Theoretical And Experimental Research On The Ultra-fast Electron Diffraction System

An ultrafast electron diffraction(UED) system with high temporal and spatial resolution is introduced in the present thesis. This system can be used to study many physical and chemical phenomena in ultra-short time scale and is an advanced method to the study of crystallite, surface, film, et al.The main contents of the thesis is presented as follow.1 The research on the theory of the UED system, especially the deflection distance under scanning, from which we get another method to measure and calculate the pulse width of electron beams. The synchronization process is analyzed, and the result is especially important to the scanning experiment.2 The electron optical design process of UED system generation I and generation II is introduced, and the main works of which include sampling of the emitting process of electrons, calculation of the electrical and magnetic field and calculation of the trajectories of electrons. After a number of calculations we got the relationship between the object and image, which is the basis of the design of ultrafast electron gun. The shape of phoeocathode was analyzed, and we found that the electrical field close to the surface of photocathode is especially important to the temporal resolution of the ultrafast electron gun, and another easier method was proposed to improve the temporal resolution of the UED system.3 The manufacture of the UED system generation I and II was introduced, and the main work done include the designing of the photocathode, magnetic focusing system, electrical deflection system, electrical image intensify system, vacuum system, control system, and scanning electrical circuit as well.4 The measurement of the UED system is introduced. The size of the electron beam measured is smaller than 100um, the deflection sensivity is 26.8mm/kV and 49.2mm/kV in the x and y direction respectively, and the azimuth angle is smaller than 1.1mrad.