| Digital holography is using the charge coupled device CCD instead of the traditional plate,record the initial light wavelengths to complete the hologram,and then using the computer calculation of complex diffraction reappearance of the original distribution of the field of the wave front,digital holographic technology to realize the whole process of holographic recording,storage,processing and digital and real-time,which provides a new way for the practical application of holographic technology,in the information security encryption,high resolution microscopy images,particle detection,play a great role in such aspects as material detection.At present,due to the limitations of CCD and other photosensitive electronic imagers in the imaging conditions,how to improve the resolution of digital holography,realize the separation of the reconstructed image from other noise components,and improve the signal-to-noise ratio of the reconstructed light field are the key problems to be solved in the development and application of digital holography.The diffraction theory of light wave is the most basic theory.To quantitatively describe the practical problem of optical information processing,diffraction calculation is needed.In this paper,different diffraction algorithms are derived in theory and the original object light wave is reconstructed by computer simulation.The different reconstruction algorithms are compared and analyzed,and the noise elimination of the reconstructed image is studied.The main work is as follows:Based on the overview of digital holography,this paper describes the development,application and research status of digital holography at home and abroad.Key research based on the Fresnel diffraction integral fast Fourier transform algorithm(S-FFT)algorithm and fast convolution algorithm(D-FFT),and two kinds of wavefront reconstruction methods: off-axis wavefront reconstruction method(1-FFT)and wavefront reconstruction method based on virtual light field(VDH4FFT),and also research the off-axis digital holographic wavefront reconstruction method to eliminate noise.MATLAB software is used to realize the simulation reproduction of digital holographic wavefront reconstruction methods 1-FFT and VDH4 FFT.The 1-FFT reconstruction method is compared with the VDH4 FFT reconstruction method,and the influence of different wavefront reconstruction methods on the holographic reconstruction effect and the influence of different noise elimination methods on theholographic reconstruction effect is analyzed.The research results show that using only a fast Fourier transform of 1-FFT of off-axis holographic reconstruction method is simple,the use of zero order interference elimination method and the step four phase shift method directly after removing noise can get the full image,but the size of its reconstruction field is represent the wavelength of light,the diffraction distance function of the number and sampling and reproduce like the reconstruction plane of the area is small,most of the area occupied by noise,the resolution of the particular observation area is very low,for some light sensitive optical precision testing no practical effect.The VDH4 FFT method of virtual field wavefront reconstruction can use more pixels to represent the local image of the observed object of the same size,the local image has a very high resolution,and the reconstruction image can fully occupy the reconstruction plane.By comparing and analyzing the calculation amount and time of the two off-axis digital holographic reconstruction methods,it is found that the calculation time of VDH4 FFT is slightly lower than that of 1-FFT method under the same resolution,and the memory occupied during calculation is also smaller than that of 1-FFT method.The digital holographic algorithm and wavefront reconstruction method are summarized.The virtual light field reconstruction method can reconstruct the object light field with high quality,and it will be widely used in the deformation detection and microimaging of materials. |
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