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Xu G.,State Key Laboratory of Transient Optics and Photonics | Xu G.,University of Chinese Academy of Sciences | Liu B.,State Key Laboratory of Transient Optics and Photonics | Liu B.,CAS Xi'an Institute of Optics and Precision Mechanic | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

In order to improve the dynamic range and the signal-noise ratio of the image intensifier, keep the flux of the screen of image intensifier constant. In the article, introduced a design of the switching power supply and tested its performance. Firstly, used a sampling amplifier amplify the feedback current signals. The feedback signals were converted into square wave signals through a digital circuit. Then, using the MOSFET in the post stage circuit produced high voltage and high speed adjustable square pulses. The frequency of the pulse is 1 kHz, the speed of the cutting edge is 20ns and the amplitude is 200V. The photoelectron emission time of the photocathode is short when the width of the high speed pulse is narrow for strong illumination. On the contrary, the time is long when the width is wide for weak illumination. The number of photoelectron is a constant no matter what kind of the illumination. It keeps the flux reaching the phosphor screen constant. © 2017 SPIE.


Ji R.,Xiamen University | Gao Y.,Tsinghua University | Liu W.,IBM | Xie X.,Microsoft | And 2 more authors.
ACM Transactions on Intelligent Systems and Technology | Year: 2015

Coming with the popularity of multimedia sharing platforms such as Facebook and Flickr, recent years have witnessed an explosive growth of geographical tags on social multimedia content. This trend enables a wide variety of emerging applications, for example, mobile location search, landmark recognition, scene reconstruction, and touristic recommendation, which range from purely research prototype to commercial systems. In this article, we give a comprehensive survey on these applications, covering recent advances in recognition and mining of geographical-aware social multimedia. We review related work in the past decade regarding to location recognition, scene summarization, tourism suggestion, 3D building modeling, mobile visual search and city navigation. At the end, we further discuss potential challenges, future topics, as well as open issues related to geo-social multimedia computing, recognition, mining, and analytics. © 2015 ACM.


Wu Y.,Nanjing University of Aeronautics and Astronautics | Wu Y.,State Key Laboratory of Transient Optics and Photonics | Yin J.,Nanjing University of Aeronautics and Astronautics | Zhu L.,Nanjing University of Aeronautics and Astronautics | Ye Z.,Nanjing University of Aeronautics and Astronautics
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2014

Reconstructed image of digital holography has problems such as serious interference of speckle noise, low contrast and so on. Thus a method based on speckle reducing anisotropic diffusion (SRAD) model and nonsubsampled contourlet transform (NSCT) is proposed for improving reconstructed image quality of digital hologram. SRAD model is adopted to eliminate speckle noise of reconstructed image. After NSCT decomposition, a low-frequency sub-band and several high-frequency sub-bands are produced. Low-frequency sub-band coefficients are adjusted based on a nonlinear gain function and an image segmentation method. In high-frequency sub-bands, edges are enhanced using a NSCT modulus maximum edge detection method. A large number of experimental results show that, compared with nonlinear diffusion denoising methods and NSCT enhancement methods proposed recently, the proposed method can more effectively eliminate speckle noise and improve the contrast of reconstructed image. Furthermore, the edges are smooth and clear. As a result, the accuracy of recognition and measurement in digital holography can be improved.


Tang W.,State Key Laboratory of Transient Optics and Photonics | Tang W.,University of Chinese Academy of Sciences | Yang W.,CAS Xi'an Institute of Optics and Precision Mechanic | Yang Y.,State Key Laboratory of Transient Optics and Photonics | And 4 more authors.
Materials Science in Semiconductor Processing | Year: 2014

A novel concept for solar electricity generation named photon-enhanced thermionic emission (PETE) was recently proposed for harvesting solar photonic and thermionic energies simultaneously. Comparative investigations showed that the conversion efficiency of PETE can theoretically exceed 40%. In this paper, an electric field-assisted PETE experiment was carried out to demonstrate the possibility of using GaAs epitaxial films in PETE solar devices. The solar photonic and thermionic effects were simulated by a red light-emitting diode array and a heat resistor, respectively. Surface electron affinity was decreased by an electric field instead of Cs/Cs-O coating. The experimental results agreed with calculated values, and a distinct enhancement was observed in the thermionic emission produced by photoexcitation compared with thermionic field emission produced by an illuminated sample and the sample emission obtained in the dark. © 2013 Elsevier Ltd.


Chen L.,Nanjing University of Aeronautics and Astronautics | Chen L.,China Jiliang University | Wang J.,Nanjing University of Aeronautics and Astronautics | Wang J.,State Key Laboratory of Transient Optics and Photonics | And 4 more authors.
Journal of Modern Optics | Year: 2013

An optical system is proposed for the controlled focus shaping of generalized cylindrical vector beams by a high-numerical-aperture lens. A segmented electro-optical filter with four concentric belts is introduced and works with a double-λ/2-plate. By controlling the rotational angle of the plate and the voltage applied to the filter with proper azimuth angle, a three-dimensional engineered focusing field, such as an electrically controlled axial-shifted focus, extended depth of focus, and a diffraction-limited optical tube, can be achieved. The main advantage of this focusing system is that the focused field can be adjusted and formed by the applied voltage and the rotational angle of the half-wave plates. It can provide a new focus shaping technique with free adjustability and flexibility. © 2013 Taylor and Francis Group, LLC.


