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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 pulsed imaging study of dental caries

    NASA Astrophysics Data System (ADS)

    Karagoz, Burcu; Altan, Hakan; Kamburoglu, Kıvanç

    2015-07-01

    Current diagnostic techniques in dentistry rely predominantly on X-rays to monitor dental caries. Terahertz Pulsed Imaging (TPI) has great potential for medical applications since it is a nondestructive imaging method. It does not cause any ionization hazard on biological samples due to low energy of THz radiation. Even though it is strongly absorbed by water which exhibits very unique chemical and physical properties that contribute to strong interaction with THz radiation, teeth can still be investigated in three dimensions. Recent investigations suggest that this method can be used in the early identification of dental diseases and imperfections in the tooth structure without the hazards of using techniques which rely on x-rays. We constructed a continuous wave (CW) and time-domain reflection mode raster scan THz imaging system that enables us to investigate various teeth samples in two or three dimensions. The samples comprised of either slices of individual tooth samples or rows of teeth embedded in wax, and the imaging was done by scanning the sample across the focus of the THz beam. 2D images were generated by acquiring the intensity of the THz radiation at each pixel, while 3D images were generated by collecting the amplitude of the reflected signal at each pixel. After analyzing the measurements in both the spatial and frequency domains, the results suggest that the THz pulse is sensitive to variations in the structure of the samples that suggest that this method can be useful in detecting the presence of caries.

  3. Visualization and classification in biomedical terahertz pulsed imaging

    NASA Astrophysics Data System (ADS)

    Löffler, Torsten; Siebert, Karsten; Czasch, Stephanie; Bauer, Tobias; Roskos, Hartmut G.

    2002-11-01

    'Visualization' in imaging is the process of extracting useful information from raw data in such a way that meaningful physical contrasts are developed. 'Classification' is the subsequent process of defining parameter ranges which allow us to identify elements of images such as different tissues or different objects. In this paper, we explore techniques for visualization and classification in terahertz pulsed imaging (TPI) for biomedical applications. For archived (formalin-fixed, alcohol-dehydrated and paraffin-mounted) test samples, we investigate both time- and frequency-domain methods based on bright- and dark-field TPI. Successful tissue classification is demonstrated.

  4. Visualization and classification in biomedical terahertz pulsed imaging.

    PubMed

    Lffler, Torsten; Siebert, Karsten; Czasch, Stephanie; Bauer, Tobias; Roskos, Hartmut G

    2002-11-01

    'Visualization' in imaging is the process of extracting useful information from raw data in such a way that meaningful physical contrasts are developed. 'Classification' is the subsequent process of defining parameter ranges which allow us to identify elements of images such as different tissues or different objects. In this paper, we explore techniques for visualization and classification in terahertz pulsed imaging (TPI) for biomedical applications. For archived (formalin-fixed, alcohol-dehydrated and paraffin-mounted) test samples, we investigate both time- and frequency-domain methods based on bright- and dark-field TPI. Successful tissue classification is demonstrated. PMID:12452576

  5. Pulsed Coherent Teragraphy: Imaging in the Terahertz Frequency Range

    NASA Astrophysics Data System (ADS)

    Bespalov, V. G.

    2016-02-01

    Principles of recording the amplitudes and phases of wave fields in the terahertz (THz) frequency range are considered and methodology and schemes used for imaging in this range are analyzed. Generation of THz radiation by femtosecond optical pulses and registration of THz electric field waveforms allow the methods for holographic recording and image restoration to be developed. Results of the experiments on reconstruction of phase characteristics of THz field by the suggested holographic method are demonstrated and the influence of the experimental parameters on the quality of image restoration in time-resolved THz holography is analyzed.

  6. 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

  7. Pulsed terahertz spectroscopy and imaging applied to inspection of explosives and inflammable liquids

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kohji; Yamaguchi, Mariko; Miyamaru, Fumiaki; Tani, Masahiko; Hangyo, Masanori; Ikeda, Takeshi; Matsushita, Akira; Koide, Kenji; Tatsuno, Michiaki; Manami, Yukio

    We carried out applied researches on the pulsed terahertz spectroscopy and the terahertz imaging to detect the C-4 explosive hidden in a mail and inflammable liquids stored in plastic bottles. We confirm that THz techniques are quite efficient at contactless and nondestructive inspection of hazardous materials used in terrorist activities.

  8. Terahertz wave reciprocal imaging

    NASA Astrophysics Data System (ADS)

    Xu, Jingzhou; Zhang, X.-C.

    2006-04-01

    A reciprocal imaging technology with an encoding/decoding image readout method allows a single detector (such as a heterodyne detector) to produce a two dimensional (2D) image simultaneously. Applying it in a pulsed terahertz imaging system could create a 2D terahertz image with 100pixels per frame which produces the same signal to noise ratio as a signal spot measurement.

  9. Non-invasive detection of murals with pulsed terahertz reflected imaging system

    NASA Astrophysics Data System (ADS)

    Yuan, Minjie; Sun, Wenfeng; Wang, Xinke; Ye, Jiasheng; Wang, Sen; Zhang, Qunxi; Zhang, Yan

    2015-11-01

    Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of "Y-type" metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals.

  10. 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.

  11. Terahertz pulsed imaging and magnetic resonance imaging as tools to probe formulation stability.

    PubMed

    Zhang, Qilei; Gladden, Lynn F; Avalle, Paolo; Zeitler, J Axel; Mantle, Michael D

    2013-01-01

    Dissolution stability over the entire shelf life duration is of critical importance to ensure the quality of solid dosage forms. Changes in the drug release profile during storage may affect the bioavailability of drug products. This study investigated the stability of a commercial tablet (Lescolr XL) when stored under accelerated conditions (40 oC/75% r.h.). Terahertz pulsed imaging (TPI) was used to investigate the structure of the tablet coating before and after the accelerated aging process. The results indicate that the coating was reduced in thickness and exhibited a higher density after being stored under accelerated conditions for four weeks. In situ magnetic resonance imaging (MRI) of the water penetration processes during tablet dissolution in a USP-IV dissolution cell equipped with an in-line UV-vis analyzer was carried out to study local differences in water uptake into the tablet matrix between the stressed and unstressed state. The drug release profiles of the Lescolr XL tablet before and after the accelerated storage stability testing were compared using a "difference" factor ?1 and a "similarity" factor ?2. The results reveal that even though the physical properties of the coating layers changed significantly during the stress testing, the coating protected the tablet matrix and the densification of the coating polymer had no adverse effect on the drug release performance. PMID:24300564

  12. Terahertz Pulsed Imaging and Magnetic Resonance Imaging as Tools to Probe Formulation Stability

    PubMed Central

    Zhang, Qilei; Gladden, Lynn F.; Avalle, Paolo; Zeitler, J. Axel; Mantle, Michael D.

    2013-01-01

    Dissolution stability over the entire shelf life duration is of critical importance to ensure the quality of solid dosage forms. Changes in the drug release profile during storage may affect the bioavailability of drug products. This study investigated the stability of a commercial tablet (Lescol® XL) when stored under accelerated conditions (40 °C/75% r.h.). Terahertz pulsed imaging (TPI) was used to investigate the structure of the tablet coating before and after the accelerated aging process. The results indicate that the coating was reduced in thickness and exhibited a higher density after being stored under accelerated conditions for four weeks. In situ magnetic resonance imaging (MRI) of the water penetration processes during tablet dissolution in a USP-IV dissolution cell equipped with an in-line UV-vis analyzer was carried out to study local differences in water uptake into the tablet matrix between the stressed and unstressed state. The drug release profiles of the Lescol® XL tablet before and after the accelerated storage stability testing were compared using a “difference” factor f1 and a “similarity” factor f2. The results reveal that even though the physical properties of the coating layers changed significantly during the stress testing, the coating protected the tablet matrix and the densification of the coating polymer had no adverse effect on the drug release performance. PMID:24300564

  13. Characterisation of historic plastics using terahertz time-domain spectroscopy and pulsed imaging.

    PubMed

    Pastorelli, Gianluca; Trafela, Tanja; Taday, Phillip F; Portieri, Alessia; Lowe, David; Fukunaga, Kaori; Strlič, Matija

    2012-05-01

    Terahertz (THz) time-domain spectroscopy and 3D THz pulsed imaging have been explored with regard to polymer materials, both commodity and historic polymers. A systematic spectroscopic study of a wide range of different polymer materials showed significant differences in their spectra. Polyolefins and polystyrenes generally exhibit lower absorption than other examined polymers, various cellulose derivates, poly(vinyl chloride), poly(methyl methacrylate), polyamide, hard rubber and phenol formaldehyde resin, the last of these exhibiting the most intense absorption over the entire range, 0.15-4.2 THz. It was also examined how the presence of plasticisers in poly(vinyl chloride), the presence of fillers in polypropylene, and the degree of branching in polyethylene and polystyrene affect the spectra; inorganic fillers in polypropylene affected the absorption most. With 3D THz pulsed imaging, features in polymer objects were explored, appearing either as integral parts of the material (coatings and pores in foams) or as a consequence of physical deterioration (cracks, delamination). All of these features of various complexities can be successfully imaged in 3D. Terahertz technology is thus shown to have significant potential for both chemical and structural characterisation of polymers, which will be of interest to heritage science, but also to the polymer industry and development of analytical technologies in general. PMID:22447218

  14. 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

  15. Non-destructive quantification of pharmaceutical tablet coatings using terahertz pulsed imaging and optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Zhong, Shuncong; Shen, Yao-Chun; Ho, Louise; May, Robert K.; Zeitler, J. Axel; Evans, Mike; Taday, Philip F.; Pepper, Michael; Rades, Thomas; Gordon, Keith C.; Müller, Ronny; Kleinebudde, Peter

    2011-03-01

    Optical coherence tomography (OCT) and terahertz pulsed imaging (TPI) are two powerful techniques allowing high quality cross-sectional images from within scattering media to be obtained non-destructively. In this paper, we report experimental results of using OCT and TPI for quantitatively characterizing pharmaceutical tablet coatings in the thickness range of 10-140 μm. We found that the spectral OCT system developed in-house has an axial resolution of 0.9 μm, and is capable of quantifying very thin coatings in the range of 10-60 μm. The upper limit of 60 μm within the tablet coating and core is owed to the strong scattering of OCT light, which has relatively short wavelengths in the range of 0.5-1.0 μm. On the other hand, TPI utilizes terahertz radiation that has substantially long wavelengths in the range of hundreds of microns, and thus is less prone to the scattering problem. Consequently TPI has been demonstrated to be able to quantify thicker coatings in the range of 40-140 μm and beyond. We concluded that OCT and TPI are two complementary analytical techniques for non-destructive and quantitative characterization of pharmaceutical tablet coatings.

  16. Terahertz pulse imaging of stratified architectural materials for cultural heritage studies

    NASA Astrophysics Data System (ADS)

    Jackson, J. Bianca; Labaune, Julien; Mourou, Gérard; Duling, Irl N.; Walker, Gillian; Bowen, John; Menu, Michel

    2011-06-01

    Terahertz pulse imaging (TPI) is a novel noncontact, nondestructive technique for the examination of cultural heritage artifacts. It has the advantage of broadband spectral range, time-of-flight depth resolution, and penetration through optically opaque materials. Fiber-coupled, portable, time-domain terahertz systems have enabled this technique to move out of the laboratory and into the field. Much like the rings of a tree, stratified architectural materials give the chronology of their environmental and aesthetic history. This work concentrates on laboratory models of stratified mosaics and fresco paintings, specimens extracted from a neolithic excavation site in Catalhoyuk, Turkey, and specimens measured at the medieval Eglise de Saint Jean-Baptiste in Vif, France. Preparatory spectroscopic studies of various composite materials, including lime, gypsum and clay plasters are presented to enhance the interpretation of results and with the intent to aid future computer simulations of the TPI of stratified architectural material. The breadth of the sample range is a demonstration of the cultural demand and public interest in the life history of buildings. The results are an illustration of the potential role of TPI in providing both a chronological history of buildings and in the visualization of obscured wall paintings and mosaics.

  17. 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

  18. Potential uses of terahertz pulse imaging in dentistry: caries and erosion detection

    NASA Astrophysics Data System (ADS)

    Longbottom, Christopher; Crawley, David A.; Cole, Bryan E.; Arnone, Donald D.; Wallace, Vincent P.; Pepper, Michael

    2002-06-01

    TeraHertz Pulse Imaging (TPI) is a relatively new imaging modality for medical and dental imaging. The aim of the present study was to make a preliminary assessment of the potential uses of TPI in clinical dentistry, particularly in relation to caries detection and the detection and monitoring of erosion. Images were obtained in vitro using a new TPI system developed by TeraView Ltd. We present data showing that TPI in vitro images of approximal surfaces of whole teeth demonstrate a distinctive shadowing in the presence of natural carious lesions in enamel. The thickness of this enamel shadowing appears to be related to lesion depth. The use of non-ionizing radiation to image such lesions non-destructively in vitro represents a significant step towards such measurements in vivo. In addition, data is presented which indicates that TPI may have a potential role in the detection and monitoring of enamel erosion. In vitro experiments on whole incisor teeth show that TPI is capable of detecting relatively small artificially induced changes in the buccal or palatal surface of the enamel of these teeth. Imaging of enamel thickness at such a resolution without ionizing radiation would represent a significant breakthrough if applicable in vivo.

  19. Density mapping and chemical component calibration development of four-component compacts via terahertz pulsed imaging.

    PubMed

    Palermo, Ryanne; Cogdill, Robert P; Short, Steven M; Drennen, James K; Taday, Philip F

    2008-01-01

    The purpose of this research was to investigate suitable procedures for generating multivariate prediction vectors for quantitative composition and density analysis of intact solid oral dosage forms using terahertz pulsed imaging (TPI) spectroscopy. Both frequency- (absorbance and refractive index) and time-domain data are presented. A set of calibration and prediction samples were created according to a quaternary mixture design with five levels of compaction at each concentration design point. Calibration models were generated by partial least-squares, type II (PLS-2) regression of the TPI spectra against nominal composition and relative density reference measurements. Quantitative frequency-domain composition calibration models were created for all crystalline components (R(2)>0.90), but the calibration models for individual amorphous components (R(2)<0.76) did not perform as well in testing. Combining both amorphous components into a single component variable for regression resulted in lower error statistics and equally good predictions of crystalline components. A non-linear attenuation of time-domain spectra was observed as a function of compaction force, which corresponded to compact density predictions (R(2)=0.948). While refractive index spectra were sensitive to density (R(2)=0.937), the absorbance spectra were not. Surface density maps were prepared based on refractive index calibrations. PMID:18053671

  20. Quantifying Pharmaceutical Film Coating with Optical Coherence Tomography and Terahertz Pulsed Imaging: An Evaluation.

    PubMed

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

    2015-10-01

    Spectral domain optical coherence tomography (OCT) has recently attracted a lot of interest in the pharmaceutical industry as a fast and non-destructive modality for quantification of thin film coatings that cannot easily be resolved with other techniques. Because of the relative infancy of this technique, much of the research to date has focused on developing the in-line measurement technique for assessing film coating thickness. To better assess OCT for pharmaceutical coating quantification, this paper evaluates tablets with a range of film coating thickness measured using OCT and terahertz pulsed imaging (TPI) in an off-line setting. In order to facilitate automated coating quantification for film coating thickness in the range of 30-200 μm, an algorithm that uses wavelet denoising and a tailored peak finding method is proposed to analyse each of the acquired A-scan. Results obtained from running the algorithm reveal an increasing disparity between the TPI and OCT measured intra-tablet variability when film coating thickness exceeds 100 μm. The finding further confirms that OCT is a suitable modality for characterising pharmaceutical dosage forms with thin film coatings, whereas TPI is well suited for thick coatings. PMID:26284354

  1. Quantifying Pharmaceutical Film Coating with Optical Coherence Tomography and Terahertz Pulsed Imaging: An Evaluation

    PubMed Central

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

    2015-01-01

    Spectral domain optical coherence tomography (OCT) has recently attracted a lot of interest in the pharmaceutical industry as a fast and non-destructive modality for quantification of thin film coatings that cannot easily be resolved with other techniques. Because of the relative infancy of this technique, much of the research to date has focused on developing the in-line measurement technique for assessing film coating thickness. To better assess OCT for pharmaceutical coating quantification, this paper evaluates tablets with a range of film coating thickness measured using OCT and terahertz pulsed imaging (TPI) in an off-line setting. In order to facilitate automated coating quantification for film coating thickness in the range of 30–200 μm, an algorithm that uses wavelet denoising and a tailored peak finding method is proposed to analyse each of the acquired A-scan. Results obtained from running the algorithm reveal an increasing disparity between the TPI and OCT measured intra-tablet variability when film coating thickness exceeds 100 μm. The finding further confirms that OCT is a suitable modality for characterising pharmaceutical dosage forms with thin film coatings, whereas TPI is well suited for thick coatings. © 2015 The Authors. Journal of Pharmaceutical Sciences published by Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:3377–3385, 2015 PMID:26284354

  2. Diffusion and swelling measurements in pharmaceutical powder compacts using terahertz pulsed imaging.

    PubMed

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

    2015-05-01

    Tablet dissolution is strongly affected by swelling and solvent penetration into its matrix. A terahertz-pulsed imaging (TPI) technique, in reflection mode, is introduced as a new tool to measure one-dimensional swelling and solvent ingress in flat-faced pharmaceutical compacts exposed to dissolution medium from one face of the tablet. The technique was demonstrated on three tableting excipients: hydroxypropylmethyl cellulose (HPMC), Eudragit RSPO, and lactose. Upon contact with water, HPMC initially shrinks to up to 13% of its original thickness before undergoing expansion. HPMC and lactose were shown to expand to up to 20% and 47% of their original size in 24 h and 13 min, respectively, whereas Eudragit does not undergo dimensional change. The TPI technique was used to measure the ingress of water into HPMC tablets over a period of 24 h and it was observed that water penetrates into the tablet by anomalous diffusion. X-ray microtomography was used to measure tablet porosity alongside helium pycnometry and was linked to the results obtained by TPI. Our results highlight a new application area of TPI in the pharmaceutical sciences that could be of interest in the development and quality testing of advanced drug delivery systems as well as immediate release formulations. PMID:25645509

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

    PubMed Central

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

    2015-01-01

    Tablet dissolution is strongly affected by swelling and solvent penetration into its matrix. A terahertz-pulsed imaging (TPI) technique, in reflection mode, is introduced as a new tool to measure one-dimensional swelling and solvent ingress in flat-faced pharmaceutical compacts exposed to dissolution medium from one face of the tablet. The technique was demonstrated on three tableting excipients: hydroxypropylmethyl cellulose (HPMC), Eudragit RSPO, and lactose. Upon contact with water, HPMC initially shrinks to up to 13% of its original thickness before undergoing expansion. HPMC and lactose were shown to expand to up to 20% and 47% of their original size in 24 h and 13 min, respectively, whereas Eudragit does not undergo dimensional change. The TPI technique was used to measure the ingress of water into HPMC tablets over a period of 24 h and it was observed that water penetrates into the tablet by anomalous diffusion. X-ray microtomography was used to measure tablet porosity alongside helium pycnometry and was linked to the results obtained by TPI. Our results highlight a new application area of TPI in the pharmaceutical sciences that could be of interest in the development and quality testing of advanced drug delivery systems as well as immediate release formulations. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:1658–1667, 2015 PMID:25645509

  4. 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.

  5. 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

  6. Terahertz imaging for non-destructive evaluation of mural paintings

    NASA Astrophysics Data System (ADS)

    Jackson, J. B.; Mourou, M.; Whitaker, J. F.; Duling, I. N.; Williamson, S. L.; Menu, M.; Mourou, G. A.

    2008-02-01

    The feasibility of applying time-domain, terahertz spectroscopic imaging to the evaluation of underdrawings and paint layers embedded within wall paintings is demonstrated. Metallic and dielectric paint patterns and a graphite drawing are resolved through both paint and plaster overlayers using a pulsed-terahertz reflectometer and imaging system. We calculated the bulk refractive indices of four common pigments and used them to confirm color domains in a terahertz-beam spectral image of a painting.

  7. 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.

  8. 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.

  9. Determination of Water Content in Dehydrated Mammalian Cells Using Terahertz Pulsed Imaging: A Feasibility Study.

    PubMed

    Chau, David Y S; Dennis, Anthony R; Lin, Hungyen; Zeitler, J Axel; Tunnacliffe, Alan

    2015-01-01

    Mammalian cells are involved in a range of biotechnological applications and more recently have been increasingly exploited in regenerative medicine. Critical to successful applications involving mammalian cells are their long-term storage and transport, for which cryopreservation in liquid nitrogen is the most frequently used strategy. However, cryopreservation suffers from high costs, difficulties in transport logistics and the use of undesirable additives (e.g. animal sera or DMSO). An alternative approach, proposed as low cost, low maintenance and process-compatible, is viable desiccation of mammalian cells. Several groups claim to have achieved this, but the extent of desiccation in the cell samples concerned is not always clear, in part because of difficulties in determining very low water content. Although several techniques exist that are frequently used to quantify the amount of water in samples (e.g. FTIR spectroscopy, thermogravimetric analysis (TGA), NMR spectroscopy), the complexity of sample preparation, as well as the costs and time constraints involved are disadvantageous. Here, we assess a novel, rapid and low cost technique, i.e. terahertz (THz) spectroscopy, for the quantification of water content within dehydrated mammalian cell samples. PMID:26511980

  10. Optimal chirped probe pulse length for terahertz pulse measurement.

    PubMed

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

    2008-08-01

    A detailed analysis of the relationship between the duration of the chirped probe pulse and the bipolar terahertz (THz) pulse length in the spectral encoding technique is carried out. We prove that there is an optimal chirped probe pulse length (or an optimal chirp rate of the chirped probe pulse) matched to the input THz pulse length and derive a rigorous relationship between them. We find that only under this restricted condition the THz signal can be correctly retrieved. PMID:18679511

  11. Industrial Applications of Terahertz Imaging

    NASA Astrophysics Data System (ADS)

    Zeitler, J. Axel; Shen, Yao-Chun

    This chapter gives a concise overview of potential industrial applications for terahertz imaging that have been reported over the past decade with a discussion of the major advantages and limitations of each approach. In the second half of the chapter we discuss in more detail how terahertz imaging can be used to investigate the microstructure of pharmaceutical dosage forms. A particular focus in this context is the nondestructive measurement of the coating thickness of polymer coated tablets, both by means of high resolution offline imaging in research and development as well as for in-line quality control during production.

  12. Scanning Terahertz Heterodyne Imaging Systems

    NASA Technical Reports Server (NTRS)

    Siegel, Peter; Dengler, Robert

    2007-01-01

    Scanning terahertz heterodyne imaging systems are now at an early stage of development. In a basic scanning terahertz heterodyne imaging system, (see Figure 1) two far-infrared lasers generate beams denoted the local-oscillator (LO) and signal that differ in frequency by an amount, denoted the intermediate frequency (IF), chosen to suit the application. The LO beam is sent directly to a mixer as one of two inputs. The signal beam is focused to a spot on or in the specimen. After transmission through or reflection from the specimen, the beams are focused to a spot on a terahertz mixer, which extracts the IF outputs. The specimen is mounted on a translation stage, by means of which the focal spot is scanned across the specimen to build up an image.

  13. Terahertz interferometric imaging of RDX

    NASA Astrophysics Data System (ADS)

    Sinyukov, Alexander M.; Barat, Robert B.; Gary, Dale E.; Michalopoulou, Zoi-Heleni; Zorych, Ivan; Zimdars, David; Federici, John F.

    2007-04-01

    Experimental results of homodyne terahertz interferometric 2-D imaging of RDX are presented. Continuous waves at 0.25-0.6 THz are used to obtain images of a C-4 sample at several THz frequencies. The performance of an N element detector array is imitated by only one detector placed at N positions. The distance between the C-4 sample and the detector array is ~30 cm. By taking interferometric images at several THz frequencies RDX can be recognized by the spectral peak at 0.82 THz. Simulations of interferometric images of two point sources of spherical waves are presented. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

  14. Imaging with a Terahertz quantum cascade laser

    NASA Astrophysics Data System (ADS)

    Darmo, Juraj; Tamosiunas, Vincas; Fasching, Gernot; Kröll, Josef; Unterrainer, Karl; Beck, Mattias; Giovannini, Marcella; Faist, Jerome; Kremser, Christian; Debbage, Paul

    2004-05-01

    We demonstrate bio-medical imaging using a Terahertz quantum cascade laser. This new optoelectronic source of coherent Terahertz radiation allows building a compact imaging system with a large dynamic range and high spatial resolution. We obtain images of a rat brain section at 3.4 THz. Distinct regions of brain tissue rich in fat, proteins, and fluid-filled cavities are resolved showing the high contrast of Terahertz radiation for biological tissue. These results suggest that continuous-wave Terahertz imaging with a carefully chosen wavelength can provide valuable data on samples of biological origin; these data appear complementary to those obtained from white-light images.

  15. Terahertz pulsed spectroscopy of paraffin-embedded brain glioma.

    PubMed

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

    2014-01-01

    The refractive indices, absorption coefficients, and complex dielectric constants of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time-domain spectroscopy (THz-TDS) system in the 0.2- to 2.0-THz range. The spectral differences between gliomas and normal brain tissues were obtained. Compared with normal brain tissue, our results indicate that paraffin-embedded brain gliomas have a higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the best THz frequencies for different methods of paraffin-embedded brain glioma imaging, such as intensity imaging, coherent imaging with continuum THz sources, and THz pulsed imaging with short-pulsed THz sources, are analyzed. PMID:25003757

  16. Terahertz pulsed spectroscopy of paraffin-embedded brain glioma

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    The refractive indices, absorption coefficients, and complex dielectric constants of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time-domain spectroscopy (THz-TDS) system in the 0.2- to 2.0-THz range. The spectral differences between gliomas and normal brain tissues were obtained. Compared with normal brain tissue, our results indicate that paraffin-embedded brain gliomas have a higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the best THz frequencies for different methods of paraffin-embedded brain glioma imaging, such as intensity imaging, coherent imaging with continuum THz sources, and THz pulsed imaging with short-pulsed THz sources, are analyzed.

  17. Terahertz metrology on power, frequency, spectroscopy, and pulse parameters

    NASA Astrophysics Data System (ADS)

    Wu, Bin; Ying, Cheng Ping; Wang, Heng Fei; Zhang, Peng; Liu, Hong Yuan; Jiang, Bin

    2015-11-01

    Terahertz metrology is becoming more and more important along with the fast development of terahertz technology. This paper reviews the research works of the groups from the physikalisch-technische bundesanstalt (PTB), National institute of standards and technology (NIST), National physical laboratory (NPL), National institute of metrology (NIM) and some other research institutes. The contents mainly focus on the metrology of parameters of power, frequency, spectrum and pulse. At the end of the paper, the prospect of terahertz metrology is predicted.

  18. Terahertz generation in plasmas using two-color laser pulses.

    PubMed

    Peñano, Joseph; Sprangle, Phillip; Hafizi, Bahman; Gordon, Daniel; Serafim, Philip

    2010-02-01

    We analyze the generation of terahertz radiation when an intense, short laser pulse is mixed with its frequency-doubled counterpart in plasma. The nonlinear coupling of the fundamental and the frequency-doubled laser pulses in plasma is shown to be characterized by a third order susceptibility which has a time dependence characteristic of the laser pulse durations. The terahertz generation process depends on the relative polarizations of the lasers and the terahertz frequency is omega approximately 1/tau(L), where tau(L) is the laser pulse duration. Since the laser pulse duration is typically in the picosecond or subpicosecond regime the resulting radiation is in the terahertz or multiterahertz regime. To obtain the third order susceptibility we solve the plasma fluid equations correct to third order in the laser fields, including both the relativistic and ponderomotive force terms. The relativistic and ponderomotive contributions to the susceptibility nearly cancel in the absence of electron collisions. Therefore, in this terahertz generation mechanism collisional effects play a critical role. Consistent with recent experimental observations, our model shows that (1) the terahertz field amplitude is proportional to I(1) square root I(2), where I(1) and I(2) are the intensities of the fundamental and second harmonic laser pulses, respectively, (2) the terahertz emission is maximized when the polarization of the laser beams and the terahertz are aligned, (3) for typical experimental parameters, the emitted terahertz field amplitude is on the order of tens of kilovolts/cm with duration comparable to that of the drive laser pulses, and (4) the direction of terahertz emission depends sensitively on experimental parameters. PMID:20365665

  19. Terahertz generation in plasmas using two-color laser pulses

    SciTech Connect

    Penano, Joseph; Sprangle, Phillip; Gordon, Daniel; Hafizi, Bahman; Serafim, Philip

    2010-02-15

    We analyze the generation of terahertz radiation when an intense, short laser pulse is mixed with its frequency-doubled counterpart in plasma. The nonlinear coupling of the fundamental and the frequency-doubled laser pulses in plasma is shown to be characterized by a third order susceptibility which has a time dependence characteristic of the laser pulse durations. The terahertz generation process depends on the relative polarizations of the lasers and the terahertz frequency is omegaapprox1/tau{sub L}, where tau{sub L} is the laser pulse duration. Since the laser pulse duration is typically in the picosecond or subpicosecond regime the resulting radiation is in the terahertz or multiterahertz regime. To obtain the third order susceptibility we solve the plasma fluid equations correct to third order in the laser fields, including both the relativistic and ponderomotive force terms. The relativistic and ponderomotive contributions to the susceptibility nearly cancel in the absence of electron collisions. Therefore, in this terahertz generation mechanism collisional effects play a critical role. Consistent with recent experimental observations, our model shows that (1) the terahertz field amplitude is proportional to I{sub 1}sq root(I{sub 2}), where I{sub 1} and I{sub 2} are the intensities of the fundamental and second harmonic laser pulses, respectively, (2) the terahertz emission is maximized when the polarization of the laser beams and the terahertz are aligned, (3) for typical experimental parameters, the emitted terahertz field amplitude is on the order of tens of kilovolts/cm with duration comparable to that of the drive laser pulses, and (4) the direction of terahertz emission depends sensitively on experimental parameters.

  20. 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.

  1. Terahertz polarization imaging based on the continuous wave terahertz radiations

    NASA Astrophysics Data System (ADS)

    Liu, Ying; Shen, Yanchun; Zhao, Guozhong

    2015-08-01

    Terahertz (THz) imaging is a hot topic in the current imaging technology. THz imaging has the advantage to penetrate most of non-metal and non-polar materials for the detection of concealed objects, while it is harmless to biological organism. Continuous wave terahertz (THz) imaging is enable to offer a safe and noninvasive imaging for the investigated objects. In this paper, THz real-time polarization imaging system is demonstrated based on the SIFIR-50 THz laser as a radiation source and a NEC Terahertz Imager as an array detector. The experimental system employs two wire grid polarizers to acquire the intensity images in four different directions. The polarization information of the measured object is obtained based on the Stokes-Mueller matrix. Imaging experiments on the currency with water mark and the hollowed-out metal ring have been done. Their polarization images are acquired and analyzed. The results show that the extracted polarization images include the valuable information which can effectively detect and recognize the different kinds of objects.

  2. Papyrus imaging with terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Labaune, J.; Jackson, J. B.; Pagès-Camagna, S.; Duling, I. N.; Menu, M.; Mourou, G. A.

    2010-09-01

    Terahertz time domain spectroscopic imaging (THz-TDSI) is a non-ionizing, non-contact and non-destructive measurement technique that has been recently utilized to study cultural heritage artifacts. We will present this technique and the results of non-contact measurements of papyrus texts, including images of hidden papyri. Inks for modern papyrus specimens were prepared using the historical binder, Arabic gum, and two common pigments used to write ancient texts, carbon black and red ochre. The samples were scanned in reflection at normal incidence with a pulse with a spectral range between 0.1 and 1.5 THz. Temporal analysis of the signals provides the depths of the layers, and their frequency spectra give information about the inks.

  3. Identification of high explosive RDX using terahertz imaging and spectral fingerprints

    NASA Astrophysics Data System (ADS)

    Liu, Jia; Fan, Wen-Hui; Chen, Xu; Xie, Jun

    2016-01-01

    We experimentally investigated the spectral fingerprints of high explosive cyclo-1,3,5- trimethylene-2,4,6-trinitramine (RDX) in terahertz frequency region. A home-made terahertz time-domain spectroscopy ranging from 0.2 THz∼ 3.4 THz was deployed. Furthermore, two sample pellets (RDX pellet and polyethylene pellet), which were concealed in an opaque envelop, could be identified by using terahertz pulse imaging system. For the purpose of distinguishing the RDX between two pellets, we further calculated the THz frequency -domain map using its spectral fingerprints. It is demonstrated that the high explosive RDX could similarly be identified using terahertz frequency-domain imaging.

  4. Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials

    NASA Astrophysics Data System (ADS)

    Strachan, Clare J.; Rades, Thomas; Newnham, David A.; Gordon, Keith C.; Pepper, Michael; Taday, Philip F.

    2004-05-01

    The application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated. The different polymorphic forms of carbamazepine and enalapril maleate exhibit distinct terahertz absorbance spectra. In contrast to crystalline indomethacin and fenoprofen calcium, amorphous indomethacin and liquid crystalline fenoprofen calcium show no absorption modes, which is likely to be due to a lack of order. These findings suggest that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations. The large spectral differences between different forms of the compounds studied is evidence that terahertz pulsed spectroscopy is well-suited to distinguishing crystallinity differences in pharmaceutical compounds.

  5. Application of terahertz pulse imaging as PAT tool for non-destructive evaluation of film-coated tablets under different manufacturing conditions.

    PubMed

    Dohi, Masafumi; Momose, Wataru; Yoshino, Hiroyuki; Hara, Yuko; Yamashita, Kazunari; Hakomori, Tadashi; Sato, Shusaku; Terada, Katsuhide

    2016-02-01

    Film-coated tablets (FCTs) are a popular solid dosage form in pharmaceutical industry. Manufacturing conditions during the film-coating process affect the properties of the film layer, which might result in critical quality problems. Here, we analyzed the properties of the film layer using a non-destructive approach with terahertz pulsed imaging (TPI). Hydrophilic tablets that become distended upon water absorption were used as core tablets and coated with film under different manufacturing conditions. TPI-derived parameters such as film thickness (FT), film surface reflectance (FSR), and interface density difference (IDD) between the film layer and core tablet were affected by manufacturing conditions and influenced critical quality attributes of FCTs. Relative standard deviation of FSR within tablets correlated well with surface roughness. Tensile strength could be predicted in a non-destructive manner using the multivariate regression equation to estimate the core tablet density by film layer density and IDD. The absolute value of IDD (Lateral) correlated with the risk of cracking on the lateral film layer when stored in a high-humidity environment. Further, in-process control was proposed for this value during the film-coating process, which will enable a feedback control system to be applied to process parameters and reduced risk of cracking without a stability test. PMID:26678177

  6. Terahertz Tools Advance Imaging for Security, Industry

    NASA Technical Reports Server (NTRS)

    2010-01-01

    Picometrix, a wholly owned subsidiary of Advanced Photonix Inc. (API), of Ann Arbor, Michigan, invented the world s first commercial terahertz system. The company improved the portability and capabilities of their systems through Small Business Innovation Research (SBIR) agreements with Langley Research Center to provide terahertz imaging capabilities for inspecting the space shuttle external tanks and orbiters. Now API s systems make use of the unique imaging capacity of terahertz radiation on manufacturing floors, for thickness measurements of coatings, pharmaceutical tablet production, and even art conservation.

  7. Terahertz techniques for solar cell imaging

    NASA Astrophysics Data System (ADS)

    Minkevi?ius, L.; Suzanovi?ien--, R.; Molis, G.; Krotkus, A.; Balakauskas, S.; Venckevi?ius, R.; Kaalynas, I.; imkien--, I.; Valuis, G.; Tamoiūnas, V.

    2013-12-01

    Rapid development in fabrication of solar cells requires innovations in characterization of the layers. Particular attention deserves structural imperfections which cannot be directly investigated by optical methods in a visible range. In this paper, we present two terahertz (THz) imaging approaches - Terahertz-Time Domain spectroscopy (THz-TDS)-based and continuous wave (CW) -based THz imaging - which can successfully serve as powerful experimental tool for versatile characterization of the solar cells.

  8. Terahertz interferometric imaging of a concealed object

    NASA Astrophysics Data System (ADS)

    Sinyukov, Alexander M.; Bandyopadhyay, Aparajita; Sengupta, Amartya; Barat, Robert B.; Gary, Dale E.; Michalopoulou, Zoi-Heleni; Zimdars, David; Federici, John F.

    2006-10-01

    Experimental results of two-dimensional homodyne terahertz interferometric imaging are presented. The performance of an N element detector array is imitated by only one detector placed at N positions. Continuous waves at 0.25-0.3 THz are used to detect concealed objects: a metal object and an RDX sample. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

  9. Inexpensive detector for terahertz imaging.

    PubMed

    Abramovich, A; Kopeika, N S; Rozban, D; Farber, E

    2007-10-10

    Glow discharge plasma, derived from direct-current gas breakdown, is investigated in order to realize an inexpensive terahertz (THz) room-temperature detector. Preliminary results for THz radiation show that glow discharge indicator lamps as room-temperature detectors yield good responsivity and noise-equivalent power. Development of a focal plane array (FPA) using such devices as detectors is advantageous since the cost of a glow discharge detector is approximately $0.2-$0.5 per lamp, and the FPA images will be diffraction limited. The detection mechanism of the glow discharge detector is found to be the enhanced diffusion current, which causes the glow discharge detector bias current to decrease when exposed to THz radiation. PMID:17932531

  10. Electromagnetic Pulse Technology: Biological and Terahertz Applications

    NASA Astrophysics Data System (ADS)

    Kumar, Prashanth

    2011-12-01

    Since the mid-1970s, the field of Electromagnetic Pulse (EMP) technology has extended to include High-Power Electromagnetic (HPE) sources/antennas. Two such EMP/HPE antennas, designed to address unique applications, are presented in this dissertation. The first is the Prolate-Spheroidal Impulse-Radiating Antenna (PSIRA). Such an antenna uses a prolate-spheroidal reflector and has two foci. A fast (≤ 100 ps), high-voltage (> 100 kV) pulse launched from the first focal point is focused into a target located at the second focal point (near-field). It has been found that these pulses are useful for a variety of biological applications, such as accelerated wound healing and skin cancer (melanoma) treatment. Two lens designs for the PSIRA are explored. The first lens, called the focusing lens, is used at the second focal point of the PSIRA to better match the focused pulses into the (biological) target medium. Analytical calculations, numerical simulations and experimental results on a five-layer, hemispherical, dielectric focusing lens are detailed. The second lens, called the launching lens, is used at the first focal point of the PSIRA. For input voltages of 100 kV or more, a switch system, i.e., switch cones, pressure vessel, hydrogen chamber and launching lens, are required to effectively launch a spherical TEM wave from the first focal point. Various switch configurations are explored. It is shown that the pressure vessel can also serve as the launching lens, which considerably simplifies the design of the switch system. Spherical and cylindrical pressure vessel designs are investigated. The second is the Switched Oscillator (SwO) antenna. A SwO is essentially an electrical, shock-excited resonant structure. The SwO is adopted as a high-power antenna to radiate high-energy pulses in the terahertz frequency range. The primary focus is to use these pulses for secure communications. Analytical calculations for the SwO are detailed. Numerical simulations are used to optimize and more thoroughly study the antenna. Various characteristic relations obtained are used to provide a deeper insight into the working of the SwO radiator.

  11. Processing and Probability Analysis of Pulsed Terahertz NDE of Corrosion under Shuttle Tile Data

    NASA Technical Reports Server (NTRS)

    Anastasi, Robert F.; Madaras, Eric I.; Seebo, Jeffrey P.; Ely, Thomas M.

    2009-01-01

    This paper examines data processing and probability analysis of pulsed terahertz NDE scans of corrosion defects under a Shuttle tile. Pulsed terahertz data collected from an aluminum plate with fabricated corrosion defects and covered with a Shuttle tile is presented. The corrosion defects imaged were fabricated by electrochemically etching areas of various diameter and depth in the plate. In this work, the aluminum plate echo signal is located in the terahertz time-of-flight data and a threshold is applied to produce a binary image of sample features. Feature location and area are examined and identified as corrosion through comparison with the known defect layout. The results are tabulated with hit, miss, or false call information for a probability of detection analysis that is used to identify an optimal processing threshold.

  12. Terahertz polarization imaging for colon cancer detection

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  13. Creating Rydberg electron wave packets using terahertz pulses

    NASA Astrophysics Data System (ADS)

    Bromage, Jake

    1999-10-01

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

  14. Array Technology for Terahertz Imaging

    NASA Technical Reports Server (NTRS)

    Reck, Theodore; Siles, Jose; Jung, Cecile; Gill, John; Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, Imran; Cooper, Ken

    2012-01-01

    Heterodyne terahertz (0.3 - 3THz) imaging systems are currently limited to single or a low number of pixels. Drastic improvements in imaging sensitivity and speed can be achieved by replacing single pixel systems with an array of detectors. This paper presents an array topology that is being developed at the Jet Propulsion Laboratory based on the micromachining of silicon. This technique fabricates the array's package and waveguide components by plasma etching of silicon, resulting in devices with precision surpassing that of current metal machining techniques. Using silicon increases the versatility of the packaging, enabling a variety of orientations of circuitry within the device which increases circuit density and design options. The design of a two-pixel transceiver utilizing a stacked architecture is presented that achieves a pixel spacing of 10mm. By only allowing coupling from the top and bottom of the package the design can readily be arrayed in two dimensions with a spacing of 10mm x 18mm.

  15. Terahertz interferometric and synthetic aperture imaging

    NASA Astrophysics Data System (ADS)

    Sinyukov, Alexander M.; Bandyopadhyay, Aparajita; Sengupta, Amartya; Barat, Robert B.; Gary, Dale E.; Michalopoulou, Zoi-Heleni; Zimdars, David; Federici, John F.

    2006-05-01

    Experimental results of homodyne terahertz interferometric 1-D and 2-D imaging are presented. Continuous waves at 0.25-0.3 THz are used to detect a metal object behind a barrier. The performance of an N element detector array is imitated by only one detector placed at N positions. The reconstructed images are in a good agreement with theoretical predictions. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

  16. 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.

  17. Terahertz imaging system with resonant tunneling diodes

    NASA Astrophysics Data System (ADS)

    Miyamoto, Tomoyuki; Yamaguchi, Atsushi; Mukai, Toshikazu

    2016-03-01

    We report a feasibility study of a terahertz imaging system with resonant tunneling diodes (RTDs) that oscillate at 0.30 THz. A pair of RTDs acted as an emitter and a detector in the system. Terahertz reflection images of opaque samples were acquired with our RTD imaging system. A spatial resolution of 1 mm, which is equal to the wavelength of the RTD emitter, was achieved. The signal-to-noise ratio (SNR) of the reflection image was improved by 6 dB by using polarization optics that reduced interference effects. Additionally, the coherence of the RTD enabled a depth resolution of less than 3 µm to be achieved by an interferometric technique. Thus, RTDs are an attractive candidate for use in small THz imaging systems.

  18. Terahertz wave imaging: horizons and hurdles

    NASA Astrophysics Data System (ADS)

    Zhang, X.-C.

    2002-11-01

    Terahertz (THz) science will profoundly impact biotechnology. It has tremendous potential for applications in imaging, medical diagnosis, health monitoring, environmental control and chemical and biological identification. THz research will become one of the most promising research areas in the 21st century for transformational advances in imaging, as well as in other interdisciplinary fields. However, terahertz wave (T-ray) imaging is still in its infancy. This paper discusses the uniqueness and limitations of T-ray imaging, identifies the major challenges impeding T-ray imaging and proposes solutions and opportunities in this field. It also concentrates on the generation, propagation and detection of T-rays by the use of femtosecond optics.

  19. Hybrid tilted-pulse-front excitation scheme for efficient generation of high-energy terahertz pulses.

    PubMed

    Pálfalvi, L; Ollmann, Z; Tokodi, L; Hebling, J

    2016-04-18

    Conception of a hybrid type tilted-pulse-front pumping scheme for the generation of high-energy terahertz pulses is presented. The proposed setup is the combination of the conventional setup containing imaging optics and the contact grating. The solution was developed for nonlinear materials requiring large pulse-front-tilt angle, like LiNbO3. Due to the creation of the pulse-front-tilt in two steps the limitations of imaging errors can be significantly reduced. Furthermore the necessary grating constant of the contact grating can be larger compared to the simple contact grating scheme making possible the fabrication of the grating profile with significantly higher precision. A detailed optimization procedure with respect to the diffraction efficiency on the contact grating is given for LiNbO3. Instructions are also given how to construct the geometry of the setup in order to minimize imaging errors. Examples are given for LiNbO3 based practically realizable, optimized schemes with reduced imaging errors and high diffraction efficiency on the contact grating. PMID:27137255

  20. Biomedical terahertz imaging with a quantum cascade laser

    NASA Astrophysics Data System (ADS)

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

    2006-04-01

    We present biomedical imaging using a single frequency terahertz imaging system based on a low threshold quantum cascade laser emitting at 3.7THz (?=81?m). With a peak output power of 4mW, coherent terahertz radiation and detection provide a relatively large dynamic range and high spatial resolution. We study image contrast based on water/fat content ratios in different tissues. Terahertz transmission imaging demonstrates a distinct anatomy in a rat brain slice. We also demonstrate malignant tissue contrast in an image of a mouse liver with developed tumors, indicating potential use of terahertz imaging for probing cancerous tissues.

