共查询到20条相似文献,搜索用时 351 毫秒
1.
利用缀饰原子方法研究了激光同位素分离涉及的一个四能级系统的布居转移过程,发现了类似于三能级系统的布居囚禁态,在此基础上分析了光泵浦过程的布居囚禁现象,提出一种能够利用基态布居及亚稳态热布居的高效率光泵浦方法并以分离轴原子为例说明该方法的优越性。 相似文献
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推导了光束在半导体光折变介质的光子晶格中演化的二能级形式, 给出了光束在其中传播时二能级方程的经典正则形式. 解析计算出了经典正则方程的不动点并对其稳定性作了分析, 计算出了拓扑结构变化的临界值. 根据二能级方程的经典正则形式做出了空间相图, 进一步分析了半导体光折变介质中光束传输的自囚禁现象, 发现有两种形式的自囚禁: 1)能级中的布居数差和相对相位都在平衡点附近振动; 2)能级中的布居数差在平衡点附近振动, 而相对相位单调变化. 分别从高频、低频、中频三个方面研究了外加周期调制对自囚禁的影响, 发现在高频调制中发生自囚禁现象的相变参数能够被周期场非常有效的调制, 使得光束在半导体光折变介质中传输时, 在非线性效应影响较小时也能够发生自囚禁.
关键词:
半导体光折变介质
自囚禁
二能级形式
周期调制 相似文献
3.
受激拉曼绝热通道(STIRAP)为我们提供了一种有效转移原子与分子中电子布居的方法.采用数值方法系统地分析了不同的四能级系统在受激拉曼迁移过程中电子布居的转移情况,计算了各种系统处于双光子共振和共振失谐时的转移率,并且讨论了在不同情况下第四能级对转移率的影响.计算结果表明,对于许多原子或分子系统,获得高的转移率所必须满足的条件是非常严格的,而有些四能级系统根本就不能获得高的转移率.( 相似文献
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基于二能级体系的速率方程,获得了非完全初始自旋偏振极化条件下的自旋偏振向上和向下 载流子布居弛豫的解析解. 基于小信号近似,给出了左、右旋圆偏振探测光的饱和吸收变化 的表达式. 此表达式中含有电子布居的初始自旋偏振度参数,因而用此表达式拟合实验数据 能够直接获取电子布居的初始自旋偏振度,而电子布居的初始自旋偏振度在自旋偏振输运研 究中是一个非常重要的关键参数. 实验获得了GaAs/AlGaAs多量子阱结构中光注入电子布居 的初始自旋偏振度及其弛豫时间常数.
关键词:
圆偏振抽运_探测技术
电子自旋偏振度
自旋偏振弛豫
GaAs量子阱 相似文献
5.
采用辍饰原子模型研究了四光子三步共振离化过程的布居囚禁,发现了一种与离化速率无关的布居囚禁。通过数值求解裸原子表象的含时薛定谔方程发现,适当选取激光频率与跃迁的失谐量,可以解除这种布居囚禁。 相似文献
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基于相干布居囚禁,提出了一种新的电磁诱导光栅物理模型, 得到了该模型下介质极化率的解析表达式. 由于相干布居囚禁引入的原子相干性, 介质极化率会形成增益、无吸收高折射率点以及暗态三个区域. 根据该理论模型, 基于87Rb的原子能级, 提出了一种新型衍射光栅实现方案, 并进行了分析与计算. 结果表明, 在无吸收高折射率点处, 这种光栅是一种纯相位光栅, 一级衍射强度可达到0.4; 在增益区域中, 发现这种光栅是相位光栅和幅度光栅组合而成的混合型光栅, 在其最大增益点, 一级衍射效率最大可达1.26, 二级衍射效率也可增加到0.31.
关键词:
相干粒子数囚禁
电磁诱导光栅
衍射效率 相似文献
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首先考虑囚禁在谐振子势中的二能级离子在Lamb-Dick级限下与驻波场的相互作用利用态选择测量来产生囚陷离卫的奇偶相干态。然后研究原子反转随时间的演化,发现其在一定条件下表现为梳形崩塌与复苏现象。 相似文献
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T. Ya. Karagodova 《Optics and Spectroscopy》2005,98(6):805-810
Specific features of the coherent population trapping effect are considered in the generalized Λ system whose lower levels are the magnetic sublevels of the fine structure levels of the thallium atom. Numerical experiments were performed aimed at examination of the coherent population trapping for the case of nontrivial, but feasible, initial populations of the upper metastable fine structure level. Such populations may be obtained, for example, due to the photodissociation of TlBr molecules. The possibility of reducing the number of resonances of the coherent population trapping in a multilevel system, which may be useful for high-resolution spectroscopy, is demonstrated. It is shown that the magnitude and shape of the resonances can be controlled by varying the orientation of the polarization vectors of the light field components with respect to each other and to a magnetic field. In addition, studying the shape of the coherent population trapping resonances for the atoms obtained by photodissociation of molecules may provide information about these molecules. 相似文献
13.
