太赫兹脉冲整形技术研究进展

太赫兹(THz)脉冲整形技术在量子理论、生物医学成像、安全检查、亚毫米波通信等领域都具有重要的学术价值和应用前景。概述了基于飞秒脉冲的整形技术和新型太赫兹辐射材料整形技术,分析了太赫兹脉冲整形器件整形技术目前的研究状况,并对各种整形方法的发展进行了展望。     

Dictionary Learning-Based Image Reconstruction for Terahertz Computed Tomography

Terahertz computed tomography (THz CT) demonstrates its advantages in aspects of nonmetallic and nonpolar materials penetration, 3D internal structure visualization, etc. To perform satisfied reconstruction results, it is necessary to obtain complete measurements from many different views. However, this process is time-consuming and we usually obtain incomplete projections for THz CT in practice, which generates artifacts in the final reconstructed images. To address this issue, dictionary learning-based THz CT reconstruction (DLTR) model is proposed in this study. Especially, the image patches are extracted from other state-of-the-art reconstructed images to train the initial dictionary by using the K-SVD algorithm. Then, the dictionary can be adaptively updated during THz CT reconstruction. Finally, the updated dictionary is used for further updating reconstructed images. In order to verify the accuracy and quality of DLTR method, the filtered back-projection (FBP), simultaneous algebraic reconstruction technique (SART), and total variation (TV) reconstruction are chosen as comparisons. The experiment results show that the DLTR method has a good capability for noise suppression and structures preservation.

     

Terahertz Computed Tomography Using A Continuous-Wave Gas Laser

A 3D continuous-wave (CW) terahertz computed tomography (CT) system employing a gas laser operating at 2.52 THz is presented. To shorten acquisition time on the premise of guaranteeing the image quality, the modified simultaneous algebraic reconstruction technique (MSART) coupled with image processing operations like the Gaussian low-pass filter (GLPF), open operation and close operation has been adopted in the paper. With the 2D results the 3D images of the samples have been also obtained. The reconstruction results illustrate the promising application prospects of this CW THz CT system.     

Wavelet Based Identification of Substances in Terahertz Tomography Measurements

In comparison to the X-ray computed tomography Terahertz technique significantly enhances the amount of the information acquired during the sample measurement. Not only amplitude, but also phase, time and spectral characteristics can be determined in THz time-domain spectroscopy. Thus, Terahertz tomography allows localization and identification of substances within the objects due to the characteristic fingerprints in this frequency range. Certainly, an appropriate data processing and comparison algorithms are crucial for the accurate identification of the substances in the measured sample. Therefore, we present a new wavelet-based identification method which is suitable even for the substances with broad absorption curves and small or no absorption peaks. The performance of this algorithm was evaluated with the help of a tomographic sample filled with four substances, which were previously characterized for the external database. The continuous wavelet transform was applied to every data cell of the tomographic measurement and compared to the database. Received sinograms were reconstructed into images which depict estimated similarity between the measured and database substances. Furthermore, we suggest a method for the reduction of spectral data after the continuous wavelet transform. This method is based on the extraction of the distinctive features in the form of ridge lines.     

Terahertz Photonics: Optoelectronic Techniques for Generation and Detection of Terahertz Waves

Optoelectronic techniques for generation and detection of terahertz (THz) signals have been reviewed. The operation principles of THz photomixer sources and THz parametric sources have been studied and recent developments in these areas have been presented. The performances of developed THz optoelectronic sources have been discussed and compared.      

太赫兹雷达技术

太赫兹雷达具有带宽大、分辨率高、多普勒敏感、抗干扰等独特优势,是目标探测领域的重要发展方向。该文首先回顾和介绍了电子学和光学太赫兹雷达系统历史、现状和最新进展,其次对太赫兹雷达目标特性从机理、计算、测量3个方面进行了梳理和概要介绍,同时阐述了太赫兹ISAR、SAR、阵列和孔径编码成像研究状况,简要介绍了太赫兹雷达在预警探测、安检反恐等领域的应用,最后对太赫兹雷达技术的发展方向进行了展望。      

基于太赫兹光谱技术的爆炸物类危险品检测

太赫兹(THz)光谱技术识别爆炸物类危险品是一种极具竞争力的新型安检方法。总结了不同研究机构的爆炸物指纹谱数据,建立了可供参考的数据库;讨论了棉布、塑料、皮革、涤纶和硬纸板等常见材料覆盖下隐蔽爆炸物的检测状况;介绍了远距离探测爆炸物的最新研究进展。最后,分析了实战场景中应用THz光谱技术检测爆炸物需要面临的混合爆炸物、复杂环境条件和远距离探测等主要问题,并对未来的发展趋势作了展望。     

太赫兹光谱技术在气体检测中的应用

相关环境污染信息在太赫兹波段内具有较强的吸收特性,使得利用太赫兹光谱技术探测大气中的污染物成为可能.概述了国内外太赫兹时域光谱技术在气体检测方面的研究历史和发展现状,介绍了不同的气体分子在太赫兹波段的吸收谱,以及对混合气体分子和同素异形体分子的识别.对太赫兹时域光谱技术在气体检测方面的研究方向进行了展望.     

Review of Anisotropic Terahertz Material Response

Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear optics regimes. Such material properties have led to a diverse array of useful polarization components in the visible and near-infrared, but mature technology is non-existent in the terahertz (THz). Here, we review several novel types of anisotropic material responses observed in the THz frequency range, including both linear and circular anisotropy, which have long-term implications for the development of THz polarization optics. We start with the extreme linear anisotropy of macroscopically aligned carbon nanotubes, arising from their intrinsically anisotropic dynamic conductivity. Magnetically induced anisotropy will then be reviewed, including the giant Faraday effects observed in semiconductors, semimetals, and two-dimensional electron systems.     

