S>>N13>neo dn3s0 n S-n.W() 未形成自激振荡或在阈值附近时可忽略受激辐 射 dt n 13(t)n-n2() A2n, s a + a A21+S2 n2()=-n +nwi t (0<t≤t0) 71 n2S32>>W13 n30 0 3  dt dn ( ) 1 13 1 3 32 nW t n S =  未形成自激振荡或在阈值附近时可忽略受激辐 射 2 2 1 2 1 1 3 2 2 ( ) ( )[ ( )]   A n t W t n n t dt dn = − −         − + =         − + W t A e W A W n n t 1 1 3 2 2 1 ( ) 1 1 1 3 2 2 1 1 1 3 2      (0 ) 0  t  t 32 1 32 31 21 2 21 21 S S A A A S   = + = +