High intensity laser interactions with near critical density target for shock ion acceleration.

We will present ion acceleration measurements from the interaction a near-infrared (λ = 1.053μm), relativistic intensity (3 × 10¹⁹ W/cm²) laser pulse with a near-critical density plasma. By controlling the front side density gradient a forward accelerated, narrow divergence (< 0.8^o) proton beam was generated with energies (> 400 keV). We also assess the effect of peak plasma density and density length scale on electron heating and beam transmission. Particle-in-cell simulations are used to investigate the ion acceleration mechanisms and to provide insight into the experimental measurements.