Quantum Coherence Of Atoms In Compact Space

Atomic coherence effect has been one continuous attention in the research between light and atoms. EIT is an important atomic coherence effect,which has been received very mature research so far, and has become an important technical means. EIT effect is achieved with a bunch of strong traveling wave field and a bunch of weak probe field, and in the two-photon resonance condition, atom media exhibit transparency effect to the probe field. When we use the standing wave field instead of the traveling wave field, dark state between the ground states becomes bright state, which cause the medium to the effect of the probe field from transparent becomes strong absorption. This strong absorption is called EIA. Currently there are three main explanations about atomic coherence effect under the standing wave driving:Electromagnetically induced grating, Four wave mixing theory and Electromagnetic induction photonic bandgap. Absorption characteristics, the refractive index and the dispersion of atom medium modulating by standing wave field, which has the characteristics of spatial distribution, can exhibits the characteristics of the spatial modulation and a a high degree of regulation. So the research of atomic coherence effects modulated by standing wave field has a very large research value.The dissertation firstly gives a brief introduction of the physical nature, development process, research status about several atomic coherence effects, such as:CPT, EIT, EIA, et, al. We know that in the study of atomic coherence effects, the optical thickness is a very important parameter. Its accuracy is related to the accuracy of the experiment. So we propose a calculation method of the optical thickness based on the Beer’s Law, and measured the atomic absorption characteristics. The experimental results agree well with theoretical simulations. This can help us to do more precise study of coherence effects in experiments. In the research of atomic coherence effects in the standing wave modulation, hot atom system is relatively easy to build than cold atoms system. However, due to the presence of thermal motion, the Doppler Effects affect the building of atomic energy band structure, so we consider to place the atom in a "limited" space to improve the doppler background. First, we give the corresponding theoretical model, simulated the relationship between the periodic absorption and the atomic coherence effect at different doppler backgrounds. Then, we experimentally analysis the doppler width of the probe field, and the absorption characteristics in a small atomic room space and conventional room space, respectively,which Correspond the theoretical simulations well. It is show that when the atom is palced in a small room space, the effect of EIA becomes weak and the effect of EIT becomes strong, especially the transparency. This corresponds to the medium can get better periodicity characteristic of the absorption modulator, and is helpful for us to improve energy band structure in hot atom systems.