Ion acceleration with few-cycle relativistic laser pulses from foil targets

Abstract

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

Development of an ultrathin liquid sheet target for laser ion acceleration at high repetition rates in the kilohertz range

“…According to the theories and experimental results, the sweet point lies in the submicrometer regime [28][29][30][31]. For few-cycle pulses, it is in the range of 100 nm [32,33]. Hence, efficient ion acceleration at a considerable repetition rate requires the development of a rapidly selfreplenishing liquid sheet target of nanometric thickness in vacuum, and with sufficient position stability in the focal plane of the high intensity laser.…”