The resolution characteristic can be obtained by the modulation transfer function （MTF） of a GaAs/GaA1As photocathode. After establishing the theoretical model of GaAs（100）-oriented atomic configuration and the fo...The resolution characteristic can be obtained by the modulation transfer function （MTF） of a GaAs/GaA1As photocathode. After establishing the theoretical model of GaAs（100）-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers, this paper calculates the trajectories of photoelectrons in a photocathode. Thus the distribution of photoelectron spots on the emit-face is obtained, which is namely the point spread function. The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function. The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length, and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration. Furthermore, the resolution is enhanced considerably by increasing the active-layer thickness, especially at high spatial frequencies. The best spatial resolution is 860 lp/mm, for the GaAs photocathode of doping concentration 1 ×10^19 cm 3 electron diffusion length 3.6 μm and the active-layer thickness 2 μm, under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode＇s resolution for preparing a high performance GaAs photocathode, and improve the resolution of a low light level image intensifier.展开更多
The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation ...The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation transfer function (MTF) were presented. The factors that influence the spatial resolution were also discussed. The results of the simulation showed that the intrinsic spatial resolution was consistent with the size of the physical pixels and a few centimeters spatial resolution could be obtained under certain circumstances.展开更多
遥感图像在成像过程中受到大气、光学系统、探测器、平台运动和电路等因素的影响,引起图像退化,图像复原算法可以改善遥感图像像质,提高图像信息的解译能力。文章介绍了调制传递函数补偿(modulation transfer function compensation,MT...遥感图像在成像过程中受到大气、光学系统、探测器、平台运动和电路等因素的影响,引起图像退化,图像复原算法可以改善遥感图像像质,提高图像信息的解译能力。文章介绍了调制传递函数补偿(modulation transfer function compensation,MTFC)算法的原理,从遥感成像的链路环节出发,分析了MTFC的原理,提出了一种星上实时遥感图像MTFC复原算法。通过卷积系数和抑噪参数的优化设计,在提高图像清晰度的同时能较好地抑制噪声;对不同卷积和抑噪参数的图像复原效果进行了对比,从主观和客观两个方面对复原图像进行了评价。实验结果表明,该算法能有效提高图像像质,增强图像的高频部分,采用不同类型的卫星遥感图像验证了算法的适应性。展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 60678043)the Research and Innovation Plan for Graduate Students of Jiangsu Higher Education Institutions,China (Grant No. CX09B 096Z)
文摘The resolution characteristic can be obtained by the modulation transfer function （MTF） of a GaAs/GaA1As photocathode. After establishing the theoretical model of GaAs（100）-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers, this paper calculates the trajectories of photoelectrons in a photocathode. Thus the distribution of photoelectron spots on the emit-face is obtained, which is namely the point spread function. The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function. The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length, and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration. Furthermore, the resolution is enhanced considerably by increasing the active-layer thickness, especially at high spatial frequencies. The best spatial resolution is 860 lp/mm, for the GaAs photocathode of doping concentration 1 ×10^19 cm 3 electron diffusion length 3.6 μm and the active-layer thickness 2 μm, under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode＇s resolution for preparing a high performance GaAs photocathode, and improve the resolution of a low light level image intensifier.
基金Supported by Natural Science Foundation of China (No.60602065)Innovation Funds of USTC for Graduate Student (No.KD2006009)
文摘The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation transfer function (MTF) were presented. The factors that influence the spatial resolution were also discussed. The results of the simulation showed that the intrinsic spatial resolution was consistent with the size of the physical pixels and a few centimeters spatial resolution could be obtained under certain circumstances.
文摘遥感图像在成像过程中受到大气、光学系统、探测器、平台运动和电路等因素的影响,引起图像退化,图像复原算法可以改善遥感图像像质,提高图像信息的解译能力。文章介绍了调制传递函数补偿(modulation transfer function compensation,MTFC)算法的原理,从遥感成像的链路环节出发,分析了MTFC的原理,提出了一种星上实时遥感图像MTFC复原算法。通过卷积系数和抑噪参数的优化设计,在提高图像清晰度的同时能较好地抑制噪声;对不同卷积和抑噪参数的图像复原效果进行了对比,从主观和客观两个方面对复原图像进行了评价。实验结果表明,该算法能有效提高图像像质,增强图像的高频部分,采用不同类型的卫星遥感图像验证了算法的适应性。
