As the photoelectric conversion material, semiconductor photocathode plays an important role in the development of vacuum photodetectors and electron sources, and the efficiency and stability of electron emission have always been the focus in photocathode applications. Photocathode is based on the external photoelectric effect. Different from the internal photoelectric effect, photoelectrons generated by light excitation inside the cathode must overcome the surface barrier to escape into the vacuum, so the level of the photoemission ability is closely related to the surface properties. The preparation process usually includes surface cleaning and activation, wherein the activation process under the ultrahigh vacuum condition is regarded as an irreversible and evolutionary process over time. How to characterize the cathode surface in situ is particularly important for understanding the mechanism of photoemission generation and degradation. Nowadays, the surface characterization methods including photoelectron spectroscopy, synchrotron x-ray characterization, electron diffraction, scanning probe microscopy, spectral response measurement, and photoreflectance spectroscopy are utilized as assisted evaluation tools to prepare photocathodes. Here, we present a newly developed integrated ultrahigh vacuum facility for photocathode preparation and in-situ characterization. With this system, the surface cleaning, activation and degradation processes for semiconductor photocathodes were effectively characterized by photoelectron spectroscopy and spectral measurement. The integrated photocathode preparation and characterization system can realize in-situ multi-information characterization in ultra-high vacuum environment, and the element composition and chemical state analysis of the specified region can be realized by using X-ray secondary electron image and micro-area analysis function, which is helpful to optimize the preparation process of photocathodes.
This paper proposes a method of infrared moving target detection and its azimuth information display based on background difference. First of all, in view of the shortcomings of the current VIBE (Visual Background Extractor) algorithm, we propose a moving target detection algorithm based on the improved visual background extraction. This improved algorithm makes full use of the temporal and spatial domain information of the image, which can not only adapt to different detection environment, but also effectively eliminate ghosting to have better detection results for small targets. Then, we design an infrared video moving target detection system based on FPGA, including three modules, namely target detection module, GPS (Global Position System) information extraction module and character superimposing module. Furthermore, the system has the function of target extraction and azimuth information display. Compared to the traditional two-dimensional(2D) infrared moving target detection, this method superimposes GPS data onto 2D image information to facilitate real-time detection so that the moving state of the target can be understood more comprehensively, which has wide application value in the sea, land and air moving target detection and location.
We numerically studied the effect of the geometric structure and Al component on the optical capture performance of gradient Al component AlxGa1 − xN photocathodes. The effects of geometric parameters, such as base radius (R), wire-to-wire spacing, cone rate, and angle of incident light, on the optical response were systematically studied based on the finite element method. In the radial direction, we study the optical response of rectangular periodic structure and hexagonal periodic structure. Simulation results show that pencil nanostructure can achieve omnidirectional and broadband light absorption of AlxGa1 − xN nanowires with hexagonal periodic structure. In addition, we used the Spicer three-step emission model to establish the photoemission efficiency of the AlxGa1 − xN nanostructure. As a result, the photocathode achieves optimal quantum efficiency when the Al component is in the range of 0 to 0.75 and sublayer thickness of 240, 180, 120, and 60 nm.
We numerically analyzed the influence of geometric structures of gradient Al component AlxGa1 − xN nanowire on their light-trapping properties, ranging from nanopillars, inverted conical frustums, to inverted hexagonal frustums. COMSOL® Multiphysics package based on the finite element method is used to systematically study the effects of geometric parameters such as base radii (R), pillar height (H), period (P), and angle of incident light on the optical absorption. The simulation results show that compared with the other nanostructure counterparts, the inverted hexagonal frustum can effectively couple photons into the nanoarrays to achieve wide spectrum and effective optical absorption for AlxGa1 − xN nanowire-based UV photocathode. The inverted hexagon frustum with optimum height can obtain an optical absorption above 95% over a wide wavelength of 200 to 380 nm and a broad angle of incident light between 0 deg and 70 deg. All these findings not only show that the gradient Al component AlxGa1 − xN material has a great potential advantage for the UV photocathode, but it also provides an efficient broadband and omni-directional light trappers for the UV photocathode.
The simulation models of gallium nitride (GaN) nanostructure arrays are designed by COMSOL Multiphysics software package based on finite element method (FEM). The effects of changes of GaN nanowires in axial geometry on photoelectron concentration distributions performance are analyzed. And the absorptivity differences of nanorods, truncated-cones and inverted-pencil structures in ultraviolet band are studied. Analysis of simulation results pointed out that both truncated-corn arrays and inverted-pencil arrays have the ability of boosting light absorption compared to nanorod arrays. Thus, such positive conclusion of the axial structure changed GaN nanowires would offer new references for the photoemission layer design of the photocathode.
