Heavy Ions Accelerated by a High Intensity, High Contrast Laser Pulse from Sub-Micrometer Metal Targets

Abstract

We performed an experiment with the high-contrast highintensity Trident laser at LANL with the particular interest of heavy ion acceleration. This laser allows the focalization of 75 J during 650 fs on a focal spot of $4.7 \mu \mathrm {m}($FWHM) to reach an intensity on target of $3\mathrm {x} 10 ^{20}\mathrm {W} /$cm2, with an intensity contrast of $10 ^{-12}$on sub-micrometric targets (60–200 nm) of Cobalt, Titanium and Germanium. The heavy ions were characterized by two Thomson parabolas (one at0° and another at 11° with the normal rear side of the target) and by an ion angular and spectral diagnostic iWasp. Thomson parabolas reveal strongly ionized $\sim 140$MeV mono-energetic ions and an optimum acceleration thickness (in energy and in number). The angular analyze performed using the iWasp and the comparison between the two TPs shows two ion beams at + /- 7° with a higher ion energy off target normal. The results show difference in the ionization state between 0 and 11°. Only one ionization state was observed on target normal and a huge number of ionization state was observed at 11°. PIC simulations were performed and show coherent results with the experiment concerning the ionization state on and off target normal and the acceleration of mono-energetic ions.