Abstract-Characterizing the Layer Structures of the Lacquerware From the Palace Museum by Terahertz Imaging in Reflection Geometry

                                                       

Hongfei Zhang, Yuanmeng Zhao, Chenyu Li, Cunlin Zhang

https://www.frontiersin.org/articles/10.3389/fphy.2021.751205/full

Chinese lacquerware is an important invention of arts and crafts in China. In this study, Chinese lacquerware is characterized using terahertz reflectometric imaging. The lacquerware studied herein comprises an ornamental wood panel covered by multiple layers of lacquers to portray motifs. For characterizing lacquerware, a terahertz time-domain spectroscopic reflectometric imaging system is proposed. The role of the proposed terahertz imaging system in highlighting the interface between layers during stratigraphic buildup in reflection geometry is proved. The proposed system provides a universal method for assessing the structural information of lacquered objects in a contactless and non-invasive manner; moreover, it provides two-dimensional images, subsurface three-dimensional images, and stratigraphic images (b-scans) in a contactless and non-invasive manner. Using the proposed system, we examine the buried layers of the lacquerware, including faults in the wooden layer and damages in the lacquerware. Research shows the promising prospects of terahertz time-domain spectroscopic reflectometric imaging as a non-destructive detection technique suited to lacquerware.

Abstract-Terahertz Absorption Properties of Two Solid Amino Acids and Their Aqueous Solutions

 

Ping Ye,  Guoyang Wang,  Yizhou Yang, Qinghao Meng, Jiahui Wang, Bo Su, Cunlin Zhang

https://www.hindawi.com/journals/ijo/2021/9203999/

A new type of embedded cyclic olefin copolymer microfluidic chip was designed and combined with terahertz (THz) technology to study the effects of glycine and arginine on the THz wave absorption characteristics. This study aims to understand the interactions between solid amino acid molecules and between amino acid and water molecules and to determine the changes in their microstructure. By observing the intensity of the time domain spectra in the range of 0.2–2.6 THz, we found that, as the concentration of glycine and arginine increased, the THz transmission gradually decreased. It can be inferred that the molecular structure and quantity of different amino acids have different influence on the hydrogen bond, which affects the absorption coefficient in solution. It was also found that the terahertz technique is able to identify the solid amino acid species better, and it can also perform some species identification for liquid amino acids. These results provide a reference for future studies on the terahertz absorption properties of amino acid samples. Moreover, Gaussian16 software was used to calculate the terahertz spectra using the density functional theory, B3LYP functional, and 6-31G basis set. Additionally, Gaussian View6 video software provided the frequency values, molecular vibration modes of the theoretical absorption peaks of glycine, arginine, and its aqueous solutions in the frequency range of 0.2–2.6 THz, which offers theoretical support for future studies.

Abstract-Diagnosis of hepatocellular carcinoma based on a terahertz signal and VMD-CWSE

Haishun Liu, Ke Zhao, Xiangyi Liu, Zhenwei Zhang, Jingyu Qian, Cunlin Zhang, and Meiyan Liang

Schematic sketch of the equipment

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-11-9-5045

A novel strategy on combining variational mode decomposition (VMD) and composite weighted-scale sample entropy (CWSE) modified from composite multiscale entropy (CMSE) is proposed to screen hepatocellular carcinoma (HCC) by measuring the terahertz (THz) pulse signals of ten normal and ten HCC serums. Eight measured HCC specimens are negative in serum biomarker alpha fetoprotein (AFP) determination. In CWSE, the time series with weighted-scales are generated from the weighted average processing in the coarse-grained time series corresponding to each scale of the CMSE algorithm. VMD served as a preprocessing method was introduced into decomposing THz signal to obtain the mode functions of specific bandwidth for identification. Final results reveal that more obtainable entropy values of CWSE for recognition in comparison to those of CMSE on the basis of the rule of statistically significant difference and effect size and also manifest the stronger discriminability than the traditional THz parameters. This study provides a new potential auxiliary tool for diagnosis HCC and develops the methodology on the discrimination for similar THz signals.