  1. Terahertz/mm wave imaging simulation software

    NASA Astrophysics Data System (ADS)

    Fetterman, M. R.; Dougherty, J.; Kiser, W. L., Jr.

    2006-10-01

    We have developed a mm wave/terahertz imaging simulation package from COTS graphic software and custom MATLAB code. In this scheme, a commercial ray-tracing package was used to simulate the emission and reflections of radiation from scenes incorporating highly realistic imagery. Accurate material properties were assigned to objects in the scenes, with values obtained from the literature, and from our own terahertz spectroscopy measurements. The images were then post-processed with custom Matlab code to include the blur introduced by the imaging system and noise levels arising from system electronics and detector noise. The Matlab code was also used to simulate the effect of fog, an important aspect for mm wave imaging systems. Several types of image scenes were evaluated, including bar targets, contrast detail targets, a person in a portal screening situation, and a sailboat on the open ocean. The images produced by this simulation are currently being used as guidance for a 94 GHz passive mm wave imaging system, but have broad applicability for frequencies extending into the terahertz region.

  2. Ultrashort pulse characterization with a terahertz streak camera.

    PubMed

    Schubert, O; Riek, C; Junginger, F; Sell, A; Leitenstorfer, A; Huber, R

    2011-11-15

    A phase-locked terahertz transient is exploited as an ultrafast phase gate for femtosecond optical pulses. We directly map out the group delay dispersion of a low-power near-infrared pulse by measuring the electro-optically induced polarization rotation as a function of wavelength. Our experiment covers the spectral window from 1.0 to 1.4 ?m and reaches a temporal precision better than 1 fs. A quantitative analysis of the detector response confirms that this streaking technique requires no reconstruction algorithm and is also well suited for the characterization of pulses spanning more than one optical octave. PMID:22089596

  3. Chirped-pulse terahertz spectroscopy for broadband trace gas sensing.

    PubMed

    Gerecht, Eyal; Douglass, Kevin O; Plusquellic, David F

    2011-04-25

    We report the first demonstration of a broadband trace gas sensor based on chirp-pulse terahertz spectroscopy. The advent of newly developed solid state sources and sensitive heterodyne detectors for the terahertz frequency range have made it possible to generate and detect precise arbitrary waveforms at THz frequencies with ultra-low phase noise. In order to maximize sensitivity, the sample gas is first polarized using sub-μs chirped THz pulses and the free inductive decays (FIDs) are then detected using a heterodyne receiver. This approach allows for a rapid broadband multi-component sensing with low parts in 10(9) (ppb) sensitivities and spectral frequency accuracy of <20 kHz in real-time. Such a system can be configured into a portable, easy to use, and relatively inexpensive sensing platform. PMID:21643150

  4. Real-Time Detection of Terahertz Pulse Amplitude and Position

    NASA Astrophysics Data System (ADS)

    Phringer, Harald; Nejim, Zeineb; Pfleger, Michael; Katletz, Stefan

    2016-02-01

    A novel and continuous detection scheme for the pulse amplitude and temporal position of a terahertz time domain system is presented. Currently, we have achieved a sampling time of 25 Hz and a resolution of less than 70 fs. The method is therefore very well suited for online measurements in production processes to monitor the thickness and inhomogeneities in the composition of non-conducting materials.

  5. Pulsed-terahertz reflectometry for health monitoring of ceramic thermal barrier coatings.

    PubMed

    Chen, Chia-Chu; Lee, Dong-Joon; Pollock, Tresa; Whitaker, John F

    2010-02-15

    Terahertz time-domain reflectometry was used to monitor the progress of a thermally grown oxide layer and stress-induced, air-filled voids at the interface of an Yttria-stabilized-zirconia ceramic thermal-barrier coating and a metal surface. The thicknesses of these internal layers, observed in scanning-electron-microscope images to increase with thermal-exposure time, have been resolved - even when changing on the order of only a few micrometers - by distinguishing not only increased delays in the arrival times of terahertz pulses reflected from this multilayer structure, but also changes in the width and shape of the pulses. These unique features can be used to predict the lifetime of thermal-barrier coatings and to indicate or warn of spallation conditions. The trends of the experimental results are also confirmed through Fresnel-reflection time-domain simulations. PMID:20389357

  6. Terahertz ISAR imaging in noise backgroud

    NASA Astrophysics Data System (ADS)

    Li, Liang-Sheng; Li, Sheng; Yin, Hong-cheng

    2013-08-01

    We investigate the ISAR imaging in background noises by using the analytical solutions and physical optics within the terahertz region. When increasing the frequency band wide, the scattering signals of the metal sphere are enhanced by the coherent measurement technique, and the background noises are effectively canceled. Furthermore, the resolution of SAR imaging is improved to precisely locate the scattering centers of objects. However, the increased band wide seemly decreases the contrast of imaging due to the discrete grids of filtered back projection algorithm.

  7. THz pulsed time-domain imaging of an oil canvas painting: a case study of a painting by Pablo Picasso

    NASA Astrophysics Data System (ADS)

    Fukunaga, Kaori; Ikari, Tomofumi; Iwai, Kikuko

    2016-02-01

    The terahertz pulsed time-domain imaging technique and near-infrared observation were applied to investigate an oil painting on canvas by Pablo Picasso. The multilayer structure is clearly observed in cross-sectional image by terahertz pulsed time-domain imaging, and particular Cubism style lines were revealed under newly painted area by near-infrared image.

  8. Terahertz polarization imaging with birefringent materials

    NASA Astrophysics Data System (ADS)

    Zhang, LiangLiang; Zhong, Hua; Deng, Chao; Zhang, CunLin; Zhao, YueJin

    2010-12-01

    We present a terahertz (THz) imaging method with a birefringent material which is sensitive to THz wave polarization. The subtle THz polarization modulations introduced by the target are extracted by the amplitudes of the two separated THz peaks passing through the birefringent material. The anisotropy of the industrial sprayed-on-foam-insulation (SOFI) is characterized by measuring its azimuthal angle dependent THz polarization response. This work demonstrated that this polarization sensitive THz imaging technique can be used for industrial inspection and biological related characterization.

  9. Terahertz real-time imaging for nondestructive detection

    NASA Astrophysics Data System (ADS)

    Zhang, LiangLiang; Karpowicz, Nick; Zhang, CunLin; Zhao, YueJin; Zhang, XiCheng

    2008-03-01

    We present a real time imaging measurement in the terahertz (THz) frequency region. The dynamic subtraction technique is used to reduce long-term optical background drift. The reflective images of two targets, a Nikon camera's lens cap and a plastic toy gun, are obtained. For the lens cap, the image data were processed to be false color images. For the toy gun, we show that even under an optically opaque canvas bag, a clear terahertz image is obtained. It is shown that terahertz real time imaging can be used to nondestructively detect concealed objects.

  10. Generation of terahertz radiation by focusing femtosecond bichromatic laser pulses in a gas or plasma

    SciTech Connect

    Chizhov, P A; Volkov, Roman V; Bukin, V V; Ushakov, A A; Garnov, Sergei V; Savel'ev-Trofimov, Andrei B

    2013-04-30

    The generation of terahertz radiation by focusing two-frequency femtosecond laser pulses is studied. Focusing is carried out both in an undisturbed gas and in a pre-formed plasma. The energy of the terahertz radiation pulses is shown to reduce significantly in the case of focusing in a plasma. (extreme light fields and their applications)

  11. Video-rate terahertz electric-field vector imaging

    SciTech Connect

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

    2014-10-13

    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.

  12. NDE Imaging of Time Differential Terahertz Waves

    NASA Technical Reports Server (NTRS)

    Trinh, Long B.

    2008-01-01

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

  13. Carrier envelope phase shifter for broadband terahertz pulses.

    PubMed

    Kawada, Yoichi; Yasuda, Takashi; Takahashi, Hironori

    2016-03-01

    We demonstrated controlled shifting of the internal phase of broadband terahertz (THz) pulses. The internal phase of an ultrashort pulse is called the carrier envelope phase (CEP), which is an important parameter in the interaction of few-cycle light pulses and matter. Our CEP shifter utilizes the ultra-broadband feature of prism wave plates. We analytically derived the amount of CEP shift achievable by the CEP shifter using Jones matrixes. THz time-domain measurements clearly showed the shift of the CEP, and the results agreed well with the calculated values. The CEP shift was as high as 2π, indicating that any CEP values can be chosen using our CEP shifter. PMID:26974097

  14. Passive terahertz imaging for security application

    NASA Astrophysics Data System (ADS)

    Guo, Lan-tao; Deng, Chao; Zhao, Yuan-meng; Zhang, Cun-lin

    2013-08-01

    The passive detection is safe for passengers and operators as no radiation. Therefore, passive terahertz (THz) imaging can be applied to human body security check. Imaging in the THz band offers the unique property of being able to identify object through a range of materials. Therefore passive THz imaging is meaningful for security applications. This attribute has always been of interest to both the civil and military marks with applications. We took advantage of a single THz detector and a trihedral scanning mirror to propose another passive THz beam scanning imaging method. This method overcame the deficiencies of the serious decline in image quality due to the movement of the focused mirror. We exploited a THz scanning mirror with a trihedral scanning mirror and an ellipsoidal mirror to streamline the structure of the system and increase the scanning speed. Then the passive THz beam scanning imaging system was developed based on this method. The parameters were set as follows: the best imaging distance was 1.7m, the image height was 2m, the image width was 1m, the minimum imaging time of per frame was 8s, and the minimum resolution was 4cm. We imaged humans with different objects hidden under their clothes, such as fruit knife, belt buckle, mobile phone, screwdriver, bus cards, keys and other items. All the tested stuffs could be detected and recognized from the image.

  15. [Study of Terahertz Amplitude Imaging Based on the Mean Absorption].

    PubMed

    Zhang, Zeng-yan; Ji, Te; Xiao, Ti-qiao; Zhao, Hong-wei; Chen, Min; Yu, Xiao-han; Tong, Ya-jun; Zhu, Hua-chun; Peng, Wei-wei

    2015-12-01

    A new method of terahertz (THz) imaging based on the mean absorption is proposed. Terahertz radiation is an electromagnetic radiation in the range between millimeter waves and far infrared. THz pulse imaging emerges as a novel tool in many fields because of its low energy and non-ionizing character, such as material, chemical, biological medicine and food safety. A character of THz imaging technique is it can get large amount of information. How to extract the useful parameter from the large amount of information and reconstruct sample's image is a key technology in THz imaging. Some efforts have been done for advanced visualization methods to extract the information of interest from the raw data. Both time domain and frequency domain visualization methods can be applied to extract information on the physical properties of samples from THz imaging raw data. The process of extracting useful parameter from raw data of the new method based on the mean absorption was given in this article. This method relates to the sample absorption and thickness, it delivers good signal to noise ratio in the images, and the dispersion effects are cancelled. A paper with a "THz" shape hole was taken as the sample to do the experiment. Traditional THz amplitude imaging methods in time domain and frequency domain are used to achieve the sample's image, such as relative reduction of pulse maximum imaging method, relative power loss imaging method, and relative power loss at specific frequency imaging method. The sample's information that reflected by these methods and the characteristics of these methods are discussed. The method base on the mean absorption within a certain frequency is also used to reconstruct sample's image. The experimental results show that this new method can well reflect the true information of the sample. And it can achieve a clearer image than the other traditional THz amplitude imaging methods. All the experimental results and theoretical analyses indicate that the method base on the mean absorption within a certain frequency can reflects sample absorb and thickness information, it can achieve good signal to noise ratio in the images. Because the absorption is mean absorption within in a certain frequency, so the method proposed in this article is especially suitable for samples with simple structure. And this new method can be a useful added tool for the other traditional THz amplitude imaging methods. PMID:26964201

  16. Ultrafast imaging of terahertz Cherenkov waves and transition-like radiation in LiNbO₃.

    PubMed

    Wang, Zhenyou; Su, FuHai; Hegmann, Frank A

    2015-03-23

    We use ultrafast phase-contrast imaging to directly observethe cone-like terahertz (THz) Cherenkov wave generated by optical rectification of femtosecond laser pulses focused into bulk lithium niobate (LiNbO₃) single crystals. The transverse imaging geometry allows the Cherenkov angle, THz wave velocity, and optical pump pulse group velocity to be measured. Furthermore, transition-like THz radiation generated by the femtosecond laser pulse at the air-crystal boundary is observed. The effect of optical pump pulse polarization on the generation of THz Cherenkov waves and transition-like radiation in LiNbO₃ is also investigated. PMID:25837145

  17. 3-D Terahertz Synthetic-Aperture Imaging and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Henry, Samuel C.

    Terahertz (THz) wavelengths have attracted recent interest in multiple disciplines within engineering and science. Situated between the infrared and the microwave region of the electromagnetic spectrum, THz energy can propagate through non-polar materials such as clothing or packaging layers. Moreover, many chemical compounds, including explosives and many drugs, reveal strong absorption signatures in the THz range. For these reasons, THz wavelengths have great potential for non-destructive evaluation and explosive detection. Three-dimensional (3-D) reflection imaging with considerable depth resolution is also possible using pulsed THz systems. While THz imaging (especially 3-D) systems typically operate in transmission mode, reflection offers the most practical configuration for standoff detection, especially for objects with high water content (like human tissue) which are opaque at THz frequencies. In this research, reflection-based THz synthetic-aperture (SA) imaging is investigated as a potential imaging solution. THz SA imaging results presented in this dissertation are unique in that a 2-D planar synthetic array was used to generate a 3-D image without relying on a narrow time-window for depth isolation cite [Shen 2005]. Novel THz chemical detection techniques are developed and combined with broadband THz SA capabilities to provide concurrent 3-D spectral imaging. All algorithms are tested with various objects and pressed pellets using a pulsed THz time-domain system in the Northwest Electromagnetics and Acoustics Research Laboratory (NEAR-Lab).

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

    SciTech Connect

    Ilyakov, I. E. Shishkin, B. V.; Kitaeva, G. Kh.; Akhmedzhanov, R. A.

    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.

  19. Single-shot terahertz spectroscopy using pulse-front tilting of an ultra-short probe pulse.

    PubMed

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

    2011-06-01

    We developed a single-shot terahertz pulse measurement technique using pulse-front tilting of an ultra-short probe pulse and demonstrated single-shot terahertz spectroscopy. A transmission grating was used to introduce a sufficiently large pulse-front tilt angle. A measuring time range of 23.8 ps was achieved. The measured temporal waveforms were corrected in consideration of the nonlinearity arising from the crossed-Nicols arrangement employed and the beam profiles of the probe and terahertz pulses. The characteristic spectrum of lactose was measured with a single terahertz pulse, and the effectiveness of our single-shot technique was confirmed by comparison with a conventional sampling method. PMID:21716352

  20. 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

  1. Theory of terahertz pulse generation through optical rectification in a nonlinear optical material with a finite size

    SciTech Connect

    Schneider, Arno

    2010-09-15

    The full analytical solutions for plane terahertz waves generated through optical rectification in a slab of a nonlinear optical material are calculated. Terahertz dispersion, absorption of both optical and terahertz waves, and multiple reflections are considered. The results are valid for an arbitrary difference between the optical group index and the terahertz refractive index, including equal indices. It is demonstrated that the full terahertz wave is freely propagating and has no contribution of a 'forced' pulse.

  2. High-speed terahertz imaging toward food quality inspection.

    PubMed

    Ok, Gyeongsik; Park, Kisang; Kim, Hyun Jung; Chun, Hyang Sook; Choi, Sung-Wook

    2014-03-01

    In contrast to conventional x-ray food inspection systems that have difficulty in detecting low-density materials, a terahertz imaging system can even identify insects and plastics embedded in a food matrix. A reflection-mode continuous-wave terahertz imaging system was therefore developed for application to food quality inspection, which requires fast, compact, and low-cost detection. High-speed operation of the terahertz imaging system was achieved through the use of a beam-steering tool. A reasonable compromise between the spatial resolution and the scan length of an aspheric f-theta scanning lens could be achieved by optimizing the lens parameters. PMID:24663370

  3. Compact, high average power, fiber-pumped terahertz source for active real-time imaging of concealed objects.

    PubMed

    Creeden, Daniel; McCarthy, John C; Ketteridge, Peter A; Schunemann, Peter G; Southward, Timothy; Komiak, James J; Chicklis, Evan P

    2007-05-14

    We have modeled and demonstrated a scalable, compact, fiber-pumped terahertz source based on difference frequency mixing (DFM) in zinc germanium phosphide (ZGP) capable of producing high average and peak-power pulses. Currently, our terahertz source produces 2 mW of average THz power and >40 W of peak power with sub-nanosecond pulses at a repetition rate of 100 kHz in the range of 2-3 THz without cryogenic cooling or ultra-fast optics. This high average power laser-based terahertz output enables the real-time imaging of concealed objects using an off-the-shelf uncooled microbolometer focal-plane array. With this THz system, we have imaged objects obscured inside in a common shipping envelope, demonstrating the potential of compact laser-based terahertz sources for use in security screening applications. PMID:19546954

  4. TeraHertz imaging of hidden paint layers on canvas.

    PubMed

    Adam, Aurèle J L; Planken, Paul C M; Meloni, Sabrina; Dik, Joris

    2009-03-01

    We show terahertz reflection images of hidden paint layers in a painting on canvas and compare the results with X-ray Radiography and In-frared Reflectography. Our terahertz measurements show strong reflections from both the canvas/paint interface and from the raw umber/lead white interface, indicating sufficient refractive-index contrast. Our results show that X-rays cannot be used to image through the lead white pigment which effectively blocks the X-rays. Although Infrared Reflectography is capable of vaguely observing the hidden paint strokes from the canvas side, we show that only terahertz imaging is capable of providing information on the thickness of the hidden paint layers. Terahertz imaging is thus shown to be a powerful imaging method for art historians, conservators and conservation scientists. PMID:19259178

  5. Interaction of Terahertz Pulses with Photoexcited Electron Plasmas on Semiconductor Surfaces

    NASA Astrophysics Data System (ADS)

    Malevich, V. L.; Sinitsyn, G. V.; Rozanov, N. N.

    2016-01-01

    The interactions of terahertz pulses of electromagnetic radiation with optically-excited free charge carrier plasmas on the surface of semiconductors are studied. The influence of the plasma layer on the Brewster effect and total internal reflection is analyzed. It is shown that the changes in transmission and reflection caused by the electron plasma layer can be used to modulate terahertz radiation.

  6. Frequency Up-Conversion Photon-Type Terahertz Imager.

    PubMed

    Fu, Z L; Gu, L L; Guo, X G; Tan, Z Y; Wan, W J; Zhou, T; Shao, D X; Zhang, R; Cao, J C

    2016-01-01

    Terahertz imaging has many important potential applications. Due to the failure of Si readout integrated circuits (ROICs) and the thermal mismatch between the photo-detector arrays and the ROICs at temperatures below 40 K, there are big technical challenges to construct terahertz photo-type focal plane arrays. In this work, we report pixel-less photo-type terahertz imagers based on the frequency up-conversion technique. The devices are composed of terahertz quantum-well photo-detectors (QWPs) and near-infrared (NIR) light emitting diodes (LEDs) which are grown in sequence on the same substrates using molecular beam epitaxy. In such an integrated QWP-LED device, photocurrent in the QWP drives the LED to emit NIR light. By optimizing the structural parameters of the QWP-LED, the QWP part and the LED part both work well. The maximum values of the internal and external energy up-conversion efficiencies are around 20% and 0.5%. A laser spot of a homemade terahertz quantum cascade laser is imaged by the QWP-LED together with a commercial Si camera. The pixel-less imaging results show that the image blurring induced by the transverse spreading of photocurrent is negligible. The demonstrated pixel-less imaging opens a new way to realize high performance terahertz imaging devices. PMID:27147281

  7. Frequency Up-Conversion Photon-Type Terahertz Imager

    PubMed Central

    Fu, Z. L.; Gu, L. L.; Guo, X. G.; Tan, Z. Y.; Wan, W. J.; Zhou, T.; Shao, D. X.; Zhang, R.; Cao, J. C.

    2016-01-01

    Terahertz imaging has many important potential applications. Due to the failure of Si readout integrated circuits (ROICs) and the thermal mismatch between the photo-detector arrays and the ROICs at temperatures below 40 K, there are big technical challenges to construct terahertz photo-type focal plane arrays. In this work, we report pixel-less photo-type terahertz imagers based on the frequency up-conversion technique. The devices are composed of terahertz quantum-well photo-detectors (QWPs) and near-infrared (NIR) light emitting diodes (LEDs) which are grown in sequence on the same substrates using molecular beam epitaxy. In such an integrated QWP-LED device, photocurrent in the QWP drives the LED to emit NIR light. By optimizing the structural parameters of the QWP-LED, the QWP part and the LED part both work well. The maximum values of the internal and external energy up-conversion efficiencies are around 20% and 0.5%. A laser spot of a homemade terahertz quantum cascade laser is imaged by the QWP-LED together with a commercial Si camera. The pixel-less imaging results show that the image blurring induced by the transverse spreading of photocurrent is negligible. The demonstrated pixel-less imaging opens a new way to realize high performance terahertz imaging devices. PMID:27147281

  8. Characteristic of Terahertz Radiation from a Counter-Pulse Scheme in a Magnetized Plasma

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    We studied a novel scheme of generating a quasi-continuous terahertz radiation from counter-propagating laser pulses colliding in a magnetized plasma. In this system, the strong ponderomotive force of colliding pulses leaves a standing oscillation of an electron current around the collision point, which acts as an antenna of the electromagnetic radiation in the terahertz frequency regime. Theoretically it was found that the terahertz amplitude scales with square of P, where P is the power of the driving pulse, while it scales just with P for a single pulse case. So the radiation intensity can be enhanced by tens of times from that of Cherenkov wake scheme driven by a single laser pulse. Furthermore it was found that, due to the growth of the central field, which is a direct result of driven-diffusion of the electric field near the cutoff, the density gradient of the plasma even increases the peak power of the terahertz radiation.

  9. 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.

  10. Metamaterial based devices for terahertz imaging

    NASA Astrophysics Data System (ADS)

    Peralta, Xomalin G.; Wanke, Michael C.; Brener, Igal; Waldman, Jerry; Goodhue, William D.; Li, J.; Azad, Abul K.; Chen, Hou-Tong; Taylor, Antoinette J.; O'Hara, John F.

    2010-02-01

    The terahertz (THz) region has been shown to have considerable application potential for spectroscopic imaging, nondestructive imaging through nonpolar, nonmetallic materials and imaging of biological materials. These applications have all been possible due to the recent progress in THz sources, detectors and measurement techniques. However, only moderate progress has been made in developing passive and active devices to control and manipulate THz radiation, which can enhance current imaging capabilities. One promising approach for implementing passive and active devices at THz frequencies are metamaterials - composite materials designed to have specific electromagnetic properties not found in naturally occurring materials. The most common implementation utilizes a metallic resonant particle periodically distributed in an insulator matrix where the periodicity is significantly smaller than the wavelength of operation. We have designed and implemented three metamaterial based devices with potential applications to THz imaging. We present an electrically-driven active metamaterial which operates as an external modulator for a ~2.8 THz CW quantum cascade laser. We obtained a modulation depth of ~60%. We also demonstrate a polarization sensitive metamaterial which can be used as a continuously variable attenuator or as a wave plate. The latter may be useful for the development of THz phase contrast imaging.

  11. Terahertz electronics for sensing and imaging applications

    NASA Astrophysics Data System (ADS)

    Shur, Michael

    2015-05-01

    Short channel field effect transistors can detect terahertz radiation. Such detection is enabled by the excitation of the plasma waves rectified due to the device nonlinearities. The resulting response has nanometer scale spatial resolution and can be modulated in the sub THz range. This technology could enable a variety of sensing, imaging, and wireless communication applications, including detection of biological and chemical hazardous agents, cancer detection, shortrange covert communications (in THz and sub-THz windows), and applications in radio astronomy. Field effect transistors implemented using III-V, III-N, Si, SiGe, and graphene have been used to detect THz radiation. Using silicon transistors in plasmonic regimes is especially appealing because of compatibility with standard readout silicon VLSI components.

  12. Amplification of terahertz pulses in gases beyond thermodynamic equilibrium

    SciTech Connect

    Schwaab, G. W.; Schroeck, K.; Havenith, M.

    2007-03-15

    In Ebbinghaus et al. [Plasma Sources Sci. Technol. 15, 72 (2006)] we reported terahertz time-domain spectroscopy in a plasma at low pressure, we observed a simultaneous absorption and amplification process within each single rotational transition. Here we show that this observation is a direct consequence of the short interaction time of the pulsed terahertz radiation with the plasma, which is shorter than the average collision time between the molecules. Thus, during the measurement time the molecular states may be considered entangled. Solution of the time-dependent Schroedinger equation yields a linear term that may be neglected for long observation times, large frequencies, or nonentangled states. We determine the restrictions for the observation of this effect and calculate the spectrum of a simple diatomic molecule. Using this model we are able to explain the spectral features showing a change from emission to absorption as observed previously. In addition we find that the amplification and absorption do not follow the typical Lambert-Beer exponential law but an approximate square law.

  13. Terahertz imaging system using high-Tc superconducting oscillation devices

    NASA Astrophysics Data System (ADS)

    Tsujimoto, M.; Minami, H.; Delfanazari, K.; Sawamura, M.; Nakayama, R.; Kitamura, T.; Yamamoto, T.; Kashiwagi, T.; Hattori, T.; Kadowaki, K.

    2012-06-01

    Microwatt power oscillation devices at sub-terahertz frequency region between 0.3 and 1.0 terahertz (THz) were fabricated from high-Tc superconducting single crystalline Bi2Sr2CaCu2O8+δ and used as a source of the transmission terahertz imaging system. As test examples, terahertz images of coins and a razor blade placed inside the brownish paper envelopes with the spatial resolution of 1 mm are presented. The signal-to-noise ratio exceeds 130 in these images. Using a simple wedge-shaped interferometer and analysing the interference fringe pattern, the wavelength of the terahertz wave is calibrated within 0.1% accuracy. This interferometer also provides a simple method to measure the absorption coefficient of the liquid sample. Two test measurements for distilled water and ethanol are demonstrated and their absorption coefficients are obtained with 99.2% accuracy. This suggests that our terahertz imaging system can be applied to many practical applications, such as biological and biomedical imaging, environmental monitoring, microanalysis of impurities, structure and dynamical analyses of large molecules and ions in solution.

  14. Subsurface nanoimaging by broadband terahertz pulse near-field microscopy.

    PubMed

    Moon, Kiwon; Park, Hongkyu; Kim, Jeonghoi; Do, Youngwoong; Lee, Soonsung; Lee, Gyuseok; Kang, Hyeona; Han, Haewook

    2015-01-14

    Combined with terahertz (THz) time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, we experimentally demonstrate a broadband THz pulse near-field microscope that provides subsurface nanoimaging of a metallic grating embedded in a dielectric film. The THz near-field microscope can obtain broadband nanoimaging of the subsurface grating with a nearly frequency-independent lateral resolution of 90 nm, corresponding to ∼ λ/3300, at 1 THz, while the AFM only provides a flat surface topography. PMID:25436437

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

    SciTech Connect

    Wang Weimin; Kawata, Shigeo; Sheng Zhengming; Zhang Jie; Li Yutong

    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}.

  16. Terahertz parametric sources and imaging applications

    NASA Astrophysics Data System (ADS)

    Yamashita, M.; Ogawa, Y.; Otani, C.; Kawase, K.

    2005-12-01

    We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of LiNbO 3 or MgO-doped LiNbO 3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We report the detailed characteristics of the oscillation and the radiation including tunability, spatial and temporal coherency, uni directivity, and efficiency. A Fourier transform limited THz-wave spectrum narrowing was achieved by introducing the injection seeding method. Further, we have developed a spectroscopic THz imaging system using a TPO, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. Several images of the envelope are recorded at different THz frequencies and then processed. The final result is an image that reveals what substances are present in the envelope, in what quantity, and how they are distributed across the envelope area. The example presented here shows the identification of three drugs, two of which illegal, while one is an over-the-counter drug.

  17. Terahertz parametric sources and imaging applications

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo; Ogawa, Yuichi; Minamide, Hiroaki; Ito, Hiromasa

    2005-07-01

    We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of LiNbO3 or MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave source with a simple configuration. We report the detailed characteristics of the oscillation and the radiation including tunability, spatial and temporal coherency, uni-directivity, and efficiency. A Fourier transform limited THz-wave spectrum narrowing was achieved by introducing the injection seeding method. Further, we have developed a spectroscopic THz imaging system using a THz-wave parametric oscillator, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. Several images of the envelope are recorded at different THz frequencies and then processed. The final result is an image that reveals what substances are present in the envelope, in what quantity, and how they are distributed across the envelope area. The example presented here shows the identification of three drugs, two of which are illegal, while one is an over-the-counter drug.

  18. Single-pixel terahertz imaging via compressed sensing

    NASA Astrophysics Data System (ADS)

    Zhao, Ya-qin; Zhang, Liang-liang; Duan, Guo-teng; Liu, Xiao-hua; Zhang, Cun-lin

    2011-08-01

    With the development of terahertz related technologies, the terahertz imaging technology will show its greater practical value in more areas. In this paper, we describe a terahertz imaging system that uses a single pixel detector in combination with a series of random masks to enable high-speed image acquisition. The image formation is based on the theory of compressed sensing (CS). When the scene under view is compressible by an algorithm like JPEG or JPEG2000, the CS theory enables us to stably reconstruct an image of the scene from fewer measurements than the number of reconstructed pixels. In this manner, we achieve sub-Nyquist image acquisition. CS theory mainly includes signal sparse representation, encoding measurement and reconstruction algorithm. CS combines sampling and compression into a single non-adaptive linear measurement process. Rather than measuring pixel samples of the scene under view, we measure inner products between the scene and a set of test functions. CS permits the reconstruction of a N-by-N pixel image using much fewer than N2 measurements. This approach eliminates the need for raster scanning of the object or the terahertz beam, while maintaining the high sensitivity of a single-element detector. We demonstrate the concept using a backward wave oscillator (BWO) which is a continuous-wave terahertz source and get a preliminary test result.

  19. Electro-optic time lensing with an intense single-cycle terahertz pulse

    SciTech Connect

    Shen, Y.; Carr, G.L.; Murphy, J.B.; Tsang, T. Y.; Wang, X.; Yang, X.

    2010-05-18

    We demonstrate that an intense single-cycle terahertz (THz) pulse can act as a time lens to phase modulate and compress a copropagating ultrashort laser pulse. By using the THz-induced phase modulation as a time lens and a glass plate as a group velocity dispersive element, we have compressed an unchirped {approx}165 fs laser pulse to {approx}45 fs.

  20. Electro-optic time lensing with an intense single-cycle terahertz pulse

    SciTech Connect

    Shen Yuzhen; Carr, G. L.; Murphy, James B.; Wang Xijie; Yang Xi; Tsang, Thomas Y.

    2010-05-15

    We demonstrate that an intense single-cycle terahertz (THz) pulse can act as a time lens to phase modulate and compress a copropagating ultrashort laser pulse. By using the THz-induced phase modulation as a time lens and a glass plate as a group velocity dispersive element, we have compressed an unchirped {approx} 165 fs laser pulse to {approx} 45 fs.

  1. Contrast improvement of terahertz images of thin histopathologic sections

    PubMed Central

    Formanek, Florian; Brun, Marc-Aurle; Yasuda, Akio

    2011-01-01

    We present terahertz images of 10 ?m thick histopathologic sections obtained in reflection geometry with a time-domain spectrometer, and demonstrate improved contrast for sections measured in paraffin with water. Automated segmentation is applied to the complex refractive index data to generate clustered terahertz images distinguishing cancer from healthy tissues. The degree of classification of pixels is then evaluated using registered visible microscope images. Principal component analysis and propagation simulations are employed to investigate the origin and the gain of image contrast. PMID:21326635

  2. Probe beam-free detection of terahertz wave by electroluminescence induced by intense THz pulse

    NASA Astrophysics Data System (ADS)

    Shin, J.; Jin, Z.; Nosaka, Y.; Nakazawa, T.; Kodama, R.

    2016-03-01

    Recently, a table-top fs laser system can generate MW terahertz (THz) pulse with its electric field higher than 100 kV/cm can be generated by several schemes. Such a strong THz field can directly drive electrons inside various materials. Here, we demonstrated a direct THz electric field detection method by measuring the electroluminescence induced by intense THz pulse inside commonly available light emitting diode. An intense THz wave obtained by the two-color laser scheme was focused onto LED along with an external DC bias to induce luminescence which we found proportional to the amplitude of the incident THz field. The scheme can be useful to realize a low-cost, probe-free THz detection and imaging system.

  3. Effect of spherical aberration and surface waves on propagation of lens-coupled terahertz pulses

    NASA Astrophysics Data System (ADS)

    Reiten, M. T.; Cheville, R. A.

    2005-03-01

    Spatiotemporal measurements of a near-single-cycle terahertz pulse emitted from a photoconductive switch terahertz (THz) source show the effects of spherical aberration and surface waves on the pulse shape. The measured phase front has a swallow-tail shape described by catastrophe theory that contributes to the concentric ring structure of THz beam profiles. A time-of-flight model shows that the pulse shape is due to propagation along a cusp caustic and enhancement of the wings of the swallow-tail pulse is caused by surface waves.

  4. Terahertz imaging and spectroscopy for landmine detection

    NASA Astrophysics Data System (ADS)

    Fitch, Michael J.; Schauki, Dunja; Kelly, Craig A.; Osiander, Robert

    2004-04-01

    Pulsed THz (100 GHz - 30 THz) Imaging Spectroscopy combines three ways of mine detection in one system, high resolution radar, depth ranging, and infrared spectroscopy. It allows minefield detection, single mine imaging, and near-zero false alarm due to the capabilities of explosives / plastic identification using spectroscopy with working distances to 1000 feet. We have previously demonstrated imaging capabilities with 1 mm spatial resolution on a rubber O-ring embedded in sand. The estimated transmission depth in moist sand is 1 to 3 cm, which should be sufficient for imaging anti-personnel mines. In this work, we present initial results investigating the feasibility of THz spectroscopy in the frequency range from 1 to 10 THz to detect and identify explosives and related compounds (ERCs). A major component of this effort is chemical modeling to obtain spectroscopic information on ERCs and environmental background. A time-domain THz system using femtosecond laser pulses is also being developed.

  5. Real-time terahertz imaging for art conservation science

    NASA Astrophysics Data System (ADS)

    Fukunaga, K.; Sekine, N.; Hosako, I.; Oda, N.; Yoneyama, H.; Sudou, T.

    2008-08-01

    A new real-time terahertz imaging system has been developed by using a quantum cascade laser source and a microbolometer focal plane detector array. The application to non-invasive analyses of cultural heritage is demonstrated with an oil paint specimen. The experimental results suggested that the terahertz imaging system can identify materials based on a spectral database with a spatial resolution of about 300 μm. The transmission imaging indicated the difference between natural and artificial ultramarine pigments. Since the size of the system is similar to a common portable infrared camera, it can be used at the place where the object is located, such as museums, and can contribute to conservation activities, such as drying process monitoring. This real-time, small, non-invasive terahertz imaging system can be used in various fundamental research fields and practical industries.

  6. High-Contrast Imaging of Graphene via Time-Domain Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Tomaino, J. L.; Jameson, A. D.; Paul, M. J.; Kevek, J. W.; van der Zande, A. M.; Barton, R. A.; Choi, H.; McEuen, P. L.; Minot, E. D.; Lee, Yun-Shik

    2012-08-01

    We demonstrate terahertz (THz) imaging and spectroscopy of single-layer graphene deposited on an intrinsic Si substrate using THz time-domain spectroscopy. A single-cycle THz pulse undergoes multiple internal reflections within the Si substrate, and the THz absorption by the graphene layer accumulates through the multiple interactions with the graphene/Si interface. We exploit the large absorption of the multiply reflected THz pulses to acquire high-contrast THz images of graphene. We obtain local sheet conductivity of the graphene layer analyzing the transmission data with thin-film Fresnel formula based on the Drude model.

  7. Characterization of photoconducting materials using variable-length picosecond terahertz pulses

    NASA Astrophysics Data System (ADS)

    Cole, Bryan E.; Hegmann, Frank A.; Williams, Jon B.; Sherwin, Mark S.; Beeman, Jeffrey W.; Haller, Eugene E.

    1999-04-01

    A source of high-intensity, ultra-short terahertz pulses has been developed. The operation and performance of a terahertz pulse-slicing system for use with the UCSB free-electron lasers are discussed. Short pulses are sliced from the microsecond long output of the free-electron laser using laser-activated semiconductor switches; the pulse length may be freely varied from a few picoseconds up to four nanoseconds. The temporal response of a heavily compensated gallium-doped germanium photoconductor has been investigated. At low excitation intensity, a recombination time of 2 +/- 0.1 ns is found. At higher THz pulse powers non-exponential relaxation is observed; the data is well modeled using a rate equation approach and including impact- ionization impact-ionization effects due to the terahertz- heated free holes.

  8. Detection and identification of illicit drugs using terahertz imaging

    NASA Astrophysics Data System (ADS)

    Lu, Meihong; Shen, Jingling; Li, Ning; Zhang, Yan; Zhang, Cunlin; Liang, Laishun; Xu, Xiaoyu

    2006-11-01

    We demonstrated an advanced terahertz imaging technique for detection and identification of illicit drugs by introducing the component spatial pattern analysis. As an explanation, the characteristic fingerprint spectra and refractive index of ketamine were first measured with terahertz time-domain spectroscopy both in the air and nitrogen. The results obtained in the ambient air indicated that some absorption peaks are not obvious or probably not dependable. It is necessary and important to present a more practical technique for the detection. The spatial distributions of several illicit drugs [3,4-methylenedioxymethamphetamine, methylenedioxyamphetamine, heroin, acetylcodeine, morphine, and ketamine], widely consumed in the world, were obtained from terahertz images using absorption spectra previously measured in the range from 0.2to2.6THz in the ambient air. The different kinds of pure illicit drugs hidden in mail envelopes were inspected and identified. It could be an effective method in the field of safety inspection.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    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.

  12. 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

  13. Efficient Cherenkov emission of broadband terahertz radiation from an ultrashort laser pulse in a sandwich structure with nonlinear core

    SciTech Connect

    Bodrov, S. B.; Bakunov, M. I.; Hangyo, M.

    2008-11-01

    A scheme for efficient generation of broadband terahertz radiation by a femtosecond laser pulse propagating in a planar sandwichlike structure is proposed. The structure consists of a thin nonlinear core cladded with prisms made of a material with low terahertz absorption. The focused into a line laser pulse propagates in the core as a leaky or waveguide mode and emits Cherenkov wedge of terahertz waves in the cladding. We developed a theory that describes terahertz generation in such a structure and calculated spatial distribution of the generated terahertz field, its energy spectrum and optical-to-terahertz conversion efficiency. The developed theory predicts the conversion efficiency of up to several percent in a 1 cm long and 1 cm wide Si-LiNbO{sub 3}-Si sandwich structure with a 20 {mu}m thick nonlinear layer pumped by 8.5 {mu}J Ti:sapphire laser with pulse duration of 100 fs.

  14. Application of image processing for terahertz time domain spectroscopy imaging quantitative detection

    NASA Astrophysics Data System (ADS)

    Li, Li-juan; Wang, Sheng; Ren, Jiao-jiao; Zhou, Ming-xing; Zhao, Duo

    2015-03-01

    According to nondestructive testing principle for the terahertz time domain spectroscopy Imaging, using digital image processing techniques, through Terahertz time-domain spectroscopy system collected images and two-dimensional datas and using a range of processing methods, including selecting regions of interest, contrast enhancement, edge detection, and defects being detected. In the paper, Matlab programming is been use to defect recognition of Terahertz, by figuring out the pixels to determine defects defect area and border length, roundness, diameter size. Through the experiment of the qualitative analysis and quantitative calculation of Matlab image processing, this method of detection of defects of geometric dimension of the sample to get a better result.

  15. Tunable, high peak power terahertz radiation from optical rectification of a short modulated laser pulse.

    PubMed

    Gordon, Daniel F; Ting, Antonio; Alexeev, Ilya; Fischer, Richard; Sprangle, Phillip; Kapetenakos, Christos A; Zigler, Arie

    2006-07-24

    A new way of generating high peak power terahertz radiation using ultra-short pulse lasers is demonstrated. The optical pulse from a titanium:sapphire laser system is stretched and modulated using a spatial filtering technique to produce a several picosecond long pulse modulated at the terahertz frequency. A collinear type II phase matched interaction is realized via angle tuning in a gallium selenide crystal. Peak powers of at least 1.5 kW are produced in a 5 mm thick crystal, and tunability is demonstrated between 0.7 and 2.0 THz. Simulations predict that 150 kW of peak power can be produced in a 5 mm thick crystal. The technique also allows for control of the terahertz bandwidth. PMID:19516863

  16. 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.

  17. Terahertz and multispectral imaging of a Tanda painting

    NASA Astrophysics Data System (ADS)

    Jackson, J. Bianca; Melis, Marcello; Walker, Gillian; Giovannacci, David; Miccoli, Matteo; Martos-Levif, Dominique; Bowen, John; Detalle, Vincent

    2015-06-01

    We systematically examined the mid-20th century Italian painting "After Fishing" (fig. 1) by Ausonio Tanda using multi-spectral (UV, RGB visible, tri-band IR), x-ray and terahertz time-domain spectroscopic imaging. THz-TDSI was performed in both transmission and reflection geometries and the results were compared.

  18. Applications of terahertz spectral imaging-diagnostics in dentistry

    NASA Astrophysics Data System (ADS)

    Zinov'ev, N. N.; Nikoghosyan, A. S.; Chamberlain, J. M.

    2006-03-01

    We present a review on terahertz diagnostics in dentistry. Time domain and spectral domain imaging studies are compared. Imaging built on mapping time-domain dependencies delivers the information on mechanisms of light transport in tissue: ballistic, quasi-ballistic and diffusive photon transfer. Imaging utilizing transform in frequency-domain provides a wealth of data on specific characterization of object: spectral and chemical content, tissue structure and composition and various kind of tissue abnormalities.

  19. Terahertz wave two-dimensional transmission imaging with a backward wave oscillator

    NASA Astrophysics Data System (ADS)

    Yuan, Hongyang; Ge, Xinhao; Zhang, Cunlin

    2008-12-01

    We present a terahertz (THz) imaging system with a Backward Wave Oscillator (BWO). BWO Continuous-Wave THz imaging is a new approach to non-destructive testing. Many materials that are opaque to visible and infrared light are transparent to THz radiation. THz wave image provides a higher spatial resolution than microwave image by having much shorter wavelength. It also poses no known harm to living organisms, making it a safe and powerful imaging technology. Unlike pulsed THz imaging, BWO THz imaging only yields intensity data without providing any depth, frequency-domain or time-domain information about the subject. However, in most cases the energy plots are sufficient for identification of targets. In exchange for the loss of depth, time-domain and frequency-domain information, BWO imaging offers a simple, fast and relatively low-cost system. In this work we show a simple Terahertz (THz) 2-dimentional scanning imaging system utilizing a BWO source tunable from 0.52 to 0.71 THz and a pyroelectric sensor detector operated in THz range. The sample is placed on an X-Z two-dimensional stage controlled by a computer. The intensity information of the terahertz wave after passing sample is collected. Two-dimensional image of the sample is obtained by raster scanning the sample in X and Z directions. A number of potential imaging applications are demonstrated using the 0.71 THz radiation, including nondestructive real-time testing for campus debit card and various articles contained in an envelop. And we present the digital image processing based on the result of the imaging system. This work reveals that a BWO THz imaging system is very practical, effective and promising in nondestructive identification and security inspections applications in future.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  1. A hybrid continuous-wave terahertz imaging system

    SciTech Connect

    Dolganova, Irina N. Zaytsev, Kirill I. Metelkina, Anna A.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

    2015-11-15

    A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc.

  2. A hybrid continuous-wave terahertz imaging system

    NASA Astrophysics Data System (ADS)

    Dolganova, Irina N.; Zaytsev, Kirill I.; Metelkina, Anna A.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

    2015-11-01

    A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc.

