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1

Error from Delay Drift in Terahertz Attenuated Total Reflection Spectroscopy  

NASA Astrophysics Data System (ADS)

In this article we discuss the influence of temporal stability on the value obtained for dielectric properties of materials measured by terahertz time-domain spectroscopy with particular emphasis on attenuated total reflection. The stability of three different terahertz attenuated total reflection spectroscopy systems is carefully characterized. The formalism for the complex refractive index extraction is presented and the effect of delay errors is calculated numerically. We found that good thermal stability of the terahertz system helps to minimize delay fluctuations and therefore the uncertainty of the resulting complex refractive index.

Soltani, A.; Probst, T.; Busch, S. F.; Schwerdtfeger, M.; Castro-Camus, E.; Koch, M.

2014-05-01

2

Reflective mode terahertz time domain spectroscopy for sealed liquid detection  

NASA Astrophysics Data System (ADS)

We built a reflective mode terahertz time domain spectroscopy system for sealed liquid detection. We used air plasma THz emitter for obtaining a high THz power of 5mW and used ZnTe electro-optic (EO) sampling for getting high sensitivity difference detection. Experiment demonstrates this system can detect the liquid in the sealed container. We measured the reflection data on the second interface between the sealed container and the inside liquid. The signals from the top interface show a relation with the refraction coefficients of the liquid in the THz region by using Fresnel's equations. The liquid can be indentified by comparing the curves of reflection and a database of known liquid refraction coefficients. In this paper, water, ethanol and ethylene glycol were detected and indentified. In additional, the data processing and analysis for getting the reflection data on the second interface are discussed.

Zhang, Zhen-Wei; Mu, Kai-Jun; Zhang, Liang-Liang; Zhang, Cun-Lin

2010-11-01

3

Physics-based processing for terahertz reflection spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

The spectra obtained from Terahertz (THz) reflection imaging can be distorted by scattering from rough interfaces, layers, and granular inclusions. Since the facets of the object being imaged are not generally aligned normal to the THz beam, the received signal is produced from diffuse scattering, which can be appreciably lower in signal strength than specular returns. These challenges can be addressed with advanced signal processing approaches based upon the coherent and incoherent combination of returns from multiple sensors and frequencies. This paper presents two examples of physics-based processing strategies applied to THz imaging spectroscopy. The first method is based on synthetic aperture processing of a 2D sensor array to provide variable depth focused images of buried inclusions (a ball bearing embedded in polyethylene sample). The second method uses correlation processing to coherently combine multiple sensors and multiple frequencies to extract material signatures from measurements of THz scattering from rough interfaces. Results for both methods show an increase in performance relative to conventional imaging or spectroscopy approaches.

Zurk, L. M.; Henry, S. C.; Schecklman, S.; Duncan, D. D.

2010-11-01

4

Nondestructive evaluation of aircraft composites using reflective terahertz time domain spectroscopy  

Microsoft Academic Search

Terahertz time domain spectroscopy in reflection configuration was assessed as a nondestructive evaluation technique for aircraft glass fiber composites. A technique for measuring the material properties of glass fiber composites using reflection geometry was demonstrated in addition to imaging of damaged glass fiber composites. Surface defects such as localized burn damage, puncture holes, and paint\\/composite removal were detected using amplitude

Christopher Stoik; Matthew Bohn; James Blackshire

2010-01-01

5

Numerical phase correction method for terahertz time-domain reflection spectroscopy  

Microsoft Academic Search

We propose a numerical method for the misplacement phase error correction in terahertz time-domain reflection spectroscopy (THz-TDRS). The developed algorithm is based on the maximum entropy principle and can be readily implemented into data processing, allowing one to reveal material parameters of the opaque materials from the THz reflection measurements. The method resolves the phase retrieval problem in the THz-TDRS

Erik M. Vartiainen; Yusuke Ino; Ryo Shimano; Makoto Kuwata-Gonokami; Yuri P. Svirko; Kai-Erik Peiponen

2004-01-01

6

Terahertz Microspectroscopy and Infrared Reflection-Absorption Spectroscopy Apparatuses at UVSOR-II  

SciTech Connect

We have recently constructed two specialized end stations, one is the terahertz microspectroscopy (THz-MS) and the other the infrared reflection-absorption spectroscopy (SR-IRAS). Both instruments have been tested using synchrotron radiation in the infrared and terahertz regions at UVSOR-II. The THz-MS station covers the wavenumber region of 15,000 -40 cm-1 with the spatial resolution as same as the wavelength. This apparatus is a powerful tool for the electrodynamics on strongly correlated materials at low temperatures and under high pressures and also for the molecular vibration imaging of living cells. On the other hand, the SR-IRAS station covers the IR range down to 300 cm-1 with a high accuracy. The change of Al-N stretching and pyramidalization modes at 423 and 460 cm-1, respectively, due to potassium doping in Alq3 molecules on an Ag surface was observed.

Kimura, Shin-ichi; Sakurai, Yoko; Nakamura, Eiken [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Mizuno, Takafumi [School of Physical Sciences, Graduate University for Advanced Studies, Okazaki 444-8585 (Japan)

2007-01-19

7

Evaluation of drug crystallinity in aqueous suspension using terahertz time-domain attenuated total reflection spectroscopy.  

PubMed

Terahertz pulsed spectroscopy has recently been demonstrated to be a novel technique for the investigation of the solid-state properties of pharmaceutical materials. In this study, we directly measured the crystallinity of a drug suspended in water, using a terahertz pulsed attenuated total reflection (ATR) method. The dihydropyridine calcium channel blocker nifedipine is classified as a poorly soluble drug; its most stable crystalline form is known as form I. Transmission spectra, collected from 0.2 to 2.0 THz (6.6 to 66 cm(-1) ), of nifedipine crystals had a strong absorption peak at 1.2 THz (40 cm(-1) ) at room temperature. When the nifedipine crystals were mixed with poloxamer 188 and suspended in water, the resulting spectra measured using the ATR method had a peak at the same frequency as in the spectra obtained in transmission mode. Furthermore, the peak area was proportional to the amount of crystals. The upward sloping baseline in the spectra, corresponding to water absorption, decreased stepwise with increasing amounts of crystalline particles. We confirmed that the spectra gave excellent quantitative results, using partial least-squares regression analysis. The results suggest the possibility of using this method for qualitative and quantitative assessments of crystalline drugs in suspension. PMID:24037861

Takebe, Gen; Kawada, Yoichi; Akiyama, Koichiro; Takahashi, Hironori; Takamoto, Hisayoshi; Hiramatsu, Mitsuo

2013-11-01

8

Design and performance of reflective ultra-broadband terahertz time-domain spectroscopy with air-biased-coherent-detection  

Microsoft Academic Search

In general, a reflective spectrometer is more suitable for the spectroscopic measurement for highly absorptive samples. We report the design and evaluation of a reflective terahertz time-domain spectroscopy (R-THz-TDS), using air as THz wave emitter and sensor, together with air-biased-coherent-detection (ABCD) method. With an 85 fs pulse amplified laser, we demonstrate a usable bandwidth from 0.5 THz to 12 THz,

I.-Chen Ho; Xiaoyu Guo; X.-C. Zhang

2010-01-01

9

Analysis of intermolecular interaction of poly(N-isopropylacrylamide) solution with attenuated total reflectance terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The terahertz attenuated total reflectance spectra of Poly(N-isopropylacrylamide) (P-NIPAAm) solutions were measured in the range of 26.5-47.3 °C. The phase-change in P-NIPAAm was observed via the temperature dependence of the spectra. The collapse of hydrogen bonds in solution was confirmed by the decrease in the signal intensities around 62 cm-1, which corresponds to fast dielectric relaxation by rotation and collision of molecules, and around 166 cm-1, which corresponds to the stretching mode of the intermolecular vibration of water molecules.

Naito, H.; Ogawa, Y.; Hoshina, H.; Sultana, S.; Kondo, N.

2012-05-01

10

Terahertz time-domain spectroscopy of biological tissues  

SciTech Connect

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)

Nazarov, M M; Shkurinov, A P; Kuleshov, E A [M. V. Lomonosov Moscow State University, Faculty of Physics, Moscow (Russian Federation); Tuchin, V V [N. G. Chernyshevskii Saratov State University, Saratov (Russian Federation)

2008-07-31

11

Analytical terahertz spectroscopy.  

PubMed

Recent progress in analytical terahertz (THz) spectroscopy is reviewed with illustrative examples showing that it is an effective method for detecting and identifying intermolecular interactions in chemical compounds, such as hydrogen bonds. The unique and characteristic properties of THz waves, their significance to both science and industry, and the bases of one of the successful fields of analytical THz spectroscopy, namely THz time-domain spectroscopy and THz imaging for chemical analysis, are described. Preliminary quantitative studies are presented to show the potential of THz spectroscopy for the detection and identification of intermolecular hydrogen bonds in unknown mixture samples. The selective detection of intramolecular hydrogen bonds and the detection of intramolecular interactions in ice are also introduced. Some brief remarks are provided on future developments, the main issues, and the prospects for analytical THz spectroscopy. PMID:18270407

Ueno, Yuko; Ajito, Katsuhiro

2008-02-01

12

Realization of metal-insulator transition and oxidation in silver nanowire percolating networks by terahertz reflection spectroscopy.  

PubMed

Metal nanowires (NWs) enable versatile applications in printed electronics and optoelectronics by serving as thin and flexible transparent electrodes. The performance of metal NWs as thin electrodes is highly correlated to the connectivity of NW meshes. The percolation threshold of metal NW films corresponds to the minimum density of NWs to form the transparent, yet conductive metal NW networks. Here, we determine the percolation threshold of silver NW (AgNW) networks by using morphological analysis and terahertz (THz) reflection spectroscopy. From the divergent behavior of carrier scattering time and the increase of carrier backscattering factor, the critical NW density at which crossover from Drude to non-Drude behavior of THz conductivity occurs can be unambiguously determined for AgNW thin films. Furthermore, the natural oxidation of AgNWs which causes the gradual reduction of the connectivity of the AgNW network is also realized by the THz spectroscopy. The selective oxidation of NW-to-NW junctions weakens the ohmic contact, and for AgNWs near a critical density, it can even lead to metal-insulator transition. The presented results offer invaluable information to accelerate the deployment of metal nanowires for next-generation electronics and optoelectronics on flexible substrates. PMID:24299073

Tsai, Yao-Jiun; Chang, Chi-Ying; Lai, Yi-Chun; Yu, Pei-Chen; Ahn, Hyeyoung

2014-01-01

13

Terahertz multistatic reflection imaging.  

PubMed

We describe a new imaging method using single-cycle pulses of terahertz (THz) radiation. This technique emulates the data collection and image processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a migration procedure to solve the inverse problem; this permits us to reconstruct the location, the shape, and the refractive index of targets. We show examples for both metallic and dielectric model targets, and we perform velocity analysis on dielectric targets to estimate the refractive indices of imaged components. These results broaden the capabilities of THz imaging systems and also demonstrate the viability of the THz system as a test bed for the exploration of new seismic processing methods. PMID:12095212

Dorney, Timothy D; Symes, William W; Baraniuk, Richard G; Mittleman, Daniel M

2002-07-01

14

Attenuated internal reflection terahertz imaging.  

PubMed

We present a terahertz (THz) imaging technique based on attenuated internal reflection, which is ideally suited for the analysis of liquid and biological samples. Inserted in a THz time-domain system, and using a high-resistivity low loss silicon prism to couple the THz wave into the sample, the detection scheme is based on the relative differential spectral phase of two orthogonal polarizations. Biological sample imaging as well as subwavelength (?/16) longitudinal resolution are demonstrated. PMID:23454932

Wojdyla, Antoine; Gallot, Guilhem

2013-01-15

15

Terahertz reflection imaging for package and personnel inspection  

NASA Astrophysics Data System (ADS)

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Because terahertz imaging employs safe non-ionizing radiation that penetrates clothing, people may be routinely scanned as well as packages. Time domain terahertz imaging can be employed in reflection mode to image beneath clothing with sub millimeter resolution. Fiber optic coupled terahertz transmitter and generator arrays can be constructed to more quickly objects such as shoes, or larger portions of the body. The application of commercially available time domain terahertz spectroscopy equipment to imaging through clothing on simulant personnel is shown to distinguish harmful from innocuous objects.

Zimdars, David; White, Jeffrey S.

2004-09-01

16

Phase-sensitive terahertz spectroscopy with backward-wave oscillators in reflection mode.  

PubMed

In this article we describe a method which allows accurate measurements of the complex reflection coefficient r = absolute value(r) x exp(i phi(R)) of a solid at frequencies of 1-50 cm(-1) (30 GHz-1.5 THz). Backward-wave oscillators are used as sources for monochromatic coherent radiation tunable in frequency. The amplitude of the complex reflection (the reflectivity) is measured in a standard way, while the phase shift, introduced by the reflection from the sample surface, is measured using a Michelson interferometer. This method is particular useful for nontransparent samples, where phase-sensitive transmission measurements are not possible. The method requires no Kramers-Kronig transformation in order to extract the sample's electrodynamic properties (such as the complex dielectric function or complex conductivity). Another area of application of this method is the study of magnetic materials with complex dynamic permeabilities different from unity at the measurement frequencies (for example, colossal-magnetoresistance materials and metamaterials). Measuring both the phase-sensitive transmission and the phase-sensitive reflection allows for a straightforward model-independent determination of the dielectric permittivity and magnetic permeability of such materials. PMID:20059151

Pronin, A V; Goncharov, Yu G; Fischer, T; Wosnitza, J

2009-12-01

17

Probing biological systems with terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy is able to probe several aspects of biological systems. Most well known is its sensitivity to water due to the strong water absorptions at terahertz frequencies. However an increasing number of studies have shown that it is not just water content that terahertz is sensitive to and that other factors such as tissue structure, molecular arrangement or even temperature can also affect the signal. Examples ranging from breast cancer spectroscopy to antibody protein spectroscopy will be presented and discussed.

Pickwell-MacPherson, Emma; Sun, Yiwen; Parrott, Edward P. J.

2012-10-01

18

Modulated orientation sensitive terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The energies of protein correlated motions lie in the far infrared or THz frequency range (lambda = 1 cm -- 50 mm, f = 0.03 -- 6 THz). The existence of correlated motions has been confirmed by neutron and inelastic x-ray scattering measurements. These techniques require large sample volumes and specialized facilities, limiting their application to systematic studies of changes in correlated motions with functional state and allosteric interactions. Standard terahertz time domain spectroscopy measurements have shown sensitivity to protein-ligand binding, oxidation state, conformation, temperature and hydration. However, the response is broad, in part from the large vibrational density of states and in part from the dielectric response contribution from surface water and side-chains. As an overall strategy to measure the correlated structural motions in protein, we use anisotropic and birefringent behavior of molecular crystals to develop a new technique called MOSTS (Modulated Orientation Sensitive Terahertz Spectroscopy). We achieve high sensitivity and mode separation, by using single molecular crystal such as sucrose and oxalic acid, and rapid modulation of the relative alignment of the terahertz polarization and the crystal axes by rotating the sample. By locking into the signal at the rotation frequency, we determine the polarization sensitive signal and map out the optically active vibrational resonances. To illustrate the technique, we compare our measured spectra with the calculated, and find a close agreement. We measure dielectric properties of oxalic acid, sucrose and protein crystals and polycarbonate sheet using standard terahertz time domain spectroscopy. We determine the absorbances in oxalic acid and sucrose crystals, using MOSTS technique. We compare the resonances in these two distinct methods. Then, we develop a protein model sample by sticking together two thin plates of sucrose and polycarbonate. We carry out standard THz-TDS and MOSTS measurements on the protein model sample. We show that we are able to isolate the vibrational modes from glassy background in protein model sample by using MOSTS.

Singh, Rohit

19

Terahertz spectroscopy of liver cirrhosis: investigating the origin of contrast  

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

20

Toward practical terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy is a promising technology for the identification of explosive and pharmaceutical substances in adverse conditions. It interacts strongly with intermolecular vibrational and rotational modes. Terahertz also passes through many common dielectric covering materials, allowing for the identification of substances in envelopes, wrapped in opaque plastic, or otherwise hidden. However, there are several challenges preventing the adoption of terahertz spectroscopy outside the laboratory. This dissertation examines the problems preventing widespread adoption of terahertz technology and attempts to resolve them. In order to use terahertz spectroscopy to identify substances, a spectrum measured of the target sample must be compared to the spectra of various known standard samples. This dissertation examines various methods that can be employed throughout the entire process of acquiring and transforming terahertz waveforms to improve the accuracy of these comparisons. The concepts developed in this dissertation directly apply to terahertz spectroscopy, but also carry implications for other spectroscopy methods, from Raman to mass spectrometry. For example, these techniques could help to lower the rate of false positives at airport security checkpoints. This dissertation also examines the implementation of several of these methods as a way to realize a fully self-contained, handheld, battery-operated terahertz spectrometer. This device also employs techniques to allow minimally-trained operators use terahertz to detect different substances of interest. It functions as a proof-of-concept of the true benefits of the improvements that have been developed in this dissertation.

Brigada, David J.

21

Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures  

SciTech Connect

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.

Azad, Abul K [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Han, Jiaguang [OSU; Lu, Xinchao [OSU; Zhang, Weili [OSU

2009-01-01

22

Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy  

Microsoft Academic Search

Terahertz (THz) time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Material properties of glass fiber composite were measured using both transmission and reflection configuration. The interaction of THz with a glass fiber composite was then analyzed, including the effects of scattering, absorption, and the index of refraction, as well as effective medium approximations. THz

Christopher D. Stoik

2008-01-01

23

Effect of surface scattering on terahertz time domain spectroscopy of chemicals  

NASA Astrophysics Data System (ADS)

The existence of unique absorption spectrum patterns for many chemicals at terahertz frequencies has opened an exciting avenue in non-contact safe detection of such materials by terahertz spectroscopy. However, scattering of THz waves, which have wavelengths on the order of material grain sizes, by surface roughness challenges the sensitivity of this detection scheme in practice. In this work, we present terahertz time domain spectroscopy results for materials with rough surfaces. Both reflection from and transmission through lactose, which has sharp absorption peaks in the terahertz regime, are studied and the effect of increasing scattering through controlled surface roughness is investigated. Such electromagnetic scattering can alter the terahertz absorption spectrum and thus obscure the detection of chemicals. Furthermore we examine electro-optic detection of terahertz signals reflected from randomly rough targets with a theoretical electromagnetic system perspective and provide a method to retrieve coherent reflection responses from rough surface targets.

Arbab, M. Hassan; Chen, Antao; Thorsos, Eric I.; Winebrenner, Dale P.; Zurk, Lisa M.

2008-02-01

24

Investigation of inflammable liquids by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

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 60 cm-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.

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

2005-07-01

25

Terahertz time-domain spectroscopy and application on peanut oils  

Microsoft Academic Search

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

Jiusheng Li; Jianquan Yao; Jianrui Li

2008-01-01

26

Terahertz spectroscopy techniques for explosives detection  

Microsoft Academic Search

Spectroscopy in the terahertz frequency range has demonstrated unique identification of both pure and military-grade explosives.\\u000a There is significant potential for wide applications of the technology for nondestructive and nonintrusive detection of explosives\\u000a and related devices. Terahertz radiation can penetrate most dielectrics, such as clothing materials, plastics, and cardboard.\\u000a This allows both screening of personnel and through-container screening. We review

Megan R. Leahy-Hoppa; Michael J. Fitch; Robert Osiander

2009-01-01

27

Measurement precision analysis for terahertz absorption spectrum of explosive materials by using terahertz transmissione spectroscopy  

NASA Astrophysics Data System (ADS)

The terahertz absorption spectrum of explosive materials can be measured by terahertz time domain spectroscopy operated in transmission mode. In this paper, the absorption characteristics of four explosive materials in spectral range of 0.1-3 THz are studied. It shows that even for the same materials, the spectral absorption peak value in the same measurement condition is a little different. So the measurement precision of the terahertz time domain spectroscopy is very important for the feature extraction and identification of explosive materials. This work investigates the measurement precision of terahertz time domain spectroscopy. Some factors that affect the measurement precision of the terahertz time domain spectroscopy are analyzed and discussed.

Yang, Zhe; Yin, Qingyan; Li, Hongguang

2013-08-01

28

Terahertz Spectroscopy of Excited Water  

NASA Astrophysics Data System (ADS)

The observation and characterization of water spectra have been intensely pursued in the astrophysical community. Its rotational transitions in the ground, (010) (v_2 = 1), (020), (100), and (001) states are primary targets of the ongoing Herschel mission. In this study, laboratory terahertz spectroscopy of water was carried out at JPL and Cologne, with the goals to measure all transitions HIFI might see and critically review and fit the lowest 5 vibrational states. DC discharge, radio frequency discharge and heating tapes were used to generate highly excited water. A total of 145 pure rotational transitions in the (000), (010), (020), (100), and (001) states of water were observed in the 293-1969 GHz region. Of these, 86 have been detected for the first time with MW accuracy. So far, the 1(1,0)-1(0,1) transition was observed for all five states; the 2(1,2)-1(0,1) transition was observed for (000), (100), and (001) but is missing for (010) (1753914 GHz) and (020) (1872972 GHz); the 1(1,1)-0(0,0) transition was observed for all states but (020) (1332967 GHz). The analysis is still in progress, and we will present the most recent fitting results to date. There are difficulties in fitting water spectra, such as the strong centrifugal distortion, which gives a non-convergent Watson Hamiltonian. In addition, the first triad states (100, 020, and 001) are strongly coupled. The latest attempt at a global fit of these 5 states using Euler series achieved a reduced RMS of 8.4 (Pickett et al. 2005, J. Mol. Spectrosc. 233, 174).

Yu, Shanshan; Pearson, John C.; Drouin, Brian J.; Walters, Adam; Müller, Holger S. P.; Brünken, Sandra

2010-06-01

29

Terahertz Spectroscopy of Large-Area Graphene  

Microsoft Academic Search

Graphene is predicted to possess exotic nonlinear electromagnetic properties, which may lead to novel terahertz (THz) applications. THz dynamic conductivity measurements allow us to probe the dynamics of such 2D quantum relativistic Dirac fermions (DF). Here, we used THz time-domain spectroscopy (TDS) to measure large-area graphene grown by chemical vapor deposition. Raman spectroscopy, as well as optical absorption spectroscopy from

L. Ren; T. Arikawa; B. F. Cruz; M. Z. Jin; J. Kono; Z. Jin; J. M. Tour; A. K. Wojcik; A. A. Belyanin; Y. Takemoto; K. Takeya; I. Kawayama; M. Tonouchi

2010-01-01

30

Pre- and post-processing for tomographic reconstruction of terahertz time-domain spectroscopy.  

PubMed

Reflection-type terahertz tomography is obtained using time-domain spectroscopy. Due to different velocities of the terahertz ray in free space and inside a sample, the tomographic transverse plane is not obtained by a simple reconstruction using time index. A pre-processing method is proposed to compensate for the different velocities of the terahertz ray for tomographic reconstruction. Maximum intensity projection, averaging, and short-time Fourier transform are proposed as post-processing methods along the depth direction for the terahertz tomography. Log-scale display is also suggested for a better visualization. Some experimental results with the pre- and post-processing are demonstrated. PMID:24105540

Hong, Hye-Jin; Park, Jinho; Park, Hochong; Son, Joo-Hiuk; Ahn, Chang-Beom

2013-08-26

31

Liquid-sheet jets for terahertz spectroscopy.  

PubMed

We investigated liquid-sheet jets with controllable thickness for application to terahertz (THz) spectroscopy. Slit-type and colliding-jet nozzles were used to generate optically flat liquid jets. The thickness of the liquid sheet was determined precisely by spectral interference and THz time-domain-spectroscopy methods. By adjusting the collision angle of the colliding-jet nozzle, we could control the thickness of the liquid sheet from 50 to 120 ?m. PMID:24977512

Kondoh, Masato; Tsubouchi, Masaaki

2014-06-16

32

Reflection imaging system with terahertz-wave parametric oscillator  

Microsoft Academic Search

We demonstrated the reflection imaging system using a terahertz-wave parametric oscillator (TPO). Reflection images were acquired on a test sample consisting of bands of aluminum film, as well as on pig tissue.

T. Ikari; K. Kawase; H. Minamide; Y. Ishikawa; H. Ito

2003-01-01

33

Terahertz Spectroscopy of Liquids and Biomolecules  

NASA Astrophysics Data System (ADS)

The terahertz regime has particular value for liquid and biomolecular spectroscopy. In the case of liquids, terahertz is sensitive to relaxational and collective motions in liquids [1-13]. Applications include determination of sugar, alcohol, and water content. While there are no narrow band identification features for liquids in the terahertz range, the ability of THz to transmit through packaging materials and high sensitivity of relative water content is considered highly appealing for its use as a method to rapidly verify labeled contents. The determination of the water, sucrose, alcohol, liquid fuel, and petroleum content using terahertz have been demonstrated [1, 10]. The fundamental findings from terahertz measurements of liquids include the hydration number associated with solutes [14, 15], the extent of the perturbation of the liquid structure by the solute [16, 17], and the role of interactions in binary liquids [13, 18] . New collective mode vibrations have been identified for alcohols [19, 20], and the changes in the relaxational dynamics due to mixing, and the role of collective vibrations in ionic liquids [21-24]. In order to achieve these many findings, sensitive measurement techniques and data analysis have been developed. In parallel, great strides in modeling have been made to effectively model the picosecond dielectric response for these highly complex systems.

George, D. K.; Markelz, A. G.

34

Extending applicability of terahertz spectroscopy for biosensing  

NASA Astrophysics Data System (ADS)

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 Spectroscopy Technique model based on thin film interference to calculate the fine structure of refractive index and absorption coefficient of biological molecules (DNA, proteins) in the THz gap. As to spectroscopy in the low THz range (3-10 cm-1), a noise source was used in free space configuration in the FT-IR set-up to obtain transmission and reflection data of biological molecules that act as fingerprints.

Parthasarathy, Ramakrishnan

35

High frequency resolution terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Sangala, Bagvanth Reddy

36

A promising diagnostic method: Terahertz pulsed imaging and spectroscopy  

PubMed Central

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.

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

2011-01-01

37

[Frequency correction in terahertz absorption spectroscopy].  

PubMed

Measurement errors in frequency domain always appear when testing samples' terahertz (THz) absorption spectrum using terahertz time-domain spectroscopy (THz-TDS) system, which is supposed to be attributed to the sampling accuracy of the high speed electro-optic sampling system In order to make the measurement have a high accuracy, the method of error correction was studied in the present article. Carbon monoxide in gas phase was employed as our standard sample, and its absorption spectrum at the pressure of 2.0 x 10(5) Pa was measured experimentally. Comparing the obtained absorption frequencies with the corresponding standard data in JPL database, we got the error values, and their distribution law shows that the values have a linear correlation with the standard absorption frequency. Based on this, the error correction model was built. Using the model to correct the experimental data, the result shows the maximum error after correction is reduced to 3.36 GHz, which is two orders of magnitude lower than the error before correction. This states that the model can be used to correct the error of the THz spectrum caused by high speed electro-optic sampling system. At last, the authors draw a conclusion that the THz-TDS system is supposed to be corrected by the terahertz spectrum of carbon monoxide before measurement, in this way, the terahertz spectrum of sample can have a high accuracy. The study contributes to the material identification and the construction of molecular spectroscopy database in THz region. PMID:24369628

Wu, Bin; Shi, Xue-shun; Sun, Qing; Deng, Yu-qiang; Wang, Heng-fei; Chen, Kun-feng

2013-09-01

38

Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy  

Microsoft Academic Search

Terahertz time domain spectroscopy was used for nondestructive evaluation of aircraft glass fiber composites stressed with bending and heating damage. Refractive index and absorption coefficients were measured for both damaged and undamaged composites. The two dimensional extent of the heat damage could be shown with either a simple phase or amplitude terahertz imaging technique.

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

2008-01-01

39

Sensing of phase transition in medium with terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

Phase state identification and phase transition registration in condensed matter are significant applications of terahertz spectroscopy. A set of fundamental and applied problems are associated with the phase state problem. Our report is devoted to the experimental analysis of the spectral characteristics of water and water solution during the phase transition from the solid state to the liquid state via the method of terahertz pulsed spectroscopy. In this work transformation of the sample spectral characteristics during the phase transition were observed and discussed. Possible application of terahertz pulsed spectroscopy as an effective instrument for phase transition sensing was considered.

Zaytsev, Kirill I.; Fokina, Irina N.; Fedorov, Aleksey K.; Yurchenko, Stanislav O.

2014-03-01

40

Terahertz wave reflective sensing and imaging  

Microsoft Academic Search

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

Hua Zhong

2006-01-01

41

Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials  

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

42

Influence of noise on the characterization of materials by terahertz time-domain spectroscopy  

Microsoft Academic Search

We analyze the contributions of various error sources to uncertainty in the far-infrared optical constants (re- fractive index and absorption coefficient) measured by terahertz (THz) time-domain spectroscopy. We focus our study on the influence of noise. This noise study is made with a thick slab of transparent material for which the THz transmitted signal exhibits temporal echoes owing to reflections

Lionel Duvillaret; Frédéric Garet; Jean-Louis Coutaz

2000-01-01

43

Tissue characterization using terahertz pulsed imaging in reflection geometry  

NASA Astrophysics Data System (ADS)

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.

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

2009-01-01

44

Papyrus imaging with terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

45

Terahertz reflection response measurement using a phonon polariton wave  

NASA Astrophysics Data System (ADS)

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.

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

2009-03-01

46

Terahertz spectroscopy of ionized air and explosive vapor  

NASA Astrophysics Data System (ADS)

In the past it has been demonstrated that terahertz spectroscopy could identify various chemical agents and explosives in solid and liquid phases. However peaks and dips in the terahertz spectra obtained from solid and liquid phases are not sharp and often ambiguous or ill-defined, as the interferences among the molecules in the solid or liquid obscure the molecule's characteristic resonances. Hence there has been considerable interest in obtaining terahertz spectrum of gas phase. Recently we have increased terahertz output power of our terahertz spectrometer, and measured terahertz spectra of gases, including water vapor, and ionized air produced by various ionization sources as well as explosive vapors. Our experiments revealed: (1) our terahertz spectrum of water vapor was highly consistent with other published data, (2) the spectra of ionized air produced by corona discharge and nuclear isotopes including Am-241, Bi-207, Ba-133, Co-60, Na-22 and Cs-137 were all different, and the characteristic spectrum changes largely depending on the type of ionization source, and (3) terahertz spectra of explosive vapor taken from TNT, PETN and RDX which were dissolved in acetonitrile or water exhibit very sharp resonance peaks and dips. We will present details of our experimental results.

Graber, Benjamin; Tao, Rongjia; Wu, Dong Ho

2011-03-01

47

Terahertz spectroscopy: Its future role in medical diagnoses  

NASA Astrophysics Data System (ADS)

Over the past two decades, terahertz radiation has received a lot of interest due to advances in emission and detection technologies in the late 1980s and early 1990s which allowed the construction of coherent source/detection regimes. This paper focuses on reviewing the use of terahertz radiation in the investigation and understanding of biological systems and medical diagnosis. In particular, research on terahertz spectroscopy of biomolecules, from amino acids to proteins is presented, and examples of potential medical applications are discussed.

Parrott, Edward Philip John; Sun, Yiwen; Pickwell-MacPherson, Emma

2011-12-01

48

Terahertz and infrared spectroscopy of gated large-area graphene.  

PubMed

We have fabricated a centimeter-size single-layer graphene device with a gate electrode, which can modulate the transmission of terahertz and infrared waves. Using time-domain terahertz spectroscopy and Fourier-transform infrared spectroscopy in a wide frequency range (10-10?000 cm(-1)), we measured the dynamic conductivity change induced by electrical gating and thermal annealing. Both methods were able to effectively tune the Fermi energy, E(F), which in turn modified the Drude-like intraband absorption in the terahertz as well as the "2E(F) onset" for interband absorption in the mid-infrared. These results not only provide fundamental insight into the electromagnetic response of Dirac fermions in graphene but also demonstrate the key functionalities of large-area graphene devices that are desired for components in terahertz and infrared optoelectronics. PMID:22663563

Ren, Lei; Zhang, Qi; Yao, Jun; Sun, Zhengzong; Kaneko, Ryosuke; Yan, Zheng; Nanot, Sébastien; Jin, Zhong; Kawayama, Iwao; Tonouchi, Masayoshi; Tour, James M; Kono, Junichiro

2012-07-11

49

Ultrabroadband terahertz spectroscopies of biomolecules and water  

NASA Astrophysics Data System (ADS)

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).

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

2013-03-01

50

Synchrotron Terahertz Spectroscopy of Solids under Extreme Conditions  

SciTech Connect

We report on the end station for terahertz spectroscopy at high pressures and low temperatures at the UVSOR Facility of the Institute for Molecular Science, and present one set of experimental results for the pressure-dependent valence transition of samarium sulfide (SmS) at the temperatures of 6 and 300 K. The end station covers the photon energy range of 5 meV to 1.2 eV with pressures of up to 6 GPa and temperatures down to 3.7 K. Using the end station, the valence transition, namely, the black-golden phase transition, of SmS was clearly observed at 0.65 GPa. From Drude and Lorentz fitting of the pressure-dependent reflectivity spectra, the carrier density at the critical pressure was found to be about 10{sup -2}/SmS at both 6 and 300 K. The carrier density appear to play an important role in the valence transition.

Kimura, Shin-ichi [UVSOR Facility, Institute for Molecular Science (BUNSHIKEN), Okazaki 444-8585 (Japan); School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585 (Japan); Mizuno, Takafumi; Iizuka, Takuya [School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585 (Japan)

2010-02-03

51

Terahertz time-domain spectroscopy of gases, liquids, and solids.  

PubMed

The techniques and methods employed in the spectroscopic characterization of gases, liquids, and solids in the terahertz frequency range are reviewed. Terahertz time-domain spectroscopy is applied to address a broadband frequency range between 100 GHz and 5 THz with a sub-10 GHz frequency resolution. The unique spectral absorption features measured can be efficiently used in material identification and sensing. Possibilities and limitations of fundamental and industrial applications are discussed. PMID:21735510

Theuer, Michael; Harsha, Srikantaiah Sree; Molter, Daniel; Torosyan, Garik; Beigang, René

2011-10-24

52

Terahertz vibrational absorption spectroscopy using microstrip-line waveguides  

NASA Astrophysics Data System (ADS)

We demonstrate that terahertz microstrip-line waveguides can be used to measure absorption spectra of polycrystalline materials with a high frequency resolution (~2 GHz) and with a spatial resolution that is determined by the microstrip-line dimensions, rather than the free-space wavelength. The evanescent terahertz-bandwidth electric field extending above the microstrip line interacts with, and is modified by, overlaid dielectric samples, thus enabling the characteristic vibrational absorption resonances in the sample to be probed. As an example, the terahertz absorption spectrum of polycrystalline lactose monohydrate was investigated; the lowest lying mode was observed at 534(+/-2) GHz, in excellent agreement with free-space measurements. This microstrip technique offers both a higher spatial and frequency resolution than free-space terahertz time-domain spectroscopy and requires no contact between the waveguide and sample.

Byrne, M. B.; Cunningham, J.; Tych, K.; Burnett, A. D.; Stringer, M. R.; Wood, C. D.; Dazhang, L.; Lachab, M.; Linfield, E. H.; Davies, A. G.

2008-11-01

53

Measurement and modeling of rough surface effects on terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

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 ?-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.

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

2010-02-01

54

Terahertz spectroscopy and imaging for material analysis in conservation science  

Microsoft Academic Search

Terahertz (THz) waves can penetrate opaque materials and fingerprint spectra appear as those in infrared bands. The technique is expected to be used as a new non-invasive analysis method for various materials. Time domain reflection imaging, in particular, uses THz pulses that propagate in specimens, and in this technique, pulses reflected from the internal boundaries of the specimen indicate the

Kaori Fukunaga; Iwao Hosako; Marcello Picollo

2010-01-01

55

Niobium direct detectors for fast and sensitive terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We report the performance of a niobium hot-electron bolometer designed for laboratory terahertz spectroscopy. The antenna-coupled detector can operate above 4.2 K and has fast (subnanosecond) response. Detailed microwave measurements of performance over a wide range of operating conditions were correlated with quantitative terahertz measurements. The maximum responsivity is 4×104 V/W with a noise equivalent power at the detector of 2×10-14 W/Hz1/2, approaching the intrinsic thermal fluctuation limit for the device. This detector enables a variety of novel laboratory spectroscopy measurements.

Reese, M. O.; Santavicca, D. F.; Prober, D. E.; True, A. B.; Schmuttenmaer, C. A.

2007-08-01

56

Niobium direct detectors for fast and sensitive terahertz spectroscopy.  

PubMed

We report the performance of a niobium hot-electron bolometer designed for laboratory terahertz spectroscopy. The antenna-coupled detector can operate above 4.2 K and has fast (subnanosecond) response. Detailed microwave measurements of performance over a wide range of operating conditions were correlated with quantitative terahertz measurements. The maximum responsivity is 4 x 10(4) VW with a noise equivalent power at the detector of 2 x 10(-14) W/Hz(12), approaching the intrinsic thermal fluctuation limit for the device. This detector enables a variety of novel laboratory spectroscopy measurements. PMID:17764371

Reese, M O; Santavicca, D F; Prober, D E; True, A B; Schmuttenmaer, C A

2007-08-01

57

Terahertz Spectroscopy of Water Vapors, Chemical Vapors and Ionized Air  

NASA Astrophysics Data System (ADS)

In the past, a few research groups have demonstrated that terahertz spectroscopy could be a useful tool for the identification of chemicals. However most of those demonstrations have been done with solid-phase or liquid-phase chemicals. There are little demonstrations for the detection and identification of chemicals in the gas-phase, as it is very difficult in part due to the presence of water-absorption lines in the terahertz frequency range. As the water absorption lines predominate in the 0.1 - 2THz spectral range, and can interfere with already weak terahertz signatures generated by chemical vapors, it is often very hard to obtain meaningful terahertz spectrum of chemical vapor. Regardless we recently have been able to obtain some terahertz spectra of chemical vapors and ionized air produced by several different ionization sources, including corona discharge and nuclear isotopes. Throughout data analysis we learned that water molecules, nitrogen and oxygen molecules play very important roles in these terahertz spectra. In this presentation we will discuss our experiments and the roles of these molecules.

