Electroporation-Induced Cell Modifications Detected with THz Time-Domain Spectroscopy

Electroporation (electropermeabilization) increases the electrical conductivity of biological cell membranes and lowers transport barriers for normally impermeant materials. Molecular simulations suggest that electroporation begins with the reorganization of water and lipid head group dipoles in the phospholipid bilayer interface, driven by an externally applied electric field, and the evolution of the resulting defects into water-filled, lipid pores. The interior of the electroporated membrane thus contains water, which should provide a signature for detection of the electropermeabilized state. In this feasibility study, we use THz time-domain spectroscopy, a powerful tool for investigating biomolecular systems and their interactions with water, to detect electroporation in human cells subjected to permeabilizing pulsed electric fields (PEFs). The time-domain response of electroporated human monocytes was acquired with a commercial THz, time-domain spectrometer. For each sample, frequency spectra were calculated, and the absorption coefficient and refractive index were extracted in the frequency range between 0.2 and 1.5 THz. This analysis reveals a higher absorption of THz radiation by PEF-exposed cells, with respect to sham-exposed ones, consistent with the intrusion of water into the cell through the permeabilized membrane that is presumed to be associated with electroporation.     

Terahertz Multivariate Spectral Analysis and Molecular Dynamics Simulations of Three Pyrethroid Pesticides

The terahertz (THz) multivariate spectral characteristics and the molecular dynamics of three pyrethroid pesticides, including deltamethrin, fenvalerate, and beta-cypermethrin, were studied in this paper. THz spectra of the pesticides were measured in frequency range of 0.06–3.5 THz by using THz time-domain spectroscopy (THz-TDS). To improve the THz spectral quality, the wavelet threshold de-noising (WTD) method was used to remove spectral noise and the spectral baseline correction (SBC) method was used to remove baseline drift. Specific absorption peaks were observed in the processed THz spectra of the three pesticides. Deltamethrin showed three peaks at 0.90, 1.49, and 2.32 THz. Fenvalerate had five peaks at 1.13, 1.43, 1.61, 1.98, and 2.58 THz. Beta cypermethrin had four peaks at 1.27, 1.84, 2.12, and 2.92 THz. The density functional theory (DFT) was used to characterize the molecular dynamics and formation mechanism of the absorption peaks. Results showed that there was a good matching effect between the THz experimental spectra and the DFT quantum calculation spectra. Based on the characterized fingerprint absorption peaks, the linear addition model was used to simulate the THz spectra of mixed pesticides. The simulated spectra of multicomponent pesticides were demonstrated to be in good agreement with those obtained by THz-TDS. By analyzing the absorption peaks of THz spectra, the composition and concentration of multicomponent pesticides could be determined. The proposed strategy presented an analytical methodology for studying the THz spectral characteristics of pesticides. In addition, this work provided experimental and theoretical basis for the detection potential of pesticides in agricultural products based on THz technology.     

偏置电压驱动下AlGaN/GaN二维电子气的宽谱太赫兹波发射

本文介绍了低温（6 K）下偏置电压加速AlGaN/GaN二维电子气产生的宽谱太赫兹波发射。根据“浅水波”等离子体波失稳理论和史密斯-珀塞尔理论,分别设计了两种器件结构。实验结果表明所观测到的太赫兹辐射与电子浓度无明显依赖关系,得到的而是自于晶格和热电子的黑体辐射。通过考虑湿度和衬底法布里-珀罗谐振腔作用,计算得到的热电子发射光谱与实验光谱良好吻合。研究结果表明通过电流驱动二维电子气产生太赫兹辐射的器件将不可避免地产生强烈的电子气加热和晶格加热问题,很难实现理论预言的等离子体波失稳与高效太赫兹发射。因此,需要设计更加精巧的器件结构才能实现高效的等离子体波激发和太赫兹发射。     

