It is clear that the simple two-level atom model is too constrained to describe the behavior of such laser, and the four-level model using center-manifold techniques seems to be a particularly attractive candidate model for describingit.

• 当J=0时，四能级的振转模型转变为二能级模型，通过理论计算的曲线我们可以清楚地看到二能级速率模型与四能级振转模型的两个主要的区别：一个FWHM(激光脉冲的全波半高宽)，从二能级模型解出来的理论曲线的全波半高宽与实验结果相比明显要窄的多；