Graber, Benjamin; Tao, Rongjia; Wu, Dong Ho

2013-03-01

58

Achromatic terahertz quarter-wave retarder in reflection mode  

NASA Astrophysics Data System (ADS)

A compact achromatic quarter-wave retarder (QWR) operating in reflection mode is designed for using in terahertz region. It is a composite device utilizing form birefringence and Fabry-Pérot (FP) interference. Under illumination of plane waves with incidence angle of 45°, from 1.8 THz to 2.8 THz, the QWR achieved only ±2° variation around 90° phase retardation, enlarging the working bandwidth of ordinary QWR greatly. An analytical model combining transmission-line (TL) theory with effective medium theory (EMT) is presented and results agree well with the time-consuming numerical calculation. The 38 ?m thick construction is simple and easy for fabrication by the existing lithographic technique and a promising application in terahertz or other frequency region is believed.

Sun, L.; Lü, Z.; Zhang, D.; Zhao, Z.; Yuan, J.

2012-02-01

59

Nondestructive Evaluation of Rubber Compounds by Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

Rubber compounds were investigated by terahertz time-domain spectroscopy. Terahertz absorption spectra of crude rubbers and additives were measured as well as those of acrylonitrile-butadiene rubber compounds, which included the additives. It was found that carbon black, which is one of the additives and serves as a filler, dominates the terahertz absorption owing to its metallic characteristics. Thus, terahertz spectroscopy is a useful method for rapid nondestructive inspection during the rubber production.

Hirakawa, Yasuyuki; Ohno, Yoshitomo; Gondoh, Toyohiko; Mori, Tetsuo; Takeya, Kei; Tonouchi, Masayoshi; Ohtake, Hideyuki; Hirosumi, Tomoya

2011-12-01

60

Silicon wafer thickness measurement using terahertz time domain spectroscopy main  

NASA Astrophysics Data System (ADS)

When measuring optical material parameters with terahertz spectroscopy the accuracy of the material parameters measured depends strongly on knowing and supplying the precise sample thickness when processing the raw terahertz data. It turns out that the terahertz data itself typically does contain accurate information as to the sample thickness. In this study we determine the accuracy with which the exact thickness of nominally 500 ?m silicon wafers can be measured using terahertz time domain spectroscopy (THz-TDS). We analyze and compare the resolution of 5 different approaches for determining sample thickness using THz-TDS data including three methods previously proposed in the literature, one novel approach and a refined implementation of an existing approach. The quantitative results and analyses of methods we present will be useful in developing far-infrared optical metrology. Conversely the quantitative results presented in this study can be used to relate uncertainty in sample thickness to uncertainty in the measured terahertz data both in the time domain and frequency domain (phase and amplitude).

Jen, Chih-Yu; Richter, Christiaan

2014-03-01

61

The intermolecular stretching vibration mode in water isotopes investigated with broadband terahertz time-domain spectroscopy  

Microsoft Academic Search

We determined the complex dielectric constants of the liquid water isotopes, H2O, D2O, and H218O at 296K from 0.2 to 7THz by terahertz time-domain attenuated total reflection spectroscopy. We extracted the dispersion of the complex susceptibility of the intermolecular stretching vibration mode around 5THz. The isotope effect on the vibration mode is clarified in its amplitude, frequency, and damping constant.

Hiroyuki Yada; Masaya Nagai; Koichiro Tanaka

2009-01-01

62

Terahertz frequency Hall measurement by magneto-optical Kerr spectroscopy in InAs  

Microsoft Academic Search

We report on the time-domain terahertz (THz) magneto-optical Kerr spectroscopy in the frequency range from 0.5 to 2.5 THz. The developed technique employs reflection geometry, enabling high-frequency noncontact Hall measurements in opaque samples. We also present a method to reveal the off-diagonal component of the complex dielectric tensor from the measured polarization-dependent THz wave forms. At a static magnetic field

R. Shimano; Y. Ino; Yu. P. Svirko; M. Kuwata-Gonokami

2002-01-01

63

Conformational changes of photoactive yellow protein monitored by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Observing the structural dynamics of proteins under conditions as close as possible to those in a living organism is essential for understanding the biological functions of proteins accurately. Here we demonstrate that terahertz spectroscopy is a convenient probe of conformational changes in proteins suspended in physiological buffer solution. We have observed that the partial unfolding of photoactive yellow protein leads to a clear increase in absorption at terahertz frequencies. Using normal mode and molecular dynamics simulations we show that this increase in absorption is related to an increase in the density of delocalised vibrational modes in the more flexible partially unfolded state.

Castro-Camus, E.; Johnston, M. B.

2008-04-01

64

Uncertainty in terahertz time-domain spectroscopy measurement  

SciTech Connect

Measurements of optical constants at terahertz--or T-ray--frequencies have been performed extensively using terahertz time-domain spectroscopy (THz-TDS). Spectrometers, together with physical models explaining the interaction between a sample and T-ray radiation, are progressively being developed. Nevertheless, measurement errors in the optical constants, so far, have not been systematically analyzed. This situation calls for a comprehensive analysis of measurement uncertainty in THz-TDS systems. The sources of error existing in a terahertz spectrometer and throughout the parameter estimation process are identified. The analysis herein quantifies the impact of each source on the output optical constants. The resulting analytical model is evaluated against experimental THz-TDS data.

Withayachumnankul, Withawat [School of Electrical and Electronic Engineering, University of Adelaide, Adelaide, South Australia 5005 (Australia); Department of Information Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520 (Thailand); Fischer, Bernd M.; Lin Hungyen; Abbott, Derek [School of Electrical and Electronic Engineering, University of Adelaide, Adelaide, South Australia 5005 (Australia)

2008-06-15

65

Terahertz imaging and spectroscopy based on hot electron bolometer (HEB) heterodyne detection  

Microsoft Academic Search

Imaging and spectroscopy at terahertz frequencies have great potential for healthcare, plasma diagnostics, and homeland security applications. Terahertz frequencies correspond to energy level transitions of important molecules in biology and astrophysics. Terahertz radiation (T-rays) can penetrate clothing and, to some extent, can also penetrate biological materials. Because of their shorter wavelengths, they offer higher spatial resolution than do microwaves or

Eyal Gerecht; Lixing You

2008-01-01

66

Papyrus imaging with terahertz time domain spectroscopy  

Microsoft Academic Search

Terahertz time domain spectroscopic imaging (THz-TDSI) is a non-ionizing, non-contact and non-destructive measurement technique\\u000a that has been recently utilized to study cultural heritage artifacts. We will present this technique and the results of non-contact\\u000a measurements of papyrus texts, including images of hidden papyri. Inks for modern papyrus specimens were prepared using the\\u000a historical binder, Arabic gum, and two common pigments

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

2010-01-01

67

Terahertz time-domain spectroscopy of organic semiconductors  

NASA Astrophysics Data System (ADS)

In this paper, we conduct transmission and reflection mode terahertz time-domain spectroscopy (THz-TDS) measurements of organic semiconductors such as ALQ3 and TBADN. THz-TDS is effective for determining the purity of the organic semiconductors based on the refractive index and spectral signatures in THz range. In order to prepare the sample for a custom built sample holder, the powder samples are pressed into pellets of 13 mm diameter and a thickness of 2 mm using a hydraulic press. The organic semiconductor, for example ALQ3 sample, is prepared as a 70% ALQ3 and 30% polyethylene (PE) concentration pellet by mixing ALQ3 and PE. The ALQ3 pellet is measured in a chamber purged with dry nitrogen to avoid the effect of water vapor absorptions in ambient air. The absorption coefficient and index of refraction are measured from the spectra of the reference THz pulse and the THz pulse after transmission through the sample. The THz spectrum is obtained by applying a fast Fourier transform to the THz waveform. Further studies were conducted by reducing the concentration of the organic semiconductor from 70% to 10% ALQ3. We also obtained the spectral signature and absorption coefficient for 50% TBADN 50% PE pellet. The spectral signatures of ALQ3 were found to be at 0.868 THz, 1.271 THz and 1.52 THz, while spectral signature of TBADN was found to be at 1.033 THz.

Hailu, Daniel M.; Aziz, Hany; Safavi-Naeini, Safieddin; Saeedkia, Daryoosh

2013-03-01

68

Far-infrared terahertz time-domain spectroscopy of flames  

Microsoft Academic Search

We present what is to our knowledge the first comprehensive far-infrared absorption measurement of f lames. These measurements, covering the region of 7 -88 wave numbers (0.2 - 2.65 THz) are only now made possible by the technique of terahertz time-domain spectroscopy. We observe a large number of absorption lines — including those of water, CH, and NH 3 —

R. A. Cheville; D. Grischkowsky

69

Terahertz pulsed imaging and spectroscopy of breast tumors  

NASA Astrophysics Data System (ADS)

We have developed a portable terahertz pulsed imaging system (TPI Imaga1000) for use in a clinical environment. The system uses photoconduction to generate and detect terahertz radiation with frequency content from 0.1-4 THz. Here, we report on a study using TPI for imaging breast tumours ex vivo. Several breast samples were imaged and parameters from the time domain impulse functions were used to provide contrast. The size and shape of tumour regions in the terahertz images were compared with the corresponding histology section. Good correlation was found for area and shape of tumour in the THz images compared to that of histology. In addition, we have also performed spectroscopy study comparing the terahertz properties (absorption coefficient and refractive index) of excised normal breast skin and breast tumor. Both the absorption coefficient and refractive index were higher for tissue containing tumor compared to normal. These changes are consistent with higher water content and structural changes, like increased cell and protein density. This study demonstrates the potential of TPI to image both invasive breast carcinomas and ductal carcinoma in situ using THz and encourages further studies.

Wallace, Vincent P.; MacPherson, Emma; Fitzgerald, Anthony J.; Lo, Thomas; Provenzano, Elena; Pinder, Sarah; Purushotham, Anand

2006-11-01

70

Terahertz spectroscopy properties of the selected engine oils  

NASA Astrophysics Data System (ADS)

Engine oil, most of which is extracted from petroleum, consist of complex mixtures of hydrocarbons of molecular weights in the range of 250-1000. Variable amounts of different additives are put into them to inhibit oxidation, improve the viscosity index, decrease the fluidity point and avoid foaming or settling of solid particles among others. Terahertz (THz) spectroscopy contains rich physical, chemical, and structural information of the materials. Most low-frequency vibrational and rotational spectra of many petrochemicals lie in this frequency range. In recent years, much attention has been paid to the THz spectroscopic studies of petroleum products. In this paper, the optical properties and spectroscopy of selected kinds of engine oil consisting of shell HELIX 10W-40, Mobilube GX 80W-90, GEELY ENGINE OIL SG 10W-30, SMA engine oil SG 5W-30, SMA engine oil SG 10W-30, SMA engine oil SG 75W-90 have been studied by the terahertz time-domain spectroscopy (THz-TDS) in the spectral range of 0.6-2.5 THz. Engine oil with different viscosities in the terahertz spectrum has certain regularity. In the THz-TDS, with the increase of viscosity, time delay is greater and with the increase of viscosity, refractive indexes also grow and their rank is extremely regular. The specific kinds of engine oil can be identified according to their different spectral features in the THz range. The THz-TDS technology has potentially significant impact on the engine oil analysis.

Zhu, Shouming; Zhao, Kun; Lu, Tian; Zhao, Songqing; Zhou, Qingli; Shi, Yulei; Zhao, Dongmei; Zhang, Cunlin

2010-11-01

71

Terahertz pulse imaging in reflection geometry of human skin cancer and skin tissue  

NASA Astrophysics Data System (ADS)

We demonstrate the application of terahertz pulse imaging (TPI) in reflection geometry for the study of skin tissue and related cancers both in vitro and in vivo. The sensitivity of terahertz radiation to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the skin and the determination of the lateral spread of skin cancer pre-operatively. By studying the terahertz pulse shape in the time domain we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC). Basal cell carcinoma has shown a positive terahertz contrast, and inflammation and scar tissue a negative terahertz contrast compared to normal tissue. In vivo measurements on the stratum corneum have enabled visualization of the stratum corneum-epidermis interface and the study of skin hydration levels. These results demonstrate the potential of terahertz pulse imaging for the study of skin tissue and its related disorders, both in vitro and in vivo.

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

2002-11-01

72

Terahertz pulse imaging in reflection geometry of human skin cancer and skin tissue  

Microsoft Academic Search

We demonstrate the application of terahertz pulse imaging (TPI) in reflection geometry for the study of skin tissue and related cancers both in vitro and in vivo. The sensitivity of terahertz radiation to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the skin and the determination of the lateral spread of skin cancer pre-operatively.

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

2002-01-01

73

Characteristics of bent terahertz antiresonant reflecting pipe waveguides.  

PubMed

Bending characteristics of the terahertz (THz) pipe waveguides are numerically investigated. Numerical results reveal that the inherent periodic feature of the loss spectrum, resulting from the antiresonant reflection guiding mechanism, is nearly unaffected under bending. However, attenuation constant of the fundamental (HE11) mode becomes polarization dependent for the bent pipe waveguide, and the polarization perpendicular to the bending plane experiences less bending losses. Moreover, unlike the straight case where a larger air-core diameter leads to a smaller attenuation constant, increasing core diameter of the bent pipe waveguide is unable to reduce attenuation constant effectively if the propagation mode is a whispering gallery mode. Finally, behavior of the bent pipe waveguide connected to a straight one is also examined in this work. PMID:24718219

Lai, Chih-Hsien; Chang, Teng; Yeh, Yi-Siang

2014-04-01

74

Terahertz BWO spectroscopy of conductors and superconductors  

SciTech Connect

Methods for direct (without the use of the Kramers-Kronig relations) measuring the dielectric response (dynamic conductivity and permittivity) spectra of dielectrics, conductors, and superconductors in the terahertz frequency range (0.03-1.5 THz) are described. The methods are realised by using BWO (backward-wave oscillator) spectrometers developed at the A.M. Prokhorov General Physics Institute, RAS. Dielectric measurements can be performed at temperatures from 2 to 1000 K in magnetic fields up to 8 T. The dielectric response spectra are investigated for a number of materials with properties determined by electron correlation effects: superconductors, one-dimensional conductors, heavy fermion systems, spin-ladder cuprates, and spin glasses. (special issue devoted to the 25th anniversary of the a.m. prokhorov general physics institute)

Gorshunov, B P; Volkov, A A; Prokhorov, A S; Spektor, I E [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Akimitsu, J [Department of Physics, Aoyama-Gakun University, Tokyo (Japan); Dressel, M [University of Stuttgart, Stuttgart (Germany); Nieuwenhuys, G [Leiden University, Leiden (Netherlands); Tomic, S [Institut za Fiziku, Zagreb (Croatia); Uchida, S [Department of Physics, University of Tokyo, Tokyo (Japan)

2007-10-31

75

Ultrabroadband terahertz spectroscopy of a liquid crystal.  

PubMed

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. PMID:23263058

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

2012-12-17

76

Application of superlattice multipliers for high-resolution terahertz spectroscopy.  

PubMed

Frequency multipliers based on superlattice (SL) devices as nonlinear elements have been developed as radiation sources for a terahertz (THz) laboratory spectrometer. Input frequencies of 100 and 250 GHz from backward wave oscillators have been multiplied up to the 11th harmonic, producing usable frequencies up to 2.7 THz. Even at these high frequencies the output power is sufficient for laboratory spectroscopy. Comparisons to conventional high-resolution microwave spectroscopy methods reveal several superior features of this new device such as very high line frequency accuracies, broadband tunability, high output power levels at odd harmonics of the input frequency up to high orders, and a robust applicability. PMID:17477648

Endres, C P; Lewen, F; Giesen, T F; Schlemmer, S; Paveliev, D G; Koschurinov, Y I; Ustinov, V M; Zhucov, A E

2007-04-01

77

Terahertz probe for spectroscopy of sub-wavelength objects.  

PubMed

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. PMID:22418501

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

2012-03-12

78

Identification and classification of chemicals using terahertz reflective spectroscopic focal-plane imaging system  

NASA Astrophysics Data System (ADS)

We present terahertz (THz) reflective spectroscopic focal-plane imaging of four explosive and bio-chemical materials (2, 4-DNT, Theophylline, RDX and Glutamic Acid) at a standoff imaging distance of 0.4 m. The 2 dimension (2-D) nature of this technique enables a fast acquisition time and is very close to a camera-like operation, compared to the most commonly used point emission-detection and raster scanning configuration. The samples are identified by their absorption peaks extracted from the negative derivative of the reflection coefficient respect to the frequency (-dr/dv) of each pixel. Classification of the samples is achieved by using minimum distance classifier and neural network methods with a rate of accuracy above 80% and a false alarm rate below 8%. This result supports the future application of THz time-domain spectroscopy (TDS) in standoff distance sensing, imaging, and identification.

Zhong, Hua; Redo-Sanchez, Albert; Zhang, X.-C.

2006-10-01

79

Terahertz spectroscopy of carbon nanotubes embedded in a deformable rubber  

NASA Astrophysics Data System (ADS)

The dielectric response and anisotropic properties of natural rubber with embedded multiwall carbon nanotubes (CNTs) are studied in the 0.2-3 THz frequency range using terahertz transmission spectroscopy. Natural rubber acts as an invisible and insulating medium in this frequency range, allowing examination of isolated CNTs. The complex dielectric function is obtained with different CNT loadings by using a superposition formula. In highly loaded composites, we find a significant increase in the imaginary part of the dielectric function, related to a change in conductivity due to percolation. The deformable rubber matrix allows the alignment of CNTs by stretching. We investigated the response of aligned nanotubes to polarized terahertz radiation and it shows the evidence of primary electron transport along the tube axis.

Rungsawang, R.; Geethamma, V. G.; Parrott, E. P. J.; Ritchie, D. A.; Terentjev, E. M.

2008-06-01

80

Terahertz Spectroscopy of Crystalline and Non-Crystalline Solids  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy of crystalline and non-crystalline solids is probably one of the most active research fields within the terahertz community. Many potential applications, amongst which spectral recognition is probably one of the most prominent, have significantly stimulated the development of commercial systems and have spurred an increased technical advancement. However, the topic is very complex and multifaceted. Therefore, it is beyond the scope of this chapter to provide a fully comprehensive review of the works performed in this area. We would rather like to demonstrate, based on some selected examples, the potential the technique holds for various different applications. A particular focus will be given to data analysis and, in particular, how we may account for effects resulting from non-ideal sample preparation.

Parrott, Edward P. J.; Fischer, Bernd M.; Gladden, Lynn F.; Zeitler, J. Axel; Jepsen, Peter U.

81

[Terahertz spectroscopy of DNA nucleobases: cytosine and thymine].  

PubMed

The absorption features of DNA nucleobases cytosine and thymine were measured by terahertz time-domain spectroscopy (THz-TDS) from 0.1 to 3.5 THz. Our experimental results clearly show that these important biomolecules exhibit distinctive absorption features in THz region. To the best of our knowledge, the subtle absorption peak of cytosine at 2.53 THz is reported for the first time. Moreover, geometry optimizations and lattice dynamic calculations on cytosine crystal were also performed with the pseudo-potential plane wave method of density functional theory by taking periodic boundary conditions into account. All measured terahertz absorption features of cytosine were assigned successfully and its absorption spectrum was reproduced according to our calculations. Furthermore, our results show that absorption features of cytosine below 3.5 THz arise from external modes in translation and rotation motions, which are dominated by the intermolecular hydrogen bonds. PMID:24409701

Yan, Hui; Fan, Wen-Hui; Zheng, Zhuan-Ping; Liu, Jia

2013-10-01

82

The detection of amoxicillin medicines by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) is a new spectroscopic technique, which improve a good complement for other spectroscopic techniques and has broad application prospects in the biomedical field. In this paper, a terahertz time-domain spectroscopy system is set up. Using this system, the amoxicillin drugs are detected, and the spectrum are analyzed.

Meng, Kun; Li, Zeren; Liu, Qiao

2011-11-01

83

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

NASA Astrophysics Data System (ADS)

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.

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

84

Broadband terahertz time-domain and Raman spectroscopy of explosives  

NASA Astrophysics Data System (ADS)

Broadband terahertz time-domain spectroscopy (THz-TDS) has been shown to be a valuable technique for the detection and analysis of explosives. In this paper, we present recent work on the use of this technique to analyse two pure explosives, 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and 1,3-dinitrato-2,2-bis(nitratomethyl)propane (PETN) and three plastic explosives (Semtex, SX2 and Metabel). For each explosive, a clear and unique spectral absorption fingerprint is found, which can be attributed to oscillations of the molecular lattice. Temperature dependent terahertz absorption measurements of RDX show that the observed vibrational modes are anharmonic in nature. Terahertz spectra are compared with Raman spectra, and the similarities and differences between the spectra produced by the two techniques are discussed. A molecular mechanics calculation approach is used to calculate vibrational intensities and frequencies, and these results are compared with experimental results at both room temperature and 4 K.

Burnett, A. D.; Fan, W. H.; Upadhya, P. C.; Cunningham, J. E.; Edwards, H. G. M.; Kendrick, J.; Munshi, T.; Hargreaves, M.; Linfield, E. H.; Davies, A. G.

2007-05-01

85

Terahertz imaging and spectroscopy for landmine detection  

NASA Astrophysics Data System (ADS)

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

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

2004-04-01

86

Determination of additive content in polymeric compounds with terahertz time-domain spectroscopy  

Microsoft Academic Search

We present terahertz transmission time-domain spectroscopy measurements on a variety of additive-polymer combinations with differing additive contents. At lower terahertz frequencies, standard polymers are transparent. When processed into compounds, their terahertz properties are distinctively affected by additives in most cases. The materials under investigation are magnesium hydroxide in linear low-density polyethylene, glass-fibres in polyamide, and calcium carbonate, silicon or silicon

S. Wietzke; C. Jansen; F. Rutz; D. M. Mittleman; M. Koch

2007-01-01

87

Coherent source terahertz-subterahertz spectroscopy: instrumentation and physics  

NASA Astrophysics Data System (ADS)

We describe instrumentation and principles of terahertz-subterahertz (THz-subTHz) spectrometers based on continuously frequency tunable coherent radiation sources – backward-wave oscillators (BWOs). The spectrometers cover frequency range from 1 cm?1 (0.03 THz) to 50 cm?1 (1.5 THz) and operate at temperatures from 2 K to 1000 K, also in magnetic fields up to 8 Tesla. We illustrate abilities of the BWO-spectroscopy by presenting some late results on dielectric, conducting, superconducting and magnetic materials.

Gorshunov, Boris P.; Zhukova, Elena S.

2014-03-01

88

Broadband terahertz time-domain and Raman spectroscopy of explosives  

Microsoft Academic Search

Broadband terahertz time-domain spectroscopy (THz-TDS) has been shown to be a valuable technique for the detection and analysis of explosives. In this paper, we present recent work on the use of this technique to analyse two pure explosives, 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and 1,3-dinitrato-2,2-bis(nitratomethyl)propane (PETN) and three plastic explosives (Semtex, SX2 and Metabel). For each explosive, a clear and unique spectral absorption

A. D. Burnett; W. H. Fan; P. C. Upadhya; J. E. Cunningham; H. G. M. Edwards; J. Kendrick; T. Munshi; M. Hargreaves; E. H. Linfield; A. G. Davies

2007-01-01

89

Terahertz Time-Domain Spectroscopy of Amino Acids and Polypeptides  

PubMed Central

Frequency-dependent absorption coefficients and refractive indices of amino acids (glycine and l-alanine) and polypeptides (polyglycine and poly-l-alanine) in the wavenumber region from 7 to 55 cm?1 were measured by terahertz time-domain spectroscopy. A vibrational band was observed at 45.5 cm?1 for polyglycine, which was assigned as an interchain mode. The reduced absorption cross sections of the amino acids and polypeptides show power-law behavior. The exponents are different between the monomers and polymers, and those of the two polypeptides suggest that the time dependences of the total dipole moments are similar in the timescale of subpico- to picoseconds.

Yamamoto, Kohji; Tominaga, Keisuke; Sasakawa, Hiroaki; Tamura, Atsuo; Murakami, Hidetoshi; Ohtake, Hideyuki; Sarukura, Nobuhiko

2005-01-01

90

Terahertz spectroscopy of methanimine and its isotopologs  

NASA Astrophysics Data System (ADS)

Context. Methanimine (CH2NH) is a simple molecule composed of methylene and imine. The molecule has been detected toward the Galactic center, star-forming regions, circumstellar envelopes, and other galaxies since 1973. In previous studies, the rest frequency of methanimine has been measured for normal species up to the 650-GHz region, but its 13CH2NH, CH2 15NH, and CH2ND isotopologs were limited to the 100-GHz region. Aims: If a rotational temperature of 100 K is assumed for methanimine, the highest intensity falls at approximately 1.5 THz. In addition to normal methanimine, the 13CH2NH, CH2 15NH, and CH2ND isotopologs in their ground-vibrational states were observed in the frequency range of 120-1600 GHz to provide accurate rest frequency information. Based on this study, the calculated rest frequencies below 2 THz should be sufficiently precise and support observations using all ALMA and Herschel/HIFI observational bands. Methods: Methanimine was generated by pyrolysis of diaminoethane (DAE) vapor at 850 °C. 13CH2NH and CH2 15NH isotopologs were measured with their natural abundance, and deuterization of DAE was performed by mixing normal DAE with deuterated water, D2O, and then pyrolyzed. This gives the deuterated isotopolog of methanimine, CH2ND. Spectral measurements were performed by using the 23 kHz source-frequency modulated terahertz spectrometer at Toho University. Results: Both a- and b-type transitions up to 1.6 THz for the three isotopologs and the normal species were measured. Rotational and centrifugal distortion constants for the three isotopologs were accurately determined. For normal species (CH2NH), both electric quadrupole and nuclear spin-rotation coupling constants for nitrogen nucleus were determined, while for the 13CH2NH and CH2ND species, only electric quadrupole-coupling constants for nitrogen nucleus were determined. Conclusions: Our spectral line frequencies are suitable for a future astronomical search for these isotopologs of methanimine. The 1? frequency accuracy up to 2 THz is lower than 100 kHz. The full line list is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/566/A28

Motoki, Yuta; Isobe, Fuya; Ozeki, Hiroyuki; Kobayashi, Kaori

2014-06-01

91

Two-dimensional Raman-terahertz spectroscopy of water  

PubMed Central

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.

Savolainen, Janne; Ahmed, Saima; Hamm, Peter

2013-01-01

92

Extraordinary control of terahertz beam reflectance in graphene electro-absorption modulators.  

PubMed

We demonstrate a graphene-based electro-absorption modulator achieving extraordinary control of terahertz reflectance. By concentrating the electric field intensity in an active layer of graphene, an extraordinary modulation depth of 64% is achieved while simultaneously exhibiting low insertion loss (?2 dB), which is remarkable since the active region of the device is atomically thin. This modulator performance, among the best reported to date, indicates the enormous potential of graphene for terahertz reconfigurable optoelectronic devices. PMID:22862777

Sensale-Rodriguez, Berardi; Yan, Rusen; Rafique, Subrina; Zhu, Mingda; Li, Wei; Liang, Xuelei; Gundlach, David; Protasenko, Vladimir; Kelly, Michelle M; Jena, Debdeep; Liu, Lei; Xing, Huili Grace

2012-09-12

93

Characteristics of nanoscale composites by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We have conducted visible pump-THz probe experiments on single wall carbon nanotubes (SWCNTs) on quartz substrates. Our results suggest an upper limit to the carrier-lifetime, which is on the order 1.5ps, limited only by the THz pulse duration. These experiments were repeated for ion-implanted, 3-4nm Si nanoclusters in quartz for which the carrier lifetime was also assessed at 1.5ps. THz time-domain spectroscopy (THz-TDS) of SWCNTs revealed that the THz pulse peak transmission changed under optical illumination.

Altan, Hakan; Huang, Feng; Federici, John F.; Lan, Aidong; Grebel, Haim

2003-08-01

94

Semiconductor Nonlinear Dynamics Study by Broadband Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

Semiconductor nonlinearity in the terahertz (THz) frequency range has been attracting considerable attention due to the recent development of high-power semiconductor-based nanodevices. However, the underlying physics concerning carrier dynamics in the presence of high-field THz transients is still obscure. This thesis introduces an ultrafast, time-resolved THz pump/THz probe approach to the study of semiconductor properties in the nonlinear regime. The carrier dynamics regarding two mechanisms, intervalley scattering and impact ionization, is observed for doped InAs on a sub-picosecond time scale. In addition, polaron modulation driven by intense THz pulses is experimentally and theoretically investigated. The observed polaron dynamics verifies the interaction between energetic electrons and a phonon field. In contrast to previous work which reports optical phonon responses, acoustic phonon modulations are addressed in this study. A further understanding of the intense field interacting with solid materials will accelerate the development of semiconductor devices. This thesis starts with the design and performance of a table-top THz spectrometer which has the advantages of ultra-broad bandwidth (one order higher bandwidth compared to a conventional ZnTe sensor) and high electric field strength (>100 kV/cm). Unlike the conventional THz time-domain spectroscopy, the spectrometer integrates a novel THz air-biased-coherent-detection (THz-ABCD) technique and utilizes selected gases as THz emitters and sensors. In comparison with commonly used electro-optic (EO) crystals or photoconductive (PC) dipole antennas, the gases have the benefits of no phonon absorption as existing in EO crystals and no carrier life time limitation as observed in PC dipole antennas. The newly development THz-ABCD spectrometer with a strong THz field strength capability provides a platform for various research topics especially on the nonlinear carrier dynamics of semiconductors. Two mechanisms, electron intervalley scattering and impact ionization of InAs crystals, are observed under the excitation of intense THz field on a sub-picosecond time scale. These two competing mechanisms are demonstrated by changing the impurity doping type of the semiconductors and varying the strength of the THz field. Another investigation of nonlinear carrier dynamics is the observation of coherent polaron oscillation in n-doped semiconductors excited by intense THz pulses. Through modulations of surface reflection with a THz pump/THz probe technique, this work experimentally verifies the interaction between energetic electrons and a phonon field, which has been theoretically predicted by previous publications, and shows that this interaction applies for the acoustic phonon modes. Usually, two transverse acoustic (2TA) phonon responses are inactive in infrared measurement, while they are detectable in second-order Raman spectroscopy. The study of polaron dynamics, with nonlinear THz spectroscopy (in the far-infrared range), provides a unique method to diagnose the overtones of 2TA phonon responses of semiconductors, and therefore incorporates the abilities of both infrared and Raman spectroscopy. This work presents a new milestone in wave-matter interaction and seeks to benefit the industrial applications in high power, small scale devices.

Ho, I.-Chen

95

Terahertz imaging of aircraft composites  

Microsoft Academic Search

Damaged aircraft composites were prepared simulating voids, delaminations, puncture holes, burns and paint removal. Terahertz time domain spectroscopy in reflection configuration was assessed as a non-destructive evaluation (NDE) technique and compared to traditional NDE techniques.

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

2009-01-01

96

Instrument independent diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

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.

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

2011-01-01

97

Instrument independent diffuse reflectance spectroscopy.  

PubMed

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. PMID:21280897

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

2011-01-01

98

Instrument independent diffuse reflectance spectroscopy  

PubMed Central

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.

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

2011-01-01

99

Characteristics of Gadolinium Oxide Nanoparticles Using Terahertz Spectroscopy (abstract)  

NASA Astrophysics Data System (ADS)

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.

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

2009-04-01

100

Terahertz absorption spectroscopy of protein-containing reverse micellar solution  

NASA Astrophysics Data System (ADS)

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.

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

2012-01-01

101

Terahertz time-domain spectroscopy of cotton sheets  

NASA Astrophysics Data System (ADS)

The transmission of cotton is measured using time-domain spectroscopy in the terahertz (THz) frequency range, from 0.1 to 1.5 THz. An effective medium approximation is used to model the combined cotton and air comprising the samples, and the refractive index of cotton fibers determined. The imaginary part of the refractive index varies across this frequency range with corresponding attenuation coefficient increasing from ˜ 2 to ˜ 12 cm-1, while the real part remains constant at n ˜ 1.144. The effect of moisture content is systematically examined and absorption of the samples determined. Concealed material detection was tested by measuring the 1.44-THz absorption band of representative substance D-Glucose embedded in cotton sheets.

Zhu, Yanhan; Holtz, Mark; Bernussi, Ayrton

2012-10-01

102

[Study on cephalosporins with terahertz time-domain spectroscopy technique].  

PubMed

Terahertz Time-Domain Spectroscopy (THz-TDS) technique has a wide range of applications in substances identification and quantitative analysis. In the present paper, we report absorption spectra and index of refraction of 14 kinds of pure cephalosporins in 0.2-2.6 THz, in which eight kinds have apparent absorption peaks, while the others have different index of refraction. Based on these results, different kinds of antibiotics can be identified. Besides, according to THz absorption spectra of both pure sample and real pills we calculated the contents of cefixime in the two pills produced by two manufacturers. Compared with the contents marked on the package, relative errors are 9.38% and 0.92%, respectively. The results manifest that THz-TDS technique is reliable and promising in medicine detection. PMID:23697105

Zhang, Man; Zhu, Si-Yuan; Li, Qing-Mei; Shen, Jing-Ling

2013-02-01

103

Application of wavelet transforms in terahertz spectroscopy of rough surface targets  

NASA Astrophysics Data System (ADS)

Previously, it has been shown that scattering of terahertz waves by surface roughness of a target can alter the terahertz absorption spectrum and thus obscure the detection of some chemicals in both transmission and reflection geometries. In this paper it is demonstrated that by employing Maximal Overlap Discrete Wavelet Transform (MODWT) coefficients, wavelet-based methods can be used to retrieve spectroscopic information from a broadband terahertz signal reflected from a rough surface target. It is concluded that while the commonly used direct frequency domain deconvolution method fails to accurately characterize and detect the resonance in the dielectric constant of rough surface lactose pellets, wavelet techniques were able to successfully identify such features.

Arbab, M. Hassan; Winebrenner, Dale P.; Thorsos, Eric I.; Chen, Antao

2010-02-01

104

Terahertz pulse imaging in reflection geometry of skin tissue using time-domain analysis techniques  

NASA Astrophysics Data System (ADS)

We demonstrate the application of Terahertz Pulse Imaging (TPI) in reflection geometry for the study of skin tissue and related cancers. The terahertz frequency regime of 0.1-100THz excites the vibrational modes of molecules, allowing for spectroscopic investigation. The sensitivity of terahertz to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the stratum corneum and the determination of the lateral spread of skin cancer pre-operatively. By studying the terahertz pulse shape in the time domain we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC). Measurements on scar tissue, which is known to contain less water than the surrounding skin, and on regions of inflammation, show a clear contrast in the THz image compared to normal skin. We discuss the time domain analysis techniques used to classify the different tissue types. Basal cell carcinoma shows a positive terahertz contrast, and inflammation and scar tissue shows a negative terahertz contrast compared to normal tissue. This demonstrates for the first time the potential of TPI both in the study of skin cancer and inflammatory related disorders.

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

2002-06-01

105

Determination of complex refractive index of thin metal films from terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Thin metal films alone or incorporated in a multilayer stack structure with dielectric films are good candidates of terahertz absorbers necessary for achieving the maximum responsivity in microbolometer devices. However, the design and optimization of these absorber structures depend on the knowledge of the complex refractive index of metal films in the terahertz frequency range, which is not easy to measure or determine from experiment. This paper presents a novel method that allows fast and reliable extraction of the complex refractive index from terahertz time-domain spectroscopy. It starts with terahertz time-domain transmission measurements, followed by Fourier transforms to obtain the transmission spectrum in the frequency range of 0.1-3 THz, and finally an extraction process using the enhanced ``on-the-downhill'' algorithm. Some experimental examples are given, all of which show good agreement with theoretical calculations. This extraction method, combined with the scattering matrix model, can help design and optimize complicated absorber structures for terahertz microbolometers.

Zhou, Da-Xiang; Parrott, E. P. J.; Paul, Douglas J.; Zeitler, J. Axel

2008-09-01

106

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

NASA Astrophysics Data System (ADS)

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.

Li, Jiusheng; Yao, Jianquan

2008-12-01

107

Terahertz spectroscopy of concrete for evaluating the critical hydration level  

NASA Astrophysics Data System (ADS)

Concrete, a mixture of cement, coarse aggregate, sand and filler material (if any), is widely used in the construction industry. Cement, mainly composed of Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S) reacts readily with water, a process known as hydration. The hydration process forms a solid material known as hardened cement paste which is mainly composed of Calcium Silicate Hydrate (C-S-H), Calcium Hydroxide and Calcium Carbonate. To quantify the critical hydration level, an accurate and fast technique is highly desired. However, in conventional XRD technique, the peaks of the constituents of anhydrated and hydrated cement cannot be resolved properly, where as Mid-infrared (MIR) spectroscopy has low penetration depth and hence cannot be used to determine the hydration level of thicker concrete samples easily. Further, MIR spectroscopy cannot be used to effectively track the formation of Calcium Hydroxide, a key by-product during the hydration process. This paper describes a promising approach to quantify the hydration dynamics of cement using Terahertz (THz) spectroscopy. This technique has been employed to track the time dependent reaction mechanism of the key constituents of cement that react with water and form the products in the hydrated cement, viz., C-S-H, Calcium Hydroxide and Calcium Carbonate. This study helps in providing an improved understanding on the hydration kinetics of cement and also to optimise the physio-mechanical characteristics of concrete.

Dash, Jyotirmayee; Ray, Shaumik; Nallappan, Kathirvel; Sasmal, Saptarshi; Pesala, Bala

2014-03-01

108

Quantitative analyses of tartaric acid based on terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Cao, Binghua; Fan, Mengbao

2010-05-01

109

Dielectric Properties of Diesel and Gasoline by Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Arik, Enis; Altan, Hakan; Esenturk, Okan

2014-06-01

110

Accuracy of sample material parameters reconstruction using terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

111

Terahertz spectroscopy of Ni-Ti alloy thin films  

NASA Astrophysics Data System (ADS)

We investigate the charge transport in nickel-titanium (Ni-Ti) alloy thin films using terahertz (THz) transmission spectroscopy. Ni-Ti alloys have peculiar mechanical properties such as shape memory effects. Electrical conductivity can be a good measure to characterize the alloy phase transitions, yet the carrier transport properties of this material are relatively unexplored in the thin film regime. We grew 60-80-nm Ni-Ti alloy films of various Ti concentrations (0- 100%) on intrinsic Si substrates by Ar plasma sputtering. We carried out THz transmission spectroscopy of the samples using broadband THz pulses. The broadband THz pulses were generated by optical rectification of femtosecond laser pulses in a 1-mm ZnTe crystal. The light source was a 1-kHz Ti:sapphire amplifier producing 800-nm femtosecond pulses (pulse energy, 1 mJ; pulse duration, 90 fs). The transmitted THz pulses were measured by either a L-He-cooled Si:Bolometer (sensitive to time-averaged THz power) or by electro-optic (EO) sampling using a 1-mm ZnTe crystal. Analyzing the power transmission data and the transmitted waveforms, we obtained the alloy resistivity as a function of Ti concentration. Sharp changes in the resistivity were observed at the Ti fractions of 22%, 44% and 62%, indicating that structural disorder is greatly enhanced when the alloy undergoes a phase transition.

