Ultrashort-laser-produced heavy ion generation via target laser-ablation cleaning

It has become apparent in the last few years that the surface contamination on laser-acceleration targets is a major impediment to the acceleration of the actual target ions. A typical target has many monolayers with a total of about 1016 atoms/cm2 of hydrogen, carbon and oxygen on the surface. We have performed experiments at the Los Alamos Trident Laser facility using one arm of the Trident laser at 150 ps to ablatively clean targets that are subsequently irradiated by the Trident TW Short-pulse arm to accelerate the bulk target ions to high energies. The 150 ps ablation pulse rids the rear of the target of its omnipresent surface contamination layer allowing the short-pulse to illuminate the target and accelerate ions via the Target Normal Sheath Acceleration (TNSA) mechanism. Our experimental results are compared to the LASNEX code and a large discrepancy is showed between the simulation and the measurements. The biggest potential inaccuracy is caused by the large scale internal speckle structure inherent in the laser beam, which can create a large intensity variability estimated to be around 3 times the nominal intensity. Also LASNEX does not model melting, lattice structures or material strengths natively, which might add a large error to a relatively rigid target like vanadium