Formation of Light-Induced Spatial Gratings of Cooled Atoms in Light Fields with Polarization Gradients

The kinetics of an atomic beam with total angular momenta J(g) = J(e) = 1/2 in the ground and excited states traveling through a resonance light field with lin perpendicular to lin configuration is analyzed. Using the framework of approximation of weak light fields, the initial kinetic Focker-Planck equations for the complete distribution function and the orientation of atoms in the ground states are derived. The kinetic equations for the stationary regime are also analyzed. It is demonstrated that atoms can be cooled down below the Doppler limit due to the radiation friction force in the case of positive detuning. Formation of spatial gratings of the density of cooled atoms (channeling effect) and of the density of light-induced magnetic momentum in the effective potential field produced due to the force of light pressure are analyzed quantitatively. The fractions of atoms trapped in channels and the degree of polarization of those atoms are estimated. It is demonstrated in particular that atoms captured in the channels possess essentially non-equilibrium momentum distribution with the half-width k(B)T(cool) = (1/2)(h) over barG gamma, this being much lower than the Doppler limit at low level of saturation.