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1

Terahertz reflection spectroscopy for the detection of explosives  

NASA Astrophysics Data System (ADS)

Terahertz (THz) technology has been demonstrated as a promising tool for detection of explosives and is being developed for aviation screening and sensing of improvised explosive devices. THz radiation is attractive for many applications due to its ability to penetrate through a wide range of dielectric materials including clothing, paper, cardboard, plastics, and wood. Of course, metals block THz waves as is the case for microwave, IR, and visible light. Our work has involved investigating the reflection spectroscopy of a variety of materials including explosives such as RDX and PETN, plastic explosive taggants such as DMDNB, and other organic materials. We have also investigated the changes of the reflection spectra in varying grades of sucrose. Spectral differences are observed between three grades of crystalline sugar in the region from 0.1 to 1 THz. By exploiting the unique spectral features, the discrimination capabilities of THz reflection spectroscopy points to the broad applicability of identifying a wide variety of materials.

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

2008-02-01

2

Reflection terahertz time-domain spectroscopy of RDX and HMX explosives  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

3

Spectroscopy: Nanoscale terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The advent of terahertz spectroscopy schemes that offer single-photon sensitivity, femtosecond time resolution and nanometre spatial resolution is creating new opportunities for investigating ultrafast charge dynamics in semiconductor structures.

Shigekawa, Hidemi; Yoshida, Shoji; Takeuchi, Osamu

2014-11-01

4

Picosecond dynamics of hydrated water in biomolecular solution revealed by terahertz time-domain attenuated total reflection spectroscopy  

Microsoft Academic Search

We propose a novel method to characterize hydration state in solution from dielectric responses in terahertz (THz) frequency region. Slower motion of hydrated water molecules than that of bulk water molecules results in the decrement in dielectric loss, which is detected using THz time-domain attenuated total reflection (TD-ATR) spectroscopy. By fitting experimental data with a dielectric function derived based on

T. Arikawa; M. Nagai; K. Tanaka

2007-01-01

5

FEATURE ARTICLE Terahertz Spectroscopy  

E-print Network

about 13 years ago with the demonstration that nearly single-cycle pulses of far-infrared radiation covers the spectral range from about 3 cm-1 to about 600 cm-1, also known as the far-infrared (far- IR#12;FEATURE ARTICLE Terahertz Spectroscopy Matthew C. Beard, Gordon M. Turner, and Charles A

6

Terahertz time-domain spectroscopy of biological tissues  

SciTech Connect

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

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

2008-07-31

7

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

PubMed

We use reflection terahertz spectroscopy to locate and produce three-dimensional images of air gaps between stones that resemble fractures, even of subwavelength thicknesses. This technique is found to be promising tool for sculpture and building damage evaluation as well as structural quality control in other dielectric materials. PMID:23338182

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

2013-01-20

8

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

PubMed

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

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

2014-01-01

9

Ultrabroadband reflective polarization convertor for terahertz waves  

NASA Astrophysics Data System (ADS)

We design and experimentally demonstrate an ultrathin, ultrabroadband, and highly efficient reflective linear polarization convertor or half-wave retarder operating at terahertz frequencies. The metamaterial-inspired convertor is composed of metallic disks and split-ring resonators placed over a ground plane. The structure exhibits three neighboring resonances, by which the linear polarization of incident waves can be converted to its orthogonal counterpart upon reflection. For an optimal design, a measured polarization conversion ratio for normal incidence is greater than 80% in the range of 0.65-1.45 THz, equivalent to 76% relative bandwidth. The mechanism for polarization conversion is explained via decomposed electric field components that couple with different resonance modes of the structure. The proposed metamaterial design for enhancing efficiency of polarization conversion has potential applications in the area of terahertz spectroscopy, imaging, and communications.

Cheng, Yong Zhi; Withayachumnankul, Withawat; Upadhyay, Aditi; Headland, Daniel; Nie, Yan; Gong, Rong Zhou; Bhaskaran, Madhu; Sriram, Sharath; Abbott, Derek

2014-11-01

10

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

11

Terahertz wide aperture reflection tomography  

NASA Astrophysics Data System (ADS)

We describe a powerful imaging modality for terahertz (THz) radiation, THz wide aperture reflection tomography (WART). Edge maps of an object's cross section are reconstructed from a series of time-domain reflection measurements at different viewing angles. Each measurement corresponds to a parallel line projection of the object's cross section. The filtered backprojection algorithm is applied to recover the image from the projection data. To our knowledge, this is the first demonstration of a reflection computed tomography technique using electromagnetic waves. We demonstrate the capabilities of THz WART by imaging the cross sections of two test objects.

Pearce, Jeremy; Choi, Hyeokho; Mittleman, Daniel M.; White, Jeff; Zimdars, David

2005-07-01

12

Reflective terahertz tunable polarization controller  

NASA Astrophysics Data System (ADS)

This paper proposes an optical device which can continuously change the polarization state of terahertz (THz) waves. The device consists of metal gate, anti-reflection coatings, liquid crystal and mirror. By changing the refractive index of liquid crystal in the interface between the metal gate and the mirror, the phase difference between two beams with orthogonal polarization is varied and a continuous phase shift is achieved. The phase shift of the device is calculated by using the finite difference time domain (FDTD) method, and the transmittance and reflectance are calculated by using the rigorous coupled wave analysis (RCWA) method. The results reveal that the structure can realize continuously tunable phase shift for THz wave at 1 THz.

Niu, Chao; Chang, Sheng-jiang

2012-07-01

13

Terahertz Time-Domain Spectroscopy  

Microsoft Academic Search

Terahertz time-domain spectroscopy (THz-TDS) is a technique in which the time-dependent electric field of a THz wave is measured after it interacts with a sample and compared to a reference measurement in which there is no sample. This technique, developed originally in the 1980's, has evolved into a powerful and versatile probing method because of the unique ways in which

Jason D. Readle

14

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

15

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.

2011-03-01

16

Picosecond dynamics of water and heavy water investigated by using terahertz time-domain attenuated total reflection spectroscopy  

Microsoft Academic Search

We have determined the complex dielectric constant of water and heavy water in the range from 0.2 to 3.5 THz from 269 to 362 K by employing THz time-domain attenuated total reflection spectroscopy. We find the THz component can be assigned not only to the Debye relaxation but also a vibration mode, which is found in other complimentary experiments.

H. Yada; M. Nagai; K. Tanaka

2007-01-01

17

TIME-RESOLVED TERAHERTZ TRANSMISSION SPECTROSCOPY OF DIELECTRICS  

E-print Network

Republic. Using the method of time-domain terahertz-transmission spectroscopy we measured the far-infrared Terahertz pulses; far infrared; time-resolved spectroscopy INTRODUCTION The time-domain terahertzTIME-RESOLVED TERAHERTZ TRANSMISSION SPECTROSCOPY OF DIELECTRICS PETR KUZEL AND JAN PETZELT

KuÂ?el, Petr

18

Compressed sensing pulse-echo mode terahertz reflectance tomography  

E-print Network

terahertz (THz) reflectance tomography, where scattered THz waveforms are measured using a high in AOS THz-TDS. © 2009 Optical Society of America OCIS codes: 110.6795, 110.3010. In classical terahertzCompressed sensing pulse-echo mode terahertz reflectance tomography Kyung Hwan Jin,1 Youngchan Kim

19

Metamaterial-Enhanced Nonlinear Terahertz Spectroscopy  

E-print Network

We demonstrate large nonlinear terahertz responses in the gaps of metamaterial split ring resonators in several materials and use nonlinear THz transmission and THz-pump/THz-probe spectroscopy to study the nonlinear responses ...

Hwang, Harold Young

20

Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

Stoik, Christopher D.

21

Terahertz time-domain spectroscopy and application on peanut oils  

NASA Astrophysics Data System (ADS)

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

Li, Jiusheng; Yao, Jianquan; Li, Jianrui

2008-12-01

22

Ultrafast semiconductor spectroscopy using terahertz electromagnetic pulses  

Microsoft Academic Search

Terahertz electromagnetic pulses can serve as a new and unique tool for various types of spectroscopy. We first characterized the temporal and spatial properties of THz pulses generated from a large-aperture photoconductive antena, and then used them for the study of the ultrafast dynamics of electrons in semiconductros. We studied the dynamics of electrons generated by femtosecond optical pulses with

Toshiaki Hattori; Satoshi Arai; Keisuke Ohta; Aya Mochiduki; Shin-ichi Ookuma; Keiji Tukamoto; Rakchanok Rungsawang

2005-01-01

23

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.

24

A promising diagnostic method: Terahertz pulsed imaging and spectroscopy  

PubMed Central

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

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

2011-01-01

25

Terahertz magneto-spectroscopy of transient plasmas in semiconductors  

Microsoft Academic Search

Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have\\u000aperformed picosecond time-resolved THz spectroscopy of transient carriers in\\u000asemiconductors. Specifically, we measured the temporal evolution of THz\\u000atransmission and reflectivity after NIR excitation. We systematically\\u000ainvestigated transient carrier relaxation in GaAs and InSb with varying NIR\\u000aintensities and magnetic fields. Using this information, we were able to\\u000adetermine the

M. A. Zudov; A. P. Mitchell; A. H. Chin; J. Kono

2002-01-01

26

Temperature-Dependent Terahertz Spectroscopy of Liquid n-alkanes  

E-print Network

Temperature-Dependent Terahertz Spectroscopy of Liquid n-alkanes Jonathan P. Laib & Daniel M alkanes. We study all of the liquid alkanes from pentane (C5) to hexadecane (C16) over the temperature-molecular interactions in non-polar hydrocarbons. Keywords Alkane . Terahertz The normal alkanes have been the subject

Mittleman, Daniel

27

Spectroscopy of Nafion in terahertz frequency range  

NASA Astrophysics Data System (ADS)

We report results on the terahertz (THz) spectroscopy of polymer Nafion. Using THz pulse spectroscopy and refined post-processing algorithms based on the ill-posed spectroscopic inverse problem analysis, we find the complex dielectric permittivity of Nafion to be in the range 0.15-1.5 THz. The results in the low-frequency (gigahertz) range agree well with known measurements. We find that the complex dielectric permittivity can be described well using the double-Debye model with relaxation times of 7.20 ± 0.05 ps and 0.12 ± 0.05 ps. This result is discussed briefly from the viewpoint of the appearance of a segregated structure in the "Nafion-water" system.

Yurchenko, Stanislav O.; Zaytsev, Kirill I.

2014-09-01

28

Reflective terahertz imaging with the TEM01 mode laser beam.  

PubMed

Reflective terahertz imaging with a first-order Hermite-Gaussian laser beam was experimentally investigated. High spatial resolution targets prepared by direct laser microprocessing were used to evaluate the performance. The reflection imaging system at 2.524 THz frequency demonstrated up to diffraction limited resolution using the single focusing mirror with the numerical aperture not smaller than 0.6. The TEM(01) mode laser beam was also applied for practical samples such as silicon solar cell terahertz (THz) imaging. It is shown that usage of appropriate optics enables us to obtain high-quality THz images with the multimode laser beam. PMID:23938412

Kašalynas, Irmantas; Venckevi?ius, Rimvydas; Tumonis, Laurynas; Voisiat, Bogdan; Seliuta, Dalius; Valušis, Gintaras; Ra?iukaitis, Gediminas

2013-08-10

29

Tissue characterization using terahertz pulsed imaging in reflection geometry  

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

30

New Development for Terahertz Spectroscopy in Lille  

NASA Astrophysics Data System (ADS)

Terahertz domain is particularly interesting for spectroscopy of atmospheric species since the rotational spectra of light molecules like water or methanol have their absorption maximum in this range. Up to few years ago the source commonly used in terahertz domain were the backward wave oscillators. These radiation sources provide relatively high output power (several milliwatts) in the frequency range up to 1.2 THz However the BWOs are not easy to handle: they need high voltage supply (2 - 6 kV), water cooling, magnetic field up to 1 Tesla, and a phase locked loop to give accurate frequency measurements. With the arrival of telescopes working in the THz range, great improvements were achieved in the development of solid state devices based on Schottky diodes. The new spectrometer in Lille take advantage of this development and is now based on a frequency multiplication chain using these devices. The spectrometer covers more than 80% of the frequency range 0.05 - 1.5 THz, and we need about 150 hours to record the spectra in this range with high resolution. We will present two short-term projects for the spectrometer. The first one is to increase the frequency range up to 1.9 THz in order to have the full coverage of Herschel telescope. The second one is to speed up the experimental setup. Recently we have shown that one can obtain high resolution and high precision broadband spectra with a high recording rate using a DDS synthesizer in the phase-locked loop of a BWO1. Such fast-scan spectroscopy is particularly interesting for unstable species2,3. Our project is to couple a DDS synthesizer with a 10 - 20 GHz reference synthesizer and a frequency multiplication chain to obtain fast-scan solid state spectrometer. This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI. This work was also done under Ukrainian-French CNRS-PICS 6051 project

Margulès, L.; Motiyenko, R. A.; Alekseev, E. A.

2014-06-01

31

Terahertz quantum well photodetectors with reflection-grating couplers  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

32

High-resolution broadband terahertz spectroscopy via electronic heterodyne detection of photonically generated terahertz frequency comb.  

PubMed

We report an alternative approach to the terahertz frequency-comb spectroscopy (TFCS) based on nonlinear mixing of a photonically generated terahertz pulse train with a continuous wave signal from an electronic synthesizer. A superlattice is used as a nonlinear mixer. Unlike the standard TFCS technique, this approach does not require a complex double-laser system but retains the advantages of TFCS-high spectral resolution and wide bandwidth. PMID:25360955

Pavelyev, D G; Skryl, A S; Bakunov, M I

2014-10-01

33

Synchrotron Terahertz Spectroscopy of Solids under Extreme Conditions  

SciTech Connect

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

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

2010-02-03

34

Ultrabroadband terahertz spectroscopies of biomolecules and water  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

35

Terahertz spectroscopy for the assessment of burn injuries in vivo.  

PubMed

A diagnosis criterion is proposed for noninvasive grading of burn injuries using terahertz radiation. Experimental results are presented from in vivo terahertz time-domain spectroscopy of second- and third-degree wounds, which are obtained in a 72-hour animal study. During this period, the change in the spectroscopic response of the burned tissue is studied. It is shown that terahertz waves are sensitive not only to the postburn formation of interstitial edema, but also to the density of skin structures derived from image processing analysis of histological sections. Based on these preliminary results, it is suggested that the combination of these two effects, as probed by terahertz spectroscopy of the tissue, may ultimately be used to differentiate partial-thickness burns that will naturally heal from those that will require surgical intervention. PMID:23860943

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

2013-07-01

36

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

37

Far-infrared signature of animal tissues characterized by terahertz time-domain spectroscopy  

E-print Network

Far-infrared signature of animal tissues characterized by terahertz time-domain spectroscopy terahertz time-domain spectroscopy characterization of various animal tissues obtained from pork and rats; 87.80.Ã?y Keywords: Terahertz time-domain spectroscopy; Animal tissue; Water content; Absorption

38

"Developing terahertz spectroscopy to be used for the study of bio-materials."  

E-print Network

"Developing terahertz spectroscopy to be used for the study of bio-materials." Tatiana Globus and medical applications. Our research encompasses optical and terahertz spectroscopy of biological;RECENT RESEARCH DEVELOPMENTS · Highly resolved sub-terahertz vibrational spectroscopy of biological

Acton, Scott

39

High-speed terahertz reflection three-dimensional imaging for nondestructive  

E-print Network

* dsyee@kriss.re.kr Abstract: We demonstrate high-speed terahertz (THz) reflection three- dimensional (3D, M. Jewariya, M. Nagai, T. Araki, and T. Yasui, "Real-time line projection for fast terahertz International Conference on Infrared Millimeter and Terahertz Waves (IRMMW-THz) (2010). 13. B. Schulkin and D

40

Fundamentals of Measurement in Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a main spectroscopic modality to fill the frequency range between a few hundred gigahertz to a few terahertz. This spectrum has been known as "terahertz gap" owing to limited accessibility by conventional electronic and optical techniques. Over the past two decades, THz-TDS has evolved substantially with enhanced compactness and stability. Since THz-TDS is becoming an industrial standard, the performance and precision of the system are of prime importance. This article provides an overview on terahertz metrology, including parameter estimation, signal processing, measurement characteristics, uncertainties, and calibrations. The overview serves as guidance for metrology and further developments of THz-TDS systems.

Withayachumnankul, Withawat; Naftaly, Mira

2014-08-01

41

Broadband terahertz spectroscopy of polypropylenes with different tacticities  

NASA Astrophysics Data System (ADS)

We apply Fourier transform terahertz spectroscopy to an investigation of polypropylenes (PPs) with different tacticities. Terahertz (THz) absorption spectra were measured for isotactic, syndiotactic, and atactic samples over a frequency range of 1–11 THz. A clear difference in the spectra of the isotactic and syndiotactic PPs was observed, while that of the atactic PP did not display any clear characteristic absorption peaks. The spectral differences are thought to originate from not only the primary structure but also intermolecular vibrations of the well-packed PP-chains in the crystal structure. Broadband THz spectroscopy offers a nondestructive, noninvasive inspection technique for general-purpose plastics.

Ariyoshi, S.; Hiroshiba, N.; Tanzawa, Y.; Ichikawa, Y.; Bae, J.

2014-12-01

42

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

43

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

44

Terahertz Spectroscopy of Water Vapors, Chemical Vapors and Ionized Air  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

45

Quality control of leather by terahertz time-domain spectroscopy.  

PubMed

We use terahertz time-domain spectroscopy, combined with effective-medium theory, to measure the moisture content and thickness of leather simultaneously. These results demonstrate that this method could become a standard quality control test for the industrial tanning process. PMID:25607861

Hernandez-Serrano, A I; Corzo-Garcia, S C; Garcia-Sanchez, E; Alfaro, M; Castro-Camus, E

2014-11-20

46

Terahertz time-domain spectroscopy characterization of the  

E-print Network

Terahertz time-domain spectroscopy characterization of the far-infrared absorption and index February 6, 2004 The far-infrared absorption and index of refraction of high-resistivity, float for the absorption of this most transparent dielectric material in the far infrared shows unprecedented transparency

47

Silicon beam splitter for far-infrared and terahertz spectroscopy  

E-print Network

Silicon beam splitter for far-infrared and terahertz spectroscopy Christopher C. Homes,1,2, * G several Mylar beam splitters to span the entire far-infrared region. In addition to superior long, effec- tively restricting it to the far-infrared region. The alkali­halide materials that are typically

Homes, Christopher C.

48

Squeezing Terahertz Light into Nanovolumes: Nanoantenna Enhanced Terahertz Spectroscopy (NETS) of Semiconductor Quantum Dots.  

PubMed

Terahertz spectroscopy has vast potentialities in sensing a broad range of elementary excitations (e.g., collective vibrations of molecules, phonons, excitons, etc.). However, the large wavelength associated with terahertz radiation (about 300 ?m at 1 THz) severely hinders its interaction with nano-objects, such as nanoparticles, nanorods, nanotubes, and large molecules of biological relevance, practically limiting terahertz studies to macroscopic ensembles of these compounds, in the form of thick pellets of crystallized molecules or highly concentrated solutions of nanomaterials. Here we show that chains of terahertz dipole nanoantennas spaced by nanogaps of 20 nm allow retrieving the spectroscopic signature of a monolayer of cadmium selenide quantum dots, a significant portion of the signal arising from the dots located within the antenna nanocavities. A Fano-like interference between the fundamental antenna mode and the phonon resonance of the quantum dots is observed, accompanied by an absorption enhancement factor greater than one million. NETS can find immediate applications in terahertz spectroscopic studies of nanocrystals and molecules at extremely low concentrations. Furthermore, it shows a practicable route toward the characterization of individual nano-objects at these frequencies. PMID:25422163

Toma, Andrea; Tuccio, Salvatore; Prato, Mirko; De Donato, Francesco; Perucchi, Andrea; Di Pietro, Paola; Marras, Sergio; Liberale, Carlo; Proietti Zaccaria, Remo; De Angelis, Francesco; Manna, Liberato; Lupi, Stefano; Di Fabrizio, Enzo; Razzari, Luca

2015-01-14

49

Terahertz Spectroscopy Comes of Age Mark Sherwin  

E-print Network

different manner, and perhaps even not at all in Germany". From talk by G. Williams #12;Terahertz (Far Wavelength 30 µm 300 µm NaCl KBr #12;Fourier-Transform IR spectrometer October 7, 2010 ITST, 1587 (1988) Not the superconducting energy gap #12;23 years later-- ITST video-rate THz

Ahlers, Guenter

50

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

Microsoft Academic Search

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

Eyal Gerecht; Lixing You

2008-01-01

51

[Applications of terahertz spectroscopy in illicit drugs detection].  

PubMed

Abstract The present paper reviewed our recent research on illicit drugs detection by using terahertz (THz) spectroscopy technique. First, we found a THz spectral database which contains 38 types of pure illicit drugs. Second, we employ the artificial neural network (ANN) and support vector machine (SVM) methods as useful automatic tools to identify the illicit drugs. Third, a theoretical and experimental method has been developed to confirm the illicit drug purity and effective component content. Forth, Gaussian Software was used for spectral analysis of some individual samples, such as MA, ketamine, heroin, etc. Fifth, we built a smart portable Terahertz time domain spectroscopy system (THz-TDS). These works provide a solid scientific foundation for illicit drug identification by using THz spectroscopy technique. And also, as a complement detection approach, it will serve public security work. PMID:24369629

He, Ting; Shen, Jing-ling

2013-09-01

52

Step-scan time-domain terahertz magneto-spectroscopy.  

PubMed

We present a novel approach for terahertz time-domain spectroscopy of magneto-optic phenomena. The setup used in this work combines a tabletop pulsed magnet and a standard terahertz time-domain spectroscopy system. The approach is based on repetitive operation of the pulsed magnet and step-wise increment of the delay time of the time-domain spectroscopy system. The method is demonstrated by plotting the magneto-transmission spectra of linearly polarized THz pulses through the hole gas of a Ge sample and the electron gas of GaAs, InSb and InAs samples. Cyclotron resonance spectra are displayed in the frequency range from 200 GHz to 2 THz and for a magnetic field up to 6 T. The GaAs spectra are analyzed in more detail using simulations based on the Drude model. PMID:22418476

Molter, D; Torosyan, G; Ballon, G; Drigo, L; Beigang, R; Léotin, J

2012-03-12

53

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

54

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

SciTech Connect

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

Kashiwagi, T.; Minami, H.; Kadowaki, K. [Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8571 (Japan); Division of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Nakade, K.; Saiwai, Y.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y. [Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8571 (Japan); Markovi?, B.; Mirkovi?, J. [Faculty of Sciences, University of Montenegro, George Washington Str., 81000 Podgorica (Montenegro); Tsujimoto, M. [Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Yamamoto, T. [National Institute for Materials Science, Wide Bandgap Materials Group, Optical and Electronic Materials Unit, Environment and Energy Materials Division, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

2014-01-13

55

Terahertz and Infrared Spectroscopy of Gated Large-Area Graphene Zhengzong Sun,  

E-print Network

Terahertz and Infrared Spectroscopy of Gated Large-Area Graphene Lei Ren, Qi Zhang, Jun Yao, Department of Mechanical Engineering and Materials Science, and ¶ Department of Physics and Astronomy, Rice and infrared waves. Using time-domain terahertz spectroscopy and Fourier- transform infrared spectroscopy

Kono, Junichiro

56

Narrow-Line Waveguide Terahertz Time-Domain Spectroscopy of Aspirin and Aspirin Precursors  

E-print Network

Narrow-Line Waveguide Terahertz Time-Domain Spectroscopy of Aspirin and Aspirin Precursors N. LAMAN modes of the molecule. Here, this technique has been demonstrated with aspirin and its precursors spectroscopy; Terahertz Time-domain spectroscopy; Far infrared; Waveguide; Aspirin; Benzoic acid. INTRODUCTION

57

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

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

58

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

59

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

60

Time-resolved terahertz spectroscopy of bulk and nanoscale semiconductors  

Microsoft Academic Search

The nature of charge carrier dynamics and conduction in bulk and nanoscale semiconducting materials is investigated with time-resolved terahertz (THz) spectroscopy (TRTS). This powerful technique uses picosecond (10-12 s) pulses of far-infrared light to map the electrodynamic response of a photoexcited material in the 0.2 - 3 THz (1012 Hz) frequency range on ultrafast time scales. We show how TRTS

David G. Cooke

2007-01-01

61

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

62

Overcoming Optical Resolution Limits in Terahertz Spectroscopy C. Alfaro, H. Koga, I. Kawayama, H. Murakami, M. Tonouchi  

E-print Network

Overcoming Optical Resolution Limits in Terahertz Spectroscopy C. Alfaro, H. Koga, I. Kawayama, H to be emitted and allow image readings to be performed by the LTEM. One hurdle faced with terahertz spectroscopy to be beneficial, not only to those labs performing terahertz spectroscopy, but hopefully in other areas

Mellor-Crummey, John

63

Application of superlattice multipliers for high-resolution terahertz spectroscopy.  

