连续波太赫兹成像系统的单幅图像超分辨重建

针对现有的太赫兹成像系统所需硬件设备复杂且昂贵的问题,设计了基于单幅图像超分辨重建的连续波太赫兹成像系统,降低设备复杂度和硬件成本。通过对该成像系统生成的太赫兹图像进行双维度预处理,降低图像处理的占用内存,提高后续处理速度。引入限制对比度自适应直方图均衡方法对太赫兹图像进行分区域对比度提升,有效解决太赫兹图像对比度低的问题。利用稀疏表示和字典学习实现太赫兹图像的超分辨重建,提出了反余割拟牛顿平滑零范数的算法解决零范数优化问题,提高了重建精度。通过对该成像系统采集的单幅太赫兹图像进行超分辨重建,在边缘强度上提高了3.232,在平均梯度对比中提高了0.300,验证了对单幅太赫兹图像超分辨重建的有效性与优越性。     

聚四氟乙烯材料的太赫兹特性

太赫兹(THz)辐射能够穿透很多对可见光不透明的非金属、非极性材料,而用X辐射对这些材料成像的对比度又相对低,因此,太赫兹成像在安全检测和生产质量控制等领域日益受到重视。对成像材料的太赫兹特性的实际测量是太赫兹成像技术的重要组成部分。利用CO_2激光抽运太赫兹激光对聚四氟乙烯材料的太赫兹吸收特性和透过光斑轮廓进行了实验研究,获得聚四氟乙烯在70.51μm,96.5μm,118.83μm,122.4μm,158.51μm,184.31μm和214.58μm波长的吸收系数。     

隐藏物的连续太赫兹反射扫描成像实验

太赫兹成像的优势在于能够穿透大多数非金属、非极性物质进行隐藏物的探测,而且不会对生物体造成伤害。其中太赫兹反射成像具有更为广泛的应用空间。由于对常见包装品和衣物的穿透能力在太赫兹反射成像系统的评估中十分重要,故利用CO2抽运太赫兹激光器所搭建的2.52THz反射扫描成像系统对剃须刀、铅笔字、5角硬币、金属纪念币和星卡等多种物体进行了穿透力实验;以纸、纸质快递信封和实验服为遮挡物,进行了成像对比分析。实验结果表明,该成像装置可以穿透单层实验服或单层纸制信封对目标成反射像,最大插入损耗近42dB。     

基于太赫兹超材料的微流体折射率传感器

设计加工了一种太赫兹超材料微流体传感器件,利用时域有限差分法（Finite Difference Time Domain,FDTD）对其在太赫兹波段的传输、谐振及传感特性进行数值模拟。采用太赫兹时域光谱系统实验研究了偏振方向对传感器灵敏度的影响。实验结果表明,当超材料谐振环开口方向与入射太赫兹波的偏振方向平行和垂直时,折射率传感灵敏度可分别达到39.29 GHz/RIU和74.43 GHz/RIU。通过等效电路模型对该超材料器件的传输和谐振特性做了分析,并进一步明确了其传感机制。该超材料器件可对微量液体（5 l/mm2）实现芯片式的折射率传感,具有较高的传感灵敏度,在化学生物传感器的设计和制造领域具有潜在的应用前景。     

太赫兹波谱与成像技术

太赫兹波谱与成像是太赫兹科学与技术的重要内容,在生物、物理、化学、安检、航空航天等领域有重要的应用前景,是近年来的研究热点。首先简单介绍了太赫兹时域光谱、时间分辨光谱和超连续谱等波谱技术,并列举了相关波谱技术对爆炸物识别和对半导体材料超快载流子动力学的研究结果。讨论了时域扫描成像、实时焦平面成像、连续波成像和被动成像等太赫兹成像技术。相应地分别给出了利用上述技术对葵花籽、玩具手枪、航天泡沫和人体的成像研究结果。     

