The Study Of Digital Holography And Its Application In Particle Field

Digital holography, digital recording of hologram and numerical reconstruction of the wave fields, offers an alternative recording and reconstruction in holography. The hologram generated by object is recorded directly by CCD and stored digitally by computer, and then reconstructed numerically. Combined with the advantages of digital feature of computer and three-dimensional image of holography, digital holography has good prospects in optical metrology and has been widely applied in various fields of science, engineering and biomedicine. Researches on digital holography and its application in particle field are the main purpose and contents of this dissertation. The work as follows, which centers about digital recording and numerical reconstruction and the analysis of reconstructed image, has been done in this dissertation.Using multiplane-model, the study of the off-axis and in-line holographic recording system of 3D object has been done, with plane reference wave, and the mathematic expressions of reconstructed image of 3D object are formulated. Reconstruction algorithms of digital holography are analyzed and experiment results are also given.The concept of "a model of volume digital hologram" is presented, and the mathematic description and the mathematical model of the volume digital hologram are given. The twin-image can be eliminated by numerical reconstruction of the volume digital hologram, and experiments have also been carried out. The theoretical analysis and experimental results show that the method presented in this dissertation to eliminate twin-image is feasible. Holographic diffraction grating of low spatial frequency is employed, and the simple off-axis holographic recording system and the method of eliminating zero-order image are presented, and experiments have been completed. The experimental results manifest the experimental method feasibilityAccording to the method of highest spatial frequency and eigenfunction analysis, for a certain CCD, the issues of allowable object size, the minimum recording distance, spatial resolution of digital holography, pixel number of object information transferring to image plane and plane holography system information capacity are studied. The quality of reconstructed image of digital holography is analyzed by a coherent optical imaging system, and the relation of lateral resolution, axis resolution and object size, speckle and the approximation problem of reconstruction algorithm are also investigated. On basis of Fourier optical theory, the process of particle holography with spherical wave recording and plane reconstructing is interpreted and the mathematical description is given.In reconstructed image analysis of digital holography of particle field, the method of two-level threshold and once time binarization is proposed to separate particle from particle field, and gradient threshold and perimeter correlation are also presented to act as the rule by which to judge if the particle is in focus or out of focus, and testing of particle field is completed. The experimental approach of velocity measurement has also been investigated for low speed particle field. The main innovation of research work is as follows:The concept of "a model of volume digital hologram" and the method of eliminating of twin-image are presented.The experimental system of digital off-axis holography and experimental method to eliminate zero-order image are presented.The method of threshold setting with two-level threshold and oncetime binarization is put forward and the criterion focus with gradient threshold and perimeter correlation is also presented. The method of particle digital holography with spherical wave recording and plane reconstructing is presented and its mathematical description is also given.