PubMed

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

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

2007-04-01

64

MYOGLOBIN FAR-INFRARED ABSORPTION AND PROTEIN HYDRATION EFFECTS STUDIED BY TERAHERTZ TIME-DOMAIN SPECTROSCOPY  

E-print Network

MYOGLOBIN FAR-INFRARED ABSORPTION AND PROTEIN HYDRATION EFFECTS STUDIED BY TERAHERTZ TIME-DOMAIN SPECTROSCOPY A Dissertation Submitted to the Faculty of Purdue University by Chenfeng Zhang In Partial............................................................................ 1 CHAPTER 2. TERAHERTZ TIME-DOMAIN SPECTROSCOPY .......................... 5 2.1. Generation

Purdue University

65

Far-Infrared Characteristics of ZnS Nanoparticles Measured by Terahertz Time-Domain Spectroscopy  

E-print Network

ARTICLES Far-Infrared Characteristics of ZnS Nanoparticles Measured by Terahertz Time-Domain Spectroscopy Jiaguang Han, Weili Zhang,*, Wei Chen,§ L. Thamizhmani, Abul K. Azad, and Zhiyuan Zhu Shanghai of terahertz time-domain spectroscopy (THz-TDS) over the frequency range from 0.3 to 3.0 THz. The effective

66

Development of Fiber-Coupled Compact Terahertz Time-Domain Spectroscopy Imaging Head  

E-print Network

. Introduction Terahertz time-domain spectroscopy (THz-TDS) utilizing THz pulses is a well-established technique, however, it is indispensable to realize fast scanning of a large area with a compact and costDevelopment of Fiber-Coupled Compact Terahertz Time-Domain Spectroscopy Imaging Head Ryotaro INOUE

Tonouchi, Masayoshi

67

POLARIZATION DEPENDENT TERAHERTZ TIME-DOMAIN SPECTROSCOPY MEASUREMENTS ON ALIGNED CARBON NANOTUBE FILMS AND FIBERS  

E-print Network

Dependent Terahertz Time-Domain Spectroscopy Measurements On Aligned Carbon Nanotube Films And Fibers are not well defined ! Carbon nanotube (CNT) fiber properties strongly determined by overall alignment of itsPOLARIZATION DEPENDENT TERAHERTZ TIME-DOMAIN SPECTROSCOPY MEASUREMENTS ON ALIGNED CARBON NANOTUBE

Mellor-Crummey, John

68

Terahertz Spectroscopy of Crystalline and Non-Crystalline Solids  

NASA Astrophysics Data System (ADS)

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

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

69

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

70

Dynamics of the stratification process in drying colloidal dispersions studied by terahertz time-domain spectroscopy.  

PubMed

We present an optical study that reveals the bulk dynamics of the stratification process in drying colloidal dispersions. Terahertz time-domain spectroscopy has been used to measure in situ solventborne and waterborne paint layers as a function of drying time. The dynamic behavior of the dry top layer and wet bottom layer thickness, as well as the bulk thickness, reflect the principal processes of the established drying mechanism. In addition, the results demonstrate stratification only when the drying process is in the evaporation controlled regime, whereas the coating is shown to remain a single layer for diffusion controlled drying. PMID:25300667

van Mechelen, J L M

2014-11-01

71

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

72

Coherent source terahertz-subterahertz spectroscopy: instrumentation and physics  

NASA Astrophysics Data System (ADS)

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

Gorshunov, Boris P.; Zhukova, Elena S.

2014-03-01

73

Research of pesticide residues on fruit by terahertz spectroscopy technology  

NASA Astrophysics Data System (ADS)

Pesticide residues on the fruit skin are measured by terahertz time-domain spectroscopy (THz-TDS) in 0.2-1.3THz. Pesticide is mainly residues for fruit, which threatens health of human, so the research about the fruit residues is absolutely important. In the experiment, a kind of pesticide carbendazim, orange, and the mixture of them are measured by THz-TDS, and then calculate absorption spectrums through Fourier transform and Fresnel formula. Experiment results indicate that THz-TDS is an effective tool for the measurement of pesticide residues on the fruit skin.

Ma, Yehao; Wang, Qiang; Wang, Xiaowei; Wang, Huali

2011-11-01

74

Two-dimensional Raman-terahertz spectroscopy of water  

PubMed Central

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

Savolainen, Janne; Ahmed, Saima; Hamm, Peter

2013-01-01

75

Semiconductor Nonlinear Dynamics Study by Broadband Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

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

Ho, I.-Chen

76

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

E-print Network

Conductivity of solvated electrons in hexane investigated with terahertz time-domain spectroscopy and recombination dynamics of quasifree electrons in liquid n-hexane and cyclohexane performed using terahertz time- uids of hexane and cyclohexane. The nature of solvated electrons in nonpolar liquids such as hexane has

Heinz, Tony F.

77

Terahertz time domain spectroscopy of phonon-depopulation based quantum cascade lasers  

E-print Network

1 Terahertz time domain spectroscopy of phonon-depopulation based quantum cascade lasers N. Jukam) 251108" #12;2 Abstract The gain and loss in a terahertz quantum cascade laser based on a longitudinal cascade lasers (QCLs) based on longitudinal-optical (LO) phonon depopulation of the lower laser level1

Boyer, Edmond

78

Effect on influenza hemagglutinin protein binding with neutralizing antibody using terahertz spectroscopy technology  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy is sensitive to probe several aspects of biological systems. We have reported the terahertz dielectric spectrum is able to identify the type of the charges in the hydrogen-bonded antibodies' networks in our previous work. Recently we demonstrate a highly sensitive THz-TDS method to monitor binding interaction of influenza hemagglutinin (HA) against its target antibody F10. The terahertz dielectric properties of HA was strongly affected by the presence of a specific antibody. Protein solution concentration or even molecular binding interaction can also affect the terahertz signal. This enables us to detect the specificity and sensitivity of antibody-antigen binding under THz radiation.

Sun, Yiwen; Zhong, Junlan; Zuo, Jian; Zhang, Cunlin

2014-11-01

79

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

E-print Network

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

Yeh, Ka-Lo

2009-01-01

80

Terahertz micro-spectroscopy using a transient mirror technique  

NASA Astrophysics Data System (ADS)

Terahertz (THz) spectroscopy of a biomolecule with spatial resolution below the diffraction limit of the radiation has been achieved by use of an all-optical, contactless transient mirror technique. A resolution of around 50 ?m is determined by the use of a test sample of gold strip lines deposited on GaAs, and the differential THz time-domain spectroscopy (THz-TDS) response of biotin has been measured in both the presence and absence of the transient mirror at room temperature. These preliminary results demonstrate the potential for use of the technique for the chemical identification and characterisation of biomolecules in small volumes with the ultimate goal being microscopic imaging of live cells. The technique may find applications in quality control for semiconductor processing, and in identifying material imperfections, i.e. small cracks in non-destructive testing. We discuss the limitations of the transient mirror technique along with several advantages over other related techniques.

Levitt, James A.; Gallant, Andrew J.; Swift, G. Peter; Dai, De Chang; Chamberlain, J. Martyn

2007-02-01

81

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

E-print Network

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

Teo, Stephanie M

2014-01-01

82

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

83

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

84

Investigation of the sol-gel transition of gelatin using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

The sol-gel transition temperature of gelatin is determined using viscoelasticity measurement and terahertz time-domain spectroscopy. From the results of the viscoelasticity measurement, the sol-gel transition temperature is determined to be 30-32 °C, and it strongly depended on the concentration. However, terahertz time-domain spectroscopy indicates a particular transition temperature of 36 °C. A distinction of these transition temperatures is attributed to the difference in the structural changes detected by these measurements.

Kawabe, Shunsuke; Seki, Munetoshi; Tabata, Hitoshi

2014-04-01

85

Terahertz pulsed spectroscopy of paraffin-embedded brain glioma  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

86

Terahertz pulsed spectroscopy of paraffin-embedded brain glioma.  

PubMed

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

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

2014-07-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2002-06-01

88

Terahertz spectroscopy of concrete for evaluating the critical hydration level  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

89

3-D Terahertz Synthetic-Aperture Imaging and Spectroscopy  

NASA Astrophysics Data System (ADS)

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

Henry, Samuel C.

90

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

91

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

92

Time-resolved terahertz spectroscopy of bulk and nanoscale semiconductors  

NASA Astrophysics Data System (ADS)

The nature of charge carrier dynamics and conduction in bulk and nanoscale semiconducting materials is investigated with time-resolved terahertz (THz) spectroscopy (TRTS). This powerful technique uses picosecond (10-12 s) pulses of far-infrared light to map the electrodynamic response of a photoexcited material in the 0.2 - 3 THz (1012 Hz) frequency range on ultrafast time scales. We show how TRTS can be used to extract the complex conductivity of a material induced by a femtosecond pump pulse, just picoseconds after excitation. A case study of a standard III-V semiconductor, GaAs, is presented to establish a baseline for TRTS in the Ultrafast Spectroscopy lab at the University of Alberta. Fundamental conduction mechanisms are investigated in dilute nitride and bismide alloys of GaAs, materials of interest for optoelectronic devices. We find that while both nitrogen and bismuth incorporation reduces the fundamental energy bandgap of GaAs, bismuth does so without deteriorating the electrical properties whereas nitrogen severely reduces the electron mobility, limiting its usefulness in future devices. This is the first measurement of electron mobility in GaAsBi, and the results should have a significant impact on the optoelectronic device community. The inherent sensitivity of the THz pulse to the conductivity of a material, sub-picosecond resolution, and noncontact nature make time-resolved terahertz spectroscopy an ideal technique for investigating carrier capture dynamics in semiconductor nanostructures. In this work, we demonstrate how THz pulses can be used to monitor this capture process directly in both quantum dot and quantum wire structures. We further show how the THz polarization can be used to probe a photoconductive anisotropy arising from a linear ordering of both quantum wire and dot-chain systems. Finally, we investigate how the confinement of charge carriers influences the electrodynamics of silicon films by varying the degree of structural disorder. A transition from free to localized behaviour is observed from bulk, crystalline silicon to silicon nanocrystals embedded in glass. The transition from metal-to-insulator can be observed directly as a suppression of the low frequency real conductivity, and can be explained using a model based on carrier backscattering.

Cooke, David G.

93

Quantitative analyses of tartaric acid based on terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

Cao, Binghua; Fan, Mengbao

2010-10-01

94

High-Q terahertz bandpass filters based on coherently interferingmetasurface reflections  

Microsoft Academic Search

We present compact and easy-to-realize terahertz bandpass filters\\u000a\\u0009with Q values in the order of 500. The filters are based on coherently\\u000a\\u0009interfering reflections from two parallel metasurfaces applied to\\u000a\\u0009the boundaries of a semiconductor disk. By changing the thickness\\u000a\\u0009of the semiconductor disk and the dimensions of the metasurface structures,\\u000a\\u0009the filter can be optimized for various terahertz frequencies.

Norman Born; Marco Reuter; Martin Koch; Maik Scheller

2013-01-01

95

High-Q terahertz bandpass filters based on coherently interfering metasurface reflections.  

PubMed

We present compact and easy-to-realize terahertz bandpass filters with Q values in the order of 500. The filters are based on coherently interfering reflections from two parallel metasurfaces applied to the boundaries of a semiconductor disk. By changing the thickness of the semiconductor disk and the dimensions of the metasurface structures, the filter can be optimized for various terahertz frequencies. Moreover, a precise tuning of the resonance frequency is possible via the temperature of the structure or its angle with respect to the propagation direction. PMID:23503256

Born, Norman; Reuter, Marco; Koch, Martin; Scheller, Maik

2013-03-15

96

Dielectric Properties of Diesel and Gasoline by Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

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

Arik, Enis; Altan, Hakan; Esenturk, Okan

2014-09-01

97

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

98

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

99

Temperature-Dependent Far-Infrared Spectra of Single Crystals of High Explosives Using Terahertz Time-Domain Spectroscopy  

E-print Network

Temperature-Dependent Far-Infrared Spectra of Single Crystals of High Explosives Using Terahertz Time-Domain Spectroscopy Jeffrey Barber, Daniel E. Hooks, and David J. Funk* DX DiVision, Los Alamos in the region from 10 to 80 cm-1 using terahertz time-domain spectroscopy. The spectra were taken

Ryan, Michael D.

100

Terahertz vibrationrotationtunneling spectroscopy of water clusters in the translational band region of liquid water  

E-print Network

, and in less detail in the mid-infrared by a variety of methods including infrared cavity ringdown spectroscopy by tuning it to spectroscopic data in six-dimensional calculations of the water dimer far-infrared spectrumTerahertz vibration­rotation­tunneling spectroscopy of water clusters in the translational band

Cohen, Ronald C.

101

Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy is distinguished from other far infrared and millimeter wave spectroscopies by its inherent phase sensitivity and sub-picosecond time resolution making it a versatile technique to study a wide range of physical phenomena. As THz spectroscopy is still a relatively new field, many aspects of THz generation mechanisms have not been fully examined. Using terahertz emission spectroscopy (TES), THz emission from ZnTe(110) was analyzed and found to be limited by two-photon absorption and free-carrier generation at high excitation fluences. Due to concerns about the continued use of fossil fuels, solar energy has been widely investigated as a promising source of renewable energy. Dye-sensitized solar cells (DSSCs) have been developed as a low-cost alternative to conventional photovoltaic solar cells. To solve the issues of the intermittency and inefficient transport associated with solar energy, researchers are attempting to adapt DSSCs for water oxidation and chemical fuel production. Both device designs incorporate sensitizer molecules covalently bound to metal oxide nanoparticles. The sensitizer, which is comprised of a chromophore and anchoring group, absorbs light and transfers an electron from its excited state to the conduction band of the metal oxide, producing an electric current. Using time-resolved THz spectroscopy (TRTS), an optical pump/THz probe technique, the efficiency and dynamics of electron injection from sensitizers to metal oxides was evaluated as a function of the chromophore, its anchoring group, and the metal oxide identity. Experiments for studying fully functioning DSSCs and water oxidation devices are also described. Bio-inspired pentafluorophenyl porphyrin chromophores have been designed and synthesized for use in photoelectrochemical water oxidation cells. Influences on the efficiency and dynamics of electron injection from the chromophores into TiO2 and SnO2 nanoparticles due to changes in both the central substituent to the porphyrin ring and degree of fluorination of ring substituents were analyzed. Due to the high reduction potentials of these sensitizers, injection into TiO2 was generally not observed. Injection timescales from the porphyrins into SnO2 depended strongly on the identity of the central substituent and were affected by competition with excited-state deactivation processes. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but is typically not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency and water stability of several alternative anchoring groups, including phosphonic acid, hydroxamic acid, acerylacetone, and boronic acid, were evaluated. While all of the anchoring groups exhibited water stability superior to carboxylate, the hydroxamate anchor had the best combination of ease of handling and electron injection efficiency. The effects on photoconductivity due to metal oxide morphology and the addition of dopants were also analyzed. Mixtures of anatase and rutile TiO 2 nanoparticles are known to exhibit cooperative effects which increase the efficiency of DSSCs and photocatalysis relative to the pure-phase materials. Through analysis of TRTS measurements, the mechanism of this synergistic effect was found to involve electron transfer from the lower-mobility, higher surface area rutile nanoparticles to anatase particles, resulting in a higher charge collection efficiency. In addition to morphology, doping has been investigated as a means of expanding the spectral range of visible absorption of photocatalysts. Doping ZnO nanowires with manganese(II) was found to significantly decrease the electron mobility, and doping with cobalt(II) increased the timescale for electron trapping. These differences can be understood by considering the changes to the band structure of ZnO effected by the dopants. Preliminary analyses of the solvent and electrolyte dependence on the electron injection rate and efficiency suggest that electron injection can be affected by

Milot, Rebecca Lee

102

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

2012-07-27

103

Terahertz time-domain spectroscopy of sulfur-containing biomolecules  

NASA Astrophysics Data System (ADS)

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 electro-optic sampling method with a ZnTe crystal. The characterization of the apparatus of THz TDS is discussed in detail. The spectral features in the THz region are different among sulfur-containing biomolecules of L,L-cystine, L-cysteine, L-methionine, and oxidized glutathione in powder. These results demonstrate that THz TDS is a promising method for studies on the low-frequency spectra of complex molecules and identification of materials. We present a calculation method to analyze the THz spectra based on a model function for dynamics of the dipoles, which allows us to obtain spectral information characterizing the low-frequency responses of the molecules. The experimental results are compared with ab initio calculations to discuss assignment of the vibrational modes.

Yamamoto, Kohji; Kabir, Md. Humayun; Tominaga, Keisuke

2005-11-01

104

Few-cycle terahertz generation and spectroscopy of nanostructures.  

PubMed

We report on new schemes for terahertz (THz) generation. The THz efficiency of photoconducting antennas can be increased by using a cavity effect for the near-infrared pump beam. The cavity is formed by a molecular beam epitaxy grown semiconductor Bragg mirror below the photoconducting layer. The optical confinement is accompanied by an electrical confinement suppressing undesired leakage currents and providing a constant electric field in the active layers. The performance of this cavity-enhanced emitter is further improved by using a mobility optimized low-temperature GaAs layer. This emitter is successfully used in a femtosecond Ti:sapphire laser cavity for highly efficient intracavity THz generation, where the photoconductive layer serves also as a saturable absorber. The broadband THz pulses generated are used for time-resolved spectroscopy of nanostructures. We study the dynamics of intersubband transitions in semiconductor quantum wells. The relaxation of carriers excited by a near-infrared pump pulse is investigated by measuring the THz absorption between the different subbands with our THz pulses. For transition energies below the optical phonon energy we find relatively long relaxation times with a strong dependence on the excited carrier density. PMID:15306518

Darmo, Juraj; Müller, Thomas; Parz, Wolfgang; Kröll, Josef; Strasser, Gottfried; Unterrainer, Karl

2004-02-15

105

Advanced birefringence measurements in standard terahertz time-domain spectroscopy.  

PubMed

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

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

2014-05-20

106

Applications of terahertz spectroscopy in the plastics industry  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

107

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

108

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

PubMed

With the ongoing proliferation of terahertz time-domain instrumentation from semiconductor physics into applied spectroscopy over the past decade, measurements at terahertz frequencies (1 THz ? 10(12) Hz ? 33 cm(-1)) have attracted a sustained growing interest, in particular the investigation of hydrogen-bonding interactions in organic materials. More recently, the availability of Raman spectrometers that are readily able to measure in the equivalent spectral region very close to the elastic scattering background has also grown significantly. This development has led to renewed efforts in performing spectroscopy at the interface between dielectric relaxation phenomena and vibrational spectroscopy. In this review, we briefly outline the underlying technology, the physical phenomena governing the light-matter interaction at terahertz frequencies, recent examples of spectroscopic studies, and the current state of the art in assigning spectral features to vibrational modes based on computational techniques. PMID:25506684

Parrott, Edward P J; Zeitler, J Axel

2015-01-01

109

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

NASA Astrophysics Data System (ADS)

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

Catapano, Ilaria; Soldovieri, Francesco

2014-05-01

110

Character research on 2.52 terahertz coaxial reflection-mode confocal scanning microscopic imaging  

NASA Astrophysics Data System (ADS)

The technology of terahertz (THz) is a major research area in the 21st century. THz imaging is an important research direction. The single-frequency continuous-wave THz technology is combined with coaxial reflection-mode confocal scanning microscopic imaging in this article. Under the given system parameters, the transverse response character of 2.52THz (118.83?m) coaxial reflection-mode confocal scanning microscopic imaging is emulated and analyzed. The results of emulation show that coaxial reflection-mode confocal scanning microscopic imaging is feasible in THz region.

Yang, Yong-fa; Li, Qi; Hu, Jia-qi

2014-12-01

111

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

NASA Astrophysics Data System (ADS)

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

Yang, Yong-fa; Li, Qi

2014-12-01

112

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

Microsoft Academic Search

We present terahertz (THz) reflective spectroscopic focal-plane imaging of four explosive and bio-chemical materials (2, 4-DNT, Theophylline, RDX and Glutamic Acid) at a standoff imaging distance of 0.4 m. The 2 dimension (2-D) nature of this technique enables a fast acquisition time and is very close to a camera-like operation, compared to the most commonly used point emission-detection and raster

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

2006-01-01

113

Reflection-type electromagnetically induced transparency analogue in terahertz metamaterials  

NASA Astrophysics Data System (ADS)

A reflection-type electromagnetically induced transparency (EIT) metamaterial is proposed, which is composed of a dielectric spacer sandwiched with metallic patterns and metallic plane. Experimental results of THz time domain spectrum (THz-TDS) exhibit a typical reflection of EIT at 0.865 THz, which are in excellent agreement with the full-wave simulations. A multi-reflection theory is adopted to analyze the physical mechanism of the reflection-type EIT, showing that the reflection-type EIT is a superposition of multiple reflection of the transmission EIT. Such a reflection-type EIT provides many applications based on the EIT effect, such as slow light devices and nonlinear elements.

Ding, Chun-Feng; Zhang, Ya-Ting; Yao, Jian-Quan; Sun, Chong-Ling; Xu, De-Gang; Zhang, Gui-Zhong

2014-12-01

114

Terahertz time-domain spectroscopy and quantitative analysis of metal gluconates.  

