Orientation observed by Zeeman spectra of dissociated atoms and the interference in photoexcitations

Abstract

In a magnetic field, the wave number of a pump laser light polarized along the field was fixed to the isolated ${\mathrm{Cs}}_{2}D{}^{1}{\ensuremath{\Sigma}}_{u}^{+}(v=46,J=54)\ensuremath{\leftarrow}X{}^{1}{\ensuremath{\Sigma}}_{g}^{+}(v=0,J=55)$ line, and the excitation spectrum of the dissociated $\mathrm{Cs}(6p{}^{2}{P}_{3/2})$ atoms was measured by scanning the wave number of a probe laser light polarized perpendicular to the field. The population of each sublevel $6p{}^{2}{P}_{{3/2,m}_{j}}$ of the dissociated atoms was determined from the line intensities in the ${m}_{j}$-resolved excitation spectrum. The unequal population between the $6p{}^{2}{P}_{3/2,+|{m}_{j}|}$ and $6p{}^{2}{P}_{3/2,\ensuremath{-}|{m}_{j}|}$ levels (atomic orientation) was observed and it was enhanced as the magnetic-field strength was increased. The atomic orientation is shown to be induced by the interference between the indirect predissociation, which occurs by a combination of the spin-orbit coupling of the $D{}^{1}{\ensuremath{\Sigma}}_{u}^{+}$ state with the ${(2)}^{3}{\ensuremath{\Pi}}_{0u}$ state and the L-uncoupling and Zeeman interactions between the ${(2)}^{3}{\ensuremath{\Pi}}_{0u}$ and dissociative ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ states, and the dissociation following a direct excitation to the ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state, which is allowed by spin-orbit coupling of the ${(2)}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state with the $B{}^{1}{\ensuremath{\Pi}}_{u}$ state. It is demonstrated that the atomic orientation is produced by the photodissociation in the presence of an external magnetic field even when all degenerated molecular $M=J,\dots{},0,\dots{},\ensuremath{-}J$ sublevels are excited by a light polarized linearly along the field.