Abstract-Image fusion based on multiscale transform and sparse representation to enhance terahertz images

Qi Mao, Yunlong Zhu, Cixing Lv, Yao Lu, Xiaohui Yan, Dongshan Wei, Shihan Yan, and Jingbo Liu

Schematic diagram of the fusion method based on MST and SR.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-17-25293

High-quality terahertz (THz) images are vital to integrated circuit (IC) manufacturing. Due to the unique sensitivity of THz waves to different materials, the images obtained from the point-spread function (PSF) model have fewer image details and less texture information in some frequency bands. This paper presents an image fusion technique to enhance the resolution of THz IC images. The source images obtained from the PSF model are processed by a fusion method combining a multiscale transform (MST) and sparse representation (SR). The low-pass band is handled by sparse representation, and the high-pass band is fused by the conventional “max-absolute” rule. From both objective and visual perspectives, four popular multiscale transforms—the Laplacian pyramid, the ratio of low-pass pyramids, the dual-tree complex wavelet transform and the curvelet transform—are thoroughly compared at different decomposition levels ranging from one to four. This work demonstrates the feasibility of using image fusion to enhance the resolution of THz IC images.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Enhanced terahertz imaging of electronic packaging materials with deconvolution algorithm

Chan Zheng;  Zheyu Song;  Shihan Yan;  Jingbo Liu;  Dongxiong Ling;  Dongshan Wei;  Jinyun Zhou

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11441/114410D/Enhanced-terahertz-imaging-of-electronic-packaging-materials-with-deconvolution-algorithm/10.1117/12.2547637.short

This paper proposes the deconvolution image restoration algorithm, which uses the point spread function constructed by the physical characteristics of the terahertz beam to reconstruct the terahertz image and improve the image resolution[1]. At the same time, by constructing a point spread function with different penetration depths in the sample, the effect of image chromatogram on the sample can also be achieved. The integrated circuit (IC) electronic package terahertz imaging results clearly show the spatial position of the pins, internal chips and defects of the electronic packages, and analyze a variety of failure defect types, which are <1% more than the actual size.

© (2020) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Calculated Terahertz Spectra of Glycine Oligopeptide Solutions Confined in Carbon Nanotubes

Dongxiong Ling, Mingkun Zhang, Jianxun Song, Dongshan Wei

https://www.mdpi.com/2073-4360/11/2/385/htm

To reduce the intense terahertz (THz) wave absorption of water and increase the signal-to-noise ratio, the THz spectroscopy detection of biomolecules usually operates using the nanofluidic channel technologies in practice. The effects of confinement due to the existence of nanofluidic channels on the conformation and dynamics of biomolecules are well known. However, studies of confinement effects on the THz spectra of biomolecules are still not clear. In this work, extensive all-atom molecular dynamics simulations are performed to investigate the THz spectra of the glycine oligopeptide solutions in free and confined environments. THz spectra of the oligopeptide solutions confined in carbon nanotubes (CNTs) with different radii are calculated and compared. Results indicate that with the increase of the degree of confinement (the reverse of the radius of CNT), the THz absorption coefficient decreases monotonically. By analyzing the diffusion coefficient and dielectric relaxation dynamics, the hydrogen bond life, and the vibration density of the state of the water molecules in free solution and in CNTs, we conclude that the confinement effects on the THz spectra of biomolecule solutions are mainly to slow down the dynamics of water molecules and hence to reduce the THz absorption of the whole solution in confined environments.

Abstract-Terahertz Spectroscopic Signatures of Microcystin Aptamer Solution Probed with a Microfluidic Chip

Mingkun Zhang, Zhongbo Yang, Mingjie Tang , Deqiang Wang , Huabin Wang, Shihan Yan , Dongshan Wei,  Hong-Liang Cui

https://www.mdpi.com/1424-8220/19/3/534

Terahertz signature detection of biological samples in aqueous solution remains a great challenge due to the strong terahertz absorption of water. Here we propose a new preparation process for fabricating a microfluidic chip and use it as an effective sensor to probe the terahertz absorption signatures of microcystin aptamer (a linear single-stranded DNA with 60 nucleotides) dissolved in TE buffer with different concentrations. The microfluidic chip made of silicon includes thousands of 2.4 μm × 2.4 μm square-cross-section channels. One repeatable terahertz absorption signature is detected and recognized around 830 GHz, fitted to a Lorentz oscillator. This signature is theorized to originate from the bending of hydrogen bonds formed between adjacent hydrated DNA bases surrounded by water molecules. Furthermore, the low-lying vibrational modes are also investigated by molecular dynamics simulations which suggest that strong resonant oscillations are highly probable in the 815–830 GHz frequency band

