Sample records for terahertz pulsed imaging

  1. Terahertz pulsed imaging in vivo

    NASA Astrophysics Data System (ADS)

    Pickwell-MacPherson, E.

    2011-03-01

    Terahertz (1012 Hz) pulsed imaging is a totally non-destructive and non-ionising imaging modality and thus potential applications in medicine are being investigated. In this paper we present results using our hand-held terahertz probe that has been designed for in vivo use. In particular, we use the terahertz probe to perform reflection geometry in vivo measurements of human skin. The hand-held terahertz probe gives more flexibility than a typical flat-bed imaging system, but it also results in noisier data and requires existing processing methods to be improved. We describe the requirements and limitations of system geometry, data acquisition rate, image resolution and penetration depth and explain how various factors are dependent on each other. We show how some of the physical limitations can be overcome using novel data processing methods.

  2. Terahertz Pulse Imaging of ex vivo Basal Cell Carcinoma

    Microsoft Academic Search

    Ruth M Woodward; Vincent P Wallace; Richard J Pye; Bryan E Cole; Donald D Arnone; Edmund H Linfield; Michael Pepper

    2003-01-01

    Terahertz pulse imaging has been used for the first time to study basal cell carcinoma ex vivo, the most common form of skin cancer. This noninvasive technique uses part of the electromagnetic spectrum in the frequency range 0.1–2.7 THz. A total of 21 samples were imaged; the study was performed blind and results were compared to histology. Each image consisted

  3. A promising diagnostic method: Terahertz pulsed imaging and spectroscopy

    PubMed Central

    Sun, Yiwen; Sy, Ming Yiu; Wang, Yi-Xiang J; Ahuja, Anil T; Zhang, Yuan-Ting; Pickwell-MacPherson, Emma

    2011-01-01

    The terahertz band lies between the microwave and infrared regions of the electromagnetic spectrum. This radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. It is strongly attenuated by water and very sensitive to water content. Unique absorption spectra due to intermolecular vibrations in this region have been found in different biological materials. These unique features make terahertz imaging very attractive for medical applications in order to provide complimentary information to existing imaging techniques. There has been an increasing interest in terahertz imaging and spectroscopy of biologically related applications within the last few years and more and more terahertz spectra are being reported. This paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques, and a number of applications such as molecular spectroscopy, tissue characterization and skin imaging are discussed. PMID:21512652

  4. TOPICAL REVIEW: Pulsed terahertz tomography

    Microsoft Academic Search

    S. Wang; X.-C. Zhang

    2004-01-01

    Terahertz time-domain spectroscopy (THz-TDS) is a coherent measurement technology. Using THz-TDS, the phase and amplitude of the THz pulse at each frequency can be determined. Like radar, THz-TDS also provides time information that allows us to develop various three-dimensional THz tomographic imaging modalities. The three-dimensional THz tomographic imagings we investigated are: terahertz diffraction tomography (THz DT), terahertz computed tomography (THz

  5. Terahertz imaging for styrofoam inspection

    Microsoft Academic Search

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

    2007-01-01

    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. Terahertz imaging for styrofoam inspection

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

    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.

  7. Neural Network-based non-destructive quantification of thin coating by terahertz pulsed imaging in the frequency domain

    Microsoft Academic Search

    Shuncong Zhong; Yaochun Shen; Michael J. Evans; Robert K. May; J. Axel Zeitler; Dipankar Dey

    2010-01-01

    Terahertz pulsed imaging (TPI) is a powerful tool for non-destructive quantification of pharmaceutical tablet coatings. In this paper, we present a Neural Network (NN) based method for extracting the coating thickness from the FFT-amplitude of the measured terahertz waveform. We demonstrate that the NN-based frequency domain method outperforms the standard “peak-finding” time-domain method, in terms of quantifying thinner coating thickness,

  8. Medical diagnostics using terahertz pulsed spectroscopy

    NASA Astrophysics Data System (ADS)

    Zaytsev, Kirill I.; Kudrin, Konstantin G.; Koroleva, Svetlana A.; Fokina, Irina N.; Volodarskaya, Svetlana I.; Novitskaya, Ekaterina V.; Perov, Artem N.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

    2014-03-01

    The paper contains recent results of studying the ability of human body disease diagnosis with terahertz time-domain spectroscopy. In vitro skin cancer samples (squamous cell carcinoma, epithelioid cell melanoma, infiltrating carcinoma) were studied experimentally with terahertz pulsed spectrometer. The parametrical in vitro images of skin cancers are presented. The ability to make early tooth cariosity diagnosis with terahertz time-domain spectroscopy was also shown experimentally. The results of studying the in vitro tooth samples are presented and discussed.

  9. Spatiotemporal shapingof terahertz pulses

    Microsoft Academic Search

    Jake Bromage; Stojan Radic; G. P. Agrawal; C. R. Stroud Jr.; P. M. Fauchet; Roman Sobolewski

    1997-01-01

    We report temporal shaping of few-cycle terahertz pulses, using a slit in a conductive screen as a high-pass filter. The filter's cutoff frequency was tuned by changing the width of the slit; the slope of the cutoff transition was altered by changing the thickness of the screen. We measured the transmission function of the filters, using large-aperture photoconducting antennas to

  10. Terahertz pulsed imaging as an advanced characterisation tool for film coatings--a review.

    PubMed

    Haaser, Miriam; Gordon, Keith C; Strachan, Clare J; Rades, Thomas

    2013-12-01

    Solid dosage forms are the pharmaceutical drug delivery systems of choice for oral drug delivery. These solid dosage forms are often coated to modify the physico-chemical properties of the active pharmaceutical ingredients (APIs), in particular to alter release kinetics. Since the product performance of coated dosage forms is a function of their critical coating attributes, including coating thickness, uniformity, and density, more advanced quality control techniques than weight gain are required. A recently introduced non-destructive method to quantitatively characterise coating quality is terahertz pulsed imaging (TPI). The ability of terahertz radiation to penetrate many pharmaceutical materials enables structural features of coated solid dosage forms to be probed at depth, which is not readily achievable with other established imaging techniques, e.g. near-infrared (NIR) and Raman spectroscopy. In this review TPI is introduced and various applications of the technique in pharmaceutical coating analysis are discussed. These include evaluation of coating thickness, uniformity, surface morphology, density, defects and buried structures as well as correlation between TPI measurements and drug release performance, coating process monitoring and scale up. Furthermore, challenges and limitations of the technique are discussed. PMID:23570960

  11. Quantitative analysis of visible surface defect risk in tablets during film coating using terahertz pulsed imaging.

    PubMed

    Niwa, Masahiro; Hiraishi, Yasuhiro

    2014-01-30

    Tablets are the most common form of solid oral dosage produced by pharmaceutical industries. There are several challenges to successful and consistent tablet manufacturing. One well-known quality issue is visible surface defects, which generally occur due to insufficient physical strength, causing breakage or abrasion during processing, packaging, or shipping. Techniques that allow quantitative evaluation of surface strength and the risk of surface defect would greatly aid in quality control. Here terahertz pulsed imaging (TPI) was employed to evaluate the surface properties of core tablets with visible surface defects of varying severity after film coating. Other analytical methods, such as tensile strength measurements, friability testing, and scanning electron microscopy (SEM), were used to validate TPI results. Tensile strength and friability provided no information on visible surface defect risk, whereas the TPI-derived unique parameter terahertz electric field peak strength (TEFPS) provided spatial distribution of surface density/roughness information on core tablets, which helped in estimating tablet abrasion risk prior to film coating and predicting the location of the defects. TPI also revealed the relationship between surface strength and blending condition and is a nondestructive, quantitative approach to aid formulation development and quality control that can reduce visible surface defect risk in tablets. PMID:24300215

  12. Quantitative analysis of the layer separation risk in bilayer tablets using terahertz pulsed imaging.

    PubMed

    Niwa, Masahiro; Hiraishi, Yasuhiro; Iwasaki, Norio; Terada, Katsuhide

    2013-08-16

    Layer separation is a critical defect in many bilayer tablets. Despite its importance for product quality, few studies have investigated its root cause. We evaluated bilayer tablets with varying layer separation tendencies using terahertz pulsed imaging (TPI) in comparison with other analytical methods such as tensile strength measurements, friability testing, scanning electron microscopy (SEM), and X-ray computed tomography (XRCT). The layer separation risk was determined by friability testing and shown to be correlated with the final compression pressure used for bilayer tablet fabrication. TPI could nondestructively detect cracks between the component layers that lead to layer separation. The adhesion integrity of the interface was quantified by the interface index, a unique value derived from the time-domain terahertz waveform. The interface index showed good correlation to the layer separation tendency and could distinguish interface quality among seven batches of bilayer tablets. In contrast, SEM and XRCT detected structural defects but could not distinguish batches with high or low layer separation risk. TPI revealed the relationship between compression pressure and interface quality. Thus, TPI can aid in quality control by providing a precise estimate of the layer separation risk and robust quality of bilayer tablet development with better understanding of layer separation. PMID:23680735

  13. Pulsed Terahertz Signal Reconstruction

    NASA Astrophysics Data System (ADS)

    Fletcher, J. R.; Swift, G. P.; Dai, DeChang; Chamberlain, J. M.; Upadhya, P. C.

    2007-12-01

    A procedure is outlined which can be used to determine the response of an experimental sample to a single, simple broadband frequency pulse in terahertz frequency time domain spectroscopy (TDS). The advantage that accrues from this approach is that oscillations and spurious signals (arising from a variety of sources in the TDS system or from ambient water vapor) can be suppressed. In consequence, small signals (arising from the interaction of the radiation with the sample) can be more readily observed in the presence of noise. Procedures for choosing key parameters and methods for eliminating further artifacts are described. In particular, the use of input functions which are based on the binomial distribution is described. These binomial functions are used to unscramble the sample response to a simple pulse: they have sufficient flexibility to allow for variations in the spectra of different terahertz sources, some of which have low frequency as well as high frequency cutoffs. The signal processing procedure is validated by simple reflection and transmission experiments using a gap between polytetrafluoroethylene (PTFE) plates to mimic a void within a larger material. It is shown that a resolution of 100?m is easily achievable in reflection geometry after signal processing.

  14. Coating and Density Distribution Analysis of Commercial Ciprofloxacin Hydrochloride Monohydrate Tablets by Terahertz Pulsed Spectroscopy and Imaging.

    PubMed

    Sakamoto, Tomoaki; Portieri, Alessia; Arnone, Donald D; Taday, Philip F; Kawanishi, Toru; Hiyama, Yukio

    2012-06-01

    Terahertz pulsed spectroscopy was used to qualitatively detect ciprofloxacin hydrochloride monohydrate (CPFX·HCl·H(2)O) in tablets, and terahertz pulsed imaging (TPI) was used to scrutinize not only the coating state but also the density distribution of tablets produced by several manufacturers. TPI was also used to evaluate distinguishability among these tablets. The same waveform, which is a unique terahertz absorption spectrum derived from pure CPFX·HCl·H(2)O, was observed in all of the crushed tablets and in pure CPFX·HCl·H(2)O. TPI can provide information about the physical states of coated tablets. Information about the uniformity of parameters such as a coating thickness and density can be obtained. In this study, the authors investigated the coating thickness distributions of film-coated CPFX·HCl·H(2)O from four different manufacturers. Unique terahertz images of the density distributions in these commercial tablets were obtained. Moreover, B-scan (depth) images show the status of the coating layer in each tablet and the density map inside the tablets. These features would reflect differences resulting from different tablet-manufacturing processes. PMID:22707994

  15. Evaluating the effect of coating equipment on tablet film quality using terahertz pulsed imaging.

    PubMed

    Haaser, Miriam; Naelapää, Kaisa; Gordon, Keith C; Pepper, Michael; Rantanen, Jukka; Strachan, Clare J; Taday, Philip F; Zeitler, J Axel; Rades, Thomas

    2013-11-01

    In this study, terahertz pulsed imaging (TPI) was employed to investigate the effect of the coating equipment (fluid bed and drum coater) on the structure of the applied film coating and subsequent dissolution behaviour. Six tablets from every batch coated with the same delayed release coating formulation under recommended process conditions (provided by the coating polymer supplier) were mapped individually to evaluate the effect of coating device on critical coating characteristics (coating thickness, surface morphology and density). Although the traditional coating quality parameter (weight gain) indicated no differences between both batches, TPI analysis revealed a lower mean coating thickness (CT) for tablets coated in the drum coater compared to fluid bed coated tablets (p<0.05). Moreover, drum coated tablets showed a more pronounced CT variation between the two sides and the centre band of the biconvex tablets, with the CT around the centre band being 22.5% thinner than the top and bottom sides for the drum coated tablets and 12.5% thinner for fluid bed coated tablets. The TPI analysis suggested a denser coating for the drum coated tablets. Dissolution testing confirmed that the film coating density was the drug release governing factor, with faster drug release for tablets coated in the fluid bed coater (98 ± 4% after 6h) compared to drum coated tablets (72 ± 6% after 6h). Overall, TPI investigation revealed substantial differences in the applied film coating quality between tablets coated in the two coaters, which in turn correlated with the subsequent dissolution performance. PMID:23563103

  16. Imaging with terahertz radiation

    NASA Astrophysics Data System (ADS)

    Chan, Wai Lam; Deibel, Jason; Mittleman, Daniel M.

    2007-08-01

    Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.

  17. Terahertz pulse generation from noble gases

    SciTech Connect

    Chen Yunqing; Yamaguchi, Masashi; Wang Mingfeng; Zhang, X.-C. [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2007-12-17

    Terahertz pulse generation in the laser-induced plasma from a series of noble gases (He, Ne, Ar, Kr, and Xe) was systematically investigated. Femtosecond laser pulses consisting of both a fundamental and its second-harmonic frequency were used for the terahertz generation. Experimental results reveal that terahertz generation efficiency of these noble gases increases with decreasing ionization potential.

  18. Spatiotemporal transformations of ultrashort terahertz pulses

    E-print Network

    Ku?el, Petr

    Spatiotemporal transformations of ultrashort terahertz pulses Petr Kuzel, Maxim A. Khazan, and Jan-cycle terahertz pulses emitted by large-aperture emitters. The spatial transformations of the beams are connected the temporal waveform and the spectrum of the pulses are altered as a result of these spa- tial transformations

  19. Continuous-wave terahertz imaging of nonmelanoma skin cancers

    NASA Astrophysics Data System (ADS)

    Joseph, Cecil Sudhir

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

  20. Applications of terahertz (THz) technology to medical imaging

    Microsoft Academic Search

    Don D. Arnone; Craig M. Ciesla; Alessandra Corchia; S. Egusa; M. Pepper; J. Martyn Chamberlain; C. Bezant; E. H. Linfield; R. Clothier; N. Khammo

    1999-01-01

    An imaging system has been developed based on pulses of Terahertz (THz) radiation generated and detected using all- optical effects accessed by irradiating semiconductors with ultrafast pulses of visible laser light. This technique, commonly referred to as T-Ray Imaging or THz Pulse Imaging (TPI), holds enormous promise for certain aspects of medical imaging. We have conducted an initial survey of

  1. Reflective terahertz imaging of porcine skin burns.

    PubMed

    Taylor, Z D; Singh, R S; Culjat, M O; Suen, J Y; Grundfest, W S; Lee, H; Brown, E R

    2008-06-01

    A reflective pulsed terahertz imaging system based on direct detection was developed and used to obtain high-resolution images of a porcine skin specimen with superficial partial-thickness (second-degree) burns. Images were also obtained of the sample through ten layers of dry medical (cotton) gauze with minimal image degradation. The burned and unburned regions of skin had large differences in terahertz reflectivity, displaying clear delineation [20 dB signal-to-noise ratio (SNR) difference signal] between both regions in the images. The terahertz images also exhibited a "halo" surrounding the burn areas that may correlate to the extent of burn injury. The system operated at a center frequency of 500 GHz with 125 GHz of 3 dB bandwidth and used whiskbroom scanning to generate images with a spatial resolution of 1.5 mm. Each pixel was acquired with a 16 ms integration time, resulting in a 40 dB postdetection SNR. The simplicity and high SNR of the reflective terahertz system are promising steps toward real-time terahertz medical imaging. PMID:18516193

  2. Investigating the use of terahertz pulsed time domain reflection imaging for the study of fabric layers of an Egyptian mummy

    NASA Astrophysics Data System (ADS)

    Fukunaga, K.; Cortes, E.; Cosentino, A.; Stã¼nkel, I.; Leona, M.; Duling, N.; Mininberg, D. T.

    2011-08-01

    This paper reports the first use of terahertz time domain reflection imaging involving textiles on part of a complete human mummy, still in original wrapping. X-ray technique has been used extensively to investigate anatomical features, since X-ray pass through the wrapping. Terahertz waves, on the other hand, can penetrate into non-metallic materials and its reflection depends on the refractive index of materials at the interface, such as textiles and the air. The mummy of Kharushere (ca. 945-712 B.C.) was examined by using Terahertz time domain reflection imaging in the Egyptian galleries of The Metropolitan Museum of Art. Experimental results suggest that the Terahetz imaging is a promising technique for probing the fabric layers surrounding Egyptian mummies, although it is still very limited in its current state. In the future it could become a useful complement to CT scanning when materials with low radiographic density and contrast are being investigated

  3. Identify paraffin-embedded brain glioma using terahertz pulsed spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Ze-ren; Meng, Kun; Chen, Tu-nan; Chen, Tao; Zhu, Li-guo; Liu, Qiao; Li, Zhao; Li, Fei; Zhong, Sen-cheng; Feng, Hua; Zhao, Jian-heng

    2015-01-01

    The refractive indices, absorption coefficients and complex dielectric constants spectra of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time domain spectroscopy (THz-TDS) system in the range of 0.2 - 2.0 THz. The spectral differences between glioma and normal brain tissues were obtained. Our results indicate that, compared with normal tissue, glioma had higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the suitable frequency components for different methods of glioma imaging (intensity imaging, coherent imaging and terahertz pulsed imaging) are analyzed.

  4. Applications of terahertz-pulsed technology in the pharmaceutical industry

    NASA Astrophysics Data System (ADS)

    Taday, Philip F.

    2010-02-01

    Coatings are applied to pharmaceutical tablets (or pills) to for either cosmetic or release control reasons. Cosmetic coatings control the colour or to mask the taste of an active ingredient; the thickness of these coating is not critical to the performance of the product. On the other hand the thickness and uniformity of a controlled release coating has been found affect the release of the active ingredient. In this work we have obtained from a pharmacy single brand of pantoprazole tablet and mapped them using terahertz pulsed imaging (TPI) prior to additional dissolution testing. Three terahertz parameters were derived for univariate analysis for each layer: coating thickness, terahertz electric field peak strength and terahertz interface index. These parameters were then correlated dissolution tested. The best fit was found to be with combined coating layer thickness of the inert layer and enteric coating. The commercial tablets showed a large variation in coating thickness.

  5. Semiconductor investigation by terahertz radiation pulses

    NASA Astrophysics Data System (ADS)

    Krotkus, Arúnas; Arlauskas, A.; Adomavi?ius, R.

    2012-10-01

    Several applications of terahertz radiation pulses for characterizing semiconductor bulk materials and structures are described. Terahertz pulses emitted at the surfaces illuminated by femtosecond laser of a tunable wavelength are demonstrated to provide information on the electron energy spectrum in the conduction band as well as on the subsurface band bending. On the other hand, by sampling the conductivity of various structures with short electrical field transient photoexcited electron dynamics can be directly studied at its initial, subpicosecond time scale. Narrow gap semiconductors InSb and InAs as well as novel materials such as GaAsBi or self-assembled InAs quantum dots were characterized by using terahertz radiation pulses.

  6. Pulsed terahertz emission from GaN/InN heterostructure

    NASA Astrophysics Data System (ADS)

    Reklaitis, Antanas

    2011-11-01

    Dynamics of the electron-hole plasma excited by the femtosecond optical pulse in wurtzite GaN/InN heterostructure is investigated by Monte Carlo simulations. The GaN/InN heterostructure for pulsed terahertz emission is suggested. The results of Monte Carlo simulations show that the power of terahertz emission from the GaN/InN heterostructure exceeds the power of terahertz emission from the surface of InN by one order of magnitude.

  7. Pulsed terahertz inspection of non-conducting sandwich composites

    NASA Astrophysics Data System (ADS)

    Lopato, P.; Chady, T.

    2013-01-01

    Pulsed terahertz inspection enables accurate, contactless and safe for operating personnel evaluation of non-conducting structures. In this paper we present results of pulsed terahertz testing of various sandwich composite structures incorporating glass and basalt fibers based skin materials and spherecore and balsa wood based core materials. Various Time-Frequency Distributions (TFD) are utilized in order to obtain most valuable defects response.

  8. Terahertz technology for imaging and spectroscopy

    NASA Astrophysics Data System (ADS)

    Crowe, T. W.; Porterfield, D. W.; Hesler, J. L.; Bishop, W. L.; Kurtz, D. S.; Hui, K.

    2006-05-01

    The terahertz region of the electromagnetic spectrum has unique properties that make it especially useful for imaging and spectroscopic detection of concealed weapons, explosives and chemical and biological materials. However, terahertz energy is difficult to generate and detect, and this has led to a technology gap in this frequency band. Nonlinear diodes can be used to bridge this gap by translating the functionality achieved at microwave frequencies to the terahertz band. Basic building blocks include low-noise mixers, frequency multipliers, sideband generators and direct detectors. These terahertz components rely on planar Schottky diodes and recently developed integrated diode circuits make them easier to assemble and more robust. The new generation of terahertz sources and receivers requires no mechanical tuning, yet achieves high efficiency and broad bandwidth. This paper reviews the basic design of terahertz transmitters and receivers, with special emphasis on the recent development of systems that are compact, easy to use and have excellent performance.

  9. Achromatic prism-type wave plate for broadband terahertz pulses.

    PubMed

    Kawada, Yoichi; Yasuda, Takashi; Nakanishi, Atsushi; Akiyama, Koichiro; Hakamata, Kento; Takahashi, Hironori

    2014-05-01

    We demonstrated achromatic half- and quarter-wave plates for broadband terahertz pulses using phase retardation by internal total reflection. Prism-type wave plates realized ultra-broadband retardation stability up to 2.5 THz, which was the limitation of our experimental setup. Novel aspects of our work were use of a 3?/4 plate as a quarter-wave plate and a multistacked prism-type (MSP) wave plate for a large-aperture THz beam. Real-time polarization imaging of two crossed bunches of hairs was performed to show the efficiency of the MSP wave plate. We clearly observed polarization dependence of the hair direction. PMID:24784105

  10. New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

    NASA Astrophysics Data System (ADS)

    Wu, Yin-Zhong; Zhao, Zong-Qing; Gu, Yu-Qiu; Wei, Lai; Cao, Lei-Feng

    2014-12-01

    A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.

  11. Spectral interference of terahertz pulses from two laser filaments in air

    NASA Astrophysics Data System (ADS)

    Chen, Yanping; Zhang, Zhelin; Zhang, Zhen; Yuan, Xiaohui; Liu, Feng; Chen, Min; Xu, Jianqiu; Yu, Jin; Sheng, Zhengming; Zhang, Jie

    2015-06-01

    Spectral interference is experimentally demonstrated by two terahertz pulses emitting from filaments induced by two successive femtosecond laser pulses in air. Here, a leading pulse is set to be weaker than a trailing pulse and their temporal separation is larger than the pulse duration of the terahertz pulses. When the leading pulse is stronger than the trailing pulse, the frequency modulation within the whole terahertz envelope is greatly deteriorated due to nonlinear effects applying on the trailing pulse through the plasmas generated by the leading pulses. Such unique terahertz spectrum may find applications in terahertz spectroscopy.

  12. Imaging of ex vivo nonmelanoma skin cancers in the optical and terahertz spectral regions optical and terahertz skin cancers imaging.

    PubMed

    Joseph, Cecil S; Patel, Rakesh; Neel, Victor A; Giles, Robert H; Yaroslavsky, Anna N

    2014-05-01

    We tested the hypothesis that polarization sensitive optical and terahertz imaging may be combined for accurate nonmelanoma skin cancer (NMSC) delineation. Nine NMSC specimens were imaged. 513 ?m and 440 nm wavelengths were used for terahertz and optical imaging, respectively. Histopathology was processed for evaluation. Terahertz reflectance of NMSC was quantified. Our results demonstrate that cross-polarized terahertz images correctly identified location of the tumours, whereas cross-polarized and polarization difference optical images accurately presented morphological features. Cross-polarized terahertz images exhibited lower reflectivity values in cancer as compared to normal tissue. Combination of optical and terahertz imaging shows promise for intraoperative delineation of NMSC. PMID:22987857

  13. Power Scaling on Efficient Generation of Ultrafast Terahertz Pulses

    Microsoft Academic Search

    Xiaodong Mu; C. I. B. Zotova; Yujie J. Ding

    2008-01-01

    We have investigated power scaling for the efficient generation of the broadband terahertz (THz) pulses. These THz short pulses are converted from ultrafast laser pulses propagating in a class of semiconductor electrooptic materials. By measuring the dependence of the THz output on the pump beam in terms of incident angle, polarization, azimuthal angle, and pump intensity, we have precisely determined

  14. Sub-surface terahertz imaging through uneven surfaces: visualizing Neolithic wall paintings in Çatalhöyük.

    PubMed

    Walker, Gillian C; Bowen, John W; Matthews, Wendy; Roychowdhury, Soumali; Labaune, Julien; Mourou, Gerard; Menu, Michel; Hodder, Ian; Jackson, J Bianca

    2013-04-01

    Pulsed terahertz imaging is being developed as a technique to image obscured mural paintings. Due to significant advances in terahertz technology, portable systems are now capable of operating in unregulated environments and this has prompted their use on archaeological excavations. August 2011 saw the first use of pulsed terahertz imaging at the archaeological site of Çatalhöyük, Turkey, where mural paintings dating from the Neolithic period are continuously being uncovered by archaeologists. In these particular paintings the paint is applied onto an uneven surface, and then covered by an equally uneven surface. Traditional terahertz data analysis has proven unsuccessful at sub-surface imaging of these paintings due to the effect of these uneven surfaces. For the first time, an image processing technique is presented, based around Gaussian beam-mode coupling, which enables the visualization of the obscured painting. PMID:23571902

  15. Direct acoustic phonon excitation by intense and ultrashort terahertz pulses

    NASA Astrophysics Data System (ADS)

    Manceau, J.-M.; Loukakos, P. A.; Tzortzakis, S.

    2010-12-01

    We report on the direct and resonant excitation of acoustic phonons in an AlGaAs intrinsic semiconductor using intense coherent and single cycle terahertz pulses created by two-color femtosecond laser pulse filamentation in air. While the electrons are left unperturbed, we follow the lattice dynamics with time-delayed optical photons tuned to the interband transition.

  16. Terahertz Imaging Quantum Dot Detector

    E-print Network

    Sheldon, Nathan D.

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.2 Terahertz Detection . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1.2.1 The Bolometer Transistors . . . . . . . . . . . . . . . . . . . . . . 46 2.6.1 The Tunnel Junction . . . . . . . . . . . . . . . . . . . . . 47 2.6.2 Single Electron Box . . . . . . . . . . . . . . . . . . . . . . 50 2.6.3 The Double Tunnel

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

    NASA Technical Reports Server (NTRS)

    Winfree, William P.; Madaras, Eric I.

    2005-01-01

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

  18. Generation of ultrafast terahertz radiation pulses on metallic nanostructured surfaces.

    PubMed

    Welsh, Gregor H; Wynne, Klaas

    2009-02-16

    A resonant "incoherent" rectification process is presented relying on the excitation of surface plasmons on a nanostructured metal surface. Excitation of gold and silver films with 800-nm femtosecond laser pulses results in the emission of terahertz radiation with an angle-dependent efficiency and an approximately third-order power dependence. It is shown that the source of this terahertz pulse generation is the surface-plasmon-assisted multiphoton ionization and ponderomotive acceleration in the evanescent field of the surface plasmon. Simple models are used to understand the forces and dynamics near the surface. PMID:19219150

  19. Terahertz imaging using full-field electrooptic sampling

    NASA Astrophysics Data System (ADS)

    Ayesheshim, Ayesheshim Kebie

    Real time terahertz imaging is emerging as an important non-destructive imaging tool for medical, quality control, security and other industrial applications. In this thesis, we demonstrate real-time full-field terahertz (THz) imaging of still, moving, and concealed objects, and real-time THz images of the field distribution on the imaging plane. A femtosecond laser pulse from an amplified Ti:sapphire laser system with a pulse duration of 100 fs, repetition rate of 1 kHz, and 800 nm center wavelength is used to generate THz pulses via optical rectification in a 15x15 mm2 by 2 mm thick [110] ZnTe crystal. The THz pulses are collimated to a 1" diameter beam using off-axis parabolic reflectors. An object is placed in the collimated THz beam, and a plastic lens is used to form an image of the object on a second ZnTe crystal (detector). The THz image is detected by free-space electro-optic sampling using a large diameter gating beam derived from the laser source. Video or still images are captured by an 8-bit (30 fps) grayscale CCD camera, and objects hidden behind paper or inside Styrofoam can be clearly seen in real-time. We also study the ring-like spatial intensity distribution of the various frequency components of the THz pulse focused in the image plane by varying the time-delay between the THz and probe beams. Methods for improving signal-to-noise such as frame averaging and dynamic subtraction are also studied.

  20. Terahertz spin current pulses controlled by magnetic heterostructures.

    PubMed

    Kampfrath, T; Battiato, M; Maldonado, P; Eilers, G; Nötzold, J; Mährlein, S; Zbarsky, V; Freimuth, F; Mokrousov, Y; Blügel, S; Wolf, M; Radu, I; Oppeneer, P M; Münzenberg, M

    2013-04-01

    In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters. PMID:23542903

  1. Compressed sensing pulse-echo mode terahertz reflectance tomography

    E-print Network

    Compressed sensing pulse-echo mode terahertz reflectance tomography Kyung Hwan Jin,1 Youngchan Kim reconstruction is accomplished using a compressed sensing ap- proach. One of the main advantages of the proposed [1] and diffraction and/or computed tomography [2]. Recently, Chan et al. proposed a compressed sens

  2. Generation and manipulation of multi-cycle terahertz pulses via optical rectification in poled lithium niobate

    NASA Astrophysics Data System (ADS)

    Lee, Yun-Shik; Amer, N.; Hurlbut, W. C.; Norton, B. J.; Danielson, J. R.

    2005-11-01

    We demonstrate control of terahertz (THz) waves developing novel devices in the THz regime: THz pulse shapers. THz technology is a relatively unexplored subject, yet the importance of THz wave manipulation cannot be emphasized enough considering its potential application to THz imaging systems, ultrafast optical signal processing, ultrahigh-speed computing, quantum information science, nanotechnology, and chemical reaction dynamics among other areas. THz time-domain spectroscopy (THz-TDS) can assess the performance of the THz pulse shapers monitoring time-dependent THz wave propagation. THz-TDS permits precise measurements not only of the amplitude but also of the phase of THz waves, thus a comprehensive assessment of the THz devices can be achieved. The phase sensitivity is also vital to many applications such as high-contrast THz imaging and quantum control of semiconductor nanostructures. We develop arbitrary THz pulse generators synthesizing THz waveforms via optical rectification in pre-engineered domain structures of poled nonlinear crystals using femtosecond lasers. The terahertz waveforms coincide with the crystal domain structures. The one dimensional nonlinear wave equation simulates the experimental results with a good qualitative agreement. The ratio of the domain length to the optical pulse length in the crystal turns out to be the crucial limiting factor to generating optimum terahertz fields and preventing waveform distortion. Optical pulse shaping techniques is integrated into the THz pulse generators to extend the scope of THz pulse shaping control. Continuously tunable narrow-band THz pulses are generated in a fanned-out periodically-poled lithium niobate crystal. We measure the free induction decay of rotational transitions in gas-phase HCl molecules using the narrow-band THz pulses. The shape of the multi-cycle THz pulses is controlled by adjusting the relative time delay and intensity between the two optical pulses.

  3. Concealed weapon identification using terahertz imaging sensors

    NASA Astrophysics Data System (ADS)

    Jacobs, Eddie L.; Moyer, Steve; Franck, Charmaine C.; DeLucia, Frank C.; Casto, Corey; Petkie, Douglas T.; Murrill, Steven R.; Halford, Carl E.

    2006-05-01

    Terahertz imaging sensors are being considered for providing a concealed weapon identification capability for military and security applications. In this paper the difficulty of this task is assessed in a systematic way. Using imaging systems operating at 640 GHz, high resolution imagery of possible concealed weapons has been collected. Information in this imagery is removed in a controlled and systematic way and then used in a human observer perception experiment. From the perception data, a calibration factor describing the overall difficulty of this task was derived. This calibration factor is used with a general model of human observer performance developed at the US Army Night Vision and Electronic Sensors Directorate to predict the task performance of observers using terahertz imaging sensors. Example performance calculations for a representative imaging sensor are shown.

  4. Enhancement of Laser-Induced Fluorescence by Intense Terahertz Pulses in Gases

    Microsoft Academic Search

    Jingle Liu; Xi-Cheng Zhang

    2011-01-01

    The enhancement of laser-induced fluorescence by in- tense terahertz pulses was studied both theoretically and experi- mentally using selected gases. Semiclassical physical picture incor- porating photoionization, electron heating, impact excitation, and dissociative recombination was used to explain the plasma dynam- ics under terahertz radiation in picosecond scale. The dependences of enhanced fluorescence on the terahertz field, laser intensity, and atomic

  5. Tunable and collimated terahertz radiation generation by femtosecond laser pulses

    SciTech Connect

    Malik, Hitendra K.; Malik, Anil K.

    2011-12-19

    A mechanism is proposed for the generation of tunable terahertz (THz) radiation under the application of two femtosecond laser pulses and an external magnetic field, where quick tunnel ionization is achieved that leads to higher plasma density evolution and large residual current for the efficient THz radiation generation. With the optimization of magnetic field, phase difference, and amplitudes of lasers' fields, a THz source can be obtained with tunable frequency and power along with a control on the direction of radiation emission.

  6. Nonlinear propagation of terahertz pulses in ammonia vapor

    NASA Astrophysics Data System (ADS)

    Fedotova, O. M.; Khasanov, O. K.; Rusetsky, G. A.; Degert, J.; Freysz, E.

    2014-11-01

    We consider the propagation of terahertz (THz) pulses resonant with the lowest rotational levels in ammonia vapors at room temperature. We demonstrate a quasisimultonic regime of propagation for two-color THz pulses (their lossless simultaneous propagation with equal group velocities and stable envelopes at finite distances, like coupled solitons). The quasisimultons are formed by two pulses synchronized in time, the first one being intense and two humped with an area multiple of 4 ? , while the another one is weaker, one humped, and with an area much less than ? . Two- and one-humped pulses have equal width and copropagate in ammonia vapor at the same group velocity. Moreover, the larger the dip of the two-hump pulse is, the weaker may be the one-humped pulse. The stability of this coupled state is provided by the fact that the two-humped pulse makes the medium transparent for the one-humped pulse. In its turn, the latter prevents the breakup of the former into separate pulses. It is established as well that a multihumped pulse with an odd or even number of humps and a hyperbolic secant pulse can behave like a simulton. In this case, the area of multihumped pulse equals to 2 n ? , where n is the number of humps in the powerful pulse structure.

  7. Goya's artwork imaging with Terahertz waves.

    PubMed

    Seco-Martorell, C; López-Domínguez, V; Arauz-Garofalo, G; Redo-Sanchez, A; Palacios, J; Tejada, J

    2013-07-29

    In this paper we use a Terahertz (THz) time-domain system to image and analyze the structure of an artwork attributed to the Spanish artist Goya painted in 1771. The THz images show features that cannot be seen with optical inspection and complement data obtained with X-ray imaging that provide evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya's known signatures is seen in the THz images. In particular, this paper demonstrates the potential of THz imaging as a complementary technique along with X-ray for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection. PMID:23938652

  8. Goya's artwork imaging with Terahertz waves

    E-print Network

    Seco, C; Arauz, G; Redo, A; Palacios, J; Tejada, J

    2013-01-01

    In this paper we use a Terahertz (THz) time-domain system to image and analize the structure of an artwork attributed to Spanish artist Goya painted in 1771. The Thz images show features that cannot be seen in the optical or X-ray images that providence evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya's known signatures is seen in the THz images that cannot be detected otherwise. This paper shows the feasibility of using THz imaging in the field of authentication and characterization of artworks. This may be of great importance in cases where both the signature and specific features that are critical for the authentication of an artwork remain hidden to visible, infrared, or X-ray inspection methods.

  9. Video-rate terahertz electric-field vector imaging

    NASA Astrophysics Data System (ADS)

    Takai, Mayuko; Takeda, Masatoshi; Sasaki, Manabu; Tachizaki, Takehiro; Yasumatsu, Naoya; Watanabe, Shinichi

    2014-10-01

    We present an experimental setup to dramatically reduce a measurement time for obtaining spatial distributions of terahertz electric-field (E-field) vectors. The method utilizes the electro-optic sampling, and we use a charge-coupled device to detect a spatial distribution of the probe beam polarization rotation by the E-field-induced Pockels effect in a ?110?-oriented ZnTe crystal. A quick rotation of the ZnTe crystal allows analyzing the terahertz E-field direction at each image position, and the terahertz E-field vector mapping at a fixed position of an optical delay line is achieved within 21 ms. Video-rate mapping of terahertz E-field vectors is likely to be useful for achieving real-time sensing of terahertz vector beams, vector vortices, and surface topography. The method is also useful for a fast polarization analysis of terahertz beams.

  10. Tunable high-efficient pulsed NH3 terahertz lasers

    NASA Astrophysics Data System (ADS)

    Jiu, Zhi-Xian; Li, Qiang; Zuo, Du-Luo; Miao, Liang; Cheng, Zu-Hai

    2012-03-01

    Experimental studies on a tunable efficient high-efficient pulsed NH3 terahertz (THz) lasers pumped by TEA CO2 lasers are presented. When NH3 is pumped by the different lines with the CO2 lasers, the generation of different terahertz radiations is discussed. The lines of the CO2 lasers are 9R(08), 9P(20), 10R(14), 10R(08), and 10R(06). To improve THz laser energy and photon conversion efficiency, different higher power of the CO2 laser can effectively improve THz laser energy and photon conversion efficiency. When the 9P(20) CO2 lasers with 9.68 J and 4.12 J pump NH3, the corresponding energy conversion efficiencies are 0.28% and 0.19%, increasing by a factor of about 1.5. The generation of terahertz radiations with energy as high as 27.29 mJ and 7.73 mJ are obtained, respectively, increasing by a factor of about 3.5. Meanwhile, for 10R(14) line, the energy conversion efficiencies increase to 8.5 times and the energy of THz lasers increase to 32 times.

  11. Laser pulse amplitude changes induced by terahertz waves under linear electro-optic effect

    SciTech Connect

    Ilyakov, I. E., E-mail: igor-ilyakov@mail.ru; Shishkin, B. V. [Institute of Applied Physics, RAS, Nizhny Novgorod 603950 (Russian Federation); Kitaeva, G. Kh. [Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Akhmedzhanov, R. A. [Institute of Applied Physics, RAS, Nizhny Novgorod 603950 (Russian Federation); N.I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation)

    2014-04-14

    Changes in the amplitude of femtosecond laser pulses and in the energy of terahertz wave radiation induced during their co-propagation in ZnTe and GaP crystals are studied theoretically and experimentally. The results show that variation of the optical field amplitude leads to changes in the laser pulse energy and spectrum shift. We investigate the quantitative correlations between variations of the optical pulse energy, spectrum, phase and terahertz radiation energy. The values of laser pulse energy change and spectrum shift are proportional to the first time derivative of the magnitude of terahertz electric field, which enables coherent electro-optic detection. A simple and convenient calibration technique for terahertz energy detectors based on the correlation between laser and terahertz energy changes is proposed and tested.

  12. Complex extreme learning machine applications in terahertz pulsed signals feature sets.

    PubMed

    Yin, X-X; Hadjiloucas, S; Zhang, Y

    2014-11-01

    This paper presents a novel approach to the automatic classification of very large data sets composed of terahertz pulse transient signals, highlighting their potential use in biochemical, biomedical, pharmaceutical and security applications. Two different types of THz spectra are considered in the classification process. Firstly a binary classification study of poly-A and poly-C ribonucleic acid samples is performed. This is then contrasted with a difficult multi-class classification problem of spectra from six different powder samples that although have fairly indistinguishable features in the optical spectrum, they also possess a few discernable spectral features in the terahertz part of the spectrum. Classification is performed using a complex-valued extreme learning machine algorithm that takes into account features in both the amplitude as well as the phase of the recorded spectra. Classification speed and accuracy are contrasted with that achieved using a support vector machine classifier. The study systematically compares the classifier performance achieved after adopting different Gaussian kernels when separating amplitude and phase signatures. The two signatures are presented as feature vectors for both training and testing purposes. The study confirms the utility of complex-valued extreme learning machine algorithms for classification of the very large data sets generated with current terahertz imaging spectrometers. The classifier can take into consideration heterogeneous layers within an object as would be required within a tomographic setting and is sufficiently robust to detect patterns hidden inside noisy terahertz data sets. The proposed study opens up the opportunity for the establishment of complex-valued extreme learning machine algorithms as new chemometric tools that will assist the wider proliferation of terahertz sensing technology for chemical sensing, quality control, security screening and clinic diagnosis. Furthermore, the proposed algorithm should also be very useful in other applications requiring the classification of very large datasets. PMID:25037827

  13. Terahertz Imaging System for Medical Applications and Related High Efficiency Terahertz Devices

    NASA Astrophysics Data System (ADS)

    Ouchi, Toshihiko; Kajiki, Kousuke; Koizumi, Takayuki; Itsuji, Takeaki; Koyama, Yasushi; Sekiguchi, Ryota; Kubota, Oichi; Kawase, Kodo

    2013-07-01

    A terahertz (THz) imaging system and high efficient terahertz sources and detectors for medical applications were developed. A fiber laser based compact time domain terahertz tomography system was developed with a high depth resolution of less than 20 ?m. Three-dimensional images of porcine skin were obtained including some physical properties such as applied skin creams. The discrimination between healthy human tissue and tumor tissue has been achieved using reflection spectra. To improve the THz imaging system, a ridge waveguide LiNbO3 based nonlinear terahertz generator was studied to achieve high output power. A ridge waveguide with 5-7 ?m width was designed for high efficiency emission from the LiNbO3 crystal by the electro-optic Cherenkov effect. Terahertz electronic sources and detectors were also realized for future imaging systems. As electronic source devices, resonant tunneling diode (RTD) oscillators with a patch antenna were fabricated using an InGaAs/InAlAs/AlAs triple barrier structure. On the other side, Schottky barrier diode (SBD) detectors with a log-periodic antenna were fabricated by thin-film technology on a Si substrate. Both devices operate above 1 THz at room temperature. This electronic THz device set could provide a future high performance imaging system.

  14. Super-resolution reconstruction of terahertz images

    NASA Astrophysics Data System (ADS)

    Li, Yue; Li, Li; Hellicar, Andrew; Guo, Y. Jay

    2008-04-01

    A prototype of terahertz imaging system has been built in CSIRO. This imager uses a backward wave oscillator as the source and a Schottky diode as the detector. It has a bandwidth of 500-700 GHz and a source power 10 mW. The resolution at 610 GHz is about 0.85 mm. Even though this imaging system is a coherent system, only the signal power is measured at the detector and the phase information of the detected wave is lost. Some initial images of tree leaves, chocolate bars and pinholes have been acquired with this system. In this paper, we report experimental results of an attempt to improve the resolution of this imaging system beyond the limitation of diffraction (super-resolution). Due to the lack of phase information needed for applying any coherent super-resolution algorithms, the performance of the incoherent Richardson-Lucy super-resolution algorithm has been evaluated. Experimental results have demonstrated that the Richardson-Lucy algorithm can significantly improve the resolution of these images in some sample areas and produce some artifacts in other areas. These experimental results are analyzed and discussed.

  15. Generation of Terahertz Radiation by Interaction of Intense Femtosecond Laser Pulses with a Metal Surface

    NASA Astrophysics Data System (ADS)

    Akhmedzhanov, R. A.; Ilyakov, I. E.; Mironov, V. A.; Oladyshkin, I. V.; Suvorov, E. V.; Fadeev, D. A.; Shishkin, B. V.

    2015-04-01

    We present the results of experimental and theoretical studies of generation of terahertz radiation during reflection of a femtosecond-long laser pulse from a metal surface. It is shown that a greater part of the experimental results (narrow directivity of the terahertz waves and dependence of its energy on the polarization and incidence angle of the laser radiation) can be interpreted within the model of ?erenkov radiation. Some new features of generation of terahertz radiation are considered, which appear during an optical breakdown of the medium near the metal surface. Structural changes in the terahertz signal, which take place in the process of formation of the near-surface plasma, are studied.

  16. Subwavelength imaging using plasmonic lenses at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Heggie, Tanner

    The effects of diffraction at terahertz frequencies limit the spatial resolution of imaging systems. One approach to achieve subwavelength resolution is near-field imaging using a subwavelength aperture, however, the low transmission through subwavelength apertures limits the sensitivity of this approach. Plasmonic lenses in the form of bullseye structures, consisting of a circular subwavelength aperture with concentric periodic corrugations, have demonstrated enhanced transmission and beam confinement. This thesis discusses the design criteria of plasmonic lenses optimized for 325 GHz. Fabrication for optical applications is traditionally achieved by nanolithography. Since the scale of plasmonic structures depends on the wavelength, precision micromilling techniques are well suited for terahertz applications. Theoretical simulations are obtained using a finite-difference time-domain solver and the performance the devices are evaluated using a customized terahertz testbed. The prospect of using plasmonic lenses in a terahertz imaging configuration for the diagnosis of cancer is also discussed.

  17. In vivo terahertz imaging of rat skin burns

    NASA Astrophysics Data System (ADS)

    Tewari, Priyamvada; Kealey, Colin P.; Bennett, David B.; Bajwa, Neha; Barnett, Kelli S.; Singh, Rahul S.; Culjat, Martin O.; Stojadinovic, Alexander; Grundfest, Warren S.; Taylor, Zachary D.

    2012-04-01

    A reflective, pulsed terahertz (THz) imaging system was used to acquire high-resolution (d10-90/ ?~1.925) images of deep, partial thickness burns in a live rat. The rat's abdomen was burned with a brass brand heated to ~220°C and pressed against the skin with contact pressure for ~10 sec. The burn injury was imaged beneath a Mylar window every 15 to 30 min for up to 7 h. Initial images display an increase in local water concentration of the burned skin as evidenced by a marked increase in THz reflectivity, and this likely correlates to the post-injury inflammatory response. After ~1 h the area of increased reflectivity consolidated to the region of skin that had direct contact with the brand. Additionally, a low reflecting ring of tissue could be observed surrounding the highly reflective burned tissue. We hypothesize that these regions of increased and decreased reflectivity correlate to the zones of coagulation and stasis that are the classic foundation of burn wound histopathology. While further investigations are necessary to confirm this hypothesis, if true, it likely represents the first in vivo THz images of these pathologic zones and may represent a significant step forward in clinical application of THz technology.

  18. Accuracy of sample material parameters reconstruction using terahertz pulsed spectroscopy

    NASA Astrophysics Data System (ADS)

    Zaytsev, Kirill I.; Gavdush, Arseniy A.; Karasik, Valeriy E.; Alekhnovich, Valentin I.; Nosov, Pavel A.; Lazarev, Vladimir A.; Reshetov, Igor V.; Yurchenko, Stanislav O.

    2014-05-01

    New experimental and theoretical results for the material parameter reconstruction using terahertz (THz) pulsed spectroscopy (TPS) are presented. The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. In order to both verify the algorithm and to estimate the reconstruction accuracy, test sample material parameters obtained with the TPS were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated for the spectral range, corresponding to the BWO sensitivity and located between 0.2 and 1.2 THz. The numerical simulations were applied for determining the material parameter reconstruction stability in the presence of white Gaussian noise in TPS waveforms as well as fluctuations in the femtosecond (FS) optical pulse duration. We report a strong dependence of the inverse problem solution stability on these factors. We found that the instability of the FS optical pulse duration used for THz pulses generation and detection limits the material parameter reconstruction with TPS.

  19. Terahertz generation by tilted-front laser pulses in weakly and strongly nonlinear regimes

    NASA Astrophysics Data System (ADS)

    Bodrov, Sergey B.; Murzanev, Aleksey A.; Sergeev, Yury A.; Malkov, Yury A.; Stepanov, Andrey N.

    2013-12-01

    Terahertz generation by femtosecond laser pulses with tilted intensity front in room-temperature and cryogenically cooled LiNbO3 crystals was investigated. The role of the interaction length and pump pulse duration was studied for weak and strong laser pump. It was shown that the optical-to-terahertz conversion efficiency is saturated as a result of the Kerr self-phase modulation of the optical pump.

  20. Field Intensity Detection of Individual Terahertz Pulses at 80 MHz Repetition Rate

    NASA Astrophysics Data System (ADS)

    Rettich, F.; Vieweg, N.; Cojocari, O.; Deninger, A.

    2015-05-01

    We present a new approach to detect the intensity of individual terahertz pulses at repetition rates as high as 80 MHz. Our setup comprises a femtosecond fiber laser, an InGaAs-based terahertz emitter, a zero-bias Schottky detector, and a high-speed data acquisition unit. The detected pulses consist of two lobes with half-widths of 1-2 ns, which is much shorter than the inverse repetition rate of the laser. The system lends itself for high-speed terahertz transmission measurements, e.g., to study wetting dynamics in real time.

  1. High-terahertz-frequency carrier generation by optical pulse for radio-over-fiber applications

    NASA Astrophysics Data System (ADS)

    Afroozeh, Abdolkarim; Jomtarak, Rangsan; Ali, Jalil; Yupapin, Preecha P.

    2011-12-01

    In this study a new design of terahertz frequency carrier generation for radio frequency identification (RFID) application is proposed. The dense wavelength-division multiplexing can be generated and obtained by using a Gaussian or soliton pulse propagating within a modified add-drop filter known as a PANDA ring resonator. The broad bandwidth of terahertz signals can be obtained and are available for useful applications, in which the use of the generated terahertz pulses for RFID application, for instance Ad-Hoc network, uses RFID. Results obtained have shown that the increase in channel capacity can be obtained and useful for the large demand of RFID applications.

  2. Field Intensity Detection of Individual Terahertz Pulses at 80 MHz Repetition Rate

    NASA Astrophysics Data System (ADS)

    Rettich, F.; Vieweg, N.; Cojocari, O.; Deninger, A.

    2015-07-01

    We present a new approach to detect the intensity of individual terahertz pulses at repetition rates as high as 80 MHz. Our setup comprises a femtosecond fiber laser, an InGaAs-based terahertz emitter, a zero-bias Schottky detector, and a high-speed data acquisition unit. The detected pulses consist of two lobes with half-widths of 1-2 ns, which is much shorter than the inverse repetition rate of the laser. The system lends itself for high-speed terahertz transmission measurements, e.g., to study wetting dynamics in real time.

  3. Towards gigawatt terahertz emission by few-cycle laser pulses

    SciTech Connect

    Wang Weimin [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Graduate School of Engineering, Utsunomiya University, 7-1-2 Yohtoh, Utsunomiya 321-8585 (Japan); Kawata, Shigeo [Graduate School of Engineering, Utsunomiya University, 7-1-2 Yohtoh, Utsunomiya 321-8585 (Japan); Sheng Zhengming; Zhang Jie [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Key Laboratory for Laser Plasmas of the Ministry of Education of China and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Li Yutong [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China)

    2011-07-15

    It is shown by analysis and simulations that an extremely powerful terahertz (THz) radiation can be produced by a few-cycle laser pulse in a tenuous plasma. The THz amplitude scales linearly with the laser amplitude as well as with the sine of the laser carrier-envelope phase, and in particular, it increases exponentially with the decrease of the laser duration. For example, the THz amplitude increases by near 2 orders of magnitude as the laser duration decreases from one and a half cycles to one cycle; a single-cycle laser of 200 TW can drive the THz radiation of 1 GW with the energy conversion efficiency higher than 10{sup -4}.

