Total (upper) and circularly polarized (lower) intensity of a Zeeman-split line. The intensities are normalized with respect to the unsplit (x_Z = 0) intensity. The total intensity plots are for an unsplit (x_Z = 0) and Zeeman-split (x_Z = 0.3, , θ = π/2 – π/30) line. The circularly polarized intensity plots are for a single propagation with constant magnetic fields, x_Z = 0.3 and θ = π/2 – π/30, that yield the curve. The curve indicated by Δx = 0.3 is the circular polarization from two propagations with a velocity shift Δx = 0.3 and oppositely oriented magnetic fields (x_Z = 0.3 and θ = ±π/2 – π/30).