作者机构：
[Hu, XM; Xu, J] 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：
In this paper we investigate the dispersive and absorptive properties of a system of three-level cascade atoms driven by a strong coherent field. Three characteristic features are found. First, for the same set of atom-light interaction parameters, the indices of refraction are large at three different frequencies where the absorption vanishes. These three frequencies are determined by the resonance transition frequencies between dressed states produced by the strong driving field. Second, negative dispersion without absorption, which leads to superluminal light propagation, is achievable in the central resonance structure of the dispersion spectrum. Third, the whole absorption spectrum displays, in general, three pairs of absorption peaks and three pairs of gain (negative absorption) peaks. The minimal spacing between dressed states determines whether the outer adjacent gain peaks are separated from each other.
作者机构：
[Hu, XM; Li, JY] 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 show that spontaneous-emission-mediated emissive multiphoton transitions provide an efficient way for the generation of squeezed light. Exemplifying the doubly driven three-level system in V configuration, we find that photon fluctuations are suppressed below the shot noise limit by more than 50%. The greatest advantage of the present scheme is that spontaneous-emission-mediated emissive multiphoton transitions are conveniently controlled by adjusting driving field parameters. Good noise reduction is achievable when the decay rate at the bare state laser transition is much larger than that at the bare state auxiliary transition, which is impossible in the previous schemes.
期刊：
EUROPEAN PHYSICAL JOURNAL A,2004年20(1):117-120 ISSN：1434-6001
通讯作者：
Napoli, A.
作者机构：
[Napoli A.; Messina A.] INFM, MIUR, Dipartimento di Scienze Fisiche, Via Archirafi, 36, 90123 Palermo, Italy;[Hu Xiang-ming] Department of Physics, Huazhong Normal University, Wuhan 430079, China
通讯机构：
[Napoli, A.] I;INFM, Via Archirafi, 36, 90123 Palermo, Italy
摘要：
The dynamics of a degenerate two-mode lossy cavity field coupled to an effective two-level atom is studied. Our main result is that the coherent energy exchange between the two modes, manifested by the system in the ideal case, is compatible with the presence of cavity damping characterizing the current experimental set-up.
关键词：
master equation;bimodal lossy cavity;generalized JC model
摘要：
The Liouville equation of a two-level atom coupled to a degenerate bimodal lossy cavity is unitarily and exactly reduced to two uncoupled Liouville equations. The first one describes a dissipative Jaynes-Cummings model and the other one a damped harmonic oscillator. Advantages related to the reduction method are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.
作者机构：
[Hu, XM; Wang, L; Kong, LB] 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.
关键词：
Population transfer;Driven systems;Inversion;Fluorescence;Relaxation;Resonance;Cavity;Atoms
摘要：
So far it has been known that the simultaneous use of two coherent fields is necessary for dynamically induced irreversibility in three-level systems. Here we show that one incoherent field and one coherent field, in principle, suffice to establish the dynamical irreversibility, which leads to population inversion on the only coherently driven transition. As the physical mechanism, the coherent field creates dressed states and the incoherent field induces selective trapping or selective excitation of either of dressed states. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 26]
作者机构：
[Hu, XM; Xu, J; Kong, LB] Cent China Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] C;Cent China Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We show that it is possible, in principle, to employ an incoherent field as a control field to achieve maximal atomic coherence for a probe field, which characterizes ultralarge index of refraction and vanishing absorption. For this purpose we consider a three-level V system in which there are two dipole transitions, of which one is weak and the other is strong. The strong probe field is applied to the weak transition and the incoherent field drives the strong transition. For such an arrangement, selective dressed-population trapping, which corresponds to maximal atomic coherence, is established by relying on the incoherent field and the spontaneous relaxation to transfer population from one dressed state to the other. This scheme as an extreme example explains that strong-field index enhancement based on selective dressed-population trapping is resistant to the control field fluctuations.
