Field Ionization Spectroscopy Of The Ultracold Rydberg Atoms And Evolution Into Ultracold Plasmas

The development of laser cooling and trapping techniques opens a new realm of cold atoms in the fields of atoms and molecules physics.It also becomes very important in the study of ultracold Rydberg atoms.Rydberg atoms,which are in states of high principal quantum number,n, are atoms with exaggerated properties,such as big electric dipole moment, long lifetime and small adjacent energy level spacing.Using the laser cooling and trapping techniques,it has become possible to excite Rydberg atoms at densities exceeding 10⁹cm^-3 and at temperatures in the micro-Kelvin range.In contrast to atom beam experiments,Rydberg atoms in a frozen Rydberg gas do not move significantly over the experimental time scales given by the Rydberg atom lifetime.In this regime,interactions are no longer masked by thermal motion.This thesis represents the production and detection of Rydberg atoms.The cold,trapped Cs atoms were excited to Rydberg states via two-photon excitation.Using field ionization method,the ion spectrum of Rydberg atoms at nS and nD states is detected by scanning the Dye laser wavelength.We also study spontaneous evolution of Rydberg atoms into ultracold plasma. The main contents are as follows:First,some basic concepts on Rydberg atom and the properties of Rydberg atoms will be introduced,and the developing process and status of ultracold Rydberg atoms are reported in summary.Second,according to the process of two-photon excitation,the experimental systems of ultracold Rydberg atoms will be introduced, including Magneto-Optical Trap and the dye laser.Third,the detailed field ionization spectra of the ultracold cesium Rydberg atoms will be illustrated.The DC Stark effect of the ionization threshold shift and the ion spectrum of Rydberg states will be obtained and discussed.Forth,we will also study the spontaneous evolution from ultracold Rydberg atoms to plasma in cesium MOT using the method of field ionization pulse.The processes of the evolution will be description and the ionization mechanisms will be analyzed partly.In this thesis we have two main achievements:1.We investigated the ion spectrum of ultracold Rydberg atoms using field ionization pulse.We obtained the field-free ionization threshold of cesium (6P_3/2) and quantum defects of S and D states by fitting experimental data.2.The spontaneous evolution from ultracold Rydberg atoms to plasma was investigated using the method of field ionization.The evolution mechanism was analyzed primarily.