General theory of laser-induced quantum beats. II. Sequential laser excitation; effects of external static fields

A general theory of laser-induced quantum beats introduced in paper I is extended to include the effects of sequential laser excitation by several lasers for atomic systems either free or subjected to external static fields. A detailed study is made of the dependence of the quantum beat signal on the polarizations of the exciting laser pulses and detected spontaneous emission. The theory is applied to the echelon excitation of sodium $\mathrm{nD}$ Rydberg states. An analysis of the Zeeman beats produced by excitation in an external magnetic field suggests new ways to measure the fine-structure interaction constant of the Rydberg levels.