Rubidium Atoms Of Saturated Absorption And Four-wave Mixing Spectral Characteristics Research

The appearance of Laser spectroscopy technology have improved the spectrurn sensitivity and resolution, which soon became an important means in the study of the light and matter interaction. Hot atoms are always used to analyze the material, while the Doppler broadening caused by the hot atoms lower the resoluton of the spectrum. However, four-wave mixing (FWM) and saturated absorption spectroscopy (SAS) can eliminate Doppler broadening and become the focus of research in this paper. Against the drawback in the application of the traditional saturated absorption, we proposed a new configuration to eliminate the drawback and made to explain theoretically. In addition, the phase conjugate degenerate four-wave mixing (PCDFWM) and forward degenerate four-wave mixing (FDFWM) in their own characteristics were analyzed and compared. Normally, the conversion efficiency of FWM is relatively low. The electromagnetically induced transparency (EIT) was used to control the generation of effective FWM. And the influence of temperature, incident power and polarization state to FWM were also studied in this paper. Conclusions are:1. The experimental study of the rubidium atomic hyperfine structure with SAS. The applications of SAS usually use rubidium atoms as sample, because SAS of the rubidium is relatively simple. However, the crossovers peaks in the SAS spectrum often swamp the real peaks, which is harmful to the application of SAS. In the convetional SAS, the probe and pump beams propagate in exactly opposite directions. We proposed a new experimental configuration different with conventional way. In this configuration, the two beams copropagate into the sample with an angle. We can displace crossovers from their original position to prevent them from overlapping real peaks by adjusting the angle between two copropagating beams from one laser source. This method helps identify the real transitions in saturation absorption spectroscopy and simplify saturated absorption spectroscopy, which is of meaning in saturation absorption application.2. The DFWM of the rubidium atoms. Depending on the optical configuration, DFWM is divided into PCDFWM and FDFWM. We compared the two type DFWM under the same experimental conditions. Concluded that the spectrum line width of the PCDFWM so narrow that we can observe the atomic hyperfine structure, but the signal intensity is relatively small. Compared with the PCDFWM, the line width of the FDFWM is too wide to distinguish the hyperfine structure, but the signal intensity is relatively large. The results of the analysis provides a reference for the choice of the configuration in the practical application.3. The Non-degenerate four-wave mixing based on EIT. The conversion efficiency of the FWM is relatively low in normal circumstances. EIT can reduce the resonant linear absorption of the medium and enhance the conversion efficiency of the FWM. We studied the influences of the temperature of the sample, the incident power and polarization to the FWM signal. Found that:(1) With increasing temperature, the signal intensity of the FWM first increases and then decreases. Because with the temperature enhanced, the resonance absorption of the sample is also enhanced.(2) The signal intensity of the FWM is proportional to the incident power.(3) The polarization of the incident beam can modulate the FWM signal. These studies above will provide references for obtaining and modulating the best FWM signal.