Ion acceleration with few cycle relativistic laser pulses from foil targets

Abstract Ion acceleration resulting from the interaction of 11 fs laser pulses ~35 mJ energy with ultrahigh contrast (<10^-10), and 10^19 W/cm^2 peak intensity foil targets made various materials thicknesses at normal (0◦) 45◦ incidence is investigated. The maximum protons reached ~1.4 MeV accelerated in propagation direction ~1.2 opposite formvar target. An conversion efficiency to proton beam estimated be as high % using a 51 nm-thick Al indicates predominance vacuum heating via Brunel’s effect an absorption mechanism involving tiny pre-plasma target front. Experimental results are reasonable agreement theoretical estimates where front side into backward well explained by Coulomb explosion charged cavity formed preplasma, while forward likely two-step process: first then further boosted through back TNSA mechanism.