Science.gov

Sample records for porous dielectric thz

  1. Dielectric THz waveguides

    NASA Astrophysics Data System (ADS)

    Dupuis, Alexandre

    In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (˜25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber

  2. Square dielectric THz waveguides.

    PubMed

    Aflakian, N; Yang, N; LaFave, T; Henderson, R M; O, K K; MacFarlane, D L

    2016-06-27

    A holey cladding dielectric waveguide with square cross section is designed, simulated, fabricated and characterized. The TOPAS waveguide is designed to be single mode across the broad frequency range of 180 GHz to 360 GHz as shown by finite-difference time domain simulation and to robustly support simultaneous TE and TM mode propagation. The square fiber geometry is realized by pulling through a heat distribution made square by appropriate furnace design. The transmitted mode profile is imaged using a vector network analyzer with a pinhole at the receiver module. Good agreement between the measured mode distribution and the calculated mode distribution is demonstrated.

  3. Extremely sub-wavelength THz metal-dielectric wire microcavities.

    PubMed

    Feuillet-Palma, Cheryl; Todorov, Yanko; Steed, Robert; Vasanelli, Angela; Biasiol, Giorgio; Sorba, Lucia; Sirtori, Carlo

    2012-12-17

    We demonstrate minimal volume wire THz metal-dielectric micro-cavities, in which all but one dimension have been reduced to highly sub-wavelength values. The smallest cavity features an effective volume of 0.4 µm(3), which is ~5.10(-7) times the volume defined by the resonant vacuum wavelength (λ = 94 µm) to the cube. When combined with a doped multi-quantum well structure, such micro-cavities enter the ultra-strong light matter coupling regime, even if the total number of electrons participating to the coupling is only in the order of 10(4), thus much less than in previous studies.

  4. Dielectric Study of Alcohols Using Broadband Terahertz Time Domain Spectroscopy (THz-TDS).

    NASA Astrophysics Data System (ADS)

    Sarkar, Sohini; Saha, Debasis; Banerjee, Sneha; Mukherjee, Arnab; Mandal, Pankaj

    2016-06-01

    Broadband Terahertz-Time Domain Spectroscopy (THz-TDS) (1-10 THz) has been utilized to study the complex dielectric properties of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-octanol. Previous reports on dielectric study of alcohols were limited to 5 THz. At THz (1 THz = 33.33 wn = 4 meV) frequency range (0.1 to 15 THz), the molecular reorientation and several intermolecular vibrations (local oscillation of dipoles) may coexist and contribute to the overall liquid dynamics. We find that the Debye type relaxations barely contribute beyond 1 THz, rather three harmonic oscillators dominate the entire spectral range. To get insights on the modes responsible for the observed absorption in THz frequency range, we performed all atom molecular dynamics (MD) using OPLS force field and ab initio quantum calculations. Combined experimental and theoretical study reveal that the complex dielectric functions of alcohols have contribution from a) alkyl group oscillation within H-bonded network ( 1 THz), b) intermolecular H-bond stretching ( 5 THz) , and c) librational motions in alcohols. The present work, therefore, complements all previous studies on alcohols at lower frequencies and provides a clear picture on them in a broad spectral range from microwave to 10 THz.

  5. Porous Dielectrics in Microelectronic Wiring Applications

    PubMed Central

    McGahay, Vincent

    2010-01-01

    Porous insulators are utilized in the wiring structure of microelectronic devices as a means of reducing, through low dielectric permittivity, power consumption and signal delay in integrated circuits. They are typically based on low density modifications of amorphous SiO2 known as SiCOH or carbon-doped oxides, in which free volume is created through the removal of labile organic phases. Porous dielectrics pose a number of technological challenges related to chemical and mechanical stability, particularly in regard to semiconductor processing methods. This review discusses porous dielectric film preparation techniques, key issues encountered, and mitigation strategies.

  6. Analysis of high voltage dielectric insulation materials of XLPE by THz-TDS system

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Yan, Zhijin; Yang, Lei; Dai, Yang; Zhang, Like; Bian, Kangkang; Hou, Lei

    2015-11-01

    In this paper, cross-linked polyethylene (XLPE) was analyzed by THz time domain spectroscopy (TDS) system at room temperature. By recording time domain signal of terahertz radiation field, frequency spectrum can be obtained by Fourier transform. Then the refractive index and dielectric constant in THz band are calculated. This proves that the THz-TDS system has a potential application for detecting the aging characteristic of XLPE.

  7. THz transmission characteristics of dielectric-filled parallel-plate waveguides

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind

    2007-04-01

    THz transmission characteristics of dielectric-filled (DF) metallic parallel-plate waveguides (PPWGs) are experimentally and theoretically investigated via the propagation of sub-ps THz pulses. It is found that a PPWG having a high-resistivity (>10 kΩ cm) silicon filling can, in fact, exhibit a higher transmission loss compared to one having a polythene filling, despite the significantly lower THz absorption in the bulk silicon. Consequently, it is shown that the key to achieving low-loss transmission in DF-PPWGs is to use a dielectric filling having not only a low absorption, but also a low refractive index. The application of this guided-wave geometry for THz spectroscopy of minute (film) substances is also predicted.

  8. THz - ToF Optical Layer Analysis (OLA) to determine optical properties of dielectric materials

    NASA Astrophysics Data System (ADS)

    Spranger, Holger; Beckmann, Jörg

    2017-02-01

    Electromagnetic waves with frequencies between 0.1 and 10 THz are described as THz-radiation (T-ray). The ability to penetrate dielectric materials makes T-rays attractive to reveal discontinuities in polymer and ceramic materials. THz-Time Domain Spectroscopy Systems (THz-TDS) are available on the market today which operates with THz-pulses transmitted and received by optically pumped semiconductor antennas. In THz-TDS the travelling time (ToF) and shape of the pulse is changed if it interacts with the dielectric material and its inherent discontinuities. A tomogram of the object under the test can be reconstructed from time of flight diffraction (ToFD) scans if a synthetic focusing aperture (SAFT) algorithm is applied. The knowledge of the base materials shape and optical properties is essential for a proper reconstruction result. To obtain these properties a model is assumed which describes the device under the test as multilayer structure composed of thin layers with different dielectric characteristics. The Optical Layer Analysis (OLA) is able to fulfill these requirements. A short description why the optical properties are crucial for meaningful SAFT reconstruction results will be given first. Afterwards the OLA will be derived and applied on representative samples to discuss and evaluate its benefits and limits.

  9. The source of THz radiation based on dielectric waveguide excited by sequence of electron bunches

    NASA Astrophysics Data System (ADS)

    Altmark, A. M.; Kanareykin, A. D.

    2016-07-01

    We present a new method for excitation of THz Cherenkov radiation in a dielectric waveguide by relativistic electron bunches. A sequence of bunches generates monochromatic radiation. The frequency of radiation is defined by the distance between the bunches. The studies were carried by using the newly updated BBU-3000 code which permits taking into account a number of additional options: an external quadrupole focusing system, group velocity of the wakefield, and the dielectric material loss factor. In this paper, we present our algorithm for optimizing the number and sequential positions of bunches for generation of narrow band high power THz radiation.

  10. Dielectric tube waveguides with absorptive cladding for broadband, low-dispersion and low loss THz guiding

    PubMed Central

    Bao, Hualong; Nielsen, Kristian; Bang, Ole; Jepsen, Peter Uhd

    2015-01-01

    Research on terahertz waveguides is experiencing a tremendous growth due to their importance for compact and robust THz systems. However, designing compact, broadband, mechanically stable and environmentally shielded THz waveguides is still a challenge due to high losses of both metals and dielectrics in this frequency range. Here we report on a novel twist on the classical tube waveguide where we deliberately introduce a thick and highly lossy cladding layer. By this we attenuate the field in the cladding and thus prevent interference with the core field. This mechanism breaks the well-known ARROW guiding mechanism, and as a result, extremely broad bandwidth and low dispersion can be achieved with a very simple design. Since the main part of the field propagates inside the air-core, the propagation loss is still kept at a very low level. Simulations, analytical modelling and experiments verify our findings. The proposed THz waveguide is robust, insensitive to external perturbation and easy to handle, and thus the design represents a significant advance of the field of THz dielectric waveguides suitable for the 0.3–1 THz band which in the future will be important for ultrafast wireless communication systems. PMID:25557284

  11. Sub-THz radiation from dielectric capillaries with reflectors

    NASA Astrophysics Data System (ADS)

    Lekomtsev, K.; Aryshev, A.; Tishchenko, A. A.; Shevelev, M.; Ponomarenko, A. A.; Karataev, P.; Terunuma, N.; Urakawa, J.

    2017-07-01

    In this report we present experimental investigations of the THz radiation generated from a corrugated and a non-corrugated capillary with reflectors, using a femtosecond electron beam of LUCX accelerator at KEK, Japan. We discuss measurements of the radiation angular distributions and their comparison with Particle In Cell simulations, and also investigate an off-central propagation of the beam in the capillaries based on experimental measurements and simulations.

  12. Tunable THz radiation source from dielectric loaded waveguide excited by nonrelativistic electron bunch trains

    NASA Astrophysics Data System (ADS)

    Li, Weiwei; He, Zhigang; Lu, Yalin; Huang, Ruixuan; Liu, Weihao; Jia, Qika; Wang, Lin

    2016-10-01

    We propose a novel scheme to generate a tunable narrow-band THz radiation. In this scheme, a train of laser pulses with THz repetition rate is used to drive a photocathode direct current (DC) gun, leading to the emission of a train of electron bunches. The electron bunch train is subsequently accelerated by the gun field and applied to selectively excite one of the modes in the dielectric loaded waveguide (DLW) structure, which is located downstream the DC gun. Thanks to the tunability of the repetition rate of laser pulses and the gun voltage, a tunable narrow-band THz radiation source can be obtained. This proposed source has the advantages of compactness, robustness and relatively high power.

  13. THz polarization radiation from electrons passing corrugated dielectric tube under non-central propagation

    NASA Astrophysics Data System (ADS)

    Ponomarenko, A. A.; Tishchenko, A. A.; Strikhanov, M. N.

    2017-07-01

    In this work we construct the theory of THz polarization radiation from electrons passing corrugated dielectric tube under non-central propagation. Fully analytical description of spectral and angular properties of radiation is obtained. In calculations we used the method of polarization currents combined with theory of perturbations assuming small distances from the central axis of the tube. Smith-Purcell and Cherenkov mechanisms of radiation are considered and analysed numerically.

  14. Giant THz surface plasmon polariton induced by high-index dielectric metasurface.

    PubMed

    Lin, Shuai; Bhattarai, Khagendra; Zhou, Jiangfeng; Talbayev, Diyar

    2017-08-29

    We use computational approaches to explore the role of a high-refractive-index dielectric TiO2 grating with deep subwavelength thickness on InSb as a tunable coupler for THz surface plasmons. We find a series of resonances as the grating couples a normally-incident THz wave to standing surface plasmon waves on both thin and thick InSb layers. In a marked contrast with previously-explored metallic gratings, we observe the emergence of a much stronger additional resonance. The mechanism of this giant plasmonic resonance is well interpreted by the dispersion of surface plasmon excited in the air\\TiO2\\InSb trilayer system. We demonstrate that both the frequency and the intensity of the giant resonance can be tuned by varying dielectric grating parameters, providing more flexible tunability than metallic gratings. The phase and amplitude of the normally-incident THz wave are spatially modulated by the dielectric grating to optimize the surface plasmon excitation. The giant surface plasmon resonance gives rise to strong enhancement of the electric field above the grating structure, which can be useful in sensing and spectroscopy applications.

  15. Beam dynamics in THz dielectric-loaded waveguides for the AXSIS project

    NASA Astrophysics Data System (ADS)

    Vinatier, T.; Assmann, R. W.; Dorda, U.; Lemery, F.; Marchetti, B.

    2017-07-01

    In this paper, we investigate with ASTRA simulations the beam dynamics in dielectric-loaded waveguides driven by THz pulses, used as linac structure for the AXSIS project. We show that the bunch properties at the linac exit are very sensitive to the phase velocity of the THz pulse and are limited by the strong phase slippage of the bunch respective to it. We also show that the bunch properties are optimized when low frequencies (< 300 GHz) are used inside the linac, and that the longitudinal focal point can be put several tens of cm away from the linac exit thanks to ballistic bunching. However, a strong asymmetry in the bunch transverse sizes remains for which a solution is still to be found. Work supported by the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement n. 609920.

  16. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

    NASA Astrophysics Data System (ADS)

    Antipov, S.; Baryshev, S. V.; Kostin, R.; Baturin, S.; Qiu, J.; Jing, C.; Swinson, C.; Fedurin, M.; Wang, D.

    2016-10-01

    We have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

  17. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

    DOE PAGES

    Antipov, S.; Baryshev, S. V.; Kostin, R.; ...

    2016-10-03

    Here, we have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measuredmore » with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.« less

  18. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

    SciTech Connect

    Antipov, S.; Baryshev, S. V.; Kostin, R.; Baturin, S.; Qiu, J.; Jing, C.; Swinson, C.; Fedurin, M.; Wang, D.

    2016-10-03

    Here, we have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

  19. Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

    SciTech Connect

    Antipov, S.; Baryshev, S. V.; Kostin, R.; Baturin, S.; Qiu, J.; Jing, C.; Swinson, C.; Fedurin, M.; Wang, D.

    2016-10-03

    Here, we have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

  20. Dielectric response of pure and doped-GaSe crystals studied by an indigenously developed broadband THz-TDS system

    NASA Astrophysics Data System (ADS)

    Das, Amit C.; Bhattacharya, S.; Mandal, K. C.; Mondal, S.; Jewariya, M.; Ozaki, T.; Bhaktha, S. N. B.; Datta, P. K.

    2016-04-01

    Publisher's Note: This paper, originally published on 12 July 2016, was replaced with a corrected/revised version on 26 July 2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. We have developed a terahertz time domain spectroscopy system (THz TDS). For THz generation, optical rectification process and for detection, electro-optic sampling processes are used. Identical < 110 > cut ZnTe crystals are used for both generation and detection of THz radiation.This spectroscopy system can be used for the noninvasive and contactless electrical and optical characterizations of various samples. In this work spectroscopic measurements of pure, Chromium and Indium doped GaSe crystals within 0.4 THz to 3 THz range are taken by the developed set-up to study the dielectric response of the samples.

  1. Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method.

    PubMed

    Dupuis, Alexandre; Allard, Jean-François; Morris, Denis; Stoeffler, Karen; Dubois, Charles; Skorobogatiy, Maksim

    2009-05-11

    We report several strategies for the fabrication of porous subwavelength fibers using low density Polyethylene plastic for low-loss terahertz light transmission applications. We also characterize transmission losses of the fabricated fibers in terahertz using a novel non-destructive directional coupler method. Within this method a second fiber is translated along the length of the test fiber to probe the power attenuation of a guided mode. The method is especially suitable for measuring transmission losses through short fiber segments, a situation in which standard cutback method is especially difficult to perform. We demonstrate experimentally that introduction of porosity into a subwavelength rod fiber, further reduces its transmission loss by as much as a factor of 10. The lowest fiber loss measured in this work is 0.01 cm(-1) and it is exhibited by the 40% porous subwavelength fiber of diameter 380 microm. For comparison, the loss of a rod-in-the-air subwavelength fiber of a similar diameter was measured to be approximately 0.1 cm(-1), while the bulk loss of a PE plastic used in the fabrication of such fibers is >or= 1 cm(-1). Finally, we present theoretical studies of the optical properties of individual subwavelength fibers and a directional coupler. From these studies we conclude that coupler setup studied in this paper also acts as a low pass filter with a cutoff frequency around 0.3 THz. Considering that the spectrum of a terahertz source used in this work falls off rapidly below 0.25 THz, the reported loss measurements are, thus, the bolometer averages over the approximately 0.25 THz-0.3 THz region.

  2. Cu-Induced Dielectric Breakdown of Porous Low-Dielectric-Constant Film

    NASA Astrophysics Data System (ADS)

    Cheng, Yi-Lung; Lee, Chih-Yen; Huang, Yao-Liang; Sun, Chung-Ren; Lee, Wen-Hsi; Chen, Giin-Shan; Fang, Jau-Shiung; Phan, Bach Thang

    2017-02-01

    Dielectric breakdown induced by Cu ion migration in porous low-k dielectric films has been investigated in alternating-polarity bias conditions using a metal-insulator-metal capacitor with Cu top metal electrode. The experimental results indicated that Cu ions migrated into the dielectric film under stress with positive polarity, leading to weaker dielectric strength and shorter time to failure (TTF). In the alternating-polarity test, the measured TTFs increased with decreasing stressing frequency, implying backward migration of Cu ions during reverse-bias stress. Additionally, compared with a direct-current stress condition, the measured TTFs were higher as the frequency was decreased to 10-2 Hz. The electric-field acceleration factor for porous low-k dielectric film breakdown in the alternating-polarity test was also found to increase. This Cu backward migration effect is effective when the stressing time under negative polarity is longer than 0.1 s.

  3. Cu-Induced Dielectric Breakdown of Porous Low-Dielectric-Constant Film

    NASA Astrophysics Data System (ADS)

    Cheng, Yi-Lung; Lee, Chih-Yen; Huang, Yao-Liang; Sun, Chung-Ren; Lee, Wen-Hsi; Chen, Giin-Shan; Fang, Jau-Shiung; Phan, Bach Thang

    2017-06-01

    Dielectric breakdown induced by Cu ion migration in porous low- k dielectric films has been investigated in alternating-polarity bias conditions using a metal-insulator-metal capacitor with Cu top metal electrode. The experimental results indicated that Cu ions migrated into the dielectric film under stress with positive polarity, leading to weaker dielectric strength and shorter time to failure (TTF). In the alternating-polarity test, the measured TTFs increased with decreasing stressing frequency, implying backward migration of Cu ions during reverse-bias stress. Additionally, compared with a direct-current stress condition, the measured TTFs were higher as the frequency was decreased to 10-2 Hz. The electric-field acceleration factor for porous low- k dielectric film breakdown in the alternating-polarity test was also found to increase. This Cu backward migration effect is effective when the stressing time under negative polarity is longer than 0.1 s.

  4. Wakefields in THz cylindrical dielectric lined waveguides driven by femtosecond electron bunches

    NASA Astrophysics Data System (ADS)

    Nie, Yuancun

    2015-01-01

    This paper reports the wakefield effects driven by a high-intensity relativistic electron bunch in a dielectric lined waveguide (DLW). A state-of-the-art electron bunch is employed to serve as the drive bunch, which has an rms length of 10 μm, i.e. 33 fs, and a charge of 200 pC. Such bunch parameters are comparable to those of DESY's FLASH and SLAC's LCLS and FACET facilities. It is demonstrated that coherent Cherenkov radiation (CCR) at the fundamental mode with frequency above 1 THz and accelerating gradient as high as 2 GV/m can be obtained in a single layer cylindrical diamond-DLW structure, as long as the geometrical parameters of the DLW are properly selected to match the drive bunch. Wakefield-induced energy modulations on the drive bunch itself are studied as well, which can be used to reduce its energy spread or to produce microbunches with much shorter length from it. The simulated results agree well with the theoretical predictions. Such wakefields can be used to accelerate or modulate electron bunches with ultra-high gradients, and produce high power THz radiations directly. These properties have potential applications in the fields of compact colliders and advanced radiation sources.

  5. Porous low dielectric constant materials for microelectronics.

    PubMed

    Baklanov, Mikhail R; Maex, Karen

    2006-01-15

    Materials with a low dielectric constant are required as interlayer dielectrics for the on-chip interconnection of ultra-large-scale integration devices to provide high speed, low dynamic power dissipation and low cross-talk noise. The selection of chemical compounds with low polarizability and the introduction of porosity result in a reduced dielectric constant. Integration of such materials into microelectronic circuits, however, poses a number of challenges, as the materials must meet strict requirements in terms of properties and reliability. These issues are the subject of the present paper.

  6. Hybrid semiconductor-dielectric metamaterial modulation for switchable bi-directional THz absorbers

    NASA Astrophysics Data System (ADS)

    Le, Ly Nguyen; Thang, Nguyen Manh; Thuy, Le Minh; Tung, Nguyen Thanh

    2017-01-01

    There is an increasing interest for electromagnetic metamaterials that show mutable absorption properties with real-time and dynamic control. In this paper, we investigate a modulation of bi-directional metamaterial absorbers that is thermally switchable at terahertz frequencies. The metamaterial absorber is composed of symmetric hybrid semiconductor-dielectric cut-wire-pair structures, whose electromagnetic responses can be actively manipulated by utilizing an external heat source. As increasing the temperature of metamaterials from 300 to 350 K, we demonstrate that the magnetic resonance can be systematically blue-shifted and overlapped with the electric resonance, which is unaffectedly settled at about 0.8 THz. This superposition provides an effective mechanism to control the absorption intensity from 43% to nearly 95%. Finite integration simulation technique, standard retrieval method, and equivalent circuit model are employed to elaborate our idea.

  7. Stimulated light emission in a dielectrically disordered composite porous matrix

    NASA Astrophysics Data System (ADS)

    Gross, E.; Künzner, N.; Diener, J.; Fujii, Minoru; Timoshenko, V. Yu.; Kovalev, D.

    2005-06-01

    We report on a medium exhibiting extremely efficient light scattering properties: a liquid network formed in a porous matrix. Liquid fragments confined in the solid matrix result in a random fluctuation of the dielectric function and act as scattering objects for photons. The optical scattering efficiency is defined by the filling factor of the liquid in the pores and its dielectric constant. The spectral dependence of the scattering length of photons indicates that the phenomenon is governed by a Mie-type scattering mechanism. The degree of the dielectric disorder of the medium, i.e. the level of opacity is tunable by the ambient vapor pressure of the dielectric substance. In the strongest scattering regime the scattering length of photons is found to be in the micrometer range. By incorporation of dye molecules in the voids of the porous layer a system exhibiting optical gain is realized. In the multiple scattering regime the optical path of diffusively propagating photons is enhanced and light amplification through stimulated emission occurs: a strong intensity enhancement of the dye emission accompanied by significant spectral narrowing is observed above the excitation threshold for a layer being in the opalescence state.

  8. Heat Induced Damage Detection by Terahertz (THz) Radiation

    NASA Astrophysics Data System (ADS)

    Rahani, Ehsan Kabiri; Kundu, Tribikram; Wu, Ziran; Xin, Hao

    2011-06-01

    Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic waves. Capability of THz electromagnetic waves in detecting heat induced damage in porous materials is investigated in this paper. Porous pumice stone blocks are subjected to long time heat exposures to produce heat induced damage in the block. The dielectric properties extracted from THz TDS (Time Domain Spectroscopy) measurements are compared for different levels of heat exposure. Experimental results show noticeable and consistent change in dielectric properties with increasing levels of heat exposure, well before its melting point.

  9. A computational component analysis of dielectric relaxation and THz spectra of water/AOT reverse micelles with different water loading

    NASA Astrophysics Data System (ADS)

    Schmollngruber, Michael; Braun, Daniel; Steinhauser, Othmar

    2016-12-01

    In this computational study, we present molecular dynamics simulations of water/aerosol-OT/isooctane reverse micelles with different water loading. We compare these systems in terms of a detailed analysis of dielectric relaxation spectra and water librations in the THz region. The spectra are decomposed into contributions by molecular species and contributions from individual water solvation shells. Additionally, micellar tumbling motion is shown to have a profound influence on the observed dielectric relaxation spectra, if relaxation by internal reorganization and micellar tumbling occurs within similar time scales. A formalism to directly quantify the effect of micellar tumbling motion on a recorded dielectric spectrum is developed. Since micellar rotational diffusion obeys the laws of hydrodynamics, this method is applicable in an experimental context as well, only knowing the viscosity of the outside medium and the average volume of the reverse micelle.

  10. Dielectric breakdown in nano-porous thin films

    NASA Astrophysics Data System (ADS)

    Borja, Juan Pablo

    Unknown to most computer users and mobile device enthusiasts, we have finally entered into a critical age of chip manufacturing. January of 2014 marks the official start of the quest by the semiconductor industry to successfully integrate sub 14nm process technology nodes in accordance to the International Technology Roadmap for Semiconductors (ITRS). The manufacturing of nano-scale features represents a major bottleneck of its own. However, a bigger challenge lies in reliably isolating the massive chip interconnect network. The present work is aimed at generating a theoretical and experimental framework to predict dielectric breakdown for thin films used in computer chip components. Here, a set of experimental techniques are presented to assess and study dielectric failure in novel thin films. A theory of dielectric breakdown in thin nano-porous films is proposed to describe combined intrinsic and metal ion catalyzed failure. This theory draws on experimental evidence as well as fundamental concepts from mass and electronic charge transport. The drift of metal species was found to accelerate intrinsic dielectric failure. The solubility of metals species such as Cu was found to range from 7.0x1025 ions/m3 to 1.86x1026 ions/m3 in 7% porous SiCOH films. The diffusion coefficient for Cu species was found to span from 4.2x10-19 m2/s to 1.86x10-21 m2/s. Ramped voltage stress experiments were used to identify intrinsic failure from metal catalyzed failure. Intrinsic breakdown is defined when time to failure against applied field ramp rate results in ∂(ln(TTF))/∂(ln(R)) ≈ -1. Intrinsic failure was studied using Au. Here, ∂(ln(TTF))/∂(ln(R)) ≈ -0.95, which is an experimental best case scenario for intrinsic failure. Au is commonly reluctant to ionize which means that failure occurs in the absence of ionic species. Metal catalyzed failure was investigated using reactive electrodes such as Cu, and Ag. Here, trends for ∂(ln(TTF))/∂(ln(R)) significantly

  11. Simultaneously coherent excitation of multi-modes THz radiation from dielectric loaded waveguide by pre-bunched electron beam

    NASA Astrophysics Data System (ADS)

    Li, Biaobin; Lu, Yalin; He, Zhigang; Li, Weiwei; Jia, Qika; Wang, Lin

    2017-02-01

    The cylindrical dielectric loaded waveguide (DLW) supports a discrete set of modes, which can be excited by electron beam passing through the structure, and the high-order modes can be the harmonics of the fundamental one by properly choosing the parameters of the DLW. By using a train of electron bunches, repeated at the fundamental frequency of the DLW, as the driving source, coherent and simultaneous excitation of multi-modes can be expected. With this proposed scheme, multi-color narrow-band THz radiation with high pulse power and high frequency can be obtained simultaneously.

  12. Functionalization and characterization of porous low-kappa dielectrics

    NASA Astrophysics Data System (ADS)

    Orozco-Teran, Rosa Amelia

    2005-12-01

    The incorporation of fluorine into SiO2 has been shown to reduce the dielectric constant of the existing materials by reducing the electrical polarizability. However, the incorporation of fluorine has also been shown to decrease film stability. Therefore, new efforts have been made to find different ways to further decrease the relative dielectric constant value of the existing low-k materials. One way to reduce the dielectric constant is by decreasing its density. This reduces the amount of polarizable materials. A good approach is increasing porosity of the film. Recently, fluorinated silica xerogel films have been identified as potential candidates for applications such as interlayer dielectric materials in CMOS technology. In addition to their low dielectric constants, these films present properties such as low refractive indices, low thermal conductivities, and high surface areas. Another approach to lower kappa is incorporating lighter atoms such as hydrogen or carbon. Silsesquioxane based materials are among them. However, additional integration issues such as damage to these materials caused by plasma etch, plasma ash, and wet etch processes are yet to be overcome. This dissertation reports the effects of triethoxyfluorosilane-based (TEFS) xerogel films when reacted with silylation agents. TEFS films were employed because they form robust silica networks and exhibit low dielectric constants. However, these films readily absorb moisture. Employing silylation reactions enhances film hydrophobicity and permits possible introduction of this film as an interlayer dielectric material. Also, this work describes the effects of SC-CO2 in combination with silylating agents used to functionalize the damaged surface of the ash-damaged MSQ films. Ashed MSQ films exhibit increased water adsorption and dielectric constants due to the carbon depletion and modification of the properties of the low-kappa material caused by interaction with plasma species. CO2 is widely used

  13. Dielectric Properties of Porous Si3N4-SiO2-BN Composites

    NASA Astrophysics Data System (ADS)

    Sun, Yinbao; Zhang, Yumin; Li, Dihong; Han, Jiecai

    Porous Si3N4-SiO2-BN composites were prepared by adding starch as both pore former and consolidator. Bruggeman effective-medium model, Maxwell-Garnett model and logarithmic model were used to describe and predict the dielectric constant of porous Si3N4-SiO2-BN ceramics. Relative dielectric constant of porous Si3N4-SiO2-BN composites decreases with the increase of apparent porosity within limits, and these models can forecast the change of the dielectric constant of the porous ceramics quite well. The minimum relative dielectric constant is 2.5 at the apparent porosity of 0.555 at room-temperature. The relationship between dielectric constant and temperature were investigated. It was found dielectric constant varied a lot with the increase of temperature, and Debye relaxation theory was employed to explain the variation of the dielectric constant with temperature increment. But the Debye relaxation theory can not explain the reason of variation of dielectric constant at the temperature range from 300°C to 900°C. To ascertain the cause of changes of dielectric constant at this temperature region, differential scanning calorimentry (DSC) measurement was performed. In this temperature region, phase transition behavior occurs at nearly 300°C in the porous composites. The new phase probably has a tidy large dielectric constant, and the dielectric constant increases sharply.

  14. A novel porous silicon-based multilayer dielectric-grating structures for diffraction-based sensing

    NASA Astrophysics Data System (ADS)

    Mo, Jiaqing; Liu, Yajun; Lv, Changwu; Lv, Xiaoyi; Jia, Zhenhong

    2014-11-01

    Porous silicon material and device has attracted more attention for use as biochemical optical sensors. In this paper, A novel porous silicon-based multilayer dielectric-grating structures by adding high-reflectivity porous silicon stacks between the substrate and grating was fabricated, and the porous silicon grating height was set to be about 200 nm, the grating period was 4 μm, the air filling factor was 50%. A new better method of preparing this porous silicon-based multilayer dielectric-grating structures have also been employed.

  15. Thermal stability of low dielectric constant porous silica films

    NASA Astrophysics Data System (ADS)

    Esposito, L.; Ottaviani, G.; Carollo, E.; Bacchetta, M.

    2005-12-01

    Thermal stability of porous-silica-based low dielectric constant, k, material deposited by chemical vapor deposition has been investigated in a wide temperature range. The films as-deposited and after heat treatments up to 600°C have Si1O1.6C1.4H2.3 composition, permittivity k ≈2.8, and porosity h ≈0.25. A skeleton of silicon dioxide and empty pores justifies the permittivity and porosity values. Permeation experiments with deuterated water vapor indicate that pores are interconnected. At 700°C, the film has Si1O1.6C1.4H1.4 composition, k ≈2.4, and h ≈0.21. Bonds with lower polarizability could be responsible for the decrease of k. Above 800°C, carbon segregation and nanoclusters formation occur.

  16. Spectral and spatial nondestructive examination of dielectric materials with THz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Beckmann, J.; von Chrzanowski, L. S.; Fratzscher, D.; Ewert, U.

    2012-05-01

    A time domain spectrometer T-ray 2000® operating in the range of 0.2-2 THz was used for Time of Flight measurements. A series of ethanol water mixtures from 10% to 90% were produced subsequently filled in polystyrene cells and analyzed in the T-ray 2000 TDS system in the reflection mode. The reflectivity of the material liquid interface is strongly influenced by the ethanol concentration in water. The reciprocal reflection coefficient of the material liquid interface was found to be a useful discriminating feature for further Probably of Detection calculations which can be used for the performance evaluation of potential THz bottle scanners. THz pulse echo (PE) measurements were performed in comparison to the established ultra sound PE technique for flaw detection of plastics. Synthetic aperture reconstructions were applied for simulated data to reconstruct the flaw shape. The results were compared with B-scan images of a high density polyethylene (HDPE) test cylinder. Existing restrictions on the quality of the back projected images and limits of the existing model are discussed in detail.

  17. Experimental Plans to Explore Dielectric Wakefield Acceleration in the THZ Regime

    SciTech Connect

    Lemery, F.; Mihalcea, D.; Piot, P.; Behrens, C.; Elsen, E.; Flottmann, K.; Gerth, C.; Kube, G.; Schmidt, B.; Osterhoff, J.; Stoltz, P.

    2011-09-07

    Dielectric wakefield accelerators have shown great promise toward high-gradient acceleration. We investigate the performances of a possible experiment under consideration at the FLASH facility in DESY to explore wakefield acceleration with an enhanced transformer ratio. The experiment capitalizes on a unique pulse shaping capability recently demonstrated at this facility. In addition, the facility incorporates a superconducting linear accelerator that could generate bunch trains with closely spaced bunches thereby opening the exploration of potential dynamical effects in dielectric wakefield accelerators.

  18. Time-dependent dielectric breakdown measurements of porous organosilicate glass using mercury and solid metal probes

    SciTech Connect

    Pei, Dongfei; Nichols, Michael T.; Shohet, J. Leon; King, Sean W.; Clarke, James S.; Nishi, Yoshio

    2014-09-01

    Time-dependent dielectric breakdown (TDDB) is one of the major concerns for low-k dielectric materials. During plasma processing, low-k dielectrics are subjected to vacuum ultraviolet photon radiation and charged-particle bombardment. To examine the change of TDDB properties, time-to-breakdown measurements are made to porous SiCOH before and after plasma exposure. Significant discrepancies between mercury and solid-metal probes are observed and have been shown to be attributed to mercury diffusion into the dielectric porosities.

  19. Simulation analysis of rectangular dielectric-loaded traveling wave amplifiers for THz sources

    NASA Astrophysics Data System (ADS)

    Wang, Changbiao

    2007-12-01

    Nonlinear simulation results for a 220-GHz rectangular dielectric-loaded traveling-wave amplifier are presented. Simulations are used to check a linear theory that is developed by phenomenological introduction of an effective dielectric parameter for electron beam channel, and it is found that the rf power gains from Pierce three-wave theory and particle simulations are in reasonable agreement. It is shown that the rf power gain during initial beam-wave interaction is positive; the falling on the initial rf power profile, which has been thought to be the rf power transferred to the beam for bunching buildup (negative gain effect), is probably resulting from numerical errors. Beam-wave interaction mechanism is analyzed by examining the evolution of beam bunching centers. Influences of various parameters on amplifier performance are examined, and transverse space-charge effect is analyzed. A symmetric excitation scheme for rf couplers is proposed, and rf field jumps on the common intersection line of vacuum, dielectric, and metal wall, which were found in rf simulations, are explained theoretically.

  20. Mechanical property changes in porous low-k dielectric thin films during processing

    SciTech Connect

    Stan, G. Gates, R. S.; Kavuri, P.; Torres, J.; Michalak, D.; Ege, C.; Bielefeld, J.; King, S. W.

    2014-10-13

    The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

  1. Mechanical property changes in porous low-k dielectric thin films during processing

    NASA Astrophysics Data System (ADS)

    Stan, G.; Gates, R. S.; Kavuri, P.; Torres, J.; Michalak, D.; Ege, C.; Bielefeld, J.; King, S. W.

    2014-10-01

    The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

  2. Study of counting characteristics of porous dielectric detectors of radiations

    NASA Astrophysics Data System (ADS)

    Lorikyan, M. P.

    2003-12-01

    Multiwire and microstrip porous detectors have been developed and investigated for DC operation. The multiwire porous detector consists of anode wires, an Al cathode and a gap between them filled with porous CsI. The microstrip porous detector consists of an insulating plate covered with metallic strips, micromesh cathode and a gap between them filled with porous CsI. For some time after being manufactured, these detectors' performances are non-stable and they have poor spatial resolution. However, after being kept in vacuum for a certain time, they spontaneously acquire stability and spatial resolution better than 100 μm and have detection efficiencies of 100% and 70% for heavily ionizing α-particles and 5.9 keV X-rays, respectively. The MWPDD performs stably at an intensity of heavily ionizing α-particles of 711 cts/(cm 2 s).

  3. Surface-Localized Sealing of Porous Ultralow-k Dielectric Films with Ultrathin (<2 nm) Polymer Coating.

    PubMed

    Yoon, Seong Jun; Pak, Kwanyong; Nam, Taewook; Yoon, Alexander; Kim, Hyungjun; Im, Sung Gap; Cho, Byung Jin

    2017-08-22

    Semiconductor integrated circuit chip industries have been striving to introduce porous ultralow-k (ULK) dielectrics into the multilevel interconnection process in order to improve their chip operation speed by reducing capacitance along the signal path. To date, however, highly porous ULK dielectrics (porosity >40%, dielectric constant (k) <2.4) have not been successfully adopted in real devices because the porous nature causes many serious problems, including noncontinuous barrier deposition, penetration of the barrier metal, and reliability issues. Here, a method that allows porous ULK dielectrics to be successfully used with a multilevel interconnection scheme is presented. The surface of the porous ULK dielectric film (k = 2.0, porosity ∼47%) could be completely sealed by a thin (<2 nm) polymer deposited by a multistep initiated chemical vapor deposition (iCVD) process. Using the iCVD process, a thin pore-sealing layer was localized only to the surface of the porous ULK dielectric film, which could minimize the increase of k; the final effective k was less than 2.2, and the penetration of metal barrier precursors into the dielectric film was completely blocked. The pore-sealed ULK dielectric film also exhibited excellent long-term reliability comparable to a dense low-k dielectric film.

  4. Optical properties of multilayered Period-Doubling and Rudin-Shapiro porous silicon dielectric heterostructures

    NASA Astrophysics Data System (ADS)

    Agarwal, V.; Mora-Ramos, Miguel E.; Alvarado-Tenorio, B.

    2009-05-01

    To investigate the optical properties in quasi-regular porous-silicon-based dielectric Period-Doubling and Rudin-Shapiro multilayer systems, we study here the reflection of light from these structures. The Period-Doubling and Rudin-Shapiro structures are fabricated in such a way that the optical thickness of each layer is one quarter of 600 and 640 nm respectively. We find that porous silicon Period-Doubling dielectric multilayers could demonstrate the optical properties similar to the classical periodic Febry-Perot interference filters with one or multiple resonant peaks, but with an advantage of having total optical thickness much lesser than the periodic structures. Additionally, light propagation in porous silicon Rudin-Shapiro structures is investigated for the first time, both theoretically and experimentally. The reflectance spectra of the structures exhibit photonic band gaps centered at predetermined wavelengths. In both cases, numerical simulation of light transmission is performed using transfer matrix method.

  5. Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

    SciTech Connect

    Im, Ji Sun; Bae, Tae-Sung; Lee, Sung Kyu; Lee, Sei-Hyun; Jeong, Euigyung; Kang, Phil Hyun; Lee, Young-Seak

    2010-11-15

    We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.

  6. Porous pSiCOH Ultralow-k Dielectrics for Chip Interconnects Prepared by PECVD

    NASA Astrophysics Data System (ADS)

    Grill, Alfred

    2009-08-01

    Porous pSiCOH materials with ultralow dielectric constants (ulk) have been developed with dielectric constants reaching values below 2.0. The pSiCOH films, composed of Si, C, O, and H atoms, are prepared by plasma-assisted chemical vapor deposition (PECVD), showing that PECVD can be used to prepare porous materials. The pSiCOH films are deposited as dual-phase materials, and the porosity is formed in them by curing the as-deposited films by thermal anneals, electron beams, or UV irradiation. The porous pSiCOH dielectrics are suitable for integration in the interconnects of VLSI chips of the 45-nm-and-beyond technology nodes, and films with dielectric constants of 2.4 have already been implemented in upcoming 45-nm products. This review discusses the fabrication of pSiCOH films and the characterization of their structure, porosity, and electrical and mechanical properties. The limitations of some of the characterization techniques of these amorphous thin films are also addressed.

  7. Image x-ray emission converters and microstrip porous dielectric x-ray detector

    SciTech Connect

    Lorikyan, M. P.

    2008-11-01

    The effective, fast, and accurate registration of x ray depends on the quality conversion of the X-quanta to photoelectrons. In this respect, of high interest are porous x-ray emission converters (PXECs). They are analogs of porous secondary electron emitters (PSEEs); the only difference is that active porous material should have high absorption properties for the X-quanta energies to be detected. Microstrip porous dielectric detector (MSPDD) is highly effective for x-ray registration without preliminary conversion of the X-quanta. Earlier it was shown that PSEE similar to PXEC has a high emission factor for 1-2 MeV {beta}-particles and 5 MeV {alpha}-particles. It was shown that MSPDDs and PSEEs are very stable.

  8. Mechanistic study of plasma damage to porous low-k: Process development and dielectric recovery

    NASA Astrophysics Data System (ADS)

    Shi, Hualiang

    Low-k dielectrics with porosity are being introduced to reduce the RC delay of Cu/low-k interconnect. However, during the O2 plasma ashing process, the porous low-k dielectrics tend to degrade due to methyl depletion, moisture uptake, and densification, increasing the dielectric constant and leakage current. This dissertation presents a study of the mechanisms of plasma damage and dielectric recovery. The kinetics of plasma interaction with low-k dielectrics was investigated both experimentally and theoretically. By using a gap structure, the roles of ion, photon, and radical in producing damage on low-k dielectrics were differentiated. Oxidative plasma induced damage was proportional to the oxygen radical density, enhanced by VUV photon, and increased with substrate temperature. Ion bombardment induced surface densification, blocking radical diffusion. Two analytical models were derived to quantify the plasma damage. Based on the radical diffusion, reaction, and recombination inside porous low-k dielectrics, a plasma altered layer model was derived to interpret the chemical effect in the low ion energy region. It predicted that oxidative plasma induced damage can be reduced by decreasing pore radius, substrate temperature, and oxygen radical density and increasing carbon concentration and surface recombination rate inside low-k dielectrics. The model validity was verified by experiments and Monte-Carlo simulations. This model was also extended to the patterned low-k structure. Based on the ion collision cascade process, a sputtering yield model was introduced to interpret the physical effect in the high ion energy region. The model validity was verified by checking the ion angular and energy dependences of sputtering yield using O2/He/Ar plasma, low-k dielectrics with different k values, and a Faraday cage. Low-k dielectrics and plasma process were optimized to reduce plasma damage, including increasing carbon concentration in low-k dielectrics, switching plasma

  9. Dielectric Anisotropy of Human Bone and CERABONE® in the Terahertz Spectral Range 0.2 to 2.5 THz

    NASA Astrophysics Data System (ADS)

    Nikoghosyan, A. S.; Ting, H.; Shen, J.; Martirosyan, R. M.; Kazaryan, M. A.; Tunyan, M. Yu.; Papikyan, A. V.; Papikyan, A. A.

    2017-04-01

    Terahertz time-domain spectroscopy (THz-TDS) was applied to study properties of a human jawbone in transmission geometry. The fiber femtosecond laser (Fx-100, IMRA) with a pulse width of 113 fs, a central wavelength of 800 nm and an average power of 120 mW was used as a laser source for pumping and detecting terahertz pulses. The refractive indices n(ω) and absorption coefficients α(ω) of the human jawbone and bone substitute Cerabone® were determined in vitro by the THz-TDS in a wide frequency range from 0.2 to 2.5 THz. It is shown that the refractive index of the human jawbone changes between the values of 2.24 and 2.36, and Cerabone® between 2.4 and 2.65. The absorption coefficient of the human jawbone depending on frequency increases from 1.7 cm-1 to 178.5 cm -1, showing several resonance absorption lines after 1.6 THz. The absorption coefficient of Cerabone® increases from zero to 80 cm-1, and the resonance absorption occurs at 1.7 THz. The experimental results indicate that n(f) and α(f) of a human jawbone change with the alteration of the direction of the linear polarization vector of the electric field of THz pulse relative to the axis of the plate of the human jawbone. The obtained results allowed us to determine the proximity of the physical properties of the Cerabone® with the natural bone matrix.

  10. Role of copper in time dependent dielectric breakdown of porous organo-silicate glass low-k materials

    NASA Astrophysics Data System (ADS)

    Zhao, Larry; Pantouvaki, Marianna; Croes, Kristof; Tőkei, Zsolt; Barbarin, Yohan; Wilson, Christopher J.; Baklanov, Mikhail R.; Beyer, Gerald P.; Claeys, Cor

    2011-11-01

    The role of copper in time dependent dielectric breakdown (TDDB) of a porous low-k dielectric with TaN/Ta barrier was investigated on a metal-insulator-metal capacitor configuration where Cu ions can drift into the low-k film by applying a positive potential on the top while they are not permitted to enter the low-k dielectric if a negative potential is applied on the top. No difference in TDDB performance was observed between the positive and negative bias conditions, suggesting that Cu cannot penetrate TaN/Ta barrier to play a critical role in the TDDB of porous low-k material.

  11. Estimating the extent of surface oxidation by measuring the porosity dependent dielectrics of oxygenated porous silicon [rapid communication

    NASA Astrophysics Data System (ADS)

    Pan, L. K.; Sun, Chang Q.; Li, C. M.

    2005-02-01

    Surface oxidation and porosity variation play significant roles in the dielectric performance of porous silicon (PS) yet discriminating the contribution of these events is a challenge. Here we present an analytical solution that covers contributions from the components of silicon oxide surface, silicon backbone and voids using a serial-parallel capacitance structure. Agreement between modeling predictions and measurement has been realized, which turns out an effective method that enables us to estimate the extent of surface oxidation of a specimen by measuring the porosity dependent dielectric response of the chemically passivated PS, and provides guidelines that could be useful for designing dielectric porous structures with surface oxidation.

  12. THz Cherenkov radiation of Josephson vortex

    NASA Astrophysics Data System (ADS)

    Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.

    2008-01-01

    It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.

  13. Enhanced integrability of porous low-permittivity dielectrics for improved reliability in copper-based interconnects

    NASA Astrophysics Data System (ADS)

    Luo, Fu

    Achieving the aggressive device performance metrics demanded by the microelectronics industry dictates the use of low dielectric constant ('low-k') insulating materials to reduce the capacitive component of the interconnect-related RC signal propagation delay. In particular, to meet interconnect performance requirements for the 65 nm node and beyond, one approach is to introduce significant levels of porosity into the interlayer dielectric (ILD) films. However, the incorporation of porosity leads to a number of integration challenges, including increased reliability issues due to the open pores distributed on the sidewalls of vias/trenches. The research discussed in this paper demonstrates that it is possible to 'seal' the sidewalls of patterned porous dielectric layers using a specially designed deposition-etch passivation process. The concept of the process is to employ selected organosilcon precursors to deposit fully dense carbon-doped oxide (CDO) type films using plasma enhanced chemical vapor deposition (PECVD) on patterned porous dielectric structures, and then to preferentially plasma etch the material built up on the via floor. In order to ensure sufficient sealing results, several deposition-etch cycles are required. Based on this concept, a systematic process development project was carried out. The properties of the resulting CDO films are discussed. The integration characteristics of the CDO film with candidate porous low-k material and with a subsequently deposited TaN barrier layer were also investigated. In addition, two unique approaches have been developed for the characterization of the sealing effectiveness of the cycled passivation process. These two approaches are based on spectroscopic ellipsometry and capacitance-voltage techniques. Both use the exposure of the passivated porous material to the vapor of an organic solvent to evaluate the responses of samples to the presence of the solvent vapor. Results from these experiments confirmed that

  14. Preparation and structure of porous dielectrics by plasma enhanced chemical vapor deposition

    SciTech Connect

    Gates, S. M.; Neumayer, D. A.; Sherwood, M. H.; Grill, A.; Wang, X.; Sankarapandian, M.

    2007-05-01

    The preparation of ultralow dielectric constant porous silicon, carbon, oxygen, hydrogen alloy dielectrics, called 'pSiCOH', using a production 200 mm plasma enhanced chemical vapor deposition tool and a thermal treatment is reported here. The effect of deposition temperature on the pSiCOH film is examined using Fourier transform infrared (FTIR) spectroscopy, dielectric constant (k), and film shrinkage measurements. For all deposition temperatures, carbon in the final porous film is shown to be predominantly Si-CH{sub 3} species, and lower k is shown to correlate with increased concentration of Si-CH{sub 3}. NMR and FTIR spectroscopies clearly detect the loss of a removable, unstable, hydrocarbon (CH{sub x}) phase during the thermal treatment. Also detected are increased cross-linking of the Si-O skeleton, and concentration changes for three distinct structures of carbon. In the as deposited films, deposition temperature also affects the hydrocarbon (CH{sub x}) content and the presence of C=O and C=C functional groups.

  15. Cellular-automata model of oxygen plasma impact on porous low-K dielectric

    NASA Astrophysics Data System (ADS)

    Rezvanov, Askar; Matyushkin, Igor V.; Gutshin, Oleg P.; Gornev, Evgeny S.

    2016-12-01

    Cellular-automata model of oxygen plasma influence on the integral properties of porous low-K dielectric is studied. The present work investigates the imitative simulation of this process. In our model we consider one isolated pore, which is simulated by cylinder with length L=200 nm and radius 1 nm ignoring the curvature factor. The simulation was performed for 2 million automata steps that correspond to 2 seconds in the real process time. Extrapolating the data to the longer time shows that more and more •CH3 groups will be replaced by the •OH groups, and over time almost all methyl groups will leave the pore surface (there is not more than 20% of the initial methyl groups amount on the first low-K dielectric 40nm after 2 seconds simulation).

  16. Bandgap measurements of low-k porous organosilicate dielectrics using vacuum ultraviolet irradiation

    SciTech Connect

    Zheng, H.; Shohet, J. L.; King, S. W.; Ryan, V.; Nishi, Y.

    2014-02-10

    Vacuum ultraviolet (VUV) photoemission spectroscopy is used to investigate the effect of VUV radiation on porous organosilicate (SiCOH) dielectrics during plasma processing. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies less than 9.0 eV was found to be beneficial in depleting accumulated charge in SiCOH films while VUV photons with higher energies did not have this effect. Moreover, VUV irradiation with 8.9 eV photons depletes the most charge. From this result, it can be concluded that 8.9 eV is the bandgap plus the electron affinity energy of SiCOH dielectrics.

  17. Determination of excitation profile and dielectric function spatial nonuniformity in porous silicon by using WKB approach.

    PubMed

    He, Wei; Yurkevich, Igor V; Canham, Leigh T; Loni, Armando; Kaplan, Andrey

    2014-11-03

    We develop an analytical model based on the WKB approach to evaluate the experimental results of the femtosecond pump-probe measurements of the transmittance and reflectance obtained on thin membranes of porous silicon. The model allows us to retrieve a pump-induced nonuniform complex dielectric function change along the membrane depth. We show that the model fitting to the experimental data requires a minimal number of fitting parameters while still complying with the restriction imposed by the Kramers-Kronig relation. The developed model has a broad range of applications for experimental data analysis and practical implementation in the design of devices involving a spatially nonuniform dielectric function, such as in biosensing, wave-guiding, solar energy harvesting, photonics and electro-optical devices.

  18. Water and ion transport in ultra-adsorbing porous magnesium carbonate studied by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Pochard, Isabelle; Frykstrand, Sara; Ahlström, Olle; Forsgren, Johan; Strømme, Maria

    2014-01-01

    Porous materials are used in application areas ranging from drug and vaccine delivery, medical implants, molecular sieves and cosmetics to catalysis and humidity control. In the present work, we employed an alternative approach to gain in-depth understanding about water interaction properties in such materials by the use of dielectric spectroscopy and thereby show that it is possible to obtain information that is not accessible from the more commonly employed water interaction analysis techniques. Specifically, the complex dielectric response of Upsalite, a novel, super-hydroscopic, high-surface area, porous magnesium carbonate material was measured in isothermal frequency scans between 10-3 and 106 Hz at controlled relative humidity (RH). We found the dielectric constant of the dry material to be 1.82. The ratio of bound to free water present in Upsalite after adsorption at room temperature was found to be high irrespective of the surrounding humidity with values ranging from ˜67% to ˜90%. We further found that OH- ions are the charge carriers responsible for the electrode polarization observed in the dielectric response and that the amount of these ions that are free to move in the material corresponds to a concentration of the order of 1-10 μmol l-1 independent of RH. Finally, the OH- diffusion coefficient displayed a drastic decrease with decreasing RH, typical of transport in unsaturated conditions. The presented results provide detailed insight about water interactions in the novel water adsorbing material under study and it is foreseen that the employed analysis methods can be used to evaluate other types of moisture adsorbing materials as well as the movement of functional species in the pores of inorganic drug delivery materials and materials tailored for adsorption of harmful charged species.

  19. Hierarchical viscosity of aqueous solution of tilapia scale collagen investigated via dielectric spectroscopy between 500 MHz and 2.5 THz

    PubMed Central

    Kawamata, H.; Kuwaki, S.; Mishina, T.; Ikoma, T.; Tanaka, J.; Nozaki, R.

    2017-01-01

    Aqueous solutions of biomolecules such as proteins are very important model systems for understanding the functions of biomolecules in actual life processes because interactions between biomolecules and the surrounding water molecules are considered to be important determinants of biomolecules’ functions. Globule proteins have been extensively studied via dielectric spectroscopy; the results indicate three relaxation processes originating from fluctuations in the protein molecule, the bound water and the bulk water. However, the characteristics of aqueous solutions of collagens have rarely been investigated. In this work, based on broadband dielectric measurements between 500 MHz and 2.5 THz, we demonstrate that the high viscosity of a collagen aqueous solution is due to the network structure being constructed of rod-like collagen molecules surrounding free water molecules and that the water molecules are not responsible for the viscosity. We determine that the macroscopic viscosity is related to the mean lifetime of the collagen-collagen interactions supporting the networks and that the local viscosity of the water surrounded by the networks is governed by the viscosity of free water as in the bulk. This hierarchical structure in the dynamics of the aqueous solution of biomolecules has been revealed for the first time. PMID:28345664

  20. Hierarchical viscosity of aqueous solution of tilapia scale collagen investigated via dielectric spectroscopy between 500 MHz and 2.5 THz

    NASA Astrophysics Data System (ADS)

    Kawamata, H.; Kuwaki, S.; Mishina, T.; Ikoma, T.; Tanaka, J.; Nozaki, R.

    2017-03-01

    Aqueous solutions of biomolecules such as proteins are very important model systems for understanding the functions of biomolecules in actual life processes because interactions between biomolecules and the surrounding water molecules are considered to be important determinants of biomolecules’ functions. Globule proteins have been extensively studied via dielectric spectroscopy; the results indicate three relaxation processes originating from fluctuations in the protein molecule, the bound water and the bulk water. However, the characteristics of aqueous solutions of collagens have rarely been investigated. In this work, based on broadband dielectric measurements between 500 MHz and 2.5 THz, we demonstrate that the high viscosity of a collagen aqueous solution is due to the network structure being constructed of rod-like collagen molecules surrounding free water molecules and that the water molecules are not responsible for the viscosity. We determine that the macroscopic viscosity is related to the mean lifetime of the collagen-collagen interactions supporting the networks and that the local viscosity of the water surrounded by the networks is governed by the viscosity of free water as in the bulk. This hierarchical structure in the dynamics of the aqueous solution of biomolecules has been revealed for the first time.

  1. Porous Polyimide Membranes Prepared by Wet Phase Inversion for Use in Low Dielectric Applications

    PubMed Central

    Kim, Soohyun; Jang, Keon-Soo; Choi, Hee-Dok; Choi, Seung-Hoon; Kwon, Seong-Ji; Kim, Il-Doo; Lim, Jung Ah; Hong, Jae-Min

    2013-01-01

    A wet phase inversion process of polyamic acid (PAA) allowed fabrication of a porous membrane of polyimide (PI) with the combination of a low dielectric constant (1.7) and reasonable mechanical properties (Tensile strain: 8.04%, toughness: 3.4 MJ/m3, tensile stress: 39.17 MPa, and young modulus: 1.13 GPa), with further thermal imidization process of PAA. PAA was simply synthesized from purified pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in two different reaction solvents such as γ-butyrolactone (GBL) and N-methyl-2-pyrrolidinone (NMP), which produce Mw/PDI of 630,000/1.45 and 280,000/2.0, respectively. The porous PAA membrane was fabricated by the wet phase inversion process based on a solvent/non-solvent system via tailored composition between GBL and NMP. The porosity of PI, indicative of a low electric constant, decreased with increasing concentration of GBL, which was caused by sponge-like formation. However, due to interplay between the low electric constant (structural formation) and the mechanical properties, GBL was employed for further exploration, using toluene and acetone vs. DI-water as a coagulation media. Non-solvents influenced determination of the PAA membrane size and porosity. With this approach, insight into the interplay between dielectric properties and mechanical properties will inform a wide range of potential low-k material applications. PMID:23615465

  2. Porous polyimide membranes prepared by wet phase inversion for use in low dielectric applications.

    PubMed

    Kim, Soohyun; Jang, Keon-Soo; Choi, Hee-Dok; Choi, Seung-Hoon; Kwon, Seong-Ji; Kim, Il-Doo; Lim, Jung Ah; Hong, Jae-Min

    2013-04-24

    A wet phase inversion process of polyamic acid (PAA) allowed fabrication of a porous membrane of polyimide (PI) with the combination of a low dielectric constant (1.7) and reasonable mechanical properties (Tensile strain: 8.04%, toughness: 3.4 MJ/m3, tensile stress: 39.17 MPa, and young modulus: 1.13 GPa), with further thermal imidization process of PAA. PAA was simply synthesized from purified pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in two different reaction solvents such as γ-butyrolactone (GBL) and N-methyl-2-pyrrolidinone (NMP), which produce Mw/PDI of 630,000/1.45 and 280,000/2.0, respectively. The porous PAA membrane was fabricated by the wet phase inversion process based on a solvent/non-solvent system via tailored composition between GBL and NMP. The porosity of PI, indicative of a low electric constant, decreased with increasing concentration of GBL, which was caused by sponge-like formation. However, due to interplay between the low electric constant (structural formation) and the mechanical properties, GBL was employed for further exploration, using toluene and acetone vs. DI-water as a coagulation media. Non-solvents influenced determination of the PAA membrane size and porosity. With this approach, insight into the interplay between dielectric properties and mechanical properties will inform a wide range of potential low-k material applications.

