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Effect of Plasma Scale Length on Multi-MeV Proton Production by Intense Laser Pulses

2001; American Physical Society; Volume: 86; Issue: 9 Linguagem: Inglês

10.1103/physrevlett.86.1769

1092-0145

A. J. Mackinnon, M. Borghesi, S. P. Hatchett, M. H. Key, P. K. Patel, H.D. Campbell, A. Schiavi, R. A. Snavely, S. C. Wilks, O. Willi,

Laser-induced spectroscopy and plasma

The influence of the plasma density scale length on the production of MeV protons from thin foil targets irradiated at $I{\ensuremath{\lambda}}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0ex}{0ex}}\mathrm{W}\mathrm{cm}{}^{\ensuremath{-}2}$ has been studied. With an unperturbed foil, protons with energy $>20\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$ were formed in an exponential energy spectrum with a temperature of $2.5\ifmmode\pm\else\textpm\fi{}0.3\mathrm{MeV}$. When a plasma with a scale length of $100\ensuremath{\mu}\mathrm{m}$ was preformed on the back of the foil, the maximum proton energy was reduced to $<5\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$ and the beam was essentially destroyed. The experimental results are consistent with an electrostatic accelerating mechanism that requires an ultrashort scale length at the back of the target.