DUAL UNDULATOR FREE-ELECTRON LASER

The harmonic property of the dual undulator free-electron laser by usi ng Madey's theorem has been analyzed. We have derived the formulas of harmonic spontaneous emission power density, small-signal gain of this new type of undulator free-electron laser and the coupling coefficien t between electrons and radiation field. From the numerical calculatio n results, we came to the conclusion that we can enhance the coupling between electrons and the radiation field by using a dual undulator, a nd hence the harmonic emission power density and gain can be increased . Furthermore, under certain conditions we can obtain not only odd but also even harmonic radiation on axis.