  3. Rôle of dielectric effects in the red-green switching of porous silicon luminescence

    NASA Astrophysics Data System (ADS)

    Chazalviel, J.-N.; Ozanam, F.; Dubin, V. M.

    1994-09-01

    Trapping of a carrier at an ionized impurity in porous silicon may be significantly hindered when the material is embedded in a high-dielectric-constant medium such as an aqueous electrolyte. This effect is estimated for a geometry of cylindrical silicon wires, and by modeling the two media with wavevector-independent dielectric constants. The self-image potential of the electron is taken into account, and the frequency dependence of the outer dielectric constant is treated in a simple manner. The results demonstrate that the impurity states are not accessible in the presence of the electrolyte, just due to the dielectric relaxation of the embedding medium. This result may apply to different kinds of localized electronic states, including those responsible for the red luminescence in dry porous silicon. This provides a plausible explanation for the red to green switching of the luminescence when the porous silicon is wet and suggests that using embedding media of intermediate dielectric constants should allow one to observe a progressive transition between red and green luminescence. Observation of porous silicon luminescence in solvents of various dielectric constants provides a preliminary test of this prediction. Le piégeage d'un porteur par une impureté ionisée dans le silicium poreux peut devenir inefficace lorsque le matériau est plongé dans un milieu de grande constante diélectrique tel qu'un électrolyte aqueux. Cet effet est estimé pour une géométrie de filaments cylindriques de silicium, les deux milieux étant modélisés par des constantes diélectriques indépendantes du vecteur d'onde. Le potentiel image de l'électron est pris en considération, et la dépendance en fréquence de la constante diélectrique du milieu extérieur est traitée de manière simple. Les résultats démontrent que les états liés sur l'impureté ne sont pas accessibles en présence de l'électrolyte, simplement en raison de la relaxation diélectrique de ce milieu

  4. Effect of vacuum ultraviolet and ultraviolet Irradiation on capacitance-voltage characteristics of low-k-porous organosilicate dielectrics

    SciTech Connect

    Sinha, H.; Lauer, J. L.; Nichols, M. T.; Shohet, J. L.; Antonelli, G. A.; Nishi, Y.

    2010-02-01

    High frequency capacitance-voltage (C-V) measurements are used to determine the effects of vacuum ultraviolet (VUV) and ultraviolet (UV) irradiation on defect states in porous low-k organosilicate (SiCOH) dielectrics. The characteristics show that VUV photons depopulate trapped electrons from defect states within the dielectric creating trapped positive charge. This is evidenced by a negative shift in the flat-band voltage of the C-V characteristic. UV irradiation reverses this effect by repopulating the defect states with electrons photoinjected from the silicon substrate. Thus, UV reduces the number of trapped positive charges in the dielectric and can effectively repair processing-induced damage.

  5. Dielectric Response at THz Frequencies of Mg Water Complexes Interacting with O3 Calculated by Density Functional Theory

    DTIC Science & Technology

    2012-10-24

    vibrational modes in the absorption spectra of various materials. A series of studies have focused on the general concept of constructing dielectric response...has a total of 3N-6 normal mode vibrations . The Schrodinger equation for the harmonic oscillations of these normal modes has known solutions. The...and m is the effective mass contributed by those atoms vibrating in the normal mode . A molecule in stable equilibrium is characterized by all

  6. Spin Coating Film Transfer and Hot-Pressing System for Uniform Dielectric Formation and Its Application to Porous Low-k Film Formation

    NASA Astrophysics Data System (ADS)

    Kawagoe, Masafumi; Adachi, Hideki; Yanagida, Takaaki; Komura, Tomoyuki; Saito, Hidenori; Sato, Norio; Kudou, Kazuhisa; Machida, Katsuyuki

    2008-01-01

    In this paper, we describe a transfer system that enables to form uniform dielectrics using spin coating film transfer and hot-pressing (STP) technology, and the applicability of a porous low-k material. The STP technology transfers a dielectric from a base film to a wafer by hot pressing in vacuum. We propose a processing unit that enables the handling of both the wafer and the base film. In the transfer unit, we also propose a scheme for transferring a dielectric to wafer uniformly. In the experiments, an organic porous low-k material, porous nanoporous polybenzoxazole dielectric (OxD) is used. The results on the film characteristics show no difference from those obtained by conventional spin coating. STP also enables planarization and sealing for patterned wafers with the porous OxD. It is confirmed that the STP process using porous OxD will be a candidate integration process.

  7. Devices and materials for THz spectroscopy: GHz CMOS circuits, periodic hole-arrays and high-frequency dielectric materials

    NASA Astrophysics Data System (ADS)

    Arenas, Daniel J.

    This dissertation is composed of three main projects, linked together by the THz region of the electromagnetic spectrum. In the first project, we detected the radiation from a silicon CMOS circuit, using a fourier transform interferometer. At the time of measurement, this 410 GHz circuit had the highest operating frequency for silicon integrated technology. The measured radiated power from the 410 GHz circuits was in the order of 0.01 muW. This circuit had radiated intensities comparable to those of commercially available black-body sources in the 400 GHz region. The high power and high emission per source area suggested possible spectroscopy applications. We also studied the optical properties of periodic hole-arrays with resonant frequencies in the THz region. Although the transmittance spectra of these structures have been extensively studied, here we present reflectance measurements that allow the analysis of the extinction/absorption spectra. The results were compared to predictions from the trapped-mode theory on the ohmic losses of these systems. Our results did not support the prediction of a suppression of the R + T spectra at the resonant frequency. Also, we studied the time-dependence of femtosecond pulses reflected from periodic hole arrays with resonant frequencies in the NIR region. Our results show that if the trapped modes theory is correct, then the lifetime of these modes are below 100 fs. Finally, in the third project, we studied the Raman active modes of various bismuth pyrochlores Bi3/2ZnNb3/2O7 (BZN), Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb 3/2O7 (BMN) and Bi3/2MgTa3/2O 7 (BMT), which have earned recent attention for high-frequency applications. The spectra of the four compositions are very similar, suggesting no major structural differences among these materials. The spectra were compared to those of other pyrochlores and specific discussions are offered for the assignment of each mode. Although there are clear differences between the spectra of

  8. Integration of porous low-k dielectrics using post porosity pore protection

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; de Marneffe, Jean-François; Verdonck, Patrick; Heylen, Nancy; Wen, Liang Gong; Wilson, Chris; Tokei, Zsolt; Boemmels, Juergen; De Gendt, Stefan; Baklanov, Mikhail R.

    2016-12-01

    Post porosity pore protection is studied as a means for low damage integration of porous low-k dielectrics. Homogeneous low-k densification is achieved using poly(methyl methacrylate) (PMMA) as a sacrificial filler. The improvement in plasma-induced damage is investigated on a plasma-enhanced chemical vapor deposition 2.0 porous organo-silicate glass, including damage from radicals and vacuum ultraviolet photons. Open pores are sealed upon polymer protection; therefore the penetration of metal species during deposition of a metal diffusion barrier is avoided. Various solutions for post metallization polymer removal are investigated, such as hydrogen remote plasma and an ultraviolet cure. The PMMA removal process is studied in order to avoid Cu wire degradation. Finally, low-k damage and barrier continuity are investigated on patterned wafers with functional circuits. By means of transmission electron microscopy inspection and electrical measurement, effective integrated k-values are extracted, giving a value k eff ~ 2.5-2.6 for the post metallization polymer removal option.

  9. Porous AlN with a Low Dielectric Constant Synthesized Based on the Physical Vapor Transport Principle

    NASA Astrophysics Data System (ADS)

    Wang, Hua-Jie; Liu, Xue-Chao; Kong, Hai-Kuan; Xin, Jun; Gao, Pan; Shi, Er-Wei

    2016-07-01

    Porous AlN with low dielectric constant has been synthesized by the sacrificial template method based on the physical vapor transport principle. It is quite different from the traditional method that mixes the matrix with a pore-forming agent and utilizes liquid-phase sintering. The method consists of two parts. Firstly, AlN powder is placed in a graphite crucible. C/AlN composite can be formed by mixing decomposed AlN vapor and volatile carbon originated from a crucible at high temperature. Secondly, pores are formed after removing carbon from the C/AlN composite by an annealing process. The structure, morphology, porosity and properties of porous AlN are characterized. It is shown the obtained porous AlN has a thermal conductivity of 37.3 W/(m K) and a reduced dielectric constant of 5.5-6.1 (at 1 MHz). The porosity measured by a mercury porosimeter is 24.09%. It has been experimentally proved that porous AlN with a sufficiently porous structure and properties can be synthesized based on the vapor-phase principle.

  10. Industrial applications of THz systems

    NASA Astrophysics Data System (ADS)

    Wietzke, S.; Jansen, C.; Jördens, C.; Krumbholz, N.; Vieweg, N.; Scheller, M.; Shakfa, M. K.; Romeike, D.; Hochrein, T.; Mikulics, M.; Koch, M.

    2009-07-01

    Terahertz time-domain spectroscopy (THz TDS) holds high potential as a non-destructive, non-contact testing tool. We have identified a plethora of emerging industrial applications such as quality control of industrial processes and products in the plastics industry. Polymers are transparent to THz waves while additives show a significantly higher permittivity. This dielectric contrast allows for detecting the additive concentration and the degree of dispersion. We present a first inline configuration of a THz TDS spectrometer for monitoring polymeric compounding processes. To evaluate plastic components, non-destructive testing is strongly recommended. For instance, THz imaging is capable of inspecting plastic weld joints or revealing the orientation of fiber reinforcements. Water strongly absorbs THz radiation. However, this sensitivity to water can be employed in order to investigate the moisture absorption in plastics and the water content in plants. Furthermore, applications in food technology are discussed. Moreover, security scanning applications are addressed in terms of identifying liquid explosives. We present the vision and first components of a handheld security scanner. In addition, a new approach for parameter extraction of THz TDS data is presented. All in all, we give an overview how industry can benefit from THz TDS completing the tool box of non-destructive evaluation.

  11. Advances in Determining Soil Matric Potential Using an Engineered Porous Ceramic and Dielectric Permittivity

    NASA Astrophysics Data System (ADS)

    Cobos, D. R.; Campbell, C. S.; Campbell, G. S.

    2007-12-01

    Soil water potential is a key parameter for determining water availability for plant growth, water flow, and soil stability. Although an in situ measurement of matric potential has been the focus of considerable research over the years, existing solutions still have many draw backs such as high maintenance, limited longevity, individual calibration requirements, high cost, and small measurement range. The objective of this research was to develop a sensor that could be used in the field to accurately measure soil matric potential without the limitations noted above. The sensor, which consisted of a dielectric sensor sandwiched between porous ceramic, was tested over a range soil types, electrical conductivties, and temperatures to calibrate and characterize its output. Data show consistent calibration curves between sensor output and actual soil matric potential over a variety of soil textures and electrical conductivities. Although temperature showed an effect on sensor output, it was low compared to overall sensor output. Likewise, salt effects were not visible in saturated matrices up to 10 dS/m. Data suggest the sensor will be an effective and robust tool to determine in situ matric potential.

  12. Electro-optical effects in porous PET films filled with liquid crystal: new possibilities for fiber optics and THZ applications.

    PubMed

    Chopik, A; Pasechnik, S; Semerenko, D; Shmeliova, D; Dubtsov, A; Srivastava, A K; Chigrinov, V

    2014-03-15

    The results of investigation of electro-optical properties of porous polyethylene terephthalate films filled with a nematic liquid crystal (5 CB) are presented. It is established that the optical response of the samples on the applied voltage drastically depends on the frequency range. At low frequencies of applied electrical field (ffc) electric field induces an overall change in the light intensity, which is typical for an electro-optical response of a liquid crystal (LC) layer in a conventional "sandwich"-like cell. The dependences of critical frequency fc, threshold voltages, and characteristic times on a pore diameter d were established. The peculiarities of electro-optical effects can be explained in the framework of the approach which connects the variations of light intensity with the corresponding changes of the effective refractive index n(eff) of a composite LC media. The unusual behavior of the electro-optical response at low frequencies is assigned to the orienting action of the specific shear flow typical for electrokinetic phenomena in polar liquids.

  13. Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses.

    PubMed

    Qiu, Song; Lyu, Hailong; Liu, Jiurong; Liu, Yuzhen; Wu, Nannan; Liu, Wei

    2016-08-10

    Porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 μm were fabricated by a solvothermal method combined with carbon reduction. The pore size of the synthesized Ni/C composite microspheres ranged from several nanometers to 50 nm. The porous Ni/C composite microspheres exhibited a saturation magnetization (MS) of 53.5 emu g(-1) and a coercivity (HC) of 51.4 Oe. When tested as an electromagnetic (EM) wave absorption material, the epoxy resin composites containing 60% and 75% porous Ni/C microspheres provided high-performance EM wave absorption at thicknesses of 3.0-11.0 and 1.6-7.0 mm in the corresponding frequency ranges of 2.0-12 and 2.0-18 GHz, respectively. The superior EM wave absorption performances of porous Ni/C composite microspheres were derived from the synergy effects generated by the magnetic loss of nickel, the dielectric loss of carbon, and the porous structure.

  14. Impact of reductive N2/H2 plasma on porous low-dielectric constant SiCOH thin films

    NASA Astrophysics Data System (ADS)

    Cui, Hao; Carter, Richard J.; Moore, Darren L.; Peng, Hua-Gen; Gidley, David W.; Burke, Peter A.

    2005-06-01

    Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2/H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2/H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film.

  15. Integration Process Development for Improved Compatibility with Organic Non-Porous Ultralow-k Dielectric Fluorocarbon on Advanced Cu Interconnects

    NASA Astrophysics Data System (ADS)

    Gu, Xun; Tomita, Yugo; Nemoto, Takenao; Miyatani, Kotaro; Saito, Akane; Kobayashi, Yasuo; Teramoto, Akinobu; Kuroda, Rihito; Kuroki, Shin-Ichiro; Kawase, Kazumasa; Nozawa, Toshihisa; Matsuoka, Takaaki; Sugawa, Shigetoshi; Ohmi, Tadahiro

    2012-05-01

    Integration of an organic non-porous ultralow-k dielectric, fluorocarbon (k= 2.2), into advanced Cu interconnects was demonstrated. The challenges of process-induced damage, such as delamination and variances of both the structure and electrical properties of the fluorocarbon during fabrication, were investigated on Cu/fluorocarbon damascene interconnects. A titanium-based barrier layer, instead of a tantalum-based barrier layer, was used to avoid delamination between Cu and fluorocarbon in Cu/fluorocarbon interconnects. A moisture-hermetic dielectric protective layer was also effective to avoid damage induced by wet chemical cleaning. On the other hand, a post-etching nitrogen plasma treatment to form a stable protective layer on the surface of the fluorocarbon was proposed for the practical minimization of damage introduction to fluorocarbon in the following damascene process, such as post-etching cleaning.

  16. Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

    SciTech Connect

    Marneffe, J.-F. de Lukaszewicz, M.; Porter, S. B.; Vajda, F.; Rutigliani, V.; Verdonck, P.; Baklanov, M. R.; Zhang, L.; Heyne, M.; El Otell, Z.; Krishtab, M.; Goodyear, A.; Cooke, M.

    2015-10-07

    Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

  17. Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

    NASA Astrophysics Data System (ADS)

    de Marneffe, J.-F.; Zhang, L.; Heyne, M.; Lukaszewicz, M.; Porter, S. B.; Vajda, F.; Rutigliani, V.; el Otell, Z.; Krishtab, M.; Goodyear, A.; Cooke, M.; Verdonck, P.; Baklanov, M. R.

    2015-10-01

    Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

  18. Mechanical reliability of porous low-k dielectrics for advanced interconnect: Study of the instability mechanisms in porous low-k dielectrics and their mediation through inert plasma induced re-polymerization of the backbone structure

    NASA Astrophysics Data System (ADS)

    Sa, Yoonki

    Continuous scaling down of critical dimensions in interconnect structures requires the use of ultralow dielectric constant (k) films as interlayer dielectrics to reduce resistance-capacitance delays. Porous carbon-doped silicon oxide (p-SiCOH) dielectrics have been the leading approach to produce these ultralow-k materials. However, embedding of porosity into dielectric layer necessarily decreases the mechanical reliability and increases its susceptibility to adsorption of potentially deleterious chemical species during device fabrication process. Among those, exposure of porous-SiCOH low-k (PLK) dielectrics to oxidizing plasma environment causes the increase in dielectric constant and their vulnerability to mechanical instability of PLKs due to the loss of methyl species and increase in moisture uptake. These changes in PLK properties and physical stability have been persisting challenges for next-generation interconnects because they are the sources of failure in interconnect integration as well as functional and physical failures appearing later in IC device manufacturing. It is therefore essential to study the fundamentals of the interactions on p-SiCOH matrix induced by plasma exposure and find an effective and easy-to-implement way to reverse such changes by repairing damage in PLK structure. From these perspectives, the present dissertation proposes 1) a fundamental understanding of structural transformation occurring during oxidative plasma exposure in PLK matrix structure and 2) its restoration by using silylating treatment, soft x-ray and inert Ar-plasma radiation, respectively. Equally important, 3) as an alternative way of increasing the thermo-mechanical reliability, PLK dielectric film with an intrinsically robust structure by controlling pore morphology is fabricated and investigated. Based on the investigations, stability of PLK films studied by time-dependent ball indentation tester under the elevated temperature, variation in film thickness and

  19. Thin film deposition at atmospheric pressure using dielectric barrier discharges: Advances on three-dimensional porous substrates and functional coatings

    NASA Astrophysics Data System (ADS)

    Fanelli, Fiorenza; Bosso, Piera; Mastrangelo, Anna Maria; Fracassi, Francesco

    2016-07-01

    Surface processing of materials by atmospheric pressure dielectric barrier discharges (DBDs) has experienced significant growth in recent years. Considerable research efforts have been directed for instance to develop a large variety of processes which exploit different DBD electrode geometries for the direct and remote deposition of thin films from precursors in gas, vapor and aerosol form. This article briefly reviews our recent progress in thin film deposition by DBDs with particular focus on process optimization. The following examples are provided: (i) the plasma-enhanced chemical vapor deposition of thin films on an open-cell foam accomplished by igniting the DBD throughout the entire three-dimensional (3D) porous structure of the substrate, (ii) the preparation of hybrid organic/inorganic nanocomposite coatings using an aerosol-assisted process, (iii) the DBD jet deposition of coatings containing carboxylic acid groups and the improvement of their chemical and morphological stability upon immersion in water.

  20. Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics.

    PubMed

    D'Angelo, Francesco; Mics, Zoltán; Bonn, Mischa; Turchinovich, Dmitry

    2014-05-19

    Terahertz-range dielectric properties of the common polymers low-density polyethylene (LDPE), cyclic olefin/ethylene copolymer (TOPAS®), polyamide-6 (PA6), and polytetrafluoroethylene (PTFE or Teflon®) are characterized in the ultra-broadband frequency window 2-15 THz, using a THz time-domain spectrometer employing air-photonics for the generation and detection of single-cycle sub-50 fs THz transients. The time domain measurements provide direct access to both the absorption and refractive index spectra. The polymers LDPE and TOPAS® demonstrate negligible absorption and spectrally-flat refractive index across the entire spectroscopy window, revealing the high potential of these polymers for applications in THz photonics such as ultra-broadband polymer-based dielectric mirrors, waveguides, and fibers. Resonant high-frequency polar vibrational modes are observed and assigned in polymers PA6 and PTFE, and their dielectric functions in the complete frequency window 2-15 THz are theoretically reproduced. Our results demonstrate the potential of ultra-broadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science.

  1. Excitation of THz hybrid modes in an elliptical dielectric rod waveguide with a cold collisionless unmagnetized plasma column by an annular electron beam

    SciTech Connect

    Rahmani, Z. Safari, S.; Heidari-Semiromi, E.

    2016-06-15

    The dispersion relation of electromagnetic waves propagating in an elliptical plasma waveguide with a cold collisionless unmagnetized plasma column and a dielectric rod is studied analytically. The frequency spectrum of the hybrid waves and the growth rate for excitation of the waves by a thin annular relativistic elliptical electron beam (TAREEB) is obtained. The effects of relative permittivity constant of dielectric rod, geometrical dimensions, plasma frequency, accelerating voltage, and current density of TAREEB on the growth rate and frequency spectra of the waveguide will be investigated.

  2. Modeling of the dielectric permittivity of porous soil media with water using statistical-physical models

    NASA Astrophysics Data System (ADS)

    Usowicz, Boguslaw; Marczewski, Wojciech; Usowicz, Jerzy B.; Łukowski, Mateusz; Lipiec, Jerzy; Stankiewicz, Krystyna

    2013-04-01

    Radiometric observations with SMOS rely on the Radiation Transfer Equations (RTE) determining the Brightness Temperature (BT) in two linear polarization components (H, V) satisfying Fresnel principle of propagation in horizontally layered target media on the ground. RTE involve variables which bound the equations expressed in Electro-Magnetic (EM) terms of the intensity BT to the physical reality expressed by non-EM variables (Soil Moisture (SM), vegetation indexes, fractional coverage with many different properties, and the boundary conditions like optical thickness, layer definitions, roughness, etc.) bridging the EM domain to other physical aspects by means of the so called tau-omega methods. This method enables joining variety of different valuable models, including specific empirical estimation of physical properties in relation to the volumetric water content. The equations of RTE are in fact expressed by propagation, reflection and losses or attenuation existing on a considered propagation path. The electromagnetic propagation is expressed in the propagation constant. For target media on the ground the dielectric constant is a decisive part for effects of propagation. Therefore, despite of many various physical parameters involved, one must effectively and dominantly rely on the dielectric constant meant as a complex variable. The real part of the dielectric constant represents effect of apparent shortening the propagation path and the refraction, while the imaginary part is responsible for the attenuation or losses. This work engages statistical-physical modeling of soil properties considering the media as a mixture of solid grains, and gas or liquid filling of pores and contact bridges between compounds treated statistically. The method of this modeling provides an opportunity of characterizing the porosity by general statistical means, and is applicable to various physical properties (thermal, electrical conductivity and dielectric properties) which

  3. Peculiarities of the dielectric response of the silver-modified-zeolite porous microstructure

    NASA Astrophysics Data System (ADS)

    Bunyatova, U.; Ozturk Koc, S.; Orbukh, V. I.; Eyvazova, G. M.; Agamaliev, Z. A.; Lebedeva, N. N.; Koçum, İ. C.; Salamov, B. G.; Ozer, M.

    2016-10-01

    The aim of this study was to characterize electrical conductivity and dielectrical properties of the silver-exchanged zeolite - natural clinoptilolite from Western part of Turkey and Azerbaijan in the range of frequencies from 200 Hz to 1 MHz and at room temperature. For a better understanding the effect of concentration and content of silver in the nanoporous zeolite volume on the conductivity, a study of the dielectric properties of an un-modified and silver-modified zeolite plates with different amounts of Ag ions and Ag nanoparticles is performed. Un-modified and three different types of the silver ion-exchanged modified clinoptilolite plates were prepared. It was found, that with increasing silver concentration, resistance of zeolite plate monotonically decreases at the same time a capacitance is increases. It is suggested an explanation of the observed frequency dependence of the capacitance and resistance of zeolite plates on the silver concentrations may be explain on the basis of an electrode-dielectric interface gap model. At the same time, the observed phenomenon can be explained by considering the fact that with increasing content of silver the conductivity increases. These results show that Ag nanoparticles play significant role for performance improvement in plasma electronic devices with zeolite cathode.

  4. Terahertz Artificial Dielectric Lens

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-03-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  5. CF3Br plasma cryo etching of low-k porous dielectric

    NASA Astrophysics Data System (ADS)

    Clemente, I.; Koehler, N.; Miakonkikh, A.; Zimmermann, S.; Schulz, S. E.; Rudenko, K.

    2016-08-01

    Process of plasma etching of CVD low-k dielectric was studied. We used CF3Br low pressure ICP plasma for etching at cryo temperatures (-20°C — -100°C), pressures (5-20 mTorr) and RF bias with effective DC voltage 80-140 V. Refractive index of film and its thickness were measured by spectral ellipsometry. Ellipsometric porosimetry was employed to compare pore size distribution before and after etching of films. Measurements show increasing of etch rate increase with decreasing sample temperature.

  6. Low-temperature dielectric measurements of confined water in porous granites

    NASA Astrophysics Data System (ADS)

    Gonçalves da Silva, Hugo; Prezas, Pedro; Vinagre, Ana; Graça, Manuel F.; Monteiro, Jorge H.; Tlemçani, Mouhaydine; Moita, Patrícia; Pinho, António; Bezzeghoud, Mourad; Mendiratta, Sushil K.; Rosa, Rui N.

    2014-05-01

    Three different granitic rocks extracted from Évora (in the south of Portugal) where used to perform dielectric measurements in the frequency range from 100 Hz to 1 MHz and temperatures 100 - 350 K. Thin cylindrical samples were prepared and circular electrodes were established using silver conductive paint. A clear anomaly appears, for T ~ 200 - 220 K, in the dielectric measurements of the samples studied. This anomaly occurs in different materials and coincides with a phase transition of supercooled water. Tightly bounded water confined in the pores of the rock do not crystallize at 273 K, but form a metastable liquid down to 200 - 220 K increasing water polarization. Below this temperature water molecules solidify and polarizability decreases. The rock presenting the most sizeable anomaly has a very low specific surface area, ~ 0.09 m2g-1, and connected porosity, ~ 1.10 %. In addition, geochemical analyses reveal almost inexistence of water molecules in its structure confirming the role of confined water in the anomaly. Comparison between saturated, oven dried, and vacuum dried samples is done. Finally, a logarithmic dependency of the critical temperature for the supercooled water phase transition with the measuring frequency is found. The authors acknowledge the support of FCT (Portuguese Science and Technology Foundation) through the project PTDC/GEO-FIQ/4178/2012.

  7. Effects of porosity on dielectric and piezoelectric properties of porous lead zirconate titanate ceramics

    SciTech Connect

    Yang Ankun; Wang Changan; Guo Rui; Huang Yong

    2011-04-11

    We report porous lead zirconate titanate ceramics fabricated by tert-butyl alcohol-based gel-casting process which show a very high thickness electromechanical coupling coefficient (0.77), high hydrostatic figure of merit (9594x10{sup -15} m{sup 2}/N), and low acoustic impedance (3.7 Mrayls). We show that the porosity effectively affects the performance of the samples in two ways: (1) a higher porosity simplifies the resonance behavior, leading to more efficient energy transduction; (2) its replacement of active ceramic phase leads to low relative permittivity, high hydrostatic figure of merit, and low acoustic impedance. It was confirmed the properties could be tailored by controlling the porosity.

  8. Dispersion characteristics of THz surface plasmons in nonlinear graphene-based parallel-plate waveguide with Kerr-type core dielectric

    NASA Astrophysics Data System (ADS)

    Yarmoghaddam, Elahe; Rakheja, Shaloo

    2017-08-01

    We theoretically model the dispersion characteristics of surface plasmons in a graphene-based parallel-plate waveguide geometry using nonlinear Kerr-type core (inter-plate) dielectric. The optical nonlinearity of graphene in the terahertz band under high light intensity is specifically included in the analysis. By solving Maxwell's equations and applying appropriate boundary conditions, we show that the waveguide supports four guided plasmon modes, each of which can be categorized as either symmetric or anti-symmetric based on the electric field distribution in the structure. Of the four guided modes, two modes are similar in characteristics to the modes obtained in the structure with linear graphene coating, while the two new modes have distinct characteristics as a result of the nonlinearity of graphene. We note that the group velocity of one of the plasmon modes acquires a negative value under high light intensity. Additionally, the optical nonlinearity of the core dielectric leads to a significant enhancement in the localization length of various plasmon modes. The description of the intra-band optical conductivity of graphene incorporates effects of carrier scatterings due to charged impurities, resonant scatterers, and acoustic phonons at 300 K. The proposed structure offers flexibility to tune the waveguide characteristics and the mode index by changing light intensity and electrochemical potential in graphene for reconfigurable plasmonic devices.

  9. Mitigation of plasma-induced damage in porous low-k dielectrics by cryogenic precursor condensation

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; de Marneffe, Jean-François; Leroy, Floriane; Lefaucheux, Philippe; Tillocher, Thomas; Dussart, Remi; Maekawa, Kaoru; Yatsuda, Koichi; Dussarrat, Christian; Goodyear, Andy; Cooke, Mike; De Gendt, Stefan; Baklanov, Mikhail R.

    2016-05-01

    The present work describes the plasma etch properties of porous organo-silicate materials at cryogenic temperature. The mechanism of plasma damage is studied by means of in situ ellipsometry and post-etch material evaluation. Using conventional volatile reactants such as SF6, it is found that low plasma damage can be achieved below  -120 °C through two main channels: pore sidewall passivation by molecular SF6 and partial condensation of non-volatile etch by-products. The protection can be enhanced by means of gas phase precursors with low saturated vapor pressure. Using C4F8, complete pore filling is achieved at  -110 °C and negligible plasma-induced damage is demonstrated on both blanket and patterned low-k films. The characteristics of the precursor condensation process are described and discussed in detail, establishing an optimal process window. It is shown that the condensation temperature can be raised by using precursors with even lower vapor pressure. The reported in situ densification through precursor condensation could enable damage-free plasma processing of mesoporous media.

  10. Electromagnetic THz Radiation Modeling by DPSM

    NASA Astrophysics Data System (ADS)

    Rahani, Ehsan Kabiri; Kundu, Tribikram

    2012-03-01

    THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated.

  11. Improving interpretation of geoelectrical signatures arising from biomineralization process in porous media: Low-frequency dielectric spectroscopy measurements on Desulfovibrio vulgaris cell suspensions

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Prodan, C.; Slater, L. D.; Bot, C.; Ntarlagiannis, D.

    2009-12-01

    Previous geophysical studies have demonstrated the sensitivity of complex conductivity measurements to microbial growth, biofilm formation, and microbial-mineral alternations, indicating that complex conductivity has the potential to serve as non-invasive tool for bioremediation monitoring. However, the inherent dielectric properties of microbes and how they might directly contribute to the geophysical responses observed during microbial-mineral transformations are not well understood. As a first step towards improving the understanding of electrical signals from microbial-mineral transformations in porous media, we studied the low frequency dielectric properties of sulfate-reducing bacteria (Desulfovibrio vulgaris) cell suspensions, a common soil borne microorganism involved in remediation of toxic metals in solution. We utilized a two-electrode dielectric spectroscopy measurement, common in biophysics applications,to acquire high quality dielectric dispersion curves of Desulfovibrio vulgaris cell suspensions over the frequency range 0.1 Hz to 1M Hz. Desulfovibrio vulgaris cell suspensions were placed between two parallel steel electrodes that are enclosed in a cylindrical glass tube, and the complex impedance of sample was measured relative to a known resistor. The measured impedance includes an electrode polarization impedance arising at the interface between electrodes and ionic solutions at low frequencies. This electrode impedance has traditionally precluded the reliable interpretation of two electrode techniques at low frequencies (< 1000 Hz). In order to obtain the true dielectric dispersion curve of sample, we adopt a simple and robust strategy to measure, analyze and remove the polarization impedance. The feasibility of this polarization removal technique was tested on water saturated glass beads. We show that the broadband dielectric response of Desulfovibrio vulgaris can be reliably determined with this approach. The measurements are modeled based on a

  12. In-situ surface and interface study of atomic oxygen modified carbon containing porous low-κ dielectric films for barrier layer applications

    NASA Astrophysics Data System (ADS)

    Bogan, J.; Lundy, R.; P. McCoy, A.; O'Connor, R.; Byrne, C.; Walsh, L.; Casey, P.; Hughes, G.

    2016-09-01

    The surface treatment of ultralow-κ dielectric layers by exposure to atomic oxygen is presented as a potential mechanism to modify the chemical composition of the dielectric surface to facilitate copper diffusion barrier layer formation. High carbon content, low-κ dielectric films of varying porosity were exposed to atomic oxygen treatments at room temperature, and x-ray photoelectron spectroscopy studies reveal both the depletion of carbon and the incorporation of oxygen at the surface. Subsequent dynamic water contact angle measurements show that the chemically modified surfaces become more hydrophilic after treatment, suggesting that the substrates have become more "SiO2-like" at the near surface region. This treatment is shown to be thermally stable up to 400 °C. High resolution electron energy loss spectroscopy elemental profiles confirm the localised removal of carbon from the surface region. Manganese (≈1 nm) was subsequently deposited on the modified substrates and thermally annealed to form surface localized MnSiO3 based barrier layers. The energy-dispersive X-ray spectroscopy elemental maps show that the atomic oxygen treatments facilitate the formation of a continuous manganese silicate barrier within dense low-k films, but significant manganese diffusion is observed in the case of porous substrates, negatively impacting the formation of a discrete barrier layer. Ultimately, the atomic oxygen treatment proves effective in modifying the surface of non-porous dielectrics while continuing to facilitate barrier formation. However, in the case of high porosity films, diffusion of manganese into the bulk film remains a critical issue.

  13. Damage by radicals and photons during plasma cleaning of porous low-k SiOCH. II. Water uptake and change in dielectric constant

    SciTech Connect

    Shoeb, Juline; Kushner, Mark J.

    2012-07-15

    Porous dielectric materials provide lower capacitances that reduce RC time delays in integrated circuits. Typical low-k materials include porous SiOCH-silicon dioxide with carbon groups, principally CH{sub 3}, lining the pores. With a high porosity, internally connected pores provide pathways for reactive species to enter into the material. Fluorocarbon plasmas are often used to etch SiOCH, a process that leaves a fluorocarbon polymer on the surface that must later be removed. During cleaning using Ar/O{sub 2} or He/H{sub 2} plasmas, reactions of radicals that diffuse into the SiOCH and photons that penetrate into the SiOCH can remove -CH{sub 3} groups. Due to its higher reactivity, cleaning with Ar/O{sub 2} plasmas removes more -CH{sub 3} groups than He/H{sub 2} plasmas, and so produce more free radical sites, such as -SiO{sub 2} Bullet (a -SiO{sub 2}-CH{sub 3} site with the -CH{sub 3} group removed).Upon exposure to humid air, these free radical sites can chemisorb H{sub 2}O to form hydrophilic Si-OH which can further physisorb H{sub 2}O through hydrogen bonding to form Si-OH(H{sub 2}O). With the high dielectric constant of water, even a small percentage of water uptake can significantly increase the effective dielectric constant of SiOCH. In this paper, we report on results from a computational investigation of the cleaning of SiOCH using Ar/O{sub 2} or He/H{sub 2} plasmas and subsequent exposure to humid air. The authors found that plasma cleaning with He/H{sub 2} mixtures produce less demethylation than cleaning with Ar/O{sub 2} plasmas, as so results in less water uptake, and a smaller increase in dielectric constant. The water that produces the increase in dielectric constant is roughly half chemisorbed and half physisorbed, the latter of which can be removed with mild heating. Sealing the pores with NH{sub 3} plasma treatment reduces water uptake and helps prevent the increase in dielectric constant.

  14. Anisotropic terahertz dielectric responses of sodium nitrate crystals.

    PubMed

    Fu, Xiaojian; Song, Youting; Sun, Changqing; Zhou, Ji

    2014-04-21

    Terahertz (THz) spectroscopy has become an effective tool to characterize the low-frequency rotational and vibrational modes of molecules. In addition, novel THz dielectric responses and optical properties on the basis of molecular rotation and vibration have attracted lots of attention because of their potential application in THz devices. In this paper, the dielectric response of low-symmetric sodium nitrate crystals in the frequency range of 0.2-1.5 THz was experimentally demonstrated. Four absorption bands at 0.23, 0.47, 0.92, and 1.15 THz were observed in the dielectric spectra and were tentatively ascribed to the rotational motion of nitrate ions. Based on the molecular rotation mechanism, the dielectric anisotropy and dielectric resonance of the crystal were discussed in detail.

  15. Atmospheric propagation of THz radiation.

    SciTech Connect

    Wanke, Michael Clement; Mangan, Michael A.; Foltynowicz, Robert J.

    2005-11-01

    In this investigation, we conduct a literature study of the best experimental and theoretical data available for thin and thick atmospheres on THz radiation propagation from 0.1 to 10 THz. We determined that for thick atmospheres no data exists beyond 450 GHz. For thin atmospheres data exists from 0.35 to 1.2 THz. We were successful in using FASE code with the HITRAN database to simulate the THz transmission spectrum for Mauna Kea from 0.1 to 2 THz. Lastly, we successfully measured the THz transmission spectra of laboratory atmospheres at relative humidities of 18 and 27%. In general, we found that an increase in the water content of the atmosphere led to a decrease in the THz transmission. We identified two potential windows in an Albuquerque atmosphere for THz propagation which were the regions from 1.2 to 1.4 THz and 1.4 to 1.6 THz.

  16. Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials

    SciTech Connect

    Wu, C. De Wolf, I.; Li, Y.; Leśniewska, A.; Varela Pedreira, O.; Marneffe, J.-F. de; Ciofi, I.; Verdonck, P.; Baklanov, M. R.; Bömmels, J.; Tőkei, Zs.; Croes, K.

    2015-10-28

    Stress-Induced Leakage Current (SILC) behavior during the dielectric degradation of ultra-porous SiOCH low-k materials was investigated. Under high voltage stress, SILC increases to a critical value before final hard breakdown. This SILC increase rate is mainly driven by the injected charges and is negligibly influenced by temperature and voltage. SILC is found to be transient and shows a t{sup −1} relaxation behavior, where t is the storage time at low voltages. This t{sup −1} transient behavior, described by the tunneling front model, is caused by both electron charging of neutral defects in the dielectric close to the cathode interface and discharging of donor defects close to the anode interface. These defects have a uniform density distribution within the probed depth range, which is confirmed by the observed flat band voltage shift results collected during the low voltage storage. By applying an additional discharging step after the low voltage storage, the trap energies and spatial distributions are derived. In a highly degraded low-k dielectric, the majority of defects have a trap depth between 3.4 eV and 3.6 eV and a density level of 1 × 10{sup 18 }eV{sup −1 }cm{sup −3}. The relation between the defect density N and the total amount of the injected charges Q is measured to be sub-linear, N ∼ Q{sup 0.45±0.07}. The physical nature of these stress-induced defects is suggested to be caused by the degradation of the Si-O based skeleton in the low-k dielectric.

  17. Properties of aqueous solutions in THz frequency range

    NASA Astrophysics Data System (ADS)

    Cherkasova, O.; Nazarov, M.; Shkurinov, A.

    2017-01-01

    Terahertz time-domain spectroscopy has been used for measuring of bovine serum albumin and glucose solutions response. The transmission and the attenuated total internal reflection geometries have been combined for analyzing the dielectric properties of aqueous solutions spectra at 0.07-3.2 THz.

  18. Microwave and THz sensing using slab-pair-based metamaterials

    SciTech Connect

    Kenanakis, G.; Shen, Nianhai; Mavidis, Ch.; Katsarakis, N.; Kafesaki, M.; Soukoulis, Costas M.; Economou, E.N.

    2012-10-15

    In this work the sensing capability of an artificial magnetic metamaterial based on pairs of metal slabs is demonstrated, both theoretically and experimentally, in the microwave regime. The demonstration is based on transmission measurements and simulations monitoring the shift of the magnetic resonance frequency as one changes a thin dielectric layer placed between the slabs of the pairs. Strong dependence of the magnetic resonance frequency on both the permittivity and the thickness of the dielectric layer under detection was observed. The sensitivity to the dielectrics′ permittivity (ε) is larger for dielectrics of low ε values, which makes the approach suitable for sensing organic materials also in the THz regime. The capability of our approach for THz sensing is also demonstrated through simulations.

  19. Three-dimensional THz lumped-circuit resonators.

    PubMed

    Todorov, Yanko; Desfond, Pascal; Belacel, Cherif; Becerra, Loïc; Sirtori, Carlo

    2015-06-29

    Our work describes a novel three dimensional meta-material resonator design for optoelectronic applications in the THz spectral range. In our resonant circuits, the capacitors are formed by double-metal regions cladding a dielectric core. Unlike conventional planar metamaterials, the electric field is perpendicular to the surface and totally confined in the dielectric core. Furthermore, the magnetic field, confined in the inductive part, is parallel to the electric field, ruling out coupling through propagation effects. Our geometry thus combines the benefit of double-metal structures that provide parallel plate capacitors, while maintaining the ability of meta-material resonators to adjust independently the capacitive and inductive parts. Furthermore, in our geometry, a constant bias can be applied across the dielectric, making these resonators very suitable for applications such as ultra-low dark current THz quantum detectors and amplifiers based on quantum cascade gain medium.

  20. Dielectric properties of porous silicon for use as a substrate for the on-chip integration of millimeter-wave devices in the frequency range 140 to 210 GHz

    NASA Astrophysics Data System (ADS)

    Sarafis, Panagiotis; Nassiopoulou, Androula Galiouna

    2014-08-01

    In this work, the dielectric properties of porous Si for its use as a local substrate material for the integration on the Si wafer of millimeter-wave devices were investigated in the frequency range 140 to 210 GHz. Broadband electrical characterization of coplanar waveguide transmission lines (CPW TLines), formed on the porous Si layer, was used in this respect. It was shown that the dielectric parameters of porous Si (dielectric permittivity and loss tangent) in the above frequency range have values similar to those obtained at lower frequencies (1 to 40 GHz). More specifically, for the samples used, the obtained values were approximately 3.12 ± 0.05 and 0.023 ± 0.005, respectively. Finally, a comparison was made between the performance of the CPW TLines on a 150-μm-thick porous Si layer and on three other radiofrequency (RF) substrates, namely, on trap-rich high-resistivity Si (trap-rich HR Si), on a standard complementary metal-oxide-semiconductor (CMOS) Si wafer (p-type, resistivity 1 to 10 Ω.cm) and on quartz.

  1. Dielectric absorption behavior of YAlO3 at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Morimoto, Takaaki; Kuroda, Yasuhiro; Ohki, Yoshimichi

    2017-10-01

    Using THz time-domain spectroscopy, optical or dielectric absorption spectra were obtained for YAlO3(100) single crystals. A sharp absorption peak appears at around 3.4 THz only when the THz electric field is parallel to the sample’s [011] axis. This peak should be due to a normal mode of vibration, to which Y largely contributes.

  2. THz Local Oscillator Technology

    NASA Technical Reports Server (NTRS)

    Mehdi, Imran

    2004-01-01

    The last decade has seen a number of technological advancements that have now made it possible to implement fully solid state local oscillator chains up to 2 THz. These chains are composed of cascaded planar multiplier stages that are pumped with W-band high power sources. The high power W-band sources are achieved by power combining MMIC amplifiers and can provide in access of 150 mW with about 10% bandwidth. Planar diode technology has also enabled novel circuit topologies that can take advantage of the high input power and demonstrate significant efficiencies well into the THz range. Cascaded chains to 1.9 THz have now been demonstrated with enough output power to successfully pump hot-electron bolometer mixers in this frequency range. An overview of the current State-of-the-Art of the local oscillator technology will be presented along with highlighting future trends and challenges.

  3. Pulsed THz spectroscopy of substance under disordered opaque cover

    NASA Astrophysics Data System (ADS)

    Trofimov, V. A.; Zagursky, D. Yu.; Zakharova, I. G.

    2016-02-01

    Remote sensing using the pulsed THz-TDS is of great interest because of its possible practical applications. Many ordinary materials (paper, for example) are transparent to THz radiation while the hazardous substances, which have to detect, possess fingerprints in this frequency range. However, cover of ordinary material can distort its spectrum in such a way that the spectrum of reflected THz pulse or transmitted THz pulse will contain absorption frequencies, which are inherent to dangerous substance (explosives, illistic drugs....), despite their absence in the material under consideration. This is a consequence of covering material influence due to its density fluctuation or its structure variation, for example. As rule, covering material structure fluctuation may be comparable with some wavelengths of the probing THz radiation. Thus, the cover can act as a disordered photonic structure with respect to incident THz pulse and its action results in additional absorption spectral lines appearance and in turn, the incorrect substance identification will take place. In this paper we discuss an influence of quasi-periodic structure with variable dielectric constant on the spectrum of a substance, which is placed behind or inside such structure. The investigation is conducted by means of computer simulation. We consider a single layer of optically active substance placed between two covers consisting of linear layers with random dielectric permittivity. Incident Gaussian pulse with a few-cycles falls on the substance covered by layers. Both transmitted pulse and reflected pulse are analyzed and their spectra are compared to those of the incident pulse. For description of a THz pulse interaction with an optically active substance covered by disordered structures we use the Maxwell's equations together with matrix-density formalism. The appearance of additional spectrum extremes due to the layered structure influence is illustrated. Computer simulation results were

  4. THz Emission Spectroscopy for THz Spintronics

    NASA Astrophysics Data System (ADS)

    Jarik Huisman, Thomas; Rasing, Theo

    2017-01-01

    Spintronics is used as the standard for the readout of magnetically stored data and also has commercial applications for writing data. The generation, control and detection of spin-polarized currents, spin-dependent electric transport, and pure spin currents on the subpicosecond (10-12 s) timescale are the next challenges in spintronics. Terahertz (THz, 1012 Hz) emission spectroscopy has proven to be an excellent tool for investigating these challenges. In this short review, we outline the functioning of this spectroscopic technique and its recent applications to spintronics.

  5. Low-noise THz MgB2 Josephson mixer

    NASA Astrophysics Data System (ADS)

    Cunnane, Daniel; Kawamura, Jonathan H.; Acharya, Narendra; Wolak, Matthäus A.; Xi, X. X.; Karasik, Boris S.

    2016-09-01

    The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The IcRn product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.

  6. Terahertz (THZ) Imaging

    DTIC Science & Technology

    2006-03-01

    beam or by moving the sample around. THz TDS is by no means confined to transmission data. It is possible to get reflective data from samples by slight...Wallace, V.P.; Fitzgerald, A.J.; Cole, B.C.; Pye , R.J.; Arnone, D.D., “Biomedical applications of THz imaging” Microwave Symposium Digest, 2004 IEEE MTT-S...2002. A perspective on state of art. 13. Wallace, V.P.; Arnone, D.A.; Woodward, R.M.; Pye RJ; “Biomedical applications of terahertz pulse

  7. A single dielectric nanolaser

    NASA Astrophysics Data System (ADS)

    Huang, Tsung-Yu; Yen, Ta-Jen

    2016-09-01

    To conquer Ohmic losses from metal and enhance pump absorption efficiency of a nanolaser based on surface plasmon polariton, we theoretically calculate the first magnetic and electric scattering coefficient of a dielectric sphere under a plane wave excitation with a dielectric constant of around 12. From this calculation, we could retrieve both negative effective permittivity and permeability of the sphere simultaneously at frequencies around 153 THz in the aids of Lewin's theory and the power distribution clearly demonstrate the expected negative Goos-Hänchen effect, which usually occurred in a negative refractive waveguide, thus creating two energy vortices to trap incident energy and then promoting the pump absorption efficiency. Meanwhile, a magnetic lasing mode at 167.3 THz is demonstrated and reveals a magnetic dipole resonance mode and a circulating energy flow within the dielectric sphere, providing a possible stopped light feedback mechanism to enable the all-dielectric nanolaser. More importantly, the corresponding mode volume is reduced to 0.01λ3 and a gain threshold of 5.1×103 is obtained. To validate our design of all-dielectric nanolaser, we employ finite-difference-time-domain simulation software to examine the behavior of the nanolaser. From simulation, we could obtain a pinned-down population inversion of 0.001 and a lasing peak at around 166.5 THz, which is very consistent with the prediction of Mie theory. Finally, according to Mie theory, we can regard the all-dielectric nanolaser as the excitation of material polariton and thus could make an analogue between lasing modes of the dielectric and metallic nanoparticles.

  8. Electromigration failure mode concerning negative resistance shift of Cu interconnects buried in porous low-k dielectric

    NASA Astrophysics Data System (ADS)

    Zheng, Hui; Yin, Binfeng; Yu, Hewei; Chen, Leigang; Gao, Lin; Zhou, Ke; Kuo, Chinte

    2017-02-01

    Electromigration failure mode concerning a negative resistance shift of 4%-11% and cathode burnout was reported for Cu interconnects buried in porous low-k in this paper. Evidence for oxidation and debonding of Ta/TaN liner at high temperature was revealed, which was demonstrated to have been enabled by the unsealed porous low-k due to moisture uptake. The cathode burnout was thus attributed to severe Joule heating induced in the insulated liner after oxidation. The resistance decay of Cu also exhibited to be mainly consistent with the calculation from specularity recovery of electron scattering at the Cu/Ta interface after oxidation and debonding of the liner, although other factors like strain relaxation may also have some contribution.

  9. Model of THz Magnetization Dynamics

    PubMed Central

    Bocklage, Lars

    2016-01-01

    Magnetization dynamics can be coherently controlled by THz laser excitation, which can be applied in ultrafast magnetization control and switching. Here, transient magnetization dynamics are calculated for excitation with THz magnetic field pulses. We use the ansatz of Smit and Beljers, to formulate dynamic properties of the magnetization via partial derivatives of the samples free energy density, and extend it to solve the Landau-Lifshitz-equation to obtain the THz transients of the magnetization. The model is used to determine the magnetization response to ultrafast multi- and single-cycle THz pulses. Control of the magnetization trajectory by utilizing the THz pulse shape and polarization is demonstrated. PMID:26956997

  10. THz identification and Bayes modeling

    NASA Astrophysics Data System (ADS)

    Sokolnikov, Andre

    2017-05-01

    THz Identification is a developing technology. Sensing in the THz range potentially gives opportunity for short range radar sensing because THz waves can better penetrate through obscured atmosphere, such as fog, than visible light. The lower scattering of THz as opposed to the visible light results also in significantly better imaging than in IR spectrum. A much higher contrast can be achieved in medical trans-illumination applications than with X-rays or visible light. The same THz radiation qualities produce better tomographical images from hard surfaces, e.g. ceramics. This effect comes from the delay in time of reflected THz pulses detection. For special or commercial applications alike, the industrial quality control of defects is facilitated with a lower cost. The effectiveness of THz wave measurements is increased with computational methods. One of them is Bayes modeling. Examples of this kind of mathematical modeling are considered.

  11. Broadband terahertz dielectric spectroscopy of alcohols

    NASA Astrophysics Data System (ADS)

    Sarkar, Sohini; Saha, Debasis; Banerjee, Sneha; Mukherjee, Arnab; Mandal, Pankaj

    2017-06-01

    We have studied the complex dielectric properties of a series of alcohols in 0.5-10 THz frequency range using THz time-domain spectroscopy. The dielectric response observed has contribution from a Debye relaxation process and three damped harmonic oscillators. Combination of experimental observations, all-atom molecular dynamics simulations and ab initio quantum calculations reveals that the complex dielectric spectra of alcohols result from a complex dynamics involving vibrational motions of several atoms across multiple interacting alcohol molecules. The major contribution comes from the fast hydrogen-bond rupture and reformation dynamics, the motion of alkyl chains, and the motions of the H-bonded OH groups.

  12. Ultrasensitive Speciation Analysis of Mercury in Rice by Headspace Solid Phase Microextraction Using Porous Carbons and Gas Chromatography-Dielectric Barrier Discharge Optical Emission Spectrometry.

    PubMed

    Lin, Yao; Yang, Yuan; Li, Yuxuan; Yang, Lu; Hou, Xiandeng; Feng, Xinbin; Zheng, Chengbin

    2016-03-01

    Rice consumption is a primary pathway for human methylmercury (MeHg) exposure in inland mercury mining areas of Asia. In addition, the use of iodomethane, a common fumigant that significantly accelerates the methylation of mercury in soil under sunlight, could increase the MeHg exposure from rice. Conventional hyphenated techniques used for mercury speciation analysis are usually too costly for most developing countries. Consequently, there is an increased interest in the development of sensitive and inexpensive methods for the speciation of mercury in rice. In this work, gas chromatography (GC) coupled to dielectric barrier discharge optical emission spectrometry (DBD-OES) was developed for the speciation analysis of mercury in rice. Prior to GC-DBD-OES analysis, mercury species were derivatized to their volatile species with NaBPh4 and preconcentrated by headspace solid phase microextraction using porous carbons. Limits of detection of 0.5 μg kg(-1) (0.16 ng), 0.75 μg kg(-1) (0.24 ng), and 1.0 μg kg(-1) (0.34 ng) were obtained for Hg(2+), CH3Hg(+), and CH3CH2Hg(+), respectively, with relative standard deviations (RSDs) better than 5.2% and 6.8% for one fiber or fiber-to-fiber mode, respectively. Recoveries of 90-105% were obtained for the rice samples, demonstrating the applicability of the proposed technique. Owing to the small size, low power, and low gas consumption of DBD-OES as well as efficient extraction of mercury species by porous carbons headspace solid phase micro-extraction, the proposed technique provides several advantages including compactness, cost-effectiveness, and potential to couple with miniature GC to accomplish the field speciation of mercury in rice compared to conventional hyphenated techniques.

  13. 3D THz hyperspectrum applied in security check-in

    NASA Astrophysics Data System (ADS)

    Damian, V.; Logofǎtu, P. C.; Vasile, T.

    2016-12-01

    We developed a measuring technology using a TDS-THz system to construct hyperspectral images of some objects, including hazardous materials. "T-rays" (the THz spectral domain of the light) have a growing importance in security and imagistic domain. Due to their property of penetrating through dielectric objects, and using non-ionizing radiations, the THz systems have become a standard for "hot-places" (airports, train stations etc.). The hyperspectral images are 3D images having 2D spatial dimension and one spectral dimension. In this way, we obtain simultaneously information about the form of the object and its molecular composition. For discriminating between substances, we must first build a database of spectra for hazardous and dangerous substances. We experiment our system on some items (among them a firecracker, a cigarette and a metal collar) and we tried to discriminate between them using the database of spectra.

  14. Coherent Cherenkov radiation as an intense THz source

    NASA Astrophysics Data System (ADS)

    Bleko, V.; Karataev, P.; Konkov, A.; Kruchinin, K.; Naumenko, G.; Potylitsyn, A.; Vaughan, T.

    2016-07-01

    Diffraction and Cherenkov radiation of relativistic electrons from a dielectric target has been proposed as mechanism for production of intense terahertz (THz) radiation. The use of an extremely short high-energy electron beam of a 4th generation light source (X-ray free electron laser) appears to be very promising. A moderate power from the electron beam can be extracted and converted into THz radiation with nearly zero absorption losses. The initial experiment on THz observation will be performed at CLARA/VELA FEL test facility in the UK to demonstrate the principle to a wider community and to develop the radiator prototype. In this paper, we present our theoretical predictions (based on the approach of polarization currents), which provides the basis for interpreting the future experimental measurements. We will also present our hardware design and discuss a plan of the future experiment.

  15. Terahertz wire grid polarizer fabricated by imprinting porous silicon.

    PubMed

    Imakita, Kenji; Kamada, Takeshi; Fujii, Minoru; Aoki, Kanna; Mizuhata, Minoru; Hayashi, Shinji

    2013-12-01

    A terahertz (THz) wire-grid polarizer is fabricated by imprinting porous Si followed by oblique evaporation of Ag. We demonstrate that it works in a wide frequency region covering from 5 to 18 THz with the extinction ratio of 10 dB. The frequency region is much wider than that of THz wire-grid polarizers fabricated by conventional imprint lithography using organic materials. The result suggests that imprinting of porous Si is a promising fabrication technique to realize low-cost wire-grid polarizers working in the THz region.

  16. In Situ Synthesis of Porous Carbons by Using Room-Temperature, Atmospheric-Pressure Dielectric Barrier Discharge Plasma as High-Performance Adsorbents for Solid-Phase Microextraction.

    PubMed

    Lin, Yao; Wu, Li; Xu, Kailai; Tian, Yunfei; Hou, Xiandeng; Zheng, Chengbin

    2015-09-21

    A one-step, template-free method is described to synthesize porous carbons (PCs) in situ on a metal surface by using a room-temperature, atmospheric-pressure dielectric barrier discharge (DBD) plasma. This method not only features high efficiency, environmentally friendliness, and low cost and simple equipment, but also can conveniently realize large-area synthesis of PCs by only changing the design of the DBD reactor. The synthesized PCs have a regulated nestlike morphology, and thus, provide a high specific surface area and high pore volume, which result in excellent adsorption properties. Its applicability was demonstrated by using a PC-coated stainless-steel fiber as a solid-phase microextraction (SPME) fiber to preconcentrate polycyclic aromatic hydrocarbons (PAHs) prior to analysis by gas chromatography with flame ionization detection (GC-FID). The results showed that the fiber exhibited excellent enrichment factors (4.1×10(4) to 3.1×10(5)) toward all tested PAHs. Thus, the PC-based SPME-GC-FID provides low limits of detection (2 to 20 ng L(-1)), good precision (<7.8%), and good recoveries (80-115%) for ultra-sensitive determination of PAHs in real water samples. In addition, the PC-coated fiber could be stable enough for more than 500 replicate extraction cycles.

