We have observed coherent Raman beat signals from a Λ-type three-level system in a sodium atomic vapor. The sample is first prepared in a coherent superposition state of the ground-state hyperfine levels, or a dark state, by resonant bichromatic radiation. A following sudden frequency shift of one of the excitation beams causes the beat signals. Detailed analytical calculations based on the three-level Liouville equations are presented and are compared with experimental results. This simple technique is particularly suited for the obtaining of information on the generated sublevel coherence, including magnitude, phase, and decay time.
© 2005 Optical Society of America
(020.1670) Atomic and molecular physics : Coherent optical effects
(020.2930) Atomic and molecular physics : Hyperfine structure
(270.1670) Quantum optics : Coherent optical effects
(300.6320) Spectroscopy : Spectroscopy, high-resolution
(300.6420) Spectroscopy : Spectroscopy, nonlinear
Ken-ichi Harada, Koji Motomura, Takanori Koshimizu, Hirotaka Ueno, and Masaharu Mitsunaga, "Coherent Raman beats from dark states," J. Opt. Soc. Am. B 22, 1105-1111 (2005)