Management of isolated superior mesenteric artery dissection

AIM: To evaluate our experience of the clinical management of spontaneous isolated superior mesenteric artery dissection (ISMAD).

miR-183调控Wnt/β-catenin信号通路影响胃癌SGC-7901细胞生物学特性的研究

背景 miR-183在胃癌、乳腺癌、膀胱癌等多种肿瘤组织中低表达,发挥抑癌基因的作用,但其在胃癌中作用机制目前尚不十分清楚.研究表明, miR-183可以通过调节Wnt/β-catenin信号通路抑制骨肉瘤细胞的生长、迁移和侵袭,而Wnt/β-catenin信号通路在胃癌中高度激活与胃癌的发生和转移密切相关.但miR-183是否调节Wnt/β-catenin信号通路影响胃癌细胞生物学特性尚不清楚.目的探讨miR-183调控Wnt/β-catenin信号通路对胃癌细胞生物学特性的影响.方法采用q RT-PCR检测miR-183在不同胃癌细胞株中的表达情况,在胃癌细胞SGC-7901中转染miR-183mimics或mimics对照,分别设为miR-183组和miR-NC组, qRT-PCR检测转染效率,噻唑蓝增殖实验检测SGC-7901细胞增殖变化,流式细胞仪检测SGC-7901细胞凋亡情况, Transwell实验检测SGC-7901细胞侵袭和迁移能力, Western blot法检测凋亡相关及Wnt/β-catenin信号通路相关蛋白表达水平.使用Wnt/β-catenin信号通路激动剂氯化锂处理过表达miR-183的SGC-7901细胞,观察SGC-7901细胞生物学特性的变化.结果与正常胃黏膜上皮GES-1细胞相比, 4株胃癌细胞中miR-183的表达水平明显降低(P <0.05).转染miR-183mimics后SGC-7901细胞中miR-183的表达水平显著升高(P<0.05).过表达miR-183后SGC-7901细胞OD值降低(P<0.05),凋亡率、Bax和Cleaved Caspase-3蛋白表达水平升高(P <0.05),侵袭和迁移细胞数减少(P<0.05),β-catenin、p-GSK-3β和Cyclin D1蛋白表达水平下调(P<0.05), GSK-3β蛋白表达水平上调(P <0.05).激活Wnt/β-catenin信号通路部分逆转了过表达miR-183对SGC-7901细胞增殖、侵袭和迁移的抑制作用及凋亡促进作用(P<0.05).结论miR-183可能通过抑制Wnt/β-catenin信号通路阻碍人胃癌SGC-7901细胞增殖、侵袭和迁移能力,促进细胞凋亡.

Phase-shift interferometry measured transmission matrix of turbid medium: Three-step phase-shifting interference better than four-step one

Transmission matrix(TM)is an important tool for controlling light focusing,imaging,and communication through turbid media.It can be measured by 3-step(TM3)or 4-step(TM4)phase-shifting interference,but the similarities and differences of the transmission matrices obtained by the two methods are rarely reported.Therefore,we make a quantitative comparison of the peak light intensity,signal-to-noise ratio,and average background of 24×24=576 focal points between paired samples(TM3-TM4)through the Wilcoxon rank sum test,and discuss the singular value of the transmission matrix and the focal peak.The comparative results of peak light intensity and signal-to-noise ratio show that there is a significant difference between the 3-step phase shift and the 4-step phase shift transmission matrixes.The focusing effect of the former is significantly better than that of the latter;interest concentrates on the focal intensity and singular value.The reciprocal of the singular value is proportional to the squared intensity,which is in accordance with singular value theory.The results of comparison of peak light intensity and signal-to-noise ratio strongly suggest that 3-step phase shift should be selected and used in applying the phase shift method to the measurement of the transmission matrix;and the singular value is of great significance in quantifying the focusing,imaging,and communication quality of the transmission matrix.

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

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.

