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1

Scattering effects in terahertz reflection spectroscopy  

Microsoft Academic Search

Recent advances in ultrafast optical laser technology have improved generation and detection of energy within the terahertz (THz) portion of the electromagnetic (EM) spectrum. One promising application of THz spectroscopy is the detection of explosive materials and chemical or biological agents. This application has been motivated by initial measurements that indicate that explosives may have unique spectral characteristics in the

L. M. Zurk; G. Sundberg; S. Schecklman; Z. Zhou; A. Chen; E. I. Thorsos

2008-01-01

2

Scattering effects in terahertz reflection spectroscopy  

NASA Astrophysics Data System (ADS)

Recent advances in ultrafast optical laser technology have improved generation and detection of energy within the terahertz (THz) portion of the electromagnetic (EM) spectrum. One promising application of THz spectroscopy is the detection of explosive materials and chemical or biological agents. This application has been motivated by initial measurements that indicate that explosives may have unique spectral characteristics in the THz region thus providing a discernible fingerprint. However, since THz wavelengths are 10's to 100's of microns in scale, rough interfaces between materials as well as the granular nature of explosives can cause frequency-dependent scattering that has the potential to alter or obscure these signatures. For reflection spectroscopy in particular the measured response may be dominated by rough surface scattering, which is in turn influenced by a number of factors including the dielectric contrast, the angle of incidence and scattering, and the operating frequency. In this paper, we present measurements of THz scattering from rough surfaces and compare these measurements with analytical and numerical scattering models. These models are then used to predict the distortion of explosive signatures due to rough surface interfaces with varying surface height deviations and correlation lengths. Implications of scattering effects on the performance of THz sensing of explosive materials are presented and discussed.

Zurk, L. M.; Sundberg, G.; Schecklman, S.; Zhou, Z.; Chen, A.; Thorsos, E. I.

2008-05-01

3

Model-Based Material Parameter Estimation for Terahertz Reflection Spectroscopy  

NASA Astrophysics Data System (ADS)

Many materials such as drugs and explosives have characteristic spectral signatures in the terahertz (THz) band. These unique signatures imply great promise for spectral detection and classification using THz radiation. While such spectral features are most easily observed in transmission, real-life imaging systems will need to identify materials of interest from reflection measurements, often in non-ideal geometries. One important, yet commonly overlooked source of signal corruption is the etalon effect -- interference phenomena caused by multiple reflections from dielectric layers of packaging and clothing likely to be concealing materials of interest in real-life scenarios. This thesis focuses on the development and implementation of a model-based material parameter estimation technique, primarily for use in reflection spectroscopy, that takes the influence of the etalon effect into account. The technique is adapted from techniques developed for transmission spectroscopy of thin samples and is demonstrated using measured data taken at the Northwest Electromagnetic Research Laboratory (NEAR-Lab) at Portland State University. Further tests are conducted, demonstrating the technique's robustness against measurement noise and common sources of error.

Kniffin, Gabriel Paul

4

FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Measurement of Refractive Index for High Reflectance Materials with Terahertz Time Domain Reflection Spectroscopy  

NASA Astrophysics Data System (ADS)

A method to measure the refractive index for high reflectance materials in the terahertz range with terahertz time domain reflection spectroscopy is proposed. In this method, the THz waveforms reflected by a silicon wafer and high reflectance sample are measured respectively. The refractive index of the silicon wafer, measured with the THz time domain transmission spectroscopy, is used as a reference in the THz time domain reflective spectroscopy. Therefore, the complex refractive index of the sample can be obtained by resorting to the known reflective index of the silicon and the Fresnel law. To improve the accuracy of the phase shift, the Kramers-Kronig transform is adopted. This method is also verified by the index of the silicon in THz reflection spectroscopy. The bulk metal plates have been taken as the sample, and the experimentally obtained metallic refractive indexes are compared with the simple Drude model.

Sun, Wen-Feng; Wang, Xin-Ke; Zhang, Yan

2009-11-01

5

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. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:4065-4071, 2013. PMID:24037861

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

2013-08-23

6

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

7

Terahertz Spectroscopy of Polymers  

NASA Astrophysics Data System (ADS)

Polymers and terahertz (THz) waves form a fruitful symbiosis: on the one hand, non-polar plastics serve as base materials for THz optics as they exhibit low absorption and excellent machinability. On the other hand, THz time-domain spectroscopy (TDS) grants access to unique information about the molecular structure and morphology of polymers, offering an immense portfolio of interesting scientific opportunities. Furthermore, contact-free, non-destructive testing with non-ionizing THz radiation could evolve as a valuable addition to or substitution of ultrasonic and X-ray characterization, especially in quality inspection and process control applications. This chapter aims to give an overview of recent activities in this field, covering both the spectroscopic analysis of polymers with THz waves as well as the non-destructive testing of plastic components with THz systems.

Jansen, Christian; Wietzke, Steffen; Koch, Martin

8

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

9

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

10

Terahertz Spectroscopy of Biomolecules  

NASA Astrophysics Data System (ADS)

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

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

2002-03-01

11

Characterization of burn injuries using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

12

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

13

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.

14

High speed terahertz reflection imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging has shown great potential in several biomedical areas such as burn imaging, detection of skin cancer, and pharmaceutical tablet imaging. The development of each of these application has been limited by slow imaging speed (tens of minutes to hours) and small scan areas (less than 10 square centimeters). Elsewhere to date, the sample itself must be mechanically raster scanned due to the free space optical coupling of femtosecond laser pulses driving the terahertz generating and detecting elements. This paper reports on the development of a freely positionable fiber optic coupled terahertz transceiver which may be raster scanned over a stationary object. Image acquisition times of less than 8 minutes for a 20x20 cm area (400 sq cm area) raster scanning a terahertz transceiver over a stationary object; and of less than 1 minute for image acquisition with a movable object raster scanning the object have been demonstrated. High speed stationary imaging will allow the practical investigation on human and animal subjects.

Zimdars, David

2005-04-01

15

Biological Sensing with Terahertz Circular Dichroism Spectroscopy.  

National Technical Information Service (NTIS)

We have developed a circular dichroism spectrometer working in the terahertz (THz) frequency regime. As THz spectroscopy is specific to collective vibrational modes in macromolecules (and collective modes in condensed, polar media such as water), the spec...

K. W. Plaxco S. J. Allen

2005-01-01

16

Temperature Dependent Terahertz Spectroscopy of Allopurinol  

NASA Astrophysics Data System (ADS)

We report terahertz (THz) characterization of allopurinol over a broad frequency range of 0.2 THz to 20 THz at different temperatures. The combined use of THz time domain spectroscopy and Fourier transform infrared spectroscopy provides complete coverage of the whole terahertz range. The results show that allopurinol has many prominent absorption signatures within terahertz range, which are determined by the structure and properties of the sample. The absorption spectra from room temperature to below liquid nitrogen temperatures are obtained. The observed blue shifts of the absorption fingerprints at low temperatures are analyzed by Bose-Einstein distribution.

Song, Qian; Han, Pengyu; Zhang, X.-C.; Zhang, Cunlin; Zhao, Yuejin

2009-05-01

17

Terahertz Spectroscopy of Complex Materials  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy is a powerful tool to investigate complex materials broadly defined. This includes artificial electromagnetic composites such as metamaterials, and correlated electron materials where the interplay between microscopic degrees of freedom leads to phenomena such as superconductivity or metal-insulator transitions. I will discuss our recent results in these areas. Metamaterials are a relatively new type of artificial composite with electromagnetic properties that derive from their sub-wavelength structure. The judicious combination of metamaterials with MEMS technology enables reconfigurable metamaterials where artificial "atoms" reorient within unit cells in response to an external stimulus. This is accomplished by fabricating planar arrays of split ring resonators on bimaterial cantilevers designed to bend out of plane in response to a thermal stimulus. In this way we can control the electric and magnetic response of these metamaterials. Vanadium dioxide (VO2) exhibits a metal-insulator transition (MIT) at a temperature (340K) that coincides with a structural phase transition. This leads to the "chicken and egg" problem. Is it the structural change or electron correlations that lead to the MIT transition? Uniaxially strained VO2 films have been fabricated to help solve this problem. In unstrained VO2 crystals the insulator to metal transition enables the electrons move freely in three dimensions. Non-contact THz-TDS conductivity measurements of strained samples reveal that the electrons prefer to move in one direction. That is, strain induces a quasi one-dimensional metallic conductivity. These results reveal the utility of terahertz spectroscopy to investigate complex materials and point the way towards future studies of hybrid composites incorporating metamaterials with quantum-based complex matter. Such multi-scale structures may offer complementary benefits where quantum materials confer additional functionality to artificial electromagnetic composites or, conversely, metamaterials serve as a novel tool to facilitate fundamental studies of the electrodynamic response of complex quantum materials.

Averitt, Richard D.

2011-04-01

18

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

19

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.

20

A promising diagnostic method: Terahertz pulsed imaging and spectroscopy.  

PubMed

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

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

2011-03-28

21

Terahertz Spectroscopy of Bacteriorhodopsin and Rhodopsin: Similarities and Differences  

PubMed Central

We studied the low-frequency terahertz spectroscopy of two photoactive protein systems, rhodopsin and bacteriorhodopsin, as a means to characterize collective low-frequency motions in helical transmembrane proteins. From this work, we found that the nature of the vibrational motions activated by terahertz radiation is surprisingly similar between these two structurally similar proteins. Specifically, at the lowest frequencies probed, the cytoplasmic loop regions of the proteins are highly active; and at the higher terahertz frequencies studied, the extracellular loop regions of the protein systems become vibrationally activated. In the case of bacteriorhodopsin, the calculated terahertz spectra are compared with the experimental terahertz signature. This work illustrates the importance of terahertz spectroscopy to identify vibrational degrees of freedom which correlate to known conformational changes in these proteins.

Balu, R.; Zhang, H.; Zukowski, E.; Chen, J.-Y.; Markelz, A. G.; Gregurick, S. K.

2008-01-01

22

Terahertz pulsed spectroscopy and imaging for pharmaceutical applications: a review.  

PubMed

The terahertz region of the electromagnetic spectrum spans the frequency range between the infrared and the microwave. Traditionally the exploitation of this spectral region has been difficult owing to the lack of suitable source and detector. Over the last ten years or so, terahertz technology has advanced considerably with both terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) instruments now commercially available. This review outlines some of the recent pharmaceutical applications of terahertz pulsed spectroscopy and imaging. The following application areas are highlighted: (1) discrimination and quantification of polymorphs/hydrates, (2) analysis of solid form transformation dynamics, (3) quantitative characterisation of tablet coatings: off-line and on-line, (4) tablet coating and dissolution, (5) spectroscopic imaging and chemical mapping. This review does not attempt to offer an exhaustive assessment of all anticipated pharmaceutical applications; rather it is an attempt to raise the awareness of the emerging opportunities and usefulness offered by this exciting technology. PMID:21237260

Shen, Yao-Chun

2011-01-13

23

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

24

Terahertz spectroscopy of explosives and simulants: RDX, PETN, sugar, and L-tartaric acid  

Microsoft Academic Search

We report on the transmission and reflection terahertz (THz) spectra of the high explosives RDX and PETN. These common military explosives are compared to simulants L-tartaric acid and sucrose, respectively. The use of these simulants enables researchers to develop many aspects of THz spectroscopy for explosives detection without the need for live explosives. Further, we discuss the effect of sample

Christopher Konek; John Wilkinson; Okan Esenturk; Edwin Heilweil; Michael Kemp

2009-01-01

25

Terahertz and mid-infrared reflectance of epitaxial graphene  

NASA Astrophysics Data System (ADS)

Epitaxial graphene grown by thermal decomposition on SiC substrate has been widely investigated as a promising material for electronics and optics. Here, we investigate the infrared (IR) optical properties of few-layer (FL) and multilayer (ML) graphene on the C-terminated face of 6H-SiC substrates [1]. Contrary to IR transmission spectroscopy, which is hampered over a large part of the IR range by the SiC reststrahlen band and multiphonon absorption, IR reflectance gives access to invaluable information from terahertz (THz) to mid-infrared (MIR). Experimental data are well fitted with an explicit model over the entire spectral range using the SiC dielectric function and the graphene optical conductivity, taking into account both intraband and interband transitions. The number of layers extracted from our data in the FL and ML graphene corroborates with the X-ray photoelectron spectroscopy (XPS) measurements. We demonstrate that this consistent and simultaneous analysis leads to precise information on the carrier properties, doping level and the number of layers, even in the case of thick ML (30 layers or more). MIR microscopy was also used to check the sample homogeneity. [1] F. Joucken et al., Phys. Rev. B 85, 161408(R) (2012).

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

2013-03-01

26

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

27

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

28

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

2012-06-07

29

Time-resolved terahertz spectroscopy of semiconductor quantum dots  

Microsoft Academic Search

Spectroscopy in the far-infrared part of the electromagnetic spectrum based on the time-domain measurements of transient terahertz pulses has become a standard experimental technique. In the first part of this thesis we present results regarding applications of this technique to the problem of near-field, sub-wavelength imaging and the effect of finite-size beams in optical pump\\/terahertz probe experiments. The second part

Georgi Dakovski

2008-01-01

30

Terahertz spectroscopy of explosives and simulants: RDX, PETN, sugar, and L-tartaric acid  

NASA Astrophysics Data System (ADS)

We report on the transmission and reflection terahertz (THz) spectra of the high explosives RDX and PETN. These common military explosives are compared to simulants L-tartaric acid and sucrose, respectively. The use of these simulants enables researchers to develop many aspects of THz spectroscopy for explosives detection without the need for live explosives. Further, we discuss the effect of sample preparation on the THz spectrum of RDX and demonstrate that experiments performed on different terahertz instruments at multiple laboratories show quantitative agreement between spectra recorded with four different instruments.

Konek, Christopher; Wilkinson, John; Esenturk, Okan; Heilweil, Edwin; Kemp, Michael

2009-05-01

31

Optical pump-terahertz probe spectroscopy of dyes in solutions: Probing the dynamics of liquid solvent or solid precipitate?  

Microsoft Academic Search

The optical pump-terahertz probe spectroscopy was used together with ab initio calculations and molecular dynamics simulations to investigate ultrafast dynamics following electronic excitation of Coumarin 153 and TBNC (2,11,20,29-tetra-tert-butyl-2,3-naphtalocyanine) dyes in polar solvents. By scanning the terahertz waveform for different pump-probe delays this experimental technique allows us to obtain two dimensional spectra directly reflecting the temporal response of the system.

Filip Kadlec; Christelle Kadlec; Petr Kuzel; Petr Slavícek; Pavel Jungwirth

2004-01-01

32

Protein Conformational State Observed through Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

We present the first demonstration of the dependence of far infrared (FIR) absorption on protein conformational state using terahertz time domain spectroscopy. FIR spectral measurements of wild type (WT) and D96N mutant bacteriorhodopsin thin films have been carried out as a function of hydration, temperature and conformational state. The results are compared to calculated spectra generated via normal mode analyses using CHARMm. The FIR absorbance is slowly increasing with frequency and without strong narrow features over the range of 2-60 cm-1. The absorption shifts in frequency with decreasing temperature as expected with a strongly anharmonic potential. Decreasing hydration shifts the absorption to higher frequencies. Ground state FIR absorbances have nearly identical frequency dependence, with the mutant having less optical density than the wild type. We use photoexcitation and thermal capture to perform measurements as a function of the M intermediate state content. In the M state the FIR absorbance of the WT increases whereas there is no change for D96N. Support was provided by ARO DAAD19-02-1-0271 and DAAD19-99-1-0198 and NSF EIA-0129731.

Chen, J. Y.; Whitmire, S. E.; Wolpert, D.; Markelz, A. G.; Hillebrecht, J. R.; Galan, J.; Birge, R. R.

2003-03-01

33

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

34

Terahertz Imaging and Spectroscopy Based on Hot Electron Bolometer (HEB) Heterodyne Detection.  

National Technical Information Service (NTIS)

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....

E. Gerecht L. You

2008-01-01

35

Terahertz transmission spectroscopy of nonpolar materials and relationship with composition and properties  

Microsoft Academic Search

Terahertz time-domain spectroscopy is used to study the properties of non-polar materials. Terahertz absorption spectra and refractive indices are measured in a number of glasses and oils. The results are correlated with material properties.

M. Naftaly; A. P. Foulds; M. R. Stringer; R. E. Miles; A. G. Davies

2004-01-01

36

Measurements of the Carrier Dynamics and Terahertz Response of Oriented Germanium Nanowires using Optical-Pump Terahertz-Probe Spectroscopy  

Microsoft Academic Search

We have measured the terahertz response of oriented germanium nanowires using ultrafast optical-pump terahertz-probe spectroscopy. We present results on the time, frequency, and polarization dependence of the terahertz response. Our results indicate intraband energy relaxation times of photoexcited carriers in the 1.5-2.0 ps range, carrier density dependent interband electron-hole recombination times in the 75-125 ps range, and carrier momentum scattering

Jared H. Strait; Paul A. George; Mark Levendorf; Martin Blood-Forsythe; Farhan Rana; Jiwoong Park

2009-01-01

37

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

38

An efficient method-development strategy for quantitative chemical imaging using terahertz pulse spectroscopy  

Microsoft Academic Search

The purpose of our research was to investigate efficient procedures for generating multivariate prediction vectors for quantitative\\u000a chemical analysis of solid dosage forms using terahertz pulse imaging (TPI) reflection spectroscopy. A set of calibration\\u000a development and validation tablet samples was created following a ternary mixture of anhydrous theophylline, lactose monohydrate,\\u000a and microcrystalline cellulose (MCC). Spectral images of one side of

Robert P. Cogdill; Steven M. Short; Ryanne Forcht; Zhenqi Shi; Yaochun Shen; Philip F. Taday; Carl A. Anderson; James K. Drennen

2006-01-01

39

Measurements of the carrier dynamics and terahertz response of oriented germanium nanowires using optical-pump terahertz-probe spectroscopy.  

PubMed

We have measured the terahertz response of oriented Germanium nanowires using ultrafast optical-pump terahertz-probe spectroscopy. We present results on the time, frequency, and polarization dependence of the terahertz response. Our results indicate intraband energy relaxation times of photoexcited carriers in the 1.5-2.0 ps range, carrier density dependent interband electron-hole recombination times in the 75-125 ps range, and carrier momentum scattering rates in the 60-90 fs range. Additionally, the terahertz response of the nanowires is strongly polarization dependent despite the subwavelength dimensions of the nanowires. The differential terahertz transmission is found to be large when the field is polarized parallel to the nanowires and very small when the field is polarized perpendicular to the nanowires. This polarization dependence of the terahertz response can be explained in terms of the induced depolarization fields and the resulting magnitudes of the surface plasmon frequencies. PMID:19594164

Strait, Jared H; George, Paul A; Levendorf, Mark; Blood-Forsythe, Martin; Rana, Farhan; Park, Jiwoong

2009-08-01

40

Measurements of the Carrier Dynamics and Terahertz Response of Oriented Germanium Nanowires using Optical-Pump Terahertz-Probe Spectroscopy  

NASA Astrophysics Data System (ADS)

We have measured the terahertz response of oriented germanium nanowires using ultrafast optical-pump terahertz-probe spectroscopy. We present results on the time, frequency, and polarization dependence of the terahertz response. Our results indicate intraband energy relaxation times of photoexcited carriers in the 1.5-2.0 ps range, carrier density dependent interband electron-hole recombination times in the 75-125 ps range, and carrier momentum scattering rates in the 60-90 fs range. Additionally, the terahertz response of the nanowires is strongly polarization dependent despite the subwavelength dimensions of the nanowires. The differential terahertz transmission is found to be large when the field is polarized parallel to the nanowires and very small when the field is polarized perpendicular to the nanowires. This polarization dependence of the terahertz response can be explained in terms of the induced depolarization fields and the resulting magnitudes of the surface plasmon frequencies.

Strait, Jared H.; George, Paul A.; Levendorf, Mark; Blood-Forsythe, Martin; Rana, Farhan; Park, Jiwoong

2009-08-01

41

Continuous wave terahertz reflection imaging of human colorectal tissue  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

42

Conformational characteristics of ?-glucan in laminarin probed by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

43

Characterization of roughness parameters of metallic surfaces using terahertz reflection spectra.  

PubMed

This paper reports on the effect of random Gaussian roughness with rms roughness values of 5-20 microm on the terahertz reflection spectra of metallic aluminum surfaces using Fourier transform IR spectroscopy. By comparing experimental data with a theoretical model based on the Kirchhoff approximation, the rms roughness of a surface is accurately determined. The rms roughness determined by this method is in good agreement with the rms roughness measured using a stylus surface profilometer. In addition, we demonstrate that this method can be used to clearly resolve rough surfaces that differ in rms roughness by approximately 1 microm. PMID:19571954

Jagannathan, Arunkumar; Gatesman, Andrew J; Giles, Robert H

2009-07-01

44

Terahertz Spectroscopy of Histidine Enantiomers and Polymorphs  

NASA Astrophysics Data System (ADS)

We have measured terahertz and powder x-ray diffraction spectra of D-histidine, L-histidine, and DL-histidine. The as-received D and L material exists in two different polymorphs: D-histidine is in the metastable monoclinic form, while L-histidine is in the stable orthorhombic form. For both the L and D enantiomers, recrystallization of the as-received material results in a mixture of the monoclinic and orthorhombic forms.

True, Alan B.; Schroeck, Konstanze; French, Timothy A.; Schmuttenmaer, Charles A.

2011-05-01

45

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

46

Applications of terahertz spectroscopy in biosystems  

Microsoft Academic Search

Terahertz (THz) spectroscopic investigations of condensed-phase\\u000a biological samples are reviewed ranging from the simple crystalline\\u000a forms of amino acids, carbohydrates and polypeptides to the more complex\\u000a aqueous forms of small proteins, DNA and RNA. Vibrationally resolved\\u000a studies of crystalline samples have revealed the exquisite sensitivity\\u000a of THz modes to crystalline order, temperature, conformational form,\\u000a peptide sequence and local solvate environment

David F. Plusquellic; Karen Siegrist; Edwin J. Heilweil; Okan Esenturk

2007-01-01

47

Ultrafast conductivity dynamics in pentacene probed using terahertz spectroscopy  

Microsoft Academic Search

We present measurements of the transient photoconductivity in pentacene single crystals using optical-pump terahertz-probe spectroscopy. We have measured the temperature and fluence dependence of the mobility of the photoexcited charge carriers with picosecond resolution. The pentacene crystals were excited at 3.0 eV, which is above the bandgap of ?2.2 eV, and the induced change in the far-infrared transmission was measured.

V. K. Thorsmølle; R. D. Averitt; X. Chi; D. J. Hilton; D. L. Smith; A. P. Ramirez; A. J. Taylor

2004-01-01

48

Ultrafast conductivity dynamics in pentacene probed using terahertz spectroscopy  

Microsoft Academic Search

We present measurements of the transient photoconductivity in pentacene single crystals using optical-pump terahertz-probe spectroscopy. We have measured the temperature and fluence dependence of the mobility of the photoexcited charge carriers with picosecond resolution. The pentacene crystals were excited at 3.0 eV, which is above the bandgap of ~2.2 eV, and the induced change in the far-infrared transmission was measured.

V. K. Thorsmølle; R. D. Averitt; X. Chi; D. J. Hilton; D. L. Smith; A. P. Ramirez; A. J. Taylor

2004-01-01

49

Terahertz time-domain spectroscopy of sulfur-containing biomolecules  

Microsoft Academic Search

We present frequency-dependent absorption coefficients and refractive indices of sulfur-containing biomolecules in the far-infrared region measured by terahertz (THz) time-domain spectroscopy (TDS). The THz radiation was generated by a surface photocurrent method with a (100)InAs wafer as a THz emitter, and its intensity was enhanced by applying a magnetic field of 1.6 T. The THz radiation was detected by the

Kohji Yamamoto; Keisuke Tominaga

2005-01-01

50

Assessing skin hydration status in haemodialysis patients using terahertz spectroscopy: a pilot/feasibility study  

NASA Astrophysics Data System (ADS)

Terahertz (THz) time-domain spectroscopy was used in vivo to measure the body reflectance with the aim of determining experimentally the influence of haemodialysis on the content of water in the human skin. For this purpose, an original methodology of determining the skin properties at THz frequencies from the reflectance was developed. A series of measurements were performed before and after dialysis with ten subjects. The results strongly indicate that the surface body hydration is not the main parameter determining the skin conductivity in the THz range.

Kadlec, Filip; Berta, Milan; Kužel, Petr; Lopot, František; Polakovi?, Vladimír

2008-12-01

51

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

52

Ultrafast Carrier Dynamics of YBCO Films with Various In-plain Orientations Investigated by Pump-probe and Terahertz Spectroscopy  

Microsoft Academic Search

In this study, we focus on the terahertz (THz) and optical responses of superconducting YBa2Cu3O7-delta (YBCO) films with various in-plane orientations. We report results and analyses of THz time domain spectroscopy and time-resolved photoinduced reflectivity experiments on four in-plane orientated superconducting YBCO films grown on yttria-stabilized zirconia substrates. Our study of the transmissions of THz time domain spectroscopy indicates a

Shyh-Shii Pai; Zen-Chi Lin; Pao-An Lin; Cheng-Chung Chi

2008-01-01

53

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

54

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

55

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

56

Ultrafast conductivity dynamics in pentacene probed using terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We present measurements of the transient photoconductivity in pentacene single crystals using optical-pump terahertz-probe spectroscopy. We have measured the temperature and fluence dependence of the mobility of the photoexcited charge carriers with picosecond resolution. The pentacene crystals were excited at 3.0 eV, which is above the bandgap of ~2.2 eV, and the induced change in the far-infrared transmission was measured. At 30 K, the carrier mobility is ?~0.4 cm2/V s and decreases to ?~0.2 cm2/V s at room temperature. The transient terahertz signal reveals the presence of free carriers that are trapped on the time scale of a few picoseconds or less, possibly through the formation of excitons, small polarons, or trapping by impurities.

Thorsmølle, V. K.; Averitt, R. D.; Chi, X.; Hilton, D. J.; Smith, D. L.; Ramirez, A. P.; Taylor, A. J.

2004-02-01

57

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

58

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

59

Dielectric relaxation of electrolyte solutions using terahertz transmission spectroscopy  

NASA Astrophysics Data System (ADS)

We use terahertz (THz) transmission spectroscopy to obtain the frequency dependent complex dielectric constants of water, methanol, and propylene carbonate, and solutions of lithium salts in these solvents. The behavior of the pure solvents is modeled with either two (water) or three (methanol and propylene carbonate) Debye relaxations. We discuss the effects of ionic solvation on the relaxation behavior of the solvents in terms of modifications to the values of the Debye parameters of the pure solvents. In this way we obtain estimates for numbers of irrotationally bound solvent molecules, the numbers of bonds broken or formed, and the effects of ions on the higher-frequency relaxations.

Asaki, M. L. T.; Redondo, A.; Zawodzinski, T. A.; Taylor, A. J.

2002-05-01

60

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

61

Spectroscopy of several drugs in the terahertz region  

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

62

High Resolution Terahertz Spectroscopy with Quantum Cascade Lasers  

NASA Astrophysics Data System (ADS)

High resolution terahertz (THz) spectroscopy is a powerful analytical tool for laboratory purposes as well as for remote sensing in astronomy, planetary research, and Earth observation. THz quantum cascade lasers (QCLs) are promising sources for implementation into THz spectrometers, in particular at frequencies above 3 THz, which is the least explored portion of the THz region. One application of QCLs in THz spectroscopy is in absorption spectrometers, where they can replace less powerful and somewhat cumbersome sources based on frequency mixing with gas lasers. Another one is using a QCL as local oscillator in a heterodyne spectrometer for remote sensing. This article will review the state-of-the art in high resolution THz spectroscopy with QCLs.

Hübers, H.-W.; Eichholz, R.; Pavlov, S. G.; Richter, H.

2013-06-01

63

Detection and identification of explosives using terahertz pulsed spectroscopic imaging  

NASA Astrophysics Data System (ADS)

The absorption spectrum of the explosive 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopy. Seven absorption features in the spectral range of 5-120 cm-1 have been observed and identified as the fingerprint of RDX. Furthermore, the spatial distribution of individual chemical substances including RDX, has been mapped out using reflection terahertz spectroscopic imaging in combination with component spatial pattern analysis. This is the terahertz spectroscopy and chemical mapping of explosives obtained using reflection terahertz measurement, and represents a significant advance toward developing a terahertz pulsed imaging system for security screening of explosives.

Shen, Y. C.; Lo, T.; Taday, P. F.; Cole, B. E.; Tribe, W. R.; Kemp, M. C.

2005-06-01

64

Photocarriers dynamics in silicon wafer studied with optical-pump terahertz-probe spectroscopy  

NASA Astrophysics Data System (ADS)

Optical pump-terahertz probe spectroscopy is employed to investigate the optical characteristics of silicon wafer. The wafer surface undergoes a phase transition from insulator to metal for terahertz wave with increasing pump fluence. The real part of the pump-induced conductivity shows strong frequency dependence, which can be well described with Drude-Smith model. Our results also demonstrate that the photoexcited Si layer acts as a broadband terahertz pulse antireflection coating with proper pump fluence. In addition, it is observed that the terahertz pulse apparently arrives at the detector earlier when silicon is optically excited.

Li, Gaofang; Li, Dong; Jin, Zuanming; Ma, Guohong

2012-09-01

65

Identification of biomolecules by terahertz spectroscopy and fuzzy pattern recognition  

NASA Astrophysics Data System (ADS)

An approach for automatic identification of terahertz (THz) spectra of biomolecules is proposed based on principal component analysis (PCA) and fuzzy pattern recognition in this paper, and THz transmittance spectra of some typical amino acid and saccharide biomolecular samples are investigated to prove its feasibility. Firstly, PCA is applied to reduce the dimensionality of the original spectrum data and extract features of the data. Secondly, instead of the original spectrum variables, the selected principal component scores matrix is fed into the model of fuzzy pattern recognition, where a principle of fuzzy closeness based optimization is employed to identify those samples. Results demonstrate that THz spectroscopy combined with PCA and fuzzy pattern recognition can be efficiently utilized for automatic identification of biomolecules. The proposed approach provides a new effective method in the detection and identification of biomolecules using THz spectroscopy.

Chen, Tao; Li, Zhi; Mo, Wei

2013-04-01

66

Identification of biomolecules by terahertz spectroscopy and fuzzy pattern recognition.  

PubMed

An approach for automatic identification of terahertz (THz) spectra of biomolecules is proposed based on principal component analysis (PCA) and fuzzy pattern recognition in this paper, and THz transmittance spectra of some typical amino acid and saccharide biomolecular samples are investigated to prove its feasibility. Firstly, PCA is applied to reduce the dimensionality of the original spectrum data and extract features of the data. Secondly, instead of the original spectrum variables, the selected principal component scores matrix is fed into the model of fuzzy pattern recognition, where a principle of fuzzy closeness based optimization is employed to identify those samples. Results demonstrate that THz spectroscopy combined with PCA and fuzzy pattern recognition can be efficiently utilized for automatic identification of biomolecules. The proposed approach provides a new effective method in the detection and identification of biomolecules using THz spectroscopy. PMID:23357678

Chen, Tao; Li, Zhi; Mo, Wei

2013-01-10

67

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

68

Terahertz tomography of a photo-induced carrier based on pump-probe spectroscopy using counterpropagation geometry.  

PubMed

A novel technique for the terahertz (THz) tomography of a photo-induced carrier that is based on optical-pump THz-probe time-resolved reflection spectroscopy using counterpropagation geometry of the pump and probe pulses has been proposed. Transient reflection due to the photo-induced carrier provides information about the physical properties and spatial distribution separately. We have experimentally demonstrated this method using a silicon wafer. The obtained complex reflection can be reproduced by the exact solution of Maxwell's equations, assuming an exponential distribution of the photo-induced carrier density. PMID:22940938

Tsubouchi, Masaaki; Nagai, Masaya; Ohshima, Yasuhiro

2012-09-01

69

Hydration dynamics of oriented DNA films investigated by time-domain terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The B to A conformational transition of highly oriented DNA films due to a hydration change is observed with time-domain terahertz spectroscopy. Wet-spun films of calf thymus and salmon DNA are investigated for different film thicknesses and for different polarizations of the terahertz radiation relative to the DNA orientation. A clear polarization dependence is observed. Asynchronous optical sampling allows recording of terahertz absorption and background spectra in a few 10 s, permitting the tracking of the dehydration dynamics on a time scale of minutes. The observation of a phase transition is corroborated by Raman spectroscopy.

Kistner, C.; André, A.; Fischer, T.; Thoma, A.; Janke, C.; Bartels, A.; Gisler, T.; Maret, G.; Dekorsy, T.

