Influence of laser irradiated spot size on energetic electron injection and proton acceleration in foil targets

McKenna, Paul and Carroll, David and Coury, Mireille and Robinson, A.P.L. and Yuan, Xiaohui and Brenner, Ceri Mae and Burza, Matthias and Gray, Ross and Quinn, Mark and Neely, David and Tresca, Olivier and Lancaster, Kate and Li, YT and Lin, XX and Wahlstrom, CG (2012) Influence of laser irradiated spot size on energetic electron injection and proton acceleration in foil targets. Applied Physics Letters, 100 (7). 074105. ISSN 0003-6951 (https://doi.org/10.1063/1.3685615)

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Abstract

The influence of irradiated spot size on laser energy coupling to electrons, and subsequently to protons, in the interaction of intense laser pulses with foil targets is investigated experimentally. Proton acceleration is characterized for laser intensities ranging from 2 x 10(18) - 6 x 10(20) W/cm(2), by (1) variation of the laser energy for a fixed irradiated spot size, and (2) by variation of the spot size for a fixed energy. At a given laser pulse intensity, the maximum proton energy is higher under defocus illumination compared to tight focus and the results are explained in terms of geometrical changes to the hot electron injection