Enhanced proton beams from ultrathin targets driven by high contrast laser pulses

Neely, D. and Foster, P. and Robinson, A. and Lindau, F. and Lundh, O. and Persson, A. and Wahlstrom, C.-G. and McKenna, P. (2006) Enhanced proton beams from ultrathin targets driven by high contrast laser pulses. Applied Physics Letters, 89 (2). 021502. ISSN 0003-6951

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Abstract

The generation of proton beams from ultrathin targets, down to 20 nm in thickness, driven with ultrahigh contrast laser pulses is explored. the conversion efficiency from laser energy into protons increases as the foil thickness is decreased, with good beam quality and high efficiencies of 1% being achieved, for protons with kinetic energy exceeding 0.9 MeV, for 100 nm thick aluminum foils at intensities of 10(19) W/cm(2) with 33 fs, 0.3 J pulses. To minimize amplified spontaneous emission (ASE) induced effects disrupting the acceleration mechanism, exceptional laser to ASE intensity contrasts of up to 1010 are achieved by introducing a plasma mirror to the high contrast 10 Hz multiterawatt laser at the Lund Laser Centre. It is shown that for a given laser energy on target, regimes of higher laser-to-proton energy conversion efficiency. can be accessed with increasing contrast. The increasing efficiency as the target thickness decreases is closely correlated to an increasing proton temperature. (c) 2006 American Institute of Physics.