  3. A hybrid continuous-wave terahertz imaging system.

    PubMed

    Dolganova, Irina N; Zaytsev, Kirill I; Metelkina, Anna A; Karasik, Valeriy E; Yurchenko, Stanislav O

    2015-11-01

    A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc. PMID:26628141

  4. Quantum theory of terahertz emission due to ultrashort pulse ionization of gases

    NASA Astrophysics Data System (ADS)

    Schuh, K.; Scheller, M.; Hader, J.; Moloney, J. V.; Koch, S. W.

    2013-12-01

    A microscopic model is developed to analyze terahertz (THz) emission after ultrashort one- and two-color laser-pulse excitations of an atomic gas. Optical Bloch equations are derived to describe the pulse-induced ionization in the many-atom system including the Coulombic scattering of the ionized electrons. The model captures the continuous transition between the tunneling and the multiphoton ionization regimes. Numerical evaluations for a wide range of pulse configurations identify optimized excitation conditions for strong THz emission.

  5. Efficient flat metasurface lens for terahertz imaging.

    PubMed

    Yang, Quanlong; Gu, Jianqiang; Wang, Dongyang; Zhang, Xueqian; Tian, Zhen; Ouyang, Chunmei; Singh, Ranjan; Han, Jiaguang; Zhang, Weili

    2014-10-20

    Metamaterials offer exciting opportunities that enable precise control of amplitude, polarization and phase of the light beam at a subwavelength scale. A gradient metasurface consists of a class of anisotropic subwavelength metamaterial resonators that offer abrupt amplitude and phase changes, thus enabling new applications in optical device design such as ultrathin flat lenses. We propose a highly efficient gradient metasurface lens based on a metal-dielectric-metal structure that operates in the terahertz regime. The proposed structure consists of slotted metallic resonator arrays on two sides of a thin dielectric spacer. By varying the geometrical parameters, the metasurface lens efficiently manipulates the spatial distribution of the terahertz field and focuses the beam to a spot size on the order of a wavelength. The proposed flat metasurface lens design is polarization insensitive and works efficiently even at wide angles of incidence. PMID:25401626

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

    SciTech Connect

    Shalaby, Mostafa E-mail: christoph.hauri@psi.ch; Hauri, Christoph P. E-mail: christoph.hauri@psi.ch

    2015-05-04

    We report on the measurement of the instantaneous Kerr nonlinearity and the retarded alignment of air molecules CO{sub 2}, N{sub 2}, and O{sub 2} 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.

  7. Simultaneous determination of thickness and refractive index based on time-of-flight measurements of terahertz pulse.

    PubMed

    Hussain, Babar; Ahmed, Mushtaq; Nawaz, M; Saleem, M; Razzaq, M; Aslam Zia, M; Iqbal, M

    2012-07-20

    We present a simple technique for simultaneous determination of thickness and refractive index of plane-parallel samples in the terahertz radiation domain. The technique uses time-of-flight measurements of the terahertz pulse. It has been employed on nine different polymers and semiconductor materials, which are transparent for terahertz frequencies. Our results of thickness measurement are in good agreement with micrometer reading. The accuracy in the determination of refractive index is on the order of two decimal points. PMID:22858978

  8. Terahertz compressive imaging with metamaterial spatial light modulators

    NASA Astrophysics Data System (ADS)

    Watts, Claire M.; Shrekenhamer, David; Montoya, John; Lipworth, Guy; Hunt, John; Sleasman, Timothy; Krishna, Sanjay; Smith, David R.; Padilla, Willie J.

    2014-08-01

    Imaging at long wavelengths, for example at terahertz and millimetre-wave frequencies, is a highly sought-after goal of researchers because of the great potential for applications ranging from security screening and skin cancer detection to all-weather navigation and biodetection. Here, we design, fabricate and demonstrate active metamaterials that function as real-time tunable, spectrally sensitive spatial masks for terahertz imaging with only a single-pixel detector. A modulation technique permits imaging with negative mask values, which is typically difficult to achieve with intensity-based components. We demonstrate compressive techniques allowing the acquisition of high-frame-rate, high-fidelity images. Our system is all solid-state with no moving parts, yields improved signal-to-noise ratios over standard raster-scanning techniques, and uses a source orders of magnitude lower in power than conventional set-ups. The demonstrated imaging system establishes a new path for terahertz imaging that is distinct from existing focal-plane-array-based cameras.

  9. Nondestructive Evaluation of Aircraft Composites Using Dielectric Properties and Imaging in the Terahertz Spectrum

    NASA Astrophysics Data System (ADS)

    Stoik, C. D.; Bohn, M. J.; Blackshire, J. L.

    2009-03-01

    Terahertz imaging and dielectric property measurements were assessed as nondestructive evaluation techniques for damage to aircraft glass fiber composites. Samples with localized heat damage showed a minimal change in refractive index or absorption coefficient; however, material blistering was detected. Voids were located by terahertz imaging using amplitude and phase techniques. Delamination depths were approximated by measuring the timing of Fabry-Perot reflections. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging.

  10. Plasmon-enhanced terahertz emission in self-assembled quantum dots by femtosecond pulses

    SciTech Connect

    Carreño, F. Antón, M. A. Melle, Sonia Calderón, Oscar G. Cabrera-Granado, E.; Egatz-Gómez, A.

    2014-02-14

    A scheme for terahertz (THz) generation from intraband transition in a self-assembled quantum dot (QD) molecule coupled to a metallic nanoparticle (MNP) is analyzed. The QD structure is described as a three-level atom-like system using the density matrix formalism. The MNP with spherical geometry is considered in the quasistatic approximation. A femtosecond laser pulse creates a coherent superposition of two subbands in the quantum dots and produces localized surface plasmons in the nanoparticle which act back upon the QD molecule via dipole-dipole interaction. As a result, coherent THz radiation with a frequency corresponding to the interlevel spacing can be obtained, which is strongly modified by the presence of the MNP. The peak value of the terahertz signal is analyzed as a function of nanoparticle's size, the MNP to QD distance, and the area of the applied laser field. In addition, we theoretically demonstrate that the terahertz pulse generation can be effectively controlled by making use of a train of femtosecond laser pulses. We show that by a proper choice of the parameters characterizing the pulse train a huge enhancement of the terahertz signal is obtained.

  11. 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.

  12. Point Spread Function Estimation for a Terahertz Imaging System

    NASA Astrophysics Data System (ADS)

    Popescu, Dan C.; Hellicar, Andrew D.

    2010-12-01

    We present a method for estimating the point spread function of a terahertz imaging system designed to operate in reflection mode. The method is based on imaging phantoms with known geometry, which have patterns with sharp edges at all orientations. The point spread functions are obtained by a deconvolution technique in the Fourier domain. We validate our results by using the estimated point spread functions to deblur several images of natural scenes and by direct comparison with a point source response. The estimations turn out to be robust and produce consistent deblurring quality over the entire depth of the focal region of the imaging system.

  13. On the role of terahertz field acceleration and beaming of surface plasmon generated ultrashort electron pulses

    SciTech Connect

    Greig, S. R. Elezzabi, A. Y.

    2014-07-28

    A mechanism for control of the energy and pitch angle of surface plasmon accelerated electron pulses is proposed. Electrons generated via multi-photon absorption in a silver film on a glass prism are ponderomotively accelerated in the surface plasmon field excited by a 30 fs, 800 nm optical pulse. Through introduction of a single-cycle terahertz (THz) pulse, the energy spectrum and trajectory of the generated electron pulse can be controlled via the THz field strength. Generated electron pulses achieve peak kinetic energies up to 1.56 keV, while utilizing an incident optical field strength five times less than comparable plasmon accelerated electron pulses. These results demonstrate that THz pulses can be utilized to achieve tunable, high energy, trajectory controlled electron pulses necessary for various applications that require ultrafast electron pulse manipulation.

  14. 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 μm excitation based on an InGaAs heterostructure Nanotechnology 24 214007 [4] Chen H-T, Padilla W J, Zide J M O, Gossard A C, Taylor A J and Averitt R D 2006 Active terahertz metamaterial devices Nature 444 597-600 [5] Hans H 1991 Microwave technology in the terahertz region Brand Conf. Proc.—European Microwave Conf. vol 1, pp 16-35 [6]Joyce H J, Docherty C J, Gao Q, Tan H H, Jagadish C, Lloyd-Hughes J, Herz L M and Johnston M B 2013 Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy Nanotechnology 24 214006 [7] Knap W, Rumyantsev S, Vitiello M S, Coquillat D, Blin S, Dyakonova N, Shur M, Teppe F, Tredicucci A and Nagatsuma T 2013 Nanometer size field effect transistors for terahertz detectors Nanotechnology 24 214002 [8] Kawano Y 2013 Wide-band frequency-tunable terahertz and infrared detection with graphene Nanotechnology 24 214004 [9]Romeo L, Coquillat D, Pea M, Ercolani D, Beltram F, Sorba L, Knap W, Tredicucci A and Vitiello M S 2013 Nanowire-based field effect transistors for terahertz detection and imaging systems Nanotechnology 24 214005 [10] Son J-H 2013 Principle and applications of terahertz molecular imaging Nanotechnology 24 214001 [11] Zhu Z, Yang X, Gu J, Jiang J, Yue W, Tian Z, Tonouchi M, Han J and Zhang W 2013 Broadband plasmon induced transparency in terahertz metamaterials Nanotechnology 24 214003 [12] Tonouchi M 2007 Cutting-edge terahertz technology Nature Photon. 1 97-105

  15. Study of freshly excised brain tissues using terahertz imaging

    PubMed Central

    Oh, Seung Jae; Kim, Sang-Hoon; Ji, Young Bin; Jeong, Kiyoung; Park, Yeonji; Yang, Jaemoon; Park, Dong Woo; Noh, Sam Kyu; Kang, Seok-Gu; Huh, Yong-Min; Son, Joo-Hiuk; Suh, Jin-Suck

    2014-01-01

    We demonstrated that tumors in freshly excised whole brain tissue could be differentiated clearly from normal brain tissue using a reflection-type terahertz (THz) imaging system. THz binary images of brain tissues with tumors indicated that the tumor boundaries in the THz images corresponded well to those in visible images. Grey and white-matter regions were distinguishable owing to the different distribution of myelin in the brain tissue. THz images corresponded closely with magnetic resonance imaging (MRI) results. The MRI and hematoxylin and eosin-stained microscopic images were investigated to account for the intensity differences in the THz images for fresh and paraffin-embedded brain tissue. Our results indicated that the THz signals corresponded to the cell density when water was removed. Thus, THz imaging could be used as a tool for label-free and real-time imaging of brain tumors, which would be helpful for physicians to determine tumor margins during brain surgery. PMID:25136506

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

    SciTech Connect

    Sajadi, Mohsen Wolf, Martin; Kampfrath, Tobias

    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.

  17. INTERFEROMETRIC IMAGING WITH TERAHERTZ PULSES. (R827122)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  18. Terahertz waves emitted from an optical fiber.

    PubMed

    Yi, Minwoo; Lee, Kanghee; Lim, Jongseok; Hong, Youngbin; Jho, Young-Dahl; Ahn, Jaewook

    2010-06-21

    We report a simple method of creating terahertz waves by applying the photo-Dember effect in a (100)-oriented InAs film coated onto the 45-degree wedged-end facet of an optical fiber. The terahertz waves are generated by infrared pulses guided through the optical fiber which is nearly in contact with a sample and then measured by a conventional photo-conductive antenna detector. Using this alignment-free terahertz source, we performed proof-of-principle experiments of terahertz time-domain spectroscopy and near-field terahertz microscopy. We obtained a bandwidth of 2 THz and 180-microm spatial resolution. Using this method, the THz imaging resolution is expected to be reduced to the size of the optical fiber core. Applications of this device can be extended to sub-wavelength terahertz spectroscopic imaging, miniaturized terahertz system design, and remote sensing. PMID:20588503

  19. Near-field imaging with tetrahertz pulses

    NASA Astrophysics Data System (ADS)

    Mitrofanov, Oleg

    2001-11-01

    High spatial resolution imaging is implemented with a novel collection mode near-field terahertz (THz) probe. Exceptional sensitivity of the probe allows imaging with spatial resolution of few microns using THz pulses with spectral content of 120 to 1500 microns. In the present study, the principle of the probe operation as well as the probe design and characteristics are described. The probe performance is related to effective detection of radiation coupled into the probe aperture. Propagation of short single-cycle electromagnetic pulses through apertures as small as 1/300 of the wavelength is experimentally and numerically studied. Finite-difference time-domain method is used to model propagation of THz pulses through the probe aperture in order to optimize the probe design. It is shown that the probe sensitivity is significantly improved if the detecting antenna measures electric field coupled through the aperture in the near-field zone rather than in the far-field zone. Effects of temporal and spectral pulse shaping are described by frequency-dependent transmission at the near- or below cutoff regimes of the aperture. Imaging schemes, properties, and artifacts are considered. The technique provides the best to date spatial resolution capabilities in the THz range of the electromagnetic spectrum.

  20. Detection and segmentation of concealed objects in terahertz images.

    PubMed

    Shen, Xilin; Dietlein, Charles R; Grossman, Erich; Popovic, Zoya; Meyer, Franois G

    2008-12-01

    Terahertz imaging makes it possible to acquire images of objects concealed underneath clothing by measuring the radiometric temperatures of different objects on a human subject. The goal of this work is to automatically detect and segment concealed objects in broadband 0.1-1 THz images. Due to the inherent physical properties of passive terahertz imaging and associated hardware, images have poor contrast and low signal to noise ratio. Standard segmentation algorithms are unable to segment or detect concealed objects. Our approach relies on two stages. First, we remove the noise from the image using the anisotropic diffusion algorithm. We then detect the boundaries of the concealed objects. We use a mixture of Gaussian densities to model the distribution of the temperature inside the image. We then evolve curves along the isocontours of the image to identify the concealed objects. We have compared our approach with two state-of-the-art segmentation methods. Both methods fail to identify the concealed objects, while our method accurately detected the objects. In addition, our approach was more accurate than a state-of-the-art supervised image segmentation algorithm that required that the concealed objects be already identified. Our approach is completely unsupervised and could work in real-time on dedicated hardware. PMID:19004716

  1. High-speed time domain terahertz security imaging

    NASA Astrophysics Data System (ADS)

    Zimdars, David; White, Jeffrey; Williamson, Steven; Stuk, G.

    2005-05-01

    Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Time domain terahertz imaging can be employed in reflection mode to image with sub millimeter resolution. Previously, single pixel acquisition times for THz waveforms was typically 20 Hz with time records of approx 80 picoseconds, which typically restricted imaging time to hours for areas on the order of 1 square foot, limiting the field practicality of the equipment. We describe and demonstrate advanced imagers with 100 Hz --> 320 picosecond, and 4000 Hz -- 20 picosecond waveform records. These systems have been demonstrated to image >600 pixels/second from a single channel. Such a system, combined with a 32 channel linear THz array, could image a 1 square foot area with 1 mm resolution in <5 seconds, performing a shoe explosives detection image in a short period of time.

  2. Terahertz quasi-near-field real-time imaging

    NASA Astrophysics Data System (ADS)

    Wang, Xinke; Cui, Ye; Hu, Dan; Sun, Wenfeng; Ye, JiaSheng; Zhang, Yan

    2009-12-01

    A terahertz (THz) quasi-near-field real-time imaging system is presented. Not only the consumption of experimental time is dramatically reduced, but also the resolution of the imaging system is improved to the magnitude of sub-wavelength of THz waves. THz images of a razor blade edge are obtained and the spatial resolution of the imaging system is discussed in detail. For checking the imaging capability of this system, three metallic plates with different sub-wavelength air hole arrays are imaged and the microstructure of these samples can be clearly observed in their THz images. It is believed that the THz quasi-near-field real-time imaging system should have tremendous applications in the THz microscopic field.

  3. The potential of terahertz imaging for cancer diagnosis: A review of investigations to date

    PubMed Central

    Yu, Calvin; Fan, Shuting; Sun, Yiwen; Pickwell-MacPherson, Emma

    2012-01-01

    The terahertz region lies between the microwave and infrared regions of the electromagnetic spectrum such that it is strongly attenuated by water and very sensitive to water content. Terahertz radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. Because of these characteristic properties, there has been an increasing interest in terahertz imaging and spectroscopy for biological applications within the last few years and more and more terahertz spectra are being reported, including spectroscopic studies of cancer. The presence of cancer often causes increased blood supply to affected tissues and a local increase in tissue water content may be observed: this acts as a natural contrast mechanism for terahertz imaging of cancer. Furthermore the structural changes that occur in affected tissues have also been shown to contribute to terahertz image contrast. This paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques. In particular investigations relating to the potential of terahertz imaging and spectroscopy for cancer diagnosis will be highlighted. PMID:23256057

  4. Target recognition in passive terahertz image of human body

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  5. 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

  6. Intense terahertz emission from relativistic circularly polarized laser pulses interaction with overdense plasmas

    SciTech Connect

    Chen, Zi-Yu; Li, Xiao-Ya; Yu, Wei

    2013-10-15

    During the interaction of a relativistic circularly polarized laser pulse with an overdense plasma target, the longitudinal motion of bunches of electrons under the action of light pressure and electrostatic restore force can emit intense terahertz (THz) pulses. This mechanism allows high pump laser intensity and large electron number participating in the emission. Two-dimensional particle-in-cell simulations are carried out to investigate the THz emission. The results suggest that such a source can produce remarkably intense THz pulses with energy of several mJ/sr and power of tens of gigawatts, which could find applications in nonlinear studies and relativistic laser-plasma interaction diagnostics.

  7. Physical mechanisms of terahertz pulse emission from photoexcited surfaces of tellurium crystals

    SciTech Connect

    Bičiūnas, A.; Arlauskas, A.; Adamonis, J.; Cicėnas, P.; Krotkus, A.

    2014-09-07

    We report on terahertz (THz) emission from tellurium crystal surfaces excited by femtosecond optical pulses. Measurements were performed on three differently cut Te samples and with different wavelength optical excitation pulses. THz pulse amplitude dependences on the azimuthal angle measured at various excitation wavelengths have evidenced that three different mechanisms are responsible for THz generation in tellurium: second order nonlinear optical rectification effect, dominating at lower excitation photon energies, as well as transverse and ordinary photo-Dember effects, which emerge at energies larger than 0.9 eV. The shapes of the azimuthal angle dependences were also explained by theoretical model.

  8. Continuous wave terahertz reflection imaging of human colorectal tissue

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    Continuous wave terahertz (THz) imaging has the potential to offer a safe, non-ionizing, and nondestructive medical imaging modality for delineating colorectal cancer. Fresh excisions of normal colon tissue were obtained from surgeries performed at the University of Massachusetts Medical School, Worcester. Reflection measurements of thick sections of colorectal tissues, mounted in an aluminum sample holder, were obtained for both fresh and formalin fixed tissues. The two-dimensional reflection images were acquired by using an optically pumped far-infrared molecular gas laser operating at 584 GHz with liquid Helium cooled silicon bolometer detector. Using polarizers in the experiment both co-polarized and cross-polarized remittance form the samples was collected. Analysis of the images showed the importance of understanding the effects of formalin fixation while determining reflectance level of tissue response. The resulting co- and cross-polarized images of both normal and formalin fixed tissues showed uniform terahertz response over the entire sample area. Initial measurements indicated a co-polarized reflectance of 16%, and a cross-polarized reflectance of 0.55% from fresh excisions of normal colonic tissues.

  9. Single attosecond pulse from terahertz-assisted high-order harmonic generation

    SciTech Connect

    Balogh, Emeric; Kovacs, Katalin; Dombi, Peter; Farkas, Gyozo; Fulop, Jozsef A.; Hebling, Janos; Tosa, Valer; Varju, Katalin

    2011-08-15

    High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.

  10. To realize the optimal probe pulse length for detection of pulsed terahertz signal with spectral-encoding technique

    NASA Astrophysics Data System (ADS)

    Peng, Xiao-Yu; Zhang, Xin-Hai; Teng, Jing-Hua; Guo, Hong-Cheng; Foo, Yong-Lim

    2011-06-01

    The approach to realize the optimal chirped probe pulse length for an arbitrary pulsed terahertz (THz) signal measured with the spectral-encoding technique was investigated by simulation. It was found that either the maximum positive peak or the absolute value of the strongest negative peak of the normalized difference between the probe spectrum modulated by THz signal and the background probe spectrum tended to be maximized when the probe pulse duration approached to the optimal value. The probe pulse length can be adjusted continuously with a pair of triangular dispersive prisms. THz signals from high-voltage biased air plasmas induced by femtosecond laser pulse were measured with minimum distortion using our simple method.

  11. Single Circularly Polarized Attosecond Pulse Generation by Intense Few Cycle Elliptically Polarized Laser Pulses and Terahertz Fields from Molecular Media

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2013-01-01

    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 (λ=4800nm) field at an intensity of ˜1014W/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 ɛ=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.

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

    SciTech Connect

    Zabolotskii, A. A.

    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.

  13. Measurement of coherent terahertz radiation for time-domain spectroscopy and imaging

    NASA Astrophysics Data System (ADS)

    Kuroda, R.; Yasumoto, M.; Sei, N.; Toyokawa, H.; Ikeura-Sekiguchi, H.; Ogawa, H.; Koike, M.; Yamada, K.

    2009-12-01

    A high-power terahertz (THz) source for THz time-domain spectroscopy (THz-TDS) and THz imaging has been developed based on an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). A THz pulse was generated as coherent synchrotron radiation (CSR) from an ultra-short electron bunch and expected to have peak power of kW-order with frequency range of 0.1-2 THz. The electro-optic (EO) sampling method with a ZnTe crystal for the THz pulse measurement has been prepared for THz-TDS system. The timing measurement between the THz pulse and a probe laser was carried out. A preliminary experiment of THz transmission imaging of an integrated circuit (IC) card has been successfully demonstrated using the THz CSR pulse and a W-band rf detector. The imaging result was experimentally compared with a result of X-ray imaging. It is confirmed that its intensity and stability are enough to perform for the THz applications.

  14. Model-based, one-sided, time-of-flight terahertz image reconstruction

    NASA Astrophysics Data System (ADS)

    Schmitt, Stephen M.; Fessler, Jeffrey A.; Fichter, Greg D.; Zimdars, David A.

    2013-03-01

    In the last decade, terahertz-mode imaging has received increased attention for non-destructive testing applica- tions due to its ability to penetrate many materials while maintaining a small wavelength. This paper describes a model-based reconstruction algorithm that is able to image defects in the spray-on foam insulation (SOFI) used in aerospace applications that has been sprayed on a re ective metal hull. In this situation, X-ray based imaging is infeasible since only one side of the hull is accessible in ight. This paper models the object as a grid of materials, each section of which has a constant index of refraction. The delay between the transmission and reception of a THz pulse is related to the integral of the index of refraction along the pulse's path, and we adapt computed tomography (CT) methods to reconstruct an image of an object's index of refraction. We present the results of our reconstruction method using real data of the timing of THz pulses passing through a block of SOFI with holes of a known location and radius. The resulting image of the block has a low level of noise, but contains artifacts due to the limited angular range of one-sided imaging and due to the narrow beam approximation used in the forward model.

  15. Time Domain Terahertz (T-Ray) Subsurface and Structural Imaging

    NASA Astrophysics Data System (ADS)

    Zimdars, David; White, Jeffrey S.; Stuk, G.; Chernovsky, A.; Fichter, G.; Sucha, G.; Williamson, S.

    2007-03-01

    The technology, methods, and examples of high speed time domain terahertz (T-Ray) imaging non-destructive examination (NDE) for 2 and 3 dimensional structural and material content characterization are discussed. T-Ray imaging can be utilized for non-contact transmission and/or monostatic reflection inspection of non-conductive materials such as plastics, foam, composites, ceramics, paper, wood and glass. Example subsurface homeland security images of concealed items in baggage and on personnel are shown. We tabulate attenuation and penetration characteristics through a selection of building materials, and demonstrate the ability of T-ray instrumentation to sub-surface image building structures such as wall framing and interior wiring and conduits.

  16. Diagnose human colonic tissues by terahertz near-field imaging

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Ma, Shihua; Wu, Xiumei; Yang, Wenxing; Zhao, Tian

    2015-03-01

    Based on a terahertz (THz) pipe-based near-field imaging system, we demonstrate the capability of THz imaging to diagnose freshly surgically excised human colonic tissues. Through THz near-field scanning the absorbance of the colonic tissues, the acquired images can clearly distinguish cancerous tissues from healthy tissues fast and automatically without pathological hematoxylin and eosin stain diagnosis. A statistical study on 58 specimens (20 healthy tissues and 38 tissues with tumor) from 31 patients (mean age: 59 years; range: 46 to 79 years) shows that the corresponding diagnostic sensitivity and specificity on colonic tissues are both 100%. Due to its capability to perform quantitative analysis, our study indicates the potential of the THz pipe-based near-field imaging for future automation on human tumor pathological examinations.

  17. InP Double Heterojunction Bipolar Transistor for broadband terahertz detection and imaging systems

    NASA Astrophysics Data System (ADS)

    Coquillat, D.; Nodjiadjim, V.; Konczykowska, A.; Dyakonova, N.; Consejo, C.; Ruffenach, S.; Teppe, F.; Riet, M.; Muraviev, A.; Gutin, A.; Shur, M.; Godin, J.; Knap, W.

    2015-10-01

    This paper presents terahertz detectors based on high performance 0.7-μm InP double heterojunction bipolar transistor (DHBT) technology and reports on the analysis of their voltage responsivity over a wide frequency range of the incoming terahertz radiation. The detectors operated without any spatial antennas to couple terahertz radiation to the device and have been characterized in the 0.25 - 3.1 THz range with the responsivities (normalized to 1 W radiant power) of 5 V/W and 200 μV/W measured at 0.35 THz and 3.11 THz, respectively. The InP DHBTs also performed as the imaging single-pixels at room temperature in the raster scanned transmission mode. A set of the sub-terahertz images of plant leaves suggest potential utility of InP DHBT detectors for terahertz imaging dedicated to non-invasive testing of plants.

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

    SciTech Connect

    Jahangiri, Fazel; Laser and Plasma Research Institute, Shahid Beheshti University, Tehran ; Hashida, Masaki; Tokita, Shigeki; Sakabe, Shuji; Department of Physics, GSS, Kyoto University, Kyoto ; Nagashima, Takeshi; Hangyo, Masanori; Institute of Laser Engineering, Osaka University, Osaka

    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.

  19. Single-shot spatiotemporal measurements of high-field terahertz pulses

    SciTech Connect

    van Tilborg, Jeroen; Schroeder, Carl; Toth, Csaba; Geddes, Cameron; Esarey, Eric; Leemans, Wim

    2011-06-17

    The electric field profiles of broad-bandwidth coherent terahertz (THz) pulses, emitted by laser-wakefield-accelerated electron bunches, are studied. The near-single-cycle THz pulses are measured with two single-shot techniques in the temporal and spatial domains. Spectra of 0-6 THz and peak fields up to {approx_equal} 0.4 MV cm{sup -1} are observed. The measured field substructure demonstrates the manifestation of spatiotemporal coupling at focus, which affects the interpretation of THz radiation as a bunch diagnostic and in high-field pump-probe experiments.

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

    SciTech Connect

    Schüler, Michael Berakdar, Jamal

    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.

  1. 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.

  2. Electronic response of graphene to an ultrashort intense terahertz radiation pulse

    NASA Astrophysics Data System (ADS)

    Ishikawa, Kenichi L.

    2013-05-01

    We have recently reported a study (Ishikawa 2010 Phys. Rev. B 82 201402) on a nonlinear optical response of graphene to a normally incident terahertz radiation pulse within the massless Dirac fermion (MDF) picture, where we have derived physically transparent graphene Bloch equations (GBE). Here we extend it to the tight-binding (TB) model and oblique incidence. The derived equations indicate that interband transitions are governed by the temporal variation of the spinor phase along the electron path in the momentum space and predominantly take place when the electron passes near the Dirac point. At normal incidence, the equations for electron dynamics within the TB model can be cast into the same form of GBE as for the MDF model. At oblique incidence, the equations automatically incorporate photon drag and satisfy the continuity equation for electron density. Single-electron dynamics strongly depend on the model and pulse parameters, but the rapid variations are averaged out after momentum-space integration. Direct current remaining after the pulse is generated in graphene irradiated by an intense monocycle terahertz pulse, even if it is linearly polarized and normally incident. The generated current depends on the carrier-envelope phase, pulse intensity and Fermi energy in a complex manner.

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

    SciTech Connect

    Daranciang, Dan; Goodfellow, John; Fuchs, Matthias; Wen, Haidan; Ghimire, Shambhu; Reis, David A.; Loos, Henrik; Fisher, Alan S.; 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.

  4. Single-cycle terahertz pulses with >0.2 V/A field amplitudes via coherent transition radiation

    SciTech Connect

    Daranciang, Dan; Goodfellow, John; Fuchs, Matthias; Ghimire, Shambhu; Wen, Haidan; Reis, David A.; Loos, Henrik; Fisher, Alan S.; Lindenberg, Aaron M.

    2011-10-03

    We demonstrate terahertz pulses with field amplitudes exceeding 0.2 V/A 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.

  5. Reflection type of terahertz imaging system using a high-T{sub c} superconducting oscillator

    SciTech Connect

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

    2014-01-13

    A reflection type of imaging system is shown at sub-terahertz frequencies generated from high-T{sub c} superconducting intrinsic Josephson junction mesa structures fabricated by single crystalline Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} to demonstrate how the sub-terahertz imaging technique using monochromatic radiation is powerful and unique for the variety of practical applications. Several examples are discussed in detail and are compared to other terahertz imaging systems.

  6. Chirp-free isolated attosecond pulse generation from an atom irradiated by a fundamental terahertz pulse synchronizing an infrared laser pulse.

    PubMed

    Jia, Cheng; Wang, Jun; Li, Qing-Yi; Guo, Fu-Ming; Chen, Ji-Gen; Zeng, Si-Liang; Yang, Yu-Jun

    2015-12-14

    We theoretically study high-order harmonic generation (HHG) and attosecond pulses from an atom irradiated synchronically by a terahertz (THz) pulse and an infrared laser pulse. For the HHG spectrum from the THz pulse alone and the combined pulse, an apparent peak-valley structure appears the platform region. Specially, for the periodic structure generated by an atom under the action of the combined pulse is originated from the interference between the electrons ionized at different instants in the laser field, which undergo many recollision and return to the core at the same time. Therefore, continuum harmonics with few chirps from the interference enhancement region can be achieved, which result in a chirp-free isolated attosecond pulse. PMID:26699012

  7. Intense terahertz-pulse generation by four-wave mixing process in induced gas plasma

    NASA Astrophysics Data System (ADS)

    Wicharn, S.; Buranasiri, P.

    2015-08-01

    In this article, we have numerically investigated an intense terahertz (THz) pulses generation in gaseous plasma based on the third-order nonlinear effect, four-wave mixing rectification (FWMR). We have proposed that the fundamental fields and second-harmonic field of ultra-short pulse lasers are combined and focused into a very small gas chamber to induce a gaseous plasma, which intense THz pulse is produced. To understand the THz generation process, the first-order multiple-scale perturbation method (MSPM) has been utilized to derive a set of nonlinear coupled-mode equations for interacting fields such as two fundamental fields, a second-harmonic field, and a THz field. Then, we have simulate the intense THz-pulse generation by using split step-beam propagation method (SS-BPM) and calculated output THz intensities. Finally, the output THz intensities generated from induced air, nitrogen, and argon plasma have been compared.

  8. Terahertz pulse detection by the GaAs Schottky diodes

    NASA Astrophysics Data System (ADS)

    Laperashvili, Tina; Kvitsiani, Orest; Imerlishvili, Ilia; Laperashvili, David

    2010-06-01

    We present the results of experimental studies of physical properties of the detection process of GaAs Schottky diodes for terahertz frequency radiation. The development of technology in the THz frequency band has a rapid progress recently. Considered as an extension of the microwave and millimeter wave bands, the THz frequency offers greater communication bandwidth than is available at microwave frequencies. The Schottky barrier contact has an important role in the operation of many GaAs devices. GaAs Schottky diodes have been the primary nonlinear device used in millimeter and sub millimeter wave detectors and receivers. GaAs Schottky diodes are especially interesting due to their high mobility transport characteristics, which allows for a large reduction of the resistance-capacitance (RC) time constant and thermal noise. In This work are investigated the electrical and photoelectric properties of GaAs Schottky diodes. Samples were obtained by deposition of different metals (Au, Ni, Pt, Pd, Fe, In, Ga, Al) on semiconductor. For fabrication metal-semiconductor (MS) structures is used original method of metal electrodepositing. In this method electrochemical etching of semiconductor surface occurs just before deposition of metal from the solution, which contains etching material and metal ions together. For that, semiconductor surface cleaning processes and metal deposition carries out in the same technological process. In the experiments as the electrolyte was used aqueous solution of chlorides. Metal deposition was carried out at room temperature.

  9. Exploration of Terahertz Imaging with Silicon MOSFETs

    NASA Astrophysics Data System (ADS)

    Lisauskas, Alvydas; Bauer, Maris; Boppel, Sebastian; Mundt, Martin; Khamaisi, Bassam; Socher, Eran; Venckevičius, Rimvydas; Minkevičius, 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- μW 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.

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

    PubMed

    Vinokurov, Nikolay A; Jeong, Young Uk

    2013-02-01

    We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the z axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the z axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the z axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device. PMID:23432259

  11. Terahertz imaging with Si MOSFET focal-plane arrays

    NASA Astrophysics Data System (ADS)

    Lisauskas, A.; Glaab, D.; Roskos, H. G.; Oejefors, E.; Pfeiffer, U. R.

    2009-02-01

    We report on imaging at terahertz frequencies using a 3x5 Si MOSFET focal-plane array (FPA) processed by a 0.25-?m CMOS technology. Each pixel of the FPA consists of a 645-GHz patch antenna coupled to a FET detector and a 43-dB voltage amplifier with a 1.6-MHz bandwidth. We achieve a typical single-pixel responsivity of 80 kV/W and a noise-equivalent power (NEP) of 300 pW/?Hz at 30-kHz. The performance data of these all-CMOS devices pave the way for the realization of broad-band THz detectors and FPAs for video-rate active imaging on the basis of established low-cost and integration-friendly CMOS technology.

  12. A waveguide high-pass filter system for measuring the spectrum of pulsed terahertz sources

    NASA Astrophysics Data System (ADS)

    Glyavin, M. Yu.; Goykhman, M. B.; Gromov, A. V.; Palitsin, A. V.; Panin, A. N.; Rodin, Yu. V.; Fil'chenkov, S. E.

    2016-05-01

    We propose a system for measuring spectra of terahertz (THz) pulses, including single pulses, which is based on high-pass filters (HPFs). The system consists of channels for measuring amplitudes of pulses (initial pulses and those transmitted via HPFs with different cutoff frequencies) and an algorithm for processing of the obtained data. The pulse spectrum is restored by using the iteration method or the amplitude-frequency method. The iteration method of spectrum restoration is applicable in the range of THz pulse durations from 10-9 s to 10-7 s. The amplitude-frequency method is applicable to THz pulses with durations exceeding 10-8 s. The system for measuring of THz pulse spectra was simulated by using the characteristics of specially developed waveguide HPFs. The relative simulation error of determining the central frequency by the amplitude-frequency method is equal to 2 · 10-6 for THz pulse durations of 10-5 s and longer.

  13. 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)

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

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

    PubMed

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

    2015-10-19

    We realize a compact two-dimensional tomographic terahertz imaging experiment involving only one photoconductive antenna (PCA) simultaneously serving as a transmitter and receiver of the terahertz radiation. A hollow-core Teflon cylinder filled with α-Lactose monohydrate powder is studied at two terahertz frequencies, far away and at a specific absorption line of the powder. This sample is placed between the antenna and a chopper wheel, which serves as back reflector of the terahertz radiation into the PCA. Amplitude and phase information of the continuous-wave (CW) terahertz radiation are extracted from the measured homodyne self-mixing (HSM) signal after interaction with the cylinder. The influence of refraction is studied by modeling the set-up utilizing ZEMAX and is discussed by means of the measured 1D projections. The tomographic reconstruction by using the Simultaneous Algebraic Reconstruction Technique (SART) allows to identify both object geometry and α-Lactose filling. PMID:26480382

  16. Waveform-controlled terahertz radiation from the air filament produced by few-cycle laser pulses.

    PubMed

    Bai, Ya; Song, Liwei; Xu, Rongjie; Li, Chuang; Liu, Peng; Zeng, Zhinan; Zhang, Zongxin; Lu, Haihe; Li, Ruxin; Xu, Zhizhan

    2012-06-22

    Waveform-controlled terahertz (THz) radiation is of great importance due to its potential application in THz sensing and coherent control of quantum systems. We demonstrated a novel scheme to generate waveform-controlled THz radiation from air plasma produced when carrier-envelope-phase (CEP) stabilized few-cycle laser pulses undergo filamentation in ambient air. We launched CEP-stabilized 10 fs-long (~1.7 optical cycles) laser pulses at 1.8 μm into air and found that the generated THz waveform can be controlled by varying the filament length and the CEP of driving laser pulses. Calculations using the photocurrent model and including the propagation effects well reproduce the experimental results, and the origins of various phase shifts in the filament are elucidated. PMID:23004609

  17. 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

  18. Numerical and simulation study of terahertz radiation generation by laser pulses propagating in the extraordinary mode in magnetized plasma

    SciTech Connect

    Jha, Pallavi; Kumar Verma, Nirmal

    2014-06-15

    A one-dimensional numerical model for studying terahertz radiation generation by intense laser pulses propagating, in the extraordinary mode, through magnetized plasma has been presented. The direction of the static external magnetic field is perpendicular to the polarization as well as propagation direction of the laser pulse. A transverse electromagnetic wave with frequency in the terahertz range is generated due to the presence of the magnetic field. Further, two-dimensional simulations using XOOPIC code show that the THz fields generated in plasma are transmitted into vacuum. The fields obtained via simulation study are found to be compatible with those obtained from the numerical model.

  19. Fast terahertz imaging using a quantum cascade amplifier

    SciTech Connect

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

    2015-07-06

    A terahertz (THz) imaging scheme based on the effect of self-mixing in a 2.9 THz quantum cascade (QC) amplifier has been demonstrated. By coupling an antireflective-coated silicon lens to the facet of a QC laser, with no external optical feedback, the laser mirror losses are enhanced to fully suppress lasing action, creating a THz QC amplifier. The addition of reflection from an external target to the amplifier creates enough optical feedback to initiate lasing action and the resulting emission enhances photon-assisted transport, which in turn reduces the voltage across the device. At the peak gain point, the maximum photon density coupled back leads to a prominent self-mixing effect in the QC amplifier, leading to a high sensitivity, with a signal to noise ratio up to 55 dB, along with a fast data acquisition speed of 20 000 points per second.

  20. 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.

  1. Gelatin embedding: a novel way to preserve biological samples for terahertz imaging and spectroscopy

    NASA Astrophysics Data System (ADS)

    Fan, Shuting; Ung, Benjamin; Parrott, Edward P. J.; Pickwell-MacPherson, Emma

    2015-04-01

    Sample dehydration has traditionally been a challenging problem in ex vivo terahertz biomedical experiments as water content changes significantly affect the terahertz properties and can diminish important contrast features. In this paper, we propose a novel method to prevent sample dehydration using gelatin embedding. By looking at terahertz image data and calculating the optical properties of the gelatin-embedded sample, we find that our method successfully preserves the sample for at least 35 h, both for imaging and spectroscopy. Our novel preservation method demonstrates for the first time the capability to simultaneously maintain sample structural integrity and prevent dehydration at room temperature. This is particularly relevant for terahertz studies of freshly excised tissues but could be beneficial for other imaging and spectroscopy techniques.

  2. Reflection terahertz time-domain imaging for analysis of an 18th century neoclassical easel painting.

    PubMed

    Koch-Dandolo, Corinna L; Filtenborg, Troels; Fukunaga, Kaori; Skou-Hansen, Jacob; Jepsen, Peter Uhd

    2015-06-01

    Terahertz time-domain imaging (THz-TDI) has been applied for imaging a hidden portrait and other subsurface composition layers of an 18th century (18C) easel painting by Nicolai Abildgaard, the most important 18C Danish neoclassical painter of historical and mythological subjects. For the first time, a real hidden portrait on an easel painting has been imaged by THz-TDI, with an unexpected richness of detail. THz C- and B-scans have been compared with images obtained by x-ray radiography and invasive cross-sectional imaging, leading to a deeper understanding of the strengths and limitations of this technique for art diagnostic purposes and defining its role among complementary tools for the investigation of art objects. We present a fast and effective method to separate single THz pulse reflections of interest from the entire signal across the image, adapted for uneven surfaces typically encountered in practical applications of the technique. Interfaces between layers of the painting have been successfully imaged, contributing substantially to the understanding of the structure of the painting. PMID:26192674

  3. Generation of high power pulsed terahertz radiation using a plasmonic photoconductive emitter array with logarithmic spiral antennas

    SciTech Connect

    Berry, Christopher W.; Hashemi, Mohammad R.; Jarrahi, Mona

    2014-02-24

    An array of 3 × 3 plasmonic photoconductive terahertz emitters with logarithmic spiral antennas is fabricated on a low temperature (LT) grown GaAs substrate and characterized in response to a 200 fs optical pump from a Ti:sapphire mode-locked laser at 800 nm wavelength. A microlens array is used to split and focus the optical pump beam onto the active area of each plasmonic photoconductive emitter element. Pulsed terahertz radiation with record high power levels up to 1.9 mW in the 0.1–2 THz frequency range is measured at an optical pump power of 320 mW. The record high power pulsed terahertz radiation is enabled by the use of plasmonic contact electrodes, enhancing the photoconductor quantum efficiencies, and by increasing the overall device active area, mitigating the carrier screening effect and thermal breakdown at high optical pump power levels.

  4. Fast, High-Resolution Terahertz Radar Imaging at 25 Meters

    NASA Technical Reports Server (NTRS)

    Cooper, Ken B.; Dengler, Robert J.; Llombart, Nuria; Talukder, Ashit; Panangadan, Anand V.; Peay, Chris S.; Siegel, Peter H.

    2010-01-01

    We report improvements in the scanning speed and standoff range of an ultra-wide bandwidth terahertz (THz) imaging radar for person-borne concealed object detection. Fast beam scanning of the single-transceiver radar is accomplished by rapidly deflecting a flat, light-weight subreflector in a confocal Gregorian optical geometry. With RF back-end improvements also implemented, the radar imaging rate has increased by a factor of about 30 compared to that achieved previously in a 4 m standoff prototype instrument. In addition, a new 100 cm diameter ellipsoidal aluminum reflector yields beam spot diameters of approximately 1 cm over a 50x50 cm field of view at a range of 25 m, although some aberrations are observed that probably arise from misaligned optics. Through-clothes images of a concealed threat at 25 m range, acquired in 5 seconds, are presented, and the impact of reduced signal-to-noise from an even faster frame rate is analyzed. These results inform the system requirements for eventually achieving sub-second or video-rate THz radar imaging.

  5. 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.

  6. Real-time passive terahertz imaging system for standoff concealed weapons imaging

    NASA Astrophysics Data System (ADS)

    Luukanen, Arttu; Grönberg, Leif; Grönholm, Markus; Lappalainen, Petteri; Leivo, Mikko; Rautiainen, Anssi; Tamminen, Aleksi; Ala-Laurinaho, Juha; Dietlein, Charles R.; Grossman, Erich N.

    2010-04-01

    The performance of stand-off imaging systems of concealed weapons in the mm-wave range remains limited by the relatively poor angular resolution using practical aperture sizes. For this reason, increasing the operating frequency of the systems is desired, but in practice is hard to realize due to the lack of affordable, low noise amplifiers well beyond 100 GHz. In this paper we present a passive terahertz imaging system which acquires passive terahertz (~200 GHz - ~1 THz) imagery near video frame rate. The system, one copy of which is built in Finland and the other in the U.S., is based on a 64 pixel linear array of superconducting antenna-coupled microbolometers operated within a commercial cryogen-free closed cycle cryocooler, and utilizes conical scanning Schmidt optics. Quantitative measurements on the imager resolution metrics (thermal, spatial and temporal) will be presented. The results from field tests at the Helsinki-Vantaa airport will be presented.

  7. Operation of a Wideband Terahertz Superconducting Bolometer Responding to Quantum Cascade Laser Pulses

    NASA Astrophysics Data System (ADS)

    Cibella, S.; Beck, M.; Carelli, P.; Castellano, M. G.; Chiarello, F.; Faist, J.; Leoni, R.; Ortolani, M.; Sabbatini, L.; Scalari, G.; Torrioli, G.; Turcinkova, D.

