Laser-Ion Lens and Accelerator (LILAC): Towards Point-Like Sources of Relativistic Ions

We report the focusing of a shaped thin target by a circular-polarized laser pulse at 10²² W/cm² intensity, to a low-emittance, quasi-monoenergetic proton beam. The target shape is designed to be simultaneously deformed and focused into a cubic micron spot by the radiation pressure during its acceleration. A simple model reminiscent of geometric optics of the ions will be described. The model predicts the self-consistent dynamics of the nanostructured thin target, as well as the target’s shape that is necessary for focusing without aberrations. Three-dimensional particle-in-cell (PIC) simulations show that the focal length and the final energy are in good agreement with the scaling laws obtained from the geometric optics model. Extensive scans of the laser and target parameters identify the stable propagation regime where the Rayleigh-Taylor-like instability is suppressed. Several simulations for different laser powers (from under a petawatt to multi-petawatt) are presented. The possibility of obtaining proton beams with densities of order 10²³/cm³ and energy density up to 2 × 10¹³ J/cm³ at the focal point is discussed.