We study a new modification of the Bragg structures based on the coupling of traveling and quasicritical waves, as well as the possibility to use it as an electrodynamic system of free-electron masers (FEMs) and lasers (FELs). It is shown that inclusion of quasicritical waves in the feedback loop allows one to improve significantly the selective characteristics of Bragg structures and ensure the stable regime of single-frequency generation at a rather large (as compared to the wavelength) transverse size of the interaction space. Simulation and “cold” electrodynamic tests performed in the millimeter- and submillimeter-wave ranges confirm high efficiency of application of such structures. Operability of the new feedback mechanism has been confirmed in a series of joint experiments performed by the Joint Institute for Nuclear Research (Dubna, Russia) and the Institute of Applied Physics (IAP) of the Russian Academy of Sciences (Nizhny Novgorod, Russia) with FEL/FEM-based generators in frequency bands from K_a to W for transverse cavity sizes of up to five wavelengths. The project of a high-power long-pulse FEL operated in the subterahertz and terahertz frequency ranges, which is developed jointly by the IAP and the Budker Institute of Nuclear Physics, is discussed. The results of modeling an electrodynamic system based on modified Bragg reflectors having diameters of 20 and 40 wavelengths for implementation of FELs in the 300 and 600 GHz ranges, respectively, are presented.

我们研究了基于行波和准临界波耦合的布拉格结构的新修改形式，以及将其用作自由电子主峰（FEM）和激光器（FEL）的电动力系统的可能性。结果表明，将准临界波包含在反馈环路中，可以显着改善布拉格结构的选择特性，并确保在较大（与波长相比）的相互作用空间横向尺寸下产生单频的稳定状态。在毫米波和亚毫米波范围内进行的仿真和“冷”电动力学测试证实了此类结构的高效应用。新的反馈机制的可操作性已在联合核研究所（杜布纳，对于最多五个波长的横向腔尺寸，从_a到W。讨论了由IAP和Budker核物理研究所联合开发的，在太赫兹和太赫兹频率范围内工作的大功率长脉冲FEL的项目。给出了基于修改后的布拉格反射器的电动系统建模结果，该反射器的直径分别为20和40个波长，以实现300 GHz和600 GHz范围内的FEL。