Collimated Ion Beam by a Laser-Illuminated Tailored Hole Target

Divergence suppression of laser-produced proton beam is demonstrated by a tailored thin-foil target with hole. When an intense short-pulse laser illuminates the thin-foil target with the hole, transverse-edge effects of an accelerated electron cloud and an ion source cloud are eliminated by a protuberant part of the hole. The edge fields of the electron cloud and the ion source cloud induce the proton-beam divergence. Therefore, the transverse proton-beam divergence is suppressed by the tailored hole target. First, this paper presents the robustness of the hole target against a contaminated proton-source layer. It may be also difficult to make the laser axis coincide with the target-hole center line in realistic experiments and uses when the target has only one hole. The 2.5-D particle-in-cell simulations present that a multiple-hole target is robust against the laser-alignment and the target-setting errors. The multiple-hole target may serve as a robust target for practical uses to produce a collimated proton beam. In addition, a method for a proton-energy-spectrum control is also proposed by using a hole-cover layer. The hole-cover layer serves a role of high-energy proton selection.