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

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

Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing

“…Recent studies have indicated that utilizing high contrast laser pulses to irradiate ultra-thin foils is a promising way to improve the proton beam quality and conversion efficiency. Much effort has been made to improve the contrast ratio of the laser pulses, by utilizing the ultra-fast Pockels cells, 12 plasma mirrors, [13][14][15] second harmonic generation (SHG), 16 etc.…”

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…Recently the development of plasma mirrors for the temporal pulse cleaning has gained attention [8,[33][34][35][36]. Hence, the laser beam is weakly focused on an antireflection coated glass plate so that the peak intensity reaches about 10 15 − 10 16 W/cm 2 .…”

Direct High-Power Laser Acceleration of Ions for Medical Applications

“…Further design improvements on such machines need to be made before they may be used as ion sources for direct acceleration. An alternative source could possibly be a solid target of micro-or nanoscale thickness, perhaps blown off by a laser pulse, as in the TNSA mechanism [7,8] and the laser-piston regime [21], followed at the appropriate time delay by an accelerating pulse of the type discussed in this Letter.…”

“…This superstrong field accelerates the ions to tens of MeV over a distance in the µm range [6]. Recent work [7] has shown that proton beams produced by this method of target normal sheath acceleration (TNSA) may be improved in energy and beam quality by the use of foils less than 1 µm in thickness [8]. In earlier experiments, employing thicker foils, a small fraction of the energy got converted to proton energy.…”