  4. Enhancement of terahertz pulse emission by optical nanoantenna.

    PubMed

    Park, Sang-Gil; Jin, Kyong Hwan; Yi, Minwoo; Ye, Jong Chul; Ahn, Jaewook; Jeong, Ki-Hun

    2012-03-27

    Bridging the gap between ultrashort pulsed optical waves and terahertz (THz) waves, the THz photoconductive antenna (PCA) is a major constituent for the emission or detection of THz waves by diverse optical and electrical methods. However, THz PCA still lacks employment of advanced breakthrough technologies for high-power THz emission. Here, we report the enhancement of THz emission power by incorporating optical nanoantennas with a THz photoconductive antenna. The confinement and concentration of an optical pump beam on a photoconductive substrate can be efficiently achieved with optical nanoantennas over a high-index photoconductive substrate. Both numerical and experimental results clearly demonstrate the enhancement of THz wave emission due to high photocarrier generation at the plasmon resonance of nanoantennas. This work opens up many opportunities for diverse integrated photonic elements on a single PCA at THz and optical frequencies. PMID:22339093

  5. Yb:YAG thin-disk chirped pulse amplification laser system for intense terahertz pulse generation.

    PubMed

    Ochi, Yoshihiro; Nagashima, Keisuke; Maruyama, Momoko; Tsubouchi, Masaaki; Yoshida, Fumiko; Kohno, Nanase; Mori, Michiaki; Sugiyama, Akira

    2015-06-01

    We have developed a 1 kHz repetition picosecond laser system dedicated for intense terahertz (THz) pulse generation. The system comprises a chirped pulse amplification laser equipped with a Yb:YAG thin-disk amplifier. At room temperature, the Yb:YAG thin-disk regenerative amplifier provides pulses having energy of over 10 mJ and spectral bandwidth of 1.2 nm. The pulse duration achieved after passage through a diffraction grating pair compressor was 1.3 ps. By employing this picosecond laser as a pump source, THz pulses having a peak frequency of 0.3 THz and 4 µJ of energy were generated by means of optical rectification in an Mg-doped LiNbO3 crystal. PMID:26072862

  6. IMAGING WITH THZ PULSES Timothy Dorney, Jon Johnson, Daniel Mittleman, Richard Baraniuk

    E-print Network

    IMAGING WITH THZ PULSES Timothy Dorney, Jon Johnson, Daniel Mittleman, Richard Baraniuk Department-time imaging system based on terahertz (THz) time-domain spectroscopy has been demonstrated. This technique-sensitive detection of the THz pulses. This paper provides a brief introduction of the state-of-the art in THz imaging

  7. Terahertz reflection imaging using Kirchhoff migration

    Microsoft Academic Search

    Timothy D. Dorney; Jon L. Johnson; J. Van Rudd; Richard G. Baraniuk; William W. Symes; Daniel M. Mittleman

    2001-01-01

    sitions. Common examples includeultrawideband radar and pulsed sonar.1--3The lattercase is of particular interest because of the complexityof the geophysical imaging problem. Image quality inground-penetrating sonar can be strongly inf luencedby factors such as scattering of the propagating acousticwaves. As a result, direct backpropagation of thediffracted wave is often untenable, and a more robustimaging algorithm must be used.3Unfortunately,because the object under

  8. 200 ns pulse high-voltage supply for terahertz field emission.

    PubMed

    Welsh, Gregor H; Turton, David A; Jones, David R; Jaroszynski, Dino A; Wynne, Klaas

    2007-04-01

    We present a method of generating 200 ns high-voltage (up to 40 kV) pulses operating at repetition rates of up to 100 kHz, which may be synchronized with laser pulses. These supplies are simple to make and were developed for ultrafast terahertz pulse generation from GaAs photoconductive antennas using a high-repetition-rate regeneratively amplified laser. We also show an improvement in signal-to-noise ratio over a continuous dc bias field and application of the supply to terahertz pulse generation. PMID:17477645

  9. Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity

    E-print Network

    Paris-Sud XI, Université de

    Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity Jean of functional frog auricular fibers by ionic contrast terahertz ICT near field microscopy. This technique

  10. Terahertz Spectroscopy and Imaging for Defense and Security Applications

    Microsoft Academic Search

    Hai-Bo Liu; Hua Zhong; Nicholas Karpowicz; Yunqing Chen; Xi-Cheng Zhang

    2007-01-01

    Terahertz (THz) radiation, which occupies a relatively unexplored portion of the electromagnetic spectrum between the mid-infrared and microwave bands, offers innovative sensing and imaging technologies that can provide information unavailable through conventional methods such as microwave and X-ray techniques. With the advancement of THz technologies, THz sensing and imaging will impact a broad range of interdisciplinary fields, including chemical and

  11. Terahertz digital holography image processing based on MAP algorithm

    NASA Astrophysics Data System (ADS)

    Chen, Guang-Hao; Li, Qi

    2015-04-01

    Terahertz digital holography combines the terahertz technology and digital holography technology at present, fully exploits the advantages in both of them. Unfortunately, the quality of terahertz digital holography reconstruction images is gravely harmed by speckle noise which hinders the popularization of this technology. In this paper, the maximum a posterior estimation (MAP) filter is harnessed for the restoration of the digital reconstruction images. The filtering results are compared with images filtered by Wiener Filter and conventional frequency-domain filters from both subjective and objective perspectives. As for objective assessment, we adopted speckle index (SPKI) and edge preserving index (EPI) to quantitate the quality of images. In this paper, Canny edge detector is also used to outline the target in original and reconstruction images, which then act as an important role in the evaluation of filter performance. All the analysis indicate that maximum a posterior estimation filtering algorithm performs superiorly compared with the other two competitors in this paper and has enhanced the terahertz digital holography reconstruction images to a certain degree, allowing for a more accurate boundary identification.

  12. Mode-selective terahertz emission from rippled air irradiated by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Shin, Junghun; Zhidkov, Alexei; Jin, Zhan; Hosokai, Tomonao; Kodama, Ryosuke

    2014-04-01

    Terahertz (THz) emission from rippled air is studied in multidimensional particle-in-cell simulations that include optical field ionization. The ionization modulation in a plasma channel produced by a laser pulse propagating along a ripple and the pulse self-focusing result in THz mode selection with the generation of intense signals having quasi-monochromatic spectral distributions.

  13. High-power femtosecond-terahertz pulse induces a wound response in mouse skin

    PubMed Central

    Kim, Kyu-Tae; Park, Jaehun; Jo, Sung Jin; Jung, Seonghoon; Kwon, Oh Sang; Gallerano, Gian Piero; Park, Woong-Yang; Park, Gun-Sik

    2013-01-01

    Terahertz (THz) technology has emerged for biomedical applications such as scanning, molecular spectroscopy, and medical imaging. Although a thorough assessment to predict potential concerns has to precede before practical utilization of THz source, the biological effect of THz radiation is not yet fully understood with scant related investigations. Here, we applied a femtosecond-terahertz (fs-THz) pulse to mouse skin to evaluate non-thermal effects of THz radiation. Analysis of the genome-wide expression profile in fs-THz-irradiated skin indicated that wound responses were predominantly mediated by transforming growth factor-beta (TGF-?) signaling pathways. We validated NF?B1- and Smad3/4-mediated transcriptional activation in fs-THz-irradiated skin by chromatin immunoprecipitation assay. Repeated fs-THz radiation delayed the closure of mouse skin punch wounds due to up-regulation of TGF-?. These findings suggest that fs-THz radiation initiate a wound-like signal in skin with increased expression of TGF-? and activation of its downstream target genes, which perturbs the wound healing process in vivo. PMID:23907528

  14. Efficient real-time detection of terahertz pulse radiation based on photoacoustic conversion by carbon nanotube nanocomposite

    NASA Astrophysics Data System (ADS)

    Chen, Sung-Liang; Chang, You-Chia; Zhang, Cheng; Ok, Jong G.; Ling, Tao; Mihnev, Momchil T.; Norris, Theodore B.; Guo, L. Jay

    2014-07-01

    Terahertz sensing plays an important role in industry, biology and material science. Most existing techniques for terahertz detection either require bulky optics or need cryogenic cooling, and the uncooled thermal detectors usually suffer from long integration times (1-1,000 ms). We propose, and experimentally demonstrate, a novel scheme based on photoacoustic detection of terahertz pulse radiation. The transient and localized heating in a carbon nanotube-polymer composite by the absorption of terahertz pulse energy produces ultrasound, which is subsequently detected by a highly sensitive acoustic sensor. In contrast to conventional thermal detectors utilizing continuous heat integration, this new method of terahertz detection responds to the energy of each individual terahertz pulse by a time-gated scheme, thus rejecting the continuous radiation from the ambient. In addition, this novel detector possesses advantages such as room-temperature operation, a fast response (~0.1 µs) allowing real-time detection, compact size (millimetre scale) and wide spectral response.

  15. Terahertz digital holography image denoising using stationary wavelet transform

    NASA Astrophysics Data System (ADS)

    Cui, Shan-Shan; Li, Qi; Chen, Guanghao

    2015-04-01

    Terahertz (THz) holography is a frontier technology in terahertz imaging field. However, reconstructed images of holograms are inherently affected by speckle noise, on account of the coherent nature of light scattering. Stationary wavelet transform (SWT) is an effective tool in speckle noise removal. In this paper, two algorithms for despeckling SAR images are implemented to THz images based on SWT, which are threshold estimation and smoothing operation respectively. Denoised images are then quantitatively assessed by speckle index. Experimental results show that the stationary wavelet transform has superior denoising performance and image detail preservation to discrete wavelet transform. In terms of the threshold estimation, high levels of decomposing are needed for better denoising result. The smoothing operation combined with stationary wavelet transform manifests the optimal denoising effect at single decomposition level, with 5×5 average filtering.

  16. Tunable terahertz radiation from an ultrashort-laser-pulse-induced discharge in biased air

    NASA Astrophysics Data System (ADS)

    Suzuki, Fuminori; Anno-Kashiwazaki, Hiroaki; Miyazawa, Jun; Ono, Shohei; Higashiguchi, Takeshi; Yugami, Noboru; Sentoku, Yasuhiko; Kodama, Ryosuke; Muggli, Patric

    2011-10-01

    Strong beams of coherent radiation are essential to induce nonlinear excitation phenomena in biology and material sciences. Optical-field-induced ionization by an ultrashort laser pulse produces ultrabroadband bursts of radiation with photon energies ranging from radio-wave at the microsecond timescale to x-ray at the attosecond timescale. As the laser pulse drives an ultrafast-discharge with high current it induces nonlinear spectral conversion in a few femtoseconds and generates terahertz electromagnetic waves. Broadband terahertz generation has been reported in air and rare gases. If the radiation frequency depends on the electron plasma density, it should vary with the laser pulse intensity, and the kind and density of the gas. However, the peak radiation frequencies reported are almost independent of those parameters. From the laser-gas interaction point of view, the terahertz generation mechanism is not enough understood. We demonstrate a frequency-tuning scheme that uses the laser pulse duration to control the ultrafast-discharge current timescale, yielding a terahertz energy of 0.1 ?J and a conversion efficiency of 10-4 by use of the homemade power supply with 60-A discharge current at 1 kHz. We also propose a simple physical model to explain the generation of terahertz radiation with the laser propagation in an ultrafast-discharge.

  17. Proposal for real-time terahertz imaging system with palm-size terahertz camera and compact quantum cascade laser

    E-print Network

    Oda, Naoki

    This paper describes a real-time terahertz (THz) imaging system, using the combination of a palm-size THz camera with a compact quantum cascade laser (QCL). The THz camera contains a 320x240 microbolometer focal plane array ...

  18. Coherent control of terahertz harmonic generation by a chirped few-cycle pulse in a quantum well

    NASA Astrophysics Data System (ADS)

    Cui, Ni; Xiang, Yang; Niu, Yueping; Gong, Shangqing

    2010-01-01

    We present results on the occurrence of ultrashort terahertz harmonic generation (THG) driven by a millimeter nonlinear chirped few-cycle laser pulse in a symmetric double quantum well. By solving the effective nonlinear Bloch equations, THG with a generic plateau and cutoff can be produced. The time-frequency characteristic of the ultrashort terahertz harmonic spectrum is analyzed in detail by means of the wavelet transform of induced dipole acceleration. Furthermore, an ultrabroad supercontinuum terahertz harmonic spectrum can be generated and an isolated ultrashort terahertz pulse can be obtained at the cutoff region by choosing the appropriate chirping rate parameters.

  19. Generation of a Strong Terahertz Radiation by Counter-Propagating Laser Pulses in a Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Hur, Min Sup; Cho, Myung-Hoon; Kim, Young-Kuk

    2014-10-01

    A novel scheme of terahertz emission from a laser-plasma system was studied by theory and PIC simulations. In this new scheme, two counter-propagating laser pulses collide in a magnetized plasma. The strong ponderomotive force of the colliding pulses induces longitudinal current, which again is partially converted to a transverse one via the external magnetic field. This current actually plays the role radiating antenna. Since the ponderomotive force of the colliding pulses is generally much stronger than that from the single pulse, the intensity of the terahertz emission from the suggested scheme can be enhanced by tens of times from the single-pulse-driven Cherenkov wake scheme. Theoretically it was found that the terahertz amplitude scales with the P-square of the driving pulse instead of just P. More than that, an interesting physics of the electric field diffusion near the cutoff was observed in the simulations and fully described theoretically. One direct result of such a driven-diffusion of the electric field is the growth of the central field, leading to increased terahertz emission with the plasma density gradient.

  20. Field-free molecular orientation with terahertz few-cycle pulses

    NASA Astrophysics Data System (ADS)

    Shu, Chuan-Cun; Yuan, Kai-Jun; Hu, Wen-Hui; Cong, Shu-Lin

    2010-06-01

    We demonstrate theoretically an efficient field-free orientation in LiH and LiCl driven by available terahertz few-cycle pulses (TFCPs). Exact results by numerically solving the time-dependent Schrödinger equation including the vibrational and rotational degrees of freedom are compared to the rigid-rotor approximation (RRA) as well as to the impulsive approximation (IA), and the effect of rotational-vibrational coupling on the both RRA and IA is examined in detail. We find that the current available TFCPs may overcome the technical limitation of terahertz half-cycle pulse for enhancing the field-free molecular orientation.

  1. Field-free molecular orientation with terahertz few-cycle pulses.

    PubMed

    Shu, Chuan-Cun; Yuan, Kai-Jun; Hu, Wen-Hui; Cong, Shu-Lin

    2010-06-28

    We demonstrate theoretically an efficient field-free orientation in LiH and LiCl driven by available terahertz few-cycle pulses (TFCPs). Exact results by numerically solving the time-dependent Schrodinger equation including the vibrational and rotational degrees of freedom are compared to the rigid-rotor approximation (RRA) as well as to the impulsive approximation (IA), and the effect of rotational-vibrational coupling on the both RRA and IA is examined in detail. We find that the current available TFCPs may overcome the technical limitation of terahertz half-cycle pulse for enhancing the field-free molecular orientation. PMID:20590197

  2. High field, high efficiency terahertz pulse generation by optical rectification

    E-print Network

    Huang, Wenqian Ronny

    2014-01-01

    The great difficulty of producing high intensity radiation in the terahertz (THz) spectral region by conventional electronics has stimulated interest in development of sources based on photonics. Optical rectification in ...

  3. Imaging of epithelial cancer in sub-terahertz electromagnetic wave.

    PubMed

    Mitobe, Kazutaka; Manabe, Motomu; Yoshimura, Noboru; Kurabayashi, Toru

    2005-01-01

    We used sub-terahertz (THz) imaging to exam two cross sections of epithelial cancer tissue embedded in paraffin using a 0.19 THz electromagnetic wave. The sub-THz imaging system was constructed with a tunnel injection transit time (TUNNETT) diode, a Schottky barrier diode detector and a X-Z stage. We examined the difference between a sub-THz wave absorption in melanoma and nevus tissue. PMID:17282146

  4. Design of fast, high-resolution terahertz imaging system based on laser and nonlinear crystal LiNbO3

    NASA Astrophysics Data System (ADS)

    Xin, Feifei; Su, Hongyan

    2015-05-01

    In this paper, we introduced the design of a fast, high-resolution terahertz imaging system based on nonlinear crystal LiNbO3. Compared with the fast developed THz pulse imaging technique, THz Continuous Wave imaging system has many advantages such as high average power, high integration, small volume, and low cost. So, THz Continuous Wave imaging system without the need of scanning system is one of the best ways to improve the imaging resolution and the speed of a THz imaging system at the same time.

  5. Air nonlinear dynamics initiated by ultra-intense lambda-cubic terahertz pulses

    NASA Astrophysics Data System (ADS)

    Shalaby, Mostafa; Hauri, Christoph P.

    2015-05-01

    We report on the measurement of the instantaneous Kerr nonlinearity and the retarded alignment of air molecules CO2, N2, and O2 triggered by an intense, lambda-cubic terahertz pulse, a diffraction- and transform-limited single-cycle pulse. The strong-field, impulsive low-frequency excitation (3.9 THz) leads to field-free alignment dynamics of these molecules thanks to the terahertz-induced transient dipole moments in the otherwise non-polar molecules. The strong coupling to the terahertz electric transient results in the excitation of coherent large amplitude long-living rotational states at room temperature and ambient pressure. Beyond fundamental investigations of nonlinear properties in gases, our results suggest a route towards field-free molecular alignment at laser intensity well below the ionization threshold.

  6. Terahertz Lasers Reveal Information for 3D Images

    NASA Technical Reports Server (NTRS)

    2013-01-01

    After taking off her shoes and jacket, she places them in a bin. She then takes her laptop out of its case and places it in a separate bin. As the items move through the x-ray machine, the woman waits for a sign from security personnel to pass through the metal detector. Today, she was lucky; she did not encounter any delays. The man behind her, however, was asked to step inside a large circular tube, raise his hands above his head, and have his whole body scanned. If you have ever witnessed a full-body scan at the airport, you may have witnessed terahertz imaging. Terahertz wavelengths are located between microwave and infrared on the electromagnetic spectrum. When exposed to these wavelengths, certain materials such as clothing, thin metal, sheet rock, and insulation become transparent. At airports, terahertz radiation can illuminate guns, knives, or explosives hidden underneath a passenger s clothing. At NASA s Kennedy Space Center, terahertz wavelengths have assisted in the inspection of materials like insulating foam on the external tanks of the now-retired space shuttle. "The foam we used on the external tank was a little denser than Styrofoam, but not much," says Robert Youngquist, a physicist at Kennedy. The problem, he explains, was that "we lost a space shuttle by having a chunk of foam fall off from the external fuel tank and hit the orbiter." To uncover any potential defects in the foam covering, such as voids or air pockets, that could keep the material from staying in place, NASA employed terahertz imaging to see through the foam. For many years, the technique ensured the integrity of the material on the external tanks.

  7. Advanced terahertz imaging system performance model for concealed weapon identification

    NASA Astrophysics Data System (ADS)

    Murrill, Steven R.; Redman, Brian; Espinola, Richard L.; Franck, Charmaine C.; Petkie, Douglas T.; De Lucia, Frank C.; Jacobs, Eddie L.; Griffin, Steven T.; Halford, Carl E.; Reynolds, Joe

    2007-04-01

    The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory (ARL) have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The details of this MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination, were reported on at the 2005 SPIE Europe Security and Defence Symposium. The focus of this paper is to report on recent advances to the base model which have been designed to more realistically account for the dramatic impact that target and background orientation can have on target observability as related to specular and Lambertian reflections captured by an active-illumination-based imaging system. The advanced terahertz-band imaging system performance model now also accounts for target and background thermal emission, and has been recast into a user-friendly, Windows-executable tool. This advanced THz model has been developed in support of the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. This paper will describe the advanced THz model and its new radiometric sub-model in detail, and provide modeling and experimental results on target observability as a function of target and background orientation.

  8. Intense terahertz pulses from SLAC electron beams using coherent transition radiation.

    PubMed

    Wu, Ziran; Fisher, Alan S; Goodfellow, John; Fuchs, Matthias; Daranciang, Dan; Hogan, Mark; Loos, Henrik; Lindenberg, Aaron

    2013-02-01

    SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/A?) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response. PMID:23464183

  9. Intense terahertz pulses from SLAC electron beams using coherent transition radiation

    NASA Astrophysics Data System (ADS)

    Wu, Ziran; Fisher, Alan S.; Goodfellow, John; Fuchs, Matthias; Daranciang, Dan; Hogan, Mark; Loos, Henrik; Lindenberg, Aaron

    2013-02-01

    SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/Å) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

  10. Intense terahertz pulses from SLAC electron beams using coherent transition radiation

    SciTech Connect

    Wu Ziran; Fisher, Alan S.; Hogan, Mark; Loos, Henrik [Accelerator Directorate, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Goodfellow, John [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Fuchs, Matthias [Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Daranciang, Dan [Department of Chemistry, Stanford University, Stanford, California 94305 (United States); Lindenberg, Aaron [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)

    2013-02-15

    SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/A) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

  11. Experimental imaging research on continuous-wave terahertz in-line digital holography

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  12. Terahertz field enhancement via coherent superposition of the pulse sequences after a single optical-rectification crystal

    SciTech Connect

    Sajadi, Mohsen, E-mail: sajadi@fhi-berlin.mpg.de; Wolf, Martin; Kampfrath, Tobias [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany)

    2014-03-03

    Terahertz electromagnetic pulses are frequently generated by optical rectification of femtosecond laser pulses. In many cases, the efficiency of this process is known to saturate with increasing intensity of the generation beam because of two-photon absorption. Here, we demonstrate two routes to reduce this effect in ZnTe(110) crystals and enhance efficiency, namely, by (i) recycling the generation pulses and by (ii) splitting each generation pulse into two pulses before pumping the crystal. In both methods, the second pulse arrives ?1?ns after the first one, sufficiently long for optically generated carriers to relax. Enhancement is achieved by coherently superimposing the two resulting terahertz fields.

  13. A CMOS focal-plane array for terahertz imaging

    Microsoft Academic Search

    U. R. Pfeiffer; E. Ojefors; A. Lisauskas; D. Glaab; F. Voltolina; V. M. F. Nzogang; P. H. Bolivar; H. G. Roskos

    2008-01-01

    A terahertz focal-plane array (FPA) for video-rate imaging applications has been fabricated in a commercially available CMOS process technology. The 3times5 pixel array uses conventional low-cost quarter-micron NMOS transistors for incoherent power detection. Each pixel has a size of 150times150 mum2 and consists of an on-chip antenna, an incoherent power detection circuit, and a 43-dB amplifier with a 1.6-MHz bandwidth.

  14. Broadband terahertz imaging of documents written with lead pencils

    NASA Astrophysics Data System (ADS)

    Abraham, E.; Younus, A.; El Fatimy, A.; Delagnes, J. C.; Nguéma, E.; Mounaix, P.

    2009-08-01

    Far infrared transmission spectra of several graphite pencil leads on paper have been measured up to 2 THz using time-domain spectroscopy. The observation of the gradual absorption depending on the graphite proportion has been assessed for different pencils from hard to soft black-marking graphite leads. The resulting graphite transmittance is used to perform two-dimensional transmission terahertz imaging of written documents.

  15. Advanced terahertz imaging system performance model for concealed weapon identification

    Microsoft Academic Search

    Steven R. Murrill; Brian Redman; Richard L. Espinola; Charmaine C. Franck; Douglas T. Petkie; Frank C. De Lucia; Eddie L. Jacobs; Steven T. Griffin; Carl E. Halford; Joe Reynolds

    2007-01-01

    The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory (ARL) have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The details of this MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation,

  16. Terahertz imaging system performance model for concealed weapon identification

    Microsoft Academic Search

    Steven R. Murrill; Eddie L. Jacobs; Steven K. Moyer; Carl E. Halford; Steven T. Griffin; Frank C. De Lucia; Douglas T. Petkie; Charmaine C. Franck

    2005-01-01

    The U.S. Army Night Vision and Electronic Sensors Directorate and the U.S. Army Research Laboratory have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is

  17. Terahertz imaging system performance model for concealed-weapon identification

    Microsoft Academic Search

    Steven R. Murrill; Eddie L. Jacobs; Steven K. Moyer; Carl E. Halford; Steven T. Griffin; Frank C. De Lucia; Douglas T. Petkie; Charmaine C. Franck

    2008-01-01

    The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination.

  18. Intense terahertz emission from atomic cluster plasma produced by intense femtosecond laser pulses

    SciTech Connect

    Jahangiri, Fazel; Hashida, Masaki; Tokita, Shigeki; Sakabe, Shuji [Advanced Research Center for Beam Science, ICR, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan and Department of Physics, GSS, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-7501 (Japan); Nagashima, Takeshi; Hangyo, Masanori [Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan)

    2011-12-26

    Terahertz (THz) emission from argon cluster plasma, generated by intense femtosecond laser pulses in the energy range of 10-70 mJ, has been investigated. THz polarization, energy dependence, and angular distribution were measured to provide an initial discussion on the mechanisms of THz emission. THz pulses of much higher energy were generated from argon clusters than from argon gas, which indicates that plasma produced from atomic clusters holds considerable promise as an intense THz source.

  19. Conversion of short optical pulses to terahertz radiation in a nonlinear medium: Experiment and theory

    SciTech Connect

    Zinov'ev, N. N.; Nikoghosyan, A. S.; Dudley, R. A.; Chamberlain, J. M. [Department of Physics, University of Durham, Durham DH1 3LE (United Kingdom) and A. F. Ioffe Physical Technical Institute, 194021 St. Petersburg (Russian Federation); Department of Microwave Engineering, Yerevan State University, Yerevan 375025 (Armenia); National Physical Laboratory, Teddington, Middlesex TW11 0LW (United Kingdom); Department of Physics, University of Durham, Durham DH1 3LE (United Kingdom)

    2007-12-15

    We report on the frequency and time domain analysis of electromagnetic terahertz radiation generated by nonlinear conversion of short optical pulses crossing boundaries of nonlinear material. Analysis and comparison with experiment have unequivocally established that the nature of collinear radiation at terahertz frequencies relates to the phenomenon of transition radiation produced by the instantaneous creation (at the input interface) and extinction (at the output interface) of the moving polarization charge formed by the nonlinear coupling of the pump electromagnetic fields. The mechanism is analogous to the phenomena of transition radiation of moving free charges, in particular, to the radiation mechanism discussed in the Tamm problem.

  20. EDITORIAL: Terahertz nanotechnology Terahertz nanotechnology

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    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 within the THz spectral region providing an additional benefit. His review describes the principle, characteristics, and applications of terahertz molecular imaging, where the use of nanoparticle probes allows dramatically enhanced sensitivity. Jiaguang Han and Weili Zhang and colleagues in China, Saudi Arabia, Japan and the US report exciting developments for optoelectronics [11]. They describe work on plasmon-induced transparency (PIT), an analogue of electromagnetically induced transparency (EIT) where interference leads to a sharp transparency window that may be useful for nonlinear and slow-light devices, optical switching, pulse delay, and storage for optical information processing. While PIT has advantages over the cumbersome experimental systems required for EIT, it has so far been constrained to very narrow band operation. Now Zhang and colleagues present the simulation, implementation, and measurement of a broadband PIT metamaterial functioning across a frequency range greater than 0.40 THz in the terahertz regime. 'We can foresee a historic breakthrough for science and technology through terahertz research,' concluded Masayoshi Tonouchi in his review over five years ago as momentum in the field was mounting [12]. He added, 'It is also noteworthy that THz research is built on many areas of science and the coordination of a range of disciplines is giving birth to a new science.' With the inherently multidisciplinary nature of nanotechnology research it is not so strange to see the marriage of the two fields form such a fruitful partnership, as this special section highlights. References [1] Williams B S, Kumar S, Hu Q and Reno J L 2006 High-power terahertz quantum-cascade lasers Electron. Lett. 42 89-91 [2] Köhler R et al 2002 Terahertz semiconductor-heterostructure laser Nature 417 156-9 [3] Mittendorff M, Xu M, Dietz R J B, K¨unzel H, Sartorius B, Schneider H, Helm M and Winnerl S 2013 Large area photoconductive THz emitter for 1.55 ?m excitation based on an InGaAs heterostructure Nanotechnology 24 214007 [4] Chen H-T, Padilla W J, Zide J M O, Gossa

  1. Terahertz interferometric synthetic aperture tomography for confocal imaging systems.

    PubMed

    Heimbeck, M S; Marks, D L; Brady, D; Everitt, H O

    2012-04-15

    Terahertz (THz) interferometric synthetic aperture tomography (TISAT) for confocal imaging within extended objects is demonstrated by combining attributes of synthetic aperture radar and optical coherence tomography. Algorithms recently devised for interferometric synthetic aperture microscopy are adapted to account for the diffraction-and defocusing-induced spatially varying THz beam width characteristic of narrow depth of focus, high-resolution confocal imaging. A frequency-swept two-dimensional TISAT confocal imaging instrument rapidly achieves in-focus, diffraction-limited resolution over a depth 12 times larger than the instrument's depth of focus in a manner that may be easily extended to three dimensions and greater depths. PMID:22513671

  2. Nonlinear cross-phase modulation with intense single-cycle terahertz pulses.

    PubMed

    Shen, Y; Watanabe, T; Arena, D A; Kao, C-C; Murphy, J B; Tsang, T Y; Wang, X J; Carr, G L

    2007-07-27

    We have demonstrated nonlinear cross-phase modulation in electro-optic crystals using intense, single-cycle terahertz (THz) radiation. Individual THz pulses, generated by coherent transition radiation emitted by subpicosecond electron bunches, have peak energies of up to 100 microJ per pulse. The time-dependent electric field of the intense THz pulses induces cross-phase modulation in electro-optic crystals through the Pockels effect, leading to spectral shifting, broadening, and modulation of copropagating laser pulses. The observed THz-induced cross-phase modulation agrees well with a time-dependent phase-shift model. PMID:17678365

  3. Nonlinear Cross-Phase Modulation with Intense Single-Cycle Terahertz Pulses

    SciTech Connect

    Shen,Y.; Watanabe, T.; Arena, D.; Kao, C.; Murphy, J.; Tsang, T.; Wang, X.; Carr, G.

    2007-01-01

    We have demonstrated nonlinear cross-phase modulation in electro-optic crystals using intense, single-cycle terahertz (THz) radiation. Individual THz pulses, generated by coherent transition radiation emitted by subpicosecond electron bunches, have peak energies of up to 100{mu}J per pulse. The time-dependent electric field of the intense THz pulses induces cross-phase modulation in electro-optic crystals through the Pockels effect, leading to spectral shifting, broadening, and modulation of copropagating laser pulses. The observed THz-induced cross-phase modulation agrees well with a time-dependent phase-shift model.

  4. Numerical studies of powerful terahertz pulse generation from a super-radiant surface wave oscillator

    SciTech Connect

    Zhang Hai [Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China); Wang Jianguo [Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China); Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China); Tong Changjiang; Li Xiaoze [Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China); Wang Guangqiang [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)

    2009-12-15

    The results of theoretical and numerical studies of coherent stimulated terahertz radiation from intense, subnanosecond electron beam are presented. The mechanism of terahertz pulse generation is associated with self-bunching of the beam and slippage of the wave over the whole electron flow. This so called Cherenkov super-radiance (SR) is used to propose a compact terahertz generator with high peak power. A large cross-section (overmoded), slow wave structure is designed to support the high power handling capability, and the mode competition is avoided by operating the device in the surface wave status. With 2.5 D particle-in-cell simulation, the 'hot' characteristics of the proposed super-radiant terahertz generator are investigated, and the numerical results show that the SR peak power could be further increased by optimizing the amplitude profile of electron pulse. Under the condition of 0.5 ns pulsewidth, 500 kV voltage, and 1.5 kA current, the 110 ps, 680 MW, and 0.14 THz SR pulse is achieved with a power efficiency of 90.67% in TM{sub 01} mode.

  5. Temperature-dependent terahertz imaging of excised oral malignant melanoma.

    PubMed

    Sim, Yookyeong Carolyn; Ahn, Kang-Min; Park, Jae Yeon; Park, Chan-Sik; Son, Joo-Hiuk

    2013-07-01

    We imaged a single case of oral malignant melanoma using terahertz (THz) reflection imaging at room temperature (20 °C) and below freezing (-20 °C). A malignant nodule beneath the oral tissue surface was visualized using 2-D and B-scan THz imaging techniques. The THz images were well correlated with the histological findings. The nodule was found to have lower water content than that of normal cells, and this water effect may have influenced the THz refractive index and absorption coefficient at 20 °C. The THz spectroscopic image of the frozen tissue at -20 °C showed better contrast because of the lack of liquid water; this implies that there are significant structural differences between malignant oral melanoma cells and normal mucosal cells. The better contrast in the frozen tissue images was due to the greater penetration of THz radiation into the sample. This temperature-dependent THz imaging approach demonstrated the feasibility of accurate imaging of the oral tumor tissue. PMID:25055305

  6. Terahertz generation by nonlinear mixing of laser pulses in a clustered gas

    SciTech Connect

    Kumar, Manoj; Tripathi, V. K. [Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)

    2011-05-15

    A scheme of terahertz (THz) generation by two collinear laser pulses of finite spot size in a clustered gas is investigated theoretically. The lasers quickly ionize the atoms of the clusters, converting them into plasma balls, and exert a ponderomotive force on the cluster electrons, producing a beat frequency longitudinal current of limited transverse extent. The current acts as an antenna to produce beat frequency terahertz radiation. As the cluster expands under the hydrodynamic pressure, plasma frequency of cluster electrons {omega}{sub pe} decreases and approaches {radical}(3) times the frequency of laser, resonant heating and expansion of clusters occurs. On further expansion of clusters as {omega}{sub pe} approaches {radical}(3) times the terahertz frequency, resonant enhancement in THz radiated power occurs.

  7. Markov chain Monte Carlo sampling based terahertz holography image denoising.

    PubMed

    Chen, Guanghao; Li, Qi

    2015-05-10

    Terahertz digital holography has attracted much attention in recent years. This technology combines the strong transmittance of terahertz and the unique features of digital holography. Nonetheless, the low clearness of the images captured has hampered the popularization of this imaging technique. In this paper, we perform a digital image denoising technique on our multiframe superposed images. The noise suppression model is concluded as Bayesian least squares estimation and is solved with Markov chain Monte Carlo (MCMC) sampling. In this algorithm, a weighted mean filter with a Gaussian kernel is first applied to the noisy image, and then by nonlinear contrast transform, the contrast of the image is restored to the former level. By randomly walking on the preprocessed image, the MCMC-based filter keeps collecting samples, assigning them weights by similarity assessment, and constructs multiple sample sequences. Finally, these sequences are used to estimate the value of each pixel. Our algorithm shares some good qualities with nonlocal means filtering and the algorithm based on conditional sampling proposed by Wong et al. [Opt. Express18, 8338 (2010)10.1364/OE.18.008338OPEXFF1094-4087], such as good uniformity, and, moreover, reveals better performance in structure preservation, as shown in numerical comparison using the structural similarity index measurement and the peak signal-to-noise ratio. PMID:25967487

  8. Developments in time-resolved ultrafast imaging and spectroscopy at terahertz frequencies

    E-print Network

    Teo, Stephanie M

    2014-01-01

    Prior to the advent of high energy pulsed femtosecond lasers, the field of terahertz (THz) spectroscopy was stagnated by the lack of both high power THz sources and sensitive THz detectors. Over the past few years, it has ...

  9. Terahertz imaging with missing data analysis for metamaterials characterization

    NASA Astrophysics Data System (ADS)

    Sokolnikov, Andre

    2012-05-01

    Terahertz imaging proves advantageous for metamaterials characterization since the interaction of THz radiation with the metamaterials produces clear patterns of the material. Characteristic "finger prints" of the crystal structure help locating defects, dislocations, contamination, etc. TDS-THz spectroscopy is one of the tools to control metamaterials design and manufacturing. A computational technique is suggested that provides a reliable way of calculation of the metamaterials structure parameters, spotting defects. Based on missing data analysis, the applied signal processing facilitates a better quality image while compensating for partially absent information. Results are provided.

  10. High conversion efficiency, high energy terahertz pulses by optical rectification in cryogenically cooled lithium niobate.

    PubMed

    Huang, Shu-Wei; Granados, Eduardo; Huang, Wenqian Ronny; Hong, Kyung-Han; Zapata, Luis E; Kärtner, Franz X

    2013-03-01

    We demonstrate highly efficient terahertz (THz) generation by optical rectification (OR) of near-optimum pump pulses centered at 1.03 ?m in cryogenically cooled lithium niobate. Using a close to optimal pulse duration of 680 fs and a pump energy of 1.2 mJ, we report conversion efficiencies above 3.8±0.4%, which is more than an order of magnitude higher than previously reported. The results confirm the advantage of using cryogenic cooling of the lithium niobate crystal that significantly reduces the THz absorption, enabling the scaling of THz pulse energies to the millijoule level via OR. PMID:23455302

  11. Terahertz imaging system performance model for concealed-weapon identification.

    PubMed

    Murrill, Steven R; Jacobs, Eddie L; Moyer, Steven K; Halford, Carl E; Griffin, Steven T; De Lucia, Frank C; Petkie, Douglas T; Franck, Charmaine C

    2008-03-20

    The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance modeling technology that couples system design parameters to observer-sensor field performance by using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support of the Defense Advanced Research Project Agencies' Terahertz Imaging Focal-Plane Technology (TIFT) program and is currently being used to guide the design and development of a 0.650 THz active-passive imaging system. This paper will describe the THz model in detail, provide and discuss initial modeling results for a prototype THz imaging system, and outline plans to calibrate and validate the model through human perception testing. PMID:18709076

  12. Terahertz imaging system performance model for concealed weapon identification

    NASA Astrophysics Data System (ADS)

    Murrill, Steven R.; Jacobs, Eddie L.; Moyer, Steven K.; Halford, Carl E.; Griffin, Steven T.; De Lucia, Frank C.; Petkie, Douglas T.; Franck, Charmaine C.

    2005-11-01

    The U.S. Army Night Vision and Electronic Sensors Directorate and the U.S. Army Research Laboratory have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance models that couple system design parameters to observer-sensor field performance using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support of the Defense Advanced Research Project Agencies' Terahertz Imaging Focal-Plane-Array Technology (TIFT) program and is presently being used to guide the design and development of a 0.650 THz active/passive imaging system. This paper will describe the THz model in detail, provide and discuss initial modeling results for a prototype THz imaging system, and outline plans to validate and calibrate the model through human perception testing.

  13. Terahertz imaging system performance model for concealed-weapon identification

    NASA Astrophysics Data System (ADS)

    Murrill, Steven R.; Jacobs, Eddie L.; Moyer, Steven K.; Halford, Carl E.; Griffin, Steven T.; De Lucia, Frank C.; Petkie, Douglas T.; Franck, Charmaine C.

    2008-03-01

    The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance modeling technology that couples system design parameters to observer-sensor field performance by using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support of the Defense Advanced Research Project Agencies' Terahertz Imaging Focal-Plane Technology (TIFT) program and is currently being used to guide the design and development of a 0.650 THz active-passive imaging system. This paper will describe the THz model in detail, provide and discuss initial modeling results for a prototype THz imaging system, and outline plans to calibrate and validate the model through human perception testing.

  14. Bolometric THz-to-IR converter for terahertz imaging

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Sergey A.; Paulish, Andrey G.; Gelfand, Alexander V.; Lazorskiy, Pavel A.; Fedorinin, Victor N.

    2011-07-01

    The quasi-optical bolometric converter of terahertz (THz) waves into infrared (IR) radiation is proposed and experimentally investigated. The converter includes an ultra-thin THz absorber (with a thickness 1/50 of the operating free-space wavelength) based on an artificial impedance surface with close to perfect resonant absorptivity at 0.3 THz and a high-performance IR emissive layer. Absorption of THz waves induces converter heating that yields enhancement of IR emission from the emissive layer. The experimental testing of the THz-to-IR converter demonstrates the applicability of a converter to THz imaging with spectral and polarization discrimination in real-time operation.

  15. Single circularly polarized attosecond pulse generation by intense few cycle elliptically polarized laser pulses and terahertz fields from molecular media.

    PubMed

    Yuan, Kai-Jun; Bandrauk, André D

    2013-01-11

    We present a method for producing a single circularly polarized attosecond pulse by an intense few cycle elliptically polarized laser pulse combined with a terahertz field from numerical solutions of the time-dependent Schrödinger equation for the molecular ion H2(+). It is found that in the presence of a 62.5 THz (?=4800??nm) field at an intensity of ?10(14)??W/cm2, a single circularly polarized 114 as pulse can be generated by an elliptical polarized laser pulse at a wavelength of 400 nm with an ellipticity of ?=0.59. The efficiency of circular polarization attosecond pulse generation is interpreted based on a classical model of single electron recollision with the parent ion. PMID:23383902

  16. AlGaN/GaN based field effect transistors for terahertz detection and imaging

    NASA Astrophysics Data System (ADS)

    Sakowicz, M.; Lifshits, M. B.; Klimenko, O. A.; Coquillat, D.; Dyakonova, N.; Teppe, F.; Gaquière, C.; Poisson, M. A.; Delage, S.; Knap, W.

    2012-03-01

    AlGaN/GaN based FETs have great potential as sensitive and fast operating detectors because of their material advantages such as high breakdown voltage, high electron mobility, and high saturation velocity. These advantages could be exploited for resonant and non-resonant terahertz detection. We have designed, fabricated, and characterized AlGaN/GaN based FETs as single pixel terahertz detectors. This work focuses on non-resonant detection and imaging using GaN field plate FETs. To evaluate their performances as terahertz detectors, we have measured the responsivity as a function of gate voltage, the azimuthal angle between the terahertz electric field, the source-to-drain direction, and the temperature. A simple analytical model of the response is developed. It is based on plasma density perturbation in the transistor channel by the incoming terahertz radiation. The model shows how the non-resonant detection signal is related to static (dc) transistor characteristics and it fully describes the experimental results on the non-resonant sub-terahertz detection by the AlGaN/GaN based FETs. The imaging performances are evaluated by scanning objects in transmission mode and an example of application of terahertz imaging as new non-destructive technique for the quality control of materials is given. Results indicate that these FETs can be considered as promising devices for terahertz detection and imaging applications.

  17. Role of nonlinear refraction in the generation of terahertz field pulses by light fields

    SciTech Connect

    Zabolotskii, A. A., E-mail: zabolotskii@iae.nsk.su [Russian Academy of Sciences, Institute of Automation and Electrometry, Siberian Branch (Russian Federation)

    2013-07-15

    The generation of microwave (terahertz) pulses without any envelope in a four-level quasi-resonant medium is considered. Two intense quasi-monochromatic laser fields lead to a partial upper-level population. Microwave field pulses cause the transition between these levels. For appropriately chosen scales, the evolution of the fields is shown to be described by the pseudo-spin evolution equations in a microwave field with the inclusion of nonlinear refraction caused by an adiabatic upper-level population. The evolution of terahertz field pulses is described outside the scope of the slow-envelope approximation. When a number of standard approximations are taken into account, this system of equations is shown to be equivalent to an integrable version of the generalized reduced Maxwell-Bloch equations or to the generalized three-wave mixing equations. The soliton solution found by the inverse scattering transform method is used as an example to show that nonlinear refraction leads to a strong compression of the microwave (terahertz) field soliton.

  18. Ultra-broadband terahertz pulses generated in the organic crystal DSTMS.

    PubMed

    Somma, Carmine; Folpini, Giulia; Gupta, Jyotsana; Reimann, Klaus; Woerner, Michael; Elsaesser, Thomas

    2015-07-15

    Electric-field transients covering the extremely wide frequency range from 0.5 to 26 THz are generated in the organic nonlinear crystal 4-N,N-dimethylamino-4'-N'-methylstilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). Parametric difference frequency mixing within the spectrum of 25-fs amplified pulses centered at 800 nm provides a highly stable broadband output with an electric-field amplitude of up to several hundred kilovolts/cm. The high stability of the terahertz pulse parameters allows for sensitive phase-resolved broadband spectroscopy of optically thick crystalline samples. PMID:26176480

  19. Photoconductive Emission and Detection of Terahertz Pulsed Radiation Using Semiconductors and Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Tani, Masahiko; Yamamoto, Kohji; Estacio, Elmer S.; Que, Christopher T.; Nakajima, Hidekazu; Hibi, Masakazu; Miyamaru, Fumiaki; Nishizawa, Seizi; Hangyo, Masanori

    2012-04-01

    Recent studies on the techniques and development of photoconductive (PC) semiconductor devices for efficient generation and detection of terahertz (THz) pulsed radiation are reported. Firstly, the optimization of PC antenna design is discussed. The PC detection of THz pulsed radiation using low-temperature grown GaAs with 1.55-?m wavelength probe is then described. Finally, the enhancement of THz radiation from InSb by using a coupling lens and magnetic field is investigated. These results reveal valuable insights on the design of an efficient, compact, and cost-effective THz time-domain spectroscopy system based on 1.55-?m fs laser sources.

  20. Enhancing the energy of terahertz radiation from plasma produced by intense femtosecond laser pulses

    SciTech Connect

    Jahangiri, Fazel [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan) [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan); Laser and Plasma Research Institute, Shahid Beheshti University, Tehran (Iran, Islamic Republic of); Hashida, Masaki; Tokita, Shigeki; Sakabe, Shuji [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan) [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan); Department of Physics, GSS, Kyoto University, Kyoto (Japan); Nagashima, Takeshi; Hangyo, Masanori [Department of Physics, GSS, Kyoto University, Kyoto (Japan) [Department of Physics, GSS, Kyoto University, Kyoto (Japan); Institute of Laser Engineering, Osaka University, Osaka (Japan)

    2013-05-13

    Terahertz (THz) radiation from atomic clusters illuminated by intense femtosecond laser pulses is investigated. By studying the angular distribution, polarization properties and energy dependence of THz waves, we aim to obtain a proper understanding of the mechanism of THz generation. The properties of THz waves measured in this study differ from those predicted by previously proposed mechanisms. To interpret these properties qualitatively, we propose that the radiation is generated by time-varying quadrupoles, which are produced by the ponderomotive force of the laser pulse.

  1. A Comparison of Terahertz Pulsed Spectroscopy and Backward-Wave Oscillator Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zaytsev, Kirill I.; Gavdush, Arseniy A.; Chernomyrdin, Nikita V.; Kruchkov, Nikita P.; Kudrin, Konstantin G.; Nosov, Pavel A.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

    2014-09-01

    This paper presents new experimental and theoretical results for the material parameter reconstruction utilizing the terahertz (THz) pulsed spectroscopy (TPS). The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. The algorithm takes into account multiple reflections of THz pulse within the flat sample during the transmission mode measurements. Therefore the samples with small thickness or low refractive index could be studied utilizing the proposed method. In order to estimate the reconstruction accuracy, test sample material parameters, obtained with the TPS, were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated.

  2. Soliton regime of generation of terahertz radiation taking into account the phase of an optical pulse

    NASA Astrophysics Data System (ADS)

    Sazonov, S. V.; Sukhorukov, A. P.; Ustinov, N. V.

    2015-01-01

    An integrable generalization of the Yajima-Oikawa system of equations has been obtained to describe the optical generation of broadband terahertz radiation in a quadratically nonlinear medium with allowance for the effect of the phase of an optical pulse on this process. The corresponding Lax pair has been found. A soliton solution has been constructed. The analysis has indicated, in particular, that the role of the phase of the optical pulse increases significantly in the vicinity of zero value of the second-order group dispersion parameter. This behavior can result in a significant increase in the efficiency of generation in the soliton regime.

  3. Generation and coherent control of pure spin currents via terahertz pulses

    SciTech Connect

    Schüler, Michael, E-mail: michael.schueler@physik.uni-halle.de; Berakdar, Jamal [Institute for Physics, Martin-Luther University Halle-Wittenberg, 06099 Halle (Germany)

    2014-04-21

    We inspect the time and spin-dependent, inelastic tunneling in engineered semiconductor-based double quantum well driven by time-structured terahertz pulses. An essential ingredient is an embedded spin-active structure with vibrational modes that scatter the pulse driven carriers. Due to the different time scales of the charge and spin dynamics, the spin-dependent electron-vibron coupling may result in pure net spin current (with negligible charge current). Heating the vibrational site may affect the resulting spin current. Furthermore, by controlling the charge dynamics, the spin dynamics and the generated spin current can be manipulated and switched on and off coherently.

  4. Method for large and rapid terahertz imaging

    DOEpatents

    Williams, Gwyn P.; Neil, George R.

    2013-01-29

    A method of large-scale active THz imaging using a combination of a compact high power THz source (>1 watt), an optional optical system, and a camera for the detection of reflected or transmitted THz radiation, without the need for the burdensome power source or detector cooling systems required by similar prior art such devices. With such a system, one is able to image, for example, a whole person in seconds or less, whereas at present, using low power sources and scanning techniques, it takes several minutes or even hours to image even a 1 cm.times.1 cm area of skin.

  5. Scalable, Low-Noise Architecture for Integrated Terahertz Imagers

    NASA Astrophysics Data System (ADS)

    Gergelyi, Domonkos; Földesy, Péter; Zarándy, Ákos

    2015-06-01

    We propose a scalable, low-noise imager architecture for terahertz recordings that helps to build large-scale integrated arrays from any field-effect transistor (FET)- or HEMT-based terahertz detector. It enhances the signal-to-noise ratio (SNR) by inherently enabling complex sampling schemes. The distinguishing feature of the architecture is the serially connected detectors with electronically controllable photoresponse. We show that this architecture facilitate room temperature imaging by decreasing the low-noise amplifier (LNA) noise to one-sixteenth of a non-serial sensor while also reducing the number of multiplexed signals in the same proportion. The serially coupled architecture can be combined with the existing read-out circuit organizations to create high-resolution, coarse-grain sensor arrays. Besides, it adds the capability to suppress overall noise with increasing array size. The theoretical considerations are proven on a 4 by 4 detector array manufactured on 180 nm feature sized standard CMOS technology. The detector array is integrated with a low-noise AC-coupled amplifier of 40 dB gain and has a resonant peak at 460 GHz with 200 kV/W overall sensitivity.

  6. Single-cycle Terahertz Pulses with >0.2 V/A Field Amplitudes via Coherent Transition Radiation

    SciTech Connect

    Daranciang, Dan; /Stanford U., Chem. Dept.; Goodfellow, John; /Stanford U. Materials Sci. Dept.; Fuchs, Matthias; /SIMES, Stanford /SLAC, PULSE; Wen, Haidan; /ANL, APS; Ghimire, Shambhu; /SLAC, PULSE; Reis, David A.; /SIMES, Sanford /SLAC, PULSE /Stanford U., Appl. Phys. Dept.; Loos, Henrik; Fisher, Alan S.; /SLAC, LCLS; Lindenberg, Aaron M.; /Stanford U. Materials Sci. Dept. /SIMES, Stanford /SLAC, PULSE

    2012-02-15

    We demonstrate terahertz pulses with field amplitudes exceeding 0.2 V/{angstrom} generated by coherent transition radiation. Femtosecond, relativistic electron bunches generated at the Linac Coherent Light Source are passed through a beryllium foil, and the emitted radiation is characterized as a function of the bunch duration and charge. Broadband pulses centered at a frequency of 10 THz with energies of 140 {mu}J are measured. These far-below-bandgap pulses drive a nonlinear optical response in a silicon photodiode, with which we perform nonlinear autocorrelations that yield information regarding the terahertz temporal profile. Simulations of the spatiotemporal profile agree well with experimental results.

