As the rapid development of back-illuminated CMOS (BI-CMOS) image sensor technology in recent years, its application prospect in the field of Low-Light-Level (LLL) night vision has been widely concerned. Therefore, LLL imaging module was developed based on BICMOS, whose 3-D noise data was obtained under different illumination conditions. The test results show that, the signal-to-noise ratio (SNR) of imaging module becomes worse with the decreasing of illumination. According to the judgement of noise, the noise power of the image in low illumination is mainly Gaussian distribution. And the image processed by spatial filtering, which efficiently reducing the imaging noise and improving the imaging quality.
Based on the study of working principle and making process of 4-transistor Backside-illuminated CMOS (4T BSI-CMOS), Signal-to-noise ratio (SNR) model are established and quantitative calculating formula is derived. In addition, factors of influencing SNR are analyzed. Two methods are presented to enhance the SNR, the one is optimizing structure of 4T BSI-CMOS image sensor to strengthen the signal and the other one is correlated double sampling to decrease fixed pattern noise (FPN). These results serve as useful guidelines to enhance the SNR of 4T BSI-CMOS and improve the image quality.
Solid low-light imaging device is an important part of night vision, which has the advantage of high resolution, high contrast and small size, and it can work 24 hours. A handheld high-resolution low-light camera is proposed based on the characteristics of GSENSE400BSI CMOS image sensor in this paper. The camera includes CMOS driver, image correction, cache, low-light image enhancement and ultra-clear format encoding, implemented on an FPGA-based hardware platform. And the camera structure is optimized designed to realize the handheld operation. Finally, the experiments show that the low-illuminance camera display the details of the target clearly under 10-2 lx illumination, with an effective display resolution of 2048×2048@60fps.
Apparent distance is a reflection of the performance of low-light night vision system, but also an important parameter indicator in the design stage of LLL night vision system. As the working environment is changing, it is difficult to accurately estimate the apparent distance. Except the parameters of the system itself and the series of parameters caused by the weather environment, the contrast of the target and background is also the important factor to affect performance of the system. In this paper, we use ICCD to test the contrast of target and background of several typical scenes in the use of low-light night vision system, and get the contrast of target and background, which is very important to the prediction of apparent distance.
Low Level Light (LLL) night vision technology is extensively applied in national defense and civil application fields. The digitization of LLL imaging is trend of light detection technology in the future. The corresponding modulation transfer function (MTF) and total system MTF model were established, base on the structure composition and operation principle. Simulation was carried out to analyze the performance of the MTF modern. Results indicate that the MCPCMOS better contrast of object. When the spatial frequency increasing, the MTF of MCP-CMOS downing faster than that of GaAs LLL image intensifier. The GaAs image intensifier shows an better image restoration capability and higher limiting resolution. The model and simulation results can provide a theoretical guidance for the fabrication and application of high imaging quality MCP-CMOS.
To achieve negative-electron-affinity state, the atomically clean surface of GaAs-based photocathode is usually activated by cesium and oxygen in the ultrahigh vacuum environment. In view of the required computer-control of evaporation flow rates, the solid oxygen dispenser instead of gaseous oxygen is urgently needed just as the regular cesium dispenser. Accordingly, the solid cesium and oxygen dispensers were applied to activate epitaxial GaAs cathode samples. Two types of solid oxygen dispensers composed of barium peroxide powder and silver oxide powder respectively are employed to improve cathode photoemission performance. The experimental results show that the barium peroxidebased oxygen dispenser can release more oxygen and bring in higher activation photocurrent and spectral response than the silver oxide-based one. The unsatisfactory feature is that the silver oxide-based oxygen dispenser released effectual oxygen gas more slowly than the barium peroxide-based oxygen dispenser. Therefore, an effective activation technique was proposed to ameliorate this unfavorable phenomenon for the silver oxide-based dispenser, which can bring out the desired symmetry of photocurrent curve shape during the Cs/O alternate activation process. The improved activation technique would provide guidance for the optimization of activation craft.