  17. THz Sources for Space

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Ward, John; Maiwald, Frank; Mehdi, Imran

    2007-01-01

    Terahertz is the primary frequency for line and continuum radiation from cool (5-100K) gas (atoms and molecules) and dust. This viewgraph presentation reviews the reasons for the interest in Terahertz Space Applications; the Terahertz Space Missions: in the past, present and planned for the future, Terahertz source requirements and examples of some JPL instruments; and a case study for a flight deliverable: THz Local Oscillators for ESA s Herschel Space Telescope

  18. THz channel characterization for future wireless gigabit indoor communication systems

    NASA Astrophysics Data System (ADS)

    Piesiewicz, Radoslaw; Jemai, Jaouhar; Koch, Martin; Kurner, Thomas

    2005-03-01

    Short range wireless communication systems are expanding at rapid rate, finding application in offices, congested urban areas and homes. Development of wireless local area networks is accompanied by a steady increase in the demand for ever higher data rates. This in turn entails the necessity to develop communication systems which operate at higher frequencies. Currently WLAN works at a few GHz, while systems operating at several ten GHz appear already feasible. It can be expected that wireless short-range communication networks will soon push towards the THz frequency range and that systems which handle high-density information and support wider bandwidth communications will be developed in a few years time. Since THz radiation is strongly absorbed by the atmosphere, working distances may be short and individual THz pico-cells may cover only single rooms or at most one building. For an indoor system of practical importance it must be robust against shadowing. Recently, flexible all-plastic mirrors, supporting specular reflections in the THz range have been demonstrated. They are cheap and easy to produce and can be used as frequency selective wall-paper to enhance the reflectivity of walls and hence facilitate non-line-of-sight communication in a THz cell. For this case the spatial and temporal characteristics of the indoor THz propagation channel in a room with randomly placed objects and moving people are derived with ray-tracing methodology and Monte Carlo simulations. Our simulations show that high-gain antennas will be needed for the realization of THz communication in indoor environments. Furthermore, indirect transmission paths between transmitter and receiver, supported by dielectric mirrors make the communication channel much more robust against shadowing.

  19. Quantitative study of rectangular waveguide behavior in the THz.

    SciTech Connect

    Rowen, Adam M.; Nordquist, Christopher Daniel; Wanke, Michael Clement

    2009-10-01

    This report describes our efforts to quantify the behavior of micro-fabricated THz rectangular waveguides on a configurable, robust semiconductor-based platform. These waveguides are an enabling technology for coupling THz radiation directly from or to lasers, mixers, detectors, antennas, and other devices. Traditional waveguides fabricated on semiconductor platforms such as dielectric guides in the infrared or co-planar waveguides in the microwave regions, suffer high absorption and radiative losses in the THz. The former leads to very short propagation lengths, while the latter will lead to unwanted radiation modes and/or crosstalk in integrated devices. This project exploited the initial developments of THz micro-machined rectangular waveguides developed under the THz Grand Challenge Program, but instead of focusing on THz transceiver integration, this project focused on exploring the propagation loss and far-field radiation patterns of the waveguides. During the 9 month duration of this project we were able to reproduce the waveguide loss per unit of length in the waveguides and started to explore how the loss depended on wavelength. We also explored the far-field beam patterns emitted by H-plane horn antennas attached to the waveguides. In the process we learned that the method of measuring the beam patterns has a significant impact on what is actually measured, and this may have an effect on most of the beam patterns of THz that have been reported to date. The beam pattern measurements improved significantly throughout the project, but more refinements of the measurement are required before a definitive determination of the beam-pattern can be made.

  20. Tunable THz metamaterials based on phase-changed materials (VO2) triggered by thermal and electrical stimuli

    NASA Astrophysics Data System (ADS)

    Crunteanu, Aurelian; Humbert, Georges; Leroy, Jonathan; Huitema, Laure; Orlianges, Jean-Christophe; Bessaudou, Annie

    2017-02-01

    One of the most peculiar characteristics of the insulator-to-metal transition (MIT) in vanadium dioxide (VO2) material is its broadband response, manifested by drastic electrical and dielectric properties changes between the insulator and metallic states on a very large frequency spectrum. We are presenting the characterization of the MIT in VO2 films over a wide range of the electromagnetic spectrum (75-110GHz, 0.1-1.4THz) and illustrate the materials' capabilities for manipulating the electromagnetic radiation in the millimeter-waves and THz domains. We demonstrate the possibility of realizing tunable THz devices by introducing this phase transition material as localized patterns in the structure of THz planar metamaterials. We designed, simulated and fabricated tunable VO2-based THz metamaterials devices which show significant variations in their THz transmission under the effect of thermal stimuli but also by applying an electrical voltage across the devices.

  1. Corrugated capillary as THz Cherenkov Smith-Purcell radiator

    NASA Astrophysics Data System (ADS)

    Lekomtsev, K. V.; Aryshev, A. S.; Tishchenko, A. A.; Ponomarenko, A. A.; Sukharev, V. M.; Terunuma, N.; Urakawa, J.; Strikhanov, M. N.

    2016-07-01

    In this article we discussed Particle In Cell electromagnetic simulations and mechanical design of dielectric capillaries that produce THz Cherenkov Smith-Purcell radiation (ChSPR), arising when a femtosecond electron multi-bunch beam propagates through corrugated and non-corrugated dielectric capillaries with metallic radiation reflectors. We investigated the influence of the four-bunch beam on the SPR field spectrum and on the ChSPR power spectrum, and the influence of the non-central beam propagation on the ChSPR power spectrum. We also discussed the design and assembly of the capillaries, constructed as sets of cylindrical rings.

  2. A review on the sub-THz/THz gyrotrons

    NASA Astrophysics Data System (ADS)

    Kumar, Nitin; Singh, Udaybir; Bera, Anirban; Sinha, A. K.

    2016-05-01

    A review on the sub-THz/THz gyrotrons is performed in this manuscript. The present development status of gyrotrons can be divided into three streams for the sake of better understanding: 1. low frequency (<35 GHz), medium power (<100 kW), small size and easy to handle gyrotrons for industrial applications, 2. very high power (1 MW or more), medium frequency (100-200 GHz) gyrotrons for plasma fusion applications, 3. low power (few tens of watt to kW), high frequency (>200 GHz) gyrotrons for various innovative applications. In this manuscript, the third stream of gyrotron development is reviewed. In last few decades several innovative applications are searched in sub-THz/THz band where the gyrotrons could be used as an efficient source of RF radiation. The applications of sub-THz/THz gyrotrons including the futuristic scope of the device are also discussed in this article. Further, several criticalities arise in the design and development when the gyrotron operation shifts toward the high frequency band. Various such design and technological challenges are also discussed here. Finally the development status of sub-THz/THz gyrotrons as per the use in various scientific and technological applications is also discussed.

  3. THz Imaging of Skin Burn: Seeing the Unseen—An Overview

    PubMed Central

    Dutta, Moumita; Bhalla, Amar S.; Guo, Ruyan

    2016-01-01

    Significance: This review article puts together all the studies performed so far in realizing terahertz (THz) spectra as a probing mechanism for burn evaluation, summarizing their experimental conditions, observations, outcomes, merits, and demerits, along with a comparative discussion of other currently used technologies to present the state of art in a condensed manner. The key features of this noncontact investigation technique like its precise burn depth analysis and the approaches it follows to convert the probed data into a quantitative measure have also been discussed in this article. Recent Advances: The current research developments in THz regime observed in device design technologies (like THz time domain spectrometer, quantum cascade THz lasers, THz single-photon detectors, etc.) and in understanding its unique properties (like nonionizing nature, penetrability through dry dielectrics, etc.) have motivated the research world to realize THz window as a potential candidate for burn detection. Critical Issues: Application of appropriate medical measure for burn injury is primarily subjective to proper estimation of burn depth. Tool modality distinguishing between partial and full-thickness burn contributing toward correct medical care is indeed awaited. Future Directions: The overview of THz imaging as a burn assessment tool as provided in this article will certainly help in further nurturing of this emerging diagnostic technique particularly in improving its detection and accompanied image processing methods so that the minute nuances captured by the THz beam can be correlated with the physiological–anatomical changes in skin structures, caused by burn, for better sensitivity, resolution, and quantitative analysis. PMID:27602253

  4. Exploration of the effects of burn parameters on THz wound imaging

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Sung, Shijun; Fishbein, Michael; Grundfest, Warren S.; Taylor, Zachary D.

    2015-08-01

    The high contrast resolution afforded by terahertz (1 THz = 1012 Hz) imaging of physiologic tissue continues to drive explorations into the utility of THz technology for burn wound detection. Although we have previously reported the use of a novel, reflective THz imaging technology to sense spatiotemporal differences in reflectivity between partial and full thickness burn wounds, no evidence exists of a one-to-one correlation between structural damage observed in histological assessments of burn severity and THz signal. For example, varying burn induction methods may all result in a common burn wound severity, however, burn features observed in parallel THz imagery may not be identical. Successful clinical translation of THz technology as a comprehensive burn guidance tool, therefore, necessitates an understanding of THz signal and its relation to wound pathophysiology. In this work, longitudinal THz imagery was acquired with a quartz (n = 2.1, 500 μm) window of cutaneous wounds induced with the same brand geometry and contact pressure but varying contact times (5, 7, and 10 seconds) in in vivo, pre-clinical rat models (n=3) over a period of 3 days. Though all burn wounds were evaluated to be deep partial thickness with histology, THz contrasts observed for each burn contact time were intrinsically unique. This is the first preliminary in vivo evidence of a many-to-one relationship between changes in THz contrast and burn severity as ascertained by histology. Future large-scale studies are required to assess whether these observed changes in THz contrast may be interpreted as physiological changes occurring over time, morphometric changes related to anatomical change, or electromagnetic changes between dielectric substrate windows and the underlying tissue.

  5. Nanowires for THz Spectroscopy

    DTIC Science & Technology

    2013-10-01

    03-D-0009 Mansoor Sheik- Bahae Prepared by: OVPR/ University Strategic Partnership MSC02 1660 1 University of New Mexico Albuquerque, New...Z39.18 00-10-2013 Technical 07/21/2010 - 04/30/2012 Nanowires for THz Spectroscopy HDTRA1-03-D-0009 Mansoor Sheik- Bahae 3 26 OVPR/University Strategic...kilogram (C/kg) second (s) kilogram (kg) kilo pascal (kPa) 3 TABLE OF CONTENTS: I . Introduction ………....…………………………………………………… 01 II

  6. THz spectroscopy of polar liquids

    NASA Astrophysics Data System (ADS)

    Libon, Imke. H.; Hempel, M.; Seitz, S.; Hecker, Nancy E.; Feldmann, Jochen; Hayd, A.; Zundel, G.; Mittleman, Daniel; Koch, M.

    1999-04-01

    The mesoscopic structure of water has long been a subject of discussion. We postulate that, on the mesoscopic scale, liquid water forms nm-size ice-like crystals and that his structure is responsible for absorption in the THz-frequency range. However, until the recent development of Thz-time domain spectroscopy (THz-TDS), it was difficult to determine the optical constants in this frequency range with a good signal-to-noise ratio and hence to study the absorption properties of water. Here we report on the optical properties of water in the frequency range 0.05-1.4 THz and discuss the mesoscopic structure of water. We use THz-TDS based on photoconductive dipole antennas gated by a 150 femtosecond laser pulses to generate and detect the THz- frequency pulses. A new theoretical approach is also presented which were use to explain the absorption behavior in the measured THz frequency range. In this theory, molecular plasma oscillations of H3O2 complexes, that are distinctly separate from the H5O2+ complexes which form an underlying crystalline lattice, are assumed to be responsible for absorption in the THz- frequency range. This model provides good agreement to our data.

  7. THz stark spectroscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Feurer, Thomas; Rohwer, Egmont; Akbarimoosavi, Maryam

    2016-09-01

    Stark spectroscopy has been pioneered many decades ago and is a unique tool to extract information on molecular constants such as changes of dipole moments or polarizabilities upon excitation. Here we introduce a new twist, i.e. THz Stark spectroscopy. In THz fields the electric field vector oscillates on time scales of picoseconds and thus much faster than in conventional Stark spectroscopy. It therefore may allow to distinguish between different electric field contributions by analyzing the dynamics of the THz response. We first demonstrate that conventional THz sources can be boosted by combination with field enhancement structures, reaching field strength of GV/m driving several different materials into the nonlinear response regime. Then we discuss THz fields influencing charge transfer in different molecules.

  8. Optically-electrically pumped THz source

    NASA Astrophysics Data System (ADS)

    Haji-Saeed, Bahareh; Khoury, Jed; Buchwald, Walter; Woods, Charles; Wentzell, Sandra; Krejca, Brian; Kierstead, John

    2010-08-01

    In this paper, we propose a design for a widely tunable solid-state optically and electrically pumped THz source based on the Smith-Purcell free-electron laser. Our design consists of a thin dielectric layer sandwiched between an upper corrugated structure and a lower layer of thin metal, semiconductor, or high electron mobility material. The lower layer is for current streaming, which replaces the electron beam in the Smith-Purcell free-electron laser design. The upper layer consists of two micro-gratings for optical pumping, and a nano-grating to couple with electrical pumping in the lower layer. The optically generated surface plasmon waves from the upper layer and the electrically induced surface plasmon waves from the lower layer are then coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

  9. High Absorptance Coatings for THz Applications

    NASA Technical Reports Server (NTRS)

    Wollack, Edward J.

    2012-01-01

    High absorptance materials find application throughout the electromagnetic spectrum as radiation terminations, calibration standards, and glint reduction coatings. Successful use of materials at millimeter through submillimeter wavelengths requires an accurate knowledge and control over their thermal, mechanical, and electromagnetic properties in order to achieve the desired response while minimizing mass and volume. In practice, the achieved blackness is intimately linked to the material properties and geometry. Here, we summarize the characteristics of a variety of tunable artificial dielectric mixtures appropriate for THz applications at room and cryogenic temperatures. Theoretical guidelines for their application will be provided in the context of the effective-medium mean-field-approximation. The performance of these coatings as elements of reflectance standards, radiometric flux calibrators, passive thermal radiators, and stray light suppression baffles for imaging systems will be reviewed.

  10. THz spectroscopy of the atmosphere

    NASA Astrophysics Data System (ADS)

    Pickett, Herbert M.

    1999-04-01

    THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing.THe IR region near 3 micrometers requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH result from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the microwave limb sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on 24 May 1998. Results from this flight will be presented.

  11. THz Spectroscopy of the Atmosphere

    NASA Technical Reports Server (NTRS)

    Pickett, Herbert M.

    2000-01-01

    THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing. The infrared region near 3 microns suffers from chemiluminescence and from spectral contamination due to water. The ultraviolet region near 300 nm requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH results from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the Microwave Limb Sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on, 24 May 1998. Results form this flight will be presented.

  12. Sapphire decelerating capillary channel integrated with antenna at frequency 0.675 THz

    NASA Astrophysics Data System (ADS)

    Ashanin, I. A.; Polozov, S. M.

    2016-07-01

    In recent years, there has been an increasing interest in THz-radiation for application in medicine (THz tomographs), in pharmaceutics (composition analysis for medicines), in introscopy of large-scale objects (ships, trains, containers) and others. THz-radiation can be generated by relativistic electron bunches passing through the Cherenkov decelerating capillary channel (circular waveguide with dielectric filling) with horn extraction. Relativistic electron beams having ∼100 µm in diameter and pulse durations of 1 ps or less (as in photoinjectors) are capable of producing substantial power of THz-radiation. High-peak power coherent Cherenkov radiation can be produced by a properly modulated high-brightness electron beam or by a single, high-density bunch having sub-wavelength dimension. The aperture of a Cherenkov decelerating structure should be comparable with the mm or sub-mm wavelength (0.1-3 mm). Different dielectric materials for the internal surface coating of the capillary channel of mm-sub-mm cross-section can be used. As is known, a frequency of 0.675 THz corresponds to the atmospheric window with high transparency. This report presents the results of electrodynamics study of the metallized sapphire decelerating Cherenkov capillary. A horn antenna attached to the metallized sapphire capillary channel at the 0.675 THz resonant frequency will be considered.

  13. Surface plasmon-polariton resonance at diffraction of THz radiation on semiconductor gratings

    NASA Astrophysics Data System (ADS)

    Spevak, I. S.; Kuzmenko, A. A.; Tymchenko, M.; Gavrikov, V. K.; Shulga, V. M.; Feng, J.; Sun, H. B.; Kamenev, Yu. E.; Kats, A. V.

    2016-08-01

    Resonance diffraction of THz hidrogen cyanide laser radiation on a semiconductor (InSb) grating is studied both experimentally and theoretically. The specular reflectivity suppression due to the resonance excitation of the THz surface plasmon-polariton is observed on a pure semiconductor grating and on semiconductor gratings covered with a thin dielectric layer. The dielectric coating of the grating results in the resonance shift and widening depending both on the layer thickness and dielectric properties. A simple analytical theory of the resonance diffraction on rather shallow gratings covered with a dielectric layer is presented, and the results are in a good accordance with the experimental data. Analytical expressions for the resonance shift and broadening are essential for the resonance properties understanding and useful for sensing data interpretation of the agents deposited on the grating surface.

  14. THz-metamaterial absorbers

    NASA Astrophysics Data System (ADS)

    Tuong Pham, Van; Park, J. W.; Vu, Dinh Lam; Zheng, H. Y.; Rhee, J. Y.; Kim, K. W.; Lee, Y. P.

    2013-03-01

    An ultrabroad-band metamaterial absorber was investigated in mid-IR regime based on a similar model in previous work. The high absorption of metamaterial was obtained in a band of 8-11.7 THz with energy loss distributed in SiO2, which is appropriate potentially for solar-cell applications. A perfect absorption peak was provided by using a sandwich structure with periodical anti-dot pattern in the IR region, getting closed to visible-band metamaterials. The dimensional parameters were examined for the corresponding fabrication. Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology, 30 October-2 November, 2012, Ha Long, Vietnam.

  15. Conceiving THz endometrial ablation: feasibility, requirements and technical challenges.

    PubMed

    Neelakanta, Perambur S; Sharma, Bharti

    2013-07-01

    Shallow-ablation of endometrial lining using microwaves has been traditionally indicated as a minimally invasive treatment option for dysfunctional uterine bleeding (DUB). Known as microwave endometrial ablation (MEA), relevant procedure is used as an alternative to hysterectomy considering its safety, simplicity and effectiveness. In lieu of the prevailing MEA techniques, it is attempted in this study to foresee the possibility of conceiving an alternative and a newer option on endometrial ablation using mm-wave/THz frequencies. Commensurate with this motivated impetus, objectively considered are merits and design issues of using electromagnetic (EM) spectrum of mm-wave/THz region toward optimal conversion of EM energy into a thermal ablative source so that, the basal layer of endometrium can be effectively destroyed in surgical contexts as necessary. Hence, the feasibility of designing appropriate TEA applicators for controlled and safe procedures so as to ablate just the unwanted tissues within a localized zone of energy field is addressed. Lastly, a quantitative analysis on the interaction of THz EM-energy versus the lossy dielectric characteristics of endometrial medium is indicated to model the underlying (THz-energy)-to-(thermal energy) transduction. Relevant prospects of conceiving TEA and the associated pros and cons are identified specific to the prospects of feasibility, requirement considerations and technical challenges.

  16. Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy

    SciTech Connect

    Minami, Yasuo; Horiuchi, Kohei; Masuda, Kaisei; Takeda, Jun; Katayama, Ikufumi

    2015-10-26

    We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si plate was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.

  17. Compact High Power THz Source

    SciTech Connect

    Geoffrey Krafft

    2003-08-01

    In this paper a new type of THz radiation source, based on recirculating an electron beam through a high gradient superconducting radio frequency cavity, and using this beam to drive a standard electromagnetic undulator, is discussed. Because the beam is recirculated, short bunches may be produced that radiate coherently in the undulator, yielding high average THz power for relatively low average beam power. Deceleration from the coherent emission, and the detuning it causes is discussed.

  18. Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe₃O₄ nano-fillers: an interface-mediated superior dielectric and EMI shielding performance.

    PubMed

    Rao, B V Bhaskara; Yadav, Prasad; Aepuru, Radhamanohar; Panda, H S; Ogale, Satishchandra; Kale, S N

    2015-07-28

    In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm(-3) is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA-SLGAPC-Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz-10 MHz, enhanced by a factor of 4 as compared to that of the PVA-SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell-Wagner-Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2-12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm(-3))(-1), indicating the promising character of this material for flexible EMI shielding applications.

  19. Frequency Selective Surface Based Bandpass Filter for THz Communication System

    NASA Astrophysics Data System (ADS)

    Das, Subrata; Reza, Khan Mamun; Habib, Md. Ahsan

    2012-11-01

    In this work, a band pass filter based on frequency selective surface (FSS) is presented. The resonance of the FSS is achieved by perforating slot type ring structure on an Aluminum layer. To ensure adequate mechanical strength, this structure is again supported by a dielectric layer. The physical dimensions of the FSS, i.e. ring radius, slot width, cell dimension and width of the layers all are responsible for the resonance behavior. In its electrical equivalent circuit, these dimensions act as inductor and capacitor. The center frequency of the designed filter is at 0.16 THz with a -3 dB bandwidth of 18 GHz. This filter can be utilized as a part of any THz communication system to achieve application specific frequency discrimination. The simulation has been carried by using commercial software-CST Microwave Studio. The performance of the fabricated FSS is evaluated by Microwave Vector Network Analyzer.

  20. Compact electron acceleration and bunch compression in THz waveguides.

    PubMed

    Wong, Liang Jie; Fallahi, Arya; Kärtner, Franz X

    2013-04-22

    We numerically investigate the acceleration and bunch compression capabilities of 20 mJ, 0.6 THz-centered coherent terahertz pulses in optimized metallic dielectric-loaded cylindrical waveguides. In particular, we theoretically demonstrate the acceleration of 1.6 pC and 16 pC electron bunches from 1 MeV to 10 MeV over an interaction distance of 20mm, the compression of a 1.6 pC 1 MeV bunch from 100 fs to 2 fs (50 times compression) over an interaction distance of about 18mm, and the compression of a 1.6 pC 10 MeV bunch from 100 fs to 1.61 fs (62 times) over an interaction distance of 42 cm. The obtained results show the promise of coherent THz pulses in realizing compact electron acceleration and bunch compression schemes.

  1. THz time domain sensing and imaging

    NASA Astrophysics Data System (ADS)

    Cheville, R. A.; Reiten, Matthew T.; O'Hara, John; Grischkowsky, Daniel R.

    2004-09-01

    Over the past decade the experimental technique of THz time domain spectroscopy (THz-TDS) has proved to be a versatile method for investigating a wide range of phenomena in the THz or far infrared spectral region from 100 GHz to 5 THz. THz-TDS has wide potential for sensing and imaging. The experimental technique is described along with recent results on THz beam propagation for long base-line THz measurements. THz imaging has been demonstrated using both quasi-optical and synthetic aperture approaches, results are presented including images of scatterers as well as non-destructive evaluation of ceramics. Two potential sensing applications of THz-TDS are discussed, thin film characterization and use of waveguides for sensing.

  2. THz Local Oscillator Sources

    NASA Astrophysics Data System (ADS)

    Mehdi, Imran; Schlecht, Erich; Chattopadhyay, Goutam; Siegel, Peter H.

    Most operational Submillimeter-wave radio telescopes, both space borne and ground based, employ local oscillator sources based on Gunn diodes followed by whisker contacted Schottky multipliers. Enough progress, however, has been made on a number of fronts to conclude that next generation of radio telescopes that become operational in the new Millennium will have a different local oscillator (LO) generation architecture. MMIC power amplifiers with impressive gain in the Ka- to-W band have enabled the use of microwave synthesizers which can then be actively multiplied to provide a frequency agile power source beyond 100 GHz. This medium power millimeter source can then be amplified to enable efficient pumping of follow-on balanced multiplier stages. Input power to the multipliers can be further enhanced by power combining to achieve close to half a Watt at W-band. An 800 GHz three-stage multiplier chain, implemented this way has demonstrated a peak output power of 1 mW. A second advance in LO generation lies in the Schottky diode varactor technology. Planar Schottky diode multipliers have now been demonstrated up to 1500 GHz and it can be assumed that most of the future multiplier chains will be based on these robust devices rather than the whisker contacted diode of the past. The ability to produce planar GaAs diode chips deep into the THz range, with submicron dimensions, has opened up a wide range of circuit design space which can be taken advantage of to improve efficiency, bandwidth, and power handling capability of the multipliers. A third breakthrough has been the demonstration of photonic based LO sources utilizing GaAs photomixers. These sources, though not yet implemented in robust space borne missions, offer a number of advantages over their electronic counterparts, including extremely broad tuning, fiber coupled components, and solid-state implementation. Another development, which holds some promise, is the use of micro-machining technology to implement

  3. Electrodynamic model of the field effect transistor application for THz/subTHz radiation detection: Subthreshold and above threshold operation

    SciTech Connect

    Dobrovolsky, V.

    2014-10-21

    Developed in this work is an electrodynamic model of field effect transistor (FET) application for THz/subTHz radiation detection. It is based on solution of the Maxwell equations in the gate dielectric, expression for current in the channel, which takes into account both the drift and diffusion current components, and the equation of current continuity. For the regimes under and above threshold at the strong inversion the response voltage, responsivity, wave impedance, power of ohmic loss in the gate and channel have been found, and the electrical noise equivalent power (ENEP) has been estimated. The responsivity is orders of magnitude higher and ENEP under threshold is orders of magnitude less than these values above threshold. Under the threshold, the electromagnetic field in the gate oxide is identical to field of the plane waves in free-space. At the same time, for strong inversion the charging of the gate capacitance through the resistance of channel determines the electric field in oxide.

  4. Monolithic THz Frequency Multipliers

    NASA Technical Reports Server (NTRS)

    Erickson, N. R.; Narayanan, G.; Grosslein, R. M.; Martin, S.; Mehdi, I.; Smith, P.; Coulomb, M.; DeMartinez, G.

    2001-01-01

    Frequency multipliers are required as local oscillator sources for frequencies up to 2.7 THz for FIRST and airborne applications. Multipliers at these frequencies have not previously been demonstrated, and the object of this work was to show whether such circuits are really practical. A practical circuit is one which not only performs as well as is required, but also can be replicated in a time that is feasible. As the frequency of circuits is increased, the difficulties in fabrication and assembly increase rapidly. Building all of the circuit on GaAs as a monolithic circuit is highly desirable to minimize the complexity of assembly, but at the highest frequencies, even a complete monolithic circuit is extremely small, and presents serious handling difficulty. This is compounded by the requirement for a very thin substrate. Assembly can become very difficult because of handling problems and critical placement. It is very desirable to make the chip big enough to that it can be seen without magnification, and strong enough that it may be picked up with tweezers. Machined blocks to house the chips present an additional challenge. Blocks with complex features are very expensive, and these also imply very critical assembly of the parts. It would be much better if the features in the block were as simple as possible and non-critical to the function of the chip. In particular, grounding and other electrical interfaces should be done in a manner that is highly reproducible.

  5. CVD Diamond Dielectric Accelerating Structures

    SciTech Connect

    Schoessow, P.; Kanareykin, A.; Gat, R.

    2009-01-22

    The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

  6. Ceramic dielectric mirrors for the terahertz range.

    PubMed

    Rutz, Frank; Koch, Martin; Micele, Lorenzo; de Portu, Goffredo

    2006-11-01

    We have produced a rigid dielectric terahertz mirror by tape casting and sintering 25 stacked ceramic layers of alumina and alumina-zirconia. Our structure shows a pronounced stop band between 0.3 and 0.38 THz. The experimental data agree well with transfer matrix calculations.

  7. THz Dynamic Nuclear Polarization NMR

    PubMed Central

    Nanni, Emilio A.; Barnes, Alexander B.; Griffin, Robert G.; Temkin, Richard J.

    2013-01-01

    Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140–600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology. PMID:24639915

  8. THz Dynamic Nuclear Polarization NMR.

    PubMed

    Nanni, Emilio A; Barnes, Alexander B; Griffin, Robert G; Temkin, Richard J

    2011-08-29

    Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140-600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology.

  9. Dielectric response of the human tooth dentine

    NASA Astrophysics Data System (ADS)

    Leskovec, J.; Filipič, C.; Levstik, A.

    2005-07-01

    Dielectric properties of tooth dentine can be well described by the model which was developed for the dielectric response to hydrating porous cement paste. It is shown that the normalized dielectric constant and the normalized specific conductivity are proportional to the model parameters ɛ and σv, indicating the deposition of AgCl in the dentine tubules during the duration of the precipitation. The fractal dimension of the tooth dentine was determined by dielectric spectroscopy.

  10. Coherent THz Pulses from Linear Accelerators

    SciTech Connect

    G.L. Carr; H. Loos; J.B. Murphy; T. Shaftan; B. Sheehy; X.-J. Wang; W.R. McKinney; M.C. Martin; G.P. Williams; K. Jordan; G. Neil

    2003-10-01

    Coherent THz pulses are being produced at several facilities using relativistic electrons from linear accelerators. The THz pulses produced at the Brookhaven accelerator have pulse energies exceeding 50 {micro}J and reach a frequency of 2 THz. The high repetition rate of the Jefferson Lab accelerator leads to an average THz power of 20 watts. Possible uses for these high power pulses are discussed.

  11. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

    PubMed Central

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

    2017-01-01

    The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy. PMID:28262731

  12. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

    NASA Astrophysics Data System (ADS)

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

    2017-03-01

    The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

  13. Laser Micromachining of THz Components

    DTIC Science & Technology

    2000-09-29

    such an instrument [3] for use on the Large Binocular Telescope now being constructed on Mount Graham, Arizona. Before operation the cell is evacuated...micromachined, 2 THz array receiver being developed for SOFIA, the Stratospheric Observatory for Far Infrared •: Astronomy [3]. Test feedhorns for the array

  14. H2/N2 plasma damage on porous dielectric SiOCH film evaluated by in situ film characterization and plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hiroshi; Takeda, Keigo; Ishikawa, Kenji; Ito, Masafumi; Sekine, Makoto; Hori, Masaru; Kaminatsui, Takeshi; Hayashi, Hisataka; Sakai, Itsuko; Ohiwa, Tokuhisa

    2011-04-01

    This study investigates the mechanism of H2/N2 plasma ashing damage of porous SiOCH films. Porous SiOCH films were treated by a H2/N2 plasma using a 100-MHz capacitively coupled plasma etcher. The impact of ions, radicals, and vacuum ultraviolet radiation on the porous SiOCH films was investigated using in situ bulk analysis techniques such as spectroscopic ellipsometry and Fourier-transform infrared spectroscopy and ex situ film characterization techniques such as dynamic secondary ion mass spectrometry and x-ray photoelectron spectroscopy. In addition, plasma analysis including vacuum ultraviolet absorption spectroscopy was performed. The film characterization and plasma analysis show that the extraction of methyl by H radicals was enhanced by light while N radicals were responsible for inhibit the extraction of Si-CH3 bonds by forming nitride layer. The H2/N2 plasma damage mechanism is discussed based on characterization of the film and plasma diagnostics.

  15. Evaluation of SiO2@CoFe2O4 nano-hollow spheres through THz pulses

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Pal, Monalisa; Serita, Kazunori; Chaudhuri, Arka; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-05-01

    We have synthesized cobalt ferrite (CFO) nanoparticles (NPs) of diameter 100 nm and nano-hollow spheres (NHSs) of diameter 100, 160, 250, and 350 nm by a facile one step template free solvothermal technique and carried out SiO2 coating on their surface following Stöber method. The phase and morphology of the nanostructures were confirmed by X-ray diffraction and transmission electron microscope. The magnetic measurements were carried out by vibrating sample magnetometer in order to study the influence of SiO2 coating on the magnetic properties of bare CFO nanostructures. Furthermore, we have applied THz time domain spectroscopy to investigate the THz absorption property of these nanostructures in the frequency range 1.0-2.5 THz. Detailed morphology and size dependent THz absorption study unfolds that the absorption property of these nanostructures sensitively carries the unique signature of its dielectric property.

  16. Long-range guided THz radiation by thin layers of water.

    PubMed

    Sczech, Robert; Rivas, Jaime Gómez; Berrier, Audrey; Giannini, Vincenzo; Pirruccio, Giuseppe; Debus, Christian; Schäfer-Eberwein, Heiko; Bolívar, Peter Haring

    2012-12-03

    We propose a novel method to guide THz radiation with low losses along thin layers of water. This approach is based on the coupling of evanescent surface fields at the opposite sides of the thin water layer surrounded by a dielectric material, which leads to a maximum field amplitude at the interfaces and a reduction of the energy density inside the water film. In spite of the strong absorption of water in this frequency range, calculations show that the field distribution can lead to propagation lengths of several centimeters. By means of attenuated total reflection measurements we demonstrate the coupling of incident THz radiation to the long-range surface guided modes across a layer of water with a thickness of 24 μm. This first demonstration paves the way for THz sensing in aqueous environments.

  17. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

    NASA Astrophysics Data System (ADS)

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

    2017-01-01

    The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process.

  18. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation.

    PubMed

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

    2017-01-09

    The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process.

  19. Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

    PubMed Central

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Vâţã, Ion

    2017-01-01

    The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process. PMID:28067289

  20. Dispersion of carbon nanotubes in melt compounded polypropylene based composites investigated by THz spectroscopy.

    PubMed

    Casini, R; Papari, G; Andreone, A; Marrazzo, D; Patti, A; Russo, P

    2015-07-13

    We investigate the use of Terahertz (THz) Time Domain Spectroscopy (TDS) as a tool for the measurement of the index dispersion of multi-walled carbon nanotubes (MWCNT) in polypropylene (PP) based composites. Samples containing 0.5% by volume concentration of non-functionalized and functionalized carbon nanotubes are prepared by melt compounding technology. Results indicate that the THz response of the investigated nanocomposites is strongly dependent on the kind of nanotube functionalization, which in turn impacts on the level of dispersion inside the polymer matrix. We show that specific dielectric parameters such as the refractive index and the absorption coefficient measured by THz spectroscopy can be both correlated to the index of dispersion as estimated using conventional optical microscopy.

  1. Improvement of passive THz camera images

    NASA Astrophysics Data System (ADS)

    Kowalski, Marcin; Piszczek, Marek; Palka, Norbert; Szustakowski, Mieczyslaw

    2012-10-01

    Terahertz technology is one of emerging technologies that has a potential to change our life. There are a lot of attractive applications in fields like security, astronomy, biology and medicine. Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. The reasons of this fact were difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. The THz waves can penetrate through various materials. However, automated processing of THz images can be challenging. The THz frequency band is specially suited for clothes penetration because this radiation does not point any harmful ionizing effects thus it is safe for human beings. Strong technology development in this band have sparked with few interesting devices. Even if the development of THz cameras is an emerging topic, commercially available passive cameras still offer images of poor quality mainly because of its low resolution and low detectors sensitivity. Therefore, THz image processing is very challenging and urgent topic. Digital THz image processing is a really promising and cost-effective way for demanding security and defense applications. In the article we demonstrate the results of image quality enhancement and image fusion of images captured by a commercially available passive THz camera by means of various combined methods. Our research is focused on dangerous objects detection - guns, knives and bombs hidden under some popular types of clothing.

  2. Complex Oxide Thin Film Metamaterial Structures for THz applications

    NASA Astrophysics Data System (ADS)

    Shreiber, D.; Cravey, R.; Cole, M. W.

    2013-03-01

    Metamaterials operating in the frequency range of 0.1-1.5 THz are of a special interest for multiple Army applications such as communications, NDE of materials, and detection of chem./bio hazards. Recently proposed dielectric metamaterials present an intriguing venue for the developments in this field due to their low propagation losses and ease of fabrication. These dielectric metamaterials were implemented in bulk and in thick films. Tunability of ferroelectric complex oxides is achieved by applied bias voltage and constitutes an additional benefit for multiple applications. However, real-life applications require usage of relatively low bias voltage which is achievable only by using a ferroelectric complex oxide thin-film. Although the physical dimensions of the thin film metamaterial structures suggest their usage in IR-optical spectrum, their very high dielectric constant provides a rare opportunity to lower their resonant frequency to the frequency range of interest. This presentation will discuss the opportunities and challenges associated with the metamaterial complex oxide thin film structures including numerical investigations of the resonant frequency shift as a function of the complex oxide thin film dielectric constant and thickness.

  3. Photo-generated THz antennas

    PubMed Central

    Georgiou, G.; Tyagi, H. K.; Mulder, P.; Bauhuis, G. J.; Schermer, J. J.; Rivas, J. Gómez

    2014-01-01

    Electromagnetic resonances in conducting structures give rise to the enhancement of local fields and extinction efficiencies. Conducting structures are conventionally fabricated with a fixed geometry that determines their resonant response. Here, we challenge this conventional approach by demonstrating the photo-generation of THz linear antennas on a flat semiconductor layer by the structured optical illumination through a spatial light modulator. Free charge carriers are photo-excited only on selected areas, which enables the realization of different conducting antennas on the same sample by simply changing the illumination pattern, thus without the need of physically structuring the sample. These results open a wide range of possibilities for the all-optical spatial control of resonances on surfaces and the concomitant control of THz extinction and local fields. PMID:24394920

  4. Frequency dependent optical and dielectric properties of zinc sulfide in Terahertz regime

    NASA Astrophysics Data System (ADS)

    Ganti, Satya R.; Sundaram, S. K.; McCloy, John S.

    2014-07-01

    Frequency dependent optical and dielectric properties for several grades of chemical vapor deposited (CVD) zinc sulfide (standard, elemental, and multi-spectral) was performed using a terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.15 THz to 2.5 THz. Zinc sulfide exhibits low frequency vibrational modes characterized by the THz-TDS. Two low-frequency phonon resonance lines were revealed at 0.78 THz and 2.20 THz. These samples were also characterized in the GHz range using a backward wave oscillator (BWO) source quasi-optical spectrometer, and the data obtained by both approaches were compared. Experimental data were also compared with an undamped harmonic oscillator model. These results compare well with the literature values obtained using other methods.

  5. Technological customization of uncooled amorphous silicon microbolometer for THz real time imaging

    NASA Astrophysics Data System (ADS)

    Pocas, S.; Deronzier, E.; Brianceau, P.; Imperinetti, P.; Dumont, G.; Roule, A.; Rabaud, W.; Meilhan, J.; Simoens, F.; Goudon, V.; Vialle, Claire; Arnaud, A.

    2013-03-01

    Terahertz uncooled antenna-coupled microbolometer focal plane arrays are being developed at CEA Leti for real time THz imaging and sensing. This detector relies on LETI amorphous silicon uncooled infrared bolometer technology that has been deeply modified to optimize sensitivity in the THz range. The main technological key lock of the pixel structure is the quarter wavelength cavity that consists in a thick dielectric layer deposited over the metalized CMOS wafer; such cavity improves significantly the optical coupling efficiency. Copper plugs connect the microbolometer level down to the CMOS readout circuit (ROIC) upper metal pads through this thick dielectric cavity. This paper explains how we have improved the copper vias technology and the challenges we have faced to customize the microbolometer while keeping a monolithically above IC technology fully compatible with standard silicon processes. The results show a very good operability and reproducibility of the contact through this thick oxide cavity. Due to these good results, we have been able to characterize a very efficient THz absorption that enables real time imaging with high sensitivity in the 1-3 THz range.

  6. A compact THz imaging system

    NASA Astrophysics Data System (ADS)

    Sešek, Aleksander; Å vigelj, Andrej; Trontelj, Janez

    2015-03-01

    The objective of this paper is the development of a compact low cost imaging THz system, usable for observation of the objects near to the system and also for stand-off detection. The performance of the system remains at the high standard of more expensive and bulkiest system on the market. It is easy to operate as it is not dependent on any fine mechanical adjustments. As it is compact and it consumes low power, also a portable system was developed for stand-off detection of concealed objects under textile or inside packages. These requirements rule out all optical systems like Time Domain Spectroscopy systems which need fine optical component positioning and requires a large amount of time to perform a scan and the image capture pixel-by-pixel. They are also almost not suitable for stand-off detection due to low output power. In the paper the antenna - bolometer sensor microstructure is presented and the THz system described. Analysis and design guidelines for the bolometer itself are discussed. The measurement results for both near and stand-off THz imaging are also presented.

  7. Electrical characterization and dielectric impedance of Au/n-CdS/p-porous GaAs/p++-GaAs thin film structures

    NASA Astrophysics Data System (ADS)

    Hamdaoui, Nejeh; Beji, Lotfi

    2017-05-01

    Current-voltage, capacitance-voltage-frequency characteristics, and impedance spectroscopy (IS) under conditions of reverse and forward bias are reported in Au/CdS/porous GaAs/GaAs devices. By comparing the C-V and C-f measurements, a possible existence of two depletion layers in our structure is discussed. In contrast to the typically expected parallel association of resistive and capacitive elements, an equivalent circuit is extracted from impedance plots, which employs the constant phase element and accounts for trap states and frequency dispersion. IS makes it possible not only to clarify the contribution of additional capacitive component due to the porous GaAs/GaAs interface by using an appropriate equivalent circuit model analysis but also to estimate a more reliable capacitance value of every junction in the structure.

  8. Non-invasive Florentine Renaissance Panel Painting Replica Structures Investigation by Using Terahertz Time-Domain Imaging (THz-TDI) Technique

    NASA Astrophysics Data System (ADS)

    Koch Dandolo, Corinna L.; Picollo, Marcello; Cucci, Costanza; Jepsen, Peter Uhd

    2016-11-01

    The potentials of the Terahertz Time-Domain Imaging (THz-TDI) technique for a non-invasive inspection of panel paintings have been considered in detail. The THz-TD data acquired on a replica of a panel painting made in imitation of Italian Renaissance panel paintings were processed in order to provide insights as to the limits and potentials of the technique in detecting different kinds of underdrawings and paint layers. Constituent layers, construction techniques, and anomalies were identified and localized by interpreting the extracted THz dielectric stratigraphy.

  9. Enhancing the low frequency THz resonances (< 1 THz) of organic molecules via electronegative atom substitution

    NASA Astrophysics Data System (ADS)

    Dash, Jyotirmayee; Ray, Shaumik; Pesala, Bala

    2015-03-01

    Terahertz (THz) technology is an active area of research with various applications in non-intrusive imaging and spectroscopy. Very few organic molecules have significant resonances below 1 THz. Understanding the origin of low frequency THz modes in these molecules and their absence in other molecules could be extremely important in design and engineering molecules with low frequency THz resonances. These engineered molecules can be used as THz tags for anti-counterfeiting applications. Studies show that low frequency THz resonances are commonly observed in molecules having higher molecular mass and weak intermolecular hydrogen bonds. In this paper, we have explored the possibility of enhancing the strength of THz resonances below 1 THz through electronegative atom substitution. Adding an electronegative atom helps in achieving higher hydrogen bond strength to enhance the resonances below 1 THz. Here acetanilide has been used as a model system. THz-Time Domain Spectroscopy (THz-TDS) results show that acetanilide has a small peak observed below 1 THz. Acetanilide can be converted to 2-fluoroacetanilide by adding an electronegative atom, fluorine, which doesn't have any prominent peak below 1 THz. However, by optimally choosing the position of the electronegative atom as in 4-fluoroacetanilide, a significant THz resonance at 0.86 THz is observed. The origin of low frequency resonances can be understood by carrying out Density Functional Theory (DFT) simulations of full crystal structure. These studies show that adding an electronegative atom to the organic molecules at an optimized position can result in significantly enhanced resonances below 1 THz.

  10. Efficient power combiner for THz radiation

    SciTech Connect

    Seidfaraji, Hamide Fuks, Mikhail I.; Christodoulou, Christos; Schamiloglu, Edl

    2016-08-15

    Most dangerous explosive materials, both toxic and radioactive, contain nitrogen salts with resonant absorption lines in the frequency range 0.3-10 THz. Therefore, there has been growing interest in remotely detecting such materials by observing the spectrum of reflected signals when the suspicious material is interrogated by THz radiation. Practical portable THz sources available today generate only 20–40 mW output power. This power level is too low to interrogate suspicious material from a safe distance, especially if the material is concealed. Hence, there is a need for sources that can provide greater power in the THz spectrum. Generating and extracting high output power from THz sources is complicated and inefficient. The efficiency of vacuum electronic microwave sources is very low when scaled to the THz range and THz sources based on scaling down semiconductor laser sources have low efficiency as well, resulting in the well known “THz gap.” The reason for such low efficiencies for both source types is material losses in the THz band. In this article an efficient power combiner is described that is based on scaling to higher frequencies a microwave combiner that increases the output power in the THz range of interest in simulation studies. The proposed power combiner not only combines the THz power output from several sources, but can also form a Gaussian wavebeam output. A minimum conversion efficiency of 89% with cophased inputs in a lossy copper power combiner and maximum efficiency of 100% in a Perfect Electric Conductor (PEC)-made power combiner were achieved in simulations. Also, it is shown that the TE{sub 01} output mode is a reasonable option for THz applications due to the fact that conductive loss decreases for this mode as frequency increases.

  11. H{sub 2}/N{sub 2} plasma damage on porous dielectric SiOCH film evaluated by in situ film characterization and plasma diagnostics

    SciTech Connect

    Yamamoto, Hiroshi; Takeda, Keigo; Ishikawa, Kenji; Hori, Masaru; Ito, Masafumi; Sekine, Makoto; Kaminatsui, Takeshi; Hayashi, Hisataka; Sakai, Itsuko; Ohiwa, Tokuhisa

    2011-04-15

    This study investigates the mechanism of H{sub 2}/N{sub 2} plasma ashing damage of porous SiOCH films. Porous SiOCH films were treated by a H{sub 2}/N{sub 2} plasma using a 100-MHz capacitively coupled plasma etcher. The impact of ions, radicals, and vacuum ultraviolet radiation on the porous SiOCH films was investigated using in situ bulk analysis techniques such as spectroscopic ellipsometry and Fourier-transform infrared spectroscopy and ex situ film characterization techniques such as dynamic secondary ion mass spectrometry and x-ray photoelectron spectroscopy. In addition, plasma analysis including vacuum ultraviolet absorption spectroscopy was performed. The film characterization and plasma analysis show that the extraction of methyl by H radicals was enhanced by light while N radicals were responsible for inhibit the extraction of Si-CH{sub 3} bonds by forming nitride layer. The H{sub 2}/N{sub 2} plasma damage mechanism is discussed based on characterization of the film and plasma diagnostics.

  12. Fabrication of THz Sensor with Metamaterial Absorber

    NASA Astrophysics Data System (ADS)

    Gonzalez, Hugo; Alves, Fabio; Karunasiri, Gamani

    The terahertz (THz) portion of the electromagnetic spectrum (0.1-10 THz) has not been fully utilized due to the lack of sensitive detectors. Real-time imaging in this spectral range has been demonstrated using uncooled infrared microbolometer cameras and external illumination provided by quantum cascade laser (QCL) based THz sources. However, the microbolometer pixels in the cameras have not been optimized to achieve high sensitivity in THz frequencies. Recently, we have developed a highly sensitive micromechanical THz sensor employing bi-material effect with an integrated metamaterial absorber tuned to the THz frequency of interest. The use of bi-material structures causes deflection on the sensor to as the absorbed THz radiation increases its temperature, which can be monitored optically by reflecting a light beam. This approach eliminates the integration of readout electronics needed in microbolometers. The absorption of THz by metamaterial can be tailored by controlling geometrical parameters. The sensors can be fabricated using conventional microelectronic materials and incorporated into pixels to form focal plane arrays (FPAs). In this presentation, characterization and readout of a THz sensor with integrated metamaterial structure will be described. Supported by DoD.

  13. Terahertz (THz) Wireless Systems for Space Applications

    NASA Technical Reports Server (NTRS)

    Hwu, Shian U.; deSilva, Kanishka B.; Jih, Cindy T.

    2013-01-01

    NASA has been leading the Terahertz (THz) technology development for the sensors and instruments in astronomy in the past 20 years. THz technologies are expanding into much broader applications in recent years. Due to the vast available multiple gigahertz (GHz) broad bandwidths, THz radios offer the possibility for wireless transmission of high data rates. Multi-Gigabits per second (MGbps) broadband wireless access based on THz waves are closer to reality. The THz signal high atmosphere attenuation could significantly decrease the communication ranges and transmittable data rates for the ground systems. Contrary to the THz applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. The manufacturing technologies for the THz electronic components are advancing and maturing. There is great potential for the NASA future high data wireless applications in environments with difficult cabling and size/weight constraints. In this study, the THz wireless systems for potential space applications were investigated. The applicability of THz systems for space applications was analyzed. The link analysis indicates that MGbps data rates are achievable with compact sized high gain antennas.

  14. Study on the THz spectrum of methamphetamine

    NASA Astrophysics Data System (ADS)

    Ning, Li; Shen, Jingling; Jinhai, Sun; Laishun, Liang; Xu, Xiaoyu; Lu, Meihong; Yan, Jia

    2005-09-01

    The spectral absorption features of methamphetamine (MA), one of the most widely consumed illicit drugs in the world, are studied experimentally by Terahertz (THz) time-domain spectroscopy (THz-TDS), and the characteristic absorption spectra are obtained in the range of 0.2 to 2.6 THz. The vibrational frequencies are calculated using the density functional theory (DFT). Theoretical results show significant agreement with experimental results, and identification of vibrational modes are given. The calculated results further confirm that the characteristic frequencies come from the collective vibrational modes. The results suggest that use of the THz-TDS technique can be an effective way to inspect for illicit drugs.

  15. High-power Broadband Organic THz Generator

    PubMed Central

    Jeong, Jae-Hyeok; Kang, Bong-Joo; Kim, Ji-Soo; Jazbinsek, Mojca; Lee, Seung-Heon; Lee, Seung-Chul; Baek, In-Hyung; Yun, Hoseop; Kim, Jongtaek; Lee, Yoon Sup; Lee, Jae-Hyeok; Kim, Jae-Ho; Rotermund, Fabian; Kwon, O-Pil

    2013-01-01

    The high-power broadband terahertz (THz) generator is an essential tool for a wide range of THz applications. Here, we present a novel highly efficient electro-optic quinolinium single crystal for THz wave generation. For obtaining intense and broadband THz waves by optical-to-THz frequency conversion, a quinolinium crystal was developed to fulfill all the requirements, which are in general extremely difficult to maintain simultaneously in a single medium, such as a large macroscopic electro-optic response and excellent crystal characteristics including a large crystal size with desired facets, good environmental stability, high optical quality, wide transparency range, and controllable crystal thickness. Compared to the benchmark inorganic and organic crystals, the new quinolinium crystal possesses excellent crystal properties and THz generation characteristics with broader THz spectral coverage and higher THz conversion efficiency at the technologically important pump wavelength of 800 nm. Therefore, the quinolinium crystal offers great potential for efficient and gap-free broadband THz wave generation. PMID:24220234

  16. Curvature Control of Silicon Microlens for THz Dielectric Antenna

    NASA Technical Reports Server (NTRS)

    Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran

    2012-01-01

    We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.

  17. Curvature Control of Silicon Microlens for THz Dielectric Antenna

    NASA Technical Reports Server (NTRS)

    Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran

    2012-01-01

    We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.

  18. Dielectric Properties of Diesel and Gasoline by Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Arik, Enis; Altan, Hakan; Esenturk, Okan

    2014-09-01

    In this study we have investigated the dielectric properties of diesel and gasoline in the Terahertz (THz) spectral region. We present frequency dependent absorption coefficients, refractive indices, and dielectric constants calculated from the transient measurements of the fuel oils between 0.1 and 1.1 THz. Observed weak absorption coefficient of fuel oils is explained by transient dipole moments induced by collisions between individual molecules. Fuel oils were modeled successfully with Debye model to investigate the relaxation dynamics after interaction with the electric field. Significant differences in relaxation times of molecules in diesel and gasoline are attributed to the differences in their intermolecular forces. Dispersion forces are much greater in diesel due to the longer hydrocarbon chains (C8-C40) compared to that (C4-C12) of the gasoline. This leads to a comparably faster relaxation right after THz electric field is applied. Clear differences in optical properties offer a simple yet effective way to discriminate fuel oils from each other by using THz spectroscopy without any danger of combustion or decomposition of the samples. Such an approach may also be used for the quality determination of either fuels. The study presents the great potential of THz spectroscopy to study very complex mixtures like fuel oils by the use of instantaneous THz wave/matter interactions and relaxation dynamics of the constituent molecules.

  19. 2D THz-THz-Raman Photon-Echo Spectroscopy of Molecular Vibrations in Liquid Bromoform.

    PubMed

    Finneran, Ian A; Welsch, Ralph; Allodi, Marco A; Miller, Thomas F; Blake, Geoffrey A

    2017-09-13

    Fundamental properties of molecular liquids are governed by long-range interactions that most prominently manifest at terahertz (THz) frequencies. Here we report the detection of nonlinear THz photon-echo (rephasing) signals in liquid bromoform using THz-THz-Raman spectroscopy. Together, the many observed signatures span frequencies from 0.5 to 8.5 THz and result from couplings between thermally populated ladders of vibrational states. The strongest peaks in the spectrum are found to be multiquantum dipole and 1-quantum polarizability transitions and may arise from nonlinearities in the intramolecular dipole moment surface driven by intermolecular interactions.

  20. Surface sealing using self-assembled monolayers and its effect on metal diffusion in porous low-k dielectrics studied using monoenergetic positron beams

    NASA Astrophysics Data System (ADS)

    Uedono, Akira; Armini, Silvia; Zhang, Yu; Kakizaki, Takeaki; Krause-Rehberg, Reinhard; Anwand, Wolfgang; Wagner, Andreas

    2016-04-01

    Surface sealing effects on the diffusion of metal atoms in porous organosilicate glass (OSG) films were studied by monoenergetic positron beams. For a Cu(5 nm)/MnN(3 nm)/OSG(130 nm) sample fabricated with pore stuffing, C4F8 plasma etch, unstuffing, and a self-assembled monolayer (SAM) sealing process, it was found that pores with cubic pore side lengths of 1.1 and 3.1 nm coexisted in the OSG film. For the sample without the SAM sealing process, metal (Cu and Mn) atoms diffused from the top Cu/MnN layer into the OSG film and were trapped by the pores. As a result, almost all pore interiors were covered with those metals. For the sample damaged by an Ar/C4F8 plasma etch treatment before the SAM sealing process, SAMs diffused into the OSG film, and they were preferentially trapped by larger pores. The cubic pore side length in these pores containing self-assembled molecules was estimated to be 0.7 nm. Through this work, we have demonstrated that monoenergetic positron beams are a powerful tool for characterizing capped porous films and the trapping of atoms and molecules by pores.

  1. THz imaging of histo-pathological samples

    NASA Astrophysics Data System (ADS)

    Knobloch, Pascal; Schmalstieg, K.; Koch, Martin; Rehberg, E.; Vauti, F.; Donhuijsen, K.

    2001-10-01

    We investigate the potential of THz imaging for the examination of histo-pathological samples. Data obtained on a pig larynx and on a human liver containing cancerous tissue are presented. Different types of tissue are clearly resolved due to their distinct spectral absorption characteristics or due to a density dependent THz transmission.

  2. Tactical systems applications for THz devices

    SciTech Connect

    McGee, R.A.

    1994-12-31

    Currently several weapons systems use millimeter wave, infrared or both for sensing. THz technology is spectrally located so as to be able to exploit the best features of MMW and infrared technology. The items for discussion are Army needs that could be addressed by THz technology. The emphasis is on active and passive sensing parameters for ``Smart`` munitions and combat vehicles.

  3. High power THz sources for nonlinear imaging

    SciTech Connect

    Tekavec, Patrick F.; Kozlov, Vladimir G.

    2014-02-18

    Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source delivers 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.

  4. Laser Micromachining Fabrication of THz Components

    NASA Technical Reports Server (NTRS)

    DrouetdAubigny, C.; Walker, C.; Jones, B.; Groppi, C.; Papapolymerou, J.; Tavenier, C.

    2001-01-01

    Laser micromachining techniques can be used to fabricate high-quality waveguide structures and quasi-optical components to micrometer accuracies. Successful GHz designs can be directly scaled to THz frequencies. We expect this promising technology to allow the construction of the first fully integrated THz heterodyne imaging arrays. At the University of Arizona, construction of the first laser micromachining system designed for THz waveguide components fabrication has been completed. Once tested and characterized our system will be used to construct prototype THz lx4 focal plane mixer arrays, magic tees, AR coated silicon lenses, local oscillator source phase gratings, filters and more. Our system can micro-machine structures down to a few microns accuracy and up to 6 inches across in a short time. This paper discusses the design and performance of our micromachining system, and illustrates the type, range and performance of components this exciting new technology will make accessible to the THz community.

  5. Majolica imaging with THz waves: preliminary results

    NASA Astrophysics Data System (ADS)

    Catapano, Ilaria; Affinito, Antonio; Guerriero, Luigi; Bisceglia, Bruno; Soldovieri, Francesco

    2016-05-01

    Recent advancements performed in the development of stable and flexible devices working at TeraHertz (THz) frequencies have opened the way at considering this technology as a very interesting noninvasive diagnostic tool in cultural heritage. In this frame, the paper aims at assessing the ability of THz imaging to gather information about preservation state and constructive modalities of majolica artworks. In particular, THz surveys have been carried out on two majolica tiles dated back to the nineteenth century and realized as building cladding at Naples (Italy). The analysis has been performed by means of the Zomega fiber-coupled THz time-domain system. This analysis corroborates the ability of THz to reconstruct irregularities of majolica tile topography, to characterize pigment and glaze losses, and to detect and localize glaze and pigment layer as well as the glaze-clay body interface.

  6. Evanescent-wave proton postaccelerator driven by intense THz pulse

    NASA Astrophysics Data System (ADS)

    Pálfalvi, L.; Fülöp, J. A.; Tóth, Gy.; Hebling, J.

