High-Resolution Spectroscopy Based on Atomic Coherences

The paper surveys the techniques of Doppler-free spectroscopy based on the creation and detection of Hertzian coherence in atomic and molecular systems. The preparation of individual atoms in a coherent superposition of states with the use of broadband optical excitation is discussed, with particular reference to excitation by pulsed tunable dye lasers. Time-resolved observations of the fluorescent light emitted by these atoms reveal the interference phenomenon known as quantum beats and enable Lande g-factors, fine and hyperfine splittings of excited levels to be determined. An account of progress in recent experiments with probe-beam monitoring and pulse trains from mode-locked dye lasers completes this review.