Abstract

Recently [1] we reported the preparation of Elliptical Dark States (EDS) which are coherent superpositions of the ground state magnetic sublevels, completely uncoupled from the elliptically polarized exciting light. The character of such a dark state, namely - the population distribution among the m-sublevels and the cross coherences between them, is determined by the ellipticity of the light. The nonuniform population distribution and high order coherences result in an anisotropic directional distribution of atomic angular momentum. In contrast to the well known uniaxial alignment (orientation) created by linearly or circularly polarized light, the angular momentum of the EDS has in general two preferential axes (the EDS axes) [2]. In this Abstract, we experimentally demonstrate for the first time the biaxial symmetry of this distribution, and prove that its spatial geometry is controlled by the polarization of the light that had created the dark state. The angular momentum distribution is probed by the CPT-Hanle configuration. The laser-induced fluorescence from a sodium atomic beam excited by elliptically polarized laser beam is measured at a right angle to both. An external magnetic field is applied, and its amplitude and direction are scanned. The calculated angular momentum distribution of the generated EDS is depicted on the left. On the right, the measured total fluorescence signal (solid line) is plotted in polar coordinates versus the magnetic field orientation angle. The shaded region represents the angular momentum distribution in the same coordinates. Two Hanle resonance dips are clearly observed when the magnetic field is parallel to the EDS axes, manifesting the biaxial geometry of the atomic angular momentum.

© 1998 IEEE