Proton acceleration with multi-peak energy spectra tailored by vortex laser

A novel flying cascaded acceleration mechanism is proposed to generate energetic proton beams with multi-peak energy spectra using a circularly polarized (CP) Laguerre-Gaussian (LG) laser pulse in three-dimensional particle-in-cell simulations. Simulations show that the protons are initially accelerated and compressed into the beam center via the radiation pressure of the CP LG (sigma(z) = -1) laser pulse. Then, they are tailored by flying dipolar electric fields in this LG laser, resulting in a multi-peak energy spectrum. Each shaped proton peak exhibits a narrow energy spread of similar to 5% and high flux of similar to 2 x 10(8) protons/MeV at giga-electron volts energy. Such a flying cascaded acceleration mechanism extends the energy spectra of proton beams from monoenergetic to multi-peak structure, thereby potentially enhancing the generation efficiency of monoenergetic proton beams for various applications, such as proton-induced spallation reactions, proton radiography, and proton therapy.