  7. Excitation of terahertz radiation by laser pulses in nonuniform plasma Thomas M. Antonsen, Jr. and John Palastro

    E-print Network

    Milchberg, Howard

    that a large fraction of laser pulse energy can be down-converted to THz levels. Research on THz radiation not lead to radiation. In addition to having a current density as a source, it is requiredExcitation of terahertz radiation by laser pulses in nonuniform plasma channels Thomas M. Antonsen

  8. Optimal Control of Quantum Rings by Terahertz Laser Pulses E. Rasanen,1,3,* A. Castro,1,3

    E-print Network

    Gross, E.K.U.

    Optimal Control of Quantum Rings by Terahertz Laser Pulses E. Ra¨sa¨nen,1,3,* A. Castro,1,3 J-dimensional semiconductor quantum-ring model is established, opening a path into coherent laser-driven single-gate qubits tailored laser-pulse sequences for logic operations [1]. Semiconductor quantum dots and quantum rings (QRs

  9. Terahertz imaging using intermediate thermal screen

    Microsoft Academic Search

    A. E. Klimov; V. V. Kubarev; V. N. Shumsky

    2010-01-01

    Parameters of THz imaging system with the intermediate thermal screen are analyzed. Experimental data on the prototype which uses the highly sensitive PbSnTe:In film as IR photodetector and the microbolometer matrix as the thermal screen are also given.

  10. Exploration of Terahertz Imaging with Silicon MOSFETs

    NASA Astrophysics Data System (ADS)

    Lisauskas, Alvydas; Bauer, Maris; Boppel, Sebastian; Mundt, Martin; Khamaisi, Bassam; Socher, Eran; Venckevi?ius, Rimvydas; Minkevi?ius, Linas; Kašalynas, Irmantas; Seliuta, Dalius; Valušis, Gintaras; Krozer, Viktor; Roskos, Hartmut G.

    2014-01-01

    We summarize three lines of development and investigation of foundry-processed patch-antenna-coupled Si MOSFETs as detectors of THz radiation: (i) Exploiting the pinciple of plasma-waved-based mixing in the two-dimensional electron gas of the transistors' channels, we demonstrate efficient detection at frequencies as high as 9 THz, much above the transit-time-limited cut-off frequencies of the devices (tens of GHz). Real-time imaging at 600 GHz with a 12 × 12 detector array is explored. (ii) Given the limited THz power usually available for applications, we explore imaging with enhanced sensitivity in heterodyne mode. We show that real-time operation of a 100 × 100-pixel heterodyne camera should be possible at 600 GHz with a better dynamic range (30 dB) than for direct power detection (20 dB), even if only a quarter-milliwatt of local-oscillator power, distributed radiatively over all detector pixels, is available. (iii) Finally, we present an all-electronic raster-scan imaging system for 220 GHz entirely based on CMOS devices, combining the CMOS detectors with an emitter circuit implemented in a 90-nm CMOS process and delivering radiation with a power on the 100- ?W scale. Considering progress in the field, we anticipate that the emitter concept of oscillator-based power generation with on-chip frequency multiplication will carry well into the sub-millimeter-wave regime.

  11. Discrete Pulse Transform of Images

    Microsoft Academic Search

    Roumen Anguelov; Inger Fabris-rotelli

    2008-01-01

    \\u000a The Discrete Pulse Transform (DPT) of images is defined by using a new class of LULU operators on multidimensional arrays.\\u000a This transform generalizes the DPT of sequences and replicates its essential properties, e.g. total variation preservation.\\u000a Furthermore, the discrete pulses in the transform capture the contrast in the original image on the boundary of their supports.\\u000a Since images are perceived

  12. A self-consistent regime of generation of terahertz radiation by an optical pulse with a tilted intensity front

    SciTech Connect

    Bugai, A N; Sazonov, S V; Shashkov, Andrei Yu

    2012-11-30

    We derived a self-consistent system of nonlinear wave equations describing the terahertz generation in dielectric uniaxial crystals by optical pulsed radiation with a tilted wavefront. The numerical analysis of the system of equations showed that the generation of a broadband one-period terahertz signal is accompanied by a red shift of the carrier frequency of the optical pulse, the magnitude of the shift being proportional to the pulse intensity. The generation efficiency with respect to energy reached a maximum at a certain distance of propagation in the crystal, after which the efficiency decreased. A satisfactory agreement was obtained between theoretical calculations and experimental data of other investigations. (generation of terahertz radiation)

  13. Quantum path control and isolated attosecond pulse generation in the combination of near-infrared and terahertz pulses

    NASA Astrophysics Data System (ADS)

    Zhong, Hui-Ying; Guo, Jing; Zhang, Hong-Dan; Du, Hui; Liu, Xue-Shen

    2015-07-01

    We present an efficient and realizable scheme for the generation of an ultrashort single attosecond (as) pulse from H atom with a 800-nm fundamental laser field combined with a terahertz (THz) field. The high-order harmonic generation (HHG) can be obtained by solving the time-dependent Schrödinger equation accurately and efficiently with time-dependent generalized pseudo-spectral (TDGPS) method. The result shows that the plateau of high-order harmonics is extended and the broadband spectra can be produced by the combined laser pulse, which can be explained by the corresponding ionization probability. The time–frequency analysis and semi-classical three-step model are also presented to further investigate this mechanism. Besides, by the superposition of the harmonics near the cutoff region, an isolated 133-as pulse can be obtained. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174108, 11104108, and 11271158).

  14. A Real-Time Terahertz Time-Domain Polarization Analyzer with 80-MHz Repetition-Rate Femtosecond Laser Pulses

    PubMed Central

    Watanabe, Shinichi; Yasumatsu, Naoya; Oguchi, Kenichi; Takeda, Masatoshi; Suzuki, Takeshi; Tachizaki, Takehiro

    2013-01-01

    We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications. PMID:23478599

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  16. Phase-sensitive terahertz emission from gas targets irradiated by few-cycle laser pulses

    NASA Astrophysics Data System (ADS)

    Wu, Hui-Chun; Meyer-ter-Vehn, Jürgen; Sheng, Zheng-Ming

    2008-04-01

    The effect of the carrier envelope phase (CEP) of few-cycle laser pulses on terahertz (THz) emission from gas targets is investigated by analysis and two-dimensional particle-in-cell simulations. For linearly polarized (LP) light, the THz amplitude depends on the CEP phase sinusoidally. For circularly polarized (CP) light, the THz amplitude is independent of the phase, but its polarization plane rotates with the phase. By measuring the THz amplitude or polarization direction, one can determine the CEP of LP or CP laser pulses, respectively. We find that when the ionization degree of atoms is lower than 10%, the phase dependence of the THz radiation is insensitive to intensity and duration of the laser pulse, which is preferable for the phase determination.

  17. Recording of Terahertz Pulses of Microsecond Duration Using the Thermoacoustic Effect

    NASA Astrophysics Data System (ADS)

    Andreev, V. G.; Vdovin, V. A.; Kalynov, Yu. K.

    2014-01-01

    We consider the possibility of using a thermoacoustic detector (TAD) for recording of high-power pulse radiation at frequencies of 0.55, 0.68, and 0.87 THz. Electromagnetic wave is transformed into an acoustic wave in a structure consisting of a 10-nm thick chromium film deposited on a quartz substrate and a layer of the immersion liquid that is in contact with the film. It is shown that for the pulse of microsecond duration (3-10 ?s) the waveform detected by the thermoacoustic detector is matched with high accuracy to the derivative of the terahertz pulse profile. For recording of electromagnetic radiation in the 0.5-0.9 THz frequency range it is possible to employ the simplified design of TAD, in which a transparent quartz substrate is in contact with a layer of water or ethanol.

  18. High-speed terahertz time-domain spectroscopy of cyclotron resonance in pulsed magnetic field.

    PubMed

    Molter, D; Ellrich, F; Weinland, T; George, S; Goiran, M; Keilmann, F; Beigang, R; Léotin, J

    2010-12-01

    We present time-resolved cyclotron resonance spectra of holes in p-Ge measured during single magnetic field pulses by using a rapid-scanning, fiber-coupled terahertz time-domain spectroscopy system. The key component of the system is a rotating monolithic delay line featuring four helicoid mirror surfaces. It allows measurements of THz spectra at up to 250 Hz repetition rate. Here we show results taken at 150 Hz. In a single 900 ms measurement 135 cyclotron resonance spectra were recorded that fully agree with what is expected from literature. PMID:21164965

  19. Directional elliptically polarized terahertz emission from air plasma produced by circularly polarized intense femtosecond laser pulses

    SciTech Connect

    Jahangiri, Fazel; Hashida, Masaki; Tokita, Shigeki; Sakabe, Shuji [Advanced Research Center for Beam Science, ICR, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan and Department of Physics, GSS, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-7501 (Japan); Nagashima, Takeshi; Hangyo, Masanori [Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan)

    2011-10-17

    We have observed directional elliptically polarized terahertz (THz) waves emitted from air plasma produced by circularly polarized femtosecond laser pulses. The spatial distribution of the THz waves shows that the radiation is strongly directed forward with a peak around the laser propagation direction. Measured THz power shows a square dependence on laser energy. We consider the parametric decay of laser light to R-waves in plasma in the presence of a spontaneous magnetic field as a possible explanation for the polarization, power dependence, and direction of the THz beam.

  20. Whispering-gallery-mode cavity for terahertz pulses

    E-print Network

    in a dielectric cylinder coupled by means of a dielectric slab waveguide. We observed repeti- tive cavity pulses of Electrical and Computer Engineering and Center for Laser and Photonics Research, Oklahoma State University-gallery-mode coupling into the cylinder. A coupled-mode theory derived for this cylindrical system and coupling

  1. Terahertz Kerr effect

    E-print Network

    Hoffmann, Matthias C.

    We have observed optical birefringence in liquids induced by single-cycle terahertz pulses with field strengths exceeding 100 kV/cm. The induced change in polarization is proportional to the square of the terahertz electric ...

  2. Simulation of Laser Pulse Driven Terahertz Generation in Inhomogeneous Plasmas

    NASA Astrophysics Data System (ADS)

    Miao, Chenlong; Palastro, John; Antonsen, Thomas

    2014-10-01

    Intense, short laser pulses propagating through plasma generate THz radiation. Full format PIC simulations and theoretical analysis are conducted to investigate two mechanisms of ponderomotively driven THz radiation: transition radiation, and slow wave phase matching enabled by corrugated plasma channels. The first mechanism occurs as a laser pulse crosses a plasma boundary and is analogous to transition radiation emitted by charged particle beams. The THz radiation resulting from this transition radiation mechanism (TRM) is characterized by conical emission and a broad spectrum with the maximum frequency occurring near the plasma frequency. The second mechanism occurs in axially periodic plasma channels. These channels support electromagnetic modes with slow wave (Floquet-type) dispersion, which can be phase matched to the ponderomotive current. The slow wave phase-matched radiation (SWPM) is characterized by lateral emission and a coherent spectrum with sharp modes at frequencies associated with the channel. Supported by US DoE.

  3. Terahertz imaging of excised oral cancer at frozen temperature

    PubMed Central

    Sim, Yookyeong Carolyn; Park, Jae Yeon; Ahn, Kang-Min; Park, Chansik; Son, Joo-Hiuk

    2013-01-01

    The feasibility of terahertz (THz) imaging at frozen temperature for the clinical application of oral cancer detection was investigated by analyzing seven oral tissues resected from four patients. The size, shape, and internal position of the oral cancers were mapped by THz radiation in the frequency range of 0.2–1.2 THz at ?20 °C and 20 °C, and compared with those identified in the histological examination. THz imaging of frozen tissue was found to offer greater sensitivity in distinguishing cancerous areas from surrounding tissue and a larger THz-frequency spectral difference between the oral cancer and normal mucosa than room-temperature THz imaging. A cancerous tumor hidden inside tissue was also detected using this method by observing the THz temporal domain waveform. The histological analysis showed that these findings resulted from cell structure deformations involving the invasion of oral tumor and neoplastic transformations of mucous cells. Therefore, a cytological approach using THz radiation at a frozen temperature might be applied to detect oral cancer. PMID:24010003

  4. Photonic crystal Fano laser: terahertz modulation and ultrashort pulse generation.

    PubMed

    Mork, J; Chen, Y; Heuck, M

    2014-10-17

    We suggest and analyze a laser with a mirror realized by Fano interference between a waveguide and a nanocavity. For small-amplitude modulation of the nanocavity resonance, the laser can be modulated at frequencies exceeding 1 THz, not being limited by carrier dynamics as for conventional lasers. For larger modulation, a transition from pure frequency modulation to the generation of ultrashort pulses is observed. The laser dynamics is analyzed by generalizing the field equation for conventional lasers to account for a dynamical mirror, described by coupled mode theory. PMID:25361259

  5. Terahertz spectroscopy of liver cirrhosis: investigating the origin of contrast

    NASA Astrophysics Data System (ADS)

    Sy, Stanley; Huang, Shengyang; Wang, Yi-Xiang J.; Yu, Jun; Ahuja, Anil T.; Zhang, Yuan-ting; Pickwell-MacPherson, Emma

    2010-12-01

    We have previously demonstrated that terahertz pulsed imaging is able to distinguish between rat tissues from different healthy organs. In this paper we report our measurements of healthy and cirrhotic liver tissues using terahertz reflection spectroscopy. The water content of the fresh tissue samples was also measured in order to investigate the correlations between the terahertz properties, water content, structural changes and cirrhosis. Finally, the samples were fixed in formalin to determine whether water was the sole source of image contrast in this study. We found that the cirrhotic tissue had a higher water content and absorption coefficient than the normal tissue and that even after formalin fixing there were significant differences between the normal and cirrhotic tissues' terahertz properties. Our results show that terahertz pulsed imaging can distinguish between healthy and diseased tissue due to differences in absorption originating from both water content and tissue structure.

  6. Bursts of Terahertz Radiation from Large-Scale Plasmas Irradiated by Relativistic Picosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Liao, G. Q.; Li, Y. T.; Li, C.; Su, L. N.; Zheng, Y.; Liu, M.; Wang, W. M.; Hu, Z. D.; Yan, W. C.; Dunn, J.; Nilsen, J.; Hunter, J.; Liu, Y.; Wang, X.; Chen, L. M.; Ma, J. L.; Lu, X.; Jin, Z.; Kodama, R.; Sheng, Z. M.; Zhang, J.

    2015-06-01

    Powerful terahertz (THz) radiation is observed from large-scale underdense preplasmas in front of a solid target irradiated obliquely with picosecond relativistic intense laser pulses. The radiation covers an extremely broad spectrum with about 70% of its energy located in the high frequency regime over 10 THz. The pulse energy of the radiation is found to be above 1 0 0 ? J per steradian in the laser specular direction at an optimal preplasma scale length around 40 - 50 ? m . Particle-in-cell simulations indicate that the radiation is mainly produced by linear mode conversion from electron plasma waves, which are excited successively via stimulated Raman scattering instability and self-modulated laser wakefields during the laser propagation in the preplasma. This radiation can be used not only as a powerful source for applications, but also as a unique diagnostic of parametric instabilities of laser propagation in plasmas.

  7. Terahertz polariton propagation in patterned materials.

    PubMed

    Stoyanov, Nikolay S; Ward, David W; Feurer, Thomas; Nelson, Keith A

    2002-10-01

    Generation and control of pulsed terahertz-frequency radiation have received extensive attention, with applications in terahertz spectroscopy, imaging and ultrahigh-bandwidth electro-optic signal processing. Terahertz 'polaritonics', in which terahertz lattice waves called phonon-polaritons are generated, manipulated and visualized with femtosecond optical pulses, offers prospects for an integrated solid-state platform for terahertz signal generation and guidance. Here, we extend terahertz polaritonics methods to patterned structures. We demonstrate femtosecond laser fabrication of polaritonic waveguide structures in lithium tantalate and lithium niobate crystals, and illustrate polariton focusing into, and propagation within, the fabricated waveguide structures. We also demonstrate a 90 degrees turn within a structure consisting of two waveguides and a reflecting face, as well as a structure consisting of splitting and recombining elements that can be used as a terahertz Mach-Zehnder interferometer. The structures permit integrated terahertz signal generation, propagation through waveguide-based devices, and readout within a single solid-state platform. PMID:12618821

  8. Speckle pattern of the images of objects exposed to monochromatic coherent terahertz radiation

    SciTech Connect

    Vinokurov, Nikolai A; Knyazev, Boris A; Kulipanov, Gennadii N [G.I. Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation); Dem'yanenko, M A; Esaev, D G [A.V.Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation); Chashchina, O I; Cherkasskii, Valerii S [Novosibirsk State University, Novosibirsk (Russian Federation)

    2009-05-31

    By using a free electron laser and a microbolometer array, real-time images are recorded for the first time in the terahertz range at the rate of up to 90 frames per second. In the case of diffusive illumination of objects by coherent monochromatic radiation, the images consist of speckles. The study of the statistical properties of speckle patterns shows that they are quite accurately described by the theory developed for speckles in the visible range. By averaging a set of images with the help of a rotating scatterer during the exposure time of a frame (20 ms) and by summing statistically independent speckle patterns of many frames, images of the acceptable quality are obtained. The possibilities of terahertz speckle photography and speckle interferometry are discussed. (terahertz radiation)

  9. Elimination of Fresnel Reflection Boundary Effects and Beam Steering in Pulsed Terahertz Computed Tomography

    NASA Astrophysics Data System (ADS)

    Mukherjee, Suman; Federici, John; Lopes, Paulo; Cabral, Miguel

    2013-09-01

    For the past few decades there has been tremendous innovation and development of Terahertz (THz) science and imaging. In particular, the technique of 3-D computed tomography has been adapted from the X-Ray to the THz range. However, the finite refractive index of materials in the THz range can severally refract probing THz beams during the acquisition of tomography data. Due to Fresnel reflection power losses at the boundaries as well as steering of the THz beam through the sample, refractive effects lead to anomalously high local attenuation coefficients near the material boundaries of a reconstructed image. These boundary phenomena can dominate the reconstructed THz-CT images making it difficult to distinguish structural defect(s) inside the material. In this paper an algorithm has been developed to remove the effects of refraction in THz-CT reconstructed images. The algorithm is successfully implemented on cylindrical shaped objects.

  10. Arbitrary terahertz pulse shaping via optical rectification in fanned-out periodically-poled lithium niobate

    NASA Astrophysics Data System (ADS)

    Lee, Yun-Shik; Danielson, J. R.; Amer, N.

    2007-02-01

    We demonstrate a novel terahertz (THz) pulse shaping technique, which guarantees ultimate flexibility for arbitrary THz pulse generation. The THz pulse shaper consists of a fanned-out periodically-poled lithium niobate (FO-PPLN) crystal-the domain width of the FO-PPLN crystal varies continuously across the lateral direction-, a spatial mask, and a spherical mirror. Optical pulses are line-focused on the FO-PPLN crystal to generate spatially separated multi-frequency components of THz pulses. The spatial mask is placed in front of the FO-PPLN crystal in order to manipulate the spatial pattern of the incident optical beam, thus to control the amplitudes of the spatially dispersed THz frequency components. Spectral resolution of this method is determined by FO-PPLN bandwidth and mask resolution: estimated practical resolution is ~0.01 THz for 1 THz bandwidth. After the spherical mirror assembles the various frequencies into a single collimated beam, a shaped THz pulse can be obtained, with the pulse shape determined by the Fourier transform of the pattern transferred by the mask. As a proof-of-principle experiment, we measured THz waveforms using metal masks. The experiment was performed using 800-nm, 100-fs pulses from a 1-kHz Ti:sapphire regenerative amplifier. We used a 5-mm long FO-PPLN sample (width = 10 mm, height = 0.5 mm) continuously tunable from 0.6 to 1.5 THz. We tested the metal masks of three different spatial patterns: low-pass filter, high-pass filter, and double slit. The experimental results show that the THz waveforms are determined by the spatial patterns of the masks.

  11. Single-shot measurement of the spectral envelope of broad-bandwidth terahertz pulses from femtosecond electron bunches

    SciTech Connect

    van Tilborg, Jeroen; Toth, Csaba; Matlis, Nicholas; Plateau, Guillaume; Leemans, Wim

    2011-06-17

    We present a new approach (demonstrated experimentally and through modeling) to characterize the spectral envelope of a terahertz (THz) pulse in a single shot. The coherent THz pulse is produced by a femtosecond electron bunch and contains information on the bunch duration. The technique, involving a single low-power laser probe pulse, is an extension of the conventional spectral encoding method (limited in time resolution to hundreds of femtoseconds) into a regime only limited in resolution by the laser pulse length (tens of femtoseconds). While only the bunch duration is retrieved (and not the exact charge profile), such a measurement provides a useful and critical parameter for optimization of the electron accelerator.

  12. Diffraction mode terahertz tomography

    DOEpatents

    Ferguson, Bradley; Wang, Shaohong; Zhang, Xi-Cheng

    2006-10-31

    A method of obtaining a series of images of a three-dimensional object. The method includes the steps of transmitting pulsed terahertz (THz) radiation through the entire object from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three-dimensional object using the detected changes in the transmitted THz radiation. The THz radiation is transmitted through the object as a two-dimensional array of parallel rays. The optical detection is an array of detectors such as a CCD sensor.

  13. Terahertz Imaging of cyclotron emission from quantum Hall conductors

    Microsoft Academic Search

    Susumu Komiyama

    2006-01-01

    Microscopy of extremely weak terahertz (THz) waves via photon-counting method is reported. A quantum-dot photon detector [1] is incorporated into a scanning terahertz microscope [2]. By using a quantum Hall detector [3] as well, measurements cover the intensity dynamic range more than five orders of magnitude. The minimum intensity reaches as lo as 10ˆ-21^ watt (one photon per one second).

  14. DEVELOPMENT OF A 4 K STIRLING-TYPE PULSE TUBE CRYOCOOLER FOR A MOBILE TERAHERTZ DETECTION SYSTEM

    SciTech Connect

    Bradley, P. E.; Gerecht, E.; Radebaugh, R. [National Institute of Standards and Technology, Boulder, Colorado, 80305 (United States); Garaway, I. [National Institute of Standards and Technology, Boulder, Colorado, 80305 (United States); Technion-Israel Institute of Technology, Haifa (Israel)

    2010-04-09

    We discuss in this paper the design and development of a 4 K Stirling-type pulse tube cryocooler for a mobile terahertz detection system. This system integrates new heterodyne detector technology at terahertz frequencies with advancements of Stirling-type pulse tube technology that brings the advent of cooled detector sensitivities in a mobile, compact, and long duration operation system without degradation of sensitivity. To achieve this goal we reduced overall system size, input power, and temperature fluctuations and mechanical vibrations in order to maintain the detector sensitivity. The Stirling-type pulse tube cryocooler developed for this system is a hybrid design employing a He-4 pulse-tube cryocooler operating at 60 Hz and 2.5 MPa average pressure that precools a He-3 pulse tube cryocooler operating at 30 Hz and 1.0 MPa average pressure to achieve 4 K cooling for the terahertz receiver. The He-4 cryocooler employs stainless steel mesh regenerators for the first stage and ErPr spheres for the second stage, while the He-3 cryocooler employs stainless mesh for the first stage and ErPr spheres for the second stage with a layered rare-earth third stage regenerator. Design details and cooler performance goals are discussed.

  15. Development of a 4 K Stirling-Type Pulse Tube Cryocooler for a Mobile Terahertz Detection System

    NASA Astrophysics Data System (ADS)

    Bradley, P. E.; Gerecht, E.; Radebaugh, R.; Garaway, I.

    2010-04-01

    We discuss in this paper the design and development of a 4 K Stirling-type pulse tube cryocooler for a mobile terahertz detection system. This system integrates new heterodyne detector technology at terahertz frequencies with advancements of Stirling-type pulse tube technology that brings the advent of cooled detector sensitivities in a mobile, compact, and long duration operation system without degradation of sensitivity. To achieve this goal we reduced overall system size, input power, and temperature fluctuations and mechanical vibrations in order to maintain the detector sensitivity. The Stirling-type pulse tube cryocooler developed for this system is a hybrid design employing a He-4 pulse-tube cryocooler operating at 60 Hz and 2.5 MPa average pressure that precools a He-3 pulse tube cryocooler operating at 30 Hz and 1.0 MPa average pressure to achieve 4 K cooling for the terahertz receiver. The He-4 cryocooler employs stainless steel mesh regenerators for the first stage and ErPr spheres for the second stage, while the He-3 cryocooler employs stainless mesh for the first stage and ErPr spheres for the second stage with a layered rare-earth third stage regenerator. Design details and cooler performance goals are discussed.

  16. High-Power Terahertz Source Opens the Door for Full-Field Video-Rate Terahertz Imaging

    SciTech Connect

    Klopf, John; Coppinger, Matthew; Sustersic, Nathan; Kolodzey, James; Williams, Gwyn

    2008-07-01

    Terahertz (THz) light, at wavelengths between electronics and photonics, promises novel imaging applications such as revealing epithelial carcinomas 1 or identifying objects hidden in clothing and packages 2. But THz imaging has been little exploited because generating source power high enough for adequate signal detection is difficult -- and because even more power is needed for most applications that require detecting scattered light rather than light transmitted straight through the target 3. The ability to image movement in real time would aid medicine by allowing the rapid viewing of multiple perspectives and larger areas for detecting skin cancer. Real-time imaging is also essential for the efficient detection, with sufficient resolution, of hidden, and possibly moving, objects. Here, in work building on our earlier demonstration that relativistic electrons can yield tens of watts of broadband THz light 4, 5, we report the first video-rate THz movies of objects observed in real t

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

    SciTech Connect

    Li, Jiang; Shi, Junkai; Xu, Baozhong; Xing, Qirong; Wang, Chingyue [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); Chai, Lu, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn; Liu, Bowen; Hu, Minglie; Li, Yanfeng, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); MOEMS Key Laboratory (Ministry of Education), Tianjin University, Tianjin 300072 (China); Fedotov, Andrey B. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Zheltikov, Aleksei M. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843 (United States)

    2014-01-20

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

  18. Terahertz technology: a boon to tablet analysis.

    PubMed

    Wagh, M P; Sonawane, Y H; Joshi, O U

    2009-05-01

    The terahertz gap has a frequency ranges from approximately 0.3 THz to approximately 10 THz in the electromagnetic spectrum which is in between microwave and infrared. The terahertz radiations are invisible to naked eye. In comparison with x-ray they are intrinsically safe, non-destructive and non-invasive. Terahertz spectroscopy enables 3D imaging of structures and materials, and the measurement of the unique spectral fingerprints of chemical and physical forms. Terahertz radiations are produced by a dendrimer based high power terahertz source and spectroscopy technologies. It resolves many of the questions left unanswered by complementary techniques, such as optical imaging, Raman and infrared spectra. In the pharmaceutical industries it enables nondestructive, internal, chemical analysis of tablets, capsules, and other dosage forms. Tablet coatings are a major factor in drug bioavailability. Therefore tablet coatings integrity and uniformity are of crucial importance to quality. Terahertz imaging gives an unparalleled certainty about the integrity of tablet coatings and the matrix performance of tablet cores. This article demonstrates the potential of terahertz pulse imaging for the analysis of tablet coating thickness by illustrating the technique on tablets. PMID:20490288

  19. Terahertz Technology: A Boon to Tablet Analysis

    PubMed Central

    Wagh, M. P.; Sonawane, Y. H.; Joshi, O. U.

    2009-01-01

    The terahertz gap has a frequency ranges from ?0.3 THz to ?10 THz in the electromagnetic spectrum which is in between microwave and infrared. The terahertz radiations are invisible to naked eye. In comparison with x-ray they are intrinsically safe, non-destructive and non-invasive. Terahertz spectroscopy enables 3D imaging of structures and materials, and the measurement of the unique spectral fingerprints of chemical and physical forms. Terahertz radiations are produced by a dendrimer based high power terahertz source and spectroscopy technologies. It resolves many of the questions left unanswered by complementary techniques, such as optical imaging, Raman and infrared spectra. In the pharmaceutical industries it enables nondestructive, internal, chemical analysis of tablets, capsules, and other dosage forms. Tablet coatings are a major factor in drug bioavailability. Therefore tablet coatings integrity and uniformity are of crucial importance to quality. Terahertz imaging gives an unparalleled certainty about the integrity of tablet coatings and the matrix performance of tablet cores. This article demonstrates the potential of terahertz pulse imaging for the analysis of tablet coating thickness by illustrating the technique on tablets. PMID:20490288

  20. Monolithic focal plane arrays for terahertz active spectroscopic imaging: an experimental study

    NASA Astrophysics Data System (ADS)

    Ortolani, Michele; Casini, Roberto; Chiarello, Fabio; Cibella, Sara; Di Gaspare, Alessandra; Evangelisti, Florestano; Foglietti, Vittorio; Giovine, Ennio; Leoni, Roberto; Torrioli, Guido; Tredicucci, Alessandro; Vitiello, Miriam S.; Scamarcio, Gaetano

    2011-01-01

    Imaging arrays of direct detectors in the 0.5-5 THz range are being experimentally developed. Terahertz active imaging with amplitude-modulated quantum cascade lasers emitting at 2.5 and 4.4 THz performed by using an antenna-coupled superconducting microbolometer. We then present two room-temperature terahertz detector technologies compatible with monolithic arrays: i) GaAs Schottky diodes with air-bridge sub-micron anodes; ii) high electron mobility transistors with sub-micron Schottky gate. Performances, requirements and fabrication costs of the different detector technologies are compared.

  1. Terahertz measurement and imaging detection of delamination and water intrusion in ground based radome panels

    NASA Astrophysics Data System (ADS)

    Zimdars, David; White, Jeffrey; Sucha, Gregg; Fichter, G.; Stuk, G.; Megdanoff, C.; Chernovsky, A.; Williamson, S. L.

    2007-04-01

    We demonstrate the location and identification of delaminations and water intrusion in advanced composite materials used in ground based radome panels, shelters and towers using time domain terahertz imaging. Water has a very high absorption in the THz spectral region in comparison to polymer foam and fiberglass, so the method is very sensitive to water intrusion. The sub-picosecond near single cycle electromagnetic images enabled identification of delaminations of the fiberglass shell and foam. We report a novel time domain terahertz non-destructive evaluation control system, which is suitably portable for applications such as field examination of radome composites.

  2. Coherent detection of multicycle terahertz pulses generated in periodically inverted GaAs structures

    NASA Astrophysics Data System (ADS)

    Lee, Yun-Shik; Hurlbut, W. C.; Vodopyanov, K. L.; Fejer, M. M.; Kozlov, V. G.

    2007-02-01

    Narrow-band, multi-cycle terahertz (THz) pulses have been generated in the pre-engineered domain structure of periodically-poled lithium niobate (PPLN) crystals. The mechanism for THz generation is quasi-phase-matching (QPM) optical rectification. Recently, THz generation of high conversion efficiency in a new material, QPM GaAs, were demonstrated using mid-IR femtosecond pulses. GaAs has several advantages for QPM THz wave generation, as compared to PPLN. First, it is highly transparent at THz frequencies (absorption coefficient below 1.5 THz < 1 cm -1). Second, the mismatch between the optical group velocity and THz phase velocity is much smaller: the corresponding group (ng) and refractive (n) indices are ng=3.431 at 2?m and n=3.61 at 1 THz. In this work, we report on generation of THz wave packets in three different types of QPM GaAs, combined with their coherent detection using two-color THz time-domain spectroscopy. The QPM GaAs structures are optically-contacted GaAs, diffusion-bonded GaAs, and all-epitaxially-grown orientation patterned GaAs. The QPM optical rectification in GaAs is a nonresonant mechanism, as opposed to widely used photoconductive antenna technique in GaAs, where THz radiation is produced via ultrafast charge transport caused by photoexcitation with femtosecond laser pulses of the near-IR range. In order to avoid linear and two-photon absorption in GaAs, we use 2?m femtosecond pulses to generate THz pulses. We measure the THz waveforms via electro-optic sampling in ZnTe using 0.8?m probe pulses. The corresponding power spectra are also measured by a THz Michelson interferometer. Frequency tunability in the range 0.8-3 THz is achieved with several structure periods.

  3. Terahertz standoff imaging testbed design and performance for concealed weapon and device identification model development

    NASA Astrophysics Data System (ADS)

    Franck, Charmaine C.; Lee, Dave; Espinola, Richard L.; Murrill, Steven R.; Jacobs, Eddie L.; Griffin, Steve T.; Petkie, Douglas T.; Reynolds, Joe

    2007-04-01

    This paper describes the design and performance of the U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate's (NVESD), active 0.640-THz imaging testbed, developed in support of the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. The laboratory measurements and standoff images were acquired during the development of a NVESD and Army Research Laboratory terahertz imaging performance model. The imaging testbed is based on a 12-inch-diameter Off-Axis Elliptical (OAE) mirror designed with one focal length at 1 m and the other at 10 m. This paper will describe the design considerations of the OAE-mirror, dual-capability, active imaging testbed, as well as measurement/imaging results used to further develop the model.

  4. Toward remote sensing with broadband terahertz waves

    NASA Astrophysics Data System (ADS)

    Clough, Benjamin W.

    Terahertz electromagnetic waves, defined as the frequency region between 0.1 and 10 terahertz on the electromagnetic spectrum, have demonstrated remarkable usefulness for imaging and chemical identification with the ability to penetrate many optically opaque barriers. Photon energies at these frequencies are relatively small (meV), which means the radiation is non-ionizing and therefore considered biologically innocuous. With the growing list of applications and demand for terahertz technology, there is a need to develop innovative terahertz sources and detectors that can overcome existing limitations in power, bandwidth, and operating range. Although terahertz radiation has demonstrated unique and exceptional abilities, it has also presented several fundamental challenges. Most notably, the water vapor absorption of terahertz waves in air at habitable altitudes is greater than 100 dB/km. There is an immediate push to utilize the material and vapor identification abilities of terahertz radiation, while extending the effective distances over which the technology can be used. Remote terahertz detection, until recently, was thought to be impossible due to the high water content in the atmosphere, limited signal collection geometries, and solid state materials necessary for generation and detection. This dissertation focuses on laser air-photonics used for sensing short pulses of electromagnetic radiation. Through the ionization process, the very air that we breathe is capable of generating terahertz field strengths greater than 1 MV/cm, useful bandwidths over 100 terahertz, and highly directional emission patterns. Following ionization and plasma formation, the emitted plasma acoustics or fluorescence can be modulated by an external field to serve as omnidirectional, broadband, electromagnetic sensor. A deeper understanding of terahertz wave-plasma interaction is used to develop methods for retrieving coherent terahertz wave information that can be encoded into plasma acoustic and fluorescence wave emission; the ultimate goal aimed at overcoming fundamental limitations of the current terahertz technology. A synthesized bichromatic field-induced laser plasma is used to study effects of electron velocity redistribution inside the plasma filament, and a technique for obtaining a direct correlation between the terahertz field and the plasma acoustic or fluorescence emission is engineered. This dissertation presents significant advances in terahertz air photonics that help to close the "THz gap" once existing between electronic and optical frequencies, and the acoustic and fluorescence detection methodologies developed provide promising new avenues for extending the useful range of terahertz wave technology.

  5. Terahertz beam steering and frequency tuning by using the spatial dispersion of ultrafast laser pulses.

    PubMed

    Maki, Ken-ichiro; Otani, Chiko

    2008-07-01

    We demonstrate a terahertz (THz) beam steering method using difference frequency generation that is based on the principle of phased array antennas. A strip-line photoconductive antenna was illuminated by two spatially dispersed beams produced from an ultrafast laser. THz radiation with a bandwidth of 65 GHz was generated from the overlapping area of the two beams, between which the frequency difference was approximately constant. We confirmed that the THz beam can be steered by tilting one of the incident pump beams so as to change their relative phase relation. The steering range of the THz beam was 29 degrees when the angle between the incident pump beams was only varied within a range of 0.155 degrees, that is, 187 times less. In addition, by laterally shifting one of the pump beams, the frequency of the THz radiation could be tuned from 0.3 to 1.7 THz. This technique can be applied to high-speed terahertz imaging and spectroscopy systems. PMID:18607423

  6. Pulsed terahertz spectroscopy of DNA, bovine serum albumin and collagen between 0.1 and 2.0 THz

    Microsoft Academic Search

    A. G. Markelz; A. Roitberg; E. J. Heilweil

    2000-01-01

    We report the first use of pulsed terahertz spectroscopy to examine low-frequency collective vibrational modes of biomolecules. Broadband absorption increasing with frequency was observed for lyophilized powder samples of calf thymus DNA, bovine serum albumin and collagen in the 0.06–2.00 THz (2–67 cm?1) frequency range, suggesting that a large number of the low-frequency collective modes for these systems are IR

  7. Terahertz Laser Based Standoff Imaging System Kurt J. Linden, William R. Neal

    E-print Network

    Massachusetts at Lowell, University of

    _gatesman@uml.edu, andriy_danylov@student.uml.edu Abstract Definition and design of a terahertz standoff imag- ing system materials such as clothing, paper, metals, or a human body. Beyond the far-infrared spectral region however explosive materials), but materials such as clothing, paper, and most packaging materials are relatively

  8. CARS Imaging of Periodically Poled Lithium Niobate Using Terahertz-Frequency Phonon Modes

    Microsoft Academic Search

    Jun-ichi Shikata; Kazuhisa Endo; A. Nawahara; S. Nagano; H. Ito

    2007-01-01

    Coherent anti-stokes Raman scattering (CARS) via terahertz-frequency optical phonon modes was successfully applied to the imaging of periodically poled lithium niobate crystals. Using spectral changes in the E-mode (50-1100 cm-1 = 1.5-33 THz), periodic structures of ferroelectric domains (period: 20 mum) were clearly mapped with CARS signals.

  9. Terahertz imaging of subjects with concealed weapons Jason C. Dickinson*a

    E-print Network

    Massachusetts at Lowell, University of

    Terahertz imaging of subjects with concealed weapons Jason C. Dickinson*a , Thomas M. Goyettea for concealed weapons detection, the Submillimeter-Wave Technology Laboratory (STL) at the University-the-fly processing. Imagery at 1.56THz of human subjects with concealed weapons are presented and discussed

  10. Non-destructive terahertz imaging of illicit drugs using spectral fingerprints

    Microsoft Academic Search

    Kodo Kawase; Yuichi Ogawa; Yuuki Watanabe; Hiroyuki Inoue

    2003-01-01

    The absence of non-destructive inspection techniques for illicit drugs hidden in mail envelopes has resulted in such drugs being smuggled across international borders freely. We have developed a novel basic technology for terahertz imaging, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. The spatial distributions of the targets are obtained from

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

    PubMed Central

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

    2015-01-01

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

  12. Mine field detection and identification using terahertz spectroscopic imaging

    NASA Astrophysics Data System (ADS)

    Osiander, Robert; Miragliotta, Joseph A.; Jiang, Zhiping; Xu, Jingzhou; Zhang, Xi-Cheng

    2003-08-01

    The spatial, temporal, and spectroscopic characteristics associated with pulsed THz (100 GHz - 70 THz) radiation provide this emerging technology with the potential for reliable identification of buried objects such as non-metallic landmines. With a suitable integration of these attributes, one can envision a THz detection platform that provides: (1) accurate identification of buried objects, and (2) a source-to-sample working distance that is sufficient for remote sensing applications. In our preliminary laboratory studies, we have demonstrated the detection capabilities of THz radiation by imaging a small rubber object embedded in a moist, sand-like soil. Despite the significant attenuation of the THz radiation via water absorption and particle scattering, the initial transmission results showed that pulsed THz imaging could identify the non-metallic object when buried in a few inches of soil. The sub-millimeter resolution observed in our THz images illustrates the potential to discriminate landmines from other buried objects. Finally, THz calculations and measurements determined that our current THz source and detector has sufficient SNR to detect a buried object to a depth of 6 inches in moist sand.

  13. Dielectric Covered Planar Antennas at Submillimeter Wavelengths for Terahertz Imaging

    NASA Technical Reports Server (NTRS)

    Chattopadhyay, Goutam; Gill, John J.; Skalare, Anders; Lee, Choonsup; Llombart, Nuria; Siegel, Peter H.

    2011-01-01

    Most optical systems require antennas with directive patterns. This means that the physical area of the antenna will be large in terms of the wavelength. When non-cooled systems are used, the losses of microstrip or coplanar waveguide lines impede the use of standard patch or slot antennas for a large number of elements in a phased array format. Traditionally, this problem has been solved by using silicon lenses. However, if an array of such highly directive antennas is to be used for imaging applications, the fabrication of many closely spaced lenses becomes a problem. Moreover, planar antennas are usually fed by microstrip or coplanar waveguides while the mixer or the detector elements (usually Schottky diodes) are coupled in a waveguide environment. The coupling between the antenna and the detector/ mixer can be a fabrication challenge in an imaging array at submillimeter wavelengths. Antennas excited by a waveguide (TE10) mode makes use of dielectric superlayers to increase the directivity. These antennas create a kind of Fabry- Perot cavity between the ground plane and the first layer of dielectric. In reality, the antenna operates as a leaky wave mode where a leaky wave pole propagates along the cavity while it radiates. Thanks to this pole, the directivity of a small antenna is considerably enhanced. The antenna consists of a waveguide feed, which can be coupled to a mixer or detector such as a Schottky diode via a standard probe design. The waveguide is loaded with a double-slot iris to perform an impedance match and to suppress undesired modes that can propagate on the cavity. On top of the slot there is an air cavity and on top, a small portion of a hemispherical lens. The fractional bandwidth of such antennas is around 10 percent, which is good enough for heterodyne imaging applications.The new geometry makes use of a silicon lens instead of dielectric quarter wavelength substrates. This design presents several advantages when used in the submillimeter-wave and terahertz bands: a) Antenna fabrication compatible with lithographic techniques. b) Much simpler fabrication of the lens. c) A simple quarter-wavelength matching layer of the lens will be more efficient if a smaller portion of the lens is used. d) The directivity is given by the lens diameter instead of the leaky pole (the bandwidth will not depend anymore on the directivity but just on the initial cavity). The feed is a standard waveguide, which is compatible with proven Schottky diode mixer/detector technologies. The development of such technology will benefit applications where submillimeter- wave heterodyne array designs are required. The main fields are national security, planetary exploration, and biomedicine. For national security, wideband submillimeter radars could be an effective tool for the standoff detection of hidden weapons or bombs concealed by clothing or packaging. In the field of planetary exploration, wideband submillimeter radars can be used as a spectrometer to detect trace concentrations of chemicals in atmospheres that are too cold to rely on thermal imaging techniques. In biomedicine, an imaging heterodyne system could be helpful in detecting skin diseases.

  14. Effect of preformed plasma on terahertz-wave emission from the plasma generated by two-color laser pulses

    SciTech Connect

    Minami, Yasuo; Nakajima, Makoto; Suemoto, Tohru [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba, 277-8581 (Japan)

    2011-02-15

    We introduced a weak prepulse 0-2 ns before the main pulse in the formation of a terahertz (THz) wave in air plasma by laser pulses composed of fundamental and second-harmonic waves. The prepulse suppressed the THz wave generated by the main pulse. We analyzed the suppression factor as a function of the time interval between the prepulse and the main pulse and found that the THz wave from the main pulse decreases immediately after the prepulse, recovers partially within several hundred picoseconds, and then recovers slowly. This suppression is attributed to the dense plasma, which absorbs and screens the generated THz wave, since the relaxation time is close to the lifetime of the fluorescence from the plasma. The results support the idea that the major mechanism of THz wave generation is explained by the plasma current model.

  15. Femtosecond pulse imaging: ultrafast optical oscilloscope

    E-print Network

    Fainman, Yeshaiahu

    waves of a shaped femtosecond pulse are mixed with those of a transform-limited pulse to generateFemtosecond pulse imaging: ultrafast optical oscilloscope P. C. Sun, Y. T. Mazurenko,* and Y 12, 1996 A nonlinear optical processor that is capable of real-time conversion of a femtosecond pulse

  16. High-energy terahertz pulses from organic crystals: DAST and DSTMS pumped at Ti:sapphire wavelength.

    PubMed

    Monoszlai, B; Vicario, C; Jazbinsek, M; Hauri, C P

    2013-12-01

    High-energy terahertz pulses are produced by optical rectification (OR) in organic crystals 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) and 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS) by a Ti:sapphire amplifier system with 0.8 ?m central wavelength. The simple scheme provides broadband spectra between 1 and 5 THz, when pumped by a collimated 60 fs near-IR pump pulse, and it is scalable in energy. Fluence-dependent conversion efficiency and damage threshold are reported, as well as optimized OR at visible wavelengths. PMID:24281521

  17. Numerical and experimental studies of mechanisms underlying the effect of pulsed broadband terahertz radiation on nerve cells

    NASA Astrophysics Data System (ADS)

    Duka, M. V.; Dvoretskaya, L. N.; Babelkin, N. S.; Khodzitskii, M. K.; Chivilikhin, S. A.; Smolyanskaya, O. A.

    2014-08-01

    We have studied the mechanisms underlying the effect of pulsed broadband terahertz radiation on the growth of neurites of sensory ganglia using a comparative analysis of measured reflection spectra of ganglion neurites (in the frequency range 0.1 – 2.0 THz) and spectra obtained by numerical simulation with CST Microwave Studio. The observed changes are shown to be mainly due to pulse energy absorption in the ganglion neurites. Of particular interest are the observed single resonance frequencies related to resonance size effects, which can be used to irradiate ganglia in order to activate their growth.

  18. Quasi-single-cycle terahertz pulses based on broadband-phase-matched difference-frequency generation in second-order nonlinear medium: high output powers and conversion efficiencies

    Microsoft Academic Search

    Yujie J. Ding

    2004-01-01

    Consider a second-order nonlinear medium in which perfect phase-matching can be achieved at one particular output wavelength for the process of the terahertz generation from a train of ultrafast laser pulses based on difference-frequency generation. We assume that the coherence lengths for the terahertz generation are sufficiently long within a wide bandwidth around this perfect phase-matching wavelength due to a

  19. Maximizing terahertz pulse amplitude from low temperature gallium arsenide photo conductive semiconductor switch

    NASA Astrophysics Data System (ADS)

    Ray, Sampad

    An antenna radiates when a time rate of change of signal arrives at the structure from a generator, after travelling through a transmitting medium. THz radiation in a photoconductive semiconductor switches (PCSS) follows the same principles. Here the signal is produced by the photoconductive action, which travels through the bulk to the metallic contacts. In the simulation analysis, therefore, one needs to analyze the substrate with semiconductor code to characterize the generated pulse and then use Maxwell's equation solver for the antenna (contact) analysis. This is because of the unavailability of a comprehensive simulation code that can solve both Maxwell's and semiconductor equations in tandem. In this study, two different commercially available simulation codes were used to optimize the THZ radiation from a GaAs PCSS. Results show that the 50 X 50 microm PCSS material produces a central frequency of 1.75 Terahertz, and a pulse amplitude of approximately 0.22 A at an optimum bias voltage of 1100 Volts. The PCSS was illuminated for 350 fs with a 0.78 microm beam, 50 Mw/cm2 in intensity. The FWHM of the generated pulse 0.4 ps, and the rise time is 0.275 ps. In the antenna analysis, results show that the rectangular patch antenna had a maximum return loss (S11) of approximately -30 dB and had multiple resonant frequencies. The maximum S11 was achieved at 5.6845 THz. The directivity of the main lobe was found out to be 6.2 dB with an angular width of 36.9 degrees. The main lobe was directed at 148 degrees. The side lobes were found out to be -6.8 dB.

  20. Two-Dimensional Terahertz Imaging System Using Hot Electron Bolometer Technology

    Microsoft Academic Search

    Dazhen Gu; Eyal Gerecht; Fernando Rodriguez-Morales; Sigfrid Yngvesson

    2006-01-01

    We present first results with a two-dimensional (2D) scanning terahertz passive heterodyne imaging system, currently under development. The imager is based on a phonon-cooled quasi-optically coupled hot electron bolometric (HEB) mixer integrated with an InP MMIC IF low-noise amplifier (LNA). A harmonic multiplier with an output power of about 250 piW is employed as the local oscillator (LO) source, resulting

  1. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...false Ultrasonic pulsed echo imaging system. 892.1560 Section...1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended...measure the duration of an acoustic pulse from the...

  2. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Intraband dynamics and terahertz emission in biased semiconductor superlattices coupled to double far-infrared pulses

    Microsoft Academic Search

    Min Li; Xian-Wu Mi

    2009-01-01

    This paper studies both the intraband polarization and terahertz emission of a semiconductor superlattice in combined dc and ac electric fields by using the superposition of two identical time delayed and phase shifted optical pulses. By adjusting the delay between these two optical pulses, our results show that the intraband polarization is sensitive to the time delay. The peak values

  3. Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances

    NASA Astrophysics Data System (ADS)

    Tuniz, Alessandro; Kaltenecker, Korbinian J.; Fischer, Bernd M.; Walther, Markus; Fleming, Simon C.; Argyros, Alexander; Kuhlmey, Boris T.

    2013-10-01

    Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells.

  4. Remote generation of high-energy terahertz pulses from two-color femtosecond laser filamentation in air

    SciTech Connect

    Wang, T.-J.; Daigle, J.-F.; Yuan, S.; Chin, S. L. [Centre d'Optique, Photonique et Laser (COPL) and Departement de physique, de genie physique et d'optique, Universite Laval, Quebec, Quebec G1V 0A6 (Canada); Theberge, F.; Chateauneuf, M.; Dubois, J.; Roy, G. [Defence Research and Development Canada-Valcartier, 2459 Pie-XI Boulevard North, Quebec, Quebec G3J 1X5 (Canada); Zeng, H. [State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062 (China)

    2011-05-15

    We experimentally investigated the dynamic behavior of remote terahertz (THz) generation from two-color femtosecond laser-induced filamentation in air. A record-high THz pulse energy of 570 nJ at frequency below 5.5 THz was measured by optimizing the pump parameters at a controllable remote distance of 16 m, while super-broadband THz (<300 THz) pulse energy was up to 2.8 {mu}J. A further energy-scaling possibility was proposed. By analyzing simultaneously the fluorescence from both neutral N{sub 2} and N{sub 2}{sup +} in the filament, we found that the enhancement of THz radiation was due principally to guiding of the weak second-harmonic pulse inside the filament of the first strong fundamental pulse.

  5. Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses

    PubMed Central

    Tokita, Shigeki; Sakabe, Shuji; Nagashima, Takeshi; Hashida, Masaki; Inoue, Shunsuke

    2015-01-01

    Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 1018?W/cm2 is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200?MV/m and 7?ps, respectively. PMID:25652694

  6. Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses.

    PubMed

    Tokita, Shigeki; Sakabe, Shuji; Nagashima, Takeshi; Hashida, Masaki; Inoue, Shunsuke

    2015-01-01

    Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 10(18)?W/cm(2) is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200?MV/m and 7?ps, respectively. PMID:25652694

  7. Pre-print of "1.56 Terahertz 2-frames per second standoff imaging" Goyette et al. OPTO 2008 in SPIE Photonics West, January 2008 Vol. 6893

    E-print Network

    Massachusetts at Lowell, University of

    : Terahertz, imaging, concealed, weapon 1. INTRODUCTION Heretofore a number of terahertz imaging systems have for the transmitter and receiver to view the subject. Special electronics were designed to allow heterodyne detection 3. Figure 1. Sample THz image of concealed weapon scan in a dB color scale. * Thomas

  8. Pulsed Interleaved Excitation Fluctuation Imaging

    PubMed Central

    Hendrix, Jelle; Schrimpf, Waldemar; Höller, Matthias; Lamb, Don C.

