Sample records for terahertz wave source

  1. Terahertz sources

    National Research Council Canada - National Science Library

    Shumyatsky, Pavel; Alfano, Robert R


    We present an overview and history of terahertz (THz) sources for readers of the biomedical and optical community for applications in physics, biology, chemistry, medicine, imaging, and spectroscopy...

  2. Energy scaling of terahertz-wave parametric sources. (United States)

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


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

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

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


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

  4. Regulatory effects of terahertz waves


    Vyacheslav F. Kirichuk; Alexey N. Ivanov


    There are modern data about biological effects of terahertz (THz) waves in this article. Items of interaction of THz waves with bio objects of different organization level. A complex of the data indicates that the realization of a THz wave effect in biosystems is possible at molecular, cellular, tissular, organ and system levels of regulation. There are data about changes in nervous and humoral regulation of an organism and metabolic effects of THz waves.

  5. Continuous-wave terahertz light from optical parametric oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Sowade, Rosita


    Continuous-wave (cw) optical parametric oscillators (OPOs) are working horses for spectroscopy in the near and mid infrared. However, in the terahertz frequency range (0.1 to 10 THz), the pump threshold is more than 100 W due to the high absorption in nonlinear crystals and thus exceeds the power of standard cw single-frequency pump sources. In this thesis the first cw OPO capable of generating terahertz radiation is demonstrated. To overcome the high threshold, the signal wave of a primary infrared process is resonantly enhanced to serve as the pump wave for a cascaded parametric process with one wave being at the terahertz frequency level. A terahertz output power of more than two microwatts is measured and tuning is achieved from 1.3 to 1.7 THz. This terahertz source emits a narrow-band, diffraction-limited beam which remains mode-hop free over more than one hour. Such a device inhibits high potential for applications in areas like astronomy, telecommunications or high-resolution spectroscopy. (orig.)

  6. Compact Tunable Narrowband Terahertz-Wave Source Based on Difference Frequency Generation Pumped by Dual Fiber Lasers in MgO:LiNbO3 (United States)

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


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

  7. Reconfigurable metamaterials for terahertz wave manipulation (United States)

    Hashemi, Mohammed R.; Cakmakyapan, Semih; Jarrahi, Mona


    Reconfigurable metamaterials have emerged as promising platforms for manipulating the spectral and spatial properties of terahertz waves without being limited by the characteristics of naturally existing materials. Here, we present a comprehensive overview of various types of reconfigurable metamaterials that are utilized to manipulate the intensity, phase, polarization, and propagation direction of terahertz waves. We discuss various reconfiguration mechanisms based on optical, electrical, thermal, and mechanical stimuli while using semiconductors, superconductors, phase-change materials, graphene, and electromechanical structures. The advantages and disadvantages of different reconfigurable metamaterial designs in terms of modulation efficiency, modulation bandwidth, modulation speed, and system complexity are discussed in detail.

  8. Experimental imaging research on continuous-wave terahertz in-line digital holography (United States)

    Huang, Haochong; Wang, Dayong; Rong, Lu; Wang, Yunxin


    The terahertz (THz) imaging is an advanced technique on the basis of the unique characteristics of terahertz radiation. Due to its noncontact, non-invasive and high-resolution capabilities, it has already shown great application prospects in biomedical observation, sample measurement, and quality control. The continuous-wave terahertz in-line digital holography is a combination of terahertz technology and in-line digital holography of which the source is a continuous-wave terahertz laser. Over the past decade, many researchers used different terahertz sources and detectors to undertake experiments. In this paper, the pre-process of the hologram is accomplished after the holograms' recording process because of the negative pixels in the pyroelectric detector and the air vibration caused by the chopper inside the camera. To improve the quality of images, the phase retrieval algorithm is applied to eliminate the twin images. In the experiment, the pin which terahertz wave can't penetrate and the TPX slice carved letters "THz" are chosen for the samples. The amplitude and phase images of samples are obtained and the twin image and noise in the reconstructed images are suppressed. The results validate the feasibility of the terahertz in-line digital holographic imaging technique. This work also shows the terahertz in-line digital holography technique's prospects in materials science and biological samples' detection.

  9. Rotatable illusion media for manipulating terahertz electromagnetic waves

    National Research Council Canada - National Science Library

    Zang, XiaoFei; Li, Zhou; Shi, Cheng; Chen, Lin; Cai, Bin; Zhu, YiMing; Li, Li; Wang, XiaoBin


    Based on composite optical transformation, we propose a rotatable illusion media with positive permittivity and permeability to manipulate terahertz waves, and a new way to realize singular parameter...

  10. Photonic generation of continuous terahertz waves and its application to sensing and communications (United States)

    Song, Ho-Jin; Shimizu, Naofumi; Kado, Yuichi; Nagatsuma, Tadao


    We show that phohtonic technologies developed for conventional fiber-optic communications have potential for use in contemporary terahertz-wave applications, such as remote sensing and wireless communications. Advanced unitravelling photodiodes (UTC-PDs) can produce output power of 0.5 mW at 350 GHz and 10 μW at 1 THz. Using the UTC-PD and other optical devices, we demonstrate a time-continuous terahertz-wave signal generator that can tune the output signal over a wide frequency range with very narrow spectral linewidth and gas-sensing with the terahertz-wave source. We also show some preliminary results for terahertz-wave wireless communications using photonic technologies.

  11. Active graphene-silicon hybrid diode for terahertz waves. (United States)

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


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

  12. Active graphene–silicon hybrid diode for terahertz waves (United States)

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


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

  13. Continuous-wave terahertz imaging of nonmelanoma skin cancers (United States)

    Joseph, Cecil Sudhir

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

  14. Radar cross section measurements using terahertz waves

    DEFF Research Database (Denmark)

    Iwaszczuk, Krzysztof; Heiselberg, Henning; Jepsen, Peter Uhd


    Radar cross sections at terahertz frequencies are measured on scale models of aircrafts. A time domain broadband THz system generates freely propagating THz pulses measured with sub-picosecond time resolution. The THz radiation is generated using fs laser pulses by optical rectification in a lith......Radar cross sections at terahertz frequencies are measured on scale models of aircrafts. A time domain broadband THz system generates freely propagating THz pulses measured with sub-picosecond time resolution. The THz radiation is generated using fs laser pulses by optical rectification...... in a lithium niobate crystal with application of the tilted wave front method, resulting in high electric field THz pulses with a broad band spectrum from 100 GHz up to 4 THz. The corresponding wave lengths are two orders of magnitude smaller than normal radars and we therefore use scale models of size 5-10 cm...... in order to measure realistic radar cross sections. RCS polar and azimuthal angle plots of F-16 and F-35 are presented....

  15. Dynamic Stimulation of Superconductivity With Resonant Terahertz Ultrasonic Waves

    CERN Document Server

    Kadin, Alan M


    An experiment is proposed to stimulate a superconducting thin film with terahertz (THz) acoustic waves, which is a regime not previously tested. For a thin film on a piezoelectric substrate, this can be achieved by coupling the substrate to a tunable coherent THz electromagnetic source. Suggested materials for initial tests are a niobium film on a quartz substrate, with a BSCCO intrinsic Josephson junction (IJJ) stack. This will create acoustic standing waves on the nm scale in the thin film. A properly tuned standing wave will enable electron diffraction across the Fermi surface, leading to electron localization perpendicular to the substrate. This is expected to reduce the effective dimensionality, and enhance the tendency for superconducting order parallel to the substrate, even well above the superconducting critical temperature. This enhancement can be observed by measuring the in-plane critical current and the perpendicular tunneling gap. A similar experiment may be carried out for a cuprate thin film, ...

  16. Active graphene?silicon hybrid diode for terahertz waves


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


    Controlling the propagation properties of the terahertz waves in graphene holds great promise in enabling novel technologies for the convergence of electronics and photonics. A diode is a fundamental electronic device that allows the passage of current in just one direction based on the polarity of the applied voltage. With simultaneous optical and electrical excitations, we experimentally demonstrate an active diode for the terahertz waves consisting of a graphene?silicon hybrid film. The di...

  17. Direct Measurements of Terahertz Meta-atoms with Near-Field Emission of Terahertz Waves (United States)

    Serita, Kazunori; Darmo, Juraj; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi


    We present the direct measurements of terahertz meta-atoms, an elementary unit of metamaterials, by using locally generated terahertz waves in the near-field region. In contrast to a conventional far-field terahertz spectroscopy or imaging, our technique features the localized emission of coherent terahertz pulses on a sub-wavelength scale, which has a potential for visualizing details of dynamics of each meta-atom. The obtained data show the near-field coupling among the meta-atoms and the impact of the electric field distribution from the excited meta-atom to neighbor meta-atoms. The observable LC resonance response is enhanced with an increase of numbers of meta-atoms. Furthermore, our approach also has a potential for visualizing the individual mode of meta-atom at different terahertz irradiation spots. These data can help us to understand the important role of the meta-atom in metamaterials and develop the novel terahertz components and devices such as active terahertz metamaterial and compact, high-sensitive bio-sensor devices.

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

    Energy Technology Data Exchange (ETDEWEB)

    Baik, Chan-Wook, E-mail:; Ahn, Ho Young; Kim, Yongsung; Lee, Jooho; Hong, Seogwoo; Lee, Sang Hun; Choi, Jun Hee; Kim, Sunil; Kim, Jong Min; Hwang, Sungwoo [Samsung Advanced Institute of Technology, Suwon 443-803 (Korea, Republic of); Jeon, So-Yeon; Yu, SeGi [Department of Physics, Hankuk University of Foreign Studies, Yongin 449-791 (Korea, Republic of); Collins, George; Read, Michael E.; Lawrence Ives, R. [Calabazas Creek Research, Inc., San Mateo, California 94404-1010 (United States)


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

  19. Observation of terahertz radiation coherently generated by acoustic waves (United States)

    Armstrong, Michael R.; Reed, Evan J.; Kim, Ki-Yong; Glownia, James H.; Howard, William M.; Piner, Edwin L.; Roberts, John C.


    Over the past decade, pioneering and innovative experiments using subpicosecond lasers have demonstrated the generation and detection of acoustic and shock waves in materials with terahertz frequencies, the highest possible frequency acoustic waves. In addition to groundbreaking demonstrations of acoustic solitons, these experiments have led to new techniques for probing the structure of thin films. Terahertz-frequency electromagnetic radiation has been used in applications as diverse as molecular and material excitations, charge transfer, imaging and plasma dynamics. However, at present, existing approaches to detect and measure the time dependence of terahertz-frequency strain waves in materials use direct optical probes-time-resolved interferometry or reflectrometry. Piezoelectric-based strain gauges have been used in acoustic shock and strain wave experiments for decades, but the time resolution of such devices is limited to ~100ps and slower, the timescale of electronic recording technology. We have recently predicted that terahertz-frequency acoustic waves can be detected by observing terahertz radiation emitted when the acoustic wave propagates past an interface between materials of differing piezoelectric coefficients. Here, we report the first experimental observation of this fundamentally new phenomenon and demonstrate that it can be used to probe structural properties of thin films.

  20. Evaluation of human hairs with terahertz wave (United States)

    Serita, Kazunori; Murakami, Hironaru; Kawayama, Iwao; Takahashi, Yoshinori; Yoshimura, Masashi; Mori, Yusuke; Tonouchi, Masayoshi


    Single human hairs using a scanning laser terahertz (THz) imaging system are evaluated. The system features near-field THz emission and far-field THz detection. A sample is set in the vicinity of a two-dimensional THz emitter, and an excitation laser beam is scanned over the emitter via a galvanometer. By detecting the transmitted THz wave pulses that are locally generated at the irradiation spots of the excitation laser, we can obtain the THz transmission image and the spectrum of the sample with imaging time of 47 s for 512×512 pixels and maximum resolution of ˜27 μm. Using the system, we succeeded in observing the specific features of single human hairs in both the THz transmittance spectra and transmission images; it was found that the THz transmittance spectrum of gray hair shows a tendency of increase while that of black hair shows a decrease with increasing frequency above 1.2 THz. We could also observe the change of the moisture retention in the hair, and it is found that cuticles play one of the important roles in keeping moisture inside the hair. Those obtained data indicate that our system can be useful for evaluating single human hairs and those kinds of microscale samples.

  1. Continuous-wave terahertz reflective off-axis digital holography (United States)

    Wan, Min; Wang, Dayong; Rong, Lu; Wang, Yunxin; Huang, Haochong; Li, Bin


    Terahertz (THz) continuous-wave digital holography is an advanced interference imaging technique that can reconstruct quantitative distributions of amplitude and phase of the sample in real time with high resolution. In this paper, a reflective off-axis holographic system is presented. A Gaussian fitting method is applied to enhance the hologram contrast and Laplacian of Gaussian filter is used to obtain the reconstructed distance automatically. Furthermore, spectrum filtering method and angular spectrum algorithm are used to obtain the complex amplitude of the one-yuan chinese metal coin. The results confirm the prospective application of terahertz digital holography in the surface morphology for reflective samples.

  2. Active terahertz wave modulator based on molybdenum disulfide (United States)

    Liu, Xin; Zhang, Bo; Wang, Guocui; Wang, Wei; Ji, Hongyu; Shen, Jingling


    A high-efficiency active terahertz wave modulator based on a molybdenum disulfide (MoS2)/germanium (Ge) structure was investigated. Spectrally broadband modulation of the THz transmission was obtained using optical control over the frequency range from 0.2 to 2.6 THz. The MoS2 monolayer structure on germanium demonstrated enhancement of the terahertz modulation depth when compared with those of bare Ge and the graphene/Ge structures. The results show that the MoS2-based modulator demonstrated even higher modulation efficiency than the graphene-based device. The modulation enhancement mechanism that originated from increased conductivity was analyzed. The optical modulation properties of the MoS2/Ge device show tremendous promise for applications in terahertz modulation and switching.

  3. Nonperiodic metallic gratings transparent for broadband terahertz waves (United States)

    Fan, Ren-Hao; Ren, Xiao-Ping; Peng, Ru-Wen; Huang, Xian-Rong; Wang, Mu

    Recently, we demonstrate both theoretically and experimentally that nonperiodic metallic gratings can become transparent for broadband terahertz waves. Quasiperiodic and disordered metallic gratings effectively weaken and even eliminate Wood's anomalies, which are the diffraction-related characters of periodic gratings. Consequently, both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity. Furthermore, we show that for a specific light source, for example, a line source, a corresponding nonperiodic transparent grating can be also designed. We expect that our findings can be applied for transparent conducting panels, perfect white-beam polarizers, antireflective conducting solar cells, and beyond. References: X. P. Ren, R. H. Fan, R. W. Peng, X. R. Huang, D. H. Xu, Y. Zhou, and Mu Wang, Physical Review B, 91, 045111 (2015); R. H. Fan, R. W. Peng, X. R. Huang, J. Li, Y. Liu, Q. Hu, Mu. Wang, and X. Zhang, Advanced Materials, 24, 1980 (2012); and X. R. Huang, R. W. Peng, and R. H. Fan. Physical Review Letters, 105, 243901 (2010).

  4. Controlling Gigahertz and Terahertz Surface Electromagnetic Waves with Metamaterial Resonators

    Directory of Open Access Journals (Sweden)

    W.-C. Chen


    Full Text Available We computationally and experimentally investigate the use of metamaterial resonators as bandpass filters and other components that enable control of guided surface electromagnetic waves. The guided surface electromagnetic wave propagates on a planar Goubau line, launched via a coplanar waveguide coupler with 50Ω impedance. Experimental samples targeted for either microwave or terahertz frequencies are measured and shown to be in excellent agreement with simulations. Metamaterial elements are designed to absorb energy only of the planar Goubau line and yield narrow-band resonances with relatively high quality factors. Two independent configurations of coupled metamaterial elements are demonstrated that modify the otherwise flat transmission spectrum of the planar Goubau line. By physically shunting the capacitive gaps of the coupled metamaterial elements, we demonstrate the potential for a large dynamic range in transmissivity, suggesting the use of this configuration for high-bandwidth terahertz communications.

  5. Continuous wave terahertz transmission imaging of nonmelanoma skin cancers. (United States)

    Joseph, Cecil S; Yaroslavsky, Anna N; Neel, Victor A; Goyette, Thomas M; Giles, Robert H


    Continuous wave terahertz imaging has the potential to offer a safe, noninvasive medical imaging modality for delineating human skin cancers. Terahertz pulse imaging (TPI) has already shown that there is contrast between basal cell carcinoma and normal skin. Continuous-wave imaging offers a simpler, lower cost alternative to TPI. The goal of this study was to investigate the feasibility of continuous wave terahertz imaging for delineating skin cancers by demonstrating contrast between cancerous and normal tissue in transmission mode. Two CO(2) optically pumped far-infrared molecular gas lasers were used for illuminating the tissue at two frequencies, 1.39 and 1.63 THz. The transmitted signals were detected using a liquid Helium cooled Silicon bolometer. Fresh skin cancer specimens were obtained from Mohs surgeries. The samples were processed and imaged within 24 hours after surgery. During the imaging experiment the samples were kept in pH-balanced saline to prevent tissue dehydration. At both THz frequencies two-dimensional THz transmission images of nonmelanoma skin cancers were acquired with spatial resolution of 0.39 mm at 1.4 THz and 0.49 mm at 1.6 THz. For evaluation purposes, hematoxylin and eosin (H&E) histology was processed from the imaged tissue. A total of 10 specimens were imaged and it was determined that for both frequencies, the areas of decreased transmission in the THz image correlated well with cancerous areas in the histopathology. Two negative controls were also imaged. The difference in transmission between normal and cancerous tissue was found to be approximately 60% at both frequencies, which suggests that contrast between normal and cancerous tissue at these frequencies is dominated by differences in water content. Our results suggest that intraoperative delineation of nonmelanoma skin cancers using continuous-wave terahertz imaging is feasible. Copyright © 2011 Wiley-Liss, Inc.

  6. Wide-aperture total absorption of a terahertz wave in a nanoperiodic graphene-based plasmon structure

    Energy Technology Data Exchange (ETDEWEB)

    Polischuk, O. V., E-mail: [Russian Academy of Sciences, Kotelnikov Institute of Radio Engineering and Electronics, Saratov Branch (Russian Federation); Melnikova, V. S. [Saratov National Research State University (Russian Federation); Popov, V. V., E-mail: [Russian Academy of Sciences, Kotelnikov Institute of Radio Engineering and Electronics, Saratov Branch (Russian Federation)


    The terahertz absorption spectrum in a periodic array of graphene nanoribbons located on the surface of a dielectric substrate with a high refractive index (terahertz prism) is studied theoretically. The total absorption of terahertz radiation is shown to occur in the regime of total internal reflection of the terahertz wave from the periodic array of graphene nanoribbons, at the frequencies of plasma oscillations in graphene, in a wide range of incidence angles of the external terahertz wave even at room temperature.

  7. Rotatable illusion media for manipulating terahertz electromagnetic waves. (United States)

    Zang, XiaoFei; Li, Zhou; Shi, Cheng; Chen, Lin; Cai, Bin; Zhu, YiMing; Li, Li; Wang, XiaoBin


    Based on composite optical transformation, we propose a rotatable illusion media with positive permittivity and permeability to manipulate terahertz waves, and a new way to realize singular parameter-independent cloaks when the incident wave with a certain width propagates from specific incident directions. The fundamental mechanism of this kind of cloak is that the illusion media can be able to avoid the incident wave interacting with the objects. Comparing with traditional transformation-coordinate-based cloaks such as cylindrical-shaped cloaks, our cloaks are independent of singular material parameters. Furthermore, this type of rotatable illusion media can be applied to design tunable miniaturized high-directivity antenna (a small antenna array covered with the rotatable illusion media appears like a large one and meanwhile, the radiation directions of the small antenna array is tunable via this rotatable illusion media). Full wave simulations are performed to confirm these points.

  8. The development of terahertz sources and their applications. (United States)

    Davies, A G; Linfield, E H; Johnston, M B


    The terahertz region of the electromagnetic spectrum spans the frequency range between the mid-infrared and the millimetre/microwave. This region has not been exploited fully to date owing to the limited number of suitable (in particular, coherent) radiation sources and detectors. Recent demonstrations, using pulsed near-infrared femtosecond laser systems, of the viability of THz medical imaging and spectroscopy have sparked international interest; yet much research still needs to be undertaken to optimize both the power and bandwidth in such THz systems. In this paper, we review how femtosecond near-infrared laser pulses can be converted into broad band THz radiation using semiconductor crystals, and discuss in depth the optimization of one specific generation mechanism based on ultra-fast transport of electrons and holes at a semiconductor surface. We also outline a few of the opportunities for a technology that can address a diverse range of challenges spanning the physical and biological sciences, and note the continuing need for the development of solid state, continuous wave, THz sources which operate at room temperature.

  9. Dual-frequency continuous-wave terahertz transmission imaging of nonmelanoma skin cancers (United States)

    Joseph, Cecil S.; Yaroslavsky, Anna N.; Lagraves, Julie L.; Goyette, Thomas M.; Giles, Robert H.


    Continuous wave terahertz imaging has the potential for diagnosing and delineating skin cancers. While contrast has been observed between cancerous and normal tissue at terahertz frequencies, the source mechanism behind this contrast is not clearly understood.1Transmission measurements of 240μm thick sections of nonmelanoma skin cancer were taken at two frequencies of 1.39 THz and 1.63 THz that lie within and outside the tryptophan absorption band, respectively. Two CO2 pumped Far-Infrared molecular gas lasers were used for illuminating the tissue while the transmitted signals were detected using a liquid Helium cooled Silicon bolometer. At both THz frequencies 2-dimensional THz transmission images of nonmelanoma skin cancers were acquired with better than 0.5mm spatial resolution. The resulting images were compared to the sample histology and showed a correlation between cancerous tissue and decreased transmission. The results of the imaging experiments will be presented and discussed.

  10. Switching terahertz waves with gate-controlled active graphene metamaterials. (United States)

    Lee, Seung Hoon; Choi, Muhan; Kim, Teun-Teun; Lee, Seungwoo; Liu, Ming; Yin, Xiaobo; Choi, Hong Kyw; Lee, Seung S; Choi, Choon-Gi; Choi, Sung-Yool; Zhang, Xiang; Min, Bumki


    The extraordinary electronic properties of graphene provided the main thrusts for the rapid advance of graphene electronics. In photonics, the gate-controllable electronic properties of graphene provide a route to efficiently manipulate the interaction of photons with graphene, which has recently sparked keen interest in graphene plasmonics. However, the electro-optic tuning capability of unpatterned graphene alone is still not strong enough for practical optoelectronic applications owing to its non-resonant Drude-like behaviour. Here, we demonstrate that substantial gate-induced persistent switching and linear modulation of terahertz waves can be achieved in a two-dimensional metamaterial, into which an atomically thin, gated two-dimensional graphene layer is integrated. The gate-controllable light-matter interaction in the graphene layer can be greatly enhanced by the strong resonances of the metamaterial. Although the thickness of the embedded single-layer graphene is more than six orders of magnitude smaller than the wavelength (metamaterial, can modulate both the amplitude of the transmitted wave by up to 47% and its phase by 32.2° at room temperature. More interestingly, the gate-controlled active graphene metamaterials show hysteretic behaviour in the transmission of terahertz waves, which is indicative of persistent photonic memory effects.

  11. Terahertz radiation source using a high-power industrial electron ...

    Indian Academy of Sciences (India)


    Mar 27, 2017 ... from such an industrial linac can first pass through an undulator to generate useful terahertz (THz) radiation, and the spent electron ..... speed and the speed of ponderomotive wave, requiring. 20. 40. 60. 80. 100. 120. 140. 1.0. 1.5. 2.0. 2.5. 3.0. 3.5. 4.0. 4.5. 5.0. Normalized emittance εn. (mm−mrad). P cen.

  12. Art Painting Diagnostic Before Restoration with Terahertz and Millimeter Waves (United States)

    Guillet, Jean-Paul; Roux, M.; Wang, K.; Ma, X.; Fauquet, F.; Balacey, H.; Recur, B.; Darracq, F.; Mounaix, P.


    Art painting diagnostic is commonly performed using electromagnetic waves at wavelengths from terahertz to X-ray. These former techniques are essential in conservation and art history research, but they could be also very useful for restoring artwork. While most studies use time domain imaging technique, in this study, a painting has been investigated using both time domain imaging (TDI) and frequency-modulated continuous wave (FMCW) system in the millimeter frequency range. By applying these systems to a painting of the eighteenth century, we detect and analyze the structure of some defects. This study underlines the differences between FMCW and TDI. We present the advantages and disadvantages of each technique on a real artwork.

  13. Filament characterization via resonance absorption of terahertz wave (United States)

    Zheng, Zhigang; Huang, Yindong; Guo, Quan; Meng, Chao; Lü, Zhihui; Wang, Xiaowei; Zhao, Jing; Meng, Congsen; Zhang, Dongwen; Yuan, Jianmin; Zhao, Zengxiu


    In this work, we characterize the transmission properties of the focusing-laser-induced filament by using terahertz (THz) time domain spectroscopy. Significant resonance absorption of the THz wave is identified, which is attributed to the dynamic screening of the ionized electrons. The polarization and intensity of the filament-generated pulse have been varied to study their influences on the resonance absorption. Our results suggest that the electron density of the filament can be determined by fitting the phase shifts and absorption properties around the absorption. This method provides not only an alternative to the plasma diagnostics with plasma frequency at the THz range, but also a supplement to the existing generation theory of THz waves from plasma.

  14. Influence of magnetic field on terahertz wave generation in photorefractive periodically poled lithium niobate crystal. (United States)

    Li, Gaofang; Li, Dong; Ma, Guohong; Liu, Weimin; Tang, Sing Hai


    By employing femtosecond pump-probe configuration, we successfully realized narrowband terahertz wave generation and detection in both photorefractive periodically poled lithium niobate (PPLN) and periodically poled Mg:LiNb(3) (PP-Mg:LN) crystal. Using an applied magnetic field, we achieved modulation of the terahertz wave in a photorefractive PPLN crystal. The terahertz wave depends strongly on the magnitude of the applied magnetic field in the photorefractive PPLN crystal. Terahertz wave independence of the magnetic field in PP-Mg:LN crystal was also identified. The interaction of the magnetic field and photorefractive PPLN crystal is believed to occur due to the Lorentz force, which results in the buildup of a space-charge field in a photorefractive PPLN crystal.

  15. Excitation of a double corrugation slow-wave structure in terahertz range

    DEFF Research Database (Denmark)

    Zhurbenko, Vitaliy; Krozer, Viktor; Kotiranta, Mikko


    problem of a terahertz double corrugation slow-wave structure is considered and practical realization of the structure using currently available technological processes is discussed. The parameters of the realized excitation structure are optimized for vacuum electronics applications while taking...

  16. Low frequency piezoresonance defined dynamic control of terahertz wave propagation. (United States)

    Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G; Bhalla, Amar S; Guo, Ruyan


    Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.

  17. FDTD-based quantitative analysis of terahertz wave detection for multilayered structures. (United States)

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


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

  18. Prism-coupled Cherenkov phase-matched terahertz wave generation using a DAST crystal. (United States)

    Suizu, Koji; Shibuya, Takayuki; Uchida, Hirohisa; Kawase, Kodo


    Terahertz (THz) wave generation based on nonlinear frequency conversion is a promising method for realizing a tunable monochromatic high-power THz-wave source. Unfortunately, many nonlinear crystals have strong absorption in the THz frequency region. This limits efficient and widely tunable THz-wave generation. The Cherenkov phase-matching method is one of the most promising techniques for overcoming these problems. Here, we propose a prism-coupled Cherenkov phase-matching (PCC-PM) method, in which a prism with a suitable refractive index at THz frequencies is coupled to a nonlinear crystal. This has the following advantages. Many crystals can be used as THz-wave emitters; the phase-matching condition inside the crystal does not have to be observed; the absorption of the crystal does not prevent efficient generation of radiation; and pump sources with arbitrary wavelengths can be employed. Here we demonstrate PCC-PM THz-wave generation using the organic crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate (DAST) and a Si prism coupler. We obtain THz-wave radiation with tunability of approximately 0.1 to 10 THz and with no deep absorption features resulting from the absorption spectrum of the crystal. The obtained spectra did not depend on the pump wavelength in the range 1300 to 1450 nm. This simple technique shows promise for generating THz radiation using a wide variety of nonlinear crystals.

  19. Atomic-Scale Time and Space Resolution of Terahertz Frequency Acoustic Waves (United States)

    Reed, Evan J.; Armstrong, Michael R.; Kim, Ki-Yong; Glownia, James H.


    Using molecular dynamics simulations and analytics, we find that strain waves of terahertz frequencies can coherently generate radiation when they propagate past an interface between materials with different piezoelectric coefficients. By considering AlN/GaN heterostructures, we show that the radiation is of detectable amplitude and contains sufficient information to determine the time dependence of the strain wave with potentially subpicosecond, nearly atomic time and space resolution. We demonstrate this phenomenon within the context of high amplitude terahertz frequency strain waves that spontaneously form at the front of shock waves in GaN crystals.

  20. Asymmetric transmission of terahertz waves using polar dielectrics. (United States)

    Serebryannikov, Andriy E; Ozbay, Ekmel; Nojima, Shunji


    Asymmetric wave transmission is a Lorentz reciprocal phenomenon, which can appear in the structures with broken symmetry. It may enable high forward-to-backward transmittance contrast, while transmission for one of the two opposite incidence directions is blocked. In this paper, it is demonstrated that ultrawideband, high-contrast asymmetric wave transmission can be obtained at terahertz frequencies in the topologically simple, i.e., one- or two-layer nonsymmetric gratings, which are entirely or partially made of a polar dielectric working in the ultralow-ε regime inspired by phonon-photon coupling. A variety of polar dielectrics with different characteristics can be used that gives one a big freedom concerning design. Simple criteria for estimating possible usefulness of a certain polar dielectric are suggested. Contrasts exceeding 80dB can be easily achieved without a special parameter adjustment. Stacking a high-ε corrugated layer with a noncorrugated layer made of a polar dielectric, one can enhance transmission in the unidirectional regime. At large and intermediate angles of incidence, a better performance can be obtained owing to the common effect of nonsymmetric diffractions and directional selectivity, which is connected with the dispersion of the ultralow-ε material. At normal incidence, strong asymmetry in transmission may occur in the studied structures as a purely diffraction effect.

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

    Energy Technology Data Exchange (ETDEWEB)

    Condori Quispe, Hugo O.; Sensale-Rodriguez, Berardi [The University of Utah, Salt Lake City, Utah 84112 (United States); Encomendero-Risco, Jimy J.; Xing, Huili Grace [University of Notre Dame, Notre Dame, Indiana 46556 (United States); Cornell University, Ithaca, New York 14853 (United States)


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

  2. Broadband terahertz wave deflection based on C-shape complex metamaterials with phase discontinuities

    KAUST Repository

    Zhang, Xueqian


    A broadband terahertz wave deflector based on metasurface induced phase discontinuities is reported. Various frequency components ranging from 0.43 to 1.0 THz with polarization orthogonal to the incidence are deflected into a broad range of angles from 25° to 84°. A Fresnel zone plate consequently developed from the beam deflector is capable of focusing a broadband terahertz radiation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Compact high-power terahertz radiation source

    Directory of Open Access Journals (Sweden)

    G. A. Krafft


    Full Text Available 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 on the return leg, is discussed. Because the beam is recirculated and not stored, short bunches may be produced that radiate coherently in the undulator, yielding exceptionally high average THz power for relatively low average beam power. Deceleration from the coherent emission, and the detuning it causes, limits the charge-per-bunch possible in such a device.

  4. Intense Terahertz Sources for 2D Spectroscopy

    DEFF Research Database (Denmark)

    Pedersen, Pernille Klarskov

    /cm. In agreement with the MD II simulations, a bleaching of the 1.4 THz is observed for the highest field strengths in a 1D spectroscopy configuration. Phonon coupling in sucrose is investigated with a 2D spectroscopy experiment based on a DSTMS and a DAST source, for which a new chopper scheme is presented...... in a molecular dynamics (MD) simulation. With this THz induced nonlinear responses and mode couplings in CsI and sucrose are investigated for increasing field strengths, and it is found that these occur for sucrose when the field strength is in the MV/cm range. THz sources based on LiNbO3, DAST, DSTMS and 2...... radiation emitted from a 2-color air plasma has a conical beam profile. With the beam profiles measured through a focal plane, this has been reconstructed in 3D showing that the beam collapses to a single spot in focus. Besides the off-axis THz radiation, a weak on-axis forward propagating mode has been...

  5. A High Precision Terahertz Wave Image Reconstruction Algorithm

    National Research Council Canada - National Science Library

    Guo, Qijia; Chang, Tianying; Geng, Guoshuai; Jia, Chengyan; Cui, Hong-Liang


    With the development of terahertz (THz) technology, the applications of this spectrum have become increasingly wide-ranging, in areas such as non-destructive testing, security applications and medical scanning, in which one of the most...

  6. Impact of the Metal Adhesion Layer on the Radiation Power of Plasmonic Photoconductive Terahertz Sources (United States)

    Turan, Deniz; Corzo-Garcia, Sofia Carolina; Yardimci, Nezih Tolga; Castro-Camus, Enrique; Jarrahi, Mona


    The use of plasmonic contact electrodes in a photoconductive terahertz source offers high optical-to-terahertz conversion efficiencies. The high efficiency is because plasmonic contact electrodes concentrate a large portion of the incident optical pump beam in close proximity to the contact electrodes. By reducing the average transport path length of the photo-generated carriers from the contact electrodes, a larger number of the photocarriers drift to the terahertz radiating elements of the photoconductive source within a sub-picosecond time scale. Therefore, higher terahertz radiation power levels are achieved compared to a similar photoconductive source without plasmonic contact electrodes. Au is a preferred metal for plasmonic contact electrodes because of the strong plasmonic enhancement factors it offers at near-infrared optical wavelengths. However, it requires an adhesion layer to stick well to most III-V semiconductor substrates used in photoconductive terahertz sources. In this paper, we analyze the impact of the Au adhesion layer on the performance of plasmonic photoconductive sources fabricated on a GaAs substrate. Our analysis suggests that Cr is the most promising adhesion layer for plasmonic contact electrodes. We show that the use of a Cr adhesion layer instead of Ti, which is used in previously demonstrated plasmonic photoconductive sources, offers up to an 80% enhancement in the generated terahertz powers. We report record-high terahertz power emissions of up to 6.7 mW from plasmonic photoconductive sources with Cr/Au contacts.

  7. Impact of the Metal Adhesion Layer on the Radiation Power of Plasmonic Photoconductive Terahertz Sources (United States)

    Turan, Deniz; Corzo-Garcia, Sofia Carolina; Yardimci, Nezih Tolga; Castro-Camus, Enrique; Jarrahi, Mona


    The use of plasmonic contact electrodes in a photoconductive terahertz source offers high optical-to-terahertz conversion efficiencies. The high efficiency is because plasmonic contact electrodes concentrate a large portion of the incident optical pump beam in close proximity to the contact electrodes. By reducing the average transport path length of the photo-generated carriers from the contact electrodes, a larger number of the photocarriers drift to the terahertz radiating elements of the photoconductive source within a sub-picosecond time scale. Therefore, higher terahertz radiation power levels are achieved compared to a similar photoconductive source without plasmonic contact electrodes. Au is a preferred metal for plasmonic contact electrodes because of the strong plasmonic enhancement factors it offers at near-infrared optical wavelengths. However, it requires an adhesion layer to stick well to most III-V semiconductor substrates used in photoconductive terahertz sources. In this paper, we analyze the impact of the Au adhesion layer on the performance of plasmonic photoconductive sources fabricated on a GaAs substrate. Our analysis suggests that Cr is the most promising adhesion layer for plasmonic contact electrodes. We show that the use of a Cr adhesion layer instead of Ti, which is used in previously demonstrated plasmonic photoconductive sources, offers up to an 80% enhancement in the generated terahertz powers. We report record-high terahertz power emissions of up to 6.7 mW from plasmonic photoconductive sources with Cr/Au contacts.

  8. Enhanced plasma wave detection of terahertz radiation using multiple high electron-mobility transistors connected in series

    KAUST Repository

    Elkhatib, Tamer A.


    We report on enhanced room-temperature detection of terahertz radiation by several connected field-effect transistors. For this enhanced nonresonant detection, we have designed, fabricated, and tested plasmonic structures consisting of multiple InGaAs/GaAs pseudomorphic high electron-mobility transistors connected in series. Results show a 1.63-THz response that is directly proportional to the number of detecting transistors biased by a direct drain current at the same gate-to-source bias voltages. The responsivity in the saturation regime was found to be 170 V/W with the noise equivalent power in the range of 10-7 W/Hz0.5. The experimental data are in agreement with the detection mechanism based on the rectification of overdamped plasma waves excited by terahertz radiation in the transistor channel. © 2010 IEEE.

  9. Arrayed silicon prism coupler for a terahertz-wave parametric oscillator. (United States)

    Kawase, K; Shikata, J; Minamide, H; Imai, K; Ito, H


    Using room-temperature parametric oscillation of a LiNbO3 crystal pumped by a Q-switched Nd:YAG laser with a simple configuration, we have realized a widely tunable coherent terahertz- (THz-) wave source in the range between 1 and 3 THz. Inasmuch as the THz wave is affected by total internal reflection at the crystal edge, we used a Si prism coupler to couple out the THz wave. We introduce an arrayed Si-prism coupler that increases the efficiency and decreases the diffraction angle. By use of the arrayed-prism coupler, there is a sixfold increase in coupling efficiency and a 40% decrease in the far-field beam diameter, compared with the use of a single-prism coupler. We discuss the negative effect of the free carriers at the Si-prism surface that is excited by the scattered pump beam, and the positive effect of cavity rotation on the unidirectional radiation of the THz wave from a Si prism.

  10. Terahertz scanning probe microscope

    NARCIS (Netherlands)

    Klapwijk, T.M.


    The invention provides aterahertz scanning probe microscope setup comprising (i) a terahertz radiation source configured to generate terahertz radiation; (ii) a terahertz lens configured to receive at least part of the terahertz radiation from the terahertz radiation source; (iii) a cantilever unit

  11. Broadband and high-efficient terahertz wave deflection based on C-shaped complex metamaterials with phase discontinuities

    KAUST Repository

    Tian, Zhen


    A terahertz metamaterial comprised of C-shaped SRRs was experimentally devised and demonstrated to exhibit high-efficient and broadband anomalous refraction with strong phase discontinuities. The generalized refraction properties of the proposed metamaterial, including the effect of various incident angles and polarizations were investigated at broad terahertz frequencies. By employing such metasurface, we demonstrated a simple method to tailor transmission and phase of terahertz wave. © 2013 IEEE.

  12. Continuous-wave terahertz reflection imaging of ex vivo nonmelanoma skin cancers (United States)

    Joseph, Cecil S.; Yaroslavsky, Anna N.; Neel, Victor A.; Goyette, Thomas M.; Giles, Robert H.


    Nonmelanoma skin cancers are the most common form of cancer. Continuous wave terahertz imaging has the potential to differentiate between nonmelanoma skin cancers and normal skin. Terahertz imaging is non-ionizing and offers a high sensitivity to water content. Contrast between cancerous and normal tissue in transmission mode has already been demonstrated using a continuous wave terahertz system. The aim of this experiment was to implement a system that is capable of reflection modality imaging of nonmelanoma skin cancers. Fresh excisions of skin cancer specimens were obtained from Mohs surgeries for this study. A CO2 optically pumped far-infrared molecular gas laser was used for illuminating the tissue at 584 GHz. The reflected signal was detected using a liquid Helium cooled Silicon bolometer. The terahertz images were compared with sample histology. The terahertz reflection images exhibit some artifacts that can hamper the specificity. The beam waist at the sample plane was measured to be 0.57 mm, and the system's signal-to-noise ratio was measured to be 65 dB.

  13. Controlling terahertz waves with meta-materials and photonic bandgap structures

    Energy Technology Data Exchange (ETDEWEB)

    Shchegolkov, Dmitry [Los Alamos National Laboratory; Azad, Abul [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Moody, Nathan A [Los Alamos National Laboratory; Simakov, Evgenya I [Los Alamos National Laboratory


    We will describe research conducted at Los Alamos National Laboratory towards developing components for controlling terahertz waves. We employ meta-materials and, particularly, meta-films, as very compact absorbers for controlling quasioptical beams. We believe that dielectric photonic bandgap structures could replace ordinary metal waveguide devices at THz, since metal structures become extremely lossy in this frequency range.

  14. Towards a Terahertz Room-Temperature Integrated Source

    DEFF Research Database (Denmark)

    Leo, Giuseppe; Gérard, Jean-Michel; Reitzenstein, Stephan


    We aim at a radically new continuous-wave, electrically pumped THz emitter. Compared to existing THz sources, this source will bring together several advantages that are far from being simultaneously available in any existing source today: compactness, roomtemperature operation, output power arou...

  15. Propagation Characteristics of Oblique Incident Terahertz Wave in Nonuniform Dusty Plasma

    Directory of Open Access Journals (Sweden)

    Yunhua Cao


    Full Text Available Propagation characteristics of oblique incident terahertz wave from the nonuniform dusty plasma are studied using the propagation matrix method. Assuming that the electron density distribution of dusty plasma is parabolic model, variations of power reflection, transmission, and absorption coefficients with frequencies of the incident wave are calculated as the wave illuminates the nonuniform dusty plasma from different angles. The effects of incident angles, number density, and radius of the dust particles on propagation characteristics are discussed in detail. Numerical results show that the number density and radius of the dust particles have very little influences on reflection and transmission coefficients and have obvious effects on absorption coefficients. The terahertz wave has good penetrability in dusty plasma.

  16. AlInGaN-Based Superlattice Terahertz Source Project (United States)

    National Aeronautics and Space Administration — WaveBand Corporation in collaboration with Virginia Commonwealth University proposes to design and fabricate a new sub-millimeter source based on an InAlGaN...

  17. Terahertz Light Source and User Area at FACET

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Z.; Li, S.Z.; Litos, M.; Fisher, A.D.; Hogan, M.J.; /SLAC


    FACET at SLAC provides high charge, high peak current, low emittance electron beam that is bunched at THz wavelength scale during its normal operation. A THz light source based coherent transition radiation (CTR) from this beam would potentially be the brightest short-pulse THz source ever constructed. Efforts have been put into building this photon source together with a user area, to provide a platform to utilize this unique THz radiation for novel nonlinear and ultrafast phenomena researches and experiments. Being a long-time underutilized portion of the electromagnetic spectrum, terahertz (100 GHz {approx} 10 THz) spectral range is experiencing a renaissance in recent years, with broad interests from chemical and biological imaging, material science, telecommunication, semiconductor and superconductor research, etc. Nevertheless, the paucity of THz sources especially strong THz radiation hinders both its commercial applications and nonlinear processes research. FACET - Facilities for Accelerator science and Experimental Test beams at SLAC - provides 23 GeV electron beam with peak currents of {approx} 20 kA that can be focused down to 100 {mu}m{sup 2} transversely. Such an intense electron beam, when compressed to sub-picosecond longitudinal bunch length, coherently radiates high intensity EM fields well within THz frequency range that are orders of magnitude stronger than those available from laboratory tabletop THz sources, which will enable a wide variety of THz related research opportunities. Together with a description of the FACET beamline and electron beam parameters, this paper will report FACET THz radiation generation via coherent transition radiation and calculated photon yield and power spectrum. A user table is being set up along the THz radiation extraction sites, and equipped with various signal diagnostics including THz power detector, Michelson interferometer, sample stages, and sets of motorized optical components. This setup will also be

  18. Terahertz wave manipulation with metamaterials based on metal and graphene

    DEFF Research Database (Denmark)

    Andryieuski, Andrei; Malureanu, Radu; Zalkovskij, Maksim


    The terahertz (THz) technology provides with exciting possibilities for spectroscopy, food quality control, defense, communication and biomedical imaging [1]. Being relatively young (the massive exploitation of the THz range began only in the beginning of 1990-ies), the THz science demands...... for active and passive materials and devices. Metamaterials, metal-dielectric artificial composites, propose wide possibilities for achieving unconventional electromagnetic properties, not found in nature. Moreover, metamaterials constructed of graphene, a monolayer of carbon atoms, allow for tunable...

  19. Broadband modulation of terahertz waves through electrically driven hybrid bowtie antenna-VO2 devices. (United States)

    Han, Chunrui; Parrott, Edward P J; Humbert, Georges; Crunteanu, Aurelian; Pickwell-MacPherson, Emma


    Broadband modulation of terahertz (THz) light is experimentally realized through the electrically driven metal-insulator phase transition of vanadium dioxide (VO2) in hybrid metal antenna-VO2 devices. The devices consist of VO2 active layers and bowtie antenna arrays, such that the electrically driven phase transition can be realized by applying an external voltage between adjacent metal wires extended to a large area array. The modulation depth of the terahertz light can be initially enhanced by the metal wires on top of VO2 and then improved through the addition of specific bowties in between the wires. As a result, a terahertz wave with a large beam size (~10 mm) can be modulated within the measurable spectral range (0.3-2.5 THz) with a frequency independent modulation depth as high as 0.9, and the minimum amplitude transmission down to 0.06. Moreover, the electrical switch on/off phase transition depends very much on the size of the VO2 area, indicating that smaller VO2 regions lead to higher modulation speeds and lower phase transition voltages. With the capabilities in actively tuning the beam size, modulation depth, modulation bandwidth as well as the modulation speed of THz waves, our study paves the way in implementing multifunctional components for terahertz applications.

  20. Manipulating of Different-Polarized Reflected Waves with Graphene-based Plasmonic Metasurfaces in Terahertz Regime. (United States)

    Deng, Li; Wu, Yongle; Zhang, Chen; Hong, Weijun; Peng, Biao; Zhu, Jianfeng; Li, Shufang


    A graphene-based plasmonic metasurface which can independently control different polarized electromagnetic waves with reasonably small losses in terahertz regime is proposed and demonstrated in this paper. This metasurface is composed of graphene based elements. Owing to anisotropic plasmonic resonance of the graphene-based elements, the reflected phases and magnitudes of orthogonally polarized waves can be independently controlled by varying dimensions of the element. Four types of graphene-based plasmonic metasurfaces with different reflected phases distributions are synthesized and simulated, exhibiting diverse functions such as polarized beam splitting, beam deflection, and linear-to-circular polarization conversion. The simulation results demonstrate excellent performances as theoretical expectation. The proposed graphene-based plasmonic metasurface can be applied to realize extremely light-weight, ultra-compact, and high-performances electromagnetic structures for diverse terahertz applications.

  1. Optical Synthesis of Terahertz and Millimeter-Wave Frequencies with Discrete Mode Diode Lasers

    CERN Document Server

    O'Brien, Stephen; Bitauld, David; Brandonisio, Nicola; Amann, Andreas; Phelan, Richard; Kelly, Brian; O'Gorman, James


    It is shown that optical synthesis of terahertz and millimeter-wave frequencies can be achieved using two-mode and mode-locked discrete mode diode lasers. These edge-emitting devices incorporate a spatially varying refractive index profile which is designed according to the spectral output desired of the laser. We first demonstrate a device which supports two primary modes simultaneously with high spectral purity. In this case sinusoidal modulation of the optical intensity at terahertz frequencies can be obtained. Cross saturation of the material gain in quantum well lasers prevents simultaneous lasing of two modes with spacings in the millimeter-wave region. We show finally that by mode-locking of devices that are designed to support a minimal set of four primary modes, we obtain a sinusoidal modulation of the optical intensity in this frequency region.

  2. Transmission properties of terahertz waves through asymmetric rectangular aperture arrays on carbon nanotube films

    Directory of Open Access Journals (Sweden)

    Yue Wang


    Full Text Available Transmission spectra of terahertz waves through a two-dimensional array of asymmetric rectangular apertures on super-aligned multi-walled carbon nanotube films were obtained experimentally. In this way, the anisotropic transmission phenomena of carbon nanotube films were observed. For a terahertz wave polarization parallel to the orientation of the carbon nanotubes and along the aperture short axis, sharp resonances were observed and the resonance frequencies coincided well with the surface plasmon polariton theory. In addition, the minima of the transmission spectra were in agreement with the location predicted by the theory of Wood’s anomalies. Furthermore, it was found that the resonance profiles through the carbon nanotube films could be well described by the Fano model.

  3. Temperature variation induced by the pulsed-periodic laser pumping under terahertz wave generation (United States)

    Kitaeva, G. Kh; Moiseenko, E. V.; Shepelev, A. V.


    During nonlinear-optical parametric frequency conversion the heat-related effects occur, considerably influencing the conversion process. We develop versatile methods for analytic and numerical calculations of thermo-optical parameters and the temperature distribution inside a non-linear crystal pumped by periodic laser pulses. As an example, numerical results are presented for a number of laser-based schemes actual for the non-linear optical terahertz wave generation and parametric frequency conversion processes.

  4. Slot-dimer babinet metamaterials as polarization shapers for terahertz waves

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Chigrin, D. N.; Lavrinenko, Andrei


    We theoretically study optical properties of free-standing metallic membranes patterned with an array of two-slot elements (dimers) comprising two rectangular slots of different dimensions and orientation. It is shown that these structures feature extraordinary optical transmission with strong an...... and spectrally selective polarization conversion capabilities. The output polarization is highly dependent on the dimer geometry, which can be used in the design of compact polarization shapers for terahertz waves....

  5. Detection and Characterization of Flaws in Sprayed on Foam Insulation with Pulsed Terahertz Frequency Electromagnetic Waves (United States)

    Winfree, William P.; Madaras, Eric I.


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

  6. Broadband diffuse terahertz wave scattering by flexible metasurface with randomized phase distribution. (United States)

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


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

  7. Advances in the biological effects of terahertz wave radiation. (United States)

    Zhao, Li; Hao, Yan-Hui; Peng, Rui-Yun


    The terahertz (THz) band lies between microwave and infrared rays in wavelength and consists of non-ionizing radiation. Both domestic and foreign research institutions, including the army, have attached considerable importance to the research and development of THz technology because this radiation exhibits both photon-like and electron-like properties, which grant it considerable application value and potential. With the rapid development of THz technology and related applications, studies of the biological effects of THz radiation have become a major focus in the field of life sciences. Research in this field has only just begun, both at home and abroad. In this paper, research progress with respect to THz radiation, including its biological effects, mechanisms and methods of protection, will be reviewed.

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

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


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

  9. Terahertz radiation source using a high-power industrial electron ...

    Indian Academy of Sciences (India)

    We propose that high-power electron beam from such an industrial linac can first pass through an undulator to generate useful terahertz (THz) radiation, and the spent electron beam coming out of the undulator can still be used for the intended industrial applications. This will enhance the utilization of a high-power industrial ...

  10. Widely tunable terahertz source based on intra-cavity frequency mixing in quantum cascade laser arrays

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Aiting; Jung, Seungyong; Jiang, Yifan; Kim, Jae Hyun; Belkin, Mikhail A., E-mail: [Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Vijayraghavan, Karun [Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); ATX Photonics, 10100 Burnet Rd., Austin, Texas 78758 (United States)


    We demonstrate a compact monolithic terahertz source continuously tunable from 1.9 THz to 3.9 THz with the maximum peak power output of 106 μW at 3.46 THz at room temperature. The source consists of an array of 10 electrically tunable quantum cascade lasers with intra-cavity terahertz difference-frequency generation. To increase fabrication yield and achieve high THz peak power output in our devices, a dual-section current pumping scheme is implemented using two electrically isolated grating sections to independently control gain for the two mid-IR pumps.

  11. Investigating Dielectric and Metamaterial Effects in a Terahertz Traveling-Wave Tube Amplifier (United States)

    Starinshak, David P.; Wilson, Jeffrey D.


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

  12. Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor. (United States)

    Yasumatsu, Naoya; Watanabe, Shinichi


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

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

    Energy Technology Data Exchange (ETDEWEB)

    Li, Ke, E-mail:; Cao, Miaomiao, E-mail: [Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China); Institute of Electronics, University of Chinese Academy of Sciences, Beijing 100190 (China); Liu, Wenxin, E-mail:; Wang, Yong, E-mail: [Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China)


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

  14. See-through Detection and 3D Reconstruction Using Terahertz Leaky-Wave Radar Based on Sparse Signal Processing (United States)

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


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

  15. Experimental study of intense radiation in terahertz region based on cylindrical surface wave resonator

    Energy Technology Data Exchange (ETDEWEB)

    Gong, Shaoyan; Ogura, Kazuo; Yambe, Kiyoyuki; Nomizu, Shintaro; Shirai, Akihiro; Yamazaki, Kosuke; Kawamura, Jun; Miura, Takuro; Takanashi, Sho; San, Min Thu [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)


    Periodical corrugations structured on a cylindrical conductor have cylindrical surface waves (CSWs), which are reflected at the corrugation ends and form a CSW-resonator. In this paper, intense radiations in terahertz region based on the CSW-resonator are reported. The CSW-resonators with upper cut off frequencies in the modern IEEE G-band (110–300 GHz) are excited by a coaxially injected annular beam in a weakly relativistic region less than 100 kV. It is shown that there exists an oscillation starting energy for the CSW-resonator. Above the starting energy, very intense terahertz radiations on the order of kW are obtained. The operation frequencies in the range of 166–173 GHz and 182–200 GHz are obtained using two types of CSW-resonator with the different corrugation amplitude. Electromagnetic properties of the CSW-resonator can be controlled by the artificial structure and may play an important role in high-intensity terahertz generations and applications.

  16. Source Modeling Sleep Slow Waves

    National Research Council Canada - National Science Library

    Michael Murphy; Brady A. Riedner; Reto Huber; Marcello Massimini; Fabio Ferrarelli; Giulio Tononi; Marcus E. Raichle


    .... Here we use high-density EEG (hd-EEG) source modeling to show that individual spontaneous slow waves have distinct cortical origins, propagate uniquely across the cortex, and involve unique subsets of cortical structures...

  17. Design rules for phase-matched terahertz surface electromagnetic wave generation by optical rectification in a nonlinear planar waveguide. (United States)

    Musin, Roman R; Xing, Qirong; Li, Yanfeng; Hu, Minglie; Chai, Lu; Wang, Qingyue; Mikhailova, Yuliya M; Nazarov, Maksim M; Shkurinov, Alexander P; Zheltikov, Aleksei M


    The theory of guided waves in metal-dielectric planar multilayer structures is applied to reduce the loss and maximize optical nonlinearity for efficient terahertz-field generation in a surface electromagnetic wave by femtosecond laser pulses confined in a (chi)((2)) nonlinear planar waveguide. For typical parameters of thin-film polymer waveguides and metal-dielectric interfaces, the optimal size of the (chi)((2)) waveguide core providing the maximum efficiency of terahertz plasmon-field generation is shown to be less than the wavelength of the optical pump field.

