【作者】 孔令波；

【导师】 胡响明；

【作者基本信息】 华中师范大学 ， 理论物理， 2003， 硕士

【摘要】 本文提出利用非相干场可以有效地控制原子相干效应。主要考虑强场折射率增强和动态不可逆性。产生这两类不同相干效应共同的物理机制是，非相干场产生选择性修饰态布居捕获或者激发，不同的条件分别是，相干场与原子发生共振和非共振耦合。 主要研究了有两个偶极跃迁的三能级Ⅴ型原子系统，其中一个偶极跃迁很弱，由强相干场耦合；另一个偶极跃迁很强，用非相干场驱动。在强相干场建立的修饰态中，调谐非相干场的中心频率，使之只与两个修饰态跃迁中的一个跃迁发生共振。于是，非相干场和原子自发衰减过程构成一个两步过程，把原子布居从一个修饰态转移到另外一个修饰态，从而产生选择性的修饰态布居捕获。如果强相干场与弱偶极跃迁发生非共振耦合，修饰态布居捕获导致布居反转，理想情况下可获得几乎完全的反转；如果发生共振耦合，修饰态布居捕获导致最大原子相干（0.5），对应原子对强相干场的无吸收高色散。类似，对于有两个偶极跃迁的三能级Λ型原子系统，在相应的条件下，非相干场可以实现选择性修饰态布居激发，在非共振情况下产生原子布居反转，理想情况下布居反转为（0.5）；如果发生共振耦合，修饰态激发导致半最大原子相干（0.25）。 本文在原理上证明了利用非相干场产生选择性修饰态布居转移可以有效地控制原子相干效应。在激光应用如此广泛的今天，也许没有必要用非相干场。然而，在实用上，一般激光场都经历自由的相位扩散，具有一定的线宽。部分相干光（极限情形为非相干光）具有实用的优势。我们的研究表明，对于部分相干光，可在比相干光更宽的中心频率范围内建立布居反转，这正是实用上更有利的。对于现实的原子模型，Ba原子的三个能态6s ¹S₀，6s6p ¹P₁，6s6p ³P₁构成Ⅴ型系统，原子Ba的三个能级6P₁，6S₀和6D₂构成Λ系统，上述方案在实验上是可行的。更多还原

【Abstract】 In this thesis we propose to utilize an incoherent field to achieve the efficient control of atomic coherence effects. These include dynamically induced irreversibility and the strong-field index enhancement. The common physical mechanism to these two coherent effects is the selective trapping or selective excitation of either of dressed states. The different conditions for these effects are off-resonant or resonant coupling of the coherent field with the atom.Consider a there-level V system in which there are two dipole transitions, of which one dipole transition is weak and the other is strong. One strong coherent field is applied to the weak transition and one incoherent field drives strong transition. For such an arrangement, the coherent field creates dressed states, and the incoherent field is tuned to be resonant with one of two dressed transitions. As a result, the incoherent pump and the decay pathway constitute a successive two-step channel transfer population from one dressed state to the other. So selective dressed-population trapping is established. When the coherent field is off-resonant with the weak dipole transition, dressed population trapping leads to population inversion, which corresponds to almost complete inversion for the ideal condition. When the coherent field is resonant with the weak dipole transition, dressed population trapping leads to maximal atomic coherence (0.5), which corresponds to ultralarge index of refraction and vanishing absorption for the strong coherent field. Similarly, a there-level A system in which there are two dipole transitions, of which the weak dipole transition is driven by a strong coherent field, and the other strong dipole transition is driven by an incoherent field. When the coupling of coherent field with weak dipole transition is off-resonant, the selective dressed population excitation by the incoherent field leads to population inversion. The inversion is 0.5 under the ideal condition. On the resonance selective dressed excitation leads to half of maximal atomic coherence (0.25).The paper shows that the efficient control of the atomic coherent effects isachieved, in principle, by employing an incoherent field to transfer selectively dressed state population. In days that lasers are so widely used, we do not necessarily use the incoherent field as a drive. However, it is well known that a laser generally experiences free phase diffusion and has a finite bandwidth. Hence the use of partially coherent (incoherent field as the limiting case) field shows practical advantage. Our results show that population inversion is obtained in a wider central frequency range than for the coherent field case, and it is more advantageous in practical applications. For atomic barium, the states 6s 1S0, 6s6p 1P1, 6s6p 3P1 constitute those levels of the V system, the states 6P1, 650 and 6D2 constitute those of the A system. Such conditions of their realization are accessible to experiment.更多还原