    2013-01-01

    Fluorescence fluctuation imaging is a powerful means to investigate dynamics, interactions, and stoichiometry of proteins inside living cells. Pulsed interleaved excitation (PIE) is the method of nanosecond alternating excitation with time-resolved detection and allows accurate, independent, and quasi-simultaneous determination of fluorescence intensities and lifetimes of different fluorophores. In this work, we combine pulsed interleaved excitation with fluctuation imaging methods (PIE-FI) such as raster image correlation spectroscopy (RICS) or number and brightness analysis (N&B). More specifically, we show that quantitative measurements of diffusion and molecular brightness of Venus fluorescent protein (FP) can be performed in solution with PIE-RICS and compare PIE-RICS with single-point PIE-FCS measurements. We discuss the advantages of cross-talk free dual-color PIE-RICS and illustrate its proficiency by quantitatively comparing two commonly used FP pairs for dual-color microscopy, eGFP/mCherry and mVenus/mCherry. For N&B analysis, we implement dead-time correction to the PIE-FI data analysis to allow accurate molecular brightness determination with PIE-NB. We then use PIE-NB to investigate the effect of eGFP tandem oligomerization on the intracellular maturation efficiency of the fluorophore. Finally, we explore the possibilities of using the available fluorescence lifetime information in PIE-FI experiments. We perform lifetime-based weighting of confocal images, allowing us to quantitatively determine molecular concentrations from 100 nM down to <30 pM with PIE-raster lifetime image correlation spectroscopy (RLICS). We use the fluorescence lifetime information to perform a robust dual-color lifetime-based FRET analysis of tandem fluorescent protein dimers. Lastly, we investigate the use of dual-color RLICS to resolve codiffusing FRET species from non-FRET species in cells. The enhanced capabilities and quantitative results provided by PIE-FI make it a powerful method that is broadly applicable to a large number of interesting biophysical studies. PMID:23972837

  9. Enhanced terahertz imaging system performance analysis and design tool for concealed weapon identification

    Microsoft Academic Search

    Steven R. Murrill; Charmaine C. Franck; Richard L. Espinola; Douglas T. Petkie; Frank C. De Lucia; Eddie L. Jacobs

    2011-01-01

    The U.S. Army Research Laboratory (ARL) and the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) have developed a terahertz-band imaging system performance model\\/tool for detection and identification of concealed weaponry. The details of the MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation,

  10. Terahertz imaging of inhomogeneous electrodynamics in single-layer graphene embedded in dielectrics

    NASA Astrophysics Data System (ADS)

    Paul, M. J.; Tomaino, J. L.; Kevek, J. W.; DeBorde, T.; Thompson, Z. J.; Minot, E. D.; Lee, Yun-Shik

    2012-08-01

    We investigate electron transport properties in large-area, single-layer graphene embedded in dielectric media, using free-space terahertz (THz) imaging and time-domain spectroscopy. Sandwiched between a thin polymethyl methacrylate (PMMA) layer and a Si substrate, graphene layers of different growth recipes exhibit distinctive spatial inhomogeneity of sheet conductivity. The non-contacting, non-destructive THz probe reveals that the PMMA layer induces a small, yet noticeable reduction in conductivity.

  11. Terahertz imaging of inhomogeneous electrodynamics in single-layer graphene embedded in dielectrics

    NASA Astrophysics Data System (ADS)

    Thompson, Zachary; Paul, Michael; Tomaino, Joeseph; Kevek, Joshua; Deborde, Tristan; Minot, Ethan; Lee, Yun-Shik

    2012-10-01

    We investigate electron transport properties in large-area, single-layer graphene embedded in dielectric media, using free-space terahertz (THz) imaging and time-domain spectroscopy. Sandwiched between a thin polymethyl methacrylate (PMMA) layer and a Si substrate, graphene layers of different growth recipes exhibit distinctive spatial inhomogeneity of sheet conductivity. The non-contacting, non-destructive THz probe reveals that the PMMA layer induces a small, yet noticeable reduction in conductivity.

  12. Modeling and Processing of Terahertz Imaging in Space Shuttle External Tank Foam Inspection

    Microsoft Academic Search

    Chien-Ping Chiou; R. Bruce Thompson; William P. Winfree; Eric I. Madaras; Jeffrey Seebo

    2006-01-01

    Recently, terahertz ray (T-ray) imaging emerged as one of the most promising techniques to inspect the space shuttle external tank foam insulation. This paper demonstrates the application of state-of-the-art computer processing and modeling technologies to assist in further refinement of this new technology. The current protocol of T-ray inspection and its limitations are first reviewed. New strategies of using signal

  13. Passive millimetre-wave imaging and how it differs from terahertz imaging.

    PubMed

    Appleby, R

    2004-02-15

    It is well known that millimetre-wave systems can penetrate poor weather, dust and smoke far better than infrared or visible systems. Imaging in this band offers the opportunity to be able to navigate and perform surveillance in these conditions of poor visibility. Furthermore, the ability to penetrate dielectrics such as plastic and cloth has opened up the opportunity of detecting weapons and contraband hidden under people's clothing. The optical properties of materials have a direct impact on the applicability of imaging systems. In the terahertz band solids have absorptions which can be assigned to vibrational modes. Lattice modes occur at the lowest frequencies and polythene, for example, has a lattice mode at 2.4 THz. Solids have no such absorptions in the millimetre bands (30-300 GHz) and image contrast is produced by differences in transmission, reflection and absorption. A novel, real-time, mechanically scanned, passive millimetre-wave imager has been designed. The antenna elements are based on a combination of a Schmidt camera and a conical scanner, both of which have their origins in optical systems. Polarization techniques, which were developed for operation in the centimetric band, are used to fold the optics. Both 35 GHz and 94 GHz versions have been constructed. PMID:15306527

  14. Real-time, continuous-wave terahertz imaging using a microbolometer focal-plane array

    NASA Technical Reports Server (NTRS)

    Hu, Qing (Inventor); Min Lee, Alan W. (Inventor)

    2010-01-01

    The present invention generally provides a terahertz (THz) imaging system that includes a source for generating radiation (e.g., a quantum cascade laser) having one or more frequencies in a range of about 0.1 THz to about 10 THz, and a two-dimensional detector array comprising a plurality of radiation detecting elements that are capable of detecting radiation in that frequency range. An optical system directs radiation from the source to an object to be imaged. The detector array detects at least a portion of the radiation transmitted through the object (or reflected by the object) so as to form a THz image of that object.

  15. Processing sequence for non-destructive inspection based on 3D terahertz images

    NASA Astrophysics Data System (ADS)

    Balacey, H.; Perraud, Jean-Baptiste; Bou Sleiman, J.; Guillet, Jean-Paul; Recur, B.; Mounaix, P.

    2014-11-01

    In this paper we present an innovative data and image processing sequence to perform non-destructive inspection from 3D terahertz (THz) images. We develop all the steps starting from a 3D tomographic reconstruction of a sample from its radiographs acquired with a monochromatic millimetre wave imaging system. Thus an automated segmentation provides the different volumes of interest (VOI) composing the sample. Then a 3D visualization and dimensional measurements are performed on these VOI, separately, in order to provide an accurate nondestructive testing (NDT) of the studied sample. This sequence is implemented onto an unique software and validated through the analysis of different objects

  16. Two-dimensional interferometric and synthetic aperture imaging with a hybrid terahertz/millimeter wave system.

    PubMed

    Su, Ke; Liu, Zhiwei; Barat, Robert B; Gary, Dale E; Michalopoulou, Zoi-Heleni; Federici, John F

    2010-07-01

    We have developed an interferometric synthetic aperture incoherent imaging system at 94 GHz, in which a high-power electronic millimeter wave source (Gunn Oscillator) is integrated with a continuous-wave terahertz (THz) photomixing detection system to achieve a high signal-to-noise ratio. Imaging of a point source located 10?m away from the detector array is presented. Two-dimensional THz reflective images of an extended object with different shapes are reconstructed with only four detectors by use of rotational synthesis. PMID:20648115

  17. Terahertz imaging system based on bessel beams via 3D printed axicons at 100GHz

    NASA Astrophysics Data System (ADS)

    Liu, Changming; Wei, Xuli; Zhang, Zhongqi; Wang, Kejia; Yang, Zhenggang; Liu, Jinsong

    2014-11-01

    Terahertz (THz) imaging technology shows great advantage in nondestructive detection (NDT), since many optical opaque materials are transparent to THz waves. In this paper, we design and fabricate dielectric axicons to generate zeroth order-Bessel beams by 3D printing technology. We further present an all-electric THz imaging system using the generated Bessel beams in 100GHz. Resolution targets made of printed circuit board are imaged, and the results clearly show the extended depth of focus of Bessel beam, indicating the promise of Bessel beam for the THz NDT.

  18. Enhanced terahertz imaging system performance analysis and design tool for concealed weapon identification

    NASA Astrophysics Data System (ADS)

    Murrill, Steven R.; Franck, Charmaine C.; Espinola, Richard L.; Petkie, Douglas T.; De Lucia, Frank C.; Jacobs, Eddie L.

    2011-11-01

    The U.S. Army Research Laboratory (ARL) and the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) have developed a terahertz-band imaging system performance model/tool for detection and identification of concealed weaponry. The details of the MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination, were reported on at the 2005 SPIE Europe Security & Defence Symposium (Brugge). An advanced version of the base model that accounts for both the dramatic impact that target and background orientation can have on target observability as related to specular and Lambertian reflections captured by an active-illumination-based imaging system, and for the impact of target and background thermal emission, was reported on at the 2007 SPIE Defense and Security Symposium (Orlando). This paper will provide a comprehensive review of an enhanced, user-friendly, Windows-executable, terahertz-band imaging system performance analysis and design tool that now includes additional features such as a MODTRAN-based atmospheric attenuation calculator and advanced system architecture configuration inputs that allow for straightforward performance analysis of active or passive systems based on scanning (single- or line-array detector element(s)) or staring (focal-plane-array detector elements) imaging architectures. This newly enhanced THz imaging system design tool is an extension of the advanced THz imaging system performance model that was developed under the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. This paper will also provide example system component (active-illumination source and detector) trade-study analyses using the new features of this user-friendly THz imaging system performance analysis and design tool.

  19. Terahertz imaging using quantum cascade lasers—a review of systems and applications

    NASA Astrophysics Data System (ADS)

    Dean, P.; Valavanis, A.; Keeley, J.; Bertling, K.; Lim, Y. L.; Alhathlool, R.; Burnett, A. D.; Li, L. H.; Khanna, S. P.; Indjin, D.; Taimre, T.; Raki?, A. D.; Linfield, E. H.; Davies, A. G.

    2014-09-01

    The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of THz radiation offering high power, high spectral purity and moderate tunability. As such, these sources are particularly suited to the application of THz frequency imaging across a range of disciplines, and have motivated significant research interest in this area over the past decade. In this paper we review the technological approaches to THz QCL-based imaging and the key advancements within this field. We discuss in detail a number of imaging approaches targeted to application areas including multiple-frequency transmission and diffuse reflection imaging for the spectral mapping of targets; as well as coherent approaches based on the self-mixing phenomenon in THz QCLs for long-range imaging, three-dimensional imaging, materials analysis, and high-resolution inverse synthetic aperture radar imaging.

  20. Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity

    NASA Astrophysics Data System (ADS)

    Masson, Jean-Baptiste; Sauviat, Martin-Pierre; Gallot, Guilhem

    2006-10-01

    The authors demonstrate the direct, noninvasive and time resolved imaging of functional frog auricular fibers by ionic contrast terahertz (ICT) near field microscopy. This technique provides quantitative, time-dependent measurement of ionic flow during auricular muscle electrical activity, and opens the way of direct noninvasive imaging of cardiac activity under stimulation. ICT microscopy technique was associated with full three-dimensional simulation enabling to measure precisely the fiber sizes. This technique coupled to waveguide technology should provide the grounds to development of advanced in vivo ion flux measurement in mammalian hearts, allowing the prediction of heart attack from change in K+ fluxes.

  1. Terahertz wideband spectroscopic imaging based on two-dimensional electro-optic sampling technique

    NASA Astrophysics Data System (ADS)

    Usami, Mamoru; Yamashita, Masatsugu; Fukushima, Kazushiro; Otani, Chiko; Kawase, Kodo

    2005-04-01

    We extended the bandwidth of a terahertz (THz) spectroscopic imaging system based on two-dimensional electro-optic sampling. By using an optical-rectification emitter, formed by a ZnTe crystal, a high-frequency component of more than 2.0THz was detected. A calibration-free procedure with polarity inversion of the THz beam ensures us precise spectroscopy: the polarity was inverted by rotating the emitter crystal. The spatial patterns of the chemicals were extracted from the THz multispectral images in the extended spectral region.

  2. Using terahertz pulse spectroscopy to study the crystalline structure of a drug: A case study of the polymorphs of ranitidine hydrochloride

    Microsoft Academic Search

    P. F. Taday; I. V. Bradley; D. D. Arnone; M. Pepper

    2003-01-01

    We describe the application of Terahertz pulse spectroscopy to polymorph identification. The particular compounds investigated were the different crystalline Forms 1 and 2 of ranitidine hydrochloride, both in the pure form and also obtained as a marketed pharmaceutical product. Identification was clear. The technique has advant- ages that excitation is not via a powerful laser source, as used in Raman

  3. Tailored terahertz pulses from a laser-modulated electron beam Michael C. Martin, John Byrd, Zhao Hao, David Robin, Fernando Sannibale, Robert W. Schoenlein,

    E-print Network

    -alpha lattices (blue), at two beam ports. Figure 3. Time domain signal of the far-IR bolometer detector output CIRCE project in Berkeley. Figure 5. Stimulated bursting emission as a function of beam current growsTailored terahertz pulses from a laser-modulated electron beam Michael C. Martin, John Byrd, Zhao

  4. Theoretical analysis and simulations of strong terahertz radiation from the interaction of ultrashort laser pulses with gases

    NASA Astrophysics Data System (ADS)

    Chen, Min; Pukhov, Alexander; Peng, Xiao-Yu; Willi, Oswald

    2008-10-01

    Terahertz (THz) radiation from the interaction of ultrashort laser pulses with gases is studied both by theoretical analysis and particle-in-cell (PIC) simulations. A one-dimensional THz generation model based on the transient ionization electric current mechanism is given, which explains the results of one-dimensional PIC simulations. At the same time the relation between the final THz field and the initial transient ionization current is shown. One- and two-dimensional simulations show that for the THz generation the contribution of the electric current due to ionization is much larger than the one driven by the usual ponderomotive force. Ionization current generated by different laser pulses and gases is also studied numerically. Based on the numerical results we explain the scaling laws for THz emission observed in the recent experiments performed by Xie [Phys. Rev. Lett. 96, 075005 (2006)]. We also study the effective parameter region for the carrier envelop phase measurement by the use of THz generation.

  5. Optically- and Electrically-Stimulated Terahertz Radiation Emission from Indium Nitride

    NASA Astrophysics Data System (ADS)

    Wilke, Ingrid; Ding, Yujie J.; Shubina, Tatiana V.

    2012-06-01

    Indium nitride is a novel narrow band gap semiconductor. The material is a potential strong source of terahertz frequency electromagnetic radiation with applications in time-domain terahertz spectroscopy and imaging systems. This article reviews recent experimental research on terahertz emission from the binary compound semiconductor indium nitride excited by near-infrared laser beams or microseconds electrical pulses. Advantages of indium nitride as terahertz radiation source material are discussed. It is demonstrated that different mechanisms contribute to the emission of terahertz radiation from indium nitride. The emission of up to 2.4 ?W of THz radiation power is observed when InN is excited with near-infrared femtosecond laser pulses at an average power of 1 W.

  6. Probing ultrafast temperature changes of aqueous solutions with coherent terahertz pulses.

    PubMed

    Backus, Ellen H G; Tielrooij, Klaas-Jan; Bonn, Mischa; Bakker, Huib J

    2014-04-01

    We introduce an infrared pump-terahertz probe technique to measure the thermalization dynamics of aqueous solutions with a time resolution <200??fs. This technique makes use of the sensitivity of the terahertz absorption to the temperature of the hydrogen bond network. The thermalization dynamics of different aqueous solutions are measured and compared to the dynamics inferred from ultrafast infrared pump-infrared probe measurements on the intramolecular stretch vibration of water. This technique can shed new light on important aspects of energy transfer and heat dynamics and is applicable to a wide range of systems. PMID:24686587

  7. Terahertz imaging system for stand-off detection of threats

    NASA Astrophysics Data System (ADS)

    Hübers, H.-W.; Semenov, A. D.; Richter, H.; Böttger, U.

    2007-04-01

    Suicide bombers and hidden bombs or explosives have become serious threats especially for mass transportation. Until now there exists no established system which can be used against these threats. Therefore new technologies especially for stand-off detection of threats are required. Terahertz (THz) rays offer an alternative inspection method, which can cope with these new challenges. Major advantages of THz radiation as compared to other spectral regions are the possibility to penetrate through clothes and that THz radiation is not harmful for human health. In this report the design and results of a THz stand-off detection system will be presented. The sensor is based on active illumination of the object and sensitive heterodyne detection of reflected and backscattered radiation. The system operates at about 0.8 THz. A THz laser is used for illumination and a superconducting hot-electron bolometric mixer for detection. The local oscillator required for heterodyne detection is a multiplied microwave source. The optical system is designed to allow for stand-off detection at 20 m with a spatial resolution less than 2 cm.

  8. Propagation through terahertz waveguides with photonic crystal boundaries

    Microsoft Academic Search

    Adam L. Bingham

    2007-01-01

    Scope and method of study. The research presented in this dissertation investigates the integration of photonic crystal lattices into parallel plate waveguides at terahertz frequencies. The experimental data was obtained by measuring the terahertz pulses through the photonic crystal waveguides in a standard terahertz time-domain spectroscopy system. The terahertz pulses were generated and detected via optoelectronic means utilizing lithographically fabricated

  9. Terahertz metrology of tree rings for dendrochronology and cultural heritage applications

    NASA Astrophysics Data System (ADS)

    Jackson, J. B.; Labaune, J.; Mourou, G.; Duling, I.; Lavier, C.; Menu, M.

    2009-07-01

    Terahertz imaging will be presented as a novel method of nondestructively measuring otherwise inaccessible tree-rings for the purpose of dendrochronologically cross-dating cultural heritage artifacts. Wood specimens were measured using time-domain terahertz pulse reflectometry. Two-dimensional images of tree-rings were generated through analysis of both time- and frequency-domain terahertz signals, which changed proportionally to the variations in wood density. Terahertz pulse separation enabled wood specimens with at least two layers of coatings (primer and/or paint) to be measured and the terahertz images were quantitatively compared to the optical photographs of related, uncoated specimen. Tree-ring series and timelines were obtained for each terahertz image with respect to the source (reference) ring series. Short ring width blocks were aligned to the reference series and combined to create an extended timeline for each terahertz image. It was determined that while spatial resolution may be improved with analysis at high frequencies, the lower signal to noise reduces the precision of the ring measurement. Constructing longer timelines from ring blocks, significantly improves the overall quality of a match.

  10. Ultrafast far-infrared dynamics probed by terahertz pulses: A frequency domain approach. I. Model systems

    E-print Network

    Ku?el, Petr

    2005 Time-resolved terahertz spectroscopy has become a widely used experimental tool ; these results serve as a basis for the interpretation of experimental results. We discuss also the cases where. © 2005 American Institute of Physics. DOI: 10.1063/1.1857851 I. INTRODUCTION The fast development

  11. Reflective Terahertz Imaging for early diagnosis of skin burn severity

    E-print Network

    TEWARI, PRIYAMVADA

    2013-01-01

    images immediate post burn and (right) three days post burn The visible pictures andpictures of a partial thickness burn on day 1, 2 & 3 and THz imagespictures of a full thickness burn on day 1, 2 & 3 and THz images

  12. Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials Using Terahertz Energy

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    This article describes a noncontact single-sided terahertz electromagnetic measurement and imaging method that simultaneously characterizes microstructural (egs. spatially-lateral density) and thickness variation in dielectric (insulating) materials. The method was demonstrated for two materials-Space Shuttle External Tank sprayed-on foam insulation and a silicon nitride ceramic. It is believed that this method can be used as an inspection method for current and future NASA thermal protection system and other dielectric material inspection applications, where microstructural and thickness variation require precision mapping. Scale-up to more complex shapes such as cylindrical structures and structures with beveled regions would appear to be feasible.

  13. Imaging of free carriers in semiconductors via optical feedback in terahertz quantum cascade lasers

    SciTech Connect

    Mezzapesa, F. P., E-mail: francesco.mezzapesa@uniba.it; Brambilla, M.; Dabbicco, M.; Scamarcio, G. [Dipartimento Interateneo di Fisica, Università degli Studi e Politecnico di Bari, via Amendola 173, 70126 Bari (Italy); CNR-IFN UOS Bari, via Amendola 173, 70126 Bari (Italy); Columbo, L. L. [Dipartimento Interateneo di Fisica, Università degli Studi e Politecnico di Bari, via Amendola 173, 70126 Bari (Italy); CNR-IFN UOS Bari, via Amendola 173, 70126 Bari (Italy); Dipartimento di Scienza ed Alta Tecnologia, Università dell'Insubria, via Valleggio 11, 22100 Como (Italy); Vitiello, M. S. [NEST, CNR - Istituto Nanoscienze and Scuola Normale Superiore, piazza San Silvestro 12, 56127 Pisa (Italy)

    2014-01-27

    To monitor the density of photo-generated charge carriers on a semiconductor surface, we demonstrate a detectorless imaging system based on the analysis of the optical feedback in terahertz quantum cascade lasers. Photo-excited free electron carriers are created in high resistivity n-type silicon wafers via low power (?40 mW/cm{sup 2}) continuous wave pump laser in the near infrared spectral range. A spatial light modulator allows to directly reconfigure and control the photo-patterned intensity and the associated free-carrier density distribution. The experimental results are in good agreement with the numerical simulations.

  14. Terahertz imaging of sub-wavelength particles with Zenneck surface waves

    NASA Astrophysics Data System (ADS)

    Navarro-Cía, M.; Natrella, M.; Dominec, F.; Delagnes, J. C.; Kužel, P.; Mounaix, P.; Graham, C.; Renaud, C. C.; Seeds, A. J.; Mitrofanov, O.

    2013-11-01

    Impact of sub-wavelength-size dielectric particles on Zenneck surface waves on planar metallic antennas is investigated at terahertz (THz) frequencies with THz near-field probe microscopy. Perturbations of the surface waves show the particle presence, despite its sub-wavelength size. The experimental configuration, which utilizes excitation of surface waves at metallic edges, is suitable for THz imaging of dielectric sub-wavelength size objects. As a proof of concept, the effects of a small strontium titanate rectangular particle and a titanium dioxide sphere on the surface field of a bow-tie antenna are experimentally detected and verified using full-wave simulations.

  15. Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis.

    PubMed

    Raki?, Aleksandar D; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Dean, Paul; Indjin, Dragan; Ikoni?, Zoran; Harrison, Paul; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Wilson, Stephen J; Linfield, Edmund H; Davies, A Giles

    2013-09-23

    The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser. PMID:24104111

  16. Imaging with a terahertz quantum cascade laser for biomedical applications

    NASA Astrophysics Data System (ADS)

    Kim, Seongsin M.; Hatami, Fariba; Kurian, Allison W.; Goddard, Lynford; Ford, James; Harris, James S.; Scalari, Giacomo; Giovannini, Marcella; Hoyler, Nicolas; Faist, Jerome; Harris, Geoff

    2005-11-01

    We investigated and demonstrated bio-medical imaging using a THz quantum cascade laser. With the THz quantum cascade laser (QCL) at 3.8 THz, we obtained large dynamic range and high spatial resolution in the transmission imaging technique. The various tissues images, such as lung, liver, and brain sections from the laboratory mouse were obtained and studied. The most important factor for this imaging scheme is to obtain high contrast with different absorption characteristics in tissues. We explored distinct images from the fat, muscles and tendon from the freshly cut tissues and investigated absorption coefficient and compared with FTIR measurement. We also demonstrated the image of distinct region of tumors progressed and normal tissues using this technique. The comparison of frequency dependent medical imaging with utilizing different wavelength of QCLs has been addressed.

  17. Bio-medical imaging with a terahertz quantum cascade laser

    NASA Astrophysics Data System (ADS)

    Kim, Seongsin M.; Hatami, Fariba; Kurian, Allison W.; Ford, James; Harris, James S.; Scalari, Giacomo; Giovannini, Marcella; Hoyler, Nicolas; Faist, Jerome; Harris, Geoff

    2006-02-01

    We investigated and demonstrated bio-medical imaging using a THz quantum cascade laser. With the THz quantum cascade laser (QCL) at 3.8 THz, we obtained large dynamic range and high spatial resolution in the transmission imaging technique. The various tissues images, such as lung, liver, and brain sections from the laboratory mouse were obtained and studied. The most important factor for this imaging scheme is to obtain high contrast with different absorption characteristics in tissues. We explored distinct images from the fat, muscles and tendon from the freshly cut tissues and investigated absorption coefficient and compared with FTIR measurement. We also demonstrated the image of distinct region of tumors progressed and normal tissues using this technique. The comparison of frequency dependent medical imaging with utilizing different wavelength of QCLs has been addressed.

  18. Screening mail for powders using terahertz technology

    NASA Astrophysics Data System (ADS)

    Kemp, Mike

    2011-11-01

    Following the 2001 Anthrax letter attacks in the USA, there has been a continuing interest in techniques that can detect or identify so-called 'white powder' concealed in envelopes. Electromagnetic waves (wavelengths 100-500 ?m) in the terahertz frequency range penetrate paper and have short enough wavelengths to provide good resolution images; some materials also have spectroscopic signatures in the terahertz region. We report on an experimental study into the use of terahertz imaging and spectroscopy for mail screening. Spectroscopic signatures of target powders were measured and, using a specially designed test rig, a number of imaging methods based on reflection, transmission and scattering were investigated. It was found that, contrary to some previous reports, bacterial spores do not appear to have any strong spectroscopic signatures which would enable them to be identified. Imaging techniques based on reflection imaging and scattering are ineffective in this application, due to the similarities in optical properties between powders of interest and paper. However, transmission imaging using time-of-flight of terahertz pulses was found to be a very simple and sensitive method of detecting small quantities (25 mg) of powder, even in quite thick envelopes. An initial feasibility study indicates that this method could be used as the basis of a practical mail screening system.

  19. Passive stand-off terahertz imaging with 1 hertz frame rate

    NASA Astrophysics Data System (ADS)

    May, T.; Zieger, G.; Anders, S.; Zakosarenko, V.; Starkloff, M.; Meyer, H.-G.; Thorwirth, G.; Kreysa, E.

    2008-04-01

    Terahertz (THz) cameras are expected to be a powerful tool for future security applications. If such a technology shall be useful for typical security scenarios (e.g. airport check-in) it has to meet some minimum standards. A THz camera should record images with video rate from a safe distance (stand-off). Although active cameras are conceivable, a passive system has the benefit of concealed operation. Additionally, from an ethic perspective, the lack of exposure to a radiation source is a considerable advantage in public acceptance. Taking all these requirements into account, only cooled detectors are able to achieve the needed sensitivity. A big leap forward in the detector performance and scalability was driven by the astrophysics community. Superconducting bolometers and midsized arrays of them have been developed and are in routine use. Although devices with many pixels are foreseeable nowadays a device with an additional scanning optic is the straightest way to an imaging system with a useful resolution. We demonstrate the capabilities of a concept for a passive Terahertz video camera based on superconducting technology. The actual prototype utilizes a small Cassegrain telescope with a gyrating secondary mirror to record 2 kilopixel THz images with 1 second frame rate.

  20. Materials for terahertz science and technology

    Microsoft Academic Search

    Bradley Ferguson; Xi-Cheng Zhang

    2002-01-01

    Terahertz spectroscopy systems use far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum. Materials research is an essential component of modern terahertz systems: novel, higher-power terahertz sources rely heavily on new materials such as quantum cascade structures. At the same time, terahertz spectroscopy and imaging provide a powerful tool for the characterization of

  1. Nonresonant ionization of oxygen molecules by femtosecond pulses: Plasma dynamics studied by time-resolved terahertz spectroscopy

    SciTech Connect

    Mics, Zoltan; Kadlec, Filip; Kuzel, Petr; Jungwirth, Pavel; Bradforth, Stephen E.; Apkarian, V. Ara [Institute of Physics, Academy of Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic (Czech Republic); Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 166 10 Prague 6 (Czech Republic); Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Department of Chemistry, University of California, Irvine, California 92697 (United States)

    2005-09-08

    We show that optical pump-terahertz probe spectroscopy is a direct experimental tool for exploring laser-induced ionization and plasma formation in gases. Plasma was produced in gaseous oxygen by focused amplified femtosecond pulses. The ionization mechanisms at 400- and 800-nm excitation wavelengths differ significantly being primarily of a multiphoton character in the former case and a strong-field process in the latter case. The generation of the plasma in the focal volume of the laser and its expansion on subnanosecond time scale is directly monitored through its density-dependent susceptibility. A Drude model used to evaluate the plasma densities and electron-scattering rates successfully captures the observations for a wide range of pump intensities. In addition, rotational fingerprints of molecular and ionic species were also observed in the spectra.

  2. A terahertz imaging system using high Tc superconducting oscillators fabricated from the Bi2212 single crystals

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Kadowaki, K.; Tsujimoto, M.; Yamamoto, T.; Markovic, B.; Mirkovic, J.

    2014-03-01

    We have developed a terahertz (THz) oscillator based on high Tc superconductor of Bi2Sr2CaCu2O8+?(Bi2212) single crystals and have succeeded in developing 30 ?W level of output power, which is continuous, monochromatic as well as stable at frequencies between 0.3 ~ 1.0 THz. Recently, for the purpose of application use of our THz oscillator, we have developed the reflection type of the imaging system in addition to the transmission imaging system reported previously. We will show the details of the system and the images obtained here as practical example and compared those with previous results. This work was supported by CREST-JST. This work is in part performed in collaboration with Dr. Wai Kwok and his group in Argonne National Lab.

  3. Nonlinear pulse compression in pulse-inversion fundamental imaging.

    PubMed

    Cheng, Yun-Chien; Shen, Che-Chou; Li, Pai-Chi

    2007-04-01

    Coded excitation can be applied in ultrasound contrast agent imaging to enhance the signal-to-noise ratio with minimal destruction of the microbubbles. Although the axial resolution is usually compromised by the requirement for a long coded transmit waveforms, this can be restored by using a compression filter to compress the received echo. However, nonlinear responses from microbubbles may cause difficulties in pulse compression and result in severe range side-lobe artifacts, particularly in pulse-inversion-based (PI) fundamental imaging. The efficacy of pulse compression in nonlinear contrast imaging was evaluated by investigating several factors relevant to PI fundamental generation using both in-vitro experiments and simulations. The results indicate that the acoustic pressure and the bubble size can alter the nonlinear characteristics of microbubbles and change the performance of the compression filter. When nonlinear responses from contrast agents are enhanced by using a higher acoustic pressure or when more microbubbles are near the resonance size of the transmit frequency, higher range side lobes are produced in both linear imaging and PI fundamental imaging. On the other hand, contrast detection in PI fundamental imaging significantly depends on the magnitude of the nonlinear responses of the bubbles and thus the resultant contrast-to-tissue ratio (CTR) still increases with acoustic pressure and the nonlinear resonance of microbubbles. It should be noted, however, that the CTR in PI fundamental imaging after compression is consistently lower than that before compression due to obvious side-lobe artifacts. Therefore, the use of coded excitation is not beneficial in PI fundamental contrast detection. PMID:17679323

  4. Generation of terahertz pulsed radiation from photoconductive emitters using 1060 nm laser excitation

    Microsoft Academic Search

    I. Hinkov; G. Harzendorf; S. Kluska; B. Hinkov; K. Kamaruzaman; R. Beigang; J. Heinrich; S. Hoefling; A. Forchel

    2007-01-01

    In this paper we report experimental results on the generation of broadband terahertz (THz) radiation using photoconductive emitters on the base of low-temperature-grown (LT) InGaAs for excitation with 1060 nm wavelength. The material properties of the semiconductor layers were investigated and the emitter function optimised. As experimental arrangement we have used a THz time-domain-spectroscopy (TDS) system. The THz spectrum reaches

  5. Adaptive terahertz imaging using a virtual transceiver and coherence weighting

    E-print Network

    Buma, Takashi

    , and D. Zimdars, "THz imaging and sensing for security applications ­ explosives, weapons, and drugs-speed inhomogeneities: The van Cittert Zernike approach and focusing criterion," J. Acoust. Soc. Am. 96(6), 3721

  6. Terahertz time-domain reflectometry of multilayered systems

    Microsoft Academic Search

    J. Bianca Jackson

    2008-01-01

    Presented in this work are applications of terahertz pulse ranging, spectroscopy and imaging to the nondestructive evaluation of three disparate multilayer systems for the detection and measurement of hidden layers, as well as the extraction of system information that will aid in its maintenance, repair or replacement. Thermal protection systems for turbine engine components were investigated. Thermal barrier coatings (TBC)

  7. Generation of widely tunable Fourier-transform-limited terahertz pulses using narrowband near-infrared laser radiation

    NASA Astrophysics Data System (ADS)

    Liu, Jinjun; Schmutz, Hansjürg; Merkt, Frédéric

    2009-07-01

    Widely tunable, Fourier-transform-limited pulses of terahertz (THz) radiation have been generated using (i) crystals of the highly nonlinear organic salt 4- N, N-dimethylamino-4'- N'-methyl stilbazolium tosylate (DAST), (ii) zinc telluride (ZnTe) crystals, (iii) gallium phosphide (GaP) crystals, and (iv) low-temperature-grown gallium arsenide (LTG-GaAs) photomixers with THz spiral antennas. Outputs from two narrowband (? ? < 1 MHz, ? ˜ 800 nm) cw titanium-doped sapphire (Ti:Sa) ring lasers with a well-controlled frequency difference were shaped into pulses using acousto-optic modulators (AOM), coupled into an optical fiber, pulse amplified in Nd:YAG-pumped Ti:Sa crystals and used as optical sources to pump the THz emitters. The THz radiation was detected over a broad frequency range and its bandwidth was determined to be ˜10 MHz. The spectroscopic potential of the THz source is illustrated by the absorption spectrum of a pure rotational transition of OCS.

  8. Single nanowire photoconductive terahertz detectors.

    PubMed

    Peng, Kun; Parkinson, Patrick; Fu, Lan; Gao, Qiang; Jiang, Nian; Guo, Ya-Nan; Wang, Fan; Joyce, Hannah J; Boland, Jessica L; Tan, Hark Hoe; Jagadish, Chennupati; Johnston, Michael B

    2015-01-14

    Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as diverse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors. PMID:25490548

  9. Terahertz holography for imaging amplitude and phase objects.

    PubMed

    Hack, Erwin; Zolliker, Peter

    2014-06-30

    A non-monochromatic THz Quantum Cascade Laser and an uncooled micro-bolometer array detector with VGA resolution are used in a beam-splitter free holographic set-up to measure amplitude and phase objects in transmission. Phase maps of the diffraction pattern are retrieved using the Fourier transform carrier fringe method; while a Fresnel-Kirchhoff back propagation algorithm is used to reconstruct the complex object image. A lateral resolution of 280 µm and a relative phase sensitivity of about 0.5 rad are estimated from reconstructed images of a metallic Siemens star and a polypropylene test structure, respectively. Simulations corroborate the experimental results. PMID:24977861

  10. Photonic time-division multiplexing (OTDM) using ultrashort picosecond pulses in a terahertz optical asymmetric demultiplexer (TOAD)

    NASA Astrophysics Data System (ADS)

    Melo, A. M.; Lima, J. L. S.; de Oliveira, R. S.; Sombra, A. S. B.

    2002-05-01

    The performance of a terahertz optical asymmetric demultiplexer (TOAD) operating with an ordinary fiber and with a DDF and DIF (dispersion decreasing and increasing fiber) configurations, for three lengths of fiber ( ?=?/2,2? and 5?) and using soliton and quasi-soliton laser profiles for the control pulse, was studied. The numerical simulations show that the increase of the fiber length leads to the decrease of the power for the first and second demultiplexed pulses and leads to a broadening of these pulses, with the exception of the TOAD operating with the DDF fiber. For the TOAD operating with a basic telecommunication fiber one see that the increase of the power of the control power lead to a strong compression of the demultiplexed pulse. Operating the TOAD using a DDF fiber one can say that the control power necessary to demultiplex the signal pulse is always lower compared with the TOAD with the normal telecommunication fiber. This is a strong suggestion that the use of the DDF fiber will allow the use of less control power. Our simulations considering the TOAD operating with a DDF and DIF with a linear profile conclude that it is possible to operate the TOAD with lower control power using a DDF fiber setup. For this device the demultiplexed pulses will present a compression on time duration and will be insensitive to the time profile of the control pulse. We also did simulations with the TOAD operating with DDF in four different profiles: hyperbolic, exponential, linear and Gaussian. For all the profiles the increase of the length of the fiber also decreases the pump power of the three first peaks for the soliton and quasi-soliton regimes. The first critical power is always lower for the quasi-soliton regime compared to the soliton regime for all profiles under consideration and all lengths of the TOAD under consideration. It was also observed that for all the profiles and lengths of fiber one has pulse compression for the switched pulse. For the ?=2? fiber with the hyperbolic profile, both soliton and quasi-soliton profiles present the lowest critical power and the highest compression factors for all the considered profiles.

  11. Terahertz tomographic imaging of XVIIIth Dynasty Egyptian sealed pottery

    E-print Network

    Paris-Sud XI, Université de

    of artworks such as fresco [1,2], canvas paintings [3,4], and old parchments [5]. However, very few studies/uniqueness of the samples and the problem of sample radiometric dating after x-ray irradiation [7]. In most THz imaging

  12. Terahertz tomographic imaging of XVIIIth Dynasty Egyptian sealed pottery.

    PubMed

    Caumes, Jean-Pascal; Younus, Ayesha; Salort, Simon; Chassagne, Bruno; Recur, Benoît; Ziéglé, Anne; Dautant, Alain; Abraham, Emmanuel

    2011-07-10

    A monochromatic millimeter-wave imaging system coupled with an infrared temperature sensor has been used to investigate historic objects preserved at the Museum of Aquitaine (France). In particular, two-dimensional and three-dimensional analyses have been performed in order to reveal the internal structure of nearly 3500-year-old sealed Egyptian jars. PMID:21743572

  13. The generation of high field terahertz radiation and its application in terahertz nonlinear spectroscopy

    E-print Network

    Yeh, Ka-Lo

    2009-01-01

    In this thesis research, I implemented a terahertz generation scheme that enables high-field near-single-cycle terahertz (THz) pulse generation via optical rectification in a LiNbO3 (LN) crystal. I also developed a method ...

  14. Terahertz spectroscopic imaging and properties of gastrointestinal tract in a rat model

    PubMed Central

    Ji, Young Bin; Kim, Sang-Hoon; Jeong, Kiyoung; Choi, Yuna; Son, Joo-Hiuk; Park, Dong Woo; Noh, Sam Kyu; Jeon, Tae-In; Huh, Yong-Min; Haam, Seungjoo; Lee, Sang Kil; Oh, Seung Jae; Suh, Jin-Suck

    2014-01-01

    We have investigated basic properties of normal gastrointestinal (GI) tract tissues, including glandular stomach (GS), fore stomach (FS), large intestine (LI), small intestine (SI), and esophagus (ESO), from a rat model using terahertz (THz) reflection imaging and spectroscopy. The THz images collected from stratified squamous epithelia (SSE) of FS and ESO show a lower peak-to-peak value compared to those from columnar epithelia (CE) of GS, LI, or SI because the SSE contains less water than CE. The refractive index and absorption coefficient of FS were less than those of GS or LI, both having values similar to those of water. Additionally, we report internal reflection THz signals from ESO, although we were unable to determine the exact interface for this internal reflection. PMID:25574429

  15. Terahertz spectroscopic imaging and properties of gastrointestinal tract in a rat model.

    PubMed

    Ji, Young Bin; Kim, Sang-Hoon; Jeong, Kiyoung; Choi, Yuna; Son, Joo-Hiuk; Park, Dong Woo; Noh, Sam Kyu; Jeon, Tae-In; Huh, Yong-Min; Haam, Seungjoo; Lee, Sang Kil; Oh, Seung Jae; Suh, Jin-Suck

    2014-12-01

    We have investigated basic properties of normal gastrointestinal (GI) tract tissues, including glandular stomach (GS), fore stomach (FS), large intestine (LI), small intestine (SI), and esophagus (ESO), from a rat model using terahertz (THz) reflection imaging and spectroscopy. The THz images collected from stratified squamous epithelia (SSE) of FS and ESO show a lower peak-to-peak value compared to those from columnar epithelia (CE) of GS, LI, or SI because the SSE contains less water than CE. The refractive index and absorption coefficient of FS were less than those of GS or LI, both having values similar to those of water. Additionally, we report internal reflection THz signals from ESO, although we were unable to determine the exact interface for this internal reflection. PMID:25574429

  16. A CMOS focal-plane array for heterodyne terahertz imaging

    Microsoft Academic Search

    Ullrich R. Pfeiffer; E. Ojefors; A. Lisaukas; D. Glaab; H. G. Roskos

    2009-01-01

    In this paper we present a focal-plane array (FPA) for heterodyne imaging at 0.65-THz in a low-cost 0.25-mum CMOS process technology. The 3times5 pixel array is fully integrated on chip and consists of differential patch antennas, NMOS square-law mixers, and 43-dB low-IF amplifiers. The NMOS square-law mixers are based on distributed resistive self-mixing and facilitate mixing well beyond the cutoff

  17. Fast terahertz imaging using a quantum cascade amplifier

    E-print Network

    Ren, Yuan; Wallis, Robert; Jessop, David Stephen; Degl'Innocenti, Riccardo; Klimont, Adam; Beere, Harvey E.; Ritchie, David A.

    2015-07-09

    spectral region3. Based on the emission driven from electron transitions between individual subbands within the conduction band of a semiconductor heterostructure, THz QC lasers have demonstrated emission frequencies from 1.2 to 5.2 THz4. Peak power over... such as the study of intrinsic stability of QC lasers15 and imaging of free carriers on the surface of semiconductors in the THz frequency region16. In the self-mixing experiment, voltage perturbation due to optical feedback, which is the difference...

  18. Transmission mode terahertz computed tomography

    DOEpatents

    Ferguson, Bradley Stuart; Wang, Shaohong; Zhang, Xi-Cheng

    2006-10-10

    A method of obtaining a series of images of a three-dimensional object by transmitting pulsed terahertz (THz) radiation through the entire object from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three-dimensional object using the detected changes in the transmitted THz radiation. The THz radiation is transmitted through the object as a scanning spot. The object is placed within the Rayleigh range of the focused THz beam and a focusing system is used to transfer the imaging plane from adjacent the object to a desired distance away from the object. A related system is also disclosed.

  19. Femtoelectron-Based Terahertz Imaging of Hydration State in a Proton Exchange Membrane Fuel Cell

    NASA Astrophysics Data System (ADS)

    Buaphad, P.; Thamboon, P.; Kangrang, N.; Rhodes, M. W.; Thongbai, C.

    2015-05-01

    Imbalanced water management in a proton exchange membrane (PEM) fuel cell significantly reduces the cell performance and durability. Visualization of water distribution and transport can provide greater comprehension toward optimization of the PEM fuel cell. In this work, we are interested in water flooding issues that occurred in flow channels on cathode side of the PEM fuel cell. The sample cell was fabricated with addition of a transparent acrylic window allowing light access and observed the process of flooding formation (in situ) via a CCD camera. We then explore potential use of terahertz (THz) imaging, consisting of femtoelectron-based THz source and off-angle reflective-mode imaging, to identify water presence in the sample cell. We present simulations of two hydration states (water and nonwater area), which are in agreement with the THz image results. A line-scan plot is utilized for quantitative analysis and for defining spatial resolution of the image. Implementing metal mesh filtering can improve spatial resolution of our THz imaging system.

  20. 3D terahertz synthetic aperture imaging of objects with arbitrary boundaries

    NASA Astrophysics Data System (ADS)

    Kniffin, G. P.; Zurk, L. M.; Schecklman, S.; Henry, S. C.

    2013-09-01

    Terahertz (THz) imaging has shown promise for nondestructive evaluation (NDE) of a wide variety of manufactured products including integrated circuits and pharmaceutical tablets. Its ability to penetrate many non-polar dielectrics allows tomographic imaging of an object's 3D structure. In NDE applications, the material properties of the target(s) and background media are often well-known a priori and the objective is to identify the presence and/or 3D location of structures or defects within. The authors' earlier work demonstrated the ability to produce accurate 3D images of conductive targets embedded within a high-density polyethylene (HDPE) background. That work assumed a priori knowledge of the refractive index of the HDPE as well as the physical location of the planar air-HDPE boundary. However, many objects of interest exhibit non-planar interfaces, such as varying degrees of curvature over the extent of the surface. Such irregular boundaries introduce refraction effects and other artifacts that distort 3D tomographic images. In this work, two reconstruction techniques are applied to THz synthetic aperture tomography; a holographic reconstruction method that accurately detects the 3D location of an object's irregular boundaries, and a split­-step Fourier algorithm that corrects the artifacts introduced by the surface irregularities. The methods are demonstrated with measurements from a THz time-domain imaging system.

  1. Standoff Detection of Hidden Explosives and Cold and Fire Arms by Terahertz Time-Domain Spectroscopy and Active Spectral Imaging (Review)

    NASA Astrophysics Data System (ADS)

    Skvortsov, L. A.

    2014-11-01

    Terahertz time-domain spectroscopy and standoff spectral imaging for detection of explosives and cold and fire arms hidden, for example, under clothing, were reviewed. Special attention was paid to different schemes for practical implementation of these methods. Progress in this direction and existing problems and the prospects for their solution were discussed. Issues related to sources and receivers of terahertz radiation were briefly discussed. It was noted that interest in quantum-cascade lasers as compact sources of terahertz radiation and the potential of using them at room temperature were increasing.

  2. Waveguide mode imaging and dispersion analysis with terahertz near-field microscopy

    NASA Astrophysics Data System (ADS)

    Mitrofanov, Oleg; Tan, Thomas; Mark, Paul R.; Bowden, Bradley; Harrington, James A.

    2009-04-01

    Propagation of terahertz waves in hollow metallic waveguides depends on the waveguide mode. Near-field scanning probe terahertz microscopy is applied to identify the mode structure and composition in dielectric-lined hollow metallic waveguides. Spatial profiles, relative amplitudes, and group velocities of three main waveguide modes are experimentally measured and matched to the HE11, HE12, and TE11 modes. The combination of near-field microscopy with terahertz time-resolved spectroscopy opens the possibility of waveguide mode characterization in the terahertz band.

  3. High-contrast coherent terahertz imaging of porcine tissue via swept-frequency feedback interferometry.

    PubMed

    Lim, Yah Leng; Taimre, Thomas; Bertling, Karl; Dean, Paul; Indjin, Dragan; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Schaider, Helmut; Prow, Tarl W; Peter Soyer, H; Wilson, Stephen J; Linfield, Edmund H; Giles Davies, A; Raki?, Aleksandar D

    2014-11-01

    There is considerable interest in the interrogation of biological tissue at terahertz (THz) frequencies, largely due to the contrast in the optical properties of different biological tissues which occur in this electro-magnetic radiation band. Of particular interest are THz biomedical images, which have the potential to highlight different information than those acquired in other frequency bands, thereby providing an augmented picture of biological structures. In this work, we demonstrate the feasibility of an interferometric biological imaging technique using a THz quantum cascade laser (QCL) operating at 2.59 THz to perform coherent imaging of porcine tissue samples. We show the potential of this new THz biomedical imaging technique for in vivo studies, by virtue of its reflection geometry and useful tissue penetration depth enabled by the large THz powers emitted by the quantum cascade laser used in this work. The observed clustering of interferometric tissue signatures opens a pathway towards automatic techniques for the discrimination of healthy tissue types for the study of normal physiology and possible therapeutic approaches. PMID:25426324

  4. CARS imaging with a single laser pulse

    Microsoft Academic Search

    Christoph Heinrich; Stefan Bernet; Monika Ritsch-Marte

    2005-01-01

    We report coherent anti-Stokes Raman scattering (CARS) microscopy with ns-pulses. The chosen wide-field geometry allows imaging of the whole field of view at once, without scanning of the sample. Tuning the difference of the two incident laser frequencies overlapping at the sample to a specific vibrational level, one can map the spatial distribution of selected Raman active molecules. Both the

  5. Terahertz time-domain reflectometry of multilayered systems

    NASA Astrophysics Data System (ADS)

    Jackson, J. Bianca

    Presented in this work are applications of terahertz pulse ranging, spectroscopy and imaging to the nondestructive evaluation of three disparate multilayer systems for the detection and measurement of hidden layers, as well as the extraction of system information that will aid in its maintenance, repair or replacement. Thermal protection systems for turbine engine components were investigated. Thermal barrier coatings (TBC) and thermally-grown oxide (TGO) thicknesses were determined with 10 micron resolution using time-of-flight and refractive index calculations. Two alternative methods of monitoring TGO growth using reflection amplitudes and spectral shifts were proposed for the prediction of TBC failure. Laser-machined defects as narrow as 50 microns were resolved in one- and two-dimensional images. The light and dark rings of trees, which reflect the changes in tree growth density over the course of a year, are measurable using pulsed terahertz beams. Tree-rings of bare and painted wood specimen were laterally and axially tomographically imaged in order to facilitate the dendrochronological cross-dating of artifacts. Comparisons were made between photographs and terahertz images to demonstrate the reliability of the technique. Historically, numerous unique artworks have been lost through the act of being covered over time. Samples of paintings, drawings and mosaics were imaged beneath layers of paint and plaster using pulsed-terahertz techniques to demonstrate the efficacy of the technique for art history and restoration. Sketch materials and pigments were measured, between 0.05 and 1.0 THz, to help identify colors in spectroscopic images. Other computational and processing methods were used to optimize the distinction between color domains. Additional time-domain terahertz applications for the examination of artwork and other artifacts were proposed.

  6. POISe: pulsed optoacoustic interferometric spectroscopy and imaging

    NASA Astrophysics Data System (ADS)

    Carp, Stefan A.; Guerra, Arnold, III; Duque, Samuel Q., Jr.; Venugopalan, Vasan

    2004-07-01

    POISe is a spectroscopic imaging technique based on the measurement of surface motion resulting from thermoelastic stress waves produced by short pulse laser irradiation of optically heterogeneous turbid samples. Here we show the capability of POISe to form tomographic images of tissue phantoms using surface displacement measurements taken at several locations following irradiation of a sample with a Q-switched Nd:YAG laser ?=1064 nm. The principal component of POISe is a modified Mach-Zehnder interferometer that provides surface displacement measurements with a temporal resolution of 4 ns and a displacement sensitivity of 0.2 nm. By performing simple image reconstructions on data sets acquired from several tissue-like phantoms, we demonstrate the ability of POISe to provide better than 250 ?m spatial resolution at depths of 6 to 8 mm in a strongly scattering medium (?'s=1/mm). This technique shows great promise for high-resolution non-invasive imaging of superficial (< 1 cm) tissue structures.

  7. Imaging with a 90 frames/s microbolometer focal plane array and high-power terahertz free electron laser

    SciTech Connect

    Dem'yanenko, M. A.; Esaev, D. G. [Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk (Russian Federation); Knyazev, B. A.; Vinokurov, N. A. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Kulipanov, G. N. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation)

    2008-03-31

    An uncooled microbolometer focal plane array (FPA) has been developed and used for imaging of objects illuminated by monochromatic coherent radiation of a free electron laser tunable in the range of 1.25-2.5 THz. A sensitivity threshold of 1.3x10{sup -3} W/cm{sup 2} was obtained for the FPA with a homemade absolute interferometric power meter. Videos up to 90 frames/s were recorded in both transmission and reflection/scattering modes. When objects were illuminated by laser radiation scattered by a rough metal surface, speckled images were observed. Good quality terahertz images were achieved through the fast rotation of the scatterer.

  8. Computed tomography image using sub-terahertz waves generated from a high-Tc superconducting intrinsic Josephson junction oscillator

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Markovi?, B.; Mirkovi?, J.; Klemm, R. A.; Kadowaki, K.

