Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions

Su, L. N. and Hu, Z. D. and Zheng, Y. and Liu, M. and Li, Y. T. and Wang, W. M. and Sheng, Z. M. and Yuan, X. H. and Xu, M. H. and Shen, Z. W. and Fan, H. T. and Chen, L. M. and Lu, X. and Ma, J. L. and Wang, X. and Wang, Z. H. and Wei, Z. Y. and Zhang, J. (2014) Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions. Physics of Plasmas, 21 (9). 093111. ISSN 1070-664X

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    Abstract

    Proton acceleration from 4μm thick aluminum foils irradiated by 30-TW Ti:sapphire laser pulses is investigated using an angle-resolved proton energy spectrometer. We find that a modulated spectral peak at ∼0.82MeV is presented at 2.5° off the target normal direction. The divergence angle of the modulated zone is 3.8°. Two-dimensional particle-in-cell simulations reveal that self-generated toroidal magnetic field at the rear surface of the target foil is responsible for the modulated spectral feature. The field deflects the low energy protons, resulting in the modulated energy spectrum with certain peaks.