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

The interaction of laser light of arbitrary polarization with systems of hi gh angular momentum is considered. We show that elliptically polarized ligh t creates an anisotropic spatial distribution of atomic and molecular angul ar momentum which is qualitatively different from the alignment and orienta tion induced by light of circular or linear polarization. Multilevel cohere nt population trapping within a manifold of ground-stare magnetic sublevels results in a nonclassical behavior of a high-J molecular rotor. The classi cal approximation for the angular momentum distribution is compared with th e exact quantum calculations, and is shown to fail in cases of long interac tion 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 d ifferent in the cases of J-->J-1 and J-->J transitions. A biaxial spatial o rientation 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 m omentum by magnetic field assisted coherent population trapping is proposed . [S1050-2947(99)01708-4].