High-energy terahertz wave parametric oscillator with a surface-emitted ring-cavity configuration.

PubMed

Yang, Zhen; Wang, Yuye; Xu, Degang; Xu, Wentao; Duan, Pan; Yan, Chao; Tang, Longhuang; Yao, Jianquan

2016-05-15

A surface-emitted ring-cavity terahertz (THz) wave parametric oscillator has been demonstrated for high-energy THz output and fast frequency tuning in a wide frequency range. Through the special optical design with a galvano-optical scanner and four-mirror ring-cavity structure, the maximum THz wave output energy of 12.9 μJ/pulse is achieved at 1.359 THz under the pump energy of 172.8 mJ. The fast THz frequency tuning in the range of 0.7-2.8 THz can be accessed with the step response of 600 μs. Moreover, the maximum THz wave output energy from this configuration is 3.29 times as large as that obtained from the conventional surface-emitted THz wave parametric oscillator with the same experimental conditions.

Research into Influence of Gaussian Beam on Terahertz Radar Cross Section of a Semicircular Boss

NASA Astrophysics Data System (ADS)

Li, Hui-Yu; Li, Qi; She, Jian-Yu; Zhao, Yong-Peng; Chen, De-Ying; Wang, Qi

2013-08-01

In radar cross section (RCS) calculation of a rough surface, the model can be simplified into the scattering of geometrically idealized bosses on a surface. Thus the problem of the RCS calculation of a rough surface is changed to the RCS calculation of the semicircular boss. The RCS measurement of scale model can help save time and money. The utilization of terahertz in RCS is attractive because of its special properties: the wavelength of the terahertz wave can help limit the size of the model in a suitable range in the measurement of the scale model and get more detailed data in the measurement of the real object. However, usually the incident beam of a terahertz source is a Gaussian beam; in the theoretical RCS estimation, usually a plane wave is assumed as the incident beam for sake of simplicity which may lead to an error between the measurement and calculation results. In this paper, the method of images is used to calculate the RCS of a semicircular boss at 2.52 THz and the results are compared to the one calculated when the incident beam is a plane wave.

Design of a LiNbO(3) ribbon waveguide for efficient difference-frequency generation of terahertz wave in the collinear configuration.

PubMed

Takushima, Y; Shin, S Y; Chung, Y C

2007-10-29

We propose and investigate a ribbon waveguide for difference-frequency generation of terahertz (THz) wave from infrared light sources. The proposed ribbon waveguide is composed of a nonlinear optic crystal and has a thickness less than the wavelength of the THz wave to support the surface-wave mode in the THz region. By utilizing the waveguide dispersion of the surface-wave mode, the phase matching condition between infrared pump, idler and THz waves can be realized in the collinear configuration. Owing to the weak mode confinement of the THz wave, the absorption coefficient can also be reduced. We design the ribbon waveguide which uses LiNbO(3) crystal and discuss the phase-matching condition for DFG of THz wave. Highly efficient THz-wave generation is confirmed by numerical simulations.

Electromagnetically induced transparency metamaterial based on spoof localized surface plasmons at terahertz frequencies

PubMed Central

Liao, Zhen; Liu, Shuo; Ma, Hui Feng; Li, Chun; Jin, Biaobing; Cui, Tie Jun

2016-01-01

We numerically and experimentally demonstrate a plasmonic metamaterial whose unit cell is composed of an ultrathin metallic disk and four ultrathin metallic spiral arms at terahertz frequencies, which supports both spoof electric and magnetic localized surface plasmon (LSP) resonances. We show that the resonant wavelength is much larger than the size of the unit particle, and further find that the resonant wavelength is very sensitive to the particle’s geometrical dimensions and arrangements. It is clearly illustrated that the magnetic LSP resonance exhibits strong dependence to the incidence angle of terahertz wave, which enables the design of metamaterials to achieve an electromagnetically induced transparency effect in the terahertz frequencies. This work opens up the possibility to apply for the surface plasmons in functional devices in the terahertz band. PMID:27277417

Monolithic Superconducting Emitter of Tunable Circularly Polarized Terahertz Radiation

NASA Astrophysics Data System (ADS)

Elarabi, A.; Yoshioka, Y.; Tsujimoto, M.; Kakeya, I.

2017-12-01

We propose an approach to controlling the polarization of terahertz (THz) radiation from intrinsic Josephson-junction stacks in a single crystalline high-temperature superconductor Bi2Sr2CaCu2O8 . Monolithic control of the surface high-frequency current distributions in the truncated square mesa structure allows us to modulate the polarization of the emitted terahertz wave as a result of two orthogonal fundamental modes excited inside the mesa. Highly polarized circular terahertz waves with a degree of circular polarization of more than 99% can be generated using an electrically controlled method. The intuitive results obtained from the numerical simulation based on the conventional antenna theory are consistent with the observed emission characteristics.

Numeric analysis of terahertz wave propagation in familiar packaging materials

NASA Astrophysics Data System (ADS)

Zhang, Lihong; Yang, Guang

2015-10-01

To assess the potential application of terahertz waves in security examination, the transmission characteristics of terahertz waves in packaging materials should be studied. This paper simulates the propagation of terahertz waves in cloth and paper, studies the changes of shape and position of crest of terahertz waves before and after these materials, and gets the law of these changes, which has potential applications in thickness measurement for the thin insulated materials; gives reflected and transmitted wave of terahertz waves, and computes reflected and transmitted coefficient, indicates the good transmission properties of these materials for terahertz waves, which provides the theoretical basis for the realization of contactless security examination of packaged post, package and people pass the important passageway (such as airport and station).

Terahertz-wave surface-emitted difference-frequency generation without quasi-phase-matching technique.

PubMed

Avetisyan, Yuri H

2010-08-01

A scheme of terahertz (THz)-wave surface-emitted difference-frequency generation (SEDFG), which lacks the drawbacks associated with the usage of periodically orientation-inverted structures, is proposed. It is shown that both material birefringence of the bulk LiNbO(3) crystal and modal birefringence of GaAs/AlAs waveguide are sufficient to obtain SEDFG up to a frequency of approximately 3THz. The simplicity of the proposed scheme, along with the fact that there is a much smaller THz-wave decay in nonlinear crystal, makes it a good candidate for the practical realization of efficient THz generation. The use of a GaAs waveguide with an oxidized AlAs layer is proposed for enhanced THz-wave SEDFG in the vicinity of the GaAs polariton resonance at 8THz.

Manipulating line waves in flat graphene for agile terahertz applications

NASA Astrophysics Data System (ADS)

Bisharat, Dia'aaldin J.; Sievenpiper, Daniel F.

2018-05-01

Reducing open waveguides enabled by surface waves, such as surface plasmon polaritons, to a one-dimensional line is attractive due to the potentially enhanced control over light confinement and transport. This was recently shown to be possible by simply interfacing two co-planar surfaces with complementary surface impedances, which support transverse-magnetic and transverse-electric modes, respectively. Attractively, the resultant "line wave" at the interface line features singular field enhancement and robust direction-dependent polarizations. Current implementations, however, are limited to microwave frequencies and have fixed functionality due to the lack of dynamic control. In this article, we examine the potential of using gate-tunable graphene sheets for supporting line waves in the terahertz regime and propose an adequate graphene-metasurface configuration for operation at room temperature and low voltage conditions. In addition, we show the occurrence of quasi-line wave under certain conditions of non-complementary boundaries and qualify the degradation in line wave confinement due to dissipation losses. Furthermore, we show the possibility to alter the orientation of the line wave's spin angular momentum on demand unlike conventional surface waves. Our results on active manipulation of electromagnetic line waves in graphene could be useful for various applications including reconfigurable integrated circuits, modulation, sensing and signal processes.

Anomalous Surface Wave Launching by Handedness Phase Control.

PubMed

Zhang, Xueqian; Xu, Yuehong; Yue, Weisheng; Tian, Zhen; Gu, Jianqiang; Li, Yanfeng; Singh, Ranjan; Zhang, Shuang; Han, Jiaguang; Zhang, Weili

2015-11-25

Anomalous launch of a surface wave with different handedness phase control is achieved in a terahertz metasurface based on phase discontinuities. The polarity of the phase profile of the surface waves is found to be strongly correlated to the polarization handedness, promising polarization-controllable wavefront shaping, polarization sensing, and environmental refractive-index sensing. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Compact four-channel terahertz demultiplexer based on directional coupling photonic crystal

NASA Astrophysics Data System (ADS)

Jiu-Sheng, Li; Han, Liu; Le, Zhang

2015-09-01

Electromagnetic polarization conveys valuable information for signal processing. Manipulation of terahertz wavelength demultiplexer exhibits tremendous potential in developing application of terahertz science and technology. We propose an approach to separate efficiently four frequencies terahertz waves based on three cascaded directional coupling two-dimensional photonic crystal waveguides. Both plane wave expansion method and finite-difference time-domain method are used to calculate and analyze the characteristics of the proposed device. The simulation results show that the designed terahertz wavelength demultiplexer can split four different wavelengths of terahertz wave into different propagation directions with high transmittance and low crosstalk. The present device is very compact and the total size is 6.8×10.6 mm2. This enables the terahertz wavelength demultiplexer to be used in terahertz wave system and terahertz wave integrated circuit fields.

Terahertz broadband polarization converter based on metamaterials

NASA Astrophysics Data System (ADS)

Li, Yonghua; Zhao, Guozhong

2018-01-01

Based on the metamaterial composed of symmetrical split resonant ring, a broadband reflective terahertz polarization converter is proposed. The numerical simulation shows that it can rotate the polarization direction of linear polarized wave 90° in the range of 0.7-1.8THz and the polarization conversion ratio is over 90%. The reflection coefficient of the two electric field components in the diagonal direction is the same and the phase difference is 180° ,which leads to the cross-polarization rotation.In order to further study the physical mechanism of high polarization conversion, we analyze the surface current distribution of the resonant ring. The polarization converter has potential applications in terahertz wave plate and metamaterial antenna design.

Active terahertz wave imaging system for detecting hidden objects

NASA Astrophysics Data System (ADS)

Gan, Yuner; Liu, Ming; Zhao, Yuejin

2016-11-01

Terahertz wave can penetrate the common dielectric materials such as clothing, cardboard boxes, plastics and so on. Besides, the low photon energy and non-ionizing characteristic of the terahertz wave are especially suitable for the safety inspection of the human body. Terahertz imaging technology has a tremendous potential in the field of security inspection such as stations, airports and other public places. Terahertz wave imaging systems are divided into two categories: active terahertz imaging systems and passive terahertz imaging systems. So far, most terahertz imaging systems work at point to point mechanical scan pattern with the method of passive imaging. The imaging results of passive imaging tend to have low contrast and the image is not clear enough. This paper designs and implements an active terahertz wave imaging system combining terahertz wave transmitting and receiving with a Cassegrain antenna. The terahertz wave at the frequency of 94GHz is created by impact ionization avalanche transit time (IMPATT) diode, focused on the feed element for Cassegrain antenna by high density polyethylene (HDPE) lens, and transmitted to the human body by Cassegrain antenna. The reflected terahertz wave goes the same way it was emitted back to the feed element for Cassegrain antenna, focused on the horn antenna of detector by another high density polyethylene lens. The scanning method is the use of two-dimensional planar mirror, one responsible for horizontal scanning, and another responsible for vertical scanning. Our system can achieve a clear human body image, has better sensitivity and resolution than passive imaging system, and costs much lower than other active imaging system in the meantime.

Strain Imaging Using Terahertz Waves and Metamaterials

DTIC Science & Technology

2016-11-01

TECHNICAL REPORT RDMR-WD-16-48 STRAIN IMAGING USING TERAHERTZ WAVES AND METAMATERIALS Henry O. Everitt and Martin S...TITLE AND SUBTITLE Strain Imaging Using Terahertz Waves and Metamaterials 5. FUNDING NUMBERS 6. AUTHOR(S) Henry O. Everitt, Martin S...predictions. 14. SUBJECT TERMS Birefringence, Terahertz Waves , Metamaterials 15. NUMBER OF PAGES 16 16. PRICE CODE 17. SECURITY

Elliptically polarized terahertz radiation from a chiral oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takeda, R.; Kida, N., E-mail: kida@k.u-tokyo.ac.jp; Sotome, M.

2015-09-28

Polarization control of terahertz wave is a challenging subject in terahertz science and technology. Here, we report a simple method to control polarization state of the terahertz wave in terahertz generation process. At room temperature, terahertz radiation from a noncentrosymmetric and chiral oxide, sillenite Bi{sub 12}GeO{sub 20}, is observed by the irradiation of linearly polarized femtosecond laser pulses at 800 nm. The polarization state of the emitted terahertz wave is found to be elliptic with an ellipticity of ∼0.37 ± 0.10. Furthermore, the ellipticity was altered to a nearly zero (∼0.01 ± 0.01) by changing the polarization of the incident linearly polarized femtosecond laser pulses.more » Such a terahertz radiation characteristic is attributable to variation of the polarization state of the emitted terahertz waves, which is induced by retardation due to the velocity mismatch between the incident femtosecond laser pulse and generated terahertz wave and by the polarization tilting due to the optical activity at 800 nm.« less

Intense terahertz radiation from relativistic laser–plasma interactions

DOE PAGES

Liao, G. Q.; Li, Y. T.; Li, C.; ...

2016-11-02

The development of tabletop intense terahertz (THz) radiation sources is extremely important for THz science and applications. This study presents our measurements of intense THz radiation from relativistic laser–plasma interactions under different experimental conditions. Several THz generation mechanisms have been proposed and investigated, including coherent transition radiation (CTR) emitted by fast electrons from the target rear surface, transient current radiation at the front of the target, and mode conversion from electron plasma waves (EPWs) to THz waves. Finally, the results indicate that relativistic laser plasma is a promising driver of intense THz radiation sources.

Visualization of terahertz surface waves propagation on metal foils

PubMed Central

Wang, Xinke; Wang, Sen; Sun, Wenfeng; Feng, Shengfei; Han, Peng; Yan, Haitao; Ye, Jiasheng; Zhang, Yan

2016-01-01

Exploitation of surface plasmonic devices (SPDs) in the terahertz (THz) band is always beneficial for broadening the application potential of THz technologies. To clarify features of SPDs, a practical characterization means is essential for accurately observing the complex field distribution of a THz surface wave (TSW). Here, a THz digital holographic imaging system is employed to coherently exhibit temporal variations and spectral properties of TSWs activated by a rectangular or semicircular slit structure on metal foils. Advantages of the imaging system are comprehensively elucidated, including the exclusive measurement of TSWs and fall-off of the time consumption. Numerical simulations of experimental procedures further verify the imaging measurement accuracy. It can be anticipated that this imaging system will provide a versatile tool for analyzing the performance and principle of SPDs. PMID:26729652

Study on spectral features of terahertz wave propagating in the air

NASA Astrophysics Data System (ADS)

Kang, Shengwu

2018-03-01

Now, Terahertz technology has been widely used in many fields, which is mainly related to imaging detection. While the frequency range of the terahertz-wave is located between microwave and visible light, whether the existing visible light principle is applicable to terahertz-wave should be studied again. Through experiment, we measure the terahertz-wave field amplitude distribution on the receiving plane perpendicular to the direction of propagation in the air and picture out the energy distribution curve; derive an energy decay formula of terahertz wave based on the results; design a terahertz wavelength apparatus using the F-P interferometer theory; test the wavelength between 1 and 3 THz from the SIFIR-50THz laser of American Corehent company; finally analyze the related factors affecting the measurement precision including the beam incident angle, mechanical vibration, temperature fluctuation and the refractive index fluctuation.

A megawatt-level surface wave oscillator in Y-band with large oversized structure driven by annular relativistic electron beam.

PubMed

Wang, Jianguo; Wang, Guangqiang; Wang, Dongyang; Li, Shuang; Zeng, Peng

2018-05-03

High power vacuum electronic devices of millimeter wave to terahertz regime are attracting extensive interests due to their potential applications in science and technologies. In this paper, the design and experimental results of a powerful compact oversized surface wave oscillator (SWO) in Y-band are presented. The cylindrical slow wave structure (SWS) with rectangular corrugations and large diameter about 6.8 times the radiation wavelength is proposed to support the surface wave interacting with annular relativistic electron beam. By choosing appropriate beam parameters, the beam-wave interaction takes place near the π-point of TM 01 mode dispersion curve, giving high coupling impedance and temporal growth rate compared with higher TM 0n modes. The fundamental mode operation of the device is verified by the particle-in-cell (PIC) simulation results, which also indicate its capability of tens of megawatts power output in the Y-band. Finally, a compact experimental setup is completed to validate our design. Measurement results show that a terahertz pulse with frequency in the range of 0.319-0.349 THz, duration of about 2 ns and radiation power of about 2.1 MW has been generated.

A simple system for 160GHz optical terahertz wave generation and data modulation

NASA Astrophysics Data System (ADS)

Li, Yihan; He, Jingsuo; Sun, Xueming; Shi, Zexia; Wang, Ruike; Cui, Hailin; Su, Bo; Zhang, Cunlin

2018-01-01

A simple system based on two cascaded Mach-Zehnder modulators, which can generate 160GHz optical terahertz waves from 40GHz microwave sources, is simulated and tested in this paper. Fiber grating filter is used in the system to filter out optical carrier. By properly adjusting the modulator DC bias voltages and the signal voltages and phases, 4-tupling optical terahertz wave can be generated with fiber grating. This notch fiber grating filter is greatly suitable for terahertz over fiber (TOF) communication system. This scheme greatly reduces the cost of long-distance terahertz communication. Furthermore, 10Gbps digital signal is modulated in the 160GHz optical terahertz wave.

Surface plasmons based terahertz modulator consisting of silicon-air-metal-dielectric-metal layers

NASA Astrophysics Data System (ADS)

Wang, Wei; Yang, Dongxiao; Qian, Zhenhai

2018-05-01

An optically controlled modulator of the terahertz wave, which is composed of a metal-dielectric-metal structure etched with circular loop arrays on both the metal layers and a photoexcited silicon wafer separated by an air layer, is proposed. Simulation results based on experimentally measured complex permittivities predict that modification of complex permittivity of the silicon wafer through excitation laser leads to a significant tuning of transmission characteristics of the modulator, forming the modulation depths of 59.62% and 96.64% based on localized surface plasmon peak and propagating surface plasmon peak, respectively. The influences of the complex permittivity of the silicon wafer and the thicknesses of both the air layer and the silicon wafer are numerically studied for better understanding the modulation mechanism. This study proposes a feasible methodology to design an optically controlled terahertz modulator with large modulation depth, high speed and suitable insertion loss, which is useful for terahertz applications in the future.

Active graphene-silicon hybrid diode for terahertz waves.

PubMed

Li, Quan; Tian, Zhen; Zhang, Xueqian; Singh, Ranjan; Du, Liangliang; Gu, Jianqiang; Han, Jiaguang; Zhang, Weili

2015-05-11

Controlling the propagation properties of the terahertz waves in graphene holds great promise in enabling novel technologies for the convergence of electronics and photonics. A diode is a fundamental electronic device that allows the passage of current in just one direction based on the polarity of the applied voltage. With simultaneous optical and electrical excitations, we experimentally demonstrate an active diode for the terahertz waves consisting of a graphene-silicon hybrid film. The diode transmits terahertz waves when biased with a positive voltage while attenuates the wave under a low negative voltage, which can be seen as an analogue of an electronic semiconductor diode. Here, we obtain a large transmission modulation of 83% in the graphene-silicon hybrid film, which exhibits tremendous potential for applications in designing broadband terahertz modulators and switchable terahertz plasmonic and metamaterial devices.

Continuous-wave terahertz imaging of nonmelanoma skin cancers

NASA Astrophysics Data System (ADS)

Joseph, Cecil Sudhir

Continuous wave terahertz imaging has the potential to offer a safe, non-invasive medical imaging modality for detecting different types of human skin cancers. Terahertz pulse imaging (TPI) has already shown that there is contrast between basal cell carcinoma and normal skin. Continuous-wave imaging offers a simpler, lower cost alternative to terahertz pulse imaging. This project aims to isolate the optimal contrast frequency for a continuous wave terahertz imaging system and demonstrate transmission based, in-vitro , imaging of thin sections of non-melanoma skin cancers and correlate the images to sample histology. The aim of this project is to conduct a proof-of-principle experiment that establishes whether continuous-wave terahertz imaging can detect differences between cancerous and normal tissue while outlining the basic requirements for building a system capable of performing in vivo tests.

Active graphene–silicon hybrid diode for terahertz waves

PubMed Central

Li, Quan; Tian, Zhen; Zhang, Xueqian; Singh, Ranjan; Du, Liangliang; Gu, Jianqiang; Han, Jiaguang; Zhang, Weili

2015-01-01

Controlling the propagation properties of the terahertz waves in graphene holds great promise in enabling novel technologies for the convergence of electronics and photonics. A diode is a fundamental electronic device that allows the passage of current in just one direction based on the polarity of the applied voltage. With simultaneous optical and electrical excitations, we experimentally demonstrate an active diode for the terahertz waves consisting of a graphene–silicon hybrid film. The diode transmits terahertz waves when biased with a positive voltage while attenuates the wave under a low negative voltage, which can be seen as an analogue of an electronic semiconductor diode. Here, we obtain a large transmission modulation of 83% in the graphene–silicon hybrid film, which exhibits tremendous potential for applications in designing broadband terahertz modulators and switchable terahertz plasmonic and metamaterial devices. PMID:25959596

Enhanced coupling of terahertz radiation to cylindrical wire waveguides.

PubMed

Deibel, Jason A; Wang, Kanglin; Escarra, Matthew D; Mittleman, Daniel

2006-01-09

Wire waveguides have recently been shown to be valuable for transporting pulsed terahertz radiation. This technique relies on the use of a scattering mechanism for input coupling. A radially polarized surface wave is excited when a linearly polarized terahertz pulse is focused on the gap between the wire waveguide and another metal structure. We calculate the input coupling efficiency using a simulation based on the Finite Element Method (FEM). Additional FEM results indicate that enhanced coupling efficiency can be achieved through the use of a radially symmetric photoconductive antenna. Experimental results confirm that such an antenna can generate terahertz radiation which couples to the radial waveguide mode with greatly improved efficiency.

Toward remote sensing with broadband terahertz waves

NASA Astrophysics Data System (ADS)

Clough, Benjamin W.

Terahertz electromagnetic waves, defined as the frequency region between 0.1 and 10 terahertz on the electromagnetic spectrum, have demonstrated remarkable usefulness for imaging and chemical identification with the ability to penetrate many optically opaque barriers. Photon energies at these frequencies are relatively small (meV), which means the radiation is non-ionizing and therefore considered biologically innocuous. With the growing list of applications and demand for terahertz technology, there is a need to develop innovative terahertz sources and detectors that can overcome existing limitations in power, bandwidth, and operating range. Although terahertz radiation has demonstrated unique and exceptional abilities, it has also presented several fundamental challenges. Most notably, the water vapor absorption of terahertz waves in air at habitable altitudes is greater than 100 dB/km. There is an immediate push to utilize the material and vapor identification abilities of terahertz radiation, while extending the effective distances over which the technology can be used. Remote terahertz detection, until recently, was thought to be impossible due to the high water content in the atmosphere, limited signal collection geometries, and solid state materials necessary for generation and detection. This dissertation focuses on laser air-photonics used for sensing short pulses of electromagnetic radiation. Through the ionization process, the very air that we breathe 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 acoustics or fluorescence can be modulated by an external field to serve as omnidirectional, broadband, electromagnetic sensor. A deeper understanding of terahertz wave-plasma interaction is used to develop methods for retrieving coherent terahertz wave information that can be encoded into plasma acoustic and fluorescence wave emission; the ultimate goal aimed at overcoming fundamental limitations of the current terahertz technology. A synthesized bichromatic field-induced laser plasma is used to study effects of electron velocity redistribution inside the plasma filament, and a technique for obtaining a direct correlation between the terahertz field and the plasma acoustic or fluorescence emission is engineered. This dissertation presents significant advances in terahertz air photonics that help to close the "THz 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.

Dispersion relation of a surface wave at a rough metal-air interface

DOE PAGES

Kotelnikov, Igor; Stupakov, Gennady

2016-11-28

Here, we derived a dispersion relation of a surface wave at a rough metal-air interface. In contrast to previous publications, we assumed that an intrinsic surface impedance due to a finite electric conductivity of the metal can be of the same order as the roughness-induced impedance. We then applied our results to the analysis of a long-standing problem of the discrepancy between the experimental data on the propagation of surface waves in the terahertz range of frequencies and the classical Drude theory.

Compact terahertz wave polarization beam splitter using photonic crystal.

PubMed

Mo, Guo-Qiang; Li, Jiu-Sheng

2016-09-01

Electromagnetic polarization conveys valuable information for signal processing. Manipulation of a terahertz wave polarization state exhibits tremendous potential in developing applications of terahertz science and technology. We propose an approach to efficiently split transverse-electric and transverse-magnetic polarized terahertz waves into different propagation directions over the frequency range from 0.9998 to 1.0007 THz. Both the plane wave expansion method and the finite-difference time-domain method are used to calculate and analyze the transmission characteristics of the proposed device. The present device is very compact and the total size is 1.02  mm×0.99  mm. This polarization beam splitter performance indicates that the structure has a potential application for forthcoming terahertz-wave integrated circuit fields.

Microfabricated Circuits for Terahertz Wave Amplification and Terahertz Biosensors

NASA Astrophysics Data System (ADS)

Fawole, Olutosin Charles

The terahertz frequency band extends from deep infrared (100 THz) down to millimeter waves (0.4 THz), and this band was mostly inaccessible due to the lack of appropriate sources and detectors. Those with access to this band had to endure the small-intensity pulsed signals (nanowatts to microwatts) that the terahertz sources of those times could provide. In recent years, however, sufficient development has led to the availability of terahertz sources with sufficient power (1-100 muW) and the ease of use these sources has in turn enabled researchers to develop newer sources, detectors, and application areas. The terahertz regime is interesting because a) many molecules have vibrational, rotation and transition absorption bands in this regime, b) the terahertz electromagnetic wavelength is sufficiently small to resolve centimeter to millimeter scale objects, and c) scattering and absorption in metals in the terahertz regime make it very challenging to devise terahertz signal processing circuits. Thus, performing terahertz reflection/transmission measurements may enable precise identification of chemicals in a sample. Furthermore, small wavelengths and strong scattering by metallic objects make imaging with terahertz waves quite attractive. Finally, the ability to devise terahertz communication circuits and links will provide access to a frequency domain that is restricted and not available to others. One of the main objectives of this work is to develop 0.75 - 1.1 terahertz (free space wavelength 272 mum - 400 ?mum) amplifiers. Another objective of this work is to explore the suitability of terahertz waves in biological imaging and sensing. The terahertz amplifiers developed in this work consisted of distributed components such as rectangular waveguides and cylindrical dielectric resonators. In contrast to discrete amplifiers, which are based on solid-state devices, distributed traveling wave amplifiers can potentially handle and produce larger powers. Three different distributed terahertz amplifier circuits were considered in this work. These were based on a) coupled dielectric resonators, b) dielectric waveguides with periodic slots, and c) metallic meandering waveguides. The result of the hot test of the last circuit on interaction with an electron beam energy source yielded an amplification of 12 dB of a -55 dBm, 0.9 terahertz signal over 1 gigahertz bandwidth. The electron beam acceleration voltage was 4.8 kV and its current was approximately 20 microamps. The terahertz biosensing system developed in this work was used to study the unique interaction of terahertz waves with the chemical and physical components of biological tissues, and the products of biochemical reactions. A terahertz near-field imaging system was also developed to image mouse brain slices, plants, and bug wings. In addition, this work also demonstrated the capabilities and limitations of terahertz waves for the real-time noninvasive monitoring of bioethanol production by yeast cells.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uryupin, S A; Frolov, A A

We have developed a theory of generation of low-frequency radiation and surface waves under the pondermotive action of a femtosecond laser pulse irradiating a conductor along the normal and focused by a cylindrical lens. It is shown that for the chosen focusing method and specified values of laser pulse duration and flux density it is possible to significantly increase the total energy of both surface waves and low-frequency radiation. (terahertz radiation)

Surface-Wave Pulse Routing around Sharp Right Angles

NASA Astrophysics Data System (ADS)

Gao, Z.; Xu, H.; Gao, F.; Zhang, Y.; Luo, Y.; Zhang, B.

2018-04-01

Surface-plasmon polaritons (SPPs), or localized electromagnetic surface waves propagating on a metal-dielectric interface, are deemed promising information carriers for future subwavelength terahertz and optical photonic circuitry. However, surface waves fundamentally suffer from scattering loss when encountering sharp corners in routing and interconnection of photonic signals. Previous approaches enabling scattering-free surface-wave guidance around sharp corners are limited to either volumetric waveguide environments or extremely narrow bandwidth, being unable to guide a surface-wave pulse (SPP wave packet) on an on-chip platform. Here, in a surface-wave band-gap crystal implemented on a single metal surface, we demonstrate in time-domain routing a surface-wave pulse around multiple sharp right angles without perceptible scattering. Our work not only offers a solution to on-chip surface-wave pulse routing along an arbitrary path, but it also provides spatiotemporal information on the interplay between surface-wave pulses and sharp corners, both of which are desirable in developing high-performance large-scale integrated photonic circuits.

Surface-emitting terahertz quantum cascade lasers with continuous-wave power in the tens of milliwatt range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Gangyi, E-mail: gangyi.xu@mail.sitp.ac.cn; Key Laboratory of Infrared Imaging Materials and Detectors, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083; Li, Lianhe

2014-03-03

We demonstrate efficient surface-emitting terahertz frequency quantum cascade lasers with continuous wave output powers of 20–25 mW at 15 K and maximum operating temperatures of 80–85 K. The devices employ a resonant-phonon depopulation active region design with injector, and surface emission is realized using resonators based on graded photonic heterostructures (GPHs). GPHs can be regarded as energy wells for photons and have recently been implemented through grading the period of the photonic structure. In this paper, we show that it is possible to keep the period constant and grade instead the lateral metal coverage across the GPH. This strategy ensures spectrally single-mode operationmore » across the whole laser dynamic range and represents an additional degree of freedom in the design of confining potentials for photons.« less

All-dielectric metalens for terahertz wave imaging.

PubMed

Jiang, Xue; Chen, Hao; Li, Zeyu; Yuan, Hongkuan; Cao, Luyao; Luo, Zhenfei; Zhang, Kun; Zhang, Zhihai; Wen, Zhongquan; Zhu, Li-Guo; Zhou, Xun; Liang, Gaofeng; Ruan, Desheng; Du, Lianghui; Wang, Lingfang; Chen, Gang

2018-05-28

Terahertz wave imaging offers promising properties for non-destructive testing applications in the areas of homeland security, medicine, and industrial inspection. However, conventional optical lenses are heavy and bulky and difficult to integrate. An all-dielectric metasurface provides an attractive way to realize a planar lens of light weight that is ultrathin and offers ease of integration. Terahertz lenses based on various metasurfaces have been studied, especially for the application of wave focusing, while there are few experimental demonstrations of terahertz wave imaging lenses based on an all-dielectric metasurface. In the present work, we propose a metalens based on an all-dielectric metasurface with a sub-wavelength unit size of 0.39λ for terahertz wave imaging and experimentally demonstrate its performance in focusing and imaging. A large numerical aperture metalens was fabricated with a focal length of 300λ, radius of 300λ, and numerical aperture of 0.707. The experimental results show that the lens can focus THz waves with an incident angle up to 48°. More importantly, clear terahertz wave images of different objects were obtained for both different cases of forward- and inverse-incident directions, which demonstrate the reversibility of the metalens for imaging. Such a metalens provides a way for realization of all-planar-lens THz imaging system, and might find application in terahertz wave imaging, information processing, microscopy, and others.

Ultrabright continuously tunable terahertz-wave generation at room temperature

PubMed Central

Hayashi, Shin'ichiro; Nawata, Kouji; Taira, Takunori; Shikata, Jun-ichi; Kawase, Kodo; Minamide, Hiroaki

2014-01-01

The hottest frequency region in terms of research currently lies in the ‘frequency gap' region between microwaves and infrared: terahertz waves. Although new methods for generating terahertz radiation have been developed, most sources cannot generate high-brightness terahertz beams. Here we demonstrate the generation of ultrabright terahertz waves (brightness ~0.2 GW/sr·cm2, brightness temperature of ~1018 K, peak power of >50 kW) using parametric wavelength conversion in a nonlinear crystal; this is brighter than many specialized sources such as far-infrared free-electron lasers (~1016 K, ~2 kW). We revealed novel parametric wavelength conversion using stimulated Raman scattering in LiNbO3 without stimulated Brillouin scattering using recently-developed microchip laser. Furthermore, nonlinear up-conversion techniques allow the intense terahertz waves to be visualized and their frequency determined. These results are very promising for extending applied research into the terahertz region, and we expect that this source will open up new research fields such as nonlinear optics in the terahertz region. PMID:24898269

Ultrabright continuously tunable terahertz-wave generation at room temperature.

PubMed

Hayashi, Shin'ichiro; Nawata, Kouji; Taira, Takunori; Shikata, Jun-ichi; Kawase, Kodo; Minamide, Hiroaki

2014-06-05

The hottest frequency region in terms of research currently lies in the 'frequency gap' region between microwaves and infrared: terahertz waves. Although new methods for generating terahertz radiation have been developed, most sources cannot generate high-brightness terahertz beams. Here we demonstrate the generation of ultrabright terahertz waves (brightness ~0.2 GW/sr·cm(2), brightness temperature of ~10(18) K, peak power of >50 kW) using parametric wavelength conversion in a nonlinear crystal; this is brighter than many specialized sources such as far-infrared free-electron lasers (~10(16) K, ~2 kW). We revealed novel parametric wavelength conversion using stimulated Raman scattering in LiNbO3 without stimulated Brillouin scattering using recently-developed microchip laser. Furthermore, nonlinear up-conversion techniques allow the intense terahertz waves to be visualized and their frequency determined. These results are very promising for extending applied research into the terahertz region, and we expect that this source will open up new research fields such as nonlinear optics in the terahertz region.

Experimental study of surface plasmon-phonon polaritons in GaAs-based microstructures

NASA Astrophysics Data System (ADS)

Galimov, A. I.; Shalygin, V. A.; Moldavskaya, M. D.; Panevin, V. Yu; Melentyev, G. A.; Artemyev, A. A.; Firsov, D. A.; Vorobjev, L. E.; Klimko, G. V.; Usikova, A. A.; Komissarova, T. A.; Sedova, I. V.; Ivanov, S. V.

2018-03-01

Optical properties of a heavily-doped GaAs epitaxial layer with a regular grating at its surface have been experimentally investigated in the terahertz spectral range. Reflectivity spectra for the layer with a profiled surface drastically differ from those for the as-grown epilayer with a planar surface. For s-polarized radiation, this difference is totally caused by the electromagnetic wave diffraction at the grating. For p-polarized radiation, additional resonant dips arise due to excitation of surface plasmon-phonon polaritons. Terahertz radiation emission under significant electron heating in an applied pulsed electric field has also been studied. Polarization measurements revealed pronounced peaks related to surface plasmon-phonon polariton resonances of the first and second order in the emission spectra.

[A Compact Source of Terahertz Radiation Based on Interaction of Electrons in à Quantum Well with an Electromagnetic Wave of a Corrugated Waveguide].

PubMed

Shchurova, L Yu; Namiot, V A; Sarkisyan, D R

2015-01-01

Coherent sources of electromagnetic waves in the terahertz frequency range are very promising for various applications, including biology and medicine. In this paper we propose a scheme of a compact terahertz source, in which terahertz radiation is generated due to effective interaction of electrons in a quantum well with an electromagnetic wave of a corrugated waveguide. We have shown that the generation of electromagnetic waves with a frequency of 1012 sec(-1) and an output power of up to 25. mW is possible in the proposed scheme.

Switchable Scattering Meta-Surfaces for Broadband Terahertz Modulation

PubMed Central

Unlu, M.; Hashemi, M. R.; Berry, C. W.; Li, S.; Yang, S.-H.; Jarrahi, M.

2014-01-01

Active tuning and switching of electromagnetic properties of materials is of great importance for controlling their interaction with electromagnetic waves. In spite of their great promise, previously demonstrated reconfigurable metamaterials are limited in their operation bandwidth due to their resonant nature. Here, we demonstrate a new class of meta-surfaces that exhibit electrically-induced switching in their scattering parameters at room temperature and over a broad range of frequencies. Structural configuration of the subwavelength meta-molecules determines their electromagnetic response to an incident electromagnetic radiation. By reconfiguration of the meta-molecule structure, the strength of the induced electric field and magnetic field in the opposite direction to the incident fields are varied and the scattering parameters of the meta-surface are altered, consequently. We demonstrate a custom-designed meta-surface with switchable scattering parameters at a broad range of terahertz frequencies, enabling terahertz intensity modulation with record high modulation depths and modulation bandwidths through a fully integrated, voltage-controlled device platform at room temperature. PMID:25028123

Fabrication of photonic amorphous diamonds for terahertz-wave applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Komiyama, Yuichiro; Abe, Hiroyuki; Kamimura, Yasushi

2016-05-09

A recently proposed photonic bandgap material, named “photonic amorphous diamond” (PAD), was fabricated in a terahertz regime, and its terahertz-wave propagation properties were investigated. The PAD structure was fabricated from acrylic resin mixed with alumina powder, using laser lithographic, micro-additive manufacturing technique. After fabrication, the resulting structure was dewaxed and sintered. The formation of a photonic bandgap at around 0.45 THz was demonstrated by terahertz time-domain spectroscopy. Reflecting the disordered nature of the random network structure, diffusive terahertz-wave propagation was observed in the passbands; the scattering mean-free path decreased as the frequency approached the band edge. The mean-free paths evaluated atmore » the band edges were close to the Ioffe-Regel threshold value for wave localization.« less

Freely Tunable Broadband Polarization Rotator for Terahertz Waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Ren-Hao; Zhou, Yu; Ren, Xiao-Ping

2014-12-28

A freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging.

Experimental observation of sub-terahertz backward-wave amplification in a multi-level microfabricated slow-wave circuit

NASA Astrophysics Data System (ADS)

Baik, Chan-Wook; Ahn, Ho Young; Kim, Yongsung; Lee, Jooho; Hong, Seogwoo; Lee, Sang Hun; Choi, Jun Hee; Kim, Sunil; Jeon, So-Yeon; Yu, SeGi; Collins, George; Read, Michael E.; Lawrence Ives, R.; Kim, Jong Min; Hwang, Sungwoo

2015-11-01

In our earlier paper dealing with dispersion retrieval from ultra-deep, reactive-ion-etched, slow-wave circuits on silicon substrates, it was proposed that splitting high-aspect-ratio circuits into multilevels enabled precise characterization in sub-terahertz frequency regime. This achievement prompted us to investigate beam-wave interaction through a vacuum-sealed integration with a 15-kV, 85-mA, thermionic, electron gun. Our experimental study demonstrates sub-terahertz, backward-wave amplification driven by an external oscillator. The measured output shows a frequency downshift, as well as power amplification, from beam loading even with low beam perveance. This offers a promising opportunity for the development of terahertz radiation sources, based on silicon technologies.

Experimental observation of sub-terahertz backward-wave amplification in a multi-level microfabricated slow-wave circuit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baik, Chan-Wook, E-mail: cw.baik@samsung.com; Ahn, Ho Young; Kim, Yongsung

2015-11-09

In our earlier paper dealing with dispersion retrieval from ultra-deep, reactive-ion-etched, slow-wave circuits on silicon substrates, it was proposed that splitting high-aspect-ratio circuits into multilevels enabled precise characterization in sub-terahertz frequency regime. This achievement prompted us to investigate beam-wave interaction through a vacuum-sealed integration with a 15-kV, 85-mA, thermionic, electron gun. Our experimental study demonstrates sub-terahertz, backward-wave amplification driven by an external oscillator. The measured output shows a frequency downshift, as well as power amplification, from beam loading even with low beam perveance. This offers a promising opportunity for the development of terahertz radiation sources, based on silicon technologies.

Subwavelength focusing of terahertz waves in silicon hyperbolic metamaterials.

PubMed

Kannegulla, Akash; Cheng, Li-Jing

2016-08-01

We theoretically demonstrate the subwavelength focusing of terahertz (THz) waves in a hyperbolic metamaterial (HMM) based on a two-dimensional subwavelength silicon pillar array microstructure. The silicon microstructure with a doping concentration of at least 10¹⁷  cm^-3 offers a hyperbolic dispersion at terahertz frequency range and promises the focusing of terahertz Gaussian beams. The results agree with the simulation based on effective medium theory. The focusing effect can be controlled by the doping concentration, which determines the real part of the out-of-plane permittivity and, therefore, the refraction angles in HMM. The focusing property in the HMM structure allows the propagation of terahertz wave through a subwavelength aperture. The silicon-based HMM structure can be realized using microfabrication technologies and has the potential to advance terahertz imaging with subwavelength resolution.

Terahertz Mapping of Microstructure and Thickness Variations

NASA Technical Reports Server (NTRS)

Roth, Donald J.; Seebo, Jeffrey P.; Winfree, William P.

2010-01-01

A noncontact method has been devised for mapping or imaging spatial variations in the thickness and microstructure of a layer of a dielectric material. The method involves (1) placement of the dielectric material on a metal substrate, (2) through-the-thickness pulse-echo measurements by use of electromagnetic waves in the terahertz frequency range with a raster scan in a plane parallel to the substrate surface that do not require coupling of any kind, and (3) appropriate processing of the digitized measurement data.

Reversed Cherenkov emission of terahertz waves from an ultrashort laser pulse in a sandwich structure with nonlinear core and left-handed cladding.

PubMed

Bakunov, M I; Mikhaylovskiy, R V; Bodrov, S B; Luk'yanchuk, B S

2010-01-18

We propose a scheme for an experimental verification of the reversed Cherenkov effect in left-handed media. The scheme uses optical-to-terahertz conversion in a planar sandwichlike structure that consists of a nonlinear core cladded with a material that exhibits left-handedness at terahertz frequencies. The focused into a line femtosecond laser pulse propagates in the core and emits Cherenkov wedge of terahertz waves in the cladding. We developed a theory that describes terahertz generation in such a structure and calculated spatial distribution of the generated terahertz field, its energy spectrum, and optical-to-terahertz conversion efficiency. The proposed structure can be a useful tool for characterization of the electromagnetic properties of metamaterials in the terahertz frequency range.

Terahertz carpet cloak based on ultrathin metasurface

NASA Astrophysics Data System (ADS)

Wei, Minggui; Yang, Quanlong; Zhang, Xueqian; Li, Yanfeng; Gu, Jianqiang; Han, Jiaguang; Zhang, Weili

2018-01-01

Ultrathin metasurfaces with local phase compensation deliver new schemes to cloaking devices. We demonstrate a remarkable large size carpet cloak realized by an ultrathin metasurface at terahertz frequencies. The metasurface cloak is constructed by periodically arranging 12 different elements. The reflected wave front is perfectly reconstructed by an ultrathin metasurface cloak, which perform well under both intensity-sensitive and phase-sensitive detectors. The invisibility is verified when the cloak is placed on a reflecting triangular surface (bump). The multi-step discrete phase design method would greatly simplify the design process and is probable to achieve large-dimension cloaks, for applications in radar and antenna systems as a thin and easy-to-fabricate solution for radio and terahertz frequencies.

Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators

DOE PAGES

Mitrofanov, Oleg; Khromova, Irina; Siday, Thomas; ...

2016-04-22

We describe the temporal evolution of the terahertz (THz) field leading to the excitation of plasmonic resonances in carbon microfibers. The field evolution is mapped in space and time for the 3/2 wavelength resonance using a subwavelength aperture THz near-field probe with an embedded THz photoconductive detector. The excitation of surface waves at the fiber tips leads to the formation of a standing wave along the fiber. Local THz time-domain spectroscopy at one of the standing wave crests shows a clear third-order resonance peak at 1.65 THz, well described by the Lorentz model. Lastly, this application of the subwavelength aperturemore » THz near-field microscopy for mode mapping and local spectroscopy demonstrates the potential of near-field methods for studies of subwavelength plasmonic THz resonators.« less

Metasurfaces in terahertz waveband

NASA Astrophysics Data System (ADS)

He, Jingwen; Zhang, Yan

2017-11-01

Metasurface, composed of subwavelength antennas, allows us to obtain arbitrary permittivity and permeability in electromagnetic (EM) waveband. It can be used to control the polarization, frequency, amplitude, and phase of the EM wave. Conventional terahertz (THz) components, such as high-impedance silicon lens, polyethylene lens, and quartz wave plate, rely on the phase accumulation along the wave propagation to reshape the THz wavefront. The metasurface employs the localized surface plasmon resonance to modulate the wavefront. Compared with conventional THz components, metasurface has the advantages of being ultrathin, ultralight, and low cost. In recent years, a large number of THz devices based on metasurface have been proposed. We review in broad outline the metasurface devices in the THz region and describe the progress of static and tunable THz field-modulated metasurfaces in detail. Finally, we discuss current challenges and opportunities in this rapidly developing research field.

Continuous-wave optical parametric oscillators on their way to the terahertz range

NASA Astrophysics Data System (ADS)

Sowade, Rosita; Breunig, Ingo; Kiessling, Jens; Buse, Karsten

2010-02-01

Continuous-wave optical parametric oscillators (OPOs) are known to be working horses for spectroscopy in the near- and mid-infrared. However, strong absorption in nonlinear media like lithium niobate complicates the generation of far-infrared light. This absorption leads to pump thresholds vastly exceeding the power of standard pump lasers. Our first approach was, therefore, to combine the established technique of photomixing with optical parametric oscillators. Here, two OPOs provide one wave each, with a tunable difference frequency. These waves are combined to a beat signal as a source for photomixers. Terahertz radiation between 0.065 and 1.018 THz is generated with powers in the order of nanowatts. To overcome the upper frequency limit of the opto-electronic photomixers, terahertz generation has to rely entirely on optical methods. Our all-optical approach, getting around the high thresholds for terahertz generation, is based on cascaded nonlinear processes: the resonantly enhanced signal field, generated in the primary parametric process, is intense enough to act as the pump for a secondary process, creating idler waves with frequencies in the terahertz regime. The latter ones are monochromatic and tunable with detected powers of more than 2 μW at 1.35 THz. Thus, continuous-wave optical parametric oscillators have entered the field of terahertz photonics.

Tutorial: Terahertz beamforming, from concepts to realizations

NASA Astrophysics Data System (ADS)

Headland, Daniel; Monnai, Yasuaki; Abbott, Derek; Fumeaux, Christophe; Withayachumnankul, Withawat

2018-05-01

The terahertz range possesses significant untapped potential for applications including high-volume wireless communications, noninvasive medical imaging, sensing, and safe security screening. However, due to the unique characteristics and constraints of terahertz waves, the vast majority of these applications are entirely dependent upon the availability of beam control techniques. Thus, the development of advanced terahertz-range beam control techniques yields a range of useful and unparalleled applications. This article provides an overview and tutorial on terahertz beam control. The underlying principles of wavefront engineering include array antenna theory and diffraction optics, which are drawn from the neighboring microwave and optical regimes, respectively. As both principles are applicable across the electromagnetic spectrum, they are reconciled in this overview. This provides a useful foundation for investigations into beam control in the terahertz range, which lies between microwaves and infrared light. Thereafter, noteworthy experimental demonstrations of beam control in the terahertz range are discussed, and these include geometric optics, phased array devices, leaky-wave antennas, reflectarrays, and transmitarrays. These techniques are compared and contrasted for their suitability in applications of terahertz waves.

Distributed source model for the full-wave electromagnetic simulation of nonlinear terahertz generation.

PubMed

Fumeaux, Christophe; Lin, Hungyen; Serita, Kazunori; Withayachumnankul, Withawat; Kaufmann, Thomas; Tonouchi, Masayoshi; Abbott, Derek

2012-07-30

The process of terahertz generation through optical rectification in a nonlinear crystal is modeled using discretized equivalent current sources. The equivalent terahertz sources are distributed in the active volume and computed based on a separately modeled near-infrared pump beam. This approach can be used to define an appropriate excitation for full-wave electromagnetic numerical simulations of the generated terahertz radiation. This enables predictive modeling of the near-field interactions of the terahertz beam with micro-structured samples, e.g. in a near-field time-resolved microscopy system. The distributed source model is described in detail, and an implementation in a particular full-wave simulation tool is presented. The numerical results are then validated through a series of measurements on square apertures. The general principle can be applied to other nonlinear processes with possible implementation in any full-wave numerical electromagnetic solver.

Design of a Tunable, Room Temperature, Continuous-Wave Terahertz Source and Detector using Silicon Waveguides

DTIC Science & Technology

2008-01-30

that will use conventional diode- or hotomultiplier-tube-based optical detectors , which are xtremely sensitive . . HEATING AND FREE-CARRIER IMITATIONS...CONTRACT NUMBER IN-HOUSE Design of a tunable, room temperature, continuous-wave terahertz source and detector using silicon waveguides 5b. GRANT...B 261Design of a tunable, room temperature, continuous-wave terahertz source and detector using silicon waveguides T. Baehr-Jones,1,* M. Hochberg,1,3

See-through Detection and 3D Reconstruction Using Terahertz Leaky-Wave Radar Based on Sparse Signal Processing

NASA Astrophysics Data System (ADS)

Murata, Koji; Murano, Kosuke; Watanabe, Issei; Kasamatsu, Akifumi; Tanaka, Toshiyuki; Monnai, Yasuaki

2018-02-01

We experimentally demonstrate see-through detection and 3D reconstruction using terahertz leaky-wave radar based on sparse signal processing. The application of terahertz waves to radar has received increasing attention in recent years for its potential to high-resolution and see-through detection. Among others, the implementation using a leaky-wave antenna is promising for compact system integration with beam steering capability based on frequency sweep. However, the use of a leaky-wave antenna poses a challenge on signal processing. Since a leaky-wave antenna combines the entire signal captured by each part of the aperture into a single output, the conventional array signal processing assuming access to a respective antenna element is not applicable. In this paper, we apply an iterative recovery algorithm "CoSaMP" to signals acquired with terahertz leaky-wave radar for clutter mitigation and aperture synthesis. We firstly demonstrate see-through detection of target location even when the radar is covered with an opaque screen, and therefore, the radar signal is disturbed by clutter. Furthermore, leveraging the robustness of the algorithm against noise, we also demonstrate 3D reconstruction of distributed targets by synthesizing signals collected from different orientations. The proposed approach will contribute to the smart implementation of terahertz leaky-wave radar.

Tunable terahertz wave generation through a bimodal laser diode and plasmonic photomixer.

PubMed

Yang, S-H; Watts, R; Li, X; Wang, N; Cojocaru, V; O'Gorman, J; Barry, L P; Jarrahi, M

2015-11-30

We demonstrate a compact, robust, and stable terahertz source based on a novel two section digital distributed feedback laser diode and plasmonic photomixer. Terahertz wave generation is achieved through difference frequency generation by pumping the plasmonic photomixer with two output optical beams of the two section digital distributed feedback laser diode. The laser is designed to offer an adjustable terahertz frequency difference between the emitted wavelengths by varying the applied currents to the laser sections. The plasmonic photomixer is comprised of an ultrafast photoconductor with plasmonic contact electrodes integrated with a logarithmic spiral antenna. We demonstrate terahertz wave generation with 0.15-3 THz frequency tunability, 2 MHz linewidth, and less than 5 MHz frequency stability over 1 minute, at useful power levels for practical imaging and sensing applications.

Development of terahertz endoscopic system for cancer detection

NASA Astrophysics Data System (ADS)

Doradla, Pallavi; Alavi, Karim; Joseph, Cecil S.; Giles, Robert H.

2016-02-01

Terahertz (THz) imaging is emerging as a robust platform for a myriad of applications in the fields of security, health, astronomy and material science. The terahertz regime with wavelengths spanning from microns to millimeters is a potentially safe and noninvasive medical imaging modality for detecting cancers. Endoscopic imaging systems provide high flexibility in examining the interior surfaces of an organ or tissue. Researchers have been working on the development of THz endoscopes with photoconductive antennas, which necessarily operate under high voltage, and require at least two channels to measure the reflected signal from the specimen. This manuscript provides the design and imperative steps involved in the development of a single-channel terahertz endoscopic system. The continuous-wave terahertz imaging system utilizes a single flexible terahertz waveguide channel to transmit and collect the back reflected intrinsic terahertz signal from the sample and is capable of operation in both transmission and reflection modalities. To determine the feasibility of using a terahertz endoscope for cancer detection, the co- and cross-polarized terahertz remittance from human colonic tissue specimens were collected at 584 GHz frequency. The two dimensional terahertz images obtained using polarization specific detection exhibited intrinsic contrast between cancerous and normal regions of fresh colorectal tissue. The level of contrast observed using endoscopic imaging correlates well with the contrast levels observed in the free space ex vivo terahertz reflectance studies of human colonic tissue. The prototype device developed in this study represents a significant step towards clinical endoscopic application of THz technology for in vivo colon cancer screening.

Flexible manipulation of terahertz wave reflection using polarization insensitive coding metasurfaces.

PubMed

Jiu-Sheng, Li; Ze-Jiang, Zhao; Jian-Quan, Yao

2017-11-27

In order to extend to 3-bit encoding, we propose notched-wheel structures as polarization insensitive coding metasurfaces to control terahertz wave reflection and suppress backward scattering. By using a coding sequence of "00110011…" along x-axis direction and 16 × 16 random coding sequence, we investigate the polarization insensitive properties of the coding metasurfaces. By designing the coding sequences of the basic coding elements, the terahertz wave reflection can be flexibly manipulated. Additionally, radar cross section (RCS) reduction in the backward direction is less than -10dB in a wide band. The present approach can offer application for novel terahertz manipulation devices.

Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor.

PubMed

Yasumatsu, Naoya; Watanabe, Shinichi

2012-02-01

We propose and develop a method to quickly and precisely determine the polarization direction of coherent terahertz electromagnetic waves generated by femtosecond laser pulses. The measurement system consists of a conventional terahertz time-domain spectroscopy system with the electro-optic (EO) sampling method, but we add a new functionality in the EO crystal which is continuously rotating with the angular frequency ω. We find a simple yet useful formulation of the EO signal as a function of the crystal orientation, which enables a lock-in-like detection of both the electric-field amplitude and the absolute polarization direction of the terahertz waves with respect to the probe laser pulse polarization direction at the same time. The single measurement finishes around two periods of the crystal rotations (∼21 ms), and we experimentally prove that the accuracy of the polarization measurement does not suffer from the long-term amplitude fluctuation of the terahertz pulses. Distribution of the measured polarization directions by repeating the measurements is excellently fitted by a gaussian distribution function with a standard deviation of σ = 0.56°. The developed technique is useful for the fast direct determination of the polarization state of the terahertz electromagnetic waves for polarization imaging applications as well as the precise terahertz Faraday or Kerr rotation spectroscopy.

Terahertz wave polarization beam splitter using a cascaded multimode interference structure.

PubMed

Li, Jiu-sheng; Liu, Han; Zhang, Le

2014-08-01

A terahertz wave polarization beam splitter, based on two cascaded multimode interference structures with different widths, is designed and numerically demonstrated. The numerical calculation results show that the designed polarization beam splitter can split transverse-electric (TE) and transverse-magnetic (TM)-polarized terahertz waves into different propagation directions with high efficiency over a frequency range from 6.40 to 6.50 THz. This polarization beam splitter shows more than a 22.06 dB extinction ratio for TE-polarization and a 31.65 dB extinction ratio for TM-polarization. Using such a polarization beam splitter, the whole length of the polarization beam splitter is reduced to about 1/12 that of a conventional design. This enables the polarization beam splitter to be used in terahertz wave integrated circuit fields.

Evanescent wave coupling in terahertz waveguide arrays.

PubMed

Reichel, K S; Sakoda, N; Mendis, R; Mittleman, D M

2013-07-15

We study energy transfer among an array of identical finite-width parallel-plate waveguides in close proximity, via evanescent wave coupling of broadband terahertz waves. We observe stronger coupling with larger plate separations and longer propagation paths. This work establishes a platform to investigate new opportunities for THz components and devices based on evanescent wave coupling.

Dispersion features of complex waves in a graphene-coated semiconductor nanowire

NASA Astrophysics Data System (ADS)

Yu, Pengchao; Fesenko, Volodymyr I.; Tuz, Vladimir R.

2018-05-01

The dispersion features of a graphene-coated semiconductor nanowire operating in the terahertz frequency band are consistently studied in the framework of a special theory of complex waves. Detailed classification of the waveguide modes was carried out based on the analysis of characteristics of the phase and attenuation constants obtained from the complex roots of characteristic equation. With such a treatment, the waves are attributed to the group of either "proper" or "improper" waves, wherein their type is determined as the trapped surface waves, fast and slow leaky waves, and surface plasmons. The dispersion curves of axially symmetric TM0n and TE0n modes, as well as nonsymmetric hybrid EH1n and HE1n modes, were plotted and analyzed in detail, and both radiative regime of leaky waves and guided regime of trapped surface waves are identified. The peculiarities of propagation of the TM modes of surface plasmons were revealed. Two subregions of existence of surface plasmons were found out where they appear as propagating and reactive waves. The cutoff conditions for higher-order TM modes of surface plasmons were correctly determined.

FDTD-based quantitative analysis of terahertz wave detection for multilayered structures.

PubMed

Tu, Wanli; Zhong, Shuncong; Shen, Yaochun; Zhou, Qing; Yao, Ligang

2014-10-01

Experimental investigations have shown that terahertz pulsed imaging (TPI) is able to quantitatively characterize a range of multilayered media (e.g., biological issues, pharmaceutical tablet coatings, layered polymer composites, etc.). Advanced modeling of the interaction of terahertz radiation with a multilayered medium is required to enable the wide application of terahertz technology in a number of emerging fields, including nondestructive testing. Indeed, there have already been many theoretical analyses performed on the propagation of terahertz radiation in various multilayered media. However, to date, most of these studies used 1D or 2D models, and the dispersive nature of the dielectric layers was not considered or was simplified. In the present work, the theoretical framework of using terahertz waves for the quantitative characterization of multilayered media was established. A 3D model based on the finite difference time domain (FDTD) method is proposed. A batch of pharmaceutical tablets with a single coating layer of different coating thicknesses and different refractive indices was modeled. The reflected terahertz wave from such a sample was computed using the FDTD method, assuming that the incident terahertz wave is broadband, covering a frequency range up to 3.5 THz. The simulated results for all of the pharmaceutical-coated tablets considered were found to be in good agreement with the experimental results obtained using a commercial TPI system. In addition, we studied a three-layered medium to mimic the occurrence of defects in the sample.

Creating Rydberg electron wave packets using terahertz pulses

NASA Astrophysics Data System (ADS)

Bromage, Jake

1999-10-01

In this thesis I present experiments in which we excited classical-limit states of an atom using terahertz pulses. In a classical-limit state, an atom's outer electron is confined to a wave packet that orbits the core along a classical trajectory. Researchers have excited states with classical traits, but wave packets localized in all three dimensions have proved elusive. Theoretical studies have shown such states can be created using terahertz pulses. Using these techniques, we created a linear-orbit wave packet (LOWP), that is three-dimensionally localized and orbits along a line on one side of the atom's core. Terahertz pulses are sub-picosecond bursts of far- infrared radiation. Unlike ultrashort optical pulses, the electric field of terahertz pulses barely completes a single cycle. Our simulations of the atom-pulse interaction show that this electric field profile is critical in determining the quality of the wave packet. To characterize our terahertz pulses, we invented dithered-edge sampling which time- resolves the electric field using a photoconductive receiver and a triggered attenuator. We also studied how pulses are distorted after propagating through metallic structures, and used our findings to design our atomic experiments. We excited wave packets in atomic sodium using a two-step process. First, we used tunable, nanosecond dye lasers to excite an extreme Stark state. Next, we used a terahertz pump pulse to coherently redistribute population among extreme Stark states in neighboring manifolds. Interference between the final states produces a localized, dynamic LOWP. To analyze the LOWP, we ionized it with a stronger terahertz probe pulse, varying the pump-probe delay to map out its motion. We observed two strong LOWP signatures. Changing the static electric field produced small changes (2%) in the orbital period that agreed with our theoretical predictions. Secondly, because the LOWP scatters off the core, the pump-probe signal depended on the direction of the kick the LOWP received from the robe pulse. These observations, combined with our detailed simulations that used sodium parameters and the actual shape of the terahertz pulse, lead us to conclude that we excited a LOWP.

