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Calibration method to improve the accuracy of THz imaging and spectroscopy in reflection geometry

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Photonics Research 2016年第3期4卷 29-35页

作者： Shuting Fan Edward P.J.Parrott Benjamin S.Y.Ung emma Pickwell-macpherson Department of Electric and Computer Engineering Hong Kong University of Science and Technology Department of Electronic Engineering The Chinese University of Hong Kong

We introduce a novel method to accurately extract the optical parameters in terahertz reflection imaging. Our method builds on standard self-referencing methods using the reflected signal from the bottom of the imaging window material to further compensate for time-dependent system fluctuations and position-dependent variation in the window thickness. Our proposed method not only improves the accuracy, but also simplifies the imaging procedure and reduces measurement times.

关键词： Calibration method to improve the accuracy of THz imaging and spectroscopy in reflection geometry THz

Terahertz photonics:techniques and applications feature issue introduction

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Photonics Research 2016年第3期4卷 1-2页

作者： emma Pickwell-macpherson Charles Schmuttenmaer Electronic Engineering The Chinese University of Hong Kong Department of Chemistry Yale University

We give an introduction to the feature issue comprised of six articles on terahertz photonics techniques and applications.

关键词： THz

Exploiting a metal wire grating in total internal reflection geometry to achieve achromatic polarization conversion

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Photonics Research 2017年第4期5卷 299-304页

作者： XUDONG LIU XUEQUAN CHEN EDWARD P.J.PARROTT emma PICKWELL-macpherson Department of Electronic Engineering Chinese University of Hong Kong

We demonstrate how a metal wire grating can work as a 45° polarization converter, a quarter-wave retarder, and a half-wave retarder over a broadband terahertz range when set up in total internal reflection geometry. Classical electromagnetic theory is applied to understand the mechanism, and equations to calculate the polarization state of reflected light are derived. We use a metal grating with a period of 20 μm and width of 10 μm on a fused silica surface: linearly polarized terahertz light incident from fused silica with a supercritical incident angle of 52° is totally reflected by the metal grating and air. The polarization of the terahertz light is rotated by 45°, 90°, and circularly polarized by simply rotating the wire grating. The performance is achromatic over the measured range of 0.1–0.7 THz and comparable to commercial visible light wave retarders.

关键词： THz

Robust and accurate terahertz time-domain spectroscopic ellipsometry

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Photonics Research 2018年第8期6卷 768-775页

作者： XUEQUAN CHEN EDWARD P.J.PARROTT ZHE HUANG HAU-PING CHAN emma PICKWELL-macpherson Department of Electronic Engineering The Chinese University of Hong Kong School of Science Zhejiang University of Science and Technology Department of Electronic Engineering City University of Hong Kong Department of Physics and Astronomy Warwick University

In this work, we show how fiber-based terahertz systems can be robustly configured for accurate terahertz ellipsometry. To this end, we explain how our algorithms can be successfully applied to achieve accurate spectroscopic ellipsometry with a high tolerance on the imperfect polarizer extinction ratio and pulse shift errors. Highly accurate characterization of transparent, absorptive, and conductive samples comprehensively demonstrates the versatility of our algorithms. The improved accuracy we achieve is a fundamental breakthrough for reflectionbased measurements and overcomes the hurdle of phase uncertainty.

关键词：光纤太赫兹椭偏仪通讯技术发展现状

A promising diagnostic method:Terahertz pulsed imaging and spectroscopy

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World Journal of Radiology 2011年第3期3卷 55-65页

作者： Ming Yiu Sy Yi-Xiang J Wang Anil T Ahuja emma Pickwell-macpherson Department of Electronic Engineering The Chinese University of Hong Kong Department of Imaging and Interventional Radiology The Chinese University of Hong Kong Department of Electronic and Computer Engineering Hong Kong University of Science and Technology

The terahertz band lies between the microwave and infrared regions of the electromagnetic *** radiation has very low photon energy and thus it does not pose any ionization hazard for biological *** is strongly attenuated by water and very sensitive to water *** absorption spectra due to intermolecular vibrations in this region have been found in different biological *** unique features make tera-hertz imaging very attractive for medical applications in order to provide complimentary information to existing imaging *** has been an increasing interest in terahertz imaging and spectroscopy of biologically related applications within the last few years and more and more terahertz spectra are being *** paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques,and a number of applications such as molecular spectroscopy,tissue characterization and skin imaging are discussed.

关键词： Biomedical Imaging Spectroscopy Terahertz

Graphene-loaded metal wire grating for deep and broadband THz modulation in total internal reflection geometry

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Photonics Research 2018年第12期6卷 1151-1157页

作者： YIWEN SUN RICCARDO DEGLJINNOCENTI DAVID A.RITCHIE HARVEY E.BEERE LONG XIAO MICHAEL RUGGIERO J.AXEL ZEITLER RAYKO I.STANTCHEV DANNI CHEN ZHENGCHUN PENG emma macpherson XUDONG LIU National-Regional Key Technology Engineering Laboratory for Medical Ultrasound Guangdong Key Laboratory for Biomedical Measurements and Ultrasound ImagingDepartment of Biomedical EngineeringSchool of MedicineShenzhen UniversityShenzhen 518060China Cavendish Laboratory University of CambridgeJ J Thomson AvenueCambridge CB30HEUK Department of Electrical Engineering and Computer Science Massachusetts Institute of TechnologyCambridgeMassachusetts 02139USA Department of Chemistry University of Vermont82 University PlaceBurlingtonVermont 05405USA Department of Chemical Engineering and Biotechnology University of CambridgePembroke StreetCambridge CB2 3RAUK Department of Electronic Engineering The Chinese University of Hong KongHong KongChina Key Laboratory of Ministry of Education for Optoelectronic Devices and Systems College of Optoelectronic EngineeringShenzhen University Shenzhen 518060China Department of Physics University of WarwickGibbet Hill RoadCoventry CV4 7ALUK

We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in TIR geometry and in the subwavelength wire grating was combined to demonstrate a ～77% modulation depth (MD) in the frequency range of 0.2–1.4 THz. This MD, achieved electrically with a SiO_2∕Si gated graphene device, was 4.5 times higher than that of the device without a metal grating in transmission geometry. By optimizing the parameters of the metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging.

关键词： modulation depth (MD) graphene Wire grating