Quantum beats in photoionization from a coherent superposition of fine-structure levels

We present a theory of quantum beats in photoionization from a coherent superposition of D3/2,5.2 levels in alkali-metal atoms. The semiclassical density-matrix formalism is used to describe both the excitation of the D3/2,5/2 levels by a two-photon resonant pulse and the subsequent photoionization by a delayed probe pulse. Quantum beats occur in the ionization signal as a function of the delay of the probe pulse. The depth of modulation is determined for different light polarizations.