Strongly oversized “three-dimensional” Bragg resonators of planar geometry for effective mode selection in high-power free-electron lasers from sub-THz to THz band

A novel scheme of Bragg resonators is proposed that implements three-dimensional (3D) scattering of wave-fluxes. The electrodynamic characteristics of resonators of this type have been studied within the framework of the coupled wave method, and high selectivity has been demonstrated under conditions of a substantial oversize along all three spatial coordinates. The results of the theoretical analysis are corroborated by modeling the spatiotemporal dynamics of the RF-field evolution in such a resonator. A comparison is made with known types of Bragg resonators, as well as photonic bandgap structures, and the advantages of the proposed resonators for use as selective elements of powerful relativistic generators are shown. The prospect of using these resonators to provide a 3D distributed feedback mechanism and, as a result, to ensure the stable single-mode generation regime in projects of high-power free-electron lasers/masers operating from sub-THz to THz bands, which are currently being developed in collaboration between the BINP RAS (Novosibirsk), the IAP RAS (Nizhny Novgorod), and the Lobachevsky State University (Nizhny Novgorod), is discussed.