中文摘要：

使用具有中间态的双光子共振非简并四波混频（NFWM）测量了Ba原子J=0和J=2的偶宇称里德伯线系，与现代实验方法不同，本方法是纯光学的方法，其光路简单，检测的是相干光，而不是电子或离子信号．当用窄带宽的激光时，本技术对里德伯能级的窄光谱结构可以获得消多普勒的分辨率．

英文摘要：

We have applied two-photon resonant nondegenerate four-wave mixing （NFWM） with a resonant intermediate state to measure the energy levels of the Ba even-parity J = 0 and J = 2 series. Differing from other experiment techniques, our method is a pure optical technique. Instead of detecting electrons or ions, the signal here is a coherent light. Two-photon resonant NFWM is a Doppler-free spectroscopy when the incident laser beams have narrow bandwidths.