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Sample records for terahertz reflection spectroscopy

  1. Reflection terahertz time-domain spectroscopy of RDX and HMX explosives

    NASA Astrophysics Data System (ADS)

    Choi, Kyujin; Hong, Taeyoon; Ik Sim, Kyung; Ha, Taewoo; Cheol Park, Byung; Hyuk Chung, Jin; Gyeong Cho, Soo; Hoon Kim, Jae

    2014-01-01

    We report on our study of RDX and HMX, two of the most commonly used explosive materials, in bulk pellets with reflection terahertz time-domain spectroscopy in the frequency range of 0.3-3 THz. The maximum entropy method was utilized to correct our raw reflection data against the phase error due to the relative displacement between the sample and the reference. Both the refractive index n and the extinction coefficient k in the terahertz region were acquired for these two explosives without a Kramers-Kronig analysis. Both RDX and HMX exhibit a series of distinct peaks not quite detectable in the more conventional transmission-type measurements due to their high terahertz absorptivity. Our results are compared with the literature data on powder samples.

  2. Terahertz Reflection Spectroscopy for Identification of Explosive Devices

    DTIC Science & Technology

    2012-12-09

    CODE 30 SAAET 6.1 Basic Research Effort Total # Name Organization PI 1 Eric I. Thorsos University of Washington Co-PIs 1 Antao Chen ...D. P. Winebrenner, A. Chen , and E. I. Thorsos, United States Patent Application Publication, US 2012/0191371 A1, July 26, 2012. January 20, 2010...Presentation (Date) Patent (Date) M. H. Arbab, D. P. Winebrenner, E. I. Thorsos, and A. Chen “Application of wavelet transforms in terahertz

  3. Transmission and Reflection Terahertz Spectroscopy of Insensitive Melt-Cast High-Explosive Materials

    NASA Astrophysics Data System (ADS)

    Palka, Norbert; Szala, Mateusz

    2016-10-01

    Currently, artillery shells and grenades that are introduced into the market are based on melt-castable insensitive high explosives (IHEs), which do not explode while they run a risk of impact, heat or shrapnel. Particles of explosives (such as hexogen, nitroguanidine and nitrotriazolone) are suspended in different proportions in a matrix of 2.4-dinitroanisole. In this paper, we investigated samples of commonly used IHEs: PAX-41, IMX-104 and IMX-101, whose internal structures were determined by a scanning electron microscope. Terahertz time domain spectroscopy was applied in both transmission and reflection configurations. At first, the complex refraction indices of four pure constituents creating IHEs were determined and became the basis of further calculations. Next, the experimentally determined transmission and reflection spectra of IHEs and pure constituents were compared with theoretical considerations. The influence of the grain size of constituent material and scattering on the reflection spectra was analysed, and good agreement between the experimental and theoretical data was achieved.

  4. Extracting Complex Refractive Index from Polycrystalline Glucose with Self-Referenced Method for Terahertz Time-Domain Reflection Spectroscopy.

    PubMed

    Zhang, Yu; Zhang, Lin; Sun, Ping; He, Yingfeng; Zou, Yun; Deng, Yuqiang

    2016-07-01

    A self-referenced method for extracting the complex refractive index of material was proposed. The method utilized signals reflected from the front and rear surfaces of a slice sample as reference and sample signals, respectively. Before using the self-referenced method, a hybrid filtering technique for eliminating systematic and random noises of time-domain terahertz reflection spectroscopy was used. A terahertz reflection spectrum of crystalline glucose was measured and three feature absorption peaks were obtained from 0.2 to 2.0 THz. We suggest that intermolecular vibrational modes may contribute to the observed absorption spectra in the THz frequency range.

  5. Rapid analysis of tetracycline hydrochloride solution by attenuated total reflection terahertz time-domain spectroscopy.

    PubMed

    Qin, Jianyuan; Xie, Lijuan; Ying, Yibin

    2017-06-01

    Despite numerous methods for the detection of antibiotic residues, they are usually destructive and require tedious pre-treatment. Terahertz time-domain spectroscopy (THz-TDS) is an emerging technology that has advantages for analyzing chemical and biological compounds since THz waves are very sensitive to the molecular vibrational modes. Here we incorporated attenuated total reflection technique into the THz-TDS and demonstrated that this technology (ATR THz-TDS) allowed to determine the complex refractive indices of tetracycline hydrochloride (TCH) solutions with high accuracy and could be used to predict their concentrations. Our results from the simple linear regression models indicated that the complex refractive index exhibited a monotonic decrease with an increase in the TCH concentration. This study will provide new knowledge about the concentration determination of a liquid sample that couldn't be elucidated with the conventional THz-TDS technologies.

  6. Sensitive monitoring of photocarrier densities in the active layer of a photovoltaic device with time-resolved terahertz reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamashita, Genki; Matsubara, Eiichi; Nagai, Masaya; Kim, Changsu; Akiyama, Hidefumi; Kanemitsu, Yoshihiko; Ashida, Masaaki

    2017-02-01

    We demonstrate the sensitive measurement of photocarriers in an active layer of a GaAs-based photovoltaic device using time-resolved terahertz reflection spectroscopy. We found that the reflection dip caused by Fabry-Pérot interference is strongly affected by the carrier profile in the active layer of the p-i-n structure. The experimental results show that this method is suitable for quantitative evaluation of carrier dynamics in active layers of solar cells under operating conditions.

  7. Mechanism of relativistic Doppler reflection from a photoinduced moving plasma front studied by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Kohno, Nanase; Itakura, Ryuji; Tsubouchi, Masaaki

    2016-10-01

    We applied terahertz (THz) time-domain spectroscopy to reveal the mechanism of the relativistic Doppler reflection of THz light from a photoinduced plasma front in a silicon wafer. The frequency upshift caused by the Doppler reflection was identified by measurement of the reflected THz waveforms and compared to the calculated results obtained using the one-dimensional finite-difference time-domain method. The relation between the energy density of the pump light and the frequency upshift was also explored. We found that the interaction time of the moving plasma front and the reflected THz pulse is a key factor in understanding the mechanism of the relativistic Doppler reflection.

  8. 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.

  9. Thickness measurement of tablet coating using continuous-wave terahertz reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Devi, Nirmala; Dash, Jyotirmayee; Ray, Shaumik; Pesala, Bala

    2016-02-01

    THz rays have higher penetration depth compared to infrared rays and hence can be effectively used to measure tablet coating thickness. In addition, THz wavelength (1 mm - 0.1 mm) provides an optimal depth resolution for the thickness measurement. This method can be non-invasive and hence ideal for inline quality monitoring. Tablet coating thickness is one of the major parameters of interest in Process Analytical Technology (PAT). In this paper, a reflection mode Continuous Wave (CW) Terahertz (THz) system has been employed to measure the tablet coating thickness. A frequency scan of the sample has been carried out from 0.1 THz to 1.1 THz and the reflection coefficient of the sample is inverse fourier transformed to obtain the tablet thickness. The calculated thickness has also been validated using the optical microscope. Results show that the thickness can be measured with considerable accuracy.

  10. Terahertz imaging of composite materials in reflection and transmission mode with a time-domain spectroscopy system

    NASA Astrophysics Data System (ADS)

    Sørgârd, Trygve R.; van Rheenen, Arthur D.; Haakestad, Magnus W.

    2016-02-01

    A fiber-coupled Terahertz time domain spectroscopy (THz-TDS) system based on photoconductive antennas, pumped by a 100-fs fiber laser, has been used to characterize materials in transmission and reflection mode. THz images are acquired by mounting the samples under investigation on an x-y stage, which is stepped through the beam while the transmitted or reflected THz waveform is captured. The samples include a carbon fiber epoxy composite and a sandwich-structured composite panel with an aramid fiber honeycomb core in between two skin layers of fiberglass reinforced plastic. The former has an artificially induced void, and from a comparison of recorded reflected time-domain signals, with and without the void, a simple model for the structure of the composite is proposed that describes the time-domain signals reasonably well.

  11. Terahertz time-domain spectroscopy of biological tissues

    SciTech Connect

    Nazarov, M M; Shkurinov, A P; Kuleshov, E A; Tuchin, V V

    2008-07-31

    Terahertz absorption spectra and dispersion of biologically important substances such as sugar, water, hemoglobin, lipids and tissues are studied. The characteristic absorption lines in the frequency range of a terahertz spectrometer (0.1-3.5 THz) are found. The refraction indices and absorption coefficients of human tooth enamel and dentine are measured. The method of terahertz phase reflection spectroscopy is developed for strongly absorbing substances. Simple and reliable methods of time-resolved terahertz spectroscopy are developed. (biophotonics)

  12. Beating the wavelength limit: three-dimensional imaging of buried subwavelength fractures in sculpture and construction materials by terahertz time-domain reflection spectroscopy.

    PubMed

    Schwerdtfeger, M; Castro-Camus, E; Krügener, K; Viöl, W; Koch, M

    2013-01-20

    We use reflection terahertz spectroscopy to locate and produce three-dimensional images of air gaps between stones that resemble fractures, even of subwavelength thicknesses. This technique is found to be promising tool for sculpture and building damage evaluation as well as structural quality control in other dielectric materials.

  13. Investigations on polarimetric terahertz frequency domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Gong, Yandong; Zhang, Banghong; Notake, Takashi; Minamide, Hiroaki; Olivo, Malini; Sugii, Shigeki

    2014-04-01

    A polarimetric Terahertz frequency-domain spectroscopy system is presented which has an additional polarization measurement function at the Terahertz band. The achromatic Terahertz waveplate, which acts as the key device in the system, is also presented.

  14. Terahertz Spectroscopy of Biomolecules

    NASA Astrophysics Data System (ADS)

    Korter, Timothy; Plusquellic, David; Hight Walker, Angela; Heilweil, Edwin

    2002-03-01

    A novel, continuous-wave (CW) terahertz spectrometer has been constructed to investigate the flexibility and dynamics of small biological molecules. Hydrogen bonding interactions, torsional vibrations, and conformational changes are expressed in this far-infrared region of the spectrum. Terahertz (THz) radiation (0 - 4 THz or 0 - 133 wavenumber) is generated at the difference frequency of two near-infrared pump lasers by optical heterodyne mixing at the surface of a solid-state photomixer. This spectrometer has been used to probe the low-frequency vibrational modes of several members of the vitamin B-complex including riboflavin, pantothenic acid, and biotin. Interpretation of these unique THz spectra has been aided by low-frequency Raman experiments as well as ab initio predictions for normal mode frequencies and intensities. Instrumental details, vitamin B-complex analyses, and preliminary results for myoglobin and other large biomolecules will be presented.

  15. Brain tumor imaging of rat fresh tissue using terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Sayuri; Fukushi, Yasuko; Kubota, Oichi; Itsuji, Takeaki; Ouchi, Toshihiko; Yamamoto, Seiji

    2016-07-01

    Tumor imaging by terahertz spectroscopy of fresh tissue without dye is demonstrated using samples from a rat glioma model. The complex refractive index spectrum obtained by a reflection terahertz time-domain spectroscopy system can discriminate between normal and tumor tissues. Both the refractive index and absorption coefficient of tumor tissues are higher than those of normal tissues and can be attributed to the higher cell density and water content of the tumor region. The results of this study indicate that terahertz technology is useful for detecting brain tumor tissue.

  16. Brain tumor imaging of rat fresh tissue using terahertz spectroscopy

    PubMed Central

    Yamaguchi, Sayuri; Fukushi, Yasuko; Kubota, Oichi; Itsuji, Takeaki; Ouchi, Toshihiko; Yamamoto, Seiji

    2016-01-01

    Tumor imaging by terahertz spectroscopy of fresh tissue without dye is demonstrated using samples from a rat glioma model. The complex refractive index spectrum obtained by a reflection terahertz time-domain spectroscopy system can discriminate between normal and tumor tissues. Both the refractive index and absorption coefficient of tumor tissues are higher than those of normal tissues and can be attributed to the higher cell density and water content of the tumor region. The results of this study indicate that terahertz technology is useful for detecting brain tumor tissue. PMID:27456312

  17. 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.

  18. 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.

  19. 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.

  20. Examining pharmaceuticals using terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Sulovská, Kateřina; Křesálek, Vojtěch

    2015-10-01

    Pharmaceutical trafficking is common issue in countries where they are under stricter dispensing regime with monitoring of users. Most commonly smuggled pharmaceuticals include trade names Paralen Plus, Modafen, Clarinase repetabs, Aspirin complex, etc. These are transported mainly from Eastern Europe (e.g. Poland, Ukraine, Russia) to countries like Czech Republic, which is said to have one of the highest number of methamphetamine producers in Europe. The aim of this paper is to describe the possibility of terahertz spectroscopy utilization as an examining tool to distinguish between pharmaceuticals containing pseudoephedrine compounds and those without it. Selected medicaments for experimental part contain as an active ingredient pseudoephedrine hydrochloride or pseudoephedrine sulphate. Results show a possibility to find a pseudoephedrine compound spectra in samples according to previously computed and experimentally found ones, and point out that spectra of same brand names pills may vary according to their expiration date, batch, and amount of absorbed water vapours from ambience. Mislead spectrum also occurs during experimental work in a sample without chosen active ingredient, which shows persistent minor inconveniences of terahertz spectroscopy. All measurement were done on the TPS Spectra 3000 instrument.

  1. Terahertz homodyne self-mixing transmission spectroscopy

    SciTech Connect

    Mohr, Till Breuer, Stefan; Blömer, Dominik; Patel, Sanketkumar; Schlosser, Malte; Birkl, Gerhard; Elsäßer, Wolfgang; Simonetta, Marcello; Deninger, Anselm; Giuliani, Guido

    2015-02-09

    A compact homodyne self-mixing terahertz spectroscopy concept is experimentally investigated and confirmed by calculations. This method provides amplitude and phase information of the terahertz radiation emitted by a photoconductive antenna in a transmission experiment where a rotating chopper wheel serves as a feedback mirror. As a proof-of-principle experiment the frequency-dependent refractive index of Teflon is measured.

  2. Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

    SciTech Connect

    Azad, Abul K; Chen, Houtong; Taylor, Antoinette; O' Hara, John F; Han, Jiaguang; Lu, Xinchao; Zhang, Weili

    2009-01-01

    The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

  3. Terahertz spectroscopy of plasmonic fractals.

    PubMed

    Agrawal, A; Matsui, T; Zhu, W; Nahata, A; Vardeny, Z V

    2009-03-20

    We use terahertz time-domain spectroscopy to study the transmission properties of metallic films perforated with aperture arrays having deterministic or stochastic fractal morphologies ("plasmonic fractals"), and compare them with random aperture arrays. All of the measured plasmonic fractals show transmission resonances and antiresonances at frequencies that correspond to prominent features in their structure factors in k space. However, in sharp contrast to periodic aperture arrays, the resonant transmission enhancement decreases with increasing array size. This property is explained using a density-density correlation function, and is utilized for determining the underlying fractal dimensionality, D(<2). Furthermore, a sum rule for the transmission resonances and antiresonances in plasmonic fractals relative to the transmission of the corresponding random aperture arrays is obtained, and is shown to be universal.

  4. Coherent two-dimensional terahertz-terahertz-Raman spectroscopy

    PubMed Central

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

    2016-01-01

    We present 2D terahertz-terahertz-Raman (2D TTR) spectroscopy, the first technique, to our knowledge, to interrogate a liquid with multiple pulses of terahertz (THz) light. This hybrid approach isolates nonlinear signatures in isotropic media, and is sensitive to the coupling and anharmonicity of thermally activated THz modes that play a central role in liquid-phase chemistry. Specifically, by varying the timing between two intense THz pulses, we control the orientational alignment of molecules in a liquid, and nonlinearly excite vibrational coherences. A comparison of experimental and simulated 2D TTR spectra of bromoform (CHBr3), carbon tetrachloride (CCl4), and dibromodichloromethane (CBr2Cl2) shows previously unobserved off-diagonal anharmonic coupling between thermally populated vibrational modes. PMID:27274067

  5. Coherent two-dimensional terahertz-terahertz-Raman spectroscopy.

    PubMed

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

    2016-06-21

    We present 2D terahertz-terahertz-Raman (2D TTR) spectroscopy, the first technique, to our knowledge, to interrogate a liquid with multiple pulses of terahertz (THz) light. This hybrid approach isolates nonlinear signatures in isotropic media, and is sensitive to the coupling and anharmonicity of thermally activated THz modes that play a central role in liquid-phase chemistry. Specifically, by varying the timing between two intense THz pulses, we control the orientational alignment of molecules in a liquid, and nonlinearly excite vibrational coherences. A comparison of experimental and simulated 2D TTR spectra of bromoform (CHBr3), carbon tetrachloride (CCl4), and dibromodichloromethane (CBr2Cl2) shows previously unobserved off-diagonal anharmonic coupling between thermally populated vibrational modes.

  6. Nondestructive analysis of structure and components of tablet coated with film by the usage of terahertz time-domain reflection spectroscopy.

    PubMed

    Takeuchi, Issei; Shimakura, Kemmaro; Ohtake, Hideyuki; Takayanagi, Jun; Tomoda, Keishiro; Nakajima, Takehisa; Terada, Hiroshi; Makino, Kimiko

    2014-01-01

    Nondestructive analysis of tablet is of great importance from the aspect of productivity and safety. In terahertz (THz) region, however, the analysis of core of coated tablet has not been progressed. In this study, we have measured a flat-surface push-pull osmotic pump tablet, having no orifice, having bilayer core and a coating film layer. The bilayer core was made from the drug layer and the push layer, and acetaminophen was contained in the drug layer as a model drug. To study its structure and components, we have obtained reflection spectra from the drug layer side and the push layer side measurements using THz time-domain reflection spectroscopy (THz-TDRS). From these results, detection of the peak of acetaminophen in the spectrum from the drug layer side measurements was confirmed. We have made ridges approximated toward the peak using a general method of linear regression analysis in both spectra. Two-sample t-test was applied to their gradients, and significant difference between the drug layer and the push layer was shown. These results suggested that THz-TDRS is applicable to the analysis of structure and component of a coated tablet.

  7. Microfluidic devices for terahertz spectroscopy of biomolecules.

    PubMed

    George, Paul A; Hui, Wallace; Rana, Farhan; Hawkins, Benjamin G; Smith, A Ezekiel; Kirby, Brian J

    2008-02-04

    We demonstrate microfluidic devices for terahertz spectroscopy of biomolecules in aqueous solutions. The devices are fabricated out of a plastic material that is both mechanically rigid and optically transparent with near-zero dispersion in the terahertz frequency range. Using a lowpower terahertz time-domain spectrometer, we experimentally measure the absorption spectra of the vibrational modes of bovine serum albumin from 0.5 - 2.5 THz and find good agreement with previously reported data obtained using large-volume solutions and a high-power free-electron laser. Our results demonstrate the feasibility of performing high sensitivity terahertz spectroscopy of biomolecules in aqueous solutions with detectable molecular quantities as small as 10 picomoles using microfluidic devices.

  8. Investigation of inflammable liquids by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Ikeda, Takeshi; Matsushita, Akira; Tatsuno, Michiaki; Minami, Yukio; Yamaguchi, Mariko; Yamamoto, Kohji; Tani, Masahiko; Hangyo, Masanori

    2005-07-01

    We have examined a nondestructive and contactless screening method for water and inflammable liquids stored in common beverage plastic bottles by the terahertz time-domain spectroscopy. No THz transmission has been observed between 10 and 60cm-1 for 45-mm-thick water in plastic bottles. Part of the THz wave, on the other hand, has been transmitted through the commercially available inflammable liquids in the same bottles. The differences in the absorption intensities and the refractive indices in the THz region, which reflect the ingredients of organic compounds, allow us to distinguish these inflammable liquids. We confirm that the screening method based on the THz transmission can be applied to classifying the commercially available inflammable liquids stored in plastic bottles and to distinguishing these inflammable liquids from water as well.

  9. Application of Terahertz Attenuated Total Reflection Spectroscopy to Detect Changes in the Physical Properties of Lactose during the Lubrication Process Required for Drug Formulation.

    PubMed

    Dohi, Masafumi; Momose, Wataru; Yamashita, Kazunari; Hakomori, Tadashi; Sato, Shusaku; Noguchi, Shuji; Terada, Katsuhide

    2017-02-01

    Manufacturing the solid dosage form of an orally administered drug requires lubrication to enhance manufacturability, ensuring that critical quality attributes such as disintegration and dissolution of the drug product are maintained during manufacture. Here, to evaluate lubrication performance during manufacture, we used terahertz attenuated total reflection (THz-ATR) spectroscopy to detect differences in the physical characteristics of the lubricated powder. We applied a simple formulation prepared by blending granulated lactose as filler with magnesium stearate as lubricant. A flat tablet was prepared using the lubricated powder to acquire sharp THz-ATR absorption peaks of the samples. First, we investigated the effects of lubricant concentration and compression pressure on preparation of the tablet and then determined the effect of the pressure applied to samples in contact with the ATR prism on sample absorption amplitude. We focused on the differences in the magnitudes of spectra at the lactose-specific frequency. Second, we conducted the dynamic lubrication process using a 120-L mixer to investigate differences in the magnitudes of absorption corresponding to the lactose-specific frequency during lubrication. In both studies, enriching the lubricated powder with a higher concentration of magnesium stearate or prolonging blending time correlated with higher magnitudes of spectra at the lactose-specific frequency. Further, in the dynamic lubrication study, the wettability and disintegration time of the tablets were compared with the absorption spectra amplitudes at the lactose-specific frequency. We conclude that THz-ATR spectroscopy is useful for detecting differences in densities caused by a change in the physical properties of lactose during lubrication.

  10. Nondestructive Evaluation of Aircraft Composites Using Terahertz Time Domain Spectroscopy

    DTIC Science & Technology

    2008-12-10

    Taday, P. F., Pepper , M. (2008). Elimination of scattering effects in spectral measurement of granulated materials using terahertz time domain...W., Ferguson , B., Rainsford, T., Mickan, S. P., & Abbott, D. (2005). Material parameter extraction for terahertz time-domain spectroscopy using... Ferguson , B., Rainsford, T., Mickan, S. P., & Abbott, D. (2005). Simple material parameter estimation via terahertz time-domain spectroscopy

  11. Terahertz time-domain spectroscopy and application on peanut oils

    NASA Astrophysics Data System (ADS)

    Li, Jiusheng; Yao, Jianquan; Li, Jianrui

    2008-12-01

    Many materials were previously studied using far-infrared Fourier transform spectroscopy (FTS) in transmission and reflection modes. Recently, there has been a remarkable effort in employing terahertz time-domain spectroscopy (THz-TDS) for investigating material properties, including environment pollutants, semiconductors, polymers, explosive materials, and gases, etc. Since the absorption coefficient and the refractive index of the material studied are directly related to the amplitude and phase respectively of the transmitted field, both parts of the complex permittivity can be obtained by THz-TDS. In this letter, the optical properties of peanut oils in the frequency range from 0.2 to 2.5 THz were studied by employing terahertz time-domain spectroscopy. Several peanut oils, such as clean unused peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling were tested. The time delays of clean unused peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling are 8.33ps, 8.46ps and 8.46ps, respectively. The refractive indices of the three oil samples show slow a decrease as the terahertz wave frequency increases. The power absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range.

  12. Extending applicability of terahertz spectroscopy for biosensing

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Ramakrishnan

    Terahertz (THz) vibrational resonance spectroscopy has recently emerged as a promising technique for fingerprinting biological molecules. Absorption spectra in this frequency range (0.1-10 THz) reflect molecular internal vibrations involving the weakest hydrogen bonds and/or non-bonded interactions, which are species specific. Of prime importance is improving detection sensitivity of molecules with low absorption characteristics in the THz gap. Also of importance is the characterization of biological molecules in the THz gap (10-25 cm-1) by physical parameters (refractive index and absorption coefficient) rather than sample dependent parameters (transmission, reflection) and extending spectroscopy to the low THz range where remote sensing is most viable. To address the sensitivity issue, it is shown that periodic arrays of rectangular slots with subwavelength width provide for local electromagnetic field enhancements due to edge effects in the low frequency range of interest, 10-25 cm-1 (300-750 GHz). Periodic structures of Au, doped Si and InSb were studied. InSb is confirmed to offer the highest results with the local power enhancements on the order of 1100 at frequency 14 cm -1. InSb and Si have large skin depths in the frequency range of interest and so the analysis of their structures was done through the Fourier expansion method of field diffracted from gratings. Au however has small skin depths at these frequencies compared to the thickness. Surface impedance boundary conditions were employed to model the Au structure, for which the Fourier expansion method was unsuitable owing to the huge magnitude of Au permittivity. The applications possibly include development of novel bio-sensors, with the strongly enhanced local electromagnetic fields leading to increased detection sensitivity, and monitoring biophysical processes such as DNA denaturation. Transmission and reflection data from parallel, independent experiments are utilized in the Interference

  13. High frequency resolution terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Sangala, Bagvanth Reddy

    2013-12-01

    A new method for the high frequency resolution terahertz time-domain spectroscopy is developed based on the characteristic matrix method. This method is useful for studying planar samples or stack of planar samples. The terahertz radiation was generated by optical rectification in a ZnTe crystal and detected by another ZnTe crystal via electro-optic sampling method. In this new characteristic matrix based method, the spectra of the sample and reference waveforms will be modeled by using characteristic matrices. We applied this new method to measure the optical constants of air. The terahertz transmission through the layered systems air-Teflon-air-Quartz-air and Nitrogen gas-Teflon-Nitrogen gas-Quartz-Nitrogen gas was modeled by the characteristic matrix method. A transmission coefficient is derived from these models which was optimized to fit the experimental transmission coefficient to extract the optical constants of air. The optimization of an error function involving the experimental complex transmission coefficient and the theoretical transmission coefficient was performed using patternsearch algorithm of MATLAB. Since this method takes account of the echo waveforms due to reflections in the layered samples, this method allows analysis of longer time-domain waveforms giving rise to very high frequency resolution in the frequency-domain. We have presented the high frequency resolution terahertz time-domain spectroscopy of air and compared the results with the literature values. We have also fitted the complex susceptibility of air to the Lorentzian and Gaussian functions to extract the linewidths.

  14. Terahertz wave reflective sensing and imaging

    NASA Astrophysics Data System (ADS)

    Zhong, Hua

    Sensing and imaging technologies using terahertz (THz) radiation have found diverse applications as they approach maturity. Since the burgeoning of this technique in the 1990's, many THz sensing and imaging investigations have been designed and conducted in transmission geometry, which provides sufficient phase and amplitude contrast for the study of the spectral properties of targets in the THz domain. Driven by rising expectations that THz technology will be a potential candidate in the next generation of security screening, remote sensing, biomedical imaging and non-destructive testing (NDT), most THz sensing and imaging modalities are being extended to reflection geometry, which offers unique and adaptive solutions, and multi-dimensional information in many real scenarios. This thesis takes an application-focused approach to the advancement of THz wave reflective sensing and imaging systems: The absorption signature of the explosive material hexahydro-1,3,5-trinitro-1,3,5triazine (RDX) is measured at 30 m---the longest standoff distance so far attained by THz time-domain spectroscopy (THz-TDS). The standoff distance sensing ability of THz-TDS is investigated along with discussions specifying the influences of a variety of factors such as propagation distance, water vapor absorption and collection efficiency. Highly directional THz radiation from four-wave mixing in laser-induced air plasmas is first observed and measured, which provides a potential solution for the atmospheric absorption effect in standoff THz sensing. The simulations of the beam profiles also illuminate the underlying physics behind the interaction of the optical beam with the plasma. THz wave reflective spectroscopic focal-plane imaging is realized the first time. Absorption features of some explosives and related compounds (ERCs) and biochemical materials are identified by using adaptive feature extraction method. Good classification results using multiple pattern recognition methods are

  15. Biological Sensing with Terahertz Circular Dichroism Spectroscopy

    DTIC Science & Technology

    2005-05-31

    S.J. and Plaxco, K.W. (2003) “Terahertz circular dichroism spectroscopy: a potential approach to unbiased, in situ life detection.” Astrobiology , 3...detection.” Astrobiology , 3, 489-504 Xu, J., Ramian, G.J., Galan, J.F., Savvidis, P.G., Scopatz, A.M., Birge, R.R., Allen, S.J. and Plaxco, K.W. (2004

  16. Application of Terahertz Time-Domain Spectroscopy in Detecting Gaps with Different Widths.

    PubMed

    Bao, Rima; Wu, Zhikui; Wang, Fang; Miao, Xinyang; Feng, Chengjing

    2017-01-01

    The characterization of fractures is of vital importance for studies in many industries. In the present work, we used terahertz reflection measurements to identify simulated gaps of different widths that resemble fractures. The time interval between pulses (Δt) was proportional to the distance between the interfaces. In addition, fast Fourier transform (FFT) corresponding to the waveforms was also employed to distinguish the gaps. The widths in frequency were found to be inversely proportional to that of the gaps. In general, both terahertz time-domain spectroscopy (THz-TDS) and terahertz frequency-domain spectroscopy (THz-FDS) can achieve the measurement of the gaps of micro size.

  17. 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

  18. 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.

  19. Terahertz and mid-infrared reflectance of epitaxial graphene

    PubMed Central

    Santos, Cristiane N.; Joucken, Frédéric; De Sousa Meneses, Domingos; Echegut, Patrick; Campos-Delgado, Jessica; Louette, Pierre; Raskin, Jean-Pierre; Hackens, Benoit

    2016-01-01

    Graphene has emerged as a promising material for infrared (IR) photodetectors and plasmonics. In this context, wafer scale epitaxial graphene on SiC is of great interest in a variety of applications in optics and nanoelectronics. Here we present IR reflectance spectroscopy of graphene grown epitaxially on the C-face of 6H-SiC over a broad optical range, from terahertz (THz) to mid-infrared (MIR). Contrary to the transmittance, reflectance measurements are not hampered by the transmission window of the substrate, and in particular by the SiC Reststrahlen band in the MIR. This allows us to present IR reflectance data exhibiting a continuous evolution from the regime of intraband to interband charge carrier transitions. A consistent and simultaneous analysis of the contributions from both transitions to the optical response yields precise information on the carrier dynamics and the number of layers. The properties of the graphene layers derived from IR reflection spectroscopy are corroborated by other techniques (micro-Raman and X-ray photoelectron spectroscopies, transport measurements). Moreover, we also present MIR microscopy mapping, showing that spatially-resolved information can be gathered, giving indications on the sample homogeneity. Our work paves the way for a still scarcely explored field of epitaxial graphene-based THz and MIR optical devices. PMID:27102827

  20. Terahertz Spectroscopy for Chemical Detection and Burn Characterization

    NASA Astrophysics Data System (ADS)

    Arbab, Mohammad Hassan

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

  1. Moisture detection in composites by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Malinowski, Paweł; Pałka, Norbert; Opoka, Szymon; Wandowski, Tomasz; Ostachowicz, Wiesław

    2015-07-01

    The application of Glass Fibre Reinforced Polymers (GFRP) in many branches of industry has been increasing steadily. Many research works focus on damage identification for structures made out of such materials. However, not only delaminations, cracks or other damage can have a negative influence of GFRP parts performance. Previous research proved that fluid absorption influences the mechanical performance of composites. GFRP parts can be contaminated by moisture or release agent during manufacturing, while fuel, hydraulic fluid and moisture ingression into the composite can be the in-service treats. In the reported research authors focus on moisture detection. There are numerous sources of moisture such as post manufacturing NDT inspection with ultrasonics coupled by water or exposition to moisture during transportation and in service. An NDT tool used for the research is a terahertz (THz) spectrometer. The device uses an electromagnetic radiation in the terahertz range (0.1-3 THz) and allows for reflection and transmission measurements. The spectrometer is equipped with moving table that allows for XY scanning of large objects such as GFRP panels. In the conducted research refractive indices were experimentally extracted from the materials of interest (water and GFRP). Time signals as well as C-scans were analysed for samples with moisture contamination. In order to be sure that the observed effects are related to moisture contamination reference measurements were conducted. The obtained results showed that the THz NDT technique can detect moisture hidden under a GFRP with multiple layers.

  2. Spectroscopy of materials for terahertz photonics

    NASA Astrophysics Data System (ADS)

    Postava, K.; Chochol, J.; Mičica, M.; Vanwolleghem, M.; Kolejak, P.; Halagačka, L.; Cada, M.; Pištora, J.; Lampin, J.-F.

    2016-12-01

    In this paper we apply the terahertz time-domain spectroscopy (THz-TDS) to obtain optical function spectra in the range from 0.06 to 3 THz. Polarization sensitivity is obtained using azimuth-controlled wire-grid polarizers. We demonstrate general methods on characterization of plasmonic semiconductors. Detail characterization of optical and magneto-optical material properties is also motivated by a need of optical isolator in THz spectral range. The technique is applied to III-V semiconductors. The typical material is a single crystal undoped InSb having the plasma frequency in the range of interest. With appropriate magnetic field (in our case 0.4 T) we observed coupling of plasma and cyclotron behavior of free electrons with gigantic magneto-optic effect in the THz spectral range.

  3. [Study on terahertz spectroscopy of Hotan jade].

    PubMed

    Maimaitiming; Ainiwaer; Xiong, Wei; Guo, Xue-jiao; Shen, Jing-ling

    2010-10-01

    Terahertz time-domain spectroscopy (THz-TDS) technique has a wide range of applications including illicit drugs and explosive detection, and organic molecules recognition. In the present paper, the spectral features of three kinds of Hotan jade were studied experimentally by THz-TDS technique and the characteristic absorption spectra and refractive index were obtained in the range of 0.2 to 2.6 THz. The experimental results show that different samples have different absorption characters, and the refractive index is 2.4-2.7 in the range of 0.2-2.6 THz. The results indicate that it is feasible to apply THz-TDS technique to identification of Hotan jade, which provides a new approach to the nondestructive examination of Hotan jade.

  4. Terahertz Spectroscopy of Biochars and Related Aromatic Compounds

    NASA Astrophysics Data System (ADS)

    Lepodise, L. M.; Horvat, J.; Lewis, R. A.

    2016-12-01

    A recent application of terahertz spectroscopy is to biochar, the agricultural charcoal produced by pyrolysis of various organic materials. Biochars simultaneously improve soil fertility and assist in carbon sequestration. Terahertz spectroscopy allows different biochars to be distinguished. However, the origin of the absorption features observed has not been clear. Given that biochar-based fertilizers are rich in aromatic compounds, we have investigated simple aromatic compounds as an approach to unravelling the complex biochar spectrum.

  5. 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.

  6. Uncertainty in Terahertz Time-Domain Spectroscopy Measurement of Liquids

    NASA Astrophysics Data System (ADS)

    Yang, Fei; Liu, Liping; Song, Maojiang; Han, Feng; Shen, Li; Hu, Pengfei; Zhang, Fang

    2017-02-01

    Terahertz time-domain spectroscopy (THz-TDS) is a significant technique for characterizing materials as it allows fast and broadband measurement of optical constants in the THz regime. The measurement precision of the constants is highly influenced by the complicated measurement procedure and data processing. Taking THz transmission measurement of liquids into account, the sources of error existing in THz-TDS process are identified. The contributions of each source to the uncertainty of optical constants in THz-TDS process are formulated, with particular emphasis on the effect of multilayer reflections and plane wave assumption. As a consequence, an analytical model is proposed for uncertainty evaluation in a THz-TDS measurement of liquids. An actual experiment with a Di 2-Ethyl Hexyl Phthalate (DEHP) sample is carried out to show that the proposed model could be a basis to evaluate the measurement precision of optical constants of liquids.

  7. Terahertz spectroscopy of the metal insulator transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Hilton, David; Prasankumar, Rohit; Cavalleri, Andrea; Fourmaux, Sylvain; Kieffer, Jean-Claude; Taylor, Antoinette; Averitt, Richard

    2006-03-01

    We employ terahertz spectroscopy to study the metal-insulator phase transition in vanadium dioxide (VO2 ). We measure the terahertz frequency conductivity in the metallic phase that has a real conductivity of 1000 &-1circ; cm-1 and a negligible imaginary conductivity. The observed conductivity dynamics are consistent with a photoinduced transition in spatially inhomogeneous regions of the film, followed by a thermally driven transition to the maximum conductivity.

  8. Continuous-wave terahertz reflective off-axis digital holography

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  9. Ultrabroadband terahertz spectroscopies of biomolecules and water

    NASA Astrophysics Data System (ADS)

    Turton, David; Harwood, Thomas; Lapthorn, Adrian; Ellis, Elizabeth; Wynne, Klaas

    2013-03-01

    We describe the use of a range of modern spectroscopic techniques—from terahertz time-domain spectroscopy (THz- TDS) to high dynamic-range femtosecond optical Kerr-effect (OKE) spectroscopy—to study the interaction of proteins, peptides, and other biomolecules with the aqueous solvent. Chemical reactivity in proteins requires fast picosecond fluctuations to reach the transition state, to dissipate energy, and (possibly) to reduce the width and height of energy barriers along the reaction coordinate. Such motions are linked with the structure and dynamics of the aqueous solvent making hydration critical to function. These dynamics take place over a huge range of timescales: from the nanosecond timescale of diffusion of water molecules in the first solvation shell of proteins, picosecond motions of amino-acid side chains, and sub-picosecond librational and phonon-like motions of water. It is shown that a large range of frequencies from MHz to THz is accessible directly using OKE resulting in the reduced anisotropic Raman spectrum and by using a combination of techniques including THz-TDS resulting in the dielectric spectrum. Using these techniques, we can now observe very significant differences in the spectra of proteins in aqueous solvent in the 3-30 THz range and more subtle differences at lower frequencies (10 GHz-3 THz).

  10. Tissue characterization using terahertz pulsed imaging in reflection geometry

    NASA Astrophysics Data System (ADS)

    Huang, S. Y.; Wang, Y. X. J.; Yeung, D. K. W.; Ahuja, A. T.; Zhang, Y.-T.; Pickwell-MacPherson, E.

    2009-01-01

    Terahertz pulsed imaging (TPI™) is a non-ionizing and non-destructive imaging technique that has been recently used to study a wide range of biological materials. The severe attenuation of terahertz radiation in samples with high water content means that biological samples need to be very thin if they are to be measured in transmission geometry. To overcome this limitation, samples could be measured in reflection geometry and this is the most feasible way in which TPI could be performed in a clinical setting. In this study, we therefore used TPI in reflection geometry to characterize the terahertz properties of several organ samples freshly harvested from laboratory rats. We observed differences in the measured time domain responses and determined the frequency-dependent optical properties to characterize the samples further. We found statistically significant differences between the tissue types. These results show that TPI has the potential to accurately differentiate between tissue types non-invasively.

  11. Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy.

    PubMed

    Stoik, Christopher D; Bohn, Matthew J; Blackshire, James L

    2008-10-13

    Terahertz time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Damage to glass fiber was studied 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 TDS transmissive 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.

  12. Terahertz reflection response measurement using a phonon polariton wave

    NASA Astrophysics Data System (ADS)

    Inoue, Hayato; Katayama, Kenji; Shen, Qing; Toyoda, Taro; Nelson, Keith A.

    2009-03-01

    We developed a new technique for the measurement of terahertz reflection responses utilizing a propagating phonon polariton wave. Frequency tunable phonon polariton waves were generated by the recently developed continuously variable spatial frequency transient grating method [K. Katayama, H. Inoue, H. Sugiya, Q. Shen, T. Taro, and K. A. Nelson, Appl. Phys. Lett. 92, 031906 (2008)]. The phonon polariton wave traveled in a ferroelectric crystal in an in-plane direction with an inclined angle of 26°, and the wave reflected at the crystal edge where a sample was positioned. The reflected polariton wave was detected by the same method as that used for the generation of the polariton waves. By comparing the reflection intensities in the presence and absence of the sample, reflectivity of the polariton wave was calculated, and the refractive index and absorption in the terahertz region were obtained.

  13. Measurement and modeling of rough surface effects on terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

    Recent improvements in sensing technology have driven new research areas within the terahertz (THz) portion of the electromagnetic (EM) spectrum. While there are several promising THz applications, several outstanding technical challenges need to be addressed before robust systems can be deployed. A particularly compelling application is the potential use of THz reflection spectroscopy for stand-off detection of drugs and explosives. A primary challenge for this application is to have sufficient signal-to-noise ratio (SNR) to allow spectroscopic identification of the target material, and surface roughness can have an impact on identification. However, scattering from a rough surface may be observed at all angles, suggesting diffuse returns can be used in robust imaging of non-cooperative targets. Furthermore, the scattering physics can also distort the reflection spectra, complicating classification algorithms. In this work, rough surface scattering effects were first isolated by measuring diffuse scattering for gold-coated sandpaper of varying roughness. Secondly, we measured scattering returns from a rough sample with a spectral signature, namely α-lactose monohydrate mixed with Teflon and pressed with sandpaper to introduce controlled roughness. For both the specular and diffuse reflection measurements, the application of traditional spectroscopy techniques provided the ability to resolve the 0.54 THz absorption peak. These results are compared with results from a smooth surface. Implications of the results on the ability to detect explosives with THz reflection spectroscopy are presented and discussed. In addition, the Small Perturbation Method (SPM) is employed to predict backscatter from lactose with a small amount of roughness.

  14. Terahertz wave reference-free transmission spectroscopy of aminophenol

    NASA Astrophysics Data System (ADS)

    Deng, Chao; Zhong, Hua; Zhang, Liangliang; Zhang, Cunlin

    2008-12-01

    We present a reference-free transmission spectroscopy of two kinds of aminophenol (Tyrosine and Phenylalanine) using terahertz time domain spectroscopy (THz-TDS). The THz band, which refers to the spectral region between 0.1 to 10 THz, offers a plethora of fingerprints of many chemical and biological materials. Within the past few years, efforts have been focused on exploiting the broadband nature of the THz time domain spectroscopy (THz-TDS) system for material identification and characterization. The conventional spectroscopic sensing method involves measuring both the terahertz signal carrying the sample information and a reference terahertz signal. In transmission geometry measurement, the absorption peaks of the sample material are found by taking the logarithm of the power spectrum of the transmitted signal beam divided by a reference power spectrum. In this work, we propose a reference-free approach to extract the absorption feature in THz transmission spectroscopy. The samples are identified by their absorption peaks extracted from the negative first-order derivative of the sample signal phase divided by the frequency. Unlike in conventional transmission spectroscopy measurement, in this method, the amplitude spectrum of the terahertz signal is not considered at all. Instead, the absorption features are extracted exclusively from the phase information by taking advantage of the almost-linear phase spectrum of terahertz pulses and the correlation between dispersion and absorption. It is also noted that the spectral phase of the terahertz pulse can be determined with far greater accuracy than the amplitude, which makes this method even more favorable. We measured two kinds of aminophenol (Tyrosine and Phenylalanine), and calculated the absorbance spectrum of each by both methods: taking the ratio between the power spectra of the sample signal and the reference signal and the reference-free phase spectrum of each material. The agreement between the positions

  15. Terahertz quantum well photodetectors with reflection-grating couplers

    SciTech Connect

    Zhang, R.; Fu, Z. L.; Gu, L. L.; Guo, X. G.; Cao, J. C.

    2014-12-08

    The design, fabrication, and characterization of terahertz (THz) quantum well photodetectors with one-dimensional reflection-grating coupler are presented. It is found that the reflection gratings could effectively couple the THz waves normally incident to the device. Compared with the 45-degree facet sample, the peak responsivity of this grating-coupled detector is enhanced by over 20%. The effects of the gratings on the photocurrent spectra are also analyzed.

  16. Continuous wave terahertz spectroscopy system with stably tunable beat source using optical switch

    NASA Astrophysics Data System (ADS)

    Eom, Joo Beom; Kim, Chihoon; Ahn, Jaesung

    2017-01-01

    A tunable beat source has been made using an optical switch module. A stably-tunable beat source for continuous wave terahertz spectroscopy system was implemented by simply connecting 16 coaxial distributed feedback laser diodes to an optical switch. The terahertz frequency was rapidly changed without frequency drifts by changing the optical path. The continuous wave terahertz frequency was tuned from 0.05 to 0.8 THz in steps of 50 GHz or 0.4 nm. We measured continuous wave terahertz waveforms emitted from the photomixers using the switched optical beat source. We also calculated the terahertz frequency peaks by taking fast Fourier transforms of the measured terahertz waveforms. By equipping the implemented tunable beat source with an optical switch, a continuous wave terahertz spectroscopy system was constructed and used to demonstrate the feasibility of continuous wave terahertz spectroscopy for nondestructive tests using the spectra of two type of Si wafers with different resistivity.

  17. Discrimination of genetically modified sugar beets based on terahertz spectroscopy.

    PubMed

    Chen, Tao; Li, Zhi; Yin, Xianhua; Hu, Fangrong; Hu, Cong

    2016-01-15

    The objective of this paper was to apply terahertz (THz) spectroscopy combined with chemometrics techniques for discrimination of genetically modified (GM) and non-GM sugar beets. In this paper, the THz spectra of 84 sugar beet samples (36 GM sugar beets and 48 non-GM ones) were obtained by using terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.2 to 1.2 THz. Three chemometrics methods, principal component analysis (PCA), discriminant analysis (DA) and discriminant partial least squares (DPLS), were employed to classify sugar beet samples into two groups: genetically modified organisms (GMOs) and non-GMOs. The DPLS method yielded the best classification result, and the percentages of successful classification for GM and non-GM sugar beets were both 100%. Results of the present study demonstrate the usefulness of THz spectroscopy together with chemometrics methods as a powerful tool to distinguish GM and non-GM sugar beets.

  18. Discrimination of genetically modified sugar beets based on terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Chen, Tao; Li, Zhi; Yin, Xianhua; Hu, Fangrong; Hu, Cong

    2016-01-01

    The objective of this paper was to apply terahertz (THz) spectroscopy combined with chemometrics techniques for discrimination of genetically modified (GM) and non-GM sugar beets. In this paper, the THz spectra of 84 sugar beet samples (36 GM sugar beets and 48 non-GM ones) were obtained by using terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.2 to 1.2 THz. Three chemometrics methods, principal component analysis (PCA), discriminant analysis (DA) and discriminant partial least squares (DPLS), were employed to classify sugar beet samples into two groups: genetically modified organisms (GMOs) and non-GMOs. The DPLS method yielded the best classification result, and the percentages of successful classification for GM and non-GM sugar beets were both 100%. Results of the present study demonstrate the usefulness of THz spectroscopy together with chemometrics methods as a powerful tool to distinguish GM and non-GM sugar beets.

  19. Terahertz spectroscopy for chemicals and biological sensing applications

    NASA Astrophysics Data System (ADS)

    Liu, Hai-Bo

    Terahertz (THz) radiation offers innovative sensing and imaging technologies that can provide information unavailable through other conventional electromagnetic techniques. With the advancement of THz technologies, THz sensing will impact a broad range of areas. This thesis focuses on the use of THz spectroscopy for sensing applications including explosives detection, pharmaceutical identification and biological characterization. Using both a THz time-domain spectroscopy (THz-TDS) system and a Fourier transform far-infrared spectrometer (FT-FIR), a THz spectral database of explosives and related compounds (ERCs) in the range of 0.1-20 THz was established. The transmission measurements show good agreement with the diffuse reflectance measurements, which are more feasible for practical applications. Density Functional Theory was employed to calculate structures and vibrational modes of several important ERCs and the calculated spectra are in good accordance with the experimental data in the 3-20 THz range. The detection and identification of the explosive RDX using diffusely reflected THz waves were also demonstrated. THz-TDS was applied successfully for pharmaceutical study, such as investigating drug interactions, as well as identifying hydrated and anhydrous drugs, based upon the intermolecular vibrational modes of drug substances. Dehydrations and complex solid state reactions of pharmaceutical materials were studied with THz-TDS and the reaction kinetics was successfully probed. These investigations have opened new avenues for using THz technologies in pharmaceutical science and industry. THz spectra of amino acids, purines and other biomolecules were recorded. Most of these solid-state biocompounds have THz spectral features in the 0.1-3.0 THz range. THz spectroscopy of solid-state proteins and bioactive protein micro suspensions in organic media was studied and their THz absorption features may reflect their collective vibrational modes which could be used to

  20. Protein-Ligand Binding Detected by Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Knab, J.; Chen, J. Y.; Mader, M.; Markelz, A.

    2004-03-01

    Established measures of protein flexibility through the B-factor use time intensive and facility limited techniques such as X-ray crystallography, NMR structure analysis and inelastic neutron scattering. We demonstrate a novel technique that may be used for determination of ligand binding for proteins as well as a measure of protein flexibility. Using the method of terahertz (THz) time domain spectroscopy, we measured the far infrared dielectric response as a function of the binding of N (1-4)-acetylglucosamine (NAG) to hen egg white lysozyme (HEWL). Vibrational modes associated with tertiary structure conformational motions lay in the THz frequency range. The THz dielectric response reflects the density and amplitude of these normal modes through dipole coupling. Transmission measurements on thin films show that while there is no change in the real part of the refractive index as a function of binding, there is a decrease in the absorbance for the HEWL+NAG thin films relative to HEWL films. This decrease can be attributed to a reduction in the flexibility of the protein with binding. These results are compared to calculated absorbance spectra.

  1. Tunable reflecting terahertz filter based on chirped metamaterial structure.

    PubMed

    Yang, Jing; Gong, Cheng; Sun, Lu; Chen, Ping; Lin, Lie; Liu, Weiwei

    2016-12-12

    Tunable reflecting terahertz bandstop filter based on chirped metamaterial structure is demonstrated by numerical simulation. In the metamaterial, the metal bars are concatenated to silicon bars with different lengths. By varying the conductivity of the silicon bars, the reflectivity, central frequency and bandwidth of the metamaterial could be tuned. Light illumination could be introduced to change the conductivity of the silicon bars. Numerical simulations also show that the chirped metamaterial structure is insensitive to the incident angle and polarization-dependent. The proposed chirped metamaterial structure can be operated as a tunable bandstop filter whose modulation depth, bandwidth, shape factor and center frequency can be controlled by light pumping.

  2. Tunable reflecting terahertz filter based on chirped metamaterial structure

    PubMed Central

    Yang, Jing; Gong, Cheng; Sun, Lu; Chen, Ping; Lin, Lie; Liu, Weiwei

    2016-01-01

    Tunable reflecting terahertz bandstop filter based on chirped metamaterial structure is demonstrated by numerical simulation. In the metamaterial, the metal bars are concatenated to silicon bars with different lengths. By varying the conductivity of the silicon bars, the reflectivity, central frequency and bandwidth of the metamaterial could be tuned. Light illumination could be introduced to change the conductivity of the silicon bars. Numerical simulations also show that the chirped metamaterial structure is insensitive to the incident angle and polarization-dependent. The proposed chirped metamaterial structure can be operated as a tunable bandstop filter whose modulation depth, bandwidth, shape factor and center frequency can be controlled by light pumping. PMID:27941833

  3. Tunable reflecting terahertz filter based on chirped metamaterial structure

    NASA Astrophysics Data System (ADS)

    Yang, Jing; Gong, Cheng; Sun, Lu; Chen, Ping; Lin, Lie; Liu, Weiwei

    2016-12-01

    Tunable reflecting terahertz bandstop filter based on chirped metamaterial structure is demonstrated by numerical simulation. In the metamaterial, the metal bars are concatenated to silicon bars with different lengths. By varying the conductivity of the silicon bars, the reflectivity, central frequency and bandwidth of the metamaterial could be tuned. Light illumination could be introduced to change the conductivity of the silicon bars. Numerical simulations also show that the chirped metamaterial structure is insensitive to the incident angle and polarization-dependent. The proposed chirped metamaterial structure can be operated as a tunable bandstop filter whose modulation depth, bandwidth, shape factor and center frequency can be controlled by light pumping.

  4. Terahertz transmission vs reflection imaging and model-based characterization for excised breast carcinomas

    PubMed Central

    Bowman, Tyler; El-Shenawee, Magda; Campbell, Lucas K.

    2016-01-01

    This work presents experimental and analytical comparison of terahertz transmission and reflection imaging modes for assessing breast carcinoma in excised paraffin-embedded human breast tissue. Modeling for both transmission and reflection imaging is developed. The refractive index and absorption coefficient of the tissue samples are obtained. The reflection measurements taken at the system’s fixed oblique angle of 30° are shown to be a hybridization of TE and TM modes. The models are validated with transmission spectroscopy at fixed points on fresh bovine muscle and fat tissues. Images based on the calculated absorption coefficient and index of refraction of bovine tissue are successfully compared with the terahertz magnitude and phase measured in the reflection mode. The validated techniques are extended to 20 and 30 μm slices of fixed human lobular carcinoma and infiltrating ductal carcinoma mounted on polystyrene microscope slides in order to investigate the terahertz differentiation of the carcinoma with non-cancerous tissue. Both transmission and reflection imaging show clear differentiation in carcinoma versus healthy tissue. However, when using the reflection mode, in the calculation of the thin tissue properties, the absorption is shown to be sensitive to small phase variations that arise due to deviations in slide and tissue thickness and non-ideal tissue adhesion. On the other hand, the results show that the transmission mode is much less sensitive to these phase variations. The results also demonstrate that reflection imaging provides higher resolution and more clear margins between cancerous and fibroglandular regions, cancerous and fatty regions, and fibroglandular and fatty tissue regions. In addition, more features consistent with high power pathology images are exhibited in the reflection mode images. PMID:27699136

  5. Terahertz transmission vs reflection imaging and model-based characterization for excised breast carcinomas.

    PubMed

    Bowman, Tyler; El-Shenawee, Magda; Campbell, Lucas K

    2016-09-01

    This work presents experimental and analytical comparison of terahertz transmission and reflection imaging modes for assessing breast carcinoma in excised paraffin-embedded human breast tissue. Modeling for both transmission and reflection imaging is developed. The refractive index and absorption coefficient of the tissue samples are obtained. The reflection measurements taken at the system's fixed oblique angle of 30° are shown to be a hybridization of TE and TM modes. The models are validated with transmission spectroscopy at fixed points on fresh bovine muscle and fat tissues. Images based on the calculated absorption coefficient and index of refraction of bovine tissue are successfully compared with the terahertz magnitude and phase measured in the reflection mode. The validated techniques are extended to 20 and 30 μm slices of fixed human lobular carcinoma and infiltrating ductal carcinoma mounted on polystyrene microscope slides in order to investigate the terahertz differentiation of the carcinoma with non-cancerous tissue. Both transmission and reflection imaging show clear differentiation in carcinoma versus healthy tissue. However, when using the reflection mode, in the calculation of the thin tissue properties, the absorption is shown to be sensitive to small phase variations that arise due to deviations in slide and tissue thickness and non-ideal tissue adhesion. On the other hand, the results show that the transmission mode is much less sensitive to these phase variations. The results also demonstrate that reflection imaging provides higher resolution and more clear margins between cancerous and fibroglandular regions, cancerous and fatty regions, and fibroglandular and fatty tissue regions. In addition, more features consistent with high power pathology images are exhibited in the reflection mode images.

  6. Coherent phonon spectroscopy of non-fully symmetric modes using resonant terahertz excitation

    SciTech Connect

    Huber, T. Huber, L.; Johnson, S. L.; Ranke, M.; Ferrer, A.

    2015-08-31

    We use intense terahertz (THz) frequency electromagnetic pulses generated via optical rectification in an organic crystal to drive vibrational lattice modes in single crystal Tellurium. The coherent modes are detected by measuring the polarization changes of femtosecond laser pulses reflecting from the sample surface, resulting in a phase-resolved detection of the coherent lattice motion. We compare the data to a model of Lorentz oscillators driven by the near-single-cycle broadband THz pulse. The demonstrated technique of optically probed coherent phonon spectroscopy with THz frequency excitation could prove to be a viable alternative to other time-resolved spectroscopic methods like standard THz time domain spectroscopy.

  7. Nondestructive Evaluation of Carbon Fiber Reinforced Polymer Composites Using Reflective Terahertz Imaging.

    PubMed

    Zhang, Jin; Li, Wei; Cui, Hong-Liang; Shi, Changcheng; Han, Xiaohui; Ma, Yuting; Chen, Jiandong; Chang, Tianying; Wei, Dongshan; Zhang, Yumin; Zhou, Yufeng

    2016-06-14

    Terahertz (THz) time-domain spectroscopy (TDS) imaging is considered a nondestructive evaluation method for composite materials used for examining various defects of carbon fiber reinforced polymer (CFRP) composites and fire-retardant coatings in the reflective imaging modality. We demonstrate that hidden defects simulated by Teflon artificial inserts are imaged clearly in the perpendicular polarization mode. The THz TDS technique is also used to measure the thickness of thin fire-retardant coatings on CFRP composites with a typical accuracy of about 10 micrometers. In addition, coating debonding is successfully imaged based on the time-delay difference of the time-domain waveforms between closely adhered and debonded sample locations.

  8. Development of the technique of terahertz pulse spectroscopy for diagnostic malignant tumors during gastrointestinal surgeries

    NASA Astrophysics Data System (ADS)

    Goryachuk, A. A.; Khodzitsky, M. K.; Borovkova, M. A.; Khamid, A. K.; Dutkinskii, P. S.; Shishlo, D. A.

    2016-08-01

    Samples of fresh excised tissues obtained from patients who had undergone gastric cancer have been investigated. Samples were consisted of cancer zone, normal zone and zone mixed of normal and cancer tissues. Their optical properties and spectral features were investigated by terahertz time-domain spectroscopy (TDS) in reflection mode. It was found that waveforms of reflected signals from normal and cancer tissues were well distinguished so it can be concluded that it is easy to discriminate gastric cancer tissue from normal by using THz TDS.

  9. Ultrabroadband terahertz spectroscopy of a liquid crystal.

    PubMed

    Vieweg, N; Fischer, B M; Reuter, M; Kula, P; Dabrowski, R; Celik, M A; Frenking, G; Koch, M; Jepsen, P U

    2012-12-17

    Liquid crystals (LCs) are becoming increasingly important for applications in the terahertz frequency range. A detailed understanding of the spectroscopic parameters of these materials over a broad frequency range is crucial in order to design customized LC mixtures for improved performance. We present the frequency dependent index of refraction and the absorption coefficients of the nematic liquid crystal 5CB over a frequency range from 0.3 THz to 15 THz using a dispersion-free THz time-domain spectrometer system based on two-color plasma generation and air biased coherent detection (ABCD). We show that the spectra are dominated by multiple strong spectral features mainly at frequencies above 4 THz, originating from intramolecular vibrational modes of the weakly LC molecules.