Jameson, A. D.; Tomaino, J. L.; Paul, M. J.; Kevek, J.; Minot, E. D.; Hemphill-Johnston, M. T.; Koretsky, M. D.; Lee, Yun-Shik

2012-02-01

112

Density of states and vibrational modes of PDMS studied by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Using time-domain spectroscopy (TDS), we performed high-precision spectroscopic measurements of polydimethylsiloxane (PDMS) in the terahertz domain. We investigated the influence of crosslinking on the terahertz absorption and refractive index, and modeled the data with vibrational density of states and coupling between photons and vibrational modes of the polymer molecules. We also investigated the influence of the temperature on PDMS, and observed the glass transition temperature, as well as the cold crystallization peak and the melting zone.

Podzorov, Alexander; Gallot, Guilhem

2010-07-01

113

Direct observation of low frequency confined acoustic phonons in silver nanoparticles: Terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time domain spectroscopy has been used to study low frequency confined acoustic phonons of silver nanoparticles embedded in poly(vinyl alcohol) matrix in the spectral range of 0.1-2.5 THz. The real and imaginary parts of the dielectric function show two bands at 0.60 and 2.12 THz attributed to the spheroidal and toroidal modes of silver nanoparticles, thus demonstrating the usefulness of terahertz time domain spectroscopy as a complementary technique to Raman spectroscopy in characterizing the nanoparticles.

Kumar, Sunil; Kamaraju, N.; Karthikeyan, B.; Tondusson, M.; Freysz, E.; Sood, A. K.

2010-07-01

114

Reflection-type pulsed terahertz imaging with a phase-retrieval algorithm  

SciTech Connect

We propose and demonstrate a scheme for two-dimensional terahertz reflection imaging using a time-domain phase-retrieval algorithm based on the dispersion relations of complex reflection coefficients. With this scheme, topographic images--as well as the dielectric functions of a structured sample--can be obtained. A composite sample made of a semiconductor and metals is characterized within depth and lateral errors of 50 {mu}m and 100 {mu}m.

Ino, Y.; Heroux, J.B.; Mukaiyama, T.; Kuwata-Gonokami, M. [Department of Applied Physics, University of Tokyo (Japan) and Solution Oriented Research for Science and Technology (JST), 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2006-01-23

115

Destructive interference effect on surface plasmon resonance in terahertz attenuated total reflection  

Microsoft Academic Search

We investigate the surface plasmon resonance at the interface between air and n-type (100) oriented-InAs as an active material with a time-domain attenuated total reflection technique with coherent terahertz pulses. The characteristic spectra of the attenuated total reflectivity and phase shift caused by surface plasmon are observed in the Otto configuration. The surface plasmon resonance frequency and the phase jump

Hideki Hirori; Masaya Nagai; Koichiro Tanaka

2005-01-01

116

Etude de la dynamique des porteurs dans des nanofils de silicium par spectroscopie terahertz  

NASA Astrophysics Data System (ADS)

Ce memoire presente une etude des proprietes de conduction electrique et de la dynamique temporelle des porteurs de charges dans des nanofils de silicium sondes par rayonnement terahertz. Les cas de nanofils de silicium non intentionnellement dopes et dopes type n sont compares pour differentes configurations du montage experimental. Les mesures de spectroscopie terahertz en transmission montre qu'il est possible de detecter la presence de dopants dans les nanofils via leur absorption du rayonnement terahertz (˜ 1--12 meV). Les difficultes de modelisation de la transmission d'une impulsion electromagnetique dans un systeme de nanofils sont egalement discutees. La detection differentielle, une modification au systeme de spectroscopie terahertz, est testee et ses performances sont comparees au montage de caracterisation standard. Les instructions et des recommendations pour la mise en place de ce type de mesure sont incluses. Les resultats d'une experience de pompe optique-sonde terahertz sont egalement presentes. Dans cette experience, les porteurs de charge temporairement crees suite a l'absorption de la pompe optique (lambda ˜ 800 nm) dans les nanofils (les photoporteurs) s'ajoutent aux porteurs initialement presents et augmentent done l'absorption du rayonnement terahertz. Premierement, l'anisotropie de l'absorption terahertz et de la pompe optique par les nanofils est demontree. Deuxiemement, le temps de recombinaison des photoporteurs est etudie en fonction du nombre de photoporteurs injectes. Une hypothese expliquant les comportements observes pour les nanofils non-dopes et dopes-n est presentee. Troisiemement, la photoconductivite est extraite pour les nanofils non-dopes et dopes-n sur une plage de 0.5 a 2 THz. Un lissage sur la photoconductivite permet d'estimer le nombre de dopants dans les nanofils dopes-n. Mots-cles: nanofil, silicium, terahertz, conductivite, spectroscopie, photoconductivite.

Beaudoin, Alexandre

117

Investigation of Chlorophyll Protein 43 and 47 Denaturation by Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate the applications of terahertz time-domain spectroscopy to distinguish conformation changes of the chlorophyll proteins CP43 and CP47 induced by the treatment of guanidine hydrochloride, light irradiation and heating. It is indicated that THz transmission spectroscopy can be used for monitoring protein denaturation and associated conformation change processes in a feasible and effective way.

Chen, Hua; Qu, Yuan-Gang; Peng, Wei-Xian; Kuang, Ting-Yun; Li, Liang-Bi; Wang, Li

2007-07-01

118

Advanced birefringence measurements in standard terahertz time-domain spectroscopy.  

PubMed

Polarization-sensitive (PS) terahertz (THz) technology can be used for investigating anisotropic materials that are opaque for visible light. A full characterization of an anisotropic material requires the extraction of the birefringence as well as the orientation of the optical axis from the measurement data. We present an approach based on THz time-domain spectroscopy (TDS) that exploits the spectral content of the THz signal for determining these two parameters from only two measurements. In contrast to an earlier approach with a more sophisticated PS-THz system and quasi-circularly polarized THz radiation, now a simple standard THz-TDS system can be employed. After a description of the mathematical model for data analysis we demonstrate the applicability of our method for a lithium niobate crystal and furthermore for a glass-fiber reinforced polymer sample, for which the orientation of the optical axis and birefringence are obtained in a spatially resolved way, showing the potential of the method also for PS-THz imaging. As no specialized setup or components are required, our approach can be easily and extensively applied for the analysis of anisotropic samples at THz frequencies. PMID:24922202

Pfleger, Michael; Roitner, Heinz; Pühringer, Harald; Wiesauer, Karin; Grün, Hubert; Katletz, Stefan

2014-05-20

119

Fiber-pigtailed terahertz time domain spectroscopy instrumentation for package inspection and security imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Because terahertz imaging employs safe non-ionizing radiation that penetrates clothing, people may be routinely scanned as well as packages. Images can have sub-millimeter resolution, superior to longer wavelength techniques. Explosives, chemical weapons, and biological agents may posses a spectral fingerprint in the terahertz regime. The application of commercially available time domain terahertz spectroscopy equipment to imaging of concealed threats within packages is shown to penetrate common packing materials and clearly image common plastic and metal threat objects.

Zimdars, David A.

2003-08-01

120

Applications of terahertz spectroscopy in the plastics industry  

NASA Astrophysics Data System (ADS)

The worldwide production volume of polymers is still rising exponentially and the number of applications for plastic components steadily increases. Yet, many branches within the polymer industry are hardly supported by non-destructive testing techniques. We demonstrate that terahertz (THz) spectroscopy could be the method of choice to ensure high-quality polymer products. Applications range from the in-line monitoring of extrusion processes and the quality control of commodities in a mass production up to a total inspection of high-tech safety relevant products. Furthermore, we present an extension to THz time-domain spectroscopy in the form of a new data extraction algorithm, which derives the absorption coefficient, the refractive index and the thickness of a sample with very high precision in a single pass. Apart from that, we discuss the ability of THz systems for quality control of polymeric compounds. Here, it is essential to monitor the additive content as well as additive inhomogeneities within the mixture. Recently, we built a fiber-coupled THz spectrometer for in-line monitoring of compounding processes. Additionally, we demonstrate the potential of THz systems for the non-destructive and contactless testing of structural components. THz imaging is capable of analyzing material thicknesses, superstructures, the quality of plastic weld joints, and of detecting flaws in components. Plastics and THz form a very fruitful symbiosis. In return, plastics industry can provide THz systems with custom-tailored components, which have very attractive properties and extremely low costs. Examples of this development are photonic crystals or polymeric Bragg filters, which have recently been demonstrated.

Wietzke, S.; Rutz, F.; Jördens, C.; Krumbholz, N.; Vieweg, N.; Jansen, C.; Wilk, R.; Koch, M.

2008-03-01

121

Final Project Report for Terahertz Spectroscopy of Complex Matter.  

National Technical Information Service (NTIS)

This project designed characterization techniques for thin films of complex matter and other materials in the terahertz spectral region extending from approximately 100 GHz to 4000 GHz (4 THz) midway between radio waves and light. THz has traditionally be...

2006-01-01

122

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

NASA Astrophysics Data System (ADS)

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

Catapano, Ilaria; Soldovieri, Francesco

2014-05-01

123

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

PubMed

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. PMID:23263043

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

2012-12-17

124

Fresnel reflection in optical components and detectors for the terahertz frequency band  

Microsoft Academic Search

Plane-parallel dielectric and semiconductor windows, beam splitters and radiation absorbers, as well as reflecting metal surfaces,\\u000a are important components used in experiments with monochromatic terahertz radiation. The wavelengths of this radiation are\\u000a longer than the wavelengths of visible light; therefore, multibeam interference becomes important in relatively transparent\\u000a components with a thickness of the order of 1 mm, which is typical

V. V. Gerasimov; B. A. Knyazev; P. D. Rudych; V. S. Cherkassky

2007-01-01

125

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

National Technical Information Service (NTIS)

The feasibility of attaining improved explosives detection and identification using complementary InN-based time-domain terahertz spectroscopy (TDTS) and laser-induced breakdown spectroscopy (LIBS) techniques employing 1550-nm femtosecond (fs) pulse techn...

A. Sampath D. Stratis-Cullum M. Wraback

2008-01-01

126

Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas  

Microsoft Academic Search

From classical charge transport equations and dipole radiation equations, we derive a simple analytical model for the signal detected in terahertz time-domain spectroscopy using photoconducting antennas. The validity of our model is checked by comparison to published calculated results and to experimental data we have measured. This expression depends mostly on the carrier lifetime in the antennas' semiconductor material and

Lionel Duvillaret; Frédéric Garet; Jean-François Roux; Jean-Louis Coutaz

2001-01-01

127

Spectroscopy and imaging system using a frequency agile ring-cavity terahertz-wave parametric oscillator  

Microsoft Academic Search

A spectroscopy and imaging system using a ring cavity terahertz (THz) wave parametric oscillator was developed. We demonstrate the differentiation of tissue types in a watery microtomed biological section using differences of water concentration. The contrast of differentiation for watery tissues was improved over that of the dried tissue.

Tomofumi Ikari; Koichi Akiyama; Hiroaki Minamide; Hiromasa Ito

2007-01-01

128

Terahertz Time Domain Spectroscopy of Phonon-Depopulation Based Quantum Cascade Lasers  

SciTech Connect

A 3.1 THz phonon depopulation-based quantum-cascade-laser is investigated using terahertz time domain spectroscopy. A gain of 25 cm{sup -1} and absorption features due to the lower laser level being populated from a parasitic electronic channel are highlighted.

Rungsawang, R.; Dhillon, S. S.; Jukam, N.; Oustinov, D.; Madeo, J.; Tignon, J. [Laboratoire Pierre Aigrain, Ecole Normale Superieure, UMR8551 CNRS, UPMC Univ. Paris 6, F-75005 Paris (France); Colombelli, R. [Institut d'Electronique Fondamentale, Universite Paris Sud, UMR8622 CNRS, 91405 Orsay (France); Dean, P.; Salih, M.; Khanna, S. P.; Linfield, E.; Davies, A. G. [School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT (United Kingdom)

2011-12-23

129

Charge carrier relaxation and effective masses in silicon probed by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Charge transport in silicon is investigated on a metal-oxide-semiconductor structure, which is driven into depletion, accumulation, or inversion. Terahertz electromodulation spectroscopy provides momentum relaxation times as well as conductivity effective masses of electrons and holes. At room temperature the conductivity effective masses of electrons and holes are close to those values reported for cryogenic temperatures.

Engelbrecht, S. G.; Reichel, A. J.; Kersting, R.

2012-12-01

130

Broadband terahertz time-domain spectroscopy of drugs-of-abuse mixtures and ‘street‘ samples  

Microsoft Academic Search

Terahertz time-domain spectroscopy is used to analyze a number of real-world drugs-of-abuse samples, common drug adulterants, and drugs systematically adulterated in the laboratory. Principle component analysis is used to cluster spectra of similar compounds, which could lead to automatic spectral recognition of illicit materials.

A. D. Burnett; Wenhui Fan; P. C. Upadhya; J. E. Cunningham; M. Hargreaves; T. Munshi; H. G. M. Edwards; E. H. Linfield; A. G. Davies

2008-01-01

131

A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons  

NASA Astrophysics Data System (ADS)

We demonstrate a band-pass resonator in the terahertz (THz) range, based on a frequency-selective designer reflector. The resonator consists of a parallel-plate waveguide, a designed groove pattern cut into the output facet of each plate, and a reflecting mirror. The patterned facet supports a spoof surface plasmon mode, which modifies the reflectivity at the waveguide output facet by interacting with the waveguide mode. By tuning the geometrical parameters of the groove pattern, the reflectivity at the patterned output facet can be increased up to ?100% for a selected frequency. Broadband THz waves are quasi-optically coupled into this resonator and reflected multiple times from the patterned facet. This leads to a narrowing of the spectrum at the selected frequency. The Q value of the resonator increases as the number of reflections on the patterned facet increases, reaching ?25 when the THz wave has experienced 12 reflections.

Liu, Jingbo; Mendis, Rajind; Mittleman, Daniel M.

2013-05-01

132

Novel modulation reflectance spectroscopy of semiconductor heterostructures  

Microsoft Academic Search

New methods of modulation reflectance spectroscopy have been proposed for investigation of semiconductor heterostructures. Current-, radio-frequency- and microwave-modulated reflectance are proposed and applied for determination of band structure features and band diagram of heterostructures of high electron mobility transistors and laser diodes. New physical contributions to formation of spectra of the modulation reflectance of light with quantum energy near the

O. A. Ryabushkin; E. I. Lonskaya; A. E. Sotnikov; M. A. Chernikov

2005-01-01

133

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

NASA Astrophysics Data System (ADS)

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.

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

2013-02-01

134

Terahertz spectroscopy of the reactive and radiative near-field zones of split ring resonator.  

PubMed

A terahertz microscope has been used to excite and observe the resonant modes of a single split ring resonator in the reactive and radiative near-field zones. The two lowest resonant modes of an isolated split ring resonator with their corresponding radiation patterns are reported; they showed good agreement to simulations. The passage from the reactive to radiative near-field zone is also discussed. Further, our result introduced a novel technique to perform terahertz time-domain spectroscopy of samples a few tens of micrometers in size by measuring the in-plane radiative near-field zone. PMID:23038582

Blanchard, F; Ooi, K; Tanaka, T; Doi, A; Tanaka, K

2012-08-13

135

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

NASA Astrophysics Data System (ADS)

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.

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

2006-03-01

136

Application of femtotechnologies and terahertz spectroscopy methods in cataract diagnostics  

NASA Astrophysics Data System (ADS)

We study the destructive action of femtosecond pulses (200 fs) on the human cataractous crystalline lens and the transmission of the cataractous lens in the terahertz spectral range of electromagnetic oscillations (0.2-1 THz) in relation to the density of the nucleus of the lens.

Sakhnov, S. N.; Leksutkina, E. V.; Smolyanskaya, O. A.; Usov, A. V.; Parakhuda, S. E.; Grachev, Ya. V.; Kozlov, S. A.

2011-08-01

137

Diffuse reflection imaging at terahertz frequencies for security applications  

Microsoft Academic Search

We report diffuse reflection imaging of concealed powdered samples in atmospheric air using a quantum cascade laser operating at 2.83 THz. The imaging system uses a helium-cooled silicon bolometer for mapping radiation diffusely reflected and scattered from samples, and a room-temperature pyroelectric sensor for simultaneously acquiring a specular image. A range of powders concealed within plastic packaging and standard FedEx

P. Dean; S. Khanna; S. Chakraborty; M. Lachab; A. G. Davies; E. H. Linfield

2007-01-01

138

Terahertz Time-Domain Spectroscopy of Solid Samples: Principles, Applications, and Challenges  

Microsoft Academic Search

Advances in ultrafast lasers and semiconductor technologies have facilitated access to the terahertz (THz) frequency range for spectroscopic and imaging purposes. THz time-domain spectroscopy (TDS) is commonly used to acquire spectral data having high signal-to-noise ratios (SNRs) over a broad range of THz frequencies. THz-TDS instrumentation is commercially available, thereby enabling novel applications of THz time-domain (TD) imaging and spectroscopy

Ryan M. Smith; Mark A. Arnold

2011-01-01

139

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

NASA Astrophysics Data System (ADS)

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)

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

2012-02-01

140

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

PubMed Central

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.

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

2013-01-01

141

Chemometrics applied to quantitative analysis of ternary mixtures by terahertz spectroscopy.  

PubMed

Chemometrics was applied to qualitative and quantitative analyses of terahertz spectra obtained in transmission mode. A series of mixtures of three pure analytes, namely, citric acid, d-(-)fructose, and ?-lactose monohydrate under various concentrations, was prepared as pressed pellets with polyethylene as binder. Then, terahertz absorbance spectra were recorded by terahertz time domain spectroscopy and analyzed. First, principal component analysis allowed one to correctly locate the samples into a ternary diagram. Second, quantitative analysis was achieved by partial least-squares (PLS) regression and artificial neural networks (ANN). The concentrations were predicted with values of relative mean square error lower than 0.9% for the three constituents. As a conclusion, chemometrics was demonstrated to be very efficient for the analysis of the ternary mixtures prepared for this study. PMID:24738647

El Haddad, Josette; de Miollis, Frederick; Bou Sleiman, Joyce; Canioni, Lionel; Mounaix, Patrick; Bousquet, Bruno

2014-05-20

142

An ion-implanted InP receiver for polarization resolved terahertz spectroscopy.  

PubMed

We report on the construction, optical alignment and performance of a receiver which is capable of recording the full polarization state of coherent terahertz radiation. The photoconductive detector was fabricated on InP which had been implanted with Fe(+) ions. The device operated successfully when it was gated with near infrared femtosecond pulses from either a Ti:sapphire laser oscillator or a 1 kHz regenerative laser amplifier. When illuminated with terahertz radiation from a typical photoconductive source, the optimized device had a signal to noise figure of 100:1 with a usable spectral bandwidth of up to 4 THz. The device was shown to be very sensitive to terahertz polarization, being able to resolve changes in polarization of 0.34 degrees. Additionally, we have demonstrated the usefulness of this device for (i) polarization sensitive terahertz spectroscopy, by measuring the birefringence of quartz and (ii) terahertz emission experiments, by measuring the polarization dependence of radiation generated by optical rectification in (110)-ZnTe. PMID:19547022

Castro-Camus, E; Lloyd-Hughes, J; Fu, L; Tan, H H; Jagadish, C; Johnston, Michael B

2007-05-28

143

Automated measurement equipment of temperature-dependent reflectivity spectra with high accuracy in the infrared and terahertz regions  

Microsoft Academic Search

Near-normal-incident reflectivity spectra in the infrared and terahertz regions give us important information of electronic structure and of lattice vibrations. To obtain the temperature-dependent reflectivity spectra with high accuracy of absolute reflectivity, we have constructed an automated measurement equipment of temperature-dependent reflectivity spectra. Using the equipment, we can obtain substantial reflectivity spectra without extrinsic effects such as surface roughness, waviness

Shin-ichi Kimura

144

A reflection sensor based on the Rayleigh anomaly of metallic grating in terahertz wave band  

NASA Astrophysics Data System (ADS)

An optical refractive index sensor based on the Rayleigh anomaly of the gold grating is demonstrated in the terahertz (THz) wave band. A pronounced peak due to the Rayleigh anomaly of the gold grating is observed in the reflection spectrum, the center wavelength of which is sensitive to the environmental refractive index on the top of the grating. The wavelength of the Rayleigh anomaly reflection peak and the corresponding sensitivity are solely determined by the period of the gold grating, the larger the period, the longer the resonance wavelength and the higher the sensitivity. Therefore, a higher sensitivity can be achieved in the THz wave band. Both theoretical and experimental investigations show that the shape and intensity of the Rayleigh anomaly reflection peaks are determined by the duty cycle of the grating, for the value of the duty cycle about 0.4, the maximum intensity of the Rayleigh anomaly reflection peak was achieved.

Yue, Lingyue; He, Jingwen; Feng, Shengfei; Wang, Xingke; Sun, Wenfeng; Zhang, Yan

2012-12-01

145

Dielectric Relaxation Dynamics of Water in Model Membranes Probed by Terahertz Spectroscopy  

PubMed Central

We study hydrated model membranes, consisting of stacked bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine lipids, using terahertz time-domain spectroscopy and infrared spectroscopy. Terahertz spectroscopy enables the investigation of water dynamics, owing to its sensitivity to dielectric relaxation processes associated with water reorientation. By controlling the number of water molecules per lipid molecule in the system, we elucidate how the interplay between the model membrane and water molecules results in different water dynamics. For decreasing hydration levels, we observe the appearance of new types of water dynamics: the collective bulklike dynamics become less pronounced, whereas an increased amount of both very slowly reorienting (i.e., irrotational) and very rapidly reorienting (i.e., fast) water molecules appear. Temperature-dependent measurements reveal the interconversion between the three distinct types of water present in the system.

Tielrooij, K.J.; Paparo, D.; Piatkowski, L.; Bakker, H.J.; Bonn, M.

2009-01-01

146

Biomedical Applications of Terahertz Spectroscopy: A Brief Review  

NASA Astrophysics Data System (ADS)

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 spectrum.

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

2008-08-01

147

Biomedical Applications of Terahertz Spectroscopy: A Brief Review  

SciTech Connect

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.

Vargas-Luna, M. [Instituto de Fisica, Universidad de Guanajuato, Loma del Bosque 103, Lomas del Campestre CP 37150 Leon Gto. (Mexico); Huerta-Franco, R. [Instituto de Investigaciones sobre el Trabajo, Av. Eugenio Garza Sada 530, Lomas del Campestre, CP 37150, Leon Gto. (Mexico)

2008-08-11

148

Single-shot measurement of a terahertz electric-field waveform using a reflective echelon mirror  

NASA Astrophysics Data System (ADS)

Single-shot measurements of terahertz (THz) electric-field waveforms are demonstrated using a reflective echelon mirror, which produces multiple probe pulses with different time-delays. The polarization rotation of the probe pulses, due to the electro-optic effect induced by the THz electric field generated from grating-coupled LiNbO3, was imaged onto a two-dimensional complementary metal-oxide-semiconductor camera. A waveform with a weak peak field strength of 0.6 kV/cm was obtained with a good signal-to-noise ratio, demonstrating precise single-shot detection of the THz electric field waveform.

Minami, Yasuo; Hayashi, Yusuke; Takeda, Jun; Katayama, Ikufumi

2013-07-01

149

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

PubMed

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. PMID:19997298

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

2009-11-01

150

Bidirectional reflectance spectroscopy. I - Theory  

Microsoft Academic Search

An approximate analytic solution is derived for the radiative transfer equation describing particulate surface light scattering, taking into account multiple scattering and mutual shadowing. Analytical expressions for the following quantities are found: bidirectional reflectance, radiance coefficient and factor, the normal, Bond, hemispherical, and physical albedos, integral phase function and phase integral, and limb-darkening profile. Scattering functions for mixtures can be

Bruce Hapke

1981-01-01

151

Terahertz surface plasmon polariton coupling on metallic gratings  

Microsoft Academic Search

Terahertz time-domain spectroscopy is used to study the nature and efficiency of coupling between surface plasmon polaritons and free-space terahertz radiation by metallic gratings made from brass rods and a grooved aluminum plate. Reflection and transmission mode measurements indicate very rapid coupling and decoupling with > 70% efficiency after accounting for scattering. Results indicate a good match to theoretical coupling

John F. O'Hara; R. D. Averitt; A. J. Taylor

2004-01-01

152

Broadband terahertz spectroscopy: principles, fundamental research and potential for industrial applications  

NASA Astrophysics Data System (ADS)

Terahertz radiation (also called T-rays) can be employed for spectroscopy and imaging, from the laboratory to industrial applications. In this paper we give an overview of how broadband optoelectronic THz techniques (i.e. using optical lasers to achieve THz generation and detection) can be implemented, and give examples of their unique use in solid-state physics, and in biological and industrial applications.

Zouaghi, W.; Thomson, M. D.; Rabia, K.; Hahn, R.; Blank, V.; Roskos, H. G.

2013-11-01

153

Fiber-coupled antennas for ultrafast coherent terahertz spectroscopy in low temperatures and high magnetic fields  

Microsoft Academic Search

For the purposes of measuring the high-frequency complex conductivity of correlated-electron materials at low temperatures and high magnetic fields, a method is introduced for performing coherent time-domain terahertz spectroscopy directly in the cryogenic bore of existing dc and pulsed magnets. Miniature fiber-coupled THz emitters and receivers are constructed and are demonstrated to work down to 1.5 K and up to

S. A. Crooker

2002-01-01

154

Doping profile recognition in silicon using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Here we demonstrate for the first time that terahertz time domain spectroscopy (THz-TDS) can be used to distinguish doping profile discrepancies in semiconductor silicon wafers. These proof of concept results suggest the suitability of the technique for in-line process control applications in both IC/photovoltaic (PV) industries. The experimental results show that THz radiation is sensitive to the implant dosage changes in the time domains.

Jen, Chih-Yu; Richter, Christiaan

2014-03-01

155

Terahertz imaging and spectroscopy of large-area single-layer graphene  

Microsoft Academic Search

We demonstrate terahertz (THz) imaging and spectroscopy of a 15x15-mm^2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is

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

2011-01-01

156

Quantitative analysis of water distribution in human articular cartilage using terahertz time-domain spectroscopy  

PubMed Central

The water distribution in human osteoarthritic articular cartilage has been quantitatively characterized using terahertz time-domain spectroscopy (THz TDS). We measured the refractive index and absorption coefficient of cartilage tissue in the THz frequency range. Based on our measurements, the estimated water content was observed to decrease with increasing depth cartilage tissue, showing good agreement with a previous report based on destructive biochemical methods.

Jung, Euna; Choi, Hyuck Jae; Lim, Meehyun; Kang, Hyeona; Park, Hongkyu; Han, Haewook; Min, Byung-hyun; Kim, Sangin; Park, Ikmo; Lim, Hanjo

2012-01-01

157

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

NASA Astrophysics Data System (ADS)

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.

Xiao-li, Zhao; Jiu-sheng, Li

2011-02-01

158

Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties  

Microsoft Academic Search

Terahertz (THz) time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of silica, Pyrex, and seven different Schott glasses. The refractive indices were analyzed using the Clausius-Mossotti equation, and the absorption coefficients in terms of the power-law model of far-infrared absorption. Relationships were observed between THz absorption and refractive indices on the one hand, and glass

M. Naftaly; R. E. Miles

2007-01-01

159

Role of low-temperature-grown GaAs substrate of photoconductive antenna in broadband terahertz time domain spectroscopy  

Microsoft Academic Search

We have investigated the detection performance of photoconductive antennas fabricated on low-temperature-grown GaAs substrate. We compared terahertz waves detected with antennas annealed at different temperatures in terahertz time domain spectroscopy. The signal detected with the antenna annealed at higher temperature showed stronger intensity. On the other hand, the spectrum detected with the antenna annealed at lower temperature showed broader bandwidth.

H. Shimosato; I. Katayama; S. Saito; M. Ashida; T. Itoh; Y. Kadoya; K. Sakai

2007-01-01

160

Ultrafast Optical-Pump Terahertz-Probe Spectroscopy of the Carrier Relaxation and Recombination Dynamics in Epitaxial Graphene  

Microsoft Academic Search

The ultrafast relaxation and recombination dynamics of photogenerated electrons and holes in epitaxial graphene are studied using optical-pump Terahertz-probe spectroscopy. The conductivity in graphene at Terahertz frequencies depends on the carrier concentration as well as the carrier distribution in energy. Time-resolved studies of the conductivity can therefore be used to probe the dynamics associated with carrier intraband relaxation and interband

Paul A. George; Jared Strait; Jahan Dawlaty; Shriram Shivaraman; Mvs Chandrashekhar; Farhan Rana; Michael G. Spencer

2008-01-01

161

Measuring the electrical properties of semiconductor nanowires using terahertz conductivity spectroscopy  

NASA Astrophysics Data System (ADS)

Accurately measuring the electronic properties of nanowires is a crucial step in the development of novel semiconductor nanowire-based devices. With this in mind, optical pump-terahertz probe (OPTP) spectroscopy is ideally suited to studies of nanowires: it provides non-contact measurement of carrier transport and dynamics at room temperature. OPTP spectroscopy has been used to assess key electrical properties, including carrier lifetime and carrier mobility, of GaAs, InAs and InP nanowires. The measurements revealed that InAs nanowires exhibited the highest mobilities and InP nanowires exhibited the lowest surface recombination velocity.

Joyce, Hannah J.; Docherty, Callum J.; Yong, Chaw-Keong; Wong-Leung, Jennifer; Gao, Qiang; Paiman, Suriati; Tan, H. Hoe; Jagadish, C.; Lloyd-Hughes, James; Herz, Laura M.; Johnston, Michael B.

2013-12-01

162

Detection of porosity of pharmaceutical compacts by terahertz radiation transmission and light reflection measurement techniques.  

PubMed

We report on the non-destructive quantification of the porosity of pharmaceutical compacts (microcrystalline cellulose tablets) by using both optical and terahertz techniques. For the full analysis of the porosity of pharmaceutical tablets, the results obtained in both cases have shown that optical and terahertz techniques are complementary. The intrinsic refractive index of microcrystalline cellulose was estimated using the effective refractive index obtained from the time delay of the THz pulse together with the Bruggeman model for effective media. Once this intrinsic refractive index is known, the unknown porosity of the tablet can be estimated with the aid of the measured effective refractive index as well as the thickness of the pharmaceutical tablet. The method was tested using a set of thirteen tablets having different porosities. It is shown that the error in the estimation of the unknown tablet's porosity is less than 1%. In addition, surface roughness was measured by using an optical interferometer and gloss by using a diffractive-optical-element based glossmeter. The measurement was achieved by scanning the tablets with a probe beam and detecting the reflected light. The surface roughness and gloss data show relatively good correlation with the porosities of the tablets. PMID:24530384

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

2014-04-25

163

Methanol-induced conformation transition of gland fibroin monitored by FTIR spectroscopy and terahertz spectroscopy.  

PubMed

Silk fibroin extracted from the gland of Bombyx mori silkworm is employed as an ideal system to investigate its conformation transition in methanol/D2O solution. The transition process was monitored by Fourier transform infrared (FTIR) spectroscopy coupled with terahertz time domain spectroscopy (THz-TDS). Analysis of FTIR spectra suggests that, with increasing time of treatment, an increasing band at 1634 cm(-1) is observed indicating the formation of ?-pleated sheets coincident with the loss of intensity of a band at 1673 cm(-1) indicating decrease of the random coil structure. In addition, there is a burst phase of 33% occurring during the first 2 minutes when the gland fibroin membranes are immersed into methanol/D2O solution. THz spectra present distinct features for conformations of silk fibroin, in combination with the results obtained from FTIR; the peaks observed at 1.54 THz (51 cm(-1)), 1.67 THz (55 cm(-1)), and 1.84 THz (61 cm(-1)) can be attributed to a ?-pleated sheet, ?-helix, and random coil, respectively. Intensity change of bands centered at 1.54 THz and 1.84 THz confirms the formation of the ?-pleated sheet and the disappearance of the random coil. Kinetic curves obtained from THz spectra indicate that the methanol-induced conformation transition from the random coil to the ?-pleated sheet is fitted with an exponential function. The results suggest that THz-TDS presents great potential as a complementary approach in studying the secondary structure of a protein, providing significant insight into the silk-spinning process in vivo. PMID:24588004

Yan, Chao; Yang, Bin; Yu, Zhicheng

2014-04-21

164

Two beam surface fluctuation specular reflection spectroscopy  

NASA Astrophysics Data System (ADS)

In surface fluctuation specular reflection spectroscopy (SFSRS) deflections of a specularly reflected laser beam are used to characterize thermally excited surface waves. Here we report on a new two beam version of SFSRS in which the deflections of two reflected laser beams from separate locations on a surface are correlated. We demonstrate that this new two beam SFSRS technique can be used to determine directly the power spectrum of height fluctuation of thermally excited surface waves over a large range of both frequencies and wavevectors. In addition, we show that the technique is well suited for materials ranging from simple liquids to complex liquids and soft solids, including turbid materials.

Raudsepp, Allan; Fretigny, Christian; Lequeux, François; Talini, Laurence

2012-01-01

165

Terahertz time domain spectroscopy of epoxy resin composite with various carbon inclusions  

NASA Astrophysics Data System (ADS)

The propagation properties of terahertz waves through epoxy resin filled with small amounts (0.25-1.5 wt.%) of commercially available carbon black (CB) and CVD made single-walled and multi-walled carbon nanotubes (CNT) have been investigated by terahertz time domain spectroscopy. High electromagnetic attenuation specified substantially with absorption of THz radiation and strongly decreasing with the decrease of frequency from 0.2 to 1.5 THz has been found for both types of CNT fillers starting from 1 wt.% of nanocarbon concentration. At the same time CB in the same concentration does not make any impact to THz transmission spectrum. The resonance dielectric dispersion has been observed for all investigated samples, which can be attributed to phonon resonance in epoxy resin matrix. The availability of Maxwell-Garnett model for epoxy resin filled with 0.25-1.5 wt.% of CNT was also addressed in the paper.

Macutkevic, J.; Seliuta, D.; Valusis, G.; Adomavicius, R.; Kuzhir, P.; Paddubskaya, A.; Shuba, M.; Maksimenko, S.; Coderoni, L.; Micciulla, F.; Sacco, I.; Bellucci, S.

2012-08-01

166

Experimental study on identifying main component in rice bran oil with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

The absorption spectra of rice bran oil in the frequency range of 0.2~1.6THz has been measured with terahertz timedomain spectroscopy (THz-TDS) at room temperature in nitrogen atmosphere. It is found that hexadecanoidc acid and octadecanoic acid contained in rice bran oil has the spectral response to terahertz waves in this frequency region. Simultaneously, the corresponding theoretical spectra were given by using DFT methods with the aid of Gaussian03. The experimental spectra are well comparable with the calculated spectra and these results mutually validated both approaches. It was found that the absorption peaks of the two molecules obtained by theoretical were in good agreement with the experimental results. The research results prove the feasibility of applying THz-TDS technique to detect and identify of main component of edible oil. Furthermore, the result s provided in this paper will help us to study the THz application to food quality evaluation or safety inspection further.

Li, Jiu-Sheng; Zhao, Xiao-Li; Li, Jian-Rui

2009-07-01

167

Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz—Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS2) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS2-lithium grease than that of lithium grease.

Tian, Lu; Zhou, Qing-Li; Zhao, Kun; Shi, Yu-Lei; Zhao, Dong-Mei; Zhao, Song-Qing; Zhao, Hui; Bao, Ri-Ma; Zhu, Shou-Ming; Miao, Qing; Zhang, Cun-Lin

2011-01-01

168

Reflectance spectroscopy and asteroid surface mineralogy  

NASA Technical Reports Server (NTRS)

Information available from reflectance spectroscopy on the surface mineralogy of asteroids is discussed. Current spectral interpretive procedures used in the investigations of asteroid mineralogy are described. Present understanding of the nature and history of asteroids is discussed together with some still unresolved issues such as the source of ordinary chondrites.

Gaffey, Michael J.; Bell, Jeffrey F.; Cruikshank, Dale P.

1989-01-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

170

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

PubMed

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

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

2011-06-01

171

Terahertz time domain spectroscopy of hollow polycarbonated metal waveguides  

NASA Astrophysics Data System (ADS)

Recently, the terahertz region of the electromagnetic spectrum has gained critical significance in various technical applications and fundamental research problems, involving nondestructive evaluation of material parameters, bio-medical imaging, remote sensing and security screening. However, for applications in which THz radiation needs to be transmitted over a long distance without atmospheric absorption, a flexible waveguide could have potential applications simplifying the propagation of THz radiation in remote locations. Different structures like rigid hollow metallic waveguides, solid wires, or short lengths of solid-core transparent dielectrics such as sapphire and plastic have already been explored for THz guiding purposes. Recently, it has been reported that Cu coated flexible, hollow polycarbonate waveguide has a low loss of less than 4 dB/m in single mode operation, at 1.89 THz. In the present study, using a broadband THz source of photoconductive antennae, we characterize the loss and dispersion profile of Cu coated flexible, hollow polycarbonate waveguide having an inner diameter of 2mm. Insertion loss and the attenuation coefficient were calculated using waveguides of lengths between 40mm and 70mm.

Bandyopadhyay, Aparajita; Sengupta, Amartya; Federici, John; Johnson, Valencia; Harrington, James

2006-03-01

172

Spectrally interleaved, comb-mode-resolved spectroscopy using swept dual terahertz combs.  