Terahertz wave techniques using a metal mesh for evaluating the components of the stratum corneum.

PubMed

Mizukoshi, Koji; Yonekura, Kazuki; Ogura, Hidehiro; Guan, Yu; Kawase, Kodo

2013-02-01

Terahertz waves are located in the region of the spectrum between milliwaves and infrared. We analyzed the feasibility of terahertz spectroscopy to inspect the compositional variations of the stratum corneum (SC). We used a terahertz time-domain spectroscopy system with the metal mesh technique. To investigate whether terahertz can inspect compositional variation of SC, we measured the terahertz frequency spectra of the SC sheet that was treated with chloroform-methanol, lipid mixture, a denaturation agent, and heating with hot air. The chloroform-methanol treatment of the SC shifted the dip position, which represents a convex downward shape of the spectra, to a higher frequency. This dip shift was reversed to an untreated position by the dose-dependent application of a lipid mixture. The heating treatment of the SC shifted the dip position to a higher frequency. The same dip shift was also induced by the application of a denaturation agent to the SC. The technique using terahertz waves with a metal mesh is effective because of its simplicity and its high degree of accuracy in detecting the amount of lipid and the protein conformation state. © 2012 John Wiley & Sons A/S.

Characterization of terahertz waves on foreign materials of composite materials

NASA Astrophysics Data System (ADS)

Im, Kwang-Hee; Kim, Sun-Kyu; Chiou, Chien-Ping; Jung, Jong-An

2018-04-01

Carbon-fiber reinforced plastics (CFRP) are widely utilized due to their comparatively high performance in engineering structures. It is well understood that a nondestructive technique would be very beneficial. A new terahertz radiation has been recognized for its importance in technological applications. Recently, T-ray (terahertz ray) advances in technology and instrumentation have provided a probing field on the electromagnetic spectrum. In carbon composites, the penetration characterization of T-ray waves was fundamentally investigated in order to measure the painting thickness. Also, another study dealt with THz scan images of honeycomb sandwich composite panels using a refractive index (n), an absorption coefficient (α), the electrical conductivity of glass fiber embedded epoxy matrix composites, and carbon fiber reinforced plastics (CFRP) skin. For experiments, a method of detecting FRP composites with impact damage is presented, which utilizes aluminum wires intertwined with woven carbon fibers as they are inserted into the surface of the CFRP honeycomb sandwich panels. Intensive characterization of T-ray for the nondestructive evaluation (NDE) of carbon composite reinforced plastics (CFRP) composites is discussed in relation to the E-field influence with CFRP composite laminates.

Generating high-power short terahertz electromagnetic pulses with a multifoil radiator.

PubMed

Vinokurov, Nikolay A; Jeong, Young Uk

2013-02-08

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the z axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the z axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the z axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

Terahertz Spectroscopy for Chemical Detection and Burn Characterization

NASA Astrophysics Data System (ADS)

Arbab, Mohammad Hassan

Terahertz (THz) frequencies represent the last frontier of the electromagnetic spectrum to be investigated by scientists. One of the main attractions of investigating this frequency range is the richness of the spectral information that can be obtained using a Terahertz Time-Domain Spectroscopy (THz-TDS) setup. Many large molecule chemicals and polymers have vibrational and rotational modes in the THz frequencies. Study of these resonance modes has revealed a wealth of new information about the intermolecular structure, and its transformation during crystallization or polymerization process. This information helps researchers develop new materials to address problems such as efficient energy conversion in polymer solar cells. Moreover, similar signature-like terahertz modes can be used for stand-off identification of substances or for nondestructive evaluation of defects in industrial applications. Finally, terahertz spectroscopy has the potential to provide a safe and non-ionizing imaging modality to study cellular and molecular events in biological and biomedical applications. The high sensitivity of terahertz waves to attenuation by both bound and free water molecules can also provides a source of signal contrast for many future biomedical imaging and diagnostic applications. In this dissertation, we aim to study and develop three such applications of terahertz spectroscopy, which form the three axes of our work: rough-surface scattering mediated stand-off detection of chemicals, characterization of burn injuries using terahertz radiation, and a new electrically tunable bandpass filter device incorporating nano-material transparent electrodes that can enable fast terahertz spectroscopy in the frequency domain.

High Speed Terahertz Modulator on the Chip Based on Tunable Terahertz Slot Waveguide

PubMed Central

Singh, P. K.; Sonkusale, S.

2017-01-01

This paper presents an on-chip device that can perform gigahertz-rate amplitude modulation and switching of broadband terahertz electromagnetic waves. The operation of the device is based on the interaction of confined THz waves in a novel slot waveguide with an electronically tunable two dimensional electron gas (2DEG) that controls the loss of the THz wave propagating through this waveguide. A prototype device is fabricated which shows THz intensity modulation of 96% at 0.25 THz carrier frequency with low insertion loss and device length as small as 100 microns. The demonstrated modulation cutoff frequency exceeds 14 GHz indicating potential for the high-speed modulation of terahertz waves. The entire device operates at room temperature with low drive voltage (<2 V) and zero DC power consumption. The device architecture has potential for realization of the next generation of on-chip modulators and switches at THz frequencies. PMID:28102306

Parametric amplification of a superconducting plasma wave

DOE PAGES

Rajasekaran, S.; Casandruc, E.; Laplace, Y.; ...

2016-07-11

Many applications in photonics require all-optical manipulation of plasma waves, which can concentrate electromagnetic energy on sub-wavelength length scales. This is difficult in metallic plasmas because of their small optical nonlinearities. Some layered superconductors support Josephson plasma waves, involving oscillatory tunnelling of the superfluid between capacitively coupled planes. Josephson plasma waves are also highly nonlinear, and exhibit striking phenomena such as cooperative emission of coherent terahertz radiation, superconductor–metal oscillations and soliton formation. In this paper, we show that terahertz Josephson plasma waves can be parametrically amplified through the cubic tunnelling nonlinearity in a cuprate superconductor. Finally, parametric amplification is sensitivemore » to the relative phase between pump and seed waves, and may be optimized to achieve squeezing of the order-parameter phase fluctuations or terahertz single-photon devices.« less

Controlling Propagation Properties of Surface Plasmon Polariton at Terahertz Frequency

NASA Astrophysics Data System (ADS)

Gupta, Barun

Despite great scientific exploration since the 1900s, the terahertz range is one of the least explored regions of electromagnetic spectrum today. In the field of plasmonics, texturing and patterning allows for control over electromagnetic waves bound to the interface between a metal and the adjacent dielectric medium. The surface plasmon-polaritons (SPPs) display unique dispersion characteristics that depend upon the plasma frequency of the medium. In the long wavelength regime, where metals are highly conductive, such texturing can create an effective medium that can be characterized by an effective plasma frequency that is determined by the geometrical parameters of the surface structure. The terahertz (THz) spectral range offers unique opportunities to utilize such materials. This thesis describes a number of terahertz plasmonic devices, both passive and active, fabricated using different techniques. As an example, inkjet printing is exploited for fabricating two-dimensional plasmonic devices. In this case, we demonstrated the terahertz plasmonic structures in which the conductivity of the metallic film is varied spatially in order to further control the plasmonic response. Using a commercially available inkjet printers, in which one cartridge is filled with conductive silver ink and a second cartridge is filled with resistive carbon ink, computer generated drawings of plasmonic structures are printed in which the individual printed dots can have differing amounts of the two inks, thereby creating a spatial variation in the conductivity. The inkjet printing technique is limited to the two-dimensional structurers. In order to expand the capability of printing complex terahertz devices, which cannot otherwise be fabricated using standard fabricating techniques, we employed 3D printing techniques. 3D printing techniques using polymers to print out the complex structures. In the realm of active plasmonic devices, a wide range of innovative approaches have been developed utilizing a variety of materials. We discuss the use of SMAs for terahertz (THz) plasmonics that allows for switching between different physical geometries corresponding to different electromagnetic responses.

Negative refractive index metamaterial with high transmission, low reflection, and low loss in the terahertz waveband.

PubMed

Suzuki, Takehito; Sekiya, Masashi; Sato, Tatsuya; Takebayashi, Yuki

2018-04-02

The refractive index is a basic parameter of materials which it is essential to know for the manipulation of electromagnetic waves. However, there are no naturally occurring materials with negative refractive indices, and high-performance materials with negative refractive indices and low losses are demanded in the terahertz waveband. In this paper, measurements by terahertz time-domain spectroscopy (THz-TDS) demonstrate a metamaterial with a negative refractive index n of -4.2 + j0.17, high transmitted power of 81.5%, low reflected power of 4.3%, and a high figure of merit (FOM = |Re(n)/Im(n)|) of 24.2 at 0.42 THz. The terahertz metamaterial with these unprecedented properties can provide various attractive terahertz applications such as superlenses with resolutions beyond the diffraction limit in terahertz continuous wave imaging.

Electro-optically Induced and Manipulated Terahertz Waves from Fe-doped InGaAs Surfaces

NASA Astrophysics Data System (ADS)

Hatem, O.

2018-03-01

We demonstrate the presence of dual simultaneous nonlinear mechanisms: field-induced optical rectification (FIOR) and field-induced surge current (FISC) for the generation of terahertz (THz) pulses from p-type and n-type Fe:In0.53Ga0.47As surfaces upon excitation with femtosecond laser pulses centered at 800 nm wavelength. Experimental investigations of the dependence of the generated THz waves on the incident angular optical polarization, optical irradiance, and the direction and magnitude of applied electric DC fields give confirming results to the proposed THz generation mechanisms. Applying external DC electric fields in the plane of the incident optical field shows efficient capability in manipulating the direction and phase of the generated THz waves, and controlling the refractive index of Fe:In0.53Ga0.47As material in the THz range, in addition to enhancing the emitted THz power up to two orders of magnitude. The fast and reliable response of Fe:In0.53Ga0.47As to the changes in the direction and magnitude of the optical and electrical fields suggests its use in amplitude and phase modulators, and ultrafast optoelectronic systems.

Terahertz amplification in RTD-gated HEMTs with a grating-gate wave coupling topology

NASA Astrophysics Data System (ADS)

Condori Quispe, Hugo O.; Encomendero-Risco, Jimy J.; Xing, Huili Grace; Sensale-Rodriguez, Berardi

2016-08-01

We theoretically analyze the operation of a terahertz amplifier consisting of a resonant-tunneling-diode gated high-electron-mobility transistor (RTD-gated HEMT) in a grating-gate topology. In these devices, the key element enabling substantial power gain is the efficient coupling of terahertz waves into and out of plasmons in the RTD-gated HEMT channel, i.e., the gain medium, via the grating-gate itself, part of the active device, rather than by an external antenna structure as discussed in previous works, therefore potentially enabling terahertz amplification with associated power gains >40 dB.

Terahertz amplification in RTD-gated HEMTs with a grating-gate wave coupling topology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Condori Quispe, Hugo O.; Sensale-Rodriguez, Berardi; Encomendero-Risco, Jimy J.

2016-08-08

We theoretically analyze the operation of a terahertz amplifier consisting of a resonant-tunneling-diode gated high-electron-mobility transistor (RTD-gated HEMT) in a grating-gate topology. In these devices, the key element enabling substantial power gain is the efficient coupling of terahertz waves into and out of plasmons in the RTD-gated HEMT channel, i.e., the gain medium, via the grating-gate itself, part of the active device, rather than by an external antenna structure as discussed in previous works, therefore potentially enabling terahertz amplification with associated power gains >40 dB.

Characteristics of a liquid-crystal-filled composite lattice terahertz bandgap fiber

NASA Astrophysics Data System (ADS)

Bai, Jinjun; Ge, Meilan; Wang, Shasha; Yang, Yanan; Li, Yong; Chang, Shengjiang

2018-07-01

A new type of terahertz fiber is presented based on composite lattice photonic crystal bandgap. The cladding is filled selectively with the nematic liquid crystal 5CB which is sensitive to the electric field. The terahertz wave can be modulated by using the electric field to control the orientation of liquid crystal molecules. The plane wave expansion method and the finite element method are employed to theoretically analyze bandgap characteristics, polarization characteristics, energy fraction and material absorption loss. The results show that this fiber structure can be used as tunable terahertz polarization controller.

Characterization of ErAs:GaAs and LuAs:GaAs Superlattice Structures for Continuous-Wave Terahertz Wave Generation through Plasmonic Photomixing

NASA Astrophysics Data System (ADS)

Yang, Shang-Hua; Salas, Rodolfo; Krivoy, Erica M.; Nair, Hari P.; Bank, Seth R.; Jarrahi, Mona

2016-07-01

We investigate the impact of ErAs:GaAs and LuAs:GaAs superlattice structures with different LuAs/ErAs nanoparticle depositions and superlattice geometries on terahertz radiation properties of plasmonic photomixers operating at a 780-nm optical wavelength. Our analysis indicates the crucial impact of carrier drift velocity and carrier lifetime on the performance of plasmonic photomixers. While higher carrier drift velocities enable higher optical-to-terahertz conversion efficiencies by offering higher quantum efficiencies, shorter carrier lifetimes allow achieving higher optical-to-terahertz conversion efficiencies by mitigating the negative impact of destructive terahertz radiation from slow photocarriers and preventing the carrier screening effect.

Enhanced coherent oscillations in the superconducting state of underdoped YB a 2 C u 3 O 6 + x induced via ultrafast terahertz excitation

DOE PAGES

Dakovski, Georgi L.; Lee, Wei -Sheng; Hawthorn, David G.; ...

2015-06-24

We utilize intense, single-cycle terahertz pulses to induce collective excitations in the charge-density-wave-ordered underdoped cuprate YBa 2Cu 3O 6+x. These excitations manifest themselves as pronounced coherent oscillations of the optical reflectivity in the transient state, accompanied by minimal incoherent quasiparticle relaxation dynamics. The oscillations occur at frequencies consistent with soft phonon energies associated with the charge-density-wave, but vanish above the superconducting transition temperature rather than that at the charge-density-wave transition. These results indicate an intimate relationship of the terahertz excitation with the underlying charge-density-wave and the superconducting condensate itself.

Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves

NASA Astrophysics Data System (ADS)

Chiadini, Francesco; Fiumara, Vincenzo; Mackay, Tom G.; Scaglione, Antonio; Lakhtakia, Akhlesh

2017-08-01

The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a dissipative plasmonic material. Correspondingly, the ESWs transmute from Dyakonov-Tamm surface waves into surface-plasmon-polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results.

Determination of tenogenic differentiation in human mesenchymal stem cells by terahertz waves for measurement of the optical property of cellular suspensions

NASA Astrophysics Data System (ADS)

Morita, Yasuyuki; Azuchi, Kosuke; Ju, Yang; Suzuki, Satoshi; Xu, Baiyao; Yamamoto, Shuhei

2014-06-01

Technology for identifying stem cell-to-tenocyte differentiation that is non-contact and non-destructive in vitro is essential in tissue engineering. It has been found that expression of various RNA and proteins produced by differentiated cells is elevated when human bone marrow mesenchymal stem cells (hBMSCs) differentiate into tenocytes. Also, such biomolecules have absorption bands in the terahertz range. Thus, we attempted to evaluate whether terahertz waves could be used to distinguish hBMSC-to-tenocyte differentiation. Terahertz time-domain spectroscopy (THz-TDS) using femtosecond laser pulses was used for terahertz measurements. HBMSCs differentiated into tenocytes with mechanical stimulation: 10% cyclical uniaxial stretching at 1 Hz for 24 or 48 h. Cellular suspensions before and after differentiation were measured with terahertz waves. Complex refractive index, consisting of a refractive index (real) and an extinction coefficient (imaginary) obtained from the transmitted terahertz signals, was evaluated before and after differentiation at 1.0 THz. As a result, the THz-TDS system enabled discrimination of hBMSC-to-tenocyte differentiation due to the marked contrast in optical parameter before and after differentiation. This is the first report of the potential of a THz-TDS system for the detection of tenogenic differentiation using a non-contact and non-destructive in vitro technique.

Ultraviolet Laser Lithography of Titania Photonic Crystals for Terahertz-Wave Modulation.

PubMed

Kirihara, Soshu; Nonaka, Koki; Kisanuki, Shoichiro; Nozaki, Hirotoshi; Sakaguchi, Keito

2018-05-18

Three-dimensional (3D) microphotonic crystals with a diamond structure composed of titania microlattices were fabricated using ultraviolet laser lithography, and the bandgap properties in the terahertz (THz) electromagnetic-wave frequency region were investigated. An acrylic resin paste with titania fine particle dispersions was used as the raw material for additive manufacturing. By scanning a spread paste surface with an ultraviolet laser beam, two-dimensional solid patterns were dewaxed and sintered. Subsequently, 3D structures with a relative density of 97% were created via layer lamination and joining. A titania diamond lattice with a lattice constant density of 240 µm was obtained. The properties of the electromagnetic wave were measured using a THz time-domain spectrometer. In the transmission spectra for the Γ-X direction, a forbidden band was observed from 0.26 THz to 0.44 THz. The frequency range of the bandgap agreed well with calculated results obtained using the plane⁻wave expansion method. Additionally, results of a simulation via transmission-line modeling indicated that a localized mode can be obtained by introducing a plane defect between twinned diamond lattice structures.

Active Terahertz Chiral Metamaterials Based on Phase Transition of Vanadium Dioxide (VO2).

PubMed

Wang, Shengxiang; Kang, Lei; Werner, Douglas H

2018-01-09

Compared with natural materials, chiral metamaterials have been demonstrated with orders of magnitude stronger chiroptical response, which provides the basis for applications such as ultracompact polarization components and plasmonic-enhanced biosensing. Terahertz chiral metamaterials that allow dynamic polarization control of terahertz waves are of great practical interest, but remain extremely rare. Here, we show that hybrid metamaterials integrated with vanadium dioxide (VO 2 ) exhibiting phase transition can enable dynamically tunable chiroptical responses at terahertz frequencies. In particular, a circular dichroism of ~40° and a maximum polarization rotation of ~200°/λ are observed around 0.7 THz. Furthermore, our study also reveals that the chiroptical response from the proposed metamaterials is strongly dependent on the phase transition of VO 2 , leading to actively controllable polarization states of the transmitted terahertz waves. This work paves the way for the development of terahertz metadevices capable of enabling active polarization manipulation.

Broadband diffuse terahertz wave scattering by flexible metasurface with randomized phase distribution

PubMed Central

Zhang, Yin; Liang, Lanju; Yang, Jing; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian; Jin, Biaobing; Liu, Weiwei

2016-01-01

Suppressing specular electromagnetic wave reflection or backward radar cross section is important and of broad interests in practical electromagnetic engineering. Here, we present a scheme to achieve broadband backward scattering reduction through diffuse terahertz wave reflection by a flexible metasurface. The diffuse scattering of terahertz wave is caused by the randomized reflection phase distribution on the metasurface, which consists of meta-particles of differently sized metallic patches arranged on top of a grounded polyimide substrate simply through a certain computer generated pseudorandom sequence. Both numerical simulations and experimental results demonstrate the ultralow specular reflection over a broad frequency band and wide angle of incidence due to the re-distribution of the incident energy into various directions. The diffuse scattering property is also polarization insensitive and can be well preserved when the flexible metasurface is conformably wrapped on a curved reflective object. The proposed design opens up a new route for specular reflection suppression, and may be applicable in stealth and other technology in the terahertz spectrum. PMID:27225031

Broadband diffuse terahertz wave scattering by flexible metasurface with randomized phase distribution.

PubMed

Zhang, Yin; Liang, Lanju; Yang, Jing; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian; Jin, Biaobing; Liu, Weiwei

2016-05-26

Suppressing specular electromagnetic wave reflection or backward radar cross section is important and of broad interests in practical electromagnetic engineering. Here, we present a scheme to achieve broadband backward scattering reduction through diffuse terahertz wave reflection by a flexible metasurface. The diffuse scattering of terahertz wave is caused by the randomized reflection phase distribution on the metasurface, which consists of meta-particles of differently sized metallic patches arranged on top of a grounded polyimide substrate simply through a certain computer generated pseudorandom sequence. Both numerical simulations and experimental results demonstrate the ultralow specular reflection over a broad frequency band and wide angle of incidence due to the re-distribution of the incident energy into various directions. The diffuse scattering property is also polarization insensitive and can be well preserved when the flexible metasurface is conformably wrapped on a curved reflective object. The proposed design opens up a new route for specular reflection suppression, and may be applicable in stealth and other technology in the terahertz spectrum.

Investigation of radiant millimeter wave/terahertz radiation from low-infrared signature targets

NASA Astrophysics Data System (ADS)

Aytaç, B.; Alkuş, Ü.; Sivaslıgil, M.; Şahin, A. B.; Altan, H.

2017-10-01

Millimeter (mm) and sub-mm wave radiation is increasingly becoming a region of interest as better methods are developed to detect in this wavelength range. The development of sensitive focal plane array (FPA) architectures as well as single pixel scanners has opened up a new field of passive detection and imaging. Spectral signatures of objects, a long standing area of interest in the Short Wave Infrared (SWIR), Mid-Wave (MWIR) and Long Wave-IR (LWIR) bands can now be assessed in the mm-wave/terahertz (THz) region. The advantage is that this form of radiation is not as adversely affected by poor atmospheric conditions compared to other bands. In this study, a preliminary experiment in a laboratory environment is performed to assess the radiance from targets with low infrared signatures in the millimeter wave/terahertz (THz) band (<1 THz). The goal of this approach is to be able to model the experimental results to better understand the mm-wave/THz signature of targets with low observability in the IR bands.

High-power, single-longitudinal-mode terahertz-wave generation pumped by a microchip Nd:YAG laser [Invited].

PubMed

Hayashi, Shin'ichiro; Nawata, Koji; Sakai, Hiroshi; Taira, Takunori; Minamide, Hiroaki; Kawase, Kodo

2012-01-30

We report on the development of a high-peak-power, single-longitudinal-mode and tunable injection-seeded terahertz-wave parametric generator using MgO:LiNbO3, which operates at room temperature. The high peak power (> 120 W) is enough to allow easy detection by commercial and calibrated pyroelectric detectors, and the spectral resolution (< 10 GHz) is the Fourier transform limit of the sub-nanosecond terahertz-wave pulse. The tunability (1.2-2.8 THz) and the small footprint size (A3 paper, 29.7 × 42 cm) are suitable for a variety of applications.

Making structured metals transparent for ultrabroadband electromagnetic waves and acoustic waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Ren-Hao; Peng, Ru-Wen; Huang, Xian-Rong

2015-07-01

In this review, we present our recent work on making structured metals transparent for broadband electromagnetic waves and acoustic waves via excitation of surface waves. First, we theoretically show that one-dimensional metallic gratings can become transparent and completely antireflective for extremely broadband electromagnetic waves by relying on surface plasmons or spoof surface plasmons. Second, we experimentally demonstrate that metallic gratings with narrow slits are highly transparent for broadband terahertz waves at oblique incidence and high transmission efficiency is insensitive to the metal thickness. Further, we significantly develop oblique metal gratings transparent for broadband electromagnetic waves (including optical waves and terahertzmore » ones) under normal incidence. In the third, we find the principles of broadband transparency for structured metals can be extended from one-dimensional metallic gratings to two-dimensional cases. Moreover, similar phenomena are found in sonic artificially metallic structures, which present the transparency for broadband acoustic waves. These investigations provide guidelines to develop many novel materials and devices, such as transparent conducting panels, antireflective solar cells, and other broadband metamaterials and stealth technologies.« less

Photoinduced Nonlinear Mixing of Terahertz Dipole Resonances in Graphene Metadevices.

PubMed

In, Chihun; Kim, Hyeon-Don; Min, Bumki; Choi, Hyunyong

2016-02-17

The first experimental demonstration of nonlinear terahertz difference-frequency generation in a hybrid graphene metadevice is reported. Decades of research have revealed that terahertz-wave generation is impossible in single-layer graphene. This limitation is overcome and nonlinear terahertz generation by ultra-short optical pulse injection is demonstrated. This device is an essential step toward atomically thin, nonlinear terahertz optoelectronic components. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Energy scaling of terahertz-wave parametric sources.

PubMed

Tang, Guanqi; Cong, Zhenhua; Qin, Zengguang; Zhang, Xingyu; Wang, Weitao; Wu, Dong; Li, Ning; Fu, Qiang; Lu, Qingming; Zhang, Shaojun

2015-02-23

Terahertz-wave parametric oscillators (TPOs) have advantages of room temperature operation, wide tunable range, narrow line-width, good coherence. They have also disadvantage of small pulse energy. In this paper, several factors preventing TPOs from generating high-energy THz pulses and the corresponding solutions are analyzed. A scheme to generate high-energy THz pulses by using the combination of a TPO and a Stokes-pulse-injected terahertz-wave parametric generator (spi-TPG) is proposed and demonstrated. A TPO is used as a source to generate a seed pulse for the surface-emitted spi-TPG. The time delay between the pump and Stokes pulses is adjusted to guarantee they have good temporal overlap. The pump pulses have a large pulse energy and a large beam size. The Stokes beam is enlarged to make its size be larger than the pump beam size to have a large effective interaction volume. The experimental results show that the generated THz pulse energy from the spi-TPG is 1.8 times as large as that obtained from the TPO for the same pumping pulse energy density of 0.90 J/cm(2) and the same pumping beam size of 3.0 mm. When the pumping beam sizes are 5.0 and 7.0 mm, the enhancement times are 3.7 and 7.5, respectively. The spi-TPG here is similar to a difference frequency generator; it can also be used as a Stokes pulse amplifier.

Study on THz wave generation from air plasma induced by quasi-square Airy beam

NASA Astrophysics Data System (ADS)

Zhang, Shijing; Zhang, Liangliang; Jiang, Guangtong; Zhang, Cunlin; Zhao, Yuejin

2018-01-01

Terahertz (THz) wave has attracted considerable attention in recent years because of its potential applications. The intense THz waves generated from air plasma induced by two-color femtosecond laser are widely used due to its high generation efficiency and broad frequency bandwidth. The parameters of the laser change the distribution of the air plasma, and then affect the generation of THz wave. In this research, we investigate the THz wave generation from air plasma induced by quasi-square Airy beam. Unlike the common Gauss beam, the quasi-square Airy beam has ability to autofocus and to increase the maximum intensity at the focus. By using the spatial light modulator (SLM), we can change the parameters of phase map to control the shape of the Airy beam. We obtain the two-color laser field by a 100-um-thick BBO crystal, then use a Golay detector to record THz wave energy. By comparing terahertz generation at different modulation depths, we find that terahertz energy produced by quasi-square Airy beam is up to 3.1 times stronger than that of Gauss beam with identical laser energy. In order to understand the influence of quasi-square Airy beam on the BBO crystal, we record THz wave energy by changing the azimuthal angle of BBO crystal with Gauss beam and Airy beam at different modulation depths. We find that the trend of terahertz energy with respect to the azimuthal angle of the BBO crystal keeps the same for different laser beams. We believe that the quasi-square Airy beam or other auto focusing beam can significantly improve the efficiency of terahertz wave generation and pave the way for its applications.

Making structured metals transparent for ultrabroadband electromagnetic waves and acoustic waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Ren-Hao; Peng, Ru-Wen, E-mail: rwpeng@nju.edu.cn; Huang, Xian-Rong

2015-07-15

In this review, we present our recent work on making structured metals transparent for broadband electromagnetic waves and acoustic waves via excitation of surface waves. First, we theoretically show that one-dimensional metallic gratings can become transparent and completely antireflective for extremely broadband electromagnetic waves by relying on surface plasmons or spoof surface plasmons. Second, we experimentally demonstrate that metallic gratings with narrow slits are highly transparent for broadband terahertz waves at oblique incidence and high transmission efficiency is insensitive to the metal thickness. Further, we significantly develop oblique metal gratings transparent for broadband electromagnetic waves (including optical waves and terahertzmore » ones) under normal incidence. In the third, we find the principles of broadband transparency for structured metals can be extended from one-dimensional metallic gratings to two-dimensional cases. Moreover, similar phenomena are found in sonic artificially metallic structures, which present the transparency for broadband acoustic waves. These investigations provide guidelines to develop many novel materials and devices, such as transparent conducting panels, antireflective solar cells, and other broadband metamaterials and stealth technologies. - Highlights: • Making structured metals transparent for ultrabroadband electromagnetic waves. • Non-resonant excitation of surface plasmons or spoof surface plasmons. • Sonic artificially metallic structures transparent for broadband acoustic waves.« less

Surface plasmon induced direct detection of long wavelength photons.

PubMed

Tong, Jinchao; Zhou, Wei; Qu, Yue; Xu, Zhengji; Huang, Zhiming; Zhang, Dao Hua

2017-11-21

Millimeter and terahertz wave photodetectors have long been of great interest due to a wide range of applications, but they still face challenges in detection performance. Here, we propose a new strategy for the direct detection of millimeter and terahertz wave photons based on localized surface-plasmon-polariton (SPP)-induced non-equilibrium electrons in antenna-assisted subwavelength ohmic metal-semiconductor-metal (OMSM) structures. The subwavelength OMSM structure is used to convert the absorbed photons into localized SPPs, which then induce non-equilibrium electrons in the structure, while the antenna increases the number of photons coupled into the OMSM structure. When the structure is biased and illuminated, the unidirectional flow of the SPP-induced non-equilibrium electrons forms a photocurrent. The energy of the detected photons is determined by the structure rather than the band gap of the semiconductor. The detection scheme is confirmed by simulation and experimental results from the devices, made of gold and InSb, and a room temperature noise equivalent power (NEP) of 1.5 × 10 -13 W Hz -1/2 is achieved.

Polarization-dependent thin-film wire-grid reflectarray for terahertz waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niu, Tiaoming; School of Information Science and Engineering, Lanzhou University, Lanzhou 730000; Upadhyay, Aditi

2015-07-20

A thin-film polarization-dependent reflectarray based on patterned metallic wire grids is realized at 1 THz. Unlike conventional reflectarrays with resonant elements and a solid metal ground, parallel narrow metal strips with uniform spacing are employed in this design to construct both the radiation elements and the ground plane. For each radiation element, a certain number of thin strips with an identical length are grouped to effectively form a patch resonator with equivalent performance. The ground plane is made of continuous metallic strips, similar to conventional wire-grid polarizers. The structure can deflect incident waves with the polarization parallel to the stripsmore » into a designed direction and transmit the orthogonal polarization component. Measured radiation patterns show reasonable deflection efficiency and high polarization discrimination. Utilizing this flexible device approach, similar reflectarray designs can be realized for conformal mounting onto surfaces of cylindrical or spherical devices for terahertz imaging and communications.« less

Continuous-wave terahertz digital holography by use of a pyroelectric array camera.

PubMed

Ding, Sheng-Hui; Li, Qi; Li, Yun-Da; Wang, Qi

2011-06-01

Terahertz (THz) digital holography is realized based on a 2.52 THz far-IR gas laser and a commercial 124 × 124 pyroelectric array camera. Off-axis THz holograms are obtained by recording interference patterns between light passing through the sample and the reference wave. A numerical reconstruction process is performed to obtain the field distribution at the object surface. Different targets were imaged to test the system's imaging capability. Compared with THz focal plane images, the image quality of the reconstructed images are improved a lot. The results show that the system's imaging resolution can reach at least 0.4 mm. The system also has the potential for real-time imaging application. This study confirms that digital holography is a promising technique for real-time, high-resolution THz imaging, which has extensive application prospects. © 2011 Optical Society of America

Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shang-Hua; Jarrahi, Mona; Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095

2015-09-28

We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more thanmore » 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.« less

Frequency-dependent absorbance of broadband terahertz wave in dense plasma sheet

NASA Astrophysics Data System (ADS)

Peng, Yan; Qi, Binbin; Jiang, Xiankai; Zhu, Zhi; Zhao, Hongwei; Zhu, Yiming

2018-05-01

Due to the ability of accurate fingerprinting and low-ionization for different substances, terahertz (THz) technology has a lot of crucial applications in material analysis, information transfer, and safety inspection, etc. However, the spectral characteristic of atmospheric gas and ionized gas has not been widely investigated, which is important for the remote sensing application. Here, in this paper, we investigate the absorbance of broadband terahertz wave in dense plasma sheet generated by femtosecond laser pulses. It was found that as the terahertz wave transmits through the plasma sheet formed, respectively, in carbon dioxide, oxygen, argon and nitrogen, spectrum presents completely different and frequency-dependent absorbance. The reasons for these absorption peaks are related to the molecular polarity, electric charge, intermolecular and intramolecular interactions, and collisional absorption of gas molecules. These results have significant implications for the remote sensing of gas medium.

Quantitative analyses of tartaric acid based on terahertz time domain spectroscopy

NASA Astrophysics Data System (ADS)

Cao, Binghua; Fan, Mengbao

2010-10-01

Terahertz wave is the electromagnetic spectrum situated between microwave and infrared wave. Quantitative analysis based on terahertz spectroscopy is very important for the application of terahertz techniques. But how to realize it is still under study. L-tartaric acid is widely used as acidulant in beverage, and other food, such as soft drinks, wine, candy, bread and some colloidal sweetmeats. In this paper, terahertz time-domain spectroscopy is applied to quantify the tartaric acid. Two methods are employed to process the terahertz spectra of different samples with different content of tartaric acid. The first one is linear regression combining correlation analysis. The second is partial least square (PLS), in which the absorption spectra in the 0.8-1.4THz region are used to quantify the tartaric acid. To compare the performance of these two principles, the relative error of the two methods is analyzed. For this experiment, the first method does better than the second one. But the first method is suitable for the quantitative analysis of materials which has obvious terahertz absorption peaks, while for material which has no obvious terahertz absorption peaks, the second one is more appropriate.

Towards terahertz detection and calibration through spontaneous parametric down-conversion in the terahertz idler-frequency range generated by a 795 nm diode laser system

NASA Astrophysics Data System (ADS)

Kornienko, Vladimir V.; Kitaeva, Galiya Kh.; Sedlmeir, Florian; Leuchs, Gerd; Schwefel, Harald G. L.

2018-05-01

We study a calibration scheme for terahertz wave nonlinear-optical detectors based on spontaneous parametric down-conversion. Contrary to the usual low wavelength pump in the green, we report here on the observation of spontaneous parametric down-conversion originating from an in-growth poled lithium niobate crystal pumped with a continuous wave 50 mW, 795 nm diode laser system, phase-matched to a terahertz frequency idler wave. Such a system is more compact and allows for longer poling periods as well as lower losses in the crystal. Filtering the pump radiation by a rubidium-87 vapor cell allowed the frequency-angular spectra to be obtained down to ˜0.5 THz or ˜1 nm shift from the pump radiation line. The presence of an amplified spontaneous emission "pedestal" in the diode laser radiation spectrum significantly hampers the observation of spontaneous parametric down-conversion spectra, in contrast to conventional narrowband gas lasers. Benefits of switching to longer pump wavelengths are pointed out, such as collinear optical-terahertz phase-matching in bulk crystals.

Study of image reconstruction for terahertz indirect holography with quasi-optics receiver.

PubMed

Gao, Xiang; Li, Chao; Fang, Guangyou

2013-06-01

In this paper, an indirect holographic image reconstruction algorithm was studied for terahertz imaging with a quasi-optics receiver. Based on the combination of the reciprocity principle and modified quasi-optics theory, analytical expressions of the received spatial power distribution and its spectrum are obtained for the interference pattern of target wave and reference wave. These results clearly give the quantitative relationship between imaging quality and the parameters of a Gaussian beam, which provides a good criterion for terahertz quasi-optics transceivers design in terahertz off-axis holographic imagers. To validate the effectiveness of the proposed analysis method, some imaging results with a 0.3 THz prototype system are shown based on electromagnetic simulation.

Electromagnetic behavior of spatial terahertz wave modulators based on reconfigurable micromirror gratings in Littrow configuration.

PubMed

Kappa, Jan; Schmitt, Klemens M; Rahm, Marco

2017-08-21

Efficient, high speed spatial modulators with predictable performance are a key element in any coded aperture terahertz imaging system. For spectroscopy, the modulators must also provide a broad modulation frequency range. In this study, we numerically analyze the electromagnetic behavior of a dynamically reconfigurable spatial terahertz wave modulator based on a micromirror grating in Littrow configuration. We show that such a modulator can modulate terahertz radiation over a wide frequency range from 1.7 THz to beyond 3 THz at a modulation depth of more than 0.6. As a specific example, we numerically simulated coded aperture imaging of an object with binary transmissive properties and successfully reconstructed the image.

Metal wires for terahertz wave guiding.

PubMed

Wang, Kanglin; Mittleman, Daniel M

2004-11-18

Sources and systems for far-infrared or terahertz (1 THz = 10(12) Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal waveguides for microwave radiation, nor dielectric fibres for visible and near-infrared radiation can be used to guide terahertz waves over a long distance, owing to the high loss from the finite conductivity of metals or the high absorption coefficient of dielectric materials in this spectral range. Furthermore, the extensive use of broadband pulses in the terahertz regime imposes an additional constraint of low dispersion, which is necessary for compatibility with spectroscopic applications. Here we show how a simple waveguide, namely a bare metal wire, can be used to transport terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity. As an example of this new waveguiding structure, we demonstrate an endoscope for terahertz pulses.

Subwavelength hybrid terahertz waveguides.

PubMed

Nam, Sung Hyun; Taylor, Antoinette J; Efimov, Anatoly

2009-12-07

We introduce and present general properties of hybrid terahertz waveguides. Weakly confined Zenneck waves on a metal-dielectric interface at terahertz frequencies can be transformed to a strongly confined yet low-loss subwavelength mode through coupling with a photonic mode of a nearby high-index dielectric strip. We analyze confinement, attenuation, and dispersion properties of this mode. The proposed design is suitable for planar integration and allows easy fabrication on chip scale. The superior waveguiding properties at terahertz frequencies could enable the hybrid terahertz waveguides as building blocks for terahertz integrated circuits.

Terahertz generation by beating two Langmuir waves in a warm and collisional plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiao-Bo; Qiao, Xin; Cheng, Li-Hong

2015-09-15

Terahertz (THz) radiation generated by beating of two Langmuir waves in a warm and collisional plasma is discussed theoretically. The critical angle between the two Langmuir waves and the critical wave-length (wave vector) of Langmuir waves for generating THz radiation are obtained analytically. Furthermore, the maximum radiation energy is obtained. We find that the critical angle, the critical wave-length, and the generated radiation energy strongly depend on plasma temperature and wave-length of the Langmuir waves. That is, the THz radiation generated by beating of two Langmuir waves in a warm and collisional plasma can be controlled by adjusting the plasmamore » temperature and the Langmuir wave-length.« less

Terahertz artificial material based on integrated metal-rod-array for phase sensitive fluid detection.

PubMed

You, Borwen; Chen, Ching-Yu; Yu, Chin-Ping; Liu, Tze-An; Hattori, Toshiaki; Lu, Ja-Yu

2017-04-17

A terahertz artificial material composed of metal rod array is experimentally investigated on its transmission spectral property and successfully incorporated into microfluidics as a miniaturized terahertz waveguide with an extended optical-path-length for label-free fluidic sensing. Theoretical and experimental characterizations of terahertz transmission spectra show that the wave guidance along the metal rod array originates from the resonance of transverse-electric-polarized waves within the metal rod slits. The extended optical path length along three layers of metal-rod-array enables terahertz waves sufficiently overlapping the fluid molecules embedded among the rods, leading to strongly enhanced phase change by approximately one order of magnitude compared with the blank metal-parallel-plate waveguide. Based on the enhanced phase sensitivity, three kinds of colorless liquid analytes, namely, acetone, methanol, and ethanol, with different dipole moments are identified in situ using the metal-rod-array-based microfluidic sensor. The detection limit in molecular amounts of a liquid analyte is experimentally demonstrated to be less than 0.1 mmol, corresponding to 2.7 μmol/mm². The phase sensitive terahertz metal-rod-array-based sensor potentially has good adaptability in lab-chip technology for various practical applications, such as industrial toxic fluid detection and medical breath inspection.

Evanescent-Wave Filtering in Images Using Remote Terahertz Structured Illumination

NASA Astrophysics Data System (ADS)

Flammini, M.; Pontecorvo, E.; Giliberti, V.; Rizza, C.; Ciattoni, A.; Ortolani, M.; DelRe, E.

2017-11-01

Imaging with structured illumination allows for the retrieval of subwavelength features of an object by conversion of evanescent waves into propagating waves. In conditions in which the object plane and the structured-illumination plane do not coincide, this conversion process is subject to progressive filtering of the components with high spatial frequency when the distance between the two planes increases, until the diffraction-limited lateral resolution is restored when the distance exceeds the extension of evanescent waves. We study the progressive filtering of evanescent waves by developing a remote super-resolution terahertz imaging system operating at a wavelength λ =1.00 mm , based on a freestanding knife edge and a reflective confocal terahertz microscope. In the images recorded with increasing knife-edge-to-object-plane distance, we observe the transition from a super-resolution of λ /17 ≃60 μ m to the diffraction-limited lateral resolution of Δ x ≃λ expected for our confocal microscope. The extreme nonparaxial conditions are analyzed in detail, exploiting the fact that, in the terahertz frequency range, the knife edge can be positioned at a variable subwavelength distance from the object plane. Electromagnetic simulations of radiation scattering by the knife edge reproduce the experimental super-resolution achieved.

Millimetre wave and terahertz technology for the detection of concealed threats: a review

NASA Astrophysics Data System (ADS)

Kemp, Michael C.

2006-09-01

There has been intense interest in the use of millimetre wave and terahertz technology for the detection of concealed weapons, explosives and other threats. Electromagnetic waves at these frequencies are safe, penetrate barriers and have short enough wavelengths to allow discrimination between objects. In addition, many solids including explosives have characteristic spectroscopic signatures at terahertz wavelengths which can be used to identify them. This paper reviews the progress which has been made in recent years and identifies the achievements, challenges and prospects for these technologies in checkpoint people screening, stand off detection of improvised explosive devices (IEDs) and suicide bombers as well as more specialized screening tasks.

FDTD Simulation on Terahertz Waves Propagation Through a Dusty Plasma

NASA Astrophysics Data System (ADS)

Wang, Maoyan; Zhang, Meng; Li, Guiping; Jiang, Baojun; Zhang, Xiaochuan; Xu, Jun

2016-08-01

The frequency dependent permittivity for dusty plasmas is provided by introducing the charging response factor and charge relaxation rate of airborne particles. The field equations that describe the characteristics of Terahertz (THz) waves propagation in a dusty plasma sheath are derived and discretized on the basis of the auxiliary differential equation (ADE) in the finite difference time domain (FDTD) method. Compared with numerical solutions in reference, the accuracy for the ADE FDTD method is validated. The reflection property of the metal Aluminum interlayer of the sheath at THz frequencies is discussed. The effects of the thickness, effective collision frequency, airborne particle density, and charge relaxation rate of airborne particles on the electromagnetic properties of Terahertz waves through a dusty plasma slab are investigated. Finally, some potential applications for Terahertz waves in information and communication are analyzed. supported by National Natural Science Foundation of China (Nos. 41104097, 11504252, 61201007, 41304119), the Fundamental Research Funds for the Central Universities (Nos. ZYGX2015J039, ZYGX2015J041), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20120185120012)

Scattering properties of electromagnetic waves from metal object in the lower terahertz region

NASA Astrophysics Data System (ADS)

Chen, Gang; Dang, H. X.; Hu, T. Y.; Su, Xiang; Lv, R. C.; Li, Hao; Tan, X. M.; Cui, T. J.

2018-01-01

An efficient hybrid algorithm is proposed to analyze the electromagnetic scattering properties of metal objects in the lower terahertz (THz) frequency. The metal object can be viewed as perfectly electrical conducting object with a slightly rough surface in the lower THz region. Hence the THz scattered field from metal object can be divided into coherent and incoherent parts. The physical optics and truncated-wedge incremental-length diffraction coefficients methods are combined to compute the coherent part; while the small perturbation method is used for the incoherent part. With the MonteCarlo method, the radar cross section of the rough metal surface is computed by the multilevel fast multipole algorithm and the proposed hybrid algorithm, respectively. The numerical results show that the proposed algorithm has good accuracy to simulate the scattering properties rapidly in the lower THz region.

Terahertz radiation by subpicosecond spin-polarized photocurrent originating from Dirac electrons in a Rashba-type polar semiconductor

NASA Astrophysics Data System (ADS)

Kinoshita, Yuto; Kida, Noriaki; Miyamoto, Tatsuya; Kanou, Manabu; Sasagawa, Takao; Okamoto, Hiroshi

2018-04-01

The spin-splitting energy bands induced by the relativistic spin-orbit interaction in solids provide a new opportunity to manipulate the spin-polarized electrons on the subpicosecond timescale. Here, we report one such example in a bulk Rashba-type polar semiconductor BiTeBr. Strong terahertz electromagnetic waves are emitted after the resonant excitation of the interband transition between the Rashba-type spin-splitting energy bands with a femtosecond laser pulse circularly polarized. The phase of the emitted terahertz waves is reversed by switching the circular polarization. This suggests that the observed terahertz radiation originates from the subpicosecond spin-polarized photocurrents, which are generated by the asymmetric depopulation of the Dirac state. Our result provides a way for the current-induced terahertz radiation and its phase control by the circular polarization of incident light without external electric fields.

Superiority of terahertz over infrared transmission through bandages and burn wound ointments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suen, Jonathan Y., E-mail: j.suen@duke.edu; Padilla, Willie J.

Terahertz electromagnetic waves have long been proposed to be ideal for spectroscopy and imaging through non-polar dielectric materials that contain no water. Terahertz radiation may thus be useful for monitoring burn and wound injury recovery, as common care treatments involve application of both a clinical dressing and topical ointment. Here, we investigate the optical properties of typical care treatments in the millimeter wave (150–300 GHz), terahertz (0.3–3 THz), and infrared (14.5–0.67 μm) ranges of the electromagnetic spectrum. We find that THz radiation realizes low absorption coefficients and high levels of transmission compared to infrared wavelengths, which were strongly attenuated. Terahertz imaging canmore » enable safe, non-ionizing, noninvasive monitoring of the healing process directly through clinical dressings and recovery ointments, minimizing the frequency of dressing changes and thus increasing the rate of the healing process.« less

Terahertz solid immersion microscopy for sub-wavelength-resolution imaging of biological objects and tissues

NASA Astrophysics Data System (ADS)

Chernomyrdin, Nikita V.; Kucheryavenko, Anna S.; Malakhov, Kirill M.; Schadko, Alexander O.; Komandin, Gennady A.; Lebedev, Sergey P.; Dolganova, Irina N.; Kurlov, Vladimir N.; Lavrukhin, Denis V.; Ponomarev, Dmitry S.; Yurchenko, Stanislav O.; Tuchin, Valery V.; Zaytsev, Kirill I.

2018-04-01

We have developed a method of terahertz (THz) solid immersion microscopy for imaging of biological objects and tissues. It relies on the solid immersion lens (SIL) employing the THz beam focusing into the evanescent-field volume and allowing strong reduction in the dimensions of the THz beam caustic. By solving the problems of the sample handling at the focal plane and raster scanning of its surface with the focused THz beam, the THz SIL microscopy has been adapted for imaging of soft tissues. We have assembled an experimental setup based on a backward-wave oscillator, as a continuous-wave source operating at the wavelength of λ = 500 μm, and a Golay cell, as a detector of the THz wave intensity. By imaging of the razor blade, we have demonstrated advanced 0.2λ-resolution of the proposed THz SIL configuration. Using the experimental setup, we have performed THz imaging of a mint leaf revealing its sub-wavelength features. The observed results highlight a potential of the THz SIL microscopy in biomedical applications of THz science and technology.

[Development of Terahertz Imaging Technology in the Assessment of Burn Injuries].

PubMed

Zhu, Xinjian; He, Xuan; Wang, Pin; Gao, Dandan; Qiu, Yan; He, Qinghua; Wu, Baoming

2016-02-01

Terahertz waves have unique properties and advantages, which makes it gain increasing attention and applications in the biomedical field. Burns is a common clinical trauma. Since the water-sensitive and non-destructive characteristics of terahertz, terahertz imaging techniques can be used to detect burns. So far, terahertz imaging technology in the assessment of burn injuries has been developed from ex vivo to in vivo, and high-resolution images can be obtained through the gauzes and plasters. In this paper, we mainly introduces the application of terahertz imaging technology and development in the assessment of burn injuries.

High energy, widely tunable Si-prism-array coupled terahertz-wave parametric oscillator with a deformed pump and optimal crystal location for angle tuning.

PubMed

Zhang, Ruiliang; Qu, Yanchen; Zhao, Weijiang; Chen, Zhenlei

2017-03-20

A high energy, widely tunable Si-prism-array coupled terahertz-wave parametric oscillator (TPO) has been demonstrated by using a deformed pump. The deformed pump is cut from a beam spot of 2 mm in diameter by a 1-mm-wide slit. In comparison with a small pump spot (1-mm diameter), the THz-wave coupling area for the deformed pump is increased without limitation to the low-frequency end of the tuning range. Besides, the crystal location is specially designed to eliminate the alteration of the output position of the pump during angle tuning, so the initially adjusted nearest pumped region to the THz-wave exit surface is maintained throughout the tuning range. The tuning range is 0.58-2.5 THz for the deformed pump, while its low frequency end is limited at approximately 1.2 THz for the undeformed pump with 2 mm diameter. The highest THz-wave output of 2 μJ, which is 2.25 times as large as that from the pump of 1 mm in diameter, is obtained at 1.15 THz under 38 mJ (300  MW/cm²) pumping. The energy conversion efficiency is 5.3×10^-5.

Smooth bridge between guided waves and spoof surface plasmon polaritons.

PubMed

Liu, Liangliang; Li, Zhuo; Gu, Changqing; Xu, Bingzheng; Ning, Pingping; Chen, Chen; Yan, Jian; Niu, Zhenyi; Zhao, Yongjiu

2015-04-15

In this work, we build a smooth bridge between a coaxial waveguide and a plasmonic waveguide with subwavelength periodically cylindrical radial grooves, to realize high-efficiency mode conversion between conventional guided waves and spoof surface plasmon polaritons in broadband. This bridge consists of a flaring coaxial waveguide connected with a metal cylindrical wire corrugated with subwavelength gradient radial grooves. Experimental results of the transmission and reflection coefficients show excellent agreement with the numerical simulations. The proposed scheme can be extended readily to other bands and the bridge structure can find potential applications in the integration of conventional microwave or terahertz devices with plasmonic circuits.

Experimental Realization of an Epsilon-Near-Zero Graded-Index Metalens at Terahertz Frequencies

NASA Astrophysics Data System (ADS)

Pacheco-Peña, Victor; Engheta, Nader; Kuznetsov, Sergei; Gentselev, Alexandr; Beruete, Miguel

2017-09-01

The terahertz band has been historically hindered by the lack of efficient generators and detectors, but a series of recent breakthroughs have helped to effectively close the "terahertz gap." A rapid development of terahertz technology has been possible thanks to the translation of revolutionary concepts from other regions of the electromagnetic spectrum. Among them, metamaterials stand out for their unprecedented ability to control wave propagation and manipulate electromagnetic response of matter. They have become a workhorse in the development of terahertz devices such as lenses, polarizers, etc., with fascinating features. In particular, epsilon-near-zero (ENZ) metamaterials have attracted much attention in the past several years due to their unusual properties such as squeezing, tunneling, and supercoupling where a wave traveling inside an electrically small channel filled with an ENZ medium can be tunneled through it, reducing reflections and coupling most of its energy. Here, we design and experimentally demonstrate an ENZ graded-index (GRIN) metamaterial lens operating at terahertz with a power enhancement of 16.2 dB, using an array of narrow hollow rectangular waveguides working near their cutoff frequencies. This is a demonstration of an ENZ GRIN device at terahertz and can open the path towards other realizations of similar devices enabling full quasioptical processing of terahertz signals.

Novel devices and systems for terahertz spectroscopy and imaging

NASA Astrophysics Data System (ADS)

Wang, Kanglin

This doctoral thesis documents my research on novel devices and systems for terahertz (THz) spectroscopy and imaging. The research is particularly focused on the manipulation of THz radiation, including subwavelength concentration and low-loss wave guiding. One of the major obstacles for THz imaging is the poor spatial resolution due to the diffraction of the long-wavelength light source. To break this restriction, we build a THz near-field microscopy system by combining apertureless near-field scanning optical microscopy (ANSOM) with terahertz time-domain spectroscopy (THz-TDS). The experimental result indicates a sub-wavelength spatial resolution of about 10 micron. Abnormal frequency response of the ANSOM probe tip is observed, and a dipole antenna model is developed to explain the bandwidth reduction of the detected THz pulses. We also observe and characterize the THz wave propagation on the near-field probe in ANSOM. These studies not only demonstrate the feasibility of ANSOM in the THz frequency range, but also provide fundamental insights into the near-field microscopy in general, such as the broadband compatibility, the propagation effects and the antenna effects. Motivated by our study of the propagation effects in THz ANSOM, we characterize the guided mode of THz pulses on a bare metal wire by directly measuring the spatial profile of electric field of the mode, and find that the wire structure can be used to guide THz waves with outstanding performance. This new broadband THz waveguide exhibits very small dispersion, extremely low attenuation and remarkable structural simplicity. These features make it especially suitable for use in THz sensing and imaging systems. The first THz endoscope is demonstrated based on metal wire waveguides. To improve the input coupling efficiency of such waveguides, we develop a photoconductive antenna with radial symmetry which can generate radially polarized THz radiation matching the waveguide mode. Through THz-TDS measurements and theoretical calculations, we study the dispersion relation of the surface waves on metal wires, which indicates the increasing importance of skin effects for surface waves in the THz frequency range.

[The Lambert-Beer's law characterization of formal analysis in Terahertz spectrum quantitative testing].

PubMed

Su, Hai-Xia; Zhang, Zhao-Hui; Zhao, Xiao-Yan; Li, Zhi; Yan, Fang; Zhang, Han

2013-12-01

The present paper discusses the Lambert-Beer' s law application in the terahertz spectrum, studies the single amino acid tablet sample (glutamine) and two kinds of amino acids mixture tablet (threonine and cystine) under the condition of different concentrations. Absorbance and absorption coefficient was analyzed in the description of the terahertz optical properties of matter. By comparing absorption coefficient and absorbance value of the single component in the vicinity of 1. 72 THz, we verified the material under two kinds of absorption characterization of quantity of THz wave absorption along with the change in the concentration. Using the index of goodness of fit R , it studied the stand or fall of linear relationship between the terahertz absorption quantity of material and concentration under two kinds of representation. This paper analyzes the two components mixture under two kinds of absorption characterization of quantity of terahertz absorption in 0. 3-2. 6 THz. Using the similarity co- efficient and the estimate concentration error as evaluation index, it has been clear that the absorbance of additivity instead of the absorption coefficient should be used during the terahertz spectrum quantitative test, and the Lambert-Beer's law application in the terahertz wave band was further clarified.

Terahertz imaging system based on a backward-wave oscillator.

PubMed

Dobroiu, Adrian; Yamashita, Masatsugu; Ohshima, Yuichi N; Morita, Yasuyuki; Otani, Chiko; Kawase, Kodo

2004-10-20

We present an imaging system designed for use in the terahertz range. As the radiation source a backward-wave oscillator was chosen for its special features such as high output power, good wave-front quality, good stability, and wavelength tunability from 520 to 710 GHz. Detection is achieved with a pyroelectric sensor operated at room temperature. The alignment procedure for the optical elements is described, and several methods to reduce the etalon effect that are inherent in monochromatic sources are discussed. The terahertz spot size in the sample plane is 550 microm (nearly the diffraction limit), and the signal-to-noise ratio is 10,000:1; other characteristics were also measured and are presented in detail. A number of preliminary applications are also shown that cover various areas: nondestructive real-time testing for plastic tubes and packaging seals; biological terahertz imaging of fresh, frozen, or freeze-dried samples; paraffin-embedded specimens of cancer tissue; and measurement of the absorption coefficient of water by use of a wedge-shaped cell.

Freely-tunable broadband polarization rotator for terahertz waves

NASA Astrophysics Data System (ADS)

Peng, Ru-Wen; Fan, Ren-Hao; Zhou, Yu; Jiang, Shang-Chi; Xiong, Xiang; Huang, Xian-Rong; Wang, Mu

It is known that commercially-available terahertz (THz) emitters usually generate linearly polarized waves only along certain directions, but in practice, a polarization rotator that is capable of rotating the polarization of THz waves to any direction is particularly desirable and it will have various important applications. In this work, we demonstrate a freely tunable polarization rotator for broadband THz waves using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized THz wave to any desired direction with nearly perfect conversion efficiency. The device performance has been experimentally demonstrated by both THz transmission spectra and direct imaging. The polarization rotation originates from multi wave interference in the three-layer grating structure based on the scattering-matrix analysis. We can expect that this active broadband polarization rotator has wide applications in analytical chemistry, biology, communication technology, imaging, etc.. Reference: R. H. Fan, Y. Zhou, X. P. Ren, R. W. Peng, S. C. Jiang, D. H. Xu, X. Xiong, X. R. Huang, and Mu Wang, Advanced Materials 27,1201(2015). Freely-tunable broadband polarization rotator for terahertz waves.

Integrated Arrays on Silicon at Terahertz Frequencies

NASA Technical Reports Server (NTRS)

Chattopadhayay, Goutam; Lee, Choonsup; Jung, Cecil; Lin, Robert; Peralta, Alessandro; Mehdi, Imran; Llombert, Nuria; Thomas, Bertrand

2011-01-01

In this paper we explore various receiver font-end and antenna architecture for use in integrated arrays at terahertz frequencies. Development of wafer-level integrated terahertz receiver front-end by using advanced semiconductor fabrication technologies and use of novel integrated antennas with silicon micromachining are reported. We report novel stacking of micromachined silicon wafers which allows for the 3-dimensional integration of various terahertz receiver components in extremely small packages which easily leads to the development of 2- dimensioanl multi-pixel receiver front-ends in the terahertz frequency range. We also report an integrated micro-lens antenna that goes with the silicon micro-machined front-end. The micro-lens antenna is fed by a waveguide that excites a silicon lens antenna through a leaky-wave or electromagnetic band gap (EBG) resonant cavity. We utilized advanced semiconductor nanofabrication techniques to design, fabricate, and demonstrate a super-compact, low-mass submillimeter-wave heterodyne frontend. When the micro-lens antenna is integrated with the receiver front-end we will be able to assemble integrated heterodyne array receivers for various applications such as multi-pixel high resolution spectrometer and imaging radar at terahertz frequencies.

Remote and in situ sensing products in chemical reaction using a flexible terahertz pipe waveguide.

PubMed

You, Borwen; Lu, Ja-Yu

2016-08-08

The feasibility of remote chemical detection is experimentally demonstrated by using a Teflon pipe as a scanning arm in a continuous-terahertz wave sensing and imaging system. Different tablets with distinct mixed ratios of aluminum and polyethylene powders are well distinguished by measuring the power reflectivities of 0.4 THz wave associated with their distinct terahertz refractive indices. Given its refractive index sensitivity and fast response, the reflective terahertz sensing system can be used to real-time trace and quantitatively analyze the ammonium-chloride aerosols produced by the chemical reaction between hydrochloric acid and ammonia vapors. With a tightly focusing terahertz beam spot, the spatial and concentration distributions of the generated chemical product are successfully mapped out by the 1D scan of the flexible pipe probe. In consideration of the responsitivity, power stability, and focused spot size of the system, its detection limit for the ammonium-chloride aerosol is estimated to be approximately 165 nmol/mm². The reliable and compact terahertz pipe scan system is potentially suitable for practical applications, such as biomedical or industrial fiber endoscopy.

