The Mechanism Of The Auto-ionization Of Ultracold ND Cs Rydberg Atoms

When the outer electrons in an atom are excited to state of a high principal quantum number, it is called Rydberg atom. It has many properties because of the high state. For instance, Rydberg atoms have huge radius of outer electron orbit (～n2), and large polarizability (～n7). There for, it is very sensitive to external electric field and magnetic field. It has a lot of superiority when we are searching for the interaction with external field and other atoms. Rydberg atoms also have some other characteristics such as low bound energy (～n-2), small energy interval (～n-3). This makes Rydberg atoms have more potential in the research of atomic and molecular physics.In this paper, there are three aspects:First, the definition of Rydberg atoms and ultracold plasmas is given. And so is the characteristics and the research development. Then is the brief introduction of the mechanism of auto-ionization during the spontaneous evolution in ultracold Rydberg atoms in repulsive potential. Second, we give the energy level of Cs atoms and detailed description of experimental system. Thirdly, some possible reasons that cause the auto-ionizatoin of Rydberg atoms are found:1, BBR-induced direct ionization; 2, redistribution from repulsive interaction to attractive interaction induced by BBR, spontaneous emission and superradiance.4,47D3/2 and 47D5/2 state Rydberg atoms is prepared. And comparison is made on the ionization spectrum and spontaneous evolution of Rydberg atoms respectively. Most importantly, initial ionization is observed. Finally, conclusions are found that superradiance is the most possibly reason to trigger redistribution of the atoms to attractive interaction from repulsive interaction.The innovations of this work are shown by two aspects as follow:1. For the initial ionization during the spontaneous evolution of Rydberg atoms in repulsive interaction region, some comprehensive analysis is made in many aspects:black body direct ionization, and black body, spontaneous emission, and superradiance induced redistribution to attractive interaction. Then the calculation of the total rate of BBR transition and BBR ionization is done.2. The excitation probabilities, the situation of the number variation of different particles, the percent conversion of plasma from Rydberg atoms are compared in different fine level,47D3/2 and 47D5/2. A qualitative explanation is made using theory of collision in the region potential. Finally we find out the main reason that cause auto-ionization of Rydberg atoms through comparing the calculation and experimental result.