Density matrix formalism is used to model two-photon free-induction decay from a ladder-type, three-level scheme with a resonant intermediate state. Counterpropagating light beams are assumed. Only the upper transition is frequency shifted out of resonance with the injected field. Results indicate departure from single-photon behavior; in particular, there is a π phase shift in the oscillations when the Rabi frequencies associated with each transition are comparable in magnitude. The theory is applied to the 32S½ (F=1) − 32P½ − 42D3/2 excitation scheme of sodium.
© 1986 Optical Society of America
M. F. Marshman, P. M. Farrell, W. R. MacGillivray, and M. C. Standage, "Two-photon free-induction decay," J. Opt. Soc. Am. B 3, 607-613 (1986)