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Acta Physica Sinica

Interference enhancement of two-photon absorption caused by a pair of coherent superposition levels in Na

Yanliang Zhang, Jiang Li, Niu Yue-Ping, Zhenrong Sun, Ding Liang-En, Zugeng Wang, (1)华东师范大学物理系,光谱学与波谱学教育部重点实验室,上海 200062; (2)陕西师范大学,物理学与信息技术学院,西安 710062

Published Jan 1, 2003• 1 citation
Publisher

Abstract

In the sodium dimer rhomb-type four-level system with a pair of coherent superposition levels, the interference enhancement of two-photon absorption caused by coherent superposition of the coupling levels is experimentally observed. The calculated results using density matrix equation are in good agreement with the experimental results.
DOI
10.7498/aps.52.345

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In this paper we report the first observation of molecular population trapping in four level systems. Constructive and destructive quantum interferences between two sum-frequncy two-photon transitions in Y- and rhomb-type four-level systems, respectively, im sodium molecules have been experimentally achieved by using only one laser source. Their energy level schemes are featured by the extremely near-resonant enhancement of the equal-frequency two-photon transitions, sharing both the initial and the intermediate levels for the Y-type, and sharing both the initial and the final levels for the rhomb-type systems. Their novel spectral effects are to show seriously restrained Doppler-free UV peak at the nominal location of the induced two-photon transition with visible fluorescence in rhomb-type schems, and to show a strong extra UV peak but null visible fluorescence in the middle between the two dipole allowed two-photon transitions.
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Atomic coherence and interference in an atomic medium exhibiting electromagnetically induced transparency may lead to enhancement or suppression of nonlinear susceptibilities. Absorptive photon switching has been observed by constructive quantum interference, which is based on the enhanced third-order, nonlinear absorption in a four-level system. In a different four-level system, suppression of the two-photon absorption by destructive quantum interference has been observed. Experiments were carried out on 87Rb atoms cooled and confined in a magneto-optical trap and the experimental results agree with theoretical calculations of simple four-level model systems.
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Electromagnetically induced transparency may lead to suppression of two-photon absorption in a four-level atomic system. This phenomenon is manifested by destructive quantum interference among multiple excitation paths created by a coherent coupling field. We report an experimental observation of such suppression of two-photon absorption in cold 87Rb{}^{87}\mathrm{Rb}87Rb atoms.