The Investigation Of Related Nonlinear Effects In Electromagnetically Induced Coherent Media

In the past decade, researchers have found that the optical properties of a media can be dramatically altered by optically inducing the medium into a coherent superposition. Such electromagnetically induced coherent media typically have large susceptibility without the resonant absorption that usually accompanies large nonlinear susceptibility. In this thesis, the related nonlinear effects of electromagnetically induced coherent media in cesium atom system are discussed systematically. By use of the bichromatic light, the light group velocity in thermal cesium vapor and trapped cold cesium cloud, the hole-burn effect in the atom near the dielectric surface are investigated. The effects of the intensity and detuning of coupling laser on the electromagnetically induced coherent media are investigated.This thesis is organized as follow:Chapter 1 presented an introduction in which the background and development of nonlinear optical effect was reviewed. The various applications of the electromagnetically induced coherent media were reviewed comprehensively.Chapter 2 presented a theory of the electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA). The absorption and dispersion curves were numerical computed by use of the density matrix equation. The decrease of absorption and increase of dispersion were predicted when probe laser beam resonant with transitions of the atom. We pointed out that EIT and EIA were the result of quantum interference in the interaction process of laser field and atomic system.In Chapter 3, by using of the double scans frequency technique in cesium atom, the spectroscopy character of electromagnetically induced transparency and electromagnetically induced absorption were studied. The content include in the line shapeinversion from EIA to EIT through the intensity coupling laser and the line shape inversion with different buffer gas pressure. The linewidth broadening was also discussed.Chapter 4 was experimental investigation of light group velocity with and without buffer gas in Cs atom system. The light storage was also investigated. We measured the light group velocity in the condition with different buffer gas pressure, different temperature, and different laser detuning.Chapter 5 presented measurement of nonlinear spectroscopy of the cesium atoms in a magneto-optical trap. The group velocity of light in the cold atoms was studied with the positive and negative detuning of probe beam.In Chapter 6, the nonlinear optical effect of atom near the dielectric surface was studied.The results include the hole-burn effect and splitting effect in nonlinear selective reflectionspectroscopy.Finally, the recapitulation work was presented.The characterized works among the above are as follows:1. We observed the splitting of electromagnetically induced absorption and slow light when the coupling laser was intense. The line shape inversion from EIA to EIT was firstly investigated with different buffer gas pressure. The result can lead to the arbitrary control of the group velocity in electromagnetically induced coherent media.2. The dispersion-like nonlinear absorption spectra of cold caesium atoms which confined in a magneto-optical trap were observed around D2 line (6Si/2,F=4—>6P3/2,F'=5) for the probe frequency near the cooling transition frequency. The behavior of the group velocity of light in the cold atoms was firstly studied with the positive and negative detuning of probe beam. The speed of a light pulse was able to arbitrarily control from subluminal (8xl03m/s) to superluminal (-1.5xl04m/s) velocity in cold caesium atoms by changing only the detuning of the probe laser.3. Considering the collisions between the atom and the walls of the cell, the spectral hole-burning was observed in nonlinear selective reflection spectroscopy. The difference of intensity and detuning of coupling laser were applied. The experimental results correspond with reasonable accuracy with the predictions derived from a theoretical explanation of the nonlinear optical susceptibility. At the same time, the splitting of selective reflection spectroscopy was studied in A three-levels system when the coupling laser was intense.