Investigation Of Purely-Long-Range State Molecule And Direct Frequency Comb Spectroscopy

In the last decade, the research on cold and ultracold molecules has received much attention because of important advances and potentially new applications in several domains such as few body physics, physical chemistry, and quantum computing. The invention of frequency comb, not only built a bridge from the microwave frequency to optical frequency but also providing a versatile spectroscopy tool with high spectral purity, excellent accuracy, and at the same time broad spectral coverage. In this thesis, with the aim of obtain high resolution spectroscopy, the dark spot magneto-optical trap technique is utilized to improvement the trapped cold atomic cloud density. The three-dimensional controllable modulation fluorescence technique is adopted to increase the sensitivity of ultracold molecules spectroscopy. Based on these techniques, we have experimentally obtained two lowest vibrational levels of ultracold cesium moleculars with purely long range states. The potential curve is represented with spectra data by using an analytical asymptotic approach. Values of atomic levels radiative lifetimes and cesium molecule ground states van der Waals coefficients are extracted, respectively. Besides serving as a clock work and frequency locking system, we used an optical frequency comb directly for spectroscopy, which named as direct frequency comb spectroscopy.Our main innovation works in this these are summarized as:1. By utilizing ark spot magneto-optical trap technique, the density of cold atomic cloud are enhanced, we increasing the coupling of photoassociation laser with cold atom. This technique provides enough sensitivity to obtain high resolution ultracold cecium molecular ro-vibrational spectroscopy.2. The amplitude-frequency translate detection technique is proposed to Study the laser induced frequency shift rate of ultracold cesium molecules. This technique used the dependence of the fluorescence losses on the laser induced frequency shift, which based on the condition of identified spectral lineshape. By using this technique, we obtained the laser induced frequency shift rate of ultracold cesium molecules, which is too small to be detected directly.3. By carrying out the three-dimensional modulation photoassociation spectroscopy, we experimentally obtained loweset levels of ultracold cesium molecules in purely long range states. We paves the way for an sensitive detection of cesium molecules in the lowest level of pure long-range state. The agreement between experimental and theoretically calculated energy positions would improve the precision of potential well. We represent the potential curve of purely long range state of cesium molecule with these this data by asymptotic analytical approach. Based on represented potential curve, values of atomic levels radiative lifetimes and cesium molecule ground states van der Waals coefficients are extracted, respectively. This facility and robust detection technique would work for other ultracold molecular samples.4. We shaped the output broadband laser of optical frequency comb, we observed the two photon spectroscopy of rubidium atoms and obtained the hyperfine constant of rubidium atoms. This method paves the way for study the ultracold and ulatrafast physics.