The Research Of Methods To Reconstruct The Digital Hologram With Computer

Digital holography is an active research topic. It substitutes numerical reconstruction for optical method to reconstruct object wave fields by computer. Numerical reconstruction overcomes the shortcoming of optical method and helps to store and process images digitally. Moreover, It makes the application of digital holography wider.In the thesis, the theorical background and methods of numerical reconstruction are introduced, the theorical background for numerical reconstruction in digital holography is scalar diffraction theory. Similar to holography, the technology of numerical reconstruction also has two steps: recording and reconstruction. It records object wave field by interference theory, But it is different in recording media from holography. After recording digital hologram with charge-coupled device (CCD),We can reconstruct the real image of the object from it by means of numerical method. It is shown that the intensity as well as the phase can be calculated from the digital sampled hologram. The thesis also explores the application of numerical reconstruction in the process of double-exposure holography.After analyzing the experiment, the author completes designing the experiment in which the Fresnel hologram is recorded with CCD. How to realize the technology with program is the focus of the research. The program is developed by Visual C++. C plus plus language has the powerful function in pointer and array and object-oriented programming (OOP) technology which are in favor of programming. Encapsulating attributes and methods as a bitmap class facilitates digital processing of the bitmap. The crux of the program is Fresnel transformation in which an inverse discrete Fourier transformation is involved. In the calculation of the transformation, the standard algorithms for fast Fourier transformation (FFT) can be applied to enhance the efficiency of the program.The image of the object is successfully reconstructed from hologram with the program. Moreover, the author proves that the image can be reconstructed from every part of a hologram.The major drawback of the method is the low spatial resolution of CCD arrays, because of which, the angle between the reference and the object waves must be limited to a few degrees. Furthermore, the dynamic range of the numerical method is not so high as that of optical reconstruction. It is expectedthat in the future CCD chips with higher resolutions will be available so that the angle between the interfering waves can be enlarged and digital holography is applied widely.