Xiaofeng Bai

Research on mechanical vibration impacts of GaAs photocathode photoemission performance

The GaAs photocathode has widely been used in optoelectronic devices such as image intensifiers, photomultiplier tubes, but these devices is inevitable to withstand a variety of mechanical vibration. In order to study the mechanical vibration impact on the photoemission performance of GaAs photocathode, GaAs photocathode image intensifier is researched in this paper. The spectral response of the GaAs photocathode before and after 5~55Hz scan frequency, 14Hz, 33Hz, 52Hz stay frequency, 5～60Hz scan frequency mechanical vibration respectively was tested, then the parameter of photocathode was calculated by MATLAB software according to quantum efficiency formula, the quantum efficiency curve were fitted. The results show that surface escape probability is increased after photocathode is subjected to mechanical vibration, so that its photoemission performance will be improved. We think this phenomenon is due to the GaAs photocathode surface Cs-O reconstruction. This finding provided a new method to enhance the photoemission performance of photocathode.

Cooperative chemisorption of K and O elements on cleaved GaAs(110) surface

Using the projected augmented wave potential by the density functional theory based upon gradual gradient approach method and the slab model, from the calculated surface, we identify the relaxed atoms sites of GaAs(110) surface, the electronic structure of elements K and O adsorpted on binding sites of ideal GaAs(110) surface have also been calculated, especially the total energy of the adsorption system. The comparison results of calculated total energy showed: for K and O elements at highest coverage of Θ=1ML on GaAs(110) surface, they were not formed to local domain of competitive chemical adsorption, while they were formed to a compound uniformity phase of cooperative chemical adsorption. Our calculated results providing theoretical basis and reference for the application of alkali oxidation adsorpted on GaAs surface to form a negative electron affinity photocathode.

A simple device for measuring the spectral transmittance of lens used in InGaAs image intensifier apparatus

In this article, in order to accurately measure the spectral transmittance of imaging lens used in InGaAs imaging apparatus, a simple device, which spectrum ranges from 400 nanometers to 2000 nanometers, based on double grating monochromator and self-collimating has been founded by using stable shortwave infrared radiant source, accurate double grating monochromator and telescope, stable silicon detector and cooled HgCdTe infrared detector. An imaging lens whose spectral transmittance has been known is measured on it. Comparing the test results to known data provided by manufacture, it is shown that the testing device founded in this article is competent to measure spectral transmittance of shortwave infrared imaging lens and which max relative deviation is no more than ±2.5%. It is worthwhile for selecting InGaAs image intensifier assembly and evaluating the quality of shortwave infrared imaging lens.

Research on mechanical shock impact of GaAs photocathode photoemission performance

The GaAs photocathode has been widely used in optoelectronic devices such as image intensifiers and photomultiplier tubes, but it is inevitable for these devices to withstand a variety of mechanical shock. In order to study the impact on the GaAs photocathode’s photoemission performance caused by mechanical shock, GaAs photocathode image intensifier is researched in this paper . The spectral response of the GaAs photocathode was tested respectively before and after several value of mechanical shock（the value of mechanical shock:55g，65g，75g，85g and 95g）.The parameter of the GaAs photocathode can be calculated and the quantum efficiency curve can be fitted as well using the MATLAB software. The results show that surface escape probability is increased after photocathode is subjected to mechanical shock, so that its photoemission performance will be improved. We think this phenomenon is due to the GaAs photocathode surface Cs-O reconstruction. This finding provided a new method to enhance the photoemission performance of photocathode.

