Abstract

The intensity of resonance laser light, forward scattered by atoms in a longitudinal, magnetic field B is expressed by optical coherences between the sublevels of the lower and upper atomic states, perturbed by the scattered light. [1]. This can be done either in a standard |J, m〉 basis, or in the representation of superposition states that form two classes: the absorbing coupled, and nonabsorbing trap states. When .J quantum numbers of the upper and lower states are equal and integer, there is only one trap state |l〉 stable with respect to the spontaneous emission. When B = 0, |l〉 is a. perfect trap and accumulates entire atomic population, hence there is no coherence between |l〉 and other coupled states, which results in zero forward scatered (FS) signal. When B≠0, however, magnetic mixing of |l〉with other superposition destroys the trap and yields nonzero forward scattered intensity. It can be demonstrated that the shape of the FS signal reflects the magnetic dependence of the trap population [2]. Forward scattering (FS) of the resonance light can be thus used for monitoring the complex trap states similarly as in fluorescence (’dark resonance’). Superiority of forward scattering method consists in the lower number of light- and magnetic-induced coulings. In Hanle effect, information about the trap |t〉 is obtained indirectly by couplings: populations of coupled states in the upper level → optical coherences → populations and coherences between states in the lower level.

© 1996 IEEE