Abstract-High-precision terahertz frequency modulated continuous wave imaging method using continuous wavelet transform

Yu Zhou

https://arxiv.org/abs/1905.12437

Inspired by the extensive application of terahertz imaging technologies in the field of aerospace, we exploit a terahertz frequency modulated continuous wave imaging method with continuous wavelet transform algorithm to detect a multilayer heat shield made of special materials. This method uses the frequency modulation continuous wave system to catch the reflected terahertz signal and then processing the image data by the continuous wavelet transform with different basis functions. By calculating the sizes of the defects area in the final images and then comparing the results with real samples, a novel and practical high-precision terahertz imaging method are demonstrated. Our method can be an effective tool for the terahertz nondestructive testing of composites, drugs and some cultural heritages

Abstract-Highly-efficient spintronic terahertz emitter enabled by metal-dielectric photonic crystal

Zheng Feng, Rui Yu, Yu Zhou, Hai Lu, Wei Tan, Hu Deng, Quancheng Liu, Zhaohui Zhai, Liguo Zhu, Jianwang Cai, Bingfeng Miao, Haifeng Ding

https://arxiv.org/abs/1807.03069

Spintronic terahertz (THz) emitter provides the advantages such as apparently broader spectrum, significantly lower cost, and more flexibility in compared with the commercial THz emitters, and thus attracts great interests recently. In past few years, efforts have been made in optimizing the material composition and structure geometry, and the conversion efficiency has been improved close to that of ZnTe crystal. One of the drawbacks of the current designs is the rather limited laser absorption - more than 50% energy is wasted and the conversion efficiency is thus limited. Here, we theoretically propose and experimentally demonstrate a novel device that fully utilizes the laser intensity and significantly improves the conversion efficiency. The device, which consists of a metal-dielectric photonic crystal structure, utilizes the interference between the multiple scattering waves to simultaneously suppress the reflection and transmission of the laser, and to reshape the laser field distributions. The experimentally detected laser absorption and THz generations show one-to-one correspondence with the theoretical calculations. We achieve the strongest THz pulse emission that presents a 1.7 times improvement compared to the currently designed spintronic emitter. This work opens a new pathway to improve the performance of spintronic THz emitter from the perspective of optics.

Abstract-High-precision terahertz frequency modulated continuous wave imaging method using continuous wavelet transform

Yu Zhou, Tianyi Wang,  Bing Dai,  Wenjun Li,  Wei Wang,  Chengwu You, Kejia Wang, Jinsong Liu; Shenglie Wang,  Zhengang Yang

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-57/issue-2/023108/High-precision-terahertz-frequency-modulated-continuous-wave-imaging-method-using/10.1117/1.OE.57.2.023108.short?SSO=1

Inspired by the extensive application of terahertz (THz) imaging technologies in the field of aerospace, we exploit a THz frequency modulated continuous-wave imaging method with continuous wavelet transform (CWT) algorithm to detect a multilayer heat shield made of special materials. This method uses the frequency modulation continuous-wave system to catch the reflected THz signal and then process the image data by the CWT with different basis functions. By calculating the sizes of the defects area in the final images and then comparing the results with real samples, a practical high-precision THz imaging method is demonstrated. Our method can be an effective tool for the THz nondestructive testing of composites, drugs, and some cultural heritages.

© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Abstract-Tunable multiband directional electromagnetic scattering from spoof Mie resonant structure

Hong-Wei Wu, Hua-Jun Chen, Hua-Feng Xu, Yu Zhou, Dong-Xiang Qi, Yue-Ke Wang

https://arxiv.org/abs/1801.04040

We demonstrate that directional electromagnetic scattering can be realized from a artificial Mie resonant structure which supports electric and magnetic dipole modes simultaneously. The directivity of the far-field radiation pattern can be switched by changing the incident light wavelength as well as tailoring the geometric parameters of the structure. Particularly, the electric quadrupole at higher frequency contribute significantly to the scattered fields, leading to enhancement of the directionality. In addition, we further design a quasiperiodic spoof Mie resonant structure by alternately inserting two materials into the slits. The results show that multi-band directional light scattering are realized by exciting multiple electric and magnetic dipole modes with different frequencies in the quasiperiodic structure. The presented design concept is general from microwave to terahertz region and can be applied for various advanced optical devices, such as antenna, metamaterial and metsurface.