基于相干层析的太赫兹成像技术研究

介绍了一种结合光学相干层析技术和太赫兹技术的太赫兹三维成像技术——太赫兹相干层析成像技术。该技术利用宽频太赫兹的弱相干原理,可以实现对待测样品进行高精度的三维成像。实验结果表明太赫兹相干层析成像技术的纵向分辨能力高于100 μm。在纵向探测精度方面,该技术相对传统的方案有了较大的提高,在高精度太赫兹无损探测领域具有巨大的应用前景。     

太赫兹动态超表面

太赫兹波段处于微波、毫米波与光波段之间，其相关技术对下一代高速通信、高分辨成像、智能感通一体等多个信息领域的发展具有重要的意义.发展太赫兹应用技术需要对太赫兹波束进行操控和信息加载.动态超表面作为一种新型的实现结构和器件，是实现该功能的重要途径之一.本文将以太赫兹动态超表面的调控功能作为分类依据，从相辅相成的材料、结构、机理及其最终表现的应用演示对幅度调控、相位调控、极化调控、波束调控、高阶非线性调控太赫兹动态超表面5个方面进行了概述，介绍了不同类型动态超表面的相似性与独特性，并对部分工作进行了指标对比.最后，展望了太赫兹动态超表面的发展趋势.本文希望更多学者可以了解太赫兹动态超表面，并促进此领域的发展.     

基于线阵扫描成像的太赫兹图像超分辨率重建

针对太赫兹扫描成像设备存在的图像清晰度差、边缘模糊等问题,提出了一种基于生成对抗网络的太赫兹图像超分辨率重建算法。首先,在处理太赫兹图像时引入限制对比度自适应直方图均衡方法,有效解决了太赫兹图像对比度低的问题;其次,在生成对抗网络的基础上,提出了一种基于增强注意力机制的残差生成对抗网络,实现了太赫兹扫描图像的超分辨率重建,提升了图像纹理和细节的重建能力;最后利用频谱归一化的U-net网络对生成器生成的重建图像进行判别,增强了训练的稳定性。实验结果表明,提出的太赫兹图像超分辨率重建算法将太赫兹线阵相机所成太赫兹图像的边缘强度提高了7%,峰值信噪比提高了13%,平均梯度提高了12%,结构相似度提高了14%,验证了该算法的优越性和有效性。     

THz主动焦平面成像系统的MRC匹配滤波器模型

太赫兹焦平面成像技术具有成像分辨率高、时间周期短、系统简单,体积小等诸多优点,在安检和工业检测等领域具有广泛的应用前景。由于目前太赫兹焦平面器件灵敏度尚低,大多只能采用主动成像模式,且目前尚没有较公认可测试的THz主动成像系统性性能评价参数及其模型,难以为其系统设计提供理论基础和方法指导。本文结合太赫兹射源及焦平面探测器特性,同时考虑目标-背景特性、大气衰减及器件衰减等影响,研究建立了太赫兹主动成像系统的最小可分辨对比度匹配滤波器模型。并结合文献示例以及实际太赫兹焦平面主动成像系统的测试结果,验证了最小可分辨对比度模型。结果表明：实验测量值和计算值基本一致,误差在合理范围之内,从而表明了本文模型的有效性。     

太赫兹超材料生物检测应用研究进展

超材料作为一种具备超常物理性质的人工复合材料,能够突破常规材料的限制,为设计先进功能材料开辟一种全新的思路。太赫兹波由于具有光子能量低、对生物物质无电离损害和分子指纹谱等特性,通过与超材料结合,可实现对生物物质高灵敏检测,越来越受到国内外学者的广泛关注。本文总结了近几年来太赫兹超材料传感器在生物分子和细胞检测领域上取得的进展,首先介绍了太赫兹超材料传感器的传感原理和性能指标,其次从超材料结构设计、衬底选择、以及与微流控和新材料结合等方面阐述了太赫兹超材料传感器在生物检测领域的发展。通过对超材料结构进行优化、采用低介电常数薄型衬底、结合微流控技术或在传感器上粘附新材料涂层,可进一步提高超材料传感器的灵敏度,并丰富其在生物医学检测上的功能。最后,对太赫兹超材料传感器的发展趋势和前景进行了展望。     

