三能级级联型介质的正常色散与反常色散  

Normal and Anomalous Dispersion in Three-level Cascade Media

作　　者：李星[1] 邹金花[1] 胡响明[1] 

机构地区：[1]华中师范大学物理科学与技术学院,湖北武汉430079

出　　处：《量子光学学报》2005年第2期47-56,共10页Journal of Quantum Optics

基　　金：国家自然科学基金(60378008)

摘　　要：建议利用三能级级联型介质实现从正常色散到反常色散的变换。在级联型介质中,两个偶极跃迁分别与两个不同的相干场耦合。探测场或者与上跃迁耦合,或者与下跃迁耦合。利用谐振展开方法把介质密度矩阵元方程组转换成在定态条件下系数不依赖时间的方程组,然后用逆矩阵求解,并用此解求得介质的吸收与色散谱。结果表明,对于每一种情形,在同一频率区域系统既能呈现正常色散,也能呈现反常色散。通过改变耦合到探测跃迁的驱动场强度,可以实现从正常色散到反常色散的转换。级联系统与Λ和V系统之间呈现两个差别。第一,如果利用Λ和V系统的两个跃迁同时与探测场耦合获得色散转换,则需要利用近简并能级,而本方案利用缀饰态获得等价的近简并能级,其间距由相应驱动场强度进行控制。第二,如果利用Λ和V系统的单个跃迁耦合探测场建立色散转换,当退耦合态起主要作用时,系统不能产生色散转换,而级联系统不涉及退耦合态。We suggest that a three-level cascade medium be used to achieve the switching from normal dispersion to anomalous dispersion. In the cascade medium, two dipole-allowed transitions are coupled by two different coherent fields, respectively. A probe field is applied either to the upper transition or to the lower transition. The equations for density matrix elements are transformed into a set of equations with time-independent coefficients in the steady state via harmonic expansion, which are solved by matrix inversion. By the solutions we obtain the absorption and dispersion spectra. It is shown that for each case, the medium exhibits either normal or anomalous dispersion at the same frequency regime. The switching from normal dispersion to anomalous dispersion is obtained by varying the intensity from couple to probe transition. The two differences lie between the proposed cascade system and the Λ and V systems. Firstly, near degenerate levels are required for the Λ and V systems when the probe field is simultaneously coupled to the two transitions to achieve dispersion switching. The present scheme is based on an equivalent realization of near degeneracy in the dressed picture, and the interval is controlled by the corresponding field. Secondly, dispersion switching does not occur in the Λ and V systems when the probe field is only coupled to either of two transitions and the decoupled state plays a dominant role. In contrast, the present scheme does not involve the decoupled state.

关 键 词：正常色散 反常色散 色散转换 三能级级联型介质 

分 类 号：O431[机械工程—光学工程]