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本文从理论上探讨了成象系统的点扩散函数(PSF)和电子光学调制传递函数(MTF)的研究。由一阶横向象差公式出发求成象系统的全MTF通常有两种方法:一是将单色PSF对有贡献的电子做能量的概率统计,得全色PSF,由此进行富里叶—贝塞尔变换,得全色MTF(记为MTF_1);二是对单色PSF直接进行富里叶—贝塞尔变换,得单色MTF;再将它对初能分布求概率统计平均值,得全色MTF(记为MTF_2)。但是,两种方法求MTF的一致性并没有得到充分的证明。本文由近贴聚焦系统和锐聚焦系统的一阶横向象差公式出发,在(r,ξ,a)和(r,ξ,v_r)两套座标系中建立象差半径的三维曲面图,用形象的手段讨论阴极透镜的PSF和MTF。
In this paper, we study the point spread function (PSF) and electron optical modulation transfer function (MTF) of imaging system theoretically. From the first-order transverse aberration formula to find the imaging system for the full MTF there are usually two ways: First, the contribution of monochromatic PSF to the contribution of electrons to do the probability of energy statistics, were panchromatic PSF, which make Fourier- Searl transform, the panchromatic MTF (MTF_1); the second is the direct monochrome PSF Fourier-Bessel transform monochromatic MTF; and then calculate the probability distribution of its primary distribution average, the whole Color MTF (denoted as MTF_2). However, the consistency of the two methods for MTF has not been fully proved. Based on the first-order transverse aberration formula of near focus focusing system and sharp focusing focusing system, a three-dimensional surface map of aberration radius is established in two sets of coordinate systems (r, ξ, a) and (r, ξ and v_r) Image Discussion of PSF and MTF of Cathode Lens.