Vacuum technology is extensively used in space science, nuclear energy, surface science, materials science, electric vacuum industry, microelectronics, semiconductor, metallurgy, and so on. More and more fields need ultra high vacuum (UHV) or extreme high vacuum (XHV) for scientific research and production. Both the rigorous vacuum processing technics and highly developed sophisticated vacuum technology are the necessities for the acquisition and conservation of UHV or XHV ambience. In this paper, a vacuum decline was analyzed and the UHV system was recovered. Using the residual gas analyzer to measure the partial pressure of residual gas and identify the type of gas, the outgassing source was found out by comparing the measure results. The UHV system was recovered back to 10<sup>-9</sup>Pa through treatment. The residual gas analyzing method can effectively identify the type of gas about outgassing, narrow the scope of outgassing subassembly, shorten the vacuum system recovery time, and improve work efficiency. The method of determining the outgassing source by residual gas analyzer can be applied in the fields of UHV and XHV, and it has a certain reference significance for further improving the system vacuum degree.
The electronic structure and optical properties of pure and P-doped cubic-blende gallium arsenide (GaAs) for different P constants (x=0, 0.125, 0.25, 0.375) have been studied by the first-principles projected augmented plane potential approach based on the density functional theory and the generalized gradient approximation method. It shows that the P-doped material has a smaller lattice constant, which resulted in a local lattice distortion. The minimum of the conduction band moves to high energy level and the band gaps gradually become wide with gradual increase concentration of P impurity. The dielectric function are calculated based on Kramers-Kroning relations. The optical property studied from the calculated absorption coefficients shows that the adsorption peaks change obviously in the visible light wavelength area for the P-doped GaAs system.
In a LIDAR system, a pulsed laser beam is propagated to a scene, and then reflected back by objects. Ideally if the beam diameter and the pulse width are close to zero, then the reflected beam in time domain is similar to a delta function, which can accurately locate an object's position. However, in a practical system, the beam has finite size. Therefore, even if the pulse width is small, an object shape will make the reflected beam stretched along the time axis, then affect system resolution. <p> </p>In this paper, we assume the beam with Gaussian shape. The beam can be formulated as a delta function convolved with a shape function, such as a rectangular function, in time domain. Then the reflected beam can be defined as a system response function convolved with the shape function. We use symmetric objects to analyze the reflected beam. Corn, sphere, and cylinder objects are used to find a LIDAR system's response function. <p> </p>The case for large beam size is discussed. We assume the beam shape is similar to a plane wave. With this assumption, we get the simplified LIDAR system response functions for the three kinds of objects. Then we use tiny spheres to emulate an arbitrary object, and study its effect to the returned beam.
The photocurrent attenuation of GaAs photocathode within one hour after activation under three different vacuum pressure (5×10<sup>-9</sup>Pa, 5×10<sup>-8</sup>Pa, 5×10<sup>-7</sup>Pa) were recorded by automatically activated monitor. The results show that: the photocurrent quickly descend in the beginning and then descend linearly at a low slope; the amplitude of the quickly descending area were 10%, 14.74% and 36%separately, with the respective slope of the linear descending area were -0.00653, -0.01132and -0.02. Three samples’ gas components of H<sub>2</sub>, CH<sub>4</sub>, CO, H<sub>2</sub>O, O<sub>2</sub>, CO<sub>2</sub> etc under the same vacuum pressure (5×10<sup>-8</sup>Pa)during photocurrent attenuation were collected by quadrupole mass spectrometer. By comparing the gas components content and the attenuation law of the photocurrent, it has been found that H<sub>2</sub>O and H<sub>2</sub> had a greater impact on the stability of GaAs photocathode in the ultra-high vacuum environment and H<sub>2</sub>O was the predominant effect. This paper has important guiding significance and reference value in studying the stability of GaAs photocathode and the improvement of semiconductor photocathode process.
