Theoretical Simulation of Polarization Effect on a Ladder-type Electromagnetically Induced Transparency in Cesium Atoms

Abstract

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

Date of Award	2020
Original language	English
Supervisor	Chin-Chun Tsai (Supervisor)