Wu Y.,Nanjing University of Aeronautics and Astronautics | Wu Y.,State Key Laboratory of Transient Optics and Photonics | Yin J.,Nanjing University of Aeronautics and Astronautics
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2013

Aiming at the problem of low contrast, blurred edges and textures, and speckle noise of reconstructed image in digital holography, an adaptive enhancement method for reconstructed image of digital holography in contourlet domain based on uniform searching particle swarm optimization is proposed. Median filtering algorithm is used to suppress speckle noise of the reconstructed image. After the contourlet decomposition, edge enhancement is performed for the band-pass directional subbands by a nonlinear gain function. While the coefficients of low-pass subbands are adjusted by the gain function based on a gray-scale transform and the local mean. The gray-scale transform aims to expand the dark areas of digital holographic image. The undetermined parameters are found by uniform searching particle swarm optimization. The fitness function takes into account the contrast, definition and peak signal-to-noise ratio of image. A large number of experimental results show that, compared with three existing enhancement methods, the proposed method can more effectively improve the contrast and definition of reconstructed image in digital holography, highlight edges and textures, and suppress speckle noise. As a result, the measurement accuracy of digital holography can be improved.


Wu Y.,Nanjing University of Aeronautics and Astronautics | Wu Y.,State Key Laboratory of Transient Optics and Photonics | Ye Z.,Nanjing University of Aeronautics and Astronautics | Wan H.,Nanjing University of Aeronautics and Astronautics
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2013

In order to suppress the speckle noise of reconstructed image in digital holography effectively and to further improve the quality of reconstructed image, a speckle noise suppression method of reconstructed image in digital holography based on dual-tree complex wavelet transform (DT-CWT) and anisotropic diffusion is proposed. The reconstructed image is decomposed through DT-CWT. Then, the low-frequency components and the high-frequency components in six directions are processed through P_Laplace diffusion and Laplacian pyramid-based nonlinear diffusion (LPND), respectively. The new reconstructed image is synthesized through inverse dual-tree complex wavelet transform (IDT-CWT). The experimental results are given, and a subjective visual comparison is made with the method of wavelet threshold shrinkage and total variation (TV) diffusion, the method of LPND, and the method combining contourlet transform with TV and adaptive contrast diffusion. While the results are evaluated quantitatively according to peak signal to noise ratio (PSNR), correlation coefficient (COR) and running time. Experimental results show that the proposed method has a better performance in speckle noise suppression and preserves the detail and textural features of original reconstructed image more efficiently.


Tang W.,State Key Laboratory of Transient Optics and Photonics | Yang W.,Chinese Academy of Sciences | Cai Z.,State Key Laboratory of Transient Optics and Photonics | Sun C.,Chinese Academy of Sciences
Advanced Materials Research | Year: 2012

An exponential doping NEA InGaAs photocathode is theoretically proposed to apply in the near infrared streak camera. The photocathode time response is calculated and analyzed by using a photoelectron non-steady method. The numerical results show that the excited electrons in the InGaAs active layer is accelerated due to the built-in electric field induced by the exponential doping structure, which shortens the transport time of minority carriers in the photocathode and thus, the time response is greatly improved. In addition, the exponential doping InGaAs photocathode possesses time response of less than 10 picoseconds and near-infrared quantum efficiency of 10%.


Zhao H.,CAS Xi'an Institute of Optics and Precision Mechanic | Zhao H.,State Key Laboratory of Transient Optics and Photonics | Li Y.,CAS Xi'an Institute of Optics and Precision Mechanic
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

In this paper, an extended cubic phase mask used to realize wave-front coding technique is derived in frequency domain. Then by splitting and re-combining the terms of the phase function, a new mask containing two conjugate cubic terms is generated and can be physically realized by shifting and superposing two cubic phase mask having relative displacement with respect to the center of the pupil plane. Simulation results indicate that this phase mask has the capability of changing the system effective bandwidth while maintaining the defocus invariance characteristic. The work reported can be extended to other phase masks and could be considered to be complementary to the existing researches. © 2012 SPIE.


Zhang Y.F.,Nanjing University of Aeronautics and Astronautics | Wu Y.Q.,State Key Laboratory of Transient Optics and Photonics
Advanced Materials Research | Year: 2013

In the reconstruction process of digital holograph, zero-order image has a bad impact on the quality of real image. In this paper, a new way to eliminate zero-order image in digital holography is proposed. Firstly, digital holography image is decomposed by contourlet transform, then remove the low frequency. The new digital holography image is obtained by inverse contourlet transform. Experiments show that, compared with spatial filtering, frequency domain filtering, laplacian filtering and eliminate zero-order image method based on wavelet, the new method proposed in this paper can eliminate zero-order image better, what's more, the real image is also strengthened in some way. © (2013) Trans Tech Publications, Switzerland.

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