    2014-02-01

    A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+? was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

  9. Incoherent sub-terahertz radiation source with a photomixer array for active imaging in smoky environments

    NASA Astrophysics Data System (ADS)

    Shimizu, Naofumi; Matsuyama, Ken; Uchida, Hidetake

    2015-03-01

    We propose a sub-terahertz (THz) illuminator suitable for use with a THz camera when exploring objects within and behind smoke at the scene of a fire. The illuminator contains a photomixer array and each photomixer generates incoherent sub-THz waves from a single-mode laser light and optical noise using photomixing. The incoherency of the generated sub-THz waves enables us to raise their intensity by increasing the number of photomixers in operation, which makes it possible to realize very bright sub-THz illumination. Consequently, objects being under searched for within or behind smoke can be clearly illuminated using the illuminator and visualized by the THz camera even though they are surrounded by thick and/or high-temperature smoke. To verify our concept, we conducted active imaging with coherent and incoherent sub-THz radiation from a photomixer array utilizing reflection geometry. Although the contrast of the image was improved by increasing number of photomixers in operation on the imaging with coherent radiation, the shape of the target was degraded by the interference pattern of the illuminated sub-THz waves. The contrast of the image when using incoherent radiation was improved without obscuring the shape of the target by increasing the number of photomixers. We also confirmed that there was good visibility for active imaging using incoherent sub-THz illumination even though thick smoke was presented. These results indicate that the use of incoherent sub-THz waves and an array of photomixers should enable a sub-THz illuminator with a high level of brightness to be used for active imaging

  10. Nonstationary time-domain statistics of multiply scattered broadband terahertz pulses

    E-print Network

    Mittleman, Daniel

    of the statistical properties of electro- magnetic waves that propagate through random media. Such studies have led and the transient na- ture of the source in pulsed experiments, the statistics of the diffusive wave necessarily

  11. Pulsed EPR Imaging of Nitroxides in Mice

    PubMed Central

    Hyodo, Fuminori; Matsumoto, Shingo; Devasahayam, Nallathamby; Dharmaraj, Christopher; Subramanian, Sankaran; Mitchell, James B.; Krishna, Murali C.

    2012-01-01

    Nitroxides, unlike trityl radicals, have shorter T2s which until now were not detectable by time-domain Electron Paramagnetic Resonance (EPR) spectrometer at 300 MHz pulsed EPR since their phase memory times were shorter than the spectrometer recovery times. In the current version of the time-domain EPR spectrometer with improved spectrometer recovery times, we tested the feasibility of detecting signals from nitroxide radicals. Several nitroxides and the trityl radical Oxo63 were tested. Among the nitroxides evaluated, deuterated 15N-Tempone (15N-PDT) was found to have the longest T2. The signal intensity profile as a function of concentration of these agents was evaluated and a bi-phasic behavior was observed; beyond a nitroxide concentration of 1.5 mM, signal intensity was found to decrease as a result of self-broadening. Imaging experiments were carried out with 15N-PDT in solutions equilibrated with 0, 5, 10 and 21% oxygen using the Single Point Imaging (SPI) modality in EPR. The image intensity in these tubes was found to depend on the oxygen concentration which in turn influences the T2 of 15N-PDT. In vivo experiments were demonstrated with 15N-PDT in anesthetized mice where the distribution and metabolism of 15N-PDT could be monitored. This study, for the first time shows the capability to image a cell-permeable nitroxide in mice using pulsed EPR in the SPI modality. PMID:19157932

  12. Improvements in Magnetic Resonance Imaging Excitation Pulse Design

    E-print Network

    Improvements in Magnetic Resonance Imaging Excitation Pulse Design by Adam Charles Zelinski;#12;Improvements in Magnetic Resonance Imaging Excitation Pulse Design by Adam Charles Zelinski Submitted inhomogeneity limitations. When magnetic spins are tilted by only a small amount, pulse transmission may

  13. Qualitative and quantitative analysis of calcium-based microfillers using terahertz spectroscopy and imaging.

    PubMed

    Abina, Andreja; Puc, Uroš; Jegli?, Anton; Prah, Jana; Venckevi?ius, Rimvydas; Kašalynas, Irmantas; Valušis, Gintaras; Zidanšek, Aleksander

    2015-10-01

    In different industrial applications, several strictly defined parameters of calcium-based microfillers such as average particle size, particle size distribution, morphology, specific surface area, polymorphism and chemical purity, play a key role in the determination of its usefulness and effectiveness. Therefore, an analytical tool is required for rapid and non-destructive characterization of calcium-based microfillers during the synthesis process or before its use in a further manufacturing process. Since spectroscopic techniques are preferred over microscopy and thermogravimetry, particularly due to its non-destructive nature and short analysis time, we applied terahertz (THz) spectroscopy to analyse calcite microfillers concentration in polymer matrix, its granulation and chemical treatment. Based on the analysis of peak absorbance amplitude, peak frequency position, and the appearance of additional spectral features, quantitative and qualitative analysis was successfully achieved. In addition, THz imaging was also applied for both quantitative and qualitative analysis of calcium-based microfillers. By using spatial distribution map, the inhomogeneity in concentration of calcium carbonate in polymer matrix was characterized. Moreover, by THz spectroscopy and imaging different calcium compounds were detected in binary mixtures. Finally, we demonstrated that the applied spectroscopic technique offers valuable results and can be, in combination with other spectroscopic and microscopic techniques, converted to a powerful rapid analytical tool. PMID:26078145

  14. Investigation of microelectromechanical systems bimaterial sensors with metamaterial absorbers for terahertz imaging

    NASA Astrophysics Data System (ADS)

    Alves, Fabio; Grbovic, Dragoslav; Karunasiri, Gamani

    2014-09-01

    One attractive option to achieve real-time terahertz (THz) imaging is a microelectromechanical systems (MEMS) bimaterial sensor with embedded metamaterial absorbers. We have demonstrated that metamaterial films can be designed using standard MEMS materials such as silicon oxide (SiOx), silicon oxinitrate (SiOxNy), and aluminum (Al) to achieve nearly 100% resonant absorption matched to the illumination source, providing structural support, desired thermomechanical properties and access to external optical readout. The metamaterial structure absorbs the incident THz radiation and transfers the heat to bimaterial microcantilevers that are connected to the substrate, which acts as a heat sink via thermal insulating legs, allowing the overall structure to deform proportionally to the absorbed power. The amount of deformation can be probed by measuring the displacement of a laser beam reflected from the sensor's metallic ground plane. Several sensor configurations have been designed, fabricated, and characterized to optimize responsivity and speed of operation and to minimize structural residual stress. Measured responsivity values as high as 1.2 deg/?W and time constants as low as 20 ms with detectable power on the order of 10 nW were obtained, indicating that the THz MEMS sensors have a great potential for real-time imaging.

  15. Investigation of high-temperature superconductors with terahertz bandwidth electrical pulses

    SciTech Connect

    Nuss, M.C.; Goossen, K.W. (AT and T Bell Labs., Holmdel, NJ (US))

    1989-12-01

    The authors summarize recent attempts to propagate ultrashort electrical pulses containing frequency components up to 1 THz on transmission lines made from thin films of the high temperature superconductor YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}. Optoelectronic generation of extremely-short electrical transients and jitter-free electooptic detection of the pulse shape and amplitude as they propagate along the superconducting line enable them to investigate the high-frequency properties of the high-T{sub c} material with high accuracy because of the long interaction lengths that are possible on transmission lines. They discuss the influence of epitaxy, surface roughness, and magnetic field on the pulse propagation. Important parameters like the magnetic penetration depth {lambda}(T) and the superconducting energy gap {Delta} are directly determined from the experimental data. The authors compare their results with weak-coupling BCS theory.

  16. Tunable narrowband terahertz emission from mastered laserelectron

    E-print Network

    Loss, Daniel

    bunch Storage ring Laser & pulse shaper Laser pulse analysis Figure 1 Principle of the experimentLETTERS Tunable narrowband terahertz emission from mastered laser­electron beam interaction S in the terahertz domain, promising candidates are nonlinear optical processes occurring when an intense laser beam

  17. Nanowire-based field effect transistors for terahertz detection and imaging systems

    NASA Astrophysics Data System (ADS)

    Romeo, L.; Coquillat, D.; Pea, M.; Ercolani, D.; Beltram, F.; Sorba, L.; Knap, W.; Tredicucci, A.; Vitiello, M. S.

    2013-05-01

    The development of self-assembled nanostructure technologies has recently opened the way towards a wide class of semiconductor integrated devices, with progressively optimized performances and the potential for a widespread range of electronic and photonic applications. Here we report on the development of field effect transistors (FETs) based on semiconductor nanowires (NWs) as highly-sensitive room-temperature plasma-wave broadband terahertz (THz) detectors. The electromagnetic radiation at 0.3?THz is funneled onto a broadband bow-tie antenna, whose lobes are connected to the source and gate FET electrodes. The oscillating electric field experienced by the channel electrons, combined with the charge density modulation by the gate electrode, results in a source-drain signal rectification, which can be read as a DC signal output. We investigated the influence of Se-doping concentration of InAs NWs on the detection performances, reaching responsivity values higher than 100 V W-1, with noise-equivalent-power of ˜10-9 W Hz-1/2. Transmission imaging experiments at 0.3 THz show the good reliability and sensitivity of the devices in a real practical application.

  18. Nanowire-based field effect transistors for terahertz detection and imaging systems.

    PubMed

    Romeo, L; Coquillat, D; Pea, M; Ercolani, D; Beltram, F; Sorba, L; Knap, W; Tredicucci, A; Vitiello, M S

    2013-05-31

    The development of self-assembled nanostructure technologies has recently opened the way towards a wide class of semiconductor integrated devices, with progressively optimized performances and the potential for a widespread range of electronic and photonic applications. Here we report on the development of field effect transistors (FETs) based on semiconductor nanowires (NWs) as highly-sensitive room-temperature plasma-wave broadband terahertz (THz) detectors. The electromagnetic radiation at 0.3?THz is funneled onto a broadband bow-tie antenna, whose lobes are connected to the source and gate FET electrodes. The oscillating electric field experienced by the channel electrons, combined with the charge density modulation by the gate electrode, results in a source-drain signal rectification, which can be read as a DC signal output. We investigated the influence of Se-doping concentration of InAs NWs on the detection performances, reaching responsivity values higher than 100 V W?¹, with noise-equivalent-power of ?10?? W Hz(?½). Transmission imaging experiments at 0.3 THz show the good reliability and sensitivity of the devices in a real practical application. PMID:23618953

  19. Terahertz spectroscopic investigations of leather in terahertz wave range

    NASA Astrophysics Data System (ADS)

    Song, Mei-jing; Li, Jiu-sheng

    2011-11-01

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

  20. Terahertz spectroscopic investigations of leather in terahertz wave range

    NASA Astrophysics Data System (ADS)

    Song, Mei-jing; Li, Jiu-sheng

    2012-03-01

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

  1. Terahertz Radiation from a Nonlinear Slab Traversed by an Optical Pulse

    SciTech Connect

    Zinov'ev, N. N. [Department of Physics, University of Durham, Durham DH1 3LE (United Kingdom); A. F. Ioffe Physical Technical Institute, 194021 St. Petersburg (Russian Federation); Nikoghosyan, A. S. [Department of Microwave Engineering, Yerevan State University, Yerevan 375025 (Armenia); Chamberlain, J. M. [Department of Physics, University of Durham, Durham DH1 3LE (United Kingdom)

    2007-01-26

    We report on the theoretical calculations considering collinear electromagnetic radiation at the propagation of an optical pulse through a slab of nonlinear material. Calculated waveforms of the radiated field fit well to the experimental dependencies showing the remarkable similarities between the radiation at nonlinear wave interaction and the radiation phenomena of moving external charges, similarly to discussed in the Tamm Problem and transition radiation of moving external charges.

  2. Observation of water trees using terahertz spectroscopy and time-domain imaging

    Microsoft Academic Search

    Ryo Sato; Marina Komatsu; Yoshimichi Ohki; Norikazu Fuse; Yoshinobu Nakamichi; Maya Mizuno; Kaori Fukunaga

    2011-01-01

    Terahertz measurements were carried out to detect water trees grown in low-density polyethylene sheets. Water absorbs light at terahertz frequencies, fairly strongly at about 5.0 THz and rather weakly from 0.1 to 1.0 THz. Using the absorption at these frequencies, observation of water trees was tried according to the following procedures. First, we made a model sample, consisting of a

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

    PubMed

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

    2014-10-01

    Experimental investigations have shown that terahertz pulsed imaging (TPI) is able to quantitatively characterize a range of multilayered media (e.g., biological issues, pharmaceutical tablet coatings, layered polymer composites, etc.). Advanced modeling of the interaction of terahertz radiation with a multilayered medium is required to enable the wide application of terahertz technology in a number of emerging fields, including nondestructive testing. Indeed, there have already been many theoretical analyses performed on the propagation of terahertz radiation in various multilayered media. However, to date, most of these studies used 1D or 2D models, and the dispersive nature of the dielectric layers was not considered or was simplified. In the present work, the theoretical framework of using terahertz waves for the quantitative characterization of multilayered media was established. A 3D model based on the finite difference time domain (FDTD) method is proposed. A batch of pharmaceutical tablets with a single coating layer of different coating thicknesses and different refractive indices was modeled. The reflected terahertz wave from such a sample was computed using the FDTD method, assuming that the incident terahertz wave is broadband, covering a frequency range up to 3.5 THz. The simulated results for all of the pharmaceutical-coated tablets considered were found to be in good agreement with the experimental results obtained using a commercial TPI system. In addition, we studied a three-layered medium to mimic the occurrence of defects in the sample. PMID:25401257

  4. Terahertz wave spectrum analysis of microstrip structure

    NASA Astrophysics Data System (ADS)

    Song, Mei-jing; Li, Jiu-sheng

    2012-03-01

    Terahertz wave is a kind of electromagnetic wave ranging from 0.1~10THz, between microwave and infrared, which occupies a special place in the electromagnetic spectrum. Terahertz radiation has a strong penetration for many media materials and nonpolar substance, for example, dielectric material, plastic, paper carton and cloth. In recent years, researchers around the world have paid great attention on terahertz technology, such as safety inspection, chemical biology, medical diagnosis and terahertz wave imaging, etc. Transmission properties of two-dimensional metal microstrip structures in the terahertz regime are presented and tested. Resonant terahertz transmission was demonstrated in four different arrays of subwavelength microstrip structure patterned on semiconductor. The effects of microstrip microstrip structure shape were investigated by using terahertz time-domain spectroscopy system. The resonant terahertz transmission has center frequency of 2.05 THz, transmission of 70%.

  5. Terahertz wave spectrum analysis of microstrip structure

    NASA Astrophysics Data System (ADS)

    Song, Mei-jing; Li, Jiu-sheng

    2011-11-01

    Terahertz wave is a kind of electromagnetic wave ranging from 0.1~10THz, between microwave and infrared, which occupies a special place in the electromagnetic spectrum. Terahertz radiation has a strong penetration for many media materials and nonpolar substance, for example, dielectric material, plastic, paper carton and cloth. In recent years, researchers around the world have paid great attention on terahertz technology, such as safety inspection, chemical biology, medical diagnosis and terahertz wave imaging, etc. Transmission properties of two-dimensional metal microstrip structures in the terahertz regime are presented and tested. Resonant terahertz transmission was demonstrated in four different arrays of subwavelength microstrip structure patterned on semiconductor. The effects of microstrip microstrip structure shape were investigated by using terahertz time-domain spectroscopy system. The resonant terahertz transmission has center frequency of 2.05 THz, transmission of 70%.

  6. Terahertz time-domain imaging of hidden defects in wooden artworks: application to a Russian icon painting.

    PubMed

    Skryl, Anton S; Jackson, J Bianca; Bakunov, Michael I; Menu, Michel; Mourou, Gerard A

    2014-02-20

    We use terahertz time-domain imaging and time-of-flight tomography to examine subsurface defects in an early-19th-century Russian icon painting. In the transmission geometry, we distinguish between native wood and higher-absorption knotted wood. In reflection, we identify a void in the wood filled with foreign filler material. By using time-of-flight tomographic analysis, we ascertain the depth of burial of the defects. This information helps us to identify the cause of surface faults in the painting, thus allowing the conservators to choose an adequate restoration strategy. PMID:24663298

  7. Pulsed-Source Interferometry in Acoustic Imaging

    NASA Technical Reports Server (NTRS)

    Shcheglov, Kirill; Gutierrez, Roman; Tang, Tony K.

    2003-01-01

    A combination of pulsed-source interferometry and acoustic diffraction has been proposed for use in imaging subsurface microscopic defects and other features in such diverse objects as integrated-circuit chips, specimens of materials, and mechanical parts. A specimen to be inspected by this technique would be mounted with its bottom side in contact with an acoustic transducer driven by a continuous-wave acoustic signal at a suitable frequency, which could be as low as a megahertz or as high as a few hundred gigahertz. The top side of the specimen would be coupled to an object that would have a flat (when not vibrating) top surface and that would serve as the acoustical analog of an optical medium (in effect, an acoustical "optic").

  8. TUNABLE TERAHERTZ GENERATION IN QUASI-PHASEMATCHED GALLIUM ARSENIDE

    Microsoft Academic Search

    Joseph E. Schaar; Konstantin L. Vodopyanov; Martin M. Fejer

    Sources of electromagnetic radiation with terahertz (THz) frequencies have been actively investigated during the last decade for applications in imaging and spectroscopic sensors. Femtosecond optical pulses have been shown to efficiently generate THz waves in quasi-phasematched (QPM) gallium arsenide (GaAs) (1). In this work we demonstrate a picosecond system creating a near diffraction-limited THz source with 1 mW of average

  9. Contactless photoconductive terahertz generation.

    PubMed

    Zhang, H; Wahlstrand, J K; Choi, S B; Cundiff, S T

    2011-01-15

    We describe a pulsed terahertz (THz) emitter that uses a rapidly oscillating, high-voltage bias across electrodes insulated from a photoconductor. Because no carriers are injected from the electrodes, trap-enhanced electric fields do not form. The resulting uniform field allows excitation with a large laser spot, lowering the carrier density for a given pulse energy and increasing the efficiency of THz generation. Compared to a dc bias, less susceptibility to damage is observed. PMID:21263507

  10. A terahertz molecular switch.

    PubMed

    Orellana, P; Claro, F

    2003-05-01

    We present time-dependent results describing the current through a molecular device, modeled as a complex with two active centers connected to leads under bias. We show that, at a properly adjusted external voltage, a passing terahertz electromagnetic pulse may cause a transition between states of finite and negligible current, suggesting that the system might be useful as a nanoscopic switch in the terahertz range. A phase diagram defining the bias region in which the transition takes place within a short time is given. As described, the physical processes involved are of an entirely different nature than those in ordinary photodetectors. PMID:12786110

  11. Carbon irradiated semi insulating GaAs for photoconductive terahertz pulse detection.

    PubMed

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S S; Mathimalar, S; Nanal, Vandana; Pillay, R G; Döhler, G H

    2015-03-01

    We report here a photoconductive material for THz detection with sub-picosecond carrier lifetime made by C12 (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C12) ions. With an increase of the irradiation dose from ~1012 /cm2 to ~1015 /cm2 the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, whereas that of usual non-irradiated SI-GaAs is ~70 picosecond. This decreased carrier lifetime has resulted in a strong improvement in THz pulse detection compared with normal SI-GaAs. Improvement in signal to noise ratio as well as in detection bandwidth is observed. Carbon irradiated SI-GaAs appears to be an economical alternative to low temperature grown GaAs for fabrication of THz devices. PMID:25836882

  12. Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials Using Terahertz Energy

    NASA Technical Reports Server (NTRS)

    Roth, Donald J (Inventor)

    2011-01-01

    A process for simultaneously measuring the velocity of terahertz electromagnetic radiation in a dielectric material sample without prior knowledge of the thickness of the sample and for measuring the thickness of a material sample using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of the terahertz electromagnetic radiation in the sample is disclosed and claimed. The process evaluates, in a plurality of locations, the sample for microstructural variations and for thickness variations and maps the microstructural and thickness variations by location. A thin sheet of dielectric material may be used on top of the sample to create a dielectric mismatch. The approximate focal point of the radiation source (transceiver) is initially determined for good measurements.

  13. Terahertz frequency spectrum characterization of coherent heterodyne time-domain spectrometer

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  14. Two-pulse biexponential-weighted 23Na imaging.

    PubMed

    Benkhedah, Nadia; Bachert, Peter; Nagel, Armin M

    2014-03-01

    A new method is proposed for acquiring 3D biexponential-weighted sodium images with two instead of three RF pulses to allow for shorter repetition time at high magnetic fields (B0?7 T) and reduced SAR. The second pulse converts single- into triple-quantum coherences in regions containing sodium ions which are restricted in mobility. Since only single-quantum coherences can be detected, an image acquired after the second pulse is intrinsically single-quantum-filtered and can be used to generate a biexponential-weighted sodium image by a weighted subtraction with the spin-density-weighted image acquired between the pulses. The proposed sequence generates biexponential-weighted sodium images of in vivo human brain with 140% higher SNR than triple-quantum-filtered sodium images and 4% higher SNR than a biexponential-weighted sequence with three RF pulses at equal acquisition time and with 1/3 lower SAR. As SAR is reduced, accordingly repetition time can be spared to obtain even higher SNR-time efficiency. In comparison to a difference image generated from two images of a double-readout sequence, the proposed two-pulse sequence yields about 14% higher SNR. Our new two-pulse biexponential-weighted sequence allows for acquisition of full 3D data sets of the human brain in vivo with a nominal resolution of (5 mm)(3) in about 10 min. PMID:24530955

  15. Two-pulse biexponential-weighted 23Na imaging

    NASA Astrophysics Data System (ADS)

    Benkhedah, Nadia; Bachert, Peter; Nagel, Armin M.

    2014-03-01

    A new method is proposed for acquiring 3D biexponential-weighted sodium images with two instead of three RF pulses to allow for shorter repetition time at high magnetic fields (B0 ? 7 T) and reduced SAR. The second pulse converts single- into triple-quantum coherences in regions containing sodium ions which are restricted in mobility. Since only single-quantum coherences can be detected, an image acquired after the second pulse is intrinsically single-quantum-filtered and can be used to generate a biexponential-weighted sodium image by a weighted subtraction with the spin-density-weighted image acquired between the pulses. The proposed sequence generates biexponential-weighted sodium images of in vivo human brain with 140% higher SNR than triple-quantum-filtered sodium images and 4% higher SNR than a biexponential-weighted sequence with three RF pulses at equal acquisition time and with 1/3 lower SAR. As SAR is reduced, accordingly repetition time can be spared to obtain even higher SNR-time efficiency. In comparison to a difference image generated from two images of a double-readout sequence, the proposed two-pulse sequence yields about 14% higher SNR. Our new two-pulse biexponential-weighted sequence allows for acquisition of full 3D data sets of the human brain in vivo with a nominal resolution of (5 mm)3 in about 10 min.

  16. Reconstruction of pulse noisy images via stochastic resonance

    PubMed Central

    Han, Jing; Liu, Hongjun; Sun, Qibing; Huang, Nan

    2015-01-01

    We investigate a practical technology for reconstructing nanosecond pulse noisy images via stochastic resonance, which is based on the modulation instability. A theoretical model of this method for optical pulse signal is built to effectively recover the pulse image. The nanosecond noise-hidden images grow at the expense of noise during the stochastic resonance process in a photorefractive medium. The properties of output images are mainly determined by the input signal-to-noise intensity ratio, the applied voltage across the medium, and the correlation length of noise background. A high cross-correlation gain is obtained by optimizing these parameters. This provides a potential method for detecting low-level or hidden pulse images in various imaging applications. PMID:26067911

  17. Reconstruction of pulse noisy images via stochastic resonance.

    PubMed

    Han, Jing; Liu, Hongjun; Sun, Qibing; Huang, Nan

    2015-01-01

    We investigate a practical technology for reconstructing nanosecond pulse noisy images via stochastic resonance, which is based on the modulation instability. A theoretical model of this method for optical pulse signal is built to effectively recover the pulse image. The nanosecond noise-hidden images grow at the expense of noise during the stochastic resonance process in a photorefractive medium. The properties of output images are mainly determined by the input signal-to-noise intensity ratio, the applied voltage across the medium, and the correlation length of noise background. A high cross-correlation gain is obtained by optimizing these parameters. This provides a potential method for detecting low-level or hidden pulse images in various imaging applications. PMID:26067911

  18. Terahertz Imaging and Remote Sensing Design for Applications in Medical Imaging

    E-print Network

    Sung, Shijun

    2013-01-01

    Normalized signal strength versus target plane depth (b) DOFtarget was translated in the ±z direction (denoted in Figure 4-1) to measure signal strengthtarget (polished aluminum plate) placed at the imaging plane. The return signal strength

  19. Antenna-coupled field-effect transistors for multi-spectral terahertz imaging up to 4.25 THz.

    PubMed

    Bauer, M; Venckevi?ius, R; Kašalynas, I; Boppel, S; Mundt, M; Minkevi?ius, L; Lisauskas, A; Valušis, G; Krozer, V; Roskos, H G

    2014-08-11

    We demonstrate for the first time the applicability of antenna-coupled field-effect transistors for the detection of terahertz radiation (TeraFETs) for multi-spectral imaging from 0.76 to 4.25 THz. TeraFETs were fabricated in a commercial 90-nm CMOS process and noise-equivalent powers of 59, 20, 63, 85 and 110?pW/?(Hz) at 0.216, 0.59, 2,52, 3.11 and 4.25 THz, respectively, have been achieved. A set of TeraFETs has been applied in raster-scan transmission and reflection imaging of pellets of sucrose and tartaric acid simulating common plastic explosives. Transmittance values are in good agreement with Fourier-transform infrared spectroscopy data. The spatial distribution of the components in the samples has been determined from the transmission data using principal component analysis. PMID:25321008

  20. Improvements in Magnetic Resonance Imaging Excitation Pulse Design

    E-print Network

    Goyal, Vivek K

    Improvements in Magnetic Resonance Imaging Excitation Pulse Design by Adam Charles Zelinski magnetic spins are tilted by only a small amount, pulse transmission may be interpreted as depositing by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Terry P. Orlando Chairman, Department Committee on Graduate Students #12;2 #12;Improvements in Magnetic

  1. Improvements in magnetic resonance imaging excitation pulse design

    E-print Network

    Zelinski, Adam Charles

    2008-01-01

    This thesis focuses on the design of magnetic resonance imaging (MRI) radio-frequency (RF) excitation pulses, and its primary contributions are made through connections with the novel multiple-system single-output (MSSO) ...

  2. Terahertz Frequency Sensing and Imaging: A Time of Reckoning Future Applications?

    Microsoft Academic Search

    DWIGHT L. WOOLARD; R. Brown; MICHAEL PEPPER; MICHAEL KEMP

    2005-01-01

    In recent years, the field of terahertz (THz) science and technology has entered a completely new phase of unprecedented expansion that is generating ever growing levels of broad-based international attention. In particular,there have been important advances in state-of-the-art THz technology and very enthusiastic growth in research activities associated with related scientific and industrial applications. One can legitimately argue that the

  3. Infrared imaging of defects heated by a sonic pulse

    NASA Astrophysics Data System (ADS)

    Favro, L. D.; Han, Xiaoyan; Ouyang, Zhong; Sun, Gang; Sui, Hua; Thomas, R. L.

    2000-06-01

    High-frequency pulsed sonic excitation is combined with an infrared camera to image surface and subsurface defects. Irreversible temperature increases on the surface of the object, resulting from localized heating in the vicinity of cracks, disbonds, or delaminations, are imaged as a function of time prior to, during, and following the application of a short pulse of sound. Pulse durations of 50 ms are sufficient to image such defects, and result in surface temperatures variations of ˜2 °C above the defect. As an example, sonic infrared images are presented for two fatigue cracks in Al and of interply delamination impact damage in a graphite-fiber-reinforced polymer composite. The shorter of the two fatigue cracks is ˜0.7 mm in length, and is tightly closed. Thus, this new technique is sensitive, and capable of rapid imaging of defects under wide surface areas of an object.

  4. Discrete Pulse Transform of images: Algorithm and applications

    Microsoft Academic Search

    Bobby Anguelov

    2008-01-01

    The Discrete Pulse Transform (DPT), a well known method for the analysis of signals, was recently extended to images. Here we propose an efficient algorithm generating DPT on a given image and discuss some applications. These include detecting objects of interest in a scene and identifying textures by granulometric curves.

  5. Nonlinear Response of the High-Temperature Superconductor YBa2Cu3O7-? to the Transmission of Intense Terahertz Pulses

    NASA Astrophysics Data System (ADS)

    Kawayama, Iwao; Glossner, Andreas; Zhang, Caihong; Kikuta, Shinya; Murakami, Hironaru; Müller, Paul; Tonouchi, Masayoshi

    2012-02-01

    High-Power Terahertz Time-Domain Spectroscopy (THz-TDS) was used to examine YBa2Cu3O7-? thin films when transmitted by intense single-cycle THz pulses. This allowed for an investigation of the nonlinear, time-resolved behavior of YBa2Cu3O7-? in the presence of strong THz electric fields for the first time. High field strengths of tens of kV cm-1 were achieved by improving the efficiency of optical rectification in LiNbO3 through the tilted-pulse-front method and by ensuring a tight focusing of the THz beam. In the case of low field strengths, the behavior of the thin films agrees with previous examinations of YBa2Cu3O7-? by means of conventional, low-power THz-TDS. However, for strong THz electric fields, it was found by analysis with the two-fluid model that the superfluid population decreases dramatically, possibly due to Cooper pair breakup. This was accompanied by a drop in the imaginary part of the conductivity in the investigated frequency range of 0.2 to 0.8 THz. The results further suggest a decrease of the effective mass of the carriers for strong THz fields.

  6. Generation of elliptically polarized terahertz waves from laser-induced plasma with double helix electrodes.

    PubMed

    Lu, Xiaofei; Zhang, X-C

    2012-03-23

    By applying a helical electric field along a plasma region, a revolving electron current is formed along the plasma and an elliptically polarized far-field terahertz wave pattern is observed. The observed terahertz wave polarization reveals the remarkable role of velocity retardation between optical pulses and generated terahertz pulses in the generation process. Extensive simulations, including longitudinal propagation effects, are performed to clarify the mechanisms responsible for polarization control of air-plasma-based terahertz sources. PMID:22540584

  7. Terahertz Quantum-Cascade Transmission-Line Metamaterials

    NASA Astrophysics Data System (ADS)

    Tavallaee, Amir Ali

    Terahertz quantum-cascade (QC) lasers operating at 0.6 - 5 THz (? ˜ 60 - 500 µm) are poised to become the dominant solid-state sources of continuous-wave (cw) far-infrared radiation enabling applications in terahertz spectroscopy, imaging, and sensing. QC-lasers are the longest wavelength semiconductor laser sources in which terahertz gain is obtained from electronic intersubband radiative transitions in GaAs/AlGaAs heterostructure quantum wells. Since their invention in 2001, rapid development has enabled demonstration of cw powers greater than 100 mW. However, challenges still remain in the areas of operating temperature, laser efficiency and power, and beam quality to name a few. The highest-temperature operation of terahertz quantum-cascade lasers (200 K pulsed, 117 K cw) depends on the use of a low-loss "metal-metal" waveguide where the active gain material is sandwiched between two metal cladding layers; a technique similar, in concept, to microstrip transmission line technology at microwave frequencies. Due to the subwavelength transverse dimensions of the metal-metal waveguide, however, obtaining a directive beam pattern and efficient out-coupling of THz power is non-trivial. This thesis reports the demonstration of a one-dimensional waveguide for terahertz quantum-cascade lasers that acts as a leaky-wave antenna and tailors laser radiation in one dimension to a directional beam. This scheme adapts microwave transmission-line metamaterial concepts to a planar structure realized in terahertz metal-metal waveguide technology and is fundamentally different from distributed feedback/photonic crystal structures that work based on Bragg scattering of propagating modes. The leaky-wave metamaterial antenna operates based on a propagating mode with an effective phase index smaller than unity such that it radiates in the surface direction via a leaky-wave mechanism. Surface emission (˜ 40° from broadside) with a single directive beam (FWHM ˜ 15°) at 2.74 THz was demonstrated from terahertz QC-lasers with leaky-wave coupler antennas which exhibited slope efficiencies ˜ 4 times greater than conventional Fabry-Perot metal-metal waveguides. Using this technique the first demonstration of beam scanning for a terahertz QC-laser was reported (from 35° - 60°) as the emission frequency varied from 2.65 - 2.81 THz. Towards the bigger goal of realizing an active terahertz metamaterial to ultimately develop "zero-index" terahertz quantum-cascade lasers immune to spatial hole burning, or "negative-index" metamaterials for superresolution terahertz imaging, a composite right-/left-handed transmission-line metamaterial based upon subwavelength metal waveguide loaded with terahertz QC material was demonstrated. Due to the addition of distributed series capacitors (realized by introducing gaps in top metallization) and shunt inductors (realized by operating in the higher-order lateral mode of the waveguide), the transmission-line metamaterial exhibits left-handed (backward waves or negative index) leaky-wave propagation from 2.3 - 2.45 THz in addition to the conventional right-handed leaky-wave behavior (from 2.6 - 3.0 THz).

  8. Nondestructive testing potential evaluation of a terahertz frequency-modulated continuous-wave imager for composite materials inspection

    NASA Astrophysics Data System (ADS)

    Cristofani, Edison; Friederich, Fabian; Wohnsiedler, Sabine; Matheis, Carsten; Jonuscheit, Joachim; Vandewal, Marijke; Beigang, René

    2014-03-01

    The sub-terahertz (THz) frequency band has proved to be a noteworthy option for nondestructive testing (NDT) of nonmetal aeronautics materials. Composite structures or laminates can be inspected for foreign objects (water or debris), delaminations, debonds, etc., using sub-THz sensors during the manufacturing process or maintenance. Given the harmless radiation to the human body of this frequency band, no special security measures are needed for operation. Moreover, the frequency-modulated continuous-wave sensor used in this study offers a very light, compact, inexpensive, and high-performing solution. An automated two-dimensional scanner carrying three sensors partially covering the 70- to 320-GHz band is operated, using two complementary measurement approaches: conventional focused imaging, where focusing lenses are used; and synthetic aperture (SA) or unfocused wide-beam imaging, for which lenses are no longer needed. Conventional focused imagery offers finer spatial resolutions but imagery is depth-limited due to the beam waist effect, whereas SA measurements allow imaging of thicker samples with depth-independent but coarser spatial resolutions. The present work is a compendium of a much larger study and describes the key technical aspects of the proposed imaging techniques and reports on results obtained from human-made samples (A-sandwich, C-sandwich, solid laminates) which include diverse defects and damages typically encountered in aeronautics multilayered structures. We conclude with a grading of the achieved results in comparison with measurements performed by other NDT techniques on the same samples.

  9. Portable pulsed electronic digital X-ray imager

    Microsoft Academic Search

    Wang Yi; Wang Jingjin; Wang Kuilu; Liu Guozhi; Zhu Guofu; Zhang Yuanlin; Du Hongliang

    1999-01-01

    A portable, pulsed electronic digital X-ray imaging device has been developed. The system is intended to be used in explosive ordnance disposal, police and customs baggage inspection and nondestructive testing (NDT). Image acquisition is performed by a charge-coupled-device (CCD) imaging sensors which view the output of an X-ray scintillation screen via an optical system. The construction of the system, its

  10. Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, 9 -11th April, 2003, Grainau, The Design and Operation of TeraHertz Sources

    E-print Network

    Kolodzey, James

    ), diode frequency multipliers (to 2.5 THz), and femtosecond optical pulse switches. Infrared emitters to microwaves, the far-infrared or TeraHertz frequency range has significant reductions in antenna sizes, and greater communication bandwidth. Commercial applications comprise thermal imaging, remote chemical sensing

  11. Characteristic responses of biological and nanoscale systems in the terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Angeluts, A. A.; Balakin, A. V.; Evdokimov, M. G.; Esaulkov, M. N.; Nazarov, M. M.; Ozheredov, I. A.; Sapozhnikov, D. A.; Solyankin, P. M.; Cherkasova, O. P.; Shkurinov, A. P.

    2014-07-01

    This paper briefly examines methods for the generation of pulsed terahertz radiation and principles of pulsed terahertz spectroscopy, an advanced informative method for studies of complex biological and nanostructured systems. Some of its practical applications are described. Using a number of steroid hormones as examples, we demonstrate that terahertz spectroscopy in combination with molecular dynamics methods and computer simulation allows one to gain information about the structure of molecules in crystals. A 'terahertz colour vision' method is proposed for analysis of pulsed terahertz signals reflected from biological tissues and it is shown that this method can be effectively used to analyse the properties of biological tissues and for early skin cancer diagnosis.

  12. Applications of Ultrafast Terahertz Pulses for Intra-ExcitonicSpectroscopy of Quasi-2D Electron-Hole Gases

    SciTech Connect

    Kaindl, Robert A.; Carnahan, Marc A.; Hagele, Daniel; Chemla, D.S.

    2006-09-02

    Excitons are of fundamental interest and of importance foropto-electronic applications of bulk and nano-structured semiconductors.This paper discusses the utilization of ultrafast terahertz (THz) pulsesfor the study of characteristic low-energy excitations of photoexcitedquasi 2D electron-hole (e-h) gases. Optical-pump THz-probe spectroscopyat 250-kHz repetition rate is employed to detect characteristic THzsignatures of excitons and unbound e-h pairs in GaAs quantum wells.Exciton and free-carrier densities are extracted from the data using atwo-component model. We report the detailed THz response and pairdensities for different photoexcitation energies resonant to heavy-holeexcitons, light-hole excitons, or the continuum of unbound pairs. Suchexperiments can provide quantitative insights into wavelength, time, andtemperature dependence of the low-energy response and composition ofoptically excited e-h gases in low-dimensionalsemiconductors.

  13. Potential for detection of explosive and biological hazards with electronic terahertz systems: One contribution of 16 to a Discussion Meeting 'The terahertz gap: the generation of far-infrared radiation and its applications'

    Microsoft Academic Search

    Min Ki Choi; Alan Bettermann; D. W. van der Weide

    2004-01-01

    The terahertz (THz) regime (0.1-10 THz) is rich with emerging possibilities in sensing, imaging and communications, with unique applications to screening for weapons, explosives and biohazards, imaging of concealed objects, water content and skin. Here we present initial surveys to evaluate the possibility of sensing plastic explosives and bacterial spores using field-deployable electronic THz techniques based on short-pulse generation and

  14. January 1, 1990 / Vol. 15, No. 1 / OPTICS LETTERS 51 Generation of terahertz-rate trains of femtosecond pulses by

    E-print Network

    Purdue University

    frequency components that are spatially dispersed within a simple lens and grating apparatus.6' 7' 9 of femtosecond pulses 6 as well as generation of femtosecond dark pulses for studies of dark-soliton propagation by reactive ion etching. This procedure yields a binary phase mask, with the phase difference given by AO= 2?r

  15. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 2, NO. 3, SEPTEMBER 1996 709 Terahertz Waveform Synthesis

    E-print Network

    Purdue University

    as generation of ultrafast bit sequences at terahertz frequencies. We present a theory which accurately predicts. Detected terahertz pulses can be as fast as a single-cycle or even half-cycle and can span a spectral range

  16. Tunable and efficient terahertz radiation generation by photomixing of two super Gaussian laser pulses in a corrugated magnetized plasma

    NASA Astrophysics Data System (ADS)

    Varshney, Prateek; Sajal, Vivek; Singh, Kunwar Pal; Kumar, Ravindra; Sharma, Navneet K.

    2015-05-01

    A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies ( ? 1 , ? 2 ) and wave numbers ( k ? 1 , k ? 2 ) in a performed corrugated plasma embedded with transverse dc magnetic field. Lasers exert a nonlinear ponderomotive force, imparting an oscillatory velocity to plasma electrons that couples with the density corrugations ( n ' = n ? 0 e i ? z ) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ˜ ? h (upper hybrid frequency). The periodicity of density corrugations is suitably chosen to transfer maximum momentum from lasers to THz radiation at phase matching conditions ? = ? 1 - ? 2 and k ? = k ? 1 - k ? 2 + ? ? . The efficiency, power, beam quality, and tunability of the present scheme exhibit high dependency upon the applied transverse dc magnetic field along with q-indices and beam width parameters ( a 0 ) of super Gaussian lasers. In the present scheme, efficiency ˜10-2 is achieved with the optimization of all these parameters.

  17. Pulsed holography for combustion diagnostics. [image reconstruction

    NASA Technical Reports Server (NTRS)

    Klein, N.; Dewilde, M. A.

    1980-01-01

    Image reconstruction and data extraction techniques were considered with respect to their application to combustion diagnostics. A system was designed and constructed that possesses sufficient stability and resolution to make quantitative data extraction possible. Example data were manually processed using the system to demonstrate its feasibility for the purpose intended. The system was interfaced with the PDP-11-04 computer for maximum design capability. It was concluded that the use of specialized digital hardware controlled by a relatively small computer provides the best combination of accuracy, speed, and versatility for this particular problem area.

  18. Terahertz Science, Technology, and Communication

    NASA Technical Reports Server (NTRS)

    Chattopadhyay, Goutam

    2013-01-01

    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.

  19. 406 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 2, NO. 4, JULY 2012 Understanding THz Pulse Propagation in the

    E-print Network

    Oklahoma State University

    THz Pulse Propagation in the Atmosphere Yihong Yang, Student Member, IEEE, Mahboubeh Mandehgar, and Daniel R. Grischkowsky, Fellow, IEEE Abstract--In this paper, we have extracted the THz refractivity of water vapor ( ( ) 1) from the complex spectra of the pre- cise coherent THz-TDS absorption measurement

  20. A spatial light modulator for terahertz beams

    SciTech Connect

    Chen, Hou-tong [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

    2009-01-01

    Spatial light modulators that control the spatial transmission of a terahertz beam either electrically or optically, have been difficult to build due to the lack of suitable materials. Here we propose the use of active terahertz metamaterials for the construction of a multi-pixel spatial modulator for terahertz beams. Our first-generation device consists of a 4 x 4 pixel array, where each pixel is an array of sub-wavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. Through terahertz transmission experiments, we show that the spatial modulator has a uniform modulation depth of around 40 percent across all pixels at the resonant frequency. Around this operating frequency, the crosstalk between pixels is negligible. This device can operate under small voltage levels, at room temperature, with low power consumption and reasonably high switching speed, and can therefore benefit future applications in terahertz imaging and communications.

  1. Plasma characterization with terahertz timedomain measurements S. P. Jamisona)

    E-print Network

    Strathclyde, University of

    Plasma characterization with terahertz time­domain measurements S. P. Jamisona) Department­domain spectral techniques are applied to the characterization of a He discharge plasma. Electro-optically sampling of the electric field of a quasi-unipolar terahertz pulse transmitted through the plasma has

  2. Combined simulated annealing and Shinnar Le Roux pulse design of slice-multiplexed RF pulses for multi-slice imaging

    NASA Astrophysics Data System (ADS)

    Lee, K. J.; Paley, M. N. J.; Wild, J. M.

    2006-09-01

    Slice-multiplexed RF pulses have recently been introduced for simultaneous multi-slice imaging. Their novel aspect is that each slice is given a different linear phase profile, and hence a different slice-rephasing requirement, by the pulse. During readout, extra slice gradients are applied such that when one slice is rephased, the others are dephased to prevent aliasing. In this paper, an improved method of designing slice-multiplexed RF pulses is presented: component pulses which are optimized with simulated annealing for a specific rephasing are combined using Shinnar-Le Roux methods. In this way, non-linearities at higher flip angles are taken into account and more slices can be excited. Bloch simulations show the phase and amplitude profile of component pulses are faithfully preserved in the multiplexed pulse. Three- and four-slice multiplex pulses are demonstrated in gradient- and spin-echo in-vivo imaging.

  3. Linear synthetic aperture modes for ultrasonic pulse-echo imaging.

    PubMed

    Lang, M; Ermert, H

    1997-05-01

    A unified approach is developed to characterize and compare the most widely used two-dimensional ultrasound pulse-echo imaging procedures. The methods of monostatic, bistatic and multistatic time-domain holography are theoretically investigated with regard to line spread functions, resolution capabilities, and the effects of multiple scattering and object inhomogeneities. Analytical derivations and computer simulations show the superiority of monostatic holography in applications such as nondestructive testing, where in most cases the assumptions generally made in the calculation of the inverse scattering formulae are justified. However, if higher order scattering and/or the spatial variations of the sound speed play a significant role, then multistatic imaging is more advantageous. A modification of this latter mode, with fixed focus on transmission, is commonly used in medical imaging B-scan systems, but implementation of the full algorithm would offer improved resolving power and reduced side lobe levels throughout the image plane. PMID:9206320

  4. Diffusion and Swelling Measurements in Pharmaceutical Powder Compacts Using Terahertz Pulsed Imaging

    E-print Network

    Yassin, Samy; Su, Ke; Lin, Hungyen; Gladden, Lynn F.; Zeitler, J. Axel

    2015-02-02

    of Eudragit, lac- tose, and HPMC using the compaction simulator. The dashed black line corresponds to the readings from the lower punch and the red line shows the forces acting on the upper punch. Yassin et al., JOURNAL OF PHARMACEUTICAL SCIENCES DOI 10... to wavelengths of 5.00 to 0.09 mm. High- resistivity silicon lenses and silicon probe optics focus the tera- hertz radiation to a diffraction-limited spot (200 :m diameter at a distance of 7 mm in front of the optics), where the sample is placed. A homemade...

  5. Quantifying pharmaceutical film coating with optical coherence tomography and terahertz pulsed imaging: an evaluation

    E-print Network

    Lin, Hungyen; Dong, Yue; Shen, Yaochun; Zeitler, J. Axel

    2015-06-11

    alcohol–polyethyleneglycol graft copolymer (Kolicoat® IR), 0.075% w/w polyoxyethylene(20) sorbitan monooleate (Polysorbate 80), 0.3% w/w glycerolmonostearate, 0.75% w/w triethylcitrate and 42.87% w/w deionised water. The tablet cores were coated in a...

  6. Characteristics of nonlinear imaging of broadband laser stacked by chirped pulses

    NASA Astrophysics Data System (ADS)

    Wang, Youwen; You, Kaiming; Chen, Liezun; Lu, Shizhuan; Dai, Zhiping; Ling, Xiaohui

    2014-11-01

    Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.

  7. Real-time terahertz imaging of nonmetallic objects for security screening and anti-counterfeiting applications

    NASA Astrophysics Data System (ADS)

    Behnken, Barry N.; Karunasiri, Gamani

    2008-10-01

    We report the use of a 160×120 pixel microbolometer camera, under illumination by a milliwatt-scale 3.6 THz quantum cascade laser, for real-time imaging of materials which are exclusively nonmetallic in character. By minimizing diffraction effects suffered by the camera system and operating the laser at bias currents approaching saturation values, an imaging scheme was developed in which overlapping samples of nonmetallic materials can be imaged with high fidelity and long persistence times. Furthermore, an examination of various security features embedded within domestic and foreign currency notes suggests that this imaging scheme could serve a future role in detection of assorted counterfeiting practices.

  8. Terahertz Polarization Imaging for Colon Cancer Detection Pallavi Doradlaa,b

    E-print Network

    Massachusetts at Lowell, University of

    for lymph node staging in rectal cancer [14]. OCT provides high resolution (1 m, depending on the incident tomography (PET) [5,6], magnetic resonance imaging (MRI) [7,8], and optical coherence tomography (OCT) [9's experience. Besides the conventional colonoscopy, CT, MRI and PET are current diagnostic imaging modalities

  9. High-speed terahertz reflection three-dimensional imaging for nondestructive

    E-print Network

    ) imaging based on electronically controlled optical sampling (ECOPS). ECOPS enables scanning of an axial is obtained, which is made of glass fiber reinforced polymer composite material and has defects such as delamination and inclusion, and is compared with an ultrasonic reflection 3D image of the sample. ©2012 Optical

  10. Recent development of terahertz wave sensing and imaging science, technology, and applications

    NASA Astrophysics Data System (ADS)

    Zhang, X.-C.

    2006-03-01

    Recent advances in THz science and technology make it one of the most promising research areas in the 21st century for sensing and imaging, as well as in other interdisciplinary fields. We believe new T-ray capabilities will impact a range of interdisciplinary fields and industrial companies, including: communications, imaging, medical diagnosis, health monitoring, environmental control, and chemical and biological identification. While microwave and X-ray imaging modalities produce density pictures, T-ray imaging provides spectroscopic information within the THz frequency range. The unique rotational and vibrational responses of materials within the THz range provide information that is generally absent in optical, X-ray and NMR images. A THz wave can easily penetrate and inspect the insides of most dielectric materials, which are opaque to visible light and low contrast to X-rays, making T-rays a useful complementary imaging source in this context. Recent developments of THz wave technologies allow us to coherently control a THz wave (phase, amplitude, and directionality). I present its impacts the physics understanding and industrial applications. Examples of imaging a long distance target (>100 meters), large scale industrial samples (>m2), or a small scale semiconductor device (a few nanometer) will be presented.

  11. Approaching real-time terahertz imaging using photo-induced reconfigurable aperture arrays

    NASA Astrophysics Data System (ADS)

    Shams, Md. Itrat Bin; Jiang, Zhenguo; Rahman, Syed; Qayyum, Jubaid; Hesler, Jeffrey L.; Cheng, Li-Jing; Xing, Huili Grace; Fay, Patrick; Liu, Lei

    2014-05-01

    We report a technique using photo-induced coded-aperture arrays for potential real-time THz imaging at roomtemperature. The coded apertures (based on Hadamard coding) were implemented using programmable illumination on semi-insulating Silicon wafer by a commercial digital-light processing (DLP) projector. Initial imaging experiments were performed in the 500-750 GHz band using a WR-1.5 vector network analyzer (VNA) as the source and receiver. Over the entire band, each array pixel can be optically turned on and off with an average modulation depth of ~20 dB and ~35 dB, for ~4 cm2 and ~0.5 cm2 imaging areas respectively. The modulation speed is ~1.3 kHz using the current DLP system and data acquisition software. Prototype imaging demonstrations have shown that a 256-pixel image can be obtained in the order of 10 seconds using compressed sensing (CS), and this speed can be improved greatly for potential real-time or video-rate THz imaging. This photo-induced coded-aperture imaging (PI-CAI) technique has been successfully applied to characterize THz beams in quasi-optical systems and THz horn antennas.

  12. Simulation of terahertz generation in corrugated plasma waveguides

    SciTech Connect

    Pearson, Andrew J.; Palastro, John; Antonsen, Thomas M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)

    2011-05-15

    We simulate the response of a corrugated plasma channel to an ultrashort laser pulse in two dimensions with the goal of demonstrating the production of terahertz frequency electromagnetic modes. Corrugated channels support electromagnetic modes that have a Floquet-type dispersion relation and thus consist of a sum of spatial harmonics with subluminal phase velocities. This allows the possibility of phase matching between the ponderomotive potential associated with the laser pulse and the electromagnetic modes of the channel. Since the bandwidth of an ultrashort pulse includes terahertz frequencies, significant excitation of terahertz radiation is possible. Here we consider realistic density profiles to obtain predictions of the terahertz power output and mode structure for a channel with periodic boundary conditions. We then estimate pulse depletion effects from our simulation results. The fraction of laser energy converted to terahertz is independent of laser pulse energy in the linear regime, and we find it to be around 1%. Extrapolating to a pulse energy of 0.5 J gives a terahertz power output of 6 mJ with a pulse depletion length of less than 20 cm.

  13. A Source for Ultrafast Continuum Infrared and Terahertz Radiation

    E-print Network

    Petersen, Poul B.

    A compact and stable method for generating high-intensity linearly polarized continuum mid-IR and terahertz light using ultrafast femtosecond (fs) laser pulses is demonstrated. Continuous light generation from <400cm?1 ...

