【作者】 王健；

【导师】 张连水； 尉长江；

【作者基本信息】 河北大学 ， 光学， 2009， 硕士

【摘要】 本文以量子力学及电磁诱导透明(Electromagnetically Induced Transparency-EIT)相关实验研究为基础,对作用场及原子能级体系进行综合分析,建立了∧-型三能级系统及准∧-型四能级系统模型。通过求解相应的密度矩阵方程,研究了EIT形成及单窗口EIT向双窗口EIT的转换过程,探讨了两种EIT系统的光开关特性,取得了创新性研究成果。值得指出的是,本文所进行的密度矩阵方程求解,未采用常用的微扰理论求解,所得结果适合于任意作用场情况。首先对双场作用下的∧-型三能级系统EIT瞬态特性进行了系统研究。该系统的瞬态探测吸收曲线表现为一种量子拍频衰减振荡形式。分别讨论了不同探测场频率处的瞬态吸收随耦合场和探测场Rabi频率的变化规律。从理论上证明了缀饰态章动信号频率只与探测场Rabi频率有关,而高频的拍频信号只与耦合场Rabi频率有关。随后研究了外加射频驱动场作用下的准∧-型四能级系统相干瞬态特性,通过求解系统的含时密度矩阵方程,研究了系统从单窗口EIT向双窗口EIT的转换过程。该过程亦表现为量子拍频衰减振荡形式,并利用缀饰态理论很好的解释了量子拍频的变化规律,指出这种量子拍频效应源于RF驱动场所引起劈裂能级间的量子相干。当探测场与相应的裸态跃迁能级共振时,拍频频率等于RF驱动场Rabi频率的二分之一；当探测场与强RF驱动场所导致的缀饰态能级跃迁共振时,拍频频率等于RF驱动场的Rabi频率。在上述研究的基础上,本文对上述两种∧-型系统的光开关特性进行了研究。结果表明,采用方波脉冲序列光学耦合场或RF驱动场,两种∧-型系统都可以实现对探测光波场的光开关作用；两者均有一定优势,∧-型三能级系统的光开关速度高于准∧-型四能级系统,而准∧-型四能级系统的开关深度明显大于∧-型三能级系统。两系统的光开关速度和开关深度会随着耦合场或RF驱动场Rabi频率的增大而增大。本工作可为光开关器件的实验研究提供理论参考。更多还原

【Abstract】 On the basis of quantum mechanics and experiments of Electromagnetically Induced Transparency (EIT), aΛ-three-level system configuration and a quasic-Λ-four-level system configuration are considered in this thesis. By numerically solving the corresponding equations of motion of the density matrix, the time-dependent probe response of an EIT and a single EIT window to double EIT windows are studied theoretically. And based on them, the optical switching property in the above both system configurations are also discussed. It is worth noting that the perturbation theory used commonly in solving density matrix equation is not employed in this thesis, thus the results fit situation which field has any strength.Firstly, The coherent transient property of an EIT inΛ-three-level configuration is studied comprehensively in this thesis. There is a coherent transient process with high quantum beats in the absorptive spectra. Then, the EIT transient properties with different probe frequencies are studied as function of Rabi frequency of both couple field and probe field. It shows that the frequency of dressed state quantum beats is mainly determined by the couple field, while the frequency of dressed state nutation is mainly determined by the probe field.Secondly, the coherent transient property of an EIT subject to a RF field driving a hyperfine transition within the ground state in a quasi-A-four-level configuration is studied, and a theoretical study of the time-dependent probe response of a single EIT window to double EIT windows is also made by numerically solving the equations of motion of the density matrix. There is also a coherent transient process with high quantum beats. This effect can be explained using the dressed state formalism. The quantum beats result from quantum coherence effect between the levels driven by RF field. The results show that when the probe field is on resonance with a bare-state transition, the beat frequency is one-half of RF Rabi frequency in transient absorption response. While the probe field is on resonance with a dressed-state transition, which results from the atom system interact with strong RF field, the beat frequency equals the RF Rabi frequency in transient absorption response.Finally, the optical switching property in the A-type configuration three or four level system is studied. Optical switching of the probe field can be achieved by applying a pulsed coupling field or RF field and both of them have their own advantage in A system. The speed of the optical switching of three-level system is much faster than that of four-level system, while the depth of the optical switching of the latter is much larger than that of the former. The speed of optical switching of the two systems can be increased by increasing Rabi frequency of coupling field or RF field. The results will provide benefits for experiment research of optical stitching equipment.更多还原