Highly Sensitive and Wide-Band Tunable Terahertz Response of Plasma Waves Based on Graphene Field Effect Transistors

PubMed Central

Wang, Lin; Chen, Xiaoshuang; Yu, Anqi; Zhang, Yang; Ding, Jiayi; Lu, Wei

2014-01-01

Terahertz (THz) technology is becoming a spotlight of scientific interest due to its promising myriad applications including imaging, spectroscopy, industry control and communication. However, one of the major bottlenecks for advancing this field is due to lack of well-developed solid-state sources and detectors operating at THz gap which serves to mark the boundary between electronics and photonics. Here, we demonstrate exceptionally wide tunable terahertz plasma-wave excitation can be realized in the channel of micrometer-level graphene field effect transistors (FET). Owing to the intrinsic high propagation velocity of plasma waves (>~108 cm/s) and Dirac band structure, the plasma-wave graphene-FETs yield promising prospects for fast sensing, THz detection, etc. The results indicate that the multiple guide-wave resonances in the graphene sheets can lead to the deep sub-wavelength confinement of terahertz wave and with Q-factor orders of magnitude higher than that of conventional 2DEG system at room temperature. Rooted in this understanding, the performance trade-off among signal attenuation, broadband operation, on-chip integrability can be avoided in future THz smart photonic network system by merging photonics and electronics. The unique properties presented can open up the exciting routes to compact solid state tunable THz detectors, filters, and wide band subwavelength imaging based on the graphene-FETs. PMID:24969065

High-resolution broadband terahertz spectroscopy via electronic heterodyne detection of photonically generated terahertz frequency comb.

PubMed

Pavelyev, D G; Skryl, A S; Bakunov, M I

2014-10-01

We report an alternative approach to the terahertz frequency-comb spectroscopy (TFCS) based on nonlinear mixing of a photonically generated terahertz pulse train with a continuous wave signal from an electronic synthesizer. A superlattice is used as a nonlinear mixer. Unlike the standard TFCS technique, this approach does not require a complex double-laser system but retains the advantages of TFCS-high spectral resolution and wide bandwidth.

Applying terahertz technology for nondestructive detection of crack initiation in a film-coated layer on a swelling tablet

PubMed Central

Momose, Wataru; Yoshino, Hiroyuki; Katakawa, Yoshifumi; Yamashita, Kazunari; Imai, Keiji; Sako, Kazuhiro; Kato, Eiji; Irisawa, Akiyoshi; Yonemochi, Etsuo; Terada, Katsuhide

2012-01-01

Here, we describe a nondestructive approach using terahertz wave to detect crack initiation in a film-coated layer on a drug tablet. During scale-up and scale-down of the film coating process, differences in film density and gaps between the film-coated layer and the uncoated tablet were generated due to differences in film coating process parameters, such as the tablet-filling rate in the coating machine, spray pressure, and gas–liquid ratio etc. Tablets using the PEO/PEG formulation were employed as uncoated tablets. We found that heat and humidity caused tablets to swell, thereby breaking the film-coated layer. Using our novel approach with terahertz wave nondestructively detect film surface density (FSD) and interface density differences (IDDs) between the film-coated layer and an uncoated tablet. We also found that a reduced FSD and IDD between the film-coated layer and uncoated tablet increased the risk of crack initiation in the film-coated layer, thereby enabling us to nondestructively predict initiation of cracks in the film-coated layer. Using this method, crack initiation can be nondestructively assessed in swelling tablets after the film coating process without conducting accelerated stability tests, and film coating process parameters during scale-up and scale-down studies can be appropriately established. PMID:25755992

Wireless Data Transmission at Terahertz Carrier Waves Generated from a Hybrid InP-Polymer Dual Tunable DBR Laser Photonic Integrated Circuit.

PubMed

Carpintero, Guillermo; Hisatake, Shintaro; de Felipe, David; Guzman, Robinson; Nagatsuma, Tadao; Keil, Norbert

2018-02-14

We report for the first time the successful wavelength stabilization of two hybrid integrated InP/Polymer DBR lasers through optical injection. The two InP/Polymer DBR lasers are integrated into a photonic integrated circuit, providing an ideal source for millimeter and Terahertz wave generation by optical heterodyne technique. These lasers offer the widest tuning range of the carrier wave demonstrated to date up into the Terahertz range, about 20 nm (2.5 THz) on a single photonic integrated circuit. We demonstrate the application of this source to generate a carrier wave at 330 GHz to establish a wireless data transmission link at a data rate up to 18 Gbit/s. Using a coherent detection scheme we increase the sensitivity by more than 10 dB over direct detection.

High-resolution reconstruction for terahertz imaging.

PubMed

Xu, Li-Min; Fan, Wen-Hui; Liu, Jia

2014-11-20

We present a high-resolution (HR) reconstruction model and algorithms for terahertz imaging, taking advantage of super-resolution methodology and algorithms. The algorithms used include projection onto a convex sets approach, iterative backprojection approach, Lucy-Richardson iteration, and 2D wavelet decomposition reconstruction. Using the first two HR reconstruction methods, we successfully obtain HR terahertz images with improved definition and lower noise from four low-resolution (LR) 22×24 terahertz images taken from our homemade THz-TDS system at the same experimental conditions with 1.0 mm pixel. Using the last two HR reconstruction methods, we transform one relatively LR terahertz image to a HR terahertz image with decreased noise. This indicates potential application of HR reconstruction methods in terahertz imaging with pulsed and continuous wave terahertz sources.

Manipulating terahertz wave by a magnetically tunable liquid crystal phase grating.

PubMed

Lin, Chia-Jen; Li, Yu-Tai; Hsieh, Cho-Fan; Pan, Ru-Pin; Pan, Ci-Ling

2008-03-03

This investigation demonstrates the feasibility of a magnetically tunable liquid crystal phase grating for the terahertz wave. The phase grating can be used as a beam splitter. The ratio of the zeroth and first-order diffracted THz-beams (0.3 THz) polarized in a direction perpendicular to that of the grooves of the grating can be tuned from 4:1 to 1:2. When the THz wave is polarized in any other direction, this device can be operated as a polarizing beam splitter.

FDTD-based computed terahertz wave propagation in multilayer medium structures

NASA Astrophysics Data System (ADS)

Tu, Wan-li; Zhong, Shun-cong; Yao, Hai-zi; Shen, Yao-chun

2013-08-01

The terahertz region of the electromagnetic spectrum spans the frequency range of 0.1THz~10THz, which means it sandwiches between the mid-infrared (IR) and the millimeter/ microwave. With the development and commercialization of terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) systems, terahertz technologies have been widely used in the sensing and imaging fields. It allows high quality cross-sectional images from within scattering media to be obtained nondestructively. Characterizing the interaction of terahertz radiation with multilayer medium structures is critical for the development of nondestructive testing technology. Currently, there was much experimental investigation of using TPI for the characterization of terahertz radiation in materials (e.g., pharmaceutical tablet coatings), but there were few theoretical researches on propagation of terahertz radiation in multilayer medium structures. Finite Difference Time Domain (FDTD) algorithm is a proven method for electromagnetic scattering theory, which analyzes continuous electromagnetic problems by employing finite difference and obtains electromagnetic field value at the sampling point to approach the actual continuous solutions. In the present work, we investigated the propagation of terahertz radiation in multilayer medium structures based on FDTD method. The model of multilayer medium structures under the THz frequency plane wave incidence was established, and the reflected radiation properties were recorded and analyzed. The terahertz radiation used was broad-band in the frequency up to 2 THz. A batch of single layer coated pharmaceutical tablets, whose coating thickness in the range of 40~100μm, was computed by FDTD method. We found that the simulation results on pharmaceutical tablet coatings were in good agreement with the experimental results obtained using a commercial system (TPI imaga 2000, TeraView, Cambridge, UK) , demonstrating its usefulness in simulating and analyzing terahertz responses from a multilayered sample.

Optically controlled dielectric properties of single-walled carbon nanotubes for terahertz wave applications.

PubMed

Smirnov, Serguei; Anoshkin, Ilya V; Demchenko, Petr; Gomon, Daniel; Lioubtchenko, Dmitri V; Khodzitsky, Mikhail; Oberhammer, Joachim

2018-06-21

Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.

Numerical analysis of THz radiation wave using upper hybrid wave wiggler

NASA Astrophysics Data System (ADS)

Malik, Pratibha; Sharma, Suresh C.; Panwar, Jyotsna; Sharma, Rinku

2018-03-01

A theory for upper hybrid wave induced by relativistic electron beam in magnetized plasma emits tuneable and coherent terahertz radiation. The nonlinear interaction with REB is used to generate terahertz radiation. The enhancement in the amplitude of THz wave is also observed when pre-bunched REB is used. The ponderomotive force applied on beam electrons due to radiation wave and upper wave wiggler modifies the dispersion relation. By solving the dispersion relation, we have derived the growth rate of the radiation wave. Numerical studies indicate that by increasing the beam energy the growth rate of the radiation wave decreases, while it increases with wiggler frequency. Besides this, the growth rate of the radiation wave increases with beam density and decreases with radiation frequency and static magnetic field.

Handheld THz security imaging

NASA Astrophysics Data System (ADS)

Duling, Irl N.

2016-05-01

Terahertz energy, with its ability to penetrate clothing and non-conductive materials, has held much promise in the area of security scanning. Millimeter wave systems (300 GHz and below) have been widely deployed. These systems have used full two-dimensional surface imaging, and have resulted in privacy concerns. Pulsed terahertz imaging, can detect the presence of unwanted objects without the need for two-dimensional photographic imaging. With high-speed waveform acquisition it is possible to create handheld tools that can be used to locate anomalies under clothing or headgear looking exclusively at either single point waveforms or cross-sectional images which do not pose a privacy concern. Identification of the anomaly to classify it as a potential threat or a benign object is also possible.

THz-wave parametric source and its imaging applications

NASA Astrophysics Data System (ADS)

Kawase, Kodo

2004-08-01

Widely tunable coherent terahertz (THz) wave generation has been demonstrated based on the parametric oscillation using MgO doped LiNbO3 crystal pumped by a Q-switched Nd:YAG laser. This method exhibits multiple advantages like wide tunability, coherency and compactness of its system. We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

Plasma physics and related challenges of millimeter-wave-to-terahertz and high power microwave generationa)

NASA Astrophysics Data System (ADS)

Booske, John H.

2008-05-01

Homeland security and military defense technology considerations have stimulated intense interest in mobile, high power sources of millimeter-wave (mmw) to terahertz (THz) regime electromagnetic radiation, from 0.1 to 10THz. While vacuum electronic sources are a natural choice for high power, the challenges have yet to be completely met for applications including noninvasive sensing of concealed weapons and dangerous agents, high-data-rate communications, high resolution radar, next generation acceleration drivers, and analysis of fluids and condensed matter. The compact size requirements for many of these high frequency sources require miniscule, microfabricated slow wave circuits. This necessitates electron beams with tiny transverse dimensions and potentially very high current densities for adequate gain. Thus, an emerging family of microfabricated, vacuum electronic devices share many of the same plasma physics challenges that are currently confronting "classic" high power microwave (HPM) generators including long-life bright electron beam sources, intense beam transport, parasitic mode excitation, energetic electron interaction with surfaces, and rf air breakdown at output windows. The contemporary plasma physics and other related issues of compact, high power mmw-to-THz sources are compared and contrasted to those of HPM generation, and future research challenges and opportunities are discussed.

Plasmon enhanced terahertz emission from single layer graphene.

PubMed

Bahk, Young-Mi; Ramakrishnan, Gopakumar; Choi, Jongho; Song, Hyelynn; Choi, Geunchang; Kim, Yong Hyup; Ahn, Kwang Jun; Kim, Dai-Sik; Planken, Paul C M

2014-09-23

We show that surface plasmons, excited with femtosecond laser pulses on continuous or discontinuous gold substrates, strongly enhance the generation and emission of ultrashort, broadband terahertz pulses from single layer graphene. Without surface plasmon excitation, for graphene on glass, 'nonresonant laser-pulse-induced photon drag currents' appear to be responsible for the relatively weak emission of both s- and p-polarized terahertz pulses. For graphene on a discontinuous layer of gold, only the emission of the p-polarized terahertz electric field is enhanced, whereas the s-polarized component remains largely unaffected, suggesting the presence of an additional terahertz generation mechanism. We argue that in the latter case, 'surface-plasmon-enhanced optical rectification', made possible by the lack of inversion symmetry at the graphene on gold surface, is responsible for the strongly enhanced emission. The enhancement occurs because the electric field of surface plasmons is localized and enhanced where the graphene is located: at the surface of the metal. We believe that our results point the way to small, thin, and more efficient terahertz photonic devices.

Terahertz wave electro-optic measurements with optical spectral filtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilyakov, I. E., E-mail: igor-ilyakov@mail.ru; Shishkin, B. V.; Kitaeva, G. Kh.

We propose electro-optic detection techniques based on variations of the laser pulse spectrum induced during pulse co-propagation with terahertz wave radiation in a nonlinear crystal. Quantitative comparison with two other detection methods is made. Substantial improvement of the sensitivity compared to the standard electro-optic detection technique (at high frequencies) and to the previously shown technique based on laser pulse energy changes is demonstrated in experiment.

Continuous wave terahertz radiation from an InAs/GaAs quantum-dot photomixer device

NASA Astrophysics Data System (ADS)

Kruczek, T.; Leyman, R.; Carnegie, D.; Bazieva, N.; Erbert, G.; Schulz, S.; Reardon, C.; Reynolds, S.; Rafailov, E. U.

2012-08-01

Generation of continuous wave radiation at terahertz (THz) frequencies from a heterodyne source based on quantum-dot (QD) semiconductor materials is reported. The source comprises an active region characterised by multiple alternating photoconductive and QD carrier trapping layers and is pumped by two infrared optical signals with slightly offset wavelengths, allowing photoconductive device switching at the signals' difference frequency ˜1 THz.

Metasurface for multi-channel terahertz beam splitters and polarization rotators

NASA Astrophysics Data System (ADS)

Zang, XiaoFei; Gong, HanHong; Li, Zhen; Xie, JingYa; Cheng, QingQing; Chen, Lin; Shkurinov, Alexander P.; Zhu, YiMing; Zhuang, SongLin

2018-04-01

Terahertz beam splitters and polarization rotators are two typical devices with wide applications ranging from terahertz communication to system integration. However, they are faced with severe challenges in manipulating THz waves in multiple channels, which is desirable for system integration and device miniaturization. Here, we propose a method to design ultra-thin multi-channel THz beam splitters and polarization rotators simultaneously. The reflected beams are divided into four beams with nearly the same density under illumination of linear-polarized THz waves, while the polarization of reflected beams in each channel is modulated with a rotation angle or invariable with respect to the incident THz waves, leading to the multi-channel polarization rotator (multiple polarization rotation in the reflective channels) and beam splitter, respectively. Reflective metasurfaces, created by patterning metal-rods with different orientations on a polyimide film, were fabricated and measured to demonstrate these characteristics. The proposed approach provides an efficient way of controlling polarization of THz waves in various channels, which significantly simplifies THz functional devices and the experimental system.

An ultrathin terahertz quarter-wave plate using planar babinet-inverted metasurface.

PubMed

Wang, Dacheng; Gu, Yinghong; Gong, Yandong; Qiu, Cheng-Wei; Hong, Minghui

2015-05-04

Metamaterials promise an exotic approach to artificially manipulate the polarization state of electromagnetic waves and boost the design of polarimetric devices for sensitive detection, imaging and wireless communication. Here, we present the design and experimental demonstration of an ultrathin (0.29λ) terahertz quarter-wave plate based on planar babinet-inverted metasurface. The quarter-wave plate consisting of arrays of asymmetric cross apertures reveals a high transmission of 0.545 with 90 degrees phase delay at 0.870 THz. The calculated ellipticity indicates a high degree of polarization conversion from linear to circular polarization. With respect to different incident polarization angles, left-handed circular polarized light, right-handed circular polarized light and elliptically polarized light can be created by this novel design. An analytical model is applied to describe transmitted amplitude, phase delay and ellipticitiy, which are in good agreement with the measured and simulated results. The planar babinet-inverted metasurface with the analytical model opens up avenues for new functional terahertz devices design.

Ultrafast terahertz control of extreme tunnel currents through single atoms on a silicon surface

NASA Astrophysics Data System (ADS)

Jelic, Vedran; Iwaszczuk, Krzysztof; Nguyen, Peter H.; Rathje, Christopher; Hornig, Graham J.; Sharum, Haille M.; Hoffman, James R.; Freeman, Mark R.; Hegmann, Frank A.

2017-06-01

Ultrafast control of current on the atomic scale is essential for future innovations in nanoelectronics. Extremely localized transient electric fields on the nanoscale can be achieved by coupling picosecond duration terahertz pulses to metallic nanostructures. Here, we demonstrate terahertz scanning tunnelling microscopy (THz-STM) in ultrahigh vacuum as a new platform for exploring ultrafast non-equilibrium tunnelling dynamics with atomic precision. Extreme terahertz-pulse-driven tunnel currents up to 107 times larger than steady-state currents in conventional STM are used to image individual atoms on a silicon surface with 0.3 nm spatial resolution. At terahertz frequencies, the metallic-like Si(111)-(7 × 7) surface is unable to screen the electric field from the bulk, resulting in a terahertz tunnel conductance that is fundamentally different than that of the steady state. Ultrafast terahertz-induced band bending and non-equilibrium charging of surface states opens new conduction pathways to the bulk, enabling extreme transient tunnel currents to flow between the tip and sample.

Ion acoustic wave assisted laser beat wave terahertz generation in a plasma channel

NASA Astrophysics Data System (ADS)

Tyagi, Yachna; Tripathi, Deepak; Walia, Keshav; Garg, Deepak

2018-04-01

Resonant excitation of terahertz (THz) radiation by non-linear mixing of two lasers in the presence of an electrostatic wave is investigated. The electrostatic wave assists in k matching and contributes to non-linear coupling. In this plasma channel, the electron plasma frequency becomes minimum on the axis. The beat frequency ponderomotive force imparts an oscillating velocity to the electrons. In the presence of an ion-acoustic wave, density perturbation due to the ion-acoustic wave couples with the oscillating velocity of the electrons and give rise to non-linear current that gives rise to an ion-acoustic wave frequency assisted THz radiation field. The normalized field amplitude of ion acoustic wave assisted THz varies inversely for ω/ωp . The field amplitude of ion acoustic wave assisted THz decreases as ω/ωp increases.

Electrically Tunable Reflective Terahertz Phase Shifter Based on Liquid Crystal

NASA Astrophysics Data System (ADS)

Yang, Jun; Xia, Tianyu; Jing, Shuaicheng; Deng, Guangsheng; Lu, Hongbo; Fang, Yong; Yin, Zhiping

2018-02-01

We present a reflective spatial phase shifter which operates at terahertz regime above 325 GHz. The controllable permittivity of the nematic liquid crystals was utilized to realize a tunable terahertz (THz) reflective phase shifter. The reflective characteristics of the terahertz electromagnetic waves and the liquid crystal parameters were calculated and analyzed. We provide the simulation results for the effect of the incident angle of the plane wave on the reflection. The experiment was carried out considering an array consisting of 30 × 30 patch elements, printed on a 20 × 20 mm quartz substrate with 1-mm thickness. The phase shifter provides a tunable phase range of 300° over the frequency range of 325 to 337.6 GHz. The maximum phase shift of 331° is achieved at 330 GHz. The proposed phase shifter is a potential candidate for THz applications, particularly for reconfigurable reflectarrays.

Dispersion of surface plasmon polaritons on metal wires in the terahertz frequency range.

PubMed

Wang, Kanglin; Mittleman, Daniel M

2006-04-21

We report the experimental and theoretical study of the dispersive behavior of surface plasmon polaritons (SPPs) on cylindrical metal surfaces in the terahertz frequency range. Time-domain measurements of terahertz SPPs propagating on metal wires reveal a unique structure that is inconsistent with a simple extrapolation of the high frequency portion of the dispersion diagram for SPPs on a planar metal surface, and also distinct from that of SPPs on metal nanowires observed at visible and near-infrared frequencies. The results are consistent with a numerical solution of Maxwell's equations, showing that the dispersive behavior of SPPs on a cylindrical metal surface at terahertz frequencies is quite different from that of SPPs on a flat surface. These findings indicate the increasing importance of skin effects for SPPs in the terahertz range, as well as the enhancement of such effects on curved surfaces.

Graphene-based terahertz metasurface with tunable spectrum splitting.

PubMed

Su, Zhaoxian; Chen, Xuan; Yin, Jianbo; Zhao, Xiaopeng

2016-08-15

We design a tunable terahertz metasurface, which consists of two different trapezoid graphene ribbons patterned in opposite directions on a gold film, separated by a thin dielectric spacer. The two kinds of graphene ribbons can cover a nearly 2π phase shift with high reflection efficiency in different spectral regions so that the metasurface can reflect different frequency waves to totally different directions. By changing the Fermi level of the graphene ribbons, the response frequency of the proposed metasurface can be adjusted, and as a result, tunable spectrum splitting can be realized. The present metasurface provides a powerful way to control terahertz waves and has potential applications in wide-angle beam splitters.

Frequency-agile terahertz-wave parametric oscillator in a ring-cavity configuration.

PubMed

Minamide, Hiroaki; Ikari, Tomofumi; Ito, Hiromasa

2009-12-01

We demonstrate a frequency-agile terahertz wave parametric oscillator (TPO) in a ring-cavity configuration (ring-TPO). The TPO consists of three mirrors and a MgO:LiNbO(3) crystal under noncollinear phase-matching conditions. A novel, fast frequency-tuning method was realized by controlling a mirror of the three-mirror ring cavity. The wide tuning range between 0.93 and 2.7 THz was accomplished. For first demonstration using the ring-TPO, terahertz spectroscopy was performed as the verification of the frequency-agile performance, measuring the transmission spectrum of the monosaccharide glucose. The spectrum was obtained within about 8 s in good comparison to those of Fourier transform infrared spectrometer.

Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition

NASA Astrophysics Data System (ADS)

Urade, Yoshiro; Nakata, Yosuke; Okimura, Kunio; Nakanishi, Toshihiro; Miyamaru, Fumiaki; Takeda, Mitsuo W.; Kitano, Masao

2016-03-01

This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide ($\\mathrm{VO}_2$), the proposed metamaterial is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition.

PubMed

Urade, Yoshiro; Nakata, Yosuke; Okimura, Kunio; Nakanishi, Toshihiro; Miyamaru, Fumiaki; Takeda, Mitsuo W; Kitano, Masao

2016-03-07

This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide (VO 2 ), the proposed meta-material is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

Quantum cascade lasers: from tool to product.

PubMed

Razeghi, M; Lu, Q Y; Bandyopadhyay, N; Zhou, W; Heydari, D; Bai, Y; Slivken, S

2015-04-06

The quantum cascade laser (QCL) is an important laser source in the mid-infrared and terahertz frequency range. The past twenty years have witnessed its tremendous development in power, wall plug efficiency, frequency coverage and tunability, beam quality, as well as various applications based on QCL technology. Nowadays, QCLs can deliver high continuous wave power output up to 5.1 W at room temperature, and cover a wide frequency range from 3 to 300 μm by simply varying the material components. Broadband heterogeneous QCLs with a broad spectral range from 3 to 12 μm, wavelength agile QCLs based on monolithic sampled grating design, and on-chip beam QCL combiner are being developed for the next generation tunable mid-infrared source for spectroscopy and sensing. Terahertz sources based on nonlinear generation in QCLs further extend the accessible wavelength into the terahertz range. Room temperature continuous wave operation, high terahertz power up to 1.9 mW, and wide frequency tunability form 1 to 5 THz makes this type of device suitable for many applications in terahertz spectroscopy, imaging, and communication.

Optically tuned terahertz modulator based on annealed multilayer MoS2.

PubMed

Cao, Yapeng; Gan, Sheng; Geng, Zhaoxin; Liu, Jian; Yang, Yuping; Bao, Qiaoling; Chen, Hongda

2016-03-08

Controlling the propagation properties of terahertz waves is very important in terahertz technologies applied in high-speed communication. Therefore a new-type optically tuned terahertz modulator based on multilayer-MoS2 and silicon is experimentally demonstrated. The terahertz transmission could be significantly modulated by changing the power of the pumping laser. With an annealing treatment as a p-doping method, MoS2 on silicon demonstrates a triple enhancement of terahertz modulation depth compared with the bare silicon. This MoS2-based device even exhibited much higher modulation efficiency than the graphene-based device. We also analyzed the mechanism of the modulation enhancement originated from annealed MoS2, and found that it is different from that of graphene-based device. The unique optical modulating properties of the device exhibit tremendous promise for applications in terahertz switch.

Nonlinear optical THz generation and sensing applications

NASA Astrophysics Data System (ADS)

Kawase, Kodo

2012-03-01

We have suggested a wide range of real-life applications using novel terahertz imaging techniques. A high-resolution terahertz tomography was demonstrated by ultra short terahertz pulses using optical fiber and a nonlinear organic crystal. We also report on the thickness measurement of very thin films using high-sensitivity metal mesh filter. Further we have succeeded in a non-destructive inspection that can monitor the soot distribution in the ceramic filter using millimeter-to-terahertz wave computed tomography. These techniques are directly applicable to the non-destructive testing in industries.

Extremely frequency-widened terahertz wave generation using Cherenkov-type radiation.

PubMed

Suizu, Koji; Koketsu, Kaoru; Shibuya, Takayuki; Tsutsui, Toshihiro; Akiba, Takuya; Kawase, Kodo

2009-04-13

Terahertz (THz) wave generation based on nonlinear frequency conversion is promising way for realizing a tunable monochromatic bright THz-wave source. Such a development of efficient and wide tunable THz-wave source depends on discovery of novel brilliant nonlinear crystal. Important factors of a nonlinear crystal for THz-wave generation are, 1. High nonlinearity and 2. Good transparency at THz frequency region. Unfortunately, many nonlinear crystals have strong absorption at THz frequency region. The fact limits efficient and wide tunable THz-wave generation. Here, we show that Cherenkov radiation with waveguide structure is an effective strategy for achieving efficient and extremely wide tunable THz-wave source. We fabricated MgO-doped lithium niobate slab waveguide with 3.8 microm of thickness and demonstrated difference frequency generation of THz-wave generation with Cherenkov phase matching. Extremely frequency-widened THz-wave generation, from 0.1 to 7.2 THz, without no structural dips successfully obtained. The tuning frequency range of waveguided Cherenkov radiation source was extremely widened compare to that of injection seeded-Terahertz Parametric Generator. The tuning range obtained in this work for THz-wave generation using lithium niobate crystal was the widest value in our knowledge. The highest THz-wave energy obtained was about 3.2 pJ, and the energy conversion efficiency was about 10(-5) %. The method can be easily applied for many conventional nonlinear crystals, results in realizing simple, reasonable, compact, high efficient and ultra broad band THz-wave sources.

Terahertz transmission properties of silicon wafers using continuous-wave terahertz spectroscopy

NASA Astrophysics Data System (ADS)

Kim, Chihoon; Ahn, Jae Sung; Ji, Taeksoo; Eom, Joo Beom

2017-04-01

We present the spectral properties of Si wafers using continuous-wave terahertz (CW-THz) spectroscopy. By using a tunable laser source and a fixed distributed-feedback laser diode (DFB-LD), a stably tunable beat source for CW-THz spectroscopy system can be implemented. THz radiation is generated in the frequency range of 100 GHz-800 GHz by photomixing in a photoconductive antenna. We also measured CW-THz waveforms by changing the beat frequency and confirmed repeatability through repeated measurement. We calculated the peaks of the THz frequency by taking fast Fourier transforms (FFTs) of measured THz waveforms. The feasibility of CW-THz spectroscopy is demonstrated by the THz spectra of Si wafers with different resistivities, mobilities, and carrier concentrations. The results show that Si wafers with a lower resistivity absorb more THz waves. Thus, we expect our CW-THz system to have the advantage of being able to perform fast non-destructive analysis.

High-efficiency terahertz polarization devices based on the dielectric metasurface

NASA Astrophysics Data System (ADS)

Zhou, Jian; Wang, JingJing; Guo, Kai; Shen, Fei; Zhou, Qingfeng; Zhiping yin; Guo, Zhongyi

2018-02-01

Metasurfaces are composed of the subwavelength structures, which can be used to manipulate the amplitude, phase, and polarization of incident electromagnetic waves efficiently. Here, we propose a novel type of dielectric metasurface based on crystal Si for realizing to manipulate the terahertz wave, in which by varying the geometric sizes of the Si micro-bricks, the transmitting phase of the terahertz wave can almost span over the entire 2π range for both of the x-polarization and y-polarization simultaneously, while keeping the similarly high-transmission amplitudes (over 90%). At the frequency of 1.0 THz, we have successfully designed a series of controllable THz devices, such as the polarization-dependent beam splitter, polarization-independent beam deflector and the focusing lenses based on the designed metasurfaces. Our designs are easy to fabricate and can be promising in developing high-efficiency THz functional devices.

Terahertz transmission resonances in complementary multilayered metamaterial with deep subwavelength interlayer spacing

NASA Astrophysics Data System (ADS)

Choi, Muhan; Kang, Byungsoo; Yi, Yoonsik; Lee, Seung Hoon; Kim, Inbo; Han, Jae-Hyung; Yi, Minwoo; Ahn, Jaewook; Choi, Choon-Gi

2016-05-01

We introduce a flexible multilayered THz metamaterial designed by using the Babinet's principle with the functionality of narrow band-pass filter. The metamaterial gives us systematic way to design frequency selective surfaces working on intended frequencies and bandwidths. It shows highly enhanced transmission of 80% for the normal incident THz waves due to the strong coupling of the two layers of metamaterial complementary to each other.

High-order modes of spoof surface plasmonic wave transmission on thin metal film structure.

PubMed

Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

2013-12-16

Recently, conformal surface plasmon (CSP) structure has been successfully proposed that could support spoof surface plasmon polaritons (SPPs) on corrugated metallic strip with ultrathin thickness [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Such concept provides a flexible, conformal, and ultrathin wave-guiding element, very promising for application of plasmonic devices, and circuits in the frequency ranging from microwave to mid-infrared. In this work, we investigated the dispersions and field patterns of high-order modes of spoof SPPs along CSP structure of thin metal film with corrugated edge of periodic array of grooves, and carried out direct measurement on the transmission spectrum of multi-band of surface wave propagation at microwave frequency. It is found that the mode number and mode bands are mainly determined by the depth of the grooves, providing a way to control the multi-band transmission spectrum. We have also experimentally verified the high-order mode spoof SPPs propagation on curved CSP structure with acceptable bending loss. The multi-band propagation of spoof surface wave is believed to be applicable for further design of novel planar devices such as filters, resonators, and couplers, and the concept can be extended to terahertz frequency range.

Frequency-dependent radiation patterns emitted by THz plasmons on finite length cylindrical metal wires.

PubMed

Deibel, Jason A; Berndsen, Nicholas; Wang, Kanglin; Mittleman, Daniel M; van der Valk, Nick C; Planken, Paul C M

2006-09-18

We report on the emission patterns from THz plasmons propagating towards the end of cylindrical metal waveguides. Such waveguides exhibit low loss and dispersion, but little is known about the dynamics of the terahertz radiation at the end of the waveguide, specifically in the near- and intermediate-field. Our experimental results and numerical simulations show that the near- and intermediate-field terahertz spectra, measured at the end of the waveguide, vary with the position relative to the waveguide. This is explained by the frequency-dependent diffraction occurring at the end of the cylindrical waveguide. Our results show that near-field changes in the frequency content of THz pulses for increasing wire-detector distances must be taken into account when studying surface waves on cylindrical waveguides.

Terahertz in-line digital holography of human hepatocellular carcinoma tissue.

PubMed

Rong, Lu; Latychevskaia, Tatiana; Chen, Chunhai; Wang, Dayong; Yu, Zhengping; Zhou, Xun; Li, Zeyu; Huang, Haochong; Wang, Yunxin; Zhou, Zhou

2015-02-13

Terahertz waves provide a better contrast in imaging soft biomedical tissues than X-rays, and unlike X-rays, they cause no ionisation damage, making them a good option for biomedical imaging. Terahertz absorption imaging has conventionally been used for cancer diagnosis. However, the absorption properties of a cancerous sample are influenced by two opposing factors: an increase in absorption due to a higher degree of hydration and a decrease in absorption due to structural changes. It is therefore difficult to diagnose cancer from an absorption image. Phase imaging can thus be critical for diagnostics. We demonstrate imaging of the absorption and phase-shift distributions of 3.2 mm × 2.3 mm × 30-μm-thick human hepatocellular carcinoma tissue by continuous-wave terahertz digital in-line holography. The acquisition time of a few seconds for a single in-line hologram is much shorter than that of other terahertz diagnostic techniques, and future detectors will allow acquisition of meaningful holograms without sample dehydration. The resolution of the reconstructions was enhanced by sub-pixel shifting and extrapolation. Another advantage of this technique is its relaxed minimal sample size limitation. The fibrosis indicated in the phase distribution demonstrates the potential of terahertz holographic imaging to obtain a more objective, early diagnosis of cancer.

Terahertz in-line digital holography of human hepatocellular carcinoma tissue

PubMed Central

Rong, Lu; Latychevskaia, Tatiana; Chen, Chunhai; Wang, Dayong; Yu, Zhengping; Zhou, Xun; Li, Zeyu; Huang, Haochong; Wang, Yunxin; Zhou, Zhou

2015-01-01

Terahertz waves provide a better contrast in imaging soft biomedical tissues than X-rays, and unlike X-rays, they cause no ionisation damage, making them a good option for biomedical imaging. Terahertz absorption imaging has conventionally been used for cancer diagnosis. However, the absorption properties of a cancerous sample are influenced by two opposing factors: an increase in absorption due to a higher degree of hydration and a decrease in absorption due to structural changes. It is therefore difficult to diagnose cancer from an absorption image. Phase imaging can thus be critical for diagnostics. We demonstrate imaging of the absorption and phase-shift distributions of 3.2 mm × 2.3 mm × 30-μm-thick human hepatocellular carcinoma tissue by continuous-wave terahertz digital in-line holography. The acquisition time of a few seconds for a single in-line hologram is much shorter than that of other terahertz diagnostic techniques, and future detectors will allow acquisition of meaningful holograms without sample dehydration. The resolution of the reconstructions was enhanced by sub-pixel shifting and extrapolation. Another advantage of this technique is its relaxed minimal sample size limitation. The fibrosis indicated in the phase distribution demonstrates the potential of terahertz holographic imaging to obtain a more objective, early diagnosis of cancer. PMID:25676705

Terahertz in-line digital holography of human hepatocellular carcinoma tissue

NASA Astrophysics Data System (ADS)

Rong, Lu; Latychevskaia, Tatiana; Chen, Chunhai; Wang, Dayong; Yu, Zhengping; Zhou, Xun; Li, Zeyu; Huang, Haochong; Wang, Yunxin; Zhou, Zhou

2015-02-01

Terahertz waves provide a better contrast in imaging soft biomedical tissues than X-rays, and unlike X-rays, they cause no ionisation damage, making them a good option for biomedical imaging. Terahertz absorption imaging has conventionally been used for cancer diagnosis. However, the absorption properties of a cancerous sample are influenced by two opposing factors: an increase in absorption due to a higher degree of hydration and a decrease in absorption due to structural changes. It is therefore difficult to diagnose cancer from an absorption image. Phase imaging can thus be critical for diagnostics. We demonstrate imaging of the absorption and phase-shift distributions of 3.2 mm × 2.3 mm × 30-μm-thick human hepatocellular carcinoma tissue by continuous-wave terahertz digital in-line holography. The acquisition time of a few seconds for a single in-line hologram is much shorter than that of other terahertz diagnostic techniques, and future detectors will allow acquisition of meaningful holograms without sample dehydration. The resolution of the reconstructions was enhanced by sub-pixel shifting and extrapolation. Another advantage of this technique is its relaxed minimal sample size limitation. The fibrosis indicated in the phase distribution demonstrates the potential of terahertz holographic imaging to obtain a more objective, early diagnosis of cancer.

Terahertz NDE for Metallic Surface Roughness Evaluation

NASA Technical Reports Server (NTRS)

Madaras, Eric I.; Anastasi, Robert F.

2006-01-01

Metallic surface roughness in a nominally smooth surface is a potential indication of material degradation or damage. When the surface is coated or covered with an opaque dielectric material, such as paint or insulation, then inspecting for surface changes becomes almost impossible. Terahertz NDE is a method capable of penetrating the coating and inspecting the metallic surface. The terahertz frequency regime is between 100 GHz and 10 THz and has a free space wavelength of 300 micrometers at 1 THz. Pulsed terahertz radiation, can be generated and detected using optical excitation of biased semiconductors with femtosecond laser pulses. The resulting time domain signal is 320 picoseconds in duration. In this application, samples are inspected with a commercial terahertz NDE system that scans the sample and generates a set of time-domain signals that are a function of the backscatter from the metallic surface. Post processing is then performed in the time and frequency domains to generate C-scan type images that show scattering effects due to surface non-uniformity.

A novel Zeonex based oligoporous-core photonic crystal fiber for polarization preserving terahertz applications

NASA Astrophysics Data System (ADS)

Islam, Md. Saiful; Sultana, Jakeya; Dinovitser, Alex; Ng, Brian W.-H.; Abbott, Derek

2018-04-01

A novel waveguide consisting of oligo-porous core photonic crystal fiber (PCF) with a kagome lattice cladding has been designed for highly birefringent and near zero dispersion flattened applications of terahertz waves. The wave guiding properties of the designed PCF including birefringence, dispersion, effective material loss (EML), core power fraction, confinement loss, and modal effective area are investigated using a full vector Finite Element Method (FEM) with Perfectly Matched Layer (PML) absorbing boundary condition. Simulation results demonstrate that an ultra-high birefringence of 0.079, low EML of 0.05 cm-1, higher core power fraction of 44% and negligible confinement loss of 7 . 24 × 10-7 cm-1 can be achieved at 1 THz. Furthermore, for the y-polarization mode a near zero flattened dispersion of 0 . 49 ± 0 . 05 ps/THz/cm is achieved within a broad frequency range of 0.8-1.7 THz. The fabrication of the proposed fiber is feasible using the existing fabrication technology. Due to favorable wave-guiding properties, the proposed fiber has potential for terahertz imaging, sensing and polarization maintaining applications in the terahertz frequency range.

Simulation and analysis of atmospheric transmission performance in airborne Terahertz communication

NASA Astrophysics Data System (ADS)

Pan, Chengsheng; Shi, Xin; Liu, Chengyang; Wang, Xue; Ding, Yuanming

2018-02-01

For the special meteorological condition of high altitude transmission; first the influence of atmospheric turbulence on the Terahertz wireless communication is analyzed, and the atmospheric constants model with increase in height is given. On this basis, the relationship between the flicker index and the high altitude horizon transmission distance of the Terahertz wave is analyzed by simulation. Then, through the analysis of high altitude path loss and noise, the high altitude wireless link model is built. Finally, the link loss budget is given according to the current Terahertz device parameters, and bit error rate (BER) performance of on-off keyed modulation (OOK) and pulse position modulation (PPM) in four Terahertz frequency bands is compared and analyzed. All these above provided theoretical reference for high-altitude Terahertz wireless communication transmission.

Ultrafast control and monitoring of material properties using terahertz pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowlan, Pamela Renee

These are a set of slides on ultrafast control and monitoring of material properties using terahertz pulses. A few of the topics covered in these slides are: How fast is a femtosecond (fs), Different frequencies probe different properties of molecules or solids, What can a THz pulse do to a material, Ultrafast spectroscopy, Generating and measuring ultrashort THz pulses, Tracking ultrafast spin dynamics in antiferromagnets through spin wave resonances, Coherent two-dimensional THz spectroscopy, and Probing vibrational dynamics at a surface. Conclusions are: Coherent two-dimensional THz spectroscopy: a powerful approach for studying coherence and dynamics of low energy resonances. Applying thismore » to graphene we investigated the very strong THz light mater interaction which dominates over scattering. Useful for studying coupled excitations in multiferroics and monitoring chemical reactions. Also, THz-pump, SHG-probe spectoscopy: an ultrafast, surface sensitive probe of atomic-scale symmetry changes and nonlinear phonon dymanics. We are using this in Bi 2Se 3 to investigate the nonlinear surface phonon dynamics. This is potentially very useful for studying catalysis.« less

Large dynamic range terahertz spectrometers based on plasmonic photomixers (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wang, Ning; Javadi, Hamid; Jarrahi, Mona

2017-02-01

Heterodyne terahertz spectrometers are highly in demand for space explorations and astrophysics studies. A conventional heterodyne terahertz spectrometer consists of a terahertz mixer that mixes a received terahertz signal with a local oscillator signal to generate an intermediate frequency signal in the radio frequency (RF) range, where it can be easily processed and detected by RF electronics. Schottky diode mixers, superconductor-insulator-superconductor (SIS) mixers and hot electron bolometer (HEB) mixers are the most commonly used mixers in conventional heterodyne terahertz spectrometers. While conventional heterodyne terahertz spectrometers offer high spectral resolution and high detection sensitivity levels at cryogenic temperatures, their dynamic range and bandwidth are limited by the low radiation power of existing terahertz local oscillators and narrow bandwidth of existing terahertz mixers. To address these limitations, we present a novel approach for heterodyne terahertz spectrometry based on plasmonic photomixing. The presented design replaces terahertz mixer and local oscillator of conventional heterodyne terahertz spectrometers with a plasmonic photomixer pumped by an optical local oscillator. The optical local oscillator consists of two wavelength-tunable continuous-wave optical sources with a terahertz frequency difference. As a result, the spectrometry bandwidth and dynamic range of the presented heterodyne spectrometer is not limited by radiation frequency and power restrictions of conventional terahertz sources. We demonstrate a proof-of-concept terahertz spectrometer with more than 90 dB dynamic range and 1 THz spectrometry bandwidth.

Optomechanical terahertz detection with single meta-atom resonator.

PubMed

Belacel, Cherif; Todorov, Yanko; Barbieri, Stefano; Gacemi, Djamal; Favero, Ivan; Sirtori, Carlo

2017-11-17

Most of the common technologies for detecting terahertz photons (>1 THz) at room temperature rely on slow thermal devices. The realization of fast and sensitive detectors in this frequency range is indeed a notoriously difficult task. Here we propose a novel device consisting of a subwavelength terahertz meta-atom resonator, which integrates a nanomechanical element and allows energy exchange between the mechanical motion and the electromagnetic degrees of freedom. An incident terahertz wave thus produces a nanomechanical signal that can be read out optically with high precision. We exploit this concept to demonstrate a terahertz detector that operates at room temperature with high sensitivity and a much higher frequency response compared to standard detectors. Beyond the technological issue of terahertz detection, our architecture opens up new perspectives for fundamental science of light-matter interaction at terahertz frequencies, combining optomechanical approaches with semiconductor quantum heterostructures.

Angle-resolved and polarization-dependent investigation of cross-shaped frequency-selective surface terahertz filters

NASA Astrophysics Data System (ADS)

Ferraro, A.; Zografopoulos, D. C.; Caputo, R.; Beccherelli, R.

2017-04-01

The spectral response of a terahertz (THz) filter is investigated in detail for different angles of incidence and polarization of the incoming THz wave. The filter is fabricated by patterning an aluminum frequency-selective surface of cross-shaped apertures on a thin foil of the low-loss cyclo-olefin polymer Zeonor. Two different types of resonances are observed, namely, a broadline resonance stemming from the transmittance of the slot apertures and a series of narrowline guided-mode resonances, with the latter being investigated by employing the grating theory. Numerical simulations of the filter transmittance based on the finite-element method agree with experimental measurements by means of THz time domain spectroscopy (THz-TDS). The results reveal extensive possibilities for tuning the guided-mode resonances by mechanically adjusting the incidence or polarization angle, while the fundamental broadline resonance is not significantly affected. Such filters are envisaged as functional elements in emerging THz systems for filtering or sensing applications.

Surface-Emitting Distributed Feedback Terahertz Quantum-Cascade Lasers in Metal-Metal Waveguides

NASA Technical Reports Server (NTRS)

Kumar, Sushil; Williams, Benjamin S.; Qin, Qi; Lee, Alan W. M.; Hu, Qing; Reno, John L.

2007-01-01

Single-mode surface-emitting distributed feedback terahertz quantumcascade lasers operating around 2.9 THz are developed in metal-metal waveguides. A combination of techniques including precise control of phase of reflection at the facets, and u e of metal on the sidewalls to eliminate higher-order lateral modes allow robust single-mode operation over a range of approximately 0.35 THz. Single-lobed far-field radiation pattern is obtained using a pi phase-shift in center of the second-order Bragg grating. A grating device operating at 2.93 THz lased up to 149 K in pulsed mode and a temperature tuning of 19 .7 GHz was observed from 5 K to 147 K. The same device lased up to 78 K in continuous-wave (cw) mode emitting more than 6 m W of cw power at 5 K. ln general, maximum temperature of pulsed operation for grating devices was within a few Kelvin of that of multi-mode Fabry-Perot ridge lasers

Statistics of multiply scattered broadband terahertz pulses.

PubMed

Pearce, Jeremy; Jian, Zhongping; Mittleman, Daniel M

2003-07-25

We describe the first measurements of the diffusion of broadband single-cycle optical pulses through a highly scattering medium. Using terahertz time-domain spectroscopy, we measure the electric field of a multiply scattered wave with a time resolution shorter than one optical cycle. This time-domain measurement provides information on the statistics of both the amplitude and phase distributions of the diffusive wave. We develop a theoretical description, suitable for broadband radiation, which adequately describes the experimental results.

THz holography in reflection using a high resolution microbolometer array.

PubMed

Zolliker, Peter; Hack, Erwin

2015-05-04

We demonstrate a digital holographic setup for Terahertz imaging of surfaces in reflection. The set-up is based on a high-power continuous wave (CW) THz laser and a high-resolution (640 × 480 pixel) bolometer detector array. Wave propagation to non-parallel planes is used to reconstruct the object surface that is rotated relative to the detector plane. In addition we implement synthetic aperture methods for resolution enhancement and compare Fourier transform phase retrieval to phase stepping methods. A lateral resolution of 200 μm and a relative phase sensitivity of about 0.4 rad corresponding to a depth resolution of 6 μm are estimated from reconstructed images of two specially prepared test targets, respectively. We highlight the use of digital THz holography for surface profilometry as well as its potential for video-rate imaging.

Numerical and theoretical analysis on the absorption properties of metasurface-based terahertz absorbers with different thicknesses.

PubMed

Wu, Kaimin; Huang, Yongjun; Wanghuang, Tenglong; Chen, Weijian; Wen, Guangjun

2015-01-10

In this paper, we numerically and theoretically discuss the novel absorption properties of a conventional metasurface-based terahertz (THz) electromagnetic (EM) absorber with different dielectric thicknesses. Two absorption modes are presented in the considered frequency band due to the increased dielectric thickness, and both modes can achieve near-unity absorptions when the dielectric layers reach additional nλ(d)/2 (n=1, 2) thicknesses, where λ(d) is the operating wavelength at the peak absorption in the dielectric slabs. The surface currents between the metasurface resonators and ground plane are not associated any longer, different from the conventional thin absorbers. Moreover, the EM wave energies are completely absorbed by the metasurface resonators and dielectric layer, and the main function of ground plane is to reflect the incident EM waves back to the resonators. The discussed novel absorption properties are analyzed and explained by classical EM theory and interference theory after numerical demonstrations. These findings can broaden the potential applications of the metasurface-based absorbers in the THz frequency range for different requirements.

Improvement of contact grating device for efficient terahertz wave generation using bi-angular filter

NASA Astrophysics Data System (ADS)

Nagashima, Keisuke; Tsubouchi, Masaaki; Ochi, Yoshihiro; Maruyama, Momoko

2018-03-01

We have proposed an improved contact grating device for generating terahertz waves efficiently and have succeeded in developing the device with a very high diffraction efficiency and a wide spectral width. This device has a bi-angular filter and a Fabry-Perot-type structure, which are composed of dielectric multilayers. The bi-angular filter is designed to reflect the 0th-order wave and transmit the-1st-order diffraction wave. Numerical calculations indicate that the new device has a maximum diffraction efficiency over 99% and a spectral width of approximately 20 nm. We measured a high efficiency of 90% over a broad spectral range using a fabricated device.

Generation of phase-locked and tunable continuous-wave radiation in the terahertz regime.

PubMed

Quraishi, Qudsia; Griebel, Martin; Kleine-Ostmann, Thomas; Bratschitsch, Rudolf

2005-12-01

Broadly tunable phase-stable single-frequency terahertz radiation is generated with an optical heterodyne photomixer. The photomixer is excited by two near-infrared CW diode lasers that are phase locked to the stabilized optical frequency comb of a femtosecond titanium:sapphire laser. The terahertz radiation emitted by the photomixer is downconverted into RF frequencies with a waveguide harmonic mixer and measurement-limited linewidths at the Hertz level are demonstrated.

Efficient terahertz wave generation from GaP crystals pumped by chirp-controlled pulses from femtosecond photonic crystal fiber amplifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jiang; Shi, Junkai; Xu, Baozhong

2014-01-20

A chirp-tunable femtosecond 10 W, 42 MHz photonic-crystal-fiber oscillator-amplifier system that is capable of delivering sub-60 fs light pulses at 1040 nm is used to demonstrate high-efficiency terahertz radiation generation via optical rectification in GaP crystals only a few millimeters in length. The optimization of the chirp of the fiber-laser pulses is shown to radically enhance the terahertz output, indicating one possible way to more efficiently use these extended nonlinear crystals in compact fiber-pumped terahertz radiation sources.

Non-destructive terahertz imaging of illicit drugs using spectral fingerprints

NASA Astrophysics Data System (ADS)

Kawase, Kodo; Ogawa, Yuichi; Watanabe, Yuuki; Inoue, Hiroyuki

2003-10-01

The absence of non-destructive inspection techniques for illicit drugs hidden in mail envelopes has resulted in such drugs being smuggled across international borders freely. We have developed a novel basic technology for terahertz imaging, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. The spatial distributions of the targets are obtained from terahertz multispectral transillumination images, using absorption spectra measured with a tunable terahertz-wave source. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

Detection and Characterization of Flaws in Sprayed on Foam Insulation with Pulsed Terahertz Frequency Electromagnetic Waves

NASA Technical Reports Server (NTRS)

Winfree, William P.; Madaras, Eric I.

2005-01-01

The detection and repair of flaws such as voids and delaminations in the sprayed on foam insulation of the external tank reduces the probability of foam debris during shuttle ascent. The low density of sprayed on foam insulation along with it other physical properties makes detection of flaws difficult with conventional techniques. An emerging technology that has application for quantitative evaluation of flaws in the foam is pulsed electromagnetic waves at terahertz frequencies. The short wavelengths of these terahertz pulses make them ideal for imaging flaws in the foam. This paper examines the application of terahertz pulses for flaw detection in foam characteristic of the foam insulation of the external tank. Of particular interest is the detection of voids and delaminations, encapsulated in the foam or at the interface between the foam and a metal backing. The technique is shown to be capable of imaging small voids and delaminations through as much as 20 cm of foam. Methods for reducing the temporal responses of the terahertz pulses to improve flaw detection and yield quantitative characterizations of the size and location of the flaws are discussed.

A honeycomb-like three-dimensional metamaterial absorber via super-wideband and wide-angle performances at millimeter wave and low THz frequencies

NASA Astrophysics Data System (ADS)

Vahidi, Alireza; Rajabalipanah, Hamid; Abdolali, Ali; Cheldavi, Ahmad

2018-04-01

Achieving wideband absorption via three-dimensional (3D) metamaterials has revealed as a new emerging innovative field of research, especially in recent years. Here, a novel 3D metamaterial absorber (MA) having a sixfold symmetry is designed which consists of periodic resistive honeycomb-like units. The proposed 3D MA exhibits a strong absorptivity above 90% in the widest bandwidth ever reported to the authors' knowledge from 50 to 460 GHz (the bandwidth ratio larger than 1:9), covering both millimeter wave and low -terahertz spectra. To understand the physical mechanism of absorption, the electric field and surface current distributions, the power loss density as well as the deteriorating effects of the high-order Floquet modes are monitored and discussed. As a distinctive feature in comparison to the similar 3D MAs, our engineered absorber provides multiple resonances, contributing to further broadening of the operating bandwidth. In addition, it is shown that the honeycomb-like MA retains its polarization-insensitive absorption in a wide range of incident wave angles and polarization angles. Due to flexibility of the design, these superior performances can be simply extended to terahertz, infrared and visible frequencies, potentially leading to many promising applications in imaging, sensing, and camouflage technology.

Material Inspection Using THz and Thermal Wave

NASA Astrophysics Data System (ADS)

Zhang, Cunlin; Mu, Kaijun; Li, Yanhong; Zhang, X.-C.

2007-03-01

Terahertz (THz) and thermal wave imaging technologies are complementary inspection modalities for use in non-contact and non-destructive evaluation. Both of them are applied in order to evaluate damages on a variety of composite samples. We will also report the test of a large number of insulation foam panels used in NASA's External Fuel Tank through pulse and CW terahertz systems. The study of defects using the two techniques in selected materials, including metal plates, carbon fibers, glass fibers, carbon silicon composites, etc is also shown.

Hybridization-induced broadband terahertz wave absorption with graphene metasurfaces.

PubMed

Mou, Nanli; Sun, Shulin; Dong, Hongxing; Dong, Shaohua; He, Qiong; Zhou, Lei; Zhang, Long

2018-04-30

Electromagnetic (EM) wave absorption plays a vital role in photonics. While metasurfaces are proposed to absorb EM waves efficiently, most of them exhibit limited bandwidth and fixed functionalities. Here, we propose a broadband and tunable terahertz (THz) absorber based on a graphene-based metasurface, which is constructed by a single layer of closely patterned graphene concentric double rings and a metallic mirror separated by an ultrathin SiO 2 layer. Plasmonic hybridization between two graphene rings significantly enlarges the absorption bandwidth, which can be further tuned by gating the graphene. Moreover, the specific design also makes our device insensitive to the incident angle and polarization state of impinging EM waves. Our results may inspire certain wave-modulation-related applications, such as THz imaging, smart absorber, tunable sensor, etc.

Terahertz photoluminescence from S.I.-GaAs by below gap excitation via EL2 level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oyama, Yutaka, E-mail: oyama@material.tohoku.ac.jp; Dezaki, Hikari; Shimizu, Yusaku

2015-01-12

Terahertz emission by radiative transitions in semi-conductors via shallow impurity states is investigated. We report on the observation of terahertz photoluminescence from S.I.-GaAs by below gap excitation via EL2 level which is located at the center of band gap. In order to investigate the terahertz wave emission mechanisms, the emission spectra and temperature dependence of the emission intensity are evaluated. It is shown that intense terahertz emission from S.I.-GaAs over 120 K is observed due to the thermal recovery of photo-quenched EL2 meta-stable state, and that the emission peak frequency looks to be attributed to the shallow level energy in GaAs.

Ultra-broadband near-field antenna for terahertz plasmonic applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polischuk, O. V., E-mail: polischuk.sfire@mail.ru; Popov, V. V., E-mail: popov-slava@yahoo.co.uk; Knap, W.

A new type of ultra-broadband near-field antenna for terahertz frequencies is proposed. This antenna is a short-period planar metal array. It is theoretically shown that irradiation of the short-period array antenna by a plane homogeneous terahertz waves excite a highly inhomogeneous near electric field near the metal array. In this case, the amplitude of the excited inhomogeneous near electric field is almost independent of frequency in the entire terahertz frequency range. The excitation of plasma oscillations in a two-dimensional electron system using the antenna under study is numerically simulated in the resonant and non-resonant plasmonic response modes. This type ofmore » antenna can be used for developing ultra-broadband plasmonic detectors of terahertz radiation.« less

Compact terahertz spectrometer based on disordered rough surfaces

NASA Astrophysics Data System (ADS)

Yang, Tao; Jiang, Bing; Ge, Jia-cheng; Zhu, Yong-yuan; Li, Xing-ao; Huang, Wei

2018-01-01

In this paper, a compact spectrometer based on disordered rough surfaces for operation in the terahertz band is presented. The proposed spectrometer consists of three components, which are used for dispersion, modulation and detection respectively. The disordered rough surfaces, which are acted as the dispersion component, are modulated by the modulation component. Different scattering intensities are captured by the detection component with different extent of modulation. With a calibration measurement process, one can reconstruct the spectra of the probe terahertz beam by solving a system of simultaneous linear equations. A Tikhonov regularization approach has been implemented to improve the accuracy of the spectral reconstruction. The reported broadband, compact, high-resolution terahertz spectrometer is well suited for portable terahertz spectroscopy applications.

An effective way to reduce water absorption to terahertz

NASA Astrophysics Data System (ADS)

Wu, Yaxiong; Su, Bo; He, Jingsuo; Zhang, Cong; Zhang, Hongfei; Zhang, Shengbo; Zhang, Cunlin

2018-01-01

Since many vibrations and rotational levels of biomolecules fall within the THz band, THz spectroscopy can be used to identify biological samples. In addition, most biomolecules need to maintain their biological activity in a liquid environment, but water as polar substance has strong absorption to the THz wave. Thus, it is difficult to detect the sample information in aqueous solution using THz wave. In order to prevent the information of biological samples were masked in the solution, many research methods were used to explore how to reduce the water absorption of terahertz. In this paper, we have developed a real-time chemical methodology through transmission Terahertz time-domain spectroscopy (THz-TDS) system. The material of Zeonor 1020r is used as substrate and cover plate, and PDMS as channel interlayer. The transmission of the empty microfluidic chip is more than 80% in the range of 0.2-2.6 THz by THz-TDS system. Then, experiments were carried out using chips, which were filled with different volumes of 1, 2- propanediol, and it has been proved that the microfluidic chip could reduce the water absorption of terahertz. Finally, in order to further explore the reduction of terahertz to water absorption, we inject different concentrations of electrolyte to the chip. The results show that with the addition of different electrolytes, terahertz transmission line has evident changes. It can be taken into account that the electrolyte has different effects about the hydrogen bonds in the aqueous solution. Some of them can promote water molecules clusters, while others destroy them. Based on the basis of microfluidic chip, the discovery of this phenomenon can provide a way that reduces water absorption of terahertz. This work has laid a solid foundation for the subsequent study in reducing water absorption of terahertz.

Characterization of an active metasurface using terahertz ellipsometry

DOE PAGES

Karl, Nicholas; Heimbeck, Martin S.; Everitt, Henry O.; ...

2017-11-06

Switchable metasurfaces fabricated on a doped epi-layer have become an important platform for developing techniques to control terahertz (THz) radiation, as a DC bias can modulate the transmission characteristics of the metasurface. To model and understand this performance in new device configurations accurately, a quantitative understanding of the bias-dependent surface characteristics is required. In this work, we perform THz variable angle spectroscopic ellipsometry on a switchable metasurface as a function of DC bias. By comparing these data with numerical simulations, we extract a model for the response of the metasurface at any bias value. Using this model, we predict amore » giant bias-induced phase modulation in a guided wave configuration. Lastly, these predictions are in qualitative agreement with our measurements, offering a route to efficient modulation of THz signals.« less

Investigating Dielectric and Metamaterial Effects in a Terahertz Traveling-Wave Tube Amplifier

NASA Technical Reports Server (NTRS)

Starinshak, David P.; Wilson, Jeffrey D.

2008-01-01

Adding material enhancements to a terahertz traveling-wave tube amplifier is investigated. Isotropic dielectrics, negative-index metamaterials, and anisotropic crystals are simulated, and plans to increase the efficiency of the device are discussed. Early results indicate that adding dielectric to the curved sections of the serpentine-shaped slow-wave circuit produce optimal changes in the cold-test characteristics of the device and a minimal drop in operating frequency. Additional results suggest that materials with simultaneously small relative permittivities and electrical conductivities are best suited for increasing the efficiency of the device. More research is required on the subject, and recommendations are given to determine the direction.

Output-Mirror-Tuning Terahertz-Wave Parametric Oscillator with an Asymmetrical Porro-Prism Resonator Configuration

NASA Astrophysics Data System (ADS)

Zhang, Ruiliang; Qu, Yanchen; Zhao, Weijiang; Liu, Chuang; Chen, Zhenlei

2017-06-01

We demonstrate a terahertz-wave parametric oscillator (TPO) with an asymmetrical porro-prism (PP) resonator configuration, consisting of a close PP corner reflector and a distant output mirror relative to the MgO:LiNbO3 crystal. Based on this cavity, frequency tuning of Stokes and the accompanied terahertz (THz) waves is realized just by rotating the plane mirror. Furthermore, THz output with high efficiency and wide tuning range is obtained. Compared with a conventional TPO employing a plane-parallel resonator of the same cavity length and output loss, the low end of the frequency tuning range is extended to 0.96 THz from 1.2 THz. The highest output obtained at 1.28 THz is enhanced by about 25%, and the oscillation threshold pump energy measured at 1.66 THz is reduced by about 4.5%. This resonator configuration also shows some potential to simplify the structure and application for intracavity TPOs.

