Generation of harmonics of intense laser radiation in a transparent collisionless plasma

The spectral composition of a relativistically strong uniform nonlinear electromagnetic wave in a transparent collisionless plasma is analyzed. The vortex and potential components of the wave field are shown to contain only odd and even harmonics, respectively; in a transparent plasma, the wave remains quasi-monochromatic, since the intensities of the harmonics decrease exponentially with increasing harmonic number. An equation that includes diffraction effects is derived to describe the propagation of wavepackets. The results obtained are compared with experimental data.