This chapter presents the coupled harmonic oscillator model in bright-bright mode coupling system by utilizing the boundary conditions of electromagnetic field combined with the microscopic behavior of electrons in metal. According to the model, the scattering parameters can be easily derived for a thin system. It can be then used to analyze the other physical parameters in the system, such as the dielectric constant, coupling strength, and so on. The correctness of the model is verified by using a simple planar structure composed of the two paralleled and staggered metal nanorods in each unit cell. The results show that physical parameters of the system can be concluded very well from the model. This indicates that the model is effective and convenient for describing bright-bright mode coupling. Then, physical regime behind the PIT and slow light effect is revealed in a system based on the model.
Top4.1 Introduction
In the field of atomic research, coherent preparation can significantly change the optical properties of gas atoms and molecular media, which provides a new way for optical research. The most notable of these is the EIT phenomenon observed by Boller et al. (1991) in strontium vapors. As early as 1976, Alzetta et al. Found a coherent population trapping (CPT) phenomenon that was closely related to the EIT phenomenon. Subsequently, in 1986, Kocharovskaya et al. (1986) found that the CPT phenomenon occurs when the pulse interval of the mode-locked laser array is equal to the fine division of the atoms by theoretical studies. They propel the light in the three-level atomic system can spread a significant distance without being absorbed phenomenon. Soon people in the experiment observed in the three-level system of light transmission is not consumed phenomenon, that is, EIT phenomenon. The working principle can be illustrated by the three-level Λ-type atom shown in Figure 1. The transition between energy level |1| and |2| is prohibited, |1| and |3| and |2|3| can transition between each other. In the absence of coupling light, the probe will be absorbed by the atoms to form absorption peaks; and in the coupled light, |2| and |3| energy transition between the level, and energy level |3| can transition to energy level |1| and |2|, respectively. Therefore, there are two paths between 1: 3 and 3. The direct transition between |1| and |3| The interphase transition between these two transition paths allows the probe light to be not absorbed by the atom so that a transparent window is formed in the transmission spectrum, that is, EIT phenomenon. The EIT phenomenon has attracted much attention because it dramatically increases the nonlinear optical polarization in the transparent window (Lukin, Hemmer, & Scully, 2000) while showing a very steep dispersion relationship and the accompanying slow light effect (Matsko, Kocharovskaya, Rostovtsev, Welch, Zibrov, & Scully, 2001). Also, the technology associated with EIT is also expected to be used in the study of quantum information processing (Novikova, Walsworth, & Xiao, 2012; Liu, Dutton, Behroozi, & Hau, 2001). However, it should be noted that in the atomic system to achieve EIT is facing very harsh conditions. First, the atomic energy level structure requires precise selection. Secondly, the need for two high light intensity of the coherent light, the detection of light and coupled light. Thirdly, the experiment is carried out in ultra-low temperature environment. Fourthly, the entire experimental device equipment, etc., these conditions limit its application in real life.
Figure 1. Three-level Λ-type atoms in the detection of light and coupled light irradiation to achieve EIT phenomenon of energy level transition diagram