Digital Holographic Diffraction Tomography And Experimental Study

Digital holographic diffraction tomography combines digital holography with diffraction tomography,which has the advantages of full field of view,non-contact,non-marking of digital holography,and the advantages of three-dimensional imaging of diffraction tomography.Compared with the traditional computed tomography technique,the imaging quality of weakly scattered microscopic sample is improved because it takes into account the diffraction effect.Besides,except the 3D morphology,digital holographic diffraction tomography can also obtain the refractive index distribution of the sample.Owing to the above advantages,digital holographic diffraction tomography has wide application prospects in biomedical measurement,optical component detection and other fields.In this paper,based on digital holographic diffraction tomography,the basic principle of diffraction tomography is studied based on Fourier diffraction projection theorem.The linear interpolation algorithm based on single assignment is proposed.The illumination direction is changed by a galvanometer,and the lens imaging characteristics is combined to optimize the imaging system.Finally,a standard sample is used to verify the effectiveness of interpolation algorithm,and the optical samples after laser ablation and live human breast cancer cells are imaged by the imaging system.The main content of this paper is as follows:The basic principle of digital holographic diffraction tomography is described.Firstly,the recording and reconstruction process of digital holography,and three kinds of reconstruction algorithms are introduced.Then the basic principle of diffraction tomography is introduced based on Fourier diffraction projection theorem.The internal characteristics of weakly scattering objects are measured.Meanwhile,two different recording methods,rotating sample and multi-angle illumination are introduced.The reconstruction algorithm in digital holographic diffraction tomography is analyzed and optimized.Aiming at the problem that the nearest neighbor interpolation algorithm is multiple assignments to reduce the accuracy of spectral information,a linear interpolation algorithm based on single assignment is proposed.This interpolation algorithm ensures that a single assignment of spectral information is obtained at each angle,and a more accurate spectral information of the object function is obtained,thereby improving the reproduction accuracy.On this basis,the positive constrained iterative algorithm is used to increase the spectral information to make up for the “missing cone” in the spectrum of multi-angle illumination.The combination of the two algorithms improves the reconstruction quality of the sample.Finally,silica microspheres with a diameter of 50 μm(n=1.4607)were used as the standard sample verification algorithm.After using linear interpolation algorithm based on single assignment,the average refractive index of the microspheres was 1.4758 and the relative error was 1.034%.Using the linear interpolation algorithm based on single assignment and the positive constraint iterative algorithm,the average refractive index of the microspheres is 1.4661 and the relative error is 0.3697%.Compared with the traditional nearest neighbor interpolation algorithm,the measurement accuracy is greatly improved.A digital holographic diffraction tomography experimental device based on galvanometer to change the illumination angle was designed and built.The galvanometer changes the illumination direction and combines the lens imaging characteristics to achieve large-angle illumination,and the illumination spot position of the object is kept constant and the brightness is relatively uniform,and the imaging quality is improved by keeping the brightness of the recorded hologram uniform.On this basis,the laser ablated optical sample polymethyl methacrylate(PMMA)was reconstructed and obtain the refractive index distribution at different depths.In the laser ablation area,the refractive index of the PMMA increases with increasing depth.Subsequently,the human breast cancer cell T47 D and human breast cancer cell MDA-MB-231 were imaged.In particular,the morphology and refractive index changes of human breast cancer cell MDA-MB-231 within 120 minutes were dynamically monitored.Digital holographic diffraction tomography provides a non-destructive and quantitative three-dimensional imaging method for optical component quality assessment,biological sample morphology and refractive index detection,and has important practical significance for detection.