    2012-06-01

    We make use of a niobium film to produce a micrometric vacuum-bridge superconducting bolometer responding to THz frequency. The bolometer works anywhere in the temperature range 2-7 K, which can be easily reached in helium bath cryostats or closed-cycle cryocoolers. In this work the bolometer is mounted on a pulse tube refrigerator and operated to measure the equivalent noise power (NEP) and the response to fast (μs) terahertz pulses. The NEP above 100 Hz equals that measured in a liquid helium cryostat showing that potential drawbacks related to the use of a pulse tube refrigerator (like mechanical and thermal oscillations, electromagnetic interference, noise) are irrelevant. At low frequency, instead, the pulse tube expansion-compression cycles originate lines at 1 Hz and harmonics in the noise spectrum. The bolometer was illuminated with THz single pulses coming either from a Quantum Cascade Laser operating at liquid nitrogen temperature or from a frequency-multiplied electronic oscillator. The response of the bolometer to the single pulses show that the device can track signals with a rise time as fast as about 450 ns.

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

    PubMed

    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

    2015-06-26

    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 100  μJ per steradian in the laser specular direction at an optimal preplasma scale length around 40-50  μm. 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. PMID:26197129

  9. Generation of Intense Narrow-Band Tunable Terahertz Radiation from Highly Bunched Electron Pulse Train

    NASA Astrophysics Data System (ADS)

    Li, Heting; Lu, Yalin; He, Zhigang; Jia, Qika; Wang, Lin

    2016-02-01

    We present the analysis and start-to-end simulation of an intense narrow-band terahertz (THz) source with a broad tuning range of radiation frequency, using a single-pass free electron laser (FEL) driven by a THz-pulse-train photoinjector. The fundamental radiation frequency, corresponding to the spacing between the electron microbunches, can be easily tuned by varying the spacing time between the laser micropulses. Since the prebunched electron beam is highly bunched at the first several harmonics, with the harmonic generation technique, the radiation frequency range can be further enlarged by several times. The start-to-end simulation results show that this FEL is capable of generating a few tens megawatts power, several tens micro-joules pulse energy, and a few percent bandwidth at the frequencies of 0.5-5 THz. In addition, several practical issues are considered.

  10. 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

  11. Technology and Applications of Terahertz Imaging Non-Destructive Examination: Inspection of Space Shuttle Sprayed On Foam Insulation

    NASA Astrophysics Data System (ADS)

    Zimdars, David; Valdmanis, J. A.; White, Jeffrey S.; Stuk, G.; Williamson, S.; Winfree, William P.; Madaras, Eric I.

    2005-04-01

    The implementation of terahertz (THz) imaging for non-destructive evaluation shows great promise in 2 and 3 dimensional non-contact inspection of non-conductive materials such as plastics, foam, composites, ceramics, paper, wood and glass. THz imaging employs safe low power non-ionizing electromagnetic pulses, which produce images with lateral resolution <200 microns, and depth resolution <50 microns. We demonstrate the detection of voids and disbonds intentionally incorporated within the sprayed on foam insulation of a space shuttle external tank mock-up segment using time domain THz imaging. Recently, highly integrated turn-key THz imaging systems have been introduced commercially. An industrially hardened THz scanning system which has been deployed to scan the space shuttle tank with small remote THz transceiver on a 30 meter fiber optic umbilical, is described.

  12. Distortion analysis of pulsed terahertz signal measured with spectral-encoding technique

    NASA Astrophysics Data System (ADS)

    Peng, Xiao-Yu; Teng, Jing-Hua; Zhang, Xin-Hai; Foo, Yong-Lim

    2010-11-01

    The principle of the spectral-encoding technique, one of the single-shot techniques for measurement of arbitrary pulsed terahertz (THz) signals, or T-rays, is demonstrated theoretically and through simulation. For single-cycle input THz pulse (bipolar wave form), THz signal could be retrieved faithfully under certain conditions, while for the multicycle input case, the THz signal cannot be retrieved without any distortion. However, there is an optimal length of the chirped-probe-pulse, corresponding to the characteristic time of the multicycle THz field, to minimize the distortion in the retrieved THz signal. Three main possible sources of distortions from both bipolar and multicycle THz signals are analyzed systematically. The first distortion originates from the mismatch of the optimal duration Tco of the chirped-probe-pulse and the T-ray length T. The second one is relevant to the spectrum bandwidth of the probe pulse. The third one occurs when the modulation depth k ?1 is not satisfied. It comes from the neglect of the quadratic term of the modulation depth k, which reflects the strength of the THz signal in the retrieving process. Possible strategies are proposed to reduce these distortions.

  13. Generation of scalable terahertz radiation from cylindrically focused laser pulses in air

    NASA Astrophysics Data System (ADS)

    Kuk, Donghoon; Yoo, Yungjun; Rosenthal, Eric; Jhajj, Nihal; Milchberg, Howard; Kim, Ki-Yong

    We have demonstrated scalable terahertz (THz) generation via cylindrical focusing of two-color laser pulses in air. In this experiment, we have used a terawatt (TW) laser system which can deliver >50 mJ, 800 nm, 50 fs pulses at a 10 Hz repetition rate. A 800 nm pulse passing through a nonlinear crystal (BBO) generates its second harmonic pulse (400 nm). Both pulses pass through a cylindrical lens and are focused together to generate a 2-dimensional plasma sheet in air. This yields two diverging THz lobes, characterized by an uncooled microbolometer. This observed radiation angle and pattern is explained by the optical-Cherenkov radiation theory. The diverging THz radiation is re-focused to yield strong THz field strengths (>20 MV/cm) at the focus. At laser energy of 40 mJ, cylindrical focusing provides THz energy of >30 microjoules, far exceeding the output produced by spherical focusing. This shows that cylindrical focusing can effectively minimize ionization-induced defocusing, previously observed in spherical focusing, and can allow scalable THz generation with relatively high laser energies (>20 mJ). Work supported by DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. 014216-001.

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

    NASA Astrophysics Data System (ADS)

    Li, Min; Mi, Xian-Wu

    2009-12-01

    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 appear again for the terahertz emission intensity due to the superposition of two optical pulses. The emission lines of terahertz blueshift and redshift in different ac electric fields and dynamic localization appears. The emission lines of THz only appear to blueshift when the biased superlattice is driven by a single optical pulse. Due to excitonic dynamic localization, the terahertz emission intensity decays with time in different dc and ac electric fields. These are features of this superlattice which distinguish it from a superlattice generated by a single optical pulse to drive it.

  15. Single-cycle coherent terahertz-pulse propagation in rigid-rotor molecular media

    NASA Astrophysics Data System (ADS)

    Marskar, Robert; Ã-sterberg, Ulf L.

    2015-08-01

    We theoretically analyze linear and nonlinear coherent propagation of linearly polarized, plane-wave, resonant single-cycle terahertz pulses through spatially extended rigid-rotor molecular media. Our model incorporates mixed state medium preparation, nonperturbative nonlinearities, saturation, coherence, memory effects, and propagation, but ignores the effects of damping. Explicit solutions are reported in the linear propagation regime. These solutions are the multilevel superposition of linear, single-cycle 0 π pulses, and appear as temporal beats in the time domain. For media initially in thermal equilibrium, the pulse and molecular beats are dispersive and broaden temporally with increased propagation distance. In the simplified limit of equal rotational line strength (an idealized situation), the emitted impulses are exact temporal copies of the input pulse. An efficient, scalable computational method for solving the reduced multilevel Maxwell-Bloch equations for molecular media is reported. This method is based on a standard differential method for the propagation equation together with an operator splitting method for the Bloch equations. It invokes neither the slowly varying envelope (SVEA) or rotating wave approximations (RWA), and incorporates a large number of possible energy eigenstates (we solve for 7744 levels). Case studies of nonlinear single-cycle pulse propagation are then provided by means of computer solutions. In the nonlinear regime, we observe strong molecular orientations and suppression of the pulse and orientational revivals predicted by linear theory. For sufficiently strong pulses, coherent bleaching effects lead to increased transmission of the driving pulse, which also bears signs of self-modulation and carrier-shock formation.

  16. Early detection of skin cancer via terahertz spectral profiling and 3D imaging.

    PubMed

    Rahman, Anis; Rahman, Aunik K; Rao, Babar

    2016-08-15

    Terahertz scanning reflectometry, terahertz 3D imaging and terahertz time-domain spectroscopy have been used to identify features in human skin biopsy samples diagnosed for basal cell carcinoma (BCC) and compared with healthy skin samples. It was found from the 3D images that the healthy skin samples exhibit regular cellular pattern while the BCC skin samples indicate lack of regular cell pattern. The skin is a highly layered structure organ; this is evident from the thickness profile via a scan through the thickness of the healthy skin samples, where, the reflected intensity of the terahertz beam exhibits fluctuations originating from different skin layers. Compared to the healthy skin samples, the BCC samples' profiles exhibit significantly diminished layer definition; thus indicating a lack of cellular order. In addition, terahertz time-domain spectroscopy reveals significant and quantifiable differences between the healthy and BCC skin samples. Thus, a combination of three different terahertz techniques constitutes a conclusive route for detecting the BCC condition on a cellular level compared to the healthy skin. PMID:27040943

  17. Frequency resolved cross-correlation between optical and terahertz pulses: application to ultrashort laser pulse characterization.

    PubMed

    Cornet, M; Degert, J; Abraham, E; Freysz, E

    2016-02-01

    We have analyzed both theoretically and experimentally the spectrum of the optical pulses produced by the interaction of optical and THz pulses in a ZnTe crystal. Recorded as a function of the delay between the two pulses, the resulting spectrogram can be viewed as a frequency resolved cross-correlation between the optical and THz pulses making it possible to characterize the optical pulse. PMID:26906866

  18. 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.

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

    SciTech Connect

    Vinokurov, Nikolai A; Knyazev, Boris A; Kulipanov, Gennadii N; Dem'yanenko, M A; Esaev, D G; Chashchina, O I; Cherkasskii, Valerii S

    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)

  20. 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.

  1. 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.

  2. 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.; Garaway, I.

    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.

  3. 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; Chai, Lu E-mail: yanfengli@tju.edu.cn; Liu, Bowen; Hu, Minglie; Li, Yanfeng E-mail: yanfengli@tju.edu.cn; Fedotov, Andrey B.; Zheltikov, Aleksei M.

    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.

  4. Investigating murals with terahertz reflective tomography

    NASA Astrophysics Data System (ADS)

    Yuan, Minjie; Sun, Wenfeng; Wang, Xinke; Wang, Sen; Zhang, Qunxi; Ye, Jiasheng; Zhang, Yan

    2015-08-01

    Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals.

  5. Spectroscopic Terahertz Imaging at Room Temperature Employing Microbolometer Terahertz Sensors and Its Application to the Study of Carcinoma Tissues

    PubMed Central

    Kašalynas, Irmantas; Venckevičius, Rimvydas; Minkevičius, Linas; Sešek, Aleksander; Wahaia, Faustino; Tamošiūnas, Vincas; Voisiat, Bogdan; Seliuta, Dalius; Valušis, Gintaras; Švigelj, Andrej; Trontelj, Janez

    2016-01-01

    A terahertz (THz) imaging system based on narrow band microbolometer sensors (NBMS) and a novel diffractive lens was developed for spectroscopic microscopy applications. The frequency response characteristics of the THz antenna-coupled NBMS were determined employing Fourier transform spectroscopy. The NBMS was found to be a very sensitive frequency selective sensor which was used to develop a compact all-electronic system for multispectral THz measurements. This system was successfully applied for principal components analysis of optically opaque packed samples. A thin diffractive lens with a numerical aperture of 0.62 was proposed for the reduction of system dimensions. The THz imaging system enhanced with novel optics was used to image for the first time non-neoplastic and neoplastic human colon tissues with close to wavelength-limited spatial resolution at 584 GHz frequency. The results demonstrated the new potential of compact RT THz imaging systems in the fields of spectroscopic analysis of materials and medical diagnostics. PMID:27023551

  6. Spectroscopic Terahertz Imaging at Room Temperature Employing Microbolometer Terahertz Sensors and Its Application to the Study of Carcinoma Tissues.

    PubMed

    Kašalynas, Irmantas; Venckevičius, Rimvydas; Minkevičius, Linas; Sešek, Aleksander; Wahaia, Faustino; Tamošiūnas, Vincas; Voisiat, Bogdan; Seliuta, Dalius; Valušis, Gintaras; Švigelj, Andrej; Trontelj, Janez

    2016-01-01

    A terahertz (THz) imaging system based on narrow band microbolometer sensors (NBMS) and a novel diffractive lens was developed for spectroscopic microscopy applications. The frequency response characteristics of the THz antenna-coupled NBMS were determined employing Fourier transform spectroscopy. The NBMS was found to be a very sensitive frequency selective sensor which was used to develop a compact all-electronic system for multispectral THz measurements. This system was successfully applied for principal components analysis of optically opaque packed samples. A thin diffractive lens with a numerical aperture of 0.62 was proposed for the reduction of system dimensions. The THz imaging system enhanced with novel optics was used to image for the first time non-neoplastic and neoplastic human colon tissues with close to wavelength-limited spatial resolution at 584 GHz frequency. The results demonstrated the new potential of compact RT THz imaging systems in the fields of spectroscopic analysis of materials and medical diagnostics. PMID:27023551

  7. 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

  8. Development and Testing of a Single Frequency Terahertz Imaging System for Breast Cancer Detection

    PubMed Central

    St. Peter, Benjamin; Yngvesson, Sigfrid; Siqueira, Paul; Kelly, Patrick; Khan, Ashraf; Glick, Stephen; Karellas, Andrew

    2013-01-01

    The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated with optical histological micrographs of the same specimens, and a mean discrimination of 73% was found for five out of six samples using Receiver Operating Characteristic (ROC) analysis. The system design and characterization is discussed in detail. The initial results are encouraging but further development of the technology and clinical evaluation is needed to evaluate its feasibility in the clinical environment. PMID:25055306

  9. 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.

  10. Enhanced Terahertz Imaging of Small Forced Delamination in Woven Glass Fibre-reinforced Composites with Wavelet De-noising

    NASA Astrophysics Data System (ADS)

    Dong, Junliang; Locquet, Alexandre; Citrin, D. S.

    2016-03-01

    Terahertz (THz) reflection imaging is applied to characterize a woven glass fibre-reinforced composite laminate with a small region of forced delamination. The forced delamination is created by inserting a disk of 25- μ m-thick Upilex film, which is below the THz axial resolution, resulting in one featured echo with small amplitude in the reflected THz pulses. Low-amplitude components of the temporal signal due to ambient water vapor produce features of comparable amplitude with features associated with the THz pulse reflected off the interfaces of the delamination and suppress the contrast of THz C- and B-scans. Wavelet shrinkage de-noising is performed to remove water-vapor features, leading to enhanced THz C- and B-scans to locate the delamination in three dimensions with high contrast.

  11. Enhanced Terahertz Imaging of Small Forced Delamination in Woven Glass Fibre-reinforced Composites with Wavelet De-noising

    NASA Astrophysics Data System (ADS)

    Dong, Junliang; Locquet, Alexandre; Citrin, D. S.

    2015-11-01

    Terahertz (THz) reflection imaging is applied to characterize a woven glass fibre-reinforced composite laminate with a small region of forced delamination. The forced delamination is created by inserting a disk of 25- ? m-thick Upilex film, which is below the THz axial resolution, resulting in one featured echo with small amplitude in the reflected THz pulses. Low-amplitude components of the temporal signal due to ambient water vapor produce features of comparable amplitude with features associated with the THz pulse reflected off the interfaces of the delamination and suppress the contrast of THz C- and B-scans. Wavelet shrinkage de-noising is performed to remove water-vapor features, leading to enhanced THz C- and B-scans to locate the delamination in three dimensions with high contrast.

  12. Room temperature terahertz wave imaging at 60 fps by frequency up-conversion in DAST crystal

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    Terahertz imaging has attracted a lot of interests for more than 10 years. But real time, high sensitive, low cost THz imaging in room temperature, which is widely needed by fields such as biology, biomedicine and homeland security, has not been fully developed yet. A lot of approaches have been reported on electro-optic (E-O) imaging and THz focal plane arrays with photoconductive antenna or micro-bolometer integrated. In this paper, we report high sensitive realtime THz image at 60 frames per second (fps) employing a commercial infrared camera, using nonlinear optical frequency up-conversion technology. In this system, a flash-lamp pumped nanosecond pulse green laser is used to pump two optical parametric oscillator systems with potassium titanyl phosphate crystals (KTP-OPO). One system with dual KTP crystals is used to generate infrared laser for the pumping of THz difference frequency generation (DFG) in a 4- Dimethylamino-N-Methyl-4-Stilbazolium Tosylate (DAST) crystal. The other one is for generation of pumping laser for THz frequency up-conversion in a second DAST crystal. The THz frequency can be tuned continuously from a few THz to less than 30 THz by controlling the angle of KTP crystals. The frequency up-converted image in infrared region is recorded by a commercial infrared camera working at 60 Hz. Images and videos are presented to show the feasibility of this technique and the real-time ability. Comparison with a general micro-bolometer THz camera shows the high sensitivity of this technique.

  13. Improved terahertz imaging with a sparse synthetic aperture array

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuopeng; Buma, Takashi

    2010-02-01

    Sparse arrays are highly attractive for implementing two-dimensional arrays, but come at the cost of degraded image quality. We demonstrate significantly improved performance by exploiting the coherent ultrawideband nature of singlecycle THz pulses. We compute two weighting factors to each time-delayed signal before final summation to form the reconstructed image. The first factor employs cross-correlation analysis to measure the degree of walk-off between timedelayed signals of neighboring elements. The second factor measures the spatial coherence of the time-delayed delayed signals. Synthetic aperture imaging experiments are performed with a THz time-domain system employing a mechanically scanned single transceiver element. Cross-sectional imaging of wire targets is performed with a onedimensional sparse array with an inter-element spacing of 1.36 mm (over four λ at 1 THz). The proposed image reconstruction technique improves image contrast by 15 dB, which is impressive considering the relatively few elements in the array. En-face imaging of a razor blade is also demonstrated with a 56 x 56 element two-dimensional array, showing reduced image artifacts with adaptive reconstruction. These encouraging results suggest that the proposed image reconstruction technique can be highly beneficial to the development of large area two-dimensional THz arrays.

  14. 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

  15. 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.

  16. Application of Terahertz Imaging and Backscatter Radiography to Space Shuttle Foam Inspection

    NASA Technical Reports Server (NTRS)

    Ussery, Warren

    2008-01-01

    Two state of the art technologies have been developed for External Fuel Tank foam inspections. Results of POD tests have shown Backscatter Radiography and Terahertz imaging detect critical defects with no false positive issue. These techniques are currently in use on the External Tank program as one component in the foam quality assurance program.

  17. Graphene based metamaterials for terahertz cloaking and subwavelength imaging

    NASA Astrophysics Data System (ADS)

    Forouzmand, Seyedali

    Graphene is a two-dimensional carbon crystal that became one of the most controversial topics of research in the last few years. The intense interest in graphene stems from recent demonstrations of their potentially revolutionary electromagnetic applications -- including negative refraction, subdiffraction imaging, and even invisibility -- which have suggested a wide range of new devices for communications, sensing, and biomedicine. In addition, it has been shown that graphene is amenable to unique patterning schemes such as cutting, bending, folding, and fusion that are predicted to lead to interesting properties. A recent proposed application of graphene is in engineering the scattering properties of objects, which may be leveraged in applications such as radar-cross-section management and stealth, where it may be required to make one object look like another object or render an object completely invisible. We present the analytical formulation for the analysis of electromagnetic interaction with a finite conducting wedge covered with a cylindrically shaped nanostructured graphene metasurface, resulting in the scattering cancellation of the dominant scattering mode for all the incident and all the observation angles. Following this idea, the cylindrical graphene metasurface is utilized for cloaking of several concentric finite conducting wedges. In addition, a wedge shaped metasurface is proposed as an alternative approach for cloaking of finite wedges. The resolution of the conventional imaging lenses is restricted by the natural diffraction limit. Artificially engineered metamaterials now offer the possibility of creating a superlens that overcomes this restriction. We demonstrate that a wire medium (WM) slab loaded with graphene sheets enables the enhancement of the near field for subwavelength imaging at terahertz (THz) frequencies. The analysis is based on the nonlocal homogenization model for WM with the additional boundary condition in the connection of wires to graphene. The principle of the operation of the proposed lens depends on the enhancement of evanescent waves, wherein the excited surface plasmons at the lower and upper graphene interfaces are coupled by an array of metallic wires. The resolution and the operating frequency of the subwavelength imaging device are mainly determined by the tunability of graphene and the structural parameters of the WM slab. The proposed structure has a resolution better than lambda/10 with the advantages of broad bandwidth, low sensitivity to losses, and tunability with respect to the chemical potential even if the distance between two graphene sheets is a significant fraction of wavelength. As a supplementary study, the performance of WM slab loaded with nanostructured graphene metasurfaces as a novel sub-diffraction imaging lens is studied. It is observed that the dual nature (capacitive/inductive) of the nanostructured graphene metasurface can be utilized to design a dual-band lens in which the subwavelength imaging simultaneously at two tunable distinct frequencies is possible. The analytical results which are presented throughout this thesis, are validated with the full-wave electromagnetic simulator, CST Microwave Studio.

  18. Parasitic antenna effect in terahertz plasmon detector array for real-time imaging system

    NASA Astrophysics Data System (ADS)

    Yang, Jong-Ryul; Lee, Woo-Jae; Ryu, Min Woo; Rok Kim, Kyung; Han, Seong-Tae

    2015-10-01

    The performance uniformity of each pixel integrated with a patch antenna in a terahertz plasmon detector array is very important in building the large array necessary for a real-time imaging system. We found a parasitic antenna effect in the terahertz plasmon detector whose response is dependent on the position of the detector pixel in the illumination area of the terahertz beam. It was also demonstrated that the parasitic antenna effect is attributed to the physical structure consisting of signal pads, bonding wires, and interconnection lines on a chip and a printed circuit board. Experimental results show that the performance of the detector pixel is determined by the sum of the effects of each parasitic antenna and the on-chip integrated antenna designed to detect signals at the operating frequency. The parasitic antenna effect can be minimized by blocking the interconnections with a metallic shield.

  19. Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser.

    PubMed

    Lui, H S; Taimre, T; Bertling, K; Lim, Y L; Dean, P; Khanna, S P; Lachab, M; Valavanis, A; Indjin, D; Linfield, E H; Davies, A G; Rakić, A D

    2014-05-01

    We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit. PMID:24784063

  20. 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.

  1. Resonant-phonon depopulation terahertz quantum cascade lasers and their application in spectroscopic imaging

    NASA Astrophysics Data System (ADS)

    Dean, P.; Salih, M.; Khanna, S. P.; Li, L. H.; Saat, N. K.; Valavanis, A.; Burnett, A.; Cunningham, J. E.; Davies, A. G.; Linfield, E. H.

    2012-09-01

    The terahertz (THz) frequency quantum cascade laser (QCL) is a semiconductor heterostructure laser that has attracted much research interest over the past decade. We report on the high performance of THz QCLs based on a three-well resonant-phonon (RP) depopulation active region (AR) and operating in the frequency range 2.7 THz to 4.0 THz. Devices, processed into surface-plasmon waveguides, lased up to 116 K in pulsed mode with threshold current densities as low as 840 Acm-2. The effects of the design frequency and laser cavity length on performance are discussed. We also report on the operation of QCLs with reduced AR thicknesses, and show, for the first time, that the AR thickness of RP QCLs processed in a surface plasmon waveguide can be reduced to as little as 5 µm. Finally, we demonstrate the use of an electrically tuneable THz QCL, based on a heterogeneous AR, for spectroscopic imaging of the high-explosive pentaerythritol tetranitrate.

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

    SciTech Connect

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

    2014-08-31

    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. (laser biophotonics)

  3. Application of threshold estimation for terahertz digital holography image denoising based on stationary wavelet transform

    NASA Astrophysics Data System (ADS)

    Cui, Shan-shan; Li, Qi; Ma, Xue

    2015-11-01

    Terahertz digital holography imaging technology is one of the hot topics in imaging domain, and it has drawn more and more public attention. Owing to the redundancy and translation invariance of the stationary wavelet transform, it has significant application in image denoising, and the threshold selection has a great influence on denoising. The denoising researches based on stationary wavelet transform are performed on the real terahertz image, with Bayesian estimation and Birge-Massart strategy applied to evaluate the threshold. The experimental results reveal that, Bayesian estimation combined with homomorphic stationary wavelet transform manifests the optimal denoising effect at 3 decomposition levels, which improves the signal-to-noise and preserves the image detail information simultaneously.

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

    PubMed Central

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

    2015-01-01

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

  5. Coherent detection for continuous terahertz wave

    NASA Astrophysics Data System (ADS)

    Yuan, Hui; Lu, Tielin; Zhang, Jingshui; Zhang, Liangliang; Zhao, Ji; Zhao, Yuejin

    2015-08-01

    In this paper we demonstrated a coherent raster-scan imaging system that can acquire phase information based on continuous terahertz imaging. It mixes the terahertz with a Fs-laser by a electro-optic crystal of ZnTe to make a hybrid modulation on the crystal to achieve continuous terahertz detection. In this way, it can not only propagate for a long distance but also achieve phase detection for continuous terahertz imaging. The surface images of objects that are under test can be obtained by the Backward-Wave Oscillator, which the output power is 10mW at 205.994GHz. With the repetition frequency of 80MHz, the output power of the MaiTai is 1.65W and 100fs pulse light at 800nm. The images can achieve diffraction-limited resolution approximately. And the simulated results show that the system can obtain phase imaging of test objects based on continuous terahertz source. The way to get the phase of the signal has significant meaning for coherent detection of continuous terahertz source.

  6. Terahertz modulation of the Faraday rotation by laser pulses via the optical Kerr effect

    NASA Astrophysics Data System (ADS)

    Subkhangulov, R. R.; Mikhaylovskiy, R. V.; Zvezdin, A. K.; Kruglyak, V. V.; Rasing, Th.; Kimel, A. V.

    2016-02-01

    The magneto-optical Faraday effect played a crucial role in the elucidation of the electromagnetic nature of light. Today it is powerful means to probe magnetism and the basic operational principle of magneto-optical modulators. Understanding the mechanisms allowing for modulation of the magneto-optical response at terahertz frequencies may have far-reaching consequences for photonics, ultrafast optomagnetism and magnonics, as well as for future development of ultrafast Faraday modulators. Here we suggest a conceptually new approach for an ultrafast tunable magneto-optical modulation with the help of counter-propagating laser pulses. Using terbium gallium garnet (Tb3Ga5O12) we demonstrate the feasibility of such magneto-optical modulation with a frequency up to 1.1 THz, which is continuously tunable by means of an external magnetic field. Besides the novel concept for ultrafast magneto-optical polarization modulation, our findings reveal the importance of accounting for propagation effects in the interpretation of pump-probe magneto-optical experiments.

  7. 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

  8. 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

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

    PubMed Central

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

    2013-01-01

    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. PMID:24162458

  10. Parametric study of broadband terahertz radiation generation based on interaction of two-color ultra-short laser pulses

    SciTech Connect

    Moradi, S.; Ganjovi, A.; Shojaei, F.; Saeed, M.

    2015-04-15

    In this work, using a two-dimensional kinetic model based on particle in cell-Monte Carlo collision simulation method, the influence of different parameters on the broadband intense Terahertz (THz) radiation generation via application of two-color laser fields, i.e., the fundamental and second harmonic modes, is studied. These two modes are focused into the molecular oxygen (O{sub 2}) with uniform density background gaseous media and the plasma channels are created. Thus, a broadband THz pulse that is around the plasma frequency is emitted from the formed plasma channel and co-propagates with the laser pulse. For different laser pulse shapes, the THz electric field and its spectrum are both calculated. The effects of laser pulse and medium parameters, i.e., positive and negative chirp pulse, number of laser cycles in the pulse, laser pulse shape, background gas pressure, and exerted DC electric field on THz spectrum are verified. Application of a negatively chirped femtosecond (40 fs) laser pulse results in four times enhancement of the THz pulse energy (2 times in THz electric field). The emission of THz radiation is mostly observed in the forward direction.

  11. Parametric study of broadband terahertz radiation generation based on interaction of two-color ultra-short laser pulses

    NASA Astrophysics Data System (ADS)

    Moradi, S.; Ganjovi, A.; Shojaei, F.; Saeed, M.

    2015-04-01

    In this work, using a two-dimensional kinetic model based on particle in cell-Monte Carlo collision simulation method, the influence of different parameters on the broadband intense Terahertz (THz) radiation generation via application of two-color laser fields, i.e., the fundamental and second harmonic modes, is studied. These two modes are focused into the molecular oxygen (O2) with uniform density background gaseous media and the plasma channels are created. Thus, a broadband THz pulse that is around the plasma frequency is emitted from the formed plasma channel and co-propagates with the laser pulse. For different laser pulse shapes, the THz electric field and its spectrum are both calculated. The effects of laser pulse and medium parameters, i.e., positive and negative chirp pulse, number of laser cycles in the pulse, laser pulse shape, background gas pressure, and exerted DC electric field on THz spectrum are verified. Application of a negatively chirped femtosecond (40 fs) laser pulse results in four times enhancement of the THz pulse energy (2 times in THz electric field). The emission of THz radiation is mostly observed in the forward direction.

  12. Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Sano, Y.; Kawayama, I.; Tabata, M.; Salek, K. A.; Murakami, H.; Wang, M.; Vajtai, R.; Ajayan, P. M.; Kono, J.; Tonouchi, M.

    2014-08-01

    Being an atomically thin material, graphene is known to be extremely susceptible to its environment, including defects and phonons in the substrate on which it is placed as well as gas molecules that surround it. Thus, any device design using graphene has to take into consideration all surrounding components, and device performance needs to be evaluated in terms of environmental influence. However, no methods have been established to date to readily measure the density and distribution of external perturbations in a quantitative and non-destructive manner. Here, we present a rapid and non-contact method for visualizing the distribution of molecular adsorbates on graphene semi-quantitatively using terahertz time-domain spectroscopy and imaging. We found that the waveform of terahertz bursts emitted from graphene-coated InP sensitively changes with the type of atmospheric gas, laser irradiation time, and ultraviolet light illumination. The terahertz waveform change is explained through band structure modifications in the InP surface depletion layer due to the presence of localized electric dipoles induced by adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene films and devices, suggesting a novel two-dimensional sensor for detecting local chemical reactions.

  13. Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy

    PubMed Central

    Sano, Y.; Kawayama, I.; Tabata, M.; Salek, K. A.; Murakami, H.; Wang, M.; Vajtai, R.; Ajayan, P. M.; Kono, J.; Tonouchi, M.

    2014-01-01

    Being an atomically thin material, graphene is known to be extremely susceptible to its environment, including defects and phonons in the substrate on which it is placed as well as gas molecules that surround it. Thus, any device design using graphene has to take into consideration all surrounding components, and device performance needs to be evaluated in terms of environmental influence. However, no methods have been established to date to readily measure the density and distribution of external perturbations in a quantitative and non-destructive manner. Here, we present a rapid and non-contact method for visualizing the distribution of molecular adsorbates on graphene semi-quantitatively using terahertz time-domain spectroscopy and imaging. We found that the waveform of terahertz bursts emitted from graphene-coated InP sensitively changes with the type of atmospheric gas, laser irradiation time, and ultraviolet light illumination. The terahertz waveform change is explained through band structure modifications in the InP surface depletion layer due to the presence of localized electric dipoles induced by adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene films and devices, suggesting a novel two-dimensional sensor for detecting local chemical reactions. PMID:25116593

  14. Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy.

    PubMed

    Sano, Y; Kawayama, I; Tabata, M; Salek, K A; Murakami, H; Wang, M; Vajtai, R; Ajayan, P M; Kono, J; Tonouchi, M

    2014-01-01

    Being an atomically thin material, graphene is known to be extremely susceptible to its environment, including defects and phonons in the substrate on which it is placed as well as gas molecules that surround it. Thus, any device design using graphene has to take into consideration all surrounding components, and device performance needs to be evaluated in terms of environmental influence. However, no methods have been established to date to readily measure the density and distribution of external perturbations in a quantitative and non-destructive manner. Here, we present a rapid and non-contact method for visualizing the distribution of molecular adsorbates on graphene semi-quantitatively using terahertz time-domain spectroscopy and imaging. We found that the waveform of terahertz bursts emitted from graphene-coated InP sensitively changes with the type of atmospheric gas, laser irradiation time, and ultraviolet light illumination. The terahertz waveform change is explained through band structure modifications in the InP surface depletion layer due to the presence of localized electric dipoles induced by adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene films and devices, suggesting a novel two-dimensional sensor for detecting local chemical reactions. PMID:25116593

  15. On-chip integration solutions of compact optics and detectors in room-temperature terahertz imaging systems

    NASA Astrophysics Data System (ADS)

    Minkevičius, Linas; TamošiÅ«nas, Vincas; Kašalynas, Irmantas; Venckevičius, Rimvydas; Madeikis, Karolis; Voisiat, Bogdan; Seliuta, Dalius; Račiukaitis, Gediminas; Valušis, Gintaras

    2015-08-01

    On-chip integrated solutions employing properties of Fresnel zone plates with integrated band-pass filters for the room temperature terahertz imaging systems are discussed. Finite-difference time-domain simulations were used to predict properties of conventional zone plates and ones with resonant filter areas as flat optics components. They are produced employing the laser direct writing and characterized by electronic THz sources and an optically pumped terahertz laser. It was shown that more than one order of magnitude detection enhancement can be observed of bow-tie-shaped InGaAs-based terahertz detectors by on-chip incorporation of the secondary diffractive optics.

  16. A Practical and Portable Solids-State Electronic Terahertz Imaging System.

    PubMed

    Smart, Ken; Du, Jia; Li, Li; Wang, David; Leslie, Keith; Ji, Fan; Li, Xiang Dong; Zeng, Da Zhang

    2016-01-01

    A practical compact solid-state terahertz imaging system is presented. Various beam guiding architectures were explored and hardware performance assessed to improve its compactness, robustness, multi-functionality and simplicity of operation. The system performance in terms of image resolution, signal-to-noise ratio, the electronic signal modulation versus optical chopper, is evaluated and discussed. The system can be conveniently switched between transmission and reflection mode according to the application. A range of imaging application scenarios was explored and images of high visual quality were obtained in both transmission and reflection mode. PMID:27110791

  17. A Practical and Portable Solids-State Electronic Terahertz Imaging System

    PubMed Central

    Smart, Ken; Du, Jia; Li, Li; Wang, David; Leslie, Keith; Ji, Fan; Li, Xiang Dong; Zeng, Da Zhang

    2016-01-01

    A practical compact solid-state terahertz imaging system is presented. Various beam guiding architectures were explored and hardware performance assessed to improve its compactness, robustness, multi-functionality and simplicity of operation. The system performance in terms of image resolution, signal-to-noise ratio, the electronic signal modulation versus optical chopper, is evaluated and discussed. The system can be conveniently switched between transmission and reflection mode according to the application. A range of imaging application scenarios was explored and images of high visual quality were obtained in both transmission and reflection mode. PMID:27110791

  18. Influences of different gases on the terahertz radiation based on the application of two-color laser pulses

    SciTech Connect

    Moradi, S.; Ganjovi, A.; Shojaei, F.; Saeed, M.

    2015-10-15

    In this work, using a two-dimensional Particle In Cell-Monte Carlo Collision simulation method, a comparative study is performed on the influences of different types of atomic and molecular gases at various background gas pressures on the generation of broadband and intense Terahertz (THz) radiation via the application of two-color laser pulses. These two modes are focused into Argon (Ar), Xenon (Xe), Nitrogen (N{sub 2}), Oxygen (O{sub 2}), and air as the background gaseous media and the plasma channel is created. It is observed that the THz radiation emission dramatically changes due to the propagation effects. A wider THz pulse is emitted from the formed plasma channel at the higher gas pressures. The significant effects of the propagation features of the emitted THz pulse on its energy at the longer lengths of the plasma channel are observed.

  19. Temporal interferences driven by a single-cycle terahertz pulse in the photodetachment dynamics of negative ions

    NASA Astrophysics Data System (ADS)

    Yang, B. C.; Robicheaux, F.

    2015-12-01

    We present theory and calculations of a real-time-domain interferometry for the photodetachment dynamics of negative ions in the presence of a single-cycle terahertz pulse. The photoelectron can follow two or more classical trajectories to arrive at a detector simultaneously allowing the electron waves to interfere quantum mechanically. Both the in-phase and antiphase oscillations can be observed in the photoelectron interferences from negative hydrogen and fluorine ions depending on the pulse strength and the observing angle. Especially, a temporal-caustic bifurcation is observed when the detection angle is not in line with the pulse polarization direction. Similar interferences and bifurcations are also expected in the angle-resolved energy spectrum, as a result of its approximate equivalence with the time-dependent electron flux at large distances.

  20. Influences of different gases on the terahertz radiation based on the application of two-color laser pulses

    NASA Astrophysics Data System (ADS)

    Moradi, S.; Ganjovi, A.; Shojaei, F.; Saeed, M.

    2015-10-01

    In this work, using a two-dimensional Particle In Cell-Monte Carlo Collision simulation method, a comparative study is performed on the influences of different types of atomic and molecular gases at various background gas pressures on the generation of broadband and intense Terahertz (THz) radiation via the application of two-color laser pulses. These two modes are focused into Argon (Ar), Xenon (Xe), Nitrogen (N2), Oxygen (O2), and air as the background gaseous media and the plasma channel is created. It is observed that the THz radiation emission dramatically changes due to the propagation effects. A wider THz pulse is emitted from the formed plasma channel at the higher gas pressures. The significant effects of the propagation features of the emitted THz pulse on its energy at the longer lengths of the plasma channel are observed.

  1. Terahertz imaging modalities of ancient Egyptian mummified objects and of a naturally mummified rat.

    PubMed

    Öhrström, Lena; Fischer, Bernd M; Bitzer, Andreas; Wallauer, Jan; Walther, Markus; Rühli, Frank

    2015-06-01

    During the last few years, terahertz (THz) imaging has been used to investigate artwork and historic artifacts. The application of THz imaging to mummy investigations is very attractive since it provides spectroscopic information over a broad frequency range and its radiation has proven to be harmless to human cells. However, compared with the current standard imaging methods in mummy imaging-X-ray and computed tomography (CT)--it remains a novel, emerging technique whose potential still needs to be fully evaluated. Here, ancient Egyptian mummified objects as well as a naturally mummified rat have been investigated by two different THz imaging systems: a broadband THz time domain imaging system and an electronic THz scanner. The obtained THz images are compared with conventional CT, X-ray, and magnetic resonance images. While the broadband THz time domain setup permits analyses of smaller samples, the electronic THz scanner allows the recording of data of thicker and larger samples at the expense of a limited spectral bandwidth. Terahertz imaging shows clear potential for mummy investigations, although currently CT imaging offers much higher spatial resolution. Furthermore, as commercial mobile THz scanners become available, THz imaging could be applied directly in museums or at excavation sites. PMID:25998647

  2. Terahertz Imaging and Backscatter Radiography Probability of Detection Study for Space Shuttle Foam Inspections

    NASA Technical Reports Server (NTRS)

    Ussery, Warren; Johnson, Kenneth; Walker, James; Rummel, Ward

    2008-01-01

    This slide presentation reviews the use of terahertz imaging and Backscatter Radiography in a probability of detection study of the foam on the external tank (ET) shedding and damaging the shuttle orbiter. Non-destructive Examination (NDE) is performed as one method of preventing critical foam debris during the launch. Conventional NDE methods for inspection of the foam are assessed and the deficiencies are reviewed. Two methods for NDE inspection are reviewed: Backscatter Radiography (BSX) and Terahertz (THZ) Imaging. The purpose of the Probability of Detection (POD) study was to assess performance and reliability of the use of BSX and or THZ as an appropriate NDE method. The study used a test article with inserted defects, and a sample of blanks included to test for false positives. The results of the POD study are reported.

  3. Terahertz emission from coherent phonons in lithium ternary chalcopyrite crystals illuminated by 1560 nm femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Takeya, K.; Takemoto, Y.; Kawayama, I.; Murakami, H.; Matsukawa, T.; Yoshimura, M.; Mori, Y.; Tonouchi, M.

    2010-07-01

    We have investigated terahertz (THz) emission from lithium ternary chalcopyrite crystals LiInSe2, LiGaSe2, LiInS2, and LiGaS2 that were illuminated by 1560 nm femtosecond pump laser pulses. Monocyclic THz emission caused by nonlinear optical effects was initially observed in all the illuminated crystals. Narrow-band THz emission from the coherent phonons were observed in LiInSe2 (2.87 THz) and LiGaSe2 (2.60 and 3.45 THz). These phonon modes were most likely caused by impulsive stimulated Raman scattering.

  4. Terahertz near-field imaging of surface plasmon waves in graphene structures

    SciTech Connect

    Mitrofanov, O.; Yu, W.; Thompson, R. J.; Jiang, Y.; Greenberg, Z. J.; Palmer, J.; Brener, I.; Pan, W.; Berger, C.; de Heer, W. A.; Jiang, Z.

    2015-09-08

    In this study, we introduce a near-field scanning probe terahertz (THz) microscopy technique for probing surface plasmon waves on graphene. Based on THz time-domain spectroscopy method, this near-field imaging approach is well suited for studying the excitation and evolution of THz plasmon waves on graphene as well as for mapping of graphene properties at THz frequencies on the sub-wavelength scale.

  5. Multi-sensor evaluation of a wooden panel painting using terahertz imaging and shearography

    NASA Astrophysics Data System (ADS)

    Groves, Roger M.; Pradarutti, Boris; Kouloumpi, Eleni; Osten, Wolfgang; Notni, Gunther

    2009-07-01

    Cultural heritage objects are increasingly being investigated using advanced non-destructive optical measurement techniques. Holographic and speckle interferometry based instrumentation allow dimensional measurement of objects at the tens of nanometer scale. For the structural diagnostics of artwork, double-exposure techniques are often used to locate defects, delaminations, voids and other structural features. Shearography is a speckle interferometry configuration that uses a close-to-common-path shearing interferometer configuration to give a direct sensitivity to displacement gradient at the object surface. This configuration is particularly useful for measurements outside the optical laboratory, as the stability requirements are much reduced compared with holography techniques. Terahertz imaging is a new category of sensor, used to investigate materials using electromagnetic radiation in the 0.1 to 10 THz frequency range. At these frequencies many materials become semi-transparent, so bulk structural diagnostics can be performed. Typically terahertz imaging is performed using a scanning pixel, or multi-pixel, sensor. In this manuscript shearography is first used to identify areas of interest of possible structural anomalies in the artwork. These regions of interest are then studied in more detail using the terahertz imaging instrument. Together the two instruments provide an analysis of both the surface and bulk structural features. The approach is demonstrated experimentally using a wooden panel painting.

  6. Combination of silicon phase masks with time-domain spectroscopy for single-scan terahertz imaging

    NASA Astrophysics Data System (ADS)

    Jolly, A.; Gokhan, F. S.; Jolly, J.-C.; Hocquet, S.; Chassagne, B.

    2015-09-01

    We demonstrate the effectiveness of silicon phase masks to implement spatially resolved, multispectral imaging capabilities in the range of terahertz frequencies, using a standard setup of basic interest for time-domain spectrometry with a single-cell source and a single-cell detector. Our principle primarily aims at the development of robust and inexpensive systems. It consists of appropriate space-to-time encoding, in order to ensure single-scan triggering and then take advantage of rapid and self-consistent measurements in the two-dimensional space. The process enables very efficient discrimination giving access to a relevant spatial resolution in the analysis of small size, planar assemblies made of inhomogeneous materials. Benchmark results are provided to validate the concept, thanks to prototyping phase masks with 2 × 2 pixels, prior evidencing actual performance limitations in the case of 3 × 3 pixels. Due to the frequency bandwidth of 0.1-1.5 THz in our setup and to the available operating conditions, currently acceptable pixel resolutions lie in the range of 3-4 mm. Numerical modeling by means of finite elements helps to discuss these numbers and to investigate the relevant theoretical issues, figuring the main propagation issues in connection with a sub-picosecond seed pulse throughout various masks. This involves diffraction and trailing edge effects when crossing the mask together with residual, parasitic reflections. Finally, we give a consistent prospective for improved performance, via realistic updates regarding the architecture of the setup and complementary post-processing. Further values for the attainable spatial resolution then range from 5 × 5 to 6 × 6 pixels.