PubMed

A series of metal gluconates (Na(+), K(+), Mg(2+), Ca(2+), Fe(2+), Cu(2+), and Zn(2+)) were investigated by terahertz (THz) time-domain spectroscopy. The absorption coefficients and refractive indices of the samples were obtained in the frequency range of 0.5-2.6 THz. The gluconates showed distinct THz characteristic fingerprints, and the dissimilarities reflect their different structures, hydrogen-bond networks, and molecular interactions. In addition, some common features were observed among these gluconates, and the similarities probably come from the similar carbohydrate anion group. The X-ray powder diffraction measurements of these metal gluconates were performed, and the copper(II) gluconate was found to be amorphous, corresponding to the monotonic increase feature in the THz absorption spectrum. The results suggest that THz spectroscopy is sensitive to molecular structure and physical form. Binary and ternary mixtures of different gluconates were quantitatively analyzed based on the Beer-Lambert law. A chemical map of a tablet containing calcium D-gluconate monohydrate and ?-lactose in the polyethylene host was obtained by THz imaging. The study shows that THz technology is a useful tool in pharmaceutical research and quality control applications. PMID:25506686

Li, Shaoxian; Yang, Jingqi; Zhao, Hongwei; Yang, Na; Jing, Dandan; Zhang, Jianbing; Li, Qingnuan; Han, Jiaguang

2015-01-01

115

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

116

Laser Original Magneto-Optical Spectroscopy of Semiconductors Using Terahertz Quantum Cascade Lasers  

E-print Network

860 Laser Original Magneto-Optical Spectroscopy of Semiconductors Using Terahertz Quantum Cascade 77005, U.S.A. Received October 7, 2005 We have used quantum-cascade lasers operating at 4.7 THz, 3.5 THz the first spectroscopic application of THz quantum-cascade lasers. Results show that these compact lasers

Kono, Junichiro

117

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

118

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

119

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. PMID:24105302

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

2013-01-01

120

Detection of melamine in foods using terahertz time-domain spectroscopy.  

PubMed

The aim of this study was to investigate the feasibility of detecting melamine in foodstuffs using terahertz imaging. The terahertz (THz) spectra and images of melamine mixtures were obtained in the frequency range of 0.1-3 THz at room temperature using THz time-domain spectroscopy. Characteristic absorption peaks of melamine were found at 2, 2.26, and 2.6 THz, and these peaks showed the same frequencies in the different food matrices. At 2 THz, the THz images of melamine were dose-dependently distinguishable from those of food components with or without the packaging materials used. The calibration curve of melamine showed a regression coefficient (R(2)) of >0.913 and a detection limit of <13%. These results suggest that terahertz imaging has the potential to be used for the qualitative detection of melamine in food as a nondestructive analytical tool. PMID:24884284

Baek, Seung Hyun; Lim, Heung Bin; Chun, Hyang Sook

2014-06-18

121

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

122

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

123

Progress of ultrafast terahertz time-domain spectroscopy: Raman inactive soft mode in quantum paraelectric SrTiO3  

NASA Astrophysics Data System (ADS)

We have measured the complex dielectric constants of quantum paraelectric SrTiO3 (STO) bulk single crystals by using the ultrafast and broadband terahertz time-domain spectroscopy (THz-TDS) with the reflection configuration. The observed complex dielectric dispersion consists of the Raman inactive TO1 soft mode and is well reproduced by damped harmonic oscillator model where the resonant frequency and the damping constant are 2.75 THz and 0.63 THz, respectively, in good agreement with the previous reports. The ultrafast THz-TDS used in this study employs the technique of high-speed asynchronous optical sampling and Cherenkov type THz generator. The sampling time of one scan is about 10 milliseconds and available frequency of the THz source is from 0.5 to 7 THz. The reflection configuration combined with the ultrafast system enabled to detect the dispersion of a STO bulk sample which has high permittivity and opaque in the THz region.

Mori, Tatsuya; Igawa, Hikaru; Kojima, Seiji

2014-03-01

124

Optical referencing in differential reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

We report a new optical set-up for difference reflectance spectroscopy (DRS) measurements based on a two-beam configuration. By normalizing the reflected intensity from the sample surface with a reference signal that is directly proportional to the incident beam intensity, the calculated DR spectra become insensitive to the instability of the light source. As a result, a significantly improved signal-to-noise ratio is obtained and DR signals in the low 10?4 range can be measured reliably. This enables an extremely high sensitivity for surface studies using optical spectroscopy.

Zaglmayr, H.; Hu, C. G.; Sun, L. D.; Zeppenfeld, P.

2014-11-01

125

Terahertz time-domain spectroscopy and its applications  

NASA Astrophysics Data System (ADS)

Mode-locked lasers can now readily produce optical pulses of femtosecond duration. In this thesis, results are presented on new methods by which these laser pulses can be exploited to measure and control electric fields on an ultrafast time scale. In addition to the development of these techniques, the resulting capability is used for time-domain far-infrared spectroscopy measurements. With respect to approaches for the detection of electric fields on the femtosecond time scale, two new detection methods based on nonlinear optical interactions with femtosecond laser pulses have been developed. In one scheme, electro-optic sampling of ultrafast electrical transients is extended to permit the capture of a complete electric-field waveform with a single femtosecond laser pulse. This is achieved by using a multichannel detection scheme combined with an experimental geometry in which the femtosecond probe pulse experiences time skew across its wave front relative to the electric field being measured. This method eliminates the need for sampling and the associated scanning of a delay line. A further development involves application of the electric field- induced optical second-harmonic generation. This process is shown to permit the characterization of the magnitude and direction of electric fields in centrosymmetric materials, such as silicon, with high sensitivity, spatial and temporal resolution. With respect to the generation of ultrashort electromagnetic transients, results are presented on the enhancement of the emission efficiency of optically gated photoconductive emitters under application of an external magnetic field. The basic mechanism of the large observed enhancements is clarified within the context of a simple model incorporating a Lorentz-Drude description of carrier dynamics together with an appropriate treatment of the radiation process for the photo-induced current transients. One important application of these capabilities is the time-domain spectroscopy in the terahertz (THz) or far- infrared spectral region. In this approach one produces a controlled electric-field waveform and measures directly in the time domain the changes in this waveform induced by the sample. The method provides access to a spectral region that is difficult to reach by conventional means. It also offers unique capabilities for probing the non- equilibrium properties of rapidly changing systems. These capabilities have permitted the study of the nature and transport of photo-generated electrons in a condensed- phase system consisting of liquid hexane. A second application illustrates the utility of controlled single- cycle THz pulses for the elucidation of fundamental questions about electromagnetic waves and their interactions. In particular, the properties of circularly polarized electromagnetic pulses with a duration approaching that of one optical cycle are investigated experimentally. The results are found to agree well with a theoretical treatment that predicts that the orthogonal components of the electric field of circularly polarized radiation satisfy a Hilbert transform relation. This new analysis provides a completely general description of polarized electromagnetic radiation, one which extends beyond the conventional quasi-monochromatic limit.

Shan, Jie

126

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

127

Terahertz Spectra of L-Ascorbic Acid and Thiamine Hydrochloride Studied by Terahertz Spectroscopy and Density Functional Theory  

NASA Astrophysics Data System (ADS)

We have investigated the terahertz spectra of L-ascorbic acid and thiamine hydrochloride measured by terahertz time-domain spectroscopy (THz-TDS) and Fourier transform infrared spectroscopy (FTIR). The measured absorption spectra were demonstrated to be in good agreement with the results simulated by Density Functional Theory (DFT) using hybrid functional B3LYP with basis set of 6-31G (d), except with slight frequency shift and few peaks missing. We presented the comparison of measured spectra by the FTIR spectroscopy employing low temperature silicon bolometer as detector and the TDS system. The measured spectra of the L-ascorbic acid showed shoulder bands at 0.25, 1.1, 1.5, 1.82, 2.03, 2.30, 2.44, 2.67, 2.97, 3.12, and 3.40 THz, respectively. The spectra of the thiamine hydrochloride show shoulder bands at 0.48, 1.11, 1.57, 1.75, 1.92, 2.08, 2.31, 2.53, 2.69, 2.85, 3.12, 3.22, and 3.31 THz. Most absorption peaks of the two samples agree with the results simulated by Density Function Theory (DFT) method of Gaussian 09 software. In our work, more spectral peaks based on experimental and theoretical results were found in comparison to that of other groups, since we employed higher sensitive FTIR measurement system and considered the effect of number of molecule unit in simulation. The study suggests that the effect of intermolecular vibration is stronger than intramolecular interaction on the absorption bands in THz region.

Jiang, Ling; Li, Miao; Li, Chun; Sun, Haijun; Xu, Li; Jin, Biaobin; Liu, Yunfei

2014-10-01

128

Biomedical Applications of Terahertz Spectroscopy: A Brief Review  

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

129

Two-band conductivity of a FeSe_{0.5}Te_{0.5} film by reflectance measurements in the terahertz and infrared range  

NASA Astrophysics Data System (ADS)

We report an infrared spectroscopy study of a 200 nm thick FeSe0.5Te0.5 film grown on LaAlO3 with Tc = 13.7 K. We analyze the 20 K normal state absolute reflectance RN measured over a broad infrared range and the reflectance ratio RS/RN, RS being the superconducting state reflectance, measured at 6 K in the terahertz range down to 12 cm?1. We show that the normal state model conductivity is given by two Drude components, one of which much broader and intense than the other. In the superconducting state, we find that a gap ? = 37 ± 3 cm?1 opens up in the narrow Drude band only, while the broad Drude band results to be ungapped, at least in the explored spectral range. Our results show that only a two-band model can coherently describe both normal and superconducting state data.

Perucchi, A.; Joseph, B.; Caramazza, S.; Autore, M.; Bellingeri, E.; Kawale, S.; Ferdeghini, C.; Putti, M.; Lupi, S.; Dore, P.

2014-12-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

131

Polarization state and Mueller matrix measurements in terahertz-time domain spectroscopy  

Microsoft Academic Search

We derive the complete formulae governing the polarization state measurement in terahertz-time domain spectroscopy (THz-TDS) by using a rotatable THz polarizer. Four Stokes parameters can be uniquely obtained by spectrally-resolved measurement in THz-TDS. Further, we propose a new approach to measure the Mueller matrix of a pure birefringent material, using THz-TDS, by rotating the material under test. Based on the

Hui Dong; Yandong Gong; Varghese Paulose; Minghui Hong

2009-01-01

132

Terahertz spectroscopy of dicyanobenzenes: Anomalous absorption intensities and spectral calculations  

NASA Astrophysics Data System (ADS)

Terahertz absorption spectra of three isomeric structures of dicyanobenzene in chloroform solution and solid phase at 298 K are reported. These spectra exhibit enhanced absorption in low THz range compared to most organic systems because of strong coupling to phonon modes. Molecular vibrational spectral calculations show strong correlation with the experiment especially for solution spectra. All intramolecular modes were assigned and intermolecular modes identified. Out-of-plane intramolecular modes at low frequency exhibit ˜75 cm -1 blue shifts as the secondary CN group moves from the para to ortho position on the benzene ring, whereas almost no frequency shift occurs for low-frequency in-plane modes.

Esenturk, O.; Evans, A.; Heilweil, E. J.

2007-07-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

134

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

PubMed

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

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

2014-01-01

135

Soft tissue differentiation by diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

136

Terahertz time-domain spectroscopy of crystalline and aqueous systems  

Microsoft Academic Search

We use ab-initio density-functional perturbation theory together with THz spectroscopy for precise prediction and assignment of vibrational modes in molecular crystals. We show that THz spectroscopy is useful for analysis of liquids and food products.

Peter Uhd Jepsen; U. Moller; Finn Eichhorn; Hannes Merbold; Jacob Riis Folkenberg; S. J. Clark

2007-01-01

137

Brill transition of nylon-6 characterized by low-frequency vibration through terahertz absorption spectroscopy  

NASA Astrophysics Data System (ADS)

With the aim of opening a route toward new applications of terahertz (THz) spectroscopy to studies of polymer science, the conformations and structural transitions of polycaprolactam (nylon-6) were investigated by THz spectroscopy in the ?, ?, pseudo-hexagonal, and amorphous phases. A Brill transition from the ? form to the pseudo-hexagonal form was detected at 160 °C from a temperature variation of the peak intensity at 6.6 THz in the second-derivative spectrum of nylon-6. In the amorphous phase, a glass transition was observed at 60 °C, and a new anomaly was found at 110 °C.

Suzuki, Hal; Ishii, Shinya; Sato, Harumi; Yamamoto, Shigeki; Morisawa, Yusuke; Ozaki, Yukihiro; Uchiyama, Tetsuji; Otani, Chiko; Hoshina, Hiromichi

2013-06-01

138

Characterization of plasma treated surfaces for food safety by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

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

Sulovská, Kate?ina; Lehocký, Marián.

2014-10-01

139

Ultrafast multi-terahertz nano-spectroscopy with sub-cycle temporal resolution  

NASA Astrophysics Data System (ADS)

Phase-locked ultrashort pulses in the rich terahertz spectral range have provided key insights into phenomena as diverse as quantum confinement, first-order phase transitions, high-temperature superconductivity and carrier transport in nanomaterials. Ultrabroadband electro-optic sampling of few-cycle field transients can even reveal novel dynamics that occur faster than a single oscillation cycle of light. However, conventional terahertz spectroscopy is intrinsically restricted to ensemble measurements by the diffraction limit. As a result, it measures dielectric functions averaged over the size, structure, orientation and density of nanoparticles, nanocrystals or nanodomains. Here, we extend ultrabroadband time-resolved terahertz spectroscopy to the sub-nanoparticle scale (10?nm) by combining sub-cycle, field-resolved detection (10?fs) with scattering-type near-field scanning optical microscopy (s-NSOM). We trace the time-dependent dielectric function at the surface of a single photoexcited InAs nanowire in all three spatial dimensions and reveal the ultrafast (<50?fs) formation of a local carrier depletion layer.

Eisele, M.; Cocker, T. L.; Huber, M. A.; Plankl, M.; Viti, L.; Ercolani, D.; Sorba, L.; Vitiello, M. S.; Huber, R.

2014-11-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

141

Far-infrared optical and dielectric response of ZnS measured by terahertz time-domain spectroscopy  

E-print Network

Far-infrared optical and dielectric response of ZnS measured by terahertz time-domain spectroscopy properties THz-TDS has shown significant ad- vantages over many of the far-infrared spectroscopy modali- ties material in the infrared and far-infrared region.1 It plays a vital role in being used as infrared windows

142

Terahertz Vibration-Rotation-Tunneling Spectroscopy of the Ammonia Dimer: Characterization of an out of Plane Vibration  

E-print Network

by tunable far-infrared laser spectroscopy, and later three more subbands10 using infrared-far-infrared cm-1 above the lowest energy E + E state. Both that work and the infrared-far-infrared doubleTerahertz Vibration-Rotation-Tunneling Spectroscopy of the Ammonia Dimer: Characterization

Cohen, Ronald C.

143

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

PubMed Central

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

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

2014-01-01

144

Wavelet denoising and reconstruction of a microneedle embedded in human skin ex-vivo using terahertz pulsed reflectance.  

PubMed

Biological tissue can show promising features in the terahertz region of the electro-magnetic spectrum but face the problem that the signal to noise ratio can be poor due to the low energy output from the measurement instrument coupled with the high absorbance of water in biological tissue. Wavelet denoising and reconstruction are known to be suitable digital signal processing filters for reflected terahertz energy when appropriate thresholds, scales and mother-wavelets are chosen. In this article, we therefore describe a Wavelet transform-based method for denoising reflections of THz energy from ex-vivo human skin with an embedded microneedle. The wavelet reconstruction was then successfully used to identify the microneedle from the reflected waveform. This technique is potentially useful to enhance in-depth analysis and visualisation of underlying skin layers, lesions and penetration depth for targeted drug delivery. PMID:25571543

Mueller-Holtz, Martin; Seker, Huseyin; Smith, Geoff

2014-08-01

145

Terahertz time domain spectroscopy of hollow polycarbonated metal waveguides  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

146

Terahertz Spectroscopy of Hydrogen-Bonded Molecular Complexes in Solution  

NASA Astrophysics Data System (ADS)

Hydrogen bonding is ubiquitous in nature and governs a wide array of chemical and biological processes. Although the hydrogen bond is well studied, its low-frequency vibrations -- the large-amplitude motions involving stretching and bending along the actual hydrogen-bond coordinates -- have been rarely investigated. These vibrations largely fall in the terahertz (THz) or far-infrared region (0.1-6 THz). Here we present pulsed THz spectroscopic investigations of intermolecular hydrogen bonding in several molecular clusters in non-aqueous solutions. In order to access spectral data above 3 THz, a pulsed THz spectrometer utilizing gallium phosphide (GaP) crystals was constructed to provide >6 THz of continuous spectral bandwidth. Molecular systems to be discussed include the mixed dimeric systems of phenol:pyridine and 4-fluorophenol:pyridine, as well as the phenol trimer. Experiments will also be presented on the 7- azaindole dimer which serves a model system for the phenomenon of excited- state double-proton transfer. In all cases, density functional theory calculations were used to assign the observed vibrational features to specific vibrational motions of the complexes. Finally, preliminary optical-pump-THz-probe experiments concerning the excited-state dynamics of these molecular complexes will be discussed.

Korter, Timothy

2005-03-01

147

Diagnosing breast cancer using diffuse reflectance spectroscopy and intrinsic fluorescence spectroscopy  

E-print Network

Using diffuse reflectance spectroscopy and intrinsic fluorescence spectroscopy, we have developed an algorithm that successfully classifies normal breast tissue, fibrocystic change, fibroadenoma, and infiltrating ductal ...

Fitzmaurice, Maryann

148

Investigation of thermal denaturation of solid oxytocin by terahertz dielectric spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

149

Far-infrared optical constants of CO2 near the critical point measured by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The optical index constants of CO2 at critical density are measured by terahertz (THz) time-domain spectroscopy (TDS-THz) in the frequency range 0.1-1.5 THz. Since supercritical CO2 is usually presented as a "universal" solvent, we systematically study the refractive index variations in the vicinity of its critical point along the critical isochore by scanning temperature from 295 to 308 K to explore the liquid, the gas, and the supercritical states. Density changes with temperature result in refractive index variations that are found to fit the Lorenz-Lorentz relationship in the THz frequency range.

Mounaix, P.; Moustakim, M.; Le Boiteux, S.; Delville, J. P.; Wunenburger, R.; Sarger, L.

2003-12-01

150

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

151

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

152

Characterization of Hydroxyapatite-Glass Composites Using Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) is presented as a tool for characterization of the hydroxyapatite (HA)-glass composites. The materials under investigation are composites of HA and a calcium zinc silicate glass. Our results show that the refractive index and dielectric constant in THz frequencies provide a reliable determination of glass content of these composites. In addition, the THz-TDS is used to morphological changes in HA during simulated body fluid (SBF) incubation. Our results demonstrate that the THz-TDS can be a promising non-destructive tool.

Yatongchai, C.; Wren, A. W.; Sundaram, S. K.

2015-01-01

153

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

PubMed

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

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

2014-06-01

154

Characterization of Hydroxyapatite-Glass Composites Using Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) is presented as a tool for characterization of the hydroxyapatite (HA)-glass composites. The materials under investigation are composites of HA and a calcium zinc silicate glass. Our results show that the refractive index and dielectric constant in THz frequencies provide a reliable determination of glass content of these composites. In addition, the THz-TDS is used to morphological changes in HA during simulated body fluid (SBF) incubation. Our results demonstrate that the THz-TDS can be a promising non-destructive tool.

Yatongchai, C.; Wren, A. W.; Sundaram, S. K.

2014-08-01

155

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

156

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

PubMed Central

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

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

2012-01-01

157

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

PubMed

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

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

2012-11-01

158

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

PubMed

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

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

2011-04-21

159

High spectral resolution reflectance spectroscopy of minerals  

USGS Publications Warehouse

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

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

1990-01-01

160

Reflectance spectroscopy of organic compounds: 1. Alkanes  

USGS Publications Warehouse

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

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

2009-01-01

161

Insulin amyloid fibrillation studied by terahertz spectroscopy and other biophysical methods  

SciTech Connect

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

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

2010-01-01

162

Terahertz polarization imaging  

Microsoft Academic Search

We present a new method to measure the polarization state of a terahertz pulse by using a modified electrooptic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and terahertz images of a plastic

Willemine A. M. van der Marel; Paul C. M. Planken

2005-01-01

163

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

164

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

165

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

166

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

167

Sub-terahertz resonance spectroscopy of biological macromolecules and cells  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

168

Reflectance anisotropy spectroscopy of magnetite (110) surfaces  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

169

Specular Reflection and Diffuse Reflectance Spectroscopy of Soils  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

170

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

171

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

Microsoft Academic Search

Imaging and spec troscopy at terahertz fre quencies have great po tential for healthcare, plasma di ag nos tics, and homeland se- cu rity ap pli ca tions. Terahertz fre quen cies cor re spond to en ergy level tran si tions of im por tant mol e cules in bi ol ogy and as tro- phys ics. Terahertz ra

Eyal Gerecht; Lixing You

2009-01-01

172

Advanced imaging and spectroscopy of biological and chemical agents at terahertz frequencies  

Microsoft Academic Search

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. Terahertz imagers based on HEB technology have sufficient sensitivity to operate in a passive imaging mode, thus eliminating the need for active illumination. HEB mixers have, therefore, become the detectors of choice for applications

E. Gerecht; D. Gu; L. You; S. Yngvesson

2007-01-01

173

Investigation of spectral gain narrowing in quantum cascade lasers using terahertz time domain spectroscopy  

E-print Network

1 Investigation of spectral gain narrowing in quantum cascade lasers using terahertz time domain;2 Abstract The spectral gain of bound-to-continuum terahertz quantum cascade lasers (QCLs) is measured,version1-16Jun2008 #12;3 Important progress on terahertz quantum cascade lasers (QCLs) has been achieved

Paris-Sud XI, Université de

174

Electron density measurement of inductively coupled plasmas by terahertz time-domain spectroscopy (THz-TDS)  

SciTech Connect

The electron densities of argon inductively coupled plasmas were measured by terahertz time-domain spectroscopy (THz-TDS). At a low pressure, the electron densities were also measured with a Langmuir-type double probe and the validity of THz-TDS electron-density measurement in a plasma has been corroborated. As the input radio-frequency (RF) power increases, the plasma density and gas temperature increase, which makes the probe measurement less reliable or even impossible, due to the large heat load to the probe surface. On the contrary, the THz-TDS measurement is unaffected by the gas temperature and becomes more reliable due to the higher electron density at higher input power for plasma generation.

Ando, Ayumi; Kurose, Tomoko; Kitano, Katsuhisa; Hamaguchi, Satoshi [Center for Atomic and Molecular Technologies, Osaka University 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Reymond, Vivien [Center for Atomic and Molecular Technologies, Osaka University 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); ENSPS, Universite de Strasboug, Boulevard Sebastien Brant BP10413 67412 Illkirch Cedex (France); Kitahara, Hideaki; Takano, Keisuke; Hangyo, Masanori [Institute of Laser Engineering, Osaka University 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Tani, Masahiko [Resarch Center for Development of Far-Infrared Region, University of Fukui 3-9-1 Bunkyo, Fukui City, Fukui Prefecture 910-8507 (Japan)

2011-10-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

176

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

177

Experimental measurements of water content in crude oil emulsions by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

We measured the water content (0.01%-0.25% w/w) in crude oil emulsions using terahertz time-domain spectroscopy (THz-TDS). To improve the precision and range of the measurements, we used 1 and 10 mm thick quartz cells. The experiments were performed at 20 °C and the THz wave was transmitted vertically to the samples and detected on the other side. The experimental results suggest linear relation for the THz absorption coefficient and the water content of the crude oil emulsions in the observed range. The linear dependence facilitates high-precision measurements of the water content of crude oil. This suggests the potential of THz-TDS in determining the water concentration in crude oil and borehole fluid identification.

