Research On CW2.52THZ3D Imaging Methods

With the development of terahertz imaging technology and the emergence ofnew imaging methods, high-quality and high-dimensional imaging has been aresearch focus among investigations into THz imaging technology which has drawnwidespread attention. THz computed tomography (CT) is a combination of THztechnology and CT, and THz digital holography applies digital holography to THztechnology. They can effectively improve the reconstructed image quality andrealize three-dimensional (3D) imaging by numerical reconstruction methods.Numerical simulation and experimental researches on3D reconstruction methods,influence factors of imaging quality and methods of improving imaging quality havebeen conducted based on the built continuous-wave (CW)2.52THz CT imagingequipment and Gabor inline digital holography imaging equipment.To realize high-quality3D imaging of CW2.52THz CT, the reconstructionalgorithms and methods of improving image quality have been numericallyinvestigated. A modified CW THz CT reconstruction algorithm has been given bycombining the modified iteration algorithm with digital image processing to reducethe required number of projections. Compressive sensing (CS) has also been appliedto the reconstruction. Experimental research on the3D reconstruction of THz CThas been made with self-made polystyrene samples, and the feasibility of3Dimaging of CW2.52THz CT has been verified.To realize high-quality2D imaging of CW2.52THz Gabor inline digitalholography, the reconstruction algorithms and methods of improving image qualityhave been investigated by numerical simulation and experimental researches. Amodified CS algorithm has been given by combining CS algorithm with negativetransformation and piecewise-nonlinear transformation function. A modifiedanalysis reconstruction algorithm has also been given by combining the angularspectrum (AS) algorithm with DC suppression method and apodization.Experimental research on the2D reconstruction of CW2.52THz Gabor inlinedigital holography has been made with watch gears and handwritten characters andthe results have been compared with the simulation results.To realize3D imaging of CW2.52THz Gabor inline digital holography, theproper parameter selection of CS reconstruction algorithm has been numericallystudied firstly. The displacement error between the reconstruction position and thereal position of the sample has been simulated and a modified CS3D iterativereconstruction algorithm has also been given by combining CS algorithm with negative transformation, apodization of the expanded hologram andpiecewise-nonlinear transformation function. Experimental research on the3Dimaging of THz digital holography has been made based on the built CW2.52THzGabor inline digital holography imaging system with self-made Teflon printedcircuit board samples and handwritten character. The feasibility of3D imaging ofTHz Gabor inline digital holography has also been verified.