PubMed

Optical frequency combs are innovative tools for broadband spectroscopy because a series of comb modes can serve as frequency markers that are traceable to a microwave frequency standard. However, a mode distribution that is too discrete limits the spectral sampling interval to the mode frequency spacing even though individual mode linewidth is sufficiently narrow. Here, using a combination of a spectral interleaving and dual-comb spectroscopy in the terahertz (THz) region, we achieved a spectral sampling interval equal to the mode linewidth rather than the mode spacing. The spectrally interleaved THz comb was realized by sweeping the laser repetition frequency and interleaving additional frequency marks. In low-pressure gas spectroscopy, we achieved an improved spectral sampling density of 2.5?MHz and enhanced spectral accuracy of 8.39 × 10(-7) in the THz region. The proposed method is a powerful tool for simultaneously achieving high resolution, high accuracy, and broad spectral coverage in THz spectroscopy. PMID:24448604

Hsieh, Yi-Da; Iyonaga, Yuki; Sakaguchi, Yoshiyuki; Yokoyama, Shuko; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Araki, Tsutomu; Yasui, Takeshi

2014-01-01

173

Spectrally interleaved, comb-mode-resolved spectroscopy using swept dual terahertz combs  

PubMed Central

Optical frequency combs are innovative tools for broadband spectroscopy because a series of comb modes can serve as frequency markers that are traceable to a microwave frequency standard. However, a mode distribution that is too discrete limits the spectral sampling interval to the mode frequency spacing even though individual mode linewidth is sufficiently narrow. Here, using a combination of a spectral interleaving and dual-comb spectroscopy in the terahertz (THz) region, we achieved a spectral sampling interval equal to the mode linewidth rather than the mode spacing. The spectrally interleaved THz comb was realized by sweeping the laser repetition frequency and interleaving additional frequency marks. In low-pressure gas spectroscopy, we achieved an improved spectral sampling density of 2.5?MHz and enhanced spectral accuracy of 8.39 × 10?7 in the THz region. The proposed method is a powerful tool for simultaneously achieving high resolution, high accuracy, and broad spectral coverage in THz spectroscopy.

Hsieh, Yi-Da; Iyonaga, Yuki; Sakaguchi, Yoshiyuki; Yokoyama, Shuko; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Araki, Tsutomu; Yasui, Takeshi

2014-01-01

174

Thermal denaturation of protein studied by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

175

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

NASA Astrophysics Data System (ADS)

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.

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

176

Total Internal Reflection with Fluorescence Correlation Spectroscopy  

Microsoft Academic Search

\\u000a The method in which total internal reflection illumination is combined with fluorescence correlation spectroscopy (TIR-FCS)\\u000a is reviewed. Included are descriptions of the conceptual basis and experimental design, as well as a variety of applications\\u000a and the theoretical models associated with these measurements. Emerging, more complex versions of TIR-FCS, related techniques,\\u000a and possible future directions for TIR-FCS are also outlined.

Nancy L. Thompson; Punya Navaratnarajah; Xiang Wang

177

Long-Range Hydration Effect of Lipid Membrane Studied by Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

The hydration state of biomolecules is believed to affect their self-assembly. The hydration state of phospholipid bilayers is studied precisely by terahertz spectroscopy, by which water perturbed by a lipid membrane is detected sensitively from the observation of the relaxation dynamics of water molecules in the subpicosecond time scale. Combined with x-ray observation of the lamellar structure of the lipid, a long-range hydration effect on up to 4-5 layers of water is confirmed. Most water molecules in the lamellae fall into the hydration water, and condensation of them is also indicated.

Hishida, M.; Tanaka, K.

2011-04-01

178

Applying terahertz time-domain spectroscopy to probe the evolution of kerogen in close pyrolysis systems  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) has been used to probe the evolutionary paths of kerogen in selected black mudstone. The evolutionary regime of kerogens (for instance, the immaturity, early maturity, middle maturity, late maturity, and catagenesis stages) can be indicated by the absorption coefficient in the THz region. The present study of identification based on THz-TDS was in good agreement with programmed pyrolysis experiments and suggests that THz technology can act as a nondestructive, contact-free tool for probing the ability to generate hydrocarbons from kerogens.

Bao, RiMa; Wu, ShiXiang; Zhao, Kun; Zheng, LunJu; Xu, ChangHong

2013-08-01

179

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

PubMed Central

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.

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

2012-01-01

180

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

NASA Astrophysics Data System (ADS)

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.

Jiang, Dejun; Zhao, Shusen; Shen, Jingling

2008-03-01

181

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

NASA Astrophysics Data System (ADS)

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 ?-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 ?-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.

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

2012-07-01

182

Torsional Vibrational Modes of Tryptophan Studied by Terahertz Time-Domain Spectroscopy  

PubMed Central

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 (?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.

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

2004-01-01

183

Atomic charge distribution in sodosilicate glasses from terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy has been used to extract the light-to-vibration coupling coefficient for sodosilicate glasses, from which it was possible to calculate the variance in the distribution of uncorrelated charges. It was found that increasing the sodium content of the glasses increased the standard deviation of the uncorrelated charge distribution in a linear fashion, and was almost an order of magnitude higher when compared to the charge distribution for pure silica reported previously, in agreement with previously published simulation data.

Parrott, Edward P. J.; Zeitler, J. Axel; Simon, Guilhem; Hehlen, Bernard; Gladden, Lynn F.; Taraskin, Sergei N.; Elliott, Stephen R.

2010-10-01

184

Multichannel terahertz time-domain spectroscopy system at 1030 nm excitation wavelength.  

PubMed

We present Terahertz (THz) imaging with a 1D multichannel time-domain spectroscopy (TDS) system which operates with a photoconductive array of 15 detection channels excited by a 1030 nm femtosecond fiber laser. The emitter and detector are photoconductive antennas based on InGaAs/InAlAs multi-layer heterostructures (MLHS). We characterized the THz optics and the resolution of the system. The performance is demonstrated by the multichannel imaging of two samples. A simultaneous measurement of 15 THz pulses with a pixel pitch of 1 mm increases the measurement speed of the TDS system by factor 15. PMID:24921495

Brahm, Anika; Wilms, Annika; Dietz, Roman J B; Göbel, Thorsten; Schell, Martin; Notni, Gunther; Tünnermann, Andreas

2014-06-01

185

Investigation of thermal denaturation of solid bovine serum albumin by terahertz dielectric spectroscopy  

NASA Astrophysics Data System (ADS)

We investigate the thermal denaturation of solid bovine serum albumin (BSA) using terahertz time domain spectroscopy (THz-TDS). When the protein 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 6.52 kJ/(K·mol), which can be an indicator for the stability of BSA during thermal denaturation process.

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

2013-10-01

186

Terahertz imaging and spectroscopy of large-area single-layer graphene  

Microsoft Academic Search

We demonstrate terahertz (THz) imaging and spectroscopy of a 15x15-mm^2\\u000asingle-layer graphene film on Si using broadband THz pulses. The THz images\\u000aclearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing\\u000aus to measure sheet conductivity with sub-mm resolution without fabricating\\u000aelectrodes. The THz carrier dynamics are dominated by intraband transitions and\\u000athe THz-induced electron motion is

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

2011-01-01

187

Causality-based method for determining the time origin in terahertz emission spectroscopy.  

PubMed

We propose a method for determining the time origin on the basis of causality in terahertz (THz) emission spectroscopy. The method is formulated in terms of the singly subtractive Kramers-Kronig relation, which is useful for the situation where not only the amplitude spectrum but also partial phase information is available within the measurement frequency range. Numerical analysis of several simulated and observed THz emission data shows that the misplacement of the time origin in THz waveforms can be detected by the method with an accuracy that is an order of magnitude higher than the given temporal resolutions. PMID:21716518

Unuma, Takeya; Ino, Yusuke; Peiponen, Kai-Erik; Vartiainen, Erik M; Kuwata-Gonokami, Makoto; Hirakawa, Kazuhiko

2011-06-20

188

Assessment of terahertz spectroscopy to detect antibiotic residues in food and feed matrices.  

PubMed

We report the use of terahertz (THz) spectroscopy to explore the spectral properties of eleven antibiotics commonly used in livestock production. Eight of the eleven antibiotics showed specific fingerprints in the frequency range between 0.1 and 2 THz. The main spectral features of two antibiotics (doxycycline and sulfapyridine) were still detectable when they were mixed with three food matrices (feed, milk, and egg powder). These preliminary results indicate that THz spectroscopy could be suitable for screening applications to detect the presence of antibiotic residues in the food industry, with the prospect to allow inspections directly on the production lines. THz spectroscopy is a non-destructive, non-contact, and real-time technique that requires very little sample preparation. Moreover, THz radiation can penetrate plastic and paper, which enables the detection of antibiotics in packaged food. PMID:21336350

Redo-Sanchez, Albert; Salvatella, Gerard; Galceran, Regina; Roldós, Eva; García-Reguero, José-Antonio; Castellari, Massimo; Tejada, Javier

2011-04-21

189

Soft tissue differentiation by diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Laser surgery gives the possibility to work remotely which leads to high precision, little trauma and high level sterility. However these advantages are coming with the lack of haptic feedback during the laser ablation of tissue. Therefore additional means are required to control tissue-specific ablation during laser surgery supporting the surgeon regardless of experience and skills. Diffuse Reflectance Spectroscopy provides a straightforward and simple approach for optical tissue differentiation. We measured diffuse reflectance from four various tissue types ex vivo. We applied Linear Discriminant Analysis (LDA) to differentiate the four tissue types and computed the area under the ROC curve (AUC). Special emphasis was taken on the identification of nerve as the most crucial tissue for maxillofacial surgery. The results show a promise for differentiating soft tissues as guidance for tissue-specific laser surgery by means of the diffuse reflectance.

Zam, Azhar; Stelzle, Florian; Nkenke, Emeka; Tangermann-Gerk, Katja; Schmidt, Michael; Adler, Werner; Douplik, Alexandre

2009-07-01

190

Effect of solvent on carrier transport in poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) studied by terahertz and infrared-ultraviolet spectroscopy  

NASA Astrophysics Data System (ADS)

The effect of solvent such as ethylene glycol (EG) on the carrier transport in poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) was studied by the combination of terahertz (THz) time-domain transmission spectroscopy (0.1-3 THz) and broadband reflectance spectroscopy (4-800 THz). While the broadband reflectance showed a plasma edge in the near-infrared, the frequency dependence of the THz conductivity of PEDOT/PSS indicated weakly localized carrier behavior. The simultaneous fitting of both spectra by the localization-modified Drude model allowed us to conclude that the significant increase in conductivity with the addition of EG is due to improved carrier mobility in the PEDOT/PSS.

Yamashita, Masatsugu; Otani, Chiko; Shimizu, Masahiro; Okuzaki, Hidenori

2011-10-01

191

Terahertz surface plasmons for subwavelength sensing and spectroscopy  

Microsoft Academic Search

At THz frequencies, certain semiconductors support confined surface plasmons (SPs). Here we show that THz surface plasmons can be utilized to overcome the diffraction limit when performing spectroscopy on very thin samples of analyte. We present measurements of SP propagation on an InSb surface overlayed with thin polymer dielectric films, and show that the SP on the InSb surface is

Tom H. Isaac; William L. Barnes; Euan Hendry

2008-01-01

192

Terahertz-frequency electrical conductivity measurements of ultrashort laser-ablated plasmas  

Microsoft Academic Search

We investigate the phase transitions of intense ultrashort laser-heated solids, from the cold solid to the hot dense plasma state, by measuring the complex electrical conductivity (or refractive index) transients at terahertz (1 THz = 1012 Hz) frequencies. Using optical-pump, terahertz-probe spectroscopy, we measured the phase shifts and absorption of terahertz probe pulses that were reflected from the warm dense

K. Y. Kim; B. Yellampelle; J. H. Glownia; A. J. Taylor; G. Rodriguez

2006-01-01

193

Insulin amyloid fibrillation studied by terahertz spectroscopy and other biophysical methods  

SciTech Connect

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.

Liu, Rui [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)] [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); He, Mingxia [College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072 (China)] [College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072 (China); Su, Rongxin, E-mail: surx@tju.edu.cn [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China) [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Tianjin Key Laboratory of Membrane Science and Desalination Technology, Tianjin University, Tianjin 300072 (China); Yu, Yanjun [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)] [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Qi, Wei; He, Zhimin [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China) [State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Tianjin Key Laboratory of Membrane Science and Desalination Technology, Tianjin University, Tianjin 300072 (China)

2010-01-01

194

Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy  

SciTech Connect

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.

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

2007-04-01

195

Speckle in active millimeter-wave and terahertz imaging and spectroscopy  

NASA Astrophysics Data System (ADS)

Wideband millimeter-wave imaging techniques and systems have been developed at Pacific Northwest National Laboratory (PNNL) for concealed weapon detection and other applications. These techniques evolved from singlefrequency 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 its 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.

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

2007-05-01

196

Terahertz Time-Domain Spectroscopy of Atmospheric Water Vapor from 0.4 to 2.7 THz.  

National Technical Information Service (NTIS)

We conducted broadband absorption measurements of atmospheric water vapor in the ground state, X (sup 1)A(sub 1) (000), from 0.4 to 2.7 THz with a pressure broadening-limited resolution of 6.2 GHz using pulsed, terahertz time-domain spectroscopy (THz-TDS)...

R. J. Foltynowicz R. E. Allman

2005-01-01

197

Frequency-Comb-Assisted Terahertz Quantum Cascade Laser Spectroscopy  

NASA Astrophysics Data System (ADS)

We report a metrological-grade THz spectroscopy based on the combination of a THz frequency-comb synthesizer (FCS) and a THz quantum cascade laser (QCL). The QCL, emitting at 2.5 THz, is phase locked to the free-space THz FCS, and its frequency is swept across a methanol transition by tuning the comb-repetition rate, which is ultimately disciplined by the Cs primary frequency standard. The absolute frequency scale provides an uncertainty of a few parts in 10-11 on the laser frequency and 10-9 on the line-center determination, ranking this technique among the most precise ever developed in the THz range.

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

2014-04-01

198

Terahertz time-domain spectroscopy and the quantitative monitoring of mechanochemical cocrystal formation  

NASA Astrophysics Data System (ADS)

Terahertz (THz) radiation probes intermolecular interactions through crystal lattice vibrations, allowing the characterization of solid materials. Thus, THz spectroscopy is a promising alternative to mainstream solid-state analytical tools such as X-ray diffraction or thermal analysis. The method provides the benefits of online measurement, remote sampling and three-dimensional imaging, all of which are attractive for quality control and security applications. In the context of pharmaceutical solids, THz spectroscopy can differentiate and quantify different forms of active pharmaceutical ingredients. Here, we apply this technique to monitor a dynamic process involving two molecular crystals. In particular, we follow the mechanochemical construction of a two-component cocrystal by grinding together phenazine (phen) and mesaconic acid (mes). To rationalize the observed changes in the spectra, we conduct lattice dynamics calculations that lead to the tentative assignment of at least one feature in the cocrystal THz spectrum.

Lien Nguyen, K.; Friš?i?, Tomislav; Day, Graeme M.; Gladden, Lynn F.; Jones, William

2007-03-01

199

Monitoring the reaction between AlCl3 and o-xylene by using terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are measured by using THz-TDS. The o-xylene carries out isomerization reaction in the presence of catalyst AlCl3. The absorption coefficient of the mixed reaction solution is extracted and analyzed in the frequency range from 0.2 THz to 1.4 THz. The temperature dependence of the absorption coefficient, which is influenced by both the dissolution of AlCl3 and the production of the two other isomer resultants, is obtained, and it can indicate the process of the isomerization reaction. The results suggest that THz spectroscopy can be used to monitor the isomerization reaction and other reactions in chemical synthesis, petrochemical and biomedical fields.

Jin, Wu-Jun; Li, Tao; Zhao, Kun; Zhao, Hui

2013-11-01

200

Sub-terahertz resonance spectroscopy of biological macromolecules and cells  

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

201

Terahertz spectroscopy of shift currents resulting from asymmetric (110)-oriented GaAs/AlGaAs quantum wells  

SciTech Connect

We report the observation and the study of an additional shift current tensor element in (110)-oriented GaAs quantum wells, which arises from an out-of-plane asymmetry of the quantum well structure. The current resulting from this tensor element is optically induced with 150 fs laser pulses and detected by measuring the simultaneously emitted terahertz radiation. This terahertz spectroscopy of shift currents is a powerful technique for symmetry investigations, which shows, for example, that our nominally symmetric (110)-oriented GaAs/AlGaAs quantum wells grown by molecular beam epitaxy are in reality asymmetric structures with different right and left interfaces.

Priyadarshi, Shekhar; Leidinger, Markus; Pierz, Klaus; Racu, Ana M.; Siegner, Uwe; Bieler, Mark [Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig (Germany); Dawson, Philip [School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom)

2009-10-12

202

Measurement of carrier concentration captured by InAs/GaAs quantum dots using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

The authors investigated the carrier dynamics of n-type modulation-doped InAs/GaAs quantum dots (QDs) using terahertz time-domain spectroscopy to estimate the total number of electrons captured by the QDs. The terahertz power absorption of the sample with QDs was less than that of the sample without QDs. This is attributed to the fact that the carriers are confined in the QDs. The experiment results were fitted into the Drude model and the number of electrons captured by QDs was determined through the difference in the numbers of free electrons of the samples with and without QDs.

Oh, Seung Jae; Kang, Chul; Maeng, Inhee; Son, Joo-Hiuk; Cho, Nam Ki; Song, Jin Dong; Choi, Won Jun; Cho, Woon-Jo; Lee, Jung Il

2007-03-01

203

Ultrafast terahertz spectroscopy for measuring carrier dynamics in nanoscale photovoltaic materials  

NASA Astrophysics Data System (ADS)

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 ?J, 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.

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

2010-02-01

204

Compact diode-laser-based system for continuous-wave and quasi-time-domain terahertz spectroscopy.  

PubMed

We present a multimodal diode-laser-based terahertz (THz) spectroscopy system. In contrast to other laser-based THz setups that provide either cw or broadband THz generation, our configuration combines the advantages of both approaches. Our low complexity setup enables fast switching from cw difference frequency generation to broadband THz emission, enabling sophisticated data analysis like much more complex time domain spectroscopy systems. PMID:21124545

Brenner, Carsten; Hofmann, Martin; Scheller, Maik; Shakfa, Mohammad Khaled; Koch, Martin; Mayorga, Iván Cámara; Klehr, Andreas; Erbert, Götz; Tränkle, Günther

2010-12-01

205

Optical Reflection Spectroscopy of GEO Objects  

NASA Technical Reports Server (NTRS)

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.

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

2013-01-01

206

Materials for terahertz science and technology  

Microsoft Academic Search

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

Bradley Ferguson; Xi-Cheng Zhang

2002-01-01

207

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

SciTech Connect

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.

Yamamoto, Kohji; Yamaguchi, Mariko; Tani, Masahiko; Hangyo, Masanori; Teramura, Satoshi; Isu, Toshiro; Tomita, Naohide [Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871 (Japan); Graduate School of Material Science, Nara Institute of Science and Technology (NAIST), 8916-5, Takayama, Ikoma, Nara, 630-0101 (Japan); International Innovation Center, Kyoto University, Yoshida-Hon-machi, Sakyo-ku, Kyoto, 606-8501 (Japan)

2004-11-29

208

Probing the sulfur content in gasoline quantitatively with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) was used for the quantitative detection of sulfur content in gasoline. Models of chemo metrics methods and partial least squares (PLS) were built to measure THz-TDS and the sulfur content. All of the samples were divided into two parts. One part was used for calibration and the other one for validation. In order to evaluate the quality of the models, the correlation coefficient ( R) and root-mean-square errors (RMSE) of calibration and validation models were calculated. The value of R and RMSE were close to 1 and 0 within acceptable levels, respectively, indicating that the combination of THz-TDS and PLS is a potential method for further quantitative detection.

Qin, FangLi; Li, Qian; Zhan, HongLei; Jin, WuJun; Liu, HongLan; Zhao, Kun

2014-07-01

209

Probing the sulfur content in gasoline quantitatively with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) was used for the quantitative detection of sulfur content in gasoline. Models of chemo metrics methods and partial least squares (PLS) were built to measure THz-TDS and the sulfur content. All of the samples were divided into two parts. One part was used for calibration and the other one for validation. In order to evaluate the quality of the models, the correlation coefficient (R) and root-mean-square errors (RMSE) of calibration and validation models were calculated. The value of R and RMSE were close to 1 and 0 within acceptable levels, respectively, indicating that the combination of THz-TDS and PLS is a potential method for further quantitative detection.

Qin, FangLi; Li, Qian; Zhan, HongLei; Jin, WuJun; Liu, HongLan; Zhao, Kun

2014-04-01

210

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

NASA Astrophysics Data System (ADS)

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.

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

2012-04-01

211

Detection of harmful residues in honey using terahertz time-domain spectroscopy.  

PubMed

Terahertz time-domain spectroscopy (THz-TDS) has been applied for the detection and discrimination of harmful chemical residues in honey. Three antibiotics (sulfapyridine, sulfathiazole, and tetracycline) and two acaricides (coumaphos and amitraz) were characterized in the THz frequency regime between 0.5 THz and 6.0 THz. All chemical substances present distinct absorption peaks. THz transmission measurements of honey mixtures with antibiotics have been performed, revealing that antibiotic residues are traceable in highly absorptive food products, such as honey, at concentrations down to 1% weight percentage, thanks to their THz fingerprints. Moreover, multiple antibiotics were identified in their mixture with honey, pointing out the potential of the technique to be used in the near future as a fast, real-time technique for detecting and discriminating multi-residues strictly related to food safety issues. PMID:24160877

Massaouti, Maria; Daskalaki, Christina; Gorodetsky, Andrei; Koulouklidis, Anastasios D; Tzortzakis, Stelios

2013-11-01

212

Time-resolved terahertz spectroscopy and Hall measurement on chromium vanadium thin films  

NASA Astrophysics Data System (ADS)

We have measured the low-frequency dynamical conductivity of Cr1-xVx thin films through the quantum phase transition at x 0.35 using terahertz time-domain spectroscopy. From Drude model fits we have determined the plasma frequency ?p of samples over concentrations x=0-0.1 and temperatures 10--300 K. We have compared these to the Hall resistance RH on the same samples and found that both reveal the opening of the spin-density wave gap. At high temperatures ?p^21/RH, but as the temperature is lowered below 75 K, 1/RH falls more rapidly than ?p^2. We will relate these observations to a theoretical model based on a realistic Fermi surface.

Farahani, Amir; Kamal, Saeid; Fullerton, Eric; Dodge, J. Steven

2010-03-01

213

Application of terahertz spectroscopy to the characterization of biological samples using birefringence silicon grating.  

PubMed

We present a device and method for performing vector transmission spectroscopy on biological specimens at terahertz (THz) frequencies. The device consists of artificial dielectric birefringence obtained from silicon microfluidic grating structures. The device can measure the complex dielectric function of a liquid, across a wide THz band of 2 to 5.5 THz, using a Fourier transform infrared spectrometer. Measurement data from a range of liquid specimens, including sucrose, salmon deoxyribonucleic acid (DNA), herring DNA, and bovine serum albumin protein solution in water are presented. The specimen handling is simple, using a microfluidic channel. The transmission through the device is improved significantly and thus the measurement accuracy and bandwidth are increased. PMID:22734784

Saha, Shimul C; Grant, James P; Ma, Yong; Khalid, Ata; Hong, Feng; Cumming, David R S

2012-06-01

214

Terahertz spectroscopy on Rb1-xFe2-ySe2  

NASA Astrophysics Data System (ADS)

Single crystals of superconducting and non-superconducting Rb1-xFe2-ySe2 [1] have been investigated by terahertz time-domain transmission spectroscopy as a function of temperature. In the superconducting samples, we observe the signatures of the superconducting transition [2] and an isosbestic point in the temperature dependence of optical conductivity in the vicinity of 100 K, which could be related to the reported phase separation in these compounds. In the non-superconducting samples, the optical conductivity exhibits features which can be interpreted in terms of spin wave excitations in agreement with neutron experiments [3].[4pt] [1] V. Tsurkan et al. Phys. Rev. B 84, 144520 (2011)[0pt] [2] A. Charnukha et al. Phys. Rev. B 85, 100504 (2012)[0pt] [3] Miaoyin Wang et al. Nature Communications 2, 580 (2011)

Wang, Zhe; Fisher, Jonas; Schmidt, Michael; Tsurkan, Vladimir; Loidl, Alois; Deisenhofer, Joachim

2013-03-01

215

Infrared spectroscopy of tunable Dirac terahertz magneto-plasmons in graphene.  

PubMed

We present infrared spectroscopy study of plasmon excitations in graphene in high magnetic fields. The plasmon resonance in patterned graphene disks splits into edge and bulk plasmon modes in magnetic fields. Remarkably, the edge plasmons develop increasingly longer lifetimes in high fields due to the suppression of backscattering. Moreover, due to the linear band structure of graphene, the splitting of the edge and bulk plasmon modes develops a strong doping dependence, which differs from the behavior of conventional semiconductor two-dimensional electron gas (2DEG) systems. We also observe the appearance of a higher order mode indicating an anharmonic confinement potential even in these well-defined circular disks. Our work not only opens an avenue for the investigation of the properties of Dirac magnetoplasmons but also supports the great potential of graphene for tunable terahertz magneto-optical devices. PMID:22690695

Yan, Hugen; Li, Zhiqiang; Li, Xuesong; Zhu, Wenjuan; Avouris, Phaedon; Xia, Fengnian

2012-07-11

216

Cooling dynamics of photoexcited carriers in Si studied using optical pump and terahertz probe spectroscopy  

NASA Astrophysics Data System (ADS)

We investigated the photoexcited carrier dynamics in Si by using optical pump and terahertz probe spectroscopy in an energy range between 2 and 25 meV. The formation dynamics of excitons from unbound e-h pairs was studied through the emergence of the 1s-2p transition of excitons at 12 meV (3 THz). We revealed the thermalization mechanism of the photoinjected hot carriers (electrons and holes) in the low-temperature lattice system by taking account of the interband and intraband scattering of carriers with acoustic and optical phonons. The overall cooling rate of electrons and holes was numerically calculated on the basis of a microscopic analysis of the phonon scattering processes, and the results well account for the experimentally observed carrier cooling dynamics. The long formation time of excitons in Si after the above-gap photoexcitation is reasonably accounted for by the thermalization process of photoexcited carriers.

Suzuki, Takeshi; Shimano, Ryo

2011-02-01

217

Terahertz imaging and spectroscopy of large-area single-layer graphene.  

PubMed

We demonstrate terahertz (THz) imaging and spectroscopy of a 15 × 15-mm2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from ?(s) = 1.7 × 10(-3) to 2.4 × 10(-3) ?(-1) (sheet resistance, ?(s) = 420 - 590 ?/sq). PMID:21263550

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

2011-01-01

218

High-speed terahertz time-domain spectroscopy based on electronically controlled optical sampling.  

PubMed

We demonstrate high-speed terahertz (THz) time-domain spectroscopy based on electronically controlled optical sampling (ECOPS). The ECOPS system utilizes two synchronized Ti:sapphire femtosecond lasers with a 100 MHz repetition frequency. The time delay between the two laser pulses is demonstrated to be rapidly swept at a scan rate of 1 kHz on a time delay window of 77 ps by using an external offset voltage applied to a locking electronics. It is shown that a THz pulse can be exactly measured by ECOPS, as is done by asynchronous optical sampling (ASOPS), and the measurement time is shortened by a factor of 50 by using ECOPS compared with ASOPS in the case of employing 100 MHz repetition-rate lasers. PMID:21081973

Kim, Youngchan; Yee, Dae-Su

2010-11-15

219

High spectral resolution reflectance spectroscopy of minerals  

USGS Publications Warehouse

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

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

1990-01-01

220

Reflectance spectroscopy of organic compounds: 1. Alkanes  

USGS Publications Warehouse

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.

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

2009-01-01

221

Characterisation of the Cartilage/Bone Interface Utilising Reflectance Spectroscopy.  

National Technical Information Service (NTIS)

Optical reflection spectra of the cartilage/bone interface from hip joints of cows were studied. When comparing to ultrasonic measurement, it was found that cartilage thickness could be extracted using optical reflectance spectroscopy. For thicker cartila...

P. A. Oberg T. Sundqvist A. Johansson M. Sundberg

2001-01-01

222

High Speed Terahertz Pulse Imaging in the Reflection Geometry and Image Quality Enhancement by Digital Image Processing  

NASA Astrophysics Data System (ADS)

We describe the formation and enhancement of two dimensional pulsed terahertz (THz) images obtained in the reflection geometry with a high-speed optical delay line. Two test objects are imaged and analyzed with respect to material information and concealed structure. Clear THz images were obtained with various imaging modes and were compared with the X-ray images. The THz image of a sample revealed material features that the X-ray image cannot distinguish. We could enhance the THz image quality using various image processing techniques, such as edge detection, de-noising, high-pass filtering, and wavelet filtering.

Shon, Chae-Hwa; Chong, Won-Yong; Jeon, Seok-Gy; Kim, Geun-Ju; Kim, Jung-Il; Jin, Yun-Sik

2008-01-01

223

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

PubMed

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. PMID:22784643

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

2012-08-01

224

Reflectance anisotropy spectroscopy of magnetite (110) surfaces  

NASA Astrophysics Data System (ADS)

Reflectance anisotropy spectroscopy (RAS) has been used to measure the optical anisotropies of bulk and thin-film Fe3O4(110) surfaces. The spectra indicate that small shifts in energy of the optical transitions, associated with anisotropic strain or electric field gradients caused by the (110) surface termination or a native oxide layer, are responsible for the strong signal observed. The RAS response was then measured as a function of temperature. A distinct change in the RAS line-shape amplitude was observed in the spectral range from 0.8 to 1.6 eV for temperatures below the Verwey transition of the crystal. Finally, thin-film magnetite was grown by molecular beam epitaxy on MgO(110) substrates. Changes in the RAS spectra were found for different film thickness, suggesting that RAS can be used to monitor the growth of magnetite (110) films in situ. The thickness dependence of the RAS is discussed in terms of various models for the origin of the RAS signal.

Fleischer, K.; Verre, R.; Mauit, O.; Sofin, R. G. S.; Farrell, L.; Byrne, C.; Smith, C. M.; McGilp, J. F.; Shvets, I. V.

2014-05-01

225

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

Microsoft Academic Search

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

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

2000-01-01

226

Very Slow Cooling Dynamics of Photoexcited Carriers in Graphene Observed by Optical-Pump Terahertz-Probe Spectroscopy  

Microsoft Academic Search

Using optical-pump terahertz-probe spectroscopy, we study the relaxation dynamics of photoexcited carriers in graphene at different temperatures. We find that at lower temperatures the tail of the relaxation transients as measured by the differential probe transmission becomes slower, extending beyond several hundred picoseconds at temperatures below 50K. We interpret the observed relaxation transients as resulting from the cooling of the

Jared H. Strait; Haining Wang; Shriram Shivaraman; Virgil Shields; Michael Spencer; Farhan Rana

2011-01-01

227

Terahertz time-domain spectroscopy: A new tool for the study of glasses in the far infrared  

Microsoft Academic Search

Terahertz time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of polycrystalline quartz, amorphous silica, Pyrex and BK7 glasses. The results were analyzed in terms of the power-law model of far-infrared absorption. Evidence of the Boson peak was seen in the absorption spectra. Relationships were observed between THz absorption and refractive indices on the one hand,

M. Naftaly; R. E. Miles

2005-01-01

228

Quantitative measurement of AMS and orange mixtures by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time domain spectroscopy (THz-TDS) is a new kind of nondestructive detection method, frequency of terahertz wave spans from a few tens of GHz to several THz, which is used to detect material because of its strong identification, it can supply rich vibration information caused by intermolecular and large intra-molecular. Ammonium sulfamate (AMS) is a kind of herbicide, it has special value for many woody plants, which can prevent annual weeds. The excess use of pesticide is a huge threaten for human health in recent years, thus the research on detection of pesticide has absolutely important meaning, in this paper, pure AMS and mixture samples of AMS and orange are measured using THz-TDS, and their absorption coefficient are calculated by the model, which is put forward based on Fresnel equation. We qualitatively analyze the absorption coefficient spectra of pure AMS, which is useful for us to identify the pesticide in agriculture products. Meanwhile, we measured 14 mixture samples of AMS and orange, the weight ratio of mixtures are from 0% to 59.9%. Nine samples are considered as calibration set and the other five samples are regarded as prediction set, to quantitatively analyze the concentration of AMS by the partial least squares (PLS), the result shows that the prediction error is less then 4.5%, in addition, the relationship of the average absorption and weight ratio are absolutely linear. The experiment demonstrates that THz-TDS is promising and efficient to quantitatively detect the component of mixtures, and it has important reference value for the detection of pesticide in agriculture food.

Wang, Qiang; Ma, Yehao; Wang, Xiaowei

2012-05-01

229

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)

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.

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

2009-12-01

230

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

NASA Astrophysics Data System (ADS)

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.

Hoshina, Hiromichi; Ishii, Shinya; Otani, Chiko

2014-07-01

231

Broadband microwave and time-domain terahertz spectroscopy of chemical vapor deposition grown graphene  

Microsoft Academic Search

We report a study of the complex AC impedance of chemical vapor deposition grown graphene. We measure the explicit frequency dependence of the complex impedance and conductance over the microwave and terahertz range of frequencies using our recently developed broadband microwave Corbino and time domain terahertz spectrometers (TDTS). We demonstrate how one may resolve a number of technical difficulties in

W. Liu; R. Valdés Aguilar; Yufeng Hao; R. S. Ruoff; N. P. Armitage

2011-01-01

232

Structure-property correlation in glasses by infrared reflectance spectroscopy  

Microsoft Academic Search

The two methods of analysis of infrared reflectance data, i.e. the Kramers-Kronig inversion and the fitting of reflectivity using classical dispersion theory, are reviewed and shown to lead to equivalent results. The potential of infrared reflectance spectroscopy for the quantitative determination of glass structure is demonstrated by showing how proper data analysis can lead to the evaluation of the fraction

E. I. Kamitsos; Y. D. Yiannopoulos; C. P. Varsamis; H. Jain

1997-01-01

233

Graphene terahertz sources and amplifiers  

Microsoft Academic Search

Plasmons in population inverted graphene can experience extremely large gain through the process of stimulated emission at terahertz frequencies. The large gain values and the small plasmon wavelengths can lead to compact terahertz plasmon lasers and amplifiers that are only a few microns in size. We present optical and terahertz spectroscopy results for carrier relaxation and recombination dynamics in graphene

F. Rana; P. A. George; J. H. Strait; J. Dawlaty

2008-01-01

234

Noncovalent interactions in paired DNA nucleobases investigated by terahertz spectroscopy and solid-state density functional theory.  

PubMed

Cocrystallized adenine and thymine derivatives, along with the pure monomeric crystals, were investigated by terahertz spectroscopy and solid-state density functional theory (DFT). The methylated nucleobase derivatives crystallize in planar hydrogen-bonded adenine-thymine pairs similar to the manner found in DNA. The spectra obtained for 1-methylthymine, 9-methyladenine, and the 1:1 cocrystal in the range of 10-100 cm(-1) clearly demonstrate that absorptions in this spectral range originate from the uniquely ordered assembly and the intermolecular interactions found in each individual crystal system. The quality of spectral reproduction for the DFT simulations of each system was clearly improved by the inclusion of an empirical correction term for London-type dispersion forces to the calculations. Notably, it was found that these weak dispersion forces in the adenine-thymine cocrystal were necessary to produce a properly converged crystal structure and meaningful simulation of the terahertz vibrational spectrum. PMID:21446683

King, Matthew D; Ouellette, Wayne; Korter, Timothy M

2011-09-01

235

Monitoring plant drought stress response using terahertz time-domain spectroscopy.  

PubMed

We present a novel measurement setup for monitoring changes in leaf water status using nondestructive terahertz time-domain spectroscopy (THz-TDS). Previous studies on a variety of plants showed the principal applicability of THz-TDS. In such setups, decreasing leaf water content directly correlates with increasing THz transmission. Our new system allows for continuous, nondestructive monitoring of the water status of multiple individual plants each at the same constant leaf position. It overcomes previous drawbacks, which were mainly due to the necessity of relocating the plants. Using needles of silver fir (Abies alba) seedlings as test subjects, we show that the transmission varies along the main axis of a single needle due to a variation in thickness. Therefore, the relocation of plants during the measuring period, which was necessary in the previous THz-TDS setups, should be avoided. Furthermore, we show a highly significant correlation between gravimetric water content and respective THz transmission. By monitoring the relative change in transmission, we were able to narrow down the permanent wilting point of the seedlings. Thus, we established groups of plants with well-defined levels of water stress that could not be detected visually. This opens up the possibility for a broad range of genetic and physiological experiments. PMID:24501000

Born, Norman; Behringer, David; Liepelt, Sascha; Beyer, Sarah; Schwerdtfeger, Michael; Ziegenhagen, Birgit; Koch, Martin

2014-04-01

236

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

NASA Astrophysics Data System (ADS)

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 ?erenkov-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 ?erenkov-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.

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

2014-01-01

237

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

PubMed

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. PMID:15260559

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

2004-07-01

238

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

PubMed Central

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.

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

2012-01-01

239

Time-domain terahertz spectroscopy and applications on drugs and explosives  

NASA Astrophysics Data System (ADS)

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.

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

240

Terahertz time-domain spectroscopy as a new tool for the characterization of dust forming plasmas  

NASA Astrophysics Data System (ADS)

We report the application of terahertz time-domain spectroscopy as a new tool for plasma diagnostics. The short broadband THz pulses were radiated from a low temperature grown GaAs emitter by free charge carriers which were generated by focusing a 20 femtosecond TiSa-laser pulse onto the emitter. For sensitive signal recording a coherent detection scheme was applied. This allowed the measurement of the amplitude and sign of the electromagnetic field of the THz pulse after passing the plasma chamber. Fourier transformation allowed us to obtain the full spectrum in the frequency domain. We compared the transmitted THz intensities of a pure argon (Ar) and an acetylene (C2H2)/argon plasma. The presence of the ethynyl-radical (CCH) and cyclopropenylidene (c-C3H2) in the (C2H2)/argon plasma could be confirmed by the observations of rotational transitions in the region from 8 to 16 cm-1 corresponding to 0.3-0.5 THz.

Ebbinghaus, S.; Schröck, K.; Schauer, J. C.; Bründermann, E.; Heyden, M.; Schwaab, G.; Böke, M.; Winter, J.; Tani, M.; Havenith, M.

2006-02-01

241

Terahertz polarization imaging  

NASA Astrophysics Data System (ADS)

We present a new method to measure the polarization state of a terahertz pulse by using a modified electro-optic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and terahertz images of a plastic coin. Both measurements show a sample-induced rotation of the terahertz electric field vector, which is surprisingly large and is a strong function of frequency. A promising aspect of our setup is the possibility of simultaneously measuring both transversal electric field components.

van der Valk, Nick C. J.; van der Marel, Willemine A. M.; Planken, Paul C. M.

2005-10-01

242

Terahertz polarization imaging.  

