Complete classification and additional saddle-point solutions for high-order above-threshold ionization induced by a strong laser field. III. Two-component fields
The complete classification of the saddle-point solutions for high-order above-threshold ionization, presented in and for a linearly polarized laser field, is generalized to the case of an arbitrary bichromatic elliptically polarized field. We first present the classification of the saddle-point solutions for the case of a monochromatic elliptically polarized driving field, which is the simplest example of the field that has two components, i.e., that evolves in the plane. For a bichromatic laser field whose elliptically polarized components have the frequencies rω and sω (r and s are integers, s>r, and ω is the fundamental frequency), the system of the saddle-point equations has 8s2 solutions per optical cycle. One-half of these solutions are the so-called backward-scattering solutions for which the direction of the electron motion is significantly affected by the rescattering. The other half are the forward-scattering solutions for which the electron is only slightly deflected during the rescattering event. For some specific field configurations, the number of saddle-point solutions can be smaller. For example, for a bicircular field, which consists of two counterrotating circularly polarized components, there are 4s(r+s) solutions, while for the corotating configuration there are 4s2 solutions. As an application, we have shown that for a monochromatic elliptically polarized laser field, all four threshold anomalies appear in the spectra of the rescattered photoelectrons.