Spatial sampling of terahertz fields with sub-wavelength accuracy via probe-beam encoding

Recently,computational sampling methods have been implemented to spatially characterize terahertz(THz)fields.Previous methods usually rely on either specialized THz devices such as THz spatial light modulators or complicated systems requiring assistance from photon-excited free carriers with high-speed synchronization among multiple optical beams.Here,by spatially encoding an 800-nm near-infrared(NIR)probe beam through the use of an optical SLM,we demonstrate a simple sampling approach that can probe THz fields with a single-pixel camera.This design does not require any dedicated THz devices,semiconductors or nanofilms to modulate THz fields.Using computational algorithms,we successfully measure 128×128 field distributions with a 62-μm transverse spatial resolution,which is 15 times smaller than the central wavelength of the THz signal(940μm).Benefitting from the noninvasive nature of THz radiation and sub-wavelength resolution of our system,this simple approach can be used in applications such as biomedical sensing,inspection of flaws in industrial products,and so on.

Autism spectrum disorders: autistic phenotypes and complicated mechanisms

Background Autism spectrum disorder (ASD),a pervasive developmental neurological disorder,is characterized by impairments in social interaction and communication,and stereotyped,repetitive patterns of interests or behaviors.The mechanism of ASDs is complex,and genetic components and epigenetic modifications play important roles.In this review,we summarized the recent progresses of ASDs focusing on the genetic and epigenetic mechanisms.We also briefly discussed current animal models of ASD and the application of high-throughput sequencing technologies in studying ASD.Data sources Original research articles and literature reviews published in PubMed-indexed journals.Results Individuals with ASDs exhibit a set of phenotypes including neurological alteration.Genetic components including gene mutation,copy-number variations,and epigenetic modifications play important and diverse roles in ASDs.The establishment of animal models and development of new-generation sequencing technologies have contributed to reveal the complicated mechanisms underlying autistic phenotypes.Conclusions Dramatic progress has been made for understanding the roles of genetic and epigenetic components in ASD.Future basic and translational studies should be carried out towards those candidate therapeutic targets.

Preference of subpicosecond laser pulses for terahertz wave generation from liquids

Terahertz(THz)wave generation from laser-induced air plasma generally requires a short temporal laser pulse.In contrast,it was observed that THz radiation from ionized liquid water prefers a longer pulse,wherein the mechanism remains unclear.We attribute the preference for longer pulse duration to the process of ionization and plasma formation in water,which is supported by a numerical simulation result showing that the highest electron density is achieved with a subpicosecond pulse.The explanation is further verified by the coincidence of our experimental result and simulation when the thickness of the water is varied.Other liquids are also tested to assure the preference for such a pulse is not exclusive to water.

Terahertz aqueous photonics

Developing efficient and robust terahertz(THz)sources is of incessant interest in the THz community for their wide applications.With successive effort in past decades,numerous groups have achieved THz wave generation from solids,gases,and plasmas.However,liquid,especially liquid water has never been demonstrated as a THz source.One main reason leading the impediment is that water has strong absorption characteristics in the THz frequency regime.A thin water film under intense laser excitation was introduced as the THz source to mitigate the considerable loss of THz waves from the absorption.Laser-induced plasma formation associated with a ponderomotive forceinduced dipole model was proposed to explain the generation process.For the one-color excitation scheme,the water film generates a higher THz electric field than the air does under the identical experimental condition.Unlike the case of air,THz wave generation from liquid water prefers a sub-picosecond(200-800 fs)laser pulse rather than a femtosecond pulse(~50 fs).This observation results from the plasma generation process in water.For the two-color excitation scheme,the THz electric field is enhanced by one-order of magnitude in comparison with the one-color case.Meanwhile,coherent control of the THz field is achieved by adjusting the relative phase between the fundamental pulse and the second-harmonic pulse.To eliminate the total internal reflection of THz waves at the water-air interface of a water film,a water line produced by a syringe needle was used to emit THz waves.As expected,more THz radiation can be coupled out and detected.THz wave generation from other liquids were also tested.

Plasma-based terahertz wave photonics in gas and liquid phases

Ultra-broadband,intense,coherent terahertz(THz)radiation can be generated,detected,and manipulated using laser-induced gas or liquid plasma as both the THz wave transmitter and detector,with a frequency coverage spanning across and beyond the whole THz gap."Such a research topic is termed plasma-based THz wave photonics in gas and liquid phases."In this paper,we review the most important experimental and theoretical works of the topic in the non-relativistic region with pump laser intensity below 1018 W/cm^(2).

