Characteristics and applications of ion streams produced by long-pulse lasers

Abstract

If a laser plasma generated on a slab target with a high Z is left to expand it becomes a very efficient source of highly charged ions. Depending on the parameters of the laser driver, ions with charge states from 1+ up to more than 50+ can be produced, with ion energies ranging from tens of electronvolts up to tens of megaelectronvolts, with no external acceleration. The ion current density may reach tens of milliamperes per square centimetres in a distance of 1 m from the target. They can be used either for a direct accelerator injection, for a hybrid ion source based on the coupling of a laser with an electron cyclotron resonance ion source for an easier evaporation and a pre-ionization of the target material with a subsequent charge state enhancement or for a direct ion implantation, as substrates for the implantation metallic and polymer materials are usually exposed to the laser produced ion streams with an appropriate tuning of the implantation regime to modify their surface properties. Although the interaction of the laser beam with the plasma is a fairly complex process certain fundamental phenomena have been identified based on a careful analysis of the charge–energy spectra of the outgoing ions.