Generation of a near-circularly-polarized pulse from a ring-current state of a Ne atom in an orthogonally polarized two-color laser field

We investigate theoretically the elliptically high-order harmonic generation from the ring-current state of the Ne atom by numerically solving the two-dimensional time-dependent Schr\"odinger equation in an orthogonally polarized two-color (OTC) laser fields. We find that the elliptically polarized harmonics can be generated by the ring-current state with nonzero angular momentum. A high-efficiency near-circularly-polarized single-atom radiation pulse can be obtained by adjusting the intensity ratio of the OTC laser fields. As the intensity ratio increases, the efficiency of the harmonics is enhanced and the ellipticity of the harmonics is increased, which is illustrated by the temporal evolution of the electronic density probability and the semiclassical three-step model. Moreover, we find that the ellipticity of a single-atom radiation pulse is sensitive to the relative phase of the OTC laser fields, which offers the possibility to control the polarization of extreme ultraviolet radiation.