High Sensitive Spectroscopy Research On Ultracold Cesium Molecule

During the past decade, the study of ultracold molecular spectroscopy has gradually extended to the high-resolution measurement of the molecular spectroscopy, the measurement of the basic physical constants, ultracold collisions, multi-body problem, high-precision frequency standard, quantum computing and many other cutting-edge issues from the simple study of ultracold molecular level, potential energy curves and molecular constants, and has aroused the great interest. With a very low temperature of ultracold molecules, Doppler-effect has been almost overcomed. It is possible to directly achieve a high-resolution molecular spectroscopy. In the study of ultra-cold molecular spectroscopy, fluorescence spectroscopy technique is a reasonable method. However, its detection sensitivity is too low to unable to meet the needs of high-precision measurements. In the thesis, the new detection techniques, three-dimensional velocity-selected modulation spectroscopy and photon counting spectroscopy, have been first offered by analyzing the main reasons of the low sensitivity. And the high sensitive ultracold cesium molecular spectroscopy has been obtained.The main innovation of the work summarized as follows:1. By using the three-dimensional velocity-selected modulation spectroscopy technique, the ultra-cold excited state Cs₂ vibrational spectroscopy with a high sensitivity has been obtained. The detection range of the present trap-loss spectroscopy has been extended to detect with 20cm^-1, and the spectroscopy data of lower lying vibrational levels have been obtained. The excited state cesium molecular coefficients C₃ and long-range potential energy curves are calculated by fitting with a theoretical formula.2. By optimizing the parameters of experiment, more high sensitivity has been achieved. As a result, the high-resolution and high-sensitive Cs₂ rovibrational spectroscopy has been obtained. And the rotational spectrum of the low-vibration quantum number (v = 1) has been observed with a very low transition probability.3. By using the photon counting technique, a near-threshold photoassociation spectroscopy has been obtained with a high sensitivity, which provides the important spectroscopy data for studying the energy curves in the near-threshold region. 4. It is operated to systematically study the dependence of the ultra-cold Cs₂ excited state rovibrational spectroscopy on the intensity of a photoassociation laser. Saturation effect was observed in our experiment. And the saturation intensities were obtained by the theoretical fitting. The difference among the saturation intensities for different rotational progressions has been found.5. It has been demonstrated a robust method of directly stabilizing diode laser frequency to the cesium atom-molecular hyperfine transitions. The trap loss fluorescence spectroscopy was applied to yield the error signal based on modulating molecules with ultralow modulation frequency.