Jin, Wu-Jun; Zhao, Kun; Yang, Chen; Xu, Chang-Hong; Ni, Hao; Chen, Shao-Hua

2013-12-01

178

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

PubMed

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

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

2012-06-01

179

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

NASA Astrophysics Data System (ADS)

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

Yamashita, G.; Matsubara, E.; Nagai, M.; Kanemitsu, Y.; Ashida, M.

2014-12-01

180

Materials for terahertz science and technology  

Microsoft Academic Search

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

Bradley Ferguson; Xi-Cheng Zhang

2002-01-01

181

High-resolution waveguide terahertz spectroscopy of partially oriented organic polycrystalline films.  

PubMed

We have characterized the terahertz (THz) vibrational spectroscopy of organic polycrystalline thin films using the new experimental technique of waveguide terahertz time domain spectroscopy (waveguide THz-TDS). The organic materials used in this study are tetracyanoquinodimethane (TCNQ) and 1,3-dicyanobenzene (13DCB). For each material, a thin film is cast onto one of the inner surfaces of a metal parallel plate waveguide (PPWG), followed by measurement of the low-frequency vibrational spectrum using waveguide THz-TDS. The vibrational spectra of the waveguide films are compared to corresponding vibrational spectra of standard pellet samples made by dispersing the organic solid in transparent polyethylene. We show how the waveguide films produce significantly narrower THz vibrational line shapes and reveal additional spectral lines that are obscured by inhomogeneous broadening effects in the pellet samples. When TCNQ waveguide films are cooled to 77 K, vibrational line widths as sharp as 25-30 gigahertz (0.83-1.0 cm(-1)) at the full width at half-maximum are observed, which are among the narrowest far-infrared line widths measured for this material. The origin of the line-narrowing effect for the waveguide films is the suppression of inhomogeneous broadening due to the planar ordering of the film on the waveguide surface. The TCNQ waveguide films are further characterized using optical microscopic evaluation to understand how film morphology affects the THz vibrational spectrum. X-ray diffraction is used to determine the orientation of the polycrystalline TCNQ films on the PPWG surface and to qualitatively explain the different vibrational line strengths observed for the ordered waveguide film relative to the random pellet. PMID:17929786

Melinger, Joseph S; Laman, N; Harsha, S Sree; Cheng, ShuFan; Grischkowsky, D

2007-11-01

182

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

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

183

Terahertz frequency upconversion via relativistic Doppler reflection from a photoinduced plasma front in a solid-state medium  

NASA Astrophysics Data System (ADS)

We propose and simulate the relativistic Doppler reflection of terahertz (THz) radiation normally incident on a plasma front in a semiconductor medium, resulting in a significant frequency upshift for the reflected radiation. The plasma front is generated by linear interband excitation of the semiconductor by a counterpropagating femtosecond optical pulse. High-resistivity silicon is identified as an ideal medium for experiments, as it possesses a desirable optical penetration depth, upshift factor, and low THz absorption and dispersion. The depletion of the optical pump pulse results in a spatiotemporal plasma profile, which leads to results that go beyond the existing analytic theory. We employ one-dimensional finite-difference time-domain simulations to predict the reflected THz pulses vs a range of realistic experimental parameters. The results indicate that a significant frequency upshift can be expected for both conventional and ultrabroadband THz pulses, and that this technique may be suitable to provide higher-bandwidth THz radiation extending into the midinfrared.

Thomson, Mark D.; Tzanova, Slava M.; Roskos, Hartmut G.

2013-02-01

184

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

185

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

NASA Astrophysics Data System (ADS)

A time-domain terahertz spectroscopic system with high source power (average power > 10 nW) and high signal-to- noise ratio (>104) was developed and used to study ultrafast electronic processes in semiconductor structures. The physics of the spectroscopy, the theoretical basis of the interferometry, the model of the electron-electromagnetic field interaction, and the principle of experimental data processing are presented. The first direct measurement of the intervalley scattering time in In 0.53Ga0.47As was performed. The intervalley scattering time constants obtained were ?L? = 35 fs and ?L? = 450 fs. The spectroscopic data showed that at low carrier density the carrier- carrier scattering is unimportant. The intervalley deformation potential was obtained from the measured intervalley scattering time constant ? L?. The transient conductivity was obtained using time-domain terahertz spectroscopy. The frequency dependent terahertz spectroscopy enabled us to uniquely determine the transient mobility and density. The transient electron mobility is ~5200 cm2/Vs, which is less than the Hall mobility. For large photocarrier densities, this discrepancy is attributed to the additional momentum relaxation associated with electron-hole scattering. Using pump pulses with wavelength of 810 run, the electron trapping time in low-temperature-grown GaAs was accurately determined. The measured trapping time is slightly larger than that observed from a band-edge pump- probe measurements. We argue that the terahertz technique provides the most reliable measure of carrier lifetime due to the unique interaction. The carrier dynamics of low-temperature-grown InGaAs bulk and InGaAs/InAlAs multiple quantum wells were investigated. We were able to differentiate the two dominant mechanisms in the electron decay process, trapping and recombination. A trapping time as fast as 1.3-2.6 ps was observed for photo-excited electrons. The effects of Be-doping and growth temperature on the trapping dynamics in both bulk and multiquantum wells were determined. The role of Be-As complexes and simple compensation were discussed. The photo-electron trapping time of isolated As defects was found to be 16-24 ps. Annealing of low-temperature- grown materials was found to dramatically decrease the recombination time of isolated As defects but hardly changed the effective trapping rate. We propose that the isolated As defects still play a major role in carrier trapping and recombination in the annealed low- temperature-grown InGaAs multi-quantum wells. However, the formation of As precipitates after annealing may dramatically decrease the recombination time of isolated As defects. The initial transient conductivity and the residual conductivity were determined using numerical methods in a quasi-static fashion. The mobility ? and the static carrier density No are uniquely determined. This allows us to calculate the initial change of the conductivity ?? i due to photoexcitation. A significant residual (t > 10ns) photoconductivity has been observed in low-temperature- grown InGaAs. This residual conductivity has significant consequences for device performance. Be-doping was shown to systematically reduce the residual conductivity and simultaneously reduce the decay time of the initial conductivity transient. The Be related defect may act in the form of a Be-As complex which may be a superior recombination center. However, it is not possible to disregard the compensation effects of the beryllium. The carrier density and mobility of a GaN sample were determined using static terahertz spectroscopy. Assuming the carrier density and mobility are independent parameters, the terahertz transmission through a multi- layer structure was calculated and shown to fit the experimental data. The values of carrier density and mobility obtained in the fitting are consistent with the Hall measurement results. A wide well-width GaAs-AlGaAs multi-quantum well structure was designed to investigate intersubband relaxation with energy separations less than LO phonon e

Chen, Yue

186

Understanding the terahertz spectra of crystalline pharmaceuticals: terahertz spectroscopy and solid-state density functional theory study of (S)-(+)-ibuprofen and (RS)-ibuprofen.  

PubMed

The potential applications of terahertz (THz) spectroscopy in the analysis of pharmaceutical products in their crystalline state have prompted the need for a more thorough understanding of the fundamental vibrational motions contributing to the THz spectra. The detection of variations in crystal structure and the reliable assignment of observed THz absorption features can be aided by the use of solid-state density functional theory (DFT). In this study, solid-state DFT with periodic boundary conditions was used to simulate the crystalline structure and assign the experimental THz spectra (10-90 cm(-1)) of the enantiomerically pure and racemic forms of the common pharmaceutical compound ibuprofen. The results clearly demonstrate the capabilities of DFT methodologies to accurately reproduce the THz spectra of large complicated molecular systems and provide insight into the internal and external vibrational motions that form the basis of THz spectroscopy. PMID:20815081

King, Matthew D; Buchanan, William D; Korter, Timothy M

2011-03-01

187

[Application of terahertz technology in medical testing and diagnosis].  

PubMed

Terahertz science and technology is increasingly emphasized in science and industry, and has progressed significantly in recent years. There is an important aspect of attention in the application of terahertz technology to medicine. The overview of the terahertz characters, terahertz spectroscopy and terahertz imaging technology is introduced. This paper focuses on reviewing the use of and research progress in terahertz spectroscopy and terahertz imaging technology in medical testing and diagnosis. Furthermore, the problems to be solved and development directions of terahertz spectroscopy and terahertz imaging technology are discussed. PMID:24159847

Qi, Na; Zhang, Zhuo-Yong; Xiang, Yu-Hong

2013-08-01

188

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

Microsoft Academic Search

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

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

2000-01-01

189

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

NASA Astrophysics Data System (ADS)

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

Wang, Qiang; Ma, Yehao; Wang, Xiaowei

2012-06-01

190

Molecular Recognition and Interaction between Uracil and Urea in Solid-State Studied by Terahertz Time-Domain Spectroscopy.  

PubMed

Using terahertz time-domain spectroscopy characterization, we observe that urea is able to recognize and interact with uracil efficiently even in the solid phase without involving water or solvents. A cocrystal configuration linked by a pair of hydrogen bonds between uracil and urea was formed. The terahertz absorption spectrum of the cocrystal shows a distinct new absorption at 0.8 THz (26.7 cm(-1)), which originates from the intermolecular hydrogen bonding. Both mechanical milling and heating can accelerate the reaction efficiently. Density functional theory was adopted to simulate the vibrational modes of the cocrystal, and the results agree well with the experimental observation. Multiple techniques, including powder X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy, were performed to investigate the reaction process, and they presented supportive evidence. This work enables in-depth understanding of recognition and interaction of urea with nucleobases and comprehension of the denaturation related to RNA. We also demonstrate that terahertz spectroscopy is an effective and alternative tool for online measurement and quality control in pharmaceutical and chemical industries. PMID:25386785

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

2014-11-20

191

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-...

192

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

193

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

NASA Astrophysics Data System (ADS)

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

Skvortsov, L. A.

2014-11-01

194

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

PubMed

This study investigated the feasibility of detecting pesticides using terahertz (THz) spectroscopy in high-density polyethylene and/or wheat flour mixtures. The absorption spectra of seven pesticides (dicofol, chlorpyrifos, chlorpyrifos-methyl, daminozide, imidacloprid, diethyldithiocarbamate, and dimethyldithiocarbamate) were measured in the frequency range 0.1 to 3 THz at room temperature. Five of the seven pesticides exhibited specific absorption peaks in the low-energy THz range. The two remaining pesticides had no specific absorption peaks in this frequency range, but they exhibited different frequency-dependent refractive indices. The absorption coefficients of imidacloprid increased with its increasing weight ratio in high-density polyethylene, and the fitted power absorptions and refractive indices using a Maxwell-Garnett effective medium model were comparable to the measured data. Imidacloprid was also identified from its characteristic absorption peaks in wheat flour mixtures, and a linear relationship between the absorption coefficient and the weight ratio was observed. Our results show the potential of detection of selected pesticides in foods, such as wheat flour, using THz spectroscopy. PMID:25474054

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

2014-12-01

195

Terahertz chiroptical spectroscopy of an ?-helical polypeptide: a molecular dynamics simulation study.  

PubMed

Vibrational spectroscopy has provided incisive information on the structure of biological molecules. Here, using a molecular dynamics simulation method, infrared vibrational circular dichroism and vibrational optical rotatory dispersion spectra of a right-handed ?-helix in the terahertz (THz) frequency range are calculated. Both the autocorrelation function of an electric dipole moment and the cross-correlation function of electric and magnetic dipole moments of the ?-helix are calculated and Fourier-transformed to obtain THz absorption and optical activity spectra, which reveal characteristic features of the helical polypeptide structure. The anharmonicity and delocalized nature of the low-frequency modes in the THz frequency domain are taken into account to obtain statistically convergent results on the THz optical activity spectra. In addition, the magnitude of the THz vibrational optical activity signal of the ?-helix is directly compared with those of typical, previously studied mid- and near-infrared chiral molecules. We anticipate that THz chiroptical spectroscopy that has not yet been demonstrated experimentally would provide highly important and complementary information on protein structure and dynamics. PMID:25343745

Choi, Jun-Ho; Cho, Minhaeng

2014-11-13

196

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

NASA Astrophysics Data System (ADS)

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

Hoshina, Hiromichi; Ishii, Shinya; Otani, Chiko

2014-07-01

197

Reflectance spectroscopy for evaluating hair follicle cycle  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

198

Transient photoconductivity in GaAs as measured by time-resolved terahertz spectroscopy Matthew C. Beard, Gordon M. Turner, and Charles A. Schmuttenmaer  

E-print Network

. INTRODUCTION Ultrafast carrier dynamics in semiconductors have been of great interest for the last few decades absorption. Time-resolved THz spectroscopy TRTS is a noncontact electrical probe capable of determiningTransient photoconductivity in GaAs as measured by time-resolved terahertz spectroscopy Matthew C

199

Combined theory of reflectance and emittance spectroscopy  

NASA Technical Reports Server (NTRS)

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

Hapke, Bruce

1995-01-01

200

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

201

Probing the dynamics of biomolecules in liquid water by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Decades of molecular dynamics and normal mode calculations suggest that proteins are rife with collective vibrational modes with ps to ns time constants. Given that proteins are "decorated" with charged groups, these motions should lead to oscillating dipoles that, in turn, will lead to strong gigahertz to terahertz absorption. Investigation of these harmonic motions by absorption spectroscopy, however, is extremely challenging due to the strong absorption of water. In response, we have developed a sensitive Vector Network Analyzer based spectrometer that operates from 65 to 700 GHz and can measure both the absorbance and refractive index of protein solutions. In order to extract the complex dielectric response of the protein in solution we employ an effective medium approximation for the mixture of the protein and aqueous buffer. The extracted dielectric response suggests that each protein molecule is surrounded by a tightly held layer of 164 +/- 5 water molecules that behave as if they are an integral part of the protein. The size of this hydration shell and the dielectric response of the solvated protein are all independent of protein concentration. Our measured dielectric response, however, does not agree with published computation models of the protein: the measurements indicate a low frequency cutoff in the density of modes of ˜250 GHz.

Vinh, Nguyen; Allen, Jim; Plaxco, Kevin

2011-03-01

202

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

PubMed

We report the use of terahertz time-domain spectroscopy (THz-TDS) to detect tetracyclines hydrochloride (TCsH) in infant milk powder for the first time. Four kinds of TCsH exhibited their unique spectral features in the region of 0.3-1.8 THz. The main spectral features of these TCsH were still detectable when mixed with infant milk powder with concentrations at 1%-50%, even in the ternary mixtures. The results from chemometrics analysis showed that qualitative and quantitative detection of TCsH in infant milk powder could be successfully achieved. The residual predictive deviation (RPD) values of all these TCsH models were all higher than 2, indicating these models were considered good and could be used in screening purposes. The RPD values of TCH, DTCH, and CTCH models were higher than 3, which were considered excellent for prediction purposes. These preliminary results indicated that THz-TDS combined with chemometrics analysis was suitable for detecting the presence of TCsH residues in a food matrix. PMID:25348376

Qin, Jianyuan; Xie, Lijuan; Ying, Yibin

2014-12-01

203

Time-domain terahertz spectroscopy and applications on drugs and explosives  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

204

Observation of the inverse giant piezoresistance effect in silicon nanomembranes probed by ultrafast terahertz spectroscopy.  

PubMed

The anomalous piezoresistance (a-PZR) effects, including giant PZR (GPZR) with large magnitude and inverse PZR of opposite, have exciting technological potentials for their integration into novel nanoelectromechanical systems. However, the nature of a-PZR effect and the associated kinetics have not been clearly determined yet. Even further, there are intense research debates whether the a-PZR effect actually exists or not; although numerous investigations have been conducted, the origin of the effect has not been clearly understood. This paper shows the existence of a-PZR and provides direct experimental evidence through the performance of well-established electrical measurements and terahertz spectroscopy on silicon nanomembranes (Si NMs). The clear inverse PZR behavior was observed in the Si NMs when the thickness was less than 40 nm and the magnitude of the PZR response linearly increased with the decreasing thickness. Observations combined with electrical and optical measurements strongly corroborate that the a-PZR effect originates from the carrier concentration changes via charge carrier trapping into strain-induced defect states. PMID:25375958

Jang, Houk; Kim, Jaeseok; Kim, Min-Seok; Cho, Jeong Ho; Choi, Hyunyong; Ahn, Jong-Hyun

2014-12-10

205

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

PubMed Central

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

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

2012-01-01

206

Reflectance Spectroscopy of Near-Earth Objects  

NASA Astrophysics Data System (ADS)

We present the preliminary results of an ongoing spectroscopic survey of near-Earth objects. To date, low-resolution CCD reflectance spectra covering the wavelength range 0.38--1 mu m have been obtained for 15 near-Earth asteroids and three cometary candidates, using the Double Imaging Spectrograph on the Apache Point Observatory 3.5-m telescope. Spectra have also been taken of two well-studied main-belt asteroids for comparison with published work. The presence of diagnostic solid-state absorption features in most of the spectra permit the examination of these objects' surface mineralogies. Goals of the study include searching for compositional relationships between near-Earth objects and possible source regions in the main asteroid belt, and the identification of plausible parent bodies for specific meteorite types. Since extinct or inactive comets may form a significant fraction of the near-Earth object population, we also examine the spectra for emission features characteristic of cometary volatiles. Significant spectral differences are noted between some of the observed objects and main-belt asteroids of otherwise similar taxonomic type. For example, the asteroid 2062 Aten is seen to have a deeper 0.9 mu m absorption band and a lower reflectivity at ~ 0.7 mu m than the typical S-type asteroid. This may indicate a more pyroxene or olivine-rich surface, less regolith (more bare rock), larger particle sizes in the regolith, or some combination of all of these influences. No cometary emission features are observed for any of these objects.

Hammergren, M.

1995-12-01

207

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

2012-09-01

208

Detection of a Coherent Longitudinal Optical Phonon in a GaAs Buffer Layer Optically Covered with a GaSb Top Epitaxial Layer Using Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate that, in a GaSb/GaAs epitaxial structure, the coherent longitudinal optical (LO) phonon in the GaAs layer optically covered with the GaSb top layer is observed utilizing terahertz spectroscopy. In the terahertz-wave measurement, the Fourier power spectrum of the terahertz waveform exhibits both the GaAs and the GaSb LO phonons; namely, the coherent LO phonon in the optically covered GaAs buffer layer is observed in the terahertz-wave measurement. This fact demonstrates that the instantaneous surface potential modulation originating from the impulsive carrier excitation by the pump pulses reaches the GaAs buffer layer. This surface potential modulation generates the coherent GaAs LO phonon.

Takeuchi, Hideo; Tsuruta, Syuichi; Nakayama, Masaaki

2011-12-01

209

Nonlinear terahertz spectroscopy of electronic and vibrational responses in condensed matter systems  

E-print Network

In this work, I describe experiments utilizing high-field terahertz (THz) pulses to initiate nonlinear responses in several classes of materials. We have developed several methods for interrogating the nonlinear THz response ...

Hwang, Harold Young

2012-01-01

210

Skin cancer detection by oblique-incidence diffuse reflectance spectroscopy  

E-print Network

Skin cancer is the most common form of cancer and it is on the rise. If skin cancer is diagnosed early enough, the survival rate is close to 90%. Oblique-incidence diffuse reflectance (OIR) spectroscopy offers a technology that may be used...

Smith, Elizabeth Brooks

2009-05-15

211

Terahertz time-domain and FTIR spectroscopy of tris-crown interaction  

NASA Astrophysics Data System (ADS)

In this letter we compare the terahertz time-domain and fourier-transform infrared spectra of tris and its mixtures with crown ether. We demonstrate the potential of all plasma-air based time-domain terahertz technique for the analysis of low-frequency vibrational spectra. The spectral features are interpreted using simulations of the crystalline structure and THz vibrational modes with the aid of the solid-state density functional theory.

Mankova, A. A.; Borodin, A. V.; Kargovsky, A. V.; Brandt, N. N.; Kuritsyn, I. I.; Luo, Q.; Sakodynskaya, I. K.; Wang, K. J.; Zhao, H.; Chikishev, A. Yu.; Shkurinov, A. P.; Zhang, X.-C.

2012-12-01

212

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

213

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

214

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

PubMed

Protein-containing reverse (PCR) micelles are suitable systems to study the properties of proteins and waters in a cell-like environment. A model for determining the structural parameters of PCR micelles, such as the aqueous cavity size and molecule number of water within the reverse micelle, is presented. The model is based on an important hypothesis that the structural parameters of the protein-unfilled reverse micelle do not change after solubilization of protein. I describe a procedure using near infrared spectroscopy of OH stretching vibration band of water to verify the hypothesis. Further, the terahertz (THz) absorption spectrum of myoglobin is derived from THz time-domain spectroscopy of the PCR micellar solution, and the states of waters in reverse micelles with and without protein are discussed on the basis of the structural parameters. The last topic is on internal dynamics of PCR micelles on timescales from femtoseconds to nanoseconds studied by femtosecond time-resolved fluorescence spectroscopy. PMID:24018326

Murakami, Hiroshi

2013-01-01

215

Technical Report: Final project report for Terahertz Spectroscopy of Complex Matter  

SciTech Connect

This project designed characterization techniques for thin films of complex matter and other materials in the terahertz spectral region extending from approximately 100 GHz to 4000 GHz (4 THz) midway between radio waves and light. THz has traditionally been a difficult region of the spectrum in which to conduct spectroscopic measurements. The “THz gap” arises from the nature of the sources and detectors used in spectroscopy both at the optical (high frequency) side and electronic (low frequency) side of the gap. To deal with the extremely rapid oscillations of the electric field in this frequency region this research project adapted techniques from both the electronics and optics technologies by fabricating microscopic antennas and driving them with short optical pulses. This research technique creates nearly single cycle pulses with extremely broad spectral bandwidth that are able to cover the THz spectral range with a single measurement. The technique of THz time domain spectroscopy (THz-TDS) has seen increasing use and acceptance in laboratories over the past fifteen years. However significant technical challenges remain in order to allow THz-TDS to be applied to measurement of solid materials, particularly thin films and complex matter. This project focused on the development and adaptation of time domain THz measurement techniques to investigate the electronic properties of complex matter in the terahertz frequency region from 25 GHz to beyond 5 THz (<1 inv. cm to >165 inv. cm). This project pursued multiple tracks in adapting THz Time Domain Spectroscopy (THz-TDS) to measurement of complex matter. The first, and most important, is development of a reliable methods to characterize the complex dielectric constant of thin films with high accuracy when the wavelength of the THz radiation is much longer than the thickness of the film. We have pursued several techniques for measurement of thin films. The most promising of these are waveguide spectroscopy and THz interferometry. Since THz spectroscopy measures the changes of the transmitted spectra, any noise on the THz signal contributes to measurement errors. The dynamic range—defined as the RMS noise of the THz detector compared to the peak THz signal—of THz spectroscopy using photoconductive antennas is extremely high, typically over 10,000. However the precision with which spectroscopic data can be measured is limited by the noise on the laser source which is typically 0.1% to 1%. For low values of the sample absorbance and for values of optical thickness less than approximately 0.01, the change in transmission approaches the measurement accuracy. The sample refractive index can be measured with better accuracy since the index causes a temporal shift of the THz pulse by an amount time shift of nd/c where n is the refractive index, d the sample thickness, and c the speed of light. Time shifts of tens of femtoseconds can generally be resolved so that index-thickness values of nd > ten microns can be accurately measured. Waveguide spectroscopy is a way to increase the path length in thin film by several orders of magnitude, and thus have a large interaction length even when the film is much less than a wavelength in thickness. Film thicknesses of 10’s of nm have been measured. THz interferometry cancels out many of the noise sources of THz spectroscopy and can thus result in measurements of films of several hundred nm in thickness and is additionally suitable for optical pump, THz probe spectroscopic techniques. A large amount of additional work was performed in support of the main project direction or to explore promising alternative avenues for research. This report discussed work on the the confinement of low density species for measurement of nanogram or picogram quantities of material. Whispering gallery mode resonators to achieve long path lengths were also investigated as were imaging techniques for sub-wavelength imaging of thin films. The report concludes with a report on investigations of fundamental issues in THz beam propagation and coupli

R. A. Cheville; D. R. Grischkowsky

2007-02-08

216

Quantitative determination of molecular structure in multilayered thin films of biaxial and lower symmetry from photon spectroscopies. I. Reflection  

E-print Network

symmetry from photon spectroscopies. I. Reflection infrared vibrational spectroscopy Atul N. Parikh-ray reflectivity, uv-visible spectroscopic ellipsometry, and infrared reflection spectroscopy. Further, the theory spectroscopy and involves quantitative decomposition of the isotropic imaginary optical function (k) spectrum

Parikh, Atul N.