  18. Contrast-enhanced continuous-terahertz-wave imaging based on superparamagnetic iron oxide nanoparticles for biomedical applications. (United States)

    Zhang, Rui; Zhang, Liangliang; Wu, Tong; Zuo, Shasha; Wang, Ruixue; Zhang, Cunlin; Zhang, Jue; Fang, Jing


    We present a novel contrast-enhanced continuous-terahertz-wave imaging modality based on magnetic induction heating of superparamagnetic iron oxide nanoparticles (SPIOs), which yields a highly sensitive increment in the reflection terahertz (THz) signal in SPIO solution upon exposure to an alternating magnetic field. In the differential and relative refection change focal-plane images before and after alternating magnetic field exposure, a dramatic contrast is demonstrated between water with and without SPIOs. This low-cost, simple, and stable contrast-enhanced continuous-THz-wave imaging system is suitable for miniaturization and real-time imaging application.

  19. Nondestructive evaluation of cork enclosures using terahertz/millimeter wave spectroscopy and imaging. (United States)

    Hor, Yew Li; Federici, John F; Wample, Robert L


    Natural cork enclosures, due to their cell structure, composition, and low moisture are fairly transparent to terahertz (THz) and millimeter waves enabling nondestructive evaluation of the cork's surface and interior. It is shown that the attenuation coefficient of the defect-free cork can be modeled with a Mie scattering model in the weakly scattering limit. Contrast in the THz images is a result of enhanced scattering of THz radiation by defects or voids as well as variations in the cork cell structure. The presence of voids, defects, and changes in grain structure can be determined with roughly 100-300 microm resolution.

  20. HfO 2 -based ferroelectric modulator of terahertz waves with graphene metamaterial (United States)

    Jiang, Ran; Wu, Zheng-Ran; Han, Zu-Yin; Jung, Hyung-Suk


    Tunable modulations of terahertz waves in a graphene/ferroelectric-layer/silicon hybrid structure are demonstrated at low bias voltages. The modulation is due to the creation/elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfO2 layer. Considering the good compatibility of HfO2 with the Si-based semiconductor process, the highly tunable characteristics of the graphene metamaterial device under ferroelectric effect open up new avenues for graphene-based high performance integrated active photonic devices compatible with the silicon technology. Project supported by the National Natural Science Foundation of China (Grant No. 11374182).

  1. Review of 3D Printed Millimeter-Wave and Terahertz Passive Devices

    Directory of Open Access Journals (Sweden)

    Bing Zhang


    Full Text Available The 3D printing technology is catching attention nowadays. It has certain advantages over the traditional fabrication processes. We give a chronical review of the 3D printing technology from the time it was invented. This technology has also been used to fabricate millimeter-wave (mmWave and terahertz (THz passive devices. Though promising results have been demonstrated, the challenge lies in the fabrication tolerance improvement such as dimensional tolerance and surface roughness. We propose the design methodology of high order device to circumvent the dimensional tolerance and suggest specific modelling of the surface roughness of 3D printed devices. It is believed that, with the improvement of the 3D printing technology and related subjects in material science and mechanical engineering, the 3D printing technology will become mainstream for mmWave and THz passive device fabrication.

  2. Terahertz Quantum Cascade Laser Based 3D Imaging Project (United States)

    National Aeronautics and Space Administration — LongWave Photonics proposes a terahertz quantum-cascade laser based swept-source optical coherence tomography (THz SS-OCT) system for single-sided, 3D,...

  3. Analysis of propagation properties of terahertz hollow-optical fiber by using time-domain spectroscopy and application for THz wave remote spectroscopy (United States)

    Ito, K.; Katagiri, T.; Matsuura, Y.


    Terahertz pulse propagation in hollow optical fibers is investigated by using terahertz time-domain spectroscopy. From evaluation of transmission loss spectra of hollow optical fiber, it is found that TM11 mode propagates as well as TE11 mode that is the lowest order mode in terahertz metal-hollow fiber. Short-time Fourier transform is also applied for investigation of mode properties and as a result, it is confirmed that the interference peaks in the loss spectra are due to mode mixing in hollow optical fibers. Finally we performed a terahertz wave remote spectroscopy using the hollow optical fiber and acquired a clear transmission spectrum of the theophylline.

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

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Sheng; Zhu, Jianfei; Jiang, Wei; Yuan, Jun; Yin, Ge; Ma, Yungui, E-mail: [State Key Lab of Modern Optical Instrumentation, Centre for Optical and Electromagnetic Research, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310058 (China); Xu, Wendao; Xie, Lijuan; Ying, Yibin [College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058 (China)


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

  5. Electrically tunable terahertz wave modulator based on complementary metamaterial and graphene

    Energy Technology Data Exchange (ETDEWEB)

    He, Xun-jun, E-mail:; Li, Teng-yue; Wang, Lei; Wang, Jian-min; Jiang, Jiu-xing [Department of Electronic Science and technology, School of Applied Sciences, Harbin University of Science and Technology, Harbin 150080 (China); Yang, Guo-hui; Meng, Fan-yi; Wu, Qun [Department of Electronic and Communications Engineering, School of Electronic Information Engineering, Harbin Institute of Technology, Harbin 150001 (China)


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

  6. Plasmonic properties of graphene-based nanostructures in terahertz waves

    Directory of Open Access Journals (Sweden)

    Do T. Nga


    Full Text Available We theoretically study the plasmonic properties of graphene on bulk substrates and graphene-coated nanoparticles. The surface plasmons of such systems are strongly dependent on bandgap and Fermi level of graphene that can be tunable by applying external fields or doping. An increase of bandgap prohibits the surface plasmon resonance for GHz and THz frequency regime. While increasing the Fermi level enhances the absorption of the graphene-based nanostructures in these regions of wifi-waves. Some mechanisms for electric-wifi-signal energy conversion devices are proposed. Our results have a good agreement with experimental studies and can pave the way for designing state-of-the-art electric graphene-integrated nanodevices that operate in the GHz–THz radiation.

  7. Transform-limited, achromatic injection-seeded terahertz-wave parametric generator

    Energy Technology Data Exchange (ETDEWEB)

    Guo, R; Minamide, H; Ito, H, E-mail: [RIKEN Advanced Science Institute, 519-1399, Aramaki Aoba, Aoba-ku, Sendai 980-0845 (Japan)


    A review to our effort on developing the transform-limited, frequency-agile terahertz-wave parametric generator (TPG) is presented. A frequency-agile THz-wave generation is realized by introducing the injection-seeding method and the optical design for the stationary dispersion-compensation The purity of the THz-wave frequency was dramatically improved to {Delta}v/v<10{sup -4}. Simultaneously, the THz-wave output was several hundred times higher than that of a conventional TPG. In addition, a wide frequency tuning with fast tuning speed were realized. The THz-wave frequency can be set randomly or scanned continuously over a frequency range from 0.6 THz to 2.4 THz with narrow linewidth of sub 100 MHz. Furthermore, a tabletop, high-performance THz-wave gas spectrometer based on this achromatic injection-seeded TPG was developed. To demonstrate the potential of this system, we performed the measurement of the absorption line due to rotational transitions of the water molecules and determined their pressure-broadening coefficient.

  8. Enhancement of terahertz-wave output from LiNbO(3) optical parametric oscillators by cryogenic cooling. (United States)

    Shikata, J; Sato, M; Taniuchi, T; Ito, H; Kawase, K


    In recent years widely tunable terahertz- (THz-) wave generation from LiNbO(3) optical parametric oscillators (OPO's) has been successfully demonstrated by use of the prism output-coupler method. However, there remains a problem of large absorption loss for generated terahertz waves inside the crystal, so we investigated the cryogenic characteristics of the OPO. We achieved 125-times-higher THz-wave output and 32% reduction of the generation threshold by cooling the crystal to 78 K. This scheme also provides direct loss measurement at THz frequency, and we found that the THz-wave enhancement mechanism is improvement of the gain as well as the reduction of the absorption coefficient.

  9. Full-State Controls of Terahertz Waves Using Tensor Coding Metasurfaces. (United States)

    Liu, Shuo; Zhang, Hao Chi; Zhang, Lei; Yang, Quan Long; Xu, Quan; Gu, Jianqiang; Yang, Yan; Zhou, Xiao Yang; Han, Jiaguang; Cheng, Qiang; Zhang, Weili; Cui, Tie Jun


    Coding metasurfaces allow us to study metamaterials from a fully digital perspective, enabling many exotic functionalities, such as anomalous reflections, broadband diffusions, and polarization conversion. Here, we propose a tensor coding metasurface at terahertz (THz) frequency that could take full-state controls of an electromagnetic wave in terms of its polarization state, phase and amplitude distributions, and wave-vector mode. Owing to the off-diagonal elements that dominant in the reflection matrix, each coding particle could reflect the normally incident wave to its cross-polarization with controllable phases, resulting in different coding digits. A 3-bit tensor coding metasurface with three coding sequences is taken as an example to show its full-state controls in reflecting a normally incident THz beam to anomalous directions with cross-polarizations and making a spatially propagating wave (PW) to surface wave (SW) conversion at the THz frequency. We show that the proposed PW-SW convertor based on the tensor coding metasurface supports both x- and y-polarized normal incidences, producing cross-polarized transverse-magnetic and transverse-electric modes of THz SWs, respectively.

  10. Terahertz Techniques

    CERN Document Server

    Bründermann, Erik; Kimmitt, Maurice FitzGerald


    Research and development in the terahertz portion of the electromagnetic spectrum has expanded very rapidly during the past fifteen years due to major advances in sources, detectors and instrumentation. Many scientists and engineers are entering the field and this volume offers a comprehensive and integrated treatment of all aspects of terahertz technology. The three authors, who have been active researchers in this region over a number of years, have designed Terahertz Techniques to be both a general introduction to the subject and a definitive reference resource for all those involved in this exciting research area.

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

    National Research Council Canada - National Science Library

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


    .... The fact limits efficient and wide tunable THz-wave generation. Here, we show that Cherenkov radiation with waveguide structure is an effective strategy for achieving efficient and extremely wide tunable THz-wave source...

  12. Millimeter- and terahertz-wave over fiber technologies for high-speed communication and non-telecom applications (United States)

    Kanno, Atsushi


    Millimeter-wave and terahertz-wave technologies are promising solutions for high-speed wireless communication as well as nondestructive imaging due to its high frequency (short wavelength) nature. In the study, we propose and demonstrate high-speed wireless communication in millimeter- and terahertz-wave bands adopted by advanced optical fiber communication technologies: combination of a radio over fiber (RoF) manner for generation of the signals and a high-speed digital signal processing implemented in a receiver. The RoF technique is also capable for a local-oscillator signal transport over the fiber to the remote sites. Fiber-remoted distributed radar system is also discussed in the paper.

  13. Radiation of terahertz electromagnetic waves from build-in nano Josephson junctions of cuprate high-T(c) superconductors. (United States)

    Lin, Shi-Zeng; Hu, Xiao


    The nano-scale intrinsic Josephson junctions in highly anisotropic cuprate superconductors have potential for generation of terahertz electromagnetic waves. When the thickness of a superconductor sample is much smaller than the wavelength of electromagnetic waves in vacuum, the superconductor renders itself as a cavity. Unlike conventional lasers, the presence of the cavity does not guarantee a coherent emission because of the internal degree of freedom of the superconductivity phase in long junctions. We study the excitation of terahertz wave by solitons in a stack of intrinsic Josephson junctions, especially for relatively short junctions. Coherent emission requires a rectangular configuration of solitons. However such a configuration is unstable against weak fluctuations, contrarily solitons favor a triangular lattice corresponding to an out-phase oscillation of electromagnetic waves. To utilize the cavity, we propose to use an array of stacks of short intrinsic Josephson junctions to generate powerful terahertz electromagnetic waves. The cavity synchronizes the plasma oscillation in different stacks and the emission intensity is predicted to be proportional to the number of stacks squared.

  14. Wave shape recovery for terahertz pulse field detection via photoconductive antenna. (United States)

    Liu, Jinsong; Zou, Si; Yang, Zhengang; Wang, Kejia; Ye, Kefei


    For photoconductive (PC) antennae used as terahertz (THz) detectors, traditional data processing methods should be improved because the space-charge and radiation field screening effects and the time dependence of photocarriers density have not been considered. Through developing a double-probe-pulse THz detection technique and using an equivalent-circuit model to describe PC antennae, we present a new method to restore the THz-field wave shape from the measurement data of currents between two electrodes on the antenna. This method is verified to be effective through building a special THz time-domain spectroscopy system with double probes. This work is significant for the accurate determination of pulse THz fields.

  15. Millimeter-wave and Terahertz Reconfigurable Radio-over-Fiber Systems

    DEFF Research Database (Denmark)

    Vegas Olmos, Juan José

    on photonic technologies enable to generate, transport and radiate in a straight forward manner microwave and millimeter wave signals. Although electronic technologies are able to sustain an increase in frequency from a technology point of view, with current developments hitting the Terahertz regime...... when deploying fiber is not an option. Radio-over-Fiber (RoF) technologies have evolved from a blue sky academic topic in the 90s to a main driver within the current quest for the 5th generation mobile systems (5G). A twist in RoF technologies is that it has found along the way niches in areas non...... purely related to communication technologies (ICT) applications: distribution of highly pure clock signals for radio telescopes, photonic-based coherent radar and fiber optic sensing. It is however in the communication arena where RoF seems to be able to provide a technological edge; RoF techniques based...

  16. High-sensitivity attenuated total internal reflection continuous-wave terahertz imaging (United States)

    Liu, Hongxiang; Wang, Yuye; Xu, Degang; Wu, Limin; Yan, Chao; Yan, Dexian; Tang, Longhuang; He, Yixin; Feng, Hua; Yao, Jianquan


    We demonstrate an attenuated total internal reflection imaging system. The surface information of the sample on top of a prism can be acquired by two-dimensionally scanning this prism moving in the vertical plane with horizontally incident continuous terahertz waves at a fixed height. The principles and feasibility of this method are investigated. The effective imaging area on the prism, image resolution and polarization dependence of contrast enhancement and stability improvement are analyzed. Examples including solid agar, distilled water and porcine tissue are presented, demonstrating the method’s advantages of high sensitivity and simple sample preparation. The experimental and theoretical results consistently show that p-polarization contributes to enhanced image contrast and more stable intensity of the attenuated total internal reflected signal.

  17. Convergence of Terahertz Sciences in Biomedical Systems

    CERN Document Server

    Kim, Yong; Han, Haewook; Han, Joon; Ahn, Jaewook; Son, Joo-Hiuk; Park, Woong-Yang; Jeong, Young


    Recent technological breakthrough in the field of Terahertz radiation has triggered new applications in biology and biomedicine. Particularly, biological applications are based on the specific spectroscopic fingerprints of biological matter in this spectral region. Historically with the discovery of new electromagnetic wave spectrum, we have always discovered new medical diagnostic imaging systems. The use of terahertz wave was not realized due to the absence of useful terahertz sources. Now after successful generation of THz waves, it is reported that a great potential for THz wave exists for its resonance with bio-molecules. There are many challenging issues such as development of THz passive and active instrumentations, understanding of THz-Bio interaction for THz spectroscopy, THz-Bio nonlinear phenomena and safety guideline, and THz imaging systems. Eventually the deeper understanding of THz-Bio interaction and novel THz systems enable us to develop powerful THz biomedical imaging systems which can contr...

  18. Terahertz Josephson plasma waves in layered superconductors: spectrum, generation, nonlinear and quantum phenomena (United States)

    Savel'ev, Sergey; Yampol'skii, V. A.; Rakhmanov, A. L.; Nori, Franco


    The recent growing interest in terahertz (THz) and sub-THz science and technology is due to its many important applications in physics, astronomy, chemistry, biology and medicine, including THz imaging, spectroscopy, tomography, medical diagnosis, health monitoring, environmental control, as well as chemical and biological identification. We review the problem of linear and nonlinear THz and sub-THz Josephson plasma waves in layered superconductors and their excitations produced by moving Josephson vortices. We start by discussing the coupled sine-Gordon equations for the gauge-invariant phase difference of the order parameter in the junctions, taking into account the effect of breaking the charge neutrality, and deriving the spectrum of Josephson plasma waves. We also review surface and waveguide Josephson plasma waves. The spectrum of these waves is presented, and their excitation is discussed. We review the propagation of weakly nonlinear Josephson plasma waves below the plasma frequency, ωJ, which is very unusual for plasma-like excitations. In close analogy to nonlinear optics, these waves exhibit numerous remarkable features, including a self-focusing effect and the pumping of weaker waves by a stronger one. In addition, an unusual stop-light phenomenon, when ∂ω/∂k ≈ 0, caused by both nonlinearity and dissipation, can be observed in the Josephson plasma waves. At frequencies above ωJ, the current-phase nonlinearity can be used for transforming continuous sub-THz radiation into short, strongly amplified, pulses. We also present quantum effects in layered superconductors, specifically, the problem of quantum tunneling of fluxons through stacks of Josephson junctions. Moreover, the nonlocal sine-Gordon equation for Josephson vortices is reviewed. We discuss the Cherenkov and transition radiations of the Josephson plasma waves produced by moving Josephson vortices, either in a single Josephson junction or in layered superconductors. Furthermore, the

  19. Frequency selective terahertz retroreflectors (United States)

    Williams, Richard James

    The use of novel optical structures operating at terahertz frequencies in industrial and military applications continues to grow. Some of these novel structures include gratings, frequency selective surfaces, metamaterials and metasurfaces, and retroreflectors. A retroreflector is a device that exhibits enhanced backscatter by concentrating the reflected wave in the direction of the source. Retroreflectors have applications in a variety of diverse fields such as aviation, radar systems, antenna technology, communications, navigation, passive identification, and metrology due to their large acceptance angles and frequency bandwidth. This thesis describes the design, fabrication, and characterization of a retroreflector designed for terahertz frequencies and the incorporation of a frequency selective surface in order to endow the retroreflector with narrow-band frequency performance. The radar cross section of several spherical lens reflectors operating at terahertz frequencies was investigated. Spherical lens reflectors with diameters ranging from 2 mm to 8 mm were fabricated from fused silica ball lenses and their radar cross section was measured at 100 GHz, 160 GHz, and 350 GHz. Crossed-dipole frequency selective surfaces exhibiting band-pass characteristics at 350 GHz fabricated from 12 um-thick Nickel screens were applied to the apertures of the spherical lens reflectors. The radar cross section of the frequency selective retroreflectors was measured at 160 GHz and 350 GHz to demonstrate proof-of-concept of narrow-band terahertz performance.

  20. Compact high-repetition-rate terahertz source based on difference frequency generation from an efficient 2-μm dual-wavelength KTP OPO (United States)

    Mei, Jialin; Zhong, Kai; Wang, Maorong; Liu, Pengxiang; Xu, Degang; Wang, Yuye; Shi, Wei; Yao, Jianquan; Norwood, Robert A.; Peyghambarian, Nasser


    A compact optical terahertz (THz) source was demonstrated based on an efficient high-repetition-rate doubly resonant optical parametric oscillator (OPO) around 2 μm with two type-II phase-matched KTP crystals in the walk-off compensated configuration. The KTP OPO was intracavity pumped by an acousto-optical (AO) Q-switched Nd:YVO4 laser and emitted two tunable wavelengths near degeneracy. The tuning range extended continuously from 2.068 μm to 2.191 μm with a maximum output power of 3.29 W at 24 kHz, corresponding to an optical-optical conversion efficiency (from 808 nm to 2 μm) of 20.69%. The stable pulsed dual-wavelength operation provided an ideal pump source for generating terahertz wave of micro-watt level by the difference frequency generation (DFG) method. A 7.84-mm-long periodically inverted quasi-phase-matched (QPM) GaAs crystal with 6 periods was used to generate a terahertz wave, the maximum voltage of 180 mV at 1.244 THz was acquired by a 4.2-K Si bolometer, corresponding to average output power of 0.6 μW and DFG conversion efficiency of 4.32×10-7. The acceptance bandwidth was found to be larger than 0.35 THz (FWHM). As to the 15-mm-long GaSe crystal used in the type-II collinear DFG, a tunable THz source ranging from 0.503 THz to 3.63 THz with the maximum output voltage of 268 mV at 1.65 THz had been achieved, and the corresponding average output power and DFG conversion efficiency were 0.9 μW and 5.86×10-7 respectively. This provides a potential practical palm-top tunable THz sources for portable applications.

  1. Output-Mirror-Tuning Terahertz-Wave Parametric Oscillator with an Asymmetrical Porro-Prism Resonator Configuration (United States)

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


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

  2. High Reliability Oscillators for Terahertz Systems Project (United States)

    National Aeronautics and Space Administration — Terahertz sources based on lower frequency oscillators and amplifiers plus a chain of frequency multipliers are the workhorse technology for NASA's terahertz...

  3. Double-stacked hyperbolic metamaterial waveguide arrays for efficient and broadband terahertz quarter-wave plates. (United States)

    Ke, Xianmin; Zhu, Hua; Li, Junhao; Chen, Lin; Li, Xun


    We demonstrate how it is possible to achieve weak dispersion in the phase delay between two orthogonal polarization states by using double-stacked hyperbolic metamaterial (HMM) waveguide arrays. The weak dispersion in the phase delay originates from the different signs of phase delay from the two different HMM waveguide arrays. The condition of dispersion-free phase delay for the transmitted waves has been theoretically derived from the transmission matrix as the propagation characteristic of the HMM waveguide is involved. We further reveal that the designed double-stacked HMM waveguide array can function as an efficient quarter-wave plate that enables the conversion of linearly polarized light to circularly polarized light within a broad frequency band. In addition, the bandwidth over which the degree of linear polarization is nearly unity and over which the angle of linear polarization is kept at approximately 45° is basically consistent with the phase bandwidth. This offers a promising approach for developing a practical polarization converter in the terahertz domain.

  4. Intense Plasma Waveguide Terahertz Sources for High-Field THz Probe Science with Ultrafast Lasers for Solid State Physics (United States)


    AFRL-AFOSR-UK-TR-2016-0029 Intense Plasma-Waveguide Terahertz Sources for High-Field THz probe science with ultrafast lasers for Solid State Physics ...Plasma-Waveguide Terahertz Sources for High-Field THz probe science with ultrafast lasers for Solid State Physics , 5a.  CONTRACT NUMBER 5b.  GRANT... Physics Matter Probe 16.  SECURITY CLASSIFICATION OF: 17.  LIMITATION OF ABSTRACT SAR 18.  NUMBER OF PAGES  11  19a.  NAME OF RESPONSIBLE PERSON

  5. Metamaterials for terahertz polarimetric devices

    Energy Technology Data Exchange (ETDEWEB)

    O' hara, John F [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Smirnova, Evgenya [Los Alamos National Laboratory; Azad, Abul [Los Alamos National Laboratory


    We present experimental and numerical investigations of planar terahertz metamaterial structures designed to interact with the state of polarization. The dependence of metamaterial resonances on polarization results in unique amplitude and phase characteristics of the terahertz transmission, providing the basis for polarimetric terahertz devices. We highlight some potential applications for polarimetric devices and present simulations of a terahertz quarter-wave plate and a polarizing terahertz beam splitter. Although this work was performed at terahertz frequencies, it may find applications in other frequency ranges as well.

  6. Real-time continuous-wave terahertz line scanner based on a compact 1 × 240 InGaAs Schottky barrier diode array detector. (United States)

    Han, Sang-Pil; Ko, Hyunsung; Kim, Namje; Lee, Won-Hui; Moon, Kiwon; Lee, Il-Min; Lee, Eui Su; Lee, Dong Hun; Lee, Wangjoo; Han, Seong-Tae; Choi, Sung-Wook; Park, Kyung Hyun


    We demonstrate real-time continuous-wave terahertz (THz) line-scanned imaging based on a 1 × 240 InGaAs Schottky barrier diode (SBD) array detector with a scan velocity of 25 cm/s, a scan line length of 12 cm, and a pixel size of 0.5 × 0.5 mm². Foreign substances, such as a paper clip with a spatial resolution of approximately 1 mm that is hidden under a cracker, are clearly detected by this THz line-scanning system. The system consists of the SBD array detector, a 200-GHz gyrotron source, a conveyor system, and several optical components such as a high-density polyethylene cylindrical lens, metal cylindrical mirror, and THz wire-grid polarizer. Using the THz polarizer, the signal-to-noise ratio of the SBD array detector improves because the quality of the source beam is enhanced.

  7. Electron beam requirements for a three-dimensional Smith-Purcell backward-wave oscillator for intense terahertz radiation

    Directory of Open Access Journals (Sweden)

    Kwang-Je Kim


    Full Text Available A Smith-Purcell device can operate as a backward-wave oscillator for intense, narrow-bandwidth, continuous wave radiation at terahertz wavelengths. We determine the requirements on electron beam current and emittance for the system to oscillate based on a three-dimensional extension of our previous two-dimensional analysis. It is found that specially designed electron beams are required with a current that exceeds a certain threshold value and a flat transverse profile that allows the beam to travel very close to the grating surface. Two methods for producing electron beams with the required characteristics are discussed.

  8. Ultrabroadband terahertz source and beamline based on coherent transition radiation

    Directory of Open Access Journals (Sweden)

    S. Casalbuoni


    Full Text Available Coherent transition radiation (CTR in the THz regime is an important diagnostic tool for analyzing the temporal structure of the ultrashort electron bunches needed in ultraviolet and x-ray free-electron lasers. It is also a powerful source of such radiation, covering an exceptionally broad frequency range from about 200 GHz to 100 THz. At the soft x-ray free-electron laser FLASH we have installed a beam transport channel for transition radiation (TR with the intention to guide a large fraction of the radiation to a laboratory outside the accelerator tunnel. The radiation is produced on a screen inside the ultrahigh vacuum beam pipe of the linac, coupled out through a diamond window and transported to the laboratory through an evacuated tube equipped with five focusing and four plane mirrors. The design of the beamline has been based on a thorough analysis of the generation of TR on metallic screens of limited size. The optical propagation of the radiation has been computed taking into account the effects of near-field (Fresnel diffraction. The theoretical description of the TR source is presented in the first part of the paper, while the design principles and the technical layout of the beamline are described in the second part. First experimental results demonstrate that the CTR beamline covers the specified frequency range and preserves the narrow time structure of CTR pulses emitted by short electron bunches.

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

    CERN Document Server

    Spencer, James


    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 CO2 lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that even lower frequency, superconducting RF seems to be the currently preferred means. Similarly, the validity of modelling 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 calculate radiation from shaped transmission lines using finite-difference, time-domain (FDTD) simulations of Maxwell’s equations coupled to Monte-Carlo techniques for both the production and transport physics of short electron pulses. Examples of THz sources that demonstrate coherent interference effects will be discussed with the goal o...

  10. Velocity-matching dispersion maps for zincblende and chalcopyrite terahertz sources (United States)

    Rowley, Joseph; Zawilski, Kevin; Schunemann, Peter; Bas, Derek; Bristow, Alan


    Pulsed terahertz radiation has been shown to be a useful diagnostic in fundamental and applied science. A common method for generating pulsed THz is by optical rectification. (110)-cut ZnGeP2 was previously demonstrated as an efficient source of broadband THz radiation for near-infrared pump pulses, while other orientations have been modeled to show equal or greater efficiency. Here we explore and compare phase-matching in ZnGeP2 to that in other commonly used near-infrared THz sources including GaAs and GaP. We experimentally demonstrate that the three most efficient orientations provide distinct phase-matching configurations and thus distinct phase-matched near-infrared and THz frequencies. Our calculations also show that thin (~100 micron) crystals of ZGP may be promising sources for phase-matched and broadband THz emission out to 9 THz for 850 nm pump pulses.

  11. Low-bias active control of terahertz waves by coupling large-area CVD graphene to a terahertz metamaterial. (United States)

    Valmorra, Federico; Scalari, Giacomo; Maissen, Curdin; Fu, Wangyang; Schönenberger, Christian; Choi, Jong Won; Park, Hyung Gyu; Beck, Mattias; Faist, Jérôme


    We propose an hybrid graphene/metamaterial device based on terahertz electronic split-ring resonators directly evaporated on top of a large-area single-layer CVD graphene. Room temperature time-domain spectroscopy measurements in the frequency range from 250 GHz to 2.75 THz show that the presence of the graphene strongly changes the THz metamaterial transmittance on the whole frequency range. The graphene gating allows active control of such interaction, showing a modulation depth of 11.5% with an applied bias of 10.6 V. Analytical modeling of the device provides a very good qualitative and quantitative agreement with the measured device behavior. The presented system shows potential as a THz modulator and can be relevant for strong light-matter coupling experiments.

  12. Detection of foreign bodies in foods using continuous wave terahertz imaging. (United States)

    Lee, Young-Ki; Choi, Sung-Wook; Han, Seong-Tae; Woo, Deog Hyun; Chun, Hyang Sook


    Foreign bodies (FBs) in food are health hazards and quality issues for many food manufacturers and enforcement authorities. In this study, continuous wave (CW) terahertz (THz) imaging at 0.2 THz with an output power of 10 mW was compared with X-ray imaging as techniques for inspection of food for FBs. High-density FBs, i.e., aluminum and granite pieces of various sizes, were embedded in a powdered instant noodle product and detected using THz and X-ray imaging. All aluminum and granite pieces (regular hexahedrons with an edge length of 1 to 5 mm) were visualized by both CW THz and X-ray imaging. THz imaging also detected maggots (length = 8 to 22 mm) and crickets (length = 35 and 50 mm), which were embedded in samples as low density FBs. However, not all sizes of maggot pieces embedded in powdered instant noodle were detected with X-ray imaging, although larger crickets (length = 50 mm and thickness = 10 mm) were detected. These results suggest that CW THz imaging has potential for detecting both high-density and low-density FBs embedded in food.

  13. EDITORIAL: Terahertz nanotechnology Terahertz nanotechnology (United States)

    Demming, Anna; Tonouchi, Masayoshi; Reno, John L.


    A useful synergy is being established between terahertz research and nanotechnology. High power sources [1-3] and detectors [4] in what was once considered the terahertz 'frequency gap' [5] in the electromagnetic spectrum have stimulated research with huge potential benefits in a range of industries including food, medicine and security, as well as fundamental physics and astrophysics. This special section, with guest editors Masayoshi Tonouchi and John Reno, gives a glimpse of the new horizons nanotechnology is broaching in terahertz research. While the wavelengths relevant to the terahertz domain range from hundreds of micrometres to millimetres, structures at the nanoscale reveal interesting low energy dynamics in this region. As a result terahertz spectroscopy techniques are becoming increasingly important in nanomaterial characterization, as demonstrated in this special section by colleagues at the University of Oxford in the UK and the Australian National University. They use terahertz spectroscopy to identify the best nanostructure parameters for specific applications [6]. The low energy dynamics in nanostructures also makes them valuable tools for terahertz detection [7]. In addition the much sought after terahertz detection over broadband frequency ranges has been demonstrated, providing versatility that has been greatly in demand, particularly in spectroscopy applications [8, 9]. Also in this special section, researchers in Germany and China tackle some of the coupling issues in terahertz time domain spectroscopy with an emitter specifically well suited for systems operated with an amplified fibre [3]. 'In medical imaging, the advantage of THz radiation is safety, because its energy is much lower than the ionization energy of biological molecules, in contrast to hazardous x-ray radiation,' explains Joo-Hiuk Son from the University of Seoul in Korea in his review [10]. As he also points out, the rotational and vibrational energies of water molecules are

  14. Terahertz in-line digital holographic multiplane imaging method (United States)

    Huang, Haochong; Wang, Dayong; Rong, Lu; Li, Weihua; Wang, Yunxin


    Terahertz waves of which frequency spans from 0.1 to 10 THz bridge the gap between the infrared spectrum and microwaves. Owing to the special features of terahertz wave, such as penetrability and non-ionizing, terahertz imaging technique is a very significant and important method for inspections and detections. Digital holography can reconstruct the amplitude and phase distributions of a sample without scanning and it already has many successful applications in the area of visible and infrared light. The terahertz in-line digital holographic multi-plane imaging system which is presented in this paper is the combination of a continuous-wave terahertz source and the in-line scheme of digital holography. In order to observe a three dimensional (3D) shape sample only a portion of which appears in good focus, the autofocusing algorithm is brought to the data process. The synthetic aperture method is also applied to provide the high resolution imaging effect in the terahertz waveband. Both intrinsic twin images and defocused objective images confuse the quality of the image in an individual reconstructed plane. In order to solve this issue, phase retrieval iteration algorithm is used for the reconstruction. In addition, the reconstructed amplitude image in each plane multiplies the mask of which the threshold depends on the values of the autofocusing curve. A sample with simple artificial structure is observed which verifies that the present method is an authentic tool to acquire the multi-plane information of a target in terahertz waves. It can expect a wide application in terahertz defect detecting, terahertz medical inspection and other important areas in the future.

  15. Fast mapping of terahertz bursting thresholds and characteristics at synchrotron light sources

    Directory of Open Access Journals (Sweden)

    Miriam Brosi


    Full Text Available Dedicated optics with extremely short electron bunches enable synchrotron light sources to generate intense coherent THz radiation. The high degree of spatial compression in this so-called low-α_{c} optics entails a complex longitudinal dynamics of the electron bunches, which can be probed studying the fluctuations in the emitted terahertz radiation caused by the microbunching instability (“bursting”. This article presents a “quasi-instantaneous” method for measuring the bursting characteristics by simultaneously collecting and evaluating the information from all bunches in a multibunch fill, reducing the measurement time from hours to seconds. This speed-up allows systematic studies of the bursting characteristics for various accelerator settings within a single fill of the machine, enabling a comprehensive comparison of the measured bursting thresholds with theoretical predictions by the bunched-beam theory. This paper introduces the method and presents first results obtained at the ANKA synchrotron radiation facility.

  16. Enhanced Cherenkov phase matching terahertz wave generation via a magnesium oxide doped lithium niobate ridged waveguide crystal (United States)

    Takeya, K.; Minami, T.; Okano, H.; Tripathi, S. R.; Kawase, K.


    When combined with a nonlinear waveguide crystal, Cherenkov phase matching allows for highly effective generation of high power and broadband terahertz (THz) waves. Using a ridged Lithium Niobate (LiNbO3) waveguide coupled with a specially designed silicon lens, we successfully generated THz waves with intensity of approximately three orders of magnitude stronger than those from conventional photoconductive antenna. The broadband spectrum was from 0.1 THz to 7 THz with a maximum dynamic range of 80 dB. The temporal shape of time domain pulse is a regular single cycle which could be used for high depth resolution time of flight tomography. The generated THz wave can also be easily monitored by compact room-temperature THz camera, enabling us to determine the spatial characteristics of the THz propagation.

  17. Enhanced Cherenkov phase matching terahertz wave generation via a magnesium oxide doped lithium niobate ridged waveguide crystal

    Directory of Open Access Journals (Sweden)

    K. Takeya


    Full Text Available When combined with a nonlinear waveguide crystal, Cherenkov phase matching allows for highly effective generation of high power and broadband terahertz (THz waves. Using a ridged Lithium Niobate (LiNbO3 waveguide coupled with a specially designed silicon lens, we successfully generated THz waves with intensity of approximately three orders of magnitude stronger than those from conventional photoconductive antenna. The broadband spectrum was from 0.1 THz to 7 THz with a maximum dynamic range of 80 dB. The temporal shape of time domain pulse is a regular single cycle which could be used for high depth resolution time of flight tomography. The generated THz wave can also be easily monitored by compact room-temperature THz camera, enabling us to determine the spatial characteristics of the THz propagation.

  18. Wind wave source functions in opposing seas

    KAUST Repository

    Langodan, Sabique


    The Red Sea is a challenge for wave modeling because of its unique two opposed wave systems, forced by opposite winds and converging at its center. We investigate the different physical aspects of wave evolution and propagation in the convergence zone. The two opposing wave systems have similar amplitude and frequency, each driven by the action of its own wind. Wave patterns at the centre of the Red Sea, as derived from extensive tests and intercomparison between model and measured data, suggest that the currently available wave model source functions may not properly represent the evolution of the local fields that appear to be characterized by a less effective wind input and an enhanced white-capping. We propose and test a possible simple solution to improve the wave-model simulation under opposing winds and waves condition. This article is protected by copyright. All rights reserved.

  19. Metamaterials for terahertz polarimetric devices

    Energy Technology Data Exchange (ETDEWEB)

    O' hara, John F [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Smirnova, Evgenya [Los Alamos National Laboratory; Azad, Abul [Los Alamos National Laboratory; Chen, Hou-tong [Los Alamos National Laboratory; Peralta, Xomalin G [SNL; Brener, Igal [SNL


    We present experimental and numerical investigations of planar terahertz metamaterial structures designed to interact with the state of polarization. The dependence of metamaterial resonances on polarization results in unique amplitude and phase characteristics of the terahertz transmission, providing the basis for polarimetric terahertz devices. We highlight some potential applications for polarimetric devices and present simulations of a terahertz quarter-wave plate and a polarizing terahertz beam splitter. Although this work was performed at tcrahertz frequencies, it may find applications in other frequency ranges as well.

  20. [Research progress in the application of biosensors by using metamaterial in terahertz wave]. (United States)

    Yan, Xin; Zhang, Xing-Fang; Liang, Lan-Ju; Yao, Jian-Quan


    In the present paper, the recent progress in terahertz metamaterials-based sensing is reviewed with the principle of metamaterial biosensor,metamaterial substrate, and structure design, respectively. The paper introduces the principle in detail, analyzes the sensitivity of the biosensor with the material and the thickness of the substrate and the structure of metamaterial. The analysis shows that we can enhance the sensitivity and resolution of biosensor by designing specific metamaterial structure, using low dielectric constant and low loss thin substrate, especially many materials have a specific response in the terahertz frequency. So, there is a large potential application for label-free sensing by using the terahertz metamaterials. This paper also presents the future development of THz metamaterial sensors.

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

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, A. A., E-mail: [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)


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

  2. Effect of continuous irradiation with terahertz electromagnetic waves of the NO frequency range on behavioral reactions of male albino rats under stress conditions. (United States)

    Kirichuk, V F; Antipova, O N; Krylova, Ya A


    We studied the effect of terahertz waves (NO frequency range, 150.176-150.664 GHz) on stress-induced variations in behavioral reactions of male albino rats during hypokinetic stress. THz irradiation was followed by partial or complete normalization of behavioral reactions of male albino rats after hypokinetic stress. The most significant effect was observed after continuous irradiation for 30 min.

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

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xuemin; Shen, Changle; Jiang, Tao; Zhan, Zhiqiang; Deng, Qinghua; Li, Weihua; Wu, Weidong, E-mail: [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, 621900, Sichuan (China); Yang, Ning; Chu, Weidong; Duan, Suqing [Institute of Applied Physics and Computational Mathematics, Beijing, 100088 (China)


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

  4. Characteristics of terahertz wave modulation using wavelength-selective photoexcitation in pentacene/Si and TIPS pentacene/Si bilayers

    Directory of Open Access Journals (Sweden)

    Hyung Keun Yoo


    Full Text Available We demonstrate the characteristics of the optical control of terahertz (THz wave transmission in photoexcited bilayers of pentacene/Si and 6,13-bis(triisopropylsilylethynyl pentacene (TIPS pentacene/Si. The modulation efficiency is influenced significantly by the photoexcitation wavelength of the optical beams. Lower optical absorption of organic materials leads to higher modulation efficiency because the photocarriers excited on Si with a higher diffusion rate and mobility are far more instrumental in increasing the modulation than the excitons generated on the organic layers. Securing a sufficient depth for carrier diffusion on organic layers is also important for increasing the THz modulation efficiency. These findings may be useful for designing highly efficient and spectrally controllable THz wave modulators.

  5. Terahertz Coherent Synchrotron Radiation from Femtosecond Laser Modulation of the Electron Beam at the Advanced Light Source

    CERN Document Server

    Byrd, John; Martin, Michael C; Robin, David; Sannibale, Fernando; Schönlein, Robert W; Zholents, Alexander; Zolotorev, Max S


    At the Advanced Light Source (ALS), the "femtoslicing" beamline is in operation since 1999 for the production of x-ray synchrotron radiation pulses with femtosecond duration. The mechanism used for generating the short x-ray pulses induces at the same time temporary structures in the electron bunch longitudinal distribution with very short characteristic length. Such structures emit intense coherent synchrotron radiation (CSR) in the terahertz frequency range. This CSR, whose measured intensity is routinely used as a diagnostics for the tune-up of the femtoslicing experiments, represents a potential source of terahertz radiation with very interesting features. Several measurements have been performed for its characterization and in this paper an updated description of the experimental results and of their interpretation is presented.

  6. Photomlxer for terahertz electromagnetic wave emission comprising quantum dots in a laser cavity

    DEFF Research Database (Denmark)


    The present invention relates to a photomixer for generating terahertz electromagnetic radiation in response to illumination by a time-modulated optical signal. The photomixer (300) comprises a carrier substrate (310) with a plurality of quantum dots arranged in an emission region (308) thereof...

  7. Source Estimation by Full Wave Form Inversion

    Energy Technology Data Exchange (ETDEWEB)

    Sjögreen, Björn [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Center for Applied Scientific Computing; Petersson, N. Anders [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Center for Applied Scientific Computing


    Given time-dependent ground motion recordings at a number of receiver stations, we solve the inverse problem for estimating the parameters of the seismic source. The source is modeled as a point moment tensor source, characterized by its location, moment tensor components, the start time, and frequency parameter (rise time) of its source time function. In total, there are 11 unknown parameters. We use a non-linear conjugate gradient algorithm to minimize the full waveform misfit between observed and computed ground motions at the receiver stations. An important underlying assumption of the minimization problem is that the wave propagation is accurately described by the elastic wave equation in a heterogeneous isotropic material. We use a fourth order accurate finite difference method, developed in [12], to evolve the waves forwards in time. The adjoint wave equation corresponding to the discretized elastic wave equation is used to compute the gradient of the misfit, which is needed by the non-linear conjugated minimization algorithm. A new source point moment source discretization is derived that guarantees that the Hessian of the misfit is a continuous function of the source location. An efficient approach for calculating the Hessian is also presented. We show how the Hessian can be used to scale the problem to improve the convergence of the non-linear conjugated gradient algorithm. Numerical experiments are presented for estimating the source parameters from synthetic data in a layer over half-space problem (LOH.1), illustrating rapid convergence of the proposed approach.

  8. Gravitational Waves, Sources and Detectors


    Schutz, B; Ricci, F


    Gravitational waves and their detection are becoming more and more important both for the theoretical physicist and the astrophysicist. In fact, technological developments have enabled the construction such sensitive detectors (bars and interferometers) that the detection of gravitational radiation could become a reality during the next few years. In these lectures we give a brief overview of this interesting and challenging field of modern physics. The topics to be covered are divided into ...

  9. Toward realizing high power semiconductor terahertz laser sources at room temperature (United States)

    Razeghi, Manijeh


    The terahertz (THz) spectral range offers promising applications in science, industry, and military. THz penetration through nonconductors (fabrics, wood, plastic) enables a more efficient way of performing security checks (for example at airports), as illegal drugs and explosives could be detected. Being a non-ionizing radiation, THz radiation is environment-friendly enabling a safer analysis environment than conventional X-ray based techniques. However, the lack of a compact room temperature THz laser source greatly hinders mass deployment of THz systems in security check points and medical centers. In the past decade, tremendous development has been made in GaAs/AlGaAs based THz Quantum Cascade Laser (QCLs), with maximum operating temperatures close to 200 K (without magnetic field). However, higher temperature operation is severely limited by a small LO-phonon energy (~ 36 meV) in this material system. With a much larger LO-phonon energy of ~ 90 meV, III-Nitrides are promising candidates for room temperature THz lasers. However, realizing high quality material for GaN-based intersubband devices presents a significant challenge. Advances with this approach will be presented. Alternatively, recent demonstration of InP based mid-infrared QCLs with extremely high peak power of 120 W at room temperature opens up the possibility of producing high power THz emission with difference frequency generation through two mid-infrared wavelengths.

  10. Multiple-beam output of a surface-emitted terahertz-wave parametric oscillator by using a slab MgO:LiNbO₃ crystal. (United States)

    Wang, Weitao; Zhang, Xingyu; Wang, Qingpu; Cong, Zhenhua; Chen, Xiaohan; Liu, Zhaojun; Qin, Zengguang; Li, Ping; Tang, Guanqi; Li, Ning; Wang, Cong; Li, Yongfu; Cheng, Wenyong


    A MgO:LiNbO₃ slab configuration for the surface-emitted terahertz-wave parametric oscillator (TPO) is presented. The pump and the oscillating Stokes beams were totally reflected at the slab surface and propagated zigzaggedly in the slab MgO:LiNbO₃ crystal. Up to five terahertz beams were emitted perpendicularly to the surface of the crystal. The total output energy of the five THz-wave beams was 3.56 times as large as that obtained from the conventional surface-emitted TPO at the same experimental conditions. The intensity distributions of the THz wave beams were measured, and they were unsymmetrical in the horizontal direction while symmetrical in the vertical direction.

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

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Gangyi, E-mail: [Institut d' Electronique Fondamentale, Univ. Paris Sud, UMR8622 CNRS, 91405 Orsay (France); Key Laboratory of Infrared Imaging Materials and Detectors, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Li, Lianhe; Giles Davies, A.; Linfield, Edmund H. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS9 2JT (United Kingdom); Isac, Nathalie; Halioua, Yacine; Colombelli, Raffaele, E-mail: [Institut d' Electronique Fondamentale, Univ. Paris Sud, UMR8622 CNRS, 91405 Orsay (France)


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

  12. Love waves excited by a moving source (United States)

    Zaslavskii, Yu. M.


    The study analyzes the characteristics of surface Love waves excited by the moment of an oscillating torsional force with a point of action that moves uniformly and rectilinearly along the free flat boundary of a medium having the structure of a "layer on a half-space." The azimuthal-angular distribution of the amplitude and Doppler shift in frequency of the wave modes is studied as a function of the motion velocity of a vibrating source and the parameters of the medium.

  13. Terahertz Spectroscopy and Imaging

    CERN Document Server

    Zeitler, Axel; Kuwata-Gonokami, Makoto


    "This book presents the current state of knowledge in the field of terahertz spectroscopy, providing a comprehensive source of information for beginners and experienced researchers alike whose interests lie in this area. The book aims to explain the fundamental physics that underpins terahertz  technology and to describe its key applications. Highlights of scientific research in the field of terahertz science are also outlined in some chapters, providing an overview as well as giving an insight into future directions for research.  Over the past decade terahertz spectroscopy has developed into one of the most rapidly growing areas of its kind, gaining an important impact across a wide range of scientific disciplines. Due to substantial advances in femtosecond laser technology, terahertz time-domain spectroscopy (THz-TDS) has established itself as the dominant spectroscopic technique for experimental scientists interested in measurements at this frequency range. In solids and liquids THz radiation is in reso...

  14. Trapping waves with terahertz metamaterial absorber based on isotropic Mie resonators. (United States)

    Yahiaoui, Riad; Hanai, Kenichiro; Takano, Keisuke; Nishida, Tsubasa; Miyamaru, Fumiaki; Nakajima, Makoto; Hangyo, Masanori


    Quasi-monodisperse dielectric particles organized in a periodic hexagonal network on an aluminum surface are exploited numerically and experimentally as a single-layered near-perfect absorber in the terahertz regime. Of particular interest are titanium dioxide (TiO(2)) microspheres because of their large dielectric permittivity and isotropic shape leading to Mie resonances with insensitive polarization. Absorption higher than 80% at normal incidence covering two distinct ranges of frequencies is demonstrated experimentally. Furthermore, the performance of the metamaterial absorber is kept over a wide range of incident angles.

  15. Modeling of a Compact Terahertz Source based on the Two-Stream Instability

    Energy Technology Data Exchange (ETDEWEB)

    Svimonishvili, Tengiz [Univ. of New Mexico, Albuquerque, NM (United States)


    THz radiation straddles the microwave and infrared bands of the electromagnetic spectrum, thus combining the penetrating power of lower-frequency waves and imaging capabilities of higher-energy infrared radiation. THz radiation is employed in various elds such as cancer research, biology, agriculture, homeland security, and environmental monitoring. Conventional vacuum electronic sources of THz radiation (e.g., fast- and slow-wave devices) either require very small structures or are bulky and expensive to operate. Optical sources necessitate cryogenic cooling and are presently capable of producing milliwatt levels of power at THz frequencies. We propose a millimeter and sub-millimeter wave source based on a well-known phenomenon called the two-stream instability. The two-beam source relies on lowenergy and low-current electron beams for operation. Also, it is compact, simple in design, and does not contain expensive parts that require complex machining and precise alignment. In this dissertation, we perform 2-D particle-in-cell (PIC) simulations of the interaction region of the two-beam source. The interaction region consists of a beam pipe of radius ra and two electron beams of radius rb co-propagating and interacting inside the pipe. The simulations involve the interaction of unmodulated (no initial energy modulation) and modulated (energy-modulated, seeded at a given frequency) electron beams. In addition, both cold (monoenergetic) and warm (Gaussian) beams are treated.

  16. Gravitational wave sources: reflections and echoes (United States)

    Price, Richard H.; Khanna, Gaurav


    The recent detection of gravitational waves has generated interest in alternatives to the black hole interpretation of sources. A subset of such alternatives involves a prediction of gravitational wave ‘echoes’. We consider two aspects of possible echoes: first, general features of echoes coming from spacetime reflecting conditions. We find that the detailed nature of such echoes does not bear any clear relationship to quasi-normal frequencies. Second, we point out the pitfalls in the analysis of local reflecting ‘walls’ near the horizon of rapidly rotating black holes.

  17. A Design of Terahertz Parallel Plate Dielectric Waveguide with Signal Line inserted for Ballistic Deflection Transistor Travelling Wave Amplifier (United States)

    Wang, H.; Knepper, R.; Hossain, N.; Marthi, P.; Milithaler, J.-F.; Margala, M.


    In this paper a new waveguide design is proposed to be implemented as part of Ballistic Deflection Transistor (BDT) Traveling Wave Amplifier Design. The BDT is designed to be operated in the Terahertz regime. Due to its relatively low transconductance (gm=200µA/V), the entire structure will consist of ten stages, with 15 BDTs/stage, to reach a total gain of 30mA/V. In this case, the total length of the transmission line will be more than 400µm. We did the investigation for different structures and materials of the transmission line. For our Parallel Plate Dielectric Waveguide with Signal Line inserted (PPDWS) design, we are able to get an average loss of 0.46dB/mm at 0.8-1.4THz from ANSYS HFSS simulation. The return loss for input and output are better than -20dB at 0.8-1.7THz. Although it is designed for our future travelling wave amplifier, it can also be used for various other THz frequency applications.

  18. Terahertz semiconductor-heterostructure laser. (United States)

    Köhler, Rüdeger; Tredicucci, Alessandro; Beltram, Fabio; Beere, Harvey E; Linfield, Edmund H; Davies, A Giles; Ritchie, David A; Iotti, Rita C; Rossi, Fausto


    Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications--for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.

  19. Scattering properties of electromagnetic waves from metal object in the lower terahertz region (United States)

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


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

  20. Engineering the Losses and Beam Divergence in Arrays of Patch Antenna Microcavities for Terahertz Sources (United States)

    Madéo, Julien; Pérez-Urquizo, Joel; Todorov, Yanko; Sirtori, Carlo; Dani, Keshav M.


    We perform a comprehensive study on the emission from finite arrays of patch antenna microcavities designed for the terahertz range by using a finite element method. The emission properties including quality factors, far-field pattern, and photon extraction efficiency are investigated for etched and non-etched structures as a function of the number of resonators, the dielectric layer thickness, and period of the array. In addition, the simulations are achieved for lossy and perfect metals and dielectric layers, allowing to extract the radiative and non-radiative contributions to the total quality factors of the arrays. Our study shows that this structure can be optimized to obtain low beam divergence (FWHM 50% while keeping a strongly localized mode. These results show that the use of these microcavities would lead to efficient terahertz emitters with a low divergence vertical emission and engineered losses.

  1. Terahertz radiation source using a high-power industrial electron linear accelerator (United States)

    Kalkal, Yashvir; Kumar, Vinit


    High-power (˜ 100 kW) industrial electron linear accelerators (linacs) are used for irradiations, e.g., for pasteurization of food products, disinfection of medical waste, etc. We propose that high-power electron beam from such an industrial linac can first pass through an undulator to generate useful terahertz (THz) radiation, and the spent electron beam coming out of the undulator can still be used for the intended industrial applications. This will enhance the utilization of a high-power industrial linac. We have performed calculation of spontaneous emission in the undulator to show that for typical parameters, continuous terahertz radiation having power of the order of μW can be produced, which may be useful for many scientific applications such as multispectral imaging of biological samples, chemical samples etc.

  2. LIGHT SOURCE: Terahertz emission in tenuous gases irradiated by ultrashort laser pulses (United States)

    Wang, Wei-Min; Sheng, Zheng-Ming; Wit, Hui-Chun; Chen, Min; Li, Chun; Zhang, Jie; Mima, K.


    Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed.

  3. Unbiased continuous wave terahertz photomixer emitters with dis-similar Schottky barriers. (United States)

    Mohammad-Zamani, Mohammad Javad; Moravvej-Farshi, Mohammad Kazem; Neshat, Mohammad


    We are introducing a new bias free CW terahertz photomixer emitter array. Each emitter consists of an asymmetric metal-semiconductor-metal (MSM) that is made of two side by side dis-similar Schottky contacts, on a thin layer of low temperature grown (LTG) GaAs, with barrier heights of difference (ΔΦ(B)) and a finite lateral spacing (s). Simulations show that when an appropriately designed structure is irradiated by two coherent optical beams of different center wavelengths, whose frequency difference (∆f) falls in a desired THz band, the built-in field between the two dis-similar potential barriers can accelerate the photogenerated carriers that are modulated by ∆ω, making each pitch in the array to act as a CW THz emitter, effectively. We also show the permissible values of s and ΔΦ(B) pairs, for which the strengths of the built-in electric field maxima fall below that of the critical of 50 V/μm- i.e., the breakdown limit for the LTG-GaAs layer. Moreover, we calculate the THz radiation power per emitter in an array. Among many potential applications for these bias free THz emitters their use in endoscopic imaging without a need for hazardous external biasing circuitry that reduces the patient health risk, could be the most important one. A hybrid numerical simulation method is used to design an optimum emitter pitch, radiating at 0.5 THz.

