Self-diffraction and phase conjugation in a gas of atoms with a hyperfine level structure

A cubic susceptibility tensor describing all nonlinear optical phenomena within a one-photon absorption line is derived for a gas of atoms with a hyperfine level structure. This tensor is valid for either degenerate or nondegenerate four-wave mixing. It thus becomes possible to study the effect of the hyperfine structure and of the nuclear spin on self-diffraction, phase conjugation, and the self-effects of steady-state light waves in resonance with a common one-photon transition. Those amplitude properties and polarization properties of the these nonlinear phenomena which stem exclusively from the hyperfine structure and the nuclear spin are determined. It thus becomes possible to experimentally identify transitions in terms of the electron angular momentum and the total angular momentum with allowance for the nuclear spin. It also becomes possible to select optimum conditions for optical image transmission and optical information processing. In several nonlinear phenomena involving degenerate four-wave mixing and the self-effects of light waves, a deviation from resonance with the hyperfine sublevels does not eliminate the effects of either the hyperfine structure itself or the nuclear spin, because of the resonance at zero frequency