Abstract-Nonperiodic metallic gratings transparent for broadband terahertz waves

Xiao-Ping Ren1, Ren-Hao Fan1,*, Ru-Wen Peng1,*, Xian-Rong Huang2,*, Di-Hu Xu1, Yu Zhou1, and Mu Wang1

• 1National Laboratory of Solid State Microstructures and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
• 2Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.045111

In this work, we demonstrate both theoretically and experimentally that nonperiodic metallic gratings can become transparent for broadband terahertz waves. It is shown that broadband high transmission appears in aperiodic metallic gratings (including quasiperiodic and disordered ones), which originates from the nonresonant excitations in the grating system. Quasiperiodic and disordered metallic gratings effectively weaken and even eliminate Wood's anomalies, which are the diffraction-related characters of periodic gratings. Consequently, both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity. An optimal condition is also achieved for broadband high transparency in aperiodic metallic gratings. Experimental measurements at the terahertz regime reasonably agree with both analytical analysis and numerical simulations. Furthermore, we show that for a specific light source, for example, a line source, a corresponding nonperiodic transparent grating can be also designed. We expect that our findings can be applied for transparent conducting panels, perfect white-beam polarizers, antireflective conducting solar cells, and beyond.

DOI: http://dx.doi.org/10.1103/PhysRevB.91.045111

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©2015 American Physical Society

Article part of CHORUS

Accepted manuscript will be available starting 12 January 2016.

Abstract-Non-periodic metallic gratings transparent for broadband terahertz waves

Xiao-Ping Ren, Ren-Hao Fan, Ru-Wen Peng, Xian-Rong Huang, Di-Hu Xu, Yu Zhou, and Mu Wang

http://journals.aps.org/prb/accepted/df07cO48H1b13926f6ed29b47501c94f9f1a79ec8

In this work, we demonstrate both theoretically and experimentally that non-periodic metallic gratings can become transparent for broadband terahertz waves. It is shown that broadband high transmission appears in aperiodic metallic gratings (including quasi-periodic and disordered ones), which originates from the non-resonant excitations in the grating system. Quasi-periodic and disordered metallic gratings effectively weaken and even eliminate Wood's anomalies, which are the diffraction-related characters of periodic gratings. Consequently, both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity. And an optimal condition is also achieved for broadband high transparency in aperiodic metallic gratings. Experimental measurements at terahertz regime reasonably agree with both analytical analysis and numerical simulations. Furthermore, we show that for a specific light source, for example, a line source, a corresponding non-periodic transparent grating can be also designed. We expect that our findings can be applied for transparent conducting panels, perfect white-beam polarizers, antireflective conducting solar cells, and beyond.

Abstract-Asymmetric transmission of terahertz waves through a graphene-loaded metal grating

Yu Zhou¹, Ye-Qing Dong¹, Ren-Hao Fan¹, Qing Hu^1,2, Ru-Wen Peng^1,a) andMu Wang¹

1 National Laboratory of Solid State Microstructures and Department of Physics, National Center of Microstructures and Quantum Manipulation, Nanjing University, Nanjing 210093, China
2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
a) Author to whom correspondence should be addressed. Electronic mail: rwpeng@nju.edu.cn
Appl. Phys. Lett. 105, 041114 (2014); http://dx.doi.org/10.1063/1.4891818

http://scitation.aip.org/content/aip/journal/apl/105/4/10.1063/1.4891818

In this work, we theoretically investigate the propagation of terahertz (THz) waves through a graphene-loaded metal grating under external magnetic field. It is found that resonant modes in the system can be converted between transverse-electric and transverse-magneticpolarizations due to Hall conductivity of graphene. As a consequence, asymmetric transmission of THz waves through this graphene-loaded metal grating is achieved. Furthermore, by adjusting either the external magnetic field or the Fermi level of graphene, such asymmetricwave propagation can be significantly tuned. The investigations may provide a unique way to achieve the graphene-loaded optodevices for THz waves.