PubMed

We present a new method to measure the polarization state of a terahertz pulse by using a modified electro-optic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and terahertz images of a plastic coin. Both measurements show a sample-induced rotation of the terahertz electric field vector, which is surprisingly large and is a strong function of frequency. A promising aspect of our setup is the possibility of simultaneously measuring both transversal electric field components. PMID:16252780

van der Valk, Nick C J; van der Marel, Willemine A M; Planken, Paul C M

2005-10-15

243

Terahertz reconfigurable devices using graphene  

NASA Astrophysics Data System (ADS)

This paper reviews the first demonstrations of broadband graphene terahertz modulators as well as recent progress on reconfigurable terahertz devices using graphene. Although atom-thick, single layer graphene is capable of efficiently tuning terahertz absorption meanwhile introducing negligible insertion loss. Recent developments in terms of transmission-mode and reflection-mode electro-absorption modulators are reviewed. Moreover, an application of these devices is presented and discussed: arrays of graphene electro-absorption modulators as electrically reconfigurable patterns for terahertz cameras.

Sensale Rodriguez, Berardi; Xing, Huili G.

2013-09-01

244

Terahertz laser frequency combs  

NASA Astrophysics Data System (ADS)

Terahertz light can be used to identify numerous complex molecules, but has traditionally remained unexploited due to the lack of powerful broadband sources. Pulsed lasers can be used to generate broadband radiation, but such sources are bulky and produce only microwatts of average power. Conversely, although terahertz quantum cascade lasers are compact semiconductor sources of high-power terahertz radiation, their narrowband emission makes them unsuitable for complex spectroscopy. In this work, we demonstrate frequency combs based on terahertz quantum cascade lasers, which combine the high power of lasers with the broadband capabilities of pulsed sources. By fully exploiting the quantum-mechanically broadened gain spectrum available to these lasers, we can generate 5 mW of terahertz power spread across 70 laser lines. This radiation is sufficiently powerful to be detected by Schottky-diode mixers, and will lead to compact terahertz spectrometers.

Burghoff, David; Kao, Tsung-Yu; Han, Ningren; Chan, Chun Wang Ivan; Cai, Xiaowei; Yang, Yang; Hayton, Darren J.; Gao, Jian-Rong; Reno, John L.; Hu, Qing

2014-06-01

245

Coherent broadband continuous-wave terahertz spectroscopy on solid-state samples  

Microsoft Academic Search

Measuring the complex dielectric function ?(omega)=?1+i?2 of solid-state samples in the terahertz frequency range with high spectral resolution remains difficult. Using a continuous-wave terahertz spectrometer based on photomixing in the frequency range from 60 GHz to 1.8 THz, we obtain the most precise data of ?(omega) reported to date for the well-studied example of alpha-lactose monohydrate. We are able to

A. Roggenbuck; H. Schmitz; A. Deninger; I. Cámara Mayorga; J. Hemberger; R. Güsten; M. Grüninger

2010-01-01

246

Probing the collective vibrational dynamics of a protein in liquid water by terahertz absorption spectroscopy  

Microsoft Academic Search

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

Jing Xu; Kevin W. Plaxco; S. James Allen

2006-01-01

247

Contact resistance dynamics at bimetallic interfaces investigated by ultrafast terahertz surface plasmon-mediated transmission spectroscopy  

Microsoft Academic Search

We study free-space terahertz pulse propagation through samples of densely packed Cu microparticles that are coated with Au nano-layers. By coating the Cu particles with Au nano-layers, the terahertz transmission is dramatically attenuated. The substantial attenuation cannot be reconciled by the inherent resistivities of the Cu and Au metals. The experimental results strongly show that the transmission attenuation arises from

K. J. Chau; A. Y. Elezzabi

2006-01-01

248

Terahertz time-domain spectroscopy of atmospheric water vapor from 0.4 to 2.7 THz.  

SciTech Connect

We conducted broadband absorption measurements of atmospheric water vapor in the ground state, X {sup 1}A{sub 1} (000), from 0.4 to 2.7 THz with a pressure broadening-limited resolution of 6.2 GHz using pulsed, terahertz time-domain spectroscopy (THz-TDS). We measured a total of seventy-two absorption lines and forty-nine lines were identified as H{sub 2}{sup 16}O resonances. All the H{sub 2}{sup 16}O lines identified were confirmed by comparing their center frequencies to experimental values available in the literature.

Allman, Ronald E.; Foltynowicz, Robert J.

2005-10-01

249

Observation of salt effects on hydration water of lysozyme in aqueous solution using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy was used to investigate the salt effect of ammonium sulfate on the dynamics of hydration water of lysozyme in aqueous solution. The absorption coefficient of lysozyme aqueous solutions containing salt was subtracted by that of the water and ammonium sulfate contained in the lysozyme solution. The results revealed that ammonium sulfate increases the absorption coefficient of the hydration water, which indicates that the dynamics of the hydration water becomes faster and/or the number of hydration water molecules decreases with increasing ammonium sulfate concentration.

Aoki, Katsuyoshi; Shiraki, Kentaro; Hattori, Toshiaki

2013-10-01

250

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

NASA Astrophysics Data System (ADS)

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.

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

2006-08-01

251

Reflectance contrast spectroscopy for distinguishing between monolayer and bilayer graphene  

NASA Astrophysics Data System (ADS)

The authors report a reflectance contrast spectroscopy study to distinguish between monolayer and bilayer graphene on silicon dioxide covered silicon substrate. They describe a setup built for reflectance measurements with high spatial resolution, which uses a combination of a pin-hole and a microscope with a high magnification objective lens. The measured reflectance contrast spectra are subsequently compared with simulations in order to identify mono/bilayer graphene.

Saigal, Nihit; Ghosh, Sandip

2013-02-01

252

Characterization of cobaltite spinels by reflectance spectroscopy  

Microsoft Academic Search

The longitudinal (LO) frequencies as well as the transversal (TO) frequencies are determined in a series of cobaltite spinels: Co3O4, ZnCo2O4, MnCo2O4, FeCo2O4, CuCo2O4, and NiCo2O4. The data were obtained from the infrared reflectance spectra of thin layers on cobalt substrate.

B. Lefez; P. Nkeng; J. Lopitaux; G. Poillerat

1996-01-01

253

Reflectance spectroscopy of organic compounds: 1. Alkanes  

Microsoft Academic Search

Reflectance spectra of the organic compounds comprising the alkane series are presented from the ultraviolet to midinfrared, 0.35 to 15.5 mum. 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

Roger N. Clark; John M. Curchin; Todd M. Hoefen; Gregg A. Swayze

2009-01-01

254

Reflectance spectroscopy of organic compounds: 1. Alkanes  

Microsoft Academic Search

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

Roger N. Clark; John M. Curchin; Todd M. Hoefen; Gregg A. Swayze

2009-01-01

255

Experimental demonstration of reflectarray antennas at terahertz frequencies.  

PubMed

Reflectarrays composed of resonant microstrip gold patches on a dielectric substrate are demonstrated for operation at terahertz frequencies. Based on the relation between the patch size and the reflection phase, a progressive phase distribution is implemented on the patch array to create a reflector able to deflect an incident beam towards a predefined angle off the specular direction. In order to confirm the validity of the design, a set of reflectarrays each with periodically distributed 360 × 360 patch elements are fabricated and measured. The experimental results obtained through terahertz time-domain spectroscopy (THz-TDS) show that up to nearly 80% of the incident amplitude is deflected into the desired direction at an operation frequency close to 1 THz. The radiation patterns of the reflectarray in TM and TE polarizations are also obtained at different frequencies. This work presents an attractive concept for developing components able to efficiently manipulate terahertz radiation for emerging terahertz communications. PMID:23481746

Niu, Tiaoming; Withayachumnankul, Withawat; Ung, Benjamin S-Y; Menekse, Hakan; Bhaskaran, Madhu; Sriram, Sharath; Fumeaux, Christophe

2013-02-11

256

Combined theory of reflectance and emittance spectroscopy  

NASA Technical Reports Server (NTRS)

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.

Hapke, Bruce

1995-01-01

257

Strong optical reflection of rare-earth garnets in the terahertz regime by reststrahlen bands  

NASA Astrophysics Data System (ADS)

The reststrahlen bands of rare-earth garnets were investigated in the terahertz regime. Through this, it was found that the crystal orientation and light polarization directly influence the reststrahlen-related dielectric absorptions of Gd3Ga5O12 (GGG), which is attributed to restriction in the vibrational motion of Gd ions. A theoretical fit to the dielectric absorption revealed that the phonon-polariton frequency in GGG crystals at around 85.5 cm-1 exhibits a narrow spectral width of 100 GHz at room temperature, as estimated using a Lorentz oscillator model. In addition, it was found that the reststrahlen bands can be readily manipulated within a range of 0.7-3.7 THz by changing the chemical composition of the garnet.

Adachi, Masaki; Yamahara, Hiroyasu; Kawabe, Shunsuke; Matsui, Hiroaki; Tabata, Hitoshi

2014-05-01

258

Terahertz near-field spectroscopy of filled subwavelength sized apertures in thin metal films.  

PubMed

We have measured terahertz near-field spectra of cesium iodide crystals as small as ~10 ?m in diameter, which were deposited on single, sub-wavelength-sized apertures created in thin gold films on a substrate. The advantage of using small apertures for terahertz microspectroscopy is that only terahertz light that has interacted with the cesium iodide is observed. We find that around the transverse optical phonon frequency of cesium iodide, the amplitude transmission is as much influenced by the refractive index as by the absorption. We show that the ability to measure in the near-field of the apertures, where signals are relatively strong, allows us to measure on sample volumes as small as ~5×10(-16) m(3). PMID:23389003

Knab, J R; Adam, A J L; Shaner, E; Starmans, H J A J; Planken, P C M

2013-01-14

259

Assessment of skin flap viability using visible diffuse reflectance spectroscopy and auto-fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

The accurate assessment of skin flap viability is vitally important in reconstructive surgery. Early identification of vascular compromise increases the change of successful flap salvage. The ability to determine tissue viability intraoperatively is also extremely useful when the reconstructive surgeon must decide how to inset the flap and whether any tissue must be discarded. Visible diffuse reflectance and auto-fluorescence spectroscopy, which yield different sets of biochemical information, have not been used in the characterization of skin flap viability simultaneously to our best knowledge. We performed both diffuse reflectance and fluorescence measurements on a reverse MacFarlane rat dorsal skin flap model to identify the additional value of auto-fluorescence spectroscopy to the assessment of flap viability. Our result suggests that auto-fluorescence spectroscopy appears to be more sensitive to early biochemical changes in a failed flap than diffuse reflectance spectroscopy, which could be a valuable complement to diffuse reflectance spectroscopy for the assessment of flap viability.

Zhu, Caigang; Chen, Shuo; Chui, Christopher Hoe-Kong; Liu, Quan

2012-12-01

260

Observation of soft-mode hardening and broadening in SrTiO3 thin films by broadband terahertz time-domain spectroscopy  

Microsoft Academic Search

Complex dielectric constants of SrTiO3 thin films have been measured using the broadband terahertz time-domain spectroscopy. The broad detection-bandwidth of the photoconductive antenna enables us to clarify soft-mode dispersions as well as the TO2 mode.

Ikufumi Katayama; Hiroshi Shimosato; Masaaki Ashida; Iwao Kawayama; Masayoshi Tonouchi; Tadashi Itoh

2007-01-01

261

Picosecond Transient Photoconductivity in Functionalized Pentacene Molecular Crystals Probed by Terahertz Pulse Spectroscopy  

NASA Astrophysics Data System (ADS)

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800nm, 100fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4ps, a power-law decay is observed consistent with dispersive transport.

Hegmann, F. A.; Tykwinski, R. R.; Lui, K. P.; Bullock, J. E.; Anthony, J. E.

2002-11-01

262

Optoelectronic difference-frequency synthesiser: terahertz-waves for high-resolution spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate a simple approach for a difference-frequency synthesiser within the terahertz domain. Two near-infrared CW diode lasers are frequency-locked to the resonances of a high finesse Fabry-Perot cavity using the Pound-Drever-Hall technique. Two acousto-optic modulators driven by RF synthesizers frequency-shift each diode laser and provide continuous tuning, modulation and switching capabilities for the difference-frequency. Terahertz-waves generated by heterodyne mixing in an ultrahigh-bandwidth photodetector are used to interrogate the rotational transitions in the ground state of the methyl-chloride.

Aballea, L.; Constantin, L. F.

2009-02-01

263

Stratified dispersive model for material characterization using terahertz time-domain spectroscopy.  

PubMed

We propose a novel terahertz material analysis approach that provides highly accurate material parameters and can be used for industrial quality control. The method treats the inspected material within its environment locally as a stratified system and describes the light-matter interaction of each layer in a realistic way. The approach is illustrated in the time-domain and frequency-domain for two potential fields of implementation of terahertz technology: quality control of (coated) paper sheets and car paint multilayers, both measured in humid air. PMID:24978754

van Mechelen, J L M; Kuzmenko, A B; Merbold, H

2014-07-01

264

Quantitative UV-Visible Diffuse Reflectance Spectroscopy of Solid Powders  

Microsoft Academic Search

In spite of difficulties in attaining high resolution, the determination of UV-VIS-NIR spectra via diffuse reflectance spectro-scopic measurements on solid powders; provides several advantages. Compounds which are difficult to obtain as suitable single crystals, or are found to be unstable or insoluble in liquid solution, can only be studied by diffuse reflectance spectroscopy. Also, since no solvents are required, any

T. H. Flint; E. A. Boudreaux

1982-01-01

265

Dependence on chirp rate and spectral resolution of the terahertz field pulse waveform measured by electro-optic detection using a chirped optical pulse and a spectrometer and its effect on terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Single-shot measurement of a terahertz field pulse waveform by electro-optic sampling using a chirped optical pulse and a spectrometer was demonstrated by and Jiang and Zhang [Appl. Phys. Lett. 72, 1945 (1998)]. We have performed an experimental and theoretical investigation into the dependence of the waveform thus measured on the chirp rate and spectral resolution. It was found that the waveform exhibits multicyclic behavior at a chirp rate of -0.24 THz2, which corresponds to a chirped-pulse width of over 10 ps, for the monocyclic original terahertz field, while it approaches the monocyclic behavior with decreasing pulse width. Further, broadening of the spectral resolution of the spectrometer gives rise to a monocyclic waveform in the chirp rate range where the waveform is expected to be multicyclic. In addition, we have derived an analytical expression for the terahertz field pulse waveform thus measured without using the method of stationary phase. The theoretical results were found to be consistent with measured ones. Finally, we examined the spectral bandwidth and resolution of terahertz spectroscopy using this method.

Murakami, H.; Shimizu, K.; Katsurada, M.; Nashima, S.

2008-11-01

266

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

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.

Whitley, Von H [Los Alamos National Laboratory; Hooks, Dan E [Los Alamos National Laboratory; Ramos, Kyle J [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Azad, A K [Los Alamos National Laboratory; Taylor, A J [Los Alamos National Laboratory; Barber, J [NON LANL; Averitt, R D [BOSTON UNIV

2008-01-01

267

Efficient generation of charges via below-gap photoexcitation of polymer-fullerene blend films investigated by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Using optical-pump terahertz-probe spectroscopy, we have investigated the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers: poly[3-hexylthiophene] (P3HT) and poly[2-methoxy-5-( 3,7 -dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) blended with [6,6]-phenyl- C61 butyric acid methyl ester (PCBM). The observed terahertz-frequency conductivity is characteristic of dispersive charge transport for photoexcitation both at the ?-?? absorption peak (560 nm for P3HT) and significantly below it (800 nm). The photoconductivity at 800 nm is unexpectedly high, which we attribute to the presence of a charge-transfer complex. We report the excitation-fluence dependence of the photoconductivity over more than four orders of magnitude, obtained by utilizing a terahertz spectrometer based upon on either a laser oscillator or an amplifier source. The time-averaged photoconductivity of the P3HT:PCBM blend is over 20 times larger than that of P3HT, indicating that long-lived hole polarons are responsible for the high photovoltaic efficiency of polymer:fullerene blends. At early times (˜ps) the linear dependence of photoconductivity upon fluence indicates that interfacial charge transfer dominates as an exciton decay pathway, generating charges with mobility of at least ˜0.1cm2V-1s-1 . At later times, a sublinear relationship shows that carrier-carrier recombination effects influence the conductivity on a longer time scale (>1?s) with a bimolecular charge annihilation constant for the blends that is approximately two to three orders of magnitude smaller than that typical for neat polymer films.

Parkinson, P.; Lloyd-Hughes, J.; Johnston, M. B.; Herz, L. M.

2008-09-01

268

Impact of pellet thickness on quantitative terahertz spectroscopy of solid samples in a polyethylene matrix.  

PubMed

Pellets composed of different weight-percent (wt-%) of lactose within a polyethylene (PE) matrix are used to examine how the physical thickness of solid samples impact analytical measurements performed over terahertz (THz) frequencies when using time-domain THz spectroscopy. Results indicate that the thickness of each pellet depends on the mass and physical properties of the individual components that comprise the pellet. Thickness of mixture pellets depends on the porosity of the individual pellet components. Porosity measurements presented here for PE and lactose give values of 25.6 ± 0.3 and 14.5 ± 0.1, respectively, which indicate that more air is trapped within the compressed PE matrix compared to that for lactose. This difference in porosity creates different pellet thicknesses for pellets of the same nominal mass but with different relative amounts of PE and lactose. For this binary matrix, the thickness of each pellet is found to be a linear combination of the compressed densities of the individual components. Analysis of the time-domain THz spectra reveals that thinner samples are confounded by a fringe pattern observed in the frequency-domain spectra. This fringe pattern is created by an etalon corresponding to the air/pellet interfaces for the sample in the optical path. Spectra collected from thicker pellets are confounded by a sloping baseline caused by scattering effects within the pellet matrix. The quantitative impact of pellet thickness is determined by comparing the mean standard error of calibration (MSEC) and mean standard error of prediction (MSEP) for a set of leave-three-out cross validation multivariate calibration models based on the partial least-squares (PLS) algorithm. Results indicate that PLS models are capable of analytical measurements with MSEC and MSEP values between 0.04 and 0.20 wt-%. Analysis of spectral variance captured within the corresponding spectral loadings for each model indicates that spectral variance is lowest for the 300 mg samples where the impact of scattering is minimal under conditions when the sample etalon is nonexistent. PMID:23438763

Namkung, Hankyu; Kim, Jaejin; Chung, Hoeil; Arnold, Mark A

2013-04-01

269

Photoexcited GaAs surfaces studied by transient terahertz time-domain spectroscopy  

Microsoft Academic Search

The transmission characteristics of an air - GaAs interface and the transient absorption and index spectra of the thin, photoexcited surface layer are investigated subsequent to excitation by a femtosecond laser pulse. We find that the total phase change and transmission of a terahertz (THz) probe pulse are dominated by interface effects. This observation has important implications in the interpretation

Michael Schall; Peter Uhd Jepsen

2000-01-01

270

Terahertz Time Domain Spectroscopy of Conformational Dynamics of Sensor Proteins: Basic Research and Pathogen Sensor Development.  

National Technical Information Service (NTIS)

We report on the research funded in part by this ARO grant towards developing an all-optical terahertz biosensor. This program is motivated by the need for fast and adaptable biosensors that do not require probe labeling. Our sensors are based on an intri...

A. G. Markelz

2004-01-01

271

Terahertz time-domain spectroscopy of surface plasmon polaritons on periodic metal arrays  

Microsoft Academic Search

This contribution focuses on surface plasmon polaritons at terahertz frequencies. The coupling to surface plasmon polaritons is provided by periodic metal arrays with different structures and distinct dimensions. For these different geometries the generation and propagation of surface plasmon polaritons are studied. A full wave calculation of the interaction of THz radiation with the metal arrays has revealed good correlation

M. Martl; J. Darmo; J. Kroll; K. Unterrainer

2007-01-01

272

Bidirectional reflectance spectroscopy. I - Theory. [of planetary surfaces  

NASA Technical Reports Server (NTRS)

An approximate analytic solution is derived for the radiative transfer equation describing particulate surface light scattering, taking into account multiple scattering and mutual shadowing. Analytical expressions for the following quantities are found: bidirectional reflectance, radiance coefficient and factor, the normal, Bond, hemispherical, and physical albedos, integral phase function and phase integral, and limb-darkening profile. Scattering functions for mixtures can be calculated, as well as corrections for comparisons of experimental transmission or reflection spectra with observational planetary spectra. The theory should be useful for the interpretation of reflectance spectroscopy of laboratory surfaces and the photometry of solar system objects.

Hapke, B.

1981-01-01

273

Spectral Identification of Impact Glasses Via NIR Reflectance Spectroscopy  

Microsoft Academic Search

Impact glasses from Haughton and other known impact sites possess what appears to be a unique NIR spectral feature that may be indicative of their impact origin. As such, it is possible that impact glasses may be identified via the use of reflectance spectroscopy alone.

M. A. Craig; G. R. Osinski; R. L. Flemming; E. A. Cloutis

2011-01-01

274

Sample rotation in diffuse reflectance Fourier transform infrared spectroscopy  

Microsoft Academic Search

An apparatus for the rotation of sample and blank in diffuse reflectance Fourier transform infrared spectroscopy has been designed and fabricated. Spectra taken with sample rotation give data with better precision by a factor of 4 than without rotation. Additionally, sample rotation saves time by eliminating the need for taking three to five spectra followed by spectrum averaging as has

Rance A. Velapoldi; Jan E. Tvedt; Alfred A. Christy

1987-01-01

275

Analytical study of spacecraft deposition contamination by internal reflection spectroscopy  

NASA Technical Reports Server (NTRS)

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.

Mookherji, T.

1972-01-01

276

Optical characteristics of biological molecules in the terahertz gap  

NASA Astrophysics Data System (ADS)

Terahertz Spectroscopy has been recently introduced as a promising technique for the collection of signature data in transmission spectra of biological materials including warfare agent simulants. To characterize material rather than sample, it is always desirable to obtain the material's optical properties as functions of frequency. In this work, we present results from parallel measurements of reflection and transmission spectra of biological molecules to enable detailed and direct calculation of refractive index and absorption coefficient spectra in the terahertz gap. DNA samples from herring and salmon as well as samples of Ovalbumin and Bacillus Subtillus spores have been characterized. The technique for simulation is described. Reflection spectra reveal resonance features similar to those demonstrated earlier for transmission, thereby affirming molecular vibrational modes in biological materials. The dispersion of refractive index and absorption coefficient is demonstrated within the Terahertz gap of 10 cm-1 to 25 cm-1.

Globus, Tatiana; Parthasarathy, Ramakrishnan; Khromova, Tatyana; Woolard, Dwight L.; Swami, Nathan; Gatesman, Andrew J.; Waldman, Jerry

2004-12-01

277

TOPICAL REVIEW: Pulsed terahertz tomography  

Microsoft Academic Search

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

S. Wang; X.-C. Zhang

2004-01-01

278

Coherent broadband continuous-wave terahertz spectroscopy on solid-state samples  

NASA Astrophysics Data System (ADS)

Measuring the complex dielectric function ?(?)=?1+i?2 of solid-state samples in the terahertz frequency range with high spectral resolution remains difficult. Using a continuous-wave terahertz spectrometer based on photomixing in the frequency range from 60 GHz to 1.8 THz, we obtain the most precise data of ?(?) reported to date for the well-studied example of ?-lactose monohydrate. We are able to determine both ?1 and ?2 due to coherent detection and show that the results are Kramers-Kronig consistent. Our analysis is based on scanning an interference pattern in frequency and relies on the high spectral resolution in the MHz range. This enables us to avoid mechanically moving parts such as a delay stage. Moreover, we show that the optical data can be used to determine both ?(?) and the sample thickness d independently.

Roggenbuck, A.; Schmitz, H.; Deninger, A.; Cámara Mayorga, I.; Hemberger, J.; Güsten, R.; Grüninger, M.

2010-04-01

279

Conformational characteristics of chiral and racemic naproxen molecules investigated by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Absorption spectra in the terahertz region between 6 and 66 cm-1 (0.2 ~ 2.0 THz) were measured for S-(+)-, R-(-) and RS-naproxen pharmaceutical molecules in crystalline form using time-domain terahertz spectroscopic (THz-TDS) technique at room temperature. Different absorption features were observed for the racemic RS-naproxen and its corresponding enantiomers (S-(+)- and R-(-)-naproxen). The observed THz absorption bands are strikingly sensitive to the change of subtle conformational structures despite that the isostructurality exists within such crystal molecules. The results show that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.

Du, Yong; Zhao, Rongjiao; Hao, Guohui; Guo, Changsheng; Hong, Zhi

2011-11-01

280

Intervalley separation in the conduction band of InGaAs measured by terahertz excitation spectroscopy  

SciTech Connect

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.

Molis, G.; Krotkus, A. [Semiconductor Physics Institute, A. Gostauto 11, Vilnius 01108 (Lithuania); Vaicaitis, V. [Laser Research Center, Vilnius University, Sauletekio 10, Vilnius 10223 (Lithuania)

2009-03-02

281

Terahertz (THz) spectroscopy of Freon-11 (CCl 3F, CFC-11) at room temperature  

NASA Astrophysics Data System (ADS)

The rotational spectrum for the lowest vibrational mode for CCl 3F has been measured in the 0.1-2 THz frequency range using a compact time-resolved terahertz spectrometer. The peak of the population spectrum for the ground state rotational manifold was observed at 0.3 THz. The observed absorption profile was modeled with rotational and vapor pressure parameters. The limits of detectivity of the compact THz system are discussed in context of atmospheric sensing.

Altan, H.; Yu, B. L.; Alfano, S. A.; Alfano, R. R.

2006-08-01

282

Stimulated terahertz emission from optically pumped graphene  

Microsoft Academic Search

We conduct time domain spectroscopy studies and shows that graphene sheet amplifies an incoming terahertz field. The graphene emission spectra dependency on laser pumping intensity shows a threshold like behavior, testifying the occurrence of the negative conductivity and the population inversion in the terahertz range, paving the way for a new class room temperature graphene based terahertz lasers.

S. Boubanga Tombet; A. Satou; T. Otsuji; V. Ryzhii

2011-01-01

283

Graphene plasmonics for subwavelength terahertz oscillators  

Microsoft Academic Search

Plasmons in population inverted graphene can experience extremely large gain through the process of stimulated emission at terahertz frequencies. The large gain values and the small plasmon wavelengths can lead to compact terahertz plasmon lasers and amplifiers that are only a few microns in size. We also present optical and terahertz spectroscopy results for carrier relaxation and recombination dynamics and

F. Rana; J. H. Strait; P. A. George; Haining Wang; J. D. Besant

2009-01-01

284

Coherently controlled terahertz source for a time domain spectroscopy system via injection current in bulk ZnSe.  

PubMed

We have observed terahertz generation via injection current induced by harmonically related two-color beams in an unbiased ZnSe bulk at room temperature using a femtosecond Ti:sapphire oscillator. The terahertz intensity is just several times smaller than that obtained via optical rectification and further enhancements are believed possible. Experimental results demonstrate that the terahertz radiation is mainly attributed to the transition from the split-off band. This conclusion provides a novel approach to effectively generate a broadband and coherently controlled terahertz radiation, which leads to practical applications of terahertz radiation via this mechanism. PMID:22330303

Lü, Zhihui; Zhang, Dongwen; Zhou, Zhaoyan; Sun, Lin; Zhao, Zengxiu; Yuan, Jianmin

2012-02-10

285

Prediction of dissolution time and coating thickness of sustained release formulations using Raman spectroscopy and terahertz pulsed imaging.  

PubMed

Raman spectroscopy was implemented successfully as a non-invasive and rapid process analytical technology (PAT) tool for in-line quantitative monitoring of functional coating. Coating experiments were performed at which diprophylline tablets were coated with a sustained release formulation based on Kollicoat SR 30 D. Using PLS a multivariate model was constructed by correlating Raman spectral data with the mean dissolution time as determined by dissolution testing and the coating thickness as measured by terahertz pulsed imaging. By performing in-line measurements it was possible to monitor the progress of the coating process and to detect the end point of the process, where the acquired coating amount was achieved for the desired MDT or coating thickness. PMID:22245221

Müller, Joshua; Brock, Daniela; Knop, Klaus; Axel Zeitler, J; Kleinebudde, Peter

2012-04-01

286

Investigation of coherent acoustic phonons in terahertz quantum cascade laser structures using femtosecond pump-probe spectroscopy  

NASA Astrophysics Data System (ADS)

The dynamics of acoustic vibrations in terahertz quantum cascade laser structures (THz-QCLs) is studied by means of femtosecond pump-probe spectroscopy. The phonon modes are characterized by the folding of the acoustic dispersion into an effective reduced Brillouin zone. An accurate identification of this dispersion allows the sample structure and periodicity to be determined with high precision on the order of 0.1%. By temperature tuning the energy of the electronic levels of the system and performing wavelength dependent measurements, we are able to study the impulsive resonant generation and detection of coherent acoustic phonon modes. These results are supported by simulations of the electronic system that well explain the experimental observations. The effects of interface (IF) roughness on coherent acoustic phonon spectra are clearly observed for equal nominal THz-QCL structures but with different interface qualities.

Bruchhausen, Axel; Lloyd-Hughes, James; Hettich, Mike; Gebs, Raphael; Grossmann, Martin; Ristow, Oliver; Bartels, Albrecht; Fischer, Milan; Beck, Mattias; Scalari, Giacomo; Faist, Jérôme; Rudra, Alok; Gallo, Pascal; Kapon, Eli; Dekorsy, Thomas

2012-08-01

287

Very slow cooling dynamics of photoexcited carriers in graphene observed by optical-pump terahertz-probe spectroscopy.  

PubMed

Using optical-pump terahertz-probe spectroscopy, we study the relaxation dynamics of photoexcited carriers in graphene at different substrate temperatures. We find that at lower temperatures the tail of the relaxation transients measured by the differential probe transmission become slower, extending beyond several hundred picoseconds below 50 K. We interpret the observed relaxation transients as resulting from the cooling of the photoexcited carriers via phonon emission. The slow cooling of the photoexcited carriers at low temperatures is attributed to the bulk of the electron and hole energy distributions moving close enough to the Dirac point that both intraband and interband scattering of carriers via optical phonon emission become inefficient for removing heat from the carriers. Our model, which includes intraband carrier scattering and interband carrier recombination and generation, agrees very well with the experimental observations. PMID:21973122

Strait, Jared H; Wang, Haining; Shivaraman, Shriram; Shields, Virgil; Spencer, Michael; Rana, Farhan

2011-11-01

288

Determination of the time origin by the maximum entropy method in time-domain terahertz emission spectroscopy.  

PubMed

We have developed a scheme for determining the time origin by the maximum entropy method (MEM) in time-domain terahertz (THz) emission spectroscopy. By applying the MEM to trial damped sinusoidal waveforms, we confirmed that the MEM gives true phase shifts across the resonance features and that its inherent uncertainty in determining the time origin is +/-15 fs for 100-fs-class excitation/sampling optical pulses. Furthermore, when the MEM was applied to a THz waveform recorded experimentally with a finite sampling interval for the Bloch oscillation in a semiconductor superlattice, a misplacement of the time origin was indeed detected with an accuracy limited by the worse of the MEM inherent uncertainty and the sampling interval. PMID:20720967

Unuma, Takeya; Ino, Yusuke; Kuwata-Gonokami, Makoto; Vartiainen, Erik M; Peiponen, Kai-Erik; Hirakawa, Kazuhiko

2010-07-19

289

Pancreatic tissue assessment using fluorescence and reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

The ability of multi-modal optical spectroscopy to detect signals from pancreatic tissue was demonstrated by studying human pancreatic cancer xenografts in mice and freshly excised human pancreatic tumor tissue. Measured optical spectra and fluorescence decays were correlated with tissue morphological and biochemical properties. The measured spectral features and decay times correlated well with expected pathological differences in normal, pancreatitis and adenocarcinoma tissue states. The observed differences between the fluorescence and reflectance properties of normal, pancreatitis and adenocarcinoma tissue indicate a possible application of multi-modal optical spectroscopy to differentiating between the three tissue classifications.

Chandra, Malavika; Heidt, David; Simeone, Diane; McKenna, Barbara; Scheiman, James; Mycek, Mary-Ann

2007-07-01

290

The quantitative monitoring of mechanochemical reaction between solid L-tartaric acid and sodium carbonate monohydrate by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Liu, Xiaohong; Liu, Guifeng; Zhao, Hongwei; Zhang, Zengyang; Wei, Yongbo; Liu, Min; Wen, Wen; Zhou, Xingtai

2011-11-01

291

Multiply scattered broadband terahertz pulses  

Microsoft Academic Search

We describe measurements of single-cycle terahertz pulse propagation in a random medium. The unique capabilities of terahertz time-domain spectroscopy permit the characterization of a multiply scattered field with unprecedented temporal resolution. With these results, we can develop a framework for understanding the statistics of broadband laser speckle. We also describe recent measurements of the polarization dynamics of these diffusively propagating

J. Pearce; Zhongping Jian; D. M. Mittleman

2004-01-01

292

Ultra-broadband coherent terahertz spectroscopy using asymmetric excitation of photoconductive structures  

Microsoft Academic Search

We report recent progress in the generation of ultra-broadband (>14.0 THz) coherent terahertz (THz) radiation, with high dynamic signal-to-noise ratio (>1000), using asymmetric excitation of carriers in biased low-temperature-grown GaAs (LT-GaAs) photoconductive structures. The generated ultrashort THz temporal wave form is characterized by both free space electro-optic sampling (using 20-?m-thick ZnTe and 150-?m-thick GaP crystals) and a LT-GaAs photoconductive receiver.

P. C. Upadhya; W. H. Fan; A. Burnett; Y. C. Shen; H. E. Beere; A. G. Davies; E. H. Linfield

2005-01-01

293

Detection and correction of the misplacement error in terahertz spectroscopy by application of singly subtractive Kramers-Kronig relations  

Microsoft Academic Search

In THz reflection spectroscopy the complex permittivity of an opaque medium is determined on the basis of the amplitude and phase of the reflected wave. There is usually a problem of phase error due to misplacement of the reference sample. Such experimental error brings inconsistency between phase and amplitude invoked by the causality principle. We propose a rigorous method to

Valerio Lucarini; Yusuke Ino; Kai-Erik Peiponen; Makoto Kuwata-Gonokami

2005-01-01

294

Comparison of Terahertz Pulse Imaging and Near-Infrared Spectroscopy for Rapid, Non-Destructive Analysis of Tablet Coating Thickness and Uniformity  

Microsoft Academic Search

In this study, coating thickness and uniformity of production-scale pharmaceutical tablets were investigated using near-infrared\\u000a (NIR) and terahertz pulse imaging (TPI) spectroscopy. Two coating formulations were considered; samples for each coating formulation\\u000a were obtained at 0, 1, 2, 3, 4, and 5% coating weight. NIR spectra were collected, and regressed with respect to batch percent\\u000a weight gain. While standard errors

Robert P. Cogdill; Ryanne N. Forcht; Yaochun Shen; Philip F. Taday; J. Richard Creekmore; Carl A. Anderson; James K. Drennen

2007-01-01

295

Evidence for linelike vortex liquid phase in Tl2Ba2CaCu2O8 probed using terahertz time-domain spectroscopy  

Microsoft Academic Search

Summary form only given. To probe the vortex state in Tl2Ba2CaCu2O8 thin films we used terahertz time-domain spectroscopy in transmission. The decrease of the oscillation frequency from 70 K to 80 K in the time-domain is shown, and the effect of a magnetic field illustrated. A drop of the Josephson plasma resonance (JPR) occurs in the frequency-domain when applying a

V. K. Thorsmolle; R. D. Averitt; M. P. Maley; M. F. Hundley; L. N. Bulaevskii; A. J. Taylor; A. E. Koshelev

2002-01-01

296

Terahertz Scattering  

NASA Astrophysics Data System (ADS)

Terahertz (THz) Time Domain Spectroscopy (TDS) measurements have the unique ability to detect both the amplitude and phase of the electric field, simultaneously. This eliminates complications introduced by Kramers-Kronig relations typically used in near-infrared spectroscopy. Many materials of interest contain resonant features in their refractive indices in the far-infrared (THz) spectrum, while their packaging materials are generally transparent. Thus, an important application for THz TDS is the ability to see inside packaging materials and detect the material features of their contents. Such applications are promising for security screening (concealed drugs, explosives, etc.) in post offices and airports as well as for non-destructive evaluation (NDE) of products on an assembly line or tissue damage due to burns or cancer [1-6].

Zurk, L. M.; Schecklman, S.

297

Superhuman Vision - Seeing with Terahertz  

NSDL National Science Digital Library

This article is an introduction to terahertz waves and imaging applications that use them. An explanation of how the reflection and absorption of these electromagnetic waves can be used to generate 3D images and identify materials is provided. The site also presents components developed to improve the performance and functionality of terahertz imaging systems.

2006-12-28

298

Terahertz wave spectrum analysis of microstrip structure  

NASA Astrophysics Data System (ADS)

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

Song, Mei-jing; Li, Jiu-sheng

2011-11-01

299

Synthesis, structure, terahertz spectroscopy and luminescent properties of copper(I) complexes with mercaptan ligands and triphenylphosphine  

NASA Astrophysics Data System (ADS)

The reactions of copper(I) halides with triphenylphosphine (PPh3) and mercaptan ligand [2-mercapto-6-nitrobenzothiazole (HMNBT), 2-amino-5-mercapto-1,3,4-thiadiazole (HAMTD) and 2-mercapto-5-methyl-benzimidazole (MMBD)] yielded seven complexes, [CuCl(HMNBT)(PPh3)2] (1), [CuX(HMNBT)(PPh3)]2 (X = Cl, Br) (2-3), [Cu(MNBT)(HMNBT)(PPh3)2] (4), [CuBr(HAMTD)(PPh3)2]·CH3OH (5) and [CuX(MMBD)(PPh3)2]·2CH3OH (X = Br, I) (6-7). These complexes were characterized by elemental analysis, X-ray diffraction, 1H NMR and 31P NMR spectroscopy. In these complexes the mercaptan ligands act as monodentate or bridged ligand with S as the coordination atom. In complexes 1 and 4, hydrogen bonds CH⋯X and weak interactions CH⋯? lead to the formation of chains and 2D network respectively, while complexes 2 and 3 are dinuclear. In 5-7, intramolecular hydrogen bonds link the [CuX(thione)(PPh3)2] molecules and the solvated methanol molecules into centrosymmetric dimers. Complexes 1-5 represent first copper(I) halide complexes of HMNBT and HAMTD. The complexes 1, 5, 6 and 7 exhibit interesting fluorescence in the solid state at room temperature and their terahertz (THz) time-domain spectroscopy was also studied.

