PROPAGATION OF REALISTIC BEAMS IN UNDERDENSE PLASMA

The effect of beam structure on propagation through underdense plasma is examined in two different examples. First, it is shown that the dis tribution of intensities within a laser beam affects how the beam defl ects in the presence of transverse plasma how. A detailed analysis of beam deflection shows that the rate scales linearly with intensity and plasma density, and inversely with plasma temperature. When the plasm a flow is subsonic, the deflection rate is proportional to the ion dam ping decrement, and scales as M/(1-M-2)(3/2): where M is the transvers e flow Mach number. When the plasma flow is supersonic, the deflection rate scales as 1/[M(M-2-1))(1/2)]. Next, the effect of beam structure on channel formation by very intense laser beams is studied. A diffra ction-limited beam with similar to 3 TW of input power forms a channel through 400 mu m of plasma, whereas when this beam is phase aberrated , channel formation does not occur.