Four Wave Mixing Spectral Technology Research And Its Application In Isotope Analysis

With the wider and deeper application of isotopes in many areas such as, archaeology, geology, environmental studies, medical studies and so on, isotope quantitative analysis is getting increasingly important. To set up a convenient, reliable and low-cost isotope measurement method has become a major issue in isotope applications.’In this dissertation, four-wave mixing (FWM) spectrometry, a kind of nonlinear spectrometry is employed to analyze isotopes. The polarization properties, dressing properties, resolution, and sensitivity of FWM spectrometry are investigated. Rubidium (Rb), cesium (Cs) and potassium (K) isotopes have been analyzed. Besides, the application of FWM spectrometry in the provenance determination of the artworks is explored. Main efforts and innovations are listed as follows:FWM with high efficiency and high resolution was realized with electro magnetically induced transparency (EIT) in the ladder-type three-level of87Rb atoms. The polarization and dressing properties of FWM were investigated. The results indicate that when all the incident beams are linear polarized, FWM is linear polarized. But when any incident beam becomes elliptical polarized, FWM is elliptical polarized. It is also found that the dressing effect gets stronger with the coupled or the probe field changing from linear to elliptical polarized. This work helps people understand the mechanism of FWM and its dressing effect, which can also be a reference in improving the efficiency and resolution of FWM.The polarization and dressing properties of degenerate four-wave mixing (DFWM) was investigated in133Cs atoms. DFWM signal intensity and its line shape were studied by altering the polarization state of one pump field. The results show that DFWM gets highest with the pump field in circular polarized, lower with the pump field in perpendicular polarized and lowest with the pump field in horizontally polarized. The theoretical simulation is in good agreement with the experimental data. Additionally, the double-peak phenomenon appearing at the strong pump beam is well explained by dressing-state theory in the two-level system. This work provides useful references for improving the efficiency of DFWM, recognizing the spectra and avoiding the spectra distortion in real applications.Several basic problems of DFWM spectrometry in isotope analysis were studied in Rb atomic vapor medium. Firstly, DFWM with forward phase-matching arrangement (FDFWM) and DFWM with phase-conjugate phase-matching arrangement (PCDFWM) were compared both theoretically and experimentally. It is found that PCDFWM is of higher resolution, while FDFWM is of higher efficiency and better SNR and stability. And then, the pump power dependence of DFWM was investigated. The results show that DFWM of Rb gets saturated at the pump power at5mW and double-peak appears at37.3mW. Besides, the effect of medium resonant absorption on DFWM was studied. The results indicate that resonant absorption decreases the DFWM intensity and complicates the isotope quantitive measurement. And therefore, the sample concentration should be set as low as possible to reduce the resonant absorption premising required SNR. Finally, Rb isotope abundance ratio in the Rb atomic vapor sample was determined. The value was confirmed by the absorption spectrometry, which indicates the feasibility of DFWM in isotope abundance ratio measurements.Rb, Cs, K isotopes in RbCl, CsCl, KCl samples, and Rb isotopes in several artworks were analyzed. Graphite furnace was employed as the atomizer. The detect limit expression of DFWM was deduced, and then, detect limit of Cs. K, and Rb were calculated as0.63pg/mL、0.325fg/mL and18.51fg/mL respectively. The low detect limit indicates the potential of DFWM in trace isotope analysis. Additionally, Rb isotope abundance ratio in RbCl were measured to be2.649+0.002, which is very close to that obtained by ICP-MS as2.67±0.02. Finally, Rb isotope abundance ratios in several terra-cotta figures were measured and used to determine their provenances, which demenstrates the potential of DFWM in archeology.