2007-06-01

70

Charge carrier dynamics of ZnSe by optical-pump terahertz-probe spectroscopy  

Microsoft Academic Search

The optical properties and transient dynamics of ZnSe were studied by terahertz time-domain spectroscopy (THz-TDS) and optical-pump terahertz probe (OPTP) spectroscopy, respectively. From the THz time-domain signal, the frequency-dependent absorption coefficient and index of refraction of ZnSe were calculated. It follows that the values appear to be similar with those in literatures. The complex permittivity and conductivity of ZnSe were

A. K. G. Tapia; N. Yamamoto; C. Ponseca Jr; K. Tominaga

2011-01-01

71

High-resolution molecular spectroscopy with 2.5 terahertz quantum cascade lasers  

Microsoft Academic Search

Quantum cascade lasers operating at about 2.5 terahertz have been implemented in a spectrometer for high resolution molecular spectroscopy. Linewidth, frequency tunability and frequency stability of the lasers were investigated by mixing their radiation with radiation from a 2.5 terahertz gas laser. Two first laser characteristics were found to be sufficient for Doppler-limited spectroscopy. For a demonstration of the spectrometer,

Sergey G. Pavlov; Heinz-Wilhelm Hübers; Michael Greiner-Bär; Heiko Richter; L. Mahler; A. Tredicucci; H. E. Beere; D. A. Ritchie

2008-01-01

72

Carrier dynamics and terahertz photoconductivity of doped silicon measured by femtosecond pump-terahertz probe spectroscopy  

Microsoft Academic Search

The carrier dynamics and terahertz photoconductivity in the n-type silicon (n-Si) as well as in the p-type Silicon (p-Si) have been investigated by using femtosecond pump-terahertz probe technique. The measurements show that the relative change\\u000a of terahertz transmission of p-Si at low pump power is slightly smaller than that of n-Si, due to the lower carrier density induced by the

Qingli Zhou; Yulei Shi; Tong Li; Bin Jin; Dongmei Zhao; Cunlin Zhang

2009-01-01

73

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

74

Continuous-wave terahertz reflection imaging of ex vivo nonmelanoma skin cancers  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

75

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

NASA Astrophysics Data System (ADS)

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 millimeter waves. We are developing hot electron bolometer (HEB) mixer receivers for heterodyne detection at terahertz frequencies. HEB detectors provide unprecedented sensitivity and spectral resolution at terahertz frequencies. We describe the development of a two-pixel focal plane array (FPA) based on HEB technology. Furthermore, we have demonstrated a fully automated, two-dimensional scanning, passive imaging system based on our HEB technology operating at 0.85 THz. Our high spectral resolution terahertz imager has a total system noise equivalent temperature difference (NE?T) value of better than 0.5 K and a spatial resolution of a few millimeters. HEB technology is becoming the basis for advanced terahertz imaging and spectroscopic technologies for the study of biological and chemical agents over the entire terahertz spectrum.

Gerecht, Eyal; You, Lixing

2008-02-01

76

Pulsed terahertz bi-directional reflection distribution function (BRDF) measurements of materials and obscurants  

NASA Astrophysics Data System (ADS)

We report a pulsed method to measure reflection and scattering from several samples with different degrees of surface roughness and material properties at terahertz frequencies. Reflection from a flat gold mirror shows that the full width half maximum (FWHM) of the terahertz beam angular spread is <4° for frequency range 0.2 THz to 3 THz with signal-to-noise of 65 dB. Measurement of a paper index card, used as a low scattering sample, shows that the reflection/scattering properties are essentially similar to the system signature response except for multiple reflections between the front and back surfaces of the sample. Sixty-grit sandpaper shows multiple scattering events with almost no signal reflected from the flat backing paper surface. Corduroy cloth shows periodic reflections in the time domain, which correspond to diffraction lobes in the spectral domain.

Lo, Shu-Zee A.; Heilweil, Edwin J.

2011-09-01

77

Time-resolved Terahertz spectroscopy using a Ti:Sapphire laser oscillator  

NASA Astrophysics Data System (ADS)

In time-resolved terahertz spectroscopy, electromagnetic radiation in the frequency range 0.3 - 3 THz (corresponding to wavelengths of 0.1 - 1.0 mm) is used to probe the dynamic properties of charge carriers within materials. When a sample material is excited using an ultrafast optical laser pulse, the terahertz probe that passes through the sample a time later reveals the subsequent behavior of the charge carriers in the sample. Real-time mapping of the dynamics can then be achieved through a pump-probe delay experiment. To date, most time-resolved terahertz spectroscopy has relied on high-power laser systems in order both to excite the sample as well as to generate the probing terahertz radiation. Here, we investigate the feasibility of adapting this technology to a relatively less expensive Ti:sapphire laser oscillator. We present preliminary data and discuss challenges going forward.

Kharel, Pradosh; Waquar, Wassam; Gagnon, Etienne

2013-03-01

78

Ultrafast terahertz spectroscopy for measuring carrier dynamics in nanoscale photovoltaic materials  

Microsoft Academic Search

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 muJ, 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

Okan Esenturk; Joseph S. Melinger; Edwin J. Heilweil

2010-01-01

79

Ultrafast optical-pump terahertz-probe spectroscopy of oriented Ge and Ge\\/Si core\\/shell nanowires  

Microsoft Academic Search

We study the time- and frequency-dependent terahertz dynamics of oriented Ge and Ge\\/Si core\\/shell nanowires using ultrafast optical-pump terahertz-probe spectroscopy, and we compare their intraband relaxation, interband recombination and momentum scattering times. ©2011 Optical Society of America OCIS codes: (320.0320) Ultrafast Optics; (300.6495) Spectroscopy, terahertz; (160.4236) Nanomaterials One-dimensional semiconductor nanowires (NWs) have generated considerable interest due to their substantial potential

Momchil T. Mihnev; Wayne Fung; Wei Lu; Theodore B. Norris

2011-01-01

80

Self-referenced method for terahertz wave time-domain spectroscopy.  

PubMed

The method allows retrieval of the absorbance of a sample without the need for a reference measurement. The method measures the dynamic variation of frequency resolution as the waveform is being acquired. In terahertz wave time-domain spectroscopy, the frequency resolution increases as the temporal window increases. Therefore, narrow absorption peaks will appear in the spectrum when the temporal window is long enough to resolve the peak. By measuring the dynamic values of each frequency component at specific points in time, a reference value and a peak value are extracted and, hence, the self-referenced is achieved. In addition, the method provides a mechanism to remove the effects of echoes, which enables arbitrary temporal window length and, thus, achieves high-resolution frequency. Examples of extraction of the water vapor lines and resonant features in gas and semiconductors are demonstrated in transmission and reflection geometries. PMID:21886193

Redo-Sanchez, Albert; Zhang, Xi-Cheng

2011-09-01

81

Bidirectional reflectance spectroscopy. I - Theory  

NASA Astrophysics Data System (ADS)

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.

1981-04-01

82

Optical pump-terahertz probe spectroscopy of dyes in solutions: probing the dynamics of liquid solvent or solid precipitate?  

PubMed

The optical pump-terahertz probe spectroscopy was used together with ab initio calculations and molecular dynamics simulations to investigate ultrafast dynamics following electronic excitation of Coumarin 153 and TBNC (2,11,20,29-tetra-tert-butyl-2,3-naphtalocyanine) dyes in polar solvents. By scanning the terahertz waveform for different pump-probe delays this experimental technique allows us to obtain two dimensional spectra directly reflecting the temporal response of the system. A distinct signal was obtained for TBNC in chloroform, 2-propanol, and n-butanol, while no signal was recorded for Coumarin 153 in either of these solvents. We explain the nonequilibrium signal detected in TBNC solutions by the presence of a solid, polycrystalline phase of the dye resulting from irradiating the solution by intense optical pulses. PMID:15267927

Kadlec, Filip; Kadlec, Christelle; Kuzel, Petr; Slavícek, Petr; Jungwirth, Pavel

2004-01-01

83

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

84

Terahertz pulsed imaging and spectroscopy of breast tumors  

Microsoft Academic Search

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

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

2006-01-01

85

Optical pump-terahertz probe spectroscopy utilizing a cavity-dumped oscillator-driven terahertz spectrometer  

Microsoft Academic Search

A terahertz spectrometer capable of steady-state and time-resolved measurements over the 0.1-3.5-THz spectral region has been built. This spectrometer routinely produces and detects terahertz pulses that exhibit signal-to-noise ratios (SNRs) greater than 6000 in the time domain and a spectral noise door of magnitude 2.7×10-4. Hence, the spectrometer achieves nearly four decades of dynamic range in the frequency domain. Two

Bret N. Flanders; David C. Arnett; Norbert F. Scherer

1998-01-01

86

Theory of selective reflection spectroscopy  

NASA Astrophysics Data System (ADS)

We present a calculation of selective reflection spectroscopy, in which the reflection coefficient of a light beam from the interface of a dielectric and an atomic vapor is evaluated as a function of the light frequency. It is shown that the reflection signal depends critically on the spatial attenuation pattern of the refracted field inside the vapor. In the linear case, where the incident laser power is below the saturation limit, we show the dependence of the peak- and center-frequencies of the reflectivity line shapes on the atomic number density. In particular, we show that our self-consistent solution leads to a previously unrecognized line shift. The effects related to saturation and velocity-changing collisions between vapor atoms are also analyzed. Permanent address: Centrum Fizyki Teoretycznej, Polska Akademia Nauk, 02-668 Warsaw, Poland

Guo, J.; Cooper, J.; Gallagher, A.; Lewenstein, M.

1994-08-01

87

Theory of selective reflection spectroscopy  

NASA Astrophysics Data System (ADS)

We present a calculation of selective reflection spectroscopy, in which the reflection coefficient of a light beam from the interface of a dielectric and an atomic vapor is evaluated as a function of the light frequency. It is shown that the reflection signal depends critically on the spatial attenuation pattern of the refracted field inside the vapor. In the linear case, where the incident laser power is below the saturation limit, we show the dependence of the peak- and center-frequencies of the reflectivity line shapes on the atomic number density. In particular, we show that our self-consistent solution leads to a previously unrecognized line shift. The effects related to saturation and velocity-changing collisions between vapor atoms are also analyzed. Permanent address: Centrum Fizyki Teoretycznej, Polska Akademia Nauk, 02-668 Warsaw, Poland.

Guo, J.; Cooper, J.; Gallagher, A.; Lewenstein, M.

1994-09-01

88

Exciton Mott transition in Si revealed by terahertz spectroscopy.  

PubMed

We investigate the exciton Mott transition in Si by using optical pump and terahertz probe spectroscopy. The density-dependent exciton ionization ratio ? is quantitatively evaluated from the analysis of dielectric function and conductivity spectra. The Mott density is clearly determined by the rapid increase in ? as a function of electron-hole (e-h) pair density, which agrees well with the value expected from the random phase approximation theory. However, exciton is sustained in the high-density metallic region above the Mott density as manifested by the 1s-2p excitonic resonance that remains intact across the Mott density. Moreover, the charge carrier scattering rate is strongly enhanced slightly above the Mott density due to nonvanishing excitons, indicating the emergence of highly correlated metallic phase in the photoexcited e-h system. Concomitantly, the loss function spectra exhibit the signature of plasmon-exciton coupling, i.e., the existence of a new collective mode of charge density excitation combined with the excitonic polarization at the proximity of Mott density. PMID:23006100

Suzuki, Takeshi; Shimano, Ryo

2012-07-26

89

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

90

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

91

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

92

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

93

Probing structure and phase-transitions in molecular crystals by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Since the introduction of ultra-fast laser techniques for the generation and detection of broadband terahertz pulses, terahertz time-domain spectroscopy has become a versatile tool for vibrational spectroscopy of molecular systems in the far-infrared. Due to their highly collective and delocalized character vibrational modes in this part of the spectrum are highly sensitive to molecular structure and arrangement within a molecular crystal. Here we utilize this sensitivity to differentiate between the enantiopure amino acid L-cysteine and its racemic crystalline DL-form. Using terahertz time-domain spectroscopy we are able to observe temperature induced solid-state phase transitions in polycrystalline DL-cysteine, as well as in polycrystalline benzoic acid. The dynamics of the transitions is studied by tracing the temperature dependency of spectral features that are assigned to certain conformational phases.

Franz, Morten; Fischer, Bernd M.; Walther, Markus

2011-12-01

94

The ultrafast photoconductive characteristics of GaAs bulk investigated by optical-pump terahertz probe spectroscopy  

Microsoft Academic Search

The ultrafast photoconductive characteristics of GaAs bulk were investigated by the optical-pump terahertz-probe spectroscopy (OPTP) at room temperature. In our experiment, a significant decrease of the terahertz transmittance has been observed when the time delay between the optical pump pulse and the terahertz probe pulse was adjusted. It can be concluded that the electronic states of the GaAs became metallic,

Bin Jin; Qing-Li Zhou; Cunlin Zhang

2008-01-01

95

Optical Properties of Laminarin Using Terahertz Time-Domain Spectroscopy (abstract)  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy is important in the study of biomolecular structure because the vibration and rotation energy of large molecules such as DNA, proteins, and polysaccharides are laid in terahertz regions. Terahertz time-domain spectroscopy (THz-TDS), using terahertz pulses generated and detected by femto-second pulses laser, has been used in the study of biomolecular dynamics, as well as carrier dynamics of semiconductors. Laminarin is a polysaccharide of glucose in brown algae. It is made up of ?(1-3)-glucan and ?(1-6)-glucan. ?-glucan is an anticancer material that activates the immune reaction of human cells and inhibits proliferation of cancer cells. ?-glucan with a single-strand structure has been reported to activate the immune reaction to a greater extent than ?-glucan with a triple-strand helix structure. We used THz-TDS to characterize the difference between single-strand and triple-strand ?-glucan. We obtained single-strand ?-glucan by chemical treatment of triple-strand ?-glucan. We measured the frequency dependent optical constants of Laminarin using THz-TDS. Power absorption of the triple-strand helix is larger than the single-strand helix in terahertz regions. The refractive index of the triple-strand helix is also larger than that of the single-strand helix.

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

2009-04-01

96

Time-domain terahertz magneto-spectroscopy of semiconductors  

NASA Astrophysics Data System (ADS)

The terahertz frequency range, 0.1-10 THz, is one of the richest frequency ranges in condensed matter spectroscopy. Many important excitations and dynamical phenomena occur in this range, including superconducting gaps, protein conformational modes, phonons, and plasmons, just to name a few. Spectroscopic studies in this region provide valuable insights into the quantum states and dynamics of confined, driven, or interacting electrons in solids. In this dissertation research I have developed a time-domain THz magneto-spectroscopy system to investigate various THz magnetic excitations in semiconductors, including a high-mobility two-dimensional electron gas (2DEG) in a GaAs quantum well and lightly-doped InSb. In the 2DEG, I have observed very long-lived (up to ˜ 50 ps) coherent THz oscillations, which correspond to a time-domain observation of cyclotron resonance. From the data both the real and imaginary parts of the conductivity can be simultaneously determined because of the phase-sensitive-detection nature of this technique. Magnetic field and temperature dependent results provide some important information on electron scattering in this system. In InSb, I have found that the THz transmittance of the sample sensitively changes with the temperature and magnetic field, showing a number of non-intuitive spectral features. In particular, I observed a sudden appearance and disappearance of transparency with increasing temperature, which resulted in a transparency window of a narrow temperature region (160-190 K), over a frequency range of 0.1-0.8 THz. Detailed theoretical simulations based on a cold magneto-plasma model demonstrate that this novel phenomenon is a manifestation of coherent interference of the cyclotron-resonance-active and cyclotron-resonance-inactive modes co-propagating through the magneto-plasma along the magnetic field direction. Finally, I have obtained some experimental results on the 1s--2p-- impurity transition at 1.6 K that provide insight on the nature of the magnetic-field-induced metal-to-insulator transition that is known to occur in this system. The materials studied in this research are highly tunable with external fields and doping and thus promising for future THz devices such as tunable THz detectors, filters, and Faraday rotators.

Wang, Xiangfend

97

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

98

Terahertz spectroscopy of human skin constituents in suspension  

NASA Astrophysics Data System (ADS)

Continuous wave terahertz imaging has the potential to offer a non-invasive medical imaging modality for detecting different types of human cancers. The aim of this study was to identify frequencies of interest for continuous wave terahertz imaging of skin cancer. The absorption characteristics of water, collagen, and elastin were studied in the range between 20 and 100cm-1. In addition, we have recorded and analyzed the teraherz absorption spectra of several substances that are present in human skin (i.e. tryptophan, tyrosine, melanin, urocanic acid, keratin) and their water suspensions with the goal of using them as biomarkers for skin cancer detection.

Joseph, Cecil; Yaroslavsky, Anna; Al-Arashi, Munir; Gatesman, Andrew; Goyette, Thomas; Giles, Robert

2008-03-01

99

Nonlinear Terahertz Spectroscopy in Solids with Single-Cycle Terahertz Pulses  

NASA Astrophysics Data System (ADS)

We present novel generation methods of intense terahertz single cycle pulses. The Cherenkov scheme with tilted wave-front technique in the LiNbO3 crystal gives us the maximum electric field larger than 1 MV/cm, which ponderomotive energy is as large as 10 eV. The ponderomotive energy is strong enough to ionize bound electronic states in solids such as donors and accepters and easy to induce nonlinear optical effects in solids.

Tanaka, K.

2013-03-01

100

Ultrafast Terahertz Spectroscopy for Measuring Carrier Dynamics in Nanoscale Photovoltaic Materials  

Microsoft Academic Search

Femtosecond pump-probe methods are useful tools for investigating\\u000a transient electronic and vibrational states of conducting materials and\\u000a molecular photochemistry. Ultraviolet and visible excitation pulses\\u000a (150 fs, 20 mu J, 400-800 nm) with time-delayed broadband terahertz\\u000a (similar to 500 GHz to 3 THz) probing pulses (Time-Resolved Terahertz\\u000a Spectroscopy; TRTS) are used to measure linear spectroscopic\\u000a transmission changes resulting from exciton and

Okan Esenturk; Joseph S. Melinger; Edwin J. Heilweil

2010-01-01

101

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

102

Ultrafast broadband mid-infrared pump, terahertz probe spectroscopy  

Microsoft Academic Search

We report a novel ultrafast optical system capable of directly pumping low energy excitations in complex materials and probing the photoinduced changes in their properties with terahertz pulses, benchmarked through mid-infrared-pump, THz-probe measurements on InSb.

K. M. Dani; J. F. O'Hara; Q. McCulloch; F. Chen; A. K. Azad; G. Dakovski; S. A. Crooker; A. J. Taylor; R. P. Prasankumar

2010-01-01

103

Terahertz pump-probe spectroscopy in YBCO thin films  

Microsoft Academic Search

Terahertz (THz) radiation is ideal for probing many different materials and processes. Photons in the THz regime have energies on the order of an meV, which is an important energy scale for many electronic processes. In this paper we will describe the use of optical rectification of 50 fs IR pulses to generate THz pulses. Using this method, spectrally broad

Anna K. Kristoffersen; H. Tiedje; Robert A. Hughes; Harold K. Haugen; Thomas Timusk; John S. Preston

2004-01-01

104

Subwavelength plastic wire terahertz time-domain spectroscopy  

Microsoft Academic Search

This work demonstrates the feasibility of a terahertz time-domain spectrometer based on a subwavelength-diameter plastic wire (SPW) for sensing applications. The dispersion property of the SPW is experimentally and theoretically studied. The SPW exhibits a low and controllable waveguide dispersion, which can be engineered by changing the core diameter, the core index, and the cladding index of the wire. Two

Borwen You; Ja-Yu Lu; Tze-An Liu; Jin-Long Peng; Ci-Ling Pan

2010-01-01

105

Terahertz Spectroscopy and Imaging for Defense and Security Applications  

Microsoft Academic Search

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

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

2007-01-01

106

Fourier Spectroscopy of Radiation of Novosibirsk Terahertz Free Electron Laser  

Microsoft Academic Search

We have investigated various spectral parameters of Novosibirsk terahertz free electron laser (FEL) in different regimes by Bruker vacuum Fourier spectrometer IFS-66v. In addition to routine wavelength measurement and calibration we studied also radiation of harmonics [1] and detailed form of FEL spectrums. Such interesting phenomena as sideband instability [2] and two wavelength generation have been demonstrated very distinctly in

V. V. Kubarev; N. A. Vinokurov; V. V. Kotenkov; G. N. Kulipanov; A. N. Matveenko; T. V. Salikova; S. S. Serednyakov; M. A. Scheglov

2006-01-01

107

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

PubMed

Detecting the aging situation of stock explosive is essentially meaningful to the research on the capability, security and stability of explosive. Existing aging explosive detection techniques, such as scan microscope technique, Fourier transfer infrared spectrum technique, gas chromatogram mass spectrum technique and so on, are either not able to differentiate whether the explosive is aging or not, or not able to image the structure change of the molecule. In the present paper, using the density functional theory (DFT), the absorb spectrum changes after the explosive aging were calculated, from which we can clearly find the difference of spectrum between explosive molecule and aging ones in the terahertz band. The terahertz time-domain spectrum (THz-TDS) system as well as its frequency spectrum resolution and measured range are analyzed. Combined with the existing experimental results and the essential characters of the terahertz wave, the application of THz-TDS technique to the detection of aging explosive was demonstrated from the aspects of feasibility, veracity and practicability. On the base of that, the authors advance the new method of aging explosive detection using the terahertz time-domain spectrum technique. PMID:21800588

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

2011-05-01

108

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

109

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

PubMed

Terahertz waves (THz, T-ray) lie between far-infrared and microwave in electromagnetic spectrum with frequency from 0.1 to 10 THz. Many explosives and illicit drugs show characteristic spectral features in the terahertz. Compared with conventional methods of detecting a variety of threats, such as weapons, explosives and illegal drugs, THz radiation is low frequency and non-ionizing, and does not give rise to safety concerns. Moreover, THz can penetrate many barrier materials, such as clothing and common packaging materials. THz technique has a great potential and advantage in antiterrorism and security inspection of explosives and illegal drugs due to the ability of high-sensitivity, nondestructive and stand-off inspection of many substances. The present paper summarizes the latest progress in the application of terahertz time domain spectroscopy (THz-TDS) to explosives and illegal drugs. Studies on RDX are discussed in details and many factors affecting experiments are also introduced. PMID:18720779

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

2008-05-01

110

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

PubMed

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

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

2013-10-09

111

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

112

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

113

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

NASA Astrophysics Data System (ADS)

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.

2013-10-01

114

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

115

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

116

Methodology and hardware of terahertz BWO-spectroscopy  

Microsoft Academic Search

Modern terahertz (THz) spectrometers based on coherent sources of radiation, the backward-wave oscillators (BWOs), cover frequencies v = 2 cm-1 - 45 cm-1 (60-1350 GHz) and allow for measurements at temperatures 2-1000 K, also in magnetic fields up to 8 Tesla (Koslov and Volkov, 1998). They are of a hybrid type and combine merits of techniques existing in neighboring microwave

I. Spektor; V. Anzin; Yu. Goncharov; B. Gorshunov; G. Gusev; G. Komandin; S. Lebedev; A. Volkov

2005-01-01

117

Measurement and analysis of the diffuse reflectance of powdered samples at terahertz frequencies using a quantum cascade laser  

NASA Astrophysics Data System (ADS)

We report terahertz (THz) diffuse reflectance measurements of bulk powdered samples at a frequency of 2.83 THz using a narrowband quantum cascade laser. Samples studied comprise polydisperse powders with absorption coefficients extending over two orders of magnitude from ~3 cm-1 to >200 cm-1. Diffuse reflectance measurements are used to obtain the effective absorption coefficient of these samples from the backscattering cross-section, predicted under the quasi-crystalline approximation (QCA) in the T-matrix formulation and in conjunction with the Percus-Yevick pair distribution function. Results are compared with effective absorption coefficients obtained from THz time-domain spectroscopy measurements on pressed pellet samples, and show good agreement over the range of effective absorption coefficients studied. We observe that the backscattering cross-section predicted under the QCA is strongly dependent on both the real and imaginary components of the complex permittivity of the sample, and we show that reliable determination of the absorption coefficient from diffuse reflectance measurements therefore requires knowledge of the sample's refractive index. This work demonstrates the applicability of diffuse reflectance measurements, using a THz frequency quantum cascade laser, to the high-resolution spectroscopic analysis of bulk powdered samples at THz frequencies.

Dean, P.; Burnett, A. D.; Tych, K.; Khanna, S. P.; Lachab, M.; Cunningham, J. E.; Linfield, E. H.; Davies, A. G.

2011-04-01

118

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

119

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

120

Terahertz time-domain spectroscopy of highT(c) superconductors  

Microsoft Academic Search

The c-axis Josephson plasma resonance (JPR) in high- Tc cuprate Tl2Ba2CaCu2O 8 (Tl-2212) superconducting thin films is unambiguously observed directly in the time-domain employing terahertz time-domain spectroscopy in transmission as a function of temperature with and without an applied c-axis magnetic field. These are the first observations of the JPR in a high- Tc material in transmission. The temperature dependence

Verner Kristian Thorsmolle

2001-01-01

121

Terahertz pump-probe spectroscopy in LT-InGaAs thin film  

Microsoft Academic Search

We perform terahertz time-domain pump-probe spectroscopy in low-temperature-grown InGaAs substrate. Temporal evolution of differential optical density shows that photoinduced carrier decays a few picoseconds at low excitation density and several picoseconds at high excitation density. These features of carriers' lifetime and amplitudes of short- and long-lifetime components directly involve emission and detection efficiencies for photoconductive switch, giving us guideline of

Masaya Nagai; Koichiro Tanaka; Akihiro Takazato; Yutaka Kadoya

2007-01-01

122

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

Microsoft Academic Search

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

Takeshi Suzuki; Ryo Shimano

2011-01-01

123

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

124

Characterization of original and expanded leaf-roots of tobacco by terahertz spectroscopy and X-ray microanalysis  

Microsoft Academic Search

Expanded leaf-roots of tobacco are used as fillers into cigarette products to reduce cost and contents of tar and nicotine and improve quality. To study the difference between expanded and original leaf-roots of tobacco, terahertz (THz) time-domain spectroscopy was used to detect the absorption spectra in the frequency range from 0.2 to 1.5 THz. Significant difference in terahertz absorption was observed

Tong-fu Su; Xin-feng Jia; Guo-zhong Zhao; Pengyu Han; Yu-jie Wang; Yongliang Li; Bin Zhou; Chao-peng Song; Jian-feng Chang; Chang-rong Gong

2008-01-01

125

Solute-induced retardation of water dynamics probed directly by terahertz spectroscopy  

PubMed Central

The dynamics of water surrounding a solute is of fundamental importance in chemistry and biology. The properties of water molecules near the surface of a bio-molecule have been the subject of numerous, sometimes controversial experimental and theoretical studies, with some suggesting the existence of rather rigid water structures around carbohydrates and proteins [Pal, S. K., Peon, J., Bagchi, B. & Zewail A. H. (2002) J. Phys. Chem. B 106, 12376–12395]. Hydrogen bond rearrangement in water occurs on the picosecond time scale, so relevant experiments must access these times. Here, we show that terahertz spectroscopy can directly investigate hydration layers. By a precise measurement of absorption coefficients between 2.3 THz and 2.9 THz we could determine the size and the characteristics of the hydration shell. The hydration layer around a carbohydrate (lactose) is determined to extend to 5.13 ± 0.24 Å from the surface corresponding to ?123 water molecules beyond the first solvation shell. Accompanying molecular modeling calculations support this result and provide a microscopic visualization. Terahertz spectroscopy is shown to probe the collective modes in the water network. The observed increase of the terahertz absorption of the water in the hydration layer is explained in terms of coherent oscillations of the hydration water and solute. Simulations also reveal a slowing down of the hydrogen bond rearrangement dynamics for water molecules near lactose, which occur on the picosecond time scale. The present study demonstrates that terahertz spectroscopy is a sensitive tool to detect solute-induced changes in the water network.

Heugen, U.; Schwaab, G.; Brundermann, E.; Heyden, M.; Yu, X.; Leitner, D. M.; Havenith, M.

2006-01-01

126

Investigating antibody interactions with a polar liquid using terahertz pulsed spectroscopy.  

PubMed

In this article, we use terahertz spectroscopy to study the dielectric properties of the peroxidase-conjugated affinity purified goat anti-cat immunoglobulin G and the fluorescein-conjugated affinity purified goat anti-cat immunoglobulin G when they interact with polar liquids. The influence of protein concentration, as well as presence of glycerol as a cosolvent, is determined by estimation of the effective hydration shell radius of the protein in solution. The dielectric spectra in this study are measured over the frequency range 0.1-1.3 THz and it is found that the dielectric properties are dependent on the type of the charges in the hydrogen-bonded antibodies' networks. Our results indicate that the terahertz dielectric properties of polar liquids are strongly affected by the presence of the antibody and suggest that the dielectric spectrum is particularly powerful in the study of structural and conformational properties of proteins. Therefore, terahertz spectroscopy is a very sensitive approach to investigate structural features of biological systems. PMID:21190675

Sun, Yiwen; Zhang, Yuanting; Pickwell-Macpherson, Emma

2011-01-01

127

Optical parameter determination of seed oil with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

The spectral characteristics of corn oil after five minutes and ten minutes of boiling in the rang from 0.2THz to 1.5THz have been measured with THz time-domain spectroscopy (THz-TDS) at room temperature in nitrogen atmosphere. A novel iterative algorithm is employed to determinate the optical properties considering the effect of the cuvette. The refractive indices of the two corn oil samples show slow a decrease as the terahertz wave frequency increases. The power absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range. The results provided in this paper will help us to study the THz application to seed oil quality and safety detection further.

Li, Jiu-Sheng; Zhao, Xiao-Li; Xu, Degeng

2009-07-01

128

Using Terahertz Spectroscopy for Observing the Kinetics of Recrystallisation of Polybutene-1  

NASA Astrophysics Data System (ADS)

This paper deals with the use of terahertz spectroscopy for observing the kinetics of recrystallisation of polybutene-1 as a suitable material for manufacturing optical elements in the terahertz region of the electromagnetic spectrum. These materials were studied from the perspective of their optical properties - the refractive index and the absorption coefficient. The time dependencies of the refractive index and the absorption coefficient were measured, because polybutene-1 is a material which recrystallises for a number of days from the date of its manufacture. The coefficients describing the recrystallisation process were calculated from the fitting function derived from the Avrami equation. In this paper, the measurement results are presented and the possibilities of the use of the studied materials are discussed.

K?esálek, V.; Gavenda, T.

2013-02-01

129

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

130

Terahertz polaritonics: High-field THz coherent control and spectroscopy  

Microsoft Academic Search

The tools of THz polaritonics are extended for improved polariton amplification and for nonlinear THz spectroscopy using amplified and focused polariton waveforms. THz coherent spectroscopy and control applications are enabled

Ka-Lo Yeh; Eric Statz; Joshua C. Vaughan; Thomas Hornung; Keith A. Nelson

2006-01-01

131

Two-dimensional-Raman-terahertz spectroscopy of water: Theory  

NASA Astrophysics Data System (ADS)

We discuss the hybrid 2D-Raman-THz spectroscopy of liquid water. This two-dimensional spectroscopy is designed to directly work in the low-frequency range of the intermolecular degrees of freedom. The information content of 2D-Raman-THz spectroscopy is similar to 2D-Raman or 2D-THz spectroscopy, but its experimental implementation should be easier. That is, 2D-Raman-THz spectroscopy is a 3rd-order nonlinear spectroscopy and as such completely avoids cascading of consecutive 3rd-order signals, which turned out to be a major difficulty in 5th-order 2D-Raman spectroscopy. On the other hand, it does not require any intense THz pump-pulse, the lack of which limits 2D-THz spectroscopy to the study of semiconductor quantum wells as the currently available pulse energies are too low for molecular systems. In close analogy to 2D-Raman spectroscopy, the 2D-Raman-THz response of liquid water is simulated from an all-atom molecular dynamics simulation, and the expected spectral features are discussed.

Hamm, Peter; Savolainen, Janne

2012-03-01

132

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

133

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

134

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

135

Terahertz transmission spectroscopy by Josephson oscillator and cold-electron bolometer  

NASA Astrophysics Data System (ADS)

For sensitive wideband spectroscopy at TeraHertz frequencies one needs a wide-range electrically tunable THz source and a sensitive detector. In this paper a superconducting normal metal cold electron bolometer (CEB) was used as a broadband sensor. Bolometers were integrated with broadband log-periodic antenna designed for 0.2-2 THz frequency range and double-dipole antennas designed for 300 and 600 GHz central frequency. A Josephson junction was used as a wide band electrically tuned terahertz cryogenic oscillator. Bicrystal YBaCuO Josephson junctions demonstrated a characteristic voltage IcRn of over 4 mV that corresponds to characteristic frequency about 2 THz. The bolometer chip is attached to a Si substrate lens at 260 mK and the oscillator chip is attached to the sapphire substrate lens at 1.8 K, with lenses facing each other at the distance of few centimeters. High signal was measured in the whole frequency range up to 1.7 THz by simple changing the bias voltage of Josephson junction from zero to 3.5 mV. A voltage response of the bolometer up to 4*108 V/W corresponds to an amplifier-limited technical noise equivalent power of the bolometer NEP=1.25*10-17 W/Hz1/2. Combining a Terahertz band Josephson junction, a high-sensitive hot electron bolometer, and a sample under test in between, makes it possible to develop a cryogenic compact Terahertz-band transmission spectrometer with a resolution below 1 GHz corresponding to the linewidth of Josephson oscillations. For frequencies below 600 GHz a conventional Nb shunted SIS junction can be used as Josephson oscillator.

Tarasov, Mikhail A.; Kuzmin, Leonid S.; Stepantsov, Evgueni; Agulo, I.; Kalabukhov, A.; Kidiyarova-Shevchenko, A.; Claeson, Tord

2004-12-01

136

Charge carrier dynamics in metalated polymers investigated by optical-pump terahertz-probe spectroscopy.  

