Research On Charge Multiplication In EMCCD And It's Application On Photon Counting Imaging

Adopting the impact ionization mechanism, EMCCD (Electron Multiplication CCD) achieved the multiplication of photo-generated charge signals in solid-state devices, and achieved all solid-state technology of devices. It is one of the key technologies of low-light imaging technology. Based on the summary of traditional CCD working principle and its deficient in low-light imaging application, it analyzed charge multiplication working principle of charge multiplication register in EMCCD, put forward mathematical model of charge multiplication, discussed the effect of charge multiplication on EMCCD imaging in low-light environment, innovatively proposes the dual-threshold principle of single-photon response model, and overcame the effect of dark current noise on single-photon detection performance of EMCCD in normal cooling condition, so that we could adopt the EMCCD to achieve photon counting imaging using low-cost thermal electrical refrigerator. The main contents of this paper studied the traditional CCD working principle, charge multiplication mechanism and model, imaging model of EMCCD, photon counting imaging principle based on EMCCD, and the experimental equipments build and experiments of EMCCD tests. Through the research on EMCCD working and its application in photon counting imaging, we could offer the theoretical basis for achieving the independence of EMCCD core technologies, so as to make some contributions to break through the technology blockage of United Kingdom and American developed countries as soon as possible.On the aspect of research on CCD working principle, it mainly studied the two-dimensional electric potential field distribution in buried-channel CCD device. Through the solutions of one-dimensional Poisson's equation and wave equation of transmission line, after obtaining the analytical expression of two-dimensional electric potential field distribution in buried-channel CCD devices, it analyzed the effects of key factors of center distance between electrodes, electrode bias voltage, charge storage capacity inside electrode on two-dimensional electric potential field distribution, and defined the two-dimensional electric potential field distribution in buried-channel CCD devices.On the aspect of principle research on achieving charge multiplication in charge multiplication register, it analyzed four points:strong electric field, large charge potential well capacity, overflow controller and DC bias phase. At the same time, according to having Markov nature during charge multiplication or not, the charge multiplication could be sorted as two modes of high-gain mode and ordinary gain mode. Under the different modes, through solutions of Markov-diffusion equation and Malthusian equation, the gain statistical characteristics and gain probability density function were obtained. After building testing system of EMCCD, we found that the size of signal charge packet inside multiplied electrode also could affect the charge multiplication process, besides the bias voltage of multiplied electrode.On the aspect of research on EMCCD imaging model, after the establishment of charge-transfer model and device model of EMCCD, we obtained the system response function and amplitude-frequency response characteristics of EMCCD, and analyzed the effects of charge multiplication process on imaging. According to the experimental testing results, it was obvious that:although the charge multiplication process did not change the distribution of amplitude-frequency response of EMCCD, it increased the detail resolution of EMCCD in low-light condition because the charge multiplication process increased the response amplitude.On the aspect of research on photon counting imaging based on EMCCD, after the establishment of discrete single-photon response model, it obtained the evidences of single-photon detection to estimate the EMCCD. Using the single-photon response model of EMCCD, it discussed the principle of achieving photon incident detection by dual-threshold principle, and gave out the selective evidences of amplitude threshold and frequency threshold. Through the efficiency and error experiments of single-photon detection, it analyzed the property of EMCCD in the mode of photon technology imaging. Through the experiment of photon counting imaging, it proved that:in the mode of photon counting, the minimum responsibility of EMCCD could achieve 0.1 charge/pixel/frame, it obviously preceded the results of the other imaging mode at the same conditions.These works of this paper are a part of research work of Natural Science Foundation project of Jiangsu Province (project NO.BK2008059)-"Research on photon counting imaging mechanism and its key technologies".These works were also supported by grants from Ministry of National Defence of China (project NO.4040508011 and NO. A2620060242).