Terahertz polarizing beam splitter based on copper grating on polyimide substrate

NASA Astrophysics Data System (ADS)

Zhang, Mengen; Li, Xiangjun; Wang, Wentao; Liu, Jianjun; Hong, Zhi

2012-12-01

A terahertz polarizing beam splitter, based on a copper grating on polyimide (PI) substrate, was fabricated by the way of laser induced and non-electrolytic plating. The good polarization characteristics of the splitter in the range of 0°-180°polarization are verified experimentally using backward wave oscillator at fixed frequency of 300GHz, and the insertion losses of 0.13dB and 0.32dB are measured for the transmitted and reflected beams, respectively. The broadband transmission of TM wave of the splitter was also measured by terahertz time-domain spectroscopy, and the extinction ratio larger than 22dB is obtained in the frequency range of 0.2-1.5THz. The experiment results are in good agreement with finite element simulation results.

Colossal terahertz nonlinearity of tunneling van der Waals gap (Conference Presentation)

NASA Astrophysics Data System (ADS)

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Ji Yeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2016-09-01

We manufactured an array of three angstrom-wide, five millimeter-long van der Waals gaps of copper-graphene-copper composite, in which unprecedented nonlinearity was observed. To probe and manipulate van der Waals gaps with long wavelength electromagnetic waves such as terahertz waves, one is required to fabricate vertically oriented van der Waals gaps sandwiched between two metal planes with an infinite length in the sense of being much larger than any of the wavelengths used. By comparison with the simple vertical stacking of metal-graphene-metal structure, in our structure, background signals are completely blocked enabling all the light to squeeze through the gap without any strays. When the angstrom-sized van der Waals gaps are irradiated with intense terahertz pulses, the transient voltage across the gap reaches up to 5 V with saturation, sufficiently strong to deform the quantum barrier of angstrom gaps. The large transient potential difference across the gap facilitates electron tunneling through the quantum barrier, blocking terahertz waves completely. This negative feedback of electron tunneling leads to colossal nonlinear optical response, a 97% decrease in the normalized transmittance. Our technology for infinitely long van der Waals gaps can be utilized for other atomically thin materials than single layer graphene, enabling linear and nonlinear angstrom optics in a broad spectral range.

Backward spoof surface wave in plasmonic metamaterial of ultrathin metallic structure.

PubMed

Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

2016-02-04

Backward wave with anti-parallel phase and group velocities is one of the basic properties associated with negative refraction and sub-diffraction image that have attracted considerable interest in the context of photonic metamaterials. It has been predicted theoretically that some plasmonic structures can also support backward wave propagation of surface plasmon polaritons (SPPs), however direct experimental demonstration has not been reported, to the best of our knowledge. In this paper, a specially designed plasmonic metamaterial of corrugated metallic strip has been proposed that can support backward spoof SPP wave propagation. The dispersion analysis, the full electromagnetic field simulation and the transmission measurement of the plasmonic metamaterial waveguide have clearly validated the backward wave propagation with dispersion relation possessing negative slope and opposite directions of group and phase velocities. As a further verification and application, a contra-directional coupler is designed and tested that can route the microwave signal to opposite terminals at different operating frequencies, indicating new application opportunities of plasmonic metamaterial in integrated functional devices and circuits for microwave and terahertz radiation.

Polarization imaging of imperfect m-plane GaN surfaces

NASA Astrophysics Data System (ADS)

Sakai, Yuji; Kawayama, Iwao; Nakanishi, Hidetoshi; Tonouchi, Masayoshi

2017-04-01

Surface polar states in m-plane GaN wafers were studied using a laser terahertz (THz) emission microscope (LTEM). Femtosecond laser illumination excites THz waves from the surface due to photocarrier acceleration by local spontaneous polarization and/or the surface built-in electric field. The m-plane, in general, has a large number of unfavorable defects and unintentional polarization inversion created during the regrowth process. The LTEM images can visualize surface domains with different polarizations, some of which are hard to visualize with photoluminescence mapping, i.e., non-radiative defect areas. The present study demonstrates that the LTEM provides rich information about the surface polar states of GaN, which is crucial to improve the performance of GaN-based optoelectronic and power devices.

Terahertz molecular resonance of cancer DNA.

PubMed

Cheon, Hwayeong; Yang, Hee-Jin; Lee, Sang-Hun; Kim, Young A; Son, Joo-Hiuk

2016-11-15

Carcinogenesis involves the chemical and structural alteration of biomolecules in cells. Aberrant methylation of DNA is a well-known carcinogenic mechanism and a common chemical modification of DNA. Terahertz waves can directly observe changes in DNA because the characteristic energies lie in the same frequency region. In addition, terahertz energy levels are not high enough to damage DNA by ionization. Here, we present terahertz molecular resonance fingerprints of DNA methylation in cancer DNA. Methylated cytidine, a nucleoside, has terahertz characteristic energies that give rise to the molecular resonance of methylation in DNA. Molecular resonance is monitored in aqueous solutions of genomic DNA from cancer cell lines using a terahertz time-domain spectroscopic technique. Resonance signals can be quantified to identify the types of cancer cells with a certain degree of DNA methylation. These measurements reveal the existence of molecular resonance fingerprints of cancer DNAs in the terahertz region, which can be utilized for the early diagnosis of cancer cells at the molecular level.

Terahertz molecular resonance of cancer DNA

NASA Astrophysics Data System (ADS)

Cheon, Hwayeong; Yang, Hee-Jin; Lee, Sang-Hun; Kim, Young A.; Son, Joo-Hiuk

2016-11-01

Carcinogenesis involves the chemical and structural alteration of biomolecules in cells. Aberrant methylation of DNA is a well-known carcinogenic mechanism and a common chemical modification of DNA. Terahertz waves can directly observe changes in DNA because the characteristic energies lie in the same frequency region. In addition, terahertz energy levels are not high enough to damage DNA by ionization. Here, we present terahertz molecular resonance fingerprints of DNA methylation in cancer DNA. Methylated cytidine, a nucleoside, has terahertz characteristic energies that give rise to the molecular resonance of methylation in DNA. Molecular resonance is monitored in aqueous solutions of genomic DNA from cancer cell lines using a terahertz time-domain spectroscopic technique. Resonance signals can be quantified to identify the types of cancer cells with a certain degree of DNA methylation. These measurements reveal the existence of molecular resonance fingerprints of cancer DNAs in the terahertz region, which can be utilized for the early diagnosis of cancer cells at the molecular level.

Terahertz time-domain spectroscopy for non-invasive assessment of water content in biological samples.

PubMed

Borovkova, Mariia; Khodzitsky, Mikhail; Demchenko, Petr; Cherkasova, Olga; Popov, Alexey; Meglinski, Igor

2018-05-01

We apply terahertz time-domain spectroscopy for the quantitative non-invasive assessment of the water content in biological samples, such as Carpinus caroliniana tree leaves and pork muscles. The developed experimental terahertz time-domain spectroscopy system operates both in transmission and reflection modes. The Landau-Looyenga-Lifshitz-based model is used for the calculation of the water concentration within the samples. The results of the water concentration measurements are compared with the results of the gravimetric measurements. The obtained results show that the water content in biological samples can be measured non-invasively, with a high accuracy, utilizing terahertz waves in transmission and reflection modes.

Plasmon resonance enhanced mid-infrared generation by graphene on gold gratings through difference frequency mixing

NASA Astrophysics Data System (ADS)

Cao, Jianjun; Kong, Yan; Gao, Shumei; liu, Cheng

2018-01-01

Graphene has been demonstrated to have extraordinary large second order nonlinear susceptibility that can be applied in generating mid-infrared (MIR) and terahertz waves through the difference frequency process. In this study, we exploit the highly localized electric fields caused by plasmon resonances to increase the nonlinear response from graphene. The proposed structure contains a graphene sheet on a gold grating substrate that sustains both surface plasmons at the near-infrared on the gold surface and plasmons at the MIR on the graphene surface. Based on finite difference time domain (FDTD) numerical simulations, more than 3 orders of magnitude improvement of the MIR generation efficiency is obtained by placing graphene sheets on a gold grating substrate under resonance conditions instead of placing them on a flat substrate. With the same gold grating substrate, MIR waves tunable from 30 to 55 THz are generated by tuning the gate voltage of the graphene sheet.

Terahertz photonic crystals

NASA Astrophysics Data System (ADS)

Jian, Zhongping

This thesis describes the study of two-dimensional photonic crystals slabs with terahertz time domain spectroscopy. In our study we first demonstrate the realization of planar photonic components to manipulate terahertz waves, and then characterize photonic crystals using terahertz pulses. Photonic crystal slabs at the scale of micrometers are first designed and fabricated free of defects. Terahertz time domain spectrometer generates and detects the electric fields of single-cycle terahertz pulses. By putting photonic crystals into waveguide geometry, we successfully demonstrate planar photonic components such as transmission filters, reflection frequency-selective filters, defects modes as well as superprisms. In the characterization study of out-of-plane properties of photonic crystal slabs, we observe very strong dispersion at low frequencies, guided resonance modes at middle frequencies, and a group velocity anomaly at high frequencies. We employ Finite Element Method and Finite-Difference Time-Domain method to simulate the photonic crystals, and excellent agreement is achieved between simulation results and experimental results.

Two-dimensional tomographic terahertz imaging by homodyne self-mixing.

PubMed

Mohr, Till; Breuer, Stefan; Giuliani, G; Elsäßer, Wolfgang

2015-10-19

We realize a compact two-dimensional tomographic terahertz imaging experiment involving only one photoconductive antenna (PCA) simultaneously serving as a transmitter and receiver of the terahertz radiation. A hollow-core Teflon cylinder filled with α-Lactose monohydrate powder is studied at two terahertz frequencies, far away and at a specific absorption line of the powder. This sample is placed between the antenna and a chopper wheel, which serves as back reflector of the terahertz radiation into the PCA. Amplitude and phase information of the continuous-wave (CW) terahertz radiation are extracted from the measured homodyne self-mixing (HSM) signal after interaction with the cylinder. The influence of refraction is studied by modeling the set-up utilizing ZEMAX and is discussed by means of the measured 1D projections. The tomographic reconstruction by using the Simultaneous Algebraic Reconstruction Technique (SART) allows to identify both object geometry and α-Lactose filling.

Predictive of the quantum capacitance effect on the excitation of plasma waves in graphene transistors with scaling limit

NASA Astrophysics Data System (ADS)

Wang, Lin; Chen, Xiaoshuang; Hu, Yibin; Wang, Shao-Wei; Lu, Wei

2015-04-01

Plasma waves in graphene field-effect transistors (FETs) and nano-patterned graphene sheets have emerged as very promising candidates for potential terahertz and infrared applications in myriad areas including remote sensing, biomedical science, military, and many other fields with their electrical tunability and strong interaction with light. In this work, we study the excitations and propagation properties of plasma waves in nanometric graphene FETs down to the scaling limit. Due to the quantum-capacitance effect, the plasma wave exhibits strong correlation with the distribution of density of states (DOS). It is indicated that the electrically tunable plasma resonance has a power-dependent V0.8TG relation on the gate voltage, which originates from the linear dependence of density of states (DOS) on the energy in pristine graphene, in striking difference to those dominated by classical capacitance with only V0.5TG dependence. The results of different transistor sizes indicate the potential application of nanometric graphene FETs in highly-efficient electro-optic modulation or detection of terahertz or infrared radiation. In addition, we highlight the perspectives of plasma resonance excitation in probing the many-body interaction and quantum matter state in strong correlation electron systems. This study reveals the key feature of plasma waves in decorated/nanometric graphene FETs, and paves the way to tailor plasma band-engineering and expand its application in both terahertz and mid-infrared regions.Plasma waves in graphene field-effect transistors (FETs) and nano-patterned graphene sheets have emerged as very promising candidates for potential terahertz and infrared applications in myriad areas including remote sensing, biomedical science, military, and many other fields with their electrical tunability and strong interaction with light. In this work, we study the excitations and propagation properties of plasma waves in nanometric graphene FETs down to the scaling limit. Due to the quantum-capacitance effect, the plasma wave exhibits strong correlation with the distribution of density of states (DOS). It is indicated that the electrically tunable plasma resonance has a power-dependent V0.8TG relation on the gate voltage, which originates from the linear dependence of density of states (DOS) on the energy in pristine graphene, in striking difference to those dominated by classical capacitance with only V0.5TG dependence. The results of different transistor sizes indicate the potential application of nanometric graphene FETs in highly-efficient electro-optic modulation or detection of terahertz or infrared radiation. In addition, we highlight the perspectives of plasma resonance excitation in probing the many-body interaction and quantum matter state in strong correlation electron systems. This study reveals the key feature of plasma waves in decorated/nanometric graphene FETs, and paves the way to tailor plasma band-engineering and expand its application in both terahertz and mid-infrared regions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07689c

Coherent and tunable terahertz radiation from graphene surface plasmon polaritons excited by an electron beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Shenggang, E-mail: liusg@uestc.edu.cn; Hu, Min; Chen, Xiaoxing

2014-05-19

Although surface plasmon polaritons (SPPs) resonance in graphene can be tuned in the terahertz regime, transforming such SPPs into coherent terahertz radiation has not been achieved. Here, we propose a graphene-based coherent terahertz radiation source with greatly enhanced intensity. The radiation works at room temperature, it is tunable and can cover the whole terahertz regime. The radiation intensity generated with this method is 400 times stronger than that from SPPs at a conventional dielectric or semiconducting surface and is comparable to that from the most advanced photonics source such as a quantum cascade laser. The physical mechanism for this strongmore » radiation is presented. The phase diagrams defining the parameters range for the occurrence of radiation is also shown.« less

Room temperature broadband terahertz gains in graphene heterostructures based on inter-layer radiative transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Linlong; Chongqing institute of green and intelligent technology, Chinese Academy of Sciences, Chongqing, 401122; Du, Jinglei, E-mail: dujl@scu.edu.cn

We exploit inter-layer radiative transitions to provide gains to amplify terahertz waves in graphene heterostructures. This is achieved by properly doping graphene sheets and aligning their energy bands so that the processes of stimulated emissions can overwhelm absorptions. We derive an expression for the gain estimation and show the gain is insensitive to temperature variation. Moreover, the gain is broadband and can be strong enough to compensate the free carrier loss, indicating graphene based room temperature terahertz lasers are feasible.

A nonlinear analysis of the terahertz serpentine waveguide traveling-wave amplifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Ke, E-mail: like.3714@163.com; Cao, Miaomiao, E-mail: mona486@yeah.net; Institute of Electronics, University of Chinese Academy of Sciences, Beijing 100190

A nonlinear model for the numerical simulation of terahertz serpentine waveguide traveling-wave tube (SW-TWT) is described. In this model, the electromagnetic wave transmission in the SW is represented as an infinite set of space harmonics to interact with an electron beam. Analytical expressions for axial electric fields in axisymmetric interaction gaps of SW-TWTs are derived and compared with the results from CST simulation. The continuous beam is treated as discrete macro-particles with different initial phases. The beam-tunnel field equations, space-charge field equations, and motion equations are combined to solve the beam-wave interaction. The influence of backward wave and relativistic effectmore » is also considered in the series of equations. The nonlinear model is used to design a 340 GHz SW-TWT. Several favorable comparisons of model predictions with results from a 3-D Particle-in-cell simulation code CHIPIC are presented, in which the output power versus beam voltage and interaction periods are illustrated. The relative error of the predicted output power is less than 15% in the 3 dB bandwidth and the relative error of the saturated length is less than 8%.The results show that the 1-D nonlinear analysis model is appropriate to solve the terahertz SW-TWT operation characteristics.« less

Feasibility of graphene CRLH metamaterial waveguides and leaky wave antennas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chu, Derrick A.; Itoh, Tatsuo; Hon, Philip W. C.

2016-07-07

The feasibility of composite right/left-handed (CRLH) metamaterial waveguides based upon graphene plasmons is demonstrated via numerical simulation. Designs are presented that operate in the terahertz frequency range along with their various dimensions. Dispersion relations, radiative and free-carrier losses, and free-carrier based tunability are characterized. Finally, the radiative characteristics are evaluated, along with its feasibility for use as a leaky-wave antenna. While CRLH waveguides are feasible in the terahertz range, their ultimate utility will require precise nanofabrication, and excellent quality graphene to mitigate free-carrier losses.

Magnetically controlled terahertz modulator based on Fe3O4 nanoparticle ferrofluids

NASA Astrophysics Data System (ADS)

Liu, Xin; Xiong, Luyao; Yu, Xiang; He, Shuli; Zhang, Bo; Shen, Jingling

2018-03-01

A multifunctional terahertz (THz) wave modulator fabricated from Fe3O4 nanoparticle ferrofluids and metamaterials was characterized in externally applied magnetic fields. Specifically, modulation depths and frequency shifts by the wave modulators were examined. A 34% THz amplitude modulation depth was demonstrated and the absorption peak of the metamaterial induced a frequency shift of 33 GHz at low magnetic field intensities. It is anticipated that this device structure and its tunable properties will have many potential applications in THz filtering, modulation, and sensing.

Operation of Terahertz Quantum-cascade Lasers at 164 K in Pulsed Mode and at 117 K in Continuous-wave Mode

NASA Technical Reports Server (NTRS)

Williams, Benjamin S.; Kumar, Sushil; Hu, Qing; Reno, John L.

2005-01-01

We report the demonstration of a terahertz quantum-cascade laser that operates up to 164 K in pulsed mode and 117 K in continuous-wave mod e at approximately 3.0 THz. The active region was based on a resonant -phonon depopulation scheme and a metal-metal waveguide was used for modal confinement. Copper to copper thermocompression wafer bonding w as used to fabricate the waveguide, which displayed improved thermal properties compared to a previous indium-gold bonding method.

Photonic-crystal diplexers for terahertz-wave applications.

PubMed

Yata, Masahiro; Fujita, Masayuki; Nagatsuma, Tadao

2016-04-04

A compact diplexer is designed using a silicon photonic-crystal directional coupler of length comparable to the incident wavelength. The diplexer theoretically and experimentally exhibits a cross state bandwidth as broad as 2% of the operation frequency, with over 40-dB isolation between the cross and bar ports. We also demonstrate 1.5-Gbit/s frequency-division communication in the 0.32- and 0.33-THz bands using a single-wavelength-sized diplexer, and discuss the transmission bandwidth. Our study demonstrates the potential for application of photonic crystals as terahertz-wave integration platforms.

Phonon-wave-induced resonance fluorescence in semiconductor nanostructures: acoustoluminescence in the terahertz range.

PubMed

Ahn, K J; Milde, F; Knorr, A

2007-01-12

Acoustic wave excitation of semiconductor quantum dots generates resonance fluorescence of electronic intersublevel excitations. Our theoretical analysis predicts acoustoluminescence, in particular, a conversion of acoustic into electromagnetic THz waves over a broad spectral range.

Single-Cycle Terahertz Pulse Generation from OH1 Crystal via Cherenkov Phase Matching

NASA Astrophysics Data System (ADS)

Uchida, Hirohisa; Oota, Kengo; Okimura, Koutarou; Kawase, Kodo; Takeya, Kei

2018-06-01

OH1 crystal is an organic nonlinear optical crystal with a large nonlinear optical constant. However, it has dispersion of refractive indices in the terahertz (THz) frequency. This limits the frequencies that satisfy the phase matching conditions for THz wave generation. In this study, we addressed the phase matching conditions for THz wave generation by combining an OH1 crystal with prism-coupled Cherenkov phase matching. We observed the generation of single-cycle THz pulses with a spectrum covering a frequency range of 3 THz. These results prove that combining prism-coupled Cherenkov phase matching with nonlinear optical crystals yields a THz wave generation method that is insusceptible to crystal dispersion.

Single-Cycle Terahertz Pulse Generation from OH1 Crystal via Cherenkov Phase Matching

NASA Astrophysics Data System (ADS)

Uchida, Hirohisa; Oota, Kengo; Okimura, Koutarou; Kawase, Kodo; Takeya, Kei

2018-03-01

OH1 crystal is an organic nonlinear optical crystal with a large nonlinear optical constant. However, it has dispersion of refractive indices in the terahertz (THz) frequency. This limits the frequencies that satisfy the phase matching conditions for THz wave generation. In this study, we addressed the phase matching conditions for THz wave generation by combining an OH1 crystal with prism-coupled Cherenkov phase matching. We observed the generation of single-cycle THz pulses with a spectrum covering a frequency range of 3 THz. These results prove that combining prism-coupled Cherenkov phase matching with nonlinear optical crystals yields a THz wave generation method that is insusceptible to crystal dispersion.

Progress in terahertz nondestructive testing: A review

NASA Astrophysics Data System (ADS)

Zhong, Shuncong

2018-05-01

Terahertz (THz) waves, whose frequencies range between microwave and infrared, are part of the electromagnetic spectrum. A gap exists in THz literature because investigating THz waves is difficult due to the weak characteristics of the waves and the lack of suitable THz sources and detectors. Recently, THz nondestructive testing (NDT) technology has become an interesting topic. This review outlines several typical THz devices and systems and engineering applications of THz NDT techniques in composite materials, thermal barrier coatings, car paint films, marine protective coatings, and pharmaceutical tablet coatings. THz imaging has higher resolution but lower penetration than ultrasound imaging. This review presents the significance and advantages provided by the emerging THz NDT technique.

Measurement of beam profiles by terahertz sensor card with cholesteric liquid crystals.

PubMed

Tadokoro, Yuzuru; Nishikawa, Tomohiro; Kang, Boyoung; Takano, Keisuke; Hangyo, Masanori; Nakajima, Makoto

2015-10-01

We demonstrate a sensor card with cholesteric liquid crystals (CLCs) for terahertz (THz) waves generated from a nonlinear crystal pumped by a table-top laser. A beam profile of the THz waves is successfully visualized as color change by the sensor card without additional electronic devices, power supplies, and connecting cables. Above the power density of 4.3  mW/cm2, the approximate beam diameter of the THz waves is measured using the hue image that is digitalized from the picture of the sensor card. The sensor card is low in cost, portable, and suitable for various situations such as THz imaging and alignment of THz systems.

Coupling of free space sub-terahertz waves into dielectric slabs using PC waveguides.

PubMed

Ghattan, Z; Hasek, T; Shahabadi, M; Koch, M

2008-04-28

The paper presents theoretical and experimental results on photonic crystal structures which work under the self-collimation condition to couple free space waves into dielectric slabs in the sub-terahertz range. Using a standard machining process, two-dimensional photonic crystal structures consisting of a square array of air holes in the dielectric medium are fabricated. One of the structures has two adjacent parallel line-defects that improve the coupling efficiency. This leads to a combination of self-collimation and directional emission of electromagnetic waves. The experimental results are in good agreement with those of the Finite- Element-Method calculations. Experimentally we achieve a coupling efficiency of 63%.

High-power terahertz quantum cascade lasers with ∼0.23 W in continuous wave mode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xuemin; Shen, Changle; Jiang, Tao

2016-07-15

Terahertz quantum cascade lasers with a record output power up to ∼0.23 W in continuous wave mode were obtained. We show that the optimal 2.9-mm-long device operating at 3.11 THz has a low threshold current density of 270 A/cm{sup 2} at ∼15 K. The maximum operating temperature arrived at ∼65 K in continuous wave mode and the internal quantum efficiencies decreased from 0.53 to 0.19 for the devices with different cavity lengths. By using one convex lens with the effective focal length of 13 mm, the beam profile was collimated to be a quasi Gaussian distribution.

Design of a GaP/Si composite waveguide for CW terahertz wave generation via difference frequency mixing.

PubMed

Saito, Kyosuke; Tanabe, Tadao; Oyama, Yutaka

2014-06-10

We design a GaP/Si composite waveguide to achieve efficient terahertz (THz) wave generation under collinear phase-matched difference frequency mixing (DFM) between near-infrared light sources. This waveguide structure provides a strong mode confinement of both near-infrared sources and THz wave, resulting in an efficient mode overlapping. The numerical results show that the waveguide can produce guided THz wave (5.93 THz) with a power conversion efficiency of 6.6×10(-4)  W(-1). This value is larger than previously obtained with the bulk GaP crystal: 0.5×10(-9)  W(-1) [J. Lightwave Technol.27, 3057 (2009)]. Our proposed composite waveguide can be achieved by bridging the telecom wavelength and THz frequency region.

Highly nonlinear organic crystal OHQ-T for efficient ultra-broadband terahertz wave generation beyond 10 THz.

PubMed

Kang, Bong Joo; Baek, In Hyung; Lee, Seung-Heon; Kim, Won Tae; Lee, Seung-Jun; Jeong, Young Uk; Kwon, O-Pil; Rotermund, Fabian

2016-05-16

We report on efficient generation of ultra-broadband terahertz (THz) waves via optical rectification in a novel nonlinear organic crystal with acentric core structure, i.e. 2-(4-hydroxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate (OHQ-T), which possesses an ideal molecular structure leading to a maximized nonlinear optical response for near-infrared-pumped THz wave generation. By systematic studies on wavelength-dependent phase-matching conditions in OHQ-T crystals of different thicknesses we are able to generate coherent THz waves with a high peak-to-peak electric field amplitude of up to 650 kV/cm and an upper cut-off frequency beyond 10 THz. High optical-to-THz conversion efficiency of 0.31% is achieved by efficient index matching with a selective pumping at 1300 nm.

Terahertz spectroscopic investigations of leather in terahertz wave range

NASA Astrophysics Data System (ADS)

Song, Mei-jing; Li, Jiu-sheng

2012-03-01

Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse are measured. Recently, material characterization using THz spectroscopy has been applied to biochemicals, pharmaceuticals, polymers and semiconductors and has given us important information. Moreover, THz imaging has progressed and is expected to be applicable for the identification of narcotics and explosives. The most important and characteristic point of THz spectroscopy is said to be its ability to observe intermolecular vibrations in contrast to infrared spectroscopy (IR), which observes intramolecular vibrations. Coherent detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. Terahertz wave spectroscopy has been used to study the properties and absorption spectra characteristic of materials. In this paper, the spectral characteristics of cow skin, pig skin sheep skin, horse skin and deer skin have been measured with terahertz time-domain spectroscopy in the range of 0.1~2.0THz. The results show that THz-TDS technology provides an important tool for quality analysis and detection of leathers.

Detection of terahertz radiation in metamaterials: giant plasmonic ratchet effect (Conference Presentation)

NASA Astrophysics Data System (ADS)

Rudin, Sergey; Rupper, Greg; Kachorovski, Valentin; Shur, Michael S.

2017-05-01

The electromagnetic wave impinging on the spatially modulated two-dimensional electron liquid (2DEL) induces a direct current (DC) when the wave amplitude modulated with the same wave vector as the 2DEL but is shifted in phase (the ratchet effect). The recent theory of this phenomenon predicted a dramatic enhancement at the plasmonic resonances and a non-trivial polarization dependence [1]. We will present the results of the numerical simulations using a hydrodynamic model exploring the helicity dependence of the DC current for silicon, InGaAs, and GaN metamaterial structures at cryogenic and room temperatures. In particular we will report on the effect of the DEL viscosity and explore the nonlinear effects at large amplitudes of the helical electromagnetic radiation impinging on the ratchet structures. We will then discuss the applications of the ratchet effect for terahertz metamaterials in order to realize ultra-sensitive terahertz (THz) radiation detectors, modulators, phase shifters, and delay lines with cross sections matching the terahertz wavelength and capable of determining the electromagnetic wave polarization and helicity. To this end, we propose and analyze the four contact ratchet devices capable of registering the two perpendicular components of the electric currents induced by the elliptically or circularly polarized radiation and analyze the load impedance effects in the structures optimized for the ratchet metamaterial THz components. The analysis is based on the hydrodynamic model suitable for the multi-gated semiconductor structures, coupled self-consistently with Poisson's equation for the electric potential. The model accounts for the effects of pressure gradients and 2DEL viscosity. Our numerical solutions are applicable to the wide ranges of electron mobility and terahertz power. [1] I. V. Rozhansky, V. Yu. Kachorovskii, and M. S. Shur, Helicity-Driven Ratchet Effect Enhanced by Plasmons, Phys. Rev. Lett. 114, 246601, 15 June 2015

Applications of surface plasmon polaritons in terahertz spectral regime

NASA Astrophysics Data System (ADS)

Zhan, Hui

This thesis presents the experimental work on the applications of surface plasmon polariton (SPP) in terahertz (THz) spectral range. Apertureless near-field optical microscopy (ANSOM) has been widely used to study the localized SPP on various material surfaces. THz ANSOM technique was recently developed to combine the THz time-domain spectroscopy and the ANSOM technique to provide a near-field detection on the localized THz surface waves with improved spatial resolution and signal-noise ratio. We have studied the metal-insulator transition in vanadium dioxide (VO2) thin film using THz ANSOM. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of metallic domains, which exist in the VO2 thin films in the vicinity of the phase transition. We experimentally investigate the propagation of guided waves in finite-width parallel-plate waveguides (PPWGs) in the terahertz spectral range. We observe the propagation of SPPs in this guiding structure, instead of the fundamental transverse electromagnetic (TEM) mode. We find that the two-dimensional (2-D) energy confinement within the finite-width PPWG increases exponentially as the plate separation is reduced. We speculate that edge plasmons play an important role in the energy confinement in this open-structure waveguide. For comparison, the infinite-width PPWGs, the plates of which are much wider than the THz beam size, are also studied with several plate separations. The free-space beam diffraction produces a Gaussian profile along the unconfined direction. The unusual electric field profiles along the vertical direction, perpendicular to the plate are observed. The field enhancement near the metal surfaces are also explained by the SPPs coupled to the metal surfaces. Based on the 2-D energy confinement in the finite-width PPWGs, we design the tapered slot waveguide by slowly tapering the plate width and slot gap. We first study the transverse component of the THz electric field, where a subwavelength 2-D energy confinement is observed. The output spot size strongly depends on the output facet size, where the slot gap and the tip width are in the same scale range. Subwavelength confinement is obtained, corresponding to lambda/4. Further confinement is limited by the spatial resolution of the detecting technique. To overcome this problem, we adapt the THz ASNOM setup to scattering-probe imaging technique, which has been proven to obtain deep subwavelength spatial resolution and great signal-noise ratio. Scattering-probe imaging setup measures the longitudinal component of the electric field of SPPs in the tapered slot waveguides. By slowly tapering the tip width and the slot gap, we squeeze a single-cycle THz pulse down to a size of 10 mum (lambda/260) by 18 mum (lambda/145), a mode area of only 2.6 x 10-5lambda2. We also observe a polarity reversal for the electric field between the guiding region near the upper and lower plates of the waveguide. This polarity flip is similar to that associated with the symmetric plasmon mode of slot waveguides.

Terahertz Radiation from Laser Created Plasma by Applying a Transverse Static Electric Field

NASA Astrophysics Data System (ADS)

Fukuda, Takuya; Katahira, Koji; Yugami, Noboru; Sentoku, Yasuhiko; Sakagami, Hitoshi; Nagatomo, Hideo

2016-10-01

Terahertz (THz) radiation, which is emitted in narrow cone in the forward direction from laser created plasma has been observed by N.Yugami et al.. Additionally, Löffler et al. have observed that a significantly increased THz emission intensity in the forward direction when the transverse static electric field is applied to the plasma. The purpose of our study is to derive the mechanism of the THz radiation from laser created plasma by applying the transverse static electric field. To study the radiation mechanism, we conducted 2D-PIC simulation. With the static electric field of 10 kV/cm and gas density of 1020 cm-3, we obtain 1.2 THz single cycle pulse radiation, whose intensity is 1.3 ×105 W/cm2. The magnetic field called ``picket fence mode'' is generated in the laser created plasma. At the boundary surface between the plasma and vacuum, the magnetic field is canceled because eddy current flows. We conclude that the temporal behavior of the magnetic field at the boundary surface radiates the THz wave.

Flat Terahertz Reflective Focusing Metasurface with Scanning Ability.

PubMed

Yi, Huan; Qu, Shi-Wei; Chen, Bao-Jie; Bai, Xue; Ng, Kung Bo; Chan, Chi Hou

2017-06-14

The ability to manipulate the propagation properties of electromagnetic waves, e.g., divergence, focusing, holography or deflection, is very significant in terahertz applications. Metasurfaces with flat structures are attractive for achieving such manipulations in terahertz band, as they feature low profile, lightweight, and ease of design and installation. Several types of terahertz reflective or transmitting metasurfaces with focusing function have been implemented recently, but none of them can provide scanning ability with controllable focus. Here, a flat reflective metasurface featuring controllable focal shift is proposed and experimentally demonstrated. Furthermore, the principle of designing a focus scanning reflective metasurface is presented and the focusing characteristics are discussed, including focus scanning along a line parallel or orthogonal to the metasurface with a large bandwidth. These interesting properties indicate that this flat reflective metasurface could play a key role in many terahertz imaging and detection systems.

Tunable terahertz waves from 4-dimethylamino-N‧-methyl-4‧-stibazolium tosylate pumped with dual-wavelength injection-seeded optical parametric generation

NASA Astrophysics Data System (ADS)

Tokizane, Yu; Nawata, Kouji; Han, Zhengli; Koyama, Mio; Notake, Takashi; Takida, Yuma; Minamide, Hiroaki

2017-02-01

We developed a widely tunable terahertz (THz)-wave source covering the sub-THz frequency by difference frequency generation using a 4-dimethylamino-N‧-methyl-4‧-stibazolium tosylate (DAST) crystal. Near-infrared waves generated by dual-wavelength injection-seeded β-BaB2O4 optical parametric generation (is-BBO-OPG) were used for pumping the DAST crystal, which had separated wavelengths in the spectrum with a difference frequency of sub-THz. Furthermore, the non-collinear phase-matching condition was designed to compensate the walk-off effect of the BBO crystal. Consequently, tunable THz-waves from 0.3 to 4 THz were generated by tuning the wavelength of one of the seeding beams. The generated sub-THz-waves were monochromatic (dν < 33 GHz) with a maximum energy of 80 pJ at 0.65 THz.

Polymer Morphological Change Induced by Terahertz Irradiation

NASA Astrophysics Data System (ADS)

Hoshina, Hiromichi; Suzuki, Hal; Otani, Chiko; Nagai, Masaya; Kawase, Keigo; Irizawa, Akinori; Isoyama, Goro

2016-06-01

As terahertz (THz) frequencies correspond to those of the intermolecular vibrational modes in a polymer, intense THz wave irradiation affects the macromolecular polymorph, which determines the polymer properties and functions. THz photon energy is quite low compared to the covalent bond energy; therefore, conformational changes can be induced “softly,” without damaging the chemical structures. Here, we irradiate a poly(3-hydroxybutylate) (PHB) / chloroform solution during solvent casting crystallization using a THz wave generated by a free electron laser (FEL). Morphological observation shows the formation of micrometer-sized crystals in response to the THz wave irradiation. Further, a 10-20% increase in crystallinity is observed through analysis of the infrared (IR) absorption spectra. The peak power density of the irradiating THz wave is 40 MW/cm2, which is significantly lower than the typical laser intensities used for material manipulation. We demonstrate for the first time that the THz wave effectively induces the intermolecular rearrangement of polymer macromolecules.

Sub-terahertz and terahertz microstrip resonant-tunneling-diode oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feiginov, Michael, E-mail: feiginov.michael@canon.co.jp

We present a theoretical analysis of traveling-wave microstrip resonant-tunneling-diode (RTD) oscillators. Such oscillators are similar to terahertz (THz) quantum-cascade lasers (QCLs) with a metal-metal waveguide and with just the active part of a single QCL period (an RTD) as their active core. Assuming realistic parameters of RTDs, we show that the microstrip RTD oscillators should be working at sub-THz and THz frequencies. Contrary to the contemporary THz QCLs, RTD microstrips are room-temperature oscillators. The major loss- and gain-enhancement mechanisms in RTD microstrips are identified.

Conditions for optimal efficiency of PCBM-based terahertz modulators

NASA Astrophysics Data System (ADS)

Yoo, Hyung Keun; Lee, Hanju; Lee, Kiejin; Kang, Chul; Kee, Chul-Sik; Hwang, In-Wook; Lee, Joong Wook

2017-10-01

We demonstrate the conditions for optimal modulation efficiency of active terahertz modulators based on phenyl-C61-butyric acid methyl ester (PCBM)-silicon hybrid structures. Highly efficient active control of the terahertz wave modulation was realized by controlling organic film thickness, annealing temperature, and laser excitation wavelength. Under the optimal conditions, the modulation efficiency reached nearly 100%. Charge distributions measured with a near-field scanning microwave microscanning technique corroborated the fact that the increase of photo-excited carriers due to the PCBM-silicon hybrid structure enables the enhancement of active modulation efficiency.

A Tri-Band Frequency Selective Surface (FSS) to Diplex Widely Separated Bands for Millimeter Wave Remote Sensing

NASA Astrophysics Data System (ADS)

Poojali, Jayaprakash; Ray, Shaumik; Pesala, Bala; Chitti, Krishnamurthy V.; Arunachalam, Kavitha

2016-10-01

A substrate-backed frequency selective surface (FSS) is presented for diplexing the widely separated frequency spectrum centered at 55, 89, and 183 GHz with varying bandwidth for spatial separation in the quasi-optical feed network of the millimeter wave sounder. A unit cell composed of a crossed dipole integrated with a circular ring and loaded inside a square ring is optimized for tri-band frequency response with transmission window at 89 GHz and rejection windows at 55 and 183 GHz. The reflection and transmission losses predicted for the optimized unit cell (728 μm × 728 μm) composed of dissimilar resonant shapes is less than 0.5 dB for transverse electric (TE) and transverse magnetic (TM) polarizations and wide angle of incidence (0°-45°). The FSS is fabricated on a 175-μm-thick quartz substrate using microfabrication techniques. The transmission characteristics measured with continuous wave (CW) terahertz transmit receive system are in good agreement with the numerical simulations.

Thermal radiation scanning tunnelling microscopy

NASA Astrophysics Data System (ADS)

de Wilde, Yannick; Formanek, Florian; Carminati, Rémi; Gralak, Boris; Lemoine, Paul-Arthur; Joulain, Karl; Mulet, Jean-Philippe; Chen, Yong; Greffet, Jean-Jacques

2006-12-01

In standard near-field scanning optical microscopy (NSOM), a subwavelength probe acts as an optical `stethoscope' to map the near field produced at the sample surface by external illumination. This technique has been applied using visible, infrared, terahertz and gigahertz radiation to illuminate the sample, providing a resolution well beyond the diffraction limit. NSOM is well suited to study surface waves such as surface plasmons or surface-phonon polaritons. Using an aperture NSOM with visible laser illumination, a near-field interference pattern around a corral structure has been observed, whose features were similar to the scanning tunnelling microscope image of the electronic waves in a quantum corral. Here we describe an infrared NSOM that operates without any external illumination: it is a near-field analogue of a night-vision camera, making use of the thermal infrared evanescent fields emitted by the surface, and behaves as an optical scanning tunnelling microscope. We therefore term this instrument a `thermal radiation scanning tunnelling microscope' (TRSTM). We show the first TRSTM images of thermally excited surface plasmons, and demonstrate spatial coherence effects in near-field thermal emission.

Terahertz Spectroscopy of Individual Single-Walled Carbon Nanotubes as a Probe of Luttinger Liquid Physics.

PubMed

Chudow, Joel D; Santavicca, Daniel F; Prober, Daniel E

2016-08-10

Luttinger liquid theory predicts that collective electron excitations due to strong electron-electron interactions in a one-dimensional (1D) system will result in a modification of the collective charge-propagation velocity. By utilizing a circuit model for an individual metallic single-walled carbon nanotube as a nanotransmission line, it has been shown that the frequency-dependent terahertz impedance of a carbon nanotube can probe this expected 1D Luttinger liquid behavior. We excite terahertz standing-wave resonances on individual antenna-coupled metallic single-walled carbon nanotubes. The terahertz signal is rectified using the nanotube contact nonlinearity, allowing for a low-frequency readout of the coupled terahertz current. The charge velocity on the nanotube is determined from the terahertz spectral response. Our measurements show that a carbon nanotube can behave as a Luttinger liquid system with charge-propagation velocities that are faster than the Fermi velocity. Understanding what determines the charge velocity in low-dimensional conductors is important for the development of next generation nanodevices.

Electrically controlled wire-channel GaN/AlGaN transistor for terahertz plasma applications

NASA Astrophysics Data System (ADS)

Cywiński, G.; Yahniuk, I.; Kruszewski, P.; Grabowski, M.; Nowakowski-Szkudlarek, K.; Prystawko, P.; Sai, P.; Knap, W.; Simin, G. S.; Rumyantsev, S. L.

2018-03-01

We report on a design of fin-shaped channel GaN/AlGaN field-effect transistors developed for studying resonant terahertz plasma oscillations. Unlike common two dimensional FinFET transistor design, the gates were deposited only to the sides of the two dimensional electron gas channel, i.e., metal layers were not deposited on the top of the AlGaN. This side gate configuration allowed us to electrically control the conductivity of the channel by changing its width while keeping the carrier density and mobility virtually unchanged. Computer simulations and analytical model describe well the general shape of the characteristics. The side gate control of the channel width of these transistors allowed us to eliminate the so-called oblique plasma wave modes and paves the way towards future terahertz detectors and emitters using high quality factor plasma wave resonances.

Design of a terahertz parametric oscillator based on a resonant cavity in a terahertz waveguide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saito, K., E-mail: k-saito@material.tohoku.ac.jp; Oyama, Y.; Tanabe, T.

We demonstrate ns-pulsed pumping of terahertz (THz) parametric oscillations in a quasi-triply resonant cavity in a THz waveguide. The THz waves, down converted through parametric interactions between the pump and signal waves at telecom frequencies, are confined to a GaP single mode ridge waveguide. By combining the THz waveguide with a quasi-triply resonant cavity, the nonlinear interactions can be enhanced. A low threshold pump intensity for parametric oscillations can be achieved in the cavity waveguide. The THz output power can be maximized by optimizing the quality factors of the cavity so that an optical to THz photon conversion efficiency, η{submore » p}, of 0.35, which is near the quantum-limit level, can be attained. The proposed THz optical parametric oscillator can be utilized as an efficient and monochromatic THz source.« less

Detecting the propagation effect of terahertz wave inside the two-color femtosecond laser filament in the air

NASA Astrophysics Data System (ADS)

Zhao, J.; Zhang, X.; Li, S.; Liu, C.; Chen, Y.; Peng, Y.; Zhu, Y.

2018-03-01

In this work, to decide the existence of terahertz (THz) wave propagation effect, THz pulses emitted from a blocked two-color femtosecond laser filament with variable length were recorded by a standard electric-optic sampling setup. The phenomenon of temporal advance of the THz waveform's peak with the increasing filament length has been observed. Together with another method of knife-edge measurement which aims at directly retrieving the THz beam diameter, both the experimental approaches have efficiently indicated the same filament range within which THz wave propagated inside the plasma column. At last, a preliminary two-dimensional near-field scanning imaging of the THz spot inside the cross section of the filament has been suggested as the third way to determine the issue of THz wave propagation effect.

Polarization control of terahertz waves generated by circularly polarized few-cycle laser pulses

NASA Astrophysics Data System (ADS)

Song, Liwei; Bai, Ya; Xu, Rongjie; Li, Chuang; Liu, Peng; Li, Ruxin; Xu, Zhizhan

2013-12-01

We demonstrate the generation and control of elliptically polarized terahertz (THz) waves from air plasma produced by circularly polarized few-cycle laser pulses. Experimental and calculated results reveal that electric field asymmetry in rotating directions of the circularly polarized few-cycle laser pulses produces the enhanced broadband transient currents, and the phase difference of perpendicular laser field components is partially inherited in the generation process of THz emission. The ellipticity of the THz emission and its major axis direction are all-optically controlled by the duration and carrier-envelope phase of the laser pulses.

NDE Imaging of Time Differential Terahertz Waves

NASA Technical Reports Server (NTRS)

Trinh, Long B.

2008-01-01

Natural voids are present in the vicinity of a conathane interface that bonds two different foam materials. These voids are out of focus with the terahertz imaging system and multiple optical reflections also make it difficult to determine their depths. However, waves passing through the top foam article at normal incidence are partially reflected at the denser conathane layer prior to total reflection at the tank s wall. Reflections embedded in the oscillating noise segment prior to the main signals can be extracted with dual applications of filtering and time derivative. Void's depth is computed from direct path's time of flight.

Dual-axis reflective continuous-wave terahertz confocal scanning polarization imaging and image fusion

NASA Astrophysics Data System (ADS)

Zhou, Yi; Li, Qi

2017-01-01

A dual-axis reflective continuous-wave terahertz (THz) confocal scanning polarization imaging system was adopted. THz polarization imaging experiments on gaps on film and metallic letters "BeLLE" were carried out. Imaging results indicate that the THz polarization imaging is sensitive to the tilted gap or wide flat gap, suggesting the THz polarization imaging is able to detect edges and stains. An image fusion method based on the digital image processing was proposed to ameliorate the imaging quality of metallic letters "BeLLE." Objective and subjective evaluation both prove that this method can improve the imaging quality.

High-contrast terahertz wave modulation by gated graphene enhanced by extraordinary transmission through ring apertures.

PubMed

Gao, Weilu; Shu, Jie; Reichel, Kimberly; Nickel, Daniel V; He, Xiaowei; Shi, Gang; Vajtai, Robert; Ajayan, Pulickel M; Kono, Junichiro; Mittleman, Daniel M; Xu, Qianfan

2014-03-12

Gate-controllable transmission of terahertz (THz) radiation makes graphene a promising material for making high-speed THz wave modulators. However, to date, graphene-based THz modulators have exhibited only small on/off ratios due to small THz absorption in single-layer graphene. Here we demonstrate a ∼50% amplitude modulation of THz waves with gated single-layer graphene by the use of extraordinary transmission through metallic ring apertures placed right above the graphene layer. The extraordinary transmission induced ∼7 times near-filed enhancement of THz absorption in graphene. These results promise complementary metal-oxide-semiconductor compatible THz modulators with tailored operation frequencies, large on/off ratios, and high speeds, ideal for applications in THz communications, imaging, and sensing.

Tunable continuous-wave terahertz generation/detection with compact 1.55 μm detuned dual-mode laser diode and InGaAs based photomixer.

PubMed

Kim, Namje; Han, Sang-Pil; Ko, Hyunsung; Leem, Young Ahn; Ryu, Han-Cheol; Lee, Chul Wook; Lee, Donghun; Jeon, Min Yong; Noh, Sam Kyu; Park, Kyung Hyun

2011-08-01

We demonstrate a tunable continuous-wave (CW) terahertz (THz) homodyne system with a novel detuned dual-mode laser diode (DML) and low-temperature-grown (LTG) InGaAs photomixers. The optical beat source with the detuned DML showed a beat frequency tuning range of 0.26 to over 1.07 THz. Log-spiral antenna integrated LTG InGaAs photomixers are used as THz wave generators and detectors. The CW THz radiation frequency was continuously tuned to over 1 THz. Our results clearly show the feasibility of a compact and fast scanning CW THz spectrometer consisting of a fiber-coupled detuned DML and photomixers operating in the 1.55-μm range.

High-precision terahertz frequency modulated continuous wave imaging method using continuous wavelet transform

NASA Astrophysics Data System (ADS)

Zhou, Yu; Wang, Tianyi; Dai, Bing; Li, Wenjun; Wang, Wei; You, Chengwu; Wang, Kejia; Liu, Jinsong; Wang, Shenglie; Yang, Zhengang

2018-02-01

Inspired by the extensive application of terahertz (THz) imaging technologies in the field of aerospace, we exploit a THz frequency modulated continuous-wave imaging method with continuous wavelet transform (CWT) algorithm to detect a multilayer heat shield made of special materials. This method uses the frequency modulation continuous-wave system to catch the reflected THz signal and then process the image data by the CWT with different basis functions. By calculating the sizes of the defects area in the final images and then comparing the results with real samples, a practical high-precision THz imaging method is demonstrated. Our method can be an effective tool for the THz nondestructive testing of composites, drugs, and some cultural heritages.

Electrically tunable terahertz wave modulator based on complementary metamaterial and graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Xun-jun, E-mail: hexunjun@hrbust.edu.cn; Li, Teng-yue; Wang, Lei

2014-05-07

In this paper, we design and numerically demonstrate an electrically controllable light-matter interaction in a hybrid material/metamaterial system consisting of an artificially constructed cross cut-wire complementary metamaterial and an atomically thin graphene layer to realize terahertz (THz) wave modulator. By applying a bias voltage between the metamaterial and the graphene layer, this modulator can dynamically control the amplitude and phase of the transmitted wave near 1.43 THz. Moreover, the distributions of current density show that this large modulation depth can be attributed to the resonant electric field parallel to the graphene sheet. Therefore, the modulator performance indicates the enormous potentialmore » of graphene for developing sophisticated THz communication systems.« less

Diffraction-limited real-time terahertz imaging by optical frequency up-conversion in a DAST crystal.

PubMed

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Takida, Yuma; Matsukawa, Takeshi; Minamide, Hiroaki

2015-03-23

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and the arts. This report describes real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in an organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate (DAST) crystal, with high resolution reaching the diffraction limit. THz-wave images were converted to the near infrared region and then captured using an InGaAs camera in a tandem imaging system. The resolution of the imaging system was analyzed. Diffraction and interference of THz wave were observed in the experiments. Videos are supplied to show the interference pattern variation that occurs with sample moving and tilting.

Role of vanguard counter-potential in terahertz emission due to surface currents explicated by three-dimensional ensemble Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Cortie, D. L.; Lewis, R. A.

2011-10-01

The discovery that short pulses of near-infrared radiation striking a semiconductor may lead to emission of radiation at terahertz frequencies paved the way for terahertz time-domain spectroscopy. Previous modeling has allowed the physical mechanisms to be understood in general terms but it has not fully explored the role of key physical parameters of the emitter material nor has it fully revealed the competing nature of the surface-field and photo-Dember effects. In this context, our purpose has been to more fully explicate the mechanisms of terahertz emission from transient currents at semiconductor surfaces and to determine the criteria for efficient emission. To achieve this purpose we employ an ensemble Monte Carlo simulation in three dimensions. To ground the calculations, we focus on a specific emitter, InAs. We separately vary distinct physical parameters to determine their specific contribution. We find that scattering as a whole has relatively little impact on the terahertz emission. The emission is found to be remarkably resistant to alterations of the dark surface potential. Decreasing the band gap leads to a strong increase in terahertz emission, as does decreasing the electron mass. Increasing the absorption dramatically influences the peak-peak intensity and peak shape. We conclude that increasing absorption is the most direct path to improve surface-current semiconductor terahertz emitters. We find for longer pump pulses that the emission is limited by a newly identified vanguard counter-potential mechanism: Electrons at the leading edge of longer laser pulses repel subsequent electrons. This discovery is the main result of our work.

Using COMSOL Multiphysics Software to Model Anisotropic Dielectric and Metamaterial Effects in Folded-Waveguide Traveling-Wave Tube Slow-Wave Circuits

NASA Technical Reports Server (NTRS)

Starinshak, David P.; Smith, Nathan D.; Wilson, Jeffrey D.

2008-01-01

The electromagnetic effects of conventional dielectrics, anisotropic dielectrics, and metamaterials were modeled in a terahertz-frequency folded-waveguide slow-wave circuit. Results of attempts to utilize these materials to increase efficiency are presented.

Terahertz waves radiated from two noncollinear femtosecond plasma filaments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Hai-Wei; Hoshina, Hiromichi; Otani, Chiko, E-mail: otani@riken.jp

2015-11-23

Terahertz (THz) waves radiated from two noncollinear femtosecond plasma filaments with a crossing angle of 25° are investigated. The irradiated THz waves from the crossing filaments show a small THz pulse after the main THz pulse, which was not observed in those from single-filament scheme. Since the position of the small THz pulse changes with the time-delay of two filaments, this phenomenon can be explained by a model in which the small THz pulse is from the second filament. The denser plasma in the overlap region of the filaments changes the movement of space charges in the plasma, thereby changingmore » the angular distribution of THz radiation. As a result, this schematic induces some THz wave from the second filament to propagate along the path of the THz wave from the first filament. Thus, this schematic alters the direction of the THz radiation from the filamentation, which can be used in THz wave remote sensing.« less

Strong emission of terahertz radiation from nanostructured Ge surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Chul; Maeng, Inhee; Kee, Chul-Sik, E-mail: cskee@gist.ac.kr

2015-06-29

Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAsmore » for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly.« less

Terahertz Quantum Cascade Laser With Efficient Coupling and Beam Profile

NASA Technical Reports Server (NTRS)

Chattopadhyay, Goutam; Kawamura, Jonathan H.; Lin, Robert H.; Williams, Benjamin

2012-01-01

Quantum cascade lasers (QCLs) are unipolar semiconductor lasers, where the wavelength of emitted radiation is determined by the engineering of quantum states within the conduction band in coupled multiple-quantum-well heterostructures to have the desired energy separation. The recent development of terahertz QCLs has provided a new generation of solid-state sources for radiation in the terahertz frequency range. Terahertz QCLs have been demonstrated from 0.84 to 5.0 THz both in pulsed mode and continuous wave mode (CW mode). The approach employs a resonant-phonon depopulation concept. The metal-metal (MM) waveguide fabrication is performed using Cu-Cu thermo-compression bonding to bond the GaAs/AlGaAs epitaxial layer to a GaAs receptor wafer.

Graphene based terahertz phase modulators

NASA Astrophysics Data System (ADS)

Kakenov, N.; Ergoktas, M. S.; Balci, O.; Kocabas, C.

2018-07-01

Electrical control of amplitude and phase of terahertz radiation (THz) is the key technological challenge for high resolution and noninvasive THz imaging. The lack of active materials and devices hinders the realization of these imaging systems. Here, we demonstrate an efficient terahertz phase and amplitude modulation using electrically tunable graphene devices. Our device structure consists of electrolyte-gated graphene placed at quarter wavelength distance from a reflecting metallic surface. In this geometry, graphene operates as a tunable impedance surface which yields electrically controlled reflection phase. Terahertz time domain reflection spectroscopy reveals the voltage controlled phase modulation of π and the reflection modulation of 50 dB. To show the promises of our approach, we demonstrate a multipixel phase modulator array which operates as a gradient impedance surface.

Recent developments in terahertz sensing technology

NASA Astrophysics Data System (ADS)

Shur, Michael

2016-05-01

Terahertz technology has found numerous applications for the detection of biological and chemical hazardous agents, medical diagnostics, detection of explosives, providing security in buildings, airports, and other public spaces, shortrange covert communications (in the THz and sub-THz windows), and applications in radio astronomy and space research. The expansion of these applications will depend on the development of efficient electronic terahertz sources and sensitive low-noise terahertz detectors. Schottky diode frequency multipliers have emerged as a viable THz source technology reaching a few THz. High speed three terminal electronic devices (FETs and HBTs) have entered the THz range (with cutoff frequencies and maximum frequencies of operation above 1 THz). A new approach called plasma wave electronics recently demonstrated an efficient terahertz detection in GaAs-based and GaN-based HEMTs and in Si MOS, SOI, FINFETs and in FET arrays. This progress in THz electronic technology has promise for a significant expansion of THz applications.

Morphology of human sweat ducts observed by optical coherence tomography and their frequency of resonance in the terahertz frequency region

NASA Astrophysics Data System (ADS)

Tripathi, Saroj R.; Miyata, Eisuke; Ishai, Paul Ben; Kawase, Kodo

2015-03-01

It is crucial to understand the various biological effects induced by terahertz (THz) electromagnetic waves with the rapid development of electronic and photonic devices operating in the THz frequency region. The presence of sweat glands plays an important role in THz wave interactions with human skin. We investigated the morphological features of sweat ducts using optical coherence tomography (OCT) to further understand such phenomena. We observed remarkable features of the ducts, such as their clear helical structure. The intersubject and intrasubject variations in the diameter of sweat ducts were considerably smaller than the variations in other structural parameters, such as length and number of turns. Based on the sweat duct dimensions and THz dielectric properties of skin measured using terahertz time-domain spectroscopy (THz-TDS), we calculated the resonating frequency of the sweat duct under the assumption of it functioning as a helical antenna. Here, we show that the resonance frequency in the axial mode of operation lies in the THz wave region with a centre frequency of 0.44 +/- 0.07 THz. We expect that these findings will further our understanding of the various health consequences of the interaction of THz waves with human beings.

Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes.

PubMed

Takida, Yuma; Nawata, Kouji; Suzuki, Safumi; Asada, Masahiro; Minamide, Hiroaki

2017-03-06

The sensitive detection of terahertz (THz)-wave radiation from compact sources at room temperature is crucial for real-world THz-wave applications. Here, we demonstrate the nonlinear optical detection of THz-wave radiation from continuous-wave (CW) resonant tunneling diodes (RTDs) at 0.58, 0.78, and 1.14 THz. The up-conversion process in a MgO:LiNbO₃ crystal under the noncollinear phase-matching condition offers efficient wavelength conversion from a THz wave to a near-infrared (NIR) wave that is detected using a commercial NIR photodetector. The minimum detection limit of CW THz-wave power is as low as 5 nW at 1.14 THz, corresponding to 2-aJ energy and 2.7 × 10³ photons within the time window of a 0.31-ns pump pulse. Our results show that the input frequency and power of RTD devices can be calibrated by measuring the output wavelength and energy of up-converted waves, respectively. This optical detection technique for compact electronic THz-wave sources will open up a new opportunity for the realization of real-world THz-wave applications.

Terahertz imaging systems: a non-invasive technique for the analysis of paintings

NASA Astrophysics Data System (ADS)

Fukunaga, K.; Hosako, I.; Duling, I. N., III; Picollo, M.

2009-07-01

Terahertz (THz) imaging is an emerging technique for non-invasive analysis. Since THz waves can penetrate opaque materials, various imaging systems that use THz waves have been developed to detect, for instance, concealed weapons, illegal drugs, and defects in polymer products. The absorption of THz waves by water is extremely strong, and hence, THz waves can be used to monitor the water content in various objects. THz imaging can be performed either by transmission or by reflection of THz waves. In particular, time domain reflection imaging uses THz pulses that propagate in specimens, and in this technique, pulses reflected from the surface and from the internal boundaries of the specimen are detected. In general, the internal structure is observed in crosssectional images obtained using micro-specimens taken from the work that is being analysed. On the other hand, in THz time-domain imaging, a map of the layer of interest can be easily obtained without collecting any samples. When realtime imaging is required, for example, in the investigation of the effect of a solvent or during the monitoring of water content, a THz camera can be used. The first application of THz time-domain imaging in the analysis of a historical tempera masterpiece was performed on the panel painting Polittico di Badia by Giotto, of the permanent collection of the Uffizi Gallery. The results of that analysis revealed that the work is composed of two layers of gypsum, with a canvas between these layers. In the paint layer, gold foils covered by paint were clearly observed, and the consumption or ageing of gold could be estimated by noting the amount of reflection. These results prove that THz imaging can yield useful information for conservation and restoration purposes.

Spatial and temporal ultrafast imaging and control of terahertz wavepackets

NASA Astrophysics Data System (ADS)

Koehl, Richard Michael

Some polar optical phonons couple strongly to far- infrared electromagnetic radiation and move at light-like speeds through dielectric media. These phonon-polaritons retain both ionic and electromagnetic character. One of the fruitful implications of this mixing is that vibrational and electronic nonlinearities in ferroelectric and other highly anharmonic media interact with traveling electromagnetic waves spanning several frequency regimes, permitting nonlinear wave mixing at infrared and optical frequencies. Nonlinear optical mixing techniques are well-developed because optical light is easy to produce, but the lack of similar far- infrared sources has stymied similar efforts at terahertz frequencies. Nonlinear interactions in this frequency regime provide information about vibrational potential energy surfaces and are very strong when the lattice vibration is associated with a phase transition. In this thesis, I review methods based on a well known nonlinear optical technique, impulsive stimulated Raman scattering (ISRS), to monitor the progress of coherent phonon polaritons in a highly nonlinear ferroelectric, lithium tantalate. I also advance multiple-pulse ISRS optical techniques to attempt to elucidate information about the ferroelectric's vibrational potential energy surface, and I discuss significant recent progress that has been made in the development of ultrafast optical tools to generate far-infrared radiation through ISRS at specified times and spatial locations and control the interactions of coherent phonon-polariton wavepackets. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

The interaction between electromagnetic fields at megahertz, gigahertz and terahertz frequencies with cells, tissues and organisms: risks and potential

PubMed Central

Begley, Ryan; Harvey, Alan R.; Hool, Livia; Wallace, Vincent P.

