Study On The Recording And Reconstructing Methods About Digital Holography

In digital holography, the holographic information is directly recorded on a charge-coupled device(CCD) camera and the optical reconstruction is replaced by a computer numerical reconstruction, so the holographic full process including recording, memory and reconstruction is entirely digital. In the small aperture and field of view measuring field, such as cell viewing, microcircuit examination, grain size analysis, experimental stress analysis, 3-D profilometry, transparent field measurement etc, digital holography can develop its advantage and achieve extensive application.Based on theoretic analysis, computer simulation and the corresponding experiment research, this paper gives some analysis about the fundamental issue of digital holography including recording sampling requirement, reconstructing separation condition, and how to improve the resolving power of measuring system and the ratio of signal to noise of reconstructing image. By analysis of various digital holographic methods and their combination, some important research results are obtained, meanwhile some experimental results are given the reasonable explain. In this paper, the main innovative ideas are as following:The relationship which is fulfilled the recording sampling and reconstructing separation requirement for the lateral size of the object and CCD, the distance between the object, CCD and the reference wave point source is given, and it can be used to estimate the recording structure parameters for both the spherical reference wave system and the plane reference wave system. Meanwhile it is proved lensless Fourier holography is an optimum digital holographic recording system in fulfilling the above recording requirement, and the lensless Fourier hologram of the full scattering object is equal to the diffracting field superposition of two point sources and the ratio of signal to noise of reconstructing light field is very lower.It is proved to combine phase-shifting technique with on-axis lensless Fourier holography is an kind of optimum method in which the conflict between the recording sampling and the reconstructing separation requirement can be eliminated, especially for recording and reconstruction large aperture digital hologram, in which on-axis holography achieves the maximum of object information recording, lensless Fourier holography makes it is easy to fulfill the recording sampling, and phase-shifting technique can solve the problem of reconstructing separation requirement and improves the ratio of signal to noise of reconstructing image. A novel recording method of multi-reference waves synthetic aperture digital holography is proposed, especially some detail analysis about the reconstructing complex amplitude superposition of sub-hologram and the reconstructing intensity superposition of sub-hologram are given. Comparing with the conventional numerical reconstructing method of direct combining sub-hologram, the former reconstructing methods are the same in improving the resolving power of reconstructing image, but the difficulty of recording and reconstruction of synthetic aperture digital holography is decreased.In the reconstruction of digital hologram, owing to the higher-order phase term of the hologram can be compensated by the reconstructing wave, a novel Fourier transformation reconstructing algorithm of the large aperture digital hologram which isn't fulfilled Fresnel diffraction condition is proposed, meanwhile the application condition and how to design recording light road are analyzed.