Study On The Gain Material With Four Energy Level Model

With the rapid development of electromagnetism and the computer science, the advantages of computational electromagnetics become more obvious. The computational electromagnetics gradually occupied the dominant position of interdisciplinary analysis of the electromagnetic problems. As one of the branches of computational electromagnetics, FDTD algorithm has many advantages such as easy to use, fast and easily programming. In this way, it is widely used in various types of electromagnetic model calculation. At the same time, in recent years, metamaterials research has made very significant progress. Especially in optical band, metamaterials has the very broad application prospects, especially compare with those ordinary materials. In this condition, for those devices which are limited by material constraints, metamaterials can take the place of the restricted materials. However, people often meet a large number of losses which might affect the practical application. In this way, how to reduce the losses of the metamaterial becomes an important issue in front of academics.This paper first put forward an improved FDTD algorithm which is used for study the gain material with a four energy levels model. This improved algorithm can not only help us observe the laser threshold and the population change of each level but also greatly reduce the time which the traditional method processing the gain model. In this way, our improved algorithm has a more widely use value. Secondly, this article combine the gain model which is based on the structure of four energy levels with cholesteric liquid crystal and put forward a simple method to observe the laser threshold of cholesteric liquid crystal laser model. This method can be used in more complex cholesteric liquid crystal laser model and other multilayer system. This method is also benefit in further understanding the laser and manufacture more efficient laser device.In this paper, the main works are as follows:1. Introduce the basic theory of traditional FDTD method and related key technologies, such as FDTD basic equations,(PML) absorbing boundary conditions. Also, we expound its advantages in electromagnetic calculation. Then, we briefly introduce the research status of electromagnetic metamaterials and cholesterol crystal with their application prospects.2. Introducing the two-dimensional gain of the four-energy level and the relevant theories, such as rate equations and the polarization equations. We also introduce the traditional method which is used to process four-level gain media and our improved algorithm which can also be utilized to process the gain media and give the corresponding numerical simulation results respectively. Then we compare these two methods and give the conclusions.3. Using two-dimensional gain media which is based on a four energy level to analyze the cholesteric liquid crystal laser device. Introducing a method, ADE-FDTD method, which can be used to observe cholesteric liquid crystal threshold and derive the related formulas. Also, we give the corresponding numerical simulation results and verify the correctness of the method.