Zeeman coherence in saturated absorption

By modulating the saturating beam polarization, it is possible to extract from the probe beam a signal which depends only on the Zeeman coherence Δm = 2 (transverse alignment), and to study velocity changing collisions which do not destroy the alignment. This type of collisions appears to be of small importance in neon, so that width of the saturated absorption curve from alignment is narrower than that from populations.