The influence of target thickness on characteristics of a forward-emitted proton beam produced by an ultrashort laser pulse

Summary form only given. Fast protons, produced by the interaction of an ultrashort (/spl les/1 ps) laser pulse (USP) with a thin foil target, are currently the subject of an intensive study. To make this prospect feasible, the proton production efficiency and proton beam characteristics must be considerably enhanced. The possible way to attain this goal is optimization of the target. We have found that, for maximizing the energies of forward-emitted protons and for minimizing the proton energy spread, the target thickness must be properly selected. It should be smaller than the hot electron range in the target but greater than the characteristic path length of the electron heat wave generated by the prepulse and the leading edge of a laser pulse. If the target thickness is smaller than the heat wave path length, both the maximum and the mean proton energies can be a decreasing function of laser energy.