Coherent Control Of Transient Evolution Of Optical Properties In A Ladder-Type Three-Level System

The study of coherent control of optical properties and optical process is one of the most important and active research front fields in international optics nowadays. 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 photo-communication, etc. In addition, Atomic coherence effects have multiple potential applications in many aspects, for example: coherence population trapping, electromagnetically induced transparency, lasing without inversion and optical quantum information storage and processing. Among numerous phenomena of atom coherence, lasing without inversion 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 the study of LWI has not only an important theoretical value, but also wide application prospects.Based on the work of the former people, we studied the lasing without inversion and coherent control of optical properties in an open Ladder-type system in this paper. This paper consists of four chapters.In Chapter 1, we explained the significance for studying coherent control and LWI, showed the basic principle of producing LWI, and introduced simply the current research state of coherent control and LWI.In Chapter 2, the effect of spontaneously generated coherence (SGC) on transient evolution of gain of lasing without inversion (LWI) and modulation role of the ratio of injection rates and exit rate on SGC-dependent gain in an open Ladder type three level system are studied by using the numerical solution of the matrix density motion equation of the system. It is shown that variation of SGC strength will makes the transient and final stationary gains having a considerable changing; when incoherent pumping presents, LWI gain increases with the ratio of injection rates and exit rate decreasing, however, when incoherent pumping is absent, the case is just the opposite; by choosing suitable values of SGC strength, the ratio of injection rates and exit rate can obtain the biggest transient and final stationary gains.In Chapter 3, in an open ladder-type resonant atomic system, variation in relative phase between probe and driving fields does not affect the transient evolution of populations, but it has remarkable effects on gain and dispersion of the probe field. No matter whether an incoherent pump is present or not, transient and stationary gains without inversion (GWI) always can be obtained by choosing an appropriate value of the relative phase. When the incoherent pump is absent,the values of transient and stationary GWIs are much larger and the time interval required to reach the stationary value is longer than those when the incoherent pump is present. Varying the exit rate and the ratio between injection rates can obviously change the phase-dependent GWI. In addition, in the transient evolution process, the phenomenon of high dispersion (refractive index) without absorption occurs at some values of relative phase. In the corresponding closed system, the stationary GWI can be obtained by choosing an appropriate value of relative phase only when incoherent pump exists, moreover the gain is smaller than that in the open system.In Chapter 4, we summarized the main research results of the paper in detail, and we put forward some ideas to the further research work.