This paper investigates the formation energy, atomic structure, electronic structure and optical properties of native point defects on n-GaN (0001) surface based on the first-principles of the density functional theory. The results find that the 𝑉𝑁 is not easy to exist and the 𝑉𝐺𝑎, 𝑁𝐺𝑎 or 𝑁𝑖 defects are most likely to appear on the n-type GaN surface. The substitutional defect 𝑁𝐺𝑎 , the interstitial defect 𝑁𝑖 and the single Ga vacancy cause the conduction band to drop and the Fermi level to enter the conduction band in a deeper extent. However, both the valence band and the conduction band move up at the same time with the increase of Ga vacancies, exhibiting p-type characteristics and reducing the n-type conductivity of the surface. The N-vacancy makes the conduction band shift upwards, which reduces the n-type metal conductivity. It is also found that the reduction of photon adsorption on the surface affects the photo-emission of the surface, which is detrimental to the optoelectronic devices with n-GaN and metal contacts. This study shows that 𝑉𝐺𝑎, 𝑁𝐺𝑎 and 𝑁𝑖 native point defects all increase the doping difficulty of n-type GaN films and have a certain value for the fabrication of high-performance optoelectronic devices with n-GaN and metal contacts.
In this paper, a 532nm laser polarization underwater target detection information processing system is designed. Firstly, combined with GPS detection, the polarization characteristic data and location information of the underwater target are obtained by laser polarization technique. Then the polarization characteristic database is established on the basis of existing polarization characteristic data. Analyze and compare the measured polarization data with the existing polarization characteristic data so as to quickly complete the target identification and classification. Finally, use the acquired location and classification information to reconstruct three-dimensional model of the measured terrain and restore underwater scene vividly. The research of this subject is of great significance for the marine resources development, underwater engineering monitoring, submarine environmental monitoring and so on.
Based on the first principles calculation, this paper systematically studies the adsorption of three gases on the wurtzite GaAs nanowires (100) surface. Compared with CH4 and H2, the surface absorbed with H2O has the lowest adsorption energy, thus it is the easiest to adsorb on the surface. The gas adsorption will result in the increase of band gaps, work functions and surface electron affinity, especially H2O adsorption system with the largest band gap of 1.34eV. The adsorption of these gases produces a dipole moment pointing from the GaAs nanowires to the residual gas molecules. For H2O molecular adsorption, which impedes the electron emission and decrease electrons emission capacity. The surface structures also reconstruct with different degrees. The residual gas adsorption can greatly affect the optical properties of the surface and undermine the performance of GaAs nanowire, particularly H2O adsorption. This work can help to understand the fading mechanism of the performance of optoelectronic devices based on GaAs nanowires.
In this paper, a novel target detection and tracking algorithm based on visual attention is proposed. Firstly, the algorithm extracts saliency map of the first frame by improved visual attention algorithm, then detects targets which moving very slowly or even close to stationary after eliminating the interference of background factors. Secondly, it makes the mean shift algorithm’s kernel fixed bandwidth to be a dynamically changing bandwidth, so it not only retains the feature of traditional mean shift algorithm and can accomplish real-time tracking, but also can reduce background interference. Thirdly, the target model is established based on the saliency map, so the model is described by a variety of features. Therefore, when the target’s single feature changes, as size or shape, it still can detect the target. Lastly, it uses the modified meanshift algorithm to track moving targets, which can reduce the probability of losing target. Experimental results show that this algorithm is applicable to image sequences of both infrared and visible light, and it has good tracking performance. What’s more, the algorithm provides the motion information of the moving targets, so it gives a possibility for accurate positioning.
The detection of foreign substances in transparent-bottled liquid is a key procedure in production. An improved algorithm based on the combination of guided filter and visual background extractor (ViBe) is proposed for the detection of foreign substances in transparent-bottled turbid liquid on the market. In the stage of image preprocessing, the image enhancement is carried out by the guided filter and then the liquid region is detected by the Hough transform. Finally, the area of the connected region is determined for the image processed by the ViBe algorithm to remove the tiny noise in detection images. The simulation results show that the proposed algorithm can not only detect foreign substances in transparent liquid but also detect foreign substances in the turbid liquid.
