title: Transition of proton energy scaling using an ultrathin target irradiated by linearly polarized femtosecond laser pulses.
abstract: Particle acceleration using ultraintense, ultrashort laser pulses is one of the most attractive topics in relativistic laser-plasma research. We report proton and/or ion acceleration in the intensity range of 5×10(19) to 3.3×10(20) W/cm2 by irradiating linearly polarized, 30-fs laser pulses on 10-to 100-nm-thick polymer targets. The proton energy scaling with respect to the intensity and target thickness is examined, and a maximum proton energy of 45 MeV is obtained when a 10-nm-thick target is irradiated by a laser intensity of 3.3×10(20) W/cm2. The proton acceleration is explained by a hybrid acceleration mechanism including target normal sheath acceleration, radiation pressure acceleration, and Coulomb explosion assisted-free expansion. The transition of proton energy scaling from I(1/2) to I is observed as a consequence of the hybrid acceleration mechanism. The experimental results are supported by two- and three-dimensional particle-in-cell simulations.
authors.affiliation: Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea and Center for Relativistic Laser Science, Institute for Basic Science (IBS), Gwangju 500-712, Korea.
authors.forename: I Jong
authors.initials: IJ
authors.lastname: Kim
authors.forename: Ki Hong
authors.initials: KH
authors.lastname: Pae
authors.forename: Chul Min
authors.initials: CM
authors.lastname: Kim
authors.forename: Hyung Taek
authors.initials: HT
authors.lastname: Kim
authors.forename: Jae Hee
authors.initials: JH
authors.lastname: Sung
authors.forename: Seong Ku
authors.initials: SK
authors.lastname: Lee
authors.forename: Tae Jun
authors.initials: TJ
authors.lastname: Yu
authors.forename: Il Woo
authors.initials: IW
authors.lastname: Choi
authors.forename: Chang-Lyoul
authors.initials: CL
authors.lastname: Lee
authors.forename: Kee Hwan
authors.initials: KH
authors.lastname: Nam
authors.forename: Peter V
authors.initials: PV
authors.lastname: Nickles
authors.forename: Tae Moon
authors.initials: TM
authors.lastname: Jeong
authors.forename: Jongmin
authors.initials: J
authors.lastname: Lee