Over-critical sharp-gradient plasma slab produced by the collision of laser-induced blast-waves in a gas jet; Application to high-energy proton acceleration

TL;DR

This paper presents a novel method to produce ultra-thin, high-density plasma slabs using colliding laser-induced blast waves in a gas jet, enhancing high-energy proton acceleration for laser applications.

Contribution

It introduces a new plasma creation scheme using counter-propagating blast waves, avoiding damage risks and enabling tailored plasma slabs for improved proton acceleration.

Findings

Density increased by over 10 times in plasma slabs.

Produced plasma slabs are a few microns thick with high density contrast.

Enhanced proton beam collimation and energy with tailored plasma slabs.

Abstract

The generation of thin and high density plasma slabs at high repetition rate is a key issue for ultra-high intensity laser applications. We present a scheme to create such plasma slabs, based on the propagation and collision in a gas jet of two counter-propagating blast waves (BW). Each BW is launched by a sudden and local heating induced by a nanosecond laser beam that propagates along the side of the jet. The resulting cylindrical BW expands perpendicular to the beam. The shock front, bent by the gas jet density gradient, pushes and compresses the plasma toward the jet center. By using two parallel ns laser beams, this scheme enables to tailor independently two opposite sides of the jet, while avoiding the damage risks associated with counterpropagating laser beams. A parametric study is performed using two and three dimensional hydrodynamic, as well as kinetic simulations. The BWs bending combined with the collision in a stagnation regime increases the density by more than 10 times and generates a very thin (down to few microns), near to over-critical plasma slab with a high density contrast (> 100), and a lifetime of a few hundred picoseconds. Two dimensional particle-in-cell simulations are used to study the influence of plasma tailoring on proton acceleration by a high-intensity sub-picosecond laser pulse. Tailoring the plasma not only at the entrance but also the exit side of the ps-pulse enhances the proton beam collimation, increases significantly the number of high energy protons, as well as their maximum energy.