NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
Laser-driven ion acceleration is often analyzed assuming that ionization reaches a steady state early in the interaction of the laser pulse with the target. This assumption breaks down for materials of high atomic number for which the ionization occurs concurrently with the acceleration process. Using particle-in-cell simulations, we have examined acceleration and simultaneous field ionization of copper ions in ultra-thin targets 20-150 nm thick irradiated by a laser pulse with intensity 1 x 1021 Wcm2. At this intensity, the laser pulse drives strong electric fields at the rear side of the target that can ionize Cu to charge states with valence L-shell or full K-shell. The highly-charged ions are produced only in a very localized region due to a significant gap between the M-and L-shells ionization potentials and can be accelerated by strong, forward-directed sections of the field. Such an ionization injection leads to well-pronounced bunches of energetic, highly-charged ions. We also find that for the thinnest target 20 nm a push by the laser further increases the ion energy gain. Thus, the field ionization, concurrent with the acceleration, offers a promising mechanism for the production of energetic, high-charge ion bunches.
Journal Article - Open Access
Scientific Reports , 9, 666, 01 Jan 0001, 01 Jan 0001,