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.
In order to know the influence of activation processes on GaAs photocathodes, three GaAs samples were activated by a fixed current of cesium source and different currents of oxygen source. The current of caesium source is same during activation to ensure initial adsorption of caesium quantum is similar, which is the base to show the difference during alternation activation of caesium and oxygen. Analysed with the activation data, it is indicated that Cs-to-O current ratio of 1.07 is the optimum ratio to obtain higher sensitivity and better stability. According to double dipole model, stable and uniform double dipole layers of GaAs-O-Cs:Cs-O-Cs are formed and negative electron affinity is achieved on GaAs surface by activation with cesium and oxygen. The analytical result is just coincident with the model. Thus there is an efficient technological method to improve sensitivity and stability of GaAs photocathode.
The gallium arsenide (GaAs) photocathode generally requires a high temperature thermal cleaning before (Cs, O) activation in order to obtain an atomic level clean surface. The process is useful to adsorb and deposit cesium and oxygen atoms. Generally considered, the photocathode needs to be cooled to 60℃ to activate for achieving better results. People usually keep the annealing time for at least 1.5 hours in practical production. In order to explore the effect of annealing time on cesium atoms which were adsorbed on GaAs photocathode, the experiment monitored the activation curves of three GaAs photocathodes samples which annealed for 0.5 hour, 1.0 hour, 1.5 hours respectively, and then compared the occurrence moment of the photocurrent and the first cesium peak by different annealing waiting time. The difference of the activation curves reflects indirectly that the photocathode surface temperature had an influence on the adsorption of cesium atoms during activation process. This phenomenon could explain from two aspects about atoms adsorption and electronic transport. The work has referential significance for experimental research and industrial production.
The simulation calculation and analysis on the electron backscattering for ion barrier films (IBFs) of Al<sub>2</sub>O<sub>3</sub> were performed by Monte Carlo methods. Simulation and experimental detection both found that electron backscattering ratio is inversely proportional to the incident electron energy, proportional to the film thickness and density. But if the film is thick enough, the back scattering ratio will not continue to increase, will maintain a relatively stable value. This work provided a theory support for fabricating high performance low-level-light device.
Ar<sup>+</sup> ion etching and X-ray photoelectron spectroscopy (XPS)depth profile analysis have been performed on the native oxide layerof GaAs(100) surface. The composition of the native oxide layer,that isthe oxide phases of gallium and arsenic, was characterized precisely. It is indicated that native oxide phases on extreme surface of GaAs(100) consist of a mixture of Ga<sub>2</sub>O<sub>3</sub>, As<sub>2</sub>O<sub>3</sub> and As<sub>2</sub>O<sub>5</sub>. Furthermore, the respective distribution of oxide phases of gallium and arsenic along the depthwere compared and analyzed.A seemingly contradictory phenomenon was found, that is As enrichment exist in total oxide layer, but the content of Ga oxide was greater than that of As oxide in the oxide layer except for the outmost surface layer.Based on the comprehensive influence of oxidation process, etching, segregation and growth process, the intrinsic mechanism of the change of oxides along etching depth was discussed. According to the analyzed results, the oxide layer of GaAs (100) surface should be divided to two layers,that is the outmost layer containing oxides of Ga and As and the intermediate layer including only oxide of Ga.The concentration of As oxides in the outmost layer and the enrichment of As in total oxide layer are derived from surface structure inhomogeneity. The throughout total oxide layer of Ga oxide is attributed to its stronger oxidability.In the present work, the system study for native oxide layer of GaAs surface provides the powerful foundation for understanding surface state of GaAs and surface treatment.
