In order to clarify the mechanism on electron multiplication of MCP, it is necessary to study the secondary electron emission properties of inner wall surface. The secondary electron emission is not completely required by materials or devices, and sometimes it can bring bad effects such as noise. In addition to the secondary electron produced by electron colliding with the inner wall, there are additional secondary electrons produced by the ionized cation colliding with the inner wall, which is the key to control the noise of MCP. In this paper, the secondary electron emission produced by the ionized cation colliding with the inner wall of MCP was analyzed after the materials were acid and alkaline treated and hydrogen reduced at high temperature. Time of Flying (ToF) was used to detect secondary electron emission yield (SEEY) of lead silicate glass surface. By comparative analyses, the influence trend of surface treatment process on the secondary electron emission yield of glass surface was acquired. It is expected to provide data supports for parameters optimization of MCP manufacture and preparation of MCP with high signal to noise ratio (SNR).
Fiber optic imaging elements is a general term for optical fiber products including fiber optic plate (FOP), fiber optic inverter (FOI), and fiber optic taper (FOT), which is a light and image transmission array made of optical glass fibers that are drawn, regularly arranged, vacuum melted-pressed, secondary thermal processed and optically processed. They are mainly used in photomultiplier devices for low-light-level night vision and particle detection equipment. Its devices have been widely used in many fields such as low-light night vision, electronics, aerospace, nuclear diagnostics, high-speed photography, etc., especially in the field of military operations at night combat, guidance, early warning, and electro-optical countermeasures. With the continuous development of glass fiber material, preparation technology and performance requirements, the optical fiber imaging element has been significantly improved, and its application field has been continuously expanded. This paper reviews the materials, structures, principles, characteristics, preparation processes and detection technologies of optic fiber imaging elements. It mainly summarizes the development situation, latest technological progress, and several major devices in optical applications. And the bottlenecks in the preparation and detection of fiber-optic imaging elements at present are analyzed. Furthermore, the development trend and challenges of fiber-optic imaging elements evolving to larger size with smaller diameter of fiber, higher contrast, higher resolution, lower distortion, ultra-short and ultra-light are prospected.
The research object of surface defects in optical glass processing is mainly focused on the surface of homogeneous monomers, but there are few reports on the surface polishing defects of composite materials with a variety of monomers with different physical and chemical properties. In this paper, the defect samples with different characteristics are obtained by changing the types of optical fiber image transmission elements, adjusting different polishing processes and parameters. The structure and morphology of the defects on the surface of optical fiber image transmission components are observed by white light interferometer and atomic force microscope. The composition at different positions and the combination of chemical elements are determined by Energy Dispersive Spectrometer (EDS). The specific reasons for the defects are analyzed, the optimal polishing process and corresponding parameters are obtained, and the mechanism of the formation of defects on the polished surface of optical fiber image transmission elements is clarified. The results of the study have a certain guiding significance for the control of polishing defects on the surface of composite materials composed of various monomers, and provide data and theoretical support for improving the polishing quality and efficiency of optical fiber image transmission components.
The existence of blemishes deteriorates the imaging quality of fiber-optic imaging elements and reduces the yield of finished products in factories. The effective detection of blemishes is a prerequisite for analyzing the causes of blemishes and preventing their generation. An independently developed detection device for fiber-optic imaging elements based on machine vision is implemented to detect blemishes automatically and accurately. The blemish distributions of three typical fiber-optic imaging elements, including a fiber-optic plate (FOP), a fiber-optic inverter (FOI), and a fiber-optic taper (FOT), are compared with each other, and the causes of blemishes in fiber-optic imaging elements are analyzed. The distribution of blemishes in the FOP is random, and the average number (AN) of blemishes in the first zone (central zone) and the second zone (outer zone) with the same area is similar. The AN of blemishes for the FOI prepared by twisting the FOP at high-temperature increases from 272.8 (FOP) to 2125.0, and the AN in the outer zone is 1542.5, higher than that in the central zone. More blemishes are generated by the twisting process, and the distribution of these blemishes is close to the outer zone. A significant amount of chicken wires is found in the outer zone, but the majority of blemishes are still spots. The AN of blemishes for the FOT prepared by stretching the FOP increases from 383.0 (FOP) to 515.0, which is attributed to the increase of the number of blemishes in the first zone from 190.8 to 427.0, but the AN of blemishes in the second zone decreases from 192.3 to 88.0. The stretching process stimulates the formation of blemishes with a distribution that is close to the central ring. These blemishes are randomly distributed inside or at the boundary of the multifiber. Most of the blemishes are still spots.