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

Abstract-Ultrafast hydrogen bond dynamics of liquid water revealed by terahertz-induced transient birefringence

Hang Zhao, Yong Tan, Liangliang Zhang, Rui Zhang, Mostafa Shalaby, Cunlin Zhang, Yuejin Zhao & Xi-Cheng Zhang

TKE measurement of liquid water.

https://www.nature.com/articles/s41377-020-00370-z

The fundamental properties of water molecules, such as their molecular polarizability, have not yet been clarified. The hydrogen bond network is generally considered to play an important role in the thermodynamic properties of water. The terahertz (THz) Kerr effect technique, as a novel tool, is expected to be useful in exploring the low-frequency molecular dynamics of liquid water. Here, we use an intense and ultrabroadband THz pulse (peak electric field strength of 14.9 MV/cm, centre frequency of 3.9 THz, and bandwidth of 1–10 THz) to resonantly excite intermolecular modes of liquid water. Bipolar THz field-induced transient birefringence signals are observed in a free-flowing water film. We propose a hydrogen bond harmonic oscillator model associated with the dielectric susceptibility and combine it with the Lorentz dynamic equation to investigate the intermolecular structure and dynamics of liquid water. We mainly decompose the bipolar signals into a positive signal caused by hydrogen bond stretching vibration and a negative signal caused by hydrogen bond bending vibration, indicating that the polarizability perturbation of water presents competing contributions under bending and stretching conditions. A Kerr coefficient equation related to the intermolecular modes of water is established. The ultrafast intermolecular hydrogen bond dynamics of water revealed by an ultrabroadband THz pump pulse can provide further insights into the transient structure of liquid water corresponding to the pertinent modes.

Abstract-Terahertz Wave Modulation by Pre-plasma Using Different Laser Wavelength

Tong Wu, Liquan Dong, Rui Zhang, Hang Zhao, Yuejin Zhao, Cunlin Zhang, Liangliang Zhang

https://link.springer.com/article/10.1007%2Fs10762-019-00618-9

We report the terahertz (THz) wave modulation from a pre-plasma using different laser wavelengths, which is intersected orthogonally to the two-color laser filament produced by 800-nm laser pulse. When the pre-plasma exists, the THz radiation excited by the two-color field decreases significantly and the modulation depth increases with the increasing modulation pulse wavelength. Moreover, the amplitude reduction at high frequency in THz spectrum and the THz wave polarization change also have the modulation pulse wavelength dependence. These results can be explained by a photocurrent model considering wavelength-dependent ionization rate. The work contributes to further understand the theoretical mechanism of THz wave generation and enrich the practical application of ultrafast THz modulator.

Abstract-The active modulation of flexible terahertz tube

Jing Liu, Hongyu Ji, Jingling Shen, Cunlin Zhang, Yuejin Zhao,


https://www.sciencedirect.com/science/article/abs/pii/S0925346719304756

We demonstrated a flexible polyimide terahertz tube that can modulate Terahertz (THz) wave efficiently based on indium oxide (In2O3) nanoparticle. The transmission of the THz pulse can be modulated using optical control over 0.2 to 2.6 THz, and the modulation depth reached up to 14%. By combining nano-indium oxide layer with metal periodic metamaterial structure, the modulation was optimized to 35%. The results show that a photo-excited tunable terahertz modulator can be realized by irradiating the structure under different intensity of the laser beam.

Abstract-Using Markov constraint and constrained least square filter to develop a novel method of passive terahertz image restoration

Yuanmeng Zhao, Xiao Sun, Cunlin Zhang, Yuejin Zhao,

https://iopscience.iop.org/article/10.1088/1742-6596/1187/4/042094

In recent years, passive terahertz imaging has gained significant attention in both research and practice. One big challenge with passive terahertz imaging is its low-quality images with high level of noise. State-of-the art image restoration methods have been developed for image denoising, such as methods based on Markov constraint and regular filter methods. Building upon these two methods, this paper develops a novel method for passive terahertz image restoration which preserves well both high frequency and low frequency information of the images. Performance of our method is evaluated using two common image criteria of the image sharpness, i.e. edge intensity and definition. Experimental results showed our method outperform state-of-the art methods for passive terahertz image restoration.

Abstract-Effect of the broken symmetry on the electromagnetic properties in the terahertz ring resonators

Lan Shi, Qingli Zhou, Wanlin Liang, GeLi, Jianhai Sun, Cunlin Zhang



https://www.sciencedirect.com/science/article/abs/pii/S0030401819303086

We experimentally and numerically demonstrate resonant behaviors of terahertz metamaterials can be tuned significantly by their asymmetry. For the ring structure cut symmetrically, transmission spectra are nearly the same as those of their individual single-ring resonators. However, three resonant dips appear in the spectra due to the broken symmetry in single-ring resonator cut asymmetrically from the top. For the asymmetrically-cut double-ring structures, the mutual coupling between four arcs results in multi-resonance dips, especially a low-frequency Fano-like resonance accompanied with a sharp peak. Our asymmetric structures could offer potential applications in terahertz frequency selectors and bio-sensors.