Assessment of Terahertz Imaging for Excised Breast Cancer Tumors with Image Morphing

This paper presents an image morphing algorithm for quantitative evaluation methodology of terahertz (THz) images of excised breast cancer tumors. Most current studies on the assessment of THz imaging rely on qualitative evaluation, and there is no established benchmark or procedure to quantify the THz imaging performance. The proposed morphing algorithm provides a tool to quantitatively align the THz image with the histopathology image. Freshly excised xenograft murine breast cancer tumors are imaged using the pulsed THz imaging and spectroscopy system in the reflection mode. Upon fixing the tumor tissue in formalin and embedding in paraffin, a formalin-fixed paraffin-embedded (FFPE) tissue block is produced. A thin slice of the block is prepared for the pathology image while another THz reflection image is produced directly from the block. We developed an algorithm of mesh morphing using homography mapping of the histopathology image to adjust the alignment, shape, and resolution to match the external contour of the tissue in the THz image. Unlike conventional image morphing algorithms that rely on internal features of the source and target images, only the external contour of the tissue is used to avoid bias. Unsupervised Bayesian learning algorithm is applied to THz images to classify the tissue regions of cancer, fat, and muscles present in xenograft breast tumors. The results demonstrate that the proposed mesh morphing algorithm can provide more effective and accurate evaluation of THz imaging compared with existing algorithms. The results also showed that while THz images of FFPE tissue are highly in agreement with pathology images, challenges remain in assessing THz imaging of fresh tissue.     

猪肉组织的近场太赫兹成像检测研究

利用搭建的基于光电导微探针的近场太赫兹(Terahertz,THz)系统对新鲜猪肉组织切片进行了成像检测研究,结果发现近场THz成像可以很好地区分猪肉组织中的脂肪组织区域和肌肉组织区域,其成像效果明显优于传统远场THz时域光谱成像系统。研究表明了基于光电导微探针的近场THz成像技术在生物样品检测方面的可行性,展示出该技术在生物医学检测领域具有很好的应用前景。     

Fiber-Drawn Metamaterial for THz Waveguiding and Imaging

In this paper, we review the work of our group in fabricating metamaterials for terahertz (THz) applications by fiber drawing. We discuss the fabrication technique and the structures that can be obtained before focusing on two particular applications of terahertz metamaterials, i.e., waveguiding and sub-diffraction imaging. We show the experimental demonstration of THz radiation guidance through hollow core waveguides with metamaterial cladding, where substantial improvements were realized compared to conventional hollow core waveguides, such as reduction of size, greater flexibility, increased single-mode operating regime, and guiding due to magnetic and electric resonances. We also report recent and new experimental work on near- and far-field THz imaging using wire array metamaterials that are capable of resolving features as small as λ/28.     

Is there a Biological Basis for Therapeutic Applications of Millimetre Waves and THz Waves?

Millimetre wave (MMW) and THz wave (THz) applications are already employed in certain industrial and medical environments for non-destructive quality control, and medical imaging, diagnosis, and therapy, respectively. The aim of the present study is to investigate if published experimental studies (in vivo and in vitro) provide evidence for “non-thermal” biological effects of MMW and THz. Such effects would occur in absence of tissue heating and associated damage and are the ones that can be exploited for therapeutic medical use. The investigated studies provide some evidence for both MMW and THz that can influence biological systems in a manner that is not obviously driven by tissue heating. However, the number of relevant studies is very limited which severely limits the drawing of any far-reaching conclusions. Furthermore, the studies have not addressed specific interaction mechanisms and do not provide hints for future mechanistic studies. Also, the studies do not indicate any specific importance regarding power density levels, frequencies, or exposure duration. It is also unclear if any specific biological endpoints are especially sensitive. Any therapeutic potential of MMW or THz has to be evaluated based on future high-quality studies dealing with physical, bio-physical, and biological aspects that have specific health-related perspectives in mind.     