作者机构：
[Hu, XM] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;Chinese Acad Sci, Shanghai Inst Opt & Fine Mech, Lab High Intens Opt, Shanghai 201800, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We analyse the physical origin of population inversion via continuous wave two-colour coherent excitation in three-level systems by dressing the inverted transition. Two different mechanisms are identified as being responsible for the population inversion. For V-configured systems and cascade (Θ) configured systems with inversion on the lower transition, the responsible mechanism is the selective trapping of dressed states, and the population inversion approaches the ideal value of 1. For Λ-configured systems and Θ-configured systems with inversion on the upper transition, population inversion is based on the selective excitation of dressed states, with the population inversion tending towards 0.5. As the essential difference between these two mechanisms, the selective trapping of dressed states occurs in systems with strong decay into dressed states while the selective excitation appears in systems with strong decay out of dressed states.
作者机构：
[Hu, XM] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;Chinese Acad Sci, Shanghai Inst Opt & Fine Mech, Lab High Intens Opt, Shanghai 201800, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We propose a scheme for the control of spontaneous emission, employing a single spontaneous channel. the decaying state of which is coupled to two long living states by two laser fields. This scheme provides a controllable way for the equivalent realization of a two-channel system and thus is easier to implement. While effects obtained previously for the two channel system such as selective elimination and spectral narrowing are preserved, two new effects are predicted. A three-peaked spectrum alternatively appears with a single ultrasharp line as either of two driven transitions is slowly detuned from one-photon resonance. Double dark lines occur in the spontaneous emission spectrum when the two driven transitions are off two-photon resonance. We also show that the phase control of spontaneous emission can be realized under significantly looser conditions. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 16]
作者机构：
[Hu, XM] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;Chinese Acad Sci, Shanghai Inst Opt & Fine Mech, Lab High Intens Opt, Shanghai 201800, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We consider strong-field index enhancement in three-level systems in which there is a strong spontaneous decay from an auxiliary level into either of two states that the probe field couples. A control field is detuned resonant with the transition between the auxiliary level and one of the dressed states produced by the strong probe field. It is shown that it is possible to achieve maximal atomic coherence, which characterizes an ultralarge index of refraction and vanishing absorption. This scheme is based on selective dressed population trapping, which is established by relying on the control field and the strong decay to transfer population from one dressed state to another through the auxiliary level. An advantage of the present scheme is that the conditions for its realization are accessible experimentally.
作者机构：
[Hu, XM] Chinese Acad Sci, Shanghai Inst Opt & Fine Mech, Lab High Intens Opt, Shanghai 201800, Peoples R China.;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] C;Chinese Acad Sci, Shanghai Inst Opt & Fine Mech, Lab High Intens Opt, Shanghai 201800, Peoples R China.
摘要：
We show that it is possible to achieve population inversion and upconversion lasing when a strong coherent field induces an exchange in the relative position of one dynamical Stark sublevel and a neighbouring level. This prediction is based on the fact that the dynamical level crossing results in a change in the direction of spontaneous emission. This provides a potential way towards short-wavelength laser generation.
作者机构：
[Hu, XM; Xiong, J; Peng, JS] 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：
A theoretical analysis of the spectral linewidth of V-type inversionless and Raman lasers is presented. First, we examine the effects of the atomic coherence between dressed states and the Autler-Townes splitting on the linewidth. It is demonstrated that near above threshold, the V inversionless laser has a narrower linewidth than that of the two-level laser. Instead of the dressed coherence, it is the Autler-Townes splitting that is responsible for the linewidth reduction though the dressed coherence determines the laser gain. Next, we explore the effects of the generated laser intensity on the linewidth. It is shown that the linewidths of the V inversionless and Raman lasers follow the usual 1/I decrease for smaller laser intensity I, but a slower decrease than 1/I for larger laser intensity. For the V Raman laser, even more surprisingly, with the laser intensity increasing, the linewidth appreciably increases as well. As a result, well above threshold, the V inversionless and Raman lasers may have a larger linewidth than that of the two-level laser. Finally, a comparison is made between the V lasers and the Λ lasers. It is found that the linewidth of the Λ inversionless laser shows a fast 1/I2 decay under optimum conditions.
