Interaction of laser radiation with free atoms

Aspects of atomic and molecular physics explored in studies of the interaction of laser radiation and free atoms are reviewed. The two-level approximation describing the resonant interaction between atoms and monochromatic light is discussed, with attention given to the Bloch equations and the dressed-atom model. The response of atomic systems (atomic beams transversely illuminated or vapors) to resonant laser excitation is treated, and pulse propagation experiments are considered. Self-induced transparency observed in pulse propagation experiments is emphasized. Multiphoton processes, including Doppler-free multiphoton excitation and resonant multiphoton ionization, are also mentioned.