Reconstruction Of Three-Dimensional Refractive Index Field Based On Multi-Wave Shearing Interferometry And Optical Tomography

With the development of science and technology, the form of information acquisition has been changing from plane to three-dimensional information. In life science, conventional optical imaging microscopy is gradually substituted by confocal microscopy, structured illumination microscopy and tomographic phase microscopy, which can provide three-dimensional information of cells and tissues. For single or multiple fluorescently-labeled samples, confocal microscopy and structured illumination microscopy can obtain perfect test results. With the help of synthetic aperture technique, stuctured illumination microscopy is even capable of super-resolution tomographic imaging. However, for transparent label-free samples, only the tomographic phase microscopy, which is based on optical interference tomography, can acquire three-dimensional structural information of the sample from its reconstructed refractive index distribution. Meanwhile, in aerodynamics, hypersonic aircraft designing has been a research hotspot. The problems are not only in the designing and simulation of aerodynamic layout, but also in the aero-optical detection of the surrounding flow field. Conventional schlieren photography or optical interferometry can only obtain the beam deflection information or wavefront distortion in a single direction. To precisely obtain the three-dimensional flow field distribution, optical interference tomography should also be introduced. Currently, the most commonly used interferometry in optical interference tomography is Mach-Zehnder or Twyman-Green interferometer, which needs further improvement in stability, dynamic range and the space occupied.In this dissertation, the reconstruction of three-dimensional refractive index distribution based on multi-wave shearing interferometry and optical tomography is proposed. On the basis of the mathematical model of three-dimensional refractive index field reconstruction, muti-wave shearing interferometry, which can provide large dynamic range and strong stablility, is employed. A three-dimensional refractive index field reconstruction system based on bi-wave off-axis radial shearing interferometer is then proposed for flow field detection and a three-dimensional refractive index field reconstruction system based on quadriwave lateral shearing interferometer is proposed for testing of cells and tissues. This research is of great significance for optical interference tomography, especially for its generalization and miniaturization. The content of this dissertation include:The research background of optical tomography is investigated and the comparison between optical projection tomography, beam deflection tomography and optical interference tomography has been carried out. According to the investigation, the technique for three-dimensional refractive index reconstruction based on multi-wave shearing interferometry and tomography is proposed.The Radon transform, which lays the foundation for computed tomography, and the Fouier slice theorem are introduced for the mathematical modelling of three-dimensional refractive index reconstruction. A comparison between the performance of the algebraic reconstruction technique and filtered backprojection algorithm is carried out, in case of different grid numbers, projection angles and the number of sampling rays.The three-dimensional refractive index field reconstruction system based on the bi-wave off-axis radial shearing interferometer is proposed for flow field detection. A novel common-path off-axis radial shearing interferometer, which can obtain steady interferogram even when the center of the wind tunnel is blocked by the model, is employed. Considering the limited-data and blocking issues in flow field detection, a biharmonic spline interpolation algebraic reconstruction technique is also proposed.The three-dimensional refractive index field reconstruction system based on the quadriwave lateral shearing interferometer is proposed for testing of cells and tissues. After investigating the cross-grating lateral shearing interferometer and the quadriwave lateral shearing interferometer based on the modified Hartmann mask, a novel quadriwave lateral shearing interferometer based on randomly encoded hybrid grating is employed to test the wavefront distortion. As the projection angle is limited using galvanometer, the iterative constraint filtered backprojection algorithm is introduced to obtain more precise reconstruction results with the help of priori information.The experiments demonstrating the three-dimensional refractive index field reconstruction systems based on the off-axis radial shearing interferometer and the quadriwave lateral shearing interferometer are carried out. A ZYGO GPI interferometer is employed to validate the wavefront measurement precision of the off-axis radial shearing interferometer and the quadriwave lateral shearing interferometer based on the randomly encoded hybrid grating. With corresponding optical tomographic technique, the three-dimensional refractive index distribution of the thermal air and the red blood cell are reconstructed eventually.