POLARIZATION GRADIENT COOLING IN A ONE-DIMENSIONAL SIGMA+-SIGMA- CONFIGURATION FOR ANY ATOMIC TRANSITION

We discuss the radiation force in a one-dimensional sigma+-sigma- laser standing wave, for transitions J --> J + DELTA J, for any J, and DELTA J = +/-1, 0, in the limit of low saturation of the atomic transition. The interaction between the radiation field and the atom produces a motion-induced orientation of the atomic ground state which grows rapidly with J. The radiative force on the atom is sensitive to this orientation. For J --> J + 1 the dissipative part of the total force is much larger than the reactive part, at low velocities, while for the other cases the two contributions are roughly equal and opposite. By using a simple method of calculation, we pin much physical insight into the mechanism of induced orientation, and give quantitative results for the size of the radiation force, including both the low-velocity friction coefficient and the velocity capture range.