ATOMIC COHERENT POPULATION TRAPPING AND ITS APPLICATION IN A RAMAN-TYPE PHOTOIONIZATION SYSTEM WITH THREE BOUND STATES
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We have studied the atomic coherent population trapping in a Raman-type, photoionization system with three bound states. The conditions for the system having two or one stable eigenstate are given. The influences of Fano asymmetric factors on the coberent population transfer are also analyzed.It is found that the property of the system having on]y one population trapping state consisting of the ground state, and one excited state, can be utilized to transfer the atomic initial population into one excited state. 相似文献
14.
研究了少周期脉冲串作用下三能级原子中的布居转移和相干布居捕获现象.在非旋波近似的情况下求解了密度矩阵方程.研究结果表明在等时间间隔的锁相脉冲作用下,系统能级的布居逐步转移并积累,系统基态相干也逐步积累.在满足脉冲重复频率为基态能级频差的整数分之一倍时,三能级系统和频率梳中两梳齿频率成分作用形成相干布居捕获现象,原子暗态布居值达到最大,介质对脉冲透明.在适当选取少周期脉冲参量的情况下,在0.5个ns的时间内三能级系统相干性演化到最大后到达稳态,相干布居捕获发生.与脉宽为100个fs的多周期脉冲相比,少周期脉冲串在介质中建立相干布居捕获的时间缩短两个数量级.由于频率梳中与三能级系统发生作用的梳频成份有相同的频移,相干布居捕获的条件双光子共振仍然满足.因而,当两基态能级频率差较大时,如果选取少周期脉冲载波频率为系统能级1至2和1至3的传输频率之和的一半ω=(ω1+ω2)/2,室温下原子热运动的引起的多普勒频移并不会破坏相干布居捕获. 相似文献
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Population trapping via quantum interference in a multi-level system driven by a coherent field is investigated. The influences of the alignment of the transition dipole moments and the energy-level separation of the upper levels are taken into account. Detailed trapping population profiles under the different conditions are given. The research result is helpful for simplifying the theoretical model and selection rational energy level system. 相似文献
16.
COHERENT POPULATION TRAPPING IN MULTILEVEL LASER-INDUCED CONTINUUM STRUCTURE SYSTEM INCLUDING CASCADE TWO-PHOTON PROCESSES
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We have investigated the atomic coherent population trapping in a mul tilevel laser-induced continuum structure system including cascade two-photon processes, in which two sets of quasicontinua of excited levels to be modeled as the Bixon-Jortner quasicontinuum are laser-embedded into a previously structu reless atomic continuum.The condition leading to the atomic coherent population trapping and the coherent population trapping state are given explicitly. And th e effects of the Fano factors, the laser intensities and the detunings on the am ount of population trapped in the atomic bound states and the populations distri buted in the two sets of quasicontinua are also examined. 相似文献
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Wanare H 《Physical review letters》2006,96(18):183601
We demonstrate the simultaneous occurrence of coherent population trapping at a series of frequencies separated by modulation frequency of phase-modulated fields. The two arms of the system are coupled to two phase-modulated fields and the response of the atomic system to such fields is calculated nonperturbatively. A judicious choice of modulation characteristics allows one to selectively switch on or off the occurrence of coherent population trapping at specific frequencies. A new technique is developed to compute two-dimensional tridiagonal matrix equations. This generalized technique provides the vital methodology needed to calculate the response of such systems in the strong modulation regime and for arbitrary field strengths. 相似文献
18.
Xiaochi Liu 《中国物理 B》2022,31(4):43201-043201
We present a coherent population trapping clock system based on laser-cooled $^{87}$Rb atoms. The clock consists of a frequency-stabilized CPT interrogation laser and a cooling laser as well as a compact magneto-optical trap, a high-performance microwave synthesizer, and a signal detection system. The resonance signal in the continuous wave regime exhibits an absorption contrast of $\sim 50$%. In the Ramsey interrogation method, the linewidth of the central fringe is 31.25 Hz. The system achieves fractional frequency stability of ${2.4\times }{{10}}^{{-11}}/\sqrt \tau $, which goes down to ${1.8\times }{{10}}^{{-13}}$ at 20000 s. The results validate that cold atom interrogation can improve the long-term frequency stability of coherent population trapping clocks and holds the potential for developing compact/miniature cold atoms clocks. 相似文献
19.
Min Xie 《Optics Communications》2009,282(9):1819-1824
We investigate quantum interferences in coherent population trapping of a cold double Λ-type four-level atomic system driven by two counterpropagating laser fields. We study both decoherence and enhanced-coherence actions resulting from the multi-transition pathways in building up the trapping state, and analyze the system operating with and without external coherences in various configurations of the atomic dipole moments. 相似文献
20.
L. V. Il’ichev 《JETP Letters》2011,93(8):442-446
The properties of a one-dimensional atomic Bose condensate are studied under the assumption that the condensation leads to
a state of velocity-selective coherent population trapping. This state is characterized by the quantum correlation (entanglement)
between the intrinsic angular momentum of an atom and its translational motion underlying nontrivial features of the condensate.
The effects of weak interatomic interaction are taken into account. The steady state of above-condensate atoms corresponding
to the slow decay of the state with coherent population trapping is found. The dynamic problem concerning the evolution of
the system of above-condensate atoms after switching off the optical field forming the state with coherent population trapping
is solved. The solution is found by the diagonalization of the Hamiltonian based on introducing the Bogoliubov quasiparticles
with the unusual dispersion law. 相似文献