  7. Application of a high-temperature superconducting detector to terahertz imaging

    NASA Astrophysics Data System (ADS)

    Hellicar, Andrew D.; Du, Jia; Hanham, Stephen M.; Li, Li

    2009-05-01

    The performance of a high temperature superconducting junction detector is evaluated. The detector has been built to explore applications of terahertz imaging. The detector device is a high-temperature superconductor (HTS) Josephson junction, which is integrated with a thin-film ring-slot antenna. The ring-slot antenna is patterned on a magnesium oxide (MgO) substrate which is compatible with the detector's YBCO superconducting material lattice. A hyper-hemispherical lens made from high resistivity float zone silicon (HRFZ-Si) is mounted on the rear side of the substrate. The lens couples energy from an imaging system onto the antenna which couples the energy into the device. An existing terahertz imaging system is used in conjunction with the detector to allow for the exploration of relevant applications. The imaging system is based on a conventional quasi-optical design with a backward-wave oscillator as the source and raster scans samples for image acquisition. The imaging capability of the system has been assessed by trialing a range of applications in both transmission and reflection modes. Applications explored include imaging concealed weapons in packaging, non-destructive testing of materials, and imaging devices through plastic structures. The results generated by the imaging system demonstrate its capability for these applications.

  8. InGaAs-based bow-tie diode for spectroscopic terahertz imaging

    NASA Astrophysics Data System (ADS)

    Kaalynas, I.; Venckevi?ius, R.; Seliuta, D.; Grigelionis, I.; Valuis, G.

    2011-12-01

    Suitability of InGaAs-based bow-tie diodes for a spectroscopic terahertz imaging is demonstrated by inspecting explosive simulators packed in a thick plastic container. The transmission images were obtained within the frequency range of 0.58-2.52 THz at room temperature using optimized bow-tie diode connection scheme. Content of sucrose and tartaric acid in the test samples was discriminated. Measured absorbance was found to be in a good correlation with Fourier spectroscopy data. Performance of room temperature THz imaging using the bow-tie diode was compared versus a commercial pyro-electric sensor.

  9. Review of Moisture and Liquid Detection and Mapping using Terahertz Imaging

    NASA Astrophysics Data System (ADS)

    Federici, John F.

    2012-02-01

    The relatively high permittivity of liquid water compared to other materials in the Terahertz (THz) range enables a contrast mechanism for the detection and imaging of moisture. In this paper, spatial mapping of moisture and liquid detection by THz imaging is reviewed. Analysis of the moisture content is discussed in terms of a double Debye model for liquid water and effective medium models for the permittivity of the dry and `wet' materials of interest. Examples from medical applications, forestry products, agriculture/ food products, and polymers are reviewed. Extraction of diffusion rates and diffusion maps from THz images are discussed.

  10. Terahertz far-field superresolution imaging through spoof surface plasmons illumination.

    PubMed

    Tang, Heng-He; Liu, Pu-Kun

    2015-12-15

    The applications of terahertz (THz) imaging are always restricted by the low resolution. We introduce here a new way to realize far-field superresolution imaging at THz frequency. Assisted by a new spoof surface plasmons (SSP) probe illumination, the images of two subwavelength separated slits can be reconstructed by a single shot. Although only 0.06? resolution is numerically demonstrated at 0.3THz, the resolution potentially can be further enhanced by scaling down the size of the SSP probe. Deep subwavelength focusing is also achieved by the SSP probe. Our work may open a new avenue for SSP-based superresolution at longer wavelengths. PMID:26670521

  11. 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.

  12. 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.

  13. Passive imaging with pulsed ultrasound insonations

    PubMed Central

    Haworth, Kevin J.; Mast, T. Douglas; Radhakrishnan, Kirthi; Burgess, Mark T.; Kopechek, Jonathan A.; Huang, Shao-Ling; McPherson, David D.; Holland, Christy K.

    2012-01-01

    Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set. PMID:22779500

  14. 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.; Rakić, 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.

  15. Spatial pattern separation of chemicals and frequency-independent components by terahertz spectroscopic imaging

    NASA Astrophysics Data System (ADS)

    Watanabe, Yuuki; Kawase, Kodo; Ikari, Tomofumi; Ito, Hiromasa; Ishikawa, Youichi; Minamide, Hiroaki

    2003-10-01

    We separated the component spatial patterns of frequency-dependent absorption in chemicals and frequency-independent components such as plastic, paper, and measurement noise in terahertz (THz) spectroscopic images, using known spectral curves. Our measurement system, which uses a widely tunable coherent THz-wave parametric oscillator source, can image at a specific frequency in the range 1-2 THz. The component patterns of chemicals can easily be extracted by use of the frequency-independent components. This method could be successfully used for nondestructive inspection for the detection of illegal drugs and devices of bioterrorism concealed, e.g., inside mail and packages.

  16. 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.

  17. 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.

  18. Feasibility demonstration of frequency domain terahertz imaging in breast cancer margin determination

    NASA Astrophysics Data System (ADS)

    Yngvesson, Sigfrid K.; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew; Khan, Ashraf

    2012-03-01

    In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This possibility of re-excision is undesirable in terms of reducing patient morbidity, emotional stress and healthcare. It has been shown that terahertz (THz) images of breast specimens can accurately differentiate between breast carcinoma, normal fibroglandular tissue, and adipose tissue. That study employed the Time-Domain Spectroscopy (TDS) technique. We are instead developing a new technique, Frequency-Domain Terahertz Imaging (FDTI). In this joint project between UMass/Amherst and UMass Medical School/Worcester (UMMS), we are investigating the feasibility of the FDTI technique for THz reflection imaging of breast cancer margins. Our system, which produces mechanically scanned images of size 2cm x 2cm, uses a THz gas laser. The system is calibrated with mixtures of water and ethanol and reflection coefficients as low as 1% have been measured. Images from phantoms and specimens cut from breast cancer lumpectomies at UMMS will be presented. Finally, there will be a discussion of a possible transition of this FDTI setup to a compact and inexpensive CMOS THz camera for use in the operating room.

  19. Terahertz sources.

    PubMed

    Shumyatsky, Pavel; Alfano, Robert R

    2011-03-01

    We present an overview and history of terahertz (THz) sources for readers of the biomedical and optical community for applications in physics, biology, chemistry, medicine, imaging, and spectroscopy. THz low-frequency vibrational modes are involved in many biological, chemical, and solid state physical processes. PMID:21456861

  20. An ultrafast carbon nanotube terahertz polarisation modulator

    NASA Astrophysics Data System (ADS)

    Docherty, Callum J.; Stranks, Samuel D.; Habisreutinger, Severin N.; Joyce, Hannah J.; Herz, Laura M.; Nicholas, Robin J.; Johnston, Michael B.

    2014-05-01

    We demonstrate ultrafast modulation of terahertz radiation by unaligned optically pumped single-walled carbon nanotubes. Photoexcitation by an ultrafast optical pump pulse induces transient terahertz absorption in nanowires aligned parallel to the optical pump. By controlling the polarisation of the optical pump, we show that terahertz polarisation and modulation can be tuned, allowing sub-picosecond modulation of terahertz radiation. Such speeds suggest potential for semiconductor nanowire devices in terahertz communication technologies.

  1. An ultrafast carbon nanotube terahertz polarisation modulator

    SciTech Connect

    Docherty, Callum J.; Stranks, Samuel D.; Habisreutinger, Severin N.; Joyce, Hannah J.; Herz, Laura M.; Nicholas, Robin J.; Johnston, Michael B.

    2014-05-28

    We demonstrate ultrafast modulation of terahertz radiation by unaligned optically pumped single-walled carbon nanotubes. Photoexcitation by an ultrafast optical pump pulse induces transient terahertz absorption in nanowires aligned parallel to the optical pump. By controlling the polarisation of the optical pump, we show that terahertz polarisation and modulation can be tuned, allowing sub-picosecond modulation of terahertz radiation. Such speeds suggest potential for semiconductor nanowire devices in terahertz communication technologies.

  2. Spectral modification of the laser emission of a terahertz quantum cascade laser induced by broad-band double pulse injection seeding

    NASA Astrophysics Data System (ADS)

    Markmann, Sergej; Nong, Hanond; Pal, Shovon; Hekmat, Negar; Scholz, Sven; Kukharchyk, Nadezhda; Ludwig, Arne; Dhillon, Sukhdeep; Tignon, Jérôme; Marcadet, Xavier; Bock, Claudia; Kunze, Ulrich; Wieck, Andreas D.; Jukam, Nathan

    2015-09-01

    We demonstrate by injection seeding that the spectral emission of a terahertz (THz) quantum cascade laser (QCL) can be modified with broad-band THz pulses whose bandwidths are greater than the QCL bandwidth. Two broad-band THz pulses delayed in time imprint a modulation on the single THz pulse spectrum. The resulting spectrum is used to injection seed the THz QCL. By varying the time delay between the THz pulses, the amplitude distribution of the QCL longitudinal modes is modified. By applying this approach, the QCL emission is reversibly switched from multi-mode to single mode emission.

  3. Non-contact weight measurement of flat-faced pharmaceutical tablets using terahertz transmission pulse delay measurements.

    PubMed

    Bawuah, Prince; Silfsten, Pertti; Ervasti, Tuomas; Ketolainen, Jarkko; Zeitler, J Axel; Peiponen, Kai-Erik

    2014-12-10

    By measuring the time delay of a terahertz pulse traversing a tablet, and hence its effective refractive index, it is possible to non-invasively and non-destructively detect the weight of tablets made of microcrystalline cellulose (MCC). Two sets of MCC tablets were used in the study: Set A (training set) consisted of 13 tablets with nominally constant height but varying porosities, whereas Set B (test set) comprised of 21 tablets with nominally constant porosity but different heights. A linear correlation between the estimated absolute weight based on the terahertz measurement and the measured weight of both sets of MCC tablets was found. In addition, it was possible to estimate the height of the tablets by utilizing the estimated absolute weight and calculating the relative change of height of each tablet with respect to an ideal tablet. A good agreement between the experimental and the calculated results was found highlighting the potential of this technique for in-line sensing of the weight, porosity and the relative change in height of the tablets compared to a reference/ideal tablet. In this context, we propose a quantitative quality control method to assess the deviations in porosity of tablets immediately after compaction. PMID:25245546

  4. Identification of tissue interaction of terahertz radiation toward functional tissue imaging

    NASA Astrophysics Data System (ADS)

    Yokus, Hamdullah; Baughman, William; Balci, Soner; Bolus, Michael; Wilbert, David; Kung, Patrick; Kim, Seongsin M.

    2013-02-01

    In recent years, many applications have been recognized for biomedical imaging techniques utilizing terahertz frequency radiation. This is largely due to the capability of unique tissue identification resulting from the nature of the interaction between THz radiation and the molecular structure of the cells. By THz identification methods, tissue changes in tooth enamel, cartilage, and malignant cancer cells have already been demonstrated. Terahertz Time-Domain Spectroscopy (THz-TDS) remains one of the most versatile methods for spectroscopic image acquisition for its ability to simultaneously determine amplitude and phase over a broad spectral range. In this study we investigate the use of THz imaging techniques to uniquely identify damage types in tissue samples for both forensic and treatment applications. Using THz-TDS imaging in both transmission and reflection schemes, we examine tissue samples which have been damaged using a variety of acids. Each method of damage causes structural deterioration to the tissue by a different mechanism, thus leaving the remaining tissue uniquely changed based on the damage type. We correlate the change in frequency spectra, phase shift for each damage type to the mechanisms and severity of injury.

  5. 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.

  6. 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.

  7. Systematic experimental study on a highly efficient terahertz source based on two-color laser-induced air plasma

    NASA Astrophysics Data System (ADS)

    Xie, Jun; Fan, Wen-Hui; Chen, Xu

    2016-05-01

    In this paper, highly efficient terahertz radiation generated by two-color femtosecond laser-induced air plasma is reported. A number of variables that can obviously influence terahertz generation and detection have been investigated systematically. The dependence on experimental parameters, including pulse energy, the rotation angle of beta-barium boron oxide (BBO) crystal, the distance between BBO crystal and laser-induced plasma, focal length, chopper frequency, and detection angle are presented, and the optimal values of these parameters have also been obtained experimentally. Finally, a highly efficient terahertz source has been achieved and can be utilized to carry out further investigation on terahertz sensing, spectroscopy, and imaging.

  8. Imaging of large-scale integrated circuits using laser-terahertz emission microscopy.

    PubMed

    Yamashita, Masatsugu; Kawase, Kodo; Otani, Chiko; Kiwa, Toshihiko; Tonouchi, Masayoshi

    2005-01-10

    We present the redesign and improved performance of the laser terahertz emission microscope (LTEM), which is a potential tool for locating electrical failures in integrated circuits. The LTEM produces an image of the THz waves emitted when the circuit is irradiated by a femtosecond laser; the amplitude of the THz emission is proportional to the local electric field. By redesigning the optical setup and improving the spatial resolution of the system to below 3 microm, we could extend its application to examining of large-scale integration circuits. As example we show the THz emission pattern of the electric field in an 8-bit microprocessor chip under bias voltage. PMID:19488334

  9. 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.

  10. Terahertz near-field imaging of electric and magnetic resonances of a planar metamaterial.

    PubMed

    Bitzer, Andreas; Merbold, Hannes; Thoman, Andreas; Feurer, Thomas; Helm, Hanspeter; Walther, Markus

    2009-03-01

    Experimental investigations of the microscopic electric and in particular the magnetic near-fields in metamaterials remain highly challenging and current studies rely mostly on numerical simulations. Here we report a terahertz near-field imaging approach which provides spatially resolved measurements of the amplitude, phase and polarization of the electric field from which we extract the microscopic magnetic near-field signatures in a planar metamaterial constructed of split-ring resonators (SRRs). In addition to studying the fundamental resonances of an individual double SRR unit we further investigate the interaction with neighboring elements. PMID:19259224

  11. Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser.

    PubMed

    Keeley, J; Dean, P; Valavanis, A; Bertling, K; Lim, Y L; Alhathlool, R; Taimre, T; Li, L H; Indjin, D; Rakić, A D; Linfield, E H; Davies, A G

    2015-03-15

    We demonstrate coherent three-dimensional terahertz imaging by frequency modulation of a quantum cascade laser in a compact and experimentally simple self-mixing scheme. Through this approach, we can realize significantly faster acquisition rates compared to previous schemes employing longitudinal mechanical scanning of a sample. We achieve a depth resolution of better than 0.1 μm with a power noise spectral density below -50  dB/Hz, for a sampling time of 10  ms/pixel. PMID:25768165

  12. The ethical dimension of terahertz and millimeter-wave imaging technologies: security, privacy, and acceptability

    NASA Astrophysics Data System (ADS)

    Ammicht Quinn, R.; Rampp, B.

    2009-05-01

    Terahertz and millimeter-wave imaging technologies, wherever they are applied to human beings, generate problems with the "naked" body. Security issues thus inevitably lead to ethical questions of privacy and intimacy. Less apparent but no less important are other issues such as discrimination and the question of reducing this problem through post processing of data; scalability; questions of controlling the controllers; questions of proliferation. Ethical research alone can not provide acceptability. However, ultimately innovative technologies will not achieve widespread and sustainable acceptance without a fundamental clarification of the ethically relevant issues.

  13. Imaging of large-scale integrated circuits using laser-terahertz emission microscopy

    NASA Astrophysics Data System (ADS)

    Yamashita, Masatsugu; Kawase, Kodo; Otani, Chiko; Kiwa, Toshihiko; Tonouchi, Masayoshi

    2005-01-01

    We present the redesign and improved performance of the laser terahertz emission microscope (LTEM), which is a potential tool for locating electrical failures in integrated circuits. The LTEM produces an image of the THz waves emitted when the circuit is irradiated by a femtosecond laser; the amplitude of the THz emission is proportional to the local electric field. By redesigning the optical setup and improving the spatial resolution of the system to below 3 μm, we could extend its application to examining of large-scale integration circuits. As example we show the THz emission pattern of the electric field in an 8-bit microprocessor chip under bias voltage.

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

    SciTech Connect

    Mezzapesa, F. P. Brambilla, M.; Dabbicco, M.; Scamarcio, G.; Columbo, L. L.; Vitiello, M. S.

    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.

  15. Effects of laser-plasma interactions on terahertz radiation from solid targets irradiated by ultrashort intense laser pulses

    SciTech Connect

    Li Chun; Zhou Mulin; Ding Wenjun; Du Fei; Liu Feng; Li Yutong; Wang Weimin; Ma Jinglong; Chen Liming; Lu Xin; Dong Quanli; Wang Zhaohua; Wei Zhiyi; Sheng Zhengming; Zhang Jie; Lou Zheng; Shi Shengcai

    2011-09-15

    Interactions of 100-fs laser pulses with solid targets at intensities of 10{sup 18} W/cm{sup 2} and resultant terahertz (THz) radiation are studied under different laser contrast ratio conditions. THz emission is measured in the specular reflection direction, which appears to decrease as the laser contrast ratio varies from 10{sup -8} to 10{sup -6}. Correspondingly, the frequency spectra of the reflected light are observed changing from second harmonic dominant, three-halves harmonic dominant, to vanishing of both harmonics. Two-dimensional particle-in-cell simulation also suggests that this observation is correlated with the plasma density scale length change. The results demonstrate that the THz emission is closely related to the laser-plasma interaction processes. The emission is strong when resonance absorption is a key feature of the interaction, and becomes much weaker when parametric instabilities dominate.

  16. Effects of laser-plasma interactions on terahertz radiation from solid targets irradiated by ultrashort intense laser pulses.

    PubMed

    Li, Chun; Zhou, Mu-Lin; Ding, Wen-Jun; Du, Fei; Liu, Feng; Li, Yu-Tong; Wang, Wei-Min; Sheng, Zheng-Ming; Ma, Jing-Long; Chen, Li-Ming; Lu, Xin; Dong, Quan-Li; Wang, Zhao-Hua; Lou, Zheng; Shi, Sheng-Cai; Wei, Zhi-Yi; Zhang, Jie

    2011-09-01

    Interactions of 100-fs laser pulses with solid targets at intensities of 10(18) W/cm(2) and resultant terahertz (THz) radiation are studied under different laser contrast ratio conditions. THz emission is measured in the specular reflection direction, which appears to decrease as the laser contrast ratio varies from 10(-8) to 10(-6). Correspondingly, the frequency spectra of the reflected light are observed changing from second harmonic dominant, three-halves harmonic dominant, to vanishing of both harmonics. Two-dimensional particle-in-cell simulation also suggests that this observation is correlated with the plasma density scale length change. The results demonstrate that the THz emission is closely related to the laser-plasma interaction processes. The emission is strong when resonance absorption is a key feature of the interaction, and becomes much weaker when parametric instabilities dominate. PMID:22060511

  17. High-speed terahertz reflection three-dimensional imaging for nondestructive evaluation.

    PubMed

    Jin, Kyong Hwan; Kim, Young-Gil; Cho, Seung Hyun; Ye, Jong Chul; Yee, Dae-Su

    2012-11-01

    We demonstrate high-speed terahertz (THz) reflection three-dimensional (3D) imaging based on electronically controlled optical sampling (ECOPS). ECOPS enables scanning of an axial range of 9 mm in free space at 1 kHz. It takes 80 s to scan a transverse range of 100 mm × 100 mm along a zigzag trajectory that consists of 200 lines using translation stages. To show applicability of the imaging system to nondestructive evaluation, a THz reflection 3D image of an artificially made sample 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. PMID:23187360

  18. Three-dimensional sparse image reconstruction for terahertz surface layer holography with random step frequency.

    PubMed

    Liu, Wei; Li, Chao; Sun, Zhaoyang; Zhang, Qunying; Fang, Guangyou

    2015-07-15

    In this Letter, a sparse image reconstruction approach is proposed for three-dimensional (3D) terahertz (THz) surface layer holography by a sharply dwindled amount of frequency samples, without reducing the high quality of the final reconstructed 3D THz images. To avoid the range ambiguity resulting from the reduction of frequency samples, a random step frequency method is adopted to evaluate the rough range profile of the 3D surface layer. With the obtained range profile, a de-ambiguity procedure is proposed to demodulate the sparse echoed data to greatly compress the maximum nonambiguous range and recover all the information for 3D holography image reconstruction. Proof-of-state experiments are performed in 0.2-THz band. The results verify the effectiveness and the efficiency of the sparse imaging scheme for THz surface layer 3D holography. PMID:26176475

  19. Foreign object detection by sub-terahertz quasi-Bessel beam imaging.

    PubMed

    Ok, Gyeongsik; Choi, Sung-Wook; Park, Kyung Hyun; Chun, Hyang Sook

    2012-01-01

    Food quality monitoring, particularly foreign object detection, has recently become a critical issue for the food industry. In contrast to X-ray imaging, terahertz imaging can provide a safe and ionizing-radiation-free nondestructive inspection method for foreign object sensing. In this work, a quasi-Bessel beam (QBB) known to be nondiffracting was generated by a conical dielectric lens to detect foreign objects in food samples. Using numerical evaluation via the finite-difference time-domain (FDTD) method, the beam profiles of a QBB were evaluated and compared with the results obtained via analytical calculation and experimental characterization (knife edge method, point scanning method). The FDTD method enables a more precise estimation of the beam profile. Foreign objects in food samples, namely crickets, were then detected with the QBB, which had a deep focus and a high spatial resolution at 210 GHz. Transmitted images using a Gaussian beam obtained with a conventional lens were compared in the sub-terahertz frequency experimentally with those using a QBB generated using an axicon. PMID:23344374

  20. Foreign Object Detection by Sub-Terahertz Quasi-Bessel Beam Imaging

    PubMed Central

    Ok, Gyeongsik; Choi, Sung-Wook; Park, Kyung Hyun; Chun, Hyang Sook

    2013-01-01

    Food quality monitoring, particularly foreign object detection, has recently become a critical issue for the food industry. In contrast to X-ray imaging, terahertz imaging can provide a safe and ionizing-radiation-free nondestructive inspection method for foreign object sensing. In this work, a quasi-Bessel beam (QBB) known to be nondiffracting was generated by a conical dielectric lens to detect foreign objects in food samples. Using numerical evaluation via the finite-difference time-domain (FDTD) method, the beam profiles of a QBB were evaluated and compared with the results obtained via analytical calculation and experimental characterization (knife edge method, point scanning method). The FDTD method enables a more precise estimation of the beam profile. Foreign objects in food samples, namely crickets, were then detected with the QBB, which had a deep focus and a high spatial resolution at 210 GHz. Transmitted images using a Gaussian beam obtained with a conventional lens were compared in the sub-terahertz frequency experimentally with those using a QBB generated using an axicon. PMID:23344374

  1. Intense, carrier frequency and bandwidth tunable quasi single-cycle pulses from an organic emitter covering the Terahertz frequency gap

    NASA Astrophysics Data System (ADS)

    Vicario, C.; Monoszlai, B.; Jazbinsek, M.; Lee, S.-H.; Kwon, O.-P.; Hauri, C. P.

    2015-09-01

    In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1-15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light.

  2. Intense, carrier frequency and bandwidth tunable quasi single-cycle pulses from an organic emitter covering the Terahertz frequency gap

    PubMed Central

    Vicario, C.; Monoszlai, B.; Jazbinsek, M.; Lee, S. -H.; Kwon, O. -P.; Hauri, C. P.

    2015-01-01

    In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1–15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light. PMID:26400005

  3. Intense, carrier frequency and bandwidth tunable quasi single-cycle pulses from an organic emitter covering the Terahertz frequency gap.

    PubMed

    Vicario, C; Monoszlai, B; Jazbinsek, M; Lee, S-H; Kwon, O-P; Hauri, C P

    2015-01-01

    In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1-15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light. PMID:26400005

  4. 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.

  5. Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K

    NASA Astrophysics Data System (ADS)

    Du, Jia; Hellicar, A. D.; Hanham, S. M.; Li, L.; Macfarlane, J. C.; Leslie, K. E.; Foley, C. P.

    2011-05-01

    A high-Tc superconducting (HTS) broadband Josephson detector has been developed and applied to millimetre wave (mm-wave) and terahertz (THz) imaging. The detector is based on a YBa2Cu3O7-x (YBCO) step-edge Josephson junction, which is coupled to a thin-film log-periodic antenna, designed for operation at 200-600 GHz, and a hemispheric silicon lens. The junction parameters have been optimised to achieve a high IcRn value so that the detector responds well to the specified frequencies at liquid nitrogen temperature (77 K). Images at ˜200 GHz and ˜600 GHz were acquired with the same detector; each demonstrated their unique properties. The results demonstrate the potential of achieving a cheaper, compact and portable multi-spectral imager based on a HTS detector.

  6. Dual-frequency imaging using an electrically tunable terahertz quantum cascade laser.

    PubMed

    Dean, Paul; Saat, Nor Kamila; Khanna, Suraj P; Salih, Mohammed; Burnett, Andrew; Cunningham, John; Linfield, Edmund H; Davies, A Giles

    2009-11-01

    We report dual-frequency transmission imaging of polycrystalline materials using an electrically tunable terahertz (THz) frequency quantum cascade laser (QCL). Using our system we are able to obtain images at both 3.05 THz and 3.24 THz in a single two-dimensional scan of a sample. By taking the difference of the natural logarithms of the transmission coefficients obtained at each frequency, the difference-attenuation coefficient is determined, and evaluated for samples of lactose monohydrate, glucose monohydrate, sucrose, and the high explosive PETN. We also demonstrate difference-intensity imaging at these frequencies by combining amplitude modulation of the QCL bias with lock-in detection. Owing to the specific molecular absorption spectra of these materials in the THz frequency range, the samples can be distinguished using our technique. PMID:19997292

  7. Ionic contrast terahertz near-field imaging of axonal water fluxes

    PubMed Central

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

    2006-01-01

    We demonstrate the direct and noninvasive imaging of functional neurons by ionic contrast terahertz near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductances and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ionic contrast terahertz microscopy technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. Water influx as small as 20 fl per ?m of axonal length can be measured. This technique should then provide grounds for the development of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules. PMID:16547134

  8. Screening mail for powders using terahertz technology

    NASA Astrophysics Data System (ADS)

    Kemp, Mike

    2011-11-01

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

  9. Backside observation of large-scale integrated circuits with multilayered interconnections using laser terahertz emission microscope

    NASA Astrophysics Data System (ADS)

    Yamashita, Masatsugu; Otani, Chiko; Kawase, Kodo; Matsumoto, Toru; Nikawa, Kiyoshi; Kim, Sunmi; Murakami, Hironaru; Tonouchi, Masayoshi

    2009-05-01

    We have developed a laser terahertz emission microscope utilizing excitation laser pulses at 1.06 μm wavelength for the inspection and localization of electrical failures in large-scale integrated circuits with multilayered interconnection structures. The system enables to measure terahertz emission images from the backside of a large-scale integrated circuits chip with a multilayered interconnection structure that prevents the observation from the front side. By comparing the terahertz emission images, we successfully distinguish a normal circuit from damaged ones with different positions of the interconnection defects without any electrical probing.

  10. 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

  11. Ultrafast far-infrared dynamics probed by terahertz pulses: A frequency-domain approach. II. Applications

    NASA Astrophysics Data System (ADS)

    Němec, H.; Kadlec, F.; Kadlec, C.; Kužel, P.; Jungwirth, P.

    2005-03-01

    We present data obtained by time-resolved terahertz spectroscopy in selected semiconducting and molecular systems exhibiting subpicosecond far-infrared dynamics. We use a frequency-domain method which eliminates the influence of instrumental functions and artifacts due to frequency mixing and yields a two-dimensional transient conductivity of the photoexcited sample. This technique enables improving the attainable experimental time resolution and allows a simple qualitative interpretation of the results without a priori modeling. The quantitative interpretation is based on the time-dependent Drude and damped harmonic oscillator models.

  12. Narrowband continuous-wave terahertz generation and imaging

    NASA Astrophysics Data System (ADS)

    Dolasinski, Brian; Powers, Peter

    2014-03-01

    The output of seeded, dual periodically poled lithium niobate (PPLN) optical parametric generators (OPG) are combined in the nonlinear crystal 4-dimthylamino-N-methyl-4-stilbazolium-tosylate (DAST) to produce a widely tunable narrowband THz source via difference frequency generation (DFG). We have demonstrated that by employing this type of configuration we are able to tune our system seamlessly, without mode-hops, from 1.5 THz to 21THz with a minimum bandwidth of 3.1 GHz. The bandwidth of the source was measured by using the THz transmission spectrum of water vapor lines over a 3-meter path length. By selecting of the DFG pump wavelength to be at 1380 nm and the signal wavelength to tune over a range from 1380 nm to 1570 nm, we produced several maxima in the output THz spectrum that was dependent on the phase matching ability of the DAST crystal and the efficiency of our pyro-electric detector. Due to the effects of dispersive phase matching, filter absorption of the THz waves, and two-photon absorption multiple band gaps in the overall spectrum occur and are discussed. Employing the dual generator scheme, we have obtained THz images at several locations in the spectrum using an infrared camera that runs at a rate of 35 frames per second. We have demonstrated the ability to image 13 THz to 20 THz under static conditions. We will present images of carbon fibers illuminated at different THz frequencies.

  13. 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

  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. A cryogen-free HTS Josephson junction detector for terahertz imaging

    NASA Astrophysics Data System (ADS)

    Du, J.; Smart, K.; Li, L.; Leslie, K. E.; Hanham, S. M.; Wang, D. H. C.; Foley, C. P.; Ji, F.; Li, X. D.; Zeng, D. Z.

    2015-08-01

    A cryogen-free terahertz (THz) imaging system based on a high-temperature superconducting (HTS) Josephson junction detector is reported. The detector was made of a YBa2Cu3O7-x step-edge Josephson junction and integrated into an on-chip thin-film antenna. The HTS Josephson detector was cooled via a commercial mechanical cryocooler; an important step towards cryogen-free THz instrumentation, which is critical for industrial acceptance. In addition, it is shown that operating the detector in a cryocooler provides improved flexibility for optimizing the detector parameters and performance due to the ability to adjust the temperature compared to liquid nitrogen cooling methods. The dc and ac characteristics, the detector responsivity and the noise-equivalent power of the detector, and resulting image quality were studied as the function of operating temperatures.

  16. Terahertz imaging and tomography as efficient instruments for testing polymer additive manufacturing objects.

    PubMed

    Perraud, J B; Obaton, A F; Bou-Sleiman, J; Recur, B; Balacey, H; Darracq, F; Guillet, J P; Mounaix, P

    2016-05-01

    Additive manufacturing (AM) technology is not only used to make 3D objects but also for rapid prototyping. In industry and laboratories, quality controls for these objects are necessary though difficult to implement compared to classical methods of fabrication because the layer-by-layer printing allows for very complex object manufacturing that is unachievable with standard tools. Furthermore, AM can induce unknown or unexpected defects. Consequently, we demonstrate terahertz (THz) imaging as an innovative method for 2D inspection of polymer materials. Moreover, THz tomography may be considered as an alternative to x-ray tomography and cheaper 3D imaging for routine control. This paper proposes an experimental study of 3D polymer objects obtained by additive manufacturing techniques. This approach allows us to characterize defects and to control dimensions by volumetric measurements on 3D data reconstructed by tomography. PMID:27140357

  17. Sequencing using pulsed field and image reconstruction.

    PubMed Central

    Noolandi, J; Forsyth, R; Shi, A C

    1993-01-01

    The use of pulsed fields in a standard manual sequencing set-up results in the separation of > 2 kb on a single gel, as compared to 300-400 bases with a dc field. However, visual reading of the sequence from a film exposed to a pulsed-field gel is not possible for more than 800-900 bases under the best conditions. The use of image reconstruction and enhancement techniques allows the reading of the M13mp18 sequence to > 1 kb, and individual bands can be identified at > 2 kb. Images Fig. 1 Fig. 4 PMID:8234263

  18. FDTD-based computed terahertz wave propagation in multilayer medium structures

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  19. Detection of foreign bodies in foods using continuous wave terahertz imaging.

    PubMed

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

    2012-01-01

    Foreign bodies (FBs) in food are health hazards and quality issues for many food manufacturers and enforcement authorities. In this study, continuous wave (CW) terahertz (THz) imaging at 0.2 THz with an output power of 10 mW was compared with X-ray imaging as techniques for inspection of food for FBs. High-density FBs, i.e., aluminum and granite pieces of various sizes, were embedded in a powdered instant noodle product and detected using THz and X-ray imaging. All aluminum and granite pieces (regular hexahedrons with an edge length of 1 to 5 mm) were visualized by both CW THz and X-ray imaging. THz imaging also detected maggots (length = 8 to 22 mm) and crickets (length = 35 and 50 mm), which were embedded in samples as low density FBs. However, not all sizes of maggot pieces embedded in powdered instant noodle were detected with X-ray imaging, although larger crickets (length = 50 mm and thickness = 10 mm) were detected. These results suggest that CW THz imaging has potential for detecting both high-density and low-density FBs embedded in food. PMID:22221375

  20. Applications of pulse radiolysis to imaging sciences

    SciTech Connect

    Meisel, D.

    1996-05-01

    Pulse radiolysis has been used over the last 3 decades to study a variety of physical and chemical systems, including those relevant to imaging processes. This review outlines the similarities between photolysis and radiolysis and highlight the differences. It focuses on time-resolved variants of the two disciplines, flash photolysis vs pulse radiolysis. The strength (and weakness) of the radiolytic techniques is their nonspecificity; the energy is always absorbed by the solvent and not the solute. Radiation chemistry principles that were developed for one discipline are easily transportable to another. The pulse radiolysis technique with a wide arsenal of detection techniques is currently used to identify short-lived intermediates and to determine their kinetic and thermodynamic properties. Together, these studies provide mechanistic insight into the behavior of physical systems. We demonstrate the utility of the approach in several areas of interest to imaging sciences: clustering of silver atoms, growth of silver halides, and medium effects on these systems.

  1. Generation of longitudinally polarized terahertz pulses with field amplitudes exceeding 2 kV/cm

    SciTech Connect

    Cliffe, M. J. Rodak, A.; Graham, D. M.; Jamison, S. P.

    2014-11-10

    We demonstrate the generation of near-single cycle longitudinally polarized terahertz radiation using a large-area radially biased photoconductive antenna with a longitudinal field amplitude in excess of 2 kV/cm. The 76 mm diameter antenna was photo-excited by a 0.5 mJ amplified near-infrared femtosecond laser system and biased with a voltage of up to 100 kV applied over concentric electrodes. Amplitudes for both the transverse and longitudinal field components of the source were measured using a calibrated electro-optic detection scheme. By tightly focusing the radiation emitted from the photoconductive antenna, we obtained a maximum longitudinal field amplitude of 2.22 kV/cm with an applied bias field of 38.5 kV/cm.

  2. Study of propagation and detection methods of terahertz radiation for spectroscopy and imaging

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Aparajita

    The applications of terahertz (THz, 1 THz is 1012 cycles per second or 300 mu m in wavelength) radiation are rapidly expanding. In particular, THz imaging is emerging as a powerful technique to spatially map a wide variety of objects with spectral features which are present for many materials in THz region. Objects buried within dielectric structures can also be imaged due to the transparency of most dielectrics in this regime. Unfortunately, the image quality in such applications is inherently influenced by the scattering introduced by the sample inhomogeneities and by the presence of barriers that reduces both the transmitted power and the spatial resolution in particular frequency components. For continued development in THz radiation imaging, a comprehensive understanding of the role of these factors on THz radiation propagation and detection is vital. This dissertation focuses on the various aspects like scattering, attenuation, frequency filtering and waveguide propagation of THz radiation and its subsequent application to a stand-off THz interferometric imager under development. Using THz Time Domain spectroscopic set-up, the effect of scattering, guided THz propagation with loss and dispersion profile of hollow-core waveguides and various filtering structures are investigated. Interferometric detection scheme and subsequent agent identification is studied in detail using extensive simulation and modeling of various imaging system parameters.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  4. Terahertz wavefront assessment based on 2D electro-optic imaging

    NASA Astrophysics Data System (ADS)

    Cahyadi, Harsono; Ichikawa, Ryuji; Degert, Jérôme; Freysz, Eric; Yasui, Takeshi; Abraham, Emmanuel

    2015-03-01

    Complete characterization of terahertz (THz) radiation becomes an interesting yet challenging study for many years. In visible optical region, the wavefront assessment has been proved as a powerful tool for the beam profiling and characterization, which consequently requires 2-dimension (2D) single-shot acquisition of the beam cross-section to provide the spatial profile in time- and frequency-domain. In THz region, the main problem is the lack of effective THz cameras to satisfy this need. In this communication, we propose a simple setup based on free-space collinear 2D electrooptic sampling in a ZnTe crystal for the characterization of THz wavefronts. In principle, we map the optically converted, time-resolved data of the THz pulse by changing the time delay between the probe pulse and the generated THz pulse. The temporal waveforms from different lens-ZnTe distances can clearly indicate the evolution of THz beam as it is converged, focused, or diverged. From the Fourier transform of the temporal waveforms, we can obtain the spectral profile of a broadband THz wave, which in this case within the 0.1-2 THz range. The spectral profile also provides the frequency dependency of the THz pulse amplitude. The comparison between experimental and theoretical results at certain frequencies (here we choose 0.285 and 1.035 THz) is in a good agreement suggesting that our system is capable of THz wavefront characterization. Furthermore, the implementation of Hartmann/Shack-Hartmann sensor principle enables the reconstruction of THz wavefront. We demonstrate the reconstruction of THz wavefronts which are changed from planar wave to spherical one due to the insertion of convex THz lens in the THz beam path. We apply and compare two different reconstruction methods: linear integration and Zernike polynomial. Roughly we conclude that the Zernike method provide smoother wavefront shape that can be elaborated later into quantitative-qualitative analysis about the wavefront distortion.

  5. Discrete spectrum terahertz imaging using bow-tie diodes: optimized antenna designs and arrays

    NASA Astrophysics Data System (ADS)

    Minkevičius, Linas; Madeikis, Karolis; Kašalynas, Irmantas; Venckevičius, Rimvydas; Seliuta, Dalius; TamošiÅ«nas, Vincas; Valušis, Gintaras

    2013-09-01

    Optimization routes to optimize the operation of InGaAs bow-tie diodes were demonstrated using simulations based on 3D finite-difference time-domain method. Calculations of the electromagnetic field amplitude distribution in a detector plane were performed. Three types of designs - bow-tie diode itself, log-periodic antenna and log-periodic antenna coupled with the bow-tie diode were analyzed; it was determined that frequency properties of such antennacoupled device can be tuned via variation of antenna shape and size. Multi-pixel InGaAs bow-tie diodes arrays of different designs - narrow band and broadband operation - were designed and fabricated. They were demonstrated to be well suited for continuous wave room temperature spectroscopic terahertz imaging at 0.58 THz and at 1.63 THz.

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

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

    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 processing and modeling are then proposed to improve on the flaw detection. Preliminary results are presented on a series of multi-dimensional signal processing operations of T-ray signals. The use of models and their comparisons with experimental data from foam samples are also included.

  7. Imaging embryonic development with ultrashort pulse microscopy

    NASA Astrophysics Data System (ADS)

    Gibbs, Holly C.; Bai, Yuqiang; Lekven, Arne C.; Yeh, Alvin T.

    2014-05-01

    We report the application of ultrashort pulse microscopy (UPM) for integrated imaging of embryonic development at the tissue, cell, and molecular length scales. The UPM is a multimodal imaging platform that utilizes the broad-power spectrum and high-peak power of 10-fs pulses to render two-photon excited signals and the short coherence gate of such pulses to render optical coherence signals. We show that ultrashort pulses efficiently excite cellular autofluorescence in developing zebrafish embryos such that tissues are readily visualized and individual cells can be monitored, providing a potential method for label-free cell tracking. We also show the ability of ultrashort pulses, without tuning, to excite a broad spectrum of fluorescent protein variants for tracking genetically labeled cell lineages in live embryos, with no apparent damage to the embryos. Molecular information at the mRNA transcript level can also be obtained from embryos that have been stained to reveal the localization of the expression of a gene using NBT/BCIP, which we show can be detected with three-dimensional resolution using a combination of two-photon and optical coherence signals. From this demonstration, we conclude that UPM is an efficient and a powerful tool for elucidating the dynamic multiparameter and multiscale mechanisms of embryonic development.

  8. 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.

    2015-08-01

    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.

  9. Near-field terahertz imaging using sub-wavelength apertures without cutoff.

    PubMed

    Liu, Shuchang; Mitrofanov, Oleg; Nahata, Ajay

    2016-02-01

    We demonstrate near-field imaging capabilities of a conical waveguide without cutoff using broadband terahertz (THz) radiation. In contrast to conventional conically tapered waveguides, which are characterized by strong suppression of transmission below the cutoff frequency, the proposed structure consists of two pieces, such that there is an adjustable gap along the length of the waveguide. We also ensure that the sidewalls are thin in the vicinity of the gap. The combination of these geometrical features allow for significantly enhanced transmission at frequencies below the cutoff frequency, without compromising the mode confinement and, consequently, the spatial resolution when used for imaging applications. We demonstrate near-field imaging with this probe simultaneously at several frequencies, corresponding to three regimes: above, near and below the cutoff frequency. We observe only mild degradation in the image quality as the frequency is reduced below the cutoff frequency. These results suggest that further refinements in the probe structure will allow for improved imaging capabilities at frequencies well below the cutoff frequency. PMID:26906843

  10. Terahertz imaging with sub-wavelength resolution by femtosecond laser filament in air

    PubMed Central

    Zhao, Jiayu; Chu, Wei; Guo, Lanjun; Wang, Zhi; Yang, Jing; Liu, Weiwei; Cheng, Ya; Xu, Zhizhan

    2014-01-01

    Terahertz (THz) imaging provides cutting edge technique in biology, medical sciences and non-destructive evaluation. However, due to the long wavelength of the THz wave, the obtained resolution of THz imaging is normally a few hundred microns and is much lower than that of the traditional optical imaging. We introduce a sub-wavelength resolution THz imaging technique which uses the THz radiation generated by a femtosecond laser filament in air as the probe. This method is based on the fact that the femtosecond laser filament forms a waveguide for the THz wave in air. The diameter of the THz beam, which propagates inside the filament, varies from 20 μm to 50 μm, which is significantly smaller than the wavelength of the THz wave. Using this highly spatially confined THz beam as the probe, THz imaging with resolution as high as 20 μm (~λ/38 at 0.4 THz) can be realized. PMID:24457525

  11. Sequencing using pulsed field and image reconstruction

    SciTech Connect

    Noolandi, J.; Forsyth, R.; Shi, An-Chang )

    1993-11-15

    The use of pulsed fields in a standard manual sequencing set-up results in the separation of >2 kb on a single gel, as compared to 300-400 bases with a dc field. However, visual reading of the sequence from a film exposed to a pulsed-field gel is not possible for more that 800-900 bases under the best conditions. The use of image reconstruction and enhancement techniques allows the reading of the M13mp18 sequence to>1 kb, and individual bands can be identified at>2 kb.

  12. 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.

  13. Terahertz NDE for Metallic Surface Roughness Evaluation

    NASA Technical Reports Server (NTRS)

    Madaras, Eric I.; Anastasi, Robert F.

    2006-01-01

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

  14. Coded Pulse Excitation for Ultrasonic Strain Imaging

    PubMed Central

    Liu, Jie; Insana, Michael F.

    2009-01-01

    Decorrelation strain noise can be significantly reduced in low echo-signal-to-noise (eSNR) conditions using coded excitation. Large time-bandwidth-product (>30) pulses are transmitted into tissue mimicking phantoms with 2.5-mm diameter inclusions that mimic the elastic properties of breast lesions. We observed a 5–10 dB improvement in eSNR that led to a doubling of the depth of focus for strain images with no reduction of spatial resolution. In high eSNR conditions, coded excitation permits the use of higher carrier frequencies and shorter correlation windows to improve the attainable spatial resolution for strain relative to that obtained with conventional short pulses. This paper summarizes comparative studies of strain imaging in noise-limited conditions obtained by short pulses and four common aperiodic codes (chirp, Barker, suboptimal, and Golay) as a function of attenuation, eSNR and applied strain. Imaging performance is quantified using SNR for displacement (SNRd), local modulation transfer function (LMTF), and contrast-to-noise ratio for strain (CNRϵ). We found that chirp and Golay codes are the most robust for imaging soft tissue deformation using matched filter decoding. Their superior performance is obtained by balancing the need for low-range lobes, large eSNR improvement, and short-code duration. PMID:15801311

  15. 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.

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

    PubMed Central

    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.; Rakić, Aleksandar D.