217

[Identification of pearl powder using microscopic infrared reflectance spectroscopy].  

PubMed

Pearl is a precious ornament and traditional Chinese medicine, which application history in China is more than 2000 years. It is well known that the chemical ingredients of shell and pearl are very similar, which all of them including calcium carbonate and various amino acids. Generally, shell powders also can be used as medicine; however, its medicinal value is much lower than that of pearl powders. Due to the feature similarity between pearl powders and shell powders, the distinguishment of them by detecting chemical composition and morphology is very difficult. It should be noted that shell powders have been often posing as pearl powders in markets, which seriously infringes the interests of consumers. Identification of pearl powder was investigated by microscopic infrared reflectance spectroscopy, and pearl powder as well as shell powder was calcined at different temperatures for different time before infrared reflectance spectroscopy analysis. The experimental results indicated that when calcined at 400 °C for 30 minutes under atmospheric pressure, aragonite in pearl powder partly transformed into calcite, while aragonite in shell powder completely transformed into calcite. At the same time, the difference in phase transition between the pearl powders 'and shell powders can be easily detected by using the microscopic infrared reflectance spectroscopy. Therefore, based on the difference in their phase transition process, infrared reflectance spectroscopy can be used to identify phase transformation differences between pearl powder and shell powder. It's more meaningfully that the proposed infrared reflectance spec- troscopy method was also investigated for the applicability to other common counterfeits, such as oyster shell powders and abalone shell powders, and the results show that the method can be a simple, efficiently and accurately method for identification of pearl powder. PMID:25532338

Zhang, Xuan; Hu, Chao; Yan, Yan; Yang, Hai-Feng; Li, Jun-Fang; Bai, Hua; Xi, Guang-Cheng; Liao, Jie

2014-09-01

218

Ultrawideband MgB2 Mixer for High-Resolution Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz high-resolution spectroscopy of interstellar molecular clouds greatly relies on the hot-electron superconducting bolometric (HEB) mixers. A frequency independent mechanism of absorption of radiation inherent in such mixers makes them the detector of choice for heterodyne receivers from 1.5 THz to 4.7 THz. The current state-of-the-art receivers use mixer devices made from an ultrathin (~ 5 nm) film of NbN with a critical temperature ~ 9-11 K. Such mixers have been deployed on a number of ground based, suborbital, and orbital platform including the HIFI instrument on the Hershel Space Observatory. Despite its popularity, good sensitivity, and well established fabrication process, the NbN HEB mixer suffers from a relatively narrow intermediate frequency (IF) bandwidth ~ 2-4 GHz which is insufficient for the spectroscopy of the Galactic center and for extragalactic line observations. As the THz heterodyne receivers are now trending upwards the “high THz” frequencies, the need in a larger IF bandwidth becomes more pressing since the same velocity resolution for a Doppler shifted line at 5 THz requires a 5-tmes greater IF bandwidth than at 1 THz. We propose to develop an HEB mixer with the IF bandwidth ~ 20 GHz or even greater using an ultrathin superconducting film of MgB2. This high critical temperature (40 K) material was discovered 11 year ago and thin films suitable for HEB device fabrication are becoming available now. Compared to NbN, the intrinsic electron-phonon relaxation time in this material is much shorter (estimated to 2-3 ps). Also, MgB2 can be fabricated on MgO buffers, which provide a perfect acoustic match between the film and the substrate that is critical for realization of the fast thermal relaxation in a mixer device. The outcome of this works will be a state-of-the-art heterodyne sensor applicable throughout the 1.5-4.7 THz frequency range with the noise temperature < 1000 K and the IF bandwidth > 10 GHz and operating at ~ 20 K. Beside the bulk substrate (c-sapphire, MgO) we will build mixer devices on MgO buffered silicon-on-insulator (SOI) wafers which are instrumental for integration of HEB mixers into micromachined waveguide array receivers. The near term application of this mixer would be on SOFIA and suborbital balloons. The higher operating temperature will be a very important factor for the future space applications as the required cryocooling can be be provided at much lower cost.

Karasik, Boris

219

Pancreatic tissue assessment using fluorescence and reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

220

Optical Fiber Sensing Based on Reflection Laser Spectroscopy  

PubMed Central

An overview on high-resolution and fast interrogation of optical-fiber sensors relying on laser reflection spectroscopy is given. Fiber Bragg-gratings (FBGs) and FBG resonators built in fibers of different types are used for strain, temperature and acceleration measurements using heterodyne-detection and optical frequency-locking techniques. Silica fiber-ring cavities are used for chemical sensing based on evanescent-wave spectroscopy. Various arrangements for signal recovery and noise reduction, as an extension of most typical spectroscopic techniques, are illustrated and results on detection performances are presented. PMID:22294902

Gagliardi, Gianluca; Salza, Mario; Ferraro, Pietro; Chehura, Edmond; Tatam, Ralph P.; Gangopadhyay, Tarun K.; Ballard, Nicholas; Paz-Soldan, Daniel; Barnes, Jack A.; Loock, Hans-Peter; Lam, Timothy T.-Y.; Chow, Jong H.; De Natale, Paolo

2010-01-01

221

Terahertz magnetospectroscopy of transient plasmas in semiconductors  

Microsoft Academic Search

Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have performed picosecond time-resolved THz spectroscopy of transient carriers in semiconductors. Specifically, we measured the temporal evolution of THz transmission and reflectivity after NIR excitation. We systematically investigated transient carrier relaxation in GaAs and InSb with varying NIR intensities and magnetic fields. Using this information, we were able to determine the

M. A. Zudov; A. P. Mitchell; A. H. Chin; J. Kono

2003-01-01

222

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

223

Pulsed Terahertz Transmission Spectroscopy of Liquid CHCl3, CCl4, and their Mixtures B. N. Flanders, R. A. Cheville, D. Grischkowsky, and N. F. Scherer*,  

E-print Network

Pulsed Terahertz Transmission Spectroscopy of Liquid CHCl3, CCl4, and their Mixtures B. N. Flanders 29, 1996X The frequency-dependent absorption coefficient of CHCl3, CCl4, and their mixtures, based on mole fraction weighted sums of the absorption coefficients of pure CHCl3 and CCl4, indicate

Scherer, Norbert F.

224

Electrically continuous graphene from single crystal copper verified by terahertz conductance spectroscopy and micro four-point probe.  

PubMed

The electrical performance of graphene synthesized by chemical vapor deposition and transferred to insulating surfaces may be compromised by extended defects, including for instance grain boundaries, cracks, wrinkles, and tears. In this study, we experimentally investigate and compare the nano- and microscale electrical continuity of single layer graphene grown on centimeter-sized single crystal copper with that of previously studied graphene films, grown on commercially available copper foil, after transfer to SiO2 surfaces. The electrical continuity of the graphene films is analyzed using two noninvasive conductance characterization methods: ultrabroadband terahertz time-domain spectroscopy and micro four-point probe, which probe the electrical properties of the graphene film on different length scales, 100 nm and 10 ?m, respectively. Ultrabroadband terahertz time-domain spectroscopy allows for measurement of the complex conductance response in the frequency range 1-15 terahertz, covering the entire intraband conductance spectrum, and reveals that the conductance response for the graphene grown on single crystalline copper intimately follows the Drude model for a barrier-free conductor. In contrast, the graphene grown on commercial copper foil shows a distinctly non-Drude conductance spectrum that is better described by the Drude-Smith model, which incorporates the effect of preferential carrier backscattering associated with extended, electronic barriers with a typical separation on the order of 100 nm. Micro four-point probe resistance values measured on graphene grown on single crystalline copper in two different voltage-current configurations show close agreement with the expected distributions for a continuous 2D conductor, in contrast with previous observations on graphene grown on commercial copper foil. The terahertz and micro four-point probe conductance values of the graphene grown on single crystalline copper shows a close to unity correlation, in contrast with those of the graphene grown on commercial copper foil, which we explain by the absence of extended defects on the microscale in CVD graphene grown on single crystalline copper. The presented results demonstrate that the graphene grown on single crystal copper is electrically continuous on the nanoscopic, microscopic, as well as intermediate length scales. PMID:25317778

Buron, Jonas D; Pizzocchero, Filippo; Jessen, Bjarke S; Booth, Timothy J; Nielsen, Peter F; Hansen, Ole; Hilke, Michael; Whiteway, Eric; Jepsen, Peter U; Bøggild, Peter; Petersen, Dirch H

2014-11-12

225

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

NASA Astrophysics Data System (ADS)

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

Aballea, L.; Constantin, L. F.

2009-02-01

226

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

227

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.  

PubMed

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. PMID:19330320

Whitley, V H; Hooks, D E; Ramos, K J; O'Hara, J F; Azad, A K; Taylor, A J; Barber, J; Averitt, R D

2009-09-01

228

Bulk-like transverse electron mobility in an array of heavily n-doped InP nanowires probed by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy is employed for the noncontact measurement of transversal mobility in InP nanowires, wherein photonic effects (waveguiding of excitation beam and propagation of terahertz beam in a complex gradient environment) were successfully deconvoluted. Monte Carlo calculations accounting for electron localization and heavy doping were used to determine electron momentum relaxation time corresponding to electron mobility ?3000 cm2/V s, which is similar to that in bulk InP. The developed approach paves a way for noncontact determination of charge mobility in advanced semiconductor nanostructures.

Ponseca, C. S.; N?mec, H.; Wallentin, J.; Anttu, N.; Beech, J. P.; Iqbal, A.; Borgström, M.; Pistol, M.-E.; Samuelson, L.; Yartsev, A.

2014-08-01

229

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

230

Terahertz tomography using quantum-cascade lasers  

E-print Network

The interfaces of a dielectric sample are resolved in reflection geometry using light from a frequency agile array of terahertz quantum-cascade lasers. The terahertz source is a 10-element linear array of third-order ...

Kao, Tsung-Yu

231

Photoexcited GaAs surfaces studied by transient terahertz time-domain spectroscopy  

Microsoft Academic Search

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

Michael Schall; Peter Uhd Jepsen

2000-01-01

232

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

2011-11-01

233

Pancreatic tumor margin detection by oblique incidence diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

In surgical treatment of pancreatic cancers, the effectiveness of the procedures largely depends on the ability to completely and precisely remove the malignant tumors. We present the ex-vivo use of oblique incidence diffuse reflectance spectroscopy (OIRDS) to detect and differentiate normal from neoplastic tissue. An OIRDS probe has been constructed to provide scattering and absorption information of the pancreatic tissue. To reveal the physiological origin of the difference in these optical signatures, the optical scattering coefficients were extracted along the pancreatic duct with 1-cm spacing. Experimental results show that OIDRS was able to successfully determinate the tumor margins based on the higher optical scattering on malignant tissue.

Garcia-Uribe, Alejandro; Chang, Cheng-Chung; Zou, Jun; Banerjee, Bhaskar; Kuczynski, John; Wang, Lihong V.

2011-03-01

234

Depth sensitive oblique polarized reflectance spectroscopy of oral epithelial tissue  

NASA Astrophysics Data System (ADS)

Identifying depth-dependent alterations associated with epithelial cancerous lesions can be challenging in the oral cavity where variable epithelial thicknesses and troublesome keratin growths are prominent. Spectroscopic methods with enhanced depth resolution would immensely aid in isolating optical properties associated with malignant transformation. Combining multiple beveled fibers, oblique collection geometry, and polarization gating, oblique polarized reflectance spectroscopy (OPRS) achieves depth sensitive detection. We report promising results from a clinical trial of patients with oral lesions suspected of dysplasia or carcinoma demonstrating the potential of OPRS for the analysis of morphological and architectural changes in the context of multilayer, epithelial oral tissue.

Jimenez, Maria K.; Lam, Sylvia; Poh, Catherine; Sokolov, Konstantin

2014-05-01

235

Glass transition dynamics of anti-inflammatory ketoprofen studied by Raman scattering and terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

A liquid-glass transition and a crystalline state of pharmaceutical racemic ketoprofen were studied by Raman scattering and the broadband terahertz time-domain spectroscopy (THz-TDS) in the frequency range from 9 to 260 cm-1. The low-frequency Raman scattering spectra clearly shows the remarkable change related to a liquid-glass transition at about Tg = 267 K. After melt-quenching at liquid nitrogen temperature, a boson peak appears at about 16.5 cm-1 near and below Tg and the intensity of quasi-elastic scattering related to structural relaxation increases markedly on heating. The crystalline racemic ketoprofen of "conformer A" shows the noncoincidence effect of mode frequencies below 200 cm-1 between Raman scattering spectra and dielectric spectra observed by THz-TDS.

Shibata, Tomohiko; Igawa, Hikaru; Kim, Tae Hyun; Mori, Tatsuya; Kojima, Seiji

2014-03-01

236

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

237

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

2012-03-01

238

Asynchronous optical sampling with GHz repetition rate femtosecond lasers for high precision terahertz spectroscopy  

Microsoft Academic Search

We report a terahertz time-domain spectrometer with 6 THz spectral coverage and 1 GHz resolution which is based on high-speed asynchronous optical sampling. High-speed asynchronous optical sampling is based on two femtosecond lasers with approximately 1 GHz repetition rate. The two lasers are stabilized in their repetition rate to an off-set frequency of approximately 2 kHz. The time delay between

T. Dekorsy; G. Klatt; R. Gebs; C. Janke; A. Bartels

2011-01-01

239

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

240

Time-Resolved Terahertz Spectroscopy with Free-Space Electro-Optic Sampling  

Microsoft Academic Search

We present a time-resolved ultrafast measurement in terahertz (THz) frequency region by means of the free-space electro-optic sampling. The fast delay scan technique is used to suppress the noise with low frequency and to improve the signal-to-noise ratio of the system. The transmission spectra of different materials are obtained. The optical properties of these materials in a THz region are

Zhang Liang-Liang; Zhao Guo-Zhong; Zhong Hua; Hu Ying; Zhang Cun-Lin

2004-01-01

241

Terahertz plasmonic Bessel beamformer  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate terahertz Bessel beamforming based on the concept of plasmonics. The proposed planar structure is made of concentric metallic grooves with a subwavelength spacing that couple to a point source to create tightly confined surface waves or spoof surface plasmon polaritons. Concentric scatterers periodically incorporated at a wavelength scale allow for launching the surface waves into free space to define a Bessel beam. The Bessel beam defined at 0.29 THz has been characterized through terahertz time-domain spectroscopy. This approach is capable of generating Bessel beams with planar structures as opposed to bulky axicon lenses and can be readily integrated with solid-state terahertz sources.

Monnai, Yasuaki; Jahn, David; Withayachumnankul, Withawat; Koch, Martin; Shinoda, Hiroyuki

2015-01-01

242

TOPICAL REVIEW: Pulsed terahertz tomography  

Microsoft Academic Search

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

S. Wang; X.-C. Zhang

2004-01-01

243

Determination of carrier concentration dependent electron effective mass and scattering time of n-ZnO thin film by terahertz time domain spectroscopy  

SciTech Connect

We demonstrated a novel and widely accessible method for determining the electron effective mass and scattering time of ZnO films with different carrier concentrations by combining terahertz time-domain spectroscopy with Hall measurement. The terahertz time domain spectroscopy (THz-TDS) transmission spectra (0.1–2THz) were well described by Drude model. It is found that electron effective mass varied from 0.23m{sub 0} to 0.26m{sub 0} as the electron concentration changes from 5.9?×?10{sup 17}?cm{sup ?3} to 4.0?×?10{sup 19}?cm{sup ?3}. The carrier concentration dependent characteristic is ascribed to the non-parabolicity of conduction band. Free carrier localization mechanism explained the discrepancy in mobilities obtained from THz-TDS and Hall measurements.

Tang, J.; Tay, C. B. [Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore); NUSNNI-Nanocore, National University of Singapore, Singapore 117576 (Singapore); Deng, L. Y. [Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore); Zhang, X. H.; Chai, J. W. [Institute of Materials and Research Engineering, Agency for Science, Technology and Research, 3 Research Link, Singapore 117602 (Singapore); Qin, H. [Department of Chemical and Bioengineering, National University of Singapore, Singapore 117542 (Singapore); Liu, H. W. [Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Venkatesan, T. [NUSNNI-Nanocore, National University of Singapore, Singapore 117576 (Singapore); Chua, S. J., E-mail: elecsj@nus.edu.sg [Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore); NUSNNI-Nanocore, National University of Singapore, Singapore 117576 (Singapore); Institute of Materials and Research Engineering, Agency for Science, Technology and Research, 3 Research Link, Singapore 117602 (Singapore)

2014-01-21

244

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

Microsoft Academic Search

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

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

2002-01-01

245

C -axis Josephson plasma resonance observed in Tl 2 Ba 2 CaCu 2 O 8 superconducting thin films by use of terahertz time-domain spectroscopy  

Microsoft Academic Search

We have unambiguously observed the c-axis Josephson Plasma Resonance (JPR) in high-T$_{c}$ cuprate Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$ superconducting thin films employing terahertz time-domain spectroscopy in transmission as a function of temperature in zero magnetic field. These are the first measurements of the JPR temperature dependence of a high-$T_{c}$ material in transmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K

V. K. Thorsmølle; R. D. Averitt; M. P. Maley; L. N. Bulaevskii; C. Helm; A. J. Taylor

2001-01-01

246

Time-Resolved Terahertz Spectroscopy with Free-Space Electro-Optic Sampling  

NASA Astrophysics Data System (ADS)

We present a time-resolved ultrafast measurement in terahertz (THz) frequency region by means of the free-space electro-optic sampling. The fast delay scan technique is used to suppress the noise with low frequency and to improve the signal-to-noise ratio of the system. The transmission spectra of different materials are obtained. The optical properties of these materials in a THz region are shown. The broadening of spectrum and chirping phenomena are illustrated. We find that polystyrene is an excellent material for the THz application.

Zhang, Liang-Liang; Zhao, Guo-Zhong; Zhong, Hua; Hu, Ying; Zhang, Cun-Lin

2004-11-01

247

Low-frequency dynamics of proteins and aqueous solutions studied by terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

We studied low-frequency spectra of hydration water molecules around the hydrophobic probe in an aqueous solution by using tetraalkylammonium cation as a probe and terahertz time-domain spectroscopic technique. The phenomenon, called dynamical transition, has been known to be universally observed among proteins and polypeptides. In this work we investigated temperature and hydration dependence of low-frequency dynamics to clarify relationships between the dynamical transition and protein structures, and its functional states. We also mention general behaviors of the lowfrequency spectra of globular proteins.

Yamamoto, Naoki; Ishihara, Akané; Kaneko, Azusa; Iguchi, Haruka; Kambara, Ohki; Tamura, Atsuo; Tominaga, Keisuke

2013-03-01

248

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

249

Reflectance difference spectroscopy of water on Cu(110)  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

250

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

251

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

252

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

PubMed Central

Abstract. Evanescent field sensing methods are currently used to detect many different types of disease markers and biologically important chemicals such as the HER2 breast cancer receptor. Hinoue et al. used Total Internal Reflection Photoacoustic Spectroscopy (TIRPAS) as a method of using the evanescent field to detect an optically opaque dye at a sample interface. Although their methods were successful at detecting dyes, the results at that time did not show a very practical spectroscopic technique, which was due to the less than typical sensitivity of TIRPAS as a spectroscopy modality given the low power (?1 to 2 W) lasers being used. Contrarily, we have used an Nd:YAG laser with a five nanosecond pulse that gives peak power of 1 MW coupled with the TIRPAS system to increase the sensitivity of this technique for biological material sensing. All efforts were focused on the eventual detection of the optically absorbing material, hemozoin, which is created as a byproduct of a malarial infection in blood. We used an optically analogous material, ?-hematin, to determine the potential for detection in the TIRPAS system. In addition, four properties which control the sensitivity were investigated to increase understanding about the sensor’s function as a biosensing method. PMID:22734742

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

2012-01-01

253

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

254

Resonant reflection spectroscopy of biomolecular arrays in muscle.  

PubMed

Sarcomeres, the functional units of contraction in striated muscle, are composed of an array of interdigitating protein filaments. Direct interaction between overlapping filaments generates muscular force, which produces animal movement. When filament length is known, sarcomere length successfully predicts potential force, even in whole muscles that contain billions of sarcomere units. Inability to perform in vivo sarcomere measurements with submicrometer resolution is a long-standing challenge in the muscle physiology field and has hampered studies of normal muscle function, adaptation, injury, aging, and disease, particularly in humans. Here, we develop theory and demonstrate the feasibility of to our knowledge a new technique that measures sarcomere length with submicrometer resolution. In this believed novel approach, we examine sarcomere structure by measuring the multiple resonant reflections that are uniquely defined by Fourier decomposition of the sarcomere protein spatial framework. Using a new supercontinuum spectroscopic system, we show close agreement between sarcomere lengths measured by resonant reflection spectroscopy and laser diffraction in an ensemble of 10 distinct muscles. PMID:25418304

Young, Kevin W; Radic, Stojan; Myslivets, Evgeny; O'Connor, Shawn M; Lieber, Richard L

2014-11-18

255

Superhuman Vision - Seeing with Terahertz  

NSDL National Science Digital Library

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

2006-12-28

256

Anatomy-Based Algorithms for Detecting Oral Cancer Using Reflectance and Fluorescence Spectroscopy  

E-print Network

OBJECTIVES: We used reflectance and fluorescence spectroscopy to noninvasively and quantitatively distinguish benign from dysplastic/malignant oral lesions. We designed diagnostic algorithms to account for differences in ...

McGee, Sasha

257

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

258

Surface excitations in surface electron spectroscopies studied by reflection electron energy-loss spectroscopy and elastic peak electron spectroscopy.  

