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Tang Y.,Xian University of Science and Technology | Tang Y.,York University | Cao X.,Xian University of Science and Technology | Liu H.,Polytechnic University of Mozambique | And 6 more authors.
Applied Optics | Year: 2012

In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 104-10-2 lx, the corresponding electron count is 1.57 × 105 - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2 × 105 lx. The clear details of presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement. © 2012 Optical Society of America. Source

Li Y.,Beijing Institute of Technology | Li Y.,Light Technology | Li Y.,North Night Vision Technology Corporation Ltd. | Chen X.,Beijing Institute of Technology | Ni G.,Beijing Institute of Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

The Microchannel plate (MCP) is the main noise source of low-level light (LLL) image intensifier. Material and the whole manufacturing process of MCP have great impact on the noises of MCP. In this paper, based on the physical mechanisms of MCP, noises of MCP are classified scientifically. By using the data obtained from the actual production and the process test, the regression equation of the noise figure of MCP is derived, and the theoretical model of MCP noise figure is established, including the background noise figure model caused by the dark current of the MCP primarily about the time of the alkali corrosion technic, the ion feedback induced noise figure model caused by the patterns of the MCP channel wall primarily about the time and temperature of the hydrogen reduction technic, and the electronic scattering noise figure model caused by the open area ratio of the MCP primarily about the time of the alkali corrosion technic. Guided by the theoretical model of noise figure, the methods of suppressing noises of MCP are obtained and the technics are optimized. Taking advantage of the new techniques, the noise figure of the third generation MCP has been reduced to below 1.8. © 2013 Copyright SPIE. Source

Tang Y.,Xian University of Science and Technology | Zhang R.,Xian University of Science and Technology | Gao H.,Xian University of Science and Technology | Liu K.,Xian University of Science and Technology | And 7 more authors.
Optics Express | Year: 2010

A partially lighbcontrolled imaging system is proposed as a novel device. It is used to improve the imaging quality at the illumination of 1979 × 105lx by means of mitigating image contrast. It consists of a High Temperature Poly-Silicon Thin Film Transistor-Liquid Crystal Display (HTPS TFT-LCD), which is set between the lens and CCD and is coupled with CCD by the optical fiber taper. The transmittance of pixelated LCD can be controlled by Field-Programmable Gate Array to realize the partially light-controlled and thus dynamic range of the imaging system can be extended. Samples of indoor objects and outdoor license plate are photographed by the prototype imaging system under strong light. The imaging results of this novel system are satisfactory with better restored details, compared with the photos taken by normal CCD camera (WAT231S2) which uses aperture and shutter to control the overall light intensity. ©2010 Optical Society of America. Source

Tian Y.,Tsinghua University | Yang Y.-G.,Tsinghua University | Pan J.-S.,North Night Vision Technology Corporation Ltd. | Li Y.-L.,Tsinghua University | Li Y.-J.,Tsinghua University
Chinese Physics C | Year: 2014

An event-counting thermal neutron imaging detector based on 3 mol % natGd2O3-doped micro-channel plate (MCP) has been developed and tested. A thermal neutron imaging experiment was carried out with a low flux neutron beam. Detection efficiency of 33% was achieved with only one doped MCP. The spatial resolution of 72 μm RMS is currently limited by the readout anode. A detector with larger area and improved readout method is now being developed. © 2014 Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd. Source

Li X.-F.,1The Key Laboratory on Night Vision Technology | Li X.-F.,North Night Vision Technology Corporation Ltd.
Guangzi Xuebao/Acta Photonica Sinica | Year: 2013

Multi-alkali photocathode in super generation image intensifier is different from previous multi-alkali photocathode between the production processes, so the photoelectric emission characteristics are different from previous multi-alkali photocathode. In this paper, through the measurement of multi-alkali photocathode spectral reflectivity and transmissivity, according to the law of conservation of energy, cathode spectral absorption rate was obtained. Spectral absorption rate indicates that, only when the photon energy greater than 1.333 eV, cathode absorption rates began to increase quickly. The cathode spectral absorption shows that cathode will not absorb any photons if light incident photon energy is less than the absorption limit, i.e. 933 nm wave absorption limit. In the cathode surface electron affinity further reduced circumstances, cathode photoemission long wave theory threshold is determined by long-wave absorption limit. In the electronic transition process after absorption of a photon, transition energies increase less than the absorption of the incident photon energy, i.e. the presence of an "energy loss". The higher energy of a photon is, the higher electronic transition energy level is, the more energy loss is. At the same time, the higher energy of a photon is; the higher-energy level transition electron, the lower electronic transition probability is. Photocathode quantum efficiency is determined by the absorption rate, the transition probability and transition level, energy loss of diffusion process and other factors, thus photocathode quantum efficiency is in the presence of long wave threshold and shortwave threshold also. Photocathode quantum efficiency in 587 nm reaches the maximum value, after that decreases with the photon energy increases, when 3.6 eV, the quantum efficiency is reduced to zero. Cathode in photon energy of 3.6 eV the absorption coefficient is still high, but due to the electronic transition probability is low, while the electron diffusion process of energy loss is big, thus in spite of cathode on lower wavelength has high absorption coefficient, but the quantum efficiency is still low. Therefore on shortwave, cathode absorbed shortwave photon energy is converted into a photoconductive, lattice vibration and other forms of energy; the photoelectric emission utilization rate is very low. Source

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