2017-01-01

Since regular radio broadcasts started in the 1920s, the exposure to human-made electromagnetic fields has steadily increased. These days we are not only exposed to radio waves but also other frequencies from a variety of sources, mainly from communication and security devices. Considering that nearly all biological systems interact with electromagnetic fields, understanding the affects is essential for safety and technological progress. This paper systematically reviews the role and effects of static and pulsed radio frequencies (100–109 Hz), millimetre waves (MMWs) or gigahertz (109–1011 Hz), and terahertz (1011–1013 Hz) on various biomolecules, cells and tissues. Electromagnetic fields have been shown to affect the activity in cell membranes (sodium versus potassium ion conductivities) and non-selective channels, transmembrane potentials and even the cell cycle. Particular attention is given to millimetre and terahertz radiation due to their increasing utilization and, hence, increasing human exposure. MMWs are known to alter active transport across cell membranes, and it has been reported that terahertz radiation may interfere with DNA and cause genomic instabilities. These and other phenomena are discussed along with the discrepancies and controversies from published studies. PMID:29212756

Hybrid metasurface for ultra-broadband terahertz modulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heyes, Jane E.; Withayachumnankul, Withawat; Grady, Nathaniel K.

2014-11-05

We demonstrate an ultra-broadband free-space terahertz modulator based on a semiconductor-integrated metasurface. The modulator is made of a planar array of metal cut-wires on a silicon-on-sapphire substrate, where the silicon layer functions as photoconductive switches. Without external excitation, the cut-wire array exhibits a Lorentzian resonant response with a transmission passband spanning dc up to the fundamental dipole resonance above 2 THz. Under photoexcitation with 1.55 eV near-infrared light, the silicon regions in the cut-wire gaps become highly conductive, causing a transition of the resonant metasurface to a wire grating with a Drude response. In effect, the low-frequency passband below 2more » THz evolves into a stopband for the incident terahertz waves. Experimental validations confirm a bandwidth of at least 100%, spanning 0.5 to 1.5 THz with -10 dB modulation depth. This modulation depth is far superior to -5 dB achievable from a plain silicon-on-sapphire substrate with effectively 25 times higher pumping energy. The proposed concept of ultra-broadband metasurface modulator can be readily extended to electrically controlled terahertz wave modulation.« less

Plasmonic waveguide with folded stubs for highly confined terahertz propagation and concentration.

PubMed

Ye, Longfang; Xiao, Yifan; Liu, Na; Song, Zhengyong; Zhang, Wei; Liu, Qing Huo

2017-01-23

We proposed a novel planar terahertz (THz) plasmonic waveguide with folded stub arrays to achieve excellent terahertz propagation performance with tight field confinement and compact size based on the concept of spoof surface plasmon polaritons (spoof SPPs). It is found that the waveguide propagation characteristics can be directly manipulated by increasing the length of the folded stubs without increasing its lateral dimension, which exhibits much lower asymptotic frequency of the dispersion relation and even tighter terahertz field confinement than conventional plasmonic waveguides with rectangular stub arrays. Based on this waveguiding scheme, a terahertz concentrator with gradual step-length folded stubs is proposed to achieve high terahertz field enhancement, and an enhancement factor greater than 20 is demonstrated. This work offers a new perspective on very confined terahertz propagation and concentration, which may have promising potential applications in various integrated terahertz plasmonic circuits and devices, terahertz sensing and terahertz nonlinear optics.

Interaction of surface plasmon polaritons and acoustic waves inside an acoustic cavity.

PubMed

Khokhlov, Nikolai; Knyazev, Grigoriy; Glavin, Boris; Shtykov, Yakov; Romanov, Oleg; Belotelov, Vladimir

2017-09-15

In this Letter, we introduce an approach for manipulation of active plasmon polaritons via acoustic waves at sub-terahertz frequency range. The acoustic structures considered are designed as phononic Fabry-Perot microresonators where mirrors are presented with an acoustic superlattice and the structure's surface, and a plasmonic grating is placed on top of the acoustic cavity so formed. It provides phonon localization in the vicinity of the plasmonic grating at frequencies within the phononic stop band enhancing phonon-light interaction. We consider phonon excitation by shining a femtosecond laser pulse on the plasmonic grating. Appropriate theoretical model was used to describe the acoustic process caused by the pump laser pulse in the GaAs/AlAs-based acoustic cavity with a gold grating on top. Strongest modulation is achieved upon excitation of propagating surface plasmon polaritons and hybridization of propagating and localized plasmons. The relative changes in the optical reflectivity of the structure are more than an order of magnitude higher than for the structure without the plasmonic film.

Polarization-sensitive electro-optic detection of terahertz wave using three different types of crystal symmetry: Toward broadband polarization spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oguchi, Kenichi; Iwasaki, Hotsumi; Okano, Makoto

2016-01-04

We investigated polarization-sensitive electro-optic (EO) detection of terahertz (THz) waves by using two uniaxial crystals: a c-cut gallium selenide and a c-cut lithium niobate crystals. We formulated a general frequency-domain description of EO detection by in-plane isotropic EO crystals, which holds regardless of the frequency. Based on this description, the polarization of THz waves can be derived by analyzing EO sampling signals measured with two orthogonal configurations of the in-plane isotropic EO crystals as well as typical (111) zinc-blende EO crystals. In addition, we experimentally demonstrated that the frequency-dependent polarization of THz waves can be reproducibly retrieved using three EOmore » crystals with different crystal symmetries and with different phase matching conditions. Our description provides essential information for practical polarization sensing in the THz frequency range as well as in the mid-infrared range.« less

THz-wave parametric sources and imaging applications

NASA Astrophysics Data System (ADS)

Kawase, Kodo

2004-12-01

We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We have also developed a novel basic technology for THz imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral trasillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

Nano-antenna in a photoconductive photomixer for highly efficient continuous wave terahertz emission

PubMed Central

Tanoto, H.; Teng, J. H.; Wu, Q. Y.; Sun, M.; Chen, Z. N.; Maier, S. A.; Wang, B.; Chum, C. C.; Si, G. Y.; Danner, A. J.; Chua, S. J.

2013-01-01

We report highly efficient continuous-wave terahertz (THz) photoconductive antenna based photomixer employing nano-gap electrodes in the active region. The tip-to-tip nano-gap electrode structure provides strong THz field enhancement and acts as a nano-antenna to radiate the THz wave generated in the active region of the photomixer. In addition, it provides good impedance matching to the THz planar antenna and exhibits a lower RC time constant, allowing more efficient radiation especially at the higher part of the THz spectrum. As a result, the output intensity of the photomixer with the new nano-gap electrode structure in the active region is two orders of magnitude higher than that of a photomixer with typical interdigitated electrodes. Significant improvement in the THz emission bandwidth was also observed. An efficient continuous wave THz source will greatly benefit compact THz system development for high resolution THz spectroscopy and imaging applications. PMID:24100840

Design, fabrication, and experimental characterization of plasmonic photoconductive terahertz emitters.

PubMed

Berry, Christopher; Hashemi, Mohammad Reza; Unlu, Mehmet; Jarrahi, Mona

2013-07-08

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation (1-8). Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors (9). Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 (10).

Higgs Mode in the d -Wave Superconductor Bi2Sr2CaCu2O8 +x Driven by an Intense Terahertz Pulse

NASA Astrophysics Data System (ADS)

Katsumi, Kota; Tsuji, Naoto; Hamada, Yuki I.; Matsunaga, Ryusuke; Schneeloch, John; Zhong, Ruidan D.; Gu, Genda D.; Aoki, Hideo; Gallais, Yann; Shimano, Ryo

2018-03-01

We investigate the terahertz (THz)-pulse-driven nonlinear response in the d -wave cuprate superconductor Bi2Sr2CaCu2O8 +x (Bi2212) using a THz pump near-infrared probe scheme in the time domain. We observe an oscillatory behavior of the optical reflectivity that follows the THz electric field squared and is markedly enhanced below Tc . The corresponding third-order nonlinear effect exhibits both A1 g and B1 g symmetry components, which are decomposed from polarization-resolved measurements. A comparison with a BCS calculation of the nonlinear susceptibility indicates that the A1 g component is associated with the Higgs mode of the d -wave order parameter.

Higgs Mode in the d -Wave Superconductor Bi 2 Sr 2 CaCu 2 O 8 + x Driven by an Intense Terahertz Pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsumi, Kota; Tsuji, Naoto; Hamada, Yuki I.

We investigated the terahertz (THz)-pulse driven nonlinear response in the d-wave cuprate superconductor Bi 2Sr 2CaCu 2O 8+x (Bi2212) using a THz pump near-infrared probe scheme in the time domain. We have observed an oscillatory behavior of the optical reflectivity that follows the THz electric field squared and is strongly enhanced below Tc. The corresponding third-order nonlinear effect exhibits both A 1g and B 1g symmetry components, which are decomposed from polarization-resolved measurements. Comparison with a BCS calculation of the nonlinear susceptibility indicates that the A 1g component is associated with the Higgs mode of the d-wave order parameter.

Higgs Mode in the d -Wave Superconductor Bi 2 Sr 2 CaCu 2 O 8 + x Driven by an Intense Terahertz Pulse

DOE PAGES

Katsumi, Kota; Tsuji, Naoto; Hamada, Yuki I.; ...

2018-03-14

We investigated the terahertz (THz)-pulse driven nonlinear response in the d-wave cuprate superconductor Bi 2Sr 2CaCu 2O 8+x (Bi2212) using a THz pump near-infrared probe scheme in the time domain. We have observed an oscillatory behavior of the optical reflectivity that follows the THz electric field squared and is strongly enhanced below Tc. The corresponding third-order nonlinear effect exhibits both A 1g and B 1g symmetry components, which are decomposed from polarization-resolved measurements. Comparison with a BCS calculation of the nonlinear susceptibility indicates that the A 1g component is associated with the Higgs mode of the d-wave order parameter.

Mode-locked laser with pulse interleavers in a monolithic photonic integrated circuit for millimeter wave and terahertz carrier generation.

PubMed

Lo, Mu-Chieh; Guzmán, Robinson; Gordón, Carlos; Carpintero, Guillermo

2017-04-15

This Letter presents a photonics-based millimeter wave and terahertz frequency synthesizer using a monolithic InP photonic integrated circuit composed of a mode-locked laser (MLL) and two pulse interleaver stages to multiply the repetition rate frequency. The MLL is a multiple colliding pulse MLL producing an 80 GHz repetition rate pulse train. Through two consecutive monolithic pulse interleaver structures, each doubling the repetition rate, we demonstrate the achievement of 160 and 320 GHz. The fabrication was done on a multi-project wafer run of a generic InP photonic technology platform.

GaSe1-xSx and GaSe1-xTex thick crystals for broadband terahertz pulses generation

NASA Astrophysics Data System (ADS)

Nazarov, M. M.; Yu. Sarkisov, S.; Shkurinov, A. P.; Tolbanov, O. P.

2011-08-01

We demonstrate the possibility of broadband THz pulse generation in mixed GaSe1-xSx and GaSe1-xTex crystals. The ordinary and extraordinary refractive indices of the crystals have been measured by the terahertz time-domain spectroscopy method, those values strongly influence the efficiency of THz generation process. The high birefringence and transparency of pure GaSe and mixed crystals allow optical rectification of femtosecond laser pulses in the several millimeters thick crystal using the еее interaction process (with two pumping waves and generated THz wave all having extraordinary polarization in the crystal).

Longitudinal terahertz wave generation from an air plasma filament induced by a femtosecond laser

NASA Astrophysics Data System (ADS)

Minami, Yasuo; Kurihara, Takayuki; Yamaguchi, Keita; Nakajima, Makoto; Suemoto, Tohru

2013-04-01

We have generated and detected a longitudinally polarized (Z-polarized) terahertz (THz) wave by focusing a conically propagating THz beam generated from a plasma filament induced by a femtosecond laser pulse. In the experiment, we observed a radially polarized field in a collimated region and Z-polarized field at focus in the time domain. The maximum value of the Z-polarized THz electric field reached 1.0 kV/cm. It was also quantitatively discussed about the Z-polarized field and the radial field at the focal point. We expect this technique to find application in THz time domain spectroscopy.

Optical-fiber-connected 300-GHz FM-CW radar system

NASA Astrophysics Data System (ADS)

Kanno, Atsushi; Sekine, Norihiko; Kasamatsu, Akifumi; Yamamoto, Naokatsu; Kawanishi, Tetsuya

2017-05-01

300-GHz frequency-modulated continuous-wave (FM-CW) radar system operated by radio over fiber technologies is configured and demonstrated. Centralized signal generator, which is based on an optical frequency comb generation, provides high-precise FM-CW radar signal. The optical signal is easy to be transported to radar heads through an optical fiber network. Optical-modulator-based optical frequency comb generator is utilized as an optical frequency multiplier from a microwave signal to a 300-GHz terahertz signal by an optical modulation technique. In the study, we discuss the configuration of the network, signal generator and remote radar head for terahertz-wave multi-static radar system.

Computed tomography image using sub-terahertz waves generated from a high-T{sub c} superconducting intrinsic Josephson junction oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kashiwagi, T., E-mail: kashiwagi@ims.tsukuba.ac.jp; Minami, H.; Kadowaki, K.

2014-02-24

A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

Target recognition in passive terahertz image of human body

NASA Astrophysics Data System (ADS)

Zhao, Ran; Zhao, Yuan-meng; Deng, Chao; Zhang, Cun-lin; Li, Yue

2014-11-01

THz radiation can penetrate through many nonpolar dielectric materials and can be used for nondestructive/noninvasive sensing and imaging of targets under nonpolar, nonmetallic covers or containers. Thus using THz systems to "see through" concealing barriers (i.e. packaging, corrugated cardboard, clothing) has been proposed as a new security screening method. Objects that can be detected by THz include concealed weapons, explosives, and chemical agents under clothing. Passive THz imaging system can detect THz wave from human body without transmit any electromagnetic wave, and the suspicious objects will become visible because the THz wave is blocked by this items. We can find out whether or not someone is carrying dangerous objects through this image. In this paper, the THz image enhancement, segmentation and contour extraction algorithms were studied to achieve effective target image detection. First, the terahertz images are enhanced and their grayscales are stretched. Then we apply global threshold segmentation to extract the target, and finally the targets are marked on the image. Experimental results showed that the algorithm proposed in this paper can extract and mark targets effectively, so that people can identify suspicious objects under clothing quickly. The algorithm can significantly improve the usefulness of the terahertz security apparatus.

Terahertz generation by difference frequency generation from a compact optical parametric oscillator

NASA Astrophysics Data System (ADS)

Li, Zhongyang; Wang, Silei; Wang, Mengtao; Wang, Weishu

2017-11-01

Terahertz (THz) generation by difference frequency generation (DFG) processes with dual idler waves is theoretically analyzed. The dual idler waves are generated by a compact optical parametric oscillator (OPO) with periodically poled lithium niobate (PPLN). The phase-matching conditions in a same PPLN for the optical parametric oscillation generating signal and idler waves and for the DFG generating THz waves can be simultaneously satisfied by selecting the poling period of PPLN. Moreover, 3-order cascaded DFG processes generating THz waves can be realized in the same PPLN. To take an example of 8.341 THz which locates in the vicinity of polariton resonances, THz intensities and quantum conversion efficiencies are calculated. Compared with non-cascaded DFG processes, THz intensities of 8.341 THz in 3-order cascaded DFG processes increase to 2.57 times. When the pump intensity equals to 20 MW/mm2, the quantum conversion efficiency of 106% in 3-order cascaded DFG processes can be realized, which exceeds the Manley-Rowe limit.

Generation of Elliptically Polarized Terahertz Waves from Antiferromagnetic Sandwiched Structure.

PubMed

Zhou, Sheng; Zhang, Qiang; Fu, Shu-Fang; Wang, Xuan-Zhang; Song, Yu-Ling; Wang, Xiang-Guang; Qu, Xiu-Rong

2018-04-01

The generation of elliptically polarized electromagnetic wave of an antiferromagnetic (AF)/dielectric sandwiched structure in the terahertz range is studied. The frequency and external magnetic field can change the AF optical response, resulting in the generation of elliptical polarization. An especially useful geometry with high levels of the generation of elliptical polarization is found in the case where an incident electromagnetic wave perpendicularly illuminates the sandwiched structure, the AF anisotropy axis is vertical to the wave-vector and the external magnetic field is pointed along the wave-vector. In numerical calculations, the AF layer is FeF2 and the dielectric layers are ZnF2. Although the effect originates from the AF layer, it can be also influenced by the sandwiched structure. We found that the ZnF2/FeF2/ZnF2 structure possesses optimal rotation of the principal axis and ellipticity, which can reach up to about thrice that of a single FeF2 layer.

Polymer Morphological Change Induced by Terahertz Irradiation

PubMed Central

Hoshina, Hiromichi; Suzuki, Hal; Otani, Chiko; Nagai, Masaya; Kawase, Keigo; Irizawa, Akinori; Isoyama, Goro

2016-01-01

As terahertz (THz) frequencies correspond to those of the intermolecular vibrational modes in a polymer, intense THz wave irradiation affects the macromolecular polymorph, which determines the polymer properties and functions. THz photon energy is quite low compared to the covalent bond energy; therefore, conformational changes can be induced “softly,” without damaging the chemical structures. Here, we irradiate a poly(3-hydroxybutylate) (PHB) / chloroform solution during solvent casting crystallization using a THz wave generated by a free electron laser (FEL). Morphological observation shows the formation of micrometer-sized crystals in response to the THz wave irradiation. Further, a 10−20% increase in crystallinity is observed through analysis of the infrared (IR) absorption spectra. The peak power density of the irradiating THz wave is 40 MW/cm2, which is significantly lower than the typical laser intensities used for material manipulation. We demonstrate for the first time that the THz wave effectively induces the intermolecular rearrangement of polymer macromolecules. PMID:27272984

Invited Article: An active terahertz polarization converter employing vanadium dioxide and a metal wire grating in total internal reflection geometry

NASA Astrophysics Data System (ADS)

Liu, Xudong; Chen, Xuequan; Parrott, Edward P. J.; Han, Chunrui; Humbert, Georges; Crunteanu, Aurelian; Pickwell-MacPherson, Emma

2018-05-01

Active broadband terahertz (THz) polarization manipulation devices are challenging to realize, but also of great demand in broadband terahertz systems. Vanadium dioxide (VO2) shows a promising phase transition for active control of THz waves and provides broadband polarization characteristics when integrated within grating-type structures. We creatively combine a VO2-based grating structure with a total internal reflection (TIR) geometry providing a novel interaction mechanism between the electromagnetic waves and the device, to realize a powerful active broadband THz polarization-controlling device. The device is based on a Si-substrate coated with a VO2 layer and a metal grating structure on top, attached to a prism for generating the TIR condition on the Si-VO2-grating interface. The grating is connected to electrodes for electrically switching the VO2 between its insulating and conducting phases. By properly selecting the incident angle of the THz waves, the grating direction, and the incident polarization state, we first achieved a broadband intensity modulator under a fused silica prism with an average modulation depth of 99.75% in the 0.2-1.1 THz region. Additionally, we realized an active ultra-broadband quarter-wave converter under a Si prism that can be switched between a 45° linear rotator and a quarter wave converter in the 0.8-1.5 THz region. This is the first demonstration of an active quarter-wave converter with ultra-broad bandwidth performance. Our work shows a highly flexible and multifunctional polarization-controlling device for broadband THz applications.

A terahertz-vibration to terahertz-radiation converter based on gold nanoobjects: a feasibility study.

PubMed

Moldosanov, Kamil; Postnikov, Andrei

2016-01-01

The need for practical and adaptable terahertz sources is apparent in the areas of application such as early cancer diagnostics, nondestructive inspection of pharmaceutical tablets, visualization of concealed objects. We outline the operation principle and suggest the design of a simple appliance for generating terahertz radiation by a system of nanoobjects - gold nanobars (GNBs) or nanorings (GNRs) - irradiated by microwaves. Our estimations confirm a feasibility of the idea that GNBs and GNRs irradiated by microwaves could become terahertz emitters with photon energies within the full width at half maximum of the longitudinal acoustic phononic DOS of gold (ca. 16-19 meV, i.e., 3.9-4.6 THz). A scheme of the terahertz radiation source is suggested based on the domestic microwave oven irradiating a substrate with multiple deposited GNBs or GNRs. The size of a nanoobject for optimal conversion is estimated to be approx. 3 nm (thickness) by approx. 100 nm (length of GNB, or along the GNR). This detailed prediction is open to experimental verification. An impact is expected onto further studies of interplay between atomic vibrations and electromagnetic waves in nanoobjects.

Predictive of the quantum capacitance effect on the excitation of plasma waves in graphene transistors with scaling limit.

PubMed

Wang, Lin; Chen, Xiaoshuang; Hu, Yibin; Wang, Shao-Wei; Lu, Wei

2015-04-28

Plasma waves in graphene field-effect transistors (FETs) and nano-patterned graphene sheets have emerged as very promising candidates for potential terahertz and infrared applications in myriad areas including remote sensing, biomedical science, military, and many other fields with their electrical tunability and strong interaction with light. In this work, we study the excitations and propagation properties of plasma waves in nanometric graphene FETs down to the scaling limit. Due to the quantum-capacitance effect, the plasma wave exhibits strong correlation with the distribution of density of states (DOS). It is indicated that the electrically tunable plasma resonance has a power-dependent V0.8 TG relation on the gate voltage, which originates from the linear dependence of density of states (DOS) on the energy in pristine graphene, in striking difference to those dominated by classical capacitance with only V0.5 TG dependence. The results of different transistor sizes indicate the potential application of nanometric graphene FETs in highly-efficient electro-optic modulation or detection of terahertz or infrared radiation. In addition, we highlight the perspectives of plasma resonance excitation in probing the many-body interaction and quantum matter state in strong correlation electron systems. This study reveals the key feature of plasma waves in decorated/nanometric graphene FETs, and paves the way to tailor plasma band-engineering and expand its application in both terahertz and mid-infrared regions.

Electron acceleration and kinetic energy tailoring via ultrafast terahertz fields.

PubMed

Greig, S R; Elezzabi, A Y

2014-11-17

We propose a mechanism for tuning the kinetic energy of surface plasmon generated electron pulses through control of the time delay between a pair of externally applied terahertz pulses. Varying the time delay results in translation, compression, and broadening of the kinetic energy spectrum of the generated electron pulse. We also observe that the electrons' kinetic energy dependence on the carrier envelope phase of the surface plasmon is preserved under the influence of a terahertz electric field.

Terahertz inline wall thickness monitoring system for plastic pipe extrusion

NASA Astrophysics Data System (ADS)

Hauck, J.; Stich, D.; Heidemeyer, P.; Bastian, M.; Hochrein, T.

2014-05-01

Conventional and commercially available inline wall thickness monitoring systems for pipe extrusion are usually based on ultrasonic or x-ray technology. Disadvantages of ultrasonic systems are the usual need of water as a coupling media and the high damping in thick walled or foamed pipes. For x-ray systems special safety requirements have to be taken into account because of the ionizing radiation. The terahertz (THz) technology offers a novel approach to solve these problems. THz waves have many properties which are suitable for the non-destructive testing of plastics. The absorption of electrical isolators is typically very low and the radiation is non-ionizing in comparison to x-rays. Through the electromagnetic origin of the THz waves they can be used for contact free measurements. Foams show a much lower absorption in contrast to acoustic waves. The developed system uses THz pulses which are generated by stimulating photoconductive switches with femtosecond laser pulses. The time of flight of THz pulses can be determined with a resolution in the magnitude of several ten femtoseconds. Hence the thickness of an object like plastic pipes can be determined with a high accuracy by measuring the time delay between two reflections on materials interfaces e.g. at the pipe's inner and outer surface, similar to the ultrasonic technique. Knowing the refractive index of the sample the absolute layer thickness from the transit time difference can be calculated easily. This method in principle also allows the measurement of multilayer systems and the characterization of foamed pipes.

Multilayer graphene-based metasurfaces: robust design method for extremely broadband, wide-angle, and polarization-insensitive terahertz absorbers.

PubMed

Rahmanzadeh, Mahdi; Rajabalipanah, Hamid; Abdolali, Ali

2018-02-01

In this study, by using an equivalent circuit method, a polarization-insensitive terahertz (THz) absorber based on multilayer graphene-based metasurfaces (MGBMs) is systematically designed, providing an extremely broad absorption bandwidth (BW). The proposed absorber is a compact, three-layer structure, comprising square-, cross-, and circular-shaped graphene metasurfaces embedded between three separator dielectrics. The equivalent-conductivity method serves as a parameter retrieval technique to characterize the graphene metasurfaces as the components of the proposed circuit model. Good agreement is observed between the full-wave simulations and the equivalent-circuit predictions. The optimum MGBM absorber exhibits >90% absorbance in an extremely broad frequency band of 0.55-3.12 THz (BW=140%). The results indicate a significant BW enhancement compared with both the previous metal- and graphene-based THz absorbers, highlighting the capability of the designed MGBM absorber. To clarify the physical mechanism of absorption, the surface current and the electric-field distributions, as well as the power loss density of each graphene metasurface, are monitored and discussed. The MGBM functionality is evaluated under a wide range of incident wave angles to prove that the proposed absorber is omnidirectional and polarization-insensitive. These superior performances guarantee the applicability of the MGBM structure as an ultra-broadband absorber for various THz applications.

Angular dependent anisotropic terahertz response of vertically aligned multi-walled carbon nanotube arrays with spatial dispersion.

PubMed

Zhou, Yixuan; E, Yiwen; Xu, Xinlong; Li, Weilong; Wang, Huan; Zhu, Lipeng; Bai, Jintao; Ren, Zhaoyu; Wang, Li

2016-12-14

Spatial dispersion effect of aligned carbon nanotubes (CNTs) in the terahertz (THz) region has significance for both theoretical and applied consideration due to the unique intrinsically anisotropic physical properties of CNTs. Herein, we report the angular dependent reflection of p-polarized THz wave from vertically aligned multi-walled CNT arrays in both experiment and theory. The spectra indicate that the reflection depends on the film thickness of vertically aligned CNTs, the incident angle, and the frequency. The calculation model is based on the spatial dispersion effect of aligned CNTs and performed with effective impedance method and the Maxwell-Garnett approximation. The results fit well with the experiment when the thickness of CNT film is thin, which reveals a coherent superposition mechanism of the CNT surface reflection and CNTs/Si interface reflection. For thick CNT films, the CNTs/Si interface response determines the reflection at small incident angles, while the CNTs surface effect dominates at large incident angles. This work investigates the spatial dispersion effect of vertically aligned CNT arrays in the THz region, and paves a way for potential anisotropic THz applications based on CNTs with oblique incidence requirements.

Angular dependent anisotropic terahertz response of vertically aligned multi-walled carbon nanotube arrays with spatial dispersion

NASA Astrophysics Data System (ADS)

Zhou, Yixuan; Yiwen, E.; Xu, Xinlong; Li, Weilong; Wang, Huan; Zhu, Lipeng; Bai, Jintao; Ren, Zhaoyu; Wang, Li

2016-12-01

Spatial dispersion effect of aligned carbon nanotubes (CNTs) in the terahertz (THz) region has significance for both theoretical and applied consideration due to the unique intrinsically anisotropic physical properties of CNTs. Herein, we report the angular dependent reflection of p-polarized THz wave from vertically aligned multi-walled CNT arrays in both experiment and theory. The spectra indicate that the reflection depends on the film thickness of vertically aligned CNTs, the incident angle, and the frequency. The calculation model is based on the spatial dispersion effect of aligned CNTs and performed with effective impedance method and the Maxwell-Garnett approximation. The results fit well with the experiment when the thickness of CNT film is thin, which reveals a coherent superposition mechanism of the CNT surface reflection and CNTs/Si interface reflection. For thick CNT films, the CNTs/Si interface response determines the reflection at small incident angles, while the CNTs surface effect dominates at large incident angles. This work investigates the spatial dispersion effect of vertically aligned CNT arrays in the THz region, and paves a way for potential anisotropic THz applications based on CNTs with oblique incidence requirements.

Systematic characterization of a 1550 nm microelectromechanical (MEMS)-tunable vertical-cavity surface-emitting laser (VCSEL) with 7.92 THz tuning range for terahertz photomixing systems

NASA Astrophysics Data System (ADS)

Haidar, M. T.; Preu, S.; Cesar, J.; Paul, S.; Hajo, A. S.; Neumeyr, C.; Maune, H.; Küppers, F.

2018-01-01

Continuous-wave (CW) terahertz (THz) photomixing requires compact, widely tunable, mode-hop-free driving lasers. We present a single-mode microelectromechanical system (MEMS)-tunable vertical-cavity surface-emitting laser (VCSEL) featuring an electrothermal tuning range of 64 nm (7.92 THz) that exceeds the tuning range of commercially available distributed-feedback laser (DFB) diodes (˜4.8 nm) by a factor of about 13. We first review the underlying theory and perform a systematic characterization of the MEMS-VCSEL, with particular focus on the parameters relevant for THz photomixing. These parameters include mode-hop-free CW tuning with a side-mode-suppression-ratio >50 dB, a linewidth as narrow as 46.1 MHz, and wavelength and polarization stability. We conclude with a demonstration of a CW THz photomixing setup by subjecting the MEMS-VCSEL to optical beating with a DFB diode driving commercial photomixers. The achievable THz bandwidth is limited only by the employed photomixers. Once improved photomixers become available, electrothermally actuated MEMS-VCSELs should allow for a tuning range covering almost the whole THz domain with a single system.

Phase-slope and phase measurements of tunable CW-THz radiation with terahertz comb for wide-dynamic-range, high-resolution, distance measurement of optically rough object.

PubMed

Yasui, Takeshi; Fujio, Makoto; Yokoyama, Shuko; Araki, Tsutomu

2014-07-14

Phase measurement of continuous-wave terahertz (CW-THz) radiation is a potential tool for direct distance and imaging measurement of optically rough objects due to its high robustness to optical rough surfaces. However, the 2π phase ambiguity in the phase measurement of single-frequency CW-THz radiation limits the dynamic range of the measured distance to the order of the wavelength used. In this article, phase-slope measurement of tunable CW-THz radiation with a THz frequency comb was effectively used to extend the dynamic range up to 1.834 m while maintaining an error of a few tens µm in the distance measurement of an optically rough object. Furthermore, a combination of phase-slope measurement of tunable CW-THz radiation and phase measurement of single-frequency CW-THz radiation enhanced the distance error to a few µm within the dynamic range of 1.834 m without any influence from the 2π phase ambiguity. The proposed method will be a powerful tool for the construction and maintenance of large-scale structures covered with optically rough surfaces.

An implemented method of asymmetric transmission for arbitrary polarization base in multi-layered chiral meta-surface

NASA Astrophysics Data System (ADS)

Xiao, Zhong-yin; Zou, Huan-ling; Xu, Kai-Kai; Tang, Jing-yao

2018-03-01

Asymmetric transmission of linearly or circularly polarized waves is a well-established property not only for three-layered chiral structures but for multi-layered ones. Here we show a method which can simultaneously implement asymmetric transmission for arbitrary base vector polarized wave in multi-layered chiral meta-surface. We systematically study the implemented method based on a multi-layered chiral structure consisting of a y-shape, a half gammadion and an S-shape in the terahertz gap. A numerical simulation was carried out, followed by an explanation of the asymmetric transmission mechanism in these structures proposed in this work. The simulated results indicate that the multi-layered chiral structure can realize a maximum asymmetric transmission of 0.89 and 0.28 for circularly and linearly polarized waves, respectively, which exhibit magnitude improvement over previous chiral metamaterials. Specifically, the maximum asymmetric transmitted coefficient of the multi-layered chiral structure is insensitivity to the incident angles from 0° to 45° for circularly polarized components. Additionally, we also study the influence of structural parameters on the asymmetric transmission effect for both linearly and circularly polarized waves in detail.

Absorber for wakefield interference management at the entrance of the wiggler of a free electron laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchlik, Matthew; Biallas, George Herman

A method for managing the broad band microwave and TeraHertz (THz) radiation in a free electron laser (FEL) having a wiggler producing power in the electromagnetic spectrum. The method includes placement of broadband microwave and TeraHertz (THz) radiation absorbers on the upstream end of the wiggler. The absorbers dampen the bounced back, broad band microwave and THz radiation returning from the surfaces outside the nose of the cookie-cutter and thus preventing broadening of the electron beam pulse's narrow longitudinal energy distribution. Broadening diminishes the ultimate laser power from the wiggler. The broadband microwave and THz radiation absorbers are placed onmore » either side of the slot in the cookie-cutter that shapes the wake field wave of the electron pulse to the slot shape of the wiggler chamber aperture. The broad band microwave and THz radiation absorber is preferably a non-porous pyrolytic grade of graphite with small grain size.« less

The interaction between electromagnetic fields at megahertz, gigahertz and terahertz frequencies with cells, tissues and organisms: risks and potential.

PubMed

Romanenko, Sergii; Begley, Ryan; Harvey, Alan R; Hool, Livia; Wallace, Vincent P

2017-12-01

Since regular radio broadcasts started in the 1920s, the exposure to human-made electromagnetic fields has steadily increased. These days we are not only exposed to radio waves but also other frequencies from a variety of sources, mainly from communication and security devices. Considering that nearly all biological systems interact with electromagnetic fields, understanding the affects is essential for safety and technological progress. This paper systematically reviews the role and effects of static and pulsed radio frequencies (10 0 -10 9 Hz), millimetre waves (MMWs) or gigahertz (10 9 -10 11 Hz), and terahertz (10 11 -10 13 Hz) on various biomolecules, cells and tissues. Electromagnetic fields have been shown to affect the activity in cell membranes (sodium versus potassium ion conductivities) and non-selective channels, transmembrane potentials and even the cell cycle. Particular attention is given to millimetre and terahertz radiation due to their increasing utilization and, hence, increasing human exposure. MMWs are known to alter active transport across cell membranes, and it has been reported that terahertz radiation may interfere with DNA and cause genomic instabilities. These and other phenomena are discussed along with the discrepancies and controversies from published studies. © 2017 The Author(s).

Terahertz vibrational signature of bacterial spores arising from nanostructure decorated endospore surface.

PubMed

Datta, Debopam; Stroscio, Michael A; Dutta, Mitra; Zhang, Weidong; Brown, Elliott R

2018-05-03

This theoretical effort is the first to explore the possible hypothesis that terahertz optical activity of Bacillus spores arises from normal vibrational modes of spore coat subcomponents in the terahertz frequency range. Bacterial strains like Bacillus and Clostridium form spores with a hardened coating made of peptidoglycan to protect its genetic material in harsh conditions. In recent years, electron microscopy and atomic force microscopy has revealed that bacterial spore surfaces are decorated with nanocylinders and honeycomb nanostructures. In this article, a simple elastic continuum model is used to describe the vibration of these nanocylinders mainly in Bacillus subtilis, which also leads to the conclusion that the terahertz signature of these spores arises from the vibration of these nanostructures. Three vibrating modes: radial/longitudinal, torsional and flexural, have been identified and discussed for the nanocylinders. The effect of bound water, which shifts the vibration frequency, is also discussed. The peptidoglycan molecule consists of polar and charged amino acids; hence, the sporal surface local vibrations interact strongly with the terahertz radiation. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Emission of terahertz waves in the interaction of a laser pulse with clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frolov, A. A., E-mail: frolov@ihed.ras.ru

2016-07-15

A theory of generation of terahertz radiation in the interaction of a femtosecond laser pulse with a spherical cluster is developed for the case in which the density of free electrons in the cluster plasma exceeds the critical value. The spectral, angular, and energy characteristics of the emitted terahertz radiation are investigated, as well as its spatiotemporal structure. It is shown that the directional pattern of radiation has a quadrupole structure and that the emission spectrum has a broad maximum at a frequency nearly equal to the reciprocal of the laser pulse duration. It is found that the total radiatedmore » energy depends strongly on the cluster size. Analysis of the spatiotemporal profile of the terahertz signal shows that it has a femtosecond duration and contains only two oscillation cycles.« less

Propagation characteristic of THz wave in camouflage net material

NASA Astrophysics Data System (ADS)

Dong, Hailong; Wang, Jiachun; Chen, Zongsheng; Lin, Zhidan; Zhao, Dapeng; Liu, Ruihuang

2017-10-01

Terahertz (THz) radar system, with excellent potentials such as high-resolution and strong penetration capability, is promising in the field of anti-camouflage. Camouflage net is processed by cutting the camouflage net material, which is fabricated on pre-processing substrate by depositing coatings with camouflage abilities in different bands, such as visible, infrared and radar. In this paper, we concentrate on the propagation characteristic of THz wave in camouflage net material. Firstly, function and structure of camouflage net were analyzed. Then the advantage and appliance of terahertz time-domain spectroscopy (THz-TDS) was introduced. And the relevant experiments were conducted by utilizing THz-TDS. The results obtained indicate that THz wave has better penetration capacity in camouflage net material, which demonstrates the feasibility of using THz radar to detect those targets covered with camouflage net.

High-performance terahertz wave absorbers made of silicon-based metamaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Sheng; Zhu, Jianfei; Jiang, Wei

2015-08-17

Electromagnetic (EM) wave absorbers with high efficiency in different frequency bands have been extensively investigated for various applications. In this paper, we propose an ultra-broadband and polarization-insensitive terahertz metamaterial absorber based on a patterned lossy silicon substrate. Experimentally, a large absorption efficiency more than 95% in a frequency range of 0.9–2.5 THz was obtained up to a wave incident angle as large as 70°. Much broader absorption bandwidth and excellent oblique incidence absorption performance are numerically demonstrated. The underlying mechanisms due to the combination of a waveguide cavity mode and impedance-matched diffraction are analyzed in terms of the field patternsmore » and the scattering features. The monolithic THz absorber proposed here may find important applications in EM energy harvesting systems such as THz barometer or biosensor.« less

Terahertz polarization converter based on all-dielectric high birefringence metamaterial with elliptical air holes

NASA Astrophysics Data System (ADS)

Zi, Jianchen; Xu, Quan; Wang, Qiu; Tian, Chunxiu; Li, Yanfeng; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili

2018-06-01

Metamaterials have been widely applied in the polarization conversion of terahertz (THz) waves. However, common plasmonic metamaterials usually work as reflective devices and have low transmissions. All-dielectric metamaterials can overcome these shortcomings. An all-dielectric metamaterial based on silicon with elliptical air holes is reported to achieve high artificial birefringence at THz frequencies. Simulations show that with appropriate structural parameters the birefringence of the dielectric metamaterial can remain flat and is above 0.7 within a broad band. Moreover, the metamaterial can be designed as a broadband quarter wave plate. A sample metamaterial was fabricated and tested to prove the validity of the simulations, and the sample could work as a quarter wave plate at 1.76 THz. The all-dielectric metamaterial that we proposed is of great significance for high performance THz polarization converters.

Superfocusing terahertz waves below lambda/250 using plasmonic parallel-plate waveguides.

PubMed

Zhan, Hui; Mendis, Rajind; Mittleman, Daniel M

2010-04-26

We experimentally demonstrate complete two-dimensional (2-D) confinement of terahertz (THz) energy in finite-width parallel-plate waveguides, defying conventional wisdom in the century-old field of microwave waveguide technology. We find that the degree of energy confinement increases exponentially with decreasing plate separation. We propose that this 2-D confinement is mediated by the mutual coupling of plasmonic edge modes, analogous to that observed in slot waveguides at optical wavelengths. By adiabatically tapering the width and the separation, we focus THz waves down to a size of 10 microm (approximately lambda/260) by 18 microm ( approximately lambda/145), which corresponds to a mode area of only 2.6 x 10(-5) lambda(2).

Monolithic dual-mode distributed feedback semiconductor laser for tunable continuous-wave terahertz generation.

PubMed

Kim, Namje; Shin, Jaeheon; Sim, Eundeok; Lee, Chul Wook; Yee, Dae-Su; Jeon, Min Yong; Jang, Yudong; Park, Kyung Hyun

2009-08-03

We report on a monolithic dual-mode semiconductor laser operating in the 1550-nm range as a compact optical beat source for tunable continuous-wave (CW) terahertz (THz) generation. It consists of two distributed feedback (DFB) laser sections and one phase section between them. Each wavelength of the two modes can be independently tuned by adjusting currents in micro-heaters which are fabricated on the top of the each DFB section. The continuous tuning of the CW THz emission from Fe(+)-implanted InGaAs photomixers is successfully demonstrated using our dual-mode laser as the excitation source. The CW THz frequency is continuously tuned from 0.17 to 0.49 THz.

Coherent Two-Dimensional Terahertz Magnetic Resonance Spectroscopy of Collective Spin Waves.

PubMed

Lu, Jian; Li, Xian; Hwang, Harold Y; Ofori-Okai, Benjamin K; Kurihara, Takayuki; Suemoto, Tohru; Nelson, Keith A

2017-05-19

We report a demonstration of two-dimensional (2D) terahertz (THz) magnetic resonance spectroscopy using the magnetic fields of two time-delayed THz pulses. We apply the methodology to directly reveal the nonlinear responses of collective spin waves (magnons) in a canted antiferromagnetic crystal. The 2D THz spectra show all of the third-order nonlinear magnon signals including magnon spin echoes, and 2-quantum signals that reveal pairwise correlations between magnons at the Brillouin zone center. We also observe second-order nonlinear magnon signals showing resonance-enhanced second-harmonic and difference-frequency generation. Numerical simulations of the spin dynamics reproduce all of the spectral features in excellent agreement with the experimental 2D THz spectra.

Telecom technology based continuous wave terahertz photomixing system with 105 decibel signal-to-noise ratio and 3.5 terahertz bandwidth.

PubMed

Göbel, Thorsten; Stanze, Dennis; Globisch, Björn; Dietz, Roman J B; Roehle, Helmut; Schell, Martin

2013-10-15

A modified photoconductive receiver significantly improves the performance of photomixing-based continuous wave (cw) THz systems driven at the optical telecommunication wavelength of 1.5 μm. The achieved signal-to-noise ratio of 105 dB at 100 GHz and 70 dB at 1 THz, both for an integration time of 200 ms, are to our knowledge the highest numbers reported in literature for any optoelectronic cw THz system, including classical setups operating at 800 nm. The developed receiver allows for combining low cost and high performance in one system for the first time to our knowledge.

Laser beat wave resonant terahertz generation in a magnetized plasma channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhasin, Lalita; Tripathi, V. K.; Kumar, Pawan, E-mail: kumarpawan-30@yahoo.co.in

Resonant excitation of terahertz (THz) radiation by nonlinear mixing of two lasers in a ripple-free self created plasma channel is investigated. The channel has a transverse static magnetic field and supports a THz X-mode with phase velocity close to the speed of light in vacuum when the frequency of the mode is close to plasma frequency on the channel axis and its value decreases with the intensity of lasers. The THz is resonantly driven by the laser beat wave ponderomotive force. The THz amplitude scales almost three half power of the intensity of lasers as the width of the THzmore » eigen mode shrinks with laser intensity.« less

[Research progress of Terahertz wave technology in quality measurement of food and agricultural products].

PubMed

Yan, Zhan-Ke; Zhang, Hong-Jian; Ying, Yi-Bin

2007-11-01

The quality concern of food and agricultural products has become more and more significant. The related technologies for nondestructive measurement or quality control of food products have been the focus of many researches. Terahertz (THz) radiation, or THz wave, the least explored region of the spectrum, is the electromagnetic wave that lies between mid-infrared and microwave radiation, which has very important research and application values. THz spectroscopy and THz imaging technique are the two main applications of THz wave. During the past decade, THz waves have been used to characterize the electronic, vibrational and compositional properties of solid, liquid and gas phase materials. Recently, THz technology has gained a lot of attention of researchers in various fields from biological spectral analysis to bio-medical imaging due to its unique features compared with microwave and optical waves. In the present paper, the properties of THz wave and its uniqueness in sensing and imaging applications were discussed. The most recent researches on THz technology used in food quality control and agricultural products inspection were summarized. The prospect of this novel technology in agriculture and food industry was also discussed.

Compact Tunable Narrowband Terahertz-Wave Source Based on Difference Frequency Generation Pumped by Dual Fiber Lasers in MgO:LiNbO3

NASA Astrophysics Data System (ADS)

Wada, Yoshio; Satoh, Takumi; Higashi, Yasuhiro; Urata, Yoshiharu

2017-12-01

We demonstrate a high-average-power, single longitudinal-mode, and tunable terahertz (THz)-wave source based on difference frequency generation (DFG) in a MgO:LiNbO3 (MgO:LN) crystal. The waves for DFG are generated using a pair of Yb-doped pulsed fiber lasers with a master oscillator power fiber amplifier configuration. The average power of the THz-wave output reaches 450 μW at 1.07 THz (280 μm) at a linewidth of 7.2 GHz, and the tunability ranges from 0.35 to 1.07 THz under the pulse repetition frequency of 500 kHz. A short burn-in test of the THz wave is also carried out, and the output power stability is within ± 5% of the averaged power without any active stabilizing technique. The combination of MgO:LN-DFG and stable and robust fiber laser sources is highly promising for the development of high-average-power THz-wave sources, particularly in the high transmission sub-THz region. This approach may enable new applications of THz-wave spectroscopy in imaging and remote sensing.

Novel Waveguide Structures in the Terahertz Frequency Range

NASA Astrophysics Data System (ADS)

Mbonye, Marx

Over the last decade, considerable research interest has peaked in realizing an efficient Terahertz (THz) waveguide for potential applications in imaging, sensing, and communications applications. Two of the promising candidates are the two-wire waveguide and the parallel-plate waveguide (PPWG). I present theoretical and experimental evidence that show that the two-wire waveguide supports low loss terahertz pulse propagation, and illustrate that the mode pattern at the end of the waveguide resembles that of a dipole. In comparison to the weakly guided Sommerfeld wave of a single wire waveguide, this two-wire structure exhibits much lower bending losses. I also observe that a commercial 300-Ohm two-wire TVantenna cable can be used for guiding frequency components of up to 0.2 THz, although these cables are generally designed to operate only up to about 800 MHz. The parallel-plate waveguide is another promising candidate that would make an efficient THz waveguide, since it has relatively low Ohmic losses. The transverse electromagnetic mode (TEM) of this waveguide has been generally preferred since it has no cutoff frequency, and therefore no group velocity dispersion. Utilizing this TEM mode, I study the reflection of THz radiation at the end of a PPWG, due to the impedance mismatch between the propagating transverse-electromagnetic mode and the free-space background. I find that for a PPWG with uniformly spaced plates, the reflection coefficient at the output face increases as the plate separation decreases, consistent with predictions by early low frequency ray optical theory. I observe this same trend in tapered PPWGs, when the input separation is fixed, and the output separation is varied. In another study, I investigate how to minimize diffraction losses in PPWGs by using plates with slightly concave surfaces. Using a simple "bouncing plane wave" analysis, I demonstrate how to determine an ideal radius of curvature for a waveguide operating at a given THz frequency. I perform a detailed experimental and simulation study that illustrates, for a waveguide with a plate separation of 1 cm, one can inhibit the diffraction around a frequency of 0.1 THz, when the surface has a curvature of 6.7 cm. Using much longer PPWGs (about 170cm), I reliably measure the overall losses in a PPWG with a radius of curvature of R=6.7 cm, and find it to be less than 1db/m around the design frequency (of 0.1 THz). This is very close to the lowest achieved loss to date with any terahertz waveguide.

Physics-Based Imaging Methods for Terahertz Nondestructive Evaluation Applications

NASA Astrophysics Data System (ADS)

Kniffin, Gabriel Paul

Lying between the microwave and far infrared (IR) regions, the "terahertz gap" is a relatively unexplored frequency band in the electromagnetic spectrum that exhibits a unique combination of properties from its neighbors. Like in IR, many materials have characteristic absorption spectra in the terahertz (THz) band, facilitating the spectroscopic "fingerprinting" of compounds such as drugs and explosives. In addition, non-polar dielectric materials such as clothing, paper, and plastic are transparent to THz, just as they are to microwaves and millimeter waves. These factors, combined with sub-millimeter wavelengths and non-ionizing energy levels, makes sensing in the THz band uniquely suited for many NDE applications. In a typical nondestructive test, the objective is to detect a feature of interest within the object and provide an accurate estimate of some geometrical property of the feature. Notable examples include the thickness of a pharmaceutical tablet coating layer or the 3D location, size, and shape of a flaw or defect in an integrated circuit. While the material properties of the object under test are often tightly controlled and are generally known a priori, many objects of interest exhibit irregular surface topographies such as varying degrees of curvature over the extent of their surfaces. Common THz pulsed imaging (TPI) methods originally developed for objects with planar surfaces have been adapted for objects with curved surfaces through use of mechanical scanning procedures in which measurements are taken at normal incidence over the extent of the surface. While effective, these methods often require expensive robotic arm assemblies, the cost and complexity of which would likely be prohibitive should a large volume of tests be needed to be carried out on a production line. This work presents a robust and efficient physics-based image processing approach based on the mature field of parabolic equation methods, common to undersea acoustics, seismology, and other areas of science and engineering. The method allows the generation of accurate 3D THz tomographic images of objects with irregular, non-planar surfaces using a simple planar scan geometry, thereby facilitating the integration of 3D THz imaging into mainstream NDE use.

Terahertz beam switching by electrical control of graphene-enabled tunable metasurface.

PubMed

Zhang, Yin; Feng, Yijun; Zhao, Junming; Jiang, Tian; Zhu, Bo

2017-10-26

Controlling the terahertz wave, especially the dynamical and full control of terahertz wavefront, is highly demanded due to the increasing development of practical devices and application systems. Recently considerable efforts have been made to fill the 'terahertz gap' with the help of artificial metamaterial or metasurface incorporated with graphene material. Here, we propose a scheme to design tunable metasurface consisting of metallic patch array on a grounded polymer substrate embedded with graphene layers to electrically control the electromagnetic beam reflection at terahertz frequency. By adjusting geometric dimension of the patch elements, 360 degree reflection phase range may be achieved, thus abrupt phase shifts can be introduced along the metasurface for tailoring the reflected wavefront. Moreover, the reflective phase gradient over the metasurface can be switched between 90 and 360 degree by controlling the Fermi energy of the embedded graphene through voltage biasing, hence dynamically switching the reflective beam directions. Numerical simulations demonstrate that either single beam or dual beam dynamically switching between normal and oblique reflection angles can be well attained at working frequency. The proposed approach will bring much freedom in the design of beam manipulation devices and may be applied to terahertz radiation control.

Terahertz electromagnetic fields (0.106 THz) do not induce manifest genomic damage in vitro.

PubMed

Hintzsche, Henning; Jastrow, Christian; Kleine-Ostmann, Thomas; Kärst, Uwe; Schrader, Thorsten; Stopper, Helga

2012-01-01

Terahertz electromagnetic fields are non-ionizing electromagnetic fields in the frequency range from 0.1 to 10 THz. Potential applications of these electromagnetic fields include the whole body scanners, which currently apply millimeter waves just below the terahertz range, but future scanners will use higher frequencies in the terahertz range. These and other applications will bring along human exposure to these fields. Up to now, only a limited number of investigations on biological effects of terahertz electromagnetic fields have been performed. Therefore, research is strongly needed to enable reliable risk assessment.Cells were exposed for 2 h, 8 h, and 24 h with different power intensities ranging from 0.04 mW/cm(2) to 2 mW/cm(2), representing levels below, at, and above current safety limits. Genomic damage on the chromosomal level was measured as micronucleus formation. DNA strand breaks and alkali-labile sites were quantified with the comet assay. No DNA strand breaks or alkali-labile sites were observed as a consequence of exposure to terahertz electromagnetic fields in the comet assay. The fields did not cause chromosomal damage in the form of micronucleus induction.

Terahertz Electromagnetic Fields (0.106 THz) Do Not Induce Manifest Genomic Damage In Vitro

PubMed Central

Hintzsche, Henning; Jastrow, Christian; Kleine-Ostmann, Thomas; Kärst, Uwe; Schrader, Thorsten; Stopper, Helga

2012-01-01

Terahertz electromagnetic fields are non-ionizing electromagnetic fields in the frequency range from 0.1 to 10 THz. Potential applications of these electromagnetic fields include the whole body scanners, which currently apply millimeter waves just below the terahertz range, but future scanners will use higher frequencies in the terahertz range. These and other applications will bring along human exposure to these fields. Up to now, only a limited number of investigations on biological effects of terahertz electromagnetic fields have been performed. Therefore, research is strongly needed to enable reliable risk assessment. Cells were exposed for 2 h, 8 h, and 24 h with different power intensities ranging from 0.04 mW/cm2 to 2 mW/cm2, representing levels below, at, and above current safety limits. Genomic damage on the chromosomal level was measured as micronucleus formation. DNA strand breaks and alkali-labile sites were quantified with the comet assay. No DNA strand breaks or alkali-labile sites were observed as a consequence of exposure to terahertz electromagnetic fields in the comet assay. The fields did not cause chromosomal damage in the form of micronucleus induction. PMID:23029508

Terahertz Modulator based on Metamaterials integrated with Metal-Semiconductor-Metal Varactors

PubMed Central

Nouman, Muhammad Tayyab; Kim, Hyun-Woong; Woo, Jeong Min; Hwang, Ji Hyun; Kim, Dongju; Jang, Jae-Hyung

2016-01-01

The terahertz (THz) band of the electromagnetic spectrum, with frequencies ranging from 300 GHz to 3 THz, has attracted wide interest in recent years owing to its potential applications in numerous areas. Significant progress has been made toward the development of devices capable of actively controlling terahertz waves; nonetheless, further advances in device functionality are necessary for employment of these devices in practical terahertz systems. Here, we demonstrate a low voltage, sharp switching terahertz modulator device based on metamaterials integrated with metal semiconductor metal (MSM) varactors, fabricated on an AlGaAs/InGaAs based heterostructure. By varying the applied voltage to the MSM-varactor located at the center of split ring resonator (SRR), the resonance frequency of the SRR-based metamaterial is altered. Upon varying the bias voltage from 0 V to 3 V, the resonance frequency exhibits a transition from 0.52 THz to 0.56 THz, resulting in a modulation depth of 45 percent with an insertion loss of 4.3 dB at 0.58 THz. This work demonstrates a new approach for realizing active terahertz devices with improved functionalities. PMID:27194128

Response to ''Comment on 'Terahertz wave generation by upper hybrid wave''' [Phys. Plasmas 18, 074701 (2011)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Monika; Kumar, Sanjay; Sharma, R. P.

2011-07-15

The comment by Stenflo and Brodin mentions two points in our recently published paper [M. Singh, S. Kumar, and R. P. Sharma, Phys. Plasmas 18, 022304 (2011)]. We have given the appropriate reply for the same here.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers

PubMed Central

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-01-01

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν ~ 1–5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06–4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers. PMID:27009375

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers.

PubMed

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-03-24

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν~1-5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06-4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers.

Linewidth and tuning characteristics of terahertz quantum cascade lasers.

PubMed

Barkan, A; Tittel, F K; Mittleman, D M; Dengler, R; Siegel, P H; Scalari, G; Ajili, L; Faist, J; Beere, H E; Linfield, E H; Davies, A G; Ritchie, D A

2004-03-15

We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.

Guided Terahertz Waves for Characterizing Explosives

DTIC Science & Technology

2009-01-01

Spectroscopy of Nanometer Water Layers,” Optics Letters 29, 1617–1619 (2004). 4 J. S. Melinger, N. Laman , S. Sree Harsha, and D. Grischkowsky, “Line...2006). 5 N. Laman , S. Sree Harsha, D. Grischkowsky, and J.S. Melinger, “7 GHz Resolution Waveguide THz Spectroscopy of Explosives Related Solids...Showing New Features,” Optics Express 16, 4094–4105 (2008). 6 J.S. Melinger, N. Laman , and D. Grischkowsky, “The Underlying Terahertz Vibrational

Terahertz detection of alcohol using a photonic crystal fiber sensor.

PubMed

Sultana, Jakeya; Islam, Md Saiful; Ahmed, Kawsar; Dinovitser, Alex; Ng, Brian W-H; Abbott, Derek

2018-04-01

Ethanol is widely used in chemical industrial processes as well as in the food and beverage industry. Therefore, methods of detecting alcohol must be accurate, precise, and reliable. In this content, a novel Zeonex-based photonic crystal fiber (PCF) has been modeled and analyzed for ethanol detection in terahertz frequency range. A finite-element-method-based simulation of the PCF sensor shows a high relative sensitivity of 68.87% with negligible confinement loss of 7.79×10 -12    cm -1 at 1 THz frequency and x -polarization mode. Moreover, the core power fraction, birefringence, effective material loss, dispersion, and numerical aperture are also determined in the terahertz frequency range. Owing to the simple fiber structure, existing fabrication methods are feasible. With the outstanding waveguiding properties, the proposed sensor can potentially be used in ethanol detection, as well as polarization-preserving applications of terahertz waves.

Propagation of terahertz pulses in random media.

PubMed

Pearce, Jeremy; Jian, Zhongping; Mittleman, Daniel M

2004-02-15

We describe measurements of single-cycle terahertz pulse propagation in a random medium. The unique capabilities of terahertz time-domain spectroscopy permit the characterization of a multiply scattered field with unprecedented spatial and temporal resolution. With these results, we can develop a framework for understanding the statistics of broadband laser speckle. Also, the ability to extract information on the phase of the field opens up new possibilities for characterizing multiply scattered waves. We illustrate this with a simple example, which involves computing a time-windowed temporal correlation between fields measured at different spatial locations. This enables the identification of individual scattering events, and could lead to a new method for imaging in random media.

High-performance sub-terahertz transmission imaging system for food inspection

PubMed Central

Ok, Gyeongsik; Park, Kisang; Chun, Hyang Sook; Chang, Hyun-Joo; Lee, Nari; Choi, Sung-Wook

2015-01-01

Unlike X-ray systems, a terahertz imaging system can distinguish low-density materials in a food matrix. For applying this technique to food inspection, imaging resolution and acquisition speed ought to be simultaneously enhanced. Therefore, we have developed the first continuous-wave sub-terahertz transmission imaging system with a polygonal mirror. Using an f-theta lens and a polygonal mirror, beam scanning is performed over a range of 150 mm. For obtaining transmission images, the line-beam is incorporated with sample translation. The imaging system demonstrates that a pattern with 2.83 mm line-width at 210 GHz can be identified with a scanning speed of 80 mm/s. PMID:26137392

Pulse sequences for efficient multi-cycle terahertz generation in periodically poled lithium niobate.

PubMed

Ravi, Koustuban; Schimpf, Damian N; Kärtner, Franz X

2016-10-31

The use of laser pulse sequences to drive the cascaded difference frequency generation of high energy, high peak-power and multi-cycle terahertz pulses in cryogenically cooled (100 K) periodically poled Lithium Niobate is proposed and studied. Detailed simulations considering the coupled nonlinear interaction of terahertz and optical waves (or pump depletion), show that unprecedented optical-to-terahertz energy conversion efficiencies > 5%, peak electric fields of hundred(s) of mega volts/meter at terahertz pulse durations of hundred(s) of picoseconds can be achieved. The proposed methods are shown to circumvent laser induced damage limitations at Joule-level pumping by 1µm lasers to enable multi-cycle terahertz sources with pulse energies > 10 milli-joules. Various pulse sequence formats are proposed and analyzed. Numerical calculations for periodically poled structures accounting for cascaded difference frequency generation, self-phase-modulation, cascaded second harmonic generation and laser induced damage are introduced. The physics governing terahertz generation using pulse sequences in this high conversion efficiency regime, limitations and practical considerations are discussed. It is shown that varying the poling period along the crystal length and further reduction of absorption can lead to even higher energy conversion efficiencies >10%. In addition to numerical calculations, an analytic formulation valid for arbitrary pulse formats and closed-form expressions for important cases are presented. Parameters optimizing conversion efficiency in the 0.1-1 THz range, the corresponding peak electric fields, crystal lengths and terahertz pulse properties are furnished.

Tunable terahertz reflection spectrum based on band gaps of GaP materials excited by ultrasonic

NASA Astrophysics Data System (ADS)

Cui, H.; Zhang, X. B.; Wang, X. F.; Wang, G. Q.

