Research on Free Electron Laser Using Dielective Resonance

在传统的自由电子激光器（FEL）中，为了使其在可见光或更短的波长范围内工作，必须使用能量电子束（高于100MeV）。因此，可见的自由电子束流将会更大。这是FEL最严重的缺点之一。本研究的主要目标是通过在摆动器的光学腔中加载气体来减少光束能量和减小可见自由电子激光器的尺寸。当气体中折射率为n^^-时，相速度为c/n^^-，则自由电子激光器的共振条件为λ =(l/n^^—nuz/c) λ。这里，λ是摆动的波长，λ是辐射波长，而nuz是摆动的轴向速度。当n大于1.001时，10MeV的电子束会产生可见光或紫外线辐射。如果负载气体没有介电谐振，则所需气体压力将高于100torr。当气体压力达到这个水平时，电子束被气体分子散射，质量（能量扩散和发射度）下降。我们建议在FEL辐射和分子跃迁之间使用适当的介电响应，以便将气体压力从100torr降低到10torr。为了评估在介电谐振气体自由电子激光器中的应用率，我们研究了近共振介质中的辐射传播方程，即带有电子束轫致的布洛赫方程。结果表明，在适当的电子束和摆动参数下，可以获得足够的速率。

In a conventional free electron laser (FEL), it is necessary to use an energy electron beam (higher than 100MeV), in order to operate it in the visible or shorter wavelength range. Therefore, the sue of the visible FEL will be larger. This is one of the most serious disadvantages for FEL. The main objective of this research is to reduce the necessary beam energy and to reduce the size of a visible FEL by loading a gas in a optical cavity in a wiggler. When the refractive index is n^^- in the gas, the phase velocity is c/n^^- and the reconance condition for FEL is then lambda=(l/n^^--nuz/c)lambdaw. Here, lambdaw is the wiggler wavelength, lambda is the radiation wavelength, and nuz is the axial velocity in the wiggler. When n is greater than 1.001, a 10MeV electron beam will generate visible or ultra-violet radiations. It there is not dielectric resonance for a loaded gas, the required gas pressure will be higher than 100torr. When the gas pressure is as high as this level, the electron beam is scatlered by the gas molecules and degrated in the quality (energy spread and emittance).We proposed the use uf an appropriate dielectric resonce between the FEL radiation and the molecular transitions in order to reduce the gas pressure from 100torr to 10torr. In order to evaluate the application rate in an dielectrically resonant gas FEL, we investigated the radiation propagation equation in a near resonance media, namely the Bloch equation with the electron beam brewsstrahlung. As a result, we found that enough rate can be obtain for moderate electron beam and wiggler parameters.