    2014-03-01

    Hadron therapy motivates research dealing with the production of particle beams with ˜100 MeV/nucleon energy and relative energy fluctuation on the order of 1%. Laser-driven accelerators produce ion beams with only tens of MeV /nucleon energy and an extremely broad spectra. Here, a novel method is proposed for postacceleration and monochromatization of particles, leaving the laser-driven accelerator, by using intense THz pulses. It is based on further developing the idea of using the evanescent field of electromagnetic waves between a pair of dielectric crystals. Simple model calculations show that the energy of a proton bunch can be increased from 40 to 56 MeV in five stages and its initially broad energy distribution can be significantly narrowed down.

  7. ASK modulator based on switchable FSS for THz applications

    NASA Astrophysics Data System (ADS)

    Kiani, Ghaffer I.; Bird, Trevor S.

    2011-04-01

    An amplitude shift keying modulator that is based on a switchable frequency selective surface (FSS) is described for THz communication. The FSS uses a square loop aperture geometry, with each unit cell having four PIN diodes across the aperture at 90 degree intervals. To minimize the effect of bias lines on the overall frequency response of the FSS, a crossed-shape negative dc bias line, which is connected to the center of the FSS unit cell, has been placed on the rear surface of the dielectric substrate. Positive dc biasing is provided from the front side of the FSS structure. Simulation results are presented for two possible operating frequencies and two principal polarizations at normal and oblique incidence. These show that a free space modulator based on the proposed FSS structure would provide about 19 dB transmission loss at 600 GHz between on and off states of the PIN diodes for both transverse electric and transverse magnetic polarizations.

  8. Slot-line end-fire antennas for THz frequencies

    NASA Technical Reports Server (NTRS)

    Ekstroem, H.; Gearhart, S.; Acharya, P. R.; Dave, H.; Rebeiz, G.; Jacobsson, S.; Kollberg, E.; Chin, G.

    1992-01-01

    Tapered slot-line endfire antennas, of BLTSA type, have been fabricated on 1.7 micron thin SiO2/Si3N4 (epsilon (sub r) = 4.5) dielectric membranes. The antenna patterns, in the E-, H-, D- and D-cross planes, were measured at 270, 348, 370, and 802 GHz using bismuth micro bolometer detectors. The antennas have approximately 12 dB directivity, and the -10 dB beam widths are 50 and 55 degrees in the E- and H-planes at 348 GHz, respectively. The measurements at millimeter/submillimeter wavelengths compare well with scale measurements at 45 GHz as well as with theoretical predictions. The overall results are encouraging and show that slot-line antennas can be fabricated for use at THz frequencies. Furthermore, it is shown that the very thin SiO2/Si3N4 membranes are strong enough to be used in practical applications.

  9. Strong coupling of THz surface plasmon polaritons to complementary metasurfaces (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Keller, Janine; Paravicini Bagliani, Gian Lorenzo; Haase, Johannes; Maissen, Curdin; Scalari, Giacomo; Faist, Jérôme

    2017-02-01

    We study the transmission of complementary THz split ring resonator (cSRR) arrays with THz time domain spectroscopy. Utilizing complementary THz metasurfaces and, varying the inter meta-atom separation, a regime of resonant coupling to surface plasmon polaritons (SPPs) is entered. The effective medium condition valid for the direct metasurface is not applicable anymore in the complementary case because of the high THz dielectric constant of gold. We observe a normalized strong coupling of 3.5% to the lattice SPP mode when tuned into resonance with the LC-mode of the cSRR at a frequency of 1.07 THz. The lattice constant is varied from 40 um to 160 um. Finite element simulations with CST MWS show the characteristic field distribution of the two modes and the intermixing of the LC-mode with the SPP-mode very clearly. Analytical modeling with a simple two oscillator model well describes the coupling. An effective relative permittivity of 11.6 for the coupled system was extracted. For broader linewidths, an apparent modulation of the effective Quality-factor can be observed which is of crucial importance for designing metasurfaces for applications. Measurements of the broader lambda/2 mode in orthogonal excitation direction reveal instead a Fano-like interaction. Rectangular array configuration reveal the excitation direction of the SPP modes being along the polarization of the exciting THz pulse. We demonstrate that the understanding of the SPP modes is fundamental for research and applications in which the metasurface has to be designed for special needs.

  10. Measurement of complex terahertz dielectric properties of polymers using an improved free-space technique

    NASA Astrophysics Data System (ADS)

    Chang, Tianying; Zhang, Xiansheng; Yang, Chuanfa; Sun, Zhonglin; Cui, Hong-Liang

    2017-04-01

    The complex dielectric properties of non-polar solid polymer materials were measured in the terahertz (THz) band by a free-space technique employing a frequency-extended vector network analyzer (VNA), and by THz time-domain spectroscopy (TDS). Mindful of THz wave’s unique characteristics, the free-space method for measurement of material dielectric properties in the microwave band was expanded and improved for application in the THz frequency region. To ascertain the soundness and utility of the proposed method, measurements of the complex dielectric properties of a variety of polymers were carried out, including polytetrafluoroethylene (PTFE, known also by the brand name Teflon), polypropylene (PP), polyethylene (PE), and glass fiber resin (Composite Stone). The free-space method relies on the determination of electromagnetic scattering parameters (S-parameters) of the sample, with the gated-reflect-line (GRL) calibration technique commonly employed using a VNA. Subsequently, based on the S-parameters, the dielectric constant and loss characteristic of the sample were calculated by using a Newtonian iterative algorithm. To verify the calculated results, THz TDS technique, which produced Fresnel parameters such as reflection and transmission coefficients, was also used to independently determine the dielectric properties of these polymer samples, with results satisfactorily corroborating those obtained by the free-space extended microwave technique.

  11. Experimental realization of a terahertz all-dielectric metasurface absorber.

    PubMed

    Liu, Xinyu; Fan, Kebin; Shadrivov, Ilya V; Padilla, Willie J

    2017-01-09

    Metamaterial absorbers consisting of metal, metal-dielectric, or dielectric materials have been realized across much of the electromagnetic spectrum and have demonstrated novel properties and applications. However, most absorbers utilize metals and thus are limited in applicability due to their low melting point, high Ohmic loss and high thermal conductivity. Other approaches rely on large dielectric structures and / or a supporting dielectric substrate as a loss mechanism, thereby realizing large absorption volumes. Here we present a terahertz (THz) all dielectric metasurface absorber based on hybrid dielectric waveguide resonances. We tune the metasurface geometry in order to overlap electric and magnetic dipole resonances at the same frequency, thus achieving an experimental absorption of 97.5%. A simulated dielectric metasurface achieves a total absorption coefficient enhancement factor of FT=140, with a small absorption volume. Our experimental results are well described by theory and simulations and not limited to the THz range, but may be extended to microwave, infrared and optical frequencies. The concept of an all-dielectric metasurface absorber offers a new route for control of the emission and absorption of electromagnetic radiation from surfaces with potential applications in energy harvesting, imaging, and sensing.

  12. Terahertz imaging in dielectric media with quasi-Bessel beams

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuopeng; Buma, Takashi

    2011-02-01

    Terahertz (THz) imaging is promising for nondestructive evaluation, since many optically opaque dielectrics are transparent to THz waves. Conventional THz imaging systems employ focusing elements such as spherical lenses and off-axis parabolas, but their fixed focal length produces an inherent trade-off between lateral resolution and depth of focus. Furthermore, image quality suffers when imaging objects located inside a dielectric medium. The air-dielectric interface introduces significant spherical aberration that degrades spatial resolution. Bessel beams are known to produce a small spot size over a large depth of focus. The contribution of our work is two-fold: (1) We demonstrate THz imaging with a significantly improved depth of focus using a zero-th order Bessel beam produced by an axicon lens. (2) We also demonstrate, for the first time to our knowledge, that Bessel beams experience reduced spherical aberration when imaging objects embedded in a dielectric medium. Imaging experiments are performed with a time-domain THz system, where a zero-th order quasi-Bessel beam is formed with an axicon lens made from high density polyethylene (HDPE). The HDPE axicon has a 50 mm diameter and an apex angle of 120 degrees. Point spread function (PSF) measurements confirm that lateral resolution is maintained over a 25 mm depth of field in air. The same lateral resolution is achieved over a 35 mm range inside a HDPE substrate. Needle objects embedded inside a thick HDPE substrate are imaged with high spatial resolution. Image contrast is significantly improved by digital filtering to reduce sidelobe levels. These promising results suggest that Bessel beams are well suited for terahertz nondestructive imaging of thick dielectric objects.

  13. The Thz Spectrum of Glycolaldehyde

    NASA Astrophysics Data System (ADS)

    Goubet, Manuel; Huet, Therese R.; Haykal, Imane; Margules, Laurent; Pirali, Olivier; Roy, Pascale

    2011-06-01

    The vibration-rotation spectrum of the ν_1-0, ν_2-0 and ν_3-0 bands of glycolaldehyde was recorded up to 12 THz, using the far-infrared beamline AILES at the synchrotron SOLEIL and a Fourier transform spectrometer coupled to a multipass cell. More than eight thousands lines were assigned, revealing the rotation structure up to J=80, K_a=38 for the ground state. The THz data were fitted simultaneously with pure rotational transitions of better accuracy observed in the microwave (1), in the millimeter-wave (2) and in the sub-millimeter-wave (3) range. In addition new data were recorded at Lille in the 150-300 GHz and 750-950 GHz range. The THz lines and the microwave - (sub)-millimeterwave lines are reproduced with a standard deviation of 2 10-4 Cm-1 and 40 KHz, respectively. Glycolaldehyde has been identified toward the galactic center (4). The vibrational state partition function can be re-evaluated according to the bands origins associated with ν_1, ν_2, and ν_3, which are observed experimentally for the first time. This work is supported by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS) and by the contract ANR-08-BLAN-0054. 1. M. Rey, J.-R. Aviles-Moreno and T. R. Huet, Chem. Phys. Lett. 430(2006) 121 ; K.-M. Marstokk and H. Mollendal, J. Mol. Struct. 5 (1970) 205. 2. R. A. H. Butler, F. C. De Lucia, D. T. Petkie, H. Mollendal, A. Horn, and E. Herbst, ApJS 134 (2001) 319. ; S. L. Widicus-Weaver, R. A. H. Butler, B. J. Drouin, D. T. Petkie, K. A. Dyl, F. C. De Lucia, and G. A. Blake, ApJ 158(2005)188. 3. P. B. Carroll, B. J. Drouin, and S. L. Widicus-Weaver, ApJ 723 (2010) 845. 4. J. M. Hollis, S. N. Vogel, L. E. Snyder, P. R. Jewell, and F. J. Lovas, ApJ 554 (2001) L81. ; M.T. Beltran, C. Codella, S. Viti, R. Niri, R. Cesaroni, ApJ 690 (2009) L93.

  14. THz dynamics of nanoconfined water by ultrafast optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Taschin, A.; Bartolini, P.; Torre, R.

    2017-01-01

    We investigated the vibrational dynamics and structural relaxation of water nanoconfined in porous silica samples with a pore size of 4 nm at different levels of hydration and temperature. We used the time-resolved optical Kerr effect (OKE), a spectroscopic technique that enables investigation of ultrafast water dynamics in a wide time (0.1-10 ps) or frequency (10-0.1 THz) window. At low hydration levels corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all investigated temperatures. Meanwhile, at full hydration we witness a partial ice formation at about 248 K that coexists with the surface water remaining in the supercooled state. At low hydration, both structural and vibrational dynamics show significant modifications compared to bulk liquid water. This is due to the strong interaction of the water molecules with silica surfaces. Inner water, however, reveals relaxation dynamics very similar to bulk water.

  15. Image reconstruction method for non-synchronous THz signals

    NASA Astrophysics Data System (ADS)

    Oda, Naoki; Okubo, Syuichi; Sudou, Takayuki; Isoyama, Goro; Kato, Ryukou; Irizawa, Akinori; Kawase, Keigo

    2014-05-01

    Image reconstruction method for non-synchronous THz signals was developed for a combination of THz Free Electron Laser (THz-FEL) developed by Osaka University with THz imager. The method employs a slight time-difference between repetition period of THz macro-pulse from THz-FEL and a plurality of frames for THz imager, so that image can be reconstructed out of a predetermined number of time-sequential frames. This method was applied to THz-FEL and other pulsed THz source, and found very effective. Thermal time constants of pixels in 320x240 microbolometer array were also evaluated with this method, using quantum cascade laser as a THz source.

  16. THz spectroscopy of D2H+

    NASA Astrophysics Data System (ADS)

    Yu, S.; Pearson, J. C.; Amano, T.; Matsushima, F.

    2017-01-01

    We extended the measurements of the rotational transitions of D2H+ up to 3 THz by using the JPL frequency multiplier chains and a TuFIR system at Toyama. D2H+ was generated in an extended negative glow discharge cell cooled to liquid nitrogen temperature. We observed five new THz lines. All the available rotational transition frequencies together with the combination differences derived from the three fundamental bands were subject to least square analysis to determine the molecular constants. New THz measurements are definitely useful for better characterization of spectroscopic properties. The improved molecular constants provide better predictions of other unobserved rotational transitions.

  17. DNA detection by THz pumping

    SciTech Connect

    Chernev, A. L.; Bagraev, N. T.; Klyachkin, L. E.; Emelyanov, A. K.; Dubina, M. V.

    2015-07-15

    DNA semiconductor detection and sequencing is considered to be the most promising approach for future discoveries in genome and proteome research which is dramatically dependent on the challenges faced by semiconductor nanotechnologies. DNA pH-sensing with ion-sensitive field effect transistor (ISFET) is well-known to be a successfully applied electronic platform for genetic research. However this method lacks fundamentally in chemical specificity. Here we develop the first ever silicon nanosandwich pump device, which provides both the excitation of DNA fragments’ self-resonant modes and the feedback for current-voltage measurements at room temperature. This device allows direct detection of singlestranded label-free oligonucleotides by measuring their THz frequency response in aqueous solution. These results provide a new insight into the nanobioelectronics for the future real-time technologies of direct gene observations.

  18. Super Dielectric Materials

    PubMed Central

    Fromille, Samuel; Phillips, Jonathan

    2014-01-01

    Evidence is provided here that a class of materials with dielectric constants greater than 105 at low frequency (<10−2 Hz), herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials. Specifically it is demonstrated that high surface area alumina powders, loaded to the incipient wetness point with a solution of boric acid dissolved in water, have dielectric constants, near 0 Hz, greater than 4 × 108 in all cases, a remarkable increase over the best dielectric constants previously measured for energy storage capabilities, ca. 1 × 104. It is postulated that any porous, electrically insulating material (e.g., high surface area powders of silica, titania, etc.), filled with a liquid containing a high concentration of ionic species will potentially be an SDM. Capacitors created with the first generated SDM dielectrics (alumina with boric acid solution), herein called New Paradigm Super (NPS) capacitors display typical electrostatic capacitive behavior, such as increasing capacitance with decreasing thickness, and can be cycled, but are limited to a maximum effective operating voltage of about 0.8 V. A simple theory is presented: Water containing relatively high concentrations of dissolved ions saturates all, or virtually all, the pores (average diameter 500 Å) of the alumina. In an applied field the positive ionic species migrate to the cathode end, and the negative ions to the anode end of each drop. This creates giant dipoles with high charge, hence leading to high dielectric constant behavior. At about 0.8 V, water begins to break down, creating enough ionic species to “short” the individual water droplets. Potentially NPS capacitor stacks can surpass “supercapacitors” in volumetric energy density. PMID:28788298

  19. Development of THz wave oscillation and its application to molecular sciences

    NASA Astrophysics Data System (ADS)

    Nishizawa, J.

    In 1967, a THz wave was generated for the first time using a free electron laser; however, the device was too expensive to be used widely. The author published the idea of THz wave generation by use of resonating vibration between paired atoms in polymer or crystal in 1965, and succeeded with K. Suto to generate a 12 THz wave in 1983. In 1999, the author invited K. Kawase and H. Ito to Sendai RIKEN to realize the concept by use of dielectrics; in 2000, they succeeded in realizing a sweep generator. In the same year, the author suggested the idea of applying the THz wave to cancer diagnosis and treatment, particularly by improving heating selectivity: This enhances the effect of medications by raising only the temperature of the cancer itself, not of the surrounding atomic pairs in the neighborhood. These applications are expected to spread quickly as powerful methodology based on molecular science. The reason for this is that the much improved waveform generated enables higher selectivity, allowing the detection of the existence of abnormal polymer near the paired atoms by measuring resonating frequency between paired atoms.

  20. s-SNOM based IR and THz spectroscopy for nanoscale material characterization

    NASA Astrophysics Data System (ADS)

    Gokus, Tobias; Huber, Andreas; Cernescu, Adrian

    Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) allows to overcome the diffraction limit of conventional light microscopy enabling optical measurements at a spatial resolution of 10nm. s-SNOM employs an externally-illuminated sharp metallic AFM tip to create a nanoscale hot-spot at its apex. The optical tip-sample near-field interaction is determined by the local dielectric properties (refractive index) of the sample and detection of the elastically tip-scattered light yields nanoscale resolved near-field images simultaneous to topography. Development of a dedicated Fourier-transform detection module for analyzing light scattered from the tip which is illuminated by a broadband laser source enables IR spectroscopy of complex polymer nanostructures. Applications presented further demonstrate characterization of embedded structural phases in biominerals (bone), organic semiconductors or functional semiconductor nanostructures.Furthermore, by extending the concept of broadband-s-SNOM spectroscopy to the THz-spectral range, we demonstrate optical near-field imaging and spectroscopy at THz-frequencies (0.5-2.5 THz) by coupling the free space beam of a dedicated THz-TDS to the s-SNOM system.

  1. Collective hydration dynamics in some amino acid solutions: A combined GHz-THz spectroscopic study

    NASA Astrophysics Data System (ADS)

    Samanta, Nirnay; Das Mahanta, Debasish; Choudhury, Samiran; Barman, Anjan; Kumar Mitra, Rajib

    2017-03-01

    A detailed understanding of hydration of amino acids, the building units of protein, is a key step to realize the overall solvation processes in proteins. In the present contribution, we have made a combined GHz (0.2-50) to THz (0.3-2.0) experimental spectroscopic study to investigate the dynamics of water at room temperature in the presence of different amino acids (glycine, L-serine, L-lysine, L-tryptophan, L-arginine, and L-aspartic acid). The THz absorption coefficient, α(ν), of amino acids follows a trend defined by their solvent accessible surface area. The imaginary and real dielectric constants obtained in GHz and THz regions are fitted into multiple Debye model to obtain various relaxation times. The ˜100 ps time scale obtained in the GHz frequency region is attributed to the rotational motion of the amino acids. In the THz region, we obtain ˜8 ps and ˜200 fs time scales which are related to the cooperative dynamics of H-bond network and partial rotation or sudden jump of the under-coordinated water molecules. These time scales are found to be dependent on the amino acid type and the cooperative motion is found to be dependent on both the hydrophobic as well as the hydrophilic residue of amino acids.

  2. Morphological study of human sweat ducts for the investigation of THz-wave interaction (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo; Tripathi, Saroj R.

    2016-03-01

    Recently, some studies reported that the sweat ducts act as a low-Q-factor helical antenna due to their helical structure, and resonate in the terahertz frequency range according to their structural parameters. According to the antenna theory, when the duct works as a helical antenna, the dimension of the helix plays a key role to determine the frequency of resonance. Therefore, the accurate determination of structural parameters of sweat duct is crucially important to obtain the reliable frequency of resonance and modes of operations. Therefore, here we performed the optical coherence tomography (OCT) of human subjects on their palm and foot to investigate the density, distribution and morphological features of sweat ducts. Moreover, we measured the dielectric properties of stratum corneum using terahertz time domain spectroscopy and based upon this information, we determined the frequency of resonance. We recruited 32 subjects for the measurement and the average duct diameter was 95±11μm. Based upon this information on diameter of duct and THz dielectric properties of stratum corneum (ɛ=5.1±1.3), we have calculated the frequency of resonance of sweat duct. Finally, we determined that the center frequency of resonance was 442±76 GHz. 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. We will also report on the EEG measurement while being shined by micro watt order THz waves.

  3. Enhancement of optics-to-THz conversion efficiency by metallic slot waveguides.

    PubMed

    Ruan, Zhichao; Veronis, Georgios; Vodopyanov, Konstantin L; Fejer, Marty M; Fan, Shanhui

    2009-08-03

    A metallic slot waveguide, with a dielectric strip embedded within, is investigated for the purpose of enhancing the optics-to-THz conversion efficiency using the difference-frequency generation (DFG) process. To describe the frequency conversion process in such lossy waveguides, a fully-vectorial coupled-mode theory is developed. Using the coupled-mode theory, we outline the basic theoretical requirements for efficient frequency conversion, which include the needs to achieve large coupling coefficients, phase matching, and low propagation loss for both the optical and THz waves. Following these requirements, a metallic waveguide is designed by considering the trade-off between modal confinement and propagation loss. Our numerical calculation shows that the conversion efficiency in these waveguide structures can be more than one order of magnitude larger than what has been achieved using dielectric waveguides. Based on the distinct impact of the slot width on the optical and THz modal dispersion, we propose a two-step method to realize the phase matching for general pump wavelengths.

  4. Spectral characterization of dielectric materials using terahertz measurement systems

    NASA Astrophysics Data System (ADS)

    Seligman, Jeffrey M.

    The performance of modern high frequency components and electronic systems are often limited by the properties of the materials from which they are made. Over the past decade, there has been an increased emphasis on the development of new, high performance dielectrics for use in high frequency systems. The development of these materials requires novel broadband characterization, instrumentation, and extraction techniques, from which models can be formulated. For this project several types of dielectric sheets were characterized at terahertz (THz) frequencies using quasi-optical (free-space) techniques. These measurement systems included a Fourier Transform Spectrometer (FTS, scalar), a Time Domain Spectrometer (TDS, vector), a Scalar Network Analyzer (SNA), and a THz Vector Network Analyzer (VNA). Using these instruments the THz spectral characteristics of dielectric samples were obtained. Polarization based anisotropy was observed in many of the materials measured using vector systems. The TDS was the most informative and flexible instrument for dielectric characterization at THz frequencies. To our knowledge, this is the first such comprehensive study to be performed. Anisotropy effects within materials that do not come into play at microwave frequencies (e.g. ~10 GHz) were found, in many cases, to increase measured losses at THz frequencies by up to an order of magnitude. The frequency dependent properties obtained during the course of this study included loss tangent, permittivity (index of refraction), and dielectric constant. The results were largely consistent between all the different systems and correlated closely to manufacturer specifications over a wide frequency range (325 GHz-1.5 THz). Anisotropic behavior was observed for some of the materials. Non-destructive evaluation and testing (NDE/NDT) techniques were used throughout. A precision test fixture was developed to accomplish these measurements. Time delay, insertion loss, and S-parameters were

  5. Evaluation of SiO{sub 2}@CoFe{sub 2}O{sub 4} nano-hollow spheres through THz pulses

    SciTech Connect

    Rakshit, Rupali Pal, Monalisa; Chaudhuri, Arka; Mandal, Kalyan; Serita, Kazunori; Tonouchi, Masayoshi

    2016-05-06

    We have synthesized cobalt ferrite (CFO) nanoparticles (NPs) of diameter 100 nm and nano-hollow spheres (NHSs) of diameter 100, 160, 250, and 350 nm by a facile one step template free solvothermal technique and carried out SiO{sub 2} coating on their surface following Stöber method. The phase and morphology of the nanostructures were confirmed by X-ray diffraction and transmission electron microscope. The magnetic measurements were carried out by vibrating sample magnetometer in order to study the influence of SiO{sub 2} coating on the magnetic properties of bare CFO nanostructures. Furthermore, we have applied THz time domain spectroscopy to investigate the THz absorption property of these nanostructures in the frequency range 1.0–2.5 THz. Detailed morphology and size dependent THz absorption study unfolds that the absorption property of these nanostructures sensitively carries the unique signature of its dielectric property.

  6. New THz opportunities based on graphene

    SciTech Connect

    Hartnagel, Hans

    2015-04-24

    Graphene is a new material of a single or multiple layer carbon structure with impressive properties. A brief introduction is initially presented. Graphene does not have a bandwidth and is a semimetal with charge carriers of zero mass. A bandgap can be formed by confining the graphene width in nanoribbon or nanoconstricition structures. For example, the induced bandgap by a 20 nm wide nanoribbon is about 50 meV. The charge carrier mass then increases, but is still very small. This material can especially be employed for various Terahertz applications. Here several examples are to be described, namely a) a THz transistor, b) the opportunities of ballistic electron resonances for THz signal generation, c) the simultaneous optical transmission and electrical conduction up to THz frequencies and d) Cascaded THz emitters. The optical advantages of multilayer graphene can be compared to ITO (Indium Tin Oxide)

  7. THz Medical Imaging: in vivo Hydration Sensing

    PubMed Central

    Taylor, Zachary D.; Singh, Rahul S.; Bennett, David B.; Tewari, Priyamvada; Kealey, Colin P.; Bajwa, Neha; Culjat, Martin O.; Stojadinovic, Alexander; Lee, Hua; Hubschman, Jean-Pierre; Brown, Elliott R.; Grundfest, Warren S.

    2015-01-01

    The application of THz to medical imaging is experiencing a surge in both interest and federal funding. A brief overview of the field is provided along with promising and emerging applications and ongoing research. THz imaging phenomenology is discussed and tradeoffs are identified. A THz medical imaging system, operating at ~525 GHz center frequency with ~125 GHz of response normalized bandwidth is introduced and details regarding principles of operation are provided. Two promising medical applications of THz imaging are presented: skin burns and cornea. For burns, images of second degree, partial thickness burns were obtained in rat models in vivo over an 8 hour period. These images clearly show the formation and progression of edema in and around the burn wound area. For cornea, experimental data measuring the hydration of ex vivo porcine cornea under drying is presented demonstrating utility in ophthalmologic applications. PMID:26085958

  8. Preparation and unique dielectric properties of nanoporous materials with well-controlled closed-nanopores.

    PubMed

    Zhao, Cuijiao; Wei, Xiaonan; Huang, Yawen; Ma, Jiajun; Cao, Ke; Chang, Guanjun; Yang, Junxiao

    2016-07-28

    Although general porous materials have a low dielectric constant, their uncontrollable opened porous structure results in high dielectric loss and poor barrier properties, thus limiting their application as interconnect dielectrics. In this study, polymeric nanoporous materials with well-controlled closed pores were prepared by incorporating polystyrene (PS) hollow nanoparticles into polyethylene (PE/HoPS). SEM images suggested a closed porous structure for PE/HoPS. In order to show the effect of the porous structure on dielectric properties, nanoporous materials with an opened or uncontrollable porous structure were prepared by etching SiO2/PE or PE/PS@SiO2 composites. PE/HoPSs composites showed an apparently lower dielectric constant and loss compared with the opened porous PE, demonstrating the advantages of a closed porous structure upon enhancing low-dielectric performance. The low dielectric performance of the PE/HoPS composites is linked with high water resistance owing to their closed porous characteristics. When incorporating 15.3 wt% HoPS (porosity: ∼6.9%), the dielectric constant reached 2.08. This value is lower than that calculated from the serial model. Our work revealed that the incorporation of HoPS not only reduces the porosity, but also alters the intrinsic properties of PE, as a result, leading to a greatly reduced dielectric constant.

  9. THz Detection and Imaging using Rydberg Atoms

    NASA Astrophysics Data System (ADS)

    Wade, Christopher; Sibalic, Nikola; Kondo, Jorge; de Melo, Natalia; Adams, Charles; Weatherill, Kevin

    2016-05-01

    Atoms make excellent electromagnetic field sensors because each atom of the same isotope is identical and has well-studied, permanent properties allowing calibration to SI units. Thus far, atoms have not generally been exploited for terahertz detection because transitions from the atomic ground state are constrained to a limited selection of microwave and optical frequencies. In contrast, highly excited `Rydberg' states allow us access to many strong, electric dipole transitions from the RF to THz regimes. Recent advances in the coherent optical detection of Rydberg atoms have been exploited by a number of groups for precision microwave electrometry Here we report the demonstration of a room-temperature, cesium Rydberg gas as a THz to optical interface. We present two configurations: First, THz-induced fluorescence offers non-destructive and direct imaging of the THz field, providing real-time, single shot images. Second, we convert narrowband terahertz photons to infrared photons with 6% quantum efficiency allowing us to use nano-Watts of THz power to control micro-Watts of laser power on microsecond timescales. Exploiting hysteresis and a room-temperature phase transition in the response of the medium, we demonstrate a latching optical memory for sub pico-Joule THz pulses.

  10. Study of Application of Thz Time Domainspectroscopy in Food Safet

    NASA Astrophysics Data System (ADS)

    Lang, Liying; Cai, Na

    In this paper, a new spectroscopy technology named terahertz time-domain spectroscopy (THz-TDS) is introduced, which is used in food safety. We describe a coherent subpicosecond THz spectroscopy system based on nonresonant optical rectification for the generation of THz radiation. As an example, we measured absorption spectrum of water vapor by THz-TDS in frequency from 0.5 to 2.5 THz, The experiment demonstrated that the spectroscopy resolution of system was up to 0.0001THz, which can be measured vegetable pesticide residual, for it neither need sample pretreatment nor cause pollution.

  11. Monte Carlo simulations of skin exposure to electromagnetic field from 10 GHz to 1 THz

    NASA Astrophysics Data System (ADS)

    Sasaki, Kensuke; Mizuno, Maya; Wake, Kanako; Watanabe, Soichi

    2017-09-01

    In this study, we present an assessment of human-body exposure to an electromagnetic field at frequencies ranging from 10 GHz to 1 THz. The energy absorption and temperature elevation were assessed by solving boundary value problems of the one-dimensional Maxwell equations and a bioheat equation for a multilayer plane model. Dielectric properties were measured in~vitro at frequencies of up to 1 THz at body temperature. A Monte Carlo simulation was conducted to assess variations of the transmittance into a skin surface and temperature elevation inside a body by considering the variation of the tissue thickness due to individual differences among human bodies. Furthermore, the impact of the dielectric properties of adipose tissue on temperature elevation, for which large discrepancies between our present measurement results and those in past works were observed, was also examined. We found that the dielectric properties of adipose tissue do not impact on temperature elevation at frequencies over 30 GHz. The potential risk of skin burn was discussed on the basis of the temperature elevation in millimeter-wave and terahertz-wave exposure. Furthermore, the consistency of the basic restrictions in the international guidelines set by ICNIRP was discussed.

  12. Method of casting patterned dielectric structures

    DOEpatents

    Poco, John F.; Hrubesh, Lawrence W.

    2001-01-01

    A pattern of dielectric structures are formed directly on a substrate in a single step using sol-gel chemistry and molding procedures. The resulting dielectric structures are useful in vacuum applications for electronic devices. Porous, lightweight structures having a high aspect ratio that are suitable for use as spacers between the faceplate and baseplate of a field emission display can be manufactured using this method.

  13. Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

    SciTech Connect

    Askari, Nasim; Eslami, Esmaeil; Mirzaie, Reza

    2015-11-15

    The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

  14. Thz Spectroscopy of D_2H^+

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Pearson, John; Amano, Takayoshi

    2015-06-01

    Pure rotational transitions of D_2H^+ observed by high-resolution spectroscopy have been limited so far to the J = 110-101 transition at 691.7 GHz, J=220-211 at 1.370 THz, and J=111-000 at 1.477 THz. As this ion is a light asymmetric-top molecule, spectroscopic characterization and prediction of other rotational transition frequencies are not straightforward. In this presentation, we extended the measurements up to 2 THz by using the JPL frequency multiplier chains, and observed three new THz lines and re-measured the three known transitions. D_2H^+ was generated in an extended negative glow discharge cell cooled to liquid nitrogen temperature. Six rotational transition frequencies together with the combination differences derived from three fundamental bands were subject to least square analysis to determine the molecular constants. New THz measurements are definitely useful for better characterization of spectroscopic properties. The improved molecular constants provide better predictions of other unobserved rotational transitions. T. Hirao and T. Amano, Ap. J.,597, L85 (2003) K. M. Evenson et al cited by O. L. Polyansky and A. R. W. McKellar, J. Chem. Phys., 92, 4039 (1990) O. Asvany et al, Phys. Rev. Lett., 100, 233004 (2008)

  15. Novel detectors for traceable THz power measurements

    NASA Astrophysics Data System (ADS)

    Müller, Ralf; Bohmeyer, Werner; Kehrt, Mathias; Lange, Karsten; Monte, Christian; Steiger, Andreas

    2014-08-01

    Several novel types of detectors for the measurement of electromagnetic radiation in the THz spectral range are described. Firstly, detectors based on pyroelectric foil coated with different absorbers have been developed focusing on the following features: high accuracy due to well-characterized absorption, high sensitivity, large area absorbers and frequency and polarization independence. A three-dimensional design with five absorptions gave an overall absorption of more than 98 %. Secondly, detectors based on pyroelectric foils with thin metal layers were realized. An absorption of 50 % can be obtained if the thickness of the layers is carefully adjusted. According to electromagnetic theory this degree of absorption is independent of the polarization and frequency of the radiation in a wide range from at least 20 GHz to 5 THz. The third type of detector is based on a new type of volume absorber with a polished front surface and a gold-coated back side. It is the absorber of choice of the standard power detector for disseminating the spectral power responsivity scale. This standard detector allows the application of a physical model to calculate its spectral responsivity in the range from 1 THz to 5 THz if the detector has been calibrated at one single frequency. Finally, a THz detector calibration facility was set up and is now in operation at PTB to calibrate detectors from customers with an uncertainty as low as 1.7 %.

  16. Antenna Enhanced Graphene THz Emitter and Detector.

    PubMed

    Tong, Jiayue; Muthee, Martin; Chen, Shao-Yu; Yngvesson, Sigfrid K; Yan, Jun

    2015-08-12

    Recent intense electrical and optical studies of graphene have pushed the material to the forefront of optoelectronic research. Of particular interest is the few terahertz (THz) frequency regime where efficient light sources and highly sensitive detectors are very challenging to make. Here we present THz sources and detectors made with graphene field effect transistors (GFETs) enhanced by a double-patch antenna and an on-chip silicon lens. We report the first experimental observation of 1-3 THz radiation from graphene, as well as more than 3 orders of magnitude performance improvements in a half-edge-contacted GFET thermoelectric detector operating at ∼2 THz. The quantitative analysis of the emitting power and its unusual charge density dependence indicate significant nonthermal noise contribution from the GFET. The polarization resolved detection measurements with different illumination geometries allow for detailed and quantitative analysis of various factors that contribute to the overall detector performance. Our experimental results represent a significant advance toward practically useful graphene THz devices.

  17. Different roles of electron beam in two stream instability in an elliptical waveguide for generation and amplification of THz electromagnetic waves

    SciTech Connect

    Safari, S.; Jazi, B.; Jahanbakht, S.

    2016-08-15

    In this work, two stream instability in a metallic waveguide with elliptical cross-section and with a hollow annular dielectric layer is studied for generation and amplification of THz electromagnetic waves. Dispersion relation of waves and their dependents to geometric dimensions and characteristics of the electron beam are analyzed. In continuation, the diagrams of growth rate for some operating frequencies are presented, so that effective factors on the growth rates, such as geometrical dimensions, dielectric constant of dielectric layer, accelerating voltage, and applied current intensity are analyzed. It is shown that while an electron beam is responsible for instability, another electron beam plays a stabilizing role.

  18. 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

  19. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

    PubMed Central

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

    2015-01-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5–10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields. PMID:25800287

  20. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

    NASA Astrophysics Data System (ADS)

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

    2015-03-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5-10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields.

  1. 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.

  2. Reflective THz and MR imaging of burn wounds: a potential clinical validation of THz contrast mechanisms

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Nowroozi, Bryan; Sung, Shijun; Garritano, James; Maccabi, Ashkan; Tewari, Priyamvada; Culjat, Martin; Singh, Rahul; Alger, Jeffry; Grundfest, Warren; Taylor, Zachary

    2012-10-01

    Terahertz (THz) imaging is an expanding area of research in the field of medical imaging due to its high sensitivity to changes in tissue water content. Previously reported in vivo rat studies demonstrate that spatially resolved hydration mapping with THz illumination can be used to rapidly and accurately detect fluid shifts following induction of burns and provide highly resolved spatial and temporal characterization of edematous tissue. THz imagery of partial and full thickness burn wounds acquired by our group correlate well with burn severity and suggest that hydration gradients are responsible for the observed contrast. This research aims to confirm the dominant contrast mechanism of THz burn imaging using a clinically accepted diagnostic method that relies on tissue water content for contrast generation to support the translation of this technology to clinical application. The hydration contrast sensing capabilities of magnetic resonance imaging (MRI), specifically T2 relaxation times and proton density values N(H), are well established and provide measures of mobile water content, lending MRI as a suitable method to validate hydration states of skin burns. This paper presents correlational studies performed with MR imaging of ex vivo porcine skin that confirm tissue hydration as the principal sensing mechanism in THz burn imaging. Insights from this preliminary research will be used to lay the groundwork for future, parallel MRI and THz imaging of in vivo rat models to further substantiate the clinical efficacy of reflective THz imaging in burn wound care.

  3. Complex dielectric properties of anhydrous polycrystalline glucose in the terahertz region

    NASA Astrophysics Data System (ADS)

    Sun, P.; Liu, W.; Zou, Y.; Jia, Qiong Z.; Li, Jia Y.

    2015-03-01

    We utilized terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric properties of solid polycrystalline material of anhydrous glucose (D-(+)-glucose with purity >99.9%). THz transmission spectra of samples were measured from 0.2 to 2.2 THz. The samples were prepared into tablets with thicknesses of 0.362, 0.447, 0.504, 0.522 and 0.626 mm, respectively. The imaginary part of the complex dielectric function of polycrystalline glucose showed that there were multiple characteristic absorption peaks at 1.232, 1.445, 1.522, 1.608, 1.811 and 1.987 THz, respectively. Moreover, for a given characteristic absorption peak, the real part of the complex dielectric function showed anomalous dispersion within the full width half maximum (FWHM) of the absorption peak. Both finite difference time-domain (FDTD) numerical simulations and experimental results showed that the complex dielectric function of anhydrous polycrystalline glucose fits well with the Lorentz dielectric mode. The plasma oscillation frequency was below the frequency of the light waves suggesting that the light waves passed through the polycrystalline glucose tablets. Calculations based on density functional theory (DFT) showed that the characteristic absorption peaks of polycrystalline glucose originated mainly from collective intermolecular vibrations such as hydrogen bonds and crystal phonon modes. The THz radiation can excite the vibrational or rotational energy levels of the biological macromolecules. This leads to changes in their spatial configuration or interactions. This study showed that THz-TDS has potential applications in biological and pharmaceutical research and food industry.

  4. Magnetic Field Assisted sub-THz Quantum Cascade Lasers

    NASA Astrophysics Data System (ADS)

    Wade, A.; Kim, Y.; Smirnov, D.; Kumar, S.; Hu, Q.; Williams, B. S.; Reno, J.

    2009-03-01

    In THz QCLs radiative transitions take place between closely-spaced 2D electronic subbands (1THz ˜ 4meV) of a multi-QW semiconductor system. THz quantum cascade lasers now cover the frequency range from 1.2 THz to 5 THz, though cryogenic cooling is still required. Further progress towards the realization of devices emitting at longer wavelengths (sub-THz QCLs) and higher temperatures may be realized in a system with additional lateral confinement. Here we use strong magnetic fields to achieve quasi-0D confinement in THz QCL based on the resonance phonon design. We studied two designs: (a) 2-well injector/2 well active region, emitting at 3 THz at B=0; and (b) 1-well injector/3-well active region, emitting at 2 THz at B=0 T. By applying the appropriate electrical bias and strong magnetic fields, we achieved laser emission at 0.8-0.9 THz at B>16 T [1], and 0.6 THz at B˜17 T, from devices a and b respectively. The ability to achieve sub-THz lasing is due to magnetic field enhanced population inversion in a quasi-0D QCL. [1] Wade, A et. al., Magnetic field assisted Terahertz quantum cascade laser operating up to 225K, Accepted for publication Nature Photonics (2009)

  5. A THz Tomography System for Arbitrarily Shaped Samples

    NASA Astrophysics Data System (ADS)

    Stübling, E.; Bauckhage, Y.; Jelli, E.; Fischer, B.; Globisch, B.; Schell, M.; Heinrich, A.; Balzer, J. C.; Koch, M.

    2017-06-01

    We combine a THz time-domain spectroscopy system with a robotic arm. With this scheme, the THz emitter and receiver can be positioned perpendicular and at defined distance to the sample surface. Our system allows the acquisition of reflection THz tomographic images of samples with an arbitrarily shaped surface.

  6. THz spectra of cortisone and the related medicine

    NASA Astrophysics Data System (ADS)

    Ma, Shihua; Ge, Min; Liu, Guifeng; Song, Xiyu; Zhang, Peng; Wang, Wenfeng

    2009-07-01

    THz-TDS are used to study four kinds of drug: cortisone, hydrocortisone, prednisone and prednisolone. The THz spectra of them are obtained and analyzed from 0.2 - 1.6 THz. The experimental results shows the four samples have the different THz spectra. Cortisone has a peak at 1.5 THz and a broad absorption peak at 0.96 THz, while hydrocortisone has a weak absorption peak that lies at 1.27 THz. At the same time the prednisone has the stronger absorption peaks than the others, and its two peaks shows at 1.24 THz and 1.5 THz. Prednisolone has a weak broad peak at 1.43 THz. The results of the theoretical calculation were performed using Gaussian 03 software with Density Functional Theory at the basis set of 6-31+G (d, p). The theoretical vibrational frequencies are compared with the experimental results, and the deviations are discussed. The THz spectra of the medicine show THz technique may be help to distinguish some different chemical bond and functional group.

  7. A THz Tomography System for Arbitrarily Shaped Samples

    NASA Astrophysics Data System (ADS)

    Stübling, E.; Bauckhage, Y.; Jelli, E.; Fischer, B.; Globisch, B.; Schell, M.; Heinrich, A.; Balzer, J. C.; Koch, M.

    2017-10-01

    We combine a THz time-domain spectroscopy system with a robotic arm. With this scheme, the THz emitter and receiver can be positioned perpendicular and at defined distance to the sample surface. Our system allows the acquisition of reflection THz tomographic images of samples with an arbitrarily shaped surface.

  8. Characterization of Micron-Scale Nanotublar Super Dielectric Materials

    DTIC Science & Technology

    2015-09-01

    MICRON-SCALE NANOTUBULAR SUPER DIELECTRIC MATERIALS by Jonathan Wayne Gandy September 2015 Thesis Advisor: Jonathan Phillips Co-Advisor...AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE CHARACTERIZATION OF MICRON-SCALE NANOTUBULAR SUPER DIELECTRIC MATERIALS 5. FUNDING NUMBERS...study focused on dielectric materials based on a novel hypothesis: that porous electrically insulating solids in which the pores are filled with liquids

  9. Plasma shock waves excited by THz radiation

    NASA Astrophysics Data System (ADS)

    Rudin, S.; Rupper, G.; Shur, M.

    2016-10-01

    The shock plasma waves in Si MOS, InGaAs and GaN HEMTs are launched at a relatively small THz power that is nearly independent of the THz input frequency for short channel (22 nm) devices and increases with frequency for longer (100 nm to 1 mm devices). Increasing the gate-to-channel separation leads to a gradual transition of the nonlinear waves from the shock waves to solitons. The mathematics of this transition is described by the Korteweg-de Vries equation that has the single propagating soliton solution.

  10. Detectivity enhancement in THz electrooptical sampling

    SciTech Connect

    Ahmed, Saima; Savolainen, Janne; Hamm, Peter

    2014-01-15

    We demonstrate and discuss a simple scheme that significantly enhances the detectivity of THz electro-optical sampling by introducing a sequence of Brewster windows that increases the ellipticity of the probe beam. By varying the window material or the number of Brewster windows, the enhancement factor can be adjusted; we demonstrate an enhancement factor of ≈20 with four ZnSe Brewster windows. The scheme is particularly useful when very small THz fields are to be measured in connection with low-repetition rate amplified Ti:S laser systems.

  11. Development of a THz spectroscopic imaging system.

    PubMed

    Usami, M; Iwamoto, T; Fukasawa, R; Tani, M; Watanabe, M; Sakai, K

    2002-11-07

    We have developed a real-time THz imaging system based on the two-dimensional (2D) electro-optic (EO) sampling technique. Employing the 2D EO-sampling technique, we can obtain THz images using a CCD camera at a video rate of up to 30 frames per second. A spatial resolution of 1.4 mm was achieved. This resolution was reasonably close to the theoretical limit determined by diffraction. We observed not only static objects but also moving ones. To acquire spectroscopic information, time-domain images were collected. By processing these images on a computer, we can obtain spectroscopic images. Spectroscopy for silicon wafers was demonstrated.

  12. Why engineer porous materials?

    PubMed

    Kelly, A

    2006-01-15

    A number of specific examples are briefly given for the use of pores in engineering materials: a porous ceramic to produce minimum thermal conduction; thin skeleton walls in silicon to produce photoluminescence; low dielectric constant materials. The desirable nature of the pores in fuel cell electrodes and sieves is described. Further examples are given in orthopaedics, prosthetic scaffolds and sound deadening and impact resistance materials. An attempt is made to describe the desirable pore size, whether open or closed, and the useful volume fraction. This short review does not deal with flexible foams.

  13. Non Destructive Thermal Analysis and In Situ Investigation of Creep Mechanism of Graphite and Ceramic Composites using Phase-sensitive THz Imaging & Nonlinear Resonant Ultrasonic Spectroscopy

    SciTech Connect

    Zhang, XI-Cheng; Hurley, David; Redo-Scanchez, Albert

    2012-11-26

    In this project, we conducted a comprehensive study on nuclear graphite properties with terahertz (THz) imaging. Graphite samples from Idaho National Laboratory were carefully imaged by continuous wave (CW) THz. The CW THz imaging of graphite shows that the samples from different billet with different fabricating conditions have different pore size and structure. Based on this result, we then used a phase sensitive THz system to study the graphite properties. In this exploration, various graphite were studied. By imaging nuclear graphite samples in reflection mode at nine different incident polarization angles using THz time-domain spectroscopy, we find that different domain distributions and levels of porosity will introduce polarization dependence in THz reflectivity. Sample with higher density is less porous and has a smaller average domain distribution. As a consequence, it is less polarization-dependent and the polarization-dependent frequency is higher. The results also show that samples oxidized at higher temperatures tend to be more polarization dependent. The graphite from the external billet is more polarization dependent compared to that from the center billet. In addition, we performed laser-based ultrasonic measurements on these graphite samples. The denser, unoxidized samples allow surface acoustic waves to propagate more rapidly than in the samples that had already undergone oxidation. Therefore, for the oxidized samples, the denser samples show less polarization-dependence, higher polarization-dependent frequency, and allow the surface acoustic waves propagate faster.

  14. Subwavelength silicon through-hole arrays as an all-dielectric broadband terahertz gradient index metamaterial

    SciTech Connect

    Park, Sang-Gil; Jeong, Ki-Hun; Lee, Kanghee; Han, Daehoon; Ahn, Jaewook

    2014-09-01

    Structuring at subwavelength scales brings out artificial media with anomalous optical features called metamaterials. All-dielectric metamaterials have high potential for practical applications over the whole electromagnetic spectrum owing to low loss and optical isotropy. Here, we report subwavelength silicon through-hole arrays as an all-dielectric gradient index metamaterial with broadband THz operation. The unit cell consists of a single subwavelength through-hole on highly resistive monocrystalline silicon. Depending on the fill-factor and period, the effective index was linearly modulated at 0.3–1.6 THz. The experimental results also demonstrate silicon gradient refractive index (Si-GRIN) lenses with parabolic index profiles through the spatial modification of a single unit cell along the radial direction. Si-GRIN lenses either focus 0.4–1.6 THz beam to the diffraction-limit or serve as a flat and thin solid immersion lens on the backside of THz photoconductive antenna for highly efficient pulse extraction. This all-dielectric gradient index metamaterial opens up opportunities for integrated THz GRIN optics.

  15. THz remote sensing for water vapor and cloud observation

    NASA Astrophysics Data System (ADS)

    Kasai, Yasuko; Ochiai, Satoshi; Mendrok, Jana; Baron, Philippe; Seta, Takamasa; Irimajiri, Yoshihisa

    Terahertz (THz) region (0.1-20 THz; 3.3-650 cm-1 ) plays important role for the Earth's radiation budget, for example, 1) Up to 75% of atmospheric OLR is beyond 650 cm-1 (19.5 THz). 2) Up to 50% of basic greenhouse effect, mainly due to the water vapor, is in THz/Far-IR. 3) Clear-sky cooling of free troposphere occurs in THz/far-IR. 4) Upper tropospheric H2O radiative feedback occurs THz/far-IR. Atmospheric radiation in THz-wave region is characterised by the emission from water vapour. In other word, THz radiation is favorable frequency for the remote sensing observation of water vapor. Furthermore, THz-wave might be powerful method to observe ice cloud because of the sensitivity of ice cloud in this frequency, example, the average size of the ice cloud -100micron is consistent to 3THz. Despite the importance for water vapor and ice cloud observation, there are not many observation so far, and still poor knowledge in the atmosphere. Main reason was the lack of the THz technology for the remote sensing observation in this frequency region. We are developing an NICT THz-wave remote sensing system to observe planetary atmosphere. Three researches are currently in progress: 1) Development of the THz-wave radiative transfer model both for clear and cloudy sky including laboratory experiment. 2) Feasibility study for satellite system 3) Development of the ground-based observation system for the demonstration in the city air. We will present the recent status of the THz remote sensing project in NICT, particularly the feasibility study for the water vapor and cloud observation system in THz-wave region from ground-based, air-borne, and satellite born system.

  16. Analysis of porous silicon

    NASA Astrophysics Data System (ADS)

    Earwaker, L. G.; Farr, J. P. G.; Grzeszczyk, P. E.; Sturland, I.; Keen, J. M.

    1985-06-01

    Porous silicon, suitable after oxidation for dielectric isolation, has been produced successfully by anodizing silicon in strong HF. The oxidized layer has been shown to have promise in device manufacture, providing high packing densities and radiation hardness. Anodizing has been carried out using both single and double cells, following the effects of current density. HF concentration and silicon resistivity. The resultant porous layers have been characterised with respect to composition and structure. The materials produced differ considerably in lattice strain, composition and reactivities. Prompt radiation analyses 19F(p,αγ), 16O(d,α), 12C(d,p), are useful for monitoring the anodizing procedures and subsequent oxidation: currently, interest centres on the mechanistic information obtained. RBS analysis using α-particles gives a much lower Si response from porous than from bulk silicon. Glancing angle proton recoil analyses reveal considerable quantities of hydrogen in the porous layers. These mutually consistent findings have considerable mechanistic significance; extensive Si-H bonding occurs following a 2 equivalent Faradaic process.

  17. Coaxial waveguide mode reconstruction and analysis with THz digital holography.

    PubMed

    Wang, Xinke; Xiong, Wei; Sun, Wenfeng; Zhang, Yan

    2012-03-26

    Terahertz (THz) digital holography is employed to investigate the properties of waveguides. By using a THz digital holographic imaging system, the propagation modes of a metallic coaxial waveguide are measured and the mode patterns are restored with the inverse Fresnel diffraction algorithm. The experimental results show that the THz propagation mode inside the waveguide is a combination of four modes TE₁₁, TE₁₂, TM₁₁, and TM₁₂, which are in good agreement with the simulation results. In this work, THz digital holography presents its strong potential as a platform for waveguide mode charactering. The experimental findings provide a valuable reference for the design of THz waveguides.

  18. Photonic-integrated circuit for continuous-wave THz generation.

    PubMed

    Theurer, Michael; Göbel, Thorsten; Stanze, Dennis; Troppenz, Ute; Soares, Francisco; Grote, Norbert; Schell, Martin

    2013-10-01

    We demonstrate a photonic-integrated circuit for continuous-wave (cw) terahertz (THz) generation. By comprising two lasers and an optical phase modulator on a single chip, the full control of the THz signal is enabled via a unique bidirectional operation technique. Integrated heaters allow for continuous tuning of the THz frequency over 570 GHz. Applied to a coherent cw THz photomixing system operated at 1.5 μm optical wavelength, we reach a signal-to-noise ratio of 44 dB at 1.25 THz, which is identical to the performance of a standard system based on discrete components.

  19. Research on THz stepped-frequency ISAR imaging

    NASA Astrophysics Data System (ADS)

    Liang, Meiyan; Zhang, Zhiheng; Zhang, Cunlin

    2016-11-01

    High resolution THz inverse synthetic aperture radar (ISAR) imaging for the aircraft is simulated using 0.22THz stepped-frequency (SF) radar system which is designed in the paper. Based on the small rotate angle and the far field approximation, the Range-Doppler algorithm is proposed to reconstruct THz ISAR image of the aircraft. The simulation results indicate that THz stepped-frequency radar can achieve high resolution ISAR images of the aircraft, the resolution of the ISAR images can reach centimeter-scale, which laid a theoretical foundation for radar imaging in THz band.

  20. Dielectric and structural characterisation of chalcogenide glasses via terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Ravagli, A.; Naftaly, M.; Craig, C.; Weatherby, E.; Hewak, D. W.

    2017-07-01

    Terahertz time-domain spectroscopy (THz TDS) was used to investigate a series of chalcogenide glasses. In particular, the dielectric properties at terahertz frequencies were determined and correlated with the glass composition. The experimental results showed a strong relationship between the dielectric properties and the polarizability of the glasses studied. A new explanation based on the coordination number of the metallic cations was proposed to understand these observations.

  1. Strong-Field THz Interactions with Wavepackets

    NASA Astrophysics Data System (ADS)

    Bucksbaum, Philip H.

    1998-03-01

    Intense THz radiation from photoconducting antennas are particularly useful for manipulating the structure and dynamics of atomic and molecular Rydberg states. We have used sub-picosecond ``half-cycle'' field pulses to follow both the radial(C. Raman, C.W.S. Conover, C.I. Sukenik, and P. H. Bucksbaum, Physical Review Letters 76), 2436 (1996). and angular motion(C.S. Raman, T.C. Weinacht, and P.H. Bucksbaum, Physical Review A 55), R3995-8 (1997). of wavepackets. The impulse imparted to an atomic electron by these pulses can also be used to produce or alter wavepacket motion. The THz radiation can be shaped by modulating optical radiation which photo-excites the antenna.(A. S. Weling et al., Appl. Phys. Lett. 64), 137, 1994. In this way we have produced intense tunable narrow-band THz radiation, which was employed to study population transfer in strongly driven Rydberg systems.(C. Raman, M. F. DeCamp and P. H. Bucksbaum, Optics Express 1) 186 (1997). The same techniques is used to arbitrarily adjust the intensity envelope of the THz pulse, alter its central frequency over a wide range, and to produce and control dispersion. When combined with active pulse-shaping and adaptive feedback techniques, wavepacket shapes and dispersion properties can be controlled.

  2. Very High Power THz Radiation Sources.

    PubMed

    Carr, G L; Martin, M C; McKinney, W R; Jordan, K; Neil, G R; Williams, G P

    2003-06-01

    We report the production of high power (20watts average, ∼ 1 Megawatt peak) broadbandTHz light based on coherent emission fromrelativistic electrons. Such sources areideal for imaging, for high power damagestudies and for studies of non-linearphenomena in this spectral range. Wedescribe the source, presenting theoreticalcalculations and their experimentalverification. For clarity we compare thissource with one based on ultrafast lasertechniques.

  3. THz local oscillator sources: performance and capabilities

    NASA Technical Reports Server (NTRS)

    Mehdi, I.; Chattopadhyah, G.; Schlecht, E.; Siegel, P.

    2002-01-01

    Frequency multiplier circuits based on planar GaAs Schottky diodes have made significant advances in the last decade. Useful power in the >1 THz range has now been demonstrated from a complete solid-state chain. This paper will review some of the technology responsible for this achievement along with presenting a brief look at future challenges.

  4. THz cavities and injectors for compact electron acceleration using laser-driven THz sources

    NASA Astrophysics Data System (ADS)

    Fakhari, Moein; Fallahi, Arya; Kärtner, Franz X.

    2017-04-01

    We present a design methodology for developing ultrasmall electron injectors and accelerators based on cascaded cavities excited by short multicycle THz pulses obtained from laser-driven THz generation schemes. Based on the developed concept for optimal coupling of the THz pulse, a THz electron injector and two accelerating stages are designed. The designed electron gun consists of a four cell cavity operating at 300 GHz and a door-knob waveguide to coaxial coupler. Moreover, special designs are proposed to mitigate the problem of thermal heat flow and induced mechanical stress to achieve a stable device. We demonstrated a gun based on cascaded cavities that is powered by only 1.1 mJ of THz energy in 300 cycles to accelerate electron bunches up to 250 keV. An additional two linac sections can be added with five and four cell cavities both operating at 300 GHz boosting the bunch energy up to 1.2 MeV using a 4-mJ THz pulse.

