title: Origin for ellipticity of high-order harmonics generated in atomic gases and the sublaser-cycle evolution of harmonic polarization.
abstract: We investigate numerically and analytically the polarization properties of high-order harmonics generated by an atom in intense elliptically polarized laser field. The offset angle of the harmonic polarization ellipse can be well described with the semiclassic "simple-man" high-harmonic generation model. The harmonic ellipticity itself, however, can be hardly understood within this model. We show that this ellipticity originates from quantum-mechanical uncertainty of the electron motion. We develop a theoretical approach describing this ellipticity and, more generally, the time evolution of the high-harmonic polarization state within the laser cycle. The analytical results are verified with the exact numerical solution; to make the comparison accurately, we develop a specific technique for separating the contributions of quantum paths in the numerical calculation.
authors.affiliation: General Physics Institute of the Russian Academy of Sciences, 38 Vavilova st., Moscow 119991, Russia. v-strelkov@fpl.gpi.ru
authors.forename: V V
authors.initials: VV
authors.lastname: Strelkov
authors.forename: A A
authors.initials: AA
authors.lastname: Gonoskov
authors.forename: I A
authors.initials: IA
authors.lastname: Gonoskov
authors.forename: M Yu
authors.initials: MY
authors.lastname: Ryabikin