The Caculation And Simulation Of Femtosecond Electron Pulses

Ultrafast electron diffraction (UED) developed rapidly, and many ultrafast dynamics investigation in different field consisting of molecule structure dynamics, chemaical reaction and biological molecule function etc have been intensively and extensively applied based on this efficient technology. In general, this method can be regarded as a special'Pump-Probe' process, where the femtosecond laser pulses excite the related material and induce the structure deformation and phase transitions, then the ultrafast electron pulses are utilized to detect and record the ultrafast dynamics in detail. Due to the ultrafast temporal resolution of the pump laser pulses and the ultrahigh spatial resolution from the electron diffraction, it is believed that the UED technology actualize the detection in submilli-A spatial scale with sub-picosecond time scale. In experiment, as the typical parameter for the time resolution in UED system, the electron pulse duration time becomes the most important in the studies of ultrafast dynamics process. Therefore, it is the core technology to suppress the space-charge-effects and compress the electron pulse duration efficiently.In our experiment, a home-made molecule4D imaging system based on ultrafast electron diffraction has been constructed, and the ultrafast electron pulse with high brightness has been observed. In this thesis, we have introduced the electron gun system, and simulated the properties of the electron beams. The main contents are presented as following.Firstly, the electron gun system, including of the high voltage electrostatic accelerating field, magnetic focusing lens and radio frequency compressing cavity has been discussed. Based on the electric field, magnetic field and RF field with Poisson Superfish software, we have calculated and simulated the electron pulses by the�'子示踪software.Secondly, Particle Tracer software is used to simulate the transverse emittance and longitudinal duration of the femtosecond electron pulses. By adjusting the pulse electron number, magnetic lens and the RF compression cavity etc, the optimized femtosecond electron pulses can be achieved.