A free-electron laser with enhanced energy spread acceptance

It is shown that by cascading wiggler sections through compensating sections a gain of N²times the gain of a single wiggler section may be attained, whereas the energy acceptance of the sections is the same as that of a single section. The relative phase shift of electrons with different energies in the compensating section is opposite that in the wiggler. A realization of a compensating section is presented. Finally, an application of this idea is considered to a free-electron laser in a storage ring. It is shown that at 0.15μm wavelength, using a 250 MeV storage ring, a gain 100 times higher may be obtained as compared to the uniform wiggler free-electron laser, for the same energy acceptance of 2.5 percent in the two cases.