  5. Design and characterization of terahertz-absorbing nano-laminates of dielectric and metal thin films

    SciTech Connect

    Bolakis, Christos; Grbovic, Dragoslav; Lavrik, Nickolay V; Karunasiri, Gamani

    2010-01-01

    A terahertz-absorbing thin-film stack, containing a dielectric Bragg reflector and a thin chromium metal film, was fabricated on a silicon substrate for applications in bi-material terahertz (THz) sensors. The Bragg reflector is to be used for optical readout of sensor deformation under THz illumination. The THz absorption characteristics of the thin-film composite were measured using Fourier transform infrared spectroscopy. The absorption of the structure was calculated both analytically and by finite element modeling and the two approaches agreed well. Finite element modeling provides a convenient way to extract the amount of power dissipation in each layer and is used to quantify the THz absorption in the multi-layer stack. The calculation and the model were verified by experimentally characterizing the multi-layer stack in the 3-5 THz range. The measured and simulated absorption characteristics show a reasonably good agreement. It was found that the composite film absorbed about 20% of the incident THz power. The model was used to optimize the thickness of the chromium film for achieving high THz absorption and found that about 50% absorption can be achieved when film thickness is around 9 nm.

  6. Nanotechnology-supported THz medical imaging.

    PubMed

    Stylianou, Andreas; Talias, Michael A

    2013-01-01

    Over the last few decades, the achievements and progress in the field of medical imaging have dramatically enhanced the early detection and treatment of many pathological conditions. The development of new imaging modalities, especially non-ionising ones, which will improve prognosis, is of crucial importance. A number of novel imaging modalities have been developed but they are still in the initial stages of development and serious drawbacks obstruct them from offering their benefits to the medical field. In the 21 (st) century, it is believed that nanotechnology will highly influence our everyday life and dramatically change the world of medicine, including medical imaging. Here we discuss how nanotechnology, which is still in its infancy, can improve Terahertz (THz) imaging, an emerging imaging modality, and how it may find its way into real clinical applications. THz imaging is characterised by the use of non-ionising radiation and although it has the potential to be used in many biomedical fields, it remains in the field of basic research. An extensive review of the recent available literature shows how the current state of this emerging imaging modality can be transformed by nanotechnology. Innovative scientific concepts that use nanotechnology-based techniques to overcome some of the limitations of the use of THz imaging are discussed. We review a number of drawbacks, such as a low contrast mechanism, poor source performance and bulky THz systems, which characterise present THz medical imaging and suggest how they can be overcome through nanotechnology. Better resolution and higher detection sensitivity can also be achieved using nanotechnology techniques.

  7. Nanotechnology-supported THz medical imaging

    PubMed Central

    Stylianou, Andreas; Talias, Michael A

    2013-01-01

    Over the last few decades, the achievements and progress in the field of medical imaging have dramatically enhanced the early detection and treatment of many pathological conditions. The development of new imaging modalities, especially non-ionising ones, which will improve prognosis, is of crucial importance. A number of novel imaging modalities have been developed but they are still in the initial stages of development and serious drawbacks obstruct them from offering their benefits to the medical field. In the 21 st century, it is believed that nanotechnology will highly influence our everyday life and dramatically change the world of medicine, including medical imaging. Here we discuss how nanotechnology, which is still in its infancy, can improve Terahertz (THz) imaging, an emerging imaging modality, and how it may find its way into real clinical applications. THz imaging is characterised by the use of non-ionising radiation and although it has the potential to be used in many biomedical fields, it remains in the field of basic research. An extensive review of the recent available literature shows how the current state of this emerging imaging modality can be transformed by nanotechnology. Innovative scientific concepts that use nanotechnology-based techniques to overcome some of the limitations of the use of THz imaging are discussed. We review a number of drawbacks, such as a low contrast mechanism, poor source performance and bulky THz systems, which characterise present THz medical imaging and suggest how they can be overcome through nanotechnology. Better resolution and higher detection sensitivity can also be achieved using nanotechnology techniques. PMID:24555052

  8. Substrate independence of THz vibrational modes of polycrystalline thin films of molecular solids in waveguide THz-TDS

    NASA Astrophysics Data System (ADS)

    Harsha, S. Sree; Melinger, Joseph. S.; Qadri, S. B.; Grischkowsky, D.

    2012-01-01

    The influence of the metal substrate on the measurement of high resolution THz vibrational modes of molecular solids with the waveguide THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two-surface passivated substrates. The independence of the observed THz vibrational modes to the metal substrate is demonstrated. Independently, surface passivation is presented as a viable experimental addition to the waveguide THz-TDS technique to aid the characterization of samples with known reactivity to metal surfaces.

  9. Novel materials, fabrication techniques and algorithms for microwave and THz components, systems and applications

    NASA Astrophysics Data System (ADS)

    Liang, Min

    This dissertation presents the investigation of several additive manufactured components in RF and THz frequency, as well as the applications of gradient index lens based direction of arrival (DOA) estimation system and broadband electronically beam scanning system. Also, a polymer matrix composite method to achieve artificially controlled effective dielectric properties for 3D printing material is studied. Moreover, the characterization of carbon based nano-materials at microwave and THz frequency, photoconductive antenna array based Terahertz time-domain spectroscopy (THz-TDS) near field imaging system, and a compressive sensing based microwave imaging system is discussed in this dissertation. First, the design, fabrication and characterization of several 3D printed components in microwave and THz frequency are presented. These components include 3D printed broadband Luneburg lens, 3D printed patch antenna, 3D printed multilayer microstrip line structure with vertical transition, THz all-dielectric EMXT waveguide to planar microstrip transition structure and 3D printed dielectric reflectarrays. Second, the additive manufactured 3D Luneburg Lens is employed for DOA estimation application. Using the special property of a Luneburg lens that every point on the surface of the Lens is the focal point of a plane wave incident from the opposite side, 36 detectors are mounted around the surface of the lens to estimate the direction of arrival (DOA) of a microwave signal. The direction finding results using a correlation algorithm show that the averaged error is smaller than 1º for all 360 degree incident angles. Third, a novel broadband electronic scanning system based on Luneburg lens phased array structure is reported. The radiation elements of the phased array are mounted around the surface of a Luneburg lens. By controlling the phase and amplitude of only a few adjacent elements, electronic beam scanning with various radiation patterns can be easily achieved

  10. Design and research for biosensing THz microfluidic chips

    NASA Astrophysics Data System (ADS)

    Fan, Ning; Su, Bo; Zhang, Cong; Zhang, Cunlin

    2016-11-01

    Many Biomolecules vibration frequencies are in terahertz (0.1THz-10THz) frequency range, so terahertz (THz) technology is an essential tool for detecting biological molecules. However, due to terahertz strongly absorbed by water, it is difficult to detect these molecules for biological and chemical liquid samples. Therefore, we present a novel detection method by combining terahertz technology with microfluidic technology. The strong absorption of water is effectively overcome by controlling the length that terahertz passes through liquid samples. What's more, a higher signal to noise ratio is obtained through using less samples. In this paper, we designed a THz microfluidic chip that is easy to be fabricated by using the materials of Zeonor and polydimethylsiloxane (PDMS). Using terahertz time-domainspectroscopy (THz-TDS) system, we find that the chip has a high transmittance above 80% in the range from 0.2 THz to 2.6 THz. Then the THz spectra of deionized water and different kinds of solutions with different concentrations in the microfluidic chip were measured, respectively. In our research, it is found that different kinds of solutions have different transmission coefficients for THz. In addition, the THz transmission and absorption spectrum changes with the concentration of the same kind of solution.

  11. Invited Article: Single-shot THz detection techniques optimized for multidimensional THz spectroscopy

    SciTech Connect

    Teo, Stephanie M.; Ofori-Okai, Benjamin K.; Werley, Christopher A.; Nelson, Keith A.

    2015-05-15

    Multidimensional spectroscopy at visible and infrared frequencies has opened a window into the transfer of energy and quantum coherences at ultrafast time scales. For these measurements to be performed in a manageable amount of time, one spectral axis is typically recorded in a single laser shot. An analogous rapid-scanning capability for THz measurements will unlock the multidimensional toolkit in this frequency range. Here, we first review the merits of existing single-shot THz schemes and discuss their potential in multidimensional THz spectroscopy. We then introduce improved experimental designs and noise suppression techniques for the two most promising methods: frequency-to-time encoding with linear spectral interferometry and angle-to-time encoding with dual echelons. Both methods, each using electro-optic detection in the linear regime, were able to reproduce the THz temporal waveform acquired with a traditional scanning delay line. Although spectral interferometry had mediocre performance in terms of signal-to-noise, the dual echelon method was easily implemented and achieved the same level of signal-to-noise as the scanning delay line in only 4.5% of the laser pulses otherwise required (or 22 times faster). This reduction in acquisition time will compress day-long scans to hours and hence provides a practical technique for multidimensional THz measurements.

  12. Photonic generation for multichannel THz wireless communication.

    PubMed

    Shams, Haymen; Fice, Martyn J; Balakier, Katarzyna; Renaud, Cyril C; van Dijk, Frédéric; Seeds, Alwyn J

    2014-09-22

    We experimentally demonstrate photonic generation of a multichannel THz wireless signal at carrier frequency 200 GHz, with data rate up to 75 Gbps in QPSK modulation format, using an optical heterodyne technique and digital coherent detection. BER measurements were carried out for three subcarriers each modulated with 5 Gbaud QPSK or for two subcarriers modulated with 10 Gbaud QPSK, giving a total speed of 30 Gbps or 40 Gbps, respectively. The system evaluation was also performed with three subcarriers modulated with 12.5 Gbaud QPSK (75 Gbps total) without and with 40 km fibre transmission. The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate. This approach increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.

  13. Time-resolved THz studies of carrier dynamics in semiconductors, superconductors, and strongly-correlated electron materials

    SciTech Connect

    Kaindl, Robert A.; Averitt, Richard D.

    2006-11-14

    materials occur at lower energies. The terahertz (THz) regime is particularly rich in such fundamental resonances. This includes ubiquitous lattice vibrations and low-energy collective oscillations of conduction charges. In nanoscale materials, band structure quantization also yields novel infrared and THz transitions, including intersubband absorption in quantum wells. The formation of excitons in turn leads to low-energy excitations analogous to inter-level transitions in atoms. In transition-metal oxides, fundamental excitation gaps arise from charge pairing into superconducting condensates and other correlated states. This motivates the use of ultrafast THz spectroscopy as a powerful tool to study light-matter interactions and microscopic processes in nanoscale and correlated-electron materials.A distinct advantage of coherent THz pulses is that the amplitude and phase of the electric field can be measured directly, as the THz fields are coherent with the fs pulses from which they are generated. Using THz time-domain spectroscopy (THz-TDS), both the real and imaginary parts of the response functions (such as the dielectric function) are obtained directly without the need for Kramers?Kronig transforms. The THz response can also be expressed in terms of absorption and refractive index, or as the optical conductivity. The optical conductivity describes the current response of a many-body system to an electric field, an ideal tool to study conducting systems. A second important advantage is the ultrafast time resolution that results from the short temporal duration of the THz time-domain sources. In particular, optical-pump THz-probe spectroscopy enables a delicate probe of the transient THz conductivity after optical photoexcitation. These experiments can provide insight into quasiparticle interactions, phase transitions, or nonequilibrium dynamics. In this chapter we will provide many such examples. Since THz spectroscopy of solids is a quickly expanding field

  14. Very high power THz radiation sources

    SciTech Connect

    Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

    2002-10-31

    We report the production of high power (20 watts average, {approx} 1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source to one based on ultrafast laser techniques.

  15. Very High Power THz Radiation Sources

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-10-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity, we compare this sources with one based on ultrafast laser techniques.

  16. THz Emission Based On Intersubband Plasmon Resonances

    SciTech Connect

    Coquelin, M.; Zobl, R.; Strasser, G.; Gornik, E.; Bakshi, P.; Umansky, V.; Heiblum, M.

    2010-01-04

    The radiative decay of collective plasma oscillations as a new mechanism for THz emission is studied. This phenomenon is based on the attractive interaction of two intersubband plasmons. This interaction can be viewed as a collective e-e scattering phenomenon. The emission results fit very well to the results of the current voltage measurements indicating that the conditions for a plasma instability are reached.

  17. Carbon Nanotube Quantum Dots as THz Detectors

    DTIC Science & Technology

    2012-12-14

    devices that are viable for wafer -scale production. We recently started testing fabrication processes using epitaxial graphene on SiC in collaboration... laser sources at four different Fig. 4 Top: Drain current versus the gate voltage for different THz field intensities. Bottom: Temperature dependence...research. The first was the small coupling between the quantum dot and the powerful (10 mW) laser source. The second was the difficulty to reproduce the

  18. New application of terahertz time-domain spectrometry (THz-TDS) to the phonon-polariton observation on ferroelectric crystals

    NASA Astrophysics Data System (ADS)

    Nishizawa, Seizi; Tsumura, Naoki; Kitahara, Hideaki; Wada Takeda, Mitsuo; Kojima, Seiji

    2002-11-01

    A new instrument for terahertz time-domain spectroscopy (THz-TDS) has been developed. It consists of a composite THz-TDS system and a high throughput (Martin-Puplett) interferometer. The instrument is for use in the qualitative study of optoelectronic constants of materials. The spectral transmission intensity and phase shift related to phonon-polariton dispersion have been measured between 100 cm-1 and 3 cm-1 on ferroelectric crystals of industrial interest. These include bismuth titanate Bi4Ti3O12 (a key material for FeRAM), lithium niobate LiNbO3 (a typical nonlinear crystal for parametric oscillator applications) and lithium heptagermanate Li2Ge7O15 for surface elastic wave filter applications. The complex dielectric constants are well reproduced by the phonon-polariton dispersion relation based on the Kurosawa formula. The instrument details and phonon-polariton dispersion results are described.

  19. THz polarization difference imaging of aqueous targets

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Bajwa, Neha; Ramirez, Lucia; Grundfest, Warren; Taylor, Zachary

    2015-08-01

    This paper describes the basic design, implementation, and testing of a polarization difference imaging system for use on aqueous targets. The ultimate performance limitation of THz imaging in many active areas of research is clutter from surface geometry. While the signal to nose ratio (SNR) of standard THz imaging systems is quite large, the signal to clutter ratio (SCR) often faced in an imaging application is orders of magnitude lower and, in many cases, lower than the contrast to noise (CNR) resulting in imagery where the contrast mechanism of interest does not significantly contribute to the overall observed contrast. To overcome these limitations we develop a system that uses a circularly polarized source and linearly polarized detectors to acquire images of transverse electric (TE) and transverse magnetic (TM) reflectivities of the target over the same field of view. Geletin based tissue mimicking phantoms are fabricated with spatially varying water content and modified with a range of surface topologies and surface roughness. TE and TM images are combined to yield self-calibrated clutter-suppressed images. The resulting image indicates that the imaging field clutter affected both polarization channels nearly equally allowing the system to resolve differences in phantom water content. This design is a step toward windowless THz imaging capability critical for clinical translation where patient imaging is dominated by clutter.

  20. Active THz inspection of water content in plants

    NASA Astrophysics Data System (ADS)

    Etayo, D.; Iriarte, J. C.; Palacios, I.; Teniente, J.; Ederra, I.; Gonzalo, R.

    2010-04-01

    The THz range offers the possibility of measuring water content. This can be useful in wine industry to control plants water levels and also to decrease irrigation costs. This paper presents a THz imaging system used to characterise water content in leaves using frequency and time domain methods from 0.14 to 0.22 THz. Our results show the possibility of getting useful information out of the preformed measurements.

  1. Optical properties of human nails in THz frequency range

    NASA Astrophysics Data System (ADS)

    Guseva, Victoria A.; Gusev, Sviatoslav I.; Demchenko, Petr S.; Sedykh, Egor A.; Khodzitsky, Mikhail K.

    2017-03-01

    This work is devoted to investigation of optical properties (dispersion of refractive index, permittivity and absorption coefficient) of human nails in THz frequency range. These data were obtained by THz time-domain spectroscopy (TDS) technique in transmission mode. These results may be used to develop non-invasive technique of human pathologies control using nail as reference sample in reflection mode of THz TDS.

  2. Time domain measurement of the THz refractivity of water vapor.

    PubMed

    Yang, Yihong; Mandehgar, Mahboubeh; Grischkowsky, D

    2012-11-19

    We report the measurement of the essentially frequency independent refractivity of water vapor from 0.1 to 1 THz, independent of the simultaneous strong THz pulse broadening and absorption. The humidity dependent transit time of THz pulses through a 170 m long round trip path was measured to a precision of 0.1 ps, using a mode-locked laser as an optical clock.

  3. Multifrequency high precise subTHz-THz-IR spectroscopy for exhaled breath research

    NASA Astrophysics Data System (ADS)

    Vaks, Vladimir L.; Domracheva, Elena G.; Pripolzin, Sergey I.; Chernyaeva, Mariya B.

    2016-09-01

    Nowadays the development of analytical spectroscopy with high performance, sensitivity and spectral resolution for exhaled breath research is attended. The method of two-frequency high precise THz spectroscopy and the method of high precise subTHz-THz-IR spectroscopy are presented. Development of a subTHz-THz-IR gas analyzer increases the number of gases that can be identified and the reliability of the detection by confirming the signature in both THz and MIR ranges. The testing measurements have testified this new direction of analytical spectroscopy to open widespread trends of its using for various problems of medicine and biology. First of all, there are laboratory investigations of the processes in exhaled breath and studying of their dynamics. Besides, the methods presented can be applied for detecting intermediate and short time living products of reactions in exhaled breath. The spectrometers have been employed for investigations of acetone, methanol and ethanol in the breath samples of healthy volunteers and diabetes patients. The results have demonstrated an increased concentration of acetone in breath of diabetes patients. The dynamic of changing the acetone concentration before and after taking the medicines is discovered. The potential markers of pre-cancer states and oncological diseases of gastrointestinal tract organs have been detected. The changes in the NO concentration in exhaled breath of cancer patients during radiotherapy as well as increase of the NH3 concentration at gastrointestinal diseases have been revealed. The preliminary investigations of biomarkers in three frequency ranges have demonstrated the advantages of the multifrequency high precise spectroscopy for noninvasive medical diagnostics.

  4. 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.

  5. Dielectric property of MoS_2 crystal in terahertz and visible regions

    NASA Astrophysics Data System (ADS)

    Yan, Xianding; Zhu, Lipeng; Zhou, Yixuan; E, Yiwen; Wang, Li; Xu, Xinlong

    2015-08-01

    Two-dimensional materials such as MoS2 have attracted much attention in recent years due to their fascinating optoelectronic properties. Dielectric property of MoS2 is desired for the optoelectronic application. In this paper, terahertz (THz) time-domain spectroscopy and ellipsometry technology are employed to investigate the dielectric response of MoS2 crystal in THz and visible region. The real and imaginary parts of the complex dielectric constant of MoS2 crystal are found to follow a Drude model in THz region, which is due to the intrinsic carrier absorption. In visible region, the general trend of the complex dielectric constant is found to be described with a Lorentz model, while two remarkable peaks are observed at 1.85 and 2.03 eV, which have been attributed to the splitting arising from the combined effect of interlayer coupling and spin-orbit coupling. This work affords the fundamental dielectric data for the future optoelectronic applications with MoS2.

  6. Dissociation of D2+ by UV and THz light pulses

    NASA Astrophysics Data System (ADS)

    Xu, Tian-Yu; He, Feng

    2013-10-01

    The dissociation of D2+ in the few-cycle UV and THz light pulses is studied by numerically simulating the time-dependent Schrödinger equation. With only the UV pulse, we find the dissociation probability does not increase monotonously with the increasing of the UV pulse intensity or duration. The UV-triggered dissociation is streaked by the time-delayed THz light pulse, i.e., the nuclear momentum oscillates with the half of the THz period when the UV-THz time delay or the carrier envelope phase of the THz pulse is scanned. The difference of the maximum and minimum nuclear momenta equals the THz laser vector potential. The classical calculation of the Newtonian equation for a mass point moving on the THz light-modified molecular potential curves reproduces the quantum simulation results and therefore intuitively explores the physical scenario: The nuclear wave packets propagate along the THz field-dressed molecular potential curves adiabatically but make a fully diabatic transition, while the THz electric field changes direction. This study offers a visual angle to understand the molecular dissociation in the strong laser field with very long wavelengths.

  7. THz quantum cascade lasers for standoff molecule detection.

    SciTech Connect

    Chow, Weng Wah; Wanke, Michael Clement; Lerttamrab, Maytee; Waldmueller, Ines

    2007-10-01

    Remote optical detection of molecules, agents, and energetic materials has many applications to national security interests. Currently there is significant interest in determining under what circumstances THz frequency coverage will aid in a complete sensing package. Sources of coherent THz frequency (i.e. 0.1 to 10 THz) electromagnetic radiation with requisite power levels, frequency agility, compactness and reliability represent the single greatest obstacle in establishing a THz technology base, but recent advances in semiconductor-based quantum cascade lasers (QCLs) offer huge improvements towards the ultimate THz source goals. This project advanced the development of narrow-linewidth THz quantum cascade lasers. We developed theoretical tools to guide the improvement of standard THz quantum cascade lasers, the investigation of nonlinear optics employing infrared QCLs, and the exploration of quantum coherence to improve QCL performance. The latter was aimed especially towards achieving high temperature operation. In addition we developed a computer algorithm capable of shifting the frequencies of an existing THz QCL to a different frequency and invented a new type of laser that may enable room temperature THz generation in a electrically driven solid-state source.

  8. 3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure

    NASA Astrophysics Data System (ADS)

    Vogt, Dominik Walter; Leonhardt, Rainer

    2016-11-01

    We demonstrate broadband, low loss, and close-to-zero dispersion guidance of terahertz (THz) radiation in a dielectric tube with an anti-reflection structure (AR-tube waveguide) in the frequency range from 0.2 to 1.0 THz. The anti-reflection structure (ARS) consists of close-packed cones in a hexagonal lattice arranged on the outer surface of the tube cladding. The feature size of the ARS is in the order of the wavelength between 0.2 and 1.0 THz. The waveguides are fabricated with the versatile and cost efficient 3D-printing method. Terahertz time-domain spectroscopy (THz-TDS) measurements as well as 3D finite-difference time-domain simulations (FDTD) are performed to extensively characterize the AR-tube waveguides. Spectrograms, attenuation spectra, effective phase refractive indices, and the group-velocity dispersion parameters β 2 of the AR-tube waveguides are presented. Both the experimental and numerical results confirm the extended bandwidth and smaller group-velocity dispersion of the AR-tube waveguide compared to a low loss plain dielectric tube THz waveguide. The AR-tube waveguide prototypes show an attenuation spectrum close to the theoretical limit given by the infinite cladding tube waveguide.

  9. Substrate Independence of THz Vibrational Modes of Polycrystalline Thin Films of Molecular Solids in Waveguide THz-TDS

    DTIC Science & Technology

    2012-01-01

    THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two...vibrational modes with wave- guide THz-TDS. The investigation of substrate dependence is performed using salicylic acid as the test molecule. This...Al and a self assembled monolayer (SAM) on Au. Salicylic acid is first characterized in the pel- let form and then compared to the absorption features

  10. Frequency-domain spectroscopy using high-power tunable THz-wave sources: towards THz sensing and detector sensitivity calibration

    NASA Astrophysics Data System (ADS)

    Takida, Yuma; Minamide, Hiroaki

    2017-05-01

    The development of reliable, high-power, frequency-tunable terahertz (THz)-wave sources is crucial for a wide variety of applications, such as spectroscopy, imaging, and sensing. In order to generate frequency-tunable THz waves at room temperature, one of the most promising methods is a wavelength conversion in nonlinear optical crystals. Here, we present our recent results on high-power, widely-tunable, frequency-agile THz-wave sources based on nonlinear parametric processes in MgO:LiNbO3 crystals. By changing the noncollinear phase-matching condition in MgO:LiNbO3, the tunability of sub-nanosecond-pumped injection-seeded THz-wave parametric generators (is-TPGs) covers the 3.65-octave frequency range from 0.37 THz up to 4.65 THz. The monochromatic THz-wave output from is-TPGs is greater than 10 kW peak power with the linewidth of approximately 3 GHz and the stability of 1%. These is-TPG systems are reliable and promising high-power tunable THz-wave sources for frequency-domain spectroscopic measurements towards THz sensing and detector sensitivity calibration.

  11. Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide.

    PubMed

    Chu, Zheng; Liu, Jinsong; Wang, Kejia

    2012-05-01

    A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100  kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60  kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed.

  12. Technology trend in real-time, uncooled image sensors for sub-THz and THz wave detection

    NASA Astrophysics Data System (ADS)

    Oda, Naoki

    2016-05-01

    The author summarizes development of uncooled microbolometer terahertz (THz) focal plane arrays (FPAs) and real-time cameras for sub-THz and THz wave detection. The array formats are 320x240 and 640x480, and the cameras have several functions, such as lock-in imaging, external-trigger imaging, image processing (pixel binning and frame integration), beam profiling and so on. The FPAs themselves are sensitive to sub-THz, THz and infrared radiations. Active imaging systems based on the imagers are described. One of them is a real-time transmission-type THz microscope which contains a THz camera and a quantum cascade laser (QCL). The other one is an active sub-THz imaging system, where a transmission imaging mode and a reflection imaging mode can be switched with one-touch operation. Strong THz emitters, such as far-infrared gas lasers and QCLs, are strongly coherent and often produce interference fringes in an image. A method of reducing the interference fringes (beam homogenizing) is described. Microbolometer FPAs developed by other groups, antenna-coupled CMOS FPA, array detectors based on GaAs high-mobility heterostructure and so on are also summarized, which operate in real-time and at room temperature. A fair method of evaluating performance of detectors with different sizes and at different wavelengths is explained and the performances of the detectors are compared.

  13. Measurements of High-Field THz Induced Photocurrents in Semiconductors

    SciTech Connect

    Wiczer, Michael; /Illinois U., Urbana

    2007-11-07

    THz pulses have provided a useful tool for probing, with time resolution, the free carriers in a system. The development of methods to produce intense THz radiation has been slow since spectroscopists and condensed matter physicists first began probing materials with THz pulses. We have developed a method for producing intense ultra-short THz pulses, which have full width half maximum of 300 fs - approximately a half cycle of THz radiation. These intense half cycle pulses (HCPs) allow us to use THz radiation not only as a probe of the free carriers in a system but also as a source of excitation to alter a system in some way. In particular, HPCs perturb free carriers considerably in short time scales but show minimal effect to individual free carriers over long time. By exposing the semiconductor indium antimonide (InSb) to our intense THz HCP radiation, we have observed non-linear optical effects which suggest the generation of new free carriers by below band-gap THz photons. This generation of free carriers appears to be caused by an avalanche multiplication process, which should amplify the number of free carriers already in the system and then induce a current in the timescale of our THz pulse. This amplification on such a short timescale suggests the possibility of an ultra-fast detector of weak above band-gap radiation. We constructed a device which detects these currents by painting an electrode structure on the surface of the semiconductor. The currents induced across the electrodes by this avalanche multiplication process were measured and compared with other measurements of this non-linear optical process. We successfully measured THz induced currents in InSb, which indicate promise towards the development of an ultra-fast detector, and we gain insight into a possible physical explanation of the THz induced free carriers we observe in InSb.

  14. Spectral Trends of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Giménez de Castro, C. G.; Kudaka, A. S.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2017-01-01

    Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 - 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 - 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

  15. THz optics and metamaterials: Design, fabrication and characterization

    NASA Astrophysics Data System (ADS)

    Turaga, Shuvan Prashant

    In the past decade, terahertz(THz) based optics and metamaterials have been extensively researched to create components and devices in the frequency range of 0.1 to 5 THz also known as 'THz gap'. Metamaterials, in particular, have realized concepts such as negative refraction, slow light and superlensing through artificially engineered media. The naturally available materials have very weak interaction of terahertz light. Therefore, the design of THz metamaterials to manipulate THz radiation is an important task towards furthering the usage of terahertz light for practical applications. The thesis involved the development of two lab facilities for fabrication and characterization. A state-of-the-art two photon lithography( TPL) system was developed which enables us to manufacture 3D structures with sub-diffraction limit resolution(280nm at 800 nm wavelength). The software was written to enable easy fabrication of multiple structures with different algorithms. For characterizing our metamaterial structures in the terahertz regime, a THz time-domain spectroscopy(THz-TDS) and imaging system was built. This transmission based spectrometer has a dynamic range of 50 dB at 0.5 THz and a bandwidth of about 2.5 THz. To demonstrate the application of these home-built facilities, the metamaterials in the THz regime were fabricated using TPL and UV lithography. To investigate conductive coupling effects in meta-atoms, a new design was proposed, fabricated and characterized. As an application of TPL, free standing polymer helices were fabricated and coated with silver electroless plating. These silver helical metamaterials have potential application as circular polarizers in the MIR and THz regimes. The aspect ratio effects of these helical metamaterials were also studied in order to improve their polarizing performance.

  16. Method for producing high dielectric strength microvalves

    DOEpatents

    Kirby, Brian J.; Reichmuth, David S.; Shepodd, Timothy J.

    2006-04-04

    A microvalve having a cast-in-place and lithographically shaped mobile, polymer monolith for fluid flow control in microfluidic devices and method of manufacture. The microvalve contains a porous fluorinated polymer monolithic element whose pores are filled with an electrically insulating, high dielectric strength fluid, typically a perfluorinated liquid. This combination provides a microvalve that combines high dielectric strength with extremely low electrical conductivity. These microvalves have been shown to have resistivities of at least 100 G.OMEGA. and are compatible with solvents such as water at a pH between 2.7 and 9.0, 1-1 propanol, acetonitrile, and acetone.

  17. 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.

  18. Silicon Micromachined Microlens Array for THz Antennas

    NASA Technical Reports Server (NTRS)

    Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, IImran; Gill, John J.; Jung-Kubiak, Cecile D.; Llombart, Nuria

    2013-01-01

    5 5 silicon microlens array was developed using a silicon micromachining technique for a silicon-based THz antenna array. The feature of the silicon micromachining technique enables one to microfabricate an unlimited number of microlens arrays at one time with good uniformity on a silicon wafer. This technique will resolve one of the key issues in building a THz camera, which is to integrate antennas in a detector array. The conventional approach of building single-pixel receivers and stacking them to form a multi-pixel receiver is not suited at THz because a single-pixel receiver already has difficulty fitting into mass, volume, and power budgets, especially in space applications. In this proposed technique, one has controllability on both diameter and curvature of a silicon microlens. First of all, the diameter of microlens depends on how thick photoresist one could coat and pattern. So far, the diameter of a 6- mm photoresist microlens with 400 m in height has been successfully microfabricated. Based on current researchers experiences, a diameter larger than 1-cm photoresist microlens array would be feasible. In order to control the curvature of the microlens, the following process variables could be used: 1. Amount of photoresist: It determines the curvature of the photoresist microlens. Since the photoresist lens is transferred onto the silicon substrate, it will directly control the curvature of the silicon microlens. 2. Etching selectivity between photoresist and silicon: The photoresist microlens is formed by thermal reflow. In order to transfer the exact photoresist curvature onto silicon, there needs to be etching selectivity of 1:1 between silicon and photoresist. However, by varying the etching selectivity, one could control the curvature of the silicon microlens. The figure shows the microfabricated silicon microlens 5 x5 array. The diameter of the microlens located in the center is about 2.5 mm. The measured 3-D profile of the microlens surface has a

  19. Application of porous silicon in terahertz technology

    NASA Astrophysics Data System (ADS)

    Lo, Shu-Zee Alencious

    In this thesis, we discuss our efforts in developing porous silicon based devices for terahertz signal processing. In the first stage of our research, we demonstrate that porous silicon samples fabricated from highly doped p-type silicon can have adjustable refractive indices ranging from 1.5--2.1 and can exhibit a resistivity that is four orders of magnitude higher than that of the silicon wafer from which they were made. We show that the porous silicon becomes stable and relatively lossless after thermal oxidation. The partially oxidized porous silicon is shown to exhibit a smooth absorption spectrum, with low absorption loss of <10 cm-1 over the entire terahertz spectrum. As a proof of concept, we fabricated, for the first time, a porous silicon based multilayered Bragg filter with reflectance of 93% and full-width at half-maximum bandwidth of 0.26 THz. Compared with other multilayered filtering techniques, porous silicon has the advantage that it can be easily fabricated, and offers the possibility of forming multilayer and graded index structures for more advanced filters. The large surface area of nanoporous silicon makes it an especially attractive platform for applications in biochemical detection and diagnostics As part of our effort in developing terahertz waveguide for biosensing, we reported the world's first porous silicon based terahertz waveguide using the principle of surface plasmon polaritons. The effect of porous silicon film thickness on the propagation of surface plasmons is explained theoretically in this thesis and is found to be in good agreement with experimental results.

  20. Towards THz medical imaging; reflective imaging of animal tissues.

    PubMed

    Singh, Rahul S; Taylor, Zachary D; Culjat, Martin O; Grundfest, Warren S; Brown, Elliott R

    2008-01-01

    A reflective THz imaging system has been developed, and features a photoconductive switch and zero-bias Schottky diode detector. The system was used to image deli meats and can distinguish between muscle and adipose tissue based on water content. This capability is a step towards the development of THz medical imaging systems.

  1. Programmatic perspectives with technical examples for THz materials characterization

    NASA Astrophysics Data System (ADS)

    Buchwald, Walter

    2011-06-01

    THz technology has a rich history of use in the field of interstellar molecule identification where a variety of molecule specific vibrational and rotational spectroscopic signatures exist and has been aggressively investigated for use in advanced radar applications because of the immediate improvement in object resolution obtained at higher frequencies. Traditionally, high power THz systems have relied upon millimeter wave sources and frequency multiplication techniques to achieve acceptable output power levels, while lower power, table top spectroscopic systems, have relied on broadband incoherent light sources. With the advent of high power lasers, advances in non-linear optics, and new material systems, a number of promising techniques for the generation, detection and manipulation of THz radiation are currently under development and are considered the enabling technologies behind a variety of advanced THz applications. This work presents a programmatic overview of current trends in THz technology of interest to a variety of government organizations. It focuses on those techniques currently under investigation for the generation and detection of THz fields motivated, for example, by such diverse applications as metamaterial spectroscopy, TH imaging, long standoff chem/bio detection and THz communications. Examples of these new techniques will be presented which in turn will motivate the need for the characterization of application specific active and passive THz components.

  2. A scanned beam THz imaging system for medical applications

    NASA Astrophysics Data System (ADS)

    Taylor, Zachary D.; Li, Wenzao; Suen, Jon; Tewari, Priyamvada; Bennett, David; Bajwa, Neha; Brown, Elliott; Culjat, Martin; Grundfest, Warren; Singh, Rahul

    2011-10-01

    THz medical imaging has been a topic of increased interest recently due largely to improvements in source and detector technology and the identification of suitable applications. One aspect of THz medical imaging research not often adequately addressed is pixel acquisition rate and phenomenology. The majority of active THz imaging systems use translation stages to raster scan a sample beneath a fixed THz beam. While these techniques have produced high resolution images of characterization targets and animal models they do not scale well to human imaging where clinicians are unwilling to place patients on large translation stages. This paper presents a scanned beam THz imaging system that can acquire a 1 cm2 area with 1 mm2 pixels and a per-pixel SNR of 40 dB in less than 5 seconds. The system translates a focused THz beam across a stationary target using a spinning polygonal mirror and HDPE objective lens. The illumination is centered at 525 GHz with ~ 125 GHz of response normalized bandwidth and the component layout is designed to optically co-locate the stationary source and detector ensuring normal incidence across a 50 mm × 50 mm field of view at standoff of 190 mm. Component characterization and images of a test target are presented. These results are some of the first ever reported for a short standoff, high resolution, scanned beam THz imaging system and represent an important step forward for practical integration of THz medical imaging where fast image acquisition times and stationary targets (patients) are requisite.

  3. The mechanism of the dielectric relaxation in water.

    PubMed

    Popov, Ivan; Ishai, Paul Ben; Khamzin, Airat; Feldman, Yuri

    2016-05-18

    Although relating to the same system, the interpretations of the water spectra from Raman and Dielectric spectroscopy present independent pictures of the nature of water. We show that in the overlap region of the two methods it is possible to combine these views into a coherent concept of what drives the dynamic features of water. In this work, we develop the idea that the dielectric relaxation in water is driven by the migration of defects through the H-bond network, leading to a Debye-like peak in the lower frequencies. The deviation from the Debye law in the higher sub-THz frequencies is traced to a global fluctuation of the same H-bond network, clearly evident in the Raman Spectra. By incorporating these two views, a mathematical formalism is presented that can aptly explicate the dielectric spectra of liquid water.

  4. THz transceiver characterization : LDRD project 139363 final report.

    SciTech Connect

    Nordquist, Christopher Daniel; Wanke, Michael Clement; Cich, Michael Joseph; Reno, John Louis; Fuller, Charles T.; Wendt, Joel Robert; Lee, Mark; Grine, Albert D.

    2009-09-01

    LDRD Project 139363 supported experiments to quantify the performance characteristics of monolithically integrated Schottky diode + quantum cascade laser (QCL) heterodyne mixers at terahertz (THz) frequencies. These integrated mixers are the first all-semiconductor THz devices to successfully incorporate a rectifying diode directly into the optical waveguide of a QCL, obviating the conventional optical coupling between a THz local oscillator and rectifier in a heterodyne mixer system. This integrated mixer was shown to function as a true heterodyne receiver of an externally received THz signal, a breakthrough which may lead to more widespread acceptance of this new THz technology paradigm. In addition, questions about QCL mode shifting in response to temperature, bias, and external feedback, and to what extent internal frequency locking can improve stability have been answered under this project.

  5. [Study on THz spectra of nicotinic acid, nicotinamide and nicotine].

    PubMed

    Yu, Bin; Huang, Zhen; Wang, Xiao-yan; Zhao, Guo-zhong

    2009-09-01

    The terahertz (THz) spectra of nicotinic acid, nicotinamide and nicotine were studied at room temperature. The time-domain THz spectra were measured. The frequency-domain spectra were obtained by fast Fourier transform (FFT). The spectral response and the dispersive relationship of refractive index in THz spectral range were obtained. The results show that the samples have obvious spectral response in THz spectral range except nicotine. The corresponding stimulated spectra were given by using density functional theory (DFT) method for both nicotinamide and nicotinic acid. The origin of the absorption peaks of nicotinic acid and nicotinamide was explored. It is thought that the absorption peak of nicotinic acid is caused by the torsion and wagging of the molecule, but the absorption peaks of nicotinamide (except 1.93 THz) are caused by intermolecular or phonon mode. It was shown that the molecule structure and vibrational modes of nicotinic acid and nicotinamide can be analyzed by the combination of simulation and experimental results.

  6. Comparative Study of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2016-04-01

    We analyze a large set of 17 solar radio bursts observed at sub-THz (0.2 and 0.4 THz) in 2012-2014 together with the new solar patrol radio telescopes (45 and 90 GHz), operated at El Leoncito, in the Argentinean Andes, allowing the derivation of complete burst spectra in this unexplored range of frequencies. We discuss the uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission. The burst spectra were completed with microwave bursts data obtained by the Radio Solar Telescope Network - RSTN. The events selection was based on GOES soft X-rays burst reported for classes stronger then C. Nearly 50 percent of the bursts exhibited a frequency increasing sub-THz spectral component. The results suggest that the THz component might be always present, with the minimum turn-over frequencies shifting to higher frequencies for larger energies of the electrons producing the emissions.

  7. Dielectric properties of amorphous phase-change materials

    NASA Astrophysics Data System (ADS)

    Chen, C.; Jost, P.; Volker, H.; Kaminski, M.; Wirtssohn, M.; Engelmann, U.; Krüger, K.; Schlich, F.; Schlockermann, C.; Lobo, R. P. S. M.; Wuttig, M.

    2017-03-01

    The dielectric function of several amorphous phase-change materials has been determined by employing a combination of impedance spectroscopy (9 kHz-3 GHz) and optical spectroscopy from the far- (20 c m-1 , 0.6 THz) to the near- (12 000 c m-1 , 360 THz) infrared, i.e., from the DC limit to the first interband transition. While phase-change materials undergo a change from covalent bonding to resonant bonding on crystallization, the amorphous and crystalline phases of ordinary chalcogenide semiconductors are both governed by virtually the same covalent bonds. Here, we study the dielectric properties of amorphous phase-change materials on the pseudobinary line between GeTe and S b2T e3 . These data provide important insights into the charge transport and the nature of bonding in amorphous phase-change materials. No frequency dependence of permittivity and conductivity is discernible in the impedance spectroscopy measurements. Consequently, there are no dielectric relaxations. The frequency-independent conductivity is in line with charge transport via extended states. The static dielectric constant significantly exceeds the optical dielectric constant. This observation is corroborated by transmittance measurements in the far infrared, which show optical phonons. From the intensity of these phonon modes, a large Born effective charge is derived. Nevertheless, it is known that crystalline phase-change materials such as GeTe possess even significantly larger Born effective charges. Crystallization is hence accompanied by a huge increase in the Born effective charge, which reveals a significant change of bonding upon crystallization. In addition, a clear stoichiometry trend in the static dielectric constant along the pseudobinary line between GeTe and S b2T e3 has been identified.

  8. THz characterization of lysozyme at different conformations

    NASA Astrophysics Data System (ADS)

    Globus, Tatiana; Khromova, Tatyana; Lobo, Rebecca; Woolard, Dwight; Swami, Nathan; Fernandez, Erik

    2005-05-01

    This work demonstrates application of Fourier Transform Infrared Spectroscopy (FTIR) technique in the low terahertz frequency range of 10-25 cm-1 to discriminate between different protein conformations and evaluate possible application of THz spectroscopy for monitoring of protein folding-unfolding process. A specific procedure developed earlier for unfolding lysozyme by salt (KSCN) precipitation and refolding the lysozyme molecules by removing of KSCN and dissolving in sodium acetate was used to prepare three different forms of lysozyme. In addition, two standard procedures were used to prepare samples in unfolded conformation: denaturation at high temperature ~95° C followed by fast freezing, and dissolution in 6 M guanidine. Thin, air dried protein films were characterized as well as material in the form of gel. Spectra reveal resonance features in transmission which represent vibrational modes in the protein samples. A great variability of spectral features for the different conformational states showed the sensitivity of vibrational frequencies to the three dimensional structure of proteins. The results obtained on liquid (gel) samples indicate that THz transmission spectroscopy can be used for monitoring folding-unfolding process in a realistic, aqueous environment.

  9. Micromachined TWTs for THz Radiation Sources

    NASA Technical Reports Server (NTRS)

    Booske, John H.; vanderWeide, Daniel W.; Kory, Carol L.; Limbach, S.; Downey, Alan (Technical Monitor)

    2001-01-01

    The Terahertz (THz) region of the electromagnetic spectrum (about 300 - 3000 GHz in frequency or about 0.1 - 1 mm free space wavelength) has enormous potential for high-data-rate communications, spectroscopy, astronomy, space research, medicine, biology, surveillance, remote sensing, industrial process control, etc. It has been characterized as the most scientifically rich, yet under-utilized, region of the electromagnetic spectrum. The most critical roadblock to full exploitation of the THz band is lack of coherent radiation sources that are powerful (0.001 - 1.0 W continuous wave), efficient (> 1%), frequency agile (instantaneously tunable over 1% bandwidths or more), reliable, and comparatively inexpensive. To develop vacuum electron device (VED) radiation sources satisfying these requirements, fabrication and packaging approaches must be heavily considered to minimize costs, in addition to the basic interaction physics and circuit design. To minimize size of the prime power supply, beam voltage must be minimized, preferably 10 kV. Solid state sources satisfy the low voltage requirement, but are many orders of magnitude below power, efficiency, and bandwidth requirements. On the other hand, typical fast-wave VED sources in this regime (e.g., gyrotrons, FELs) tend to be large, expensive, high voltage and very high power devices unsuitable for most of the applications cited above. VEDs based on grating or inter-digital (ID) circuits have been researched and developed. However, achieving forward-wave amplifier operation with instantaneous fractional bandwidths > 1% is problematic for these devices with low-energy (< 15 kV) electron beams. Moreover, the interaction impedance is quite low unless the beam-circuit spacing is kept particularly narrow, often leading to significant beam interception. One solution to satisfy the THz source requirements mentioned above is to develop micromachined VEDs, or "micro-VEDs". Among other benefits, micro-machining technologies

  10. Dielectric metasurfaces

    NASA Astrophysics Data System (ADS)

    Valentine, Jason

    While plasmonics metasurfaces have seen much development over the past several years, they still face throughput limitations due to ohmic losses. On the other hand, dielectric resonators and associated metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will present our recent efforts to harness this freedom using metasurfaces formed from silicon and fabricated using CMOS-compatible techniques. Operating in the telecommunications band, I will discuss how we have used this platform to realize a number of novel functionalities including wavefront control, near-perfect reflection, and high quality factor resonances. In many cases the optical performance of these silicon-based metasurfaces can surpass their plasmonic counterparts. Furthermore, for some cases the surfaces are more amenable to large-area fabrication techniques.

  11. Artificial high birefringence in all-dielectric gradient grating for broadband terahertz waves

    PubMed Central

    Chen, Meng; Fan, Fei; Xu, Shi-Tong; Chang, Sheng-Jiang

    2016-01-01

    Subwavelength dielectric gratings are widely applied in the phase and polarization manipulation of light. However, the dispersion of the normal dielectric gratings is not flat while their birefringences are not enough in the THz regime. In this paper, we have fabricated two all-dielectric gratings with gradient grids in the THz regime, of which artificial birefringence is much larger than that of the equal-grid dielectric grating demonstrated by both experiments and simulations. The transmission and dispersion characteristics are also improved since the gradient grids break the periodicity of grating lattices as a chirp feature. From 0.6–1.4 THz, a broadband birefringence reaches 0.35 with a low dispersion and good linearity of phase shift, and the maximum phase shift is 1.4π. Furthermore, these gradient gratings are applied as half-wave plates and realize a linear polarization conversion with a conversion rate over 99%, also much higher than the equal-grid gratings. These gradient gratings show great advantages compared to the periodic gratings and provide a new way in the designing of artificial birefringence material. PMID:27934962

  12. Magnetic Fano resonances by design in symmetry broken THz meta-foils

    PubMed Central

    Wu, Jianfeng; Moser, Herbert O.; Li, Rujiang; Yang, Yihao; Jing, Liqiao; Chen, Hongsheng; Breese, Mark B. H.

    2017-01-01

    Magnetic Fano resonances in there-dimensional symmetry broken meta-foils at THz frequencies are theoretically and experimentally studied. Sharp Fano resonances occur due to the interference between different resonances and can be designed by choosing geometric parameters of the meta-foil. At the Fano resonances, the meta-foil supports antisymmetric modes, whereas, at the main resonance, only a symmetric mode exists. The meta-foil is left-handed at the Fano resonances and shows sharp peaks of the real part of the refractive index in transmission with small effective losses opening a way to very sensitive high-speed sensing of dielectric changes in the surrounding media and of mechanical configuration. PMID:28150797

  13. Magnetic Fano resonances by design in symmetry broken THz meta-foils

    NASA Astrophysics Data System (ADS)

    Wu, Jianfeng; Moser, Herbert O.; Li, Rujiang; Yang, Yihao; Jing, Liqiao; Chen, Hongsheng; Breese, Mark B. H.

    2017-02-01

    Magnetic Fano resonances in there-dimensional symmetry broken meta-foils at THz frequencies are theoretically and experimentally studied. Sharp Fano resonances occur due to the interference between different resonances and can be designed by choosing geometric parameters of the meta-foil. At the Fano resonances, the meta-foil supports antisymmetric modes, whereas, at the main resonance, only a symmetric mode exists. The meta-foil is left-handed at the Fano resonances and shows sharp peaks of the real part of the refractive index in transmission with small effective losses opening a way to very sensitive high-speed sensing of dielectric changes in the surrounding media and of mechanical configuration.

  14. Temperature-dependent time-domain THz spectroscopic study of spinel NiCo2O4 thin films

    NASA Astrophysics Data System (ADS)

    Silwal, Punam; Shan, Tianqi; Kim, Daeho; Talbayev, Diyar

    2013-03-01

    The unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order makes the spinel NiCo2O4 an attractive material for various technological applications. Our previous study showed that high quality epitaxial spinel NiCo2O4 films on MgAl2O4 (001) substrate exhibit metallic behavior accompanied by ferrimagnetic order. The electrical properties of these films can be tuned from metallic to insulating by changing the growth temperature. The comprehensive understanding of the microscopic details of carrier transport in these films requires the study of frequency-dependent optical properties. Terahertz time-domain spectroscopy (THz TDS) can determine the frequency dependent complex dielectric constant, refractive index, and optical conductivity. We used THz TDS to measure the optical properties of NiCo2O4 in the 0.2 - 2.7 THz spectral region. The complex conductivities display a Drude-type frequency response. The extrapolated DC conductivity is consistent with our previous work. The temperature- and growth-condition dependent Drude parameters provide further insight in the metal-insulator transition in these materials.

  15. Spiral Antenna-Coupled Microbridge Structures for THz Application.

    PubMed

    Gou, Jun; Zhang, Tian; Wang, Jun; Jiang, Yadong

    2017-12-01

    Bolometer sensor is a good candidate for THz imaging due to its compact system, low cost, and wideband operation. Based on infrared microbolometer structures, two kinds of antenna-coupled microbridge structures are proposed with different spiral antennas: spiral antenna on support layer and spiral antenna with extended legs. Aiming at applications in detection and imaging, simulations are carried out mainly for optimized absorption at 2.52 THz, which is the radiation frequency of far-infrared CO2 lasers. The effects of rotation angle, line width, and spacing of the spiral antenna on THz wave absorption of microbridge structures are discussed. Spiral antenna, with extended legs, is a good solution for high absorption rate at low absorption frequency and can be used as electrode lead simultaneously for simplified manufacturing process. A spiral antenna-coupled microbridge structure with an absorption rate of more than 75% at 2.52 THz is achieved by optimizing the structure parameters. This research demonstrates the use of different spiral antennas for enhanced and tunable THz absorption of microbridge structures and provides an effective way to fabricate THz microbolometer detectors with great potential in the application of real-time THz imaging.

  16. Water-vapor detection using asynchronous THz sampling.

    PubMed

    Brown, Michael S; Fiechtner, Gregory J; Rudd, J V; Zimdars, David A; Warmuth, Matthew; Gord, James R

    2006-03-01

    The use of a fiber-coupled terahertz (THz) transmitter/receiver pair for spectroscopic detection of water vapor is investigated. Transmission signals of an alumina cylinder demonstrate that the measurement approach can be applied in a windowless ceramic combustor. First, a conventional commercial transmitter/receiver pair is used to make measurements for frequencies to 1.25 THz. Water-vapor absorption is clearly evident within the alumina transparency window and is readily modeled using existing databases. A variety of data-acquisition schemes is possible using THz instrumentation. To assess signal-collection techniques, a prototype THz transmitter/receiver pair is then used with the asynchronous optical-sampling (ASOPS) technique to obtain asynchronous THz-sampling signals to 1 THz without the need for an optomechanical delay line. Two mode-locked Ti:sapphire lasers operating at slightly different repetition rates are used for pumping the transmitter and receiver independently to permit a complete time-domain THz signal to be recorded. The resulting repetitive phase walkout is demonstrated by collecting power spectra of room air that exhibit water-vapor absorption.

  17. Photoconductive ultrafast low gap materials: pulsed THz emitters and detectors

    NASA Astrophysics Data System (ADS)

    Petrov, Branko; Fekecs, Andre; Chicoine, Martin; Schiettekatte, Francois; Ares, Richard; Morris, Denis

    2014-03-01

    Commonly photoconductive (PC) switches used for pulsed THz generation and detection are made on GaAs which works at 800 nm. However, there is a need for PC materials compatible with laser sources emitting at 1550 nm since they are of high interest for fiber-coupled devices to be integrated in THz imaging and spectroscopy systems. We have developed such materials based on low bandgap III-V semiconductors. With our novel approach, based on cold-implantation of heavy ions followed by a rapid thermal annealing (RTA) treatment, it was possible to obtain high resistivity (up to 2500 Ω . cm) and short lifetime (<1ps) materials. THz PC antennas were made on these materials and their characteristics were studied by using a THz time-domain spectroscopy (TDS) setup. The impact of the RTA process and different electrode designs were investigated in order to compare the characteristics of PC antennas in terms of amplitude, bandwidth, and signal to noise ratio. For the emitters, bias-voltage and pump-power dependences are shown. Remarkably high electric field (>50 kV/cm) could be applied for increased emission of pulsed THz radiation due to the high resistivity of our materials. Our THz-TDS setup offers measurement capabilities from 0.1 to 3 THz.

  18. Design and simulations of CAEP THz FEL resonator

    NASA Astrophysics Data System (ADS)

    Dou, Yuhuan; Shu, Xiaojian; Deng, Derong; Yang, Xingfan; Li, Ming

    2015-02-01

    A high power China Academy of Engineering Physics(CAEP) THz free electron laser (FEL) is designed and optimized in a radiation frequency range of 1~3 THz and average output power of about 10 W. The main work focuses on the optimization of different schemes through physical analysis. The wiggler peak field strength and electron beam energy have been selected with eleven frequencies ranging from 1 THz to 3 THz. It is found that the values of the gain and output power of the cavity are largest at 2.6 THz. So we can test the facility at this frequency. While the value of the output power is less than the design goal at the lower frequency region of about 1.0 THz due to the serious slippage between the electron bunch and radiation pulse. To increase the output power at the lower frequency region, the scheme of elliptical hole-coupling optical resonator is proposed to solve this problem. The simulation results show that the elliptical hole-coupling output is effective and applicable for the THz FEL and the output power can be increased by more than 30%.

  19. Reflective terahertz (THz) imaging: system calibration using hydration phantoms

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Garritano, James; Lee, Yoon Kyung; Tewari, Priyamvada; Sung, Shijun; Maccabi, Ashkan; Nowroozi, Bryan; Babakhanian, Meghedi; Sanghvi, Sajan; Singh, Rahul; Grundfest, Warren; Taylor, Zachary

    2013-02-01

    Terahertz (THz) hydration sensing continues to gain traction in the medical imaging community due to its unparalleled sensitivity to tissue water content. Rapid and accurate detection of fluid shifts following induction of thermal skin burns as well as remote corneal hydration sensing have been previously demonstrated in vivo using reflective, pulsed THz imaging. The hydration contrast sensing capabilities of this technology were recently confirmed in a parallel 7 Tesla Magnetic Resonance (MR) imaging study, in which burn areas are associated with increases in local mobile water content. Successful clinical translation of THz sensing, however, still requires quantitative assessments of system performance measurements, specifically hydration concentration sensitivity, with tissue substitutes. This research aims to calibrate the sensitivity of a novel, reflective THz system to tissue water content through the use of hydration phantoms for quantitative comparisons of THz hydration imagery.Gelatin phantoms were identified as an appropriate tissue-mimicking model for reflective THz applications, and gel composition, comprising mixtures of water and protein, was varied between 83% to 95% hydration, a physiologically relevant range. A comparison of four series of gelatin phantom studies demonstrated a positive linear relationship between THz reflectivity and water concentration, with statistically significant hydration sensitivities (p < .01) ranging between 0.0209 - 0.038% (reflectivity: %hydration). The THz-phantom interaction is simulated with a three-layer model using the Transfer Matrix Method with agreement in hydration trends. Having demonstrated the ability to accurately and noninvasively measure water content in tissue equivalent targets with high sensitivity, reflective THz imaging is explored as a potential tool for early detection and intervention of corneal pathologies.

  20. THz-Pulse-Induced Selective Catalytic CO Oxidation on Ru.

    PubMed

    LaRue, Jerry L; Katayama, Tetsuo; Lindenberg, Aaron; Fisher, Alan S; Öström, Henrik; Nilsson, Anders; Ogasawara, Hirohito

    2015-07-17

    We demonstrate the use of intense, quasi-half-cycle THz pulses, with an associated electric field component comparable to intramolecular electric fields, to direct the reaction coordinate of a chemical reaction by stimulating the nuclear motions of the reactants. Using a strong electric field from a THz pulse generated via coherent transition radiation from an ultrashort electron bunch, we present evidence that CO oxidation on Ru(0001) is selectively induced, while not promoting the thermally induced CO desorption process. The reaction is initiated by the motion of the O atoms on the surface driven by the electric field component of the THz pulse, rather than thermal heating of the surface.

  1. Room temperature strong light-matter coupling in 3D THz meta-atoms (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Paulillo, Bruno; Manceau, Jean-Michel; Li, Lianhe; Linfield, Edmund; Colombelli, Raffaele

    2016-04-01

    We demonstrate strong light-matter coupling at room temperature in the terahertz (THz) spectral region using 3D meta-atoms with extremely sub-wavelength volumes. Using an air-bridge fabrication scheme, we have implemented sub-wavelength 3D THz micro-resonators that rely on suspended loop antennas connected to semiconductor-filled patch cavities. We have experimentally shown that they possess the functionalities of lumped LC resonators: their frequency response can be adjusted by independently tuning the inductance associated the antenna element or the capacitance provided by the metal-semiconductor-metal cavity. Moreover, the radiation coupling and efficiency can be engineered acting on the design of the loop antenna, similarly to conventional RF antennas. Here we take advantage of this rich playground in the context of cavity electrodynamics/intersubband polaritonics. In the strong light-matter coupling regime, a cavity and a two-level system exchange energy coherently at a characteristic rate called the vacuum Rabi frequency ΩR which is dominant with respect to all other loss mechanisms involved. The signature, in the frequency domain, is the appearance of a splitting between the bare cavity and material system resonances: the new states are called upper and a lower polariton branches. So far, most experimental demonstrations of strong light-matter interaction between an intersubband transition and a deeply sub-wavelength mode in the THz or mid-infrared ranges rely on wavelength-scale or larger resonators such as photonic crystals, diffractive gratings, dielectric micro-cavities or patch cavities. Lately, planar metamaterials have been used to enhance the light-matter interaction and strongly reduce the interaction volume by engineering the electric and magnetic resonances of the individual subwavelength constituents. In this contribution we provide evidence of strong coupling between a THz intersubband transition and an extremely sub-wavelength mode (≈λ/10

  2. Josephson broadband spectroscopy to 1 THz

    NASA Astrophysics Data System (ADS)

    Edstam, J.; Olsson, H. K.

