We show that the parity of the order of the harmonics generated by a bichromatic field with commensurate frequencies may be related to the invariance properties of the time-dependent Hamiltonian with respect to some suitable transformations. To simplify the mathematical treatment, we have used a simple model atom to perform calculations that show the effects of the relative phase of the driving fields. Harmonic generation has been described as a two-step process that involves replicas of the Stark levels. In agreement with other previous treatments in which other model atoms were used, we have found that a small contamination of the fundamental harmonic can produce significant modifications of the emission spectra.
© 1999 Optical Society of America
S. Bivona, R. Burlon, and C. Leone, "Symmetries in harmonic generation by a two-color field: an application to a simple model atom," J. Opt. Soc. Am. B 16, 986-993 (1999)