计及声子辅助跃迁的单量子点中的非线性法拉第偏转

利用一束弱线性π偏振探测光在与其平行的磁场作用下所形成的两偏振分量,在半导体单量子点中考虑声子辅助跃迁去构建环形四能级电磁感应透明介质模型.利用多重尺度法,解析研究发现:仅考虑系统的线性效应,随着耦合光强度的增加,介质对探测光的吸收迅速减少,形成透明窗口,并且透明窗口的宽度随之增大;进一步地,在相同的外加磁场下探测光的非线性法拉第偏转方向与线性法拉第偏转相反,且偏转角更大.随着声子辅助跃迁强度的增加,线性和非线性法拉第偏转角都会逐渐变小,并且非线性法拉第偏转角减小的更多.这说明系统中的声子辅助跃迁能有效地调制探测光的法拉第偏转.我们的研究可能对于弱光条件下的光信息处理和传输具有潜在的应用价值.     

半导体三量子点电磁感应透明介质中的非线性法拉第偏转

利用一束弱线性π偏振探测光在与其平行的磁场作用下所形成的两偏振分量,然后结合量子点间的隧穿耦合,构建了五能级M型半导体三量子点分子电磁感应透明介质.通过研究该体系的线性光学性质发现,操控量子点间隧穿耦合强度可有效调节系统中隧穿诱导透明窗口的宽度,并实现对介质的反常色散与正常色散的"开关"调节效应.随后,对体系非线性法拉第效应的研究发现,在相同的外加磁场下探测光的非线性法拉第偏转方向与线性法拉第偏转相反且非线性法拉第偏转角更大.     

四能级原子系统中非线性电磁感应吸收的理论研究

在n型四能级原子系统中,研究了电磁感应吸收的非线性理论.结果表明:探测光的拉比频率和衰减分配系数A影响非线性吸收,进而影响介质吸收.当探测光光强较弱时,介质吸收和线性吸收一致,均表现为电磁感应吸收特征;当探测光光强增大时,介质吸收和线性吸收不再一致,介质吸收曲线将会呈现出烧孔现象;当探测光光强增大到控制光(或信号光)光强时,介质吸收表现出很大的增益现象.同时,非线性吸收受到衰减分配系数A的影响,即使在探测场很弱的条件下,随着A值的减小,介质吸收由电磁感应吸收现象表 关键词： 电磁感应吸收 非线性吸收 增益现象 n型四能级原子系统     

里德伯原子中非厄米电磁诱导光栅引起的弱光孤子偏折及其操控

基于里德伯-电磁感应透明系统实现了具有宇称-时间对称的电磁感应诱导光栅,并研究了系统中探测光场在到达光栅前形成孤子的过程以及经过光栅时引起的偏折现象.发现由于里德伯-电磁感应透明系统具有很强的非线性光学效应,因此只需要很少的输入探测光能量就能形成稳定的光孤子.此外还发现,通过改变电磁感应诱导光栅的增益/损耗系数、光栅周期、以及体系的克尔非线性非局域度都可以有效地改变探测光孤子的偏折程度和状态,实现对弱光孤子偏折的主动操控.本文的研究结果可为未来利用宇称-时间对称的电磁感应诱导光栅实现全光控制和光信息处理等相关应用提供一定的理论依据.     

计及激子-双激子相干下半导体单量子点中的空间光孤子对

考虑激子-双激子的相干效应, 解析地研究了半导体单量子点中探测光和信号光的吸收特性和非线性传播特性.结果发现, 在线性条件下, 单量子点中出现电磁感应透明现象; 进一步分析可得, 电磁感应透明所呈现的是单窗口或双窗口或光学增益均可通过调节控制光强加以控制.在非线性条件下, 弱信号光诱导弱探测光产生两个分量, 这两个分量在系统中所激发的自克尔和交叉克尔 非线性效应与系统的衍射效应相平衡从而形成稳定的亮-亮, 亮-暗, 暗-暗等空间光孤子对. 关键词： 半导体量子点 电磁感应透明 空间光孤子对     

电磁感应透明介质中的弱光空间暗孤子环

利用多重尺度方法,解析地研究了Λ型三能级冷原子气及一束较强耦合光组成的电磁感应透明介质体系中的非线性动力学性质.结果表明：一束较弱的探测光能在电磁感应透明介质中形成弱光空间暗孤子,当弱光空间暗孤子沿轴向传播时,它会逐渐演化成一个稳定的弱光空间暗孤子环,这是衍射效应和自散焦效应相互平衡的结果. 关键词： 电磁感应透明 弱光空间暗孤子环 多重尺度方法     

里德伯电磁感应透明中的相位

本文在典型的里德伯电磁感应透明系统中研究弱探测场在相互作用原子系统中的传播特性,重点关注基于偶极阻塞效应的探测场相位的合作光学非线性行为.通过与探测场透射率和光子关联作对比,发现相位的光学响应具有新特性:共振和Autler-Townes劈裂条件下相位对入射场强和初始光子关联不敏感,而在两者之间的频率范围内相位响应具有非线性特征,尤其在经典光频率处最显著.此外,提高主量子数和原子密度都会促进相位的非线性效应.综上,与探测场透射率和光子关联一样,相位可以作为合作光学非线性的另一个标识来刻画非线性现象,对里德伯电磁感应透明研究是一个有力的补充.     

