Recent progress of terahertz sensing and imaging

Abstract

In this presentation, I will present a few topics related to terahertz (THz) sensing. The first one is related to the development of THz absorber made by metal-plated Spirulina microcoils. Spirulina is a type of algae with a spiral shape, with a length of 40–300 μm and a helical inner diameter of 25–35 μm. Iyoda, Kamata et al. have applied 0.3 μm-thick metal plating to this and shown that it worked as a sort of functional material in the THz region. Moreover, we have revealed its temporal response by THz-TDS and shown that it absorbed a broadband THz radiation and reemitted a part of the energy by axial and dipole mode radiation. Here, I will present that it works as a phase-randomizing absorber with low reflection when we make it by including many microcoils in collaboration with PANAC Co. Ltd. In fact, the reflected temporal profiles by a single input pulse showed the combination of small multiple pulses. Moreover, the reflection signal was about about one order smaller than that of Eccosorb® (AN-72) that is a de facto standard absorber in THz region. These results suggest that this microcoil absorber can be a good absorber with phase-randomizing functionality and a good for future THz high-speed wireless telecommunication.
The second topic is the further development of a walk-through body scanner. We have developed the imaging system by combining THz-band FMCW radar and a polygon mirror, and successfully visualized concealed objects of pedestrians at real walking speed. However, for practical use, it is also necessary to enable measurement of the front and back using multiple units. In this presentation, we will show the simultaneous imaging of the front and back with the same optical unit using a double-path optical system. The system has two optical paths coaxialized by a beam splitter, and when a pedestrian passes through these optical paths, both the front and the back can be measured. We will show the results of the simultaneous imaging.