  10. Terahertz probe for spectroscopy of sub-wavelength objects.

    PubMed

    Mitrofanov, Oleg; Renaud, Cyril C; Seeds, Alwyn J

    2012-03-12

    A system of two probes is designed for terahertz (THz) time-domain spectroscopy of sub-wavelength size objects. A twin-needle probe confines broadband THz pulses spatially by means of surface plasmon waves to a sub-wavelength spot smaller than 10 microns. The confined pulses are detected within the near-field zone of the twin-needle probe by a sub-wavelength aperture probe. The system allows THz spectroscopy to be applied to single micrometer-size objects in the 1-2.5THz region.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  12. Diffraction-limited ultrabroadband terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Baillergeau, M.; Maussang, K.; Nirrengarten, T.; Palomo, J.; Li, L. H.; Linfield, E. H.; Davies, A. G.; Dhillon, S.; Tignon, J.; Mangeney, J.

    2016-05-01

    Diffraction is the ultimate limit at which details of objects can be resolved in conventional optical spectroscopy and imaging systems. In the THz spectral range, spectroscopy systems increasingly rely on ultra-broadband radiation (extending over more 5 octaves) making a great challenge to reach resolution limited by diffraction. Here, we propose an original easy-to-implement wavefront manipulation concept to achieve ultrabroadband THz spectroscopy system with diffraction-limited resolution. Applying this concept to a large-area photoconductive emitter, we demonstrate diffraction-limited ultra-broadband spectroscopy system up to 14.5 THz with a dynamic range of 103. The strong focusing of ultrabroadband THz radiation provided by our approach is essential for investigating single micrometer-scale objects such as graphene flakes or living cells, and besides for achieving intense ultra-broadband THz electric fields.

  13. Diffraction-limited ultrabroadband terahertz spectroscopy

    PubMed Central

    Baillergeau, M.; Maussang, K.; Nirrengarten, T.; Palomo, J.; Li, L. H.; Linfield, E. H.; Davies, A. G.; Dhillon, S.; Tignon, J.; Mangeney, J.

    2016-01-01

    Diffraction is the ultimate limit at which details of objects can be resolved in conventional optical spectroscopy and imaging systems. In the THz spectral range, spectroscopy systems increasingly rely on ultra-broadband radiation (extending over more 5 octaves) making a great challenge to reach resolution limited by diffraction. Here, we propose an original easy-to-implement wavefront manipulation concept to achieve ultrabroadband THz spectroscopy system with diffraction-limited resolution. Applying this concept to a large-area photoconductive emitter, we demonstrate diffraction-limited ultra-broadband spectroscopy system up to 14.5 THz with a dynamic range of 103. The strong focusing of ultrabroadband THz radiation provided by our approach is essential for investigating single micrometer-scale objects such as graphene flakes or living cells, and besides for achieving intense ultra-broadband THz electric fields. PMID:27142959

  14. Terahertz pulsed imaging and spectroscopy for biomedical and pharmaceutical applications.

    PubMed

    Wallace, Vincent P; Taday, Philip F; Fitzgerald, Anthony J; Woodward, Ruth M; Cluff, Julian; Pye, Richard J; Arnone, Donald D

    2004-01-01

    Terahertz (THz) radiation lies between the infrared and microwave regions of the electromagnetic spectrum. Advances in THz technology have opened up many opportunities in this scientifically and technologically important spectroscopic region. The THz frequency range excites large amplitude vibrational modes of molecules as well as probing the weak interactions between them. Here we describe two techniques that utilize THz radiation, terahertz pulsed imaging (TPI) and terahertz pulsed spectroscopy (TPS). Both have a variety of possible applications in biomedical imaging and pharmaceutical science. TPI, a non-invasive imaging technique, has been used to image epithelial cancer ex vivo and recently in vivo. The diseased tissue showed a change in absorption compared to normal tissue, which was confirmed by histology. To understand the origins of the differences seen between diseased and normal tissue we have developed a TPS system. TPS has also been used to study solids of interest in the pharmaceutical industry. One particularly interesting example is ranitidine hydrochloride, which is used in treatment of stomach ulcers. Crystalline ranitidine has two polymorphic forms known as form 1 and form 2. These polymorphs have the same chemical formula but different crystalline structure that give rise to different physiochemical properties of the material. Using TPS it is possible to rapidly distinguish between the two polymorphic forms.

  15. Terahertz electromodulation spectroscopy of electron transport in GaN

    NASA Astrophysics Data System (ADS)

    Engelbrecht, S. G.; Arend, T. R.; Zhu, T.; Kappers, M. J.; Kersting, R.

    2015-03-01

    Time-resolved terahertz (THz) electromodulation spectroscopy is applied to investigate the high-frequency transport of electrons in gallium nitride at different doping concentrations and densities of threading dislocations. At THz frequencies, all structures reveal Drude transport. The analysis of the spectral response provides the fundamental transport properties, such as the electron scattering time and the electrons' conductivity effective mass. We observe the expected impact of ionized-impurity scattering and that scattering at threading dislocations only marginally affects the high-frequency mobility.

  16. Spectroscopy of several drugs in the terahertz region

    NASA Astrophysics Data System (ADS)

    Liu, Guifeng; Ma, Shihua; Song, Xiyu; Zhang, Peng; Li, Haixia; Wang, Wenfeng

    2009-07-01

    We use terahertz time-domain spectroscopy (THz-TDS) to measure the absorption spectra of six drugs, atenolol, furosemide, tropicamide, lobeline hydrochloride, propranolol hydrochloride, and promethazine hydrochloride, in the frequency range of 0.3 THz to 2.0 THz. Furosemide, tropicamide, and promethazine hydrochloride show distinct absorption features, whereas atenolol, lobeline hydrochloride, and propranolol hydrochloride exhibit no obvious absorption peaks. The use of THz-TDS makes it possible to rapidly distinguish the drugs with characteristic absorption peaks. Our results demonstrate that THz-TDS is highly sensitive to the structure and spatial arrangement of molecules. As a result, THz-TDS will have potential exploitation in pharmaceutical fields.

  17. Terahertz electromodulation spectroscopy of electron transport in GaN

    SciTech Connect

    Engelbrecht, S. G.; Arend, T. R.; Kersting, R.; Zhu, T.; Kappers, M. J.

    2015-03-02

    Time-resolved terahertz (THz) electromodulation spectroscopy is applied to investigate the high-frequency transport of electrons in gallium nitride at different doping concentrations and densities of threading dislocations. At THz frequencies, all structures reveal Drude transport. The analysis of the spectral response provides the fundamental transport properties, such as the electron scattering time and the electrons' conductivity effective mass. We observe the expected impact of ionized-impurity scattering and that scattering at threading dislocations only marginally affects the high-frequency mobility.

  18. Characterization of Wheat Varieties Using Terahertz Time-Domain Spectroscopy

    PubMed Central

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

    2015-01-01

    Terahertz (THz) spectroscopy and multivariate data analysis were explored to discriminate eight wheat varieties. The absorption spectra were measured using THz time-domain spectroscopy from 0.2 to 2.0 THz. Using partial least squares (PLS), a regression model for discriminating wheat varieties was developed. The coefficient of correlation in cross validation (R) and root-mean-square error of cross validation (RMSECV) were 0.985 and 1.162, respectively. In addition, interval PLS was applied to optimize the models by selecting the most appropriate regions in the spectra, improving the prediction accuracy (R = 0.992 and RMSECV = 0.967). Results demonstrate that THz spectroscopy combined with multivariate analysis can provide rapid, nondestructive discrimination of wheat varieties. PMID:26024421

  19. Two-dimensional Raman-terahertz spectroscopy of water

    PubMed Central

    Savolainen, Janne; Ahmed, Saima; Hamm, Peter

    2013-01-01

    Two-dimensional Raman-terahertz (THz) spectroscopy is presented as a multidimensional spectroscopy directly in the far-IR regime. The method is used to explore the dynamics of the collective intermolecular modes of liquid water at ambient temperatures that emerge from the hydrogen-bond networks water forming. Two-dimensional Raman-THz spectroscopy interrogates these modes twice and as such can elucidate couplings and inhomogeneities of the various degrees of freedoms. An echo in the 2D Raman-THz response is indeed identified, indicating that a heterogeneous distribution of hydrogen-bond networks exists, albeit only on a very short 100-fs timescale. This timescale appears to be too short to be compatible with more extended, persistent structures assumed within a two-state model of water. PMID:24297930

  20. 3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure

    NASA Astrophysics Data System (ADS)

    Vogt, Dominik Walter; Leonhardt, Rainer

    2016-11-01

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

  1. Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamakawa, H.; Miyamoto, T.; Morimoto, T.; Yada, H.; Kinoshita, Y.; Sotome, M.; Kida, N.; Yamamoto, K.; Iwano, K.; Matsumoto, Y.; Watanabe, S.; Shimoi, Y.; Suda, M.; Yamamoto, H. M.; Mori, H.; Okamoto, H.

    2016-02-01

    In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroelectrics include charge degrees of freedom, so that they are sometimes conductive, complicating dielectric measurements. This makes difficult the exploration of electronic-type ferroelectrics and the understanding of their ferroelectric nature. Here, we show unambiguous evidence for electronic ferroelectricity in the charge-order (CO) phase of a prototypical ET-based molecular compound, α-(ET)2I3 (ET:bis(ethylenedithio)tetrathiafulvalene), using a terahertz pulse as an external electric field. Terahertz-pump second-harmonic-generation(SHG)-probe and optical-reflectivity-probe spectroscopy reveal that the ferroelectric polarization originates from intermolecular charge transfers and is inclined 27° from the horizontal CO stripe. These features are qualitatively reproduced by the density-functional-theory calculation. After sub-picosecond polarization modulation by terahertz fields, prominent oscillations appear in the reflectivity but not in the SHG-probe results, suggesting that the CO is coupled with molecular displacements, while the ferroelectricity is electronic in nature. The results presented here demonstrate that terahertz-pump optical-probe spectroscopy is a powerful tool not only for rapidly controlling polarizations, but also for clarifying the mechanisms of ferroelectricity.

  2. 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.

  3. 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.

  4. Aeronautics composite material inspection with a terahertz time-domain spectroscopy system

    NASA Astrophysics Data System (ADS)

    Ospald, Frank; Zouaghi, Wissem; Beigang, René; Matheis, Carsten; Jonuscheit, Joachim; Recur, Benoit; Guillet, Jean-Paul; Mounaix, Patrick; Vleugels, Wouter; Bosom, Pablo Venegas; González, Laura Vega; López, Ion; Edo, Rafael Martínez; Sternberg, Yehuda; Vandewal, Marijke

    2014-03-01

    The usability of pulsed broadband terahertz radiation for the inspection of composite materials from the aeronautics industry is investigated, with the goal of developing a mobile time-domain spectroscopy system that operates in reflection geometry. A wide range of samples based on glass and carbon fiber reinforced plastics with various types of defects is examined using an imaging system; the results are evaluated both in time and frequency domain. The conductivity of carbon fibers prevents penetration of the respective samples but also allows analysis of coatings from the reflected THz pulses. Glass fiber composites are, in principle, transparent for THz radiation, but commonly with significant absorption for wavelengths >1 THz. Depending on depth, matrix material, and size, defects like foreign material inserts, delaminations, or moisture contamination can be visualized. If a defect is not too deep in the sample, its location can be correctly identified from the delay between partial reflections at the surface and the defect itself.

  5. Surface-enhanced terahertz spectroscopy using gold rod structures resonant with terahertz waves.

    PubMed

    Ueno, Kosei; Nozawa, Sho; Misawa, Hiroaki

    2015-11-02

    Terahertz (THz) spectroscopy is a promising method to measure the spectrum of low-frequency modes of molecules or ensembles, such as crystals and polymers, including proteins. However, the main drawback of THz spectroscopy is its extremely low sensitivity. In the present study, we report on signal enhancement in THz spectroscopy achieved by depositing amino acid molecules or their derivatives on a gold rod structured silicon substrate whose localized surface plasmon resonance is exhibited in the THz frequency region. The distinct peaks derived from the enhancement of the inherent spectrum based on a molecular crystal were clearly observed when a longitudinal plasmon resonance mode of the gold rod structure was excited and the plasmon resonance band overlapped the molecular/intermolecular vibrational mode. We discuss the mechanism by which surface-enhanced THz spectroscopy was induced from the viewpoint of the enhancement of light-matter coupling due to plasmon excitation and the modulation of the plasmon band by dipole coupling between the plasmon dipole and molecular/intermolecular vibrational modes.

  6. Characteristics of Gadolinium Oxide Nanoparticles Using Terahertz Spectroscopy (abstract)

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  7. Characteristics of Gadolinium Oxide Nanoparticles Using Terahertz Spectroscopy

    SciTech Connect

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

    2009-04-19

    The penetration property of the terahertz electromagnetic (THz) wave is relevant to its use. We used the THz wave spectroscopy system which easily penetrates some materials that do not contain water, e.g., plastic and ceramics. The system has been developed for several purposes, including measuring the properties of semiconductors and bio-materials, and detecting plastic bombs and ceramic knives at airports. It is also used for medical imaging systems, such as magnetic resonance imaging (MRI), at some research institutes. It can show not only the difference in amplitude, but also the difference of the phase of each point of sample. MRI technology usually uses contrast agents to enhance the quality of the image. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), made with a heavy metal ion, is commonly used as a clinical MRI contrast agent. Gadolinium oxide (Gd{sub 2}O{sub 3}) nanoparticle is a new contrast agent. It serves to equip the core of each particle with antibodies or ligands. It can freely circulate in blood vessels without amassing in the liver or lungs. This study shows the characteristics of gadolinium oxide nanoparticles to further advance terahertz medical imaging.

  8. Nitrocellulose membrane sample holder using for terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaojing; Liu, Shangjian; Wang, Cuicui; Zuo, Jian; Zhang, Cunlin

    2016-11-01

    Terahertz (THz) technology has promising applications for the detection and identification of materials because it has a great advantage in measuring material fingerprint spectrum. Terahertz time-domain spectroscopy (THz-TDS) is a key technique that is applied to spectroscopic measurement of materials. However, it is difficult to press a pellet with small mass of sample and a bulking medium such as polyethylene (PE) powder usually need to be added. Characteristic absorption peaks of the solution in liquid cell is hard to be observed due to the interaction between materials and water molecules. Therefore, one method using the hydrophilic nitrocellulose (NC) membrane as a sample holder was applied to detect samples in an aqueous medium by THz-TDS. In this study, the α-lactose samples were mixed with 20 μl of deionized water and then applied directly onto the double-layered NC membrane sample holder. This mixture is located on the gap of two piece of NC membranes. Firstly the NC membranes with different pore sizes were tested in the experiment. And then the α-lactose solutions with different concentrations were measured on the NC with different pore sizes. Consequently, the small mass of samples can be detected and the characteristic absorption peaks become stronger with the increase of NC pore size. Moreover, compared to the traditional pellet-making and liquid cell detection, this membrane method is more convenient and easy to operate.

  9. [Detection of amino acids based on terahertz spectroscopy].

    PubMed

    Tang, Zhong-feng; Lin, Hai-tao; Chen, Xiao-wei; Zhang, Zeng-fang

    2009-09-01

    Terahertz (THz) is the frequency region ranging from 0.1 to 2.0 THz, which lies in the far-infrared region. Compared to Fourier transform infrared spectra (FTIR), terahertz time-domain spectra (THz-TDS) has low energy, high signal-to-noise ratio (SNR) and is non-ionizing radiation. Low-frequency vibrational modes of some amino acids, such as torsional and collective vibrational modes and hydrogen-bond modes, exist in the THz region. Amino acids are important organic compounds and are the fundamental components of proteins. Amino acids can exist with a highly ordered crystal structure linked by hydrogen intermolecular bonds in the solid phase. The absorption spectra of amino acids in the THz region show marked differences while mid-infrared absorption spectra usually show very little difference. Up to now, absorption spectra of twenty kinds of amino acids have been studied by many researchers using THz technique; the quantitative analysis of amino acids by THZ-TDS is also included. Investigation of THz spectra of amino acids are of fundamental interests, and will lead to further understanding of low-frequency vibrations of protein/DNA and relevant biological reactions and activities. In the present paper, the latest progress in absorption spectra of amino acids determined by THz spectroscopy is reviewed and a database is built. Some brief remarks on future developments in and prospects for THz application in amino acids are also provided.

  10. Reflectance spectroscopy for soil analysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Over the last three decades or more, researchers have estimated soil properties using visible and near infrared (VNIR) diffuse reflectance spectroscopy (DRS), with varying results. This presentation reviews the history and state-of –the art of VNIR-DRS, including relative estimation accuracy for var...

  11. Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields

    NASA Astrophysics Data System (ADS)

    Noe, G. Timothy; Katayama, Ikufumi; Katsutani, Fumiya; Allred, James J.; Horowitz, Jeffrey A.; Sullivan, David M.; Zhang, Qi; Sekiguchi, Fumiya; Woods, Gary L.; Hoffmann, Matthias C.; Nojiri, Hiroyuki; Takeda, Jun; Kono, Junichiro

    2016-12-01

    We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.

  12. Instrument independent diffuse reflectance spectroscopy.

    PubMed

    Yu, Bing; Fu, Henry L; Ramanujam, Nirmala

    2011-01-01

    Diffuse reflectance spectroscopy with a fiber optic probe is a powerful tool for quantitative tissue characterization and disease diagnosis. Significant systematic errors can arise in the measured reflectance spectra and thus in the derived tissue physiological and morphological parameters due to real-time instrument fluctuations. We demonstrate a novel fiber optic probe with real-time, self-calibration capability that can be used for UV-visible diffuse reflectance spectroscopy in biological tissue in clinical settings. The probe is tested in a number of synthetic liquid phantoms over a wide range of tissue optical properties for significant variations in source intensity fluctuations caused by instrument warm up and day-to-day drift. While the accuracy for extraction of absorber concentrations is comparable to that achieved with the traditional calibration (with a reflectance standard), the accuracy for extraction of reduced scattering coefficients is significantly improved with the self-calibration probe compared to traditional calibration. This technology could be used to achieve instrument-independent diffuse reflectance spectroscopy in vivo and obviate the need for instrument warm up and post∕premeasurement calibration, thus saving up to an hour of precious clinical time.

  13. The coating curing properties study using terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Ren, Jiaojiao; Zhao, Duo; Li, Lijuan

    2015-10-01

    Coating curing curve is one of the most important methods to reflect the coating curing properties. It is of great significance for the coating curing properties. In this paper, by using the reflective Terahertz (THz) time-domain spectroscope technique, the curing properties of coating with different thicknesses are studied. Three different parameters used for studying the properties of coating curing curve are proposed in this paper. They are respectively the differential time of flight, power spectrum and amplitude for reflective THz time-domain waveform. In this paper, two kinds of coating (with different thicknesses) curing properties curves are established and the relative errors from three parameter analysis methods are compared respectively. This study shows that the study on coating curing properties curves by using the power spectrum of reflective THz time-domain waveform is superior to the amplitude parameter method. But for the thick coating, the differential time of flight for the reflective THz time-domain waveform can also better reflect the coating curing properties.

  14. Spectroscopic study of terahertz reflection and transmission properties of carbon-fiber-reinforced plastic composites

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Shi, Changcheng; Ma, Yuting; Han, Xiaohui; Li, Wei; Chang, Tianying; Wei, Dongshan; Du, Chunlei; Cui, Hong-Liang

    2015-05-01

    Carbon-fiber-reinforced plastic (CFRP) composites are widely used in aerospace and concrete structure reinforcement due to their high strength and light weight. Terahertz (THz) time-domain spectroscopy is an attractive tool for defect inspection in CFRP composites. In order to improve THz nondestructive testing of CFRP composites, we have carried out systematic investigations of THz reflection and transmission properties of CFRP. Unidirectional CFRP composites with different thicknesses are measured with polarization directions 0 deg to 90 deg with respect to the fiber direction, in both reflection and transmission modes. As shown in the experiments, CFRP composites are electrically conducting and therefore exhibit a high THz reflectivity. In addition, CFRP composites have polarization-dependent reflectivity and transmissivity for THz radiation. The reflected THz power in the case of parallel polarization is nearly 1.8 times higher than for perpendicular polarization. At the same time, in the transmission of THz wave, a CFRP acts as a Fabry-Pérot cavity resulting from multiple internal reflections from the CFRP-air interfaces. Moreover, from the measured data, we extract the refractive index and absorption coefficient of CFRP composites in the THz frequency range.

  15. Adaptive optics instrumentation in submillimeter/terahertz spectroscopy with a flexible polyvinylidene fluoride cladding hollow waveguide

    NASA Astrophysics Data System (ADS)

    Hidaka, Takehiko; Ishikawa, Akihiro; Kojou, Jun-Ichiro; Ikari, Tomofumi; Ishikawa, Yoh-Ichi; Minamide, Hiroaki; Kudoh, Akito; Nishizawa, Jun-Ichi; Ito, Hiromasa

    2007-08-01

    A simple instrument has been developed to carry out temperature dependent submillimeter/terahertz-wave spectroscopy using a polyvinylidene fluoride flexible hollow waveguide and an eggplant-shape launching lens.

  16. Nondestructive Evaluation of Carbon Fiber Reinforced Polymer Composites Using Reflective Terahertz Imaging

    PubMed Central

    Zhang, Jin; Li, Wei; Cui, Hong-Liang; Shi, Changcheng; Han, Xiaohui; Ma, Yuting; Chen, Jiandong; Chang, Tianying; Wei, Dongshan; Zhang, Yumin; Zhou, Yufeng

    2016-01-01

    Terahertz (THz) time-domain spectroscopy (TDS) imaging is considered a nondestructive evaluation method for composite materials used for examining various defects of carbon fiber reinforced polymer (CFRP) composites and fire-retardant coatings in the reflective imaging modality. We demonstrate that hidden defects simulated by Teflon artificial inserts are imaged clearly in the perpendicular polarization mode. The THz TDS technique is also used to measure the thickness of thin fire-retardant coatings on CFRP composites with a typical accuracy of about 10 micrometers. In addition, coating debonding is successfully imaged based on the time-delay difference of the time-domain waveforms between closely adhered and debonded sample locations. PMID:27314352

  17. Terahertz absorption spectroscopy of protein-containing reverse micellar solution

    NASA Astrophysics Data System (ADS)

    Murakami, H.; Toyota, Y.; Nishi, T.; Nashima, S.

    2012-01-01

    Terahertz time-domain spectroscopy has been carried out for AOT/isooctane reverse micellar solution with myoglobin at the water-to-surfactant molar ratios ( w0) of 0.2 and 4.4. The amplitude of the absorption spectrum increases with increasing the protein concentration at w0 = 0.2, whereas it decreases at w0 = 4.4. The molar extinction coefficients of the protein-filled reverse micelle, and the constituents, i.e., myoglobin, water, and AOT, have been derived by use of the structural parameters of the micellar solution. The experimental results are interpreted in terms of hydration onto the protein and surfactant in the reverse micelle.

  18. Terahertz spectroscopy of ground state HD18O

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Pearson, John C.; Drouin, Brian J.; Miller, Charles E.; Kobayashi, Kaori; Matsushima, Fusakazu

    2016-10-01

    Terahertz absorption spectroscopy was employed to measure the ground state pure rotational transitions of the water isotopologue HD18O . A total of 105 pure rotational transitions were observed in the 0.5-5.0 THz region with ∼ 100 kHz accuracy for the first time. The observed positions were fit to experimental accuracy using the Euler series expansion of the asymmetric-top Hamiltonian together with the literature Microwave, Far-IR and IR data in the ground state and ν2 . The new measurements and predictions reported here support the analysis of astronomical observations by high-resolution spectroscopic telescopes such as SOFIA and ALMA where laboratory rest frequencies with uncertainties of 1 MHz or less are required for proper analysis of velocity resolved astrophysical data.

  19. Terahertz devices, spectroscopy, and signal processing for biosensing

    NASA Astrophysics Data System (ADS)

    Smiley, Brianna; Marotto, Amanda; Balci, Soner; Park, Seung Jo; Güngördü, M. Zeki; Maleski, Alex; Mollah, A. Shahab; Philip, Elizabath; Kung, Patrick; Kim, Yonghyun; Kim, Seongsin M.

    2016-09-01

    Sub-wavelength metamaterial structures are of great fundamental and practical interest because of their ability to manipulate the propagation of electromagnetic waves. Here we investigate the metamaterials composed of titanium and copper split-ring resonators for use in detection of living cells. Terahertz spectroscopy was utilized to detect a change in resonance frequencies of the bio-sensor in the presence of MDA-MB-231 breast cancer cells in culture in real time. The shift in frequency showed dependency upon cell density. We applied circuit model to interpret the resonance peak shift observed, and not only do we see shifts in resonance frequency but also in capacitance and resistance as time progresses.

  20. 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.

  1. 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.

  2. Terahertz reflection and emission associated with nonequilibrium surface plasmon polaritons in n-GaN

    NASA Astrophysics Data System (ADS)

    Melentyev, G. A.; Shalygin, V. A.; Moldavskaya, M. D.; Panevin, V. Yu; Vorobjev, L. E.; Firsov, D. A.; Nykänen, H.; Riuttanen, L.; Svensk, O.; Suihkonen, S.

    2015-01-01

    Surface plasmon polaritons are investigated in heavily doped n-GaN epitaxial layers. The grating etched on the surface of the epitaxial layer is used to convert photons into the surface plasmon polaritons and vice versa. The spectral study of reflection demonstrates the possibility of nonequilibrium surface plasmon polaritons excitation due to terahertz radiation scattering on the grating. Terahertz electroluminescence is investigated under lateral electric field. The luminescence spectrum demonstrates a significant contribution of nonequilibrium surface plasmon polariton scattering to terahertz radiation emission.

  3. Research of biological liquid albumin based on terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Shuai; Liu, Shang-jian; Zuo, Jian; Zhang, Cun-lin

    2016-11-01

    There is no corresponding fingerprint characteristic spectrum detecting complex ensemble biological samples in liquid, in the paper, such urine of kidney disease patients as samples of the research, using terahertz time-domain spectroscopy emphatically explores response characteristics of the urine albumin in the terahertz spectrum characteristics, and combined with stoichiometric method, we find a certain kind of relationship between terahertz spectrum data and the content of urine albumin, which offsets the defects of other spectroscopy in measuring liquid protein, and in accordance with hospital clinical data. This study established a semi-qualitative method of using terahertz spectroscopy in detecting non-purification of biological liquid sample, which provides a simple, nondestructive, cheap and fast reference method in identifying the early nephropathy for medical test.

  4. Highly precise determination of optical constants in olive oil using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Jiusheng; Yao, Jianquan

    2008-12-01

    Recently, there has been a remarkable effort in employing terahertz (THz) spectroscopy for investigating material properties. Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse are measured. Coherent detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. In this letter, the terahertz absorption spectra and the refractive indices of olive oil were measured by using terahertz time-domain spectroscopy (THz-TDS) in the frequency range extending from 0.2 to 2.5 THz. The terahertz dielectric properties of olive oil were characterized by THz-TDS, and the consistency with the known parameters was identified. A novel iterative algorithm improves the existing data extraction algorithms and further enhances the accuracy of the parameter extraction for terahertz time-domain spectroscopy. The results obtained in this study suggest that the THz-TDS method is a useful tool for vegetable oils characterization in the far infrared region. This method can be applied not only to terahertz time-domain spectroscopy but also to any kind of optical constant measurement in the time domain.

  5. Cartilage analysis by reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Laun, T.; Muenzer, M.; Wenzel, U.; Princz, S.; Hessling, M.

    2015-07-01

    A cartilage bioreactor with analytical functions for cartilage quality monitoring is being developed. For determining cartilage composition, reflection spectroscopy in the visible (VIS) and near infrared (NIR) spectral region is evaluated. Main goal is the determination of the most abundant cartilage compounds water, collagen I and collagen II. Therefore VIS and NIR reflection spectra of different cartilage samples of cow, pig and lamb are recorded. Due to missing analytical instrumentation for identifying the cartilage composition of these samples, typical literature concentration values are used for the development of chemometric models. In spite of these limitations the chemometric models provide good cross correlation results for the prediction of collagen I and II and water concentration based on the visible and the NIR reflection spectra.

  6. 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.

  7. Dielectric Properties of Diesel and Gasoline by Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Arik, Enis; Altan, Hakan; Esenturk, Okan

    2014-09-01

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

  8. Discrimination of transgenic soybean seeds by terahertz spectroscopy

    PubMed Central

    Liu, Wei; Liu, Changhong; Chen, Feng; Yang, Jianbo; Zheng, Lei

    2016-01-01

    Discrimination of genetically modified organisms is increasingly demanded by legislation and consumers worldwide. The feasibility of a non-destructive discrimination of glyphosate-resistant and conventional soybean seeds and their hybrid descendants was examined by terahertz time-domain spectroscopy system combined with chemometrics. Principal component analysis (PCA), least squares-support vector machines (LS-SVM) and PCA-back propagation neural network (PCA-BPNN) models with the first and second derivative and standard normal variate (SNV) transformation pre-treatments were applied to classify soybean seeds based on genotype. Results demonstrated clear differences among glyphosate-resistant, hybrid descendants and conventional non-transformed soybean seeds could easily be visualized with an excellent classification (accuracy was 88.33% in validation set) using the LS-SVM and the spectra with SNV pre-treatment. The results indicated that THz spectroscopy techniques together with chemometrics would be a promising technique to distinguish transgenic soybean seeds from non-transformed seeds with high efficiency and without any major sample preparation. PMID:27782205

  9. Discrimination of transgenic soybean seeds by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Liu, Changhong; Chen, Feng; Yang, Jianbo; Zheng, Lei

    2016-10-01

    Discrimination of genetically modified organisms is increasingly demanded by legislation and consumers worldwide. The feasibility of a non-destructive discrimination of glyphosate-resistant and conventional soybean seeds and their hybrid descendants was examined by terahertz time-domain spectroscopy system combined with chemometrics. Principal component analysis (PCA), least squares-support vector machines (LS-SVM) and PCA-back propagation neural network (PCA-BPNN) models with the first and second derivative and standard normal variate (SNV) transformation pre-treatments were applied to classify soybean seeds based on genotype. Results demonstrated clear differences among glyphosate-resistant, hybrid descendants and conventional non-transformed soybean seeds could easily be visualized with an excellent classification (accuracy was 88.33% in validation set) using the LS-SVM and the spectra with SNV pre-treatment. The results indicated that THz spectroscopy techniques together with chemometrics would be a promising technique to distinguish transgenic soybean seeds from non-transformed seeds with high efficiency and without any major sample preparation.

  10. Quantitative analyses of tartaric acid based on terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Cao, Binghua; Fan, Mengbao

    2010-10-01

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

  11. 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.

  12. Tunable terahertz wave Goos-Hänchen shift of reflected terahertz wave from prism-metal-polymer-metal multilayer structure

    NASA Astrophysics Data System (ADS)

    Li, Jiu-Sheng; Wu, Jing-fang; Zhang, Le

    2015-01-01

    We propose a scheme to manipulate the Goos-Hänchen shift of a terahertz wave reflected from the prism-metal-polymer-metal interface via external voltage bias. By adjusting the external voltage bias, the refractive index of the nonlinear polymer can be changed, so the lateral Goos-Hänchen shift is dynamically tuned. The relation among the Goos-Hänchen shift, prism and the nonlinear polymer is investigated in theory analysis and simulation. Using this scheme, the Goos-Hänchen shift can be tuned without changing the original structure of the proposed device. Numerical calculation results further indicate that the proposed structure has the potential application for the integrated terahertz wave switch.

  13. Broadband terahertz time-domain spectroscopy : crystalline and glassy drug materials

    NASA Astrophysics Data System (ADS)

    Kojima, Seiji; Shibata, Tomohiko; Igawa, Hikaru; Mori, Tatsuya

    2014-03-01

    Low-energy IR active modes of glassy and crystalline drug materials were studied by the broadband Terahertz Time Domain Spectroscopy (THz-TDS) in the frequency range from 0.5 to 6.5 THz using a Cherenkov type THz generator. In order to determine the real and imaginary parts of complex dielectric constant, all samples were measured by the transmission using a pure pellet without mixing polyethylene. For glassy indomethacine, the broadband THz spectrum of real part of dielectric constant shows step-wise decrease with the increase of frequency, while the imaginary part shows a broad peak at about 3 THz reflecting quenched glassy disordered structure. The observed spectra of crystalline racemic ketoprofen show the noncoincidence of peak frequencies between low-frequency Raman scattering and THz absorbance spectra. It can be attributed to the fact that the mutual exclusion principle between Raman and IR activities holds below 6 THz.

  14. Terahertz polariton propagation in patterned materials.

    PubMed

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

    2002-10-01

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

  15. Terahertz spectroscopy of dry, hydrated, and thermally denatured biological macromolecules

    NASA Astrophysics Data System (ADS)

    Lipscomb, Dawn; Echchgadda, Ibtissam; Ibey, Bennett L.; Beier, Hope; Thomas, Robert J.; Peralta, Xomalin; Wilmink, Gerald J.

    2012-03-01

    Terahertz time-domain spectroscopy (THz-TDS) is an effective technique to probe the intermolecular and collective vibrational modes of biological macromolecules at THz frequencies. To date, the vast majority of spectroscopic studies have been performed on dehydrated biomolecular samples. Given the fact that all biochemical processes occur in aqueous environments and water is required for proper protein folding and function, we hypothesize that valuable information can be gained from spectroscopic studies performed on hydrated biomolecules in their native conformation. In this study, we used a THz-TDS system that exploits photoconductive techniques for THz pulse generation and freespace electro-optical sampling approaches for detection. We used the THz spectrometer to measure the time-dependent electric field of THz waves upon interaction with water, phosphate buffered saline (PBS), and collagen gels. By comparing these waveforms with references, we simultaneously determined each sample's index of refraction (n) and absorption coefficients (μa) as a function of frequency. Our data show that the properties we measure for the water, PBS and collagen are comparable to those reported in the literature. In the future, we plan to examine the effect that both temperature and pH have on the optical properties of other biological macromolecules. Studies will also be performed to compare our results to those generated using molecular dynamics simulations.

  16. Improved Sensitivity MEMS Cantilever Sensor for Terahertz Photoacoustic Spectroscopy

    PubMed Central

    Coutu, Ronald A.; Medvedev, Ivan R.; Petkie, Douglas T.

    2016-01-01

    In this paper, a microelectromechanical system (MEMS) cantilever sensor was designed, modeled and fabricated to measure the terahertz (THz) radiation induced photoacoustic (PA) response of gases under low vacuum conditions. This work vastly improves cantilever sensitivity over previous efforts, by reducing internal beam stresses, minimizing out of plane beam curvature and optimizing beam damping. In addition, fabrication yield was improved by approximately 50% by filleting the cantilever’s anchor and free end to help reduce high stress areas that occurred during device fabrication and processing. All of the cantilever sensors were fabricated using silicon-on-insulator (SOI) wafers and tested in a custom built, low-volume, vacuum chamber. The resulting cantilever sensors exhibited improved signal to noise ratios, sensitivities and normalized noise equivalent absorption (NNEA) coefficients of approximately 4.28 × 10−10 cm−1·WHz−1/2. This reported NNEA represents approximately a 70% improvement over previously fabricated and tested SOI cantilever sensors for THz PA spectroscopy. PMID:26907280

  17. Determining Phthalic Acid Esters Using Terahertz Time Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, L.; Shen, L.; Yang, F.; Han, F.; Hu, P.; Song, M.

    2016-09-01

    In this report terahertz time domain spectroscopy (THz-TDS) is applied for determining phthalic acid esters (PAEs) in standard materials. We reported the THz transmission spectrum in the frequency range of 0.2 to 2.0 THz for three PAEs: di-n-butyl phthalate (DBP), di-isononyl phthalate (DINP), and di-2-ethylhexyl phthalate ester (DEHP). The study provided the refractive indices and absorption features of these materials. The absorption spectra of three PAEs were simulated by using Gaussian software with Density Functional Theory (DFT) methods. For pure standard PAEs, the values of the refractive indices changed between 1.50 and 1.60. At 1.0 THz, the refractive indices were 1.524, 1.535, and 1.563 for DINP, DEHP, and DBP, respectively. In this experiment different concentrations of DBP were investigated using THz-TDS. Changes were measured in the low THz frequency range for refractive indices and characteristic absorption. The results indicated that THz-TDS is promising as a new method in determining PAEs in many materials. The results of this study could be used to support the practical application of THz-TDS in quality detection and food monitoring. In particular, this new technique could be used in detecting hazardous materials and other substances present in wine or foods.

  18. Terahertz and Infrared Laboratory Spectroscopy in Support of NASA Missions

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan

    2015-06-01

    The JPL molecular spectroscopy group supports NASA programs encompassing Astrophysics, Atmospheric Science, and Planetary Science. Ongoing activities include measurement and analysis of molecular spectra in the terahertz and infrared regions under conditions akin to the remote environments under study in NASA missions. This presentation will show the implementation of state-of-the-art spectroscopic techniques to fulfill spectroscopic demands of the Herschel Space Observatory and the Orbiting Carbon Observatory re-flight (OCO-2). A demonstrative example of the significantly improved frequency predictions for the H_3O^+ ground state high-J transitions will be given. This work was critical to Herschel's successful identification of highly excited metastable H_3O^+ Terahertz lines with J=K up to 11, one of the Herschel mission's many surprising observational results. The observation and subsequent laboratory work revealed that (1) these highly excited H_3O^+ lines had already been observed by European Southern Observatory's Atacama Pathfinder Experiment telescope a few years before but had been classified as U-lines; (2) the H_3O^+ number density was previously underestimated by an order of magnitude, due to ignorance of the population in the metastable states. A second example focuses on O_2, an important absorber from the microwave through the deep UV. This work is motivated by the challenge of developing an accurate and complete spectroscopic characterization of molecular oxygen across a wide frequency range for current and planned Earth atmospheric observations. Especially, OCO-2 utilizes the O_2 A-band for air mass calibration; extremely accurate O_2 molecular data, i.e., line positions with uncertainty on the order of MHz for the A-band around 13000 wn, are required to fulfill the demand of the proposed 0.25% precision for the carbon dioxide concentration retrievals. G. Pilbratt, J. Riedinger, T. Passvogel, G. Crone, D. Doyle, U. Gageur et al. A&A, 518, L1 (2010

  19. Laminated helmet materials characterization by terahertz kinetics spectroscopy

    NASA Astrophysics Data System (ADS)

    Rahman, Anis; Rahman, Aunik K.

    2015-05-01

    High speed acquisition of reflected terahertz energy constitutes a kinetics spectrum that is an effective tool for layered materials' deformation characterization under ballistic impact. Here we describe utilizing the kinetics spectrum for quantifying a deformation event due to impact in material used for Soldier's helmet. The same technique may be utilized for real-time assessment of trauma by measuring the helmet wore by athletes. The deformation of a laminated material (e.g., a helmet) is dependent on the nature of impact and projectile; thus can uniquely characterize the impact condition leading to a diagnostic procedure based on the energy received by an athlete during an impact. We outline the calibration process for a given material under ballistic impact and then utilize the calibration for extracting physical parameters from the measured kinetics spectrum. Measured kinetics spectra are used to outline the method and rationale for extending the concept to a diagnosis tool. In particular, captured kinetics spectra from multilayered plates subjected to ballistic hit under experimental conditions by high speed digital acquisition system. An algorithm was devised to extract deformation and deformation velocity from which the energy received on the skull was estimated via laws of nonrelativistic motion. This energy is assumed to be related to actual injury conditions, thus forming a basis for determining whether the hit would cause concussion, trauma, or stigma. Such quantification may be used for diagnosing a Soldier's trauma condition in the field or that of an athlete's.

  20. Terahertz-visible two-photon rotational spectroscopy of cold OD-

    NASA Astrophysics Data System (ADS)

    Lee, Seunghyun; Hauser, Daniel; Lakhmanskaya, Olga; Spieler, Steffen; Endres, Eric S.; Geistlinger, Katharina; Kumar, Sunil S.; Wester, Roland

    2016-03-01

    We present a method to measure rotational transitions of molecular anions in the terahertz domain by sequential two-photon absorption. Ion excitation by bound-bound terahertz absorption is probed by absorption in the visible on a bound-free transition. The visible frequency is tuned to a state-selective photodetachment transition of the excited anions. This provides a terahertz action spectrum for just a few hundred molecular ions. To demonstrate this we measure the two lowest rotational transitions, J =1 ←0 and J =2 ←1 of OD- anions in a cryogenic 22-pole trap. We obtain rotational transition frequencies of 598 596.08(19) MHz for J =1 ←0 and 1 196 791.57(27) MHz for J =2 ←1 of OD-, in good agreement with their only previous measurement. This two-photon scheme opens up terahertz rovibrational spectroscopy for a range of molecular anions, in particular for polyatomic and cluster anions.

  1. Origin and quantification of differences between normal and tumor tissues observed by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Sayuri; Fukushi, Yasuko; Kubota, Oichi; Itsuji, Takeaki; Ouchi, Toshihiko; Yamamoto, Seiji

    2016-09-01

    The origin of the differences in the refractive index observed between normal and tumor tissues using terahertz spectroscopy has been described quantitatively. To estimate water content differences in tissues, we prepared fresh and paraffin-embedded samples from rats. An approximately 5% increase of water content in tumor tissues was calculated from terahertz time domain spectroscopy measurements compared to normal tissues. A greater than 15% increase in percentage of cell nuclei per unit area in tumor tissues was observed by hematoxylin and eosin stained samples, which generates a higher refractive index of biological components other than water. Both high water content and high cell density resulted in higher refractive index by approximately 0.05 in tumor tissues. It is predicted that terahertz spectroscopy can also be used to detect brain tumors in human tissue due to the same underlying mechanism as in rats.

  2. Terahertz time-domain and low-frequency Raman spectroscopy of organic materials.

    PubMed

    Parrott, Edward P J; Zeitler, J Axel

    2015-01-01

    With the ongoing proliferation of terahertz time-domain instrumentation from semiconductor physics into applied spectroscopy over the past decade, measurements at terahertz frequencies (1 THz ≡ 10(12) Hz ≡ 33 cm(-1)) have attracted a sustained growing interest, in particular the investigation of hydrogen-bonding interactions in organic materials. More recently, the availability of Raman spectrometers that are readily able to measure in the equivalent spectral region very close to the elastic scattering background has also grown significantly. This development has led to renewed efforts in performing spectroscopy at the interface between dielectric relaxation phenomena and vibrational spectroscopy. In this review, we briefly outline the underlying technology, the physical phenomena governing the light-matter interaction at terahertz frequencies, recent examples of spectroscopic studies, and the current state of the art in assigning spectral features to vibrational modes based on computational techniques.

  3. Terahertz spectroscopy and detection of brain tumor in rat fresh-tissue samples

    NASA Astrophysics Data System (ADS)

    Yamaguchi, S.; Fukushi, Y.; Kubota, O.; Itsuji, T.; Yamamoto, S.; Ouchi, T.

    2015-03-01

    Terahertz (THz) spectroscopy and imaging of biomedical samples is expected to be an important application of THz analysis techniques. Identification and localization of tumor tissue, imaging of biological samples, and analysis of DNA by THz spectroscopy have been reported. THz time-domain spectroscopy (TDS) is useful for obtaining the refractive index over a broad frequency range. However, THz-TDS spectra of fresh tissue samples are sensitive to procedures such as sample preparation, and a standardized measurement protocol is required. Therefore, in this work, we establish a protocol for measurements of THz spectra of fresh tissue and demonstrate reliable detection of rat brain tumor tissue. We use a reflection THz-TDS system to measure the refractive index spectra of the samples mounted on a quartz plate. The tissue samples were measured immediately after sectioning to avoid sample denaturalization during storage. Special care was taken in THz data processing to eliminate parasitic reflections and reduce noise. The error level in our refractive index measurements was as low as 0.02 in the frequency range 0.8-1.5 THz. With increasing frequency, the refractive index in the tumor and normal regions monotonically decreased, similarly to water, and it was 0.02 higher in the tumor regions. The spectral data suggest that the tumor regions have higher water content. Hematoxylin-eosin stained images showed that increased cell density was also responsible for the observed spectral features. A set of samples from 10 rats showed consistent results. Our results suggest that reliable tumor detection in fresh tissue without pretreatment is possible with THz spectroscopy measurements. THz spectroscopy has the potential to become a real-time in vivo diagnostic method.

  4. Terahertz nano-spectroscopy and imaging of superfluid surface plasmons in conventional and anisotropic superconductors

    NASA Astrophysics Data System (ADS)

    Stinson, H. T.; Wu, J. S.; Jiang, B. Y.; Fei, Z.; Rodin, A. S.; Chapler, B.; McLeod, A. S.; Castro Neto, A.; Lee, Y. S.; Fogler, M. M.; Basov, D. N.

    2015-03-01

    We numerically model near-field spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors in the infrared and terahertz regime. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting gap in Bardeen-Cooper-Schrieffer superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the c-axis plasma frequency, and thus the c-axis superfluid density, of layered unconventional superconductors such as cuprates and pnictides with identical spatial resolution. We discuss the development of a cryogenic terahertz near-field microscope designed to perform these proposed experiments.

  5. Characterization of primary and permanent teeth using terahertz spectroscopy

    PubMed Central

    Yetimoĝlu, N Ö; Altan, H

    2014-01-01

    Objectives: To analyse teeth samples by using terahertz time-domain spectroscopy (THz-TDS) system that was developed in the laboratory to measure the properties of sliced teeth sections in transmission mode. Methods: Using home-built THz-TDS system, we analysed a total of 25 teeth samples (9 primary and 16 permanent teeth). For transmission measurements, the refractive index and absorptive properties of the teeth sections were calculated. Difference between groups was tested using Mann–Whitney U-test statistics at the specific frequency of 0.5 THz, which was at the midpoint of the bandwidth. Median and minimum–maximum values were given as descriptive statistics. Type-I error rate was taken as α = 0.05. Results: Median refractive index values for permanent and primary teeth were found to be 2.53 and 2.54, respectively. Median absorption coefficient values for permanent and primary teeth were found to be 26.29 and 29.67, respectively. Median refractive index values for both healthy and carious teeth were found to be 2.54. Median absorption coefficient values for healthy and carious teeth were found to be 26.52 and 27.13, respectively. Although higher median absorption coefficient values were found for primary and carious teeth than those of permanent and healthy teeth, the differences were insignificant (p > 0.05). In addition, no statistical differences were found for refractive index values among different groups (p > 0.05). Conclusions: THz imaging has the potential to be used in assessing dental structures. PMID:24940807

  6. 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

    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.

  7. Analysis of 3D-printed metal for rapid-prototyped reflective terahertz optics

    NASA Astrophysics Data System (ADS)

    Headland, Daniel; Withayachumnankul, Withawat; Webb, Michael; Ebendorff-Heidepriem, Heike; Luiten, Andre; Abbott, Derek

    2016-07-01

    We explore the potential of 3D metal printing to realize complex conductive terahertz devices. Factors impacting performance such as printing resolution, surface roughness, oxidation, and material loss are investigated via analytical, numerical, and experimental approaches. The high degree of control offered by a 3D-printed topology is exploited to realize a zone plate operating at 530 GHz. Reflection efficiency at this frequency is found to be over 90%. The high-performance of this preliminary device suggest that 3D metal printing can play a strong role in guided-wave and general beam control devices in the terahertz range.

  8. Highly sensitive terahertz spectroscopy of residual pesticide using nano-antenna

    NASA Astrophysics Data System (ADS)

    Lee, Dong-Kyu; Kim, Giyoung; Son, Joo-Hiuk; Seo, Minah

    2016-02-01

    In this report, a novel type of highly sensitive small molecule sensing tool has been employed to detect residual pesticide molecules including e. g. methomyl using terahertz (THz) time-domain spectroscopy (TDS) system with nano-slotantenna array. Enhance THz wave by the nano-slot-antenna array induces strong THz field enhancement around nano antenna and thus increases an absorption cross section leading to the detection sensitivity upto ppm level even in solution state. Measured spectrums in transmission and reflection show an excellent performance in both sensitivity and selectivity. We also tested the performance of our nano-antenna array in reflection imaging geometry to simply detect the contained residual pesticide at the real fruit surface as it is, without any extraction or sampling preprocess. The clear difference in the obtained THz reflection image distinguishes the stained area with methomyl from the bare area. Our observation can offer the possibility for further application as a prompt and an accurate small molecule monitoring tool in real time. A quantitative analysis tool for such small molecule can be also developed by this method.

  9. Precise Determination of Thicknesses of Multilayer Polyethylene Composite Materials by Terahertz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Palka, Norbert; Krimi, Soufiene; Ospald, Frank; Miedzinska, Danuta; Gieleta, Roman; Malek, Marcin; Beigang, Rene

    2015-06-01

    The multilayer structure of an ultra-high molecular weight polyethylene (UHMWPE) composite material was investigated in the terahertz (THz) spectral range by means of time-domain spectroscopy (TDS) technique. Such structures consist of many alternating layers of fibers, each being perpendicular to the other and each having a thickness of about 50 μm. Refractive indices of two composite samples and of a sample composed of four single layers (plies) having the same fiber orientation were determined for two orthogonal orientations of the electric field in a transmission TDS system. The birefringence of a single layer was measured, and the origin of this phenomenon is discussed. Using the TDS system in reflection, the formation of many pulses shifted in time was observed originating from reflections from interfaces of successive layers caused by the periodic modulation of the refractive index along the propagation of the THz radiation. This phenomenon is theoretically described and simulated by means of a transfer matrix method (TMM). A time-domain fitting procedure was used to determine thicknesses of all layers of the composite material. The reconstructed waveform based on the optimized thicknesses shows very good agreement with the measured waveform, with typical differences between measurements and simulations between 3 and 7 μm (depending on the sample). As a result, we were able to determine the thicknesses of all layers of two multilayer (~200 plies) structures by means of the reflection TDS technology with high accuracy.

  10. A novel analytical method for pharmaceutical polymorphs by terahertz spectroscopy and the optimization of crystal form at the discovery stage.

    PubMed

    Ikeda, Yukihiro; Ishihara, Yoko; Moriwaki, Toshiya; Kato, Eiji; Terada, Katsuhide

    2010-01-01

    A novel analytical method for the determination of pharmaceutical polymorphs was developed using terahertz spectroscopy. It was found out that each polymorph of a substance showed a specific terahertz absorption spectrum. In particular, analysis of the second derivative spectrum was enormously beneficial in the discrimination of closely related polymorphs that were difficult to discern by powder X-ray diffractometry. Crystal forms that were obtained by crystallization from various solvents and stored under various conditions were specifically characterized by the second derivative of each terahertz spectrum. Fractional polymorphic transformation for substances stored under stressed conditions was also identified by terahertz spectroscopy during solid-state stability test, but could not be detected by powder X-ray diffractometry. Since polymorphs could be characterized clearly by terahertz spectroscopy, further physicochemical studies could be conducted in a timely manner. The development form of compound examined was determined by the results of comprehensive physicochemical studies that included thermodynamic relationships, as well as chemical and physicochemical stability. In conclusion, terahertz spectroscopy, which has unique power in the elucidation of molecular interaction within a crystal lattice, can play more important role in physicochemical research. Terahertz spectroscopy has a great potential as a tool for polymorphic determination, particularly since the second derivative of the terahertz spectrum possesses high sensitivity for pharmaceutical polymorphs.

  11. Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Milot, Rebecca Lee

    Terahertz spectroscopy is distinguished from other far infrared and millimeter wave spectroscopies by its inherent phase sensitivity and sub-picosecond time resolution making it a versatile technique to study a wide range of physical phenomena. As THz spectroscopy is still a relatively new field, many aspects of THz generation mechanisms have not been fully examined. Using terahertz emission spectroscopy (TES), THz emission from ZnTe(110) was analyzed and found to be limited by two-photon absorption and free-carrier generation at high excitation fluences. Due to concerns about the continued use of fossil fuels, solar energy has been widely investigated as a promising source of renewable energy. Dye-sensitized solar cells (DSSCs) have been developed as a low-cost alternative to conventional photovoltaic solar cells. To solve the issues of the intermittency and inefficient transport associated with solar energy, researchers are attempting to adapt DSSCs for water oxidation and chemical fuel production. Both device designs incorporate sensitizer molecules covalently bound to metal oxide nanoparticles. The sensitizer, which is comprised of a chromophore and anchoring group, absorbs light and transfers an electron from its excited state to the conduction band of the metal oxide, producing an electric current. Using time-resolved THz spectroscopy (TRTS), an optical pump/THz probe technique, the efficiency and dynamics of electron injection from sensitizers to metal oxides was evaluated as a function of the chromophore, its anchoring group, and the metal oxide identity. Experiments for studying fully functioning DSSCs and water oxidation devices are also described. Bio-inspired pentafluorophenyl porphyrin chromophores have been designed and synthesized for use in photoelectrochemical water oxidation cells. Influences on the efficiency and dynamics of electron injection from the chromophores into TiO2 and SnO2 nanoparticles due to changes in both the central substituent to

  12. Broadband terahertz anti-reflective structure fabricated by femtosecond laser drilling technique

    NASA Astrophysics Data System (ADS)

    Zhang, Yibin; Yuan, Minghui; Chen, Lin; Cai, Bin; Yang, Rui; Zhu, Yiming

    2016-02-01

    We fabricated several reverse conical holes on high-resistivity silicon substrate with different power and pulse number of femtosecond laser, and investigated their patterns and features by using scanning electron microscope (SEM). Then, we chose one of the experimental parameters prepared a reverse conical anti-reflection structure sample with period of 90 μm. Terahertz Time-domain Spectroscopy (THz-TDS) was used to test its properties. Compared with the nonstructural high-resistivity silicon, the transmission of structural high-resistivity silicon increases by the maximum of 14% in the range 0.32-1.30 THz. Furthermore, we simulated the sample by finite integral method (FIM). The simulated results show good consistency with experimental results. The transmission effect of the reverse conical holes were optimized via simulation. Results show that the related transmission effect can be improved by increasing the pulse numbers and decreasing the spot size of the femtosecond laser. The different transmission window can also be tuned by changing the reverse conical structure of different periods.

  13. Compact Femtosecond Pulse Approach to Explosives Detection Combining InN-Based Time Domain Terahertz Spectroscopy and Laser-Induced Breakdown Spectroscopy

    DTIC Science & Technology

    2008-08-01

    Terahertz radiation field amplitude as a function of sample rotation angle for nonpolar GaN samples with varying stacking fault densities (top). Conceptual...1E6cm-1 (MOCVD), V m- GaN : SFD ~3E6cm-1 (MBE), V TH z si gn al (d V/ V ) sample angle (deg) Figure 2. Terahertz radiation field amplitude as a...Compact Femtosecond Pulse Approach to Explosives Detection Combining InN-Based Time Domain Terahertz Spectroscopy and Laser- Induced

  14. Application of Terahertz Time-Domain Spectroscopy in nondestructive testing of adhesion quality

    NASA Astrophysics Data System (ADS)

    Zhao, Duo; Ren, Jiaojiao; Qao, Xiaoli; Li, Lijuan

    2015-10-01

    Multilayer composites assembled flexibly with have important effect on the performance and safety of aircrafts. The nondestructive detection on the adhesion layer is an important index to evaluate the quality of aircraft assembly. Terahertz Time-Domain Spectroscopy (THz-TDS) is a newly developed spectroscopy technique based on femtosecond laser technology which currently applied to qualitative analysis as a means of security detection and material identification. Compared with the traditional tensile testing, the detection of defects in the adhesion layer could be nondestructive, visible, positioning and more accurate. The spectral analysis on the material to be assembled was done respectively. The testing model was established in accord with the extracted optical parameters. With the employment of a reflective THz-TDS device, X-Y spot scanning was done to obtain waveforms of every location on an assembled sample. Layered analysis was done by selecting region of interest in time domain waveforms. Conclusions of Time- Frequency spectrum analysis and scanning imaging performance are relatively satisfying through the experiments. The defects could be located and analyzed accurately and efficiently. The research reveals that THz-TDS (0.1THz~5THz) has good testing performance on the adhesion quality of multilayer composites.

  15. Advances in terahertz spectroscopy of high-T(c) superconductors

    NASA Astrophysics Data System (ADS)

    Corson, John Frederick

    Over the past 15 years much effort has been expended in the search for an understanding of the high temperature cuprate superconductors. As yet, however, the underlying mechanism of superconductivity in the cuprates remains undiscovered. In fact, there exists no satisfactory explanation of the normal state out of which the superconductivity arises. One experimental probe, important in investigating both of these phenomena, has been the optical conductivity. A gap exists, however, in the measured spectra of the cuprates in the crucial range 0.1 THz < nu < 1.0 THz, where hv ≈ kBT. The absence of such data prevents a full understanding of the optical conductivity. Using a coherent experimental technique, known as time-domain terahertz spectroscopy, we have measured the conductivity of an important cuprate system, Bi2Sr2CaCu2Og+delta (BSCCO). These measurements cover the frequency range from 0.1--1.0 THz and a wide range of doping delta. These measurements enable a step forward in our understanding of both the superconducting and normal states of BSCCO, as well as the transition between them. In the superconducting state, we find that the conductivity includes an additional contribution beyond the conventional two: the normal fluid (quasiparticles) and the superconducting condensate. We observe a low frequency collective mode (v ≈ 0.3 THz) whose spectral weight varies with temperature proportionally to that of the condensate. The fraction of the condensate spectral weight which is drawn into the collective mode increases greatly with increased with doping. Furthermore, once the collective mode contribution is recognized we are able to extract the transport scattering rate of the quasiparticles, 1/tau. We find 1/tau to vary approximately as kBT/ h below Tc. The transition from the superconducting to the normal state proceeds by the loss of phase coherence of the superconducting order parameter. This process continues to temperatures more than 10 degrees K above the

  16. Goos-Hänchen shifts of reflected terahertz wave on a COC-air interface.

    PubMed

    Li, Qingmei; Zhang, Bo; Shen, Jingling

    2013-03-11

    Goos-Hänchen (GH) shifts of terahertz wave reflected on the Cyclo-Olefin Copolymer (COC)-air interface was investigated in simulation and experiment. The relationship between the GH shifts with the incident angle and the frequency of incident wave were calculated to get a reference for the simulation and experiment. The reflected GH shift was measured on the COC-air interface when a terahertz wave with the frequency of 0.206 THz was incident to a COC double-prism. By changing the thickness of the air layer we find experimentally and simulatively that the GH shift and the energy of the reflected wave increases with the increase of the air layer thickness. The study of GH shift can provide useful information for applications of THz waves in sensor and power delivery systems.

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

    PubMed

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

    2011-05-01

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

  18. Detection of Threat Materials Using Terahertz Waveguides and Long Pathlength Terahertz Spectroscopy

    DTIC Science & Technology

    2015-05-01

    measurement methods to improve the resolution, detection sensitivity, and fundamental understanding of THz vibrational fingerprint resonances in threat...order to resolve the underlying THz vibrational spectra explosives related materials. This ability to resolve underlying fingerprint resonances had not...Technical Digest (Optical Society of America, Washington, D.C., 2011), CThEE7. 4. “Guided wave terahertz characterization of fingerprint lines in threat

  19. Crystallization of amorphous lactose at high humidity studied by terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    McIntosh, Alexander I.; Yang, Bin; Goldup, Stephen M.; Watkinson, Michael; Donnan, Robert S.

