Detection And Processing Based On Digital Spectrum Analysis In Digital Holography

Holography is a technique for recording a hologram to obtain the wavefront of an object wave and then reconstructing both the three-dimensional(3D)and quantitative phase images of the object.With the combination of the modern charged coupled device(CCD)and computer image processing technology,digital holography(DH)can effectively realize the quantitatively recording of interferogram,data storage,processing and reconstruction,which improves the efficiency and quality of holographic imaging.Comparing with the common imaging thechnologies,the lensless structure of DH avoids various aberration,furthermore,DH has a lot of other advantages including non-contact,wide-field and high precision.Therefore,DH has been widely used in microscopic imaging,3D object recognition,deformation detection,surface inspection,particle field analysis,and so on.This paper mainly introduces the basic theory of recording a reconstruction of an object wave in phase-shifting digital holography(PSDH).By using the common wavefront calculation formula in two-step and three-step PSDH,the object wavefront can be retrieved.By spectrum analysis,the tilt error of reference beam is theoretically deduced and eliminated in in-line PSDH,and the recording conditions are also improved.Finally,the auto-focusing process of holographic imaging is realized by focusing evaluation function of frequency field by analyzing the distribution of spectrum,which greatly improves the accuracy and efficiency of holographic reconstruction.The main contents of this dissertation are as follows.(1)A robust digital holography recording design is presented to complete the work of switching between in-line and off-axis recording methods.We precisely monitor and control the off-axis angle between the reference beam and object beam by introducing a supervising unit.By the Fourier analysis on the interferograms recorded by the supervising unit and using the corresponding equations,the off-axis angle can be calculated accurately and then chosen for the best recording angle that the original reconstructed image can be separated justly.For in-line PSDH,the error affecting the slight tilt of the reference beam can be eliminated completely because the tilt angle is detected by another independent device.The availability and effectiveness of this design are verified by a series of experiments.(2)The focusing evaluation function in frequency field is constructed to detect the reconstructed distance of digital holographic imaging precisely.By comparing our function with several other focusing evaluation functions in both simulations and experiments,the availability and effectiveness of evaluation function in frequency filed are verified.