PubMed

We report charge carrier dynamics in solid films of a series of metalated polymers based on Pt- and 4,7-di-2'-thienyl-2,1,3,-benzothiadiazole or 4,7-di-2'-thienothienyl-2,1,3,-benzothiadiazole upon photoexcitation of the pi-pi* transition using optical-pump terahertz-probe spectroscopy. Subpicosecond generated charge carriers recombine within 100 ps, but bound excitons persist. Application of the Drude-Smith model allows for estimation of the intrinsic mobility and internal quantum yield of charge carrier generation in these films. Thermal annealing is found to have no effect on nanometer scale charge transport. PMID:19886608

Cunningham, Paul D; Hayden, L Michael; Yip, Hin-Lap; Jen, Alex K-Y

2009-11-26

137

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

138

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

139

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

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

140

Simultaneous composition and thickness measurement of paper using terahertz time-domain spectroscopy.  

PubMed

We present a noncontact method for quantitative composition and thickness monitoring of flat sheet products using terahertz time-domain spectroscopy. We apply the method to obtain simultaneous measurement of thickness and moisture content of paper sheets. The paper is modeled as an effective medium of water mixed with fibers, and model parameters are estimated from fits to the measured transmission amplitude. We demonstrate the method on two different paper samples and obtain uncertainties that are comparable with existing sensor technology. Monte Carlo simulations indicate that these uncertainties can be reduced further by at least an order of magnitude. PMID:19935977

Mousavi, Payam; Haran, Frank; Jez, David; Santosa, Fadil; Dodge, John Steven

2009-11-20

141

Terahertz magneto-optical spectroscopy in HgTe thin films  

NASA Astrophysics Data System (ADS)

Thin films of HgTe have been systematically investigated using continuous frequency terahertz spectroscopy in external magnetic fields. In these experiments, full control of the polarization state can be achieved including Faraday rotation and ellipticity. We present the details of the experimental procedure and of the data analysis. Besides the cyclotron resonance, an additional mode is observed in the zero-gap sample. The results at high temperatures can be well understood within the classical Drude model of the dynamic conductivity. Possible dimensionality of the charge dynamics at low temperatures is discussed.

Shuvaev, A. M.; Astakhov, G. V.; Brüne, C.; Buhmann, H.; Molenkamp, L. W.; Pimenov, A.

2012-12-01

142

A versatile and reconfigurable setup for all-terahertz time-resolved pump-probe spectroscopy  

NASA Astrophysics Data System (ADS)

A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.

Elezzabi, A. Y.; Maraghechi, P.

2012-05-01

143

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

2011-02-18

144

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

145

Optical pump Terahertz probe transmission spectroscopy of YBCO thin films  

Microsoft Academic Search

Our facility uses optical pump THz probe transmission spectroscopy to study the quasiparticle dynamics in Yttrium Barium Copper Oxide (YBCO) thin films. The recovery of the film exhibits two components, a fast response on the order of several ps and a long tail that lasts nanoseconds. In this presentation, the behaviour of the film in both the fast and long

Anna Kristoffersen; John Nam

2005-01-01

146

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

147

Optical pump-terahertz spectroscopy of condensed phase reaction dynamics  

Microsoft Academic Search

The general theoretical and experimental principles of optical pump-THz probe spectroscopy of chemical reactions in liquids is presented. Background on specific difficulties encountered in the experimental observation is reviewed. Chiefly, signal-to-noise ratios currently limit the quality of information that can be extracted from optical pump-THz prove data on chemical reactions. This issue is shown to be connected to the assumption

Bret N. Flanders; Norbert F. Scherer

1998-01-01

148

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

149

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

150

Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy.  

PubMed

We present a new method for data acquisition in time-resolved terahertz spectroscopy experiments. Our approach is based on simultaneous collection of reference and differential THz scans. Both the optical THz generation beam and the pump beam are modulated at two different frequencies that are not harmonic with respect to each other. Our method allows not only twice as fast data acquisition but also minimization of noise connected to slowly varying laser power fluctuations and timing instabilities. Our use of the nonlinear crystal N-benzyl-2-methyl-4-nitroaniline (BNA) enables time-resolved THz spectroscopy to beyond 5 THz, thereby highlighting that the presented method is especially valuable at higher frequencies where phase errors in the data acquisition become increasingly important. PMID:19997441

Iwaszczuk, Krzysztof; Cooke, David G; Fujiwara, Masazumi; Hashimoto, Hideki; Jepsen, Peter Uhd

2009-11-23

151

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

152

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

NASA Astrophysics Data System (ADS)

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 recombination. We report the electron-hole recombination times in epitaxial graphene for the first time. Our results show that carrier cooling occurs on sub-picosecond time scales and that interband recombination times are carrier density dependent.

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

2008-12-01

153

Ultrafast optical-pump terahertz-probe spectroscopy of the carrier relaxation and recombination dynamics in epitaxial graphene.  

PubMed

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 recombination. We report the electron-hole recombination times in epitaxial graphene for the first time. Our results show that carrier cooling occurs on subpicosecond time scales and that interband recombination times are carrier density dependent. PMID:19367881

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

2008-12-01

154

Terahertz spectroscopy and solid-state density functional theory simulations of the improvised explosive oxidizers potassium nitrate and ammonium nitrate.  

PubMed

Terahertz spectroscopy provides a noninvasive and nondestructive method for detecting and identifying concealed explosives. In this work, the room-temperature and cryogenic terahertz spectra of two common improvised explosive oxidizers, namely, potassium nitrate (KN) and ammonium nitrate (AN), are presented, along with detailed solid-state density functional theory (DFT) analyses of the crystalline structures and spectral features. At both 294 and 78 K, KN exhibits two terahertz absorption features below 100 cm(-1) that have been assigned through DFT simulations to arise from hindered nitrate rotations in the KN-II crystalline polymorph. The terahertz spectrum of AN exhibits a pronounced temperature dependence. The 294 K spectrum is free of any absorptions, whereas the 78 K spectrum consists of several narrow and intense peaks. The origin of this large difference is the polymorphic transition that occurs during cooling of AN, where room-temperature AN-IV is converted to AN-V at 255 K. The 78 K terahertz spectrum of AN is assigned here to various ion rotations and translations in the AN-V polymorph lattice. The analysis of the room-temperature AN-IV terahertz spectrum proved to be more complicated. The solid-state DFT simulations predicted that the room-temperature crystal structure of AN is not very well described using the standard Pmmn space-group symmetry as previously believed. The AN-IV polymorph actually belongs to the Pmn2(1) space group, and the perceived Pmmn symmetry results from vibrational averaging through nitrate rotations. This newly observed Pmn2(1) crystal symmetry for room-temperature AN is the reason for the absence of absorption features in the 294 K terahertz spectrum of AN and provides new insight into the polymorphic transitions of this ionic solid. PMID:22007790

Witko, Ewelina M; Buchanan, William D; Korter, Timothy M

2011-10-18

155

Using Terahertz Spectroscopy to Study Systems with Solar Energy Applications  

NASA Astrophysics Data System (ADS)

Biomimetic solar water oxidation systems are being developed as renewable alternatives to fossil fuels. One possible design incorporates thin-film dye-sensitized nanoparticle photoanades to capture and convert visible light to charge carriers and catalysts to facilitate water oxidation. The physical properties of the dye are important due to its position as the light absorber and electron transfer initiator. Given the role that porphyrins play in photosynthesis and their synthetic tunability, they are promising components for these photoanodes. Time-Resolved THz Spectroscopy (TRTS), an optical pump/THz probe technique, is a non-contact electrical probe with proven usefulness for studying electron transfer and conductivity on a sub-picosecond timescale. Using TRTS, the efficiency and dynamics of electron injection from porphyrin dyes into metal oxide surfaces was found to be strongly influenced by the structure and photophysical properties of the dye.

Milot, Rebecca L.; Moore, Gary F.; Martini, Lauren A.; Brudvig, Gary W.; Crabtree, Robert H.; Schmuttenmaer, Charles A.

2013-06-01

156

The ultrafast photoconductive characteristics of GaAs bulk investigated by optical-pump terahertz probe spectroscopy  

NASA Astrophysics Data System (ADS)

The ultrafast photoconductive characteristics of GaAs bulk were investigated by the optical-pump terahertz-probe spectroscopy (OPTP) at room temperature. In our experiment, a significant decrease of the terahertz transmittance has been observed when the time delay between the optical pump pulse and the terahertz probe pulse was adjusted. It can be concluded that the electronic states of the GaAs became metallic, when the optical excitation occurred on the surface of the GaAs material. Since we expect only the free carrier response in the terahertz range, the decrease of the transmittance is obviously assigned to the appearance of the high electronic conductivity due to the increasing free carriers. Furthermore, it was found that transmittance of the terahertz radiation decreased with the increase of the optical pump power due to the more optical generated carriers under the higher power. We can also find that the carrier recombination time of the GaAs became shorter while the power of the optical pump was lowered.

Jin, Bin; Zhou, Qing-Li; Zhang, Cunlin

2008-12-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

158

Photoinduced metallic state in VO2 proved by the terahertz pump-probe spectroscopy  

Microsoft Academic Search

We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation induced an ultrafast decrease of the transmittance of the terahertz radiation within 0.7 ps. Since we expect only the free carrier response in the terahertz range, the decrease of the transmittance is

M. Nakajima; N. Takubo; Z. Hiroi; Y. Ueda; T. Suemoto

2008-01-01

159

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

PubMed

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

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

2012-03-25

160

Spectroscopy study of ephedrine hydrochloride and papaverine hydrochloride in terahertz range  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

161

Material thickness optimization for transmission-mode terahertz time-domain spectroscopy.  

PubMed

The thickness of a sample material for a transmission-mode terahertz time-domain spectroscopy (THz-TDS) measurement is the subject of interest in this paper. A sample that is too thick or too thin can raise the problem of measurement uncertainty. Although greater thickness allows the terahertz radiation--or T-rays--to interact more with bulk material, the SNR rolls off with thickness due to signal attenuation. A sample that is too thin renders itself nearly invisible to T-rays, in such a way that the system can hardly sense the difference between the sample and a free space path. The optimal trade-off is analyzed and revealed in this paper, where our approach is to find the optimal thickness that results in the minimal uncertainty of measured optical constants. The derived model for optimal thickness is supported by the results from experiments performed with polyvinyl chloride (PVC), high-density polyethylene (HDPE), and lactose samples. PMID:18545443

Withayachumnankul, Withawat; Fischer, Bernd M; Abbott, Derek

2008-05-12

162

Terahertz radiation from Er,O-codoped GaAs surface grown by organometallic vapor phase epitaxy  

NASA Astrophysics Data System (ADS)

Ultrafast carrier dynamics and terahertz radiation from Er,O-codoped GaAs (GaAs:Er,O) have been investigated by pump and probe reflectance and time-domain terahertz spectroscopy. In pump and probe reflectance measurements, GaAs:Er,O showed faster relaxation time (0.37-0.56 ps) of photoexcited carriers than undoped GaAs. In terahertz spectroscopy, the radiated terahertz amplitude decreased and the decay time of transient photocurrent became long with increasing Er concentration. The Er concentration dependence was understood by additional electron scattering due to the Er doping. The fast relaxation time and the terahertz radiation properties suggest new applications of GaAs:Er,O for the terahertz frequency region.

Shimada, K.; Terai, Y.; Takemoto, S.; Hidaka, K.; Fujiwara, Y.; Suzuki, M.; Tonouchi, M.

2008-03-01

163

Terahertz time-domain spectroscopy of high-T(c) superconductors  

NASA Astrophysics Data System (ADS)

The c-axis Josephson plasma resonance (JPR) in high- Tc cuprate Tl2Ba2CaCu2O 8 (Tl-2212) superconducting thin films is unambiguously observed directly in the time-domain employing terahertz time-domain spectroscopy in transmission as a function of temperature with and without an applied c-axis magnetic field. These are the first observations of the JPR in a high- Tc material in transmission. The temperature dependence of the JPR in zero field indicates d-wave symmetry of the superconducting order parameter in the dirty limit. In a c-axis magnetic field, the JPR is sensitive to the ordering of pancake vortices along the c-axis and is an excellent tool to study the vortex structure. Using the JPR to study the interlayer phase coherence, I find direct evidence for a linelike vortex liquid phase in Tl-2212. The ordering of the vortex lattice is studied as a function of applied ab-plane current at different temperatures in a c-axis magnetic field. The ordering decreases with increased current in the vortex solid phase, but then increases when driving it into the flux-flow state near the melting transition. Using dc transport measurements the c- axis resistivity in irradiated and pristine Bi2Sr2CaCu2O 8-? is measured as a function of in- plane field component at fixed out-of-plane component B? in the vortex liquid phase. The average length of vortex line segments inside columnar defects as a function of filling factor f = B ?/B? is then determined. The maximum length, ~15 interlayer distances, is reached near f ~ 0.35. Time-resolved optical-pump terahertz-probe spectroscopy is employed to measure ultrafast conductivity dynamics in hole-doped transition metal oxide thin films. Measurements on La0.7M0.3MnO3 (M = Ca, Sr) from 10 K to ~0.9Tc reveal a two-component relaxation. A fast, ~2 ps, conductivity decrease arises from optically induced modification of the effective phonon temperature. The slower component, related to spin-lattice relaxation, has a lifetime that increases upon approaching Tc from below in accordance with an increasing spin specific heat. For T << Tc, ??/?T is primarily determined by thermally disordered phonons while spin fluctuations dominate near Tc. For YBCO thin films, optical-pump terahertz-probe spectroscopy was used to study the dynamics of superconducting pairs and quasiparticles following photoexcitation. In particular, by following the dynamic changes of the imaginary conductivity, the phase coherent recovery time was directly measured. This recovery occurs on a picosecond timescale.

Thorsmolle, Verner Kristian

164

Total internal reflection with fluorescence correlation spectroscopy  

Microsoft Academic Search

Total internal reflection–fluorescence correlation spectroscopy (TIR-FCS) is an emerging technique that is used to measure events at or near an interface, including local fluorophore concentrations, local translational mobilities and the kinetic rate constants that describe the association and dissociation of fluorophores at the interface. TIR-FCS is also an extremely promising method for studying dynamics at or near the basal membranes

Bridgett L Steele; Nancy L Thompson

2007-01-01

165

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

166

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

167

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

168

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

169

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

170

Surface metallic states in ultrathin Bi(001) films studied with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Dynamical response of surface metallic states in single crystalline ultrathin Bi(001) films on Si(111) 7 × 7 surface was investigated at a spectral range of 0.1-12 THz by broadband terahertz time-domain spectroscopy. The observed transmittance increased with a decrease in the thickness, without showing a gap structure. The measured complex dielectric dispersion was analyzed using a Drude model, and the plasma frequency (?p) and damping constant (?) were found to be inversely proportional to the thickness. The results strongly indicate the existence of surface metallic states, whose carrier density and damping constant are estimated to be 3.08 × 1019 cm-3 and 4.83 × 102 THz, respectively.

Yokota, K.; Takeda, J.; Dang, C.; Han, G.; McCarthy, D. N.; Nagao, T.; Hishita, S.; Kitajima, M.; Katayama, I.

2012-06-01

171

Exciton dissociation in polymer field-effect transistors studied using terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We have used terahertz time-domain spectroscopy to investigate photoinduced charge generation in conjugated polymer field-effect transistors. Our measurements show that excitons dissociate in the accumulation layer under the application of a gate voltage, with a quantum efficiency of ˜0.1 for an average gate field of ˜1×108Vm-1 . The transistor history is found to affect the exciton dissociation efficiency, which decreases as holes are increasingly trapped in the accumulation layer. The quantum efficiency of charge formation from excitons is compared with the two contrasting models proposed by Onsager and Arkhipov based on the assumption that field-induced exciton dissociation is assisted by the Brownian diffusive motion or an initial excess energy supplied by excited vibrational modes, respectively.

Lloyd-Hughes, J.; Richards, T.; Sirringhaus, H.; Johnston, M. B.; Herz, L. M.

2008-03-01

172

Low-frequency Spectra of a Phospholipid Bilayer Studied by Terahertz Time-domain Spectroscopy  

NASA Astrophysics Data System (ADS)

We have investigated the low-frequency spectra of a phospholipid bilayer composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) by terahertz time-domain spectroscopy (THz-TDS). We focused on the temperature and hydration dependence of the low-frequency spectra of a gel-phase sample. The spectra of the dehydrated and hydrated samples showed shoulder bands at 45 and 30 cm-1, respectively. In contrast to the dehydrated sample, in the hydrated sample spectra the slope of the temperature change of the absorption coefficient increased sharply around 240 K. This result suggests that water molecules affect the change in the low-frequency dynamics. We obtained the absorption coefficient difference spectra for different hydration levels to clarify the mechanism of the spectral change.

Andachi, Tomoyo; Yamamoto, Naoki; Tamura, Atsuo; Tominaga, Keisuke

2013-08-01

173

Terahertz-time domain spectroscopy for the detection of PCR amplified DNA in aqueous solution.  

PubMed

In this work we present a label free quantitative detection method for DNA samples amplified by polymerase chain reaction (PCR) in aqueous medium using terahertz-time domain spectroscopy (THz-TDS) in the frequency range from 0.3 to 1.2 THz. The DNA samples of 133 and 697 base pairs were prepared using PCR. We measured the absorption coefficients of DNA solutions in the concentration range of 0-0.3 ng ?l(-1). For both DNA types, the absorption coefficients decreased with increasing DNA concentrations. The average change in absorption coefficients compared to buffer within the frequency range of 0.8-1.0 THz showed a linear behavior. Our results demonstrate that THz-TDS can detect PCR amplified DNA in aqueous solution with a minimum concentration of 0.1 ng ?l(-1) and a minimum sample volume of 10 ?l. PMID:22189821

Arora, Arun; Luong, Trung Quan; Krüger, Matthias; Kim, Young Jun; Nam, Chang-Hoon; Manz, Andreas; Havenith, Martina

2011-12-21

174

EDITORIAL: Terahertz nanotechnology Terahertz nanotechnology  

NASA Astrophysics Data System (ADS)

A useful synergy is being established between terahertz research and nanotechnology. High power sources [1-3] and detectors [4] in what was once considered the terahertz 'frequency gap' [5] in the electromagnetic spectrum have stimulated research with huge potential benefits in a range of industries including food, medicine and security, as well as fundamental physics and astrophysics. This special section, with guest editors Masayoshi Tonouchi and John Reno, gives a glimpse of the new horizons nanotechnology is broaching in terahertz research. While the wavelengths relevant to the terahertz domain range from hundreds of micrometres to millimetres, structures at the nanoscale reveal interesting low energy dynamics in this region. As a result terahertz spectroscopy techniques are becoming increasingly important in nanomaterial characterization, as demonstrated in this special section by colleagues at the University of Oxford in the UK and the Australian National University. They use terahertz spectroscopy to identify the best nanostructure parameters for specific applications [6]. The low energy dynamics in nanostructures also makes them valuable tools for terahertz detection [7]. In addition the much sought after terahertz detection over broadband frequency ranges has been demonstrated, providing versatility that has been greatly in demand, particularly in spectroscopy applications [8, 9]. Also in this special section, researchers in Germany and China tackle some of the coupling issues in terahertz time domain spectroscopy with an emitter specifically well suited for systems operated with an amplified fibre [3]. 'In medical imaging, the advantage of THz radiation is safety, because its energy is much lower than the ionization energy of biological molecules, in contrast to hazardous x-ray radiation,' explains Joo-Hiuk Son from the University of Seoul in Korea in his review [10]. As he also points out, the rotational and vibrational energies of water molecules are within the THz spectral region providing an additional benefit. His review describes the principle, characteristics, and applications of terahertz molecular imaging, where the use of nanoparticle probes allows dramatically enhanced sensitivity. Jiaguang Han and Weili Zhang and colleagues in China, Saudi Arabia, Japan and the US report exciting developments for optoelectronics [11]. They describe work on plasmon-induced transparency (PIT), an analogue of electromagnetically induced transparency (EIT) where interference leads to a sharp transparency window that may be useful for nonlinear and slow-light devices, optical switching, pulse delay, and storage for optical information processing. While PIT has advantages over the cumbersome experimental systems required for EIT, it has so far been constrained to very narrow band operation. Now Zhang and colleagues present the simulation, implementation, and measurement of a broadband PIT metamaterial functioning across a frequency range greater than 0.40 THz in the terahertz regime. 'We can foresee a historic breakthrough for science and technology through terahertz research,' concluded Masayoshi Tonouchi in his review over five years ago as momentum in the field was mounting [12]. He added, 'It is also noteworthy that THz research is built on many areas of science and the coordination of a range of disciplines is giving birth to a new science.' With the inherently multidisciplinary nature of nanotechnology research it is not so strange to see the marriage of the two fields form such a fruitful partnership, as this special section highlights. References [1] Williams B S, Kumar S, Hu Q and Reno J L 2006 High-power terahertz quantum-cascade lasers Electron. Lett. 42 89-91 [2] Köhler R et al 2002 Terahertz semiconductor-heterostructure laser Nature 417 156-9 [3] Mittendorff M, Xu M, Dietz R J B, K¨unzel H, Sartorius B, Schneider H, Helm M and Winnerl S 2013 Large area photoconductive THz emitter for 1.55 ?m excitation based on an InGaAs heterostructure Nanotechnology 24 214007 [4] Chen H-T, Padilla W J, Zide J M O, Gossa

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

2013-05-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

176

High-resolution terahertz spectroscopy of Sr2CrReO6 at cryogenic temperatures and high magnetic fields  

NASA Astrophysics Data System (ADS)

Temperature and magnetic field dependent terahertz spectroscopies have proven useful in elucidating the interplay between structure charge, and magnetism in complex oxide systems. To this end, we are developing a turn-key, continuous-wave (CW) terahertz transmission spectrometer operating from 6 K to 300 K and in fields up to 9 T. Fiber-coupled photoconductive switches operate from 200 GHz to 1.8 THz in the cryogenic and high-field sample environment -- eliminating the need to align a THz beam through multiple cryostat windows. In this work we compare CW-THz measurements on epitaxial thins films of Sr2CrReO6, a double-perovskite ferrimagnet, with conventional THz time-domain spectroscopy.

Daughton, D. R.; Higgins, R.; Yano, S.; Du, C. H.; Hauser, A. J.; Adur, R.; Lucy, J. M.; Wang, H. L.; Pelekhov, D. V.; Johnston-Halperin, E.; Yang, F. Y.; Hammel, P. C.

2013-03-01

177

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

178

Prediction of vitamin C using FTIR-ATR terahertz spectroscopy combined with interval partial least squares (iPLS) regression  

Microsoft Academic Search

In this study FTIR-ATR terahertz (THz) spectroscopy combined with interval PLS (iPLS) regression was used to measure concentration of vitamin C in aqueous solution. iPLS regression was used to select the efficient spectral regions and variables to develop calibration model. The performance of the iPLS model was then compared to that of full-spectrum PLS model. The result obtained by iPLS

Diding Suhandy; Meinilwita Yulia; Yuichi Ogawa; Naoshi Kondo

2011-01-01

179

High-Resolution Terahertz Spectroscopy by a Compact Radiation Source Based on Photomixing with Diode Lasers in a Photoconductive Antenna  

Microsoft Academic Search

We demonstrate generation of continuous-wave terahertz radiation and its application to molecular spectroscopy. The radiation source is based on the photomixing of two diode laser beams in a low-temperature-grown GaAs photoconductive antenna, which offered output power of several tens of nanowatts at frequencies up to 2 THz with its long term frequency stability being about 5 MHz. The pure rotational

Shuji Matsuura; Masahiko Tani; Hajime Abe; Kiyomi Sakai; Hiroyuki Ozeki; Shuji Saito

1998-01-01

180

Photo-induced insulator-metal phase transition observed by the terahertz pump-probe spectroscopy  

Microsoft Academic Search

We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation at 800 nm induced an ultrafast decrease of the transmittance of the terahertz pulse within 0.7 ps, and then the transmittance decreases gradually up to 100 ps. The decrease of the transmittance

Makoto Nakajima; Naoko Takubo; Zenji Hiroi; Yutaka Ueda; Tohru Suemoto

2009-01-01

181

Study of photo-induced phenomena in VO 2 by terahertz pump-probe spectroscopy  

Microsoft Academic Search

The ultrafast terahertz response to the photoexcitation in vanadium dioxide was investigated using the optical-pump terahertz-probe technique at room temperature. The optical excitation at 790nm induced an ultrafast decrease of the transmittance of the terahertz pulses corresponding to the increase of the electronic conductivity within 0.7ps, and then the transmittance decreases gradually up to 100ps. This two-step behavior is very

M. Nakajima; N. Takubo; Z. Hiroi; Y. Ueda; T. Suemoto

2009-01-01

182

Ultrafast carrier transport in GaAs measured by optical pump-terahertz probe spectroscopy  

Microsoft Academic Search

Femtosecond optical pump-terahertz probe studies of carrier dynamics and transport characteristics in semi-insulating GaAs have been investigated under different pump powers at room temperature. The transmission of the terahertz pulse is monitored as a function of delay time between pump and probe pulse, we found that because the more optical generated carriers under the higher power, the terahertz transmission decreased

Hai-Yan Yang; Yu-Lei Shi; Qing-Li Zhou; Dong-Mei Zhao; Lei Li; Cun-Lin Zhang

2009-01-01

183

Carrier dynamics of doped silicon measured by femtosecond pump-terahertz probe spectroscopy  

Microsoft Academic Search

The carrier dynamics and terahertz photoconductivity in the n-type silicon (n-Si) as well as in the p-type Silicon (p- Si) have been investigated by using femtosecond pump-terahertz probe technique. The measurements show that the relative change of terahertz transmission of p-Si at low pump power is slightly lower than that of n-Si, due to the lower carrier density induced by

Qingli Zhou; Yulei Shi; Tong Li; Bin Jin; Dongmei Zhao; Cunlin Zhang

2010-01-01

184

Terahertz-wave spectroscopy for precise histopathological imaging of tumor and non-tumor lesions in paraffin sections.  

PubMed

Terahertz (THz; 10(12) Hz) waves have a frequency from 0.1 to 10 THz between the visible light and microwave domains. THz waves are expected to be useful for analysis of the histological features, without any staining procedure that is an indispensable prerequisite for optical microscopy. It has been demonstrated that THz transmittances at cancer and normal tissues are different. However, spectroscopy that is currently used is applicable for imaging only small areas at fixed-wavelength. In this study, we have developed a spectrometer employing a gallium phosphide (GaP) THz-generator and applied it to examine large areas of tissue specimens using a wide range of wavelengths. We thus examined the whole areas of two paraffin sections (metastatic liver cancer and acute myocardial infarction) in a frequency range of 1 to 6 THz, and compared the THz images of ordinary paraffin sections with the histological features detected by microscopy. THz imaging showed striking contrasts between cancerous and non-cancerous regions at 3.7 THz. Likewise, the precise imaging was achieved in the infarct myocardium at 3.6 THz. Images of THz transmittances in optimal wavelength were well matched with HE histological features both in cancer and myocardial tissues. Cancer regions showed higher transmittance than non-cancerous regions in liver. Old scar regions showed low transmittance, and necrotic regions showed relatively higher transmittance than normal myocardial areas. Thus, THz imaging precisely reflects tissue conditions such as tumor, non-tumor tissues, tissue degeneration and fibrosis. The newly established THz spectroscopy would be useful for pathological diagnosis of routinely processed specimens. PMID:21467828

Miura, Yasuhiro; Kamataki, Akihisa; Uzuki, Miwa; Sasaki, Tetsuo; Nishizawa, Jun-ichi; Sawai, Takashi

2011-01-01

185

Photoinduced metallic state in VO2 proved by the terahertz pump-probe spectroscopy  

NASA Astrophysics Data System (ADS)

We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation induced an ultrafast decrease of the transmittance of the terahertz radiation within 0.7 ps. Since we expect only the free carrier response in the terahertz range, the decrease of the transmittance is unambiguously assigned to the appearance of the high electronic conductivity due to free carriers. The conductivity increases more than ten times in the picosecond time range after photoexcitation and it is concluded that the electronic states are metallic.

Nakajima, M.; Takubo, N.; Hiroi, Z.; Ueda, Y.; Suemoto, T.

2008-01-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

187

Solvation dynamics of model peptides probed by terahertz spectroscopy. Observation of the onset of collective network motions.  

PubMed

We have studied the solvation of model peptides at low hydration levels by terahertz absorption spectroscopy. We have recorded the concentration-dependent terahertz absorption coefficients of N-acetyl-glycine-amide (NAGA), N-acetyl-glycine-methylamide (NAGMA), N-acetyl-leucine-amide (NALA), N-acetyl-leucine-methylamide (NALMA), and N-acetyl-tryptophan-amide (NATA) in aqueous solution. We find a dramatic decrease in the THz absorption, if the number of water molecules per solute is less than 18-20. This change is taken as a signature for the breakdown of peptide-water network motions, which supports the hypothesis that a minimum number of hydration waters is required to activate these motions. This is well below a monolayer coverage of the model peptides. It is interesting to note that the required hydration level corresponds to the number of water molecules which are required for biological functionality. PMID:19275262

Born, Benjamin; Weingärtner, Hermann; Bründermann, Erik; Havenith, Martina

2009-03-18

188

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

189

High Count Rates with Total Internal Reflection Fluorescence Correlation Spectroscopy  

Microsoft Academic Search

We achieved photon count rates per molecule as high as with commonly used confocal fluorescence correlation spectroscopy instruments using a new total internal reflection fluorescence correlation spectroscopy system based on an epi-illumination configuration.

Kai Hassler; Tiemo Anhut; Rudolf Rigler; Michael Gösch; Theo Lasser

2005-01-01

190

Study on silicon nanostructure based solar cell by ultrafast terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Recently, Silicon nanowires(Si NWs) have been suggested as a promising candidate for solar energy harvesting. The Si NWs have the advantage of enhancing the optical absorption for broadband spectra, which increases the optical absorption significantly. It is of crucial importance for high efficiency solar cell. We applied the transient optical-pump THz emission spectroscopy to research Si NWs fabricated by chemical etching and to analyse the THz radiation mechanism. The experiment datas indicated that Si NWs enhance the optical absorption significantly. And the lifetime and dynamics properties of photoexcited carriers are important to the photovoltaic conversion efficiency of solar cell. Here the optical-pump terahertz-probe system was employed to study the ultrafast dynamics and transport properties of photoexcited carriers in Si NWs. The experiment results shown that carrier lifetime in Si NWs is approximate 0.7ns, and it reduces optical energy-conversion efficiencies of solar cell. However, compared to other silicon nanostructures, Si NWs fabricated by chemical etching have relative high values for both the carrier lifetime and mobility. The detailed analysis of the optical absorption and carriers dynamics would be significant for optimizing configuration of the silicon nanostructures.

Peng, Longyao; Zhu, Liguo; Tang, Hao; Meng, Kun; Zhong, Sencheng; Li, Zeren; Zhang, Rongzhu

2013-08-01

191

[Simultaneous quantitative determination of multicomponents in tablets based on terahertz time-domain spectroscopy].  

PubMed

Terahertz time-domain spectroscopy (THz-TDS) combined with chemometric modeling methods was used to perform quantitative analysis of both active pharmaceutical ingredient (API) and excipient concentrations of multicomponent pharmaceutical mixtures. The THz spectra of ternary mixtures formulated with anhydrous theophylline, lactose monohydrate, magnesium stearate and quaternary mixtures composed of acetaminophen, lactose monohydrate, microcrystalline cellulose and soluble starch were measured using THz-TDS. Two multivariate calibration methods, principal component regression (PCR) and partial least squares (PLS) regression, were employed to correlate THz absorbance spectra with the pharmaceutical tablet concentrations. Both API and excipient concentrations of mixtures were predicted simultaneously, and the PLS method provides better result than PCR method. The correlation coefficients of calibration (Rcal) and validation (Rval) for ternary mixtures' components, anhydrous theophylline and lactose monohydrate, were all more than 0.98. The Rcal and Rval for quaternary mixtures' components, acetaminophen, lactose monohydrate, microcrystalline cellulose and soluble starch, were all more than 0.93, 0.98, 0.63 and 0.86, respectively. Experimental results show that THz-TDS combined with chemometrics is feasible in nondestructive quantitative analysis of multicomponent mixtures, and it can be widely applied in the fields of pharmaceutical analysis and others. PMID:23905323

Chen, Tao; Li, Zhi; Mo, Wei; Hu, Fang-Rong

2013-05-01

192

New Frontiers in Optical Science: Terahertz Spectroscopy ot Two Dimensional Systems  

NASA Astrophysics Data System (ADS)

Terahertz (THz) radiation is electromagnetic radiation whose frequency lies between the microwave and infrared regions of the spectrum. Naturally occurring THz radiation fills up the space of everyday life providing warmth, yet this part of the spectrum remains the least explored region mainly due to the technical difficulties. The technological gap, however, has been rapidly diminishing for the last two decades. The new and exciting frontier of the THz science and technology has encroached on many different disciplines producing a broad range of applications such as medical imaging, sensing of biochemical agents, and ultra-high speed communication. Furthermore, the unique and advanced techniques of the THz spectroscopy have been proved to be a powerful tool to investigate the material properties inaccessible until recently. For example, THz waves strongly interact with electrons and holes in two dimensional systems, in which their dynamics are governed mainly by many-body Coulomb interactions. I will present our experimental studies demonstrating remarkable quantum effects in semiconductor nanostructures and exotic charge carrier dynamics in graphene.