    2014-01-01

    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

  17. High-speed terahertz reflection three-dimensional imaging using beam steering.

    PubMed

    Yee, Dae-Su; Jin, Kyong Hwan; Yahng, Ji Sang; Yang, Ho-Soon; Kim, Chi Yup; Ye, Jong Chul

    2015-02-23

    High-speed terahertz (THz) reflection three-dimensional (3D) imaging is demonstrated using electronically-controlled optical sampling (ECOPS) and beam steering. ECOPS measurement is used for scanning an axial range of 7.8 mm in free space at 1 kHz scan rate while a transverse range of 100 × 100 mm(2) is scanned using beam steering instead of moving an imaging target. Telecentric f-θ lenses with axial and non-axial symmetry have been developed for beam steering. It is experimentally demonstrated that the non-axially symmetric lens has better characteristics than the axially symmetric lens. The total scan time depends on the number of points in a transverse range. For example, it takes 40 s for 200 × 200 points and 10 s for 100 × 100 points. To demonstrate the application of the imaging technique to nondestructive testing, THz 3D tomographic images of a glass fiber reinforced polymer sample with artificial internal defects have been acquired using the lenses for comparison. PMID:25836537

  18. In vivo confirmation of hydration based contrast mechanisms for terahertz medical imaging using MRI

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Sung, Shijun; Garritano, James; Nowroozi, Bryan; Tewari, Priyamvada; Ennis, Daniel B.; Alger, Jeffery; Grundfest, Warren; Taylor, Zachary

    2014-09-01

    Terahertz (THz) detection has been proposed and applied to a variety of medical imaging applications in view of its unrivaled hydration profiling capabilities. Variations in tissue dielectric function have been demonstrated at THz frequencies to generate high contrast imagery of tissue, however, the source of image contrast remains to be verified using a modality with a comparable sensing scheme. To investigate the primary contrast mechanism, a pilot comparison study was performed in a burn wound rat model, widely known to create detectable gradients in tissue hydration through both injured and surrounding tissue. Parallel T2 weighted multi slice multi echo (T2w MSME) 7T Magnetic Resonance (MR) scans and THz surface reflectance maps were acquired of a full thickness skin burn in a rat model over a 5 hour time period. A comparison of uninjured and injured regions in the full thickness burn demonstrates a 3-fold increase in average T2 relaxation times and a 15% increase in average THz reflectivity, respectively. These results support the sensitivity and specificity of MRI for measuring in vivo burn tissue water content and the use of this modality to verify and understand the hydration sensing capabilities of THz imaging for acute assessments of the onset and evolution of diseases that affect the skin. A starting point for more sophisticated in vivo studies, this preliminary analysis may be used in the future to explore how and to what extent the release of unbound water affects imaging contrast in THz burn sensing.

  19. Planar Circulator for Sub-Terahertz-Wave Reflection-Geometry Imaging

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Yamamoto, Hiroshi; Muramoto, Yoshifumi; Ishibashi, Tadao

    2011-11-01

    A planar circulator circuit (PCC) implementing a 180° hybrid circuit for reflection-geometry sub-terahertz-wave imaging has been developed. The PCC is evaluated by measuring its signal transfer characteristics at around 300 GHz. A resonant behavior with a unidirectional cycling transmittance is observed in the PCC at around 270 GHz, indicating the proper function of the PCC as a circulator. The peak signal-to-background ratio is measured to be about 10. The PCC is integrated with a uni-traveling-carrier photodiode and a Schottky barrier diode to construct a photonic transceiver module. The characteristics of the PCC in the module are also evaluated by measuring images of a test sample. Although the image resolution decreases with signal frequency deviation from the resonant condition, it is confirmed that a practical contrast can be obtained for a bandwidth of about 40 GHz. Using the fabricated transceiver, the in vivo imaging of a human finger at 270 GHz is successfully demonstrated.

  20. Terahertz Wide-Angle Imaging and Analysis on Plane-wave Criteria Based on Inverse Synthetic Aperture Techniques

    NASA Astrophysics Data System (ADS)

    Gao, Jing Kun; Qin, Yu Liang; Deng, Bin; Wang, Hong Qiang; Li, Jin; Li, Xiang

    2016-04-01

    This paper presents two parts of work around terahertz imaging applications. The first part aims at solving the problems occurred with the increasing of the rotation angle. To compensate for the nonlinearity of terahertz radar systems, a calibration signal acquired from a bright target is always used. Generally, this compensation inserts an extra linear phase term in the intermediate frequency (IF) echo signal which is not expected in large-rotation angle imaging applications. We carried out a detailed theoretical analysis on this problem, and a minimum entropy criterion was employed to estimate and compensate for the linear-phase errors. In the second part, the effects of spherical wave on terahertz inverse synthetic aperture imaging are analyzed. Analytic criteria of plane-wave approximation were derived in the cases of different rotation angles. Experimental results of corner reflectors and an aircraft model based on a 330-GHz linear frequency-modulated continuous wave (LFMCW) radar system validated the necessity and effectiveness of the proposed compensation. By comparing the experimental images obtained under plane-wave assumption and spherical-wave correction, it also showed to be highly consistent with the analytic criteria we derived.

  1. Terahertz Wide-Angle Imaging and Analysis on Plane-wave Criteria Based on Inverse Synthetic Aperture Techniques

    NASA Astrophysics Data System (ADS)

    Gao, Jing Kun; Qin, Yu Liang; Deng, Bin; Wang, Hong Qiang; Li, Jin; Li, Xiang

    2016-01-01

    This paper presents two parts of work around terahertz imaging applications. The first part aims at solving the problems occurred with the increasing of the rotation angle. To compensate for the nonlinearity of terahertz radar systems, a calibration signal acquired from a bright target is always used. Generally, this compensation inserts an extra linear phase term in the intermediate frequency (IF) echo signal which is not expected in large-rotation angle imaging applications. We carried out a detailed theoretical analysis on this problem, and a minimum entropy criterion was employed to estimate and compensate for the linear-phase errors. In the second part, the effects of spherical wave on terahertz inverse synthetic aperture imaging are analyzed. Analytic criteria of plane-wave approximation were derived in the cases of different rotation angles. Experimental results of corner reflectors and an aircraft model based on a 330-GHz linear frequency-modulated continuous wave (LFMCW) radar system validated the necessity and effectiveness of the proposed compensation. By comparing the experimental images obtained under plane-wave assumption and spherical-wave correction, it also showed to be highly consistent with the analytic criteria we derived.

  2. Nonresonant coherent control: Intersubband excitations manipulated by a nonresonant terahertz pulse

    NASA Astrophysics Data System (ADS)

    Folpini, Giulia; Morrill, Drew; Somma, Carmine; Reimann, Klaus; Woerner, Michael; Elsaesser, Thomas; Biermann, Klaus

    2015-08-01

    We present an approach for controlling quantum coherences in condensed matter by interaction with a nonresonant optical control field. Coherent intersubband (IS) excitations of electrons in GaAs/AlGaAs quantum wells are manipulated by a strong nonresonant terahertz (THz) field as demonstrated by phase-resolved two-color two-dimensional spectroscopy. In the linear regime of IS response, we observe a THz-induced enhancement of the midinfrared (MIR) IS absorption and a dispersive perturbed free induction decay caused by a THz-induced blueshift of the IS polarization. In the regime of IS Rabi oscillations, the THz field causes pronounced phase shifts of the coherently emitted MIR field, while the IS Rabi frequency remains unaffected. Such behavior is accounted for by a full solution of the Maxwell-Bloch equations, treating the THz and MIR fields without approximations. Our control scheme paves the way for THz control of IS emitters and holds potential for an extension to other systems.

  3. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ultrasonic pulsed echo imaging system. 892.1560... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project...

  4. CARS imaging with a single laser pulse

    NASA Astrophysics Data System (ADS)

    Heinrich, Christoph; Bernet, Stefan; Ritsch-Marte, Monika

    2005-09-01

    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 CARS signal of the surrounding solvent can be excited (negative contrast) as well as the signal of the structure embedded by the solvent (positive contrast). As a biological sample we used slices of a sunflower seed and tuned to the vibrational transition of its ingredient - linoleic acid - at 2870 cm-1 which corresponds to the strongest C-H stretching vibration. Even with a single pair of laser pulses of 3 ns duration it was possible to acquire a rough, but still meaningful image.

  5. Thermal Effusivity Tomography from Pulsed Thermal Imaging

    SciTech Connect

    Sun, Jiangang

    2006-12-01

    The software program generates 3D volume distribution of thermal effusivity within a test material from one-sided pulsed thermal imaging data. Thsi is the first software capable of accurate, fast and automated thermal tomographic imaging of inhomogeneous materials to produce 3D images similar to those obtained from 3D X-ray CT (all previous thermal-imaging software can only produce 2D results). Because thermal effusivity is an intrisic material property that is related to material constituent, density, conductivity, etc., quantitative imaging of effusivity allowed direct visualization of material's internal constituent/structure and damage distributions, thereby potentially leading to quantitative prediction of other material properties such as strength. I can be therefre be used for 3D imaging of material structure in fundamental material studies, nondestructive characterization of defects/flaws in structural engineering components, health monitoring of material damage and degradation during service, and medical imaging and diagnostics. This technology is one-sided, non contact and sensitive to material's thermal property and discontinuity. One major advantage of this tomographic technology over x-ray CT and ultrasounds is its natural efficiency for 3D imaging of the volume under a large surface area. This software is implemented with a method for thermal computed tomography of thermal effusivity from one-sided pulsed thermal imaging (or thermography) data. The method is based on several solutions of the governing heat transfer equation under pulsed thermography test condition. In particular, it consists of three components. 1) It utilized the thermal effusivity as the imaging parameter to construct the 3D image. 2) It established a relationship between the space (depth) and the time, because thermography data are in the time domain. 3) It incorporated a deconvolution algorithm to solve the depth porfile of the material thermal effusivity from the measured (temporal) surface temperature data. The predicted effusivity is a direct function of depth, not an average or convolved parameter, so it is an accurate (and more sensitive) representation of local property along depth.

  6. Thermal Effusivity Tomography from Pulsed Thermal Imaging

    Energy Science and Technology Software Center (ESTSC)

    2006-12-01

    The software program generates 3D volume distribution of thermal effusivity within a test material from one-sided pulsed thermal imaging data. Thsi is the first software capable of accurate, fast and automated thermal tomographic imaging of inhomogeneous materials to produce 3D images similar to those obtained from 3D X-ray CT (all previous thermal-imaging software can only produce 2D results). Because thermal effusivity is an intrisic material property that is related to material constituent, density, conductivity, etc.,more » quantitative imaging of effusivity allowed direct visualization of material's internal constituent/structure and damage distributions, thereby potentially leading to quantitative prediction of other material properties such as strength. I can be therefre be used for 3D imaging of material structure in fundamental material studies, nondestructive characterization of defects/flaws in structural engineering components, health monitoring of material damage and degradation during service, and medical imaging and diagnostics. This technology is one-sided, non contact and sensitive to material's thermal property and discontinuity. One major advantage of this tomographic technology over x-ray CT and ultrasounds is its natural efficiency for 3D imaging of the volume under a large surface area. This software is implemented with a method for thermal computed tomography of thermal effusivity from one-sided pulsed thermal imaging (or thermography) data. The method is based on several solutions of the governing heat transfer equation under pulsed thermography test condition. In particular, it consists of three components. 1) It utilized the thermal effusivity as the imaging parameter to construct the 3D image. 2) It established a relationship between the space (depth) and the time, because thermography data are in the time domain. 3) It incorporated a deconvolution algorithm to solve the depth porfile of the material thermal effusivity from the measured (temporal) surface temperature data. The predicted effusivity is a direct function of depth, not an average or convolved parameter, so it is an accurate (and more sensitive) representation of local property along depth.« less

  7. Thermal Effusivity Tomography from Pulsed Thermal Imaging

    Energy Science and Technology Software Center (ESTSC)

    2008-11-05

    The software program generates 3D volume distribution of thermal effusivity within a test material from one—sided pulsed thermal imaging data. Thsi is the first software capable of accurate, fast and automated thermal tomographic imaging of inhomogeneoirs materials to produce 3D images similar to those obtained from 3D X—ray CT (all previous thepnal—imaging software can only produce 20 results) . Because thermal effusivity is an Intrisic material property that is related to material constituent, density, conductivity,more » etc., quantitative imaging of eftusivity allowed direct visualization of material’s internal constituent/structure and damage distributions, thereby potentially leading to quantitative prediction of other material properties such as strength. I can be therefre be used for 3D imaging of material structure in fundamental material studies, nondestructive characterization of defects/flaws in structural engineering components, health monitoring of material damage and degradation during service, and medical imaging and diagnostics. This technology is one—sided, non contact and sensitive to material’s thermal property and discontinuity. One major advantage of this tomographic technology over x-ray CT and ultrasounds is its natural efficiency for 3D imaging of the volume under a large surface area. This software is implemented with a method for thermal computed tomography of thermal effusivity from one—sided pulsed thermal imaging (or thermography) data. The method is based on several solutions of the governing heat transfer equation under pulsed thermography test condition. In particular, it consists of three components. 1) It utilized the thermal effusivity as the imaging parameter to construct the 3D image. 2) It established a relationship between the space (depth) and the time, because thermography data are in the time domain. 3) It incorporated a deconvolution algorithm to solve the depth porfile of the material thermal effusivity from the measured (temporal) surface temperature data. The predicted effusivity is a direct function of depth, not an average or convolved parameter, so it is an accurate (and more sensitive) representation of local property along depth.« less

  8. Terahertz spectroscopy and imaging for cultural heritage management: state of art and perspectives

    NASA Astrophysics Data System (ADS)

    Catapano, Ilaria; Soldovieri, Francesco

    2014-05-01

    Non-invasive diagnostic tools able to provide information on the materials and preservation state of artworks are crucial to help conservators, archaeologists and anthropologists to plan and carry out their tasks properly. In this frame, technological solutions exploiting Terahertz (THz) radiation, i.e., working at frequencies ranging from 0.1 to 10 THz, are currently deserving huge attention as complementary techniques to classical analysis methodologies based on electromagnetic radiations from X-rays to mid infrared [1]. The main advantage offered by THz spectroscopy and imaging systems is referred to their capability of providing information useful to determine the construction modality, the history life and the conservation state of artworks as well as to identify previous restoration actions [1,2]. In particular, unlike mid- and near-infrared spectroscopy, which provides fingerprint absorption spectra depending on the intramolecular behavior, THz spectroscopy is related to the structure of the molecules of the investigated object. Hence, it can discriminate, for instance, the different materials mixed in a paint [1,2]. Moreover, THz radiation is able to penetrate several materials which are opaque to both visible and infrared materials, such as varnish, paint, plaster, paper, wood, plastic, and so on. Accordingly, it is useful to detect hidden objects and characterize the inner structure of the artwork under test even in the direction of the depth, while avoiding core drillings. In this frame, THz systems allow us to discriminate different layers of materials present in artworks like paints, to obtain images providing information on the construction technique as well as to discover risk factors affecting the preservation state, such as non-visible cracks, hidden molds and air gaps between the paint layer and underlying structure. Furthermore, adopting a no-ionizing radiation, THz systems offer the not trivial benefit of negligible long term risks to the molecular stability of the exposed objects and humans. Recently, the interest on THz technology is also growing up thanks to the development of flexible and compact commercial systems having source and detector probes coupled by means of optical fiber cables and that do not require complex optical alignments. These features allow us to reconfigure the measurement configuration easily; thus transmission, normal reflection and oblique reflection data can be collected according to the constrains and objective of the survey to be performed. Moreover, they open the way to on field applications. An example of last generation THz systems is the Fiber-Coupled Terahertz Time Domain System (FICO) marketed by Z-Omega and available at the Institute of Electromagnetic Sensing of the Environment. Such a system is designed to perform both transmission and reflection spectroscopy and imaging measurements in the range from 60GHz to 3THz; with a waveform acquisition speed up to 500Hz. A review of the literature assessing potentialities and open challenges of THz spectroscopy and imaging in the frame of cultural heritage preservation will be provided at the conferences, with a specific focus on the diagnostic capabilities of last generation systems. REFERENCES [1] K. Fukunaga, I. Hosako, Innovative non-invasive analysis techniques for cultural heritage using terahertz technology, C. R. Physique, vol. 11, pp.519-526, 2010. [2] G.Fillippidis, M. Massaouti, A. Selimis, E.J. Gualda, J.M. Manceau, S. Tzortzakis, Nonlinear imaging and THz diagnostic tools in the service of Cultural Heritage, Appl. Phys. A, vol.106, pp.257-263, 2012.

  9. Early detection of germinated wheat grains using terahertz image and chemometrics

    NASA Astrophysics Data System (ADS)

    Jiang, Yuying; Ge, Hongyi; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong

    2016-02-01

    In this paper, we propose a feasible tool that uses a terahertz (THz) imaging system for identifying wheat grains at different stages of germination. The THz spectra of the main changed components of wheat grains, maltose and starch, which were obtained by THz time spectroscopy, were distinctly different. Used for original data compression and feature extraction, principal component analysis (PCA) revealed the changes that occurred in the inner chemical structure during germination. Two thresholds, one indicating the start of the release of α-amylase and the second when it reaches the steady state, were obtained through the first five score images. Thus, the first five PCs were input for the partial least-squares regression (PLSR), least-squares support vector machine (LS-SVM), and back-propagation neural network (BPNN) models, which were used to classify seven different germination times between 0 and 48 h, with a prediction accuracy of 92.85%, 93.57%, and 90.71%, respectively. The experimental results indicated that the combination of THz imaging technology and chemometrics could be a new effective way to discriminate wheat grains at the early germination stage of approximately 6 h.

  10. Early detection of germinated wheat grains using terahertz image and chemometrics

    PubMed Central

    Jiang, Yuying; Ge, Hongyi; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong

    2016-01-01

    In this paper, we propose a feasible tool that uses a terahertz (THz) imaging system for identifying wheat grains at different stages of germination. The THz spectra of the main changed components of wheat grains, maltose and starch, which were obtained by THz time spectroscopy, were distinctly different. Used for original data compression and feature extraction, principal component analysis (PCA) revealed the changes that occurred in the inner chemical structure during germination. Two thresholds, one indicating the start of the release of α-amylase and the second when it reaches the steady state, were obtained through the first five score images. Thus, the first five PCs were input for the partial least-squares regression (PLSR), least-squares support vector machine (LS-SVM), and back-propagation neural network (BPNN) models, which were used to classify seven different germination times between 0 and 48 h, with a prediction accuracy of 92.85%, 93.57%, and 90.71%, respectively. The experimental results indicated that the combination of THz imaging technology and chemometrics could be a new effective way to discriminate wheat grains at the early germination stage of approximately 6 h. PMID:26892180

  11. Early detection of germinated wheat grains using terahertz image and chemometrics.

    PubMed

    Jiang, Yuying; Ge, Hongyi; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong

    2016-01-01

    In this paper, we propose a feasible tool that uses a terahertz (THz) imaging system for identifying wheat grains at different stages of germination. The THz spectra of the main changed components of wheat grains, maltose and starch, which were obtained by THz time spectroscopy, were distinctly different. Used for original data compression and feature extraction, principal component analysis (PCA) revealed the changes that occurred in the inner chemical structure during germination. Two thresholds, one indicating the start of the release of α-amylase and the second when it reaches the steady state, were obtained through the first five score images. Thus, the first five PCs were input for the partial least-squares regression (PLSR), least-squares support vector machine (LS-SVM), and back-propagation neural network (BPNN) models, which were used to classify seven different germination times between 0 and 48 h, with a prediction accuracy of 92.85%, 93.57%, and 90.71%, respectively. The experimental results indicated that the combination of THz imaging technology and chemometrics could be a new effective way to discriminate wheat grains at the early germination stage of approximately 6 h. PMID:26892180

  12. Theoretical analysis of conditions for observation of plasma oscillations in semiconductors from pulsed terahertz emission

    SciTech Connect

    Reklaitis, Antanas

    2014-08-28

    Oscillations of electron-hole plasma generated by femtosecond optical pulse in freestanding semiconductor are studied using hydrodynamic model and Monte Carlo simulations. The conditions required for the observation of coherent plasma oscillations in THz emission from semiconductor are determined. It is shown that several conditions have to be fulfilled in order to observe coherent plasma oscillations. First, the intensity of the optical pulse must exceed some threshold value. Second, the optical absorption depth must exceed the thickness of the built-in electric field region. Third, the generation of electron-hole pairs with uniform illumination is required, i.e., the laser beam with the flattop intensity profile has to be used. It is found that the duration of the optical pulse does not play a vital role in the development of plasma oscillations.

  13. Nonlinear terahertz coherent excitation of vibrational modes of liquids

    NASA Astrophysics Data System (ADS)

    Allodi, Marco A.; Finneran, Ian A.; Blake, Geoffrey A.

    2015-12-01

    We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm-1), and in carbon tetrachloride at 6.50 THz (217 cm-1), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies.

  14. Nonlinear terahertz coherent excitation of vibrational modes of liquids.

    PubMed

    Allodi, Marco A; Finneran, Ian A; Blake, Geoffrey A

    2015-12-21

    We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm(-1)), and in carbon tetrachloride at 6.50 THz (217 cm(-1)), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies. PMID:26696055

  15. 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.; Knyazev, B. A.; Vinokurov, N. A.; Kulipanov, G. N.

    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.

  16. 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.; Marković, B.; Mirković, 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+δ was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

  17. 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.

  18. A non-imaging polarized terahertz passive system for detecting and identifying concealed explosives

    NASA Astrophysics Data System (ADS)

    Karam, Mostafa A.; Meyer, Doug

    2011-06-01

    Existing terahertz THz systems for detecting concealed explosives are not capable of identifying explosive type which leads to higher false alarm rates. Moreover, some of those systems are imaging systems that invade personal privacy, and require more processing and computational resources. Other systems have no polarization preference which makes them incapable of capturing the geometric features of an explosive. In this study a non-imaging polarized THz passive system for detecting and identifying concealed explosives overcoming the forgoing shortcomings is developed. The system employs a polarized passive THz sensor in acquiring emitted data from a scene that may have concealed explosives. The acquired data are decomposed into their natural resonance frequencies, and the number of those frequencies is used as criteria in detecting the explosive presence. If the presence of an explosive is confirmed, a set of physically based retrieval algorithms is used in extracting the explosive dielectric constant/refractive index value from natural resonance frequencies and amplitudes of associated signals. Comparing the refractive index value against a database of refractive indexes of known explosives identifies the explosive type. As an application, a system having a dual polarized radiometer operating within the frequency band of 0.62- 0.82 THz is presented and used in detecting and identifying person borne C-4 explosive concealed under a cotton garment. The system showed higher efficiencies in detecting and identifying the explosive.

  19. 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/μW 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.

  20. Terahertz real-time imaging uncooled array based on antenna- and cavity-coupled bolometers.

    PubMed

    Simoens, François; Meilhan, Jérôme

    2014-03-28

    The development of terahertz (THz) applications is slowed down by the availability of affordable, easy-to-use and highly sensitive detectors. CEA-Leti took up this challenge by tailoring the mature infrared (IR) bolometer technology for optimized THz sensing. The key feature of these detectors relies on the separation between electromagnetic absorption and the thermometer. For each pixel, specific structures of antennas and a resonant quarter-wavelength cavity couple efficiently the THz radiation on a broadband range, while a central silicon microbridge bolometer resistance is read out by a complementary metal oxide semiconductor circuit. 320×240 pixel arrays have been designed and manufactured: a better than 30 pW power direct detection threshold per pixel has been demonstrated in the 2-4 THz range. Such performance is expected on the whole THz range by proper tailoring of the antennas while keeping the technological stack largely unchanged. This paper gives an overview of the developed bolometer-based technology. First, it describes the technology and reports the latest performance characterizations. Then imaging demonstrations are presented, such as real-time reflectance imaging of a large surface of hidden objects and THz time-domain spectroscopy beam two-dimensional profiling. Finally, perspectives of camera integration for scientific and industrial applications are discussed. PMID:24567477

  1. Application of terahertz spectroscopy imaging for discrimination of transgenic rice seeds with chemometrics.

    PubMed

    Liu, Wei; Liu, Changhong; Hu, Xiaohua; Yang, Jianbo; Zheng, Lei

    2016-11-01

    Discrimination of genetically modified organisms is increasingly demanded by legislation and consumers worldwide. The feasibility of a non-destructive discrimination of transgenic rice seeds from its non-transgenic counterparts was examined by terahertz spectroscopy imaging system combined with chemometrics. Principal component analysis (PCA), least squares support vector machines (LS-SVM), PCA-back propagation neural network (PCA-BPNN), and random forest (RF) models with the first and second derivative and standard normal variate transformation (SNV) pre-treatments were applied to classify rice seeds based on genotype. The results demonstrated that differences between non-transgenic and transgenic rice seeds did exist, and an excellent classification (accuracy was 96.67% in the prediction set) could be achieved using the RF model combined with the first derivative pre-treatment. The results indicated that THz spectroscopy imaging together with chemometrics would be a promising technique to identify transgenic rice seeds with high efficiency and without any sample preparation. PMID:27211665

  2. Terahertz Real-Time Imaging Uncooled Arrays Based on Antenna-Coupled Bolometers or FET Developed at CEA-Leti

    NASA Astrophysics Data System (ADS)

    Simoens, François; Meilhan, Jérôme; Nicolas, Jean-Alain

    2015-10-01

    Sensitive and large-format terahertz focal plane arrays (FPAs) integrated in compact and hand-held cameras that deliver real-time terahertz (THz) imaging are required for many application fields, such as non-destructive testing (NDT), security, quality control of food, and agricultural products industry. Two technologies of uncooled THz arrays that are being studied at CEA-Leti, i.e., bolometer and complementary metal oxide semiconductor (CMOS) field effect transistors (FET), are able to meet these requirements. This paper reminds the followed technological approaches and focuses on the latest modeling and performance analysis. The capabilities of application of these arrays to NDT and security are then demonstrated with experimental tests. In particular, high technological maturity of the THz bolometer camera is illustrated with fast scanning of large field of view of opaque scenes achieved in a complete body scanner prototype.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  4. Long-lived field-free molecular orientation driven by modulated few-cycle terahertz pulses

    NASA Astrophysics Data System (ADS)

    Yu, Jie; Liu, Yong; Su, Qian-Zhen; Cong, Shu-Lin

    2012-09-01

    We present a theoretical scheme used for achieving an efficient long-lived field-free molecular orientation by utilizing two modulated few-cycle THz pulses with an appropriate delay time. The exact numerical calculations are performed by solving the time-dependent Schrödinger equation including the vibrational and rotational degrees of freedom, with the LiH molecule as an example. The results show that the orientation degree and the orientation duration are strongly related to the period of envelope Tp, the central frequency ωL and the phase of envelope ϕ of the modulated few-cycle THz pulses. A long-lived and efficient field-free molecular orientation can be realized by adjusting these laser parameters which is available in the current experiment. The effect of temperature on molecular orientation is also discussed.

  5. Laser Pulse Driven Terahertz Generation via Resonant Transition Radiation (RTR) in inhomogeneous Plasmas

    NASA Astrophysics Data System (ADS)

    Miao, Chenlong; Palastro, John; Antonsen, Thomas

    2015-11-01

    Intense, short laser pulses propagating through inhomogeneous plasma can ponderomotively drive THz radiation via a resonant transition radiation mechanism (RTR) for THz generation as the laser pulses cross a plasma boundary. Simulations and theoretical analysis demonstrate that the THz emission is low frequency, broad band, coherent and conical. Simulation results show that this radiation is insensitive to the plasma length and density above 1.5x1018 cm-3 for the laser parameters we use and assuming a sharp plasma boundary. The effect of density ramps is also considered and shown that an upward ramp enhances the radiated energy while a downward ramp diminishes it. According to the model we developed, the radiation at a given frequency is generated at the resonant point in the plasma ramp where its frequency matches the local plasma frequency. The radiation must then tunnel out of the plasma to the turning point. The results from our model matches well with the simulation using the full format PIC code TurboWAVE, showing that the amount of radiation reaches maximum at a certain ramp length. As an example, a fixed driver pulse (1.66 J) excites THz radiation of 280.7 μJ in a 400 μm increasing density ramp. Work supported by USDOE grant DESC0010741.

  6. Terahertz Spectroscopy and Imaging at the Nanoscale for Biological and Security Applications

    NASA Astrophysics Data System (ADS)

    Bowen, John W.

    The chemical specificity of terahertz spectroscopy, when combined with techniques for sub-wavelength sensing, is giving new understanding of processes occurring at the nanometre scale in biological systems and offers the potential for single molecule detection of chemical and biological agents and explosives. In addition, terahertz techniques are enabling the exploration of the fundamental behaviour of light when it interacts with nanoscale optical structures, and are being used to measure ultrafast carrier dynamics, transport and localisation in nanostructures.

  7. Terahertz beat oscillation of plasmonic electrons interacting with femtosecond light pulses

    NASA Astrophysics Data System (ADS)

    Zhang, Xinping; He, Jianfang; Wang, Yimeng; Liu, Feifei

    2016-01-01

    Plasmon resonance in nanostructured metals is in essence collective oscillation of free electrons, which is driven by optical electric fields and oscillates at nearly the same frequency as the excitation photons. This is the basic physics for the currently extensively interested topics in optical metamaterials, optical switching, and logic optical “circuits” with potential applications in optical communication and optical computation. We present here an interference effect between photons and plasmon electrons, which is observed as multi-cycle beat-oscillation. The beat frequency is in the range of 3~4 THz, which is equal to the difference between optical frequency of the photons and oscillation frequency of the plasmon electrons. Such beat oscillation evolves in a time scale of more than 1 ps, which is much longer than the optical pulse length, implying interaction between photons and pure damping plasmon-electrons. The discovered mechanisms might be important for exploring new approaches for THz generation.

  8. Terahertz beat oscillation of plasmonic electrons interacting with femtosecond light pulses.

    PubMed

    Zhang, Xinping; He, Jianfang; Wang, Yimeng; Liu, Feifei

    2016-01-01

    Plasmon resonance in nanostructured metals is in essence collective oscillation of free electrons, which is driven by optical electric fields and oscillates at nearly the same frequency as the excitation photons. This is the basic physics for the currently extensively interested topics in optical metamaterials, optical switching, and logic optical "circuits" with potential applications in optical communication and optical computation. We present here an interference effect between photons and plasmon electrons, which is observed as multi-cycle beat-oscillation. The beat frequency is in the range of 3~4 THz, which is equal to the difference between optical frequency of the photons and oscillation frequency of the plasmon electrons. Such beat oscillation evolves in a time scale of more than 1 ps, which is much longer than the optical pulse length, implying interaction between photons and pure damping plasmon-electrons. The discovered mechanisms might be important for exploring new approaches for THz generation. PMID:26732478

  9. Review of Terahertz Tomography Techniques

    NASA Astrophysics Data System (ADS)

    Guillet, J. P.; Recur, B.; Frederique, L.; Bousquet, B.; Canioni, L.; Manek-Hnninger, I.; Desbarats, P.; Mounaix, P.

    2014-04-01

    Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.

  10. 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.

  11. 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.

  12. Terahertz beat oscillation of plasmonic electrons interacting with femtosecond light pulses

    PubMed Central

    Zhang, Xinping; He, Jianfang; Wang, Yimeng; Liu, Feifei

    2016-01-01

    Plasmon resonance in nanostructured metals is in essence collective oscillation of free electrons, which is driven by optical electric fields and oscillates at nearly the same frequency as the excitation photons. This is the basic physics for the currently extensively interested topics in optical metamaterials, optical switching, and logic optical “circuits” with potential applications in optical communication and optical computation. We present here an interference effect between photons and plasmon electrons, which is observed as multi-cycle beat-oscillation. The beat frequency is in the range of 3~4 THz, which is equal to the difference between optical frequency of the photons and oscillation frequency of the plasmon electrons. Such beat oscillation evolves in a time scale of more than 1 ps, which is much longer than the optical pulse length, implying interaction between photons and pure damping plasmon-electrons. The discovered mechanisms might be important for exploring new approaches for THz generation. PMID:26732478

  13. 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").

  14. 21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... features of continuous wave doppler-effect technology with pulsed-echo effect technology and is intended to... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1550 Ultrasonic pulsed doppler...

  15. 21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... features of continuous wave doppler-effect technology with pulsed-echo effect technology and is intended to... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1550 Ultrasonic pulsed doppler...

  16. 21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... features of continuous wave doppler-effect technology with pulsed-echo effect technology and is intended to... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1550 Ultrasonic pulsed doppler...

  17. 21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... features of continuous wave doppler-effect technology with pulsed-echo effect technology and is intended to... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1550 Ultrasonic pulsed doppler...

  18. Terahertz antenna electronic chopper.

    PubMed

    Sterczewski, L A; Grzelczak, M P; Plinski, E F

    2016-01-01

    In this paper, we present an electronic circuit used to bias a photoconductive antenna that generates terahertz radiation. The working principles and the design process for the device are discussed in detail. The noise and shape of the wave measurements for a built device are considered. Furthermore, their impact on a terahertz pulse and its spectra is also examined. The proposed implementation is simple to build, robust and offers a real improvement over THz instrumentation due to the frequency tuning. Additionally, it provides for galvanic isolation and ESD protection. PMID:26827336

  19. Terahertz antenna electronic chopper

    NASA Astrophysics Data System (ADS)

    Sterczewski, L. A.; Grzelczak, M. P.; Plinski, E. F.

    2016-01-01

    In this paper, we present an electronic circuit used to bias a photoconductive antenna that generates terahertz radiation. The working principles and the design process for the device are discussed in detail. The noise and shape of the wave measurements for a built device are considered. Furthermore, their impact on a terahertz pulse and its spectra is also examined. The proposed implementation is simple to build, robust and offers a real improvement over THz instrumentation due to the frequency tuning. Additionally, it provides for galvanic isolation and ESD protection.

  20. Discrimination and identification of RDX/PETN explosives by chemometrics applied to terahertz time-domain spectral imaging

    NASA Astrophysics Data System (ADS)

    Bou-Sleiman, J.; Perraud, J.-B.; Bousquet, B.; Guillet, J.-P.; Palka, N.; Mounaix, P.

    2015-10-01

    Detection of explosives has always been a priority for homeland security. Jointly, terahertz spectroscopy and imaging are emerging and promising candidates as contactless and safe systems. In this work, we treated data resulting from hyperspectral imaging obtained by THz-time domain spectroscopy, with chemometric tools. We found efficient identification and sorting of targeted explosives in the case of pure and mixture samples. In this aim, we applied to images Principal Component Analysis (PCA) to discriminate between RDX, PETN and mixtures of the two materials, using the absorbance as the key-parameter. Then we applied Partial Least Squares-Discriminant Analysis (PLS-DA) to each pixel of the hyperspectral images to sort the explosives into different classes. The results clearly show successful identification and categorization of the explosives under study.

  1. 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.

  2. 21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550 Section 892.1550 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification....

  3. How to take your pulse (image)

    MedlinePlus

    ... the blood pulsing beneath your fingers. Use a watch or clock with a second hand. Count the beats you ... the blood pulsing beneath your fingers. Use a watch or clock with a second hand. Count the beats you ...

  4. Imaging of broadband terahertz beams using an array of antenna-coupled microbolometers operating at room temperature.

    PubMed

    Oden, Jonathan; Meilhan, Jérome; Lalanne-Dera, Jérémy; Roux, Jean-François; Garet, Frédéric; Coutaz, Jean-Louis; Simoens, François

    2013-02-25

    We present results of 2D real-time imaging of terahertz (THz) beam generated by a photoconductive antenna driven by a femtosecond oscillator. The detector, operating at room temperature, is a 320 x 240 array of antenna-coupled microbolometers with integrated CMOS read-out electronics delivering 25 images per second. High quality images of broadband THz beams covering the 0.1-2 THz range are recorded while maintaining a signal-to-noise ratio of 10 for detected THz power as low as 25 nW. The compactness of the easy-to-use uncooled camera makes it very useful for the alignment of systems such as THz time-domain spectrometers and for the characterization of emitters, optics and other components. PMID:23482016

  5. Continuous-wave terahertz field imaging based on photonics-based self-heterodyne electro-optic detection.

    PubMed

    Hisatake, Shintaro; Nagatsuma, Tadao

    2013-07-01

    We demonstrate a photonics-based self-heterodyne electro-optic field imaging technique at terahertz (THz) frequency. An optical intensity beat generated by mixing two frequency-detuned free-running lasers is used for both the generation and the detection. The frequency of the beat for detection is shifted by an optical frequency shifter to realize coherent heterodyne measurement with free-running lasers. Neither mechanical delay lines nor phase-locked synthesizers are required for the amplitude and the phase imaging of the THz field, and the system simplicity is thus improved. The amplitude and phase of the THz field (125 GHz) radiated from a horn antenna are simultaneously imaged, and the standard deviation of the phase measurement is found to be 0.18 rad. PMID:23811911

  6. Superconducting phase shifter in the development of a Terahertz Imaging Radar System. Final technical report, August 1986-January 1987

    SciTech Connect

    Baliga, S.; Radparvar, M.; Faris, S.M.

    1987-10-01

    A Terahertz Imaging Radar System which exploits superconductive electronics for all of its major components is described in this report. In particular, the importance of the superconducting millimeter(mm)-wave phase shifter in the development of such systems was fully investigated. The experimental and theoretical results presented are better than the authors expected to achieve under Phase I of the project. Conventional technology is unable to provide the high frequencies required to obtain small apertures for target acquisition. Superconducting technology offers a high-performance, very broadband and low-power, mm- and sub-mm wave phase shifter based on superconducting microstrips. The physics of the non-equilibrium superconductivity underlying the operation of the superconducting microstrip phase shifter has been studied. Theoretical analysis and numerous experimental results show that superconducting stripline modulation leading to phase velocity reduction and subsequent phase shift is achievable by quasi-particle injection. A digital N-bit phase shifter based on the superconducting microstrip transmission line is proposed for development. The implementations of such a mm and sub-mm wave phase shifter will fulfill a crucial need in the development of the Terahertz Imaging Radar.

  7. 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.

  8. 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

  9. Reconstruction of pulse noisy images via stochastic resonance

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  10. Generation of Terahertz Radiation from Fe-doped InGaAsP Using 800 nm to 1550 nm Pulsed Laser Excitation

    NASA Astrophysics Data System (ADS)

    Hatem, O.; Freeman, J. R.; Cunningham, J. E.; Cannard, P. J.; Robertson, M. J.; Linfield, E. H.; Davies, A. G.; Moodie, D. G.

    2016-05-01

    We demonstrate efficient generation of terahertz (THz) frequency radiation by pulsed excitation, at wavelengths between 800 and 1550 nm, of photoconductive (PC) switches fabricated using Fe-doped InGaAsP wafers, grown by metal organic chemical vapor deposition (MOCVD). Compared to our previous studies of Fe-doped InGaAs wafers, Fe:InGaAsP wafers exhibited five times greater dark resistivity to give a value of 10 kΩ cm, and Fe:InGaAsP PC switches produced five times higher THz power emission. The effect of Fe-doping concentration (between 1E16 and 1.5E17 cm-3) on optical light absorption (between 800 and 1600 nm), on resistivity, and on THz emission is also discussed.

  11. Terahertz sources and detectors

    NASA Astrophysics Data System (ADS)

    Crowe, Thomas W.; Porterfield, David W.; Hesler, Jeffrey L.; Bishop, William L.; Kurtz, David S.; Hui, Kai

    2005-05-01

    Through the support of the US Army Research Office we are developing terahertz sources and detectors suitable for use in the spectroscopy of chemical and biological materials as well as for use in imaging systems to detect concealed weapons. Our technology relies on nonlinear diodes to translate the functionality achieved at microwave frequencies to the terahertz band. Basic building blocks that have been developed for this application include low-noise mixers, frequency multipliers, sideband generators and direct detectors. These components rely on planar Schottky diodes and integrated diode circuits and are therefore easy to assemble and robust. They require no mechanical tuners to achieve high efficiency and broad bandwidth. This paper will review the range of performance that has been achieved with these terahertz components and briefly discuss preliminary results achieved with a spectroscopy system and the development of sources for imaging systems.

  12. Terahertz spectroscopic imaging using noncollinear electro-optic sampling and a multistep mirror without shifting the object

    NASA Astrophysics Data System (ADS)

    Itani, Norihiko; Maruyama, Kazunori; Hasegawa, Shin-ya; Wakana, Shinichi

    2012-10-01

    We previously developed a high-speed terahertz spectroscopic imaging method based on electro-optic sampling with a noncollinear geometry of the THz beam and probe laser beam and using a multistep mirror in the path of the probe beam. We set the incident probe laser into MAST at a 45° angle, to prevent interference between adjacent beams. However, this produced beam vignetting, so imaging had to be performed twice, between sample movements, and this increased the imaging time accordingly. Thus, we improved the probe-laser imaging system after reflecting from the MAST to correct for the effects of diffraction. This prevents interference from adjacent beams and allows the angle of incidence on the MAST to be set to 0°, enabling the entire sample surface to be imaged in one measurement. As a result, we are able to perform measurements in 40 seconds, half the time of the previous method, and obtain a 28x28-pixel spectral image with spatial resolution of 1.07 mm. To verify the imaging performance, we also measured test samples, showing that the shape and thickness of items inside an opaque plastic case can be distinguished using amplitude and phase images, and metallic foreign objects can be detected. We also evaluated the method and were able to show the validity of the spectral imaging results by distinguishing the transmission or blocking of arbitrary frequency components.

  13. Terahertz Mapping of Microstructure and Thickness Variations

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  14. Photoinduced Nonlinear Mixing of Terahertz Dipole Resonances in Graphene Metadevices.

    PubMed

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

    2016-02-01

    The first experimental demonstration of nonlinear terahertz difference-frequency generation in a hybrid graphene metadevice is reported. Decades of research have revealed that terahertz-wave generation is impossible in single-layer graphene. This limitation is overcome and nonlinear terahertz generation by ultra-short optical pulse injection is demonstrated. This device is an essential step toward atomically thin, nonlinear terahertz optoelectronic components. PMID:26639550

  15. Apertureless near-field terahertz imaging using the self-mixing effect in a quantum cascade laser

    NASA Astrophysics Data System (ADS)

    Dean, Paul; Mitrofanov, Oleg; Keeley, James; Kundu, Iman; Li, Lianhe; Linfield, Edmund H.; Giles Davies, A.

    2016-02-01

    We report two-dimensional apertureless near-field terahertz (THz) imaging using a quantum cascade laser (QCL) source and a scattering probe. A near-field enhancement of the scattered field amplitude is observed for small tip-sample separations, allowing image resolutions of ˜1 μm (˜λ/100) and ˜7 μm to be achieved along orthogonal directions on the sample surface. This represents the highest resolution demonstrated to date with a THz QCL. By employing a detection scheme based on self-mixing interferometry, our approach offers experimental simplicity by removing the need for an external detector and also provides sensitivity to the phase of the reinjected field.

  16. Antenna-coupled microbolometer based uncooled 2D array and camera for 2D real-time terahertz imaging

    NASA Astrophysics Data System (ADS)

    Simoens, F.; Meilhan, J.; Gidon, S.; Lasfargues, G.; Lalanne Dera, J.; Ouvrier-Buffet, J. L.; Pocas, S.; Rabaud, W.; Guellec, F.; Dupont, B.; Martin, S.; Simon, A. C.

    2013-09-01

    CEA-Leti has developed a monolithic large focal plane array bolometric technology optimized for 2D real-time imaging in the terahertz range. Each pixel consists in a silicon microbolometer coupled to specific antennas and a resonant quarter-wavelength cavity. First prototypes of imaging arrays have been designed and manufactured for optimized sensing in the 1-3.5THz range where THz quantum cascade lasers are delivering high optical power. NEP in the order of 1 pW/sqrt(Hz) has been assessed at 2.5 THz. This paper reports the steps of this development, starting from the pixel level, to an array associated monolithically to its CMOS ROIC and finally a stand-alone camera. For each step, modeling, technological prototyping and experimental characterizations are presented.

  17. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section 892.1560 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... pulsed sound beam into body tissue to determine the depth or location of the tissue interfaces and...

  18. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section 892.1560 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... pulsed sound beam into body tissue to determine the depth or location of the tissue interfaces and...

  19. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section 892.1560 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... pulsed sound beam into body tissue to determine the depth or location of the tissue interfaces and...

  20. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section 892.1560 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... pulsed sound beam into body tissue to determine the depth or location of the tissue interfaces and...

  1. Clutter discrimination algorithm simulation in pulse laser radar imaging

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-mei; Li, Huan; Guo, Hai-chao; Su, Xuan; Zhu, Fule

    2015-10-01

    Pulse laser radar imaging performance is greatly influenced by different kinds of clutter. Various algorithms are developed to mitigate clutter. However, estimating performance of a new algorithm is difficult. Here, a simulation model for estimating clutter discrimination algorithms is presented. This model consists of laser pulse emission, clutter jamming, laser pulse reception and target image producing. Additionally, a hardware platform is set up gathering clutter data reflected by ground and trees. The data logging is as clutter jamming input in the simulation model. The hardware platform includes a laser diode, a laser detector and a high sample rate data logging circuit. The laser diode transmits short laser pulses (40ns FWHM) at 12.5 kilohertz pulse rate and at 905nm wavelength. An analog-to-digital converter chip integrated in the sample circuit works at 250 mega samples per second. The simulation model and the hardware platform contribute to a clutter discrimination algorithm simulation system. Using this system, after analyzing clutter data logging, a new compound pulse detection algorithm is developed. This new algorithm combines matched filter algorithm and constant fraction discrimination (CFD) algorithm. Firstly, laser echo pulse signal is processed by matched filter algorithm. After the first step, CFD algorithm comes next. Finally, clutter jamming from ground and trees is discriminated and target image is produced. Laser radar images are simulated using CFD algorithm, matched filter algorithm and the new algorithm respectively. Simulation result demonstrates that the new algorithm achieves the best target imaging effect of mitigating clutter reflected by ground and trees.

