Using the activation and evaluation system for negative electron affinity (NEA) photocathode, the Cs activation was finished for GaN photocathode, and the Cs, O activations was completed by using the alternate method of Cs source continues, O source intermittent for the cathode sample, the photocurrent curve was gotten during the activation process. Based on the characteristics of NEA and the formation of cathode surface barrier, the evolution of GaN photocathode surface barrier before and after activation was analyzed. After the GaN photocathode being purified, the adsorption of cesium is a key step for getting the NEA surface. With Cs alone, the electron affinity potential change of 3.0eV can be obtained, and the vacuum energy level can be moved to approximately 1.0eV below the bottom of conduction band. Together with Cs, O processing can further reduce the vacuum energy level by 0.2eV.
The solutions to the engineering problems were provided according to the innovation principle based on the theory of TRIZ. The ultra high vacuum test and evaluation system for the preparation of negative electron affinity (NEA) photocathode has the characteristics of complex structure and powerful functions. Segmentation principle, advance function principle, curved surface principle, dynamic characteristics principle and nested principle adopted by the design of ultra high vacuum test and evaluation system for cathode preparation were analyzed. The applications of the physical contradiction and the substance-field analysis method of the theory of TRIZ in the cathode preparation ultra high vacuum test and evaluation system were discussed.
Negative electron affinity (NEA) GaN photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive threshold and so on. The quantum efficiency is an important parameter for the preparation and evaluation of NEA GaN photocathode. The varied doping GaN photocathode has the directional inside electric field within the material, so the higher quantum efficiency can be obtained. The varied doping NEA GaN photocathode has better photoemission performance. According to the photoemission theory of NEA GaN photocathode, the quantum efficiency formulas for uniform doping and varied doping NEA GaN photocathodes were given. In the certain condition, the quantum efficiency formula for varied doping GaN photocathode consists with the uniform doping. The activation experiment was finished for varied doping GaN photocathode. The cleaning method and technics for varied doping GaN photocathode were given in detail. To get an atom clean surface, the heat cleaning must be done after the chemical cleaning. Using the activation and evaluation system for NEA photocathode, the varied doping GaN photocathode was activated with Cs and O, and the photocurrent curve for varied doping GaN photocathode was gotten.
Thermal stability technology of signal processing circuit infrared sight is studied under temperature shock. Model parameters and geometry is configured for FPGA devices (EP1C20F400C8), solder material and PCB. Signal circuit boards of full array BGA distribution are simulated and analyzed by thermal shock and waveform through engineering finite element analysis software. Because solders of the whole model have strong stress along Y direction, initial stress constraints along Y direction are primarily considered when the partial model of single solder is imposed by thermal load. When absolute thermal loads stresses of diagonal nodes with maximum strains are separated from the whole model, interpolation is processed according to thermal loads circulation. Plastic strains and thermal stresses of nodes in both sides of partial model are obtained. The analysis results indicate that with thermal load circulation, maximum forces of each circulation along Y direction are increasingly enlarged and with the accumulation of plastic strains of danger point, the composition will become invalid in the end.
For varied doping GaN photocathode, from bulk to surface the doping concentrations are distributed from high to low. The varied doping GaN photocathode may produce directional inside electric field within the material, so the higher quantum efficiency can be obtained. The photoemission surface of varied doping GaN photocathode is very important to the high quantum efficiency, but the forming process of the surface state after Cs activation or Cs/O activation has been not known completely. Encircling the photoemission mechanism of varied GaN photocathode, considering the experiment phenomena during the activation and the successful activation results, the varied GaN photocathode surface model [GaN(Mg):Cs]:O-Cs after activation with cesium and oxygen was given. According to GaN photocathode activation process and the change of electronic affinity, the comparatively ideal NEA property can be achieved by Cs or Cs/O activation, and higher quantum efficiency can be obtained. The results show: The effective NEA characteristic of GaN can be gotten only by Cs. [GaN(Mg):Cs] dipoles form the first dipole layer, the positive end is toward the vacuum side. In the activation processing with Cs/O, the second dipole layer is formed by O-Cs dipoles, A O-Cs dipole includes one oxygen atom and two Cs atoms, and the positive end is also toward the vacuum side，thus the escape of electrons can be promoted.
The development of infrared optical materials is always closely related to the research and exploration of material science. The infrared optical domes bears shock and produces stress when the infrared optical domes mounted on the missile moving at a high speed is shocked by high temperature. According to aerodynamics theory and thermo shock theory, the surge current will be transferred to optical parts through holding up layer and warms the surface of optical parts when infrared optical parts are shocked by high temperature. A compress stress is formed on the hot external surface of optical parts forms and a tension stress is formed on the internal surface or optical parts under the circumstance of the edge of optical parts being fixed. The windows of optical parts become curvature radius of lens with the function of pressure difference which can cause aberration change. The brittle fracture of material will be caused if peak stress is beyond the strength which is permitted for infrared materials. Therefore, limits to design of windows thickness is proposed in this paper.
