通讯机构：
[Hu, MM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We study spontaneous emission of a three-level cascade atom driven by a pair of bichromatic fields of equal frequency differences. The fluorescence spectra from the cascade transitions depend strongly on the difference between the relative phases of two bichromatic fields. Selective and almost complete elimination of fluorescence spectra is achieved simply by varying the difference phase.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
关键词：
absorption and dispersion;phase dependence and independence;multiple switching from normal to anomalous dispersion
摘要：
The phase dependence and independence of the response of a trichromatically driven two-level medium to an arbitrarily intense probe field have been studied. The sum of the relative phases of the sideband components of the trichromatic field compared to the central component plays a crucial role in the response of the medium. For a weak probe field, as the sum of the relative phases changes from 0 to π, multiple switching can be achieved, in which switching from normal to anomalous dispersion occurs in multiple separate frequency regimes. The remarkable dependence on the sum phase is also shown for a strong probe field. On the other hand, when the sum of the two relative phases is fixed, the changes in the respective phases have no influence on the response of the medium.
通讯机构：
[Hu, Xiangming] H;Huazhong Normal Univ, Dept Phys, Luoyu Rd 152, Wuhan 430079, Peoples R China.
摘要：
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states.
摘要：
We examine the phase-dependent effects in resonance fluorescence of a two-level atom driven by a trichromatic modulated field. It is shown that the fluorescence spectrum depends crucially on the sum of relative phases of the sideband components compared to the central component, not simply on the respective phases. The appearance or disappearance of the central peak and the selective elimination of the sideband peaks are achieved simply by varying the sum phase. Once the sum phase is fixed, the spectrum keeps its features unchanged regardless of the respective relative phases.
作者机构：
[Hu, XM; Zou, JH; Li, X; Du, D; Cheng, GL] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We present a theoretical analysis of trichromatic phase manipulation of electromagnetically induced transparency and show that it is possible to obtain double switching, in which switching from normal to anomalous dispersion occurs in two separate frequency regimes. In particular, a four-level system in the N configuration is considered, in which electromagnetically induced transparency is established in the Λ subsystem and the additional transition is connected to the probe transition and is coupled by a trichromatic field. It is shown that the sum of the relative phases of the sideband components compared to that of the central component plays a crucial role in the absorption and dispersion spectra. Normal dispersion with negligible absorption or anomalous dispersion with small gain can be achieved in multiple-frequency regimes by varying the sum of the relative phases. When the sum phase is changed from 0 to π, switching from normal to anomalous dispersion occurs in the two different frequency regimes. On the other hand, so long as we fix the sum of two relative phases, the absorption and dispersion spectra keep their own features unchanged no matter how we vary the respective relative phases.
作者机构：
[Hu, XM; Zou, JH; Li, X; Du, D; Cheng, GL] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We study the dependence of absorption and dispersion spectra on amplitudes and phases of the driving fields in multiple electromagnetically induced transparency. For this purpose we consider trichromatic excitation in a three-level Λ atomic system, in which a trichromatic control laser and a monochromatic probe laser are applied to two different transitions, respectively. We numerically calculate the absorption and dispersion spectra. Two characteristic features are found. Firstly, the central transparency can be made to appear or to disappear by utilizing the amplitudes and phases of the driving components. Secondly, so long as we fix the sum of two relative phases of two sideband excitation components to the central component, the absorption and dispersion spectra keep their own lineshapes unchanged no matter how we vary the respective relative phases.
作者机构：
[Hu, XM; Zou, JH; Li, X; Du, D; Cheng, GL] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We study two-photon absorption in a three-level ladder atomic system driven by a pair of bichromatic fields of equal frequency differences. The high-frequency component of one bichromatic field and the low-frequency component of the other are on two-photon resonance. The transition probability is calculated by employing the method of harmonic expansion and matrix inversion. Unexpectedly, when the sums of the phases of the different pairs of field components on the two-photon resonance are equal to each other, two-photon absorption is dramatically suppressed and the atomic system becomes transparent against two-photon absorption. Physically, due to dynamical Stark splitting, the two-photon transitions induced by the different pairs of field components experience different dressed states with phase difference of π. As a result, destructive interference occurs between the two pathways and leads to the inhibition of two-photon absorption.
期刊：
Journal of Physics B: Atomic, Molecular and Optical Physics,2004年37(2):345-356 ISSN：0953-4075
通讯作者：
Hu, X.-M.
作者机构：
[Hu, XM; Zhang, JP] Department of Physics, Huazhong Normal University, Wuhan 430079, China
通讯机构：
Department of Physics, Huazhong Normal University, China
摘要：
Quantum interference has been predicted to occur in a three-level Λ system with near-degenerate dipole allowed transitions, which are coupled to the same linearly polarized incoherent field. For the Λ system with two degenerate lower levels, we show that (a) quantum interference of incoherent pump processes leads to coherent population trapping (CPT), and (b) when two coherent fields are applied to two transitions on two-photon resonance, CPT appears when the amplitudes and phases of the applied coherent fields and the polarization angle of the incoherent field satisfy certain conditions. Further, the physical mechanism and the above conditions for CPT are presented.
