Research On The Resolution Of GaAs Photocathode And Image Intensifier

The researches on the electron transport and resolution of uniform-doping and exponential-doping GaAs photocathode, and the application of GaAs photocathode in image intensifier were carried out in this thesis.By establishing the atomic fundamental structure unit and ionized impurity scattering formula, the transport of photoelectrons in the uniform-doping transmission-mode GaAs photocathode was simulated. The influence of the electron diffusion length, the doping concentration, and the photocathode thickness on the dispersive spot and the ratio of the number of photoelectrons reaching the emission surface to the number of exited photoelectrons at the emission surface of GaAs photocathode were analyzed. The optimum values of the photocathode thickness, the doping concentration, and the electron diffusion length were explored. Considering the factors of reflectivity, transmisstivity, and absorption coefficient of GaAlAs window-layer and GaAs active-layer, the modulation transfer function of uniform-doping GaAs photocathode was calculated, and the influence of photocathode structure parameters on modulation transfer function was analyzed.Based on the photoelectron transport model of uniform-doping transmission-mode GaAs photocathode, the atomic fundamental structure unit and ionized impurity scattering formula of exponential-doping GaAs photocathode were established. Considering the different positions of excitated photoelectrons in the radiation range of400-900nm, the trajectories of photoelectrons in photocathode were simulated, and the influence of exponential-doping structure on the energy spread, emergence angle spread, the modulation transfer function and the photoemission efficiency of GaAs photocathode was analyzed. By establishing the electric field penetration model, the influence of electric field penetration on the electron distribution, the photoemission efficiency, and the modulation transfer function were analyzed. The photoemission performance of GaAs photocathode operating in low light level image intensifier was researched.Considering the energy spread and emergence angle spread of photoelectrons, the modulation transfer function of pre-proximity focusing system was researched assuming that the initial energy distribution and angle distribution of photoelectrons escaped from GaAs photocathode obey Beta distributions and Lambert distributions respectively. The influence of proximity voltage and distance on the pre-proximity focusing system was analyzed. According to the theory of secondary electron emission, the energy spread and angle spread of secondary electron in microchannel plate were established. The influences of microchannel plate opening area ratio, oblique angle, ending spoiling electrode depth, and thickness on the resolution and modulation transfer function of the low light level image intensifier were researched. A perfect resolution theory of GaAs photocathode low light level image intensifier was established consequently.In order to verify the theoretical model, the halo effect and resolution of low light level image intensifier with GaAs photocathode were investigated. The halo effects of super second-and third-generation image intensifier were tested and compared by analyzing the gray value curves of the collected halo effect. The influence of pro-proximity pulse voltage on image intensifiers halo effect was researched by respectively changing the high and low level voltage and duty ratio. Besides, the halo effects of low light level image intensifiers with different doping GaAs photocathode were analyzed. Moreover, the resolutions of low light level image intensifiers consisting of uniform-doping and exponential-doping GaAs photocathode were calculated respectively. Then the influence of GaAs photocathode on image intensifier resolution was analyzed, and the availability of the resolution theory model of low light level image intensifier with GaAs photocathode was verified indirectly.