2018-02-01

Tunable terahertz (THz) reflection spectrum, ranged from 0.2 to 8 THz, in band gaps of gallium phosphide (GaP) materials excited by ultrasonic is investigated in the present paper, in which tunable ultrasonic and terahertz wave collinear transmission in the same direction is postulated. Numerical simulation results show that, under the acousto-optic interaction, band gaps of transverse optical phonon polariton dispersion curves are turned on, this leads to a dis-propagation of polariton in GaP bulk. On the other side, GaP material has less absorption to THz wave according to experimental studies, as indicates that THz wave could be reflected by the band gaps spontaneously. The band gaps width and acousto-optic coupling strength are proportional with ultrasonic frequency and its intensity in ultrasonic frequency range of 0-250 MHz, in which low-frequency branch of transverse optical phonon polariton dispersion curves demonstrate periodicity and folding as well as. With the increase of ultrasonic frequency, frequency of band gap is blue-shifted, and total reflectivity decreased with -1-order and -2-order reflectivity decrease. The band gaps converge to the restrahlen band infinitely with frequency of ultrasonic exceeding over 250 MHz, total reflectivity of which is attenuated. As is show above, reflection of THz wave can be accommodated by regulating the frequency and its intensity of ultrasonic frequency. Relevant technology may be available in tunable THz frequency selection and filtering.

Observation of broadband terahertz wave generation from liquid water

NASA Astrophysics Data System (ADS)

Jin, Qi; E, Yiwen; Williams, Kaia; Dai, Jianming; Zhang, X.-C.

2017-08-01

Bulk liquid water is a strong absorber in the terahertz (THz) frequency range, due to which liquid water has historically been sworn off as a source for THz radiation. Here, we experimentally demonstrate the generation of broadband THz waves from liquid water excited by femtosecond laser pulses. Our measurements reveal the critical dependence of the THz field upon the relative position between the water film and the focal point of the laser beam. The THz radiation from liquid water shows distinct characteristics when compared with the THz radiation from air plasmas with single color optical excitation. First, the THz field is maximized with the laser beam of longer pulse durations. In addition, the p-polarized component of the emitted THz waves will be influenced by the polarization of the optical excitation beam. It is also shown that the energy of the THz radiation is linearly dependent on the excitation pulse energy.

Wide modulation bandwidth terahertz detection in 130 nm CMOS technology

NASA Astrophysics Data System (ADS)

Nahar, Shamsun; Shafee, Marwah; Blin, Stéphane; Pénarier, Annick; Nouvel, Philippe; Coquillat, Dominique; Safwa, Amr M. E.; Knap, Wojciech; Hella, Mona M.

2016-11-01

Design, manufacturing and measurements results for silicon plasma wave transistors based wireless communication wideband receivers operating at 300 GHz carrier frequency are presented. We show the possibility of Si-CMOS based integrated circuits, in which by: (i) specific physics based plasma wave transistor design allowing impedance matching to the antenna and the amplifier, (ii) engineering the shape of the patch antenna through a stacked resonator approach and (iii) applying bandwidth enhancement strategies to the design of integrated broadband amplifier, we achieve an integrated circuit of the 300 GHz carrier frequency receiver for wireless wideband operation up to/over 10 GHz. This is, to the best of our knowledge, the first demonstration of low cost 130 nm Si-CMOS technology, plasma wave transistors based fast/wideband integrated receiver operating at 300 GHz atmospheric window. These results pave the way towards future large scale (cost effective) silicon technology based terahertz wireless communication receivers.

Strong terahertz emission by optical rectification of shaped laser pulse in transversely magnetized plasma

NASA Astrophysics Data System (ADS)

Singh, Ram Kishor; Singh, Monika; Rajouria, Satish Kumar; Sharma, R. P.

2017-07-01

This communication presents a theoretical model for efficient terahertz (THz) radiation generation by the optical rectification of shaped laser pulse in transversely magnetised ripple density plasma. The laser beam imparts a nonlinear ponderomotive force to the electron and this force exerts a nonlinear velocity component in both transverse and axial directions which have spectral components in the THz range. These velocity components couple with the pre-existing density ripple and give rise to a strong nonlinear current density which drives the THz wave in the plasma. The THz yield increases with the increasing strength of the background magnetic field and the sensitivity depends on the ripple wave number. The emitted power is directly proportional to the square of the amplitude of the density ripple. For exact phase matching condition, the normalised power of the generated THz wave can be achieved of the order of 10-4.

Tunable terahertz wave-plate based on dual-frequency liquid crystal controlled by alternating electric field.

PubMed

Yu, Jian-Ping; Chen, Sai; Fan, Fei; Cheng, Jie-Rong; Xu, Shi-Tong; Wang, Xiang-Hui; Chang, Sheng-Jiang

2018-01-22

In this work, the optically anisotropic property of dual-frequency liquid crystals (DFLC) in terahertz (THz) regime has been experimentally investigated, which indicates that the refractive index and birefringence of DFLC can be continuously modulated by both the alternating frequency and intensity of the alternating electric field. This tunability originates from the rotation of DFLC molecules induced by alternating electric fields. The results show that by modulating the alternating frequency from 1 kHz to 100 kHz under 30 kV/m electric field, the 600 μm thickness DFLC cell can play as a tunable quarter-wave plate above 0.68 THz, or a half-wave plate above 1.33 THz. Besides, it can be viewed as a tunable THz phase shifter from 0 to π. Therefore, due to its novel tuning mechanism, DFLC will be of great significance in dynamic manipulating on THz phase and polarization.

Multi-physics analysis of hybrid graphene/semiconductor plasmonic terahertz sources (Conference Presentation)

NASA Astrophysics Data System (ADS)

Nafari, Mona; Aizin, Gregory R.; Jornet, Josep M.

2017-05-01

Wireless data rates have doubled every eighteen months for the last three decades. Following this trend, Terabit-per-second links will become a reality within the next five years. In this context, Terahertz (THz) band (0.1-10 THz) communication is envisioned as a key technology of the next decade. Despite major progress towards developing THz sources, compact signal generators above 1 THz able to efficiently work at room temperature are still missing. Recently, the use of hybrid graphene/semiconductor high-electron-mobility transistors (HEMT) has been proposed as a way to generate Surface Plasmon Polariton (SPP) waves at THz frequencies. Compact size, room-temperature operation and tunability of the graphene layer, in addition to possibility for large scale integration, motivate the exploration of this approach. In this paper, a simulation model of hybrid graphene/semiconductor HEMT-based THz sources is developed. More specifically, first, the necessary conditions for the so-called Dyakonov-Shur instability to arise within the HEMT channel are derived, and the impact of imperfect boundary conditions is analyzed. Second, the required conditions for coupling between a confined plasma wave in the HEMT channel and a SPP wave in graphene are derived, by starting from the coupling analysis between two 2DEG. Multi-physics simulation are conducted by integrating the hydrodynamic equations for the description of the HEMT device with Maxwell's equations for SPP modeling. Extensive results are provided to analyze the impact of different design elements on the THz signal source. This work will guide the experimental fabrication and characterization of the devices.

Markets, Availability, Notice, and Technical Performance of Terahertz Systems: Historic Development, Present, and Trends

NASA Astrophysics Data System (ADS)

Hochrein, Thomas

2015-03-01

Although a lot of work has already been done under the older terms "far infrared" or "sub-millimeter waves", the term "terahertz" stands for a novel technique offering many potential applications. The latter term also represents a new generation of systems with the opportunity for coherent, time-resolved detection. In addition to the well-known technical opportunities, an historical examination of Internet usage, as well as the number of publications and patent applications, confirms ongoing interest in this technique. These activities' annual growth rate is between 9 % and 21 %. The geographical distribution shows the center of terahertz activities. A shift from the scientific to more application-oriented research can be observed. We present a survey among worldwide terahertz suppliers with special focus on the European region and the use of terahertz systems in the field of measurement and analytical applications. This reveals the current state of terahertz systems' commercial and geographical availability as well as their costs, target markets, and technical performance. Component cost distribution using the example of an optical pulsed time-domain terahertz system gives an impression of the prevailing cost structure. The predication regarding prospective market development, decreasing system costs and higher availability shows a convenient situation for potential users and interested customers. The causes are primarily increased competition and larger quantities in the future.

Modulated scattering technique in the terahertz domain enabled by current actuated vanadium dioxide switches

PubMed Central

Vitale, W. A.; Tamagnone, M.; Émond, N.; Le Drogoff, B.; Capdevila, S.; Skrivervik, A.; Chaker, M.; Mosig, J. R.; Ionescu, A. M.

2017-01-01

The modulated scattering technique is based on the use of reconfigurable electromagnetic scatterers, structures able to scatter and modulate an impinging electromagnetic field in function of a control signal. The modulated scattering technique is used in a wide range of frequencies up to millimeter waves for various applications, such as field mapping of circuits or antennas, radio-frequency identification devices and imaging applications. However, its implementation in the terahertz domain remains challenging. Here, we describe the design and experimental demonstration of the modulated scattering technique at terahertz frequencies. We characterize a modulated scatterer consisting in a bowtie antenna loaded with a vanadium dioxide switch, actuated using a continuous current. The modulated scatterer behavior is demonstrated using a time domain terahertz spectroscopy setup and shows significant signal strength well above 0.5 THz, which makes this device a promising candidate for the development of fast and energy-efficient THz communication devices and imaging systems. Moreover, our experiments allowed us to verify the operation of a single micro-meter sized VO2 switch at terahertz frequencies, thanks to the coupling provided by the antenna. PMID:28145523

[Aging explosive detection using terahertz time-domain spectroscopy].

PubMed

Meng, Kun; Li, Ze-ren; Liu, Qiao

2011-05-01

Detecting the aging situation of stock explosive is essentially meaningful to the research on the capability, security and stability of explosive. Existing aging explosive detection techniques, such as scan microscope technique, Fourier transfer infrared spectrum technique, gas chromatogram mass spectrum technique and so on, are either not able to differentiate whether the explosive is aging or not, or not able to image the structure change of the molecule. In the present paper, using the density functional theory (DFT), the absorb spectrum changes after the explosive aging were calculated, from which we can clearly find the difference of spectrum between explosive molecule and aging ones in the terahertz band. The terahertz time-domain spectrum (THz-TDS) system as well as its frequency spectrum resolution and measured range are analyzed. Combined with the existing experimental results and the essential characters of the terahertz wave, the application of THz-TDS technique to the detection of aging explosive was demonstrated from the aspects of feasibility, veracity and practicability. On the base of that, the authors advance the new method of aging explosive detection using the terahertz time-domain spectrum technique.

Characteristics of Gadolinium Oxide Nanoparticles Using Terahertz Spectroscopy (abstract)

NASA Astrophysics Data System (ADS)

Lee, Dongkyu; Maeng, Inhee; Oh, Seung Jae; Kim, Taekhoon; Cho, Byung Kyu; Lee, Kwangyeol; Son, Joo-Hiuk

2009-04-01

The penetration property of the terahertz electromagnetic (THz) wave is relevant to its use. We used the THz wave spectroscopy system which easily penetrates some materials that do not contain water, e.g., plastic and ceramics. The system has been developed for several purposes, including measuring the properties of semiconductors and bio-materials, and detecting plastic bombs and ceramic knives at airports. It is also used for medical imaging systems, such as magnetic resonance imaging (MRI), at some research institutes. It can show not only the difference in amplitude, but also the difference of the phase of each point of sample. MRI technology usually uses contrast agents to enhance the quality of the image. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), made with a heavy metal ion, is commonly used as a clinical MRI contrast agent. Gadolinium oxide (Gd2O3) nanoparticle is a new contrast agent. It serves to equip the core of each particle with antibodies or ligands. It can freely circulate in blood vessels without amassing in the liver or lungs. This study shows the characteristics of gadolinium oxide nanoparticles to further advance terahertz medical imaging.

Chemical recognition of gases and gas mixtures with terahertz waves.

PubMed

Jacobsen, R H; Mittleman, D M; Nuss, M C

1996-12-15

A time-domain chemical-recognition system for classifying gases and analyzing gas mixtures is presented. We analyze the free induction decay exhibited by gases excited by far-infrared (terahertz) pulses in the time domain, using digital signal-processing techniques. A simple geometric picture is used for the classif ication of the waveforms measured for unknown gas species. We demonstrate how the recognition system can be used to determine the partial pressures of an ammonia-water gas mixture.

Chemical recognition of gases and gas mixtures with terahertz waves

NASA Astrophysics Data System (ADS)

Jacobsen, R. H.; Mittleman, D. M.; Nuss, M. C.

1996-12-01

A time-domain chemical-recognition system for classifying gases and analyzing gas mixtures is presented. We analyze the free induction decay exhibited by gases excited by far-infrared (terahertz) pulses in the time domain, using digital signal-processing techniques. A simple geometric picture is used for the classification of the waveforms measured for unknown gas species. We demonstrate how the recognition system can be used to determine the partial pressures of an ammonia-water gas mixture.

Millimeter-wave and terahertz integrated circuit antennas

NASA Technical Reports Server (NTRS)

Rebeiz, Gabriel M.

1992-01-01

This paper presents a comprehensive review of integrated circuit antennas suitable for millimeter and terahertz applications. A great deal of research was done on integrated circuit antennas in the last decade and many of the problems associated with electrically thick dielectric substrates, such as substrate modes and poor radiation patterns, have been understood and solved. Several new antennas, such as the integrated horn antenna, the dielectric-filled parabola, the Fresnel plate antenna, the dual-slot antenna, and the log-periodic and spiral antennas on extended hemispherical lenses, have resulted in excellent performance at millimeter-wave frequencies, and are covered in detail in this paper. Also, a review of the efficiency definitions used with planar antennas is given in detail in the appendix.

Anharmonic Damping of Terahertz Acoustic Waves in a Network Glass and Its Effect on the Density of Vibrational States

NASA Astrophysics Data System (ADS)

Baldi, G.; Giordano, V. M.; Ruta, B.; Dal Maschio, R.; Fontana, A.; Monaco, G.

2014-03-01

We report the observation, by means of high-resolution inelastic x-ray scattering, of an unusually large temperature dependence of the sound attenuation of a network glass at terahertz frequency, an unprecedentedly observed phenomenon. The anharmonicity can be ascribed to the interaction between the propagating acoustic wave and the bath of thermal vibrations. At low temperatures the sound attenuation follows a Rayleigh-Gans scattering law. As the temperature is increased the anharmonic process sets in, resulting in an almost quadratic frequency dependence of the damping in the entire frequency range. We show that the temperature variation of the sound damping accounts quantitatively for the temperature dependence of the density of vibrational states.

Stable high absorption metamaterial for wide-angle incidence of terahertz wave

NASA Astrophysics Data System (ADS)

Du, Qiujiao; Zeng, Zuoxun; Xiang, Dong; Lv, Tao; Zhang, Guangyong; Yang, Hongwu

2014-04-01

We propose a metamaterial based on metallic Jerusalem cross and cross-wire structures for realizing relatively stable high absorption with respect to the wide angle incidence of both polarized terahertz (THz) waves. Numerical simulations are carried out to verify the proposed absorber. For both transverse electric and transverse magnetic polarizations, absorptions around 0.93 THz reach nearly up to unity under normal incidence and maintain above 97% over a wide incidence angle range. The THz absorber can be easily micro-fabricated due to a thickness about 40 times smaller than operating wavelength. The proposed metamaterial is a promising candidate as absorbing element in THz thermal imager, due to its wide angle, stable high absorption and very thin thickness.

Ultrafast Terahertz Nonlinear Optics of Landau Level Transitions in a Monolayer Graphene

NASA Astrophysics Data System (ADS)

Yumoto, Go; Matsunaga, Ryusuke; Hibino, Hiroki; Shimano, Ryo

2018-03-01

We investigated the ultrafast terahertz (THz) nonlinearity in a monolayer graphene under the strong magnetic field using THz pump-THz probe spectroscopy. An ultrafast suppression of the Faraday rotation associated with inter-Landau level (LL) transitions is observed, reflecting the Dirac electron character of nonequidistant LLs with large transition dipole moments. A drastic modulation of electron distribution in LLs is induced by far off-resonant THz pulse excitation in the transparent region. Numerical simulation based on the density matrix formalism without rotating-wave approximation reproduces the experimental results. Our results indicate that the strong light-matter coupling regime is realized in graphene, with the Rabi frequency exceeding the carrier wave frequency and even the relevant energy scale of the inter-LL transition.

Characterization of plasma treated surfaces for food safety by terahertz spectroscopy

NASA Astrophysics Data System (ADS)

Sulovská, Kateřina; Lehocký, Marián.

2014-10-01

A physico-chemical approach to modify surfaces not only for use in medicine, but also for preservation of food is nowadays widely studied to lower the risks of increased number of bacterial pathogens that are in a direct contact with people. Food safety is very important part of preserving sustainability during crises, especially after the enterohaemorrhagic Escherichia coli outbreak in Europe in 2011. One of the possibility how we can protect food against various pathogens is the modification of packing materials that are directly in contact with preserved food. This contribution deals with the characterization of modified surfaces with antibacterial properties via Terahertz spectroscopy. For the purpose of this paper, three monomers were used for grafting onto air radiofrequency plasma activated low density polyethylene surface, which created a brush-like structure. Next, the antibacterial agents, Irgasan and Chlorhexidine, were anchored to these surfaces. These antibacterial agents were selected for supposed effect on two most frequently occurring bacterial strains - Escherichia coli and Staphylococcus aureus. Materials were further tested for the presence of antibacterial agent molecules, in our case by means of terahertz spectroscopy. Each material was tested on two spectroscopes - the SPECTRA and the OSCAT terahertz instruments.

Sub-wavelength terahertz beam profiling of a THz source via an all-optical knife-edge technique.

PubMed

Phing, Sze Ho; Mazhorova, Anna; Shalaby, Mostafa; Peccianti, Marco; Clerici, Matteo; Pasquazi, Alessia; Ozturk, Yavuz; Ali, Jalil; Morandotti, Roberto

2015-02-25

Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (<100 nm-thickness) of photo carriers is induced on the surface of the terahertz generation crystal, which acts as an all-optical, virtual blade for terahertz near-field imaging via a knife-edge technique. Remarkably, and in spite of the fact that the proposed approach does not require any mechanical probe, such as tips or apertures, we are able to demonstrate the imaging of a terahertz source with deeply sub-wavelength features (<30 μm) directly in its emission plane.

Video-rate terahertz electric-field vector imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takai, Mayuko; Takeda, Masatoshi; Sasaki, Manabu

We present an experimental setup to dramatically reduce a measurement time for obtaining spatial distributions of terahertz electric-field (E-field) vectors. The method utilizes the electro-optic sampling, and we use a charge-coupled device to detect a spatial distribution of the probe beam polarization rotation by the E-field-induced Pockels effect in a 〈110〉-oriented ZnTe crystal. A quick rotation of the ZnTe crystal allows analyzing the terahertz E-field direction at each image position, and the terahertz E-field vector mapping at a fixed position of an optical delay line is achieved within 21 ms. Video-rate mapping of terahertz E-field vectors is likely to bemore » useful for achieving real-time sensing of terahertz vector beams, vector vortices, and surface topography. The method is also useful for a fast polarization analysis of terahertz beams.« less

Terahertz modulation based on surface plasmon resonance by self-gated graphene

NASA Astrophysics Data System (ADS)

Qian, Zhenhai; Yang, Dongxiao; Wang, Wei

2018-05-01

We theoretically and numerically investigate the extraordinary optical transmission through a terahertz metamaterial composed of metallic ring aperture arrays. The physical mechanism of different transmission peaks is elucidated to be magnetic polaritons or propagation surface plasmons with the help of surface current and electromagnetic field distributions at respective resonance frequencies. Then, we propose a high performance terahertz modulator based on the unique PSP resonance and combined with the metallic ring aperture arrays and a self-gated parallel-plate graphene capacitor. Because, to date, few researches have exhibited gate-controlled graphene modulation in terahertz region with low insertion losses, high modulation depth and low control voltage at room temperature. Here, we propose a 96% amplitude modulation with 0.7 dB insertion losses and ∼5.5 V gate voltage. Besides, we further study the absorption spectra of the modulator. When the transmission of modulator is very low, a 91% absorption can be achieved for avoiding damaging the source devices.

Performance analysis of higher mode spoof surface plasmon polariton for terahertz sensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Haizi; Tu, Wanli; Zhong, Shuncong, E-mail: zhongshuncong@hotmail.com

2015-04-07

We investigated the spoof surface plasmon polaritons (SSPPs) on 1D grooved metal surface for terahertz sensing of refractive index of the filling analyte through a prism-coupling attenuated total reflection setup. From the dispersion relation analysis and the finite element method-based simulation, we revealed that the dispersion curve of SSPP got suppressed as the filling refractive index increased, which cause the coupling resonance frequency redshifting in the reflection spectrum. The simulated results for testing various refractive indexes demonstrated that the incident angle of terahertz radiation has a great effect on the performance of sensing. Smaller incident angle will result in amore » higher sensitive sensing with a narrower detection range. In the meanwhile, the higher order mode SSPP-based sensing has a higher sensitivity with a narrower detection range. The maximum sensitivity is 2.57 THz/RIU for the second-order mode sensing at 45° internal incident angle. The proposed SSPP-based method has great potential for high sensitive terahertz sensing.« less

Graphene surface emitting terahertz laser: Diffusion pumping concept

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davoyan, Arthur R., E-mail: davoyan@seas.upenn.edu; Morozov, Mikhail Yu.; Popov, Vyacheslav V.

2013-12-16

We suggest a concept of a tunable graphene-based terahertz (THz) surface emitting laser with diffusion pumping. We employ significant difference in the electronic energy gap of graphene and a typical wide-gap semiconductor, and demonstrate that carriers generated in the semiconductor can be efficiently captured by graphene resulting in population inversion and corresponding THz lasing from graphene. We develop design principles for such a laser and estimate its performance. We predict up to 50 W/cm{sup 2} terahertz power output for 100 kW/cm{sup 2} pump power at frequency around 10 THz at room temperature.

Broadband, Spectrally Flat, Graphene-based Terahertz Modulators.

PubMed

Shi, Fenghua; Chen, Yihang; Han, Peng; Tassin, Philippe

2015-12-02

Advances in the efficient manipulation of terahertz waves are crucial for the further development of terahertz technology, promising applications in many diverse areas, such as biotechnology and spectroscopy, to name just a few. Due to its exceptional electronic and optical properties, graphene is a good candidate for terahertz electro-absorption modulators. However, graphene-based modulators demonstrated to date are limited in bandwidth due to Fabry-Perot oscillations in the modulators' substrate. Here, a novel method is demonstrated to design electrically controlled graphene-based modulators that can achieve broadband and spectrally flat modulation of terahertz beams. In our design, a graphene layer is sandwiched between a dielectric and a slightly doped substrate on a metal reflector. It is shown that the spectral dependence of the electric field intensity at the graphene layer can be dramatically modified by optimizing the structural parameters of the device. In this way, the electric field intensity can be spectrally flat and even compensate for the dispersion of the graphene conductivity, resulting in almost invariant absorption in a wide frequency range. Modulation depths up to 76% can be achieved within a fractional operational bandwidth of over 55%. It is expected that our modulator designs will enable the use of terahertz technology in applications requiring broadband operation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Terahertz quasi time-domain spectroscopy based on telecom technology for 1550 nm.

PubMed

Kohlhaas, Robert B; Rehn, Arno; Nellen, Simon; Koch, Martin; Schell, Martin; Dietz, Roman J B; Balzer, Jan C

2017-05-29

We present a fiber-coupled terahertz quasi time-domain spectroscopy system driven by a laser with a central wavelength of 1550 nm. By using a commercially available multimode laser diode in combination with state-of-the-art continuous wave antennas, a bandwidth of more than 1.8 THz is achieved. The peak signal-to-noise ratio is around 60 dB. A simulation based on the optical spectrum of the laser diode and the transfer function of the THz path is in agreement with the experimental results. The system is used to extract the refractive index from two different samples and the results indicate that the performance is up to 1.8 THz comparable to a terahertz time-domain spectroscopy system.

The importance of scattering, surface potential, and vanguard counter-potential in terahertz emission from gallium arsenide

NASA Astrophysics Data System (ADS)

Cortie, D. L.; Lewis, R. A.

2012-06-01

It is well established that under excitation by short (<1 ps), above-band-gap optical pulses, semiconductor surfaces may emit terahertz-frequency electromagnetic radiation via photocarrier diffusion (the dominant mechanism in InAs) or photocarrier drift (dominant in GaAs). Our three-dimensional ensemble Monte Carlo simulations allow multiple physical parameters to vary over wide ranges and provide unique direct insight into the factors controlling terahertz emission. We find for GaAs (in contrast to InAs), scattering and the surface potential are key factors. We further delineate in GaAs (as in InAs) the role of a vanguard counter-potential. The effects of varying dielectric constant, band-gap, and effective mass are similar in both emitter types.

The role of optical rectification in the generation of terahertz radiation from GaBiAs

NASA Astrophysics Data System (ADS)

Radhanpura, K.; Hargreaves, S.; Lewis, R. A.; Henini, M.

2009-06-01

We report on a detailed study of the emission of terahertz-frequency electromagnetic radiation from layers of GaBiyAs1-y (0≤y<0.04) grown by molecular beam epitaxy on (311)B and (001) GaAs substrates. We measure two orthogonally polarized components of the terahertz radiation emitted under excitation by ultrashort near-infrared laser pulses in both transmission and reflection geometries as a function of the crystal rotation about its surface normal as well as the effect of in-plane magnetic field and pump fluence on the terahertz emission. We conclude that the principal mechanism for terahertz generation is via optical rectification rather than transient currents.

Ultra-high Q terahertz whispering-gallery modes in a silicon resonator

NASA Astrophysics Data System (ADS)

Vogt, Dominik Walter; Leonhardt, Rainer

2018-05-01

We report on the first experimental demonstration of terahertz (THz) whispering-gallery modes (WGMs) with an ultra-high quality factor of 1.5 × 104 at 0.62 THz. The WGMs are observed in a high resistivity float zone silicon spherical resonator coupled to a sub-wavelength silica waveguide. A detailed analysis of the coherent continuous wave THz spectroscopy measurements combined with a numerical model based on Mie-Debye-Aden-Kerker theory allows us to unambiguously identify the observed higher order radial THz WGMs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sterczewski, L. A., E-mail: lukasz.sterczewski@pwr.edu.pl; Grzelczak, M. P.; Plinski, E. F.

In this paper, we present an electronic circuit used to bias a photoconductive antenna that generates terahertz radiation. The working principles and the design process for the device are discussed in detail. The noise and shape of the wave measurements for a built device are considered. Furthermore, their impact on a terahertz pulse and its spectra is also examined. The proposed implementation is simple to build, robust and offers a real improvement over THz instrumentation due to the frequency tuning. Additionally, it provides for galvanic isolation and ESD protection.

Bending and coupling losses in terahertz wire waveguides.

PubMed

Astley, Victoria; Scheiman, Julianna; Mendis, Rajind; Mittleman, Daniel M

2010-02-15

We present an experimental study of several common perturbations of wire waveguides for terahertz pulses. Sommerfeld waves retain significant signal strength and bandwidth even with large gaps in the wire, exhibiting more efficient recoupling at higher frequencies. We also describe a detailed study of bending losses. For a given turn angle, we observe an optimum radius of curvature that minimizes the overall propagation loss. These results emphasize the impact of the distortion of the spatial mode on the radiative bend loss.

Fast continuous tuning of terahertz quantum-cascade lasers by rear-facet illumination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hempel, Martin, E-mail: hempel@pdi-berlin.de; Röben, Benjamin; Schrottke, Lutz

2016-05-09

GaAs-based terahertz quantum-cascade lasers (QCLs) are continuously tuned in their emission frequency by illuminating the rear facet with a near-infrared, high-power diode laser. For QCLs emitting around 3.1 THz, the maximum tuning range amounts to 2.8 GHz for continuous-wave operation at a heat sink temperature of 55 K, while in pulsed mode 9.1 and 8.0 GHz are achieved at 35 and 55 K, respectively.

Disturbing the coherent dynamics of an excitonic polarization with strong terahertz fields

NASA Astrophysics Data System (ADS)

Drexler, M. J.; Woscholski, R.; Lippert, S.; Stolz, W.; Rahimi-Iman, A.; Koch, M.

2014-11-01

We present a paper based on combining four-wave mixing and strong fields in the terahertz frequency range to monitor the time evolution of a disturbed excitonic polarization in a multiple quantum well system. Our findings not only confirm a lower field-dependent ionization threshold for higher excitonic states, but furthermore provide experimental evidence for intraexcitonic Rabi flopping in the time domain. These measurements correspond to the picture of a reversible and irreversible transfer as previously predicted by a microscopic theory.

Low-coherence terahertz tomography based on spatially separated counterpropagating beams with allowance for probe radiation absorption in the medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandrosov, V I

2015-10-31

This paper analyses low-coherence tomography of absorbing media with the use of spatially separated counterpropagating object and reference beams. A probe radiation source based on a broadband terahertz (THz) generator that emits sufficiently intense THz waves in the spectral range 90 – 350 μm and a prism spectroscope that separates out eight narrow intervals from this range are proposed for implementing this method. This allows media of interest to be examined by low-coherence tomography with counterpropagating beams in each interval. It is shown that, according to the Rayleigh criterion, the method is capable of resolving inhomogeneities with a size nearmore » one quarter of the coherence length of the probe radiation. In addition, the proposed tomograph configuration allows one to determine the average surface asperity slope and the refractive index and absorption coefficient of inhomogeneities 180 to 700 mm in size, and obtain spectra of such inhomogeneities in order to determine their chemical composition. (laser applications and other topics in quantum electronics)« less

Observation of Gate-Tunable Coherent Perfect Absorption of Terahertz Waves in Graphene

NASA Astrophysics Data System (ADS)

Kocabas, Coskun; Kakenov, Nurbek; Balci, Osman; Takan, Taylan; Ozkan, Vedat Ali; Altan, Hakan

We report experimental observation of electrically tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode, and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1 eV and to achieve a critical coupling condition at 2.8 THz with absorption of 100 %. With the enhanced THz absorption, we were able to measure the Fermi energy dependence of the transport scattering time of highly doped graphene. Furthermore, we demonstrate flexible active THz surfaces that yield large modulation in the THz reflectivity with low insertion losses. We anticipate that the gate-tunable CPA will lead to efficient active THz optoelectronics applications. This work was partially supported by the Scientific and Technological Research Council of Turkey (TUBITAK) Grant No. 114F379 and the European Research Council (ERC) Consolidator Grant ERC-682723 SmartGraphene. N.K. acknowledges the TUBITAK-BIDEB 2215.

High performance terahertz metasurface quantum-cascade VECSEL with an intra-cryostat cavity

DOE PAGES

Xu, Luyao; Curwen, Christopher A.; Reno, John L.; ...

2017-09-04

A terahertz quantum-cascade (QC) vertical-external-cavity surface-emitting-laser (VECSEL) is demonstrated with over 5 mW power in continuous-wave and single-mode operation above 77 K, in combination with a near-Gaussian beam pattern with full-width half-max divergence as narrow as ~5° × 5°, with no evidence of thermal lensing. This is realized by creating an intra-cryostat VECSEL cavity to reduce the cavity loss and designing an active focusing metasurface reflector with low power dissipation for efficient heat removal. Compared with a conventional quantumcascade laser based on a metal-metal waveguide, the intra-cryostat QC-VECSEL exhibits significant improvements in both output power level and beam pattern. Also,more » the intra-cryostat configuration newly allows evaluation of QC-VECSEL operation vs. temperature, showing a maximum pulsed mode operating temperature of 129 K. While the threshold current density in the QC-VECSEL is worse in comparison to a conventional edge-emitting metal-metal waveguide QClaser, the beam quality, slope efficiency, maximum power, and thermal resistance are all significantly improved.« less

[The Detection of Ultra-Broadband Terahertz Spectroscopy of InP Wafer by Using Coherent Heterodyne Time-Domain Spectrometer].

PubMed

Zhang, Liang-liang; Zhang, Rui; Xu, Xiao-yan; Zhang, Cun-lin

2016-02-01

Indium Phosphide (InP) has attracted great physical interest because of its unique characteristics and is indispensable to both optical and electronic devices. However, the optical property of InP in the terahertz range (0. 110 THz) has not yet been fully characterized and systematically studied. The former researches about the properties of InP concentrated on the terahertz frequency between 0.1 and 4 THz. The terahertz optical properties of the InP in the range of 4-10 THz are still missing. It is fairly necessary to fully understand its properties in the entire terahertz range, which results in a better utilization as efficient terahertz devices. In this paper, we study the optical properties of undoped (100) InP wafer in the ultra-broad terahertz frequency range (0.5-18 THz) by using air-biased-coherent-detection (ABCD) system, enabling the coherent detection of terahertz wave in gases, which leads to a significant improvement on the dynamic range and sensitivity of the system. The advantage of this method is broad frequency bandwidth from 0.2 up to 18 THz which is only mainly limited by laser pulse duration since it uses ionized air as terahertz emitter and detector instead of using an electric optical crystal or photoconductive antenna. The terahertz pulse passing through the InP wafer is delayed regarding to the reference pulse and has much lower amplitude. In addition, the frequency spectrum amplitude of the terahertz sample signal drops to the noise floor level from 6.7 to 12.1 THz. At the same time InP wafer is opaque at the frequencies spanning from 6.7 to 12.1 THz. In the frequency regions of 0.8-6.7 and 12.1-18 THz it has relativemy low absorption coefficient. Meanwhile, the refractive index increases monotonously in the 0.8-6.7 THz region and 12.1-18 THz region. These findings will contribute to the design of InP based on nonlinear terahertz devices.

Energy scaling and extended tunability of terahertz wave parametric oscillator with MgO-doped near-stoichiometric LiNbO₃ crystal.

PubMed

Wang, Yuye; Tang, Longhuang; Xu, Degang; Yan, Chao; He, Yixin; Shi, Jia; Yan, Dexian; Liu, Hongxiang; Nie, Meitong; Feng, Jiachen; Yao, Jianquan

2017-04-17

A widely tunable, high-energy terahertz wave parametric oscillator based on 1 mol. % MgO-doped near-stoichiometric LiNbO₃ crystal has been demonstrated with 1064 nm nanosecond pulsed laser pumping. The tunable range of 1.16 to 4.64 THz was achieved. The maximum THz wave output energy of 17.49 μJ was obtained at 1.88 THz under the pump energy of 165 mJ/pulse, corresponding to the THz wave conversion efficiency of 1.06 × 10^-4 and the photon conversion efficiency of 1.59%, respectively. Moreover, under the same experimental conditions, the THz output energy of TPO with MgO:SLN crystal was about 2.75 times larger than that obtained from the MgO:CLN TPO at 1.60 THz. Based on the theoretical analysis, the THz energy enhancement mechanism in the MgO:SLN TPO was clarified to originate from its larger Raman scattering cross section and smaller absorption coefficient.

Determination of plane stress state using terahertz time-domain spectroscopy

PubMed Central

Wang, Zhiyong; Kang, Kai; Wang, Shibin; Li, Lin'an; Xu, Ningning; Han, Jiaguang; He, Mingxia; Wu, Liang; Zhang, Weili

2016-01-01

THz wave has been increasingly applied in engineering practice. One of its outstanding advantages is the penetrability through certain optically opaque materials, whose interior properties could be therefore obtained. In this report, we develop an experimental method to determine the plane stress state of optically opaque materials based on the stress-optical law using terahertz time-domain spectroscopy (THz-TDS). In this method, two polarizers are combined into the conventional THz-TDS system to sense and adjust the polarization state of THz waves and a theoretical model is established to describe the relationship between phase delay of the received THz wave and the plane stress applied on the specimen. Three stress parameters that represent the plane stress state are finally determined through an error function of THz wave phase-delay. Experiments were conducted on polytetrafluoroethylene (PTFE) specimen and a reasonably good agreement was found with measurement using traditional strain gauges. The presented results validate the effectiveness of the proposed method. The proposed method could be further used in nondestructive tests for a wide range of optically opaque materials. PMID:27824112

Determination of plane stress state using terahertz time-domain spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Zhiyong; Kang, Kai; Wang, Shibin; Li, Lin'an; Xu, Ningning; Han, Jiaguang; He, Mingxia; Wu, Liang; Zhang, Weili

2016-11-01

THz wave has been increasingly applied in engineering practice. One of its outstanding advantages is the penetrability through certain optically opaque materials, whose interior properties could be therefore obtained. In this report, we develop an experimental method to determine the plane stress state of optically opaque materials based on the stress-optical law using terahertz time-domain spectroscopy (THz-TDS). In this method, two polarizers are combined into the conventional THz-TDS system to sense and adjust the polarization state of THz waves and a theoretical model is established to describe the relationship between phase delay of the received THz wave and the plane stress applied on the specimen. Three stress parameters that represent the plane stress state are finally determined through an error function of THz wave phase-delay. Experiments were conducted on polytetrafluoroethylene (PTFE) specimen and a reasonably good agreement was found with measurement using traditional strain gauges. The presented results validate the effectiveness of the proposed method. The proposed method could be further used in nondestructive tests for a wide range of optically opaque materials.

Low frequency piezoresonance defined dynamic control of terahertz wave propagation

NASA Astrophysics Data System (ADS)

Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G.; Bhalla, Amar S.; Guo, Ruyan

2016-11-01

Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.

Low frequency piezoresonance defined dynamic control of terahertz wave propagation.

PubMed

Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G; Bhalla, Amar S; Guo, Ruyan

2016-11-30

Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO 3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.

Wide-aperture aspherical lens for high-resolution terahertz imaging

NASA Astrophysics Data System (ADS)

Chernomyrdin, Nikita V.; Frolov, Maxim E.; Lebedev, Sergey P.; Reshetov, Igor V.; Spektor, Igor E.; Tolstoguzov, Viktor L.; Karasik, Valeriy E.; Khorokhorov, Alexei M.; Koshelev, Kirill I.; Schadko, Aleksander O.; Yurchenko, Stanislav O.; Zaytsev, Kirill I.

2017-01-01

In this paper, we introduce wide-aperture aspherical lens for high-resolution terahertz (THz) imaging. The lens has been designed and analyzed by numerical methods of geometrical optics and electrodynamics. It has been made of high-density polyethylene by shaping at computer-controlled lathe and characterized using a continuous-wave THz imaging setup based on a backward-wave oscillator and Golay detector. The concept of image contrast has been implemented to estimate image quality. According to the experimental data, the lens allows resolving two points spaced at 0.95λ distance with a contrast of 15%. To highlight high resolution in the THz images, the wide-aperture lens has been employed for studying printed electronic circuit board containing sub-wavelength-scale elements. The observed results justify the high efficiency of the proposed lens design.

The effect of beam pre-bunching on the excitation of terahertz plasmons in a parallel plane guiding system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Suresh C.; Malik, Pratibha

2015-04-15

The excitation of terahertz (THz) plasmons by a pre-bunched relativistic electron beam propagating in a parallel plane semiconducting guiding system is studied. It is found that the n-InSb semiconductor strongly supports the confined surface plasmons in the terahertz frequency range. The growth rate and efficiency of the THz surface plasmons increase linearly with modulation index and show the largest value as modulation index approaches unity. Moreover, the growth rate of the instability scales as one-third power of the beam density and inverse one-third power of the THz radiation frequency.

Excitation of terahertz radiation by an electron beam in a dielectric lined waveguide with rippled dielectric surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tripathi, Deepak; Uma, R.; Tripathi, V. K.

A relativistic electron beam propagating through a dielectric lined waveguide, with ripple on the dielectric surface, excites a free electron laser type instability where ripple acts as a wiggler. The spatial modulation of permittivity in the ripple region couples a terahertz radiation mode to a driven mode of lower phase velocity, where the beam is in Cerenkov resonance with the slow mode. Both the modes grow at the expanse of beam energy. The terahertz frequency increases as the beam velocity increases. The growth rate of the instability goes as one third power of beam density.

Laser beat wave excitation of terahertz radiation in a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chauhan, Santosh; Parashar, Jetendra, E-mail: j.p.parashar@gmail.com

2014-10-15

Terahertz (THz) radiation generation by nonlinear mixing of lasers, obliquely incident on a plasma slab is investigated. Two cases are considered: (i) electron density profile is parabolic but density peak is below the critical density corresponding to the beat frequency, (ii) plasma boundaries are sharp and density is uniform. In both cases, nonlinearity arises through the ponderomotive force that gives rise to electron drift at the beat frequency. In the case of inhomogeneous plasma, non zero curl of the nonlinear current density gives rise to electromagnetic THz generation. In case of uniform plasma, the sharp density variation at the plasmamore » boundaries leads to radiation generation. In a slab width of less than a terahertz wavelength, plasma density one fourth of terahertz critical density, laser intensities ∼10{sup 17 }W/cm{sup 2} at 1 μm, one obtains the THz intensity ∼1 GW/cm{sup 2} at 3 THz radiation frequency.« less

Role of nonlinear refraction in the generation of terahertz field pulses by light fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zabolotskii, A. A., E-mail: zabolotskii@iae.nsk.su

2013-07-15

The generation of microwave (terahertz) pulses without any envelope in a four-level quasi-resonant medium is considered. Two intense quasi-monochromatic laser fields lead to a partial upper-level population. Microwave field pulses cause the transition between these levels. For appropriately chosen scales, the evolution of the fields is shown to be described by the pseudo-spin evolution equations in a microwave field with the inclusion of nonlinear refraction caused by an adiabatic upper-level population. The evolution of terahertz field pulses is described outside the scope of the slow-envelope approximation. When a number of standard approximations are taken into account, this system of equationsmore » is shown to be equivalent to an integrable version of the generalized reduced Maxwell-Bloch equations or to the generalized three-wave mixing equations. The soliton solution found by the inverse scattering transform method is used as an example to show that nonlinear refraction leads to a strong compression of the microwave (terahertz) field soliton.« less

Influence of the electron density on the characteristics of terahertz waves generated under laser–cluster interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frolov, A. A., E-mail: frolov@ihed.ras.ru

2016-12-15

A theory of generation of terahertz radiation under laser–cluster interaction, developed earlier for an overdense cluster plasma [A. A. Frolov, Plasma Phys. Rep. 42. 637 (2016)], is generalized for the case of arbitrary electron density. The spectral composition of radiation is shown to substantially depend on the density of free electrons in the cluster. For an underdense cluster plasma, there is a sharp peak in the terahertz spectrum at the frequency of the quadrupole mode of a plasma sphere. As the electron density increases to supercritical values, this spectral line vanishes and a broad maximum at the frequency comparable withmore » the reciprocal of the laser pulse duration appears in the spectrum. The dependence of the total energy of terahertz radiation on the density of free electrons is analyzed. The radiation yield is shown to increase significantly under resonance conditions, when the laser frequency is close to the eigenfrequency of the dipole or quadrupole mode of a plasma sphere.« less

Investigating the use of terahertz pulsed time domain reflection imaging for the study of fabric layers of an Egyptian mummy

NASA Astrophysics Data System (ADS)

Fukunaga, K.; Cortes, E.; Cosentino, A.; Stã¼nkel, I.; Leona, M.; Duling, N.; Mininberg, D. T.

2011-08-01

This paper reports the first use of terahertz time domain reflection imaging involving textiles on part of a complete human mummy, still in original wrapping. X-ray technique has been used extensively to investigate anatomical features, since X-ray pass through the wrapping. Terahertz waves, on the other hand, can penetrate into non-metallic materials and its reflection depends on the refractive index of materials at the interface, such as textiles and the air. The mummy of Kharushere (ca. 945-712 B.C.) was examined by using Terahertz time domain reflection imaging in the Egyptian galleries of The Metropolitan Museum of Art. Experimental results suggest that the Terahetz imaging is a promising technique for probing the fabric layers surrounding Egyptian mummies, although it is still very limited in its current state. In the future it could become a useful complement to CT scanning when materials with low radiographic density and contrast are being investigated

Absolute Thickness Measurements on Coatings Without Prior Knowledge of Material Properties Using Terahertz Energy

NASA Technical Reports Server (NTRS)

Roth, Don J.; Cosgriff, Laura M.; Harder, Bryan; Zhu, Dongming; Martin, Richard E.

2013-01-01

This study investigates the applicability of a novel noncontact single-sided terahertz electromagnetic measurement method for measuring thickness in dielectric coating systems having either dielectric or conductive substrate materials. The method does not require knowledge of the velocity of terahertz waves in the coating material. The dielectric coatings ranged from approximately 300 to 1400 m in thickness. First, the terahertz method was validated on a bulk dielectric sample to determine its ability to precisely measure thickness and density variation. Then, the method was studied on simulated coating systems. One simulated coating consisted of layered thin paper samples of varying thicknesses on a ceramic substrate. Another simulated coating system consisted of adhesive-backed Teflon adhered to conducting and dielectric substrates. Alumina samples that were coated with a ceramic adhesive layer were also investigated. Finally, the method was studied for thickness measurement of actual thermal barrier coatings (TBC) on ceramic substrates. The unique aspects and limitations of this method for thickness measurements are discussed.

A non-destructive method for quality control of the pellet distribution within a MUPS tablet by terahertz pulsed imaging.

PubMed

Novikova, Anna; Markl, Daniel; Zeitler, J Axel; Rades, Thomas; Leopold, Claudia S

2018-01-01

Terahertz pulsed imaging (TPI) was applied to analyse the inner structure of multiple unit pellet system (MUPS) tablets. MUPS tablets containing different amounts of theophylline pellets coated with Eudragit® NE 30 D and with microcrystalline cellulose (MCC) as cushioning agent were analysed. The tablets were imaged by TPI and the results were compared to X-ray microtomography. The terahertz pulse beam propagates through the tablets and is back-reflected at the interface between the MCC matrix and the coated pellets within the tablet causing a peak in the terahertz waveform. Cross-section images of the tablets were extracted at different depths and parallel to the tablet faces from 3D terahertz data to visualise the surface-near structure of the MUPS tablets. The images of the surface-near structure of the MUPS tablets were compared to X-ray microtomography images at the same depths. The surface-near structure could be clearly resolved by TPI at depths between 24 and 152μm below the tablet surface. An increasing amount of pellets within the MUPS tablets appears to slightly decrease the detectability of the pellets within the tablets by TPI. TPI was shown to be a non-destructive method for the detection of pellets within the tablets and could resolve structures thicker than 30μm. In conclusion, a proof-of-concept was provided for TPI as a method of quality control for MUPS tablets. Copyright © 2017 Elsevier B.V. All rights reserved.

Monitoring leaf water content with THz and sub-THz waves.

PubMed

Gente, Ralf; Koch, Martin

2015-01-01

Terahertz technology is still an evolving research field that attracts scientists with very different backgrounds working on a wide range of subjects. In the past two decades, it has been demonstrated that terahertz technology can provide a non-invasive tool for measuring and monitoring the water content of leaves and plants. In this paper we intend to review the different possibilities to perform in-vivo water status measurements on plants with the help of THz and sub-THz waves. The common basis of the different methods is the strong absorption of THz and sub-THz waves by liquid water. In contrast to simpler, yet destructive, methods THz and sub-THz waves allow for the continuous monitoring of plant water status over several days on the same sample. The technologies, which we take into focus, are THz time domain spectroscopy, THz continuous wave setups, THz quasi time domain spectroscopy and sub-THz continuous wave setups. These methods differ with respect to the generation and detection schemes, the covered frequency range, the processing and evaluation of the experimental data, and the mechanical handling of the measurements. Consequently, we explain which method fits best in which situation. Finally, we discuss recent and future technological developments towards more compact and budget-priced measurement systems for use in the field.

Ultrathin Terahertz Quarter-wave plate based on Split Ring Resonator and Wire Grating hybrid Metasurface.

PubMed

Nouman, Muhammad Tayyab; Hwang, Ji Hyun; Jang, Jae-Hyung

2016-12-13

Planar metasurface based quarter-wave plates offer various advantages over conventional waveplates in terms of compactness, flexibility and simple fabrication; however they offer very narrow bandwidth of operation. Here, we demonstrate a planar terahertz (THz) metasurface capable of linear to circular polarization conversion and vice versa in a wide frequency range. The proposed metasurface is based on horizontally connected split ring resonators and is realized on an ultrathin (0.05λ) zeonor substrate. The fabricated quarter waveplate realizes linear to circular polarization conversion in two broad frequency bands comprising 0.64-0.82 THz and 0.96-1.3 THz with an insertion loss ranging from -3.9 to -10 dB. By virtue of ultrathin sub wavelength thickness, the proposed waveplate design is well suited for application in near field THz optical systems. Additionally, the proposed metasurface design offers novel transmission phase characteristics that present further opportunities to realize dynamic polarization control of incident waves.

Ultrathin Terahertz Quarter-wave plate based on Split Ring Resonator and Wire Grating hybrid Metasurface

PubMed Central

Nouman, Muhammad Tayyab; Hwang, Ji Hyun; Jang, Jae-Hyung

2016-01-01

Planar metasurface based quarter-wave plates offer various advantages over conventional waveplates in terms of compactness, flexibility and simple fabrication; however they offer very narrow bandwidth of operation. Here, we demonstrate a planar terahertz (THz) metasurface capable of linear to circular polarization conversion and vice versa in a wide frequency range. The proposed metasurface is based on horizontally connected split ring resonators and is realized on an ultrathin (0.05λ) zeonor substrate. The fabricated quarter waveplate realizes linear to circular polarization conversion in two broad frequency bands comprising 0.64–0.82 THz and 0.96–1.3 THz with an insertion loss ranging from −3.9 to −10 dB. By virtue of ultrathin sub wavelength thickness, the proposed waveplate design is well suited for application in near field THz optical systems. Additionally, the proposed metasurface design offers novel transmission phase characteristics that present further opportunities to realize dynamic polarization control of incident waves. PMID:27958358

Terahertz imaging with sub-wavelength resolution by femtosecond laser filament in air

PubMed Central

Zhao, Jiayu; Chu, Wei; Guo, Lanjun; Wang, Zhi; Yang, Jing; Liu, Weiwei; Cheng, Ya; Xu, Zhizhan

2014-01-01

Terahertz (THz) imaging provides cutting edge technique in biology, medical sciences and non-destructive evaluation. However, due to the long wavelength of the THz wave, the obtained resolution of THz imaging is normally a few hundred microns and is much lower than that of the traditional optical imaging. We introduce a sub-wavelength resolution THz imaging technique which uses the THz radiation generated by a femtosecond laser filament in air as the probe. This method is based on the fact that the femtosecond laser filament forms a waveguide for the THz wave in air. The diameter of the THz beam, which propagates inside the filament, varies from 20 μm to 50 μm, which is significantly smaller than the wavelength of the THz wave. Using this highly spatially confined THz beam as the probe, THz imaging with resolution as high as 20 μm (~λ/38 at 0.4 THz) can be realized. PMID:24457525

Heterogeneously integrated III-V/silicon dual-mode distributed feedback laser array for terahertz generation.

PubMed

Shao, Haifeng; Keyvaninia, Shahram; Vanwolleghem, Mathias; Ducournau, Guillaume; Jiang, Xiaoqing; Morthier, Geert; Lampin, Jean-Francois; Roelkens, Gunther

2014-11-15

We demonstrate an integrated distributed feedback (DFB) laser array as a dual-wavelength source for narrowband terahertz (THz) generation. The laser array is composed of four heterogeneously integrated III-V-on-silicon DFB lasers with different lengths enabling dual-mode lasing tolerant to process variations, bias fluctuations, and ambient temperature variations. By optical heterodyning the two modes emitted by the dual-wavelength DFB laser in the laser array using a THz photomixer composed of an uni-traveling carrier photodiode (UTC-PD), a narrow and stable carrier signal with a frequency of 0.357 THz is generated. The central operating frequency and the emitted terahertz wave linewidth are analyzed, along with their dependency on the bias current applied to the laser diode and ambient temperature.

Sparsity based terahertz reflective off-axis digital holography

NASA Astrophysics Data System (ADS)

Wan, Min; Muniraj, Inbarasan; Malallah, Ra'ed; Zhao, Liang; Ryle, James P.; Rong, Lu; Healy, John J.; Wang, Dayong; Sheridan, John T.

2017-05-01

Terahertz radiation lies between the microwave and infrared regions in the electromagnetic spectrum. Emitted frequencies range from 0.1 to 10 THz with corresponding wavelengths ranging from 30 μm to 3 mm. In this paper, a continuous-wave Terahertz off-axis digital holographic system is described. A Gaussian fitting method and image normalisation techniques were employed on the recorded hologram to improve the image resolution. A synthesised contrast enhanced hologram is then digitally constructed. Numerical reconstruction is achieved using the angular spectrum method of the filtered off-axis hologram. A sparsity based compression technique is introduced before numerical data reconstruction in order to reduce the dataset required for hologram reconstruction. Results prove that a tiny amount of sparse dataset is sufficient in order to reconstruct the hologram with good image quality.

Characteristics of Gadolinium Oxide Nanoparticles Using Terahertz Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Dongkyu; Maeng, Inhee; Son, Joo-Hiuk

2009-04-19

The penetration property of the terahertz electromagnetic (THz) wave is relevant to its use. We used the THz wave spectroscopy system which easily penetrates some materials that do not contain water, e.g., plastic and ceramics. The system has been developed for several purposes, including measuring the properties of semiconductors and bio-materials, and detecting plastic bombs and ceramic knives at airports. It is also used for medical imaging systems, such as magnetic resonance imaging (MRI), at some research institutes. It can show not only the difference in amplitude, but also the difference of the phase of each point of sample. MRImore » technology usually uses contrast agents to enhance the quality of the image. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), made with a heavy metal ion, is commonly used as a clinical MRI contrast agent. Gadolinium oxide (Gd{sub 2}O{sub 3}) nanoparticle is a new contrast agent. It serves to equip the core of each particle with antibodies or ligands. It can freely circulate in blood vessels without amassing in the liver or lungs. This study shows the characteristics of gadolinium oxide nanoparticles to further advance terahertz medical imaging.« less

Continuous Beam Steering Through Broadside Using Asymmetrically Modulated Goubau Line Leaky-Wave Antennas.

PubMed

Tang, Xiao-Lan; Zhang, Qingfeng; Hu, Sanming; Zhuang, Yaqiang; Kandwal, Abhishek; Zhang, Ge; Chen, Yifan

2017-09-15

Goubau line is a single-conductor transmission line, featuring easy integration and low-loss transmission properties. Here, we propose a periodic leaky-wave antenna (LWA) based on planar Goubau transmission line on a thin dielectric substrate. The leaky-wave radiations are generated by introducing periodic modulations along the Goubau line. In this way, the surface wave, which is slow-wave mode supported by the Goubau line, achieves an additional momentum and hence enters the fast-wave region for radiations. By employing the periodic modulations, the proposed Goubau line LWAs are able to continuously steer the main beam from backward to forward within the operational frequency range. However, the LWAs usually suffer from a low radiation efficiency at the broadside direction. To overcome this drawback, we explore both transversally and longitudinally asymmetrical modulations to the Goubau line. Theoretical analysis, numerical simulations and experimental results are given in comparison with the symmetrical LWAs. It is demonstrated that the asymmetrical modulations significantly improve the radiation efficiency of LWAs at the broadside. Furthermore, the measurement results agree well with the numerical ones, which experimentally validates the proposed LWA structures. These novel Goubau line LWAs, experimentally demonstrated and validated at microwave frequencies, show also great potential for millimeter-wave and terahertz systems.

Terahertz NDE for Under Paint Corrosion Detection and Evaluation

NASA Technical Reports Server (NTRS)

Anastasi, Robert F.; Madaras, Eric I.

2005-01-01

Corrosion under paint is not visible until it has caused paint to blister, crack, or chip. If corrosion is allowed to continue then structural problems may develop. Identifying corrosion before it becomes visible would minimize repairs and costs and potential structural problems. Terahertz NDE imaging under paint for corrosion is being examined as a method to inspect for corrosion by examining the terahertz response to paint thickness and to surface roughness.

Prism-coupled Cherenkov phase-matched terahertz wave generation using a DAST crystal.

PubMed

Suizu, Koji; Shibuya, Takayuki; Uchida, Hirohisa; Kawase, Kodo

2010-02-15

Terahertz (THz) wave generation based on nonlinear frequency conversion is a promising method for realizing a tunable monochromatic high-power THz-wave source. Unfortunately, many nonlinear crystals have strong absorption in the THz frequency region. This limits efficient and widely tunable THz-wave generation. The Cherenkov phase-matching method is one of the most promising techniques for overcoming these problems. Here, we propose a prism-coupled Cherenkov phase-matching (PCC-PM) method, in which a prism with a suitable refractive index at THz frequencies is coupled to a nonlinear crystal. This has the following advantages. Many crystals can be used as THz-wave emitters; the phase-matching condition inside the crystal does not have to be observed; the absorption of the crystal does not prevent efficient generation of radiation; and pump sources with arbitrary wavelengths can be employed. Here we demonstrate PCC-PM THz-wave generation using the organic crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate (DAST) and a Si prism coupler. We obtain THz-wave radiation with tunability of approximately 0.1 to 10 THz and with no deep absorption features resulting from the absorption spectrum of the crystal. The obtained spectra did not depend on the pump wavelength in the range 1300 to 1450 nm. This simple technique shows promise for generating THz radiation using a wide variety of nonlinear crystals.

Corrugated metal surface with pillars for terahertz surface plasmon polariton waveguide components

NASA Astrophysics Data System (ADS)

Zhang, Ying; Xu, Yuehong; Tian, Chunxiu; Xu, Quan; Zhang, Xueqian; Li, Yanfeng; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili

2018-01-01

In the terahertz regime, due to perfect conductivity of most metals, it is hard to realize a strong confinement of Surface plasmon polaritons (SPPs) although a propagation loss could be sufficiently low. We experimentally demonstrated a structure with periodic pillars arranged on a thin metal surface that supports bound modes of spoof SPPs at terahertz (THz) frequencies. By using scanning near-field THz microscopy, the electric field distribution above the metal surface within a distance of 130 μm was mapped. The results proved that this structure could guide spoof SPPs propagating along subwavelength waveguides, and at the same time reduce field expansion into free space. Further, for the development of integrated optical circuits, several components including straight waveguide, S-bend, Y-splitter and directional couplers were designed and characterized by the same method. We believe that the waveguide components proposed here will pave a new way for the development of flexible, wideband and compact photonic circuits operating at THz frequencies.

THz-wave sensing via pump and signal wave detection interacted with evanescent THz waves.

PubMed

Akiba, Takuya; Kaneko, Naoya; Suizu, Koji; Miyamoto, Katsuhiko; Omatsu, Takashige

2013-09-15

We report a novel sensing technique that uses an evanescent terahertz (THz) wave, without detecting the THz wave directly. When a THz wave generated by Cherenkov phase matching via difference frequency generation undergoes total internal reflection, the evanescent THz wave is subject to a phase change and an amplitude decrease. The reflected THz wave, under the influence of the sample, interferes with the propagating THz wave and the changing electric field of the THz wave interacts with the electric field of the pump waves. We demonstrate a sensing technique for detecting changes in the electric field of near-infrared light, transcribed from changes in the electric field of a THz wave.

Hyperbolic spoof plasmonic metasurfaces

DOE PAGES

Yang, Yihao; Jing, Liqiao; Shen, Lian; ...

2017-08-25

Hyperbolic metasurfaces have recently emerged as a new research frontier because of the unprecedented capabilities to manipulate surface plasmon polaritons (SPPs) and many potential applications. But, thus far, the existence of hyperbolic metasurfaces has neither been observed nor predicted at low frequencies because noble metals cannot support SPPs at longer wavelengths. Here, we propose and experimentally demonstrate spoof plasmonic metasurfaces with a hyperbolic dispersion, where the spoof SPPs propagate on complementary H-shaped, perfectly conducting surfaces at low frequencies. Therefore, non-divergent diffractions, negative refraction and dispersion-dependent spin-momentum locking are observed as the spoof SPPs travel over the hyperbolic spoof plasmonic metasurfacesmore » (HSPMs). The HSPMs provide fundamental new platforms to explore the propagation and spin of spoof SPPs. They show great capabilities for designing advanced surface wave devices such as spatial multiplexers, focusing and imaging devices, planar hyperlenses, and dispersion-dependent directional couplers, at both microwave and terahertz frequencies.« less

Dispersion characteristics of plasmonic waveguides for THz waves

NASA Astrophysics Data System (ADS)

Markides, Christos; Viphavakit, Charusluk; Themistos, Christos; Komodromos, Michael; Kalli, Kyriacos; Quadir, Anita; Rahman, Azizur

2013-05-01

Today there is an increasing surge in Surface Plasmon based research and recent studies have shown that a wide range of plasmon-based optical elements and techniques have led to the development of a variety of active switches, passive waveguides, biosensors, lithography masks, to name just a few. The Terahertz (THz) frequency region of the electromagnetic spectrum is located between the traditional microwave spectrum and the optical frequencies, and offers a significant scientific and technological potential in many fields, such as in sensing, in imaging and in spectroscopy. Waveguiding in this intermediate spectral region is a major challenge. Amongst the various THz waveguides suggested, the metal-clad waveguides supporting surface plasmon modes waves and specifically hollow core structures, coated with insulating material are showing the greatest promise as low-loss waveguides for their use in active components and as well as passive waveguides. The H-field finite element method (FEM) based full-vector formulation is used to study the vectorial modal field properties and the complex propagation characteristics of Surface Plasmon modes of a hollow-core dielectric coated rectangular waveguide structure. Additionally, the finite difference time domain (FDTD) method is used to estimate the dispersion parameters and the propagation loss of the rectangular waveguide.

