• Q.K. Jia
  USTC/NSRL, Hefei, Anhui

The formula of spontaneous emission in free-electron laser is derived from the one dimensional Maxwell equation in the time domain. The effective start-up noise power of Self-Amplified Spontaneous Emission (SASE) process is given, it includes the incoherent spontaneous emission contribution, which is equal to the spontaneous undulator radiation in the first power gain length, and it also includes the coherent spontaneous emission contribution. The short pulse case is analysed.