    1994-05-01

    We demonstrate the operation of a ``Josephson Broadband Spectrometer'' (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.

  3. Development of SIS Mixers for 1 THz

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, J.; Kooi, J.; Chattopadhyay, G.; Bumble, B.; LeDuc, H. G.; Stern, J. A.

    1998-01-01

    SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4 Delta/h). However, the performance degrades rapidly above the gap frequency of niobium (2 Delta/h approx. 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.

  4. Free-standing THz electromagnetic metamaterials.

    PubMed

    Moser, H O; Kong, J A; Jian, L K; Chen, H S; Liu, G; Bahou, M; Kalaiselvi, S M P; Maniam, S M; Cheng, X X; Wu, B I; Gu, P D; Chen, A; Heussler, S P; bin Mahmood, Shahrain; Wen, L

    2008-09-01

    Using micromanufactured S-shaped gold strings suspended in free space by means of window-frames, we experimentally demonstrate an electromagnetic meta-material (EM(3)) in which the metallic structures are no longer embedded in matrices or deposited on substrates such that the response is solely determined by the geometrical parameters and the properties of the metal. Two carefully aligned and assembled window-frames form a bi-layer chip that exhibits 2D left-handed pass-bands corresponding to two different magnetic resonant loops in the range of 1.4 to 2.2 THz as characterized by Fourier transform interferometry and numerical simulation. Chips have a comparably large useful area of 56 mm(2). Our results are a step towards providing EM(3) that fulfill the common notions of a material.

  5. Coupleurs fibres - metasurfaces aux frequences THz

    NASA Astrophysics Data System (ADS)

    Girard, Martin

    Metamaterials are a class of arficial materials where the electromagnetic properties can be tailored during the design process. Currently demonstrated properties are varied, ranging from frequency filters to enhancement of quentum effects such as photon spin Hall effect. While these materials are mastered from a theoretical point of view, their fabrication is much more complicated. It is generally accepted that metamaterial elements must be under the effective medium limit (Lambda < lambda/10). Moreover, assembly of a 3D periodical system becomes much more complicated for small elements. For this reason, metamaterials are usually printed in 2D, on a surface, which are called metasurfaces. Generally, these are produced for the THz frequencies (˜ 1012 Hz) or lower to have a large wavelength and thus easy fabrication. Working at THz frequencies also carries additional problems. Absorption in traditional optical mediums is typically large (for exemple, BK7 glass has losses of 20 dB / cm) and powers supplied by THz sources are generally weak ( 100 muW for a THz-TDS standard source). Metasurfaces can thus play an important role by replacing traditional mediums. Moreover, we can use the resonant properties of metamaterials to produce sensors and other devices. Currently, the metasurfaces are used in conjuction with a free-space beam instead of a typical waveguide, which may be problematic when implementing devices. A simple solution to this problem is to use the metamaterial as a standard coupler by placing a waveguide above the metasurface. As stated before, we generally consider metasurfaces as effective mediums, where the permittivity is insensitive to the angle of the incident beam. However, a large amount of publications on this subject shows that this is not respected. This can have a huge impact on properties of a coupler based on such a material. First, modelisation is not a simple 2D mode calculation with a simple expression for permittivity. Second, contra

  6. Superconducting Solenoid for Superfast THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bragin, A. V.; Khrushchev, S. V.; Kubarev, V. V.; Mezencev, N. A.; Tsukanov, V. M.; Sozinov, G. I.; Shkaruba, V. A.

    This project is related to new spectroscopy method in little-developed THz range. The method is founded on using of a free electron laser (NovoFEL) with high spectral power radiation which can be smoothly tuned in desirable range of spectrum. The objects of research of this method are fast processes in physics, chemical and biological reactions. Uniform magnetic field of 6 T value in the research area can considerably increase possibilities of this method. The magnetic field will modulate radiation of free molecules induction on characteristic frequencies of the Zeeman splitting that gives more possibilities of identification of molecules having even weak magnetic momentum. Moreover, the use of magnetic field allows essentially increase sensitivity of this method due to almost complete separation of weak measuring signals from powerful radiation of the laser. A superconducting solenoid was developed for this method. Its design and peculiarities are described in this paper.

  7. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging.

    PubMed

    Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P; Zolliker, Peter

    2016-02-06

    In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8-14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed.

  8. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging

    PubMed Central

    Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P.; Zolliker, Peter

    2016-01-01

    In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8–14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. PMID:26861341

  9. Perspective: Ultrafast magnetism and THz spintronics

    SciTech Connect

    Walowski, Jakob; Münzenberg, Markus

    2016-10-14

    This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

  10. Perspective: Ultrafast magnetism and THz spintronics

    NASA Astrophysics Data System (ADS)

    Walowski, Jakob; Münzenberg, Markus

    2016-10-01

    This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

  11. Porous media

    SciTech Connect

    Bullien, F.A.L. . Dept. of Chemical Engineering)

    1992-01-01

    The unique property of a porous medium, the one that distinguishes it from other solid bodies on the one hand and from simple conduits on the other, is its complicated pore structure. Fluid flow, diffusion, and electrical conduction in porous media take place within extremely complicated microscopic boundaries that in the past made a rigorous solution of the equations of change in the capillary network practically impossible. The past state of affairs is one of the reasons why some of the brilliant and successful practitioners in the field of flow through porous media have tried, as much as possible, to stick with the continuum approach in which no attention is paid to pores or pore structure. Another reason is that the continuum approach is often adequate for the phenomenological description of macroscopic transport processes in porous media. This book has been written with the primary purpose of presenting in an organized manner the most pertinent information available on the role of pore structure and then putting it to use in the interpretation of experimental data and the results of model calculations.

  12. Dielectric metamaterials with toroidal dipolar response

    DOE PAGES

    Basharin, Alexey A.; Kafesaki, Maria; Economou, Eleftherios N.; ...

    2015-03-27

    Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here, we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. In addition, we show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials’ macroscopic response. Due to the unique field configuration of the toroidal mode, the proposed metamaterialsmore » could serve as a platform for sensing or enhancement of light absorption and optical nonlinearities.« less

  13. Dielectric Metamaterials with Toroidal Dipolar Response

    NASA Astrophysics Data System (ADS)

    Basharin, Alexey A.; Kafesaki, Maria; Economou, Eleftherios N.; Soukoulis, Costas M.; Fedotov, Vassili A.; Savinov, Vassili; Zheludev, Nikolay I.

    2015-01-01

    Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here, we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. We show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials' macroscopic response. Because of the unique field configuration of the toroidal mode, the proposed metamaterials could serve as a platform for sensing or enhancement of light absorption and optical nonlinearities.

  14. FLUTE: A versatile linac-based THz source

    SciTech Connect

    Nasse, M. J.; Schuh, M.; Schwarz, M.; Naknaimueang, S.; Mathis, Y.-L.; Rossmanith, R.; Wesolowski, P.; Huttel, E.; Plech, A.; Schmelling, M.; Mueller, A.-S.

    2013-02-15

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short ({approx}1 ps) THz pulses (up to {approx}4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range ({approx}100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

  15. FLUTE: a versatile linac-based THz source.

    PubMed

    Nasse, M J; Schuh, M; Naknaimueang, S; Schwarz, M; Plech, A; Mathis, Y-L; Rossmanith, R; Wesolowski, P; Huttel, E; Schmelling, M; Müller, A-S

    2013-02-01

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (~1 ps) THz pulses (up to ~4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (~100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

  16. The Jefferson Lab High Power THz User Facility

    SciTech Connect

    John Klopf; Amelia Greer; Joseph Gubeli; George Neil; Michelle D. Shinn; Timothy Siggins; David W. Waldman; Gwyn Williams; Alan Todd; Vincent Christina; Oleg Chubar

    2007-04-27

    We describe here, a high power (100 Watt average, 10 MW peak) broadband THz facility based on emission from sub-picosecond bunches of relativistic electrons and the beam transport system that delivers this beam in to a user laboratory.

  17. High power THz sources and applications at ENEA-Frascati

    NASA Astrophysics Data System (ADS)

    Gallerano, G. P.; Doria, A.; Giovenale, E.; Spassovsky, I.

    2014-01-01

    ENEA has a long term expertise in the development of powerful short-pulse mm-wave and THz radiation sources driven by free electrons. Various electron-wave interaction schemes were successfully tested in the past, including Cerenkov and Smith-Purcell radiators as well as undulator devices. Two THz-FEL sources are currently available, covering altogether the spectral range from 90 GHz to 0.7 THz. Recently a novel Electro-Magnetic pulser, capable of providing both nanosecond THz electromagnetic (EM) radiation pulses and electrostatic (ES) pulses with identical time duration in one device has been designed and is currently under development. The pulser will allow, for the first time, direct comparison of EM and ES pulses on biological systems with peak electric fields that are significantly higher than any reported to date.

  18. 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.

  19. Highly-efficient THz generation using nonlinear plasmonic metasurfaces

    NASA Astrophysics Data System (ADS)

    Tymchenko, M.; Gomez-Diaz, J. S.; Lee, J.; Belkin, M. A.; Alù, A.

    2017-10-01

    Nonlinear metasurfaces loaded with multi-quantum-well (MQW) heterostructures constitute a rapidly progressing class of optical devices that combine high nonlinear generation efficiency with an ultrathin profile. Here, we introduce and discuss terahertz (THz) difference-frequency generation (DFG) using MQW-based plasmonic metasurfaces and present a comprehensive theory for their rigorous electromagnetic analysis. We explicitly take into account complex phenomena associated with the local intensity saturation of intersubband transitions and identify fundamental upper-bounds for DFG conversion efficiency. Using this framework, we design and analyze a nonlinear DFG metasurface providing giant DFG nonlinear response and conversion efficiency up to 0.01% at 5.8 THz. Such metasurface can be used to generate 0.15 mW of THz power using pump intensities in the kW cm-2 range. We envision that such DFG metasurfaces can become a platform for uncooled, compact, and highly-efficient continuous-wave THz sources.

  20. High precision spectroscopy and imaging in THz frequency range

    NASA Astrophysics Data System (ADS)

    Vaks, Vladimir L.

    2014-03-01

    Application of microwave methods for development of the THz frequency range has resulted in elaboration of high precision THz spectrometers based on nonstationary effects. The spectrometers characteristics (spectral resolution and sensitivity) meet the requirements for high precision analysis. The gas analyzers, based on the high precision spectrometers, have been successfully applied for analytical investigations of gas impurities in high pure substances. These investigations can be carried out both in absorption cell and in reactor. The devices can be used for ecological monitoring, detecting the components of chemical weapons and explosive in the atmosphere. The great field of THz investigations is the medicine application. Using the THz spectrometers developed one can detect markers for some diseases in exhaled air.

  1. Tunable THz perfect absorber using graphene-based metamaterials

    NASA Astrophysics Data System (ADS)

    Faraji, Mahboobeh; Moravvej-Farshi, Mohammad Kazem; Yousefi, Leila

    2015-11-01

    A tunable THz absorber, with absorbance more than 90% is proposed, and numerically characterized. The absorber structure is based on metamaterials with unit cells consisting of two patterned graphene layers separated by a 5-nm thick layer of Al2O3. Numerical results show that when the chemical potential of the top graphene microribbons are tuned by an external variable bias and that of the lower graphene fishnet is kept at μC=0, frequency of the absorption peaks can be tuned as desired, therefore we can have a tunable or switchable absorber. The proposed absorber can have applications in designing tunable reflective THz filters or tunable THz switches and modulators. It can also be used for cloaking objects in THz range.

  2. Calculations for Tera-Hertz (THZ) Radiation Sources

    SciTech Connect

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    We explore possibilities for THz sources from 0.3-30 THz. While still inaccessible, this broad gap is even wider for advanced acceleration schemes extending from X or, at most, W band RF at the low end up to CO{sub 2} lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that lower frequency, superconducting RF is currently preferred. Similarly, the validity of modeling techniques varies greatly over this range of frequencies but generally mandates coupling Maxwell's equations to the appropriate device transport physics for which there are many options. Here we study radiation from undulatory-shaped transmission lines using finite-difference, time-domain (FDTD) simulations. Also, we present Monte-Carlo techniques for pulse generation. Examples of THz sources demonstrating coherence are shown with the goal of optimizing on-chip THz radiators for applications that may lead to accelerators.

  3. SUB-THz RADIATION MECHANISMS IN SOLAR FLARES

    SciTech Connect

    Fleishman, Gregory D.; Kontar, Eduard P.

    2010-02-01

    Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

  4. THz time-domain spectroscopy imaging for mail inspection

    NASA Astrophysics Data System (ADS)

    Zhang, Liquan; Wang, Zhongdong; Ma, Yanmei; Hao, Erjuan

    2011-08-01

    Acquiring messages from the mail but not destroying the envelope is a big challenge in the war of intelligence. If one can read the message of the mail when the envelope is closed, he will benefit from the message asymmetry and be on a good wicket in the competition. In this paper, we presented a transmitted imaging system using THz time-domain spectroscopy technology. We applied the system to image the mail inside an envelope by step-scanning imaging technology. The experimental results show that the THz spectroscopy can image the mail in an envelope. The words in the paper can be identified easily from the background. We also present the THz image of a metal blade in the envelope, in which we can see the metal blade clearly. The results show that it is feasible of THz Time-Domain Spectroscopy Imaging for mail inspection applications.

  5. THz QCL self-mixing interferometry for biomedical applications

    NASA Astrophysics Data System (ADS)

    Rakić, Aleksandar D.; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Wilson, Stephen J.; Nikolić, Milan; Valavanis, Alexander; Indjin, Dragan; Linfield, Edmund H.; Davies, A. Giles; Ferguson, Blake; Walker, Graeme; Schaider, Helmut; Soyer, H. Peter

    2014-09-01

    In this paper, we introduce the self-mixing phenomenon in terahertz quantum cascade lasers (THz QCLs) and present recent advancements in the development of coherent THz imaging and sensing systems that exploit the self-mixing effect. We describe an imaging method which utilises the interferometric nature of optical feedback in a THz QCL to employ it as a homodyning transceiver. This results in a highly sensitive and compact scheme. Due to the inherently low penetration depth of THz radiation in hydrated biological tissue, imaging of superficial skin is an ideal application for this technique. We present results for imaging of excised skin tissue, showing high-contrast between different tissue types and pathologies.

  6. Anisotropic dielectric relaxation of the water confined in nanotubes for terahertz spectroscopy studied by molecular dynamics simulations.

    PubMed

    Qi, Wenpeng; Chen, Jige; Yang, Junwei; Lei, Xiaoling; Song, Bo; Fang, Haiping

    2013-07-03

    The dynamics and structure of the hydrogen-bond network in confined water are of importance in understanding biological and chemical processes. Recently, terahertz (THz) time domain spectroscopy was widely applied for studying the kinetics of molecules and the hydrogen-bond network in water. However, the characteristics of the THz spectroscopy varying with respect to the confinement and the mechanism underlying the variation are still unclear. Here, on the basis of molecular dynamics simulations, the relationship between the anisotropic dielectric relaxation and the structure of the water confined in a carbon nanotube (CNT) was investigated. The results show that there are two preferred hydrogen-bond orientations of the confined water in the nanotube: (1) parallel to the CNT axis and (2) perpendicular to the CNT axis, which are clearly different. Moreover, the response of the orientations to the increment of the CNT diameters is opposite, leading to the opposite variations of the dielectric relaxation times along the two directions. The anisotropy in the relaxation time can be presented by the anisotropic dielectric permittivity which is able to be observed through THz spectroscopy. The anormal behaviors above are attributed to the special structure of the water close to the nanotube wall due to the confinement and hydrophobicity of CNT. These studies contribute an important step in understanding the THz experiments of water in nanoscales, and designing a chamber for specific chemical and biological reactions by controlling the diameters and materials of the nanotube.

  7. Analysis of cavity and window for THz gyrotron

    SciTech Connect

    Alaria, Mukesh Kumar; Mukherjee, P.; Rao, R.R.; Sinha, A.K. E-mail: aksinha@ceeri.ernet.in

    2011-07-01

    In this paper study of cavity and window has been carried out using Ansoft HFSS for Terahertz Gyrotron. Eigen mode analysis of the cavity has been carried out at 1 THz. An idea about the operating modes in the cavity of the Gyrotron and obtained the simulated Eigen frequency and field pattern of the modes. The design of window for 1 THz Gyrotron has also been carried out using HFSS. The simulated results have also been compared with ST microwave studio. (author)

  8. Nanoscale Imaging Technology for THz Frequency Transmission Microscopy

    DTIC Science & Technology

    2014-12-16

    Nanoscale Imaging Technology for THz Frequency Transmission Microscopy final progress report The views, opinions and/or findings contained in this...Irvine 5171 California Avenue, Suite 150 Irvine, CA 92697 -7600 30-Jun-2014 ABSTRACT Final Report: Nanoscale Imaging Technology for THz Frequency...Francisco, CA. 10. Peter Burke “Nanochannel Trap Arrays for Monitoring Single Mitochondrion Behavior”,NCI-NIBIB Point of Care Technologies for

  9. Rotational Spectroscopy for Astrophysical Applications: the Thz Frequency Region

    NASA Astrophysics Data System (ADS)

    Puzzarini, Cristina; Cazzoli, Gabriele

    2011-06-01

    Recent missions, such as the Herschel Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA), have pointed out the need for precise and accurate frequency measurements and spectroscopic parameters in the THz range. In the present contribution, the THz spectrometer working at the University of Bologna and its applications are presented. The focus is here on the accuracy of the retrieved transition frequencies of neutral as well as ionic species and on line-broadening investigations.

  10. Co-integrated microfluidic and THz functions for biochip devices

    NASA Astrophysics Data System (ADS)

    Laurette, S.; Treizebre, A.; Bocquet, B.

    2011-06-01

    TeraHertz (THz) spectroscopy is becoming an alternative way to probe biological interactions in real-time conditions. However, accurate and reproducible THz measurements of aqueous solutions, largely represented in life sciences, remain difficult. A THz microsystem which couples both electromagnetic and microfluidic integrated functions is presented here. Its technological process is accurately detailed and enables easy designs of advanced THz and microfluidic functions. It is composed of the deposition of gold wires on a glass wafer to guide the THz waves. Then, a whole silicon wafer is bonded by using a thermosensitive-polymer thermo-compression. Silicon is deep-etched to create the microchannels which are finally covered with a second glass wafer. This bonding-etching process enables huge freedom and independence for electromagnetic and microfluidic designs. The technological process characterization has shown that the manufactured biochip is compatible with pressures up to 37 bar. First measurements with empty and water-filled channels have been carried out and have shown the ability to perform THz spectroscopy inside the chip. Then, first measurements on proteins have been performed and shown the system ability to probe protein concentration. This kind of microfluidic microsystem, allowing complex design for integrated electronic and microfluidic circuits, defines a true new instrumental way for life science investigations.

  11. Investigation on 2.45-THz array transmission imaging

    NASA Astrophysics Data System (ADS)

    Yao, Rui; Li, Qi; Ding, Shenghui; Wang, Qi

    2009-07-01

    THz transmission imaging is considered as a promising detection measure and imaging method with wide application prospect in security inspection and counter-terrorism. And high-speed array imaging is a very important direction. In this paper, 2.45-THz transmission imaging experiments are made by applying a 124×124 array detector. The 2.45-THz CW CO2-pumped laser is used as illumination source and its output power is about 17mW. Some undersize articles (gasket, screw and nut) are chosen as objects. THz imaging experiments are respectively demonstrated through 1-2 pieces of paper and two kinds of envelopes to show the imaging effect. The original data is acquired and some image processing methods (5-frame average, median filtering, etc) are used to improve the image effect. Finally the THz images obtained are basically clear. The experimental results show that utilizing the setup designed for 2.45-THz imaging, the images are fast generated and objects' contours are clear through paper and envelop.

  12. The physical theory and propagation model of THz atmospheric propagation

    NASA Astrophysics Data System (ADS)

    Wang, R.; Yao, J. Q.; Xu, D. G.; Wang, J. L.; Wang, P.

    2011-02-01

    Terahertz (THz) radiation is extensively applied in diverse fields, such as space communication, Earth environment observation, atmosphere science, remote sensing and so on. And the research on propagation features of THz wave in the atmosphere becomes more and more important. This paper firstly illuminates the advantages and outlook of THz in space technology. Then it introduces the theoretical framework of THz atmospheric propagation, including some fundamental physical concepts and processes. The attenuation effect (especially the absorption of water vapor), the scattering of aerosol particles and the effect of turbulent flow mainly influence THz atmosphere propagation. Fundamental physical laws are illuminated as well, such as Lamber-beer law, Mie scattering theory and radiative transfer equation. The last part comprises the demonstration and comparison of THz atmosphere propagation models like Moliere(V5), SARTre and AMATERASU. The essential problems are the deep analysis of physical mechanism of this process, the construction of atmospheric propagation model and databases of every kind of material in the atmosphere, and the standardization of measurement procedures.

  13. Non-Destructive Evaluation (NDE) Applications of THz Radiation

    NASA Astrophysics Data System (ADS)

    Zimdars, David

    2005-03-01

    The technology and applications of time domain terahertz (THz) imaging to non-destructive evaluation (NDE) will be discussed. THz imaging has shown great promise in 2 and 3 dimensional non-contact inspection of non-conductive materials such as plastics, foam, composites, ceramics, paper, wood and glass. THz imaging employs safe low power non-ionizing electromagnetic pulses, with lateral resolution < 200 um, and depth resolution < 50 um. THz pulses can be analyzed spectroscopically to reveal chemical content. Recently, highly integrated turn-key THz imaging systems have been introduced commercially. We will demonstrate the detection of voids and disbonds intentionally incorporated within the sprayed on foam insulation of a space shuttle external tank mock-up segments. An industrially hardened THz scanning system which has been deployed to scan the space shuttle tank with small remote transceiver will be described. Additional terahertz security imaging applications for the detection of weapons and explosives will also be discussed, as well as the application of terahertz sensors for high speed industrial process monitoring and quality control.

  14. Computational Investigations of THz Transmittance in the Atmosphere

    NASA Astrophysics Data System (ADS)

    Yang, Xingyu; Calhoun, Casey; Calhoun, Ronald

    2016-06-01

    With the recent scientific advancements in Terahertz (THz) wave propagation and reception technology, there has been significant development in new possibilities for using THz waves - offering new possibilities in THz detection and ranging. A first foundational step toward this goal is to better understand THz transmittance in the turbulent atmosphere. In this project, a frequency modulation pattern of THz waves was created by utilizing a system of shifting frequency based on temperature, air humidity, and distance of transmission. The total path loss of the wave in air, based on the wave spread and molecular absorption, was then modeled using radiative transfer theory, onto a set of JavaHAWK filtered-HITRAN data representative of an air sample. This data was used to generate a path loss matrix, which was then used to optimize frequency of transmission for the specific conditions. The concept to be evaluated is whether adaptive frequency modulated THz might usefully decrease transmission losses by adjusting to atmospheric conditions (such as local variations in temperature and humidity).

  15. Mid-IR to THz polaritonics: realizing novel materials for nanophotonics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Caldwell, Joshua D.

    2016-09-01

    The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based surface plasmon materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. Beyond this, the limited availability of high efficiency optical sources, refractive and compact optics in the mid-infrared to THz spectral regions make nanophotonic advancements imperative. One highly promising alternative are polar dielectric crystals whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Due to the wide array of high quality crystalline species and varied crystal structures, a wealth of unanticipated optical properties have recently been reported. However, these materials also have some limitations, primarily in the limited spectral bandwidth of operation for any given material. This talk will discuss recent advancements to improve the material lifetime and to induce additional functionality through isotopic enrichment and hybridization of polaritonic modes for realizing low-loss, actively tunable/modulated nanophotonic materials.

  16. Low-Noise Thz Niobium SIS Mixers

    NASA Astrophysics Data System (ADS)

    Bin, Mei

    1997-09-01

    This thesis describes the development of low-noise heterodyne receivers at THz frequencies for submillimeter astronomy using Nb-based superconductor-insulator-superconductor (SIS) tunneling junctions. The mixers utilize a quasi-optical configuration which consists of a planar twin-slot antenna and antisymmetrically-fed two-junctions on an antireflection-coated silicon hyperhemispherical lens. On-chip integrated tuning circuits, in the form of microstrip lines, are used to obtain maximum coupling efficiency in the designed frequency band. To reduce the rf losses in the integrated tuning circuits above the superconducting Nb gap frequency (~700 GHz), normal-metal Al is used to replace Nb as the tuning circuits. To account the rf losses in the microstrip lines, we calculated the surface impedance of the Al films using the nonlocal anomalous skin effect for finite thickness films. Nb films were calculated using the Mattis-Bardeen theory in the extreme anomalous limit. Our calculations show that the losses of the Al and Nb microstrip lines are about equal at 830 GHz. For Al-wiring and Nb-wiring mixers both optimized at 1050 GHz, the RF coupling efficiency of Al-wiring mixer is higher than that of Nb-wiring one by almost 50%. We have designed both Nb-wiring and Al-wiring mixers below and above the gap frequency. A Fourier transform spectrometer (FTS) has been constructed especially for the study of the frequency response of SIS receivers. This FTS features large aperture size (10 inch) and high frequency resolution (114 MHz). The FTS spectra, obtained using the SIS receivers as direct detectors on the FTS, agree quite well with our theoretical simulations. We have also, for the first time, measured the FTS heterodyne response of an SIS mixer at sufficiently high resolution to resolve the LO and the sidebands. Heterodyne measurements of our SIS receivers with Nb-wiring or Al-wiring have yielded results which are among the best reported to date for broadband heterodyne

  17. Intense THz radiation produced in organic salt crystals for high-field applications

    NASA Astrophysics Data System (ADS)

    Vicario, C.; Ruchert, C.; Hauri, C. P.

    2013-03-01

    Organic stilbazolium salt crystals pumped by intense, ultrashort mid-infrared laser have been investigated for efficient THz generation by optical rectification. In this paper we present our latest results in view of the generation of single-cycle and high-field THz transient in the THz gap (0.1-10 THz). The organic rectifiers like DAST, OH1 and DSTMS combine extremely large optical susceptibility with excellent velocity matching between the infrared pump and the THz radiation. Our simple collinear conversion scheme provides THz beams with excellent focusing properties and single cycle electric field larger than 1.5 MV/cm and magnetic field strength beyond 0.5 Tesla. The source can potentially cover the full THz gap at field strength which is barely provided by other THz sources. The THz pulse is carrier-envelope phase stable and the polarity of the field can be easily inverted.

  18. Generation of efficient THz radiation by optical rectification in DAST crystal using tunable femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Venkatesh, Mottamchetty; Thirupugalmani, K.; Rao, K. S.; Brahadeeswaran, S.; Chaudhary, A. K.

    2017-03-01

    We report the efficient THz generation by optical rectification from an indigenously grown organic DAST crystal using the 140 fs oscillator laser pulses tunable in between 780 and 850 nm. The generated THz pulse profile and powers have been measured using the photoconductive (PC) antennas and pyroelectric detector, respectively. The highest THz peak amplitude and power is obtained at 825 nm central wavelength. We have theoretically explained the enhancement of THz radiation based on the matching of average optical group refractive index and average THz refractive index of the DAST crystal at 825 nm. In addition, the dependence of THz peak amplitude and THz power on laser power have been carried out. The measured quantum conversion efficiency (QCE) of 0.5 and 1.5 THz bands are of the order 3.7 × 10-3, 1.4 × 10-3, respectively. Finally, an attempt has been made to study the effect of polarizations on generated THz signal.

  19. Photo-induced spatial modulation of THz waves: opportunities and limitations.

    PubMed

    Kannegulla, Akash; Shams, Md Itrat Bin; Liu, Lei; Cheng, Li-Jing

    2015-12-14

    Programmable conductive patterns created by photoexcitation of semiconductor substrates using digital light processing (DLP) provides a versatile approach for spatial and temporal modulation of THz waves. The reconfigurable nature of the technology has great potential in implementing several promising THz applications, such as THz beam steering, THz imaging or THz remote sensing, in a simple, cost-effective manner. In this paper, we provide physical insight about how the semiconducting materials, substrate dimension, optical illumination wavelength and illumination size impact the performance of THz modulation, including modulation depth, modulation speed and spatial resolution. The analysis establishes design guidelines for the development of photo-induced THz modulation technology. Evolved from the theoretical analysis, a new mesa array technology composed by a matrix of sub-THz wavelength structures is introduced to maximize both spatial resolution and modulation depth for THz modulation with low-power photoexcitation by prohibiting the lateral diffusion of photogenerated carriers.

  20. PECVD of low-dielectric constant films for ULSI

    NASA Astrophysics Data System (ADS)

    Shimogaki, Yukihiro

    1998-10-01

    We studied the reduction mechanism of the dielectric constant of F-doped silicon oxide films prepared by PECVD from SiH_4/N_2O/CF4 mixture. From the estimation of the dielectric constant at various frequencies, ranging from 1MHz to 100THz, using CV measurement, Kramers-Kronig relation and the square of the refractive index, we suggest that the dielectric constant due to ionic and electronic polarization is not the dominant factor in decreasing the dielectric constant. It is important to remove -OH in films to obtain very low dielectric constant F-doped silicon oxide films, because Si-OH is the main factor of the orientational polarization in silicon oxide films made by PECVD. To investigate the reaction mechanism which controls the film structure, we changed the residence time of gas in chamber by varying the flow rate. When the residence time in chamber decreases, the film deposition rate increases. We tried to explain flow rate dependency of the deposition rate using a simple CSTR (continuous stirred tank reactor) model. It can be concluded that there are two paths to deposit the films. One route is a deposition by the precursors with poor step coverage profile, and the other route is deposition through intermediates formed by gas phase reactions that contribute to have better step coverage. The overall gas phase reaction rate constant was estimated from these kinetic studies. Same approach was also carried out on the PECVD of C:F film deposition.

  1. Dielectric Susceptibility of Liquid Water: Microscopic Insights from Coherent and Incoherent Neutron Scattering

    NASA Astrophysics Data System (ADS)

    Arbe, A.; Malo de Molina, P.; Alvarez, F.; Frick, B.; Colmenero, J.

    2016-10-01

    The analysis of neutron scattering results on H dynamics (H2O ) and the dynamic structure factor (D2O ) around the intermolecular peak and at intermediate length scales in terms of the susceptibilities reveals three processes (diffusive, local relaxational and vibrational) at frequencies below 3 THz, to which the contributions commonly invoked in dielectric studies can be directly mapped. We achieve a unified description of the results from both techniques, clarifying the nature of the molecular motions involved in the dielectric spectra and their impact on the structural relaxation.

  2. Chiral THz metamaterial with tunable optical activity

    SciTech Connect

    Zhou, Jiangfeng; Taylor, Antoinette; O' Hara, John; Chowdhury, Roy; Zhao, Rongkuo; Soukoullis, Costas M

    2010-01-01

    Optical activity in chiral metamaterials is demonstrated in simulation and shows actively tunable giant polarization rotation at THz frequencies. Electric current distributions show that pure chirality is achieved by our bi-Iayer chiral metamaterial design. The chirality can be optically controlled by illumination with near-infrared light. Optical activity, occurring in chiral materials such as DNA, sugar and many other bio-molecules, is a phenomenon of great importance to many areas of science including molecular biology, analytical chemistry, optoelectronics and display applications. This phenomenon is well understood at an effective medium level as a magnetic/electric moment excited by the electric/magnetic field of the incident electromagnetic (EM) wave. Usually, natural chiral materials exhibit very weak optical activity e.g. a gyrotropic quartz crystal. The optical activity of chiral metamaterials, however, can be five orders of magnitude stronger. Chiral metamaterials are made of sub-wavelength resonators lacking symmetry planes. The asymmetry allows magnetic moments to be excited by the electric field of the incident EM wave and vice versa. Recently, chiral metamaterials have been demonstrated and lead to prospects in giant optical activity, circular dichroism, negative refraction and reversing the Casmir force. These fascinating optical properties require strong chirality, which may be designed through the microscopic structure of chiral metamaterials. However, these metamaterials have a fixed response function, defined by the geometric structuring, which limits their ability to manipulate EM waves. Active metamaterials realize dynamic control of response functions and have produced many influential applications such as ultra-fast switching devices, frequency and phase modulation and memory devices. Introducing active designs to chiral metamaterials will give additional freedom in controlling the optical activity, and therefore enable dynamic manipulation

  3. Dielectric response of wurtzite gallium nitride in the terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Hibberd, M. T.; Frey, V.; Spencer, B. F.; Mitchell, P. W.; Dawson, P.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.; Graham, D. M.

    2016-12-01

    We report on the characterization of the intrinsic, anisotropic, dielectric properties of wurtzite gallium nitride in the spectral range of 0.5-11 THz, using terahertz time-domain spectroscopy. The ordinary (ε˜⊥) and extraordinary (ε˜∥) components of the complex dielectric function were determined experimentally for a semi-insulating, m-plane gallium nitride single crystal, providing measurements of the refractive indices (n⊥,∥) and absorption coefficients (α⊥,∥) . These material parameters were successfully modeled by considering the contribution of the optical phonon modes, measured using Raman spectroscopy, to the dielectric function, giving values for the relative static dielectric constants of ε0⊥ = 9.22 ± 0.02 and ε0∥ = 10.32 ± 0.03 for wurtzite gallium nitride.

  4. Intrinsic dielectric properties of magnetodielectric La2CoMnO6

    NASA Astrophysics Data System (ADS)

    Silva, R. X.; Moreira, R. L.; Almeida, R. M.; Paniago, R.; Paschoal, C. W. A.

    2015-06-01

    Manganite with a double perovskite structure is an attractive material because of its interesting magnetoelectric and dielectric responses. In particular, colossal dielectric constant (CDC) behavior has been observed in La2CoMnO6 (LCMO) at radio frequencies and at room temperature. In this paper, we used infrared-reflectivity spectroscopy to study a LCMO ceramic obtained through a modified Pechini's method to determine the phonon contribution to the intrinsic dielectric response of the system and to investigate the CDC origin. The analysis of the main polar modes and of the obtained phonon parameters indicate that the CDC effect of LCMO is of pure extrinsic origin. In addition, we estimated the dielectric constant and the quality factor of the material in the microwave region to be ɛ's ˜ 16 and Qu × f ˜ 124 THz, which verifies that LCMO is appropriate for application in microwave devices and circuitry.

  5. Grating THz laser with optical pumping

    NASA Astrophysics Data System (ADS)

    Khoury, Jed; Haji-saeed, Bahareh; Woods, Charles; Kierstead, John

    2010-04-01

    In this paper, we present a design for a widely tunable solid-state optically and electrically pumped THz laser based on the Smith-Purcell free-electron laser. In the free-electron laser, an energetic electron beam pumps a metallic grating to generate surface plasmons. Our solid-state optically pumped design consists of a thin layer of dielectic, such as SiNx, sandwiched between a corrugated structure and a thin metal or semiconductor layer. The lower layer is for current streaming, and replaces the electron beam in the original design. The upper layer consists of one micro-grating for coupling the electromagnetic field in, another for coupling out, and a nano-grating for coupling with the current in the lower layer for electromagnetic field generation. The surface plasmon waves generated from the upper layer by an external electromagnetic field, and the lower layer by the applied current, are coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

  6. The Kassel Laboratory Astrophysics Thz Spectrometrs

    NASA Astrophysics Data System (ADS)

    Chantzos, Johanna; Herberth, Doris; Kutzer, Pia; Muster, Christoph; Fuchs, Guido W.; Giesen, Thomas

    2016-06-01

    We present a brief overview of the recently established laboratory astrophysics group in Kassel/Germany with a focus on our THz technology. After an outline of our laboratory equipment and recent projects the talk will focus on our new fast spectral scan technique for molecular jet experiments. Here, a new test setup for broadband fast sweep spectrometry in the MW to submm wavelength region has been realized and can be applied to identify transient molecules in a supersonic jet. An arbitrary waveform generator (AWG) is used to generate chirped pulses with a linear frequency sweep in the MHz regime. Pulse durations are of a few microseconds. These pulses are up-converted in frequency, e.g. into the 50 GHz microwave frequency range utilizing a synthesizer, or using a synthesizer plus standard amplifier multiplier chain (AMC) to reach the 100-300 GHz region. As test, NH_3 has been measured between 18-26 GHz in a supersonic jet of 500 μ s duration. Acetonitrile (CH_3CN) was tested in the (90-110) GHz range. The spectrometer is capable of providing fast, broadband and low-noise measurements. Experiments with non-stabel molecular production conditions can greatly benefit from these advantages. The setup enables the study of Van-der-Waals-clusters, as well as carbon chain molecules and small metal-containing refractory molecules when combined with appropriate molecule sources.

  7. THz Spectroscopy and Spectroscopic Database for Astrophysics

    NASA Technical Reports Server (NTRS)

    Pearson, John C.; Drouin, Brian J.

    2006-01-01

    Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular database maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

  8. THz Spectroscopy and Spectroscopic Database for Astrophysics

    NASA Technical Reports Server (NTRS)

    Pearson, John C.; Drouin, Brian J.

    2006-01-01

    Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular data base maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

  9. Nonphasematched broadband THz amplification and reshaping in a dispersive chi(3) medium.

    PubMed

    Koys, Martin; Noskovicova, Eva; Velic, Dusan; Lorenc, Dusan

    2017-06-12

    We theoretically investigate non-phasematched broadband THz amplification in dispersive chi(3) media. A short 100 fs pump pulse is interacting with a temporally matched second harmonic pulse and a weak THz signal through the four wave mixing process and a significant broadband THz amplification and reshaping is observed. The pulse evolution dynamics is explored by numerically solving a set of generalized Nonlinear Schroedinger equations. The influence of incident pulse chirp, pulse duration and the role of wavelength, THz seed frequency and losses are evaluated separately. It is found that a careful choice of incident parameters can provide a broadband THz output and/or a significant increase of THz peak power.

  10. Strong terahertz absorption in all-dielectric Huygens’ metasurfaces

    NASA Astrophysics Data System (ADS)

    Cole, Michael A.; Powell, David A.; Shadrivov, Ilya V.

    2016-10-01

    We propose an all dielectric metamaterial that acts as a perfect terahertz absorber without a ground plane. The unit cell consists of a dielectric cylinder embedded in a low index material. In order to achieve near-perfect terahertz absorption (99.5%) we employ impedance matching of the electric and magnetic resonances within the cylinders of the Huygens’ metasurface. The impedance matching is controlled by changing the aspect ratio between the height and diameter of the cylinder. We show that the absorption resonance can be tuned to particular frequencies from 0.3 to 1.9 THz via changing the geometry of the structure while keeping a nearly constant aspect ratio of the cylinders.

  11. Strong terahertz absorption in all-dielectric Huygens' metasurfaces.

    PubMed

    Cole, Michael A; Powell, David A; Shadrivov, Ilya V

    2016-09-19

    We propose an all dielectric metamaterial that acts as a perfect terahertz absorber without a ground plane. The unit cell consists of a dielectric cylinder embedded in a low index material. In order to achieve near-perfect terahertz absorption (99.5%) we employ impedance matching of the electric and magnetic resonances within the cylinders of the Huygens' metasurface. The impedance matching is controlled by changing the aspect ratio between the height and diameter of the cylinder. We show that the absorption resonance can be tuned to particular frequencies from 0.3 to 1.9 THz via changing the geometry of the structure while keeping a nearly constant aspect ratio of the cylinders.

  12. THz-Raman spectroscopy for explosives, chemical, and biological detection

    NASA Astrophysics Data System (ADS)

    Carriere, James T. A.; Havermeyer, Frank; Heyler, Randy A.

    2013-05-01

    Raman and Terahertz spectroscopy are both widely used for their ability to safely and remotely identify unknown materials. Each approach has its advantages and disadvantages. Traditional Raman spectroscopy typically measures molecular energy transitions in the 200-5000cm-1 region corresponding to sub-molecular stretching or bending transitions, while Terahertz spectroscopy measures molecular energy transitions in the 1-200cm-1 region (30GHz - 6THz) that correspond to low energy rotational modes or vibrational modes of the entire molecule. Many difficult to detect explosives and other hazardous chemicals are known to have multiple relatively strong transitions in this "Terahertz" (<200cm-1, <6THz) regime, suggesting this method as a powerful complementary approach for identification. However, THz signal generation is often expensive, many THz spectroscopy systems are limited to just a few THz range, and strong water absorption bands in this region can act to mask certain transitions if great care isn't taken during sample preparation. Alternatively, low-frequency or "THz-Raman" spectroscopy, which covers the ~5cm-1 to 200cm-1 (150GHz - 6 THz) regions and beyond, offers a powerful, compact and economical alternative to probe these low energy transitions. We present results from a new approach for extending the range of Raman spectroscopy into the Terahertz regime using an ultra-narrow-band volume holographic grating (VHG) based notch filter system. An integrated, compact Raman system is demonstrated utilizing a single stage spectrometer to show both Stokes and anti-Stokes measurements down to <10cm-1 on traditionally difficult to detect explosives, as well as other chemical and biological samples.

  13. Fractal analysis of electroviscous effect in charged porous media

    NASA Astrophysics Data System (ADS)

    Liang, Mingchao; Yang, Shanshan; Cui, Xiaomin; Li, Yongfeng

    2017-04-01

    An electroviscous effect is an important phenomenon making flow resistance larger in electrically charged capillaries or porous media. Thus, the study of this phenomenon is very meaningful in various scientific and engineering fields. In this work, based on the fractal characteristics of porous media, a theoretical apparent viscosity model is expressed in terms of the solid surface zeta potential, physical properties (viscosity, dielectric constant, and conductivity) of the electrolyte solution, maximum pore radius, pore fractal dimension, and tortuosity fractal dimension of porous media. A reasonably good match is found between the results from the fractal model and the available experimental data reported in the literature.

  14. Measuring THz QCL feedback using an integrated monolithic transceiver.

    SciTech Connect

    Wanke, Michael Clement

    2010-08-01

    THz quantum cascade lasers are of interest for use as solid-state local-oscillators in THz heterodyne receiver systems, especially for frequencies exceeding 2 THz and for use with non-cryogenic mixers which require mW power levels. Among other criteria, to be a good local oscillator, the laser must have a narrow linewidth and excellent frequency stability. Recent phase locking measurements of THz QCLs to high harmonics of microwave frequency reference sources as high as 2.7 THz demonstrate that the linewidth and frequency stability of QCLs can be more than adequate. Most reported THz receivers employing QCLs have used discrete source and detector components coupled via mechanically aligned free-space quasioptics. Unfortunately, retroreflections of the laser off of the detecting element can lead to deleterious feedback effects. Using a monolithically integrated transceiver with a Schottky diode monolithically integrated into a THz QCL, we have begun to explore the sensitivity of the laser performance to feedback due to retroreflections of the THz laser radiation. The transceiver allows us to monitor the beat frequency between internal Fabry-Perot modes of the QCL or between a QCL mode and external radiation incident on the transceiver. When some of the power from a free running Fabry-Perot type QCL is retroreflected with quasi-static optics we observe frequency pulling, mode splitting and chaos. Given the lack of calibrated frequency sources with sufficient stability and power to phase lock a QCL above a couple THz, attempts have been made to lock the absolute laser frequency by locking the beat frequency of a multimoded laser. We have phase locked the beat frequency between Fabry-Perot modes to an {approx}13 GHz microwave reference source with a linewidth less than 1 Hz, but did not see any improvment in stability of the absolute frequency of the laser. In this case, when some laser power is retroreflected back into the laser, the absolute frequency can be pulled

  15. Detection and identification of substances using noisy THz signal

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Zakharova, Irina G.; Zagursky, Dmitry Yu.; Varentsova, Svetlana A.

    2017-05-01

    We discuss an effective method for the detection and identification of substances using a high noisy THz signal. In order to model such a noisy signal, we add to the THz signal transmitted through a pure substance, a noisy THz signal obtained in real conditions at a long distance (more than 3.5 m) from the receiver in air. The insufficiency of the standard THz-TDS method is demonstrated. The method discussed in the paper is based on time-dependent integral correlation criteria calculated using spectral dynamics of medium response. A new type of the integral correlation criterion, which is less dependent on spectral characteristics of the noisy signal under investigation, is used for the substance identification. To demonstrate the possibilities of the integral correlation criteria in real experiment, they are applied for the identification of explosive HMX in the reflection mode. To explain the physical mechanism for the false absorption frequencies appearance in the signal we make a computer simulation using 1D Maxwell's equations and density matrix formalism. We propose also new method for the substance identification by using the THz pulse frequency up-conversion and discuss an application of the cascade mechanism of molecules high energy levels excitation for the substance identification.

  16. First tests of THz transmission through a Diamond Anvil Cell

    SciTech Connect

    John Klopf

    2011-01-24

    The THz source generated by the accelerator driver for the Jefferson Lab Free Electron Laser is unique in the world in its ability to deliver a high average power beam of ultrashort (<500 fs FWHM) broadband THz pulses. The spectrum of this source presents an ideal probe for many low energy phenomena, and the time structure enables measurement of dynamic processes with sub-ps resolution. An outline of the range of potential applications for this THz source as a probe of sub-ps dynamics in materials under extreme conditions will be presented. To demonstrate the capabilities of this source for just such experiments, the first set of tests to characterize the transmission of the THz beam through a diamond anvil cell (DAC) have been performed. These preliminary results will be presented along with a description of the optical design used to deliver the THz beam into and out of the DAC. The current design will be compared with other possible techniques and the plans for the next set of measurements will also be given.

  17. Non-destructive sub-THz CW imaging

    NASA Astrophysics Data System (ADS)

    Karpowicz, Nicholas; Zhong, Hua; Xu, Jingzhou; Lin, Kuang-I.; Hwang, Jenn-Shyong; Zhang, Xi-Cheng

    2005-03-01

    A simple, compact CW sub-THz imaging system, utilizing a 0.2 and 0.6 THz Gunn diode source is presented. A silicon beam lead diode detector and a Golay cell are used for the detection. Various results are presented, which show that the CW THz imaging modality is suitable for diverse applications, such as non-destructive testing and security. The key components of the system include the Gunn diode assembly, an optical chopper, a polyethylene lens, a detector, a lock-in amplifier, and two translation stages. The beam from the Gunn diode is focused on the sample being imaged by the polyethylene lens, the transmitted or reflected beam is measured by the detector. The energy transmitted through the sample at each point in the plane of the sample is detected. Since the system has relatively few components compared to pulsed THz imaging systems, it is less expensive and easier to design and operate, although it does not provide depth or spectral information about the sample. Since no time-delay scans take place, scanning can be done quickly compared to a time-domain system, limited by the maximum velocity of the translation stages and response of the detectors. It provides information about the macroscopic features of hidden structures within materials that are transparent to sub THz radiation, such as space shuttle insulating foam, articles of clothing, and luggage.

  18. A BRIGHT IMPULSIVE SOLAR BURST DETECTED AT 30 THz

    SciTech Connect

    Kaufmann, P.; Fernandes, L. O. T.; Kudaka, A. S.; De Souza, R. V.; Valio, A.; Raulin, J.-P.; White, S. M.; Freeland, S. L.; Marcon, R.; Aballay, J. L.; Fernandez, G.; Godoy, R.; Marun, A.; Gimenez de Castro, C. G.

    2013-05-10

    Ground- and space-based observations of solar flares from radio wavelengths to gamma-rays have produced considerable insights but raised several unsolved controversies. The last unexplored wavelength frontier for solar flares is in the range of submillimeter and infrared wavelengths. Here we report the detection of an intense impulsive burst at 30 THz using a new imaging system. The 30 THz emission exhibited remarkable time coincidence with peaks observed at microwave, mm/submm, visible, EUV, and hard X-ray wavelengths. The emission location coincides with a very weak white-light feature, and is consistent with heating below the temperature minimum in the atmosphere. However, there are problems in attributing the heating to accelerated electrons. The peak 30 THz flux is several times larger than the usual microwave peak near 9 GHz, attributed to non-thermal electrons in the corona. The 30 THz emission could be consistent with an optically thick spectrum increasing from low to high frequencies. It might be part of the same spectral component found at sub-THz frequencies whose nature remains mysterious. Further observations at these wavelengths will provide a new window for flare studies.

  19. Perspective: Echoes in 2D-Raman-THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Hamm, Peter; Shalit, Andrey

    2017-04-01

    Recently, various spectroscopic techniques have been developed, which can measure the 2D response of the inter-molecular degrees of freedom of liquids in the THz regime. By employing hybrid Raman-THz pulse sequences, the inherent experimental problems of 2D-Raman spectroscopy are circumvented completely, culminating in the recent measurement of the 2D-Raman-THz responses of water and aqueous salt solutions. This review article focuses on the possibility to observe echoes in such experiments, which would directly reveal the inhomogeneity of the typically extremely blurred THz bands of liquids, and hence the heterogeneity of local structures that are transiently formed, in particular, in a hydrogen-bonding liquid such as water. The generation mechanisms of echoes in 2D-Raman-THz spectroscopy are explained, which differ from those in "conventional" 2D-IR spectroscopy in a subtle but important manner. Subsequently, the circumstances are discussed, under which echoes are expected, revealing a physical picture of the information content of an echo. That is, the echo decay reflects the lifetime of local structures in the liquid on a length scale that equals the delocalization length of the intermolecular modes. Finally, recent experimental results are reviewed from an echo perspective.

  20. THz near-field imaging of biological tissues employing synchrotronradiation

    SciTech Connect

    Schade, Ulrich; Holldack, Karsten; Martin, Michael C.; Fried,Daniel

    2004-12-23

    Terahertz scanning near-field infrared microscopy (SNIM) below 1 THz is demonstrated. The near-field technique benefits from the broadband and highly brilliant coherent synchrotron radiation (CSR) from an electron storage ring and from a detection method based on locking onto the intrinsic time structure of the synchrotron radiation. The scanning microscope utilizes conical wave guides as near-field probes with apertures smaller than the wavelength. Different cone approaches have been investigated to obtain maximum transmittance. Together with a Martin-Puplett spectrometer the set-up enables spectroscopic mapping of the transmittance of samples well below the diffraction limit. Spatial resolution down to about lambda/40 at 2 wavenumbers (0.06 THz) is derived from the transmittance spectra of the near-field probes. The potential of the technique is exemplified by imaging biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 mu-m at about 12 wave numbers (0.36 THz). The THz near-field images reveal distinct structural differences of leaves from different plants investigated. The technique presented also allows spectral imaging of bulky organic tissues. Human teeth samples of various thicknesses have been imaged between 2 and 20 wavenumbers (between 0.06and 0.6 THz). Regions of enamel and dentin within tooth samples are spatially and spectrally resolved, and buried caries lesions are imaged through both the outer enamel and into the underlying dentin.

  1. Structure and performance of dielectric films based on self-assembled nanocrystals with a high dielectric constant

    SciTech Connect

    Huang, LM; Liu, SY; Van Tassell, BJ; Liu, XH; Byro, A; Zhang, HN; Leland, ES; Akins, DL; Steingart, DA; Li, J; O'Brien, S

    2013-09-24

    Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a discrete one-dimensional unit, it becomes a challenge to capture potential enhancements in dielectric performance in two or three dimensions, frequently due to surface effects or the presence of discontinuities. This is a recurring theme in nanoparticle film technology when applied to the realm of thin film semiconductor and device electronics. We present the use of chemically synthesized. (Ba; Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm(2) and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network post assembly. The intercrystal void space (low k dielectric volume fraction) is minimized, while simultaneously promoting intercrystal connectivity and maximizing volume fraction of the high k dielectric component. Furfuryl alcohol, which has good affinity to the surface of. (Ba; Sr ) TiO3 nanocrystals and miscibility with a range of solvents, is demonstrated

  2. Dielectric behaviors of typical benzene monosubstitutes, bromobenzene and benzonitrile.

    PubMed

    Shikata, Toshiyuki; Sugimoto, Natsuki; Sakai, Yuji; Watanabe, Junji

    2012-10-18

    The dielectric behaviors of typical benzene monosubstitutes, bromobenzene (Br-Bz) and benzonitrile (NC-Bz), were investigated up to 3 THz in the pure liquid state over a temperature range from 10 to 60 °C to understand differences in molecular motions of these simple, planar molecules bearing rather different electric dipole moments: 1.72 and 4.48 D for Br-Bz and NC-Bz in gaseous state, respectively. Temperature dependence of spin-lattice relaxation time (T(1)) for (13)C NMR and viscosities for these liquids were also determined to obtain information for molecular motions. Moreover, depolarized Rayleigh scattering (DRS) experiments were carried out for both liquids at 20 °C to determine frequency dependencies of optical susceptibilities up to 8 THz directly relating to rotational motions of their molecular planes. Most Br-Bz molecules rotate freely over a temperature range examined, showing a Kirkwood correlation factor close to g(K) ∼ 1.0 at dielectric Debye-type relaxation times (ca. 18 ps at 20 °C) essentially identical to microscopic (dielectric) relaxation times evaluated from T(1)(13)C NMR data. A small amount of Br-Bz molecules forms dimeric intermolecular associations in an antiparallel configuration of dipole moments. On the other hand, NC-Bz molecules form stable dimers in the antiparallel dipole configuration at a population much higher than that of Br-Bz because of a markedly greater dipole moment than that of Br-Bz. A major dielectric relaxation mechanism for NC-Bz found at ca. 70 ps at 20 °C results from the dissociation process of dimers with a lifetime longer than a rotational relaxation time, observable as a minor dielectric relaxation mechanism at ca. 12 ps at 20 °C, of individual monomeric NC-Bz molecules without the formation of dimers. The formation of stable dimers in an antiparallel configuration is responsible for the observed small g(K) values, ca. 0.5, and disagreement between major (or minor) dielectric relaxation times and

  3. THz Pulse Detection by Multilayered GeTe/Sb2Te3.

    PubMed

    Makino, Kotaro; Kuromiya, Shota; Takano, Keisuke; Kato, Kosaku; Nakajima, Makoto; Saito, Yuta; Tominaga, Junji; Iida, Hitoshi; Kinoshita, Moto; Nakano, Takashi

    2016-11-30

    We proposed and demonstrated terahertz (THz) pulse detection by means of multilayered GeTe/Sb2Te3 phase-change memory materials that are also known as a multilayer topological insulator-normal insulator (MTN) system. THz time-domain spectroscopy measurement was performed for MTN films with different multilayer repetitions as well as a conventional as-grown Ge-Te-Sb (GST) alloy film. It was found that MTNs absorb THz waves and that the absorption coefficient depends on the number of layers, while the as-grown GST alloy film was almost transparent for THz waves. Simple MTN-based THz detection devices were fabricated, and the THz-induced change in the current signal was measured when a DC bias voltage was applied between the electrodes. We confirmed that irradiation of THz pulse causes a decrease in the resistance of the MTNs. This result indicates that our devices are capable of THz detection.

  4. Characteristics of THz carrier dynamics in GaN thin film and ZnO nanowires by temperature dependent terahertz time domain spectroscopy measurement

    NASA Astrophysics Data System (ADS)

    Balci, Soner; Baughman, William; Wilbert, David S.; Shen, Gang; Kung, Patrick; Kim, Seongsin Margaret

    2012-12-01

    We present a comprehensive study of the characteristics of carrier dynamics using temperature dependent terahertz time domain spectroscopy. By utilizing this technique in combination with numerical calculations, the complex refractive index, dielectric function, and conductivity of n-GaN, undoped ZnO NWs, and Al-doped ZnO NWs were obtained. The unique temperature dependent behaviors of major material parameters were studied at THz frequencies, including plasma frequency, relaxation time, carrier concentration and mobility. Frequency and temperature dependent carrier dynamics were subsequently analyzed in these materials through the use of the Drude and the Drude-Smith models.

  5. Novel Materials with Effective Super Dielectric Constants for Energy Storage

    NASA Astrophysics Data System (ADS)

    Cortes, Francisco Javier Quintero; Phillips, Jonathan

    2015-05-01

    To test a theory of the recently discovered phenomenon of super dielectric behavior at very low frequency, the dielectric constants of several `pastes', composed of porous alumina powders filled to the point of incipient wetness with water containing dissolved sodium chloride, were measured. The effective dielectric low frequency constants of some of the pastes were greater than 1010, dramatically higher than that of any material ever reported. Moreover, the total energy density reported for one capacitor generated with NaCl-based super dielectric material is marginally higher than found in any prior report. These results are consistent with this recently postulated model of low frequency super dielectric behavior in porous, non-conductive materials saturated with ion-containing liquids: upon the application of an electric field, ions dissolved in the saturating liquid contained in the pores will travel to the ends of pore-filling liquid droplets creating giant dipoles. The fields of these giant dipoles oppose the applied field, reducing the net field created per unit of charge on the capacitor plates, effectively increasing charge/voltage ratio, hence capacitance. This is simply a version of the theory of `polarizable media' found in most classic texts on electromagnetism. Other observations reported here include (1) the impact of ion concentration on dielectric values, (2) a maximum voltage similar to that associated with the electrical breakdown of water, (3) the loss of capacitance upon drying, (4) the recovery of capacitance upon the addition of water to a dry super dielectric material, and (5) the linear relationship between capacitance and inverse thickness. All observations are consistent with the earlier proposed model of the super dielectric phenomenon. An extrapolation of results suggests this technology can lead to energy density greater than the best lithium-ion battery.