Lee, Yun-Shik

2011-10-01

193

Pulsed and widely tunable terahertz sources for security: imaging and spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz imaging and spectroscopy are being studied for inspecting packages and personnel, but advanced THz sources with much greater power are needed to increase the signal-to-noise ratio, and much greater frequency bandwidth to obtain more information about the target. Photomixing in resonant laser-assisted field emission is a new method that shows potential for increasing both the output power and frequency bandwidth by more than an order of magnitude. Tunneling electrons have a resonance with a radiation field, so a highly focused laser diode (670 nm, 30 mW) increases the emitted current enough to be seen with an oscilloscope, in good agreement with simulations. The electron-emitting tip is much smaller than optical wavelengths, so the surface potential follows each cycle of the incident radiation. Electron emission responds to the electric field with a delay ?< 2 fs, and the current-voltage characteristics of field emission are highly nonlinear. Thus, photomixing in laser-assisted field emission can cause current oscillations that may be tuned from DC to 500 THz (1/delay). A field emission current density of 1012 A/m2 can be generated using a 20 pJ 70 fs pulse from a Ti:sapphire laser, to provide 200 W THz pulses. Microwave prototypes for 1-10 GHz are now being tested.

Hagmann, Mark J.; McBride, B. A.; Hagmann, Zulaima S.

2004-09-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

195

Investigating the position isomerism effect of dihydroxybenzoic acid compounds by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Far-infrared vibrational absorption of a series of dihydroxybenzoic acid (DHBA) compounds with different substituted hydroxy group at different positions have been investigated using terahertz time-domain spectroscopy (THz-TDS) at room temperature. The experimental results show large difference among absorption spectra of different DHBA (2,3-DHBA, 2,4-DHBA, 2,5-DHBA, 2,6-DHBA) compounds in 0.2 ~ 2.0 THz region, which probably originated from the difference of intra-molecular and inter-molecular hydrogen bonds due to the presence of two hydroxyl group in different positions with respect to the carboxylic group in different DHBAs. All the experimental DHBAs vibrational modes showed distinct fingerprint absorption in THz region and theorectical calculation based on density functional theory (DFT) was carried out to assist the analysis and assignment of the vibrational modes. The results indicate that THz-TDS technology can not only give a new experimental method to identify and characterize the position isomerism effect of hydroxyl group between such different kinds of DHBAs from molecule-level, but also provide a useful suggestion for further assessing the possible relationships between the DHBAs vibrational properties and the effects of the substituted hydroxy group position to better know their biochemical activities in food, pharmaceutical and cosmetic fields.

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

2011-11-01

196

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

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

197

Solid Material Characterization of Freeze-Dried Gabexate Mesilate Containing D-Mannitol by Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

The purpose of the present study is to characterize polymorphic forms and intermolecular interactions of freeze-dried pharmaceuticals containing additives by terahertz (THz) spectroscopy as a, process analytical technology tool in the pharmaceutical industry. Freeze-dried gabexate mesilate/D-mannitol products containing 17-75 mol% gabexate mesilate were obtained using a conventional freeze-dryer. Freeze-dried products and physical mixtures of gabexate mesilate and mannitol with various drug contents were characterized by X-ray powder diffraction (XRD) analysis, differential scanning calorimetry (DSC) and THz. The XRD and DSC results indicated that freeze-dried mannitol was obtained as a mixture of ? and ? forms of mannitol from a plain solution, but the freeze-dried product of the gabexate mesilate/mannitol mixture consisted of crystalline gabexate mesilate and the pure ? form of mannitol. Similar to the results of XRD and DSC, THz before the freeze-drying of gabexate mesilate was almost the same as that after. In contrast, the THz of mannitol before freeze-drying had specific peaks due to the ? form, but that after had peaks due to ? and ? forms. To clarify the polymorphic forms of the freeze-dried products, the THz were analyzed by least squares regression. The calibration models used to predict the amounts of gabexate mesilate and mannitol had sufficient accuracy and linearity, respectively. Two decomposed THz in FGMs had specific peaks due to the ? form of mannitol or gabexate mesilate.

Otsuka, Makoto; Fukura, Naomi; Abe, Hiroyuki

2013-02-01

198

Electron transfer in hydrogenated nanocrystalline silicon observed by time-resolved terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We report on the ultrafast carrier dynamics in hydrogenated nanocrystalline silicon (nc-Si:H) using time-resolved terahertz spectroscopy. Photoexcitation at 407 nm primarily produces charge carriers in the a-Si phase, but they undergo a rapid electron transfer to the c-Si phase prior to complete thermalization into the band-tail states of a-Si. We studied the carrier dynamics on a range of nc-Si:H samples with varying crystalline volume fractions (Xc) and mapped out the carrier dynamics with sub-ps resolution. Our measurements are consistent with a model in which electrons are first trapped at interface states at the a-Si-c-Si boundary prior to being thermally emitted into the c-Si phase. Wavelength and temperature dependent measurements are consistent with our model. The phenomena observed here have implications toward solar cell structures that utilize an amorphous material as an absorber layer, previously thought to have a mobility value too low to attain effective charge transport in a device.

Bergren, Matthew R.; Simonds, Brian J.; Yan, Baojie; Yue, Guozhen; Ahrenkiel, Richard; Furtak, Thomas E.; Collins, Reuben T.; Taylor, P. Craig; Beard, Matthew C.

2013-02-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

200

TERAHERTZ SPECTROSCOPY AND GLOBAL ANALYSIS OF H{sub 3}O{sup +}  

SciTech Connect

Eight ground-state inversion transitions of H{sub 3}O{sup +} in the 0.9-1.6 THz region have been measured using the frequency multiplier submillimeter spectrometer at Jet Propulsion Laboratory. The accuracy of these measurements is estimated to be 300 kHz. The ions were generated in a dc discharge through a gas mixture of a few mTorr of H{sub 2} and 30 mTorr of H{sub 2}O. A multistate analysis was carried out for H{sub 3}O{sup +}, which includes the lines observed in this work, previous submillimeter and terahertz inversion transitions in the ground state, and previous infrared data on all the four vibrational fundamental bands. Accurate molecular parameters were obtained with taking into account the strong Coriolis interaction between the symmetric OH stretching mode ({nu}{sub 1}) and the doubly degenerate asymmetric OH stretching mode ({nu}{sub 3}). Fequency predictions, particularly for high-J transitions in the ground state and in the {nu}{sub 1} and {nu}{sub 3} fundamental bands, have been greatly improved by including {approx} 200 more high-J transitions in our analysis, which were excluded in previous analyses. The more precise measurements and new predictions reported here will support the analyses of astronomical observations by the future high-resolution spectroscopy telescopes, such as Herschel, SOFIA, and ALMA.

Yu Shanshan; Drouin, Brian J.; Pearson, John C.; Pickett, Herbert M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)], E-mail: shanshan.yu@jpl.nasa.gov

2009-01-15

201

Probing free electrons in non-polar liquids by time-domain terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Time-domain terahertz spectroscopy has been demonstrated to be a powerful method to study the nature and dynamics of charge carriers in semiconductors. It offers the possibility of obtaining the real and imaginary parts of the frequency-dependent conductivity for systems with short carrier lifetime, as well as the capability to follow the temporal evolution of the carriers subsequent to their creation by an excitation pulse. In this paper, we present application of the technique to examine solvated electrons in non-polar liquids created by photo-ionization with a femtosecond laser pulse. Results of measurements in neat n-hexane and n-hexane with the electron scavenger CCl4 will be presented. Parameters for the scattering rate of quasi-free electrons are determined from a fit of the complex conductivity to a Drude model. Pump-probe measurements yield the decay rate of the free electron density and indicate a non-geminate recombination mechanism in the neat liquid. The energetics of the solvated electron states are investigated through the temperature dependence of the free electron density. For n-hexane an energy difference of 150 meV is inferred for the quasi-free state relative to that of the bound state of the solvated electron.

Knoesel, E.; Shan, J.; Weling, A.; Heinz, T. F.; Bonn, M.

2000-03-01

202

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

203

Dendrimer based terahertz time-domain spectroscopy and applications in molecular characterization  

NASA Astrophysics Data System (ADS)

Electro-optic Dendrimer is used to generate milliwatts of terahertz power by difference frequency method. A terahertz time-domain spectrometer (THz-TDS) has been designed around this source that exhibits wide broadband terahertz range, ˜0.1 to 35 THz. Examples of molecular characterization are discussed for three common explosives and the vibrational states of Fullerenes. The explosives' spectra are unique for each explosive that allow detection and identification of the species. The Fullerenes C60 and H2@C60 also exhibit distinctively different spectra and absorbance states indicating that the THz-TDS is suitable for probing increased number of vibrational states expected from molecular vibrations.

Rahman, Anis

2011-12-01

204

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

205

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

206

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

207

Ultrafast insulator–metal phase transition in vanadium dioxide studied using optical pump–terahertz probe spectroscopy.  

PubMed

We studied the ultrafast dynamic behavior of the photoinduced insulator–metal phase transition in VO2 thin film using optical pump–terahertz probe spectroscopy with different excitation fluences and at different temperatures. We observed two processes in the insulator–metal phase transition in VO2: a fast process and a slow process. The fast process is a nonthermal process, which is ascribed to the nucleation of the metal phase, while the slow process is strongly affected by temperature and is ascribed to the thermally driven growth and coalescence of metal domains in VO2. The transient complex conductivity spectra at different delay times are also investigated. PMID:23014464

Liu, H W; Wong, L M; Wang, S J; Tang, S H; Zhang, X H

2012-10-17

208

Time-resolved formation of excitons and electron-hole droplets in si studied using terahertz spectroscopy.  

PubMed

We investigated the formation dynamics of excitons and electron-hole (e-h) droplets (EHDs) in Si by using broadband terahertz time-domain spectroscopy. The formation of indirect excitons in Si was studied by observing their 1S-2P transition. Changes in surface plasmon resonance of the EHDs showed a gradual condensation from homogeneous e-h plasma at e-h densities above the exciton-Mott transition. Excitonic correlations were shown to exist prior to EHD condensation even above the Mott density. PMID:19792534

Suzuki, Takeshi; Shimano, Ryo

2009-07-31

209

Feasibility of spectroscopy by saturable reflection  

Microsoft Academic Search

The central frequencies and widths of overlapping lines in an absorption spectrum may be deduced from laser light reflected by a plane slab of sample material. Reflected waves from exit and entrance faces interfere, producing an alternating pattern of reflectance extrema as the thickness is varied. An increase in the laser intensity partially saturates the absorption line and causes a

William H. Thomason; James D. Macomber

1976-01-01

210

Noninvasive Inspection of C-4 Explosive in Mails by Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

We have measured the refractive index, extinction coefficient, and absorption coefficient of the explosive C-4 by THz time-domain spectroscopy and examined its applicability to detecting C-4 in mails. The explosive C-4, which is used in almost all mail-bomb terrorist activities, shows six THz bands in the frequency region from 5 to 90 cm-1 (150 GHz-2.7 THz). The 26.9 cm-1 band is very strong and can be used as a fingerprint of C-4. We confirmed that the THz absorption spectrum of C-4 hidden inside an envelope coincides essentially with that of C-4 itself. We also examined the applicability of the THz reflection spectroscopy to C-4 detection by calculating the reflectance spectra. Our results demonstrate that the THz techniques are very promising for counterterrorism against C-4 mail bombs.

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

2004-03-01

211

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

Microsoft Academic Search

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

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

2003-01-01

212

Picosecond transient photoconductivity in functionalized pentacene molecular crystals probed by terahertz pulse spectroscopy.  

PubMed

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800 nm, 100 fs 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 300 K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4 ps, a power-law decay is observed consistent with dispersive transport. PMID:12485104

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

2002-11-11

213

Characteristics of chiral and racemic ketoprofen drugs using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Absorption spectra of chiral S-(+)- and racemic RS-ketoprofen pharmaceutical molecules in crystalline form were recorded in the terahertz region between 6 and 66 cm-1 (0.2 ~ 2.0 THz) by using time-domain terahertz spectroscopic (THz-TDS) measurement. Different distinctive absorption features were observed which are strikingly sensitive to the change of subtle conformational structures within such isostructural crystal molecules. The results suggest that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.

Du, Yong; Liu, Jianjun; Hong, Zhi

2013-08-01

214

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

215

Spectroscopy of terahertz radiation using high-Q photonic crystal microcavities  

NASA Astrophysics Data System (ADS)

We report observation of high-Q resonance in the photoresponse of a detector embedded in the 2D photonic crystal slab (PCS) microcavity illuminated by terahertz radiation. The detector and PCS are fabricated from a single GaAs wafer in a unified process. The influence of the period of PCS lattice, microcavity geometry, and detector location on the resonant photoresponse is studied. The resonance is found to originate from coupling of the fundamental PCS microcavity photon mode to the detector. The phenomenon can be exploited to devise a spectrometer-on-a-chip for terahertz range.

Muravev, V. M.; Gusikhin, P. A.; Tsydynzhapov, G. E.; Fortunatov, A. A.; Kukushkin, I. V.

2012-12-01

216

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

217

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

218

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

219

Terahertz spectroscopy with a holographic Fourier transform spectrometer plus array detector using coherent synchrotron radiation  

SciTech Connect

By use of coherent terahertz synchrotron radiation, we experimentally tested a holographic Fourier transform spectrometer coupled to an array detector to determine its viability as a spectral device. Somewhat surprisingly, the overall performance strongly depends on the absorptivity of the birefringent lithium tantalate pixels in the array detector.

Nikolay I. Agladz, John Klopf, Gwyn Williams, Albert J. Sievers

2010-06-01

220

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

221

Terahertz time domain spectroscopy (THz-TDS) of hydrated biomolecular polymers and monomers  

NASA Astrophysics Data System (ADS)

Terahertz Time Domain Spectroscopy (THz-TDS) was utilized to obtain the complex dielectric spectra of hydrated biomolecules, betwixt the frequency range of 50 GHz to 2 THz. Two biological systems are observed; nucleic acid and carbohydrates. Monomers and polymers will be of interest for both. Utilizing both the Debye relaxation model and the suspension model, we observed both the mobility of biomolecules in solution as well as the influence they have on their surrounding water. Nucleotides and glucose (monomers) were found to have a small part in the overall dynamics of the polymers. Hydrated nucleotides were shown to form transition materials. The pyrimidine nucleotides act much like an ion where they break up the original structure of water and set up a less complicated structure (smaller main relaxation times than water) than water. Purine nucleotides act more like a hydrogen bond building material they set up a more complex hydrogen bond network (larger main relaxation times than water) than water. These nucleotides were shown to have an influence in water out to four water layers. The concentration studies that were preformed on native DNA, shows that concentration in the hydrated state is an important factor in the dielectric response. In addition, it was found that impurities in our samples did not play an important role in the dielectric response of our DNA solutions. Native DNA was shown to have a reach of six hydration layers. The influence temperature has on DNA solutions was observed, temperature has a large influence on hydrated DNA. It was found that hydrated DNA is more susceptible to change in temperature then that of bulk water. The main relaxation time increases at a much larger proportion to that of water. Using two synthetic DNA molecules with the same structure but different compositions and two carbohydrates with different structures but the same composition we found that the structure of a biopolymer is the most domination factor, rather than that of composition. It was determined that the length of the synthetic DNA was more important than that of the composition. Similarly, for the hydrated carbohydrate structures the amount of helices determines the amount hydrophobic dielectric behavior.

Glancy, Paul Michael

222

Using solid-state density functional theory and terahertz spectroscopy to spectroscopically distinguish the various hydrohalide salts of 5-(4-pyridyl)tetrazole  

NASA Astrophysics Data System (ADS)

The crystal structures and experimental terahertz spectroscopy of the isostructural hydrobromide and hydrochloride salts of 5-(4-pyridyl)tetrazole were reproduced using solid-state density functional theory as implemented in CRYSTAL09. The effect of the halide size was investigated to determine the influence on the low energy lattice and molecular vibrations exhibited in the region from 10 to 100 cm-1, known as the terahertz (THz) region. Using solid-state DFT, the normal modes of these THz vibrations were determined and it was shown that the mass and size of the halide anion has a significant effect in this region. A trend was observed in the frequencies in the terahertz region, such that increasing the mass of the anion, produces an overall red shift in the frequency.

Pellizzeri, Steven; Delaney, Sean P.; Korter, Timothy M.; Zubieta, Jon

2013-10-01

223

Propagation through terahertz waveguides with photonic crystal boundaries  

Microsoft Academic Search

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

Adam L. Bingham

2007-01-01

224

Ultrafast optical modulation of terahertz metamaterials  

Microsoft Academic Search

We have characterized the ultrafast dynamical properties of split ring resonators by utilizing optical pump–terahertz probe spectroscopy on a subpicosecond timescale. The experimental results show that the pump-induced relative changes in terahertz peak transmission, as well as the dynamical transmission spectra, are different when the terahertz electric vector is perpendicular and parallel to the gap of the split ring resonator.

Qingli Zhou; Yulei Shi; Aihua Wang; Lei Li; Dongmei Zhao; Jianfeng Liu; Huijuan Sun; Cunlin Zhang

2011-01-01

225

Relating Plant Carbon Exchange with Reflectance Spectroscopy  

NASA Astrophysics Data System (ADS)

One important aspect of climate change research is to monitor and model ecosystem carbon dynamics. Spectral reflectance data from satellites, aircraft, and in situ measurements have shown capabilities to track exchanges of carbon, water and energy between terrestrial ecosystems and the atmosphere. A key element of this study is to relate spectral characteristics of leaves, measured at high-spectral resolution, to their biological activity such as photosynthetic rate (calculated from CO2 exchange). In this research, the biological activity and spectral reflectance of leaves were monitored over the course of a full diurnal cycle using simultaneous gas-exchange and high spectral resolution measurements. An experimental model based on step-wise linear regression was created (adjusted R-square value 0.984) by applying statistical tools to study the relationship between plant photosynthesis and spectral reflectance indices. Indices which were shown to be statistically significant to photosynthesis, such as PSRI, PRI, EVI, WBI, etc., demonstrate the various biochemical parameters that may contribute to changes in the photosynthetic activity over the diurnal cycle. This carbon exchange/reflectance model, created using in situ techniques, can then be applied to crop-level canopy reflectance acquired via high-spectral resolution instruments from aircraft and satellite.

Long, S. A.; Huemmrich, K. F.; Corp, L.

2010-12-01

226

Screening mail for powders using terahertz technology  

NASA Astrophysics Data System (ADS)

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

Kemp, Mike

2011-10-01

227

Does Spectral Format Matter in Diffuse Reflection Spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

228

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

229

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

230

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

231

Finite pump-beam-size effects in optical pump-terahertz probe spectroscopy  

Microsoft Academic Search

Finite pump-beam size in optical pump-terahertz (THz) probe experiments introduces distortions in both the signal amplitude and the spectral form. We show both experimentally and analytically that the pump beam must be 3-4 times larger than the THz probe beam for a one-photon excitation process to achieve <10% spectral distortion. Our experiments use thin samples of single-crystal ZnTe or CdTe.

Georgi L. Dakovski; Brian Kubera; Song Lan; Jie Shan

2006-01-01

232

Inter\\/intra molecular dynamics in gases and liquids studied by terahertz time-domain spectroscopy  

Microsoft Academic Search

This thesis presents a description of the low-frequency terahertz (THz) absorption spectrum of a variety of materials that are of interest to many biological and chemical processes. The work described here encompasses the development of time-domain THz spectrometers, based on amplified Ti: Sapphire lasers systems as well as mode-locked Erbium doped fiber lasers as the driving source. These systems were

Xuying Xin

2007-01-01

233

Time-Resolved Terahertz Spectroscopy of Free Carrier Nonlinear Dynamics in Semiconductors  

Microsoft Academic Search

Nonlinear dynamics of free carriers in direct bandgap semiconductors at terahertz (THz) frequencies is studied using the intense few-cycle source available at the Advanced Laser Light Source (ALLS). Techniques such as Z-scan and optical-pump\\/THz-probe are employed to explore nonlinear interactions in an n-doped InGaAs thin film and a photoexcited GaAs sample, respectively. The physical mechanism that gives rise to such

G. Sharma; L. Razzari; F. H. Su; F. Blanchard; A. Ayesheshim; T. L. Cocker; L. V. Titova; H. C. Bandulet; T. Ozaki; J.-C. Kieffer; R. Morandotti; M. Reid; F. A. Hegmann

2010-01-01

234

Imaging of osteoarthritis using a hand-held terahertz probe  

Microsoft Academic Search

A hand-held terahertz (THz) probe system is being developed for medical use by Teraview Ltd. We use this prototype system to investigate the terahertz characteristics of osteoarthritis (OA). Excised femoral knee joints with symptoms of osteoarthritis were measured. In this paper we analyze the typical terahertz response of the diseased samples and explain how the reflected terahertz pulse could be

K. W. C. Kan; Wing-Sze Lee; W. H. Cheung; E. Pickwell-MacPherson

2009-01-01

235

Reflectance spectroscopy of interplanetary dust particles  

NASA Astrophysics Data System (ADS)

Reflectance spectra were collected from chondritic interplanetary dust particles (IDPs), a polar micrometeorite, Allende (CV3) meteorite matrix, and mineral standards using a microscope spectrophotometer. Data were acquired over the 380-1100 nm wavelength range in darkfield mode using a halogen light source, particle aperturing diaphrams, and photomultiplier tube (PMT) detectors. Spectra collected from titanium oxide (Ti4O7), magnetite (Fe3O4), and Allende matrix establish that it is possible to measure indigenous reflectivities of micrometer-sized (>5 ?m in diameter) particles over the visible (VIS) wavelength range 450-800 nm. Below 450 nm, small particle effects cause a fall-off in signal into the ultraviolet (UV). Near-infrared (IR) spectra collected from olivine and pyroxene standards suggest that the ˜1 ?m absorption features of Fe-bearing silicates in IDPs can be detected using microscope spectrophotometry. Chondritic IDPs are dark objects (<15% reflectivity) over the VIS 450-800 nm range. Large (>1 ?m in diameter) embedded and adhering single mineral grains make IDPs significantly brighter, while surficial magnetite formed by frictional heating during atmospheric entry makes them darker. Most chondritic smooth (CS) IDPs, dominated by hydrated layer silicates, exhibit generally flat spectra with slight fall-off towards 800 nm, which is similar to type CI and CM meteorites and main-belt C-type asteroids. Most chondritic porous (CP) IDPs, dominated by anhydrous silicates (pyroxene and olivine), exhibit generally flat spectra with a slight rise towards 800 nm, which is similar to outer P and D asteroids. The most C-rich CP IDPs rise steeply towards 800 nm with a redness comparable to that of the outer asteroid object Pholus (Binzel, 1992). Chondritic porous IDPs are the first identified class of meteoritic materials exhibiting spectral reflectivities (between 450 and 800 nm) similar to those of P and D asteroids. Although large mineral grains, secondary magnetite, and small particle effects complicate interpretation of IDP reflectance spectra, microscope spectrophotometry appears to offer a rapid, nondestructive technique for probing the mineralogy of IDPs, comparing them with meteorites, investigating their parent body origins, and identifying IDPs that may have been strongly heated during atmospheric entry.

Bradley, J. P.; Keller, L. P.; Brownlee, D. E.; Thomas, K. L.

1996-05-01

236

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

2011-10-14

237

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

NASA Astrophysics Data System (ADS)

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 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 such that both intraband and interband scattering of carriers via optical phonon emission becomes 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.

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

2011-11-01

238

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

PubMed

We show that optical pump-terahertz probe spectroscopy is a direct experimental tool for exploring laser-induced ionization and plasma formation in gases. Plasma was produced in gaseous oxygen by focused amplified femtosecond pulses. The ionization mechanisms at 400- and 800-nm excitation wavelengths differ significantly being primarily of a multiphoton character in the former case and a strong-field process in the latter case. The generation of the plasma in the focal volume of the laser and its expansion on subnanosecond time scale is directly monitored through its density-dependent susceptibility. A Drude model used to evaluate the plasma densities and electron-scattering rates successfully captures the observations for a wide range of pump intensities. In addition, rotational fingerprints of molecular and ionic species were also observed in the spectra. PMID:16178600

Mics, Zoltan; Kadlec, Filip; Kuzel, Petr; Jungwirth, Pavel; Bradforth, Stephen E; Apkarian, V Ara

2005-09-01

239

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

SciTech Connect

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

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

2005-09-08

240

Non-Destructive Evaluation Method of Pharmaceutical Tablet by Terahertz-Time-Domain Spectroscopy: Application to Sound-Alike Medicines  

NASA Astrophysics Data System (ADS)

To evaluate terahertz time-domain spectroscopy (THz-TDS) as a promising tool for discriminating pharmaceutical tablets, THz-TDS has been applied for discrimination between pharmaceutical tablets with sound-alike names. Two sets of medicine tablets with sound-alike names, that is, Amaryl and Almarl, Zyloric and Zantac, are examined in this study. Based on the difference in THz absorption spectra, we have succeeded in distinguishing between sound-alike medicine tablets clearly for each set. The results in this study suggest that THz-TDS is a useful tool that is indispensable for medical security maintenance, such as a non-destructive way to prevent mix-up of medicine.

Kawase, Masaya; Yamamoto, Kohji; Takagi, Keita; Yasuda, Ryohei; Ogawa, Masafumi; Hatsuda, Yasutoshi; Kawanishi, Sonoyo; Hirotani, Yoshihiko; Myotoku, Michiaki; Urashima, Yoko; Nagai, Katsuhito; Ikeda, Kenji; Konishi, Hiroki; Yamakawa, Junji; Tani, Masahiko

2013-09-01

241

Observation of TO1 soft mode in SrTiO3 films by terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

We have measured the dielectric properties of pulsed-laser-deposited SrTiO3 (STO) thin films by terahertz (THz) time-domain spectroscopy in the frequency range from 80 GHz to 1.5 THz at temperatures from 20 to 290 K. The measured frequency dispersion of the dielectric constant of the STO thin films show a clear Lorentzian oscillator behavior below 180 K and softening of the ferroelectric soft mode of the STO thin films takes place with decreasing temperature. Both eigen frequency and damping of the soft phonon mode show a peak nearly at 110 K that can be attributed to the effect on the Ti-O-Ti bending in STO thin film due to the starting of tilting in oxygen octahedra near the cubic to tetragonal phase transition. Dielectric strength saturates near the temperature 60 K, however, that is a point of further investigation.

Misra, M.; Kotani, K.; Kawayama, I.; Murakami, H.; Tonouchi, M.

2005-10-01

242

Characterization of apparent superluminal effects in the focus of an axicon lens using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

We describe time-resolved measurements of the propagating interference pattern at the focus of an axicon lens. The technique of terahertz time-domain spectroscopy permits a direct observation of the electric field within the line focus formed by a converging conical wave front. We extract the apparent superluminal velocity of this pulse from the peak of the time-domain waveform, and also in the frequency domain by Fourier transform. From these measurements, we conclude that pulse reshaping, arising from strong frequency-dependent propagation effects, does not play a substantial role. As a result, tracking the peak of the pulse in the time domain is a valid method for determining the average group velocity of the disturbance. We also elucidate a new mechanism which influences the value of the superluminal velocity, involving the curvature of the incident wave front.

Lloyd, James; Wang, Kanglin; Barkan, Adrian; Mittleman, Daniel M.

2003-04-01

243

Photo-induced insulator-metal phase transition observed by the terahertz pump-probe spectroscopy  

NASA Astrophysics Data System (ADS)

We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation at 800 nm induced an ultrafast decrease of the transmittance of the terahertz pulse within 0.7 ps, and then the transmittance decreases gradually up to 100 ps. The decrease of the transmittance is assigned to the appearance of the high electric conductivity due to metallic state. The conductivity increases more than ten times in the picoseconds time range after photoexcitation and it is concluded that the metallic electronic states appear. The rapid and gradual changes of the electric conductivity are very similar to the previous reports of the time resolved X-ray and electron diffractions. This fact indicates that the increase of the electric conductivity and the change of the lattice structure proceed in parallel. It is suggested that the photo-induced insulator-metal phase transition is of the Peierls type.

Nakajima, Makoto; Takubo, Naoko; Hiroi, Zenji; Ueda, Yutaka; Suemoto, Tohru

2009-02-01

244

Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs  

Microsoft Academic Search

The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz emission spectroscopy and optical-pump terahertz-probe spectroscopy. Terahertz emission spectroscopy measurements, coupled with Monte Carlo simulations of terahertz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump terahertz-probe spectroscopy and

J. Lloyd-Hughes; S. K. E. Merchant; L. Fu; H. H. Tan; C. Jagadish; E. Castro-Camus; M. B. Johnston

2006-01-01

245

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

246

Diffuse reflectance spectroscopy of fibrous proteins.  

PubMed

UV-visible diffuse reflectance (DR) spectra of the fibrous proteins wool and feather keratin, silk fibroin and bovine skin collagen are presented. Natural wool contains much higher levels of visible chromophores across the whole visible range (700-400 nm) than the other proteins and only those above 450 nm are effectively removed by bleaching. Both oxidative and reductive bleaching are inefficient for removing yellow chromophores (450-400 nm absorbers) from wool. The DR spectra of the four UV-absorbing amino acids tryptophan, tyrosine, cystine and phenylalanine were recorded as finely ground powders. In contrast to their UV-visible spectra in aqueous solution where tryptophan and tyrosine are the major UV absorbing species, surprisingly the disulphide chromophore of solid cystine has the strongest UV absorbance measured using the DR remission function F(R)(?). The DR spectra of unpigmented feather and wool keratin appear to be dominated by cystine absorption near 290 nm, whereas silk fibroin appears similar to tyrosine. Because cystine has a flat reflectance spectrum in the visible region from 700 to 400 nm and the powder therefore appears white, cystine absorption does not contribute to the cream colour of wool despite the high concentration of cystine residues near the cuticle surface. The disulphide absorption of solid L: -cystine in the DR spectrum at 290 nm is significantly red shifted by ~40 nm relative to its wavelength in solution, whereas homocystine and lipoic acid showed smaller red shifts of 20 nm. The large red shift observed for cystine and the large difference in intensity of absorption in its UV-visible and DR spectra may be due to differences in the dihedral angle between the crystalline solid and the solvated molecules in solution. PMID:22218994

Millington, Keith R

2012-01-05

247

Inspection of milk components by terahertz attenuated total reflectance (THz-ATR) spectrometer equipped temperature controller  

Microsoft Academic Search

It was confirmed that THz spectroscopy has a potential for quantitative analysis of milk fat, total solid, lactose, milk protein, casein and somatic cell. We investigated the correlation between the absorption spectrum of raw milk in the THz region and the measured milk contents by the Partial Least Square (PLS) regression and full cross validation as test for the calibration

Hirotaka Naito; Yuichi Ogawa; Keiichiro Shiraga; Naoshi Kondo; Tsunao Hirai; Ikuo Osaka; Asuka Kubota

2011-01-01

248

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

249

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

250

Carrier dynamics in self-assembled ErAs nanoislands embedded in GaAs measured by optical-pump terahertz-probe spectroscopy  

Microsoft Academic Search

We use optical-pump terahertz (THz)-probe spectroscopy to study carrier dynamics in self-assembled ErAs nanoislands embedded in GaAs and deposited in a superlattice structure. Measurements are performed at several pump fluences on samples with different superlattice periods, enabling a determination of the time-dependent conductivity. Subpicosecond carrier capture times are obtained, indicating the potential of these devices as time-domain THz detectors with

R. P. Prasankumar; A. Scopatz; D. J. Hilton; A. J. Taylor; R. D. Averitt; J. M. Zide; A. C. Gossard

2005-01-01

251

Terahertz time-domain spectroscopy characterization of the far-infrared absorption and index of refraction of high-resistivity, float-zone silicon  

Microsoft Academic Search

The far-infrared absorption and index of refraction of high-resistivity, float-zone, crystalline silicon has been measured by terahertz time-domain spectroscopy. The measured new upper limit for the absorption of this most transparent dielectric material in the far infrared shows unprecedented transparency over the range from 0.5 to 2.5 THz and a well-resolved absorption feature at 3.6 THz. The index of refraction

Jianming Dai; Jiangquan Zhang; Weili Zhang; D. Grischkowsky

2004-01-01

252

FDTD-based computed terahertz wave propagation in multilayer medium structures  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

253

Can Litter Decomposability Be Predicted by near Infrared Reflectance Spectroscopy?  

Microsoft Academic Search

Several decomposition experiments were used to explore the potential of near infrared reflectance spectroscopy (NIRS) for predicting litter decomposability. A first experiment was conducted on a calibration set, and predictive equations were established between the NIR spectral data of the initial litters and the decay descriptors. These equations were then applied to two validation sets. The 34 litters of the

Dominique Gillon; Richard Joffre; Adamou Ibrahima

1999-01-01

254

Factors affecting soil phosphorus and potassium estimation by reflectance spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

Visible and near infrared (VNIR) diffuse reflectance spectroscopy has potential in site-specific measurement of soil properties. However, previous studies have reported VNIR estimates of plant available soil phosphorus (P) and potassium (K) to be of variable accuracy. In this study, we used a databa...

