Collisionless absorption in sharp-edged plasmas

The absorption of subpicosecond, obliquely incident laser light is studied using a 11/2D particle-in-cell code. Density scale lengths from L/=0. 01 to 2 and laser irradiances between I^2=10^14 and 10^18 W cm^-2 m^2 are considered. ``Vacuum heating'' F. Brunel, Phys. Rev. Lett. 59, 52 (1987) dominates over resonance absorption for scale lengths L/0. 1, and is most efficient when v₎ₒ₂/c3. 1 (L/) ^2. Absorbed energy is carried mainly by a ``superhot'' electron population with U₇₎ₓ (I^2) ^1/3--1/2.