Strong plasma wave excitation by a ‘‘chirped’’ laser beat wave

A modification of the plasma beat-wave excitation scheme is proposed, aimed at a significant increase of the resulting plasma wave amplitude. The modification employs two laser beams with a down-chirped beat frequency that follows, on the average, the amplitude-dependent frequency of the intense plasma wave. Numerical and analytical calculations that support the proposed scheme are presented. Also, new analytical solutions for the constant beat-frequency case are obtained. Finally, a plausible experimental setup is suggested, where one of two CO2 laser beams attains the necessary frequency chirp by passing through a diffraction grating pair.