As the core component of image intensifier, the electronic multiplication performance of microchannel plate determines the ability of the device to detect weak signals. The theoretical model of electron gain is the theoretical basis for the secondary electron multiplication of microchannel plates. It has important theoretical significance for the research of high performance microchannel plates and image intensifiers. In this paper, the theoretical model and simulation of electron gain in microchannel plates are reviewed. The electronic gain model and the modified theoretical model of the "energy proportional hypothesis" are emphatically introduced. On the basis of the model, some improvements are made and good simulation results are obtained. The behaviors of electron transport, collision and multiplication in microchannels based on the theoretical model of electronic gain and Monte Carlo stochastic calculation method are summarized. The differences among the three models are analyzed, and the problems existing in the theoretical model and simulation of electronic gain at present are analyzed. Finally, aiming at the shortcomings of theoretical model and simulation, the direction of improvement and optimization is put forward.
The s parameter of the gain theory of microchannel plate directly affects the value of each secondary electron emission coefficient. The electron gain is the accumulation of all secondary electrons, so the s parameter has an important influence on the theoretical value of the electron gain. In this paper, two kinds of clad glass and the same core glass materials are used to fabricate two kinds of microchannel plates under the same process conditions, and measured the electronic gain values. Meanwhile, the theoretical model of the electronic gain of the microchannel plates is established by Monto Carlo stochastic mathematical method, and the s parameters of two kinds of microchannel plates were fitted by the model combined with the measured electronic gain values. On the fitted value of S parameters, the variation of the microchannel plates gain and electron transit time with the microchannel plates applied voltage at both ends, channel bias angle, channel length-to-diameter ratio and output electrode penetration depth is simulated, and compared with the corresponding measured results, the coincidence is high. The relationship between electron gain with bias angle and output electrode depth, and the relationship between Gain with Length/Diameter ratio under different voltage is obtained. Besides, this paper get the relationship between Electron transit time and Full width at half maximum (FWHM) with the different Voltages. The results of this study provide support for the calculation of theoretical electron gain of microchannel plates in different clad glass systems.
Micro-channel plate is an electronic multiplier element with two-dimensional hollow glass tube array structure, which has been widely used in low-light-level night vision imaging, particle detection and other devices. Bulk resistance of microchannel plate is an important performance index, which affects the electronic multiplication performance, dynamic response range and time resolution of micro-channel plate. There are many literatures about the influence of the preparation process of microchannel plate on bulk resistance, but few reports about the influence of the working conditions of microchannel plate on bulk resistance. In this paper, we mainly study the influence of micro-channel plate voltage and ambient temperature on bulk resistance, and analyze the mechanism of the change by tunneling. The results show that: 1) The change of working conditions leads to the change of the bulk resistance of the micro-channel plate. The higher the temperature and the voltage of the micro-channel plate, the lower the bulk resistance of micro-channel plate. The larger the original bulk resistance, the smaller the change rate of the micro-channel plate is. 2) The phenomenon that the resistance of micro-channel plate varies with the use conditions conforms to the mechanism of tunneling conduction.
Optic fiber imaging elements are used in weak visible light, X-ray imaging and high-energy particle detection imaging devices. They play an important role as input and output window materials of image intensifiers. Optic fiber imaging elements are arrays of tens of millions of micron-scale single optical fibers arranged regularly. The fabrication process requires several times of fiber drawing and secondary thermal processing such as hot melting pressure, torsion, and stretching. After these processes, there may be spots and linear chicken filaments that are called defects existed on the interface among the fibers and multi-fibers. Due to these defects, the quality of imaging is seriously reduced, and even the misjudgment or omission of image signal recognition can are caused. How to detect such defects has no an ideal solution. Currently, non-quantitative microscopic observation is generally used. This method, however, is high in misjudgment and low in detection efficiency. In this paper, a device for automatic detection of optical fiber image defects based on machine vision algorithms, including its working principle, structure, detection steps and characteristics are introduced. The device not only can automatically measure the size of each defect, but also can count the defect distribution according to the quality zones. The test results are stable and accurate. It is especially suitable for batch detection and research of optic fiber imaging elements.
X-ray photoelectron spectroscopy (XPS) was used to study the microporous surface elements change in content and
chemical states of microchannel plates before and after hydrogen reduction. The results show that the oxygen charge
states include mixture of bridging oxygen (BO), non-bridging oxygen (NBO), and hydrogen oxide (-OH), and BO is the
main charge state, that Si, Pb and Bi are also bonded with F to produce fluoride except bonding with oxygen before
hydrogen reduction. After hydrogen reduction, the binding state of O and Si unchanged. The [BO] and [NBO] decrease,
and [OH] increases obviously. Si fluoride reacts with H2O and produces amounts of ≡Si-O- at high temperature. The lead
exists in mixture of Pb0 and Pb2+, and the Bi mainly exists in bond of Bi0 in surface region of the reduced samples. The signals of K2p and Na1s emerged again in the reduced samples. It is the change in content and chemical states of
microchannel plates after hydrogen reducing processing that the secondary electron emission yield after reduction is 1.5
times higher than that of samples before reduction, and the bulk resistivity obviously drops by 3~4 order.