PubMed

Surface excitations, in addition to bulk excitation, undergone by signal electrons in surface electron spectroscopies, such as Auger electron spectroscopy, and X-ray photoelectron spectroscopy, play an important role in the formation of electron spectra. Those inelastic scattering processes not only induce decay in the peak intensity, but also form background appearing in the lower kinetic energy side of relevant peaks. Information on surface excitation is essential in addition to bulk excitations for the quantification of material surfaces by surface electron spectroscopies, and extensive studies have been devoted to it. In this report, we introduce the basics of the study of surface excitations by reflection electron energy loss spectroscopy (REELS) and elastic peak electron spectroscopy (EPES). The application of several approaches within the schemes of EPES analysis and REELS analysis to the experimental determination of inelastic scattering parameters, such as the surface excitation parameter (SEP), differential SEP (DSEP), inelastic mean free path (IMFP), and dielectric function, are also introduced. Information useful to calculate the values of the IMFP and SEP using predictive equations is provided in Supporting Information as well. PMID:20145317

Nagatomi, Takaharu; Tanuma, Shigeo

2010-01-01

259

Dielectric characterization of [Fe(NH2-trz)3]Br2•H2O thermal spin crossover compound by terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

The complex optical index refraction of an iron (II) spin-crossover coordination polymer is measured in the Terahertz frequency range by Terahertz time-domain spectroscopy (THz-TDS). By scanning the temperature from 288 to 333 K, we have recorded the evolution of the THz spectrum within the low spin - high spin thermal hysteresis loop. We were able to simultaneously infer the refractive index and absorption variations. The low spin-high spin transition has a marked spectral signature in the millimeter wavelength. In the 0.1-0.6 THz frequency range, the variation of real and imaginary part of the index of refraction is 6% and 20%, respectively. A marked absorption is observed above 500 GHz. The THz-TDS provides a clear direct fingerprint of this class of materials, which are interestingly potential candidates for optical data storage and processing devices.

Mounaix, P.; Lascoux, N.; Degert, J.; Freysz, E.; Kobayashi, A.; Daro, N.; Létard, J.-F.

2005-12-01

260

Gain measurements of scattering-assisted terahertz quantum cascade lasers  

E-print Network

Using terahertz time-domain spectroscopy, the gain of scattering-assisted terahertz quantum cascade lasers is measured. By examining the intersubband gain and absorption over a wide range of bias voltages, we experimentally ...

Hu, Qing

261

A diffuse reflectance spectroscopy system to study biological tissues  

NASA Astrophysics Data System (ADS)

Diffuse reflectance spectroscopy (DRS) is a technique that allows the study of the structural and biochemical condition of tissues in a noninvasive-nonionizing way. DRS has been widely used in biomedical applications, mainly as an alternative to biopsy. Generally, the technique consists in the irradiation of a specific zone of a tissue with a reference spectrum. Then, the reemitted by the tissue light is detected. The changes suffered by the backscattered spectrum (after light-tissue interaction) with respect to the incident one carry information about the tissue properties. This work presents a novel system designed and developed to use DRS in biomedical applications. The system uses a LED as a light source and a specially designed optical fiber probe as a mean to deliver the light to the tissue surface, and to collect the reemitted photons from the studied sample. This probe was designed to accomplish two different tasks: to increase the sensitivity of the diagnosis; and to study the radial dependence of the backscattered light. The measuring probe was built in a way that allows taking readings when the exerted pressure on the tissue reaches certain predetermined values.

de la Cadena, A.; Stolik, S.; de la Rosa, J. M.

2013-11-01

262

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

263

Low-frequency vibration study of amino acids using terahertz spectroscopy and solid-state density functional theory  

NASA Astrophysics Data System (ADS)

Understanding the low-frequency normal modes of amino acids, the building blocks of proteins, is crucial to reveal the vibration-function relationship in the macromolecular system. Recent advances in terahertz spectroscopy (THz) and solid-state density functional theory (DFT) have ensured an accurate description of low-frequency modes of amino acids. New knowledge people have learnt so far is that the inter- and intra-molecular vibrations are strongly mixed with each other in the THz region through the vibrational coordinate mixing. Rich information is believed embedded in this phenomenon. We introduce a generalized mode-analysis method that allows for the accurate decomposition of a normal mode of interest into the three intermolecular translations, three principal librations and various intrinsic intramolecular vibrations. This mode-analysis method will be demonstrated in the crystalline C60 systems and then applied to shed light on the nature of low-frequency phonons of glycine, diglycine and triglycine. This method helps reveal new intramolecular vibrational modes on the first hand, and more importantly, illuminate a new phenomenon of the frequency distribution of intramolecular vibrations (FDIV). FDIV describes the possible broad distributions of important intramolecular vibrations in the low-frequency normal modes. The FDIV concept may indicate an additional mechanism for the intramolecular vibrations to become thermally active and participate in various biological functions.

Zhang, Feng; Tominaga, Keisuke; Hayashi, Michitoshi; Wang, Houng-Wei

2014-11-01

264

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

2013-05-31

265

Near-Infrared Reflectance Spectroscopy is a Rapid, Cost-Effective Predictor  

E-print Network

Near-Infrared Reflectance Spectroscopy is a Rapid, Cost-Effective Predictor of Seagrass Nutrients + Business Media, Inc. 2006 Abstract Near-infrared reflectance spectroscopy was used to analyze nutrient com to the laboratory, and separated into leaf and root/rhizome fractions. They were dried, ground, and near-infrared

Marsh, Helene

266

DIFFUSE REFLECTANCE MID-INFRARED SPECTROSCOPY (DRIFTS) OF SOILS UNDER DIFFERENT TILLAGE AND CROP ROTATION REGIMES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Diffuse reflectance mid-infrared spectroscopy (DRIFTS) has been used successfully to quantify soil organic carbon and soil biological properties. In this study we aimed to use DRIFTS as well as diffuse reflectance near infrared spectroscopy to test if spectral differences can be used to characterize...

267

Attenuated total reflection Infrared spectroscopy applied to the study of mineral  

E-print Network

Attenuated total reflection ­ Infrared spectroscopy applied to the study of mineral ­ aqueous spectroscopy (ATR-IR) to the environmentally important mineral ­ aqueous electrolyte interface being ATR-IR. hal-00685193,version1-4Apr2012 Author manuscript, published in "Infrared Spectroscopy

Boyer, Edmond

268

Qualitative Analysis of Collective Mode Frequency Shifts in L-alanine using Terahertz Spectroscopy  

PubMed Central

We have observed collective mode frequency shifts in the phonon absorbance spectra of deuterium-substituted L-alanine isotopologues. Terahertz (THz) absorbance spectra were acquired at room temperature in the spectral range of 66–90 cm?1, or 2.0–2.7 THz, for L-alanine (L-Ala) and four L-Ala compounds in which hydrogen atoms (atomic mass = 1 amu) were substituted with deuterium atoms (atomic mass = 2 amu): L-Ala-2-d, L-Ala-3,3,3-d3, L-Ala-2,3,3,3-d4 and L-Ala-d7. The absorbance maxima of two L-Ala collective modes in this spectral range were recorded for multiple spectral measurements of each compound, and the magnitude of each collective mode frequency shift due to increased mass of these specific atoms was evaluated for statistical significance. Calculations were performed which predict the THz absorbance frequencies based on the estimated reduced mass of the modes. The shifts in absorbance maxima were correlated with the location(s) of the substituted deuterium atom(s) in the L-alanine molecule, and the atoms contributing to the absorbing delocalized mode in the crystal structure were deduced using statistics described herein. The statistical analyses presented also indicate that the precision of the method allows reproducible frequency shifts as small as 1 cm?1, or 0.03 THz to be observed, and that these shifts are not random error in the measurement. PMID:19331431

Taulbee, Anita R.; Heuser, Justin A.; Spendel, Wolfgang U.; Pacey, Gilbert E.

2009-01-01

269

Characterization of hollow polycarbonate metal waveguides using Terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2006-02-01

270

Probing the vibrational dynamics of proteins in liquid water by terahertz absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Biomolecules solvated in their biologically milieu are expected to exhibit strong absorption in the terahertz range that contain information on their global and subglobal collective vibrational modes and global dynamical correlations among solvent water molecules and the protein. Measurements in this region, however, are challenging due to due to the strong absorption of water and often sever interference artifacts. In response, we have developed, with Virginia Diode Inc., a highly sensitive Vector Network Analyzer system for probing collective dynamics in aqueous solution. Using this we explore the complex dielectric response from 0.07 to 0.70 THz that directly probes such questions as the hydration level around proteins and the large scale vibrational modes of biological polymers. We make a direct comparison to the existing molecular dynamic simulations and normal mode calculations and investigate the dependence of the low frequency dynamics on protein concentration and solvent pH. Our measurements shed light on the macromolecular motions in a biologically relevant water environment.

Quang Vinh, Nguyen; Plaxco, Kevin W.; Allen, S. James

2010-03-01

271

Terahertz quantum cascade laser based optical coherence tomography  

E-print Network

The interfaces of a dielectric sample are resolved in reflection geometry using light from a frequency agile array of terahertz quantum-cascade lasers. The terahertz source is a 10-element linear array of third-order ...

Lee, Alan W. M.

272

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

273

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

PubMed

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

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

2014-05-01

274

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

Microsoft Academic Search

We present measurements of the transient photoconductivity in pentacene single crystals using optical pump THz-probe spectroscopy. The temperature and fluence dependence of both photoinduced mobility and its dynamics are characterized.

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

2003-01-01

275

Hydration and hydrogen bond network of water around hydrophobic surface investigated by terahertz spectroscopy.  

PubMed

Water conformation around hydrophobic side chains of four amino acids (glycine, L-alanine, L-aminobutyric acid, and L-norvaline) was investigated via changes in complex dielectric constant in the terahertz (THz) region. Each of these amino acids has the same hydrophilic backbone, with successive additions of hydrophobic straight methylene groups (-CH2-) to the side chain. Changes in the degree of hydration (number of dynamically retarded water molecules relative to bulk water) and the structural conformation of the water hydrogen bond (HB) network related to the number of methylene groups were quantitatively measured. Since dielectric responses in the THz region represent water relaxations and water HB vibrations at a sub-picosecond and picosecond timescale, these measurements characterized the water relaxations and HB vibrations perturbed by the methylene apolar groups. We found each successive straight -CH2- group on the side chain restrained approximately two hydrophobic hydration water molecules. Additionally, the number of non-hydrogen-bonded (NHB) water molecules increased slightly around these hydrophobic side chains. The latter result seems to contradict the iceberg model proposed by Frank and Evans, where water molecules are said to be more ordered around apolar surfaces. Furthermore, we compared the water-hydrophilic interactions of the hydrophilic amino acid backbone with those with the water-hydrophobic interactions around the side chains. As the hydrophobicity of the side chain increased, the ordering of the surrounding water HB network was altered from that surrounding the hydrophilic amino acid backbone, thereby diminishing the fraction of NHB water and ordering the surrounding tetrahedral water HB network. PMID:25527962

Shiraga, K; Suzuki, T; Kondo, N; Ogawa, Y

2014-12-21

276

Hydration and hydrogen bond network of water around hydrophobic surface investigated by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Water conformation around hydrophobic side chains of four amino acids (glycine, L-alanine, L-aminobutyric acid, and L-norvaline) was investigated via changes in complex dielectric constant in the terahertz (THz) region. Each of these amino acids has the same hydrophilic backbone, with successive additions of hydrophobic straight methylene groups (-CH2-) to the side chain. Changes in the degree of hydration (number of dynamically retarded water molecules relative to bulk water) and the structural conformation of the water hydrogen bond (HB) network related to the number of methylene groups were quantitatively measured. Since dielectric responses in the THz region represent water relaxations and water HB vibrations at a sub-picosecond and picosecond timescale, these measurements characterized the water relaxations and HB vibrations perturbed by the methylene apolar groups. We found each successive straight -CH2- group on the side chain restrained approximately two hydrophobic hydration water molecules. Additionally, the number of non-hydrogen-bonded (NHB) water molecules increased slightly around these hydrophobic side chains. The latter result seems to contradict the iceberg model proposed by Frank and Evans, where water molecules are said to be more ordered around apolar surfaces. Furthermore, we compared the water-hydrophilic interactions of the hydrophilic amino acid backbone with those with the water-hydrophobic interactions around the side chains. As the hydrophobicity of the side chain increased, the ordering of the surrounding water HB network was altered from that surrounding the hydrophilic amino acid backbone, thereby diminishing the fraction of NHB water and ordering the surrounding tetrahedral water HB network.

Shiraga, K.; Suzuki, T.; Kondo, N.; Ogawa, Y.

2014-12-01

277

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

278

Noninvasive express diagnostics of pulmonary diseases based on control of patient's gas emission using methods of IR and terahertz laser spectroscopy  

NASA Astrophysics Data System (ADS)

Pulmonary diseases diagnostics always occupies one of the key positions in medicine practices. A large variety of high technology methods are used today, but none of them cannot be used for early screening of pulmonary diseases. We discuss abilities of methods of IR and terahertz laser spectroscopy for noninvasive express diagnostics of pulmonary diseases on a base of analysis of absorption spectra of patient's gas emission, in particular, exhaled air. Experience in the field of approaches to experimental data analysis and hard-ware realization of gas analyzers for medical applications is also discussed.

Starikova, M. K.; Bulanova, A. A.; Bukreeva, E. B.; Karapuzikov, A. A.; Karapuzikov, A. I.; Kistenev, Y. V.; Klementyev, V. M.; Kolker, D. B.; Kuzmin, D. A.; Nikiforova, O. Y.; Ponomarev, Yu. N.; Sherstov, I. V.; Boyko, A. A.

2013-11-01

279

Terahertz superconductor metamaterial  

NASA Astrophysics Data System (ADS)

We characterize the behavior of split ring resonators made up of high transition temperature yttrium barium copper oxide superconductor using terahertz time-domain spectroscopy measurements and numerical simulations. The superconductor metamaterial is found to show a remarkable change in the transmission spectra at the fundamental inductive-capacitive resonance as the temperature dips below the critical transition temperature. This resonance switching effect is normally absent in traditional metamaterials made up of regular metals. The temperature-dependent resonance behavior of the superconducting metamaterial would lead to development of low loss terahertz switches at cryogenic temperatures.

Gu, Jianqiang; Singh, Ranjan; Tian, Zhen; Cao, Wei; Xing, Qirong; He, Mingxia; Zhang, Jingwen W.; Han, Jiaguang; Chen, Hou-Tong; Zhang, Weili

2010-08-01

280

Reflectance spectroscopy in planetary science: Review and strategy for the future  

NASA Technical Reports Server (NTRS)

Reflectance spectroscopy is a remote sensing technique used to study the surfaces and atmospheres of solar system bodies. It provides first-order information on the presence and amounts of certain ions, molecules, and minerals on a surface or in an atmosphere. Reflectance spectroscopy has become one of the most important investigations conducted on most current and planned NASA Solar System Exploration Program space missions. This book reviews the field of reflectance spectroscopy, including information on the scientific technique, contributions, present conditions, and future directions and needs.

Mccord, Thomas B. (editor)

1987-01-01

281

Determination of plant silicon content with near infrared reflectance spectroscopy  

PubMed Central

Silicon (Si) is one of the most common elements in the earth bedrock, and its continental cycle is strongly biologically controlled. Yet, research on the biogeochemical cycle of Si in ecosystems is hampered by the time and cost associated with the currently used chemical analysis methods. Here, we assessed the suitability of Near Infrared Reflectance Spectroscopy (NIRS) for measuring Si content in plant tissues. NIR spectra depend on the characteristics of the present bonds between H and N, C and O, which can be calibrated against concentrations of various compounds. Because Si in plants always occurs as hydrated condensates of orthosilicic acid (Si(OH)4), linked to organic biomolecules, we hypothesized that NIRS is suitable for measuring Si content in plants across a range of plant species. We based our testing on 442 samples of 29 plant species belonging to a range of growth forms. We calibrated the NIRS method against a well-established plant Si analysis method by using partial least-squares regression. Si concentrations ranged from detection limit (0.24 ppmSi) to 7.8% Si on dry weight and were well predicted by NIRS. The model fit with validation data was good across all plant species (n = 141, R2 = 0.90, RMSEP = 0.24), but improved when only graminoids were modeled (n = 66, R2 = 0.95, RMSEP = 0.10). A species specific model for the grass Deschampsia cespitosa showed even slightly better results than the model for all graminoids (n = 16, R2 = 0.93, RMSEP = 0.015). We show for the first time that NIRS is applicable for determining plant Si concentration across a range of plant species and growth forms, and represents a time- and cost-effective alternative to the chemical Si analysis methods. As NIRS can be applied concurrently to a range of plant organic constituents, it opens up unprecedented research possibilities for studying interrelations between Si and other plant compounds in vegetation, and for addressing the role of Si in ecosystems across a range of Si research domains. PMID:25309567

Smis, Adriaan; Ancin Murguzur, Francisco Javier; Struyf, Eric; Soininen, Eeva M.; Herranz Jusdado, Juan G.; Meire, Patrick; Bråthen, Kari Anne

2014-01-01

282

The Use of Terahertz Spectroscopy in Biomolecular T. Harwood & Dr E. Ellis  

E-print Network

into close contact with the crystal to ensure close contact and good interaction between molecules and the evanescent wave. To reduce absorbance from liquid water, aqueous samples were dried directly onto the crystal complex molecules. Analysis of amino acids L-Cysteine and L-Serine show the potential of THz spectroscopy

Greenaway, Alan

283

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

284

Non-invasive detection of oral cancer using reflectance and fluorescence spectroscopy  

E-print Network

In vivo reflectance and fluorescence spectra were collected from patients with oral lesions, as well as healthy volunteers, in order to evaluate the potential of spectroscopy to serve as a non-invasive tool for the detection ...

McGee, Sasha Alanda

2008-01-01

285

Fiber-based swept-source terahertz radar.  

PubMed

We demonstrate an all-terahertz swept-source imaging radar operated at room temperature by using terahertz fibers for radiation delivery and with a terahertz-fiber directional coupler acting as a Michelson interferometer. By taking advantage of the high water reflection contrast in the low terahertz regime and by electrically sweeping at a high speed a terahertz source combined with a fast rotating mirror, we obtained the living object's distance information with a high image frame rate. Our experiment showed that this fiber-based swept-source terahertz radar could be used in real time to locate concealed moving live objects with high stability. PMID:20436563

Huang, Yu-Wei; Tseng, Tzu-Fang; Kuo, Chung-Chiu; Hwang, Yuh-Jing; Sun, Chi-Kuang

2010-05-01

286

Terahertz emission spectroscopy of laser-induced spin dynamics in TmFeO3 and ErFeO3 orthoferrites  

NASA Astrophysics Data System (ADS)

Using the examples of laser-induced spin-reorientation phase transitions in TmFeO3 and ErFeO3 orthoferrites, we demonstrate that terahertz emission spectroscopy can obtain novel information about ultrafast laser-induced spin dynamics, which is not accessible by more common all-optical methods. The power of the method is evidenced by the fact that, in addition to the expected quasi-ferromagnetic and quasi-antiferromagnetic modes of the iron sublattices, terahertz emission spectroscopy enables detection of a resonance optically excited at an unexpected frequency of ˜0.3-0.35 THz. By recording how the amplitude and phase of the excited oscillations depend on temperature and applied magnetic field, we show that the unexpected mode has all the features of a spin resonance of the Fe3 + ions. We suggest that it can be assigned to transitions between the multiplet sublevels of the 6A1 ground state of the Fe+3 ions occupying rare-earth positions.

Mikhaylovskiy, R. V.; Hendry, E.; Kruglyak, V. V.; Pisarev, R. V.; Rasing, Th.; Kimel, A. V.

2014-11-01

287

Dynamic coupling-decoupling crossover in the current-driven vortex-state in Tl[sub 2]Ba[sub 2]CaCu[sub 2]O[sub 8]studied using terahertz time-domain spectroscopy  

Microsoft Academic Search

Employing terahertz time-domain spectroscopy in transmission, they have measured the Josephson plasma resonance in TlBaCaCuO high-T{sub c} thin films, and studied the current-driven coupling-decoupling crossover in the driven vortex lattice.

V. K. Thorsmølle; R. D. Averitt; I. S. Aranson; M. P. Maley; L. N. Bulaevski; Antoinette J. Taylor

2004-01-01

288

Tethered bilayer lipid membranes studied by simultaneous attenuated total reflectance infrared spectroscopy and electrochemical impedance spectroscopy  

PubMed Central

The formation of tethered lipid bilayer membranes (tBLMs) from unilamelar vesicles of egg yolk phosphatidylcholine (EggPC) on mixed self–assembled monolayers (SAMs) from varying ratios of 6-mercaptohexanol and EO3Cholesteryl on gold has been monitored by simultaneous attenuated total reflectance fourier transform infrared (ATR–FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The influence of the lipid orientation (and hence the anisotropy) of lipids on a gold film on the dichroic ratio was studied by simulations of spectra with a matrix method for anisotropic layers. It is shown that for certain tilt angles of the dielectric tensor of the adsorbed anisotropic layer dispersive and negative absorption bands are possible. The experimental data indicates that the structure of the assemblies obtained varies with varying SAM composition. On SAMs with a high content of EO3Cholesteryl, tBLMs with reduced fluidity are formed. For SAMs with high content of 6-mercaptohexanol, the results are consistent with the adsorption of flattened vesicles, while spherical vesicles have been found in a small range of surface compositions. The kinetics of the adsorption process is consistent with the assumption of spherical vesicles as long–living intermediates for surfaces of high 6-mercaptohexanol content. No long–living spherical vesicles have been detected for surfaces with large fraction of EO3Cholesteryl tethers. The observed differences between the surfaces suggest that for the formation of tBLMs (unlike supported BLMs) no critical surface coverage of vesicles is needed prior to lipid bilayer formation. PMID:17388505

Erbe, Andreas; Bushby, Richard J.; Evans, Stephen D.; Jeuken, Lars J. C.

2013-01-01

289

Infrared/Terahertz double resonance spectroscopy of CH3F and CH3Cl at atmospheric pressure  

E-print Network

A new method for highly selective remote sensing of atmospheric trace polar molecular gases is described. Based on infrared/terahertz double resonance spectroscopic techniques, the molecule- specific coincidence between the lines of a CO2 laser and rotational-vibrational molecular absorption transitions provide two dimensions of recognition specificity: infrared coincidence frequency and the corresponding terahertz frequency whose absorption strength is modulated by the laser. Atmospheric pressure broadening expands the molecular recognition "specificity matrix" by simultaneously relaxing the infrared coincidence requirement and strengthening the corresponding terahertz signature. Representative double resonance spectra are calculated for prototypical molecules CH3F and CH3Cl and their principal isotopomers, from which a heuristic model is developed to estimate the specificity matrix and double resonance signature strength for any polar molecule.

Dane J. Phillips; Elizabeth A. Tanner; Frank C. De Lucia; Henry O. Everitt

2012-05-12

290

Reflectance spectroscopy of pigmented cutaneous benign and malignant lesions  

NASA Astrophysics Data System (ADS)

For the DRS measurements of skin benign, dysplastic and malignant lesions in vivo we applied halogen lamp (LS-1, OceanOptics Inc, Dunedin, Fl, USA) as a continuous light source in the region of 400-900 nm, optical probe (6+1 fibers) for the delivery of illumination and diffuse reflected light from the skin investigated and microspectrometer USB4000 (OceanOptics Inc., Dunedin, Fl, USA) for a storage and display of the spectra detected. As a diffuse reflectance standard Spectralon® plate was used to calibrate the spectrometer. The reflectance spectra obtained from normal skin in identical anatomic sites of different patients have similar spectral shape features, slightly differ by the reflectance intensity at different wavelengths, depending on the particular patient' skin phototype. One could find diagnostically important spectral features, related to specific intensity changes for a given wavelength due to specific pigments appearance, slope changes by value and sign for the reflectance spectra curves in a specific spectral range, disappearance or manifestation of minima, related to hemoglobin absorption at 410-420 nm, 543, 575 nm. Based on the observed peculiarities multispectral analysis of the reflectance spectra of the different lesions was used and diagnostically specific features are found. Discrimination using the DRS data obtained between benign compound and dermal nevi (45 cases), dysplastic nevi (17 cases) and pigmented malignant melanoma (41 cases) lesions is achieved with a diagnostic accuracy of 96 % for the benign nevi vs. MM, and 90 % for the dysplastic nevi vs. MM.