太赫兹频率下镁掺杂对氧化锌纳米粉体介电性能的影响

利用偶极天线LT-GaAs发射的太赫兹时域光谱(THz-TDS)研究单晶氧化锌、未掺杂和Mg掺杂的ZnO纳米粉末(粒子)在室温下的太赫兹光谱特性。在0.2~2 THz频率范围内研究了样品的功率吸收和折射率。结果发现,镁掺杂提高了样品材料的吸收效率,同时降低了氧化锌材料的折射率。相比较氧化锌单晶,未掺杂和Mg掺杂氧化锌纳米颗粒的太赫兹介电性质呈现类似的行为,该结果与横向光学E1(TO)声子模式有关。     

New Class of Efficient Terahertz Generators: Effective Terahertz Spectral Filling by Complementary Tandem Configuration of Nonlinear Organic Crystals

Intense table‐top terahertz (THz) sources, which have progressed tremendously in the last decade, are becoming more important for advanced THz science to study light–matter interactions and subsequent applications. Nonlinear optical organic crystals exhibit great potential for intense broadband THz wave generation due to their large nonlinearities and advantageous phase‐matching characteristics. However, the phonon‐induced absorption of most organic crystals in the THz region leads to undesired modulation of the spectrum and limits the THz output efficiency. To overcome such drawbacks, phonon‐mode engineering by modification of molecular structures is suggested, but intrinsic limitations still remain. Here, an efficient alternative approach has been recently proposed for generating intense broadband THz waves based on a tandem configuration that combines two complementary nonlinear organic crystals. Such configuration compensates for the spectral gap of the generated THz waves mainly caused by phonon absorption and additionally enhances the optical‐to‐THz conversion efficiency. The proposed organic tandem generator indicates a substantial enhancement of the peak‐to‐peak THz electric field due to effective spectral filling at phonon absorption gaps. As a result, such tandem configuration provides a versatile platform to generate gapless broadband THz spectra with suppressed phonon absorption and contributes to advancing the development of intense broadband coherent THz sources.     

Polarization Maintaining Air-Core Bandgap Fibers for Terahertz Wave Guiding

A polarization-maintaining air-core bandgap polymer fiber is proposed for low-loss terahertz (THz) wave guiding. The polarized guided modes are confined in an asymmetric core by a bandgap of periodic arrangement of square holes with round corners in the cladding. The guiding properties, including transmission bandwidth, numerical aperture, phase-index birefringence, modal absorption loss, and bend loss, are systematically investigated. The influence of background polymers on guiding properties is demonstrated in detail. Numerical simulations reveal that, while maintaining a relatively high phase-index birefringence (of the order of 10^-3 ), the THz fiber shows a significant suppression of absorption loss of the background polymers (by a factor of more than 25) due to the bandgap effect that repels the modal power from the absorbent polymers. The proposed THz fiber has potential for guiding intense THz waves for polarization-sensitive applications.     

太赫兹矩形波导与共面波导耦合结构设计

太赫兹（THz）波位于微波与红外光波之间,现有微波和光波段波导技术应用正在向THz波段拓展。但是,由于水汽对THz波的强吸收及制造工艺等原因,THz器件主要是平面结构,而THz源及其传输需要用矩形波导。因此,矩形波导与共面波导之间的转换结构成为决定元件和系统性能的关键部分。该设计利用脊波导进行阻抗匹配及电磁场模式转换,实现THz波矩形波导到共面波导的高效率耦合。结果表明,在0.2~0.4 THz频段内,该转换结构的传输系数(S₂₁)高于?3 dB,可以对THz电磁场进行高效率转换。该结果可用于太赫兹分子探测、太赫兹通信等领域,为0.2 THz以上太赫兹的模式转换提供了一种可行方案。     

Multi-band circuit model of tunable THz absorber based on graphene sheet and ribbons