SrFe12O19 based ceramics with ultra-low dielectric loss in the millimetre-wave band

NASA Astrophysics Data System (ADS)

Yu, Chuying; Zeng, Yang; Yang, Bin; Wylde, Richard; Donnan, Robert; Wu, Jiyue; Xu, Jie; Gao, Feng; Abrahams, Isaac; Reece, Mike; Yan, Haixue

2018-04-01

Non-reciprocal devices such as isolators and circulators, based mainly on ferromagnetic materials, require extremely low dielectric loss in order for strict power-link budgets to be met for millimetre (mm)-wave and terahertz (THz) systems. The dielectric loss of commercial SrFe12O19 hexaferrite was significantly reduced to below 0.002 in the 75-170 GHz band by thermal annealing. While the overall concentration of Fe2+ and oxygen vacancy defects is relatively low in the solid, their concentration at the surface is significantly higher, allowing for a surface sensitive technique such as XPS to monitor the Fe3+/Fe2+ redox reaction. Oxidation of Fe2+ and a decrease in oxygen vacancies are found at the surface on annealing, which are reflected in the bulk sample by a small change in the unit cell volume. The significant decrease in the dielectric loss property can be attributed to the decreased concentration of charged defects such as Fe2+ and oxygen vacancies through the annealing process, which demonstrated that thermal annealing could be effective in improving the dielectric performance of ferromagnetic materials for various applications.

Terahertz wide aperture reflection tomography.

PubMed

Pearce, Jeremy; Choi, Hyeokho; Mittleman, Daniel M; White, Jeff; Zimdars, David

2005-07-01

We describe a powerful imaging modality for terahertz (THz) radiation, THz wide aperture reflection tomography (WART). Edge maps of an object's cross section are reconstructed from a series of time-domain reflection measurements at different viewing angles. Each measurement corresponds to a parallel line projection of the object's cross section. The filtered backprojection algorithm is applied to recover the image from the projection data. To our knowledge, this is the first demonstration of a reflection computed tomography technique using electromagnetic waves. We demonstrate the capabilities of THz WART by imaging the cross sections of two test objects.

Component pattern analysis of chemicals using multispectral THz imaging system

NASA Astrophysics Data System (ADS)

Kawase, Kodo; Ogawa, Yuichi; Watanabe, Yuki

2004-04-01

We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

Extremely low-loss, dispersion flattened porous-core photonic crystal fiber for terahertz regime

NASA Astrophysics Data System (ADS)

Islam, Saiful; Islam, Mohammad Rakibul; Faisal, Mohammad; Arefin, Abu Sayeed Muhammad Shamsul; Rahman, Hasan; Sultana, Jakeya; Rana, Sohel

2016-07-01

A porous-core octagonal photonic crystal fiber (PC-OPCF) with ultralow effective material loss (EML), high core power fraction, and ultra flattened dispersion is proposed for terahertz (THz) wave propagation. At an operating frequency of 1 THz and core diameter of 345 μm, simulation results display an extremely low EML of 0.047 cm-1, 49.1% power transmission through core air holes, decreased confinement loss with the increase of frequency, and dispersion variation of 0.15 ps/THz/cm. In addition, the proposed PCF can successfully operate in single-mode condition. All the simulations are performed with finite-element modeling package, COMSOL v4.2. The design can be fabricated using a stacking and drilling method. Thus, the proposed fiber has the potential of being an effective transmission medium of broadband THz waves.

Terahertz Magnon-Polaritons in TmFeO3.

PubMed

Grishunin, Kirill; Huisman, Thomas; Li, Guanqiao; Mishina, Elena; Rasing, Theo; Kimel, Alexey V; Zhang, Kailing; Jin, Zuanming; Cao, Shixun; Ren, Wei; Ma, Guo-Hong; Mikhaylovskiy, Rostislav V

2018-04-18

Magnon-polaritons are shown to play a dominant role in the propagation of terahertz (THz) waves through TmFeO 3 orthoferrite, if the frequencies of the waves are in the vicinity of the quasi-antiferromagnetic spin resonance mode. Both time-domain THz transmission and emission spectroscopies reveal clear beatings between two modes with frequencies slightly above and slightly below this resonance, respectively. Rigorous modeling of the interaction between the spins of TmFeO 3 and the THz light shows that the frequencies correspond to the upper and lower magnon-polariton branches. Our findings reveal the previously ignored importance of propagation effects and polaritons in such heavily debated areas as THz magnonics and THz spectroscopy of electromagnons. It also shows that future progress in these areas calls for an interdisciplinary approach at the interface between magnetism and photonics.

RT-CW: widely tunable semiconductor THz QCL sources

NASA Astrophysics Data System (ADS)

Razeghi, M.; Lu, Q. Y.

2016-09-01

Distinctive position of Terahertz (THz) frequencies (ν 0.3 -10 THz) in the electromagnetic spectrum with their lower quantum energy compared to IR and higher frequency compared to microwave range allows for many potential applications unique to them. Especially in the security side of the THz sensing applications, the distinct absorption spectra of explosives and related compounds in the range of 0.1-5 THz makes THz technology a competitive technique for detecting hidden explosives. A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range will greatly boost the THz applications for the diagnosis and detection of explosives. Here we present a new strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based intracavity DFG. Room temperature continuous wave operation with electrical frequency tuning range of 2.06-4.35 THz is demonstrated.

Numerical simulation of turbulence and terahertz magnetosonic waves generation in collisionless plasmas

NASA Astrophysics Data System (ADS)

Kumar, Narender; Singh, Ram Kishor; Sharma, Swati; Uma, R.; Sharma, R. P.

2018-01-01

This paper presents numerical simulations of laser beam (x-mode) coupling with a magnetosonic wave (MSW) in a collisionless plasma. The coupling arises through ponderomotive non-linearity. The pump beam has been perturbed by a periodic perturbation that leads to the nonlinear evolution of the laser beam. It is observed that the frequency spectra of the MSW have peaks at terahertz frequencies. The simulation results show quite complex localized structures that grow with time. The ensemble averaged power spectrum has also been studied which indicates that the spectral index follows an approximate scaling of the order of ˜ k-2.1 at large scales and scaling of the order of ˜ k-3.6 at smaller scales. The results indicate considerable randomness in the spatial structure of the magnetic field profile which gives sufficient indication of turbulence.

Recording of Terahertz Pulses of Microsecond Duration Using the Thermoacoustic Effect

NASA Astrophysics Data System (ADS)

Andreev, V. G.; Vdovin, V. A.; Kalynov, Yu. K.

2014-01-01

We consider the possibility of using a thermoacoustic detector (TAD) for recording of high-power pulse radiation at frequencies of 0.55, 0.68, and 0.87 THz. Electromagnetic wave is transformed into an acoustic wave in a structure consisting of a 10-nm thick chromium film deposited on a quartz substrate and a layer of the immersion liquid that is in contact with the film. It is shown that for the pulse of microsecond duration (3-10 μs) the waveform detected by the thermoacoustic detector is matched with high accuracy to the derivative of the terahertz pulse profile. For recording of electromagnetic radiation in the 0.5-0.9 THz frequency range it is possible to employ the simplified design of TAD, in which a transparent quartz substrate is in contact with a layer of water or ethanol.

Investigation of Layer Structure of the Takamatsuzuka Mural Paintings by Terahertz Imaging Technique

NASA Astrophysics Data System (ADS)

Inuzuka, M.; Kouzuma, Y.; Sugioka, N.; Fukunaga, K.; Tateishi, T.

2017-04-01

Terahertz imaging can be a powerful tool in conservation science for cultural heritages. In this study, a new terahertz imaging system was applied to the Takamatsuzuka mural painting of a blue dragon, and the condition of the plaster layer was diagnosed. As a result, the locations where the plaster layer appears solid on the surface but in actuality may have peeled off the underlying tuff stone were revealed and viewed as two-dimensional images.

Far-field characteristics of the square grooved-dielectric lens antenna for the terahertz band.

PubMed

Pan, Wu; Zeng, Wei

2016-09-10

In order to improve the gain and directionality of a terahertz antenna, a square grooved-dielectric lens antenna based on a Fresnel zone plate is proposed. First, a diagonal horn, which is adopted as the primary feed antenna, is designed. Then, the far-field characteristics of the lens antenna are studied by using Fresnel-Kirchhoff diffraction theory and the paraxial approximation. The effects of the full-wave period, the focus diameter ratio, the subregion, and the dielectric substrate thickness on radiation characteristics are studied. The experimental results show that the proposed lens antenna has axisymmetric radiation patterns. The gain is over 26.1 dB, and the 3 dB main lobe beam width is lower than 5.6° across the operation band. The proposed lens antenna is qualified for applications in terahertz wireless communication systems.

Near-zero dispersion flattened, low-loss porous-core waveguide design for terahertz signal transmission

NASA Astrophysics Data System (ADS)

Sultana, Jakeya; Islam, Md. Saiful; Atai, Javid; Islam, Muhammad Rakibul; Abbott, Derek

2017-07-01

We demonstrate a photonic crystal fiber with near-zero flattened dispersion, ultralower effective material loss (EML), and negligible confinement loss for a broad spectrum range. The use of cyclic olefin copolymer Topas with improved core confinement significantly reduces the loss characteristics and the use of higher air filling fraction results in flat dispersion characteristics. The properties such as dispersion, EML, confinement loss, modal effective area, and single-mode operation of the fiber have been investigated using the full-vector finite element method with the perfectly matched layer absorbing boundary conditions. The practical implementation of the proposed fiber is achievable with existing fabrication techniques as only circular-shaped air holes have been used to design the waveguide. Thus, it is expected that the proposed terahertz waveguide can potentially be used for flexible and efficient transmission of terahertz waves.

A modified hexagonal photonic crystal fiber for terahertz applications

NASA Astrophysics Data System (ADS)

Islam, Md. Saiful; Sultana, Jakeya; Faisal, Mohammad; Islam, Mohammad Rakibul; Dinovitser, Alex; Ng, Brian W.-H.; Abbott, Derek

2018-05-01

We present a Zeonex based highly birefringent and dispersion flattened porous core photonic crystal fiber (PC-PCF) for polarization preserving applications in the terahertz region. In order to facilitate birefringence, an array of elliptical shaped air holes surrounded by porous cladding is introduced. The porous cladding comprises circular air-holes in a modified hexagonal arrangement. The transmission characteristics of the proposed PCF are investigated using a full-vector finite element method with perfectly matched layer (PML) absorbing boundary conditions. Simulation results show a high birefringence of 0.086 and an ultra-flattened dispersion variation of ± 0.03 ps/THz/cm at optimal design parameters. Besides, a number of other important wave-guiding properties including frequency dependence of the effective material loss (EML), confinement loss, and effective area are also investigated to assess the fiber's effectiveness as a terahertz waveguide.

Fast and High Dynamic Range Imaging with Superconducting Tunnel Junction Detectors

NASA Astrophysics Data System (ADS)

Matsuo, Hiroshi

2014-08-01

We have demonstrated a combined test of the submillimeter-wave SIS photon detectors and GaAs-JFET cryogenic integrated circuits. A relatively large background photo-current can be read out by fast-reset integrating amplifiers. An integration time of 1 ms enables fast frame rate readout and large dynamic range imaging, with an expected dynamic range of 8,000 in 1 ms. Ultimate fast and high dynamic range performance of superconducting tunnel junction detectors (STJ) will be obtained when photon counting capabilities are employed. In the terahertz frequencies, when input photon rate of 100 MHz is measured, the photon bunching gives us enough timing resolution to be used as phase information of intensity fluctuation. Application of photon statistics will be a new tool in the terahertz frequency region. The design parameters of STJ terahertz photon counting detectors are discussed.

Terahertz parametric sources and imaging applications

NASA Astrophysics Data System (ADS)

Kawase, Kodo; Ogawa, Yuichi; Minamide, Hiroaki; Ito, Hiromasa

2005-07-01

We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of LiNbO3 or MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave source with a simple configuration. We report the detailed characteristics of the oscillation and the radiation including tunability, spatial and temporal coherency, uni-directivity, and efficiency. A Fourier transform limited THz-wave spectrum narrowing was achieved by introducing the injection seeding method. Further, we have developed a spectroscopic THz imaging system using a THz-wave parametric oscillator, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. Several images of the envelope are recorded at different THz frequencies and then processed. The final result is an image that reveals what substances are present in the envelope, in what quantity, and how they are distributed across the envelope area. The example presented here shows the identification of three drugs, two of which are illegal, while one is an over-the-counter drug.

[An effective method for improving the imaging spatial resolution of terahertz time domain spectroscopy system].

PubMed

Zhang, Zeng-yan; Ji, Te; Zhu, Zhi-yong; Zhao, Hong-wei; Chen, Min; Xiao, Ti-qiao; Guo, Zhi

2015-01-01

Terahertz radiation is an electromagnetic radiation in the range between millimeter waves and far infrared. Due to its low energy and non-ionizing characters, THz pulse imaging emerges as a novel tool in many fields, such as material, chemical, biological medicine, and food safety. Limited spatial resolution is a significant restricting factor of terahertz imaging technology. Near field imaging method was proposed to improve the spatial resolution of terahertz system. Submillimeter scale's spauial resolution can be achieved if the income source size is smaller than the wawelength of the incoming source and the source is very close to the sample. But many changes were needed to the traditional terahertz time domain spectroscopy system, and it's very complex to analyze sample's physical parameters through the terahertz signal. A method of inserting a pinhole upstream to the sample was first proposed in this article to improve the spatial resolution of traditional terahertz time domain spectroscopy system. The measured spatial resolution of terahertz time domain spectroscopy system by knife edge method can achieve spatial resolution curves. The moving stage distance between 10 % and 90 Yo of the maximum signals respectively was defined as the, spatial resolution of the system. Imaging spatial resolution of traditional terahertz time domain spectroscopy system was improved dramatically after inserted a pinhole with diameter 0. 5 mm, 2 mm upstream to the sample. Experimental results show that the spatial resolution has been improved from 1. 276 mm to 0. 774 mm, with the increment about 39 %. Though this simple method, the spatial resolution of traditional terahertz time domain spectroscopy system was increased from millimeter scale to submillimeter scale. A pinhole with diameter 1 mm on a polyethylene plate was taken as sample, to terahertz imaging study. The traditional terahertz time domain spectroscopy system and pinhole inserted terahertz time domain spectroscopy system were applied in the imaging experiment respectively. The relative THz-power loss imaging of samples were use in this article. This method generally delivers the best signal to noise ratio in loss images, dispersion effects are cancelled. Terahertz imaging results show that the sample's boundary was more distinct after inserting the pinhole in front of, sample. The results also conform that inserting pinhole in front of sample can improve the imaging spatial resolution effectively. The theoretical analyses of the method which improve the spatial resolution by inserting a pinhole in front of sample were given in this article. The analyses also indicate that the smaller the pinhole size, the longer spatial coherence length of the system, the better spatial resolution of the system. At the same time the terahertz signal will be reduced accordingly. All the experimental results and theoretical analyses indicate that the method of inserting a pinhole in front of sample can improve the spatial resolution of traditional terahertz time domain spectroscopy system effectively, and it will further expand the application of terahertz imaging technology.

Electrically Tunable Goos-Hänchen Effect with Graphene in the Terahertz Regime

DOE PAGES

Fan, Yuancheng; Shen, Nian-Hai; Zhang, Fuli; ...

2016-07-14

Goos-Hänchen (G-H) effect is of great interest in the manipulation of optical beams. However, it is still fairly challenging to attain efficient controls of the G-H shift for diverse applications. Here, we propose a mechanism to realize tunable G-H shift in the terahertz regime with electrically controllable graphene. Taking monolayer graphene covered epsilon-near-zero metamaterial as a planar model system, it is found that the G-H shift for the orthogonal s-polarized and p-polarized terahertz beams at oblique incidence are positive and negative, respectively. The G-H shift can be modified substantially by electrically controlling the Fermi energy of the monolayer graphene. Reversely,more » the Fermi energy dependent G-H effect can also be used as a strategy for measuring the doping level of graphene. In addition, the G-H shifts of the system are of strong frequency-dependence at oblique angles of incidence, therefore the proposed graphene hybrid system can potentially be used for the generation of terahertz “rainbow”, a flat analog of the dispersive prism in optics. The proposed scheme of hybrid system involving graphene for dynamic control of G-H shift will have potential applications in the manipulation of terahertz waves.« less

Wireless multi-level terahertz amplitude modulator using active metamaterial-based spatial light modulation.

PubMed

Rout, Saroj; Sonkusale, Sameer

2016-06-27

The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation.

Screening mail for powders using terahertz technology

NASA Astrophysics Data System (ADS)

Kemp, Mike

2011-11-01

Following the 2001 Anthrax letter attacks in the USA, there has been a continuing interest in techniques that can detect or identify so-called 'white powder' concealed in envelopes. Electromagnetic waves (wavelengths 100-500 μm) in the terahertz frequency range penetrate paper and have short enough wavelengths to provide good resolution images; some materials also have spectroscopic signatures in the terahertz region. We report on an experimental study into the use of terahertz imaging and spectroscopy for mail screening. Spectroscopic signatures of target powders were measured and, using a specially designed test rig, a number of imaging methods based on reflection, transmission and scattering were investigated. It was found that, contrary to some previous reports, bacterial spores do not appear to have any strong spectroscopic signatures which would enable them to be identified. Imaging techniques based on reflection imaging and scattering are ineffective in this application, due to the similarities in optical properties between powders of interest and paper. However, transmission imaging using time-of-flight of terahertz pulses was found to be a very simple and sensitive method of detecting small quantities (25 mg) of powder, even in quite thick envelopes. An initial feasibility study indicates that this method could be used as the basis of a practical mail screening system.

THz-wave generation via stimulated polariton scattering in KTiOAsO4 crystal.

PubMed

Wang, Weitao; Cong, Zhenhua; Liu, Zhaojun; Zhang, Xingyu; Qin, Zengguang; Tang, Guanqi; Li, Ning; Zhang, Yuangeng; Lu, Qingming

2014-07-14

A terahertz parametric oscillator based on KTiOAsO(4) crystal is demonstrated for the first time. With the near-forward scattering configuration X(ZZ)X + Δφ, the polarizations of the pump, the Stokes and the generated THz waves are parallel to the z-axis of the crystal KTA. When the incident angle θext of the pump wave is changed from 1.875° to 6.500°, the THz wave is intermittently tuned from 3.59 to 3.96 THz, from 4.21 to 4.50 THz, from 4.90 to 5.16 THz, from 5.62 to 5.66 THz and from 5.92 to 6.43 THz. The obtained maximum THz wave energy is 627 nJ at 4.30 THz with a pump energy of 100 mJ. It is believed that the terahertz wave generation is caused by the stimulated scattering of the polaritons associated with the most intensive transverse A(1) mode of 233.8 cm(-1). Four much weaker transverse A(1) modes of 132.9 cm(-1), 156.3 cm(-1),175.1 cm(-1), and 188.4 cm(-1) cause four frequency gaps, from 3.97 THz to 4.20 THz, from 4.51 to 4.89 THz, from 5.17 to 5.61 THz and from 5.67 to 5.91 THz, respectively.

Terahertz-radiation generation and detection in low-temperature-grown GaAs epitaxial films on GaAs (100) and (111)A substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru; Buriakov, A. M.

The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity ofmore » the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.« less

Spoof surface plasmon based planar antennas for the realization of Terahertz hotspots

PubMed Central

Zhang, Yusheng; Han, Zhanghua

2015-01-01

Novel spoof surface plasmon based terahertz (THz) antennas are realized using a few number of rectangular grooves perforated in ultrathin metal stripes and the properties of them, including both scattering cross sections and field enhancement, are numerically analyzed. The dependence of these properties on the incident angle and groove number is discussed and the results show that sharp resonances in scattering cross section spectra associated with strong local field enhancement can be achieved. These resonances are due to the formation of Fabry-Perot resonances of the spoof surface plasmon mode and it is found that the order of resonance exhibiting strongest field enhancements is found to coincide with the number of grooves at normal incidence, due to hybridization of the antenna resonance with the individual groove resonance. The terahertz hotspots within the grooves at resonances due to the local field enhancement may open up new possibilities for the investigation of terahertz-matter interactions and boost a variety of THz applications including novel sensing and THz detections. The planar stripe antennas with sharper resonances than dipolar-like resonances, together with their ease of fabrication may also promise new design methodology for metamaterials. PMID:26691003

All-dielectric rod antenna array for terahertz communications

NASA Astrophysics Data System (ADS)

Withayachumnankul, Withawat; Yamada, Ryoumei; Fujita, Masayuki; Nagatsuma, Tadao

2018-05-01

The terahertz band holds a potential for point-to-point short-range wireless communications at sub-terabit speed. To realize this potential, supporting antennas must have a wide bandwidth to sustain high data rate and must have high gain and low dissipation to compensate for the free space path loss that scales quadratically with frequency. Here we propose an all-dielectric rod antenna array with high radiation efficiency, high gain, and wide bandwidth. The proposed array is integral to a low-loss photonic crystal waveguide platform, and intrinsic silicon is the only constituent material for both the antenna and the feed to maintain the simplicity, compactness, and efficiency. Effective medium theory plays a key role in the antenna performance and integrability. An experimental validation with continuous-wave terahertz electronic systems confirms the minimum gain of 20 dBi across 315-390 GHz. A demonstration shows that a pair of such identical rod array antennas can handle bit-error-free transmission at the speed up to 10 Gbit/s. Further development of this antenna will build critical components for future terahertz communication systems.

Interferometric Control of Dual-Band Terahertz Perfect Absorption Using a Designed Metasurface

NASA Astrophysics Data System (ADS)

Kang, Ming; Zhang, Huifang; Zhang, Xueqian; Yang, Quanlong; Zhang, Weili; Han, Jiaguang

2018-05-01

The coherent perfect absorber (CPA), a time-reversed counterpart to the laser emission, could cause all energy fed to the system to be absorbed. It can also be used as an absorptive interferometer, which could provide applications in controllable optical energy transfer. Here, in order to achieve a terahertz CPA, we propose a designed metasurface and experimentally demonstrate that it can serve as a polarization-insensitive CPA at a one-frequency channel under normal symmetric excitation, while a transverse-electric CPA at two-frequency channels around oblique 40° symmetric incidence. Such phenomena in this system can be attributed to Fano resonance consisting of interacting one bright and one dark mode under normal incidence and an additional operative dark mode under oblique symmetric excitation. The experimental results find good agreement with the fitted coupled-mode theory. Moreover, we show that the output amplitude can be effectively tuned from 0 to 1 only by varying the relative phase between the two input waves. The designed CPA could find potential application in effectively controlling absorption for terahertz imaging and terahertz switches.

Generation of tunable narrow-band surface-emitted terahertz radiation in periodically poled lithium niobate.

PubMed

Weiss, C; Torosyan, G; Avetisyan, Y; Beigang, R

2001-04-15

Generation of tunable narrow-band terahertz (THz) radiation perpendicular to the surface of periodically poled lithium niobate by optical rectification of femtosecond pulses is reported. The generated THz radiation can be tuned by use of different poling periods and different observation angles, limited only by the available bandwidth of the pump pulse. Typical bandwidths were 50-100 GHz, depending on the collection angle and the number of periods involved.

Quantitative analysis of visible surface defect risk in tablets during film coating using terahertz pulsed imaging.

PubMed

Niwa, Masahiro; Hiraishi, Yasuhiro

2014-01-30

Tablets are the most common form of solid oral dosage produced by pharmaceutical industries. There are several challenges to successful and consistent tablet manufacturing. One well-known quality issue is visible surface defects, which generally occur due to insufficient physical strength, causing breakage or abrasion during processing, packaging, or shipping. Techniques that allow quantitative evaluation of surface strength and the risk of surface defect would greatly aid in quality control. Here terahertz pulsed imaging (TPI) was employed to evaluate the surface properties of core tablets with visible surface defects of varying severity after film coating. Other analytical methods, such as tensile strength measurements, friability testing, and scanning electron microscopy (SEM), were used to validate TPI results. Tensile strength and friability provided no information on visible surface defect risk, whereas the TPI-derived unique parameter terahertz electric field peak strength (TEFPS) provided spatial distribution of surface density/roughness information on core tablets, which helped in estimating tablet abrasion risk prior to film coating and predicting the location of the defects. TPI also revealed the relationship between surface strength and blending condition and is a nondestructive, quantitative approach to aid formulation development and quality control that can reduce visible surface defect risk in tablets. Copyright © 2013 Elsevier B.V. All rights reserved.

Real-time continuous-wave terahertz line scanner based on a compact 1 × 240 InGaAs Schottky barrier diode array detector.

PubMed

Han, Sang-Pil; Ko, Hyunsung; Kim, Namje; Lee, Won-Hui; Moon, Kiwon; Lee, Il-Min; Lee, Eui Su; Lee, Dong Hun; Lee, Wangjoo; Han, Seong-Tae; Choi, Sung-Wook; Park, Kyung Hyun

2014-11-17

We demonstrate real-time continuous-wave terahertz (THz) line-scanned imaging based on a 1 × 240 InGaAs Schottky barrier diode (SBD) array detector with a scan velocity of 25 cm/s, a scan line length of 12 cm, and a pixel size of 0.5 × 0.5 mm². Foreign substances, such as a paper clip with a spatial resolution of approximately 1 mm that is hidden under a cracker, are clearly detected by this THz line-scanning system. The system consists of the SBD array detector, a 200-GHz gyrotron source, a conveyor system, and several optical components such as a high-density polyethylene cylindrical lens, metal cylindrical mirror, and THz wire-grid polarizer. Using the THz polarizer, the signal-to-noise ratio of the SBD array detector improves because the quality of the source beam is enhanced.

THz wavefront manipulation based on metal waveguides

NASA Astrophysics Data System (ADS)

Wu, Mengru; Lang, Tingting; Shen, Changyu; Shi, Guohua; Han, Zhanghua

2018-07-01

In this paper, two waveguiding structures for arbitrary wavefront manipulation in the terahertz spectral region were proposed, designed and characterized. The first structure consists of parallel stack copper plates forming an array of parallel-plate waveguides (PPWGs). The second structure is three-dimensional metal rectangular waveguides array. The phase delay of the input wave after passing through the waveguide array is mainly determined by the effective index of the waveguides. Therefore, the waveguide array can be engineered using different core width distribution to generate any desired light beam. Examples, working at the frequency of 0.3 THz show that good focusing phenomenon with different focus lengths and spot sizes were observed, as well as arbitrarily tilted propagation of incident plane waves. The structure introduces a new method to perform wavefront manipulation, and can be utilized in many important applications in terahertz imaging and communication systems.

A Design of Terahertz Parallel Plate Dielectric Waveguide with Signal Line inserted for Ballistic Deflection Transistor Travelling Wave Amplifier

NASA Astrophysics Data System (ADS)

Wang, H.; Knepper, R.; Hossain, N.; Marthi, P.; Milithaler, J.-F.; Margala, M.

2017-10-01

In this paper a new waveguide design is proposed to be implemented as part of Ballistic Deflection Transistor (BDT) Traveling Wave Amplifier Design. The BDT is designed to be operated in the Terahertz regime. Due to its relatively low transconductance (gm=200µA/V), the entire structure will consist of ten stages, with 15 BDTs/stage, to reach a total gain of 30mA/V. In this case, the total length of the transmission line will be more than 400µm. We did the investigation for different structures and materials of the transmission line. For our Parallel Plate Dielectric Waveguide with Signal Line inserted (PPDWS) design, we are able to get an average loss of 0.46dB/mm at 0.8-1.4THz from ANSYS HFSS simulation. The return loss for input and output are better than -20dB at 0.8-1.7THz. Although it is designed for our future travelling wave amplifier, it can also be used for various other THz frequency applications.

Water vapor: An extraordinary terahertz wave source under optical excitation

NASA Astrophysics Data System (ADS)

Johnson, Keith; Price-Gallagher, Matthew; Mamer, Orval; Lesimple, Alain; Fletcher, Clark; Chen, Yunqing; Lu, Xiaofei; Yamaguchi, Masashi; Zhang, X.-C.

2008-09-01

In modern terahertz (THz) sensing and imaging spectroscopy, water is considered a nemesis to be avoided due to strong absorption in the THz frequency range. Here we report the first experimental demonstration and theoretical implications of using femtosecond laser pulses to generate intense broadband THz emission from water vapor. When we focused an intense laser pulse in water vapor contained in a gas cell or injected from a gas jet nozzle, an extraordinarily strong THz field from optically excited water vapor is observed. Water vapor has more than 50% greater THz generation efficiency than dry nitrogen. It had previously been assumed that the nonlinear generation of THz waves in this manner primarily involves a free-electron plasma, but we show that the molecular structure plays an essential role in the process. In particular, we found that THz wave generation from H2O vapor is significantly stronger than that from D2O vapor. Vibronic activities of water cluster ions, occurring naturally in water vapor, may possibly contribute to the observed isotope effect along with rovibrational contributions from the predominant monomers.

Transmission line model and fields analysis of metamaterial absorber in the terahertz band.

PubMed

Wen, Qi-Ye; Xie, Yun-Song; Zhang, Huai-Wu; Yang, Qing-Hui; Li, Yuan-Xun; Liu, Ying-Li

2009-10-26

Metamaterial (MM) absorber is a novel device to provide near-unity absorption to electromagnetic wave, which is especially important in the terahertz (THz) band. However, the principal physics of MM absorber is still far from being understood. In this work, a transmission line (TL) model for MM absorber was proposed, and with this model the S-parameters, energy consumption, and the power loss density of the absorber were calculated. By this TL model, the asymmetric phenomenon of THz absorption in MM absorber is unambiguously demonstrated, and it clarifies that strong absorption of this absorber under studied is mainly related to the LC resonance of the split-ring-resonator structure. The distribution of power loss density in the absorber indicates that the electromagnetic wave is firstly concentrated into some specific locations of the absorber and then be strongly consumed. This feature as electromagnetic wave trapper renders MM absorber a potential energy converter. Based on TL model, some design strategies to widen the absorption band were also proposed for the purposes to extend its application areas.

Extended design window of resonant plasma-wave transistor for terahertz emitter by considering degenerate carrier velocity model with Fermi-Dirac distribution

NASA Astrophysics Data System (ADS)

Park, Jong Yul; Kim, Sung-Ho; Rok Kim, Kyung

2015-06-01

In this work, we propose extended design window which is helpful to judge whether the plasma-wave transistor (PWT) operates as a resonant terahertz (THz) electromagnetic (EM) wave emitter. When metal-oxide-semiconductor field-effect transistor (MOSFET) is on strong inversion which is believed to be an operation regime of PWT THz emitter, Boltzmann statistics is no longer valid and degenerate Fermi-Dirac distribution should be considered. Based on degenerate carrier velocity model, we report the increased maximum channel length (Lmax) to 17 nm for strained silicon (s-Si) PWT with assuming μ = 500 cm2·V-1·s-1. As mobility is enhanced, it is possible to observe two emission spectrums [fundamental (N = 1) and third (N = 3) harmonics] in a specific operation range. Theoretically, increment of Lmax for enhanced μ is limited to near 35 nm by the Pauli’s principle in the case of s-Si PWT. This theoretical value of Lmax should be compromised by considering actual PWT operation voltage for gate oxide breakdown.

Single-cycle powerful megawatt to gigawatt terahertz pulse radiated from a wavelength-scale plasma oscillator

NASA Astrophysics Data System (ADS)

Wu, Hui-Chun; Sheng, Zheng-Ming; Zhang, Jie

2008-04-01

We propose a scheme to generate single-cycle powerful terahertz (THz) pulses by ultrashort intense laser pulses obliquely incident on an underdense plasma slab of a few THz wavelengths in thickness. THz waves are radiated from a transient net current driven by the laser ponderomotive force in the plasma slab. Analysis and particle-in-cell simulations show that such a THz source is capable of providing power of megawatts to gigawatts, field strength of MV/cm-GV/cm, and broad tunability range, which is potentially useful for nonlinear and high-field THz science and applications.

Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies

NASA Astrophysics Data System (ADS)

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Jiyeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2015-09-01

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ /10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

Integrated planar terahertz resonators for femtomolar sensitivity label-free detection of DNA hybridization.

PubMed

Nagel, Michael; Bolivar, Peter Haring; Brucherseifer, Martin; Kurz, Heinrich; Bosserhoff, Anja; Büttner, Reinhard

2002-04-01

A promising label-free approach for the analysis of genetic material by means of detecting the hybridization of polynucleotides with electromagnetic waves at terahertz (THz) frequencies is presented. Using an integrated waveguide approach, incorporating resonant THz structures as sample carriers and transducers for the analysis of the DNA molecules, we achieve a sensitivity down to femtomolar levels. The approach is demonstrated with time-domain ultrafast techniques based on femtosecond laser pulses for generating and electro-optically detecting broadband THz signals, although the principle can certainly be transferred to other THz technologies.

A hybrid continuous-wave terahertz imaging system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolganova, Irina N., E-mail: in.dolganova@gmail.com; Zaytsev, Kirill I., E-mail: kirzay@gmail.ru; Metelkina, Anna A.

2015-11-15

A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc.

Two-path plasmonic interferometer with integrated detector

DOEpatents

Dyer, Gregory Conrad; Shaner, Eric A.; Aizin, Gregory

2016-03-29

An electrically tunable terahertz two-path plasmonic interferometer with an integrated detection element can down convert a terahertz field to a rectified DC signal. The integrated detector utilizes a resonant plasmonic homodyne mixing mechanism that measures the component of the plasma waves in-phase with an excitation field that functions as the local oscillator in the mixer. The plasmonic interferometer comprises two independently tuned electrical paths. The plasmonic interferometer enables a spectrometer-on-a-chip where the tuning of electrical path length plays an analogous role to that of physical path length in macroscopic Fourier transform interferometers.

Ultrasonic control of terahertz radiation via lattice anharmonicity in LiNbO3

NASA Astrophysics Data System (ADS)

Poolman, R. H.; Ivanov, A. L.; Muljarov, E. A.

2011-06-01

We propose a tunable terahertz (THz) filter using the resonant acousto-optic (RAO) effect. We present a design based on a transverse optical (TO) phonon mediated interaction between a coherent acoustic wave and the THz field in LiNbO3. We predict a tunable range for the filter of up to 4 THz via the variation of the acoustic frequency between 0.1 and 1 GHz. The RAO effect in this case is due to cubic and quartic anharmonicities between TO phonons and the acoustic field. The effect of the interference between the anharmonicities is also discussed.

Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies.

PubMed

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Jiyeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2015-09-18

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ/10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

Efficient Terahertz Wide-Angle NUFFT-Based Inverse Synthetic Aperture Imaging Considering Spherical Wavefront.

PubMed

Gao, Jingkun; Deng, Bin; Qin, Yuliang; Wang, Hongqiang; Li, Xiang

2016-12-14

An efficient wide-angle inverse synthetic aperture imaging method considering the spherical wavefront effects and suitable for the terahertz band is presented. Firstly, the echo signal model under spherical wave assumption is established, and the detailed wavefront curvature compensation method accelerated by 1D fast Fourier transform (FFT) is discussed. Then, to speed up the reconstruction procedure, the fast Gaussian gridding (FGG)-based nonuniform FFT (NUFFT) is employed to focus the image. Finally, proof-of-principle experiments are carried out and the results are compared with the ones obtained by the convolution back-projection (CBP) algorithm. The results demonstrate the effectiveness and the efficiency of the presented method. This imaging method can be directly used in the field of nondestructive detection and can also be used to provide a solution for the calculation of the far-field RCSs (Radar Cross Section) of targets in the terahertz regime.

Planar Holographic Metasurfaces for Terahertz Focusing

PubMed Central

Kuznetsov, Sergei A.; Astafev, Mikhail A.; Beruete, Miguel; Navarro-Cía, Miguel

2015-01-01

Scientists and laymen alike have always been fascinated by the ability of lenses and mirrors to control light. Now, with the advent of metamaterials and their two-dimensional counterpart metasurfaces, such components can be miniaturized and designed with additional functionalities, holding promise for system integration. To demonstrate this potential, here ultrathin reflection metasurfaces (also called metamirrors) designed for focusing terahertz radiation into a single spot and four spaced spots are proposed and experimentally investigated at the frequency of 0.35 THz. Each metasurface is designed using a computer-generated spatial distribution of the reflection phase. The phase variation within 360 deg is achieved via a topological morphing of the metasurface pattern from metallic patches to U-shaped and split-ring resonator elements, whose spectral response is derived from full-wave electromagnetic simulations. The proposed approach demonstrates a high-performance solution for creating low-cost and lightweight beam-shaping and beam-focusing devices for the terahertz band. PMID:25583565

A view of metals through the terahertz window

NASA Astrophysics Data System (ADS)

Dodge, Steve

2006-05-01

As electrons move through a metal, interaction with their environment tends to slow them down, causing the Drude peak in the optical conductivity to become narrower. The resulting peak width is typically in the terahertz frequency range that sits between microwaves the far infrared, too fast for conventional electronics and too slow for conventional infrared spectroscopy. With femtosecond laser techniques, however, coherent, broadband terahertz radiation can now be generated and detected with exquisite sensitivity, providing a new window onto electronic interactions in metals. I will discuss the application of this technique to a variety of metallic systems, including elemental lead, the nearly magnetic oxide metal CaRuO3, and CrV alloys that span the quantum phase transition from spin-density wave to paramagnetic metal. M. A. Gilmore, S. Kamal, D. M. Broun, and J. S. Dodge, Appl. Phys. Lett. 88, 141910 (2006).

Nonlinear terahertz devices utilizing semiconducting plasmonic metamaterials

DOE PAGES

Seren, Huseyin R.; Zhang, Jingdi; Keiser, George R.; ...

2016-01-26

The development of responsive metamaterials has enabled the realization of compact tunable photonic devices capable of manipulating the amplitude, polarization, wave vector and frequency of light. Integration of semiconductors into the active regions of metallic resonators is a proven approach for creating nonlinear metamaterials through optoelectronic control of the semiconductor carrier density. Metal-free subwavelength resonant semiconductor structures offer an alternative approach to create dynamic metamaterials. We present InAs plasmonic disk arrays as a viable resonant metamaterial at terahertz frequencies. Importantly, InAs plasmonic disks exhibit a strong nonlinear response arising from electric field-induced intervalley scattering, resulting in a reduced carrier mobilitymore » thereby damping the plasmonic response. here, we demonstrate nonlinear perfect absorbers configured as either optical limiters or saturable absorbers, including flexible nonlinear absorbers achieved by transferring the disks to polyimide films. Nonlinear plasmonic metamaterials show potential for use in ultrafast terahertz (THz) optics and for passive protection of sensitive electromagnetic devices.« less

Nonlinear terahertz devices utilizing semiconducting plasmonic metamaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seren, Huseyin R.; Zhang, Jingdi; Keiser, George R.

The development of responsive metamaterials has enabled the realization of compact tunable photonic devices capable of manipulating the amplitude, polarization, wave vector and frequency of light. Integration of semiconductors into the active regions of metallic resonators is a proven approach for creating nonlinear metamaterials through optoelectronic control of the semiconductor carrier density. Metal-free subwavelength resonant semiconductor structures offer an alternative approach to create dynamic metamaterials. We present InAs plasmonic disk arrays as a viable resonant metamaterial at terahertz frequencies. Importantly, InAs plasmonic disks exhibit a strong nonlinear response arising from electric field-induced intervalley scattering, resulting in a reduced carrier mobilitymore » thereby damping the plasmonic response. here, we demonstrate nonlinear perfect absorbers configured as either optical limiters or saturable absorbers, including flexible nonlinear absorbers achieved by transferring the disks to polyimide films. Nonlinear plasmonic metamaterials show potential for use in ultrafast terahertz (THz) optics and for passive protection of sensitive electromagnetic devices.« less

Terahertz reflection interferometry for automobile paint layer thickness measurement

NASA Astrophysics Data System (ADS)

Rahman, Aunik; Tator, Kenneth; Rahman, Anis

2015-05-01

Non-destructive terahertz reflection interferometry offers many advantages for sub-surface inspection such as interrogation of hidden defects and measurement of layers' thicknesses. Here, we describe a terahertz reflection interferometry (TRI) technique for non-contact measurement of paint panels where the paint is comprised of different layers of primer, basecoat, topcoat and clearcoat. Terahertz interferograms were generated by reflection from different layers of paints on a metallic substrate. These interferograms' peak spacing arising from the delay-time response of respective layers, allow one to model the thicknesses of the constituent layers. Interferograms generated at different incident angles show that the interferograms are more pronounced at certain angles than others. This "optimum" angle is also a function of different paint and substrate combinations. An automated angular scanning algorithm helps visualizing the evolution of the interferograms as a function of incident angle and also enables the identification of optimum reflection angle for a given paint-substrate combination. Additionally, scanning at different points on a substrate reveals that there are observable variations from one point to another of the same sample over its entire surface area. This ability may be used as a quality control tool for in-situ inspection in a production line. Keywords: Terahertz reflective interferometry, Paint and coating layers, Non-destructive

Metal-insulator transition properties of sputtered silicon-doped and un-doped vanadium dioxide films at terahertz range

NASA Astrophysics Data System (ADS)

Zhang, Huafu; Wu, Zhiming; Niu, Ruihua; Wu, Xuefei; he, Qiong; Jiang, Yadong

2015-03-01

Silicon-doped and un-doped vanadium dioxide (VO2) films were synthesized on high-purity single-crystal silicon substrates by means of reactive direct current magnetron sputtering followed by thermal annealing. The structure, morphology and metal-insulator transition properties of silicon-doped VO2 films at terahertz range were measured and compared to those of un-doped VO2 films. X-ray diffraction and scanning electron microscopy indicated that doping the films with silicon significantly affects the preferred crystallographic orientation and surface morphologies (grain size, pores and characteristics of grain boundaries). The temperature dependence of terahertz transmission shows that the transition temperature, hysteresis width and transition sharpness greatly depend on the silicon contents while the transition amplitude was relatively insensitive to the silicon contents. Interestingly, the VO2 film doped with a silicon content of 4.6 at.% shows excellent terahertz switching characteristics, namely a small hysteresis width of 4.5 °C, a giant transmission modulation ratio of about 82% and a relatively low transition temperature of 56.1 °C upon heating. This work experimentally indicates that silicon doping can effectively control not only the surface morphology but also the metal-insulator transition characteristics of VO2 films at terahertz range.

A microfabricated low-profile wideband antenna array for terahertz communications.

PubMed

Luk, K M; Zhou, S F; Li, Y J; Wu, F; Ng, K B; Chan, C H; Pang, S W

2017-04-28

While terahertz communications are considered to be the future solutions for the increasing demands on bandwidth, terahertz equivalents of radio frequency front-end components have not been realized. It remains challenging to achieve wideband, low profile antenna arrays with highly directive beams of radiation. Here, based on the complementary antenna approach, a wideband 2 × 2 cavity-backed slot antenna array with a corrugated surface is proposed. The approach is based on a unidirectional antenna with a cardiac radiation pattern and stable frequency characteristics that is achieved by integrating a series-resonant electric dipole with a parallel-resonant magnetic dipole. In this design, the slots work as magnetic dipoles while the corrugated surface radiates as an array of electric dipoles. The proposed antenna is realized at 1 THz operating frequency by stacking multiple metallized layers using the microfabrication technology. S-parameter measurements of this terahertz low-profile metallic antenna array demonstrate high efficiency at terahertz frequencies. Fractional bandwidth and gain are measured to be 26% and 14 dBi which are consistent with the simulated results. The proposed antenna can be used as the building block for larger antenna arrays with more directive beams, paving the way to develop high gain low-profile antennas for future communication needs.

Terahertz NDE of Stressed Composite Overwrapped Pressure Vessels - Initial Testing

NASA Technical Reports Server (NTRS)

Madaras, Eric I.; Seebo, Jeffrey P.; Anatasi, Robert F.

2009-01-01

Terahertz radiation nondestructive evaluation was applied to a set of Kevlar composite overwrapped pressure vessel bottles that had undergone a series of thermal and pressure tests to simulate stress rupture effects. The bottles in these nondestructive evaluation tests were bottles that had not ruptured but had survived various times at the elevated load and temperature levels. Some of the bottles showed evidence of minor composite failures. The terahertz radiation did detect visible surface flaws, but did not detect any internal chemical or material degradation of the thin overwraps.

Planar Submillimeter-Wave Mixer Technology with Integrated Antenna

NASA Technical Reports Server (NTRS)

Chattopadhyay, Gautam; Mehdi, Imran; Gill, John J.; Lee, Choonsup; lombart, Muria L.; Thomas, Betrand

2010-01-01

High-performance mixers at terahertz frequencies require good matching between the coupling circuits such as antennas and local oscillators and the diode embedding impedance. With the availability of amplifiers at submillimeter wavelengths and the need to have multi-pixel imagers and cameras, planar mixer architecture is required to have an integrated system. An integrated mixer with planar antenna provides a compact and optimized design at terahertz frequencies. Moreover, it leads to a planar architecture that enables efficient interconnect with submillimeter-wave amplifiers. In this architecture, a planar slot antenna is designed on a thin gallium arsenide (GaAs) membrane in such a way that the beam on either side of the membrane is symmetric and has good beam profile with high coupling efficiency. A coplanar waveguide (CPW) coupled Schottky diode mixer is designed and integrated with the antenna. In this architecture, the local oscillator (LO) is coupled through one side of the antenna and the RF from the other side, without requiring any beam sp litters or diplexers. The intermediate frequency (IF) comes out on a 50-ohm CPW line at the edge of the mixer chip, which can be wire-bonded to external circuits. This unique terahertz mixer has an integrated single planar antenna for coupling both the radio frequency (RF) input and LO injection without any diplexer or beamsplitters. The design utilizes novel planar slot antenna architecture on a 3- mthick GaAs membrane. This work is required to enable future multi-pixel terahertz receivers for astrophysics missions, and lightweight and compact receivers for planetary missions to the outer planets in our solar system. Also, this technology can be used in tera hertz radar imaging applications as well as for testing of quantum cascade lasers (QCLs).

Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging

NASA Astrophysics Data System (ADS)

Cocker, Tyler L.; Peller, Dominik; Yu, Ping; Repp, Jascha; Huber, Rupert

2016-11-01

Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated by combining scanning tunnelling microscopy with so-called lightwave electronics, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.

Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging

PubMed Central

Yu, Ping; Repp, Jascha; Huber, Rupert

2017-01-01

Watching a single molecule move on its intrinsic time scale—one of the central goals of modern nanoscience—calls for measurements that combine ultrafast temporal resolution1–8 with atomic spatial resolution9–30. Steady-state experiments achieve the requisite spatial resolution, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy9–11 or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution27–29. But tracking the dynamics of a single molecule directly in the time domain faces the challenge that single-molecule excitations need to be confined to an ultrashort time window. A first step towards overcoming this challenge has combined scanning tunnelling microscopy with so-called ‘lightwave electronics”1–8, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on time scales faster even than that of a single cycle of light. Here we use such ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state and thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record ~100 fs snapshot images of the structure of the orbital involved, and to reveal through pump-probe measurements coherent molecular vibrations at terahertz frequencies directly in the time domain and with sub-angstrom spatial resolution. We anticipate that the combination of lightwave electronics1–8 and atomic resolution of our approach will open the door to controlling electronic motion inside individual molecules at optical clock rates. PMID:27830788

Real-time terahertz wave imaging by nonlinear optical frequency up-conversion in a 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal

NASA Astrophysics Data System (ADS)

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

2014-03-01

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and arts. In this letter, we report on real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal. The active projection-imaging system consisted of (1) THz wave generation, (2) THz-near-infrared hybrid optics, (3) THz wave up-conversion, and (4) an InGaAs camera working at 60 frames per second. The pumping laser system consisted of two optical parametric oscillators pumped by a nano-second frequency-doubled Nd:YAG laser. THz-wave images of handmade samples at 19.3 THz were taken, and videos of a sample moving and a ruler stuck with a black polyethylene film moving were supplied online to show real-time ability. Thanks to the high speed and high responsivity of this technology, real-time THz imaging with a higher signal-to-noise ratio than a commercially available THz micro-bolometer camera was proven to be feasible. By changing the phase-matching condition, i.e., by changing the wavelength of the pumping laser, we suggest THz imaging with a narrow THz frequency band of interest in a wide range from approximately 2 to 30 THz is possible.

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron

PubMed Central

Yuan, Xuesong; Zhu, Weiwei; Zhang, Yu; Xu, Ningsheng; Yan, Yang; Wu, Jianqiang; Shen, Yan; Chen, Jun; She, Juncong; Deng, Shaozhi

2016-01-01

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun. PMID:27609247

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron.

PubMed

Yuan, Xuesong; Zhu, Weiwei; Zhang, Yu; Xu, Ningsheng; Yan, Yang; Wu, Jianqiang; Shen, Yan; Chen, Jun; She, Juncong; Deng, Shaozhi

2016-09-09

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

Performance assessment of a data processing chain for THz imaging

NASA Astrophysics Data System (ADS)

Catapano, Ilaria; Ludeno, Giovanni; Soldovieri, Francesco

2017-04-01

Nowadays, TeraHertz (THz) imaging is deserving huge attention as very high resolution diagnostic tool in many applicative fields, among which security, cultural heritage, material characterization and civil engineering diagnostics. This widespread use of THz waves is due to their non-ionizing nature, their capability of penetrating into non-metallic opaque materials, as well as to the technological advances, which have allowed the commercialization of compact, flexible and portable systems. However, the effectiveness of THz imaging depends strongly on the adopted data processing aimed at improving the imaging performance of the hardware device. In particular, data processing is required to mitigate detrimental and unavoidable effects like noise, signal attenuation, as well as to correct the sample surface topography. With respect to data processing, we have proposed recently a strategy involving three different steps aimed at reducing noise, filtering out undesired signal introduced by the adopted THz system and performing surface topography correction [1]. The first step regards noise filtering and exploits a procedure based on the Singular Value Decomposition (SVD) [2] of the data matrix, which does not require knowledge of noise level and it does not involve the use of a reference signal. The second step aims at removing the undesired signal that we have experienced to be introduced by the adopted Z-Omega Fiber-Coupled Terahertz Time Domain (FICO) system. Indeed, when the system works in a high-speed mode, an undesired low amplitude peak occurs always at the same time instant from the beginning of the observation time window and needs to be removed from the useful data matrix in order to avoid a wrong interpretation of the imaging results. The third step of the considered data processing chain is a topographic correction, which needs in order to image properly the samples surface and its inner structure. Such a procedure performs an automatic alignment of the first peak of the measured waveforms by exploiting the a-priori information on the focus distance at which the specimen under test must be located during the measurement phase. The usefulness of the proposed data processing chain has been widely assessed in the last few months by surveying several specimens made by different materials and representative of objects of interest for civil engineering and cultural heritage diagnostics. At the conference, we will show in detail the signal processing chain and present several achieved results. REFERENCES [1] I. Catapano, F. Soldovieri, "A Data Processing Chain for Terahertz Imaging and Its Use in Artwork Diagnostics". J Infrared Milli Terahz Waves, pp.13, Nov. 2016. [2] M. Bertero and P. Boccacci (1998), Introduction to Inverse Problems in Imaging, Bristol: Institute of Physics Publishing.

Theoretical analysis of terahertz generation from a compact optical parametric oscillator based on adhesive-free-bonded periodically inverted KTiOPO4 plates

NASA Astrophysics Data System (ADS)

Li, Zhongyang; Wang, Silei; Wang, Mengtao; Yuan, Bin; Wang, Weishu

2017-10-01

Terahertz (THz) generation by difference frequency generation (DFG) processes with dual signal waves is theoretically analyzed. The dual signal waves are generated by an optical parametric oscillator (OPO) with periodically inverted KTiOPO4 (KTP) plates based on adhesive-free-bonded (AFB) technology. The phase-matching conditions in a same AFB KTP composite for the OPO generating signals and idlers and for the DFG generating THz wave can be simultaneously satisfied by selecting the thickness of each KTP plate. Moreover, 4-order cascaded DFG processes can be realized in the same AFB KTP composite. The cascaded Stokes interaction processes generating THz photons and the cascaded anti-Stokes interaction processes consuming THz photons are investigated from coupled wave equations. Take an example of 3.106 THz which locates in the vicinity of polariton resonances, THz intensities and quantum conversion efficiencies are calculated. Compared with non-cascaded DFG processes, THz intensities of 3.106 THz in 4-order cascaded DFG processes increase to 5.56 times. When the pump intensity equals 20 MW mm-2, the quantum conversion efficiency of 259% in 4-order cascaded DFG processes can be realized, which exceeds the Manley-Rowe limit.

Terahertz imaging with compressive sensing

NASA Astrophysics Data System (ADS)

Chan, Wai Lam

Most existing terahertz imaging systems are generally limited by slow image acquisition due to mechanical raster scanning. Other systems using focal plane detector arrays can acquire images in real time, but are either too costly or limited by low sensitivity in the terahertz frequency range. To design faster and more cost-effective terahertz imaging systems, the first part of this thesis proposes two new terahertz imaging schemes based on compressive sensing (CS). Both schemes can acquire amplitude and phase-contrast images efficiently with a single-pixel detector, thanks to the powerful CS algorithms which enable the reconstruction of N-by- N pixel images with much fewer than N2 measurements. The first CS Fourier imaging approach successfully reconstructs a 64x64 image of an object with pixel size 1.4 mm using a randomly chosen subset of the 4096 pixels which defines the image in the Fourier plane. Only about 12% of the pixels are required for reassembling the image of a selected object, equivalent to a 2/3 reduction in acquisition time. The second approach is single-pixel CS imaging, which uses a series of random masks for acquisition. Besides speeding up acquisition with a reduced number of measurements, the single-pixel system can further cut down acquisition time by electrical or optical spatial modulation of random patterns. In order to switch between random patterns at high speed in the single-pixel imaging system, the second part of this thesis implements a multi-pixel electrical spatial modulator for terahertz beams using active terahertz metamaterials. The first generation of this device consists of a 4x4 pixel array, where each pixel is an array of sub-wavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. The spatial modulator has a uniform modulation depth of around 40 percent across all pixels, and negligible crosstalk, at the resonant frequency. The second-generation spatial terahertz modulator, also based on metamaterials with a higher resolution (32x32), is under development. A FPGA-based circuit is designed to control the large number of modulator pixels. Once fully implemented, this second-generation device will enable fast terahertz imaging with both pulsed and continuous-wave terahertz sources.

Self-consistent modeling of terahertz waveguide and cavity with frequency-dependent conductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Y. J.; Chu, K. R., E-mail: krchu@yahoo.com.tw; Thumm, M.

The surface resistance of metals, and hence the Ohmic dissipation per unit area, scales with the square root of the frequency of an incident electromagnetic wave. As is well recognized, this can lead to excessive wall losses at terahertz (THz) frequencies. On the other hand, high-frequency oscillatory motion of conduction electrons tends to mitigate the collisional damping. As a result, the classical theory predicts that metals behave more like a transparent medium at frequencies above the ultraviolet. Such a behavior difference is inherent in the AC conductivity, a frequency-dependent complex quantity commonly used to treat electromagnetics of metals at opticalmore » frequencies. The THz region falls in the gap between microwave and optical frequencies. However, metals are still commonly modeled by the DC conductivity in currently active vacuum electronics research aimed at the development of high-power THz sources (notably the gyrotron), although a small reduction of the DC conductivity due to surface roughness is sometimes included. In this study, we present a self-consistent modeling of the gyrotron interaction structures (a metallic waveguide or cavity) with the AC conductivity. The resulting waveguide attenuation constants and cavity quality factors are compared with those of the DC-conductivity model. The reduction in Ohmic losses under the AC-conductivity model is shown to be increasingly significant as the frequency reaches deeper into the THz region. Such effects are of considerable importance to THz gyrotrons for which the minimization of Ohmic losses constitutes a major design consideration.« less

Terahertz acoustic phonon detection from a compact surface layer of spherical nanoparticles powder mixture of aluminum, alumina and multi-walled carbon nanotube

NASA Astrophysics Data System (ADS)

Abouelsayed, A.; Ebrahim, M. R.; El hotaby, W.; Hassan, S. A.; Al-Ashkar, Emad

2017-10-01

We present terahertz spectroscopy study on spherical nanoparticles powder mixture of aluminum, alumina, and MWCNTs induced by surface mechanical attrition treatment (SMAT) of aluminum substrates. Surface alloying of AL, Al2O3 0.95% and MWCNTs 0.05% powder mixture was produced during SMAT process, where a compact surface layer of about 200 μm due to ball bombardment was produced from the mixture. Al2O3 alumina powder played a significant role in MWCNTs distribution on surface, those were held in deformation surface cites of micro-cavities due to SMAT process of Al. The benefits are the effects on resulted optical properties of the surface studied at the terahertz frequency range due to electrical isolation confinement effects and electronic resonance disturbances exerted on Al electronic resonance at the same range of frequencies. THz acoustic phonon around 0.53-0.6 THz (17-20 cm-1) were observed at ambient conditions for the spherical nanoparticles powder mixture of Al, Al2O3 and MWCNTs. These results suggested that the presence of Al2O3 and MWCNTs during SMAT process leads to the optically detection of such acoustic phonon in the THz frequency range.

[The error analysis and experimental verification of laser radar spectrum detection and terahertz time domain spectroscopy].

PubMed

Liu, Wen-Tao; Li, Jing-Wen; Sun, Zhi-Hui

2010-03-01

Terahertz waves (THz, T-ray) lie between far-infrared and microwave in electromagnetic spectrum with frequency from 0.1 to 10 THz. Many chemical agent explosives show characteristic spectral features in the terahertz. Compared with conventional methods of detecting a variety of threats, such as weapons and chemical agent, THz radiation is low frequency and non-ionizing, and does not give rise to safety concerns. The present paper summarizes the latest progress in the application of terahertz time domain spectroscopy (THz-TDS) to chemical agent explosives. A kind of device on laser radar detecting and real time spectrum measuring was designed which measures the laser spectrum on the bases of Fourier optics and optical signal processing. Wedge interferometer was used as the beam splitter to wipe off the background light and detect the laser and measure the spectrum. The result indicates that 10 ns laser radar pulse can be detected and many factors affecting experiments are also introduced. The combination of laser radar spectrum detecting, THz-TDS, modern pattern recognition and signal processing technology is the developing trend of remote detection for chemical agent explosives.

Terahertz surface plasmon-polaritons in one-dimensional graphene based Fibonacci photonic superlattices

NASA Astrophysics Data System (ADS)

Namdar, Abdolrahman; Feizollahi Onsoroudi, Rana; Khoshsima, Habib; Sahrai, Mostafa

2018-03-01

The surface plasmon-polaritons in one-dimensional graphene-based Fibonacci photonic superlattices in the terahertz frequency range have been theoretically investigated. Our numerical study shows that surface plasmon-polaritons can be realized in both transverse electric and transverse magnetic polarizations. It is shown that these modes are manageable by varying the quasi-periodic generation orders which play a critical role in the occurrence of surface modes. In addition, the effect of thickness of cap layer and chemical potential of graphene sheets on surface plasmon-polaritons and their electric field distribution are studied. We have verified the excitation of surface plasmon-polaritons by using the attenuated total reflection method. This inspection confirms that all the predicted surface modes in the dispersion curves are actually excitable with this method.