    2013-02-01

    We report the first use of terahertz time-domain spectroscopy (THz-TDS) to study the hydration and crystallization of an amorphous molecular solid at high humidity. Lactose in its amorphous and monohydrate forms exhibits different terahertz spectra due to the lack of long range order in the amorphous material. This difference allowed the transformation of amorphous lactose to its monohydrate form at high humidity to be studied in real time. Spectral fitting of frequency-domain data allowed kinetic data to be obtained and the crystallization was found to obey Avrami kinetics. Bulk changes during the crystallization could also be observed in the time-domain.

  20. Analysis of drugs-of-abuse and explosives using terahertz time-domain and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Burnett, Andrew; Fan, Wenhui; Upadhya, Prashanth; Cunningham, John; Linfield, Edmund; Davies, Giles; Edwards, Howell; Munshi, Tasnim; O'Neil, Andrew

    2006-02-01

    We demonstrate that, through coherent measurement of the transmitted terahertz electric fields, broadband (0.3-8THz) time-domain spectroscopy can be used to measure far-infrared vibrational modes of a range of illegal drugs and high explosives that are of interest to the forensic and security services. Our results show that these absorption features are highly sensitive to the structural and spatial arrangement of the molecules. Terahertz frequency spectra are also compared with high-resolution low-frequency Raman spectra to assist in understanding the low frequency inter- and intra-molecular vibrational modes of the molecules.

  1. Terahertz spectroscopy of native-conformation and thermally denatured bovine serum albumin (BSA).

    PubMed

    Yoneyama, H; Yamashita, M; Kasai, S; Kawase, K; Ueno, R; Ito, H; Ouchi, T

    2008-07-07

    Proteins are expected to exhibit collective vibrational modes at terahertz frequencies. We have developed a promising approach to measure these motions by using a membrane device to hold samples. Samples of bovine serum albumin (BSA) in native and thermally denatured conformations were measured using terahertz time-domain spectroscopy. Clear differences were observed in transmittance and phase between native-conformation BSA samples and thermally denatured BSA samples. Time-domain data shows that samples exhibited relative time shifts when compared with a standard. Results suggest that there were differences in dielectric responses in the BSA samples, and these are probably associated with molecular conformational changes in the membrane device.

  2. In vivo terahertz pulsed spectroscopy of dysplastic and non-dysplastic skin nevi

    NASA Astrophysics Data System (ADS)

    Zaytsev, Kirill I.; Chernomyrdin, Nikita V.; Kudrin, Konstantin G.; Gavdush, Arseniy A.; Nosov, Pavel A.; Yurchenko, Stanislav O.; Reshetov, Igor V.

    2016-08-01

    The results of the in vivo terahertz (THz) pulsed spectroscopy (TPS) of pigmentary skin nevi are reported. Observed THz dielectric permittivity of healthy skin and dysplastic and non-dysplastic skin nevi exhibits significant contrast in THz frequency range. Dysplastic skin nevus is a precursor of melanoma, which is reportedly the most dangerous cancer of the skin. Therefore, the THz dielectric spectroscopy is potentially an effective tool for non-invasive early diagnosis of melanomas of the skin.

  3. Time-resolved single-shot terahertz time-domain spectroscopy for ultrafast irreversible processes

    NASA Astrophysics Data System (ADS)

    Zhai, Zhao-Hui; Zhong, Sen-Cheng; Li, Jun; Zhu, Li-Guo; Meng, Kun; Li, Jiang; Liu, Qiao; Peng, Qi-Xian; Li, Ze-Ren; Zhao, Jian-Heng

    2016-09-01

    Pulsed terahertz spectroscopy is suitable for spectroscopic diagnostics of ultrafast events. However, the study of irreversible or single shot ultrafast events requires ability to record transient properties at multiple time delays, i.e., time resolved at single shot level, which is not available currently. Here by angular multiplexing use of femtosecond laser pulses, we developed and demonstrated a time resolved, transient terahertz time domain spectroscopy technique, where burst mode THz pulses were generated and then detected in a single shot measurement manner. The burst mode THz pulses contain 2 sub-THz pulses, and the time gap between them is adjustable up to 1 ns with picosecond accuracy, thus it can be used to probe the single shot event at two different time delays. The system can detect the sub-THz pulses at 0.1 THz-2.5 THz range with signal to noise ratio (SNR) of ˜400 and spectrum resolution of 0.05 THz. System design was described here, and optimizations of single shot measurement of THz pulses were discussed in detail. Methods to improve SNR were also discussed in detail. A system application was demonstrated where pulsed THz signals at different time delays of the ultrafast process were successfully acquired within single shot measurement. This time resolved transient terahertz time domain spectroscopy technique provides a new diagnostic tool for irreversible or single shot ultrafast events where dynamic information can be extracted at terahertz range within one-shot experiment.

  4. Near-Field Orientation Sensitive Terahertz Micro-Spectroscopy of Single Crystals

    NASA Astrophysics Data System (ADS)

    Acbas, Gheorghe; Singh, Rohit; Snell, Edward; Markelz, Andrea

    2012-02-01

    We present spectroscopic imaging studies of molecular crystals. These measurements examine the anisotropy of the intra and inter-molecular vibrational modes of single crystals at terahertz frequencies. The method is based on the technique developed in [1-2] for sub-wavelength resolution time domain terahertz spectroscopy (THz TDS), with added polarization orientation dependent measurements and hydration control. This method allows us to study the spectroscopic properties of small single crystals with sizes down to 20 micrometers. In addition, mapping the spectroscopic information at such small spatial scales allows us to reduce the water absorption and interference artifacts that usually affect protein THz TDS measurements. We show the polarization sensitive terahertz absorption spectra in the (0.3-3THz) range of sucrose, oxalic acid and lysozyme protein crystals. *M. A. Seo, et. al., Opt. Express, 15(19):11781--11789, 09 (2007) *J. R Knab, et. al., App. Phys. Lett.,97, 031115 (2010)

  5. [Application of terahertz time domain spectroscopy to explosive and illegal drug].

    PubMed

    Liu, Gui-Feng; Zhao, Hong-Wei; Ge, Min; Wang, Wen-Feng

    2008-05-01

    Terahertz waves (THz, T-ray) lie between far-infrared and microwave in electromagnetic spectrum with frequency from 0.1 to 10 THz. Many explosives and illicit drugs show characteristic spectral features in the terahertz. Compared with conventional methods of detecting a variety of threats, such as weapons, explosives and illegal drugs, THz radiation is low frequency and non-ionizing, and does not give rise to safety concerns. Moreover, THz can penetrate many barrier materials, such as clothing and common packaging materials. THz technique has a great potential and advantage in antiterrorism and security inspection of explosives and illegal drugs due to the ability of high-sensitivity, nondestructive and stand-off inspection of many substances. The present paper summarizes the latest progress in the application of terahertz time domain spectroscopy (THz-TDS) to explosives and illegal drugs. Studies on RDX are discussed in details and many factors affecting experiments are also introduced.

  6. Leaf water dynamics of Arabidopsis thaliana monitored in-vivo using terahertz time-domain spectroscopy

    PubMed Central

    Castro-Camus, E.; Palomar, M.; Covarrubias, A. A.

    2013-01-01

    The declining water availability for agriculture is becoming problematic for many countries. Therefore the study of plants under water restriction is acquiring extraordinary importance. Botanists currently follow the dehydration of plants comparing the fresh and dry weight of excised organs, or measuring their osmotic or water potentials; these are destructive methods inappropriate for in-vivo determination of plants' hydration dynamics. Water is opaque in the terahertz band, while dehydrated biological tissues are partially transparent. We used terahertz spectroscopy to study the water dynamics of Arabidopsis thaliana by comparing the dehydration kinetics of leaves from plants under well-irrigated and water deficit conditions. We also present measurements of the effect of dark-light cycles and abscisic acid on its water dynamics. The measurements we present provide a new perspective on the water dynamics of plants under different external stimuli and confirm that terahertz can be an excellent non-contact probe of in-vivo tissue hydration. PMID:24105302

  7. Leaf water dynamics of Arabidopsis thaliana monitored in-vivo using terahertz time-domain spectroscopy.

    PubMed

    Castro-Camus, E; Palomar, M; Covarrubias, A A

    2013-10-09

    The declining water availability for agriculture is becoming problematic for many countries. Therefore the study of plants under water restriction is acquiring extraordinary importance. Botanists currently follow the dehydration of plants comparing the fresh and dry weight of excised organs, or measuring their osmotic or water potentials; these are destructive methods inappropriate for in-vivo determination of plants' hydration dynamics. Water is opaque in the terahertz band, while dehydrated biological tissues are partially transparent. We used terahertz spectroscopy to study the water dynamics of Arabidopsis thaliana by comparing the dehydration kinetics of leaves from plants under well-irrigated and water deficit conditions. We also present measurements of the effect of dark-light cycles and abscisic acid on its water dynamics. The measurements we present provide a new perspective on the water dynamics of plants under different external stimuli and confirm that terahertz can be an excellent non-contact probe of in-vivo tissue hydration.

  8. Emulation and design of terahertz reflection-mode confocal scanning microscopy based on virtual pinhole

    NASA Astrophysics Data System (ADS)

    Yang, Yong-fa; Li, Qi

    2014-12-01

    In the practical application of terahertz reflection-mode confocal scanning microscopy, the size of detector pinhole is an important factor that determines the performance of spatial resolution characteristic of the microscopic system. However, the use of physical pinhole brings some inconvenience to the experiment and the adjustment error has a great influence on the experiment result. Through reasonably selecting the parameter of matrix detector virtual pinhole (VPH), it can efficiently approximate the physical pinhole. By using this approach, the difficulty of experimental calibration is reduced significantly. In this article, an imaging scheme of terahertz reflection-mode confocal scanning microscopy that is based on the matrix detector VPH is put forward. The influence of detector pinhole size on the axial resolution of confocal scanning microscopy is emulated and analyzed. Then, the parameter of VPH is emulated when the best axial imaging performance is reached.

  9. Biomedical Applications of Terahertz Spectroscopy: A Brief Review

    SciTech Connect

    Vargas-Luna, M.; Huerta-Franco, R.

    2008-08-11

    The Terahertz (THz) window of the electromagnetic spectrum has been partially explored but almost unexploited commercially. In recent years there has been an increased interest and a technological boost in THz research for detection systems, material characterization and imaging. Among many hot topics the researchers are interested in medical applications, and protein characterization. We present a general overview of the field showing some of the handicaps and promises of this region of the electromagnetic spectru000.

  10. Narrow band, large angular width resonant reflection from a periodic high index grid at terahertz frequency.

    PubMed

    Parriaux, Olivier; Kämpfe, Thomas; Garet, Frédéric; Coutaz, Jean-Louis

    2012-12-17

    The property of a thin silicon membrane with periodic air slits of definite depth and width to exhibit under normal incidence a close to 100% ultra-narrow band reflection peak is demonstrated experimentally in the terahertz frequency range on a single-crystal silicon grid fabricated by submillimeter microsystem technology. An analysis based on the true modes supported by the grid reveals the nature of such resonances and permits to sort out those exhibiting ultra-narrow band.

  11. New terahertz dielectric spectroscopy for the study of aqueous solutions

    NASA Astrophysics Data System (ADS)

    George, Deepu K.; Charkhesht, Ali; Vinh, N. Q.

    2015-12-01

    We present the development of a high precision, tunable far-infrared (terahertz) frequency-domain dielectric spectrometer for studying the dynamics of biomolecules in aqueous solutions in the gigahertz-to-terahertz frequency. As an important benchmark system, we report on the measurements of the absorption and refractive index for liquid water in the frequency range from 5 GHz to 1.12 THz (0.17-37.36 cm-1 or 0.268-60 mm). The system provides a coherent radiation source with power up to 20 mW in the gigahertz-to-terahertz region. The dynamic range of our instrument reaches 1012 and the system achieves a spectral resolution of less than 100 Hz. The temperature of samples can be controlled precisely with error bars of ±0.02 °C from 0 °C to 90 °C. Given these attributes, our spectrometer provides unique capabilities for the accurate measurement of even very strongly absorbing materials such as aqueous solutions.

  12. New terahertz dielectric spectroscopy for the study of aqueous solutions.

    PubMed

    George, Deepu K; Charkhesht, Ali; Vinh, N Q

    2015-12-01

    We present the development of a high precision, tunable far-infrared (terahertz) frequency-domain dielectric spectrometer for studying the dynamics of biomolecules in aqueous solutions in the gigahertz-to-terahertz frequency. As an important benchmark system, we report on the measurements of the absorption and refractive index for liquid water in the frequency range from 5 GHz to 1.12 THz (0.17-37.36 cm(-1) or 0.268-60 mm). The system provides a coherent radiation source with power up to 20 mW in the gigahertz-to-terahertz region. The dynamic range of our instrument reaches 10(12) and the system achieves a spectral resolution of less than 100 Hz. The temperature of samples can be controlled precisely with error bars of ±0.02 °C from 0 °C to 90 °C. Given these attributes, our spectrometer provides unique capabilities for the accurate measurement of even very strongly absorbing materials such as aqueous solutions.

  13. New terahertz dielectric spectroscopy for the study of aqueous solutions

    SciTech Connect

    George, Deepu K.; Charkhesht, Ali; Vinh, N. Q.

    2015-12-15

    We present the development of a high precision, tunable far-infrared (terahertz) frequency-domain dielectric spectrometer for studying the dynamics of biomolecules in aqueous solutions in the gigahertz-to-terahertz frequency. As an important benchmark system, we report on the measurements of the absorption and refractive index for liquid water in the frequency range from 5 GHz to 1.12 THz (0.17–37.36 cm{sup −1} or 0.268–60 mm). The system provides a coherent radiation source with power up to 20 mW in the gigahertz-to-terahertz region. The dynamic range of our instrument reaches 10{sup 12} and the system achieves a spectral resolution of less than 100 Hz. The temperature of samples can be controlled precisely with error bars of ±0.02 °C from 0 °C to 90 °C. Given these attributes, our spectrometer provides unique capabilities for the accurate measurement of even very strongly absorbing materials such as aqueous solutions.

  14. Detection of NaCl solutions using terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Cuicui; Liu, Shangjian; Zhao, Xiaojing; Zuo, Jian; Zhang, Cunlin

    2016-11-01

    Terahertz spectrum is corresponding with vibration and rotation of liquid molecules. It is suitable to identify and research the liquid molecular dynamics. As a powerful spectral detection technology, terahertz time-domain spectroscopy (THz- TDS) is widely used in solution detection. The absorption coefficient, refractive index and dielectric function of solutions can be extracted based on terahertz time-domain spectroscopy. NaCl exists in most biological tissues, and it is very important for life. In this paper, we detected NaCl solutions with different concentrations at room temperature by THz-TDS technique in the range of 0.2-1.5 THz. The liquid cell with a thickness of 0.2mm is made of quartz. A linear increase of the real and imaginary part of the dielectric function was observed when compared with pure water with increasing concentrations of NaCl solutions. We fitted the terahertz dielectric function of the NaCl solutions by Debye model, Where the dielectric relaxation time can be obtained. By means of dielectric relaxation process, it was found that the characteristic time of molecular movement and the information related to the liquid molecular structure and movement was obtained.

  15. Low temperature-grown GaAs carrier lifetime evaluation by double optical pump terahertz time-domain emission spectroscopy.

    PubMed

    Mag-Usara, Valynn Katrine; Funkner, Stefan; Niehues, Gudrun; Prieto, Elizabeth Ann; Balgos, Maria Herminia; Somintac, Armando; Estacio, Elmer; Salvador, Arnel; Yamamoto, Kohji; Hase, Muneaki; Tani, Masahiko

    2016-11-14

    We present the use of a "double optical pump" technique in terahertz time-domain emission spectroscopy as an alternative method to investigate the lifetime of photo-excited carriers in semiconductors. Compared to the commonly employed optical pump-probe transient photo-reflectance, this non-contact and room temperature characterization technique allows relative ease in achieving optical alignment. The technique was implemented to evaluate the carrier lifetime in low temperature-grown gallium arsenide (LT-GaAs). The carrier lifetime values deduced from "double optical pump" THz emission decay curves show good agreement with data obtained from standard transient photo-reflectance measurements on the same LT-GaAs samples grown at 250 °C and 310 °C.

  16. Monitoring PM2.5 in the Atmosphere by Using Terahertz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhan, Honglei; Zhao, Kun; Bao, Rima; Xiao, Lizhi

    2016-09-01

    The real-time monitoring of the air pollution with multiple sources is of great significance for pollution control and environmental protection. In this paper, we presented a study of terahertz time-domain spectroscopy (THz-TDS) as a direct tool for monitoring the component and content of PM2.5 in atmosphere. Due to the THz absorption, the intensities of the peaks in THz-TDS decreased with the augment of PM2.5 and were proportional to the PM2.5 content. The ratio of absorbance A to PM2.5 reflected a basically unchanged tendency, indicating the little change of principal elements under the pollution degree. In the high-pollution condition, a lot of SO2 from vehicle and factory was emitted into air. The elements, such as S and O from anions, had a stronger absorption effect in THz range. Based on the absorbance spectra, the absorption tendencies with PM2.5 over the whole range were validated by principal component analysis and the quantitative model with a high correlation was built by using back propagation artificial neural network. BPANN model improved the precision of linear fitting between peak intensities and PM2.5. The research demonstrates that THz-TDS is a promising tool for fast, direct, and reliable monitoring in environmental applications.

  17. Obtaining spectrally selective images of objects in attenuated total reflection regime in real time in visible and terahertz ranges

    NASA Astrophysics Data System (ADS)

    Gerasimov, V. V.; Knyazev, B. A.; Cherkassky, V. S.

    2010-06-01

    An imaging attenuated total reflection (ATR) spectrometer for the terahertz range is created for the first time. The spectrometer uses a powerful free-electron laser. Images are recorded with a microbolom-eter detector array as a source of frequency tunable monochromatic radiation. Recording spectrally selective images of dynamic objects at a rate of 20 frames per second in the visible and terahertz ranges is demonstrated. In the terahertz range, images of the interdiffusion of liquids with strongly differing optical constants are obtained. Optimal configurations for the operation of the ATR spectrometer are found. Merits and demerits of the method are considered, as well as ways of improving the quality of image.

  18. Ultrafast terahertz modulation characteristic of tungsten doped vanadium dioxide nanogranular film revealed by time-resolved terahertz spectroscopy

    SciTech Connect

    Xiao, Yang; Zhai, Zhao-Hui; Zhu, Li-Guo E-mail: huangwanxia@scu.edu.cn; Li, Jun; Peng, Qi-Xian; Li, Ze-Ren; Shi, Qi-Wu; Huang, Wan-Xia E-mail: huangwanxia@scu.edu.cn; Yue, Fang; Hu, Yan-Yan

    2015-07-20

    The ultrafast terahertz (THz) modulation characteristic during photo-induced insulator-to-metal transition (IMT) of undoped and tungsten (W)-doped VO{sub 2} film was investigated at picoseconds time scale using time-resolved THz spectroscopy. W-doping slows down the photo-induced IMT dynamic processes (both the fast non-thermal process and the slow metallic phase propagation process) in VO{sub 2} film and also reduces the pump fluence threshold of photo-induced IMT in VO{sub 2} film. Along with the observed broadening of phase transition temperature window of IMT in W-doped VO{sub 2}, we conclude that W-doping prevents metallic phase domains from percolation. By further extracting carrier properties from photo-induced THz conductivity at several phase transition times, we found that the electron-electron correlation during IMT is enhanced in W-doped VO{sub 2}.

  19. Tunable terahertz reflection of graphene via ionic liquid gating.

    PubMed

    Wu, Yang; Qiu, Xuepeng; Liu, Hongwei; Liu, Jingbo; Chen, Yuanfu; Ke, Lin; Yang, Hyunsoo

    2017-03-03

    We report a highly efficient tunable THz reflector in graphene. By applying a small gate voltage (up to ±3 V), the reflectance of graphene is modulated from a minimum of 0.79% to a maximum of 33.4% using graphene/ionic liquid structures at room temperature, and the reflection tuning is uniform within a wide spectral range (0.1-1.5 THz). Our observation is explained by the Drude model, which describes the THz wave-induced intraband transition in graphene. This tunable reflectance of graphene may contribute to broadband THz mirrors, deformable THz mirrors, variable THz beam splitters and other optical components.

  20. Tunable terahertz reflection of graphene via ionic liquid gating

    NASA Astrophysics Data System (ADS)

    Wu, Yang; Qiu, Xuepeng; Liu, Hongwei; Liu, Jingbo; Chen, Yuanfu; Ke, Lin; Yang, Hyunsoo

    2017-03-01

    We report a highly efficient tunable THz reflector in graphene. By applying a small gate voltage (up to ±3 V), the reflectance of graphene is modulated from a minimum of 0.79% to a maximum of 33.4% using graphene/ionic liquid structures at room temperature, and the reflection tuning is uniform within a wide spectral range (0.1–1.5 THz). Our observation is explained by the Drude model, which describes the THz wave-induced intraband transition in graphene. This tunable reflectance of graphene may contribute to broadband THz mirrors, deformable THz mirrors, variable THz beam splitters and other optical components.

  1. Terahertz Spectroscopy of Intrinsic Biomarkers for Non-Melanoma Skin Cancer

    DTIC Science & Technology

    2009-01-01

    Terahertz spectroscopy of intrinsic biomarkers for non-melanoma skin cancer . Cecil S. Joseph1*, Anna N. Yaroslavsky2, Munir Al-Arashi2,Thomas...offer a safe, non-invasive medical imaging modality for detecting different types of human cancers . The aim of this study was to identify intrinsic...biomarkers for non-melanoma skin cancer and their absorption frequencies. Knowledge of these frequencies is a prerequisite for the optimal development of

  2. Detection of pesticides residues in rapeseed oil by terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Xiao-li, Zhao; Jiu-sheng, Li

    2011-02-01

    The absorption spectra of panax notoginseng and glycyrrhiza in the frequency range of 0.2~1.6THz has been measured with terahertz time-domin spectroscopy at room temperature. Simultaneously, the corresponding theoretical spectra were given by using density functional theory methods. It was found that the absorption peaks of the two molecules obtained by theoretical were in good agreement with the experimental results.

  3. Identification of cellulosic fibers and determination of their blend ratio using terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Kurabayashi, Toru; Shuhama, Hayato; Yodokawa, Shinichi; Kosaka, Satoru

    2017-01-01

    We demonstrate a method for identifying fabric fibers and their blend ratio using terahertz spectroscopy. The absorption spectra of cellulosic fibers are discriminative due to the types of crystallized cellulose in each type of fiber when the samples are prepared by cutting the fibers to 0.2 mm lengths. The blend ratio of two different fibers was quantified using principal component analysis of the first derivative of the spectra, followed by multiple classification analysis.

  4. 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.

  5. Terahertz Spectroscopy Applied for Investigation of Water Structure.

    PubMed

    Penkov, Nikita; Shvirst, Nikolay; Yashin, Valery; Fesenko, Eugeny; Fesenko, Eugeny

    2015-10-01

    The absorption spectra of liquid water and various aqueous solutions were analyzed in a terahertz frequency domain (from 6 to 200 cm(-1)) which characterize the collective dynamics of water molecules. Particular attention was paid to the relaxation process in the range of ∼6-80 cm(-1). The physical essence of this process on the molecular level is still unclear. We found that the amplitude of this relaxation process correlates with the degree of destruction of water structure. The obtained data allowed us to interpret this process as a monomolecular relaxation of free water molecules. On the basis of a consideration of the water polarization in the electric field, we proposed a method of calculation of the amount of free water molecules in solution.

  6. 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.

  7. Far-infrared in vivo signature of human skin by terahertz time-domain spectroscopy using waveform rebuilding technology

    NASA Astrophysics Data System (ADS)

    Li, Xiangjun; Liu, Jianjun; Hong, Zhi

    2010-11-01

    We present terahertz time-domain spectroscopy characterization of human thumb skin in reflection measurement mode with waveform rebuilding technology. The thumb skin contacts one side of a high resistive silicon wafer with 3 mm thick, and here is an orthogonal incidence of the THz pulse putting on the other side of the wafer. We rebuild the time domain signal from silicon-skin interface as a sample signal by the signal from the air-silicon interface as a reference and a Fresnel transform function between them. Material parameters were calculated by minimizing the difference between the measured sample waveform and a rebuilt one in time domain. The double Debye model parameters for the thumb skin were fitted. The method has potential to research complex layer-structures in skin if a precise model is built.

  8. Linearity of Air-Biased Coherent Detection for Terahertz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Tianwu; Iwaszczuk, Krzysztof; Wrisberg, Emil Astrup; Denning, Emil Vosmar; Jepsen, Peter Uhd

    2016-06-01

    The performance of air-biased coherent detection (ABCD) in a broadband two-color laser-induced air plasma system for terahertz time-domain spectroscopy (THz-TDS) has been investigated. Fundamental parameters of the ABCD detection, including signal-to-noise ratio (SNR), dynamic range (DR), and linearity of detection have been characterized. Moreover, the performance of a photomultiplier tube (PMT) and an avalanche photodiode (APD) as photodetector in the ABCD have been compared. We have observed nonlinear behavior of PMT detector, which leads to artificial gain factor in TDS spectroscopy. The APD turns out to have superior linearity and three times higher dynamic compared to the PMT.

  9. [Preliminary research on insect damage detection in pecans using terahertz spectroscopy].

    PubMed

    Li, Bin; Wang, Ning; Zhang, Wei-Li; Zhao, Chun-Jiang; Zhang, Bao-Hua

    2014-05-01

    Pecan is an important nut in US, however, the inner insect influences pecan's quality a lot. To realize the nondestructive detection of insect damage in American pecans rapidly and efficiently, preliminary research on insect damage detection in pecans was conducted based on terahertz spectroscopy. Firstly, a set of native pecan nuts were collected and were manually sliced with a thickness of about 1, 2 and 3 mm and with a size of about 2 cm(length) X 1 cm(width) for every pecan nutmeat; Pecan shell and inner separator were also cut into the same size. Secondly, the absorption spectra of the nutmeat slices, shell, and inner separator were collected using THz time-domain spectroscopy (THz-TDS) developed by a group of researchers at Oklahoma State University, and the spectral characteristic of the slices was analyzed. Thirdly, the absorption spectra of the alive manduca sexta and dry pecan weevil were collected, and due to the high contents in the insects, very obvious spectral characteristics were found. Finally, the transmission experiment was conducted with the whole pecans. The results from the preliminary study show a potential application of THz technology for insect damage detection. This research provides a reference for further understanding terahertz and exploring sample preparation methods, test methods, data acquisition and optical parameters calculation methods, and developing nondestructive detection system for insect damage in American pecans based on terahertz technology.

  10. Characterization of plasma treated surfaces for food safety by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Sulovská, Kateřina; Lehocký, Marián.

    2014-10-01

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

  11. A terahertz time-domain spectrometer for simultaneous transmission and reflection measurements at normal incidence.

    PubMed

    Brunner, Fabian D J; Schneider, Arno; Günter, Peter

    2009-11-09

    We present a versatile terahertz time-domain spectrometer which allows reflection measurements at normal incidence and double pass transmission measurements in a single experimental setup. Two different modes for transmission measurements are demonstrated for precise measurements of transparent high or low refractive index materials, respectively. The refractive indices and absorption coefficients of cesium iodide, potassium bromide, sodium chloride, polytetrafluoroethylene (PTFE, Teflon), and silicon have been measured in the frequency range between 1.4 and 4.7 THz. The parameters of the Lorentz oscillator functions describing the phonon polariton dispersions of CsI and KBr have been determined.

  12. Compact terahertz time domain spectroscopy system with diffraction-limited spatial resolution

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinichi; Shimano, Ryo

    2007-10-01

    A compact and rigid terahertz time domain spectroscopy system is presented. The size of the device is 20mm diameter times 61mm length with four parabolic-shaped concave mirrors dug in it to effectively focus a terahertz beam on a sample. The device has no chromatic aberration over the whole bandwidth of the beam (0.3-2THz), and an effective numerical aperture of about 0.45 is achieved, which has a capability to image the structure whose size is almost the same as the wavelength. Frequency resolved images clearly show this performance. We also show that quantitative retrieval of the complex refractive index of the structure as small as twice of the wavelength is possible.

  13. High-harmonic and terahertz wave spectroscopy (HATS) for aligned molecules

    NASA Astrophysics Data System (ADS)

    Huang, Yindong; Meng, Chao; Zhao, Jing; Wang, Xiaowei; Lü, Zhihui; Zhang, Dongwen; Yuan, Jianmin; Zhao, Zengxiu

    2016-12-01

    We present the experimental and theoretical details of our recent published letter Huang et al (2015 Phys. Rev. Lett. 115 123002) on synchronized high-harmonic and terahertz-wave spectroscopy (HATS) from nonadiabatically aligned nitrogen molecules in dual-color laser fields. By associating alignment-angle dependent terahertz wave generation (TWG) with high harmonic generation (HHG), the angular differential photoionization cross section (PICS) for molecules can be reconstructed. The angles at which the PICS’s minima are located show great convergence between the theoretical predictions and the experimentally deduced results when choosing a suitable internuclear distance. We also show the optimal relative phase between the dual-color laser fields for TWG does not change with the alignment angle at a precision of about 50 attoseconds. This all-optical method provides an alternative for investigating molecular structures and dynamics.

  14. Terahertz spectroscopy of low-dimensional nanomaterials: nonlinear emission and ultrafast electrodynamics

    NASA Astrophysics Data System (ADS)

    Luo, Liang; Wang, Jigang

    2015-08-01

    Nonlinear and non-equilibrium properties of low-dimensional quantum materials are fundamental in nanoscale science yet transformative in nonlinear imaging/photonic technology today. These have been poorly addressed in many nano-materials despite of their well-established equilibrium optical and transport properties. The development of ultrafast terahertz (THz) sources and nonlinear spectroscopy tools facilitates understanding these issues and reveals a wide range of novel nonlinear and quantum phenomena that are not expected in bulk solids or atoms. In this paper, we discuss our recent discoveries in two model photonic and electronic nanostructures to solve two outstanding questions: (1) how to create nonlinear broadband terahertz emitters using deeply subwavelength nanoscale meta-atom resonators? (2) How to access one-dimensional (1D) dark excitons and their non-equilibrium correlated states in single-walled carbon nanotubes (SWMTs)?

  15. Conformational characteristics of β-glucan in laminarin probed by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Shin, Hee Jun; Oh, Seung Jae; Kim, Sung In; Won Kim, Ha; Son, Joo-Hiuk

    2009-03-01

    We measured the binding-state-dependent power absorptions, refractive indices, and dielectric constants of triple-stranded helices (TSHs) and single-stranded helices (SSHs) β-glucans in laminarin using terahertz time-domain spectroscopy (TDS). The SSH β-glucan was obtained from a TSH β-glucan laminarin by a chemical treatment with NaOH solution. The power absorption of TSH β-glucan increased more rapidly than that of the SSH β-glucan with the frequency increment. The refractive index and dielectric constants of TSH β-glucan were also larger than those of the SSH β-glucan. This result implies that terahertz-TDS is a very effective method in classifying the conformational state of β-glucans.

  16. Terahertz Spectroscopy of Low-Dimensional Nanomaterials: Nonlinear Emission and Ultrafast Electrodynamics

    DOE PAGES

    Luo, Liang; Wang, Jigang

    2016-01-01

    Nonlinear and non-equilibrium properties of low-dimensional quantum materials are fundamental in nanoscale science yet transformative in nonlinear imaging/photonic technology today. These have been poorly addressed in many nano-materials despite of their well-established equilibrium optical and transport properties. The development of ultrafast terahertz (THz) sources and nonlinear spectroscopy tools facilitates understanding these issues and reveals a wide range of novel nonlinear and quantum phenomena that are not expected in bulk solids or atoms. In this paper, we discuss our recent discoveries in two model photonic and electronic nanostructures to solve two outstanding questions: (1) how to create nonlinear broadband terahertz emittersmore » using deeply subwavelength nanoscale meta-atom resonators? (2) How to access one-dimensional (1D) dark excitons and their non-equilibrium correlated states in single-walled carbon nanotubes (SWMTs)?« less

  17. Terahertz Spectroscopy of Low-Dimensional Nanomaterials: Nonlinear Emission and Ultrafast Electrodynamics

    SciTech Connect

    Luo, Liang; Wang, Jigang

    2016-01-01

    Nonlinear and non-equilibrium properties of low-dimensional quantum materials are fundamental in nanoscale science yet transformative in nonlinear imaging/photonic technology today. These have been poorly addressed in many nano-materials despite of their well-established equilibrium optical and transport properties. The development of ultrafast terahertz (THz) sources and nonlinear spectroscopy tools facilitates understanding these issues and reveals a wide range of novel nonlinear and quantum phenomena that are not expected in bulk solids or atoms. In this paper, we discuss our recent discoveries in two model photonic and electronic nanostructures to solve two outstanding questions: (1) how to create nonlinear broadband terahertz emitters using deeply subwavelength nanoscale meta-atom resonators? (2) How to access one-dimensional (1D) dark excitons and their non-equilibrium correlated states in single-walled carbon nanotubes (SWMTs)?

  18. [Terahertz time-domain spectroscopy of alpha endosulfan persistent organic pollutant].

    PubMed

    Hou, Di-bo; Yue, Fei-heng; Kang, Xu-sheng; Huang, Ping-jie; Zhang, Guang-xin

    2012-05-01

    Frequency-dependent absorption coefficient spectrum and refractive index spectrum of alpha endosulfan, a kind of persistent organic pollutants, are presented in the terahertz frequency region by terahertz (THz) time-domain spectroscopy (TDS). The spectral features in the THz region have a number of unique characteristic absorption peaks. The result demonstrates that THz-TDS is a promising method to identify materials. Then we adopted density functional calculation method to analyze theoretic absorption coefficients of single alpha endosulfan molecule within 0.2-2 THz. The results show that absorption peaks at 1.68, 1.91 THz in theoretical calculation correspond to 1.7, 1.88 THz in the experiment. Finally, vibrational modes and approximate assignments were discussed, showing that these matched peaks are caused by intramolecular vibrational modes of alpha endosulfan. Others might be related to intermolecular vibrational modes or combined vibrational modes.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  20. Transmission and reflection of terahertz plasmons in two-dimensional plasmonic devices

    DOE PAGES

    Sydoruk, Oleksiy; Choonee, Kaushal; Dyer, Gregory Conrad

    2015-03-10

    We found that plasmons in two-dimensional semiconductor devices will be reflected by discontinuities, notably, junctions between gated and non-gated electron channels. The transmitted and reflected plasmons can form spatially- and frequency-varying signals, and their understanding is important for the design of terahertz detectors, oscillators, and plasmonic crystals. Using mode decomposition, we studied terahertz plasmons incident on a junction between a gated and a nongated channel. The plasmon reflection and transmission coefficients were found numerically and analytically and studied between 0.3 and 1 THz for a range of electron densities. At higher frequencies, we could describe the plasmons by a simplifiedmore » model of channels in homogeneous dielectrics, for which the analytical approximations were accurate. At low frequencies, however, the full geometry and mode spectrum had to be taken into account. Moreover, the results agreed with simulations by the finite-element method. As a result, mode decomposition thus proved to be a powerful method for plasmonic devices, combining the rigor of complete solutions of Maxwell's equations with the convenience of analytical expressions.« less

  1. Transmission and reflection of terahertz plasmons in two-dimensional plasmonic devices

    SciTech Connect

    Sydoruk, Oleksiy; Choonee, Kaushal; Dyer, Gregory Conrad

    2015-03-10

    We found that plasmons in two-dimensional semiconductor devices will be reflected by discontinuities, notably, junctions between gated and non-gated electron channels. The transmitted and reflected plasmons can form spatially- and frequency-varying signals, and their understanding is important for the design of terahertz detectors, oscillators, and plasmonic crystals. Using mode decomposition, we studied terahertz plasmons incident on a junction between a gated and a nongated channel. The plasmon reflection and transmission coefficients were found numerically and analytically and studied between 0.3 and 1 THz for a range of electron densities. At higher frequencies, we could describe the plasmons by a simplified model of channels in homogeneous dielectrics, for which the analytical approximations were accurate. At low frequencies, however, the full geometry and mode spectrum had to be taken into account. Moreover, the results agreed with simulations by the finite-element method. As a result, mode decomposition thus proved to be a powerful method for plasmonic devices, combining the rigor of complete solutions of Maxwell's equations with the convenience of analytical expressions.

  2. Exploiting total internal reflection geometry for efficient optical modulation of terahertz light

    NASA Astrophysics Data System (ADS)

    Liu, Xudong; Parrott, Edward P. J.; Ung, Benjamin S.-Y.; Pickwell-MacPherson, Emma

    2016-10-01

    Efficient methods to modulate terahertz (THz) light are essential for realizing rapid THz imaging and communication applications. Here we report a novel THz modulator which utilizes the evanescent wave in a total internal reflection setup coupled with a conductive interface to enhance the attenuation efficiency of THz light. This approach makes it possible to achieve close to 100% modulation with a small interface conductivity of 12 mS. The frequency dependence of this technique is linked to the optical properties of the materials: a material with close to frequency independent conductivity that is also controllable will result in an achromatic modulation response, and the device performance can be optimized further by tuning the internal reflection angle. In this work, we focus on applying the technique in the terahertz frequency range. Using an LED array with a pump intensity of 475 mW/cm2 to produce carriers in a silicon wafer, we have achieved a modulation depth of up to 99.9% in a broad frequency range of 0.1 THz-0.8 THz. The required pumping power for the generation of the required free carriers is low because the sheet conductivity needed is far less than required for traditional transmission techniques. Consequently, the device can be modulated by an LED making it a very practical, low cost, and scalable solution for THz modulation.

  3. [The error analysis and experimental verification of laser radar spectrum detection and terahertz time domain spectroscopy].

    PubMed

    Liu, Wen-Tao; Li, Jing-Wen; Sun, Zhi-Hui

    2010-03-01

    Terahertz waves (THz, T-ray) lie between far-infrared and microwave in electromagnetic spectrum with frequency from 0.1 to 10 THz. Many chemical agent explosives show characteristic spectral features in the terahertz. Compared with conventional methods of detecting a variety of threats, such as weapons and chemical agent, THz radiation is low frequency and non-ionizing, and does not give rise to safety concerns. The present paper summarizes the latest progress in the application of terahertz time domain spectroscopy (THz-TDS) to chemical agent explosives. A kind of device on laser radar detecting and real time spectrum measuring was designed which measures the laser spectrum on the bases of Fourier optics and optical signal processing. Wedge interferometer was used as the beam splitter to wipe off the background light and detect the laser and measure the spectrum. The result indicates that 10 ns laser radar pulse can be detected and many factors affecting experiments are also introduced. The combination of laser radar spectrum detecting, THz-TDS, modern pattern recognition and signal processing technology is the developing trend of remote detection for chemical agent explosives.

  4. Thermal denaturation of protein studied by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Fu, Xiuhua; Li, Xiangjun; Liu, Jianjun; Du, Yong; Hong, Zhi

    2012-12-01

    In this study, the absorption spectra of native or thermal protein were measured in 0.2-1.4THz using terahertz time-domain spectroscopy (THz-TDS) system at room temperature, their absorption spectra and the refractive spectra were obtained. Experimental results indicate that protein both has strong absorption but their characteristics were not distinct in the THz region, and the absorption decreased during thermal denatured state. In order to prove protein had been denatured, we used Differential scanning calorimeter (DSC) measured their denatured temperature, from their DSC heating traces, collagen Td=101℃, Bovine serum albumin Td=97℃. While we also combined the Fourier transform infrared spectrometer (FTIR) to investigate their secondary and tertiary structure before and after denatuation, but the results did not have the distinct changes. We turned the absorption spectra and the refractive spectra to the dielectric spectra, and used the one-stage Debye model simulated the terahertz dielectric spectra of protein before and after denaturation. This research proved that the terahertz spectrum technology is feasible in testing protein that were affected by temperature or other factors which can provide theoretical foundation in the further study about the THz spectrum of protein and peptide temperature stability.

  5. Anisotropic optical response of optically opaque elastomers with conductive fillers as revealed by terahertz polarization spectroscopy

    PubMed Central

    Okano, Makoto; Watanabe, Shinichi

    2016-01-01

    Elastomers are one of the most important materials in modern society because of the inherent viscoelastic properties due to their cross-linked polymer chains. Their vibration-absorbing and adhesive properties are especially useful and thus utilized in various applications, for example, tires in automobiles and bicycles, seismic dampers in buildings, and seals in a space shuttle. Thus, the nondestructive inspection of their internal states such as the internal deformation is essential in safety. Generally, industrial elastomers include various kinds of additives, such as carbon blacks for reinforcing them. The additives make most of them opaque in a wide spectral range from visible to mid-infrared, resulting in that the nondestructive inspection of the internal deformation is quite difficult. Here, we demonstrate transmission terahertz polarization spectroscopy as a powerful technique for investigating the internal optical anisotropy in optically opaque elastomers with conductive additives, which are transparent only in the terahertz frequency region. The internal deformation can be probed through the polarization changes inside the material due to the anisotropic dielectric response of the conductive additives. Our study about the polarization-dependent terahertz response of elastomers with conductive additives provides novel knowledge for in situ, nondestructive evaluation of their internal deformation. PMID:28008942

  6. Anisotropic optical response of optically opaque elastomers with conductive fillers as revealed by terahertz polarization spectroscopy

    NASA Astrophysics Data System (ADS)

    Okano, Makoto; Watanabe, Shinichi

    2016-12-01

    Elastomers are one of the most important materials in modern society because of the inherent viscoelastic properties due to their cross-linked polymer chains. Their vibration-absorbing and adhesive properties are especially useful and thus utilized in various applications, for example, tires in automobiles and bicycles, seismic dampers in buildings, and seals in a space shuttle. Thus, the nondestructive inspection of their internal states such as the internal deformation is essential in safety. Generally, industrial elastomers include various kinds of additives, such as carbon blacks for reinforcing them. The additives make most of them opaque in a wide spectral range from visible to mid-infrared, resulting in that the nondestructive inspection of the internal deformation is quite difficult. Here, we demonstrate transmission terahertz polarization spectroscopy as a powerful technique for investigating the internal optical anisotropy in optically opaque elastomers with conductive additives, which are transparent only in the terahertz frequency region. The internal deformation can be probed through the polarization changes inside the material due to the anisotropic dielectric response of the conductive additives. Our study about the polarization-dependent terahertz response of elastomers with conductive additives provides novel knowledge for in situ, nondestructive evaluation of their internal deformation.

  7. [Identification of Six Isomers of Dimethylbenzoic Acid by Using Terahertz Time-Domain Spectroscopy Technique].

    PubMed

    Liu, Jian-wei; Shen, Jing-ling; Zhang, Bo

    2015-11-01

    In this paper, the absorption spectra of 6 isomers of dimethylbenzoic acid, which were widely used in chemical and pharmaceutical production as intermediate substance, were measured by using the terahertz time-domain spectroscopy (THz-TDS) system in the range 0.2-2.2 THz at room temperature. The experimental results show that the six measured isomers present apparent different spectral response. However, the results of using infrared spectroscopy indicates that different isomers show high similarity in absorption spectra in the range 1450-1700 cm⁻¹. The vibrational frequencies are calculated by using the density functional theory (DFT), and identification of vibrational modes are given. It is clear that the absorption peaks of the 6 isomers in the range 1450-1700 cm⁻¹ come from the stretching vibration of benzene ring and C==O, while the absorption peaks in the terahertz range are caused by the relative wagging of benzene ring and all the chains out of plane, which lead to the different absorption characteristics of the 6 isomers in the range 0.2-2.2 THz. The results suggest that the difference and similarity of the absorption spectra observed in the two different frequency range are resulted from the difference and similarity of the molecular structures of the six isomers. By using the different absorption characteristics, we can identify the six isomers of dimethylbenzoic acid effectively. Our study indicates that it is feasible to distinguish the isomers by using terahertz and infrared spectroscopy technique. It provides an effective way to identify different isomers and test the purity of the intermediate substance in the process of production quickly and accurately.

  8. Terahertz nano-spectroscopy and imaging of super?uid surface plasmons in conventional and anisotropic superconductors

    NASA Astrophysics Data System (ADS)

    Stinson, H. T.; Wu, J. S.; Jiang, B. Y.; Fei, Z.; Rodin, A. S.; Chapler, B.; McLeod, A. S.; Castro Neto, A.; Lee, Y. S.; Fogler, M. M.; Basov, D. N.

    We numerically model near-field spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors in the infrared and terahertz regime. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting gap in Bardeen-Cooper-Schrieffer superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the c-axis plasma frequency, and thus the c-axis superfluid density, of layered unconventional superconductors such as cuprates and pnictides with identical spatial resolution. We discuss the development of a cryogenic terahertz near-field microscope designed to perform these proposed experiments, and recent proof of principle results at room temperature.

  9. Investigation of thermal denaturation of solid oxytocin by terahertz dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Xiangjun; Yang, Xiaojie; Liu, Jianjun; Du, Yong; Hong, Zhi

    2014-07-01

    We investigate the thermal denaturation of solid oxytocin using terahertz time domain spectroscopy(THz-TDS). When the peptide is heated up from 25°C to 107°C and cooled down to 25°C again, an irreversible decrease in its THz absorption coefficient and refractive index is observed. The corresponding frequency-dependent permittivity during heating is fitted by the Debye model with single relaxation time. The relaxation times during temperature rising agree very well with Arrhenius equation with the activation energy of 3.12kJ/(K•mol) as an indicator for its thermal denaturation difficulty.

  10. Quantitative analysis of the mixtures of illicit drugs using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Jiang, Dejun; Zhao, Shusen; Shen, Jingling

    2008-03-01

    A method was proposed to quantitatively inspect the mixtures of illicit drugs with terahertz time-domain spectroscopy technique. The mass percentages of all components in a mixture can be obtained by linear regression analysis, on the assumption that all components in the mixture and their absorption features be known. For illicit drugs were scarce and expensive, firstly we used common chemicals, Benzophenone, Anthraquinone, Pyridoxine hydrochloride and L-Ascorbic acid in the experiment. Then illicit drugs and a common adulterant, methamphetamine and flour, were selected for our experiment. Experimental results were in significant agreement with actual content, which suggested that it could be an effective method for quantitative identification of illicit drugs.

  11. Label-free monitoring of interaction between DNA and oxaliplatin in aqueous solution by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Wu, Xiaojun; E, Yiwen; Xu, Xinlong; Wang, Li

    2012-07-01

    We demonstrated the feasibility of applying terahertz time-domain spectroscopy (THz-TDS) to monitor the molecular reactions in aqueous solutions of anticancer drug oxaliplatin with λ-DNA and macrophages DNA. The reaction time dependent refractive index and absorption coefficient were extracted and analyzed. The reaction half-decaying time of about 4.0 h for λ-DNA and 12.9 h for M-DNA was established. The results suggest that the THz-TDS detection could be an effective label-free technique to sense the molecular reaction in aqueous solutions and could be very useful in biology, medicine, and pharmacy industry.

  12. Characterization of crystal transformation in the solid-state by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Ge, Min; Wang, Wenfeng; Zhao, Hongwei; Zhang, Zengyan; Yu, Xiaohan; Li, Wenxin

    2007-08-01

    Terahertz time-domain spectroscopy (THz-TDS) was utilized to investigate crystal transformation between p-benzoquinone and p-dihydroxybenzene in the solid-state. This process can be clearly visualized by THz spectral patterns of the pure starting compounds and the products at different conditions. The observed results were further confirmed by characteristic X-ray powder diffraction and mid-infrared spectra. The extent of crystal-to-crystal transformation was quantified by the absorption intensity ratio according to the Beer-Lambert law. THz-TDS was demonstrated to be a promising and complementary method in analyzing solid-state reactions.

  13. Terahertz time-domain spectroscopy for monitoring the curing of dental composites

    PubMed Central

    Schwerdtfeger, Michael; Lippert, Sina; Koch, Martin; Berg, Andreas; Katletz, Stefan; Wiesauer, Karin

    2012-01-01

    We apply terahertz (THz) time-domain spectroscopy for monitoring the curing process of three different light-curing dental composites. Exact knowledge of the sample thickness is required for a precise determination of the THz dielectric parameters, as the materials exhibit shrinkage when they are cured. We find very small but significant changes of the THz refractive index and absorption coefficient during stepwise light exposure. The changes in the refractive index are correlated with changes in the density of the materials. Furthermore, the refractive index and the sample thickness are found to give the most reliable result for monitoring the curing process of the dental composites. PMID:23162722

  14. Investigation on optical properties of BSA protein on single-layer graphene using terahertz spectroscopy technology

    NASA Astrophysics Data System (ADS)

    Yang, Shengxin; Du, Pengju; Sun, Yiwen

    2016-11-01

    Terahertz (THz) spectroscopy is sensitive to probe several aspects of biological systems. In THz frequency, electrically controllable Drude-like intraband absorption makes graphene a promising platform for building graphene-based optoelectronic devices such as THz biosensor. In this work, BSA protein thin films were spin-coated and incubated on single-layer graphene. IR lasers with different power were used as the pump light to stimulate the sandwich-like sample respectively. The graphene monolayer complex conductivity was calculated using the transmission method. The novel optical properties of single-layer graphene and BSA protein on graphene in the THz range will be discussed in this paper.

  15. Vibrational frequencies of anti-diabetic drug studied by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Du, S. Q.; Li, H.; Xie, L.; Chen, L.; Peng, Y.; Zhu, Y. M.; Li, H.; Dong, P.; Wang, J. T.

    2012-04-01

    By using terahertz time-domain spectroscopy, the absorption spectra of seven anti-diabetic pills have been investigated. For gliquidone, glipizide, gliclazide, and glimepiride, an obvious resonance peak is found at 1.37 THz. Furthermore, to overcome the limit of density functional theory that can analyze the normal mode frequencies of the ground state of organic material, we also present a method that relies on pharmacophore recognition, from which we can obtain the resonance peak at 1.37 THz can be attributed to the vibration of sulfonylurea group. The results indicate that the veracity of density functional theory can be increased by combining pharmacophore recognition.

  16. Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy.

    PubMed

    Yu, B; Zeng, F; Yang, Y; Xing, Q; Chechin, A; Xin, X; Zeylikovich, I; Alfano, R R

    2004-03-01

    The low-frequency torsional modes, index of refraction, and absorption of a tryptophan film and pressed powders from 0.2 to 2.0 THz (6.6-66 cm(-1)) were measured by terahertz time-domain spectroscopy at room temperature. It was found that there were two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The associated relaxation lifetimes ( approximately 1 ps) for these modes of the tryptophan molecule were measured. Using a density-functional calculation, the origins of the observed torsional vibrations were assigned to the chain and ring of the tryptophan molecule.

  17. Isothermal crystallization of poly(3-hydroxybutyrate) studied by terahertz two-dimensional correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Hoshina, Hiromichi; Ishii, Shinya; Morisawa, Yusuke; Sato, Harumi; Noda, Isao; Ozaki, Yukihiro; Otani, Chiko

    2012-01-01

    The isothermal crystallization of poly(3-hydroxybutylate) (PHB) was studied by monitoring the temporal evolution of terahertz absorption spectra in conjunction with spectral analysis using two-dimensional correlation spectroscopy. Correlation between the absorption peaks and the sequential order of the changes in spectral intensity extracted from synchronous and asynchronous plots indicated that crystallization of PHB at 90 °C is a two step process, in which C-H...O=C hydrogen bonds are initially formed before well-defined crystal structures are established.

  18. In-vitro terahertz spectroscopy of rat skin under the action of dehydrating agents

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Aleksandr S.; Kolesnikova, Ekaterina A.; Tuchina, Daria K.; Terentyuk, Artem G.; Nazarov, Maxim; Skaptsov, Alexander A.; Shkurinov, Alexander P.; Tuchin, Valery V.

    2014-01-01

    In the paper we present the results of study of rat skin and rat subcutaneous tumor under the action of dehydrating agents in terahertz (THz) range (15-30 THz). Frustrated Total Internal Reflection (FTIR) spectra were obtained with infrared Fourier spectrometer Nicolet 6700 and then they were recalculated in the transmittance spectra with Omnic software. Experiments were carried out with healthy and xenografted tumor in skin tissue in vitro. As the dehydrating agents 100% glycerol, 40%-water glucose solution, PEG-600, and propylene glycol were used. To determine the effect of the optical clearing agent (OCA), the alterations of terahertz transmittance for the samples were analyzed. The results have shown that PEG-600 and 40%-glucose water solution are the most effective dehydrating agent. The transmittance of healthy skin after PEG-600 application increased approximately by 6% and the transmittance of tumor tissue after PEG- 600 and 40%-glucose water solution application increased approximately by 8%. Obtained data can be useful for further application of terahertz radiation for tumor diagnostics.

  19. In vivo spectroscopy of healthy skin and pathology in terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Zaytsev, Kirill I.; Kudrin, Konstantin G.; Reshetov, Igor V.; Gavdush, Arseniy A.; Chernomyrdin, Nikita V.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

    2015-01-01

    Biomedical applications of terahertz (THz) technology and, in particular, THz pulsed spectroscopy have attracted considerable interest in the scientific community. A lot of papers have been dedicated to studying the ability for human disease diagnosis, including the diagnosis of human skin cancers. In this paper we have studied the THz material parameters and THz dielectric properties of human skin and pathology in vivo, and THz pulsed spectroscopy has been utilized for this purpose. We have found a contrast between material parameters of basal cell carcinoma and healthy skin, and we have also compared the THz material parameters of dysplastic and non-dysplastic pigmentary nevi in order to study the ability for early melanoma diagnosis. Significant differences between the THz material parameters of healthy skin and pathology have been detected, thus, THz pulsed spectroscopy promises to be become an effective tool for non-invasive diagnosis of skin neoplasms.

  20. Infrared and Terahertz Spectroscopy of Strongly Correlated Electron Systems under Extreme Conditions

    NASA Astrophysics Data System (ADS)

    Kimura, Shin-ichi; Okamura, Hidekazu

    2013-02-01

    Owing to its high brilliance, infrared and terahertz synchrotron radiation (IR/THz-SR) has emerged as a powerful tool for spectroscopy under extreme (i.e., technically more difficult) experimental conditions such as high pressure, high magnetic field, high spatial resolution, and a combination of these. The methodologies for pressure- and magnetic-field-dependent spectroscopy and microscopy using IR/THz-SR have advanced rapidly worldwide. By applying them to strongly correlated electron systems (SCESs), many experimental studies have been performed on their electronic structures and phonon/molecular vibration modes under extreme conditions. Here, we review the recent progress of methodologies of IR/THz-SR spectroscopy and microscopy, and the experimental results on SCESs and other systems obtained under extreme conditions.

  1. Excitation of plasmonic terahertz photovoltaic effects in a periodic two-dimensional electron system by the attenuated total reflection method

    SciTech Connect

    Fateev, D. V. Mashinsky, K. V.; Bagaeva, T. Yu.; Popov, V. V.

    2015-01-15

    The problem of the rectification of terahertz radiation due to plasmonic nonlinearities in a periodic two-dimensional electron system upon the excitation of plasma oscillations by the attenuated total reflection method is solved. This model allows the independent study of different plasmonic rectification mechanisms, i.e., plasmonic electron drag and plasmonic ratchet effects.

  2. Non-contact measurement of the electrical conductivity and coverage density of silver nanowires for transparent electrodes using Terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Park, Sung-Hyeon; Chung, Wan-Ho; Kim, Hak-Sung

    2017-02-01

    In this work, a terahertz time-domain spectroscopy (THz-TDS) imaging technique was used for non-contact measurement of the conductivity and coverage density (D C) of silver nanowires (SNWs) as transparent electrodes. The reflection mode of THz-TDS with an incident angle of 30° was used, and the sheet resistance (R sh) of SNW films was measured using the four-point probe method. The correlations between the THz reflection ratio and R sh were studied by comparing the results of the four-point probe method and the measured THz reflection ratios. Also, the D C of SNWs was evaluated using THz waveforms with a general refractivity formula. This result matched well with a conventional approximation method using a scanning electron microscope image. Furthermore, defects in the SNWs could be easily detected using the THz-TDS imaging technique. The non-contact THz-TDS measurement method that we developed is expected to be a promising technique for non-contact measurement of the R sh and D C for transparent conductive electrodes.

  3. Analysis of blood plasma at terahertz frequencies

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Terahertz time-domain spectroscopy in the 0.05-2.5 THz frequency range was employed to analyze blood plasma samples obtained from laboratory animals with experimental diabetes and from healthy controls. It was found that transmission and reflection coefficients of samples from rats with diabetes differed significantly from control values in both amplitude and phase. The cause of the detected differences is discussed with respect to variation in the terahertz response of water.

  4. [Applications of terahertz spectroscopy and imaging techniques in food safety inspection].

    PubMed

    Shen, Fei; Ying, Yi-Bin

    2009-06-01

    With the development of ultra-fast laser technology and the further understanding of the mechanism behind the interaction of terahertz radiation and materials, THz radiation is actively developed as a new-style technology for a wide range of applications. Currently THz spectroscopy and imaging techniques show great promise in security detection, medical diagnosis, wireless communication, pharmaceutical and many other areas. Because of the growing importance of food safety issues, the detection technology of food safety is also faced with great opportunities and challenges, while THz spectroscopy and imaging techniques provide a new solution to the problem. Compared to other technologies, THz radiation with higher signal-to-noise ratio and wide dynamic range can simultaneously obtain both frequency-domain and time-domain information of the sample which relates to the information of physical structure and chemical composition of materials. Above all THz radiation features unique advantages in food safety inspection. In the present paper, the brief concept of terahertz radiation was introduced, while the properties and technical methods of THz wave were also discussed. The most recent progress in THz technology used in food safety inspection was summarized. The prospect and restricted factors of this novel technology in food industry were also discussed.

  5. Insulin amyloid fibrillation studied by terahertz spectroscopy and other biophysical methods

    SciTech Connect

    Liu, Rui; He, Mingxia; Su, Rongxin; Yu, Yanjun; Qi, Wei; He, Zhimin

    2010-01-01

    Assembly and fibrillation of amyloid proteins are believed to play a key role in the etiology of various human diseases, including Alzheimer's, Parkinson's, Huntington's and type II diabetes. Insights into conformational changes and formation processes during amyloid fibrillation are essential for the clinical diagnosis and drug discovery. To study the changes in secondary, tertiary, quaternary structures, and the alteration in the collective vibrational mode density of states during the amyloid fibrillation, bovine insulin in 20% acetic acid was incubated at 60 {sup o}C, and its multi-level structures were followed by various biophysical techniques, including circular dichroism (CD), thioflavin T fluorescence (ThT), dynamic light scattering (DLS), electron microscopy, and terahertz (THz) absorption spectroscopy. The experimental data demonstrated a transformation of {alpha}-helix into {beta}-sheet starting at 26 h. This was followed by the aggregation of insulin, as shown by ThT binding, with a transition midpoint at 41 h, and by the bulk formation of mature aggregates after about 71 h. THz is a quick and non-invasive technique, which has the advantage of allowing the study of the conformational state of biomolecules and tissues. We first applied THz spectroscopy to study the amyloid fibrillation. At the terahertz frequency range of 0.2-2.0 THz, there was an apparent increase in both the absorbance and refractive index in THz spectra. Thus, THz is expected to provide a new way of looking into amyloid fibrillation.

