Formation of a plasma density profile near the critical surface under the action of a ponderomotive force

An analysis is made of planar steady-state isothermal flow of a plasma subject to the ponderomotive force of laser radiation incident normally on a critical surface. It is shown that transition through the Jouguet point can be continuous or by creation of a shock wave, depending on the plasma velocity and density in the supercritical region. A continuous transition occurs when the plasma velocity and density and the laser radiation intensity satisfy two relationships. The density and the velocity exhibit discontinuities when these relationships are disobeyed. The discontinuities make it possible to select that of the two solutions differing in respect of the sign of the velocity which corresponds to a shock compression wave. In the continuous solution case both directions of motion are possible.