Terahertz (THz) absorbers due to the high potential of providing reliable applications in modern devices and technology are increasingly being investigated. Recently, a dual-band THz absorber based on a graphene sheet and ribbons has been proposed in which the results were obtained using Full-wave simulations and its authors have not provided any specific design method. In this work, we have proposed and investigated that tunable THz absorber by its circuit model. A developed transmission line method beside the analytical circuit model of graphene continues sheet and periodic arrays of graphene ribbons are used to obtain analytical expressions for the circuit model. Here, first of all, we have compared the results of the proposed method with the results of that paper and secondly, using impedance matching concept we have proposed multi-band tunable THz absorber with near-unity absorption by the same structure. Then, we have compared the results of our circuit method with the Full-wave simulations. In either case, our proposed method in addition to excellent performance in terms of runtime and memory sources, has an acceptable agreement with the results of the Full-wave simulations. The proposed method is general and can be applied to design and simulate the other sub-wavelength structures.     

维甲酸和叶酸的太赫兹光谱

利用太赫兹时域光谱技术（THz-TDS）在室温下对两种抗肿瘤维生素类药物维甲酸和叶酸在0.2～1.8 THz范围内进行了光谱测量,得到对应的吸收谱和折射率谱,发现叶酸和维甲酸在太赫兹波段都有明显的特征吸收峰,可作为其在太赫兹波段的指纹谱用于药物分子识别。同时,采用Gaussian03软件进行了单分子的密度泛函理论模拟,模拟中采用B3LYP结合高斯型基组6～31 G（d,p）,理论计算与实验结果基本吻合。另外,采用Gaussian-View3.0对叶酸和维甲酸在THz波段的特征吸收峰进行了指认。结果证明:利用太赫兹光谱技术结合密度泛函理论模拟对两种抗肿瘤维生素类药物分子识别及其新药研制具有一定的参考意义。     

Room-Temperature AlGaN/GaN Terahertz Plasmonic Detectors with a Zero-Bias Grating

In this paper, we present sensitivity measurement as well as measured and calculated absorption spectra for AlGaN/GaN THz plasmonic detector made of a metallic grating in-between two ohmic contacts. Detectors with different grating patterns have been fabricated and their sensitivity, reaching 1.9 μA/W at 77 K and 0.7 μA/W at 300 K, measured with a voltage applied between the ohmic contacts. It is the first time that such a detector shows THz detection with no voltage applied on the grating, namely with a bidimensional electron gas (2DEG) having a homogeneous electron density. These results are consistent with detection by drag-effect rectification. Measurements held between 0.648 and 0.690 THz show that the dependence of the sensitivity on the frequency follows the absorption spectrum, indicating that absorption is a crucial step in the detection process. Further simulations of absorption spectra show the tunability offered by such detector and allow us to predict frequency behavior for grating-biased detectors as well, in which the rectification is mainly governed by ratchet effect.     

飞秒激光的等离子体吸收太赫兹特性研究

在利用飞秒激光器产生太赫兹波的过程中,等离子体本身会对太赫兹波能量进行吸收,其吸收特性在太赫兹波雷达探测、等离子体隐身、电磁干扰研究等方面有着广泛的应用前景。结合理论分析设计了一种等离子体吸收太赫兹波的测量系统,提出等离子体粒子间相互碰撞吸收是导致等离子体吸收太赫兹波的主要原因,并在实验测量研究中发现等离子体密度大小、光学透镜焦距长短以及入射飞秒激光与倍频晶体晶轴角度是影响吸收程度的主要因素,这些研究为等离子体吸收应用提供了更加全面的理论支撑,有助于推动太赫兹波技术在军事及民用领域的快速发展。     

垂直双空芯宽带太赫兹偏振分离器

针对太赫兹波的特点,利用折射率匹配耦合原理,设计了一种垂直双空芯结构的偏振分离器件。与传统的分离器件相比,它具有以下优点:（1）双芯折射率匹配度高,使得对应的偏振模式所需要的分离长度很短;（2）采用双空气纤芯结构,降低材料对太赫兹波的吸收损耗;（3）通过设计,令其发生耦合的两个纤芯相互垂直,从而使y偏振模的折射率曲线部分重合,大大扩展了工作带宽的范围,其工作带宽达到了0.17 THz。此外,由于器件结构简单对称,降低了光纤的设计和制备难度,使其在太赫兹网络中具有很高的应用价值。     

