五能级原子开放系统中的多波混频共存特性

研究了受强缀饰场作用的五能级原子系统所产生的多波混频共存特性.研究发现,通过调节激光束方向,沿同一方向出射的八波混频、双缀饰四波混频和单缀饰六波混频信号因共用能级的原子相干产生而出现竞争现象,通过控制缀饰场减弱四波混频和六波混频信号强度,可以达到增强八波混频信号的目的.还对级联和并联两种不同缀饰方式下双缀饰四波混频过程的差别进行了详细分析. 关键词： 双缀饰四波混频 单缀饰六波混频 八波混频 抑制增强     

受限原子极化相干缀饰四波混频光谱

研究了两电介质面间级联四能级系统原子的缀饰四波混频(FWM)光谱.在缀饰场的作用下FWM信号可产生Autler-Townes (AT)分裂,分裂所产生的峰及凹陷的线型及缀饰场对FWM信号的抑制与增强效应均受原子极化相干及受限原子与光场相互作用瞬态机制的调制.     

受限原子极化相干缀饰四波混频光谱

研究了两电介质面间级联四能级系统原子的缀饰四波混频(FWM)光谱.在缀饰场的作用下FWM信号可产生Autler-Townes (AT)分裂,分裂所产生的峰及凹陷的线型及缀饰场对FWM信号的抑制与增强效应均受原子极化相干及受限原子与光场相互作用瞬态机制的调制.     

基于简并四波混频的双信道双频段增益谱

基于大规模光通信中频分复用的需求,本文以热原子的简并四波混频为模型,研究了具有双频段特性的双信道增益光谱.一束缀饰场诱导激发态能级发生分裂,由于量子干涉效应,四波混频信号的增益在双光子共振处被抑制,从而使增益谱线的包络由单频段转变为"M"型的双频段结构.同时,缀饰场还提高了相干基态的原子布居,进一步增强了四波混频信号的强度.最终实验上在铯原子气室内获得了一对具备双频段的双信道高增益光谱,并通过调节缀饰场的强度和频率失谐,实现了对双增益峰频率间隔的有效操控.     

中间态引入量子干涉的三光子共振非简并六波混频

理论研究了五能级系统中三光子共振非简并六波混频(NSWM) 由于中间能级加入耦合光场而产生的量子干涉效应. 分析了耦合光场对三光子共振NSWM信号以及频谱的影响. 研究发现, 在强耦合场作用下, NSWM的频谱出现了Autler-Townes分裂, 它反映的是两个缀饰态的能级, 量子干涉可以使NSWM信号被抑制或增强. 提出利用量子干涉对NSWM信号产生增强作用, 可以由耦合场产生的缀饰态代替原子固有能级, 成为三光子共振的中间态, 从而控制耦合场来选择三光子共振的中间态的位置.     

利用简并四波混频系统通过畸变介质传输图象研究

本文在研究光折晶体多波混频的基础上,从理论和实验上提出了利用简并四波混频系统单次通过畸变介质传输图象的方法,文末并给出了初步的实验结果。     

在缀饰场中四能级“Ladder”系统的布局数转移

利用"反直觉"频率啁啾激光脉冲分析了偶能级ladder系统的布局数迁移,其中在缀饰激光场作用下N-2个中间态进行耦合.作为偶能级ladder系统的代表,我们着重分析了四能级ladder系统.研究发现如果缀饰激光场足够强且发生共振,则在能级1和能级4之间发生完全布局数迁移必须要求有一个恰当的脉冲叠加面积,调谐pump激光和stokes激光,使其中一个缀饰中间态发生共振,则可以使这个四能级系统简化为三能级系统.     

布里渊增强四波混频时域特性的理论研究

通过对布里渊增强四波混频(BEFWM)瞬态耦合波方程的数值求解，描述了共轭输出光的时域调制行为.同时，对能量耦合过程中起决定性作用的声学波的时空演化特征进行了模拟与分析，由此给出BEFWM时域特性物理机理的解释.研究表明，共轭光输出强度的波动与介质内声波场的分布和起伏相关联，共轭光波形调制现象的强弱取决于介质声子寿命、信号及抽运光强度、有效作用长度等诸多参数.     

简并四波混频信号的饱和效应

本文由光学Bloch方程和密度矩阵方程出发,研究了二能级系统共振型简并四波混频(DFWM)的饱和效应,给出了DFWM信号强度与泵浦光强度的函数关系.饱和泵浦光强的大小取决于纵向弛豫时间T1和横向弛豫时T2.对理论结果与相应实验进行了比较,表明二者符合得很好.     

最优的双轴晶体非简并四波混频变频共轭波的产生

研究了双轴晶体中通过非简并四波混频产生可变频的共轭波.在KTP中共轭波有各种匹配类型.若选择合适的匹配方向及泵浦和探测波矢的合适角度,使由于离散效应引起的所有光线之间偏离得到最好的补偿.从而增加晶体的有效长度,并显著改善能量的转换效率,得到各种匹配类型的最佳工作条件.     