255

EXTENSION FORAGE TESTING USING NEAR INFRARED REFLECTANCE SPECTROSCOPY  

Microsoft Academic Search

SUMMARY Near infrared reflectance spectroscopy (NIRS) was evaluated for its accuracy in analyzing the nutritive value of tropical grass hays made by Florida livestock producers. From 1982 to 1987, a unique set of producer hays was obtained representing four tropical grass species, and an unknown range of maturities, fertilization schemes, weather conditions, and hay making and storage procedures. General NIRS

W. F. Brown; J. E. Moore; W. E. Kunkle; C. G. Chambliss; K. M. Portier

256

Compositional analysis of biomass feedstocks by near infrared reflectance spectroscopy  

Microsoft Academic Search

Near infrared reflectance spectroscopy (NIRS) has been used extensively in lignocellulose analysis of forages and should be useful in predicting the chemical composition of biomass feedstocks. We determined the chemical composition of several woody and herbaceous feedstocks (121 samples in total) in the laboratory and used these data to calibrate an NIR spectrometer. Samples were analysed for ethanol extractives, ash,

Matt A. Sanderson; Foster Agblevor; Michael Collins; David K. Johnson

1996-01-01

257

Terahertz sources and detectors  

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

258

Phase-Sensitive Reflective Imaging Device in the mm-wave and Terahertz Regions  

NASA Astrophysics Data System (ADS)

Two Free Electron Laser sources have been developed at ENEA-Frascati for a variety of applications: A Compact Free Electron Laser (C-FEL) that provides coherent radiation in the frequency range between 90 and 150 GHz Gallerano et al. (Infrared Phys. and Techn. 40:161, 1999), and a second source, FEL-CATS, which utilizes a peculiar radio-frequency structure to generate coherent emission in the range 0.4 to 0.7 THz Doria et al. (Phys. Rev. Lett 93:264801, 2004). The high peak power of several kW in 15 to 50 ps pulses, makes these sources particularly suitable for the assessment of exposure limits in biological systems and for long range detection. In this paper we present a phase-sensitive reflective imaging device in the mm-wave and THz regions, which has proven to be a valuable tool in the biological Ramundo-Orlando et al. (Bioelectromagnetics 28:587-598, 2007), environmental Doria et al. (2005) and art conservation fields Gallerano et al. (2008). Different setups have been tested at different levels of spatial resolution to image objects from a few centimeter square to larger sizes. Images have been compared to identify and characterize the contrast mechanism.

Gallerano, Gian Piero; Doria, Andrea; Germini, Marzia; Giovenale, Emilio; Messina, Giovanni; Spassovsky, Ivan P.

2009-12-01

259

Studies of adipocere using attenuated total reflectance infrared spectroscopy  

Microsoft Academic Search

Attenuated total reflectance (ATR) infrared spectroscopy has been used to characterize pig adipocere formation. The compositions\\u000a of adipocere samples obtained by burial of pig adipose tissue in soil and in mock coffins were compared with that of the original\\u000a adipose tissue using this technique. The ART spectra show that bands resulting from triglyceride and fatty acid C=O stretching\\u000a are particularly

B. H. Stuart; L. Craft; S. L. Forbes; B. B. Dent

2005-01-01

260

Magnetic circular dichroism in reflection electron energy loss spectroscopy?  

SciTech Connect

We evaluate the possibility of using dichroic electron energy loss spectroscopy (DEELS) as an alternative to x-ray magnetic circular dichroism (XMCD). It is well known that electron energy loss spectroscopy and x-ray absorption spectroscopy provide similar information. A simple semiclassical model suggests that reflection DEELS might have a magnetic sensitivity similar to that of XMCD. This sensitivity will be reduced, however, by multiple scattering of the probe electron before and after the energy loss event. Thus, it is difficult to predict the magnitude of the DEELS effect. Experiments were performed at the {ital L} edges of polycrystalline Fe, Co, and Ni thin-film samples prepared {ital in} {ital situ} with a uniaxial magnetic bias. Even in these most favorable cases, the DEELS effect is limited to less than one-tenth of related effects in XMCD. {copyright} {ital 1996 American Vacuum Society}

Harp, G.R. [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States); Farrow, R.F.; Marks, R.F. [IBM Research Division, Almaden Research Center, San Jose, California 95120-6099 (United States)

1996-07-01

261

Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy.  

PubMed

We have performed a comparative study of ultrafast charge carrier dynamics in a range of III-V nanowires using optical pump-terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm² V?¹ s?¹, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s?¹. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10?? cm s?¹. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices. PMID:23619012

Joyce, Hannah J; Docherty, Callum J; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Lloyd-Hughes, James; Herz, Laura M; Johnston, Michael B

2013-04-25

262

Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We have performed a comparative study of ultrafast charge carrier dynamics in a range of III–V nanowires using optical pump–terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm2 V?1 s?1, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s?1. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 105? cm s?1. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices.

Joyce, Hannah J.; Docherty, Callum J.; Gao, Qiang; Tan, H. Hoe; Jagadish, Chennupati; Lloyd-Hughes, James; Herz, Laura M.; Johnston, Michael B.

2013-05-01

263

Intense ultrashort terahertz pulses: generation and applications  

NASA Astrophysics Data System (ADS)

Ultrashort terahertz pulses derived from femtosecond table-top sources have become a valuable tool for time-resolved spectroscopy during the last two decades. Until recently, the pulse energies and field strengths of these pulses have been generally too low to allow for the use as pump pulses or the study of nonlinear effects in the terahertz range. In this review article we will describe methods of generation of intense single cycle terahertz pulses with emphasis on optical rectification using the tilted-pulse-front pumping technique. We will also discuss some applications of these intense pulses in the emerging field of nonlinear terahertz spectroscopy.

Hoffmann, Matthias C.; András Fülöp, József

2011-03-01

264

Reflective mesoscopic spectroscopy for noninvasive detection of reflective index alternations at nano-scale  

NASA Astrophysics Data System (ADS)

Cancer has been one of the most serious threats to human life. However, there is no substantial improvement in overall treatment of cancer patients. One of the key reasons is the unavailability of convenient method to detect cellular alterations in ultra-early stage of carcinogenesis processes, where genetic aberrations at nano-scale have not yet resulted in histological changes. In this paper, we described an optical method based on reflective mesoscopic spectroscopy for ultra-early cancer detection. According to mesoscopic light transport theory, photons propagating in one dimension (1D) within a weakly disordered medium have the non-self-averaging effect. Reflected signal after 1D propagating is sensitive to any length scale of refractive index fluctuations due to multiple interferences of light waves travelling along 1D trajectory. The principle of mesoscopic spectroscopy for perceiving reflective index fluctuations at length scale of nanometers is introduced. A system for the measurement of reflective mesoscopic spectroscopy based on spatial-incoherence broadband source and spectrometer is established. Simulations on light propagation in cell-emulating model with controlled refractive index distribution are done by finite-difference time-domain (FDTD) approach.

Tao, Yuanhao; Ding, Zhihua

2011-01-01

265

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

266

Analysis of surface plasmon excitation at terahertz frequencies with highly doped graphene sheets via attenuated total reflection  

NASA Astrophysics Data System (ADS)

Excitation of surface plasmons supported by doped graphene sheets at terahertz frequencies is investigated numerically. To alleviate the momentum mismatch between the highly confined plasmon modes and the incident radiation, it is proposed to increase the surface conductivity of graphene through high doping levels or with few-layer graphene. For currently achievable doping levels, our analysis shows that surface plasmons on monolayer graphene may be excited at operating frequencies up to about 10 THz (~41.3 meV) with a high-index coupling prism, and higher frequencies/energies are possible for few-layer graphene. These highly confined surface modes are promising for sensing and waveguiding applications in the terahertz regime.

How Gan, Choon

2012-09-01

267

Applications of Terahertz Time-Domain Reflectometry  

NASA Astrophysics Data System (ADS)

A reflection-type terahertz (THz) time-domain spectroscopy (TDS) is applied to non-contact and non-destructive diagnosis of the surface and inner-structure of test samples. Raster scan imaging and THz optical coherence tomography (THz-OCT) are demonstrated for a bank bill, a high voltage cable and an indented impression on a memo-pad paper. The watermark of the bank bill, the indented impression, and a flaw in the cable are detected successfully. These results indicate that THz imaging is potentially useful for the analysis of surfaces and inner-structures of products made with various materials.

Kitahara, Hideaki; Takano, Keisuke; Ikeda, Takeshi; Tani, Masahiko; Hangyo, Masanori

268

Ultrafast high-field carrier transport in GaAs measured by femtosecond pump-terahertz probe spectroscopy  

Microsoft Academic Search

Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers and at electric fields up to 15 kV\\/cm. The pump-induced attenuation of terahertz transmission reduces obviously at high field, and the carrier relaxation time is also found to be correlated with photoinjected carrier density and electric field. These effects can be

Yulei Shi; Qing-Li Zhou; Cunlin Zhang; Bin Jin

2008-01-01

269

[SPAD prediction of leave based on reflection spectroscopy].  

PubMed

Handheld SPAD meter is often used to measure chlorophyll content of plant and nitrogen level for some species. For plant production automation, however, it loses its popularity due to its point-by-point checking. The authors need to monitor the growing conditions of plant remotely, instantly and nondestructively. In the test, we examined optical fiber reflection spectroscopy used to measure chlorophyll content of some plant leaves, or for their SPAD prediction. The authors picked 120 leaves randomly from our campus ground or trees, among which 70 samples were chosen as calibration set and others as verification set. Each sample was water-cleaned and air-dried. To locate each measuring point precisely when using SPAD meter and spectrometer, the authors drew a circle with a diameter of 10 mm on each leave to be measured. By comparing the spectral curves of various leaves, the authors found that the spectral band between 650-750 nm was significant for SPAD modeling since this range of spectral data of leaves with the same SPAD reading was close to each other. It was showed that leave color was an unnecessary factor for SPAD prediction by reflection spectroscopy. Besides, the authors discovered that LED's narrow spectral range used by SPAD meter should be concerned because optical fiber spectrometer has much more wide spectral range. Based on this awareness, the authors designed an adjustment factor of light to linearly rebuild spectrometer's reflective intensity so that it reached zero outside the band 650-750 nm. Moreover, leave thickness was another influential factor for SPAD prediction since the light of SPAD meter goes through the leave while the reflective spectrometer does not. First, an equation for SPAD prediction was built with uncertain parameters. Then, a standard genetic algorithm was designed with Visual Basic 6.0 for parameter optimization. As a result, the optimal reflection band was narrowed within 683.24-733.91 nm. The result showed that leave thickness strongly affects the precision of SPAD prediction. Through the modification of leave thickness, the regression coefficient (R2) of calibration set and verification set reached 0.865 8 and 0.916 1 respectively. The test showed that optical fiber reflection spectroscopy is useful for SPAD prediction and can be used to develop remote SPAD sensor. PMID:19810542

Yang, Hai-Qing; Yao, Jian-Song; He, Yong

2009-06-01

270

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

271

Carrier dynamics in self-assembled ErAs nanoislands embedded in GaAs measured by optical-pump terahertz-probe spectroscopy  

NASA Astrophysics Data System (ADS)

We use optical-pump terahertz (THz)-probe spectroscopy to study carrier dynamics in self-assembled ErAs nanoislands embedded in GaAs and deposited in a superlattice structure. Measurements are performed at several pump fluences on samples with different superlattice periods, enabling a determination of the time-dependent conductivity. Subpicosecond carrier capture times are obtained, indicating the potential of these devices as time-domain THz detectors with performance comparable to low-temperature grown GaAs and superior control of material parameters.

Prasankumar, R. P.; Scopatz, A.; Hilton, D. J.; Taylor, A. J.; Averitt, R. D.; Zide, J. M.; Gossard, A. C.

2005-05-01

272

Effect of oxygen stoichiometry on the insulator-metal phase transition in vanadium oxide thin films studied using optical pump-terahertz probe spectroscopy  

NASA Astrophysics Data System (ADS)

Using optical pump-terahertz probe spectroscopy, we studied the dynamic behaviors of photoinduced insulator-metal phase transition in vanadium oxide thin films with different oxygen stoichiometry. We found that the insulator-metal phase transition of vanadium dioxide is very sensitive to oxygen stoichiometry: the increased oxygen content in vanadium oxide will reduce the magnitude of phase transition and change the dynamics of the phase transition. The transient complex photoconductivity of vanadium oxide thin films is investigated and analyzed with Drude-Smith model, supplying insight of the dynamic process of phase transition in vanadium oxide thin films.

Liu, H. W.; Wong, L. M.; Wang, S. J.; Tang, S. H.; Zhang, X. H.

2013-10-01

273

Terahertz imaging of burned tissue  

NASA Astrophysics Data System (ADS)

There are over 2 million reported burn injuries each year in the United States with 75,000 of these incidents resulting in hospitalization. Current medical imaging modalities have limited capabilities to assess initial burn damage and monitor healing progress. Some of these limitations can be attributed to modality occlusion from bandages, dried tissue and/or blood and inflammation. Since terahertz radiation can see through textiles and bandages1, previous studies2,3 suggested that terahertz radiation, in a reflectance configuration, could be used for non-invasive analysis of tissue thermal damage and healing status. In this study, we perform an analysis of the terahertz absorption and reflection properties of the tissue constituents comprising a wound area, and provide a feasibility assessment of the capabilities of terahertz imaging to provide a clinical tool for initial burn analysis and healing progress.

Dougherty, Joseph P.; Jubic, Gregory D.; Kiser, William L., Jr.

2007-02-01

274

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

275

High Resolution Dispersive Fourier Transform Spectroscopy for Pollutant Gases at Millimeter Wave and Terahertz Frequencies  

Microsoft Academic Search

Dispersive Fourier transform spectroscopy (DFTS) provides us with a very precise method of measuring the absorption and refractive index spectra of pollutant gases. This paper presents the rotational transition lines of sulfur dioxide gas as a function of varying pressure using DFTS for the very first time. The relationship between the variation of the pressure and the change in the

N. N. Almoayed; M. N. Afsar

2007-01-01

276

Terahertz Reflection Spectroscopy of Aqueous NaCl and LiCl Solutions  

NASA Astrophysics Data System (ADS)

We present spectroscopic measurements of the full dielectric function of aqueous solutions of sodium chloride and lithium chloride at concentrations approaching their solubility limits at room temperature. We find that the dielectric properties of the two salts are rather different at THz frequencies. Whereas both the real and imaginary part of the permittivity of NaCl increases with concentration, we see that the imaginary part of the permittivity of LiCl (related to the absorption) decreases with increasing salt concentration. We relate these changes to the behavior of slow and fast Debye relaxation processes in the solutions.

Jepsen, Peter Uhd; Merbold, Hannes

2010-04-01

277

Autofluorescence and diffuse reflectance patterns in cervical spectroscopy  

NASA Astrophysics Data System (ADS)

Fluorescence and diffuse reflectance spectroscopy are two new optical technologies, which have shown promise to aid in the real time, non-invasive identification of cancers and precancers. Spectral patterns carry a fingerprint of scattering, absorption and fluorescence properties in tissue. Scattering, absorption and fluorescence in tissue are directly affected by biological features that are diagnostically significant, such as nuclear size, micro-vessel density, volume fraction of collagen fibers, tissue oxygenation and cell metabolism. Thus, analysis of spectral patterns can unlock a wealth of information directly related with the onset and progression of disease. Data from a Phase II clinical trial to assess the technical efficacy of fluorescence and diffuse reflectance spectroscopy acquired from 850 women at three clinical locations with two research grade optical devices is calibrated and analyzed. Tools to process and standardize spectra so that data from multiple spectrometers can be combined and analyzed are presented. Methodologies for calibration and quality assurance of optical systems are established to simplify design issues and ensure validity of data for future clinical trials. Empirically based algorithms, using multivariate statistical approaches are applied to spectra and evaluated as a clinical diagnostic tool. Physically based algorithms, using mathematical models of light propagation in tissue are presented. The presented mathematical model combines a diffusion theory in P3 approximation reflectance model and a 2-layer fluorescence model using exponential attenuation and diffusion theory. The resulting adjoint fluorescence and reflectance model extracts twelve optical properties characterizing fluorescence efficiency of cervical epithelium and stroma fluorophores, stromal hemoglobin and collagen absorption, oxygen saturation, and stromal scattering strength and shape. Validations with Monte Carlo simulations show that adjoint model extracted optical properties of the epithelium and the stroma can be estimated accurately. Adjoint model is applied to 926 clinical measurements from 503 patients. Mean values of extracted optical properties have demonstrated to characterize the biological changes associated with dysplastic progression. Finally, penalized logistic regression algorithms are applied to discriminate dysplastic stages in tissue based on extracted optical features. This work provides understandable and interpretable information regarding predictive and generalization ability of optical spectroscopy in neoplastic changes using a minimum subset of optical measurements. Ultimately these methodologies would facilitate the transfer of these optical technologies into clinical practice.

Marin, Nena Maribel

278

Intense ultrashort terahertz pulses: generation and applications  

Microsoft Academic Search

Ultrashort terahertz pulses derived from femtosecond table-top sources have become a valuable tool for time-resolved spectroscopy during the last two decades. Until recently, the pulse energies and field strengths of these pulses have been generally too low to allow for the use as pump pulses or the study of nonlinear effects in the terahertz range. In this review article we

Matthias C. Hoffmann; József András Fülöp

2011-01-01

279

Optical Pump-Terahertz Probe Spectroscopy of Condensed Phase Reaction Dynamics  

Microsoft Academic Search

The general theoretical and experimental principles of optical pump-THz probe spectroscopy of chemical reactions in liquids is presented. Background on specific difficulties encountered in the experimental observation is reviewed. Chiefly, signal-to-noise ratios currently limit the quality of information that can be extracted from optical pump-THz probe data on chemical reactions. This issue is shown to be connected to the assumption

Bret N. Flanders; Norbert F. Scherer

280

Ultrafast optical pump terahertz-probe spectroscopy of strongly correlated electron materials  

Microsoft Academic Search

We have used optical-pump far-infrared probe spectroscopy to probe the low energy electron dynamics of high temperature superconductors and colossal magnetoresistance manganites. For the superconductor YBa2Cu3O7, picosecond conductivity measurements probe the interplay between Cooper-pairs and quasiparticles. In optimally doped films, the recovery time for long-range phase-coherent pairing increases from 1.5 ps at 4K to 3.5 ps near Tc, consistent with

R. D. Averitt; Antoinette J. Taylor; V. K. Thorsmølle; Quanxi Jia; A. I. Lobad; S. A. Trugman

2001-01-01

281

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

282

Laboratory Studies of Organic Compounds With Reflectance Spectroscopy  

NASA Astrophysics Data System (ADS)

In order to properly interpret reflectance spectra of any solar system surface from the earth to the Oort cloud, laboratory spectra of candidate materials for comparative analysis are needed. Although the common cosmochemical species (H2O, CO2, CO, NH3, and CH4) are well represented in the spectroscopic literature, comparatively little reflectance work has been done on organics from room to cryogenic temperatures at visible to near infrared wavelengths. Reflectance spectra not only enhance weak or unseen transmission features, they are also more analogous to spectra obtained by spacecraft that are imaging such bodies as giant planet moons, kuiper belt objects, centaurs, comets and asteroids, as well as remote sensing of the earth. The USGS Spectroscopy Laboratory is measuring reflectance spectra of organic compounds from room to cryogenic temperatures over the spectral range of 0.35 to 15.5 microns. This region encompasses the fundamental absorptions and many overtones and combinations of C, H, O, and N molecular bonds. Because most organic compounds belong to families whose members have similar structure and composition, individual species identification within a narrow wavelength range may be ambiguous. By measuring spectral reflectance of the pure laboratory samples from the visible through the near and mid-infrared, absorption bands unique to each can be observed, cataloged, and compared to planetary reflectance data. We present here spectra of organic compounds belonging to five families: the alkanes, alkenes, alkynes, aromatics, and cyanides. Common to all of these are the deep C-H stretch fundamental absorptions, which shift shortward from 3.35+ microns in alkanes to 3.25+ microns in aromatics, to 3.2+ microns in alkenes, and down to 3.0+ microns in alkynes. Mid-IR absorptions due to C-H bending deformations at 6.8+ and 7.2+ microns are also identified. In the near infrared these stretching and bending fundamentals yield a diagnostic set of combination absorptions at approximately 2.3 microns, as well as the first C-H stretching overtones at 1.6 to 1.7 microns, and even the second stretching overtones at 1.2+ microns. Additionally, the spectral properties of these organic materials have applications to remote sensing of terrestrial environments, including hazardous waste and disaster site characterization.

Curchin, J. M.; Clark, R. N.; Hoefen, T. M.

2007-12-01

283

Observation of Terahertz Vibrations in the Nitrogenase FeMo-cofactor via Femtosecond Pump Probe Spectroscopy  

PubMed Central

We have used Impulsive Coherent Vibrational Spectroscopy (ICVS) to study the FeMo-cofactor of nitrogenase from Azotobacter vinelandii as the extracted small molecule ‘FeMoco’. In the ICVS experiment, a 15 fs visible laser pulse pumps the sample to an excited electronic state, and a second <10 fs pulse probes the change in transmission as a function of the time delay. FeMoco was observed to relax to the ground state by a single exponential decay with a time constant of ~200 fs. Superimposed on this relaxation are oscillations caused by the coherent excitation of vibrational modes in both excited and ground electronic states. Fourier transformation reveals the FeMoco vibrational frequencies that are coherently excited by the short laser pulse. The frequencies obtained by the ICVS technique were compared with values from normal mode calculations. The strongest ICVS bands are at 215 and 420 cm?1. The 420 cm?1 band is attributed to Fe-S stretching motion, whereas the 215 cm?1 band, which is the strongest feature in the spectrum, is attributed to a breathing mode of FeMoco. Over the years, nitrogenase and FeMoco have resisted characterization by resonance Raman spectroscopy. The current results demonstrate the promise of ICVS as an alternative probe of FeMoco dynamics.

Delfino, Ines; Cerullo, Giulio; Cannistraro, Salvatore; Manzoni, Cristian; Polli, Dario; Dapper, Christie; Newton, William E.; Guo, Yisong; Cramer, Stephen P.

2011-01-01

284

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

285

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

286

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

287

Enhanced terahertz transmission by surface plasmon resonance  

NASA Astrophysics Data System (ADS)

The surface plasmon resonance (SPR) between metal and dielectric material has a good enhancement on electromagnetic wave transmission. In this paper, a series of two-dimension (2D) metal gratings and spiral structures with different geometrical size were experimentally tested by Terahertz time-domain spectroscopy (THz-TDS). The experiment results show that the 2D metal gratings have almost 70% increment on terahertz transmission than the pure silicon substrate in the range of 0.2-2.5THz, which indicates a strong coupling in the terahertz range, and the resonance mode shows a blue shift. On the other hand, the influence of different radiation directions was analyzed. It presents that the slightly higher transmission can be achieved when terahertz wave radiate from the front side than the back side. It reveals that surface plasmon resonance can enhance the terahertz transmission efficiently and has potential applications in security imaging, biological analysis and spectroscopy.

Wen, Yongzheng; Yang, Jiancheng; Yu, Xiaomei; Zhao, Yuejin; Liu, Xiaohua; Dong, Liquan

2012-02-01

288

Terahertz time-domain spectroscopy of D-glucose in the solution states  

NASA Astrophysics Data System (ADS)

THz transmission spectrums of different glucose solution with concentration from 1% to 70% were measured on the condition of room temperature and fewer than 4% humidity in the nitrogen environment. According to the physical model of the THz optical parameters, their refractive indexes and absorption coefficients were gotten. The results showed that with the increase of glucose concentration, the THz absorption coefficients of solution decrease linearly. The fitting relations among the refractive index, the extinction coefficient, absorption coefficient and its concentration at the frequency of 0.33, 0.6 and 0.8 THz were acquired individually. Their correlation coefficients were larger than 0.95. Analysis and discussion about them were given. The THz time domain spectroscopy technologies could realize an accuracy measurement for the concentration of glucose solution. This work was meaningful to the exploration of THz spectral response of biological samples.

Jiang, Zhao-feng; Wang, Yi-xin; Li, Xi-hui; Lu, Cheng-zhen; Liu, Wei; Sun, Ping; Miao, Lu

2013-08-01

289

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

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

290

Terahertz Surface Waves Propagating on Metals with Sub-wavelength Structure and Grating Reliefs  

NASA Astrophysics Data System (ADS)

Due to their long propagation length at a metal surface in the far infrared, surface plasmons make potentially feasible the design and realization of 2D integrated terahertz systems over a metallic substrate. In this article, we present a review of recent works dedicated to surface plasmon properties on structured metallic surfaces. We study excitation, propagation, diffraction and reflection of terahertz surface plasmon on shallow gratings and of spoof plasmons on deep sub-wavelength structures. The analysis of the experimental data supplied by terahertz time-domain spectroscopy allows us to point out the main parameters that govern this diffraction process and the propagation of a surface plasmon over a flat or corrugated metal surface.

Nazarov, M.; Coutaz, J.-L.

2011-10-01

291

Ultrafast optical pump terahertz-probe spectroscopy of strongly correlated electron materials.  

SciTech Connect

We have used optical-pump far-infrared probe spectroscopy to probe the low energy electron dynamics of high temperature superconductors and colossal magnetoresistance manganites. For the superconductor YBa2Cu3O7, picosecond conductivity measurements probe the interplay between Cooper-pairs and quasiparticles. In optimally doped films, the recovery time for long-range phase-coherent pairing increases from {approx}1.5 ps at 4K to {approx}3.5 ps near Tc, consistent with the closing of the superconducting gap. For underdoped films, the measured recovery time is temperature independent (3.5 ps) in accordance with the presence of a pseudogap. Ultrafast picosecond measurements of optically induced changes in the absolute conductivity of La0:7M0:3MnO3 thin films (M = Ca, Sr) from 10K to {approx}0.9Tc reveal a two-component relaxation. A fast, {approx}2 ps, conductivity decrease arises from optically induced modification of the effective phonon temperature. The slower component, related to spin-lattice relaxation, has a lifetime that increases upon approaching Tc from below in accordance with an increasing spin specific heat. Our results indicate that for T<

Averitt, R. D. (Richard D.); Taylor, Antoinette J.,; Thorsmølle, V. K. (Verner K.); Jia, Quanxi; Lobad, A. I.; Trugman, S. A. (Stuart A.)

2001-01-01

292

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

293

Myoglobin far-infrared absorption and protein hydration effects studied by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Absorption measurements were made of the heme protein myoglobin mixed with water from 1.2 to 98 wt% (weight percentage) in the frequency range 0.1-2.0 THz, using THz time-domain spectroscopy. It was found that the absorption is dominated by the water content, but even the driest specimens with hydration level below 4 wt% have a nearly continuous spectrum without identifiable sharp features. Inhomogeneous broadening plus the intrinsically high spectral density of vibrational modes in the region below 2.0 THz apparently combine to obscure the lowest frequency vibrational modes expected for protein molecules of this size. A continuous absorption spectrum for hydrated protein samples suggests that the absorption mechanisms are similar to those in liquid water, and hinders the spectroscopic identification of biomolecules in this frequency range. The interaction of proteins with an aqueous environment leads to a thin region of "biological water" whose molecules have properties that differ from bulk water, in particular reduced absorption of far-infrared radiation caused by protein-induced perturbation of the water dipole moment. Based on the myoglobin far-infrared absorption measurements, the effect of biological water on myoglobin is carefully studied. Measurements show that absorption per protein molecule is increased by the presence of biological water. Analysis shows greater THz absorption when compared to a non-interacting protein-water model. Including the suppressed absorption of biological water leads to a substantial hydration-dependent increase in absorption per protein molecule over a wide range of concentration and frequencies, meaning that water increases the protein's polarizability.

Zhang, Chenfeng

294

Security applications of terahertz technology  

NASA Astrophysics Data System (ADS)

Recent events have accelerated the quest for ever more effective security screening to detect an increasing variety of threats. Many techniques employing different parts of the electromagnetic spectrum from radio up to X- and gammaray are in use. Terahertz radiation, which lies between microwave and infrared, is the last part to be exploited for want, until recently, of suitable sources and detectors. This paper describes practical techniques for Terahertz imaging and spectroscopy which are now being applied to a variety of applications. We describe a number of proof-of-principle experiments which show that Terahertz imaging has the ability to use very low levels of this non-ionising radiation to detect hidden objects in clothing and common packing materials and envelopes. Moreover, certain hidden substances such as plastic explosives and other chemical and biological agents may be detected from their characteristic Terahertz spectra. The results of these experiments, coupled with availability of practical Terahertz systems which operate outside the laboratory environment, demonstrate the potential for Terahertz technology in security screening and counterterrorism.

Kemp, Michael C.; Taday, P. F.; Cole, Bryan E.; Cluff, J. A.; Fitzgerald, Anthony J.; Tribe, William R.

2003-08-01

295

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

296

A novel ultrafast terahertz wave modulator based on nonlinear medium  

NASA Astrophysics Data System (ADS)

A novel terahertz wave modulator based on guided wave resonance structure is demonstrated. The terahertz wave modulator consists of a prism-metal-polymer-metal multilayer structure. An external pump laser across the large third-order nonlinear susceptibility polymer layer modulates the energy coupling efficiency of incoming terahertz wave into guided wave resonance at fixed input angles. The reflection intensity of the terahertz-beam in the proposed structure can be flexibly tuned from near unity to zero, which is very fast on the order of ten picoseconds. This provides a strategy for constructing and studying ultrafast low-power integrated terahertz wave devices.

Li, Jiu-sheng

2013-06-01

297

Ultrafast high-field carrier transport in GaAs measured by femtosecond pump-terahertz probe spectroscopy  

Microsoft Academic Search

Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers and at electric fields up to 15 kV\\/cm. The pump-induced attenuation of THz transmission reduces obviously at high field, and the carrier relaxation time is also found to be correlated with photo-injected carrier density and electric field. These effects can be

Yulei Shi; Qing-Li Zhou; Cunlin Zhang; Bin Jin

2009-01-01

298

Optical two-photon absorption in GaAs measured by optical-pump terahertz-probe spectroscopy  

Microsoft Academic Search

Time-resolved terahertz experiments in a novel setup were used for a direct observation of the competition between the single- and two-photon absorption in highly excited GaAs. The experiments were carried out near 800nm where the single photon absorption usually dominates. The crystal surface was excited by femtosecond laser pulses with fluences up to 4.2mJ\\/cm2 , for which the single-photon absorption

F. Kadlec; H. Nemec; P. Kuzel

2004-01-01

299

Noninvasive measurements of carotenoids in bovine udder by reflection spectroscopy  

NASA Astrophysics Data System (ADS)

For a long time, the antioxidative status in cattle has been discussed as an indicator for stress conditions resulting from disease or exertion. Until now, invasive approaches have been necessary to obtain blood samples or biopsy materials and gain insights into the antioxidative status of cattle. Due to these efforts and the costs of the analyses, serial sampling is feasible in an experimental setting, but not for measurements on a routine basis. The present study focuses on the feasibility of an innovative, noninvasive spectroscopic technique that allows in vivo measurements of carotenoids in the skin by reflection spectroscopy. To this end, in a first trial, repeated measurements of the carotenoid concentration of the udder skin were performed on 25 healthy cattle from different breeds. Carotenoid concentrations showed highly significant differences between individual animals (P<0.001), although they were kept under the same environmental conditions and received the same diet. The carotenoid concentrations in "sensitive" and "robust" cows (evaluated by a temperament test) differed significantly (P<0.005), with higher concentrations observed in robust cows.

Klein, Julia; Darvin, Maxim E.; Müller, Kerstin E.; Lademann, Jürgen

2012-10-01

300

Diffuse reflectance spectroscopy: towards clinical application in breast cancer.  

PubMed

Diffuse reflectance spectroscopy (DRS) is a promising new technique for breast cancer diagnosis. However, inter-patient variation due to breast tissue heterogeneity may interfere with the accuracy of this technique. To tackle this issue, we aim to determine the diagnostic accuracy of DRS in individual patients. With this approach, DRS measurements of normal breast tissue in every individual patient are directly compared with measurements of the suspected malignant tissue. Breast tissue from 47 female patients was analysed ex vivo by DRS. A total of 1,073 optical spectra were collected. These spectra were analyzed for each patient individually as well as for all patients collectively and results were compared to the pathology analyses. Collective patient data analysis for discrimination between normal and malignant breast tissue resulted in a sensitivity of 90 %, a specificity of 88 %, and an overall accuracy of 89 %. In the individual analyses all measurements per patient were categorized as either benign or malignant. The discriminative accuracy of these individual analyses was nearly 100 %. The diagnosis was classified as uncertain in only one patient. Based on the results presented in this study, we conclude that the analysis of optical characteristics of different tissue classes within the breast of a single patient is superior to an analysis using the results of a cohort data analysis. When integrated into a biopsy device, our results demonstrate that DRS may have the potential to improve the diagnostic workflow in breast cancer. PMID:23225143

Evers, Daniel J; Nachabe, Rami; Vranken Peeters, Marie-Jeanne; van der Hage, Jos A; Oldenburg, Hester S; Rutgers, Emiel J; Lucassen, Gerald W; Hendriks, Benno H W; Wesseling, Jelle; Ruers, Theo J M

2012-12-06

301

Probing skin interaction with hydrogen peroxide using diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Hydrogen peroxide is an important oxidizing agent in biological systems. In dermatology, it is frequently used as topical antiseptic, it has a haemostatic function, it can cause skin blanching, and it can facilitate skin tanning. In this work, we investigated skin interaction with hydrogen peroxide, non-invasively, using diffuse reflectance spectroscopy. We observed transient changes in the oxyhaemoglobin and deoxyhaemoglobin concentrations as a result of topical application of dilute H2O2 solutions to the skin, with changes in deoxyhaemoglobin concentration being more pronounced. Furthermore, we did not observe any appreciable changes in melanin absorption properties as well as in the skin scattering properties. We also found no evidence for production of oxidized haemoglobin forms. Our observations are consistent with an at least partial decomposition of hydrogen peroxide within the stratum corneum and epidermis, with the resulting oxygen and/or remaining hydrogen peroxide inducing vasoconstriction to dermal blood vessels and increasing haemoglobin oxygen saturation. An assessment of the effects of topical application of hydrogen peroxide to the skin may serve as the basis for the development of non-invasive techniques to measure skin antioxidant capacity and also may shed light onto skin related disorders such as vitiligo.

