Thin-foil expansion into a vacuum.

The collisionless expansion into a vacuum of a thin foil heated by an ultrashort laser pulse and adiabatically cooling down is studied with a particular emphasis on the structure of the accelerating field and on the resultant ion energy spectrum. For late times, a double layer structure at the ion front becomes the dominant feature. The dependence of the maximum ion velocity on the thin foil width is established. The effect of a two-temperature electron distribution function is discussed.