Accurate and fast detection of infrared (IR) dim target has very important meaning for infrared precise guidance, early warning, video surveillance, etc. In this paper, some basic principles and the implementing flow charts of a series of algorithms for target detection are described. These algorithms are traditional two-frame difference method, improved three-frame difference method, background estimate and frame difference fusion method, and building background with neighborhood mean method. On the foundation of above works, an infrared target detection software platform which is developed by OpenCV and MFC is introduced. Three kinds of tracking algorithms are integrated in this software. In order to explain the software clearly, the framework and the function are described in this paper. At last, the experiments are performed for some real-life IR images. The whole algorithm implementing processes and results are analyzed, and those algorithms for detection targets are evaluated from the two aspects of subjective and objective. The results prove that the proposed method has satisfying detection effectiveness and robustness. Meanwhile, it has high detection efficiency and can be used for real-time detection.
Accurate and fast detection of infrared (IR) dim target has very important meaning for infrared precise guidance, early
warning, video surveillance, etc. In this paper, some basic principles and the implementing flow charts of a series of
algorithms for target detection are described. These algorithms are traditional two-frame difference method, improved
three-frame difference method, background estimate and frame difference fusion method, and building background with
neighborhood mean method. On the foundation of above works, an infrared target detection software platform which is
developed by OpenCV and MFC is introduced. Three kinds of tracking algorithms are integrated in this software. In
order to explain the software clearly, the framework and the function are described in this paper. At last, the experiments
are performed for some real-life IR images. The whole algorithm implementing processes and results are analyzed, and
those algorithms for detection targets are evaluated from the two aspects of subjective and objective. The results prove
that the proposed method has satisfying detection effectiveness and robustness. Meanwhile, it has high detection
efficiency and can be used for real-time detection.
KEYWORDS: Detection and tracking algorithms, Video, Infrared radiation, Filtering (signal processing), Infrared search and track, Infrared imaging, Video processing, Infrared technology, Software development, Microsoft Foundation Class Library
In this paper, some basic principles and the implementing flow charts of a series of algorithms for target tracking are
described. On the foundation of above works, a moving target tracking software base on the OpenCV is developed by the
software developing platform MFC. Three kinds of tracking algorithms are integrated in this software. These two
tracking algorithms are Kalman Filter tracking method and Camshift tracking method. In order to explain the software
clearly, the framework and the function are described in this paper. At last, the implementing processes and results are
analyzed, and those algorithms for tracking targets are evaluated from the two aspects of subjective and objective. This
paper is very significant in the application of the infrared target tracking technology.
This paper describes an infrared network video monitoring system based on Linux OS. Firstly, we design the hardware
system that we needed. Secondly, the software platform is introduced in this paper. The Linux operate system is applied
in our software solution. Finally, the application software design process is introduced in the paper. The system can be
used to encode the picture captured from infrared CCD, and then send the picture to another same embedded system to
decode the picture, and finally display it on the LCD and achieve the goal of the infrared video's remote monitoring. As
the infrared CCD would not be affect by the dim light, this monitoring system could be used all day long.
This paper describes the way to design an embedded network infrared video monitoring system based on Linux OS.
Firstly, we make a comparison of the hardware solution between some regular monitoring systems, and then design the
hardware system that we needed. Our hardware system uses the i.mx27 processor with the ARM9 core. Secondly, the
software platform is introduced in this paper. The Linux operate system is applied in our software solution. According to
the characteristic of Linux OS, we download uboot to the demo board, transplant the Linux kernel and jffs2 file system to
the embedded system, and briefly compile and download drivers. Finally, the application software design process is
introduced in the paper. The system can be used to encode the picture captured from infrared CCD, and then send the
picture to another same embedded system to decode the picture, and finally display it on the LCD and achieve the goal of
the infrared video's remote monitoring. As the infrared CCD would not be affect by the dim light, this monitoring system
could be used all day long.
The micro-channel plate (MCP) is an important part to imaging quality of image intensifier. In order to obtained high
quality of optoelectronic image devices, the microchannel plate (MCP) should be evaluated before assembled in the
devices. A new method for noise power factor determination of MCP is described in this paper. The measurements are in
accordance with theory and experiments reported. The system consists of vacuum chamber, electron gun, high voltage
supply, imaging luminance meter, control units, signal processing circuit, A/D converter, D/A converter, communication
unit, industrial computer and measurement software.
In this paper, some basic principles and the implementing flow charts of a series of algorithms for target detecting are
described. Then, according to actual needs and the comparison results of those algorithms, some of them are optimized
in combination with the image pre-processing. On the foundation of above works, a moving target detecting and tracking
software base on the OpenCV is developed by the software developing platform MFC. Three kinds of detecting
algorithms are integrated in this software. These three detecting algorithms are Frame Difference method, Background
Estimation method and Mixture Gaussian Modeling method. In order to explain the software clearly, the framework and
the function are described in this paper. At last, the implementing processes and results are analyzed, and those
algorithms for detecting targets are evaluated from the two aspects of subjective and objective. This paper is very
significant in the application of the infrared target detecting technology.
