An optical cavity design for a compact wave-undulator based-FEL

We have considered a novel scheme of wave undulator FEL. The system employs a recirculated radiation pulse serving as undulator provided by a high power laser. Non conventional electron acceleration schemes promise nowadays high gradient acceleration yielding the GeV on the scale of few centimeters, however these solutions might solve the problem of the accelerator length, but not that associated with the saturation length and thus of the length of the undulator, which remains on the order of tens of meters. The option of wave-undulator based FEL might provide a valid solution in the future.