Zonios, George; Dimou, Aikaterini; Galaris, Dimitrios

2008-01-01

302

Aerosol collection and analysis using diffuse reflectance infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Infrared spectroscopy is routinely employed for the identification of organic molecules and, more recently, for the classification of biological materials. We have developed a sample collection method that facilitates infrared analysis of airborne particulates using a diffuse reflectance (DR) technique. Efforts are underway to extend the method to include simultaneous analysis of vapor phase organics by using adsorbent substrates compatible with the DR technique. This series of laboratory results provides proof-of-principle for both the sample collection and data collection processes. Signal processing of the DR spectra is shown to provide rapid qualitative identification of representative aerosol materials, including particulate matter commonly found in the environment. We compare the results for such materials as bacterial spores, pollens and molds, clays and dusts, smoke and soot. Background correction analysis is shown to be useful for differentiation and identification of these constituents. Issues relating to complex mixtures of environmental samples under highly variable conditions are considered. Instrumentation development and materials research are now underway with the aim of constructing a compact sampling system for near real-time monitoring of aerosol and organic pollutants. A miniature, tilt-compensated Fourier transform spectrometer will provide spectroscopic interrogation. A series of advanced digital signal processing methods are also under development to enhance the sensor package. The approach will be useful for industrial applications, chemical and biological agent detection, and environmental monitoring for chemical vapors, hazardous air pollutants, and allergens.

Samuels, Alan C.; Wong, Diane M.; Meyer, Gerald J.; Roelant, Geoffrey J.; Williams, Barry R.; Miles, Ronald W., Jr.; Manning, Christopher J.

2004-08-01

303

Studies of protein-protein and protein-water interactions by small angle x-ray scattering, terahertz spectroscopy, ASMOS, and computer simulation  

NASA Astrophysics Data System (ADS)

The protein folding problem has been one of the most challenging subjects in biological physics due to its complexity. Energy landscape theory based on statistical mechanics provides a thermodynamic interpretation of the protein folding process. We have been working to answer fundamental questions about protein-protein and protein-water interactions, which are very important for describing the energy landscape surface of proteins correctly. At first, we present a new method for computing protein-protein interaction potentials of solvated proteins directly from SAXS data. An ensemble of proteins was modeled by Metropolis Monte Carlo and Molecular Dynamics simulations, and the global X-ray scattering of the whole model ensemble was computed at each snapshot of the simulation. The interaction potential model was optimized and iterated by a Levenberg-Marquardt algorithm. Secondly, we report that terahertz spectroscopy directly probes hydration dynamics around proteins and determines the size of the dynamical hydration shell. We also present the sequence and pH-dependence of the hydration shell and the effect of the hydrophobicity. On the other hand, kinetic terahertz absorption (KITA) spectroscopy is introduced to study the refolding kinetics of ubiquitin and its mutants. KITA results are compared to small angle X-ray scattering, tryptophan fluorescence, and circular dichroism results. We propose that KITA monitors the rearrangement of hydrogen bonding during secondary structure formation. Finally, we present development of the automated single molecule operating system (ASMOS) for a high throughput single molecule detector, which levitates a single protein molecule in a 10 microm diameter droplet by the laser guidance. I also have performed supporting calculations and simulations with my own program codes.

Kim, Seung Joong

304

A novel reflector of AZO thin films applicable for terahertz devices  

NASA Astrophysics Data System (ADS)

Despite the wide application of transparent conducting oxides in visible range, their properties and application in the terahertz range have not yet been extensively investigated. In this paper, we present a special AZO thin film - made reflector, which possesses both high reflectance in broad terahertz frequency band and high transmittance in visible range. The experimental data of the AZO films was in a good agreement to that of transfer matrix calculations. Meanwhile, the terahertz reflector of the AZO films used as reference was well verified in terahertz reflection measurement. The terahertz reflector of the AZO films is very suitable for the multispectral terahertz systems.

Lai, Wei-En; Zhu, Yao-Hua; Zhang, Huai-Wu; Wen, Qi-Ye

2013-04-01

305

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

2013-03-26

306

Terahertz superconducting plasmonic hole array.  

PubMed

We demonstrate a superconductor array of subwavelength holes with active thermal control over the resonant transmission induced by surface plasmon polaritons. The array was lithographically fabricated on a high-temperature yttrium barium copper oxide superconductor and characterized by terahertz time-domain spectroscopy. We observe a clear transition from a virtual excitation of the surface plasmon mode to a real surface plasmon mode. The highly controllable superconducting plasmonic crystals may find promising applications in the design of low-loss, large- dynamic-range amplitude modulation and surface-plasmon-based terahertz devices. PMID:21042358

Tian, Zhen; Singh, Ranjan; Han, Jiaguang; Gu, Jianqiang; Xing, Qirong; Wu, Judy; Zhang, Weili

2010-11-01

307

Optical two-photon absorption in GaAs measured by optical-pump terahertz-probe spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved terahertz experiments in a novel setup were used for a direct observation of the competition between the single- and two-photon absorption in highly excited GaAs. The experiments were carried out near 800nm where the single photon absorption usually dominates. The crystal surface was excited by femtosecond laser pulses with fluences up to 4.2mJ/cm2 , for which the single-photon absorption saturates and the two-photon absorption becomes the leading absorption mechanism. The two-photon absorption coefficient ? , its anisotropy and the depth profile of the photoexcited carriers were determined.

Kadlec, F.; N?mec, H.; Kužel, P.

2004-09-01

308

Terahertz Technology: A Boon to Tablet Analysis  

PubMed Central

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

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

2009-01-01

309

Elastomeric silicone substrates for terahertz fishnet metamaterials  

NASA Astrophysics Data System (ADS)

In this work, we characterize the electromagnetic properties of polydimethylsiloxane (PDMS) and use this as a free-standing substrate for the realization of flexible fishnet metamaterials at terahertz frequencies. Across the 0.2-2.5 THz band, the refractive index and absorption coefficient of PDMS are estimated as 1.55 and 0-22 cm-1, respectively. Electromagnetic modeling, multi-layer flexible electronics microfabrication, and terahertz time-domain spectroscopy are used in the design, fabrication, and characterization of the metamaterials, respectively. The properties of PDMS add a degree of freedom to terahertz metamaterials, with the potential for tuning by elastic deformation or integrated microfluidics.

Khodasevych, I. E.; Shah, C. M.; Sriram, S.; Bhaskaran, M.; Withayachumnankul, W.; Ung, B. S. Y.; Lin, H.; Rowe, W. S. T.; Abbott, D.; Mitchell, A.

2012-02-01

310

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

311

Novosibirsk terahertz free electron laser: instrumentation development and experimental achievements  

NASA Astrophysics Data System (ADS)

Nowadays, the Novosibirsk free electron laser (NovoFEL) is the most intense radiation source in the terahertz spectral range. It operates in the continuous mode with a pulse repetition rate of up to 11.2 MHz (5.6 MHz in the standard mode) and an average power of up to 500 W. The radiation wavelength can be precisely tuned from 120 to 240 mm with a relative line width of 0.3-1%, which corresponds to the Fourier transform limit for a micropulse length of 40-100 ps. The laser radiation is plane-polarized and completely spatially coherent. The radiation is transmitted to six user stations through a nitrogen-filled beamline. Characteristics of the NovoFEL radiation differ drastically from those of conventional low-power (and often broadband) terahertz sources, which enables obtaining results impossible with other sources, but necessitates the development of special experimental equipment and techniques. In this paper, we give a review of the instrumentation developed for control and detection of high-power terahertz radiation and for the study of interaction of the radiation with matter. Quasi-optic elements and systems, one-channel detectors, power meters, real-time imagers, spectroscopy devices and other equipment are described. Selected experimental results (continuous optical discharge, material and biology substance ablation, real-time imaging attenuated total reflection spectroscopy, speckle metrology, polarization rotation by an artificial chiral structure, terahertz radioscopy and imaging) are also presented in the paper. In the near future, after commissioning another four electron racetracks and two optical resonators, intense radiation in the range from 5 to 240 µm will be available for user experiments.

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

2010-05-01

312

Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs  

NASA Astrophysics Data System (ADS)

The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz emission spectroscopy and optical-pump terahertz-probe spectroscopy. Terahertz emission spectroscopy measurements, coupled with Monte Carlo simulations of terahertz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump terahertz-probe spectroscopy and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, it was demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch terahertz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast terahertz photonic devices.

Lloyd-Hughes, J.; Merchant, S. K. E.; Fu, L.; Tan, H. H.; Jagadish, C.; Castro-Camus, E.; Johnston, M. B.

2006-12-01

313

Homeland Security, Medical, Pharmaceutical and Non-destructive Testing Applications of Terahertz Radiation  

Microsoft Academic Search

The terahertz region of the electromagnetic spectrum (300GHz-10THz) spans the region between radio and light. Recent advances in terahertz source, detector and systems technology are enabling new applications across a number of fields, based on both terahertz imaging and spectroscopy. This paper reviews our recent work on the development of practical systems and applications in security screening for the detection

Michael Kemp

2005-01-01

314

Terahertz radar cross section measurements.  

PubMed

We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies. Our RCS measurements are performed on a scale model aircraft of size 5-10 cm in polar and azimuthal configurations, and correspond closely to RCS measurements with conventional radar on full-size objects. The measurements are performed in a terahertz time-domain system with freely propagating terahertz pulses generated by tilted pulse front excitation of lithium niobate crystals and measured with sub-picosecond time resolution. The application of a time domain system provides ranging information and also allows for identification of scattering points such as weaponry attached to the aircraft. The shapes of the models and positions of reflecting parts are retrieved by the filtered back projection algorithm. PMID:21164990

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

2010-12-01

315

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

316

Assessing Carotenoid Content in Plant Leaves with Reflectance Spectroscopy  

Microsoft Academic Search

Spectral reflectance of maple, chestnut and beech leaves in a wide range of pigment content and composition was investigated to devise a nondestructive technique for total carotenoid (Car) content estimation in higher plant leaves. Reciprocal reflectance in the range 510 to 550 nm was found to be closely related to the total pigment con- tent in leaves. The sensitivity of

Anatoly A. Gitelson; Yoav Zur; Olga B. Chivkunova; Mark N. Merzlyak

2002-01-01

317

Application of Reflectance Spectroscopy for Analysis of Higher Plant Pigments  

Microsoft Academic Search

Nondestructive techniques developed by the authors for assessment of chlorophylls, carotenoids, and anthocyanins in higher plant leaves and fruits are presented. The spectral features of leaf reflectance in the visible and near infrared regions are briefly considered. For pigment analysis only reflectance values at several specific wavelengths are required. The chlorophyll (Chl) content over a wide range of its changes

M. N. Merzlyak; A. A. Gitelson; O. B. Chivkunova; A. E. Solovchenko; S. I. Pogosyan

2003-01-01

318

Electromagnetic scattering calculations for terahertz sensing  

NASA Astrophysics Data System (ADS)

This paper presents predictions of classical electromagnetic scattering from granular material illuminated by a terahertz (THz) source. Random media models are created to represent the explosive grains, air voids and filler material commonly found in explosive devices. These constituents can cause significant volume scattering that may alter or obscure the chemical response of the explosive, thus impacting THz detection of explosives. Furthermore, the air-explosive interface may have significant roughness, and scattering from this interface may be a dominant factor - particularly in reflection spectroscopy. The volume scattering is calculated using the Quasi-Crystalline Approximation (QCA) and a Finite Difference Time Domain (FDTD) calculation; the FDTD method is also used to estimate the rough surface scattering. Results from these calculations are provided for mixtures that are representative of common classes of explosives.

Zurk, L. M.; Orlowski, B.; Sundberg, G.; Winebrenner, D. P.; Thorsos, E. I.; Chen, A.

2007-02-01

319

Influence of terahertz waves on the fiber direction of CFRP composite laminates  

NASA Astrophysics Data System (ADS)

The importance of Carbon-fiber reinforced plastics (CFRP) are widely utilized due to more high performance in engineering structures. It was well known that a nondestructive technique would be very beneficial. A new terahertz radiation has been recognized for their importance in technological applications. Recently, T-ray (terahertz ray) advances of technology and instrumentation has provided a probing field on the electromagnetic spectrum. The THz-TDS can be considered as a useful tool using general non-conducting materials; however it is quite limited to conducting materials. In order to solve various material properties, the index of refraction (n) and the absorption coefficient (?) are derived in reflective and transmission configuration using the terahertz time domain spectroscopy. However, the T-ray is limited in order to penetrate a conducting material to some degree. Here, the T-ray would not go through easily the CFRP composite laminates since carbon fibers are electrically conducting while the epoxy matrix is not. So, investigation of terahertz time domain spectroscopy (THz TDS) was made and reflection and transmission configurations were studied for a 48-ply thermoplastic PPS (poly-phenylene sulfide)-based CFRP solid laminate. It is found that the electrical conductivity of CFRP composites depends on the direction of unidirectional fibers. Also, the T-ray could penetrate a CFRP composite laminate a few ply based on the E-filed (Electrical field) of carbon fibers. The terahertz scanning images were made at the angles ranged from 0° to 180° with respect to the nominal fiber axis. So, the images were mapped out based on the electrical field (E-field) direction in the CFRP solid laminates. Also, using two-dimensional spatial Fourier transform, interface C-scan images were transformed into quantitatively angular distribution plots to show the fiber orientation information therein and to predict the orientation of the ply.

Im, Kwang-Hee; Hsu, David K.; Chiou, Chien-Ping; Barnard, Daniel J.; Yang, In-Young; Park, Je-Woong

2013-01-01

320

Assessing carotenoid content in plant leaves with reflectance spectroscopy.  

PubMed

Spectral reflectance of maple, chestnut and beech leaves in a wide range of pigment content and composition was investigated to devise a nondestructive technique for total carotenoid (Car) content estimation in higher plant leaves. Reciprocal reflectance in the range 510 to 550 nm was found to be closely related to the total pigment content in leaves. The sensitivity of reciprocal reflectance to Car content was maximal in a spectral range around 510 nm; however, chlorophylls (Chl) also affect reflectance in this spectral range. To remove the Chl effect on the reciprocal reflectance at 510 nm, a reciprocal reflectance at either 550 or 700 nm was used, which was linearly proportional to the Chl content. Indices for nondestructive estimation of Car content in leaves were devised and validated. Reflectances in three spectral bands, 510+/-5 nm, either 550+/-15 nm or 700+/-7.5 nm and the near infrared range above 750 nm are sufficient to estimate total Car content in plant leaves nondestructively with a root mean square error of less than 1.75 nmol/cm2. PMID:11950093

Gitelson, Anatoly A; Zur, Yoav; Chivkunova, Olga B; Merzlyak, Mark N

2002-03-01

321

Measurement of Hydrogen in an Alumina Ceramic by Total Reflection Infrared Spectroscopy.  

National Technical Information Service (NTIS)

Alumina-based ceramics used as high voltage insulators in neutron generator tubes have been found to outgas hydrogen under thermal treatment. In this study these ceramics were examined by infrared spectroscopy using a total reflection technique to identif...

D. R. Tallant

1981-01-01

322

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

323

Tunable terahertz fishnet metamaterial  

NASA Astrophysics Data System (ADS)

This paper describes and demonstrates a terahertz (THz) frequency tunable fishnet metamaterial (TFMM) using an electrically controlled polymer dispersed liquid crystal (PDLC) matrix. In contrast to other PDLC-based devices, the TFMM employs a novel method for encapsulating PDLC using a thin (1.5 ?m) polyimide ``skin layer'' to form a uniform surface for metal electrodes while minimizing the Fabry-Perot effect of the skin layer on the TFMM measurements. The tunability was verified by measuring the frequency shift in the reflection coefficient (0.01 THz), with an observed minimum negative refractive index of -15 at 0.55 THz.

Chang, Cheng-Ling; Wang, Wei-Chih; Lin, Hong-Ren; Ju Hsieh, Feng; Pun, Yue-Bun; Chan, Chi-Hou

2013-04-01

324

Terahertz Spectroscopy of the Bending Vibrations of Acetylene 12C2H2 and 12C2D2  

NASA Astrophysics Data System (ADS)

Several fundamental interstellar molecules, e.g., C2H2, CH4 and C3, are completely symmetric molecules and feature no permanent dipole moment and no pure rotation spectrum. As a result they have only previously been observed in the infrared. However, directly observing them with the rest of the molecular column especially when the source is spatially resolved would be very valuable in understanding chemical evolution. Vibrational difference bands provide a means to detect symmetric molecules with microwave precision using terahertz techniques. Herschel, SOFIA and ALMA have the potential to identify a number of vibrational difference bands of light symmetric species. This paper reports laboratory results on 12C2H2 and 12C2D2. Symmetric acetylene isotopologues have two bending modes, the trans bending and the cis bending. Their difference bands are allowed and occur in the microwave, terahertz, and far-infrared wavelengths, with band origins at 3500 GHz for 12C2H2 and 900 GHz for 12C2D2. Twenty 12C2H2 P branch high-J transitions and two hundred and fifty-one 12C2D2 P Q and R branch transitions have been measured in the 0.2 - 1.6 THz region with precision of 50 to 100 kHz. These lines were modeled together with prior data on the pure bending levels. Significantly improved molecular parameters were obtained for 12C2H2 and 12C2D2 with the combined data set, and new frequency and intensity predictions were made to support astrophysics applications. The research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. S. Y. was supported by an appointment to the NASA Postdoctoral Program, administrated by Oak Ridge Associated Universities through a contract with NASA.

Yu, Shanshan; Drouin, B.; Pearson, J.

2009-12-01

325

Application of near infrared reflectance spectroscopy to predict meat and meat products quality: A review  

Microsoft Academic Search

Over the past three decades, near infrared reflectance (NIR) spectroscopy has been proved to be one of the most efficient and advanced tools for the estimation of quality attributes in meat and meat products. This review focuses on the use of NIR spectroscopy to predict different meat properties, considering the literature published mainly in the last decade. Firstly, the potential

N. Prieto; R. Roehe; P. Lavín; G. Batten; S. Andrés

2009-01-01

326

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

327

Efficient estimation of reflectance parameters from imaging spectroscopy.  

PubMed

In this paper, we address the problem of efficiently recovering reflectance parameters from a single multispectral or hyperspectral image. To do so, we propose a shapelet based estimator that employs shapelets to recover the shading in the image. The optimization setting presented is based upon a three-step process. The first of these concerns the recovery of the surface reflectance and the specular coefficients through a constrained optimization approach. Second, we update the illuminant power spectrum using a simple least-squares formulation. Third, the shading is computed directly once the updated illuminant power spectrum is obtained. This yields a computationally efficient method that achieves speed-ups of nearly an order of magnitude over its closest alternative without compromising performance. We provide results on illuminant power spectrum computation, shading recovery, skin recognition and replacement of the scene illuminant, and object reflectance in real-world images. PMID:23782809

Gu, Lin; Robles-Kelly, Antonio A; Zhou, Jun

2013-06-14

328

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

2012-02-13

329

Quantitative reflection spectroscopy at the human ocular fundus  

NASA Astrophysics Data System (ADS)

A new model of the reflection of the human ocular fundus on the basis of the adding-doubling method, an approximate solution of the radiative transport equation, is described. This model enables the calculation of the concentrations of xanthophyll in the retina, of melanin in the retinal pigment epithelium and the choroid, and of haemoglobin in the choroid from fundus reflection spectra. The concentration values found in 12 healthy subjects are in excellent agreement with published data. In individual cases of pathologic fundus alterations, possible benefits to the ophthalmologic diagnostics are demonstrated.

Hammer, Martin; Schweitzer, Dietrich

2002-01-01

330

AUTONOMOUS ROVER REFLECTANCE SPECTROSCOPY WITH DOZENS OF TARGETS  

Microsoft Academic Search

Future planetary rovers will travel autonomously over the visible horizon where data collection se- quences cannot be scripted in advance. These rovers would benefit from an ability to autonomously iden- tify science targets and deploy sensors. We present an automatic method for measuring rocks using a VIS\\/NIR reflectance spectrometer and solar illumi- nation. Our approach leverages an automatic image- based

Francisco Calderon; David R. Thompson; David Wettergreen

331

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

332

Diffuse reflectance spectroscopy of pre- and post-treated oral submucous fibrosis: an in vivo study  

NASA Astrophysics Data System (ADS)

Oral submucous fibrosis (OSF) is a high risk precancerous condition characterized by changes in the connective tissue fibers of the lamina propria and deeper parts leading to stiffness of the mucosa and restricted mouth opening, fibrosis of the lining mucosa of the upper digestive tract involving the oral cavity, oro- and hypo-pharynx and the upper two-thirds of the oesophagus. Optical reflectance measurements have been used to extract diagnostic information from a variety of tissue types, in vivo. We apply diffuse reflectance spectroscopy to quantitatively monitor tumour response to chemotherapy. Twenty patients with submucous fibrosis were diagnosed with diffuse reflectance spectroscopy and treated with the chemotherapy drug, Dexamethasone sodium phosphate and Hyaluronidase injection for seven weeks and after the treatment they were again subjected to the diffuse reflectance spectroscopy. The major observed spectral alterations on pre and post treated submucous fibrosis is an increase in the diffuse reflectance from 450 to 600 nm. Normal mucosa has showed higher reflectance when compared to the pre and post-treated cases. The spectral changes were quantified and correlated to conventional diagnostic results viz., maximum mouth opening, tongue protrusion and burning sensation. The results of this study suggest that the diffuse reflectance spectroscopy may also be considered as complementary optical techniques to monitor oral tissue transformation.

Sivabalan, S.; Ponranjini Vedeswari, C.; Jayachandran, S.; Koteeswaran, D.; Pravda, C.; Aruna, P.; Ganesan, S.

2010-02-01

333

Analysis of thin film multilayer structures by reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

The optical transfer matrix formulation was applied to the analysis of thin solid film multilayer structures used in infrared detection device technology. Our analysis is similar to optimization techniques applied to optical multilayer coatings, i.e., performing simulation of spectra and obtaining best fits to experimental spectral data (targets). We present, as a example, the application of the transfer matrix method to determine the thickness of HgCdTe films attached with epoxy to CdZnTe carriers, using normal incidence reflectance spectra. MID Infrared reflection spectra were obtained using a NICOLET Magna IR 750 Fourier Transform Infrared Spectrometer, equipped with a SPECTRATECH, Inc., microscope, taking care to operate in the linear response range of the detector. The obtained thickness values of HgCdTe films and epoxy layers agree very well with those measured by photographic techniques.

Syllaios, A. J.; Bessire, D. R.; Dreiske, P. D.; Liao, P.-K.; Chandra, D.; Schaake, H. F.

1998-06-01

334

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

335

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

336

Pigmented skin lesions by VIS-NIR reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

The increase in the incidence of pigmented skin lesions in the last decade together with the fact that early detection could allow a mortality reduction has lead to the development of spectrometric diagnostic techniques applicable to dermatology. These techniques are based on the evidence that the presence of malignant cells should somehow alter the optical characteristics of epidermis with respect to the healthy one and a different reflectance spectrum should appear. The subjectivity of the clinical observation by the specialist is, in this way, substituted by an objective technique, with the improve of the specificity and the sensitivity. The aim of this work is to obtain a skin reflectance database of both benign and malignant lesions as well as of healthy skin which permits to establish algorithms and discrimination rules for a more objective identification of different pigmented skin lesions. The measure system consists of a portable visible near infrared (600-1000 nm) spectrometer (AVS-USB200, Avantes), a tungsten halogen lamp (HL-200) and fiber optics reflection probes. The parameters of that system and their variability has been tested in steady state conditions by using neutral filters and a white reference tile. A reproducibility study of both normal and pigmented skin diffuse reflectance spectra has been carried out. After that a small scale study of selected subjects have been conducted. This study has comprised the collection of spectra from different skin pigmented lesions and the clinical evaluation of its lesions characteristics by the dermatologist. The results after the analysis of the collected data are presented.

Cordo Chinea, Monica; Sendra, José R.; Lopez Silva, Sonnia M.; Viera Ramirez, Agustin

2003-04-01

337

Mars surface composition from reflectance spectroscopy: A summary  

Microsoft Academic Search

Visible and near-infrared (0.3--2.6 ..mu..m) reflectance spectra of the martian surface have been obtained primarily from earth-based telescopic observations, and multispectral images have been obtained both from spacecraft and earth-based observations. Observations in this wavelength region have confirmed the bimodal albedo distribution of surface materials, first observed visually. All spectra of Mars are characterized by strong Fe\\/sup 3 +\\/ absorptions

Robert B. Singer; Thomas B. McCord; Roger N. Clark; John B. Adams; Robert L. Huguenin

1979-01-01

338

TERAHERTZ SPECTROSCOPY OF THE BENDING VIBRATIONS OF ACETYLENE {sup 12}C{sub 2}H{sub 2}  

SciTech Connect

Twenty P-branch transitions of {sup 12}C{sub 2}H{sub 2} have been measured in the 0.8-1.6 THz region of its bending vibrational difference band. The accuracy of these measurements is estimated to be 100 kHz. The {sup 12}C{sub 2}H{sub 2} molecules were generated under room temperature by passing 150 mTorr H{sub 2}O vapor through calcium carbide (CaC{sub 2}) powder. The observed transitions were modeled together with prior far-infrared data involving the bending levels with SIGMA{sub t}V{sub t} (t = 4,5)<=2. Frequency predictions of {sup 12}C{sub 2}H{sub 2} in the terahertz region have been greatly improved by adding the first data of 'microwave' precision. The new measurements and predictions reported here will facilitate the analyses of astronomical observations by the high spectral resolution telescopes such as Herschel, SOFIA, and ALMA.

Yu Shanshan; Drouin, Brian J.; Pearson, John C., E-mail: shanshan.yu@jpl.nasa.go [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2009-11-01

339

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

340

Breast cancer tissue diagnosis at terahertz frequencies  

NASA Astrophysics Data System (ADS)

This paper investigates the feasibility of using terahertz pulsed imaging to detect breast cancer in a reflection imaging geometry. Spectroscopic terahertz data is used to simulate the reflected time domain response functions of healthy fibrous breast tissue and breast cancer tissue. Previously we have looked at the refractive index and absorption coefficient separately to characterize tissues. In this work we investigate their combined effects and identify parameters of the simulated reflected impulse response function and corresponding spectroscopic properties with a view to improving our ability to distinguish between the fibrous and cancer tissues in the breast.

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

2012-02-01

341

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

342

Understanding the composition of the lunar mare through reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

In order to quantify the spectral behavior of maturity variations in the mare, spectral trends of nearly 10,000 craters in six mare regions are examined. Radiative transfer theory is used to model these trends in order to better understand their causes. The maturity trends are confirmed to be more parallel than radial as previously suggested, and this fact is exploited to develop a new algorithm for determination of iron content in mare regions. This new mare iron algorithm better compensates for maturity than previous methods, and uncertainties due to maturity variations are less than 0.5 wt% FeO. Measured optical constants of synthetic glasses of lunar-like compositions are used to predict the optical constants of any glass of an arbitrary combination of FeO and TiO 2 content. These optical constants are employed along with radiative transfer theory to determine composition from telescopic spectra of three regional lunar pyroclastic deposits which are likely to contain large amounts of glass: the Aristarchus Plateau, Mare Humorum, and Sulpicius Gallus. The imaginary coefficient of the complex index of refraction ( k ) is derived from reflectance spectra of 30 pyroxenes. Modified Gaussian modeling is applied to these k spectra to obtain two continuum parameters and nine Gaussian parameters that describe the 1, 2, and 1.2 mm crystal field absorptions. Multiple regression results indicate that the continuum and Gaussian parameters are well predicted by pyroxene FeO and CaO contents; thus, a method to predict a complete pyroxene k spectrum from its FeO and CaO concentrations is developed. The ability of radiative transfer modeling to reproduce reflectance spectra of known composition, and extract compositional information from reflectance spectra, is examined. This model is tested using spectra of mineral mixtures, nine lunar mare soil samples studied by the Lunar Soil Characterization Consortium, and the Apollo 11 landing site. The model is able to accurately reproduce reflectance spectra of mineral mixtures, and can accurately predict mineral abundances, mineral chemistry, and particle size. Modeling of lunar spectra suggests pyroxene chemistry can have as large an effect on spectral shape as mineral abundance, and improved methods for modeling agglutinates and some pyroxenes are necessary.

Denevi, Brett Wilcox

2007-08-01

343

Detection of propranolol in pharmaceutical formulations by diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

This paper describes an analytical reflectometric method that has an objective not only the industrial quality control but also to detect possible falsifications and/or adulterations of propranolol in pharmaceutical formulations. The method is based on the diffuse reflectance measurements of the colored product (III) of the spot test reaction between propranolol hydrochloride (I) and 2,6-dichloroquinone-4-chloroimide (II) using filter paper as solid support. Spot test conditions have been investigated using experimental design in order to identify and optimize the critical factors. The factors evaluated were DCQ concentration, propranolol solvent and DCQ solvent. The best reaction conditions were achieved with the addition of 30 ?L of propranolol solution in ethanol 35% (v/v) and 30 ?L of DCQ solution at 70 mg mL -1 in acetone, in this order. All reflectance measurements were carried out at 500 nm and the linear range was from 8.45 × 10 -4 to 8.45 × 10 -2 mol L -1 ( r = 0.998). The limit of detection was 1.01 × 10 -4 mol L -1. No interference was observed from the assessed excipients and drugs. The method was applied to determine propranolol in commercial brands of pharmaceuticals. The results obtained by the proposed method were favorably compared with those given by the British Pharmacopoeia procedure.

Gotardo, Mara Andréia; Tognolli, João Olímpio; Pezza, Helena Redigolo; Pezza, Leonardo

2008-04-01

344

Terahertz and far-infrared synchrotron spectroscopy and global modeling of methyl mercaptan, CH3(32)SH.  

PubMed

In this work, terahertz and Fourier transform far-infrared (FTFIR) synchrotron spectra of methyl mercaptan, CH(3)SH, have been investigated in order to provide new laboratory information for enhanced observations of this species in interstellar molecular clouds and star-forming regions. Like its methanol cousin, methyl mercaptan has particularly rich spectra associated with its large-amplitude internal rotation that extend throughout the THz and FIR regions. We have recorded new spectra for CH(3)SH from 1.1-1.5 and 1.790-1.808 THz at the University of Cologne as well as high-resolution FTFIR synchrotron spectra from 50-550 cm(-1) at 0.001 cm(-1) resolution on the far-IR beam-line at the Canadian Light Source. Assignments are reported for rotational quantum numbers up to J ? 40 and K ? 15, and torsional states up to v(t) = 2 for the THz measurements and v(t) = 3 for the FTFIR observations. The THz and FTFIR measurements together with literature results have been combined in a global analysis of a dataset comprising a total of 1725 microwave and THz frequencies together with ~18000 FTFIR transitions, ranging up to v(t) = 2 and J(max) = 30 for MW?THz and 40 for FTFIR. The global fit employs 78 torsion-rotation parameters and has achieved a weighted standard deviation of ~1.1. A prediction list (v(t) ? 2, J ? 45 and K ? 20) has been generated from the model giving essentially complete coverage of observable CH(3)(32)SH transitions within the bandwidths of major new astronomical facilities such as HIFI (Heterodyne Instrument for the Far Infrared) on the Herschel Space Observatory, ALMA (Atacama Large Millimeter Array), SOFIA (Stratospheric Observatory For Infrared Astronomy) and APEX (Atacama Pathfinder Experiment) to close to spectroscopic accuracy. PMID:22979865

Xu, Li-Hong; Lees, R M; Crabbe, G T; Myshrall, J A; Müller, H S P; Endres, C P; Baum, O; Lewen, F; Schlemmer, S; Menten, K M; Billinghurst, B E

2012-09-14

345

Optical Characteristics of Biological Molecules in the Terahertz Gap.  

National Technical Information Service (NTIS)

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 ...

D. Woolard N. Swami R. Parthasarathy T. Globus T. Khromova

2004-01-01

346

Determination of the composition of styrene, isoprene, butadiene terpolymer by IR attenuated total reflection (ATR) spectroscopy  

NASA Astrophysics Data System (ADS)

A rapid method for quantitative determination of the composition of statistical terpolymers of styrene, butadiene, and isoprene by IR attenuated total reflection (ATR) spectroscopy is described. A quantitative model is designed with the aid of 1 H NMR spectroscopy. This method does not require that the test samples be dissolved or their thickness be monitored precisely, and records the IR spectrum of the rubber rapidly (<5 min). It is easily reproduced and has good convergence. The relative error is less than 5 %.

Orlov, A. S.; Mashukov, V. I.; Rakitin, A. R.; Novikova, E. S.

2012-07-01

347

Application of infrared spectroscopy (attenuated total reflection) for monitoring enzymatic activity on substrate films  

Microsoft Academic Search

Infrared film analysis, a method based on infrared spectroscopy in the mode of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), is demonstrated as a novel analytical method for monitoring enzymatic activity on surface-attached substrate films in the mid infrared range (400–4000 cm?1). The ATR-FTIR technique is sensitive to molecules within a distance of approximately 1 ?m from the ATR

Torben Snabe; Steffen Bjørn Petersen

2002-01-01

348

Terahertz vector beam generation using segmented nonlinear optical crystals with threefold rotational symmetry.  

