级联三能级介质中非线性光学信号的增强

揭示非最大相干可能比最大相干产生更有效的非线性频率转换. 为此以三能级级联系统(没有最大相干)为例计算其非线性光学信号的强度, 并与三能级Λ型系统(具有最大相干)进行比较. 利用非微扰方法计算表明, 在双光子共振和相同参数的条件下, 级联系统产生的非线性光学信号的最大强度约是Λ系统的两倍. 利用缀饰态表象分析表明, 两个系统中耦合跃迁的自发辐射及其介入的不可逆三光子过程具有相反的作用. 它们在级联系统中加强非线性转换, 而在Λ系统中削弱非线性转换. 关键词： 电磁感应透明 非线性光学过程 双光子共振     

级联三能级模型下超短脉冲激光与分子相互作用的动力学研究

通过求解麦克斯韦-布洛赫方程，研究了超短脉冲激光和一维对称π共轭分子材料(4,4′-二甲氨基二苯乙烯分子)的相互作用.该分子材料具有较强的非线性光学性质，其分子的电子结构和电偶极矩是在密度泛函理论水平上利用从头计算方法得到的.研究结果表明，慢变幅近似和旋波近似不能很好地描述超短脉冲在该分子介质中的传播.在单光子共振情况下，保持入射脉冲的脉冲宽度不变，当小面积脉冲在该分子介质中传播时，二能级模型可以较好地描述脉冲激光与该分子体系的相互作用过程.但对于大面积脉冲激光，由于较明显地产生了分子的二次激发，此时分子 关键词： 超短脉冲激光 4′-二甲氨基二苯乙烯分子 三能级模型 麦克斯韦-布洛赫方程     

A semi-classical approach to two-frequency solitons in a three-level cascade atomic system

A semi-classical theory of two intense optical fields interacting with a third-order non-linear medium composed of a three-level cascade atomic system is presented. It is predicted that non-linear atom-field interactions allow the formation of two-frequency bright, dark and grey spatial solitons. We demonstrate through numerical simulations and analytic stability analysis that the bright and grey solitons are stable.     

Generation of entanglement via atomic coherence in a two-mode three-level cascade atomic system

The generation of continuous variable entanglement via atomic coherence in a two-mode three-level cascade atomic system is discussed according to the entanglement criterion proposed by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)]. Atomic coherence between the top and bottom levels is induced with two photons of a strong external pump field. It shows that entanglement for the two-mode field in the cavity can be generated under certain conditions. Moreover, by means of the input-output theory, we show that the two-mode entanglement could also be approached at the output.     

两色超短脉冲激光与级联三能级分子体系相互作用的动力学研究

在不采用旋波近似和慢变幅近似的条件下,采用时域有限差分法和预估矫正法求解Maxwell-Bloch方程,对两色2π超短脉冲激光在级联三能级有机分子体系(4,4′-二甲氨基二苯乙烯分子)中传播的动力学过程进行了数值模拟.该有机分子属于一维对称体系,其电子结构和电学参量在密度泛函水平上给出.在低能量范围内,该分子可以简化为三能级体系.我们研究了在不同共振条件下,两色超短脉冲的时空演化特性和三能级体系各个能级粒子数占有率的分布情况.     

Optical power limiting of ultrashort hyper-Gaussian pulses in cascade three-level system

Propagation of strong femtosecond hyper-Gaussian pulses in a cascade three-level molecular system is studied by solving numerically the Maxwell–Bloch equations by the iterative predictor-corrector finite-difference time-domain method.Optical power limiting behavior induced by strong nonlinear two-photon absorption is observed for different orders of the femtosecond hyper-Gaussian pulses. Pulses of a higher order temporal profile are found to have a wider power range of optical limiting but a larger output saturation intensity. Both the output saturation value and the damage threshold of optical power limiting decrease with pulse duration increasing. The decrease of the pulse area along the pulse propagation is much slower than that obtained from the two-photon area theorem due to invalidity of the slowly varying amplitude approximation and the monochromatic field hypothesis.     

Dynamics of cascade three-level system interacting with the classical and quantized field

We study the exact solutions of the cascade three-level atom interacting with a single mode classical and quantized field with different initial conditions of the atom. For the semiclassical model, it is found that if the atom is initially in the middle level, the time-dependent populations of the upper and lower levels are always equal. This dynamical symmetry exhibited by the classical field is spoiled on quantization of the field mode. To reveal this non-classical effect, a Euler matrix formalism is developed to solve the dressed states of the cascade Jaynes-Cummings model (JCM). Possible modification of such an effect on the collapse and revival phenomenon is also discussed by taking the quantized field in a coherent state     

Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4＇-bis（dimethylamino） stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.     

Two-phonon process in a three-level system

The dynamical behaviour of level filling and occupation numbers of photon modes is examined rigorously. A “quantum expression” for the Rabi frequency is obtained.     

