Experimental and computational characterization of hydrodynamic expansion of a preformed plasma from thin-foil target for laser-driven proton acceleration

We characterize the electron density distributions of performed plasma for laser-accelerated proton generation. The preformed plasma of a titanium target 3 mu m thick is generated by prepulse and amplifed spontaneous emission (ASE) of a high-intensity Ti:sapphire laser and is measured with an interferometer using a second harmonic probe beam. High-energy protons are obtained by reducing the size of the performed plasma by changing the ASE duration before main pulse at the front side (laser incidence side) of the target. Simulation results with two-dimensional radiation hydrodynamic code are close to the experimental results for low-density region similar to 4 x 10(19) cm(-3) at the front side. In the high-density region near to the target surface, the interferometry underestimates the density due to the substantial refraction. The characterization of hydrodynamic expansion with the interferometer and simulation is a useful tool for investigation of high-energy proton generation.