Borisova, E.; Jeliazkova, Al.; Pavlova, E.; Troyanova, P.; Kundurdjiev, T.; Pavlova, P.; Avramov, L.

2014-10-01

291

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

PubMed Central

The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p?=?1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p?=?0.98) and less so for normal breast (p?=?0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues. PMID:25010734

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

2014-01-01

292

Use of finite difference time domain simulations and Debye theory for modelling the terahertz reflection response of normal and tumour breast tissue.  

PubMed

The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues. PMID:25010734

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

2014-01-01

293

Terahertz Spectroscopy of 2,4-Dinitrotoluene over a Wide Temperature Range (7-245 K).  

PubMed

Previous THz spectroscopy of the TNT explosive precursor, 2,4-dinitrotoluene (DNT), has been restricted to room temperature (apart from one set of data at 11 K). Here, for the first time, we investigate the spectrum as the temperature is systematically varied, from 7 to 245 K. Many new features appear in the spectrum on cooling below room temperature. As well as the five absorption lines observed previously, we observe five additional lines. In addition, a new room-temperature line at 8.52 THz (281 cm(-1)) is observed. Six of the lines red-shift with temperature and four of them blue-shift. The blue shift is explained by interplay between intramolecular and intermolecular hydrogen bonds. The variation in line width and line intensity with temperature is not systematic, although a conspicuous decrease in line intensity with temperature is observed in all cases. Modeling with hybrid PBE0 and TPSSh functionals helps identify absorption modes. PMID:25565292

Lepodise, Lucia M; Horvat, Joseph; Lewis, R A

2015-01-15

294

Study of paraffin-embedded colon cancer tissue using terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

In this work, samples of non-neoplastic and adenocarcinoma-affected human colon tissue samples were analyzed using multipoint transmission time-domain THz spectroscopy (THz-TDS) to sort out the contrast-contributing factors other than water, the main contrast mechanism factor in in-vivo or in freshly excised bio-tissue. Solving the electromagnetic inverse problem through THz-TDS and, analyzing the transmittance spectra that yielded the frequency-dependent absorption coefficient ? and refractive index n of non-neoplastic and neoplastic tissues, we show that it is possible to distinguish between non-neoplastic and neoplastic regions in paraffin-embedded dehydrated. Results and discussion are presented.

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

2015-01-01

295

Quantification of Nitrogen Status in Rice by Least Squares Support Vector Machines and Reflectance Spectroscopy  

Microsoft Academic Search

The estimation of nitrogen status non-destructively in rice was performed using canopy spectral reflectance with visible and\\u000a near-infrared reflectance (Vis\\/NIR) spectroscopy. The canopy spectral reflectance of rice grown with different levels of nitrogen\\u000a inputs was determined at several important growth stages. This study was conducted at the experiment farm of Zhejiang University,\\u000a Hangzhou, China. The soil plant analysis development (SPAD)

Yongni Shao; Chunjiang Zhao; Yidan Bao; Yong He

296

Doppler-shifted reflections of X rays in beamfoil spectroscopy  

NASA Technical Reports Server (NTRS)

Carbon foils were positioned at roughly 10 deg to the conventional perpendicular position so that the spectrometer would view the beam on emergence from the foil, with no radiation shielded by a bowed or wrinkled foil or by the foil holder. Extraneous peaks due to reflected radiation were detected in the spectrum obtained with the tilted foil. A large satellite appears longward of the spectral line and is attributed to Doppler-shifted radiation reflected from the foil surface. Special tests arranged to validate the origin of the satellites are described. The relative intensity of the reflected radiation compared with the direct radiation observed is at variance with the relative intensities reported for longer wavelengths. The reasons for this, possible effects of spectrometer geometry, and applications in the investigation or generation of polarization remain to be investigated

Bernstein, E. M.; Mcintyre, L. C., Jr.

1976-01-01

297

Carrier dynamics in bulk ZnO. II. Transient photoconductivity measured by time-resolved terahertz spectroscopy  

E-print Network

thin-film transistor,4 and electron-transport material in nanostructured solar cells.5­7 Electron to improving their perfor- mance. Carrier dynamics in ZnO bulk crystals, thin films, nano- wiresCarrier dynamics in bulk ZnO. II. Transient photoconductivity measured by time-resolved terahertz

298

Terahertz spectroscopy of N$^{18}$O and isotopic invariant fit of several nitric oxide isotopologs  

E-print Network

A tunable far-infrared laser sideband spectrometer was used to investigate a nitric oxide sample enriched in 18O between 0.99 and 4.75 THz. Regular, electric dipole transitions were recorded between 0.99 and 2.52 THz, while magnetic dipole transitions between the 2Pi(1/2) and 2Pi(3/2) spin-ladders were recorded between 3.71 and 4.75 THz. These data were combined with lower frequency data of N(18)$O (unlabeled atoms refer to (14)N and (16)O, respectively), with rotational data of NO, (15)NO, N(17)O, and (15)N(18)O, and with heterodyne infrared data of NO to be subjected to one isotopic invariant fit. Rotational, fine and hyperfine structure parameters were determined along with vibrational, rotational, and Born-Oppenheimer breakdown corrections. The resulting spectroscopic parameters permit prediction of rotational spectra suitable for the identification of various nitric oxide isotopologs especially in the interstellar medium by means of rotational spectroscopy.

Müller, Holger S P; Takahashi, Kazumasa; Tomaru, Kazuko; Matsushima, Fusakazu

2014-01-01

299

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

300

Terahertz Time Domain Spectroscopy of Simple Astrophysically Relevant Ices: the Structure of the Ice  

NASA Astrophysics Data System (ADS)

International astronomical facilities, in particular the Herschel Space Telescope, SOFIA and ALMA, are currently characterizing the interstellar medium (ISM) by collecting a huge amount of new THz spectral data that must be compared to THz laboratory spectra to be interpreted. The latter, however, are largely lacking, and this severely restricts the scientific impact of the astronomical observations. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar relevant ice analogs in the range between 0.3 - 7 THz. The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm^{-1}). The THz region of the electromagnetic spectrum is dominated by large amplitude motions, such as phonon modes and intermolecular vibrations, along with high-frequency torsional motions of individual species. This talk will focus on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H_{2}O, CO_{2}, CO, CH_{3}OH, NH_{3}, CH_{4}). Different temperatures, mixing ratios, and matrix isolation experiments will be shown. The ultimate goal of this research project is to provide the scientific community with an extensive THz ice-database, which will allow quantitative studies of the ISM, and guide future astronomical observations of species in the solid phase.

Ioppolo, Sergio; Allodi, Marco A.; McGuire, Brett A.; Kelley, Matthew J.; Blake, Geoffrey A.

2013-06-01

301

ChemCam Passive Reflectance Spectroscopy at Gale Crater, Mars  

NASA Astrophysics Data System (ADS)

The Laser-Induced Breakdown Spectrometer (LIBS) portion of the ChemCam instrument on the Mars Science Laboratory Curiosity rover uses 3 dispersive spectrometers to cover the ultraviolet (240-342 nm), visible (382-469 nm) and visible/near-infrared (474-906 nm) spectral regions at high spectral (<0.5nm) and spatial (0.65mrad) resolution. In active LIBS mode, light emitted from a laser-generated plasma is dispersed onto these spectrometers and used to detect elemental emission lines. Typical observations include 3 msec-exposure 'dark' spectra (acquired with the LIBS laser off) used to remove the background signal from the LIBS measurement. Similar 'passive' observations of the ChemCam calibration target holder can be made at similar times of day and at identical exposure times (to minimize variations from dark current). Because this target exhibits ~95% flat reflectance in the ~400-900 nm region, radiance spectra ratios (surface/calibration target) can be normalized to known calibration target lab spectra to produce relative reflectance spectra (400-900 nm) with an estimated accuracy of 10-20%. Initial results replicated the known spectral shape and overall reflectance values of the ChemCam calibration targets and green color chip on the Mastcam calibration target. Dust contamination was evident, although dust on the ChemCam calibration targets is minimized by their tilted placement on the rover deck. All ChemCam targets that were sunlit during LIBS acquisition (~80% of all measurements) provide 'dark' spectra for which relative reflectance spectra can be obtained. Owing to the dusty nature of the Gale landing sites, passive spectra observed to date exhibit spectral shapes indicative of ferric phases, similar to spectra of palagonitic soils. Most spectra are bracketed in reflectance by typical 'bright' and 'dark' spectra from the OMEGA and CRISM orbital spectrometers. Preliminary Mastcam reflectance spectra are similar, providing additional confidence regarding the first-order calibration of the ChemCam spectra. The spectral similarity to palagonitic soils is consistent with the results from the CheMin instrument for Rocknest sands. Changes in the 535 nm band depth are likely indicative of differences in the relative amount of ferric iron in crystalline phases. More strongly negative spectral slopes > 600 nm are typical of lower-reflectance, less dusty rock surfaces, whereas positive slopes < 600 nm are consistent with higher-reflectance, dustier surfaces. ChemCam elemental detections of Ca- and S-bearing veins correlate to high reflectance targets with some dust contamination. Spectra of the John_Klein and Cumberland drill tailings, as well as brushed and broken rock surfaces in the Yellowknife Bay area, exhibit much less 'red' spectral features, including inflections near 550 nm that are consistent with a number of ferrous and ferric iron-bearing clay mineral phases, similar to CheMin results. Ongoing work with ChemCam passive spectra will include efforts to utilize the UV spectral range (sensitive to iron content), investigate photometric effects of illumination variations on the calibration targets, and dust mitigation efforts. As Curiosity traverses toward Mt. Sharp, passive spectra will be used as an additional tool to remotely track variations in surface chemistry and mineralogy, particularly for iron-bearing sulfate, oxide, and clay minerals.

Johnson, J. R.; Bell, J. F.; Cloutis, E.; Bender, S.; Blaney, D. L.; Ehlmann, B. L.; Gasnault, O.; Kinch, K. M.; Le Mouelic, S.; Rice, M. S.; Wiens, R. C.; DeFlores, L.; Team, M.

2013-12-01

302

Review of Terahertz Tomography Techniques  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

303

Terahertz time-domain reflectometry of multilayered systems  

NASA Astrophysics Data System (ADS)

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

Jackson, J. Bianca

304

Polarization modulation of terahertz electromagnetic radiation by four-contact photoconductive antenna.  

PubMed

Generation and modulation of circularly polarized terahertz electromagnetic radiation have been demonstrated by using a four-contact photoconductive antenna and a total-reflection Si prism. The quality of the circularly polarized terahertz pulsed radiation has been evaluated by using a polarization sensitive terahertz time-domain spectroscopy system. The characteristic of the dynamic modulation between the left and right circularly polarized states of the THz radiation is also evaluated. The ellipticity of the modulated circularly polarized THz radiation without a polarizer is not as good as that of the non-modulated because of the non-uniform bias field distribution and the asymmetric pump laser intensity profile on the photoconductive gap. PMID:19516602

Hirota, Yuichi; Hattori, Ryo; Tani, Masahiko; Hangyo, Masanori

2006-05-15

305

Review in terahertz spectral analysis Josette El Haddad, Bruno Bousquet, Lionel Canioni, Patrick Mounaix  

E-print Network

analytical technique. Keywords: Terahertz spectroscopy; far infrared spectroscopy; vibrational spectroscopy diagnostics[8]. Ranging between far infrared and microwaves (cf. Fig. 1), THz spectroscopy is a powerful tool]. THz spectroscopy is generally considered as being different from conventional far- infrared

Paris-Sud XI, Université de

306

Propagation of terahertz pulses in photoexcited media: Analytical theory for layered systems  

E-print Network

­terahertz probe spectroscopy has become a widely used experimental tool for the investigation of the ultrafast far-infrared-domain terahertz spectroscopy uses broadband picosecond pulses of far infrared radiation with frequencies most these terahertz pulses are used to probe changes of the far-infrared susceptibility or conductivity spectrum initi

KuÂ?el, Petr

307

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

308

Point contact Andreev reflection spectroscopy on ferromagnet/superconductor bilayers  

NASA Astrophysics Data System (ADS)

We performed point contact spectroscopy experiment by pushing gold tip on the ferromagnetic side of Nb/Pd0.84Ni0.16 bilayers. Several contacts have been measured at temperature 4.2 K evidencing a wide variety of features (zero bias peak, conductance dips, etc.) appearing in the differential conductance spectra at energies up to Nb energy gap. A theoretical model has been developed within the scattering theory for ferromagnetic/superconductor heterostructures to fit experimental data. All different features can be consistently explained in our model by taking into account the spin polarization as well as the thickness of the ferromagnetic layer. We also show that we can give very precise estimation of such ferromagnetic characteristics.

Giubileo, F.; Romeo, F.; Citro, R.; Di Bartolomeo, A.; Attanasio, C.; Cirillo, C.; Polcari, A.; Romano, P.

2014-08-01

309

Terahertz metamaterials  

DOEpatents

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

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

2014-08-12

310

Employing time-resolved terahertz spectroscopy to analyze carrier dynamics in thin-film Cu{sub 2}ZnSn(S,Se){sub 4} absorber layers  

SciTech Connect

We report the application of time-resolved terahertz spectroscopy (TRTS) to measure photoexcited carrier lifetimes and mobility, and to determine recombination mechanisms in Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) thin films fabricated from nanocrystal inks. Ultrafast time resolution permits tracking the evolution of carrier density to determine recombination rates and mechanisms. The carrier generation profile was manipulated by varying the photoexcitation wavelength and fluence to distinguish between surface, Shockley-Read-Hall (SRH), radiative, and Auger recombination mechanisms and determine rate constants. Surface and SRH recombination are the dominant mechanisms for the air/CZTSSe/SiO{sub 2}/Si film stack. Diffusion to, and then recombination at, the air-CZTSSe interface occurred on the order of 100 picoseconds, while SRH recombination lifetimes were 1–2 nanoseconds. TRTS measurements can provide information that is complementary to conventional time-resolved photoluminescence measurements and can direct the design of efficient thin film photovoltaics.

Guglietta, Glenn W.; Baxter, Jason B. [Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104 (United States); Choudhury, Kaushik Roy; Caspar, Jonathan V. [DuPont Central Research and Development, Experimental Station, Wilmington, Delaware 19880 (United States)

2014-06-23

311

Bidirectional reflectance spectroscopy. [for Moon, asteroid, Europa, and Oberon  

NASA Technical Reports Server (NTRS)

An analytical model is developed for the opposition effects (heiligenshein) in the case of light scattering from a semi-infinite, particulate medium with particles that are large relative to the wavelength. The effect is common for natural materials, and comprises a bright surge in light diffusively reflected from a surface at near zero phase. A generalized expression is devised for the extinction coefficient of a particulate medium. Models are developed for step function and hyperbolic tangent distributions of light scattered from a stratified medium and exhibiting the opposition effect. A maximum brightness amplitude increase of 0.753 is projected for the effect. Greater values must have other causes. To illustrate the theory it is fitted to observations of the Moon, an asteroid, and a satellite of Uranus; Europa is also discussed.

Hapke, Bruce

1987-01-01

312

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

Microsoft Academic Search

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

Ravin Gnanasambandam; A Proctor

2000-01-01

313

Transmission Features of Frequency-Selective Components in the Far Infrared Determined by Terahertz Time-Domain Spectroscopy  

Microsoft Academic Search

Transmission and phase-shift characteristics of dichroic high-pass filters with cutoff frequencies as high as 1.11 THz and of a cross-shaped grid bandpass filter with a resonance frequency of 280 GHz were measured with an electro-optic sampling terahertz time-domain spectrometer operating between 0.1 and 2 THz. Good agreement with transmission theories is found. We also compare the transmission performance of cascaded

Carsten Winnewisser; Frank Lewen; Jochen Weinzierl; Hanspeter Helm

1999-01-01

314

In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy  

NASA Astrophysics Data System (ADS)

We present results from the anodization of an aluminum single crystal [Al(111)] and an aluminum alloy [Al 6060] studied by in situ x-ray reflectivity, in situ electrochemical impedance spectroscopy and ex situ scanning electron microscopy. For both samples, a linear increase of oxide film thickness with increasing anodization voltage was found. However, the slope is much higher in the single crystal case, and the break-up of the oxide film grown on the alloy occurs at a lower anodization potential than on the single crystal. The reasons for these observations are discussed as are the measured differences observed for x-ray reflectivity and electrochemical impedance spectroscopy.

Bertram, F.; Zhang, F.; Evertsson, J.; Carlà, F.; Pan, J.; Messing, M. E.; Mikkelsen, A.; Nilsson, J.-O.; Lundgren, E.

2014-07-01

315

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

316

Cavity enhanced terahertz modulation  

SciTech Connect

We present a versatile concept for all optical terahertz (THz) amplitude modulators based on a Fabry-Pérot semiconductor cavity design. Employing the high reflectivity of two parallel meta-surfaces allows for trapping selected THz photons within the cavity and thus only a weak optical modulation of the semiconductor absorbance is required to significantly damp the field within the cavity. The optical switching yields to modulation depths of more than 90% with insertion efficiencies of 80%.

Born, N., E-mail: norman.born@physik.uni-marburg.de [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States); Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany); Scheller, M.; Moloney, J. V. [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States)] [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States); Koch, M. [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany)] [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany)

2014-03-10

317

Morphotropic phase transition studies in by far-infrared reflectance spectroscopy  

Microsoft Academic Search

The morphotropic phase transition in the system has been studied by far-infrared reflectance spectroscopy. The reflectance measurements are performed on compositions with x = 0.0, 0.10, 0.20, 0.30, 0.35, 0.40 and 0.525 at room temperature in the frequency range . The spectrum is fitted with a model based on the factorized form of the dielectric function. The dependences of the

V Sivasubramanian; V R K Murthy; B Viswanathan; M Sieskind

1996-01-01

318

Characterization of molecular and biomolecular layers on diamond thin films by infrared reflection-absorption spectroscopy  

Microsoft Academic Search

We explore the use of single-bounce infrared reflection-absorption spectroscopy (IRRAS) to characterize molecular and biomolecular layers on doped and undoped diamond thin films on silicon substrates. Experimental measurements of thin layers of poly(methyl methacrylate) (PMMA) as a function of polarization and angle of incidence were used to characterize the intensity, frequency, and symmetry of the vibrational features. Fresnel multilayer reflectivity

Robert J. Hamers; Courtney Stavis; Ankit Pokhrel; Ryan Franking; Rose E. Ruther; Xiaoyu Wang; Michelle C. Cooperrider; Hongjun Zheng; John A. Carlisle; James E. Butler

2011-01-01

319

Weathering Grade Classification of Granite Stone Monument Using Reflectance Spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

320

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

321

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

PubMed

A series of 33 different polycyclic aromatic hydrocarbons (PAHs) were studied by far infrared spectroscopy (terahertz spectroscopy) in the spectral range comprised between 600 and 50 cm(-1). In addition to common PAHs like naphthalene, anthracene, phenanthrene, fluoranthene, picene, pyrene, benzo[?]pyrene, and perylene, also quite unusual PAHs were studied like tetracene, pentacene, acenaphtene, acenaphtylene, triphenylene, and decacyclene. A series of alkylated naphthalenes and anthracenes were studied as well as methypyrene. Partially or totally hydrogenated PAHs were also object of the present investigation, ranging from tetrahydronaphthalene (tetralin) to decahydronaphthalene (decalin), 9,10-dihydroanthracene, 9,10-dihydrophenanthrene, hexahydropyrene, and dodecahydrotriphenylene. Finally, the large and quite rare PAHs coronene, quaterrylene, hexabenzocoronene, and dicoronylene were studied by far infrared spectroscopy. The resulting reference spectra were used in the interpretation of the chemical structure of asphaltenes (as extracted from a heavy petroleum fraction and from bitumen), the chemical structures of other petroleum fractions known as DAE (distillate aromatic extract) and RAE (residual aromatic extract), and a possible interpretation of components of the chemical structure of anthracite coal. Asphaltenes, heavy petroleum fractions, and coal were proposed as model compounds for the interpretation of the emission spectra of certain proto-planetary nebulae (PPNe) with a good matching in the mid infrared between the band pattern of the PPNe emission spectra and the spectra of these oil fractions or coal. Although this study was finalized in an astrochemical context, it may find application also in the petroleum and coal chemistry. PMID:23603577

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

2013-07-01

322

Atmospheric absorption of terahertz radiation and water vapor continuum effects  

E-print Network

Atmospheric absorption of terahertz radiation and water vapor continuum effects David M. Slocum a April 2013 Keywords: Water vapor Absorption Continuum Terahertz Spectroscopy a b s t r a c t The water vapor continuum absorption spectrum was investigated using Fourier Trans- form Spectroscopy

Massachusetts at Lowell, University of

323

Reflectance and Thermal Infrared Spectroscopy of Mars: Relationship Between ISM and TES for Compositional Determinations  

NASA Technical Reports Server (NTRS)

Reflectance spectroscopy has demonstrated that high albedo surfaces on Mars contain heavily altered materials with some component of hematite, poorly crystalline ferric oxides, and an undefined silicate matrix. The spectral properties of many low albedo regions indicate crystalline basalts containing both low and high calcium pyroxene, a mineralogy consistent with the basaltic SNC meteorites. The Thermal Emission Spectrometer (TES) experiment on the Mars Geochemical Surveyor has acquired critical new data relevant to surface composition and mineralogy, but in a wavelength region that is complementary to reflectance spectroscopy. The essence of the completed research was to analyze TES data in the context of reflectance data obtained by the French ISM imaging spectrometer experiment in 1989. This approach increased our understanding of the complementary nature of these wavelength regions for mineralogic determinations using actual observations of the martian surface. The research effort focused on three regions of scientific importance: Syrtis Major-Isidis Basin, Oxia Palus-Arabia, and Valles Marineris. In each region distinct spatial variations related to reflectance, and in derived mineralogic information and interpreted compositional units were analyzed. In addition, specific science questions related to the composition of volcanics and crustal evolution, soil compositions and pedogenic processes, and the relationship between pristine lithologies and weathering provided an overall science-driven framework for the work. The detailed work plan involved colocation of TES and ISM data, extraction of reflectance and emissivity spectra from areas of known reflectance variability, and quantitative analysis using factor analysis and statistical techniques to determine the degree of correspondence between these different wavelength regions. Identified coherent variations in TES spectroscopy were assessed against known atmospheric effects to validate that the variations are due to surface properties. With this new understanding of reflectance and emission spectroscopy, mineralogic interpretations were derived and applied to the science objectives of the three regions.

