Multiphoton ionization of atoms in two-color laser field and coherent polarization control of terahertz waves

Abstract

Within the framework of the Keldysh theory, the multiphoton ionization of atoms subjected to a perturbation by a high intensity two-color laser radiation field of an arbitrary polarization is considered. The dependence of the net photoelectron current, generated due to the interaction of an intense elliptically polarized two-color laser field with an atom, on the ratio of the second and fundamental harmonic amplitudes, their relative phase, and an angle between harmonics is found. The parameters maximizing the net photoelectron current are specified. Properties of polarization and spectral intensity of terahertz radiation and also possibility of the coherent control of terahertz waves polarization through the relative phase between harmonics in a two-color scheme are investigated. Using the ‘imaginary-time’ method, extremal subbarrier trajectories of the photoelectron moving in an elliptically polarized two-color laser field and the Coulomb correction to the total ionization rate are derived and discussed. The asymptotic expressions for the total ionization rate and the net photoelectron current obtained in the paper for the qualitative explanation of experiments on the generation of terahertz radiation in gases can be used.