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全息术能够还原观察物体的三维立体图象,在全息思想的启发指导下,Mollenstedt等在透射电镜中利用二次曝光拍摄电子全息图,但所作为同轴全息,虚实象重合难以分辨(1—2)。Tonomura等采用单晶作为分束板进行电子全息,结果在记录介质中包含了单晶的内部信息(3—4)。Bates等人利用某衍射束作“参考光束’来获取电子全息,此时衍射束并不为简单调制波,而是包括了样品的全部信息,不能起到真正的参考束作用,且衍射束,透射束强弱相差太大,难于拍摄优质全息图象(5—6)。鉴于上述电子全息工作中所存在的原理性缺陷,本文提出采用静电透射棱镜,在电子束入射样品前分束来实现离轴电子全息对材料学的研究具有重要的现实意义。根据全息学原理,全息过程中波前再现的放大率为:
Holography can restore the observation of three-dimensional images of objects, under the guidance of the holographic thought inspired by Mollenstedt et al in the transmission electron microscopy of the use of double exposure of the electronic hologram, but as a co-holographic, virtual reality is difficult to distinguish (1- 2). Tonomura et al. Used single crystal as the electron beam holdup. As a result, the single crystal internal information (3-4) was included in the recording medium. Bates et al. Use a diffracted beam as the “reference beam” to acquire the electron hologram. In this case, the diffracted beam is not a simple modulation wave, but includes all the information of the sample and can not serve as a real reference beam. The diffraction beam, In view of the above principle of electronic holography defects exist, this paper proposed the use of electrostatic transmission prism, beam splitting to achieve the sample before the electron beam incident The research on the material science of off-axis electronic holography has important practical significance.According to the principle of holography, the magnification of wavefront reproduction in holographic process is: