Measurement of 7Li/6Li Isotope Ratio Using Phase-Conjugate Degenerate Four-Wave Mixing in a Graphite Furnace

To obtain a Doppler-free resolution, we employ phase-conjugate degenerate four-wave mixing (PCDFWM) to isotope selectively analyze ⁶Li and ⁷Li in a graphite furnace atomizer. After the investigation of concentration and power dependences of PCDFWM, the optimal sample concentration and power conjugation are determined. Under the optimized conditions, we measured ⁷Li/⁶Li isotope ratio in Li standard solution with PCDFWM to be 11.571 ± 0.003, which is in good agreement with the value calculated by atomic absorption spectroscopy but has a preferable resolution. The detection limit as 15.54 ng/mL is achieved. The information obtained from this paper suggests that PCDFWM is a reliable laser spectroscopic technique with high resolution in isotope ratio measurement and trace analysis for various applications such as geochemical exploration.