Non-Confocal 3D Reconstruction in Volumetric Scattering Scenario

Real-time scattering imaging technology is of great importance for transportation in extreme weather, scientific research in the deep ocean, emergency rescue in heavy smoke, and so on. Among existing volumetric scattering imaging methods, time-of-flight (ToF) methods based on confocal imaging architecture, isolating or modeling scattering photons, present the best visual reconstruction ability. However, these methods rely on the long acquisition time to capture more effective photons and thus fail to deal with real-time imaging tasks. In this article, aiming at providing both high-speed and high-quality scattering reconstruction, a dual optical coupling scattering transmission model is proposed to accurately describe the spatial and temporal propagation of scattered photons in the non-confocal imaging architecture. Then, a non-confocal boundary migration model (NBMM) is designed to establish the mapping between scattered measurement and object information. Besides, using the special characteristic of the temporal transfer matrix, a depth reconstruction method based on re-focusing is developed to recover the 3D structure of the object. Finally, a non-confocal imaging system is built to capture photons for all pixels simultaneously and verify the effectiveness of the proposed method. The experimental results show that the proposed method can recover 3D objects located at a one-way scattering length of 22.2 transport mean free paths (TMFPs), corresponding to the round-trip scattering length of 44.4 TMFPs, which is 6.9 times more than typical non-confocal methods. It operates 600 times faster than confocal methods and only requires 100 ms exposure time, which is very beneficial to a variety of real-time scattering applications.