  4. Observation of Gate-Tunable Coherent Perfect Absorption of Terahertz Waves in Graphene (United States)

    Kocabas, Coskun; Kakenov, Nurbek; Balci, Osman; Takan, Taylan; Ozkan, Vedat Ali; Altan, Hakan

    We report experimental observation of electrically tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode, and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1 eV and to achieve a critical coupling condition at 2.8 THz with absorption of 100 %. With the enhanced THz absorption, we were able to measure the Fermi energy dependence of the transport scattering time of highly doped graphene. Furthermore, we demonstrate flexible active THz surfaces that yield large modulation in the THz reflectivity with low insertion losses. We anticipate that the gate-tunable CPA will lead to efficient active THz optoelectronics applications. This work was partially supported by the Scientific and Technological Research Council of Turkey (TUBITAK) Grant No. 114F379 and the European Research Council (ERC) Consolidator Grant ERC-682723 SmartGraphene. N.K. acknowledges the TUBITAK-BIDEB 2215.

  5. Terahertz Quantum Cascade Laser With Efficient Coupling and Beam Profile (United States)

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


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

  6. Analysis and Simulation of Generating Terahertz Surface Waves in Laser-Assisted Field Emission (United States)

    Hagmann, Mark; Kumar, Gagan; Pandey, Shashank; Nahata, Ajay


    When the radiation from two lasers is focused on a field emission diode the electric field from the radiation is superimposed on the applied DC field, and the nonlinear dependence of the emitted current on the electric field causes the current to oscillate at the difference frequency for the two lasers. Finite Difference-Time Domain simulations and analytical solutions for a paraboloidal model of the field emission tip show that the current oscillations create a transverse-magnetic (TM) surface wave on the tip. The analytical solution for the TM fields in paraboloidal coordinates consists of products of regular and irregular Coulomb wave functions. The width of the tip is much smaller than the skin depth so interior and exterior solutions are required and a summation of the products is required to satisfy the boundary conditions at the surface of the tip. The simulations are consistent with the analytical solution and show that there is a quasi-stationary region near the apex, a transition region where the surface waves are formed, and the far-field where the waves propagate outward on the tip.

  7. Complex space source theory of spatially localized electromagnetic waves

    CERN Document Server

    Seshadri, SR


    The author highlights that there is a need obtain exact full-wave solutions that reduce to the paraxial beams in the appropriate limit. Complex Space Source Theory of Spatially Localized Electromagnetic Waves treats the exact full-wave generalizations of all the basic types of paraxial beam solutions. These are developed by the use of Fourier and Bessel transform techniques and the complex space source theory of spatially localized electromagnetic waves is integrated as a branch of Fourier optics.

  8. Terahertz Radome Inspection

    Directory of Open Access Journals (Sweden)

    Fabian Friederich


    Full Text Available Radomes protecting sensitive radar, navigational, and communications equipment of, e.g., aircraft, are strongly exposed to the environment and have to withstand harsh weather conditions and potential impacts. Besides their significance to the structural integrity of the radomes, it is often crucial to optimize the composite structures for best possible radio performance. Hence, there exists a significant interest in non-destructive testing techniques, which can be used for defect inspection of radomes in field use as well as for quality inspection during the manufacturing process. Contactless millimeter-wave and terahertz imaging techniques provide millimeter resolution and have the potential to address both application scenarios. We report on our development of a three-dimensional (3D terahertz imaging system for radome inspection during industrial manufacturing processes. The system was designed for operation within a machining center for radome manufacturing. It simultaneously gathers terahertz depth information in adjacent frequency ranges, from 70 to 110 GHz and from 110 to 170 GHz by combining two frequency modulated continuous-wave terahertz sensing units into a single measurement device. Results from spiraliform image acquisition of a radome test sample demonstrate the successful integration of the measurement system.

  9. Linear and nonlinear properties of chalcogenide glasses in the terahertz frequency

    DEFF Research Database (Denmark)

    Zalkovskij, Maksim; Malureanu, Radu; Popescu, A.


    Terahertz (THz) waves have the potential to improve a wide range of devices in the space, defense and semiconductor industries as well as offering the possibility of investigating various molecules of interest in biology, medicine, art etc. For this reason, THz sources, detectors and passive linear...

  10. Influence of the electron density on the characteristics of terahertz waves generated under laser–cluster interaction

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, A. A., E-mail: [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)


    A theory of generation of terahertz radiation under laser–cluster interaction, developed earlier for an overdense cluster plasma [A. A. Frolov, Plasma Phys. Rep. 42. 637 (2016)], is generalized for the case of arbitrary electron density. The spectral composition of radiation is shown to substantially depend on the density of free electrons in the cluster. For an underdense cluster plasma, there is a sharp peak in the terahertz spectrum at the frequency of the quadrupole mode of a plasma sphere. As the electron density increases to supercritical values, this spectral line vanishes and a broad maximum at the frequency comparable with the reciprocal of the laser pulse duration appears in the spectrum. The dependence of the total energy of terahertz radiation on the density of free electrons is analyzed. The radiation yield is shown to increase significantly under resonance conditions, when the laser frequency is close to the eigenfrequency of the dipole or quadrupole mode of a plasma sphere.

  11. High-energy and ultra-wideband tunable terahertz source with DAST crystal via difference frequency generation (United States)

    He, Yixin; Wang, Yuye; Xu, Degang; Nie, Meitong; Yan, Chao; Tang, Longhuang; Shi, Jia; Feng, Jiachen; Yan, Dexian; Liu, Hongxiang; Teng, Bing; Feng, Hua; Yao, Jianquan


    We have demonstrated a high-energy and broadly tunable monochromatic terahertz (THz) source based on difference frequency generation (DFG) in DAST crystal. A high-energy dual-wavelength optical parametric oscillator with two KTP crystals was constructed as a light source for DFG, where the effect of blue light was first observed accompanying with tunable dual-wavelength pump light due to different nonlinear processes. The THz frequency was tuned randomly in the range of 0.3-19.6 THz. The highest energy of 870 nJ/pulse was obtained at 18.9 THz under the intense pump intensity of 247 MW/cm2. The THz energy dips above 3 THz have been analyzed and mainly attributed to the resonance absorption induced by lattice vibration in DAST crystal. The dependence of THz output on the input energy was studied experimentally, and THz output saturation was observed. Furthermore, tests of transmission spectroscopy of four typical samples were demonstrated with this ultra-wideband THz source.

  12. Domain-Reversed Lithium Niobate Single-Crystal Fibers are Potentially for Efficient Terahertz Wave Generation

    Directory of Open Access Journals (Sweden)

    Yalin Lu


    Full Text Available Nonlinear frequency conversion remains one of the dominant approaches to efficiently generate THz waves. Significant material absorption in the THz range is the main factor impeding the progress towards this direction. In this research, a new multicladding nonlinear fiber design was proposed to solve this problem, and as the major experimental effort, periodic domain structure was introduced into lithium niobate single-crystal fibers by electrical poling. The introduced periodic domain structures were nondestructively revealed using a crossly polarized optical microscope and a confocal scanning optical microscope for quality assurance.

  13. A new class of electrically tunable metamaterial terahertz modulators. (United States)

    Yan, Rusen; Sensale-Rodriguez, Berardi; Liu, Lei; Jena, Debdeep; Xing, Huili Grace


    Switchable metamaterials offer unique solutions for efficiently manipulating electromagnetic waves, particularly for terahertz waves, which has been difficult since naturally occurring materials rarely respond to terahertz frequencies controllably. However, few terahertz modulators demonstrated to date exhibit simultaneously low attenuation and high modulation depth. In this letter we propose a new class of electrically-tunable terahertz metamaterial modulators employing metallic frequency-selective-surfaces (FSS) in conjunction with capacitively-tunable layers of electrons, promising near 100% modulation depth and graphene, Si, MoS(2), oxides etc, thus opening up myriad opportunities for realizing high performance switchable metamaterials over an ultra-wide terahertz frequency range.

  14. Study of rectangular beam folded waveguide traveling-wave tube for terahertz radiation (United States)

    Lu, Fengying; Zhang, Changqing; Grieser, Manfred; Wang, Yong; Lü, Suye; Zhao, Guohui


    To gain higher power with a lower cathode current density and a simpler structure, a novel rectangular beam folded waveguide traveling-wave tube (RB-FW-TWT) operating at 220 GHz is proposed and analyzed in this paper and compared with the normal circular beam (CB) FW TWT. The dispersion characteristic was investigated based on an equivalent circuit model. The interaction impedance and the S-parameter of a RB-FW traveling-wave tube were analyzed by numerical simulations. A 3-D particle-in-cell code CST particle studio was introduced to analyze the performance of RB-FW TWT. The influence of the initial electron energy, frequency, input power, guiding magnetic field, and aspect ratio of the RB tunnel on the circuit performance was observed, and physical explanations were given. It reveals that the output power of RB-FW can reach 51.1 dBm, 8.4% dBm higher than a CB-FW, with a 3 dB bandwidth of 35 GHz when the beam voltage and current are set to 14.25 kV and 140 mA, respectively. An aspect ratio of 0.4 is recommended to optimize the high-frequency properties and circuit performance.

  15. Terahertz Frequency Metrology for Spectroscopic Applications: a Review (United States)

    Consolino, L.; Bartalini, S.; De Natale, P.


    We provide an overview on terahertz (THz) frequency metrology, starting from the nowadays available continuous wave THz sources, discussing their main features such as tunability, spectral purity, and frequency referencing to the primary frequency standards. A comparison on the achieved results in high-precision molecular spectroscopy is given and discussed, and finally, a special emphasis poses on the future developments of this upcoming field.

  16. Minimum Lens Size Supporting the Leaky-Wave Nature of Slit Dipole Antenna at Terahertz Frequency

    Directory of Open Access Journals (Sweden)

    Niamat Hussain


    Full Text Available We designed a slit dipole antenna backed by an extended hemispherical silicon lens and investigated the minimum lens size in which the slit dipole antenna works as a leaky-wave antenna. The slit dipole antenna consists of a planar feeding structure, which is a center-fed and open-ended slot line. A slit dipole antenna backed by an extended hemispherical silicon lens is investigated over a frequency range from 0.2 to 0.4 THz with the center frequency at 0.3 THz. The numerical results show that the antenna gain responses exhibited an increased level of sensitivity to the lens size and increased linearly with increasing lens radius. The lens with the radius of 1.2λo is found to be the best possible minimum lens size for a slit dipole antenna on an extended hemispherical silicon lens.

  17. Near optimal graphene terahertz non-reciprocal isolator

    National Research Council Canada - National Science Library

    Tamagnone, Michele; Moldovan, Clara; Poumirol, Jean-Marie; Kuzmenko, Alexey B; Ionescu, Adrian M; Mosig, Juan R; Perruisseau-Carrier, Julien


    .... Here we report the design, fabrication and measurement of a terahertz non-reciprocal isolator for circularly polarized waves based on magnetostatically biased monolayer graphene, operating in reflection...

  18. Handbook of terahertz technologies devices and applications

    CERN Document Server

    Song, Ho-Jin


    Terahertz waves, which lie in the frequency range of 0.1-10 THz, have long been investigated in a few limited fields, such as astronomy, because of a lack of devices for their generation and detection. Several technical breakthroughs made over the last couple of decades now allow us to radiate and detect terahertz waves more easily, which has triggered the search for new uses of terahertz waves in many fields, such as bioscience, security, and information and communications technology. The book covers some of the technical breakthroughs in terms of device technologies. It discusses not only th

  19. Terahertz deconvolution

    National Research Council Canada - National Science Library

    Walker, Gillian C; Bowen, John W; Labaune, Julien; Jackson, J-Bianca; Hadjiloucas, Sillas; Roberts, John; Mourou, Gerard; Menu, Michel


    The ability to retrieve information from different layers within a stratified sample using terahertz pulsed reflection imaging and spectroscopy has traditionally been resolution limited by the pulse width available...

  20. Real-time terahertz wave imaging by nonlinear optical frequency up-conversion in a 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal (United States)

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


    Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and arts. In this letter, we report on real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal. The active projection-imaging system consisted of (1) THz wave generation, (2) THz-near-infrared hybrid optics, (3) THz wave up-conversion, and (4) an InGaAs camera working at 60 frames per second. The pumping laser system consisted of two optical parametric oscillators pumped by a nano-second frequency-doubled Nd:YAG laser. THz-wave images of handmade samples at 19.3 THz were taken, and videos of a sample moving and a ruler stuck with a black polyethylene film moving were supplied online to show real-time ability. Thanks to the high speed and high responsivity of this technology, real-time THz imaging with a higher signal-to-noise ratio than a commercially available THz micro-bolometer camera was proven to be feasible. By changing the phase-matching condition, i.e., by changing the wavelength of the pumping laser, we suggest THz imaging with a narrow THz frequency band of interest in a wide range from approximately 2 to 30 THz is possible.

  1. Terahertz spectra revealing the collective excitation mode in charge-density-wave single crystal LuFe{sub 2}O{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiumei; Jin, Zuanming; Lin, Xian; Ma, Guohong [Department of Physics, Shanghai University (China); Cheng, Zhenxiang [Institute for Superconducting and Electronic Materials, University of Wollongong, NSW (Australia); Balakrishnan, Geetha [Department of Physics, University of Warwick, Coventry (United Kingdom)


    A low-energy collective excitation mode in charge-ordered multiferroic LuFe{sub 2}O{sub 4} is reported via terahertz time-domain spectroscopy. Upon cooling from 300 to 40 K, the central resonance frequency showed a pronounced hardening from 0.85 to 1.15 THz. In analogy to the well-known low-energy optical properties of LuFe{sub 2}O{sub 4}, this emerging resonance was attributed to the charge-density-wave (CDW) collective excitations. By using the Drude-Lorentz model fitting, the CDW collective mode becomes increasingly damped with the increasing temperature. Furthermore, the kinks of the CDW collective mode at the magnetic transition temperature are analyzed, which indicate the coupling of spin order with electric polarization. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Terahertz antenna technology for space applications

    CERN Document Server

    Choudhury, Balamati; Jha, Rakesh Mohan


    This book explores the terahertz antenna technology towards implementation of compact, consistent and cheap terahertz sources, as well as the high sensitivity terahertz detectors. The terahertz EM band provides a transition between the electronic and the photonic regions thus adopting important characteristics from these regimes. These characteristics, along with the progress in semiconductor technology, have enabled researchers to exploit hitherto unexplored domains including satellite communication, bio-medical imaging, and security systems. The advances in new materials and nanostructures such as graphene will be helpful in miniaturization of antenna technology while simultaneously maintaining the desired output levels. Terahertz antenna characterization of bandwidth, impedance, polarization, etc. has not yet been methodically structured and it continues to be a major research challenge. This book addresses these issues besides including the advances of terahertz technology in space applications worldwide,...

  3. Energy scaling and extended tunability of terahertz wave parametric oscillator with MgO-doped near-stoichiometric LiNbO3 crystal. (United States)

    Wang, Yuye; Tang, Longhuang; Xu, Degang; Yan, Chao; He, Yixin; Shi, Jia; Yan, Dexian; Liu, Hongxiang; Nie, Meitong; Feng, Jiachen; Yao, Jianquan


    A widely tunable, high-energy terahertz wave parametric oscillator based on 1 mol. % MgO-doped near-stoichiometric LiNbO3 crystal has been demonstrated with 1064 nm nanosecond pulsed laser pumping. The tunable range of 1.16 to 4.64 THz was achieved. The maximum THz wave output energy of 17.49 μJ was obtained at 1.88 THz under the pump energy of 165 mJ/pulse, corresponding to the THz wave conversion efficiency of 1.06 × 10-4 and the photon conversion efficiency of 1.59%, respectively. Moreover, under the same experimental conditions, the THz output energy of TPO with MgO:SLN crystal was about 2.75 times larger than that obtained from the MgO:CLN TPO at 1.60 THz. Based on the theoretical analysis, the THz energy enhancement mechanism in the MgO:SLN TPO was clarified to originate from its larger Raman scattering cross section and smaller absorption coefficient.

  4. Modeling terahertz heating effects on water

    DEFF Research Database (Denmark)

    Kristensen, Torben T.L.; Withayachumnankul, Withawat; Jepsen, Peter Uhd


    We apply Kirchhoff’s heat equation to model the influence of a CW terahertz beam on a sample of water, which is assumed to be static. We develop a generalized model, which easily can be applied to other liquids and solids by changing the material constants. If the terahertz light source is focused...

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

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


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

  6. Source illusion devices for flexural Lamb waves using elastic metasurfaces

    CERN Document Server

    Liu, Yongquan; Liu, Fu; Diba, Owen; Lamb, Alistair; Li, Jensen


    Metamaterials with the transformation method has greatly promoted the development in achieving invisibility and illusion for various classical waves. However, the requirement of tailor-made bulk materials and extreme constitutive parameters associated to illusion designs hampers its further progress. Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form-invariance in usual transformation methods. We demonstrate metasurfaces for shifting, transforming and splitting a point source with "space-coiling" structures. The effects are found to be broadband and robust against a change of source position, with agreement from numerical simulations and Huygens-Fresnel theory. The proposed approach provides an avenue to generically manipulate guided elastic waves in solids, and is...

  7. Elastic Wave Radiation from a Line Source of Finite Length

    Energy Technology Data Exchange (ETDEWEB)

    Aldridge, D.F.


    Straightforward algebraic expressions describing the elastic wavefield produced by a line source of finite length are derived in circular cylindrical coordinates. The surrounding elastic medium is assumed to be both homogeneous and isotropic, anc[ the source stress distribution is considered axisymmetic. The time- and space-domain formulae are accurate at all distances and directions from the source; no fa-field or long-wavelength assumptions are adopted for the derivation. The mathematics yield a unified treatment of three different types of sources: an axial torque, an axial force, and a radial pressure. The torque source radiates only azirnuthally polarized shear waves, whereas force and pressure sources generate simultaneous compressional and shear radiation polarized in planes containing the line source. The formulae reduce to more familiar expressions in the two limiting cases where the length of the line source approaches zero and infinity. Far-field approximations to the exact equations indicate that waves radiated parallel to the line source axI.s are attenuated relative to those radiated normal to the axis. The attenuation is more severe for higher I?equencies and for lower wavespeeds. Hence, shear waves are affected more than compressional waves. This fi-equency- and directiondependent attenuation is characterized by an extremely simple mathematical formula, and is readily apparent in example synthetic seismograms.

  8. High frequency ion sound waves associated with Langmuir waves in type III radio burst source regions

    Directory of Open Access Journals (Sweden)

    G. Thejappa


    Full Text Available Short wavelength ion sound waves (2-4kHz are detected in association with the Langmuir waves (~15-30kHz in the source regions of several local type III radio bursts. They are most probably not due to any resonant wave-wave interactions such as the electrostatic decay instability because their wavelengths are much shorter than those of Langmuir waves. The Langmuir waves occur as coherent field structures with peak intensities exceeding the Langmuir collapse thresholds. Their scale sizes are of the order of the wavelength of an ion sound wave. These Langmuir wave field characteristics indicate that the observed short wavelength ion sound waves are most probably generated during the thermalization of the burnt-out cavitons left behind by the Langmuir collapse. Moreover, the peak intensities of the observed short wavelength ion sound waves are comparable to the expected intensities of those ion sound waves radiated by the burnt-out cavitons. However, the speeds of the electron beams derived from the frequency drift of type III radio bursts are too slow to satisfy the needed adiabatic ion approximation. Therefore, some non-linear process such as the induced scattering on thermal ions most probably pumps the beam excited Langmuir waves towards the lower wavenumbers, where the adiabatic ion approximation is justified.

  9. Fourcross shaped metamaterial filters fabricated from high temperature superconducting YBCO and Au thin films for terahertz waves (United States)

    Demirhan, Y.; Alaboz, H.; Nebioğlu, M. A.; Mulla, B.; Akkaya, M.; Altan, H.; Sabah, C.; Ozyuzer, L.


    In this study, we present a new, unique fourcross shaped metamaterial terahertz (THz) filter fabricated from both gold thin films and YBa2Cu3O7-d high T c superconducting thin films. A commercial electromagnetic simulation software, CST Microwave Studio, is used to design and optimize the metamaterial filter structures. The proposed fourcross shaped rectangular filter structure consists of periodic metallic rings where strip lines are located at the sides of the ring. Fourcross metamaterial filters are fabricated by using e-beam lithography and ion beam etching techniques. Terahertz time-domain spectroscopy measurements validated the design predictions for both the center frequencies and bandwidths of the resonances due to the fourcross structures. The resonance switching of the transmission spectra was investigated by lowering the temperature below the critical transition temperature. This resonance switching effect is not observed in filters made up of metals. This novel fourcross rectangular resonator with a temperature-dependent resonance behavior holds great potential for active, tunable and low loss THz devices for imaging, sensing, and detection applications.

  10. ULF waves in other magnetospheres - observations and possible source mechanisms (United States)

    Khurana, K. K.


    Five other planets besides the Earth (Mercury, Jupiter, Saturn, Uranus and Neptune) in our solar system are now known to possess internal magnetic fields. The exploration of these planets by the Mariner, Pioneer, Voyager and Ulysses spacecraft has revealed that all of them possess fully expressed magnetospheres which share several similarities in their structures with the Earth's magnetosphere. This paper presents an overview of the work done so far in the field of the ULF waves in the magnetospheres of Mercury, Jupiter, Saturn and Uranus. To give an idea of the expected wave periods, gyroperiods of the dominant ion species and the fundamental periods of the standing Alfven waves are presented as functions of L parameter in these magnetospheres. In the magnetosphere of Mercury, ULF waves were observed in the vicinity of the magnetopause and in the inner magnetosphere with frequencies in the range of 0.1-0.5 Hz. In the magnetosphere of Jupiter, at least three different types of wave sources are observed. Near the dayside and the dawn magnetopause, waves with periods 5-20 min and amplitudes between 5 and 10 nT are observed which may be caused by an interaction between the corotating outflowing plasma and the antisunward moving plasma from the magnetosheath. In Saturn's magnetosphere, ULF waves have been observed to be strongly confined to the plasma sheet and have wave periods in the range of 5-60 minutes. The calculated fundamental has a wave period of 5-6 hours in the region where these waves were observed. The ULF waves have extremely small amplitudes (approximately = 0.3 nT) in the magnetosphere of Uranus. These waves were also seen to be confined to the low magnitude latitudes and have periods much shorter than that of the fundamental of a standing Alfven wave.

  11. Fully guided-wave photon pair source for quantum applications


    Vergyris, Panagiotis; Kaiser, Florian; Gouzien, Elie; Sauder, Grégory; Lunghi, Tommaso; Tanzilli, Sébastien


    We report a fully guided-wave source of polarisation entangled photons based on a periodically poled lithium niobate waveguide mounted in a Sagnac interferometer. We demonstrate the source's quality by converting polarisation entanglement to postselection-free energy-time entanglement for which we obtain a near-optimal $S$-parameter of $2.75 \\pm 0.02$, i.e. a violation of the Bell inequality by more than 35 standard deviations. The exclusive use of guided-wave components makes our source comp...

  12. Source Illusion Devices for Flexural Lamb Waves Using Elastic Metasurfaces (United States)

    Liu, Yongquan; Liang, Zixian; Liu, Fu; Diba, Owen; Lamb, Alistair; Li, Jensen


    Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form invariance in usual transformation methods. We demonstrate compact and simple-to-implement metasurfaces for shifting, transforming, and splitting a point source. The effects are measured to be broadband and robust against a change of source positions, with agreement from numerical simulations and the Huygens-Fresnel theory. The proposed method is potentially useful for applications such as nondestructive testing, high-resolution ultrasonography, and advanced signal modulation.

  13. Source modelling at the dawn of gravitational-wave astronomy (United States)

    Gerosa, Davide


    The age of gravitational-wave astronomy has begun. Gravitational waves are propagating spacetime perturbations ("ripples in the fabric of space-time") predicted by Einstein's theory of General Relativity. These signals propagate at the speed of light and are generated by powerful astrophysical events, such as the merger of two black holes and supernova explosions. The first detection of gravitational waves was performed in 2015 with the LIGO interferometers. This constitutes a tremendous breakthrough in fundamental physics and astronomy: it is not only the first direct detection of such elusive signals, but also the first irrefutable observation of a black-hole binary system. The future of gravitational-wave astronomy is bright and loud: the LIGO experiments will soon be joined by a network of ground-based interferometers; the space mission eLISA has now been fully approved by the European Space Agency with a proof-of-concept mission called LISA Pathfinder launched in 2015. Gravitational-wave observations will provide unprecedented tests of gravity as well as a qualitatively new window on the Universe. Careful theoretical modelling of the astrophysical sources of gravitational-waves is crucial to maximize the scientific outcome of the detectors. In this Thesis, we present several advances on gravitational-wave source modelling, studying in particular: (i) the precessional dynamics of spinning black-hole binaries; (ii) the astrophysical consequences of black-hole recoils; and (iii) the formation of compact objects in the framework of scalar-tensor theories of gravity. All these phenomena are deeply characterized by a continuous interplay between General Relativity and astrophysics: despite being a truly relativistic messenger, gravitational waves encode details of the astrophysical formation and evolution processes of their sources. We work out signatures and predictions to extract such information from current and future observations. At the dawn of a revolutionary

  14. Estimation of seabed shear-wave velocity profiles using shear-wave source data. (United States)

    Dong, Hefeng; Nguyen, Thanh-Duong; Duffaut, Kenneth


    This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements.

  15. New Sources of Gravitational Waves During Inflation

    Energy Technology Data Exchange (ETDEWEB)

    Senatore, Leonardo; Silverstein, Eva; /Stanford U., Phys. Dept. /SLAC; Zaldarriaga, Matias; /Princeton, Inst. Advanced Study


    We point out that detectable inflationary tensor modes can be generated by particle or string sources produced during inflation, consistently with the requirements for inflation and constraints from scalar fluctuations. We show via examples that this effect can dominate over the contribution from quantum fluctuations of the metric, occurring even when the inflationary potential energy is too low to produce a comparable signal. Thus a detection of tensor modes from inflation does not automatically constitute a determination of the inflationary Hubble scale.

  16. Narrowband Metamaterial Absorber for Terahertz Secure Labeling (United States)

    Nasr, Magued; Richard, Jonathan T.; Skirlo, Scott A.; Heimbeck, Martin S.; Joannopoulos, John D.; Soljacic, Marin; Everitt, Henry O.; Domash, Lawrence


    Flexible metamaterial films, fabricated by photolithography on a thin copper-backed polyimide substrate, are used to mark or barcode objects securely. The films are characterized by continuous-wave terahertz spectroscopic ellipsometry and visualized by a scanning confocal imager coupled to a vector network analyzer that constructed a terahertz spectral hypercube. These films exhibit a strong, narrowband, polarization- and angle-insensitive absorption at wavelengths near 1 mm. Consequently, the films are nearly indistinguishable at visible or infrared wavelengths and may be easily observed by terahertz imaging only at the resonance frequency of the film.

  17. Energy loss of terahertz electromagnetic waves by nano-sized connections in near-self-complementary metallic checkerboard patterns (United States)

    Takano, Keisuke; Tanaka, Yoku; Moreno, Gabriel; Chahadih, Abdallah; Ghaddar, Abbas; Han, Xiang-Lei; Vaurette, François; Nakata, Yosuke; Miyamaru, Fumiaki; Nakajima, Makoto; Hangyo, Masanori; Akalin, Tahsin


    The design of a self-complementary metallic checkerboard pattern achieves broadband, dispersion-less, and maximized absorption, concentrating in deep subwavelength resistive connections between squares, without any theoretical limitation on the energy absorbing area. Here, we experimentally and numerically investigate the electromagnetic response in the limit of extremely small connections. We show that finite conductivity and randomness in a near-self-complementary checkerboard pattern play a crucial role in producing a frequency-independent energy loss in the terahertz frequency region. Here, metals behave like an almost perfect conductor. When the checkerboard pattern approaches the perfect self-complementary pattern, the perfect conductor approximation spontaneously breaks down, owing to the finite conductivity at the nano-scale connection, leading to broadband absorption. It is also shown that the random connections between metallic squares also lead to broadband and maximized energy loss through scattering loss, similar to finite conductivity.

  18. Compact fiber-pigtailed InGaAs photoconductive antenna module for terahertz-wave generation and detection. (United States)

    Han, Sang-Pil; Kim, Namje; Ko, Hyunsung; Ryu, Han-Cheol; Park, Jeong-Woo; Yoon, Young-Jong; Shin, Jun-Hwan; Lee, Dong Hun; Park, Sang-Ho; Moon, Seok-Hwan; Choi, Sung-Wook; Chun, Hyang Sook; Park, Kyung Hyun


    We propose a compact fiber-pigtailed InGaAs photoconductive antenna (FPP) module having an effective heat-dissipation solution as well as a module volume of less than 0.7 cc. The heat-dissipation of the FPP modules when using a heat-conductive printed circuit board (PCB) and an aluminium nitride (AlN) submount, without any cooling systems, improve by 40% and 85%, respectively, when compared with a photoconductive antenna chip on a conventional PCB. The AlN submount is superior to those previously reported as a heat-dissipation solution. Terahertz time-domain spectroscopy (THz-TDS) using the FPP module perfectly detects the absorption lines of water vapor in free space and an α-lactose sample.

  19. Semiconductor terahertz technology devices and systems at room temperature operation

    CERN Document Server

    Carpintero, G; Hartnagel, H; Preu, S; Raisanen, A


    Key advances in Semiconductor Terahertz (THz) Technology now promises important new applications enabling scientists and engineers to overcome the challenges of accessing the so-called "terahertz gap".  This pioneering reference explains the fundamental methods and surveys innovative techniques in the generation, detection and processing of THz waves with solid-state devices, as well as illustrating their potential applications in security and telecommunications, among other fields. With contributions from leading experts, Semiconductor Terahertz Technology: Devices and Systems at Room Tempe

  20. Source-wave analysis by using AE method

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kyung Sok; Choi, Chang Jung; Yang, Sung Pil; Jung, Hyoun Chel; Lee, Do Yun; Kim, Tae Youl; Kim Hyoung Taek [Chosun University, Kwangju (Korea, Republic of)


    At this study, we used AE method which is advantage in inspecting structures to study the fracture toughness, the source location and the quantitative analysis of the specimen made by ASTM standard for developing the stabilized measuring performance system. AE measurement system was worked to obtain acoustic emission energy from the specimen which was shown in the Time-Energy domain and that was a raid increasement at yielding point. This point`s load was determined as the yielding point of AE. At this loading, the fracture toughness, by AE method were compared with those prescribed by ASTM and the comparison shows earlier yielding point by AE test than those by ASTM about 85%. Also, we found source location by calculating wave velocity and time duration. For the quantitative analysis, a detected wave obtained by the testing device(MISTRAS 2001 system) was transformed into source wave by using deconvolution method. And in the evaluation of a default by deconvolution method, the volume of the default was calculated 2.65 x 10{sup -4} {mu}m. These test results were used in setting up this system for testing other materials, and the source wave transformed by deconvolution included the property of the default. Using the method we think that the wave is classified into the kind of default. 14 refs., 5 tabs., 24 figs. (author)

  1. Practical microstructured and plasmonic terahertz waveguides (United States)

    Markov, Andrey

    The terahertz frequency range, with frequencies lying between 100 GHz and 10 THz, has strong potential for various technological and scientific applications such as sensing, imaging, communications, and spectroscopy. Most terahertz (THz) sources are immobile and THz systems use free-space propagation in dry air where losses are minimal. Designing efficient THz waveguides for flexible delivery of broadband THz radiation is an important step towards practical applications of terahertz techniques. THz waveguides can be very useful on the system integration level when used for connection of the diverse THz point devices, such as sources, filters, sensor cells, detectors, etc. The most straightforward application of waveguides is to deliver electromagnetic waves from the source to the point of detection. Cumbersome free-space optics can be replaced by waveguides operating in the THz range, which could lead to the development of compact THz time domain spectroscopy systems. Other promising applications of THz waveguides are in sensing and imaging. THz waveguides have also been shown to operate in subwavelength regimes, offering mode confinement in waveguide structures with a size smaller than the diffraction limit, and thus, surpassing the resolution of free-space THz imaging systems. In order to design efficient terahertz waveguides, the frequency dependent loss and dispersion of the waveguide must be minimized. A possible solution would be to increase the fraction of mode power propagating through air. In this thesis, the usage of planar porous air/dielectric waveguides and metal wire/dielectric hybrid terahertz fibers will be discussed. First, I present a novel design of a planar porous low-loss waveguide, describe its fabrication, and characterize it in view of its potential applications as a low-loss waveguide and sensor in the THz spectral range. The waveguide structure features a periodic sequence of layers of thin (25-50 mum) polyethylene film that are separated

  2. Detection of Terahertz Radiation

    DEFF Research Database (Denmark)


    The present invention relates to a system for detecting terahertz radiation, a camera device, and a method for detecting terahertz radiation.......The present invention relates to a system for detecting terahertz radiation, a camera device, and a method for detecting terahertz radiation....

  3. Metasurfaces in terahertz waveband (United States)

    He, Jingwen; Zhang, Yan


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

  4. Fully guided-wave photon pair source for quantum applications (United States)

    Vergyris, P.; Kaiser, F.; Gouzien, E.; Sauder, G.; Lunghi, T.; Tanzilli, S.


    We report a fully guided-wave source of polarisation entangled photons based on a periodically poled lithium niobate waveguide mounted in a Sagnac interferometer. We demonstrate the source’s quality by converting polarisation entanglement to postselection-free energy-time entanglement for which we obtain a near-optimal S-parameter of 2.75 ± 0.02, i.e. a violation of the Bell inequality by more than 35 standard deviations. The exclusive use of guided-wave components makes our source compact and stable which is a prerequisite for increasingly complex quantum applications. Additionally, our source offers a great versatility in terms of photon pair emission spectrum and generated quantum state, making it suitable for a broad range of quantum applications such as cryptography and metrology. In this sense, we show how to use our source for chromatic dispersion measurements in optical fibres which opens new avenues in the field of quantum metrology.

  5. Ultrathin Six-Band Polarization-Insensitive Perfect Metamaterial Absorber Based on a Cross-Cave Patch Resonator for Terahertz Waves. (United States)

    Cheng, Yong Zhi; Huang, Mu Lin; Chen, Hao Ran; Guo, Zhen Zhong; Mao, Xue Song; Gong, Rong Zhou


    A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA), composed of a metal cross-cave patch resonator (CCPR) placed over a ground plane, was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up to 95% at six resonance frequencies. Owing to the ultra-narrow band resonance absorption of the structure, the designed PMMA also exhibits a higher Q factor (>65). In addition, the absorption properties can be kept stable for both normal incident transverse magnetic (TM) and transverse electric (TE) waves. The physical mechanism behind the observed high-level absorption is illustrated by the electric and power loss density distributions. The perfect absorption originates mainly from the higher-order multipolar plasmon resonance of the structure, which differs sharply from most previous studies of PMMAs. Furthermore, the resonance absorption properties of the PMMA can be modified and adjusted easily by varying the geometric parameters of the unit cell.

  6. Ultrathin Six-Band Polarization-Insensitive Perfect Metamaterial Absorber Based on a Cross-Cave Patch Resonator for Terahertz Waves

    Directory of Open Access Journals (Sweden)

    Yong Zhi Cheng


    Full Text Available A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA, composed of a metal cross-cave patch resonator (CCPR placed over a ground plane, was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up to 95% at six resonance frequencies. Owing to the ultra-narrow band resonance absorption of the structure, the designed PMMA also exhibits a higher Q factor (>65. In addition, the absorption properties can be kept stable for both normal incident transverse magnetic (TM and transverse electric (TE waves. The physical mechanism behind the observed high-level absorption is illustrated by the electric and power loss density distributions. The perfect absorption originates mainly from the higher-order multipolar plasmon resonance of the structure, which differs sharply from most previous studies of PMMAs. Furthermore, the resonance absorption properties of the PMMA can be modified and adjusted easily by varying the geometric parameters of the unit cell.

  7. Design of a plasmonic-organic hybrid slot waveguide integrated with a bowtie-antenna for terahertz wave detection

    CERN Document Server

    Zhang, Xingyu; Subbaraman, Harish; Pan, Zeyu; Chen, Chin-Ta; Chen, Ray T


    Electromagnetic (EM) wave detection over a large spectrum has recently attracted significant amount of attention. Traditional electronic EM wave sensors use large metallic probes which distort the field to be measured and also have strict limitations on the detectable RF bandwidth. To address these problems, integrated photonic EM wave sensors have been developed to provide high sensitivity and broad bandwidth. Previously we demonstrated a compact, broadband, and sensitive integrated photonic EM wave sensor, consisting of an organic electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW) modulator integrated with a gold bowtie antenna, to detect the X band of the electromagnetic spectrum. However, due to the relative large RC constant of the silicon PCW, such EM wave sensors can only work up to tens of GHz. In this work, we present a detailed design and discussion of a new generation of EM wave sensors based on EO polymer refilled plasmonic slot waveguides in conjunction with bowtie ...

  8. Terahertz Science, Technology, and Communication (United States)

    Chattopadhyay, Goutam


    The term "terahertz" has been ubiquitous in the arena of technology over the past couple of years. New applications are emerging every day which are exploiting the promises of terahertz - its small wavelength; capability of penetrating dust, clouds, and fog; and possibility of having large instantaneous bandwidth for high-speed communication channels. Until very recently, space-based instruments for astrophysics, planetary science, and Earth science missions have been the primary motivator for the development of terahertz sensors, sources, and systems. However, in recent years the emerging areas such as imaging from space platforms, surveillance of person-borne hidden weapons or contraband from a safe stand-off distance and reconnaissance, medical imaging and DNA sequencing, and in the world high speed communications have been the driving force for this area of research.

  9. Two-color surface-emitting lasers by a GaAs-based coupled multilayer cavity structure for coherent terahertz light sources (United States)

    Lu, Xiangmeng; Ota, Hiroto; Kumagai, Naoto; Minami, Yasuo; Kitada, Takahiro; Isu, Toshiro


    Two-color surface-emitting lasers were fabricated using a GaAs-based coupled multilayer cavity structure grown by molecular beam epitaxy. InGaAs/GaAs multiple quantum wells were introduced only in the upper cavity for two-mode emission in the near-infrared region. Two-color lasing of the device was successfully demonstrated under pulsed current operations at room temperature. We also observed good temporal coherence of the two-color laser light using a Michelson interferometer. A coherent terahertz source is expected when a wafer-bonded coupled cavity consisting of (0 0 1) and non-(0 0 1) epitaxial films is used for the two-color laser device, in which the difference-frequency generation can be enabled by the second-order nonlinear response in the lower cavity.

  10. Terahertz frequency spectrum characterization of coherent heterodyne time-domain spectrometer (United States)

    Zhao, Ji; Zhang, Liang-liang; Luo, Yi-man; Wu, Tong; Zhang, Cunlin; Zhao, Yue-jin


    Terahertz wave which can provide innovative sensing and imaging techniques can obtain spectroscopic information unavailable at other wavelengths. The terahertz air-biased-coherent-detection (ABCD) method can achieve the third-order nonlinear susceptibility tensor to produce field-induced optical second harmonic photons. Therefore, the intense terahertz wave generated and detected by the laser-induced air plasma provides a promising ultra-broadband terahertz source and sensor for spectroscopy and imaging technique. Aiming at that purpose, an understanding of the frequency spectrum characterization of terahertz pulse is crucial. In this work, we investigated the variation of the THz pulse bandwidth measured through the third harmonic generation using the coherent detection scheme, by increasing the optical probe pulse power and biased electric field. A bandwidth broadening of the measured THz pulse is observed by increasing either the probe pulse power or the bias voltage strength. We speculate that a pulse shape change of the probe beam and a saturation effect during the second-harmonic generation might cause the bandwidth broaden with probe power. To further investigate the mechanism, we fixed the power of probe laser at 150mW and changed the bias voltage. The results show that the frequency spectrum width becomes wider gradually with the increasing of the bias voltage. A theoretical explaination shows that the bandwidth broadening with bias field might be introduced by a pulse shape change of the bias field induced second harmonic wave. This study reveals that we can control THz intensity and bandwidth by changing probe power and bias voltage in the ABCD system.

  11. A scheme for a terahertz traveling-wave amplifier working with the TE11 mode in a circular waveguide

    Energy Technology Data Exchange (ETDEWEB)

    Chang, L.H., E-mail:; Wang, Ch.; Luo, G.H.; Yu, T.C.; Liu, Z.K.; Yeh, M.S.; Lin, M.C.; Lin, Y.H.; Chung, F.T.; Chang, M.H.; Chen, L.J.; Lo, C.H.; Tsai, M.H.


    To enlarge the interaction structure to a feasible dimension and to decrease the required magnetic field to an available strength, the gyrotron devices at THz frequencies must be designed with a high-order-mode interaction, which is weaker in a beam–wave interaction and more susceptible to mode competition. Using the same interaction structure (a circular waveguide) as in the gyrotron traveling-wave amplifier (gyro-TWT), but replacing the axial magnetic field of the gyro-TWT with a tapered helical magnetic field, we found that the gyrating electrons are able to perform strong interaction with the TE11 mode in the THz region. Through an example case, we explored the behavior of the particles and wave fields as in a beam–wave interaction under a modified scheme of the gyro-TWT with a numerical simulation code. The equations required for the simulation are presented. The simulation result of the example case indicates that, through the TE11 beam–wave interaction under the presented scheme, more than one quarter of the beam energy can be converted to the wave at 612.7 GHz and to heat, dissipated on the waveguide wall, of radius 2.5 cm.

  12. Plasma and radio waves from Neptune: Source mechanisms and propagation (United States)

    Wong, H. K.


    This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

  13. Magnetic flux tubes as sources of wave generation (United States)

    Musielak, Z. E.; Rosner, R.; Ulmschneider, P.


    The structure of solar, and very likely stellar, surface magnetic fields is highly inhomogeneous: at the photospheric level, the fields are locally strong, and show concentration into a flux tube structure. In this case, the wave energy generated in stellar convection zones may be largely carried away by flux tube waves, which can then become important sources for the heating of the outer atmospheric layers. Such flux tube wave generation may help to explain the UV and X-ray fluxes observed by the IUE and Einstein observatories. The generation of longitudinal tube waves in magnetic flux tubes embedded in an otherwise magnetic field-free, turbulent, and stratified medium was considered. It is shown that compressible tube waves are generated by dipole emission and that the generation efficiency is a strong function of the magnetic field strength. Energy flux calculations are presented for different magnetic flux tubes, and show how the results depend on the magnetic field strength and the characteristics of the convective turbulence.

  14. Perfect terahertz absorber using fishnet based metafilm

    Energy Technology Data Exchange (ETDEWEB)

    Azad, Abul Kalam [Los Alamos National Laboratory; Shchegolkov, Dmitry Yu [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; Smirnova, E I [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory


    We present a perfect terahertz (THz) absorber working for a broad-angle of incidence. The two fold symmetry of rectangular fishnet structure allows either complete absorption or mirror like reflection depending on the polarization of incident the THz beam. Metamaterials enable the ability to control the electromagnetic wave in a unique fashion by designing the permittivity or permeability of composite materials with desired values. Although the initial idea of metamaterials was to obtain a negative index medium, however, the evolution of metamaterials (MMs) offers a variety of practically applicable devices for controlling electromagnetic wave such as tunable filters, modulators, phase shifters, compact antenna, absorbers, etc. Terahertz regime, a crucial domain of the electromagnetic wave, is suffering from the scarcity of the efficient devices and might take the advantage of metamaterials. Here, we demonstrate design, fabrication, and characterization of a terahertz absorber based on a simple fishnet metallic film separated from a ground mirror plane by a dielectric spacer. Such absorbers are in particular important for bolometric terahertz detectors, high sensitivity imaging, and terahertz anechoic chambers. Recently, split-ring-resonators (SRR) have been employed for metamaterial-based absorbers at microwave and THz frequencies. The experimental demonstration reveals that such absorbers have absorptivity close to unity at resonance frequencies. However, the downside of these designs is that they all employ resonators of rather complicated shape with many fine parts and so they are not easy to fabricate and are sensitive to distortions.

  15. The effects of magnetic fringe fields on beam dynamics in a beam transport line of a terahertz FEL source

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Han [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, Hubei (China); Xiong, Yongqian, E-mail: [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, Hubei (China); Pei, Yuanji [National Synchrotron Radiation laboratory, University of Science and Technology of China, Hefei 230029, Anhui (China)


    The transport line used in a terahertz FEL device has to transport electron beam through the entire system efficiently and meet the requirements of the beam parameters at the undulator entrance. Due to space limitations, the size of the magnets (five quadrupoles and two bending magnets) employed in the transport line was limited, and some devices were densely packed. In this paper, analyses of the effect of fringe fields and magnetic interference of magnets are presented. 3D models of these magnets are built and their linear optical properties are compared with those obtained by hard edge models. The results indicated that the effects of these factors are significant and they would cause a mismatch of the beam at the exit of the transport line under the preliminary lattice design. To solve this problem, the beam was re-matched using the particle swarm optimization algorithm.

  16. High Power Room Temperature Terahertz Local Oscillator Project (United States)

    National Aeronautics and Space Administration — We propose to build a high-power, room temperature compact continuous wave terahertz local oscillator for driving heterodyne receivers in the 1-5 THz frequency...

  17. Formation and propagation of Love waves in a surface layer with a P-wave source. Technical report

    Energy Technology Data Exchange (ETDEWEB)

    Florence, A.L.; Miller, S.A.


    The objective of this research is to investigate experimentally, and support with theoretical calculations, the formation and propagation of Love waves from a P-wave source due to scattering at material heterogeneities. The P-wave source is a spherical piezoelectric crystal cast in a surface layer of rock simulant overlaying a higher impedance granite substrate. Excitation of the piezoelectric crystal with a known voltage applies a spherical compressional pulse of known amplitude to the surrounding medium. Lateral heterogeneities cast in the surface layer convert incident P-wave energy into shear waves. The horizontally polarized shear waves (SH waves) trapped in the surface layer wave guide are the Love waves we will measure at the surface.

  18. An Analytical Method of Auxiliary Sources Solution for Plane Wave Scattering by Impedance Cylinders

    DEFF Research Database (Denmark)

    Larsen, Niels Vesterdal; Breinbjerg, Olav


    Analytical Method of Auxiliary Sources solutions for plane wave scattering by circular impedance cylinders are derived by transformation of the exact eigenfunction series solutions employing the Hankel function wave transformation. The analytical Method of Auxiliary Sources solution thus obtained...

  19. Terahertz metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Hou-tong [Los Alamos National Laboratory; Taylor, Antoineete J [Los Alamos National Laboratory; Azad, Abul K [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory


    In this paper we present our recent developments in terahertz (THz) metamaterials and devices. Planar THz metamaterials and their complementary structures fabricated on suitable substrates have shown electric resonant response, which causes the band-pass or band-stop property in THz transmission and reflection. The operational frequency can be further tuned up to 20% upon photoexcitation of an integrated semiconductor region in the splitring resonators as the metamaterial elements. On the other hand, the use of semiconductors as metamaterial substrates enables dynamical control of metamaterial resonances through photoexcitation, and reducing the substrate carrier lifetime further enables an ultrafast switching recovery. The metamaterial resonances can also be actively controlled by application of a voltage bias when they are fabricated on semiconductor substrates with appropriate doping concentration and thickness. Using this electrically driven approach, THz modulation depth up to 80% and modulation speed of 2 MHz at room temperature have been demonstrated, which suggests practical THz applications.

  20. Terahertz polarization imaging for colon cancer detection (United States)

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


    Continuous wave terahertz (THz) imaging has the potential to offer a safe, noninvasive medical imaging modality for delineating colorectal cancer. The terahertz reflectance measurements of fresh 3 - 5 mm thick human colonic excisions were acquired using a continuous-wave polarization imaging technique. A CO2 optically pumped Far- Infrared molecular gas laser operating at 584 GHz was used to illuminate the colon tissue, while the reflected signals were detected using a liquid Helium cooled silicon bolometer. Both co-polarized and cross-polarized remittance from the samples was collected using wire grid polarizers in the experiment. The experimental analysis of 2D images obtained from THz reflection polarization imaging techniques showed intrinsic contrast between cancerous and normal regions based on increased reflection from the tumor. Also, the study demonstrates that the cross-polarized terahertz images not only correlates better with the histology, but also provide consistent relative reflectance difference values between normal and cancerous regions for all the measured specimens.

  1. An overview of gravitational waves theory, sources and detection

    CERN Document Server

    Auger, Gerard


    This book describes detection techniques used to search for and analyze gravitational waves (GW). It covers the whole domain of GW science, starting from the theory and ending with the experimental techniques (both present and future) used to detect them. The theoretical sections of the book address the theory of general relativity and of GW, followed by the theory of GW detection. The various sources of GW are described as well as the methods used to analyse them and to extract their physical parameters. It includes an analysis of the consequences of GW observations in terms of astrophysics as well as a description of the different detectors that exist and that are planned for the future. With the recent announcement of GW detection and the first results from LISA Pathfinder, this book will allow non-specialists to understand the present status of the field and the future of gravitational wave science

  2. Optimization of sources for focusing wave energy in targeted formations

    KAUST Repository

    Jeong, C


    We discuss a numerical approach for identifying the surface excitation that is necessary to maximize the response of a targeted subsurface formation. The motivation stems from observations in the aftermath of earthquakes, and from limited field experiments, whereby increased oil production rates were recorded and were solely attributable to the induced reservoir shaking. The observations suggest that focusing wave energy to the reservoir could serve as an effective low-cost enhanced oil recovery method. In this paper, we report on a general method that allows the determination of the source excitation, when provided with a desired maximization outcome at the targeted formation. We discuss, for example, how to construct the excitation that will maximize the kinetic energy in the target zone, while keeping silent the neighbouring zones. To this end, we cast the problem as an inverse-source problem, and use a partial-differential- equation-constrained optimization approach to arrive at an optimized source signal. We seek to satisfy stationarity of an augmented functional, which formally leads to a triplet of state, adjoint and control problems. We use finite elements to resolve the state and adjoint problems, and an iterative scheme to satisfy the control problem to converge to the sought source signal. We report on one-dimensional numerical experiments in the time domain involving a layered medium of semi-infinite extent. The numerical results show that the targeted formation\\'s kinetic energy resulting from an optimized wave source could be several times greater than the one resulting from a blind source choice, and could overcome the mobility threshold of entrapped reservoir oil. © 2010 Nanjing Geophysical Research Institute.

  3. Accurate source location from P waves scattered by surface topography (United States)

    Wang, N.; Shen, Y.


    Accurate source locations of earthquakes and other seismic events are fundamental in seismology. The location accuracy is limited by several factors, including velocity models, which are often poorly known. In contrast, surface topography, the largest velocity contrast in the Earth, is often precisely mapped at the seismic wavelength (> 100 m). In this study, we explore the use of P-coda waves generated by scattering at surface topography to obtain high-resolution locations of near-surface seismic events. The Pacific Northwest region is chosen as an example. The grid search method is combined with the 3D strain Green's tensor database type method to improve the search efficiency as well as the quality of hypocenter solution. The strain Green's tensor is calculated by the 3D collocated-grid finite difference method on curvilinear grids. Solutions in the search volume are then obtained based on the least-square misfit between the 'observed' and predicted P and P-coda waves. A 95% confidence interval of the solution is also provided as a posterior error estimation. We find that the scattered waves are mainly due to topography in comparison with random velocity heterogeneity characterized by the von Kάrmάn-type power spectral density function. When only P wave data is used, the 'best' solution is offset from the real source location mostly in the vertical direction. The incorporation of P coda significantly improves solution accuracy and reduces its uncertainty. The solution remains robust with a range of random noises in data, un-modeled random velocity heterogeneities, and uncertainties in moment tensors that we tested.

  4. The role of terahertz surface plasmons in the scattering pattern of electromagnetic waves in an unstable elliptical plasma antenna (United States)

    Safari, S.; Jazi, B.


    The scattering phenomenon of plane waves from an unstable elliptical plasma antenna is investigated. The role of surface plasmon excitation in the scattering pattern is studied. In the antenna mentioned above, there is a metallic rod with dielectric cover embedded in a long plasma column with an elliptical cross section. The antenna is considered unstable because of the injection of an electron beam into the plasma layer. The effects of applied accelerating voltage and applied current intensity on the scattering pattern and resonance frequency are investigated. The geometrical structure and its effect on the scattering cross section and creation of new resonance frequency are studied.

  5. Broadband terahertz polarization rotator based on a twisted parallel plate waveguide

    DEFF Research Database (Denmark)

    Kristensen, T. Bjørk; Iwaszczuk, Krzysztof; Jepsen, Peter Uhd


    A broadband polarization rotator for terahertz waves is developed by 3D printing. The device is based on a twisted parallel plate waveguide.......A broadband polarization rotator for terahertz waves is developed by 3D printing. The device is based on a twisted parallel plate waveguide....

  6. The Feasibility of Monitoring Continuous Wave Sources with Seismic Arrays

    Energy Technology Data Exchange (ETDEWEB)

    Claassen, J.P.; Elbring, G.; Ladd, M.


    This paper identifies and explores the technical requirements and issues associated with remotely monitoring continuous wave (CW) sources with seismic arrays. Potential approaches to this monitoring problem will be suggested and partially evaluated to expose the monitoring challenges which arise when realistic local geologies and cultural noise sources are considered. The selective directionality and the adaptive noise cancellation properties of arrays are required to observe weak signals while suppressing a colored background punctuated with an unknown distribution of point and sometimes distributive sources. The array is also required to characterize the emitters and propagation environment so as to properly focus on the CW sources of interest while suppressing the remaining emitters. The proper application of arrays requires an appreciation of the complexity of propagation in a non-homogeneous earth. The heterogeneity often limits the available spatial coherence and therefore the size of the army. This adversely impacts the array gain and the array's ability to carefully resolve various emitters. Arrays must also contend with multipath induced by the source and the heterogeneous earth. If the array is to focus on an emitter and realize an enhancement in the signal to noise ratio, methods must be sought to coherently add the desired signal components while suppressing interference which may be correlated with the desired signal. The impact of these and other issues on army design and processing are described and discussed.

  7. Propagation Modeling of Point Source Excited Magnetoinductive Waves Based on a New Plane Wave Expansion Approach

    Directory of Open Access Journals (Sweden)

    Feng Liu


    Full Text Available The signal fading in wireless underground sensor networks (WUSNs, which is caused by lossy media such as soil and sand, can be reduced by applying technology of magnetoinductive (MI propagation. This technology can effectively establish a communication at very low frequency (VLF. In contrast to the previous studies in the literature, which mostly focus on the propagation of plane waves, we propose a new approach based on the plane wave expansion (PWE to model the near field MI waves. The proposed approach is based on excitation of a point source, which is a common case in a practical WUSN. The frequent usage of square lattice MI structure is investigated. To verify the mathematical derivation, the simulation of time domain based on the fourth-order Runge-Kutta (RK method is carried out. Simulation results show that the new model can provide a precise prediction to the MI wave’s propagation, with the computation load being one-tenth of that of the time domain simulation. The characteristics of the propagation of the MI waves are presented and discussed. Finally, the reflection on the edge of the MI structure is reduced by analysing the terminal matching conditions and calculating a method for matching impedances.

