Light pressure of time-dependent fields in plasmas

Abstract

An expression of the light pressure Π is derived for the case of a nearly monochromatic electromagnetic wave with arbitrarily time‐dependent amplitude. Thereby Π is defined as the time‐averaged force density exerted on a plasma by the wave. The resulting equations are valid for both transverse and longitudinal waves. The light pressure turns out to consist of two components: the well‐known gradient‐type term and a new nonstationary solenoidal term. This is true for warm as well as cold plasmas. The importance of the new term for the generation of static magnetic fields is shown, and a model in which shear forces may result is given. Formulas for the nonstationary light pressure developed previously are discussed.