  6. Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy.

    PubMed

    Hsieh, Yi-Da; Nakamura, Shota; Abdelsalam, Dahi Ghareab; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Hindle, Francis; Yasui, Takeshi

    2016-06-15

    Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident.

  7. Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy

    PubMed Central

    Hsieh, Yi-Da; Nakamura, Shota; Abdelsalam, Dahi Ghareab; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Hindle, Francis; Yasui, Takeshi

    2016-01-01

    Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident. PMID:27301319

  8. Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Hsieh, Yi-Da; Nakamura, Shota; Abdelsalam, Dahi Ghareab; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Hindle, Francis; Yasui, Takeshi

    2016-06-01

    Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident.

  9. Thermal denaturation of CP43 studied by Fourier transform-infrared spectroscopy and terahertz time-domain spectroscopy.

    PubMed

    Qu, Yuangang; Chen, Hua; Qin, Xiaochun; Li, Liangbi; Wang, Li; Kuang, Tingyun

    2007-12-01

    Thermal denaturation of CP43 was studied by Fourier transform-infrared (FT-IR) spectroscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and terahertz time-domain spectroscopy (THz-TDS). Under heat treatment, the secondary structure of CP43 changed, and the main thermal transition occurred at 59 degrees C. During the process, CP43 aggregated at first, and then with increasing temperature degraded. The low-frequency collective vibrational modes of CP43 changed with increasing temperature and decreasing mass. THz-TDS is a new technique used to study the conformational state of a molecule, and it is the first use of this technique to study the photosynthesis membrane proteins in this paper. The results presented here demonstrate that THz-TDS has both advantages and disadvantages in monitoring the thermal denaturation of membrane proteins, which is important in applying THz-TDS technique to study of biomolecules.

  10. Sub-terahertz resonance spectroscopy of biological macromolecules and cells

    NASA Astrophysics Data System (ADS)

    Globus, Tatiana; Moyer, Aaron; Gelmont, Boris; Khromova, Tatyana; Sizov, Igor; Ferrance, Jerome

    2013-05-01

    Recently we introduced a Sub-THz spectroscopic system for characterizing vibrational resonance features from biological materials. This new, continuous-wave, frequency-domain spectroscopic sensor operates at room temperature between 315 and 480 GHz with spectral resolution of at least 1 GHz and utilizes the source and detector components from Virginia Diode, Inc. In this work we present experimental results and interpretation of spectroscopic signatures from bacterial cells and their biological macromolecule structural components. Transmission and absorption spectra of the bacterial protein thioredoxin, DNA and lyophilized cells of Escherichia coli (E. coli), as well as spores of Bacillus subtillis and B. atrophaeus have been characterized. Experimental results for biomolecules are compared with absorption spectra calculated using molecular dynamics simulation, and confirm the underlying physics for resonance spectroscopy based on interactions between THz radiation and vibrational modes or groups of modes of atomic motions. Such interactions result in multiple intense and narrow specific resonances in transmission/absorption spectra from nano-gram samples with spectral line widths as small as 3 GHz. The results of this study indicate diverse relaxation dynamic mechanisms relevant to sub-THz vibrational spectroscopy, including long-lasting processes. We demonstrate that high sensitivity in resolved specific absorption fingerprints provides conditions for reliable detection, identification and discrimination capability, to the level of strains of the same bacteria, and for monitoring interactions between biomaterials and reagents in near real-time. Additionally, it creates the basis for the development of new types of advanced biological sensors through integrating the developed system with a microfluidic platform for biomaterial samples.

  11. Subwavelength film sensing based on terahertz anti-resonant reflecting hollow waveguides.

    PubMed

    You, Borwen; Lu, Ja-Yu; Liou, Jia-Hong; Yu, Chin-Ping; Chen, Hao-Zai; Liu, Tze-An; Peng, Jin-Long

    2010-08-30

    A simple dielectric hollow-tube has been experimentally demonstrated at terahertz range for bio-molecular layer sensing based on the anti-resonant reflecting wave-guidance mechanism. We experimentally study the dependence of thin-film detection sensitivity on the optical geometrical parameters of tubes, different thicknesses and tube wall refractive indices, and on different resonant frequencies. A polypropylene hollow-tube with optimized sensitivity of 0.003 mm/μm is used to sense a subwavelength-thick (λ/225) carboxypolymethylene molecular overlayer on the tube's inner surface, and the minimum detectable quantity of molecules could be down to 1.22 picomole/mm(2). A double-layered Fabry-Pérot model is proposed for calculating the overlayer thicknesses, which agrees well with the experimental results.

  12. Non-destructive inspections of illicit drugs in envelope using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

    The absorption spectra of two illicit drugs, methylenedioxyamphetarnine (MDA) and methamphetamine (MA), within and without two conventional envelopes are studied using terahertz time-domain spectroscopy technique. The characteristic absorption spectra of MDA and MA are obtained in the range of 0.2 THz to 2.5 THz. MDA has an obvious absorption peak at 1.41 THz while MA has obvious absorption peaks at 1.23 THz, 1.67 THz, 1.84 THz and 2.43 THz. We find that the absorption peaks of MDA and MA within the envelopes are almost the same as those without the envelopes respectively although the two envelopes have some different absorption in THz waveband. This result indicates that the type of illicit drugs in envelopes can be determined by identifying their characteristic absorption peaks, and THz time-domain spectroscopy is one of the most powerful candidates for illicit drugs inspection.

  13. Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators

    DOE PAGES

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

    2016-04-22

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

  14. Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators

    SciTech Connect

    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 aperture THz near-field microscopy for mode mapping and local spectroscopy demonstrates the potential of near-field methods for studies of subwavelength plasmonic THz resonators.

  15. Application of terahertz spectroscopy for characterization of biologically active organic molecules in natural environment

    NASA Astrophysics Data System (ADS)

    Karaliūnas, Mindaugas; Jakštas, Vytautas; Nasser, Kinan E.; Venckevičius, Rimvydas; Urbanowicz, Andrzej; Kašalynas, Irmantas; Valušis, Gintaras

    2016-09-01

    In this work, a comparative research of biologically active organic molecules in its natural environment using the terahertz (THz) time domain spectroscopy (TDS) and Fourier transform spectroscopy (FTS) systems is carried out. Absorption coefficient and refractive index of Nicotiana tabacum L. leaves containing nicotine, Cannabis sativa L. leaves containing tetrahydrocannabinol, and Humulu lupulus L. leaves containing α-acids, active organic molecules that obtain in natural environment, were measured in broad frequency range from 0.1 to 13 THz at room temperature. In the spectra of absorption coefficient the features were found to be unique for N. tabacum, C. sativa and H. lupulus. Moreover, those features can be exploited for identification of C. sativa sex and N. tabacum origin. The refractive index can be also used to characterize different species.

  16. Terahertz spectroscopy for the study of paraffin-embedded gastric cancer samples

    NASA Astrophysics Data System (ADS)

    Wahaia, Faustino; Kasalynas, Irmantas; Seliuta, Dalius; Molis, Gediminas; Urbanowicz, Andrzej; Carvalho Silva, Catia D.; Carneiro, Fatima; Valusis, Gintaras; Granja, Pedro L.

    2015-01-01

    Terahertz (THz) spectroscopy constitute promising technique for biomedical applications as a complementary and powerful tool for diseases screening specially for early cancer diagnostic. The THz radiation is not harmful to biological tissues. As increased blood supply in cancer-affected tissues and consequent local increase in tissue water content makes THz technology a potentially attractive. In the present work, samples of healthy and adenocarcinoma-affected gastric tissue were analyzed using transmission time-domain THz spectroscopy (THz-TDS). The work shows the capability of the technique to distinguish between normal and cancerous regions in dried and paraffin-embedded samples. Plots of absorption coefficient α and refractive index n of normal and cancer affected tissues, are presented and the conditions for discrimination between normal and affected tissues are discussed.

  17. Estimation of crystallinity of trehalose dihydrate microspheres by usage of terahertz time-domain spectroscopy.

    PubMed

    Takeuchi, Issei; Tomoda, Keishiro; Nakajima, Takehisa; Terada, Hiroshi; Kuroda, Hideki; Makino, Kimiko

    2012-09-01

    Crystalline state of pharmaceutical materials is of great importance in the preparation of pharmaceutics because their physicochemical properties affect bioavailability, quality of products, therapeutic level, and manufacturing process. In this study, we have estimated the crystallinity of trehalose dihydrate microspheres by measuring terahertz (THz) spectroscopy. The commercially available trehalose dihydrate takes in general a crystalline state, but trehalose dihydrate microspheres prepared by using spray-drying method are in an amorphous state. We have prepared amorphous anhydrous trehalose by using melt-quenched method from crystalline trehalose dihydrate. We have measured the absorbance of trehalose dihydrate containing amorphous anhydrous trehalose (0%, 25%, 50%, 75%, and 100%) using THz time-domain spectroscopy (THz-TDS) to prepare calibration curves. Using the calibration curves, we have estimated the crystallinity of trehalose dihydrate microspheres prepared by using spray-drying method. Our results suggest that THz-TDS is well suited to distinguish crystallinity differences in pharmaceutical compounds.

  18. 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.

  19. Reflection imaging in the millimeter-wave range using a video-rate terahertz camera

    NASA Astrophysics Data System (ADS)

    Marchese, Linda E.; Terroux, Marc; Doucet, Michel; Blanchard, Nathalie; Pancrati, Ovidiu; Dufour, Denis; Bergeron, Alain

    2016-05-01

    The ability of millimeter waves (1-10 mm, or 30-300 GHz) to penetrate through dense materials, such as leather, wool, wood and gyprock, and to also transmit over long distances due to low atmospheric absorption, makes them ideal for numerous applications, such as body scanning, building inspection and seeing in degraded visual environments. Current drawbacks of millimeter wave imaging systems are they use single detector or linear arrays that require scanning or the two dimensional arrays are bulky, often consisting of rather large antenna-couple focal plane arrays (FPAs). Previous work from INO has demonstrated the capability of its compact lightweight camera, based on a 384 x 288 microbolometer pixel FPA with custom optics for active video-rate imaging at wavelengths of 118 μm (2.54 THz), 432 μm (0.69 THz), 663 μm (0.45 THz), and 750 μm (0.4 THz). Most of the work focused on transmission imaging, as a first step, but some preliminary demonstrations of reflection imaging at these were also reported. In addition, previous work also showed that the broadband FPA remains sensitive to wavelengths at least up to 3.2 mm (94 GHz). The work presented here demonstrates the ability of the INO terahertz camera for reflection imaging at millimeter wavelengths. Snapshots taken at video rates of objects show the excellent quality of the images. In addition, a description of the imaging system that includes the terahertz camera and different millimeter sources is provided.

  20. Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy

    SciTech Connect

    Sheen, David M.; McMakin, Douglas L.; Hall, Thomas E.

    2007-04-01

    Wideband millimeter-wave imaging techniques and systems have been developed at PNNL for concealed weapon detection and other applications. These techniques evolved from single-frequency millimeter-wave holographic imaging methods to wideband three-dimensional planar and cylindrical techniques and systems. The single-frequency holographic method was derived from optical and ultrasonic holography techniques. Speckle is highly significant in this case, and is caused by constructive and destructive interference from multiple scattering locations or depths within a single resolution cell. The wideband three-dimensional techniques developed at PNNL significantly reduce the speckle effect through the use of high depth resolution obtained from the wide bandwidth of the illumination. For these techniques, speckle can still be significant in some cases and affect image quality. In this paper, we explore the situations in which speckle occurs and it's relationship to lateral and depth resolution. This will be accomplished through numerical simulation and demonstrated in actual imaging results. Speckle may also play a significant role in altering reflection spectra in wideband terahertz spectra. Reflection from rough surfaces will generate speckle, which will result in significant variation in the reflection spectrum as measured over very wide bandwidths. This effect may make if difficult to interpret spectral absorption features from general reflectance data. In this paper, physical optics numerical simulation techniques will be used to model the reflection from arbitrary random surfaces and explore the effect of the surface on the reflection spectra and reconstructed image. Laboratory imaging and numerical modeling results in the millimeter-wave through the terahertz frequency ranges are presented.

  1. Diffuse reflectance spectroscopy of liver tissue

    NASA Astrophysics Data System (ADS)

    Reistad, Nina; Nilsson, Jan; Vilhelmsson Timmermand, Oskar; Sturesson, Christian; Andersson-Engels, Stefan

    2015-06-01

    Diffuse reflectance spectroscopy (DRS) with a fiber-optic contact probe is a cost-effective, rapid, and non-invasive optical method used to extract diagnosis information of tissue. By combining commercially available VIS- and NIR-spectrometers with various fiber-optic contact-probes, we have access to the full wavelength range from around 400 to 1600 nm. Using this flexible and portable spectroscopy system, we have acquired ex-vivo DRS-spectra from murine, porcine, and human liver tissue. For extracting the tissue optical properties from the measured spectra, we have employed and compared predictions from two models for light propagation in tissue, diffusion theory model (DT) and Monte Carlo simulations (MC). The focus in this work is on the capacity of this DRS-technique in discriminating metastatic tumor tissue from normal liver tissue as well as in assessing and characterizing damage to non-malignant liver tissue induced by preoperative chemotherapy for colorectal liver metastases.

  2. Ultrafast terahertz spectroscopy for measuring carrier dynamics in nanoscale photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Esenturk, Okan; Lane, Paul A.; Melinger, Joseph S.; Heilweil, Edwin J.

    2010-02-01

    Femtosecond pump-probe methods are useful tools for investigating transient electronic and vibrational states of conducting materials and molecular photochemistry. Ultraviolet and visible excitation pulses (<150 fs, <20 μJ, 400-800 nm) with time-delayed broadband terahertz (~500 GHz to 3 THz) probing pulses (Time-Resolved Terahertz Spectroscopy; TRTS) are used to measure linear spectroscopic transmission changes resulting from exciton and free carrier population in organic semiconducting thin films. Picosecond timescale exciton geminate recombination and longer-time free-carrier conduction in semiconductor polymers and nanolayered donor-acceptor films are discussed. Systems investigated with terahertz probe pulses include thiophene-based polymers (P3HT, PBTTT) studied as drop and spin-cast films on transparent quartz substrates. The relative conductivity of these films increases with increasing P3HT polymer molecular weight, structural regularity, and the fused rings in PBTTT further increases conduction. Recent studies of composite and nanolayered films (by vapor deposition) containing alternating Zn-phthalocyanine (ZnPc) and buckminsterfullerene (C60) also yield high conduction that scales linearly with the number of interfaces and total film thickness. We find evidence for a short-lived charge transfer state of C60 that decays within several picoseconds of excitation. In contrast, both composite and multilayered films exhibit long-lived THz dynamics that depends on the composition and structure of the films. The optimum composition for charge transfer within composite films is observed for a ~1:1 blend of ZnPc with C60 and a 4:1 blend of P3HT with Phenyl C61 Butyric Acid Methyl Ester (PCBM) while an increase in charge photo-generation with decreasing layer thickness (2 nm) exhibits the strongest THz signal. These findings parallel results for FET polymer transistor devices pointing to the advantage of optically measuring material properties before device test.

  3. Light distribution modulated diffuse reflectance spectroscopy

    PubMed Central

    Huang, Pin-Yuan; Chien, Chun-Yu; Sheu, Chia-Rong; Chen, Yu-Wen; Tseng, Sheng-Hao

    2016-01-01

    Typically, a diffuse reflectance spectroscopy (DRS) system employing a continuous wave light source would need to acquire diffuse reflectances measured at multiple source-detector separations for determining the absorption and reduced scattering coefficients of turbid samples. This results in a multi-fiber probe structure and an indefinite probing depth. Here we present a novel DRS method that can utilize a few diffuse reflectances measured at one source-detector separation for recovering the optical properties of samples. The core of innovation is a liquid crystal (LC) cell whose scattering property can be modulated by the bias voltage. By placing the LC cell between the light source and the sample, the spatial distribution of light in the sample can be varied as the scattering property of the LC cell modulated by the bias voltage, and this would induce intensity variation of the collected diffuse reflectance. From a series of Monte Carlo simulations and phantom measurements, we found that this new light distribution modulated DRS (LDM DRS) system was capable of accurately recover the absorption and scattering coefficients of turbid samples and its probing depth only varied by less than 3% over the full bias voltage variation range. Our results suggest that this LDM DRS platform could be developed to various low-cost, efficient, and compact systems for in-vivo superficial tissue investigation. PMID:27375931

  4. Light distribution modulated diffuse reflectance spectroscopy.

    PubMed

    Huang, Pin-Yuan; Chien, Chun-Yu; Sheu, Chia-Rong; Chen, Yu-Wen; Tseng, Sheng-Hao

    2016-06-01

    Typically, a diffuse reflectance spectroscopy (DRS) system employing a continuous wave light source would need to acquire diffuse reflectances measured at multiple source-detector separations for determining the absorption and reduced scattering coefficients of turbid samples. This results in a multi-fiber probe structure and an indefinite probing depth. Here we present a novel DRS method that can utilize a few diffuse reflectances measured at one source-detector separation for recovering the optical properties of samples. The core of innovation is a liquid crystal (LC) cell whose scattering property can be modulated by the bias voltage. By placing the LC cell between the light source and the sample, the spatial distribution of light in the sample can be varied as the scattering property of the LC cell modulated by the bias voltage, and this would induce intensity variation of the collected diffuse reflectance. From a series of Monte Carlo simulations and phantom measurements, we found that this new light distribution modulated DRS (LDM DRS) system was capable of accurately recover the absorption and scattering coefficients of turbid samples and its probing depth only varied by less than 3% over the full bias voltage variation range. Our results suggest that this LDM DRS platform could be developed to various low-cost, efficient, and compact systems for in-vivo superficial tissue investigation.

  5. Label-free detection and characterization of the binding of hemagglutinin protein and broadly neutralizing monoclonal antibodies using terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Sun, Yiwen; Zhong, Junlan; Zhang, Cunlin; Zuo, Jian; Pickwell-MacPherson, Emma

    2015-03-01

    Hemagglutinin (HA) is the main surface glycoprotein of the influenza A virus. The H9N2 subtype influenza A virus is recognized as the most possible pandemic strain as it has crossed the species barrier, infecting swine and humans. We use terahertz spectroscopy to study the hydration shell formation around H9 subtype influenza A virus's HA protein (H9 HA) as well as the detection of antigen binding of H9 HA with the broadly neutralizing monoclonal antibody. We observe a remarkable concentration dependent nonlinear response of the H9 HA, which reveals the formation process of the hydration shell around H9 HA molecules. Furthermore, we show that terahertz dielectric properties of the H9 HA are strongly affected by the presence of the monoclonal antibody F10 and that the terahertz dielectric loss tangent can be used to detect the antibody binding at lower concentrations than the standard ELISA test.

  6. Tunnelling current-voltage characteristics of Angstrom gaps measured with terahertz time-domain spectroscopy

    PubMed Central

    Kim, Joon-Yeon; Kang, Bong Joo; Bahk, Young-Mi; Kim, Yong Seung; Park, Joohyun; Kim, Won Tae; Rhie, Jiyeah; Han, Sanghoon; Jeon, Hyeongtag; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

    2016-01-01

    Quantum tunnelling becomes inevitable as gap dimensions in metal structures approach the atomic length scale, and light passing through these gaps can be used to examine the quantum processes at optical frequencies. Here, we report on the measurement of the tunnelling current through a 3-Å-wide metal-graphene-metal gap using terahertz time-domain spectroscopy. By analysing the waveforms of the incident and transmitted terahertz pulses, we obtain the tunnelling resistivity and the time evolution of the induced current and electric fields in the gap and show that the ratio of the applied voltage to the tunnelling current is constant, i.e., the gap shows ohmic behaviour for the strength of the incident electric field up to 30 kV/cm. We further show that our method can be extended and applied to different types of nanogap tunnel junctions using suitable equivalent RLC circuits for the corresponding structures by taking an array of ring-shaped nanoslots as an example. PMID:27357346

  7. The Development of a Semtex-H Simulant for Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Greenall, N.; Valavanis, A.; Desai, H. J.; Acheampong, D. O.; Li, L. H.; Cunningham, J. E.; Davies, A. G.; Linfield, E. H.; Burnett, A. D.

    2016-11-01

    The development and use of terahertz (THz) frequency spectroscopy systems for security screening has shown an increased growth over the past 15 years. In order to test these systems in real-world situations, safe simulants of illicit materials, such as Semtex-H, are required. Ideally, simulants should mimic key features of the material of interest, such that they at least resemble or even appear indistinguishable from the materials of interest to the interrogating technique(s), whilst not having hazardous or illicit properties. An ideal simulant should have similar physical properties (malleability, density, surface energy and volatility to the material of interest); be non-toxic and easy to clean and decontaminate from surfaces; be recyclable or disposable; and be useable in a public environment. Here, we present a method for developing such an explosive simulant (for Semtex-H) based on a database of THz spectra of common organic molecules, and the use of a genetic algorithm to select a mixture of compounds automatically to form such a simulant. Whilst we focus on a security application, this work could be applied to various other contexts, where the material of interest is dangerous, impractical or costly. We propose four mixtures that could then be used to test the spectral response of any instrument, working at terahertz frequencies, without the need for an explosive substance.

  8. Discrimination of Transgenic Rice containing the Cry1Ab Protein using Terahertz Spectroscopy and Chemometrics

    NASA Astrophysics Data System (ADS)

    Xu, Wendao; Xie, Lijuan; Ye, Zunzhong; Gao, Weilu; Yao, Yang; Chen, Min; Qin, Jianyuan; Ying, Yibin

    2015-07-01

    Spectroscopic techniques combined with chemometrics methods have proven to be effective tools for the discrimination of objects with similar properties. In this work, terahertz time-domain spectroscopy (THz-TDS) combined with discriminate analysis (DA) and principal component analysis (PCA) with derivative pretreatments was performed to differentiate transgenic rice (Hua Hui 1, containing the Cry1Ab protein) from its parent (Ming Hui 63). Both rice samples and the Cry1Ab protein were ground and pressed into pellets for terahertz (THz) measurements. The resulting time-domain spectra were transformed into frequency-domain spectra, and then, the transmittances of the rice and Cry1Ab protein were calculated. By applying the first derivative of the THz spectra in conjunction with the DA model, the discrimination of transgenic from non-transgenic rice was possible with accuracies up to 89.4% and 85.0% for the calibration set and validation set, respectively. The results indicated that THz spectroscopic techniques and chemometrics methods could be new feasible ways to differentiate transgenic rice.

  9. Discrimination of Transgenic Rice containing the Cry1Ab Protein using Terahertz Spectroscopy and Chemometrics

    PubMed Central

    Xu, Wendao; Xie, Lijuan; Ye, Zunzhong; Gao, Weilu; Yao, Yang; Chen, Min; Qin, Jianyuan; Ying, Yibin

    2015-01-01

    Spectroscopic techniques combined with chemometrics methods have proven to be effective tools for the discrimination of objects with similar properties. In this work, terahertz time-domain spectroscopy (THz-TDS) combined with discriminate analysis (DA) and principal component analysis (PCA) with derivative pretreatments was performed to differentiate transgenic rice (Hua Hui 1, containing the Cry1Ab protein) from its parent (Ming Hui 63). Both rice samples and the Cry1Ab protein were ground and pressed into pellets for terahertz (THz) measurements. The resulting time-domain spectra were transformed into frequency-domain spectra, and then, the transmittances of the rice and Cry1Ab protein were calculated. By applying the first derivative of the THz spectra in conjunction with the DA model, the discrimination of transgenic from non-transgenic rice was possible with accuracies up to 89.4% and 85.0% for the calibration set and validation set, respectively. The results indicated that THz spectroscopic techniques and chemometrics methods could be new feasible ways to differentiate transgenic rice. PMID:26154950

  10. Parallel-Plate Waveguide Terahertz Time Domain Spectroscopy for Ultrathin Conductive Films

    NASA Astrophysics Data System (ADS)

    Razanoelina, M.; Kinjo, R.; Takayama, K.; Kawayama, I.; Murakami, H.; Mittleman, Daniel M.; Tonouchi, M.

    2015-12-01

    Development of techniques for characterization of extremely thin films is an important challenge in terahertz (THz) science and applications. Spectroscopic measurements of materials on the nanometer scale or of atomic layer thickness (2D materials) require a sufficient terahertz wave-matter interaction length, which is challenging to achieve in conventional transmission geometry. Waveguide-based THz spectroscopy offers an alternative method to overcome this problem. In this paper, we investigate a new parallel-plate waveguide (PPWG) technique for measuring dielectric properties of ultrathin gold films, in which we mount the thin film sample at the center of the waveguide. We discuss a model of THz dielectric parameter extraction based on waveguide theory and analyze the response of thin films for both transverse magnetic (TM) and transverse electric (TE) waveguide modes. In contrast to other waveguide methods, our approach enables comparison of the material response with different electromagnetic field distributions without significantly changing the experimental setup. As a result, we demonstrate that TE modes have a better sensitivity to the properties of the thin film. For prototype test samples, optical parameters extracted using our method are in good agreement with literature values.

  11. Multiple regimes of carrier cooling in photoexcited graphene probed by time-resolved terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Frenzel, A. J.; Gabor, N. M.; Herring, P. K.; Fang, W.; Kong, J.; Jarillo-Herrero, P.; Gedik, N.

    2013-03-01

    Energy relaxation and cooling of photoexcited charge carriers in graphene has recently attracted significant attention due to possible hot carrier effects, large quantum efficiencies, and photovoltaic applications. However, the details of these processes remain poorly understood, with many conflicting interpretations reported. Here we use time-resolved terahertz spectroscopy to explore multiple relaxation and cooling regimes in graphene in order to elucidate the fundamental physical processes which occur upon photoexcitation of charge carriers. We observe a novel negative terahertz photoconductivity that results from the unique linear dispersion and allows us to measure the electron temperature with ultrafast time resolution. Additionally, we present measurements of the relaxation dynamics over a wide range of excitation fluence. By varying the pump photon energy, we demonstrate that cooling dynamics of photoexcited carriers depend on the amount of energy deposited in the graphene system by the pump pulse, not the number of absorbed photons. The data suggest that fundamentally different regimes are encountered for different excitation fluences. These results may provide a unifying framework for reconciling various measurements of energy relaxation and cooling in graphene.

  12. The Development of a Semtex-H Simulant for Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Greenall, N.; Valavanis, A.; Desai, H. J.; Acheampong, D. O.; Li, L. H.; Cunningham, J. E.; Davies, A. G.; Linfield, E. H.; Burnett, A. D.

    2017-03-01

    The development and use of terahertz (THz) frequency spectroscopy systems for security screening has shown an increased growth over the past 15 years. In order to test these systems in real-world situations, safe simulants of illicit materials, such as Semtex-H, are required. Ideally, simulants should mimic key features of the material of interest, such that they at least resemble or even appear indistinguishable from the materials of interest to the interrogating technique(s), whilst not having hazardous or illicit properties. An ideal simulant should have similar physical properties (malleability, density, surface energy and volatility to the material of interest); be non-toxic and easy to clean and decontaminate from surfaces; be recyclable or disposable; and be useable in a public environment. Here, we present a method for developing such an explosive simulant (for Semtex-H) based on a database of THz spectra of common organic molecules, and the use of a genetic algorithm to select a mixture of compounds automatically to form such a simulant. Whilst we focus on a security application, this work could be applied to various other contexts, where the material of interest is dangerous, impractical or costly. We propose four mixtures that could then be used to test the spectral response of any instrument, working at terahertz frequencies, without the need for an explosive substance.

  13. Spectroscopy study of ephedrine hydrochloride and papaverine hydrochloride in terahertz range

    NASA Astrophysics Data System (ADS)

    Deng, Fusheng; Shen, Jingling; Wang, Guangqin; Liang, Meiyan

    2008-12-01

    The terahertz(THz) fingerprint spectra of Ephedrine Hydrochloride and Papaverine Hydrochloride have been measured using THz time-domain Spectroscopy (THz-TDS) system in the region of 0.2~2.6 THz. To explain the spectra, both gas-phase simulation methods and solid-state simulation methods were performed in the efforts to extract pictures of the molecular interior vibrational modes. By comparing the results of various gas-phase simulation methods, It was found that using the semi-empirical theory is more applicable than the density functional theory (DFT) for some chemical compounds. In the solid-state calculations, solid-state density functional theory (DFT) was employed to obtain the vibration frequencies and Difference-Dipole Method (DDM) was used to calculate the corresponding infrared (IR) intensity. In the process of calculating the IR intensity of Papaverine Hydrochloride in terahertz range, we found that the results by Hirshfeld partitioning method agree better with the experiments than the ones derived from Mulliken atomic charges. Moreover, the accuracy of simulation results depends on the basis sets and grid size being chosen.

  14. Terahertz Circular Dichroism Spectroscopy: A Potential Approach to the In Situ Detection of Life's Metabolic and Genetic Machinery

    NASA Astrophysics Data System (ADS)

    Xu, Jing; Ramian, Gerald J.; Galan, Jhenny F.; Savvidis, Pavlos G.; Scopatz, Anthony Michael; Birge, Robert R.; Allen, S. James; Plaxco, Kevin W.

    2003-11-01

    We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regardless of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules (>500 atoms) as the catalysts with which they perform their metabolic and replicative functions. We also argue that nearly all such macromolecules will absorb strongly at terahertz frequencies and exhibit significant circular dichroism, and that this circular dichroism unambiguously distinguishes biological from abiological materials. Lastly, we describe several approaches to the fabrication of a terahertz circular dichroism spectrometer and provide preliminary experimental indications of their feasibility. Because terahertz circular dichroism signals arise from the molecular machinery necessary to carry out life's metabolic and genetic processes, this life-detection method differs fundamentally from more well-established approaches based on the detection of isotopic fractionation, "signature" carbon compounds, disequilibria, or other by-products of metabolism. Moreover, terahertz circular dichroism spectroscopy detects this machinery in a manner that makes few, if any, assumptions as to its chemical nature or the processes that it performs.

  15. Time domain terahertz spectroscopy of semiconductor bulk and multiple quantum wells structures

    NASA Astrophysics Data System (ADS)

    Chen, Yue

    A time-domain terahertz spectroscopic system with high source power (average power > 10 nW) and high signal-to- noise ratio (>104) was developed and used to study ultrafast electronic processes in semiconductor structures. The physics of the spectroscopy, the theoretical basis of the interferometry, the model of the electron-electromagnetic field interaction, and the principle of experimental data processing are presented. The first direct measurement of the intervalley scattering time in In 0.53Ga0.47As was performed. The intervalley scattering time constants obtained were τLΓ = 35 fs and τLΓ = 450 fs. The spectroscopic data showed that at low carrier density the carrier- carrier scattering is unimportant. The intervalley deformation potential was obtained from the measured intervalley scattering time constant τ LΓ. The transient conductivity was obtained using time-domain terahertz spectroscopy. The frequency dependent terahertz spectroscopy enabled us to uniquely determine the transient mobility and density. The transient electron mobility is ~5200 cm2/Vs, which is less than the Hall mobility. For large photocarrier densities, this discrepancy is attributed to the additional momentum relaxation associated with electron-hole scattering. Using pump pulses with wavelength of 810 run, the electron trapping time in low-temperature-grown GaAs was accurately determined. The measured trapping time is slightly larger than that observed from a band-edge pump- probe measurements. We argue that the terahertz technique provides the most reliable measure of carrier lifetime due to the unique interaction. The carrier dynamics of low-temperature-grown InGaAs bulk and InGaAs/InAlAs multiple quantum wells were investigated. We were able to differentiate the two dominant mechanisms in the electron decay process, trapping and recombination. A trapping time as fast as 1.3-2.6 ps was observed for photo-excited electrons. The effects of Be-doping and growth temperature on the

  16. Rapid and label-free detection and assessment of bacteria by terahertz time-domain spectroscopy.

    PubMed

    Yang, Xiang; Wei, Dongshan; Yan, Shihan; Liu, Yueping; Yu, Shu; Zhang, Mingkun; Yang, Zhongbo; Zhu, Xiaoyan; Huang, Qing; Cui, Hong-Liang; Fu, Weiling

    2016-10-01

    Here we demonstrated the potential and applicability of terahertz (THz) spectroscopy to detect four commonly found bacteria in the infectious diseases. Besides the different spectral characteristics between bacterial species, THz absorption differences for living bacteria, dead bacteria and bacterial powder of the same species were also investigated. Our results revealed that small differences in water contents between bacterial cells account for distinct discrepancies of the absorption coefficients, which can be used for bacterial species identification. Furthermore, living and dead bacteria showed different absorption coefficients as a result of their different hydration levels, suggesting that THz spectroscopy can be used to rapidly assess the living state of bacteria under test. Our results clearly demonstrated the ability of THz spectroscopy for time-saving and label-free detection of bacteria with minimal sample preparation, potentially to be utilized for point-of-care tests in the near future. Schematic representation of bacterial detection by THz spectroscopy. Different bacteria have distinctive absorption coefficients as a result of their different water contents.

  17. A review of the electrical properties of semiconductor nanowires: insights gained from terahertz conductivity spectroscopy

    NASA Astrophysics Data System (ADS)

    Joyce, Hannah J.; Boland, Jessica L.; Davies, Christopher L.; Baig, Sarwat A.; Johnston, Michael B.

    2016-10-01

    Accurately measuring and controlling the electrical properties of semiconductor nanowires is of paramount importance in the development of novel nanowire-based devices. In light of this, terahertz (THz) conductivity spectroscopy has emerged as an ideal non-contact technique for probing nanowire electrical conductivity and is showing tremendous value in the targeted development of nanowire devices. THz spectroscopic measurements of nanowires enable charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities to be measured with high accuracy and high throughput in a contact-free fashion. This review spans seminal and recent studies of the electronic properties of nanowires using THz spectroscopy. A didactic description of THz time-domain spectroscopy, optical pump–THz probe spectroscopy, and their application to nanowires is included. We review a variety of technologically important nanowire materials, including GaAs, InAs, InP, GaN and InN nanowires, Si and Ge nanowires, ZnO nanowires, nanowire heterostructures, doped nanowires and modulation-doped nanowires. Finally, we discuss how THz measurements are guiding the development of nanowire-based devices, with the example of single-nanowire photoconductive THz receivers.

  18. Intrinsic carrier multiplication efficiency in bulk Si crystals evaluated by optical-pump/terahertz-probe spectroscopy

    SciTech Connect

    Yamashita, G.; Nagai, M. E-mail: ashida@mp.es.osaka-u.ac.jp; Ashida, M. E-mail: ashida@mp.es.osaka-u.ac.jp; Matsubara, E.; Kanemitsu, Y.

    2014-12-08

    We estimated the carrier multiplication efficiency in the most common solar-cell material, Si, by using optical-pump/terahertz-probe spectroscopy. Through close analysis of time-resolved data, we extracted the exact number of photoexcited carriers from the sheet carrier density 10 ps after photoexcitation, excluding the influences of spatial diffusion and surface recombination in the time domain. For incident photon energies greater than 4.0 eV, we observed enhanced internal quantum efficiency due to carrier multiplication. The evaluated value of internal quantum efficiency agrees well with the results of photocurrent measurements. This optical method allows us to estimate the carrier multiplication and surface recombination of carriers quantitatively, which are crucial for the design of the solar cells.

  19. Density Detection of Aligned Nanowire Arrays Using Terahertz Time-Domain Spectroscopy.

    PubMed

    Xiang, Wenfeng; Wang, Xin; Liu, Yuan; Zhang, JiaQi; Zhao, Kun

    2016-12-01

    A rapid technique is necessary to quantitatively detect the density of nanowire (NW) and nanotube arrays in one-dimensional devices which have been identified as useful building blocks for nanoelectronics, optoelectronics, biomedical devices, etc. Terahertz (THz) time-domain spectroscopy was employed in this research to detect the density of aligned Ni NW arrays. The transmitted amplitude of THz peaks and optical thickness of NW arrays was found to be the effective parameters to analyze the density change of NW arrays. Owing to the low multiple scattering and high order of Ni NW arrays, a linear relationship was observed for the transmitted amplitude and optical thickness regarding NW density, respectively. Therefore, THz technique may be used as a promising tool to characterize the density of one-dimensional structures in the large-scale integrated nanodevice fabrication.

  20. Ultrafast conductivity in a low-band-gap polyphenylene and fullerene blend studied by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Němec, Hynek; Nienhuys, Han-Kwang; Perzon, Erik; Zhang, Fengling; Inganäs, Olle; Kužel, Petr; Sundström, Villy

    2009-06-01

    Time-resolved terahertz spectroscopy and Monte Carlo simulations of charge-carrier motion are used to investigate photoinduced transient conductivity in a blend of a low-band-gap polyphenylene copolymer and fullerene derivative. The optical excitation pulse generates free holes delocalized on polymer chains. We show that these holes exhibit a very high initial mobility as their initial excess energy facilitates their transport over defects (potential barriers) on polymer chains. The conductivity then drops down rapidly within 1 ps, and we demonstrate that this decrease occurs essentially by two mechanisms. First, the carriers loose their excess energy and they thus become progressively localized between the on-chain potential barriers—this results in a mobility decay with a rate of (180fs)-1 . Second, carriers are trapped at defects (potential wells) with a capture rate of (860fs)-1 . At longer time scales, populations of mobile and trapped holes reach a quasiequilibrium state and further conductivity decrease becomes very slow.

  1. Absolute terahertz power measurement of a time-domain spectroscopy system.

    PubMed

    Globisch, Björn; Dietz, Roman J B; Göbel, Thorsten; Schell, Martin; Bohmeyer, Werner; Müller, Ralf; Steiger, Andreas

    2015-08-01

    We report on, to the best of our knowledge, the first absolute terahertz (THz) power measurement of a photoconductive emitter developed for time-domain spectroscopy (TDS). The broadband THz radiation emitted by a photoconductor optimized for the excitation with 1550-nm femtosecond pulses was measured by an ultrathin pyroelectric thin-film (UPTF) detector. We show that this detector has a spectrally flat transmission between 100 GHz and 5 THz due to special conductive electrodes on both sides of the UPTF. Its flat responsivity allows the calibration with a standard detector that is traceable to the International System of Units (SI) at the THz detector calibration facility of PTB. Absolute THz power in the range from below 1 μW to above 0.1 mW was measured.

  2. Hyper sausage neuron: Recognition of transgenic sugar-beet based on terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Jianjun; Li, Zhi; Hu, Fangrong; Chen, Tao; Du, Yong; Xin, Haitao

    2015-01-01

    This paper presents a novel approach for identification of terahertz (THz) spectral of genetically modified organisms (GMOs) based on Hyper Sausage Neuron (HSN), and THz transmittance spectra of some typical transgenic sugar-beet samples are investigated to demonstrate its feasibility. Principal component analysis (PCA) is applied to extract features of the spectrum data, and instead of the original spectrum data, the feature signals are fed into the HSN pattern recognition, a new multiple weights neural network (MWNN). The experimental result shows that the HSN model not only can correctly classify different types of transgenic sugar-beets, but also can reject identity non similar samples in the same type. The proposed approach provides a new effective method for detection and identification of GMOs by using THz spectroscopy.

  3. The Vibrational Spectra of Bactericide molecules: Terahertz Spectroscopy and Density Functional Theory Calculations

    NASA Astrophysics Data System (ADS)

    Wang, Xiaowei; Wang, Qiang

    2011-02-01

    In the room temperature and nitrogen conditions, we presented well-resolved absorption spectra and indexes of refraction of bactericide molecules in the far infrared radiation (FIR) spectral region recorded by terahertz time-domain spectroscopy (THz-TDS). As illustrative examples we discussed the absorption spectra of captan and folpet in THz region. The absorption coefficient and index of refraction of them were obtained. Meanwhile, density functional theory (DFT) with software package Gaussian 03 using B3LYP theory was employed for optimization and vibration analysis. With the help of Gaussian View 3.09, the distinct absorption peaks of those molecules were assigned with reliable accuracy. They were caused by intermolecular hydrogen-bonding, molecular torsion or vibration modes, absorption of water molecules, etc. As the absorption spectra are highly sensitive to the overall structure and configuration of the molecules, the THz-TDS procedure can provide a direct fingerprint of the molecular structure or conformational state of a compound.

  4. Multiwavelength terahertz-wave parametric generator for one-pulse spectroscopy

    NASA Astrophysics Data System (ADS)

    Murate, Kosuke; Hayashi, Shin’ichiro; Kawase, Kodo

    2017-03-01

    In this study, the simultaneous generation of multiwavelength terahertz (THz) waves by an injection-seeded THz parametric generator (is-TPG) was achieved for the first time. The output and stability of the multiwavelength THz waves were equivalent to those of the THz waves generated via a single-wavelength is-TPG. Spatial separation of frequencies and high-sensitivity detection were achieved by converting the THz waves to near-infrared detection beams. Furthermore, one-pulse spectroscopy of saccharides was realized, and a dynamic range of more than 60 dB was obtained. The results demonstrated the possibility of using the is-TPG to significantly shorten the measurement times of spectroscopic systems.

  5. Nonlinear terahertz spectroscopy of Higgs mode in s-wave superconductors

    NASA Astrophysics Data System (ADS)

    Matsunaga, Ryusuke; Shimano, Ryo

    2017-02-01

    We review our recent experiments of ultrafast dynamics in s-wave superconductors Nb1-x Ti x N by using nonlinear terahertz (THz) spectroscopy. The free oscillation of the Higgs mode, i.e. the amplitude mode of the superconducting order parameter, is observed after instantaneous injection of quasiparticles at the superconducting gap edge by an intense monocycle THz pulse. The ultrafast nonequilibrium dynamics of the order parameter under the strong AC driving field with the photon energy tuned below the superconducting gap is also investigated. A resonant nonlinear interaction between the Higgs mode and the electromagnetic field is revealed, as manifested by an efficient THz third-harmonic generation from the superconductor.

  6. Identification of Transgenic Organisms Based on Terahertz Spectroscopy and Hyper Sausage Neuron

    NASA Astrophysics Data System (ADS)

    Liu, J.; Li, Zh.; Hu, F.; Chen, T.; Du, Y.; Xin, H.

    2015-03-01

    This paper presents a novel approach for identifi cation of terahertz (THz) spectra of genetically modifi ed organisms (GMOs) based on hyper sausage neuron (HSN), and THz transmittance spectra of some typical transgenic sugarbeet samples are investigated to demonstrate its feasibility. Principal component analysis (PCA) is applied to extract features of the spectrum data, and instead of the original spectrum data, the feature signals are fed into the HSN pattern recognition, a new multiple weights neural network (MWNN). The experimental result shows that the HSN model not only can correctly classify different types of transgenic sugar-beets, but also can reject nonsimilar samples of the same type. The proposed approach provides a new effective method for detection and identification of genetically modified organisms by using THz spectroscopy.

  7. Non-destructive testing of composite materials using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Yakovlev, Egor V.; Zaytsev, Kirill I.; Chernomyrdin, Nikita V.; Gavdush, Arsenii A.; Zotov, Arsen K.; Nikonovich, Maxim Y.; Yurchenko, Stanislav O.

    2016-04-01

    Development of novel methods for non-destructive evaluation of composite materials (CMs) at manufacturing and operational stages remains challenging problem of applied physics, optics and material science. In this paper, we have considered the ability to use the terahertz (THz) time-domain spectroscopy (TDS) for non-destructive evaluation of CMs. By combining the TDS technique with appropriate methods of solving the inverse ill-posed problems, we have shown that TDS could be applied for CM testing. At first, we have demonstrated that TDS could be used to control the polymerization process and, as a consequence, the CM binder curing. Secondary, we have shown the ability to detect the internal defects (non-impregnated voids) inside the CMs via the TDS-based THz time-of-flight tomography. Thereby, the results of our study allow highlighting the prospective of non-destructive evaluation of CMs using the TDS.

  8. Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

    SciTech Connect

    Kamaraju, N. Taylor, A. J.; Prasankumar, R. P.; Pan, W.; Reno, J.; Ekenberg, U.; Gvozdić, D. M.; Boubanga-Tombet, S.; Upadhya, P. C.

    2015-01-19

    Two-dimensional hole gases (2DHGs) have attracted recent attention for their unique quantum physics and potential applications in areas including spintronics and quantum computing. However, their properties remain relatively unexplored, motivating the use of different techniques to study them. We used terahertz magneto-optical spectroscopy to investigate the cyclotron resonance frequency in a high mobility 2DHG, revealing a nonlinear dependence on the applied magnetic field. This is shown to be due to the complex non-parabolic valence band structure of the 2DHG, as verified by multiband Landau level calculations. We also find that impurity scattering dominates cyclotron resonance decay in the 2DHG, in contrast with the dominance of superradiant damping in two-dimensional electron gases. Our results shed light on the properties of 2DHGs, motivating further studies of these unique 2D nanosystems.

  9. Far-infrared vibrational modes of DNA components studied by terahertz time-domain spectroscopy.

    PubMed

    Fischer, B M; Walther, M; Uhd Jepsen, P

    2002-11-07

    The far-infrared dielectric function of a wide range of organic molecules is dominated by vibrations involving a substantial fraction of the atoms forming the molecule and motion associated with intermolecular hydrogen bond vibrations. Due to their collective nature such modes are highly sensitive to the intra- and intermolecular structure and thus provide a unique fingerprint of the conformational state of the molecule and effects of its environment. We demonstrate the use of terahertz time-domain spectroscopy (THz-TDS) for recording the far-infrared (0.5-4.0 THz) dielectric function of the four nucleobases and corresponding nucleosides forming the building blocks of deoxyribose nucleic acid (DNA). We observe numerous distinct spectral features with large differences between the molecules in both frequency-dependent absorption coefficient and index of refraction. Assisted by results from density-functional calculations we interpret the origin of the observed resonances as vibrations of hydrogen bonds between the molecules.

  10. Rapid determination of saponification value and polymer content of vegetable and fish oils by terahertz spectroscopy.

    PubMed

    Jiang, Feng Ling; Ikeda, Ikuo; Ogawa, Yuichi; Endo, Yasushi

    2012-01-01

    A rapid method for determining the saponification value (SV) and polymer content of vegetable and fish oils using the terahertz (THz) spectroscopy was developed. When the THz absorption spectra for vegetable and fish oils were measured in the range of 20 to 400 cm⁻¹, two peaks were seen at 77 and 328 cm⁻¹. The level of absorbance at 77 cm⁻¹ correlated well with the SV. When the THz absorption spectra of thermally treated high-oleic safflower oils were measured, the absorbance increased with heating time. The polymer content in thermally treated oil correlated with the absorbance at 77 cm⁻¹. These results demonstrate that the THz spectrometry is a suitable non-destructive technique for the rapid determination of the SV and polymer content of vegetable and fish oils.

  11. Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

    SciTech Connect

    Kamaraju, N.; Pan, W.; Ekenberg, U.; Gvozdić, D. M.; Boubanga-Tombet, S.; Upadhya, P. C.; Reno, J.; Taylor, A. J.; Prasankumar, R. P.

    2015-01-21

    Two-dimensional hole gases (2DHGs) have attracted recent attention for their unique quantum physics and potential applications in areas including spintronics and quantum computing. However, their properties remain relatively unexplored, motivating the use of different techniques to study them. We then used terahertz magneto-optical spectroscopy to investigate the cyclotron resonance frequency in a high mobility 2DHG, revealing a nonlinear dependence on the applied magnetic field. This is shown to be due to the complex non-parabolic valence band structure of the 2DHG, as verified by multiband Landau level calculations. We also found that impurity scattering dominates cyclotron resonance decay in the 2DHG, in contrast with the dominance of superradiant damping in two-dimensional electron gases. Our results shed light on the properties of 2DHGs, motivating further studies of these unique 2D nanosystems.

  12. Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

    DOE PAGES

    Kamaraju, N.; Pan, W.; Ekenberg, U.; ...

    2015-01-21

    Two-dimensional hole gases (2DHGs) have attracted recent attention for their unique quantum physics and potential applications in areas including spintronics and quantum computing. However, their properties remain relatively unexplored, motivating the use of different techniques to study them. We then used terahertz magneto-optical spectroscopy to investigate the cyclotron resonance frequency in a high mobility 2DHG, revealing a nonlinear dependence on the applied magnetic field. This is shown to be due to the complex non-parabolic valence band structure of the 2DHG, as verified by multiband Landau level calculations. We also found that impurity scattering dominates cyclotron resonance decay in the 2DHG,more » in contrast with the dominance of superradiant damping in two-dimensional electron gases. Our results shed light on the properties of 2DHGs, motivating further studies of these unique 2D nanosystems.« less

  13. Degradation diagnosis of ultrahigh-molecular weight polyethylene with terahertz-time-domain spectroscopy

    SciTech Connect

    Yamamoto, Kohji; Yamaguchi, Mariko; Tani, Masahiko; Hangyo, Masanori; Teramura, Satoshi; Isu, Toshiro; Tomita, Naohide

    2004-11-29

    We investigated ultrahigh-molecular-weight-polyethylene (UHMWPE) samples prepared by various conditions with terahertz-time-domain spectroscopy (THz-TDS). Degradation of the virgin UHMWPE samples by {gamma} irradiation induced a drastic increase of the absorption ranging continuously over the THz region. The increase of the absorption continuum is interpreted to originate in the oxidation of the amorphous region within the sample. Only slight THz spectral changes induced by the {gamma} irradiation were, however, observed for the UHMWPE samples doped with 0.1 and 0.3 wt % vitamin E. This result agrees with the earlier indication that vitamin E has an antidegradation effect on UHMWPE. The present result shows that the THz-TDS can be used for the quality control of UHMWPE by monitoring the absorption continuum in the THz region.

  14. Doppler-Limited Spectroscopy with a Decade-Spanning Terahertz Frequency Comb

    NASA Astrophysics Data System (ADS)

    Finneran, Ian A.; Good, Jacob T.; Holland, Daniel; Carroll, Brandon; Allodi, Marco A.; Blake, Geoffrey

    2015-06-01

    We report the generation and detection of a decade-spanning TeraHertz (THz) frequency comb (0.15-2.4 THz) using two Ti:Sapphire femtosecond laser oscillators and ASynchronous OPtical Sampling THz Time-Domain Spectroscopy (ASOPS-THz-TDS). The measured linewidth of the comb at 1.5 THz is 3 kHz over a 60 second acquisition. With time-domain detection of the comb, we measure three transitions of water vapor at 10 mTorr between 1-2 THz with an average Doppler-limited fractional uncertainty of 5.9×10-8. Significant improvements in bandwidth, resolution, and sensitivity are possible with existing technologies and will enable future studies of jet-cooled hydrogen-bonded clusters.

  15. Terahertz spectroscopy of brain tissue from a mouse model of Alzheimer's disease

    NASA Astrophysics Data System (ADS)

    Shi, Lingyan; Shumyatsky, Pavel; Rodríguez-Contreras, Adrián; Alfano, Robert

    2016-01-01

    The terahertz (THz) absorption and index of refraction of brain tissues from a mouse model of Alzheimer's disease (AD) and a control wild-type (normal) mouse were compared using THz time-domain spectroscopy (THz-TDS). Three dominating absorption peaks associated to torsional-vibrational modes were observed in AD tissue, at about 1.44, 1.8, and 2.114 THz, closer to the peaks of free tryptophan molecules than in normal tissue. A possible reason is that there is more free tryptophan in AD brain tissue, while in normal brain tissue more tryptophan is attached to other molecules. Our study suggests that THz-absorption modes may be used as an AD biomarker fingerprint in brain, and that THz-TDS is a promising technique for early diagnosis of AD.

  16. Measuring the Elasticity of Poly‐l‐Proline Helices with Terahertz Spectroscopy

    PubMed Central

    Ruggiero, Michael T.; Sibik, Juraj; Orlando, Roberto; Zeitler, J. Axel

    2016-01-01

    Abstract The rigidity of poly‐l‐proline is an important contributor to the stability of many protein secondary structures, where it has been shown to strongly influence bulk flexibility. The experimental Young's moduli of two known poly‐l‐proline helical forms, right‐handed all‐cis (Form I) and left‐handed all‐trans (Form II), were determined in the crystalline state by using an approach that combines terahertz time‐domain spectroscopy, X‐ray diffraction, and solid‐state density functional theory. Contrary to expectations, the helices were found to be considerably less rigid than many other natural and synthetic polymers, as well as differing greatly from each other, with Young's moduli of 4.9 and 9.6 GPa for Forms I and II, respectively. PMID:27121300

  17. Collective vibrational modes in biological molecules investigated by terahertz time-domain spectroscopy.

    PubMed

    Walther, M; Plochocka, P; Fischer, B; Helm, H; Uhd Jepsen, P

    2002-01-01

    We present well-resolved absorption spectra of biological molecules in the far-IR (FIR) spectral region recorded by terahertz time-domain spectroscopy (THz-TDS). As an illustrative example we discuss the absorption spectra of benzoic acid, its monosubstitutes salicylic acid (2-hydroxy-benzoic acid), 3- and 4-hydroxybenzoic acid, and aspirin (acetylsalicylic acid) in the spectral region between 18 and 150 cm(-1). The spectra exhibit distinct features originating from low-frequency vibrational modes caused by intra- or intermolecular collective motion and lattice modes. Due to the collective origin of the observed modes the absorption spectra are highly sensitive to the overall structure and configuration of the molecules, as well as their environment. The THz-TDS procedure can provide a direct fingerprint of the molecular structure or conformational state of a compound.

  18. Terahertz spectroscopy of brain tissue from a mouse model of Alzheimer’s disease

    PubMed Central

    Shi, Lingyan; Shumyatsky, Pavel; Rodríguez-Contreras, Adrián; Alfano, Robert

    2016-01-01

    Abstract. The terahertz (THz) absorption and index of refraction of brain tissues from a mouse model of Alzheimer’s disease (AD) and a control wild-type (normal) mouse were compared using THz time-domain spectroscopy (THz-TDS). Three dominating absorption peaks associated to torsional–vibrational modes were observed in AD tissue, at about 1.44, 1.8, and 2.114 THz, closer to the peaks of free tryptophan molecules than in normal tissue. A possible reason is that there is more free tryptophan in AD brain tissue, while in normal brain tissue more tryptophan is attached to other molecules. Our study suggests that THz-absorption modes may be used as an AD biomarker fingerprint in brain, and that THz-TDS is a promising technique for early diagnosis of AD. PMID:26818714

  19. Crystallization Kinetics of Lead Halide Perovskite Film Monitored by In Situ Terahertz Spectroscopy.

    PubMed

    Park, S J; Kim, A R; Hong, J T; Park, J Y; Lee, S; Ahn, Y H

    2017-01-19

    Vibrational modes in the terahertz (THz) frequency range are good indicators of lead halide perovskite's crystallization phase. We performed real-time THz spectroscopy to monitor the crystallization kinetics in the perovskite films. First, THz absorptance was measured while the perovskite film was annealed at different temperatures. By analyzing the Avrami exponent, we observed an abrupt dimensionality switch (from 1D to 2D) with increasing temperature starting at approximately 90 °C. We also monitored the laser-induced crystallinity enhancement of the preannealed perovskite film. The THz absorptance increased initially, then subsequently decayed over a couple of hours, although the enhancement factor varies depending on the film crystallinity. In particular, the Avrami analysis implied that the light-induced crystallization was assisted by the 1D diffusion processes. The activation photon energy was measured at 2.3 eV, which indicated that enhanced crystallization originated from the photoinduced structural change of residual lead iodide at the grain boundary.

  20. Relaxation dynamics of surface-adsorbed water molecules in nanoporous silica probed by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Yu-Ru; Liu, Kao-Hsiang; Mou, Chung-Yuan; Sun, Chi-Kuang

    2015-08-01

    Relaxation dynamics of an exclusively adsorbed water molecule in mesoporous silica MCM-41-S was studied by using terahertz spectroscopy. With the temperature controlled from 0 to 50 °C, we observed strongly frequency- and temperature-dependent dielectric relaxation responses, implying that, unlike ice, surface-adsorbed water molecules retained flourishing picosecond dynamics. Based on the Debye relaxation model, a relaxation time constant was found to increase from 1.77 to 4.83 ps when the water molecule was cooled from 50 to 0 °C. An activation energy of ˜15 kJ/mol, which was in close agreement with a hydrogen-bonding energy, was further extracted from the Arrhenius analysis. Combined with previous molecular dynamics simulations, our results indicate that the reorientation relaxation originated from the "flip-flop" rotation of a three hydrogen-bonded surface-adsorbed water molecule.

  1. Quantitative Analysis for Monitoring Formulation of Lubricating Oil Using Terahertz Time-Domain Transmission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Tian, Lu; Zhao, Kun; Zhou, Qing-Li; Shi, Yu-Lei; Zhang, Cun-Lin

    2012-04-01

    The quantitative analysis of zinc isopropyl-isooctyl-dithiophosphate (T204) mixed with lube base oil from Korea with viscosity index 70 (T204-Korea70) is presented by using terahertz time-domain spectroscopy (THz-TDS). Compared with the middle-infrared spectra of zinc n-butyl-isooctyl-dithiophosphate (T202) and T204, THz spectra of T202 and T204 show the weak broad absorption bands. Then, the absorption coefficients of the T204-Korea70 system follow Beer's law at the concentration from 0.124 to 4.024%. The experimental absorption spectra of T204-Korea70 agree with the calculated ones based on the standard absorption coefficients of T204 and Korea70. The quantitative analysis enables a strategy to monitor the formulation of lubricating oil in real time.

  2. Optical Reflection Spectroscopy of GEO Objects

    NASA Technical Reports Server (NTRS)

    Seitzer, Patrick; Cardona, Tammaso; Lederer, Susan M.; Cowardin, Heather; Abercromby, Kira J.; Barker, Edwin S.; Bedard, Donald

    2013-01-01

    We report on optical reflection spectroscopy of geosynchronous (GEO) objects in the US Space Surveillance Network (SSN) catalog. These observations were obtained using imaging spectrographs on the 6.5-m Magellan telescopes at the Las Campanas Observatory in Chile. Our goal is to determine the composition of these objects by comparing these spectral observations with ground-based laboratory measurements of spacecraft materials. The observations are all low resolution (1 nm after smoothing) obtained through a 5 arcsecond wide slit and using a grism as the dispersing element. The spectral range covered was from 450 nm to 800 nm. All spectra were flux calibrated using observations of standard stars with the exact same instrumental setup. An effort was made to obtain all observations within a limited range of topocentric phase angle, although the solar incident angle is unknown due to the lack of any knowledge of the attitude of the observed surface at the time of observation.

