Proposed hole-target for improving maximum proton energy driven by a short intense laser pulse

By using particle-in-cell simulations, a new method for energetic collimated proton generation via intense short pulse laser-thin foil interactions is presented. To enhance the electron heating efficiency, a small hole is bored at the center of a thin foil target. The small hole combines target heating mechanisms effectively, which results in a high proton maximum energy. While an ultraintense, ultrashort laser pulse propagates through a small hole (diameter<laser spot size), the laser pulse drives electrons pulled out from the hole inner wall effectively inside the hole. When these electrons leave the target, a strong sheath field is formed between the electrons and the target rear surface and this accelerates protons from the rear surface of the target. The effective combination of the laser longitudinal ponderomotive force with the transverse heating (by E field) mechanism results in highly efficient electron heating of the hole target. When the rear part of the hole is filled with a proton-electron contamination layer, energetic collimated protons are produced. The scaling of the maximum proton energy of a hole target over a wide range of laser pulse intensities is presented and compared with that of a simple planar target.