Terahertz Phonon Mode Engineering of Highly Efficient Organic Terahertz Generators

For terahertz (THz) wave generators based on organic electrooptic crystals, their intrinsic phonon modes are playing an essential role in THz generation characteristics. Here, this study proposes an effective design strategy for THz phonon mode engineering of organic electrooptic salt crystals for efficient optical‐to‐THz frequency conversion. To reduce phonon‐mode intensity, strongly electronegative trifluoromethyl group acting as strong hydrogen‐bond acceptor is incorporated into molecular anions. New 2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐(trifluoromethyl)benzenesulfonate (HMQ‐4TFS) crystals exhibit a relatively small absorption coefficient in the THz spectral range between 0.5 and 4 THz, which is attributed to suppressed molecular vibrations due to strong hydrogen bonds involving the 4TFS anion. In addition, HMQ‐4TFS crystals possess a very large macroscopic optical nonlinearity, comparable (or even higher) to benchmark stilbazolium crystals. Based on the low‐intensity THz phonon modes and the large optical nonlinearity, a 0.37 mm thick HMQ‐4TFS crystal pumped with 150 fs infrared laser pulses facilitates very efficient THz wave generation by optical rectification, delivering 23 times higher peak‐to‐peak THz electric field than the widely used standard inorganic ZnTe crystal (1.0 mm thick) and a broader spectral bandwidth. Therefore, strongly electronegative groups introduced into molecular salt electrooptic crystals provide a very promising design strategy of THz phonon mode engineering for developing intense broadband THz sources.     

碳类烟幕材料对太赫兹波的衰减特性

为获得太赫兹波对碳类烟幕的穿透特性,采用压片法分别将不同比例混合的石墨粉和KBr、碳黑粉和KBr进行压片,利用太赫兹时域光谱仪在0.2~1.1 THz频率范围内测试压片样品的太赫兹透射光谱,进而获得样品在该频率范围内的吸收系数。研究发现:随着频率的增大,样品的吸收系数均逐渐增大,且在同一频率处,其均随碳类粉末掺杂比例的增加而增大;与石墨相比,相同掺杂比例的碳黑样品具有更大的吸收系数。结果表明,太赫兹波具有较强的穿透石墨烟幕的能力,但其对碳黑烟幕的穿透能力较弱,利用碳黑有望进行太赫兹波段烟幕的研制。     

鞣花酸的太赫兹光谱研究

鞣花酸是一种存在于多种植物中的天然多酚组分,近年来越来越多的实验证实鞣花酸在抑制癌细胞增长和诱导癌细胞凋亡方面有很好的效果,同时也具有抗氧化和抗辐射等作用,在抗癌药品及保健药品中占有重要地位。因此对鞣花酸的研究有着重要的意义。太赫兹时域光谱技术（THz－TDS）是一种新型的时间分辨相干探测技术,本文利用太赫兹时域光谱技术研究了鞣花酸在0.2－2.4THz波段的光谱特性,得到了鞣花酸的吸收谱和折射率谱,并利用密度泛函理论(DFT)进行了模拟计算。研究发现,鞣花酸在该波段有光谱响应,分别在0.44、0.73、0.99、1.26、1.58、1.87和2.19THz频率处出现了反常色散现象和吸收峰。可以作为检测鞣花酸存在的定量分析依据,为药品及食品检测提供指导。     

Optimized Optical Rectification and Electro-optic Sampling in ZnTe Crystals with Chirped Femtosecond Laser Pulses

We report on optimization of the intensity of THz signals generated and detected by optical rectification and electro-optic sampling in dispersive, nonlinear media. Addition of a negative prechirp to the femtosecond laser pulses used in the THz generation and detection processes in 1-mm thick ZnTe crystals leads to an increase of the THz intensity of more than 30% at low laser intensity and up to 60% at higher laser intensity. Dispersion compensation in the ZnTe crystal, which becomes significant for laser pulses with durations much less than 100 fs, is responsible for the enhanced generation and detection efficiency at low excitation intensity, and our simulations indicate that two-photon absorption is responsible for the increased efficiency enhancement observed at high excitation intensity.     