Based on the studies of the GaAs photocathode, the surface model of the InGaAs photocathode is investigated and the
energy distributions of electrons reaching the band bending region, reaching the surface and emitting into vacuum are
calculated. We use the quantum efficiency formula to fit the experimental curves, and obtain the performance parameters
of the photocathode and the surface barrier parameters. The results show that the electron escape probability is seriously
influenced by energy distribution and plays an important role in the research of high quantum efficiency as well. After
the theoretical calculation, the energy range of electrons crossing the BBR broaden, the peak of the electron energy
distribution shifts forward to low energy, the number of low energy electrons increases obviously; The surface barriers of
the InGaAs photocathode is similar to that of the GaAs photocathode. The height of barrier II not only decreases the
number of electrons, but also makes the width of electron energy distribution narrow. The prepared transmission-mode
InGaAs photocathode contains 20% InAs and 80% GaAs. This combination of InGaAs photocathodes is widely used in
the weak light detection field, such as night vision technology, forest fire prevention and harsh climate monitoring.
In order to improve the electronic gain and luminance gain of low-light-level image intensifiers, microchannel plates(MCP) are adopted as the electron multiplier mechanism. According to the relevant experimental analysis, the resistance between channels is a limited value. Due to there are resistive coupling between any two adjacent channel of MCP, the electron transmission and the electron multiplication in a certain channel will be interfered by its adjacent channels, This phenomenon would affect the quality of image transmission and field of view of image intensifier. In low-light condition, the input current of MCP is small, the current gain of each channel is same, MCP has the area of linear current amplification and distortion-free image transmission. But when input current is large and close to saturation, lower current in channels has more current gain, leading to the contrast change of the image. This paper analyzes the transmission properties of electrons in the channels. It is proved that there is an electrical relationship between adjacent channels,throuht the circuit equations with relevant circuit parameters such as the resistance of secondary electron emission layer, resistance of resistive layer, the resistance between two adjacent channels, and so on. The analysis method and research results provide technical guidance for the improvement of electronic gain, luminance uniformity and preparation process of MCP.
The 3<sup>rd</sup> generation low-light-level image intensifiers should be aged for 100 hours before its normal use. In order to know the influence of ageing processing on GaAs photocathodes, five 3<sup>rd</sup> generation low-light-level image intensifiers were aged with the life testing instrument of low-light-level image intensifier in an experiment. With the spectral response testing instrument, the intensifiers were measured for totally 8 times to get their spectral response respectively before they were aged and in a half year after aged, and to calculate the integral sensitivity according to the spectral response curves. Based on the fluctuating spectral response curves and the varying integral sensitivity, it was indicated that the aged intensifiers up to standard had more stable photocathode sensitivity, smaller decrease in their spectral response curves, while those not up to standard had more obvious decline as a whole in their spectral response curves. Additionally, the threshold wavelength of all intensifiers was moving toward shortwave. The degeneration of GaAs photocathode resulted from the instability of the Cs-O layer on GaAs photocathode surface. During the ageing processing, the lack of a longtime light radiation on Cs-O layer, the widening surface barrier and the decreasing escape probability led to less photoelectronic emission and lower sensitivity. Moreover, the destruction of dipole layer resulted in smaller bending of surface band and higher vacuum level, so that the electrons in impurity level could not escape and the threshold wavelength moved toward shortwave. Thus the ageing processing played a role of picking out the 3<sup>rd</sup> generation low-light-level image intensifiers to get rid of the products not up to standard and to put the photocathodes of products up to standard into a relatively stable random failure period.
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.