Qiu, Qi-Ming; Liu, Min; Li, Zhong-Feng; Jin, Qiong-Hua; Huang, Xu; Zhang, Zhen-Wei; Zhang, Cun-Lin; Meng, Qing-Xuan

2014-03-01

300

Characteristics of HfO2 and SiO2 on p-type silicon wafers using terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The effect of high-? dielectric HfO2 films on 200 mm diameter p-type silicon substrates was investigated and compared with conventional dielectric material, SiO2. We employed all-optical characterization methods using terahertz (THz) time-domain spectroscopy and visible cw pump/THz probe spectroscopy. Measurements were performed on two sets of samples, each set containing both HfO2 and SiO2 coated wafers with varying thickness of oxide layer. One set had a protective coating of either photoresist or Si3N4 deposition above the oxide layer which in turn was on a heavily doped p+ layer on p-type silicon. The samples exhibited similar linear transmission in the THz frequency range studied. However, when using an Ar+-ion laser as an optical pump source, differential measurements (with and without the pump source) showed that the transmission was far smaller for the high-? dielectric HfO2 films than its conventional dielectric SiO2 counterparts, indicating the presence of large photo-generated carrier density in the p-type substrate.

Altan, H.; Sengupta, A.; Pham, D.; Grebel, H.; Federici, J. F.

2007-05-01

301

Terahertz quantum cascade lasers with metal-metal waveguides.  

SciTech Connect

Quantum cascade lasers that operate in the underdeveloped terahertz spectral range (1-10 THz) promise to contribute to applications in sensing, spectroscopy, and imaging. We describe our development of terahertz quantum cascade lasers based on the resonant-phonon depopulation concept and that use low-loss metal-metal waveguides for optical confinement. Two- and three-dimensional finite-element simulations of terahertz metal-metal waveguides are used to demonstrate their high modal confinement even for very narrow ridges. Also, simulations predict high facet reflectivities due to the modal impedance mismatch with free space at the sub-wavelength waveguide aperture of these metal-metal waveguides. Finally, we report the demonstration of a 2.8 THz laser that operates up to 97 K in continuous-wave mode fabricated using a Cu-Cu thermocompression bonding technique.

Kohen, Stephen (Massachusetts Institute of Technology, Cambridge, MA); Kumar, Sushil (Massachusetts Institute of Technology, Cambridge, MA); Williams, Benjamin S. (Massachusetts Institute of Technology, Cambridge, MA); Reno, John Louis; Hu, Qing (Massachusetts Institute of Technology, Cambridge, MA)

2005-03-01

302

Diagnostic Screening of Urban Soil Contaminants Using Diffuse Reflectance Spectroscopy  

Microsoft Academic Search

\\u000a There is increasing demand for cheap and rapid screening tests for soil contaminants in environmental consultancies. Diffuse\\u000a infrared reflectance spectroscopy in the visible–near-infrared (vis–NIR) and mid-infrared (MIR) has the potential to meet\\u000a this demand. The aims of this chapter are to develop diagnostic screening tests for heavy metals and polycyclic aromatic hydrocarbons\\u000a (PAHs) in soil using vis–NIR and MIR diffuse

J. G. Bray; R. A. Viscarra Rossel; A. B. McBratney

303

Analysis of remote reflection spectroscopy to monitor plant health  

NASA Astrophysics Data System (ADS)

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.

Woodhouse, R.; Heeb, M.; Berry, W.; Hoshizaki, T.; Wood, M.

1994-11-01

304

Diffuse reflectance spectroscopy for in vivo pediatric brain tumor detection  

NASA Astrophysics Data System (ADS)

The concept of using diffuse reflectance spectroscopy to distinguish intraoperatively between pediatric brain tumors and normal brain parenchyma at the edge of resection cavities is evaluated using an in vivo human study. Diffuse reflectance spectra are acquired from normal and tumorous brain areas of 12 pediatric patients during their tumor resection procedures, using a spectroscopic system with a handheld optical probe. A total of 400 spectra are acquired at the rate of 33 Hz from a single investigated site, from which the mean spectrum and the standard deviation are calculated. The mean diffuse reflectance spectra collected are divided into the normal and the tumorous categories in accordance with their corresponding results of histological analysis. Statistical methods are used to identify those spectral features that effectively separated the two tissue categories, and to quantify the spectral variations induced by the motion of the handheld probe during a single spectral acquisition procedure. The results show that diffuse reflectance spectral intensities between 600 and 800 nm are effective in terms of differentiating normal cortex from brain tumors. Furthermore, probe movements induce large variations in spectral intensities (i.e., larger standard deviation) between 400 and 600 nm.

Lin, Wei-Chiang; Sandberg, David I.; Bhatia, Sanjiv; Johnson, Mahlon; Oh, Sanghoon; Ragheb, John

2010-11-01

305

Broadband transmission of terahertz radiations in thin silica tube  

Microsoft Academic Search

Hollow-core thin silica tubes based on antiresonant guiding mechanism are studied with Terahertz (THz) time domain spectroscopy (TDS) setup. By controlling the parameters of the waveguide, broad transmission windows, up to 580 GHz, is demonstrated at terahertz frequencies.

E. Nguema; D. Ferachou; G. Humbert; J.-L. Auguste; J.-M. Blondy

2010-01-01

306

Assessing human skin with diffuse reflectance spectroscopy and colorimetry  

NASA Astrophysics Data System (ADS)

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.

Seo, InSeok; Liu, Yang; Bargo, Paulo R.; Kollias, Nikiforos

2012-02-01

307

Highly sensitive strain detection in silicon by reflectance anisotropy spectroscopy  

NASA Astrophysics Data System (ADS)

Reflectance anisotropy spectroscopy (RAS) measurements were performed on strained silicon (Si) stripes cut from crystalline silicon wafers. Strains were externally applied using a device developed especially for the study of layers and layered structures. The dependence of the RAS signal intensity on strain was measured for (100), (110), and (111) silicon wafers strained along [001] and [011]. In these configurations, the RAS spectra show a derivativelike structure at 3.4 eV, which increases in amplitude linearly with strain. While RAS line shapes depend on the orientation of the Si wafer and the crystallographic directions along which strains are applied, RAS intensities depend on strain magnitude. Strains as low as 10-5 can be measured, which is two orders of magnitude smaller than those detected with standard techniques such as Raman, piezoelectroreflectance spectroscopy (PERS), or x-ray diffraction (XRD). The experimental RAS spectra are found to be in good agreement with spectra calculated on the basis of the spectral response of the published piezo-optical tensor components. It is concluded that RAS provides a highly sensitive tool for the detection of strain induced bulk anisotropies. Strain calibrated RAS spectra can be used for strain-stress characterization of semiconductor layers and microstructures with a higher efficiency than that achieved by Raman, PERS, and XRD. Combined with growth techniques, RAS spectroscopy can be also used for in situ control of strain during semiconductor growth.

Papadimitriou, D.; Richter, W.

2005-08-01

308

Characterization of hollow polycarbonate metal waveguides using Terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

In recent times, terahertz (THz) or the far-infrared region of the electromagnetic spectrum has gained critical significance due to many potential applications including medical diagnostics, nondestructive evaluation of material parameters, chemical sensing, remote sensing and security screening. However with the development of various applications, the need of guided systems for the transmission of THz radiation have posed a challenge, as a flexible waveguide could simplify the propagation and detection of THz waves in remote locations without atmospheric absorption. Different structures, such as, rigid hollow metallic waveguides, solid wires, or short lengths of solid-core transparent dielectrics such as sapphire and plastic have already been explored for THz guiding to characterize their individual loss and dispersion profile. Recently, it has been reported that copper coated flexible, hollow polycarbonate waveguide has low loss of less than 4 dB/m with single mode operation at 1.89 THz. In the present study, using a broadband THz source of photoconductive antennae, we characterize the loss and dispersion profile of hollow core polycarbonate metal waveguides in the frequency range of 0.2 to 1.2 THz.

Bandyopadhyay, Aparajita; Sengupta, Amartya; Johnson, Valencia; Harrington, James A.; Federici, John F.

2006-03-01

309

Wiener bounds for complex permittivity in terahertz spectroscopy: case study of two-phase pharmaceutical tablets.  

PubMed

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. PMID:20132608

Tuononen, Heikki; Fukunaga, Kaori; Kuosmanen, Marko; Ketolainen, Jarkko; Peiponen, Kai-Erik

2010-01-01

310

Ultralow surface recombination velocity in InP nanowires probed by terahertz spectroscopy.  

PubMed

Using transient terahertz photoconductivity measurements, we have made noncontact, room temperature measurements of the ultrafast charge carrier dynamics in InP nanowires. InP nanowires exhibited a very long photoconductivity lifetime of over 1 ns, and carrier lifetimes were remarkably insensitive to surface states despite the large nanowire surface area-to-volume ratio. An exceptionally low surface recombination velocity (170 cm/s) was recorded at room temperature. These results suggest that InP nanowires are prime candidates for optoelectronic devices, particularly photovoltaic devices, without the need for surface passivation. We found that the carrier mobility is not limited by nanowire diameter but is strongly limited by the presence of planar crystallographic defects such as stacking faults in these predominantly wurtzite nanowires. These findings show the great potential of very narrow InP nanowires for electronic devices but indicate that improvements in the crystallographic uniformity of InP nanowires will be critical for future nanowire device engineering. PMID:22962963

Joyce, Hannah J; Wong-Leung, Jennifer; Yong, Chaw-Keong; Docherty, Callum J; Paiman, Suriati; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Lloyd-Hughes, James; Herz, Laura M; Johnston, Michael B

2012-10-10

311

Terahertz spectroscopy of the explosive taggant 2,3-dimethyl-2,3-dinitrobutane.  

PubMed

The terahertz spectrum of the crystalline explosive taggant 2,3-dimethyl-2,3-dinitrobutane (C(6)H(12)N(2)O(4)) has been investigated as an alternative means of detecting solid-state explosives. The room-temperature spectrum exhibits two broad absorption features centered at 38.3 and 49.2 cm(-1). Once the sample is cooled to liquid-nitrogen temperatures, the resolution of three additional peaks occurs, with absorption maxima now appearing at 40.1, 47.5, 56.6, 63.9, and 73.6 cm(-1). Solid-state density functional theory simulations, both with and without London force dispersion corrections, have been used for the assignment of the experimental cryogenic THz spectrum to specific molecular motions in the crystalline solid. The B3LYP hybrid density functional paired with the 6-311G(2d,2p) basis set provides an excellent reproduction of the experimental data revealing that the THz spectrum arises from a mixture of intramolecular torsional vibrations localized primarily in the nitro groups and intermolecular lattice vibrations composed of rigid molecular rotations. PMID:22646742

Witko, Ewelina M; Korter, Timothy M

2012-06-28

312

Terahertz near-field probe incorporating a ?/100 aperture for time-domain spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

Achieving high spatial resolutions for imaging with terahertz (THz) waves requires near-field probes, such as a sub-wavelength aperture probe. Bethe's theory of transmission through a sub-wavelength aperture of size a predicts that the transmitted electric field scales as E?a3. This strong dependence limits the size of apertures that can be employed and hence the spatial resolution. This dependence however changes for the evanescent field components in very close proximity (~1?m for THz waves) to the aperture, as shown by electromagnetic simulations. To exploit this effect in a THz near-field probe, we developed a photoconductive THz near-field detector structure, which incorporates a thinned photo-conductive detector region and a distributed Bragg reflector between the detector and the aperture plane. Near-field probes are manufactured with different aperture sizes to investigate transmission of THz pulses through apertures as small as 3?m. The experimental results confirm that the transmitted field amplitude, and therefore the sensitivity, increases by about one order of magnitude for the new probes. A 3?m aperture probe with a spatial resolution of ?/100 at 1THz is demonstrated.

Macfaden, Alexander J.; Reno, John L.; Brener, Igal; Mitrofanov, Oleg

2013-12-01

313

Physics and capabilities of terahertz spectroscopy to study the water-biomolecule interaction  

NASA Astrophysics Data System (ADS)

We have conducted the first study of the use of terahertz radiation to precisely identify pre-melting, melting, polymerization, depolymerization and the influence of polar water in sulfur by scanning frequency as a parametric function of temperature, and including identifying precursor and intermediate states. This spectroscopic study has also identified the orthorhombic-monoclinic phase transformation, and the melting of the superheated orthorhombic phase. This work also reports detection of a water absorption indicating a perturbation of the water molecules, associated with solvation spheres of the inter-chain dynamics, as a precursor to a transition, and supporting our earlier results showing the transducing capabilities of conglomerates of water molecules. Through a study of the fine structure of the water absorption, we are able to determine information about local polarization effects which contribute to the transducing properties of water relative to a ligand. The above inorganic polymer study is applied to the understanding of the response of biomolecules to thermal and chemical influences, and data are included giving optical, electrical, and pH properties of the DNA-water system, showing a major conformational transition at ~43°C, and various forms of reconformation of DNA macromolecule due to chemical perturbation. Our results include findings aimed at complementing existing inhibitors that are intended to prevent retrovirus/phage invasion of the host cell DNA.

Vezzoli, G. C.

2007-09-01

314

Infrared reflectance spectroscopy on thin films: Interference effects  

NASA Astrophysics Data System (ADS)

Laboratory simulations of processes on astronomical surfaces that use infrared reflectance spectroscopy of thin films to analyze their composition and structure often ignore important optical interference effects which often lead to erroneous measurements of absorption band strengths and give an apparent dependence of this quantity on film thickness, index of refraction and wavelength. We demonstrate these interference effects experimentally and show that the optical depths of several absorption bands of thin water ice films on a gold mirror are not proportional to film thickness. We describe the method to calculate accurately band strengths from measured absorbance spectra using the Fresnel equations for two different experimental cases, and propose a way to remove interference effects by performing measurements with P-polarized light incident at Brewster's angle.

Teolis, B. D.; Loeffler, M. J.; Raut, U.; Famá, M.; Baragiola, R. A.

2007-09-01

315

Reflectance difference spectroscopy of water on Cu(110)  

NASA Astrophysics Data System (ADS)

The adsorption of H2O on Cu(110) was probed by means of reflectance difference spectroscopy (RDS) in the energy range between 1.5 and 9.3 eV and by scanning tunneling microscopy (STM). The adsorption of water on the pristine Cu(110) substrate mainly induces changes in the Cu surface state related optical transitions. Furthermore, the H2O adsorbate modifies the Cu bulk transitions. In particular, our investigations demonstrate that the coverage-dependent phase transition from 1D pentamer chains to a (7 × 8) superstructure can be monitored by means of RDS. In the vacuum-UV range, new RD features assigned to Cu bulk transitions were detected. Adsorption on the metal surface strongly modifies or quenches the H2O HOMO-LUMO transition, whereby a distinct RD feature of the water molecules themselves in the vacuum-UV range is absent.

Denk, M.; Hohage, M.; Sun, L. D.; Zeppenfeld, P.; Esser, N.; Cobet, C.

2014-09-01

316

Terahertz waves emitted from an optical fiber.  

PubMed

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

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

2010-06-21

317

Andreev reflection spectroscopy of iron-based superconductors  

NASA Astrophysics Data System (ADS)

After a reign of over two decades by the cuprate superconductors, several new families of iron-based high-temperature superconductors have recently been discovered. Essential to a superconductor is the nature of the superconducting gap, its value, its structure, and its temperature dependence. Point contact Andreev reflection (PCAR) spectroscopy operating in the ballistic limit is one of few techniques that can quantitatively measure the gap of these new Fe-based superconductors and its temperature dependence. In SmFeAsO1-xFx (0.15 <= x <= 0.30), we have determined a single gap 2?/kBTC 3.5-3.6 close to the BCS s-wave prediction and with a BCS-like temperature dependence.ootnotetextT. Y. Chen, Z. Tesanovic, R. H. Liu, X. H. Chen, and C. L. Chien, Nature, 453, 1224 (2008) These results will be compared with various theoretical possibilities and those obtained by other measurements, such as ARPES and penetration depth. While the principles of the PCAR spectroscopy are well established, poor contact control and ballistic heating might lead to the appearance of spurious gaps and pseudogaps in PCAR measurements. In collaboration with T. Y. Chen, S. X. Huang and Z. Tesanovic at JHU and R. H. Liu and X. H. Chen at USTC.

Chien, C. L.

2009-03-01

318

Total internal reflection photoacoustic spectroscopy for the detection of ?-hematin  

NASA Astrophysics Data System (ADS)

Evanescent field sensing methods are currently used to detect many different types of disease markers and biologically important chemicals such as the HER2 breast cancer receptor. Hinoue et al. used Total Internal Reflection Photoacoustic Spectroscopy (TIRPAS) as a method of using the evanescent field to detect an optically opaque dye at a sample interface. Although their methods were successful at detecting dyes, the results at that time did not show a very practical spectroscopic technique, which was due to the less than typical sensitivity of TIRPAS as a spectroscopy modality given the low power (~1 to 2 W) lasers being used. Contrarily, we have used an Nd:YAG laser with a five nanosecond pulse that gives peak power of 1 MW coupled with the TIRPAS system to increase the sensitivity of this technique for biological material sensing. All efforts were focused on the eventual detection of the optically absorbing material, hemozoin, which is created as a byproduct of a malarial infection in blood. We used an optically analogous material, ?-hematin, to determine the potential for detection in the TIRPAS system. In addition, four properties which control the sensitivity were investigated to increase understanding about the sensor's function as a biosensing method.

Goldschmidt, Benjamin S.; Sudduth, Amanda S. M.; Samson, Edward B.; Whiteside, Paul J. D.; Bhattacharyya, Kiran D.; Viator, John A.

2012-06-01

319

Development of components for cost effective terahertz measurement system: terahertz quantum cascade laser and terahertz quantum well infrared photo-detector  

Microsoft Academic Search

Terahertz imaging and spectroscopy have attracted a lot of attention in recent years, because monocycle terahertz radiation can be generated using an ultra-short pulse laser and semiconductor device technologies. The availability of monocycle terahertz radiation sources has encouraged innovative research and development activities worldwide in an extremely wide range of applications, from security to medical systems. However, the fundamental device

Iwao Hosako; Norihiko Sekine; Mikhail Patrashin; Hiroaki Yasuda

2007-01-01

320

Reflection Image Spectroscopy across the Andean subduction zone  

NASA Astrophysics Data System (ADS)

This paper presents new insights into the South American subduction zone from reprocessed seismic images. We applied a 3D Kirchhoff prestack depth migration scheme to data sets containing different narrow frequency ranges in order to extract additional details from seismic reflection images. This approach accounts for the effects of scattering on the seismic image, especially for structures below a heterogeneous overburden. The reflection image in such environments will differ significantly when focusing on different frequency ranges due to the frequency dependence of scattering that is likely to be present. The narrow frequency range images uncover reflectors in one frequency range that are masked in another range. Furthermore, the images enable for instance the characterization of the medium in terms of scatterer concentration and thus improve the structural interpretation. The analysis of these images might help to distinguish between small-scale structures in the high-frequency band and large-scale structures in the low-frequency band. We call this imaging approach Reflection Image Spectroscopy (RIS). We applied the RIS approach to the ANCORP'96 data set, an onshore deep seismic reflection profile across the South American Central Andes. The narrow frequency range images revealed additional details that we interpret as features directly linked to fluid migration processes in the subduction zone. Furthermore, structural details of the oceanic crust and the overlying mantle and crust are revealed. From the narrow-frequency range images we interpret that the top of the so called Nazca reflector at 70 km depth marks the upper limit of the hydrated mantle wedge, whereas the bottom of the reflector represents the top of the subducted oceanic crust. The compilation of our results with local earthquake data confirms this interpretation. Similar features observed in another deep seismic profile (PRECORP'95) support this interpretation, too. Furthermore, the RIS images show a highly reflective heterogeneous zone between the Nazca reflector at 70 km depth and a prominent mid-crustal Bright Spot (Quebrada Blanca Bright Spot) at about 30 km depth. We associate this zone with a complex network of ascending fluids or partial melts, initiated by ascending fluids released from the subducted oceanic plate. This observation links the Quebrada Bright Spot directly to the dehydrating oceanic plate.

Yoon, M.; Buske, S.; Shapiro, S. A.; Wigger, P.

2009-07-01

321

Asymmetric planar terahertz metamaterials  

SciTech Connect

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.

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

2010-01-01

322

Morphology effects on charge generation and recombination dynamics at ZnPc:C60 bulk hetero-junctions using time-resolved terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The influence of growth temperature induced phase segregation and crystallinity in ZnPc:C60 blend films on the charge generation and recombination dynamics is investigated with optical-pump terahertz-probe spectroscopy. While an ultrafast photo-induced charge generation process is observed for all morphologies, a subsequent sub-nanosecond photoconductivity rise depends on crystallinity and phase segregation. For higher intensities, the signal is dominated by a morphology-dependent bimolecular recombination process. High local mobilities of minimal ? ~ 0.3 cm2/Vs are found. The increase of photoconductivity with film growth temperature correlates with formerly observed device photocurrent improvements.

Bartelt, Andreas F.; Strothkämper, Christian; Schindler, Wolfram; Fostiropoulos, Konstantinos; Eichberger, Rainer

2011-10-01

323

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)

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.

Balci, Soner; Baughman, William; Wilbert, David S.; Shen, Gang; Kung, Patrick; Kim, Seongsin Margaret

2012-12-01

324

Strong correlation of electronic and lattice excitations in GaAs/AlGaAs semiconductor quantum wells revealed by two-dimensional terahertz spectroscopy.  

PubMed

Coulomb-mediated interactions between intersubband excitations of electrons in GaAs/AlGaAs double quantum wells and longitudinal optical phonons are studied by two-dimensional spectroscopy in the terahertz frequency range. The multitude of diagonal and off-diagonal peaks in the 2D spectrum gives evidence of strong polaronic signatures in the nonlinear response. A quantitative theoretical analysis reveals a dipole coupling of electrons to the polar lattice that is much stronger than in bulk GaAs, due to a dynamic localization of the electron wave function by scattering processes. PMID:21902366

Kuehn, W; Reimann, K; Woerner, M; Elsaesser, T; Hey, R; Schade, U

2011-08-01

325

Multiple Internal Reflection Fourier Transform Infrared Spectroscopy Studies of Thiocyanate Adsorption on Silver and Gold.  

National Technical Information Service (NTIS)

Conducting silver and gold coatings on silicon Attenuated Total Reflectance (ATR) plates have been employed as transparent electrodes to monitor in situ surface electrochemistry. The multiple internal reflection Fourier transform infrared spectroscopy (MI...

D. B. Parry J. M. Harris K. Ashley

1989-01-01

326

Terahertz calculations for the Australian synchrotron  

SciTech Connect

The development of terahertz radiation (T-rays) is spurring new applications in spectroscopy and imaging. To maximize the use of T-rays in more applications, a high average terahertz power is needed. Rather than using fast diodes or laser sources, this paper will show that a synchrotron can generate high average power T-rays. This is achieved by creating an electron bunch in the synchrotron ring with high intensity in the terahertz frequency region via Thomson scattering.

Chien Aun Chan; Samuel P. Mickan; Gwyn P. Williams; Derek Abbott

2004-03-01

327

[Detection of pear firmness using near infrared diffuse reflectance spectroscopy].  

PubMed

The objective of the present research was to study the potential of NIR diffuse reflectance spectroscopy as a way for nondestructive measurement of the firmness of "Xueqing" pear. NIR spectral data were collected in the spectral region between 800 nm and 2,630 nm, but only the data between 800 nm and 2,500 nm were used for the analysis. Spectral data smoothing of different gaps using Savitsky-Goaly method was discussed both qualitatively and quantitatively. The results showed that the smoothing of NIR original spectra had little influence on spectral data analysis. Statistical models were developed using partial least square method. Models for three kinds of mathematical treatments of spectra (original, first derivative and second derivative) were established in three spectral regions: 800-2,500 nm, 800-1,890 nm and 832-872 nm. The original spectra showed better results than the first derivative spectra and second derivative in all the three spectral regions. And for the three spectral regions, the full wavelength range of 800-2,500 nm offered the best result. The PLS model of original spectra in the range of 800-2,500 nm gave best predictions of pear firmness, with correlation coefficient (r) of 0.869 and root mean square errors of calibration (RMSEC) of 3.88 N for the calibration sample set and with correlation coefficient (r) of 0.840 and root mean square error of prediction (RMSEP) of 4.26 N for the validation sample set. The results of the study show that NIR diffuse reflectance specroscopy can be used to predict the firmness of "Xueqing" pear. PMID:16961225

Fu, Xia-ping; Ying, Yi-bin; Liu, Yan-de; Lu, Hui-shan

2006-06-01

328

Infrared Internal Reflection Spectroscopy of Silicon Dioxide on Silicon  

NASA Astrophysics Data System (ADS)

The oxidation of silicon forms the basis of a multibillion dollar electronics industry. With increasing miniaturization required for the next generation of integrated circuits, understanding the structure of thin oxides and the oxide-silicon interface has become increasingly important. In contrast to analytical tools such as X-ray photoelectron spectroscopy that use high energy radiation capable of altering the structure under study, infrared spectroscopy uses benign low energy radiation to probe molecular bonds. I devised a previously unrecognized application of infrared internal reflection spectroscopy to analyze oxides as thin as 10A on silicon. The technique exploits displacement continuity in a thin low refractive index material sandwiched between two high refractive index materials to achieve an unprecedented spectral amplification. Spectra of the thin oxides revealed peaks at 1080 and 1240 cm^{-1}. The 1080-cm^{-1} peak was an asymmetrical Si-O-Si stretching vibration. With the aid of an infrared polarizer, experiments on a variety of oxides identified the 1240-cm^{ -1} peak as a longitudinal optical phonon mode. The experiments also supported a similar interpretation of the 1230-cm^{-1} peak in oxygen-containing silicon that had been spuriously attributed to a variety of origins such as crystobalite or combination modes of interstitial oxygen. One of the more interesting results of this research is that it showed that there was negligible native oxide growth (native oxide defined as SiO_{ rm x} with 1 <=q x <=q 2) within the typical time scale of electronics processing. A native oxide of 10 -15A is generally thought to form instantly on exposure of the clean silicon surface to air at room temperature. This oxide has been considered the cause of a variety of problems in silicon processing. The "native oxide" here is attributed to an ellipsometric artifact of surface roughness and to adsorbed contamination such as water and hydrocarbons. Because adsorbed contamination is less tightly bound to the silicon surface than oxide, this finding has far-ranging processing ramifications.

Olsen, John Edward

329

Intramyocardial oxygen transport by quantitative diffuse reflectance spectroscopy in calves  

NASA Astrophysics Data System (ADS)

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.

Lindbergh, Tobias; Larsson, Marcus; Szabó, Zoltán; Casimir-Ahn, Henrik; Strömberg, Tomas

2010-03-01

330

Broadband terahertz transmission within the air channel of thin-wall pipe.  

PubMed

We report broadband transmissions of terahertz radiations through the air channel of thin-wall pipe. The impacts of the wall thickness and of the refractive index of the material on the transmission window bandwidth are investigated. An extension of the bandwidth by at least 5.5 times is reported with a commercial drinking straw. The salient properties of the antiresonant reflecting guiding mechanism are studied with the terahertz time domain spectroscopy method, including the reduction of the attenuation coefficient of the propagated field by 60 times the material absorption coefficient. PMID:21593889

Nguema, Edwin; Férachou, Denis; Humbert, Georges; Auguste, Jean-Louis; Blondy, Jean-Marc

2011-05-15

331

Terahertz/mm wave imaging simulation software  

NASA Astrophysics Data System (ADS)

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.

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

2006-10-01

332

Magnetoplasmon resonances in polycrystalline bismuth as seen via time-domain terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We report the magnetic-field-dependent far-infrared reflectivity of polycrystalline bismuth. We observe four distinct absorptions that we attribute to magnetoplasmon resonances, which are collective modes of an electron-hole liquid in a magnetic field and become optical and acoustic resonances of the electron-hole system in the small-field limit. Acoustic mode are only when the masses of distinct components are very different, which is the case in bismuth. In a polycrystal, where the translational symmetry is broken, a big shift of spectral weight to an acoustic plasmon is possible. This enables us to detect an associated plasma edge. Although the polycrystal sample has grains of randomly distributed orientations, our reflectivity results can be explained by invoking only two, clearly distinct, series of resonances. In the limit of zero field, the optical modes of these two series converge onto plasma frequencies measured in a monocrystal along the main optical axes.

Levallois, Julien; Chudzi?ski, Piotr; Hancock, Jason N.; Kuzmenko, Alexey B.; van der Marel, Dirk

2014-04-01

333

Characterization of atherosclerotic plaque by reflection spectroscopy and thermography: a comparison  

Microsoft Academic Search

Many methods for detecting and measuring vulnerable atherosclerotic plaques have been proposed. These include reflection spectroscopy, thermography, ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI). This paper presents an analysis and a comparison of two of these methods, near-infrared reflection spectroscopy (NIRS) and thermography. Most of the published literature evaluate methods statistically. A more analytic approach will make it

Magnus B. Lilledahl; Olav A. Haugen; Lise L. Randeberg; Lars O. Svaasand

2005-01-01

334

Solvent-induced backbone fluctuations and the collective librational dynamics of lysozyme studied by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

THz spectroscopy is used to investigate the dynamics of the globular protein hen egg white lysozyme under varying hydration and temperature conditions. An analysis of the experimental spectra has revealed that the amount of solvent in the hydration shell has a strong influence on the low-frequency protein conformational dynamics and also the arrangement of hydrogen bonds in the protein secondary structure. Furthermore at a hydration level >0.2 we identify collective backbone fluctuations in the protein secondary structure that are not present at low hydration. It is possible that these solvent induced modes are important for the biological function of the protein.

Woods, K. N.

2010-03-01

335

Suppression of spectral interferences due to water-vapor rotational transitions in terahertz time-domain spectroscopy.  

PubMed

Absorption lines of atmospheric water vapor are commonly present in terahertz spectra measured in ambient air. These spectral interferences are caused by the rotational transitions of water molecules. In this study, we develop an effective method for suppression of the water-vapor effects by modeling the absorption lines using Lorentzian line shape and spectroscopic parameters extracted from the HITRAN database and then subtracting them iteratively in the frequency domain. The free-space terahertz pulse and the absorbance spectrum of an explosive material are restored successfully in the experimental verification. PMID:18552956

Wang, Yingxin; Zhao, Ziran; Chen, Zhiqiang; Zhang, Yan; Zhang, Li; Kang, Kejun

2008-06-15

336

Diffuse Reflectance Spectroscopy for Total Carbon Analysis of Hawaiian Soils  

NASA Astrophysics Data System (ADS)

Accurate assessment of total carbon (Ct) content is important for fertility and nutrient management of soils, as well as for carbon sequestration studies. The non-destructive analysis of soils by diffuse reflectance spectroscopy (DRS) is a potential supplement or alternative to the traditional time-consuming and costly combustion method of Ct analysis, especially in spatial or temporal studies where sample numbers are large. We investigate the use of the visible to near-infrared (VNIR) and mid-infrared (MIR) spectra of soils coupled with chemometric analysis to determine their Ct content. Our specific focus is on Hawaiian soils of agricultural importance. Though this technique has been introduced to the soil community, it has yet to be fully tested and used in practical applications for all soil types, and this is especially true for Hawaii. In short, DRS characterizes and differentiates materials based on the variation of the light reflected by a material at certain wavelengths. This spectrum is dependent on the material’s composition, structure, and physical state. Multivariate chemometric analysis unravels the information in a set of spectra that can help predict a property such as Ct. This study benefits from the remarkably diverse soils of Hawaii. Our sample set includes 216 soil samples from 145 pedons from the main Hawaiian Islands archived at the National Soil Survey Center in Lincoln, NE, along with more than 50 newly-collected samples from Kauai, Oahu, Molokai, and Maui. In total, over 90 series from 10 of the 12 soil orders are represented. The Ct values of these samples range from < 1% - 55%. We anticipate that the diverse nature of our sample set will ensure a model with applicability to a wide variety of soils, both in Hawaii and globally. We have measured the VNIR and MIR spectra of these samples and obtained their Ct values by dry combustion. Our initial analyses are conducted using only samples obtained from the Lincoln archive. In this preliminary case, we use Partial Least Squares (PLS) regression with cross validation to develop a prediction model for soils of unknown carbon content given only their spectral signature. We find R2 values of greater than 0.93 for the MIR spectra and 0.87 for the VNIR spectra, indicating a strong ability to correlate a soil’s spectrum with its Ct content. We build on these encouraging results by continuing chemometric analyses using the full data set, different data subsets, separate model calibration and validation groups, combined VNIR and MIR spectra, and exploring different data pretreatment options and variations to the PLS parameters.

McDowell, M. L.; Bruland, G. L.; Deenik, J. L.; Grunwald, S.; Uchida, R.

2010-12-01

337

Terahertz Spectroscopy as a non contact estimation technique of defect states in high dielectric constant materials  

NASA Astrophysics Data System (ADS)

A large number of gate dielectric materials have been examined during the past few years to replace Silicon dioxide in the MOSFET industry to reduce gate leakage currents for microfabrication of devices. Among them, Hafnium based materials have become a very promising candidate. In the reported work, the effect of Hafnium dioxide films on p-type silicon substrates has been investigated and compared with conventional dielectric material, Silicon dioxide, using CW visible pump/THz probe spectroscopy. Drude analysis of the experimentally obtained differential transmission spectra evaluates the electric permittivity of the interfacial layer and the calculated defect density is found to be higher for HfO2 than for SiO2 which agrees with Hall measurements. Additional measurements on Silicon Nitride deposition and photoresist coated p+ Silicon on p-type silicon wafers without any oxide gave an interfacial defect density 50 times higher than that of SiO2/p+ interface. Results indicate that the mobility of the layer underneath Hafnium is less than that of Silicon. Hence the present study emphasizes the advantage of THz spectroscopy as a non-contact tool for semiconductor metrological applications.

Sengupta, Amartya; Bandyopadhyay, Aparajita; Altan, Hakan; Federici, John; Grebel, Haim

2006-03-01

338

Point contact Andreev reflection spectroscopy for measuring spin polarization  

NASA Astrophysics Data System (ADS)

The Co-Pt systems have been extensively studied because of their potential applications in spintronic devices. We have experimentally measured transport spin polarization (PC) using Point Contact Andreev Reflection (PCAR) spectroscopy and magnetic properties of Co1-xPt x alloys. All films with x varying from 0 to 100% and a thickness of ˜1000 A were grown on Si substrates covered with ˜250 A of SiO 2 by magnetron sputtering (Ref. [1]). We have also performed band-structure calculations of the spin polarization in the same Co-Pt system. We have demonstrated that the experimental and theoretical results are in reasonably good agreement. We have compared the PCAR results with the tunneling spin polarization (TSP) values recently reported by Kaiser et al. (Ref. [1]) and showed that the overall trend of PCAR spin polarization is almost the same as for TSP with Al 2O3 barrier, but it is very different from the TSP with ALN barrier. We have performed X-ray Diffraction (XRD) experiments on these alloys and found that they, in general, exhibited face centered cubic crystallographic structure. Furthermore, our results renounce the idea of a direct relationship between the spin polarization and the magnetic moment for these alloys. We were surprised to find that pure Pt films showed obvious magnetic signatures both from PCAR spectroscopy and magnetization measurements, while TSP was found to be zero for pure Pt electrodes (Ref. [1]). The Co-based Heusler alloys are also of special interest for possible spintronic applications due to their high Curie temperatures and high magnetic moment per unit cell. Co2FeSi is especially promising as a candidate half-metal as it has a Curie temperature of approximately 1100 K and the integer magnetic moment of 6 muB per unit cell (Ref. [2]). The samples have been prepared by arc melting of stoichiometric quantities of pure metals in argon atmosphere followed by annealing in sealed quartz tubes at 1300 K. We have experimentally measured PC in Co2FeSi and Co2Mn0.5Fe0.5Si using PCAR spectroscopy. We found that spin polarization for these two alloys was significantly lower than that predicted by theoretical studies. We have attributed this reduction in spin polarization to the defects and disorder in the crystallographic structure within the Heusler alloys. Moreover, we have also experimentally demonstrated that doping with Mn in Co2FeSi did not improve spin polarization for this alloy. Spin diffusion length (Lsf) is of fundamental importance for spin dependent transport and spintronic devices. So far, most of the measurements of Lsf in nonmagnetic metals have been done in the lateral non-local geometry, with the chemical potential difference characterizing the spin imbalance. We have experimentally demonstrated spin transport studies in Heusler/Au bilayers using PCAR spectroscopy. Variable thickness Au films were deposited on top of the Heusler alloys and the PCAR spectroscopy was then used to probe PC on the Au side. In our approach Lsf was measured directly with PCAR spectroscopy. A spin polarized current was injected from a ferromagnetic electrode, Co2Mn0.5Fe0.5Si Heusler alloy, into Au films of variable thickness. The spin current, which gradually decays with the increased thickness of the film, was measured with a superconducting Nb tip. We developed a phenomenological theory which allowed us to determine Lsf in such a system. We found L sf in Au to be on the order of 312+/-36 nm at 4 K, comparable to the results obtained by other techniques using conventional ferromagnetic spin injectors. Similar results were obtained with a Gd single crystal. One of the potential advantages of this new technique, however, is the ability to do the point contact measurements on the side of the normal electrode, which should allow one to do the complete measurement of spin diffusion length by consequentially measuring the spin polarization in a normal metal as a function of thickness in a single sample. This experimental demonstration may be considered as the first step in this direction. (Abstract shortened b

Faiz, Muhammad Muzummal

339

Terahertz technology in biology and medicine  

Microsoft Academic Search

Terahertz irradiation and sensing is being applied for the first time to a wide range of fields outside the traditional niches of space science, molecular line spectroscopy, and plasma diagnostics. This paper surveys some of the terahertz measurements and applications of interest in the biological and medical sciences.

