Unlimited energy gain in the laser-driven radiation pressure dominant acceleration of ions

Bulanov, S. V.; Echkina, E. Yu.*; Esirkepov, T. Z.; Inovenkov, I. N.*; Kando, Masaki; Pegoraro, F.*; Korn, G.*

The energy of the ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced by a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region increasing the energy and the longitudinal velocity of the remaining ions. In the relativistic limit, the ions become phase-locked with respect to the electromagnetic wave resulting in an unlimited ion energy gain. This effect and the use of optimal laser pulse shape provide a new approach for great enhancing the energy of laser accelerated ions.