WGM Resonators for Terahertz-to-Optical Frequency Conversion

NASA Technical Reports Server (NTRS)

Strekalov,Dmitry; Savchenkov, Anatoliy; Matsko, Andrey; Nu, Nan

2008-01-01

Progress has been made toward solving some practical problems in the implementation of terahertz-to-optical frequency converters utilizing whispering-gallery-mode (WGM) resonators. Such frequency converters are expected to be essential parts of non-cryogenic terahertz- radiation receivers that are, variously, under development or contemplated for a variety of applications in airborne and spaceborne instrumentation for astronomical and military uses. In most respects, the basic principles of terahertz-to-optical frequency conversion in WGM resonators are the same as those of microwave (sub-terahertz)-to-optical frequency conversion in WGM resonators, various aspects of which were discussed in the three preceeding articles. To recapitulate: In a receiver following this approach, a preamplified incoming microwave signal (in the present case, a terahertz signal) is up-converted to an optical signal by a technique that exploits the nonlinearity of the electromagnetic response of a whispering-gallery-mode (WGM) resonator made of LiNbO3 or another suitable electro-optical material. Upconversion takes place by three-wave mixing in the resonator. To ensure the required interaction among the optical and terahertz signals, the WGM resonator must be designed and fabricated to function as an electro-optical modulator while simultaneously exhibiting (1) resonance at the required microwave and optical operating frequencies and (2) phase matching among the microwave and optical signals circulating in the resonator. Downstream of the WGM resonator, the up-converted signal is processed photonically by use of a tunable optical filter or local oscillator and is then detected. The practical problems addressed in the present development effort are the following: Satisfaction of the optical and terahertz resonance-frequency requirement is a straightforward matter, inasmuch as the optical and terahertz spectra can be measured. However, satisfaction of the phase-matching requirement is more difficult. The approach followed in the present development is to perform computer simulations of the microwave and optical signals circulating in the resonator to test for phase matching. To enable excitation of the terahertz WGM resonator mode, it is also necessary to ensure phase matching between that mode and the incoming terahertz radiation. In the present development, the incoming signal is coupled into the WGM resonator via a tapered waveguide in the form of a fused silica rod. The phase-matching requirement is satisfied at one point along the taper; the rod is positioned with this point in proximity to the WGM resonator. To maximize the conversion efficiency, it is necessary to maximize the spatial overlap among the terahertz and optical modes in the WGM resonator. In the absence of a special design effort to address this issue, there would be little such overlap because, as a consequence of a large difference between wavelengths, the optical and terahertz modes would be concentrated at different depths from the rim of a WGM resonator. In the present development, overlap is ensured by constructing the WGM resonator as a ring (see figure) so thin that the optical and terahertz modes are effectively forced to overlap.

Terahertz Optical Gain Based on Intersubband Transitions in Optically-Pumped Semiconductor Quantum Wells: Coherent Pumped-Probe Interactions

NASA Technical Reports Server (NTRS)

Liu, Ansheng; Ning, Cun-Zheng

1999-01-01

Terahertz optical gain due to intersubband transitions in optically-pumped semiconductor quantum wells (QW's) is calculated nonperturbatively. We solve the pump- field-induced nonequilibrium distribution function for each subband of the QW system from a set of rate equations that include both intrasubband and intersubband relaxation processes. The gain arising from population inversion and stimulated Raman processes is calculated in a unified manner. We show that the coherent pump and signal wave interactions contribute significantly to the THz gain. Because of the optical Stark effect and pump-induced population redistribution, optical gain saturation at larger pump intensities is predicted.

Spatial pattern separation of chemicals and frequency-independent components by terahertz spectroscopic imaging

NASA Astrophysics Data System (ADS)

Watanabe, Yuuki; Kawase, Kodo; Ikari, Tomofumi; Ito, Hiromasa; Ishikawa, Youichi; Minamide, Hiroaki

2003-10-01

We separated the component spatial patterns of frequency-dependent absorption in chemicals and frequency-independent components such as plastic, paper, and measurement noise in terahertz (THz) spectroscopic images, using known spectral curves. Our measurement system, which uses a widely tunable coherent THz-wave parametric oscillator source, can image at a specific frequency in the range 1-2 THz. The component patterns of chemicals can easily be extracted by use of the frequency-independent components. This method could be successfully used for nondestructive inspection for the detection of illegal drugs and devices of bioterrorism concealed, e.g., inside mail and packages.

Real-time, continuous-wave terahertz imaging using a microbolometer focal-plane array

NASA Technical Reports Server (NTRS)

Hu, Qing (Inventor); Min Lee, Alan W. (Inventor)

2010-01-01

The present invention generally provides a terahertz (THz) imaging system that includes a source for generating radiation (e.g., a quantum cascade laser) having one or more frequencies in a range of about 0.1 THz to about 10 THz, and a two-dimensional detector array comprising a plurality of radiation detecting elements that are capable of detecting radiation in that frequency range. An optical system directs radiation from the source to an object to be imaged. The detector array detects at least a portion of the radiation transmitted through the object (or reflected by the object) so as to form a THz image of that object.

A Hybrid Circuit for Spoof Surface Plasmons and Spatial Waveguide Modes to Reach Controllable Band-Pass Filters

PubMed Central

Zhang, Qian; Zhang, Hao Chi; Wu, Han; Cui, Tie Jun

2015-01-01

We propose a hybrid circuit for spoof surface plasmon polaritons (SPPs) and spatial waveguide modes to develop new microwave devices. The hybrid circuit includes a spoof SPP waveguide made of two anti-symmetric corrugated metallic strips and a traditional substrate integrated waveguide (SIW). From dispersion relations, we show that the electromagnetic waves only can propagate through the hybrid circuit when the operating frequency is less than the cut-off frequency of the SPP waveguide and greater than the cut-off frequency of SIW, generating efficient band-pass filters. We demonstrate that the pass band is controllable in a large range by designing the geometrical parameters of SPP waveguide and SIW. Full-wave simulations are provided to show the large adjustability of filters, including ultra wideband and narrowband filters. We fabricate a sample of the new hybrid device in the microwave frequencies, and measurement results have excellent agreements to numerical simulations, demonstrating excellent filtering characteristics such as low loss, high efficiency, and good square ratio. The proposed hybrid circuit gives important potential to accelerate the development of plasmonic integrated functional devices and circuits in both microwave and terahertz frequencies. PMID:26552584

A Hybrid Circuit for Spoof Surface Plasmons and Spatial Waveguide Modes to Reach Controllable Band-Pass Filters.

PubMed

Zhang, Qian; Zhang, Hao Chi; Wu, Han; Cui, Tie Jun

2015-11-10

We propose a hybrid circuit for spoof surface plasmon polaritons (SPPs) and spatial waveguide modes to develop new microwave devices. The hybrid circuit includes a spoof SPP waveguide made of two anti-symmetric corrugated metallic strips and a traditional substrate integrated waveguide (SIW). From dispersion relations, we show that the electromagnetic waves only can propagate through the hybrid circuit when the operating frequency is less than the cut-off frequency of the SPP waveguide and greater than the cut-off frequency of SIW, generating efficient band-pass filters. We demonstrate that the pass band is controllable in a large range by designing the geometrical parameters of SPP waveguide and SIW. Full-wave simulations are provided to show the large adjustability of filters, including ultra wideband and narrowband filters. We fabricate a sample of the new hybrid device in the microwave frequencies, and measurement results have excellent agreements to numerical simulations, demonstrating excellent filtering characteristics such as low loss, high efficiency, and good square ratio. The proposed hybrid circuit gives important potential to accelerate the development of plasmonic integrated functional devices and circuits in both microwave and terahertz frequencies.

Millimeter wave and terahertz dielectric properties of biological materials

NASA Astrophysics Data System (ADS)

Khan, Usman Ansar

Broadband dielectric properties of materials can be employed to identify, detect, and characterize materials through their unique spectral signatures. In this study, millimeter wave, submillimeter wave, and terahertz dielectric properties of biological substances inclusive of liquids, solids, and powders were obtained using Dispersive Fourier Transform Spectroscopy (DFTS). Two broadband polarizing interferometers were constructed to test materials from 60 GHz to 1.2 THz. This is an extremely difficult portion of the frequency spectrum to obtain a material's dielectric properties since neither optical nor microwave-based techniques provide accurate data. The dielectric characteristics of liquids such as cyclohexane, chlorobenzene, benzene, ethanol, methanol, 1,4 dioxane, and 10% formalin were obtained using the liquid interferometer. Subsequently the solid interferometer was utilized to determine the dielectric properties of human breast tissues, which are fixed and preserved in 10% formalin. This joint collaboration with the Tufts New England Medical Center demonstrated a significant difference between the dielectric response of tumorous and non-tumorous breast tissues across the spectrum. Powders such as anthrax, flour, talc, corn starch, dry milk, and baking soda have been involved in a number of security threats and false alarms around the globe in the last decade. To be able to differentiate hoax attacks and serious security threats, the dielectric properties of common household powders were also examined using the solid interferometer to identify the powders' unique resonance peaks. A new sample preparation kit was designed to test the powder specimens. It was anticipated that millimeter wave and terahertz dielectric characterization will enable one to clearly distinguish one powder from the other; however most of the powders had relatively close dielectric responses and only Talc had a resonance signature recorded at 1.135 THz. Furthermore, due to polarization and birefringence effects, it was determined that one can not utilize the dielectric properties of powder-containing packages to differentiate hoax attacks and serious security threats.

Interaction of surface plasmon polaritons in heavily doped GaN microstructures with terahertz radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melentev, G. A., E-mail: gamelen@spbstu.ru; Shalygin, V. A.; Vorobjev, L. E.

2016-03-07

We present the results of experimental and theoretical studies of the surface plasmon polariton excitations in heavily doped GaN epitaxial layers. Reflection and emission of radiation in the frequency range of 2–20 THz including the Reststrahlen band were investigated for samples with grating etched on the sample surface, as well as for samples with flat surface. The reflectivity spectrum for p-polarized radiation measured for the sample with the surface-relief grating demonstrates a set of resonances associated with excitations of different surface plasmon polariton modes. Spectral peculiarities due to the diffraction effect have been also revealed. The characteristic features of themore » reflectivity spectrum, namely, frequencies, amplitudes, and widths of the resonance dips, are well described theoretically by a modified technique of rigorous coupled-wave analysis of Maxwell equations. The emissivity spectra of the samples were measured under epilayer temperature modulation by pulsed electric field. The emissivity spectrum of the sample with surface-relief grating shows emission peaks in the frequency ranges corresponding to the decay of the surface plasmon polariton modes. Theoretical analysis based on the blackbody-like radiation theory well describes the main peculiarities of the observed THz emission.« less

Frequency of resonance of human sweat duct in different modes of operation

NASA Astrophysics Data System (ADS)

Tripathi, Saroj R.; Takahashi, Shogo; Kinumura, Kento; Kawase, Kodo

2018-02-01

Recently, some studies have demonstrated that the sweat ducts present in the skin play a significant role in terahertz (THz) wave interaction with human beings. It was reported that the sweat ducts act as a low-Q-factor helical antenna due to their helical structure, and resonate in the sub-terahertz frequency range according to their structural parameters, such as helix diameter and helix length. According to the antenna theory, a helical antenna resonates in two different modes of operation known as normal mode and axial mode and the dimension of the helix plays a key role to determine the frequency of resonance. Therefore, here we performed the optical coherence tomography (OCT) of number of human subjects on their palm and foot to investigate the density, distribution and morphological features of sweat ducts. Moreover, we calculated the dielectric properties of human skin using terahertz time domain spectroscopy. Based on the structural parameters of human sweat ducts and its THz dielectric properties of surrounding medium, we computed the frequency of resonance of sweat duct in different modes of operation and we found that these ducts resonate in subterahertz frequency region. We believe that these findings will facilitate further investigation of the THz-skin interaction and provide guidelines for safety levels with respect to human exposure to electromagnetic waves at these frequencies.

Quasi-resonant enhancement of a grazing diffracted wave and deep suppression of specular reflection on shallow metal gratings in terahertz

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tymchenko, M., E-mail: mtymchenko@utexas.edu; Gavrikov, V. K.; Spevak, I. S.

2015-06-29

We report on a previously unexamined anomaly at diffraction of THz radiation on metal gratings. This anomaly consists in a nearly complete redirection of energy to a non-specular homogeneous diffraction order propagating at a specific grazing angle and deep suppression of the specular reflection. We show that this anomaly is located far enough from the well-known one caused by the resonant excitation of the surface plasmon-polariton. The effect under consideration is of general nature and can exist in all spectrum regions; however, it is especially pronounced in THz region, where it should be taken into account when analyzing relevant experimentalmore » results.« less

Improving microwave antenna gain and bandwidth with phase compensation metasurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Ke; Yang, Zhongjie; Feng, Yijun, E-mail: yjfeng@nju.edu.cn

Metasurface, as a planar version of artificial metamaterial, provide an effective way to manipulate electromagnetic wave propagation. Here, we present a transparent metasurface for compensating the out-of-phase radiation from a microstrip patch antenna to improve its radiation gain and bandwidth. Based on the equivalence principle of Huygens’ surface, we propose metasurface composed of both inductive and capacitive resonant elements which could produce high transmission with variable phase characteristics. Such metasurface mounted on a patch antenna can transform the spherical-like phase profile generated from the patch into an in-phase planar one. A prototype antenna has been fabricated and validated the squeezedmore » radiation pattern with suppressed sidelobes as well as enhanced impedance bandwidth due to strong near-field coupling. As operating at around 5.7 GHz, the proposed antenna may have potential application in wireless communication systems especially for point-to-point data transmission. It is believed that the design methodology could also be scaled to other frequency bands such as millimeter or terahertz wave.« less

Theory of injection locking and rapid start-up of magnetrons, and effects of manufacturing errors in terahertz traveling wave tubes

NASA Astrophysics Data System (ADS)

Pengvanich, Phongphaeth

In this thesis, several contemporary issues on coherent radiation sources are examined. They include the fast startup and the injection locking of microwave magnetrons, and the effects of random manufacturing errors on phase and small signal gain of terahertz traveling wave amplifiers. In response to the rapid startup and low noise magnetron experiments performed at the University of Michigan that employed periodic azimuthal perturbations in the axial magnetic field, a systematic study of single particle orbits is performed for a crossed electric and periodic magnetic field. A parametric instability in the orbits, which brings a fraction of the electrons from the cathode toward the anode, is discovered. This offers an explanation of the rapid startup observed in the experiments. A phase-locking model has been constructed from circuit theory to qualitatively explain various regimes observed in kilowatt magnetron injection-locking experiments, which were performed at the University of Michigan. These experiments utilize two continuous-wave magnetrons; one functions as an oscillator and the other as a driver. Time and frequency domain solutions are developed from the model, allowing investigations into growth, saturation, and frequency response of the output. The model qualitatively recovers many of the phase-locking frequency characteristics observed in the experiments. Effects of frequency chirp and frequency perturbation on the phase and lockability have also been quantified. Development of traveling wave amplifier operating at terahertz is a subject of current interest. The small circuit size has prompted a statistical analysis of the effects of random fabrication errors on phase and small signal gain of these amplifiers. The small signal theory is treated with a continuum model in which the electron beam is monoenergetic. Circuit perturbations that vary randomly along the beam axis are introduced through the dimensionless Pierce parameters describing the beam-wave velocity mismatch (b), the gain parameter (C), and the cold tube circuit loss ( d). Our study shows that perturbation in b dominates the other two in terms of power gain and phase shift. Extensive data show that standard deviation of the output phase is linearly proportional to standard deviation of the individual perturbations in b, C and d.

Terahertz parametric sources and imaging applications

NASA Astrophysics Data System (ADS)

Yamashita, M.; Ogawa, Y.; Otani, C.; Kawase, K.

2005-12-01

We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of LiNbO 3 or MgO-doped LiNbO 3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We report the detailed characteristics of the oscillation and the radiation including tunability, spatial and temporal coherency, uni directivity, and efficiency. A Fourier transform limited THz-wave spectrum narrowing was achieved by introducing the injection seeding method. Further, we have developed a spectroscopic THz imaging system using a TPO, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. Several images of the envelope are recorded at different THz frequencies and then processed. The final result is an image that reveals what substances are present in the envelope, in what quantity, and how they are distributed across the envelope area. The example presented here shows the identification of three drugs, two of which illegal, while one is an over-the-counter drug.

Terahertz field-induced ionization and perturbed free induction decay of excitons in bulk GaAs

NASA Astrophysics Data System (ADS)

Murotani, Yuta; Takayama, Masayuki; Sekiguchi, Fumiya; Kim, Changsu; Akiyama, Hidefumi; Shimano, Ryo

2018-03-01

We investigated the interaction between an intense terahertz (THz) pulse and excitons in bulk GaAs by using THz pump near-infrared (NIR) optical probe spectroscopy. We observed a clear spectral oscillation in the NIR transient absorption spectra at low temperature, which is interpreted as the THz pump-induced perturbed free induction decay (PFID) of the excitonic interband polarization. We performed a numerical simulation based on a microscopic theory and identified that the observed PFID signal originates from the THz field-induced ionization of excitons. Using a real-space representation of the excitonic wave function, we visualized how the ionization of an exciton proceeds under the intense single-cycle THz electric field. We also calculated the nonlinear susceptibility with the lowest-order perturbation theory assuming a weak THz pump, which showed a similar spectral feature with that obtained by the full treatment to field-induced ionization process. This coincidence is attributed to the fact that 1s-excitonic interband polarization is modified predominantly through interactions with the p-wave component of the excitonic wave function. A simple phenomenological expression of the PFID signal is presented to discuss effects of the THz pump pulse duration on the spectral oscillation.

UV-LIGA microfabrication process for sub-terahertz waveguides utilizing multiple layered SU-8 photoresist

NASA Astrophysics Data System (ADS)

Malekabadi, Ali; Paoloni, Claudio

2016-09-01

A microfabrication process based on UV LIGA (German acronym of lithography, electroplating and molding) is proposed for the fabrication of relatively high aspect ratio sub-terahertz (100-1000 GHz) metal waveguides, to be used as a slow wave structure in sub-THz vacuum electron devices. The high accuracy and tight tolerances required to properly support frequencies in the sub-THz range can be only achieved by a stable process with full parameter control. The proposed process, based on SU-8 photoresist, has been developed to satisfy high planar surface requirements for metal sub-THz waveguides. It will be demonstrated that, for a given thickness, it is more effective to stack a number of layers of SU-8 with lower thickness rather than using a single thick layer obtained at lower spin rate. The multiple layer approach provides the planarity and the surface quality required for electroforming of ground planes or assembly surfaces and for assuring low ohmic losses of waveguides. A systematic procedure is provided to calculate soft and post-bake times to produce high homogeneity SU-8 multiple layer coating as a mold for very high quality metal waveguides. A double corrugated waveguide designed for 0.3 THz operating frequency, to be used in vacuum electronic devices, was fabricated as test structure. The proposed process based on UV LIGA will enable low cost production of high accuracy sub-THz 3D waveguides. This is fundamental for producing a new generation of affordable sub-THz vacuum electron devices, to fill the technological gap that still prevents a wide diffusion of numerous applications based on THz radiation.

Terahertz radiation generation by beating of two laser beams in a collisional plasma with oblique magnetic field

NASA Astrophysics Data System (ADS)

Hematizadeh, Ayoob; Jazayeri, Seyed Masud; Ghafary, Bijan

2018-02-01

A scheme for excitation of terahertz (THz) radiation is presented by photo mixing of two super-Gaussian laser beams in a rippled density collisional magnetized plasma. Lasers having different frequencies and wave numbers but the same electric fields create a ponderomotive force on the electrons of plasma in the beating frequency. Super-Gaussian laser beam has the exclusive features such as steep gradient in laser intensity distribution, wider cross-section in comparison with Gaussian profiles, which make stronger ponderomotive force and higher THz radiation. The magnetic field is considered oblique to laser beams propagation direction; in this case, depending on the phase matching conditions different mode waves can propagate in plasma. It is found that amplitude and efficiency of the emitted THz radiation not only are sensitive to the beating frequency, collision frequency, and magnetic field strength but to the angle between laser beams and static magnetic field. The efficiency of THz radiation can be optimized in a certain angle.

Investigation of terahertz waves propagating through far infrared/CO2 laser stealth-compatible coating based on one-dimensional photonic crystal

NASA Astrophysics Data System (ADS)

Wang, Qichao; Wang, Jiachun; Zhao, Dapeng; Zhang, Jikui; Li, Zhigang; Chen, Zongsheng; Zeng, Jie; Miao, Lei; Shi, Jiaming

2016-11-01

We propose a new method to disclose the camouflaged targets coated with far infrared/CO2 laser stealth-compatible coating by utilizing terahertz (THz) radar. A coating based on one-dimensional photonic crystal (1DPC) with a defect mode is specially designed and successfully prepared, which possesses a high reflectivity in 8-14 μm waveband and a low reflectivity at 10.6 μm, by alternating thin films of Ge, ZnSe and Si. The propagation characteristic of 0.3-2 THz wave at incident angle from 0° to 80° in such PC coating is investigated theoretically based on characteristic matrix method. The maximal transmittance is up to 92%, and the absorptivity keeps lower than 0.5% over the whole band. The results are verified by experiments, which demonstrate the feasibility of using THz radar to detect the targets covered with such stealth-compatible coatings.

Ultra-wideband high-efficiency reflective linear-to-circular polarization converter based on metasurface at terahertz frequencies.

PubMed

Jiang, Yannan; Wang, Lei; Wang, Jiao; Akwuruoha, Charles Nwakanma; Cao, Weiping

2017-10-30

The polarization conversion of electromagnetic (EM) waves, especially linear-to-circular (LTC) polarization conversion, is of great significance in practical applications. In this study, we propose an ultra-wideband high-efficiency reflective LTC polarization converter based on a metasurface in the terahertz regime. It consists of periodic unit cells, each cell of which is formed by a double split resonant square ring, dielectric layer, and fully reflective gold mirror. In the frequency range of 0.60 - 1.41 THz, the magnitudes of the reflection coefficients reach approximately 0.7, and the phase difference between the two orthogonal electric field components of the reflected wave is close to 90° or -270°. The results indicate that the relative bandwidth reaches 80% and the efficiency is greater than 88%, thus, ultra-wideband high-efficiency LTC polarization conversion has been realized. Finally, the physical mechanism of the polarization conversion is revealed. This converter has potential applications in antenna design, EM measurement, and stealth technology.

Ultrathin Six-Band Polarization-Insensitive Perfect Metamaterial Absorber Based on a Cross-Cave Patch Resonator for Terahertz Waves

PubMed Central

Cheng, Yong Zhi; Huang, Mu Lin; Chen, Hao Ran; Guo, Zhen Zhong; Mao, Xue Song; Gong, Rong Zhou

2017-01-01

A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA), composed of a metal cross-cave patch resonator (CCPR) placed over a ground plane, was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up to 95% at six resonance frequencies. Owing to the ultra-narrow band resonance absorption of the structure, the designed PMMA also exhibits a higher Q factor (>65). In addition, the absorption properties can be kept stable for both normal incident transverse magnetic (TM) and transverse electric (TE) waves. The physical mechanism behind the observed high-level absorption is illustrated by the electric and power loss density distributions. The perfect absorption originates mainly from the higher-order multipolar plasmon resonance of the structure, which differs sharply from most previous studies of PMMAs. Furthermore, the resonance absorption properties of the PMMA can be modified and adjusted easily by varying the geometric parameters of the unit cell. PMID:28772951

Nonperiodic metallic gratings transparent for broadband terahertz waves

NASA Astrophysics Data System (ADS)

Fan, Ren-Hao; Ren, Xiao-Ping; Peng, Ru-Wen; Huang, Xian-Rong; Wang, Mu

Recently, we demonstrate both theoretically and experimentally that nonperiodic metallic gratings can become transparent for broadband terahertz waves. Quasiperiodic and disordered metallic gratings effectively weaken and even eliminate Wood's anomalies, which are the diffraction-related characters of periodic gratings. Consequently, both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity. Furthermore, we show that for a specific light source, for example, a line source, a corresponding nonperiodic transparent grating can be also designed. We expect that our findings can be applied for transparent conducting panels, perfect white-beam polarizers, antireflective conducting solar cells, and beyond. References: X. P. Ren, R. H. Fan, R. W. Peng, X. R. Huang, D. H. Xu, Y. Zhou, and Mu Wang, Physical Review B, 91, 045111 (2015); R. H. Fan, R. W. Peng, X. R. Huang, J. Li, Y. Liu, Q. Hu, Mu. Wang, and X. Zhang, Advanced Materials, 24, 1980 (2012); and X. R. Huang, R. W. Peng, and R. H. Fan. Physical Review Letters, 105, 243901 (2010).

Performance modeling of terahertz (THz) and millimeter waves (mmW) pupil plane imaging

NASA Astrophysics Data System (ADS)

Mohammadian, Nafiseh; Furxhi, Orges; Zhang, Lei; Offermans, Peter; Ghazi, Galia; Driggers, Ronald

2018-05-01

Terahertz- (THz) and millimeter-wave sensors are becoming more important in industrial, security, medical, and defense applications. A major problem in these sensing areas is the resolution, sensitivity, and visual acuity of the imaging systems. There are different fundamental parameters in designing a system that have significant effects on the imaging performance. The performance of THz systems can be discussed in terms of two characteristics: sensitivity and spatial resolution. New approaches for design and manufacturing of THz imagers are a vital basis for developing future applications. Photonics solutions have been at the technological forefront in THz band applications. A single scan antenna does not provide reasonable resolution, sensitivity, and speed. An effective approach to imaging is placing a high-performance antenna in a two-dimensional antenna array to achieve higher radiation efficiency and higher resolution in the imaging systems. Here, we present the performance modeling of a pupil plane imaging system to find the resolution and sensitivity efficiency of the imaging system.

All-dielectric band stop filter at terahertz frequencies

NASA Astrophysics Data System (ADS)

Yin, Shan; Chen, Lin

2018-01-01

We design all-dielectric band stop filters with silicon subwavelength rod and block arrays at terahertz frequencies. Supporting magnetic dipole resonances originated from the Mia resonance, the all-dielectric filters can modulate the working band by simply varying the structural geometry, while eliminating the ohmic loss induced by the traditional metallic metamaterials and uninvolved with the complicated mechanism. The nature of the resonance in the silicon arrays is clarified, which is attributed to the destructive interference between the directly transmitted waves and the waves emitted from the magnetic dipole resonances, and the resonance frequency is determined by the dielectric structure. By particularly designing the geometrical parameters, the profile of the transmission spectrum can be tailored, and the step-like band edge can be obtained. The all-dielectric filters can realize 93% modulation of the transmission within 0.04 THz, and maintain the bandwidth of 0.05 THz. This work provides a method to develop THz functional devices, such as filters, switches and sensors.

New 2D diffraction model and its applications to terahertz parallel-plate waveguide power splitters

PubMed Central

Zhang, Fan; Song, Kaijun; Fan, Yong

2017-01-01

A two-dimensional (2D) diffraction model for the calculation of the diffraction field in 2D space and its applications to terahertz parallel-plate waveguide power splitters are proposed in this paper. Compared with the Huygens-Fresnel principle in three-dimensional (3D) space, the proposed model provides an approximate analytical expression to calculate the diffraction field in 2D space. The diffraction filed is regarded as the superposition integral in 2D space. The calculated results obtained from the proposed diffraction model agree well with the ones by software HFSS based on the element method (FEM). Based on the proposed 2D diffraction model, two parallel-plate waveguide power splitters are presented. The splitters consist of a transmitting horn antenna, reflectors, and a receiving antenna array. The reflector is cylindrical parabolic with superimposed surface relief to efficiently couple the transmitted wave into the receiving antenna array. The reflector is applied as computer-generated holograms to match the transformed field to the receiving antenna aperture field. The power splitters were optimized by a modified real-coded genetic algorithm. The computed results of the splitters agreed well with the ones obtained by software HFSS verify the novel design method for power splitter, which shows good applied prospects of the proposed 2D diffraction model. PMID:28181514

A tunable dual-wavelength pump source based on simulated polariton scattering for terahertz-wave generation

NASA Astrophysics Data System (ADS)

Sun, Bo; Liu, Jinsong; Yao, Jianquan; Li, Enbang

2013-11-01

We propose a dual-wavelength pump source by utilizing stimulated polariton scattering in a LiNbO3 crystal. The residual pump and the generated tunable Stokes waves can be combined to generate THz-wave generation via difference frequency generation (DFG). With a pump energy of 49 mJ, Stokes waves with a tuning range from 1067.8 to 1074 nm have been generated, and an output energy of up to 14.9 mJ at 1070 nm has been achieved with a conversion efficiency of 21.7%. A sum frequency generation experiment was carried out to demonstrate the feasibility of the proposed scheme for THz-wave DFG.

Intensity modulation of a terahertz bandpass filter: utilizing image currents induced on MEMS reconfigurable metamaterials.

PubMed

Hu, Fangrong; Fan, Yixing; Zhang, Xiaowen; Jiang, Wenying; Chen, Yuanzhi; Li, Peng; Yin, Xianhua; Zhang, Wentao

2018-01-01

We experimentally demonstrated a tunable terahertz bandpass filter based on microelectromechanical systems (MEMS) reconfigurable metamaterials. The unit cell of the filter consists of two split-ring resonators (SRRs) and a movable bar. Initially, the movable bar situates at the center of the unit cell, and the filter has two passbands whose central frequencies locate at 0.65 and 0.96 THz. The intensity of the two passbands can be actively modulated by the movable bar, and a maximum modulation depth of 96% is achieved at 0.96 THz. The mechanism of tunability is investigated using the finite-integration time-domain method. The result shows that the image currents induced on the movable bar are opposite the resonance currents induced on the SRRs and, thus, weaken the oscillating intensity of the resonance currents. This scheme paves the way to dynamically control and switch the terahertz wave at some constant frequencies utilizing induced image currents.

Broadband non-polarizing terahertz beam splitters with variable split ratio

NASA Astrophysics Data System (ADS)

Wei, Minggui; Xu, Quan; Wang, Qiu; Zhang, Xueqian; Li, Yanfeng; Gu, Jianqiang; Tian, Zhen; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili

2017-08-01

Seeking effective terahertz functional devices has always aroused extensive attention. Of particular interest is the terahertz beam splitter. Here, we have proposed, designed, manufactured, and tested a broadband non-polarizing terahertz beam splitter with a variable split ratio based on an all-dielectric metasurface. The metasurface was created by patterning a dielectric surface of the N-step phase gradient and etching to a few hundred micrometers. The conversion efficiency as high as 81% under the normal incidence at 0.7 THz was achieved. Meanwhile, such a splitter works well over a broad frequency range. The split ratio of the proposed design can be continuously tuned by simply shifting the metasurface, and the angle of emergences can also be easily adjusted by choosing the step of phase gradients. The proposed design is non-polarizing, and its performance is kept under different polarizations.

Design and simulation of a sub-terahertz folded-waveguide extended interaction oscillator

NASA Astrophysics Data System (ADS)

Liu, Wenxin; Zhang, Zhaochuan; Zhao, Chao; Guo, Xin; Liao, Suying

2017-06-01

In this paper, an interesting type of a two-section folded wave-guide (TSFW) slow wave structure (SWS) for the development of sub-Terahertz (sub-THz) extended interaction oscillator (EIO) is proposed. In this sub-THz device, the prebunching electron beam is produced by the TSFW SWS, which results in the enhancement of the output power. To verify this concept, the TSFW for sub-THz EIO is developed, which includes the design, simulation, and some fabrications. A small size of electron optics system (EOS), the TSFW SWS for beam-wave interactions, and the output structure are studied with simulations. Through the codes Egun and Superfish, the EOS is designed and optimized. With a help of CST studio and 3D particle-in-cell (PIC) simulation CHIPIC, the characteristics of beam-wave interaction generated by the TSFW are studied. The results of PIC simulation show that the output power is remarkably enhanced by a factor of 3, which exceeds 200 W at the frequency of 108 GHz. Based on the optimum parameters, the TSFW is manufactured with a high speed numerical mill, and the test transmission characteristic |S21| is 13 dB. At last, the output structure with a pill-box window is optimized, fabricated, integrated, and tested, and the result shows that the voltage standing-wave ratio of the window is about 2.2 at an operating frequency of 108 GHz. This design and simulation can provide an effective method to develop high power THz sources.

Temporal dynamics of frequency-tunable graphene-based plasmonic grating structures for ultra-broadband terahertz communication

NASA Astrophysics Data System (ADS)

Jornet, Josep Miquel; Thawdar, Ngwe; Woo, Ethan; Andrello, Michael A.

2017-05-01

Terahertz (THz) communication is envisioned as a key wireless technology to satisfy the need for 1000x faster wireless data rates. To date, major progress on both electronic and photonic technologies are finally closing the so-called THz gap. Among others, graphene-based plasmonic nano-devices have been proposed as a way to enable ultra-broadband communications above 1THz. The unique dynamic complex conductivity of graphene enables the propagation of Surface Plasmon Polariton (SPP) waves at THz frequencies. In addition, the conductivity of graphene and, thus, the SPP propagation properties, can be dynamically tuned by means of electrostatic biasing or material doping. This result opens the door to frequency-tunable devices for THz communications. In this paper, the temporal dynamics of graphene-enhanced metallic grating structures used for excitation and detection of SPP waves at THz frequencies are analytically and numerically modeled. More specifically, the response of a metallic grating structure built on top of a graphene-based heterostructure is analyzed by taking into account the grating period and duty cycle and the Fermi energy of the graphene layer. Then, the interfacial charge transfer between a metallic back-gate and the graphene layer in a metal/dielectric/graphene stack is analytically modeled, and the range of achievable Fermi energies is determined. Finally, the rate at which the Fermi energy in graphene can be tuned is estimated starting from the transmission line model of graphene. Extensive numerical and simulation results with COMSOL Multi-physics are provided. The results show that the proposed structure enables dynamic frequency systems with THz bandwidths, thus, enabling resilient communication techniques such as time-hopping THz modulations.

Open Resonator for Summation of Powers in Sub-Terahertz and Terahertz Frequencies

NASA Astrophysics Data System (ADS)

Kuz'michev, I. K.; Yeryomka, V. D.; May, A. V.; Troshchilo, A. S.

2017-03-01

Purpose: Study of excitation features for the first higher axialasymmetric type oscillations in an open resonator connected into the waveguide transmission line. Design/methodology/approach: To determine the efficiency of higher oscillation excitation in the resonator by using the highest wave of a rectangular waveguide, the coefficient of the antenna surface utilization is used. The coefficient of reflection from the open resonator is determined by the known method of summation of the partial coefficients of reflection from the resonant system. Findings: The excitation efficiency of the first higher axial asymmetric type TEM10q oscillations in an open resonator connected into the waveguide transmission line, using the TE20 type wave, is considered. The research efforts were made with accounting for the electromagnetic field vector nature. It is shown that for certain sizes of exciting coupler the excitation efficiency of the working excitation is equal to 0.867. Besides, this resonant system has a single frequency response within a wide band of frequencies. Due to this, it can be applied for summation of powers for individual sources of oscillations. Since this resonant system allows separating the matching functions as to the field and coupling, it is possible to provide any prescribed coupling of sources with a resonant volume. For this purpose, one- dimensional diffraction gratings (E-polarization) are used. Conclusions: With the matched excitation of axially asymmetric modes of oscillations the resonant system has an angular and frequency spectrum selection that is of great practical importance for powers summation. By application of one- dimensional diffraction gratings (E-polarization), located in apertures of coupling elements, the active elements can be matched with the resonant volume.

Optimized two- and three-colour laser pulses for the intense terahertz wave generation

NASA Astrophysics Data System (ADS)

Zhang, Lei; Wang, Guo-Li; Zhou, Xiao-Xin

2016-11-01

Based on the photocurrent model, we perform a theoretical study on the optimization of terahertz (THz) wave emission from argon gas irradiated by the two- and three-colour laser fields. To obtain stronger THz radiation for the given conditions, a genetic algorithm method is applied to search for the optimum laser parameters. For the two-colour field, our optimizations reveal two types of optimal scheme, and each one dominates the THz generation in different regions of intensity ratio for a given total laser intensity. One scheme is the combination of a fundamental laser pulse and its second harmonic, while the other is the fundamental pulse with its fourth harmonic. For each scheme, the optimal intensity ratio and phase delay are obtained. For the three-colour case, our optimization shows that the excellent waveform for the strongest THz radiation is composed of a fundamental laser pulse, and its second, third harmonics, with appropriate intensity ratio and carrier-envelope phase. Such a 3-colour field can generate strong THz radiation comparable with a 10-colour sawtooth wave [Martínez et al., Phys. Rev. Lett. 114, 183901 (2015)]. The physical mechanisms for the enhancement of THz wave emission in gases are also discussed in detail. Our results give helpful guidance for intense THz generation with tabletop femtosecond laser device in experiment.

Semiconductor quantum well irradiated by a two-mode electromagnetic field as a terahertz emitter

NASA Astrophysics Data System (ADS)

Mandal, S.; Liew, T. C. H.; Kibis, O. V.

2018-04-01

We study theoretically the nonlinear optical properties of a semiconductor quantum well (QW) irradiated by a two-mode electromagnetic wave consisting of a strong resonant dressing field and a weak off-resonant driving field. In the considered strongly coupled electron-field system, the dressing field opens dynamic Stark gaps in the electron energy spectrum of the QW, whereas the driving field induces electron oscillations in the QW plane. Since the gapped electron spectrum restricts the amplitude of the oscillations, the emission of a frequency comb from the QW appears. Therefore, the doubly driven QW operates as a nonlinear optical element which can be used, particularly, for optically controlled generation of terahertz radiation.

Terahertz Near-Field Imaging Using Enhanced Transmission through a Single Subwavelength Aperture

NASA Astrophysics Data System (ADS)

Ishihara, Kunihiko; Ikari, Tomofumi; Minamide, Hiroaki; Shikata, Jun-ichi; Ohashi, Keishi; Yokoyama, Hiroyuki; Ito, Hiromasa

2005-07-01

We demonstrate terahertz (THz) near-field imaging using resonantly enhanced transmission of THz-wave radiation (λ˜ 200 μm) through a bull’s eye structure (a single subwavelength aperture surrounded by concentric periodic grooves in a metal plate). The bull’s eye structure shows extremely large enhanced transmission, which has the advantage for a single subwavelength aperture. The spatial resolution for the bull’s eye structure (with an aperture diameter d=100 μm) is evaluated in the near-field region, and a resolution of 50 μm (corresponding to λ/4) is achieved. We obtain the THz near-field images of the subwavelength metal pattern with a spatial resolution below the diffraction limit.

Terahertz wireless communications based on photonics technologies.

PubMed

Nagatsuma, Tadao; Horiguchi, Shogo; Minamikata, Yusuke; Yoshimizu, Yasuyuki; Hisatake, Shintaro; Kuwano, Shigeru; Yoshimoto, Naoto; Terada, Jun; Takahashi, Hiroyuki

2013-10-07

There has been an increasing interest in the application of terahertz (THz) waves to broadband wireless communications. In particular, use of frequencies above 275 GHz is one of the strong concerns among radio scientists and engineers, because these frequency bands have not yet been allocated at specific active services, and there is a possibility to employ extremely large bandwidths for ultra-broadband wireless communications. Introduction of photonics technologies for signal generation, modulation and detection is effective not only to enhance the bandwidth and/or the data rate, but also to combine fiber-optic (wired) and wireless networks. This paper reviews recent progress in THz wireless communications using telecom-based photonics technologies towards 100 Gbit/s.

Glycerol dehydration of native and diabetic animal tissues studied by THz-TDS and NMR methods

PubMed Central

Smolyanskaya, O. A.; Schelkanova, I. J.; Kulya, M. S.; Odlyanitskiy, E. L.; Goryachev, I. S.; Tcypkin, A. N.; Grachev, Ya. V.; Toropova, Ya. G.; Tuchin, V. V.

2018-01-01

The optical clearing method has been widely used for different spectral ranges where it provides tissue transparency. In this work, we observed the enhanced penetration of the terahertz waves inside biological samples (skin, kidney, and cornea) treated with glycerol solutions inducing changes of optical and dielectric properties. It was supported by the observed trend of free-to-bound water ratio measured by the nuclear magnetic resonance (NMR) method. The terahertz clearing efficiency was found to be less for diabetic samples than for normal ones. Results of the numerical simulation proved that pulse deformation is due to bigger penetration depth caused by the reduction of absorption and refraction at optical clearing. PMID:29541513

Low-loss polarization-maintaining terahertz fiber based on central air hole movements

NASA Astrophysics Data System (ADS)

Wu, Zhiqing; Li, Qingzhi; Xia, Handing; Shi, Zhaohua; Zhou, Xiaoyan; Deng, Qinghua; Wu, Weidong

2018-04-01

We report a type of single-hole core photonic crystal fiber for low-loss polarization-maintaining terahertz (THz) wave guidance. Simulation results show that high birefringence at a level of 10 - 2 can be obtained by a design of minor position adjustment of the central air hole. Low effective material loss can be achieved because of the introduced central air hole. The strategy of the central air hole movements is also applicable for the three-hole core THz photonic crystal fibers. Other transmission characteristics including single-mode condition, power fraction, confinement loss, and dispersion were discussed in detail. It is quite clear that the proposal facilitates the fabrication process due to the simple structure.

High frequency modulation and injection locking of terahertz quantum cascade lasers

NASA Astrophysics Data System (ADS)

Gu, L.; Wan, W. J.; Zhu, Y. H.; Fu, Z. L.; Li, H.; Cao, J. C.

2017-06-01

Due to intersubband transitions, the quantum cascade laser (QCL) is free of relaxations and able to work under fast modulations. In this work, the authors investigate the fast modulation properties of a continuous wave (cw) terahertz QCL emitting around 3 THz (˜100 μm). Both simulation and experimental results show that the 3 dB modulation bandwidth for the device can reach 11.5 GHz and the modulation response curve is relatively flat upto ˜16 GHz. The radio frequency (RF) injection measurements verify that around the laser threshold the inter-mode beat note interacts strongly with the RF signal and the laser can be modulated at the round trip frequency of 15.5 GHz.

Photonic crystals at visible, x-ray, and terahertz frequencies

NASA Astrophysics Data System (ADS)

Prasad, Tushar

Photonic crystals are artificial structures with a periodically varying refractive index. This property allows photonic crystals to control the propagation of photons, making them desirable components for novel photonic devices. Photonic crystals are also termed as "semiconductors of light", since they control the flow of electromagnetic radiation similar to the way electrons are excited in a semiconductor crystal. The scale of periodicity in the refractive index determines the frequency (or wavelength) of the electromagnetic waves that can be manipulated. This thesis presents a detailed analysis of photonic crystals at visible, x-ray, and terahertz frequencies. Self-assembly and spin-coating methods are used to fabricate colloidal photonic crystals at visible frequencies. Their dispersion characteristics are examined through theoretical as well as experimental studies. Based on their peculiar dispersion property called the superprism effect, a sensor that can detect small quantities of chemical substances is designed. A photonic crystal that can manipulate x-rays is fabricated by using crystals of a non-toxic plant virus as templates. Calculations show that these metallized three-dimensional crystals can find utility in x-ray optical systems. Terahertz photonic crystal slabs are fabricated by standard lithographic and etching techniques. In-plane superprism effect and out-of-plane guided resonances are studied by terahertz time-domain spectroscopy, and verified by numerical simulations.

Investigation of Fiber Waviness in a Thick Glass Composite Beam Using THz NDE

NASA Technical Reports Server (NTRS)

Anastasi, Robert F.

2008-01-01

Fiber waviness in laminated composite material is introduced during manufacture because of uneven curing, resin shrinkage, or ply buckling caused by bending the composite lay-up into its final shape prior to curing. The resulting waviness has a detrimental effect on mechanical properties, therefore this condition is important to detect and characterize. Ultrasonic characterization methods are difficult to interpret because elastic wave propagation is highly dependent on ply orientation and material stresses. By comparison, the pulsed terahertz response of the composite is shown to provide clear indications of the fiber waviness. Pulsed Terahertz NDE is an electromagnetic inspection method that operates in the frequency range between 300 GHz and 3 THz. Its propagation is influenced by refractive index variations and interfaces. This work applies pulsed Terahertz NDE to the inspection of a thick composite beam with fiber waviness. The sample is a laminated glass composite material approximately 15mm thick with a 90-degree bend. Terahertz response from the planar section, away from the bend, is indicative of a homogeneous material with no major reflections from internal plies, while the multiple reflections at the bend area correspond to the fiber waviness. Results of these measurements are presented for the planar and bend areas.

Three-Dimensional Terahertz Coded-Aperture Imaging Based on Single Input Multiple Output Technology.

PubMed

Chen, Shuo; Luo, Chenggao; Deng, Bin; Wang, Hongqiang; Cheng, Yongqiang; Zhuang, Zhaowen

2018-01-19

As a promising radar imaging technique, terahertz coded-aperture imaging (TCAI) can achieve high-resolution, forward-looking, and staring imaging by producing spatiotemporal independent signals with coded apertures. In this paper, we propose a three-dimensional (3D) TCAI architecture based on single input multiple output (SIMO) technology, which can reduce the coding and sampling times sharply. The coded aperture applied in the proposed TCAI architecture loads either purposive or random phase modulation factor. In the transmitting process, the purposive phase modulation factor drives the terahertz beam to scan the divided 3D imaging cells. In the receiving process, the random phase modulation factor is adopted to modulate the terahertz wave to be spatiotemporally independent for high resolution. Considering human-scale targets, images of each 3D imaging cell are reconstructed one by one to decompose the global computational complexity, and then are synthesized together to obtain the complete high-resolution image. As for each imaging cell, the multi-resolution imaging method helps to reduce the computational burden on a large-scale reference-signal matrix. The experimental results demonstrate that the proposed architecture can achieve high-resolution imaging with much less time for 3D targets and has great potential in applications such as security screening, nondestructive detection, medical diagnosis, etc.

Ultrafast terahertz spectroscopy study of a Kondo insulating thin-film Sm B6 : Evidence for an emergent surface state

NASA Astrophysics Data System (ADS)

Zhang, Jingdi; Yong, Jie; Takeuchi, Ichiro; Greene, Richard L.; Averitt, Richard D.

2018-04-01

We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound Sm B6 , a prototype Kondo insulator. Temperature-dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ˜T*=20 K , well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20 K) suggests the emergence of a surface state with an effective electron mass of 0.1 me . The conductivity dynamics following optical excitation is also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20 K, indicative of another channel opening up in the low-energy electrodynamics. Taken together, these results are consistent with the onset of a surface state well below the crossover temperature (100 K) after long-range coherence of the f -electron Kondo lattice is established.

Tunable Terahertz Metamaterials with Germanium Telluride Components

DTIC Science & Technology

2016-03-24

emerging field with many exciting applications. THz waves can be used to locate explosives and illicit drugs in security applications, or DNA and...17 Fig. 7. Absorbance spectra of various drugs and explosives. The resonant peaks of each material are clearly distinguishable [22...holder designed with help from the school model shop

Subwavelength prestressed microcantilevers based metamaterials for efficient manipulation of terahertz waves

DTIC Science & Technology

2015-07-01

for the fluid flow controlled MEMS metamaterial with PDMS chamber. (b)-(d) shows the cantilever deformation with respect to increasing fluid flow...Firstly the metamaterial was integrated with a polydimethylsiloxane fluidic channel and the injection flow rate was varied from 0 to 5 ml/min

Towards Terahertz MMIC Amplifiers: Present Status and Trends

NASA Technical Reports Server (NTRS)

Samoska, Lorene

2006-01-01

This viewgraph presentation surveys the fastest Monolithic Millimeter-wave Integrated Circuit (MMIC) amplifiers to date; summarize previous solid state power amp results to date; reviews examples of MMICs, reviews Power vs. Gate periphery and frequency; Summarizes previous LNA results to date; reviews Noise figure results and trends toward higher frequency

Information hiding and retrieval in Rydberg wave packets using half-cycle pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murray, J. M.; Pisharody, S. N.; Wen, H.

We demonstrate an information hiding and retrieval scheme with the relative phases between states in a Rydberg wave packet acting as the bits of a data register. We use a terahertz half-cycle pulse (HCP) to transfer phase-encoded information from an optically accessible angular momentum manifold to another manifold which is not directly accessed by our laser pulses, effectively hiding the information from our optical interferometric measurement techniques. A subsequent HCP acting on these wave packets reintroduces the information back into the optically accessible data register manifold which can then be read out.

On-chip sub-terahertz surface plasmon polariton transmission lines with mode converter in CMOS

PubMed Central

Liang, Yuan; Yu, Hao; Wen, Jincai; Apriyana, Anak Agung Alit; Li, Nan; Luo, Yu; Sun, Lingling

2016-01-01

An on-chip low-loss and high conversion efficiency plasmonic waveguide converter is demonstrated at sub-THz in CMOS. By introducing a subwavelength periodic corrugated structure onto the transmission line (T-line) implemented by a top-layer metal, surface plasmon polaritons (SPP) are established to propagate signals with strongly localized surface-wave. To match both impedance and momentum of other on-chip components with TEM-wave propagation, a mode converter structure featured by a smooth bridge between the Ground coplanar waveguide (GCPW) with 50 Ω impedance and SPP T-line is proposed. To further reduce area, the converter is ultimately simplified to a gradual increment of groove with smooth gradient. The proposed SPP T-lines with the converter is designed and fabricated in the standard 65 nm CMOS process. Both near-field simulation and measurement results show excellent conversion efficiency from quasi-TEM to SPP modes in a broadband frequency range. The converter achieves wideband impedance matching (<−9 dB) with excellent transmission efficiency (averagely −1.9 dB) from 110 GHz–325 GHz. The demonstrated compact and wideband SPP T-lines with mode converter have shown great potentials to replace existing waveguides as future on-chip THz interconnects. To the best of the author’s knowledge, this is the first time to demonstrate the (sub)-THz surface mode conversion on-chip in CMOS technology. PMID:27444782

Wideband response of a terahertz-millimeter imager based on a 384x288 pixel uncooled bolometric detector

NASA Astrophysics Data System (ADS)

Terroux, Marc; Marchese, Linda; Bolduc, Martin; Mercier, Luc; Chevalier, Claude; Gagnon, Lucie; Tremblay, Bruno; Généreux, Francis; Paultre, Jacques-Edmond; Provençal, Francis; Beaupré, Patrick; Desroches, Yan; Châteauneuf, François; Bergeron, Alain

2017-11-01

In the past, bolometer-based imagers have been used for earth observation. Uncooled-bolometer based imagers are especially well suited for this due to their low power consumption. NIRST (New Infra-Red Sensor Technology), an example of an imager based on uncooled bolometers, monitors high temperature events on the ground related to fires and volcanic events, and will measure their physical parameters and takes measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities. NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um.

Probing and controlling terahertz-driven structural dynamics with surface sensitivity

DOE PAGES

Bowlan, Pamela Renee; Bowlan, J.; Trugman, S. A.; ...

2017-03-17

Intense, single-cycle terahertz (THz) pulses are powerful tools to understand and control material properties through low-energy resonances, such as phonons. Combining this with optical second harmonic generation (SHG) makes it possible to observe the resulting ultrafast structural changes with surface sensitivity. This makes SHG an ideal method to probe phonon dynamics in topological insulators (TI), materials with unique surface transport properties. Here, we resonantly excite a phonon mode in the TI Bi 2Se 3with THz pulses and use SHG to separate the resulting symmetry changes at the surface from the bulk. Furthermore, we coherently control the lattice vibrations with amore » pair of THz pulses. Lastly, our work demonstrates a versatile, table-top tool to probe and control phonon dynamics in a range of systems, particularly at surfaces and interfaces.« less

Artworks characterization at THz frequencies: preliminary results via the Fiber-Coupled Terahertz Time Domain System

NASA Astrophysics Data System (ADS)

Catapano, Ilaria; Soldovieri, Francesco

2015-04-01

In the research field of art and archaeology, scientific observation and analysis are hugely demanded to gather as more information as possible on the materials and techniques used to create artworks as well as in previous restoration actions. In this frame, diagnostic tools exploiting electromagnetic waves deserve massive interest tanks to their ability to provide non-invasive and possibly contactless characterization of the investigated objects. Among the electromagnetic diagnostic technologies, those working at frequencies belonging to the 0.1-10 THz range are currently deserving an increased attention since THz waves are capable of penetrating into optically opaque materials (up to the preparation layers), without direct contact and by involving sufficiently low energy to be considered as perfectly non-invasive in practice [1,2]. Moreover, being THz non-ionizing radiations, a moderate exposure to them implies minor long term risks to the molecular stability of the historical artifact and humans. Finally, recent developments of THz technology have allowed the commercialization of compact, flexible and portable systems. One of them is the Fiber-Coupled Terahertz Time Domain System (FICO) developed by Z-Omega, acquired by the Institute of Electromagnetic Sensing of the Environment (IREA) in 2013. This system works in the range from 60GHz to 3THz with a waveform acquisition speed up to 500Hz, it is equipped with fiber optic coupled transmitting and receiving probes and, few months ago, has been potentiated by means of an automatic positioning system enabling to scan a 150mm x 150mm area. In the frame of the IREA research activities regarding cultural heritage, the FICO system is currently adopted to perform both spectroscopy and imaging, which are the two kind of analysis wherein THz technology can be profitably explored [3]. In particular, THz spectroscopy is used to distinguish different artists materials by exploiting their peculiar fingerprint in the absorption spectra, while imaging includes THz tomography and it is considered to obtain non-invasive cross-section images of the artwork under test. Preliminary experiments regarding laboratory designed objects and not precious artworks have been carried out at the IREA laboratory mainly to trace measurements protocols and deeply investigate the diagnostic capabilities of the FICO system. The obtained results will be illustrated and discussed at the conference. REFERENCES [1] K. Fukunaga and I. Hosako, Innovative non-invasive analysis techniques for cultural heritage using terahertz technology, C.R. Physique 11, 519-526, 2010. [2] M. Perenzoni and D. J. Paul, Physics and Applications of Terahertz Radiation, Springer Series in Optical Sciences 173, 2014. [3] J.P. Guillet, B. Recur, L. Frederique, B. Bousquet, L. Canioni, I. Manek-Hönninger, P. Desbarats, P.Mounaix, Review of Terahertz Tomography Techniques, J. Infrared MilliTerahz Waves 35, 382-411, 2014.

Active Metamaterials for Terahertz Communication and Imaging

NASA Astrophysics Data System (ADS)

Rout, Saroj

In recent years there has been significant interest in terahertz (THz) systems mostly due to their unique applications in communication and imaging. One of the primary reason for this resurgence is the use of metamaterials to design THz devices due to lack of natural materials that can respond to this electromagnetic spectrum, the so-called ''THz gap''. Even after years of intense research, THz systems are complex and expensive, unsuitable for mainstream applications. This work focuses on bridging this gap by building all solid-state THz devices for imaging and communication applications in a commercial integrated circuit (IC) technology. One such canonical device is a THz wave modulator that can be used in THz wireless communication devices and as spatial light modulator (SLM) for THz imaging systems. The key contribution of this thesis is a metamaterial based THz wave modulator fabricated in a commercial gallium arsenide (GaAs) process resonant at 0.46 THz using a novel approach of embedding pseudomorphic high electron mobility transistors (pHEMTs) in metamaterial and demonstrate modulation values over 30%, and THz modulation at frequencies up to 10 MHz. Using the THz wave modulator, we fabricated and experimentally demonstrated an all solid-state metamaterial based THz spatial light modulator (SLM) as a 2x2 pixel array operating around 0.46 THz, by raster scanning an occluded metal object in polystyrene using a single-pixel imaging setup. This was an important step towards building an low-voltage (1V), low power, on-chip integrable THz imaging device. Using the characterization result from the THz SLM, we computationally demonstrated a multi-level amplitude shift keying (ASK) terahertz wireless communication system using spatial light modulation instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. We show two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR). We have computationally demonstrated a novel pictorial modulation technique showing N/log2(N) improvement in bandwidth using a N-tile SLM compared to standard spatial modulation using a single-pixel detector. Finally, we demonstrate a path to realize a terahertz focal plane array (FPA) using a commercial 0.18 mum CMOS foundry process. Through EM simulation and circuit simulation we have demonstrated a metamaterial based THz detectors at 230-325 GHz that can be used in a focal plane array.

Measurement of Absorption Coefficient of Paraformaldehyde and Metaldehyde with Terahertz Spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, J.; Xia, T.; Chen, Q.; Sun, Q.; Deng, Y.; Wang, C.

2018-03-01

The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as "fingerprints" to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient-mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.

Fabrication of broadband antireflection coating at terahertz frequency using a hot emboss method

NASA Astrophysics Data System (ADS)

Li, YunZhou; Cai, Bin; Zhu, YiMing

2014-11-01

We fabricated a terahertz anti-reflective structure on a polystylene by using a hot-embossing method. Polystylene was spin-coated onto a silicon substrate and then transformed by using a metallic mould comprising a bunch of Chinese acupuncture needles. The transformation layer yielded gradient refractive index profiles on the substrate which can reduce the surface reflection effectively. The samples were evaluated by a terahertz time-domain spectroscope. Compared with a bare silicon substrate, we observed an increase of ~30% in the transmittance. We also observed broader bandwidth properties compared with a single-layer antireflective structure. The process imposes no substrate limiting; i.e., it has great potential to be applied onto various THz devices.

Advances in the biological effects of terahertz wave radiation.

PubMed

Zhao, Li; Hao, Yan-Hui; Peng, Rui-Yun

2014-01-01

The terahertz (THz) band lies between microwave and infrared rays in wavelength and consists of non-ionizing radiation. Both domestic and foreign research institutions, including the army, have attached considerable importance to the research and development of THz technology because this radiation exhibits both photon-like and electron-like properties, which grant it considerable application value and potential. With the rapid development of THz technology and related applications, studies of the biological effects of THz radiation have become a major focus in the field of life sciences. Research in this field has only just begun, both at home and abroad. In this paper, research progress with respect to THz radiation, including its biological effects, mechanisms and methods of protection, will be reviewed.

Analog of electromagnetically induced transparency at terahertz frequency based on a bilayer-double-H-metamaterial

NASA Astrophysics Data System (ADS)

Wang, Yue'e.; Li, Zhi; Hu, Fangrong

2018-01-01

We designed a bilayer-double-H-metamaterials (BDHM) composed of two layers of metal and two layers of dielectric to analog a spectral response of electromagnetically induced transparency (EIT) at terahertz frequency. By changing the incident angle, the BDHM exhibits an EIT-like spectral response. The tunable spectral performances and modulation mechanism of the transparent peak are theoretically investigated using full-wave electromagnetic simulation software. The physical mechanism of the EIT-like effect is based on the constructive and destructive interference between the induced electrical dipoles. Our work provides a new way to realize the EIT-like effect only by changing the incident angles of the metamaterials. The potential applications include tunable filters, sensors, attenuators, switches, and so on.

Continuous tuning of two-section, single-mode terahertz quantum-cascade lasers by fiber-coupled, near-infrared illumination

NASA Astrophysics Data System (ADS)

Hempel, Martin; Röben, Benjamin; Niehle, Michael; Schrottke, Lutz; Trampert, Achim; Grahn, Holger T.

2017-05-01

The dynamical tuning due to rear facet illumination of single-mode, terahertz (THz) quantum-cascade lasers (QCLs) which employ distributed feedback gratings are compared to the tuning of single-mode QCLs based on two-section cavities. The THz QCLs under investigation emit in the range of 3 to 4.7 THz. The tuning is achieved by illuminating the rear facet of the QCL with a fiber-coupled light source emitting at 777 nm. Tuning ranges of 5.0 and 11.9 GHz under continuous-wave and pulsed operation, respectively, are demonstrated for a single-mode, two-section cavity QCL emitting at about 3.1 THz, which exhibits a side-mode suppression ratio better than -25 dB.

A metamaterial terahertz modulator based on complementary planar double-split-ring resonator

NASA Astrophysics Data System (ADS)

Wang, Chang-hui; Kuang, Deng-feng; Chang, Sheng-jiang; Lin, Lie

2013-07-01

A metamaterial based on complementary planar double-split-ring resonator (DSRR) structure is presented and demonstrated, which can optically tune the transmission of the terahertz (THz) wave. Unlike the traditional DSRR metamaterials, the DSRR discussed in this paper consists of two split rings connected by two bridges. Numerical simulations with the finite-difference time-domain (FDTD) method reveal that the transmission spectra of the original and the complementary metamaterials are both in good agreement with Babinet's principle. Then by increasing the carrier density of the intrinsic GaAs substrate, the magnetic response of the complementary special DSRR metamaterial can be weakened or even turned off. This metamaterial structure is promised to be a narrow-band THz modulator with response time of several nanoseconds.