Research On The Operating Modes Of The EMCCD And It's Applications In Photon Counting Imaging

For a long time, the low light level imaging technology plays an extremely important role in many aspects such as scientific research and military warfare. As a representative of the traditional low light level imaging technology, the Intensified Charge Coupled Device (ICCD) still plays a leading role at present. However, with the increasing demand of application in harsh environments, the requirements of technological innovation in low light level imaging appear gradually. The Electron Multiplying Charge Coupled Device (EMCCD) is the outcome of this technological innovation.Adopting the impact ionization mechanism, EMCCDs achieve the multiplication of photon-generated charge signals in solid-state devices and all solid-state technology of devices. It is one of the key technologies of low-light imaging technology innovating. As a new type of low light level imaging device, the Electron Multiplying CCDs combine the normal CCDs and the charge multiplication. With the advantages of small volume, low noise, high sensitivity, high dynamic and the capability of single photon detecting, the EMCCD has great development potential and application prospect in the low light level imaging. And it is an effective way to achieve photon counting imaging. However, due to the technology blockage of the developed countries, such as United Kingdom and American, independent research on EMCCDs is extremely important. The research of Electron Multiplying CCD in our country is just at the initial stage. In order to offer the theoretical basis for achieving the independence of the EMCCD core technologies, this paper is mainly about researches on working principle, operating modes, noise analysis, photon counting mode and photon image restoration of the EMCCD.This paper starts from the basic structure and working principle of Electron Multiplying CCDs. The charge multiplication working principle and charge transfer mode of the Charge Carrier Multiplier (CCM) in EMCCDs are analyzed in detail. There are three operating modes in EMCCDs for different external environmental conditions. The specific applying situations, working principles, multiplication gain settings, noise sources and the SNR of the three modes are all analyzed. The analysis and simulation of charge transfer in the CCM are achieved by building equivalent circuit model and the IC model which can be used to simulate charge transfer on computer is also achieved. Based on the Probability Generating Function (PGF) and its properties, the Probability Distribution Function (PDF) of multiple CCM stages in the EMCCD is deduced. The effects of parameters to the excess noise in charge transfer process such as the input signal and the multiplication gain are discussed, which lay a theoretical foundation for the model building of excess noise.The noises in the EMCCD imaging system are discussed in detail in this paper in this paper, especially the generation mechanism of the four main kinds of noise, and its restraining method and effect to the system SNR. The working principle of Multi Pinned Phase (MPP) mode is analyzed in depth with its applications in the EMCCD. The mathematical model of excess noise is deduced from the definition of excess noise by the properties of series system. So the approximate value of excess noise factor at high gains is obtained and the model of total noise of EMCCDs is established, which lays a foundation for further study in the multiplication and noise analysis of the photon counting mode in EMCCDs.Based on the property of photons and the basic principle of photon counting imaging, further study of the photon counting mode of EMCCDs is carried out in this paper. The working principle, the proportion of counted photons, the three kinds of error count and the three kinds of noise in the photon counting mode in EMCCDs are discussed in detail. The corresponding quantitative models are built. Then the multiplying performance, gain factor, photon transfer curve and response characteristics of the EMCCD are tested by experiments. The experimental results show that EMCCDs can response efficiently under the illumination of 10-6 Lux and even lower illumination, and it has the capability of real-time and dynamic detection of the single photon signal.Based on characteristics of the photon counting mode of EMCCDs, the working principle of the threshold method is analyzed. Principles and algorithms of the dual-threshold method which are used for photon image reconstruction with EMCCDs in normal cooling are improved. The calculation formulas of the amplitude and frequency thresholds are deduced in detail.Since the grey level of photon images cannot be reconstructed by the threshold method and the coincidence losses can not be avoided, the Bayesian statistical method is proposed with its specific algorithm to reconstruct photon images under extremely low illumination with EMCCDs. Finally, the effects of photon image reconstruction are compared using the single threshold method, the dual-threshold method and the Bayesian statistical method by experiments under four different illumination.