  8. 3D Printed Terahertz Focusing Grating Couplers (United States)

    Jahn, David; Weidenbach, Marcel; Lehr, Jannik; Becker, Leonard; Beltrán-Mejía, Felipe; Busch, Stefan F.; Balzer, Jan C.; Koch, Martin


    We have designed, constructed and characterized a grating that focuses electromagnetic radiation at specific frequencies out of a dielectric waveguide. A simple theoretical model predicts the focusing behaviour of these chirped gratings, along with numerical results that support our assumptions and improved the grating geometry. The leaky waveguide was 3D printed and characterized at 120 GHz demonstrating its potential for manipulating terahertz waves.

  9. Accurate source location from waves scattered by surface topography (United States)

    Wang, Nian; Shen, Yang; Flinders, Ashton; Zhang, Wei


    Accurate source locations of earthquakes and other seismic events are fundamental in seismology. The location accuracy is limited by several factors, including velocity models, which are often poorly known. In contrast, surface topography, the largest velocity contrast in the Earth, is often precisely mapped at the seismic wavelength (>100 m). In this study, we explore the use of P coda waves generated by scattering at surface topography to obtain high-resolution locations of near-surface seismic events. The Pacific Northwest region is chosen as an example to provide realistic topography. A grid search algorithm is combined with the 3-D strain Green's tensor database to improve search efficiency as well as the quality of hypocenter solutions. The strain Green's tensor is calculated using a 3-D collocated-grid finite difference method on curvilinear grids. Solutions in the search volume are obtained based on the least squares misfit between the "observed" and predicted P and P coda waves. The 95% confidence interval of the solution is provided as an a posteriori error estimation. For shallow events tested in the study, scattering is mainly due to topography in comparison with stochastic lateral velocity heterogeneity. The incorporation of P coda significantly improves solution accuracy and reduces solution uncertainty. The solution remains robust with wide ranges of random noises in data, unmodeled random velocity heterogeneities, and uncertainties in moment tensors. The method can be extended to locate pairs of sources in close proximity by differential waveforms using source-receiver reciprocity, further reducing errors caused by unmodeled velocity structures.

  10. Methods of localization of Lamb wave sources on thin plates (United States)

    Turkaya, Semih; Toussaint, Renaud; Kvalheim Eriksen, Fredrik; Daniel, Guillaume; Grude Flekkøy, Eirik; Jørgen Måløy, Knut


    Signal localization techniques are ubiquitous in both industry and academic communities. We propose a new localization method on plates which is based on energy amplitude attenuation and inverted source amplitude comparison. This inversion is tested on synthetic data using Lamb wave propagation direct model and on experimental dataset (recorded with 4 Brüel & Kjær Type 4374 miniature piezoelectric shock accelerometers (1-26 kHz frequency range)). We compare the performance of the technique to the classical source localization algorithms, arrival time localization, time reversal localization, localization based on energy amplitude. Furthermore, we measure and compare the accuracy of these techniques as function of sampling rate, dynamic range, geometry, Signal to Noise Ratio, and we show that this very versatile technique works better than classical ones over the sampling rates 100kHz - 1MHz. Experimental phase consists of a glass plate having dimensions of 80cmx40cm with a thickness of 1cm. Generated signals due to a wooden hammer hit or a steel ball hit are captured by sensors placed on the plate on different locations with the mentioned sensors. Numerical simulations are done using dispersive far field approximation of plate waves. Signals are generated using a hertzian loading over the plate. Using imaginary sources outside the plate boundaries the effect of reflections is also included. This proposed method, can be modified to be implemented on 3d environments, monitor industrial activities (e.g boreholes drilling/production activities) or natural brittle systems (e.g earthquakes, volcanoes, avalanches).

  11. Source mechanisms and near-source wave propagation from broadband seismograms

    Directory of Open Access Journals (Sweden)

    J. Perrot


    Full Text Available Recording seismic events at teleseismic distances with broadband and high dynamic range instruments provides new high-quality data that allow us to interpret in more detail the complexity of seismic rupture as well as the heterogeneous structure of the medium surrounding the source where waves are initially propagating. Wave propagation analysis is performed by ray tracing in a local cartesian coordinate system near the source and in a global spherical coordinate system when waves enter the mantle. Seismograms are constructed at each station for a propagation in a 2.5-D medium. Many phases can be included and separately analyzed; this is one of the major advantages of ray tracing compared to other wave propagation techniques. We have studied four earthquakes, the 1988 Spitak Armenia Earthquake (Ms = 6.9, the 1990 Iran earthquake (Ms = 7.7, the 1990 romanian earthquake (Ms = 5.8 and the 1992 Erzincan, Turkey earthquake (Ms = 6.8. These earthquakes exhibit in different ways the complexity of the rupture and the signature of the medium surrounding the source. The use of velocity seismograms, the time derivative of displacement, increases the difficulty of the fit between synthetic seismograms and real seismograms but provides clear evidence for a need of careful time delay estimations of the different converted phases. We find that understanding of the seismic rupture as well as the influence of the medium surrounding the source for teleseismically recorded earthquakes requires a multi-stop procedure: starting with ground displacement seismograms, one is able to give a first description of the rupture as well as of the first-order influence of the medium. Then, considering the ground velocity seismograms makes the fit more difficult to obtain but increases our sensitivity to the rupture process and early converted phases. With increasing number of worldwide broadband stations, a complex rupture description is possible independently of field

  12. Electron cyclotron wave sources and applications for fusion (United States)

    Thomassen, K. I.


    Advances in magnetic fusion research have come as often from the use of new technologies as from the invention of ideas and discovery of phenomena that are then applied to new experiments. The technologies needed for plasma production, heating, confinement, and control have largely been developed and are a major factor in the success of our current experiments. These include high vacuum techniques, normal and superconducting magnets, particle beams, pellet fueling devices, and rf sources in the ion cylotron and lower hybrid range of frequencies. One area where development is especially required, and where the potential impact on fusion research is large, is that of electron cyclotron wave (ECW) sources in the 100-600 GHz range. This journal issue is devoted to methods for ECW generation and transmission, and to applications including heating, current drive, profile shaping, and instability control. To help focus these articles the requirements(1) for a system to heat the Compact Ignition Tokamak (CIT) were used to define the necessary technology. Somewhat lower frequencies, but similar power, is anticipated(2) for the International Thermonuclear Experimental Reactor (ITER), and for future large devices of that class, should they use ECW sources in them.

  13. Rewinding the waves: tracking underwater signals to their source. (United States)

    Kadri, Usama; Crivelli, Davide; Parsons, Wade; Colbourne, Bruce; Ryan, Amanda


    Analysis of data, recorded on March 8th 2014 at the Comprehensive Nuclear-Test-Ban Treaty Organisation's hydroacoustic stations off Cape Leeuwin Western Australia, and at Diego Garcia, reveal unique pressure signatures that could be associated with objects impacting at the sea surface, such as falling meteorites, or the missing Malaysian Aeroplane MH370. To examine the recorded signatures, we carried out experiments with spheres impacting at the surface of a water tank, where we observed almost identical pressure signature structures. While the pressure structure is unique to impacting objects, the evolution of the radiated acoustic waves carries information on the source. Employing acoustic-gravity wave theory we present an analytical inverse method to retrieve the impact time and location. The solution was validated using field observations of recent earthquakes, where we were able to calculate the eruption time and location to a satisfactory degree of accuracy. Moreover, numerical validations confirm an error below 0.02% for events at relatively large distances of over 1000 km. The method can be developed to calculate other essential properties such as impact duration and geometry. Besides impacting objects and earthquakes, the method could help in identifying the location of underwater explosions and landslides.

  14. Wave equation based microseismic source location and velocity inversion (United States)

    Zheng, Yikang; Wang, Yibo; Chang, Xu


    The microseismic event locations and velocity information can be used to infer the stress field and guide hydraulic fracturing process, as well as to image the subsurface structures. How to get accurate microseismic event locations and velocity model is the principal problem in reservoir monitoring. For most location methods, the velocity model has significant relation with the accuracy of the location results. The velocity obtained from log data is usually too rough to be used for location directly. It is necessary to discuss how to combine the location and velocity inversion. Among the main techniques for locating microseismic events, time reversal imaging (TRI) based on wave equation avoids traveltime picking and offers high-resolution locations. Frequency dependent wave equation traveltime inversion (FWT) is an inversion method that can invert velocity model with source uncertainty at certain frequency band. Thus we combine TRI with FWT to produce improved event locations and velocity model. In the proposed approach, the location and model information are interactively used and updated. Through the proposed workflow, the inverted model is better resolved and the event locations are more accurate. We test this method on synthetic borehole data and filed data of a hydraulic fracturing experiment. The results verify the effectiveness of the method and prove it has potential for real-time microseismic monitoring.

  15. Active metamaterials terahertz modulators and detectors

    CERN Document Server

    Rout, Saroj


    This book covers the theoretical background and experimental methods for engineers and physicist to be able to design, fabricate and characterize terahertz devices using metamaterials. Devices utilize mainstream semiconductor foundry processes to make them for communication and imaging applications. This book will provide engineers and physicists a comprehensive reference to construct such devices with general background in circuits and electromagnetics. The authors describe the design and construction of electromagnetic (EM) devices for terahertz frequencies (108-1010cycles/sec) by embedding solid state electronic devices into artificial metamaterials where each unit cell is only a fraction of the wavelength of the incident EM wave. The net effect is an electronically tunable bulk properties with effective electric (permittivity) and magnetic (permeability) that can be utilized to make novel devices to fill the terahertz gap.

  16. Liquid-metal-based metasurface for terahertz absorption material: Frequency-agile and wide-angle (United States)

    Song, Q. H.; Zhu, W. M.; Wu, P. C.; Zhang, W.; Wu, Q. Y. S.; Teng, J. H.; Shen, Z. X.; Chong, P. H. J.; Liang, Q. X.; Yang, Z. C.; Tsai, D. P.; Bourouina, T.; Leprince-Wang, Y.; Liu, A. Q.


    Terahertz metasurface absorption materials, which absorb terahertz wave through subwavelength artificial structures, play a key role in terahertz wave shielding and stealth technology, etc. However, most of the metasurface absorption materials in terahertz suffer from limited tuning range and narrow incident angle characteristics. Here, we demonstrate a liquid-metal-based metasurface through microfluidic technology, which functions as a terahertz absorption material with broadband tunability and wide-angle features. The proposed terahertz metasurface absorption material exhibits an experimental tuning range from 0.246 THz to 0.415 THz (the tuning range of central frequency reaches 51.1%), and the tuning range maintains at high level with wide-angle response up to 60°.

  17. Terahertz Spectroscopy of Dilute Gases Using Bi2 Sr2 CaCu2 O8 +δ Intrinsic Josephson-Junction Stacks (United States)

    Sun, Hancong; Yang, Zhibao; Kinev, Nickolay V.; Kiselev, Oleg S.; Lv, Yangyang; Huang, Ya; Hao, Luyao; Zhou, Xianjing; Ji, Min; Tu, Xuecou; Zhang, Caihong; Li, Jun; Rudau, Fabian; Wieland, Raphael; Hampp, Johannes S.; Kizilaslan, Olcay; Koelle, Dieter; Jin, Biaobing; Chen, Jian; Kang, Lin; Xu, Weiwei; Kleiner, Reinhold; Koshelets, Valery P.; Wang, Huabing; Wu, Peiheng


    We report on spectrometric gas detection using terahertz waves radiated from Bi2 Sr2 CaCu2 O8 +δ (BSCCO) intrinsic Josephson-junction stacks. The emission frequency is varied by changing the bias current through and thus the voltage across the emitter. For the terahertz detection, both bolometric and heterodyne detection methods are employed. Clear absorption dips of water and ammonia vapor on the terahertz spectrum are obtained with both detection methods. With the bolometric scheme, we achieve a frequency resolution of about 1 GHz, which is on the order of the frequency resolution of systems employing terahertz time-domain spectroscopy. With the more stable heterodyne detection scheme, the minimum detectable gas pressure is around 0.001 mbar for H2O and about 0.07 mbar for NH3 . The smallest observable absorption linewidths are in the range of 4 to 5 MHz. Our results suggest that the frequency-tunable BSCCO emitters can be convenient sources for potential terahertz applications in spectroscopy for frequencies between roughly 0.4 and 2 THz.

  18. Analysis of photonic crystal and multi-frequency terahertz microstrip patch antenna

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Lechen, E-mail: [The 41st Research Institute of CETC, Qingdao 266555, Shandong Province (China); Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu Province (China); Key Laboratory of Nanodevices and Applications, Chinese Academy of Science, Suzhou 215123, Jiangsu Province (China); Shi, Xueshun [The 41st Research Institute of CETC, Qingdao 266555, Shandong Province (China); Science and Technology on Electronic Test and Measurement Laboratory, Qingdao 266555, Shandong Province (China); Chen, Kunfeng [The 41st Research Institute of CETC, Qingdao 266555, Shandong Province (China); Fu, Kai; Zhang, Baoshun [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu Province (China); Key Laboratory of Nanodevices and Applications, Chinese Academy of Science, Suzhou 215123, Jiangsu Province (China)


    In this paper, two-dimensional photonic crystals working at terahertz (THz) frequency is analyzed, a multi-frequency terahertz microstrip patch antenna on photonic crystal substrate is presented and its electromagnetic wave propagation phenomenon is investigated. The proposed antenna can work at five frequency points' scope at terahertz frequency regions, and the radiation efficiency is as high as ∼96%. The photonic crystal structure of the substrate is used to enhance the gain, directivity and radiation efficiency of the antenna.

  19. Shear Wave Generation and Modeling Ground Motion From a Source Physics Experiment (SPE) Underground Explosion (United States)

    Pitarka, Arben; Mellors, Robert; Rodgers, Arthur; Vorobiev, Oleg; Ezzedine, Souheil; Matzel, Eric; Ford, Sean; Walter, Bill; Antoun, Tarabay; Wagoner, Jeffery; Pasyanos, Mike; Petersson, Anders; Sjogreen, Bjorn


    We investigate the excitation and propagation of far-field (epicentral distance larger than 20 m) seismic waves by analyzing and modeling ground motion from an underground chemical explosion recorded during the Source Physics Experiment (SPE), Nevada. The far-field recorded ground motion is characterized by complex features, such as large azimuthal variations in P- and S-wave amplitudes, as well as substantial energy on the tangential component of motion. Shear wave energy is also observed on the tangential component of the near-field motion (epicentral distance smaller than 20 m) suggesting that shear waves were generated at or very near the source. These features become more pronounced as the waves propagate away from the source. We address the shear wave generation during the explosion by modeling ground motion waveforms recorded in the frequency range 0.01-20 Hz, at distances of up to 1 km. We used a physics based approach that combines hydrodynamic modeling of the source with anelastic modeling of wave propagation in order to separate the contributions from the source and near-source wave scattering on shear motion generation. We found that wave propagation scattering caused by the near-source geological environment, including surface topography, contributes to enhancement of shear waves generated from the explosion source. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-06NA25946/ NST11-NCNS-TM-EXP-PD15.

  20. Graphene hyperlens for terahertz radiation

    DEFF Research Database (Denmark)

    Andryieuski, Andrei; Chigrin, D.; Novitsky, Andrey


    We propose the structured graphene terahertz hyperlens that allows overcoming natural diffraction limit and resolving subwavelength features. The proposed hyperlens can have applications in terahertz spectroscopy and imaging.......We propose the structured graphene terahertz hyperlens that allows overcoming natural diffraction limit and resolving subwavelength features. The proposed hyperlens can have applications in terahertz spectroscopy and imaging....

  1. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies (United States)

    Simons, Rainee N.; Wintucky, Edwin G.


    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37-42 GHz) and V/W-band (71- 76 GHz) satellite-to-ground signals.

  2. Characterization of burn injuries using terahertz time-domain spectroscopy (United States)

    Arbab, M. Hassan; Dickey, Trevor C.; Winebrenner, Dale P.; Chen, Antao; Mourad, Pierre D.


    The accuracy rates of the clinical assessment techniques used in grading burn injuries remain significantly low for partial thickness burns. In this paper, we present experimental results from terahertz characterization of 2nd and 3rd degree burn wounds induced on a rat model. Reflection measurements were obtained from the surface of both burned and normal skin using pulsed terahertz spectroscopy. Signal processing techniques are described for interpretation of the acquired terahertz waveform and differentiation of burn wounds. Furthermore, the progression of burn injuries is shown by comparison between acute characterization and 72-hours survival studies. While the water content of healthy and desiccated skin has been considered as a source of terahertz signal contrast, it is demonstrated that other biological effects such as formation of post-burn interstitial edema as well as the density of the discrete scattering structures in the skin (such as hair follicles, sweat glands, etc.) play a significant role in the terahertz response of the burn wounds.

  3. Strong emission of terahertz radiation from nanostructured Ge surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Chul; Maeng, Inhee; Kee, Chul-Sik, E-mail: [Integrated Optics Laboratory, Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Leem, Jung Woo; Yu, Jae Su, E-mail: [Department of Electronics and Radio Engineering, and Institute for Wareable Convergence Electronics, Kyung Hee University, Gyeonggi-do 446-701 (Korea, Republic of); Kim, Tae Heon; Lee, Jong Seok [Department of Physics and Photon Science, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)


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

  4. EDITORIAL: Photonic terahertz technology (United States)

    Lisauskas, Alvydas; Löffler, Torsten; Roskos, Hartmut G.


    In recent years, when reading newspapers and journals or watching TV, one has been able to find feature presentations dealing with the prospects of terahertz (THz) technology and its potential impact on market applications. THz technology aims to fill the THz gap in the electro-magnetic spectrum in order to make the THz frequency regime, which spans the two orders of magnitude from 100 GHz to 10 THz, accessible for applications. From the lower-frequency side, electronics keeps pushing upwards, while photonic approaches gradually improve our technological options at higher frequencies. The popular interest reflects the considerable advances in research in the THz field, and it is mainly advances in the photonic branch, with the highlight being the development of the THz quantum cascade laser, which in recent years have caught the imagination of the public, and of potential users and investors. This special issue of Semiconductor Science and Technology provides an overview of key scientific developments which currently represent the cutting edge of THz photonic technology. In order to be clear about the implications, we should define exactly what we mean by 'THz photonic technology', or synonymously 'THz photonics'. It is characterized by the way in which THz radiation (or a guided THz wave) is generated, namely by the use of lasers. This may be done in one of two fundamentally different schemes: (i) by laser action in the terahertz frequency range itself (THz lasers), or (ii) by down-conversion processes (photomixing) involving the radiation of lasers which operate in the visible, near-infrared or infrared spectral ranges, either in pulsed or continuous-wave mode. The field of THz photonics has grown so considerably that it is out of the question to cover all its aspects in a single special issue of a journal. We have elected, instead, to focus our attention on two types of development with a potentially strong impact on the THz field: first, on significant advances

  5. Towards terahertz microscopy

    NARCIS (Netherlands)

    Van der Valk, N.C.J.


    Terahertz (=1012 Hz) radiation is a form of electromagnetic radiation that is at this moment used rarely for imaging purposes. However, there are indeed reasons to assume that imaging with terahertz radiation could be very useful. First, many materials, such as paper, plastics and clothing are

  6. Terahertz polarization imaging

    NARCIS (Netherlands)

    Van der Valk, N.C.J.; Van der Marel, W.A.M.; Planken, P.C.M.


    We present a new method to measure the polarization state of a terahertz pulse by using a modified electrooptic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results:

  7. Terahertz sources based on intracavity parametric frequency down-conversion using quasi-phase-matched gallium arsenide (United States)

    Schaar, Joseph Eden

    Three types of micro-structured GaAs have been used to generate THz radiation by parametric frequency down-conversion: (i) orientation-patterned GaAs, OP-GaAs, (ii) optically contacted GaAs wafers, OC-GaAs, and (iii) diffusion-bonded GaAs plates, DB-GaAs. THz frequencies between 0.5--3.5 THz were generated using the various GaAs samples. THz average powers as large as 1 mW generated from a pump power of 8.5 W, corresponding to an optical-to-THz power conversion efficiency of 1.2 x 10-4, were observed by placing the GaAs inside a doubly resonant synchronously pumped optical parametric oscillator. The quantum conversion efficiencies were as large as 1.2%. The parametric conversion efficiency for THz generation is inherently small since the ratio of the THz and optical frequencies is small. Difference-frequency generation (DFG) between the intracavity signal and idler waves generated the THz radiation. The doubly resonant optical parametric oscillator (DRO) resonated the signal and idler pulses, with picosecond-scale pulse widths and greater than 50 W of average power in each wave at lambda ≈ 2 microm. The frequency splitting between the signal and idler waves was tuned by adjusting the temperature of the DRO gain material, periodically poled LiNbO3 (PPLN). The bandwidths of the resonant signal and idler waves were between 100--200 GHz since the OPO process used Type-II QPM where the signal and idler fields were orthogonally polarized. Designs for maximizing the THz power for both the singly and doubly resonant OPOs were described yielding expressions for the THz, signal, idler, and pump powers in terms of crystal length, optical beam size, and optical absorption coefficient. A THz-cascading process was observed during which the THz wave was amplified in the GaAs crystal by multiple pairs of infrared waves. Quantum-mechanically, THz cascading corresponds to the generation of multiple THz photons from a single infrared photon. For proper designs of the OPO

  8. Gauge-invariant theory of quasiparticle and condensate dynamics in response to terahertz optical pulses in superconducting semiconductor quantum wells. II. (s +p )-wave superconductivity in the strong spin-orbit coupling limit (United States)

    Yu, T.; Wu, M. W.


    We investigate the quasiparticle and condensate dynamics in response to the terahertz (THz) optical pulses in the strong spin-orbit-coupled (s +p )-wave superconducting semiconductor quantum wells by using the gauge-invariant optical Bloch equations in the quasiparticle approximation. Both the dynamics of triplet and singlet superconductivity are studied in response to the THz optical pulses. Specifically, for the triplet superconductivity, we predict that in the (s +p )-wave superconducting (100) quantum wells, with the vector potential parallel to the quantum wells, the optical field can cause the total spin polarization of Cooper pairs, oscillating with the frequency of the optical field. The direction of the total Cooper-pair spin polarization is shown to be parallel to the vector potential. For the singlet superconductivity, we show that due to the large spin-orbit coupling in InSb (100) quantum wells, there exist two Fermi surfaces including the inner and outer ones. In this specific configuration, the superconducting momentum can be tuned to be larger than the inner Fermi momentum but smaller than the outer one. We find that in this regime, the dynamics of the Higgs mode and charge imbalance shows different features in comparison with the conventional s -wave case.

  9. Micromachined components for terahertz frequency applications

    CERN Document Server

    Parkhurst, G M


    lithographic technology for the fabrication of terahertz circuits, the integration of an active solid state device is explored. The device chosen for this work is the resonant tunnel diode (RTD). Some background discussion of the operation of these devices as oscillators is presented, and techniques for full integration of devices into a waveguide, using processes which are completely compatible with semiconductor manufacturing technology, are explored experimentally. Two main problems prevent the use of the terahertz frequency band (defined for present purposes as 100GHz - 10THz) in a wider range of applications. The first is the absence of a convenient, cheap solid-state source of power and the second is the significant cost of conventional passive components. In this Thesis, the second issue is addressed in detail, describing developments in the fabrication and characterisation of low cost lithographically-produced terahertz frequency passive components. An extensive study of the use of ultra-thick UV phot...

  10. Enhanced terahertz detection using multiple GaAs HEMTs connected in series

    KAUST Repository

    Elkhatib, Tamer A.


    We report here, for the first time, on enhanced nonresonant detection of terahertz radiation using multiple InGaAs/GaAs high-electron-mobility transistors (HEMTs) connected in series and biased by a direct drain current. A 1.63 THz (184 mum) response is proportional to the number of detecting transistors operating in saturation region at the same gate-source bias voltage. The experimental data are in agreement with the detection mechanism based on the rectification of overdamped plasma waves excited by radiation in channels of devices.

  11. Design of Integrated Circuits Approaching Terahertz Frequencies

    DEFF Research Database (Denmark)

    Yan, Lei

    In this thesis, monolithic microwave integrated circuits(MMICs) are presented for millimeter-wave and submillimeter-wave or terahertz(THz) applications. Millimeter-wave power generation from solid state devices is not only crucial for the emerging high data rate wireless communications but also...... are designed based on the monolithic membrane supported Schottky diodes, which is under development at Chalmers University of Technology, Sweden. To simplify the baseband circuitry, the received IF signal from the subharmonic mixer is further amplified and downconverted to the DC range with a low noise...

  12. The synoptic setting and possible energy sources for mesoscale wave disturbances (United States)

    Uccellini, Louis W.; Koch, Steven E.


    Published data on 13 cases of mesoscale wave disturbances and their environment were examined to isolate common features for these cases and to determine possible energy sources for the waves. These events are characterized by either a singular wave of depression or wave packets with periods of 1-4 h, horizontal wavelengths of 50-500 km, and surface-pressure perturbation amplitudes of 0.2-7.0 mb. These wave events are shown to be associated with a distinct synoptic pattern (including the existence of a strong inversion in the lower troposphere and the propagation of a jet streak toward a ridge axis in the upper troposphere) while displaying little correlation with the presence of convective storm cells. The observed development of the waves is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.

  13. Terahertz broadband polarization converter based on metamaterials (United States)

    Li, Yonghua; Zhao, Guozhong


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

  14. Tailoring Terahertz Propagation by Phase and Amplitude Control in Metasurfaces (United States)

    Zheng, Jingjing; Zhang, Xueqian; Liu, Lixiang; Li, Quan; Singh, Leena; Han, Jiaguang; Yan, Fengping; Zhang, Weili


    Metasurfaces have been very successful at demonstrating the ability to control the wave propagation over the broad electromagnetic spectrum in recent years. The output wavefronts can be controlled at will, by encoding specially designed abrupt changes of electromagnetic parameters into the metasurfaces, such as phase and amplitude. Constituted by a single- or few-layer of planar structures, metasurfaces are straightforward in design and fabrication, thus promising many credible applications. Moreover, such control concept can be further extended to the surface wave regime. In this review, we present our recent progress on metasurfaces capable of tailoring the propagation of both free-space and surface terahertz waves. Following an introduction of the basic concept and theory, a number of unique terahertz metasurfaces are presented, showing the ability to device ultra-thin and compact functional terahertz components.

  15. An Experimental Investigation of the Wave Pattern Generated by a Moving Pressure Source: Solitary Capillary-Gravity Waves (United States)

    Duncan, J. H.; Diorio, J. D.; Lisiewski, A.; Harris, R.


    The wave pattern generated by a small pressure source moving across a water surface at speeds less than the minimum phase speed for linear gravity-capillary waves (cmin = 23 cm/s) was investigated experimentally. The resulting wave pattern was measured using cinematic shadowgraph and laser-induced fluorescence (LIF) techniques. The results show the existence of several distinct behavioral states. At low speeds, no wave behavior is observed and the pattern resembles the symmetric stationary condition. However, at a critical speed, but still below cmin, the pattern undergoes a sudden transition to an asymmetric state with a stationary, 2D solitary wave that forms behind the pressure source. This solitary wave is elongated in the cross-stream relative to the stream-wise direction and resembles gravity-capillary ``lumps'' observed in previous numerical calculations. As the translation speed approaches cmin, another time-dependent behavior is observed characterized by periodic ``shedding'' from a V-shaped solitary wave pattern. This work will be discussed in conjunction with the recent numerical calculations of T. Akylas and his research group.

  16. Features of the scattering of focused terahertz radiation from the probe of a terahertz near-field microscope (United States)

    Trukhin, V. N.; Samoylov, L. L.; Khor'kov, D. P.


    The scattering of pulsed terahertz radiation from metallic probes in the form of thin cylinders and cones with a small opening angle, which are used in apertureless terahertz near-field microscopes, has been investigated. The extrema of the waveform of pulsed terahertz radiation scattered from a free probe are linearly shifted with a change in the vertical position of the probe, and the spectral distribution is characterized by an inversely proportional frequency dependence. In the presence of a reflecting surface under the probe, when new excitation and detection directions appear, the spectrum of scattered terahertz radiation does not differ from the spectrum of the incident radiation. The experimental data are in mutual agreement with the theoretical results obtained within the model of the generation of diffraction edge waves at the interface of inhomogeneous excitation between the excitation region and shadow region.

  17. Review of Anisotropic Terahertz Material Response


    ARIKAWA, T.; Zhang, Q.; Ren, L; Belyanin, A. A.; Kono, J.


    Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear optics regimes. Such material properties have led to a diverse array of useful polarization components in the visible and near-infrared, but mature technology is non-existent in the terahertz (THz). Here, we review several novel types of aniso...

  18. Extraction of terahertz emission from a grating-coupled high-electron-mobility transistor

    Institute of Scientific and Technical Information of China (English)

    Zhou Yu; Li Xinxing; Tan Renbing; Xue Wei; Huang Yongdan; Lou Shitao; Zhang Baoshun; Qin Hua


    In a grating-coupled high-electron-mobility transistor,weak terahertz emission with wavelength around 400μm was observed by using a Fourier-transform spectrometer.The absolute terahertz emission power was extracted from a strong background blackbody emission by using a modulation technique.The power of terahertz emission is proportional to the drain-source current,while the power of blackbody emission has a distinct relation with the electrical power.The dependence on the drain-source bias and the gate voltage suggests that the terahertz emission is induced by accelerated electrons interacting with the grating.

  19. Graphene hyperlens for terahertz radiation

    DEFF Research Database (Denmark)

    Andryieuski, Andrei; Lavrinenko, Andrei; Chigrin, Dmitry N.


    We propose a graphene hyperlens for the terahertz (THz) range. We employ and numerically examine a structured graphene-dielectric multilayered stack that is an analog of a metallic wire medium. As an example of the graphene hyperlens in action, we demonstrate an imaging of two point sources...... separated by a distance λ0/5. An advantage of such a hyperlens as compared to a metallic one is the tunability of its properties by changing the chemical potential of graphene. We also propose a method to retrieve the hyperbolic dispersion, check the effective medium approximation, and retrieve...

  20. Laser Source for Atomic Gravity Wave Detector Project (United States)

    National Aeronautics and Space Administration — Develop an Atom Interferometry-based gravity wave detector (vs Optical Interferometry). Characterize a high power laser. Use Goddard Space Flight Center Mission...

  1. A wave generation toolbox for the open‐source CFD library: OpenFoam

    DEFF Research Database (Denmark)

    Jacobsen, Niels Gjøl; Fuhrman, David R.; Fredsøe, Jørgen


    The open‐source CFD library OpenFoam® contains a method for solving free surface Newtonian flows using the Reynolds averaged Navier–Stokes equations coupled with a volume of fluid method. In this paper, it is demonstrated how this has been extended with a generic wave generation and absorption...... method termed ‘wave relaxation zones’, on which a detailed account is given. The ability to use OpenFoam for the modelling of waves is demonstrated using two benchmark test cases, which show the ability to model wave propagation and wave breaking. Furthermore, the reflection coefficient from outlet...... made freely available through the OpenFoam‐Extend Community....

  2. Nanoscale Terahertz Emission Spectroscopy

    DEFF Research Database (Denmark)

    Pedersen, Pernille Klarskov; Kim, Hyewon; Colvin, Vicki L.

    By utilizing plasmonic coupling to an AFM probe, we demonstrate Laser Terahertz Emission Nanoscopy (LTEN) with sub-20 nm resolution. We demonstrate the resolution by imaging a single gold nanorod on an InAs substrate.......By utilizing plasmonic coupling to an AFM probe, we demonstrate Laser Terahertz Emission Nanoscopy (LTEN) with sub-20 nm resolution. We demonstrate the resolution by imaging a single gold nanorod on an InAs substrate....

  3. Monitoring Theophylline Concentrations in Saline Using Terahertz ATR Spectroscopy

    Directory of Open Access Journals (Sweden)

    Kei Takeya


    Full Text Available To assess the possibility of terahertz technology for the determination of drug concentration in blood, we endeavored to apply a terahertz (THz attenuated total reflection (ATR method to measure the levels of theophylline in saline. A change in reflected THz wave amplitude was observed in a theophylline concentration-dependent manner. This result was obtained with simple measurements of comparisons of the amplitude of the reflected wave, and suggests that it is possible to monitor concentration changes of drugs in liquid material using THz ATR measurements.

  4. Light diffraction by a slit and grooves with a point source model based on wave dynamics (United States)

    Hong, Jian-Shiung; Chen, Kuan-Ren


    A point source model based on wave dynamics is proposed to study the fundamental light diffraction physics by a subwavelength slit and grooves in a metallic film. In this model, two opposite traveling waves are considered in each indentation; the resultant outgoing wave can propagate along the film surface to couple each other or radiate into free space as a point source. With small-system simulations, the tangential electric field at each opening determines its source temporal phase; then the energy conservation of each point source radiation and of the total radiant wave determine the source amplitudes. Besides these, this model reveals more physics regarding the wave interactions. In the strong-wave-coupling case studied, the surface waves created by the grooves flow into the slit and delay the Fabry-Pérot-like resonance. When adding the grooves concentrates the light field into a directional beam, the total transmitted energy through the slit significantly decreases. However, the energy in the original nearby grooves increases so that the groove radiation increasingly shares the transmitted energy. As the total transmitted energy decreases, the slit radiation energy decreases further due to the energy conservation. In the weak-wave-coupling cases, the groove radiation still interferes with that from the slit; as a result, the diffracted light is split into two beams. It is interesting to find that, due to the groove radiation, the slit radiation energy is enhanced to become larger than that transmitted through it. Detailed physical interpretations will be given.

  5. A focused electric spark source for non-contact stress wave excitation in solids. (United States)

    Dai, Xiaowei; Zhu, Jinying; Haberman, Michael R


    A focused electric spark is used as a non-contact acoustic source to excite stress waves in solids. The source consists of an electric spark source located at the near focus of an ellipsoidal reflector that focuses the acoustic disturbance generated by the spark source to the far focal point. Experimental studies using both contact and non-contact sensors indicate that the source has the capability to excite the Rayleigh surface wave and impact-echo mode (S1-zero-group-velocity Lamb mode) in a 250 mm thick concrete slab and to enable fully air-coupled testing of concrete specimens.

  6. Rayleigh Wave Velocity Measurements Using Broad Band Frequency Sources. (United States)


    Heukelom 4I and Foster 1960, Chang and Ballard 1973, Ballard and McLean 1975). The procedure for measuring the Rayleigh wave velocity has consisted... Heukelom , W., and Foster, C. R. 1960. "Dynamic Testing of Pavements," Journal, Soil Mechanics and Foundations Division, American Society of Civil Engineers

  7. Wave field synthesis of moving virtual sound sources with complex radiation properties. (United States)

    Ahrens, Jens; Spors, Sascha


    An approach to the synthesis of moving virtual sound sources with complex radiation properties in wave field synthesis is presented. The approach exploits the fact that any stationary sound source of finite spatial extent radiates spherical waves at sufficient distance. The angular dependency of the radiation properties of the source under consideration is reflected by the amplitude and phase distribution on the spherical wave fronts. The sound field emitted by a uniformly moving monopole source is derived and the far-field radiation properties of the complex virtual source under consideration are incorporated in order to derive a closed-form expression for the loudspeaker driving signal. The results are illustrated via numerical simulations of the synthesis of the sound field of a sample moving complex virtual source.

  8. Ultra-flexible polarization-insensitive multiband terahertz metamaterial absorber. (United States)

    Chen, Xu; Fan, Wenhui


    A thin-flexible and polarization-insensitive multiband terahertz metamaterial absorber (MMA) has been investigated. Each unit cell of the MMA consists of two metallic structures, which include the top metal resonator ring and the bottom metal ground plane, separated by a thin-flexible dielectric spacer. Finite element simulation indicates that this MMA has three high absorption peaks in the terahertz region, with absorptivities of 89% at 0.72 THz, 98% at 1.4 THz, and 85% at 2.3 THz. However, because of its rotationally symmetric structure, this MMA is polarization-insensitive and can perform very well at a wide range of incident angles, namely, 30° for transverse electric waves and 40° for transverse magnetic waves. The thin-flexible device structure and good performance shows that this MMA is very promising to disguise objects and make them less detectable to radar in the terahertz region.

  9. Sources and sinks separating domains of left- and right-traveling waves: Experiment versus amplitude equations


    Alvarez, Roberto; van Hecke, Martin; van Saarloos, Wim


    In many pattern forming systems that exhibit traveling waves, sources and sinks occur which separate patches of oppositely traveling waves. We show that simple qualitative features of their dynamics can be compared to predictions from coupled amplitude equations. In heated wire convection experiments, we find a discrepancy between the observed multiplicity of sources and theoretical predictions. The expression for the observed motion of sinks is incompatible with any amplitude equation descri...

  10. Graphene based salisbury screen for terahertz absorber (United States)

    Min Woo, Jeong; Kim, Min-Sik; Woong Kim, Hyun; Jang, Jae-Hyung


    A graphene-based, multiband absorber operating in terahertz (THz) frequency range was demonstrated. Graphene film was transferred onto the top of a flexible polymer substrate backed with a gold reflector. The graphene acts as a resistive film that partially attenuates and reflects THz waves. The destructive interference between THz waves reflected from graphene and backside reflector gives rise to perfect absorbance at multiple frequencies. To enhance the absorbance on/off ratio (AR), the conductivity of graphene was varied using a chemical doping method. The resulting p-doped, graphene-based THz absorber exhibited absorbance at maxima and AR higher than 0.95 and 25 dB, respectively.

  11. Wave chaos and enhancement of coherent radiation with rippled waveguides in a photoconductive antenna (United States)

    Kim, Christopher

    Time-domain terahertz spectroscopy is now a well-established technique. Of the many methods available for a terahertz source for terahertz spectroscopy, the most widely used may be the GaAs-based photoconductive antenna, as it provides relatively high power at terahertz frequencies, commercially available up to 150 microW, and a wide-bandwidth, approximately 70 GHz to 3.5 THz. One of the limitations for developing more accurate and sensitive terahertz interrogation techniques is the lack of higher power sources. Because of our research interests in terahertz spectroscopy, we investigated detailed design and fabrication parameters involved in the photoconductive antenna, which exploits the surface plasma oscillation to produce a wideband pulse. The investigation enabled us to develop a new photoconductive antenna that is capable of generating a high power terahertz beam, at least twenty times stronger than those currently available. Throughout this research, it was discovered that antenna electrodes with particular geometries could produce superradiance, also known as the Dicke effect. Chaotic electrodes with a predisposition to lead charge-carriers into chaotic trajectories, e.g. rippled geometry, were exploited to reduce undesirable heat effects by driving thermal-electrons away from the terahertz generation site, i.e. the location of the surface plasma, while concentrating the removed charge-carriers in separate locations slightly away from the surface plasma. Then, spontaneous emission of coherent terahertz radiation may occur when the terahertz pulse generated by the surface plasma stimulates the concentrated carriers. This spontaneous emission enhanced the total coherent terahertz beam strength, as it occurs almost simultaneously with the primary terahertz beam. In principle, the spontaneous emission power increases as N2 , with the number N of dipole moments resulted from the concentrated charge carriers. Hence, if the design parameters are optimized, it may

  12. Chorus whistler wave source scales as determined from multipoint Van Allen Probe measurements (United States)

    Agapitov, Oleksiy; Mozer, Forrest; Blum, Lauren; Bonnell, John; Wygant, John


    Whistler-mode chorus waves are a particularly important process in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The key parameters for both nonlinear and quasi-linear treatment of wave-particle interactions are the temporal and spatial scales of the wave source region and coherence of the wave field perturbations. Both of these scales, the source scale and the coherence scale, are not well-established experimentally, mostly because of a lack of VLF waveform data. We present an unprecedentedly long interval of coordinated VLF waveform measurements (sampled at 16384 s-1) aboard the two Van Allen Probes spacecraft. The cross spacecraft distance varied from about 100 up to 5000 km. Using time-domain correlation techniques, the chorus source regions have been determined to be about 450-550 km for upper band chorus waves with amplitude less than 100 pT and up to 1000 km for larger amplitude lower band chorus waves. The ratio between wave amplitudes measured on the two spacecraft is also examined and reveals that the wave amplitude distribution within a region of chorus element generation can be well approximated by the Gaussian with the characteristic distance r0 around 300 km. This work was supported by the JHU/APL contract 922613 (RBSP-EFW) and NASA Grant NNX16AF85G.

  13. An effective way to reduce water absorption to terahertz (United States)

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


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

  14. Measurement of absolute frequency of continuous-wave terahertz radiation in real time using a free-running, dual-wavelength mode-locked, erbium-doped fibre laser. (United States)

    Hu, Guoqing; Mizuguchi, Tatsuya; Zhao, Xin; Minamikawa, Takeo; Mizuno, Takahiko; Yang, Yuli; Li, Cui; Bai, Ming; Zheng, Zheng; Yasui, Takeshi


    A single, free-running, dual-wavelength mode-locked, erbium-doped fibre laser was exploited to measure the absolute frequency of continuous-wave terahertz (CW-THz) radiation in real time using dual THz combs of photo-carriers (dual PC-THz combs). Two independent mode-locked laser beams with different wavelengths and different repetition frequencies were generated from this laser and were used to generate dual PC-THz combs having different frequency spacings in photoconductive antennae. Based on the dual PC-THz combs, the absolute frequency of CW-THz radiation was determined with a relative precision of 1.2 × 10-9 and a relative accuracy of 1.4 × 10-9 at a sampling rate of 100 Hz. Real-time determination of the absolute frequency of CW-THz radiation varying over a few tens of GHz was also demonstrated. Use of a single dual-wavelength mode-locked fibre laser, in place of dual mode-locked lasers, greatly reduced the size, complexity, and cost of the measurement system while maintaining the real-time capability and high measurement precision.

  15. Correction of stress-depended changes of glucoproteid platelet receptors activity by electromagnetic radiation of terahertz range

    Directory of Open Access Journals (Sweden)

    V.F. Kirichuk


    Full Text Available The research goal is correction of stress-depended changes of glucoproteid (Gp platelet receptors activity by electromagnetic radiation of terahertz range. Influence of electromagnetic waves of terahertz range at the frequency of molecular spectrum of radiation and absorption of nitrogen oxide on lectin-induced platelet aggregation of white rats in the stressed condition was investigated

  16. Introduction to the Issue on Current Trends in Terahertz Photonics and Applications

    DEFF Research Database (Denmark)


    Since the last special issue on terahertz science and technology, nearly three years have been passed. During this period, while there have been further developments in terahertz (THz) sources, detectors, materials, and applications, there have been new discoveries. The purpose of this issue of t...

  17. Optical waveguide mode control by nanoslit-enhanced terahertz field

    DEFF Research Database (Denmark)

    Novitsky, Andrey; Zalkovskij, Maksim; Malureanu, Radu


    In this Letter we propose a scheme providing control over an optical waveguide mode by a terahertz (THz) wave. The scheme is based on an optimization of the overlap between the optical waveguide mode and the THz field, with the THz field strength enhanced by the presence of a metallic nanoslit...

  18. Gauge-invariant theory of quasiparticle and condensate dynamics in response to terahertz optical pulses in superconducting semiconductor quantum wells. I. s -wave superconductivity in the weak spin-orbit coupling limit (United States)

    Yu, T.; Wu, M. W.


    We investigate the quasiparticle and condensate dynamics in response to the terahertz optical pulses in the weak spin-orbit-coupled s -wave superconducting semiconductor quantum wells by using the gauge-invariant optical Bloch equations in the quasiparticle approximation. Specifically, in the Bloch equations, not only can the microscopic description for the quasiparticle dynamics be realized, but also the dynamics of the condensate is included, with the superfluid velocity and the effective chemical potential naturally incorporated. We reveal that the superfluid velocity itself can contribute to the pump of quasiparticles (pump effect), with its rate of change acting as the drive field to drive the quasiparticles (drive effect). We find that the oscillations of the Higgs mode with twice the frequency of the optical field are contributed dominantly by the drive effect but not the pump effect as long as the driven superconducting momentum is less than the Fermi momentum. This is in contrast to the conclusion from the Liouville or Bloch equations in the literature, in which the drive effect on the anomalous correlation is overlooked with only the pump effect considered. Furthermore, in the gauge-invariant optical Bloch equations, the charge neutrality condition is consistently considered based on the two-component model for the charge, in which the charge imbalance of quasiparticles can cause the fluctuation of the effective chemical potential for the condensate. It is predicted that during the optical process, the quasiparticle charge imbalance can be induced by both the pump and drive effects, leading to the fluctuation of the chemical potential. This fluctuation of the chemical potential is further demonstrated to directly lead to a relaxation channel for the charge imbalance even with the elastic scattering due to impurities. This is very different from the previous understanding that in the isotropic s -wave superconductivity, the impurity scattering cannot cause

  19. Oblique propagation of whistler mode waves in the chorus source region (United States)

    Santolík, O.; Gurnett, D. A.; Pickett, J. S.; Chum, J.; Cornilleau-Wehrlin, N.


    Whistler mode chorus has been shown to play a role in the process of local acceleration of electrons in the outer Van Allen radiation belt. Most of the quasi-linear and nonlinear theoretical studies assume that the waves propagate parallel to the terrestrial magnetic field. We show a case where this assumption is invalid. We use data from the Cluster spacecraft to characterize propagation and spectral properties of chorus. The recorded high-resolution waveforms show that chorus in the source region can be formed by a succession of discrete wave packets with decreasing frequency that sometimes change into shapeless hiss. These changes occur at the same time in the entire source region. Multicomponent measurements show that waves in both these regimes can be found at large angles to the terrestrial magnetic field. The hiss intervals contain waves propagating less than one tenth of a degree from the resonance cone. In the regime of discrete wave packets the peak of the wave energy density is found at a few degrees from the resonance cone in a broad interval of azimuth angles. The wave intensity increases with the distance from the magnetic field minimum along a given field line, indicating a gradual amplification of chorus in the source region.

  20. Source and listener directivity for interactive wave-based sound propagation. (United States)

    Mehra, Ravish; Antani, Lakulish; Kim, Sujeong; Manocha, Dinesh


    We present an approach to model dynamic, data-driven source and listener directivity for interactive wave-based sound propagation in virtual environments and computer games. Our directional source representation is expressed as a linear combination of elementary spherical harmonic (SH) sources. In the preprocessing stage, we precompute and encode the propagated sound fields due to each SH source. At runtime, we perform the SH decomposition of the varying source directivity interactively and compute the total sound field at the listener position as a weighted sum of precomputed SH sound fields. We propose a novel plane-wave decomposition approach based on higher-order derivatives of the sound field that enables dynamic HRTF-based listener directivity at runtime. We provide a generic framework to incorporate our source and listener directivity in any offline or online frequency-domain wave-based sound propagation algorithm. We have integrated our sound propagation system in Valve's Source game engine and use it to demonstrate realistic acoustic effects such as sound amplification, diffraction low-passing, scattering, localization, externalization, and spatial sound, generated by wave-based propagation of directional sources and listener in complex scenarios. We also present results from our preliminary user study.

  1. Asymmetric planar terahertz metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Ramjan [Los Alamos National Laboratory; Al - Naib, Ibraheem A. I. [PHILIPPS UNIV; Koch, Martin [PHILIPPS UNIV; Zhang, Weili [OKLAHOMA STATE UNIV


    Using terahertz time-domain spectroscopy, we report an experimental observation of three distinct resonances in split ring resonators (SRRs) for both vertical and horizontal electric field polarizations at normal incidence. Breaking the symmetry in SRRs by gradually displacing the capacitive gap from the centre towards the comer of the ring allows for an 85% modulation of the fundamental inductive-capacitive (LC) resonance. Increasing asymmetry leads to the evolution of an otherwise inaccessible high quality factor electric quadrupole resonance that can be exploited for bio-sensing applications in the terahertz region.

  2. On the comparsion of the Spherical Wave Expansion-to-Plane Wave Expansion and the Sources Reconstruction Method for Antenna Diagnostics

    DEFF Research Database (Denmark)

    Alvarez, Yuri; Cappellin, Cecilia; Las-Heras, Fernando


    A comparison between two recently developed methods for antenna diagnostics is presented. On one hand, the Spherical Wave Expansion-to-Plane Wave Expansion (SWE-PWE), based on the relationship between spherical and planar wave modes. On the other hand, the Sources Reconstruction Method (SRM), based...

  3. In vivo estimation of elastic wave parameters using phase-stabilized swept source optical coherence elastography (United States)

    Manapuram, Ravi Kiran; Aglyamov, Salavat R.; Monediado, Floredes M.; Mashiatulla, Maleeha; Li, Jiasong; Emelianov, Stanislav Y.; Larin, Kirill V.


    We report a highly sensitive method based on phase-stabilized swept source optical coherence elastography (PhS-SSOCE) to measure elastic wave propagation in soft tissues in vivo. The waves were introduced using a mechanical stimulus and were assessed using the phase response of the swept source optical coherence tomography signal. The technique was utilized to measure age-related changes in elastic flexural wave velocity and attenuation in mice cornea in vivo. Results demonstrate that the wave velocity increases with animal age, supporting previous observations that stiffness of mice cornea gradually increases with age. Our studies suggest that the PhS-SSOCE technique could potentially be used to obtain biomechanical properties of ocular tissues in vivo.

  4. Terahertz Magnetic Modulator based on Magnetically-Clustered Nanoparticles

    CERN Document Server

    Shalaby, Mostafa; Ozturk, Yavuz; Al-Naib, Ibraheem; Hauri, Christoph P; Morandotti, Roberto


    Random orientation of liquid-suspended magnetic nanoparticles (Ferrofluid) gives rise to zero net magnetic orientation. An external magnetic field tends to align them into clusters, leading to a strong linear dichroism on a propagating wave. Using 10 nm-sized Fe3O4, we experimentally realize a polarization-sensitive magnetic modulator operating at terahertz wavelengths. We reached a modulation depth of 66% using a field of 35 mT. The proposed concept offers a solution towards fundamental terahertz magnetic modulators.

  5. Determination of terahertz permittivity of dehydrated biological samples (United States)

    He, Yuezhi; Liu, Kai; Au, Corinna; Sun, Qiushuo; Parrott, Edward P. J.; PickWell-MacPherson, Emma


    A key step in transforming terahertz imaging to a practical medical imaging modality lies in understanding the interactions between terahertz (THz) waves and biological tissues. Most of the models in the literature use the permittivity of liquid water to simulate the THz-tissue interactions, but they often neglect contributions from the biological background such as proteins and lipids because dehydrated biological samples are experimentally difficult to prepare. In this work, we present a method to prepare thin and flat dehydrated samples which can be easily handled and measured in a transmission setup. Our results will provide fundamental parameters for modelling THz-tissue interactions.

  6. Terahertz metamaterials for linear polarization conversion and anomalous refraction. (United States)

    Grady, Nathaniel K; Heyes, Jane E; Chowdhury, Dibakar Roy; Zeng, Yong; Reiten, Matthew T; Azad, Abul K; Taylor, Antoinette J; Dalvit, Diego A R; Chen, Hou-Tong


    Polarization is one of the basic properties of electromagnetic waves conveying valuable information in signal transmission and sensitive measurements. Conventional methods for advanced polarization control impose demanding requirements on material properties and attain only limited performance. We demonstrated ultrathin, broadband, and highly efficient metamaterial-based terahertz polarization converters that are capable of rotating a linear polarization state into its orthogonal one. On the basis of these results, we created metamaterial structures capable of realizing near-perfect anomalous refraction. Our work opens new opportunities for creating high-performance photonic devices and enables emergent metamaterial functionalities for applications in the technologically difficult terahertz-frequency regime.

  7. Dynamics of Langmuir and ion-sound waves in type III solar radio sources (United States)

    Robinson, P. A.; Willes, A. J.; Cairns, I. H.


    The study traces the evolution of Langmuir and ion-sound waves in type III sources, incorporating linear growth, linear damping, and nonlinear electrostatic decay. Improved estimates are obtained for the wavenumber range of growing waves and the nonlinear coupling coefficient for the decay process. It is shown that the conditions in the solar wind do not allow a steady state to be attained; instead, bursty linear and nonlinear interactions take place, consistent with the highly inhomogeneous and impulsive waves actually observed. Nonlinear growth is found to be rapid enough to saturate the growth of the parent Langmuir waves in the available interaction time. The competing processes of nonlinear wave collapse and quasi-linear relaxation are discussed, and it is concluded that neither is responsible for the saturation of Langmuir growth.

  8. The influence of damping and source terms on solutions of nonlinear wave equations

    Directory of Open Access Journals (Sweden)

    Mohammad A. Rammaha


    Full Text Available We discuss in this paper some recent development in the study of nonlinear wave equations. In particular, we focus on those results that deal with wave equations that feature two competing forces.One force is a damping term and the other is a strong source. Our central interest here is to analyze the influence of these forces on the long-time behavior of solutions.

  9. Seasonal variation and sources of atmospheric gravity waves in the Antarctic

    Directory of Open Access Journals (Sweden)

    Kaoru Sato


    Full Text Available In the last recent ten years, our knowledge of gravity waves in the Antarctic has been significantly improved through numerous studies using balloon and satellite observations and high-resolution model simulations. In this report, we introduce results from two studies which were performed as a part of the NIPR project "Integrated analysis of the material circulation in the Antarctic atmosphere-cryosphere-ocean" (2004-2009, i.e., Yoshiki et al. (2004 and Sato and Yoshiki (2008. These two studies focused on the seasonal variation and sources of the gravity waves in the Antarctic, because horizontal wavelengths and phase velocities depend largely on the wave sources. The former study used original high-resolution data from operational radiosonde observations at Syowa Station. In the lowermost stratosphere, gravity waves do not exhibit characteristic seasonal variation; instead, the wave energy is intensified when lower latitude air intrudes into the area near Syowa Station in the upper troposphere. This intrusion is associated with blocking events or developed synoptic-scale waves. In the lower and middle stratosphere, the gravity wave energy is maximized in spring and particularly intensified when the axis of the polar night jet approaches Syowa Station. The latter study is based on intensive radiosonde observation campaigns that were performed in 2002 at Syowa Station as an activity of JARE-43. Gravity wave propagation was statistically examined using two dimensional (i.e., vertical wavenumber versus frequency spectra in each season. It was shown that the gravity waves are radiated upward and downward from an unbalanced region of the polar night jet. This feature is consistent with the gravity-wave resolving GCM simulation.

