Light-to-plasma Momentum Transfer

The momentum of light in a plasma and the momentum transfer from light to plasma is calculated for a uniform plane of light incident into a uniform plasma. At low irradiance, the Minkowski and Abraham expressions for photon momentum are shown to be equivalent. We evaluate relativistic electron motion at a high irradiance for a plasma and show that most light momentum is transferred to the electrons associated with motion parallel to the light propagation at an irradiance corresponding to the reduced vector potential ao = 3.7 (reduced irradiance 2 X 10^19 W cm^-2 um^2). Our results show that to ensure the maximum momentum transfer from photons to electrons in motion parallel to the k-direction for fixed laser pulse energy, the laser focusing should be adjusted to achieve ao = 3.7, even if tighter focusing, and thus higher ao values, are possible.