Spontaneously Coherent Theoretical Study Of The Optical Properties Of The Ladder-type Level System

In general, when a system is prepared in a specified quantum state, scheme for achieving a predetermined quantum state by excitation with laser pulse to control transferring process is called quantum coherent control. Quantum coherent control is one of the most important and active research front fields in international lasing physics nowadays. There are many ways to produce quantum coherent control, in which spontaneously induced coherence is an important one. In many level systems, such as a closed A-type system or a closed V-type system and nearly equispaced Ladder-type system, there are many researches of the effects of spontaneously induced coherence. In this paper, the model is limited in a nearly equispaced Ladder-type system, we explained the effects of spontaneously induced coherence on the optical properties, such as population inversion and absorption, and so on.This paper consists of five chapters. In chapter 1, we explained the basic principle of producing spontaneously induced coherence, and introduced simply the current research state find the main contents for the important study subject at present. In chapter 2, we gave the nearly equispaced Ladder-type system model and the density-matrix equations in a rotating frame after taking the effects of spontaneously induced coherence into account. In chapter 3, we studied the effects of spontaneously induced coherence on population inversion. Firstly, we simply introduced the effects of spontaneously induced coherence on the population inversion of A-type system and V-type system. Secondly, basing on those ways, we studied the effects of spontaneously induced coherence on the population inversion in Ladder-type system. We found that population inversion can be greatly enhanced on one of the optical transitions due to spontaneously induced coherence. Furthermore, we find, within suitable parameters regions, that such coherence can also lead to unexpected population inversion on both of the optical transitions. In chapter 4, we studied the effects of spontaneously induced coherence on absorption properties. Firstly, we gave the definition of electromagnetically induced absorption (EIA) and introduced theway of obtaining EIA using transfer of coherence (TOC) and transfer of population (TOP). Secondly, we discussed the effects of spontaneously induced coherence on the absorption properties of nearly equispaced Ladder-type system and found that EIA can occur due to the effects of spontaneously induced coherence. In chapter 5, we summarized the main and important conclusions obtained in the study of present paper.