  10. Terahertz generation from graphite

    NARCIS (Netherlands)

    Ramakrishnan, G.; Chakkittakandy, R.; Planken, P.C.M.


    Generation of subpicosecond terahertz pulses is observed when graphite surfaces are illuminated with femtosecond near-infrared laser pulses. The nonlinear optical generation of THz pulses from graphite is unexpected since, in principle, the material possesses a centre of inversion symmetry.

  11. Graphene geometric diodes for terahertz rectennas (United States)

    Zhu, Zixu; Joshi, Saumil; Grover, Sachit; Moddel, Garret


    We demonstrate a new thin-film graphene diode called a geometric diode that relies on geometric asymmetry to provide rectification at 28 THz. The geometric diode is coupled to an optical antenna to form a rectenna that rectifies incoming radiation. This is the first reported graphene-based antenna-coupled diode working at 28 THz, and potentially at optical frequencies. The planar structure of the geometric diode provides a low RC time constant, on the order of 10-15 s, required for operation at optical frequencies, and a low impedance for efficient power transfer from the antenna. Fabricated geometric diodes show asymmetric current-voltage characteristics consistent with Monte Carlo simulations for the devices. Rectennas employing the geometric diode coupled to metal and graphene antennas rectify 10.6 µm radiation, corresponding to an operating frequency of 28 THz. The graphene bowtie antenna is the first demonstrated functional antenna made using graphene. Its response indicates that graphene is a suitable terahertz resonator material. Applications for this terahertz diode include terahertz-wave and optical detection, ultra-high-speed electronics and optical power conversion.

  12. A 1D cylindrical kinetic wave code for helicon plasma sources (United States)

    Kamenski, I. V.; Borg, G. G.


    We describe a 1D plasma kinetic code UFEM, which is specifically designed for the treatment of radiofrequency wave excitation and propagation in cylindrical low temperature plasmas. The code should find extensive application in the design and study of helicon wave driven plasma sources which are increasingly used for industrial plasma processing. The code includes the effects of collisional dissipation and the important parallel electron dynamics, such as Landau damping, that are necessary for the description of wave absorption. It employs a finite element discretization of rf fields in terms of electromagnetic potentials that is suitable for wave calculations in the lower hydrid range of frequencies where helicon waves typically propagate. Finite Larmor radius effects are known to be negligible in industrial plasma sources. These are therefore neglected leading to a considerable simplification of the dielectric tensor; in particular, the complex issue of the equilibrium gradient terms is avoided. The user can choose from a menu of several standard antenna types so that antenna optimizations can be readily performed. Four different variations of cylindrical system geometry can be used. The important issues of complex antenna near-fields and short wavelength modes can be treated fully self-consistently. We also perform a benchmark of the UFEM and ISMENE 5 codes for four different wave conditions over the Alfvén to lower hybrid frequency ranges. Finally we conclude with a presentation of code results for the conditions of a typical helicon plasma source driven by a realistic antenna.

  13. AGILE Observations of the Gravitational-wave Source GW170104 (United States)

    Verrecchia, F.; Tavani, M.; Ursi, A.; Argan, A.; Pittori, C.; Donnarumma, I.; Bulgarelli, A.; Fuschino, F.; Labanti, C.; Marisaldi, M.; Evangelista, Y.; Minervini, G.; Giuliani, A.; Cardillo, M.; Longo, F.; Lucarelli, F.; Munar-Adrover, P.; Piano, G.; Pilia, M.; Fioretti, V.; Parmiggiani, N.; Trois, A.; Del Monte, E.; Antonelli, L. A.; Barbiellini, G.; Caraveo, P.; Cattaneo, P. W.; Colafrancesco, S.; Costa, E.; D'Amico, F.; Feroci, M.; Ferrari, A.; Morselli, A.; Pacciani, L.; Paoletti, F.; Pellizzoni, A.; Picozza, P.; Rappoldi, A.; Vercellone, S.


    The LIGO/Virgo Collaboration (LVC) detected on 2017 January 4 a significant gravitational-wave (GW) event (now named GW170104). We report in this Letter the main results obtained from the analysis of hard X-ray and gamma-ray data of the AGILE mission that repeatedly observed the GW170104 localization region (LR). At the LVC detection time T 0 AGILE observed about 36% of the LR. The gamma-ray imaging detector did not reveal any significant emission in the energy range 50 MeV-30 GeV. Furthermore, no significant gamma-ray transients were detected in the LR that was repeatedly exposed over timescales of minutes, hours, and days. We also searched for transient emission using data near T 0 of the omnidirectional detector MCAL operating in the energy band 0.4-100 MeV. A refined analysis of MCAL data shows the existence of a weak event (that we call “E2”) with a signal-to-noise ratio of 4.4σ lasting about 32 ms and occurring 0.46 ± 0.05 s before T 0. A study of the MCAL background and of the false-alarm rate of E2 leads to the determination of a post-trial significance between 2.4σ and 2.7σ for a temporal coincidence with GW170104. We note that E2 has characteristics similar to those detected from the weak precursor of GRB 090510. The candidate event E2 is worth consideration for simultaneous detection by other satellites. If associated with GW170104, it shows emission in the MeV band of a short burst preceding the final coalescence by 0.46 s and involving ˜10-7 of the total rest mass energy of the system.

  14. AGILE Observations of the Gravitational-wave Source GW170104

    Energy Technology Data Exchange (ETDEWEB)

    Verrecchia, F.; Pittori, C.; Lucarelli, F. [ASI Space Science Data Center (SSDC), via del Politecnico, I-00133 Roma (Italy); Tavani, M.; Ursi, A.; Argan, A.; Evangelista, Y.; Minervini, G.; Cardillo, M.; Piano, G. [INAF-IAPS, via del Fosso del Cavaliere 100, I-00133 Roma (Italy); Donnarumma, I. [ASI, via del Politecnico snc, I-00133 Roma (Italy); Bulgarelli, A.; Fuschino, F.; Labanti, C.; Fioretti, V. [INAF-IASF-Bologna, via Gobetti 101, I-40129 Bologna (Italy); Marisaldi, M. [Birkeland Centre for Space Science, Department of Physics and Technology, University of Bergen, Bergen (Norway); Giuliani, A. [INAF-IASF Milano, via E.Bassini 15, I-20133 Milano (Italy); Longo, F. [Dipartimento di Fisica, Università di Trieste and INFN, via Valerio 2, I-34127 Trieste (Italy); Munar-Adrover, P. [Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Pilia, M. [INAF, Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047 Selargius (Italy); and others


    The LIGO/Virgo Collaboration (LVC) detected on 2017 January 4 a significant gravitational-wave (GW) event (now named GW170104). We report in this Letter the main results obtained from the analysis of hard X-ray and gamma-ray data of the AGILE mission that repeatedly observed the GW170104 localization region (LR). At the LVC detection time T {sub 0} AGILE observed about 36% of the LR. The gamma-ray imaging detector did not reveal any significant emission in the energy range 50 MeV–30 GeV. Furthermore, no significant gamma-ray transients were detected in the LR that was repeatedly exposed over timescales of minutes, hours, and days. We also searched for transient emission using data near T {sub 0} of the omnidirectional detector MCAL operating in the energy band 0.4–100 MeV. A refined analysis of MCAL data shows the existence of a weak event (that we call “E2”) with a signal-to-noise ratio of 4.4 σ lasting about 32 ms and occurring 0.46 ± 0.05 s before T {sub 0}. A study of the MCAL background and of the false-alarm rate of E2 leads to the determination of a post-trial significance between 2.4σ and 2.7σ for a temporal coincidence with GW170104. We note that E2 has characteristics similar to those detected from the weak precursor of GRB 090510. The candidate event E2 is worth consideration for simultaneous detection by other satellites. If associated with GW170104, it shows emission in the MeV band of a short burst preceding the final coalescence by 0.46 s and involving ∼10{sup −7} of the total rest mass energy of the system.

  15. A catalogue of potentially bright close binary gravitational wave sources (United States)

    Webbink, Ronald F.

    This is a current print-out of results of a survey, undertaken in the spring of 1985, to identify those known binary stars which might produce significant gravitational wave amplitudes at earth, either dimensionless strain amplitudes exceeding a threshold h = 10-21, or energy fluxes exceeding F = 10-12 erg cm-2 s-1. All real or putative binaries brighter than a certain limiting magnitude (calculated as a function of primary spectral type, orbital period, orbital eccentricity, and bandpass) are included. All double degenerate binaries and Wolf-Rayet binaries with known or suspected orbital periods have also been included. The catalog consists of two parts: a listing of objects in ascending order of Right Ascension (Equinox B1950), followed by an index, listing of objects by identification number according to all major stellar catalogs. The object listing is a print-out of the spreadsheets on which the catalog is currently maintained. It should be noted that the use of this spreadsheet program imposes some limitations on the display of entries. Text entries which exceed the cell size may appear in truncated form, or may run into adjacent columns. Greek characters are not available; they are represented here by the first two or three letters of their Roman names, the first letter appearing as a capital or lower-case letter according to whether the capital or lower-case Greek character is represented. Neither superscripts nor subscripts are available; they appear here in normal position and type-face. The index provides the Right Ascension and Declination of objects sorted by catalogue number.

  16. Frequencies of wave packets of whistler-mode chorus inside its source region: a case study

    Directory of Open Access Journals (Sweden)

    O. Santolik


    Full Text Available Whistler-mode chorus is a structured wave emission observed in the Earth's magnetosphere in a frequency range from a few hundreds of Hz to several kHz. We investigate wave packets of chorus using high-resolution measurements recorded by the WBD instrument on board the four Cluster spacecraft. A night-side chorus event observed during geomagnetically disturbed conditions is analyzed. We identify lower and upper frequencies for a large number of individual chorus wave packets inside the chorus source region. We investigate how these observations are related to the central position of the chorus source which has been previously estimated from the Poynting flux measurements. We observe typical frequency bandwidths of chorus of approximately 10% of the local electron cyclotron frequency. Observed time scales are around 0.1 s for the individual wave packets. Our results indicate a lower occurrence probability for lower frequencies in the vicinity of the central position of the source compared to measurements recorded closer to the outer boundaries of the source. This is in agreement with recent research based on the backward wave oscillator theory.

  17. Experimental Realization of an Epsilon-Near-Zero Graded-Index Metalens at Terahertz Frequencies (United States)

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


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

  18. Dynamic of Langmuir and Ion-Sound Waves in Type 3 Solar Radio Sources (United States)

    Robinson, P. A.; Willes, A. J.; Cairns, I. H.


    The evolution of Langmuir and ion-sound waves in type 3 sources is investigated, incorporating linear growth, linear damping, and nonlinear electrostatic decay. Improved estimates are obtained for the wavenumber range of growing waves and the nonlinear coupling coefficient for the decay process. The resulting prediction for the electrostatic decay threshold is consistent with the observed high-field cutoff in the Langmuir field distribution. It is shown that the conditions in the solar wind do not allow a steady state to be attained; rather, bursty linear and nonlinear interactions take place, consistent with the highly inhomogeneous and impulsive waves actually observed. Nonlinear growth is found to be fast enough to saturate the growth of the parent Langmuir waves in the available interaction time. The resulting levels of product Langmuir and ion-sound waves are estimated theoretically and shown to be consistent with in situ ISEE 3 observations of type 3 events at 1 AU. Nonlinear interactions slave the growth and decay of product sound waves to that of the product Langmuir waves. The resulting probability distribution of ion-sound field strengths is predicted to have a flat tail extending to a high-field cutoff. This prediction is consistent with statistics derived here from ISEE 3 observations. Agreement is also found between the frequencies of the observed waves and predictions for the product S waves. The competing processes of nonlinear wave collapse and quasilinear relaxation are discussed, and it is concluded that neither is responsible for the saturation of Langmuir growth. When wave and beam inhomogeneities are accounted for, arguments from quasi-linear relaxation yield an upper bound on the Langmuir fields that is too high to be relevant. Nor are the criteria for direct wave collapse of the beam-driven waves met, consistent with earlier simulation results that imply that this process is not responsible for saturation of the beam instability. Indeed, even

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

    Energy Technology Data Exchange (ETDEWEB)

    Suen, Jonathan Y., E-mail:; Padilla, Willie J. [Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708 (United States)


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

  20. Terahertz circular Airy vortex beams. (United States)

    Liu, Changming; Liu, Jinsong; Niu, Liting; Wei, Xuli; Wang, Kejia; Yang, Zhengang


    Vortex beams have received considerable research interests both in optical and millimeter-wave domain since its potential to be utilized in the wireless communications and novel imaging systems. Many well-known optical beams have been demonstrated to carry orbital angular momentum (OAM), such as Laguerre-Gaussian beams and high-order Bessel beams. Recently, the radially symmetric Airy beams that exhibit an abruptly autofocusing feature are also demonstrated to be capable of carrying OAM in the optical domain. However, due to the lack of efficient devices to manipulate terahertz (THz) beams, it could be a challenge to demonstrate the radially symmetric Airy beams in the THz domain. Here we demonstrate the THz circular Airy vortex beams (CAVBs) with a 0.3-THz continuous wave through 3D printing technology. Assisted by the rapidly 3D-printed phase plates, individual OAM states with topological charge l ranging from l = 0 to l = 3 and a multiplexed OAM state are successfully imposed into the radially symmetric Airy beams. We both numerically and experimentally investigate the propagation dynamics of the generated THz CAVBs, and the simulations agree well with the observations.

  1. Equivalent circuit analysis of terahertz metamaterial filters

    KAUST Repository

    Zhang, Xueqian


    An equivalent circuit model for the analysis and design of terahertz (THz) metamaterial filters is presented. The proposed model, derived based on LMC equivalent circuits, takes into account the detailed geometrical parameters and the presence of a dielectric substrate with the existing analytic expressions for self-inductance, mutual inductance, and capacitance. The model is in good agreement with the experimental measurements and full-wave simulations. Exploiting the circuit model has made it possible to predict accurately the resonance frequency of the proposed structures and thus, quick and accurate process of designing THz device from artificial metamaterials is offered. ©2011 Chinese Optics Letters.

  2. Graphene and Graphene Metamaterials for Terahertz Absorbers

    DEFF Research Database (Denmark)

    Andryieuski, Andrei; Pizzocchero, Filippo; Booth, Tim


    Graphene, due to the possibility to tune its conductivity, is the promising material for a range of the terahertz (THz) applications, such as tunable reflectors, absorbers, modulators, filters and polarization converters. Subwavelength structuring of graphene in order to form metamaterials allows...... for even more control over the THz waves. In this poster presentation I will show an elegant way to describe the graphene metamaterials and the design of graphene based absorbers. I will also present our recent experimental results on the graphene absorbers characterization....

  3. Electrical slow waves in the mouse oviduct are dependent on extracellular and intracellular calcium sources (United States)

    Dixon, Rose Ellen; Britton, Fiona C.; Baker, Salah A.; Hennig, Grant W.; Rollings, Christina M.; Sanders, Kenton M.


    Spontaneous contractions of the myosalpinx are critical for oocyte transport along the oviduct. Slow waves, the electrical events that underlie myosalpinx contractions, are generated by a specialized network of pacemaker cells called oviduct interstitial cells of Cajal (ICC-OVI). The ionic basis of oviduct pacemaker activity is unknown. Intracellular recordings and Ca2+ imaging were performed to examine the role of extracellular and intracellular Ca2+ sources in slow wave generation. RT-PCR was performed to determine the transcriptional expression of Ca2+ channels. Molecular studies revealed most isoforms of L- and T-type calcium channels (Cav1.2,1.3,1.4,3.1,3.2,3.3) were expressed in myosalpinx. Reduction of extracellular Ca2+ concentration ([Ca2+]o) resulted in the abolition of slow waves and myosalpinx contractions without significantly affecting resting membrane potential (RMP). Spontaneous Ca2+ waves spread through ICC-OVI cells at a similar frequency to slow waves and were inhibited by reduced [Ca2+]o. Nifedipine depolarized RMP and inhibited slow waves; however, pacemaker activity returned when the membrane was repolarized with reduced extracellular K+ concentration ([K+]o). Ni2+ also depolarized RMP but failed to block slow waves. The importance of ryanodine and inositol 1,4,5 trisphosphate-sensitive stores were examined using ryanodine, tetracaine, caffeine, and 2-aminoethyl diphenylborinate. Results suggest that although both stores are involved in regulation of slow wave frequency, neither are exclusively essential. The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitor cyclopiazonic acid inhibited pacemaker activity and Ca2+ waves suggesting that a functional SERCA pump is necessary for pacemaker activity. In conclusion, results from this study suggest that slow wave generation in the oviduct is voltage dependent, occurs in a membrane potential window, and is dependent on extracellular calcium and functional SERCA pumps. PMID:21881003

  4. Electrical slow waves in the mouse oviduct are dependent on extracellular and intracellular calcium sources. (United States)

    Dixon, Rose Ellen; Britton, Fiona C; Baker, Salah A; Hennig, Grant W; Rollings, Christina M; Sanders, Kenton M; Ward, Sean M


    Spontaneous contractions of the myosalpinx are critical for oocyte transport along the oviduct. Slow waves, the electrical events that underlie myosalpinx contractions, are generated by a specialized network of pacemaker cells called oviduct interstitial cells of Cajal (ICC-OVI). The ionic basis of oviduct pacemaker activity is unknown. Intracellular recordings and Ca(2+) imaging were performed to examine the role of extracellular and intracellular Ca(2+) sources in slow wave generation. RT-PCR was performed to determine the transcriptional expression of Ca(2+) channels. Molecular studies revealed most isoforms of L- and T-type calcium channels (Cav1.2,1.3,1.4,3.1,3.2,3.3) were expressed in myosalpinx. Reduction of extracellular Ca(2+) concentration ([Ca(2+)](o)) resulted in the abolition of slow waves and myosalpinx contractions without significantly affecting resting membrane potential (RMP). Spontaneous Ca(2+) waves spread through ICC-OVI cells at a similar frequency to slow waves and were inhibited by reduced [Ca(2+)](o). Nifedipine depolarized RMP and inhibited slow waves; however, pacemaker activity returned when the membrane was repolarized with reduced extracellular K(+) concentration ([K(+)](o)). Ni(2+) also depolarized RMP but failed to block slow waves. The importance of ryanodine and inositol 1,4,5 trisphosphate-sensitive stores were examined using ryanodine, tetracaine, caffeine, and 2-aminoethyl diphenylborinate. Results suggest that although both stores are involved in regulation of slow wave frequency, neither are exclusively essential. The sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) pump inhibitor cyclopiazonic acid inhibited pacemaker activity and Ca(2+) waves suggesting that a functional SERCA pump is necessary for pacemaker activity. In conclusion, results from this study suggest that slow wave generation in the oviduct is voltage dependent, occurs in a membrane potential window, and is dependent on extracellular calcium and functional

  5. Attenuation modelling of bulk waves generated by a point source in an isotropic medium

    Energy Technology Data Exchange (ETDEWEB)

    Ramadas, C. [Composites Research Center, R and D, Pune (India)


    Attenuation of a bulk wave, generated by a point source, propagating in an isotropic medium, is due to the geometry and nature of the material involved. In numerical simulations, if the complete domain of propagation is modeled, then it captures the attenuation of a wave caused due to its geometry. To model the attenuation of the wave caused due to the nature of the material, it is required to know the material'attenuation coefficient. Since experimental measurement on attenuation of a wave involves both the effects of geometry and material, a method based on curve fitting to estimate the material'attenuation coefficient from effective attenuation coefficient, is proposed. Using the material'attenuation coefficient in the framework of Rayleigh damping model, numerical modeling on attenuation of both the bulk waves - longitudinal and shear excited by a point source was carried out. It was shown that the proposed method captures the attenuation of bulk waves caused on account of geometry as well as nature of the material.

  6. Effects of near-source heterogeneity on wave fields emanating from crustal sources observed at regional and teleseismic distances (United States)

    Avants, Megan S.

    Near-source path effects imprint the wave field emanating from a seismic source and, if not well resolved, can obscure the details of source characteristics determined from observations of the seismic waves at regional and teleseismic distances (≥200 km). These effects are particularly strong for crustal sources such as shallow earthquakes and underground nuclear explosions. First, I explore 2D effects of random seismic P-wave velocity heterogeneity resulting from volumetric heterogeneity in the upper mantle and variability of the Moho on the amplitude decay of the regional phase Pn. Results indicate that the pattern of amplitude decay due to geometric spreading for a simple Earth model is more complex than that for an Earth model containing strong heterogeneity in the mantle lid. Next, I implement the representation theorem in a method which collects displacement and strain components output from a 3D finite difference program capable of including realistic surface topography and geologic structure in a 3D velocity model, and calculates teleseismic 3D Green functions (3DGFs) to specified receiver locations. Green functions produced from a 3D source model match Green functions produced from a 1D source model for theoretical source-receiver geometries. This new method is then applied to the problem of constraining the source depth and location of the three nuclear tests conducted by North Korea, by using a realistic topography model for the mountainous test region to calculate 3DGFs for several possible locations of each event. Amplitude ratios of P and pP from 3DGFs are correlated to those in observed stacked traces. Results show a sensitivity of this method to source depth and location across the test site region with source depths slightly greater than published estimates, but relative locations consistent with other studies. Finally, I determine a rupture model of the 2008 Wenchuan earthquake using 3DGFs calculated in a velocity model containing the dramatic

  7. Prediction of Near-Field Wave Attenuation Due to a Spherical Blast Source (United States)

    Ahn, Jae-Kwang; Park, Duhee


    Empirical and theoretical far-field attenuation relationships, which do not capture the near-field response, are most often used to predict the peak amplitude of blast wave. Jiang et al. (Vibration due to a buried explosive source. PhD Thesis, Curtin University, Western Australian School of Mines, 1993) present rigorous wave equations that simulates the near-field attenuation to a spherical blast source in damped and undamped media. However, the effect of loading frequency and velocity of the media have not yet been investigated. We perform a suite of axisymmetric, dynamic finite difference analyses to simulate the propagation of stress waves induced by spherical blast source and to quantify the near-field attenuation. A broad range of loading frequencies, wave velocities, and damping ratios are used in the simulations. The near-field effect is revealed to be proportional to the rise time of the impulse load and wave velocity. We propose an empirical additive function to the theoretical far-field attenuation curve to predict the near-field range and attenuation. The proposed curve is validated against measurements recorded in a test blast.

  8. Skeletonized inversion of surface wave: Active source versus controlled noise comparison

    KAUST Repository

    Li, Jing


    We have developed a skeletonized inversion method that inverts the S-wave velocity distribution from surface-wave dispersion curves. Instead of attempting to fit every wiggle in the surface waves with predicted data, it only inverts the picked dispersion curve, thereby mitigating the problem of getting stuck in a local minimum. We have applied this method to a synthetic model and seismic field data from Qademah fault, located at the western side of Saudi Arabia. For comparison, we have performed dispersion analysis for an active and controlled noise source seismic data that had some receivers in common with the passive array. The active and passive data show good agreement in the dispersive characteristics. Our results demonstrated that skeletonized inversion can obtain reliable 1D and 2D S-wave velocity models for our geologic setting. A limitation is that we need to build layered initial model to calculate the Jacobian matrix, which is time consuming.

  9. Swope Supernova Survey 2017a (SSS17a), the optical counterpart to a gravitational wave source. (United States)

    Coulter, D A; Foley, R J; Kilpatrick, C D; Drout, M R; Piro, A L; Shappee, B J; Siebert, M R; Simon, J D; Ulloa, N; Kasen, D; Madore, B F; Murguia-Berthier, A; Pan, Y-C; Prochaska, J X; Ramirez-Ruiz, E; Rest, A; Rojas-Bravo, C


    On 2017 August 17, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer detected gravitational waves emanating from a binary neutron star merger, GW170817. Nearly simultaneously, the Fermi and INTEGRAL telescopes detected a gamma-ray transient, GRB 170817A. 10.9 hours after the gravitational wave trigger, we discovered a transient and fading optical source, Swope Supernova Survey 2017a (SSS17a), coincident with GW170817. SSS17a is located in NGC 4993, an S0 galaxy at a distance of 40 megaparsecs. The precise location of GW170817 provides an opportunity to probe the nature of these cataclysmic events by combining electromagnetic and gravitational-wave observations. Copyright © 2017, American Association for the Advancement of Science.


    Directory of Open Access Journals (Sweden)

    Vasily D. Syten’ky


    Full Text Available The paper presents results of the mathematical synthesis of the method of passive location of a seismic wave source. The method employs measurements of regular attenuation of seismic oscillation amplitudes. If it is impossible to determine the location of a seismic event by means of direct measurements, indirect measurements are needed. A priori information for the mathematical synthesis was obtained from functional equations showing inverse proportions of measured amplitudes, arbitrary effective attenuation coefficients and corresponding coordinates. An original method was applied to process the data. The method providing for passive location of seismic waves sources has been developed; it is called the radial basic method. In the one-dimensional case, a distance is determined on the basis of seismic oscillation amplitudes measured by two seismographs that are located at a known base distance coinciding with the direction to the source of seismic waves. The distance is calculated from the receiver that is nearest to the source. If the base distance and the direct line between the seismograph and the seismic wave source do not coincide, a projection of the distance between the receivers to the given straight line is taken into account.Three seismographs were placed at mutually perpendicular base distances in a plane (i.e. the two-dimensional space. This allowed us to obtain an analytical equation for determining the direction to the seismic wave source using measured amplitudes. The value of the angle is taken into account when calculating the distance.For the seismic wave source located in the three-dimensional space, transition equations for combined coordinate systems (i.e. the Descartes (Cartesian, at the axes of which the seismographs were placed, and the spherical coordinate systems were applied, and analytical equations were obtained for determination of coordinates, such as distance/polar radius, elevation


    Directory of Open Access Journals (Sweden)

    Vasily D. Syten’ky


    Full Text Available The paper presents results of the mathematical synthesis of the method of passive location of a seismic wave source. The method employs measurements of regular attenuation of seismic oscillation amplitudes. If it is impossible to determine the location of a seismic event by means of direct measurements, indirect measurements are needed. A priori information for the mathematical synthesis was obtained from functional equations showing inverse proportions of measured amplitudes, arbitrary effective attenuation coefficients and corresponding coordinates. An original method was applied to process the data. The method providing for passive location of seismic waves sources has been developed; it is called the radial basic method. In the one-dimensional case, a distance is determined on the basis of seismic oscillation amplitudes measured by two seismographs that are located at a known base distance coinciding with the direction to the source of seismic waves. The distance is calculated from the receiver that is nearest to the source. If the base distance and the direct line between the seismograph and the seismic wave source do not coincide, a projection of the distance between the receivers to the given straight line is taken into account.Three seismographs were placed at mutually perpendicular base distances in a plane (i.e. the two-dimensional space. This allowed us to obtain an analytical equation for determining the direction to the seismic wave source using measured amplitudes. The value of the angle is taken into account when calculating the distance.For the seismic wave source located in the three-dimensional space, transition equations for combined coordinate systems (i.e. the Descartes (Cartesian, at the axes of which the seismographs were placed, and the spherical coordinate systems were applied, and analytical equations were obtained for determination of coordinates, such as distance/polar radius, elevation

  12. Coherent Polarization Control of THz Waves Generated from Asymmetrically Ionized Gases

    Energy Technology Data Exchange (ETDEWEB)

    Dai Jianming; Zhang, X-C [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Karpowicz, Nicholas, E-mail: [Max-Planck Institute for Quantum Optics, Garching (Germany)


    Unlike polarization control of optical waves, lossless control over the polarization of broadband terahertz waves remained challenging. We recently found that the polarization of terahertz waves generated from gas plasma excited by femtosecond fundamental pulse ({omega}) and its second harmonic (2{omega}) could be coherently controlled by changing the relative phase between the {omega} and 2{omega} pulses. In particular, when the {omega} and 2{omega} pulses are both circularly polarized (or close to it), the photo-excited electrons exhibit different trajectories as the relative phase between the two optical pulses changes, and subsequently terahertz polarization angle can be controlled arbitrarily through the relative phase while the intensity of the emitted terahertz wave is kept constant. This new finding may enable fast terahertz wave modulation and coherent control of nonlinear responses excited by intense terahertz waves with controllable polarization.

  13. Integrated CARS source based on seeded four-wave mixing in silicon nitride

    NARCIS (Netherlands)

    Epping, J.P.; Kues, M.; van der Slot, Petrus J.M.; Lee, Christopher James; Fallnich, C.; Boller, Klaus J.


    We present a theoretical investigation of an integrated nonlinear light source for coherent anti-Stokes Raman scattering (CARS) based on silicon nitride waveguides. Wavelength tunable and temporally synchronized signal and idler pulses are obtained by using seeded four-wave mixing. We find that the

  14. Source depopulation potential and surface-wave tomography using a crosscorrelation method in a scattering medium

    NARCIS (Netherlands)

    Gouedard, P.; Roux, P.; Campillo, M.; Verdel, A.R.; Yao, H.; Van der Hilst, R.D.


    We use seismic prospecting data on a 40 × 40 regular grid of sources and receivers deployed on a 1 km × 1 km area to assess the feasibility and advantages of velocity analysis of the shallow subsurface by means of surface-wave tomography with Green's functions estimated from crosscorrelation. In a


    NARCIS (Netherlands)

    Noorishad, Parisa; Yatawatta, Sarod


    The application of orthonormal basis functions such as Prolate Spheroidal Wave Functions (PSWF) for accurate source modeling in radio astronomy has been comprehensively studied. They are of great importance for high fidelity, high dynamic range imaging with new radio telescopes as well as

  16. Near optimal graphene terahertz non-reciprocal isolator (United States)

    Tamagnone, Michele; Moldovan, Clara; Poumirol, Jean-Marie; Kuzmenko, Alexey B.; Ionescu, Adrian M.; Mosig, Juan R.; Perruisseau-Carrier, Julien


    Isolators, or optical diodes, are devices enabling unidirectional light propagation by using non-reciprocal optical materials, namely materials able to break Lorentz reciprocity. The realization of isolators at terahertz frequencies is a very important open challenge made difficult by the intrinsically lossy propagation of terahertz radiation in current non-reciprocal materials. Here we report the design, fabrication and measurement of a terahertz non-reciprocal isolator for circularly polarized waves based on magnetostatically biased monolayer graphene, operating in reflection. The device exploits the non-reciprocal optical conductivity of graphene and, in spite of its simple design, it exhibits almost 20 dB of isolation and only 7.5 dB of insertion loss at 2.9 THz. Operation with linearly polarized light can be achieved using quarter-wave plates as polarization converters. These results demonstrate the superiority of graphene with respect to currently used terahertz non-reciprocal materials and pave the way to a novel class of optimal non-reciprocal devices.

  17. Terahertz wavefront manipulating by double-layer graphene ribbons metasurface (United States)

    Zhao, Hongliang; Chen, Zhihong; Su, Fei; Ren, Guangjun; Liu, Fei; Yao, Jianquan


    It was recently presented that the phase gradient metasurface can focus the reflection in terahertz range. However, narrow bandwidth and complex tuning method are still challenges. For instance, the size is difficult to be changed once the device is built. We propose a tunable double-layer graphene ribbons array (DLGRA) metasurface which has great potentials for applications in terahertz wavefront control. By changing the Fermi level of each graphene ribbon independently, the DLGRA separated by a bonding agent and a thin dielectric spacer can achieve nearly 2 π phase shift with high reflection efficiency. A reflector which can focus terahertz waves over a broad frequency range is demonstrated numerically by the DLGRA. Intriguingly, through a lateral shift between the nearby graphene ribbons, the variation of coupling induces a shift of focusing frequency. Hence, this approach increases the frequency range to a higher degree than the fixed state. The proposed metasurface provides an effective way for manipulating terahertz waves in a broad frequency range.

  18. Recent Progress in Terahertz Metasurfaces (United States)

    Al-Naib, Ibraheem; Withayachumnankul, Withawat


    In the past decade, the concept of metasurfaces has gradually dominated the field of metamaterials owing to their fascinating optical properties and simple planar geometries. At terahertz frequencies, the concept has been driven further by the availability of advanced micro-fabrication technologies that deliver sub-micron accuracy, well below the terahertz wavelengths. Furthermore, terahertz spectrometers with high dynamic range and amplitude and phase sensitivity provide valuable information for the study of metasurfaces in general. In this paper, we review recent progress in terahertz metasurfaces mainly in the last 5 years. The first part covers nonuniform metasurfaces that perform beamforming in reflection and transmission. In addition, we briefly overview four different methodologies that can be utilized in realizing high-quality-factor metasurfaces. We also describe two recent approaches to tuning the frequency response of terahertz metasurfaces using graphene as an active medium. Finally, we provide a brief summary and outlook for future developments in this rapidly progressing field.

  19. Study of atmospheric gravity waves and infrasonic sources using the USArray Transportable Array pressure data (United States)

    Hedlin, Michael; de Groot-Hedlin, Catherine; Hoffmann, Lars; Alexander, M. Joan; Stephan, Claudia


    The upgrade of the USArray Transportable Array (TA) with microbarometers and infrasound microphones has created an opportunity for a broad range of new studies of atmospheric sources and the large- and small-scale atmospheric structure through which signals from these events propagate. These studies are akin to early studies of seismic events and the Earth's interior structure that were made possible by the first seismic networks. In one early study with the new dataset we use the method of de Groot-Hedlin and Hedlin (2015) to recast the TA as a massive collection of 3-element arrays to detect and locate large infrasonic events. Over 2,000 events have been detected in 2013. The events cluster in highly active regions on land and offshore. Stratospherically ducted signals from some of these events have been recorded more than 2,000 km from the source and clearly show dispersion due to propagation through atmospheric gravity waves. Modeling of these signals has been used to test statistical models of atmospheric gravity waves. The network is also useful for making direct observations of gravity waves. We are currently studying TA and satellite observations of gravity waves from singular events to better understand how the waves near ground level relate to those observed aloft. We are also studying the long-term statistics of these waves from the beginning of 2010 through 2014. Early work using data bandpass filtered from 1-6 hr shows that both the TA and satellite data reveal highly active source regions, such as near the Great Lakes. de Groot-Hedlin and Hedlin, 2015, A method for detecting and locating geophysical events using clusters of arrays, Geophysical Journal International, v203, p960-971, doi: 10.1093/gji/ggv345.

  20. Analogical device for a rough localization of gravitational-wave sources

    Energy Technology Data Exchange (ETDEWEB)

    Frasca, S. (Rome Univ. (Italy). Ist. di Fisica)

    The response of a gravitational cylindrical antenna depends, besides on the values of the intensity of the wave and the sensitivity of the antenna, on the angle between the direction of the source and the axis of the antenna and on the polarization angle of the wave. In this paper, a device (gravitational astrolabe) than can roughly compute the angular part of the response is presented. It gives the zone of the sky toward which a given antenna is ''directed'' at a certain time, the angle of polarization that is best ''received'' and solves easily a number of similar problems.

  1. Analogical device for a rough localization of gravitational-wave sources

    Energy Technology Data Exchange (ETDEWEB)

    Frasca, S.

    The response of a gravitational cylindrical antenna depends, besides on the values of the intensity of the wave and the sensitivity of the antenna, on the angle between the direction of the source and the axis of the antenna and on the polarization angle of the wave. In this paper a device (gravitational astrolabe) that can roughly compute the angular part of the response is presented. It gives the zone of the sky toward which a given antenna is directed at a certain time, the angle of polarization that is best received and solves easily a number of similar problems.

  2. Quantitative estimation of minimum offset for multichannel surface-wave survey with actively exciting source (United States)

    Xu, Y.; Xia, J.; Miller, R.D.


    Multichannel analysis of surface waves is a developing method widely used in shallow subsurface investigations. The field procedures and related parameters are very important for successful applications. Among these parameters, the source-receiver offset range is seldom discussed in theory and normally determined by empirical or semi-quantitative methods in current practice. This paper discusses the problem from a theoretical perspective. A formula for quantitatively evaluating a layered homogenous elastic model was developed. The analytical results based on simple models and experimental data demonstrate that the formula is correct for surface wave surveys for near-surface applications. ?? 2005 Elsevier B.V. All rights reserved.

  3. Controlling Propagation Properties of Surface Plasmon Polariton at Terahertz Frequency (United States)

    Gupta, Barun

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

  4. On an inverse source problem for enhanced oil recovery by wave motion maximization in reservoirs

    KAUST Repository

    Karve, Pranav M.


    © 2014, Springer International Publishing Switzerland. We discuss an optimization methodology for focusing wave energy to subterranean formations using strong motion actuators placed on the ground surface. The motivation stems from the desire to increase the mobility of otherwise entrapped oil. The goal is to arrive at the spatial and temporal description of surface sources that are capable of maximizing mobility in the target reservoir. The focusing problem is posed as an inverse source problem. The underlying wave propagation problems are abstracted in two spatial dimensions, and the semi-infinite extent of the physical domain is negotiated by a buffer of perfectly-matched-layers (PMLs) placed at the domain’s truncation boundary. We discuss two possible numerical implementations: Their utility for deciding the tempo-spatial characteristics of optimal wave sources is shown via numerical experiments. Overall, the simulations demonstrate the inverse source method’s ability to simultaneously optimize load locations and time signals leading to the maximization of energy delivery to a target formation.

  5. Terahertz and Mid Infrared

    CERN Document Server

    Shulika, Oleksiy; Detection of Explosives and CBRN (Using Terahertz)


    The reader will find here a timely update on new THz sources and detection schemes as well as concrete applications to the detection of Explosives and CBRN. Included is a method to identify hidden RDX-based explosives (pure and plastic ones) in the frequency domain study by Fourier Transformation, which has been complemented by the demonstration of improvement of the quality of the images captured commercially available THz passive cameras. The presented examples show large potential for the detection of small hidden objects at long distances (6-10 m).  Complementing the results in the short-wavelength range, laser spectroscopy with a mid-infrared, room temperature, continuous wave, DFB laser diode and high performance DFB QCL have been demonstrated to offer excellent enabling sensor technologies for environmental monitoring, medical diagnostics, industrial and security applications.  From the new source point of view a number of systems have been presented - From superconductors to semiconductors, e.g. Det...

  6. Source Redshifts from Gravitational-Wave Observations of Binary Neutron Star Mergers

    Directory of Open Access Journals (Sweden)

    C. Messenger


    Full Text Available Inspiraling compact binaries as standard sirens will become an invaluable tool for cosmology when we enter the gravitational-wave detection era. However, a degeneracy in the information carried by gravitational waves between the total rest-frame mass M and the redshift z of the source implies that neither can be directly extracted from the signal; only the combination M(1+z, the redshifted mass, can be directly extracted from the signal. Recent work has shown that for third-generation detectors, a tidal correction to the gravitational-wave phase in the late-inspiral signal of binary neutron star systems can be used to break the mass-redshift degeneracy. Here, we propose to use the signature encoded in the postmerger signal allowing the accurate extraction of the intrinsic rest-frame mass of the source, in turn permitting the determination of source redshift and luminosity distance. The entirety of this analysis method and any subsequent cosmological inference derived from it would be obtained solely from gravitational-wave observations and, hence, would be independent of the cosmological distance ladder. Using numerical simulations of binary neutron star mergers of different mass, we model gravitational-wave signals at different redshifts and use a Bayesian parameter estimation to determine the accuracy with which the redshift and mass can be extracted. We find that for a known illustrative neutron star equation of state and using the Einstein telescope, the median of the 1σ confidence regions in redshift corresponds to ∼10%–20% uncertainties at redshifts of z<0.04.

  7. Interpretation of the mathematical source of the energy-flow of love-wave. Love ha no energy ryuryogen

    Energy Technology Data Exchange (ETDEWEB)

    Tazime, K. (Hokkaido Univ., Sapporo (Japan))


    This paper gives a mathematical discussion of the energy flow of wave using the function which represents cylindrical SH wave originating from a linear source as a fundamental solution of two-dimensional inhomogeneous wave equation. The formula representing the energy flow density of cylindrical wave is manipulated by means of this solution and the following results are obtained: first, the source of the cylindrical wave can be converted from a linear one to a planar one; second, the energy flow generated from the source is subject to conditions of all boundary surfaces; third, in virtue of the conservation of energy flow, the inhomogeneous transmitted wave can be generated by total reflection; fourth, the energy flow of love wave is subject to conditions of all boundary planes including the free surface, its source being also able to be converted from a linear one to a planar one; fifth, it is proved that the energy flow of Love wave originating from the source as SH wave is conserved throughout the space in which it propagates. 9 refs., 8 figs.

  8. Controlling software development of CW terahertz target scattering properties measurements based on LabVIEW (United States)

    Fan, Chang-Kun; Li, Qi; Zhou, Yi; Zhao, Yong-Peng; Chen, De-Ying


    With the development of terahertz technology and increasing studies on terahertz target scattering properties, research on terahertz target scattering properties measurements attracts more and more attention. In this paper, to solve problems in the detection process, we design a controlling software for Continuous-Wave (CW) terahertz target scattering properties measurements. The software is designed and programmed based on LabVIEW. The software controls the whole system, involving the switch between the target and the calibration target, the rotation of target, collection, display and storage of the initial data and display, storage of the data after the calibration process. The experimental results show that the software can accomplish the expected requirement, enhance the speed of scattering properties measurements and reduce operation errors.

  9. Ultra-broadband near-field antenna for terahertz plasmonic applications

    Energy Technology Data Exchange (ETDEWEB)

    Polischuk, O. V., E-mail:; Popov, V. V., E-mail: [Russian Academy of Sciences, Saratov Branch of the Kotel’nikov Institute of Radio Engineering and Electronics (Russian Federation); Knap, W. [Université Montpellier 2 and CNRS, Laboratoire Charles Coulomb, UMR 5221 (France)


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

  10. An Inverse Source Problem for a One-dimensional Wave Equation: An Observer-Based Approach

    KAUST Repository

    Asiri, Sharefa M.


    Observers are well known in the theory of dynamical systems. They are used to estimate the states of a system from some measurements. However, recently observers have also been developed to estimate some unknowns for systems governed by Partial differential equations. Our aim is to design an observer to solve inverse source problem for a one dimensional wave equation. Firstly, the problem is discretized in both space and time and then an adaptive observer based on partial field measurements (i.e measurements taken form the solution of the wave equation) is applied to estimate both the states and the source. We see the effectiveness of this observer in both noise-free and noisy cases. In each case, numerical simulations are provided to illustrate the effectiveness of this approach. Finally, we compare the performance of the observer approach with Tikhonov regularization approach.

  11. Polarization insensitive terahertz metamaterial absorber. (United States)

    Grant, J; Ma, Y; Saha, S; Lok, L B; Khalid, A; Cumming, D R S


    We present the simulation, implementation, and measurement of a polarization insensitive resonant metamaterial absorber in the terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us to maximize absorption by varying the dielectric material and thickness and, hence, the effective electrical permittivity and magnetic permeability. Experimental absorption of 77% and 65% at 2.12 THz (in the operating frequency range of terahertz quantum cascade lasers) is observed for a spacer of polyimide or silicon dioxide respectively. These metamaterials are promising candidates as absorbing elements for thermally based terahertz imaging.

  12. Near Source Energy Partitioning for Regional Waves in 2D and 3D Models (United States)


    wave, it must propagate with post critical angle at the Moho discontinuity. However, in the waveguide and especially in the near-source region...reflections on the free surface and interfaces such as the Moho discontinuity. Although the energy exists at short distances, the steep incident angle...left of these lines has incidence angles steeper than the critical angle on the Moho and the energy will leak to the upper mantle through multiple

  13. Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers. (United States)

    Consolino, L; Taschin, A; Bartolini, P; Bartalini, S; Cancio, P; Tredicucci, A; Beere, H E; Ritchie, D A; Torre, R; Vitiello, M S; De Natale, P


    Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO(3) waveguide and covering the 0.1-6 THz frequency range. We show that even a small fraction (laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.

  14. Source parameter inversion for wave energy focusing to a target inclusion embedded in a three-dimensional heterogeneous halfspace

    KAUST Repository

    Karve, Pranav M.


    We discuss a methodology for computing the optimal spatio-temporal characteristics of surface wave sources necessary for delivering wave energy to a targeted subsurface formation. The wave stimulation is applied to the target formation to enhance the mobility of particles trapped in its pore space. We formulate the associated wave propagation problem for three-dimensional, heterogeneous, semi-infinite, elastic media. We use hybrid perfectly matched layers at the truncation boundaries of the computational domain to mimic the semi-infiniteness of the physical domain of interest. To recover the source parameters, we define an inverse source problem using the mathematical framework of constrained optimization and resolve it by employing a reduced-space approach. We report the results of our numerical experiments attesting to the methodology\\'s ability to specify the spatio-temporal description of sources that maximize wave energy delivery. Copyright © 2016 John Wiley & Sons, Ltd.

  15. Terahertz (THZ) Imaging (United States)


    Especially for thin films of material the absorption and time delay of a THz pulse are mostly too low to be detected. 48. Nemec, H.; Kuzel, P.; Khazan, M...the summary) states that the use of thin ZnTe electro-optic sensors for coherent characterization of a freely propagating terahertz beam...on a GaAs wafer is determined by the diameter of the gating- 40 beam-induced thin photo carrier layer. With a dynamic aperture created on a GaAs

  16. Modeling Volcanic Eruption Parameters by Near-Source Internal Gravity Waves. (United States)

    Ripepe, M; Barfucci, G; De Angelis, S; Delle Donne, D; Lacanna, G; Marchetti, E


    Volcanic explosions release large amounts of hot gas and ash into the atmosphere to form plumes rising several kilometers above eruptive vents, which can pose serious risk on human health and aviation also at several thousands of kilometers from the volcanic source. However the most sophisticate atmospheric models and eruptive plume dynamics require input parameters such as duration of the ejection phase and total mass erupted to constrain the quantity of ash dispersed in the atmosphere and to efficiently evaluate the related hazard. The sudden ejection of this large quantity of ash can perturb the equilibrium of the whole atmosphere triggering oscillations well below the frequencies of acoustic waves, down to much longer periods typical of gravity waves. We show that atmospheric gravity oscillations induced by volcanic eruptions and recorded by pressure sensors can be modeled as a compact source representing the rate of erupted volcanic mass. We demonstrate the feasibility of using gravity waves to derive eruption source parameters such as duration of the injection and total erupted mass with direct application in constraining plume and ash dispersal models.

  17. A Numerical Study on the Excitation of Guided Waves in Rectangular Plates Using Multiple Point Sources

    Directory of Open Access Journals (Sweden)

    Wenbo Duan


    Full Text Available Ultrasonic guided waves are widely used to inspect and monitor the structural integrity of plates and plate-like structures, such as ship hulls and large storage-tank floors. Recently, ultrasonic guided waves have also been used to remove ice and fouling from ship hulls, wind-turbine blades and aeroplane wings. In these applications, the strength of the sound source must be high for scanning a large area, or to break the bond between ice, fouling and plate substrate. More than one transducer may be used to achieve maximum sound power output. However, multiple sources can interact with each other, and form a sound field in the structure with local constructive and destructive regions. Destructive regions are weak regions and shall be avoided. When multiple transducers are used it is important that they are arranged in a particular way so that the desired wave modes can be excited to cover the whole structure. The objective of this paper is to provide a theoretical basis for generating particular wave mode patterns in finite-width rectangular plates whose length is assumed to be infinitely long with respect to its width and thickness. The wave modes have displacements in both width and thickness directions, and are thus different from the classical Lamb-type wave modes. A two-dimensional semi-analytical finite element (SAFE method was used to study dispersion characteristics and mode shapes in the plate up to ultrasonic frequencies. The modal analysis provided information on the generation of modes suitable for a particular application. The number of point sources and direction of loading for the excitation of a few representative modes was investigated. Based on the SAFE analysis, a standard finite element modelling package, Abaqus, was used to excite the designed modes in a three-dimensional plate. The generated wave patterns in Abaqus were then compared with mode shapes predicted in the SAFE model. Good agreement was observed between the

  18. An Adaptive Observer-Based Algorithm for Solving Inverse Source Problem for the Wave Equation

    KAUST Repository

    Asiri, Sharefa M.


    Observers are well known in control theory. Originally designed to estimate the hidden states of dynamical systems given some measurements, the observers scope has been recently extended to the estimation of some unknowns, for systems governed by partial differential equations. In this paper, observers are used to solve inverse source problem for a one-dimensional wave equation. An adaptive observer is designed to estimate the state and source components for a fully discretized system. The effectiveness of the algorithm is emphasized in noise-free and noisy cases and an insight on the impact of measurements’ size and location is provided.

  19. Integrating a Traveling Wave Tube into an AECR-U ion source

    Energy Technology Data Exchange (ETDEWEB)

    Covo, Michel Kireeff; Benitez, Janilee Y.; Ratti, Alessandro; Vujic, Jasmina L.


    An RF system of 500W - 10.75 to 12.75 GHz was designed and integrated into the Advanced Electron Cyclotron Resonance - Upgrade (AECR-U) ion source of the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. The AECR-U produces ion beams for the Cyclotron giving large flexibility of ion species and charge states. The broadband frequency of a Traveling Wave Tube (TWT) allows modifying the volume that couples and heats the plasma. The TWT system design and integration with the AECR-U ion source and results from commissioning are presented.

  20. Gyrotrons for High-Power Terahertz Science and Technology at FIR UF (United States)

    Idehara, Toshitaka; Sabchevski, Svilen Petrov


    In this review paper, we present the recent progress in the development of a series of gyrotrons at the Research Center for Development of Far-Infrared Region, University of Fukui, that have opened the road to many novel applications in the high-power terahertz science and technology. The current status of the research in this actively developing field is illustrated by the most representative examples in which the developed gyrotrons are used as powerful and frequency-tunable sources of coherent radiation operating in a continuous-wave regime. Among them are high-precision spectroscopic techniques (most notably dynamic nuclear polarization-nuclear magnetic resonance, electron spin resonance, X-ray detected magnetic resonance, and studies of the hyperfine splitting of the energy levels of positronium), treatment and characterization of advanced materials, and new medical technologies.

  1. Intense terahertz emission from molecular beam epitaxy-grown GaAs/GaSb(001)

    Energy Technology Data Exchange (ETDEWEB)

    Sadia, Cyril P.; Laganapan, Aleena Maria; Agatha Tumanguil, Mae; Estacio, Elmer; Somintac, Armando; Salvador, Arnel [National Institute of Physics, University of the Philippines Diliman, Quezon City 1101 (Philippines); Que, Christopher T. [Physics Department, De La Salle University, 2401 Taft Avenue, Manila 1004 (Philippines); Yamamoto, Kohji; Tani, Masahiko [Research Center for Development of Far-Infrared Region, University of Fukui, Fukui 910-8507 (Japan)


    Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

  2. Synthesis of Directional Sources Using Wave Field Synthesis, Possibilities, and Limitations

    Directory of Open Access Journals (Sweden)

    Corteel E


    Full Text Available The synthesis of directional sources using wave field synthesis is described. The proposed formulation relies on an ensemble of elementary directivity functions based on a subset of spherical harmonics. These can be combined to create and manipulate directivity characteristics of the synthesized virtual sources. The WFS formulation introduces artifacts in the synthesized sound field for both ideal and real loudspeakers. These artifacts can be partly compensated for using dedicated equalization techniques. A multichannel equalization technique is shown to provide accurate results thus enabling for the manipulation of directional sources with limited reconstruction artifacts. Applications of directional sources to the control of the direct sound field and the interaction with the listening room are discussed.

  3. New technique for generating light source array in tilted wave interferometer (United States)

    Li, Jia; Shen, Hua; Zhu, Rihong; Lu, Qing


    Smaller and lighter optical systems with better performance can be built by the use of freeform optics. However, most optical systems were constrained to traditional surfaces for the accurate metrology of freeform surface is a challenge so far unsolved. One high-precision approach to measure freeform surface with less time and expense is using tilted wave interferometer. A lens array is placed in the test path of the interferometer, which can generate light source array that locally compensate the gradient of test surface. But each source generated by lens array is not ideal spherical wave which contains aberrations. In addition, the sources cannot be activated individually during the measurement, so that it is impossible to perform an irregular source array according to the gradient variation of each test surface. Thus, a novel technique based on fiber array is proposed for generating irregular source array. Whereas, the position deviation of each fiber and phase difference produced by the length of each fiber affect the measurement result. In this paper, the consequences of above errors are analyzed. A calibration method can obtain the exact spatial coordinates of each fiber is suggested to calculate the position deviation of each fiber. Meanwhile, a method based on Mach-Zehnder interference system is presented, which can get phase difference produced by the length of each fiber accurately. Afterwards, the data obtained by the two calibration methods are introduced into the mathematical model of system error for eliminating the measurement error introduced by the use of fiber array. An elliptical mirror is measured by our tilted wave interferometer based on fiber array showing the feasibility of the proposed methods.

  4. Mapping the sources of the seismic wave field at Kilauea volcano, Hawaii, using data recorded on multiple seismic Antennas (United States)

    Almendros, J.; Chouet, B.; Dawson, P.; Huber, Caleb G.


    Seismic antennas constitute a powerful tool for the analysis of complex wave fields. Well-designed antennas can identify and separate components of a complex wave field based on their distinct propagation properties. The combination of several antennas provides the basis for a more complete understanding of volcanic wave fields, including an estimate of the location of each individual wave-field component identified simultaneously by at least two antennas. We used frequency-slowness analyses of data from three antennas to identify and locate the different components contributing to the wave fields recorded at Kilauea volcano, Hawaii, in February 1997. The wave-field components identified are (1) a sustained background volcanic tremor in the form of body waves generated in a shallow hydrothermal system located below the northeastern edge of the Halemaumau pit crater; (2) surface waves generated along the path between this hydrothermal source and the antennas; (3) back-scattered surface wave energy from a shallow reflector located near the southeastern rim of Kilauea caldera; (4) evidence for diffracted wave components originating at the southeastern edge of Halemaumau; and (5) body waves reflecting the activation of a deeper tremor source between 02 hr 00 min and 16 hr 00 min Hawaii Standard Time on 11 February.

  5. Terahertz imaging for styrofoam inspection (United States)

    Pradarutti, B.; Riehemann, S.; Notni, G.; Tünnermann, A.


    Imaging of styrofoam with the help of ultrashort Terahertz pulses is investigated. With a combination of pulse amplitude and time delay imaging it is possible to speed up the measurement about two orders of magnitudes.

  6. An Analytical Method of Auxiliary Sources Solution for Plane Wave Scattering by Impedance Cylinders - A Reference Solution for the Numerical Method of Auxiliary Sources

    DEFF Research Database (Denmark)

    Larsen, Niels Vesterdal; Breinbjerg, Olav


    To facilitate the validation of the numerical Method of Auxiliary Sources an analytical Method of Auxiliary Sources solution is derived in this paper. The Analytical solution is valid for transverse magnetic, and electric, plane wave scattering by circular impedance Cylinders, and it is derived...... of the numerical Method of Auxiliary Sources for a range of scattering configurations....... with their singularities at different positions away from the origin. The transformation necessitates a truncation of the wave transformation but the inaccuracy introduced hereby is shown to be negligible. The analytical Method of Auxiliary Sources solution is employed as a reference to investigate the accuracy...