The gallium arsenide (GaAs) photocathode was generally cleaned by radiant heating, direct heating, ion bombardment annealing, and so on. In this paper, the radiant heating method, namely thermal cleaning method, was adopted for GaAs photocathode surface purification. Using this method could obtain an atomic clean surface, ensure the integrity of the GaAs surface lattice, and guarantee the uniformity of surface cleaning effect at the same time. But because the accurate measurement of the GaAs photocathode surface temperature in the vacuum system was very difficult, the residual gas analyzer (RGA) was used in this experiment to monitor the residual gas composition in ultrahigh vacuum during the thermal cleaning process and determine the thermal cleaning temperature by the partial pressure curves of As and Ga. It was found that the first peaks of As and Ga elements both appeared after heating about one hour, accompanied with H<sub>2</sub>O, N<sub>2</sub>/CO, CO<sub>2</sub> and other common gas. According to partial pressure curves of H<sub>2</sub>O, N<sub>2</sub>/CO, CO<sub>2</sub> and the heating time, it could be judged that the temperature at that time was not high, which should be under 150°C.After thermal cleaning experiment of three GaAs photocathodes, it was found that the peak value of As partial pressure at low temperature was generally within 10<sup>-11</sup>mbar~10<sup>-10</sup>mbar, and the peak value was at 10<sup>-10</sup>mbar at high temperature. Sometimes it was appeared that the peak value of As partial pressure at low temperature was even higher than the peak value at high temperature. The As volatilization phenomenon occurred at low temperature indicated that the elemental As exist on the GaAs photocathode surface or near surface after the chemical etching process, and the As could volatilize from GaAs photocathode at low temperature in the beginning of thermal cleaning. This research has guiding significance for further understanding the thermal cleaning mechanism of GaAs photocathode and improving the thermal cleaning technology.
Photocurrent of GaAs photocathode activated with Cs and O was tested by auto-activation monitor, the fitting curves of photocurrent showed that the photocurrent of the photocathode after the first activation declines exponentially, and then declines linearly with very small slope |<i>k</i><sub>1</sub>|; the photocurrent after the second activation rises exponentially, and then declines linearly with a slope|<i>k</i><sub>2</sub>| which is a bit larger than |<i>k</i><sub>1</sub>|.Based on the mechanism difference between twice annealing of the photocathode, the degeneration behavior of the photocathode was analyzed by three-dipoles model and XPS test after the first activation and succedent thermal cleaning. It is indicated that Cs<sub>2</sub>O dipoles on the surface are saturated after the photocathode was activated for the first time, the remained Cs and Cs<sub>2</sub>O in the ultra-high vacuum chamber which deposited on the photocathode surface will prevent the emission of photoelectrons. The photocathode surface with Cs and O reconstructed when it was annealing for the second time, a lot of Cs<sub>2</sub>O dipoles changed into more stable GaAs-O-Cs dipoles, and this phenomenon would happened immediately as soon as the photocathode was activating for the second time. After the residual Cs and Cs<sub>2</sub>O dipoles depleted, the neutral gas CO<sub>2</sub>, H<sub>2</sub>O, O<sub>2</sub>, damaging the surface dipoles layer, are the main factors resulted in the decline of photocurrent. Due to the instable Cs<sub>2</sub>O dipoles on the surface of photocathode have greater chances of converting into stable GaAs-O-Cs dipoles when photocathode was activated for the first time, the photocurrent declines more slowly compared with the second activation. The discussion for the phenomenon is of great significance for exploring the photoemission mechanism of Ⅲ-Ⅴ semiconductors.
Local invariant feature extraction, as one of the main problems in the field of computer vision, has been widely applied to image matching, splicing and target recognition etc. Lowe’s scale invariant feature transform (known as SIFT) algorithm has attracted much attention due to its invariance to scale, rotation and illumination. However, SIFT is not robust to affine deformations, because it is based on the DoG detector which extracts keypoints in a circle region. Besides, the feature descriptor is represented by a 128-dimensional vector, which means that the algorithm complexity is extremely large especially when there is a great quantity of keypoints in the image. In this paper, a new feature descriptor, which is robust to affine deformations, is proposed. Considering that circles turn to be ellipses after affine deformations, some improvements have been made. Firstly, the Gaussian image pyramids are constructed by convoluting the source image and the elliptical Gaussian kernel with two volatile parameters, orientation and eccentricity. In addition, the two parameters are discretely selected in order to imitate the possibilities of the affine deformation, which can make sure that anisotropic regions are transformed into isotropic ones. Next, all extreme points can be extracted as the candidates for the affine-invariant keypoints in the image pyramids. After accurate keypoints localization is performed, the secondary moment of the keypoints’ neighborhood is calculated to identify the elliptical region which is affineinvariant, the same as SIFT, the main orientation of the keypoints can be determined and the feature descriptor is generated based on the histogram constructed in this region. At last, the PCA method for the 128-dimensional descriptor’s reduction is used to improve the computer calculating efficiency. The experiments show that this new algorithm inherits all SIFT’s original advantages, and has a good resistance to affine deformations; what’s more, it is more effective in calculation and storage requirement.
