Research On The Analysis And Experimental Method Of The Gate Characteristics Of Image Intensifier

As a powerful tool to detect ultrafast phenomenon, high-speed photographic devices with high time resolution are being widely concerned. Meanwhile, with the development of gating technology, image intensifiers working under gating mode are being extensively studied as a practical solution for ultrafast detection because of its high time resolution up to 10 ? 10s. Currently there have been many papers reporting the use of gated image intensifier (GII) to inspect ultrafast phenomenon in biological, chemical or physical processes and the discovery of new features. The mechanism of GII mainly lies in that the image intensifier can be controlled by applying electrical gate pulse to a specific electrode of it. Therefore the core technology of GII is the interaction between electrical gate pulse and image intensifier which includes: the physical mechanism how gate pulses control the image intensifier, the generation of high-speed high-voltage gate pulse, the coupling between gate pulse and electrode of image intensifier and the influence on width and delay of output optical gain induced by gate pulse, etc. Currently, the worldwide research of GII mainly focuses on the characteristics of gating mode of microchannel plate (MCP) electrode of image intensifier while the research of photo-cathode gating mode of image intensifier is very rare. This thesis mainly focused on the fundamental physical processes of photo-cathode gating mode of image intensifier and the measurement. By analyzing theoretically and researching experimentally, we studied the gain characteristics of GII under photo-cathode gating mode. The work and features of the thesis are listed as follows:Theoretically, three sub-processes were analyzed in detail when photo electrons propagate in image intensifier. Three sub-processes are: acceleration at photo cathode, multiplication at MCP and acceleration at anode. Each sub-process has been established a model and simulated. The whole dynamic process of photo electrons was considered comprehensively and a mapping in time domain was proposed in order to deduce the relationship between optical gain of image intensifier and .input gate pulse. Meanwhile, the tilting and broadening effects of optical gain curve were predicted compared with the shape of gate pulse.Experimentally, by referring to typical schematic of cross correlation measurement and combining the specific features of image intensifier, a measurement based on femtosecond ultrashort pulse and optical-electrical cross correlation was proposed. And the whole gating-characteristics measurement system was divided into optical and electrical two sub-systems. The details of the theory, design and realization of each subsystem were given. Then by utilizing the realized gating-characteristics measurement system, the gain characteristics of photo-cathode gated image intensifier was measured.Theory and experimental research both indicate that the output optical gain of photo-cathode gated image intensifier has changed with input gate pulse. The rear edge of optical gain shape is larger than that of front edge when the shape of input gate pulse is symmetric, which leads to the tilting effect of gain shape. Moreover, contrary to the condition of MCP gating mode, the measured width of output optical gain of image intensifier has broadened to 6.4ns compared with the 6.0ns width of input gate pulse, which is consistent with theoretical prediction.Compared with traditional electrical method of measurement of gating characteristics, a novel optical-electrical cross-correlation method was proposed in this thesis to study the optical characteristics of image intensifier, which used one femtosecond fiber mode locked laser pulse to generate photo electrons from photo cathode with very narrow time width. This method is helpful to understand the image intensifier directly, eliminate the systematic error and uncertainty in traditional electrical method. Therefore, it can represent the true gain performance of system better. By utilizing this optical-electrical cross-correlation method, we can more accurately study the optical gain characteristics of gated image intensifier, better understand the distortion brought by the system when used to record ultrafast processes and help to retrieve the original pictures from the distorted ones.