Abstract-Dual-band ultrasensitive terahertz sensor based on tunable graphene metamaterial absorber

 

Tao Chen, Weijie Jiang, Xianhua Yin, 

https://www.sciencedirect.com/science/article/abs/pii/S0749603621000963

In this paper, we propose a dual-band tunable absorber with a graphene-dielectric-metal structure as a sensor in the terahertz (THz) region. The finite element method (FEM) based on the CST microwave studio software is used in modeling and numerical analysis. Strong interaction between graphene surface plasmon resonance (SPR) and the absorber gives rise to two ultra-narrow perfect absorption peaks, and the position of the resonance frequencies can be adjusted by tuning the chemical potential of graphene in a wide range. In addition, the high symmetry of the absorber brings polarization and angle insensitivity, in which an absorption rate of over 90% can be obtained when the oblique incident angle is close to 80° in the transverse magnetic (TM) mode. For refractive index sensing, the simulation results show that the proposed structure achieves the maximum sensitivity, Q factor, and figure-of-merit (FOM) of 2.475 THz per refractive index unit (THz/RIU), 216.29, and 76.89 RIU−1, respectively. Therefore, we believe that the proposed sensor with such high performance has a promising application for biomedical diagnosis and environmental monitoring.

Abstract-Achromatic terahertz Airy beam generation with dielectric metasurfaces

 

Qingqing Cheng , Juncheng Wang, Ling Ma, Zhixiong Shen, Jing Zhang, Xiaoying Zheng ,Tao Chen, Ye Yu, Dong Yu, Qiong He, Wei Hu, Tao Li, Songlin Zhuang,  Lei Zhou

https://www.degruyter.com/view/journals/nanoph/ahead-of-print/article-10.1515-nanoph-2020-0536/article-10.1515-nanoph-2020-0536.xml?rskey=WV2s5h&result=7&tab_body=abstract

Airy beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

Abstract-Identification terahertz spectra for the dyestuffs based on principal component analysis and Savitzky-Golay filter

Haishun Liu, Zhenwei Zhang, Yuping Yang, Tao Chen, Cunlin Zhang,



https://www.sciencedirect.com/science/article/pii/S0030402618310519

Terahertz time-domain spectroscopy (THz-TDS) was employed to measure the absorption spectra for three types of dyestuff at the frequency range of 0.3~2.2 THz. The raw spectra data were implemented dimensionality reduction by using principal component analysis (PCA). Depending on the weak cluster trend determined by the score plot, different levels of Savitzky-Golay (SG) smoothing combined with PCA processing was performed for elevating the recognition rate. The recognition effects were assessed by fuzzy c-means (FCM) and k-means clustering techniques, which consistently demonstrated the combination of polynomial order 1 and window size 5 for SG smoothing achieved the highest accuracy of 94.44%. For k-means and FCM clustering, the identification accuracies of raw spectra were 87.5% and 84.72% respectively, realizing the elevation recognition rate by using SG smoothing with polynomial order 1 and window size 5. Our results suggested SG smoothing coupled with PCA was a potent method to cope with THz spectra recognition for dyestuffs.

Abstract-Experimental and theoretical investigations of tartaric acid isomers by terahertz spectroscopy and density functional theory

Tao Chen, Qin Zhang, Zhi Li, Xianhua Yin, Fangrong Hu,

https://www.sciencedirect.com/science/article/pii/S1386142518306334

The terahertz (THz) absorption spectra of l-, d-, and dl-tartaric acid have been measured in the frequency range from 0.2 to 2.0 THz by terahertz time-domain spectroscopy (THz-TDS). The characteristic absorption peaks of these three tartaric acid isomers were obtained, which showed remarkable difference between enantiomers (l- and d-tartaric acid) and the racemic compound (dl-tartaric acid) in their peak frequencies. In parallel with the experimental study, theoretical calculations on isolated-molecule and unit cell of tartaric acids using density functional theory (DFT) were also performed for simulating the experimental THz spectrum features, which were in good agreement with the experimental data. Results demonstrate that THz-TDS can distinguish the tiny diversity between tartaric acid chiral isomers and its racemic compound, and provided an effective method for molecular identification in biological and biomedical engineering.

