Consider an atom interacting with the field detuned below the transition from atomic states F g = 1 2 and F e = 3 2 ( ℏ ℏ ω ω f i e l d < E e g ). The variation of the polarization along z results in a variation in the light shifts of the atomic Zeeman sublevels with z. The Clebsch-Gordan coefficient connecting the | g , m F = − − 1 2 ⟩ ⟩ state to the | e , m F = − − 3 2 ⟩ ⟩ state is 3 times larger than connecting the | g , m F = 1 2 ⟩ ⟩ state to the | e , m F = − − 1 2 ⟩ ⟩ state. Thus for σ σ − − polarization the light shift is three times larger for the | g , m F = − − 1 2 ⟩ ⟩ state than for the | e , m F = 1 2 ⟩ ⟩ state. The situation is reversed for σ σ + polarization, with the light shift being three times larger for the | g , m F = 1 2 ⟩ ⟩ state than the | e , m F = − − 1 2 ⟩ ⟩ state. When the polarization is linear, there is no difference in the light shifts between the two states. Thus the energies of the states will oscillate in z with period λ λ 2 .