PubMed

We propose and demonstrate a simple method for cylindrical vector beam generation in the terahertz frequency region using optical rectification in segmented nonlinear crystals with threefold rotational symmetry. We used segmented GaP(111) plates to generate the terahertz cylindrical vector beam, and obtained clear evidence of the beam generation with a terahertz camera. By this method, a broadband terahertz cylindrical vector beam can be generated, and the radial and azimuth modes can be easily switched. We also report on the direct observation of the longitudinal electric field components at the focal point using a terahertz time-domain spectroscopy technique. PMID:23037339

Imai, Ryo; Kanda, Natsuki; Higuchi, Takuya; Zheng, Zhu; Konishi, Kuniaki; Kuwata-Gonokami, Makoto

2012-09-24

349

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

350

Phase-resolved reflectance spectroscopy on layered turbid media  

NASA Astrophysics Data System (ADS)

In this study, we investigate the influence of layered tissue structures on the phase-resolved reflectance. As a particular example, we consider the affect of the skin, skull, and meninges on noninvasive blood oxygenation determination of the brain. In this case, it's important to know how accurate one can measure the absorption coefficient of the brain through the enclosing layers of different tissues. Experiments were performed on layered gelatin tissue phantoms and the results compared to diffusion theory. It is shown that when a high absorbing medium is placed on top of a low absorbing medium, the absorption coefficient of the lower layer is accessible. In the inverse case, where a low absorbing medium is placed on top of a high absorbing medium, the absorption coefficient of the underlying medium can only be determined if the differences in the absorption coefficient are small, or the top layer is very thin. Investigations on almost absorption and scattering free layers, like the cerebral fluid filled arachnoid, reveal that the determination of the absorption coefficient is barely affected by these kinds of structures.

Hielscher, Andreas H.; Liu, Hanli; Chance, Britton; Tittel, Frank K.; Jacques, Steven L.

1995-05-01

351

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

352

Terahertz Dynamics of Quantum-Confined Electrons in Carbon Nanomaterials  

NASA Astrophysics Data System (ADS)

Low-dimensional carbon nanostructures, such as single-wall carbon nanotubes (SWCNTs) and graphene, offer new opportunities for terahertz science and technology. Being zero-gap systems with a linear, photon-like energy dispersion, metallic SWCNTs and graphene exhibit a variety of extraordinary properties. Their DC and linear electrical properties have been extensively studied in the last decade, but their unusual finite-frequency, nonlinear, and/or non-equilibrium properties are largely unexplored, although they are predicted to be useful for new terahertz device applications. Terahertz dynamic conductivity measurements allow us to probe the dynamics of such photon-like electrons, or massless Dirac fermions. Here, we use terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy to investigate terahertz conductivities of one-dimensional and two-dimensional electrons, respectively, in films of highly aligned SWCNTs and gated large-area graphene. In SWCNTs, we observe extremely anisotropic terahertz conductivities, promising for terahertz polarizer applications. In graphene, we demonstrate that terahertz and infrared properties sensitively change with the Fermi energy, which can be controlled by electrical gating and thermal annealing.

Ren, Lei; Zhang, Qi; Nanot, Sébastien; Kawayama, Iwao; Tonouchi, Masayoshi; Kono, Junichiro

2012-08-01

353

Mars surface composition from reflectance spectroscopy: A summary  

SciTech Connect

Visible and near-infrared (0.3--2.6 ..mu..m) reflectance spectra of the martian surface have been obtained primarily from earth-based telescopic observations, and multispectral images have been obtained both from spacecraft and earth-based observations. Observations in this wavelength region have confirmed the bimodal albedo distribution of surface materials, first observed visually. All spectra of Mars are characterized by strong Fe/sup 3 +/ absorptions from the near-UV to about 0.75 ..mu..m. Darker regions show this effect to a lesser degree, and are interpreted to be less oxidized materials. In addition, dark areas have Fe/sup 2 +/ absorptions near 1.0 ..mu..m, attributed primarily to olivines and pyroxenes. There is evidence at infrared wavelengths for highly dessicated mineral hydrates and for H/sub 2/O-ice and/or adsorbed H/sub 2/O. Observations of the north polar cap show a strong H/sub 2/O-ice spectral signature but no spectral evidence for CO/sub 2/-ice, while only CO/sub 2/-ice has been identified in spectra of the south polar cap. While the brightest materials on Mars are widespread and correlate with aeolian dust, darker materials show greater mineralogic variability and are thought to be closer in petrology and physical location to their parent rock. At present the best model for the dark materials is somewhat oxidized basaltic or ultramafic rock, regionally variable in composition and details of oxidation. The bright materials appear to be finer-grained assemblages of primarily highly oxygen-sharing dessicated mineral hydrate, some ferric oxides, and other less major constituents, including a small amount of relatively unaltered mafic material. The bright materials seem likely to be primary and/or secondary alteration products of the basaltic or ultramafic dark materials.

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

1979-12-30

354

Wall relaxation of spin-polarized sodium measured by reflection spectroscopy  

NASA Astrophysics Data System (ADS)

Using reflection spectroscopy of optically pumped sodium vapor, we have performed what is to our knowledge the first direct measurement of the spatially inhomogeneous spin polarization near a glass surface. On the basis of a theoretical description of the reflection at an inhomogeneous, anisotropic medium, we deduce the magnitude of the small residual magnetization at the surface from an analysis of the optical line shape. This allows us to specify the depolarizing properties of the surface.

Grafström, Stefan; Suter, Dieter

1995-10-01

355

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

356

Negative-index metamaterial with polymer-embedded wire-pair structures at terahertz frequencies.  

PubMed

Experimental demonstrations of metamaterials with negative index of refraction have been limited to microwave and IR frequencies. In this work, a freestanding multilayer thin-film metamaterial showing a strong negative index of refraction at terahertz frequencies is fabricated and characterized. The metamaterial consists of periodically arranged H-shaped wire-pair resonant structures separated by a 14.5-microm-thick and enclosed between two 26-microm-thick layers of benzocyclobutene polymer. Complex reflection and transmission parameters of the metamaterial are measured via terahertz time-domain spectroscopy and are used for the extraction of refractive material properties. Our results show good agreement with finite element field simulations. PMID:19015708

Awad, Mohammad; Nagel, Michael; Kurz, Heinrich

2008-11-15

357

Conductivity peak, relaxation dynamics, and superconducting gap of YBa{sub 2}Cu{sub 3}O{sub 7} studied by terahertz and femtosecond optical spectroscopies  

SciTech Connect

Recent measurements at microwave, terahertz (THz), and infrared frequencies have revealed a peak in {sigma}{sub 1} below {ital T}{sub {ital c}}. Based on our THz measurements, which were performed on high quality, single crystal films of YBCO (900 and 500 A), we have found that {sigma}{sub 1} features a peak which increases in amplitude and shifts to lower temperatures as frequency changes from 1.2 to 0.4 THz. Although the quasiparticle relaxation time extracted from these results using the two-fluid Drude model exhibits an enhancement below {ital T}{sub {ital c}}, the analysis may not be adequate to account for the strong frequency dependence of the conductivity peak by the competition between the drop in scattering rate and the decreasing normal fluid density with temperature. On the contrary, we were able to account for the frequency dependent {sigma}{sub 1} by fitting with Mattis-Bardeen theory (modified to include scattering) using a slower average rate of increase of the anisotropic gap than for the BCS case as temperature decreases below {ital T}{sub {ital c}}. This is consistent with the higher normal fluid density (higher than Gorter-Casimir values) from the two-fluid model interpretation of our THz results. Thus, we have found evidence of BCS coherence factors in a high-{ital T}{sub {ital c}} superconductor with a slower than BCS gap increase below {ital T}{sub {ital c}}. We have discussed the role of coherence factors to account for the presence of the conductivity peak and the absence of the peak in NMR relaxation rate. Furthermore, we have presented a model for the quasiparticle relaxation time measured by the femtosecond pump-probe spectroscopy. This model allowed us to find a fit to the temperature-dependent energy gap function which is also consistent with the slower gap increase below {ital T}{sub {ital c}}.

Frenkel, A.; Gao, F.; Liu, Y.; Whitaker, J.F.; Uher, C. [Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States); Hou, S.Y.; Phillips, J.M. [AT& T Bell Laboratory, Murray Hill, New Jersey 07974 (United States)

1996-07-01

358

Terahertz and Far-Infrared Spectroscopy of High-J Transitions of the Ground and v_2 = 1 States of NH_3  

NASA Astrophysics Data System (ADS)

Since its first detection in 1968, ammonia was discovered as a major constituent of several planetary atmospheres. More recently, ammonia has been suggested in the atmosphere of cool brown Dwarf and is expected to be present in quantity in the atmospheres of many newly discovered exoplanets and brown dwarf stars where temperatures are in the order of 1000 K For such temperatures, spectroscopic knowledge of ammonia's IR spectrum needs to be improved both in term of line positions and intensities. Even for the two lowest vibrational levels (ground state and v_2 = 1) its large amplitude inversion motion complicates the spectral modelling and the experimental dataset have been (up to now) limited to low quantum numbers (J of about 20). We associated experimental results obtained from far infrared techniques and terahertz spectroscopy to obtain accurate energies for highly excited J levels (as high as J=35) in the ground state and v_2 = 1. This work significantly increases the experimental dataset available to support astronomical observations; we will present the techniques developed in this work as well as the spectral analysis and fit of the new dataset. P. Delorme, X. Delfosse, L. Albert, et al., Astronomy and Astrophysics, 482, 961 (2008) M.J. Burgdorf, G.S. Orton, T. Encrenaz, G.R. Davis, S.D. Sidher, E. Lellouch, B.M. Swinyard, Planetary and Space Science, 52, 379 (2004). O. Pirali and M. Vervloet, Chemical Physics Letters, 423, 376--381 (2006) F. Matsushima, H. Odashima, D. Wang, S. Tsunekawa, and K. Takagi, Jpn. J. Appl. Phys. 33, 315 (1994) B.J. Drouin, F.W. Maiwald, and J.C. Pearson, Rev. Sci. Instrum., 76, 093113 (2005)

Pirali, O.; Martin, M.-A.; Vervloet, M.; Balcon, D.; Yu, S.; Pearson, J.; Drouin, B.; Endres, C. P.; Shiraishi, T.; Kobayashi, K.; Matsushima, F.

2010-06-01

359

Subwavelength hybrid terahertz waveguides.  

PubMed

We introduce and present general properties of hybrid terahertz waveguides. Weakly confined Zenneck waves on a metal-dielectric interface at terahertz frequencies can be transformed to a strongly confined yet low-loss subwavelength mode through coupling with a photonic mode of a nearby high-index dielectric strip. We analyze confinement, attenuation, and dispersion properties of this mode. The proposed design is suitable for planar integration and allows easy fabrication on chip scale. The superior waveguiding properties at terahertz frequencies could enable the hybrid terahertz waveguides as building blocks for terahertz integrated circuits. PMID:20052215

Nam, Sung Hyun; Taylor, Antoinette J; Efimov, Anatoly

2009-12-01

360

Quantitative evaluation of pigment particles in organic layers by fibre-optics diffuse-reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Fibre-optics diffuse-reflectance spectroscopy was used to evaluate pigment quantity in art glazes. Measurements are non-invasive, without any contact, and can be performed in situ, without moving the work of art under investigation from its conservation place. Reflectance spectra are processed using Kubelka Munk theory in order to obtain scattering and absorption parameters of the samples. Assuming a linear dependance of these optical properties with the pigment volume concentration of the paint layers, we were able to evaluate pigment quantities in the samples from reflectance measurements. Results are in excellent agreement with those obtained by X-ray diffraction and micro-X-ray fluorescence.

Dupuis, G.; Menu, M.

2005-02-01

361

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...

362

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

363

Determination of energy band gap of nanocrystalline SbSI using diffuse reflectance spectroscopy  

Microsoft Academic Search

Twelve methods of determining energy band gap (Eg) of semiconductors using diffuse reflectance spectroscopy have been applied in investigations of sonochemically produced antimony sulfoiodide (SbSI) consisting of nanowires. It has been proved that the best method of determining Eg is based on simultaneous fitting of many mechanisms of absorption to the spectral dependence of Kubelka-Munk function evaluated from the diffuse

M. Nowak; B. Kauch; P. Szperlich

2009-01-01

364

Total Internal Reflection with Fluorescence Correlation Spectroscopy: Combined Surface Reaction and Solution Diffusion  

Microsoft Academic Search

Total internal reflection with fluorescence correlation spectroscopy (TIR-FCS) is a method for measuring the surface association\\/dissociation rates and absolute densities of fluorescent molecules at the interface of solution and a planar substrate. This method can also report the apparent diffusion coefficient and absolute concentration of fluorescent molecules very close to the surface. An expression for the fluorescence fluctuation autocorrelation function

Tammy E. Starr; Nancy L. Thompson

2001-01-01

365

Ligand-Receptor Kinetics Measured by Total Internal Reflection with Fluorescence Correlation Spectroscopy  

Microsoft Academic Search

Total internal reflection excitation used in combination with fluorescence correlation spectroscopy (TIR-FCS) is a method for characterizing the dynamic behavior and absolute concentrations of fluorescent molecules near or at the interface of a planar substrate and a solution. In this work, we demonstrate for the first time the use of TIR-FCS for examining the interaction kinetics of fluorescent ligands in

Alena M. Lieto; Randall C. Cush; Nancy L. Thompson

2003-01-01

366

Time-resolved reflectance spectroscopy for nondestructive assessment of fruit and vegetable quality  

Microsoft Academic Search

In the majority of food and feed, due to the microscopic spatial changes in the refractive index, visible (VIS) and near infrared (NIR) light undergoes multiple scattering events and the overall light distribution is determined more by scattering rather than absorption. Conventional steady state VIS\\/NIR reflectance spectroscopy can provide information on light attenuation, which depends both on light absorption and

Alessandro Torricelli; Lorenzo Spinelli; Maristella Vanoli; Anna Rizzolo; Paola Eccher Zerbini

2007-01-01

367

In-situ reflectance spectroscopy - analysing techniques for high-resolution pigment logging in sediment cores  

Microsoft Academic Search

The temporal resolution of marine proxy data is limited by analytically required sample size. We present in-situ reflectance spectroscopy techniques (usually applied in remote sensing) to analyse the organic fraction of marine and terrestrial sediment. From absorption band depths, photosynthesis pigment variations are derived for sediments from the upwelling region off Peru, where productivity is related to the annual variability

Bert Rein; Frank Sirocko

2002-01-01

368

Examination of passive films on metals with X-ray reflection absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Passive oxide layers on iron, nickel, copper and on their alloys were investigated with X-ray reflection absorption spectroscopy. As specimens, polished bulk metals and thin films on float glass substrates were used. The specimens were electrochemically passivated in alkaline electrolytes at some characteristic potentials and subsequently investigated with X-rays at glancing angles below as well as above the critical angle.

Borthen, P.; Hecht, D.; Abels, J.-M.; Strehblow, H.-H.

1995-02-01

369

Application of NIR reflectance spectroscopy for the identification of pharmaceutical excipients  

Microsoft Academic Search

For manufacturing of medicaments, all ingredients must be reliably identified. Wet chemistry methods for identification of cellulose ethers, used by the Pharmacopoea Europea, is time consuming and expensive. To distinguish microcristalline and powdered cellulose, only unspecific sedimentation properties are used. However, applications as well as technological and pharmacokinetic properties of cellulose and various cellulose ethers are different.NIR reflectance spectroscopy speeds

K Krämer; S Ebel

2000-01-01

370

Reflectance spectroscopy detects management and landscape differences in soil carbon and nitrogen  

Technology Transfer Automated Retrieval System (TEKTRAN)

Many studies document the successful calibration of visible and near infrared (VNIR) diffuse reflectance spectroscopy (DRS) to various soil properties. However, few studies have reported on the use of VNIR DRS to detect treatment differences in controlled experiments. Therefore, our objective in thi...

371

Prediction of olive quality using FT-NIR spectroscopy in reflectance and transmittance modes  

Technology Transfer Automated Retrieval System (TEKTRAN)

The objective of this research was to use FT-NIR spectroscopy to predict the firmness, oil content and color of two olive (Olea europaea L) varieties (‘Ayvalik’ and ‘Gemlik’). Spectral measurements were performed on the intact olives for the wavelengths of 780-2500 nm in reflectance and for 800-1725...

372

Near infrared reflectance spectroscopy (NIRS) could be used for characterization of soil nematode community  

Microsoft Academic Search

Studying soil nematofauna provides useful information on soil status and functioning but requires high taxonomic expertise. Near infrared reflectance (NIR) spectroscopy (NIRS) has been reported to allow fast and inexpensive determination of numerous soil attributes. Thus the present study aimed at assessing the potential of NIRS for determining the abundance and diversity of soil nematodes in a set of 103

Bernard G. Barthès; Didier Brunet; Bodovololona Rabary; Oumar Ba; Cécile Villenave

2011-01-01

373

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

374

Study of thermal behaviour of lac resin using specular reflectance spectroscopy  

Microsoft Academic Search

Purpose – To determine molecular level changes occurring in lac resin, due to the effect of thermal stress at different levels of temperature and baking times. Design\\/methodology\\/approach – Films of lac resin were applied on tin panels and baked at 100 and 200°C for different time intervals. The baked films were examined by specular reflectance spectroscopy, as they were otherwise

D. Bhatia; P. C. Sarkar; M. Alam

2006-01-01

375

Investigating Ultrasonic Diffraction Grating Spectroscopy and Reflection Techniques for Characterizing Slurry Properties  

SciTech Connect

The objectives of the project are to investigate the use of (1) ultrasonic diffraction grating spectroscopy (UDGS) to measure the velocity of sound in a liquid or slurry and the particle size of a slurry and (2) shear wave reflection techniques to measure the viscosity of a slurry.

Greenwood, Margaret S.; Bond, Leonard J.; Burgess, Lloyd; Brodsky, Anatol

2003-06-01

376

Assessment of Various Organic Matter Properties by Infrared Reflectance Spectroscopy of Sediments and Filters  

Microsoft Academic Search

The goal of this work was to evaluate the capability of infrared reflectance spectroscopy for a fast quantification of the elemental and molecular compositions of sedimentary and particulate organic matter (OM). A partial least-squares (PLS) regression model was used for analysis and values were compared to those obtained by traditional methods (i.e., elemental, humic and HPLC analyses). PLS tools are

G. Alaoui; M. Leger; J. Gagne; L. Tremblay

2009-01-01

377

Electrode/Electrolyte Interphase Study Using Polarization Modulated FT-IR Reflection Absorption Spectroscopy.  

National Technical Information Service (NTIS)

The polarization modulated Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS) is applied to the studies of adsorption and oxidation of Carbon monoxide (CO) on a platinum electrode in 0.5M sulfuric acid and of adsorption of cyanide on...

K. Kunimatsu H. Seki W. G. Golden J. G. Gordon M. R. Philpott

1986-01-01

378

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

379

Experimental Investigation on Terahertz Spectra of Amphetamine Type Stimulants  

NASA Astrophysics Data System (ADS)

The spectral absorption features of three amphetamine-type stimulants (ATS) belonging to illicit drugs have been studied with terahertz (THz) time-domain spectroscopy (THz-TDS) and the characteristic absorption spectra (fingerprint spectra) are obtained in the range from 0.2 to 2.5 THz. Fingerprint spectra of illicit drugs in terahertz band are bases to detect and to inspect nondestructively illicit drugs with terahertz technique. With fingerprint spectra of illicit drugs and strong penetrability for cloths, paper bags and leathered or plastic luggage terahertz technique would be better than other techniques in illicit drugs detection and inspection. Thus, this work would contribute to the building of corresponding fingerprint spectra database of illicit drugs and provide experimental bases for using of terahertz detection apparatus in drugs nondestructive detection and inspection in the future.

Sun, Jin-Hai; Shen, Jing-Ling; Liang, Lai-Shun; Xu, Xiao-Yu; Liu, Hai-Bo; Zhang, Cun-Lin

2005-12-01

380

A new, low temperature long-pass cell for mid-infrared to terahertz spectroscopy and synchrotron radiation use  

NASA Astrophysics Data System (ADS)

A new cell has been designed for accurate spectroscopic measurements in the 80-400 K temperature range with variable path lengths from 3 to more than 141 m. The spectral coverage at these temperatures ranges from the visible to less than 10 cm-1, thanks to the use of diamond windows. The design of the cryostat and vacuum setups allows vibration-free operation. The equipment provides temperature homogeneity and pressure control to better than 2% over the 100-400 K and the 0.1-1000 mbar ranges. Remote-controlled opto-mechanical systems enable in situ adjustments as well as changes of the optical path length within half an hour, in order to optimize measurement time in an open user facility. It allows then to meet the specific requirements of high resolution measurements on the Far-Infrared AILES beamline at SOLEIL as well at the LISA facility, in Créteil, in the mid-IR. This new instrument opens up the way for many experiments in the field of high-resolution gas-phase IR spectroscopy, in particular, in quantitative spectroscopy for atmospheric applications: measurements of absorption line parameters (absolute intensities, cross sections, and pressure-induced widths) using Fourier transform spectroscopy. The design and performance of the equipment are briefly presented and illustrated on spectroscopic examples.

Kwabia Tchana, Fridolin; Willaert, Fabrice; Landsheere, Xavier; Flaud, Jean-Marie; Lago, Leatitia; Chapuis, Mylène; Herbeaux, Christian; Roy, Pascale; Manceron, Laurent

2013-09-01

381

Amplifying mirrors for terahertz plasmons  

NASA Astrophysics Data System (ADS)

Semiconductor plasmons have long held out a promise for terahertz generation, but competitive plasmonic mechanisms have yet to be found. Here, we introduce amplifying terahertz mirrors: planar interfaces for two-dimensional electron channels that amplify plasmons in the presence of electron drift. In contrast to existing formulations, we develop a rigorous mode matching technique that takes the complete mode spectrum into account. Mirrors are characterized by plasmon reflection and transmission coefficients whose values can increase with drift. Amplitude and power coefficients are determined, and conditions are found for their values to exceed unity. Resonators based on different combinations of amplifying mirrors are investigated, and an asymmetric configuration (consisting of two different electron channels confined between conducting planes) whose roundtrip gain can exceed unity is identified. The unusual conditions needed for oscillation are examined in detail and the general advantages of asymmetric arrangements are highlighted. Finally, the potential of mode matching as a universal tool for plasmonics is discussed.

Sydoruk, O.; Syms, R. R. A.; Solymar, L.

2012-11-01

382

TOPICAL REVIEW: Biomedical applications of terahertz technology  

Microsoft Academic Search

We review the development of terahertz (THz) technology and describe a typical system used in biomedical applications. By considering where the THz regime lies in the electromagnetic spectrum, we see that THz radiation predominantly excites vibrational modes that are present in water. Thus, water absorption dominates spectroscopy and imaging of soft tissues. However, there are advantages of THz methods that

E. Pickwell; V. P. Wallace

2006-01-01

383

Interaction of terahertz radiation with surface and interface plasmon-phonons in AlGaAs/GaAs and GaN/Al2O3 heterostructures  

NASA Astrophysics Data System (ADS)

Surface phonon and plasmon-phonon polariton characteristics of GaAs, Al x Ga1- x As/GaAs, and GaN/Al2O3 layered structures are investigated by means of terahertz radiation reflection spectroscopy. The strong resonant absorption peaks and selective emission of the THz radiation dependent upon the lattice composition and free electron density in these layered structures are experimentally observed and analyzed.

Požela, J.; Požela, K.; Šil?nas, A.; Širmulis, E.; Jucien?, V.

2013-01-01

384

Determination of the carrier concentration in doped n-GaAs layers by Raman and light reflection spectroscopies  

Microsoft Academic Search

The carrier concentrations in Si-doped n-GaAs films have been determined by Raman and light reflection spectroscopies. The data obtained are in good agreement with the results of Hall measurements. It is shown that the light reflection and Raman spectroscopies supplement each other in determination of carrier concentrations in the range 1017-1019 cm-3.

L. P. Avakyants; P. Yu. Bokov; N. A. Volchkov; I. P. Kazakov; A. V. Chervyakov

2007-01-01

385

Detection of colon cancer by terahertz techniques  

NASA Astrophysics Data System (ADS)

Normal and cancer affected samples of colon tissue have been measured using transmission time-domain terahertz spectroscopy and continuous wave terahertz imaging. We show that it is possible to distinguish between normal and cancerous regions in the samples when they are fixed in formalin or embedded in paraffin. Plots of the refractive index of normal and cancer affected tissues as well as 2-D transmission THz images are shown. Experimental results will be presented and the conditions for discrimination between normal and affected tissue will be discussed.

Wahaia, Faustino; Valusis, Gintaras; Bernardo, Luis M.; Almeida, Abílio; Moreira, J. Agostinho; Lopes, Patricia C.; Macutkevic, Jan; Kasalynas, Irmantas; Seliuta, Dalius; Adomavicius, Ramunas; Henrique, Rui; Lopes, Machado

2011-05-01

386

Reflection of cylindrical surface waves.  

PubMed

The reflection of the radially polarized surface wave on a metal wire at an abrupt end is derived. This theory allows for straightforward calculation of the reflection coefficient, including the phase and the amplitude, which will prove useful to the many applications in nanoplasmonics and terahertz spectroscopy. The theory shows excellent quantitative agreement with past comprehensive numerical simulations for small wires and for predicting the minima in reflection for larger wires. Using this theory, the wavelength dependent reflection is calculated for gold rods of diameter 10 nm, 26 nm and 85 nm, from which the Fabry-Perot resonance wavelengths are found. The Fabry-Perot resonances show good agreement with experimentally measured surface plasmon resonances in nanorods. This demonstrates the predictive ability of the theory for applications involving widely-used nanorods, optical antennas and plasmonic resonators. PMID:20372593

Gordon, Reuven

2009-10-12

387

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

388

Terahertz surface plasmon polariton generation with metallic gratings and silicon prisms  

Microsoft Academic Search

Terahertz time-domain spectroscopy is used to generate surface plasmon polaritons via metallic gratings and silicon prisms. Grating measurements indicate efficient, narrowband coupling. Prism measurements show broadband coupling with substantial promise for guided-wave spectroscopy applications.

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

2005-01-01

389

Evaluation of contact status between probe and skin for noninvasive blood sensing with NIR reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

In non-invasive blood sensing with near-infrared (NIR) reflectance spectroscopy, optical probe usually directly contacts skin to eliminate specular reflection. Due to the direct contact, changes in contact pressure can lead to changes in internal structure and components distribution of the measured site, and thus introduces great interference into the final results. In this paper, we use self-made AOTF spectrophotometer to investigate the changes of reflectance spectrum with changing contact status for tissues in vitro (fresh porcine skin) and in vivo (two volunteers' left palms) at wavelengths ranging from 1100 nm to 1700 nm. The results show that with increasing degree of contact, energy of reflectance spectrum gradually decreases and the trend goes stable with time. However, the decreasing degree is related to wavelengths, which potentially suggests an indirect relevance with changes of components in tissues. Meanwhile, the results provide a practical solution to determining the optimum contact status between probe and skin.

Qiu, Qingjun; Xu, Kexin; Jiang, Jingying; Chen, Wen Liang

2004-07-01

390

[Sugar characterization of mini-watermelon and rapid sugar determination by near infrared diffuse reflectance spectroscopy].  

PubMed

In the present paper, the distribution of sugar level within the mini-watermelon was studied, a new sugar characterization method of mini-watermelon using average sugar level, the highest sugar level and the lowest sugar level index is proposed. Feasibility of nondestructive determination of mini-watermenlon sugar level using diffuse reflectance spectroscopy information was investigated by an experiment. PLS models for measuring the 3 sugar levels were established. The results obtained by near infrared spectroscopy agreed with that of the new method established above. PMID:23156764

Wang, Shuo; Yuan, Hong-fu; Song, Chun-feng; Xie, Jin-chun; Li, Xiao-yu; Feng, Le-ping

2012-08-01

391

Accurate determination of optical coefficients from chemical samples using terahertz time-domain spectroscopy and effective medium theory.  

PubMed

A technique for calculating the optical constants of powdered materials that have been pressed into pellets along with a diluent such as polyethylene, as is commonly used in the spectroscopy community, is introduced. The simple Beer-Lambert law typically used to calculate the optical constants has the inherent weakness that it treats the absorbing medium as a single nonporous solid, as opposed to a dielectric material embedded within a medium. This leads to a systematic underestimation of both the absorption coefficient and the refractive index, especially at low filling factors. Effective medium theory provides a way to calculate more accurate optical constants and produces similar optical constants across a wide range of filling factors, including crucially at the low filling factors commonly used experimentally. The technique can also be extended to estimate the porosity of the samples and provide a true, preparation-independent value for the optical properties of the sample material. PMID:19953174

Parrott, Edward P; Zeitler, J Axel; Gladden, Lynn F

2009-12-01

392

Terahertz wave filter based on photonic crystal  

NASA Astrophysics Data System (ADS)

In the past decade, spectroscopy and imaging in the terahertz region (0.1-10 THz) of the electromagnetic spectrum has been applied in both basic research and potential industrial applications, such as medical diagnosis, security screening, radio astronomy, atmospheric studies, short-range indoor communication, chemical, biological sensing, medical and biological imaging, and detection of explosives. In this paper, we design a narrow bandpass terahertz wave filter using three kinds of two-dimensional photonic crystals. By using finite-difference time-domain (FDTD) method, we examined the transmittance spectra for the proposed terahertz wave filter. The simulated results show that the proposed filter exhibit excellent transmission performance such as high transmission at the central frequency, adjustable bandpass, and good rejection of the sideband frequencies.

Liu, Yu-hang; Li, Jiu-sheng

2011-11-01

393

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

394

Investigation of Terra Cotta artefacts with terahertz  

NASA Astrophysics Data System (ADS)

Terahertz Time Domain Imaging has been used in the last few years for the investigation of cultural heritage. In this article, the authors demonstrate the possibility to apply it for the investigation of clay artifacts. Tomographic images were obtained of a model in reflection, and an Egyptian vessel in transmission.

Labaune, Julien; Jackson, J. Bianca; Fukunaga, Kaori; White, Jeffrey; D'Alessandro, Laura; Whyte, Alison; Menu, Michel; Mourou, Gerard

2011-10-01

395

Leaky and bound modes in terahertz metasurfaces made of transmission-line metamaterials  

NASA Astrophysics Data System (ADS)

Prism coupling and reflection spectroscopy are used to characterize bound modes within composite right/left handed terahertz metamaterial waveguides. The cavity antenna model is used to understand the polarization dependence of the radiative coupling to TM00 and TM01 waveguide modes. Furthermore, the cavity model along with transmission-line theory is used to derive a surface impedance model for a waveguide array metasurface. Qualitative agreement with the experiment is observed, including a mode splitting for p-polarized surface waves at the light line and the existence of s-polarized magnetic spoof surface plasmons.

Hon, Philip W. C.; Liu, Zhijun; Itoh, Tatsuo; Williams, Benjamin S.

2013-01-01

396

Investigating Ultrasonic Diffraction Grating Spectroscopy and Reflection Techniques for Characterizing Slurry Properties  

SciTech Connect

The particle size of a slurry and the viscosity of a liquid or slurry are both difficult to measure on-line and in real time. The objectives of this research are to develop the following methods for such measurements: (1) ultrasonic diffraction grating spectroscopy (UDGS) to measure the particle size of a slurry, (2) UDGS to measure the velocity of sound in a slurry using reflection from a grating as opposed to ultrasound traveling through a possibly dense slurry, and (3) shear wave reflection techniques to measure the viscosity of a slurry.

Greenwood, Margaret S.; Burgess, Lloyd

2004-06-01

397

Infrared reflectance spectroscopy and thermographic investigations of the Shroud of Turin.  

PubMed

In this paper we present the results of the IR investigations of the controversial Turin Shroud. Reflectance spectroscopy in the 3-5- and 8-14-microm bands was attempted in situ using commercial equipment with moderate success. Spectral comparisons are made between laboratory reflectance data and selected Shroud features. Infrared thermographic imaging was accomplished with an enhanced contrast technique using external illumination. Due to the spectral similarities of most features observed, we show that the results are inconclusive. The IR imagery yielded results that are consistent with expectations with no anomalies observed. PMID:20221156

Accetta, J S; Baumgart, J S

1980-06-15

398

Application of backward diffuse reflection spectroscopy for monitoring the state of tissues in photodynamic therapy  

SciTech Connect

The application of backward diffuse reflection (BDR) spectroscopy for in vivo monitoring the degree of haemoglobin oxygenation and concentration of photosensitisers in tissues subjected to photodynamic therapy is demonstrated. A simple experimental technique is proposed for measuring diffuse reflection spectra. The measurements are made under steady-state conditions using a fibreoptic probe with one transmitting and one receiving fibre separated by a fixed distance. Although this approach does not ensure the separation of contributions of scattering and absorption to the spectra being measured, it can be used for estimating the degree of haemoglobin oxygenation and concentration of photosensitisers in the tissues. Simple expressions for estimating the concentration of photosensitisers from the BDR spectra are presented and the accuracy of this approach is analysed. The results of application of BDR spectroscopy for monitoring various photosensitisers are considered. (special issue devoted to multiple radiation scattering in random media)

Stratonnikov, Aleksandr A; Meerovich, G A; Ryabova, A V; Savel'eva, T A; Loshchenov, V B [Natural Science Center, A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2006-12-31

399

Modelling of sensory and instrumental texture parameters in processed cheese by near infrared reflectance spectroscopy.  

