Elimination Of The Twin Image And The Point Source Scanning In The In-line Digital Holography

Digital holography is a new method for three-dimensional imaging,and it's products of the traditional optical holography,photoelectric detection technology and computer technology,which replaces the traditional recording material with the photoelectrical device,and implements digitalization of recording and reconstruction process.On the one hand full field of view,non-contact,high-speed,real-time,being access to the phase information.On the other hand,holography has lots of unique advantages then the traditional optical holography,such as simple reconstruction in the computer,quantitative measurement,easy processing,easy storage,and so on.However,compared with traditional optical holography,the resolution of digital holography is limited.Using in-line digital holography can improve the utilization rate of the CCD spatial bandwidth and record large size range of the object.But object light and reference light propagation in the same optical system,which leads to the twin image and real image aliasing,and more difficult to remove.The image quality of digital holography is affected by the limitation of coherent length of the light source,the pixel pitch and aperture size of the detector.In order to improve the quality of reconstructed image,two major problems have to be solved: elimination of the twin image and enhance the spatial resolution.In this dissertation,new approaches,ranging from recording architectures to algorithms,are presented to these issues.To verify the feasibility of the proposed methods,theoretical analysis and experimental demonstration has been provided.The main content of the thesis is organized as follows: 1.Optimizing the phase retrieval algorithm for elimination of the twin image in the in-line digital holography,it has the better application in the optical system of point light source illumination.With normalized hologram as the initial information,the amplitude and phase of the object is used as a constraint in the object plane,and the amplitude of digital holography is used as a constraint in the recording plane.The simulation and experimental results verify the approach with good accuracy.It is reasonable to believe that it will become an effective approach to eliminate the twin image in the in-line digital holography.2.Study for the relationship of system resolution and CCD pixel size when using the minimum recording distance.First,theoretical analysis the two case of using the plane wave or spherical wave illumination when satisfy the sampling theorem,CCD pixel size how to effect the resolution;Then,through the simulation verifies the correctness of the theoretical analysis.3.Proposing a method based on the point source scanning to realize sub-pixel shifting,optimize the optical system and algorithm.Through moving the point source,multiple holograms with sub-pixel shifts are captured.These holograms are merged together to obtained a high resolution hologram by a synthesizing algorithm.Then,the high resolution reconstructed image of the object can be obtained by the angular spectrum algorithm.The feasibility of the proposed method is demonstrated by theoretical analysis?simulation and experiments.