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     

若干参数对瞬态电磁感应透明的影响

研究了原子梯形三能级系统的瞬态电磁感应透明特性,分析了系统各种参数,诸如瞬态作用时间、泵浦场和探测场的拉比频率、激光线宽及消相碰撞等因素对瞬态电磁感应透明的影响。结果表明：在不考虑激光线宽及消相碰撞时,探测场的吸收随时间在零吸收附近作类似于阻尼减幅振荡,系统可实现无反转放大;随着泵浦场的拉比频率的减小及上能级驰豫速率的增大,感应透明将减弱。在考虑到激光线宽及消相碰撞等非相干因素时,对于一定的瞬态作用时间,感应透明将随着探测场拉比频率的增大而减弱。     

四能级原子介质中Goos-Hänchen位移的相干控制

通过外加驱动光场的调控改变腔中四能级原子介质的色散-吸收关系, 从而来调控反射光和透射光的Goos-Hänchen位移. 研究表明介质可同时对探测光场进行放大和吸收,在介质对探测光的吸收和放大相互抵消 (即介质呈现透明特性)的区域附近,对Goos-Hänchen位移的控制比强吸收或强放大特性下要灵敏, 可以实现位移的突变和增强.     

四能级原子介质中Goos-Hnchen位移的相干控制

通过外加驱动光场的调控改变腔中四能级原子介质的色散-吸收关系,从而来调控反射光和透射光的Goos-Hanchen位移.研究表明介质可同时对探测光场进行放大和吸收,在介质对探测光的吸收和放大相互抵消(即介质呈现透明特性)的区域附近,对Goos-Hanchen位移的控制比强吸收或强放大特性下要灵敏,可以实现位移的突变和增强.     

控制场对M型原子系统吸收色散性质的影响

运用数值模拟方法讨论了控制场的变化对M型五能级原子系统相对于探测场的吸收和色散等光学性质的影响.结果表明,改变控制场拉比频率时,系统的吸收和色散性质会发生规律性变化.在特定区域会呈现电磁感应透明窗口,其中透明窗口的数量与外加控制场数目成正比,而透明窗口宽度与拉比频率大小相关,拉比频率越大,透明窗口越平坦,当拉比频率减小,透明窗口变窄同时介质色散增强可获得慢光速光脉冲.     

控制场对M型原子系统吸收色散性质的影响

运用数值模拟方法讨论了控制场的变化对M型五能级原子系统相对于探测场的吸收和色散等光学性质的影响.结果表明,改变控制场拉比频率时,系统的吸收和色散性质会发生规律性变化.在特定区域会呈现电磁感应透明窗口,其中透明窗口的数量与外加控制场数目成正比,而透明窗口宽度与拉比频率大小相关,拉比频率越大,透明窗口越平坦,当拉比频率减小,透明窗口变窄同时介质色散增强可获得慢光速光脉冲.     

准Λ型四能级原子系统中的烧孔和光学双稳现象

研究了准Λ型四能级原子与两光场相互作用系统中的量子干涉效应.发现在弱探测场下系统驱动场拉比频率改变时,其色散曲线会呈现出烧孔现象,吸收增益曲线会出现全增益区以及宽而平坦的电磁感应透明窗口.另外,色散曲线随探测场拉比频率相位的演化会呈现出光学双稳态效应.     

倒Y型四能级原子系统中电磁诱导透明的相干控制

研究了倒Y型四能级原子系统中相干控制电磁诱导透明.应用微扰理论给出一阶近似条件下,不同控制场原子系统对探测光场响应的解析式及电磁诱导透明窗宽度的解析式.在探测场为弱场时,分析了系统中控制光场强度、耦合光场强度及其失谐量对电磁诱导透明窗的影响.研究发现电磁诱导透明窗随控制光场强度的增强变宽,而随耦合光场强度的增强变窄,当探测光场与耦合光场偏离双光子共振时,透明窗外的吸收增加,透明窗变宽.在弱探测场、弱控制场条件下,分析了初始时刻原子处在相干叠加态时的相对相位、相对强度与探测场和控制场的相对相位等对系统吸收特性及透明窗的影响.结果表明探测场与控制场的相对相位对吸收的影响与相干叠加态中两能级之间几率幅的相对相位对吸收的影响作用相反,系统在两下能级干涉极大时,存在一个很宽的透明带.应用缀饰态理论和量子相干理论对所得结果进行了解释.     

