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

Yogo, Akifumi; Daido, Hiroyuki; Bulanov, S. V.; Nemoto, Koshichi*; Oishi, Yuji*; Nayuki, Takuya*; Fujii, Takashi*; Ogura, Koichi; Orimo, Satoshi; Sagisaka, Akito; Ma, J.-L.; Esirkepov, T. Z.; Mori, Michiaki; Nishiuchi, Mamiko; Pirozhkov, A. S.; Nakamura, Shu*; Noda, Akira*; Nagatomo, Hideo*; Kimura, Toyoaki; Tajima, Toshiki

The duration-controlled amplified spontaneous emission with intensity of W/cm is used to convert a 7.5 m thick polyimide foil into a near-critical plasma, in which the -polarized, 45 fs, W/cm 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 generation of the quasistatic magnetic field on the target rear side with the magnetic pressure inducing and sustaining a charge separation electrostatic field.