The Investigation Of Cooling Neutral Atom By Partially Coherent Light

In the recent twenty years, the researches on laser cooling and trapping neutral atoms and related applications attracted more and more attentions, and many fruitful results have been achieved. However, in the previous studies, the laser beams used to cool atoms are usually coherent. In this thesis, the cooling and trapping neutral atoms by partially coherent laser beams is investigated. The influences of coherence degree of laser beam on the temperature of cold atoms in the MOT is obtained experimentally. The results are analyzed theoretically. The main contents of the thesis are as follows:In the first chapter, an introduction to the historical background and developments of laser cooling is presented. Then the research background and the purpose of this study are introduced briefly.In the second chapter, the atomic energy level structure of rubidium atom is discussed. The basic principle of the interaction force between atom and laser, the laser cooling and trapping in magneto-optical trap are introduced briefly.In chapter 3, the theory and method to obtain partially coherent light is introduced. We use the crystal to modulate the phase distribution of the laser. By changing the voltage applied on the crystal, the degree of coherence of laser beam can be controlled.In chapter 4, the experimental setup of laser cooling is described. Each parts of the experimental setup are introduced in detail, including the main structures and the operating principles of the semiconductor diode laser system, frequency stabilization, magnetic system, and time-of-flight measurement method of the temperature of cold atoms. Then the experimental procedure and results of cooling atom by partially coherent laser in the magneto-optical trap are presented. By analyzing the results, we find out that with the decrease of the coherence degree of the laser beam, the temperature of cold atoms in the MOT increases.In chapter 5, a brief conclusion is presented. The main results of the thesis are summarized and an outlook is given.