Peter H. Siegel

2004-01-01

340

Metal wires for terahertz wave guiding  

Microsoft Academic Search

Sources and systems for far-infrared or terahertz (1THz = 1012Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal

Kanglin Wang; Daniel M. Mittleman

2004-01-01

341

Studies of Planetary Materials Using Cryogenic Reflectance Spectroscopy  

NASA Astrophysics Data System (ADS)

Current and planned spacecraft missions to Mars and the Outer Solar System rely on laboratory measurements to facilitate interpretation of remote-sensing data. Solar system objects typically occupy environments far from terrestrial ambient conditions. Compositional studies based on infrared spectroscopy are particularly dependent on laboratory work, as many planetary materials exhibit changes in spectral behavior due to extremes of temperature, pressure, and other influences. The conditions at the surfaces of icy satellites, for example, are difficult to reproduce except under tightly controlled specifications. This is illustrated by comparing the visible and near-infrared reflectance of several materials measured at cryogenic temperatures. Water ice, which is of interest for most solid bodies of the outer solar system, exhibits strong temperature dependence, as does methane ice (Grundy and Schmitt, 1998; Grundy et al., 2002). Hydrated materials, such as salts anticipated to be abundant at Europa, and ammonia hydrates relevant to the Saturnian satellites, also display strong variations with temperature (Dalton and Clark, 1998; McCord et al., 1999; Dalton, 2001). Pyroxenes and olivines, found in rocky bodies including the moon, meteorites, and Mars, also change with temperature (Singer and Roush, 1985; Moroz et al., 2000; Hinrichs and Lucey, 2002). We have initiated a program investigating temperature sensitivity of planetary materials in support of spacecraft missions. Measurements are performed in a cryogenic vacuum environment chamber with a compressed helium cryostat capable of maintaining temperatures as low as 10 Kelvin. We will report on materials such as sulfate hydrates, which display profound spectral changes at low temperatures, and other materials we have measured, such as calcium carbonate, iron sulfide, and tholins (Roush and Dalton, 2002). While many materials are expected to show only modest variations, careful measurement and analysis of planetary materials in the laboratory is necessary to confirm interpretations of remotely-sensed spectra of solar system objects.

Dalton, J. B.; Roush, T. L.; Jamieson, C. S.

2002-09-01

342

Terahertz Spectroscopy of Molecules in the Interstellar Medium and around Stars - Sure Bets and Challenges  

NASA Astrophysics Data System (ADS)

In the very near future, powerful new observatories willrevolutionize broad band astronomical spectroscopy at THz frequencies. These include the Herschel Space Observatory, the Atacama Large Millimeter Array and, at somewhat lower, GHz, frequencies the Expanded Very Large Array. The latter two, ``radio''-style interferometers will allow sub-arcsecond, high spectral resolution imaging with total instantaneous observing bandwidths up to 100 times larger than present day facilities. This will allow comprehensive multi-transition/multi species studies that offer new approaches to a variety of astrophysical/chemical areas all of which are dependent on the availability of extensive laboratory data. To give a few examples: For many interesting sources it will be possible to get a complete astrochemical ``fingerprint'' in a single observing session with high-quality images of the distributions of the individual species! Targets include the extremely molecule-rich hot molecular cores around protostellar objects and emission from vibrationally excited lines from the innermost circumstellar envelopes of nearby asymptotic branch branch stars which will be imaged with a resolution better than the stellar diameter. Complete, high spectral resolution scans of various keystone objects over the whole 480-1250 and 1410-1920 GHz ranges will be conducted by the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel. These include lines from various important hydride species and, importantly, water vapor that are not observable from the ground. Organic molecules have hundreds of GHz/THz lines. However, due to the generally low abundances and large partition functions of ``new'' (yet to identified) very complex species, all of these are weak and have to be picked out of a thicket of also weak rotational lines from within relatively low energy vibrationally excited levels from various isotopologues of known species. Here, comprehensive model spectra of all the species known to exist in a source have to be constructed to ``weed out'' the contaminants. This requires comprehensive laboratory data, which as of now is far from existing. Moreover, Herschel will allow access to types of transitions, e.g., vibrational ones from carbon chain species, for which spectroscopic data has yet to be obtained. I shall give an overview of the challenges and great opportunities of astronomical molecular spectroscopy in the coming years and the crucial role of laboratory spectroscopy.

Menten, Karl M.

2009-06-01

343

Simultaneous time and wavelength resolved spectroscopy under two-colour near infrared and terahertz excitation.  

PubMed

Time and wavelength resolved spectroscopy requires optical sources emitting very short pulses and a fast detection mechanism capable of measuring the evolution of the output spectrum as a function of time. We use table-top Ti:sapphire lasers and a free-electron laser (FEL) emitting ps pulses as excitation sources and a streak camera coupled to a spectrometer for detection. One of the major aspects of this setup is the synchronization of pulses from the two lasers which we describe in detail. Optical properties of the FEL pulses are studied by autocorrelation and electro-optic sampling measurements. We discuss the advantages of using this setup to perform photoluminescence quenching in semiconductor quantum wells and quantum dots. Carrier redistribution due to pulsed excitation in these heterostructures can be investigated directly. Sideband generation in quantum wells is also studied where the intense FEL pulses facilitate the detection of the otherwise weak nonlinear effect. PMID:22047280

Bhattacharyya, J; Wagner, M; Zybell, S; Winnerl, S; Stehr, D; Helm, M; Schneider, H

2011-10-01

344

Holography and phase retrieval in terahertz imaging  

NASA Astrophysics Data System (ADS)

In this paper, we present review and latest results obtained in the scope of terahertz holographic and other methods for phase retrieval in terahertz imaging. Not only accurate change of amplitude, but also rigorous phase retrieval is essential for precise calculation of optical parameters of the samples in terahertz range. Pulse terahertz holography introduced some years ago shows itself as perfect method for overall-object phase retrieval technique, but in the same time it allows measurement with low signal to noise that leads to less precise derivation of sample optical parameters. And certainly just point-by-point terahertz time-domain spectroscopy provides the most precise information of sample phase, but it is rather time consuming and has low spatial resolution as well. The other possible way assumes, in contrary to pulse terahertz holography and spectroscopy, using narrow-band continuous terahertz source, which tunability might also make the measurement process easier. And diffraction patterns registered with microbolometer array or any other terahertz intensity sensor placed at several different distances from the object and/or taken for several different terahertz frequencies are used for phase retrieval in this case. We present both numerical predictions and experimental results for the proposed methods, estimate the achievable spatial and other limits of the techniques and compare them to the others used in different spectral ranges.

Petrov, Nikolay V.; Gorodetsky, Andrei A.; Bespalov, Victor G.

2013-09-01

345

Use of Finite Difference Time Domain Simulations and Debye Theory for Modelling the Terahertz Reflection Response of Normal and Tumour Breast Tissue  

PubMed Central

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.

Fitzgerald, Anthony J.; Pickwell-MacPherson, Emma; Wallace, Vincent P.

2014-01-01

346

The determination of thin film thickness using reflectance spectroscopy  

Microsoft Academic Search

The reflectance spectrum of a coated polycarbonate sample was used to determine the film thickness of a polymeric coating. Absolute reflectance spectra were acquired over the range 400-800 nm using a Cary 5000 UV-Vis-NIR spectrophotometer and 'VW' absolute specular reflectance accessory. Based on the interference fringes observed, the thickness of the film was calculated to be 4.95 µm.

Andrew R. Hind; Lisette Chomette

347

Reflectance spectroscopy: quantitative analysis techniques for remote sensing applications.  

USGS Publications Warehouse

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

Clark, R. N.; Roush, T. L.

1984-01-01

348

Reflectance Spectroscopy: Quantitative Analysis Techniques for Remote Sensing Applications  

Microsoft Academic Search

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 optical path length and the implications for use in modeling reflectance spectra are presented. It is shown that the mean optical path length in a particulate

Roger N. Clark; Ted L. Roush

1984-01-01

349

THz spectroscopy and imaging in security applications  

Microsoft Academic Search

We compared terahertz transmission spectra of explosives measured by means of Time Domain Spectroscopy (TDS) and an Optical Parametric Oscillator-based system (OPO). Reflection spectra of pure explosives were measured in reflection configuration by means of TDS in the range 0.3–2.5THz. We also analyzed influence of the surface roughness on reflectance and phase spectra of RDX-plastic based explosives. Next, we present

Norbert Palka; Mieczyslaw Szustakowski; Marcin Kowalski; Tomasz Trzcinski; Radoslaw Ryniec; Marek Piszczek; Wieslaw Ciurapinski; Marek Zyczkowski; Przemyslaw Zagrajek; Janusz Wrobel

2012-01-01

350

Detection of Soil Surface Contaminants by Infrared Reflection Spectroscopy  

SciTech Connect

A benchtop Fourier transform infrared spectrometer and specular reflection accessory has been used to record reflection spectra of several chemical compounds coating a loamy, psamment soil. Unpolarized reflection spectra were recorded between 4600 and 500 cm-1 with a resolution of 4 cm-1 for the compounds dimethyl methylphosphonate, trimethyl phosphate, methylphosphonic acid, 2,2'-thiodiethanol, diazinon, diesel fuel, and ammonium nitrate mixed separately into soil samples with concentrations of 10, 5, and 1 mg of analyte per gram of soil. The soil reflection spectra are compared to liquid or solid transmission spectra of the pure compound and frequency shifts and relative intensity changes for the absorption features are noted. As an example of detection sensitivity, we have estimated that we can detect one of the C - H stretch modes of dimethyl methylphosphonate with a signal-to-noise (peak-to-peak) of 3 for 300 nanograms of analyte on the surface layer of soil in the focal spot of the reflectance accessory. We also estimate that the flux of infrared photons reaching the soil is 1018/sec. We have recorded polarization resolved reflection spectra of the uncoated soil and coarse and fine grained sands as a function of angle of incidence and reflection and have determined the degree of polarization for light reflected off of these materials at frequencies associated with volume scattering and surface scattering features. As might be expected, the volume scattering features show a significant depolarization of the light--degree of polarization after reflection is < 20%--and the surface scattering features retain a much higher degree of polarization upon reflection, > 75%. We have also recorded polarization resolved spectra of tributyl phosphate on the soil and found significant differences between the s- and p-polarized spectra. This fact could be used to employ polarization modulation detection to improve detection sensitivity.

Blake, Thomas A. (BATTELLE (PACIFIC NW LAB)); Gassman, Paul L. (BATTELLE (PACIFIC NW LAB)); S.D. Christensen, A.J. Sedlacek

2002-01-01

351

Detection of soil surface contaminants by infrared reflection spectroscopy  

NASA Astrophysics Data System (ADS)

A benchtop Fourier transform infrared spectrometer and specular reflection accessory have been used to record reflection spectra of several chemical compounds coating a loamy, psamment soil. Unpolarized reflection spectra were recorded between 4600 and 500 cm-1 with a resolution of 4 cm-1 for the compounds dimethyl methylphosphonate, trimethyl phosphate, methylphosphonic acid, 2,2'-thiodiethanol, diazinon, diesel fuel, and ammonium nitrate mixed separately into soil samples with concentrations of 10, 5, and 1 mg of analyte per gram of soil. The soil reflection spectra are compared to liquid or solid transmission spectra of the pure compound and frequency shifts and relative intensity changes for the absorption features are noted. As an example of detection sensitivity, we have estimated that we can detect 300 nanograms of dimethyl methylphosphonate on the surface layer of soil in the focal spot (15 mm2) of the reflection accessory using one of DMMP's C - H stretch modes. The signal-to-noise (peak-to-peak) of this spectral feature under these circumstances would be 3/1. We also estimate that the flux of infrared photons reaching the soil is 1014 photons/sec/cm-1. We have recorded polarization-resolved reflection spectra of the uncoated soil and coarse and fine grained quartz sands as a function of angle of incidence and reflection and have determined the degree of polarization for light reflected off of these materials at frequencies associated with volume scattering and surface scattering features. As might be expected, the volume scattering features show a significant depolarization of the light - degree of polarization after reflection is < 20% - and the surface scattering features retain a much higher degree of polarization upon reflection, > 75%. We have also recorded polarization resolved spectra of tributyl phosphate on the soil and found significant differences between the s- and p-polarized spectra. This fact could be used to employ polarization modulation detection to improve detection sensitivity.

Blake, Thomas A.; Gassman, Paul L.

2002-02-01

352

The excitation and emission of terahertz surface plasmon polaritons on metal wire waveguides  

Microsoft Academic Search

The development of effective techniques for guiding pulsed terahertz radiation is essential for the continued development of terahertz spectroscopy and imaging applications based on the technique of time-domain spectroscopy. Terahertz surface plasmon polaritons (SPPs) can be excited and guided on cylindrical metal wires with low loss and dispersion. This propagating surface wave, known as a Sommerfeld wave, possesses radial polarization,

Jason A. Deibel; Kanglin Wang; Matthew Escarra; Nicholas Berndsen; Daniel M. Mittleman

2008-01-01

353

Cavity enhanced terahertz modulation  

NASA Astrophysics Data System (ADS)

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%.

Born, N.; Scheller, M.; Koch, M.; Moloney, J. V.

2014-03-01

354

Photoinduced insulator-metal phase transition and the metallic phase propagation in VO2 films investigated by time-resolved terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The particle size and film thickness dependence of the photoinduced insulator-metal phase transition in VO2 films has been studied systematically by time-resolved terahertz spectroscopy at room temperature. It is found that the dynamical photoinduced phase transition from insulator to metal consists of two processes: a 1.7 ps fast process and a slow process with a typical time constant of 40 ps. Both of the two processes show particle size independence. The 40 ps slow process is revealed to arise from the longitudinal propagation of the metallic phase from the photoexcited surface to the interior of the VO2 film. A phase boundary propagation speed with a magnitude of ˜2400 m/s is obtained, which is close to the velocity of sound in solid materials and coincides with the prediction of diffusionless phase transformation. Our experimental results clearly establish the entire procedure of photoinduced phase change in the VO2 film.

Xue, Xin; Jiang, Meng; Li, Gaofang; Lin, Xian; Ma, Guohong; Jin, Ping

2013-11-01

355

Hierarchy of bound states in the one-dimensional ferromagnetic Ising chain CoNb2O6 investigated by high-resolution time-domain terahertz spectroscopy.  

PubMed

Kink bound states in the one-dimensional ferromagnetic Ising chain compound CoNb2O6 have been studied using high-resolution time-domain terahertz spectroscopy in zero applied magnetic field. When magnetic order develops at low temperature, nine bound states of kinks become visible. Their energies can be modeled exceedingly well by the Airy function solutions to a 1D Schrödinger equation with a linear confining potential. This sequence of bound states terminates at a threshold energy near 2 times the energy of the lowest bound state. Above this energy scale we observe a broad feature consistent with the onset of the two particle continuum. At energies just below this threshold we observe a prominent excitation that we interpret as a novel bound state of bound states--two pairs of kinks on neighboring chains. PMID:24745454

Morris, C M; Valdés Aguilar, R; Ghosh, A; Koohpayeh, S M; Krizan, J; Cava, R J; Tchernyshyov, O; McQueen, T M; Armitage, N P

2014-04-01

356

Hierarchy of Bound States in the One-Dimensional Ferromagnetic Ising Chain CoNb2O6 Investigated by High-Resolution Time-Domain Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

Kink bound states in the one-dimensional ferromagnetic Ising chain compound CoNb2O6 have been studied using high-resolution time-domain terahertz spectroscopy in zero applied magnetic field. When magnetic order develops at low temperature, nine bound states of kinks become visible. Their energies can be modeled exceedingly well by the Airy function solutions to a 1D Schrödinger equation with a linear confining potential. This sequence of bound states terminates at a threshold energy near 2 times the energy of the lowest bound state. Above this energy scale we observe a broad feature consistent with the onset of the two particle continuum. At energies just below this threshold we observe a prominent excitation that we interpret as a novel bound state of bound states—two pairs of kinks on neighboring chains.

Morris, C. M.; Valdés Aguilar, R.; Ghosh, A.; Koohpayeh, S. M.; Krizan, J.; Cava, R. J.; Tchernyshyov, O.; McQueen, T. M.; Armitage, N. P.

2014-04-01

357

Terahertz reflectometry of burn wounds in a rat model  

PubMed Central

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.

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

2011-01-01

358

UV Reflection Spectroscopy for In-Situ Polymer Reaction Monitoring Using Bifurcated Optical Fiber.  

National Technical Information Service (NTIS)

UV reflection spectroscopy can be utilized as a characterization tool for monitoring reactions in certain polymers, which lack high quantum yield and thus, the application of fluorescence technique is impractical. This paper describes our recent developme...

H. J. Paik D. K. Hestermann N. H. Sung

1995-01-01

359

Fluorescence and Diffuse Reflectance Spectroscopy for Breast Cancer Diagnosis During Core Needle Biopsy.  

National Technical Information Service (NTIS)

The goal of this project is to explore the potential of using tissue fluorescence and diffuse reflectance spectroscopy for breast cancer detection during a core needle breast biopsy. Both empirically based and model based approaches have been explored for...

C. Zhu

2007-01-01

360

Infrared Reflection Spectroscopy Study of Orientational Behavior in Poly(3-Methylthiophene) on a Pt Surface.  

National Technical Information Service (NTIS)

Infrared reflection-absorption spectroscopy (IRRAS) has been used to obtain the vibrational spectra of thin films of poly(3-methylthiophene) electrochemically polymerized on a platinum surface. Clear orientational effects, with the thiophene rings oriente...

X. Q. Yang T. Inagaki J. Chen T. A. Skotheim Y. Okamoto

1987-01-01

361

Water Adsorption on Diamond (110) Studied by Multiple Internal Reflection Infrared Spectroscopy.  

National Technical Information Service (NTIS)

The adsorption of water on a natural, type IIa diamond (110) surface is studied by multiple internal reflection infrared spectroscopy (MIRIRS). Similar results are observed for the hydrogen-free, and hydrogen-terminated diamond (110) surfaces. Exposure of...

M. McGonigal J. N. Russell P. E. Pehrsson H. Maguire J. E. Butler

1993-01-01

362

Terahertz imaging applied to cancer diagnosis.  

PubMed

We report on terahertz (THz) time-domain spectroscopy imaging of 10 microm thick histological sections. The sections are prepared according to standard pathological procedures and deposited on a quartz window for measurements in reflection geometry. Simultaneous acquisition of visible images enables registration of THz images and thus the use of digital pathology tools to investigate the links between the underlying cellular structure and specific THz information. An analytic model taking into account the polarization of the THz beam, its incidence angle, the beam shift between the reference and sample pulses as well as multiple reflections within the sample is employed to determine the frequency-dependent complex refractive index. Spectral images are produced through segmentation of the extracted refractive index data using clustering methods. Comparisons of visible and THz images demonstrate spectral differences not only between tumor and healthy tissues but also within tumors. Further visualization using principal component analysis suggests different mechanisms as to the origin of image contrast. PMID:20671358

Brun, M-A; Formanek, F; Yasuda, A; Sekine, M; Ando, N; Eishii, Y

2010-08-21

363

Electronic THz reflection spectroscopy for detecting energetic materials  

Microsoft Academic Search

We report the first 10-450 GHz single pixel reflection spectra of several energetic materials (explosives). These are measured with an all-electronic reflection spectrometer, and we compare them to those of common objects and human skin to show differences in dielectric contrast. This instrument uses microwave sources to drive picosecond GaAs nonlinear transmission lines and sampling detectors, so it can form

V. Agrawal; T. Bork; S. Kee; D. W. Van Der Weide

1998-01-01

364

Total internal reflection fluorescence microscopy imaging-guided confocal single-molecule fluorescence spectroscopy  

PubMed Central

We have developed an integrated spectroscopy system combining total internal reflection fluorescence microscopy imaging with confocal single-molecule fluorescence spectroscopy for two-dimensional interfaces. This spectroscopy approach is capable of both multiple molecules simultaneously sampling and in situ confocal fluorescence dynamics analyses of individual molecules of interest. We have demonstrated the calibration with fluorescent microspheres, and carried out single-molecule spectroscopy measurements. This integrated single-molecule spectroscopy is powerful in studies of single molecule dynamics at interfaces of biological and chemical systems.

Zheng, Desheng; Kaldaras, Leonora; Lu, H. Peter

2012-01-01

365

Longitudinal current modulated light reflectance spectroscopy of semiconductor laser heterostructures  

Microsoft Academic Search

In this work we introduce new effective method of modulation spectroscopy for investigation of high power semiconductor laser heterostructures and compare it with traditional photoreflectance and photoluminescence methods. We present experimental results for AlGaAs\\/GaAs semiconductor laser heterostructure with strained InGaAs quantum well grown on n+-GaAs substrate.

O. A. Ryabushkin; A. Y. Romanyuk; M. A. Chernikov; A. E. Sotnikov; P. Trubenko; N. Moshegov; A. Ovtchinnikov

2003-01-01

366

Determination of styrene-butadiene rubber composition by attenuated total internal reflection infrared spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Orlov, A. S.; Kiselev, S. A.; Kiseleva, E. A.; Budeeva, A. V.; Mashukov, V. I.

2013-03-01

367

Dermal carotenoid measurements via pressure mediated reflection spectroscopy.  

PubMed

We describe a reflection-based method for the quantitative detection of carotenoid antioxidants in living human skin. The skin tissue site of interest is illuminated with broad-band white light spanning the spectral range from 350-850 nm and the spectral composition of the diffusively reflected light is analyzed in real time. Topical pressure is applied to temporarily squeeze blood out of the illuminated tissue volume. In this way the influence of oxy-hemoglobin on the reflection spectra is effectively reduced. After a short optical clearing time the carotenoid absorption becomes easily discernable in a 460-500 nm spectral window and its optical density can be calculated with high accuracy. Our empirical methodology provides a non-invasive rapid determination of skin carotenoid levels, can be used to monitor skin carotenoid concentration changes over time in response to carotenoid containing natural or supplemental diets, and is easily adaptable for applications in clinical and field settings. PMID:22331637

Ermakov, Igor V; Gellermann, Werner

2012-07-01

368

Investigation of the enzymatic digestion of plant cell walls using reflectance Fourier Transform Infrared spectroscopy  

Microsoft Academic Search

A method has been developed to determine the reflectance Fourier Transform Infrared spectra of plant cells grown in vitro and of the protoplasts released from such cells by enzymatic digestion. It is demonstrated that there is a smooth and reproducible transition in spectral detail as enzymatic digestion procedes. Reflectance Fourier Transform Infrared spectroscopy has been used to monitor the progress

J. Hopkinson; C. Moustou; K. A. Charlwood; J. E. Newbery; B. V. Charlwood

1985-01-01

369

Reflectance spectroscopy of mineral samples at IAS\\/Orsay laboratory  

Microsoft Academic Search

In the last 20 years, imaging spectrometry in the visible and infrared onboard spacecraft has become an essential technique to study surfaces of planetary objects, prior and in addition to in-situ investigations. Remote sensing experiments analysing the sunlight reflected or emitted by planetary surfaces can be used to derive the mineralogical composition and physical properties of the natural surfaces observed.

G. Bonello; J. P. Bibring; S. Erard; L. D'Hendecourt; J. M. Bardintzeff; B. Platevoet

2003-01-01

370

Monitoring bruise age using visible diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

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.

McMurdy, John W.; Duffy, Susan; Crawford, Gregory P.

2007-03-01

371

Far infrared (terahertz) spectroscopy of a series of polycyclic aromatic hydrocarbons and application to structure interpretation of asphaltenes and related compounds.  

PubMed

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[?]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. PMID:23603577

Cataldo, Franco; Angelini, Giancarlo; García-Hernández, D Aníbal; Manchado, Arturo

2013-07-01

372

Authentication of Rice Using Near-Infrared Reflectance Spectroscopy  

Microsoft Academic Search

Cereal Chem. 80(3):346-349 The authentication of rice (Korean domestic rice vs. foreign rice) has been attempted using near-infrared spectroscopy (NIRS). Two sample sets (n1 = 280 and n2 = 200) were used to obtain calibration equations and the spectral regions used for this study were 500-600 nm, 700-900nm, and 980-2,498 nm. Modified partial least square (MPLS) regression was used to

Sang Sook Kim; Mee-Ra Rhyu; Jae Min Kim; Sang-Hyo Lee

2003-01-01

373

Mid-Infrared and Near-Infrared Diffuse Reflectance Spectroscopy for Soil Carbon Measurement  

Microsoft Academic Search

Diffuse reflectance spectroscopy offers a nondestruc- tive means for measurement of C in soils based on the The ability to inventory soil C on landscapes is limited by the reflectance spectra of illuminated soil. Both the NIR ability to rapidly measure soil C. Diffuse reflectance spectroscopic (400-2500 nm) and MIR (2500-25 000 nm) region have analysis in the near-infrared (NIR,

G. W. McCarty; J. B. Reeves III; V. B. Reeves; R. F. Follett; J. M. Kimble

2002-01-01

374

Catheter based mid-infrared reflectance and reflectance generated absorption spectroscopy  

DOEpatents

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.

Holman, Hoi-Ying N

2013-10-29

375

ChemCam Passive Reflectance Spectroscopy at Gale Crater, Mars  

NASA Astrophysics Data System (ADS)

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 first-order calibration of the ChemCam spectra. The spectral similarity to palagonitic soils is consistent with the results from the CheMin instrument for Rocknest sands. Changes in the 535 nm band depth are likely indicative of differences in the relative amount of ferric iron in crystalline phases. More strongly negative spectral slopes > 600 nm are typical of lower-reflectance, less dusty rock surfaces, whereas positive slopes < 600 nm are consistent with higher-reflectance, dustier surfaces. ChemCam elemental detections of Ca- and S-bearing veins correlate to high reflectance targets with some dust contamination. Spectra of the John_Klein and Cumberland drill tailings, as well as brushed and broken rock surfaces in the Yellowknife Bay area, exhibit much less 'red' spectral features, including inflections near 550 nm that are consistent with a number of ferrous and ferric iron-bearing clay mineral phases, similar to CheMin results. Ongoing work with ChemCam passive spectra will include efforts to utilize the UV spectral range (sensitive to iron content), investigate photometric effects of illumination variations on the calibration targets, and dust mitigation efforts. As Curiosity traverses toward Mt. Sharp, passive spectra will be used as an additional tool to remotely track variations in surface chemistry and mineralogy, particularly for iron-bearing sulfate, oxide, and clay minerals.

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

376

Measuring Black Hole Spin Using X-Ray Reflection Spectroscopy  

NASA Astrophysics Data System (ADS)

I review the current status of X-ray reflection (a.k.a. broad iron line) based black hole spin measurements. This is a powerful technique that allows us to measure robust black hole spins across the mass range, from the stellar-mass black holes in X-ray binaries to the supermassive black holes in active galactic nuclei. After describing the basic assumptions of this approach, I lay out the detailed methodology focusing on "best practices" that have been found necessary to obtain robust results. Reflecting my own biases, this review is slanted towards a discussion of supermassive black hole (SMBH) spin in active galactic nuclei (AGN). Pulling together all of the available XMM-Newton and Suzaku results from the literature that satisfy objective quality control criteria, it is clear that a large fraction of SMBHs are rapidly-spinning, although there are tentative hints of a more slowly spinning population at high (M>5×107 M ?) and low (M<2×106 M ?) mass. I also engage in a brief review of the spins of stellar-mass black holes in X-ray binaries. In general, reflection-based and continuum-fitting based spin measures are in agreement, although there remain two objects (GRO J1655-40 and 4U 1543-475) for which that is not true. I end this review by discussing the exciting frontier of relativistic reverberation, particularly the discovery of broad iron line reverberation in XMM-Newton data for the Seyfert galaxies NGC 4151, NGC 7314 and MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk reflection, this detection of reverberation demonstrates that future large-area X-ray observatories such as LOFT will make tremendous progress in studies of strong gravity using relativistic reverberation in AGN.

Reynolds, Christopher S.

2013-08-01

377

Reflectance spectroscopy of mineral samples at IAS/Orsay laboratory  

NASA Astrophysics Data System (ADS)

In the last 20 years, imaging spectrometry in the visible and infrared onboard spacecraft has become an essential technique to study surfaces of planetary objects, prior and in addition to in-situ investigations. Remote sensing experiments analysing the sunlight reflected or emitted by planetary surfaces can be used to derive the mineralogical composition and physical properties of the natural surfaces observed. This technique was successfully used on many probes and will be improved as a main contribution of future missions to study several Solar System objects as Mercury (BEPI-COLOMBO), Venus (VENUS-EXPRESS), the Moon (SMART-1), Mars (MARS-EXPRESS, MRO...), Asteroids (ROSETTA, DAWN...), giant planet satellites (GALILEO, CASSINI) and comets (ROSETTA), increasing our knowledge of the formation and evolution of each object and leading to constrain the Solar System own ones. Nevertheless, the detection of diagnostic features in the spectrum acquired in order to identify mineral species needs the support of spectral database made with earth natural samples. Furthermore, the reflectance spectrum deconvolution to mineral abundance in an unambiguous way is difficult because the spectra can be complex non-linear functions of grain size, abundance, material opacity, and type of mixtures (intra, intimate, area mixtures). Ground support laboratory measurements are thus essential to interpret the spectra in terms of main chemical composition and improve the radiative transfer in particulate media modelling to deduce relative abundances. As part as some past and future instruments and being greatly concerned by the scientific background of surface geology topic, the IAS laboratory in Orsay develops a facility to achieve these goals. It consists of a Brücker IFS66V FTIR spectrometer combined with two Graseby toolkits that permit to measure reflectance of mineral samples (solid or powder). The first one is mounted in a fix biconical configuration, whereas the second one is a bi-directional configuration with variable incident and emergent angles ranging from 10 to 80°. The samples are selected, provided and prepared by the laboratoire de pétrologie which expertise is greatly needed to interpret the instruments data reduction in terms of geological history and geophysical mechanisms. Further investigations can be made with microprobe, X-ray diffraction or SEM coupled to EDS facilities present on the campus. We present first results on natural slabs of basalt polished with different abrasive powders compared to mechanically crushed powders separated into different particle size ranges of the same material and diffusion properties of natural aerial and fluvial eroded sands. We discuss the implication on reflectance spectra analysis and further investigations to be made.

Bonello, G.; Bibring, J. P.; Erard, S.; D'Hendecourt, L.; Bardintzeff, J. M.; Platevoet, B.

2003-04-01

378

Reflectance Spectroscopy of Functional Ag-Cu Thin Films: Correlation of Reflectivity with Cu Content  

NASA Astrophysics Data System (ADS)

We have investigated the optical properties of sputter-deposited silver-copper alloy thin films on silicon substrates at room temperature. We found that alloying copper with silver can significantly improve the metal's surface morphology, keeping its infrared reflectivity same as that of pure silver film. However at the same time, it worsens in the blue parts of the spectrum. The reflection in Ag-Cu thin films is interpreted in terms of a simple model describing its trend due to alloying. The experimental results and the speculations reveal a prospect for the improvement and optimization of solar reflectors.

Das, Sayantan; Alford, T. L.

2013-04-01

379

Analytical alignment tolerances for off-plane reflection grating spectroscopy  

NASA Astrophysics Data System (ADS)

Future NASA X-ray Observatories will shed light on a variety of high-energy astrophysical phenomena. Off-plane reflection gratings can be used to provide high throughput and spectral resolution in the 0.3-1.5 keV band, allowing for unprecedented diagnostics of energetic astrophysical processes. A grating spectrometer consists of multiple aligned gratings intersecting the converging beam of a Wolter-I telescope. Each grating will be aligned such that the diffracted spectra overlap at the focal plane. Misalignments will degrade both spectral resolution and effective area. In this paper we present an analytical formulation of alignment tolerances that define grating orientations in all six degrees of freedom. We verify our analytical results with raytrace simulations to fully explore the alignment parameter space. We also investigate the effect of misalignments on diffraction efficiency.

Allured, Ryan; McEntaffer, Randall T.

2013-12-01

380

Terahertz technology: a boon to tablet analysis.  

PubMed

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

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

2009-05-01

381

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

SciTech Connect

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

Schneider, Arno [Institute of Quantum Electronics, ETH Zurich, Zurich (Switzerland)

2010-09-15

382

Weathering Grade Classification of Granite Stone Monument Using Reflectance Spectroscopy  

NASA Astrophysics Data System (ADS)

Stone monument has been placed in field and exposed to rain and wind. This outdoor environment and air pollution induced weathering of stone monument. Weathering grade classification is necessary to manage and conserve stone monuments. Visual interpretation by geologist and laboratory experiments using specimens fallen off from the monument to avoid damage on the monument have been applied to classify weathering grade conventionally. Rocks and minerals absorb some particular wavelength ranges of electromagnetic energy by electronic process and vibrational process of composing elements and these phenomena produce intrinsic diagnostic spectral reflectance curve. Non-destructive technique for weathering degree assessment measures those diagnostic absorption features of weathering products and converts the depths of features related to abundance of the materials to relative weathering degree. We selected granite outcrop to apply conventional six folded weathering grade classification method using Schmidt hammer rebound teste. The correlations between Schmidt hammer rebound values and absorption depths of iron oxides such as ferric oxide in the vicinity of 0.9 micrometer wavelength and clay minerals such as illite and kaolinite in the vicinity of 2.2 micrometer wavelength, representative weathering products of granite, were analyzed. The Schmidt hammer rebound value decreased according to increase of absorption depths induced from those weathering products. Weathering grade classification on the granite stone monument was conducted by using absorption depths of weathering products This research is supported from National Research Institute of Cultural Heritage and we appreciate for this.

Hyun, C.; Roh, T.; Choi, M.; Park, H.

2009-05-01

383

Mars surface composition from reflectance spectroscopy - A summary  

NASA Technical Reports Server (NTRS)

Visible and near-infrared reflectance spectra and multispectral maps of the Martian surface are discussed, and implications of the data for the composition of the Martian surface are considered. Spacecraft and earth-based telescopic observations have confirmed the generally bimodal albedo distribution of the planet, dividing the surface into bright and dark regions. Mars spectra are characterized by the presence of strong Fe(+3) absorption, which is attributed to various ferric oxide minerals. Interpretations of the spectra from the dark regions indicate a basaltic or ultramafic source rock. Evidence for water ice or a highly desiccated metal hydrate has been obtained, along with evidence for CO2-ice only in the south polar cap. Mariner 9 observations of Martian dust suggest the presence of rather acidic rock or mineral particles, or a montmorillonite-type clay. Prospects for the future study of Martian surface composition include continuing earth-based spectrophotometric studies, and high-spectral-resolution mapping of a significant portion of the surface by the Galileo spacecraft and the next Mars mission.

Singer, R. B.; Clark, R. N.; Mccord, T. B.; Adams, J. B.; Huguenin, R. L.

1979-01-01

384

Standoff detection of explosive materials by differential reflection spectroscopy  

NASA Astrophysics Data System (ADS)

It is shown that 2, 4, 6-Trinitrotoluene (TNT) displays strong and distinct structures in differential reflectograms, near 420 nm and 250 nm. These characteristic peaks are not observed from approximately two dozen organic and inorganic substances which we tested and which may be in or on a suitcase. This exclusivity infers an ideal technique for explosives detection in mass transit and similar locations. The described technique for detection of explosives is fast, inexpensive, reliable, portable, and is applicable from some distance, that is, it does not require contact with the surveyed substance. Moreover, we have developed a curve discrimination program for field applications of the technique. Other explosives such as 1, 3, 5-trinitro-1, 3, 5 triazacyclohexane (RDX), 1, 3, 5, 7-Tetranitro-1, 3, 5, 7- tetraazacyclooctane (HMX), 2, 4, 6, N-Tetranitro-N-methylaniline (Tetryl), Pentaerythritol tetranitrate (PETN), and nitroglycerin have also been investigated and demonstrate similar, but unique, characteristic spectra. The technique utilizes near-ultraviolet to visible light reflected from two spots on the same sample surface yielding a differential reflectogram corresponding to the absorption of the sample. The origin of the spectra is attributed to the highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) transitions of the respective explosive molecule. Experiments using transmission spectrophotometry have also been performed to compliment and confirm the specific transitions. The results are supported by computer modeling of the molecular orbitals that yield UV and visible transitions.

Fuller, Anna M.; Hummel, Rolf E.; Schöllhorn, Claus; Holloway, Paul H.

2006-10-01

385

Polymer stabilized liquid crystal phase shifter for terahertz waves.  

PubMed

We propose an electrically tunable phase shifter for terahertz frequencies. The device is based on a polymer stabilized liquid crystal which allows for a simple device geometry. The polymer stabilized liquid crystal enables continuous tuning of the introduced phase shift with only one pair of electrodes. By characterizing the device with terahertz time-domain spectroscopy we demonstrate a phase shift up to 2.5 terahertz, only slightly changed properties of the neat liquid crystal and significantly reduced response times. PMID:23736457

Altmann, Kristian; Reuter, Marco; Garbat, Katarzyna; Koch, Martin; Dabrowski, Roman; Dierking, Ingo

2013-05-20

386

Determination of pectin degree of esterification by diffuse reflectance Fourier transform infrared spectroscopy  

Microsoft Academic Search

A diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) method was developed to measure the degree of esterification (DE) of commercial pectin samples. The relationship between infrared spectroscopy data and titrimetrically determined DE values was investigated. The ester carbonyl band area (C?O) occurring at a mean frequency of 1756 cm?1 had the highest correlation (R2=0.822) with the mean DE of the

Ravin Gnanasambandam; A Proctor

2000-01-01

387

Terahertz spectroscopy in the pseudo-Kagome system Cu3Bi(SeO3)2O2Br  

NASA Astrophysics Data System (ADS)

Terahertz (THz) transmission spectra have been measured as a function of temperature and magnetic field on single crystals of Cu3Bi(SeO3)2O2Br. In time-domain THz spectra without magnetic field, two resonance absorptions are observed below the magnetic ordering temperature TN˜27.4 K. The corresponding resonance frequencies increase with decreasing temperature and reach energies of 1.28 and 1.23 meV at 3.5 K. Multifrequency electron spin resonance transmission spectra as a function of the applied magnetic field show the field dependence of four magnetic resonance modes, which can be modeled as a ferromagnetic resonance including demagnetization and anisotropy effects.

Wang, Zhe; Schmidt, M.; Goncharov, Y.; Tsurkan, V.; Krug von Nidda, H.-A.; Loidl, A.; Deisenhofer, J.

2012-11-01

388

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

SciTech Connect

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

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

2006-09-02

389

Diffuse reflectance spectroscopy: a clinical study of tuberculin skin tests reading  

NASA Astrophysics Data System (ADS)

Diffuse reflectance spectroscopy is a technique widely used to determine optical properties of tissues: scattering and absorption coefficients. In this study, we present the development of a low-cost optical instrument usable in a clinical environment based upon the spatially resolved diffuse reflectance spectroscopy approach. This instrument has been used in a clinical study to support the diagnosis of tuberculosis. The idea is to establish a new scanning method for an early detection of inflammation due to a reagent injection, before the onset of visual signs. Results comparing the instrumental and classical clinical readings are presented.

Koenig, Anne; Grande, Sophie; Dahel, Karima; Planat-Chrétien, Anne; Poher, Vincent; Goujon, Catherine; Dinten, Jean-Marc

2013-02-01

390

[Application of near-infrared diffuse reflectance spectroscopy to the detection and identification of transgenic corn].  

