Coherent Formation Of Ultracold Ground State Molecules

The realization of laser cooling and trapping of neutral atoms directly propels the vigorous development in ultracold atomic and molecular physics during the past decade. The potential advantages of applications ranging from optical frequency standards, basic physical constants measurements to quantum information, directly prompt the investigations on ultracold cesium molecules to be an intensely research field in the world. The primary technique for formation of ultra-cold molecules is through association of ultracold atoms via the optical fields to magnetic fields. In this thesis, with the aim of formation the ultracold cesium ground state molecule, the scheme of stimulated Raman photoassociation of ultracold atoms is utilized. The femetosecond optical frequency comb is implemented to coherently lock the frequencies of photoassociation laser and the Raman laser. Thus, the coherent transfer of ultra-cold cesium molecules from the excited state to the ground state is realized, and the ultracold cesium ground state molecules are obtained. In addition, highly sensitive detection of ultracold cesium ground state molecules is performed using the improved trap loss spectroscopy technology. At the same time, the relative energy level properties of the ultracold cesium molecular excited states have been systematically studied. Based on the formation of ultracold cesium molecules in the excited states by photoassociation technology, the ro-vibrational spectra with the lowest vibrational quantum number are obtained, the light-induced frequency shift of the cesium molecular resonance energy levels are investigated and precisely measured by using double photoassociation spectra.The main innovation works are summarized as follows:1. The controllable three-dimensional fluorescence modulation spectroscopy techniques are proposed to enhance the detection sensitivity of trap loss spectroscopy. Thus the ro-vibrational spectra of the lowest vibrational level v=0,1in the out well of cesium molecular pure long-range state are highly sensitively detected. Relative spectral data and molecular constants are obtained. The experimental bases are well laid for the formation of ultra-cold cesium ground state molecules.2. The scheme of establishing a precise optical ruler by using a frequency shifter is devised. The laser induced ro-vibraional energy level shifts for the cesium molecules are observed. The dependences of laser induced frequency shifts and the line-width broadenings on the laser intensity are systematically demonstrated. Theoretical supports are given for choosing the intensities of the photoassociation laser and Raman laser in the two two-color photoassociation technology.3. The coherent locking of different lasers is realized by using the femtosecond optical frequency comb system. A long-term stability of the laser frequency on the atomic and molecular transition line is achieved, consequently provides a critical technical support for the formation of ultracold cesium molecules in the ground triplet state.4. Based on the coherent locking of the photoassociation laser and Raman laser via the optical frequency comb system, the ultracold cesium molecules populated in the ground triplet state are prepared by two-color photoassociation technology, the ro-vibrational spectra and molecular constants for the ground triplet cesium molecules are derived.