Abstract-All-dielectric metalens for terahertz wave imaging

Xue Jiang, Hao Chen, Zeyu Li, Hongkuan Yuan, Luyao Cao, Zhenfei Luo, Kun Zhang, Zhihai Zhang, Zhongquan Wen, Li-guo Zhu, Xun Zhou, Gaofeng Liang, Desheng Ruan, Lianghui Du, Lingfang Wang, Gang Chen,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-11-14132

Terahertz wave imaging offers promising properties for non-destructive testing applications in the areas of homeland security, medicine, and industrial inspection. However, conventional optical lenses are heavy and bulky and difficult to integrate. An all-dielectric metasurface provides an attractive way to realize a planar lens of light weight that is ultrathin and offers ease of integration. Terahertz lenses based on various metasurfaces have been studied, especially for the application of wave focusing, while there are few experimental demonstrations of terahertz wave imaging lenses based on an all-dielectric metasurface. In the present work, we propose a metalens based on an all-dielectric metasurface with a sub-wavelength unit size of 0.39λ for terahertz wave imaging and experimentally demonstrate its performance in focusing and imaging. A large numerical aperture metalens was fabricated with a focal length of 300λ, radius of 300λ, and numerical aperture of 0.707. The experimental results show that the lens can focus THz waves with an incident angle up to 48°. More importantly, clear terahertz wave images of different objects were obtained for both different cases of forward- and inverse-incident directions, which demonstrate the reversibility of the metalens for imaging. Such a metalens provides a way for realization of all-planar-lens THz imaging system, and might find application in terahertz wave imaging, information processing, microscopy, and others.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Enhancement of Real-Time THz Imaging System Based on 320 × 240 Uncooled Microbolometer Detector

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• Xing Zheng
• , Zhiming Wu,
•  Jun Gou
• , Ziji Liu
• , Jun Wang
• , Jie Zheng
• , Zhenfei Luo
• , Weiqing Chen
• , Dongcheng Que,

http://link.springer.com/article/10.1007%2Fs10762-016-0287-4

A real-time terahertz (THz) imaging system was demonstrated based on a 320 × 240 uncooled microbolometer detector combined with a 2.52 THz far-infrared CO2 laser. On the top of micro-bridge structure (35 × 35 μm2), a 10 nm nickel-chromium (NiCr) thin film was deposited to enhance THz absorption, which was fabricated by a combined process of magnetron sputtering and reactive ion etching (RIE). By mechanical simulation using design of experiment (DOE) method, the minimum deformation was optimized to 0.0385 μm, and a measured deformation of 0.097 μm was achieved in the fabrication. The fabricated micro-bridge pixel was used for THz detection, and a responsivity of 1235 V/W was achieved with a noise equivalent power (NEP) of 87.4 pW/Hz1/2. THz imaging of metal gasket covered by label paper, paper clip in an envelope, and watermark of a banknote was demonstrated by a combination of histogram equalization (HE) and linear enhancement algorithm.