  3. Effects of multivalent hexacyanoferrates and their ion pairs on water molecule dynamics measured with terahertz spectroscopy.

    PubMed

    DiTucci, Matthew J; Böhm, Fabian; Schwaab, Gerhard; Williams, Evan R; Havenith, Martina

    2017-02-27

    The valency of aqueous solutes plays a large role in determining the extent of ion-water dynamics, which can greatly influence the chemical and physical properties of solutions. In these experiments, broadband Fourier transform terahertz spectroscopy is used to probe perturbations to the low-frequency dynamics of water molecules by three different multivalent hexacyanoferrate salts. K3Fe(CN)6, K4Fe(CN)6 and Na4Fe(CN)6 were investigated as a function of concentration up to their solubility limits using spectral subtractions and fitting with damped harmonic lineshapes. Regions with subtle nonlinearities in amplitude with respect to solute concentration provide insight into ion-pairing events. The extent of nonlinearity suggests that ion pairs are major constituents in solution for all concentrations measured and is consistent with ion-pairing observed at millimolar concentrations by potentiometric and spectroscopic measurements. A lower estimate for the number of water molecules that are influenced by each ion is obtained from the damped harmonic fits. Values of 19, 28 and 25 water molecules with perturbed dynamics are obtained for KFe(CN)6(2-), KFe(CN)6(3-) and NaFe(CN)6(3-) ion pairs, respectively. These values represent dynamical perturbations into a second solvation shell and are consistent with the long-range structural effects observed in recent aqueous nanodrop spectroscopy experiments. Furthermore, the spectral absorptions for hexacyanoferrates are in agreement with a wide range of solutes studied previously using the developing methodology for interpreting terahertz spectra.

  4. Probing charge transfer and hot carrier dynamics in organic solar cells with terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Cunningham, Paul D.; Lane, Paul A.; Melinger, Joseph S.; Esenturk, Okan; Heilweil, Edwin J.

    2016-04-01

    Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (α-6T) as the electron donors and buckminsterfullerene (C60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy in conjunction with TRTS, these two contributions can be disentangled. The sub-picosecond photo-induced conductivity decay dynamics of C60 were revealed to be caused by auto-ionization: the intrinsic process by which charge is generated in molecular solids. In donor-acceptor blends, the long-lived photo-induced conductivity is used for weight fraction optimization of the constituents. In nanoscale multilayer films, the photo-induced conductivity identifies optimal layer thicknesses. In films of ZnPc/C60, electron transfer from ZnPc yields hot charges that localize and become less mobile as they thermalize. Excitation of high-lying Franck Condon states in C60 followed by hole-transfer to ZnPc similarly produces hot charge carriers that self-localize; charge transfer clearly precedes carrier cooling. This picture is contrasted to charge transfer in α-6T/C60, where hole transfer takes place from a thermalized state and produces equilibrium carriers that do not show characteristic signs of cooling and self-localization. These results illustrate the value of terahertz spectroscopic methods for probing charge transfer reactions.

  5. High spectral resolution reflectance spectroscopy of minerals

    USGS Publications Warehouse

    Clark, R.N.; King, T.V.V.; Klejwa, M.; Swayze, G.A.; Vergo, N.

    1990-01-01

    The reflectance spectra of minerals are studied as a function of spectral resolution in the range from 0.2 to 3.0 ??m. Selected absorption bands were studied at resolving powers (??/????) as high as 2240. At resolving powers of approximately 1000, many OH-bearing minerals show diagnostic sharp absorptions at the resolution limit. At low resolution, some minerals may not be distinguishable, but as the resolution is increased, most can be easily identified. As the resolution is increased, many minerals show fine structure, particularly in the OH-stretching overtone region near 1.4 ??m. The fine structure can enhance the ability to discriminate between minerals, and in some cases the fine structure can be used to determine elemental composition. The study shows that high-resolution reflectance spectroscopy of minerals may prove to be a very important tool in the laboratory, in the field using field-portable spectrometers, from aircraft, and from satellites looking at Earth or other planetary surfaces. -from Authors

  6. Reflectance spectroscopy of organic compounds: 1. Alkanes

    USGS Publications Warehouse

    Clark, R.N.; Curchin, J.M.; Hoefen, T.M.; Swayze, G.A.

    2009-01-01

    Reflectance spectra of the organic compounds comprising the alkane series are presented from the ultraviolet to midinfrared, 0.35 to 15.5 /??m. Alkanes are hydrocarbon molecules containing only single carbon-carbon bonds, and are found naturally on the Earth and in the atmospheres of the giant planets and Saturn's moon, Titan. This paper presents the spectral properties of the alkanes as the first in a series of papers to build a spectral database of organic compounds for use in remote sensing studies. Applications range from mapping the environment on the Earth, to the search for organic molecules and life in the solar system and throughout the. universe. We show that the spectral reflectance properties of organic compounds are rich, with major diagnostic spectral features throughout the spectral range studied. Little to no spectral change was observed as a function of temperature and only small shifts and changes in the width of absorption bands were observed between liquids and solids, making remote detection of spectral properties throughout the solar system simpler. Some high molecular weight organic compounds contain single-bonded carbon chains and have spectra similar to alkanes even ' when they fall into other families. Small spectral differences are often present allowing discrimination among some compounds, further illustrating the need to catalog spectral properties for accurate remote sensing identification with spectroscopy.

  7. Investigation of the terahertz vibrational modes of ZIF-8 and ZIF-90 with terahertz time-domain spectroscopy.

    PubMed

    Tan, Nicholas Y; Ruggiero, Michael T; Orellana-Tavra, Claudia; Tian, Tian; Bond, Andrew D; Korter, Timothy M; Fairen-Jimenez, David; Zeitler, J Axel

    2015-11-18

    We present experimental and computational evidence that gate-opening modes for zeolitic imidazole frameworks can be observed at terahertz frequencies. Our work highlights the critical importance to correctly optimise the crystal structure prior to computational lattice dynamics analysis. The results support the hypothesis that the low energy vibrational modes do indeed play a significant role in host-guest interactions for ZIFs, such as gas loading.

  8. Diagnosis of Breast Cancer Using Fluorescence and Reflectance Spectroscopy

    DTIC Science & Technology

    2004-09-01

    breast cancer based on fluorescence and diffuse reflectance spectroscopy . Our first objective include was to characterize the fluorescence properties of...device based on fluorescence and diffuse reflectance spectroscopy has the advantage of being fast, quantitative, and minimally invasive, and has the...Fluorescence and diffuse reflectance spectroscopy in the ultraviolet-visible wavelength range were made with a multi-separation probe at three illumination

  9. Temperature dependence of the point defect properties of GaN thin films studied by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Fang, HeNan; Zhang, Rong; Liu, Bin; Li, YeCao; Fu, DeYi; Li, Yi; Xie, ZiLi; Zhuang, Zhe; Zheng, YouDou; Wu, JingBo; Jin, BiaoBing; Chen, Jian; Wu, PeiHeng

    2013-11-01

    The dielectric functions of GaN for the temperature and frequency ranges of 10-300 K and 0.3-1 THz are obtained using terahertz time-domain spectroscopy. It is found that there are oscillations of the dielectric functions at various temperatures. Physically, the oscillation behavior is attributed to the resonance states of the point defects in the material. Furthermore, the dielectric functions are well fitted by the combination of the simple Drude model together with the classical damped oscillator model. According to the values of the fitting parameters, the concentration and electron lifetime of the point defects for various temperatures are determined, and the temperature dependences of them are in accordance with the previously reported result. Therefore, terahertz time-domain spectroscopy can be considered as a promising technique for investigating the relevant characteristics of the point defects in semiconductor materials.

  10. Investigating tautomeric polymorphism in crystalline anthranilic acid using terahertz spectroscopy and solid-state density functional theory.

    PubMed

    Delaney, Sean P; Witko, Ewelina M; Smith, Tiffany M; Korter, Timothy M

    2012-08-02

    Terahertz spectroscopy is sensitive to the interactions between molecules in the solid-state and recently has emerged as a new analytical tool for investigating polymorphism. Here, this technique is applied for the first time to the phenomenon of tautomeric polymorphism where the crystal structures of anthranilic acid (2-aminobenzoic acid) have been investigated. Three polymorphs of anthranilic acid (denoted Forms I, II and III) were studied using terahertz spectroscopy and the vibrational modes and relative polymorph stabilities analyzed using solid-state density functional theory calculations augmented with London dispersion force corrections. Form I consists of both neutral and zwitterionic molecules and was found to be the most stable polymorph as compared to Forms II and III (both containing only neutral molecules). The simulations suggest that a balance between steric interactions and electrostatic forces is responsible for the favoring of the mixed neutral/zwitterion solid over the all neutral or all zwitterion crystalline arrangements.

  11. Terahertz Spectroscopy of CrH (X 6Σ+) and AlH (X 1Σ+)

    NASA Astrophysics Data System (ADS)

    Halfen, D. T.; Ziurys, L. M.

    2016-12-01

    New laboratory measurements of hydrides have been carried out using terahertz direct absorption spectroscopy. Spin components of the N=2≤ftarrow 1 transition of the free radical CrH (X 6Σ+) have been recorded in the range 730-734 GHz, as well as a new measurement of the J=2≤ftarrow 1 line of AlH (X 1Σ+) near 755 GHz. Both species were created in an AC discharge of H2, argon, and metal vapor. For CrH, the chromium source was Cr(CO)6, while AlH was produced from Al(CH3)3. The J=4.5≤ftarrow 3.5 and 3.5≤ftarrow 2.5 fine-structure components were recorded for CrH, each which consists of resolved proton hyperfine doublets. For AlH, the two main quadrupole components, F=4.5≤ftarrow 3.5 and 3.5≤ftarrow 2.5, of the J=2≤ftarrow 1 transition were observed as blended features. These data were analyzed with previous 1≤ftarrow 0 millimeter/submillimeter measurements with 6Σ and 1Σ Hamiltonians for chromium and aluminum hydrides, respectively, and rotational, fine-structure (CrH only), and hyperfine constants were derived. The new measurements have resulted in refined spectroscopic parameters for both species, as well as direct measurement of the respective 2≤ftarrow 1 rotational transitions. This work also resolves a 10 MHz discrepancy in the frequency of the AlH line. CrH and AlH have already been observed in the photospheres of stars via their electronic transitions. These data will facilitate their discovery at submillimeter/terahertz wavelengths in circumstellar envelopes and perhaps in diffuse clouds.

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

    SciTech Connect

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

    2015-10-26

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

  13. Terahertz time domain spectroscopy allows contactless monitoring of grapevine water status

    PubMed Central

    Santesteban, Luis G.; Palacios, Inés; Miranda, Carlos; Iriarte, Juan C.; Royo, José B.; Gonzalo, Ramón

    2015-01-01

    Agriculture is the sector with the greatest water consumption, since food production is frequently based on crop irrigation. Proper irrigation management requires reliable information on plant water status, but all the plant-based methods to determine it suffer from several inconveniences, mainly caused by the necessity of destructive sampling or of alteration of the plant organ due to contact installation. The aim of this work is to test if terahertz (THz) time domain reflectance measurements made on the grapevine trunk allows contactless monitoring of plant status. The experiments were performed on a potted 14-years-old plant, using a general purpose THz emitter receiver head. Trunk THz time-domain reflection signal proved to be very sensitive to changes in plant water availability, as its pattern follows the trend of soil water content and trunk growth variations. Therefore, it could be used to contactless monitor plant water status. Apart from that, THz reflection signal was observed to respond to light conditions which, according to a specifically designed girdling experiment, was caused by changes in the phloem. This latter results opens a promising field of research for contactless monitoring of phloem activity. PMID:26082791

  14. Molecular recognition and interaction between uracil and urea in solid-state studied by terahertz time-domain spectroscopy.

    PubMed

    Yang, Jingqi; Li, Shaoxian; Zhao, Hongwei; Song, Bo; Zhang, Guoxin; Zhang, Jianbing; Zhu, Yiming; Han, Jiaguang

    2014-11-20

    Using terahertz time-domain spectroscopy characterization, we observe that urea is able to recognize and interact with uracil efficiently even in the solid phase without involving water or solvents. A cocrystal configuration linked by a pair of hydrogen bonds between uracil and urea was formed. The terahertz absorption spectrum of the cocrystal shows a distinct new absorption at 0.8 THz (26.7 cm(-1)), which originates from the intermolecular hydrogen bonding. Both mechanical milling and heating can accelerate the reaction efficiently. Density functional theory was adopted to simulate the vibrational modes of the cocrystal, and the results agree well with the experimental observation. Multiple techniques, including powder X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy, were performed to investigate the reaction process, and they presented supportive evidence. This work enables in-depth understanding of recognition and interaction of urea with nucleobases and comprehension of the denaturation related to RNA. We also demonstrate that terahertz spectroscopy is an effective and alternative tool for online measurement and quality control in pharmaceutical and chemical industries.

  15. Adaptive sampling dual terahertz comb spectroscopy using dual free-running femtosecond lasers

    PubMed Central

    Yasui, Takeshi; Ichikawa, Ryuji; Hsieh, Yi-Da; Hayashi, Kenta; Cahyadi, Harsono; Hindle, Francis; Sakaguchi, Yoshiyuki; Iwata, Tetsuo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Minoshima, Kaoru; Inaba, Hajime

    2015-01-01

    Terahertz (THz) dual comb spectroscopy (DCS) is a promising method for high-accuracy, high-resolution, broadband THz spectroscopy because the mode-resolved THz comb spectrum includes both broadband THz radiation and narrow-line CW-THz radiation characteristics. In addition, all frequency modes of a THz comb can be phase-locked to a microwave frequency standard, providing excellent traceability. However, the need for stabilization of dual femtosecond lasers has often hindered its wide use. To overcome this limitation, here we have demonstrated adaptive-sampling THz-DCS, allowing the use of free-running femtosecond lasers. To correct the fluctuation of the time and frequency scales caused by the laser timing jitter, an adaptive sampling clock is generated by dual THz-comb-referenced spectrum analysers and is used for a timing clock signal in a data acquisition board. The results not only indicated the successful implementation of THz-DCS with free-running lasers but also showed that this configuration outperforms standard THz-DCS with stabilized lasers due to the slight jitter remained in the stabilized lasers. PMID:26035687

  16. Preliminary study on quality evaluation of pecans with terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Bin; Cao, Wei; Mathanker, Sunil; Zhang, Weili; Wang, Ning

    2010-11-01

    This paper reports a preliminary work on a feasibility study of applying terahertz (THz) technology for pecan quality evaluation. A set of native pecan nuts collected in 2009 were used during the experiment. Each pecan nutmeat was manually sliced at a thickness of about 1mm, 2mm, and 3mm and a size of about 2cm (length) ×1cm (width). Pecan shell and inner separator were also cut into the same size. The absorption spectra for the nutmeat slices, shell, and inner separator were collected using a THz time-domain spectroscopy (THz-TDS) developed by a group of researchers at Oklahoma State University. The test results show that nutmeat, shell, and inner separator had different absorption characteristics within the bandwidth of 0.2-2.0 THz. To study the capability of insect damage detection of the THz spectroscopy, the absorption spectra of insects (living manduca sexta and dry pecan weevil) were also collected. Due to high water contents in the insects, very obvious spectral characteristics were found. The results from the preliminary study show a potential of THz technology applied for quality detection of bio-products. However, since bio-products mostly have high water content and are handled under an environment with certain levels of water content, practical issues needs to be further investigated to make the THz technology a feasible tool for quality evaluation.

  17. Feasibility of using terahertz spectroscopy to detect seven different pesticides in wheat flour.

    PubMed

    Maeng, Inhee; Baek, Seung Hyun; Kim, Hwa Yeon; Ok, Gyeong-Sik; Choi, Sung-Wook; Chun, Hyang Sook

    2014-12-01

    This study investigated the feasibility of detecting pesticides using terahertz (THz) spectroscopy in high-density polyethylene and/or wheat flour mixtures. The absorption spectra of seven pesticides (dicofol, chlorpyrifos, chlorpyrifos-methyl, daminozide, imidacloprid, diethyldithiocarbamate, and dimethyldithiocarbamate) were measured in the frequency range 0.1 to 3 THz at room temperature. Five of the seven pesticides exhibited specific absorption peaks in the low-energy THz range. The two remaining pesticides had no specific absorption peaks in this frequency range, but they exhibited different frequency-dependent refractive indices. The absorption coefficients of imidacloprid increased with its increasing weight ratio in high-density polyethylene, and the fitted power absorptions and refractive indices using a Maxwell-Garnett effective medium model were comparable to the measured data. Imidacloprid was also identified from its characteristic absorption peaks in wheat flour mixtures, and a linear relationship between the absorption coefficient and the weight ratio was observed. Our results show the potential of detection of selected pesticides in foods, such as wheat flour, using THz spectroscopy.

  18. Narrow-line waveguide terahertz time-domain spectroscopy of aspirin and aspirin precursors.

    PubMed

    Laman, N; Harsha, S Sree; Grischkowsky, D

    2008-03-01

    Low frequency vibrational modes of pharmaceutical molecules are dependent on the molecule as a whole and can be used for identification purposes. However, conventional Fourier transform far-infrared spectroscopy (FT-IR) and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recently developed, resulting in sharper spectral features. Waveguide THz-TDS consists of forming an ordered polycrystalline film on a metal plate and incorporating that plate in a parallel-plate waveguide, where the film is probed by THz radiation. The planar order of the film on the metal surface strongly reduces the inhomogeneous broadening, while cooling the waveguide to 77 K reduces the homogeneous broadening. This combination results in sharper absorption lines associated with the vibrational modes of the molecule. Here, this technique has been demonstrated with aspirin and its precursors, benzoic acid and salicylic acid, as well as the salicylic acid isomers 3- and 4-hydroxybenzoic acid. Linewidths as narrow as 20 GHz have been observed, rivaling single crystal measurements.

  19. Separation of overlapping vibrational peaks in terahertz spectra using two-dimensional correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Hoshina, Hiromichi; Ishii, Shinya; Otani, Chiko

    2014-07-01

    In this study, the terahertz (THz) absorption spectra of poly(3-hydroxybutyrate) (PHB) were measured during isothermal crystallization at 90-120 °C. The temporal changes in the absorption spectra were analyzed using two-dimensional correlation spectroscopy (2DCOS). In the asynchronous plot, cross peaks were observed around 2.4 THz, suggesting that two vibrational modes overlap in the raw spectrum. By comparing this to the peak at 2.9 THz corresponding to the stretching mode of the helical structure of PHB and the assignment obtained using polarization spectroscopy, we concluded that the high-frequency band could be attributed to the vibration of the helical structure and the low-frequency band to the vibration between the helical structures. The exact frequencies of the overlapping vibrational bands and their assignments provide a new means to inspect the thermal behavior of the intermolecular vibrational modes. The large red-shift of the interhelix vibrational mode suggests a large anharmonicity in the vibrational potential.

  20. EDITORIAL: Terahertz nanotechnology Terahertz nanotechnology

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  1. 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.

  2. Specular Reflection and Diffuse Reflectance Spectroscopy of Soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Studies on the occurrence and effects of specular reflection in mid-infrared spectra of soils have shown that distortions due to specular reflection occur for both organic (humic acid) and non-organic fractions (carbonates, silica, ashed fraction of soil). The results demonstrated explain why the s...

  3. Biomolecular solvation study of proteins in liquid water by a wide range gigahertz-to-terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Charkhesht, Ali; George, Deepu; Nguyen, Vinh

    Solvent dynamics within biomolecular solvation layers play a major role in enzyme activity, but obtaining an accurate and quantitative picture of solvent activity around proteins is challenging. Due to the strong absorption of water in the gigahertz-to-terahertz frequencies, it is challenging to study properties of the solvent dynamics as well as conformational changes protein in water. We have developed a highly sensitive dielectric gigahertz-to-terahertz frequency-domain spectroscopy system for probing the collective dynamics of proteins and solvent. Using this technique, we investigate the complex dielectric response of bovine serum albumin and lysozyme proteins in aqueous environment on a wide frequency range from 0.1 GHz up to 2 THz. We explore the conformation flexibility of proteins and compare the hydration dynamics around proteins to understand the effects of surface-mediated solvent dynamics, relationships among different measures of interfacial solvent dynamics, and protein-mediated solvent dynamics.

  4. Ultrahigh photoconductivity of bandgap-graded CdSxSe1−x nanowires probed by terahertz spectroscopy

    PubMed Central

    Liu, Hongwei; Lu, Junpeng; Yang, Zongyin; Teng, Jinghua; Ke, Lin; Zhang, Xinhai; Tong, Limin; Sow, Chorng Haur

    2016-01-01

    Superiorly high photoconductivity is desirable in optoelectronic materials and devices for information transmission and processing. Achieving high photoconductivity via bandgap engineering in a bandgap-graded semiconductor nanowire has been proposed as a potential strategy. In this work, we report the ultrahigh photoconductivity of bandgap-graded CdSxSe1−x nanowires and its detailed analysis by means of ultrafast optical-pump terahertz-probe (OPTP) spectroscopy. The recombination rates and carrier mobility are quantitatively obtained via investigation of the transient carrier dynamics in the nanowires. By analysis of the terahertz (THz) spectra, we obtain an insight into the bandgap gradient and band alignment to carrier transport along the nanowires. The demonstration of the ultrahigh photoconductivity makes bandgap-graded CdSxSe1−x nanowires a promising candidate as building blocks for nanoscale electronic and photonic devices. PMID:27263861

  5. Conductivity of solvated electrons in hexane investigated with terahertz time-domain spectroscopy.

    PubMed

    Knoesel, Ernst; Bonn, Mischa; Shan, Jie; Wang, Feng; Heinz, Tony F

    2004-07-01

    We present investigations of the transient photoconductivity and recombination dynamics of quasifree electrons in liquid n-hexane and cyclohexane performed using terahertz time-domain spectroscopy (THz-TDS). Quasifree electrons are generated by two-photon photoionization of the liquid using a femtosecond ultraviolet pulse, and the resulting changes in the complex conductivity are probed by a THz electromagnetic pulse at a variable delay. The detection of time-domain wave forms of the THz electric field permits the direct determination of both the real and the imaginary part of the conductivity of the electrons over a wide frequency range. The change in conductivity can be described by the Drude model, thus yielding the quasifree electron density and scattering time. The electron density is found to decay on a time scale of a few hundred picoseconds, which becomes shorter with increasing excitation density. The dynamics can be described by a model that assumes nongeminate recombination between electrons and positive ions. In addition, a strong dependence of the quasifree electron density on temperature is observed, in agreement with a two-state model in which the electron may exist in either a quasifree or a bound state.

  6. Determination of plane stress state using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Zhiyong; Kang, Kai; Wang, Shibin; Li, Lin'an; Xu, Ningning; Han, Jiaguang; He, Mingxia; Wu, Liang; Zhang, Weili

    2016-11-01

    THz wave has been increasingly applied in engineering practice. One of its outstanding advantages is the penetrability through certain optically opaque materials, whose interior properties could be therefore obtained. In this report, we develop an experimental method to determine the plane stress state of optically opaque materials based on the stress-optical law using terahertz time-domain spectroscopy (THz-TDS). In this method, two polarizers are combined into the conventional THz-TDS system to sense and adjust the polarization state of THz waves and a theoretical model is established to describe the relationship between phase delay of the received THz wave and the plane stress applied on the specimen. Three stress parameters that represent the plane stress state are finally determined through an error function of THz wave phase-delay. Experiments were conducted on polytetrafluoroethylene (PTFE) specimen and a reasonably good agreement was found with measurement using traditional strain gauges. The presented results validate the effectiveness of the proposed method. The proposed method could be further used in nondestructive tests for a wide range of optically opaque materials.

  7. Distinguishing Gasoline Engine Oils of Different Viscosities Using Terahertz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Adbul-Munaim, Ali Mazin; Reuter, Marco; Koch, Martin; Watson, Dennis G.

    2015-07-01

    Terahertz-time-domain spectroscopy (THz-TDS) in the range of 0.5-2.0 THz was evaluated for distinguishing among gasoline engine oils of three different grades (SAE 5W-20, 10W-40, and 20W-50) from the same manufacturer. Absorption coefficient showed limited potential and only distinguished ( p < 0.05) the 20W-50 grade from the other two grades in the 1.7-2.0-THz range. Refractive index data demonstrated relatively flat and consistently spaced curves for the three oil grades. ANOVA results confirmed a highly significant difference ( p < 0.0001) in refractive index among each of the three oils across the 0.5-2.0-THz range. Linear regression was applied to refractive index data at 0.25-THz intervals from 0.5 to 2.0 THz to predict kinematic viscosity. All seven linear regression models, intercepts, and refractive index coefficients were highly significant ( p < 0.0001). All models had a similar fit with R 2 ranging from 0.9773 to 0.9827 and RMSE ranging from 6.33 to 7.75. The refractive indices at 1.25 THz produced the best fit. The refractive indices of these oil samples were promising for identification and distinction of oil grades.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  9. Electron density characterization of inductively-coupled argon plasmas by the terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Jang, Dogeun; Uhm, Han Sup; Jang, Donggyu; Hur, Min Sup; Suk, Hyyong

    2016-12-01

    Inductively-coupled plasmas (ICP) in the high electron density regime of the order of 1013 cm-3 are generated and their electron density characteristics are investigated by the terahertz time-domain spectroscopy (THz-TDS) method. In this experiment, the plasma was produced by RF (13.56 MHz) with an applied RF power of 300-550 W and the argon gas pressure was in the range of 0.3-1.1 Torr. We generated the THz wave by focusing a femtosecond laser pulse in air with a DC electric field. As a plasma diagnostic tool, the THz-TDS method is found to successfully provide the plasma density information in the high-density regime, where other available plasma diagnostic tools are very limited. In addition, the analytical model based on the ambipolar diffusion equation is compared with experimental observations to explain the behavior of the electron density in the ICP source, where the plasma density is shown to be related to the applied RF power and gas pressure. The analytical result from the model is found to be in good agreement with the THz-TDS result.

  10. Boson peak dynamics of glassy glucose studied by integrated terahertz-band spectroscopy

    NASA Astrophysics Data System (ADS)

    Kabeya, Mikitoshi; Mori, Tatsuya; Fujii, Yasuhiro; Koreeda, Akitoshi; Lee, Byoung Wan; Ko, Jae-Hyeon; Kojima, Seiji

    2016-12-01

    We performed terahertz time-domain spectroscopy, low-frequency Raman scattering, and Brillouin light scattering on vitreous glucose to investigate the boson peak (BP) dynamics. In the spectra of α (ν ) /ν2 [ α (ν ) is the absorption coefficient], the BP is clearly observed around 1.1 THz. Correspondingly, the complex dielectric constant spectra show a universal resonancelike behavior only below the BP frequency. As an analytical scheme, we propose the relative light-vibration coupling coefficient (RCC), which is obtainable from the combination of the far-infrared and Raman spectra. The RCC reveals that the infrared light-vibration coupling coefficient CIR(ν ) of the vitreous glucose behaves linearly on frequency which deviates from Taraskin's model of CIR(ν ) =A +B ν2 [S. N. Taraskin et al., Phys. Rev. Lett. 97, 055504 (2006), 10.1103/PhysRevLett.97.055504]. The linearity of CIR(ν ) might require modification of the second term of the model. The measured transverse sound velocity shows an apparent discontinuity with the flattened mode observed in the inelastic neutron scattering study [N. Violini et al., Phys. Rev. B 85, 134204 (2012), 10.1103/PhysRevB.85.134204] and suggests a coupling between the transverse acoustic and flattened modes.

  11. Comparative study of boson peak in normal and secondary alcohols with terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Yomogida, Yoshiki; Sato, Yuki; Nozaki, Ryusuke; Mishina, Tomobumi; Nakahara, Jun'ichiro

    2010-05-01

    Using terahertz (THz) time-domain spectroscopy, we measured the complex permittivity of some normal (1-propanol, 1-butanol, and 1-pentanol) and secondary alcohols (2-propanol, 2-butanol, and 2-pentanol) in the frequency ranges from 0.2 to 2.5 THz at temperatures from 253 to 323 K. For all the samples, the complex permittivity in the THz region includes the following three components: (i) a high frequency side of dielectric relaxation processes, (ii) a broad mode around 1 THz, and (iii) a low frequency side of an intermolecular vibration mode located above 2.5 THz. The mode around 1 THz is recognized as a boson peak which is related to the local structure of disordered materials. The intensity of the boson peak in secondary alcohols is higher than that in normal alcohols. On the other hand, the number of carbon atoms slightly affects the appearance of the boson peak. These observations indicate that the position of an OH group in a molecule has a profound effect on the local structures in monohydric alcohols.

  12. Determination of plane stress state using terahertz time-domain spectroscopy

    PubMed Central

    Wang, Zhiyong; Kang, Kai; Wang, Shibin; Li, Lin'an; Xu, Ningning; Han, Jiaguang; He, Mingxia; Wu, Liang; Zhang, Weili

    2016-01-01

    THz wave has been increasingly applied in engineering practice. One of its outstanding advantages is the penetrability through certain optically opaque materials, whose interior properties could be therefore obtained. In this report, we develop an experimental method to determine the plane stress state of optically opaque materials based on the stress-optical law using terahertz time-domain spectroscopy (THz-TDS). In this method, two polarizers are combined into the conventional THz-TDS system to sense and adjust the polarization state of THz waves and a theoretical model is established to describe the relationship between phase delay of the received THz wave and the plane stress applied on the specimen. Three stress parameters that represent the plane stress state are finally determined through an error function of THz wave phase-delay. Experiments were conducted on polytetrafluoroethylene (PTFE) specimen and a reasonably good agreement was found with measurement using traditional strain gauges. The presented results validate the effectiveness of the proposed method. The proposed method could be further used in nondestructive tests for a wide range of optically opaque materials. PMID:27824112

  13. Feasibility of terahertz time-domain spectroscopy to detect tetracyclines hydrochloride in infant milk powder.

    PubMed

    Qin, Jianyuan; Xie, Lijuan; Ying, Yibin

    2014-12-02

    We report the use of terahertz time-domain spectroscopy (THz-TDS) to detect tetracyclines hydrochloride (TCsH) in infant milk powder for the first time. Four kinds of TCsH exhibited their unique spectral features in the region of 0.3-1.8 THz. The main spectral features of these TCsH were still detectable when mixed with infant milk powder with concentrations at 1%-50%, even in the ternary mixtures. The results from chemometrics analysis showed that qualitative and quantitative detection of TCsH in infant milk powder could be successfully achieved. The residual predictive deviation (RPD) values of all these TCsH models were all higher than 2, indicating these models were considered good and could be used in screening purposes. The RPD values of TCH, DTCH, and CTCH models were higher than 3, which were considered excellent for prediction purposes. These preliminary results indicated that THz-TDS combined with chemometrics analysis was suitable for detecting the presence of TCsH residues in a food matrix.

  14. New Versions of Terahertz Radiation Sources for Dynamic Nuclear Polarization in Nuclear Magnetic Resonance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bratman, V. L.; Kalynov, Yu. K.; Makhalov, P. B.; Fedotov, A. E.

    2014-01-01

    Dynamic nuclear polarization in strong-field nuclear magnetic resonance (NMR) spectroscopy requires terahertz radiation with moderate power levels. Nowadays, conventional gyrotrons are used almost exclusively to generate such radiation. In this review paper, we consider alternative variants of electronic microwave oscillators which require much weaker magnetic fields for their operation, namely, large-orbit gyrotrons operated at high cyclotron-frequency harmonics and Čerenkov-type devices, such as a backward-wave oscillator and a klystron frequency multiplier with tubular electron beams. Additionally, we consider the possibility to use the magnetic field created directly by the solenoid of an NMR spectrometer for operation of both the gyrotron and the backward-wave oscillator. Location of the oscillator in the spectrometer magnet makes it superfluous to use an additional superconducting magnet creating a strong field, significantly reduces the length of the radiation transmission line, and, in the case of Čerenkov-type devices, allows one to increase considerably the output-signal power. According to our calculations, all the electronic devices considered are capable of ensuring the power required for dynamic nuclear polarization (10 W or more) at a frequency of 260 GHz, whereas the gyrotrons, including their versions proposed in this paper, remain a single option at higher frequencies.

  15. Magnetization-free measurements of spin orientations in orthoferrites using terahertz time domain spectroscopy

    SciTech Connect

    Suemoto, Tohru Nakamura, Keita; Kurihara, Takayuki; Watanabe, Hiroshi

    2015-07-27

    The spin orientation during spin reorientation phase transition in a weak ferromagnetic orthoferrite Dy{sub x}Er{sub 1−x}FeO{sub 3} (x = 0.7) has been studied by using terahertz time domain spectroscopy under zero and weak external magnetic fields. The spin orientation angle was deduced from the ratio of the absorption intensity of quasi-ferromagnetic and quasi-antiferromagnetic modes, which appear around 0.25 and 0.4 THz, respectively. Between 11.4 and 17.9 K, this material showed a rotation-type reorientation transition rather than Morin-type transition. The temperature and magnetic field dependence of the orientation angle of the magnetic moment was found to follow a simple model assuming a linear temperature dependence of the anisotropy parameter. It has been also shown that this method is insensitive to the domain structure with opposite polarity and that it allows measurement without macroscopic magnetization.

  16. Simultaneous prediction of density and moisture content of wood by terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Inagaki, Tetsuya; Ahmed, Belal; Hartley, Ian D.; Tsuchikawa, Satoru; Reid, Matthew

    2014-11-01

    In this study, demonstration of simultaneous prediction of solid wood density and moisture content, both of which are critical in manufacturing operations, of 4 species (Aspen, Birch, Hemlock and Maple) was accomplished using terahertz time-domain spectroscopy (THz-TDS). THz measurements of wood at various moisture contents were taken for two orientations of the THz field (parallel and perpendicular) with respect to the visible grain. The real and imaginary parts of the dielectric function averaged over the frequency range of 0.1 to 0.2 THz had strong correlation with density and moisture content of the wood. We extend a model that has been applied previously to oven-dry wood to include the effects of moisture below the fiber saturation point by combining two effective medium models, which allows the dielectric function of water, air and oven-dry cell wall material to be modeled to give an effective dielectric function for the wood. A strong correlation between measured and predicted values for density and moisture content were observed.

  17. Characterization and Classification of Coals and Rocks Using Terahertz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Hu, Ke-xiang; Zhang, Lei; Yu, Xiao; Ding, En-jie

    2017-02-01

    Being the key unaddressed problem in unmanned mining condition, a new method for the coal-rock interface recognition was proposed in the study. Firstly, terahertz time-domain spectroscopy (THz-TDS) was employed to measure 10 kinds of coals/rocks which were common in China. Secondly, the physical properties of coals/rocks such as absorption coefficient spectra, refractive index, and dielectric properties in THz band were studied. The different responses in THz range caused by diverse components in coals/rocks were discussed, and the dielectric property of coals/rocks in THz band was well fitted by the Lorentz model. Finally, by the means of principal component analysis (PCA), support vector machine (SVM), and THz spectral data, the recognition rate of coals/rocks reaches to 100 % and the recognition rate of different bituminous coals reaches to 97.5 %. The experimental results show that the proposed method is fast, stable, and accurate for the detection of coal-rock interface and could be a promising tool for the classification of different bituminous coals.

  18. Time-domain terahertz spectroscopy and applications on drugs and explosives

    NASA Astrophysics Data System (ADS)

    Fan, W. H.; Zhao, W.; Cheng, G. H.; Burnett, A. D.; Upadhya, P. C.; Cunningham, J. E.; Linfield, E. H.; Davies, A. G.

    2008-03-01

    Many materials of interest to the forensic and security services, such as explosives, drugs and biological agents, exhibit characteristic spectral features in the terahertz (THz) frequency range. These spectral features originate from inter-molecular interactions, involving collective motions of molecules. Broadband THz time-domain spectroscopy (THz-TDS) system have been used to analyze a number of drugs-of-abuse and explosives that are of interest to the forensic and security services. These samples ranged from crystalline powders, pressed into pellets, to thin sheets of plastic explosives, and all being measured in transmission geometry in the frequency range 0.1 - 8 THz. To well understand the nature of the observed spectral features and the effects of thermal broadening on these far-infrared signatures, temperature-dependent THz-TDS measurements have also been performed at temperatures as low as 4 K, especially for two types of cocaine. Well-resolved low-frequency absorption peaks were observed in the frequency range 0.1 - 3 THz with high resolution. Some of absorption peaks were found clearly to become more intense and shift to higher frequencies as the temperature was reduced. The results confirm that the low-frequency collective modes are highly sensitive to the structural and spatial arrangement of molecules. Furthermore, a number of common postal packaging materials made from paper, cardboard, even several types of plastic, have been tested with drug sample to assess the ability of THz-TDS in a hostile detection environment.

  19. Probing phase transitions in simvastatin with terahertz time-domain spectroscopy.

    PubMed

    Tan, Nicholas Y; Zeitler, J Axel

    2015-03-02

    Simvastatin is known to exist in at least three polymorphic forms. The nature of polymorphism in simvastatin is ambiguous, as the crystal structures of the polymorphs do not show any significant change in crystal packing or molecular conformation. We utilize terahertz time-domain spectroscopy to characterize each of the polymorphs and probe the phase transitions in the range of 0.2-3.0 THz and for temperatures ranging from 90 to 390 K. In form III, vibrational modes are observed at 1.0, 1.25, and 1.7 THz. For form I, we find that the spectrum is dominated by a baseline corresponding to libration-vibration motions coupled to the dielectric relaxations, which is characteristic of a disordered hydrogen bonding material but with additional broad vibrational modes at 0.8 and 1.4 THz. In addition, the baseline shifts with temperature similar to that observed in disordered materials. This background absorption exhibits pronounced changes around the phase transition temperatures at 232 and 272 K. The results are in agreement with molecular dynamics simulations, which indicate that changes in the rotational freedom of the ester tail in the molecule govern the polymorphism in simvastatin.

  20. Angle-dependent terahertz time-domain spectroscopy of amino acid single crystals.

    PubMed

    Rungsawang, Rakchanok; Ueno, Yuko; Tomita, Isao; Ajito, Katsuhiro

    2006-10-26

    The measurement of absorption spectra using angle-dependent terahertz (THz) time-domain spectroscopy for amino acid single crystals of l-cysteine and l-histidine is reported for the first time. Linearly polarized THz radiation enables us to observe angle-dependent far-infrared absorption spectra of amino acid single crystals and determine the direction of the oscillating dipole of the molecules in the 20-100 cm(-1) range. By comparing the THz spectra of a single crystal and powder, we found that there was a clear hydrogen-bond peak in the crystal spectrum as a result of the larger hydrogen-bond network. The low-temperature THz spectra of amino acid microcrystals showed more intermolecular vibrational modes than those measured at room temperature. An ab initio frequency calculation of a single amino acid molecule was used to predict the intramolecular vibrational modes. The validity of the calculation models was confirmed by comparing the results with experimentally obtained data in the Raman spectral region.

  1. Observing the Temperature Dependent Transition of the GP2 Peptide Using Terahertz Spectroscopy

    PubMed Central

    Sun, Yiwen; Zhu, Zexuan; Chen, Siping; Balakrishnan, Jega; Abbott, Derek; Ahuja, Anil T.; Pickwell-MacPherson, Emma

    2012-01-01

    The GP2 peptide is derived from the Human Epidermal growth factor Receptor 2 (HER2/nue), a marker protein for breast cancer present in saliva. In this paper we study the temperature dependent behavior of hydrated GP2 at terahertz frequencies and find that the peptide undergoes a dynamic transition between 200 and 220 K. By fitting suitable molecular models to the frequency response we determine the molecular processes involved above and below the transition temperature (TD). In particular, we show that below TD the dynamic transition is dominated by a simple harmonic vibration with a slow and temperature dependent relaxation time constant and that above TD, the dynamic behavior is governed by two oscillators, one of which has a fast and temperature independent relaxation time constant and the other of which is a heavily damped oscillator with a slow and temperature dependent time constant. Furthermore a red shifting of the characteristic frequency of the damped oscillator was observed, confirming the presence of a non-harmonic vibration potential. Our measurements and modeling of GP2 highlight the unique capabilities of THz spectroscopy for protein characterization. PMID:23209703

  2. The qualitative identification of different alfalfa breed in same forage series by the terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Fang; Guo, Shuai

    2016-01-01

    In order to enriching the means of discriminating alfalfa and achieving the goal of nondestructive testing, terahertz time-domain spectroscopy (THz-TDS) was applied to explore and reveal the property characteristic of different alfalfa varieties in the same series. Six kinds of alfalfa were prepared for experiment and analysis, and these samples are classed as two series, namely caoyuan series and gannong series. In the result, the time-domain spectra were tested, and then the refractive indices and absorption coefficients was calculated, respectively. These spectrums showed an apparent difference between these two series, and to verify this classification, two statistical methods, partial least squares (PLS) and cluster analysis (CA), were performed to investigate. Finally, these methods yielded a classification result, and we found it classified gannong series and caoyuan series. All these result showed THz technology combined with statistical method can be an effective method for nondestructive identification of alfalfa breed with tiny different properties, and lay a foundation for establishing a forage database.

  3. Terahertz Time-Domain Spectroscopy for In Situ Monitoring of Ceramic Nuclear Waste Forms

    NASA Astrophysics Data System (ADS)

    Clark, Braeden M.; Sundaram, S. K.

    2016-10-01

    The use of terahertz time-domain spectroscopy (THz-TDS) is presented as a non-contact method for in situ monitoring of ceramic waste forms. Single-phase materials of zirconolite (CaZrTi2O7), pyrochlore (Nd2Ti2O7), and hollandite (BaCs0.3Cr2.3Ti5.7O16 and BaCs0.3CrFeAl0.3Ti5.7O16) were characterized. The refractive index and dielectric properties in THz frequencies demonstrate the ability to distinguish between these materials. Differences in processing methods show distinct changes in both the THz-TDS spectra and optical and dielectric properties of these ceramic phases. The temperature dependence of the refractive index and relative permittivity of pyrochlore and zirconolite materials in the range of 25-200 °C is found to follow an exponential increasing trend. This can also be used to monitor the temperature of the ceramic waste forms on storage over extended geological time scales.

  4. Ultrafast conductivity dynamics in pentacene probed using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Thorsmolle, Verner; Averitt, Richard; Chi, Xiaoliu; Smith, Darryl; Ramirez, Arthur; Antoinette, Taylor

    2003-03-01

    We present measurements of the transient photoconductivity in pentacene single crystals using optical-pump THz-probe spectroscopy. We have measured the temperature and fluence dependence of the mobility of the photoexcited charge carriers with picosecond resolution. The pentacene crystals were excited at 3.0 eV which is above the bandgap of ˜2.2 eV and the induced change in the far-infrared transmission was measured. At 30 K, the carrier mobility is μ 0.42 cm^2/Vs and decreases to μ 0.21 cm^2/Vs at room temperature. These values are comparable to values found in functionalized pentacene.(F.A. Hegmann, R.R. Tykwinski, K.P.H Lui, J.E. Bullock, and J.E. Anthony, Phys. Rev. Lett. 89), 227403 (2002). The transient terahertz signal reveals the presence of free carriers that are trapped on the timescale of a few ps or less, possibly through the formation of excitons, small polarons, or trapping by impurities.

  5. Determination of the complex refractivity of Au, Cu and Al in terahertz and far-infrared regions from reflection spectra measurements

    NASA Astrophysics Data System (ADS)

    Mou, Yuan; Wu, Zhen-sen; Gao, Yan-qing; Yang, Zhi-qiang; Yang, Qiu-jie; Zhang, Geng

    2017-01-01

    A scheme to determine the complex refractivity of gold (Au), Copper (Cu) and Aluminum (Al) from measurements of ellipsometer and spectrometer are proposed in this paper. The reflection spectra of the metals from 4 THz to 40 THz are measured with spectrometer. The determined refractivity by Kramers-Kronig (KK) algorithm coincides with the measured results from ellipsometer in far infrared region. Drude model is invited to make the wing correction on the terahertz reflection spectra, which helps to eliminate the effects of the noises from spectrometer on KK algorithm. The calculated refractive indexes from measured spectra in terahertz region are in consistent with those from corrected reflection spectra. The advantage of the scheme is to obtain terahertz dispersion properties based on limited information in infrared region.

  6. Attenuated total reflection far-ultraviolet spectroscopy

    NASA Astrophysics Data System (ADS)

    Ozaki, Yukihiro; Morisawa, Yusuke; Goto, Takeyoshi; Tanabe, Ichiro

    2016-09-01

    Recently, far-ultraviolet (FUV) spectroscopy of solid and liquid states has been a matter of keen interest because it provides new possibilities for studying electronic structures and transitions of almost all kinds of molecules. It has also great potential for a variety of applications from quantitative and qualitative analysis of aqueous solutions to environmental and geographical analyses. This review describes the state-of- the-art of FUV spectroscopy; an introduction to FUV spectroscopy, the development of FUV spectrometers, investigations on electronic transitions and structure, its various applications, and future prospects.

  7. Si-prism-array coupled terahertz-wave parametric oscillator with pump light totally reflected at the terahertz-wave exit surface.

    PubMed

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

    2016-09-01

    A Si-prism-array coupled terahertz (THz)-wave parametric oscillator with the pump totally reflected at the THz-wave exit surface (PR-Si-TPO) is demonstrated by manufacturing an 800 nm air gap between the crystal and the Si-prism array. Influence on the total reflection of the pump from the Si prisms is eliminated and efficient coupling of the THz wave is ensured by using this air gap. When the THz-wave frequency varies from 1.8 to 2.3 THz, compared with a Si-prism-array coupled TPO (Si-TPO) with the pump transmitting through the crystal directly, the THz-wave output energy is enhanced by 20-50 times, and the oscillating threshold is reduced by 10%-35%. Furthermore, the high end of the THz-wave frequency tuning range of the PR-Si-TPO is expanded to 3.66 THz compared with 2.5 THz for the Si-TPO.

  8. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Anomalous behaviours of terahertz reflected waves transmitted from GaAs induced by optical pumping

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Lei; Zhou, Qing-Li; Zhao, Dong-Mei; Zhang, Cun-Lin

    2009-12-01

    Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers. It is observed that, at high pump powers, the reflection peaks flip to the opposite polarity and dramatically enhance as the pump arrival time approaches the reflected wave of the terahertz pulse. The abnormal polarity-flip and enhancement can be interpreted by the pump-induced enhancement in the photoconductivity of GaAs and half-wave loss. Moreover, the carrier relaxation processes and surface states filling in GaAs are also studied in these measurements.

  9. Terahertz cyclotron resonance spectroscopy of an AlGaN/GaN heterostructure using a high-field pulsed magnet and an asynchronous optical sampling technique

    NASA Astrophysics Data System (ADS)

    Spencer, B. F.; Smith, W. F.; Hibberd, M. T.; Dawson, P.; Beck, M.; Bartels, A.; Guiney, I.; Humphreys, C. J.; Graham, D. M.

    2016-05-01

    The effective mass, sheet carrier concentration, and mobility of electrons within a two-dimensional electron gas in an AlGaN/GaN heterostructure were determined using a laboratory-based terahertz cyclotron resonance spectrometer. The ability to perform terahertz cyclotron resonance spectroscopy with magnetic fields of up to 31 T was enabled by combining a high-field pulsed magnet with a modified asynchronous optical sampling terahertz detection scheme. This scheme allowed around 100 transmitted terahertz waveforms to be recorded over the 14 ms magnetic field pulse duration. The sheet density and mobility were measured to be 8.0 × 1012 cm-2 and 9000 cm2 V-1 s-1 at 77 K. The in-plane electron effective mass at the band edge was determined to be 0.228 ± 0.002m0.

  10. Application of terahertz time-domain spectroscopy combined with chemometrics to quantitative analysis of imidacloprid in rice samples

    NASA Astrophysics Data System (ADS)

    Chen, Zewei; Zhang, Zhuoyong; Zhu, Ruohua; Xiang, Yuhong; Yang, Yuping; Harrington, Peter B.

    2015-12-01

    Terahertz time-domain spectroscopy (THz-TDS) has been utilized as an effective tool for quantitative analysis of imidacloprid in rice powder samples. Unlike previous studies, our method for sample preparation was mixing imidacloprid with rice powder instead of polyethylene. Then, terahertz time domain transmission spectra of these mixed samples were measured and the absorption coefficient spectra of the samples with frequency range extending from 0.3 to 1.7 THz were obtained. Asymmetric least square (AsLS) method was utilized to correct the slope baselines that are presented in THz absorption coefficient spectra and improve signal-to-noise ratio of THz spectra. Chemometrics methods, including partial least squares (PLS), support vector regression (SVR), interval partial least squares (iPLS), and backward interval partial least squares (biPLS), were used for quantitative model building and prediction. To achieve a reliable and unbiased estimation, bootstrapped Latin partition was chosen as an approach for statistical cross-validation. Results showed that the mean value of root mean square error of prediction (RMSEP) for PLS (0.5%) is smaller than SVR (0.7%), these two methods were based on the whole absorption coefficient spectra. In addition, PLS performed a better performance with a lower RMSEP (0.3%) based on the THz absorption coefficient spectra after AsLS baseline correction. Alternatively, two methods for variable selection, namely iPLS and biPLS, yielded models with improved predictions. Comparing with conventional PLS and SVR, the mean values of RMSEP were 0.4% (iPLS) and 0.3% (biPLS) by selecting the informative frequency ranges. The results demonstrated that an accurate quantitative analysis of imidacloprid in rice powder samples could be achieved by terahertz time-domain transmission spectroscopy combined with chemometrics. Furthermore, these results demonstrate that THz time-domain spectroscopy can be used for quantitative determinations of other

  11. Fiber-remote reflectance spectroscopy with an optimized diffuse reflectance sensor system

    SciTech Connect

    Driver, R.D.; Grim, K.P.; Dewey, G.; Brubaker, M.L.

    1995-12-31

    A diffuse reflectance spectroscopy system is described which can operate in a contact and non-contact mode on powders, slurries and other diffusely scattering materials. Diffuse reflectance spectra are presented for a number of samples including common household materials. A comparison is made of the probe with a Bio-Rad diffuse reflectance accessory. Second derivative spectra are shown of a calibration mixture of polymer additives. The use of the diffuse reflectance system for non-destructive tablet hardness measurements is discussed. Sensor multiplexing for diffuse reflectance spectroscopy, is reviewed.

  12. Fiber-remote reflectance spectroscopy with an optimized diffuse reflectance sensor system

    NASA Astrophysics Data System (ADS)

    Driver, Richard D.; Grim, Kirk P.; Dewey, G.; Brubaker, M. L.

    1995-01-01

    A diffuse reflectance spectroscopy system is described which can operate in a contact and non- contact mode on powders, slurries and other diffusely scattering materials. Diffuse reflectance spectra are presented for a number of samples including common household materials. A comparison is made of the probe with a Bio-Rad diffuse reflectance accessory. Second derivative spectra are shown of a calibration mixture of polymer additives. The use of the diffuse reflectance system for non-destructive tablet hardness measurements is discussed. Sensor multiplexing for diffuse reflectance spectroscopy is reviewed.

  13. Detection and quantification of multiple molecular species in mainstream cigarette smoke by continuous-wave terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Bigourd, Damien; Cuisset, Arnaud; Hindle, Francis; Matton, Sophie; Fertein, Eric; Bocquet, Robin; Mouret, Gaël

    2006-08-01

    Continuous-wave terahertz spectroscopy by photomixing is applied to the analysis of mainstream cigarette smoke. Using the wide tunability of the source, spectral signatures of hydrogen cyanide (HCN), carbon monoxide (CO), formaldehyde (H2CO), and water (H2O) have been observed from 500 to 2400GHz. The fine spectral purity allows direct concentration measurement from the pure rotational transitions of HCN and CO. The quantification of the measurement was validated by the means of a calibration gas containing CO. The potential of this technique for trace gas detection is demonstrated with an estimated detection limit of HCN equal to 9 parts in 106.

  14. Detection and quantification of multiple molecular species in mainstream cigarette smoke by continuous-wave terahertz spectroscopy.

    PubMed

    Bigourd, Damien; Cuisset, Arnaud; Hindle, Francis; Matton, Sophie; Fertein, Eric; Bocquet, Robin; Mouret, Gaël

    2006-08-01

    Continuous-wave terahertz spectroscopy by photomixing is applied to the analysis of mainstream cigarette smoke. Using the wide tunability of the source, spectral signatures of hydrogen cyanide (HCN), carbon monoxide (CO), formaldehyde (H2CO), and water (H2O) have been observed from 500 to 2400 GHz. The fine spectral purity allows direct concentration measurement from the pure rotational transitions of HCN and CO. The quantification of the measurement was validated by the means of a calibration gas containing CO. The potential of this technique for trace gas detection is demonstrated with an estimated detection limit of HCN equal to 9 parts in 10(6).

  15. Detection of Methomyl, a Carbamate Insecticide, in Food Matrices Using Terahertz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Baek, Seung Hyun; Kang, Ju Hee; Hwang, Yeun Hee; Ok, Kang Min; Kwak, Kyungwon; Chun, Hyang Sook

    2016-05-01

    The aim of this study was to investigate the feasibility of detecting methomyl, a carbamate insecticide, in food matrices (wheat and rice flours) using terahertz time-domain spectroscopy (THz-TDS). In the frequency range 0.1-3 THz, the characteristic THz absorption peaks of methomyl at room temperature were detected at 1 (33.4 cm-1), 1.64 (54.7 cm-1), and 1.89 (63.0 cm-1) THz. For detailed spectral analysis, the vibrational frequency and intensity of methomyl were calculated using solid-state density functional theory to mimic molecular interactions in the solid state. Qualitatively, the simulated spectrum was in good agreement with the experimental spectrum. Analysis of the individual absorption modes revealed that all of the features in the THz spectrum of methomyl were mainly generated from intermolecular vibrations. The peak appearing at 1 THz (33.4 cm-1) was then selected and tested for its suitability as a fingerprint for detecting methomyl in food matrices. Its absorbance was dose-dependently distinguishable from that of wheat and rice flours. The calibration curve of methomyl had a regression coefficient of >0.974 and a detection limit of <3.74 %. Accuracy and precision expressed as recovery and relative standard deviation in interday repeatability were in the ranges 78.0-96.5 and 2.83-4.98 %, respectively. Our results suggest that THz-TDS can be used for the rapid detection of methomyl in foods, but its sensitivity needs to be improved.

  16. CaCO3, its reaction and carbonate rocks: terahertz spectroscopy investigation

    NASA Astrophysics Data System (ADS)

    Zhan, Honglei; Wu, Shixiang; Zhao, Kun; Bao, Rima; Xiao, Lizhi

    2016-10-01

    Carbonate-rich rocks cover a primary part of the earth’s petroleum geology reservoir. The study of carbonate has special significance and more effective study methods are now needed. In order to improve the availability of carbonate rock detection, terahertz (THz) spectroscopy was employed to investigate relevant materials in Na2CO3  +  CaCl2  =  CaCO3  +  2NaCl, which is often used to generate CaCO3. By comparing the materials composited with different ions, it can be revealed that Ca2+, \\text{CO}32- , Na+ and Cl- have respective absorption features at different frequencies. Furthermore, by utilizing a conservation equation it can be observed that the average refractive indices of Na2CO3 as well as CaCl2 equal those of CaCO3 and NaCl in the entire range. Combining the absorption and refractive effect of the materials in the reaction can comprehensively characterize the different substances and reveal the inner interaction during the reaction. THz spectra can deduce the process of molecule rearrangement in the chemical reaction of long-term rock evolution. Besides, the absorption features of the real carbonate rock collected from the nearest town of Sinan county, Guizhou province in Yunnan-Guizhou plateau validate the peaks’ central frequencies of ions and the principal components of carbonates, which can be in agreement with the SEM-EDS analysis. This research will supply a spectral tool to identify the particles in the rock and deduce an evolution of petroleum carbonate reservoir.

  17. Protein and water confined in nanometer-scale reverse micelles studied by near infrared, terahertz, and ultrafast visible spectroscopies.

    PubMed

    Murakami, Hiroshi

    2013-01-01

    Protein-containing reverse (PCR) micelles are suitable systems to study the properties of proteins and waters in a cell-like environment. A model for determining the structural parameters of PCR micelles, such as the aqueous cavity size and molecule number of water within the reverse micelle, is presented. The model is based on an important hypothesis that the structural parameters of the protein-unfilled reverse micelle do not change after solubilization of protein. I describe a procedure using near infrared spectroscopy of OH stretching vibration band of water to verify the hypothesis. Further, the terahertz (THz) absorption spectrum of myoglobin is derived from THz time-domain spectroscopy of the PCR micellar solution, and the states of waters in reverse micelles with and without protein are discussed on the basis of the structural parameters. The last topic is on internal dynamics of PCR micelles on timescales from femtoseconds to nanoseconds studied by femtosecond time-resolved fluorescence spectroscopy.

  18. Characterization of Degradation Using Reflectance Spectroscopy (Postprint)

    DTIC Science & Technology

    2013-08-01

    could be performed in field. Fourier transform infrared (FTIR) devices have been developed with in field inspection capabilities [4]. Spectroscopy is a...the data to be transformed to a linear model. In these cases, all the techniques for linear models may be applied such as PCA and PLS [6, 7]. These...number of molecules of that oscillator type. This is known as the Lorentz model in dispersion analysis 1597 This article is copyrighted as indicated in

  19. Does Spectral Format Matter in Diffuse Reflection Spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Near- and more recently, mid-infrared diffuse reflectance spectroscopy have come to be extensively used to determine the composition of products ranging from forages to drugs. In these methods, spectra are generally collected as (Reflectance or R) and transformed to log (1/R) according to the Beer-...

  20. Estimating soil quality indicators with diffuse reflectance spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rapid estimation of soil quality is needed for determining and mapping soil variability in site-specific management. One technology that can fulfill this need is diffuse reflectance spectroscopy, which measures light reflected from the soil in the visible and near infrared wavelength bands. Reflecta...

