Features of ion generation using Nd-glass laser

Abstract

Charge state and energy distributions of ions generated by a 3J∕30ns Nd-glass laser were measured at a distance of 3.7m from the target for seven different elements of the Periodic Table and for two different laser power densities (of the order of 1011 and 1012W∕cm2). Two groups of elements were found: highly charged ions with ionization potentials in the range of 500–1000eV were registered for all elements between C12 and Fe56; at the same time, ions with about-one-order-less ionization potentials were registered for elements between Ge74 and Ta181. The most probable reason for such a big difference is the recombination losses of ions during laser-produced plasma expansion into vacuum. Verification of recombination losses in the case of Ta181 target has shown no losses at distances longer than 32.5cm from the target, so recombination processes should take place at shorter distances. Current densities, pulse durations, energy ranges, and numbers of ions with different charge states were found for all elements by normalizing charge state distributions to total ion currents. Two different ion groups exist for all elements and laser power densities used in experiments: the faster group has a very weak dependence of energy on ion charge state, and the energies of the slower group are proportional to the charge states with high accuracy.