Enhanced laser intensity and ion acceleration due to self-focusing in relativistically transparent ultrathin targets

Frazer, T. P. and Wilson, R. and King, M. and Butler, N. M. H. and Carroll, D. C. and Duff, M. J. and Higginson, A. and Jarrett, J. and Davidson, Z. E. and Armstrong, C. and Liu, H. and Neely, D. and Gray, R. J. and McKenna, P. (2020) Enhanced laser intensity and ion acceleration due to self-focusing in relativistically transparent ultrathin targets. Physical Review Research. ISSN 2643-1564 (In Press)

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    Abstract

    Laser-driven proton acceleration from ultrathin foils is investigated experimentally using F/3 and F/1 focusing. Higher energies achieved with F/3 are shown via simulations to result from self-focusing of the laser light in expanding foils that become relativistically transparent, enhancing the intensity. The increase in proton energy is maximised for an optimum initial target thickness, and thus expansion profile, with no enhancement occurring for targets that remain opaque, or with F/1 focusing to close to the laser wavelength. The effect is shown to depend on the drive laser pulse duration.