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

Duration-controlled amplified spontaneous emission with an intensity of 10¹³0.3em0exW∕cm² is used to convert a 7.5-μm-thick polyimide foil into a near-critical plasma, in which the p-polarized, 45-fs, 10¹⁹-W∕cm² laser pulse generates 3.8-MeV protons, emitted at some angle between the target normal and the laser propagation direction of 45^∘{}. 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.