Arbitrary orientation of atoms and molecules via coherent population trapping by elliptically polarized light

Abstract

The interaction of laser light of arbitrary polarization with systems of high angular momentum is considered. We show that elliptically polarized light creates an anisotropic spatial distribution of atomic and molecular angular momentum which is qualitatively different from the alignment and orientation induced by light of circular or linear polarization. Multilevel coherent population trapping within a manifold of ground-state magnetic sublevels results in a nonclassical behavior of a high-$J$ molecular rotor. The classical approximation for the angular momentum distribution is compared with the exact quantum calculations, and is shown to fail in cases of long interaction times and high intensities of the exciting light. In these limits, the quantum uncertainty defines the spatial width of the angular distribution. The applicability of the classical treatment is analyzed and found to be different in the cases of $\stackrel{\ensuremath{\rightarrow}}{J}J\ensuremath{-}1$ and $\stackrel{\ensuremath{\rightarrow}}{J}J$ transitions. A biaxial spatial orientation with two preferential axes of rotation is experimentally created in sodium atoms via coherent population trapping by elliptically polarized light. A method for producing an arbitrary orientation of atomic angular momentum by magnetic field assisted coherent population trapping is proposed.