Abstract-Temporal and Spatial Variability of Water Status in Plant Leaves by Terahertz Imaging

Zheyu Song,  Shihan Yan,   Ziyi Zang,  Yun Fu, Dongshan Wei,  Hong-Liang Cui,  Puxiang Lai,

https://ieeexplore.ieee.org/document/8403254/

Water and its distribution and transport dynamics in green plant leaves are vital to the growth of plants. Owing to the high sensitivity of terahertz (THz) wave to water, THz spectroscopy has great advantages in analyzing the water status of plant leaves. This paper presents a new approach to estimate the water status of plant leaves by the THz time-domain spectroscopy (THz-TDS) technique. Spatial distribution of THz transmission amplitudes located in vein xylem and mesophyll of all three kinds of leaves including wintersweet, ginkgo, and bamboo is detected by THz-TDS measurements. Based on the transmission amplitude, reconstructed THz images show that the water loss in the basal leaf region is more than that in the distal region during the natural drying process for all three plants. A good agreement is reached between the THz imaging method and the direct water weight measurement. To illustrate the accuracy and the sensitivity of the THz technique, the temporal and spatial variations of the water content in the damaged ginkgo leaf with a wound by cutting are also investigated for comparison. The water flow from the basal region to the distal region of the leaf is inferred according to the variation of THz transmission amplitude with the leaf region in different dehydration periods, which is consistent with the string-of-lakes model prediction. This paper shows the feasibility of using THz technology to monitor the temporal and spatial variability of the water status in plant leaves.

Abstract-Terahertz time-domain spectroscopy of chondroitin sulfate

Changcheng Shi, Yuting Ma, Jin Zhang, Dongshan Wei, Huabin Wang, Xiaoyu Peng, Mingjie Tang, Shihan Yan, Guokun Zuo, Chunlei Du, and Hongliang Cui

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-3-1350&origin=search

Chondroitin sulfate (CS), derived from cartilage tissues, is an important type of biomacromolecule. In this paper, the terahertz time-domain spectroscopy (THz-TDS) was investigated as a potential method for content detection of CS. With the increase of the CS content, the THz absorption coefficients of the CS/polyethylene mixed samples linearly increase. The refractive indices of the mixed samples also increase when the CS content increases. The extinction coefficient of CS demonstrates the THz frequency dependence to be approximately the power of 1.4, which can be explained by the effects of CS granular solids on THz scattering.

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

Abstract-Label-free protein detection using terahertz time-domain spectroscopy

Xiaohui Han, Shihan Yan, Ziyi Zang, Dongshan Wei, Hong-Liang Cui, and Chunlei Du

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-3-994

Protein analysis is the foundation to understanding the mechanisms of complex biological processes. As one of the most widely used techniques to determine protein species and contents, protein dot blot aids biology research but needs corresponding antibodies for marking. A label-free detection method based on terahertz time-domain spectroscopy (THz-TDS) is proposed and demonstrated to improve this traditional technology. A membrane loaded with protein samples is directly scanned using a transmission THz-TDS system for spectral imaging. Different kinds of proteins can be distinguished by the refractive index extracted from the THz transmission spectrum. The intensity or shade imaged with the THz transmission spectrum can help detect the protein quantitatively. The feasibility of this new protein assay is demonstrated by the results of systematic testing with actual samples prepared with the dot-blot protocol.