法拉第效应旋光不可逆性的实验验证

现有的法拉第效应实验装置仅能验证光单方向通过介质时,偏转角变化量与磁场间的正比关系,却无法验证法拉第效应旋光的不可逆性.重新设计光路,可测量线偏振光二次通过介质后的旋光角,与单次通过介质时的旋光角进行比较,实验结果可验证法拉第效应旋光的不可逆性.     

交叉克尔非线性对二阶非线性诱导透明的影响

考虑耦合介质存在交叉克尔非线性的情形下，研究了交叉克尔效应对耦合双谐振腔中二阶非线性诱导透明的影响.首先给出了描述体系理论模型的哈密顿量，再通过对海森堡-朗之万方程进行线性化，得到了探测场的透射率，进而得出系统的吸收和色散关系.研究结果表明，在交叉克尔非线性强度较小时，可忽略其对诱导透明的影响;随着交叉克尔非线性强度的增大，诱导透明窗口宽度随之快速变窄.此外，吸收曲线中还出现了双吸收峰.进一步增强交叉克尔非线性，导致原本出现的诱导透明消失，并在新吸收峰处产生了新的诱导透明，新的诱导透明的吸收零点位置随着交叉克尔非线性增加而向左偏移.这些结果可能在不透明介质的窄窗口光传输和提高光学腔的性能方面提供一些参考.     

非线性光学效应与光速减慢

激光技术的发展为极限光速的测量和应用提供了有效工具。本主要介绍了与光速减慢有关的非线性光学知识和光速减慢的实验原理及方法。光速减慢实验中用到的低温Na原子气在探测激光和耦合激光的共同作用下处于量子相干态－－一种非线性极化状态,由于电磁感应透明效应（EIT）,探测光可以使介质的折射率改变并能透过Na原子气,使极限光速的测量和应用变为实现。     

Steady-state linear optical properties and Kerr nonlinear optical response of a four-level quantum dot with phonon-assisted transition

The linear optical properties and Kerr nonlinear optical response in a four-level loop configuration Ga As/Al Ga As semiconductor quantum dot are analytically studied with the phonon-assisted transition(PAT). It is shown that the changes among a single electromagnetically induced transparency(EIT) window, a double EIT window and the amplification of the probe field in the absorption curves can be controlled by varying the strength of PAT κ. Meanwhile, double switching from the anomalous dispersion regime to the normal dispersion regime can likely be achieved by increasing the Rabi energy of the external optical control field. Furthermore, we demonstrate that the group velocity of the probe field can be practically regulated by varying the PAT and the intensity of the optical control field. In the nonlinear case, it is shown that the large SPM and XPM can be achieved as linear absorption vanishes simultaneously, and the PAT can suppress both third-order self-Kerr and the cross-Kerr nonlinear effect of the QD. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength, and may provide some new possibilities for technological applications.     

Dynamics of coupled ultraslow optical solitons in a coherent four-state double-${\sf \Lambda}$ system

We present a systematical investigation, both analytical and numerical, on the dynamics of two nearly lossless and distortion-free weak nonlinear optical pulses in a cold, lifetime-broadened four-state double-Λ system via electromagnetically induced transparency. Starting from theequations of motion of atomic response and probe fields, we give a detail derivation of two coupled nonlinear Schrödinger equations that control the nonlinear evolution of two probe field envelopes by means of a standard method of multiple-scales. We show that stable optical solitons with very slow propagating velocity can be generated under very low input light intensity when working in the transparency window of probe absorption spectrum induced by two continuous-wave control fields. We demonstrate that coupled optical soliton pairs are possible in the system through cross-phase modulational instability and mutual trapping effect of solitons. We provide various coupled optical soliton pair solutions explicitly and analyze their stability numerically.     

Nonlinear cascade-configuration multi-wave mixing scheme based on electromagnetically induced transparency

A nonlinear optical cascade-configuration multi-wave mixing (CCMWM) scheme is presented and analysed for the generation of coherent light in a six-level atomic system in the context of electromagnetically induced transparency (EIT). A detailed semi-classical study of the propagation of the generated mixing and probe fields is demonstrated. We show by numerical simulations that EIT is capable of suppressing linear and nonlinear photon absorption. The analytical dependence of the generated mixing field on the probe field and the respective detuning is also predicted. Such a nonlinear optical process can be used for generating coherent short-wavelength radiation.     

