Optimum Target Position of Ion Production in Ultrashort-Pulse Laser Interaction with Foil Targets under the Existence of Prepulses

摘要

It was found that ion production during ultrashort-pulse laser interaction with foil targets is most efficient when the target is positioned behind the waist of the laser, and if the main laser pulse is accompanied by prepulses that evaporate the target. The maximum proton energy was 1.2 MeV when the target was positioned 0.3 mm behind the waist, while it was 0.25 MeV at the waist. A model is proposed in which a prepulse ablates the surface of the target. The resultant neutral gas guides the head of the main pulse caused by the Kerr effect while it is ionized, so the ion generation is more efficient than that without a prepulse.