Two-beam free-electron laser

A model of a free electron laser (FEL) amplifier operating simultaneously with two electron beams of different energy is presented. The electron beam energies are chosen so that the fundamental resonance of the higher energy beam is at a harmonic of the lower energy beam. By seeding the lower energy FEL interaction with its fundamental radiation wavelength, an improved coherence of the unseeded higher energy FEL emission is predicted. This method may offer an important alternative to those seeding proposals for FELs currently under development in the xuv and x-ray regions of the spectrum.

Figure 1

The critical value of $R_n$, above which the shorter wavelength harmonic field has a higher gain than the longer wavelength, as a function of wiggler parameter $a_w$, for $n=3$, 5.

Figure 2

The scaled radiation intensities ${\mid A_1\mid }^2$ and ${\mid A_3\mid }^2$ as a function of scaled distance $\overline{z}$ through the FEL interaction region for $n=3$.

Figure 3

The bunching parameters $\mid b_{1,3}\mid$ and $\mid b_{\phi }\mid$ as a function of scaled distance $\overline{z}$ through the FEL interaction region for $n=3$.

Figure 4

The driving terms $S_{\phi }$ and $S_{3\vartheta }$ of the harmonic field $A_3$ as a function of scaled distance through the FEL interaction region for $n=3$.

Figure 5

The scaled radiation intensities ${\mid A_1\mid }^2,{\mid A_3\mid }^2$, and ${\mid A_5\mid }^2$ as a function of scaled distance $\overline{z}$ through the FEL interaction region for $n=5$.