Gain-assisted giant Kerr nonlinearity in a ${\sf \Lambda}$-type system with two-folded lower levels

We propose a four-level Λ scheme with a one-mode active Raman gain core and two-folded lower levels to obtain new linear and nonlinear optical responses. We show that this scheme is fundamentally different from that based on electromagnetically induced transparency (EIT). Firstly, it is gain-assisted and thus capable of eliminating all attenuation of probe field. Furthermore, due to the quantum interference effect introduced by a coupling field a gain doublet appears in gain spectrum, and hence the distortion of the probe field during propagation can be effectively avoided. In addition, in such system a large and rapidly responding Kerr nonlinearity can be produced, which is much (more than 10 times) larger than that obtained in the EIT-based scheme with the same energy-level configuration.     

Interference enhancement of resonant magneto-optical effects

The influence of spectral interference of different nature on resonant Faraday rotation is studied using as examples the effect of electromagnetically induced transparency in pure discrete atomic transitions and the transparency windows of autoionization resonances of gaseous media. A common numerical criterion for a substantial effect of spectral interference and coherence of atomic transitions on magneto-optical phenomena is established. A direct relationship between the polarization ellipse rotation angle of cw monochromatic light and reduction of the light pulse group velocity resulting from a strong frequency dispersion of the resonant refractive index is found. The known experimental data on ultraslow light pulses indicate the possibility of interference enhancement of the Faraday effect by a factor of 10⁶?10⁷.     

Optical Multi-wave Mixing Process Based on Electromagnetically Induced Transparency

In this paper, we propose and analyze an optical multi-wave mixing scheme for the generation of coherent light in a five-level atomic system in the context of electromagnetically induced transparency. A detailed semiclassical study of the propagation of generated mixing and probe fields is demonstrated. The analytical dependence of the generated mixing field on the probe field and the respective detuning is predicted. Such a nonlinear optical process can be used for generating short-wavelength radiation at low pump intensities.     

Gain-assisted large and rapidly responding Kerr Effect using a room-temperature active Raman gain medium

A four-level N scheme with a two-mode active Raman gain core is investigated for large and rapidly responding Kerr effect enhancement at room temperature. The new scheme is fundamentally different from the electromagnetically induced transparency (EIT-)based ultraslow-wave Kerr effect enhancement scheme. It eliminates the requirement of group velocity matching and multispecies medium. It also eliminates significant probe field attenuation or distortion associated with weakly driven EIT-based schemes. We show that a probe field can acquire a large, frequency tunable, gain-assisted nonlinear phase shift and yet travel with gain-assisted superluminal propagation velocity. This raises the possibility of rapidly responding, frequency tunable nonlinear phase switching and phase gates for information science.     

Optical switching by controlling the double-dark resonances in a N-tripod five-level atom

We have investigated the optical switching in a five-level atom in a novel configuration of electromagnetically induced transparency. This N-tripod type level scheme combines the attractive features of cross-phase modulation appearing in N-type atoms with the ability to slow light pulses associated with tripod atoms. The addition of a new driving field to the usual tripod configuration allows to control the double-dark resonances which appear in the four-level tripod system and thus enables to manipulate the probe absorption and dispersion properties. We have studied the temporal dynamics of two pulses, a probe pulse and a switch propagating pulse through the sample. In the presence of the switching field, a deep in the absorption at resonance due to one-photon electromagnetically induced transparency appears and the atomic system is transparent to the probe field, which propagates at a very small group velocity. By tuning the fields, one of the usual double-dark resonances appearing in tripod system can be controlled (Stark-shifted) and the medium, which is transparent in the absence of the control field, will become highly absorptive. The linear and cross-phase modulation susceptibilities have been calculated and we predict the possibility to realize two-photon switching and giant cross-phase modulation. Finally we address the question about the generation of an entangled coherent state and we show that the giant cross-phase modulation provided by this N-tripod atomic system can be used for realizing polarization quantum phase gates.     

Matching group velocity of bright and/or dark solitons via double-dark resonances

We propose a scheme which can generate group velocity matching bright and/or dark solitons in a four-level tripod configuration atomic system via double-dark resonances. It is shown that the linear absorption properties can be controlled by the controlling fields. For the nonlinear case, the optical soliton can form in the first and second electromagnetically induced transparency windows and their group velocities can be matched under the condition of equal half Rabi frequencies of the two controlling fields. We also show that adjusting the amplitude and group velocity of the soliton as well as the bright and dark solitons conversion can be realized.