Development of a Tunable Gas-Loaded Free-Electron Laser

本研究计划的目的是研究将气体介质引入摆动或波动磁场区域的自由电子激光器的性能。在FEL摆动器中放置气体会改变相位匹配条件。这是由于气体引入了折射率，从而延缓了电磁波的相速度。通过改变气体的压力，从而改变折射率，振荡波长可以被调谐，可能从红外线到紫外线，而不改变电子束的能量或摆动器的参数。除了可调性之外，气体还可以显著降低束流能量，从而降低加速器的成本和尺寸，并提高FEL的单位长度增益。作为对气体的FEL性能计划的一部分，将对气体中电子共振附近操作的影响进行调查。在这种情况下，可以在相对较低的气体密度下获得高折射率。还将研究使用具有轴上孔的干涉仪反射镜的可能性，以促进紧凑的在线高增益系统的发展。此外，实验将提供有关皮秒电子束在高达一个大气压的气体中传播的信息；研究利用高发射度光束提高FEL增益的方法；研究了轴上孔干涉仪的光学特性。

The objective of this research program is to investigate the performance of a free-electron laser for which a gaseous medium has been introduced into the region of the wiggler, or undulating magnetic field. Placing a gas in an FEL wiggler alters the phase matching condition. This is a consequence of the fact that the gas introduces an index of refraction which retards the phase velocity of the electromagnetic wave. By changing the pressure of the gas, and so changing the index of refraction, the oscillation wavelength can be tuned, potentially from the infrared to the ultraviolet, without altering either the energy of the electron beam or the wiggler parameters. In addition to the tunability, the gas allows for a significant reduction in beam energy, resulting in a lower cost and size for the accelerator, and a higher gain per unit length for the FEL. As part of the program on FEL performance with a gas, there will be an investigation of the effects of operating near an electronic resonance in the gas. In this case a high refractive index can be obtained at relatively low gas densities. There will also be a study of the possibility of using interferometer mirrors with on-axis holes to facilitate development of a compact in-line, high-gain system. In addition, the experiments will provide information concerning the propagation of picosecond electron beams through gases at up to one atmosphere pressure; investigate methods for increasing FEL gain with high emittance beams; and study the optical properties of interferometers with on-axis holes.