Virtual Source Extended Range Points Migration Method for Auto-Focusing 3-D Terahertz Imaging

This letter presents an auto-focusing imaging algorithm for terahertz (THz) band imaging by extending the range point migration (RPM) method using a dielectric lens model. The traditional THz time-domain spectroscopy (THz-TDS) imaging system has an essential problem for depth dependence of the azimuth resolution, which becomes more crucial in subsurface imaging, because the depth of target is unknown in most cases. This letter thus introduces an RPM-based auto-focusing imaging method using an equivalent virtual source model to accurately represent both near- and far-range areas from the focal point. Experimental validation using THz-TDS demonstrated that the proposed algorithm accurately compensates image distortions by out-of-focus effect with much lower complexity than traditional radar-imaging approaches.