According to the response of photoelectric device to a light source, the formula of spectral matching factor of low-lightlevel
and infrared fusion optoelectronic detector-object combination is deduced. The spectral matching factors of photo
cathode and infrared detector for green vegetation are calculated and compared. Through the analysis of results it shows that
spectral matching factor has influence on the performance of low light level and infrared fusion night vision system.
This paper details a method for measuring the MTF for optoelectronic detector. A description of a test facility for testing
and evaluating MTF is given. We use a knife-edge target to measure MTF. The Pentium III computer system takes the
charge of controlling and calculating.
LLL night vision system is a sort of the photoelectric imaging system. In this paper, the fundamental theory and
conception about visual simulation software platform Creator-Vega is introduced, which is an applied tool and can
simulate the workflow of the LLL sensor in the night vividly. Combined with using VC functional software, an
application software frame is set up. The interface and functional menus of software are proposed in the paper. The
software can provide the evaluation for design of LLL night vision system. The performance simulation results of
photoelectric imaging device are given.
In this paper, firstly the spectral response of transmission-type GaAs photocathode is measured online by the spectral response-testing instrument. Then the cathode is sealed in the third generation intensifier and put into the instrument again to get another spectral response curve. The variation of spectral response curves was compared. The results show that through the seal process, the spectral response in the long wavelength decrease. Based on these curves, the spectral matching factors of GaAs photocathode for green vegetation and rough concrete are calculated. The calculated performance parameters show that the variation of the spectral response in the seal process is an important influence factor on the performance of the intensifier in the use of night vision.
In this paper, firstly the spectral response of transmission-type GaAs photocathode is measured online by the spectral response-testing instrument. Then the cathode is sealed in the third generation intensifier and put into the instrument again to get another spectral response curve. The variation of spectral response curves was compared. The results show that through the seal process, the spectral response in the long wavelength decrease. Based on these curves, the spectral matching factors of GaAs photocathode for green vegetation and rough concrete are calculated. The calculated performance parameters show that the variation of the spectral response in the seal process is an important influence factor on the performance of the intensifier in the use of night vision.
In this paper, the research intention and design principle of CY-1R night vision helmet are explained which fills
the gaps in active-passive combined night vision field in our country. The structure, composition, mechanism and
overall performance of the goggle are analyzed. It is a new type device consisting of laser illuminator system,
special optical system and high performance low-level-light intensifier. Based on these characteristics, the
sensitivity of the system is high and the image observed is very clear. Taking advantage of it, we can complete the
military operation under any atrocious weather conditions.
According to the spectral response formula of multialkali photocathode, a simulation of spectral response of super S25 and new S25 photocathodes is carried out. Some characteristic parameters are obtained. The internal mechanism of good properities and some technical methods, which could probably be used in production, are discussed through analyzing the results of the simulation, which is referential to the research in the theory and technological process.
Spectral response curves of photoemission materials and spectral matching factors between detectors and reflecting spectrum of scenes are of importance in the study of detectors and imaging devices. For studying the two questions an automatic spectral recording system was developed and the schematic diagram of the system was demonstrated in this paper. A lot of experiments by use of the system were made to obtain spectral response curves and characteristic parameters of multi-alkali and GaAs:Cs-O photocathodes during activation procedure and these experimental results were given. It was found that electron affinity of Na2KSb, Na2KSb+Cs and [Na2KSb+Cs]+Sb+Cs multi-alkali photocathodes were 0.70-0.91eV, 0.35-0.41eV and 0.33eV respectively calculated from threshold wavelength of spectral response curves and quantum yield during preparation. On-line spectral response measurements of GaAs:Cs-O reflection-mode photocathodes during activation process and decay procedure were carried. The prepared GaAs:Cs-O reflection-mode photocathodes which used national p-type GaAs substrate can obtain 1025μA/lm sensitivity.
In this paper, the present status and developing tendency of night vision device of helmet are reviewed. The research intention and design principle of CY-1R night vision goggle are explained which fills the gaps in active-passive combined night vision field in our country. The structure, composition, mechanism and overall performance of the goggle are analyzed. Based on these characteristics, the sensitivity of the system is high and the image observed is very clear. Taking advantage of it, we can complete the military operation under any atrocious weather conditions.