Ghost spintronic THz-emitter-array microscope

Terahertz(THz)waves show great potential in nondestructive testing,biodetection and cancer imaging.Despite recent progress in THz wave near-field probes/apertures enabling raster scanning of an object’s surface,an efficient,nonscanning,noninvasive,deep subdiffraction imaging technique remains challenging.Here,we demonstrate THz near-field microscopy using a reconfigurable spintronic THz emitter array(STEA)based on the computational ghost imaging principle.By illuminating an object with the reconfigurable STEA followed by computing the correlation,we can reconstruct an image of the object with deep subdiffraction resolution.By applying an external magnetic field,inline polarization rotation of the THz wave is realized,making the fused image contrast polarization-free.Time-of-flight(TOF)measurements of coherent THz pulses further enable objects at different distances or depths to be resolved.The demonstrated ghost spintronic THz-emitter-array microscope(GHOSTEAM)is a radically novel imaging tool for THz near-field imaging,opening paradigm-shifting opportunities for nonintrusive label-free bioimaging in a broadband frequency range from 0.1 to 30 THz(namely,3.3-1000 cm^(−1)).

Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation- enhanced-emission-of-fluorescence: a review

With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its capability to acquire chemical spectral signatures non-invasively. However, advanced THz remote sensing techniques are obstructed by quite a few factors, such as THz waves being strongly absorbed by water vapor in the ambient air, difficulty to generate intense broadband coherent THz source remotely, and hard to transmit THz waveform information remotely without losing the signal to noise ratio, etc. In this review, after introducing different THz air-photonics techniques to overcome the difficulties of THz remote sensing, we focus mainly on theoretical and experimental methods to improve THz generation and detection performance for the purpose of remote sensing through tailoring the generation and detection media, air-plasma. For the THz generation part, auto-focusing ring-Airy beam was introduced to enhance the THz wave generation yield from two-color laser induced air plasma. By artificially modulated exotic wave packets, it is exhibited that abruptly auto-focusing beam induced air-plasma can give an up to 5.3-time-enhanced THz wave pulse energy compared to normal Gaussian beam induced plasma under the same conditions. At the same time, a red shift on the THz emission spectrum is also observed. A simulation using an interference model to qualitatively describe these behaviors has be developed. For the THz detection part, the results of THz remote sensing at 30 m using THz-radiation-enhanced-emission- of-fluorescence (THz-REEF) technique are demonstrated, which greatly improved from the 10 m demonstration last reported. The THz-REEF technique in the counter-propagation geometry was explored, which is proved to be more practical for stand-off detections than co-propagation geometry. We found that in the counter- propagating geometry the maximum amplitude of the REEF signal is comparable to that in the co-propagating case, whereas the time resolved REEF trace significantly changes. By performing the study with different plasmas, we observed that in the counter-propagating geometry the shape of the REEF trace depends strongly on the plasma length and electron density. A new theoretical model suggesting that the densest volume of the plasma does not contribute to the fluorescence enhancement is proposed to reproduce the experimental measurements. Our results further the understanding of the THz-plasma interaction and highlight the potential of THz-REEF technique in the plasma detection applications.

One Dimensional Stochastic Differential Equations with Distributional Drifts

In this paper we study the existence, pathwise uniqueness and homeomorphism flow of strong solutions to a class of one dimensional SDEs driven by infinitely many Brownian motions, and with Yamada- Watanabe diffusion coefficients and distributional drift coefficients.

