Numerical Investigations Of High-Gain Short-Wavelength Free-Electron Laser

High gain FEL has been proved to be by far the only method to generate free-electron-laser (FEL) of which the frequency lies in ultraviolet or even X-Ray regime. It has a great number of applications in chemistry, biological molecular structure studies, nano-science, atomic and molecular physics and etc. As a highly active research topic, several projects have been proposed for high gain FEL.However, due to its complex structure and unusual technical difficulties, high gain FEL typically demands hundreds of millions of dollar's investigation. Therefore a thorough theoretical analysis as well as computational simulation must have been done before any practical construction. There are several different schemes for high gain FEL, each has certain attractive point, while none of which can be considered superior over others. This makes it very important to analyze various working schemes in the generating of highly coherent, high-stability, and high-intensity X-Ray FEL.This dissertation focus on the theoretical analysis and numerical simulation of short-wavelength high gain FEL, including principle theories of FEL and methods of numerical simulation, programming for numerical study of one-dimensional FEL, semi-analytic calculation and optimization of HGHG, analysis and compare of several working schemes of high gain FEL, parameter-optimization of cascaded HGHG as well as methods on its numerical calculation, and some design work for the XFEL project in NSRL. Furthermore, due to the highly promising future of THz light-sources, the last chapter is designated to the analysis of long wavelength radiation generated by insertion device in the storage ring, derivation of relevant theories, and numerical studies based on parameters of NSRL, in the hope of its application in Optical Klystron and efficiently generating FIR.To rapidly analyze the character of different XFEL schemes, a time dependent program TDH1D is written. This program can analyze the longitudinal coherence, the bandwidth, the signal-noise ratio, and etc. On the other hand, some popular FEL code such as TDA3D and Genesis, can not calculate the power of high harmonic FEL and for this reason we upgrade TDH1D to make it capable of completing such kind of work. TDH1D follows "macro particle" simulation way, and imports the slow varying evolution approximation(SVEA) and makes average among one undulator period.Based on the 1D HGHG theory deduced by Prof. Jia Qika, a program HG1D is written for semi-analytic calculation and optimization of HGHG. By HG1D we optimized the seed laser power and the dispersive section for SDUV-FEL, and theoretically analyzed the affection on saturation power and saturation length by seed laser power and dispersive strength.