  2. Self-imaging effect in photonic quasicrystal waveguides: Application to 3 dB power splitter for terahertz waves

    NASA Astrophysics Data System (ADS)

    Xu, Feixiang; Zou, Qiushun; Zhou, Quancheng; Wang, Tongbiao; Yu, Tianbao; Liu, Nianhua

    2016-05-01

    We report that self-imaging effect still can be achieved in photonic quasicrystal waveguides (PtQCWs) just as it does in photonic crystal waveguides. As a possible application of the results, a new kind of compact 3 dB PtQCWs-based power splitters based on this effect for terahertz waves with symmetric interference is presented and analyzed. The finite element method is used to calculate the distributions of stable-state electric field and evaluate transmission efficiency of these structures. The calculated results show that the proposed device provides a new compact model for exporting efficiently THz wave with a broad bandwidth to two channels averagely and can be extended to new designs of PtQCW devices.

  3. Highly Sensitive Vibrational Imaging by Femtosecond Pulse Stimulated Raman Loss

    PubMed Central

    Zhang, Delong; Slipchenko, Mikhail N.; Cheng, Ji-Xin

    2011-01-01

    Nonlinear vibrational imaging of live cells and organisms is demonstrated by detecting femtosecond pulse stimulated Raman loss. Femtosecond pulse excitation produced a 12 times larger stimulated Raman loss signal than picosecond pulse excitation. The large signal allowed real-time imaging of the conversion of deuterated palmitic acid into lipid droplets inside live cells, and three-dimensional sectioning of fat storage in live C. elegans. With the majority of the excitation power contributed by the Stokes beam in the 1.0 to 1.2 μm wavelength range, photodamage of biological samples was not observed. PMID:21731798

  4. SAR image quality using advanced pulse compression noise (APCN)

    NASA Astrophysics Data System (ADS)

    Govoni, Mark A.; Elwell, Ryan A.

    2014-05-01

    This work demonstrates the feasibility of using the advanced pulse compression noise (APCN) radar waveform for synthetic aperture radar (SAR). Using a simple image formation process (IFP), we not only show that we can successfully form images using the APCN waveform, but we grow our understanding of how different combinations of APCN waveforms and side lobe weighting functions impact SAR image quality. In this paper, an analysis is presented that compares the target range point spread function (PSF) for several simulated SAR images.

  5. 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.

  6. Faraday rotation imaging microscope with microsecond pulse magnet

    NASA Astrophysics Data System (ADS)

    Suwa, Masayori; Tsukahara, Satoshi; Watarai, Hitoshi

    2015-11-01

    We have fabricated a high-performance Faraday rotation (FR) imaging microscope that uses a microsecond pulse magnet comprising an insulated gated bipolar transistor and a 2 μF capacitor. Our microscope produced images with greater stability and sensitivity than those of previous microscopes that used millisecond pulse magnet; these improvements are likely due to high repetition rate and negligible Joule heating effects. The mechanical vibrations in the magnet coil caused by the pulsed current were significantly reduced. The present FR microscope constructed an averaged image from 1000 FR images within 10 min under 1.7 T. Applications of the FR microscope to discriminating three benzene derivatives in micro-capillaries and oscillation-free imaging of spherical polystyrene and polymethyl methacrylate microparticles demonstrated its high performance.

  7. Terahertz metamaterials

    SciTech Connect

    Peralta, Xomalin Guaiuli; Brener, Igal; O'Hara, John; Azad, Abul; Smirnova, Evgenya; Williams, John D.; Averitt, Richard D.

    2014-08-12

    Terahertz metamaterials comprise a periodic array of resonator elements disposed on a dielectric substrate or thin membrane, wherein the resonator elements have a structure that provides a tunable magnetic permeability or a tunable electric permittivity for incident electromagnetic radiation at a frequency greater than about 100 GHz and the periodic array has a lattice constant that is smaller than the wavelength of the incident electromagnetic radiation. Microfabricated metamaterials exhibit lower losses and can be assembled into three-dimensional structures that enable full coupling of incident electromagnetic terahertz radiation in two or three orthogonal directions. Furthermore, polarization sensitive and insensitive metamaterials at terahertz frequencies can enable new devices and applications.

  8. Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Stoik, Christopher D.

    Terahertz (THz) time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Material properties of glass fiber composite were measured using both transmission and reflection configuration. The interaction of THz with a glass fiber composite was then analyzed, including the effects of scattering, absorption, and the index of refraction, as well as effective medium approximations. THz TDS, in both transmission and reflection configuration, was used to study composite damage, including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by THz TDS transmission and reflection imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the main pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging.

  9. Real-time imaging of moving living objects using a compact terahertz scanner

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    In this study, we design a compact terahertz (THz) reflection scanner with a scan rate of 20 frames/s. This scanner is based on a benzocyclobutene-embedded InGaAs Schottky barrier diode detector having a maximum responsivity of 300 V/W at 250 GHz and a minimum noise equivalent power of 38 pW/\\sqrt{\\text{Hz}} . With this scanner, details such as sharp head and tail and wrinkled segments in a moving caterpillar are observed. The thin and thick parts of the moving caterpillar that are presented in light gray and dark gray, respectively, on the gray scale are also well distinguished.

  10. The SPARC linear accelerator based terahertz source

    SciTech Connect

    Chiadroni, E.; Bacci, A.; Bellaveglia, M.; Boscolo, M.; Castellano, M.; Cultrera, L.; Di Pirro, G.; Ferrario, M.; Ficcadenti, L.; Filippetto, D.; Gatti, G.; Pace, E.; Rossi, A. R.; Vaccarezza, C.; Catani, L.; Cianchi, A.; Marchetti, B.; Mostacci, A.; Palumbo, L.; Ronsivalle, C.; and others

    2013-03-04

    Ultra-short electron beams, produced through the velocity bunching compression technique, are used to drive the SPARC linear accelerator based source, which relies on the emission of coherent transition radiation in the terahertz range. This paper reports on the main features of this radiation, as terahertz source, with spectral coverage up to 5 THz and pulse duration down to 200 fs, with an energy per pulse of the order of several micro-joule, and as electron beam longitudinal diagnostics.

  11. Wavelet Domain Radiofrequency Pulse Design Applied to Magnetic Resonance Imaging

    PubMed Central

    Huettner, Andrew M.; Mickevicius, Nikolai J.; Ersoz, Ali; Koch, Kevin M.; Muftuler, L. Tugan; Nencka, Andrew S.

    2015-01-01

    A new method for designing radiofrequency (RF) pulses with numerical optimization in the wavelet domain is presented. Numerical optimization may yield solutions that might otherwise have not been discovered with analytic techniques alone. Further, processing in the wavelet domain reduces the number of unknowns through compression properties inherent in wavelet transforms, providing a more tractable optimization problem. This algorithm is demonstrated with simultaneous multi-slice (SMS) spin echo refocusing pulses because reduced peak RF power is necessary for SMS diffusion imaging with high acceleration factors. An iterative, nonlinear, constrained numerical minimization algorithm was developed to generate an optimized RF pulse waveform. Wavelet domain coefficients were modulated while iteratively running a Bloch equation simulator to generate the intermediate slice profile of the net magnetization. The algorithm minimizes the L2-norm of the slice profile with additional terms to penalize rejection band ripple and maximize the net transverse magnetization across each slice. Simulations and human brain imaging were used to demonstrate a new RF pulse design that yields an optimized slice profile and reduced peak energy deposition when applied to a multiband single-shot echo planar diffusion acquisition. This method may be used to optimize factors such as magnitude and phase spectral profiles and peak RF pulse power for multiband simultaneous multi-slice (SMS) acquisitions. Wavelet-based RF pulse optimization provides a useful design method to achieve a pulse waveform with beneficial amplitude reduction while preserving appropriate magnetization response for magnetic resonance imaging. PMID:26517262

  12. 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.

  13. 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.

  14. Generation of 0.3 mW high-power broadband terahertz pulses from GaP crystal pumped by negatively chirped femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Li, Jiang; Chai, Lu; Shi, Junkai; Liu, Feng; Liu, Bowen; Xu, Baozhong; Hu, Minglie; Li, Yanfeng; Xing, Qirong; Wang, Chingyue; Fedotov, A. B.; Zheltikov, A. M.

    2013-12-01

    Based on optical rectification in a 3 mm GaP crystal with a femtosecond photonic crystal fiber amplifier as the pump source, a detailed experimental investigation on the influence of the chirp characteristics of the pump pulses on the THz wave generation efficiency is conducted. It is shown that a higher THz generation efficiency can be achieved using negatively chirped pulses rather than de-chirped pulses. In the chosen geometry, using 21 W pump pulses with a negative chirp of -2.3 10-3 ps2, broadband THz radiation with an average power of 0.3 mW is obtained, which is, to the best of our knowledge, the highest value reported so far for high-repetition-rate THz pulses generated by collinear optical rectification. The higher THz generation efficiency by negatively chirped pulses is explained by a pulse-narrowing mechanism in the nonlinear crystal.

  15. Pulse Processing System for the RADMAP Radiation Modulation Aperture Imager

    SciTech Connect

    Myjak, Mitchell J.; Rohrer, John S.; Morris, Scott J.; Woodring, Mitchell L.; Ely, James H.

    2007-12-31

    We are currently developing a portable radiation imager for emergency responders. The instrument contains a position-sensitive photomultiplier tube with a thin CsI(Na) scintillator and a tungsten radiation modulation aperture. As part of this project, we have designed a novel pulse processing system to record the amplitude and position of incident events. This system consists of four charge-to-pulse-width converters that transfer time-modulated digital pulses to a field-programmable gate array. The design can process data at count rates exceeding 40,000 events per second and transmit data over an Ethernet link at 1 Gb/sec.

  16. PUPA: a pulse programming assistant for NMR imaging

    SciTech Connect

    Foxvog, D.; Li, X.; Vargas, J.E.; Bourne, J.R.; Sztipanovits, J.; Mushlin, R.; Harrison, C.G.

    1987-12-01

    The design of pulse programs for magnetic resonance imaging (MRI) experiments is tedious and complex, requiring a deep understanding of the interactions that exist between magnetic fields generated during an MRI experiment. This paper describes an intelligent system that understands how to construct the multichannel temporal sequences of pulses needed to control an MRI experiment. PUPA, the PUlse Programmers Assistant, provides assistance to a relatively naive user of MRI systems. Knowledge is coded in the form of rules and semantic networks. A natural language facility and menu system are provided for communication with the user.

  17. Pulsed laser linescanner for a backscatter absorption gas imaging system

    DOEpatents

    Kulp, Thomas J.; Reichardt, Thomas A.; Schmitt, Randal L.; Bambha, Ray P.

    2004-02-10

    An active (laser-illuminated) imaging system is described that is suitable for use in backscatter absorption gas imaging (BAGI). A BAGI imager operates by imaging a scene as it is illuminated with radiation that is absorbed by the gas to be detected. Gases become "visible" in the image when they attenuate the illumination creating a shadow in the image. This disclosure describes a BAGI imager that operates in a linescanned manner using a high repetition rate pulsed laser as its illumination source. The format of this system allows differential imaging, in which the scene is illuminated with light at least 2 wavelengths--one or more absorbed by the gas and one or more not absorbed. The system is designed to accomplish imaging in a manner that is insensitive to motion of the camera, so that it can be held in the hand of an operator or operated from a moving vehicle.

  18. Image fusion by pulse couple neural network with shearlet

    NASA Astrophysics Data System (ADS)

    Geng, Peng; Wang, Zhengyou; Zhang, Zhigang; Xiao, Zhong

    2012-06-01

    The shearlet representation forms a tight frame which decomposes a function into scales and directions, and is optimally sparse in representing images with edges. An image fusion method is proposed based on the shearlet transform. Firstly, transform the image A and image B by the shearlets. Secondly, a pulse couple neural network (PCNN) is used for the frequency subbands, which uses the number of output pulses from the PCNN's neurons to select fusion coefficients. Finally, an inverse shearlet transform is applied on the new fused coefficients to reconstruct the fused image. Some experiments are performed in images such as multi-focus images, multi-sensor images, medical images and multispectral images comparing the proposed algorithm with the wavelet, contourlet and nonsubsampled contourlet method based on the PCNN. The experimental results show that the proposed algorithm can not only extract more important visual information from source images, but also effectively avoid the introduction of artificial information. It significantly outperforms the traditional multiscale transform image fusion methods in terms of both visual quality and objective evaluation criteria such as MI and QAB/F.

  19. Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators

    DOE PAGESBeta

    Mitrofanov, Oleg; Khromova, Irina; Siday, Thomas; Thompson, Robert J.; Ponomarev, Andrey N.; Brener, Igal; Reno, John L.

    2016-04-22

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

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

    SciTech Connect

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

    2014-02-24

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

  1. Terahertz spectroscopy of pigmentary skin nevi in vivo

    NASA Astrophysics Data System (ADS)

    Zaitsev, K. I.; Chernomyrdin, N. V.; Kudrin, K. G.; Reshetov, I. V.; Yurchenko, S. O.

    2015-09-01

    Pigmentary skin nevi are studied in vivo using terahertz pulsed spectroscopy. Dielectric parameters of healthy skin and dysplastic and nondysplastic nevi are reconstructed and analyzed. The fact that complex permittivities of the samples substantially differ in the terahertz spectral range can be used for early noninvasive diagnostics of dysplastic nevi, which are precursors of melanoma (the most dangerous skin cancer). A method is proposed to identify various dysplastic and nondysplastic nevi using the analysis of terahertz dielectric characteristics. It is demonstrated that terahertz pulsed spectroscopy is promising for early noninvasive diagnostics of dysplastic nevi and melanomas of the skin.

  2. 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.

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

    SciTech Connect

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

    2015-05-21

    A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies (ω{sub 1}, ω{sub 2}) and wave numbers (k{sup →}{sub 1}, k{sup →}{sub 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{sup ′}=n{sub α0}e{sup iαz}) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ∼ω{sub 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 ω=ω{sub 1}−ω{sub 2} and k{sup →}=k{sup →}{sub 1}−k{sup →}{sub 2}+α{sup →}. 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{sub 0}) of super Gaussian lasers. In the present scheme, efficiency ∼10{sup −2} is achieved with the optimization of all these parameters.

  4. 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.

  5. Pulse Waveform Analysis of Chinese Pulse Images and Its Association with Disability in Hypertension.

    PubMed

    Gomes Ribeiro Moura, Nathalia; Sá Ferreira, Arthur

    2016-04-01

    Hypertension affects functional capacity and quality of life. Pulse wave analysis (PWA) quantifies the pulse waveform's propagation and its changes resulting from arterial remodeling. Pulse image analysis (PIA) in traditional Chinese medicine contributes to pattern differentiation and therapeutic intervention. This protocol study evaluates the relationships between the parameters of both PWA and PIA to identify patterns in patients with hypertension and the associations of those patterns with functional capacity. In this observational, cross-sectional study protocol 40 patients were subjected to clinical and laboratorial examinations to assess the risk factors for cardiovascular disease and pattern differentiation. PWA was noninvasively performed at the radial artery to estimate the pulse wave's velocity, arterial compliance, and reflection index. PIA using the "simultaneous pressing" method was performed to assess nine indicators. Handgrip strength and physical activity was assessed as functional outcomes. We hypothesized that interactions between patterns and pulse images affect the PWA parameters and that the functional outcomes are weakly associated with personal, hemodynamic and risk factors for cardiovascular disease. Performing a PIA in patients with hypertension might allow the identification of early target-organ damage, standardization of the PIA based on the PWA, and unification of the pulse diagnosis. PMID:27079231

  6. Direct imaging of hot spot in Bi2Sr2CaCu2O8+δ mesa terahertz sources

    NASA Astrophysics Data System (ADS)

    Benseman, Timothy; Gray, Ken; Koshelev, Alexei; Kwok, Wai-Kwong; Welp, Ulrich; Vlasko-Vlasov, Vitalii; Kadowaki, Kazuo; Minami, Hidetoshi

    2013-03-01

    Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi2Sr2CaCu2O8+δ (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. When electrical power is applied to these devices, it is thought that hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power from Bi-2212 stacks. In order to better understand these hot spots, we have performed a thermal imaging study of BSCCO stacks which generate approximately 50 microwatts of radiation power at 0.59 THz. Utilizing the temperature-dependent 612nm fluorescence line of Eu3+, we are able to directly measure the temperature distribution at the top surface of these stacks with a resolution of +/- 1K. The images reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission. This research was funded by the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  7. Image reconstruction with sub-diffraction resolution in radio vision devices of millimeter and terahertz range using receiving arrays and image scanning

    NASA Astrophysics Data System (ADS)

    Vystavkin, Alexander N.; Pestryakov, Andrey V.; Bankov, Sergey E.; Chebotarev, Vladimir M.

    2009-09-01

    The method of image reconstruction with sub-diffraction resolution in radio vision devices (RVD) of shortwave millimeter and terahertz frequency range is proposed. The method is based on image scanning using two-dimensional receiving element array of RVD when array and image move circularly in common plane relatively each to other (rotating or not rotating) with small eccentricity between their centers. The results of scanning are signals reading out by detectors of array receiving elements. Each signal is proportional to the integral of two functions product. One function is a perfect image field distribution of the observed object received by RVD without diffraction distortion. Another one is RVD optical (quasioptical) transfer function comprising beams delivering incident radiation to detectors of array. The second function takes into account whole received radiation beam paths from RVD input to each detector including the effect of diffraction and reciprocal circular scanning of array and image. The image of observed object itself can be found solving inverse ill-posed problem determined by mentioned above integral relations. The estimation using computer simulation has shown that proposed method permits to increase resolution up to ten times in comparison with the case of diffraction restriction. The method is aimed at radioastronomy telescopes and RVD's for the security, medical diagnostics and other systems.

  8. Pulse-modulation imaging-review and performance analysis.

    PubMed

    Chen, D G; Matolin, D; Bermak, A; Posch, C

    2011-02-01

    In time-domain or pulse-modulation (PM) imaging, the incident light intensity is not encoded in amounts of charge, voltage, or current as it is in conventional image sensors. Instead, the image data are represented by the timing of pulses or pulse edges. This method of visual information encoding optimizes the phototransduction individually for each pixel by abstaining from imposing a fixed integration time for the entire array. Exceptionally high dynamic range (DR) and improved signal-to-noise ratio (SNR) are immediate benefits of this approach. In particular, DR is no longer limited by the power-supply rails as in conventional complementary metal-oxide semiconductor (CMOS) complementary metal-oxide semiconductor active pixel sensors, thus providing relative immunity to the supply-voltage scaling of modern CMOS technologies. In addition, PM imaging naturally supports pixel-parallel analog-to-digital conversion, thereby enabling high temporal resolution/frame rates or an asynchronous event-based array readout. The applications of PM imaging in emerging areas, such as sensor network, wireless endoscopy, retinal prosthesis, polarization imaging, and energy harvesting are surveyed to demonstrate the effectiveness of PM imaging in low-power, high-performance machine vision, and biomedical applications of the future. The evolving design innovations made in PM imaging, such as high-speed arbitration circuits and ultra-compact processing elements, are expected to have even wider impacts in disciplines beyond CMOS image sensors. This paper thoroughly reviews and classifies all common PM image sensor architectures. Analytical models and a universal figure of merit - image quality and dynamic range to energy complexity factor are proposed to quantitatively assess different PM imagers across the entire spectrum of PM architectures. PMID:23850979

  9. Underwater pulsed laser range-gated imaging model and its effect on image degradation and restoration

    NASA Astrophysics Data System (ADS)

    Youwei, Huang; Fengmei, Cao; Weiqi, Jin; Su, Qiu

    2014-06-01

    The imaging of underwater objects illuminated by artificial light has been of long-standing interest to investigators working in oceanographic environments. Pulsed lasers together with range-gated technology have been widely used for underwater optical imaging applications. In order to describe the formation of underwater range-gated images, a pulsed laser underwater imaging model based on pulse spatial and temporal broadening is proposed. Experiments based on a self-assembled laser range-gated imaging system were implemented in our laboratory. Results show good agreements between experiments and simulations. Both results also confirm higher image contrast toward the tail region of the target-reflected light. Furthermore, experiments on underwater image blur and restoration are also implemented and show good image recovery results. The modulation transfer function-based restoration mechanism also implies a way to eliminate the blur effect caused by light forward scattering.

  10. A novel method to suppress noise in marine radar images based on pulse-pulse correlation

    NASA Astrophysics Data System (ADS)

    Ding, Xianwen; Chen, Peng; He, Shengqi; Zheng, Zongsheng

    2011-11-01

    As the X-band marine radar often suffers from interference of electromagnetic waves of the same frequency transmitted by radars in its vicinity, the acquired images frequently contain co-channel interference noise. The noise degrades the quality of the marine radar images and is unfavorable to the processing and interpretation of the marine radar images. To suppress the noise in marine radar images, a novel method based on pulse-pulse correlation is proposed. This method includes three steps: threshold segmentation, noise extraction and noise fixing. In the threshold segmentation step, the threshold T is calculated based on the K distribution sea clutter model. In the noise extraction step, a 33 window is applied. By using the window, the pixels of noise can be extracted, and at the same time the pixels of non-noise can be discarded. In the noise fixing step, the strategy of piecewise interpolation is applied. At the region near to the image center, the triangulation with linear interpolation algorithm is applied; at the region far from the image center, the nearest neighbor algorithm is applied. The real X band marine radar image was used to test the performance of the proposed method. The obtained results show that the proposed method is able to reduce the co-channel interference noise from the marine radar images significantly and keep the information of objects in the images such as ships and islands. Besides, the proposed method can be fast in speed of operation.

  11. 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.

  12. Wall Painting Investigation by Means of Non-invasive Terahertz Time-Domain Imaging (THz-TDI): Inspection of Subsurface Structures Buried in Historical Plasters

    NASA Astrophysics Data System (ADS)

    Dandolo, Corinna Ludovica Koch; Jepsen, Peter Uhd

    2016-02-01

    Characterization of subsurface features of wall paintings is important in conservation and technical art history as well as in building archaeology and architecture fields. In this study, an area of the apsidal wall painting of Nebbelunde Church (Rødby, Denmark) has been investigated by means of terahertz time-domain imaging (THz-TDI). Subsurface structures have been detected at different depths inside the lime-based plaster of the wall painting until approximately 1 cm from the surface. The surface morphology of the buried structures has been 3D imaged in detail, providing a substantial contribution in their characterization.

  13. Analysis of a seventeenth-century panel painting by reflection terahertz time-domain imaging (THz-TDI): contribution of ultrafast optics to museum collections inspection

    NASA Astrophysics Data System (ADS)

    Koch Dandolo, Corinna L.; Filtenborg, Troels; Skou-Hansen, Jacob; Jepsen, Peter Uhd

    2015-11-01

    Terahertz time-domain imaging (THz -TDI) has been applied for nondestructive visualization of a hidden painting and other subsurface composition layers of a seventeenth-century panel painting belonging to the National Gallery of Denmark. Plan-type and cross-sectional scans realized by THz have been compared with images obtained by X-radiography, thus helping in a deep understanding of the strengths and limitations of this technique for art diagnostic purposes and in defining its rule among the other complementary investigation tools for nondestructive inspection of art pieces.

  14. Terahertz waveform generation for S21-parameter measurements using a fiber-coupled optical pulse shaper.

    PubMed

    Rämer, Jan-Martin; von Freymann, Georg

    2015-11-30

    A THz time-domain spectroscopy-based vector network analyzer for S21-parameter measurements is presented providing THz waveforms as input signal for waveguide-coupled devices under test. We integrate an optical pulse shaper into the emitter arm and fiber-couple the photoconductive antennas to allow for flexible usage. The pulse-shaping capabilities are demonstrated by realizing all 5 bit combinations of a 0.5 THz signal. Furthermore, we can set the center wavelength of the resulting THz spectrum. Finally, we apply the shaped THz waveforms to test the response of a low-noise amplifier. PMID:26698720

  15. Ultrahigh polarimetric image contrast enhancement for skin cancer diagnosis using InN plasmonic nanoparticles in the terahertz range

    NASA Astrophysics Data System (ADS)

    Ney, Michael; Abdulhalim, Ibrahim

    2015-12-01

    Mueller matrix imaging sensitivity, to delicate water content changes in tissue associated with early stages of skin cancer, is demonstrated by numerical modeling to be enhanced by localized surface plasmon resonance (LSPR) effects at the terahertz (THz) range when InN nanoparticles (NPs) coated with Parylene-C are introduced into the skin. A skin tissue model tailored for THz wavelengths is established for a Monte Carlo simulation of polarized light propagation and scattering, and a comparative study based on simulated Mueller matrices is presented considering different NPs' parameters and insertion into the skin methods. The insertion of NPs presenting LSPR in the THz is demonstrated to enable the application of polarization-based sample characterization techniques adopted from the scattering dominated visible wavelengths domain for the, otherwise, relatively low scattering THz domain, where such approach is irrelevant without the NPs. Through these Mueller polarimetry techniques, the detection of water content variations in the tissue is made possible and with high sensitivity. This study yields a limit of detection down to 0.0018% for relative changes in the water content based on linear degree of polarization-an improvement of an order of magnitude relative to the limit of detection without NPs calculated in a previous ellipsometric study.

  16. A terahertz confocal microscope for far-field thermal radiation detection and near-field sub-wavelength imaging

    NASA Astrophysics Data System (ADS)

    Weng, Qianchun; Yang, Le; Xu, Jie; Qian, Qingbai; Yu, Haochi; Zhang, Bo; An, Zhenghua; Zhu, Ziqiang; Lu, Wei

    2015-11-01

    We present a novel scattering-type scanning near-field optical microscope (s-SNOM) operating in the terahertz (THz) wavelength. A home-made ultra-high sensitive detector named charge sensitive infrared phototransistor (CSIP, detection wavelength ~15 μm) is equipped for spontaneous thermal radiation detection (external illumination should be avoided). Thermal emission from room-temperature objects is collected by a cassegrain objective lens placed above the sample, and focused to a pinhole (d=250 μm) which is kept in liquid-helium (LHe) temperature(4.2 K). With the background radiation from environment efficiently blocked by the low-temperature pinhole, the detector is only sensitive to the THz radiation from a small spot (~λ) on sample surface (the confocal point). As a result, thermal radiation spontaneously emitted by object itself is measured with an excellent spatial resolution of ~14 μm (diffraction-limit). For overcoming the diffraction limit by detecting the near-field evanescent waves, this THz microscope is combined with a home-built atomic-force microscope (AFM). With sharp AFM tip (<100 nm) scattering the evanescent waves with an improved tip-modulation method, we successfully obtained thermal near-field images with a spatial resolution of ~100 nm, which is already less than 1% of the detection wavelength (15 μm). This THz s-SNOM should be a powerful tool for various material research down to the nanometer scale.

  17. "All air-plasma" terahertz spectroscopy.

    PubMed

    Clough, Benjamin; Liu, Jingle; Zhang, X-C

    2011-07-01

    We demonstrate terahertz wave generation and detection capabilities up to 6 THz without the need for solid state materials, biased electrodes, or forward propagating signal collection. An "all air-plasma" terahertz system is used to encode explosive material resonant signatures into the 357 nm nitrogen fluorescence line of a bichromatic field-induced laser plasma filament. These results show the practicability to extend these measurements to remote locations where terahertz pulse information is no longer limited by water vapor absorption, phonon resonance, or signal collection directionality. PMID:21725424

  18. Giant enhancement of terahertz emission from nanoporous GaP

    SciTech Connect

    Atrashchenko, A. Korotchenkov, A.; Evtikhiev, V. P.; Arlauskas, A.; Adomavičius, R.; Krotkus, A.; Ulin, V. P.; Belov, P.

    2014-11-10

    In this paper, we have studied the emission of terahertz radiation from nanoporous semiconductor matrices of GaP excited by the femtosecond laser pulses. We observe 3–4 orders of magnitude increase of terahertz radiation emission from the nanoporous matrix compared to bulk material. The effect is mainly related to drastic increase of the sample surface and pinning of conducting electrons to surface states. This result opens up a promising way to create powerful sources of terahertz radiation using nanoporous semiconductors.

  19. Imaging of isolated molecules with ultrafast electron pulses.

    PubMed

    Hensley, Christopher J; Yang, Jie; Centurion, Martin

    2012-09-28

    Imaging isolated molecules in three dimensions with atomic resolution is important for elucidating complex molecular structures and intermediate states in molecular dynamics. This goal has so far remained elusive due to the random orientation of molecules in the gas phase. We show that three-dimensional structural information can be retrieved from multiple electron diffraction patterns of aligned molecules. The molecules are aligned impulsively with a femtosecond laser pulse and probed with a femtosecond electron pulse two picoseconds later, when the degree of alignment reaches a maximum. PMID:23030087

  20. Elliptically polarized terahertz radiation from a chiral oxide

    SciTech Connect

    Takeda, R.; Kida, N. Sotome, M.; Okamoto, H.

    2015-09-28

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

  1. ICARUS: imaging pulse compression algorithm through remapping of ultrasound.

    PubMed

    Biagi, Elena; Dreoni, Nicola; Masotti, Leonardo; Rossi, Iacopo; Scabia, Marco

    2005-02-01

    In this work we tackle the problem of applying to echographic imaging those synthetic aperture focusing techniques (SAFT) in the frequency domain commonly used in the field of synthetic aperture radars (SAR). The aim of this research is to improve echographic image resolution by using chirp transmit signals, and by performing pulse compression in both dimensions (depth and lateral). The curved geometry present in the unfocused radio-frequency (RF) ultrasonic image is the main cause of inaccuracy in the direct application of frequency domain SAFT algorithms to echographic imaging. The focusing method proposed in this work, after pulse compression in the depth dimension, performs lateral focusing in the mixed depth-lateral spatial frequency domain by means of a depth variant remapping followed by lateral pulse compression. This technique has the advantage of providing a resolution that is uniform in nonfrequency selective attenuation media, and improved with respect to conventional time domain SAFT, without requiring the acquisition and processing of channel data necessary for the most advanced synthetic transmit aperture techniques. Therefore, the presented method is suitable for easy real-time implementation with current generation hardware. PMID:15801314

  2. 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.

  3. Theory of a laser-plasma method for detecting terahertz radiation

    SciTech Connect

    Frolov, A. A.; Borodin, A. V.; Esaulkov, M. N.; Kuritsyn, I. I.; Shkurinov, A. P.

    2012-06-15

    A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation.

  4. Tunable focus graphene-based terahertz lens

    NASA Astrophysics Data System (ADS)

    Li, Jiu-Sheng

    2016-01-01

    To extend the usage of the terahertz wave, we present a simple method for variable focus length terahertz wave lens based on graphene. The focus length of the graphene-based terahertz lens can be tunable by changing the applied electric field without change the configuration. To demonstrate the feasibility of the approach, numerical simulation performed with the aid of the finite element method is used to evaluate the terahertz performance of the proposed device. With an appropriate design, the focal length of the proposed device can be tuned from 7.3 μm to 15.2 μm. The total size of the present graphene lens is only 3.5 μm×13 μm. It is believed to be applicable for future communication, imaging and sensing in terahertz range.

  5. A spatial light modulator for terahertz beams

    SciTech Connect

    Chen, Hou-tong; Taylor, Antoinette J

    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.

  6. Enhanced terahertz transmission by surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Wen, Yongzheng; Yang, Jiancheng; Yu, Xiaomei; Zhao, Yuejin; Liu, Xiaohua; Dong, Liquan

    2012-03-01

    The surface plasmon resonance (SPR) between metal and dielectric material has a good enhancement on electromagnetic wave transmission. In this paper, a series of two-dimension (2D) metal gratings and spiral structures with different geometrical size were experimentally tested by Terahertz time-domain spectroscopy (THz-TDS). The experiment results show that the 2D metal gratings have almost 70% increment on terahertz transmission than the pure silicon substrate in the range of 0.2-2.5THz, which indicates a strong coupling in the terahertz range, and the resonance mode shows a blue shift. On the other hand, the influence of different radiation directions was analyzed. It presents that the slightly higher transmission can be achieved when terahertz wave radiate from the front side than the back side. It reveals that surface plasmon resonance can enhance the terahertz transmission efficiently and has potential applications in security imaging, biological analysis and spectroscopy.

  7. Pulsed Raman fiber laser and multispectral imaging in three dimensions.

    PubMed

    Andersen, Joachim F; Busck, Jens; Heiselberg, Henning

    2006-08-20

    Raman scattering in single-mode optical fibers is exploited to generate multispectral light from a green nanolaser with high pulse repetition rate. Each pulse triggers a picosecond camera and measures the distance by time-of-flight in each of the 0.5 Mpixels. Three-dimensional images are then constructed with submillimeter accuracy for all visible colors. The generation of a series of Stokes peaks by Raman scattering in a Si fiber is discussed in detail and the laser radar technique is demonstrated. The data recording takes only a few seconds, and the high accuracy 3D color imaging works at ranges up to approximately 200 m. Applications for optical tomography in highly scattering media such as water and human tissue are mentioned. PMID:16892124

  8. Terahertz Sensing of Materials

    NASA Astrophysics Data System (ADS)

    Xuan, G.; Ghosh, S.; Kim, S.; Lv, P.-C.; Buma, T.; Weng, B.; Barner, K.; Kolodzey, J.

    2007-06-01

    Biomolecules such as DNA and proteins exhibit a wealth of modes in the Terahertz (THz) range from the rotational, vibrational and stretching modes of biomolecules. Many materials such as drywall that are opaque to human eyes are transparent to THz. Therefore, it can be used as a powerful tool for biomolecular sensing, biomedical analysis and through-the-wall imaging. Experiments were carried out to study the absorption of various materials including DNA and see-through imaging of drywall using FTIR spectrometer and Time Domain Spectroscopy (TDS) system.

  9. Transmission Spectra and Generation of Terahertz Pulses in SiO2-GaSe, TiO2-GaSe, Ga2O3-GaSe, and GaSe:S Structures

    NASA Astrophysics Data System (ADS)

    Bereznaya, S. A.; Zarubin, A. N.; Korotchenko, Z. V.; Prudaev, I. A.; Red'kin, R. A.; Sarkisov, S. Yu.; Tolbanov, O. P.

    2015-12-01

    Thin amorphous SiO2, TiO2, and Ga2O3 films were deposited on the surface of GaSe crystals by thermal and magnetron sputtering. It was found that under different technological conditions, the SiO2 and TiO2 layers on the surface of GaSe crack, while the Ga2O3 compound forms perfect films. A comparison of the transmission spectra and generation efficiency of terahertz pulses was made for the SiO2-GaSe, TiO2-GaSe, and Ga2O3-GaSe structures and for the GaSe:S 0.9 wt % and GaSe:S 7 wt % crystals. It was found that an increase in the concentration of sulfur in the GaSe:S crystals results in a decrease in the efficiency of generation of terahertz radiation by optical rectification of femtosecond laser pulses. Among the films deposited on the surface of GaSe, the SiO2 film has the least impact on the efficiency of generation.

  10. Pulsed photoacoustic flow imaging with a handheld system

    NASA Astrophysics Data System (ADS)

    van den Berg, Pim J.; Daoudi, Khalid; Steenbergen, Wiendelt

    2016-02-01

    Flow imaging is an important technique in a range of disease areas, but estimating low flow speeds, especially near the walls of blood vessels, remains challenging. Pulsed photoacoustic flow imaging can be an alternative since there is little signal contamination from background tissue with photoacoustic imaging. We propose flow imaging using a clinical photoacoustic system that is both handheld and portable. The system integrates a linear array with 7.5 MHz central frequency in combination with a high-repetition-rate diode laser to allow high-speed photoacoustic imaging-ideal for this application. This work shows the flow imaging performance of the system in vitro using microparticles. Both two-dimensional (2-D) flow images and quantitative flow velocities from 12 to 75 mm/s were obtained. In a transparent bulk medium, flow estimation showed standard errors of ˜7% the estimated speed; in the presence of tissue-realistic optical scattering, the error increased to 40% due to limited signal-to-noise ratio. In the future, photoacoustic flow imaging can potentially be performed in vivo using fluorophore-filled vesicles or with an improved setup on whole blood.

  11. Nonlinear terahertz superconducting plasmonics

    SciTech Connect

    Wu, Jingbo; Liang, Lanju; Jin, Biaobing E-mail: tonouchi@ile.osaka-u.ac.jp Kang, Lin; Xu, Weiwei; Chen, Jian; Wu, Peiheng E-mail: tonouchi@ile.osaka-u.ac.jp; Zhang, Caihong; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi E-mail: tonouchi@ile.osaka-u.ac.jp; Wang, Huabing

    2014-10-20

    Nonlinear terahertz (THz) transmission through subwavelength hole array in superconducting niobium nitride (NbN) film is experimentally investigated using intense THz pulses. The good agreement between the measurement and numerical simulations indicates that the field strength dependent transmission mainly arises from the nonlinear properties of the superconducting film. Under weak THz pulses, the transmission peak can be tuned over a frequency range of 145 GHz which is attributed to the high kinetic inductance of 50 nm-thick NbN film. Utilizing the THz pump-THz probe spectroscopy, we study the dynamic process of transmission spectra and demonstrate that the transition time of such superconducting plasmonic device is within 5 ps.

  12. Update to pulse sequences for interventional MR imaging.

    PubMed

    Derakhshan, Jamal J; Duerk, Jeffrey L

    2005-08-01

    The motivations for developing MR-guided minimally invasive therapy include its excellent soft tissue contrast, tomographic imaging in any direction (as opposed to projection imaging as in fluoroscopy), the absence of ionizing radiation,the abundance of contrast mechanisms (including bright blood pulse sequences that lead to excellent vessel conspicuity without exogenous contrast agent injection), the ability to obtain physiologic information such as perfusion, and an overall excellent safety profile. The main pulse sequences used today for interventional MR imaging are T1/T2-weighted FISP and TrueFISP, T2-weighted turbo spin-echo, and T1-weighted FLASH. The specific clinical question, the underlying pathophysiology,and the procedure to be performed dictate which sequence is used. Each of these sequences has been written to acquire data in conventional rectilinear trajectories, radial k-space paths, or even spirals. In many ways, the questions being researched in interventional MR imaging have been dictated by the primary issues in greatest need of resolution or that most directly facilitate new clinical development. A decade ago, research focused on exploration of new scan strategies for contrast and temporal resolution. Advancements in the last decade have made it possible to acquire and display greater than 10 images per second in realtime with millimeter resolution in all three directions. This temporal and spatial resolution is considered high enough to guide most interventions. With this capability, other research has focused on instrument tracking. The field has gone from the capability to track a single coil and superimpose it on a previously acquired roadmap to systems that follow, adapt, and provide high-resolution images due to the advent of multichannel receiver systems, improved graphics, higher processor speeds, and increases in speed and quantity of memory. Hence, instruments can be reliably identified and tracked and the information can be used to update pulse sequence parameters in real time, thereby opening new opportunities for interventional MR imaging that extend from biopsy and thermal therapy to image-guided vascular and cardiac procedures. Today, we see such issues as RF heating of wires used for device localization and the noise generated by rapid switching of MR gradients being significant obstacles yet to overcome to allow the full strength of MR-guided interventions to be realized clinically. It is anticipated that these topics will emerge as critical concepts in the next decade of interventional MR imaging research. PMID:16084410

  13. Single pulse frequency compounding protocol for superharmonic imaging

    NASA Astrophysics Data System (ADS)

    Danilouchkine, M. G.; van Neer, P. L. M. J.; Verweij, M. D.; Matte, G. M.; Vletter, W. B.; van der Steen, A. F. W.; de Jong, N.

    2013-07-01

    Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the 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 (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. 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 a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third 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 the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. 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.

  14. Terahertz detection and carbon nanotubes

    SciTech Connect

    Leonard, Francois

    2014-06-11

    Researchers at Sandia National Laboratories, along with collaborators from Rice University and the Tokyo Institute of Technology, are developing new terahertz detectors based on carbon nanotubes that could lead to significant improvements in medical imaging, airport passenger screening, food inspection and other applications.

  15. Terahertz detection and carbon nanotubes

    ScienceCinema

    Leonard, Francois

    2014-06-13

    Researchers at Sandia National Laboratories, along with collaborators from Rice University and the Tokyo Institute of Technology, are developing new terahertz detectors based on carbon nanotubes that could lead to significant improvements in medical imaging, airport passenger screening, food inspection and other applications.

  16. 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.

  17. 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.

  18. Imaging with and without time resolution using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Liu, Xuejun

    Femtosecond laser pulses were applied to four-wave mixing (FWM) microscopy with lateral resolution and to image one-dimensional ballistic electron transport in gold films with time resolution. The FWM microscope was illuminated with synchronized pulses from a Ti:sapphire laser and an optical parametric oscillator (OPO). The OPO was set up as part of the thesis and delivered an average power of about 60 mW tunable from 1 micron to 1.3 microns at pulse durations between 100 fs and 200 fs. The FWM microscope was designed to detect the long wavelength signal (infrared stimulated parametric emission, IR SPE) to probe electronic resonances of target molecules. A polarization sensitive detection scheme was applied to suppress the nonresonant background. The SPE signal proved to be insensitive to photo-bleaching, which is an inherent limiting factor in fluorescence microscopy. The FWM microscope was also applied to determine the real and imaginary part of the third-order susceptibilities of various dyes and solvents. Time-resolved fs pump-probe measurements were performed on thin Au films to image ballistic electron transport in these films. Damped oscillations in the transient reflectivity signals were observed, and are attributed to anisotropic ballistic electron motion and back-scattering at the film boundaries. A theoretical model based on a modified Fermi-liquid theory can explain the observed oscillation periods as a result of ballistic transport in directions determined by the actual shape of the Fermi surface of Au.

  19. Terahertz wave opto-mechanical scanner for security application

    NASA Astrophysics Data System (ADS)

    Deng, Chao; Zheng, Yongju; Zhang, Cunlin

    2010-11-01

    This paper describes a new opto-mechanical scanner that is hopeful for terahertz imaging in security applications. The target of using this scanner is portal screening of personnel for high-resolution imaging of concealed threat objects. It is not only applied to active terahertz imaging but also applied to passive Terahertz imaging. Terahertz wave can penetrate many materials that are opaque to visible and infrared light, such as plastics, cardboard, textiles and so on. So the terahertz imaging technology has a potential to be applicable in security inspection at airports, stations and other public place. Now, the most terahertz imaging system works at point to point mechanical scan pattern. The speed of this raster scan is too slow to apply in practical field. 2-D terahertz array detector can be applied to real time imaging. But at present their cost is prohibitively high. Fortunately low cost, high performance, opto-mechanically scanner is able to meet the current requirements. An opto-mechanical scanner should be able to rapidly scan a 2-D image of the scene. It also should have high optical efficiency so that an image system can achieve the required thermal sensitivity with the minimum number of receivers. These ensure that it can easily operate at any wavelength, and be active or passive. The opto-mechanically scanning can meets these requirements and is being developed into a high performance, low-cost prototype system that will meet the future needs for terahertz security.

  20. Terahertz inverse synthetic aperture radar (ISAR) imaging with a quantum cascade laser transmitter.

    PubMed

    Danylov, Andriy A; Goyette, Thomas M; Waldman, Jerry; Coulombe, Michael J; Gatesman, Andrew J; Giles, Robert H; Qian, Xifeng; Chandrayan, Neelima; Vangala, Shivashankar; Termkoa, Krongtip; Goodhue, William D; Nixon, William E

    2010-07-19

    A coherent transceiver using a THz quantum cascade (TQCL) laser as the transmitter and an optically pumped molecular laser as the local oscillator has been used, with a pair of Schottky diode mixers in the receiver and reference channels, to acquire high-resolution images of fully illuminated targets, including scale models and concealed objects. Phase stability of the received signal, sufficient to allow coherent image processing of the rotating target (in azimuth and elevation), was obtained by frequency-locking the TQCL to the free-running, highly stable optically pumped molecular laser. While the range to the target was limited by the available TQCL power (several hundred microwatts) and reasonably strong indoor atmospheric attenuation at 2.408 THz, the coherence length of the TQCL transmitter will allow coherent imaging over distances up to several hundred meters. Image data obtained with the system is presented. PMID:20721012

  1. Ultrafast quantum spin-state switching in the Co-octaethylporphyrin molecular magnet with a terahertz pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Farberovich, Oleg V.; Mazalova, Victoria L.