  14. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Diffraction of terahertz waves after passing through a Fresnel lens

    Microsoft Academic Search

    Yu-Lei Shi; Qing-Li Zhou; Cun-Lin Zhang

    2009-01-01

    The spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory. The simulation shows that the transmitted terahertz waveforms compress with increasing propagation distance, and the multi-frequency focusing phenomenon at different focal points is observed. Additionally, the distribution of terahertz fields in a plane perpendicular to the axis

  15. Active terahertz metamaterials

    SciTech Connect

    Chen, Hou-tong [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

    2009-01-01

    In this paper we present an overview of research in our group in terahertz (THz) metamaterials and their applications. We have developed a series of planar metamaterials operating at THz frequencies, all of which exhibit a strong resonant response. By incorporating natural materials, e.g. semiconductors, as the substrates or as critical regions of metamaterial elements, we are able to effectively control the metamaterial resonance by the application of external stimuli, e.g., photoexcitation and electrical bias. Such actively controllable metamaterials provide novel functionalities for solid-state device applications with unprecedented performance, such as THz spectroscopy, imaging, and many others.

  16. High Power Terahertz Conductive Antenna with Chaotic Electrodes

    NASA Astrophysics Data System (ADS)

    Kim, Christopher; Graber, Benjamin; Wu, Dong Ho

    2015-03-01

    Time domain terahertz spectroscopy (TDTS) is now widely adopted and being used for various purposes, including chemical and material analysis as well as detection of hazardous materials in the laboratories. While there are several different methods available to generate a wideband terahertz pulse for the TDTS, currently a terahertz photoconductive antenna may be the most popular one, as it can produce a wideband terahertz pulse very efficiently. However our experimental investigation indicates that the conventional photoconductive antenna with a pair of parallel electrodes can produce a terahertz pulse at most about 100 micro-Watts. When attempted to produce a higher power terahertz pulse the antenna may experience irrevocable failure. In order to overcome this problem we recently redesigned the photoconductive antenna and implemented electrodes that lead to a chaotic trajectories of charged particles. With the new electrodes we have demonstrated a high power (>2 mW) coherent terahertz beam, and we found that the lifetime of the antenna is also substantially longer than that of the conventional antenna. In this talk I will present our experimental results and disclose some of our new antenna designs. Supported by DTRA and Naval Research Laboratory.

  17. Portable terahertz scanner for imaging and spectroscopy using InP-related devices

    NASA Astrophysics Data System (ADS)

    Park, Kyung Hyun; Kim, Namje; Lee, Il-Min; Moon, Kiwon; Lee, Eui Su; Ko, Hyunsung; Lee, Won-Hui; Han, Sang-Pil

    2015-03-01

    Our recent studies in regards of developing portable THz scanner for imaging and spectroscopy systems are presented. In the course, high power tunable continuous wave (CW) THz emitter and high sensitivity THz receiver platforms are presented. Those platforms can be realized with tunable optical beating source, broadband photomixer, arrayed photomixer and Schottky barrier diode, evanescently-coupled photodiodes with high saturation current, and semiconductor optical amplifier (SOA) integrated optical beating source. On the system level, our recent THz thickness measurement systems and the THz line scanner imaging system are presented.

  18. HIGH RESOLUTION SAR IMAGING USING RANDOM PULSE TIMING Dehong Liu, Petros T. Boufounos

    E-print Network

    Boufounos, Petros T.

    HIGH RESOLUTION SAR IMAGING USING RANDOM PULSE TIMING Dehong Liu, Petros T. Boufounos Mitsubishi resolution imaging of a large area. However, current strip-map SAR designs, relying on uniform pulsing in the azimuth resolution using the proposed approach, without compromise on the range length of the imaged area

  19. Single pulse frequency compounding protocol for superharmonic imaging

    NASA Astrophysics Data System (ADS)

    Danilouchkine, Mikhail G.; van Neer, Paul L. M. J.; Matte, Guillaume M.; Verweij, Martin D.; de Jong, Nico

    2011-03-01

    Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations demonstrated that the angle between the main and grating lobe amounted to 90°. The difference in the fundamental pressure level between those lobes was equal to -26.8 dB. Those results suggest that the superharmonic content in the grating lobe was acceptably low. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the 3rd harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited an absence of the multiple reflection artifacts in the focal and post-focal regions. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual pulse technique, while the full frame rate is maintained.

  20. Far infrared / Terahertz micromechanical imaging-array sensors based on nano-scale optical measurement technology

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-min; Wang, Bei; Lu, Xu; Liang, Er-jun; Yang, Guo-guang

    2011-08-01

    This paper describes a new concept related to the MEMS(Micro Electro Mechanical system) imaging-array sensors with the structure of micro-cantilever-arrays for detecting far IR and THz radiation. The measure principle is based on an improved optical lever and the core component is a set of micro-displacement measuring device with nano-degree displacement measurement. The amplification coefficient of this improved optical cantilever can reach 102~103 times, combined with a high resolving power to 10-10m. Compared with focal plane arrays sensors, these tape sensors have the ability to measure deformations of micro-cantilever-arrays caused by far IR or THz radiation directly, which can increase the radiation detector sensitivity. The validity of this method is proved by practical experiments. Imaging-array sensors, based on this measure principle, can be made into a new-type MEMS Far IR or THz sensors.

  1. Contrast ratio optimisation in terahertz optical asymmetric demultiplexers

    NASA Astrophysics Data System (ADS)

    Tang, J. M.; Spencer, P. S.; Rees, P.; Shore, K. A.

    2000-08-01

    Numerical simulations are undertaken to optimise the contrast ratios of terahertz optical asymmetric demultiplexer (TOAD) devices subject to frequency-detuned signal and control picosecond optical pulses. Optimum control pulse widths and pulse energies as well as optimum small-signal gains of semiconductor optical amplifiers (SOAs) are identified for achieving maximum contrast ratios in TOAD devices.

  2. Application of laser pulse stretching scheme for efficiently delivering laser energy in photoacoustic imaging

    NASA Astrophysics Data System (ADS)

    Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

    2012-06-01

    High-energy and short-duration laser pulses are desirable to improve the photoacoustic image quality when imaging deeply seated lesions. In many clinical applications, the high-energy pulses are coupled to tissue using optical fibers. These pulses can damage fibers if the damage threshold is exceeded. While keeping the total energy under the Food and Drug Administration limit for avoiding tissue damage, it is necessary to reduce the peak intensity and increase the pulse duration for minimizing fiber damage and delivering sufficient light for imaging. We use laser-pulse-stretching to address this problem. An initial 17-ns pulse was stretched to 27 and 37 ns by a ring-cavity laser-pulse-stretching system. The peak power of the 37-ns stretched pulse reduced to 42% of the original, while the fiber damage threshold was increased by 1.5-fold. Three ultrasound transducers centered at 1.3-, 3.5-, and 6-MHz frequencies were simulated, and the results showed that the photoacoustic signal of a 0.5-mm-diameter target obtained with 37-ns pulse was about 98, 91, and 80%, respectively, using the same energy as the 17-ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding transducers showed that the image quality was not affected by stretching the pulse.

  3. Application of laser pulse stretching scheme for efficiently delivering laser energy in photoacoustic imaging

    PubMed Central

    Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

    2012-01-01

    Abstract. High-energy and short-duration laser pulses are desirable to improve the photoacoustic image quality when imaging deeply seated lesions. In many clinical applications, the high-energy pulses are coupled to tissue using optical fibers. These pulses can damage fibers if the damage threshold is exceeded. While keeping the total energy under the Food and Drug Administration limit for avoiding tissue damage, it is necessary to reduce the peak intensity and increase the pulse duration for minimizing fiber damage and delivering sufficient light for imaging. We use laser-pulse-stretching to address this problem. An initial 17-ns pulse was stretched to 27 and 37 ns by a ring-cavity laser-pulse-stretching system. The peak power of the 37-ns stretched pulse reduced to 42% of the original, while the fiber damage threshold was increased by 1.5-fold. Three ultrasound transducers centered at 1.3-, 3.5-, and 6-MHz frequencies were simulated, and the results showed that the photoacoustic signal of a 0.5-mm-diameter target obtained with 37-ns pulse was about 98, 91, and 80%, respectively, using the same energy as the 17-ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding transducers showed that the image quality was not affected by stretching the pulse. PMID:22734748

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  5. Interaction of Terahertz Radiation with Ferroelectrics

    NASA Astrophysics Data System (ADS)

    Nelson, Keith

    2007-03-01

    Ferroelectric crystals have long been used as acoustic transducers and receivers. An extensive toolset has been developed for MHz-frequency acoustic wave generation, control, guidance, and readout. In recent years, an analogous toolset has been developed for terahertz wave transduction and detection. Femtosecond optical pulses irradiate ferroelectric crystals to generate responses in the 0.1-5 THz frequency range that are admixtures of electromagnetic and polar lattice vibrational excitations called phonon-polaritons. Spatiotemporal femtosecond pulse shaping may be used to generate additional optical pulses that arrive at specified times and sample locations for control and manipulation of the THz waves. Femtosecond laser machining may be used for fabrication of waveguides, resonators, and other structures that are integrated into the ferroelectric host crystal. Finally, real-space imaging of the THz fields can be executed with variably delayed femtosecond probe pulses, permitting direct visualization of THz wave spatial and temporal evolution. This ``polaritonics'' toolset enables multiplexed generation of arbitrary THz waveforms and use of the waveforms within the ferroelectric host crystal or after projection into free space or an adjacent medium. The polaritonics platform will be reviewed and several new developments and applications will be presented. These include spectroscopy of relaxor ferroelectrics, whose temperature-dependent dielectric responses in the GHz-THz regime reveal complex polarization dynamics on well separated fast and slow time scales; direct measurement of phonon-polariton lattice vibrational displacements through femtosecond time-resolved x-ray diffraction; generation of high polariton field amplitudes and pulse energies; use of large-amplitude polariton waves to drive nonlinear lattice vibrational responses; and enhancement of optical-to-THz conversion efficiency through a pseudo-phase-matching approach that circumvents the very large disparity between refractive index values at optical and THz frequencies.

  6. Optimization of a Hardware Implementation for Pulse Coupled Neural Networks for Image Applications

    E-print Network

    Warde, Cardinal

    Pulse Coupled Neural Networks are a very useful tool for image processing and visual applications, since it has the advantages of being invariant to image changes as rotation, scale, or certain distortion. Among other ...

  7. Characterization of burn injuries using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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.

  8. Wide dynamic range pulse modulation image sensor for on-chip bioimaging applications

    Microsoft Academic Search

    Takashi Tokuda; David C. Ng; Hideki Okamoto; Keiichiro Kagawa; Jun Ohta; Masahiro Nunoshita

    2004-01-01

    Image sensors with a pulse modulation measurement scheme are fabricated for bioimaging and biosensing applications. We designed pulse modulation photosensors and a 64×64-pixel image sensor. We demonstrated the feasibility of the pulse modulation measurement scheme for biosensing applications. We obtained a dynamic range of 120 dB and minimum sensing intensity level of 2 nW\\/cm2. We also confirmed that 0.2% of

  9. Applying laser pulse stretching technique on photoacoustic imaging for efficiently delivering laser energy

    NASA Astrophysics Data System (ADS)

    Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

    2012-02-01

    High-energy and short-duration outputs from lasers are desirable to improve the photoacoustic image quality when imaging deeply-seated lesions. In many clinical applications, optical fibers are used to couple the high-energy laser pulse to tissue. These high peak intensity pulses can damage an optical fiber input face if the damage threshold is exceeded. It is necessary to reduce the peak intensity to minimize the fiber damage and to delivery sufficient light for imaging. In this paper, a laser-pulse-stretching technique is introduced to reduce the peak intensity of laser pulses. To demonstrate the technique, an initial 17ns pulse was stretched to 37ns by a ring-cavity laser-pulse-stretching system, and the laser peak power reduced to 42%. The stretched pulse increased the fiber damage threshold by 1.5-fold. Three ultrasound transducers centered at 1.3MHz, 3.5MHz, 6MHz frequencies were simulated and the results showed that the photoacoustic signal of 0.5mm-diameter target obtained with 37ns pulse was about 98%, 91% and 80% respectively using the same energy as with the 17ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding ultrasound transducers showed that the image quality was not affected by stretching the pulse.

  10. Wavelet restoration of medical pulse-echo ultrasound images in an EM framework

    Microsoft Academic Search

    James Ng; Richard Prager; Nick Kingsbury; Graham Treece; Andrew Gee

    2007-01-01

    The clinical utility of pulse-echo ultrasound images is severely limited by inherent poor resolution that impacts negatively on their diagnostic potential. Research into the enhancement of image quality has mostly been concentrated in the areas of blind image restoration and speckle removal, with little regard for accurate modeling of the underlying tissue reflectivity that is imaged. The acoustic response of

  11. Propagation through terahertz waveguides with photonic crystal boundaries

    NASA Astrophysics Data System (ADS)

    Bingham, Adam L.

    Scope and method of study. The research presented in this dissertation investigates the integration of photonic crystal lattices into parallel plate waveguides at terahertz frequencies. The experimental data was obtained by measuring the terahertz pulses through the photonic crystal waveguides in a standard terahertz time-domain spectroscopy system. The terahertz pulses were generated and detected via optoelectronic means utilizing lithographically fabricated transmitting and receiving antennas and a femtosecond laser. Findings and conclusions. The main findings of this research are that metallic photonic crystal waveguides are a potential two-dimensional interconnect, and photonic waveguides act as an excellent guided-wave filter. The photonic crystal waveguides demonstrate attenuation approximating that of a comparable metallic waveguide, and demonstrate the capability to integrate guided-wave components with a high level of performance. The photonic waveguides act as a powerful filter, and the mode-matching theory allows complete design control over the waveguides.

  12. Tunable high-power terahertz radiation generation in three-level atomic and molecular systems

    SciTech Connect

    Avetissian, H. K.; Avchyan, B. R.; Mkrtchian, G. F. [Centre of Strong Fields Physics, Yerevan State University, Yerevan 0025 (Armenia)

    2010-12-15

    A scheme is presented for generation of powerful coherent terahertz radiation by multiphoton resonant excitation of three-level hydrogenlike atoms and homonuclear diatomic molecules or molecular ions with strong laser pulses. The results of analytical and numerical investigations of the problem show that with the proposed mechanism one can achieve the implementation of widely tunable powerful terahertz sources, which may open new perspectives for terahertz science and its applications.

  13. Flexible waveguide enabled single-channel terahertz endoscopic system

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Colorectal cancer is the third most commonly diagnosed cancer in the world. The current standard of care for colorectal cancer is the conventional colonoscopy, which relies exclusively on the Physician's experience. Continuous wave terahertz (THz) imaging has the potential to offer a safe, noninvasive medical imaging modality for detecting cancers. The current study demonstrates the design and development of a prototype terahertz endoscopic system based on flexible metal-coated terahertz waveguides. A CO2 pumped Far-Infrared molecular gas laser operating at 584 GHz frequency was used for illuminating the tissue, while the reflected signals were detected using liquid Helium cooled silicon bolometer. The continuous-wave terahertz imaging system utilizes a single waveguide channel to transmit the radiation and collect the back reflected intrinsic terahertz signal from the sample and is capable of operation in both transmission and reflection modalities. The two dimensional reflectance images obtained using a prototype terahertz endoscopic system showed intrinsic contrast between cancerous and normal regions of the colorectal tissue, thereby demonstrating the potential impact of terahertz imaging for in vivo cancer detection.

  14. Communication: SHG-detected circular dichroism imaging using orthogonal phase-locked laser pulses

    NASA Astrophysics Data System (ADS)

    Jarrett, Jeremy W.; Liu, Xiaoying; Nealey, Paul F.; Vaia, Richard A.; Cerullo, Giulio; Knappenberger, Kenneth L.

    2015-04-01

    We demonstrate a novel method for second harmonic generation-detected circular dichroism (CD) imaging based on the use of phase-locked, temporally delayed femtosecond laser pulses. The polarization state of the fundamental wave was controllably changed over 2? rad by using a birefringent delay line, which provided attosecond inter-pulse delays for orthogonal phase-locked replicas; the achievable phase stability was 14 as. By introducing either a positive or negative delay of ˜667 as, we induced a ±?/2 phase shift between the orthogonally polarized pulses, resulting in left circularly polarized or right circularly polarized light. CD imaging performance using the pulse sequence was compared to results obtained for plasmonic nanoantennas using a rotating quarter-wave plate. The pulse sequence is expected to simplify polarization-resolved optical imaging by reducing experimental artifacts and decreasing image acquisition times. This method can be easily extended to other CD spectroscopy measurements.

  15. Short pulse laser propagation through tissues for biomedical imaging

    Microsoft Academic Search

    Champak Das; Ashish Trivedi; Kunal Mitra; Tuan Vo-Dinh

    2003-01-01

    An experimental and numerical study is performed to analyse short pulse laser propagation through tissue phantoms with and without inhomogeneities embedded in it. Short pulse laser probing techniques have distinct advantages over conventional very large pulse width or cw lasers primarily due to the additional information conveyed about the tissue interior by the temporal variation of the observed signal. Both

  16. Superradiant Terahertz Emission by Dipolaritons

    NASA Astrophysics Data System (ADS)

    Kyriienko, O.; Kavokin, A. V.; Shelykh, I. A.

    2013-10-01

    Dipolaritons are mixed light-matter quasiparticles formed in double quantum wells embedded in microcavities. Because of resonant coupling between direct and indirect excitons via electronic tunneling, dipolaritons possess large dipole moments. Resonant excitation of the cavity mode by a short pulse of light induces oscillations of the indirect exciton density with a characteristic frequency of Rabi flopping. This results in oscillations of a classical Hertz dipole array which generate supperradiant emission on a terahertz (THz) frequency. The resulting THz signal may be enhanced using the supplementary THz cavity in the weak coupling regime.

  17. 64 ?W pulsed terahertz emission from growth optimized InGaAs/InAlAs heterostructures with separated photoconductive and trapping regions

    NASA Astrophysics Data System (ADS)

    Dietz, Roman J. B.; Globisch, Björn; Gerhard, Marina; Velauthapillai, Ajanthkrishna; Stanze, Dennis; Roehle, Helmut; Koch, Martin; Göbel, Thorsten; Schell, Martin

    2013-08-01

    We present results on optimized growth temperatures and layer structure design of high mobility photoconductive Terahertz (THz) emitters based on molecular beam epitaxy grown In0.53Ga0.47As/In0.52Al0.48As multilayer heterostructures (MLHS). The photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer and with a Golay cell. We measured a THz bandwidth in excess of 4 THz and average THz powers of up to 64 ?W corresponding to an optical power-to-THz power conversion efficiency of up to 2 × 10-3.

  18. MREIT conductivity imaging of canine head using multi-echo pulse sequence

    NASA Astrophysics Data System (ADS)

    Han, Y. Q.; Meng, Z. J.; Jeong, W. C.; Kim, Y. T.; Minhas, A. S.; Kim, H. J.; Nam, H. S.; Kwon, O.; Woo, E. J.

    2010-04-01

    In magnetic resonance electrical impedance tomography (MREIT), we measure induced magnetic flux densities subject to multiple injection currents to reconstruct cross-sectional conductivity images. Spin echo pulse sequence has been widely used in MREIT and produce postmortem and in vivo conductivity images of animal and human subjects. The image quality depends on the SNR of the measured magnetic flux density image. In order to reduce the scan time and current amplitude while keeping the image quality, we have developed a multi-echo pulse sequence for MREIT. In this study, we show results of canine head MREIT imaging experiments using the multi-echo pulse sequence. Compared to the injection current nonlinear encoding (ICNE) pulse sequence, it provides a higher SNR of MR magnitude images by combining multiple echo signals. Noise in measured magnetic flux density data is significantly reduced due to an increased current injection time over multiple echo signals. These allow us to significantly decrease the total scan time. Reconstructed conductivity images of a canine head show enhanced conductivity contrast between gray and white matter using the multi-echo pulse sequence. In our future work, we will focus on in vivo human and disease model animal experiments using the new MREIT pulse sequence.

  19. Generation and spectral manipulation of coherent terahertz radiation with two-stage optical rectification.

    PubMed

    Chen, Ching-Wei; Lin, Yu-Shian; Huang, Jung Y; Chang, Chen-Shiung; Pan, Ci-Ling; Yan, Li; Lee, Chao-Kuei

    2008-09-01

    We propose and experimentally demonstrate the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the terahertz field injected from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of coherent THz radiation. The technique is also potentially useful for generating high-power single-cycle terahertz pulses, usually limited by the pulse walk-off effect of the nonlinear optical crystal used. PMID:18773040

  20. Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

    PubMed Central

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

    2013-01-01

    In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10. PMID:23892574

  1. Development of tunable terahertz quantum cascade wire lasers

    E-print Network

    Qin, Qi, Ph. D. Massachusetts Institute of Technology

    2012-01-01

    For a long time, terahertz (THz) radiation has been of great interest to scientific community because of its spectroscopic and imaging applications based on its unique properties, such as the capabilities to penetrate many ...

  2. Identification of biological tissue using chirped probe THz imaging

    Microsoft Academic Search

    B. Ferguson; S. Wang; D. Gray; D. Abbott; X.-C Zhang

    2002-01-01

    We consider the application of pulsed THz imaging systems in biomedical diagnostics and mail\\/packaging inspection. The sub-millimetre spectroscopic measurements obtained from T-ray systems contain a wealth of information about the sample under test. We demonstrate that different types of tissue can be classified based on their terahertz response measured with the chirped probe pulse technique. We demonstrate the performance of

  3. Study of terahertz intensity dependence on time resolved dynamic fringes in the interferometric autocorrelation setup

    NASA Astrophysics Data System (ADS)

    Venkatesh, M.; Chaudhary, A. K.

    2014-10-01

    Terahertz signal is generated from Low temperature gallium arsenide photoconductive dipole antennas (gap = 5?m, length = 20?m) by focusing 15 fs laser pulses and applying 12V DC across it. Terahertz intensity is detected by Pyroelectric detector (THZ1.5MB-USB). The collinear autocorrelation arrangement provides dynamic fringes which are allowed to be incident on photoconductive antennas to study the variation in terahertz intensity with respect to delay between laser pulses. Interestingly, the profile of THz intensity variation was similar to interferometric autocorrelation signal of laser pulses. The THz power attenuation with its propagation distance in atmosphere was measured.

  4. Terahertz-field-induced second harmonic generation through Pockels effect in zinc telluride crystal.

    PubMed

    Cornet, Marion; Degert, Jérôme; Abraham, Emmanuel; Freysz, Eric

    2014-10-15

    We report on the second harmonic generation (SHG) of a near-infrared pulse in a zinc telluride crystal through the Pockels effect induced by an intense terahertz pulse. The temporal and angular behaviors of the SHG have been measured and agree well with theoretical predictions. This phenomenon, so far overlooked, makes it possible to generate second harmonic through cascading of two second-order nonlinear phenomena in the near-infrared and terahertz ranges. We also show how this cascading process can be used to sample terahertz pulses. PMID:25361120

  5. Mesoscopic structuring and dynamics of alcohol/water solutions probed by terahertz time-domain spectroscopy and pulsed field gradient nuclear magnetic resonance.

    PubMed

    Li, Ruoyu; D'Agostino, Carmine; McGregor, James; Mantle, Michael D; Zeitler, J Axel; Gladden, Lynn F

    2014-08-28

    Terahertz and PFG-NMR techniques are used to explore transitions in the structuring of binary alcohol/water mixtures. Three critical alcohol mole fractions (x1, x2, x3) are identified: methanol (10, 30, 70 mol %), ethanol (7, 15, 60 mol %), 1-propanol (2, 10, 50 mol %), and 2-propanol (2, 10, 50 mol %). Above compositions of x1 no isolated alcohol molecules exist, and below x1 the formation of large hydration shells around the hydrophobic moieties of the alcohol is favored. The maximum number of water molecules, N0, in the hydration shell surrounding a single alcohol molecule increases with the length of the carbon chain of the alcohol. At x2 the greatest nonideality of the liquid structure exists with the formation of extended hydrogen bonded networks between alcohol and water molecules. The terahertz data show the maximum absorption relative to that predicted for an ideal mixture at that composition, while the PFG-NMR data exhibit a minimum in the alkyl chain self-diffusivity at x2, showing that the alcohol has reached a minimum in diffusion when this extended alcohol-water network has reached the highest degree of structuring. At x3 an equivalence of the alkyl and alcohol hydroxyl diffusion coefficients is determined by PFG-NMR, suggesting that the molecular mobility of the alcohol molecules becomes independent of that of the water molecules. PMID:25117060

  6. Strip Velocity Measurements for Gated X-Ray Imagers Using Short Pulse Lasers

    SciTech Connect

    Ross, P. W. [NSTec; Cardenas, M. [NSTec; Griffin, M. [NSTec; Mead, A. [NSTec; Silbernagel, C. T. [NSTec; Bell, P. [LLNL; Haque, S. H. [UNR

    2013-09-01

    Strip velocity measurements of gated X-ray imagers are presented using an ultra-short pulse laser. Obtaining time-resolved X-ray images of inertial confinement fusion shots presents a difficult challenge. One diagnostic developed to address this challenge is the gated X-ray imagers. The gated X-ray detectors (GXDs) developed by Lawrence Livermore National Laboratory and Los Alamos National Laboratory use a microchannel plate (MCP) coated with a gold strip line, which serves as a photocathode. GXDs are used with an array of pinholes, which image onto various parts of the GXD image plane. As the pulse sweeps over the strip lines, it creates a time history of the event with consecutive images. In order to accurately interpret the timing of the images obtained using the GXDs, it is necessary to measure the propagation of the pulse over the strip line. The strip velocity was measured using a short pulse laser with a pulse duration of approximately 1-2 ps. The 200nm light from the laser is used to illuminate the GXD MCP. The laser pulse is split and a retroreflective mirror is used to delay one of the legs. By adjusting the distance to the mirror, one leg is temporally delayed compared to the reference leg. The retroreflective setup is calibrated using a streak camera with a 1 ns full sweep. Resolution of 0.5 mm is accomplished to achieve a temporal resolution of ~5 ps on the GXD strip line.

  7. Integrated heterodyne terahertz transceiver

    DOEpatents

    Lee, Mark (Albuquerque, NM); Wanke, Michael C. (Albuquerque, NM)

    2009-06-23

    A heterodyne terahertz transceiver comprises a quantum cascade laser that is integrated on-chip with a Schottky diode mixer. An antenna connected to the Schottky diode receives a terahertz signal. The quantum cascade laser couples terahertz local oscillator power to the Schottky diode to mix with the received terahertz signal to provide an intermediate frequency output signal. The fully integrated transceiver optimizes power efficiency, sensitivity, compactness, and reliability. The transceiver can be used in compact, fieldable systems covering a wide variety of deployable applications not possible with existing technology.

  8. Integrated heterodyne terahertz transceiver

    DOEpatents

    Wanke, Michael C. (Albuquerque, NM); Lee, Mark (Albuquerque, NM); Nordquist, Christopher D. (Albuquerque, NM); Cich, Michael J. (Albuquerque, NM)

    2012-09-25

    A heterodyne terahertz transceiver comprises a quantum cascade laser that is integrated on-chip with a Schottky diode mixer. A terahertz signal can be received by an antenna connected to the mixer, an end facet or sidewall of the laser, or through a separate active section that can amplify the incident signal. The quantum cascade laser couples terahertz local oscillator power to the Schottky diode to mix with the received terahertz signal to provide an intermediate frequency output signal. The fully integrated transceiver optimizes power efficiency, sensitivity, compactness, and reliability. The transceiver can be used in compact, fieldable systems covering a wide variety of deployable applications not possible with existing technology.

  9. Development of a novel acoustic lens based pulse echo ultrasound imaging system

    NASA Astrophysics Data System (ADS)

    Sinha, Saugata; Rao, Navalgund A.

    2014-03-01

    Acoustic lens based focusing technology where the image reconstruction is achieved through the focusing of an acoustic lens, can potentially replace time consuming and expensive electronic focusing technology for producing high resolution real time ultrasound (US) images. A novel acoustic lens focusing based pulse echo US imaging system is explored here. In the system, a Polyvinylidene fluoride (PVDF) film transducer generates plane wave which is backscattered by the object and focused by a spherical acoustic lens on to a linear array of transducers. To improve the anticipated low signal to noise ratio (SNR) of the received US signal due to the low electromechanical coupling coefficient of the PVDF film, here we explored the possibility of implementing pulse compression technique using linear frequency modulated (FM) signals or chirp signals. Comparisons among the different SNR values obtained with short pulse and after pulse compression with chirp signal show a clear improvement of the SNR for the compressed pulse. The preliminary results show that the SNR achieved for the compressed pulse depends on time bandwidth product of the input chirp and the spectrum of the US transducers. The axial resolution obtained with compressed pulse improved with increasing sweep bandwidth of input chirp signals, whereas the lateral resolution remained almost constant. This work demonstrates the feasibility of using a PVDF film transducer as an US transmitter in an acoustic lens focusing based imaging system and implementing pulse compression technique into the same setup to improve SNR of the received US signal.

  10. CMOS Architecture of Synchronous Pulse-Coupled Neural Network and Its Application to Image Processing

    E-print Network

    Wilamowski, Bogdan Maciej

    Processing Yasuhiro Ota Bogdan M. Wilamowski Image Information Products Hdqrs. College of Engineering MINOLTA the five key axon properties of (i) threshold of excitation, (ii) refractory period, (iii) constant pulse

  11. Development of the Ultrashort Pulse Nonlinear Optical Microscopy Spectral Imaging System 

    E-print Network

    Lee, Anthony Chien-der

    2012-10-19

    by broadband sub-10-fs pulses. This dissertation will discuss the development of two spectral imaging systems using the principles of nonlinear optical microscopy for pixel-by-pixel spectral segmentation of multiple fluorescent spectra. The first spectral...

  12. Correlation chemical shift imaging with low-power adiabatic pulses and constant-density spiral trajectories

    E-print Network

    Andronesi, Ovidiu C.

    In this work we introduce the concept of correlation chemical shift imaging (CCSI). Novel CCSI pulse sequences are demonstrated on clinical scanners for two-dimensional Correlation Spectroscopy (COSY) and Total Correlation ...

  13. Pulse

    MedlinePLUS

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the patient's heart is pumping. ... exercise, the pulse rate gives information about your fitness ...

  14. Electronic imaging of high-energy nanosecond x-ray pulse accelerators

    Microsoft Academic Search

    Graham W. Smith; John D. Bell; Calvin L. G. Seymour

    2003-01-01

    Electronic imaging has been undertaken upon a selection of AWE's high power x-ray pulse accelerators used for radiation effects testing on electronic components and small sub-systems. Principally an experimental configuration, based upon a pinhole scintillator combination, has been implemented to test the feasibility of recording by an electronic imaging system for high energy (3MeV) and high dose (>16krads) x-ray pulse

  15. In vivo photoacoustic imaging of blood vessels with a pulsed laser diode

    Microsoft Academic Search

    Roy G. M. Kolkman; Wiendelt Steenbergen; Ton G. van Leeuwen

    2006-01-01

    Photoacoustic imaging is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophores such as hemoglobin in blood. For this technique, usually large and costly Q-switched Nd:YAG lasers are used. These lasers provide a pulse energy of at least several milliJoules. In search of alternative light sources, we

  16. Development of a new pulsed source for photoacoustic imaging based on aperiodically poled lithium niobate

    PubMed Central

    Yankelevich, Diego; González, J. E.; Cudney, Roger S.; Ríos, Luis A.; Marcu, Laura

    2014-01-01

    We present the development of a source of deep-red radiation for photoacoustic imaging. This source, which is based on two cascaded wavelength conversion processes in aperiodically poled lithium niobate, emits 10 nanosecond pulses of over 500 µJ at 710 nm. Photoacoustic images were obtained from phantoms designed to mimic the optical and acoustic properties of oral tissue. Results indicate this device is a viable source of optical pulses for photoacoustic applications. PMID:24575341

  17. Imaging the Cardiovascular Pulse Dept. of Computer Sc.

    E-print Network

    . Univ. of Houston Houston, TX ipavlidi@central.uh.edu Abstract We have developed a novel method to measure human cardiac pulse at a distance. It is based on the information contained in the thermal signal of cardiac pulse is widely used in health care, sport training, sleep studies, and psycho- physiological

  18. Application of Hilbert-Huang Transform for Improved Defect Detection in Terahertz NDE of Shuttle Tiles

    NASA Technical Reports Server (NTRS)

    Anastasi, Robert F.; Madaras, Eric I.

    2005-01-01

    Terahertz NDE is being examined as a method to inspect the adhesive bond-line of Space Shuttle tiles for defects. Terahertz signals are generated and detected, using optical excitation of biased semiconductors with femtosecond laser pulses. Shuttle tile samples were manufactured with defects that included repair regions unbond regions, and other conditions that occur in Shuttle structures. These samples were inspected with a commercial terahertz NDE system that scanned a tile and generated a data set of RF signals. The signals were post processed to generate C-scan type images that are typically seen in ultrasonic NDE. To improve defect visualization the Hilbert-Huang Transform, a transform that decomposes a signal into oscillating components called intrinsic mode functions, was applied to test signals identified as being in and out of the defect regions and then on a complete data set. As expected with this transform, the results showed that the decomposed low-order modes correspond to signal noise while the high-order modes correspond to low frequency oscillations in the signal and mid-order modes correspond to local signal oscillations. The local oscillations compare well with various reflection interfaces and the defect locations in the original signal.

  19. Perfect terahertz absorber using fishnet based metafilm

    SciTech Connect

    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

    2009-01-01

    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.

  20. Short pulse laser propagation through tissues for biomedical imaging

    NASA Astrophysics Data System (ADS)

    Das, Champak; Trivedi, Ashish; Mitra, Kunal; Vo-Dinh, Tuan

    2003-07-01

    An experimental and numerical study is performed to analyse short pulse laser propagation through tissue phantoms with and without inhomogeneities embedded in it. Short pulse laser probing techniques have distinct advantages over conventional very large pulse width or cw lasers primarily due to the additional information conveyed about the tissue interior by the temporal variation of the observed signal. Both the scattered temporal transmitted and reflected optical signals are measured experimentally using a streak camera for samples irradiated with a short pulse laser source. Parametric study involving different scattering and absorption coefficients of tissue phantoms and inhomogeneities as well as the detector position and orientation is performed. The temporal and spatial profiles of the scattered optical signals are compared with the numerical modelling results obtained by solving the transient radiative transport equation using the discrete ordinates technique.

  1. Interaction of Terahertz Radiation with Ferroelectrics

    Microsoft Academic Search

    Keith Nelson

    2007-01-01

    Ferroelectric crystals have long been used as acoustic transducers and receivers. An extensive toolset has been developed for MHz-frequency acoustic wave generation, control, guidance, and readout. In recent years, an analogous toolset has been developed for terahertz wave transduction and detection. Femtosecond optical pulses irradiate ferroelectric crystals to generate responses in the 0.1-5 THz frequency range that are admixtures of

  2. Nonlinear terahertz spectroscopy of electronic and vibrational responses in condensed matter systems

    E-print Network

    Hwang, Harold Young

    2012-01-01

    In this work, I describe experiments utilizing high-field terahertz (THz) pulses to initiate nonlinear responses in several classes of materials. We have developed several methods for interrogating the nonlinear THz response ...

  3. Subsurface imaging for panel paintings inspection: A comparative study of the ultraviolet, the visible, the infrared and the terahertz spectra

    NASA Astrophysics Data System (ADS)

    Bendada, A.; Sfarra, S.; Ibarra-Castanedo, C.; Akhloufi, M.; Caumes, J.-P.; Pradere, C.; Batsale, J.-C.; Maldague, X.

    2015-03-01

    Infrared (IR) reflectography has been used for many years for the detection of underdrawings on panel paintings. Advances in the fields of IR sensors and optics have impelled the wide spread use of IR reflectography by several recognized Art Museums and specialized laboratories around the World. The transparency or opacity of a painting is the result of a complex combination of the optical properties of the painting pigments and the underdrawing material, as well as the type of illumination source and the sensor characteristics. For this reason, recent researches have been directed towards the study of multispectral approaches that could provide simultaneous and complementary information of an artwork. The present work relies on non-simultaneous multispectral inspection using a set of detectors covering from the ultraviolet to the terahertz spectra. It is observed that underdrawings contrast increases with wavelength up to 1700 nm and, then, gradually decreases. In addition, it is shown that IR thermography, i.e., temperature maps or thermograms, could be used simultaneously as an alternative technique for the detection of underdrawings besides the detection of subsurface defects.

  4. CONTRAST-TO-TISSUE RATIO IMPROVEMENT BY TRANSMITTED OPTIMIZED BINARY SIGNAL IN ULTRASOUND PULSE INVERSION IMAGING

    E-print Network

    Paris-Sud XI, Université de

    .6556590 ABSTRACT Ultrasound contrast imaging has provided more accurate medical diagnoses. One of the most used. INTRODUCTION Since the 1960s, medical ultrasound imaging has become an essential tool for clinical diagnosisCONTRAST-TO-TISSUE RATIO IMPROVEMENT BY TRANSMITTED OPTIMIZED BINARY SIGNAL IN ULTRASOUND PULSE

  5. Integrated processing of contrast pulse sequencing ultrasound imaging for enhanced active contrast of hollow gas filled silica nanoshells

    E-print Network

    Kummel, Andrew C.

    Integrated processing of contrast pulse sequencing ultrasound imaging for enhanced active contrast. Imaging of the microshells in an animal model was facilitated by novel image processing. Although signal in still images and near the borders of the tumor with live images. Image processing techniques

  6. Characterization of pulsed (plasma focus) neutron source with image plate and application to neutron radiography

    SciTech Connect

    Andola, Sanjay; Niranjan, Ram; Rout, R. K.; Kaushik, T. C.; Gupta, S. C. [Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Shaikh, A. M. [Raja Ramanna Fellow, Solid State Physics Division (India)

    2013-02-05

    Plasma focus device of Mather type developed in house has been used first time for neutron radiography of different objects. The device gives (1.2{+-}0.3) Multiplication-Sign 10{sup 9} neutrons per pulse produced by D-D fusion reaction with a pulse width of 50{+-}5 ns. The method involves exposing sample to be radiographed to thermalized D-D neutrons and recording the image on Fuji-film BAS-ND image plates. The thermal neutron component of the moderated beam was estimated using two image plates: a conventional IP for X-rays and gamma rays, and an IP doped with Gd for detecting neutrons.

  7. Characterization of pulsed (plasma focus) neutron source with image plate and application to neutron radiography

    NASA Astrophysics Data System (ADS)

    Andola, Sanjay; Niranjan, Ram; Shaikh, A. M.; Rout, R. K.; Kaushik, T. C.; Gupta, S. C.

    2013-02-01

    Plasma focus device of Mather type developed in house has been used first time for neutron radiography of different objects. The device gives (1.2±0.3) ×109 neutrons per pulse produced by D-D fusion reaction with a pulse width of 50±5 ns. The method involves exposing sample to be radiographed to thermalized D-D neutrons and recording the image on Fuji-film BAS-ND image plates. The thermal neutron component of the moderated beam was estimated using two image plates: a conventional IP for X-rays and gamma rays, and an IP doped with Gd for detecting neutrons.

  8. Use of attosecond electron pulses to image electronic motion in atoms and molecules

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2013-09-01

    We investigate theoretically the direct imaging of coherent electronic motion in atoms and molecules using attosecond electron pulses. The theories of time-resolved ultrafast electron diffraction and (e, 2e) momentum spectroscopy as well as the requisite conditions for carrying out time-resolved measurements to obtain timedependent images are discussed. Results of simulations showing images of the motions of coherent superposition states in both the hydrogen atom and the hydrogen molecular ion are shown, thus indicating the capability of ultrafast electron pulses to investigate time-dependent electron dynamics.

  9. Terahertz Physics

    NASA Astrophysics Data System (ADS)

    Lewis, R. A.

    2013-01-01

    1. Introduction; Part I. Basics: 2. Oscillations; 3. Combining oscillations; 4. Light; 5. Matter; 6. Interaction of light and matter; Part II. Components: 7. Sources; 8. Optics; 9. Detectors; Part III. Applications: 10. Spectroscopy; 11. Imaging; Glossary; Appendices; Index.

  10. Electro-optic crystal mosaics for the generation of terahertz radiation

    DOEpatents

    Carrig, Timothy J. (Los Alamos, NM); Taylor, Antoinette J. (Los Alamos, NM); Stewart, Kevin R. (Schenectady, NY)

    1996-01-01

    Apparatus for the generation of high energy terahertz radiation is presented and comprises laser means effective to produce subpicosecond optical pulses and a mosaic comprising a plurality of planar electro-optic crystals fastened together edge to edge in the form of a grid. The electro-optic crystals are in optical communication with the subpicosecond optical pulses, and behave as a single large electro-optic crystal, producing high energy terahertz radiation by way of optical rectification.

  11. Terahertz wave generation from gas plasma using a phase compensator with attosecond phase-control accuracy

    SciTech Connect

    Dai Jianming; Zhang, X.-C. [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2009-01-12

    We report the use of a precise phase compensator for the generation of intense terahertz waves from laser-induced gas plasma excited by a femtosecond pulse ({omega}) and its second harmonic (2{omega}) at both close contact and standoff distances. The attosecond accuracy phase-control capability of the device enables further optimization of the terahertz emission from gas plasma and elimination of the temporal walkoff between the {omega} and 2{omega} pulses traveling in dispersive media, resulting in intense terahertz generation at a distance of over 100 m by sending the optical beams far away and focusing them locally.

  12. Coherent Polarization Control of Terahertz Waves Generated from Two-Color Laser-Induced Gas Plasma

    SciTech Connect

    Dai Jianming; Karpowicz, Nicholas; Zhang, X.-C. [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2009-07-10

    Electrons ionized from an atom or molecule by circularly or elliptically polarized femtosecond omega and 2omega pulses exhibit different trajectory orientations as the relative phase between the two pulses changes. Macroscopically, the polarization of the terahertz wave emitted during the ionization process was found to be coherently controllable through the optical phase. This new finding can be completely reproduced by numerical simulation and may enable fast terahertz wave modulation and coherent control of nonlinear responses excited by intense terahertz waves with controllable polarization.

  13. Real-time imaging of two-dimensional cardiac strain using a harmonic phase magnetic resonance imaging (HARP-MRI) pulse sequence

    Microsoft Academic Search

    Smita Sampath; J. Andrew Derbyshire; Ergin Atalar; Nael F. Osman; Jerry L. Prince

    2003-01-01

    The harmonic phase (HARP) method provides automatic and rapid analysis of tagged magnetic resonance (MR) images for quantification and visualization of myocardial strain. In this article, the development and implementation of a pulse se- quence that acquires HARP images in real time are described. In this pulse sequence, a CINE sequence of images with 1-1 spatial modulation of magnetization (SPAMM)

  14. Freely tunable broadband polarization rotator for terahertz waves.

    PubMed

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

    2015-02-18

    A freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging. PMID:25545177

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

    Microsoft Academic Search

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

    2011-01-01

    Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques\\u000a for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used\\u000a in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic\\u000a waves. Capability of THz electromagnetic waves in detecting heat induced

  16. Terahertz NDE for Under Paint Corrosion Detection and Evaluation

    NASA Technical Reports Server (NTRS)

    Anastasi, Robert F.; Madaras, Eric I.

    2005-01-01

    Corrosion under paint is not visible until it has caused paint to blister, crack, or chip. If corrosion is allowed to continue then structural problems may develop. Identifying corrosion before it becomes visible would minimize repairs and costs and potential structural problems. Terahertz NDE imaging under paint for corrosion is being examined as a method to inspect for corrosion by examining the terahertz response to paint thickness and to surface roughness.

  17. Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

    NASA Astrophysics Data System (ADS)

    Azad, Abul K.; Chen, Hou-Tong; Taylor, Antoinette J.; O'Hara, John F.; Han, Jiaguang; Lu, Xinchao; Zhang, Weili

    2009-02-01

    The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays made from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottky diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

  18. Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

    SciTech Connect

    Azad, Abul K [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Han, Jiaguang [OSU; Lu, Xinchao [OSU; Zhang, Weili [OSU

    2009-01-01

    The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

  19. A Versatile High Speed 250 MHz Pulse Imager for Biomedical Applications

    PubMed Central

    Epel, Boris; Sundramoorthy, Subramanian V.; Mailer, Colin; Halpern, Howard J.

    2009-01-01

    A versatile 250 MHz pulse electron paramagnetic resonance (EPR) instrument for imaging of small animals is presented. Flexible design of the imager hardware and software makes it possible to use virtually any pulse EPR imaging modality. A fast pulse generation and data acquisition system based on general purpose PCI boards performs measurements with minimal additional delays. Careful design of receiver protection circuitry allowed us to achieve very high sensitivity of the instrument. In this article we demonstrate the ability of the instrument to obtain three dimensional images using the electron spin echo (ESE) and single point imaging (SPI) methods. In a phantom that contains a 1 mM solution of narrow line (16 ?T, peak-to-peak) paramagnetic spin probe we achieved an acquisition time of 32 seconds per image with a fast 3D ESE imaging protocol. Using an 18 minute 3D phase relaxation (T2e) ESE imaging protocol in a homogeneous sample a spatial resolution of 1.4 mm and a standard deviation of T2e of 8.5% were achieved. When applied to in vivo imaging this precision of T2e determination would be equivalent to 2 torr resolution of oxygen partial pressure in animal tissues. PMID:19924261

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

    PubMed

    Phing, Sze Ho; Mazhorova, Anna; Shalaby, Mostafa; Peccianti, Marco; Clerici, Matteo; Pasquazi, Alessia; Ozturk, Yavuz; Ali, Jalil; Morandotti, Roberto

    2015-01-01

    Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (<100?nm-thickness) of photo carriers is induced on the surface of the terahertz generation crystal, which acts as an all-optical, virtual blade for terahertz near-field imaging via a knife-edge technique. Remarkably, and in spite of the fact that the proposed approach does not require any mechanical probe, such as tips or apertures, we are able to demonstrate the imaging of a terahertz source with deeply sub-wavelength features (<30??m) directly in its emission plane. PMID:25711343

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

    PubMed Central

    Phing, Sze Ho; Mazhorova, Anna; Shalaby, Mostafa; Peccianti, Marco; Clerici, Matteo; Pasquazi, Alessia; Ozturk, Yavuz; Ali, Jalil; Morandotti, Roberto

    2015-01-01

    Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (<100?nm-thickness) of photo carriers is induced on the surface of the terahertz generation crystal, which acts as an all-optical, virtual blade for terahertz near-field imaging via a knife-edge technique. Remarkably, and in spite of the fact that the proposed approach does not require any mechanical probe, such as tips or apertures, we are able to demonstrate the imaging of a terahertz source with deeply sub-wavelength features (<30??m) directly in its emission plane. PMID:25711343

  2. Pulsing mercury arc lamps for uncaging and fast imaging

    Microsoft Academic Search

    Winfried Denk

    1997-01-01

    It is shown that the light intensity from a mercury short arc light bulb can be boosted to about 100 times its steady-state value for a period of about 1 ms by superimposing a current pulse of up to 100 amperes in magnitude and 1–2 ms in duration on a simmer current of 3 amperes. The output spectrum changes in

  3. Methodological Advances on Pulse Measurement Through Functional Imaging

    E-print Network

    ], photoplethysmography [13] and Doppler ultrasound [8], focus on the vascular periphery. One main characteristic of all that moves the heart's muscle and the thermo-mechanical effects of pulse propaga- tion in the vascular because it focuses on the source (heart). Other commonly used methods, such as piezoelectric probing [3

  4. Time resolved imaging of a pulsed plasma discharge in water

    Microsoft Academic Search

    P. Ceccato; O. Guaitella; Lucas Shaper; Bill Graham; A. Rousseau

    2009-01-01

    Plasma discharges inside water have been widely used for pulsed power applications such as water high voltage lines and switches. More recently underwater plasma discharges have been proved to be very efficient as an advanced oxidations process. The plasma inside water is a source of useful chemical compound such as hydrogen peroxide and hydroxyl radical that can be used for

  5. Co-registered pulse-echo/photoacoustic transvaginal probe for real time imaging of ovarian tissue.

    PubMed

    Kumavor, Patrick D; Alqasemi, Umar; Tavakoli, Behnoosh; Li, Hai; Yang, Yi; Sun, Xiaoguang; Warych, Edward; Zhu, Quing

    2013-06-01

    We present the design and construction of a prototype imaging probe capable of co-registered pulse-echo ultrasound and photoacoustic (optoacoustic) imaging in real time. The probe consists of 36 fibers of 200 micron core diameter each that are distributed around a commercial transvaginal ultrasound transducer, and housed in a protective shield. Its performance was demonstrated by two sets of experiments. The first set involved imaging of blood flowing through a tube mimicking a blood vessel, the second set involved imaging of human ovaries ex vivo. The results suggest that the system along with the probe has great potential for imaging and characterizing of ovarian tissue in vivo. PMID:23450770

  6. Temporal self-imaging effects: theory and application for multiplying pulse repetition rates

    Microsoft Academic Search

    José Azaña; Miguel A. Muriel

    2001-01-01

    A time-domain equivalent of the spatial Talbot or self-imaging phenomenon appears when a periodic temporal signal propagates through a dispersive medium under first-order dispersion conditions. The effect is of great interest because it can be applied for multiplying the repetition rate of an arbitrary periodic pulse train without distorting the individual pulse features and essentially without loss of energy. In

  7. Ultrafast opto-terahertz photonic crystal modulator.

    PubMed

    Fekete, L; Kadlec, F; Kuzel, P; Nemec, H

    2007-03-15

    We present an agile optically controlled switch or modulator of terahertz (THz) radiation. The element is based on a one-dimensional photonic crystal with a GaAs wafer inserted in the middle as a defect layer. The THz electric field is enhanced in the photonic structure at the surfaces of the GaAs wafer. Excitation of the front GaAs surface by ultrashort 810 nm laser pulses then leads to an efficient modulation of the THz beam even at low photocarrier concentrations (approximately 10(16) cm(-3)). The response time of the element to pulsed photoexcitation is about 130 ps. PMID:17308600

  8. Spectrally modulated stimulated Raman scattering imaging with an angle-to-wavelength pulse shaper

    PubMed Central

    Zhang, Delong; Slipchenko, Mikhail N.; Leaird, Daniel E.; Weiner, Andrew M.; Cheng, Ji-Xin

    2013-01-01

    The stimulated Raman scattering signal is often accompanied by unwanted background arising from other pump-probe modalities. We demonstrate an approach to overcome this challenge based on spectral domain modulation, enabled by a compact, cost-effective angle-to-wavelength pulse shaper. The pulse shaper switches between two spectrally narrow windows, which are cut out of a broadband femtosecond pulse and selected for on- and off- Raman resonance excitation, at 2.1 MHz frequency for detection of stimulated Raman scattering signal. Such spectral modulation reduced the unwanted pump-probe signals by up to 20 times and enabled stimulated Raman scattering imaging of molecules in a pigmented environment. PMID:23736639

  9. Mode locking at terahertz frequencies using a distributed Bragg reflector laser with a sampled grating.

    PubMed

    Hou, Lianping; Haji, Mohsin; Marsh, John H

    2013-04-01

    We present a highly reproducible method of producing terahertz (THz) optical pulses using a class of mode-locked AlGaInAs/InP laser operating in the 1.55 ?m wavelength range. The device uses a sample grating distributed Bragg reflector to provide strong frequency selectivity at the mode-locked frequency while the distributed reflectors relax the fabrication tolerances and ensure the cavity can self adjust to being an integral number of mode-locked periods in length. The measured devices provide nearly transform-limited pulse trains at 640 GHz or 1.28 THz with a high degree of controllability and operate with consistent performance over a wide range of drive conditions. Being low cost and compact sources of THz radiation, these lasers will open up many applications, including systems for high-speed optical communication and THz imaging. PMID:23546261

  10. Spectroscopic Imaging with Improved Gradient Modulated Constant Adiabadicity Pulses on High-Field Clinical Scanners

    PubMed Central

    Andronesi, Ovidiu C.; Ramadan, Saadallah; Ratai, Eva-Maria; Jennings, Dominique; Mountford, Carolyn E.; Sorensen, A. Gregory

    2011-01-01

    The purpose of this work was to design and implement constant adiabadicity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood, 1997) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (Frequency Offset Corrected Inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of line-shapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy. PMID:20163975

  11. Optical and terahertz energy concentration on the nanoscale in plasmonics

    NASA Astrophysics Data System (ADS)

    Rusina, Anastasia

    We introduce an approach to implement full coherent control on nanometer length scales. It is based on spatiotemporal modulation of the surface plasmon polariton (SPP) fields at the thick edge of a nanowedge. The SPP wavepackets propagating toward the sharp edge of this nanowedge are compressed and adiabatically concentrated at a nanofocus, forming an ultrashort pulse of local fields. The profile of the focused waveform as a function of time and one spatial dimension is completely coherently controlled. We establish the principal limits for the nanoconcentration of the terahertz (THz) radiation in metal/dielectric waveguides and determine their optimum shapes required for this nanoconcentration. We predict that the adiabatic compression of THz radiation from the initial spot size of vacuum wavelength R0 ? lambda0 ? 300 microm to the unprecedented final size of R = 100--250 nm can be achieved, while the THz radiation intensity is increased by a factor of 10 to 250. This THz energy nanoconcentration will not only improve the spatial resolution and increase the signal/noise ratio for THz imaging and spectroscopy, but in combination with the recently developed sources of powerful THz pulses, will allow the observation of nonlinear THz effects and a variety of nonlinear spectroscopies (such as two-dimensional spectroscopy), which are highly informative. This should find a wide spectrum of applications in science, engineering, biomedical research and environmental monitoring. We also develop a theory of the spoof plasmons propagating at the interface between a dielectric and a real conductor. The deviation from a perfect conductor is introduced through a finite skin depth. The possibilities of guiding and focusing of spoof plasmons are considered. Geometrical parameters of the structure are found which provide a good guiding of such modes. Moreover, the limit on the concentration by means of planar spoof plasmons in case of non-ideal metal is established. These properties of spoof plasmons are of great interest for THz technology. INDEX WORDS: Nanoplasmonics, Surface plasmon polaritons, Adiabatic concentration, Full coherent control on nanoscale, Nanowedge, Terahertz, Coaxial waveguide, Spoof plasmons, Nanoscale, Nanofocus, Terahertz (THz) energy nanoconcentration

  12. Significant Radiation Enhancement in Photoconductive Terahertz Emitters by Incorporating Plasmonic Contact Electrodes

    E-print Network

    Berry, Christopher W; Unlu, Mehmet; Jarrahi, Mona

    2012-01-01

    Even though the terahertz spectrum is well suited for chemical identification, material characterization, biological sensing and medical imaging, practical development of these applications has been hindered by the attributes of terahertz sources, namely low output power and poor efficiency. Here, we demonstrate that use of plasmonic contact electrodes can significantly enhance the optical-to-terahertz conversion efficiency in a photoconductive terahertz emitter. The use of plasmonic contact electrodes offers nanoscale carrier transport path lengths for the photocarriers, enabling efficient collection of the majority of carriers in a sub-picosecond time-scale. It also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. We experimentally demonstrated 50 times higher terahertz radiation power from a plasmon...

