Continuous-Wave Terahertz Holographic Diffraction Tomography Based on Multiple Scattering Forward Model

Terahertz waves exhibit the great potential applications due to their particular properties. Also, diffraction tomography (DT) is an effective way to detect the internal three-dimensional structure of the sample. The terahertz DT (THz-DT) is an attractive and growing technique. However, when the samples to be measured are with complex internal structures or high refractive index contrast, the multiple scattering effect is a challenging problem, and even becomes more serious because of the large wavelength of the THz wave, which makes the first-order Born/Rytov approximation hardly to be satisfied and brings severe distortions to the reconstruction results. In this paper, the continuous-wave THz-DT based on digital holography is presented including the multiple scattering effect, which can further improve the reconstruction fidelity. The multiple scattering forward model is introduced to describe the propagation process of the THz wave inside the sample, and the modified split-step beam propagation method is presented, which evolves from its original version as one of the main forward models for the visible optical DT. Both the reconstruction accuracy and computation efficiency are achieved higher. Then, the simulations and experiments of THz-DT are performed, and three-dimensional reconstruction results with more fine structures are obtained by applying the correspondingly developed optimization-based nonlinear inverse scattering algorithm. To our best knowledge, it is the first time to apply the multiple scattering forward model into THz DT to improve the reconstruction fidelity. Besides, the capacity of the proposed method to enable sparse-angle reconstruction is also demonstrated by reducing the number of rotation angles, which is particularly important for real-time measurement applications.