PubMed

This study investigated the application of near infrared (NIR) reflectance spectroscopy to the measurement of texture (sensory and instrumental) in experimental processed cheese samples. Spectra (750 to 2498 nm) of cheeses were recorded after 2 and 4 weeks storage at 4 degrees C. Trained assessors evaluated 9 sensory properties, a texture profile analyser (TPA) was used to record 5 instrumental parameters and cheese 'meltability' was measured by computer vision. Predictive models for sensory and instrumental texture parameters were developed using partial least squares regression on raw or pre-treated spectral data. Sensory attributes and instrumental texture measurements were modelled with sufficient accuracy to recommend the use of NIR reflectance spectroscopy for routine quality assessment of processed cheese. PMID:16433962

Blazquez, Carmen; Downey, Gerard; O'Callaghan, Donal; Howard, Vincent; Delahunty, Conor; Sheehan, Elizabeth; Everard, Colm; O'Donnell, Colm P

2006-02-01

400

Near-infrared diffuse reflectance spectroscopy and neural networks for measuring nutritional parameters in chocolate samples  

Microsoft Academic Search

A rapid and non-destructive method has been developed for the characterization of chocolate samples based on diffuse reflectance near-infrared Fourier transform spectroscopy (DRIFTS) and artificial neural networks (ANNs). This methodology provides a potentially useful alternative to time-consuming chemical methods of analysis. To assess its utility, 36 chocolate samples purchased from the Spanish market were analyzed for the determination of the

J. Moros; F. A. Iñón; S. Garrigues; M. de la Guardia

2007-01-01

401

Surface barrier modulation and diffuse reflectance spectroscopy of MoO 3–WO 3 thick films  

Microsoft Academic Search

Diffuse reflectance spectroscopy in the UV–vis–NIR is employed to study the electronic transitions in MoO3–WO3 mixed oxide. The spectroscopic results were then related to the temperature profile of the surface barrier. The electronic absorptions appear to increase after reducing treatments and to decrease after oxidation. This variation of oxygen-related defects changes the doping level, which in turn, affects the dependence

C. Malagù; M. C. Carotta; S. Morandi; S. Gherardi; G. Ghiotti; A. Giberti; G. Martinelli

2006-01-01

402

Prediction of indigestible cell wall fraction of grass silage by near infrared reflectance spectroscopy  

Microsoft Academic Search

Samples of grass silages harvested at different maturities of primary growth (n=27) and regrowth (n=25) of timothy-meadow fescue swards, and samples from commercial dairy farms (n=42) were used to explore the potential of near infrared reflectance spectroscopy (NIRS) in predicting indigestible neutral detergent fibre (INDF) and digestible neutral detergent fibre (DNDF) content. The silages were analysed for cell wall (neutral

J. Nousiainen; S. Ahvenjärvi; M. Rinne; M. Hellämäki; P. Huhtanen

2004-01-01

403

X-ray Background Signals in Total Reflection X-ray Fluorescence Spectroscopy  

Microsoft Academic Search

Total Reflection X-ray Fluorescence Spectroscopy (TXRF) is widely used for wafer surface analysis. An important figure of merit is its sensitivity, defined as 3*signal\\/sqrt(background). Since the signals can be small compared to the background, it is essential to fully understand the background components when considering possible improvements. This talk describes recent experimental and theoretical progress in understanding the X-ray background

N. Takaura; A. Waldhauer; S. Brennan; P. Pianetta; S. S. Laderman; A. Fischer-Colbrie

1996-01-01

404

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

405

Time-resolved reflectance spectroscopy for non-destructive assessment of food quality  

Microsoft Academic Search

In the majority of most food and feed, visible, and near infrared light undergoes multiple scattering events and the overall\\u000a light distribution is determined more by scattering rather than absorption due to the microscopic spatial changes in the refractive\\u000a index. Conventional steady state reflectance spectroscopy can provide information on light attenuation, which depends both\\u000a on light absorption and light scattering,

Alessandro Torricelli; Lorenzo Spinelli; Davide Contini; Maristella Vanoli; Anna Rizzolo; Paola Eccher Zerbini

2008-01-01

406

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

407

Discriminant analysis of vegetable oils by near-infrared reflectance spectroscopy  

Microsoft Academic Search

Discriminant analysis of four vegetable oil types (cotton-seed, peanut, soybean and canola) was performed by near-infrared\\u000a reflectance spectroscopy. The objective of this study was to provide an alternate method to differentiate vegetable oil types\\u000a and to classify unknown oil samples. Second derivative spectra of the vegetable oils were subjected to discriminate analysis\\u000a with Mahalanobis distances principles. A four-wavelength (1704, 1802,

Karen M. Bewig; Andrew D. Clarke; Craig Roberts; Nan Unklesbay

1994-01-01

408

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

409

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

410

Quasi-DC Terahertz Electrical Conductivity Measurements of Dense Aluminum Plasma  

Microsoft Academic Search

We report on our investigation of electrical transport in ultrashort laser-heated aluminum. By measuring the complex electrical conductivity at terahertz (THz = 10^12 Hz) frequencies, we explore the dependence of electrical transport across the material phase transition from the cold solid to the dense plasma state. Using optical-pump, terahertz-probe spectroscopy, we measure the phase shifts and absorption of terahertz probe

George Rodriguez; Balakishore Yellampalle; James Glownia; Antoinette Taylor; Ki-Yong Kim

2007-01-01

411

Using near-infrared reflectance spectroscopy to investigate the effects of a moorland wildfire in the uplands of the UK  

Microsoft Academic Search

Reflectance spectroscopy has been used to predict a range of soil parameters including organic matter composition, soil carbon concentrations, and soil respiration. Its use as a low cost, rapid and non-destructive method also makes it highly favourable when investigating soil properties. Reflectance spectra contain information that reflects the composition of the sample. This technique can also be used to investigate

G. Clay; F. Worrall

2009-01-01

412

Quantitative reflectance spectroscopy of buddingtonite from the Cuprite mining district, Nevada  

SciTech Connect

Buddingtonite, an ammonium-bearing feldspar diagnostic of volcanic-hosted alteration, can be identified and, in some cases, quantitatively measured using short-wave infrared (SWIR) reflectance spectroscopy. In this study over 200 samples from Cuprite, Nevada, were evaluated by X ray diffraction, chemical analysis, scanning electron microscopy, and SWIR reflectance spectroscopy with the objective of developing a quantitative remote-sensing technique for rapid determination of the amount of ammonium or buddingtonite present, and its distribution across the site. Based upon the Hapke theory of radiative transfer from particulate surfaces, spectra from quantitative, physical mixtures were compared with computed mixture spectra. We hypothesized that the concentration of ammonium in each sample is related to the size and shape of the ammonium absorption bands and tested this hypothesis for samples of relatively pure buddingtonite. We found that the band depth of the 2.12-micron NH4 feature is linearly related to the NH4 concentration for the Cuprite buddingtonite, and that the relationship is approximately exponential for a larger range of NH4 concentrations. Associated minerals such as smectite and jarosite suppress the depth of the 2.12-micron NH4 absorption band. Quantitative reflectance spectroscopy is possible when the effects of these associated minerals are also considered.

Felzer, B.; Hauff, P.; Goetz, A.F.H. [Univ. of Colorado, Boulder, CO (United States)

1994-02-01

413

Optical pump terahertz probe studies of semiconducting polymers  

Microsoft Academic Search

Optical-pump terahertz-probe spectroscopy (OPTP) has been applied to study charge generation, transport and the evolution of the photo-induced excited states in thin film organic semiconductors, with emphasis on their relevance to photovoltaic technology. In these experiments the response of the photoexcited material to the AC electric field of a terahertz (THz) pulse was measured. From this response, the evolution of

Paul D. Cunningham

2010-01-01

414

Effect of metal permittivity on resonant properties of terahertz metamaterials  

Microsoft Academic Search

We investigate the effect of metal permittivity on resonant transmission of metamaterials by terahertz time- domain spectroscopy. Our experimental results on double split-ring resonators made from different metals confirm the recent numerical simulations (Phys. Rev. E 65, 036622 (2002)) that metamaterials exhibit permittivity-dependent resonant properties. In the terahertz regime, the measured inductive-capacitive resonance is found to strengthen with a higher

Ranjan Singh; Abul K. Azad; John F. O'Hara; Antoinette J. Taylor; Weili Zhang

2008-01-01

415

Chemical sensing and imaging with pulsed terahertz radiation  

Microsoft Academic Search

Over the past decade, terahertz spectroscopy has evolved into a versatile tool for chemically selective sensing and imaging\\u000a applications. In particular, the potential to coherently generate and detect short, and hence, broadband terahertz pulses\\u000a led to the development of efficient and compact spectrometers for this interesting part of the electromagnetic spectrum, where\\u000a common packaging materials are transparent and many chemical

Markus Walther; Bernd M. Fischer; Alex Ortner; Andreas Bitzer; Andreas Thoman; Hanspeter Helm

2010-01-01

416

Optical Nerve Detection by Diffuse Reflectance Spectroscopy for Feedback Controlled Oral and Maxillofacial Laser Surgery  

PubMed Central

Background Laser surgery lacks haptic feedback, which is accompanied by the risk of iatrogenic nerve damage. It was the aim of this study to investigate diffuse reflectance spectroscopy for tissue differentiation as the base of a feedback control system to enhance nerve preservation in oral and maxillofacial laser surgery. Methods Diffuse reflectance spectra of nerve tissue, salivary gland and bone (8640 spectra) of the mid-facial region of ex vivo domestic pigs were acquired in the wavelength range of 350-650 nm. Tissue differentiation was performed using principal component (PC) analysis followed by linear discriminant analysis (LDA). Specificity and sensitivity were calculated using receiver operating characteristic (ROC) analysis and the area under curve (AUC). Results Five PCs were found to be adequate for tissue differentiation with diffuse reflectance spectra using LDA. Nerve tissue could be differed from bone as well as from salivary gland with AUC results of greater than 88%, sensitivity of greater than 83% and specificity in excess of 78%. Conclusions Diffuse reflectance spectroscopy is an adequate technique for nerve identification in the vicinity of bone and salivary gland. The results set the basis for a feedback system to prevent iatrogenic nerve damage when performing oral and maxillofacial laser surgery.

2011-01-01

417

Characterization of material degradation in ceramic matrix composites using infrared reflectance spectroscopy  

SciTech Connect

Ceramic matrix composite materials for thermal protection systems are required to maintain operational performance in extreme thermal and mechanical environments. In-service inspection of materials capable of assessing the degree and extent of damage and degradation will be required to ensure the safety and readiness of future air vehicles. Infrared reflectance spectroscopy is an established material characterization technique capable of extracting information regarding the chemical composition of substances. The viability of this technique as a potentially powerful nondestructive evaluation method capable of monitoring degradation in thermal protection system materials subjected to extreme mechanical and thermal environments is analyzed. Several oxide-based and non-oxide-based ceramic matrix composite materials were stressed to failure in a high temperature environment and subsequently measured using infrared reflectance spectroscopy. Spectral signatures at locations along the length of the samples were compared resulting in distinct and monotonic reflectance peak changes while approaching the fracture point. The chemical significance of the observed signatures and the feasibility of infrared reflectance nondestructive evaluation techniques are discussed.

Cooney, Adam T.; Flattum-Riemers, Richard Y. [Air Force Research Laboratory, Materials and Manufacturing Directorate, NonDestructive Evaluation Branch, Wright-Patterson AFB, OH (United States); Scott, Benjamin J. [Universal Technology Corporation, Dayton, OH (United States)

2011-06-23

418

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

PubMed

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

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

2012-03-01

419

Particular features of the application of IR reflection spectroscopy methods in studies in archeology and paleontology  

NASA Astrophysics Data System (ADS)

We have considered an optical model of a porous rough surface with optical properties of objects (bone, flint) that are typical of archeology and paleontology. We have formulated an approach that makes it possible to perform mathematical processing of the IR reflection spectra of objects of this kind using standard algorithms and determine criteria that ensure obtaining reliable information on objects with a rough surface in the course of interpretation of frequencies in their IR reflection spectra. The potential of the approach has been demonstrated using as an example an investigation by the IR Fourier-transform reflection spectroscopy of mineralization processes of mammoth tusks from two paleolithic sites (14000 and 16000 BCE) located by the town of Yudinovo, Bryansk oblast, Russia.

Zolotarev, V. M.; Khlopachev, G. A.

2013-06-01

420

Water-induced modifications of GaP(100) and InP(100) surfaces studied by photoelectron spectroscopy and reflection anisotropy spectroscopy  

NASA Astrophysics Data System (ADS)

In this work, we investigate the initial interaction of water and oxygen with different surface reconstructions of GaP(100) applying photoelectron spectroscopy, low-energy electron diffraction, and reflection anisotropy spectroscopy. Surfaces were prepared by metal-organic vapour phase epitaxy, transferred to ultra-high vacuum, and exposed to oxygen or water vapour at room temperature. The (2 4) reconstructed, Ga-rich surface is more sensitive and reactive to adsorption, bearing a less ordered surface reconstruction upon exposure and indicating a mixture of dissociative and molecular water adsorption. The p(2 2)=c(4 2) P-rich surface, on the other hand, is less reactive, but shows a new surface symmetry after water adsorption. Correlating findings of photoelectron spectroscopy with reflection anisotropy spectroscopy could pave the way towards optical in-situ monitoring of electrochemical surface modifications with reflection anisotropy spectroscopy.

May, Matthias M.; Supplie, Oliver; Höhn, Christian; Zabka, Wolf-Dietrich; Lewerenz, Hans-Joachim; van de Krol, Roel; Hannappel, Thomas

2013-09-01

421

Terahertz real-time imaging for nondestructive detection  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

422

Terahertz Plasmonic Structures  

NASA Astrophysics Data System (ADS)

Here, we review the background physics of surface plasmons and plasmonic devices. In doing so, we describe how terahertz radiation can be used to excite plasmonic effects. These effects are shown to be beneficial for applications such as terahertz waveguiding, sensing, imaging and wavefront engineering.

Baragwanath, Adam J.; Gallant, Andrew J.; Chamberlain, J. Martyn

423

An efficient optically pumped terahertz laser without metal-mesh mirrors  

Microsoft Academic Search

The efficiency of a simply designed optically pumped terahertz laser is studied experimentally. The terahertz laser cavity only consists of a quartz glass tube, an antireflection-coated Ge window and a SiO2 window. The Ge crystal acts as the high-reflectivity mirror of terahertz radiation and the input coupler of pump laser instead of complicated metal-mesh mirrors. The Ge crystal is near

Liang Miao; Duluo Zuo; Yanzhao Lu; Zuhai Cheng

2010-01-01

424

Mid-IR fiber-optic reflectance spectroscopy for identifying the finish on wooden furniture.  

PubMed

Mid-IR fiber-optic reflectance spectroscopy (FORS) is a totally noninvasive infrared analytical technique allowing the investigation of artworks without the need for any sampling. The development and optimization of this analytical methodology can provide a tool that is capable of supporting conservators during the first steps of their interventions, yielding fast results and dramatically reducing the number of samples needed to identify the materials involved. Furthermore, since reflection IR spectra suffer from important spectral anomalies that complicate accurate spectral interpretation, it is important to characterize known reference materials and substrates in advance. This work aims to verify the possibility of investigating and identifying the most widely used wood finishes by means of fiber-optic (chalcogenide and metal halides) mid-infrared spectroscopy. Two historically widely employed wood finishes (beeswax, shellac) and two modern ones (a hydrogenated hydrocarbon resin and a microcrystalline wax) were investigated in an extended IR range (from 1000 to 6000 cm(-1)) with reflectance spectroscopy and with FORS. The broad spectral response of the MCT detector was exploited in order to include overtones and combination bands from the NIR spectral range in the investigation. The reflectance spectra were compared with those collected in transmission mode in order to highlight modifications to shapes and intensities, to assign absorptions, and finally to select "marker" bands indicating the presence of certain finishing materials, even when applied onto a substrate such as wood, which shows many absorptions in the mid-infrared region. After the characterization, the different products were applied to samples of aged pear wood and investigated with the same techniques in order to check the ability of mid-IR FORS to reveal the presence and composition of the product on the wooden substrate. PMID:21394452

Poli, T; Chiantore, O; Nervo, M; Piccirillo, A

2011-03-11

425

Investigation of the electrical and optical properties of iridium oxide by reflectance FTIR spectroscopy and density functional theory calculations  

Microsoft Academic Search

Variable angle reflectance FTIR spectroscopy was used to investigate the optical properties of iridium oxide thin films deposited on glass substrates in the near-IR spectral region. The reflectance was studied as a function of incident angle and wavenumber for p-polarized radiation. The Drude free-electron model along with the Fresnel equations of reflection were utilized to fit the experimental reflectance FTIR

Scott H. Brewer; Dwi Wicaksana; Jon-Paul Maria; Angus I. Kingon; Stefan Franzen

2005-01-01

426

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

NASA Astrophysics Data System (ADS)

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 plasma. To characterize the THz field, we developed and used a single-shot, high-temporal-resolution THz diagnostic capable of measuring free-space electromagnetic pulse fields in time and space. Due to relatively large focal spot sizes of the THz probe (~mm), mainly limited by the diffraction properties of THz radiation, the optical pump pulse was weakly focused onto the target in order to overfill the THz probe spot size with a peak intensity of ~1013 W/cm2. In contrast to the previous measurements of conductivities at optical frequencies, our THz non-contact probe method can directly measure quasi-DC electrical conductivities, providing insight into the transport nature of warm dense matter and any present discrepancies with the Drude model. In case of warm dense aluminum, we observe a noticeable deviation from the Drude model even in the ~1013 W/cm2 laser intensity regime. In addition, we observe strong coherent THz emission produced by a current surge in the laser-produced plasma.

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

2006-05-01

427

Quasi-DC Terahertz Electrical Conductivity Measurements of Dense Aluminum Plasma  

NASA Astrophysics Data System (ADS)

We report on our investigation of electrical transport in ultrashort laser-heated aluminum. By measuring the complex electrical conductivity at terahertz (THz = 10^12 Hz) frequencies, we explore the dependence of electrical transport across the material phase transition from the cold solid to the dense plasma state. Using optical-pump, terahertz-probe spectroscopy, we measure the phase shifts and absorption of terahertz probe pulses that are reflected from the warm (0.1˜3 eV) dense plasma. To characterize the THz field, we develop and use a single-shot, high temporal-resolution THz diagnostic capable of measuring free-space electromagnetic pulse fields in time and space. In contrast to the previous measurements of conductivities at optical frequencies, our THz non-contact probe method can directly measure quasi-DC electrical conductivities, providing insight into the transport nature of warm dense matter without dependence on conductivity models for extrapolation. Full hydrodynamic laser-foil calculations and THz Helmholtz wave equation calculations of the THz probe field show that deep penetration across the plasma gradient and into the dense solid is achieved with the THz probe. The technique demonstrates a new promising ultrafast time-resolved diagnostic capability for extracting conductivity transport.

Rodriguez, George; Yellampalle, Balakishore; Glownia, James; Taylor, Antoinette; Kim, Ki-Yong

2007-11-01

428

Methodologies and Techniques for Detecting Extraterrestrial (Microbial) Life Terahertz Circular Dichroism Spectroscopy: A Potential Approach to the In Situ Detection of Life' s Metabolic and Genetic Machinery  

Microsoft Academic Search

We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regard- less of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules ( .500 atoms) as the catalysts with which they perform their metabolic and replicative

JING XU; GERALD J. RAMIAN; JHENNY F. GALAN; PAVLOS G. SAVVIDIS; ANTHONY MICHAEL SCOPATZ; ROBERT R. BIRGE; S. JAMES ALLEN; KEVIN W. PLAXCO

429

FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Reversible Conformational Changes of PsbO Protein Detected by Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

We used a terahertz time-domain spectroscope (THz-TDS) to detect the reversible conformational changes of PsbO protein induced by N-bromosuccinimide and Guanidine Hydrochloride. The veracity and sensitivity are confirmed by the fluorescence emission spectra. The results demonstrate that THz-TDS has both advantages and disadvantages in monitoring the denaturation process of proteins, which is important in applying THz-TDS technique to studying biomolecules.

Chen, Hua; Chen, Gui-Ying; Li, Shu-Qin; Wang, Li

2009-08-01

430

Infrared reflectance spectroscopy as a characterization probe for polymer surfaces and interfaces  

NASA Astrophysics Data System (ADS)

Only recently has external reflectance infrared spectroscopy been used to acquire structural information at the molecular level at air-liquid interfaces, and particularly to characterize in situ molecular chains adsorbed at the air-water interface. This technique has been applied for the determination of chain orientation, chain conformation and packing density of small molecules such as phospholipids, fatty acids and fatty alcohols on the surface of water, and more recently of macromolecular systems. Vibrational spectroscopy, a nondestructive technique, is especially successful in the determination of the conformational order or disorder of alkyl chains (e.g. trans/gauche ratio) as well as in the evaluation of coil, helical or extended conformations in poly(amino acids). In this thesis work, the construction of a microcomputer controlled Langmuir trough optically coupled to a FT-IR instrument has allowed the direct investigation of molecular films spread at air-liquid interfaces. Order-disorder transitions and relaxation behaviors in vinyl comb-like polymeric Langmuir films have been examined using simultaneously external reflection infrared spectroscopy and surface tensiometry. The structures of several poly(amino acid) films have also been studied as a function of surface packing density at the air-water interface.

Riou, Sophie Annick

1998-12-01

431

In situ differential reflectance spectroscopy of thin crystalline films of PTCDA on different substrates  

SciTech Connect

We report an investigation of the excitonic properties of thin crystalline films of the archetypal organic semiconductor PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) grown on poly- and single crystalline surfaces. A sensitive setup capable of measuring the optical properties of ultrathin organic molecular crystals via differential reflectance spectroscopy (DRS) is presented. This tool allows to carry out measurements in situ, i.e., during the actual film growth, and over a wide spectral range, even on single crystalline surfaces with high symmetry or metallic surfaces, where widely used techniques like reflection anisotropy spectroscopy (RAS) or fluorescence excitation spectroscopy fail. The spectra obtained by DRS resemble mainly the absorption of the films if transparent substrates are used, which simplifies the analysis. In the case of mono- to multilayer films of PTCDA on single crystalline muscovite mica(0001) and Au(111) substrates, the formation of the solid state absorption from monomer to dimer and further to crystal-like absorption spectra can be monitored.

Proehl, Holger; Nitsche, Robert; Dienel, Thomas; Leo, Karl; Fritz, Torsten [Institut fuer Angewandte Photophysik, Technische Universitaet Dresden, D-01062 Dresden (Germany)

2005-04-15

432

Use of a coherent fiber bundle for multi-diameter single fiber reflectance spectroscopy  

PubMed Central

Multi-diameter single fiber reflectance (MDSFR) spectroscopy enables quantitative measurement of tissue optical properties, including the reduced scattering coefficient and the phase function parameter ?. However, the accuracy and speed of the procedure are currently limited by the need for co-localized measurements using multiple fiber optic probes with different fiber diameters. This study demonstrates the use of a coherent fiber bundle acting as a single fiber with a variable diameter for the purposes of MDSFR spectroscopy. Using Intralipid optical phantoms with reduced scattering coefficients between 0.24 and 3 mm?1, we find that the spectral reflectance and effective path lengths measured by the fiber bundle (NA = 0.40) are equivalent to those measured by single solid-core fibers (NA = 0.22) for fiber diameters between 0.4 and 1.0 mm (r ? 0.997). This one-to-one correlation may hold for a 0.2 mm fiber diameter as well (r = 0.816); however, the experimental system used in this study suffers from a low signal-to-noise for small dimensionless reduced scattering coefficients due to spurious back reflections within the experimental system. Based on these results, the coherent fiber bundle is suitable for use as a variable-diameter fiber in clinical MDSFR quantification of tissue optical properties.

Hoy, C. L.; Gamm, U. A.; Sterenborg, H. J. C. M.; Robinson, D. J.; Amelink, A.

2012-01-01

433

In vivo characterization of myocardial infarction using fluorescence and diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

We explore the feasibility of using combined fluorescence and diffuse reflectance spectroscopy to characterize a myocardial infarct at different developing stages. An animal study is conducted using rats with surgically induced myocaridal infarction (MI). In vivo fluorescence spectra at 337-nm excitation and diffuse reflectance between 400 and 900 nm are measured from the heart. Spectral acquisition is performed: 1. for normal heart tissue; 2. for the area immediately surrounding the infarct; and 3. for the infarcted tissue itself, one, two, three, and four weeks into MI development. Histological and statistical analyses are used to identify unique pathohistological features and spectral alterations associated with the investigated regions. The main alterations (p<0.05) in diffuse reflectance spectra are identified primarily between 450 and 600 nm. The dominant fluorescence alterations are increases in peak fluorescence intensity at 400 and 460 nm. The extent of these spectral alterations is related to the duration of the infarction. The findings of this study support the concept that optical spectroscopy could be useful as a tool to noninvasively determine the in vivo pathophysiological features of a myocardial infarct and its surrounding tissue, thereby providing real-time feedback to surgeons during various surgical interventions for MI.

Ti, Yalin; Chen, Poching; Lin, Wei-Chiang

2010-05-01

434

Membrane extraction of Rab proteins by GDP dissociation inhibitor characterized using attenuated total reflection infrared spectroscopy.  

PubMed

Membrane trafficking is regulated by small Ras-like GDP/GTP binding proteins of the Rab subfamily (Rab GTPases) that cycle between membranes and cytosol depending on their nucleotide state. The GDP dissociation inhibitor (GDI) solubilizes prenylated Rab GTPases from and shuttles them between membranes in the form of a soluble cytosolic complex. We use attenuated total reflection-Fourier transform infrared spectroscopy to directly observe extraction of Rab GTPases from model membranes by GDI. In their native form, most Rab GTPases are doubly geranylgeranylated at the C terminus to achieve localization to the membrane. We find that monogeranylgeranylated Rab35 and Rab1b reversibly bind to a negatively charged model membrane. Correct folding and GTPase activity of the membrane-bound protein can be evaluated. The dissociation kinetics depends on the C-terminal sequence and charge of the GTPases. The attenuated total reflection experiments show that GDI genuinely accelerates the intrinsic Rab membrane dissociation. The extraction process is characterized and occurs in a nucleotide-dependent manner. Furthermore, we find that phosphocholination of Rab35, which is catalyzed by the Legionella pneumophila protein AnkX, interferes with the ability of GDI to extract Rab35 from the membrane. The attenuated total reflection-Fourier transform infrared spectroscopy approach enables label-free investigation of the interaction between GDI and Rab GTPases in a membrane environment. Thereby, GDI is revealed to actively extract monogeranylgeranylated membrane-bound Rab GTPases and, thus, is not merely a solubilization factor. PMID:23898197

Gavriljuk, Konstantin; Itzen, Aymelt; Goody, Roger S; Gerwert, Klaus; Kötting, Carsten

2013-07-29

435

Use of a coherent fiber bundle for multi-diameter single fiber reflectance spectroscopy.  

PubMed

Multi-diameter single fiber reflectance (MDSFR) spectroscopy enables quantitative measurement of tissue optical properties, including the reduced scattering coefficient and the phase function parameter ?. However, the accuracy and speed of the procedure are currently limited by the need for co-localized measurements using multiple fiber optic probes with different fiber diameters. This study demonstrates the use of a coherent fiber bundle acting as a single fiber with a variable diameter for the purposes of MDSFR spectroscopy. Using Intralipid optical phantoms with reduced scattering coefficients between 0.24 and 3 mm(-1), we find that the spectral reflectance and effective path lengths measured by the fiber bundle (NA = 0.40) are equivalent to those measured by single solid-core fibers (NA = 0.22) for fiber diameters between 0.4 and 1.0 mm (r ? 0.997). This one-to-one correlation may hold for a 0.2 mm fiber diameter as well (r = 0.816); however, the experimental system used in this study suffers from a low signal-to-noise for small dimensionless reduced scattering coefficients due to spurious back reflections within the experimental system. Based on these results, the coherent fiber bundle is suitable for use as a variable-diameter fiber in clinical MDSFR quantification of tissue optical properties. PMID:23082287

Hoy, C L; Gamm, U A; Sterenborg, H J C M; Robinson, D J; Amelink, A

2012-09-12

436

Hygrothermal degradation of 3-glycidoxypropyltrimethoxysilane films studied by neutron and X-ray reflectivity and attenuated total reflection infrared spectroscopy.  

SciTech Connect

Thin films of organosilanes have great technological importance in the areas of adhesion promotion, durability, and corrosion resistance. However, it is well-known that water can degrade organosilane films, particularly at elevated temperatures. In this work, X-ray and neutron reflectivity (XR and NR) were combined with attenuated total reflection infrared (ATR-IR) spectroscopy to study the chemical and structural changes within thin films of (3-glycidoxypropyl)trimethoxysilane (GPS) after exposure for various periods of time to air saturated with either D{sub 2}O or H{sub 2}O at 80 C. For NR and XR, ultrathin ({approx}100 {angstrom}) films were prepared by spin-coating. Both D{sub 2}O and H{sub 2}O provide neutron scattering contrast with GPS. Variations in the neutron scattering length density (SLD) profiles (a function of mass density and atomic composition) with conditioning time were measured after drying the samples out and also swelled with H{sub 2}O or D{sub 2}O vapor at room temperature. For samples that were dried out prior to measurement, little or no change was observed for H{sub 2}O conditioning up to 3.5 days, but large changes were observed after 30 days of conditioning. The range of conditioning time for this structural change was narrowed to between 4 and 10 days with XR. The SLD profiles indicated that the top portion of the GPS film was transformed into a thick low-density layer after conditioning, but the bottom portion showed little structural change. A previous NR study of as-prepared GPS films involving swelling with deuterated nitrobenzene showed that the central portion of the film has much lower cross-link density than the region nearest the substrate. The present data show that the central portion also swells to a much greater extent with water and hydrolyzes more rapidly. The chemical degradation mechanism was identified by IR as hydrolysis of siloxane bonds. For ATR-IR, GPS films were prepared by dip-coating, which resulted in a greater and more variable thickness than for the spin-coated samples. The IR spectra revealed an increase in vicinal silanol generation over the first 3 days of conditioning followed by geminal silanol generation. Thus, the structural change detected by NR and XR roughly coincided with the onset of geminal silanol generation. Finally, little change in the reflectivity data was observed for films conditioned with D{sub 2}O at 80 C for 1 month. This indicates that hydrolysis of Si-O-Si is much slower with D{sub 2}O than with H{sub 2}O.

Tallant, David Robert; Garcia, Manuel Joseph; Majewski, Jaroslaw (Los Alamos National Lab, Los Alamos, NM); Kent, Michael Stuart; Yim, Hyun

2005-05-01

437

Characterization of surface functionality of coals by photoacoustic FTIR (PAIFT) spectroscopy, reflectance infrared microspectrometry, and X-ray photoelectron spectroscopy  

SciTech Connect

This paper illustrates detection by the technique of PhotoAcoustic Infrared Fourier Transform (PAIFT) spectroscopy of new carbonyl-type functionality at the surfaces of powdered bituminous coals, generated by both base-promoted and by thermal decomposition of precursor peroxide species, postulated as ubiquitous constituents at the surfaces of all except the most freshly prepared samples. In artificially oxidized coals, there are quantitative associations between the level of carbonyl content revealed by PAIFT spectra and plastic properties of the coals. Maceral components and mineral inclusions have been identified and characterized in sectioned, polished surfaces of Canadian bituminous coals using reflection FTIR microspectrometry; this direct examination shows promise for real-time monitoring of various reactions at surfaces.

Lynch, B.M.; Lancaster, L.; Mac Phee, J.A.

1987-04-01

438

Detection of nanoparticles by means of reflection electron energy loss spectroscopy depth profiling  

NASA Astrophysics Data System (ADS)

The various studies of nanoparticles are of great importance because of the wide application of nanotechnology. The shape and structure of the nanoparticles can be determined by transmission electron microscopy (TEM) and their chemistry by electron energy loss spectroscopy. TEM sample preparation is an expensive and difficult procedure, however. Surface sensitive, analytical techniques, such as Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are well applicable to detect the atoms that make up the nanoparticles, but cannot determine whether particle formation occurred. On the other hand, reflection electron energy loss spectroscopy (REELS) probes the electronic structures of atoms, which are strongly different for the atoms being in solution or in precipitated form. If the particle size is in the nm range, plasmon resonance can be excited in it, which appears as a loss feature in REELS spectrum. Thus, by measuring AES (XPS) spectra parallel with those of REELS, besides the atomic concentrations the presence of the nanoparticles can also be identified. As an example, the appearance of nanoparticles during ion beam induced mixing of C/Si layer will be shown.

Menyhard, M.

2013-10-01

439

Reflections  

NSDL National Science Digital Library

In this quick activity, Dracula has a hole in his house and learners help solve the problem by using a mirror and protractor to reflect incoming light out of his house. This activity introduces learners to vocabulary associated with light and optics including reflected ray, angle of incident, and angle of reflection. This Dracula-themed activity also works well during Halloween.

Little, Carlyn; Lahart, David; Meyers, Ted; Weisblat, Brooks

1997-01-01

440

Reflections  

NSDL National Science Digital Library

In this activity, learners play a game and use pattern blocks to explore mirror images and reflection. First, learners play the mirror game and try to follow everything the "leader" does but in a way that will look like a mirror image (reflections, not copies). Then, learners make reflections of each other's pattern block designs.

Exploratorium

2010-01-01

441

Terahertz spectrum of gallic acid  

NASA Astrophysics Data System (ADS)

Gallic acid is natural polyphenol compound found in many green plants. More and more experiments have demonstrated that the gallic acid has comprehensive applications. In the field of medicine, the gallic acid plays an important role in antianaphylaxis, antineoplastic, antimycotic, anti-inflammatory, antivirotic, antiasthmatic and inhibiting the degradation of insulin. It also has a lot of applications in chemical industry, food industry and light industry. So it is important to study the terahertz time-domain spectroscopy of gallic acid. Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technology based on the femtosecond laser. In this work, the spectral characteristics of gallic acid in the range of 0.4 THz to 2.6 THz have been measured by THz-TDS. We obtained its absorption and refraction spectra at room temperature. The vibration abso