    2016-05-01

    Molecular spin crossover switches are the objects of intense theoretical and experimental studies in recent years. This interest is due to the fact that these systems allow one to control their spin state by applying an external photo-, thermo-, piezo-, or magnetic stimuli. The greatest amount of research is currently devoted to the study of the effect of the photoexcitation on the bi-stable states of spin crossover single molecular magnets (SMMs). The main limitation of photo-induced bi-stable states is their short lifetime. In this paper we present the results of a study of the spin dynamics of the Co-octaethylporphyrin (CoOEP) molecule in the Low Spin (LS) state and the High Spin (HS) state induced by applying the magnetic pulse of 36.8 T. We show that the spin switching in case of the HS state of the CoOEP molecule is characterized by a long lifetime and is dependent on the magnitude and duration of the applied field. Thus, after applying an external stimuli the system in the LS state after the spin switching reverts to its ground state, whereas the system in the HS state remains in the excited state for a long time. We found that the temperature dependency of magnetic susceptibility shows an abrupt thermal spin transition between two spin states at 40 K. Here the proposed theoretical approach opens the way to create modern devices for spintronics with the controllable spin switching process.

  2. CMOS detector arrays in a virtual 10-kilopixel camera for coherent terahertz real-time imaging.

    PubMed

    Boppel, Sebastian; Lisauskas, Alvydas; Max, Alexander; Krozer, Viktor; Roskos, Hartmut G

    2012-02-15

    We demonstrate the principle applicability of antenna-coupled complementary metal oxide semiconductor (CMOS) field-effect transistor arrays as cameras for real-time coherent imaging at 591.4 GHz. By scanning a few detectors across the image plane, we synthesize a focal-plane array of 100×100 pixels with an active area of 20×20 mm2, which is applied to imaging in transmission and reflection geometries. Individual detector pixels exhibit a voltage conversion loss of 24 dB and a noise figure of 41 dB for 16 μW of the local oscillator (LO) drive. For object illumination, we use a radio-frequency (RF) source with 432 μW at 590 GHz. Coherent detection is realized by quasioptical superposition of the image and the LO beam with 247 μW. At an effective frame rate of 17 Hz, we achieve a maximum dynamic range of 30 dB in the center of the image and more than 20 dB within a disk of 18 mm diameter. The system has been used for surface reconstruction resolving a height difference in the μm range. PMID:22344098

  3. A Concealed Barcode Identification System Using Terahertz Time-domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Guan, Yu; Yamamoto, Manabu; Kitazawa, Toshiyuki; Tripathi, Saroj R.; Takeya, Kei; Kawase, Kodo

    2015-03-01

    We present a concealed terahertz barcode/chipless tag to achieve remote identification through an obstructing material using terahertz radiation. We show scanned terahertz reflection spectral images of barcodes concealed by a thick obstacle. A concealed and double- side printed terahertz barcode structure is proposed, and we demonstrate that our design has better performance in definition than a single-side printed barcode using terahertz time-domain spectroscopy. This technique combines the benefits of a chipless tag to read encoded information covered by an optically opaque material with low cost and a simple fabrication process. Simulations are also described, along with an explanation of the principle of the terahertz barcode identification system.

  4. Terahertz absorption and reflection imaging of carcinoma-affected colon tissues embedded in paraffin

    NASA Astrophysics Data System (ADS)

    Wahaia, Faustino; Kasalynas, Irmantas; Venckevicius, Rimvydas; Seliuta, Dalius; Valusis, Gintaras; Urbanowicz, Andrzej; Molis, Gediminas; Carneiro, Fatima; Carvalho Silva, Catia D.; Granja, Pedro L.

    2016-03-01

    In the present study, dehydrated human colon tissues embedded in paraffin were studied at THz frequency. A compact THz imaging system with high numerical aperture optics was developed for the analysis of adenocarcinoma-affected colon sections, in transmission and reflection geometry. A comprehensive analysis of the THz images revealed a contrast up to 23% between the neoplastic and control tissues. Absorption and reflection THz images demonstrated the possibility to distinguish adenocarcinoma-affected areas even without water in the tissue, as the main contrast mechanism in THz measurements has been observed to be water absorption in in vivo or freshly excised tissues. The present results corroborate with previous histologic findings in the same tissues, and confirm that the contrast prevails even in dehydrated tissues.

  5. 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.

  6. Real-time, T-ray imaging using a sub-terahertz gyrotron

    NASA Astrophysics Data System (ADS)

    Han, Seong-Tae; Torrezan, Antonio C.; Sirigiri, Jagadishwar R.; Shapiro, Michael A.; Temkin, Richard J.

    2012-06-01

    We demonstrated real-time, active, T-ray imaging using a 0.46 THz gyrotron capable of producing 16 W in continuous wave operation and a pyroelectric array camera with 124-by-124 pixels. An expanded Gaussian beam from the gyrotron was used to maintain the power density above the detection level of the pyroelectric array over the area of the irradiated object. Real-time imaging at a video rate of 48 Hz was achieved through the use of the built-in chopper of the camera. Potential applications include fast scanning for security purposes and for quality control of dry or frozen foods.

  7. Active terahertz metamaterials

    SciTech Connect

    Chen, Hou-tong; O' Hara, John F; Taylor, Antoinette J

    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.

  8. Fourier Analysis and Structure Determination. Part II: Pulse NMR and NMR Imaging.

    ERIC Educational Resources Information Center

    Chesick, John P.

    1989-01-01

    Uses simple pulse NMR experiments to discuss Fourier transforms. Studies the generation of spin echoes used in the imaging procedure. Shows that pulse NMR experiments give signals that are additions of sinusoids of differing amplitudes, frequencies, and phases. (MVL)

  9. Features of plasma glow in low pressure terahertz gas discharge

    SciTech Connect

    Bratman, V. L.; Golubev, S. V.; Izotov, I. V.; Kalynov, Yu. K.; Koldanov, V. A.; Razin, S. V.; Litvak, A. G.; Sidorov, A. V.; Skalyga, V. A.; Zorin, V. G.; Lobachevsky State University of Nizhny Novgorod , 23 Gagarina st., 603950 Nizhny Novgorod

    2013-12-15

    Investigations of the low pressure (1–100 Torr) gas discharge in the powerful (1 kW) quasi-optical terahertz (0.55 THz) wave beams were made. An intense afterglow was observed after the end of gyrotron terahertz radiation pulse. Afterglow duration significantly exceeded radiation pulse length (8 μs). This phenomenon could be explained by the strong dependence of the collisional-radiative recombination rate (that is supposed to be the most likely mechanism of electron losses from the low pressure terahertz gas discharge) on electron temperature.

  10. 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.

  11. Production of high power femtosecond terahertz radiation

    SciTech Connect

    Neil, George R.; Carr, G.L.; Gubeli III, Joseph F.; Jordan, K.; Martin, Michael C.; McKinney, Wayne R.; Shinn, Michelle; Tani, Masahiko; Williams, G.P.; Zhang, X.-C.

    2003-07-11

    The terahertz (THz) region of the electromagnetic spectrum is attracting interest for a broad range of applications ranging from diagnosing electron beams to biological imaging. Most sources of short pulse THz radiation utilize excitation of biased semiconductors or electro-optic crystals by high peak power lasers. For example, this was done by using an un-doped InAs wafer irradiated by a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. Microwatt levels of THz radiation were detected when excited with FEL pulses at 1.06 mm wavelength and 10W average power. Recently substantially higher powers of femtosecond THz pulses produced by synchrotron emission were extracted from the electron beamline. Calculations and measurements confirm the production of coherent broadband THz radiation from relativistic electrons with an average power of nearly 20W, a world record in this wavelength range by a factor of 10,000. We describe the source, presenting theoretical calculations and their experimental verification. Potential applications of this exciting new source include driving new non-linear phenomena, performing pump-probe studies of dynamical properties of novel materials, and studying molecular vibrations and rotations, low frequency protein motions, phonons, superconductor band gaps, electronic scattering, collective electronic excitations (e.g., charge density waves), and spintronics.

  12. Effects of frame rate and image resolution on pulse rate measured using multiple camera imaging photoplethysmography

    NASA Astrophysics Data System (ADS)

    Blackford, Ethan B.; Estepp, Justin R.

    2015-03-01

    Non-contact, imaging photoplethysmography uses cameras to facilitate measurements including pulse rate, pulse rate variability, respiration rate, and blood perfusion by measuring characteristic changes in light absorption at the skin's surface resulting from changes in blood volume in the superficial microvasculature. Several factors may affect the accuracy of the physiological measurement including imager frame rate, resolution, compression, lighting conditions, image background, participant skin tone, and participant motion. Before this method can gain wider use outside basic research settings, its constraints and capabilities must be well understood. Recently, we presented a novel approach utilizing a synchronized, nine-camera, semicircular array backed by measurement of an electrocardiogram and fingertip reflectance photoplethysmogram. Twenty-five individuals participated in six, five-minute, controlled head motion artifact trials in front of a black and dynamic color backdrop. Increasing the input channel space for blind source separation using the camera array was effective in mitigating error from head motion artifact. Herein we present the effects of lower frame rates at 60 and 30 (reduced from 120) frames per second and reduced image resolution at 329x246 pixels (one-quarter of the original 658x492 pixel resolution) using bilinear and zero-order downsampling. This is the first time these factors have been examined for a multiple imager array and align well with previous findings utilizing a single imager. Examining windowed pulse rates, there is little observable difference in mean absolute error or error distributions resulting from reduced frame rates or image resolution, thus lowering requirements for systems measuring pulse rate over sufficient length time windows.

  13. Laser terahertz emission microscopy studies of a polysilicon solar cell under the illumination of continuous laser light

    NASA Astrophysics Data System (ADS)

    Salek, Khandoker Abu; Nakanishi, Hidetoshi; Ito, Akira; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi

    2014-03-01

    Terahertz wave-emission properties of a polysilicon solar cell excited by femtosecond laser pulses were visualized by laser terahertz emission microscopy (LTEM). The effects on the terahertz emissions of continuous-wave (cw) laser illumination of the solar cell at two wavelengths (808 and 365 nm) were examined under conditions of reverse and zero bias. The amplitude of the terahertz pulses in the presence of illumination was lower than that in its absence, and it decreased with increasing illumination power. The photovoltaic effect was smaller for cw laser illumination at the shorter wavelength. These phenomena can be explained in terms of screening of the electric field in the depletion layer of the p-n junction, as a result of the presence of photoexcited carriers. In addition, the LTEM images permitted the visualization of the crystalline grain structure of the solar cell and the dynamics of photocarriers, and they reflected the local electric field distribution in the cell. LTEM was therefore shown to be a promising technique for the evaluation and inspection of solar cells.

  14. Vanadium dioxide for terahertz devices

    NASA Astrophysics Data System (ADS)

    Charipar, Nicholas; Kim, Heungsoo; Mathews, Scott; Pique, Alberto

    We investigate VO2 as a material for ultrafast sub-millimeter wave devices. This material exhibits a semiconductor to metal transition (SMT) at ~68 °C which results in a dramatic increase in carrier density (~1019 -1023 cm-3). The SMT transition can be induced thermally, electrically, or optically enabling strong interactions and unique device operation. This transition has been exploited for numerous microwave/terahertz devices such as tunable filters and modulators. However due to its low carrier mobility (~ 0 . 1 cm2/V-s) and long recovery times (~ ns), VO2 has been largely ignored as a possible material for millimeter wave and terahertz pulse generation even though the SMT can occur within 100 fs. VO2 thin film devices were fabricated and characterized. These devices were capable of generating ~1 ps electrical pulses. We will present details on the ultrafast switching behaviors of VO2 along with the design and fabrication of terahertz emitter based on the SMT of VO2. This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program.

  15. Laser micromachining of silicon: a new technique for fabricating terahertz imaging arrays

    NASA Astrophysics Data System (ADS)

    Walker, Christopher K.; Hungerford, A. L.; Narayanan, Gopal; Groppi, C.; Bloomstein, Theodore M.; Palmacci, S. T.; Stern, Margaret B.; Curtin, Jane E.

    1998-07-01

    One of the main obstacles encountered in designing low noise, high efficiency, heterodyne receivers and local oscillator sources at submillimeter wavelengths is the quality and cost of waveguide structures. At wavelengths shorter than 400 micrometers, rectangular waveguide structures, feed-horns, and backshorts become extremely difficult to fabricate using standard machining techniques. We have used a new laser milling technique to fabricate high quality, THz waveguide components and feedhorns. Once metallized, the structures have the properties of standard waveguide components. Unlike waveguide components made using silicon wet-etching techniques, laser-etched components can have almost any cross section, from rectangular to circular. Under computer control, the entire waveguide structure (including the corrugated feedhorn a submillimeter-wave mixer or multiplier can be fabricated to micrometer tolerances in a few hours. Laser etching permits the direct scaling of successful waveguide multiplier and mixer designs to THz frequencies. Since the entire process is computer controlled, the cost of fabricating submillimeter waveguide components is significantly reduced. With this new laser etching process, the construction of high performance waveguide array receivers at THz frequencies becomes tractable. In this paper we will describe the laser etching technique and discuss how it can be used to construct THz imaging arrays. We will also describe the construction of a prototype 810 GHz mixer which utilizes these new construction techniques.

  16. In vivo photoacoustic imaging of blood vessels with a pulsed laser diode.

    PubMed

    Kolkman, Roy G M; Steenbergen, Wiendelt; van Leeuwen, Ton G

    2006-09-01

    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 investigated the use of a small and compact pulsed laser diode to image blood vessels. We proved that a pulsed laser diode can be applied for imaging blood vessels in vivo. PMID:16721626

  17. Terahertz Scattering

    NASA Astrophysics Data System (ADS)

    Zurk, L. M.; Schecklman, S.

    Terahertz (THz) Time Domain Spectroscopy (TDS) measurements have the unique ability to detect both the amplitude and phase of the electric field, simultaneously. This eliminates complications introduced by Kramers-Kronig relations typically used in near-infrared spectroscopy. Many materials of interest contain resonant features in their refractive indices in the far-infrared (THz) spectrum, while their packaging materials are generally transparent. Thus, an important application for THz TDS is the ability to see inside packaging materials and detect the material features of their contents. Such applications are promising for security screening (concealed drugs, explosives, etc.) in post offices and airports as well as for non-destructive evaluation (NDE) of products on an assembly line or tissue damage due to burns or cancer [1-6].

  18. Terahertz metamaterials

    SciTech Connect

    Chen, Hou-tong; Taylor, Antoineete J; Azad, Abul K; O' Hara, John F

    2009-01-01

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

  19. 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.

  20. Evaluation of human hairs with terahertz wave

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  1. Infrared imaging diagnostics for intense pulsed electron beam

    SciTech Connect

    Yu, Xiao; Shen, Jie; Liu, Wenbin; Zhong, Haowen; Zhang, Jie; Zhang, Gaolong; Le, Xiaoyun; Qu, Miao; Yan, Sha

    2015-08-15

    Infrared imaging diagnostic method for two-dimensional calorimetric diagnostics has been developed for intense pulsed electron beam (IPEB). By using a 100-μm-thick tungsten film as the infrared heat sink for IPEB, the emitting uniformity of the electron source can be analyzed to evaluate the efficiency and stability of the diode system. Two-dimensional axisymmetric finite element method heat transfer simulation, combined with Monte Carlo calculation, was performed for error estimation and optimization of the method. The test of the method was finished with IPEB generated by explosive emission electron diode with pulse duration (FWHM) of 80 ns, electron energy up to 450 keV, and a total beam current of over 1 kA. The results showed that it is possible to measure the cross-sectional energy density distribution of IPEB with energy sensitivity of 0.1 J/cm{sup 2} and spatial resolution of 1 mm. The technical details, such as irradiation protection of bremsstrahlung γ photons and the functional extensibility of the method were discussed in this work.

  2. Hidden object detection: security applications of terahertz technology

    NASA Astrophysics Data System (ADS)

    Tribe, William R.; Newnham, David A.; Taday, Philip F.; Kemp, Michael C.

    2004-04-01

    Recent events have led to dramatic changes to the methods employed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new Recent events have led to dramatic changes to the methods employed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new technologies that can be applied to security screening, either to simplify or speed up the checking process, or to provide additional functionality. Terahertz (THz) technology is a promising, emerging candidate. In previous publications we have shown how our THz pulsed imaging systems can be used to image threat items, and have demonstrated that explosive materials have characteristic THz spectra. We have also demonstrated that nonmetallic weaponry can be imaged when concealed beneath clothing. In this work we examine more closely the properties of barrier and potential confusion materials. We demonstrate that barrier materials have smooth spectra with relatively low attenuation. We further demonstrate that the terahertz spectra of several common chemicals and medicines are distinct from those of threat materials.

  3. 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.

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

    PubMed Central

    Wang, Tianheng; Kumavor, Patrick D.

    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

  5. 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.

  6. Pulse

    MedlinePlus

    ... pulse rate can help determine if the patient's heart is pumping. Pulse measurement has other uses as well. During or immediately after exercise, the pulse rate gives information about your fitness level and health.

  7. Noncontact imaging photoplethysmography to effectively access pulse rate variability

    NASA Astrophysics Data System (ADS)

    Sun, Yu; Hu, Sijung; Azorin-Peris, Vicente; Kalawsky, Roy; Greenwald, Stephen

    2013-06-01

    Noncontact imaging photoplethysmography (PPG) can provide physiological assessment at various anatomical locations with no discomfort to the patient. However, most previous imaging PPG (iPPG) systems have been limited by a low sample frequency, which restricts their use clinically, for instance, in the assessment of pulse rate variability (PRV). In the present study, plethysmographic signals are remotely captured via an iPPG system at a rate of 200 fps. The physiological parameters (i.e., heart and respiration rate and PRV) derived from the iPPG datasets yield statistically comparable results to those acquired using a contact PPG sensor, the gold standard. More importantly, we present evidence that the negative influence of initial low sample frequency could be compensated via interpolation to improve the time domain resolution. We thereby provide further strong support for the low-cost webcam-based iPPG technique and, importantly, open up a new avenue for effective noncontact assessment of multiple physiological parameters, with potential applications in the evaluation of cardiac autonomic activity and remote sensing of vital physiological signs.

  8. Terahertz radiation from a laser plasma filament

    SciTech Connect

    Wu, H.-C.; Meyer-ter-Vehn, J.; Ruhl, H.; Sheng, Z.-M.

    2011-03-15

    By the use of two-dimensional particle-in-cell simulations, we clarify the terahertz (THz) radiation mechanism from a plasma filament formed by an intense femtosecond laser pulse. The nonuniform plasma density of the filament leads to a net radiating current for THz radiation. This current is mainly located within the pulse and the first cycle of the wakefield. As the laser pulse propagates, a single-cycle and radially polarized THz pulse is constructively built up forward. The single-cycle shape is mainly due to radiation damping effect.

  9. Broadband terahertz amplification in a heterogeneous quantum cascade laser.

    PubMed

    Bachmann, Dominic; Leder, Norbert; Rösch, Markus; Scalari, Giacomo; Beck, Mattias; Arthaber, Holger; Faist, Jérôme; Unterrainer, Karl; Darmo, Juraj

    2015-02-01

    We demonstrate a broadband terahertz amplifier based on ultrafast gain switching in a quantum cascade laser. A heterogeneous active region is processed into a coupled cavity metal-metal waveguide device and provides broadband terahertz gain that allows achieving an amplification bandwidth of more than 500 GHz. The temporal and spectral evolution of a terahertz seed pulse, which is generated in an integrated emitter section, is presented and an amplification factor of 21 dB is reached. Furthermore, the quantum cascade amplifier emission spectrum of the emerging sub-nanosecond terahertz pulse train is measured by time-domain spectroscopy and reveals discrete modes between 2.14 and 2.68 THz. PMID:25836170

  10. Focus and Alignment Tolerance in a Photoconductive Terahertz Source

    NASA Astrophysics Data System (ADS)

    Paz-Martínez, Gaudencio; Garduño-Mejía, Jesus; Kolokoltsev, Oleg V.; Treviño-Palacios, Carlos G.; Qureshi, Naser

    2015-09-01

    Robust coupling between a pulsed laser beam and a photoelectric circuit is an important issue in the development of miniaturized, integrated, and embedded terahertz instrumentation. Here, we present a study of the effect of varying the focus and alignment parameters of an excitation laser pulse on the emission characteristics of a standard Hertzian-dipole type terahertz photoelectric source. The objective is to quantify the tolerance of a terahertz time-domain spectroscopy system, and we study the variation of peak amplitude, waveform, phase, and energy distribution as a function of excitation position and defocus. We find that a terahertz source can be made relatively tolerant to variations in focus, alignment, and details of the geometry of the photoelectric system, providing a window for a more robust field operation.

  11. Nonlinear restoration of pulse and high noisy images via stochastic resonance

    NASA Astrophysics Data System (ADS)

    Sun, Qibing; Liu, Hongjun; Huang, Nan; Wang, Zhaolu; Han, Jing; Li, Shaopeng

    2015-11-01

    We propose a novel scheme for restoring pulse and high noisy images using stochastic resonance, which is based on the modulation instability and provides a cross-correlation gain higher than 8. As opposed to previously reported designs, this unique approach employs a continuous noise and pulse signal for the generation of modulation instability. The visibility and quality of output images can be improved by appropriately adjusting the system parameters. This provides a simple and feasible method for detecting low-level or hidden pulse images in various imaging applications.

  12. Nonlinear restoration of pulse and high noisy images via stochastic resonance

    PubMed Central

    Sun, Qibing; Liu, Hongjun; Huang, Nan; Wang, Zhaolu; Han, Jing; Li, Shaopeng

    2015-01-01

    We propose a novel scheme for restoring pulse and high noisy images using stochastic resonance, which is based on the modulation instability and provides a cross-correlation gain higher than 8. As opposed to previously reported designs, this unique approach employs a continuous noise and pulse signal for the generation of modulation instability. The visibility and quality of output images can be improved by appropriately adjusting the system parameters. This provides a simple and feasible method for detecting low-level or hidden pulse images in various imaging applications. PMID:26530885

  13. Double half RF pulses for reduced sensitivity to eddy currents in UTE imaging.

    PubMed

    Josan, Sonal; Pauly, John M; Daniel, Bruce L; Pauly, Kim Butts

    2009-05-01

    Ultrashort echo time imaging with half RF pulse excitation is challenging as eddy currents induced by the slice-select gradient distort the half pulse slice profile. This work presents two pulses with T(2)-dependent slice profiles that are less sensitive to eddy currents. The double half pulse improves the slice selectivity for long T(2) components, while the inverted double half pulse suppresses the unwanted long T(2) signal. Thus, both approaches prevent imperfect cancellation of out-of-slice signal from contaminating the desired slice. Experimental results demonstrate substantially improved slice selectivity and R(2)* quantitation accuracy with these pulses. These pulses are effective in making short T(2) imaging and quantitation less sensitive to eddy currents and provide an alternative to time-consuming gradient characterization. PMID:19235919

  14. 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.

  15. High dynamic velocity range particle image velocimetry using multiple pulse separation imaging.

    PubMed

    Persoons, Tim; O'Donovan, Tadhg S

    2011-01-01

    The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods. PMID:22346564

  16. High Dynamic Velocity Range Particle Image Velocimetry Using Multiple Pulse Separation Imaging

    PubMed Central

    Persoons, Tim; O’Donovan, Tadhg S.

    2011-01-01

    The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods. PMID:22346564

  17. Detection of colon cancer by terahertz techniques

    NASA Astrophysics Data System (ADS)

    Wahaia, Faustino; Valusis, Gintaras; Bernardo, Luis M.; Almeida, Abílio; Moreira, J. Agostinho; Lopes, Patricia C.; Macutkevic, Jan; Kasalynas, Irmantas; Seliuta, Dalius; Adomavicius, Ramunas; Henrique, Rui; Lopes, Machado

    2011-05-01

    Normal and cancer affected samples of colon tissue have been measured using transmission time-domain terahertz spectroscopy and continuous wave terahertz imaging. We show that it is possible to distinguish between normal and cancerous regions in the samples when they are fixed in formalin or embedded in paraffin. Plots of the refractive index of normal and cancer affected tissues as well as 2-D transmission THz images are shown. Experimental results will be presented and the conditions for discrimination between normal and affected tissue will be discussed.

  18. 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 2π 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 ±π/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.

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

    PubMed

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

    2015-04-21

    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 2π 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 ±π/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. PMID:25903859

  20. Integrated heterodyne terahertz transceiver

    DOEpatents

    Lee, Mark; Wanke, Michael C.

    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.

  1. Integrated heterodyne terahertz transceiver

    DOEpatents

    Wanke, Michael C.; Lee, Mark; Nordquist, Christopher D.; Cich, Michael J.

    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.

  2. Imaging the coupling of terahertz radiation to a high electron mobility transistor in the near-field

    NASA Astrophysics Data System (ADS)

    Ortolani, M.; di Gaspare, A.; Giovine, E.; Evangelisti, F.; Foglietti, V.; Doria, A.; Gallerano, G. P.; Giovenale, E.; Messina, G.; Spassovsky, I.; Lanzieri, C.; Peroni, M.; Cetronio, A.

    2009-03-01

    We used AlGaN/GaN high electron mobility transistors as room-temperature direct detectors of radiation at 0.15 THz from a free electron laser, hence 5 times higher than their cutoff frequency of 30 GHz. By near-field active mapping we investigated the antenna-like coupling of the radiation to the transistor channel. We formulate a model for the detection based on self-mixing in the transistor channel. The noise equivalent power is found in the range of 10^{-7} W/Hz^{0.5} without any optimization of the device responsivity. Present day AlGaN/GaN fabrication technology may provide operation at higher frequency, integration of amplifiers for improved responsivity and fast switches for multiplexing, which make the detector here described the basic element of a monolithic terahertz focal plane array.

  3. Broadband terahertz generation using the semiconductor-metal transition in VO2

    NASA Astrophysics Data System (ADS)

    Charipar, Nicholas A.; Kim, Heungsoo; Mathews, Scott A.; Piqué, Alberto

    2016-01-01

    We report the design, fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2 (vanadium dioxide). With the appropriate geometry, picosecond electrical pulses are generated by illuminating 120 nm thick VO2 with 280 fs pulses from a femtosecond laser. These ultrafast electrical pulses are used to drive a simple dipole antenna, generating broadband terahertz radiation.

  4. Contrast imaging by non-overlapping dual frequency band transmit pulse complexes.

    PubMed

    Hansen, Rune; Angelsen, Bjørn A J

    2011-02-01

    SURF contrast imaging, as described previously in the literature, is a contrast agent detection technique achieved by processing of the received signals from transmitted dual frequency band pulse complexes with overlapping high-frequency (HF) and low-frequency (LF) pulses. The transmitted HF pulses are used for image reconstruction, whereas the transmitted LF pulses are used to manipulate the scattering properties of the contrast agent. As with harmonic contrast agent detection techniques, nonlinear wave propagation will, in most situations, also limit the specificity with the SURF contrast technique when transmitting overlapping HF and LF pulses. The present paper proposes an alternative SURF contrast imaging technique using transmit dual frequency band pulse complexes with non-overlapping HF and LF pulses. If the frequency of the LF manipulation pulse is close to the bubble resonance frequency, numerical simulations indicate a significant ring-down effect of the LF bubble radius response. Utilizing this bubble ring-down effect and transmitting the HF pulse just after the LF pulse, a contrast agent specificity approaching infinity accompanied by a contrast agent sensitivity only for contrast bubbles having resonance frequencies within a narrow frequency range may be obtained. PMID:21342814

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

    PubMed

    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

  6. 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

  7. Terahertz emission from a two-color plasma filament in a slot waveguide

    SciTech Connect

    Dietze, D.; Unterrainer, K.; Darmo, J.

    2012-02-27

    Terahertz emission in forward direction from a long two-color filament placed in the center of a slot waveguide is reported. The waveguide improves the collection and imaging of the generated THz radiation. By tuning the plate separation and position of the waveguide along the filament axis, the emitted mode can be matched to the collection optics. We achieved an increase of the detected electric field by 40% and of the THz pulse energy by four times compared to the case without waveguide.

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

    SciTech Connect

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

    2014-07-31

    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. (laser biophotonics)

  9. Terahertz wave generation from spontaneously formed nanostructures in silver nanoparticle ink.

    PubMed

    Kato, Kosaku; Takano, Keisuke; Tadokoro, Yuzuru; Nakajima, Makoto

    2016-05-01

    We demonstrate terahertz pulse generation from silver nanoparticle ink, originally developed for printed electronics, under irradiation by femtosecond laser pulses. Using metal nanoparticle ink, metallic nanostructures can be easily made in a large area without lithographic techniques. Terahertz pulses were emitted from the baked ink, having spontaneously formed nanostructures of ∼100  nm. From the results of the baking temperature dependence and the polarization measurement, the terahertz generation is attributed to the nonlinear polarization induced by the enhanced local fields around these nanostructures. This study paves the way for the future development of terahertz emitters which have resonances in both the near-infrared light and the terahertz wave, by combining micrometer-scale structures drawn by an inkjet printer and nanometer-scale structures formed during the baking process. PMID:27128090

  10. Terahertz surface emission from Cu{sub 2}ZnSnSe{sub 4} thin film photovoltaic material excited by femtosecond laser pulses

    SciTech Connect

    Zhao, Zhenyu Han, Qifeng; Zhang, Jingtao; Shi, Wangzhou; Niehues, Gudrun; Funkner, Stefan; Yamamoto, Kohji; Tani, Masahiko; Estacio, Elmer; Guo, Qixin

    2014-12-08

    We observed efficient terahertz (THz) emission from sol-gel grown Cu{sub 2}ZnSnSe{sub 4} (CZTSe) thin films using THz time domain spectroscopy technique. The THz emission bandwidth exceeds 2 THz with a dynamic range of 20 dB in the amplitude spectrum. The THz emission amplitude from CZTSe is found to be independent of external magnetic fields. Comparing the polarity of THz emission waveforms of CZTSe and GaAs, we suggest that the acceleration of photo-carriers in the surface accumulation layer of CZTSe is the dominant mechanism of radiation emission. Optical excitation fluence dependence measurements show that the saturation fluence of the CZTSe thin film reaches 1.48 μJ/cm{sup 2}.

  11. 64 μW pulsed terahertz emission from growth optimized InGaAs/InAlAs heterostructures with separated photoconductive and trapping regions

    SciTech Connect

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

    2013-08-05

    We present results on optimized growth temperatures and layer structure design of high mobility photoconductive Terahertz (THz) emitters based on molecular beam epitaxy grown In{sub 0.53}Ga{sub 0.47}As/In{sub 0.52}Al{sub 0.48}As 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 μW corresponding to an optical power-to-THz power conversion efficiency of up to 2 × 10{sup −3}.

  12. Theoretical foundations of detection of terahertz radiation in laser-plasma interactions

    SciTech Connect

    Frolov, A. A.

    2013-02-15

    A theory is developed enabling one to calculate the temporal profile and spectrum of a terahertz wave packet from the energy of the second harmonic of optical radiation generated during the nonlinear interaction between terahertz and circularly polarized laser pulses in the skin layer of an overdense plasma. It is shown that the spectral and temporal characteristics of the envelope of the second harmonic of optical radiation coincide with those of the terahertz pulse only at small durations of the detecting laser radiation. For long laser pulses, the temporal profile and spectrum of the second harmonic are mainly determined by the characteristics of optical radiation at the carrier frequency.

  13. Shadowgraphic imaging of metal drilling with a long pulse excimer laser

    NASA Astrophysics Data System (ADS)

    Schoonderbeek, Aart; Biesheuvel, Cornelis A.; Hofstra, Ramon M.; Boller, Klaus-Jochen; Meijer, Johan

    2003-11-01

    A shadowgraphic imaging technique is used for studying the interaction between the laser beam and the material during laser drilling. The used laser is a XeCl excimer laser with a nearly diffraction limited beam and 175 ns pulse length. We studied how and when the material is removed. Holes are drilled with a series of pulses in aluminum and Hastelloy X. The shadowgraphic images show the development of a shockwave whose expansion is in agreement with theory. Both the removal of material at different times after the start of the laser pulse and the material removal for different pulses during the drilling process are shown. Material removal occurs by vaporization as well as melt ejection. Our experiments show the same amount of removed material for drilling with different cover gases. The shadowgraphic images show that the larger part of the material is removed after the end of the laser pulse.

  14. Dynamic control of metamaterials at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Shrekenhamer, David

    Progress in the field of metamaterials has started coming to a point where the field may finally begin to emerge as a viable solution to many electromagnetic challenges facing the community. No where is that more true then at terahertz frequencies where there lies an immense opportunity for growth. The development of mature technologies within this region of the electromagnetic spectrum would provide a valuable resource to become available for a multitude of applications. In order to achieve this, the necessary first steps of identifying viable materials and paths to integrate these with metamaterials will need to be completed. In this dissertation, we examine several different paths to achieve dynamic metamaterial electromagnetic response at terahertz frequencies, and demonstrate several paths to package these devices into imaging systems. In Chapter 1, we introduce the basic theory and design principles of metamaterials. We also describe the experimental techniques involved in the study of terahertz metamaterials. Chapter 2 presents a computational and experimental study investigating the integration of high electron mobility transistors with metamaterials allowing for high speed modulation of incident terahertz radiation. In Chapters 3 and 4, we investigate several different paths to create tunable terahertz metamaterial absorbers. Chapter 3 presents an investigation where we encapsulate a metametarial absorber unit cell with liquid crystals. We study both computationally and experimentally the tuning mechanism of the absorber as the liquid crystal refractive index is controlled as a function of the applied electric field strength and modulation frequency. In Chapter 4, we form a doped semiconducting metamaterial spatial light modulator with multi-color super-pixels composed of arrays of electronically controlled terahertz metamaterial absorbers. We computationally and experimentally study the independent tunability of each pixel in the spatial array and demonstrate high speed modulation. Chapter 5 introduces a multiplex imaging approach by using a terahertz spatial light modulator to enable terahertz imaging with a single pixel detector. We demonstrate the capability for high speed image acquisition, currently only limited by the commerical software used to reconfigure the spatial masks. We also configure the system to capture high fidelity images of varying complexity. In Chapter 6, we show how a metamaterial absorber can be implemented into a detector focal plane array for high sensitivity, low mutual coupling, and broad angle performance. Finally, we summarize in Chapter 7 the achievments of the research presented and highlight the direction of future work.

  15. Strip Velocity Measurements for Gated X-Ray Imagers Using Short Pulse Lasers

    SciTech Connect

    Ross, P. W.; Cardenas, M.; Griffin, M.; Mead, A.; Silbernagel, C. T.; Bell, P.; Haque, S. H.

    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.

  16. EDITORIAL: Photonic terahertz technology

    NASA Astrophysics Data System (ADS)

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

    2005-07-01

    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 magnitude from 100 GHz to 10 THz, accessible for applications. From the lower-frequency side, electronics keeps pushing upwards, while photonic approaches gradually improve our technological options at higher frequencies. The popular interest reflects the considerable advances in research in the THz field, and it is mainly advances in the photonic branch, with the highlight being the development of the THz quantum cascade laser, which in recent years have caught the imagination of the public, and of potential users and investors. This special issue of Semiconductor Science and Technology provides an overview of key scientific developments which currently represent the cutting edge of THz photonic technology. In order to be clear about the implications, we should define exactly what we mean by 'THz photonic technology', or synonymously 'THz photonics'. It is characterized by the way in which THz radiation (or a guided THz wave) is generated, namely by the use of lasers. This may be done in one of two fundamentally different schemes: (i) by laser action in the terahertz frequency range itself (THz lasers), or (ii) by down-conversion processes (photomixing) involving the radiation of lasers which operate in the visible, near-infrared or infrared spectral ranges, either in pulsed or continuous-wave mode. The field of THz photonics has grown so considerably that it is out of the question to cover all its aspects in a single special issue of a journal. We have elected, instead, to focus our attention on two types of development with a potentially strong impact on the THz field: first, on significant advances of the technology itself, and second, on specific applications considered capable of fostering the transmutation of THz technology as a whole into a market technology. We decided for reasons of conciseness to leave out technologies which require more than table-top equipment (free-electron lasers, THz sources based on electrons accelerated to relativistic speed, etc) as well as fairly mature techniques (such as backward-wave oscillators which, although they are not strictly lasers, also exhibit gain). More difficult was the decision not to consider fascinating ideas for novel sources and detectors which until now have existed only on paper or have just entered the process of fundamental investigation. As we ourselves are working on such a concept (the Bloch-gain laser), we are fully aware of the fact that some of these ideas may have a strong impact on the field of THz photonics in the near future. After selection of the topics we wanted to cover, we contacted colleagues who are prominent in their respective fields of research and are grateful that most of them responded positively, expressing their willingness to share their knowledge with the readers of this journal. They took care not only to describe their own work but to give ample reference to the status of their respective specialized field of work. Before summarizing the contributions, we want to address all colleagues in the field who feel that they should have been asked to contribute but were not. To you we want to apologize. We can only hope for your understanding of the constraints of this endeavour. The collection of invited contributions is grouped into five topics. The first is entitled 'Pulsed THz Systems' and contains four papers dealing with the state of the art in source and detector development of measurement systems employing femtosecond Ti:sapphire lasers. The first paper, by Planken et al, describes the state of the art of the most common types of optoelectronic THz systems, namely those with femtosecond lasers operating at high repetition rate (~100 MHz). The system described by Planken et al was initially optimized for high-speed pixel-by-pixel THz imaging, which they do not describe here but rather focus on developments in THz microscopy. The second paper, by Kübler et al, presents pioneering work towards ultra-wide-bandwidth THz pulses which exhibit spectral content reaching far into the mid-IR, tremendously widening the covered frequency range, and hence shortening the time resolution, of THz spectroscopy. The third paper, by Löffler et al, deals with the state of the art in THz measurement systems relying on amplified laser pulses. Finally, Krotkus et al focus on low-temperature-grown (LT) GaAs, arguably the most important material for ultrafast optoelectronic switching and present in many THz sources and detectors, and in other emerging materials of similar kind. This leads directly to the second topic of this collection of papers, 'Continuous-Wave Photomixing Technology', based on THz-wave generation by down-conversion of continuous-wave (cw) laser radiation. This newer branch of THz photonics opens the possibility of obtaining tunable narrow-band THz radiation and of detecting it with high signal-to-noise ratio at room temperature. CW photomixing has received much attention over the last few years mainly because it has the potential to provide the compact and low-cost THz measurement systems needed for market applications beyond the scientific realm, with the sources of light for mixing being semiconductor (or fibre) lasers with or without optical amplifiers. Six papers outline recent developments in this subfield. We should also point towards a seventh paper, by Kawase et al, which is to be found in the section on 'Chemical and Biochemical Recognition', and which discusses an interesting hybrid approach generating tunable quasi-cw THz radiation with the help of nanosecond laser pulses. Of the six papers mentioned, the first, by Tani et al, summarizes the state of the art which relies on single-point LT-GaAs photoconductive antennae as THz sources and detectors driven by semiconductor lasers operating at wavelengths around 0.8 m. As laser-induced damage to the sources currently limits the achievable output power, researchers have early-on tried to develop travelling-wave mixers with distributed THz-power generation. Michael describes the status quo of this approach. The replacement of lifetime-limited photoconductive antennae with transit-time-limited p-i-n photomixers can be another way towards higher conversion efficiency if the RC frequency roll-off can be controlled. Döhler et al introduce a novel lumped-element device, a quasi-ballistic cascaded p-i-n photomixer, which promises a significantly better conversion efficiency than standard LT-GaAs photomixers at all frequencies. At laser wavelengths in the telecommunication windows, especially at 1.55 m, where InP-based compound semiconductors exhibit an extremely favourable electron mobility, p-i-n mixers have already established themselves as a powerful THz source. The group of Ito et al have set the standards here and describe their achievements in the fourth paper of this subtopic. The challenge remains to develop a similarly effective optoelectronic detector for these operating wavelengths. This, as Brown et al show in their contribution, turns out to be mainly a materials research issue, and as novel ultrafast materials such as those containing ErAs clusters emerge, so do sensitive detectors and photoconductive sources. The section closes with a paper by Hoffmann et al, which is more speculative in its scope but targets a fascinating goal: THz photomixing directly in a dual-colour semiconductor laser itself, and thus the ultimate miniaturization of a THz source based on photomixing. The third topic is 'THz Laser Technology' and addresses direct laser action at THz frequencies. Hübers et al guide the reader into the topic with a paper presenting the state of the art and the potential of lasers based on germanium and silicon. Tredicucci et al then review their development of the THz quantum cascade laser, the THz radiation source which more than any other currently transforms the field of THz technology. Their paper and the following one by Hu et al, who have introduced major improvements of the laser scheme and the waveguiding technology, present the state of the art of these lasers and discuss their future potential. One of the main challenges will be to raise the operation temperature further, and to bring it as close to room temperature as possible. These improvements will require a more advanced theoretical understanding of how these lasers work. The papers of Hu et al and the following one by Indjin et al address this question and describe the present status of theory. With this, we leave THz sources and detectors and come to research targeting the application of THz radiation. We have, given the space restraints and the fact that the focus of this journal is on semiconductor technology, decided to address only a single field of strong current interest, 'Chemical and Biochemical Recognition'. Other developing areas, such as THz radar and tomography, aiming at the sensing and diagnostics of surfaces and the inner structure of THz-transparent objects, or semiconductor wafer diagnostics and various other THz measurement modalities, are not covered. Not at all because we might consider them to be less important; quite on the contrary we are certain that they will make a big impact in real-world applications. The field of chemical and biochemical recognition was singled out because in the recent past there was controversial discussion as to what THz spectroscopic signatures to expect, especially from soft and solid chemical or biochemical matter, and the time seems to have come now to review some of the hard data obtained in the mean time. The topic covers the identification and analysis of chemical and biochemical substances, with a strong motivation stemming from the fact that the knowledge gained by this research opens up broad application areas in such lucrative markets as pharmaceutics, genetics, medical imaging and security screening. It may be interesting to note that until one or two years ago, a buzzword of applications-related research would have been 'biomedical imaging', especially of cancerous tissue or teeth, but for whatever reason none of the researchers contacted by us were interested to represent this subfield here, which seems to indicate that it is not considered to be a hot topic at present. The first two papers in this section, by Fischer et al and Shen et al, set the stage with an overview of chemical recognition in absorption and reflection spectroscopy, respectively. Kawase et al then demonstrate drug identification with their unique quasi-cw parametric THz system. While the scope of this paper is already security-oriented, Federici et al go further along this line by discussing not only drug detection but also sensing of explosives and weapons. The section closes with a paper by Nagel et al on the detection of DNA-binding states and on the system improvements implemented by this group on the way towards cost-effective sensing. This brings us to the final theme, 'THz Microscopy, Imaging, and Photonic Crystals'. The three papers in this section deal with three different aspects of THz technology which represent current progress in the use of THz radiation. The first paper, by Cho et al, as well as the one by Planken et al in the section on 'Pulsed THz Systems', discusses developments aiming towards THz microscopy, and reviews the latest results in achieving ultrahigh spatial resolution at THz frequencies. The next paper, by Karpowicz et al, comes back to the issue of THz imaging, which was already addressed by authors of papers in the preceding section, and presents a systematic comparison between two imaging and sensing modalities, time-domain optoelectronic imaging and more conventional GHz all-electronic imaging. This study of high practical interest is followed by the final contribution, by Jian et al, which discusses the development and characterization of photonic crystals for THz frequencies. We hope that this special issue will provide the readers of this journal with a good overview of the current status of THz photonics. We also hope that we, the Guest Editors and the authors of the papers, will succeed in conveying the fascination of this field of research which comes equally from its interdisciplinarity and from the fact that fundamental and applied research go hand in hand, strongly impacting on each other. For those working in this field it is highly gratifying to help make the last under-used window of the electro-magnetic spectrum accessible for applications.

  17. Development of a new pulsed source for photoacoustic imaging based on aperiodically poled lithium niobate.

    PubMed

    Yankelevich, Diego; González, J E; Cudney, Roger S; Ríos, Luis A; Marcu, Laura

    2014-02-01

    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

  18. 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

  19. A polarization-independent broadband terahertz absorber

    SciTech Connect

    Shi, Cheng; Zang, XiaoFei E-mail: ymzhu@usst.edu.cn; Wang, YiQiao; Chen, Lin; Cai, Bin; Zhu, YiMing E-mail: ymzhu@usst.edu.cn

    2014-07-21

    A highly efficient broadband terahertz absorber is designed, fabricated, and experimentally as well as theoretically evaluated. The absorber comprises a heavily doped silicon substrate and a well-designed two-dimensional grating. Due to the destructive interference of waves and diffraction, the absorber can achieve over 95% absorption in a broad frequency range from 1 to 2 THz and for angles of incidence from 0° to 60°. Such a terahertz absorber is also polarization-independent due to its symmetrical structure. This omnidirectional and broadband absorber have potential applications in anti-reflection coatings, imaging systems, and so on.

  20. Perfect terahertz absorber using fishnet based metafilm

    SciTech Connect

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

    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.