Laser ion acceleration via control of the near-critical density target

Abstract

Duration-controlled amplified spontaneous emission with an intensity of ${10}^{13}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ is used to convert a $7.5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick polyimide foil into a near-critical plasma, in which the $p$-polarized, $45\text{\ensuremath{-}}\mathrm{fs}$, ${10}^{19}\text{\ensuremath{-}}\mathrm{W}∕{\mathrm{cm}}^{2}$ laser pulse generates $3.8\text{\ensuremath{-}}\mathrm{MeV}$ protons, emitted at some angle between the target normal and the laser propagation direction of 45\ifmmode^\circ\else\textdegree\fi{}. Particle-in-cell simulations reveal that the efficient proton acceleration is due to the generation of a quasistatic magnetic field on the target rear side with magnetic pressure inducing and sustaining a charge separation electrostatic field.