  1. Doping profile measurements in silicon using terahertz time domain spectroscopy (THz-TDS) via electrochemical anodic oxidation

    NASA Astrophysics Data System (ADS)

    Tulsyan, Gaurav

    Doping profiles are engineered to manipulate device properties and to determine electrical performances of microelectronic devices frequently. To support engineering studies afterward, essential information is usually required from physically characterized doping profiles. Secondary Ion Mass Spectrometry (SIMS), Spreading Resistance Profiling (SRP) and Electrochemical Capacitance Voltage (ECV) profiling are standard techniques for now to map profile. SIMS yields a chemical doping profile via ion sputtering process and owns a better resolution, whereas ECV and SRP produce an electrical doping profile detecting free carriers in microelectronic devices. The major difference between electrical and chemical doping profiles is at heavily doped regions greater than 1020 atoms/cm3. At the profile region over the solubility limit, inactive dopants induce a flat plateau and detected by electrical measurements only. Destructive techniques are usually designed as stand-alone systems to study impurities. For an in-situ process control purpose, non-contact methods, such as ellipsometry and non-contact capacitance voltage (CV) techniques are current under development. In this theses work, terahertz time domain spectroscopy (THz-TDS) is utilized to achieve electrical doping profile in both destructive and non-contact manners. In recent years the Terahertz group at Rochester Institute Technology developed several techniques that use terahertz pulses to non-destructively map doping profiles. In this thesis, we study a destructive but potentially higher resolution version of the terahertz based approach to map the profile of activated dopants and augment the non-destructive approaches already developed. The basic idea of the profile mapping approach developed in this MS thesis is to anodize, and thus oxidize to silicon dioxide, thin layers (down to below 10 nm) of the wafer with the doping profile to be mapped. Since the dopants atoms and any free carriers in the silicon oxide thin

  2. 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)

  3. Terahertz Desorption Emission Spectroscopy (THz DES) - ‘ALMA in the Lab’

    NASA Astrophysics Data System (ADS)

    Emile Auriacombe, Olivier Bruno Jacques; Fraser, Helen; Ellison, Brian; Ioppolo, Sergio; Rea, Simon

    2016-06-01

    ALMA is revolutionising our scope to identify and locate molecules that have been desorbed from ices, particularly complex organic molecules (COMS), which provide a vital link between interstellar and prebiotic chemistry. Explaining the existence of these molecules in star-forming regions relies on an empirical understanding of the chemistry that underpins their formation:- do COMS form predominantly in the solid-phase and then desorb to the gas phase, or do only “smaller” species, radials or ions desorb and then undergo gas-phase chemical reactions to generate larger COMS?-are the rotational state populations in COMS only attributable to equilibrium chemistry, or could their formation mechanisms and desorption processes affect the rotational state occupancy of these molecules, thereby directly tying certain species to solid-state origins?We have developed a novel laboratory method - THz Desorption Emission Spectroscopy (THz-DES) that combines “traditional” laboratory astrophysics high-vacuum ice experiments with a sensitive high-spectral-resolution terahertz total-power heterodyne radiometer 1,2, partially mirroring the spectral range of ALMA band 7 (275- 373 GHz). Ices are grown in situ on a cold-plate, situated in a vacuum cell, then (thermally) desorbed. The sub-mm emission spectra of the resultant gas-phase molecules are detected as a function of time, temperature, or distance from the surface. Our first THz DES results will be shown for pure and binary ice systems including H2O, N2O and CH3OH. They show good correlation with established methods e.g. TPD, with the advantage of exploiting the molecular spectroscopy to unravel surface dynamics, state-occupancy, and unequivocal molecular identification, as well as concurrently measuring desorption barriers and molecular yields. We will extend our technique to a broader frequency range, enabling us to detect radical and ion desorption, to differentiate between A and E populations of CH3OH or ortho

  4. Reflectance spectroscopy for evaluating hair follicle cycle

    NASA Astrophysics Data System (ADS)

    Liu, Caihua; Guan, Yue; Wang, Jianru; Zhu, Dan

    2014-02-01

    Hair follicle, as a mini-organ with perpetually cycling of telogen, anagen and catagen, provides a valuable experimental model for studying hair and organ regeneration. The transition of hair follicle from telogen to anagen is a significant sign for successful regeneration. So far discrimination of the hair follicle stage is mostly based on canonical histological examination and empirical speculation based on skin color. Hardly a method has been proposed to quantitatively evaluate the hair follicle stage. In this work, a commercial optical fiber spectrometer was applied to monitor diffuse reflectance of mouse skin with hair follicle cycling, and then the change of reflectance was obtained. Histological examination was used to verify the hair follicle stage. In comparison with the histological examination, the skin diffuse reflectance was relatively high for mouse with telogen hair follicles; it decreased once hair follicles transited to anagen stage; then it increased reversely at catagen stage. This study provided a new method to quantitatively evaluate the hair follicle stage, and should be valuable for the basic and therapeutic investigations on hair regeneration.

  5. Optimization of diffuse reflectance infrared spectroscopy accessories

    SciTech Connect

    Hirschfeld, T.

    1986-11-01

    The value of diffuse reflectance as an infrared or near-infrared spectroscopic sampling procedure has been limited by the low efficiency of accessories designed for it. In terms of signal-to-noise ratio, these average 2-6% for integrating spheres and 10-12% for various ellipsoidal mirror arrangements. Much better performances, up to 37% efficiency, can be obtained by optimizing a concentric confocal ellipsoidal mirror arrangement by using a very large central opening in the amular collector mirror, and adapting the throughput of the detector to the geometry of the collected beam.

  6. Combined theory of reflectance and emittance spectroscopy

    NASA Technical Reports Server (NTRS)

    Hapke, Bruce

    1995-01-01

    The theory in which either or both reflected sunlight and thermally emitted radiation contribute to the power received by a detector viewing a particulate medium, such as a powder in the laboratory or a planetary regolith, is considered theoretically. This theory is of considerable interest for the interpretation of data from field or spacecraft instruments that are sensitive to the near-infrared region of the spectrum, such as NIMS (near-infrared mapping spectrometer) and VIMS (visual and infrared mapping spectrometer), as well as thermal infrared detectors.

  7. Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yulei; Zhou, Qing-li; Zhang, Cunlin

    2010-11-01

    The ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs have been investigated in detail by using terahertz pump-emission technique. Through theoretical modeling based on Hertz vector potential, it is found that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed subsequent to the excitation of pump pulse, and our modeling gives successful analyses for the dynamics of photogenerated carriers in the GaAs. We attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperaturedependent measurements are also performed to verify this model.

  8. Enhancement of water retention in UV-exposed fuel-cell proton exchange membranes studied using terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Ray, Shaumik; Devi, Nirmala; Dash, Jyotirmayee; Rambabu, Gutru; Bhat, Santoshkumar D.; Pesala, Bala

    2016-02-01

    Proton Exchange Membrane (PEM) fuel cells are increasingly gaining importance as a clean energy source. PEMs need to possess high proton conductivity and should be chemically and mechanically stable in the fuel cell environment. Proton conductivity of PEM in fuel cells is directly proportional to water content in the membrane. Among the various PEMs available, Nafion has high proton conductivity even with low water content compared to SPEEK (Sulfonated Poly(ether ether ketone)) but is also expensive. SPEEK membranes and it's composites have better mechanical properties and have comparatively higher thermal stability. Operating the fuel cell at higher temperatures and at the same time maintaining the water content of the membrane is always a great challenge. In this paper, to increase water retention capacity, Nafion, SPEEK and it's composite (SPEEK PSSA-CNT) membranes are exposed to Ultra-Violet (UV) radiation for varied times. Terahertz Spectroscopy, in both pulsed and CW mode has been used as an efficient tool to quantify the water retention of the membrane. Results using Terahertz spectroscopy show that even though the initial water absorption capacity of Nafion membranes is more, SPEEK membranes and it's composites show considerable improvement in the water retention capacity upon high intensity UV irradiation.

  9. Gas-Phase Terahertz Spectroscopy and the Study of Complex Interstellar Chemistry

    NASA Astrophysics Data System (ADS)

    Braakman, Rogier

    2010-11-01

    Terahertz spectroscopy holds great promise in the advancement of the field of astrochemistry. The sensitive observation of interstellar THz radiation is expected to lower detection limits and allow the study of larger and more complex species than is currently possible at millimeter wavelengths, which will place further constraints on chemical models and permit a direct comparison to the organic compounds seen in carbonaceous chondrites. With the successful recent launch of the Herschel Space Telescope, which will give high-fidelity access to interstellar THz radiation for the first time, and the completion of the Atacama Large Millimeter Array (ALMA) by 2013, the THz astronomy era is upon us. Unfortunately, laboratory THz spectroscopy presents significant challenges and will be soon be lagging behind the newly available observational platforms. Technologies to extend the capabilities of high-resolution spectroscopic systems into the THz domain are actively being pursued on many fronts, but affordable systems that are broadly tunable, sensitive and achieve the necessary resolution are not yet available. The work in this thesis should therefore be seen as part of the effort in the transition from centimeter-/millimeter-wave to THz spectroscopy that is currently taking place in the astrochemistry community. As part of this thesis, observational searches for the complex organics hydroxyacetone (CH3COCH2OH), 2-cyanoethanol (OHCH 2CH2CN) and methoxyacetonitrile (CH3OCH2 CN) were attempted at millimeter wavelengths. The unsuccessful nature of these searches highlight the current limits of studying interstellar chemistry using pure rotational spectroscopy. The characterization of the laboratory spectra of these molecules is nonetheless important as it will aid in the assignment and description of the rotational substructure and band shapes of their THz torsional spectra, features that may allow their interstellar detection; and this thesis presents methods by which such

  10. Using Terahertz pulse spectroscopy to study the crystalline structure of a drug: a case study of the polymorphs of ranitidine hydrochloride.

    PubMed

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

    2003-04-01

    We describe the application of Terahertz pulse spectroscopy to polymorph identification. The particular compounds investigated were the different crystalline Forms 1 and 2 of ranitidine hydrochloride, both in the pure form and also obtained as a marketed pharmaceutical product. Identification was clear. The technique has advantages that excitation is not via a powerful laser source, as used in Raman spectroscopy, so phase changes or photochemical reactions in polymorphs do not occur. Terahertz absorption spectral interpretation and instrumentation are similar to basic Fourier transform infrared (FTIR) spectroscopy and therefore easy to understand. The sample preparation techniques used are the same as those used in FTIR and Raman spectroscopies. The data obtained is complementary to Raman Spectroscopy. As the selection rules are different between the two techniques, we are able to obtain new data set directly related to crystalline structure adding to that obtained by Raman spectroscopy. Terahertz pulse spectroscopy provides information on low-frequency intermolecular vibrational modes; these are difficult to assess in Raman spectroscopy due to the proximity of the laser exciting line. It is concluded that the method has a wide range of applications in pharmaceutical science including formulation, high throughput screening, and inspection in storage.

  11. Characteristics of chiral and racemic ketoprofen drugs using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Du, Yong; Liu, Jianjun; Hong, Zhi

    2013-08-01

    Absorption spectra of chiral S-(+)- and racemic RS-ketoprofen pharmaceutical molecules in crystalline form were recorded in the terahertz region between 6 and 66 cm-1 (0.2 ~ 2.0 THz) by using time-domain terahertz spectroscopic (THz-TDS) measurement. Different distinctive absorption features were observed which are strikingly sensitive to the change of subtle conformational structures within such isostructural crystal molecules. The results suggest that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.

  12. High spectral resolution reflectance spectroscopy of minerals

    NASA Technical Reports Server (NTRS)

    Clark, Roger N.; King, Trude V. V.; Klejwa, Matthew; Swayze, Gregg A.; Vergo, Norma

    1990-01-01

    The reflectance spectra of minerals are studied as a function of spectral resolution in the range from 0.2 to 3.0 microns. Selected absorption bands were studied at resolving powers as high as 2240. At resolving powers of approximately 1000, many OH-bearing minerals show diagnostic sharp absorptions at the resolution limit. At low resolution, some minerals may not be distinguishable, but as the resolution is increased, most can be easily identified. As the resolution is increased, many minerals show fine structure, particularly in the OH-stretching overtone region near 1.4 micron. The fine structure can enhance the ability to discriminate between minerals, and in some cases the fine structure can be used to determine elemental composition.

  13. Electrically continuous graphene from single crystal copper verified by terahertz conductance spectroscopy and micro four-point probe.

    PubMed

    Buron, Jonas D; Pizzocchero, Filippo; Jessen, Bjarke S; Booth, Timothy J; Nielsen, Peter F; Hansen, Ole; Hilke, Michael; Whiteway, Eric; Jepsen, Peter U; Bøggild, Peter; Petersen, Dirch H

    2014-11-12

    The electrical performance of graphene synthesized by chemical vapor deposition and transferred to insulating surfaces may be compromised by extended defects, including for instance grain boundaries, cracks, wrinkles, and tears. In this study, we experimentally investigate and compare the nano- and microscale electrical continuity of single layer graphene grown on centimeter-sized single crystal copper with that of previously studied graphene films, grown on commercially available copper foil, after transfer to SiO2 surfaces. The electrical continuity of the graphene films is analyzed using two noninvasive conductance characterization methods: ultrabroadband terahertz time-domain spectroscopy and micro four-point probe, which probe the electrical properties of the graphene film on different length scales, 100 nm and 10 μm, respectively. Ultrabroadband terahertz time-domain spectroscopy allows for measurement of the complex conductance response in the frequency range 1-15 terahertz, covering the entire intraband conductance spectrum, and reveals that the conductance response for the graphene grown on single crystalline copper intimately follows the Drude model for a barrier-free conductor. In contrast, the graphene grown on commercial copper foil shows a distinctly non-Drude conductance spectrum that is better described by the Drude-Smith model, which incorporates the effect of preferential carrier backscattering associated with extended, electronic barriers with a typical separation on the order of 100 nm. Micro four-point probe resistance values measured on graphene grown on single crystalline copper in two different voltage-current configurations show close agreement with the expected distributions for a continuous 2D conductor, in contrast with previous observations on graphene grown on commercial copper foil. The terahertz and micro four-point probe conductance values of the graphene grown on single crystalline copper shows a close to unity correlation, in

  14. Terahertz spectroscopy with a holographic Fourier transform spectrometer plus array detector using coherent synchrotron radiation

    SciTech Connect

    Nikolay I. Agladz, John Klopf, Gwyn Williams, Albert J. Sievers

    2010-06-01

    By use of coherent terahertz synchrotron radiation, we experimentally tested a holographic Fourier transform spectrometer coupled to an array detector to determine its viability as a spectral device. Somewhat surprisingly, the overall performance strongly depends on the absorptivity of the birefringent lithium tantalate pixels in the array detector.

  15. Probing the conformational changes of proteins in liquid water by dielectric terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Charkhesht, Ali; George, Deepu; Vinh, Nguyen

    2015-03-01

    Proteins solvated in their biological milieu are expected to exhibit strong absorption in the terahertz range that contain information on their global and sub-global collective vibrational modes (conformational dynamics) and global dynamical correlations among solvent water molecules and proteins. Measurements in this region, however, are challenging due to the strong absorption of water and often severe interference artifacts. In response, we have developed a highly sensitive dielectric terahertz frequency-domain system and a terahertz-time domain system for probing the collective dynamics in aqueous solution. Using these techniques we explore the complex dielectric response from 5 GHz up to 3 THz that directly probes such questions as the hydration level around proteins and the large scale vibrational modes of biological polymers. We make a direct comparison to the existing molecular dynamic simulations and normal mode calculations and investigate the dependence of the terahertz frequency dynamics on protein concentration. Our measurements shed light on the macromolecular motions in a biologically relevant water environment.

  16. Accessing deep optical properties of skin using diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Koenig, Anne; Roig, Blandine; Le Digabel, Jimmy; Josse, Gwendal; Dinten, Jean-Marc

    2015-07-01

    Diffuse reflectance spectroscopy characterizes composition and structure of tissues by determining their scattering and absorption properties. We have developed in our laboratory a low-cost spatially resolved diffuse reflectance spectroscopy instrument. We present in this study some results showing how to adapt this technology on multi-layered tissues. First of all, a method enabling determination of scattering and absorption properties of multi-layered phantoms is described; the adaptation of the initial methodology to focus on deep layers is especially detailed. Then some preliminary results obtained on a panel of volunteer's redness faces are presented.

  17. Terahertz Frequency-Domain Spectroscopy of Low-Pressure Acetonitrile Gas by a Photomixing Terahertz Synthesizer Referenced to Dual Optical Frequency Combs

    NASA Astrophysics Data System (ADS)

    Hsieh, Yi-Da; Kimura, Hiroto; Hayashi, Kenta; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Yasui, Takeshi

    2016-09-01

    A terahertz (THz) frequency synthesizer based on photomixing of two near-infrared lasers with a sub-THz to THz frequency offset is a powerful tool for spectroscopy of polar gas molecules due to its broad spectral coverage; however, its frequency accuracy and resolution are relatively low. To tune the output frequency continuously and widely while maintaining its traceability to a frequency standard, we developed a photomixing THz synthesizer phase-locked to dual optical frequency combs (OFCs). While the phase-locking to dual OFCs ensured continuous tuning within a spectral range of 120 GHz, in addition to the traceability to the frequency standard, use of a broadband uni-traveling carrier photodiode for photomixing enabled the generation of CW-THz radiation within a frequency range from 0.2 to 1.5 THz. We demonstrated THz frequency-domain spectroscopy of gas-phase acetonitrile CH3CN and its isotope CH3 13CN in the frequency range of 0.600-0.720 THz using this THz synthesizer. Their rotational transitions were assigned with a frequency accuracy of 8.42 × 10-8 and a frequency resolution of 520 kHz. Furthermore, the concentration of the CH3CN gas at 20 Pa was determined to be (5.41 ± 0.05) × 1014 molecules/cm3 by curve fitting analysis of the measured absorbance spectrum, and the mixture ratio of the mixed CH3CN/CH3 13CN gas was determined to be 1:2.26 with a gas concentration of 1014-1015 molecules/cm3. The developed THz synthesizer is highly promising for high-precision THz-FDS of low-pressure molecular gases and will enable the qualitative and quantitative analyses of multiple gases.

  18. Polarization orientation dependence of the far infrared spectra of oriented single crystals of 1,3,5,-trinitro-s-triazine (RDX) using terahertz-time-domain spectroscopy

    SciTech Connect

    Whitley, Von H; Hooks, Dan E; Ramos, Kyle J; O' Hara, John F; Azad, A K; Taylor, A J; Barber, J; Averitt, R D

    2008-01-01

    The far infrared spectra of (100), (010), and (001)-oriented RDX single crystals were measured as the crystal was rotated about the axis perpendicular to the polarization plane of the incident radiation. Absorption measurements were taken at temperatures of both 20 K and 295 K for all rotations using terahertz time-domain spectroscopy. A number of discrete absorptions were found ranging from 10-100 cm(-1) (0.3-3 THz). The absorptions are highly dependent on the orientation of the terahertz polarization with respect to crystallographic axes.

  19. Apollo 17 Soil Characterization for Reflectance Spectroscopy

    NASA Technical Reports Server (NTRS)

    Taylor, L. A.; Pieters, C.; Patchen, A.; Morris, R. V.; Keller, L. P.; Wentworth, S.; McKay, D. S.

    1999-01-01

    It is the fine fractions that dominate the observed spectral signatures of bulk lunar soil, and the next to the smallest size fractions are the most similar to the overall properties of the bulk soil. Thus, our Lunar Soil Characterization Consortium has concentrated on understanding the inter-relations of compositional, mineralogical, and optical properties of the <45-micron size fraction and its component sizes (20-44 micron, 10-20 micron, and <10 micron size fractions). To be able to generalize our results beyond the particular sample set studied, it is necessary to quantitatively identify the observed effects of space weathering and evaluate the processes involved. For this, it is necessary to know the chemistry of each size fraction, modal abundances of each phase, average compositions of the minerals and glasses, I(sub s)/FeO values, reflectance spectra, and the physical makeup of the individual particles and their patinas. This characterization includes the important dissection of the pyroxene minerals into four separate populations, with data on both modes and average chemical compositions. Armed with such data, it should be possible to effectively isolate spectral effects of space weathering from spectral properties related to mineral and glass chemistry. Four mare soils from the Apollo 17 site were selected for characterization based upon similarities in bulk composition and their contrasting maturities, ranging from immature to submature to mature. The methodology of our characterization has been discussed previously. Results of the Apollo 17 mare soils, outlined herein, are being prepared for publication in MAPS. As shown, with decreasing grain size, the agglutinitic (impact) glass content profoundly increases. This is the most impressive change for the mare soils. In several soils we have examined, there is an over two-fold increase in the agglutinitic glass contents between the 90-150- micron and the 10-20-micron size fractions. Accompanying this

  20. Fabrication of photonic amorphous diamonds for terahertz-wave applications

    NASA Astrophysics Data System (ADS)

    Komiyama, Yuichiro; Abe, Hiroyuki; Kamimura, Yasushi; Edagawa, Keiichi

    2016-05-01

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

  1. Does the spectral format matter in diffuse reflection spectroscopy?

    PubMed

    Reeves, James B

    2009-06-01

    Near-infrared, and more recently, mid-infrared diffuse reflection spectroscopy (more commonly and erroneously called reflectance spectroscopy) have come to be extensively used to determine the composition of products ranging from forages and drugs to soils. In these methods, spectra are generally collected as reflectance or R and transformed to log (1/reflectance). However, some near-infrared researchers do not transform the data, but use the data directly as reflectance. As it is generally held that procedures such as partial least squares regression do not work well with nonlinear data and the log (1/reflectance) transformation is held to be a best effort at linearization for near-infrared diffuse reflection spectral data, the question arises as to why then does not everyone transform the data? The objective of this work was to investigate this question using near-infrared and mid-infrared spectra in various formats. Calibrations were developed using spectral data from forages in several formats: reflectance, log (1/reflectance), non-background corrected single beam spectra, interferograms, and Kubelka-Munk transformed data. Calibrations were developed using both non-pretreated spectra and using data pretreatments such as derivatives. Results showed that calibrations using partial least squares regression did not require any specific data format. Accurate calibrations were developed for fiber, digestibility, and protein measures in forages using any of the aforementioned spectral formats including non-background-corrected single beam spectra and even interferograms. While calibrations could be developed using any of the formats, results indicated that those using Kubelka-Munk and especially interferograms did not perform as well as the others, although they were still quite good. In conclusion, results using forage spectra indicated that accurate and equivalent calibrations can be developed using diffuse reflectance data, with (reflectance) or without background

  2. Nondestructive evaluation of crystallized-particle size in lactose-powder by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamauchi, Satoshi; Hatakeyama, Sakura; Imai, Yoh; Tonouchi, Masayoshi

    2014-03-01

    Transmission-type terahertz time-domain spectroscopy is applied to evaluate crystallized lactose particle of size below 30 μm, which is far too small compared to the wavelength of incident terahertz (THz)-wave. The THz-absorption spectrum of lactose is successfully deconvoluted by Lorentzian to two spectra with peaks at 17.1 cm-1 (0.53 THz) and 45.6 cm-1 (1.37 THz) derived from α-lactose monohydrate, and a spectrum at 39.7 cm-1 (1.19 THz) from anhydrous β-lactose after removal of the broad-band spectrum by polynomial cubic function. Lactose is mainly crystallized into α-lactose monohydrate from the supersaturated solution at room temperature with a small amount of anhydrous β-lactose below 4%. The absorption feature is dependent on the crystallized particle size and the integrated intensity ratio of the two absorptions due to α-lactose monohydrate is correlated in linear for the size.

  3. Soil phosphorus and potassium estimation by reflectance spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Visible and near infrared (VNIR) diffuse reflectance spectroscopy has potential in site-specific measurement of soil properties. However, previous studies have reported VNIR estimates of plant available soil phosphorus (P) and potassium (K) to be of variable accuracy. In this study, we used a databa...

  4. Instrumentation for Reflectance Spectroscopy and Microspectroscopy with Application to Astrobiology

    NASA Technical Reports Server (NTRS)

    Mouroulis, Pantazis; Blaney, Diana L.; Green, Robert O.

    2008-01-01

    We present instrument concepts for in-situ reflectance spectroscopy over a spatial resolution range from several meters to tens of micrometers. These have been adapted to the low mass and power requirements of rover or similar platforms. Described are a miniaturized imaging spectrometer for rover mast, a combined mast and arm point spectrometer, and an imaging microspectrometer for the rover arm.

  5. Analytical study of spacecraft deposition contamination by internal reflection spectroscopy

    NASA Technical Reports Server (NTRS)

    Mookherji, T.

    1972-01-01

    Infrared absorption spectra of ten individual contaminant materials and four binary mixtures of these have been studied using the internal reflection spectroscopy technique. The effect of ultraviolet radiation on these contaminants has also been studied. It has been observed that all siloxanes, silanes, and esters are drastically affected by ultraviolet irradiation. In most cases polymerization and tar formation results.

  6. Estimating a soil quality index with VNIR reflectance spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sensor-based approaches to assessment and quantification of soil quality are important to facilitate cost-effective, site-specific soil management. The objective of this research was to evaluate the ability of visible, near-infrared (VNIR) diffuse reflectance spectroscopy to estimate multiple soil q...

  7. Factors affecting soil phosphorus and potassium estimation by reflectance spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Visible and near infrared (VNIR) diffuse reflectance spectroscopy has potential in site-specific measurement of soil properties. However, previous studies have reported VNIR estimates of plant available soil phosphorus (P) and potassium (K) to be of variable accuracy. In this study, we used a databa...

  8. Ultra-broadband terahertz spectroscopy of InP wafer using coherent heterodyne time domain spectrometer

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoyan; Zhang, Liangliang; Zhang, Cunlin

    2015-08-01

    Indium Phosphide (InP) has attracted great physical interest because of its unique characteristics and is indispensable to both optical and electronic devices. In this paper, we study the optical properties of undoped (100) InP wafer in the ultra-broad terahertz frequency range (0.5-18 THz) by using air-biased-coherent-detection (ABCD) system. It is observed that InP wafer is opaque at the frequencies spanning from 6.7 THz to 12.1 THz. In the frequency regions of 0.8-6.7 THz and 12.1-18 THz it has relatively low absorption coefficient. Meanwhile, the refractive index increases monotonously in the 0.8-6.7 THz region and 12.1-18 THz region. These findings will contribute to the design of InP based component for nonlinear terahertz devices.

  9. Intervalley separation in the conduction band of InGaAs measured by terahertz excitation spectroscopy

    SciTech Connect

    Molis, G.; Krotkus, A.; Vaicaitis, V.

    2009-03-02

    Spectral dependencies of terahertz radiation from the femtosecond laser-illuminated surfaces of Ga{sub x}In{sub 1-x}As (x=1, 0.8, and 0.47) have been investigated experimentally at high optical fluencies and laser wavelengths ranging from 600 to 800 nm. The terahertz pulse amplitude increased with the increasing laser photon energy due to larger excess energies of photoexcited electrons and more efficient spatial separation of electrons and holes at the illuminated surface. This increase was stopped with the onset of electron transitions to subsidiary conduction band valleys. Analysis of these experiments was used for evaluating the energy positions of the X and L conduction band valleys in Ga{sub x}In{sub 1-x}As alloys as a function of their composition.

  10. Collective dynamics of lysozyme in water: terahertz absorption spectroscopy and comparison with theory.

    PubMed

    Xu, Jing; Plaxco, Kevin W; Allen, S James

    2006-11-30

    To directly measure the low-frequency vibrational modes of proteins in biologically relevant water environment rather than previously explored dry or slightly hydrated phase, we have developed a broadband terahertz spectrometer suitable for strongly attenuating protein solutions. Radiation is provided by harmonic multipliers (up to 0.21 THz), a Gunn oscillator (at 0.139 THz), and the UCSB free-electron lasers (up to 4.8 THz). Our spectrometer combines these intense sources with a sensitive cryogenic detector and a variable path length sample cell to detect radiation after it is attenuated by more than 7 orders of magnitudes by the aqueous sample. Using this spectrometer, we have measured the molar extinction of solvated lysozyme between 0.075 and 3.72 THz (2.5-124 cm(-1)), and we made direct comparison to several published theoretical models based on molecular dynamics simulations and normal-mode analysis. We confirm the existence of dense, overlapping normal modes in the terahertz frequency range. Our observed spectrum, while in rough qualitative agreement with these models, differs in detail. Further, we observe a low-frequency cutoff in terahertz dynamics between 0.2 and 0.3 THz, and we see no evidence of a predicted normal mode at approximately 0.09 THz for the protein.

  11. Probing the collective vibrational dynamics of a protein in liquid water by terahertz absorption spectroscopy.

    PubMed

    Xu, Jing; Plaxco, Kevin W; Allen, S James

    2006-05-01

    Biological polymers are expected to exhibit functionally relevant, global, and subglobal collective modes in the terahertz (THz) frequency range (i.e., picosecond timescale). In an effort to monitor these collective motions, we have experimentally determined the absorption spectrum of solvated bovine serum albumin (BSA) from 0.3 to 3.72 THz (10-124 cm(-1)). We successfully extract the terahertz molar absorption of the solvated BSA from the much stronger attenuation of water and observe in the solvated protein a dense, overlapping spectrum of vibrational modes that increases monotonically with increasing frequency. We see no evidence of distinct, strong, spectral features, suggesting that no specific collective vibrations dominate the protein's spectrum of motions, consistent with the predictions of molecular dynamics simulations and normal mode analyses of a range of small proteins. The shape of the observed spectrum resembles the ideal quadratic spectral density expected for a disordered ionic solid, indicating that the terahertz normal mode density of the solvated BSA may be modeled, to first order, as that of a three-dimensional elastic nanoparticle with an aperiodic charge distribution. Nevertheless, there are important detailed departures from that of a disordered inorganic solid or the normal mode densities predicted for several smaller proteins. These departures are presumably the spectral features arising from the unique molecular details of the solvated BSA. The techniques used here and measurements have the potential to experimentally confront theoretical calculations on a frequency scale that is important for macromolecular motions in a biologically relevant water environment.

  12. Probe conformational dynamics of proteins in aqueous solutions by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Vinh, Nguyen Q.

    2016-10-01

    Proteins solvated in their biologically milieu are expected to exhibit strong absorption in the terahertz frequencies, that contain information on their global and sub-global collective vibrational modes (conformational dynamics) and global dynamic correlations among solvent water and proteins. The dynamics play an important role in enzymatic activities of proteins, but obtaining an accurate and quantitative pictures of these activities, however, is challenging due to the strong absorption of water. In response, we have developed the world's highest precision, highest sensitivity terahertz-frequency domain spectrometer and a standard terahertz-time domain system to probe the collective dynamics of proteins in aqueous solutions. Operating over the frequency range from 5 GHz up to 3 THz, our spectrometers provide an unparalleled ability to probe directly such questions as the hydration level, the dynamics of water and hydrated proteins over the 100 fs to 1 ns timescale. Employing an effective medium approximation to describe the complex dielectric response of the solvated proteins in solution we find that proteins are surrounded by a loosely and tightly held layers of water molecules that behave as if they are an integral part of the protein. The number of water molecules in the protein hydration shells varies with proteins, which can tell us the average surface structure of proteins. These measurements shed light on the macromolecular motions of proteins in their biologically relevant environment.

  13. Electrical transport properties of (La,Pr,Ca)MnO3 nanowires investigated using terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Nguyen, T. V. A.; Hattori, A. N.; Nagai, M.; Nakamura, T.; Ashida, M.; Tanaka, H.

    2016-03-01

    The electrical transport properties of a 100-nm-width (La,Pr,Ca)MnO3 nanowire sample were investigated using terahertz (THz) time domain spectroscopy. When the electric field of incident THz pulses was parallel to the nanowires, we obtained their intrinsic THz conductivity. The temperature-dependent dc conductivity and metallic fraction were simultaneously estimated by analyzing the THz conductivity using a metal-insulator composite model. The evaluated dc conductivity closely reproduced that measured by electrical probe measurement. The metallic fraction showed the evolution of electric domains from the metallic state at temperatures below 100 K to the insulating state at temperatures above 150 K through a coexistence region, which was in consistence with the phase-separated scenario.

  14. Charge transport in thin layer Na x CoO2 (x ˜ 0.63) studied by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Němec, H.; Knížek, K.; Jirák, Z.; Hejtmánek, J.; Soroka, M.; Buršík, J.

    2016-09-01

    Charge transport in Na0.63CoO2 thin film deposited by a spin-coating method was investigated experimentally by time-domain terahertz spectroscopy and theoretically using Monte Carlo calculations of charge response in nano-structured materials. The dominating type of transport mechanism over the entire investigated range of temperatures (20-300 K) is a metallic-like conductivity of charges partly confined in constituting nano-sized grains. Due to the granular character of our thin film, the scattering time at low temperatures is limited by scattering on grain boundaries and the conductivity is strongly suppressed due to capture of a major fraction of charge carriers in deep traps. Nevertheless, our experimental setup and the applied model allowed us to distinguish the parameters related to the grain interior from those influenced by grain boundaries, and to conclude that the metallic type of conductivity is the intrinsic property relevant to single crystal materials.

  15. Glass transition dynamics of anti-inflammatory ketoprofen studied by Raman scattering and terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Shibata, Tomohiko; Igawa, Hikaru; Kim, Tae Hyun; Mori, Tatsuya; Kojima, Seiji

    2014-03-01

    A liquid-glass transition and a crystalline state of pharmaceutical racemic ketoprofen were studied by Raman scattering and the broadband terahertz time-domain spectroscopy (THz-TDS) in the frequency range from 9 to 260 cm-1. The low-frequency Raman scattering spectra clearly shows the remarkable change related to a liquid-glass transition at about Tg = 267 K. After melt-quenching at liquid nitrogen temperature, a boson peak appears at about 16.5 cm-1 near and below Tg and the intensity of quasi-elastic scattering related to structural relaxation increases markedly on heating. The crystalline racemic ketoprofen of "conformer A" shows the noncoincidence effect of mode frequencies below 200 cm-1 between Raman scattering spectra and dielectric spectra observed by THz-TDS.

  16. Evaluation of effective electric permittivity and magnetic permeability in metamaterial slabs by terahertz time-domain spectroscopy.

    PubMed

    Minowa, Yosuke; Fujii, Takashi; Nagai, Masaya; Ochiai, Tetsuyuki; Sakoda, Kazuaki; Hirao, Kazuyuki; Tanaka, Koichiro

    2008-03-31

    We established a novel method to evaluate effective optical constants by terahertz (THz) time domain spectroscopy and suggested a strict definition of optical constants and an expression for electromagnetic energy loss following the second law of thermodynamics. We deduced the effective optical constants of phosphor bronze wire grids in the THz region experimentally and theoretically. The results depend strongly on the polarization of the THz waves. When the electric field is parallel to the wires, we observed Drude-like electric permittivities with a plasma frequency reduced by a factor of 10(-3), whereas when the field is perpendicular, the sample behaved as a simple dielectric film. We also observed unexpected magnetic permeabilities, which originate from the non-resonant real magnetic response of finite size-conductors.

  17. Investigation of pharmaceutical drugs and caffeine-containing foods using Fourier and terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    KaraliÅ«nas, Mindaugas; Venckevičius, Rimvydas; Kašalynas, Irmantas; Puc, Uroš; Abina, Andreja; Jeglič, Anton; Zidanšek, Aleksander; Valušis, Gintaras

    2015-08-01

    Several pharmaceutical drugs, such as alprazolam, ibuprofen, acetaminophen, activated carbon and others, and caffeine-containing foods were tested using terahertz (THz) time domain spectroscopy in the range from 0.3 to 2 THz. The dry powder of pharmaceutical drugs was mixed with HDPE and pressed into the pellets using hydraulic press. The coffee grounds were also pressed into the pellets after ball-milling and mixing with HDPE. The caffeine containing liquid foods were dried out on the paper strips of various stacking. Experiments allow one to determine characteristic spectral signatures of the investigated substances within THz range caused by active pharmaceutical ingredients, like in the case of caffeine, as well as supporting pharmaceutical ingredients. Spectroscopic THz imaging approach is considered as a possible option to identify packaged pharmaceutical drugs. The caffeine spectral features in the tested caffeine containing foods are difficult to observed due to the low caffeine concentration and complex caffeine chemical surrounding.

  18. Flexibility and non-destructive conductivity measurements of Ag nanowire based transparent conductive films via terahertz time domain spectroscopy.

    PubMed

    Hwang, Gyujeong; Balci, Soner; Güngördü, M Zeki; Maleski, Alex; Waters, Joseph; Lee, Sunjong; Choi, Sangjun; Kim, Kyoungkook; Cho, Soohaeng; Kim, Seongsin M

    2017-02-20

    Highly stable and flexible transparent electrodes are fabricated based on silver nanowires (AgNWs) on both polyethylene-terephthalate (PET) and polyimide (PI) substrates. Terahertz time domain spectroscopy (THz-TDS) was utilized to probe AgNW films while bended with a radius 5 mm to discover conductivity of bended films which was further analyzed through Drude-Smith model. AgNW films experience little degradation in conductivity (<3%) before, after, and during 1000 bending cycles. Highly stable AgNW flexible electrodes have broad applications in flexible optoelectronic and electronic devices. THz-TDS is an effective technique to investigate the electrical properties of the bended and flattened conducting films in a nondestructive manner.

  19. [Identification of pearl powder using microscopic infrared reflectance spectroscopy].

    PubMed

    Zhang, Xuan; Hu, Chao; Yan, Yan; Yang, Hai-Feng; Li, Jun-Fang; Bai, Hua; Xi, Guang-Cheng; Liao, Jie

    2014-09-01

    Pearl is a precious ornament and traditional Chinese medicine, which application history in China is more than 2000 years. It is well known that the chemical ingredients of shell and pearl are very similar, which all of them including calcium carbonate and various amino acids. Generally, shell powders also can be used as medicine; however, its medicinal value is much lower than that of pearl powders. Due to the feature similarity between pearl powders and shell powders, the distinguishment of them by detecting chemical composition and morphology is very difficult. It should be noted that shell powders have been often posing as pearl powders in markets, which seriously infringes the interests of consumers. Identification of pearl powder was investigated by microscopic infrared reflectance spectroscopy, and pearl powder as well as shell powder was calcined at different temperatures for different time before infrared reflectance spectroscopy analysis. The experimental results indicated that when calcined at 400 °C for 30 minutes under atmospheric pressure, aragonite in pearl powder partly transformed into calcite, while aragonite in shell powder completely transformed into calcite. At the same time, the difference in phase transition between the pearl powders 'and shell powders can be easily detected by using the microscopic infrared reflectance spectroscopy. Therefore, based on the difference in their phase transition process, infrared reflectance spectroscopy can be used to identify phase transformation differences between pearl powder and shell powder. It's more meaningfully that the proposed infrared reflectance spec- troscopy method was also investigated for the applicability to other common counterfeits, such as oyster shell powders and abalone shell powders, and the results show that the method can be a simple, efficiently and accurately method for identification of pearl powder.

  20. Optical fiber sensing based on reflection laser spectroscopy.

    PubMed

    Gagliardi, Gianluca; Salza, Mario; Ferraro, Pietro; Chehura, Edmond; Tatam, Ralph P; Gangopadhyay, Tarun K; Ballard, Nicholas; Paz-Soldan, Daniel; Barnes, Jack A; Loock, Hans-Peter; Lam, Timothy T-Y; Chow, Jong H; De Natale, Paolo

    2010-01-01

    An overview on high-resolution and fast interrogation of optical-fiber sensors relying on laser reflection spectroscopy is given. Fiber Bragg-gratings (FBGs) and FBG resonators built in fibers of different types are used for strain, temperature and acceleration measurements using heterodyne-detection and optical frequency-locking techniques. Silica fiber-ring cavities are used for chemical sensing based on evanescent-wave spectroscopy. Various arrangements for signal recovery and noise reduction, as an extension of most typical spectroscopic techniques, are illustrated and results on detection performances are presented.

  1. Low-frequency spectra of the hexamethylbenzene/tetracyanoethylene electron donor-acceptor complexes in solution studied by terahertz time-domain spectroscopy.

    PubMed

    Yamamoto, Kohji; Kabir, Md Humayun; Hayashi, Michitoshi; Tominaga, Keisuke

    2005-05-07

    We have measured the frequency dependent extinction coefficients and refractive indices of electron donor-acceptor (EDA) complexes consisting of hexamethylbenzene (HMB; electron donor) and tetracyanoethylene (TCNE; electron acceptor) in the low-frequency region by terahertz time-domain spectroscopy (THz-TDS). A mixture of the 1:1 (DA) and 2:1 (D2A) EDA complexes exist in carbon tetrachloride solution, and we successfully obtained the spectral components of the 1:1 and 2:1 EDA complexes separately by analyzing the concentration dependence of the THz spectra. The 1:1 and 2:1 complexes show quite different THz spectra of the extinction coefficient, reflecting unique features of dynamics, fluctuations and intermolecular interactions of these complexes. Polarization-selective THz-TDS on the crystalline DA complex shows two peaks at 53 and 70 cm(-1) in the spectral component perpendicular to the crystal axis. On the other hand, the crystalline D2A complex exhibits peaks at 42 and 50 cm(-1) in the perpendicular spectral component. We compare the obtained spectra of the crystalline complex and the results of molecular orbital calculations at the HF/6-31G(d) level of theory to discuss the intermolecular vibrational modes of the complexes.

  2. The quantitative monitoring of mechanochemical reaction between solid L-tartaric acid and sodium carbonate monohydrate by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Xiaohong; Liu, Guifeng; Zhao, Hongwei; Zhang, Zengyang; Wei, Yongbo; Liu, Min; Wen, Wen; Zhou, Xingtai

    2011-11-01

    The solid-state reaction of chiral tartaric acid and alkali carbonate was studied by terahertz time-domain spectroscopy (THz-TDS). The sodium tartrate dihydrate was synthesized with high efficiency by mechanical grinding in the solid-state without waste that is particularly sustainable and environmentally benign. Distinct THz absorptions were observed for reactants and products. It indicates that THz spectroscopy is sensitive to different materials and crystal structures. The characteristic THz absorption peak at 1.09 THz of L (+)-Tartaric acid was selected for quantitative analysis. The reaction kinetics could be expressed by the Second-order equation and the Jander equation, which is consistent with a three-dimensional diffusion mechanism. The combination of multi-techniques including synchrotron radiation X-ray powder diffraction (SRXRPD), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM) was used to investigate the grinding process and presented supporting evidences. The results demonstrate that THz spectroscopy technique has great potential applications in process monitoring and analysis in pharmaceutical and chemical synthesis industry.

  3. Nondestructive evaluation of cork enclosures using terahertz/millimeter wave spectroscopy and imaging.

    PubMed

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

    2008-01-01

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

  4. Depth-resolved measurements with elliptically polarized reflectance spectroscopy

    PubMed Central

    Bailey, Maria J.; Sokolov, Konstantin

    2016-01-01

    The ability of elliptical polarized reflectance spectroscopy (EPRS) to detect spectroscopic alterations in tissue mimicking phantoms and in biological tissue in situ is demonstrated. It is shown that there is a linear relationship between light penetration depth and ellipticity. This dependence is used to demonstrate the feasibility of a depth-resolved spectroscopic imaging using EPRS. The advantages and drawbacks of EPRS in evaluation of biological tissue are analyzed and discussed. PMID:27446712

  5. Reflectance spectroscopy of gold nanoshells: computational predictions and experimental measurements

    NASA Astrophysics Data System (ADS)

    Lin, Alex W. H.; Lewinski, Nastassja A.; Lee, Min-Ho; Drezek, Rebekah A.

    2006-10-01

    Gold nanoshells are concentric spherical constructs that possess highly desirable optical responses in the near infrared. Gold nanoshells consist of a thin outer gold shell and a silica core and can be used for both diagnostic and therapeutic purposes by tuning the optical response through changing the core-shell ratio as well as the overall size. Although optical properties of gold nanoshells have already been well documented, the reflectance characteristics are not well understood and have not yet been elucidated by experimental measurements. Yet, in order to use gold nanoshells as an optical contrast agent for scattering-based optical methods such as reflectance spectroscopy, it is critical to characterize the reflectance behavior. With this in mind, we used a fiber-optic-based spectrometer to measure diffuse reflectance of gold nanoshell suspensions from 500 nm to 900 nm. Experimental results show that gold nanoshells cause a significant increase in the measured reflectance. Spectral features associated with scattering from large angles ( 180°) were observed at low nanoshell concentrations. Monte Carlo modeling of gold nanoshells reflectance demonstrated the efficacy of using such methods to predict diffuse reflectance. Our studies suggest that gold nanoshells are an excellent candidate as optical contrast agents and that Monte Carlo methods are a useful tool for optimizing nanoshells best suited for scattering-based optical methods.

  6. Terahertz plasmonic Bessel beamformer

    SciTech Connect

    Monnai, Yasuaki; Shinoda, Hiroyuki; Jahn, David; Koch, Martin; Withayachumnankul, Withawat

    2015-01-12

    We experimentally demonstrate terahertz Bessel beamforming based on the concept of plasmonics. The proposed planar structure is made of concentric metallic grooves with a subwavelength spacing that couple to a point source to create tightly confined surface waves or spoof surface plasmon polaritons. Concentric scatterers periodically incorporated at a wavelength scale allow for launching the surface waves into free space to define a Bessel beam. The Bessel beam defined at 0.29 THz has been characterized through terahertz time-domain spectroscopy. This approach is capable of generating Bessel beams with planar structures as opposed to bulky axicon lenses and can be readily integrated with solid-state terahertz sources.

  7. Determination of carrier concentration dependent electron effective mass and scattering time of n-ZnO thin film by terahertz time domain spectroscopy

    SciTech Connect

    Tang, J.; Tay, C. B.; Deng, L. Y.; Zhang, X. H.; Chai, J. W.; Qin, H.; Liu, H. W.; Venkatesan, T.; Chua, S. J.

    2014-01-21

    We demonstrated a novel and widely accessible method for determining the electron effective mass and scattering time of ZnO films with different carrier concentrations by combining terahertz time-domain spectroscopy with Hall measurement. The terahertz time domain spectroscopy (THz-TDS) transmission spectra (0.1–2THz) were well described by Drude model. It is found that electron effective mass varied from 0.23m{sub 0} to 0.26m{sub 0} as the electron concentration changes from 5.9 × 10{sup 17} cm{sup −3} to 4.0 × 10{sup 19} cm{sup −3}. The carrier concentration dependent characteristic is ascribed to the non-parabolicity of conduction band. Free carrier localization mechanism explained the discrepancy in mobilities obtained from THz-TDS and Hall measurements.

  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. Reflectance spectroscopy for noninvasive evaluation of hair follicle stage

    NASA Astrophysics Data System (ADS)

    Liu, Caihua; Guan, Yue; Wang, Jianru; Zhong, Xiewei; Liu, Xiuli; Zhu, Dan

    2015-05-01

    Hair follicle offers an excellent model for systems biology and regenerative medicine. So far, the stages of hair follicle growth have been evaluated by histological examination. In this work, a noninvasive spectroscopy was proposed by measuring the diffuse reflectance of mouse skin and analyzing the melanin value. Results show that the skin diffuse reflectance was relatively high when hair follicles were at the telogen stage and at the beginning of the anagen stage, and decreased with the progression of the anagen stage. When the hair follicle entered into the catagen stage, the diffuse reflectance gradually increased. The changes in the melanin content of skin had contrary dynamics. Substages of the hair follicle cycle could be distinguished by comparing the changes in melanin value with the histological examination. This study provided a new method for noninvasive evaluation of the hair follicle stage, and should be valuable for basic and therapeutic investigations on hair regeneration.

  10. Quantitative analysis of binary polymorphs mixtures of fusidic acid by diffuse reflectance FTIR spectroscopy, diffuse reflectance FT-NIR spectroscopy, Raman spectroscopy and multivariate calibration.

    PubMed

    Guo, Canyong; Luo, Xuefang; Zhou, Xiaohua; Shi, Beijia; Wang, Juanjuan; Zhao, Jinqi; Zhang, Xiaoxia

    2017-03-10

    Vibrational spectroscopic techniques such as infrared, near-infrared and Raman spectroscopy have become popular in detecting and quantifying polymorphism of pharmaceutics since they are fast and non-destructive. This study assessed the ability of three vibrational spectroscopy combined with multivariate analysis to quantify a low-content undesired polymorph within a binary polymorphic mixture. Partial least squares (PLS) regression and support vector machine (SVM) regression were employed to build quantitative models. Fusidic acid, a steroidal antibiotic, was used as the model compound. It was found that PLS regression performed slightly better than SVM regression in all the three spectroscopic techniques. Root mean square errors of prediction (RMSEP) were ranging from 0.48% to 1.17% for diffuse reflectance FTIR spectroscopy and 1.60-1.93% for diffuse reflectance FT-NIR spectroscopy and 1.62-2.31% for Raman spectroscopy. The results indicate that diffuse reflectance FTIR spectroscopy offers significant advantages in providing accurate measurement of polymorphic content in the fusidic acid binary mixtures, while Raman spectroscopy is the least accurate technique for quantitative analysis of polymorphs.

  11. Reflective mesoscopic spectroscopy for noninvasive detection of reflective index alternations at nano-scale

    NASA Astrophysics Data System (ADS)

    Tao, Yuanhao; Ding, Zhihua

    2011-01-01

    Cancer has been one of the most serious threats to human life. However, there is no substantial improvement in overall treatment of cancer patients. One of the key reasons is the unavailability of convenient method to detect cellular alterations in ultra-early stage of carcinogenesis processes, where genetic aberrations at nano-scale have not yet resulted in histological changes. In this paper, we described an optical method based on reflective mesoscopic spectroscopy for ultra-early cancer detection. According to mesoscopic light transport theory, photons propagating in one dimension (1D) within a weakly disordered medium have the non-self-averaging effect. Reflected signal after 1D propagating is sensitive to any length scale of refractive index fluctuations due to multiple interferences of light waves travelling along 1D trajectory. The principle of mesoscopic spectroscopy for perceiving reflective index fluctuations at length scale of nanometers is introduced. A system for the measurement of reflective mesoscopic spectroscopy based on spatial-incoherence broadband source and spectrometer is established. Simulations on light propagation in cell-emulating model with controlled refractive index distribution are done by finite-difference time-domain (FDTD) approach.

  12. Picosecond charge transport in rutile at high carrier densities studied by transient terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Zajac, V.; Němec, H.; Kužel, P.

    2016-09-01

    We study terahertz photoconductivity of a rutile single crystal between 10 and 300 K under strong photoexcitation by femtosecond pulses at 266 nm. A marked dependence of the carrier mobility on the carrier density is observed leading to highly complex transport phenomena on a picosecond time scale. We develop a general model of carrier photoconductive response in the case of time dependent inhomogeneous distribution of carrier density and mobility. This allows us to assess an important role of both electrons and holes in the response of photoexcited rutile. At low temperatures, the carrier mobility is initially reduced due to the electron-hole scattering and increases by one order of magnitude upon ambipolar diffusion of the carriers into deeper regions of the sample. At room temperature, contributions of transient hot optical phonons and/or of midinfrared polaron excitations with charge-density-dependent dielectric strength emerge in the photoconductivity spectra.

  13. Excited-state charging energies in quantum dots investigated by terahertz photocurrent spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Shibata, K.; Nagai, N.; Ndebeka-Bandou, C.; Bastard, G.; Hirakawa, K.

    2016-06-01

    We have investigated the excited-state (ES) charging energies in quantum dots (QDs) by measuring a terahertz (THz)-induced photocurrent in a single-electron transistor (SET) geometry that contains a single InAs QD between metal nanogap electrodes. A photocurrent is produced in the QD SETs through THz intersublevel transitions and the subsequent resonant tunneling. We have found that the photocurrent exhibits stepwise change even within one Coulomb blockaded region as the electrochemical potential in the QD is swept by the gate voltage. From the threshold for the photocurrent generation, we have determined the charging energies for adding an electron in the photoexcited state in the QD. Furthermore, the charging energies for the ESs with different electron configurations are clearly resolved. The present THz photocurrent measurements are essentially dynamical experiments and allow us to analyze electronic properties in off-equilibrium states in the QD.

  14. Dipolar resonances in conductive carbon micro-fibers probed by near-field terahertz spectroscopy

    DOE PAGES

    Khromova, I.; Navarro-Cia, M.; Brener, I.; ...

    2015-07-13

    In this study, we observe dipole resonances in thin conductive carbon micro-fibers by detecting an enhanced electric field in the near-field of a single fiber at terahertz (THz) frequencies. Time-domain analysis of the electric field shows that each fiber sustains resonant current oscillations at the frequency defined by the fiber's length. Strong dependence of the observed resonance frequency and degree of field enhancement on the fibers' conductive properties enable direct non-contact probing of the THz conductivity in single carbon micro-fibers. We find the conductivity of the fibers to be within the range of 1– 5∙104 S/m. This approach is suitablemore » for experimental characterization of individual doped semiconductor resonators for THz metamaterials and devices.« less

  15. Dipolar resonances in conductive carbon micro-fibers probed by near-field terahertz spectroscopy

    SciTech Connect

    Khromova, I.; Navarro-Cia, M.; Brener, I.; Reno, J. L.; Ponomarev, A.; Mitrofanov, O.

    2015-07-13

    In this study, we observe dipole resonances in thin conductive carbon micro-fibers by detecting an enhanced electric field in the near-field of a single fiber at terahertz (THz) frequencies. Time-domain analysis of the electric field shows that each fiber sustains resonant current oscillations at the frequency defined by the fiber's length. Strong dependence of the observed resonance frequency and degree of field enhancement on the fibers' conductive properties enable direct non-contact probing of the THz conductivity in single carbon micro-fibers. We find the conductivity of the fibers to be within the range of 1– 5∙104 S/m. This approach is suitable for experimental characterization of individual doped semiconductor resonators for THz metamaterials and devices.

  16. Terahertz spectroscopy on Faraday and Kerr rotations in a quantum anomalous Hall state

    PubMed Central

    Okada, Ken N.; Takahashi, Youtarou; Mogi, Masataka; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S.; Ogawa, Naoki; Kawasaki, Masashi; Tokura, Yoshinori

    2016-01-01

    Electrodynamic responses from three-dimensional topological insulators are characterized by the universal magnetoelectric term constituent of the Lagrangian formalism. The quantized magnetoelectric coupling, which is generally referred to as topological magnetoelectric effect, has been predicted to induce exotic phenomena including the universal low-energy magneto-optical effects. Here we report the experimental indication of the topological magnetoelectric effect, which is exemplified by magneto-optical Faraday and Kerr rotations in the quantum anomalous Hall states of magnetic topological insulator surfaces by terahertz magneto-optics. The universal relation composed of the observed Faraday and Kerr rotation angles but not of any material parameters (for example, dielectric constant and magnetic susceptibility) well exhibits the trajectory towards the fine structure constant in the quantized limit. PMID:27436710

  17. Terahertz spectroscopy on Faraday and Kerr rotations in a quantum anomalous Hall state.

    PubMed

    Okada, Ken N; Takahashi, Youtarou; Mogi, Masataka; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S; Ogawa, Naoki; Kawasaki, Masashi; Tokura, Yoshinori

    2016-07-20

    Electrodynamic responses from three-dimensional topological insulators are characterized by the universal magnetoelectric term constituent of the Lagrangian formalism. The quantized magnetoelectric coupling, which is generally referred to as topological magnetoelectric effect, has been predicted to induce exotic phenomena including the universal low-energy magneto-optical effects. Here we report the experimental indication of the topological magnetoelectric effect, which is exemplified by magneto-optical Faraday and Kerr rotations in the quantum anomalous Hall states of magnetic topological insulator surfaces by terahertz magneto-optics. The universal relation composed of the observed Faraday and Kerr rotation angles but not of any material parameters (for example, dielectric constant and magnetic susceptibility) well exhibits the trajectory towards the fine structure constant in the quantized limit.

  18. Anisotropic Differential Reflectance Spectroscopy of Thin GeSe

    NASA Astrophysics Data System (ADS)

    Matson, Joseph; Woods, Grace; Churchill, Hugh

    2017-01-01

    Atomically thin monochalcogenides are predicted to exhibit a two-dimensional structural phase transition. This phase transition could be useful for designing new phase change memory devices. The critical temperature is dependent on the material as well as the thickness, and is predicted to occur just above room temperature for monolayer GeSe. We used differential reflectance spectroscopy on thin samples of GeSe to measure changes in the optical anisotropy with temperature as a signature of this phase transition. We constructed an apparatus for temperature-depedendent spectroscopy of micro-scale GeSe samples, and measured anisotropic optical absorption of thin GeSe. We observed a decrease in optical anisotropy of GeSe at elevated temperatures, which may be a first indication of the continuous transition from a rectangular to a square lattice in that material. This work was supported by NSF REU Grant #EEC-1359306.

  19. Reflection of terahertz monochromatic surface plasmon-polaritons by a plane mirror

    NASA Astrophysics Data System (ADS)

    Gerasimov, V. V.; Knyazev, B. A.; Nikitin, A. K.

    2017-02-01

    Using a free electron laser developed in Novosibirsk, we have studied the reflection of monochromatic (λ = 130 μm) surface plasmon-polaritons (SPPs) from a plane mirror attached to a waveguiding surface. It is found that 100 % SPP reflection occurs not only in the perpendicular position of the mirror relative to the surface, but also when the mirror is deflected from the normal by the angle α being smaller than the limiting angle α* proportional to the SPP wave vector. When the mirror is deflected by the angle greater than α*, SPPs on a perfectly smooth surface must transform into a bulk wave, while, in the experiment, the SPP reflection coefficient decreases gradually to zero with increasing α, which is a manifestation of dispersion of the wave vector of monochromatic SPPs, caused by their scattering on the inhomogeneities of a real surface.

  20. Depth Profile Determination of Stratified Layers Using Internal Reflection Spectroscopy

    NASA Astrophysics Data System (ADS)

    Shick, Robert Adam

    It is the purpose of this project to develop a method to quantitatively determine depth profile information using internal reflection spectroscopy. The theory allowing depth profile information to be recovered from variable angle attenuated total reflection (VA-ATR) spectroscopy is shown for both perpendicular and parallel polarization. The major approximation is that the extinction coefficient must be small, so that the field decay due to distance and absorption are comparable. The errors invoked by these approximations are evaluated by comparison with exact optical simulations using dispersion theory. Having shown that the newly developed method is theoretically feasible, it is important to show that it is a viable technique with current instrumentation. It is shown that VA-ATR Fourier transform infrared spectroscopy is a valuable technique to recover depth profile information on the molecular level. A number of known step profiles are measured to determine the limits of applicability for this method. Thickness results obtained using the internal reflection technique are compared with thickness determination using a stylus profilometer. It is shown that the results using p-polarization are somewhat more realistic than s -polarization. The VA-ATR infrared technique was used to investigate the interaction and diffusion of poly(2,6-dimethyl-1,4 -phenylene oxide), PPO, and polystyrene, PS. Optical theory was employed to clarify the effect of the local interactions on the infrared spectra. Optical theory was also used to determine composition profiles at various times of inter -diffusion. It was observed that migration occurred between the PPO and the PS layer, even below the glass transition of the PPO. This migration proceeded linearly with time ^{1/2} which is an indication of Fickian diffusion, although the profiles had some additional non-Fickian characteristics.

