOSECOND LASER INTERACTING WITHA CONTROLLED PREFORMED PLASMA

The efficiency of the conversion from laser energy into aluminium K-sh ell line energy hhs been measured for different interaction regimes of a sub-picosecond laser pulse with controlled preformed plasmas. We co mpare the cases of thermal plasmas for which transient ionization effe cts are dominant to non-thermal plasmas in which both transient and no n-Maxwellian effects are present. In a first experiment, a low-intensi ty green laser pulse (400 fs, 10(16) W cm(-2)) is normally incident on a preformed plasma previously generated by a similar laser pulse. In a second experiment a high-intensity p-polarized green pulse (400 fs, 5 x 10(17) W cm(-2)) is sent with a large incidence angle on the prefo rmed plasma. We have observed in these experiments that the conversion efficiency (He-alpha or Li-like lines from aluminium) scales as tau(X )(3), where tau(X) is the duration of the x-ray emission measured at t he full width half maximum, and that this scaling was not affected by non-Maxwellian effects.