Research Of Micro-structure Measurement Method Based On Digital Holography

With the rapid development of computer technology and the improvement of CCD’s spatial resolution, the theory of digital holography develops unceasingly and the applications of digital holographic technology-gets more attention. The application areas of digital holographic interferometry include topography measurement, deformation measurement,3D image recognition. With the progress of the industrial technology, the methods of non-destructive and whole-field measurement with higher precision are eagerly needed. The digital holographic interferometric technique can meet these requirements.In this paper, the basic theories and technologies of optical holography and digital holography are introduced, and the Fresnel diffraction theory is also reviewed. The spatial frequency domain filtering method and the light intensity subtracting method for diminishing the zeroth-order light intensity and the conjugate image in the reconstruction field of digital hologram are discussed;The principle of double-exposure method for testing the deformation of object is given; The ordinary double-exposure digital holographic interferometry can only measure small deformation of object, large deformation produces too dense interferometric fringe which is impossible to be visualized. To overcome this limitation of the double-exposure digital holographic interferometry, the digital holographic measurement method of object with continuous and large deformation is proposed; The experimental setup of digital holographic measurement system is built up; After verifying the testing experiment on eliminating zeroth-order light and the conjugate image to improve the quality of digital hologram reconstructed image, the digital holograms of intermediate typical states of continuous and large deformation object are recorded; Combining and reconstructing digital holograms of two adjacent typical states of object, the interferometric fringe pattern, which representing the deformation distribution between the two adjacent typical states of object, is made with computer; By analyzing the fringes in the interferometric pattern, the function relating deformation quantity and the position on object is obtained through the function-fitting-method; Properly adding the functions of intermediate typical state deformation, the functions that reflecting the deformations of intermediate typical states relative to the initial state of object are finally achieved. At the end, the sources of measurement error and the method to decrease the errors are also put forwarded.