Spatially coherent radiation from a coaxial free-electron laser with a resonator composed of one-dimensional and two-dimensional Bragg mirrors

It is shown that the application of a resonator composed of one-dimensional and two-dimensional coaxial Bragg mirrors provides a spatially coherent radiation from a hollow electron beam with a transverse size several orders of magnitude larger than the wavelength. The two-dimensional Bragg mirror placed at the cathodic end of the resonator synchronizes the radiation across the hollow electron beam. The standard one-dimensional Bragg mirror placed at the collector end closes the feedback loop and reduces ohmic losses to as low as 5–10% of the lasing power.