The generation of the coherent THz radiation in long undulators at the resonant wavelength is affected by the relatively broad spectrum of radiation that results in poor temporal coherence. The presence of the waveguide can essentially modify the continuous undulator radiation spectrum by converting it to a discrete one when radiation diffraction size exceeds the vacuum-chamber dimensions. In this paper the effect of a small radius circular waveguide on helical undulator radiation in the THz region is examined. It is shown that under certain conditions the presence of the waveguide can lead to radiation energy redistribution between the waveguide modes, enhancing the single resonance mode.

中文翻译：

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波导中太赫兹螺旋波荡器辐射的模式增强

长波荡器中谐振波长的相干太赫兹辐射的产生受到相对较宽的辐射光谱的影响，导致时间相干性较差。当辐射衍射尺寸超过真空室尺寸时，波导的存在可以通过将其转换为离散辐射光谱来实质上修改连续波荡器辐射光谱。在本文中，研究了小半径圆形波导对太赫兹区域中螺旋波荡器辐射的影响。结果表明，在某些条件下，波导的存在会导致波导模式之间的辐射能量重新分布，增强了单谐振模式。