  6. Preliminary results of non-contact THz imaging of cornea

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Garritano, James; Bajwa, Neha; Deng, Sophie; Hubschman, Jean-Pierre; Grundfest, Warren S.; Taylor, Zachary D.

    2015-03-01

    This paper presents a novel THz optical design that allows the acquisition of THz reflectivity maps of in vivo cornea without the need for a field flattening window and preliminary imaging results of in vivo rabbit cornea. The system's intended use is to sense small changes in corneal tissue water content (CTWC) that can be precursors for a host of diseases and pathologies. Unique beam optics allows the scanning of a curved surface at normal incidence while keeping the source detector and target stationary. Basic system design principles are discussed and image sets of spherical calibration targets and corneal phantom models are presented. The presented design will enable, for the first time, non-contact THz imaging of animal and human cornea.

  7. Temperature-dependent THz vibrational spectra of clenbuterol hydrochloride

    NASA Astrophysics Data System (ADS)

    Yang, YuPing; Lei, XiangYun; Yue, Ai; Zhang, Zhenwei

    2013-04-01

    Using the high-resolution Terahertz Time-domain spectroscopy (THz-TDS) and the standard sample pellet technique, the far-infrared vibrational spectra of clenbuterol hydrochloride (CH), a β 2-adrenergic agonist for decreasing fat deposition and enhancing protein accretion, were measured in temperature range of 77-295 K. Between 0.2 and 3.6 THz (6.6-120.0 cm-1), seven highly resolved spectral features, strong line-narrowing and a frequency blue-shift were observed with cooling. However, ractopamine hydrochloride, with some structural and pharmacological similarities to clenbuterol hydrochloride, showed no spectral features, indicating high sensitivity and strong specificity of THz-TDS. These results could be used for the rapid and nondestructive CH residual detection in food safety control.

  8. Through-container THz sensing: applications for biodetection

    NASA Astrophysics Data System (ADS)

    Cook, David J.; Decker, Brian K.; Dadusc, Gami; Allen, Mark G.

    2004-02-01

    The potential container penetrating capabilities of THz radiation leads to possible applications for container penetrating sensors for biological hazards. Such an approach requires the presence of distinct THz frequency resonances in the target compounds coupled with sufficiently transparent container materials to allow through container sensing. The results of a THz spectroscopic survey of container and clothing materials are presented along with spectra of materials that were chosen as simulants and markers for illicit biological substances. The spectroscopic data presented show at least partial transparency for materials commonly used for clothing and packaging. We also measure distinct spectral signatures in dipicolinic acid, calcium dipicolinate, peptidoglycan, and 2,6-diaminopimelic acid, biologically significant molecules that are indicative of hazardous spore forming bacteria. These spectra differ significantly from those of the container materials to provide a potential contrast mechanism which could be used for identification.

  9. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

    NASA Astrophysics Data System (ADS)

    Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

    2017-03-01

    Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

  10. Relative Infrared (IR) and Terahertz (THz) Signatures of Common Explosives

    SciTech Connect

    Sharpe, Steven W.; Johnson, Timothy J.; Sheen, David M.; Atkinson, David A.

    2006-11-13

    Pacific Northwest National Laboratory (PNNL) has recently recorded the infrared (IR) and far-infrared (sometimes called the terahertz, THz) spectral signatures of four common explosives, in the condensed phase. The signatures of RDX, PETN, TNT and Tetryl were recorded both in the infrared and the THz domains, using Fourier transform infrared (FTIR) spectroscopy. Samples consisted of thin films and were made by depositing and subsequent evaporation of an acetone-explosive mixture. The complete spectrum spanned the range from 4,000 to 8 cm-1 at 2.0 cm-1 spectral resolution. Preliminary results in the infrared agree with those of previous workers, while the THz signatures are one order of magnitude weaker than the strongest IR bands.

  11. Fiber-Drawn Metamaterial for THz Waveguiding and Imaging

    NASA Astrophysics Data System (ADS)

    Atakaramians, Shaghik; Stefani, Alessio; Li, Haisu; Habib, Md. Samiul; Hayashi, Juliano Grigoleto; Tuniz, Alessandro; Tang, Xiaoli; Anthony, Jessienta; Lwin, Richard; Argyros, Alexander; Fleming, Simon C.; Kuhlmey, Boris T.

    2017-09-01

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

  12. Active tunable plasmonically induced polarization conversion in the THz regime

    NASA Astrophysics Data System (ADS)

    Ling, Furi; Yao, Gang; Yao, Jianquan

    2016-10-01

    A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications.

  13. Method for the production of wideband THz radiation

    DOEpatents

    Krafft, Geoffrey A.

    2008-01-01

    A method for the production of extremely wide bandwidth THz radiation comprising: delivering an electron beam from a source to an undulator that does not deflect the angle or transversely move the electron beam; and optimizing the undulator to yield peak emission in the middle of the THz band (1 THz). These objectives are accomplished by magnetically bending the orbit of the incoming electron beam in the undulator according to the function x(z)=x.sub.o exp(-z.sup.2/2.sigma..sup.2) and controlling the transverse magnetic field to be B(z)=B.sub.0(1-z.sup.2/.sigma..sup.2)exp(-z.sup.2/2.sigma..sup.2).

  14. Optimization of THz Radiation Generation from a Laser Wakefield Accelerator

    SciTech Connect

    Plateau, G. R.; Matlis, N. H.; Toth, C.; Geddes, C. G. R.; Schroeder, C. B.; Tilborg, J. van; Albert, O.; Esarey, E.; Leemans, W. P.

    2009-01-22

    Ultrashort terahertz pulses with energies in the {mu}J range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because these electron bunches are ultrashort (<50 fs), they can radiate coherently (coherent transition radiation--CTR) in a wide bandwidth ({approx}1-10 THz) yielding high intensity terahertz pulses. In addition to providing a non-invasive bunch-length diagnostic and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and an electro-optic technique which were used to characterize these THz pulses.

  15. 2.7 THz Balanced Waveguide HEB Mixer

    NASA Astrophysics Data System (ADS)

    Boussaha, Faouzi; Kawamura, Jonathan; Stern, Jeffery; Jung-Kubiak, Cecile

    2014-09-01

    We report on the development of a waveguide-based balanced superconducting mixer for operation near 2.7 THz. The mixer employs a pair of NbN hot-electron bolometers defined on 6 μm-thick silicon substrate that follows a 90° hybrid coupler. To produce the critical structures of the coupler and waveguide embedding circuit, we have utilized silicon micromachining techniques based on deep reactive ion etching. Operating near 4.2 K bath temperature, we have measured a minimum uncorrected DSB receiver noise temperature of less than 2000 K using Callen-Welton formula and local oscillator sideband noise rejection better than 13 3 dB at 2.74 THz. The concept is suitable for building arrays, readily scalable for higher frequencies up 5 THz, and could accommodate other mixer technologies, such as room-temperature Schottky diode mixers.

  16. Self-organization approach for THz polaritonic metamaterials

    SciTech Connect

    Reyes-Coronado, A.; Acosta, M.F.; Merino, R.I.; Orera,, V.M.; Kenanakis, G.; Katsarakis, n.; Kafesaki, M.; Mavidis, Ch.; Garcia de Abajo, J.; Economou, E.N.; Soukoulis, Costas M.

    2012-06-15

    In this paper we discuss the fabrication and the electromagnetic (EM) characterization of anisotropic eutectic metamaterials, consisting of cylindrical polaritonic LiF rods embedded in either KCl or NaCl polaritonic host. The fabrication was performed using the eutectics directional solidification self-organization approach. For the EM characterization the specular reflectance at far infrared, between 3 THz and 11 THz, was measured and also calculated by numerically solving Maxwell equations, obtaining good agreement between experimental and calculated spectra. Applying an effective medium approach to describe the response of our samples, we predicted a range of frequencies in which most of our systems behave as homogeneous anisotropic media with a hyperbolic dispersion relation, opening thus possibilities for using them in negative refractive index and imaging applications at THz range.

  17. 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.

  18. Cooling of radiative quantum dot excitons by THz-radiation

    NASA Astrophysics Data System (ADS)

    Boxberg, Fredrik; Tulkki, Jukka; Yusa, Go; Sakaki, Hiroyuki

    2007-04-01

    Yusa et al. reported an anomalous cooling of radiative quantum dot (QD) excitons by THz-radiation in [Proc. 24th ICPS, 1083 (1998)] We have analyzed this experiment using continuum elasticity, multi-band kṡp and spin-resolved Monte-Carlo methods. We show that the unexpected discovery is related to hole relaxation via piezo-electric potential minima, induced in the QD sample by InP stressor islands. The THz-radiation gives rise to a drift of dark excitons from the piezo-electric minima to radiative states in the deformation potential minimum. This increases the QD ground state luminescence at the expense of the luminescence from higher QD states. We reproduce also the delayed flash of QD ground state luminescences when a THz-radiation pulse hits the sample even ˜ 1 s after switching off the carrier generation.

  19. Radiative Characteristics of On-Chip Terahertz (THz) Structures

    SciTech Connect

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    Previously, we explored possibilities for producing narrow-band THz radiation using either free or bound electrons (solid state) in micro-undulatory configurations [1] because integrated circuit technology appeared well matched to this region extending from about 300 GHz to 30 THz. This range [2]-[3] has largely been neglected until recently because it runs from the limit of WR-3 waveguide around 300 GHz up to CO{sub 2} lasers where the laser regime becomes dominant. There are mainly two approaches for generating THz radiation, i.e. through free or bound electron (BE) implementations. In this paper, emphasis is on producing this radiation using bound electrons via IC technology but in close analogy to free electron lasers (FELs) that are comparatively immense, expensive, need high power and have low efficiencies [4].

  20. Active tunable plasmonically induced polarization conversion in the THz regime

    PubMed Central

    Ling, Furi; Yao, Gang; Yao, Jianquan

    2016-01-01

    A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications. PMID:27734912

  1. New developments in THz quartz enhanced photoacoustic spectroscopy

    NASA Astrophysics Data System (ADS)

    Spagnolo, Vincenzo; Patimisco, Pietro; Sampaolo, Angelo; Giglio, Marilena; Vitiello, Miriam S.; Scamarcio, Gaetano; Tittel, Frank K.

    2016-09-01

    We will report on new developments of quartz-enhanced photo-acoustic (QEPAS) sensor employing THz quantum cascade laser (QCLs). The extension of the QEPAS technique in the THz range was made possible by the realization of custom made QTFs. With the aim to improve the QTF acousto-electric transduction efficiency, we designed and realized new QTF designs. A detailed analysis of the quality factor, the resonance frequency and the electrical resistance of custom quartz tuning forks (QTFs) with different geometrical parameters is reported. The custom QTFs were employed in QEPAS sensors using THz QCLs as the laser excitation sources and targeting CH3OH and H2S. Minimum detection limits of a few tens of ppb and normalized noise equivalent absorption factors down to 3.75×10-11 cm-1W/Hz½ were achieved.

  2. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

    NASA Astrophysics Data System (ADS)

    Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

    2016-11-01

    Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

  3. Computed tomography using broadband Bessel THz beams and phase contrast.

    PubMed

    Bitman, Assaf; Goldring, Sharone; Moshe, Inon; Zalevsky, Zeev

    2014-04-01

    We present new results demonstrating the capability of performing computed tomography (CT) using broadband Bessel terahertz (THz) beams. Nondiffractive beams such as these exhibit propagation-invariant lines of focus with an extended depth-of-field compared to conventional Gaussian beams. Using this property, we demonstrate a considerable improvement in the 3D reconstruction image of a synthetic sample through the backprojection algorithm. Only when THz Bessel beams are used, a full reconstruction of the object structure is made. Moreover, we use phase-contrast mechanism which improves the spatial resolution and reconstructed images. Our results highlight the potential in using nondiffractive Bessel beams to significantly improve 3D-image reconstruction of THz CT.

  4. Two color laser driven THz generation in clustered plasma

    NASA Astrophysics Data System (ADS)

    Malik, Rakhee; Uma, R.; Kumar, Pawan

    2017-07-01

    A scheme of terahertz (THz) generation, using nonlinear mixing of two color laser (fundamental ω1 and slightly frequency shifted second harmonic ω2 ) in clustered plasma, is investigated. The lasers exert ponderomotive force on cluster electrons and drive density perturbations at 2 ω1 and ω2-ω1 . The density perturbations beat with the oscillatory velocities to produce nonlinear current at ω2-2 ω1 , generating THz radiation. The radiation is enhanced due to cluster plasmon resonance and by phase matching introduced through a density ripple. The generation involves third order nonlinearity and does not require a magnetic field or inhomogeneity to sustain it. We report THz power conversion efficiency ˜ 10-4 at 1 μm and 0.5 μm wavelengths with intensity ˜ 3 ×1014W/cm 2 .

  5. Filling the THz Gap - High Power Sources and Applications

    SciTech Connect

    Gwyn Williams

    2006-02-01

    Electromagnetic waves centered at a frequency of 1 THz lie between photonics on the one hand and electronics on the other, and are very hard to generate and detect. However, since the THz part of the spectrum is energetically equivalent to many important physical, chemical and biological processes including superconducting gaps and protein dynamical processes, it is of great interest to facilitate experimental research in this region. This has stimulated major steps in the past decade for filling this gap in the usable spectrum. In this review paper we describe the evolution of a new generation of sources that boost the average power available in the THz region by more than a million-fold, making this region routinely accessible for the first time. This is achieved using two enhancement factors, namely relativistic electrons and super-radiance. We will also point to the scientific potential for discovery that is now enabled in this region.

  6. THz Communications using Photonics and Electronic Devices: the Race to Data-Rate

    NASA Astrophysics Data System (ADS)

    Ducournau, Guillaume; Szriftgiser, Pascal; Pavanello, Fabio; Peytavit, Emilien; Zaknoune, Mohammed; Bacquet, Denis; Beck, Alexandre; Akalin, Tahsin; Lampin, Jean-François; Lampin, Jean-François

    2015-02-01

    With the mass development of mobile data transfers, wireless communications have recently entered a new area: the carrier frequency is now entering the THz region. After a brief overview of context and key features of THz communication, focus is given on photonic-based THz emitters based on quasi-optic UTC-PDs. A special design of wideband photomixer is presented and its applications for narrow bandwidth THz generation. Using this photomixer, communication links at 200, 400 and 600 GHz are presented.

  7. Identifying the distinct phases of THz waves from K-valley electrons in graphite

    SciTech Connect

    Irfan, Muhammad; Yim, Jong-Hyuk Jho, Young-Dahl; Kim, Changyoung

    2013-12-04

    The polarity change of THz electromagnetic waves radiated from single-crystalline graphite and polycrystalline graphite films has been studied to identify the main generation mechanism in conventional reflective THz time-domain spectroscopy scheme. The excitation wavelength variation around the K-valley produces no significant changes in THz field strength. We further found that THz waves become fully dispersed without polarity change in lateral detection geometry.

  8. Measuring the dielectric properties of soil-organic mixtures using coaxial impedance dielectric reflectometry

    NASA Astrophysics Data System (ADS)

    Francisca, Franco M.; Montoro, Marcos A.

    2012-05-01

    Contamination of soils with non-aqueous phase liquids (NAPLs) is frequently produced by accidental spills and storage tanks or pipes leakage. The main goals dealing with soil and groundwater contamination include determining the extension of the affected zone, monitoring the contaminant plume and quantifying the pollution degree. The objective of this work is to evaluate the potential of dielectric permittivity measurements to detect the presence of NAPLs in sands. Tested samples were fine, medium, coarse and silty sand with different volumetric contents of water and paraffin oil. The dielectric permittivity was measured by means of a Coaxial Impedance Dielectric Reflectometry method in specimens with either known fluid content or at different stages during immiscible displacement tests. A simplified method was developed to quantify the amount of oil from dielectric permittivity measurements and effective mixture media models. Obtained results showed that groundwater contamination with NAPL and the monitoring of immiscible fluid displacement in saturated porous media can be clearly identified from dielectric measurements. Finally, very accurate results can be obtained when computing the contamination degree with the proposed method in comparison with the real volumetric content of NAPL (r2 > 90%).

  9. Commercial perspective in THz spectroscopy, sensing and imaging (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Bouyé, Clémentine; Taoudi, Sarah; Cochard, Jacques; d'Humières, Benoît

    2017-02-01

    For their ability to be transmitted by materials opaque in the visible and IR ranges (clothes, plastic, …), for being non-ionizing, for providing sub-mm resolution imaging, for the specific signatures of numerous materials, Terahertz waves - ranging from 200 GHz to 10 THz - have been raising the interest of industrials for about fifteen years. This study focuses on the penetration of THz technologies into the industrial applications driving the THz market growth at short and long term: Non Destructive testing (NDT), Defense and Security, Biomedical. For 15 years, Terahertz technologies have been continuously tested on a wide variety of applications. Thanks to these ongoing feasibility studies, manufacturers and end-users gained a deeper knowledge about the abilities and the limitations of the different Terahertz systems (Time-Domain spectroscopy, Frequency-Domain spectroscopy, Time-Domain reflectometry, etc). The demand from end-users is more qualified and is segmented as follows: 1. Detection of objects and defects on large areas 2. Thickness measurement on large areas 3. Chemical and Structural characterization of small objects and defects on small areas (2D) or volumes (3D) Each of these 3 functions leads to a specific family of THz systems with distinct requirements in terms of performance and cost: 1. Detection: cheap and compact imaging systems. 2. Thickness measurement: cost-effective and high speed systems. 3. Characterization: high resolution, high reliability and real-time sensing systems. This article will present the existing and incoming THz systems and components addressing each function. Terahertz technologies are currently finding their place on the market, outside research and scientific applications. The objective of this article is to identify the industrial applications where THz techniques will be adopted and to provide market growth perspectives.

  10. Characterization of dielectric materials

    DOEpatents

    King, Danny J.; Babinec, Susan; Hagans, Patrick L.; Maxey, Lonnie C.; Payzant, Edward A.; Daniel, Claus; Sabau, Adrian S.; Dinwiddie, Ralph B.; Armstrong, Beth L.; Howe, Jane Y.; Wood, III, David L.; Nembhard, Nicole S.

    2017-06-27

    A system and a method for characterizing a dielectric material are provided. The system and method generally include applying an excitation signal to electrodes on opposing sides of the dielectric material to evaluate a property of the dielectric material. The method can further include measuring the capacitive impedance across the dielectric material, and determining a variation in the capacitive impedance with respect to either or both of a time domain and a frequency domain. The measured property can include pore size and surface imperfections. The method can still further include modifying a processing parameter as the dielectric material is formed in response to the detected variations in the capacitive impedance, which can correspond to a non-uniformity in the dielectric material.

  11. THz and sub THz (MMW)-over-Fiber Data Links and Radar Technology

    DTIC Science & Technology

    2016-11-30

    propagation loss in free-space or transmission line, and their inherent straight-line path of propagation affects connections and synchronization between the...Chan-Shan Yang, and Ci-Ling Pan*, “ Correlation Approach to Propagation of Terahertz Pulse in Dielectrics for Material Characterization,” IEEE Photon

  12. THz and sub-THz (MMW)-over-Fiber Data Links and Radar Technology

    DTIC Science & Technology

    2016-12-05

    propagation loss in free-space or transmission line, and their inherent straight-line path of propagation affects connections and synchronization between the...Chan-Shan Yang, and Ci-Ling Pan*, “ Correlation Approach to Propagation of Terahertz Pulse in Dielectrics for Material Characterization,” IEEE Photon

  13. Optical and THz reflectance investigations of organic solar cells

    NASA Astrophysics Data System (ADS)

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Galagan, Yulia

    2016-04-01

    Two Organic Photovoltaic devices having a photoactive layer containing Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, 99%), and the layer sequences - glass/ITO/ZnO/PAL/PEDOT:PSS/Ag/encapsulation were non-destructively investigated by diffuse optical spectral reflectance, THz spectroscopy and THz imaging. The proposed methods proved to be powerful tools to support quality assurance in organic solar cells development, facilitating both the localization of manufacturing defects and the device degradation, as they are combined with "classical" evaluation means.

  14. Very high power THz radiation at Jefferson Lab

    SciTech Connect

    Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

    2002-03-31

    We report the production of high power (20 watts average, {approx};1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  15. Very high Power THz radiation at Jefferson Lab

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-03-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  16. Very high power THz radiation at Jefferson Lab.

    PubMed

    Carr, G L; Martin, Michael C; McKinney, Wayne R; Jordan, K; Neil, George R; Williams, G P

    2002-11-07

    We report the production of high power (20 W average, approximately 1 MW peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with that based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to those produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  17. Functional multi-band THz meta-foils

    PubMed Central

    Wu, Jianfeng; Moser, Herbert O.; Xu, Su; Jian, Linke; Banas, Agnieszka; Banas, Krzysztof; Chen, Hongsheng; Bettiol, Andrew A.; Breese, Mark B. H.

    2013-01-01

    In this paper, we present the first experimental demonstration of double- and triple-band negative refraction index meta-foils in the terahertz (THz) region. Multi-band meta-foils constructed by multi-cell S-string resonators in a single structure exhibit simultaneously negative permittivity and negative permeability responses at multiple frequencies. The phenomena are confirmed by numerical simulations and Fourier transform infrared spectroscopy measurements. The flexible, freestanding multi-band meta-foils provide a promising candidate for the development of multi-frequency THz materials and devices. PMID:24346309

  18. Resonant metamaterial detectors based on THz quantum-cascade structures

    PubMed Central

    Benz, A.; Krall, M.; Schwarz, S.; Dietze, D.; Detz, H.; Andrews, A. M.; Schrenk, W.; Strasser, G.; Unterrainer, K.

    2014-01-01

    We present the design, fabrication and characterisation of an intersubband detector employing a resonant metamaterial coupling structure. The semiconductor heterostructure relies on a conventional THz quantum-cascade laser design and is operated at zero bias for the detector operation. The same active region can be used to generate or detect light depending on the bias conditions and the vertical confinement. The metamaterial is processed directly into the top metal contact and is used to couple normal incidence radiation resonantly to the intersubband transitions. The device is capable of detecting light below and above the reststrahlenband of gallium-arsenide corresponding to the mid-infrared and THz spectral region. PMID:24608677

  19. Free-Space Imaging Technology For THz Beams

    DTIC Science & Technology

    2006-05-31

    1513, 2001. • B. Ferguson , S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, “THz wave computed tomography,” Optics Letters, 27, 1312, 2002. • THz...measurement of time-domain with phase and timing data provides tomographic imaging with spectroscopic information. REFERENCES [1] B. Ferguson and X.-C. Zhang...spatiotemporal terahertz field imaging,” Optics Letters 23(14), pp. 1114–1116, 1998. [11] D. D. Arnone, C. M. Ciesla, A. Corchia, S. Egusa, M. Pepper

  20. 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.

  1. Experimental and Theoretical Study of Carnosine in THz Range

    NASA Astrophysics Data System (ADS)

    Yan, Hai-Tao; Wang, Wei-Ning

    2005-12-01

    The characteristic fingerprints of carnosine from 0.2 to 2.6 THz are first measured by terahertz time-domain spectroscopy at room temperature. For the pure carnosine, the refractive index varies between 1.79 and 1.85 with the average value 1.84, while for the carnosine-polyethylene mixture, four absorption peaks centred at 1.37, 1.56, 1.85 and 2.49 THz are detected. A comparison of the theoretical predictions using the density functional theory with the experimental results shows satisfactory agreement except somewhat blue shift.

  2. Independent component analysis applications on THz sensing and imaging

    NASA Astrophysics Data System (ADS)

    Balci, Soner; Maleski, Alexander; Nascimento, Matheus Mello; Philip, Elizabath; Kim, Ju-Hyung; Kung, Patrick; Kim, Seongsin M.

    2016-05-01

    We report Independent Component Analysis (ICA) technique applied to THz spectroscopy and imaging to achieve a blind source separation. A reference water vapor absorption spectrum was extracted via ICA, then ICA was utilized on a THz spectroscopic image in order to clean the absorption of water molecules from each pixel. For this purpose, silica gel was chosen as the material of interest for its strong water absorption. The resulting image clearly showed that ICA effectively removed the water content in the detected signal allowing us to image the silica gel beads distinctively even though it was totally embedded in water before ICA was applied.

  3. Tailoring dielectric resonator geometries for directional scattering and Huygens’ metasurfaces

    DOE PAGES

    Campione, Salvatore; Basilio, Lorena I.; Warne, Larry K.; ...

    2015-01-28

    In this paper we describe a methodology for tailoring the design of metamaterial dielectric resonators, which represent a promising path toward low-loss metamaterials at optical frequencies. We first describe a procedure to decompose the far field scattered by subwavelength resonators in terms of multipolar field components, providing explicit expressions for the multipolar far fields. We apply this formulation to confirm that an isolated high-permittivity dielectric cube resonator possesses frequency separated electric and magnetic dipole resonances, as well as a magnetic quadrupole resonance in close proximity to the electric dipole resonance. We then introduce multiple dielectric gaps to the resonator geometrymore » in a manner suggested by perturbation theory, and demonstrate the ability to overlap the electric and magnetic dipole resonances, thereby enabling directional scattering by satisfying the first Kerker condition. We further demonstrate the ability to push the quadrupole resonance away from the degenerate dipole resonances to achieve local behavior. These properties are confirmed through the multipolar expansion and show that the use of geometries suggested by perturbation theory is a viable route to achieve purely dipole resonances for metamaterial applications such as wave-front manipulation with Huygens’ metasurfaces. Our results are fully scalable across any frequency bands where high-permittivity dielectric materials are available, including microwave, THz, and infrared frequencies.« less

  4. Tailoring dielectric resonator geometries for directional scattering and Huygens’ metasurfaces

    SciTech Connect

    Campione, Salvatore; Basilio, Lorena I.; Warne, Larry K.; Sinclair, Michael B.

    2015-01-28

    In this paper we describe a methodology for tailoring the design of metamaterial dielectric resonators, which represent a promising path toward low-loss metamaterials at optical frequencies. We first describe a procedure to decompose the far field scattered by subwavelength resonators in terms of multipolar field components, providing explicit expressions for the multipolar far fields. We apply this formulation to confirm that an isolated high-permittivity dielectric cube resonator possesses frequency separated electric and magnetic dipole resonances, as well as a magnetic quadrupole resonance in close proximity to the electric dipole resonance. We then introduce multiple dielectric gaps to the resonator geometry in a manner suggested by perturbation theory, and demonstrate the ability to overlap the electric and magnetic dipole resonances, thereby enabling directional scattering by satisfying the first Kerker condition. We further demonstrate the ability to push the quadrupole resonance away from the degenerate dipole resonances to achieve local behavior. These properties are confirmed through the multipolar expansion and show that the use of geometries suggested by perturbation theory is a viable route to achieve purely dipole resonances for metamaterial applications such as wave-front manipulation with Huygens’ metasurfaces. Our results are fully scalable across any frequency bands where high-permittivity dielectric materials are available, including microwave, THz, and infrared frequencies.

  5. Resonant dielectric metamaterials

    DOEpatents

    Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

    2014-12-02

    A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

  6. Inductive dielectric analyzer

    NASA Astrophysics Data System (ADS)

    Agranovich, Daniel; Polygalov, Eugene; Popov, Ivan; Ben Ishai, Paul; Feldman, Yuri

    2017-03-01

    One of the approaches to bypass the problem of electrode polarization in dielectric measurements is the free electrode method. The advantage of this technique is that, the probing electric field in the material is not supplied by contact electrodes, but rather by electromagnetic induction. We have designed an inductive dielectric analyzer based on a sensor comprising two concentric toroidal coils. In this work, we present an analytic derivation of the relationship between the impedance measured by the sensor and the complex dielectric permittivity of the sample. The obtained relationship was successfully employed to measure the dielectric permittivity and conductivity of various alcohols and aqueous salt solutions.

  7. Method of making dielectric capacitors with increased dielectric breakdown strength

    DOEpatents

    Ma, Beihai; Balachandran, Uthamalingam; Liu, Shanshan

    2017-05-09

    The invention is directed to a process for making a dielectric ceramic film capacitor and the ceramic dielectric laminated capacitor formed therefrom, the dielectric ceramic film capacitors having increased dielectric breakdown strength. The invention increases breakdown strength by embedding a conductive oxide layer between electrode layers within the dielectric layer of the capacitors. The conductive oxide layer redistributes and dissipates charge, thus mitigating charge concentration and micro fractures formed within the dielectric by electric fields.

  8. Far-infrared dispersion of the complex dielectric constant in ferroelectric near-stoichiometric LiNbO3:Ce

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Ling, Furi; Zuo, Zhigao; Liu, Jinsong; Yao, Jianquan

    2011-10-01

    The dielectric properties of near-stoichiometric LiNbO3:Ce (near-SLN:Ce) single crystal have been investigated by using terahertz time domain spectroscopy (THz-TDS) in a frequency range of 0.7-1.6 THz at room temperature. When coupled with an applied external optical field, a photorefractive effect was observed, resulting in the modulation of the complex dielectric constant for near-SLN:Ce. The variation of the refractive index |Δn| has a linear relationship in scale with the applied light intensity accompanied with an abrupt decrease. These findings were attributed to the internal space charge field of photorefraction and the light-induced domain reversal in the crystal.

  9. Far-infrared dispersion of complex dielectric constant in the ferroelectric near-stoichiometric LiNbO 3 :Fe

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Ling, Furi; Tian, Xiaoguang; Zhao, Haitao; Liu, Jinsong; Yao, Jianquan

    2011-09-01

    The dielectric properties of near-stoichiometric LiNbO 3:Fe single crystal have been investigated by using a terahertz time domain spectroscopy (THz-TDS) in a frequency range of 0.7-1.6 THz at room temperature. When coupled with an applied external optical field, an obvious photorefractive effect was observed, resulting in the modulation of the complex dielectric constant for near-SLN:Fe. The variation of refractive index |Δ n| has a linear relationship on scale with the applied light intensity accompanied with a steplike decrease. These findings were attributed to the internal space charge field of photorefraction and the light-induced domain reversal in the crystal.

  10. Thin InSb layers with metallic gratings: a novel platform for spectrally-selective THz plasmonic sensing.

    PubMed

    Lin, Shuai; Bhattarai, Khagendra; Zhou, Jiangfeng; Talbayev, Diyar

    2016-08-22

    We present a computational study of terahertz optical properties of a grating-coupled plasmonic structure based on micrometer-thin InSb layers. We find two strong absorption resonances that we interpret as standing surface plasmon modes and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The observed surface plasmon modes are well described by a simple theory of the air/InSb/air tri-layer. The plasmonic response of the grating/InSb structure is highly sensitive to the dielectric environment and the presence of an analyte (e.g., lactose) at the InSb interface, which is promising for terahertz plasmonic sensor applications. We determine the sensor sensitivity to be 7200 nm per refractive index unit (or 0.06 THz per refractive index unit). The lower surface plasmon mode also exhibits a splitting when tuned in resonance with the vibrational mode of lactose at 1.37 THz. We propose that such interaction between surface plasmon and vibrational modes can be used as the basis for a new sensing modality that allows the detection of terahertz vibrational fingerprints of an analyte.

  11. Metamaterial Demonstrates Both a High Refractive Index and Extremely Low Reflection in the 0.3-THz Band

    NASA Astrophysics Data System (ADS)

    Ishihara, Koki; Suzuki, Takehito

    2017-09-01

    Communication and imaging in the terahertz waveband have advanced rapidly in offering industrial applications. However, optical elements such as collimated lenses in the terahertz waveband are bulky compared with the wavelength due to the lack of naturally occurring substances with a high refractive index and low loss. It is essential to miniaturize optical elements in the terahertz waveband for industrial application. Metamaterials consisting of subwavelength structures can arbitrarily control permittivity and permeability and provide a range of refractive indices. Here, we demonstrate a metamaterial with both a high refractive index and extremely low reflection consisting of symmetrically aligned paired cut metal wires with 18,800 units on the front and back surfaces of a dielectric substrate. Measurements by terahertz time-domain spectroscopy (THz-TDS) confirm a high effective refractive index of 6.66 + j0.123, extremely low reflection power of 1.16%, and the unprecedented high figure of merit (FOM = | n real/ n imag|) of above 300 in the 0.3-THz band. Components with such specifications would enable miniature, high-performance optical elements in the terahertz waveband such as ultrathin flat antennas with high directivity. Further, the concept of the metamaterial with both a high refractive index and extremely low reflection potentially offers a wide range of attractive applications such as solid immersion lenses and cloaking devices.

  12. Metamaterial Demonstrates Both a High Refractive Index and Extremely Low Reflection in the 0.3-THz Band

    NASA Astrophysics Data System (ADS)

    Ishihara, Koki; Suzuki, Takehito

    2017-07-01

    Communication and imaging in the terahertz waveband have advanced rapidly in offering industrial applications. However, optical elements such as collimated lenses in the terahertz waveband are bulky compared with the wavelength due to the lack of naturally occurring substances with a high refractive index and low loss. It is essential to miniaturize optical elements in the terahertz waveband for industrial application. Metamaterials consisting of subwavelength structures can arbitrarily control permittivity and permeability and provide a range of refractive indices. Here, we demonstrate a metamaterial with both a high refractive index and extremely low reflection consisting of symmetrically aligned paired cut metal wires with 18,800 units on the front and back surfaces of a dielectric substrate. Measurements by terahertz time-domain spectroscopy (THz-TDS) confirm a high effective refractive index of 6.66 + j0.123, extremely low reflection power of 1.16%, and the unprecedented high figure of merit (FOM = |n real/n imag|) of above 300 in the 0.3-THz band. Components with such specifications would enable miniature, high-performance optical elements in the terahertz waveband such as ultrathin flat antennas with high directivity. Further, the concept of the metamaterial with both a high refractive index and extremely low reflection potentially offers a wide range of attractive applications such as solid immersion lenses and cloaking devices.

  13. Design of terahertz metal-dielectric-metal waveguide with microfluidic sensing stub

    NASA Astrophysics Data System (ADS)

    Li, Xiangjun; Song, Jian; Zhang, John X. J.

    2016-02-01

    We design a terahertz (THz) metal-dielectric-metal (MDM) waveguide sensor with embedded microfluidic channel suitable for sensing the refractive index variations in liquid. The transmission properties are described using transmission line model (TLM) and numerically simulated using finite-difference time domain (FDTD) method. The sensing characteristics of the structure are systematically analyzed through the examination of the transmission spectrum. The results reveal a series of pronounced resonance peaks in the transmission spectrum, which has linear relationship with the refractive index variation of the material under investigation. For detecting the presence of various cancer cells flowing through the microfluidic channel, we designed and optimized the structural parameters of the THz-MDM sensor and achieved a theoretical value of the refractive index detection sensitivity as high as 0.457 THz/RIU for a 20 μm × 24 μmcross-section channel. This work shows great promise toward realizing a compact THz refractive index sensor with high sensitivity for identifying the signatures of biological samples in liquid.

  14. THz optical design considerations and optimization for medical imaging applications

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Garritano, James; Bajwa, Neha; Nowroozi, Bryan; Llombart, Nuria; Grundfest, Warren; Taylor, Zachary D.

    2014-09-01

    THz imaging system design will play an important role making possible imaging of targets with arbitrary properties and geometries. This study discusses design consideration and imaging performance optimization techniques in THz quasioptical imaging system optics. Analysis of field and polarization distortion by off-axis parabolic (OAP) mirrors in THz imaging optics shows how distortions are carried in a series of mirrors while guiding the THz beam. While distortions of the beam profile by individual mirrors are not significant, these effects are compounded by a series of mirrors in antisymmetric orientation. It is shown that symmetric orientation of the OAP mirror effectively cancels this distortion to recover the original beam profile. Additionally, symmetric orientation can correct for some geometrical off-focusing due to misalignment. We also demonstrate an alternative method to test for overall system optics alignment by investigating the imaging performance of the tilted target plane. Asymmetric signal profile as a function of the target plane's tilt angle indicates when one or more imaging components are misaligned, giving a preferred tilt direction. Such analysis can offer additional insight into often elusive source device misalignment at an integrated system. Imaging plane tilting characteristics are representative of a 3-D modulation transfer function of the imaging system. A symmetric tilted plane is preferred to optimize imaging performance.

  15. Broadband THz Spectroscopy of 2D Nanoscale Materials

    NASA Astrophysics Data System (ADS)

    Chen, Lu; Tripathi, Shivendra; Huang, Mengchen; Hsu, Jen-Feng; D'Urso, Brian; Lee, Hyungwoo; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    Two-dimensional (2D) materials such as graphene and transition-metal dichalcogenides (TMDC) have attracted intense research interest in the past decade. Their unique electronic and optical properties offer the promise of novel optoelectronic applications in the terahertz regime. Recently, generation and detection of broadband terahertz (10 THz bandwidth) emission from 10-nm-scale LaAlO3/SrTiO3 nanostructures created by conductive atomic force microscope (c-AFM) lithography has been demonstrated . This unprecedented control of THz emission at 10 nm length scales creates a pathway toward hybrid THz functionality in 2D-material/LaAlO3/SrTiO3 heterostructures. Here we report initial efforts in THz spectroscopy of 2D nanoscale materials with resolution comparable to the dimensions of the nanowire (10 nm). Systems under investigation include graphene, single-layer molybdenum disulfide (MoS2), and tungsten diselenide (WSe2) nanoflakes. 1. Y. Ma, et al., Nano Lett. 13, 2884 (2013). We gratefully acknowledge financial support from the following agencies and grants: AFOSR (FA9550-12-1-0268 (JL, PRI), FA9550-12-1-0342 (CBE)), ONR (N00014-13-1-0806 (JL, CBE), N00014-15-1-2847 (JL)), NSF DMR-1124131 (JL, CBE) and DMR-1234096 (CBE).

  16. High-resolution waveguide THz spectroscopy of biological molecules.

    PubMed

    Laman, N; Harsha, S Sree; Grischkowsky, D; Melinger, Joseph S

    2008-02-01

    Low-frequency vibrational modes of biological molecules consist of intramolecular modes, which are dependent on the molecule as a whole, as well as intermolecular modes, which arise from hydrogen-bonding interactions and van der Waals forces. Vibrational modes thus contain important information about conformation dynamics of biological molecules, and can also be used for identification purposes. However, conventional Fourier transform infrared spectroscopy and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recently developed, resulting in sharper features. For this technique, an ordered polycrystalline film of the molecule is formed on a metal sample plate. This plate is incorporated into a metal parallel-plate waveguide and probed via waveguide THz-TDS. The planar order of the film reduces the inhomogeneous broadening, and cooling of the samples to 77K reduces the homogenous broadening. This combination results in the line-narrowing of THz vibrational modes, in some cases to an unprecedented degree. Here, this technique has been demonstrated with seven small biological molecules, thymine, deoxycytidine, adenosine, D-glucose, tryptophan, glycine, and L-alanine. The successful demonstration of this technique shows the possibilities and promise for future studies of internal vibrational modes of large biological molecules.

  17. 2.52-THz scanning reflection imaging and image preprocessing

    NASA Astrophysics Data System (ADS)

    Li, Qi; Yao, Rui; Yin, Qiquo; Shan, Jixin; Wang, Qi

    2008-12-01

    Terahertz radiation has high penetration capability and will not cause harmful ionization to human beings; therefore THz reflection imaging has wide application prospect in security inspection and counter-terrorism. However the reflection signal in THz active imaging is weak and the sensitivity of existing detectors in this wave band is low. In this paper the 2.52-THz laser reflection imaging system based on scanning imaging is constructed. The FIR laser of SIFIR-50FPL made by Coherent Inc in America is chosen as the THz radiation source and its power is about 30mW. The detector of P4-42 made by the Molectron Corporation is adopted, which works at the room temperature with the spectral range from 1nm to over 1mm. The imaging experiments on knives and some other objects are made utilizing this system. The images of concealed objects are obtained and the images are clearer after image preprocessing. The experimental results show that this imaging system has wide application potential in security inspection.

  18. New THz sources for bio-medical imaging

    NASA Astrophysics Data System (ADS)

    Harris, James S., Jr.; Gu, Anjia; Kim, Seongsin M.

    2007-02-01

    We present an evaluation of new terahertz sources for biomedical imaging based upon quantum cascade lasers (QCL) and orientation patterned gallium arsenide (OP-GaAs) optical parametric oscillator (OPO). The recently developed terahertz quantum cascade laser emits a peak output power of up to 40mW at 3.7 THz (λ=81μm). Utilizing coherent terahertz radiation greatly improves the signal to noise ratio of the detection, where it provides a relatively large dynamic range and high spatial resolution. We demonstrated biomedical imaging of malignant tissue contrast in an image of a mouse liver with developed tumors with a THz imaging system based on a QCL. In addition, images of various tissues, such as lung, liver, and brain sections from the laboratory mouse were also obtained. We also explored distinct images from fat, muscle and tendon and measured the absorption coefficient and compared this with FTIR measurements. Another recent technological advance in THz source is based on cascaded optical down-conversion in an OP-GaAs OPO, which provides a tunable THz source over a broad wavelength range with an average power of 1mW at room temperature (RT). The tunability of the OPO source provides additional imaging modes through the ability to excite molecular vibrations and obtain biochemical and structural information in addition to normal absorption or reflectivity contrast.

  19. Investigations on time stability of passive THz imaging

    NASA Astrophysics Data System (ADS)

    Kowalski, Marcin; Palka, Norbert; Zyczkowski, Marek; Szustakowski, Mieczyslaw

    2014-10-01

    Terahertz radiation is within the frequency range from 100 GHz to 10THz. This radiation has specific characteristics in terms of imaging. The radiation is harmless to the human body because the energy transferred by electromagnetic waves in this range of frequencies are very small thus there is no ionization of matter. The development of imaging devices and exploration of new spectral bands is a chance to introduce new equipment for assuring public safety. It has been proved that objects hidden under clothing can be detected and visualized using terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. In order to determine the properties of terahertz imaging for detection of hidden objects several aspects need to be considered. Taking into account the fact that the image captured by the terahertz camera reflects the spatial distribution of the relative temperature of the observed objects, the effect of the measurement time on the imaging capabilities should be examined. A very important aspect is the influence of the type (material composition) of coating material, as well as the type of an object hidden under clothing (size and material). The purpose of the studies is to investigate the time stability of passive THz imaging on 250 GHz for detection of concealed objects. In the article, we present the measurement setup, the measurement methodology as well as the initial results of measurements with various types of clothing and test objects.

  20. Very high Power THz radiation from Relativistic Electrons

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-08-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques.

  1. THz time-domain spectroscopy for tokamak plasma diagnostics

    SciTech Connect

    Causa, F.; Zerbini, M.; Buratti, P.; Gabellieri, L.; Pacella, D.; Romano, A.; Tuccillo, A. A.; Tudisco, O.; Johnston, M.; Doria, A.; Gallerano, G. P.; Giovenale, E.

    2014-08-21

    The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

  2. THz time-domain spectroscopy for tokamak plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Causa, F.; Zerbini, M.; Johnston, M.; Buratti, P.; Doria, A.; Gabellieri, L.; Gallerano, G. P.; Giovenale, E.; Pacella, D.; Romano, A.; Tuccillo, A. A.; Tudisco, O.

    2014-08-01

    The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

  3. New algorithm for the passive THz image quality enhancement

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Trofimov, Vladislav V.

    2016-04-01

    We propose a new approach for THz image quality enhancing using correlation function between the image under consideration and a standard image. The standard image moves in two directions along a image under analysis. As a result, 2 D correlation function is obtained. Multiplying this function by color number belonging to a grey scale, we restore the image under the analysis. This allows to suppress a noise on a new image. This method allows to see the person clothes details that it means multi-times increasing of the passive THz camera temperature resolution. We discuss a choice of standard image characteristics for an achievement of correlation function for high contrast. Other feature of our approach arises from a possibility of a person image coming to the THz camera by using a computer processing of the image only. It means that we can "decrease" a distance between a person and the passive THz camera. This algorithm is very convenient for using and has a high performance.

  4. Optimizing the sensitivity of porous thin film optical sensors

    NASA Astrophysics Data System (ADS)

    Mackay, Tom G.

    2012-10-01

    We considered a porous thin film as a platform for optical sensing. It is envisaged that the porous thin filmbecomes infiltrated by a fluid containing an agent to be sensed. The basis for detection of this agent to besensed is provided by changes in the optical properties of the infiltrated porous thin film. Provided that thepore sizes are much smaller than the wavelengths involved, the infiltrated porous thin film may be regardedas a homogenized composite material. Using the well-established Bruggeman homogenization formalism, thesensitivity of such an optical sensor was investigated theoretically. The sensitivity was considered in relation tothe optical properties of the porous thin film and the infiltrating fluid, the porosity of the thin film, and theshape of the pores. For the case of an isotropic dielectric porous thin film of relative permittivity ɛa and anisotropic dielectric fluid of relative permittivity ɛb, the sensitivity was found to be maximized if: (i) the contrast between ɛa and ɛb was maximized; (ii) mid-range values of porosity were used; (iii) the regime 0 < ɛb < 1 with ɛa » 1 pertained, for example; and (iv) pores which have elongated spheroidal shapes were incorporated.

  5. Performances of THz cameras with enhanced sensitivity in sub-terahertz region

    NASA Astrophysics Data System (ADS)

    Oda, Naoki; Ishi, Tsutomu; Kurashina, Seiji; Sudou, Takayuki; Morimoto, Takao; Miyoshi, Masaru; Doi, Kohei; Goto, Hideki; Sasaki, Tokuhito; Isoyama, Goro; Kato, Ryukou; Irizawa, Akinori; Kawase, Keigo

    2015-05-01

    Uncooled microbolometer-type 640x480 and 320x240 Terahertz (THz) focal plane arrays (FPAs) with enhanced sensitivity in sub-THz region are developed, and incorporated into 640x480 and 320x240 cameras, respectively. The pixel in the THz-FPA has such a structure that an area sensitive to electromagnetic wave is suspended above read-out integrated circuit (ROIC). A thin metallic layer is formed on the top of the sensitive area, while a thick metallic layer is formed on the surface of ROIC. The structure composed of the thin metallic layer and the thick metallic layer behaves as an optical cavity. The THz-FPAs reported in this paper have a modified pixel structure which has several times longer optical-cavity length than NEC's previous pixel does, by forming a thick SiN layer on the ROIC. The extended optical-cavity structure is favorable for detecting electromagnetic wave with lower frequency. Consequently, the Minimum Detectable Power per pixel (MDP) is improved ten times in sub-THz region, especially 0.5-0.6 THz. This paper presents spectral frequency dependences of MDP values for THz-FPA with the modified pixel structure and THz-FPA with the previous pixel structure, using THz free electron laser (FEL) developed by Osaka University. The modification of pixel structure extends high sensitivity region to lower frequency region, such as sub-THz region, and the wider spectral coverage of THz camera surely expands its applicability

  6. THz time-domain spectroscopy on plant oils and animal fats

    NASA Astrophysics Data System (ADS)

    Hu, Ying; Guo, Lantao; Wang, Xiaohong; Zhang, Xi Cheng

    2005-01-01

    Terahertz (THz) radiation, generated by ultra short laser pulses, occupies a broad band on electromagnetic spectrum chart. This radiation band belongs to far-infrared. It is a new research field of studying THz radiation interacting with materials especially with biomaterials. The paper shows experimental results of five plant oil samples from different kind of plants and two kinds of animal fat samples by using THz-TDS (THz time-domain spectroscopy) technology. The refraction indices and the absorption coefficients of these samples are measured in the range from 0.2 to 2.0 THz. The results show that different oils have different refraction indices. For oil samples, refraction indices decrease slowly while their coefficients of absorption increase with the increases of THz frequency. For the animal fat samples, the refraction indices show almost no change while the absorption coefficients increase with the increasing THz frequency. The absorption coefficients increase with the increasing temperature.

  7. Probe beam-free detection of terahertz wave by electroluminescence induced by intense THz pulse

    NASA Astrophysics Data System (ADS)

    Shin, J.; Jin, Z.; Nosaka, Y.; Nakazawa, T.; Kodama, R.

    2016-03-01

    Recently, a table-top fs laser system can generate MW terahertz (THz) pulse with its electric field higher than 100 kV/cm can be generated by several schemes. Such a strong THz field can directly drive electrons inside various materials. Here, we demonstrated a direct THz electric field detection method by measuring the electroluminescence induced by intense THz pulse inside commonly available light emitting diode. An intense THz wave obtained by the two-color laser scheme was focused onto LED along with an external DC bias to induce luminescence which we found proportional to the amplitude of the incident THz field. The scheme can be useful to realize a low-cost, probe-free THz detection and imaging system.

  8. Beam profile and spectral characteristic of THz wave in free space

    NASA Astrophysics Data System (ADS)

    Zhao, Guozhong; Yang, Kun; Wu, Meng; Wu, Lizhong

    2008-12-01

    Beam profile and spectral characteristic of terahertz (THz) wave in free space are presented in this paper. The beam width of THz wave at the focus point of parabolic mirror is obtained by means of the narrow-slit measurement. By the spectroscopic imaging, we present the transverse mode distribution of THz beam on the cross-section of focus point. Our experimental results show that the centre wavelength of THz spectra has a distinguished red-shift when it is far away the centre of THz focus point. The spectral range of THz wave far from the focus point is less than that of the centre. This kind of spectral characteristic of THz wave is closely related to the diffraction effect of electromagnetic wave.

  9. [Application of THz technology to nondestructive detection of agricultural product quality].

    PubMed

    Jiang, Yu-ying; Ge, Hong-yi; Lian, Fei-yu; Zhang, Yuan; Xia, Shan-hong

    2014-08-01

    With recent development of THz sources and detector, applications of THz radiation to nondestructive testing and quality control have expanded in many fields, such as agriculture, safety inspection and quality control, medicine, biochemistry, communication etc. Compared with other detection technique, being a new kind of technique, THz radiation has low energy, good perspectivity, and high signal-to-noise ratio, and thus can obtain physical, chemical and biological information. This paper first introduces the basic concept of THz radiation and the major properties, then gives an extensive review of recent research progress in detection of the quality of agricultural products via THz technique, analyzes the existing shortcomings of THz detection and discusses the outlook of potential application, finally proposes the new application of THz technique to detection of quality of stored grain.

  10. Revealing plasma oscillation in THz spectrum from laser plasma of molecular jet.

    PubMed

    Li, Na; Bai, Ya; Miao, Tianshi; Liu, Peng; Li, Ruxin; Xu, Zhizhan

    2016-10-03

    Contribution of plasma oscillation to the broadband terahertz (THz) emission is revealed by interacting two-color (ω/2ω) laser pulses with a supersonic jet of nitrogen molecules. Temporal and spectral shifts of THz waves are observed as the plasma density varies. The former owes to the changing refractive index of the THz waves, and the latter correlates to the varying plasma frequency. Simulation of considering photocurrents, plasma oscillation and decaying plasma density explains the broadband THz spectrum and the varying THz spectrum. Plasma oscillation only contributes to THz waves at low plasma density owing to negligible plasma absorption. At the longer medium or higher density, the combining effects of plasma oscillation and absorption results in the observed low-frequency broadband THz spectra.

  11. Effective dielectric and elastic properties of nanoporous low-k media

    NASA Astrophysics Data System (ADS)

    Hermann, H.

    2010-07-01

    This paper presents a mathematically defined characterization of random porous media including random self-similarity and surface fractality. The initial two-phase structure is transformed into a three-phase system by introducing the internal surface layer as the third phase. Effective medium theories are utilized to calculate macroscopic dielectric and elastic properties. The dependence of both the static dielectric constant and Young's modulus on geometrical parameters is analyzed for different combinations of bulk and interface properties. It is shown that the modification of the properties of the internal surface layer is a promising way to improve the effective constants of the materials. The obtained analytical expressions are also used to determine confined regions in the space of structural parameters where pre-specified property combinations are realized. The results are discussed in terms of possible applications of nanometer-scale porous interlayer dielectrics with an ultralow dielectric constant and sufficient mechanical stiffness for future semiconducting devices.

  12. Dielectric loss of liquid hydrocarbons in the millimetre and submillimetre wavelength regions

    NASA Astrophysics Data System (ADS)

    Richter, W.; Schiel, D.

    1984-05-01

    The dielectric-loss tangent of liquid cyclohexane, n-hexane, n-heptane and n-octane has been determined in the frequency range 4-300 cm -1 (120 GHz-9 THz) by means of power absorption measurements using rapid-scan FTS. The results agree with literature data for cyclohexane obtained with dispersive FTS and link up well with existing microwave results, corroborating the existence of a low-frequency dielectric-loss maximum with the n-alkanes. The origin of the dielectric loss of these low-loss liquids is considered to be due to relaxational processes of weak permanent dipoles and low-lying intramolecular vibrations in the case of the n-alkanes, and to interaction-induced absorption in the case of cyclohexane.

  13. Tunable terahertz multichannel filter based on one-dimensional superconductor-dielectric photonic crystals

    SciTech Connect

    Liu, Yang; Yi, Lin

    2014-12-14

    By means of the transfer matrix method, the transmission properties of one-dimensional photonic crystals (PCs) consisting of superconductor and dielectric have been systematically investigated within the terahertz frequency range (0.1–10 THz). It is shown that comb-like resonant peaks in transmission band can be formed without adding any defect layer in superconductor-dielectric PCs, which means that such a one-dimensional periodic structure can serve as a tunable terahertz multichannel filter by using the PCs passband. Furthermore, the influences coming from the period of the structure, the thickness of the components, the permittivity of the dielectric layers, temperature, and the normal conducting electrons on the filtering properties are also numerically investigated.

  14. Transmission enhancement of THz pulse through Ag2O-Ag layer detected by THz-TDS

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Li, Wang

    2008-12-01

    We used terahertz time-domain spectroscopy (THz-TDS) to probe the enhancement transmission of Ag2O-Ag compound. Using a 500μm- GaAs substrate attaching to the sample, the evanescent wave is coupled to the far field. And the transmitted amplitude is enhanced, corresponding to the frequent shift and spectra broadening.

  15. [Reseach on THz Time Domain Spectrum of Photo-Induced Insulator-Metal Phase Transition of VO₂ Films].

    PubMed

    Wang, Chang-lei; Wu, Shuai; Li, Yan-feng; Liu, Bo-wen; Hu, Ming-lie; Chai, Lu; Xing, Qi-rong; Wang, Qing-yue

    2015-11-01

    Vanadium dioxide (VO₂) film will be phase-transitioned from insulator into metal, accompanied with dramatic change on conductivity, which is named as photo-induced insulator-metal phase transition. Such phase transition of VO₂ film has important application potentials in modulators or other functional devices for terahertz waves. In this paper, the transmission spectrum variations before and after the photo-induced insulator-metal phase transition of vanadium dioxide film are investigated, and the phase transition properties in terahertz(THz) region are analyzed. In the experiment, the phase transition of the VO₂ film was induced by a continuous wave (CW) laser source and a femtosecond (fs) laser source, respectively. Obvious changes on the THz waveforms were observed for the both mentioned means of excitation, and the amplitude attenuation, as well as the signal distortion, was intensified with the increase of the impinging optical power. The fast Fourier transform (FFT) spectra of the transmitted THz time-domain signals were analyzed and it was found that the amplitude of the transmitted spectrum decreased synchronously with the increase of the optical power, accompanied with deformation of the spectrum line shape at the same time. The reason was that the macroscopic dielectric properties of the VO₂ film approached gradually to that of a metal as laser power was increased. A parameter, transmission modulation function, was defined in the paper as the amplitude difference between the transmission spectra of the VO₂ film before and after the laser excitation, to describe the dispersivity of the photo-induced phase transition more clearly. From the curve of the transmission modulation function, strong frequency-dependent properties at THz frequencies were found to vary regularly with the incident light power. After furthermore comparison, it was found that, though the insulator-metal phase transition could be trigged by both CW laser source and fs laser

  16. Efficient THZ Source Based on Cascaded Optical Down-Conversion in Orientation-Patterned GaAs Structures

    DTIC Science & Technology

    2008-11-20

    techniques for generating THz radiation [5], none of them provides a THz source which is simultaneously ( i ) compact, (ii) highly efficient, (iii...are very attractive for QPM THz-wave generation because of several appealing properties, namely ( i ) small THz absorption coefficient (smaller by an...with periodically- inverted crystalline orientation were used for QPM THz generation: ( i ) diffusion-bonded GaAs (DB-GaAs) [49], produced by

  17. Improved Dielectric Films For Capacitors

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

    1994-01-01

    Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

  18. Fabrication of Polyurethane Dielectric Actuators

    DTIC Science & Technology

    2005-01-01

    a summary of a 3 year Technology Investment Fund Project entitled “Dielectric Polymer Actuators for Active/ Passive Vibration Isolation”, which was...completed in March 2005. The purpose of this project was to investigate dielectric polymer materials for potential use in active/ passive vibration...devices and systems based on dielectric polymer actuators. Keywords: dielectric actuators, electroactive polymers , Technology Investment Fund 1

  19. Emission of Coherent THz-Radiation from Superconductors.

    NASA Astrophysics Data System (ADS)

    Welp, Ulrich

    2008-03-01

    Josephson junctions naturally convert dc-voltages into high-frequency electromagnetic radiation, with 1 mV corresponding to 0.483 THz, and many such junctions emitting in phase at the same frequency can produce useful emission power. Stacks of junctions with unsurpassed packing density occur naturally in the layered high temperature superconductor Bi2Sr2CaCu2O8, in which the superconducting CuO2-layers are coupled through the intrinsic Josephson effect. However, achieving synchronization of the high-frequency oscillations of all the junctions in the stack has so far been a major challenge. We demonstrate that coherent continuous-wave THz-radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 μW at frequencies up to 0.85 THz. The available power is potentially much larger, as there is evidence that 20 μW of power are pumped into the observed THz cavity resonance. The emission persists up to temperatures of ˜50 K. Emission does not require the application of a magnetic field, significantly simplifying the design of superconducting THz-sources. In fact, a single applied D.C. current leads to the efficient excitation of continuous coherent THz-radiation. This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357 -- Basic Energy Sciences, the Japanese Ministry of Education, Culture, Sports, Science and Technology, and the Turkish TUBITAK under Project No. 106T053. In collaboration with L. Ozyuzer, A. E. Koshelev, C. Kurter, N. Gopalsami, Q. Li, M. Tachiki, K. Kadowaki, T. Yamamoto, H. Minami, H. Yamaguchi, T. Tachiki, K. E. Gray, W

  20. Tunable and reconfigurable THz devices for advanced imaging and adaptive wireless communication

    NASA Astrophysics Data System (ADS)

    Liu, L.; Shams, M. I. B.; Jiang, Z.; Rahman, S.; Hesler, J. L.; Cheng, L.-J.; Fay, P.