Abstract-Resonance coupling and optical modulation properties in terahertz asymmetric double-wire structures

Ge Li, Qingli Zhou, Wanlin Liang, Cunlin Zhang,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108261P/Resonance-coupling-and-optical-modulation-properties-in-terahertz-asymmetric-double/10.1117/12.2502510.short

The spectral characteristics of the asymmetric double-wire structures have been investigated in the terahertz (THz) range. Based on the THz time-domain spectroscopy system, the spectral of the samples has been measured. It is shown that a transparent peak appears in the transmission spectrum which indicate that a resonance coupling exist between the two metal bars. Furthermore, we study the optical modulation properties when the pump light irradiates on the sample by using optical pump-terahertz probe technique (OPTP). The measured results indicate that the pump light can realize an optical switch effect to modulate the transmittance of THz wave. When adjusting the time delay between the optical pump and the terahertz probe pulses, the transmittance of THz wave varies, indicating the photoexcited carriers in the substrate have great influence on the resonance characteristics of the structure. Our obtained results indicate optical modulation method could provide the functionally potential applications in the terahertz modulators and filters.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Study on asymmetric terahertz metamaterials for biosensing

Wanlin Liang, Qingli Zhou, Ge Li, Cunlin Zhang

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108261Q/Study-on-asymmetric-terahertz-metamaterials-for-biosensing/10.1117/12.2502511.short

Recently, the terahertz biosensors based on metamaterials have attracted much attention due to the fact that metamaterials are sensitive to the local enhancement of electromagnetic field and the changes of the surrounding dielectric environment. In order to obtain the resonances with the high quality factor for biosensing, here we designed, simulated, and fabricated the metamaterial structures composed of a series of the asymmetric “double” circular arc (DASR) structures. The experimental data show there are three sharp resonance dips named Fano resonance in the terahertz transmission spectra. In the previous study of asymmetric double rings, we studied the effect of different cutting widths on the transmission characteristics of terahertz when the samples were placed at 0 degrees. Here, the spectral characteristics and polarization conversion characteristics of the samples after 90 degrees were studied. We found that when the sample rotated by 90 degrees only two resonance dips exist in the transmission spectrum. As the separation of asymmetric arcs gradually increases, two resonance frequencies also show blue-shift. To further analyze the reasons for the changes in the transmission spectrum at different angles of sample placement, we present the surface currents and the electromagnetic field distributions in those structures. Our obtained results indicate the terahertz metamaterial has great potential in application of biosensing field.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Terahertz Wave Generation From Noble Gas Plasmas Induced by a Wavelength-Tunable Femtosecond Laser

Hang Zhao, Liangliang Zhang, Suxia Huang, Shijing Zhang, Cunlin Zhang

https://ieeexplore.ieee.org/document/8340859

We investigated the effects of pump wavelength on terahertz wave generation via two-color laser-induced plasma in various gas targets including nitrogen and noble gases. The terahertz energy was measured as functions of pump wavelength, input pulse energy, gas species, and pressure. The results suggest that the plasmas in the heavier gases induced by relatively longer wavelength lasers are more likely to generate higher energy terahertz waves. However, the existence of phase slippage in the neutral gases causes distinct fluctuations in the terahertz energy as the gas pressure increases. Meanwhile, the terahertz waves produced in the heavier gas are more likely to saturate at relatively higher pressures or incident optical powers. We propose an ionization rate formula associated with the gas species and pump wavelength to theoretically explain the validity of the experimental results. As a result, the terahertz pulse energy approaches a maximum value of 0.099 μJ per pulse in xenon with a 1500-nm excitation laser, and the terahertz wave to optical pulse energy conversion efficiency reaches 5.6 × 10 -3 , which is an order of magnitude higher than that of a conventional 800-nm pump laser.

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-Dimensionality Reduction for Identification of Hepatic Tumor Samples Based on Terahertz Time-Domain Spectroscopy

