Unlimited Ion Acceleration by Radiation Pressure

The energy of ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region resulting in an increase in the ion energy and in the ion longitudinal velocity. In the relativistic limit, the ions become phase locked with respect to the electromagnetic wave resulting in unlimited ion energy gain.

Figure 1

(a) Laser pulse, reflected radiation, and MLT shown as a superposition of the ion density and the electric field $z$ component in the ($x,y$) plane at $t=112.5(2\pi /\omega )$. (b) Electron and ion energy and the normalized Langmuir frequency corresponding to the ion density versus time. Inset: Ion energy spectrum at $t=600(2\pi /\omega )$.