Numerical Investigation of the Rippling Effect at the Interaction of an Ultrashort Laser Pulse with Inhomogeneous Plasma

The interaction of ps and fs laser pulses of subrelativistic intensity (∼1016–1017 W/cm2) with inhomogeneous plasma was studied using a two‐fluid hydrodynamic computer code. It was found that action of ponderomotive forces induced by the laser pulse near the plasma critical surface results in the ion density rippling of characteristic life time ∼10−11 s. The rippling effect is the cause of back reflection of the laser pulse and leads to a strong decrease in the efficiency of energy transfer to plasma. This effect can be significantly suppresed by use of the laser radiation composed of some (>2) slightly different wavelengths or with the use of nonmonochromatic radiation. In the range of subrelativistic laser intensities the rippling effect does not appear for laser pulses shorter than ∼100 fs.