Acceleration of Protons from a Double-Layer or Multi-Ion-Mixed Foil Irradiated by Ultraintense Lasers

摘要

Acceleration of protons by the radiation pressure of a circularly polarized laser pulsewith the intensity up to 10^(21) W/cm^2 from a double-layer or multi-ion-mixed thin foil is investigatedby two-dimensional particle-in-cell simulations. The double-layer foil is composed of a heavy ionlayer and a proton layer. It is found that the radiation pressure acceleration can be classifiedinto three regimes according to the laser intensity due to the different critical intensities for lasertransparency with different ion species. When the laser intensity is moderately high, the laserpushes the electrons neither so slowly nor so quickly that the protons can catch up with theelectrons, while the heavy ions cannot. Therefore, the protons can be accelerated efficiently. Theproton beam generated from the double-layer foil is of better quality and higher energy than thatfrom a pure proton foil with the same areal electron density. When the laser intensity is relativelylow, both the protons and heavy ions are accelerated together, which is not favorable to the protonacceleration. When the laser intensity is relatively high, neither the heavy ions nor the protonscan be accelerated efficiently due to the laser transparency through the target.