A kind of graphene film metamaterial for terahertz absorbers

A kind of functional graphene thin film metamaterial on a metal-plane separated by a thick dielectric layer is designed for terahertz (THz) absorbers. We investigate the properties of the graphene metamaterial with different interlayers in the 0–3 THz range. The simulation results show that the absorption rate reaches up to 99.9% at the frequency of 1.917 THz. Changing the period to 80 μm×18 μm can get a narrow-band high quality factor (Q) absorber. We present a novel theoretical interpretation based on the standing wave field theory, which shows that the coherent superposition of incident and reflection rays produces standing waves, and the field energy is localized inside the thick spacers and dissipates through the metal-planes.     

Polarization-independent Metamaterial Absorber for Terahertz Frequency

We present the design, fabrication, as well as the characterization of the large incident angle and polarization independent terahertz (THz) metamaterial absorber. The designed absorber consists of metallic cross structure and a metallic ground plane separated with a dielectric as a spacer, this structure shows a strong resonance at terahertz frequency. The influences of the structural parameters (including period, cross width and spacer thickness) on the absorption are discussed. An optimized structure is fabricated and characterized, and a good agreement between simulation and experimental result is obtained. The metamaterial absorbers are potential candidates as absorbing elements for terahertz imaging and other fields of terahertz technology.     

基于超材料结构的高Q太赫兹滤波器

在半导体微纳工艺基础上研究了基于镜像非对称结构超材料太赫兹(THz)滤波器的性能。通过时域有限差分理论,模拟分析了滤波器工作频率下太赫兹电场强度和电流密度在微结构的分布,并阐述了微结构太赫兹波电磁共振的机理。基于太赫兹滤波器电磁损耗机制和微纳加工工艺条件,设计并优化器件开口环结构,使相邻开口环中产生电磁场的干涉相消,减少太赫兹辐射损耗,提高品质因子Q值。采用太赫兹时域光谱(THz-TDS)系统测试了滤波器的太赫兹透射特性,实验结果表明,在工作频率0.923 THz下,镜像非对称结构的平面太赫兹滤波器品质因子达到12.5。同时,研究了太赫兹电场方向对滤波器性能的影响。高Q太赫兹滤波器的研制为制备高速太赫兹电调制器等太赫兹器件提供了重要的实验依据。     

Topology-Based Prediction of Pathway Dysregulation Induced by Intense Terahertz Pulses in Human Skin Tissue Models

The strong interaction between terahertz (THz) radiation and biological systems has motivated the development of several biomedical technologies, including imaging and spectroscopy applications with promising potential for improved disease diagnosis. This interaction mechanism also implies that external excitation with intense pulses of THz energy could couple to important biological structures and induce significant downstream phenotypic effects. In this study, we expose human skin tissue models to a prolonged train of high-intensity THz pulses and measure the resulting global differential gene expression. From these data, signal pathway perturbation analysis identified pathways that are predicted to be significantly dysregulated, including the cytokine-cytokine receptor interaction and glioma pathways, and further identified the gene-level mechanisms predominantly responsible. These results indicate that induction of an inflammatory-like response and suppression of division/differentiation in cancer are possible. These effects could be further explored and characterized in different types of normal and cancerous tissues to determine potential novel clinical applicability of intense THz pulses.     

Microstructure Functional Devices-Effectively Manipulate Terahertz Waves

Terahertz (THz) technology promises important applications including imaging, spectroscopy, and communications. However, one of limitations at present for advancing THz applications is the lack of efficient devices to manipulate THz waves. Here, our recent important progresses in THz functional devices based on artificial microstructures, such as photonic crystal, metamaterial, and plasmonic structures, have been reviewed in this paper, involving the THz modulator, isolator, and sensor. These THz microstructure functional devices exhibit great promising potential in THz application systems.