High efficiency proton beam generation through target thickness control in femtosecond laser-plasma interactions

Green, J. S. and Robinson, A. P. L. and Booth, N. and Carroll, D. C. and Dance, R. J. and Gray, R. J. and MacLellan, D. A. and McKenna, P. and Murphy, C. D. and Rusby, D. and Wilson, L. (2014) High efficiency proton beam generation through target thickness control in femtosecond laser-plasma interactions. Applied Physics Letters, 104 (21). 214101. ISSN 0003-6951

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    Abstract

    Bright proton beams with maximum energies of up to 30MeV have been observed in an experiment investigating ion sheath acceleration driven by a short pulse (<50 fs) laser. The scaling of maximum proton energy and total beam energy content at ultra-high intensities of ∼10<sup>21</sup> W cm<sup>-2</sup> was investigated, with the interplay between target thickness and laser pre-pulse found to be a key factor. While the maximum proton energies observed were maximised for lm-thick targets, the total proton energy content was seen to peak for thinner, 500 nm, foils. The total proton beam energy reached up to 440 mJ (a conversion efficiency of 4%), marking a significant step forward for many laser-driven ion applications. The experimental results are supported by hydrodynamic and particle-in-cell simulations.