NONLINEAR ABSORPTION OF INTENSE LASER-LIGHT BY COLLECTIVE PLASMA EXCITATIONS

The absorption of high-intensity laser light in a plasma has been studied with the aim of calculating the collective contribution to the inverse bremsstrahlung process. This contribution arises from the electron cloud oscillating, at the laser frequency, through the almost stationary distribution of ions. Plasma waves can be excited and their energy dissipated through subsequent collisions. The calculation is performed in a frame where the electrons are stationary and the oscillatory motion is transferred to the ions. The expression derived for collective absorption involves a sum over multiphoton terms, and shows resonances whenever the plasma frequency is an exact multiple of the laser frequency. When compared with the standard inverse bremsstrahlung expression, it shows that collective effects only become significant in the extreme intensity limit. © 1990 American Institute of Physics.