基于N-A型原子系统的1→N型分束器

分析N-A型原子系统的原子极化率,结果表明即使在全共振条件下,EIT效应并不一定产生,介质对信号场的色散和吸收关系与所有场的复拉比频率有关.信号场传播方程的解析分析表明,此系统可以把一束光分成不同频率的N束光,并且其强度和相位是可控的.暗态极化子分析表明它还可以用作1→N量子分束器,产生多体纠缠态.     

准A型四能级原子系统中的烧孔和光学双稳现象

研究了准A型四能级原子与两光场相互作用系统中的量子干涉效应．发现在弱探测场下系统驱动场拉比频率改变时，其色散曲线会呈现出烧孔现象，吸收增益曲线会出现全增益区以及宽而平坦的电磁感应透明窗口．另外，色散曲线随探测场拉比频率相位的演化会呈现出光学双稳态效应．     

Controllable amplification and absorption properties in coupled-double-quantum-wells with tunneling-induced interference

We investigate optical amplification and absorption properties under a closed-loop double-Λ configuration in an asymmetric semiconductor coupled-double-quantum-well (CDQW) nanostructure based on interband transitions (IBTs). In the proposed CDQW scheme, the amplification, absorption or zero-absorption (transparency) of the probe field and the signal field can be realized with realistic experimental parameters by appropriately adjusting the relative phase, the two pump Rabi energies, the probe detuning, and the Fano-interference strength, respectively. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters.     

Amplification without population inversion in a three-level Λ-type system with an external coherent magnetic field

In this Letter, we investigate the amplification without inversion (AWI) in a new scheme, a three-level Λ-type system which the two lower states are coupled by an external magnetic field. We find that, owing to the presence of the external magnetic field, the absorption of the probing field is very sensitive to the relative phase of the probing and the pumping fields. By appropriately choosing the Rabi frequency of the pumping field, the Lamor frequency of the external magnetic field and the relative phase, AWI can be realized.     

Absorption and dispersion by a multiple driven two-level atom

We investigate the absorption and dispersion properties of a two-level atom driven by a polychromatic field. The driving field is composed of a strong resonant (carrier) frequency component and a large number of symmetrically detuned sideband fields (modulators). A rapid increase in the absorption at the central frequency and the collapse of the response of the system from multiple frequencies to a single frequency are predicted to occur when the Rabi frequency of the modulating fields is equal to the Rabi frequency of the carrier field. These are manifestations of the undressing or a disentanglement of the atomic and driving field states, that leads to a collapse of the atom to its ground state. Our calculation permits consideration of the question of the undressing of the driven atom by a multiple-modulated field and the predicted spectra offer a method of observing undressing. Moreover, we find that the absorption and dispersion spectra split into multiplets whose structures depend on the Rabi frequency of the modulating fields. The spectral features can jump between different resonance frequencies by changing the Rabi frequency of the modulating fields or their initial phases, which can have potential applications as a quantum frequency filter. Received 23 October 2001 and Received in final form 31 January 2002     

On the inversionless amplification in the proximity of transitions from autoionization levels

The results of theoretical investigations of the line shape for the absorption (amplification) of a weak optical signal in the proximity of the system of autoionization atomic levels are reported. The best conditions and regions of existence of the inversionless amplification in the proximity of transitions from these atomic levels are determined depending on the energy defect between them, the Fano parameters, and the generalized Rabi frequencies, as well as on the incoherent pumping power. The problem of dynamics of atomic level occupancy for the pulse excitation is solved. It is demonstrated that the effect of the inversionless amplification for the transient mode can considerably exceed its own steady-state value.     

