A wide range of chemical and biological agents - such as explosives, drugs, and tissues - have unique spectral signatures at THz frequencies, which can be unambiguously identified using THz imaging. Existing T-ray imaging technologies can be mainly categorized as pulsed THz time-domain imaging and CW THz imaging. For so many years, researchers have been striving to develop new technologies that could inherit the merits of both methods and offer a fast response to desired frequency bands for multispectral THz imaging, preferably in real time. While decent progress has been made in the THz sources (especially, QCLs), THz imaging technologies somehow lag behind mainly due to the fact that natural materials do not show much response in the THz frequency range. Metamaterials (MMs) - artificial structures in which the electromagnetic responses can be engineered by design to access a frequency range - can show strong responses in the THz regime, offering a flexible and relatively cheap route to image in THz using designer sensor imaging arrays based on MMs. The multicolor T-ray imaging setup using a THz hyperspectral MM-FPA and a set of QCL sources. The MM-FPAs, which absorb THz radiation at multiple bands (2.5 THz, 3.4 THz, and 4.3 THz here), can then be paired with the tunable QCL sources in accordance with different applications such as frequency selective material identification of concealed chemical substances and cancerous tissue diagnosis.

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Tiger Tao, "Real-time multispectral T-ray imaging using metamaterials (Conference Presentation)," Proc. SPIE 10656, Image Sensing Technologies: Materials, Devices, Systems, and Applications V, 1065618 (Presented at SPIE Commercial + Scientific Sensing and Imaging: April 18, 2018; Published: 14 May 2018); https://doi.org/10.1117/12.2304562.5783313354001.