 Haishun Liu,  Zhenwei Zhang, Xin Zhang,  Yuping Yang, Zhuoyong Zhang, Xiangyi Liu, Fan Wang,  Yiding Han, Cunlin Zhang

https://ieeexplore.ieee.org/document/8333778/

Terahertz time-domain spectroscopy (THz-TDS) combining with chemometrics methods was proposed for the identification of hepatic tumors. Two linear compression methods, principle component analysis and locality preserving projections (LPPs), and a nonlinear method, Isomap, were used to reduce the dimensionality of the measured dataset. Comparing two-dimensional (2-D) data reduced by these three dimensionality reduction techniques, only 2-D Isomap plot could separate the distances between two classes for the THz time-domain data and LPP had capacity of distinguishing two types of samples building on frequency-domain data. The best classification accuracies from 2-D time-domain data were 99.81±0.30% and 99.69±0.61% given by Isomap probabilistic neural network (PNN) and Isomap support vector machine (SVM), respectively, while the best classification results of 2-D frequency-domain data were 100.00±0.00%, 99.75±0.32% provided by LPP-PNN, LPP-SVM. The results showed that Isomap and LPP are appropriate techniques to reflect the nonlinear manifold of the THz data. The THz technology either in time-domain or frequency-domain coupled with Isomap-PNN or LPP-PNN could offer a potential procedure to identify hepatic tumors.

Abstract-Excitation-wavelength dependent terahertz wave polarization control in laser-induced filament

Liangliang Zhang, Shijing Zhang, Rui Zhang, Tong Wu, Yuejin Zhao, Cunlin Zhang, and X.-C. Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-32346

We examine the terahertz (THz) emission from air filament driven by two-color lasers with relatively longer wavelengths than 800 nm. The THz energy dependence on the input laser energy increases more rapidly with a longer laser wavelength, and the scaling laws of THz energy as a function of fundamental wavelength vary for different optical powers, which is theoretically validated by considering the optical wavelength-dependent ionization rate. Furthermore, the THz polarization undergoes a continuous rotation as a function of the laser wavelength, since the relative phase and polarization of the two pulses are adjusted through changing the excitation wavelength in the frequency doubling crystal. Our results contribute to the understanding of THz wave generation in a femtosecond laser filament and suggest a practical way to control the polarization of terahertz pulses for potential applications.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Influence of asymmetric structures on electromagnetic response characteristics of terahertz metamaterials

Lan Shi; Qingli Zhou,  Changxiang Liu, Huijuan Sun, Chenyu Li, Cunlin Zhang


https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10459/104590H/Influence-of-asymmetric-structures-on-electromagnetic-response-characteristics-of-terahertz/10.1117/12.2284372.pdf

Asymmetric split-ring resonators (SRRs) exhibit different resonant modes and phenomena that do not have in symmetric structure, such as Fano resonance, electromagnetic induced transparency, and plasma resonance hybridization. The asymmetric SRR was first confirmed to produce narrow linewidth resonance and has a high quality factor. Then it extends to the terahertz and near infrared bands. It has been found that the most common way to modulate the electromagnetic response characteristics is to change the asymmetry of the SRR and the coupling strength between the resonators. Here we use the finite-difference time-domain (FDTD) method to simulate the electromagnetic response characteristics of asymmetric structures. When the polarization direction along the bottom bar of the U-shaped structure, there are two similar resonance dips like those in typical SRR structure. When the incident wave is perpendicular to the bottom bar, there is only one dipole resonance. However, with the broken of the symmetry, the resonant behaviors will change. In horizontal direction, both the resonant frequency and transmittance has changed. In the vertical polarization, there are three resonant dips in transmission spectrum. Meanwhile a sharp window appears in transmission spectrum. In addition, when we turn the bottom bar of the U-shaped structure into the arc shape, we just find very slight change in frequency-shift and modulation depth in both cases, showing the impact of the short arc is nearly equivalent to the linear dipole resonance. Our obtained results indicate that we could tune the electromagnetic resonances in metamaterials and the interaction mechanism with terahertz wave.

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Studies on the trapped-mode resonant properties in asymmetric terahertz metamaterial

Wei Chen,  Qingli Zhou,  Chenyu Li, Lan Shi,  Changxiang Liu, Cunlin Zhang

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10459/104590D/Studies-on-the-trapped-mode-resonant-properties-in-asymmetric-terahertz/10.1117/12.2284323.pdf

Artificial metamaterials with appropriate design can exhibit unique electromagnetic phenomena which do not exist in natural materials. Some studies have shown that the method of breaking the geometric symmetry is capable to modify the electromagnetic responses. Here, we simulated and measured the transmission spectra of period arrays of subwavelength double-bar structure. The obtained results show the trapped-mode resonance with Fano-shaped spectrum can be induced in terahertz metamaterial with asymmetric double-bar structure, accompanied with a metamaterial induced transparency window between two resonant dips. And the bar spacing and lattice constant have great impact on the coupling strength concerned with the transparency position and spectral lineshape. We attribute there are two mechanisms together determine the coupling pattern between the bar array and the terahetz wave, the coupling between the bars of the same unit cell and the coupling between the bars of the neighbouring cells. Our obtained results indicate that such metamaterial with very simple configuration could also provide the potential application in the field of terahertz slow-light devices, amplitude and phase modulators.