  13. Distinguishing of different kinds of gunpowder using various methods based on terahertz radiation

    NASA Astrophysics Data System (ADS)

    Gavenda, Tomáš; K?esálek, Vojt?ch

    2014-10-01

    This article provides information about using terahertz radiation based methods such as time-domain spectroscopy, ATR spectroscopy and terahertz reflection imaging for distinguishing of different kinds of gunpowder. The findings in this article prove that gunpowder does not have any sharp peaks in terahertz region of electromagnetic spectrum up to 2.5 THz, but also prove that distinguishing of different kinds of gunpowder is possible using different methods based on terahertz radiation. All presented results are connected to absorbance of gunpowder and other measured materials, because comparison of absorbance analysis is essential for distinguishing of gunpowder samples.

  14. Pulse Density Modulation: Synthetic Formation Of Binary Images And Holograms

    NASA Astrophysics Data System (ADS)

    Broja, M.; Weissbach, S.; Wyrowski, F.; Bryngdahl, O.

    1987-01-01

    A large portion of our world concerned with manipulation and communication of information has turned binary. A consequence has been hardware with improved SNR. A demand and interest for binary coding procedures has arisen from this trend. Several 1-0 schemes in electronics like PWM, PPM, and PCM have been extended to 2-D optical counterparts in a straightforward way. In contrast to these cases with equidistant sampling we will also discuss situations with nonequidistant sampling where the information is coded by the positions of the pulses in such a way that the two dimensions are inseparable. This implies that no constant carrier frequency is introduced. In pulse density modu-lation (POM) the pulse separations are inversely proportional to the local signal level. Characteristic for POM is that a large number of degrees of freedom exists. They have to be handled by the coding algorithm. We will show examples how these degrees of freedom can be coupled to certain directional properties of the 2-0 signal.

  15. Terahertz quantum cascade lasers

    E-print Network

    Williams, Benjamin S. (Benjamin Stanford), 1974-

    2003-01-01

    The development of the terahertz frequency range has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) ...

  16. Broadband terahertz photonics

    E-print Network

    Burghoff, David Patrick

    2014-01-01

    In recent years, quantum cascade lasers have emerged as mature semiconductor sources of light in the terahertz range, the frequency range spanning 1 to 10 THz. Though technological development has pushed their operating ...

  17. Faraday rotation dispersion microscopy imaging of diamagnetic and chiral liquids with pulsed magnetic field.

    PubMed

    Suwa, Masayori; Nakano, Yusuke; Tsukahara, Satoshi; Watarai, Hitoshi

    2013-05-21

    We have constructed an experimental setup for Faraday rotation dispersion imaging and demonstrated the performance of a novel imaging principle. By using a pulsed magnetic field and a polarized light synchronized to the magnetic field, quantitative Faraday rotation images of diamagnetic organic liquids in glass capillaries were observed. Nonaromatic hydrocarbons, benzene derivatives, and naphthalene derivatives were clearly distinguished by the Faraday rotation images due to the difference in Verdet constants. From the wavelength dispersion of the Faraday rotation images in the visible region, it was found that the resonance wavelength in the UV region, which was estimated based on the Faraday B-term, could be used as characteristic parameters for the imaging of the liquids. Furthermore, simultaneous acquisition of Faraday rotation image and natural optical rotation image was demonstrated for chiral organic liquids. PMID:23581712

  18. Chemical-specific imaging of shallowly buried objects using femtosecond laser pulses.

    PubMed

    Strycker, B D; Wang, K; Springer, M; Sokolov, A V

    2013-07-10

    We demonstrate that objects buried in sand (1 to 4 mm deep) may be selectively imaged according to their chemical composition through spectral analysis of the laser-induced breakdown signal. The signal is generated by loosely focused femtosecond laser pulses having energies ranging from 0.5 to 2.5 mJ. We determine the depth from which a spectral signal may be measured as a function of pulse energy. Having in mind applications to remote sensing, chemical-specific imaging of shallowly buried objects may find use in various fields ranging from space exploration to landmine detection. PMID:23852190

  19. Terahertz Schottky Multiplier Sources

    NASA Technical Reports Server (NTRS)

    Schlecht, Erich T.

    2007-01-01

    This viewgraph presentation reviews the multiplier source technologies and the status/Performance of THz multiplier sources. An example of a THz application is imaging radar. The presentation reviews areas of requirements for THz sources: (1) Figures of merit, (i.e., Frequency Terahertz for high resolution Bandwidth of at least 15 GHz for high range resolution Efficiency (i.e., minimize power supply requirements) (2) Output power: (i.e., Milliwatts below 800 GHz, 10s of microwatts above 1 THz, 1-2 microwatts near 2 THz (3) Mechanical--stability, compact, low mass (4) Environmental -- radiation, vibration, thermal. Several sources for 0.3 - 2 THz are reviewed: FIR lasers, quantum cascade lasers (QCL), backward-wave oscillator (BWO), and Multiplier sources. The current state of the art (SoA) is shown as Substrateless Technology. It also shows where the SoA is for devices beyond 1 THz. The presentation concludes by reviewing the options for future development, and 2 technology roadmaps

  20. Pulse-modulated second harmonic imaging microscope quantitatively demonstrates marked increase of collagen in tumor after chemotherapy

    E-print Network

    Raja, Anju M.

    Pulse-modulated second harmonic imaging microscopes (PM-SHIMs) exhibit improved signal-to-noise ratio (SNR) over conventional SHIMs on sensitive imaging and quantification of weak collagen signals inside tissues. We quantify ...

  1. The development of a pulsed laser imaging system for natural gas leak detection

    NASA Astrophysics Data System (ADS)

    Kulp, Thomas J.

    The detection of gas leaks represents a critical operation performed regularly by the gas industry to maintain the integrity and safety of its vast network of piping, both above and below the ground. We are developing a technology that allows the real-time imaging of gas plumes in a television format. Termed backscatter absorption gas imaging (BAGI), the technique operates by illuminating a scene with infrared laser radiation having a wavelength that is absorbed by the gas to be detected (in this case, methane). Backscattered laser radiation is used to create a video image of the scene. If a leak of the target gas is present in the field-of-view of the camera, it attenuates a portion of the backscatter and creates a dark cloud in the video picture. The specific purpose of this project is to investigate a new method of accomplishing BAGI using a pulsed laser source. The pulsed laser imager under development in this project is expected to have a range (greater than or equal to 40 m) and sensitivity (less than 10 ppm-m) that will surpass the respective attributes of a scanned continuous wave laser imager. The pulsed system will operate by flooding (rather than scanning) the imaged scene with pulses of laser radiation. Imaging will be accomplished using a focal-plane array camera that operates in a snapshot format. The higher power of the pulsed laser source and the more effective collection optics of the focal-plane array-based receiver will allow the performance enhancements to be achieved.

  2. Generation of Intense Terahertz Radiation via Optical Methods

    Microsoft Academic Search

    François Blanchard; Gargi Sharma; Luca Razzari; Xavier Ropagnol; Heidi-Christina Bandulet; François Vidal; Roberto Morandotti; Jean-Claude Kieffer; Tsuneyuki Ozaki; Henry Tiedje; Harold Haugen; Matt Reid; Frank Hegmann

    2011-01-01

    The development of new sources in the terahertz (THz) spectral region has attracted much attention over the past 20 years. In particular, the last three years have seen a surge of new laser-based techniques for generating intense, few-cycle THz pulses in the microjoule energy range, thus paving the way to the study of the nonlinear optical properties of various materials

  3. Ondes terahertz : le cha^inon manquant Bertrand Gauvreau

    E-print Network

    Meunier, Michel

    ., Stancampiano, C. V., & Blumenthal, D. (1980). Picosecond microwave pulse generation. Appl. Phys. Lett., 38, F. W., & McIntosh, K. A. (1993). Coherent millimeter-wave generation by heterodyne conversion in low-1456. 18. Siegel, P. H. (2002). Terahertz technology. IEEE Transactions on Microwave Technology

  4. Advantage of terahertz radiation versus X-ray to detect hidden organic materials in sealed vessels

    NASA Astrophysics Data System (ADS)

    Bessou, Maryelle; Duday, Henri; Caumes, Jean-Pascal; Salort, Simon; Chassagne, Bruno; Dautant, Alain; Ziéglé, Anne; Abraham, Emmanuel

    2012-10-01

    Terahertz imaging and conventional X-ray have been used to investigate a sealed Ancient Egyptian jar preserved at the Museum of Aquitaine (France). Terahertz radiation revealed an unknown content that could not have been visualized by X-ray. By comparison with a model object, we concluded that this content was composed of organic materials explaining their relative radiolucency.

  5. Terahertz emission from black silicon

    Microsoft Academic Search

    P. Hoyer; M. Theuer; R. Beigang; E.-B. Kley

    2008-01-01

    We report on a terahertz emitter made out of black silicon. The black surface structure absorbs the whole optical pump power in the very surface. In contrast to expectations for indirect semiconductors, the black structure shows an emission in the terahertz range. The emitted radiation of the black silicon crystal is characterized for different parameters using terahertz time-domain spectroscopy.

  6. Fast simulation and optimization of pulse-train chemical exchange saturation transfer (CEST) imaging.

    PubMed

    Xiao, Gang; Sun, Phillip Zhe; Wu, Renhua

    2015-06-21

    Chemical exchange saturation transfer (CEST) MRI has been increasingly applied to detect dilute solutes and physicochemical properties, with promising in vivo applications. Whereas CEST imaging has been implemented with continuous wave (CW) radio-frequency irradiation on preclinical scanners, pulse-train irradiation is often chosen on clinical systems. Therefore, it is necessary to optimize pulse-train CEST imaging, particularly important for translational studies. Because conventional Bloch-McConnell formulas are not in the form of homogeneous differential equations, the routine simulation approach simulates the evolving magnetization step by step, which is time consuming. Herein we developed a computationally efficient numerical solution using matrix iterative analysis of homogeneous Bloch-McConnell equations. The proposed algorithm requires simulation of pulse-train CEST MRI magnetization within one irradiation repeat, with 99% computation time reduction from that of conventional approach under typical experimental conditions. The proposed solution enables determination of labile proton ratio and exchange rate from pulse-train CEST MRI experiment, within 5% from those determined from quantitative CW-CEST MRI. In addition, the structural similarity index analysis shows that the dependence of CEST contrast on saturation pulse flip angle and duration between simulation and experiment was 0.98??±??0.01, indicating that the proposed simulation algorithm permits fast optimization and quantification of pulse-train CEST MRI. PMID:26020414

  7. Fast simulation and optimization of pulse-train chemical exchange saturation transfer (CEST) imaging

    NASA Astrophysics Data System (ADS)

    Xiao, Gang; Zhe Sun, Phillip; Wu, Renhua

    2015-06-01

    Chemical exchange saturation transfer (CEST) MRI has been increasingly applied to detect dilute solutes and physicochemical properties, with promising in vivo applications. Whereas CEST imaging has been implemented with continuous wave (CW) radio-frequency irradiation on preclinical scanners, pulse-train irradiation is often chosen on clinical systems. Therefore, it is necessary to optimize pulse-train CEST imaging, particularly important for translational studies. Because conventional Bloch–McConnell formulas are not in the form of homogeneous differential equations, the routine simulation approach simulates the evolving magnetization step by step, which is time consuming. Herein we developed a computationally efficient numerical solution using matrix iterative analysis of homogeneous Bloch–McConnell equations. The proposed algorithm requires simulation of pulse-train CEST MRI magnetization within one irradiation repeat, with 99% computation time reduction from that of conventional approach under typical experimental conditions. The proposed solution enables determination of labile proton ratio and exchange rate from pulse-train CEST MRI experiment, within 5% from those determined from quantitative CW-CEST MRI. In addition, the structural similarity index analysis shows that the dependence of CEST contrast on saturation pulse flip angle and duration between simulation and experiment was 0.98??±??0.01, indicating that the proposed simulation algorithm permits fast optimization and quantification of pulse-train CEST MRI.

  8. Pulse compression technique for simultaneous HIFU surgery and ultrasonic imaging: A preliminary study

    PubMed Central

    Jeong, Jong Seob; Chang, Jin Ho; Shung, K. Kirk

    2013-01-01

    In an ultrasound image-guided High Intensity Focused Ultrasound (HIFU) surgery, reflected HIFU waves received by an imaging transducer should be suppressed for real-time simultaneous imaging and therapy. In this paper, we investigate the feasibility of pulse compression scheme combined with notch filtering in order to minimize these HIFU interference signals. A chirp signal modulated by the Dolph-Chebyshev window with 3–9 MHz frequency sweep range is used for B-mode imaging and 4 MHz continuous wave is used for HIFU. The second order infinite impulse response notch filters are employed to suppress reflected HIFU waves whose center frequencies are 4 MHz and 8 MHz. The prototype integrated HIFU/imaging transducer that composed of three rectangular elements with a spherically con-focused aperture was fabricated. The center element has the ability to transmit and receive 6 MHz imaging signals and two outer elements are only used for transmitting 4 MHz continuous HIFU wave. When the chirp signal and 4 MHz HIFU wave are simultaneously transmitted to the target, the reflected chirp signals mixed with 4 MHz and 8 MHz HIFU waves are detected by the imaging transducer. After the application of notch filtering with pulse compression process, HIFU interference waves in this mixed signal are significantly reduced while maintaining original imaging signal. In the single scanline test using a strong reflector, the amplitude of the reflected HIFU wave is reduced to ?45 dB. In vitro test, with a sliced porcine muscle shows that the speckle pattern of the restored B-mode image is close to that of the original image. These preliminary results demonstrate the potential for the pulse compression scheme with notch filtering to achieve real-time ultrasound image-guided HIFU surgery. PMID:22356771

  9. Quantitative sodium imaging with a flexible twisted projection pulse sequence.

    PubMed

    Lu, Aiming; Atkinson, Ian C; Claiborne, Theodore C; Damen, Frederick C; Thulborn, Keith R

    2010-06-01

    The quantification of sodium MR images from an arbitrary intensity scale into a bioscale fosters image interpretation in terms of the spatially resolved biochemical process of sodium ion homeostasis. A methodology for quantifying tissue sodium concentration using a flexible twisted projection imaging sequence is proposed that allows for optimization of tradeoffs between readout time, signal-to-noise ratio efficiency, and sensitivity to static field susceptibility artifacts. The gradient amplitude supported by the slew rate at each k-space radius regularizes the readout gradient waveform design to avoid slew rate violation. Static field inhomogeneity artifacts are corrected using a frequency-segmented conjugate phase reconstruction approach, with field maps obtained quickly from coregistered proton imaging. High-quality quantitative sodium images have been achieved in phantom and volunteer studies with real isotropic spatial resolution of 7.5 x 7.5 x 7.5 mm(3) for the slow T(2) component in approximately 8 min on a clinical 3-T scanner. After correcting for coil sensitivity inhomogeneity and water fraction, the tissue sodium concentration in gray matter and white matter was measured to be 36.6 +/- 0.6 micromol/g wet weight and 27.6 +/- 1.2 micromol/g wet weight, respectively. PMID:20512862

  10. Hidden images of holography: wavefront reconstruction of abnormalities within pulsed holographic recording

    NASA Astrophysics Data System (ADS)

    Richardson, Martin

    2014-02-01

    Unplanned images recorded within holographic space are of candid interest that can reshape audience definition crossing intellectual boundaries. This paper details three examples of off-axis Pulsed Laser transmission holograms that involve holographic portraits. These are movie director Martin Scorsese, former Royal Photographic Society President Mike Austin and a unique recently discovered early pulsed recording of Nick Phillips together with Anton Furst recorded in 1977. Each example was made when operating conditions for the pulsed ruby lasers were optimum, offering a coherence of several meters time-compressed into 25 ns. This gave rise to not only the portrait capture but also others present during the recording session inside the room. This optimum condition captured more than was intended resulting in images that, until now, have remained un-documented.

  11. A compact, short-pulse laser for near-field, range-gated imaging

    SciTech Connect

    Zutavern, F.J.; Helgeson, W.D.; Loubriel, G.M. [Sandia National Labs., Albuquerque, NM (United States); Yates, G.J.; Gallegos, R.A.; McDonald, T.E. [Los Alamos National Lab., NM (United States)

    1996-12-31

    This paper describes a compact laser, which produces high power, wide-angle emission for a near-field, range-gated, imaging system. The optical pulses are produced by a 100 element laser diode array (LDA) which is pulsed with a GaAs, photoconductive semiconductor switch (PCSS). The LDA generates 100 ps long, gain-switched, optical pulses at 904 nm when it is driven with 3 ns, 400 A, electrical pulses from a high gain PCSS. Gain switching is facilitated with this many lasers by using a low impedance circuit to drive an array of lasers, which are connected electrically in series. The total optical energy produced per pulse is 10 microjoules corresponding to a total peak power of 100 kW. The entire laser system, including prime power (a nine volt battery), pulse charging, PCSS, and LDA, is the size of a small, hand-held flashlight. System lifetime, which is presently limited by the high gain PCSS, is an active area of research and development. Present limitations and potential improvements will be discussed. The complete range-gated imaging system is based on complementary technologies: high speed optical gating with intensified charge coupled devices (ICCD) developed at Los Alamos National Laboratory (LANL) and high gain, PCSS-driven LDAs developed at Sandia National Laboratories (SNL). The system is designed for use in highly scattering media such as turbid water or extremely dense fog or smoke. The short optical pulses from the laser and high speed gating of the ICCD are synchronized to eliminate the back-scattered light from outside the depth of the field of view (FOV) which may be as short as a few centimeters. A high speed photodiode can be used to trigger the intensifier gate and set the range-gated FOV precisely on the target. The ICCD and other aspects of the imaging system are discussed in a separate paper.

  12. Imaging monitored loosening of dense fibrous tissues using high-intensity pulsed ultrasound.

    PubMed

    Yeh, Chia-Lun; Li, Pai-Chi; Shih, Wen-Pin; Huang, Pei-Shin; Kuo, Po-Ling

    2013-10-01

    Pulsed high-intensity focused ultrasound (HIFU) is proposed as a new alternative treatment for contracture of dense fibrous tissue. It is hypothesized that the pulsed-HIFU can release the contracted tissues by attenuating tensile stiffness along the fiber axis, and that the stiffness reduction can be quantitatively monitored by change of B-mode images. Fresh porcine tendons and ligaments were adapted to an ex vivo model and insonated with pulsed-HIFU for durations ranging from 5 to 30 min. The pulse length was 91 µs with a repetition frequency of 500 Hz, and the peak rarefactional pressure was 6.36 MPa. The corresponding average intensities were kept around 1606 W cm(-2) for ISPPA and 72.3 W cm(-2) for ISPTA. B-mode images of the tissues were acquired before and after pulsed-HIFU exposure, and the changes in speckle intensity and organization were analyzed. The tensile stiffness of the HIFU-exposed tissues along the longitudinal axis was examined using a stretching machine. Histology examinations were performed by optical and transmission electron microscopy. Pulsed-HIFU exposure significantly decreased the tensile stiffness of the ligaments and tendons. The intensity and organization of tissue speckles in the exposed region were also decreased. The speckle changes correlated well with the degree of stiffness alteration. Histology examinations revealed that pulsed-HIFU exposure probably damages tissues via a cavitation-mediated mechanism. Our results suggest that pulsed-HIFU with a low duty factor is a promising tool for developing new treatment strategies for orthopedic disorders. PMID:24018912

  13. Passive millimetre-wave imaging and how it differs from terahertz imaging: One contribution of 16 to a Discussion Meeting 'The terahertz gap: the generation of far-infrared radiation and its applications'

    Microsoft Academic Search

    R. Appleby

    2004-01-01

    It is well known that millimetre-wave systems can penetrate poor weather, dust and smoke far better than infrared or visible systems. Imaging in this band offers the opportunity to be able to navigate and perform surveillance in these conditions of poor visibility. Furthermore, the ability to penetrate dielectrics such as plastic and cloth has opened up the opportunity of detecting

  14. Use of pulsed Doppler tissue imaging to assess regional left ventricular diastolic dysfunction in hypertrophic cardiomyopathy

    Microsoft Academic Search

    Sergio Severino; Pio Caso; Maurizio Galderisi; Luigi De Simone; Antonio Petrocelli; Oreste de Divitiis; Nicola Mininni

    1998-01-01

    In this study, regional diastolic patterns and their relations with transmitral Doppler inflow were investigated in hypertrophic cardiomyopathy (HC) by pulsed Doppler tissue imaging (DTI). Doppler echocardiography and DTI of basal septum and lateral wall (apical 4-chamber view) were performed in 20 patients (15 men and 5 women) with HC and in 10 healthy subjects (7 men and 3 women).

  15. A STUDY OF PULSE-ECHO IMAGE FORMATION USING NON-QUADRATIC

    E-print Network

    Illinois at Urbana-Champaign, University of

    -Champaign, 405 North Mathews,Urbana, IL 61801 USA Abstract: Objective: B-mode imaging is a standard way of presenting results when pulse-echo data acquisition is used. Inverse approaches have been explored techniques (e.g., B-mode and synthetic aperture focusing techniques (SAFT)). Methodology: Two- dimensional

  16. Pulse Image Processing Using Centripetal Autowaves Jason M. Kinser and Chau Nguyen

    E-print Network

    Kinser, Jason M.

    used here is a unified cortical model (UCM) that contains only the similarities from the different by interference amongst objects in the input space. Here the marriage of curvature flow with pulse image centripetal autowaves to extract a similar target signature without the problems of interference. 2. CORTICAL

  17. Combustion Diagnostics with Terahertz Tomography

    NASA Astrophysics Data System (ADS)

    Schroeder, Nicholas; Eichorn, Fin; Deibel, Jason

    2008-10-01

    The objective of this project is to capture the spectroscopic signature and temperature of combustion process as a function of position using terahertz (THz) time-domain spectroscopy and imaging. The development of a system that can monitor the temperature of an exhaust plume and its chemical make-up as a function of position would be of immeasurable value to the further development of jet engines and their mid-life diagnostics. Current techniques available require different set-ups for each measurement, position and chemical. Our approach to tomographic reconstruction consists of utilizing 8 separate THz transmitter- receiver pairs arranged around the object, allowing all of the tomographic slices to be taken at the same instant. We will present preliminary data demonstrating THz tomographic imaging of solid objects and calibration of spectroscopic and thermal measurement capabilities by THz characterization of water vapors and flames. We will further show ongoing work to produce a THz tomographic reconstruction of a simple flame.

  18. RF Pulse Design for Parallel Excitation in Magnetic Resonance Imaging 

    E-print Network

    Liu, Yinan

    2012-07-16

    ? ?= (2.1) where ? is the gyromagnetic ratio. For 1H, ? = 42.58MHz/Tesla. 5 Figure 2.1. Precession of a nuclear spin about an external magnetic field. The imaging of an object relies on the bulk precession of the hydrogen spins in water...

  19. In vivo pulsed magneto-motive ultrasound imaging using high-performance magnetoactive contrast nanoagents.

    PubMed

    Mehrmohammadi, Mohammad; Shin, Tae-Hyun; Qu, Min; Kruizinga, Pieter; Truby, Ryan L; Lee, Jae-Hyun; Cheon, Jinwoo; Emelianov, Stanislav Y

    2013-11-21

    Previously, pulsed magneto-motive ultrasound (pMMUS) imaging has been introduced as a contrast-agent-assisted ultrasound-based imaging modality capable of visualizing biological events at the cellular and molecular level. In pMMUS imaging, a high intensity pulsed magnetic field is used to excite cells or tissue labeled with magnetic nanoparticles. Then, ultrasound (US) imaging is used to monitor the mechanical response of the tissue to an externally applied magnetic field (i.e., tissue displacement). Signal to noise ratio (SNR) in pMMUS imaging can be improved by using superparamagnetic nanoparticles with larger saturation magnetization. Metal-doped magnetic nanoparticles with enhanced tunable nanomagnetism are suitable candidates to improve the SNR and, therefore, sensitivity of pMMUS imaging, which is essential for in vivo pMMUS imaging. In this study, we demonstrate the capability of pMMUS imaging to identify the presence and distribution of zinc-doped iron oxide nanoparticles in live nude mice bearing A431 (human epithelial carcinoma) xenograft tumors. PMID:24080913

  20. In vivo Pulsed Magneto-motive Ultrasound Imaging Using High-performance Magnetoactive Contrast Nanoagents

    PubMed Central

    Mehrmohammadi, Mohammad; Shin, Tae-Hyun; Qu, Min; Kruizinga, Pieter; Truby, Ryan L.; Lee, Jae-Hyun

    2014-01-01

    Previously, pulsed magneto-motive ultrasound (pMMUS) imaging has been introduced as a contrast-agent-assisted ultrasound-based imaging modality capable of visualizing biological events at the cellular and molecular level. In pMMUS imaging, a high intensity pulsed magnetic field is used to excite cells or tissue labeled with magnetic nanoparticles. Then, ultrasound (US) imaging is used to monitor the mechanical response of the tissue to an externally applied magnetic field (i.e., tissue displacement). Signal to noise ratio (SNR) in pMMUS imaging can be improved by using superparamagnetic nanoparticles with larger saturation magnetization. Metal-doped magnetic nanoparticles with enhanced tunable nanomagnetism are suitable candidates to improve the SNR and, therefore, sensitivity of pMMUS imaging, which is essential for in vivo pMMUS imaging. In this study, we demonstrate the capability of pMMUS imaging to identify the presence and distribution of zinc-doped iron oxide nanoparticles in live nude mice bearing A431 (human epithelial carcinoma) xenograft tumors. PMID:24080913

  1. The development of a pulsed laser imaging system for natural gas leak detection

    SciTech Connect

    Kulp, T.J.

    1995-05-01

    The detection of gas leaks represents a critical operation performed regularly by the gas industry to maintain the integrity and safety of its vast network of piping, both above and below the ground. We are developing a technology that allows the real-time imaging of gas plumes in a television format. Termed backscatter absorption gas imaging (BAGI), the technique operates by illuminating a scene with infrared laser radiation having a wavelength that is absorbed by the gas to be detected (in this case, methane). Backscattered laser radiation is used to create a video image of the scene. If a leak of the target gas is present in the field-of-view of the camera, it attenuates a portion of the backscatter and creates a dark cloud in the video picture. The specific purpose of this project is to investigate a new method of accomplishing BAGI using a pulsed laser source. The efficacy of using BAGI to detect natural gas leaks has already been demonstrated using a first-generation gas imaging technology that was developed at Lawrence Livermore National Laboratories. That technique accomplishes imaging by scanning a continuous-wave infrared laser (infrared helium-neon laser, emitting at 3.39 {mu}m) across a scene at real-time video rates as the scene is imaged by a scanned infrared camera. The primary limitation to the use of that system is the weak output energy of the helium neon laser (30 mW). The pulsed laser imager under development in this project is expected to have a range ({ge}40 m) and sensitivity (<10 ppm-m) that will surpass the respective attributes of the scanned imager. The pulsed system will operate by flooding (rather than scanning) the imaged scene with pulses of laser radiation. Imaging will be accomplished using a focal-plane array camera that operates in a snapshot format. The higher power of the pulsed laser source and the more effective collection optics of the focal-plane array-based receiver will allow the performance enhancements to be achieved.

  2. An Exploration of the Utilities of Terahertz Waves for the Nde of Composites

    NASA Astrophysics Data System (ADS)

    Hsu, David K.; Im, Kwang-Hee; Chiou, Chien-Ping; Barnard, Daniel J.

    2011-06-01

    We report an investigation of terahertz waves for the nondestructive evaluation of composite materials and structures. The modalities of the terahertz radiation used were time domain spectroscopy (TDS) and continuous wave (CW). The composite materials and structures investigated include both non-conducting polymeric composites and carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse can detect a crack hidden behind a larger crack. This was demonstrated in thick GFRP laminates containing double saw slots. In carbon composites the penetration of terahertz waves is quite limited and the detection of flaws is strongly affected by the angle between the electric field vector of the terahertz waves and the intervening fiber directions. The structures tested in this study include both solid laminates and honeycomb sandwiches. The defects and anomalies investigated by terahertz waves were foreign material inclusions, simulated disbond and delamination, mechanical impact damage, heat damage, and water or hydraulic fluid ingression. The effectiveness and limitations of terahertz radiation for the NDE of composites are discussed.

  3. Generation of coherent terahertz radiation in ultrafast laser-gas interactions

    SciTech Connect

    Kim, Ki-Yong [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)

    2009-05-15

    The generation of intense terahertz radiation in ultrafast laser-gas interactions is studied on a basis of transient electron current model. When an ultrashort pulse laser's fundamental and its second harmonic fields are mixed to ionize a gas, a nonvanishing, directional photoelectron current can be produced, which simultaneously emits terahertz radiation in the far field. Here, the generation mechanism is examined with an analytic derivation and numerical simulations, in which tunneling ionization and subsequent electron motion in the combined laser field play a key role. In the simulations, three types of laser-gas interactions are considered: (i) mixing the fundamental and its second harmonic fields, (ii) mixing nonharmonic, two-color fields, and (iii) focusing single-color, few-cycle pulses. In these interactions, terahertz generation and other nonlinear effects driven by the transient current are investigated. In particular, anticorrelation between terahertz and second (or third) harmonic generation is observed and analyzed.

  4. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    Microsoft Academic Search

    Yu-Lei Shi; Qing-Li Zhou; Cun-Lin Zhang

    2009-01-01

    This paper investigates the ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs in detail by using a terahertz pump-emission technique. Based on theoretical modelling, it finds that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed after the excitation of pump

  5. Novel Waveguide Structures in the Terahertz Frequency Range

    NASA Astrophysics Data System (ADS)

    Mbonye, Marx

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

  6. Asymmetric Cherenkov radiation for improved terahertz generation in the Si-prism-coupled LiNbO3 layer.

    PubMed

    Bakunov, M I; Mashkovich, E A; Svinkina, E V

    2014-12-15

    We show that a Cherenkov emission of terahertz waves from a femtosecond optical pulse propagating in a LiNbO(3) crystal can be strongly spatially asymmetric with respect to the direction of the optical pulse propagation. We propose using this phenomenon to improve the spectral characteristics of one of the most efficient optical-to-terahertz converters: a thin LiNbO(3) layer attached to a Si-prism outcoupler. PMID:25502995

  7. Optical design of the short pulse x-ray imaging and microscopy time-angle correlated diffraction beamline at the Advanced Photon Source

    E-print Network

    Evans, Paul G.

    Optical design of the short pulse x-ray imaging and microscopy time-angle correlated diffraction://rsi.aip.org/about/rights_and_permissions #12;REVIEW OF SCIENTIFIC INSTRUMENTS 84, 053103 (2013) Optical design of the short pulse x-ray imaging April 2013; published online 10 May 2013) The short pulse x-ray imaging and microscopy beamline is one

  8. Terahertz radiation mixer

    DOEpatents

    Wanke, Michael C. (Albuquerque, NM); Allen, S. James (Santa Barbara, CA); Lee, Mark (Albuquerque, NM)

    2008-05-20

    A terahertz radiation mixer comprises a heterodyned field-effect transistor (FET) having a high electron mobility heterostructure that provides a gatable two-dimensional electron gas in the channel region of the FET. The mixer can operate in either a broadband pinch-off mode or a narrowband resonant plasmon mode by changing a grating gate bias of the FET. The mixer can beat an RF signal frequency against a local oscillator frequency to generate an intermediate frequency difference signal in the microwave region. The mixer can have a low local oscillator power requirement and a large intermediate frequency bandwidth. The terahertz radiation mixer is particularly useful for terahertz applications requiring high resolution.

  9. Imaging sensitivity of three kind of high-sensitivity imaging cameras under short-pulsed light illumination

    Microsoft Academic Search

    Hideyuki TAKAHASHI; Kouichi SAWADA; Koki ABE; Yoshimi TAKAO; Kazutoshi WATANABE

    *** Abstract: As a part of a development of an optical system that enables us to precisely observe negative phototactic fish in situ, characteristics of three different types of a high-sensitivity camera were investigated under short-pulsed light illuminations of different colors. These three types of a camera were Image Intensifier connected with CCD camera, EB-CCD camera, and HARP camera and

  10. Generation of terahertz radiation by a surface ballistic photocurrent in semiconductors under subpicosecond laser excitation

    SciTech Connect

    Ziaziulia, P. A., E-mail: palz@tut.by [Belarussian State University (Belarus); Malevich, V. L. [National Academy of Sciences of Belarus, Stepanov Institute of Physics (Belarus); Manak, I. S. [Belarussian State University (Belarus); Krotkus, A. [Center for Physical Sciences and Technology (Lithuania)

    2012-02-15

    An analytical model describing the onset of a surface ballistic photocurrent in cubic semiconductors under femtosecond laser excitation is proposed. It is shown that the contribution of the photocurrent component parallel to the surface to the generation of terahertz pulses may be comparable to the contribution of the perpendicular component. Consideration of the cubic symmetry of a semiconductor leads to the azimuthal anisotropy of terahertz generation.

  11. High-speed all-optical terahertz polarization switching by a transient plasma phase modulator

    SciTech Connect

    Wen Haidan [SLAC National Accelerator Laboratory, PULSE Institute, Menlo Park, California 94025 (United States); Daranciang, Dan [Department of Chemistry, Stanford University, Stanford, California 94305 (United States); Lindenberg, Aaron M. [SLAC National Accelerator Laboratory, PULSE Institute, Menlo Park, California 94025 (United States); Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States)

    2010-04-19

    We demonstrate high-speed all-optical polarization switching of broadband terahertz frequency electromagnetic fields with subpicosecond switch-on time. This is achieved through the use of a two-plasma configuration in an orthogonal geometry in which one plasma modulates the relative phase of a two-color optical pump field, enabling rapid terahertz polarization modulation at rates limited by the repetition-rate of the control pulse.

  12. Thin film characterization using terahertz differential time-domain spectroscopy and double modulation

    Microsoft Academic Search

    Samuel P. Mickan; Kwang-Su Lee; Toh-Ming Lu; Edward Barnat; Jesper Munch; Derek Abbott; Xi-Cheng Zhang

    2001-01-01

    Characterizing the optical and dielectric properties of thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonics systems and micro-opto-electro-mechanical systems (MOEMS). Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz (THz) radiation to detect phase changes of less than 0.6 femtoseconds (fs) and absorption changes

  13. Hepatic vein transit time of an ultrasound contrast agent: simplified procedure using pulse inversion imaging.

    PubMed

    Bang, N; Nielsen, M B; Rasmussen, A N; Osterhammel, P A; Pedersen, J F

    2001-08-01

    The aim of this study was to ascertain whether a new ultrasound technique, namely pulse inversion imaging, could assess the arrival of a contrast agent in the hepatic veins, and to describe possible advantages of this procedure in determining transit time over a previously described method based upon spectral Doppler quantification. 15 subjects were scanned using pulse inversion imaging. A bolus injection of 2.5 g Levovist (Schering AG, Berlin, Germany) 300 mg x ml(-1) was given into an antecubital vein. Median transit times of 16 s (range 14-20 s) were found in patients with liver cirrhosis (n=4), 22 s (range 16-27 s) in patients with focal liver lesions (n=8) and 31 s (range 30-32 s) in control subjects (n=3). The maximum interobserver variation was 2 s and the maximum intraobserver variation was 3 s (n=10). Transit time was assessed by both pulse inversion imaging and spectral Doppler quantification in six patients. Comparison of the two methods showed transit times within 2 s apart in five patients and within 5 s apart in one patient. In conclusion, it is possible to assess transit time using pulse inversion imaging. This method is simpler than a previously described method requiring computer analysis. Moreover, several liver veins can be assessed simultaneously. Different transit times were observed in different liver veins in two patients with liver tumours. A short transit time (<27 s) appears to be found only in patients with liver disease. After transit time assessment, it is possible to use the injected contrast agent for late phase imaging of the liver parenchyma. PMID:11511501

  14. Step-scan time-domain terahertz magneto-spectroscopy.

    PubMed

    Molter, D; Torosyan, G; Ballon, G; Drigo, L; Beigang, R; Léotin, J

    2012-03-12

    We present a novel approach for terahertz time-domain spectroscopy of magneto-optic phenomena. The setup used in this work combines a tabletop pulsed magnet and a standard terahertz time-domain spectroscopy system. The approach is based on repetitive operation of the pulsed magnet and step-wise increment of the delay time of the time-domain spectroscopy system. The method is demonstrated by plotting the magneto-transmission spectra of linearly polarized THz pulses through the hole gas of a Ge sample and the electron gas of GaAs, InSb and InAs samples. Cyclotron resonance spectra are displayed in the frequency range from 200 GHz to 2 THz and for a magnetic field up to 6 T. The GaAs spectra are analyzed in more detail using simulations based on the Drude model. PMID:22418476

  15. Generation of Terahertz Radiation in LED Heterostructures with Multiple InGaN/GaN Quantum Wells at Two-Photon Excitation by Femtosecond

    NASA Astrophysics Data System (ADS)

    Prudaev, I. A.; Sarkisov, S. Yu.; Tolbanov, O. P.; Kosobutsky, A. V.

    2015-06-01

    The results of experiments on the generation of terahertz radiation in the nitride LED structures at optical excitation by ultrashort laser pulses are presented. The dependences of the emission spectra on the structural parameters of samples and intensity of laser pulses are studied. An increase in the amplitude and the shift of the frequency spectra of terahertz pulses to higher frequencies with increasing number of quantum wells in the heterostructure is found.

  16. Waveguide piezoelectric micromachined ultrasonic transducer array for short-range pulse-echo imaging

    NASA Astrophysics Data System (ADS)

    Lu, Y.; Tang, H.; Wang, Q.; Fung, S.; Tsai, J. M.; Daneman, M.; Boser, B. E.; Horsley, D. A.

    2015-05-01

    This paper presents an 8 × 24 element, 100 ?m-pitch, 20 MHz ultrasound imager based on a piezoelectric micromachined ultrasonic transducer (PMUT) array having integrated acoustic waveguides. The 70 ?m diameter, 220 ?m long waveguides function both to direct acoustic waves and to confine acoustic energy, and also to provide mechanical protection for the PMUT array used for surface-imaging applications such as an ultrasonic fingerprint sensor. The imager consists of a PMUT array bonded with a CMOS ASIC using wafer-level conductive eutectic bonding. This construction allows each PMUT in the array to have a dedicated front-end receive amplifier, which together with on-chip analog multiplexing enables individual pixel read-out with high signal-to-noise ratio through minimized parasitic capacitance between the PMUT and the front-end amplifier. Finite element method simulations demonstrate that the waveguides preserve the pressure amplitude of acoustic pulses over distances of 600 ?m. Moreover, the waveguide design demonstrated here enables pixel-by-pixel readout of the ultrasound image due to improved directivity of the PMUT by directing acoustic waves and creating a pressure field with greater spatial uniformity at the end of the waveguide. Pulse-echo imaging experiments conducted using a one-dimensional steel grating demonstrate the array's ability to form a two-dimensional image of a target.

  17. 3-D photoacoustic and pulse echo imaging of prostate tumor progression in the mouse window chamber

    PubMed Central

    Bauer, Daniel R.; Olafsson, Ragnar; Montilla, Leonardo G.; Witte, Russell S.

    2011-01-01

    Understanding the tumor microenvironment is critical to characterizing how cancers operate and predicting their response to treatment. We describe a novel, high-resolution coregistered photoacoustic (PA) and pulse echo (PE) ultrasound system used to image the tumor microenvironment. Compared to traditional optical systems, the platform provides complementary contrast and important depth information. Three mice are implanted with a dorsal skin flap window chamber and injected with PC-3 prostate tumor cells transfected with green fluorescent protein. The ensuing tumor invasion is mapped during three weeks or more using simultaneous PA and PE imaging at 25 MHz, combined with optical and fluorescent techniques. Pulse echo imaging provides details of tumor structure and the surrounding environment with 100-?m3 resolution. Tumor size increases dramatically with an average volumetric growth rate of 5.35 mm3?day, correlating well with 2-D fluorescent imaging (R = 0.97, p < 0.01). Photoacoustic imaging is able to track the underlying vascular network and identify hemorrhaging, while PA spectroscopy helps classify blood vessels according to their optical absorption spectrum, suggesting variation in blood oxygen saturation. Photoacoustic and PE imaging are safe, translational modalities that provide enhanced depth resolution and complementary contrast to track the tumor microenvironment, evaluate new cancer therapies, and develop molecular contrast agents in vivo. PMID:21361696

  18. Pulsed light imaging for wide-field dosimetry of photodynamic therapy in the skin

    NASA Astrophysics Data System (ADS)

    Davis, Scott C.; Sexton, Kristian; Chapman, Michael Shane; Maytin, Edward; Hasan, Tayyaba; Pogue, Brian W.

    2014-03-01

    Photodynamic therapy using aminoluvelinic acid (ALA) is an FDA-approved treatment for actinic keratoses, pre-cancerous skin lesions which pose a significant risk for immunocompromised individuals, such as organ transplant recipients. While PDT is generally effective, response rates vary, largely due to variations in the accumulation of the photosensitizer protoporphyrin IX (PpIX) after ALA application. The ability to quantify PpIX production before treatment could facilitate the use of additional interventions to improve outcomes. While many groups have demonstrated the ability to image PpIX in the clinic, these systems generally require darkening the room lights during imaging, which is unpopular with clinicians. We have developed a novel wide-field imaging system based on pulsed excitation and gated acquisition to image photosensitizer activity in the skin. The tissue is illuminated using four pulsed LED's to excite PpIX, and the remitted light acquired with a synchronized ICCD. This approach facilitates real-time background subtraction of ambient light, precluding the need to darken the exam room. Delivering light in short bursts also allows the use of elevated excitation intensity while remaining under the maximum permissible exposure limits, making the modality more sensitive to photosensitizer fluorescence than standard approaches. Images of tissue phantoms indicate system sensitivity down to 250nM PpIX and images of animals demonstrate detection of PpIX fluorescence in vivo under normal room light conditions.

  19. Pulse wave imaging in normal, hypertensive and aneurysmal human aortas in vivo: a feasibility study.

    PubMed

    Li, Ronny X; Luo, Jianwen; Balaram, Sandhya K; Chaudhry, Farooq A; Shahmirzadi, Danial; Konofagou, Elisa E

    2013-07-01

    Arterial stiffness is a well-established biomarker for cardiovascular risk, especially in the case of hypertension. The progressive stages of an abdominal aortic aneurysm (AAA) have also been associated with varying arterial stiffness. Pulse wave imaging (PWI) is a noninvasive, ultrasound imaging-based technique that uses the pulse wave-induced arterial wall motion to map the propagation of the pulse wave and measure the regional pulse wave velocity (PWV) as an index of arterial stiffness. In this study, the clinical feasibility of PWI was evaluated in normal, hypertensive, and aneurysmal human aortas. Radiofrequency-based speckle tracking was used to estimate the pulse wave-induced displacements in the abdominal aortic walls of normal (N = 15, mean age 32.5 ± 10.2 years), hypertensive (N = 13, mean age 60.8 ± 15.8 years), and aneurysmal (N = 5, mean age 71.6 ± 11.8 years) human subjects. Linear regression of the spatio-temporal variation of the displacement waveform in the anterior aortic wall over a single cardiac cycle yielded the slope as the PWV and the coefficient of determination r(2) as an approximate measure of the pulse wave propagation uniformity. The aortic PWV measurements in all normal, hypertensive, and AAA subjects were 6.03 ± 1.68, 6.69 ± 2.80, and 10.54 ± 6.52 m s(-1), respectively. There was no significant difference (p = 0.15) between the PWVs of the normal and hypertensive subjects while the PWVs of the AAA subjects were significantly higher (p < 0.001) compared to those of the other two groups. Also, the average r(2) in the AAA subjects was significantly lower (p < 0.001) than that in the normal and hypertensive subjects. These preliminary results suggest that the regional PWV and the pulse wave propagation uniformity (r(2)) obtained using PWI, in addition to the PWI images and spatio-temporal maps that provide qualitative visualization of the pulse wave, may potentially provide valuable information for the clinical characterization of aneurysms and other vascular pathologies that regionally alter the arterial wall mechanics. PMID:23770991

  20. Nonlinear imaging of lipid membrane alterations elicited by nanosecond pulsed electric fields

    NASA Astrophysics Data System (ADS)

    Moen, Erick K.; Beier, Hope T.; Thompson, Gary L.; Armani, Andrea M.; Ibey, Bennett L.

    2015-03-01

    Second Harmonic Generation (SHG) imaging is a useful tool for examining the structure of interfaces between bulk materials. Recently, this technique was applied to detecting subtle perturbations in the structure of cellular membranes following nanosecond pulsed electric field (nsPEF) exposure. Monitoring the cell's outer membrane as it is exposed to nsPEF via SHG has demonstrated that nanoporation is likely the root cause for size-specific, increased cytoplasmic membrane permeabilization. It is theorized that the area of the membrane covered by these pores is tied to pulse intensity or duration. The extent of this effect along the cell's surface, however, has never been measured due to its temporal brevity and minute pore size. By enhancing the SHG technique developed and elucidated previously, we are able to obtain this information. Further, we vary the pulse width and amplitude of the applied stimulus to explore the mechanical changes of the membrane at various sites around the cell. By using this unique SHG imaging technique to directly visualize the change in order of phospholipids within the membrane, we are able to better understand the complex response of living cells to electric pulses.

  1. Optimization of Contrast-to-Tissue Ratio Through Pulse Windowing in Dual-Frequency "Acoustic Angiography" Imaging.

    PubMed

    Lindsey, Brooks D; Shelton, Sarah E; Dayton, Paul A

    2015-07-01

    Early-stage tumors in many cancers are characterized by vascular remodeling, indicative of transformations in cell function. We have previously presented a high-resolution ultrasound imaging approach to detecting these changes that is based on microbubble contrast agents. In this technique, images are formed from only the higher harmonics of microbubble contrast agents, producing images of vasculature alone with 100- to 200-?m resolution. In this study, shaped transmit pulses were used to image the higher broadband harmonic echoes of microbubble contrast agents, and the effects of varying pulse window and phasing on microbubble and tissue harmonic echoes were evaluated using a dual-frequency transducer in vitro and in vivo. An increase in the contrast-to-tissue ratio of 6.8 ± 2.3 dB was observed in vitro using an inverted pulse with a cosine window relative to a non-inverted pulse with a rectangular window. The increase in mean image intensity resulting from contrast enhancement in vivo in five rodents was 13.9 ± 3.0 dB greater for an inverted cosine-windowed pulse and 17.8 ± 3.6 dB greater for a non-inverted Gaussian-windowed pulse relative to a non-inverted pulse with a rectangular window. Implications for pre-clinical and diagnostic imaging are discussed. PMID:25819467

  2. Terahertz ambipolar dual-wavelength quantum cascade laser.

    PubMed

    Lever, L; Hinchcliffe, N M; Khanna, S P; Dean, P; Ikonic, Z; Evans, C A; Davies, A G; Harrison, P; Linfield, E H; Kelsall, R W

    2009-10-26

    Terahertz frequency quantum cascade lasers (THz QCLs) are compact solid-state sources of terahertz radiation that were first demonstrated in 2002. They have a broad range of potential applications ranging from gas sensing and non-destructive testing, through to security and medical imaging, with many polycrystalline compounds having distinct fingerprint spectra in the terahertz frequency range. In this article, we demonstrate an electrically-switchable dual-wavelength THz QCL which will enable spectroscopic information to be obtained within a THz QCL-based imaging system. The device uses the same active region for both emission wavelengths: in forward bias, the laser emits at 2.3 THz; in reverse bias, it emits at 4 THz. The corresponding threshold current densities are 490 A/cm(2) and 330 A/cm(2), respectively, with maximum operating temperatures of 98K and 120 K. PMID:19997216

  3. Photoexcited GaAs surfaces studied by transient terahertz time-domain spectroscopy

    Microsoft Academic Search

    Michael Schall; Peter Uhd Jepsen

    2000-01-01

    The transmission characteristics of an air - GaAs interface and the transient absorption and index spectra of the thin, photoexcited surface layer are investigated subsequent to excitation by a femtosecond laser pulse. We find that the total phase change and transmission of a terahertz (THz) probe pulse are dominated by interface effects. This observation has important implications in the interpretation

  4. Femtosecond pulse shaping enables detection of optical Kerr-effect (OKE) dynamics for molecular imaging

    PubMed Central

    Robles, Francisco E.; Fischer, Martin C.; Warren, Warren S.

    2014-01-01

    We apply femtosecond pulse shaping to generate optical pulse trains that directly access a material’s nonlinear refractive index (n2) and can thus determine time-resolved optical Kerr-effect (OKE) dynamics. Two types of static pulse trains are discussed: The first uses two identical fields delayed in time, plus a pump field at a different wavelength. Time-resolved OKE dynamics are retrieved by monitoring the phase of the interference pattern produced by the two identical fields in the Fourier-domain (FD) as a function of pump–probe–time–delay (where the probe is one of the two identical fields). The second pulse train uses three fields with equal time delays, but with the center field phase shifted by ?/2. In this pulse scheme, changes on a sample’s nonlinear refractive index produce a new frequency in the FD signal, which in turn yields background-free intensity changes in the conjugate (time) domain and provides superior signal-to-noise ratios. The demonstrated sensitivity improvements enable, for the first time to our knowledge, molecular imaging based on OKE dynamics. PMID:25121875

  5. Real-Time Pulse Echo and Photoacoustic Imaging Using an Ultrasound Array and In-line Reflective Illumination

    E-print Network

    Witte, Russell S.

