The fundamental coherent radiation emission processes from a bunched charged particles beam are outlined. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles, a prebunched electron beam can emit spontaneously coherent radiation proportional to the number of particles—squared, through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke’s). The coherent SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated superradiance in the presence of a seed-injected radiation field. In this review, these coherent radiation emission processes for both single bunch and periodically bunched beams are considered in a model of radiation mode expansion. The general model of coherent spontaneous emission is extended to the nonlinear regime, particularly for undulator (wiggler) interaction: tapering-enhanced stimulated-superradiant amplification (TESSA). Processes of SP-SR and TESSA take place in tapered wiggler seed-injected free-electron lasers (FELs). In such FELs, operating in the x-ray regime, these processes are convoluted with other effects. However these fundamental emission concepts are useful guidelines for the strategy of wiggler tapering efficiency and power enhancement. Based on this model, previous theories and experiments are reviewed on coherent radiation sources based on SP-SR (coherent undulator radiation, synchrotron radiation, Smith-Purcell radiation, etc.), in the THz regime and on-going works on tapered wiggler efficiency-enhancement concepts in all optical frequency regimes up to x rays.

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束电子束的超辐射和受激超辐射发射

概述了束状带电粒子束的基本相干辐射发射过程。与来自随机电子束的自发辐射与粒子数量成正比相反，预束缚电子束可以通过（自发）超辐射（SP- SR）（在Dicke的意义上）。在存在注入种子的辐射场的情况下，通过激发超辐射的过程甚至可以进一步增强束状电子束的相干SP-SR发射。在这篇综述中，在辐射模式扩展模型中考虑了单束和周期性束的这些相干辐射发射过程。相干自发发射的一般模型扩展到非线性状态，尤其是对于波状波（维格勒）相互作用：逐渐增强的刺激超辐射放大（TESSA）。SP-SR和TESSA的过程是在锥形摆动的种子注入的自由电子激光器（FEL）中进行的。在以X射线形式运行的此类FEL中，这些过程会产生其他影响。但是，这些基本的发射概念对于摆动式渐缩效率和功率增强策略是有用的指导原则。在此模型的基础上，回顾了基于SP-SR的相干辐射源（相干波幅辐射，同步加速器辐射，Smith-Purcell辐射等）的先前理论和实验，