双频场作用下三能级原子的动力学行为

求得双频场作用下串接型三能级原子系统哈密顿量的本征函数和本征值.从而给出任意初始原子态和任意偏调情况下,原子系统随时间的演化公式.研究了能级布居数和原子极化与光强的关系.揭示了原子初始条件和光场相对相位对原子动力学行为的影响.在相对相位为π时,原子场耦合最小,在特殊情况下为零.     

运动级联型三能级原子双光子过程的熵演化

研究了运动级联型三能级原子与单模场双光子相互作用过程中场(原子)熵的演化特性. 讨论了当运动原子初始处于相干叠加态时,原子运动、场模函数、初始场的平均光子数n对场熵演化的影响. 结果表明：熵演化的周期依赖于原子的运动和场模函数的取值,而初始场的平均光子数n只影响最大和次最小熵值,不改变熵演化的周期. 关键词： 双光子 运动Ξ型三能级原子 熵     

Enhanced squeezing and entanglement in a non-degenerate three-level cascade laser with injected squeezed light

We consider a non-degenerate three-level cascade laser coupled to a two-mode squeezed vacuum reservoir via the lossy single-port mirror. Applying the pertinent master equation, we analyze the effects of the injected squeezed light on the quadrature squeezing, entanglement and normalized intensity difference fluctuations. We show that the injected squeezed light considerably enhances the degree of squeezing and entanglement in the two-mode light for certain initial conditions. Moreover, the injected squeezed light increases the mean photon number where the squeezing and entanglement is significant. We also show that the presence of the injected squeezed light greatly reduces the noise in the intensity difference.     

Dynamical hysteresis in a three-level atomic system

We have experimentally investigated dynamical hysteresis behavior by changing the sweeping frequency of the cavity input field in the optical bistability of rubidium atoms (in a three-level atomic-type configuration) inside an optical cavity. The shape, width (or area), and direction of the hysteresis cycle are sensitive functions of the sweeping frequency for such an optical bistable system.     

级联三能级原子与单模场相互作用下的腔场谱

研究了高Q腔内级联三能级原子与单模光场相互作用模型的腔场谱.结果表明,原子初态处于上能级时，随R=g2/g1的增大,真空场的拉比峰个数按2→6→4→2→4的规律变化，在R1时，所有的拉比峰都消失.在初始场较弱时,腔场谱可出现3峰、5峰或7峰.在初始场很强时,腔场谱中只有单一的经典共振峰.如果原子初态处在中能级且R=1,腔场谱为简单的对称双峰结构，与标准J-C模型的谱相似. 关键词： 级联三能级原子 单模光场 腔场谱     

Intensity correlations in filtered phase-diffusing light

Light undergoing phase diffusion displays a Lorentzian line shape: Here, electrical filtering techniques are used to examine the correlations among different spectral regions under this line shape. The experiment involves delayed self-heterodyne measurements of the output from a single-mode semiconductor laser. Two filters are tuned to isolate the signal contributions from opposite wings of the spectrum, and the transmitted intensities are shown to be strongly correlated in some regimes and strongly anticorrelated in others.     

二项式光场与级联三能级原子的量子纠缠

利用量子熵理论，研究了二项式光场与级联三能级原子的量子纠缠，讨论了光场与原子的初始参量对其量子纠缠性质的影响.结果表明，利用二项式光场的特性，可以揭示从相干态到数态之间的所有态光场与三能级原子相互作用时的量子纠缠性质.选择适当的系统参数可以制备稳定的光场-原子qutrit纠缠态. 关键词： 二项式光场 级联三能级原子 光场熵 量子纠缠     

Optical multistability and ground-state coherence in a three-level system

The interaction of a three-level atomic medium with two degenerate sublevels in the ground state with a coherent radiation field in a ring cavity is investigated. We pay specific attention to atomic coherence within the ground-state doublet, and introduce separate decay rates for the ground-state coherence and the population difference. If the atomic density exceeds a critical value, the system exhibits symmetric bistability. In addition, in certain regions of parameter space we find symmetry-breaking branches, yielding optical multistability. We propose physical mechanisms for the symmetric as well as for the symmetry-breaking instability.Work supported by the Swiss National Science Foundation     

Fifth-order attosecond polarization beats using twin color-locked noisy lights in cascade three-level system with Doppler-free approach

Fifth-order attosecond sum-frequency polarization beat (FASPB) is studied in a cascade three level system with the phase-conjugation fourth-order coherence function theory. An improved schematic diagram of geometry, which is different from that inducing fifth-order femtosecond different-frequency polarization beat(FFDPB), is used to obtain FASPB. By analyzing the cases that pump beams have either narrow or broad bandwidth, it is found that the temporal behavior of the sum-frequency polarization beat signal depends on the properties of the lasers and transverse relaxation rate of the atomic energy-level system. Finally,the cascaded four-wave mixing (FWM) processes and the difference between attosecond and femtosecond polarization beats have been discussed, it is found that cascaded or sequential lower processes can often obscure the direct fifth-order polarization beat processes.