Theoretical Study Of Coherent Control Of Lasing Without Inversion In An Open Four-level Atomic System

The atomic coherent effect is a result of the interaction between the electromagnetic field and atom. The study for the atomic coherent effect has an important research value in the quantum optics field, and is one of the physical hot subjects in the recent years. The study of coherent control has not only an important theoretical value, but also wide application prospects in many fields, such as quantum optics, nonlinear optics, quantum information and optical communication, etc. In addition, atomic coherence effects have multiple potential applications in many aspects, for example electromagnetically induced transparency (EIT), lasing without inversion (LWI) and optical quantum information storage and processing. Among numerous phenomena of atom coherence, lasing without inversion (LWI) has received tremendous attention. As a new method of producing laser, LWI can obtain laser light in spectral domains, e.g. the x-ray evenγ-ray range, where conventional methods based on population inversion are not available or are difficult to implement, so LWI has wide application prospects.We at first put forward a model of an open quasiΛ-type four-level atomic system and we studied the lasing without inversion and coherent control of optical properties in the system. Then we investigated the effect of spontaneously generated coherence and the relative phase on the gain,dispersion and population differences.This paper consists of four chapters.In Chapter 1, we explained the significance for studying coherent control and LWI, and showed the basic principle of producing LWI. We introduced the simply current research state of coherent control and LWI.In Chapter 2, we gave the model of an open quasiΛ-type four-level atomic system and investigated the effect of spontaneously generated coherence on the gain of lasing without inversion from different respects by using the numerical calculation results of the system in the steady state. The study results show that, the switching from absorption to lasing without inversion (LWI) and the enhancement of the LWI gain can be realized by adjusting the strength of SGC; varying of the two factors p1 and p 2 which represent the SGC effect will produce remarkable different influence on the LWI gain. We also find that, the LWI gain is much larger in open system than that in the corresponding closed system; moreover, when the incoherent pump field is absent, the LWI gain can be obtained in the open system but can't in the closed system.In chapter 3, the effect of the relative phaseΦbetween the probe and driving fields on gain and dispersion from different aspects in an open quasiΛ-type four-level system by the numerical solution of the steady state is investigated. The results show that by adjusting the value of the relative phase the LWI gain and dispersion can be periodically amplified and attenuated; High dispersion (refractive index) without absorption can be achieved; The dispersion curve corresponding toΦ=αis similar to the gain curve corresponding toΦ=α+π/2; When the probe field is on resonance, the largest lasing without inversion gain can be obtained by adjusting the relative phase. The effect of the atomic exit and injection rates on the LWI gain for different values of the relative phase was also studied.In Chapter 4, we summarized the main research results of the paper, and we put forward a suggestion to the further research work of the open quasiΛ-type four-level atomic system.