ANGULAR SPECTRUM PROPERTY OF SPONTANEOUS EMISSION IN A TWO-DIMENSIONAL UNDULATOR FREE-ELECTRON LASER
二维摆动磁场自由电子激光自发辐射的频谱特性

The angular spectrum of spontaneous emission in a wo-dimensional undulator free-electron laser is analyzed theoretically. Numerical calcularion shows that the s-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l = s. so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electon laser can be realized selectively.