title: Proton acceleration from microdroplet spray by weakly relativistic femtosecond laser pulses.
abstract: Angular distribution of protons is measured from ethanol droplet spray irradiated by linearly polarized 150 fs laser pulses at an intensity of 1.1 x 10(16)W/cm2. Fast protons (with energies >16 keV ) with an anisotropic distribution can be observed only in or near the polarization plane of the laser fields, while the slow protons (with energies <or=16 keV ) emit with nearly an isotropic distribution. Two-dimensional particle-in-cell simulations suggest that three groups of protons originate from different acceleration regimes in the laser-droplet interaction. The first group with the highest energies is accelerated backwards by the anisotropic charge-separation field near the front surface (laser-droplet interaction side) due to the resonance absorption; the second group (forward emission) is generated by the target-normal sheath acceleration mechanism; and the third group, with the lowest energies, is accelerated by the hydrodynamic expansion of the droplet plasmas.
authors.affiliation: Key Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's of Republic, China.
authors.forename: Xiao-Yu
authors.initials: XY
authors.lastname: Peng
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Zheng
authors.forename: Zheng-Ming
authors.initials: ZM
authors.lastname: Sheng
authors.forename: Miao-Hua
authors.initials: MH
authors.lastname: Xu
authors.forename: Zhi-Yuan
authors.initials: ZY
authors.lastname: Zheng
authors.forename: Tian-Jiao
authors.initials: TJ
authors.lastname: Liang
authors.forename: Yu-Tong
authors.initials: YT
authors.lastname: Li
authors.forename: Quan-Li
authors.initials: QL
authors.lastname: Dong
authors.forename: Xiao-Hui
authors.initials: XH
authors.lastname: Yuan
authors.forename: Ying-Jun
authors.initials: YJ
authors.lastname: Li
authors.forename: Han-Ming
authors.initials: HM
authors.lastname: Li