Higher-order modes excitation in generator with photonic crystal

We revealed physical processes responsible for the excitation of higher-order modes in volume free-electron laser with photonic crystal. We discovered the new approach for the selection of the electromagnetic modes in volume free-electron laser with photonic crystal based on the choice of the emitter configuration. This approach allows essential multiplying the generation frequency. We found that the regimes with developed higher-order modes are accompanied by complex squeezed-like beam dynamics. Also, we present the results of the optimization of volume free-electron laser with photonic crystal in terms of excitation of high-order modes. In particular, we investigated the influence of the location of electron beams on the excitation of photonic crystal eigenmodes. Keywords: Electron beam, Distributed feedback, Volume free-electron laser, Photonic crystal, Higher-order modes, Modes selection, Sub-terahertz radiation