Abstract-Tunable terahertz wave difference frequency generation in a graphene/AlGaAs surface plasmon waveguide

Tao Chen, Liangling Wang, Lijuan Chen, Jing Wang, Haikun Zhang, and Wei Xia

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-6-3-186

Graphene-based surface plasmon waveguides (SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs SPW structure for terahertz wave difference frequency generation (DFG) under near-infrared pumps. The composite waveguide, which supports single-mode operation at terahertz frequencies and guides two pumps by a high-index-contrast AlGaAs/AlO𝑥$\mathrm{AlGaAs}/{\mathrm{AlO}}_x$ structure, can confine terahertz waves tightly and realize good mode field overlap of three waves. The phase-matching condition is satisfied via artificial birefringence in an AlGaAs/AlO𝑥$\mathrm{AlGaAs}/{\mathrm{AlO}}_x$ waveguide together with the tunability of graphene, and the phase-matching terahertz wave frequency varies from 4 to 7 THz when the Fermi energy level of graphene changes from 0.848 to 2.456 eV. Based on the coupled-mode theory, we investigate the power-normalized conversion efficiency for the tunable terahertz wave DFG process by using the finite difference method under continuous wave pumps, where the tunable bandwidth can reach 2 THz with considerable conversion efficiency. To exploit the high peak powers of pulses, we also discuss optical pulse evolutions for pulse-pumped terahertz wave DFG processes.

© 2018 Chinese Laser Press

Abstract-Highly Sensitive Detection of Carbendazim by Using Terahertz Time-Domain Spectroscopy Combined With Metamaterial

 Binyi Qin,  Zhi Li,  Fangrong Hu,  Cong Hu,  Tao Chen,  Huo Zhang,   Yonghong Zhao

http://ieeexplore.ieee.org/document/8252737/

The rapid and sensitive detection of pesticide residue is essential for ensuring the food safety of consumers. However, there are many disadvantages for current approaches to detect pesticide residue, such as complex pre-treatment and low sensitivity. In this paper, we demonstrate a highly sensitive carbendazim detection method by using terahertz time-domain spectroscopy (THz-TDS) combined with metamaterial. The metamaterial composed of metal ohm ring arrays, is applied in detecting different concentrations of carbendazim. Resonant peaks of metamaterial move to a lower frequency as the concentration increases. The results illustrate that metamaterial can detect trace amounts of carbendazim, as small as 5 mg/L, which is about 104 times enhancement compared to the squash method for THz-TDS detection. It also means that metamaterial combined with THz-TDS is a potential new approach for food quality and safety control.

Abstract-Identification of genetically modified cotton seeds by terahertz spectroscopy with MPGA-SVM

• Binyi Qin^a, b, 
• Zhi Li^a, c,  
• Tao Chen^c, 
• Yu Chen^d

• ^a School of Mechano-Electronic Engineering, Xidian University, Xi’an, Shanxi 710071, China
• ^b School of Electronics and Communication Engineering, Yulin Normal University, Yulin, Guangxi 537000, China
• ^c Guangxi Key Laboratory of Automatic Detecting Technology and Instruments, School of Electronic Engineering and Automation, Guilin University of Electronic Technology, Guilin, Guangxi 541004, China
• ^d SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China

