High-density (> 10(23)/cm(3)) relativistic electron plasma confined between two laser pulses in a thin foil

The nonlinear interaction of two counterpropagating high-intensity laser pu lses in thin foil targets is investigated theoretically and by simulation. The two laser pulses have circular polarization and illuminate the foil nor mally from both sides. They create a spatially confined relativistic electr on plasma. An analytical stationary solution is derived for the special cas e in which the polarization of the two beams rotates in the same direction. The solutions depend on the relative phase of the two pulses. In general, the foil oscillates as a whole; the oscillation frequency is derived analyt ically. High order harmonics are found when frequencies and/or polarization s are changed. For same polarization and frequencies omega (L) and 2 omega (L) of the two incident pulses, a harmonics spectrum is found in which each third harmonic (third, sixth, etc.) is absent. Under certain conditions, a n instability occurs which can destroy the foil. (C) 2001 American Institut e of Physics.