PubMed

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. PMID:16395887

Rui, Yu-kui; Luo, Yun-bo; Huang, Kun-lun; Wang, Wei-min; Zhang, Lu-da

2005-10-01

391

Effect of data pretreatment on the noninvasive blood glucose measurement by diffuse reflectance NIR spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Heise, H. Michael; Marbach, Ralf

1994-01-01

392

Optimized external IR reflection spectroscopy for quantitative determination of borophosphosilicate glass parameters  

Microsoft Academic Search

Infrared (IR) external reflection spectroscopy has been optimized for the quantitative determination of composition and film thickness of borophosphosilicate glass (BPSG) deposited on silicon wafer substrates. The precision of the partial least-squares calibrations for boron and phosphorus contents and thin-film thickness were measured as the cross-validated standard error of prediction statistic. The results showed that BPSG IR reflection spectra collected

Lizhong Zhang; James E. Franke; Thomas M. Niemczyk; David M. Haaland

1997-01-01

393

Investigation of the enzymatic digestion of plant cell walls using reflectance Fourier Transform Infrared spectroscopy.  

PubMed

A method has been developed to determine the reflectance Fourier Transform Infrared spectra of plant cells grown in vitro and of the protoplasts released from such cells by enzymatic digestion. It is demonstrated that there is a smooth and reproducible transition in spectral detail as enzymatic digestion procedes. Reflectance Fourier Transform Infrared spectroscopy has been used to monitor the progress of protoplast release during enzymatic digestion of cell wall material. PMID:24254073

Hopkinson, J; Moustou, C; Charlwood, K A; Newbery, J E; Charlwood, B V

1985-12-01

394

Analysis of depth profiles of hydrogen isotopes in structural materials via reflected electron spectroscopy  

Microsoft Academic Search

Methods for measuring the layer-by-layer profiles of hydrogen in structural materials based on interpretation of the energy\\u000a spectra of electrons reflected within a given spatial angle are discussed. Elastically reflected spectroscopy makes it possible\\u000a to determine the hydrogen isotope content, but its implementation requires an energy resolution on the order of 1 eV. In the\\u000a experimental implementation of the method

V. P. Afanas’ev; M. V. Afanas’ev; A. A. Batrakov; W. Bohmeyer; D. Naujoks; A. V. Lubenchenko; A. Markin

2011-01-01

395

Terahertz polarization imaging for colon cancer detection  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

396

Diffuse Reflectance Spectroscopy of Human Skin Using a Commercial Fiber Optic Spectrometer  

NASA Astrophysics Data System (ADS)

Diffuse reflectance spectroscopy is a reliable and easy to implement technique in human tissue characterization. In this work we evaluate the performance of the commercial USB4000 miniature fiber optic spectrometer in the in-vivo measurement of the diffuse reflectance spectra of different healthy skin sites and lesions in a population of 54 volunteers. Results show, that this spectrometer reproduces well the typical signatures of skin spectra over the 400-1000 nm region. Remarkable spectral differences exist between lesions and normal surrounding skin. A diffusion-based model was used to simulate reflectance spectra collected by the optical probe of the system.

Atencio, J. A. Delgado; Rodríguez, M. Cunill; Montiel, S. Vázquez Y.; Gutiérrez, J. L.; Martínez, F.; Gutiérrez, B.; Orozco, E.; Castro, Jorge; Rodríguez, A. Cornejo

2008-08-01

397

Reflectance and Thermal Infrared Spectroscopy of Mars: Relationship Between ISM and TES for Compositional Determinations  

NASA Technical Reports Server (NTRS)

Reflectance spectroscopy has demonstrated that high albedo surfaces on Mars contain heavily altered materials with some component of hematite, poorly crystalline ferric oxides, and an undefined silicate matrix. The spectral properties of many low albedo regions indicate crystalline basalts containing both low and high calcium pyroxene, a mineralogy consistent with the basaltic SNC meteorites. The Thermal Emission Spectrometer (TES) experiment on the Mars Geochemical Surveyor has acquired critical new data relevant to surface composition and mineralogy, but in a wavelength region that is complementary to reflectance spectroscopy. The essence of the completed research was to analyze TES data in the context of reflectance data obtained by the French ISM imaging spectrometer experiment in 1989. This approach increased our understanding of the complementary nature of these wavelength regions for mineralogic determinations using actual observations of the martian surface. The research effort focused on three regions of scientific importance: Syrtis Major-Isidis Basin, Oxia Palus-Arabia, and Valles Marineris. In each region distinct spatial variations related to reflectance, and in derived mineralogic information and interpreted compositional units were analyzed. In addition, specific science questions related to the composition of volcanics and crustal evolution, soil compositions and pedogenic processes, and the relationship between pristine lithologies and weathering provided an overall science-driven framework for the work. The detailed work plan involved colocation of TES and ISM data, extraction of reflectance and emissivity spectra from areas of known reflectance variability, and quantitative analysis using factor analysis and statistical techniques to determine the degree of correspondence between these different wavelength regions. Identified coherent variations in TES spectroscopy were assessed against known atmospheric effects to validate that the variations are due to surface properties. With this new understanding of reflectance and emission spectroscopy, mineralogic interpretations were derived and applied to the science objectives of the three regions.

Boyce, Joseph (Technical Monitor); Mustard, John

2004-01-01

398

INVESTIGATING ULTRASONIC DIFFRACTION GRATING SPECTROSCOPY AND REFLECTION TECHNIQUES FOR CHARACTERIZING SLURRY PROPERTIES  

EPA Science Inventory

The objectives of the project are to investigate the use of (1) ultrasonic diffraction grating spectroscopy (UDGS) for measuring the particle size of a slurry and (2) shear wave reflection techniques to measure the viscosity of a slurry. For the first topic, the basic principle...

399

Absorption and Scattering Coefficients: A Biophysical-Chemistry Experiment Using Reflectance Spectroscopy  

ERIC Educational Resources Information Center

A biophysical-chemistry experiment, based on the reflectance spectroscopy for calculating the absorption and scattering coefficients of leaves is described. The results show that different plants species exhibit different values for both the coefficients because of their different pigment composition.

Cordon, Gabriela B.; Lagorio, M. Gabriela

2007-01-01

400

Fluorescence and Diffuse Reflectance Spectroscopy for Breast Cancer Diagnosis During Core Needle Biopsy.  

National Technical Information Service (NTIS)

The goal of this project is to exploit the potential of using fluorescence and diffuse reflectance spectroscopy for breast cancer detection during a core needle breast biopsy. A novel side-firing fiber optic probe has been developed for use in a vacuum-as...

C. Zhu

2006-01-01

401

Percutaneous Penetration Enhancement in Vivo Measured by Attenuated Total Reflectance Infrared Spectroscopy  

Microsoft Academic Search

A novel application of attenuated total reflectance IR Spectroscopy (ATR-IR) was used to monitor the outer several microns of the stratum corneum (SC) and, thereby, demonstrate enhanced percutaneous absorption in vivo in man. 4-Cyanophenol (CP) as a model permeant yielded a unique IR signal, distinct from those of the stratum corneum and the vehicle components. CP was administered for 1,

Vivien H. W. Mak; Russell O. Potts; Richard H. Guy

1990-01-01

402

Attenuated total reflection mid-infrared spectroscopy for clinical chemistry applications using silver halide fibers  

Microsoft Academic Search

The quantitative analysis of biotic fluids can be carried out using attenuated total reflection mid-infrared spectroscopy based on silver halide fibers, because good optical throughput can be achieved especially in the fingerprint region of the mid-infrared spectral range. The advantages and prospects of this technique using biofluids or dry films, obtained from such aqueous solutions, are discussed in the context

H. M Heise; L Küpper; L. N Butvina

1998-01-01

403

Detailed mapping of biaxial orientation in polyethylene terephthalate bottles using polarised attenuated total reflection FTIR spectroscopy  

Microsoft Academic Search

Polarised attenuated total reflection FTIR spectroscopy has been used for detailed orientation mapping of 2l polyethylene terephthalate bottles subjected to different preform heating times. The results for the bottle with the standard preform heating time reveal significant surface orientation variations along the bottle hoop and length directions, with the inner bottle surface also showing consistently greater chain orientation in the

Matthew R. Smith; Sharon J. Cooper; Derek J. Winter; Neil Everall

2006-01-01

404

Near-Infrared Reflectance Spectroscopy Prediction of Leaf and Mineral Concentrations in Alfalfa  

Microsoft Academic Search

but still required equation redevelopment each year. concentration be limited to predicting a closed popula- Near-infrared reflectance spectroscopy accurately predicted total ash and Ca, K, and P of leaves and stems of alfalfa hay and research tion from which the calibration samples originated. This samples but was less consistent in prediction of Mg and S and micro- work demonstrated the

James L. Halgerson; Craig C. Sheaffer; Neal P. Martin; Paul R. Peterson; Salli J. Weston

2004-01-01

405

Real time, in-situ temperature monitoring using diffuse reflectance spectroscopy  

SciTech Connect

Real time temperature measurements have been performed on both GaAs and silicon substrates during wafer processing using a technique based upon diffuse reflectance spectroscopy (DRS). Good temperature resolution ({+-}O.4 {degrees}C) and rapid updates have enabled the process control potential of the device to be demonstrated.

Booth, J.L.; Beard, B.T. [Thermionics Northwest, Inc., Port Townsend, WA (United States); Pearsall, T.P.; Wang, Z.Z. [Washington Univ., Seattle, WA (United States). Dept. of Electrical Engineering; Stevens, J.E.; Blain, M.G.; Meisenheimer, T.L. [Sandia National Labs., Albuquerque, NM (United States)

1996-11-01

406

Effect of hemolysis on oxygen and hematocrit measurements by near infrared reflectance spectroscopy  

Microsoft Academic Search

A short review of the principles of near infrared reflectance spectroscopy (NIRS) in whole blood is followed by a discussion on the influence of hemolysis. The increase of free plasmahemoglobin (PHb) has a strong influence on the continuous measurement of hematocrit and oxygen saturation (O2S) by NIRS. In view of the relative stability of hematocrit values in vivo this effect

F. Neudel; S. Takatani; H. Reul; G. Rau

2002-01-01

407

Determining levels of steviol glycosides in the leaves of Stevia rebaudiana by near infrared reflectance spectroscopy  

Microsoft Academic Search

The sweet diterpene glycosides extracted from the leaves of Stevia rebaudiana (Bert) Bertoni are of increasing interest in recent years as possible sugar substitutes. Our objectives were to investigate the application of near infrared reflectance spectroscopy (NIRS) in analysis of steviol glycosides (SGs) concentration (w\\/w) dry basis in S. rebaudiana leaves, using high-pressure liquid chromatography (HPLC) as the reference method.

L. K. Hearn; P. P. Subedi

2009-01-01

408

Large drop in dielectric constant at ferrimagnetic ordering of CoCr2O4 thin film as observed by terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

Multiferroic spinel CoCr2O4 shows ferrimagnetic transition at ˜95 K and, at further low temperatures, it shows development of magnetic spin spirals simultaneous to a ferroelectric transition. We have deposited epitaxial CoCr2O4 thin film on MgO (100) substrate and studied the film using temperature dependent terahertz (THz) time-domain spectroscopy. There is a large drop in the dielectric constant (?1) to nearly half of its initial value at ferrimagnetic transition of CoCr2O4 thin films in the THz frequency range. This is contrary to few earlier studies by capacitance measurements which showed no significant change in the dielectric constant (?1) at ferrimagnetic transition [1]. At lower temperatures, two dielectric anomalies were observed in the temperature dependent ?1, which correspond to the onset of short-range magnetic spin spirals (˜50 K) and the long-range ordering of the spirals at lower temperature (˜26 K). Our results indicate a magnetoelectric effect at the ferrimagnetic transition of CoCr2O4 thin film in THz frequency range. [1] G. Lawes et al., Phys. Rev. B 74, 24413 (2006).

Mavani, K. R.; Nagai, M.; Shirai, M.; Tanaka, K.; Rana, D. S.; Kawayama, I.; Tonouchi, M.

2008-03-01

409

In vivo detection of epileptic brain tissue using static fluorescence and diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Diffuse reflectance and fluorescence spectroscopy are used to detect histopathological abnormalities of an epileptic brain in a human subject study. Static diffuse reflectance and fluorescence spectra are acquired from normal and epileptic brain areas, defined by electrocorticography (ECoG), from pediatric patients undergoing epilepsy surgery. Biopsy specimens are taken from the investigated sites within an abnormal brain. Spectral analysis reveals significant differences in diffuse reflectance spectra and the ratio of fluorescence and diffuse reflectance spectra from normal and epileptic brain areas defined by ECoG and histology. Using these spectral differences, tissue classification models with accuracy above 80% are developed based on linear discriminant analysis. The differences between the diffuse reflectance spectra from the normal and epileptic brain areas observed in this study are attributed to alterations in the static hemodynamic characteristics of an epileptic brain, suggesting a unique association between the histopathological and the hemodynamic abnormalities in an epileptic brain.

Yadav, Nitin; Bhatia, Sanjiv; Ragheb, John; Mehta, Rupal; Jayakar, Prasanna; Yong, William; Lin, Wei-Chiang

2013-02-01

410

Infrared and terahertz studies of polar phonons and magnetodielectric effect in multiferroic BiFeO3 ceramics  

Microsoft Academic Search

BiFeO3 ceramics were investigated by means of infrared reflectivity and time domain terahertz transmission spectroscopy at temperatures 20-950K , and the magnetodielectric effect was studied at 10-300K with the magnetic field up to 9T . Below 175K , the sum of polar phonon contributions to the permittivity corresponds to the value of measured permittivity below 1MHz . At higher temperatures,

S. Kamba; D. Nuzhnyy; M. Savinov; J. Sebek; J. Petzelt; J. Prokleska; R. Haumont; J. Kreisel

2007-01-01

411

Plasmonic photoconductive detectors for enhanced terahertz detection sensitivity.  

PubMed

A photoconductive terahertz detector based on plasmonic contact electrodes is presented. The use of plasmonic electrodes mitigates the inherent tradeoff between high quantum efficiency and ultrafast operation of the employed photoconductor, enabling significantly higher detection sensitivities compared to conventional photoconductive terahertz detectors. Prototypes of comparable photoconductive detectors with and without plasmonic contact electrode gratings were fabricated and characterized in a time-domain terahertz spectroscopy setup under the same operation conditions. The experimental results show that the plasmonic photoconductive detector offers more than 30 times higher terahertz detection sensitivities compared to the comparable conventional photoconductive detector without plasmonic contact electrodes over 0.1-1.5 THz frequency band. PMID:23938568

Wang, Ning; Hashemi, Mohammad R; Jarrahi, Mona

2013-07-15

412

Terahertz study of 1,3,5-trinitro-s-triazine by time-domain and Fourier transform infrared spectroscopy  

NASA Astrophysics Data System (ADS)

This letter describes the use of THz time-domain spectroscopy (TDS) applied in transmission to the secondary explosive 1,3,5 trinitro-s-triazine. Samples were also subjected to Fourier transform infrared spectroscopy over the same range for comparison. A detailed spectroscopy study is presented. General agreement between results from both methods confirms the absorption features found. A comparison study with computer molecular simulations shows that THz-TDS is sensitive to collective modes or vibrational modes of material.

Huang, Feng; Schulkin, Brian; Altan, Hakan; Federici, John F.; Gary, Dale; Barat, Robert; Zimdars, David; Chen, Minghan; Tanner, D. B.

2004-12-01

413

Investigation of the mineralization process of biosystems by IR diffuse reflection spectroscopy methods  

NASA Astrophysics Data System (ADS)

Particular features of the application of Fourier-transform IR diffuse reflection spectroscopy methods to the in situ investigation of spectra of porous rough objects have been considered. The reciprocal influence of the scattering and absorption of porous objects on the formation of the impurity-band contour in the diffuse reflection spectrum when the impurity center is in the vicinity of the fundamental IR absorption band has been analyzed. Using methods of Fourier-transform IR diffuse reflection spectroscopy, processes of mineralization of fragments of mammoth tusks from a multilayer paleolithic site at Yudinovo (Bryansk oblast, Russia) and fragments of mammoth tusks from Yakutia (Russia) have been investigated. Particular features of mineralization processes (carbonate formation and silicification) on the surface and in the volume of objects at different conditions of their burial (humidity, temperature, soil acidity) have been studied.

Zolotarev, V. M.

2014-04-01

414

Terahertz spectroscopy and solid-state density functional theory calculation of anthracene: Effect of dispersion force on the vibrational modes  

NASA Astrophysics Data System (ADS)

The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D* have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D* simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D* data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D* produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D*.

Zhang, Feng; Hayashi, Michitoshi; Wang, Houng-Wei; Tominaga, Keisuke; Kambara, Ohki; Nishizawa, Jun-ichi; Sasaki, Tetsuo

2014-05-01

415

Terahertz spectroscopy and solid-state density functional theory calculation of anthracene: effect of dispersion force on the vibrational modes.  

PubMed

The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D(*) have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D(*) simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D(*) data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D(*) produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D(*). PMID:24811648

Zhang, Feng; Hayashi, Michitoshi; Wang, Houng-Wei; Tominaga, Keisuke; Kambara, Ohki; Nishizawa, Jun-ichi; Sasaki, Tetsuo

2014-05-01

416

Quantum Cascade Terahertz Emitters for Subsurface Defect Detection  

NASA Astrophysics Data System (ADS)

The transmission and penetration capability of electromagnetic waves with terahertz frequencies promises nondestructive subsurface inspection capabilities using low energy, non-harmful radiation. The development of compact and portable terahertz frequency radiation sources and detectors is crucial to the practical implementation of future terahertz based nondestructive evaluation tools for aerospace, medical, security, and electronic industries. Recent progress in the bandstructure engineering of multi-quantum well heterostructures offers the potential to design miniature, efficient, high power, and direct terahertz emitters using standard semiconductor materials and fabrication techniques. Using a recently developed terahertz spectrometer, combined with near and mid-infrared spectroscopy data, we report on the transmission characteristics of aerospace coatings over a broad spectrum from near-infrared to terahertz frequencies. The design of quantum cascade emitters based on the obtained transmission data is presented.

Cooney, Adam T.; Sarangan, Andrew M.; Nelson, Thomas R.; Alkuwari, Rashid; Powers, Peter E.; Rodriguez, Andres; Kleeman, Mark; Lamont, Gary; Blackshire, James L.; Haus, Joseph W.

2006-03-01

417

[The research progress in determining lignocellulosic content by near infrared reflectance spectroscopy technology].  

PubMed

Near infrared reflectance spectroscopy technology, as a new analytic method, can be used to determine the content of lignin, cellulose and hemi-cellulose which is faster, effective, easier to operate, and more accurate than the traditional wet chemical methods. Nowadays it has been widely used in measuring the composition of lignocelluloses in woody plant and herbaceous plant. The domestic and foreign research progress in determining the lignin, cellulose and hemi-cellulose content in woody plant ( wood and bamboo used as papermaking raw materials and wood served as potential biomass energy) and herbaceous plant (forage grass and energy grass) by near infrared reflectance spectroscopy technology is comprehensively summarized and the advances in method studies of measuring the composition of lignocelluloses by near infrared reflectance spectroscopy technology are summed up in three aspects, sample preparation, spectral data pretreatment and wavelength selection methods, and chemometric analysis respectively. Four outlooks are proposed combining the development statues of wood, forage grass and energy grass industry. First of all, the authors need to establish more feasible and applicable models for a variety of uses which can be used for more species from different areas, periods and anatomical parts. Secondly, comprehensive near infrared reflectance spectroscopy data base of grass products quality index needs to be improved to realize on-line quality and process control in grassproducts industry, which can guarantee the quality of the grass product. Thirdly, the near infrared reflectance spectroscopy quality index model of energy plant need to be built which can not only contribute to breed screening, but also improve the development of biomass industry. Besides, modeling approaches are required to be explored and perfected any further. Finally, the authors need to try our best to boost the advancement in the determination method of lignin, cellulose and hemi-cellulose by near infrared reflectance spectroscopy from the laboratory to the practical applications. Along with the method of determining the lignin, cellulose and hemi-cellulose by near infrared spectroscopy being unceasingly perfected and matured, this technique will actively have a positive effect on the development of papermaking, forage grass and energy grass industry. PMID:24611371

Du, Juan; An, Dong; Xia, Tian; Huang, Yan-Hua; Li, Hong-Chao; Zhang, Yun-Wei

2013-12-01

418

An efficient cavity for optically pumped terahertz lasers  

NASA Astrophysics Data System (ADS)

The efficiency of a simply designed cavity for optically pumped pulsed terahertz lasers is studied experimentally. A coated Ge and a crystal quartz act as the input and output windows, respectively. The thickness of the Ge window is designed according to etalon effects to maximize terahertz reflectivity. NH3 is filled in the cavity as the active medium. When NH3 is pumped by the 10P(32) line of a TEA CO2 laser, intense 151.5 ?m terahertz radiation is emitted. As high as 19.6 mJ terahertz radiation is extracted from 1.57 J pump energy. The corresponding photon conversion efficiency reaches 35.3%.

Miao, Liang; Zuo, Duluo; Jiu, Zhixian; Cheng, Zuhai

2010-08-01

419

Time-dependent diffuse reflectance spectroscopy for in vivo characterization of pediatric epileptogenic brain lesions  

NASA Astrophysics Data System (ADS)

Optical spectroscopy for in vivo tissue diagnosis is performed traditionally in a static manner; a snap shot of the tissue biochemical and morphological characteristics is captured through the interaction between light and the tissue. This approach does not capture the dynamic nature of a living organ, which is critical to the studies of brain disorders such as epilepsy. Therefore, a time-dependent diffuse reflectance spectroscopy system with a fiber-optic probe was designed and developed. The system was designed to acquire broadband diffuse reflectance spectra (240 ~ 932 nm) at an acquisition rate of 33 Hz. The broadband spectral acquisition feature allows simultaneous monitoring of various physiological characteristics of tissues. The utility of such a system in guiding pediatric epilepsy surgery was tested in a pilot clinical study including 13 epilepsy patients and seven brain tumor patients. The control patients were children undergoing suregery for brain tumors in which measurements were taken from normal brain exposed during the surgery. Diffuse reflectance spectra were acquired for 12 seconds from various parts of the brain of the patients during surgery. Recorded spectra were processed and analyzed in both spectral and time domains to gain insights into the dynamic changes in, for example, hemodynamics of the investigated brain tissue. One finding from this pilot study is that unsynchronized alterations in local blood oxygenation and local blood volume were observed in epileptogenic cortex. These study results suggest the advantage of using a time-dependent diffuse reflectance spectroscopy system to study epileptogenic brain in vivo.

Oh, Sanghoon; Ragheb, John; Bhatia, Sanjiv; Sandberg, David; Johnson, Mahlon; Fernald, Bradley; Lin, Wei-Chiang

2008-03-01

420

Diffuse reflectance spectroscopy measurements for tissue-type discrimination during deep brain stimulation  

NASA Astrophysics Data System (ADS)

Diffuse reflectance spectroscopy as a method for improving intracerebral guidance during functional neurosurgery has been investigated. An optical probe was developed for measurements during stereotactic and functional neurosurgery in man. The aim of the study was to investigate the spectral differences between white and grey matter and between white matter and functional targets. Diffuse reflectance spectroscopy measurements in ten patients were recorded at incremental steps towards and in three different functional targets (STN, GPi and Zi). The recorded spectra along the trajectory were sorted into white or grey matter, based on preoperative MRI images or the recorded spectral shape and intensity. The difference between tissue types was calculated as a quotient. Significant intensity differences between white and grey matter were found to be at least 14% (p < 0.05) and 20% (p < 0.0001) for MRI and spectral-sorted data respectively. The reflectance difference between white matter and the functional targets of GPi was higher than for STN and Zi. The results indicate that diffuse reflectance spectroscopy has a potential to be developed to a suitable complement to other intracerebral guidance methods.

Antonsson, Johan; Eriksson, Ola; Blomstedt, Patric; Bergenheim, A. Tommy; Hariz, Marwan I.; Richter, Johan; Zsigmond, Peter; Wårdell, Karin

2008-06-01

421

Measurement of dielectric properties in gigahertz to terahertz frequency range  

Microsoft Academic Search

Measurement of the dielectric constant of thin film in the frequency range of gigahertz (GHz) to terahertz (THz) is crucial for future integrated circuit (IC) interconnect technology. This research focuses on the use of time domain terahertz pulse technology for such characterization. In particular, the goniometric phase shift of a reflected electro magnetic pulse as a function of incident angle

Ming Li

2000-01-01

422

High-speed time domain terahertz security imaging  

Microsoft Academic Search

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Time domain terahertz imaging can be employed in reflection mode to image with sub millimeter resolution. Previously, single pixel acquisition times for THz waveforms

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

2005-01-01

423

Dual-band bandpass terahertz wave filter based on microstrip resonant structure  

NASA Astrophysics Data System (ADS)

The terahertz (THz) band, which refers to the spectral region between 0.1 and 10THz, covers the fingerprints of many chemical and biological materials. Within the past few years, there are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology, nanotechnology, space science, security, chemical and biological sensing, terahertz wave communications, and medical diagnostics. For potential applications, the functional devices, such as beam polarizers, switchs and filters, are crucial components for a terahertz system. Terahertz wave filter based on two kinds of microstrip resonant structures, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. The experimental results for the frequency dependence of the transmittance of the terahertz wave filter show that the terahertz wave transmittance peak is of 79.5% at 0.5THz and 82.5% at 0.81THz.

Liu, Yu-hang; Li, Jiu-sheng

2011-11-01

424

Reflectance spectroscopy for evaluating optical clearing efficacy of skin in vivo  

NASA Astrophysics Data System (ADS)

Chemical agents with high refractive index, hyperosmotic, and biocompatibility are introduced into tissue, which will reduce the scattering of tissue, and enhance the penetration of light in tissue. Diffuse reflectance, as a common method, has been applied to assess optical clearing of skin in vivo, but the scattering characteristic during the in-vivo optical clearing process has not been valuated quantitatively. In this work, a diffuse reflectance spectroscopy, based on a lookuptable (LUT) based inverse model, is applied to calculate the reduced scattering coefficient and absorption coefficient of skin. Optical clearing agents (OCAs) were topically treated on mouse skin in vivo. The diffuse reflectance during optical clearing was recorded, and the optical properties can be extracted by the reflectance spectroscopy. The results show that the diffuse reflectance spectra and the reduced scattering coefficient are decreased obviously, whilst the absorption coefficient is increased after the application of OCAs. This study provides evident directly for explore the mechanisms of optical clearing of skin in vivo.

Zhong, Xiewei; Wang, Jing; Shi, Rui; Zhu, Dan

2013-02-01

425

Mahan excitons in degenerate wurtzite InN: Photoluminescence spectroscopy and reflectivity measurements  

NASA Astrophysics Data System (ADS)

Unintentionally degenerately doped n -type hexagonal wurtzite InN samples were studied by using Fourier-transform photoluminescence spectroscopy and reflectivity measurements. We found in luminescence overlapping band acceptor (e,A0) transitions related to two different acceptors with a strong enhancement of their intensities close to the Fermi energy of the electrons recombining with the localized holes. Our explanation is in terms of a Fermi-edge singularity of the electrons due to strongly increased electron-hole scattering. Electron-hole pairs with such resonantly enhanced oscillator strengths have been referred to as Mahan excitons. Temperature-dependent reflectivity measurements confirm this interpretation.

Feneberg, Martin; Däubler, Jürgen; Thonke, Klaus; Sauer, Rolf; Schley, Pascal; Goldhahn, Rüdiger

2008-06-01

426

Development of techniques for advanced optical contamination measurement with internal reflection spectroscopy, phase 1, volume 1  

NASA Technical Reports Server (NTRS)

The feasibility of monitoring volatile contaminants in a large space simulation chamber using techniques of internal reflection spectroscopy was demonstrated analytically and experimentally. The infrared spectral region was selected as the operational spectral range in order to provide unique identification of the contaminants along with sufficient sensitivity to detect trace contaminant concentrations. It was determined theoretically that a monolayer of the contaminants could be detected and identified using optimized experimental procedures. This ability was verified experimentally. Procedures were developed to correct the attenuated total reflectance spectra for thick sample distortion. However, by using two different element designs the need for such correction can be avoided.

Hayes, J. D.

1972-01-01

427

Influence of contact state on NIR diffuse reflectance spectroscopy in vivo  

NASA Astrophysics Data System (ADS)

In the practice of non-invasive blood glucose measurement by near-infrared (NIR) diffuse reflectance spectroscopy, an optical probe usually directly contacts skin in order to eliminate specular reflection. In this paper, the influence of contact state on the diffuse reflectance in vivo and the variation trend of diffuse reflectance with contact time under the same contact pressure, are investigated at wavelengths ranging from 1100 to 1700 nm. The result shows that the diffuse reflectance decreases with increasing contact pressure under the contact state. At a certain applied pressure, the diffuse reflectance fluctuates significantly at the beginning of contact, and the fluctuation becomes stable with elapsing contacting time. It is our aim in this paper to find out the optimal contact state and optimal measuring time, in order to reduce the influence of contact pressure on diffuse reflectance measurements. It is found from our experiments that, for in vivo measurement, the optimal contact state appears when the skin is pressed to about 0.5 mm by the probe, where the probe contacts the palm entirely, and that the optimal measuring time is at the 30th second since the probe contacting with the measuring site. Putting the above conclusions into practice, the repeatability of spectra is improved greatly.

Chen, Wenliang; Liu, Rong; Xu, Kexin; Wang, Ruikang K.

2005-08-01

428

Optical phase detection in a 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate crystal for terahertz time domain spectroscopy system at 1.55 ?m wavelength  

NASA Astrophysics Data System (ADS)

We report the electro-optic detection of terahertz (THz) pulses in a 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate crystal (DAST) using optical phase detection technique and femtosecond optical pulses at telecom wavelength. A THz time-domain spectroscopy system based on 1.55 ?m wavelength fiber laser pulses that integrates an ion-irradiated In0.53Ga0.47As photoconductive antenna as the emitter and a DAST electro-optic crystal as the detector is shown to provide a detection bandwidth of 5 THz.

Martin, M.; Mangeney, J.; Crozat, P.; Mounaix, P.

2010-09-01

429

Application of transcutaneous diffuse reflectance spectroscopy in the measurement of blood glucose concentration  

NASA Astrophysics Data System (ADS)

In this paper, the propagation characteristics of near-infrared (NIR) light in the palm tissue are analyzed, and the principle and feasibility of using transcutaneous diffuse reflectance spectroscopy for non-invasive blood glucose detection are presented. An optical probe suitable for measuring the diffuse reflectance spectrum of human palm and a non-invasive blood glucose detection system using NIR spectroscopy are designed. Based on this system, oral glucose tolerance tests are performed to measure the blood glucose concentrations of two young healthy volunteers. The partial least square calibration model is then constructed by all individual experimental data. The final result shows that correlation coefficients of the two experiments between the predicted blood glucose concentrations and the reference blood glucose concentrations are 0.9870 and 0.9854, respectively. The root mean square errors of prediction of full cross validation are 0.54 and 0.52 mmol/l, respectively.

Chen, Wenliang; Liu, Rong; Cui, Houxin; Xu, Kexin; Lv, Lina

2004-07-01

430

Monitoring of landfill leachate dispersion using reflectance spectroscopy and ground-penetrating radar.  

PubMed

The utility of ground-penetrating radar and reflectance spectroscopy in the monitoring of landfill sites has been investigated. Strong correlations between red edge inflection position and chlorophyll and heavy metal concentrations have been demonstrated from grassland species affected by leachate contamination of the soil adjacent to the landfill test site. This study demonstrated that reflectance spectroscopy can identify vegetation affected by leachate-contaminated soil at a range of spatial resolutions. To identify the vegetation affected by leachate contamination, the spectroradiometer must have contiguous bands at sufficient spectral resolution over the critical wave range that measures chlorophyll absorption and the red edge (between 650 and 750 nm). The utility of ground-penetrating radar data to identify leachate escaping from breakout points in the contaminant wall has also been demonstrated. An integrated approach using these techniques, combined with field and borehole sampling and contaminant migration modeling, offers a possible cost-effective monitoring approach for landfill sites. PMID:14524467

Splajt, T; Ferrier, G; Frostick, L E

2003-09-15

431

Estimation of grain yield by near-infrared reflectance spectroscopy in durum wheat  

Microsoft Academic Search

Near-infrared Reflectance Spectroscopy (NIRS) is widely used for routine, non-destructive assessment of grain quality in cereals. In this work, we assess the use of NIRS as an indirect indicator of grain yield (GY) in durum wheat grown in Mediterranean conditions. Plants were grown under rain-fed conditions in two sites in NW Syria, Breda and Tel Hadya, and a third trial

J. P. Ferrio; E. Bertran; M. M. Nachit; J. Català; J. L. Araus

2004-01-01

432

TOTAL INTERNAL REFLECTION WITH FLUORESCENCE CORRELATION SPECTROSCOPY: APPLICATIONS TO SUBSTRATE-SUPPORTED PLANAR MEMBRANES  

PubMed Central

In this review paper, the conceptual basis and experimental design of total internal reflection with fluorescence correlation spectroscopy (TIR-FCS) is described. The few applications to date of TIR-FCS to supported membranes are discussed, in addition to a variety of applications not directly involving supported membranes. Methods related, but not technically equivalent, to TIR-FCS are also summarized. Future directions for TIR-FCS are outlined.

Thompson, Nancy L.; Wang, Xiang; Navaratnarajah, Punya

2009-01-01

433

Determination of free fatty acids in palm oil by near-infrared reflectance spectroscopy  

Microsoft Academic Search

A near-infrared (NIR) spectroscopy calibration was developed for the determination of free fatty acids (FFA) in crude palm\\u000a oil and its fractions based on the NIR reflectance approach. A range of FFA concentrations was prepared by hydrolyzing oil\\u000a with 0.15% (w\\/w) lipase in an incubator at 60°C (200 rpm). Sample preparation was performed in Dutch cup, and the spectra\\u000a were

Y. B. Che Man; M. H. Moh

1998-01-01

434

The potential of diffuse reflectance spectroscopy for the determination of carbon inventories in soils  

Microsoft Academic Search

Investigations have shown that near- and mid-infrared reflectance spectroscopy can accurately determine organic-C in soil. Efforts have also demonstrated that both can differentiate between organic and inorganic-C in soils, but the mid-infrared produces more accurate calibrations. Nevertheless, the greatest benefit would come with in situ determinations where factors such as particle size, sample heterogeneity and moisture can be important. While

J. Reeves; G. McCarty; T. Mimmo

2002-01-01

435

Quantitative analysis of borophosphosilicate glass films on silicon using infrared external reflection--absorption spectroscopy  

Microsoft Academic Search

Borophosphosilicate glass (BPSG) dielectric thin films deposited on both bare and oxide-coated undoped silicon wafers have been analyzed using infrared external reflection--absorption spectroscopy (IRRAS). The partial least-squares (PLS1) algorithm was used to simultaneously determine boron content, phosphorous content, and film thickness, with standard errors of prediction of 0.08 wt %, 0.11 wt %, and 24 A, respectively, in the BPSG

James E. Franke; L. Zhang; T. M. Niemczyk; D. M. Haaland; K. J. Radigan

1995-01-01

436

Validation of Reflectance Infrared Spectroscopy as a Quantitative Method to Measure Percutaneous Absorption In Vivo  

Microsoft Academic Search

Attenuated total-reflectance infrared (ATR-IR) spectroscopy has been used to follow the penetration of a model compound (4-cyanophenol; CP) across human stratum corneum (SC) in vivo, in man. CP was administered for periods of 1, 2, or 3 hr, either (a) as a 10% (w\\/v) solution in propylene glycol or (b) in an identical vehicle which also contained 5% (v\\/v) oleic

Naruhito Higo; Aarti Naik; D. Bommi Bommannan; Russell O. Potts; Richard H. Guy

1993-01-01

437

Non-destructive detection of lead glass alteration by reflectance spectroscopy  

Microsoft Academic Search

A non-destructive technique giving an early diagnosis of glass degradation is presented here. It allows to implement a new sol-gel method that stops further deterioration of the glass and avoid the classical removing of crusts. Reflectance spectroscopy in the visible range is used with a portable fiber-optics spectrophotometer in a back-scattered configuration and underlines very fine levels of glass alteration.

Mady Elias; Cécile Charbonneau; Jean Marc Frigerio

2007-01-01

438

Combined use of hyperspectral VNIR reflectance spectroscopy and kriging to predict soil variables spatially  

Microsoft Academic Search

Hyperspectral visible near infrared reflectance spectroscopy (VNIRRS) and geostatistical methods are considered for precision\\u000a soil mapping. This study evaluated whether VNIR or geostatistics, or their combined use, could provide efficient approaches\\u000a for assessing the soil spatially and associated reductions in sample size using soil samples from a 32 ha area (800 × 400 m)\\u000a in northern Turkey. Soil variables considered were CaCO3, organic matter,

A. Volkan Bilgili; Fevzi Akbas; Harold M. van Es

2011-01-01

439

Reflection-absorption infrared spectroscopy of ethylene on palladium (111) at high pressure  

Microsoft Academic Search

The adsorption of ethylene adsorbed on Pd(111) at ? 300 K is studied using reflection-absorption infrared spectroscopy which confirms the formation of an ethylidyne species because of the presence of vibrational mode at 1329 cm?1 with a less-intense peak at 1089 cm?1. The 1329 cm?1 methyl mode is well away from any vibrational modes of gas-phase ethylene, which allows the

M. Kaltchev; A. W. Thompson; W. T. Tysoe

1997-01-01

440

Instrumental requirements for blood glucose sensing based on diffuse reflectance NIR spectroscopy  

NASA Astrophysics Data System (ADS)

The study on the magnitude of spectral change in blood glucose measurements with diffuse reflectance NIR spectroscopy is presented. Spectral change is estimated by a Monte Carlo simulation and measurements of absorbance spectra of aqueous glucose solution. Required sensitivity of spectrophotometers for monitoring the changein the blood glucose concentration as small as 10mg/dL has been obtained using the estimated change in the absorbance spectrum and mean pathlength of light in tissue.

Arimoto, Hidenobu; Ota, Tomohiro; Tarumi, Masatoshi; Yamada, Yukio

2003-07-01

441

Predicting Oleic and Linoleic Acid Content of Single Peanut Seeds using Near-Infrared Reflectance Spectroscopy  

Microsoft Academic Search

One objective of peanut breeders is to develop cultivars with elevated oleic acid content (.740 g kg21). Testing single seeds for oleic acid content is possible using gas chromatography (GC), but it is time-consuming and requires cutting a portion of the seed which could reduce germination. Using single, intact peanut seeds, we developed a near-infrared reflectance spectroscopy (NIR) calibration equation

Barry L. Tillman; Daniel W. Gorbet; George Person

2006-01-01