| People research on and explore physical world, in other words, investigate its related characteristics. The measurement precision of physical constant is improved, which will promote people's deep understanding of physical world. These precision measurements are often using spectroscopic techniques, so it is very important to surmount Doppler effect from atoms movement. For the hot atoms in a vapor cell, various sub-Doppler techniques, such as the saturated absorption spectroscopy, the polarization spectroscopy, and the two-photon spectroscopy and so on, are adopted, but which are all focus on the spectroscopy between atomic ground states and excited states. Recently, based on the virtue of the excited states Doppler-free spectra due to velocity selection mechanism by usual optical-optical double-resonance (OODR) technique, they are widely used in laser frequency stabilization, the measurements of hyperfine structure and excited state lifetime, and hyperfine structure constant and so forth. In addition, with the development of laser cooling technique, especially magneto-optical trap (MOT) became a standard tool for cooling and trapping neutral atoms, it greatly promotes the progress of cold atom physics and the related fields. Due to lower and narrower velocity distribution of cold atoms, Doppler effect is eliminated, so more precise measurements are possibly realized, for example, atomic energy structure and some physical constants.Based on the ladder-type cesium atomic system, we investigated the spectroscopy between atomic excited states and new-type two-color magneto-optical trap. Our main works in this thesis are as follows:(1) Using the new double-resonance optical-pumping (DROP) technique, the signal-to-noise of the excited states spectrum is greatly improved, and employing atomic coherence effect such as electromagnetically induced transparency (EIT), the linewidth of DROP spectrum is obviously suppressed; the experimental results are consistent with the conclusions from theoretical analysis.(2) In ladder-type EIT system, EIT signals without Doppler background are obtained when keeping the probe laser locked and scanning the coupling laser, which correspond to the hyperfine transitions between excited states, and are interpreted based on a multilevel ladder-type EIT model.(3) The DROP spectrum is investigated under the condition of one-photon frequency detuning, and applied to the frequency detuning control and laser frequency stabilization of794.6nm (6P32-8S12transition) cooling laser in cesium two-color MOT.(4) A two-color cesium MOT is realized for replacing any pair of852.3nm cooling laser beams in a standard cesium MOT with794.6nm cooling laser beams only coupling the excited states (6P,,-8S12, transition), and can efficiently cool and trap atoms on both the red and blue sides of two-photon resonance. We measured the dependency of two-color MOT on the experimental parameters. Based on the diamond-type atomic system, and also realized a background-free fluorescence detection of cold atoms directly using fluorescence generated in the two-photon cooling process.The above works are all based on ladder-type atomic system, the studies on the DROP and EIT in a room-temperature vapor cell will be helpful to the deep understanding the physical mechanism of two-color MOT, especially for the investigation of quantum coherence in it. It is also possible to directly generate twin beam (or correlated photon pairs) in this two-color MOT based on a diamond-configuration four-wave mixing process, which is important for quantum communication and quantum information processing.
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