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

Abstract-Detection of DNA oligonucleotides with base mutations by terahertz spectroscopy and microstructures

Mingjie Tang,  Mingkun Zhang, Shihan Yan,  Liangping Xia, Zhongbo Yang, Chunlei Du, Hong-Liang Cui, Dongshan Wei,

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0191515

DNA oligonucleotides with a 5-base mutation at the 3'-terminus were investigated by terahertz (THz) spectroscopy in a marker-free manner. The four single-stranded oligonucleotides with 17nt have been detected with specificity on a microfluidic chip, and corroborated by spectral measurements with split-ring resonators. The number of hydrogen bonds formed between the oligonucleotide and its surrounding water molecules, deemed a key contribution to the THz absorption of biological solutions, was explored by molecular dynamics simulations to explain the experimental findings. Our work underlies the feasibility of THz spectroscopy combined with microstructures for marker-free detection of DNA, which may form the basis of a prospective diagnostic tool for studying genic mutation.

Abstract-Terahertz Scattering and Spectroscopic Characteristics of Polymethacrylimide Microstructures

Liyun Xing , Hong-Liang Cui * , Jing Bai * , Zhenxiong Zhou * , Qingyu Zhou * , Dongshan Wei , Chunlei Du , Jun Yin , Songnian Zhang

https://www.preprints.org/manuscript/201708.0058/v1

We carried out systematic measurements of Polymethacrylimide (PMI)’s Terahertz (THz) spectroscopic and scattering parameters with various thicknesses and models. The Terahertz time domain spectroscopy (THz-TDS) would be useful as a nondestructive testing (NDT) tool for PMI. While the index of refraction is very close to that of air, with flat frequency dependency, the attenuation constant exhibits a remarkable strong frequency variation, suggesting a scattering dominated attenuation process. Based on the Mie scattering model, we gave the satisfactory explanation: the THz wave propagating through the PMI suffer scattering from the micro sized particles, and the sizes of the particles (shown to obey a normal distribution) determine the frequency characteristics of the interaction.

Abstract-Enhancement Effects of the Terahertz Near-Field Microscopy

Jian Huang 1,†

, Zhongbo Yang 1,†

, Dongshan Wei 1,* , Chunlei Du 1

 and Hong-Liang Cui 1,2,* 

1 Chongqing Key Laboratory of Multi-scale Manufacturing Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China2 College of Instrumentation Science and Electrical Engineering, Jilin University, Changchun 130061, China† These authors contributed equally to this work

http://www.mdpi.com/2076-3417/5/4/1745

Terahertz near-field detection based and imaging on a nanotip has drawn wide attention following extensive applications of terahertz imaging technologies. Through the local enhanced electric field created by a terahertz nanotip in the near field, it is very likely to attain superior detection sensitivity and higher spatial resolution. This paper simulates the local enhancement effects of the terahertz near-field microscopy using a two-dimension finite difference time domain (2D-FDTD) method. Factors that influence the enhancement effects are investigated and analyzed in detail. Simulation results show that the size of the nanotip apex, the apex-substrate distance, dielectric properties of the substrate and the detected sample, etc., have significant impacts on the electric field enhancement and spatial resolution of the terahertz near-field nanotip, which can be explained from the effective polarizability of the nanotip-sample/substrate system.

Abstract-Room temperature broadband terahertz gains in graphene heterostructures based on inter-layer radiative transitions

                            

Linlong Tang^1,2, Jinglei Du^1,a), Haofei Shi^2,b), Dongshan Wei² and Chunlei Du^2,c)
 HIDE AFFILIATIONS
1 Key Laboratory of High Energy Density Physics and Technology, College of Physics and Technology, Sichuan University, Chengdu, 610064, China
2 Chongqing institute of green and intelligent technology, Chinese Academy of Sciences, Chongqing, 401122, China
http://scitation.aip.org/content/aip/journal/adva/4/10/10.1063/1.4900487
a) Electronic mail: dujl@scu.edu.cn
b) Electronic mail: shi@cigit.ac.cn
c) Electronic mail: cldu@cigit.ac.cn

We exploit inter-layer radiative transitions to provide gains to amplify terahertz waves in graphene heterostructures. This is achieved by properly doping graphene sheets and aligning their energy bands so that the processes of stimulated emissions can overwhelm absorptions. We derive an expression for the gain estimation and show the gain is insensitive to temperature variation. Moreover, the gain is broadband and can be strong enough to compensate the free carrier loss, indicating graphene based room temperature terahertz lasers are feasible.