KEYWORDS: Signal to noise ratio, Image intensifiers, Filtering (signal processing), Digital filtering, Optical filters, Signal processing, Interference (communication), Image filtering, Luminescence, Computing systems
A signal-noise ratio (SNR) testset for image intensifiers is reconstructed. The signal processing module, computer module and measurement software of testset are redeveloped. The frequency spectrum measurement of noise of image intensifiers is achieved by integrating fast Fouier transform (FFT) with hardware filter and infinite impulse response digital filter (IIR DF). The improved testset is used to analyze frequency spectra of noise of image intensifiers. The results are given and analyzed. The measurement method of SNR is discussed basing on the obtained frequency spectra of noise.
As compared with III generation intensifiers, IV generations have bigger sensitivity and much broader spectral response for low light level imaging detectors. IV generation intensifier properties are improved for NEA photo-cathode sensitivity and spectral response. In this paper, a new method is introduced to increase NEA photo-cathode sensitivity and expand infrared response. In the method, spectral response of GaAs:Cs-O NEA photo-cathode is controlled with automatic survey instrument of dynamic spectral response on photo-electronic materials. During processing NEA photo-cathode, it is observed that sensitivity rises slowly when photo-cathode is illuminated with incident ambient radiation, and infrared sensitivity begins reduction when photo-cathode is measured with automatic survey instrument. The reduction of infrared sensitivity has influenced on spectral matching factor of photo-cathode-object combination and detecting distance and has resulted in the practical use of low light level night vision instrument. During processing NEA photo-cathode with Cs-O layer, we can keep watching spectral response change with automatic survey instrument: when sensitivity rises slowly as photo-cathode is illuminated with incident ambient radiation and infrared sensitivity reaches a highest peak value, we can achieve optimum GaAs:Cs-O photo-cathode for low light level imaging detectors. We studied the thickness of a layer GaAs:Cs-O photo-cathode with take off X-Ray photo-electron spectroscopy, it is clear that the thickness of Cs-O layer is about 0.7~1.0 nm.
Since influences of each factor on temperature increase can be reflected by heat flow equation, study of it is helpful to optimal design for uncooled infrared focal plane arrays (UIFPA). But presently there is no more particular discussion of heat flow equation and no frank graphs as reference. In this paper particular discussions of influencing factors are given and for the first time 2-D and 3-D graphs are used to frankly show the degree of influences from different angle of view. Schemes on the optimal design of UIFPA are also given. According to graphs the maximum of temperature increase is obtained only when UIFPA is modulated at certain value which is less than cut-off modulation frequency. In 3-D graphs distinct curves are obtained in different range of thermal conductance and heat capacity and the optimal temperature increase value is achieved only when thermal conductance and heat capacity make thermal response time meet optimal condition. Optimal condition and formula can be deduced with given graphs and multifold approaches of optimal design of thermal isolation structure are discussed. It is proved that in optimal condition temperature increase can achieved 10-1 level. It is clear that data provided by 2-D and 3-D graphs is valuable to evaluate optimal range for UIFPA.
It has been known for some time that the technology of the uncooled infrared thermal imaging system could provide a low-cost, compact-structure, low-power consumption thermal imaging device. This paper describes the theoretic limitation modal of the uncooled thermal imager's performance; temperature fluctuation noise limit is explored and presented. NETD affected by the detector structure and the noise is calculated theoretically. The theoretical curves of the relation between NETD and detector temperature, background temperature, thermal conductance and the area of the pixel are presented.
In this paper, the fundamental theory about visual range of LLL imaging system is described. Based on the revised apparent distance detecting equation and combined with the research intention and design principle of night vision goggle, the relation of parameters which have an influence on performances of system are analyzed. The visual range of the goggle under the specific circumstances is estimated, which proves the revised apparent distance detecting equation is effective and the design of the system is feasible.
In this paper, we propose a set of effective algorithms to automatically detect the lung cancer cells in the cytological color image of examines' sputum smears. To increase the stability and efficiency of the detection of the cancer cells, a hierarchical processing architecture is adopted for the segmentation and recognition. For segmentation, RGB space and Lab space are combined to segment cell. By this method, both the nucleus and cytoplasm of cancer cells can be separated from background. Then, the candidate cancer cells are selected using some morphological features of nuclei, the purpose of this step is to pick out most of non cancer cells and leave a few doubtful cells for further verification, therefore improve the efficiency of the whole recognition process. As the last step, all the candidate cell, some statistic parameters in different color space are calculated, which are used as features for recognition. Experiment results are given.
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