  1. Depth sensitive oblique polarized reflectance spectroscopy of oral epithelial tissue

    NASA Astrophysics Data System (ADS)

    Jimenez, Maria K.; Lam, Sylvia; Poh, Catherine; Sokolov, Konstantin

    2014-05-01

    Identifying depth-dependent alterations associated with epithelial cancerous lesions can be challenging in the oral cavity where variable epithelial thicknesses and troublesome keratin growths are prominent. Spectroscopic methods with enhanced depth resolution would immensely aid in isolating optical properties associated with malignant transformation. Combining multiple beveled fibers, oblique collection geometry, and polarization gating, oblique polarized reflectance spectroscopy (OPRS) achieves depth sensitive detection. We report promising results from a clinical trial of patients with oral lesions suspected of dysplasia or carcinoma demonstrating the potential of OPRS for the analysis of morphological and architectural changes in the context of multilayer, epithelial oral tissue.

  2. Analysis of remote reflection spectroscopy to monitor plant health

    NASA Astrophysics Data System (ADS)

    Woodhouse, R.; Heeb, M.; Berry, W.; Hoshizaki, T.; Wood, M.

    1994-11-01

    Remote non-contact reflection spectroscopy is examined as a method for detecting stress in Controlled Ecological Life Support System CELSS type crops. Lettuce (Latuca Sativa L. cv. Waldmans Green) and wheat (Triticum Aestivum L. cv. Yecora Rojo) were grown hydroponically. Copper and zinc treatments provided toxic conditions. Nitrogen, phosphorous, and potassium treatments were used for deficiency conditions. Water stress was also induced in test plants. Reflectance spectra were obtained in the visible and near infrared (400nm to 2600nm) wavebands. Numerous effects of stress conditions can be observed in the collected spectra and this technique appears to have promise as a remote monitor of plant health, but significant research remains to be conducted to realize the promise.

  3. Analysis of remote reflection spectroscopy to monitor plant health.

    PubMed

    Woodhouse, R; Heeb, M; Berry, W; Hoshizaki, T; Wood, M

    1994-11-01

    Remote non-contact reflection spectroscopy is examined as a method for detecting stress in Controlled Ecological Life Support System CELSS type crops. Lettuce (Lactuca [correction of Latuca] Sativa L. cv. Waldmans Green) and wheat (Triticum Aestivum L. cv. Yecora Rojo) were grown hydroponically. Copper and zinc treatments provided toxic conditions. Nitrogen, phosphorous, and potassium treatments were used for deficiency conditions. Water stress was also induced in test plants. Reflectance spectra were obtained in the visible and near infrared (400nm to 2600nm) wavebands. Numerous effects of stress conditions can be observed in the collected spectra and this technique appears to have promise as a remote monitor of plant health, but significant research remains to be conducted to realize the promise.

  4. Hydrodynamic potential-modulated reflectance spectroscopy: theory and experiment.

    PubMed

    Wang, R L; Peter, L M; Qiu, F L; Fisher, A C

    2001-05-15

    This article describes the development and application of a new electrochemical methodology based on potential-modulated UV-vis reflectance spectroscopy (PMRS). The device configuration is based upon a thin-layer flow-through channel cell incorporating a platinum working electrode. Reagent solutions are pumped through the cell under well-defined hydrodynamic conditions and electrolyzed at the platinum working electrode. Measurements are presented for linear sweep and fixed dc potentials with a superimposed small amplitude sinusoidal potential perturbation. A UV-vis source is employed to irradiate the electrode region, and the resulting reflected signal is analyzed using a phase sensitive detector. Experimental studies using tris(4-bromophenyl) amine (TBPA) in acetonitrile are presented which quantify the relationship between the absorption spectrum and reflected light intensity as a function of the transport rate, electrolysis reactions, and the modulation frequency of the incident irradiation. The experimental results are analyzed using numerical simulations based on a finite difference strategy. These permit the quantitative prediction of the concentration distribution of reagents within the cell. A fast Fourier transform (FFT) routine was used to analyze the frequency response of the numerically predicted reflectance signal. Excellent agreement was observed between the numerical predictions and experimental observations.

  5. 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.

  6. Effect of in-material losses on terahertz absorption, transmission, and reflection in photonic crystals made of polar dielectrics

    SciTech Connect

    Serebryannikov, Andriy E.; Nojima, S.; Alici, K. B.; Ozbay, Ekmel

    2015-10-07

    The effect of the material absorption factor on terahertz absorption (A), transmittance (T), and reflectance (R) for slabs of PhC that comprise rods made of GaAs, a polar dielectric, is studied. The main goal was to illustrate how critical a choice of the absorption factor for simulations is and to indicate the importance of the possible modification of the absorption ability by using either active or lossy impurities. The spectra of A, T, and R are strongly sensitive to the location of the polaritonic gap with respect to the photonic pass and stop bands connected with periodicity that enables the efficient combination of the effects of material and structural parameters. It will be shown that the spectra can strongly depend on the utilized value of the material absorption factor. In particular, both narrow and wide absorption bands may appear owing to a variation of the material parameters with a frequency in the vicinity of the polaritonic gap. The latter are often achieved at wideband suppression of transmission, so that an ultra-wide stop band can appear as a result of adjustment of the stop bands having different origin. The results obtained at simultaneous variation of the absorption factor and frequency, and angle of incidence and frequency, indicate the possibility of the existence of wide ranges of tolerance, in which the basic features do remain. This allows for mitigating the accuracy requirements for the absorption factor in simulations and promises the efficient absorption of nonmonochromatic waves and beams with a wide angular spectrum. Suppression of narrowband effects in transmission is demonstrated at rather large values of the absorption factor, when they appear due to either the defect modes related to structural defects or dispersion inspired variations of the material parameters in the vicinity of the polaritonic gap. Comparison with auxiliary structures helps one to detect the common features and differences of homogeneous slabs and slabs of a

  7. Assessing human skin with diffuse reflectance spectroscopy and colorimetry

    NASA Astrophysics Data System (ADS)

    Seo, InSeok; Liu, Yang; Bargo, Paulo R.; Kollias, Nikiforos

    2012-02-01

    Colorimetry has been used as an objective measure of perceived skin color by human eye to document and score physiological responses of the skin from external insults. CIE color space values (L*, a* and b*) are the most commonly used parameters to correlate visually perceived color attributes such as L* for pigment, a* for erythema, and b* for sallowness of the skin. In this study, we investigated the relation of Lab color scale to the amount of major skin chromophores (oxy-, deoxyhemoglobin and melanin) calculated from diffuse reflectance spectroscopy. Thirty two healthy human subjects with ages from 20 to 70 years old, skin types I-VI, were recruited for the study. DRS and colorimetry measurements were taken from the left and right cheeks, and on the right upper inner arm. The melanin content calculated from 630-700 nm range of DRS measurements was shown to correlate with the lightness of skin (L*) for most skin types. For subjects with medium-to-light complexion, melanin measured at the blue part spectrum and hemoglobin interfered on the relation of lightness of the skin color to the melanin content. The sallowness of the skin that is quantified by the melanin contribution at the blue part spectrum of DRS was found to be related to b* scale. This study demonstrates the importance of documenting skin color by assessing individual skin chromophores with diffuse reflectance spectroscopy, in comparison to colorimetry assessment.

  8. Transient terahertz spectroscopy of excitons and unbound carriers in quasi two-dimensional electron-hole gases

    SciTech Connect

    Kaindl, Robert A.; Hagele, D.; Carnahan, M. A.; Chemla, D. S.

    2008-09-11

    We report a comprehensive experimental study and detailed model analysis of the terahertz (THz) dielectric response and density kinetics of excitons and unbound electron-hole pairs in GaAs quantum wells. A compact expression is given, in absolute units, for the complex-valued THz dielectric function of intra-excitonic transitions between the 1s and higher-energy exciton and continuum levels. It closely describes the THz spectra of resonantly generated excitons. Exciton ionization and formation are further explored, where the THz response exhibits both intra-excitonic and Drude features. Utilizing a two-component dielectric function, we derive the underlying exciton and unbound pair densities. In the ionized state, excellent agreement is found with the Saha thermodynamic equilibrium, which provides experimental verification of the two-component analysis and density scaling. During exciton formation, in turn, the pair kinetics is quantitatively described by a Saha equilibrium that follows the carrier cooling dynamics. The THz-derived kinetics is, moreover, consistent with time-resolved luminescence measured for comparison. Our study establishes a basis for tracking pair densities via transient THz spectroscopy of photoexcited quasi-2D electron-hole gases.

  9. Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy.

    PubMed

    Joyce, Hannah J; Docherty, Callum J; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Lloyd-Hughes, James; Herz, Laura M; Johnston, Michael B

    2013-05-31

    We have performed a comparative study of ultrafast charge carrier dynamics in a range of III-V nanowires using optical pump-terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm² V⁻¹ s⁻¹, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s⁻¹. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10⁵  cm s⁻¹. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices.

  10. Study on intelligent recognition detection technology of debond defects for ceramic matrix composites based on terahertz time domain spectroscopy.

    PubMed

    Ren, Jiaojiao; Li, Lijuan; Zhang, Dandan; Qiao, Xiaoli; Lv, Qiongying; Cao, Guohua

    2016-09-10

    With the wide use of high-temperature-resistant ceramic matrix composites (CMCs) in aviation and space flight, it is important to detect the quality of the bonding. This paper used terahertz (THz) time-domain spectroscopy nondestructive testing technology to inspect the bonding defects of the CMC. This paper puts forward a method-extraction method, which is applied to make samples to simulate the bonding defect of CMC by embedding polytetrafluoroethylene (PTFE) sheets with 0.12 mm thickness into the adhesive layer and extracting it after curing and presetting the bonding defects. On the basis of the classical and analytical algorithms, such as the maximum in time-domain and power spectrum integration, through further study in the THz spectral characteristics of bonding samples for CMC, we specifically introduce the upper debond coefficient, lower debond coefficient, average absorption coefficient for the frequency domain, centroid coefficient for the frequency domain, and other characteristics. By optimizing the THz detection characteristics set, as a sample, we adopt the neural network intelligent recognition algorithm to detect the upper and lower debond defects in samples and realize the intelligent identification for CMC debond defects.

  11. Terahertz spectroscopy of two-dimensional electron-hole pairs: probing Mott physics of magneto-excitons

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Gao, Weilu; Watson, John; Manfra, Michael; Kono, Junichiro

    2015-03-01

    Density-dependent Coulomb interactions can drive electron-hole (e - h) pairs in semiconductors through an excitonic Mott transition from an excitonic gas into an e - h plasma. Theoretical studies suggest that these interactions can be strongly modified by an external magnetic field, including the absence of inter-exciton interactions in the high magnetic field limit in two dimensions, due to an e - h charge symmetry, which results in ultrastable magneto-excitons. Here, we present a systematic experimental study of e - h pairs in photo-excited undoped GaAs quantum wells in magnetic fields with ultrafast terahertz spectroscopy. We simultaneously monitored the dynamics of the intraexcitonic 1 s-2 p transition (which splits into 1 s-2p+ and 1 s-2p- transitions in a magnetic field) and the cyclotron resonance of unbound electrons and holes up to 10 Tesla. We found that the 1 s-2p- absorption feature is robust at high magnetic fields even under high excitation fluences, indicating magnetically enhanced stability of excitons. We will discuss the Mott physics of magneto-excitons as a function of temperature, e - h pair density, optical pump delay time, as well as magnetic field, and also compare two-dimensional excitons in GaAs quantum wells with three-dimensional excitons in bulk GaAs.

  12. Determination of the optical properties of melanin-pigmented human skin equivalents using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Lipscomb, Dawn; Echchgadda, Ibtissam; Peralta, Xomalin G.; Wilmink, Gerald J.

    2013-02-01

    Terahertz time-domain spectroscopy (THz-TDS) methods have been utilized in previous studies in order to characterize the optical properties of skin and its primary constituents (i.e., water, collagen, and keratin). However, similar experiments have not yet been performed to investigate whether melanocytes and the melanin pigment that they synthesize contribute to skin's optical properties. In this study, we used THz-TDS methods operating in transmission geometry to measure the optical properties of in vitro human skin equivalents with or without normal human melanocytes. Skin equivalents were cultured for three weeks to promote gradual melanogenesis, and THz time domain data were collected at various time intervals. Frequency-domain analysis techniques were performed to determine the index of refraction (n) and absorption coefficient (μa) for each skin sample over the frequency range of 0.1-2.0 THz. We found that for all samples as frequency increased, n decreased exponentially and the μa increased linearly. Additionally, we observed that skin samples with higher levels of melanin exhibited greater n and μa values than the non-pigmented samples. Our results indicate that melanocytes and the degree of melanin pigmentation contribute in an appreciable manner to the skin's optical properties. Future studies will be performed to examine whether these contributions are observed in human skin in vivo.

  13. Evaluation of Penicillium digitatum sterilization using non-equilibrium atmospheric pressure plasma by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Hiraoka, Takehiro; Ebizuka, Noboru; Takeda, Keigo; Ohta, Takayuki; Kondo, Hiroki; Ishikawa, Kenji; Kawase, Kodo; Ito, Masafumi; Sekine, Makoto; Hori, Masaru

    2011-10-01

    Recently, the plasma sterilization has attracted much attention as a new sterilization technique that takes the place of spraying agricultural chemicals. The conventional methods for sterilization evaluation, was demanded to culture the samples for several days after plasma treatment. Then, we focused on Terahertz time-domain spectroscopy (THz-TDS). At the THz region, vibrational modes of biological molecules and fingerprint spectra of biologically-relevant molecules were also observed. In this study, our purpose was measurement of the fingerprint spectrum of the Penicillium digitatum (PD) spore and establishment of sterilization method by THz-TDS. The sample was 40mg/ml PD spore suspensions which dropped on cover glass. The atmospheric pressure plasma generated under the conditions which Ar gas flow was 3slm, and alternating voltage of 6kV was applied. The samples were exposed the plasma from 10mm distance for 10 minutes. We could obtain the fingerprint spectrum of the PD spore from 0.5 to 0.9THz. This result indicated the possibility of in-situ evaluation for PD sterilization using THz-TDS.

  14. Low-frequency vibration study of amino acids using terahertz spectroscopy and solid-state density functional theory

    NASA Astrophysics Data System (ADS)

    Zhang, Feng; Tominaga, Keisuke; Hayashi, Michitoshi; Wang, Houng-Wei

    2014-11-01

    Understanding the low-frequency normal modes of amino acids, the building blocks of proteins, is crucial to reveal the vibration-function relationship in the macromolecular system. Recent advances in terahertz spectroscopy (THz) and solid-state density functional theory (DFT) have ensured an accurate description of low-frequency modes of amino acids. New knowledge people have learnt so far is that the inter- and intra-molecular vibrations are strongly mixed with each other in the THz region through the vibrational coordinate mixing. Rich information is believed embedded in this phenomenon. We introduce a generalized mode-analysis method that allows for the accurate decomposition of a normal mode of interest into the three intermolecular translations, three principal librations and various intrinsic intramolecular vibrations. This mode-analysis method will be demonstrated in the crystalline C60 systems and then applied to shed light on the nature of low-frequency phonons of glycine, diglycine and triglycine. This method helps reveal new intramolecular vibrational modes on the first hand, and more importantly, illuminate a new phenomenon of the frequency distribution of intramolecular vibrations (FDIV). FDIV describes the possible broad distributions of important intramolecular vibrations in the low-frequency normal modes. The FDIV concept may indicate an additional mechanism for the intramolecular vibrations to become thermally active and participate in various biological functions.

  15. Far-infrared spectroscopic characterization of explosives for security applications using broadband terahertz time-domain spectroscopy.

    PubMed

    Fan, W H; Burnett, A; Upadhya, P C; Cunningham, J; Linfield, E H; Davies, A G

    2007-06-01

    Broadband terahertz time-domain spectroscopy (THz-TDS) has been used to measure the far-infrared (FIR) vibrational spectra of several commonly used pure explosives, including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3-dinitrato-2,2-bis(nitratomethyl)propane (PETN), and two types of plastic explosive, SEMTEX and SX2. A number of distinct absorption peaks, originating from FIR-active vibrational modes of these polycrystalline energetic materials, were observed in the frequency range 0.3-7.5 THz (10-250 cm(-1)). In addition, the temperature-dependent FIR vibrational spectra of PETN were measured between 4 K and 296 K with several well-resolved absorption peaks observed across this temperature range. We find that as the temperature is reduced, the observed absorption peaks resolve into narrower features and shift towards higher frequencies. The temperature dependence of the spectra is explained in terms of the anharmonicity of the vibrational potentials of crystalline compounds, and an empirical fit is given to describe the peak shift with temperature.

  16. Autofluorescence and diffuse reflectance patterns in cervical spectroscopy

    NASA Astrophysics Data System (ADS)

    Marin, Nena Maribel

    Fluorescence and diffuse reflectance spectroscopy are two new optical technologies, which have shown promise to aid in the real time, non-invasive identification of cancers and precancers. Spectral patterns carry a fingerprint of scattering, absorption and fluorescence properties in tissue. Scattering, absorption and fluorescence in tissue are directly affected by biological features that are diagnostically significant, such as nuclear size, micro-vessel density, volume fraction of collagen fibers, tissue oxygenation and cell metabolism. Thus, analysis of spectral patterns can unlock a wealth of information directly related with the onset and progression of disease. Data from a Phase II clinical trial to assess the technical efficacy of fluorescence and diffuse reflectance spectroscopy acquired from 850 women at three clinical locations with two research grade optical devices is calibrated and analyzed. Tools to process and standardize spectra so that data from multiple spectrometers can be combined and analyzed are presented. Methodologies for calibration and quality assurance of optical systems are established to simplify design issues and ensure validity of data for future clinical trials. Empirically based algorithms, using multivariate statistical approaches are applied to spectra and evaluated as a clinical diagnostic tool. Physically based algorithms, using mathematical models of light propagation in tissue are presented. The presented mathematical model combines a diffusion theory in P3 approximation reflectance model and a 2-layer fluorescence model using exponential attenuation and diffusion theory. The resulting adjoint fluorescence and reflectance model extracts twelve optical properties characterizing fluorescence efficiency of cervical epithelium and stroma fluorophores, stromal hemoglobin and collagen absorption, oxygen saturation, and stromal scattering strength and shape. Validations with Monte Carlo simulations show that adjoint model extracted

  17. Terahertz time-domain spectroscopy of two-dimensional electron gasses at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Curtis, Jeremy A.

    This dissertation covers two projects that were in the logical path to studying decoherence in a high mobility GaAs two--dimensional electron gas at high magnetic fields. The first project is the ultrafast non--degenerate pump--probe spectroscopic study of bulk GaAs in the Split Florida Helix at the National High Magnetic Field Laboratory at Florida State University. This project was undertaken as a proof of concept that ultrafast optics could be done in the Split Florida Helix so that we might study a high mobility two dimensional electron gas using THz time--domain spectroscopy at high magnetic fields, which is a much more complicated measurement than the pump--probe discussed here. This demonstration was a success. We completed the first ultrafast optical study of any kind in the Florida Split Helix. We collected differential reflection data from this bulk sample that exhibited electronic and oscillatory components. These components were treated independently in the analysis by treating the electronic dynamics with a four level approximation. The electronic transition rates were extracted and agreed well with published values. This agreement is a demonstration that the spectrometer functioned as desired. The oscillatory response was found to be a result of the emission of coherent phonons upon electronic transition between the four levels. The frequency of the oscillatory response was extracted and agreed well with the theoretical value. The second project is the study of the temperature dependence of the cyclotron decay lifetimes in a Landau quantized GaAs high mobility two dimensional electron gas using THz time--domain spectroscopy at relatively low magnetic field (1.25 T). We find that the cyclotron decay lifetimes decrease monotonically with increasing temperature from 0.4 K to 100 K and that the primary pulse amplitudes increase from 0.4 K to 1.2 K, saturates above 1.2 K up to 50 K, and decreases rapidly above 50 K. We attribute this rapid drop in

  18. Terahertz and Infrared Spectroscopy of Room-Temperature Imidazolium-Based Ionic Liquids.

    PubMed

    Yamada, Toshiki; Tominari, Yukihiro; Tanaka, Shukichi; Mizuno, Maya

    2015-12-24

    The terahertz- and infrared-frequency vibrational modes of various room-temperature imidazolium-based ionic liquids with molecular anions were examined extensively. We found that the molar-concentration-normalized absorption coefficient spectra in the low-wavenumber range for imidazolium cations with different alkyl-chain lengths were nearly identical for the same anion. Regarding the overall view of a wide range of imidazolium-based ionic liquids, we found that the reduced mass of the combination of an imidazolium-ring cation and the anion and the force constant play significant roles in determining the central frequency of the broad absorption band. In addition to these findings, we also discuss the correlation between the (+)C-H stretching vibrational modes in the 3000-3300 cm(-1) range of the infrared spectra and the intermolecular vibrational band in the low-wavenumber range. Finally, we describe some interesting characteristics of the intermolecular vibrational band observed in a wide range of imidazolium-based ionic liquids.

  19. Wiener bounds for complex permittivity in terahertz spectroscopy: case study of two-phase pharmaceutical tablets.

    PubMed

    Tuononen, Heikki; Fukunaga, Kaori; Kuosmanen, Marko; Ketolainen, Jarkko; Peiponen, Kai-Erik

    2010-01-01

    The terahertz measurement technique has become popular in the field of pharmaceutical technology for tablet quality inspection. Spectral data obtained from the tablets is based on the utilization of Fresnel's formulas for an ideal slab. However, a tablet is a porous medium. Hence, in the THz gap one has to assume that a tablet constitutes at least an effective medium if the Fresnel theory is applied in quantitative permittivity spectra analysis. Hence, it is suggested that one should consider instead of the permittivity of homogeneous media the concept of effective permittivity in the THz terminology of porous tablets. Usually the fill factor of a component of a tablet is known but not the detailed bulk structure. Nevertheless, it is possible to estimate the complex effective permittivity of a tablet with the aid of so-called Wiener bounds. The idea of this article is to present a modification of Wiener bounds applied to the estimation of the real and imaginary part of the permittivity of the pure component of a tablet. As an example, the effective complex permittivity of a starch acetate tablet is considered.

  20. Qualitative analysis of collective mode frequency shifts in L-alanine using terahertz spectroscopy.

    PubMed

    Taulbee, Anita R; Heuser, Justin A; Spendel, Wolfgang U; Pacey, Gilbert E

    2009-04-01

    We have observed collective mode frequency shifts in deuterium-substituted L-alanine, three of which have previously only been calculated. Terahertz (THz) absorbance spectra were acquired at room temperature in the spectral range of 66-90 cm(-1), or 2.0-2.7 THz, for L-alanine (L-Ala) and four L-Ala compounds in which hydrogen atoms (atomic mass = 1 amu) were substituted with deuterium atoms (atomic mass = 2 amu): L-Ala-2-d, L-Ala-3,3,3-d(3), L-Ala-2,3,3,3-d(4), and L-Ala-d(7). The absorbance maxima of two L-Ala collective modes in this spectral range were recorded for multiple spectral measurements of each compound, and the magnitude of each collective mode frequency shift due to increased mass of these specific atoms was evaluated for statistical significance. Calculations were performed which predict the THz absorbance frequencies based on the estimated reduced mass of the modes. The shifts in absorbance maxima were correlated with the location(s) of the substituted deuterium atom(s) in the L-alanine molecule, and the atoms contributing to the absorbing delocalized mode in the crystal structure were deduced using statistics described herein. The statistical analyses presented also indicate that the precision of the method allows reproducible frequency shifts as small as 1 cm(-1) or 0.03 THz to be observed and that these shifts are not random error in the measurement.

  1. Time-resolved terahertz spectroscopy of electrically conductive metal-organic frameworks doped with redox active species

    NASA Astrophysics Data System (ADS)

    Alberding, Brian G.; Heilweil, Edwin J.

    2015-09-01

    Metal-Organic Frameworks (MOFs) are three-dimensional coordination polymers that are well known for large pore surface area and their ability to adsorb molecules from both the gaseous and solution phases. In general, MOFs are electrically insulating, but promising opportunities for tuning the electronic structure exist because MOFs possess synthetic versatility; the metal and organic ligand subunits can be exchanged or dopant molecules can be introduced into the pore space. Two such MOFs with demonstrated electrical conductivity are Cu3(1,3,5-benzenetricarboxylate)2, a.k.a HKUST-1, and Cu[Ni(pyrazine-2,3-dithiolate)2]. Herein, these two MOFs have been infiltrated with the redox active species 7,7,8,8-tetracyanoquinodimethane (TCNQ) and iodine under solution phase conditions and shown to produce redox products within the MOF pore space. Vibrational bands assignable to TCNQ anion and triiodide anion have been observed in the Mid-IR and Terahertz ranges using FTIR Spectroscopy. The MOF samples have been further investigated by Time-Resolved Terehertz Spectroscopy (TRTS). Using this technique, the charge mobility, separation, and recombination dynamics have been followed on the picosecond time scale following photoexcitation with visible radiation. The preliminary results show that the MOF samples have small inherent photoconductivity with charge separation lifetimes on the order of a few picoseconds. In the case of HKUST-1, the MOF can also be supported by a TiO2 film and initial results show that charge injection into the TiO2 layer occurs with a comparable efficiency to the dye sensitizer N3, [cis-Bis(isothiocyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylato ruthenium(II)], and therefore this MOF has potential as a new light absorbing and charge conducting material in photovoltaic devices.

  2. 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

  3. Hydration and hydrogen bond network of water around hydrophobic surface investigated by terahertz spectroscopy.

    PubMed

    Shiraga, K; Suzuki, T; Kondo, N; Ogawa, Y

    2014-12-21

    Water conformation around hydrophobic side chains of four amino acids (glycine, L-alanine, L-aminobutyric acid, and L-norvaline) was investigated via changes in complex dielectric constant in the terahertz (THz) region. Each of these amino acids has the same hydrophilic backbone, with successive additions of hydrophobic straight methylene groups (-CH2-) to the side chain. Changes in the degree of hydration (number of dynamically retarded water molecules relative to bulk water) and the structural conformation of the water hydrogen bond (HB) network related to the number of methylene groups were quantitatively measured. Since dielectric responses in the THz region represent water relaxations and water HB vibrations at a sub-picosecond and picosecond timescale, these measurements characterized the water relaxations and HB vibrations perturbed by the methylene apolar groups. We found each successive straight -CH2- group on the side chain restrained approximately two hydrophobic hydration water molecules. Additionally, the number of non-hydrogen-bonded (NHB) water molecules increased slightly around these hydrophobic side chains. The latter result seems to contradict the iceberg model proposed by Frank and Evans, where water molecules are said to be more ordered around apolar surfaces. Furthermore, we compared the water-hydrophilic interactions of the hydrophilic amino acid backbone with those with the water-hydrophobic interactions around the side chains. As the hydrophobicity of the side chain increased, the ordering of the surrounding water HB network was altered from that surrounding the hydrophilic amino acid backbone, thereby diminishing the fraction of NHB water and ordering the surrounding tetrahedral water HB network.

  4. Terahertz Spectroscopy and Solid-State Density Functional Theory Calculations of Cyanobenzaldehyde Isomers.

    PubMed

    Dash, Jyotirmayee; Ray, Shaumik; Nallappan, Kathirvel; Kaware, Vaibhav; Basutkar, Nitin; Gonnade, Rajesh G; Ambade, Ashootosh V; Joshi, Kavita; Pesala, Bala

    2015-07-23

    Spectral signatures in the terahertz (THz) frequency region are mainly due to bulk vibrations of the molecules. These resonances are highly sensitive to the relative position of atoms in a molecule as well as the crystal packing arrangement. To understand the variation of THz resonances, THz spectra (2-10 THz) of three structural isomers: 2-, 3-, and 4-cyanobenzaldehyde have been studied. THz spectra obtained from Fourier transform infrared (FTIR) spectrometry of these isomers show that the resonances are distinctly different especially below 5 THz. For understanding the intermolecular interactions due to hydrogen bonds, four molecule cluster simulations of each of the isomers have been carried out using the B3LYP density functional with the 6-31G(d,p) basis set in Gaussian09 software and the compliance constants are obtained. However, to understand the exact reason behind the observed resonances, simulation of each isomer considering the full crystal structure is essential. The crystal structure of each isomer has been determined using X-ray diffraction (XRD) analysis for carrying out crystal structure simulations. Density functional theory (DFT) simulations using CRYSTAL14 software, utilizing the hybrid density functional B3LYP, have been carried out to understand the vibrational modes. The bond lengths and bond angles from the optimized structures are compared with the XRD results in terms of root-mean-square-deviation (RMSD) values. Very low RMSD values confirm the overall accuracy of the results. The simulations are able to predict most of the spectral features exhibited by the isomers. The results show that low frequency modes (<3 THz) are mediated through hydrogen bonds and are dominated by intermolecular vibrations.

  5. 3D measurements of live cells via digital holographic microscopy and terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Park, Jun Yong; Oser, Dorian; Iapozzuto, Peter; Norbury, Sean; Mahajan, Supriya; Khmaladze, Alexander; Sharikova, Anna

    2016-03-01

    This is a study of the central nervous system (CNS) cells, including brain micro vascular endothelial cells (BMV) that constitute the blood brain barrier, and C6 glial cells that are the predominant cell in the brain. The cells are exposed to various chemicals by non-invasive, label-free methods. Digital holographic microscopy (DHM) is a technique that records an interference pattern between an object and reference waves, so that the computationally reconstructed holographic image contains both amplitude and phase information, and 3D images are obtained. The measurement of cell cultures by digital holographic microscopy yields information about cell death mechanisms, since these processes are correlated with individual cell volume. Our in-house DHM combines a visible (red) laser source with a conventional microscope base, and LabVIEW-run data processing. Terahertz spectral signatures are associated with structural changes in molecules and provide complementary information about cells. Both CNS cells BMV and C6 cells are treated with the drug "Methamphetamine" (METH), which induces apoptosis in neuronal cells and exhibits decrease in cell volume, a characteristic of cells undergoing apoptosis (induced cell death). METH can cause CNS cell death by cross-talk between mitochondria-, endoplasmic reticulum-, and receptor-mediated apoptotic events, all of which results in drug induced changes in neuroplasticity and significant neuropathology. Doxorubicin (DOX), a popular anticancer drug, is used as a control. We observe that METH treatment resulted in more pronounced cell volume shrinkage in both the BMV and C6 cells, as compared to DOX-induced cell apoptosis.

  6. Reduction of effective terahertz focal spot size by means of nested concentric parabolic reflectors

    SciTech Connect

    Neumann, V. A.; Laurita, N. J.; Pan, LiDong; Armitage, N. P.

    2015-09-15

    An ongoing limitation of terahertz spectroscopy is that the technique is generally limited to the study of relatively large samples of order 4 mm across due to the generally large size of the focal beam spot. We present a nested concentric parabolic reflector design which can reduce the terahertz focal spot size. This parabolic reflector design takes advantage of the feature that reflected rays experience a relative time delay which is the same for all paths. The increase in effective optical path for reflected light is equivalent to the aperture diameter itself. We have shown that the light throughput of an aperture of 2 mm can be increased by a factor 15 as compared to a regular aperture of the same size at low frequencies. This technique can potentially be used to reduce the focal spot size in terahertz spectroscopy and enable the study of smaller samples.

  7. Phase-Sensitive Reflective Imaging Device in the mm-wave and Terahertz Regions

    NASA Astrophysics Data System (ADS)

    Gallerano, Gian Piero; Doria, Andrea; Germini, Marzia; Giovenale, Emilio; Messina, Giovanni; Spassovsky, Ivan P.

    2009-12-01

    Two Free Electron Laser sources have been developed at ENEA-Frascati for a variety of applications: A Compact Free Electron Laser (C-FEL) that provides coherent radiation in the frequency range between 90 and 150 GHz Gallerano et al. (Infrared Phys. and Techn. 40:161, 1999), and a second source, FEL-CATS, which utilizes a peculiar radio-frequency structure to generate coherent emission in the range 0.4 to 0.7 THz Doria et al. (Phys. Rev. Lett 93:264801, 2004). The high peak power of several kW in 15 to 50 ps pulses, makes these sources particularly suitable for the assessment of exposure limits in biological systems and for long range detection. In this paper we present a phase-sensitive reflective imaging device in the mm-wave and THz regions, which has proven to be a valuable tool in the biological Ramundo-Orlando et al. (Bioelectromagnetics 28:587-598, 2007), environmental Doria et al. (2005) and art conservation fields Gallerano et al. (2008). Different setups have been tested at different levels of spatial resolution to image objects from a few centimeter square to larger sizes. Images have been compared to identify and characterize the contrast mechanism.

  8. Quantification of tissue oxygenation levels using diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    B. S., Suresh Anand; N., Sujatha

    2010-12-01

    Tumor growth is characterized by increased metabolic activity. The light absorption profile of hemoglobin in dysplastic tissue is different from a normal tissue. Neovascularization is a hallmark of many diseases and can serve as a predictive biomarker for the detection of cancers. Spectroscopic techniques can provide information about the metabolic and morphological changes related to the progression of neoplasia. Diffuse reflectance spectroscopy (DRS) measures the absorption and scattering properties of a biological tissue and this method can provide clinically useful information for the early diagnosis of epithelial precancers. We used tissue simulating phantoms with absorbing and scattering molecules for the determination of total hemoglobin concentration, hemoglobin oxygen saturation and intensity difference between the deoxy and oxy hemoglobin bands. The results show promising approach for the differentiating normal and malignant states of a tissue.

  9. Quantification of tissue oxygenation levels using diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    B. S., Suresh Anand; N., Sujatha

    2011-08-01

    Tumor growth is characterized by increased metabolic activity. The light absorption profile of hemoglobin in dysplastic tissue is different from a normal tissue. Neovascularization is a hallmark of many diseases and can serve as a predictive biomarker for the detection of cancers. Spectroscopic techniques can provide information about the metabolic and morphological changes related to the progression of neoplasia. Diffuse reflectance spectroscopy (DRS) measures the absorption and scattering properties of a biological tissue and this method can provide clinically useful information for the early diagnosis of epithelial precancers. We used tissue simulating phantoms with absorbing and scattering molecules for the determination of total hemoglobin concentration, hemoglobin oxygen saturation and intensity difference between the deoxy and oxy hemoglobin bands. The results show promising approach for the differentiating normal and malignant states of a tissue.

  10. Analysis of silage composition by near-infrared reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Reeves, James B., III; Blosser, Timothy H.; Colenbrander, V. F.

    1991-02-01

    Two studies were performed to investigate the feasibility of using near infrared reflectance spectroscopy (NIRS) with undried silages. In the first study silages were analyzed for major components (e. g. dry matter crude protein and other forms of nitrogen fiber and in vitro digestible dry matter) and short chain fatty acids (SCFA). NIRS was found to operate satisfactorily except for some forms of nitrogen and SCFA. In study two various methods of grinding spectral regions and sample presentation were examined. Undried Wiley ground samples in a rectangular cell gave the best overall results for non-dry ice undried grinds with wavelengths between 1100 and 2498 nm. Silages scanned after drying however produced the best results. Intact samples did not perform as well as ground samples and wavelengths below 1100 nm were of little use. 2 .

  11. Laboratory Studies of Organic Compounds With Reflectance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Curchin, J. M.; Clark, R. N.; Hoefen, T. M.

    2007-12-01

    In order to properly interpret reflectance spectra of any solar system surface from the earth to the Oort cloud, laboratory spectra of candidate materials for comparative analysis are needed. Although the common cosmochemical species (H2O, CO2, CO, NH3, and CH4) are well represented in the spectroscopic literature, comparatively little reflectance work has been done on organics from room to cryogenic temperatures at visible to near infrared wavelengths. Reflectance spectra not only enhance weak or unseen transmission features, they are also more analogous to spectra obtained by spacecraft that are imaging such bodies as giant planet moons, kuiper belt objects, centaurs, comets and asteroids, as well as remote sensing of the earth. The USGS Spectroscopy Laboratory is measuring reflectance spectra of organic compounds from room to cryogenic temperatures over the spectral range of 0.35 to 15.5 microns. This region encompasses the fundamental absorptions and many overtones and combinations of C, H, O, and N molecular bonds. Because most organic compounds belong to families whose members have similar structure and composition, individual species identification within a narrow wavelength range may be ambiguous. By measuring spectral reflectance of the pure laboratory samples from the visible through the near and mid-infrared, absorption bands unique to each can be observed, cataloged, and compared to planetary reflectance data. We present here spectra of organic compounds belonging to five families: the alkanes, alkenes, alkynes, aromatics, and cyanides. Common to all of these are the deep C-H stretch fundamental absorptions, which shift shortward from 3.35+ microns in alkanes to 3.25+ microns in aromatics, to 3.2+ microns in alkenes, and down to 3.0+ microns in alkynes. Mid-IR absorptions due to C-H bending deformations at 6.8+ and 7.2+ microns are also identified. In the near infrared these stretching and bending fundamentals yield a diagnostic set of combination

  12. 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.

  13. Sub-terahertz frequency-domain spectroscopy reveals single-grain mobility and scatter influence of large-area graphene.

    PubMed

    Cervetti, Christian; Heintze, Eric; Gorshunov, Boris; Zhukova, Elena; Lobanov, Svyatoslav; Hoyer, Alexander; Burghard, Marko; Kern, Klaus; Dressel, Martin; Bogani, Lapo

    2015-04-24

    The response of individual domains in wafer-sized chemical vapor deposition graphene is measured by contactless sub-terahertz interferometry, observing the intrinsic optical conductance and reaching very high mobility values. It is shown that charged scatterers limit the mobility, validating previous theoretical predictions, and sub-terahertz quality assessment is demonstrated, as necessary for large-scale applications in touchscreens, as well as wearable and optoelectronic devices.

  14. Resonant Reflection Spectroscopy of Biomolecular Arrays in Muscle

    PubMed Central

    Young, Kevin W.; Radic, Stojan; Myslivets, Evgeny; O’Connor, Shawn M.; Lieber, Richard L.

    2014-01-01

    Sarcomeres, the functional units of contraction in striated muscle, are composed of an array of interdigitating protein filaments. Direct interaction between overlapping filaments generates muscular force, which produces animal movement. When filament length is known, sarcomere length successfully predicts potential force, even in whole muscles that contain billions of sarcomere units. Inability to perform in vivo sarcomere measurements with submicrometer resolution is a long-standing challenge in the muscle physiology field and has hampered studies of normal muscle function, adaptation, injury, aging, and disease, particularly in humans. Here, we develop theory and demonstrate the feasibility of to our knowledge a new technique that measures sarcomere length with submicrometer resolution. In this believed novel approach, we examine sarcomere structure by measuring the multiple resonant reflections that are uniquely defined by Fourier decomposition of the sarcomere protein spatial framework. Using a new supercontinuum spectroscopic system, we show close agreement between sarcomere lengths measured by resonant reflection spectroscopy and laser diffraction in an ensemble of 10 distinct muscles. PMID:25418304

  15. Highly Resolved Sub-Terahertz Vibrational Spectroscopy of Biological Macromolecules and Bacteria Cells

    DTIC Science & Technology

    2016-07-01

    TR-1385 Waleed Maswadeh Richard Vanderbeek Raphael Moon RESEARCH AND TECHNOLOGY DIRECTORATE Ashish Tripathi LEIDOS, INC. Gunpowder, MD...0022 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Maswadeh, Waleed; Vanderbeek, Richard; Moon , Raphael (ECBC); Tripathi, Ashish...Chemical Biological Center (ECBC) Spectroscopy Branch RDCB-DRI-S ATTN: Maswadeh, W. Vanderbeek, R. Moon , R

  16. Noninvasive express diagnostics of pulmonary diseases based on control of patient's gas emission using methods of IR and terahertz laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Starikova, M. K.; Bulanova, A. A.; Bukreeva, E. B.; Karapuzikov, A. A.; Karapuzikov, A. I.; Kistenev, Y. V.; Klementyev, V. M.; Kolker, D. B.; Kuzmin, D. A.; Nikiforova, O. Y.; Ponomarev, Yu. N.; Sherstov, I. V.; Boyko, A. A.

    2013-11-01

    Pulmonary diseases diagnostics always occupies one of the key positions in medicine practices. A large variety of high technology methods are used today, but none of them cannot be used for early screening of pulmonary diseases. We discuss abilities of methods of IR and terahertz laser spectroscopy for noninvasive express diagnostics of pulmonary diseases on a base of analysis of absorption spectra of patient's gas emission, in particular, exhaled air. Experience in the field of approaches to experimental data analysis and hard-ware realization of gas analyzers for medical applications is also discussed.

  17. Improved thickness estimation of liquid water using Kramers-Kronig relations for determination of precise optical parameters in terahertz transmission spectroscopy.

    PubMed

    Son, Heyjin; Choi, Da-Hye; Park, Gun-Sik

    2017-02-20

    In terahertz transmission spectroscopy, there is a typical problem of thickness uncertainty, which hampers to determine precise optical parameters of samples. In order to resolve this experimental problem, a method optimizing sample thickness using singly subtractive Kramers-Kronig relations is proposed. For tens of micrometers thick water samples, we improved the accuracy of sample thickness by an order of magnitude (up to sub-micrometer) using the algorithm leading to obtain precise optical parameters of water. The broad applicability of the method is demonstrated for measuring various materials in addition to highly absorbing liquid water in the spectral range from 0.3 to 1.6 THz.

  18. Characteristics of THz carrier dynamics in GaN thin film and ZnO nanowires by temperature dependent terahertz time domain spectroscopy measurement

    NASA Astrophysics Data System (ADS)

    Balci, Soner; Baughman, William; Wilbert, David S.; Shen, Gang; Kung, Patrick; Kim, Seongsin Margaret

    2012-12-01

    We present a comprehensive study of the characteristics of carrier dynamics using temperature dependent terahertz time domain spectroscopy. By utilizing this technique in combination with numerical calculations, the complex refractive index, dielectric function, and conductivity of n-GaN, undoped ZnO NWs, and Al-doped ZnO NWs were obtained. The unique temperature dependent behaviors of major material parameters were studied at THz frequencies, including plasma frequency, relaxation time, carrier concentration and mobility. Frequency and temperature dependent carrier dynamics were subsequently analyzed in these materials through the use of the Drude and the Drude-Smith models.

  19. 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.

  20. 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.

  1. Asymmetric planar terahertz metamaterials

    SciTech Connect

    Singh, Ramjan; Al - Naib, Ibraheem A. I.; Koch, Martin; Zhang, Weili

    2010-01-01

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

  2. A study on the protection to relics and the related problems with diffuse reflectance spectroscopy.

    PubMed

    Wang, Liqin; Liang, Guozheng; Dang, Gaochao

    2005-03-01

    The application of diffuse reflectance spectroscopy to relic protection is studied by using a self-made fiber optics reflectance spectrophotometer. The major work done includes: (1) the composition of pigment on colored relics and its changes are identified; (2) the change on metal surface is monitored; (3) the reflectance spectrum characteristics of relic protection materials are studied. The results tell that diffuse reflectance spectroscopy is a new protection technique, characterized by its quickness and non-destructiveness to the relic.

  3. Noninvasive measurements of carotenoids in bovine udder by reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Klein, Julia; Darvin, Maxim E.; Müller, Kerstin E.; Lademann, Jürgen

    2012-10-01

    For a long time, the antioxidative status in cattle has been discussed as an indicator for stress conditions resulting from disease or exertion. Until now, invasive approaches have been necessary to obtain blood samples or biopsy materials and gain insights into the antioxidative status of cattle. Due to these efforts and the costs of the analyses, serial sampling is feasible in an experimental setting, but not for measurements on a routine basis. The present study focuses on the feasibility of an innovative, noninvasive spectroscopic technique that allows in vivo measurements of carotenoids in the skin by reflection spectroscopy. To this end, in a first trial, repeated measurements of the carotenoid concentration of the udder skin were performed on 25 healthy cattle from different breeds. Carotenoid concentrations showed highly significant differences between individual animals (P<0.001), although they were kept under the same environmental conditions and received the same diet. The carotenoid concentrations in "sensitive" and "robust" cows (evaluated by a temperament test) differed significantly (P<0.005), with higher concentrations observed in robust cows.

  4. Probing skin interaction with hydrogen peroxide using diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Zonios, George; Dimou, Aikaterini; Galaris, Dimitrios

    2008-01-01

    Hydrogen peroxide is an important oxidizing agent in biological systems. In dermatology, it is frequently used as topical antiseptic, it has a haemostatic function, it can cause skin blanching, and it can facilitate skin tanning. In this work, we investigated skin interaction with hydrogen peroxide, non-invasively, using diffuse reflectance spectroscopy. We observed transient changes in the oxyhaemoglobin and deoxyhaemoglobin concentrations as a result of topical application of dilute H2O2 solutions to the skin, with changes in deoxyhaemoglobin concentration being more pronounced. Furthermore, we did not observe any appreciable changes in melanin absorption properties as well as in the skin scattering properties. We also found no evidence for production of oxidized haemoglobin forms. Our observations are consistent with an at least partial decomposition of hydrogen peroxide within the stratum corneum and epidermis, with the resulting oxygen and/or remaining hydrogen peroxide inducing vasoconstriction to dermal blood vessels and increasing haemoglobin oxygen saturation. An assessment of the effects of topical application of hydrogen peroxide to the skin may serve as the basis for the development of non-invasive techniques to measure skin antioxidant capacity and also may shed light onto skin related disorders such as vitiligo.

  5. Aerosol collection and analysis using diffuse reflectance infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Samuels, Alan C.; Wong, Diane M.; Meyer, Gerald J.; Roelant, Geoffrey J.; Williams, Barry R.; Miles, Ronald W., Jr.; Manning, Christopher J.

    2004-08-01

    Infrared spectroscopy is routinely employed for the identification of organic molecules and, more recently, for the classification of biological materials. We have developed a sample collection method that facilitates infrared analysis of airborne particulates using a diffuse reflectance (DR) technique. Efforts are underway to extend the method to include simultaneous analysis of vapor phase organics by using adsorbent substrates compatible with the DR technique. This series of laboratory results provides proof-of-principle for both the sample collection and data collection processes. Signal processing of the DR spectra is shown to provide rapid qualitative identification of representative aerosol materials, including particulate matter commonly found in the environment. We compare the results for such materials as bacterial spores, pollens and molds, clays and dusts, smoke and soot. Background correction analysis is shown to be useful for differentiation and identification of these constituents. Issues relating to complex mixtures of environmental samples under highly variable conditions are considered. Instrumentation development and materials research are now underway with the aim of constructing a compact sampling system for near real-time monitoring of aerosol and organic pollutants. A miniature, tilt-compensated Fourier transform spectrometer will provide spectroscopic interrogation. A series of advanced digital signal processing methods are also under development to enhance the sensor package. The approach will be useful for industrial applications, chemical and biological agent detection, and environmental monitoring for chemical vapors, hazardous air pollutants, and allergens.

  6. Intramyocardial oxygen transport by quantitative diffuse reflectance spectroscopy in calves

    NASA Astrophysics Data System (ADS)

    Lindbergh, Tobias; Larsson, Marcus; Szabó, Zoltán; Casimir-Ahn, Henrik; Strömberg, Tomas

    2010-03-01

    Intramyocardial oxygen transport was assessed during open-chest surgery in calves by diffuse reflectance spectroscopy using a small intramuscular fiber-optic probe. The sum of hemo- and myoglobin tissue fraction and oxygen saturation, the tissue fraction and oxidation of cytochrome aa3, and the tissue fraction of methemoglobin were estimated using a calibrated empirical light transport model. Increasing the oxygen content in the inhaled gas, 21%-50%-100%, in five calves (group A) gave an increasing oxygen saturation of 19+/-4%, 24+/-5%, and 28+/-8% (p<0.001, ANOVA repeated measures design) and mean tissue fractions of 1.6% (cytochrome aa3) and 1.1% (hemo- and myoglobin). Cardiac arrest in two calves gave an oxygen saturation lower than 5%. In two calves (group B), a left ventricular assistive device (LVAD pump) was implanted. Oxygen saturation in group B animals increased with LVAD pump speed (p<0.001, ANOVA) and with oxygen content in inhaled gas (p<0.001, ANOVA). The cytochrome aa3 oxidation level was above 96% in both group A and group B calves, including the two cases involving cardiac arrest. In conclusion, the estimated tissue fractions and oxygenation/oxidation levels of the myocardial chromophores during respiratory and hemodynamic provocations were in agreement with previously presented results, demonstrating the potential of the method.

  7. Diffuse reflectance spectroscopy: towards clinical application in breast cancer.

    PubMed

    Evers, Daniel J; Nachabe, Rami; Vranken Peeters, Marie-Jeanne; van der Hage, Jos A; Oldenburg, Hester S; Rutgers, Emiel J; Lucassen, Gerald W; Hendriks, Benno H W; Wesseling, Jelle; Ruers, Theo J M

    2013-01-01

    Diffuse reflectance spectroscopy (DRS) is a promising new technique for breast cancer diagnosis. However, inter-patient variation due to breast tissue heterogeneity may interfere with the accuracy of this technique. To tackle this issue, we aim to determine the diagnostic accuracy of DRS in individual patients. With this approach, DRS measurements of normal breast tissue in every individual patient are directly compared with measurements of the suspected malignant tissue. Breast tissue from 47 female patients was analysed ex vivo by DRS. A total of 1,073 optical spectra were collected. These spectra were analyzed for each patient individually as well as for all patients collectively and results were compared to the pathology analyses. Collective patient data analysis for discrimination between normal and malignant breast tissue resulted in a sensitivity of 90 %, a specificity of 88 %, and an overall accuracy of 89 %. In the individual analyses all measurements per patient were categorized as either benign or malignant. The discriminative accuracy of these individual analyses was nearly 100 %. The diagnosis was classified as uncertain in only one patient. Based on the results presented in this study, we conclude that the analysis of optical characteristics of different tissue classes within the breast of a single patient is superior to an analysis using the results of a cohort data analysis. When integrated into a biopsy device, our results demonstrate that DRS may have the potential to improve the diagnostic workflow in breast cancer.

  8. Diffuse reflectance spectroscopy for the measurement of tissue oxygen saturation.

    PubMed

    Sircan-Kucuksayan, A; Uyuklu, M; Canpolat, M

    2015-12-01

    Tissue oxygen saturation (StO2) is a useful parameter for medical applications. A spectroscopic method has been developed to detect pathologic tissues, due to a lack of normal blood circulation, by measuring StO2. In this study, human blood samples with different levels of oxygen saturation have been prepared and spectra were acquired using an optical fiber probe to investigate the correlation between the oxygen saturation levels and the spectra. A linear correlation between the oxygen saturation and ratio of the intensities (760 nm to 790 nm) of the spectra acquired from blood samples has been found. In a validation study, oxygen saturations of the blood samples were estimated from the spectroscopic measurements with an error of 2.9%. It has also been shown that the linear dependence between the ratio and the oxygen saturation of the blood samples was valid for the blood samples with different hematocrits. Spectra were acquired from the forearms of 30 healthy volunteers to estimate StO2 prior to, at the beginning of, after 2 min, and at the release of total vascular occlusion. The average StO2 of a forearm before and after the two minutes occlusion was significantly different. The results suggested that optical reflectance spectroscopy is a sensitive method to estimate the StO2 levels of human tissue. The technique developed to measure StO2 has potential to detect ischemia in real time.

  9. Lifetime, mobility, and diffusion of photoexcited carriers in ligand-exchanged lead selenide nanocrystal films measured by time-resolved terahertz spectroscopy.

    PubMed

    Guglietta, Glenn W; Diroll, Benjamin T; Gaulding, E Ashley; Fordham, Julia L; Li, Siming; Murray, Christopher B; Baxter, Jason B

    2015-02-24

    Colloidal semiconductor nanocrystals have been used as building blocks for electronic and optoelectronic devices ranging from field-effect transistors to solar cells. Properties of the nanocrystal films depend sensitively on the choice of capping ligand to replace the insulating synthesis ligands. Thus far, ligands leading to the best performance in transistors result in poor solar cell performance, and vice versa. To gain insight into the nature of this dichotomy, we used time-resolved terahertz spectroscopy measurements to study the mobility and lifetime of PbSe nanocrystal films prepared with five common ligand-exchange reagents. Noncontact terahertz spectroscopy measurements of conductivity were corroborated by contacted van der Pauw measurements of the same samples. The films treated with different displacing ligands show more than an order of magnitude difference in the peak conductivities and a bifurcation of time dynamics. Inorganic chalcogenide ligand exchanges with sodium sulfide (Na2S) or ammonium thiocyanate (NH4SCN) show high mobilities but nearly complete decay of transient photocurrent in 1.4 ns. In contrast, ligand exchanges with 1,2-ethylenediamine (EDA), 1,2-ethanedithiol (EDT), and tetrabutylammonium iodide (TBAI) show lower mobilities but longer carrier lifetimes, resulting in longer diffusion lengths. This bifurcated behavior may explain the divergent performance of field-effect transistors and photovoltaics constructed from nanocrystal building blocks with different ligand exchanges.

  10. Recent Progress in Terahertz Metasurfaces

    NASA Astrophysics Data System (ADS)

    Al-Naib, Ibraheem; Withayachumnankul, Withawat

    2017-03-01

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

  11. Microfluidic Devices for Terahertz Spectroscopy of Live Cells Toward Lab-on-a-Chip Applications.

    PubMed

    Tang, Qi; Liang, Min; Lu, Yi; Wong, Pak Kin; Wilmink, Gerald J; Zhang, Donna; Xin, Hao

    2016-04-04

    THz spectroscopy is an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. Cells are transported, trapped and concentrated into the THz exposure region by applying an AC bias signal while the chip maintains a steady temperature at 37 °C by resistive heating. We conduct some preliminary experiments on E. coli and T-cell solution and compare the transmission spectra of empty channels, channels filled with aqueous media only, and channels filled with aqueous media with un-concentrated and concentrated cells.

  12. Electron Dynamics in Nanocrystalline TiO2 and ZnO Measured by Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Schmuttenmaer, Charles; Baxter, Jason

    2009-03-01

    Understanding the microscopic details of carrier transport in nanocrystalline colloidal thin films is required for complete understanding of a variety of photochemical and photoelectrochemical cells utilizing interpenetrating networks. Measuring the photoconductivity in these materials, however, is a challenging problem because of the inherent difficulty of attaching wires to nanometer-sized objects. Furthermore, picosecond carrier dynamics play an important role in efficient charge separation and transport, but the low temporal resolution of traditional methods used to determine their photoconductivity precludes their use in studying sub-ps to ps dynamics. This talk will present recent advances utilizing THz spectroscopy to investigate and elucidate the microscopic behavior of carrier dynamics within the context of materials for energy applications such as dye-sensitized solar cells and solar-driven cells for catalytic chemistry.

  13. Microfluidic Devices for Terahertz Spectroscopy of Live Cells Toward Lab-on-a-Chip Applications

    PubMed Central

    Tang, Qi; Liang, Min; Lu, Yi; Wong, Pak Kin; Wilmink, Gerald J.; D. Zhang, Donna; Xin, Hao

    2016-01-01

    THz spectroscopy is an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. Cells are transported, trapped and concentrated into the THz exposure region by applying an AC bias signal while the chip maintains a steady temperature at 37 °C by resistive heating. We conduct some preliminary experiments on E. coli and T-cell solution and compare the transmission spectra of empty channels, channels filled with aqueous media only, and channels filled with aqueous media with un-concentrated and concentrated cells. PMID:27049392

  14. Study of paraffin-embedded colon cancer tissue using terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Wahaia, Faustino; Kasalynas, Irmantas; Seliuta, Dalius; Molis, Gediminas; Urbanowicz, Andrzej; Carvalho Silva, Catia D.; Carneiro, Fatima; Valusis, Gintaras; Granja, Pedro L.

    2015-01-01

    In this work, samples of non-neoplastic and adenocarcinoma-affected human colon tissue samples were analyzed using multipoint transmission time-domain THz spectroscopy (THz-TDS) to sort out the contrast-contributing factors other than water, the main contrast mechanism factor in in-vivo or in freshly excised bio-tissue. Solving the electromagnetic inverse problem through THz-TDS and, analyzing the transmittance spectra that yielded the frequency-dependent absorption coefficient α and refractive index n of non-neoplastic and neoplastic tissues, we show that it is possible to distinguish between non-neoplastic and neoplastic regions in paraffin-embedded dehydrated. Results and discussion are presented.

  15. Broadband terahertz dynamics of propylene glycol monomer and oligomers

    NASA Astrophysics Data System (ADS)

    Koda, Shota; Mori, Tatsuya; Kojima, Seiji

    2016-12-01

    We investigated the broadband terahertz spectra (0.1-5.0 THz) of glass-forming liquids, propylene glycol (PG), its oligomers poly (propylene glycol)s (PPGs), and poly (propylene glycol) diglycidyl ether (PPG-de) using broadband terahertz time-domain spectroscopy and low-frequency Raman scattering. The numerical value of the dielectric loss at around 1.5 THz, which is the peak position of broad peaks in all samples, decreased as the molecular weight increased. Furthermore, the peak at around 1.5 THz is insensitive to the molecular weight. For PPGs, the side chain effect of the oligomer was observed in the terahertz region. Based on the experimental and calculation results for the PPGs and PPG-de, whose end groups are epoxy groups, the beginnings of the increases in the observed dielectric loss above 3.5 THz of the PPGs are assigned to the OH bending vibration. The higher value of the dielectric loss in the terahertz region for the PPG-de can be the tail of a broad peak located in the MHz region. The difference between the Raman susceptibility and dielectric loss reflects the difference in the observable molecular dynamics between the infrared and Raman spectroscopies.

  16. Near- and Mid-Infrared Reflectance Spectroscopy for the Quantitative and Qualitative Analysis of Agricultural Products

    Technology Transfer Automated Retrieval System (TEKTRAN)

    For several decades near-infrared diffuse reflectance spectroscopy (NIRS) has been used to determine the composition of a variety of agricultural products. More recently, diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) has similarly been shown to be able to determine the co...

  17. Fluorescence and Diffuse Reflectance Spectroscopy for Breast Cancer Diagnosis During Core Needle Biopsy

    DTIC Science & Technology

    2007-09-01

    The goal of this project is to explore the potential of using tissue fluorescence and diffuse reflectance spectroscopy for breast cancer detection...sensor based on tissue fluorescence and diffuse reflectance spectroscopy as an adjunct diagnostic tool, which has the potential to provide guidance for core needle breast biopsy.

  18. 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.

  19. 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.

  20. Terahertz spectroscopy of N18O and isotopic invariant fit of several nitric oxide isotopologs

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Kobayashi, Kaori; Takahashi, Kazumasa; Tomaru, Kazuko; Matsushima, Fusakazu

    2015-04-01

    A tunable far-infrared laser sideband spectrometer was used to investigate a nitric oxide sample enriched in 18O between 0.99 and 4.75 THz. Regular, electric dipole transitions were recorded between 0.99 and 2.52 THz, while magnetic dipole transitions between the 2Π1/2 and 2Π3/2 spin-ladders were recorded between 3.71 and 4.75 THz. These data were combined with lower frequency data of N18 O (unlabeled atoms refer to 14 N and 16 O, respectively), with rotational data of NO, 15 NO, N17 O, and 15 N18 O, and with heterodyne infrared data of NO to be subjected to one isotopic invariant fit. Rotational, fine and hyperfine structure parameters were determined along with vibrational, rotational, and Born-Oppenheimer breakdown corrections. The resulting spectroscopic parameters permit prediction of rotational spectra suitable for the identification of various nitric oxide isotopologs especially in the interstellar medium by means of rotational spectroscopy.