    2016-09-01

    In this paper, we report on two different approaches that have been explored to realize tunable and reconfigurable THz devices for advanced imaging and adaptive wireless communication. The first approach makes use of electronically tunable varactor diodes. Frequency tunable THz antennas based on this approach have been successfully demonstrated for the first time in G-band, enabling the development of spectroscopic THz detectors and focal-plane imaging arrays. The second approach takes advantages of optical THz spatial modulation based on photo-induced free carriers in semiconductors. Using this approach, high-performance tunable THz modulators/attenuators, reconfigurable masks for THz coded aperture imaging, and photo-induced Fresnel-zone-plate antennas for dynamic THz beam steering and forming have been successfully demonstrated. Our recent study also shows that by employing the so-called mesa array technique, sub-wavelength spatial resolution and higher than 100 dB modulation depth can be achieved, making it possible to develop tunable THz devices (e.g., tunable filters) with performance and versatility far beyond those realized by conventional approaches. On the basis of the above investigation, the prospects of high-speed near-field THz imaging, real-time ultra-sensitive heterodyne imaging and prototype adaptive THz wireless communication links will be discussed.

  1. Hydration dependence of conformational dielectric relaxation of lysozyme.

    PubMed

    Knab, Joseph; Chen, Jing-Yin; Markelz, Andrea

    2006-04-01

    Dielectric response of hen egg white lysozyme is measured in the far infrared (5-65 cm-1, 0.15-1.95 THz, 0.6-8.1 meV) as a function of hydration. The frequency range is associated with collective vibrational modes of protein tertiary structure. The observed frequency dependence of the absorbance is broad and glass-like. For the entire frequency range, there is a slight increase in both the absorbance and index of refraction with increasing hydration for <0.27 h (mass of H2O per unit mass protein). At 0.27 h, the absorbance and index begin to increase more rapidly. This transition corresponds to the point where the first hydration shell is filled. The abrupt increase in dielectric response cannot be fully accounted for by the additional contribution to the dielectric response due to bulk water, suggesting that the protein has not yet achieved its fully hydrated state. The broad, glass-like response suggests that at low hydrations, the low frequency conformational hen egg white lysozyme dynamics can be described by a dielectric relaxation model where the protein relaxes to different local minima in the conformational energy landscape. However, the low frequency complex permittivity does not allow for a pure relaxational mechanism. The data can best be modeled with a single low frequency resonance (nu approximately 120 GHz=4 cm-1) and a single Debye relaxation process (tau approximately .03-.04 ps). Terahertz dielectric response is currently being considered as a possible biosensing technique and the results demonstrate the required hydration control necessary for reliable biosensor applications.

  2. The presence of two electron beams in a Cherenkov maser and their different behavior for generation and amplification of THz electromagnetic waves

    NASA Astrophysics Data System (ADS)

    Hajijamali-Arani, Zeinab; Jazi, Bahram

    2017-04-01

    The wave propagation in a cylindrical metallic waveguide including a dielectric tube is investigated. Two electron beams with opposite velocities are injected in the system as energy sources. It is shown that one of the electron beams is responsible for Cherenkov radiation, the other one is as the stabilizer. The dispersion relation of the waves, impedance of the waves, operating frequency of the system and time growth rate of THz waves are investigated. The effects of relative permittivity constant of dielectric tube, the geometrical dimensions, and the accelerating voltage on time growth rate are investigated. The effective factors on the frequency spectra of the waveguide will be presented too. It is obtained that the time growth rate of the waves increases with increasing the dielectric permittivity and thickness of the dielectric tube. In addition, with increasing the accelerating voltage the time growth rate has opposite behavior in some of the branches of the dispersion graphs. The power obtained in the excitation process for one branch of the dispersion graphs is presented. The graph of variations of transported power with respect to the wave frequency is plotted.

  3. Cast dielectric composite linear accelerator

    DOEpatents

    Sanders, David M.; Sampayan, Stephen; Slenes, Kirk; Stoller, H. M.

    2009-11-10

    A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

  4. Polarimetric scattering behavior of rough dielectric materials at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Digiovanni, David Anthony

    Technologies in the terahertz region of the spectrum are finding increased usage in areas such as communications, remote sensing, and imaging, For example, driven by the promise of greater data transfer rates, free-space communication that traditionally operate in the radio and microwave bands are being developed at terahertz frequencies. Successful transition of communication systems to higher frequencies, particularly for systems located in indoor or urban environments, will require a thorough understanding of the reflection, transmission, absorption, and scattering behavior of a wide variety of materials and surface types. Scattering properties of rough surfaces have been studied extensively at radio and microwave frequencies, however, such properties have only recently become of interest at higher frequencies. The goal of this thesis was to develop a better understanding of electromagnetic scattering from dielectric rough surfaces at millimeter wavelengths and terahertz frequencies. This goal was achieved by measuring the polarimetric scattering behavior of dielectric materials and comparing the measured data to predictions made by rough surface scattering theory. The dielectric properties and the roughness of the samples were tailored in order to provide a controlled parameter space to investigate. Fully polarimetric radar imagery of the rough surfaces were acquired at 160 GHz, 240 GHz, and 1.55 THz. The backscattering measurements were collected as a function of polarization, incident angle, and frequency. The applicability of various rough surface scattering theories was determined for the different roughness regimes studied.

  5. Multilayer Dielectric Transmissive Optical Phase Modulator

    NASA Technical Reports Server (NTRS)

    Keys, Andrew Scott; Fork, Richard Lynn

    2004-01-01

    A multilayer dielectric device has been fabricated as a prototype of a low-loss, low-distortion, transmissive optical phase modulator that would provide as much as a full cycle of phase change for all frequency components of a transmitted optical pulse over a frequency band as wide as 6.3 THz. Arrays of devices like this one could be an alternative to the arrays of mechanically actuated phase-control optics (adaptive optics) that have heretofore been used to correct for wave-front distortions in highly precise optical systems. Potential applications for these high-speed wave-front-control arrays of devices include agile beam steering, optical communications, optical metrology, optical tracking and targeting, directional optical ranging, and interferometric astronomy. The device concept is based on the same principle as that of band-pass interference filters made of multiple dielectric layers with fractional-wavelength thicknesses, except that here there is an additional focus on obtaining the desired spectral phase profile in addition to the device s spectral transmission profile. The device includes a GaAs substrate, on which there is deposited a stack of GaAs layers alternating with AlAs layers, amounting to a total of 91 layers. The design thicknesses of the layers range from 10 nm to greater than 1 micrometer. The number of layers and the thickness of each layer were chosen in a computational optimization process in which the wavelength dependences of the indices of refraction of GaAs and AlAs were taken into account as the design was iterated to maximize the transmission and minimize the group-velocity dispersion for a wavelength band wide enough to include all significant spectral components of the pulsed optical signal to be phase modulated.

  6. Pulsed THz TDS of objects covered by disordered structure

    NASA Astrophysics Data System (ADS)

    Trofimov, V. A.; Zakharova, I. G.; Zagursky, D. Y.; Varentsova, Svetlana A.

    2016-05-01

    Using both computer simulation and physical experiment, we demonstrate principal limitations of standard Time Domain Spectroscopy based on a broadband THz pulse for the detection and identification of substance placed inside the disordered structure. The interaction of a THz pulse with a disordered layered structure was simulated in order to show the influence of the disordered layers on the spectral characteristics of the transmitted and reflected signals. Spectral characteristics of these signals were analyzed in a direct comparison with the incident pulse spectrum. We showed that a disordered structure disturbs the reflected pulse spectrum dramatically. To avoid this, we used the integral correlation criteria in real experiment. Computer simulation results were confirmed by physical experiment. We provided the experiments with paper bag, and ordinary sheets of paper, and napkins.

  7. Distribution of multiband THz wireless signals over fiber

    NASA Astrophysics Data System (ADS)

    Shams, Haymen; Gonzalez-Guerrero, Luis; Fice, Martyn; Yang, Zhen; Renaud, Cyril; Seeds, Alywn

    2017-01-01

    Terahertz wireless communication is receiving great interest from researchers and industries, thanks to the new spectral windows between 0.1 and 1 THz offering opportunities for ultra-high-data-rate wireless transmission. Wavelength division multiplexing for wireless-over-fiber is foreseen as an enabling technique to support connection between base stations and a central station. This paper reviews architectures for photonic distribution and generation of multiband signals for sub- THz wireless communications, giving rates up to 100 Gb/s (20 Gb/s per band) using the full spectrum between 220 GHz and 280 GHz for downlink wireless transmission, and 10 Gb/s for uplink using on-off keying.

  8. 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.

  9. THz imaging of majolica tiles and biological attached marble fragments

    NASA Astrophysics Data System (ADS)

    Catapano, Ilaria; Soldovieri, Francesco

    2016-04-01

    Devices exploiting waves in the frequency range from 0.1 THz to 10 THz (corresponding to a free-space wavelength ranging from 30 μm to 3 mm) deserve attention as diagnostic technologies for cultural heritage. THz waves are, indeed, non-ionizing radiations capable of penetrating into non-metallic materials, which are opaque to both visible and infrared waves, without implying long term risks to the molecular stability of the exposed objects and humans. Moreover, THz surveys involve low poewr probing waves, are performed without contact with the object and, thanks to the recent developments, which have allowed the commercialization of compact, flexible and portable systems, maybe performed in loco (i.e. in the place where the artworks are usually located). On the other hand, THz devices can be considered as the youngest among the sensing and imaging electromagnetic techniques and their actual potentialities in terms of characterization of artworks is an ongoing research activity. As a contribution within this context, we have performed time of flight THz imaging [1,2] on ceramic and marble objects. In particular, we surveyed majolica tiles produced by Neapolitan ceramists in the 18th and 19th centuries with the aim to gather information on their structure, constructive technique and conservation state. Moreover, we investigated a Marmo di Candoglia fragment in order to characterize the biological attach affecting it. All the surveys were carried out by using the Fiber-Coupled Terahertz Time Domain System (FICO) developed by Z-Omega and available at the Institute of Electromagnetic Sensing of the Environment (IREA). This system is equipped with fiber optic coupled transmitting and receiving probes and with an automatic positioning system enabling to scan a 150 mm x 150 mm area under a reflection measurement configuration. Based on the obtained results we can state that the use of THz waves allows: - the reconstruction of the object topography; - the geometrical

  10. Characterization of a THz CW spectrometer pumped at 1550 nm

    NASA Astrophysics Data System (ADS)

    Yeo, Woon-Gi; Nahar, Niru K.

    2015-07-01

    We present an evaluation of a cost-effective THz CW spectrometer pumped at 1550 nm wavelengths with a fixed delay line. To study the spectral competence of the spectrometer, transmission data is obtained for various organic and inorganic samples. Spectral comparisons of the samples are presented by using THz time domain spectroscopy and vector network analyzer (VNA). Despite the capability of highly resolved transmission spectroscopy, our current system reveals the uncertainty in interferometric output data for phase analysis. Here, we identify the effect of fringing space of raw output data toward frequency resolution, phase analysis, and data acquisition time. We also propose the proper delay line setup for phase analysis for this type of spectrometers.

  11. Porous Shape Memory Polymers

    PubMed Central

    Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.

    2013-01-01

    Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038

  12. Tailored Porous Materials

    SciTech Connect

    BARTON,THOMAS J.; BULL,LUCY M.; KLEMPERER,WALTER G.; LOY,DOUGLAS A.; MCENANEY,BRIAN; MISONO,MAKOTO; MONSON,PETER A.; PEZ,GUIDO; SCHERER,GEORGE W.; VARTULI,JAMES C.; YAGHI,OMAR M.

    1999-11-09

    Tailoring of porous materials involves not only chemical synthetic techniques for tailoring microscopic properties such as pore size, pore shape, pore connectivity, and pore surface reactivity, but also materials processing techniques for tailoring the meso- and the macroscopic properties of bulk materials in the form of fibers, thin films and monoliths. These issues are addressed in the context of five specific classes of porous materials: oxide molecular sieves, porous coordination solids, porous carbons, sol-gel derived oxides, and porous heteropolyanion salts. Reviews of these specific areas are preceded by a presentation of background material and review of current theoretical approaches to adsorption phenomena. A concluding section outlines current research needs and opportunities.

  13. Porous Shape Memory Polymers.

    PubMed

    Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C; Wilson, Thomas S; Maitland, Duncan J

    2013-02-04

    Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use.

  14. Emerging electronic devices for THz sensing and imaging

    NASA Astrophysics Data System (ADS)

    Fay, P.; Xie, Y.; Zhao, Y.; Jiang, Z.; Rahman, S.; Xing, H.; Sensale-Rodriguez, B.; Liu, L.

    2014-09-01

    Continuing advances in scaling of conventional semiconductor devices are enabling mainstream electronics to operate in the millimeter-wave through THz regime. At the same time, however, novel devices and device concepts are also emerging to address the key challenges for systems in this frequency range, and may offer performance and functional advantages for future systems. In addition to new devices, advances in integration technology and novel system concepts also promise to provide substantial system-level performance and functionality enhancements. Several emerging devices and device concepts, as well as circuit-level concepts to take advantage of them, are discussed. Based on unconventional semiconductor device structures and operational principles, these devices offer the potential for significantly improved system sensitivity and frequency coverage. When combined in arrays, features such as polarimetric detection and frequency tunability for imaging can be achieved. As examples of emerging devices for millimeter-wave through THz sensing and imaging, heterostructure backward diodes in the InAs/AlSb/GaSb material system and GaN-based plasma-wave high electron mobility transistors (HEMTs) will be discussed. Based on interband tunneling, heterostructure backward diodes offer significantly increased sensitivity and extremely low noise for direct detection applications, and have been demonstrated with cutoff frequencies exceeding 8 THz. The plasma-wave HEMT is an emerging device concept that, by leveraging plasma-wave resonances in the two-dimensional electron gas within the channel of the HEMT, offers the prospect for both tunable narrowband detection as well as low-noise amplification at frequencies well into the THz. These emerging devices are both amenable to direct integration within compact planar radiating structures such as annular slot antennas for realization of polarimetric detection and frequency tuning for spectroscopy and imaging.

  15. Slot-Antenna Coupled Microbolometer Arrays for THz Radiation

    DTIC Science & Technology

    2000-09-29

    properties for 2.5THz-CH 3OH laser radiation were microbolometers ), and each bolometer is connected in investigated at room temperature . The detected voltage...configuration of the infrared frequency region, because of its room - single slot antenna coupled microbolometer . The temperature operation and easy...Vol. X 3 slot antenna coupled microbolometer array and a 3 pp.773-776, Jun.1979. 2. D. F. Filpovic, W. Y. Ali-Ahmad, and G. M. Rebeiz, " Millimeter - two

  16. Electrical dynamic modulation of THz radiation based on superconducting metamaterials

    NASA Astrophysics Data System (ADS)

    Li, Chun; Wu, Jingbo; Jiang, Shoulu; Su, Runfeng; Zhang, Caihong; Jiang, Chengtao; Zhou, Gaochao; Jin, Biaobing; Kang, Lin; Xu, Weiwei; Chen, Jian; Wu, Peiheng

    2017-08-01

    We demonstrate an electrically tunable superconducting metamaterial capable of modulating terahertz waves dynamically. The device is based on electromagnetically induced transparency-like metamaterials, and the maximum modulation depth reaches 79.8% in the transmission window. Controlled by an electrical sinusoidal signal, such a device could achieve a modulation speed of approximately 1 MHz. The superior property and simplicity of design make this device promising for the development of high performance THz systems.

  17. Terahertz (THz) Radar: A Solution for Degraded Visibility Environments (DVE)

    DTIC Science & Technology

    2016-11-01

    for an object to be detectable. In addition, while the frequency is 3 high for a true radar, the frequency is sufficiently low for the radiation ...THz) frequencies. Preliminary measurements are encouraging and validate the system’s relatively high resolution and ability to tune the frequency...system must be capable of overcoming the visual obscurants and providing high -resolution images of the environment in order to facilitate the decision

  18. Broadband Sources in the 1-3 THz Range

    NASA Technical Reports Server (NTRS)

    Mehdi, Imran; Ward, John; Maestrini, Alain; Chattopadhyay, Goutam; Schlecht, Erich; Thomas, Bertrand; Lin, Robert; Lee, Choonsup; Gill, John

    2009-01-01

    Broadband electronically tunable sources in the terahertz range are a critical technology for enabling space-borne as well as ground-based applications. By power-combining MMIC amplifier and frequency tripler chips, we have recently demonstrated >1 mW of output power at 900 GHz. This source provides a stepping stone to enable sources in the 2-3 THz range than can sufficiently pump multi-pixel imaging arrays.

  19. Correlated Particle Motion and THz Spectral Response of Supercritical Water

    NASA Astrophysics Data System (ADS)

    Śmiechowski, Maciej; Schran, Christoph; Forbert, Harald; Marx, Dominik

    2016-01-01

    Molecular dynamics simulations of supercritical water reveal distinctly different distance-dependent modulations of dipolar response and correlations in particle motion compared to ambient conditions. The strongly perturbed H-bond network of water at supercritical conditions allows for considerable translational and rotational freedom of individual molecules. These changes give rise to substantially different infrared spectra and vibrational density of states at THz frequencies for densities above and below the Widom line that separates percolating liquidlike and clustered gaslike supercritical water.

  20. All-dielectric periodic terajet waveguide using an array of coupled cuboids

    SciTech Connect

    Minin, I. V. Minin, O. V.; Pacheco-Peña, V. Beruete, M.

    2015-06-22

    In this paper, the recently proposed technique to produce photonic jets (terajets at terahertz (THz) frequencies) using 3D dielectric cuboids is applied in the design of a mesoscale cuboid-chain waveguide. The chains are basically designed with several dielectric cubes with side λ{sub 0} placed periodically along the axial z-axis and separated by an air-gap. Based on this, a systematic study of the focusing properties and wave guiding of this chain is performed when the air-gap between the dielectric cubes is changed from 0.25λ{sub 0} to 3λ{sub 0} with the best performance achieved at 2.5λ{sub 0}. An analysis when losses are included in the cubes is also done, demonstrating a robust performance. Finally, the wave guiding is experimentally demonstrated at sub-THz frequencies with a good agreement with numerical results. The simulation results of focusing and transport properties are carried out using Finite Integration Technique. The results here presented may be scaled to any frequency ranges such as millimeter, sub-millimeter, and optical frequencies.

  1. Frequency-agile THz-wave generation and detection system using nonlinear frequency conversion at room temperature.

    PubMed

    Guo, Ruixiang; Ikar'i, Tomofumi; Zhang, Jun; Minamide, Hiroaki; Ito, Hiromasa

    2010-08-02

    A surface-emitting THz parametric oscillator is set up to generate a narrow-linewidth, nanosecond pulsed THz-wave radiation. The THz-wave radiation is coherently detected using the frequency up-conversion in MgO: LiNbO(3) crystal. Fast frequency tuning and automatic achromatic THz-wave detection are achieved through a special optical design, including a variable-angle mirror and 1:1 telescope devices in the pump and THz-wave beams. We demonstrate a frequency-agile THz-wave parametric generation and THz-wave coherent detection system. This system can be used as a frequency-domain THz-wave spectrometer operated at room-temperature, and there are a high possible to develop into a real-time two-dimensional THz spectral imaging system.

  2. Progress Towards Chirped-Pulse Fourier Transform Thz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Douglass, Kevin O.; Plusquellic, David F.; Gerecht, Eyal

    2010-06-01

    New opportunities are provided by the development of higher power THz frequency multiplier sources, the development of a broadband Chirped-Pulse FTMW spectroscopy technique at microwave and mm Wave frequencies, and recently demonstrated heterodyne hot electron bolometer detection technology in the THz frequency region with near quantum noise-limited performance and high spectral resolution. Combining these three technologies and extending the chirped-pulse technique to 0.85 THz enables a host of new applications. NIST is currently pursing applications as a point sensor for greenhouse gases, volatile organic compounds, and potentially human breath. The generation and detection of phase stable chirped pulses at 850 GHz will be demonstrated. A description of the experimental setup and preliminary data will be presented for nitrous oxide. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S. Shipman and B.H. Pate, Rev.Sci.Instrum. 79 (2008) 053103. E. Gerecht, D. Gu, L. You, K.S. Yngvesson, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES. 56, (2008) 1083.

  3. THz Time-Domain Spectroscopy of Complex Interstellar Ice Analogs

    NASA Astrophysics Data System (ADS)

    Ioppolo, Sergio; McGuire, Brett A.; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey

    2014-06-01

    It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 - 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, and CH4) compared to more complex molecules (e.g., HCOOH, CH3COOH, CH3CHO, (CH3)2CO, HCOOCH3, and HCOOC2H5). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.

  4. Comparison of objects detection capabilities in LWIR and THz ranges

    NASA Astrophysics Data System (ADS)

    Kowalski, Marcin; Kastek, Mariusz; Szustakowski, Mieczyslaw

    2015-10-01

    Multispectral systems for detection of concealed dangerous objects are becoming more popular because of their higher effectiveness compared to mono-spectral systems. So far, the problem of detecting objects hidden under clothing was considered only in the case of airports but it is becoming more important for public places like metro stations, and government buildings. Exploration of new spectral bands as well as development of technology result in introduction of new solutions - both mono and multispectral. It has been proved that objects hidden under clothing can be detected and visualized using terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. Limited range is another issue of passive imagers. On the other hand new infrared cameras offer sufficient parameters to detect objects covered with fabrics in some conditions, as well as high image quality and big pixel resolutions. The purpose of the studies is to investigate and compare the possibilities of using passive cameras operating in long wavelength infrared (LWIR) and THz spectral ranges for detection of concealed objects. For the purpose of investigations, commercial imagers operating in 6.5-11.7 μm and 250GHz (1.25mm) were used. In the article, we present the measurement setup and the results of measurements in various operating conditions. Theoretical studies of both spectral bands focused on detection of objects with passive imagers are also presented.

  5. Quantum-dot micropillars for parametric THz emission

    NASA Astrophysics Data System (ADS)

    Mariani, S.; Andronico, A.; Favero, I.; Ducci, S.; Todorov, Y.; Sirtori, C.; Kamp, M.; Claudon, J.; Gérard, J. M.; Wang, T.; Jepsen, P. U.; Leo, G.

    2013-01-01

    We report on the design, fabrication and optical investigation of AlGaAs microcavities for THz Difference Frequency Generation (DFG) between Whispering Gallery Modes (WGMs), where the pump and DFG wavelengths (λ ≍ 1.3 μm and λ ≍ 75-150 μm, respectively) lie on opposite sides of the Restrahlen band. For the pump modes, we demonstrate CW lasing of quantum-dot layers under electrical injection at room temperature. We control the number of lasing WGMs via vertical notches on the pillars sidewalls, providing a selection mechanism for funneling the power only to the modes contributing to DFG. In parallel with the optimization of the pump lasers and in order to validate design and material parameters before the DFG experiments, we have performed linear measurements on two sets of passive samples. For the telecom range, the micropillars have been integrated with waveguides for distributed coupling and characterized via transmission measurements. In the THz range we have measured reflectivity spectra on 2D arrays of identical cylinders. In both cases, we demonstrate a good agreement between experimental results and simulations. On a more speculative note, we numerically show that etching a hole along the pillar axis can facilitate phase matching, while single-lobe farfield pattern can be obtained for the THz mode by micro-structuring the metallic ground plane around the microcavity. Finally, we suggest a real-time fine-tuning mechanism for the forthcoming active devices.

  6. Experimental Validation of Plasma Metasurfaces as Tunable THz Reflectors

    NASA Astrophysics Data System (ADS)

    Colon Quinones, Roberto; Underwood, Thomas; Cappelli, Mark

    2016-10-01

    Measurements are presented which validate the use of plasma metasurfaces (PMs) as potential tunable THz reflectors. The PM considered here is an n x n array of laser produced plasma kernels generated by focusing the fundamental output from a 2 J/p Q-switched Nd:YAG laser through a multi-lens array (MLA) and into a gas of varying pressure. An M Squared Firefly-THz laser is used to generate a collimated pulse of THz light, which is then directed to the PM at varying angles of incidence. The reflected energy is measured using a Gentec-EO SDX-1187 joulemeter probe to characterize the surface impedance or reflectivity. In this presentation, we will compare the measured reflectance to values obtained from theoretical predictions and 3D finite-difference time-domain (FDTD) simulations. Work supported by the Air Force Office of Scientific Research (AFOSR). R. Colon Quinones and T. Underwood acknowledge the support of the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

  7. Systems Analysis for Thermal Infrared ` THz Torch' Applications

    NASA Astrophysics Data System (ADS)

    Hu, Fangjing; Sun, Jingye; Brindley, Helen E.; Liang, Xiaoxin; Lucyszyn, Stepan

    2015-05-01

    The ` THz Torch' concept was recently introduced by the authors for providing secure wireless communications over short distances within the thermal infrared (10-100 THz). Unlike conventional systems, thermal infrared can exploit front-end thermodynamics with engineered blackbody radiation. For the first time, a detailed power link budget analysis is given for this new form of wireless link. The mathematical modeling of a short end-to-end link is provided, which integrates thermodynamics into conventional signal and noise power analysis. As expected from the Friis formula for noise, it is found that the noise contribution from the pyroelectric detector dominates intrinsic noise. From output signal and noise voltage measurements, experimental values for signal-to-noise ratio (SNR) are obtained and compared with calculated predictions. As with conventional communications systems, it is shown for the first time that the measured SNR and measured bit error rate found with this thermodynamics-based system resembles classical empirical models. Our system analysis can serve as an invaluable tool for the development of thermal infrared systems, accurately characterizing each individual channel and, thus, enables the performance of multi-channel ` THz Torch' systems to be optimized.

  8. Mechanical detection of electron spin resonance beyond 1 THz

    SciTech Connect

    Takahashi, Hideyuki; Ohmichi, Eiji; Ohta, Hitoshi

    2015-11-02

    We report the cantilever detection of electron spin resonance (ESR) in the terahertz (THz) region. This technique mechanically detects ESR as a change in magnetic torque that acts on the cantilever. The ESR absorption of a tiny single crystal of Co Tutton salt, Co(NH{sub 4}){sub 2}(SO{sub 4}){sub 2}⋅6H{sub 2}O, was observed in frequencies of up to 1.1 THz using a backward travelling wave oscillator as a THz-wave source. This is the highest frequency of mechanical detection of ESR till date. The spectral resolution was evaluated with the ratio of the peak separation to the sum of the half-width at half maximum of two absorption peaks. The highest resolution value of 8.59 ± 0.53 was achieved at 685 GHz, while 2.47 ± 0.01 at 80 GHz. This technique will not only broaden the scope of ESR spectroscopy application but also lead to high-spectral-resolution ESR imaging.

  9. High sensitive THz superconducting hot electron bolometer mixers and transition edge sensors

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Miao, W.; Zhou, K. M.; Guo, X. H.; Zhong, J. Q.; Shi, S. C.

    2016-11-01

    Terahertz band, which is roughly defined as 0.1 THz to 10 THz, is an interesting frequency region of the electromagnetic spectrum to be fully explored in astronomy. THz observations play key roles in astrophysics and cosmology. High sensitive heterodyne and direct detectors are the main tools for the detection of molecular spectral lines and fine atomic structure spectral lines, which are very important tracers for probing the physical and chemical properties and dynamic processes of objects such as star and planetary systems. China is planning to build an THz telescope at Dome A, Antarctica, a unique site for ground-based THz observations. We are developing THz superconducting hot electron bolometer (HEB) mixers and transition edge sensors (TES), which are quantum limited and back-ground limited detectors, respectively. Here we first introduce the working principles of superconducting HEB and TES, and then mainly present the results achieved at Purple mountain Observatory.

  10. A tunable continuous wave (CW) and short-pulse optical source for THz brain imaging applications

    NASA Astrophysics Data System (ADS)

    Bakopoulos, P.; Karanasiou, I.; Pleros, N.; Zakynthinos, P.; Uzunoglu, N.; Avramopoulos, H.

    2009-10-01

    We demonstrate recent advances toward the development of a novel 2D THz imaging system for brain imaging applications both at the macroscopic and at the bimolecular level. A frequency-synthesized THz source based on difference frequency generation between optical wavelengths is presented, utilizing supercontinuum generation in a highly nonlinear optical fiber with subsequent spectral carving by means of a fiber Fabry-Perot filter. Experimental results confirm the successful generation of THz radiation in the range of 0.2-2 THz, verifying the enhanced frequency tunability properties of the proposed system. Finally, the roadmap toward capturing functional brain information by exploiting THz imaging technologies is discussed, outlining the unique advantages offered by THz frequencies and their complementarity with existing brain imaging techniques.

  11. THz wave parametric oscillator with a surface-emitted ring-cavity configuration

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    A surface-emitted ring-cavity terahertz (THz) wave parametric oscillator has been demonstrated for high-energy THz output and fast frequency tuning. Through the special optical design with a Galvano optical scanner and four-mirror ring-cavity structure, a maximum THz output of 12.9 μJ/pulse is achieved at 1.359 THz under the pump pulse energy of 172.8 mJ with the repetition rate of 10 Hz. A further research on the performance of the SE ring-cavity TPO has done to explore more characteristics of THz output. The THz pulse instability and the influence of cavity loss has analyzed. Moreover, the pump depletion rate of the ring-cavity configuration is much lower than the conventional surface-emitted terahertz wave parametric oscillator at the same experimental conditions.

  12. 1.6 THz heterodyne receiver for the far infrared space telescope

    NASA Astrophysics Data System (ADS)

    Cherednichenko, S.; Kroug, M.; Merkel, H.; Khosropanah, P.; Adam, A.; Kollberg, E.; Loudkov, D.; Gol'Tsman, G.; Voronov, B.; Richter, H.; Huebers, H.-W.

    2002-08-01

    A low noise heterodyne receiver is being developed for the terahertz range using a phonon-cooled hot-electron bolometric mixer based on 3.5 nm thick superconducting NbN film. In the 1-2 GHz intermediate frequency band the double-sideband receiver noise temperature was 450 K at 0.6 THz, 700 K at 1.6 THz and 1100 K at 2.5 THz. In the 3-8 GHz IF band the lowest receiver noise temperature was 700 K at 0.6 THz, 1500 K at 1.6 THz and 3000 K at 2.5 THz while it increased by a factor of 3 towards 8 GHz.

  13. Strongly Enhanced THz Emission caused by Localized Surface Charges in Semiconducting Germanium Nanowires

    PubMed Central

    Lee, Woo-Jung; Ma, Jin Won; Bae, Jung Min; Jeong, Kwang-Sik; Cho, Mann-Ho; Kang, Chul; Wi, Jung-Sub

    2013-01-01

    A principal cause of THz emission in semiconductor nanostructures is deeply involved with geometry, which stimulates the utilization of indirect bandgap semiconductors for THz applications. To date, applications for optoelectronic devices, such as emitters and detectors, using THz radiation have focused only on direct bandgap materials. This paper reports the first observation of strongly enhanced THz emission from Germanium nanowires (Ge NWs). The origin of THz generation from Ge NWs can be interpreted using two terms: high photoexcited electron-hole carriers (Δn) and strong built-in electric field (Eb) at the wire surface based on the relation . The first is related to the extensive surface area needed to trigger an irradiated photon due to high aspect ratio. The second corresponds to the variation of Fermi-level determined by confined surface charges. Moreover, the carrier dynamics of optically excited electrons and holes give rise to phonon emission according to the THz region. PMID:23760467

  14. Characterization of dielectric properties of nanocellulose from wood and algae for electrical insulator applications.

    PubMed

    Le Bras, David; Strømme, Maria; Mihranyan, Albert

    2015-05-07

    Cellulose is one of the oldest electrically insulating materials used in oil-filled high-power transformers and cables. However, reports on the dielectric properties of nanocellulose for electrical insulator applications are scarce. The aim of this study was to characterize the dielectric properties of two nanocellulose types from wood, viz., nanofibrillated cellulose (NFC), and algae, viz., Cladophora cellulose, for electrical insulator applications. The cellulose materials were characterized with X-ray diffraction, nitrogen gas and moisture sorption isotherms, helium pycnometry, mechanical testing, and dielectric spectroscopy at various relative humidities. The algae nanocellulose sample was more crystalline and had a lower moisture sorption capacity at low and moderate relative humidities, compared to NFC. On the other hand, it was much more porous, which resulted in lower strength and higher dielectric loss than for NFC. It is concluded that the solid-state properties of nanocellulose may have a substantial impact on the dielectric properties of electrical insulator applications.

  15. High birefringence, low loss terahertz photonic crystal fibres with zero dispersion at 0.3 THz

    NASA Astrophysics Data System (ADS)

    Yin, Guo-Bing; Li, Shu-Guang; Wang, Xiao-Yan; Liu, Shuo

    2011-09-01

    A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.

  16. DOE-NSF-NIH Workshop on Opportunities in THz Science, February 12-14, 2004

    SciTech Connect

    Sherwin, M.A.; Bucksbaum, P.H.; Schmuttenmaer, C. A.; Allen, J.; Biedron, S.; Carr, L.; Chamberlain, M.; Crowe, T.; DeLucia, F.; Hu, Q.; Jones, B.; Noordham, B.; Norris, T.; Orenstein, J.; Unterrainer, K.; Van der Meer, L.; Wilke, I.; Williams, G.; Zhang, X.-C.; Cheville, A.; Markelz, A.; Parks, B.; Plancken, P.; Shan, J.; Austin, B.; Basov, D.; Citrin, D.; Grundfest, W.; Heinz, T.; Kono, J.; Mittleman, D.; Siegel, P.; Taylor, T.; Jones, B.; Markelz, A.; Martin, M.; Nelson, K.; Smith, T.; Williams, G.; Allen, M.; Averitt, R.; Brunel, L.; Heilweil, T.; Heyman, J.; Jepsen, P.; Kaind, R.; Leemans, W.; Mihaly, L.; Rangan, C.; Tom, H.; Wallace, V.; Zimdars, D.

    2004-02-14

    This is the report of the Workshop on Opportunities in THz Science, held on February 12-14, 2004 in Arlington, VA. This workshop brought together researchers who use or produce THz radiation for physics, chemistry, biology, medicine, and materials science to discuss new research opportunities and common resource needs. The charge from the sponsors of the workshop was to focus on basic science questions within these disciplines that have and can be answered using THz radiation.

  17. THz spectroscopic studies of materials using the FTIR technique: experiment and simulation

    NASA Astrophysics Data System (ADS)

    Lepodise, Lucia Malebogo

    2014-04-01

    Terahertz (THz) radiation has remained the least developed part of the electromagnetic spectrum for quite a long time and thus it was traditionally known as the 'terahertz gap'. The progress of research in this field has been hindered by lack of powerful sources and detectors as compared to both the sources and detectors for the electronic and optical sides of the terahertz radiation region. However, the research on the THz field has intensified in recent years due to a number of emerging interesting technologies and owing to its unique properties. It has several advantages over its counterparts like X-ray and hence it has attracted much interest in a variety of applications scientifically and commercially. THz work has been recently focused in the low frequency region (0.1-3 THz). This is the region where most of the THz spectral features of many materials lie. Studies in this frequency range have been seen revolutionizing the THz field giving it a pool of potential applications which are still yet to be realized. The low frequency THz region (0.1-3 THz) is accessible through the use of the THz-TDS technique and this technique is the mostly used to date. The value of this method is evident throughout the work published in terahertz research and thus its use prevails over other techniques. Many materials show some spectral features in the much higher frequency region (up to 21 THz), but however this frequency range has not attracted much attention in comparison to the low frequency range which of course is more rich in THz spectral features. Furthermore, although the low frequency THz region has been quite extensively studied, the concentration has been at room temperature with a few temperature-dependence studies mostly done at particular temperatures rather than over a wide range.

  18. Complete presentation of the Gouy phase shift with the THz digital holography.

    PubMed

    Wang, Xinke; Sun, Wenfeng; Cui, Ye; Ye, Jiasheng; Feng, Shengfei; Zhang, Yan

    2013-01-28

    Three dimensional information of the Gouy phase shift in a converging spherical terahertz (THz) beam is directly observed by using a THz balanced electro-optic holographic imaging system. The major properties of the Gouy phase shift are presented, including the longitudinal and transverse distributions, relationships with the frequency and the f-number, influence on the THz polarization. The imaging technique supplies an accurate and comprehensive measurement method for observing and understanding the Gouy phase shift.

  19. Towards high-power single-cycle THz laser for initiating high-field-sensitive phenomena.

    PubMed

    Ruchert, Clemens; Ardana, Fernando; Trisorio, Alexandre; Vicario, Carlo; Hauri, Christoph P

    2011-01-01

    Powerful THz radiation confined in one field period or less is an adequate tool for triggering nonlinear actions. We show results towards the realization of a tunable high-power THz source based on a laser-driven frequency conversion scheme in plasma and nonlinear crystals. A powerful THz source in combination with the future X-ray Free Electron Laser facility in Switzerland (SwissFEL) holds promise for exciting experiments in a variety of different research areas.

  20. Longitudinal phase space manipulation of an ultrashort electron beam via THz IFEL interaction

    NASA Astrophysics Data System (ADS)

    Moody, J. T.; Li, R. K.; Musumeci, P.; Scoby, C. M.; To, H.

    2012-12-01

    A scheme where a laser locked THz source is used to manipulate the longitudinal phase space of an ultrashort electron beam using an IFEL interaction is investigated. The efficiency of THz source based on the pulse front tilt optical rectification scheme is increased by cryogenic cooling to achieve sufficient THz power for compression and synchronization. Start-to-end simulations describing the evolution of the beam from the cathode to the compression point after the undulator are presented.

  1. Development of a Compact sub-THz Gyrotron FU CW CI for Application to High Power THz Technologies

    NASA Astrophysics Data System (ADS)

    Idehara, Toshitaka; Mudiganti, Jagadish C.; Agusu, La; Kanemaki, Tomohiro; Ogawa, Isamu; Fujiwara, Toshimichi; Matsuki, Yoh; Ueda, Keisuke

    2012-07-01

    For application of high frequency gyrotron to high power THz technology, Gyrotron FU CW series is being developed in FIR FU. Gyrotron FU CW CI is developed as one of sub-THz gyrotrons included in the series. The advantage of the gyrotron is compactness using a compact superconducting magnet and compact power supply system, which makes the accesses of the gyrotron to applied large-scale devices easier and extends the applications of gyrotron to wider fields. The designed frequency and cavity mode are 394.5 GHz and TE26 mode for application to the 600 MHz DNP-NMR spectroscopy. As the operation results, the frequency and the output power were 394.03 GHz and around 30 W, respectively, which are available for the application to the 600 MHz DNP-NMR measurement. In addition, this gyrotron can operate at many other frequencies and cavity modes for application to high power THz technologies in wide fields. In this paper, the design and the operation results including long pulse or CW mode are presented.

  2. PREFACE: Dielectrics 2011

    NASA Astrophysics Data System (ADS)

    Vaughan, Alun; Lewin, Paul

    2011-08-01

    In 2011, the biennial meeting of the Dielectrics Group of the IOP, Dielectrics 2011, was held for the first time in a number of years at the University of Kent at Canterbury. This conference represents the most recent in a long standing series that can trace its roots back to a two-day meeting that was held in the spring of 1968 at Gregynog Hall of the University of Wales. In the intervening 43 years, this series of meetings has addressed many topics, including dielectric relaxation, high field phenomena, biomaterials and even molecular electronics, and has been held at many different venues within the UK. However, in the early 1990s, a regular venue was established at the University of Kent at Canterbury and, it this respect, this year's conference can be considered as "Dielectrics coming home". The format for the 2011 meeting followed that established at Dielectrics 2009, in breaking away from the concept of a strongly themed event that held sway during the mid 2000s. Rather, we again adopted a general, inclusive approach that was based upon four broad technical areas: Theme 1: Insulation/HV Materials Theme 2: Dielectric Spectroscopy Theme 3: Modelling Dielectric Response Theme 4: Functional Materials The result was a highly successful conference that attracted more than 60 delegates from eight countries, giving the event a truly international flavour, and which included both regular and new attendees; it was particularly pleasing to see the number of early career researchers at the meeting. Consequently, the organizing committee would like to thank our colleagues at the IOP, the invited speakers, our sponsors and all the delegates for making the event such a success. Finally, we look forward to convening again in 2013, when we will be returning to The University of Reading. Prof Alun Vaughan and Prof Paul Lewin, Editors

  3. Pore-size dependent THz absorption of nano-confined water.

    PubMed

    Sun, Chi-Kuang; You, Borwen; Huang, Yu-Ru; Liu, Kao-Hsiang; Sato, Shusaku; Irisawa, Akiyoshi; Imamura, Motoki; Mou, Chung-Yuan

    2015-06-15

    We performed a THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21, of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk-water-like THz absorption behavior in the core water region and a solid-like THz absorption behavior in the interfacial water region.

  4. THz generation from elliptically-focused two-color laser pulses at 1 kHz

    NASA Astrophysics Data System (ADS)

    Yoo, Yungjun; Kuk, Donghoon; Zhong, Zheqiang; Kim, Ki-Yong

    2017-01-01

    We have generated high-power terahertz (THz) radiation by elliptical focusing of two-color femtosecond laser pulses in air at a 1-kHz repetition rate. Elliptical focusing produces a 2-dimensional plasma sheet, emitting two diverging THz radiation lobes in the far field. Such radiation is collimated and refocused by a combination of cylindrical and off-axis parabolic mirrors. Here the distances between the 2-D plasma sheet, cylindrical mirror, and off-axis parabolic mirror are carefully adjusted to minimize the THz spot size at the refocus. The refocused THz field strength is estimated by measuring the THz energy, beam spot size, and waveform. Here an uncooled microbolometer camera with real-time lock-in imaging is used to monitor and measure the focused THz beam profiles with a high signal-to-noise ratio at a broad range of THz (1 40 THz) frequencies. High-pressure gas (N2 and Ar) jets puffed in air are also tested as laser targets to boost the output THz energy even further. This material is based upon work supported by the Air Force Office of Scientific Research under Award Number FA9550-16-1-0163.

  5. Tunable, Room Temperature CMOS-Compatible THz Emitters Based on Nonlinear Mixing in Microdisk Resonators

    NASA Astrophysics Data System (ADS)

    Sinha, Raju; Karabiyik, Mustafa; Ahmadivand, Arash; Al-Amin, Chowdhury; Vabbina, Phani Kiran; Shur, Michael; Pala, Nezih

    2016-03-01

    We propose and investigate in detail a novel tunable, compact, room temperature terahertz (THz) emitter using individual microdisk resonators for both optical and THz waves with the capability of radiating THz field in 0.5-10 THz range with tuning frequency resolution of 0.05 THz. Enhanced THz generation is achieved by employing a nonlinear optical disk resonator with a high value of second-order nonlinearity ( χ (2)) in order to facilitate the difference-frequency generation (DFG) via nonlinear mixing with the choice of two appropriate input infrared optical waves. Efficient coupling of infrared waves from bus to the nonlinear disk is ensured by satisfying critical coupling condition. Phase matching condition for efficient DFG process is also met by employing modal phase matching technique. Our simulations show that THz output power can be reached up to milliwatt (mW) level with high optical to THz conversion efficiency. The proposed source is Silicon on Insulator (SoI) technology compatible enabling the monolithic integration with Si complementary metal-oxide-semiconductor (CMOS) electronics including plasmonic THz detectors.

  6. Experimental 0.22 THz Stepped Frequency Radar System for ISAR Imaging

    NASA Astrophysics Data System (ADS)

    Liang, Mei Yan; Zhang, Cun Lin; Zhao, Ran; Zhao, Yue Jin

    2014-09-01

    High resolution inverse synthetic aperture radar (ISAR) imaging is demonstrated by using a 0.22 THz stepped-frequency (SF) imaging radar system. The synthesis bandwidth of the terahertz (THz) SF radar is 12 GHz, which are beneficial for high resolution imaging. The resolution of ISAR image can reach centimeter-scale with the use of Range-Doppler algorithm (RDA). Results indicate that high resolution ISAR imaging is realized by using 0.22THz SF radar coupled with turntable scanning, which can provide foundations for further research on high-resolution radar image in the THz band.

  7. Enhancement of intensity in a periodically layered metal-dielectric waveguide with magnetized plasma

    NASA Astrophysics Data System (ADS)

    Hasanbeigi, A.; Ashrafi, A.; Mehdian, H.

    2017-07-01

    Recently, a periodically layered metal-dielectric structure was introduced as a new type of tunable radiation source by Adamo et al. [Phys. Rev. Lett. 103, 113901 (2009); J. Opt. 12, 024012 (2010)]. It is anticipated that the proposed structure forms an important part of future THz systems. In this paper, the effect of plasma, as an extra controlling parameter, on this radiation source has been investigated. The results of the numerical calculations show that the presence of plasma can lead to a significant increase in the output power, and therefore, the device can be tuned over a wide frequency range by changing the plasma density.

  8. Plasmas, Dielectrics and the Ultrafast: First Science and Operational Experience at FACET

    SciTech Connect

    Clarke, C.I.; Adli, E.; Corde, S.; Decker, F.J.; England, R.J.; Erickson, R.; Fisher, A.; Gessner, S.; Hast, C.; Hogan, M.J.; Li, S.Z.; Lipkowitz, N.; Litos, M.; Nosochkov, Y.; Seeman, J.; Sheppard, J.C.; Tudosa, I.; White, G.; Wienands, U.; Woodley, M.; Wu, Z.; /SLAC /UCLA

    2012-09-14

    FACET (Facility for Advanced Accelerator and Experimental Tests) is an accelerator R&D test facility that has been recently constructed at SLAC National Accelerator Laboratory. The facility provides 20 GeV, 3 nC electron beams, short (20 {micro}m) bunches and small (20 {micro}m wide) spot sizes, producing uniquely high power beams. FACET supports studies from many fields but in particular those of Plasma Wakefield Acceleration and Dielectric Wakefield Acceleration. FACET is also a source of THz radiation for material studies. We present the FACET design, initial operating experience and first science from the facility.

  9. Experimental study on the dielectric properties of polyacrylate dielectric elastomer

    NASA Astrophysics Data System (ADS)

    Qiang, Junhua; Chen, Hualing; Li, Bo

    2012-02-01

    The dielectric constant of elastomeric dielectric material is an essential physical parameter, whose value may affect the electromechanical deformation of a dielectric elastomer actuator. Since the dielectric constant is influenced by several external factors as reported before, and no certain value has been confirmed to our knowledge, in the present paper, on the basis of systematical comparison of recent past literature, we conducted extensive works on the measurement of dielectric properties of VHB films, involving five influencing factors: prestretch (both equal and unequal biaxial), electrical frequency, electrode material, stress relaxation time and temperature. Experimental results directly show that the dielectric response changes according to these factors, based on which we investigate the significance of each factor, especially the interaction of two external conditions on the dielectric constant of deformable dielectric, by presenting a physical picture of the mechanism of polarization.

  10. Ellipsometric characterization of nanocrystals in porous silicon

    NASA Astrophysics Data System (ADS)

    Petrik, P.; Fried, M.; Vázsonyi, É.; Lohner, T.; Horváth, E.; Polgár, O.; Basa, P.; Bársony, I.; Gyulai, J.

    2006-10-01

    Porous silicon layers (PSLs) were prepared by electrochemical etching of p-type single-crystalline silicon (c-Si) wafers having different dopant concentrations to obtain systematically changing sizes of nanocrystals (walls). The microstructure of the porous material was characterized using spectroscopic ellipsometry with multi-layer effective medium approximation (EMA) models. The dielectric function of PSL is conventionally calculated using EMA mixtures of c-Si and voids. The porosity is described by the concentration of voids. Some PSL structures can be described only by adding fine-grained polycrystalline silicon (nc-Si) reference material to the EMA model. Modified model dielectric functions (MDF) of c-Si have been shown to fit composite materials containing nanocrystalline regions, either by fitting only the broadening parameter or also other parameters of the parametric oscillator in MDF. The broadening parameter correlates with the long-range order in the crystalline material, and, as a consequence, with the size of nanocrystals. EMA and MDF models were used to describe systematically changing nanostructure of PSLs. Volume fraction of nc-Si in EMA and broadening parameter in MDF provide information on the nanocrystal size. The longer-term goal of this work is to provide a method for the quantitative characterization of nanocrystal size using quick, sensitive and non-destructive optical techniques.

  11. Porous organic molecules

    NASA Astrophysics Data System (ADS)

    Holst, James R.; Trewin, Abbie; Cooper, Andrew I.

    2010-11-01

    Most synthetic materials that show molecular-scale porosity consist of one-, two- or three-dimensional networks. Porous metal-organic frameworks in particular have attracted a lot of recent attention. By contrast, discrete molecules tend to pack efficiently in the solid state, leaving as little empty space as possible, which leads to non-porous materials. This Perspective discusses recent developments with discrete organic molecules that are porous in the solid state. Such molecules, which may be either crystalline or amorphous, can be categorized as either intrinsically porous (containing permanent covalent cavities) or extrinsically porous (inefficiently packed). We focus on the possible advantages of organic molecules over inorganic or hybrid systems in terms of molecular solubility, choice of components and functionalities, and structural mobility and responsiveness in non-covalent extended solids. We also highlight the potential for 'undiscovered' porous systems among the large number of cage-like organic molecules that are already known.

  12. Influence of porosity on electrical properties of low-k dielectrics irradiated with vacuum-ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Choudhury, F. A.; Nguyen, H. M.; Baklanov, M. R.; de Marneffe, J. F.; Li, W.; Pei, D.; Benjamin, D. I.; Zheng, H.; King, S. W.; Lin, Y.-H.; Fung, H.-S.; Chen, C.-C.; Nishi, Y.; Shohet, J. L.

    2016-09-01

    During plasma processing, low-k dielectrics are exposed to high levels of vacuum ultraviolet (VUV) radiation emitted from the plasma. The porous structure of these materials makes them more sensitive to modification because of their low density and consequently deep penetration of active species into the film. Here, we investigate the changes to electrical properties of porous low-k dielectrics as a function of porosity after VUV irradiation. Organosilicate low-k films of porosities between 30% and 50% were exposed to synchrotron VUV radiation at 8 eV with a fluence of approximately 5 × 1014 photons/cm2. Capacitance-voltage measurements showed an increase in the dielectric constant along with a flat-band voltage shift. FTIR results show methyl depletion as well as water uptake after VUV treatment. These show that deterioration of the electrical properties after VUV exposure and the degree of damage are found to be higher for the more porous films.

  13. Plasma damage effects on low-k porous organosilicate glass

    NASA Astrophysics Data System (ADS)

    Ren, H.; Antonelli, G. A.; Nishi, Y.; Shohet, J. L.

    2010-11-01

    Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si-(CH3)x bonds. It was found that both charged-particle bombardment and radiation from the ECR plasma damage these bonds. Ellipsometric measurements showed that both the dielectric thickness and the dielectric constant changed during plasma exposure. In addition, both plasma-induced swelling and UV-exposure shrinking effects were observed. The plasma-induced swelling occurs at the surface of the dielectric without changing the porosity of the dielectric, while UV-induced shrinking changes the porosity significantly.

  14. Plasma damage effects on low-k porous organosilicate glass

    SciTech Connect

    Ren, H.; Shohet, J. L.; Antonelli, G. A.; Nishi, Y.

    2010-11-15

    Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si-(CH{sub 3}){sub x} bonds. It was found that both charged-particle bombardment and radiation from the ECR plasma damage these bonds. Ellipsometric measurements showed that both the dielectric thickness and the dielectric constant changed during plasma exposure. In addition, both plasma-induced swelling and UV-exposure shrinking effects were observed. The plasma-induced swelling occurs at the surface of the dielectric without changing the porosity of the dielectric, while UV-induced shrinking changes the porosity significantly.

  15. Dielectric relaxation and polar phonon softening in relaxor ferroelectric PbMg1/3Ta2/3O3

    NASA Astrophysics Data System (ADS)

    Kamba, S.; Nuzhnyy, D.; Veljko, S.; Bovtun, V.; Petzelt, J.; Wang, Y. L.; Setter, N.; Levoska, J.; Tyunina, M.; Macutkevic, J.; Banys, J.

    2007-10-01

    Relaxor ferroelectric PbMg1/3Ta2/3O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz), and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz-90 THz at temperatures 100-490 K; the THz and IR spectra were studied from 20 to 900 K. A diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below the Burns temperature Td in the THz range; it slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel-Fulcher laws, respectively. The degree of the B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm≅180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range, and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry, which can be assigned to the presence of the polar clusters below Td. Infrared spectra above Td still reveal more modes than predicted by selection rules in the paraelectric phase of the Fm3¯m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β″-perovskite sublattice.

  16. Dielectric Constant of Suspensions

    NASA Astrophysics Data System (ADS)

    Mendelson, Kenneth S.; Ackmann, James J.

    1997-03-01

    We have used a finite element method to calculate the dielectric constant of a cubic array of spheres. Extensive calculations support preliminary conclusions reported previously (K. Mendelson and J. Ackmann, Bull. Am. Phys. Soc. 41), 657 (1996).. At frequencies below 100 kHz the real part of the dielectric constant (ɛ') shows oscillations as a function of the volume fraction of suspension. These oscillations disappear at low conductivities of the suspending fluid. Measurements of the dielectric constant (J. Ackmann, et al., Ann. Biomed. Eng. 24), 58 (1996). (H. Fricke and H. Curtis, J. Phys. Chem. 41), 729 (1937). are not sufficiently sensitive to show oscillations but appear to be consistent with the theoretical results.

  17. PREFACE: Dielectrics 2013

    NASA Astrophysics Data System (ADS)

    Hadjiloucas, Sillas; Blackburn, John

    2013-11-01

    This volume records the 42nd Dielectrics Group Proceedings of the Dielectrics Conference that took place at the University of Reading UK from 10-12 April 2013. The meeting is part of the biennial Dielectrics series of the Dielectrics Group, and formerly Dielectrics Society, and is organised by the Institute of Physics. The conference proceedings showcase some of the diversity and activity of the Dielectrics community worldwide, and bring together contributions from academics and industrial researchers with a diverse background and experiences from the Physics, Chemistry and Engineering communities. It is interesting to note some continuing themes such as Insulation/HV Materials, Dielectric Spectroscopy, Dielectric Measurement Techniques and Ferroelectric materials have a growing importance across a range of technologically important areas from the Energy sector to Materials research, Semiconductor and Electronics industries, and Metrology. We would like to thank all of our colleagues and friends in the Dielectrics community who have supported this event by contributing manuscripts and participating in the event. The conference has provided excellent networking opportunities for all delegates. Our thanks go also to our theme chairs: Dr Stephen Dodd (University of Leicester) on Insulation/HV Materials, Professor Darryl Almond (University of Bath) on Dielectric Spectroscopy, Dr John Blackburn (NPL) on Dielectric Measurement Techniques and Professor Anthony R West (University of Sheffield) on Ferroelectric Materials. We would also like to thank the other members of the Technical Programme Committee for their support, and refereeing the submitted manuscripts. Our community would also like to wish a full recovery to our plenary speaker Prof John Fothergill (City University London) who was unexpectedly unable to give his talk as well as thank Professor Alun Vaughan for stepping in and giving an excellent plenary lecture in his place at such very short notice. We are also

  18. Dielectric assist accelerating structure

    NASA Astrophysics Data System (ADS)

    Satoh, D.; Yoshida, M.; Hayashizaki, N.

    2016-01-01

    A higher-order TM02 n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 M Ω /m at room temperature.

  19. Superdirective dielectric nanoantennas

    NASA Astrophysics Data System (ADS)

    Krasnok, Alexander E.; Simovski, Constantin R.; Belov, Pavel A.; Kivshar, Yuri S.

    2014-06-01

    We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%.

  20. Controlling birefringence in dielectrics

    NASA Astrophysics Data System (ADS)

    Danner, Aaron J.; Tyc, Tomáš; Leonhardt, Ulf

    2011-06-01

    Birefringence, from the very essence of the word itself, refers to the splitting of light rays into two parts. In natural birefringent materials, this splitting is a beautiful phenomenon, resulting in the perception of a double image. In optical metamaterials, birefringence is often an unwanted side effect of forcing a device designed through transformation optics to operate in dielectrics. One polarization is usually implemented in dielectrics, and the other is sacrificed. Here we show, with techniques beyond transformation optics, that this need not be the case, that both polarizations can be controlled to perform useful tasks in dielectrics, and that rays, at all incident angles, can even follow different trajectories through a device and emerge together as if the birefringence did not exist at all. A number of examples are shown, including a combination Maxwell fisheye/Luneburg lens that performs a useful task and is achievable with current fabrication materials.