IODINE LASER PRODUCTION OF HIGHLY-CHARGED TA IONS

The results of systematic studies of multiply charged Ta ion productio n with the fundamental frequency of an iodine laser (lambda = 1.315 mu m), and its 2nd (0.657 mu m) and 3rd (0.438 mu m) harmonics are summa rized and discussed. Short laser pulse (350 ps) and a focus spot diame ter of 100 mu m allowed for the laser power densities in the range of 5 x 10(13) - 1.5 x 10(15) W/cm(2). Corpuscular diagnostics were based on time-of-flight methods; two types of ion collectors and a cylindric al electrostatic ion energy analyzer were used. The Ta ions with charg e state up to 55+ were registered in the distance of 210 cm; the maxim um amplitude of the signal of a high energy ion group was found to bel ong to the ions with the charge state around 43+, depending on the las er power density. The ion energy distribution was measured for all thr ee wavelengths, however, in a different energy range; the maximum regi stered ion energy was 8.8 MeV. The occurrence of highly charged ions i n the far expansion zone is discussed in view of the mechanism of char ge distribution ''freezing'' during two-temperature isothermal plasma expansion.