Theoretical Explanation of the Apparent Two-state Behaviour Observed in NaD2Line Optical Nutation Signals

Observations of optical nutations from the NaD2 line excited by resonant, π-polarized light have indicated that the oscillations consist of essentially one frequency. Considering the complexity of the energy-level configuration associated with this line, the experimental results are surprising. However, it is shown that this pseudo-two-state behaviour is predicted by both a semiclassical theory and a completely quantum electrodynamic approach when the intensity of the light is above a moderately valued threshold, namely, when the power broadening is greater than the hyperfine splitting of the upper states.