When an intense electromagnetic wave is incident obliquely on a sharply bounded overdense plasma, strong energy absorption can be accounted for by the electrons that are dragged into the vacuum and sent back into the plasma with velocities v≃$v_{\mathrm{osc}}$. This mechanism is more efficient than usual resonant absorption for $v_{\mathrm{osc}/\mathrm{\omega }>\mathrm{L}}$, with L being the density gradient length. In the very high-intensity ${\mathrm{CO}}_2$-laser–target interaction, this mechanism may account for most of the energy absorption.

• Received 22 September 1986

DOI:https://doi.org/10.1103/PhysRevLett.59.52