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博士候選人公開演講

Multi-photon processes in the atomic system of Cesium

演講者 : 阮氏垂 博士候選人 (成大物理系)
演講時間 : 2022 / 06 / 24 15:00
理學教學新大樓物理系3F 36369會議室
理學教學新大樓物理系3F 36369會議室位於 ...
Atom-light interactions in multi-photon system bring about enormously interesting phenomena, which in turn develop into techniques for studying fundamental properties of the atomic structure, the generation of nonlinear optics, and optical-quantum manipulation for potential applications in the future quantum information world. Among them, the quantum interference of the so-called electromagnetically induced transparency (EIT) has become a key technique that paves the way for the above applications. In this talk, we focus on the fundamental properties of the spectra of light-atom interactions in a multiple-level system with two- and three-photon sources. We will present the polarization effect on the ladder-type EIT in the Cs atom. In this experiment, the polarization plane of the two applied fields is aligned at different relative angles to observe the corresponding change in the obtained spectra. The results reveal that the polarization of the applied fields causes a prominent change in relative intensity ratios. We observe the peak height ratio (normalized to 44'4" peak height) of  I45'4”/44'4"≈2 and I44'3"/44'4≈7.4 as the two polarization change from parallel to perpendicular. The experimental results are confirmed by the simulation and well explained when taking into account the optical pumping effect, two-photon transition probability, dephasing rate, the change in Rabi frequency as polarization change as well as the velocity contribution. The consecutive work based on the extension of the previous one forms a Ξ−V four-wave mixing (FWM) configuration. We perform a theoretical model using the density matrix approach to describe the interaction of this system and the characteristics of the generated FWM signal. The three-photon resonance condition and the dressed state picture in the weak probe field approximation together establish a set of equations that is useful in explaining most of the properties of the generated FWM signal, such as the differences between laser scanning schemes, estimation of resonance positions, peak shape and peak intensity for the stationary atoms. The optimal FWM signal is obtained when the two control Rabi frequencies are closely equal. A detuning-caused enhancement of FWM is also observed in the calculation. The discussion of FWM in thermal vapor with velocity averaging and neighboring hyperfine transition are included for clarity although they either suppress the signal or create negligible contributions.