Terahertz radiation-enhanced-emission-of-fluorescence

Terahertz （THz） wave science and technology have been found countless applications in biomedical imaging, security screening, and non-destructive testing as they approach maturity. However, due to the challenge of high ambient moisture absorption, the development of remote open-air broadband THz spectroscopy technology is lagging behind the compelling need that exists in homeland security, astronomy and environmental monitoring. Furthermore, the underlying physical mechanisms behind the interaction between the THz wave and laserinduced plasma which responds strongly to electromag- netic waves have not been fully understood. This review aims to explain the light-plasma interaction at THz frequencies within a semiclassical framework along with experimental study of the femtosecond-laser- induced nitrogen plasma fluorescence under the illumination of single-cycle THz pulses. The results indicate that THz-radiation-enhanced-emission-of-fluorescence （THz- REEF） is dominated by electron kinetics in the THz field and the electron-impact excitation of gas molecules/ions. The information of the time-dependent THz field can be recovered from the measured time-resolved THz-REEF from single-color laser induced plasma with the help of the bias as local oscillator. The calculations and experimental verification lead to complete understanding of the science behind these effects and push forward to extend their capabilities in related applications such as remote THz sensing, plasma diagnostics and ultrafast photoluminescence modulation. Systematic studies in selected gases including neon, argon, krypton, xenon, methane （CH4）, ethane （C2H6）, propane （C3H8）, and n-butane （C4Hlo） gases were performed to obtain an improved understanding of the THz-REEF. The dependences of the enhanced fluorescence on the THz field, laser excitation intensity, gas pressure, and intrinsic atomic properties were experimentally characterized. Both narrow line emission and broad continuum emission of the gas plasma were enhanced by the THz field. Their fluorescence enhancement ratios and time-resolved enhanced fluorescence were largely dependent on the scattering cross section and ionization potential of atoms. For the first time, we demonstrated a novel ＇all-optical＇ technique of broadband THz wave remote sensing by coherently manipulating the fluorescence emission from asymmetrically ionized gas plasma that interacted with THz waves. By studying the ultrafast electron dynamics under the single cycle THz radiation, we found that the fluorescence emission from laser-induced air plasma was highly dependent on the THz electric field and the symmetry of the electron drift velocity distribution created by two-color laser fields. The time-resolved THz-REEF can be tailored by switching the relative two-color phase and laser polarizations. Owing to the high atmospheric transparency and omni-directional emission pattern of fluorescence, this technique can be used to measure THz pulses at standoff distances with minimal water vapor absorption and unlimited directionality for optical signal collection. The coherent THz wave detection at a distance of 10 m had been demonstrated. The combination of this method and previously demonstrated remote THz genera- tion would eventually make remote THz spectroscopy available. We also introduced a unique plasma diagnostic method utilizing the THz-wave-enhanced fluorescence emission from the excited atoms or molecules. The electron relaxation time and plasma density were deduced through applying the electron impact excitation/ionization and electron-ion recombination processes to the measured time-delay-dependent enhanced fluorescence. The electron collision dynamics of nitrogen plasma excited at different gas pressures and laser pulse energies were systematically investigated. This plasma diagnostic method offers picosecond temporal resolution and is capable of omnidirectional optical signal collection. The ultrafast quenching dynamics of laser-pulseinduced photoluminescence in semiconductors under the radiation of single-cycle THz pulses was studied. It was found that the quenching in both cadmium telluride （CdTe） and gallium arsenide （GaAs） was linearly proportional to the intensity of incident THz waves and reaches up to 17% and 4% respectively at the peak intensity of 13 MW/cm2. The THz-wave-induced heating of the carriers and lattice and the subsequent decreased efficiency of photocarrier generation and recombination were most likely to be responsible for the quenching. This is potentially useful for the applications ofa non-invasive ultrafast light modulator for photoluminescence devices with picoseconds switching time in the fields of the light-emitting devices and optical communication.

Generation and detection of pulsed terahertz waves in gas： from elongated plasmas to microplasmas

The past two decades have seen an exponential growth of interest in one of the least explored region of the electromagnetic spectrum, the terahertz （THz） frequency band, ranging from to 0.1 to 10 THz. Once only the realm of astrophysicists studying the background radiation of the universe, THz waves have become little by little relevant in the most diverse fields, such as medical imaging, industrial inspection, remote sensing, fundamental science, and so on. Remarkably, THz wave radiation can be generated and detected by using ambient air as the source and the sensor. This is accomplished by creating plasma under the illumination of intense femtosecond laser fields. The integration of such a plasma source and sensor in THz time-domain techniques allows spectral measurements covering the whole THz gap （0.1 to 10 THz）, further increasing the impact of this scientific tool in the study of the four states of matter. In this review, the authors introduce a new paradigm for implementing THz plasma techniques. Specifically, we replaced the use of elongated plasmas, ranging from few mm to several cm, with sub-mm plasmas, which will be referred to as microplasmas, obtained by focusing ultrafast laser pulses with high numerical aperture optics （NA from 0.1 to 0.9）. The experimental study of the THz emission and detection from laser-induced plasmas of submillimeter size are presented. Regarding the microplasma source, one of the interesting phenomena is that the main direction of THz wave emission is almost orthogonal to the laser propagation direction, unlike that of elongated plasmas. Perhaps the most important achievement is the demonstra- tion that laser pulse energies lower than 1 μJ are sufficientto generate measurable THz pulses from ambient air, thus reducing the required laser energy requirement of two orders of magnitude compared to the state of art. This significant decrease in the required laser energy will make plasma-based THz techniques more accessible to the scientific community, as well as opening new potential industrial applications. Finally, experimental observations of THz radiation detection with microplasmas are also presented. As fully coherent detection was not achieved in this work, the results presented herein are to be considered a first step to understand the peculiarities involved in using the micro- plasma as a THz sensor.

