A Pulse Length and Intensity Study of Proton Generation from Microtube Foil Targets

Intense lasers interacting with solid foils can drive ~TV/m electric fields, accelerating ions to MeV energies. Simulations and experimental data [1] , [2] show that the ion energies and numbers can increase using structured targets. In this study, we experimentally observe that structured targets can dramatically enhance proton acceleration in the target normal sheath acceleration (TNSA) regime. At the Texas Petawatt Laser, we compared proton acceleration from a 1µm Ag flat foil, to microtube structures 3D printed on the front side of Ag foils. A pulse length (140 – 500 fs) and intensity ( [6 – 20] ×10 20 W/cm 2 ) study optimized laser parameters, where microtube targets increase the proton cutoff energy by ~2× and the energetic proton yield (>1.5 MeV) by ~3×. Radiation-hydrodynamic simulations indicate that for sufficiently high laser energy, the pre-pulse shutters the microtubes with an overcritical plasma, damping their performance, in good agreement with the experimental optimum. 2D EPOCH simulations are performed, with and without the pre-plasma profile imported, to better understand the coupling of laser energy to the microtube targets.