Spectral modification in ultra-short pulses induced by ionization fronts and relativistic plasma waves

Weak spectral modification in short-pulses due to field-induced ionization and relativistic plasma wake fields has been studied, Analytic models and numerical simulations are presented. It is shown that the laser spectrum is blue-shifted for moderate laser intensities and red-shifted for ultra-high laser intensities. The model results are shown to be in good agreement with the simulation. (C) 1997 Elsevier Science B.V.