Enhanced or suppressed six-wave mixing in a five-level atomic system

We show the enhancement and suppression of a six-wave mixing (SWM) signal in the electromagnetically induced transparency in a five-level ⁸⁵Rb atomic system. The results show the Autler—Townes splitting and the enhancement or suppression of SWM, which are caused respectively by a self-dressing effect and by an external dressing effect in the presence of mutual dressing between two SWM signals. In addition, we observe the polarization dependence of the enhancement and suppression of the SWM signals.     

Resonantly enhanced continuous-wave four-wave mixing with spontaneously generated coherence in a five-state cold atomic medium

Using Schroedinger-Maxwell formalism, we propose and analyse a continuous-wave four-wave mixing (FWM) scheme for the generation of coherent light in a five-state double-A atomic system with or without spontaneously generated coherence (SGC) based on electromagnetically induced transparency (EIT). We derive the corresponding explicit analytical expressions for the generated FWM field under the steady-state condition. The influence of hyperfine sublevel and SGC effect on the amplitude of the generated FWM field is predicted in detail via the derived analytical expressions. We also give a brief discussion on the experimental realization of the proposed scheme.     

Modulation of four-wave mixing via photonic band gap

The dressed four-wave mixing （FWM） in a four-level S5Rb atomic system, experimentally demon- strated in this paper, is comprised by two coexisting processes. One is emission signal due to enhanced nonlinear via electromagnetically induced transparency （EIT）. The other is the Bragg reflection of probe beam because of the created photonic band gap （PBG）, which is affected by both linear and third-order nonlinear susceptibility. Moreover, we have demonstrated that different experimental parameters can significantly influence the measured signal with flexibly controlled PBG. These studies are found useful for understanding the fundamental mechanisms in generated FWM processing.     

Atomic coherence in nondegenerate four-wave mixing

Two-photon resonant nondegenerate four-wave mixing (NFWM) with the addition of a coupling field in Ba atomic vapour has been studied. We find that coherence of the atomic level transitions leads to suppression of the NFWM signal, giving rise to a dip with a linewidth that is linearly proportional to the intensity of the coupling field.     

Dual-dressed four-wave mixing and dressed six-wave mixing in a five-level atomic system

We study the co-existing four-wave mixing (FWM) process with two dressing fields and the six-wave mixing (SWM) process with one dressing field in a five-level system with carefully arranged laser beams. We also show two kinds of doubly dressing mechanisms in the FWM process. FWM and SWM signals propagatingalong the same direction compete with each other. With the properly controlled dressing fields, the FWM signals can be suppressed, while the SWM signals have been enhanced.     

Enhancement of four-wave mixing process in a four-level double semiconductor quantum well

The time-dependent four-wave mixing（FWM） is analyzed in a four-level double semiconductor quantum well. The results show that both the amplitude and the conversion efficiency of the FWM field are enhanced with increasing the strength of two-photon Rabi frequency. Interestingly, when the one-photon detuning becomes stronger the control field corresponding to the maximum efficiency increases. Such a controlled enhanced FWM may be used to generate coherent short-wave length radiation, and it can have potential applications in quantum control and communications.     

Manipulation of multiple electromagnetically induced two-photon transparency in a six-level atomic system

In the five-level K-type atomic system, by using another control field to couple the excited level of the coupling transition to the sixth higher excited level, a six-level atomic system is constructed. In this system, the multiple electromagnetically induced two-photon transparency has been investigated. What is more, if choosing the parameters of the control fields properly the triple transparency window will reduce to a double one which means that the multiple electromagnetically induced two-photon transparency can be manipulated in this system. The physical interpretation of these phenomena is given in terms of the dressed states and the dark states.     

Absorption and dispersion control in a five-level M-type atomic system

We investigate the steady optical response of a coherently driven five-level M-type atomic system in three different situations.When all three coupling fields have the same zero detuning,we just find one deep transparency window accompanied by a steep normal dispersion in the probe absorption and dispersion spectra.When two coupling fields are detuned from the relevant transitions to the same extent,however,a second deep transparency window may be observed in the presence of a narrow absorption line of linewidth ～50 kHz.In this case,two single-photon far-detuned transitions can be replaced by a two-photon resonant transition,so the five-level M system in fact reduces into a four-level quasi-Λ system.Finally,we note that no deep transparency windows and no narrow absorption lines can be found when all three coupling fields have unequal detunings.     

Enhancing and suppressing four‐wave mixing in electromagnetically induced transparency window

We demonstrate the enhancement and suppression of four‐wave mixing (FWM) in an electromagnetically induced transparency (EIT) window in Y‐type ⁸⁵Rb atomic system. The generated two‐photon FWM signal can be selectively enhanced and suppressed via an EIT window. The EIT of probe as well as the enhancement and suppression of FWM signals can be modified by the sequential‐cascade double dressing. The influence of different probe polarization configurations is also studied. Different polarization states of the probe laser can select different transitions among Zeeman sublevels and different dressing strengths. Copyright © 2010 John Wiley & Sons, Ltd.