The Study Of Jitter Between Laser And Rf In Mev Ultrafast Electron Diffraction

The real-time observation of space and time on atomic scale(100 fs)is of great significance to the research of natural science.MeV ultrafast electron diffraction(MeV UED)technology,at the same time with the femtosecond laser pulses of high temporal resolution and high spatial resolution of electron diffraction,so it is an effective method to study the structure of atomic scale material changes.In recent years,with the rapid development of the accelerator field,the concept of MeV UED is put forward,Universities and research institutions are establishing their prototype devices.The performance of these devices is largely limited by the high brightness of electron beam(MeV)and its high stability in charge,energy and peak current.Therefore,it is very important to calibrate these parameters accurately by using highprecision measurement methods.On the one hand,this paper presents a new method,which can be widely used in MeV UED devices and improve its resolution.Based on the principle of Einstein's photoelectric effect,using ultra-short laser pulse excited photocathode RF gun surface emitting electron beam and the electron beam are accelerated by the microwave electric field,relying on the microwave cavity deflection(RF deflecting cavity)to measure the longitudinal length of the electron beam.We use GPT(General Particle Tracer,GPT)software to quantitatively simulate the performance of the electron beam after accelerating by the RF electric field,finding that different injected phase of the laser corresponding to the different flight time of the beam to the RF deflecting cavity,and finally quantitatively finding the linear relationship between the RF acceleration phase and the longitudinal length compression effect of electron beam(bunches).Based on these theories and quantitatively calculation,we built a MeV UED prototype device,experiments showed that the phase jitter of the laser-to-RF is relatively large,on the analysis and studies of the causes of the result,and then built the improved device,eventually for the first time in the world get 270 femtosecond phase jitter.Onthe other hand,the study based on the jitter experiment has guided the phase of the device of single crystal gold pump-probe experimental and observed the heating process of the gold lattice.The paper introduces us through different methods to try and improve the laser and microwave phase jitter measurement experiment,not only for the first time found and proved that the new physics,which has a linear relationship between electron beam-to-microwave phase jitter and phase jitter of the laser-to-microwave,and ultimately improve the performance of new machines,getting the high time of 40 fs time resolution.Finally,the experimental study of MeV UED was conducted.