For the characteristics such as wide bandgap, low dielectric constant, ability to bear high temperature, ability to resist radiation etc., GaN material can be used for UV solar blind detection in very rigorous environments. But for a long time, the preparation technology for GaN material has been still keeping it from being used extensively. GaN photocathode with good future is developed slowly in the field of UV detection. The key method of obtaining effective photoemission is to reduce the vacuum energy level of GaN emission surface, make it lower than bulk conduction band minimum. Negative electron affinity (NEA) GaN photocathode can convert the light under 365 nm to the photoelectrons that can be sent to the free space. The surface potential of NEA GaN photocathode is made up of two straight line sections with different slope. As the first dipole layer, [GaN(Mg):Cs] dipole brings 3.0 eV decline of the vacuum energy level, make the GaN photocathode surface obtain about -1.0 eV effective negative electron affinity. The second dipole O-Cs makes effective electron affinity reduce further to - 1.2 eV. The results show: near 37% quantum efficiency can be gotten at the wavelength 200 nm for reflection-mode GaN photocathode, and the quantum efficiency reaches up to 13% at 290 nm in transmission mode. The large quantum efficiency and high stability are very good properties for UV detection devices employing GaN photoemitter.
In the preparation process for negative electron affinity (NEA) GaN photocathode, the surface cleanness is very important to activation, it influences the sensitivity and stability of NEA GaN photocathode. The traditional corrosion methods based on oxidizing and dissolving can't remove oxygen (O) and carbon (C) on GaN surface effectively. How to get an ideal atom clean surface is still an important question at present. The cleaning techniques for GaN photocathode was studied by using NEA photocathode activation system and XPS surface analysis system. The experiment sample is p-type GaN doped with Mg, doped concentration is 1.37×10<sup>17</sup> cm<sup>-3</sup>, the transfer rate is 3.08 cm<sup>2</sup>/V-S, and the thickness of activation layer is 0.51 μm, the substrate is 300 μm thick sapphire. The sample was dealed with chemical cleaning depuration at first. And to get the atom clean surface, the vacuum heat cleaning process was needed. The methods of chemical cleaning and the vacuum heating cleaning were given in detail. According to the X-ray photoelectron spectroscopy of GaN surface after chemical cleaning and the vacuum degree curve of the activation chamber during the heat cleaning, the cleaning effect and the cleaning mechanism were discussed. After the effective chemical cleaning and the heating of 700 Centigrade degree about 20 minutes in ultrahigh vacuum system, the oxides and carbon contaminants on cathode surface can be removed effectively, and the ideal atom clean surface can be obtained. The purpose of heating depuration process is that not only to get the atom clean GaN surface, but also to guarantee the contents of Ga, N on GaN surface stabilize and to keep the system ultra-high vacuum degree. Because of the volatilization of oxide and carbon impurity on the cathode surface, the vacuum degree curve drops with the rising of temperature on the whole.
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
Negative electron affinity (NEA) Gallium Nitride (GaN) photocathode is an ideal new kind of UV photocathode. NEA
GaN photocathode is widely used in such fields as high-performance ultraviolet photoelectric detector, electron beam
lithography etc. The preparation of negative electron affinity gallium nitride photocathode relates to the growth
technology, the cleaning method, the activation method and the evaluation of photocathode. The mainstream growth
technology of GaN photocathode such as metal organic chemistry vapor phase deposits technology, molecule beam
epitaxial technology and halide vapor phase epitaxial technology were discussed. The chemical cleaning method and the
heat cleaning method for GaN photocathode were given in detail. After the chemical cleaning, the atom clean surface
was gotten by a 700 °C heat about 20 minutes in the vacuum system. The activation of GaN photocathode can be realized
with only Cs or with Cs/O alternately. Using the activation and evaluation system for NEA photocathode, the
photocurrent curve during Cs activation process for GaN photocathode was gotten. The evaluation of photocathode can
be done by measuring the quantum efficiency. Employing the UV spectral response measurement instrument, the
spectral response and quantum efficiency of NEA GaN photocathode were measured. The measured quantum efficiency
of reflection-mode NEA GaN photocathode reached up to 37% at 230 nm.
Gallium Nitride (GaN) photocathodes are potentially attractive as UV detective materials and electron sources. Based on
the activation and evaluation system for GaAs photocathode, which consists of ultra-high vacuum (UHV) activation
chamber, multi-information measurement system, X-ray photoelectron spectroscopy (XPS), and ultraviolet ray photoelectron
spectroscopy (UPS), the control and measurement system for the activation of UV photocathodes was
developed. The developed system, which consists of Xenon lamp, monochromator with scanner, signal-processing
module, power control unit of Cs and O source, A/D adapter, digital I/O card, computer and software, can control the
activation of GaN photocathodes and measure on-line the spectral response curves of GaN photocathodes. GaN materials
on sapphire substrate were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with p-type Mg doping. The
GaN materials were activated by Cs-O. The spectral response and quantum efficiency (QE) were measured and
calculated. The experiment results are discussed.