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

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shenggang, E-mail:; Hu, Min; Chen, Xiaoxing; Zhang, Ping; Gong, Sen; Zhao, Tao; Zhong, Renbin [Terahertz Research Centre, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054 (China); Cooperative Innovation Centre of Terahertz Science, Chengdu, Sichuan 610054 (China); Zhang, Chao [Terahertz Research Centre, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054 (China); Cooperative Innovation Centre of Terahertz Science, Chengdu, Sichuan 610054 (China); School of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2522 (Australia)


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

  8. Multi-source and multi-directional shear wave generation with intersecting steered ultrasound push beams. (United States)

    Nabavizadeh, Alireza; Song, Pengfei; Chen, Shigao; Greenleaf, James F; Urban, Matthew W


    Elasticity imaging is becoming established as a means of assisting in diagnosis of certain diseases. Shear wave-based methods have been developed to perform elasticity measurements in soft tissue. Comb-push ultrasound shear elastography (CUSE) is one of these methods that apply acoustic radiation force to induce the shear wave in soft tissues. CUSE uses multiple ultrasound beams that are transmitted simultaneously to induce multiple shear wave sources into the tissue, with improved shear wave SNR and increased shear wave imaging frame rate. We propose a novel method that uses steered push beams (SPB) that can be applied for beam formation for shear wave generation. In CUSE beamforming, either unfocused or focused beams are used to create the propagating shear waves. In SPB methods we use unfocused beams that are steered at specific angles. The interaction of these steered beams causes shear waves to be generated in more of a random nature than in CUSE. The beams are typically steered over a range of 3 to 7° and can either be steered to the left (-θ) or right (+θ).We performed simulations of 100 configurations using Field II and found the best configurations based on spatial distribution of peaks in the resulting intensity field. The best candidates were ones with a higher number of the intensity peaks distributed over all depths in the simulated beamformed results. Then these optimal configurations were applied on a homogeneous phantom and two different phantoms with inclusions. In one of the inhomogeneous phantoms we studied two spherical inclusions with 10 and 20 mm diameters, and in the other phantom we studied cylindrical inclusions with diameters ranging from 2.53 to 16.67 mm. We compared these results with those obtained using conventional CUSE with unfocused and focused beams. The mean and standard deviation of the resulting shear wave speeds were used to evaluate the accuracy of the reconstructions by examining bias with nominal values for the phantoms

  9. A broadband LED source in visible to short-wave-infrared wavelengths for spectral tumor diagnostics (United States)

    Hayashi, Daiyu; van Dongen, Anne Marie; Boerekamp, Jack; Spoor, Sandra; Lucassen, Gerald; Schleipen, Jean


    Various tumor types exhibit the spectral fingerprints in the absorption and reflection spectra in visible and especially in near- to short-wave-infrared wavelength ranges. For the purpose of spectral tumor diagnostics by means of diffuse reflectance spectroscopy, we developed a broadband light emitting diode (LED) source consisting of a blue LED for optical excitation, Lu3Al5O12:Ce3+,Cr3+ luminescent garnet for visible to near infrared emissions, and Bismuth doped GeO2 luminescent glass for near-infrared to short-wave infrared emissions. It emits broad-band light emissions continuously in 470-1600 nm with a spectral gap at 900-1000 nm. In comparison to the currently available broadband light sources like halogen lamps, high-pressure discharge lamps and super continuum lasers, the light sources of this paper has significant advantages for spectral tissue diagnostics in high-spectral stability, improved light coupling to optical fibers, potential in low light source cost and enabling battery-drive.

  10. Terahertz Imaging of Subjects With Concealed Weapons

    National Research Council Canada - National Science Library

    Dickinson, Jason C; Goyette, Thoms M; Gatesman, Andrew J; Joseph, Cecil S; Root, Zachary G; Giles, Robert H; Waldman, Jerry; Nixon, William E


    .... Two contrasting techniques were used to collect the imagery. Both methods made use of in-house transceivers, consisting of two ultra-stable far-infrared lasers, terahertz heterodyne detection systems, and terahertz anechoic chambers...

  11. Resonant metallic nanostructures for enhanced terahertz spectroscopy

    KAUST Repository

    Toma, A.


    We present our recent studies on terahertz resonant dipole nanoantennas. Exploiting the localization and enhancement capabilities of these devices, we introduce an effective method to perform terahertz spectroscopy on an extremely small number of nano-objects.

  12. Cherenkov emission of terahertz surface plasmon polaritons from a superluminal optical spot on a structured metal surface. (United States)

    Bakunov, M I; Tsarev, M V; Hangyo, M


    We propose to launch terahertz surface plasmon polaritons on a structured metal surface by using a femtosecond laser pulse obliquely incident on a strip of an electro-optic material deposited on the surface. The laser pulse creates a nonlinear polarization that moves along the strip with a superluminal velocity and emits surface terahertz waves via the Cherenkov radiation mechanism. We calculate the radiated fields and frequency distribution of the radiated energy for a grooved perfect-conductor surface with a GaAs strip illuminated by Ti:sapphire laser. This technique can be used to perform surface terahertz spectroscopy.

  13. Deep Rapid Optical Follow-Up of Gravitational Wave Sources with the Dark Energy Camera (United States)

    Cowperthwaite, Philip


    The detection of an electromagnetic counterpart associated with a gravitational wave detection by the Advanced LIGO and VIRGO interferometers is one of the great observational challenges of our time. The large localization regions and potentially faint counterparts require the use of wide-field, large aperture telescopes. As a result, the Dark Energy Camera, a 3.3 sq deg CCD imager on the 4-m Blanco telescope at CTIO in Chile is the most powerful instrument for this task in the Southern Hemisphere. I will report on the results from our joint program between the community and members of the dark energy survey to conduct rapid and efficient follow-up of gravitational wave sources. This includes systematic searches for optical counterparts, as well as developing an understanding of contaminating sources on timescales not normally probed by traditional untargeted supernova surveys. I will additionally comment on the immense science gains to be made by a joint detection and discuss future prospects from the standpoint of both next generation wide-field telescopes and next generation gravitational wave detectors.

  14. Theoretical study of terahertz generation from atoms and aligned molecules driven by two-color laser fields

    CERN Document Server

    Chen, Wenbo; Meng, Chao; Liu, Jinlei; Zhou, Zhaoyan; Zhang, Dongwen; Yuan, Jianmin; Zhao, Zengxiu


    We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second harmonic field by solving time-dependent Schr\\"odinger equation (TDSE). The comparisons between one-, two-, and three- dimensional TDSE numerical simulations show that initial ionized wave-packet and its subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles. We also present the dependence of the optimum phase delay and yield of terahertz radiation on the laser intensity, wavelength, duration, and the ratio of two-color laser components. Terahertz wave generation from model hydrogen molecules are further investigated by comparing with high harmonic emission. It is found that the terahertz yield is following the alignment dependence of ionization rate, while the optimal two-color phase delays varies by a small amount when the alignment angle changes from 0 to 90 degrees, which reflects alignment dependence of attosecond electron d...

  15. Planar Holographic Metasurfaces for Terahertz Focusing (United States)

    Kuznetsov, Sergei A.; Astafev, Mikhail A.; Beruete, Miguel; Navarro-Cía, Miguel


    Scientists and laymen alike have always been fascinated by the ability of lenses and mirrors to control light. Now, with the advent of metamaterials and their two-dimensional counterpart metasurfaces, such components can be miniaturized and designed with additional functionalities, holding promise for system integration. To demonstrate this potential, here ultrathin reflection metasurfaces (also called metamirrors) designed for focusing terahertz radiation into a single spot and four spaced spots are proposed and experimentally investigated at the frequency of 0.35 THz. Each metasurface is designed using a computer-generated spatial distribution of the reflection phase. The phase variation within 360 deg is achieved via a topological morphing of the metasurface pattern from metallic patches to U-shaped and split-ring resonator elements, whose spectral response is derived from full-wave electromagnetic simulations. The proposed approach demonstrates a high-performance solution for creating low-cost and lightweight beam-shaping and beam-focusing devices for the terahertz band.

  16. Uncertainties in the 2004 Sumatra-Andaman source through nonlinear stochastic inversion of tsunami waves (United States)

    Gopinathan, D.; Venugopal, M.; Roy, D.; Rajendran, K.; Guillas, S.; Dias, F.


    Numerical inversions for earthquake source parameters from tsunami wave data usually incorporate subjective elements to stabilize the search. In addition, noisy and possibly insufficient data result in instability and non-uniqueness in most deterministic inversions, which are barely acknowledged. Here, we employ the satellite altimetry data for the 2004 Sumatra-Andaman tsunami event to invert the source parameters. We also include kinematic parameters that improve the description of tsunami generation and propagation, especially near the source. Using a finite fault model that represents the extent of rupture and the geometry of the trench, we perform a new type of nonlinear joint inversion of the slips, rupture velocities and rise times with minimal a priori constraints. Despite persistently good waveform fits, large uncertainties in the joint parameter distribution constitute a remarkable feature of the inversion. These uncertainties suggest that objective inversion strategies should incorporate more sophisticated physical models of seabed deformation in order to significantly improve the performance of early warning systems.

  17. Stable grid refinement and singular source discretization for seismic wave simulations

    Energy Technology Data Exchange (ETDEWEB)

    Petersson, N A; Sjogreen, B


    An energy conserving discretization of the elastic wave equation in second order formulation is developed for a composite grid, consisting of a set of structured rectangular component grids with hanging nodes on the grid refinement interface. Previously developed summation-by-parts properties are generalized to devise a stable second order accurate coupling of the solution across mesh refinement interfaces. The discretization of singular source terms of point force and point moment tensor type are also studied. Based on enforcing discrete moment conditions that mimic properties of the Dirac distribution and its gradient, previous single grid formulas are generalized to work in the vicinity of grid refinement interfaces. These source discretization formulas are shown to give second order accuracy in the solution, with the error being essentially independent of the distance between the source and the grid refinement boundary. Several numerical examples are given to illustrate the properties of the proposed method.

  18. Influence of the multipole order of the source on the decay of an inertial wave beam in a rotating fluid (United States)

    Machicoane, Nathanael; Cortet, Pierre-Philippe; Voisin, Bruno; Moisy, Frederic


    Inertial wave beams emitted from localized sources are relevant to a broad range of geo and astrophysical flows. These beams are excited at critical lines, where the local slope of solid boundaries equals the propagation angle of the wave, in rotating fluid domains affected by a global harmonic forcing (e.g. precession, libration, tidal motion). We show here theoretically and experimentally that the decay of the amplitude of such wave beams depends on the multipole order of the source. We analyze the far-field viscous decay of a two-dimensional inertial wave beam emitted by a harmonic line source in a rotating fluid. By identifying the relevant conserved quantities along the wave beam, we show how the beam structure and decay exponent are governed by the multipole order of the source. Two wavemakers are considered experimentally, a pulsating and an oscillating cylinder, aiming to produce a monopole and a dipole source, respectively. The relevant conserved quantity which discriminates between these two sources is the instantaneous flow rate along the wave beam, which is non-zero for the monopole and zero for the dipole. For each source, the beam structure and decay exponent, measured using particle image velocimetry, are found in good agreement with the predictions.

  19. Open source acceleration of wave optics simulations on energy efficient high-performance computing platforms (United States)

    Beck, Jeffrey; Bos, Jeremy P.


    We compare several modifications to the open-source wave optics package, WavePy, intended to improve execution time. Specifically, we compare the relative performance of the Intel MKL, a CPU based OpenCV distribution, and GPU-based version. Performance is compared between distributions both on the same compute platform and between a fully-featured computing workstation and the NVIDIA Jetson TX1 platform. Comparisons are drawn in terms of both execution time and power consumption. We have found that substituting the Fast Fourier Transform operation from OpenCV provides a marked improvement on all platforms. In addition, we show that embedded platforms offer some possibility for extensive improvement in terms of efficiency compared to a fully featured workstation.

  20. All-integrated terahertz modulators (United States)

    Degl'Innocenti, Riccardo; Kindness, Stephen J.; Beere, Harvey E.; Ritchie, David A.


    Terahertz (0.1-10 THz corresponding to vacuum wavelengths between 30 μm and 3 mm) research has experienced impressive progress in the last few decades. The importance of this frequency range stems from unique applications in several fields, including spectroscopy, communications, and imaging. THz emitters have experienced great development recently with the advent of the quantum cascade laser, the improvement in the frequency range covered by electronic-based sources, and the increased performance and versatility of time domain spectroscopic systems based on full-spectrum lasers. However, the lack of suitable active optoelectronic devices has hindered the ability of THz technologies to fulfill their potential. The high demand for fast, efficient integrated optical components, such as amplitude, frequency, and polarization modulators, is driving one of the most challenging research areas in photonics. This is partly due to the inherent difficulties in using conventional integrated modulation techniques. This article aims to provide an overview of the different approaches and techniques recently employed in order to overcome this bottleneck.

  1. Multilayer Graphene for Waveguide Terahertz Modulator

    DEFF Research Database (Denmark)

    Khromova, I.; Andryieuski, Andrei; Lavrinenko, Andrei


    We study terahertz to infrared electromagnetic properties of multilayer graphene/dielectric artificial medium and present a novel concept of terahertz modulation at midinfrared wavelengths. This approach allows the realization of high-speed electrically controllable terahertz modulators based...... on hollow waveguide sections filled with multilayer graphene....

  2. Homogeneous spectral spanning of terahertz semiconductor lasers with radio frequency modulation. (United States)

    Wan, W J; Li, H; Zhou, T; Cao, J C


    Homogeneous broadband and electrically pumped semiconductor radiation sources emitting in the terahertz regime are highly desirable for various applications, including spectroscopy, chemical sensing, and gas identification. In the frequency range between 1 and 5 THz, unipolar quantum cascade lasers employing electron inter-subband transitions in multiple-quantum-well structures are the most powerful semiconductor light sources. However, these devices are normally characterized by either a narrow emission spectrum due to the narrow gain bandwidth of the inter-subband optical transitions or an inhomogeneous broad terahertz spectrum from lasers with heterogeneous stacks of active regions. Here, we report the demonstration of homogeneous spectral spanning of long-cavity terahertz semiconductor quantum cascade lasers based on a bound-to-continuum and resonant phonon design under radio frequency modulation. At a single drive current, the terahertz spectrum under radio frequency modulation continuously spans 330 GHz (~8% of the central frequency), which is the record for single plasmon waveguide terahertz lasers with a bound-to-continuum design. The homogeneous broadband terahertz sources can be used for spectroscopic applications, i.e., GaAs etalon transmission measurement and ammonia gas identification.

  3. THz wave emission microscope (United States)

    Yuan, Tao

    Sensing and imaging using Terahertz (THz) radiation has attracted more and more interest in the last two decades thanks to the abundant material 'finger prints' in the THz frequency range. The low photon energy also makes THz radiation an attractive tool for nondestructive evaluation of materials and devices, biomedical applications, security checks and explosive screening. Due to the long wavelength, the far-field THz wave optical systems have relatively low spatial resolution. This physical limitation confines THz wave sensing and imaging to mostly macro-size samples. To investigate local material properties or micro-size structures and devices, near-field technology has to be employed. In this dissertation, the Electro-Optical THz wave emission microscope is investigated. The basic principle is to focus the femtosecond laser to a tight spot on a thin THz emitter layer to produce a THz wave source with a similar size as the focus spot. The apparatus provides a method for placing a THz source with sub-wavelength dimension in the near-field range of the investigated sample. Spatial resolution to the order of one tenth of the THz wavelength is demonstrated by this method. The properties of some widely used THz wave emission materials under tight focused pump light are studied. As an important branch of THz time domain spectroscopy (THz-TDS), THz wave emission spectroscopy has been widely used as a tool to investigate the material physics, such as energy band structure, carrier dynamics, material nonlinear properties and dynamics. As the main work of this dissertation, we propose to combine the THz wave emission spectroscopy with scanning probe microscopy (SPM) to build a tip-assisted THz wave emission microscope (TATEM), which is a valuable extension to current SPM science and technology. Illuminated by a femtosecond laser, the biased SPM tip forms a THz wave source inside the sample beneath the tip. The source size is proportional to the apex size of the tip so

  4. The expected spins of gravitational wave sources with isolated field binary progenitors (United States)

    Zaldarriaga, Matias; Kushnir, Doron; Kollmeier, Juna A.


    We explore the consequences of dynamical evolution of field binaries composed of a primary black hole (BH) and a Wolf-Rayet (WR) star in the context of gravitational wave (GW) source progenitors. We argue, from general considerations, that the spin of the WR-descendent BH will be maximal in a significant number of cases due to dynamical effects. In other cases, the spin should reflect the natal spin of the primary BH which is currently theoretically unconstrained. We argue that the three currently published LIGO systems (GW150914, GW151226, LVT151012) suggest that this spin is small. The resultant effective spin distribution of gravitational wave sources should thus be bi-model if this classic GW progenitor channel is indeed dominant. While this is consistent with the LIGO detections thus far, it is in contrast to the three best-measured high-mass X-ray binary (HMXB) systems. A comparison of the spin distribution of HMXBs and GW sources should ultimately reveal whether or not these systems arise from similar astrophysical channels.

  5. Finite-fault source inversion using teleseismic P waves: Simple parameterization and rapid analysis (United States)

    Mendoza, C.; Hartzell, S.


    We examine the ability of teleseismic P waves to provide a timely image of the rupture history for large earthquakes using a simple, 2D finite‐fault source parameterization. We analyze the broadband displacement waveforms recorded for the 2010 Mw∼7 Darfield (New Zealand) and El Mayor‐Cucapah (Baja California) earthquakes using a single planar fault with a fixed rake. Both of these earthquakes were observed to have complicated fault geometries following detailed source studies conducted by other investigators using various data types. Our kinematic, finite‐fault analysis of the events yields rupture models that similarly identify the principal areas of large coseismic slip along the fault. The results also indicate that the amount of stabilization required to spatially smooth the slip across the fault and minimize the seismic moment is related to the amplitudes of the observed P waveforms and can be estimated from the absolute values of the elements of the coefficient matrix. This empirical relationship persists for earthquakes of different magnitudes and is consistent with the stabilization constraint obtained from the L‐curve in Tikhonov regularization. We use the relation to estimate the smoothing parameters for the 2011 Mw 7.1 East Turkey, 2012 Mw 8.6 Northern Sumatra, and 2011 Mw 9.0 Tohoku, Japan, earthquakes and invert the teleseismic P waves in a single step to recover timely, preliminary slip models that identify the principal source features observed in finite‐fault solutions obtained by the U.S. Geological Survey National Earthquake Information Center (USGS/NEIC) from the analysis of body‐ and surface‐wave data. These results indicate that smoothing constraints can be estimated a priori to derive a preliminary, first‐order image of the coseismic slip using teleseismic records.

  6. A kilonova as the electromagnetic counterpart to a gravitational-wave source (United States)

    Smartt, S. J.; Chen, T.-W.; Jerkstrand, A.; Coughlin, M.; Kankare, E.; Sim, S. A.; Fraser, M.; Inserra, C.; Maguire, K.; Chambers, K. C.; Huber, M. E.; Krühler, T.; Leloudas, G.; Magee, M.; Shingles, L. J.; Smith, K. W.; Young, D. R.; Tonry, J.; Kotak, R.; Gal-Yam, A.; Lyman, J. D.; Homan, D. S.; Agliozzo, C.; Anderson, J. P.; Angus, C. R.; Ashall, C.; Barbarino, C.; Bauer, F. E.; Berton, M.; Botticella, M. T.; Bulla, M.; Bulger, J.; Cannizzaro, G.; Cano, Z.; Cartier, R.; Cikota, A.; Clark, P.; De Cia, A.; Della Valle, M.; Denneau, L.; Dennefeld, M.; Dessart, L.; Dimitriadis, G.; Elias-Rosa, N.; Firth, R. E.; Flewelling, H.; Flörs, A.; Franckowiak, A.; Frohmaier, C.; Galbany, L.; González-Gaitán, S.; Greiner, J.; Gromadzki, M.; Guelbenzu, A. Nicuesa; Gutiérrez, C. P.; Hamanowicz, A.; Hanlon, L.; Harmanen, J.; Heintz, K. E.; Heinze, A.; Hernandez, M.-S.; Hodgkin, S. T.; Hook, I. M.; Izzo, L.; James, P. A.; Jonker, P. G.; Kerzendorf, W. E.; Klose, S.; Kostrzewa-Rutkowska, Z.; Kowalski, M.; Kromer, M.; Kuncarayakti, H.; Lawrence, A.; Lowe, T. B.; Magnier, E. A.; Manulis, I.; Martin-Carrillo, A.; Mattila, S.; McBrien, O.; Müller, A.; Nordin, J.; O’Neill, D.; Onori, F.; Palmerio, J. T.; Pastorello, A.; Patat, F.; Pignata, G.; Podsiadlowski, Ph.; Pumo, M. L.; Prentice, S. J.; Rau, A.; Razza, A.; Rest, A.; Reynolds, T.; Roy, R.; Ruiter, A. J.; Rybicki, K. A.; Salmon, L.; Schady, P.; Schultz, A. S. B.; Schweyer, T.; Seitenzahl, I. R.; Smith, M.; Sollerman, J.; Stalder, B.; Stubbs, C. W.; Sullivan, M.; Szegedi, H.; Taddia, F.; Taubenberger, S.; Terreran, G.; van Soelen, B.; Vos, J.; Wainscoat, R. J.; Walton, N. A.; Waters, C.; Weiland, H.; Willman, M.; Wiseman, P.; Wright, D. E.; Wyrzykowski, Ł.; Yaron, O.


    Gravitational waves were discovered with the detection of binary black-hole mergers and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of ‑1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90–140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

  7. Active terahertz metamaterial devices (United States)

    Chen, Houtong; Padilla, Willie John; Averitt, Richard Douglas; O'Hara, John F.; Lee, Mark


    Metamaterial structures are taught which provide for the modulation of terahertz frequency signals. Each element within an array of metamaterial (MM) elements comprises multiple loops and at least one gap. The MM elements may comprise resonators with conductive loops and insulated gaps, or the inverse in which insulated loops are present with conductive gaps; each providing useful transmissive control properties. The metamaterial elements are fabricated on a semiconducting substrate configured with a means of enhancing or depleting electrons from near the gaps of the MM elements. An on to off transmissivity ratio of about 0.5 is achieved with this approach. Embodiments are described in which the MM elements incorporated within a Quantum Cascade Laser (QCL) to provide surface emitting (SE) properties.

  8. Review of terahertz technology development at INO (United States)

    Dufour, Denis; Marchese, Linda; Terroux, Marc; Oulachgar, Hassane; Généreux, Francis; Doucet, Michel; Mercier, Luc; Tremblay, Bruno; Alain, Christine; Beaupré, Patrick; Blanchard, Nathalie; Bolduc, Martin; Chevalier, Claude; D'Amato, Dominic; Desroches, Yan; Duchesne, François; Gagnon, Lucie; Ilias, Samir; Jerominek, Hubert; Lagacé, François; Lambert, Julie; Lamontagne, Frédéric; Le Noc, Loïc; Martel, Anne; Pancrati, Ovidiu; Paultre, Jacques-Edmond; Pope, Tim; Provençal, Francis; Topart, Patrice; Vachon, Carl; Verreault, Sonia; Bergeron, Alain


    Over the past decade, INO has leveraged its expertise in the development of uncooled microbolometer detectors for infrared imaging to produce terahertz (THz) imaging systems. By modifying its microbolometer-based focal plane arrays to enhance absorption in the THz bands and by developing custom THz imaging lenses, INO has developed a leading-edge THz imaging system, the IRXCAM-THz-384 camera, capable of exploring novel applications in the emerging field of terahertz imaging and sensing. Using appropriate THz sources, results show that the IRXCAM-THz-384 camera is able to image a variety of concealed objects of interest for applications such as non-destructive testing and weapons detections. By using a longer wavelength (94 GHz) source, it is also capable of sensing the signatures of various objects hidden behind a drywall panel. This article, written as a review of THz research at INO over the past decade, describes the technical components that form the IRXCAM-THz-384 camera and the experimental setup used for active THz imaging. Image results for concealed weapons detection experiments, an exploration of wavelength choice on image quality, and the detection of hidden objects behind drywall are also presented.

  9. Modeling terahertz heating effects on water. (United States)

    Kristensen, Torben T L; Withayachumnankul, Withawat; Jepsen, Peter U; Abbott, Derek


    We apply Kirchhoff's heat equation to model the influence of a CW terahertz beam on a sample of water, which is assumed to be static. We develop a generalized model, which easily can be applied to other liquids and solids by changing the material constants. If the terahertz light source is focused down to a spot with a diameter of 0.5 mm, we find that the steady-state temperature increase per milliwatt of transmitted power is 1.8?C/mW. A quantum cascade laser can produce a CW beam in the order of several milliwatts and this motivates the need to estimate the effect of beam power on the sample temperature. For THz time domain systems, we indicate how to use our model as a worst-case approximation based on the beam average power. It turns out that THz pulses created from photoconductive antennas give a negligible increase in temperature. As biotissue contains a high water content, this leads to a discussion of worst-case predictions for THz heating of the human body in order to motivate future detailed study. An open source Matlab implementation of our model is freely available for use at

  10. Self-attraction into spinning eigenstates of a mobile wave source by its emission back-reaction (United States)

    Labousse, Matthieu; Perrard, Stéphane; Couder, Yves; Fort, Emmanuel


    The back-reaction of a radiated wave on the emitting source is a general problem. In the most general case, back-reaction on moving wave sources depends on their whole history. Here we study a model system in which a pointlike source is piloted by its own memory-endowed wave field. Such a situation is implemented experimentally using a self-propelled droplet bouncing on a vertically vibrated liquid bath and driven by the waves it generates along its trajectory. The droplet and its associated wave field form an entity having an intrinsic dual particle-wave character. The wave field encodes in its interference structure the past trajectory of the droplet. In the present article we show that this object can self-organize into a spinning state in which the droplet possesses an orbiting motion without any external interaction. The rotation is driven by the wave-mediated attractive interaction of the droplet with its own past. The resulting "memory force" is investigated and characterized experimentally, numerically, and theoretically. Orbiting with a radius of curvature close to half a wavelength is shown to be a memory-induced dynamical attractor for the droplet's motion.

  11. Terahertz wireless communications based on photonics technologies. (United States)

    Nagatsuma, Tadao; Horiguchi, Shogo; Minamikata, Yusuke; Yoshimizu, Yasuyuki; Hisatake, Shintaro; Kuwano, Shigeru; Yoshimoto, Naoto; Terada, Jun; Takahashi, Hiroyuki


    There has been an increasing interest in the application of terahertz (THz) waves to broadband wireless communications. In particular, use of frequencies above 275 GHz is one of the strong concerns among radio scientists and engineers, because these frequency bands have not yet been allocated at specific active services, and there is a possibility to employ extremely large bandwidths for ultra-broadband wireless communications. Introduction of photonics technologies for signal generation, modulation and detection is effective not only to enhance the bandwidth and/or the data rate, but also to combine fiber-optic (wired) and wireless networks. This paper reviews recent progress in THz wireless communications using telecom-based photonics technologies towards 100 Gbit/s.

  12. A flexible and wearable terahertz scanner (United States)

    Suzuki, D.; Oda, S.; Kawano, Y.


    Imaging technologies based on terahertz (THz) waves have great potential for use in powerful non-invasive inspection methods. However, most real objects have various three-dimensional curvatures and existing THz technologies often encounter difficulties in imaging such configurations, which limits the useful range of THz imaging applications. Here, we report the development of a flexible and wearable THz scanner based on carbon nanotubes. We achieved room-temperature THz detection over a broad frequency band ranging from 0.14 to 39 THz and developed a portable THz scanner. Using this scanner, we performed THz imaging of samples concealed behind opaque objects, breakages and metal impurities of a bent film and multi-view scans of a syringe. We demonstrated a passive biometric THz scan of a human hand. Our results are expected to have considerable implications for non-destructive and non-contact inspections, such as medical examinations for the continuous monitoring of health conditions.

  13. Tunable terahertz metamaterial with a graphene reflector (United States)

    Deng, Guangsheng; Xia, Tianyu; Yang, Jun; Qiu, Longzhen; Yin, Zhiping


    An hybrid graphene/metamaterial(MM) structure by directly depositing single-layer graphene on bottom of a SiO2/Si substrate of the electric ring resonators is proposed and theoretically investigated in the terahertz(THz) region. Our calculated results show that the presence of the graphene strongly changes the THz MM transmittance in the frequency range from 0.1 to 1.7 THz, and a modulation depth of 80% or above is reached on the whole frequency range except a narrow band. The tunability of the proposed structure is mainly dependent on the transmission bands between two neighboring resonance frequencies, which is different from the conventional graphene MM structure based on single resonance dip. Moreover, the energy absorption in graphene layer plays an important role in THz wave modulation. This easy-to-fabricate structure shows potential applications in developing broadband transmission modulators and sensors.

  14. Refined Source Terms in WAVEWATCH III with Wave Breaking and Sea Spray Forecasts (United States)


    dissipation and breaking, nonlinear wave-wave interaction, bottom friction, wave- mud interaction, wave-current interaction as well as sea spray flux. These...interaction. J. Fluid Mech., 211, 463–495. Banner, M.L., J.R. Gemmrich and D.M. Farmer (2002) Multiscale measurements of ocean wave breaking...of the equilibrium range in wind-generated gravity waves. J. Fluid Mech. 156, 505–531. Schwendeman, M., J. Thomson, and J.R. Gemmrich (2014) Wave

  15. Global existence and nonexistence for the viscoelastic wave equation with nonlinear boundary damping-source interaction

    KAUST Repository

    Said-Houari, Belkacem


    The goal of this work is to study a model of the viscoelastic wave equation with nonlinear boundary/interior sources and a nonlinear interior damping. First, applying the Faedo-Galerkin approximations combined with the compactness method to obtain existence of regular global solutions to an auxiliary problem with globally Lipschitz source terms and with initial data in the potential well. It is important to emphasize that it is not possible to consider density arguments to pass from regular to weak solutions if one considers regular solutions of our problem where the source terms are locally Lipschitz functions. To overcome this difficulty, we use an approximation method involving truncated sources and adapting the ideas in [13] to show that the existence of weak solutions can still be obtained for our problem. Second, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term, then the solution ceases to exist and blows up in finite time provided that the initial data are large enough.

  16. Accessibility condition of wave propagation and multicharged ion production in electron cyclotron resonance ion source plasma. (United States)

    Kato, Yushi; Yano, Keisuke; Nishiokada, Takuya; Nagaya, Tomoki; Kimura, Daiju; Kumakura, Sho; Imai, Youta; Hagino, Shogo; Otsuka, Takuro; Sato, Fuminobu


    A new tandem type source of electron cyclotron resonance (ECR) plasmas has been constructing for producing synthesized ion beams in Osaka University. Magnetic mirror field configuration with octupole magnets can be controlled to various shape of ECR zones, namely, in the 2nd stage plasma to be available by a pair mirror and a supplemental coil. Noteworthy correlations between these magnetic configurations and production of multicharged ions are investigated in detail, as well as their optimum conditions. We have been considering accessibility condition of electromagnetic and electrostatic waves propagating in ECR ion source plasma, and then investigated their correspondence relationships with production of multicharged ions. It has been clarified that there exits efficient configuration of ECR zones for producing multicharged ion beams experimentally, and then has been suggested from detail accessibility conditions on the ECR plasma that new resonance, i.e., upper hybrid resonance, must have occurred.

  17. Accurate source location from waves scattered by surface topography: Applications to the Nevada and North Korean test sites (United States)

    Shen, Y.; Wang, N.; Bao, X.; Flinders, A. F.


    Scattered waves generated near the source contains energy converted from the near-field waves to the far-field propagating waves, which can be used to achieve location accuracy beyond the diffraction limit. In this work, we apply a novel full-wave location method that combines a grid-search algorithm with the 3D Green's tensor database to locate the Non-Proliferation Experiment (NPE) at the Nevada test site and the North Korean nuclear tests. We use the first arrivals (Pn/Pg) and their immediate codas, which are likely dominated by waves scattered at the surface topography near the source, to determine the source location. We investigate seismograms in the frequency of [1.0 2.0] Hz to reduce noises in the data and highlight topography scattered waves. High resolution topographic models constructed from 10 and 90 m grids are used for Nevada and North Korea, respectively. The reference velocity model is based on CRUST 1.0. We use the collocated-grid finite difference method on curvilinear grids to calculate the strain Green's tensor and obtain synthetic waveforms using source-receiver reciprocity. The `best' solution is found based on the least-square misfit between the observed and synthetic waveforms. To suppress random noises, an optimal weighting method for three-component seismograms is applied in misfit calculation. Our results show that the scattered waves are crucial in improving resolution and allow us to obtain accurate solutions with a small number of stations. Since the scattered waves depends on topography, which is known at the wavelengths of regional seismic waves, our approach yields absolute, instead of relative, source locations. We compare our solutions with those of USGS and other studies. Moreover, we use differential waveforms to locate pairs of the North Korea tests from years 2006, 2009, 2013 and 2016 to further reduce the effects of unmodeled heterogeneities and errors in the reference velocity model.

  18. Formation of aerial standing wave field using ultrasonic sources consisting of multiple stripe-mode transverse vibrating plates (United States)

    Naito, Koki; Asami, Takuya; Miura, Hikaru


    Intense aerial acoustic waves can be produced by an ultrasonic source consisting of a transverse vibrating plate and an external jutting driving point. Previously, we studied the dimensional parameters of vibrating plates to produce stripe-mode patterns and thereby determine the plate dimensions that generate high-quality patterns. In this research, we use four transverse vibrating plates as ultrasonic sources to produce intense standing wave fields in air. As a result, an aerial standing wave field was formed in the field surrounded by four vibrating plates. Furthermore, for a total input power of 30 W for the two ultrasonic sources, a very strong (sound pressure level, 167 dB) wave field is obtained.

  19. THz wave generation and imaging for industrial applications (United States)

    Kawase, K.; Shibuya, T.; Suizu, K.; Hayashi, S.


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

  20. WASS: An open-source pipeline for 3D stereo reconstruction of ocean waves (United States)

    Bergamasco, Filippo; Torsello, Andrea; Sclavo, Mauro; Barbariol, Francesco; Benetazzo, Alvise


    Stereo 3D reconstruction of ocean waves is gaining more and more popularity in the oceanographic community and industry. Indeed, recent advances of both computer vision algorithms and computer processing power now allow the study of the spatio-temporal wave field with unprecedented accuracy, especially at small scales. Even if simple in theory, multiple details are difficult to be mastered for a practitioner, so that the implementation of a sea-waves 3D reconstruction pipeline is in general considered a complex task. For instance, camera calibration, reliable stereo feature matching and mean sea-plane estimation are all factors for which a well designed implementation can make the difference to obtain valuable results. For this reason, we believe that the open availability of a well tested software package that automates the reconstruction process from stereo images to a 3D point cloud would be a valuable addition for future researches in this area. We present WASS (, an Open-Source stereo processing pipeline for sea waves 3D reconstruction. Our tool completely automates all the steps required to estimate dense point clouds from stereo images. Namely, it computes the extrinsic parameters of the stereo rig so that no delicate calibration has to be performed on the field. It implements a fast 3D dense stereo reconstruction procedure based on the consolidated OpenCV library and, lastly, it includes set of filtering techniques both on the disparity map and the produced point cloud to remove the vast majority of erroneous points that can naturally arise while analyzing the optically complex nature of the water surface. In this paper, we describe the architecture of WASS and the internal algorithms involved. The pipeline workflow is shown step-by-step and demonstrated on real datasets acquired at sea.

  1. Strain Imaging Using Terahertz Waves and Metamaterials (United States)


    NOT TO BE CONSTRUED AS AN OFFICIAL DEPARTMENT OF THE ARMY POSITION UNLESS SO DESIGNATED BY OTHER AUTHORIZED DOCUMENTS. TRADE NAMES USE...uu Polarization ............................................ 7 8. 500 μm Region of Sample MM6 for ux Polarization...8 9. 500 μm Region of Sample MM6 Mueller Matrix Prediction for ux Transmission

  2. Metasurfaces for Terahertz Waves Polarization Control

    DEFF Research Database (Denmark)

    Lavrinenko, Andrei; Malureanu, Radu; Zalkovskij, Maksim

    metamaterials-based THz components have been proposed and show good potential for applications [1,2]. Especially fruitful appears to be two-dimensional metamaterials or metasurfaces due to fabrication simplifications and practically the same as bulk metamaterials functionalities. In the talk we will focus...... on employment of THz metasurfaces as polarizers and polarization converters, absorbers and conducting layers with enhanced transmittance, dichroic and chiral reconfigurable systems, waveplates and broadband filters. As the unified approach we employ the transmission line theory providing a needed level...... to several cm2) 2μm-thick Ni film. Depending on arrangement of both slits and their sizes different optical properties of such metasurface can be acquired. We demonstrate linear polarization filtering with the parallel slits dimmers, and more complex chiral behaviour of dimers, when non-equal slits are non...

  3. Electrically tunable terahertz metamaterials based on graphene stacks array (United States)

    Liu, Hanqing; Liu, Peiguo; Bian, Li-an; Liu, Chenxi; Zhou, Qihui; Chen, Yuwei


    With the ability of tuning chemical potential via gate voltage, the permittivity of graphene stack can be dynamically adjusted over a wide range. In this paper, we design electrically tunable metamaterials based on the graphene/Al2O3 stacks array, which can achieve a good modulation of resonant frequency and peak value in terahertz region. Due to the enlargement of plasmonic resonance response and the broaden distribution of electric field, our proposed structures perform a better tunability compared with traditional metamaterials loaded monolayer graphene. Since the dipole-dipole coupling between adjacent stacks strengthens immensely as reduces the filling factor of array, the modulated capacity could be further improved. It is found that for oblique incidence, the transmission property is also sensitive to the chemical potential of graphene as well as the polarization direction of incident terahertz wave. These results could be very instructive for the potential applications in voltage-sensitive devices, tunable sensors and photovoltaic switches.

  4. Sparsity based terahertz reflective off-axis digital holography (United States)

    Wan, Min; Muniraj, Inbarasan; Malallah, Ra'ed; Zhao, Liang; Ryle, James P.; Rong, Lu; Healy, John J.; Wang, Dayong; Sheridan, John T.


    Terahertz radiation lies between the microwave and infrared regions in the electromagnetic spectrum. Emitted frequencies range from 0.1 to 10 THz with corresponding wavelengths ranging from 30 μm to 3 mm. In this paper, a continuous-wave Terahertz off-axis digital holographic system is described. A Gaussian fitting method and image normalisation techniques were employed on the recorded hologram to improve the image resolution. A synthesised contrast enhanced hologram is then digitally constructed. Numerical reconstruction is achieved using the angular spectrum method of the filtered off-axis hologram. A sparsity based compression technique is introduced before numerical data reconstruction in order to reduce the dataset required for hologram reconstruction. Results prove that a tiny amount of sparse dataset is sufficient in order to reconstruct the hologram with good image quality.

  5. Source-receiver two-way wave extrapolation for prestack exploding-reflector modelling and migration

    KAUST Repository

    Alkhalifah, Tariq Ali


    Most modern seismic imaging methods separate input data into parts (shot gathers). We develop a formulation that is able to incorporate all available data at once while numerically propagating the recorded multidimensional wavefield forward or backward in time. This approach has the potential for generating accurate images free of artiefacts associated with conventional approaches. We derive novel high-order partial differential equations in the source-receiver time domain. The fourth-order nature of the extrapolation in time leads to four solutions, two of which correspond to the incoming and outgoing P-waves and reduce to the zero-offset exploding-reflector solutions when the source coincides with the receiver. A challenge for implementing two-way time extrapolation is an essential singularity for horizontally travelling waves. This singularity can be avoided by limiting the range of wavenumbers treated in a spectral-based extrapolation. Using spectral methods based on the low-rank approximation of the propagation symbol, we extrapolate only the desired solutions in an accurate and efficient manner with reduced dispersion artiefacts. Applications to synthetic data demonstrate the accuracy of the new prestack modelling and migration approach.

  6. An open source tool to analyse heat waves using flow analogues and weather regimes (United States)

    Radanovics, Sabine; Jézéquel, Aglaé; Alvarez-Castro, Carmen; Yiou, Pascal; Hempelmann, Nils; Ehbrecht, Carsten; Nangini, Cathy; Vautard, Robert


    Studies on the relation of atmospheric circulation patterns and heat waves using flow analogues or weather regimes often miss an assessment of the uncertainties related to internal climate variability and the analysis method itself because of the limited length of the data sets used. However, considering this type of uncertainty is important when interpreting changes found in a transient climate using this type of methods. We used several hundreds of years long preindustrial control runs of CMIP5 climate models to address this issue in a constant model climate. Several heat waves over central Europe as simulated by the climate model were selected and then reconstructed using circulation analogues, that is by searching for days with similar pressure fields in the simulation and recombining the temperatures of these similar days to form uchronic events. The variance of these uchronic events is supposed to vary with the rarity of the original event. We therefore present the relationship between the variance of the uchronic events and the distance between the original event and its analogues. Further we present the variation of the distances due to internal climate variability. Weather regimes are typical atmospheric circulation patterns obtained for example using a cluster analysis. Each day is then assigned to a cluster, the weather regime. The frequency of the weather regimes is supposed to be constant in a constant climate, but variations of these frequencies can occur due to internal climate variability. We therefore show these variations for the weather regimes associated with the heat waves. The web processing service (WPS) flyingpigeon is an open source WPS featuring processes for studying weather extremes and climate change impacts. Flyingpigeon is part of the open source project birdhouse, a collection of WPSs following the Open Geospatial Consortium (OGC) standard and available on github. The WPS allowed to first select the data sets needed from the ESGF

  7. Fiber-based source for multiplex-CARS microscopy based on degenerate four-wave mixing. (United States)

    Gottschall, Thomas; Baumgartl, Martin; Sagnier, Aude; Rothhardt, Jan; Jauregui, Cesar; Limpert, Jens; Tünnermann, Andreas


    We present a fiber-based laser source for multiplex coherent anti-Stokes Raman scattering (CARS) microscopy. This source is very compact and potentially alignment-free. The corresponding pump and Stokes pulses for the CARS process are generated by degenerate four-wave mixing (FWM) in photonic-crystal fibers. In addition, an ytterbium-doped fiber laser emitting spectrally narrow 100 ps pulses at 1035 nm wavelength serves as pump for the FWM frequency conversion. The FWM process delivers narrow-band pulses at 648 nm and drives a continuum-like spectrum ranging from 700 to 820 nm. With the presented source vibrational resonances with energies between 1200 cm-1 and 3200 cm-1 can be accessed with a resolution of 10 cm-1. Additionally, the temporal characteristics of the FWM output have been investigated by a cross-correlation setup, revealing the suitability of the emitted pulses for CARS microscopy. This work marks a significant step towards a simple and powerful all-fiber, maintenance-free multiplex-CARS source for real-world applications outside a laboratory environment.

  8. Subwavelength micropillar array terahertz lasers. (United States)

    Krall, Michael; Brandstetter, Martin; Deutsch, Christoph; Detz, Hermann; Andrews, Aaron Maxwell; Schrenk, Werner; Strasser, Gottfried; Unterrainer, Karl


    We report on micropillar-based terahertz lasers with active pillars that are much smaller than the emission wavelength. These micropillar array lasers correspond to scaled-down band-edge photonic crystal lasers forming an active photonic metamaterial. In contrast to photonic crystal lasers which use significantly larger pillar structures, lasing emission is not observed close to high-symmetry points in the photonic band diagram, but in the effective medium regime. We measure stimulated emission at 4 THz for micropillar array lasers with pillar diameters of 5 µm. Our results not only demonstrate the integration of active subwavelength optics in a terahertz laser, but are also an important step towards the realization of nanowire-based terahertz lasers.

  9. Moisture detection in composites by terahertz spectroscopy (United States)

    Malinowski, Paweł; Pałka, Norbert; Opoka, Szymon; Wandowski, Tomasz; Ostachowicz, Wiesław


    The application of Glass Fibre Reinforced Polymers (GFRP) in many branches of industry has been increasing steadily. Many research works focus on damage identification for structures made out of such materials. However, not only delaminations, cracks or other damage can have a negative influence of GFRP parts performance. Previous research proved that fluid absorption influences the mechanical performance of composites. GFRP parts can be contaminated by moisture or release agent during manufacturing, while fuel, hydraulic fluid and moisture ingression into the composite can be the in-service treats. In the reported research authors focus on moisture detection. There are numerous sources of moisture such as post manufacturing NDT inspection with ultrasonics coupled by water or exposition to moisture during transportation and in service. An NDT tool used for the research is a terahertz (THz) spectrometer. The device uses an electromagnetic radiation in the terahertz range (0.1-3 THz) and allows for reflection and transmission measurements. The spectrometer is equipped with moving table that allows for XY scanning of large objects such as GFRP panels. In the conducted research refractive indices were experimentally extracted from the materials of interest (water and GFRP). Time signals as well as C-scans were analysed for samples with moisture contamination. In order to be sure that the observed effects are related to moisture contamination reference measurements were conducted. The obtained results showed that the THz NDT technique can detect moisture hidden under a GFRP with multiple layers.

  10. Investigation of Terahertz Emission from BiVO4 /Au Thin Film Interface

    NARCIS (Netherlands)

    Kumar, N.; Abdi, F.F.; Trzesniewski, B.; Smith, W.A.; Planken, P.C.M.; Adam, A.J.L.


    We demonstrate emission of terahertz pulses from a BiVO4/Au thin film interface, illuminated with femtosecond laser pulses. Based on the experimental observations, we propose that the most likely cause of the THz emission is the Photo-Dember effect caused by the standing wave intensity distribution

  11. Extremely low-loss single-mode photonic crystal fiber in the terahertz regime

    DEFF Research Database (Denmark)

    Islam, Raonaqul; Hasanuzzaman, G. K M; Sadath, Md Anwar


    This paper presents an updated design and numerical characterization of a rotated porous-core hexagonal photonic crystal fiber (PCF) for single-mode terahertz (THz) wave guidance. The simulation results are found using an efficient finite element method (FEM) which show a better and ultra...

  12. Polarization-stable dual-color DFB fibre laser system for CW terahertz generation

    DEFF Research Database (Denmark)

    Eichhorn, Finn; Petersen, Jens Engholm; Jepsen, Peter Uhd

    The terahertz, or THz, frequency range represents a gap in technology as well as knowledge in the electromagnetic spectrum. The THz spectral range is here loosely defined as frequencies between 100 GHz and 10 THz. Electromagnetic waves at THz frequencies interact strongly with metals, ceramics...

  13. Terahertz Solitons in Biomolecular Systems and their Excitation by External Electromagnetic Field

    Directory of Open Access Journals (Sweden)

    Bugay А.N.


    Full Text Available Nonlinear dynamics of charge and acoustic excitations in cellular microtubules is considered. Different types of nonlinear solitary waves were studied taking account for dissipation. The mechanism of electro-acoustic pulse excitation by external electromagnetic field of terahertz frequency is recognized.

  14. Physics and applications of terahertz radiation

    CERN Document Server

    Paul, Douglas


    This book covers the latest advances in the techniques employed to manage the THz radiation and its potential uses. It has been subdivided in three sections: THz Detectors, THz Sources, Systems and Applications. These three sections will allow the reader to be introduced in a logical way to the physics problems of sensing and generation of the terahertz radiation, the implementation of these devices into systems including other components and finally the exploitation of the equipment for real applications in some different field. All of the sections and chapters can be individually addressed in order to deepen the understanding of a single topic without the need to read the whole book. The THz Detectors section will address the latest developments in detection devices based on three different physical principles: photodetection, thermal power detection, rectification. The THz Sources section will describe three completely different generation methods, operating in three separate scales: quantum cascade lasers...

  15. Broadband terahertz fiber directional coupler

    DEFF Research Database (Denmark)

    Nielsen, Kristian; Rasmussen, Henrik K.; Jepsen, Peter Uhd


    We present the design of a short broadband fiber directional coupler for terahertz (THz) radiation and demonstrate a 3 dB coupler with a bandwidth of 0:6 THz centered at 1:4 THz. The broadband coupling is achieved by mechanically downdoping the cores of a dual-core photonic crystal fiber by micro......We present the design of a short broadband fiber directional coupler for terahertz (THz) radiation and demonstrate a 3 dB coupler with a bandwidth of 0:6 THz centered at 1:4 THz. The broadband coupling is achieved by mechanically downdoping the cores of a dual-core photonic crystal fiber...

  16. A terahertz grid frequency doubler


    Moussessian, Alina; Wanke, Michael C.; Li, Yongjun; Chiao, Jung-Chih; Allen, S. James; Crowe, Thomas W.; Rutledge, David B.


    We present a 144-element terahertz quasi-optical grid frequency doubler. The grid is a planar structure with bow-tie antennas as a unit cell, each loaded with a planar Schottky diode. The maximum output power measured for this grid is 24 mW at 1 THz for 3.1-μs 500-GHz input pulses with a peak input power of 47 W. An efficiency of 0.17% for an input power of 6.3 W and output power of 10.8 mW is measured. To date, this is the largest recorded output power for a multiplier at terahertz frequenci...

  17. NATO Advanced Research Workshop on Terahertz and Mid Infrared Radiation

    CERN Document Server

    Pereira, Mauro F; Terahertz and Mid Infrared Radiation


    Terahertz (THz) and Mid-Infrared (MIR) radiation  (TERA-MIR) can be transmitted through nearly any material without causing biological harm. Novel and rapid methods of detection can be created with devices operation in these spectral ranges allowing scanning for weapons, detecting hidden explosives (including plastic landmines), controlling the quality of food and a host of other exciting applications.  This book focuses on mathematical and physical aspects of the field, on unifying these two spectral domains (THz and MIR) with regard to common sources, detectors, materials and applications, and on key interdisciplinary topics. The main THz and MIR source is the quantum cascade laser (QCL). Thus significant attention is paid to the challenge of turning this advanced technology into affordable commercial devices so as to exploit its enormous potential. However other alternatives to THz QCLs are also presented, e.g.  sub-terahertz imaging from avalanching GaAs bipolar transistors, Josephson junctions as THz ...

  18. Low-threshold terahertz molecular laser optically pumped by a quantum cascade laser

    Directory of Open Access Journals (Sweden)

    A. Pagies


    Full Text Available We demonstrate a low-threshold, compact, room temperature, and continuous-wave terahertz molecular laser optically pumped by a mid-infrared quantum cascade laser. These characteristics are obtained, thanks to large dipole transitions of the active medium: NH3 (ammonia in gas state. The low-power (<60 mW laser pumping excites the molecules, thanks to intense mid-infrared transitions around 10.3 μm. The molecules de-excite by stimulated emission on pure inversion “umbrella-mode” quantum transitions allowed by the tunnel effect. The tunability of the quantum cascade laser gives access to several pure inversion transitions with different rotation states: we demonstrate the continuous-wave generation of ten laser lines around 1 THz. At 1.07 THz, we measure a power of 34 μW with a very low-threshold of 2 mW and a high differential efficiency of 0.82 mW/W. The spectrum was measured showing that the linewidth is lower than 1 MHz. To our knowledge, this is the first THz molecular laser pumped by a solid-state source and this result opens the way for compact, simple, and efficient THz source at room temperature for imaging applications.

  19. Ion Bernstein instability as a possible source for oxygen ion cyclotron harmonic waves (United States)

    Min, Kyungguk; Denton, Richard E.; Liu, Kaijun; Gary, S. Peter; Spence, Harlan E.


    This paper demonstrates that an ion Bernstein instability can be a possible source for recently reported electromagnetic waves with frequencies at or near the singly ionized oxygen ion cyclotron frequency, ΩO+, and its harmonics. The particle measurements during strong wave activity revealed a relatively high concentration of oxygen ions (˜15%) whose phase space density exhibits a local peak at energy ˜20 keV. Given that the electron plasma-to-cyclotron frequency ratio is ωpe/Ωe≳1, this energy corresponds to the particle speed v/vA≳0.3, where vA is the oxygen Alfvén speed. Using the observational key plasma parameters, a simplified ion velocity distribution is constructed, where the local peak in the oxygen ion velocity distribution is represented by an isotropic shell distribution. Kinetic linear dispersion theory then predicts unstable Bernstein modes at or near the harmonics of ΩO+ and at propagation quasi-perpendicular to the background magnetic field, B0. If the cold ions are mostly protons, these unstable modes are characterized by a low compressibility (|δB∥|2/|δB|2≲0.01), a small phase speed (vph˜0.2vA), a relatively small ratio of the electric field energy to the magnetic field energy (between 10-4 and 10-3), and the Poynting vector directed almost parallel to B0. These linear properties are overall in good agreement with the properties of the observed waves. We demonstrate that superposition of the predicted unstable Bernstein modes at quasi-perpendicular propagation can produce the observed polarization properties, including the minimum variance direction on average almost parallel to B0.

  20. Direct simulations of outdoor blast wave propagation from source to receiver (United States)

    Nguyen-Dinh, M.; Lardjane, N.; Duchenne, C.; Gainville, O.


    Outdoor blast waves generated by impulsive sources are deeply affected by numerous physical conditions such as source shape or height of burst in the near field, as well as topography, ground nature, or atmospheric conditions at larger distances. Application of classical linear acoustic methods may result in poor estimates of peak overpressures at intermediate ranges in the presence of these conditions. Here, we show, for the first time, that converged direct fully nonlinear simulations can be produced at a reasonable CPU cost in two-dimensional axisymmetric geometry from source location to more than 500 m/kg^{1/3}. The numerical procedure is based on a high-order finite-volume method with adaptive mesh refinement for solving the nonlinear Euler equations with a detonation model. It is applied to a real outdoor pyrotechnic site. A digital terrain model is built, micro-meteorological conditions are included through an effective sound speed, and a ground roughness model is proposed in order to account for the effects of vegetation and unresolved scales. Two-dimensional axisymmetric simulations are performed for several azimuths, and a comparison is made with experimental pressure signals recorded at scaled distances from 36 to 504 m/kg^{1/3}. The relative importance of the main physical effects is discussed.

