Generalized Navier-Stokes equations and light-induced gas-kinetic effects

We present a general formalism for the description of gas-kinetic effects of light in a single-component gas, by elimination of rapid variables in the evolution equations. These equations contain both Boltzmann terms describing velocity-changing collisions and radiative transitions. The general result is a set of generalized Navier-Stokes equations for the density, the temperature, and the hydrodynamic velocity. The effects of the incident radiation on the transport properties of the gas are illustrated by deriving explicit transport equations in a simple model case. This shows that both the intensity and the intensity gradient serve as a thermodynamic force.