Taking GaAs and GaN as representation, negative electron affinity (NEA) photocathode has many virtues,
such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution,
adjustive long-wave threshold, great potential to extend the long-wave spectral response waveband. Therefore it plays
more and more important effect in high performance image intensifiers and polarized electron sources. GaN NEA
photocathode and GaAs NEA photocathode are very similar because they all belong to III-V compound. But, GaN
photocathode and GaAs photocathode have many difference in such aspects as preparation process, activation manners,
stability and application field etc. In this paper, using the multi-information measurement and evaluation system of
photocathode, the preparation processes of native reflection-mode GaN photocathode and GaAs photocathode are
studied. The different activation manners of GaN photocathode and GaAs photocathode are compared and analyzed. The
spectral response and stability of the two kind of photocathode are compared also. The experiments indicate: the
atomically clean degree of NEA photocathode surface and the structure of activation layer are the main factors that
influence photocathode sensitivity and stability after activation. GaN photocathode and GaAs photocathode have good
NEA property and large quantum yield. Compare with GaAs photocathode, GaN photocathode has high stability, and the
decay of the quantum yield is comparatively slow.
Multi-frame infrared image restoration is concerned with the improvement of imagery acquired in the presence of varying degradations. The degradations can arise from a variety of factors: common examples include undersampling of the image data, uncontrolled platform or scene motion, system aberrations and instabilities, noise characteristic of the infrared detector. In this paper, the mathematic models of infrared image blur and sampling and noise models are discussed. The multi-frame infrared image restoration problem is discussed, too. We show the origin and restoration
infrared images which are used in the application of multi-frame infrared image restoration. By assessing subjectively
and objectively to restoration images, we have verified this kind of model and the feasibility of the multi-frame infrared
A new algorithm which is suitable for FPGA to the real-time infrared image enhancement is proposed in this paper. In
order to reduce Infrared image noise, we use the accumulation of the combining sequential neighbor frames, and use the
nonlinear expanding of gray histogram to enhance contrast ratio. This kind of algorithm has considered infrared image
characteristic and vision characteristic of the human eye synthetically, and guarantee real-time character of image
process, at the same time, also give consideration to the advantage of the FPGA design. This method can be realized
easily on hardware without damaged enhancement result. Finally, quality of enhanced image is evaluated through a
model. It has verified the enhancement result of this kind of algorithm, and offered reliable assurance for further
treatment of the infrared image. Use in the image system of the infrared video, the effect of image Enhancement is
Iterative infrared image restoration is concerned with the improvement of infrared imagery acquired in the presence of
varying degradations. The degradations can arise from a variety of factors: common examples include undersampling of
the infrared image data, uncontrolled platform or scene motion, system aberrations and instabilities, noise characteristic
of the infrared detector. In this paper, the mathematic models of infrared image blur and sampling and noise models are
discussed. The iterative infrared image restoration problem is discussed, too. We show the origin and restoration infrared
images which are used in the application of iterative infrared image restoration. By assessing subjectively and
objectively to restoration infrared images, we have verified this kind of model and the feasibility of the iterative infrared
Two gradient-doping GaAs photocathodes were designed and activated, the achieved highest integral sensitivity for the
gradient-doping cathode is 2178μA/lm, which is much higher than that of uniform-doping cathode. The increase in the
integral sensitivity is attributed to the electric field induced in the active layer of gradient-doping cathode. We analyze
the transported mechanism of gradient-doping cathodes and solve the quantum efficiency equations of exponential-doping
cathode, which is a special gradient-doping cathode with a constant induced electric field, from the one-dimensional
continuity equations. According to these equations, we calculate the theoretical quantum yield of the
exponential-doping cathodes, and compare the performance of exponential-doping cathodes with that of uniform-doping
cathodes. The theoretical results show that the exponential-doping structure can increase the quantum yield of
photocathodes evidently, for the transmission-mode cathodes the increase is even more pronounced.
This article introduces motion detection and estimation of low-level-light video sequence, and, motion detection, motion
estimation and variational problem. Low-level-light video sequence different form others, the time and space domain
noise in the signal not only limit the lowest illuminance of the system but also make the image show random glitter. In
this paper how to improve the signal-to-noise ratio (SNR) of low light level image is discussed too. The results show that
models and estimation algorithms in low-level-light video sequence can lead to improve reliability and accuracy of the
The edge detector operator of image intensifier is a key problem for fluorescent image processing. This paper is intended
to serve for three purposes: (1). To present the general problem of Fluorescent image in a sufficient depth and extent, (2)
to present a complete algorithm for image processing including image sharpening and gradient operator. (3). to search
for a edge detector optimal for fluorescent image processing of image intensifier. It is expected that a edge detector
operator could provide a generic and robust solution to the reticle fluorescent noise images matching problem, which
could be an important breakthrough in computer vision, photogrammetry, and pattern recognition.
The novel approach to the image noise problem of reticle images based on impact condition in low-level-light weapon
sight is proposed in this paper. The condition and process of the low-level-light weapon sight impact experiment were
analyzed, and then averaging algorithm of reticle images consists of two parts has been applied on the experiment. First
averaging and smoothing using a rotating mask methods were operated on Gaussian noise, to obtain a matching precision
with in 0.05 mil. Second the well known efficient median filtering smoothing method is performed to obtain the higher
matching precision. The potential of this averaging method is shown in the experimental results of reticle images in low-level-light weapon sight based on impact condition.