Digital Holographic Diffraction Tomography Based On Multi-angle Illuminination

Digital holographic diffraction tomography is one of the research hotspots in the field of optical imaging in recent years.It is a new type of three-dimensional imaging technology that combines the advantages of digital holography and diffraction tomography.It not only has the advantages of digital holography full field of view,non-contact,non-destructive,and non-marking,but also has the advantage of diffraction tomography for high precision and quantitative three dimensional imaging of small samples.At present,digital holographic diffraction tomography imaging technology has been applied in the field of biomedicine,micro-optical device detection,temperature field and other fields,and has important research significance and application prospects.The imaging process of digital holographic diffraction tomography is divided into two steps.First,digital holography is used to obtain the hologram of the sample under different illumination angles.The holograms are numerically reproduced to obtain the scattered field distributions of the sample in different directions.Then based on the scattered data of multi-angle scattering as the basic data,the refractive index distribution of the object can be reconstructed by using the diffraction tomography algorithm.This paper analyzes the theory of digital holographic diffraction tomography,and studies the optimization of digital holographic diffraction tomography quality under multi-angle illumination,the construction of experimental system and the verification of imaging.The main contents are as follows:The theoretical model of digital holographic diffraction tomography is clarified.On the one hand,the digital holographic imaging technology is analyzed.The main aim is to record and reproduce pre-amplified off-axis Fresnel digital holography,and recording the corresponding hologram at different angles of illumination.The numerical reconstruction algorithm can obtain the complex amplitude distribution under each illumination angle.On the other hand,On the other hand,the theoretical model of optical diffraction tomography is described.The relationship between the complex amplitude distribution obtained from various angles and the three-dimensional spectrum of the object function is analyzed.Three-dimensional imaging reconstruction algorithm optimized for optical diffraction tomography.Due to the problem of spectral point discretization in the three-dimensional frequency domain of the object function,a nearest neighbor interpolation algorithm based on single assignment is proposed;meanwhile,in the digital holographic diffraction tomography imaging system based on multi-angle illumination,the recording angle of the detector is limited by the numerical aperture of the system,a problem of “missing cone spectrum” occurs in the frequency domain of the three-dimensional object function.To solve this problem,the method of positive constrained iteration is studied to recover the missing spectrum,and the accuracy of 3D reconstruction is improved by the nearest neighbor interpolation algorithm and the positive constrained iterative algorithm.A digital holography-based diffraction tomography system was designed and built.On the basis of pre-amplifying the imaging system of off-axis Fresnel image digital holography,an experimental system for multi-angle illumination samples was designed,including two experimental systems based on translational scanning and galvanometric scanning,and a program to control LabVIEW and image acquisition equipment CCD was programmed.According to the theory of optical diffraction tomography,the transparent sample is placed in a weakly scattered field environment to satisfy the approximate conditions of first-order Rytov in optical diffraction tomography.Based on this analysis,we used a matching liquid with a specific refractive index to match the surrounding environment of the sample and verified the effectiveness of the digital holographic diffraction tomography algorithm for three-dimensional imaging.The imaging technology provides an effective method for non-destructive and quantitative measurement of the internal structure of micro samples.