Coulomb driven energy boost of heavy ions for laser plasma acceleration

Abstract: An unprecedented increase of kinetic energy of laser accelerated heavy ions is demonstrated. Ultra thin gold foils have been irradiated by an ultra short laser pulse at an intensity of $6\times 10<sup>{19}$ W/cm$<sup>{2}$. Highly charged gold ions with kinetic energies up to $&gt; 200$ MeV and a bandwidth limited energy distribution have been reached by using $1.3$ Joule laser energy on target. $1$D and $2$D Particle in Cell simulations show how a spatial dependence on the ions ionization leads to an enhancement of the accelerating electrical field. Our theoretical model considers a varying charge density along the target normal and is capable of explaining the energy boost of highly charged ions, leading to a higher efficiency in laser acceleration of heavy ions.