COLLISIONLESS ABSORPTION IN SHARP-EDGED PLASMAS

The absorption of subpicosecond, obliquely incident laser light is studied using a 1 1/2 D particle-in-cell code. Density scale lengths from L/lambda = 0.01 to 2 and laser irradiances between I-lambda-2 = 10(14) and 10(18) W cm2-mu-m2 are considered. "Vacuum heating" [F. Brunel, Phys. Rev. Lett. 59, 52 (1987)] dominates over resonance absorption for scale lengths L/lambda < 0.1, and is most efficient when upsilon(osc)/c congruent-to 3.1 (L/lambda)2. Absorbed energy is carried mainly by a "superhot" electron population with U(hot) approximately (I-lambda-2)1/3-1/2.