用于太赫兹高速直接调制技术研究进展

分析了近年来太赫兹直接调制技术的发展情况,技术特点以及应用前景。随着外调制技术的快速发展,调制速率有大幅度的提高,并且与目前主流的基于肖特基二极管等固态器件太赫兹发射链路易于集成等特点,已被认为是一种在太赫兹高速通信领域中具有应前景的太赫兹调制技术。     

A Review on Terahertz Communications Research

The increasing demand of unoccupied and unregulated bandwidth for wireless communication systems will inevitably lead to the extension of operation frequencies toward the lower THz frequency range. Higher carrier frequencies will allow for fast transmission of huge amounts of data as needed for new emerging applications. Despite the tremendous hurdles that have to be overcome with regard to sources and detectors, circuit and antenna technology and system architecture to realize ultrafast data transmission in a scenario with extensive transmission loss, a new area of research is beginning to form. In this article we give an overview of emerging technologies and system research that might lead to ubiquitous THz communication systems in the future.     

太赫兹真空器件中的微加工技术和微封装技术

当工作频率升高至太赫兹频段时,真空器件的结构尺寸缩小至毫米级甚至微米级.传统的精密加工方法已经不能满足要求,这就要求采用新的加工技术即微细加工技术以保证很高的尺寸精度和表面光洁度.本文介绍了三种主要的微细加工技术,LIGA、UV(紫外)LIGA和深反应离子刻蚀,阐述了这三种加工技术的工艺流程、特点以及其应用情况,并举例说明各加工技术在太赫兹真空器件中的一些应用.     

Terahertz Direct Modulation Techniques for High-speed Communication Systems

Terahertz communication technology can provide abundant frequency resources,strong confidentiality,antijamming capability,communication tracking capability and ...     

太赫兹回旋管的现状及其发展

太赫兹回旋管一种具有重要发展前景的高功率太赫兹源。简要介绍了回旋管的结构和基本原理,并且评述了国内外太赫兹回旋管的发展状况和趋势;同时指出了太赫兹回旋管发展中存在的关键问题及一些建议。     

THz信号处理与分析的研究现状和发展展望

本文对THz信号的特点、THz信号的产生技术、THz信号的探测技术、THz时域光谱(THz-TDS)技术、THz信号的处理技术,以及THz 信号应用技术等当前的研究现状进行了综述,并对未来可能的发展做了展望.     

激光反射层析成像技术的研究进展

激光反射层析成像技术是一种通过不同角度下激光在物体深度方向的一维时间流信号积分重建目标二维轮廓图像的远距离成像技术,其重建图像的空间分辨率只与探测器的带宽、激光的脉冲宽度和噪声有关,与作用距离、光学接收孔径无关,是现阶段实现远距离空间目标探测的最可行手段。介绍了激光反射层析成像的基础理论问题、投影数据处理方法、图像重建算法、探测成像实验系统以及成像实验研究等问题,总结和对比了国内外的研究进展,探讨了需要重点解决的问题,并展望了激光反射层析成像技术未来的研究方向。     

Review of Terahertz Technology Readiness Assessment and Applications

Technological progress in Terahertz (THz) instrumentation in recent years has produced commercial THz systems with excellent performance, smaller footprint, easier to use operation and more reliable than their homemade laboratory predecessors. Form factor, weight, and data rate are, perhaps, the parameters that have shown the highest improvements in recent years. These parameters also have a major impact on practical application outside the laboratory environment. However, gaps still exists between proof of concepts demonstrated in the laboratory and application requirements in a real environment. The readiness of a technology can be assessed using the Technology Readiness Level (TRL) criterion, which considers nine readiness levels starting from basic concepts at TRL=1 up to full deployment at TRL=9. Applications of THz technology in spectroscopic characterization score high in TRL (7-9) because most of the progress of THz technology has been mainly focused in developing THz instrumentation for spectroscopy. Applications of THz for non-destructive evaluation applications score lower (TRL 5-6) due to higher requirements in terms of performance, especially data rate and form factor in imaging applications. Applications in the medical field have been studied with promising results but they are still in early stages of development, thus, TRL is low (1-4). The progress in THz technology is generating systems with better performance (faster acquisition rates, higher signal-to-noise ratio, bandwidth), broader availability of form factors and configurations, and tighter integration with particular applications. This progress will reduce the gap between the capabilities of the technology and the high-demanding requirements of applications in environments such as quality control and in-line production control in the manufacturing industry.     

A Review on Applications of Integrated Terahertz Systems

A review on Terahertz end-to-end systems with an emphasis on integrated approaches is presented.Four major catalogs of THz integrated systems,including THz comm...     

Terahertz Time-Domain Spectroscopy of Solids: A Review

Recent development of the terahertz time domain spectroscopy (THz-TDS) and its application to solids have been reviewed. This spectroscopy is unique in that the time-domain wave forms are measured at first and the complex optical constants are deduced directly by the Fourier transformation of them without resort to the Kramers-Kronig analysis. Various types of the THz-TDS systems are briefly described. Applications of the THz-TDS to various solids, i.e., semiconductors, superconductors, polymers, photonic crystals, and so on are also presented to demonstrate how widely this spectroscopy is applicable to characterization of solids.