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

Abstract

The generation of proton beams from ultrathin targets, down to 20nm 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 0.9MeV, for 100nm thick aluminum foils at intensities of 1019W∕cm2 with 33fs, 0.3J 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 10Hz 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.