研究级联三能级系统中的极化拍频技术 ,发现其对能级差的测量精度决定于光学跃迁的均匀增宽 ,在符合拍频条件下 ,两独立光源拍频的频差可以超出激光线宽 ,激光绝对频率的测量精度可达到与激光线宽同一量级。 To study the polarization beat technique in cascaded three-level system, we find that the measurement accuracy of the difference in level is determined by the uniform broadening of optical transition. Under the condition of beat frequency, the frequency difference of beat frequency of two independent light sources can exceed the laser Linewidth, laser absolute frequency measurement accuracy can be achieved with the laser linewidth the same order of magnitude.