High Intensity Laser Proton Acceleration with Underdense Targets

Abstract

Laser driven sources of high energy ions commonly use thin solid foils. However, recently experiments have shown that a gaseous target can produce proton beams with characteristics comparable to those obtained with solid targets. In underdense laser proton acceleration, volume effects dominate the acceleration, while in target normal sheath acceleration, the electric field value at the rear target side is directly related to the electron surface density. Using Particle‐In‐Cell simulations, we have studied in detail proton acceleration with high intensity laser pulses interacting with underdense plasmas. Underdense laser ion acceleration strongly depends on the length of the plasma, the laser pulse duration and intensity. A two‐step acceleration process has been observed: first, ions are accelerated in volume by electric fields generated by hot electrons, second, the ion energy is boosted in a strong electrostatic shock propagating along the descending density profile.