四能级Tripod-型原子系统中量子相干导致的交叉Kerr非线性效应

计算了四能级Tripod-型原子系统中探针光极化率随其频率失谐量的变化曲线.结果表明,当触发光作用于该系统的一个共振跃迁能级时,可使探针光的吸收和色散在其电磁感应透明(Electromagnetically Induced Transparency,EIT)窗口(由耦合光产生)处发生显著变化.随着触发光Rabi频率的增加,探针光在EIT窗口的吸收显著降低,色散显著增加.这种由触发光引起的探针光极化率的变化对应着三阶Kerr非线性光学效应,这一效应在偏振量子相位门中有着潜在的应用价值.     

四能级原子系统中的电磁诱导吸收

以三个电偶极跃迁(中间跃迁作为探测跃迁、两边分别是耦合跃迁和控制跃迁)构成N型四能级系统为例，研究介质对探测光的吸收.揭示了在N型四能级系统中，既可产生电磁诱导吸收又可产生电磁诱导透明.这不仅取决于非相干转移率的大小，而且还取决于耦合场、控制场的强度和第四个简并能级的衰减速率大小. 关键词： 电磁诱导吸收 电磁诱导透明 原子相干的自发转移 能级的衰减速率     

驱动场相位扩散对三能级梯型系统无反转激光的影响

在旋波、慢变振幅近似下,求解考虑了驱动场相位扩散后的系统密度矩阵运动方程,并给出了这个三能级梯型系统稳态线性解析解.利用得到的稳态线性解析解分析驱动场相位扩散是如何影响该系统输出无反转激光的.对稳态线性解析解数值计算的结果显示:由于驱动场相位扩散会导致无反转激光增益减小;即使由于驱动场相位扩散引起的线宽足够大,在该系统中仍能够获得无反转激光;线宽往往是破坏无反转激光产生和折射率的提高;因驱动场相位扩散导致无反转激光增益的减小,并不是总能够通过增大驱动场的Rabi频率得到补偿.     

基于自发辐射相干实现光学前驱动场

研究一个具有两个靠得足够近激发能级的双Lambda模型, 在矩形脉冲中分离出光学前驱动场. 当耦合场是大失谐时, 该原子系统在自发辐射相干效应的影响下产生一个透明窗口并伴随着陡峭的色散曲线. 因此, 由于透明窗口中的慢光效应可以使光学前驱动场从主脉冲场中分离出来. 另外, 我们通过调控脉冲波形序列研究探测场相位和幅值的累积光学前驱动波. 数值结果表明: 由于累积光前驱动场与脉冲主场的相长干涉大大地提高瞬态脉冲的能量.     

Atomic Tunneling Effect in Two-Component Bose-Einstein Condensates with a Coupling Drive

In this paper, we have studied the atomic population difference and the atomic tunneling current of twocomponent Bose-Einstein condensates with a coupling drive. It is found that when the two-component Bose-Einstein condensates are initially in the coherent states, the atomic population difference may exhibit the step structure, in which the numbers of the step increase with the decrease of the Rabi frequency and with the increment of the initial phase difference. The atomic population difference may exhibit collapses, and revivals, in which their periods are affected dramatically by the Rabi frequency and the initial phase difference. The atomic tunneling current may exhibit damping oscillation behaviors, and exist the step structure for the time range of 10-10 ～ 10-9 second.     

Phase-dependent gain and absorption properties of mid- to far-infrared lights in three-coupled-quantum-wells

We investigate the phase-dependent gain and absorption behaviors of mid- to far-infrared lights under a cascade configuration in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the amplification of the probe and signal fields, i.e., the far- and mid-infrared waves, can be realized with realistic experimental parameters. The gain-absorption spectra are strongly dependent on the relative phase of the applied laser fields. The influences of the probe detuning and the two pump Rabi energies on the gain-absorption responses of two weak far- and mid-infrared light fields are also discussed in details. The results show that amplifications of the far- and mid- infrared waves can be achieved by adjusting the relative phase, the probe detuning, and the two pump Rabi energies appropriately. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. For practical applications, this investigation may provide a new possibility for realizing the efficient gain of far- and mid-infrared waves in the solid-state materials.