MeV proton beam driven by a high-intensity laser

Summary form only given. The interaction of compact high-intensity subpicosecond lasers with matter has been studied for several years, having numerous applications such as table-top electron accelerators. However, only recently an interest has developed in ion acceleration, with potential applications for the initiation of nuclear reactions on a tabletop. Critical for ion acceleration is the efficiency of laser-energy conversion into a high-energy electron component, since the latter through charge separation can produce the requisite strong electrostatic fields. Thermal expansion of a laser-driven plasma and ponderomotive electron expulsion constitute the most well-known examples of electrostatic field production. While the former mechanism has been observed for many years, the latter one has only recently been observed in experiments with gas targets. For the gas targets, when the laser pulse duration /spl tau/ is long, /spl tau/>r/sub 0//c, where r/sub 0/ is the laser focal spot radius and c is the speed of light, the radial component of the pondermotive force dominates, and ions are accelerated radially.