  1. Automatic Wave Equation Migration Velocity Analysis by Focusing Subsurface Virtual Sources

    KAUST Repository

    Sun, Bingbing


    Macro velocity model building is important for subsequent pre-stack depth migration and full waveform inversion. Wave equation migration velocity analysis (WEMVA) utilizes the band-limited waveform to invert for the velocity. Normally, inversion would be implemented by focusing the subsurface offset common image gathers (SOCIGs). We re-examine this concept with a different perspective: In subsurface offset domain, using extended Born modeling, the recorded data can be considered as invariant with respect to the perturbation of the position of the virtual sources and velocity at the same time. A linear system connecting the perturbation of the position of those virtual sources and velocity is derived and solved subsequently by Conjugate Gradient method. In theory, the perturbation of the position of the virtual sources is given by the Rytov approximation. Thus, compared to the Born approximation, it relaxes the dependency on amplitude and makes the proposed method more applicable for real data. We demonstrate the effectiveness of the approach by applying the proposed method on both isotropic and anisotropic VTI synthetic data. A real dataset example verifies the robustness of the proposed method.

  2. Comparison of femtosecond laser and continuous wave UV sources for protein-nucleic acid crosslinking. (United States)

    Fecko, Christopher J; Munson, Katherine M; Saunders, Abbie; Sun, Guangxing; Begley, Tadhg P; Lis, John T; Webb, Watt W


    Crosslinking proteins to the nucleic acids they bind affords stable access to otherwise transient regulatory interactions. Photochemical crosslinking provides an attractive alternative to formaldehyde-based protocols, but irradiation with conventional UV sources typically yields inadequate product amounts. Crosslinking with pulsed UV lasers has been heralded as a revolutionary technique to increase photochemical yield, but this method had only been tested on a few protein-nucleic acid complexes. To test the generality of the yield enhancement, we have investigated the benefits of using approximately 150 fs UV pulses to crosslink TATA-binding protein, glucocorticoid receptor and heat shock factor to oligonucleotides in vitro. For these proteins, we find that the quantum yields (and saturating yields) for forming crosslinks using the high-peak intensity femtosecond laser do not improve on those obtained with low-intensity continuous wave (CW) UV sources. The photodamage to the oligonucleotides and proteins also has comparable quantum yields. Measurements of the photochemical reaction yields of several small molecules selected to model the crosslinking reactions also exhibit nearly linear dependences on UV intensity instead of the previously predicted quadratic dependence. Unfortunately, these results disprove earlier assertions that femtosecond pulsed laser sources provide significant advantages over CW radiation for protein-nucleic acid crosslinking.

  3. Tunable and Broadband Differential Phase Sections in Terahertz Frequency Range (United States)

    Kosiak, O. S.; Bezborodov, V. I.; Kuleshov, Ye. M.; Nesterov, P. K.


    Purpose: Studying the quasioptical tunable and broadband differential phase section (DPS) consisting of several birefringent elements (BE) on the basis of form birefringence effect. Design/methodology/approach: Using the polarization scattering matrix method, the impact of the mutual rotation axis of anisotropy of several BE by the amount of phase shift and the position of the plane of anisotropy of resulting DPS is considered. Findings: The DPS tunable in a wide range are shown to be possibly implemented in the case of quarter- wave DPS of two, and in the case of half-wave DPS of three, identical non-tunable BE. The analysis has shown to the possibility of creating a broadband quarter-wave and half-wave DPS. Conclusions: Experimental research has confirmed the possibility of constructing a tunable and broadband DPS. On this basis, tunable and broadband polarization converters, rotators of polarization plane, polarization phase shifters and frequency shifters in the terahertz frequency range can be created.

  4. High power microwave source with a three dimensional printed metamaterial slow-wave structure

    Energy Technology Data Exchange (ETDEWEB)

    French, David M.; Shiffler, Don [Air Force Research Laboratory, Directed Energy Directorate, Albuquerque, New Mexico 871117 (United States)


    For over the last decade, the concept of metamaterials has led to new approaches for considering the interaction of radiation with complex structures. However, practical manifestations of such a device operating at high power densities have proven difficult to achieve due to the resonant nature of metamaterials and the resultant high electric fields, which place severe constraints on manufacturing the slow wave structures. In this paper, we describe the first experimental manifestation of a high power microwave device utilizing a metallic slow wave structure (metamaterial-like) fabricated using additive manufacturing. The feasibility of utilizing additive manufacturing as a technique for building these relatively complicated structures has thus been demonstrated. The MW class microwave source operates in the C-band and shows frequency tunablility with electron beam voltage. The basic electromagnetic characteristics of this device, the construction using additive manufacturing, and the basic performance as a microwave oscillator are considered. Due to the tunable nature of the device, it shows promise not only as an oscillator but also as a microwave amplifier. Therefore, the dispersive characteristics and a discussion of the anticipated gain is included as it relates to an amplifier configuration.

  5. High power microwave source with a three dimensional printed metamaterial slow-wave structure. (United States)

    French, David M; Shiffler, Don


    For over the last decade, the concept of metamaterials has led to new approaches for considering the interaction of radiation with complex structures. However, practical manifestations of such a device operating at high power densities have proven difficult to achieve due to the resonant nature of metamaterials and the resultant high electric fields, which place severe constraints on manufacturing the slow wave structures. In this paper, we describe the first experimental manifestation of a high power microwave device utilizing a metallic slow wave structure (metamaterial-like) fabricated using additive manufacturing. The feasibility of utilizing additive manufacturing as a technique for building these relatively complicated structures has thus been demonstrated. The MW class microwave source operates in the C-band and shows frequency tunablility with electron beam voltage. The basic electromagnetic characteristics of this device, the construction using additive manufacturing, and the basic performance as a microwave oscillator are considered. Due to the tunable nature of the device, it shows promise not only as an oscillator but also as a microwave amplifier. Therefore, the dispersive characteristics and a discussion of the anticipated gain is included as it relates to an amplifier configuration.

  6. High-frequency torsional Alfvén waves as an energy source for coronal heating (United States)

    Srivastava, Abhishek Kumar; Shetye, Juie; Murawski, Krzysztof; Doyle, John Gerard; Stangalini, Marco; Scullion, Eamon; Ray, Tom; Wójcik, Dariusz Patryk; Dwivedi, Bhola N.


    The existence of the Sun’s hot atmosphere and the solar wind acceleration continues to be an outstanding problem in solar-astrophysics. Although magnetohydrodynamic (MHD) modes and dissipation of magnetic energy contribute to heating and the mass cycle of the solar atmosphere, yet direct evidence of such processes often generates debate. Ground-based 1-m Swedish Solar Telescope (SST)/CRISP, Hα 6562.8 Å observations reveal, for the first time, the ubiquitous presence of high frequency (~12-42 mHz) torsional motions in thin spicular-type structures in the chromosphere. We detect numerous oscillating flux tubes on 10 June 2014 between 07:17 UT to 08:08 UT in a quiet-Sun field-of-view of 60” × 60” (1” = 725 km). Stringent numerical model shows that these observations resemble torsional Alfvén waves associated with high frequency drivers which contain a huge amount of energy (~105 W m-2) in the chromosphere. Even after partial reflection from the transition region, a significant amount of energy (~103 W m-2) is transferred onto the overlying corona. We find that oscillating tubes serve as substantial sources of Alfvén wave generation that provide sufficient Poynting flux not only to heat the corona but also to originate the supersonic solar wind.

  7. Ultra-directional source of longitudinal acoustic waves based on a two-dimensional solid/solid phononic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Morvan, B.; Tinel, A.; Sainidou, R.; Rembert, P. [Laboratoire Ondes et Milieux Complexes, UMR CNRS 6294, Université du Havre, 75 rue Bellot, 76058 Le Havre (France); Vasseur, J. O.; Hladky-Hennion, A.-C. [Institut d' Electronique, de Micro-électronique et de Nanotechnologie, UMR CNRS 8520, Cité Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Swinteck, N.; Deymier, P. A. [Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721 (United States)


    Phononic crystals (PC) can be used to control the dispersion properties of acoustic waves, which are essential to direct their propagation. We use a PC-based two-dimensional solid/solid composite to demonstrate experimentally and theoretically the spatial filtering of a monochromatic non-directional wave source and its emission in a surrounding water medium as an ultra-directional beam with narrow angular distribution. The phenomenon relies on square-shaped equifrequency contours (EFC) enabling self-collimation of acoustic waves within the phononic crystal. Additionally, the angular width of collimated beams is controlled via the EFC size-shrinking when increasing frequency.

  8. Observational constraints on multimessenger sources of gravitational waves and high-energy neutrinos. (United States)

    Bartos, Imre; Finley, Chad; Corsi, Alessandra; Márka, Szabolcs


    Many astronomical sources of intense bursts of photons are also predicted to be strong emitters of gravitational waves (GWs) and high-energy neutrinos (HENs). Moreover some suspected classes, e.g., choked gamma-ray bursts, may only be identifiable via nonphoton messengers. Here we explore the reach of current and planned experiments to address this question. We derive constraints on the rate of GW and HEN bursts based on independent observations by the initial LIGO and Virgo GW detectors and the partially completed IceCube (40-string) HEN detector. We then estimate the reach of joint GW+HEN searches using advanced GW detectors and the completed km(3) IceCube detector to probe the joint parameter space. We show that searches undertaken by advanced detectors will be capable of detecting, constraining, or excluding, several existing models with 1 yr of observation. © 2011 American Physical Society

  9. Exact solutions for the source-excited cylindrical electromagnetic waves in a nonlinear nondispersive medium. (United States)

    Es'kin, V A; Kudrin, A V; Petrov, E Yu


    The behavior of electromagnetic fields in nonlinear media has been a topical problem since the discovery of materials with a nonlinearity of electromagnetic properties. The problem of finding exact solutions for the source-excited nonlinear waves in curvilinear coordinates has been regarded as unsolvable for a long time. In this work, we present the first solution of this type for a cylindrically symmetric field excited by a pulsed current filament in a nondispersive medium that is simultaneously inhomogeneous and nonlinear. Assuming that the medium has a power-law permittivity profile in the linear regime and lacks a center of inversion, we derive an exact solution for the electromagnetic field excited by a current filament in such a medium and discuss the properties of this solution.

  10. Problems with the sources of the observed gravitational waves and their resolution

    Directory of Open Access Journals (Sweden)

    Dolgov A.D.


    Full Text Available Recent direct registration of gravitational waves by LIGO and astronomical observations of the universe at redshifts 5-10 demonstrate that the standard astrophysics and cosmology are in tension with the data. The origin of the source of the GW150914 event, which presumably is a binary of coalescing black holes with masses about 30 solar masses, each with zero spin, as well as the densely populated universe at z= 5-10 by superheavy black holes, blight galaxies, supernovae, and dust does not fit the standard astrophysical picture. It is shown here that the model of primordial black hole (PBH formation, suggested in 1993, nicely explains all these and more puzzles, including those in contemporary universe, such as MACHOs and the mass spectrum of the observed solar mass black holes.. The mass spectrum and density of PBH is predicted. The scenario may possibly lead to abundant antimatter in the universe and even in the Galaxy.

  11. Problems with the sources of the observed gravitational waves and their resolution (United States)

    Dolgov, A. D.


    Recent direct registration of gravitational waves by LIGO and astronomical observations of the universe at redshifts 5-10 demonstrate that the standard astrophysics and cosmology are in tension with the data. The origin of the source of the GW150914 event, which presumably is a binary of coalescing black holes with masses about 30 solar masses, each with zero spin, as well as the densely populated universe at z= 5-10 by superheavy black holes, blight galaxies, supernovae, and dust does not fit the standard astrophysical picture. It is shown here that the model of primordial black hole (PBH) formation, suggested in 1993, nicely explains all these and more puzzles, including those in contemporary universe, such as MACHOs and the mass spectrum of the observed solar mass black holes.. The mass spectrum and density of PBH is predicted. The scenario may possibly lead to abundant antimatter in the universe and even in the Galaxy.

  12. A global wave parameter database for geophysical applications. Part 2: Model validation with improved source term parameterization (United States)

    Rascle, Nicolas; Ardhuin, Fabrice


    A multi-scale global hindcast of ocean waves is presented that covers the years 1994-2012, based on recently published parameterizations for wind sea and swell dissipation [Ardhuin, F., Rogers, E., Babanin, A., Filipot, J.-F., Magne, R., Roland, A., van der Westhuysen, A., Queffeulou, P., Lefevre, J.-M., Aouf, L., Collard, F., 2010. Semi-empirical dissipation source functions for wind-wave models: Part I. Definition, calibration and validation. J. Phys. Oceanogr. 40 (9), 1917-1941]. Results from this hindcast include traditional wave parameters, like the significant wave height and mean periods, and we particularly consider the accuracy of the results for phenomenal sea states, with significant heights above 14 m. Using unbiased winds, there is no evidence of a bias in wave heights even for this very high range. Various spectral moments were also validated, including the surface Stokes drift and mean square slopes that are relevant for wave-current interactions modelling and remote sensing, and also spectra of seismic noise sources. The estimation of these parameters is made more accurate by the new wave growth and dissipation parameterizations. Associated air-sea fluxes of momentum and energy are significantly different from what is obtained with the WAM-Cycle 4 parameterization, with a roughness that is practically a function of wind speed only. That particular output of the model does not appear very realistic and will require future adjustments of the generation and dissipation parameterizations.

  13. Giant amplification of terahertz plasmons in a double-layer graphene (United States)

    Morozov, M. Yu; Moiseenko, I. M.; Popov, V. V.


    The amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. The plasmon wave in a symmetric double-layer graphene structure splits into two branches with a symmetric and an antisymmetric distribution of tangential to graphene component of the electric field across the plane of symmetry of the structure. It is shown that, normalized to the wavelength, the terahertz plasmon amplification factor of the symmetric mode in the double-layer graphene structure could be greater than that in a single graphene layer by four orders of magnitude.

  14. Wave propagation speeds and source term influences in single and integral porosity shallow water equations

    Directory of Open Access Journals (Sweden)

    Ilhan Özgen


    Full Text Available In urban flood modeling, so-called porosity shallow water equations (PSWEs, which conceptually account for unresolved structures, e.g., buildings, are a promising approach to addressing high CPU times associated with state-of-the-art explicit numerical methods. The PSWE can be formulated with a single porosity term, referred to as the single porosity shallow water model (SP model, which accounts for both the reduced storage in the cell and the reduced conveyance, or with two porosity terms: one accounting for the reduced storage in the cell and another accounting for the reduced conveyance. The latter form is referred to as an integral or anisotropic porosity shallow water model (AP model. The aim of this study was to analyze the differences in wave propagation speeds of the SP model and the AP model and the implications of numerical model results. First, augmented Roe-type solutions were used to assess the influence of the source terms appearing in both models. It is shown that different source terms have different influences on the stability of the models. Second, four computational test cases were presented and the numerical models were compared. It is observed in the eigenvalue-based analysis as well as in the computational test cases that the models converge if the conveyance porosity in the AP model is close to the storage porosity. If the porosity values differ significantly, the AP model yields different wave propagation speeds and numerical fluxes from those of the BP model. In this study, the ratio between the conveyance and storage porosities was determined to be the most significant parameter.

  15. The 2017 terahertz science and technology roadmap (United States)

    Dhillon, S. S.; Vitiello, M. S.; Linfield, E. H.; Davies, A. G.; Hoffmann, Matthias C.; Booske, John; Paoloni, Claudio; Gensch, M.; Weightman, P.; Williams, G. P.; Castro-Camus, E.; Cumming, D. R. S.; Simoens, F.; Escorcia-Carranza, I.; Grant, J.; Lucyszyn, Stepan; Kuwata-Gonokami, Makoto; Konishi, Kuniaki; Koch, Martin; Schmuttenmaer, Charles A.; Cocker, Tyler L.; Huber, Rupert; Markelz, A. G.; Taylor, Z. D.; Wallace, Vincent P.; Axel Zeitler, J.; Sibik, Juraj; Korter, Timothy M.; Ellison, B.; Rea, S.; Goldsmith, P.; Cooper, Ken B.; Appleby, Roger; Pardo, D.; Huggard, P. G.; Krozer, V.; Shams, Haymen; Fice, Martyn; Renaud, Cyril; Seeds, Alwyn; Stöhr, Andreas; Naftaly, Mira; Ridler, Nick; Clarke, Roland; Cunningham, John E.; Johnston, Michael B.


    Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz-30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to ‘real world’ applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

  16. Wave

    DEFF Research Database (Denmark)

    Ibsen, Lars Bo


    Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many...... times smaller it remains very high. For example, whilst there is enough potential wave power off the UK to supply the electricity demands several times over, the economically recoverable resource for the UK is estimated at 25% of current demand; a lot less, but a very substantial amount nonetheless....

  17. Traveling-Wave Tube Amplifier for THz Frequencies

    DEFF Research Database (Denmark)

    Kotiranta, Mikko; Krozer, Viktor; Zhurbenko, Vitaliy

    The lack of a compact and powerful terahertz source has been hindering the application of terahertz radiation in many fields. Frequency multipliers can be used in conjunction with an electronic solid-state source to obtain power levels up to around 1 mW. A higher power may be generated with vacuu...

  18. Standing Alfvén waves with m ≫ 1 in an axisymmetric magnetosphere excited by a stochastic source

    Directory of Open Access Journals (Sweden)

    A. S. Leonovich


    Full Text Available In the framework of an axisymmetric magnetospheric model, we have constructed a theory for broad-band standing Alfvén waves with large azimuthal wave number m » 1 excited by a stochastic source. External currents in the ionosphere are taken as the oscillation source. The source with statistical properties of "white noise" is considered at length. It is shown that such a source drives oscillations which also have the "white noise" properties. The spectrum of such oscillations for each harmonic of standing Alfvén waves has two maxima: near the poloidal and toroidal eigenfrequencies of the magnetic shell of the observation. In the case of a small attenuation in the ionosphere the maximum near the toroidal frequency is dominated, and the oscillations are nearly toroidally polarized. With a large attenuation, a maximum is dominant near the poloidal frequency, and the oscillations are nearly poloidally polarized.Key words. Ionosphere-magnetosphere interaction · Wave propagation · Magnetospheric physics · MHD waves and instabilities

  19. Terahertz antireflection coatings using metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Hou-tong [Los Alamos National Laboratory; Zhou, Jiangfeng [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Azad, Abul K [Los Alamos National Laboratory; Chen, Frank [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory


    We demonstrate terahertz metamaterial antireflection coatings (ARCs) that significantly reduce the reflection and enhance the transmission at an interface of dielectric media. They are able to operate over a wide range of incidence angles for both TM and TE polarizations. Experiments and finite-element simulations will be presented and discussed.

  20. Terahertz near-field microspectroscopy

    NARCIS (Netherlands)

    Knab, J.R.; Adam, A.J.L.; Chakkittakandy, R.; Planken, P.C.M.


    Using near-field, terahertz time-domain spectroscopy (THz-TDS), we investigate how the addition of a dielectric material into a subwavelength-diameter, cylindrical waveguide affects its transmission properties. The THz electric near-field is imaged with deep subwavelength resolution as it emerges

  1. Terahertz radar cross section measurements

    DEFF Research Database (Denmark)

    Iwaszczuk, Krzysztof; Heiselberg, Henning; Jepsen, Peter Uhd


    We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies. Our RCS measurements are performed on a scale model aircraft of size 5-10 cm in polar and azimuthal configurations, and correspond closely to RCS measurements with conventional radar...

  2. A Perfect Terahertz Metamaterial Absorber


    Bagheri, Alireza; Moradi, Gholamreza


    In this paper the design for an absorbing metamaterial with near unity absorbance in terahertz region is presented. The absorber's unit cell structure consists of two metamaterial resonators that couple to electric and magnetic fields separately. The structure allows us to maximize absorption by varying dielectric material and thickness and, hence the effective electrical permittivity and magnetic permeability.

  3. Terahertz computed tomography in three-dimensional using a pyroelectric array detector (United States)

    Li, Bin; Wang, Dayong; Zhou, Xun; Rong, Lu; Huang, Haochong; Wan, Min; Wang, Yunxin


    Terahertz frequency range spans from 0.1 to 10 THz. Terahertz radiation can penetrate nonpolar materials and nonmetallic materials, such as plastics, wood, and clothes. Then the feature makes the terahertz imaging have important research value. Terahertz computed tomography makes use of the penetrability of terahertz radiation and obtains three-dimensional object projection data. In the paper, continuous-wave terahertz computed tomography with a pyroelectric array detectoris presented. Compared with scanning terahertz computed tomography, a pyroelectric array detector can obtain a large number of projection data in a short time, as the acquisition mode of the array pyroelectric detector omit the projection process on the vertical and horizontal direction. With the two-dimensional cross-sectional images of the object are obtained by the filtered back projection algorithm. The two side distance of the straw wall account for 80 pixels, so it multiplied by the pixel size is equal to the diameter of the straw about 6.4 mm. Compared with the actual diameter of the straw, the relative error is 6%. In order to reconstruct the three-dimensional internal structure image of the straw, the y direction range from 70 to 150 are selected on the array pyroelectric detector and are reconstructed by the filtered back projection algorithm. As the pixel size is 80 μm, the height of three-dimensional internal structure image of the straw is 6.48 mm. The presented system can rapidly reconstruct the three-dimensional object by using a pyroelectric array detector and explores the feasibility of on non-destructive evaluation and security testing.

  4. Graphene based tunable metamaterial absorber and polarization modulation in terahertz frequency. (United States)

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


    Graphene can be utilized in designing tunable terahertz devices due to its tunability of sheet conductivity. In this paper, we combine the metamaterial having unit cell of cross-shaped metallic resonator with the double layer graphene wires to realize polarization independent absorber with spectral tuning at terahertz frequency. The absorption performance with a peak frequency tuning range of 15% and almost perfect peak absorption has been demonstrated by controlling the Fermi energy of the graphene that can be conveniently achieved by adjusting the bias voltage on the graphene double layers. The mechanism of the proposed absorber has been explored by a transmission line model and the tuning is explained by the changing of the effective inductance of the graphene wires under gate voltage biasing. Further more, we also propose a polarization modulation scheme of terahertz wave by applying similar polarization dependent absorbers. Through the proposed polarization modulator, it is able to electrically control the reflected wave with a linear polarization of continuously tunable azimuth angle of the major axis from 0° to 90° at the working frequency. These design approaches enable us to electrically control the absorption spectrum and the polarization state of terahertz waves more flexibly.

  5. Design and analysis of perfect terahertz metamaterial absorber by a novel dynamic circuit model. (United States)

    Hokmabadi, Mohammad Parvinnezhad; Wilbert, David S; Kung, Patrick; Kim, Seongsin M


    Metamaterial terahertz absorbers composed of a frequency selective layer followed by a spacer and a metallic backplane have recently attracted great attention as a device to detect terahertz radiation. In this work, we present a quasistatic dynamic circuit model that can decently describe operational principle of metamaterial terahertz absorbers based on interference theory of reflected waves. The model comprises two series LC resonance components, one for resonance in frequency selective surface (FSS) and another for resonance inside the spacer. Absorption frequency is dominantly determined by the LC of FSS while the spacer LC changes slightly the magnitude and frequency of absorption. This model fits perfectly for both simulated and experimental data. By using this model, we study our designed absorber and we analyze the effect of changing in spacer thickness and metal conductivity on absorption spectrum.

  6. Strong terahertz field generation, detection, and application

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki-Yong [Univ. of Maryland, College Park, MD (United States)


    This report describes the generation and detection of high-power, broadband terahertz (THz) radiation with using femtosecond terawatt (TW) laser systems. In particular, this focuses on two-color laser mixing in gases as a scalable THz source, addressing both microscopic and macroscopic effects governing its output THz yield and radiation profile. This also includes the characterization of extremely broad THz spectra extending from microwaves to infrared frequencies. Experimentally, my group has generated high-energy (tens of microjoule), intense (>8 MV/cm), and broadband (0.01~60 THz) THz radiation in two-color laser mixing in air. Such an intense THz field can be utilized to study THz-driven extremely nonlinear phenomena in a university laboratory.

  7. Strong terahertz field generation, detection, and application

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki-Yong [Univ. of Maryland, College Park, MD (United States)


    This report describes the generation and detection of high-power, broadband terahertz (THz) radiation with using femtosecond terawatt (TW) laser systems. In particular, this focuses on two-color laser mixing in gases as a scalable THz source, addressing both microscopic and macroscopic effects governing its output THz yield and radiation profile. This also includes the characterization of extremely broad THz spectra extending from microwaves to infrared frequencies. Experimentally, my group has generated high-energy (tens of microjoule), intense (>8 MV/cm), and broadband (0.01~60 THz) THz radiation in two-color laser mixing in air. Such an intense THz field can be utilized to study THz-driven extremely nonlinear phenomena in a university laboratory.

  8. Terahertz beam switching by electrical control of graphene-enabled tunable metasurface. (United States)

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


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

  9. Modeling of thermal wave propagation in damaged composites with internal source (United States)

    Ciampa, Francesco; Angioni, Stefano L.; Pinto, Fulvio; Scarselli, Gennaro; Almond, Darrel P.; Meo, Michele


    SMArt Thermography exploits the electrothermal properties of multifunctional smart structures, which are created by embedding shape memory alloy (SMA) wires in traditional carbon fibre reinforced composite laminates (known as SMArt composites), in order to detect the structural flaws using an embedded source. Such a system enables a built-in, fast, cost-effective and in-depth assessment of the structural damage as it overcomes the limitations of standard thermography techniques. However, a theoretical background of the thermal wave propagation behaviour, especially in the presence of internal structural defects, is needed to better interpret the observations/data acquired during the experiments and to optimise those critical parameters such as the mechanical and thermal properties of the composite laminate, the depth of the SMA wires and the intensity of the excitation energy. This information is essential to enhance the sensitivity of the system, thus to evaluate the integrity of the medium with different types of damage. For this purpose, this paper aims at developing an analytical model for SMArt composites, which is able to predict the temperature contrast on the surface of the laminate in the presence of in-plane internal damage (delamination-like) using pulsed thermography. Such a model, based on the Green's function formalism for one-dimensional heat equation, takes into account the thermal lateral diffusion around the defect and it can be used to compute the defect depth within the laminate. The results showed good agreement between the analytical model and the measured thermal waves using an infrared (IR) camera. Particularly, the contrast temperature curves were found to change significantly depending on the defect opening.

  10. Infrared observations of gravitational-wave sources in Advanced LIGO's second observing run (United States)

    Pound Singer, Leo; Kasliwal, Mansi; Lau, Ryan; Cenko, Bradley; Global Relay of Observatories Watching Transients Happen (GROWTH)


    Advanced LIGO observed gravitational waves (GWs) from a binary black hole merger in its first observing run (O1) in September 2015. It is anticipated that LIGO and Virgo will soon detect the first binary neutron star mergers. The most promising electromagnetic counterparts to such events are kilonovae: fast, faint transients powered by the radioactive decay of the r-process ejecta. Joint gravitational-wave and electromagnetic observations of such transients hold the key to many longstanding problems, from the nature of short GRBS to the cosmic production sites of the r-process elements to "standard siren" cosmology. Due to the large LIGO/Virgo error regions of 100 deg2, synoptic survey telescopes have dominated the search for LIGO counterparts. Due to the paucity of infrared instruments with multi-deg2 fields of view, infrared observations have been lacking. Near-infrared emission should not only be a more robust signature of kilonovae than optical emission (independent of viewing angle), but should also be several magnitudes brighter and be detectable for much longer, weeks after merger rather than days. In Advanced LIGO's second observing run, we used the FLAMINGOS-2 instrument on Gemini-South to hunt for the near-infrared emission from GW sources by targeted imaging of the most massive galaxies in the LIGO/Virgo localization volumes. We present the results of this campaign, rates, and interpretation of our near-infrared imaging and spectroscopy. We show that leveraging large-scale structure and targeted imaging of the most massive ~10 galaxies in a LIGO/Virgo localization volume may be a surprisingly effective strategy to find the electromagnetic counterpart.

  11. Separation of radiated sound field components from waves scattered by a source under non-anechoic conditions

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren; Jacobsen, Finn


    A method of estimating the sound field radiated by a source under non-anechoic conditions has been examined. The method uses near field acoustic holography based on a combination of pressure and particle velocity measurements in a plane near the source for separating outgoing and ingoing wave...... components. The outgoing part of the sound field is composed of both radiated and scattered waves. The method compensates for the scattered components of the outgoing field on the basis of the boundary condition of the problem, exploiting the fact that the sound field is reconstructed very close...... to the source. Thus the radiated free-field component is estimated simultaneously with solving the inverse problem of reconstructing the sound field near the source. The method is particularly suited to cases in which the overall contribution of reflected sound in the measurement plane is significant....

  12. WASS: an open-source stereo processing pipeline for sea waves 3D reconstruction (United States)

    Bergamasco, Filippo; Benetazzo, Alvise; Torsello, Andrea; Barbariol, Francesco; Carniel, Sandro; Sclavo, Mauro


    Stereo 3D reconstruction of ocean waves is gaining more and more popularity in the oceanographic community. In fact, recent advances of both computer vision algorithms and CPU processing power can now allow the study of the spatio-temporal wave fields with unprecedented accuracy, especially at small scales. Even if simple in theory, multiple details are difficult to be mastered for a practitioner so that the implementation of a 3D reconstruction pipeline is in general considered a complex task. For instance, camera calibration, reliable stereo feature matching and mean sea-plane estimation are all factors for which a well designed implementation can make the difference to obtain valuable results. For this reason, we believe that the open availability of a well-tested software package that automates the steps from stereo images to a 3D point cloud would be a valuable addition for future researches in this area. We present WASS, a completely Open-Source stereo processing pipeline for sea waves 3D reconstruction, available at Our tool completely automates the recovery of dense point clouds from stereo images by providing three main functionalities. First, WASS can automatically recover the extrinsic parameters of the stereo rig (up to scale) so that no delicate calibration has to be performed on the field. Second, WASS implements a fast 3D dense stereo reconstruction procedure so that an accurate 3D point cloud can be computed from each stereo pair. We rely on the well-consolidated OpenCV library both for the image stereo rectification and disparity map recovery. Lastly, a set of 2D and 3D filtering techniques both on the disparity map and the produced point cloud are implemented to remove the vast majority of erroneous points that can naturally arise while analyzing the optically complex nature of the water surface (examples are sun-glares, large white-capped areas, fog and water areosol, etc). Developed to be as fast as possible, WASS

  13. Terahertz generation from Cu ion implantation into lithium niobate

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuhua, E-mail: [Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan university of Science and Technology, Wuhan 430081 (China); Wang, Ruwu; Yuan, Jie [Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan university of Science and Technology, Wuhan 430081 (China); Wang, Yumei [Department of Nephrology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022 (China)


    In this letter, the authors present first observation of terahertz generation from Cu implantation of lithium niobate crystal substrate. Lithium niobate single crystal is grown by Czochralski method. Metal nanoparticles synthesized by Cu ion implantation were implanted into lithium niobate single crystal using metal vapor vacuum arc (MEVVA) ion source. 1 kHz, 35 fs laser pulse centred at 800 nm was focused onto the samples. The supercontinuum spectra of the sample are obtained. Terahertz was generated via this kind of sample and investigated using the electro-optical sampling technique. The findings suggest that under the investigated implantation parameter, a strong spectral component in excess of 0.46 THz emission was found from Cu ion implantation of lithium niobate. -- Highlights: • We first observation of terahertz generation from Cu implantation of lithium niobate crystal substrate. • Lithium niobate single crystal is grown by Czochralski method. Cu nanoparticles in lithium niobate have been formed by using MEVVA ion source. • The THz bandwidth and center from this kind of sample were determined.

  14. Long period slow MHD waves in the solar wind source region


    Dwivedi, B. N.; Srivastava, A. K.


    We consider compressive viscosity and thermal conductivity to study the propagation and dissipation of long period slow longitudinal MHD waves in polar coronal holes. We discuss their likely role in the line profile narrowing, and in the energy budget for coronal holes and the solar wind. We compare the contribution of longitudinal MHD waves with high frequency Alfven waves.

  15. Application of the Method of Auxiliary Sources for the Analysis of Plane-Wave Scattering by Impedance Spheres

    DEFF Research Database (Denmark)

    Karamehmedovic, Mirza; Breinbjerg, Olav


    The Method of Auxiliary Sources (MAS) is applied to 3D scattering problems involving spherical impedance scatterers. The MAS results are compared with the reference spherical wave expansion (SWE) solution. It is demonstrated that good agreement is achieved between the MAS and SWE results....

  16. Terahertz focusing of multiple wavelengths by graphene metasurfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Liming, E-mail: [Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601 (Australia); School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2612 (Australia); Zarate, Yair; Shadrivov, Ilya V. [Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601 (Australia); Hattori, Haroldo T. [School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2612 (Australia); Neshev, Dragomir N.; Powell, David A. [Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601 (Australia); Centre for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS), Australian National University, Canberra, ACT 2601 (Australia)


    Metasurfaces can achieve nearly arbitrary wavefront control based on manipulation of the wave phase profile. We propose a metasurface based on double graphene cut-wire resonators which can cover the complete 2π phase region with high reflection efficiency. This full phase coverage is essential for efficient wavefront manipulation, without reflecting energy into unwanted channels. A mirror capable of focusing multiple wavelengths is demonstrated numerically based on the proposed structure. The mirror can effectively focus terahertz (THz) waves from 1.2 to 1.9 THz to the same focal point by changing the Fermi level of each graphene resonator separately. The presented metasurface could provide a powerful platform for controlling THz waves, including focusing, beam steering, beam shaping, and holography.

  17. Group bound long waves as a source of infragravity energy in the surf zone (United States)

    Masselink, Gerhard


    Measurements of water surface elevation and cross-shore currents were made under moderate-energy conditions ( Hrms = 1.1 m and Tz = 7.5 s) on a low-gradient macrotidal beach in central Queensland, Australia. The infragravity signal (BLW) that lags approximately 5 s behind the wind wave envelope. The BLW decouples from the wind wave groups as the incident waves break. The released BLW then travels onshore through the surf zone as a free wave and reflects some distance seaward (5 m) of the shoreline. The superposition of the released BLW and the reflected leaky wave results in standing wave motion in the inner surf zone. Coherence-spectra suggest that about 40% of the incoming infragravity energy is forced by the wind wave envelope.

  18. Widely Tunable Terahertz Phase Modulation with Gate-Controlled Graphene Metasurfaces

    Directory of Open Access Journals (Sweden)

    Ziqi Miao


    Full Text Available As the basis of a diverse set of photonic applications, such as hologram imaging, polarization, and wave front manipulation, the local phase control of electromagnetic waves is fundamental in photonic research. However, currently available bulky, passive, range-limited phase modulators pose an obstacle in photonic applications. Here, we propose a new mechanism to achieve a wide phase modulation range, with graphene used as a tunable loss to drive an underdamped to overdamped resonator transition. Based on this mechanism, we present widely tunable phase modulation in the terahertz regime, realized in gate-tuned ultrathin reflective graphene metasurfaces. A one-port resonator model, supported by full-wave simulations, explains the underlying physics of the discovered extreme phase modulation and indicates general strategies for designing tunable photonic devices. As an example, we demonstrate a gate-tunable terahertz (THz polarization modulator with a graphene metasurface. Our findings establish the possibility for photonic applications based on active phase manipulation.

  19. Application of distributed point source method (DPSM) to wave propagation in anisotropic media (United States)

    Fooladi, Samaneh; Kundu, Tribikram


    Distributed Point Source Method (DPSM) was developed by Placko and Kundu1, as a technique for modeling electromagnetic and elastic wave propagation problems. DPSM has been used for modeling ultrasonic, electrostatic and electromagnetic fields scattered by defects and anomalies in a structure. The modeling of such scattered field helps to extract valuable information about the location and type of defects. Therefore, DPSM can be used as an effective tool for Non-Destructive Testing (NDT). Anisotropy adds to the complexity of the problem, both mathematically and computationally. Computation of the Green's function which is used as the fundamental solution in DPSM is considerably more challenging for anisotropic media, and it cannot be reduced to a closed-form solution as is done for isotropic materials. The purpose of this study is to investigate and implement DPSM for an anisotropic medium. While the mathematical formulation and the numerical algorithm will be considered for general anisotropic media, more emphasis will be placed on transversely isotropic materials in the numerical example presented in this paper. The unidirectional fiber-reinforced composites which are widely used in today's industry are good examples of transversely isotropic materials. Development of an effective and accurate NDT method based on these modeling results can be of paramount importance for in-service monitoring of damage in composite structures.

  20. gprMax: Open source software to simulate electromagnetic wave propagation for Ground Penetrating Radar (United States)

    Warren, Craig; Giannopoulos, Antonios; Giannakis, Iraklis


    gprMax is open source software that simulates electromagnetic wave propagation, using the Finite-Difference Time-Domain (FDTD) method, for the numerical modelling of Ground Penetrating Radar (GPR). gprMax was originally developed in 1996 when numerical modelling using the FDTD method and, in general, the numerical modelling of GPR were in their infancy. Current computing resources offer the opportunity to build detailed and complex FDTD models of GPR to an extent that was not previously possible. To enable these types of simulations to be more easily realised, and also to facilitate the addition of more advanced features, gprMax has been redeveloped and significantly modernised. The original C-based code has been completely rewritten using a combination of Python and Cython programming languages. Standard and robust file formats have been chosen for geometry and field output files. New advanced modelling features have been added including: an unsplit implementation of higher order Perfectly Matched Layers (PMLs) using a recursive integration approach; diagonally anisotropic materials; dispersive media using multi-pole Debye, Drude or Lorenz expressions; soil modelling using a semi-empirical formulation for dielectric properties and fractals for geometric characteristics; rough surface generation; and the ability to embed complex transducers and targets.

  1. Terahertz applications: trends and challenges (United States)

    Robin, Thierry; Bouye, Clementine; Cochard, Jacques


    The objective of our work [1] was to determine the opportunities and challenges for Terahertz application development for the next years with a focus on systems: for homeland security and for Non Destructive Testing (NDT). Terahertz radiation has unique abilities and has been the subject of extensive research for many years. Proven concepts have emerged for numerous applications including Industrial NDT, Security, Health, Telecommunications, etc. Nevertheless, there has been no widely deployed application and Businesses based on THz technologies are still in their infancy. Some technological, market and industrial barriers are still to be broken. We summarize the final analysis and data: study of the technology trends and major bottlenecks per application segment, main challenges to be addressed in the next years, key opportunities for THz technologies based on market needs and requirements.

  2. Review in terahertz spectral analysis


    El Haddad, Josette; Bousquet, Bruno; Canioni, Lionel; Mounaix, Patrick


    International audience; Nowadays terahertz spectroscopy is a well-established technique and recent progresses in technology demonstrated that this new technique is useful for both fundamental research and industrial applications. Varieties of applications such as imaging, non destructive testing, quality control are about to be transferred to industry supported by permanent improvements from basic research. Since chemometrics is today routinely applied to IR spectroscopy, we discuss in this p...

  3. Ultrabroadband terahertz conductivity of Si nanocrystal films

    DEFF Research Database (Denmark)

    Cooke, D. G.; Meldrum, A.; Jepsen, P. Uhd


    The terahertz conductivity of silicon nanoparticles embedded in glass with varying density is studied with ultra-broadband terahertz spectroscopy on picosecond time scales following fs optical excitation. The transition from relatively isolated charge carriers to densities which allow inter...... the applicability of this simple model to the conductivity of nanoparticle ensembles over the entire THz spectral window....

  4. Submillimeter Wave Antenna With Slow Wave Feed Line

    DEFF Research Database (Denmark)

    Zhurbenko, Vitaliy; Krozer, Viktor; Kotiranta, Mikko


    Submillimeter wave radiation, which is also referred to as terahertz radiation, has not been extensively explored until recently due to a lack of reliable components and devices in this frequency range. Current advances in technology have made it possible to explore this portion of the electromag...

  5. Nanoscale Laser Terahertz Emission Microscopy

    DEFF Research Database (Denmark)

    Klarskov, Pernille; Kim, Hyewon; Colvin, Vicki L.


    Laser terahertz emission microscopy (LTEM) has become a powerful tool for studying ultrafast dynamics and local fields in many different types of materials. This technique, which relies on acceleration of charge carriers in a material upon femtosecond excitation, can provide insight into the phys......Laser terahertz emission microscopy (LTEM) has become a powerful tool for studying ultrafast dynamics and local fields in many different types of materials. This technique, which relies on acceleration of charge carriers in a material upon femtosecond excitation, can provide insight...... into the physics of charge transport, built-in fields, grain boundaries or surface states. We describe a new implementation of LTEM with a spatial resolution in the nanoscale regime based on a scattering-type near-field tip-based approach. We observe a spectral reshaping of the signal compared to conventional LTEM......-size-limited spatial resolution of ∼20 nm by imaging a gold nanorod using terahertz emission from the underlying substrate. This work enables for the first time the possibility of performing LTEM measurements on individual nanostructures....

  6. Teleseismic P wave attenuation and nuclear explosion source functions inferred from Yellowknife Array data (United States)

    Chun, Kin-Yip; Zhu, Tianfei; West, Gordon F.


    We report here the results of a comprehensive seismic attenuation investigation along the paths connecting Canada's Yellowknife seismic array (YKA) with seven active nuclear explosion testing areas. The data consist of more than 600 explosion-generated teleseismic P wave records. A dual time-frequency averaging technique is used to take advantage of the array recording characteristics without the drawback of the conventional beam-forming, excessive annihilation of high-frequency signal energies. The dual averaging technique, deployed in conjunction with a multiwindow spectral analysis method, yields smooth amplitude spectra whose falloff at high frequencies suffers little from spectral leakage due to the familiar presence of a prominent low-frequency plateau. Measured in terms of t*, the highest attenuation (0.66 s) is found along the path which originates from the Tuamotu test area; somewhat less attenuating are the two paths which depart from the Pahute Mesa (0.59 s) and Yucca Flat (0.50 s) nuclear test areas, both located within the U.S. Nevada Test Site. We find t* for these three paths to be substantially (up to 0.21 s) higher than recently published estimates (e.g., Der et al., 1985). We attribute these disparities largely to differences in spectral leakage control capability between the conventional single window and the improved multiwindow spectral analysis methods. The least attenuating paths all originate from the Soviet test areas: Novaya Zemlya (NZ), west Kazakhstan, Degelen Mountain (DM), and Shagan River (SR). The last two of these test areas, DM and SR, are both located in east Kazakhstan. The P wave signatures of the Soviet explosions are rich in high-frequency (>4.5 Hz) energies, and the YKA data (0.5-8.0 Hz) support a frequency-dependent t* whose value at high frequencies (>4.5 Hz) is as small as 0.17 s. To gain a grasp of the ramifications of the t* disparity between the multiple-window and the single-window results, we have compared explosion

  7. Generation of high-power terahertz radiation by nonlinear photon-assisted tunneling transport in plasmonic metamaterials (United States)

    Chen, Pai-Yen; Salas, Rodolfo; Farhat, Mohamed


    We propose an optoelectronic terahertz oscillator based on the quantum tunneling effect in a plasmonic metamaterial, utilizing a nanostructured metal-insulator-metal (MIM) tunneling junction. The collective resonant response of meta-atoms can achieve >90% optical absorption and strongly localized optical fields within the MIM plasmonic nanojunction. By properly tailoring the radiation aperture, the nonlinear quantum conductance induced by the metamaterial-enhanced, photon-assisted tunneling may produce miliwatt-level terahertz radiation through the optical beating (or heterodyne down conversion) of two lasers with a slight frequency offset. We envisage that the interplay between photon-assisted tunneling and plasmon coupling within the MIM metamaterial/diode may substantially enhance the modulated terahertz photocurrent, and may therefore realize a practical high-power, room-temperature source in applications of terahertz electronics.

  8. Narrow-band tunable terahertz emission from ferrimagnetic Mn{sub 3-x}Ga thin films

    Energy Technology Data Exchange (ETDEWEB)

    Awari, N. [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden (Germany); University of Groningen, 9747 AG Groningen (Netherlands); Kovalev, S., E-mail:, E-mail:, E-mail:; Fowley, C., E-mail:, E-mail:, E-mail:; Green, B.; Yildirim, O.; Lindner, J.; Fassbender, J.; Deac, A. M.; Gensch, M. [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden (Germany); Rode, K., E-mail:, E-mail:, E-mail:; Lau, Y.-C.; Betto, D.; Thiyagarajah, N.; Coey, J. M. D. [CRANN, AMBER and School of Physics, Trinity College Dublin, Dublin 2 (Ireland); Gallardo, R. A. [Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, 2390123 Valparíso (Chile)


    Narrow-band terahertz emission from coherently excited spin precession in metallic ferrimagnetic Mn{sub 3-x}Ga Heusler alloy nanofilms has been observed. The efficiency of the emission, per nanometer film thickness, is comparable or higher than that of classical laser-driven terahertz sources based on optical rectification. The center frequency of the emission from the films can be tuned precisely via the film composition in the range of 0.20–0.35 THz, making this type of metallic film a candidate for efficient on-chip terahertz emitters. Terahertz emission spectroscopy is furthermore shown to be a sensitive probe of magnetic properties of ultra-thin films.

  9. A global wave parameter database for geophysical applications. Part 2: Model validation with improved source term parameterization


    Rascle, Nicolas; Ardhuin, Fabrice


    A multi-scale global hindcast of ocean waves is presented that covers the years 1994-2012, based on recently published parameterizations for wind sea and swell dissipation [Ardhuin, F., Rogers, E., Babanin, A., Filipot, J.-F., Magne, R., Roland, A., van der Westhuysen, A., Queffeulou, P., Lefevre, J.-M., Aouf, L., Collard, F., 2010. Semi-empirical dissipation source functions for wind-wave models: Part I. Definition, calibration and validation. J. Phys. Oceanogr. 40 (9), 1917-1941]. Results f...

  10. New terahertz dielectric spectroscopy for the study aqueous solutions

    CERN Document Server

    George, Deepu K; Vinh, N Q


    We present a development of a high precision, tunable far-infrared (terahertz) frequency-domain dielectric spectrometer for studying the dynamics of biomolecules in aqueous solutions in the gigahertz-to-terahertz frequency. As a first application we report on the measurement of the absorption and refractive index for liquid water in the frequency range from 5 GHz to 1.12 THz (0.17 to 37.36 cm-1 or 0.268 to 60 mm). The system provides a coherent radiation source with a power up to 20 mW in the gigahertz-to-terahertz region. The power signal-to-noise ratio of our instrument reaches 1015 and the system achieves a spectral resolution of less than 100 Hz. The temperature of samples can be controlled precisely with an error bars of 0.02 oC from above 0 oC to 90 oC. Given these attributes, our spectrometer provides unique capabilities for the accurate measurement of even very strongly absorbing materials such as aqueous solutions.

  11. Investigation of the Frohlich hypothesis with high intensity terahertz radiation (United States)

    Weightman, Peter


    This article provides an update to recent reviews of the Frohlich hypothesis that biological organisation is facilitated by the creation of coherent excited states driven by a flow of free energy provided by metabolic processes and mediated by molecular motions in the terahertz range. Sources of intense terahertz radiation have the potential to test this hypothesis since if it is true the growth and development of sensitive systems such as stem cells should be influenced by irradiation with intense terahertz radiation. A brief survey of recent work shows that it is not yet possible to make an assessment of the validity of the Frohlich hypothesis. Under some conditions a variety of cell types respond to irradiation with intense THz radiation in ways that involve changes in the activity of their DNA. In other experiments very intense and prolonged THz radiation has no measureable effect on the behavior of very sensitive systems such as stem cells. The wide variation in experimental conditions makes it impossible to draw any conclusions as to characteristics of THz radiation that will induce a response in living cells. It is possible that in environments suitable for their maintenance and growth cells are capable of compensating for any effects caused by exposure to THz radiation up to some currently unknown level of THz peak power.

  12. Characterization of Material Properties at Terahertz Frequencies

    National Research Council Canada - National Science Library

    Giles, Robert H


    ... a decade. Research in modeling radar requires design of a wide range of measurements systems using current submillimeter-wave source/detector technology, establishment of precise calibration standards...

  13. Noise sources and improved performance of a mid-wave infrared uncooled silicon carbide optical photodetector. (United States)

    Lim, Geunsik; Manzur, Tariq; Kar, Aravinda


    An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 μm by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 μm. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The noise mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, noise equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 μm, the experimental detectivity of the optical photodetector of this study was found to be 1.07×10(10)  cm·Hz(1/2)/W, while the theoretical value was 1.11×10(10)  cm·Hz(1/2)/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation source with a temperature of 25°C and theoretical calculations, respectively.

  14. Magneto- to Electroactive Transmutation of Spin Waves in ErMnO3 (United States)

    Chaix, L.; de Brion, S.; Petit, S.; Ballou, R.; Regnault, L.-P.; Ollivier, J.; Brubach, J.-B.; Roy, P.; Debray, J.; Lejay, P.; Cano, A.; Ressouche, E.; Simonet, V.


    The low-energy dynamical properties of the multiferroic hexagonal perovskite ErMnO3 have been studied by inelastic neutron scattering as well as terahertz and far infrared spectroscopies on a synchrotron source. From these complementary techniques, we have determined the magnon and crystal field spectra and identified a zone center magnon excitable only by the electric field of an electromagnetic wave. Using a comparison with the isostructural YMnO3 compound and crystal field calculations, we propose that this dynamical magnetoelectric process is due to the hybridization of a magnon with an electroactive crystal field transition.

  15. On the source-frequency dependence of fracture-orientation estimates from shear-wave transmission experiments (United States)

    Santos, Leo K.; de Figueiredo, J. J. S.; Omoboya, Bode; Schleicher, Jörg; Stewart, Robert R.; Dyaur, Nikolay


    Shear-wave propagation through anisotropic fractured or cracked media can provide valuable information about these fracture swarms and their orientations. The main goal of this work is to recover information about fracture orientation based on the shear waveforms (S-waveforms). For this study, we carried out ultrasonic S-wave measurements in a synthetic physical model made of epoxy resin (isotropic matrix proxy), with small cylindrical rubber strips as inclusions (artificial cracks) inserted in it to simulate a homogeneous anisotropic medium. In these experiments, we used low, intermediate, and high frequency shear-wave sources, with frequencies 90, 431, and 840 kHz. We integrated and interpreted the resulting S-wave seismograms, cross-correlation panels and anisotropic parameter-analysis curves. We were able to estimate the crack orientation in single-orientation fracture zones. The high frequency peaks associated with scattered S-waves provided interpretable information about the fracture orientations when the propagation direction was parallel to the fracture plane. The analysis was possible utilizing results from frequency-versus-polarization-angle curves. Moreover, we applied a bandpass filtering process to the intermediate and high frequency seismograms in order to obtain low frequency seismograms. A spectral analysis using frequency-wavenumber (F-K) spectra supports this filtering process. The results obtained using an analysis of cross-correlograms and the Thomsen parameter γ extracted from filtered high-frequency data were quite similar to those obtained using a low-frequency source. This highlighted the possibility of using less expensive high-frequency sources to recover information about the fracture set.

  16. Detection of terahertz radiation using submicron field effect transistors and their use for inspection applications (United States)

    Delgado Notario, J. A.; Javadi, E.; Velázquez, J. E.; Diez, E.; Meziani, Y. M.; Fobelets, K.


    We investigated room temperature detection of terahertz radiation by using two different types of transistors (Strained Silicon Modulation field effect transistor, GaAs PHEMT). Experimental results show a good level of response under excitation at 0.3 THz. Competitive performance parameters were obtained (NEP and responsivity) in comparison with other detectors. Enhancement of the photoresponse signal by imposing a dc drain-to-source current (Ids) was observed experimentally. Inspection of hidden objects by using those devices within a terahertz imaging setup was demonstrated at 300 GHz and a better image was obtained under Ids.

  17. Terahertz (THz) Wireless Systems for Space Applications (United States)

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


    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.

  18. Terahertz pulsed imaging study of dental caries (United States)

    Karagoz, Burcu; Altan, Hakan; Kamburoglu, Kıvanç


    Current diagnostic techniques in dentistry rely predominantly on X-rays to monitor dental caries. Terahertz Pulsed Imaging (TPI) has great potential for medical applications since it is a nondestructive imaging method. It does not cause any ionization hazard on biological samples due to low energy of THz radiation. Even though it is strongly absorbed by water which exhibits very unique chemical and physical properties that contribute to strong interaction with THz radiation, teeth can still be investigated in three dimensions. Recent investigations suggest that this method can be used in the early identification of dental diseases and imperfections in the tooth structure without the hazards of using techniques which rely on x-rays. We constructed a continuous wave (CW) and time-domain reflection mode raster scan THz imaging system that enables us to investigate various teeth samples in two or three dimensions. The samples comprised of either slices of individual tooth samples or rows of teeth embedded in wax, and the imaging was done by scanning the sample across the focus of the THz beam. 2D images were generated by acquiring the intensity of the THz radiation at each pixel, while 3D images were generated by collecting the amplitude of the reflected signal at each pixel. After analyzing the measurements in both the spatial and frequency domains, the results suggest that the THz pulse is sensitive to variations in the structure of the samples that suggest that this method can be useful in detecting the presence of caries.

  19. Transition radiation from graphene plasmons by a bunch beam in the terahertz regime. (United States)

    Zhang, Kai-Chun; Chen, Xiao-Xing; Sheng, Chang-Jian; Ooi, Kelvin J A; Ang, Lay Kee; Yuan, Xue-Song


    The terahertz band is an increasingly important spectrum in a wide range of applications from bioimaging and medical diagnostics to security and wireless communications. We propose a tunable terahertz coherent radiation source based on graphene plasmon-induced transition radiation. The transition radiation in terahertz regime arises from the graphene plasmons, which are excited by a normally incident bunched electron beam. We analyze the field-intensities and spectral-angular distributions of the transition radiation with respect to Fermi energy, substrate dielectric permittivity, and electron bunch energy for both the coherent and incoherent radiation. The effect of electron bunching on the radiation pattern is discussed. The mechanism of plasmon frequency-selective transition radiation is discovered.

  20. A New Method for Simulating Power Flow Density Focused by a Silicon Lens Antenna Irradiated with Linearly Polarized THz Wave

    Directory of Open Access Journals (Sweden)

    Catur Apriono


    Full Text Available A terahertz system uses dielectric lens antennas for focusing and collimating beams of terahertz wave radiation. Linearly polarized terahertz wave radiation has been widely applied in the terahertz system. Therefore, an accurate method for analyzing the power flow density in the dielectric lens antenna irradiated with the linearly polarized terahertz wave radiation is important to design the terahertz systems. In optics, ray-tracing method has been used to calculate the power flow density by a number density of rays. In this study, we propose a method of ray-tracing combined with Fresnel’s transmission, including transmittance and polarization of the terahertz wave radiation to calculate power flow density in a Silicon lens antenna. We compare power flow density calculated by the proposed method with the regular ray-tracing method. When the Silicon lens antenna is irradiated with linearly polarized terahertz wave radiation, the proposed method calculates the power flow density more accurately than the regular ray-tracing.

