Effects Of Vacuum-Induced Coherence On Properties Of Multi-level Atomic Systems

An absorbing atomic medium is rendered transparent for a resonant probe field by a strong control field. This phenomenon is termed as electromagnetically induced transparency (EIT), which comes from the atomic coherence induced by the coherent fields. Under the condition of the EIT, the atomic systems display many important optical properties, such as subluminal ,superluminal, giant nonlinear optics and so on. In addition, when the two highest-lying levels of the atom are nearly degenerate and coupled by the same vacuum radiation field to the intermediate state, the system can create a vacuum-induced coherence (VIC) due to the quantum interference between the two spontaneous decay channels. VIC have important effects on transparent spectra, radiation spectra and dispersion properties. In this thesis,we mainly studied the effects of VIC on the absorption properties and dispersion properties in a three-levelΛ-type atom and a four-level inverted Y-type atom. The present paper is organized as follows:. In the first Chapter, We give an introduction of the research background and the purpose of my thesis.In Chapter 2, we use the two-level atomic system to show the semiclassical theory of laser-matter interaction, which is the basis technique for the following discussions. Based on the semiclassical theory, we show the phenomenon of the electromagnetically induced transparency (EIT), which is induced by the atomic coherence.In the following Chapter, we mainly investigate the effects of the VIC on the optical properties of a three-level atom, and give the physical explanation. In the last chapter, we mainly show that the vacuum-induced coherence can suppress the single- and two-photon transparency at resonance and lead to single-photon probe gain at other frequency. Meanwhile, it is shown that the single- and two-photon absorption spectra can be drastically modulated by the relative phase between the probe and coupling fields.