<title>Numerical analysis of space charge effect influence on physical temporal characteristics of femtosecond streak image tubes</title>

Abstract

Theoretical investigation mainly on the physical temporal resolution of our newly designed femtosecond streak image tube has been made by means of numerical simulation, in which the influence of space charge effect on the nature and extent of intensity-dependent temporal broadening has been taken into account. The study includes simulating the emission of a great number of photoelectrons as a statistical sample from the position corresponding to the actual photocathode in terms of Monte Carlo method in proper probability, tracing these electrons trajectories by resolving the electron motion equation in the electron optics focusing system in the streak tube and dealing with the repulsion among these electrons i.e. space charge effect simultaneously, and finally analyzing the position distribution of the electrons statistically to come into conclusion. Through the agency of the step above can the photoelectrons' behavior inside the streak tube including the response of space- and time-dependent quasi-Delta functions in the focusing system be obtained principally. The result has shown that the space charge effect is the essential obstacle on the improvement of streak tube's performance both in temporal resolution and in dynamic range. Our theoretical estimate has indicated that considering the serious influence of space charge effect when streak tube works under illumination of the domain of few tens femtosecond the temporal resolution of less than 100 fs with acceptable dynamic range is expectable. Also the distortion of a waveform with FWHM is a few tenths picosecond is discussed which is due to the electron pulse's transformation dispersion and space charge effect and is more concerned in practice uses.