||Theoretical Simulation of Polarization Effect on a Ladder-type Electromagnetically Induced Transparency in Cesium Atoms
||Department of Physics
||Nguyen Thi Ly Ly
Electromagnetically induced transparency
optical Bloch equation
Electromagnetically induced transparency (EIT) is a quantum interference effect that allows light to propagate by creating a transparency window at the resonance of atoms that are usually highly absorbed. This thesis theoretically simulates the polarization and temperature dependence of the EIT spectrum of Cesium atoms on the ladder-type 6S_(1/2)-6P_(3/2)-11S_(1/2) transition. The optical Bloch-equation for the system is constructed and solved to obtain the steady-state solution of the matrix elements, which contains the coherence information between the atom and the external optical fields. The absorption coefficient can be derived from the imaginary part of susceptibility for this system. In order to study the polarization effect in the EIT system, three different polarization combinations of probe and coupling fields were applied, namely σ^+-σ^-, σ^+-π, and σ^+-σ^+.The results show that when the polarization of the two fields is changed (varied), the allowed two photon-transition paths and the reshaped population distribution of Zeeman-sublevels are the key effects of changing the EIT signal. Therefore, the EIT peak can be enhanced or reduced under different polarization combinations. The influence of temperature on the EIT signal is investigated by changing the Maxwell population distribution of the system. The temperature ranges from ultra-cold (1mK, such as the temperature in a magneto optical trap) to room temperature (300K). At ultra-cold temperature, the average speed of atoms is around 0 m/s, and the non-optical energy transform process (mainly is collision) is negligible, so the optical pumping efficiency is very high. However, at room temperature, the average speed of atoms is much larger (193.36 m/s), and the impact of collisions is great, so the optical pumping rate is very low. We found that the linewidth of the EIT signal at room temperature is narrower than the linewidth at ultra-cold temperature, while the line shape at high temperature contains additional absorption wings on both sides of the EIT signal. This is the phenomena of quantum interference. The unusual peak signal when changing polarization and temperature will provide some ideas for future experiments and applications in other fields.
TABLE OF CONTENTS IV
LIST OF TABLES VI
LIST OF FIGURES VII
LIST OF ABBREVIATIONS XI
CHAPTER 1: INTRODUCTION 1
CHAPTER 2: THEORY OF ELECTROMAGNETICALLY INDUCED TRANSPARENCY 3
2.1. Interaction of light and atoms 3
2.1.1. Deriving the EIT Hamiltonian 3
2.1.2. Density matrix 6
2.1.3. The Von Neuman Equation 8
2.1.4. Density matrix approaches to three-level system 10
2.1.5. The susceptibility of the system and absorption in EIT 12
2.2. The influent factors on EIT signal 16
2.2.1. Doppler effect in EIT 16
2.2.2. Wavelength mismatch 18
2.2.3. Transition probability and Rabi frequency 22
2.2.4. Optical pumping 25
CHAPTER 3: SIMULATION RESULT 32
3.1. Model testing 32
3.1.1 Experiment setup 32
3.1.2 Experimental and simulation result 34
3.2. Simulation results under different polarization combinations 40
3.3. Temperature dependence 45
CHAPTER 4: CONCLUSION AND SUGGESTIONS FOR FURTHER WORK 49
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