  1. Cross-Shaped Terahertz Metal Mesh Filters: Historical Review and Results

    Directory of Open Access Journals (Sweden)

    Arline M. Melo


    Full Text Available Terahertz frequencies experiments has motivated the development of new sources, detectors and optical components. Here we will present a review of THz bandpass filters ranging from 0.4 to 10 THz. We also demonstrate our fabrication process, simulations and experimental results.

  2. Terahertz chiral metamaterial based on twisted closed ring resonators (United States)

    Stojanović, Danka B.; Beličev, Petra P.; Gligorić, Goran; Hadžievski, Ljupčo


    We present a chiral metamaterial (CMM) made of periodically distributed compact elements in a form of twisted closed ring resonators designed to be operational in terahertz (THz) frequency range. We analyze the three observed resonances in the absorption spectra and electric field distribution of linearly polarized incident electromagnetic waves. It has been shown that they arise due to excitation of symmetric and antisymmetric modes and are dependent on the geometry of resonant elements as well as the periodicity of the system. For the case of incident circularly polarized waves, a phenomenon of circular dichroism was observed, and its origin and dependency on the geometrical parameters and metal and dielectric losses was examined. This study indicates that the proposed CMM has a high potential for applications in the design of different THz components.

  3. Hybrid Computational Simulation and Study of Terahertz Pulsed Photoconductive Antennas (United States)

    Emadi, R.; Barani, N.; Safian, R.; Nezhad, A. Zeidaabadi


    A photoconductive antenna (PCA) has been numerically investigated in the terahertz (THz) frequency band based on a hybrid simulation method. This hybrid method utilizes an optoelectronic solver, Silvaco TCAD, and a full-wave electromagnetic solver, CST. The optoelectronic solver is used to find the accurate THz photocurrent by considering realistic material parameters. Performance of photoconductive antennas and temporal behavior of the excited photocurrent for various active region geometries such as bare-gap electrode, interdigitated electrodes, and tip-to-tip rectangular electrodes are investigated. Moreover, investigations have been done on the center of the laser illumination on the substrate, substrate carrier lifetime, and diffusion photocurrent associated with the carriers temperature, to achieve efficient and accurate photocurrent. Finally, using the full-wave electromagnetic solver and the calculated photocurrent obtained from the optoelectronic solver, electromagnetic radiation of the antenna and its associated detected THz signal are calculated and compared with a measurement reference for verification.

  4. A kind of graphene film metamaterial for terahertz absorbers (United States)

    Gao, Run-mei; Xu, Zong-cheng; Ding, Chun-feng; Yao, Jian-quan


    A kind of functional graphene thin film metamaterial on a metal-plane separated by a thick dielectric layer is designed for terahertz (THz) absorbers. We investigate the properties of the graphene metamaterial with different interlayers in the 0-3 THz range. The simulation results show that the absorption rate reaches up to 99.9% at the frequency of 1.917 THz. Changing the period to 80 μm×18 μm can get a narrow-band high quality factor ( Q) absorber. We present a novel theoretical interpretation based on the standing wave field theory, which shows that the coherent superposition of incident and reflection rays produces standing waves, and the field energy is localized inside the thick spacers and dissipates through the metal-planes.

  5. Circuit modeling of graphene absorber in terahertz band (United States)

    Taghvaee, Hamid Reza; Nasari, Hadiseh; Abrishamian, Mohammad Sadegh


    Here we develop and extend a transmission line method (TLM) to analyze the performance of graphene assisted metamaterial (GM) devices working in the terahertz (THz) band. We demonstrate that a circuit model can be presented for different parts of the device including graphene and also the patterned metallic sheet by analyzing the distribution of surface induced current. In pursuit of evaluating the efficiency and accuracy of our proposed method, we compare its results, obtained from an easy to implement MATLAB code for a typical GM absorber with those obtained from full wave simulations. The excellence of the proposed method in terms of computation time (showing more than 3 orders of magnitude reduction in run time) and memory resource besides producing results with acceptable agreement with the results of full wave simulation (with an error less than 5%) versus incident angle, dielectric thickness and chemical potential, nominates it as a promising approach to simulate other graphene-based devices.

  6. Numerical earthquake model of the 31 October 2013 Ruisui, Taiwan, earthquake: Source rupture process and seismic wave propagation (United States)

    Lee, Shiann-Jong; Huang, Hsin-Hua; Shyu, J. Bruce H.; Yeh, Te-Yang; Lin, Tzu-Chi


    We build a numerical earthquake model, including numerical source and wave propagation models, to understand the rupture process and the ground motion time history of the 2013 ML 6.4 Ruisui earthquake in Taiwan. This moderately large event was located in the Longitudinal Valley, a suture zone of the Philippine Sea Plate and the Eurasia Plate. A joint source inversion analysis by using teleseismic body wave, GPS coseismic displacement and near field ground motion data was performed first. The inversion results derived from a western dipping fault plane indicate that the slip occurred in depths between 10 and 20 km. The rupture propagated from south to north and two asperities were resolved. The largest one was located approximately 15 km north of the epicenter with a maximum slip about 1 m. A 3D seismic wave propagation simulation based on the spectral-element method was then carried out by using the inverted source model. A strong rupture directivity effect in the northern area of the Longitudinal Valley was found, which was due to the northward rupture process. Forward synthetic waveforms could explain most of the near-field ground motion data for frequencies between 0.05 and 0.2 Hz. This numerical earthquake model not only helps us confirm the detailed rupture processes on the Central Range Fault but also gives contribution to regional seismic hazard mitigation for future large earthquakes.

  7. Developing and exploiting a unique seismic dataset from South African gold mines for source characterization and wave propagation

    CSIR Research Space (South Africa)



    Full Text Available stream_source_info Julia_2008.pdf.txt stream_content_type text/plain stream_size 28067 Content-Encoding UTF-8 stream_name Julia_2008.pdf.txt Content-Type text/plain; charset=UTF-8 DEVELOPING AND EXPLOITING A UNIQUE... SEISMIC DATASET FROM SOUTH AFRICAN GOLD MINES FOR SOURCE CHARACTERIZATION AND WAVE PROPAGATION Jordi Julià1, Andrew A. Nyblade1, Rengin Gök2, William R. Walter2, Lindsay Linzer3, and Ray Durrheim3 Penn State University1, Lawrence Livermore National...

  8. Environmental Hydrocarbon Harvesting for Micro-Scale Power Sources using Thermopower Waves (United States)


    harvesting from fugitive emissions has been made, with breakthroughs in catalysis and reactor design extending thermopower waves to liquid fuels for the first...configurations. Progress towards energy harvesting from fugitive emissions has been made, with breakthroughs in catalysis and have enabled the...harvesting from fugitive emissions has been made, with breakthroughs in catalysis and have enabled the extension of thermopower waves to liquid fuels for

  9. Simulation of blast wave propagation from source to long distance with topography and atmospheric effects (United States)

    Nguyen-Dinh, Maxime; Gainville, Olaf; Lardjane, Nicolas


    We present new results for the blast wave propagation from strong shock regime to the weak shock limit. For this purpose, we analyse the blast wave propagation using both Direct Numerical Simulation and an acoustic asymptotic model. This approach allows a full numerical study of a realistic pyrotechnic site taking into account for the main physical effects. We also compare simulation results with first measurements. This study is a part of the french ANR-Prolonge project (ANR-12-ASTR-0026).

  10. Numerical Prediction of Wave Patterns Due to Motion of 3D Bodies by Kelvin-Havelock Sources

    Directory of Open Access Journals (Sweden)

    Ghassemi Hassan


    Full Text Available This paper discusses the numerical evaluation of the hydrodynamic characteristics of submerged and surface piercing moving bodies. Generally, two main classes of potential methods are used for hydrodynamic characteristic analysis of steady moving bodies which are Rankine and Kelvin-Havelock singularity distribution. In this paper, the Kelvin- Havelock sources are used for simulating the moving bodies and then free surface wave patterns are obtained. Numerical evaluation of potential distribution of a Kelvin-Havelock source is completely presented and discussed. Numerical results are calculated and presented for a 2D cylinder, single source, two parallel moving source, sphere, ellipsoid and standard Wigley hull in different situation that show acceptable agreement with results of other literatures or experiments.

  11. Terahertz Tools Advance Imaging for Security, Industry (United States)


    Picometrix, a wholly owned subsidiary of Advanced Photonix Inc. (API), of Ann Arbor, Michigan, invented the world s first commercial terahertz system. The company improved the portability and capabilities of their systems through Small Business Innovation Research (SBIR) agreements with Langley Research Center to provide terahertz imaging capabilities for inspecting the space shuttle external tanks and orbiters. Now API s systems make use of the unique imaging capacity of terahertz radiation on manufacturing floors, for thickness measurements of coatings, pharmaceutical tablet production, and even art conservation.

  12. Using COMSOL Multiphysics Software to Model Anisotropic Dielectric and Metamaterial Effects in Folded-Waveguide Traveling-Wave Tube Slow-Wave Circuits (United States)

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


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

  13. Theoretical and Experimental Study on the Permittivity of CdTe in the Terahertz Band

    Directory of Open Access Journals (Sweden)

    Sun Wang


    Full Text Available The phonon dispersion spectrum, eigenvector, and lattice vibration frequency of cadmium telluride with a zinc blende structure have been investigated using the density functional theory, and the permittivity of cadmium telluride crystal is numerically calculated. The permittivity of the crystal is measured using the terahertz time-domain spectroscopy system. The experimental results are consistent with the theoretical calculations on the modified local density approximation, the general gradient approximation, and the modified general gradient approximation. Finally, the differences among the three approximate exchange correlation potentials indicate that in the terahertz region, the permittivity of cadmium telluride is dominantly contributed by the coupling between electron and phonon; however, the phonon frequencies of transverse wave and longitudinal wave were sensitive to electron density distribution.

  14. Terahertz pulse shaping through propagation in a gas of symmetric top molecules (United States)

    Hamraoui, K.; Babilotte, P.; Billard, F.; Hertz, E.; Faucher, O.; Coudert, L. H.; Sugny, D.; Lavorel, B.


    Symmetric top molecules of methyl iodide are irradiated with a terahertz pulse generated by a two-color plasma and shaped by a short propagation in air. Free-induction decay is emitted by the excited molecular sample and then propagates in air before detection. The experimental data show that the input terahertz (THz) pulse undergoes strong reshaping through absorption and dispersion. This leads to narrow wave packets at revival times due to the excitation of high rotational energy levels. Typically, a THz burst of duration ≃15 -20 ps is produced periodically, with a central frequency of ≃1 THz and a width that can be as narrow as 60-80 GHz. Pulse shaping based on propagation can be useful for quantum control in molecules. We provide a theoretical description of this wave propagation based on the Maxwell-Bloch equation. The observed experimental signal is in good agreement with the numerical simulations.

  15. A three-dimensional all-metal terahertz metamaterial perfect absorber (United States)

    Wu, Meng; Zhao, Xiaoguang; Zhang, Jingdi; Schalch, Jacob; Duan, Guangwu; Cremin, Kevin; Averitt, Richard D.; Zhang, Xin


    We present a three-dimensional terahertz metamaterial perfect absorber (MPA) that exhibits a high quality factor and is polarization insensitive. The unit cell is composed of two orthogonally oriented copper stand-up split ring resonators deposited on a copper ground plane with capacitive gaps in free space away from the substrate. Near unity (99.6%) absorption at ˜1.65 THz is experimentally obtained in excellent agreement with simulation results. The quality factor is ˜37, which is quite large for a terahertz MPA because of reduced material losses in the all-metal structure. According to simulation results, the MPA is insensitive to the polarization of the incident wave, and more than 90% absorption can be achieved for angles of incidence up to 60° for both TE and TM polarized incident THz waves.

  16. Probing the critical zone using passive- and active-source estimates of subsurface shear-wave velocities (United States)

    Callahan, R. P.; Taylor, N. J.; Pasquet, S.; Dueker, K. G.; Riebe, C. S.; Holbrook, W. S.


    Geophysical imaging is rapidly becoming popular for quantifying subsurface critical zone (CZ) architecture. However, a diverse array of measurements and measurement techniques are available, raising the question of which are appropriate for specific study goals. Here we compare two techniques for measuring S-wave velocities (Vs) in the near surface. The first approach quantifies Vs in three dimensions using a passive source and an iterative residual least-squares tomographic inversion. The second approach uses a more traditional active-source seismic survey to quantify Vs in two dimensions via a Monte Carlo surface-wave dispersion inversion. Our analysis focuses on three 0.01 km2 study plots on weathered granitic bedrock in the Southern Sierra Critical Zone Observatory. Preliminary results indicate that depth-averaged velocities from the two methods agree over the scales of resolution of the techniques. While the passive- and active-source techniques both quantify Vs, each method has distinct advantages and disadvantages during data acquisition and analysis. The passive-source method has the advantage of generating a three dimensional distribution of subsurface Vs structure across a broad area. Because this method relies on the ambient seismic field as a source, which varies unpredictably across space and time, data quality and depth of investigation are outside the control of the user. Meanwhile, traditional active-source surveys can be designed around a desired depth of investigation. However, they only generate a two dimensional image of Vs structure. Whereas traditional active-source surveys can be inverted quickly on a personal computer in the field, passive source surveys require significantly more computations, and are best conducted in a high-performance computing environment. We use data from our study sites to compare these methods across different scales and to explore how these methods can be used to better understand subsurface CZ architecture.

  17. Low-Γ Jets from Compact Stellar Mergers: Candidate Electromagnetic Counterparts to Gravitational Wave Sources (United States)

    Lamb, Gavin P.; Kobayashi, Shiho


    Short gamma-ray bursts (GRBs) are believed to be produced by relativistic jets from mergers of neutron stars (NSs) or NSs and black-holes (BHs). If the Lorentz-factors Γ of jets from compact stellar mergers follow a similar power-law distribution to those observed for other high-energy astrophysical phenomena (e.g., blazars, active galactic nuclei), the population of jets should be dominated by low-Γ outflows. These jets will not produce prompt gamma-rays, but jet energy will be released as X-ray/optical/radio transients when they collide with the ambient medium. Using Monte Carlo simulations, we study the properties of such transients. Approximately 78% of merger jets \\lt 300 Mpc result in failed GRBs if the jet Γ follows a power-law distribution of index -1.75. X-ray/optical transients from failed GRBs will have broad distributions of their characteristics: light-curves peak {t}p˜ 0.1{--}10 days after a merger; flux peaks for X-ray {10}-6 {mJy}≲ {F}x≲ {10}-2 mJy; and optical flux peaks at 14≲ {m}g≲ 22. X-ray transients are detectable by Swift XRT, and ˜ 85 % of optical transients will be detectable by telescopes with limiting magnitude {m}g≳ 21, for well localized sources on the sky. X-ray/optical transients are followed by radio transients with peak times narrowly clustered around {t}p˜ 10 days, and peak flux of ˜10-100 mJy at 10 GHz and ˜0.1 mJy at 150 MHz. By considering the all-sky rate of short GRBs within the LIGO/Virgo range, the rate of on-axis orphan afterglows from failed GRBs should be 2.6(26) per year for NS-NS(NS-BH) mergers, respectively. Since merger jets from gravitational-wave (GW) trigger events tend to be directed to us, a significant fraction of GW events could be associated with the on-axis orphan afterglow.

  18. Pulsed Terahertz Spectroscopy of Biomolecules (United States)

    Markelz, A. G.; Heilweil, E. J.


    Measurements of the collective vibrational modes associated with the 3D tertiary structure of biomolecules were undertaken using pulse terahertz spectroscopy. Transmission measurements of calf thymus DNA (CT-DNA), bovine serum albumin (BSA), and collagen were made for 2 cm-1 to 45 cm-1. For all three biomolecules, low frequency absorption bands could be distinguished from a broadband absorption increasing with frequency. For lyophilized powder samples, features appear at 15 cm-1 and 22 cm-1 for CT-DNA, 10 cm-1 for BSA, and 8 cm-1 and 12 cm-1 for collagen. Measurements were performed as a function of hydration and conformation.

  19. Plasmonic and nanophotonics sensors from visible to terahertz (United States)

    Hassani, Alireza

    The global research objective of this thesis is to demonstrate design of novel compact and ultra-sensitive plasmonic sensors operating anywhere from the visible to the THz spectral ranges. The enabling technologies for such sensors are photonic bandgap and microstructured waveguides and fibers containing metallic inclusions. We achieve the stated global objective by systematically addressing several smaller problems. Firstly, this thesis demonstrates plasmonic excitation in metalized microstructured fibers in the context of bio-chemical sensing with enhanced microfluidics for visible and IR ranges. Furthemore, this basic design concept is generalized for the use with photonic bandgap fibers and waveguides; major advantages of using photonic bandgap waveguides in place of Total Internal Reflection (TIR) fibers for plasmonic sensing are discovered. In the first chapter, we discuss the theory of surface plasmons, surface plasmon excitation and sensing methodologies. In the second chapter we show that using microstructured fibers one can solve much easier the problem of phase matching between the surface plasmon wave and fiber core mode, which is common when standard TIR fibers are used. Moreover, the use of microstructured fibers enables integration of the microfluidics and optics during drawing step thus simplifying considerably the sensor fabrication and operation. Furthermore, the different shapes of the metalized surface to enhance the plasmonic excitation were explored with an aim to enhance sensitivity. In the third chapter, the design of photonic crystal waveguide-based surface plasmon resonance sensor is proposed. By judicious design of a photonic crystal waveguide, the effective refractive index of a core mode can be made considerably smaller than that of the core material, thus enabling efficient phase matching with a plasmon, high sensitivity, and high coupling efficiency from an external Gaussian source, at any wavelength of choice from the visible to near

  20. Acousto-optic modulation and deflection of terahertz electromagnetic radiation in nonpolar liquids (United States)

    Nikitin, P. A.; Voloshinov, V. B.; Gerasimov, V. V.; Knyazev, B. A.


    The results of a series of experiments on controlled deflection of electromagnetic radiation of a free-electron laser upon diffraction by an acoustic wave in nonpolar liquids are presented. Acoustic and optical properties of liquids that are transparent in the terahertz range are discussed. It is demonstrated that nonpolar liquids may turn out to be a more efficient acousto-optic interaction medium than dielectric crystals or semiconductors.

  1. Detection of terahertz radiation in metamaterials: giant plasmonic ratchet effect (Conference Presentation) (United States)

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


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

  2. Source for the traveling planetary waves in the polar winter mesosphere and lower thermosphere: vertical coupling versus in-situ instability. (United States)

    Lu, X.; Chen, C.; Chu, X.; Nguyen, V.; Smith, A. K.


    In the polar winter stratosphere, a group of eastward propagating planetary waves (relative to ground) are generated by the instability of the polar vortex and dominate the variability of chemistry and dynamics of the atmosphere. The strong polar vortex consisting of strong eastward winds support the propagation of these planetary waves until they reach the critical filtering level in the upper stratosphere. However, lidar measurements at McMurdo (78S), Antarctica illustrate the significant signatures of the planetary waves up to 110 km, making it intriguring to identify the wave source. The SD-WACCM well reproduces both local and global structure of these planeaty waves as compared with the ground-based lidar and satellite (MLS), which is thus used to derive the EP flux induced by these planetary waves. In addition to a region of positive EP flux divergence in the stratosphere where we expect to have the stratospheric planetary waves generated, a localized EP flux divergence is also found in the mesosphere and lower thermosphere (MLT) at high latitudes, which likely triggers the generation the waves locally or amplifies those waves that survive from the critical level filtering. By incorporating the background winds from SD-WACCM, a stand-alone mechanistic model with gravity wave effect parameterized is applied to investigate the relative importance of the vertical propagation and in-situ instability to the generation of the planetary waves in the mesosphere and lower thermosphere and whether and how there two processes are coupled together. The gravity wave effect on planetary waves is also addressed. This study provides insights on the vertical wave coupling via wave-wave and wave-mean interactions in the polar winter region.

  3. Applications of laser wakefield accelerator-based light sources (United States)

    Albert, Félicie; Thomas, Alec G. R.


    Laser-wakefield accelerators (LWFAs) were proposed more than three decades ago, and while they promise to deliver compact, high energy particle accelerators, they will also provide the scientific community with novel light sources. In a LWFA, where an intense laser pulse focused onto a plasma forms an electromagnetic wave in its wake, electrons can be trapped and are now routinely accelerated to GeV energies. From terahertz radiation to gamma-rays, this article reviews light sources from relativistic electrons produced by LWFAs, and discusses their potential applications. Betatron motion, Compton scattering and undulators respectively produce x-rays or gamma-rays by oscillating relativistic electrons in the wakefield behind the laser pulse, a counter-propagating laser field, or a magnetic undulator. Other LWFA-based light sources include bremsstrahlung and terahertz radiation. We first evaluate the performance of each of these light sources, and compare them with more conventional approaches, including radio frequency accelerators or other laser-driven sources. We have then identified applications, which we discuss in details, in a broad range of fields: medical and biological applications, military, defense and industrial applications, and condensed matter and high energy density science.

  4. Voltage adjusting characteristics in terahertz transmission through Fabry-Pérot-based metamaterials

    Directory of Open Access Journals (Sweden)

    Jun Luo


    Full Text Available Metallic electric split-ring resonators (SRRs with featured size in micrometer scale, which are connected by thin metal wires, are patterned to form a periodically distributed planar array. The arrayed metallic SRRs are fabricated on an n-doped gallium arsenide (n-GaAs layer grown directly over a semi-insulating gallium arsenide (SI-GaAs wafer. The patterned metal microstructures and n-GaAs layer construct a Schottky diode, which can support an external voltage applied to modify the device properties. The developed architectures present typical functional metamaterial characters, and thus is proposed to reveal voltage adjusting characteristics in the transmission of terahertz waves at normal incidence. We also demonstrate the terahertz transmission characteristics of the voltage controlled Fabry-Pérot-based metamaterial device, which is composed of arrayed metallic SRRs. To date, many metamaterials developed in earlier works have been used to regulate the transmission amplitude or phase at specific frequencies in terahertz wavelength range, which are mainly dominated by the inductance-capacitance (LC resonance mechanism. However, in our work, the external voltage controlled metamaterial device is developed, and the extraordinary transmission regulation characteristics based on both the Fabry-Pérot (FP resonance and relatively weak surface plasmon polariton (SPP resonance in 0.025-1.5 THz range, are presented. Our research therefore shows a potential application of the dual-mode-resonance-based metamaterial for improving terahertz transmission regulation.

  5. Combining historical eyewitness accounts on tsunami-induced waves and numerical simulations for getting insights in uncertainty of source parameters (United States)

    Rohmer, Jeremy; Rousseau, Marie; Lemoine, Anne; Pedreros, Rodrigo; Lambert, Jerome; benki, Aalae


    Recent tsunami events including the 2004 Indian Ocean tsunami and the 2011 Tohoku tsunami have caused many casualties and damages to structures. Advances in numerical simulation of tsunami-induced wave processes have tremendously improved forecast, hazard and risk assessment and design of early warning for tsunamis. Among the major challenges, several studies have underlined uncertainties in earthquake slip distributions and rupture processes as major contributor on tsunami wave height and inundation extent. Constraining these uncertainties can be performed by taking advantage of observations either on tsunami waves (using network of water level gauge) or on inundation characteristics (using field evidence and eyewitness accounts). Despite these successful applications, combining tsunami observations and simulations still faces several limitations when the problem is addressed for past tsunamis events like 1755 Lisbon. 1) While recent inversion studies can benefit from current modern networks (e.g., tide gauges, sea bottom pressure gauges, GPS-mounted buoys), the number of tide gauges can be very scarce and testimonies on tsunami observations can be limited, incomplete and imprecise for past tsunamis events. These observations often restrict to eyewitness accounts on wave heights (e.g., maximum reached wave height at the coast) instead of the full observed waveforms; 2) Tsunami phenomena involve a large span of spatial scales (from ocean basin scales to local coastal wave interactions), which can make the modelling very demanding: the computation time cost of tsunami simulation can be very prohibitive; often reaching several hours. This often limits the number of allowable long-running simulations for performing the inversion, especially when the problem is addressed from a Bayesian inference perspective. The objective of the present study is to overcome both afore-described difficulties in the view to combine historical observations on past tsunami-induced waves

  6. Point Spread Function Estimation for a Terahertz Imaging System

    Directory of Open Access Journals (Sweden)

    Popescu DanC


    Full Text Available We present a method for estimating the point spread function of a terahertz imaging system designed to operate in reflection mode. The method is based on imaging phantoms with known geometry, which have patterns with sharp edges at all orientations. The point spread functions are obtained by a deconvolution technique in the Fourier domain. We validate our results by using the estimated point spread functions to deblur several images of natural scenes and by direct comparison with a point source response. The estimations turn out to be robust and produce consistent deblurring quality over the entire depth of the focal region of the imaging system.

  7. Terahertz saturable absorbers from liquid phase exfoliation of graphite


    Bianchi, Vezio; Carey, Tian; Viti, Leonardo; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles; Tredicucci, Alessandro; Yoon, Duhee; Karagiannidis, Panagiotis; Lombardi, Lucia; Tomarchio, Flavia; Ferrari, Andrea C.; Torrisi, Felice; Vitiello, Miriam S.


    Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. Here we report the fabrication of THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite. Open-aperture z-scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at TH...

  8. Source characterization for an explosion during the 2009 eruption of Redoubt Volcano from very-long-period seismic waves (United States)

    Haney, Matthew M.; Chouet, Bernard A.; Dawson, Phillip B.; Power, John A.


    The 2009 eruption of Redoubt produced several very-long-period (VLP) signals associated with explosions. We invert for the source location and mechanism of an explosion at Redoubt volcano using waveform methods applied to broadband recordings. Such characterization of the source carries information on the geometry of the conduit and the physics of the explosion process. Inversions are carried out assuming the volcanic source can be modeled as a point source, with mechanisms described by a) a set of 3 orthogonal forces, b) a moment tensor consisting of force couples, and c) both forces and moment tensor components. We find that the source of the VLP seismic waves during the explosion is well-described by either a combined moment/force source located northeast of the crater and at an elevation of 1.6 km ASL or a moment source at an elevation of 800 m to the southwest of the crater. The moment tensors for the solutions with moment and force and moment-only share similar characteristics. The source time functions for both moment tensors begin with inflation (pressurization) and execute two cycles of deflation-reinflation (depressurization–repressurization). Although the moment/force source provides a better fit to the data, we find that owing to the limited coverage of the broadband stations at Redoubt the moment-only source is the more robust and reliable solution. Based on the moment-only solution, we estimate a volume change of 19,000 m3 and a pressure change of 7 MPa in a dominant sill and an out-of-phase volume change of 5000 m3 and pressure change of 1.8 MPa in a subdominant dike at the source location. These results shed new light on the magmatic plumbing system beneath Redoubt and complement previous studies on Vulcanian explosions at other volcanoes.

  9. Metal Mesh Filters for Terahertz Receivers Project (United States)

    National Aeronautics and Space Administration — The technical objective of this SBIR program is to develop and demonstrate metal mesh filters for use in NASA's low noise receivers for terahertz astronomy and...

  10. Investigating murals with terahertz reflective tomography (United States)

    Yuan, Minjie; Sun, Wenfeng; Wang, Xinke; Wang, Sen; Zhang, Qunxi; Ye, Jiasheng; Zhang, Yan


    Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals.

  11. Optically Modulated Multiband Terahertz Perfect Absorber

    DEFF Research Database (Denmark)

    Seren, Huseyin R.; Keiser, George R.; Cao, Lingyue


    response of resonant metamaterials continues to be a challengingendeavor. Resonant perfect absorbers have flourished as one of the mostpromising metamaterial devices with applications ranging from power har-vesting to terahertz imaging. Here, an optically modulated resonant perfectabsorber is presented...

  12. Estimation of earthquake source parameters in the Kachchh seismic zone, Gujarat, India, using three component S-wave spectra (United States)

    Nagamani, Durgada; Mandal, Prantik


    Earthquake source parameters and crustal Q0 values for the 138 selected local events of (Mw{:}2.5{-}4.4) the 2001 Bhuj earthquake sequence have been computed through inversion modelling of S-waves from three-component broadband seismometer data. SEISAN software has been used to locate the identified local earthquakes, which were recorded at least three or more stations of the Kachchh seismological network. Three component spectra of S-wave are being inverted by using the Levenberg-Marquardt non-linear inversion technique, wherein the inversion scheme is formulated based on ω 2 source model. SAC Software (seismic analysis code) is being utilized for calculating three-component displacement and velocity spectra of S-wave. The displacement spectra are used for estimating corner frequency (in Hz) and long period spectral level (in nm-s). These two parameters play a key role in estimating earthquake source parameters. The crustal {Q}0 values have been computed simultaneously for each component of three-component broadband seismograph. The estimated seismic moment (M0) and source radius ( r) using S-wave spectra range from 7.03E+12 to 5.36E+15 N-m and 178.56 to 565.21 m, respectively. The corner frequencies for S-wave vary from 3.025 to 7.425 Hz. We also estimated the radiated energy (ES) using velocity spectra, which is varying from 2.76E+06 to 4.07E+11 Joules. The estimated apparent stress drop and static stress drop values range from 0.01 to 2.56 and 0.53 to 36.79 MPa, respectively. Our study also reveals that estimated Q0 values vary from 119.0 to 7229.5, with an average Q0 value of 701. Another important parameter, by which the earthquake rupture process can be recognized, is Zuniga parameter. It suggests that most of the Kachchh events follow the frictional overshoot model. Our estimated static stress drop values are higher than the apparent stress drop values. And the stress drop values are quite larger for intraplate earthquakes than the interplate earthquakes.

  13. Modification of sonic boom wave forms during propagation from the source to the ground. (United States)

    Bass, Henry E; Raspet, Richard; Chambers, James P; Kelly, Mark


    A number of physical processes work to modify the shape of sonic boom wave forms as the wave form propagates from the aircraft to a receiver on the ground. These include frequency-dependent absorption, nonlinear steepening, and scattering by atmospheric turbulence. In the past two decades, each of these effects has been introduced into numerical prediction algorithms and results compared to experimental measurements. There is still some disagreement between measurements and prediction, but those differences are now in the range of tens of percent. The processes seem to be understood. The present understanding of sonic boom evolution will be presented along with experimental justification.

  14. Double Osbnd Ne-Mg white dwarfs merging as the source of the powerfull gravitational waves for LIGO/VIRGO type interferometers (United States)

    Lipunov, V. M.


    New strong non-spiralling-in gravitational wave (GW) source for LIGO/VIRGO detectors are proposed. Double Osbnd Ne-Mg white dwarf mergers can produce strong gravitational waves with frequencies in the several hundreds Hz range. Such events can be followed by a Super Nova type Ia.

  15. Comparison between off-resonance and electron Bernstein waves heating regime in a microwave discharge ion source

    Energy Technology Data Exchange (ETDEWEB)

    Castro, G.; Di Giugno, R.; Miracoli, R. [INFN- Laboratori Nazionali del Sud, via S. Sofia 62, 95123 Catania (Italy); Universita degli Studi di Catania, Dipartimento di Fisica e Astronomia, V. S. Sofia 64, 95123 Catania (Italy); Mascali, D. [INFN- Laboratori Nazionali del Sud, via S. Sofia 62, 95123 Catania (Italy); CSFNSM, Viale A. Doria 6, 95125 Catania (Italy); Romano, F. P. [INFN- Laboratori Nazionali del Sud, via S. Sofia 62, 95123 Catania (Italy); CNR-IBAM Via Biblioteca 4, 95124 Catania (Italy); Celona, L.; Gammino, S.; Lanaia, D.; Ciavola, G. [INFN- Laboratori Nazionali del Sud, via S. Sofia 62, 95123 Catania (Italy); Serafino, T. [CSFNSM, Viale A. Doria 6, 95125 Catania (Italy); Di Bartolo, F. [Universita di Messina, Ctr. da Papardo-Sperone, 98100 Messina (Italy); Gambino, N. [INFN- Laboratori Nazionali del Sud, via S. Sofia 62, 95123 Catania (Italy); Universita degli Studi di Catania, Dipartimento di Fisica e Astronomia, V. S. Sofia 64, 95123 Catania (Italy); IET-Institute of Energy Technology, LEC-Laboratory for Energy Conversion, ETH Zurich, Sonneggstrasse 3, CH-8092 Zurich (Switzerland)


    A microwave discharge ion source (MDIS) operating at the Laboratori Nazionali del Sud of INFN, Catania has been used to compare the traditional electron cyclotron resonance (ECR) heating with an innovative mechanisms of plasma ignition based on the electrostatic Bernstein waves (EBW). EBW are obtained via the inner plasma electromagnetic-to-electrostatic wave conversion and they are absorbed by the plasma at cyclotron resonance harmonics. The heating of plasma by means of EBW at particular frequencies enabled us to reach densities much larger than the cutoff ones. Evidences of EBW generation and absorption together with X-ray emissions due to high energy electrons will be shown. A characterization of the discharge heating process in MDISs as a generalization of the ECR heating mechanism by means of ray tracing will be shown in order to highlight the fundamental physical differences between ECR and EBW heating.

  16. Semiempirical Dissipation Source Functions for Ocean Waves. Part 1: Definition, Calibration, and Validation (United States)


    1274-1298. —. .and I. R Young. 21X13: Revisiting the Pierson-Moskowit7 asymptotic limits for fully developed wind waves. J. / VIVA Oce- anogr...stale of the art . Prog. Oceanogr., 75,603-674, doi:10.1016/j.pocean.2007.05.005 Wu, C. H.. and H. M. Nepf. 2002: Breaking criteria and energy losses

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

    Directory of Open Access Journals (Sweden)

    Changbiao Wang


    Full Text Available 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.

  18. The theory of magnetohydrodynamic wave generation by localized sources. III - Efficiency of plasma heating by dissipation of far-field waves. [in solar corona (United States)

    Collins, William


    The fraction of radiation emitted by Alfven waves is calculated by using two separate methods to determine whether the Alfven flux generated in the photosphere is sufficient to heat the corona. One method employs a set of scaling laws for the fluxes as functions of plasma and source parameters; the second method consist of a procedure for calculating the flux in each waveband from the interaction of vector-harmonic components of an arbitrary applied forcing. Both methods indicate that the Alfven flux accounts roughly for half of the total emission. The need to reexamine estimates of the amount of Alfven flux reaching the corona based on observations of plasma disturbances in the photosphere is emphasized.

  19. Ultrasensitive terahertz metamaterial sensor based on spoof surface plasmon. (United States)

    Chen, Xu; Fan, Wenhui


    A planar terahertz metamaterial sensor consisting of a corrugated metal stripe perforated by three rectangular grooves is proposed and investigated numerically. Due to the formation of Fabry-Perot resonance of the spoof surface plasmons mode on the corrugated metal stripe, the extremely sharp resonance in transmission spectrum associated with strong local field enhancement and high quality factor can be realized and exploited for ultrasensitive sensing. Since the intense interaction between electromagnetic waves and analyte materials, the frequency sensitivity of 1.966 THz per refractive index unit and the figure of merit of 19.86 can be achieved. Meanwhile, the film thickness sensitivity of this metamaterial sensor is higher than 52.5 GHz/μm when the analyte thickness is thinner than 4 μm. More interestingly, we find that the metal thickness has a great effect on the sensor performance. These findings open up opportunities for planar metamaterial structures to be developed into practical sensors in terahertz regime.

  20. Numerical simulation of broadband vortex terahertz beams propagation (United States)

    Semenova, V. A.; Kulya, M. S.; Bespalov, V. G.


    Orbital angular momentum (OAM) represents new informational degree of freedom for data encoding and multiplexing in fiber and free-space communications. OAM-carrying beams (also called vortex beams) were successfully used to increase the capacity of optical, millimetre-wave and radio frequency communication systems. However, the investigation of the OAM potential for the new generation high-speed terahertz communications is also of interest due to the unlimited demand of higher capacity in telecommunications. Here we present a simulation-based study of the propagating in non-dispersive medium broadband terahertz vortex beams generated by a spiral phase plate (SPP). The algorithm based on scalar diffraction theory was used to obtain the spatial amplitude and phase distributions of the vortex beam in the frequency range from 0.1 to 3 THz at the distances 20-80 mm from the SPP. The simulation results show that the amplitude and phase distributions without unwanted modulation are presented in the wavelengths ranges with centres on the wavelengths which are multiple to the SPP optical thickness. This fact may allow to create the high-capacity near-field communication link which combines OAM and wavelength-division multiplexing.

  1. Response of asymmetric carbon nanotube network devices to sub-terahertz and terahertz radiation

    Energy Technology Data Exchange (ETDEWEB)

    Gayduchenko, I., E-mail:, E-mail: [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); National Research Centre “Kurchatov Institute,” Moscow 123128 (Russian Federation); Kardakova, A.; Voronov, B.; Finkel, M. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Fedorov, G., E-mail:, E-mail: [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Moscow Institute of Physics and Technology (State University), Dolgoprudny 141700 (Russian Federation); Jiménez, D. [Departament d' Enginyeria Electrònica, Escola d' Enginyeria, Universitat Autònoma de Barcelona, 08193 Bellaterra (Spain); Morozov, S. [Moscow Institute of Physics and Technology (State University), Dolgoprudny 141700 (Russian Federation); Presniakov, M. [National Research Centre “Kurchatov Institute,” Moscow 123128 (Russian Federation); Goltsman, G. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Moscow Institute of Electronics and Mathematics, National Research University Higher School of Economics, Moscow 109028 (Russian Federation)


    Demand for efficient terahertz radiation detectors resulted in intensive study of the asymmetric carbon nanostructures as a possible solution for that problem. It was maintained that photothermoelectric effect under certain conditions results in strong response of such devices to terahertz radiation even at room temperature. In this work, we investigate different mechanisms underlying the response of asymmetric carbon nanotube (CNT) based devices to sub-terahertz and terahertz radiation. Our structures are formed with CNT networks instead of individual CNTs so that effects probed are more generic and not caused by peculiarities of an individual nanoscale object. We conclude that the DC voltage response observed in our structures is not only thermal in origin. So called diode-type response caused by asymmetry of the device IV characteristic turns out to be dominant at room temperature. Quantitative analysis provides further routes for the optimization of the device configuration, which may result in appearance of novel terahertz radiation detectors.

  2. Wavelength-agile high-power sources via four-wave mixing in higher-order fiber modes. (United States)

    Demas, J; Prabhakar, G; He, T; Ramachandran, S


    Frequency doubling of conventional fiber lasers in the near-infrared remains the most promising method for generating integrated high-peak-power lasers in the visible, while maintaining the benefits of a fiber geometry; but since the shortest wavelength power-scalable fiber laser sources are currently restricted to either the 10XX nm or 15XX nm wavelength ranges, accessing colors other than green or red remains a challenge with this schematic. Four-wave mixing using higher-order fiber modes allows for control of dispersion while maintaining large effective areas, thus enabling a power-scalable method to extend the bandwidth of near-infrared fiber lasers, and in turn, the bandwidth of potential high-power sources in the visible. Here, two parametric sources using the LP0,7 and LP0,6 modes of two step-index multi-mode fibers are presented. The output wavelengths for the sources are 880, 974, 1173, and 1347 nm with peak powers of 10.0, 16.2, 14.7, and 6.4 kW respectively, and ~300-ps pulse durations. The efficiencies of the sources are analyzed, along with a discussion of wavelength tuning and further power scaling, representing an advance in increasing the bandwidth of near-infrared lasers as a step towards high-peak-power sources at wavelengths across the visible spectrum.

  3. A Broadband Metasurface-Based Terahertz Flat-Lens Array

    KAUST Repository

    Wang, Qiu


    A metasurface-based terahertz flat-lens array is proposed, comprising C-shaped split-ring resonators exhibiting locally engineerable phase discontinuities. Possessing a high numerical aperture, the planar lens array is flexible, robust, and shows excellent focusing characteristics in a broadband terahertz frequency. It could be an important step towards the development of planar terahertz focusing devices for practical applications.

  4. Plasmonic Terahertz Amplification in Graphene-Based Asymmetric Hyperbolic Metamaterial

    Directory of Open Access Journals (Sweden)

    Igor Nefedov


    Full Text Available We propose and theoretically explore terahertz amplification, based on stimulated generation of plasmons in graphene asymmetric hyperbolic metamaterials (AHMM, strongly coupled to terahertz radiation. In contrast to the terahertz amplification in resonant nanocavities, AHMM provides a wide-band THz amplification without any reflection in optically thin graphene multilayers.

  5. Enhanced terahertz emission from thin film semiconductor/metal interfaces

    NARCIS (Netherlands)

    Ramakrishnan, G.


    Terahertz light is electromagnetic radiation, similar to visible light. The photons that the terahertz light is comprised of carry a much smaller amount of energy compared to the visible light photons. Unlike visible light, terahertz light can pass through materials like plastic, cardboards, wood

  6. A New Wave Equation Based Source Location Method with Full-waveform Inversion

    KAUST Repository

    Wu, Zedong


    Locating the source of a passively recorded seismic event is still a challenging problem, especially when the velocity is unknown. Many imaging approaches to focus the image do not address the velocity issue and result in images plagued with illumination artifacts. We develop a waveform inversion approach with an additional penalty term in the objective function to reward the focusing of the source image. This penalty term is relaxed early to allow for data fitting, and avoid cycle skipping, using an extended source. At the later stages the focusing of the image dominates the inversion allowing for high resolution source and velocity inversion. We also compute the source location explicitly and numerical tests show that we obtain good estimates of the source locations with this approach.

  7. A Source-Model Technique for analysis of wave guiding along chains of metallic nanowires in layered media. (United States)

    Szafranek, Dana; Leviatan, Yehuda


    A method for determining the modes that can be guided along infinite chains of metallic nanowires when they are embedded, as in most realistic set-ups, in layered media is presented. The method is based on a rigorous full-wave frequency-domain Source-Model Technique (SMT). The method allows efficient determination of the complex propagation constants and the surface-plasmon type modal fields. Sample results are presented for silver nanowires with circular and triangle-like cross-sections lying in an air-Si-glass layered structure.

  8. Rapid calculation of acoustic fields from arbitrary continuous-wave sources. (United States)

    Treeby, Bradley E; Budisky, Jakub; Wise, Elliott S; Jaros, Jiri; Cox, B T


    A Green's function solution is derived for calculating the acoustic field generated by phased array transducers of arbitrary shape when driven by a single frequency continuous wave excitation with spatially varying amplitude and phase. The solution is based on the Green's function for the homogeneous wave equation expressed in the spatial frequency domain or k-space. The temporal convolution integral is solved analytically, and the remaining integrals are expressed in the form of the spatial Fourier transform. This allows the acoustic pressure for all spatial positions to be calculated in a single step using two fast Fourier transforms. The model is demonstrated through several numerical examples, including single element rectangular and spherically focused bowl transducers, and multi-element linear and hemispherical arrays.

  9. Reverse scan as a source of information in square wave voltammetry


    Zelić, Marina


    Under the influence of recently published articles, reverse scans in square wave voltammetry were applied in a study of Eu3+/EU2+ redox system at increasing concentrations of several electrolytes, and gradually changing frequency or step potential. The electrode response is highly affected by all these factors and two peaks can appear though only one electroactive species is present in the solution and one electron included in the process, whereas adsorption of the reactant or product is not ...

  10. Terahertz-based target typing.

    Energy Technology Data Exchange (ETDEWEB)

    Lyo, Sungkwun Kenneth; Wanke, Michael Clement; Reno, John Louis; Shaner, Eric Arthur; Grine, Albert D.; Barrick, Todd A.


    The purpose of this work was to create a THz component set and understanding to aid in the rapid analysis of transient events. This includes the development of fast, tunable, THz detectors, along with filter components for use with standard detectors and accompanying models to simulate detonation signatures. The signature effort was crucial in order to know the spectral range to target for detection. Our approach for frequency agile detection was to utilize plasmons in the channel of a specially designed field-effect transistor called the grating-gate detector. Grating-gate detectors exhibit narrow-linewidth, broad spectral tunability through application of a gate bias, and no angular dependence in their photoresponse. As such, if suitable sensitivity can be attained, they are viable candidates for Terahertz multi-spectral focal plane arrays.

  11. Absorber for terahertz radiation management (United States)

    Biallas, George Herman; Apeldoorn, Cornelis; Williams, Gwyn P.; Benson, Stephen V.; Shinn, Michelle D.; Heckman, John D.


    A method and apparatus for minimizing the degradation of power in a free electron laser (FEL) generating terahertz (THz) radiation. The method includes inserting an absorber ring in the FEL beam path for absorbing any irregular THz radiation and thus minimizes the degradation of downstream optics and the resulting degradation of the FEL output power. The absorber ring includes an upstream side, a downstream side, and a plurality of wedges spaced radially around the absorber ring. The wedges form a scallop-like feature on the innermost edges of the absorber ring that acts as an apodizer, stopping diffractive focusing of the THz radiation that is not intercepted by the absorber. Spacing between the scallop-like features and the shape of the features approximates the Bartlett apodization function. The absorber ring provides a smooth intensity distribution, rather than one that is peaked on-center, thereby eliminating minor distortion downstream of the absorber.

  12. Novel Observational Technique of Gravitational Wave (GW) Events: Detecting and Locating Electromagnetic Counterparts to GW Sources using Dust Scattering Halos (United States)

    Nederlander, Richard; Paerels, Frits


    We discuss a novel observational technique for detecting and locating the electromagnetic counterpart to its GW source, providing astronomers with a several-hour reprieve after a GW event’s occurrence. The technique relies on identifying a dust scattering halo caused by GW-produced X-rays scattering off Galactic dust clouds. The travel time delay of these scattered photons makes them detectable for up to several hours after the prompt event, and the location of the gravitational wave source will be at the geometric center of the halo. The center can be determined with precision sufficient enough to allow the host galaxy to be discerned. This novel technique will be especially relevant for binary black-hole mergers because their counterparts have, as of now, been difficult to detect.

  13. Hydrodynamic Modeling of Free Surface Interactions and Implications for P and Rg Waves Recorded on the Source Physics Experiments (United States)

    Larmat, C. S.; Rougier, E.; Knight, E.; Yang, X.; Patton, H. J.


    A goal of the Source Physics Experiments (SPE) is to develop explosion source models expanding monitoring capabilities beyond empirical methods. The SPE project combines field experimentation with numerical modelling. The models take into account non-linear processes occurring from the first moment of the explosion as well as complex linear propagation effects of signals reaching far-field recording stations. The hydrodynamic code CASH is used for modelling high-strain rate, non-linear response occurring in the material near the source. Our development efforts focused on incorporating in-situ stress and fracture processes. CASH simulates the material response from the near-source, strong shock zone out to the small-strain and ultimately the elastic regime where a linear code can take over. We developed an interface with the Spectral Element Method code, SPECFEM3D, that is an efficient implementation on parallel computers of a high-order finite element method. SPECFEM3D allows accurate modelling of wave propagation to remote monitoring distance at low cost. We will present CASH-SPECFEM3D results for SPE1, which was a chemical detonation of about 85 kg of TNT at 55 m depth in a granitic geologic unit. Spallation was observed for SPE1. Keeping yield fixed we vary the depth of the source systematically and compute synthetic seismograms to distances where the P and Rg waves are separated, so that analysis can be performed without concern about interference effects due to overlapping energy. We study the time and frequency characteristics of P and Rg waves and analyse them in regard to the impact of free-surface interactions and rock damage resulting from those interactions. We also perform traditional CMT inversions as well as advanced CMT inversions, developed at LANL to take into account the damage. This will allow us to assess the effect of spallation on CMT solutions as well as to validate our inversion procedure. Further work will aim to validate the developed

  14. Terahertz spectrum splitting by a graphene-covered array of rectangular grooves. (United States)

    Tavakol, Mohammad Reza; Saba, Amirhossein; Jafargholi, Amir; Khavasi, Amin


    We propose a bidirectional terahertz (THz) spectrum splitter using a practically simple metamaterial structure consisting of rectangular grooves covered by graphene. Thanks to the graphene optoelectronic tunability and by adjusting the grooves width, this structure provides nearly 2π phase shift. At the same time, the reflection efficiency is acceptable throughout the phase shifts. We design each of the meta-atoms using a circuit model, and then we synthesize the final supercell based on the generalized Snell's law so that the structure reflects different frequency waves to totally different directions. The full-wave simulations demonstrate the beam splitting with a remarkable efficiency of around 80%.

  15. Ultrafast terahertz electrodynamics of photonic and electronic nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Liang [Iowa State Univ., Ames, IA (United States)


    This thesis summarizes my work on using ultrafast laser pulses to study Terahertz (THz) electrodynamics of photonic and electronic nanostructures and microstructures. Ultrafast timeresolved (optical, NIR, MIR, THz) pump-probe spectroscopy setup has been successfully built, which enables me to perform a series of relevant experiments. Firstly, a novel high e ciency and compact THz wave emitter based on split-ring-resonators has been developed and characterized. The emitter can be pumped at any wavelength by tailoring the magnetic resonance and could generate gapless THz waves covering the entire THz band. Secondly, two kinds of new photonic structures for THz wave manipulation have been successfully designed and characterized. One is based on the 1D and 2D photo-imprinted di ractive elements. The other is based on the photoexcited double-split-ring-resonator metamaterials. Both structures are exible and can modulate THz waves with large tunability. Thirdly, the dark excitons in semiconducting singlewalled carbon nanotubes are studied by optical pump and THz probe spectroscopy, which provides the rst insights into the THz responses of nonequilibrium excitonic correlations and dynamics from the dark ground states in carbon nanotubes. Next, several on-going projects are brie y presented such as the study of ultrafast THz dynamics of Dirac fermions in topological insulator Bi2Se3 with Mid-infrared excitation. Finally, the thesis ends with a summary of the completed experiments and an outlook of the future plan.

  16. Spectral-element simulations of three-dimensional seismic wave propagation and applications to source and structural inversions (United States)

    Liu, Qinya

    This thesis presents a concise introduction to the spectral-element method and its applications to the simulation of seismic wave propagation in 3-D earth models. The spectral-element method is implemented in the regional scale for a 3-D integrated southern California velocity model. Significantly better waveform fits are achieved for the 3-D synthetics calculated compare to the 1-D synthetics generated from the 1-D standard southern California model, especially for many basin stations where strong amplifications are observed due to the very low wave-speed sediments. A hypothetical earthquake rupturing from northeast to southwest at the southern end of the San Andreas fault is simulated to improve our understanding of the seismic hazards in the Salton Trough region. With the improved 3-D Green's function, we perform source inversions for both the source mechanisms and event depths of Mw ≥ 3.5 earthquakes in southern California. The inversion results generally agree well with the results obtained by other traditional methods, but with significantly more stations used in the inversions. Time shifts are generally required to align the data and the synthetics, which provides a great dataset for the improvement of the 3-D velocity models in southern California. We use the adjoint method to formulate the tomographic inverse problem based upon a 3-D initial model. We calculate the sensitivity kernels, a key component of the tomographic inversion, that relate the perturbations of observations to the perturbations of the model parameters. These kernels are constructed by the interaction of the regular forward wavefield and the adjoint wavefield generated by putting the time-reversed signals at the receivers as simultaneous adjoint sources. We compute the travel-time sensitivity kernels for typical phases in both regional and global problems for educational purposes, and outline the procedures of applying the conjugate-gradient method to solve both source and structural

  17. Reconfigurable terahertz grating with enhanced transmission of TE polarized light

    Directory of Open Access Journals (Sweden)

    J. W. He


    Full Text Available We demonstrate an optically reconfigurable grating with enhanced transmission of TE-polarized waves in the terahertz (THz waveband. This kind of grating is realized by projecting a grating image onto a thin Si wafer with a digital micromirror device (DMD. The enhanced transmission is caused by a resonance of the electromagnetic fields between the photoexcited strips. The position of the transmission peak shifts with the variation of the period and duty cycle of the photoinduced grating, which can be readily controlled by the DMD. Furthermore, a flattened Gaussian model was applied to describe the distribution of the photoexcited free carriers in the Si wafer, and the simulated transmittance spectra are shown to be in good agreement with the experimental results. In future, the photoexcited carriers could also be used to produce THz diffractive elements with reconfigurable functionality.

  18. Terahertz IFEL/FEL Microbunching for Plasma Beatwave Accelerators

    CERN Document Server

    Sung, Chieh; Joshi, Chandrashekhar; Musumeci, Pietro; Pellegrini, Claudio; Ralph, Joseph; Reiche, Sven; Rosenzweig, James E; Tochitsky, Sergei Ya


    In order to obtain monoenergetic acceleration of electrons, phase-locked injection using electron microbunches shorter than the accelerating structure is necessary. For a laser-driven plasma beatwave accelerator experiment, we propose to microbunch the electrons by interaction with terahertz (THz) radiation in an undulator via two mechanisms– free electron laser (FEL) and inverse free electron laser (IFEL). Since the high power FIR radiation will be generated via difference frequency mixing in GaAs by the same CO2 beatwave used to drive the plasma wave, electrons could be phase-locked and pre-bunched into a series of microbunches separated with the same periodicity. Here we examine the criteria for undulator design and present simulation results for both IFEL and FEL approaches. Using different CO2 laser lines, electrons can be microbunched with different periodicity 300 – 100 mm suitable for injection into plasma densities in the range 1016 – 1017 cm-3, respectively. The requiremen...

  19. Reconfigurable terahertz grating with enhanced transmission of TE polarized light (United States)

    He, J. W.; Wang, X. K.; Xie, Z. W.; Xue, Y. Z.; Wang, S.; Zhang, Y.


    We demonstrate an optically reconfigurable grating with enhanced transmission of TE-polarized waves in the terahertz (THz) waveband. This kind of grating is realized by projecting a grating image onto a thin Si wafer with a digital micromirror device (DMD). The enhanced transmission is caused by a resonance of the electromagnetic fields between the photoexcited strips. The position of the transmission peak shifts with the variation of the period and duty cycle of the photoinduced grating, which can be readily controlled by the DMD. Furthermore, a flattened Gaussian model was applied to describe the distribution of the photoexcited free carriers in the Si wafer, and the simulated transmittance spectra are shown to be in good agreement with the experimental results. In future, the photoexcited carriers could also be used to produce THz diffractive elements with reconfigurable functionality.

  20. Research on Novel High-Power Microwave/Millimeter Wave Sources and Applications (United States)


    theoretical support for the experiments at UC Davis aimed at the development of a zero-drive stable W-band gyrotron traveling-wave amplifier (Gyro- TWT ). The...this gyro- TWT ; namely, a new type of electron gun based on the robust, long-lived, clean, low work function, high current density thermionic cathodes...recently developed at UC Davis under the sponsorship of MURI-04. This is an electron gun to be used for the zero-drive stable Gyro- TWT . Our