-charge-induced acceleration of ions emitted by laser-irradiated surfaces

Pulsed-laser-irradiated surfaces sometimes emit positive ions at energies several volts higher than one would expect, even at modest (<0.1 J/cm2) fluences. A mechanism that can account for this phenomenon is discussed. Intense surface photoemission of electrons during the laser pulse leads to the formation of a space-charge layer near the surface. If the laser fluence were constant, the ions would accelerate and subsequently decelerate as they pass through this steady potential well. As the laser pulse ends, however, some ions may undergo extended acceleration as this space-charge layer moves away from the surface. The maximum possible ion acceleration is analytically calculated and the acceleration for a range of realistic experimental parameters is numerically predicted.