Ebook: Ultraviolet and Soft X-Ray Free-Electron Lasers: Introduction to Physical Principles, Experimental Results, Technological Challenges

In the introduction accelerator-based light sources are considered and a comparison is made between free-electron lasers and conventional quantum lasers. The motion and radiation of relativistic electrons in undulator magnets is discussed. The principle of a low-gain free-electron laser is explained and the pendulum equations are introduced that characterize the electron dynamics in the field of a light wave. The differential equations of the high-gain FEL are derived from the Maxwell equations of electrodynamics. Analytical and numerical solutions of the FEL equations are presented and important FEL parameters are defined, such as gain length, FEL bandwidth and saturation power. A detailed numerical study of the all-important microbunching process is presented. The mechanism of Self Amplified Spontaneous Emission is described theoretically and illustrated with numerous experimental results. Three-dimensional effects such as betatron oscillations and optical diffraction are addressed and their impact on the FEL performance is analyzed. The world’s first soft X-ray FEL, the user facility FLASH at DESY, is described in some detail in order to give an impression of the complexity of such an accelerator-based light source. Finally, the physical and technological challenges of X-ray FELs are addressed while some of the more involved calculations are put into the appendices, where also supplementary material can be found.

The main goal of the book is to provide a systematic and didactic approach to the physics and technology of free-electron lasers. Numerous figures are used for illustrating the underlying ideas and concepts, and many links to other fields of physics are provided. After an introduction to undulator radiation and the low-gain FEL, the one-dimensional theory of the high-gain FEL is developed in a systematic way. Particular emphasis is put on explaining and justifying the various assumptions and approximations that are needed to obtain the differential equations governing the FEL dynamics. The predictive power of the 1D FEL theory is demonstrated with numerous examples and figures, including exponential gain, saturation and FEL bandwidth. One of the most important features of a high-gain FEL, the formation of microbunches, is studied at length and illustrated with several figures. 3D corrections to the 1D theory are discussed. The process of self amplified spontaneous emission (SASE) is explained mathematically, and many experimental results are shown. The layout of the world’s first SASE FEL in the soft X-ray regime, FLASH, is described in some detail and the technological challenges of X-ray FELs are outlined. Important concepts of accelerator physics are explained while some of the more involved mathematical computations are put into the appendices.