Toward remote sensing with broadband terahertz waves

This paper studies laser air-photonics used for remote sensing of short pulses of electromagnetic radiation at terahertz frequency. Through the laser ionization process, the air is capable of generating terahertz field strengths greater than 1 MV/cm, useful bandwidths over 100 terahertz, and highly directional emission patterns. Following ionization and plasma formation, the emitted plasma acoustic or fluorescence can be modulated by an external terahertz field to serve as omnidirectional, broad- band, electromagnetic sensor. These results help to close the ＂terahertz gap＂ once existing between electronic and optical frequencies, and the acoustic and fluorescence detection methodologies developed provide promising new avenues for extending the useful range of terahertz wave technology. Our experimental results indicate that by hearing the sound or seeing the fluorescence, coherent detection of broadband terahertz wave at remote distance is feasible.

Application of broadband terahertz spectroscopy in semiconductor nonlinear dynamics

Semiconductor nonlinearity in the range of terahertz （THz） frequency has been attracting considerable attention due to the recent development of high-power semiconductor-based nanodevices. However, the underlying physics concerning carrier dynamics in the presence of high-field THz transients is still obscure. This paper introduces an ultrafast, time-resolved THz pump/THz probe approach to study semiconductor properties in a nonlinear regime. The cartier dynamics regarding two mechanisms, intervalley scattering and impact ionization, was observed for doped InAs on a sub-picosecond time scale. In addition, polaron modulation driven by intense THz pulses was experimentally and theoretically investigated. The observed polaron dynamics verifies the interaction between energetic electrons and a phonon field. In contrast to previous work which reported optical phonon responses, acoustic phonon modulations were addressed in this study. A further understanding of the intense field interacting with solid materials will accelerate the development of semiconductor devices. This paper can be divided into 4 sections. Section 1 starts with the design and performance of a table-top THz spectrometer, which has the advantages of ultraroad bandwidth （one order higher bandwidth compared to a conventional ZnTe sensor） and high electric field strength （〉 100kV/cm）. Unlike the conventional THz timedomain spectroscopy, the spectrometer integrated a novel THz air-biased-coherent-detection （THz-ABCD） technique and utilized gases as THz emitters and sensors. In comparison with commonly used electro-optic （EO） crystals or photoconductive （PC） dipole antennas, the gases have the benefits of no phonon absorption as existing in EO crystals and no carrier life time limitation as observed in PC dipole antennas. In Section 2, the newly development THz-ABCD spectrometer with a strong THz field strength capability provides a platform for various research topics especially on the nonlinear carrier dynamics of semiconductors. Two mechanisms, electron intervalley scattering and impact ionization of InAs crystals, were observed under the excitation of intense THz field on a sub-picosecond time scale. These two competing mechanisms were demonstrated by changing the impurity doping type of the semiconductors and varying the strength of the THz field. Another investigation of nonlinear carrier dynamics in Section 3 was the observation of coherent polaron oscillation in n-doped semiconductors excited by intense THz pulses. Through modulations of surface reflection with a THz pump/THz probe technique, this work experimentally verifies the interaction between energetic electrons and a phonon field, which has been theoretically predicted by previous publications, and shows that this interaction applies for the acoustic phonon modes. Usually, two transverse acoustic （2TA） phonon responses are inactive in infrared measurement, while they are detectable in second-order Raman spectroscopy. The study ofpolaron dynamics, with nonlinear THz spectroscopy （in the far- infrared range）, provides a unique method to diagnose the overtones of 2TA phonon responses of semiconductors, and therefore incorporates the abilities of both infrared and Raman spectroscopy. Finally, some conclusions were presented in Section 4. In a word, this work presents a new milestone in wave-matter interaction and seeks to benefit the industrial applications in high power, small scale devices.