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Resonance coupling and polarization conversion in terahertz metasurfaces with twisted split-ring resonator pairs

Chenyu Li, Chun-Chieh Chang, Qingli Zhou, Cunlin Zhang, and Hou-Tong Chen

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-21-25842

We investigate edge-coupling of twisted split-ring resonator (SRR) pairs in the terahertz (THz) frequency range. Using a simple coupled-resonator model we show that such a system exhibits resonance splitting and cross-polarization conversion. Numerical simulations and experimental measurements agree well with theoretical calculations, verifying the resonance splitting as a function of the coupling strength given by the SRR separation. We further show that a metal ground plane can be integrated to significantly enhance the resonance coupling, which enables the effective control of resonance splitting and the efficiency and bandwidth of the cross-polarization conversion. Our findings improve the fundamental understanding of metamaterials with a view of accomplishing metamaterial functionalities with enhanced performance, which is of great interest in realizing THz functional devices required in a variety of applications.

© 2017 Optical Society of America

Abstract-Composite multiscale entropy analysis of reflective terahertz signals for biological tissues

Rui Zhang, Yuezhi He, Kai Liu, Liangliang Zhang, Shijing Zhang, Emma Pickwell-MacPherson, Yuejin Zhao, and Cunlin Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-20-23669

We demonstrate a composite multiscale entropy (CMSE) method of terahertz (THz) signal complexity analysis to distinguish different biological tissues. The THz signals reflected from fresh porcine skin and muscle tissues were measured and analyzed. The statistically significant difference and separation of the two tissues based on several parameters were analyzed and compared for THz spectroscopy and imaging, which verified the better performance of the CMSE method and further enhancement of the contrast among THz signals that interact with different tissues. This process provides a better analysis and discrimination method for THz spectroscopy and imaging in biomedical applications.

© 2017 Optical Society of America

Abstract-Investigate the effects of EG doping PEDOT/PSS on transmission and anti-reflection properties using terahertz pulsed spectroscopy

Yiwen Sun, Shengxin Yang, Pengju Du, Fei Yan, Junle Qu, Zexuan Zhu, Jian Zuo, and Cunlin Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-3-1723&origin=search

The conductivity of poly(3,4-ethylene dioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) is significantly enhanced on adding some organic solvent such as ethylene glycol (EG). In this paper, the optoelectronic properties of EG doped PEDOT/PSS on transmission and anti-reflection effects are investigated in detail by terahertz time domain spectroscopy (THz-TDS). The transmission line circuit theory gives us an insight into the THz transmission mechanisms of the main and second pulses. In particular, we show that the conductivities of 10% EG doped PEDOT/PSS are nearly frequency independent from 0.3 to 1.5 THz. To demonstrate applications of this property, we design and fabricate broadband terahertz neutral density filters and anti-reflection coatings based on 10% EG doped PEDOT/PSS thin films with varying thickness. Our measurements highlight the capability of THz-TDS to characterize the conductivity of EG doped PEDOT/PSS, which is essential for broadband optoelectronic devices in THz region.

© 2017 Optical Society of America

Abstract-THz Spectroscopic Identification of Red Mineral Pigments in Ancient Chinese Artworks

Yuping Yang, Dongwei Zhai, Zhenwei Zhang, Cunlin Zhang

https://link.springer.com/article/10.1007%2Fs10762-017-0408-8

Nondestructive analysis of historical objects is of significance for cultural heritage conservation. In this paper, terahertz time-domain spectroscopy (THz-TDS) was used to distinguish seven red mineral pigments used in ancient Chinese artworks. Two absorption features of natural minerals HgS and four highly resolved spectral features of mineral pigment Pb3O4 were observed and identified as their fingerprints in the range 0.2 to 3.0 THz, based on which the spatial distribution of individual chemical substances including cinnabar, vermilion, and red lead were clearly revealed at various frequencies using terahertz spectroscopy imaging. Moreover, a noncontact evaluation of thickness changing and dehydration of a wet painting was monitored by inferring time delay as well as signal amplitude of THz pulses transmitted through the painting. In order to demonstrate the feasibility of THz-TDS and THz imaging for authentic artworks detection, a complete set of THz analysis of two nineteenth century wall paintings discovered in the Fuchen Temple of the Forbidden City, Beijing, was performed and the results indicate that THz measurement techniques provide a noninvasive and nondestructive solution for the care, preservation, and restoration of cultural relics.