http://www.sciencedirect.com/science/article/pii/S003040261730699X

The purpose of this paper was to propose a method that combines support vector machine (SVM) and multi-population genetic algorithm (MPGA) for identifying Genetically modified (GM) cotton seeds with THz spectroscopy. The parameters of SVM were tuned by using MPGA. Comparing previous reports of THz-TDS for GM crops detection, we used a larger sample size and more evaluation criterions (i.e. confusion matrix, average accuracy and 95th percentile of accuracy) in the experiment. Principal component analysis (PCA) was utilized to reduce dimensions of THz absorbance spectra, and then used the result of PCA as the input of different classifiers. When the input dimensionality of MPGA-SVM was 12, recall, precision and F-score were more than 97.9%, 96% and 0.9796, respectively, and accuracy was 99%. To further study the performance of MPGA-SVM with different input dimensionality, different number of principal components (ranged from 2 to 16 at intervals of 2) was selected. In addition, the proposed method was compared with traditional classifiers (decision trees (DT), k-nearest neighbor (KNN) and discriminant analysis (DA)). All the results showed that MPGA-SVM has better performance than other classifier. Thus, MPGA-SVM combined with THz spectroscopy is a potential identification tool for GM cotton seeds detection.

Abstract-Terahertz pulsed spectroscopy of paraffin-embedded brain glioma

Kun Meng ; Tu-nan Chen ; Tao Chen ; Li-guo Zhu ; Qiao Liu ; Zhao Li ; Fei Li; Sen-cheng Zhong ; Ze-ren Li ; Hua Feng ; Jian-heng Zhao

[-] Author Affiliationshttp://biomedicaloptics.spiedigitallibrary.org/article.aspx?articleid=1887716

Kun Meng

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

China Academy of Engineering Physics, Terahertz Research Center, Mianyang, Sichuan 621900, China

Tu-nan Chen

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

Third Military Medical University, Southwest Hospital, Department of Neurosurgery, No. 30, Gaotanyan Street, Shapingba, Chongqing 400038, China

Tao Chen, Jian-heng Zhao

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

Li-guo Zhu, Qiao Liu, Sen-cheng Zhong, Ze-ren Li

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

China Academy of Engineering Physics, Terahertz Research Center, Mianyang, Sichuan 621900, China

Zhao Li, Fei Li, Hua Feng

Third Military Medical University, Southwest Hospital, Department of Neurosurgery, No. 30, Gaotanyan Street, Shapingba, Chongqing 400038, China

J. Biomed. Opt. 19(7), 077001 (Jul 07, 2014). doi:10.1117/1.JBO.19.7.077001

History: Received April 11, 2014; Revised June 4, 2014; Accepted June 13, 2014

Text Size: A A A

 Open Access

Abstract.  The refractive indices, absorption coefficients, and complex dielectric constants of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time-domain spectroscopy (THz-TDS) system in the 0.2- to 2.0-THz range. The spectral differences between gliomas and normal brain tissues were obtained. Compared with normal brain tissue, our results indicate that paraffin-embedded brain gliomas have a higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the best THz frequencies for different methods of paraffin-embedded brain glioma imaging, such as intensity imaging, coherent imaging with continuum THz sources, and THz pulsed imaging with short-pulsed THz sources, are analyzed.

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Abstract-Terahertz gas sensing based on a simple one-dimensional photonic crystal cavity with high-quality factors

Tao Chen, Zhanghua Han, Jianjun Liu, and Zhi Hong  »View Author Affiliations

Applied Optics, Vol. 53, Issue 16, pp. 3454-3458 (2014)
http://dx.doi.org/10.1364/AO.53.003454

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-16-3454

We report in this paper terahertz gas sensing using a simple 1D photonic crystal cavity. The resonant frequencies of the cavity depend linearly on the refractive index of the ambient gas, which can then be measured by monitoring the resonance shift. Although quite easy to manufacture, this cavity exhibits high-quality factors, facilitating the realization of high sensitivity in the gas refractive index sensing. In our experiment, 6% of the change of hydrogen concentration in air, which corresponds to a refractive index change of 1.4×10−5, can be steadily detected, and different gas samples can be easily identified. Our experimental results are consistent with the theoretically calculated spectral responses of the cavity using the transfer matrix method.

© 2014 Optical Society of America