Abstract

Multiphoton processes in a strong optical field, such as ionization and harmonic generation, have attracted both experimental and theoretical interest in recent years. In the tunneling ionization regime, a very simple physical picture called a two step model or a returning electron model[1,2], fairly well predicts the general aspects of such important phenomena as non sequential double ionization and the cutoff of high-order harmonics. This model straightforwardly predicts not only the enhancements of high-order harmonics and of ion yield but also the extension of the cutoff-order of harmonics when two optical fields of different frequencies are coherently superimposed.

© 1994 Optical Society of America