| With the wider application of isotopes in disciplines such as geology, bio-medicine, archeology, environmental science and so on, isotope measurement and analysis has become a matter of growing concern. How to get a fast, reliable, low cost measurement method to the isotopes has become an important research topic in isotope applications. In this dissertation, degenerate four-wave mixing (DFWM), a nonlinear spectroscopy is employed to analyze isotopes. The Li isotope ratio is measured firstly. The optimal condition during the measurement is explored. Then the grating mechanism in DFWM is depth studied. Based on the theory, the rubidium (Rb) and cesium (Cs) isotopes are also measured. Finally, the wavefront distortion correction is studied according to the property of the phase conjugation. The main effects and innovations are as follow:The Li isotopes were measured accurately. First, the effect characteristics of the sample concentration and the incident powers on the DFWM signal were investigated. Then changing the concentration and observing the optimal powers, the results showed that the corresponding optimal powers should be changed when different concentration samples were measured. Under the optimal conditions, the isotope ratio was measured as 11.645±0.002.The value was close to the result of the atomic absorption spectroscopy (AAS). It proved the credibility of the result. On this base, we measured the Li isotopes in the actual rock samples. The results indicated that the presence of other elements in the sample would lead to line broadening and reduce spectral resolution. And different types of rock led to broadening different. This affected the correctness of the measurement. This study demonstrated the feasibility of DFWM for isotope measurements. It has an instructive impact on actual sample measurement.The Electromagnetically induced grating (EIG) mechanism during the process of phase conjugate degenerate four-wave mixing (PCDFWM) was investigated in the Rb atoms. The experimental results showed that the influence of the coherence grating was greater than the population grating. Then the characteristic of DFWM signal with the temperature was studied.We analyzed the effect of the temperature on the atomic number density and spectral line width. In addition, the influencing characteristics of the incident light polarization to the DFWM signal were researched. The relationship between the signal polarization and the incident light polarization was derived by using the third-order nonlinear susceptibility. This study provides a useful reference for improving DFWM efficiency.The graphite furnace was used as an atomizer. We obtained the detection limit of DFWM and studied the effect of the matrix effect and the resonance absorption on it. First, we calculated the detection limit of Rb in RbCl as 7.02 ng/mL. Then the matrix effect was studied in the graphite furnace by adding different concentrations of nitric acid (HNO3), sodium nitrate (NaNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3) in RbCl solution. The result confirmed that the signal intensity was related to the concentration and the ionization potential of the atoms. By comparing the detection limits of the original solution and the one with matrix modifier, it was found that the matrix modifier could effectively reduce the detection limit. This study has important reference value to the practical application of DFWM.Take the Rb atomic vapor as sample, according to the theory of phase conjugation, the influence of the detecting light intensity distribution to the phase conjugate signal intensity distribution was studied. The results verified the consistency of the light intensity distribution of the detecting light and the phase conjugate signal. Besides, producing a vortex beam by using the spiral phase plate, adding a distortion medium in the light path, the results showed that the DFWM can effectively correct the wavefront aberrations. The research has significant meaning for the optical signal generation and spatial transmission. |
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