The studies of quantum efficiency, electronic energy distribution and stability are highly concerned in the application
of Negative electron affinity (NEA) gallium nitride (GaN) photocathodes while the resolution of photocathodes are
concerned rarely. The resolutions of some image intensifiers are smaller than computational value partly because of
ignoring the resolution of photocathodes. To a certain extent, the resolutions of image intensifiers are influenced by
photocathodes. Electronic transverse diffusion is the main cause of decreasing the resolution of photocathodes whereas
the exponential-doping structure can reduce its influence. In this paper, the resolution characteristics of photocathodes
have been studied by using the modulation transfer function (MTF) method. The MTF expressions of transmission-mode
exponential-doping photocathodes have been obtained by solving the two-dimensional continuity equations. According
to the MTF expressions, the resolution characteristics between exponential-doping and uniform-doping GaN
photocathodes are calculated theoretically and analyzed comparatively. At the same time, the relationships between
resolution and thickness of the emission layer T<sub>e</sub>, electron diffusion length L<sub>D</sub> are researched in detail. The calculated results show that, compared with the uniform-doping photocathode, the exponential-doping structure can increase the
resolution of photocathode evidently. The resolution of exponential-doping GaN photocathode is improved distinctly
when the spatial frequency varies from 400 to 800 lp/mm. The MTF characteristics approach gradually when f increases
or decreases. Let f =600 lp/mm, the resolution increases by 20%-48% approximately. The constant built-in electric field
for exponential-doping GaN photocathode can increase the resolution of photocathode. The improvement of resolution is
different from decreasing T<sub>e</sub>, L<sub>D</sub> or increasing the recombination velocity of back-interface which are at the cost of reducing the quantum efficiency of photocathode. Therefore, the MTF expressions of transmission-mode
exponential-doping photocathode play a positive role in improving the resolution of ultraviolet detector and optimizing
the structural design of GaN photocathode.
In order to know more about the surface state of GaAs(100) epitaxial wafer during a storage period of two years, the
XPS analysis was carried out four times on the surface, respectively polished by chemical etching, stored in desiccator
for half a year, one year and two years. The results indicated that even after cleaned by proper etchant solutions, the fresh
surface was slightly oxidized with Ga<sub>2</sub>O<sub>3</sub>, As<sub>2</sub>O<sub>3</sub> and organic contaminant. The epi-wafer was always exposed to air during the storage period, so more and more oxides turned out. The mixed oxide layer comprised of C-OR, COOR, Ga<sub>2</sub>O<sub>3</sub>, As<sub>2</sub>O<sub>3</sub> and As<sub>2</sub>O<sub>5</sub> appeared after only half a year. In the ageing process of two years, the oxide types of gallium or arsenic did not change with stable content of Ga<sub>2</sub>O<sub>3</sub> and remarkably fluctuating relative contents of As<sub>2</sub>O<sub>3</sub> and As<sub>2</sub>O<sub>5</sub>. Based on the intensity ratio of Ga 3d-Ga<sub>2</sub>O<sub>3</sub> to Ga 3d-GaAs, the thickness of oxide layer was estimated. The oxide layer generated after chemical polishing was very thin, just only 0.435nm thick, and then it grew rapidly, approximately 1.822nm after one year while almost no change any more subsequently. It was indicated that after the epi-wafer was
stored for one year, because of volatile As<sub>2</sub>O<sub>3</sub> or As<sub>2</sub>O<sub>5</sub>, there remained a large amount of Ga<sub>2</sub>O<sub>3</sub> in oxide layer, which prevented the reactions between bulk material and oxide layer with oxygen. So native oxide layer plays a role as passive film to protect epi-wafer against the environment during a long storage period.
