This paper proposed a "high-speed imaging + digital processing" evaluation method to solve the problem of scintillation noise of low light image intensifiers under low illumination, which fills the gap in the quantitative evaluation of scintillation noise characteristics under low illumination in China. It was found that the scintillation noise is mainly characterized by scintillations with a diameter over 50μm and a duration of sub-microsecond or less. The frequency and the brightness of the scintillations are used to quantitatively evaluate scintillation noise. The effects of the input illuminance and luminous gain on the scintillation noise of the domestic low light image intensifier were investigated by the proposed method. With the increase of input illuminance, the frequency of scintillation noise increases linearly, and the brightness does not change obviously. As the luminous gain of the image intensifier increases, the frequency of scintillation noise increases linearly, but the rate of increase in scintillation frequency is higher than that of luminous gain increase. Based on the characteristics of scintillation noise, such as size, duration, intensity, and the variation law with various conditions, the scintillation noise of the image intensifier can be further studied. The quantitative evaluation method of scintillation noise based on scintillation noise frequency and average equivalent input electron quantity proposed in this paper is of great significance to the breakthrough of scintillation noise and the improvement of the performance of image tubes under low illumination in the future.
Silvaco simulation software was used to study the influence of applied bias on the energy band of field-assisted GaSb/GaAs photocathode under different thicknesses and p-type doping concentrations of GaAs emission layer. The simulation results demonstrated that only 2V applied bias voltage can perfectly eliminate the barrier at the heterojunction interface and will not cause a large dark current when the GaSb layer was p-type with the doping concentration of 1×1019 cm-3 and the GaAs emission layer was gradient doping. The GaAs emitting layer with gradient doping consists of a GaAs layer with a thickness of 0.2 μm and a doping concentration of 1×1016 cm-3, GaAs layer with a thickness of 0.2 μm and a doping concentration of 1×1017 cm-3, and GaAs layer with a thickness of 0.2 μm and a doping concentration of 1×1018 cm-3. This simulation study provides theoretical guidance for the preparation of field-assisted GaSb/GaAs photocathode.
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