High illumination resolution test of low-light-level image intensifier

High illumination resolution, which directly determines the applied characteristic of night vision system in flashlight or high light level condition, is an important performance parameter for evaluating the characteristic of low light level image intensifier used in high light level condition. In this article, according to the limited resolution test technique, the test principle, test condition and test method to high illumination resolution are described in detail associated with operation mode and protective way of low light level image intensifier. Test system for measuring the high illumination resolution has been founded based on the limited resolution test system. The value of high illumination for measuring the high illumination resolution has been calculated in theory and measured by illuminometer. High illumination resolution of low light level image intensifiers have been measured in test system, results show that high illumination resolution test system is satisfied the need for measuring high illumination resolution of low light level image intensifier, and test system output light illumination must be greater than 1×103 lux. Light of high illumination, which can be correctly measured by illuminometer, is transferred legitimately. That is worthwhile to evaluate the operational characteristic of low light level image intensifier.

Analysis of output signal to noise ratio’s uniformity for low light level image intensifier assembly

Output signal to noise ratio, which is an important technical index for evaluating low light level image intensifier assembly, decides the detectability of night vision system used in low light level condition. In this article, for evaluating the uniformity of output signal to noise ratio, the end surface of image intensifier assembly has been divided into some section on which the output signal to noise ratio is measured according to the method to signal to noise ratio. It can be concluded form the output signal to noise ratio on each section that the output signal to noise ratio is good uniform in central area of end surface, but the output signal to noise ratio is worse for whole end surface. To explore the main reason for worse uniformity of output signal to noise ratio, sensitivity of image intensifier on each section has been also designed and analyzed. It has been proven by testing the sensitivity of image intensifier that the uniformity of output signal to noise ratio is related to sensitivity’s uniformity, the output signal to noise ratio is uniform on the section which sensitivity is uniform, and the output signal to noise ratio is worse uniform on the section which sensitivity is also worse uniform. The uniformity of output signal to noise ratio can be improved by choosing good photocathode which sensitivity’s uniformity is better. The result in this article is value for improving the application characteristic of low light level image intensifier assembly.

Research on voltage characteristic of the third generation low-light-level image intensifier tube's output signal to noise ratio

Signal to noise ratio is an important parameter to evaluate the 3rd generation low-light-level image intensifier. In this article, voltage in different poles have been changed respectively, output signal to noise ratio referring to different voltages have been studied, and the relationship between each voltage and output signal to noise ratio has been analyzed. The study results show that voltage of photocathode is not less than 150 V, voltage of MCP is between 800 V and 900 V, and voltage of screen is between 5000 V and 6000 V while output signal to noise ratio of filmed image intensifier is optimized. The study in this article is worthwhile for developing signal to noise ratio of the 3rd low-light-level image intensifier sufficiently.

New half-film method for measuring Al2O3 film MTF of 3rd generation image intensifier

In 3rd generation image intensifier, Al₂O₃ film on the input of MCP is a serious influence factor on device MTF due to its electron scattering process. There are no reportes about how to measure the MTF of Al₂O₃ film. In this paper a new Half-film comparssion test method is creatively established for determing the film MTF, which overcomes the difficulty of measuring super thin film less than a few nm. In this way, the MTF curves of 10nm Al₂O₃ film can be accurately obtained. The measurement results show that 10nm Al₂O₃ film obviously decay the MTF performance of the 3rd generation image intensifier and take an important role in the improvement work of 3rd generation image intensifier MTF and resolution performances.

Measurement and analysis of signal to noise ratio for image intensifier tube, 18mm microchannel plate

Output signal to noise ratio is an important technical index for evaluating detectability of microchannel plate image intensifier tube, and the characteristic for detecting of microchannel plate image intensifier tube restricts the detectability of the night vision system. It has been proved in theory and in practice that the value of output signal to noise ratio of image intensifier tube equipped for night vision system decides the farthest distance and imaging definition of system which used under low light level in square root way. In this article, method and device for measuring the output signal to noise ratio of 18mm microchannel plate image intensifier tube has been introduced in detail. Output signal to noise ratio values of several 18mm microchannel plate image intensifier tube selected have been measured. Contacting to work condition of image intensifier tube, relationship between voltage of cathode, microchannel plate, screen and output signal to noise ratio of 18mm microchannel plate image intensifier tube bas been studied, which is available for other image intensifier tube.