环烯烃共聚物空芯微结构太赫兹光纤的设计与制造

以环烯烃共聚物（cyclic-olefin copolymer,COC）材料为基质,设计、制造了一种空芯多孔包层太赫兹（THz）纤维。利用comsol 软件模拟了芯径为6 mm 的光纤在0.2~1.5 THz 波段的损耗特性,结果表明:在0.85~1.5 THz 波段存在多个低损耗频带,而且在0.85~1.1 THz 波段有低于3 dB/m 的三个窗口;特别是在0.99 THz,损耗达到0.208 dB/m。芯径为3 mm、4.8 mm 和6 mm 的光纤在0.8~1.5 THz 波段的损耗特性对比分析表明:该COC 微结构多孔包层空芯纤维的损耗随着光纤外径的增加而减小。把设计的太赫兹纤维外径放大7 倍达到7 cm,据此设计制造了光纤预制棒成型专用模具。借助热挤出成型方法得到了结构完整、孔洞表面光滑,长度为22 cm 的空芯多孔包层预制棒。利用该实验室独有的微结构光纤拉丝塔,成功获得了微结构保持完好的光纤样品。损耗分析结果表明:6 mm 芯径的光纤样品在1.27 THz 的平均损耗为2.175 dB/m,与该频率的理论损耗（1.95 dB/m）接近。     

盐酸吗啡的太赫兹光谱和理论仿真分析

采用太赫兹时域光谱(THz-TDS)技术测量了盐酸吗啡原料药、4种辅料、中间体、成药在0.2～2 THz波段的光谱.盐酸吗啡原料药特征吸收峰为0.75 THz,1.17 THz,1.76 THz,原料药到成药的THz光谱发生了改变,中间体和成药的吸收谱有非常高的一致性,说明包衣对成药的THz光谱没有显著影响.采用密度泛...     

太赫兹波传播过程中横模分布的成像

研究了焦点位置附近太赫兹波的横模分布,目的在于了解系统中太赫兹波的横向分布情况,为进行太赫兹光谱和成像实验提供依据。通过太赫兹波逐点扫描成像,对经常被用来放置测试样品位置附近的太赫兹波横模分布情况进行了定性的分析。利用“狭缝法"测量了太赫兹光束的束宽。结果表明,太赫兹波在焦点附近不同位置的横向分布有较大差异,在焦点处对应于最长波长1.5 mm的最小光斑直径约为1.0 mm,这说明太赫兹波的聚焦有一定的限度。实验确定了系统中放置样品的最佳位置,对开展太赫兹光谱和成像研究有参考价值。     

FOX-7太赫兹波吸收特性及理论计算

为了研究新型高能钝感材料1,1-二氨基-2,2-二硝基乙烯(FOX-7)的分子结构特性,采用太赫兹时域光谱技术对FOX-7在0.2~2.3 THz波谱范围内的吸收光谱进行了探测,得到了待测样品的太赫兹吸收谱线,确定了其特征吸收峰的位置.基于密度泛函理论(DFT)对FOX-7单分子和晶体结构在小于2.4 THz范围内的吸收光谱进行了模拟计算,结果表明分子间相互作用对FOX-7吸收峰的形成起到很大的作用.完成了对实验光谱中特征吸收峰振动模式的分析和指认:1.59 THz处吸收峰的光谱特征主要由―NO2和―NH2的摆动造成,2.12 THz 处吸收峰光谱特征的产生包含―NO2和―NH2的摆动以及各自的扭动.