Iodine laser production of highly charged Ta ions

The results of systematic studies of multiply charged Ta ion production 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 summarized and discussed. Short laser pulse (350 ps) and a focus spot diameter 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 cylindrical electrostatic ion energy analyzer were used. The Ta ions with charge state up to 55+ were registered in the distance of 210 cm; the maximum amplitude of the signal of a high energy ion group was found to belong to the ions with the charge state around 43+, depending on the laser power density. The ion energy distribution was measured for all three wavelengths, however, in a different energy range; the maximum registered ion energy was 8.8 MeV. The occurrence of highly charged ions in the far expansion zone is discussed in view of the mechanism of charge distribution ''freezing'' during two-temperature isothermal plasma expansion.