The AlGaN/GaN with thin GaN surface was grown by metalorganic chemical vapor deposition (MOCVD). And one of
two AlGaN/GaN photocathode samples was etched by molten KOH about 40s, and its reflectivity and transmittance are
tested. The thickness of AlGaN and GaN layers are fitted by the matrix formula for thin film optics, and the GaN
thickness of them are 7nm and 2.5nm respectively. And etch speed of GaN are got in molten KOH at about 400°C. Then
the etched and original AlGaN/GaN photocathode samples are activated by Cs/O in the same way. The spectral response
and the result of simulation show that the cut-off wavelength of the etched AlGaN/GaN deviate to the short-wave. And
the quantum efficiency decline with the GaN thickness decrease.
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 3<sup>rd</sup>-generation low-light image intensifier failure theory, if the radiation gain of the
ultraviolet image intensifier tube is defined as 1,000cd/m<sup>2</sup>, 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<sup>-6</sup>
W/m<sup>2</sup>, with the radiance gain linear interval between 3.0×10<sup>-6</sup> W/m<sup>2</sup> ～4.6×10<sup>-5</sup> W/m<sup>2</sup>; and that of the double MCP ultraviolet image intensifier tubes is 4×10<sup>-7 </sup>W/m<sup>2</sup>, with the radiance gain linear interval between 4.0×10<sup>-7 </sup>W/m2 ～2.0×10<sup>-5</sup> W/m<sup>2</sup>. 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<sup>-5</sup> 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
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.
The UV radiation of spectrum range of 200~320nm almost is zero on the earth surface because UV radiation is
greatly absorbed by ozone in atmosphere. So this spectrum range is called "Solar Blind Range". Because Solar Blind
UV(SBUV) can't be influenced by atmosphere, it is easy to detect them as soon as SBUV radiation objects appear in the
earth surface. If UV photoelectric image devices are used to observe them, high contrast picture will be acquired, that
bright object's image lie in full black background. It is easy to identify the picture by human eye or other optical sensor
(CCD). A solar blind UV(Ultra Violet) image intensifier tube(SBUV-IIT) is a special image intensifier tube, which was
developed on double proximity focused Generation low-light-level image intensifier tube. It only responses spectrum
range of 200~320 nm., SBUV-IIT can be used to observe UV faint radiation object, because UV sensitivity is high and
response time is rapid and radiation gain is high. Low-altitude-flying missile can be observed by detecting its tail fog
with SBUV-IIT, because its tail fog emits plenty of SBUV. By this way high contrast UV picture can be acquired to
achieve missile warning, and this way has been widely used in foreign ordnance equipment.
SBUV-IIT has been described in this paper. It is double proximity focused MCP (Micro-channel plate) image
intensifier tube. It is 18mm active diameter of photocathode and phosphor screen. Input and output window is quartz
glass and fiber optics faceplate respective. Photocathode material and phosphor screen is tellurium cesium compound
and P20. It has been developed with a limiting UV resolution of 39 line pair per millimeter, and spectral response of
200~320 nm, photocathode maximum sensitivity of 29.5 milli-ampere per watt at wavelength 254 nm and a mass of
35g. It can be coupled with CCD easily. It has been well suited for fingerprint identify and camera system, It'll be used
for UV hail testing, UV earthquake forecasting and so on.