    Real-Time Pulse Echo and Photoacoustic Imaging Using an Ultrasound Array and In-line Reflective, enabling real- time PA and PE imaging. Based on this concept, we describe results from three types of PEDs MHz linear array. Real-time PA and PE images of a 127-µm diameter wire were consistent with our

  6. Scaling behavior of ultrafast two-color terahertz generation in plasma gas targets: energy and pressure dependence.

    PubMed

    Rodriguez, George; Dakovski, Georgi L

    2010-07-01

    Ultrafast terahertz emission from two-color generated laser plasma gas targets is studied using air and the noble gases (neon, argon, krypton, and xenon) as the generation media. Terahertz output pulse energy and power spectra are measured as function of gas species, gas pressure, and input pulse energy up to 6 mJ per pulse using a 40-fs 1-kHz Ti:sapphire laser system as the drive source. Terahertz pulse energies approaching 1 microJ per pulse with spectral content out to 40 THz and pulse duration of 35 fs is reported. A simple one dimensional transient photocurrent ionization model is used to calculate the spectra showing good agreement with experiments. PMID:20639998

  7. Plasma imaging and spectroscopy diagnostics developed on 100-500kA pulsed power devices

    Microsoft Academic Search

    DANIEL B. SINARS; LEV GREGORIAN; DAVID A. HAMMER; YITZHAK MARON

    2004-01-01

    We discuss the development of high-resolution plasma imaging and spectroscopy diagnostics for the soft X-ray and ultraviolet energy ranges developed and used on 100-500 kA pulsed power facilities. Requiring just a few people to run and modest infrastructure investment, these facilities are cost-effective test beds for new ideas and technologies as well as for training students. Most of the diagnostics

  8. RF-modulated pulsed fiber optic lidar transmitter for improved underwater imaging and communications

    Microsoft Academic Search

    F. Kimpel; Y. Chen; J.-L. Fouron; M. Akbulut; D. Engin; S. Gupta

    2011-01-01

    We present results on the design, development and initial testing of a fiber-optic based RF-modulated lidar transmitter operating at 532nm, for underwater imaging application in littoral waters. The design implementation is based on using state-of-the-art high-speed FPGAs, thereby producing optical waveforms with arbitrary digital-RF-modulated pulse patterns with carrier frequencies >= 3GHz, with a repetition rate of 0.5-1MHz, and with average

  9. Imaging CO2 laser radar - A comparison of three techniques: LFM pulse compression, FMCW, CW

    NASA Astrophysics Data System (ADS)

    Meyzonnette, Jean Louis; Saccomani, Georges

    1989-06-01

    This paper describes the breadboard of a coherent imaging IR radar, which is based upon the use of a continuous wave CO2 laser and can operate in three different modes involving frequency modulation/demodulation processing techniques; linear frequency modulation (or chirp) pulse compression, FMCW (triangular frequency modulation) and CW (offset homodyne). In each mode of operation, this laser radar delivers two-dimensional images of a scene, coded in range and/or Doppler velocity, and/or reflectance. After recalling the basic principles of these techniques, their experimental implementation is described and their performances are compared.

  10. Frequency selective terahertz retroreflectors

    NASA Astrophysics Data System (ADS)

    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.

  11. EDITORIAL: Photonic terahertz technology

    Microsoft Academic Search

    Alvydas Lisauskas; Torsten Löffler; Hartmut G. Roskos

    2005-01-01

    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

  12. Paper terahertz wave plates.

    PubMed

    Scherger, Benedikt; Scheller, Maik; Vieweg, Nico; Cundiff, Steven T; Koch, Martin

    2011-12-01

    We present a low-cost terahertz wave plate based on form birefringence fabricated using ordinary paper. Measurements of the transfer function of the wave plate between polarizers closely agree with predictions based on the measured complex indices of refraction of the effective medium. For the design frequency, the dependence on wave plate angle also agrees with theory. PMID:22273881

  13. Searching for terahertz waves

    NASA Astrophysics Data System (ADS)

    2010-09-01

    A scheme for the remote sensing of terahertz waves over distances of tens of metres could have important applications in security and biology. Xi-Cheng Zhang from the Rensselaer Polytechnic Institute spoke to Nature Photonics about his group's latest work in this field.

  14. Fluorescence imaging beyond the ballistic regime by ultrasound pulse guided digital phase conjugation.

    PubMed

    Si, Ke; Fiolka, Reto; Cui, Meng

    2012-10-01

    Fluorescence imaging has revolutionized biomedical research over the past three decades. Its high molecular specificity and unrivaled single molecule level sensitivity have enabled breakthroughs in a variety of research fields. For in vivo applications, its major limitation is the superficial imaging depth as random scattering in biological tissues causes exponential attenuation of the ballistic component of a light wave. Here we present fluorescence imaging beyond the ballistic regime by combining single cycle pulsed ultrasound modulation and digital optical phase conjugation. We demonstrate a near isotropic 3D localized sound-light interaction zone. With the exceptionally high optical gain provided by the digital optical phase conjugation system, we can deliver sufficient optical power to a focus inside highly scattering media for not only fluorescence imaging but also a variety of linear and nonlinear spectroscopy measurements. This technology paves the way for many important applications in both fundamental biology research and clinical studies. PMID:23241552

  15. Fluorescence imaging beyond the ballistic regime by ultrasound-pulse-guided digital phase conjugation

    NASA Astrophysics Data System (ADS)

    Si, Ke; Fiolka, Reto; Cui, Meng

    2012-10-01

    Fluorescence imaging has revolutionized biomedical research over the past three decades. Its high molecular specificity and unrivalled single-molecule-level sensitivity have enabled breakthroughs in a number of research fields. For in vivo applications its major limitation is its superficial imaging depth, a result of random scattering in biological tissues causing exponential attenuation of the ballistic component of a light wave. Here, we present fluorescence imaging beyond the ballistic regime by combining single-cycle pulsed ultrasound modulation and digital optical phase conjugation. We demonstrate a near-isotropic three-dimensional localized sound-light interaction zone. With the exceptionally high optical gain provided by the digital optical phase conjugation system, we can deliver sufficient optical power to a focus inside highly scattering media for not only fluorescence imaging but also a variety of linear and nonlinear spectroscopy measurements. This technology paves the way for many important applications in both fundamental biology research and clinical studies.

  16. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 4, NO. 2, MARCH/APRIL 1998 353 Optical Pump-Terahertz Probe Spectroscopy

    E-print Network

    Scherer, Norbert F.

    -terahertz probe data on h111i GaAs samples are presented, demonstrating the applicability of this spectrometer. This spectrometer routinely produces and detects terahertz pulses that exhibit signal-to-noise ratios (SNR's) greater than 6000 in the time domain and a spectral noise floor of magnitude 2.7 2 1004 . Hence

  17. Short Repetition Time Multiband Echo-Planar Imaging with Simultaneous Pulse Recording Allows Dynamic Imaging of the Cardiac Pulsation Signal

    PubMed Central

    Tong, Yunjie; Hocke, Lia M.; Frederick, Blaise deB.

    2014-01-01

    Purpose Recently developed simultaneous multislice echoplanar imaging (EPI) sequences permit imaging of the whole brain at short repetition time (TR), allowing the cardiac fluctuations to be fully sampled in blood-oxygen-level dependent functional MRI (BOLD fMRI). A novel low computational analytical method was developed to dynamically map the passage of the pulsation signal through the brain and visualize the whole cerebral vasculature affected by the pulse signal. This algorithm is based on a simple combination of fast BOLD fMRI and the scanner's own built-in pulse oximeter. Methods Multiple, temporally shifted copies of the pulse oximeter data (with 0.08 s shifting step and coverage of a 1-s span) were downsampled and used as cardiac pulsation regressors in a general linear model based analyses (FSL) of the fMRI data. The resulting concatenated z-statistics maps show the voxels that are affected as the cardiac signal travels through the brain. Results Many voxels were highly correlated with the pulsation regressor or its temporally shifted version. The dynamic and static cardiac pulsation maps obtained from both the task and resting state scans, resembled cerebral vasculature. Conclusion The results demonstrated: (i) cardiac pulsation significantly affects most voxels in the brain; (ii) combining fast fMRI and this analytical method can reveal additional clinical information to functional studies. PMID:24272768

  18. Accuracy of pulsed arterial spin labeling magnetic resonance imaging in the human brain : tag width and timing effects

    E-print Network

    Bolar, Divya Sanam

    2007-01-01

    Arterial spin labeling (ASL) is the only non-invasive magnetic resonance imaging (MRI) technique that allows absolute quantification of cerebral blood flow (CBF). It involves using radiofrequency pulses designed to invert ...

  19. Energy scaling of a tunable terahertz parametric oscillator with a surface emitted configuration

    NASA Astrophysics Data System (ADS)

    Wang, Y. Y.; Li, Z. X.; Li, J. Q.; Yan, C.; Chen, T. N.; Xu, D. G.; Shi, W.; Feng, H.; Yao, J. Q.

    2014-12-01

    A high-energy THz-wave output has been experimentally demonstrated with a terahertz-wave parametric oscillator based on a surface-emitted configuration. Through optimizing the cavity length and pump beam size, the maximum THz-wave output energy of 854?nJ?pulse?1 was obtained at 1.62?THz. The conversion efficiency was 0.57? × ?10–5, corresponding to the photon conversion efficiency of 0.099%. The THz beam profile was measured with a THz imager, which had a Gaussian profile. The measured beam diameter sizes were 423??m and 258??m in the horizontal and vertical directions, respectively. A wide tunable range from 0.75 to 2.81?THz was realized.

  20. Ultrafast THz-pulse-induced tunneling dynamics in an STM

    NASA Astrophysics Data System (ADS)

    Jelic, Vedran; Cocker, Tyler L.; Hoffman, James R.; Gupta, Manisha; Miller, Reginald; Molesky, Sean J.; Burgess, Jacob A. J.; De Los Reyes, Glenda B.; Titova, Lyubov V.; Tsui, Ying Y.; Freeman, Mark R.; Hegmann, Frank A.

    2014-03-01

    We have recently developed an ultrafast terahertz-pulse-coupled scanning tunneling microscope (THz-STM) that can image nanoscale dynamics with simultaneous 0.5 ps temporal resolution and 2 nm spatial resolution under ambient conditions. Broadband THz pulses that are focused onto the metallic tip of an STM induce sub-picosecond voltage transients across the STM junction, producing a rectified current signal due to the nonlinear tunnel junction currentvoltage (I-V) relationship. We use the Simmons model to simulate a tunnel junction I-V curve whereby a THz pulse induces an ultrafast voltage transient, generating milliamp-level rectified currents over sub-picosecond timescales. The nature of the ultrafast field emission tunneling regime achieved in the THz-STM is discussed.

  1. Terahertz technology and application for explosives detection

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Li, Xiao-feng; Li, Xi-lai; Wang, Hong-shui; Xu, Li-guo

    2007-12-01

    Terahertz (THz) radiation, which occupies a large portion of the electromagnetic spectrum between infrared and microwave bands, offers innovations imaging and sensing technologies that can provide information not available through conventional methods such as microwave, X-ray imaging and NMR(nuclear magnetic resonance). T-ray imaging can give not only the density picture but also the phase information within the frequency domain. T-ray imaging has several advantages over other sensing and imaging techniques, so it has many important scientific, industrial and medical applications. In this paper, we study the feasibility of using THz sensing and imaging for mine detection. The principal features of THz radiation and its unique advantage in mine detection are investigated. Some difficult issues, which are not resolved yet, are discussed. The military applications and development trend of the THz spectroscopy are briefly forecasted.

  2. RF-modulated pulsed fiber optic lidar transmitter for improved underwater imaging and communications

    NASA Astrophysics Data System (ADS)

    Kimpel, F.; Chen, Y.; Fouron, J.-L.; Akbulut, M.; Engin, D.; Gupta, S.

    2011-03-01

    We present results on the design, development and initial testing of a fiber-optic based RF-modulated lidar transmitter operating at 532nm, for underwater imaging application in littoral waters. The design implementation is based on using state-of-the-art high-speed FPGAs, thereby producing optical waveforms with arbitrary digital-RF-modulated pulse patterns with carrier frequencies >= 3GHz, with a repetition rate of 0.5-1MHz, and with average powers >=5W (at 532nm). Use of RF-modulated bursts above 500MHz, instead of single optical pulse lidar detection, reduces the effect of volumetric backscatter for underwater imaging application, leading to an improved signal-to-noise-ratio (SNR) and contrast, for a given range. Initial underwater target detection tests conducted at Patuxent River Naval Air Station, MD, in a large water-tank facility, validates the advantages of this hybrid-lidar-radar (HLR) approach for improved underwater imaging, over a wide range of turbidity levels and both white and black targets. The compact, robust and power-efficient fiber laser architecture lends very well to lidar sensor integration on unmanned-underwater-vehicle (UUV) platforms. HLR transmitters can also provide similar advantages in active-sensing situations dominated by continuous backscatter, e.g. underwater communications, imaging through smoke and fire environment, rotor-craft landing in degraded visual environment, and pointing-tracking of active-EO sensors through fog.

  3. Live-Cell Superresolution Imaging by Pulsed STED Two-Photon Excitation Microscopy

    PubMed Central

    Takasaki, Kevin T.; Ding, Jun B.; Sabatini, Bernardo L.

    2013-01-01

    Two-photon laser scanning microscopy (2PLSM) allows fluorescence imaging in thick biological samples where absorption and scattering typically degrade resolution and signal collection of one-photon imaging approaches. The spatial resolution of conventional 2PLSM is limited by diffraction, and the near-infrared wavelengths used for excitation in 2PLSM preclude the accurate imaging of many small subcellular compartments of neurons. Stimulated emission depletion (STED) microscopy is a superresolution imaging modality that overcomes the resolution limit imposed by diffraction and allows fluorescence imaging of nanoscale features. Here, we describe the design and operation of a superresolution two-photon microscope using pulsed excitation and STED lasers. We examine the depth dependence of STED imaging in acute tissue slices and find enhancement of 2P resolution ranging from approximately fivefold at 20 ?m to approximately twofold at 90-?m deep. The depth dependence of resolution is found to be consistent with the depth dependence of depletion efficiency, suggesting resolution is limited by STED laser propagation through turbid tissue. Finally, we achieve live imaging of dendritic spines with 60-nm resolution and demonstrate that our technique allows accurate quantification of neuronal morphology up to 30-?m deep in living brain tissue. PMID:23442955

  4. A pulse coupled neural network segmentation algorithm for reflectance confocal images of epithelial tissue.

    PubMed

    Harris, Meagan A; Van, Andrew N; Malik, Bilal H; Jabbour, Joey M; Maitland, Kristen C

    2015-01-01

    Automatic segmentation of nuclei in reflectance confocal microscopy images is critical for visualization and rapid quantification of nuclear-to-cytoplasmic ratio, a useful indicator of epithelial precancer. Reflectance confocal microscopy can provide three-dimensional imaging of epithelial tissue in vivo with sub-cellular resolution. Changes in nuclear density or nuclear-to-cytoplasmic ratio as a function of depth obtained from confocal images can be used to determine the presence or stage of epithelial cancers. However, low nuclear to background contrast, low resolution at greater imaging depths, and significant variation in reflectance signal of nuclei complicate segmentation required for quantification of nuclear-to-cytoplasmic ratio. Here, we present an automated segmentation method to segment nuclei in reflectance confocal images using a pulse coupled neural network algorithm, specifically a spiking cortical model, and an artificial neural network classifier. The segmentation algorithm was applied to an image model of nuclei with varying nuclear to background contrast. Greater than 90% of simulated nuclei were detected for contrast of 2.0 or greater. Confocal images of porcine and human oral mucosa were used to evaluate application to epithelial tissue. Segmentation accuracy was assessed using manual segmentation of nuclei as the gold standard. PMID:25816131

  5. Terahertz emission from YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films

    SciTech Connect

    Siders, J.L.W.; Gosnell, T.R.; Trugman, S.A.; Taylor, A.J.

    1998-12-31

    We report the first observation of terahertz emission from unbiased YBa{sub 2}Cu{sub 3}O{sub 7} thin films at room temperature excited by 1.5 eV femotosecond laser pulses. The strength of the radiated terahertz field depends on the incident angle ({theta}) and depends linearly on incident power. The terahertz emission also depends strongly on the rotation of the film about its surface normal (azimuthal angle, {phi}). The strong anisotropy, with 4{phi} symmetry is demonstrated for different polarizations (incident and detected) and found to be consistent with optical rectification. Because YBCO is centrosymmetric, the second order nonlinear susceptibility vanishes. The next order term in the nonlinear polarizations is the electric quadrupole source term which describes the observed data quite well. The terahertz radiation was found to decrease with decreasing oxygen content, indicating that the carriers in the doped sample enhance the nonlinearity responsible for the terahertz emission.

  6. Time resolved imaging of magnetization dynamics in hard disk writer yokes excited by bipolar current pulses

    SciTech Connect

    Yu, W., E-mail: w.yu@exeter.ac.uk; Keatley, P. S.; Hicken, R. J. [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Gubbins, M. A. [Research and Development, Seagate Technology, 1 Disc Drive, Springtown Industrial Estate, Derry BT48 0BF, Northern Ireland (United Kingdom); Czoschke, P. J.; Lopusnik, R. [Recording Heads Operation, Seagate Technology, 7801 Computer Avenue South, Bloomington, Minnesota 55435 (United States)

    2014-05-07

    A partially built hard disk writer structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied by time and vector resolved scanning Kerr microscopy. All three time dependent components of the magnetization were recorded simultaneously as a bipolar current pulse with 1?MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously.

  7. Terahertz emission from cubic semiconductor induced by a transient anisotropic photocurrent

    NASA Astrophysics Data System (ADS)

    Malevich, V. L.; Ziaziulia, P. A.; Adomavi?ius, R.; Krotkus, A.; Malevich, Y. V.

    2012-10-01

    Terahertz emission from the surfaces of narrow-gap semiconductors excited by femtosecond laser pulses was described in terms of a transient interband photoconductivity. It has been found that the nonparabolicity of the electron dispersion law as well as the optical alignment of the photoexcited carrier momenta result in anisotropic photocurrent with a component perpendicular to the surface dc electric field even in semiconductors with a cubic symmetry. This lateral transient photocurrent component is the strongest during the first few hundreds of femtoseconds after the photoexcitation and causes the emission of terahertz radiation pulses with an amplitude dependent on the angle between the optical field and the crystallographic axes. In the case of InAs the contribution of this component explains experimental results of both the azimuthal anisotropy of the emitted terahertz pulse amplitude and its dependence on the exciting photon energy.

  8. Nd:YAG Pulsed Laser based flaw imaging techniques for noncontact NDE of an aluminum plate

    NASA Astrophysics Data System (ADS)

    Park, Woong-Ki; Lee, Changgil; Park, Seunghee

    2012-04-01

    Recently, the longitudinal, shear and surface waves have been very widely used as a kind of ultrasonic wave exploration methods to identify internal defects of metallic structures. The ultrasonic wave-based non-destructive testing (NDT) is one of main non-destructive inspection techniques for a health assessment about nuclear power plant, aircraft, ships, and/or automobile manufacturing. In this study, a noncontact pulsed laser-based flaw imaging NDT technique is implemented to detect the damage of a plate-like structure and to identify the location of the damage. To achieve this goal, the Nd:YAG pulsed laser equipment is used to generate a guided wave and scans a specific area to find damage location. The Nd: YAG pulsed laser is used to generate Lamb wave and piezoelectric sensors are installed to measure structural responses. Ann aluminum plate is investigated to verify the effectiveness and the robustness of the proposed NDT approach. A notch is a target to detect, which is inflicted on the surface of an aluminum plate. The damagesensitive features are extracted by comparing the time of flight of the guided wave obtained from an acoustic emission (AE) sensor and make use of the flaw imaging techniques of the aluminum plate.

  9. High Speed Imaging of Bubble Clouds Generated in Pulsed Ultrasound Cavitational Therapy—Histotripsy

    PubMed Central

    Xu, Zhen; Raghavan, Mekhala; Hall, Timothy L.; Chang, Ching-Wei; Mycek, Mary-Ann; Fowlkes, J. Brian; Cain, Charles A.

    2009-01-01

    Our recent studies have demonstrated that mechanical fractionation of tissue structure with sharply demarcated boundaries can be achieved using short (<20 ?s), high intensity ultrasound pulses delivered at low duty cycles. We have called this technique histotripsy. Histotripsy has potential clinical applications where noninvasive tissue fractionation and/or tissue removal are desired. The primary mechanism of histotripsy is thought to be acoustic cavitation, which is supported by a temporally changing acoustic backscatter observed during the histotripsy process. In this paper, a fast-gated digital camera was used to image the hypothesized cavitating bubble cloud generated by histotripsy pulses. The bubble cloud was produced at a tissue-water interface and inside an optically transparent gelatin phantom which mimics bulk tissue. The imaging shows the following: 1) Initiation of a temporally changing acoustic backscatter was due to the formation of a bubble cloud; 2) The pressure threshold to generate a bubble cloud was lower at a tissue-fluid interface than inside bulk tissue; and 3) at higher pulse pressure, the bubble cloud lasted longer and grew larger. The results add further support to the hypothesis that the histotripsy process is due to a cavitating bubble cloud and may provide insight into the sharp boundaries of histotripsy lesions. PMID:18019247

  10. Chirp-pulse-compression three-dimensional lidar imager with fiber optics.

    PubMed

    Pearson, Guy N; Ridley, Kevin D; Willetts, David V

    2005-01-10

    A coherent three-dimensional (angle-angle-range) lidar imager using a master-oscillator-power-amplifier concept and operating at a wavelength of 1.5 microm with chirp-pulse compression is described. A fiber-optic delay line in the local oscillator path enables a single continuous-wave semiconductor laser source with a modulated drive waveform to generate both the constant-frequency local oscillator and the frequency chirp. A portion of this chirp is gated out and amplified by a two-stage fiber amplifier. The digitized return signal was compressed by cross correlating it with a sample of the outgoing pulse. In this way a 350-ns, 10-microJ pulse with a 250-MHz frequency sweep is compressed to a width of approximately 8 ns. With a 25-mm output aperture, the lidar has been used to produce three-dimensional images of hard targets out to a range of approximately 2 km with near-diffraction-limited angular resolution and submeter range resolution. PMID:15678779

  11. Effect of excitation pulse width on thermoacoustic signal characteristics and the corresponding algorithm for optimization of imaging resolution

    NASA Astrophysics Data System (ADS)

    Lou, Cunguang; Nie, Liming; Xu, Dong

    2011-10-01

    Thermoacoustic (TA) signal amplitude, waveform, and spatial resolution related to width of the excitation pulse were theoretically explained and simulated by finite-difference time-domain (FDTD) method. TA signals and the reconstructed TA images were compared under variable microwave pulse widths tunable from 400 to 1200 ns to analyze the relationships. The peak-to-peak interval of TA signals increase and the spatial resolution of TA images decrease with the increment of the excitation pulse width in the long pulse region. Also, the experimental results clearly reveal that the TA conversion efficiency decrease with increasing microwave pulse duration under the same peak power, which have a good agreement with the theoretical predication and FDTD simulation.

  12. Terahertz scattering from granular material Lisa M. Zurk,1,

    E-print Network

    Hayden, L. Michael

    application is the use of THz spectroscopy to detect the presence of explosive materials. Initial measurements detection: First, does significant energy in the THz wave field in explosive granular sys- tems (or, more August 17, 2007 Terahertz (THz) imaging is emerging as a potentially powerful method of detecting

  13. Ultrashort microwave pulsed thermoacoustic imaging for tumor localization over whole breast

    NASA Astrophysics Data System (ADS)

    Ji, Zhong; Fu, Yong; Lou, Cunguang

    2014-09-01

    Microwave-induced thermoacoustic imaging (TAI) has attracted considerable interest as a promising imaging modality. Previous studies show that TAI has great potential for use in breast tumor detection with high contrast and high spatial resolution, nevertheless it requires high energy density and possesses small field of view (FOV). In this paper, a ultrashort microwave pulse (USMP) TAI system was employed for quality imaging with much less energy density required , and simultaneously, large enough FOV was obtained to cover the whole breast. The experimental results clearly demonstrate that the new USMP TAI system can be used for three-dimensional (3-D) localization of deep breast tumors with low microwave radiation dose over the whole breast.

  14. Development of high-speed polarizing imaging system for operation in high pulsed magnetic field.

    PubMed

    Katakura, I; Tokunaga, M; Matsuo, A; Kawaguchi, K; Kindo, K; Hitomi, M; Akahoshi, D; Kuwahara, H

    2010-04-01

    A high-speed polarizing microscope system combined with a 37 T pulse magnet has been developed. This system was applied to successfully visualize the field-induced collapse of charge-orbital ordering in a layered manganite La(1/2)Sr(3/2)MnO(4). Quantitative analyses of the obtained polarizing microscope images provided clear evidence of this transition in contrast to rather moderate changes in magnetization and magnetoresistance. The ability of this system to carry out quantitative analysis was further tested through the observation of Faraday rotation in a Tb(3)Ga(5)O(12) crystal. The Verdet constant determined from the polarizing images is in reasonable agreement with that in literature. Local intensity analyses of the images indicate that we can investigate magneto-optical signals within an accuracy of 0.85% in an area of 9.6 x 9.6 microm(2). PMID:20441339

  15. Development of high-speed polarizing imaging system for operation in high pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Katakura, I.; Tokunaga, M.; Matsuo, A.; Kawaguchi, K.; Kindo, K.; Hitomi, M.; Akahoshi, D.; Kuwahara, H.

    2010-04-01

    A high-speed polarizing microscope system combined with a 37 T pulse magnet has been developed. This system was applied to successfully visualize the field-induced collapse of charge-orbital ordering in a layered manganite La1/2Sr3/2MnO4. Quantitative analyses of the obtained polarizing microscope images provided clear evidence of this transition in contrast to rather moderate changes in magnetization and magnetoresistance. The ability of this system to carry out quantitative analysis was further tested through the observation of Faraday rotation in a Tb3Ga5O12 crystal. The Verdet constant determined from the polarizing images is in reasonable agreement with that in literature. Local intensity analyses of the images indicate that we can investigate magneto-optical signals within an accuracy of 0.85% in an area of 9.6×9.6 ?m2.

  16. Synchronizing terahertz wave generation with attosecond bursts.

    PubMed

    Zhang, Dongwen; Lü, Zhihui; Meng, Chao; Du, Xiyu; Zhou, Zhaoyan; Zhao, Zengxiu; Yuan, Jianmin

    2012-12-14

    We perform a joint measurement of terahertz waves and high-harmonics generated from argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase delay between the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics. PMID:23368313

  17. Time-resolved imaging of pulse-induced magnetization reversal with a microwave assist field

    PubMed Central

    Rao, Siddharth; Rhensius, Jan; Bisig, Andre; Mawass, Mohamad-Assaad; Weigand, Markus; Kläui, Mathias; Bhatia, Charanjit S.; Yang, Hyunsoo

    2015-01-01

    The reversal of the magnetization under the influence of a field pulse has been previously predicted to be an incoherent process with several competing phenomena such as domain wall relaxation, spin wave-mediated instability regions, and vortex-core mediated reversal dynamics. However, there has been no study on the direct observation of the switching process with the aid of a microwave signal input. We report a time-resolved imaging study of magnetization reversal in patterned magnetic structures under the influence of a field pulse with microwave assistance. The microwave frequency is varied to demonstrate the effect of resonant microwave-assisted switching. We observe that the switching process is dominated by spin wave dynamics generated as a result of magnetic instabilities in the structures, and identify the frequencies that are most dominant in magnetization reversal. PMID:26023723

  18. An imaging proton spectrometer for short-pulse laser plasma experiments

    SciTech Connect

    Chen, H; Hazi, A; van Maren, R; Chen, S; Fuchs, J; Gauthier, M; Rygg, J R; Shepherd, R

    2010-02-09

    Ultra intense short pulse laser pulses incident on solid targets can generate energetic protons. In additions to their potentially important applications such as in cancer treatments and proton fast ignition, these protons are essential to understand the complex physics of intense laser plasma interaction. To better understand these laser-produced protons, we designed and constructed a novel, spatially imaging proton spectrometer that will not only provide at high-resolution the energy distribution, but also the protons angular characteristics. The information obtained from this spectrometer compliments those from other methods using radiochromic film packs, CR39 films and other protons spectrometers. The basic characterizations and example data from this diagnostics will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, as part of the Cimarron project funded by LDRD-09SI11.

  19. Terahertz Mach-Zehnder interferometer based on a hollow-core metallic ridge waveguide

    NASA Astrophysics Data System (ADS)

    Gerhard, M.; Beigang, R.; Rahm, M.

    2015-04-01

    While terahertz time-domain spectroscopy directly measures amplitude and phase of pulsed terahertz electric fields, the use of more compact terahertz continuous wave sources requires interferometric measurement techniques to obtain phase information. Since constructive and destructive interference are governed by the relative phase of the superimposing fields the phase information can be retrieved from the amplitude modulation signal at the output of the interferometer. Here, we present phase-sensitive measurements of terahertz electric fields in a Mach-Zehnder interferometer that is integrated in a hollow-core metallic ridge waveguide. With lactose in one of the interferometer arms, we measured the modulated amplitude spectrum of the interferometer output signal which carries information about the dielectric properties of the investigated lactose. We explain the measured transmission spectra and the observed dielectric resonances by analytic and numerical means and further confirmed the results by a spectroscopic reference measurement of lactose in a conventional waveguide.

  20. Characterization of terahertz emission from laser-induced air plasma under different pump power

    NASA Astrophysics Data System (ADS)

    Luo, Yi-man; Zhang, Liang-liang; Zhao, Ji; Zhang, Cun-lin

    2013-08-01

    The characterization of the emission of terahertz (THz) waves generated by four-wave mixing in the presence of laser-induced air plasma under different pump power is presented. In our experiment, terahertz is detected using THz Air-Biased Coherent Detection (THz-ABCD) method. Red-shift is observed in frequency spectra with enhanced pump power and the bandwidth is narrowing down. Then the localized terahertz radiation along the plasma was studied, by constricting the emission area with a pinhole. The spatio-frequency dependent of THz emission from laser-induced air plasma is observed. These phenomena are explained by intense self-phase modulation of the optical pulse in the plasma. This study reveals that terahertz spectrum can be controlled by changing the pump power to get useful frequency range.

  1. Terahertz Circular Photonic Crystal Fiber

    Microsoft Academic Search

    Liang Wang; Dongxiao Yang; Yin Chen; Zhineng Li

    2006-01-01

    Terahertz (THz) circular photonic crystal fiber (CPCF) with the similar distribution of air holes as that in variable-size circular photonic crystal in polyethylene material was introduced. Guiding and dispersion properties of the CPCF with different parameters have been accurately computed. Results show that the CPCF is a useful terahertz waveguide which has good ability to confine THz fields, low group-velocity

  2. Introducing the Stratospheric Terahertz Observatory

    E-print Network

    Weinreb, Sander

    Introducing the Stratospheric Terahertz Observatory Glenn Jones Jan. 30, 2008 Microwave Group #12;Stratospheric Terahertz Observatory Long duration balloon flight from Antartica: at 120,000 ft higher spatial and spectral resolution Herschel Space Observatory and SOFIA Broader beam able to map much

  3. A Novel Pulse Measurement System by Using Laser Triangulation and a CMOS Image Sensor

    PubMed Central

    Wu, Jih-Huah; Chang, Rong-Seng; Jiang, Joe-Air

    2007-01-01

    This paper presents a novel, non-invasive, non-contact system to measure pulse waveforms of artery via applying laser triangulation method to detect skin surface vibration. The proposed arterial pulsation measurement (APM) system chiefly consists of a laser diode and a low cost complementary metal-oxide semiconductor (CMOS) image sensor. Laser triangulation and centroid method are combined with the Fast Fourier Transform (FFT) in this study. The shape and frequency of the arterial pulsation can be detected rapidly by using our APM system. The relative variation of the pulse at different measurement points near wrist joint is used as a prognostic guide in traditional Chinese medicine (TCM). An extensive series of experiments was conducted to evaluate the performance of the designed APM system. From experimental results, the pulse amplitude and frequency at the Chun point (related to the small intestine) of left hand showed an obvious increase after having food. In these cases, the peak to peak amplitudes and the frequencies of arterial pulsations range from 38 to 48 ?m and from 1.27 to 1.35 Hz, respectively. The height of arterial pulsations on the area near wrist joint can be estimated with a resolution of better than 4 ?m. This research demonstrates that applying a CMOS image sensor in designing a non-contact, portable, easy-to-use, low cost pulse measurement system is feasible. Also, the designed APM system is well suited for evaluating and pre-diagnosing the health of a human being in TCM clinical practice.

  4. Photosynthesis assessment in microphytobenthos using conventional and imaging pulse amplitude modulation fluorometry.

    PubMed

    Vieira, Sónia; Ribeiro, Lourenço; Jesus, Bruno; Cartaxana, Paulo; da Silva, Jorge Marques

    2013-01-01

    Imaging pulse amplitude modulated (Imaging-PAM) fluorometry is a breakthrough in the study of spatial heterogeneity of photosynthetic assemblages. However, Imaging and conventional PAM uses a different technology, making comparisons between these techniques doubtful. Thereby, photosynthetic processes were comparatively assessed using conventional (Junior PAM and PAM 101) and Imaging-PAM on intertidal microphytobenthos (MPB; mud and sand) and on cork oak leaves. Lower values of ? (initial slope of the rETR, relative photosynthetic electron transport rate) vs E (incident photosynthetic active radiation) curve), ETR(max) (maximum relative ETR), E(k) (light saturation parameter) and F(v)/F(m) (maximum quantum efficiency of photosystem II of dark-adapted samples) were obtained using the Imaging-PAM. The level of discrepancy between conventional and Imaging-PAM systems was dependent on the type of sample, being more pronounced for MPB muddy sediments. This may be explained by differences in the depth integration of the fluorescence signal related to the thickness of the photosynthetic layer and in the light attenuation coefficients of downwelling irradiance. An additional relevant parameter is the taxonomic composition of the MPB, as cyanobacteria present in sandy sediments rendered different results with red and blue excitation light fluorometers. These findings emphasize the caution needed when interpreting chlorophyll fluorescence data of MPB communities. PMID:22891982

  5. Three-dimensional multispectral hand-held optoacoustic imaging with microsecond-level delayed laser pulses

    NASA Astrophysics Data System (ADS)

    Deán-Ben, X. L.; Bay, Erwin; Razansky, Daniel

    2015-03-01

    Three-dimensional hand-held optoacoustic imaging comes with important advantages that prompt the clinical translation of this modality, with applications envisioned in cardiovascular and peripheral vascular disease, disorders of the lymphatic system, breast cancer, arthritis or inflammation. Of particular importance is the multispectral acquisition of data by exciting the tissue at several wavelengths, which enables functional imaging applications. However, multispectral imaging of entire three-dimensional regions is significantly challenged by motion artefacts in concurrent acquisitions at different wavelengths. A method based on acquisition of volumetric datasets having a microsecond-level delay between pulses at different wavelengths is described in this work. This method can avoid image artefacts imposed by a scanning velocity greater than 2 m/s, thus, does not only facilitate imaging influenced by respiratory, cardiac or other intrinsic fast movements in living tissues, but can achieve artifact-free imaging in the presence of more significant motion, e.g., abrupt displacements during handheld-mode operation in a clinical environment.

  6. Potential for detection of explosive and biological hazards with electronic terahertz systems.

    PubMed

    Choi, Min Ki; Bettermann, Alan; van der Weide, D W

    2004-02-15

    The terahertz (THz) regime (0.1-10 THz) is rich with emerging possibilities in sensing, imaging and communications, with unique applications to screening for weapons, explosives and biohazards, imaging of concealed objects, water content and skin. Here we present initial surveys to evaluate the possibility of sensing plastic explosives and bacterial spores using field-deployable electronic THz techniques based on short-pulse generation and coherent detection using nonlinear transmission lines and diode sampling bridges. We also review the barriers and approaches to achieving greater sensing-at-a-distance (stand-off) capabilities for THz sensing systems. We have made several reflection measurements of metallic and non-metallic targets in our laboratory, and have observed high contrast relative to reflection from skin. In particular, we have taken small quantities of energetic materials such as plastic explosives and a variety of Bacillus spores, and measured them in transmission and in reflection using a broadband pulsed electronic THz reflectometer. The pattern of reflection versus frequency gives rise to signatures that are remarkably specific to the composition of the target, even though the target's morphology and position is varied. Although more work needs to be done to reduce the effects of standing waves through time-gating or attenuators, the possibility of mapping out this contrast for imaging and detection is very attractive. PMID:15306524

  7. Cavity enhanced terahertz modulation

    SciTech Connect

    Born, N., E-mail: norman.born@physik.uni-marburg.de [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States); Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany); Scheller, M.; Moloney, J. V. [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States)] [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States); Koch, M. [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany)] [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany)

    2014-03-10

    We present a versatile concept for all optical terahertz (THz) amplitude modulators based on a Fabry-Pérot semiconductor cavity design. Employing the high reflectivity of two parallel meta-surfaces allows for trapping selected THz photons within the cavity and thus only a weak optical modulation of the semiconductor absorbance is required to significantly damp the field within the cavity. The optical switching yields to modulation depths of more than 90% with insertion efficiencies of 80%.

  8. Pulse splitter-based nonlinear microscopy for live-cardiomyocyte imaging

    NASA Astrophysics Data System (ADS)

    Wang, Zhonghai; Qin, Wan; Shao, Yonghong; Ma, Siyu; Borg, Thomas K.; Gao, Bruce Z.

    2014-02-01

    Second harmonic generation (SHG) microscopy is a new imaging technique used in sarcomeric-addition studies. However, during the early stage of cell culture in which sarcomeric additions occur, the neonatal cardiomyocytes that we have been working with are very sensitive to photodamage, the resulting high rate of cell death prevents systematic study of sarcomeric addition using a conventional SHG system. To address this challenge, we introduced use of the pulse-splitter system developed by Na Ji et al. in our two photon excitation fluorescence (TPEF) and SHG hybrid microscope. The system dramatically reduced photodamage to neonatal cardiomyocytes in early stages of culture, greatly increasing cell viability. Thus continuous imaging of live cardiomyocytes was achieved with a stronger laser and for a longer period than has been reported in the literature. The pulse splitter-based TPEF-SHG microscope constructed in this study was demonstrated to be an ideal imaging system for sarcomeric addition-related investigations of neonatal cardiomyocytes in early stages of culture.

  9. Comparison of parabolic filtration methods for 3D filtered back projection in pulsed EPR imaging

    NASA Astrophysics Data System (ADS)

    Qiao, Zhiwei; Redler, Gage; Epel, Boris; Halpern, Howard J.

    2014-11-01

    Pulse electron paramagnetic resonance imaging (Pulse EPRI) is a robust method for noninvasively measuring local oxygen concentrations in vivo. For 3D tomographic EPRI, the most commonly used reconstruction algorithm is filtered back projection (FBP), in which the parabolic filtration process strongly influences image quality. In this work, we designed and compared 7 parabolic filtration methods to reconstruct both simulated and real phantoms. To evaluate these methods, we designed 3 error criteria and 1 spatial resolution criterion. It was determined that the 2 point derivative filtration method and the two-ramp-filter method have unavoidable negative effects resulting in diminished spatial resolution and increased artifacts respectively. For the noiseless phantom the rectangular-window parabolic filtration method and sinc-window parabolic filtration method were found to be optimal, providing high spatial resolution and small errors. In the presence of noise, the 3 point derivative method and Hamming-window parabolic filtration method resulted in the best compromise between low image noise and high spatial resolution. The 3 point derivative method is faster than Hamming-window parabolic filtration method, so we conclude that the 3 point derivative method is optimal for 3D FBP.

  10. Combined multiphoton imaging and automated functional enucleation of porcine oocytes using femtosecond laser pulses.

    PubMed

    Kuetemeyer, Kai; Lucas-Hahn, Andrea; Petersen, Bjoern; Lemme, Erika; Hassel, Petra; Niemann, Heiner; Heisterkamp, Alexander

    2010-01-01

    Since the birth of "Dolly" as the first mammal cloned from a differentiated cell, somatic cell cloning has been successful in several mammalian species, albeit at low success rates. The highly invasive mechanical enucleation step of a cloning protocol requires sophisticated, expensive equipment and considerable micromanipulation skill. We present a novel noninvasive method for combined oocyte imaging and automated functional enucleation using femtosecond (fs) laser pulses. After three-dimensional imaging of Hoechst-labeled porcine oocytes by multiphoton microscopy, our self-developed software automatically identified the metaphase plate. Subsequent irradiation of the metaphase chromosomes with the very same laser at higher pulse energies in the low-density-plasma regime was used for metaphase plate ablation (functional enucleation). We show that fs laser-based functional enucleation of porcine oocytes completely inhibited the parthenogenetic development without affecting the oocyte morphology. In contrast, nonirradiated oocytes were able to develop parthenogenetically to the blastocyst stage without significant differences to controls. Our results indicate that fs laser systems have great potential for oocyte imaging and functional enucleation and may improve the efficiency of somatic cell cloning. PMID:20799808

  11. Combined multiphoton imaging and automated functional enucleation of porcine oocytes using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Kuetemeyer, Kai; Lucas-Hahn, Andrea; Petersen, Bjoern; Lemme, Erika; Hassel, Petra; Niemann, Heiner; Heisterkamp, Alexander

    2010-07-01

    Since the birth of ``Dolly'' as the first mammal cloned from a differentiated cell, somatic cell cloning has been successful in several mammalian species, albeit at low success rates. The highly invasive mechanical enucleation step of a cloning protocol requires sophisticated, expensive equipment and considerable micromanipulation skill. We present a novel noninvasive method for combined oocyte imaging and automated functional enucleation using femtosecond (fs) laser pulses. After three-dimensional imaging of Hoechst-labeled porcine oocytes by multiphoton microscopy, our self-developed software automatically identified the metaphase plate. Subsequent irradiation of the metaphase chromosomes with the very same laser at higher pulse energies in the low-density-plasma regime was used for metaphase plate ablation (functional enucleation). We show that fs laser-based functional enucleation of porcine oocytes completely inhibited the parthenogenetic development without affecting the oocyte morphology. In contrast, nonirradiated oocytes were able to develop parthenogenetically to the blastocyst stage without significant differences to controls. Our results indicate that fs laser systems have great potential for oocyte imaging and functional enucleation and may improve the efficiency of somatic cell cloning.

  12. Multi-component pulsed-laser shearography using optical fiber imaging-bundles

    NASA Astrophysics Data System (ADS)

    Groves, Roger M.; James, Stephen W.; Tatam, Ralph P.

    2003-11-01

    Shearography is a full-field non-contact optical technique usually used for the identification of the location of defects in non-destructive testing. Shearography is sensitive to displacement gradient, a parameter closely related to the surface strain. To fully characterise the surface strain requires the determination of six orthogonal components of displacement gradient and this is achieved in shearography by measuring from three, or more, illumination, or viewing, directions and from a minimum of two directions of applied shear, followed by a coodinate transformation to the orthogonal components. In this paper the authors use illumination from a single direction using dual pulsed injection-seeded Nd:YAG lasers, and view the object from four directions. The images from the four viewing directions are ported to a single interferometer head using a four-leg optical fiber imaging bundle. At the interferometer head the four views are spatially-multiplexed into a single image, pass through the interferometer head and are recorded by a single high resolution dual-framing camera. The direction of applied shear in the interferometer head is adjustable to allow measurements from the two shear directions. Experimental results are presented of displacement gradient from this pulsed laser shearography instrument.

  13. Comparison of Parabolic Filtration Methods for 3D Filtered Back Projection in Pulsed EPR Imaging

    PubMed Central

    Qiao, Zhiwei; Redler, Gage; Epel, Boris; Halpern, Howard J

    2015-01-01

    Pulse electron paramagnetic resonance imaging (Pulse EPRI) is a robust method for noninvasively measuring local oxygen concentrations in vivo. For 3D tomographic EPRI, the most commonly used reconstruction algorithm is filtered back projection (FBP), in which the parabolic filtration process strongly influences image quality. In this work, we designed and compared 7 parabolic filtration methods to reconstruct both simulated and real phantoms. To evaluate these methods, we designed 3 error criteria and 1 spatial resolution criterion. It was determined that the 2 point derivative filtration method and the two-ramp-filter method have unavoidable negative effects resulting in diminished spatial resolution and increased artifacts respectively. For the noiseless phantom the rectangular-window parabolic filtration method and sinc-window parabolic filtration method were found to be optimal, providing high spatial resolution and small errors. In the presence of noise, the 3 point derivative method and Hamming-window parabolic filtration method resulted in the best compromise between low image noise and high spatial resolution. The 3 point derivative method is faster than Hamming-window parabolic filtration method, so we conclude that the 3 point derivative method is optimal for 3D FBP. PMID:25314081

  14. Usefulness of Pulsed Arterial Spin Labeling MR Imaging in Mesial Temporal Lobe Epilepsy

    PubMed Central

    Lim, Young-Min; Cho, Yong-Won; Shamim, Sadat; Solomon, Jeffrey; Birn, Rasmus; Luh, Wen Ming; Gaillard, William D.; Ritzl, Eva K.; Theodore, William H.

    2008-01-01

    Summary Purpose Arterial spin labeling (ASL) is a developing magnetic resonance imaging (MRI) method for noninvasive measurement of cerebral blood flow (CBF). The purpose of this study was to evaluate the usefulness of ASL for detecting interictal temporal hypoperfusion in temporal lobe epilepsy (TLE). ASL-derived CBF measurements were compared with those derived from H215O positron emission tomography (PET). Methods 11 normal controls and 10 patients with medically intractable TLE were studied. Pulsed ASL (PASL) with quantitative imaging of perfusion using a single subtraction, second version (QUIPSS II) was performed in all subjects and H215O PET was performed in patients. Regional CBF values in the mesial and lateral temporal lobes were measured utilizing quantitative analysis of perfusion images. A perfusion asymmetry index (AI) was calculated for each region. Results In patients, mean CBF in the mesial temporal lobe was not significantly different between PASL and H215O PET, and ipsilateral mesial temporal CBF was lower than contralateral CBF with both techniques. PASL detected significant mesial temporal perfusion asymmetry agreeing with EEG laterality in four patients. H215O PET found ipsilateral interictal hypoperfusion in three. Both scans found unilateral hypoperfusion in one patient with bilateral EEG discharges. Conclusions Pulsed ASL may be a promising approach to detecting interictal hypoperfusion in TLE. This method has potential as a clinical alternative to H215O PET due to noninvasiveness and easy accessibility. PMID:19041041

  15. Pulse splitter-based nonlinear microscopy for live-cardiomyocyte imaging

    PubMed Central

    Wang, Zhonghai; Qin, Wan; Shao, Yonghong; Ma, Siyu; Borg, Thomas K.; Gao, Bruce Z.

    2015-01-01

    Second harmonic generation (SHG) microscopy is a new imaging technique used in sarcomeric-addition studies. However, during the early stage of cell culture in which sarcomeric additions occur, the neonatal cardiomyocytes that we have been working with are very sensitive to photodamage, the resulting high rate of cell death prevents systematic study of sarcomeric addition using a conventional SHG system. To address this challenge, we introduced use of the pulse-splitter system developed by Na Ji et al. in our two photon excitation fluorescence (TPEF) and SHG hybrid microscope. The system dramatically reduced photodamage to neonatal cardiomyocytes in early stages of culture, greatly increasing cell viability. Thus continuous imaging of live cardiomyocytes was achieved with a stronger laser and for a longer period than has been reported in the literature. The pulse splitter-based TPEF-SHG microscope constructed in this study was demonstrated to be an ideal imaging system for sarcomeric addition-related investigations of neonatal cardiomyocytes in early stages of culture. PMID:25767692

  16. Directional terahertz emission from corrugated InAs structures

    NASA Astrophysics Data System (ADS)

    Yim, Jong-Hyuk; Jeong, Hoonil; Irfan, Muhammad; Lee, Eun-Hye; Song, Jin-Dong; Jho, Young-Dahl

    2013-08-01

    We have designed and fabricated a new type of terahertz (THz) emitter that radiates THz waves along the surface-normal direction because of the lateral distributions of the transient electric dipoles. The excitation and measurements were performed using a conventional THz time-domain spectroscopy scheme with femtosecond optical pulses. The corrugated mirror patterns on the InAs layers made the radiation directional along the surface-normal direction, and the emission efficiency was controlled by adjustment of the pattern width.

  17. Coherent Terahertz Control of Vertical Transport in Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Vänskä, O.; Tittonen, I.; Koch, S. W.; Kira, M.

    2015-03-01

    Coherent-control protocols are introduced to selectively transport electrons, excitons, or pure two-particle correlations through semiconductor interfaces. The scheme is tested in a double-quantum-well structure where a sequence of terahertz pulses is applied to induce the vertical excitation transfer between the wells. Using a microscopic theory, it is shown that efficient and highly selective transfer can be realized even in the presence of the unavoidable scattering and dephasing processes.

  18. Terahertz Cherenkov radiation from ultrafast magnetization in terbium gallium garnet

    NASA Astrophysics Data System (ADS)

    Gorelov, S. D.; Mashkovich, E. A.; Tsarev, M. V.; Bakunov, M. I.

    2013-12-01

    We report an experimental observation of terahertz Cherenkov radiation from a moving magnetic moment produced in terbium gallium garnet by a circularly polarized femtosecond laser pulse via the inverse Faraday effect. Contrary to some existing theoretical predictions, the polarity of the observed radiation unambiguously demonstrates the paramagnetic, rather than diamagnetic, nature of the ultrafast inverse Faraday effect. From measurements of the radiation field, the Verdet constant in the subpicosecond regime is ˜3-10 times smaller than its table quasistatic value.

  19. Ultrafast Coherent Terahertz Spectroscopy in High Magnetic Fields

    Microsoft Academic Search

    S. A. Crooker; A. J. Taylor

    2002-01-01

    With an aim towards measuring the high-frequency complex conductivity of correlated electron materials in the regime of low temperatures and high magnetic fields, we introduce a method for performing time-domain terahertz spectroscopy directly in the cryogenic bore of existing dc and pulsed-field magnets. Miniature, fiber-coupled THz emitters and receivers are constructed and are demonstrated to work down to 5 K

  20. Terahertz plasmonic composites.

    PubMed

    Nemat-Nasser, Syrus C; Amirkhizi, Alireza V; Padilla, Willie J; Basov, Dimitri N; Nemat-Nasser, Sia; Bruzewicz, Derek; Whitesides, George

    2007-03-01

    The dielectric response of a polymer matrix composite can be substantially modified and tuned within a broad frequency band by integrating within the material an artificial plasmon medium composed of periodically distributed, very thin, electrically conducting wires. In the microwave regime, such plasmon/polymer composites have been studied analytically, computationally, and experimentally. This work reports the design, fabrication, and characterization of similar composites for operation at terahertz frequencies. Such composites require significant reduction in the thickness and spacing of the wires. We used numerical modeling to design artificial effective plasmonic media with turn-on frequencies in the terahertz range. Prototype samples were produced by lithographically embedding very thin gold strips into a PDMS [poly(dimethylsiloxane)] matrix. These samples were characterized with a Fourier-transform infrared interferometer using the frequency-dependent transmission and Kramers-Kronig relations to determine the electromagnetic properties. We report the characterization results for a sample, demonstrating excellent agreement between theory, computer design, and experiment. To our knowledge this is the first demonstration of the possibility of creating composites with tuned dielectric response at terahertz frequencies. PMID:17500816