Within the frame of the ABCD formulation of propagator of a time-dependent quantum system, the ABCD law is extended to the so-called effective ABCD system which effective beam quality factor is conservative;

• 对于某一方向上品质因子守恒的情况，可以通过解析某一方向品质因子守恒的充要方程，找到原子激光的ABCD形式的传播子。