Investigation of ultra-broadband terahertz time-domain spectroscopy with terahertz wave gas photonics

Recently, air plasma, produced by focusing an intense laser beam to ionize atoms or molecules, has been demonstrated to be a promising source of broadband terahertz waves. However, simultaneous broadband and coherent detection of such broadband terahertz waves is still challenging. Electroptical sampling and photoconductive antennas are the typical approaches for terahertz wave detection. The bandwidth of these detection methods is limited by the phonon resonance or carrier＇s lifetime. Unlike solid-state detectors, gaseous sensors have several unique features, such as no phonon resonance, less dispersion, no Fabry-Perot effect, and a continuous renewable nature. The aim of this article is to review the development of a broadband terahertz time-domain spectrometer, which has both a gaseous emitter and sensor mainly based on author＇s recent investigation. This spectrometer features high efficiency, perceptive sensitivity, broad bandwidth, adequate signal-to-noise ratio, sufficient dynamic range, and controllable polarization. The detection of terahertz waves with ambient air has been realized through a third order nonlinear optical process： detecting the second harmonic photon that is produced by mixing one terahertz photon with two fundamental photons. In this review, a systematic investigation of the mechanism of broadband terahertz wave detection was presented first. The dependence of the detection efficiency on probe pulse energy, bias field strength, gas pressure and third order nonlinear susceptibility of gases were experimentally demonstrated with selected gases. Detailed discussions of phase matching and Gouy phase shift were presented by considering the focused condition of Gaussian beams. Furthermore, the bandwidth dependence on probe pulse duration was also demonstrated. Over 240 times enhancement of dynamic range had been accomplished with n-hexane vapor compared to conventional air sensor. Moreover, with sub-20 fs laser pulses delivered from a hollow fiber pulse compressor, an ultra-broad spectrum covering from 0.3 to 70 THz was also showed. In addition, a balanced detection scheme using a polarization dependent geometry was developed by author to improve signal-to-noise ratio and dynamic range of conventional terahertz air-biased-coherent-detection （ABCD） systems. Utilizing the tensor property of third order nonlinear susceptibility, second harmonic pulses with two orthogonal polarizations was detected by two separated photomultiplier tubes （PMTs）. The differential signal from these two PMTs offers a realistic method to reduce correlated laser fluctuation, which circumvents signal-to-noise ratio and dynamic range of conventional terahertz ABCD systems. A factor of two improvement of signal-to-noise ratio was experimentally demonstrated. This paper also introduces a unique approach to directly produce a broadband elliptically polarized terahertz wave from laser-induced plasma with a pair of double helix electrodes. The theoretical and experimental results demonstrated that velocity mismatch between excitation laser pulses and generated terahertz waves plays a key role in the properties of the elliptically polarized terahertz waves and confirmed that the far-field terahertz emission pattern is associated with a coherent process. The results give insight into the important influence of propagation effects on terahertz wave polarization control and complete the mechanism of terahertz wave generation from laserinduced plasma. This review provides a critical understanding of broadband terahertz time-domain spectroscopy （THz-TDS） and introduces further guidance for scientific applications of terahertz wave gas photonics.

Anti-reflection implementations for terahertz waves

Undesired reflection caused by impedance mismatch can lead to significant power loss and other unwanted effects. In the terahertz regime, anti-reflection method has evolved from simple quarter-wave antireflection coating to sophisticated metamaterial device and photonic structures. In this paper, we examined and compared the theories and techniques of several antireflection implementations for terahertz waves, with emphasis on gradient index photonic structures. A comprehensive study is presented on the design, fabrication and evaluation of this new approach.

Preface to the special issue on Terahertz Wave Science, Technology, and Application

I am delighted to introduce the first special issue on Terahertz （THz） Wave Science, Technology, and Application. This issue contains five review and research papers, all written by former Ph.D students, Dr. Xiaofei Lu, Dr. Jingle Liu, Dr. Benjamin Clough, Dr. I-Chen Ho, and Dr. Yuting W. Chen, at the Center of THz Research, Rensselaer Polytechnic Institute. These gifted scientists and engineers are among the most brilliant students that have graduated in the THz community in the past four years. This issue covers research frontiers from THz antireflection silicon structure （Dr. Chen）, remote sensing （Dr. Liu）, and THz wave air photonics （Dr. Lu） to nonlinear THz wavematter interaction （Dr. Ho）, and THz enhanced acoustics （Dr. Clough）.