Zhipeng Hou

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 calculation of cathode electron scattering radius in the generation III image intensifier

In the proximity focusing imaging system, the clear degree of images characterized by electronic scattering radius which could directly decide the resolution. In generation Ⅲ image intensifier, ion barrier film on the input of MCP is a serious influence factor on device resolution due to its electron scattering process. In this paper the electronic scattering radius would calculate at the single electron scattering, large electron scattering, and having ion barrier film electron scattering. Through comparing, it is found that the electron scattering radius is significantly larger at having an ion barrier film on the input of MCP. The results of calculation show that reducing the gap cathode-MCP and increasing the cathode voltage could reduce electron scattering radius, so as to improve the resolution of generation Ⅲ image intensifier.

Research on detectable threshold of double MCP ultraviolet image intensifier tube

In order to research the influence of the quantity of the Micro-Channel Plates (MCP) on the detectable threshold of the ultraviolet image intensifier tube, the wide spectrum image intensifier gain tester produced by Nanjing University of Science and Technology is employed to test the relation curves between self-made one single MCP ultraviolet image intensifier tube, two double MCP ultraviolet image intensifier tubes, and photocathode incidence radiation illumination respectively. With reference to the 3rd-generation low-light image intensifier failure theory, if the radiation gain of the ultraviolet image intensifier tube is defined as 1,000cd/m2, the tube will lose the effect of image intensification, when the corresponding photocathode incidence radiation illumination will be the minimum detectable threshold. Viewed from the test results, the minimum detectable threshold of the single MCP ultraviolet image intensifier tube is 3.0×10-6 W/m2, with the radiance gain linear interval between 3.0×10-6 W/m2 ～4.6×10-5 W/m2; and that of the double MCP ultraviolet image intensifier tubes is 4×10-7 W/m2, with the radiance gain linear interval between 4.0×10-7 W/m2 ～2.0×10-5 W/m2. The test results were analyzed on the basis of the MCP self-saturation effect, concluding that the saturation current density of the single-unit MCP is a fixed , but there may be certain difference among the saturation current density of different MCPs due to different materials and manufacturing processes. The test results show that the maximum of the radiation gain linear interval of the three ultraviolet image intensifier tubes are at the magnitude of 10-5 W/m2, and the non-significant differences also verified the theory. In the double MCP ultraviolet image intensifier tubes, the photocathode-produced photocurrent is multiplied in passing the first MCP and then reaches the second MCP, so the second MCP will reach the state of current saturation earlier than the first MCP, making the minimum detectable threshold of the double MCP ultraviolet image intensifier tubes is lower than that of the single ultraviolet image intensifier tube by one order of magnitude, with the linear gain interval increasing by one magnitude, and the absolute of the corresponding radiation gain of the same radiation illumination within the linear gain interval increasing by 10 times, verifying that the double MCPs can detect much lower and weaker ultraviolet radiation and realize the high gain theory. The research results has certain guiding effect towards the promotion and application of the double ultraviolet image intensifier tubes, and has great significance on enhancing the high ultraviolet radiation detection and imaging technology.

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.

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.

Performance of low-light-level night vision device affected by backscattered electron from ion barrier film

In order to suggest the performance of low-light-level night vision device affected by backscattered electron from ion barrier film(IBF), in this paper, based on the idea of Monte-Carlo, the track of electron impinging and rebounding on ion barrier film is simulated. The Lambert distribution and Beta distribution are used to calculate electron’s emission. The Mott cross section and the Bethe formula rewrited by Joy are used to describe and calculate the elastic and inelastic scattering electron traversing in the film. With the statistic of the total transmitted electron and the discussion on the effect of cathode voltage, proximity between ion barrier film and photocathode on performance of low-light-level night vision device, we get the point diffusion function of ion barrier film, and we conclude that in low light level backscattered electron hardly affect working of image intensifier and higher cathode voltage, closer proximity between cathode and ion film will reduce the impact of backscattered electron in high light level.

The report on performance of image intensifier affected by gas on surface

In order to illustrate the performance of intensifier affected by gas on surface, the kovar ring surface has been tested by XPS. According the result, gas type and quantity are calculated. With the theory of thermal and electron stimulated gas desorption, the remaining gas on surface after thermal and electron treatment is reckoned and the surface outgassing rate is evaluated on the assumption that the image intensifier is working in the 10-3lx environment. Then, the performance of image intensifier is evaluated by the effect of gas on the surface at last.