  1. Three-dimensional terahertz computed tomography of human bones.

    PubMed

    Bessou, Maryelle; Chassagne, Bruno; Caumes, Jean-Pascal; Pradère, Christophe; Maire, Philippe; Tondusson, Marc; Abraham, Emmanuel

    2012-10-01

    Three-dimensional terahertz computed tomography has been used to investigate dried human bones such as a lumbar vertebra, a coxal bone, and a skull, with a direct comparison with standard radiography. In spite of lower spatial resolution compared with x-ray, terahertz imaging clearly discerns a compact bone from a spongy one, with strong terahertz absorption as shown by additional terahertz time-domain transmission spectroscopy.

  2. 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.

  3. Fiber-based swept-source terahertz radar.

    PubMed

    Huang, Yu-Wei; Tseng, Tzu-Fang; Kuo, Chung-Chiu; Hwang, Yuh-Jing; Sun, Chi-Kuang

    2010-05-01

    We demonstrate an all-terahertz swept-source imaging radar operated at room temperature by using terahertz fibers for radiation delivery and with a terahertz-fiber directional coupler acting as a Michelson interferometer. By taking advantage of the high water reflection contrast in the low terahertz regime and by electrically sweeping at a high speed a terahertz source combined with a fast rotating mirror, we obtained the living object's distance information with a high image frame rate. Our experiment showed that this fiber-based swept-source terahertz radar could be used in real time to locate concealed moving live objects with high stability.

  4. Terahertz Microscope

    DTIC Science & Technology

    2010-05-01

    Science, 2009. 9. Reference: 1. Ferguson , B., Zhang, X.-C. Materials for terahertz science and technology, Nature Materials 1, 26 - 33 (01 Sep 2002...interaction, Phys. Rev. Lett., 71, 2725-2728 (1993). 21. Woolard D.L., Brown R., Pepper M., Kemp M., Terahertz frequency sensing and imaging: a time

  5. Determination of plant silicon content with near infrared reflectance spectroscopy

    PubMed Central

    Smis, Adriaan; Ancin Murguzur, Francisco Javier; Struyf, Eric; Soininen, Eeva M.; Herranz Jusdado, Juan G.; Meire, Patrick; Bråthen, Kari Anne

    2014-01-01

    Silicon (Si) is one of the most common elements in the earth bedrock, and its continental cycle is strongly biologically controlled. Yet, research on the biogeochemical cycle of Si in ecosystems is hampered by the time and cost associated with the currently used chemical analysis methods. Here, we assessed the suitability of Near Infrared Reflectance Spectroscopy (NIRS) for measuring Si content in plant tissues. NIR spectra depend on the characteristics of the present bonds between H and N, C and O, which can be calibrated against concentrations of various compounds. Because Si in plants always occurs as hydrated condensates of orthosilicic acid (Si(OH)4), linked to organic biomolecules, we hypothesized that NIRS is suitable for measuring Si content in plants across a range of plant species. We based our testing on 442 samples of 29 plant species belonging to a range of growth forms. We calibrated the NIRS method against a well-established plant Si analysis method by using partial least-squares regression. Si concentrations ranged from detection limit (0.24 ppmSi) to 7.8% Si on dry weight and were well predicted by NIRS. The model fit with validation data was good across all plant species (n = 141, R2 = 0.90, RMSEP = 0.24), but improved when only graminoids were modeled (n = 66, R2 = 0.95, RMSEP = 0.10). A species specific model for the grass Deschampsia cespitosa showed even slightly better results than the model for all graminoids (n = 16, R2 = 0.93, RMSEP = 0.015). We show for the first time that NIRS is applicable for determining plant Si concentration across a range of plant species and growth forms, and represents a time- and cost-effective alternative to the chemical Si analysis methods. As NIRS can be applied concurrently to a range of plant organic constituents, it opens up unprecedented research possibilities for studying interrelations between Si and other plant compounds in vegetation, and for addressing the role of Si in ecosystems across a range of Si

  6. Femtosecond terahertz time-domain spectroscopy at 36 kHz scan rate using an acousto-optic delay

    NASA Astrophysics Data System (ADS)

    Urbanek, B.; Möller, M.; Eisele, M.; Baierl, S.; Kaplan, D.; Lange, C.; Huber, R.

    2016-03-01

    We present a rapid-scan, time-domain terahertz spectrometer employing femtosecond Er:fiber technology and an acousto-optic delay with attosecond precision, enabling scanning of terahertz transients over a 12.4-ps time window at a waveform refresh rate of 36 kHz, and a signal-to-noise ratio of 1.7 × 105 / √{ H z } . Our approach enables real-time monitoring of dynamic THz processes at unprecedented speeds, which we demonstrate through rapid 2D thickness mapping of a spinning teflon disc at a precision of 10 nm/ √{ H z } . The compact, all-optical design ensures alignment-free operation even in harsh environments.

  7. On Ultrafast Time-Domain TeraHertz Spectroscopy in the Condensed Phase: Linear Spectroscopic Measurements of Hydrogen-Bond Dynamics of Astrochemical Ice Analogs and Nonlinear TeraHertz Kerr Effect Measurements of Vibrational Quantum Beats

    NASA Astrophysics Data System (ADS)

    Allodi, Marco A.

    Much of the chemistry that affects life on planet Earth occurs in the condensed phase. The TeraHertz (THz) or far-infrared (far-IR) region of the electromagnetic spectrum (from 0.1 THz to 10 THz) has been shown to provide unique possibilities in the study of condensed-phase processes. The goal of this work is to expand the possibilities available in the THz region and undertake new investigations of fundamental interest to chemistry. Since we are fundamentally interested in condensed-phase processes, this thesis focuses on two areas where THz spectroscopy can provide new understanding: astrochemistry and solvation science. To advance these fields, we had to develop new instrumentation that would enable the experiments necessary to answer new questions in either astrochemistry or solvation science. We first developed a new experimental setup capable of studying astrochemical ice analogs in both the TeraHertz (THz), or far-Infrared (far-IR), region (0.3 - 7.5 THz; 10 - 250 wavenumbers) and the mid-IR (400 - 4000 wavenumbers). The importance of astrochemical ices lies in their key role in the formation of complex organic molecules, such as amino acids and sugars in space. Thus, the instruments are capable of performing variety of spectroscopic studies that can provide especially relevant laboratory data to support astronomical observations from telescopes such as the Herschel Space Telescope, the Stratospheric Observatory for Infrared Astronomy (SOFIA), and the Atacama Large Millimeter Array (ALMA). The experimental apparatus uses a THz time-domain spectrometer, with a 1750/875 nm plasma source and a GaP detector crystal, to cover the bandwidth mentioned above with 10 GHz (0.3 wavenumber) resolution. Using the above instrumentation, experimental spectra of astrochemical ice analogs of water and carbon dioxide in pure, mixed, and layered ices were collected at different temperatures under high-vacuum conditions with the goal of investigating the structure of the ice

  8. Reflectance spectroscopy in planetary science: Review and strategy for the future

    NASA Technical Reports Server (NTRS)

    Mccord, Thomas B. (Editor)

    1987-01-01

    Reflectance spectroscopy is a remote sensing technique used to study the surfaces and atmospheres of solar system bodies. It provides first-order information on the presence and amounts of certain ions, molecules, and minerals on a surface or in an atmosphere. Reflectance spectroscopy has become one of the most important investigations conducted on most current and planned NASA Solar System Exploration Program space missions. This book reviews the field of reflectance spectroscopy, including information on the scientific technique, contributions, present conditions, and future directions and needs.

  9. Reflectance spectroscopy: quantitative analysis techniques for remote sensing applications.

    USGS Publications Warehouse

    Clark, R.N.; Roush, T.L.

    1984-01-01

    Several methods for the analysis of remotely sensed reflectance data are compared, including empirical methods and scattering theories, both of which are important for solving remote sensing problems. The concept of the photon mean path length and the implications for use in modeling reflectance spectra are presented.-from Authors

  10. Size-dependent electron transfer from PbSe quantum dots to SnO2 monitored by picosecond Terahertz spectroscopy.

    PubMed

    Cánovas, Enrique; Moll, Puck; Jensen, Søren A; Gao, Yunan; Houtepen, Arjan J; Siebbeles, Laurens D A; Kinge, Sachin; Bonn, M

    2011-12-14

    We report the direct and unambiguous determination of electron transfer rates and efficiencies from PbSe quantum dots (QDs) to mesoporous SnO2 films. We monitor the time-dependent electron density within the oxide with picosecond time resolution using Terahertz spectroscopy, following optical excitation of the QDs using a femtosecond laser pulse. QD-oxide electron transfer occurs with efficiencies of ∼2% in our samples under 800 nm pumping with a marked dependence on QD size, ranging from ∼100 ps injection times for the smallest, ∼2 nm diameter QDs, to ∼1 ns time scale for ∼7 nm QDs. The size-dependent electron transfer rates are modeled within the framework of Marcus theory and the implications of the results for device design are discussed.

  11. Employing time-resolved terahertz spectroscopy to analyze carrier dynamics in thin-film Cu{sub 2}ZnSn(S,Se){sub 4} absorber layers

    SciTech Connect

    Guglietta, Glenn W.; Baxter, Jason B.; Choudhury, Kaushik Roy; Caspar, Jonathan V.

    2014-06-23

    We report the application of time-resolved terahertz spectroscopy (TRTS) to measure photoexcited carrier lifetimes and mobility, and to determine recombination mechanisms in Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) thin films fabricated from nanocrystal inks. Ultrafast time resolution permits tracking the evolution of carrier density to determine recombination rates and mechanisms. The carrier generation profile was manipulated by varying the photoexcitation wavelength and fluence to distinguish between surface, Shockley-Read-Hall (SRH), radiative, and Auger recombination mechanisms and determine rate constants. Surface and SRH recombination are the dominant mechanisms for the air/CZTSSe/SiO{sub 2}/Si film stack. Diffusion to, and then recombination at, the air-CZTSSe interface occurred on the order of 100 picoseconds, while SRH recombination lifetimes were 1–2 nanoseconds. TRTS measurements can provide information that is complementary to conventional time-resolved photoluminescence measurements and can direct the design of efficient thin film photovoltaics.

  12. Softening of infrared-active mode of perovskite BaZrO{sub 3} proved by terahertz time-domain spectroscopy

    SciTech Connect

    Helal, M. A.; Mori, T.; Kojima, S.

    2015-05-04

    The low-frequency infrared-active optical modes were studied in a barium zirconate, BaZrO{sub 3}, single crystal with the perovskite structure using terahertz (THz) time-domain spectroscopy (TDS). The real and imaginary parts of the dielectric constants were accurately determined in the frequency range between 0.2 and 2.7 THz. Upon cooling from room temperature to 8 K, the lowest-frequency TO1 mode at 2.32 THz showed a pronounced softening to 1.94 THz. The real part of the dielectric constant at 0.5 THz determined by THz-TDS obeys Barrett's relation, and the existence of a plateau confirms that the quantum effects lead to saturation of the soft mode frequencies of the TO1 and TO2 modes below ≈20 K. This is reminiscent of incipient ferroelectrics with the perovskite structure such as CaTiO{sub 3}.

  13. Temperature and carrier-density dependence of electron-hole scattering in silicon investigated by optical-pump terahertz-probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Terashige, T.; Yada, H.; Matsui, Y.; Miyamoto, T.; Kida, N.; Okamoto, H.

    2015-06-01

    We measured the optical conductivity σ ˜(ω ) spectra of photodoped silicon by optical-pump terahertz-probe spectroscopy and analyzed them with a two-carrier Drude model. Taking into account the values of electron (hole)-phonon scattering rates previously reported in chemically doped silicon, we evaluated the electron-hole scattering rates γe -h. From 293 to 90 K , the magnitudes and temperature dependence of γe -h were successfully reproduced by a theoretical model including the effects of Rutherford scattering, Coulomb screening, and Pauli exclusion. This suggests that these three factors dominate electron-hole scattering processes in silicon. Below 90 K , γe -h becomes larger than that of the theoretical curve, which is attributable to a prolongation of the relaxation time of hot carriers.

  14. Review of Terahertz Tomography Techniques

    NASA Astrophysics Data System (ADS)

    Guillet, J. P.; Recur, B.; Frederique, L.; Bousquet, B.; Canioni, L.; Manek-Hönninger, 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.

  15. 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.

  16. Diffuse reflectance spectroscopy study of in vitro tissue for nasopharyngeal carcinoma diagnosis

    NASA Astrophysics Data System (ADS)

    Xu, Zhihong; Lin, Xueliang; Ge, Xiaosong; Lin, Duo; Huang, Wei

    2016-10-01

    Diffuse reflectance spectroscopy is a non-contact, non-invasive, and low-cost optical technique that provides real-time feedback about the absorptive characteristics and the microstructure properties of biological tissue. This optical technique shows the potential for monitoring metabolic status associated with malignancy transformation. Nasopharyngeal carcinoma (NPC) is the third most frequently diagnosed cancer associated with virus and is the most common male malignancy with a characteristic regional and racial distribution worldwide. This paper investigates the current screening state of nasopharyngeal malignancies and also provides an overview on the applications of diffuse reflectance spectroscopy in the cancer detection. Furthermore, the latest research relevant to the diagnosis of NPC in vitro tissue using diffuse reflectance spectroscopy is introduced. The results of diffuse reflectance spectroscopy are summarized, showing a significant experimental and clinical value for further NPC detection in vivo in the future.

  17. Use of Finite Difference Time Domain Simulations and Debye Theory for Modelling the Terahertz Reflection Response of Normal and Tumour Breast Tissue

    PubMed Central

    Fitzgerald, Anthony J.; Pickwell-MacPherson, Emma; Wallace, Vincent P.

    2014-01-01

    The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues. PMID:25010734

  18. Determination of styrene-butadiene rubber composition by attenuated total internal reflection infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Orlov, A. S.; Kiselev, S. A.; Kiseleva, E. A.; Budeeva, A. V.; Mashukov, V. I.

    2013-03-01

    A rapid method for determining the composition of styrene-butadiene rubber using attenuated total internal reflection infrared spectroscopy was proposed. PMR and 13C NMR spectroscopy and infrared transmission spectroscopy were used as absolute techniques for determining the compositions of calibration samples. It was shown that the method was applicable to a wide range of styrene-butadiene rubbers, did not require additional sample preparation, and was easily reproducible.

  19. Far infrared (terahertz) spectroscopy of a series of polycyclic aromatic hydrocarbons and application to structure interpretation of asphaltenes and related compounds

    NASA Astrophysics Data System (ADS)

    Cataldo, Franco; Angelini, Giancarlo; García-Hernández, D. A.; Manchado, Arturo

    2013-07-01

    A series of 33 different polycyclic aromatic hydrocarbons (PAHs) were studied by far infrared spectroscopy (terahertz spectroscopy) in the spectral range comprised between 600 and 50 cm-1. In addition to common PAHs like naphthalene, anthracene, phenanthrene, fluoranthene, picene, pyrene, benzo[α]pyrene, and perylene, also quite unusual PAHs were studied like tetracene, pentacene, acenaphtene, acenaphtylene, triphenylene, and decacyclene. A series of alkylated naphthalenes and anthracenes were studied as well as methypyrene. Partially or totally hydrogenated PAHs were also object of the present investigation, ranging from tetrahydronaphthalene (tetralin) to decahydronaphthalene (decalin), 9,10-dihydroanthracene, 9,10-dihydrophenanthrene, hexahydropyrene, and dodecahydrotriphenylene. Finally, the large and quite rare PAHs coronene, quaterrylene, hexabenzocoronene, and dicoronylene were studied by far infrared spectroscopy. The resulting reference spectra were used in the interpretation of the chemical structure of asphaltenes (as extracted from a heavy petroleum fraction and from bitumen), the chemical structures of other petroleum fractions known as DAE (distillate aromatic extract) and RAE (residual aromatic extract), and a possible interpretation of components of the chemical structure of anthracite coal. Asphaltenes, heavy petroleum fractions, and coal were proposed as model compounds for the interpretation of the emission spectra of certain proto-planetary nebulae (PPNe) with a good matching in the mid infrared between the band pattern of the PPNe emission spectra and the spectra of these oil fractions or coal. Although this study was finalized in an astrochemical context, it may find application also in the petroleum and coal chemistry.

  20. Far infrared (terahertz) spectroscopy of a series of polycyclic aromatic hydrocarbons and application to structure interpretation of asphaltenes and related compounds.

    PubMed

    Cataldo, Franco; Angelini, Giancarlo; García-Hernández, D Aníbal; Manchado, Arturo

    2013-07-01

    A series of 33 different polycyclic aromatic hydrocarbons (PAHs) were studied by far infrared spectroscopy (terahertz spectroscopy) in the spectral range comprised between 600 and 50 cm(-1). In addition to common PAHs like naphthalene, anthracene, phenanthrene, fluoranthene, picene, pyrene, benzo[α]pyrene, and perylene, also quite unusual PAHs were studied like tetracene, pentacene, acenaphtene, acenaphtylene, triphenylene, and decacyclene. A series of alkylated naphthalenes and anthracenes were studied as well as methypyrene. Partially or totally hydrogenated PAHs were also object of the present investigation, ranging from tetrahydronaphthalene (tetralin) to decahydronaphthalene (decalin), 9,10-dihydroanthracene, 9,10-dihydrophenanthrene, hexahydropyrene, and dodecahydrotriphenylene. Finally, the large and quite rare PAHs coronene, quaterrylene, hexabenzocoronene, and dicoronylene were studied by far infrared spectroscopy. The resulting reference spectra were used in the interpretation of the chemical structure of asphaltenes (as extracted from a heavy petroleum fraction and from bitumen), the chemical structures of other petroleum fractions known as DAE (distillate aromatic extract) and RAE (residual aromatic extract), and a possible interpretation of components of the chemical structure of anthracite coal. Asphaltenes, heavy petroleum fractions, and coal were proposed as model compounds for the interpretation of the emission spectra of certain proto-planetary nebulae (PPNe) with a good matching in the mid infrared between the band pattern of the PPNe emission spectra and the spectra of these oil fractions or coal. Although this study was finalized in an astrochemical context, it may find application also in the petroleum and coal chemistry.

  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. Doppler-shifted reflections of X rays in beamfoil spectroscopy

    NASA Technical Reports Server (NTRS)

    Bernstein, E. M.; Mcintyre, L. C., Jr.

    1976-01-01

    Carbon foils were positioned at roughly 10 deg to the conventional perpendicular position so that the spectrometer would view the beam on emergence from the foil, with no radiation shielded by a bowed or wrinkled foil or by the foil holder. Extraneous peaks due to reflected radiation were detected in the spectrum obtained with the tilted foil. A large satellite appears longward of the spectral line and is attributed to Doppler-shifted radiation reflected from the foil surface. Special tests arranged to validate the origin of the satellites are described. The relative intensity of the reflected radiation compared with the direct radiation observed is at variance with the relative intensities reported for longer wavelengths. The reasons for this, possible effects of spectrometer geometry, and applications in the investigation or generation of polarization remain to be investigated

  3. [Terahertz Spectroscopic Identification with Deep Belief Network].

    PubMed

    Ma, Shuai; Shen, Tao; Wang, Rui-qi; Lai, Hua; Yu, Zheng-tao

    2015-12-01

    Feature extraction and classification are the key issues of terahertz spectroscopy identification. Because many materials have no apparent absorption peaks in the terahertz band, it is difficult to extract theirs terahertz spectroscopy feature and identify. To this end, a novel of identify terahertz spectroscopy approach with Deep Belief Network (DBN) was studied in this paper, which combines the advantages of DBN and K-Nearest Neighbors (KNN) classifier. Firstly, cubic spline interpolation and S-G filter were used to normalize the eight kinds of substances (ATP, Acetylcholine Bromide, Bifenthrin, Buprofezin, Carbazole, Bleomycin, Buckminster and Cylotriphosphazene) terahertz transmission spectra in the range of 0.9-6 THz. Secondly, the DBN model was built by two restricted Boltzmann machine (RBM) and then trained layer by layer using unsupervised approach. Instead of using handmade features, the DBN was employed to learn suitable features automatically with raw input data. Finally, a KNN classifier was applied to identify the terahertz spectrum. Experimental results show that using the feature learned by DBN can identify the terahertz spectrum of different substances with the recognition rate of over 90%, which demonstrates that the proposed method can automatically extract the effective features of terahertz spectrum. Furthermore, this KNN classifier was compared with others (BP neural network, SOM neural network and RBF neural network). Comparisons showed that the recognition rate of KNN classifier is better than the other three classifiers. Using the approach that automatic extract terahertz spectrum features by DBN can greatly reduce the workload of feature extraction. This proposed method shows a promising future in the application of identifying the mass terahertz spectroscopy.

  4. Quantitative reflection spectroscopy at the human ocular fundus

    NASA Astrophysics Data System (ADS)

    Hammer, Martin; Schweitzer, Dietrich

    2002-01-01

    A new model of the reflection of the human ocular fundus on the basis of the adding-doubling method, an approximate solution of the radiative transport equation, is described. This model enables the calculation of the concentrations of xanthophyll in the retina, of melanin in the retinal pigment epithelium and the choroid, and of haemoglobin in the choroid from fundus reflection spectra. The concentration values found in 12 healthy subjects are in excellent agreement with published data. In individual cases of pathologic fundus alterations, possible benefits to the ophthalmologic diagnostics are demonstrated.

  5. Frequency selective terahertz retroreflectors

    NASA Astrophysics Data System (ADS)

    Williams, Richard James

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

  6. Determining Water Content of Geologic Materials Using Reflectance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Milliken, R. E.; Mustard, J. F.

    2004-03-01

    TGA data and reflectance spectra are used to track changes in water absorptions as a function of absolute water content. Calculating band depth areas of absorptions in VIS-NIR data may prove useful for quantifying the water content of Mars' surface.

  7. Identification of thermal degradation using probabilistic models in reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Criner, A. K.; Cherry, A. J.; Cooney, A. T.; Katter, T. D.; Banks, H. T.; Hu, Shuhua; Catenacci, Jared

    2015-03-01

    Different probabilistic models of molecular vibration modes are considered to model the reflectance spectra of chemical species through the dielectric constant. We discuss probability measure estimators in parametric and nonparametric models. Analyses of ceramic matrix composite samples that have been heat treated for different amounts of times are compared. We finally compare these results with the analysis of vitreous silica using nonparametric models.

  8. Monitoring bruise age using visible diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    McMurdy, John W.; Duffy, Susan; Crawford, Gregory P.

    2007-02-01

    The ability to determine the age of a bruise of unknown age mechanism is important in matters of domestic and child abuse and forensics. While physicians are asked to make clinical judgment on the age of a bruise using color and tenderness, studies have shown that a physicians estimate is highly inaccurate and in cases no better than chance alone. We present here the temporal progression of reflection spectrum collected from accidentally inflicted contusions in adult and child study participants with a synopsis of the observed phenomena. Reflection spectra collected using a portable fiber optic reflection spectrometer can track the increase in extravasated hemoglobin from trauma caused blood vessel rupture and subsequent removal of this hemoglobin occurring concurrent with an increase in the absorption attributed to the breakdown product bilirubin. We hypothesize that this time dependent pattern can be used to determine the age of an unknown bruise in an individual provided rate constant information for the patient can be determined in a controlled calibration bruise. Using reflection spectra to estimate bruise age can provide a rapid and noninvasive method to improve the ability of physicians in dating the age of a contusion.

  9. Three-dimensional invisibility cloaks functioning at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Cao, Wei; Zhou, Fan; Liang, Dachuan; Gu, Jianqiang; Han, Jiaguang; Sun, Cheng; Zhang, Weili

    2014-05-01

    Quasi-three-dimensional invisibility cloaks, comprised of either homogeneous or inhomogeneous media, are experimentally demonstrated in the terahertz regime. The inhomogeneous cloak was lithographically fabricated using a scalable Projection Microstereolithography process. The triangular cloaking structure has a total thickness of 4.4 mm, comprised of 220 layers of 20 μm thickness. The cloak operates at a broad frequency range between 0.3 and 0.6 THz, and is placed over an α-lactose monohydrate absorber with rectangular shape. Characterized using angular-resolved reflection terahertz time-domain spectroscopy, the results indicate that the terahertz invisibility cloak has successfully concealed both the geometrical and spectroscopic signatures of the absorber, making it undetectable to the observer. The homogeneous cloaking device made from birefringent crystalline sapphire features a large concealed volume, low loss, and broad bandwidth. It is capable of hiding objects with a dimension nearly an order of magnitude larger than that of its lithographic counterpart, but without involving complex and time-consuming cleanroom processing. The cloak device was made from two 20-mm-thick high-purity sapphire prisms. The cloaking region has a maximum height 1.75 mm with a volume of approximately 5% of the whole sample. The reflected TM beam from the cloak shows nearly the same profile as that reflected by a flat mirror.

  10. ChemCam Passive Reflectance Spectroscopy at Gale Crater, Mars

    NASA Astrophysics Data System (ADS)

    Johnson, J. R.; Bell, J. F.; Cloutis, E.; Bender, S.; Blaney, D. L.; Ehlmann, B. L.; Gasnault, O.; Kinch, K. M.; Le Mouelic, S.; Rice, M. S.; Wiens, R. C.; DeFlores, L.; Team, M.

    2013-12-01

    The Laser-Induced Breakdown Spectrometer (LIBS) portion of the ChemCam instrument on the Mars Science Laboratory Curiosity rover uses 3 dispersive spectrometers to cover the ultraviolet (240-342 nm), visible (382-469 nm) and visible/near-infrared (474-906 nm) spectral regions at high spectral (<0.5nm) and spatial (0.65mrad) resolution. In active LIBS mode, light emitted from a laser-generated plasma is dispersed onto these spectrometers and used to detect elemental emission lines. Typical observations include 3 msec-exposure 'dark' spectra (acquired with the LIBS laser off) used to remove the background signal from the LIBS measurement. Similar 'passive' observations of the ChemCam calibration target holder can be made at similar times of day and at identical exposure times (to minimize variations from dark current). Because this target exhibits ~95% flat reflectance in the ~400-900 nm region, radiance spectra ratios (surface/calibration target) can be normalized to known calibration target lab spectra to produce relative reflectance spectra (400-900 nm) with an estimated accuracy of 10-20%. Initial results replicated the known spectral shape and overall reflectance values of the ChemCam calibration targets and green color chip on the Mastcam calibration target. Dust contamination was evident, although dust on the ChemCam calibration targets is minimized by their tilted placement on the rover deck. All ChemCam targets that were sunlit during LIBS acquisition (~80% of all measurements) provide 'dark' spectra for which relative reflectance spectra can be obtained. Owing to the dusty nature of the Gale landing sites, passive spectra observed to date exhibit spectral shapes indicative of ferric phases, similar to spectra of palagonitic soils. Most spectra are bracketed in reflectance by typical 'bright' and 'dark' spectra from the OMEGA and CRISM orbital spectrometers. Preliminary Mastcam reflectance spectra are similar, providing additional confidence regarding the

  11. Cavity enhanced terahertz modulation

    SciTech Connect

    Born, N.; Scheller, M.; Moloney, J. V.; Koch, M.

    2014-03-10

    We present a versatile concept for all optical terahertz (THz) amplitude modulators based on a Fabry-Pérot semiconductor cavity design. Employing the high reflectivity of two parallel meta-surfaces allows for trapping selected THz photons within the cavity and thus only a weak optical modulation of the semiconductor absorbance is required to significantly damp the field within the cavity. The optical switching yields to modulation depths of more than 90% with insertion efficiencies of 80%.

  12. Interaction of Sensitizing Dyes with Nanostructured TiO2 Film in Dye-Sensitized Solar Cells Using Terahertz Spectroscopy

    PubMed Central

    Ghann, William; Rahman, Aunik; Rahman, Anis; Uddin, Jamal

    2016-01-01

    The objective of this investigation was to shed light on the nature of interaction of different organic dyes and an inorganic dye, Ruthenium (II) polypyridine complex, with TiO2 nanoparticles. TiO2 is commonly deployed as an efficient energy transfer electrode in dye sensitized solar cells. The efficiency of dye sensitized solar cells is a function of the interaction of a dye with the electrode material such as TiO2. To the best of our knowledge the present study is the first effort in the determination of terahertz absorbance signals, investigation of real-time dye permeation kinetics, and the surface profiling and 3D imaging of dye sensitized TiO2 films. Herein, we report that the terahertz spectra of the natural dye sensitized TiO2 films were distinctively different from that of the inorganic dye with prominent absorption of natural dyes occurring at approximately the same wavelength. It was observed that the permeation of the natural dyes were more uniform through the layers of the mesoporous TiO2 compared to the inorganic dye. Finally, defects and flaws on TiO2 film were easily recognized via surface profiling and 3D imaging of the films. The findings thus offer a new approach in characterization of dye sensitized solar cells. PMID:27443236

  13. Reflection Electron Energy Loss Spectroscopy of Iron Monosilicide

    NASA Astrophysics Data System (ADS)

    Parshin, A. S.; Igumenov, A. Yu.; Mikhlin, Yu. L.; Pchelyakov, O. P.; Zhigalov, V. S.

    2017-02-01

    X-ray photoelectron spectra, reflection electron energy loss spectra, and inelastic electron scattering cross section spectra of iron monosilicide FeSi are investigated. It is shown that the spectra of inelastic electron scattering cross section have advantages over the reflection electron energy loss spectra in studying the processes of electron energy losses. An analysis of the fine structure of the inelastic electron scattering cross section spectra allows previously unresolved peaks to be identified and their energy, intensity, and nature to be determined. The difference between energies of fitting loss peaks in the spectra of inelastic electron scattering cross section of FeSi and pure Fe are more substantial than the chemical shifts in X-ray photoelectron spectra, which indicates the possibility of application of the fine structure of the spectra of inelastic electron scattering cross section for elemental analysis.

  14. Microwave Reflection Spectroscopy of a Two-Dimensional Electron Gas

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Liu, Ruiyuan; Du, Lingjie; Du, Rui-Rui; Pfeiffer, Loren; West, Ken

    Cyclotron resonance (CR) is a standard method to determine the carrier effective mass in two-dimensional electron systems, typically by measuring/analyzing the absorption or transmission signal. Here we report a microwave spectrometer utilizing the reflection signal. In our experiment setup based on a top-loading helium3 cryostat and a superconducting solenoid, the microwave (up to 40GHz) is sent down via a coax cable to the sample surface, and the reflection signal is then collected by the same cable and fed upward to a directional coupler, and being detected. We demonstrate the applicability of the spectrometer by measuring the CR of high-mobility electrons or holes in GaAs/AlGaAs quantum wells. The construction of spectrometer, preliminary data, and brief discussions will be presented. The work at Rice was supported by Welch Foundation Grant C-1682.

  15. Terahertz reflectometry of burn wounds in a rat model

    PubMed Central

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

    2011-01-01

    We present sub-millimeter wave reflectometry of an experimental rat skin burn model obtained by the Terahertz Time-Domain Spectroscopy (THz-TDS) technique. Full thickness burns, as confirmed by histology, were created on rats (n = 4) euthanized immediately prior to the experiments. Statistical analysis shows that the burned tissue exhibits higher reflectivity compared to normal skin over a frequency range between 0.5 and 0.7 THz (p < 0.05), likely due to post-burn formation of interstitial edema. Furthermore, we demonstrate that a double Debye dielectric relaxation model can be used to explain the terahertz response of both normal and less severely burned rat skin. Finally, our data suggest that the degree of conformation between the experimental burn measurements and the model for normal skin can potentially be used to infer the extent of burn severity. PMID:21833370

  16. Optical characterization of volcanic ash using diffuse reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Bravo, D. Kelly; Falcón, Nelsón; Narea, Freddy J.; Muñoz, Rafael A.; Muñoz, Aaron A.

    2013-11-01

    The determination of the optical parameters are important for remote sensing and aircraft, in this case allow the difference between a cloud composed solely of water and water plus ash. Therefore, this research is intended to determine the optical properties of the ash four active volcanoes, by studying the spectral resolution reflectance interpreting the results in the approximation of Kubelka - Munk equation through the transfer equation radiative. The results allow classifying these ashes depending on their place of origin.

  17. [Application of near infrared reflectance spectroscopy to predict meat chemical compositions: a review].

    PubMed

    Tao, Lin-Li; Yang, Xiu-Juan; Deng, Jun-Ming; Zhang, Xi

    2013-11-01

    In contrast to conventional methods for the determination of meat chemical composition, near infrared reflectance spectroscopy enables rapid, simple, secure and simultaneous assessment of numerous meat properties. The present review focuses on the use of near infrared reflectance spectroscopy to predict meat chemical compositions. The potential of near infrared reflectance spectroscopy to predict crude protein, intramuscular fat, fatty acid, moisture, ash, myoglobin and collagen of beef, pork, chicken and lamb is reviewed. This paper discusses existing questions and reasons in the current research. According to the published results, although published results vary considerably, they suggest that near-infrared reflectance spectroscopy shows a great potential to replace the expensive and time-consuming chemical analysis of meat composition. In particular, under commercial conditions where simultaneous measurements of different chemical components are required, near infrared reflectance spectroscopy is expected to be the method of choice. The majority of studies selected feature-related wavelengths using principal components regression, developed the calibration model using partial least squares and modified partial least squares, and estimated the prediction accuracy by means of cross-validation using the same sample set previously used for the calibration. Meat fatty acid composition predicted by near-infrared spectroscopy and non-destructive prediction and visualization of chemical composition in meat using near-infrared hyperspectral imaging and multivariate regression are the hot studying field now. On the other hand, near infrared reflectance spectroscopy shows great difference for predicting different attributes of meat quality which are closely related to the selection of calibration sample set, preprocessing of near-infrared spectroscopy and modeling approach. Sample preparation also has an important effect on the reliability of NIR prediction; in particular

  18. Early detection and differentiation of venous and arterial occlusion in skin flaps using visible diffuse reflectance spectroscopy and autofluorescence spectroscopy.

    PubMed

    Zhu, Caigang; Chen, Shuo; Chui, Christopher Hoe-Kong; Tan, Bien-Keem; Liu, Quan

    2016-02-01

    Our previous preclinical study demonstrated that both visible diffuse reflectance and autofluorescence spectroscopy, each of which yields a different set of physiological information, can predict skin flap viability with high accuracy in a MacFarlane rat dorsal skin flap model. In this report, we further evaluated our technique for the early detection and differentiation of venous occlusion and arterial occlusion in a rat groin flap model. We performed both diffuse reflectance and autofluorescence measurements on the skin flap model and statistically differentiated between flaps with and without occlusions as well as between flaps with venous occlusion and those with arterial occlusion based on these non-invasive optical measurements. Our preliminary results suggested that visible diffuse reflectance and autofluorescence spectroscopy can be potentially used clinically to detect both venous and arterial occlusion and differentiate one from the other accurately at an early time point.

  19. Early detection and differentiation of venous and arterial occlusion in skin flaps using visible diffuse reflectance spectroscopy and autofluorescence spectroscopy

    PubMed Central

    Zhu, Caigang; Chen, Shuo; Chui, Christopher Hoe-Kong; Tan, Bien-Keem; Liu, Quan

    2016-01-01

    Our previous preclinical study demonstrated that both visible diffuse reflectance and autofluorescence spectroscopy, each of which yields a different set of physiological information, can predict skin flap viability with high accuracy in a MacFarlane rat dorsal skin flap model. In this report, we further evaluated our technique for the early detection and differentiation of venous occlusion and arterial occlusion in a rat groin flap model. We performed both diffuse reflectance and autofluorescence measurements on the skin flap model and statistically differentiated between flaps with and without occlusions as well as between flaps with venous occlusion and those with arterial occlusion based on these non-invasive optical measurements. Our preliminary results suggested that visible diffuse reflectance and autofluorescence spectroscopy can be potentially used clinically to detect both venous and arterial occlusion and differentiate one from the other accurately at an early time point. PMID:26977363

  20. Diffuse reflectance spectroscopy of pre- and post-treated oral submucous fibrosis: an in vivo study

    NASA Astrophysics Data System (ADS)

    Sivabalan, S.; Ponranjini Vedeswari, C.; Jayachandran, S.; Koteeswaran, D.; Pravda, C.; Aruna, P.; Ganesan, S.

    2010-02-01

    Oral submucous fibrosis (OSF) is a high risk precancerous condition characterized by changes in the connective tissue fibers of the lamina propria and deeper parts leading to stiffness of the mucosa and restricted mouth opening, fibrosis of the lining mucosa of the upper digestive tract involving the oral cavity, oro- and hypo-pharynx and the upper two-thirds of the oesophagus. Optical reflectance measurements have been used to extract diagnostic information from a variety of tissue types, in vivo. We apply diffuse reflectance spectroscopy to quantitatively monitor tumour response to chemotherapy. Twenty patients with submucous fibrosis were diagnosed with diffuse reflectance spectroscopy and treated with the chemotherapy drug, Dexamethasone sodium phosphate and Hyaluronidase injection for seven weeks and after the treatment they were again subjected to the diffuse reflectance spectroscopy. The major observed spectral alterations on pre and post treated submucous fibrosis is an increase in the diffuse reflectance from 450 to 600 nm. Normal mucosa has showed higher reflectance when compared to the pre and post-treated cases. The spectral changes were quantified and correlated to conventional diagnostic results viz., maximum mouth opening, tongue protrusion and burning sensation. The results of this study suggest that the diffuse reflectance spectroscopy may also be considered as complementary optical techniques to monitor oral tissue transformation.

  1. Catheter based mid-infrared reflectance and reflectance generated absorption spectroscopy

    DOEpatents

    Holman, Hoi-Ying N

    2013-10-29

    A method of characterizing conditions in a tissue, by (a) providing a catheter that has a light source that emits light in selected wavenumbers within the range of mid-IR spectrum; (b) directing the light from the catheter to an area of tissue at a location inside a blood vessel of a subject; (c) collecting light reflected from the location and generating a reflectance spectra; and (d) comparing the reflectance spectra to a reference spectra of normal tissue, whereby a location having an increased number of absorbance peaks at said selected wavenumbers indicates a tissue inside the blood vessel containing a physiological marker for atherosclerosis.

  2. Carrier Dynamics in CsPbBr_3 Nanocrystals in Presence of Electron and Hole Acceptors: a Time Resolved Terahertz Spectroscopy Study.

    NASA Astrophysics Data System (ADS)

    Sarkar, Sohini; Banerjee, Sneha; Reddy, Yettapu Gurivi; Ravi, Vikash Kumar; Nag, Angshuman; Mandal, Pankaj

    2016-06-01

    Study of lead halide perovskites is a burgeoning field of research owing to their applications in solar cells and myriads of other light harvesting and emitting devices. In this work we have employed Terahertz time domain spectroscopy (THz-TDS) and time-resolved THz spectroscopy (TRTS) to study dielectric properties and carrier dynamics occurring within CsPbBr_3 perovskite nanocrystals (NCs) in presence of electron and hole acceptor molecules. The THz-TDS spectrum of CsPbBr_3 NCs features a strong and broad band with a peak around 3.4 THz which originates from multiple IR-active optical phonon modes of the nature of Pb-Br stretching and Br-Pb-Br bending vibrations. We observed very efficient electron and/or hole transfer in presence of either an electron or a hole acceptor, or both. Also, in presence of either an electron or hole acceptor the diffusion length reduces to half (4.1 μm) in comparison to parent NCs (9.2 μm). In presence of both, electron and hole acceptor molecules the diffusion length reduces to 0.6 μm. Considerable decrease in mobility values is also observed for the NCs in presence of electron and hole acceptor molecules. Details of the study will be discussed in the talk.

  3. Understanding the composition of the lunar mare through reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Denevi, Brett Wilcox

    2007-08-01

    In order to quantify the spectral behavior of maturity variations in the mare, spectral trends of nearly 10,000 craters in six mare regions are examined. Radiative transfer theory is used to model these trends in order to better understand their causes. The maturity trends are confirmed to be more parallel than radial as previously suggested, and this fact is exploited to develop a new algorithm for determination of iron content in mare regions. This new mare iron algorithm better compensates for maturity than previous methods, and uncertainties due to maturity variations are less than 0.5 wt% FeO. Measured optical constants of synthetic glasses of lunar-like compositions are used to predict the optical constants of any glass of an arbitrary combination of FeO and TiO 2 content. These optical constants are employed along with radiative transfer theory to determine composition from telescopic spectra of three regional lunar pyroclastic deposits which are likely to contain large amounts of glass: the Aristarchus Plateau, Mare Humorum, and Sulpicius Gallus. The imaginary coefficient of the complex index of refraction ( k ) is derived from reflectance spectra of 30 pyroxenes. Modified Gaussian modeling is applied to these k spectra to obtain two continuum parameters and nine Gaussian parameters that describe the 1, 2, and 1.2 mm crystal field absorptions. Multiple regression results indicate that the continuum and Gaussian parameters are well predicted by pyroxene FeO and CaO contents; thus, a method to predict a complete pyroxene k spectrum from its FeO and CaO concentrations is developed. The ability of radiative transfer modeling to reproduce reflectance spectra of known composition, and extract compositional information from reflectance spectra, is examined. This model is tested using spectra of mineral mixtures, nine lunar mare soil samples studied by the Lunar Soil Characterization Consortium, and the Apollo 11 landing site. The model is able to accurately

  4. Detection of propranolol in pharmaceutical formulations by diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Gotardo, Mara Andréia; Tognolli, João Olímpio; Pezza, Helena Redigolo; Pezza, Leonardo

    2008-04-01

    This paper describes an analytical reflectometric method that has an objective not only the industrial quality control but also to detect possible falsifications and/or adulterations of propranolol in pharmaceutical formulations. The method is based on the diffuse reflectance measurements of the colored product (III) of the spot test reaction between propranolol hydrochloride (I) and 2,6-dichloroquinone-4-chloroimide (II) using filter paper as solid support. Spot test conditions have been investigated using experimental design in order to identify and optimize the critical factors. The factors evaluated were DCQ concentration, propranolol solvent and DCQ solvent. The best reaction conditions were achieved with the addition of 30 μL of propranolol solution in ethanol 35% (v/v) and 30 μL of DCQ solution at 70 mg mL -1 in acetone, in this order. All reflectance measurements were carried out at 500 nm and the linear range was from 8.45 × 10 -4 to 8.45 × 10 -2 mol L -1 ( r = 0.998). The limit of detection was 1.01 × 10 -4 mol L -1. No interference was observed from the assessed excipients and drugs. The method was applied to determine propranolol in commercial brands of pharmaceuticals. The results obtained by the proposed method were favorably compared with those given by the British Pharmacopoeia procedure.

  5. Study of electronic transitions by using attenuated total reflectance spectroscopy in the far-UV region

    NASA Astrophysics Data System (ADS)

    Morisawa, Yusuke; Tachibana, Shin; Ehara, Masahiro; Ozaki, Yukihiro

    2016-09-01

    The wavelength region shorter than 200 nm, far-ultraviolet (FUV) region, is very rich in information about the electronic states and structure of a molecule. Since the molar absorption coefficient is very high ( 105 mol-1 dm3 cm-1) in the FUV region, the electronic states and structure mainly for gas molecules has been investigated for a long time. On the other hand, as to molecules in the condensed phase transmittance spectra could not measure because of high molecular density, and reflection spectroscopy has been used to observe spectra of solid samples in the FUV region. However, for liquid samples generally either absorption spectroscopy or specular reflection spectroscopy was difficult to observe. Accordingly, FUV spectroscopy for liquid samples has been a relatively undeveloped research area. To solve the above difficulties of FUV spectroscopy we have recently developed a totally new UV spectrometer based on attenuated total reflection (ATR) that enables us to measure spectra of liquid and solid samples in the 140-280 nm region. This paper shows the studies by the attenuated total reflection far-ultraviolet (ATR-FUV) spectroscopy. These investigations elucidate the electronic structure and electronic transition in the FUV region for molecules such as n- and branched alkanes, alcohols, ketones, amides, and nylons in the liquid or solid phase. The consistent assignments were performed with a help of quantum chemical calculation.

  6. Total reflection X-ray photoelectron spectroscopy as a semiconductor lubricant elemental analysis method

    NASA Astrophysics Data System (ADS)

    Alshehabi, Abbas; Sasaki, Nobuharu; Kawai, Jun

    2015-12-01

    Photoelectron spectra from a typical hard disk storage media device (HDD) were measured at total reflection and non-total reflection at unburnished, acetone-cleaned, and argon-sputtered conditions. F, O, N, and C usually making the upper layer of a typical hard disk medium were detected. Enhancement of the photoelectron emission of the fluorocarbon lubricant was observed at total reflection. Pt and Co were only found by non-total X-ray photoelectron spectroscopy (XPS) because they are constituents of a deeper region than the top and interface regions. Argon-sputtered, ultrasonic acetone-cleaned, and unburnished top layers were compared at total and non-total reflection conditions. Total reflection X-ray photoelectron spectroscopy (TRXPS) is demonstrated to be a powerful tool for storage media lubrication layer chemical state analysis, reliable for industrial quality control application , and reproducible.

  7. Noninvasive particle sizing using camera-based diffuse reflectance spectroscopy.

    PubMed

    Abildgaard, Otto Højager Attermann; Frisvad, Jeppe Revall; Falster, Viggo; Parker, Alan; Christensen, Niels Jørgen; Dahl, Anders Bjorholm; Larsen, Rasmus

    2016-05-10

    Diffuse reflectance measurements are useful for noninvasive inspection of optical properties such as reduced scattering and absorption coefficients. Spectroscopic analysis of these optical properties can be used for particle sizing. Systems based on optical fiber probes are commonly employed, but their low spatial resolution limits their validity ranges for the coefficients. To cover a wider range of coefficients, we use camera-based spectroscopic oblique incidence reflectometry. We develop a noninvasive technique for acquisition of apparent particle size distributions based on this approach. Our technique is validated using stable oil-in-water emulsions with a wide range of known particle size distributions. We also measure the apparent particle size distributions of complex dairy products. These results show that our tool, in contrast to those based on fiber probes, can deal with a range of optical properties wide enough to track apparent particle size distributions in a typical industrial process.

  8. Thermal infrared reflectance and emission spectroscopy of quartzofeldspathic glasses

    USGS Publications Warehouse

    Byrnes, J.M.; Ramsey, M.S.; King, P.L.; Lee, R.J.

    2007-01-01

    This investigation seeks to better understand the thermal infrared (TIR) spectral characteristics of naturally-occurring amorphous materials through laboratory synthesis and analysis of glasses. Because spectra of glass phases differ markedly from their mineral counterparts, examination of glasses is important to accurately determine the composition of amorphous surface materials using remote sensing datasets. Quantitatively characterizing TIR (5-25 ??m) spectral changes that accompany structural changes between glasses and mineral crystals provides the means to understand natural glasses on Earth and Mars. A suite of glasses with compositions analogous to common terrestrial volcanic glasses was created and analyzed using TIR reflectance and emission techniques. Documented spectral characteristics provide a basis for comparison with TIR spectra of other amorphous materials (glasses, clays, etc.). Our results provide the means to better detect and characterize glasses associated with terrestrial volcanoes, as well as contribute toward understanding the nature of amorphous silicates detected on Mars. Copyright 2007 by the American Geophysical Union.

  9. Recent developments in people screening using terahertz technology: seeing the world through terahertz eyes

    NASA Astrophysics Data System (ADS)

    Kemp, Michael C.; Glauser, Antony; Baker, Colin

    2006-05-01

    Terahertz radiation, which lies between microwave and infrared, has been shown to have the potential to use very low levels of this non-ionising radiation to detect and identify objects, such as weapons and explosives, hidden under clothing. This paper describes recent work on the development of prototype systems using terahertz to provide new capabilities in people screening. In particular, it explores how hyperspectral terahertz imaging and the use of both specularly reflected and scattered terahertz radiation can enhance the detection of threat objects.

  10. High-resolution terahertz spectroscopy with a noise radiation source based on high-T c superconductors

    NASA Astrophysics Data System (ADS)

    Sobakinskaya, E.; Vaks, V. L.; Kinev, N.; Ji, M.; Li, M. Y.; Wang, H. B.; Koshelets, V. P.

    2017-01-01

    Stochastic fields can play a ‘constructive’ role in their interaction with quantum systems. In this paper, we demonstrate that the phase-diffusion field (PDF) in the terahertz range (THz) induces macroscopic polarization in molecular gas. We explain the observed effect using a simple model in which the PDF is treated as a series of ultrashort pulses of a regular signal, resulting in transient absorption in molecular gas. The experimental investigation of this effect is carried out using ammonia, and the PDF is generated by an oscillator based on stacks of Bi2Sr2CaCu2O8 intrinsic Josephson junctions. These radiation sources do not require a phase-lock loop system to provide high resolution, which simplifies the spectrometer considerably. The PDF radiation sources open up new horizons for the development of compact high-resolution THz spectrometers and applications thereof.

  11. Time-Domain Terahertz Spectroscopy (0.3 - 7.5 THz) of Molecular Ices of Simple Alcohols

    NASA Astrophysics Data System (ADS)

    McGuire, Brett A.; Ioppolo, Sergio; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey

    2014-06-01

    We have recently constructed a time-domain TeraHertz (THz) spectrometer for the study of molecular ices in the far-infrared. Here, we present the results of a study of amorphous and crystalline ices of simple alcohols from methanol (CH_3OH) through butanol (CH_3(CH_2)_3OH) in the region of 0.3 - 7.5 THz. We examine the effects of the length and degree of branching of the carbon chain on the observed spectra arising from the bulk, large-amplitude motions which are prominent in this spectral region. We also discuss these results in an astrochemical context: the application of these spectra to astronomical observations of interstellar ices with Herschel PACS/SPIRE and SOFIA.

  12. Double vibronic process in the quantum spin ice candidate Tb2Ti2O7 revealed by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Constable, E.; Ballou, R.; Robert, J.; Decorse, C.; Brubach, J.-B.; Roy, P.; Lhotel, E.; Del-Rey, L.; Simonet, V.; Petit, S.; deBrion, S.

    2017-01-01

    The origin of quantum fluctuations responsible for the spin liquid state in Tb2Ti2O7 has remained a long-standing problem. By synchrotron-based terahertz measurements, we show evidence of strong coupling between the magnetic and lattice degrees of freedom that provides a path to the quantum melting process. As revealed by hybrid crystal electric field-phonon excitations that appear at 0.67 THz below 200 K, and around 0.42 THz below 50 K, the double vibronic process is unique for Tb3 + in the titanate family due to adequate energy matching and strong quadrupolar moments. The results suggest that lattice motion can indeed be the driving force behind spin flips within the hybridized ground and first excited states, promoting quantum terms in the effective Hamiltonian that describes Tb2Ti2O7 .

  13. Cryogenic Reflectance Spectroscopy in Support of Planetary Missions

    NASA Technical Reports Server (NTRS)

    Dalton, J. B.

    2002-01-01

    Present understanding of planetary composition is based primarily on remotely-sensed data, and in particular upon ultraviolet, visible, and infrared spectroscopy. Spectra acquired by telescopic and spacecraft instruments are compared to laboratory measurements of pure materials in order to identify surface components based on characteristic absorption features. Cryogenic spectral measurements are necessary for the study of worlds beyond the Earth's orbit. While some materials exhibit only small spectral changes as a function of temperature, many others are strongly temperature-dependent. For example, hydrated salts exhibit different spectral behavior under conditions appropriate to Europa than at terrestrial temperatures. The icy satellites of the outer solar system contain significant quantities of volatile ices which do not even exist at standard temperature and pressure (STP). A comprehensive spectral database of ices and minerals covering a wide temperature range will have applications ranging from the study of comets and Kuiper Belt objects to outer planet satellites and the polar regions of Mars. Efforts are presently underway at NASA-Ames to develop capabilities which will contribute to such a database. As spacecraft instruments feature increasing spatial and spectral resolution, appropriate laboratory reference spectra become increasingly critical to accurate interpretation of the spacecraft data.

  14. Terahertz Spectroscopy of the Bending Vibrations of Acetylene 12C2H2 and 12C2D2

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Drouin, B.; Pearson, J.

    2009-12-01

    Several fundamental interstellar molecules, e.g., C2H2, CH4 and C3, are completely symmetric molecules and feature no permanent dipole moment and no pure rotation spectrum. As a result they have only previously been observed in the infrared. However, directly observing them with the rest of the molecular column especially when the source is spatially resolved would be very valuable in understanding chemical evolution. Vibrational difference bands provide a means to detect symmetric molecules with microwave precision using terahertz techniques. Herschel, SOFIA and ALMA have the potential to identify a number of vibrational difference bands of light symmetric species. This paper reports laboratory results on 12C2H2 and 12C2D2. Symmetric acetylene isotopologues have two bending modes, the trans bending and the cis bending. Their difference bands are allowed and occur in the microwave, terahertz, and far-infrared wavelengths, with band origins at 3500 GHz for 12C2H2 and 900 GHz for 12C2D2. Twenty 12C2H2 P branch high-J transitions and two hundred and fifty-one 12C2D2 P Q and R branch transitions have been measured in the 0.2 - 1.6 THz region with precision of 50 to 100 kHz. These lines were modeled together with prior data on the pure bending levels. Significantly improved molecular parameters were obtained for 12C2H2 and 12C2D2 with the combined data set, and new frequency and intensity predictions were made to support astrophysics applications. The research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. S. Y. was supported by an appointment to the NASA Postdoctoral Program, administrated by Oak Ridge Associated Universities through a contract with NASA.

  15. The view of AGN-host alignment via reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Middleton, Matthew J.; Parker, Michael L.; Reynolds, Christopher S.; Fabian, Andrew C.; Lohfink, Anne M.

    2016-04-01

    The fuelling of active galactic nuclei (AGN) - via material propagated through the galactic disc or via minor mergers - is expected to leave an imprint on the alignment of the sub-pc disc relative to the host galaxy's stellar disc. Determining the inclination of the inner disc usually relies on the launching angle of the jet; here instead we use the inclination derived from reflection fits to a sample of AGN. We determine the distorting effect of unmodelled Fe XXV/XXVI features and, via extensive simulations, determine the difference in disc inclination resulting from the use of RELXILL compared to REFLIONX. We compare inner disc inclinations to those for the host galaxy stellar disc derived from the Hubble formula and, via Monte Carlo simulations, find a strong lack of a correlation (at ≫5σ) implying either widespread feeding via mergers if we assume the sample to be homogeneous, or that radiative disc warps are distorting our view of the emission. However, we find that by removing a small (˜1/5) subset of AGN, the remaining sample is consistent with random sampling of an underlying 1:1 correlation (at the 3σ level). A heterogenous sample would likely imply that our view is not dominated by radiative disc warps but instead by different feeding mechanisms with the majority consistent with coplanar accretion (although this may be the result of selection bias), whilst a smaller but not insignificant fraction may have been fuelled by minor mergers in the recent history of the host galaxy.

  16. In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy

    SciTech Connect

    Bertram, F. Evertsson, J.; Messing, M. E.; Mikkelsen, A.; Lundgren, E.; Zhang, F.; Pan, J.; Carlà, F.; Nilsson, J.-O.

    2014-07-21

    We present results from the anodization of an aluminum single crystal [Al(111)] and an aluminum alloy [Al 6060] studied by in situ x-ray reflectivity, in situ electrochemical impedance spectroscopy and ex situ scanning electron microscopy. For both samples, a linear increase of oxide film thickness with increasing anodization voltage was found. However, the slope is much higher in the single crystal case, and the break-up of the oxide film grown on the alloy occurs at a lower anodization potential than on the single crystal. The reasons for these observations are discussed as are the measured differences observed for x-ray reflectivity and electrochemical impedance spectroscopy.

  17. [Application of near-infrared diffuse reflectance spectroscopy to the detection and identification of transgenic corn].

    PubMed

    Rui, Yu-kui; Luo, Yun-bo; Huang, Kun-lun; Wang, Wei-min; Zhang, Lu-da

    2005-10-01

    With the rapid development of the GMO, more and more GMO food has been pouring into the market. Much attention has been paid to GMO labeling under the controversy of GMO safety. Transgenic corns and their parents were scanned by continuous wave of near infrared diffuse reflectance spectroscopy range of 12000-4000 cm(-1); the resolution was 4 cm(-1); scanning was carried out for 64 times; BP algorithm was applied for data processing. The GMO food was easily resolved. Near-infrared diffuse reflectance spectroscopy is unpolluted and inexpensive compared with PCR and ELISA, so it is a very promising detection method for GMO food.

  18. Effect of data pretreatment on the noninvasive blood glucose measurement by diffuse reflectance NIR spectroscopy

    NASA Astrophysics Data System (ADS)

    Heise, Herbert M.; Marbach, Ralf

    1994-01-01

    Recent progress in spectroscopy and chemometrics have brought in-vitro blood glucose analysis into clinical reach. Parallel to these efforts noninvasive experiments by NIR- spectroscopy have also been proposed and carried out. A specially designed and optimized accessory for diffuse reflectance measurements in the spectral range of 9000 - 5000 cm-1 was used. The spectral data and reference concentration values were obtained using oral glucose tolerance tests. Calibration results are provided for log(1/R) and single beam spectra. In addition, the effects of smoothing and the use of derivative filtering were evaluated. The best results were achieved by multivariate PLS-modeling with raw data from single beam reflectance spectra.

  19. Terahertz Analysis of Quinacridone Pigments

    NASA Astrophysics Data System (ADS)

    Squires, A. D.; Kelly, M.; Lewis, R. A.

    2017-03-01

    We present terahertz spectroscopy and analysis of two commercially available quinacridone pigments in the 0.5-4.5 THz range. Our results show a clear distinction between quinacridone red and magenta pigments. We reveal four definite absorptions in the terahertz regime common to both pigments, but offset between the pigments by ˜0.2 THz. The lowest-energy line in each pigment is observed to increase in frequency by ˜0.1 THz as the temperature is reduced from 300 to 12 K.

  20. Reflectance spectroscopy: application of the Kubelka-Munk theory to the rates of photoprocesses of powders.

    PubMed

    Simmons, E L

    1976-04-01

    The Kubelka-Munk theory of reflectance spectroscopy is used to derive an approximate equation that describes the rate of the photoprocess of a powdered sample in terms of the remission function. The equation is compared with one obtained using the particle model theory of diffuse reflectance and with experimental data for the photochemical reaction of powdered K(3)[Fe(C(2)O(4))(3)]-3H(2)O.