Self-Referenced Method for Geometrical Distortion Removal in THz Time-Domain Reflection Imaging (original) (raw)

IEEE Transactions on Terahertz Science and Technology

In this article, we develop a method for removing the phase drift induced by physically distorted object in terahertz timedomain reflection imaging (THz-TDRI). The proposed approach is defined as self-referenced, as it does not rely on any numerical parameter optimization nor extra instrumental components, and it is based on the unique manipulation of time-domain imaging data. In fact, we demonstrate that the problem can be solved assuming a linear contribution of the temporal shift induced by surface curvature. We illustrate how the self-referenced method is modeled and implemented, and we report the results obtained on two objects with different characteristics: a tilted and highly reflective surface, and a warped and heterogeneous surface. The proposed method demonstrates how to successfully remove the phase alterations induced on the reflected electric field, and how to repair the heavily corrupted images in the frequency-domain. Index Terms-Image restoration, phase variation problem, reflection geometry, terahertz time-domain reflection imaging (THz-TDS). I. INTRODUCTION T HE use of electromagnetic radiation at terahertz frequencies (from 0.1 to 10 THz) is becoming highly popular, mostly thanks to the increased availability of stable devices. A valuable characteristic of THz radiation is that it can penetrate a wide range of nonconducting materials, including plastics, polymers, and ceramics [1], [2], [3]. It is strongly absorbed by polar molecules, such as water [4], reflected by metals [5], and at the same time, it is not ionizing and harmless for biological tissues [6]. For these reasons, THz-waves are broadly applicable in many disciplines, such as bio-medicine, agriculture, and security and communication services [7], [8], [9]. Terahertz time-domain spectroscopy (THz-TDS) is appreciated especially in the field of material studies because it enables