A laser parameter study on enhancing proton generation from microtube foil targets

The interaction of an intense laser with a solid foil target can drive ∼ TV/m electric fields, accelerating ions to MeV energies. In this study, we experimentally observe that structured targets can dramatically enhance proton acceleration in the target normal sheath acceleration regime. At the Texas Petawatt Laser facility, we compared proton acceleration from a 1 μ m flat Ag foil, to a fixed microtube structure 3D printed on the front side of the same foil type. A pulse length (140–450 fs) and intensity ((4–10) × 10 20 W/cm 2 ) study found an optimum laser configuration (140 fs, 4 × 10 20 W/cm 2 ), in which microtube targets increase the proton cutoff energy by 50% and the yield of highly energetic protons ( > 10 MeV) by a factor of 8 × . When the laser intensity reaches 10 21 W/cm 2 , the prepulse shutters the microtubes with an overcritical plasma, damping their performance. 2D particle-in-cell simulations are performed, with and without the preplasma profile imported, to better understand the coupling of laser energy to the microtube targets. The simulations are in qualitative agreement with the experimental results, and show that the prepulse is necessary to account for when the laser intensity is sufficiently high.