Boyce, Joseph (Technical Monitor); Mustard, John

2004-01-01

324

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

325

Use of Near Infrared Reflectance Spectroscopy (NIRS) for Predicting Soil Fertility and Historical Management  

Microsoft Academic Search

This study tests the potential of near infrared reflectance spectroscopy (NIRS) for predicting soil fertility and management history from topsoil (0–10 cm deep) spectra. Soil fertility was assessed by measuring the growth of a test plant, and soil management history was determined through inquiries with farmers. Moreover, NIRS predictive value was compared with that of a group of topsoil parameters:

Grégoire T. Freschet; Bernard G. Barthès; Didier Brunet; Edmond Hien; Dominique Masse

2011-01-01

326

Prediction of digestible organic matter of grass silage by near infrared reflectance spectroscopy  

E-print Network

Prediction of digestible organic matter of grass silage by near infrared reflectance spectroscopy I Klemetti M Hellämäki J Nousiainen Valio Ltd, Farm Services, PO Box 390, 00101 Helsinki, Finland Grass to estimate the nutritive value of grass silage as accurately as possible and with low cost. Annually more

Paris-Sud XI, Université de

327

RELAB (REFLECTANCE EXPERIMENT LABORATORY): A NASA MULTIUSER SPECTROSCOPY FACILITY. Carl M. Pieters  

E-print Network

to near-infrared wavelengths, and 2) a Nicolet 870 Nexus FTIR spectrometer for a) near- to far- infrared- to far-infrared measure- ments. Components of the system are shown in Figure 3. Much of this systemRELAB (REFLECTANCE EXPERIMENT LABORATORY): A NASA MULTIUSER SPECTROSCOPY FACILITY. Carlé M. Pieters

Hiroi, Takahiro

328

Near infrared reflectance spectroscopy to predict energy value of compound feeds for swine and ruminants  

Microsoft Academic Search

Near infrared reflectance spectroscopy (NIRS) was compared with analytical methods for predicting chemical composition, digestibility and energy content of compound feeds for swine and ruminants. The study investigated numerous widely diversified feeds with known in vivo measurements (87 swine and 80 ruminant feeds). Accuracy of prediction of the energy values of swine and ruminant feeds using NIRS was slightly better

Jocelyne Aufrère; Dominique Graviou; C. Demarquilly; J. M. Perez; J. Andrieu

1996-01-01

329

Measurement of Trans-Fatty Acids in Cereal Products Without Oil Extraction Using NIR Reflectance Spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

Near infrared (NIR) reflectance spectroscopy was evaluated as a rapid technique, to determine the trans-fatty acid content of ground cereal products. NIR spectra were obtained with a dispersive spectrometer and trans-fatty acids determined by modified AOAC Method 996.01. First derivative PLS1 mode...

330

Infrared Reflection Absorption Spectroscopy Study of CO Adsorption and Reaction on Oxidized Pd(100)  

E-print Network

to the adsorption energies of oxygen, the heats of formation of the bulk oxides, and the metal particle sizesInfrared Reflection Absorption Spectroscopy Study of CO Adsorption and Reaction on Oxidized Pd(100 oxidation on Pt group metals at temperatures between 450 and 600 K and pressures between 1 and 300 Torr

Goodman, Wayne

331

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...

332

Nondestructive Olive Quality Detection Using FT-NIR Spectroscopy in Reflectance Mode  

Technology Transfer Automated Retrieval System (TEKTRAN)

Quality features (firmness, oil content and color in terms of hue and chroma) of two olive (Olea europaea L) varieties (‘Ayvalik’ and ‘Gemlik’) were predicted using Fourier transform near-infrared (FT-NIR) spectroscopy. Reflectance measurements of intact olives were performed using a bifurcated fibe...

333

Cis and trans fatty acid determination directly in ground cereal products by NIR reflectance spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

The potential of near infrared (NIR) reflectance spectroscopy for prediction of cis- and trans-fatty acids directly in ground cereal products was investigated. NIR spectra (400-2498 nm) of ground cereal products were obtained with a dispersive spectrometer and trans-fatty acids, cis-fatty acids an...

334

Characterization of Si3N4/Si(111) thin films by reflectance difference spectroscopy  

NASA Astrophysics Data System (ADS)

Si3N4 has become an important material with great technological and scientific interests. The lattice symmetry and the crystallinity quality of Si3N4 thin films are fundamental parameters that must be determined for different applications. In order to evaluate the properties of Si3N4 films, we used reflectance difference spectroscopy/reflectance anisotropy spectroscopy (RDS/RAS) to measure the optical anisotropy of Si3N4 thin films (1–2 nm) grown by nitridation of two different Si(111) substrates, one with a 4.2° miscut off towards the [11\\bar{2}] direction and another one with a nonintentional miscut. We demonstrate that, by modifying the measurement optical setup, we could increase the RD sensitivity and clearly display the optical response corresponding to the hexagonal symmetry of the Si3N4 thin layer. Our results are in good agreement with reflection high energy electron diffraction (RHEED) measurements for both misoriented and oriented substrates.

Lastras-Martínez, Luis Felipe; Ulloa-Castillo, Nicolás Antonio; Herrera-Jasso, Rafael; Balderas-Navarro, Raúl Eduardo; Lastras-Martínez, Alfonso; Pandikunta, Mahesh; Ledyaev, Oleg; Kuryatkov, Vladimir; Nikishin, Sergey

2015-02-01

335

Diagnostics of pigmented skin tumors based on laser-induced autofluorescence and diffuse reflectance spectroscopy  

SciTech Connect

Results of investigation of cutaneous benign and malignant pigmented lesions by laser-induced autofluorescence spectroscopy (LIAFS) and diffuse reflectance spectroscopy (DRS) are presented. The autofluorescence of human skin was excited by a 337-nm nitrogen laser. A broadband halogen lamp (400-900 nm) was used for diffuse reflectance measurements. A microspectrometer detected in vivo the fluorescence and reflectance signals from human skin. The main spectral features of benign (dermal nevi, compound nevi, dysplastic nevi) and malignant (melanoma) lesions are discussed. The combined usage of the fluorescence and reflectance spectral methods to determine the type of the lesion, which increases the total diagnostic accuracy, is compared with the usage of LIAFS or DRS only. We also applied colorimetric transformation of the reflectance spectra detected and received additional evaluation criteria for determination of type of the lesion under study. Spectra from healthy skin areas near the lesion were detected and changes between healthy and lesion skin spectra were revealed. The influence of the main skin pigments on the detected spectra is discussed and evaluation of possibilities for differentiation between malignant and benign lesions is performed based on their spectral properties. This research shows that the non-invasive and high-sensitive in vivo detection by means of appropriate light sources and detectors should be possible, related to the real-time determination of existing pathological conditions. (special issue devoted to application of laser technologies in biophotonics and biomedical studies)

Borisova, E; Avramov, L [Institute of Electronics, Bulgarian Academy of Sciences, Sofia (Bulgaria); Troyanova, P [National Oncological Diagnostic Center, Sofia (Bulgaria); Pavlova, P [Technical University Sofia, branch Plovdiv (Bulgaria)

2008-06-30

336

Real-time control of quantum dot laser growth using reflectance anisotropy spectroscopy  

NASA Astrophysics Data System (ADS)

Reflectance and reflectance anisotropy spectroscopy (RAS) were used to control in-situ the complex MOCVD growth process of both InGaAs/GaAs quantum dots (QDs) and lasers with such QDs in the active region. Spectra and transients yield online information on details of quantum dot and cavity formation, like InGaAs monolayer deposition prior to QD formation and evolution of the cavity resonance. The data were used to develop laser devices including the first electrically driven vertical cavity surface emitting QD laser (QD VCSEL) grown by using MOCVD.

Pohl, U. W.; Pötschke, K.; Kaiander, I.; Zettler, J.-T.; Bimberg, D.

2004-12-01

337

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. PMID:20490288

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

2009-01-01

338

Reflection electron energy loss spectroscopy during initial stages of Ge growth on Si by molecular beam epitaxy  

E-print Network

Reflection electron energy loss spectroscopy during initial stages of Ge growth on Si by molecular for publication 23 October 1990) Using a conventional reflection high-energy electron diffraction gun together intensities from Si L2 s and Ge L2,3 core losses with reflection electron diffraction data in order to analyze

Atwater, Harry

339

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

340

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

341

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

342

Reconciling Differences in Global Iron Estimates Using Gamma-ray\\/Neutron and Reflectance Spectroscopy  

Microsoft Academic Search

Iron abundance is a key petrologic discriminator for interpretation of airless body surfaces from both remote and field perspectives. Independent measurements of iron abundance from gamma-ray\\/neutron and reflectance spectroscopy are available for the Moon. However, there are significant discrepancies between these two data products for many locations (e.g., South Pole-Atken, Tycho, etc.) [Lawrence et al., 2002]. In some cases, these

J. Cahill; J. J. Hagerty; D. J. Lawrence

2010-01-01

343

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. PMID:19269331

Thompson, Nancy L.; Wang, Xiang; Navaratnarajah, Punya

2009-01-01

344

Prediction of milk fatty acid composition by near infrared reflectance spectroscopy  

Microsoft Academic Search

Near-infrared reflectance spectroscopy (NIRS) (700–2500 nm) was used to predict milk fatty acid (FA) composition. Broad FA variability was ensured by using experimental cow milk derived from different feeding regimes (pasture and preserved forages with or without lipid supplements). Detailed FA composition was analyzed by gas chromatography. Predictive equations (354 samples) were developed for liquid and oven-dried milk samples using modified

Mauro Coppa; Anne Ferlay; Christine Leroux; Michel Jestin; Yves Chilliard; Bruno Martin; Donato Andueza

2010-01-01

345

Application of Diffuse Reflectance FT-IR Spectroscopy for the Surface Study of Kevlar Fibers  

NASA Astrophysics Data System (ADS)

The surfaces of Kevlar-49 aramid fibers, being used in high-performance composite materials, have been characterized by diffuse reflectance Fourier transform infrared (FT-IR) spectroscopy. Enhancement of the surface selectivity of the technique has been achieved using KBr overlayers. The water absorbed by both the skin and the core of the fibers has been characterized by using this technique and the accessibility of the fiber functional groups has been evaluated.

Chatzi, E. G.; Ishida, H.; Koenig, J. L.

1985-12-01

346

Terahertz traveling-wave microtube  

NASA Astrophysics Data System (ADS)

Microwave Technologies is developing a revolutionary miniature terahertz traveling-wave microtube (TTM) that will provide sub-millimeter wave radiation for many civilian and military applications. This new concept uses a dielectric microtube in conjunction with a microscopic electron beam. The electron beam is produced by a single micron-sized emitter, which lies underneath the microtube to produce high-power terahertz electromagnetic radiation. The TTM should be easily fabricated using state-of-the-art solid-state technology, and will be a pioneering step towards combining vacuum tube technology with solid-state microfabrication technology. Some of the applications for these exciting new devices include terahertz high-resolution radar, THz chemical and biological sensing, commercial THz line-of-sight networking and ultrahigh-speed computers. A key application of the device under development will be as a miniature terahertz source for biological and chemical spectroscopy. We present detailed numerical and computational analysis of this concept. We also present initial experimental testing of a dielectric microtube designed to operate at 0.1 THz. Once successfully developed, TTMs will be the basis for a new generation of high power terahertz sources capable of producing ultrahigh frequency radiation with high efficiency in an amazingly compact and lightweight package.

Velazco, Jose E.; Ceperley, Peter H.; Foshee, James F.

2004-09-01

347

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

NASA Technical Reports Server (NTRS)

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, Benjamin; Hauff, Phoebe; Goetz, Alexander F. H.

1994-01-01

348

Titanium-silicon oxide film structures for polarization-modulated infrared reflection absorption spectroscopy  

PubMed Central

We present a titanium-silicon oxide film structure that permits polarization modulated infrared reflection absorption spectroscopy on silicon oxide surfaces. The structure consists of a ~6 nm sputtered silicon oxide film on a ~200 nm sputtered titanium film. Characterization using conventional and scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy and X-ray reflectometry is presented. We demonstrate the use of this structure to investigate a selectively protein-resistant self-assembled monolayer (SAM) consisting of silane-anchored, biotin-terminated poly(ethylene glycol) (PEG). PEG-associated IR bands were observed. Measurements of protein-characteristic band intensities showed that this SAM adsorbed streptavidin whereas it repelled bovine serum albumin, as had been expected from its structure. PMID:20418963

Dunlop, Iain E.; Zorn, Stefan; Richter, Gunther; Srot, Vesna; Kelsch, Marion; van Aken, Peter A.; Skoda, Maximilian; Gerlach, Alexander; Spatz, Joachim P.; Schreiber, Frank

2010-01-01

349

[Application of Fourier transform attenuated total reflection infrared spectroscopy in analysis of pulp and paper industry].  

PubMed

As one of the most powerful tools to investigate the compositions of raw materials and the property of pulp and paper, infrared spectroscopy has played an important role in pulp and paper industry. However, the traditional transmission infrared spectroscopy has not met the requirements of the producing processes because of its disadvantages of time consuming and sample destruction. New technique would be needed to be found. Fourier transform attenuated total reflection infrared spectroscopy (ATR-FTIR) is an advanced spectroscopic tool for nondestructive evaluation and could rapidly, accurately estimate the production properties of each process in pulp and paper industry. The present review describes the application of ATR-FTIR in analysis of pulp and paper industry. The analysis processes will include: pulping, papermaking, environmental protecting, special processing and paper identifying. PMID:21595211

Zhang, Yong; Cao, Chun-yu; Feng, Wen-ying; Xu, Ming; Su, Zhen-hua; Liu, Xiao-meng; Lü, Wei-jun

2011-03-01

350

Scanning Terahertz Heterodyne Imaging Systems  

NASA Technical Reports Server (NTRS)

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

Siegel, Peter; Dengler, Robert

2007-01-01

351

Terahertz Sensing of Materials  

NASA Astrophysics Data System (ADS)

Biomolecules such as DNA and proteins exhibit a wealth of modes in the Terahertz (THz) range from the rotational, vibrational and stretching modes of biomolecules. Many materials such as drywall that are opaque to human eyes are transparent to THz. Therefore, it can be used as a powerful tool for biomolecular sensing, biomedical analysis and through-the-wall imaging. Experiments were carried out to study the absorption of various materials including DNA and see-through imaging of drywall using FTIR spectrometer and Time Domain Spectroscopy (TDS) system.

Xuan, G.; Ghosh, S.; Kim, S.; Lv, P.-C.; Buma, T.; Weng, B.; Barner, K.; Kolodzey, J.

2007-06-01

352

Active terahertz metamaterials  

SciTech Connect

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

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

2009-01-01

353

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

354

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

355

Terahertz polarization imaging for colon cancer detection  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

356

New insights into the role of water in biological function: studying solvated biomolecules using terahertz absorption spectroscopy in conjunction with molecular dynamics simulations.  

PubMed

In life science, water is the ubiquitous solvent, sometimes even called the "matrix of life". There is increasing experimental and theoretical evidence that solvation water is not a passive spectator in biomolecular processes. New experimental techniques can quantify how water interacts with biomolecules and, in doing so, differs from "bulk" water. Terahertz (THz) absorption spectroscopy has turned out to be a powerful tool to study (bio)molecular hydration. The main concepts that have been developed in the recent years to describe the underlying solute-induced sub-picosecond dynamics of the hydration shell are discussed herein. Moreover, we highlight recent findings that show the significance of hydrogen bond dynamics for the function of antifreeze proteins and for molecular recognition. In all of these examples, a gradient of water motion toward functional sites of proteins is observed, the so-called "hydration funnel". By means of molecular dynamics simulations, we provide new evidence for a specific water-protein coupling as the cause of the observed dynamical heterogeneity. The efficiency of the coupling at THz frequencies is explained in terms of a two-tier (short- and long-range) solute-solvent interaction. PMID:25127002

Conti Nibali, Valeria; Havenith, Martina

2014-09-17

357

Large drop in dielectric constant at ferrimagnetic ordering of CoCr2O4 thin film as observed by terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

Multiferroic spinel CoCr2O4 shows ferrimagnetic transition at ˜95 K and, at further low temperatures, it shows development of magnetic spin spirals simultaneous to a ferroelectric transition. We have deposited epitaxial CoCr2O4 thin film on MgO (100) substrate and studied the film using temperature dependent terahertz (THz) time-domain spectroscopy. There is a large drop in the dielectric constant (?1) to nearly half of its initial value at ferrimagnetic transition of CoCr2O4 thin films in the THz frequency range. This is contrary to few earlier studies by capacitance measurements which showed no significant change in the dielectric constant (?1) at ferrimagnetic transition [1]. At lower temperatures, two dielectric anomalies were observed in the temperature dependent ?1, which correspond to the onset of short-range magnetic spin spirals (˜50 K) and the long-range ordering of the spirals at lower temperature (˜26 K). Our results indicate a magnetoelectric effect at the ferrimagnetic transition of CoCr2O4 thin film in THz frequency range. [1] G. Lawes et al., Phys. Rev. B 74, 24413 (2006).

Mavani, K. R.; Nagai, M.; Shirai, M.; Tanaka, K.; Rana, D. S.; Kawayama, I.; Tonouchi, M.

2008-03-01

358

Spiral-type terahertz antennas and the manifestation of the Mushiake principle  

E-print Network

Spiral-type terahertz antennas and the manifestation of the Mushiake principle Ranjan Singh1 on the experimental and theoretical study of the resonant eigenmodes of spiral-type terahertz antennas. The analysis reflection and transmission coefficient. This property makes the spiral-type terahertz antenna not only

Oklahoma State University

359

Ultra-broadband terahertz time-domain ellipsometric spectroscopy utilizing GaP and GaSe emitters and an epitaxial layer transferred photoconductive detector  

SciTech Connect

We present a reflection-type ultra-broadband terahertz (THz) time-domain spectroscopic ellipsometry system covering the frequency range of 0.5–30 THz. GaP (110) and z-cut GaSe crystals are used as emitters to generate the THz and mid-infrared pulses, respectively, and a photoconductive antenna switch using a low-temperature grown GaAs epitaxial layer transferred on Si substrate was used as a detector. By changing the emitter between the GaP and GaSe crystals, the measurable frequency range can be easily switched from the 0.5–7.8 THz range to the 7.8–30 THz range without additional optical alignment. We demonstrated the measurement of the dielectric function in a p-type InAs wafer and the optical conductivity of an indium tin oxide (ITO) thin film. The obtained carrier density and the mobility of the ITO thin film show good agreement with that obtained by the Hall measurement.

Yamashita, Masatsugu, E-mail: m-yama@riken.jp; Takahashi, Hideki; Otani, Chiko [RIKEN Center for Advanced Photonics, 519-1399 Aobaaramaki, Aoba-ku, Sendai 980-0845 (Japan); Ouchi, Toshihiko [Corporate R and D Headquarters, Canon Inc., 30-2 Shimomaruko 3-Chome, Ohta-ku, Tokyo 145-8501 (Japan)

2014-02-03

360

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

361

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.

Carlyn Little

1997-01-01

362

Atmospheric absorption of terahertz radiation and water vapor continuum effects  

E-print Network

Atmospheric absorption of terahertz radiation and water vapor continuum effects David M. Slocum a vapor Absorption Continuum Terahertz Spectroscopy a b s t r a c t The water vapor continuum absorption. The absorption coefficient as a function of frequency was determined and compared with theoretical predictions

Massachusetts at Lowell, University of

363

Broadband reflectance spectroscopy for establishing a quantitative metric of vascular leak using the Miles assay  

NASA Astrophysics Data System (ADS)

Monitoring the physiological effects of biological mediators on vascular permeability is important for identifying potential targets for antivascular leak therapy. This therapy is relevant to treatments for pulmonary edema and other disorders. Current methods of quantifying vascular leak are in vitro and do not allow repeated measurement of the same animal. Using an in vivo diffuse reflectance optical method allows pharmacokinetic analysis of candidate antileak molecules. Here, vascular leak is assessed in mice and rats by using the Miles assay and introducing irritation both topically using mustard oil and intradermally using vascular endothelial growth factor (VEGF). The severity of the leak is assessed using broadband diffuse reflectance spectroscopy with a fiber reflectance probe. Postprocessing techniques are applied to extract an artificial quantitative metric of leak from reflectance spectra at vascular leak sites on the skin of the animal. This leak metric is calculated with respect to elapsed time from irritation in both mustard oil and VEGF treatments on mice and VEGF treatments on rats, showing a repeatable increase in leak metric with leak severity. Furthermore, effects of pressure on the leak metric are observed to have minimal effect on the reflectance spectra, while spatial positioning showed spatially nonuniform leak sites.

McMurdy, John; Reichner, Jonathan; Mathews, Zara; Markey, Mary; Intwala, Sunny; Crawford, Gregory

2009-09-01

364

Remote identification of the invasive tunicate Didemnum vexillum using reflectance spectroscopy.  

PubMed

Benthic coverage of the invasive tunicate Didemnum vexillum on Georges Bank is largely unknown. Monitoring of D. vexillum coverage is vital to understanding the impact this invasive species will have on the productive fishing grounds of Georges Bank. Here we investigate using reflectance spectroscopy as a method for remote identification of D. vexillum. Using two different systems, a NightSea Dive-Spec and a combination of LED light sources with a hyperspectral radiometer, we collected in-situ measurements of reflectance from D. vexillum colonies. In comparison to reflectance spectra of other common benthic substrates, D. vexillum appears to have a unique spectral signature between 500 and 600 nm. Measuring the slope of the spectrum between these wavelengths appears to be the most robust method for spectral identification. Using derivative analysis or principal component analysis, the reflectance spectra of D. vexillum can be identified among numerous other spectra of common benthic substrates. An optical system consisting of a radiometer, light source, and camera was deployed on a remotely operated vehicle to test the feasibility of using reflectance to assess D. vexillum coverage. Preliminary results, analyzed here, prove the method to be successful for the areas we surveyed and open the way for its use on large-scale surveys. PMID:23478782

Leeuw, Thomas; Newburg, Seth O; Boss, Emmanuel S; Slade, Wayne H; Soroka, Michael G; Pederson, Judith; Chryssostomidis, Chryssostomos; Hover, Franz S

2013-03-10

365

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

366

Design and Signature Analysis of Remote Trace-Gas Identification Methodology Based on Infrared-Terahertz Double-Resonance Spectroscopy  

NASA Astrophysics Data System (ADS)

The practicality of a newly proposed infrared-terahertz (IR-THz) double-resonance (DR) spectroscopic technique for remote trace-gas identification is explored. The strength of the DR signatures depends on known molecular parameters from which a combination of pump-probe transitions may be identified to recognize a specific analyte. Atmospheric pressure broadening of the IR and THz trace-gas spectra relaxes the stringent pump coincidence requirement, allowing many DR signatures to be excited, some of which occur in the favorable atmospheric transmission windows below 500 GHz. By designing the DR spectrometer and performing a detailed signal analysis, the pump-probe power requirements for detecting trace amounts of methyl fluoride, methyl chloride, or methyl bromide may be estimated for distances up to 1 km. The strength of the DR signature increases linearly with pump intensity but only as the square root of the probe power because the received signal is in the Townes noise limit. The concept of a specificity matrix is introduced and used to quantify the recognition specificity and calculate the probability of false positive detection of an interferent.

Tanner, Elizabeth A.; Phillips, Dane J.; Persons, Christopher M.; De Lucia, Frank C.; Everitt, Henry O.

2014-11-01

367

Terahertz spectroscopy and solid-state density functional theory calculation of anthracene: Effect of dispersion force on the vibrational modes  

SciTech Connect

The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D{sup *} have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D{sup *} simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D{sup *} data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D{sup *} produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D{sup *}.

Zhang, Feng; Tominaga, Keisuke, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp [Molecular Photoscience Research Center, Kobe University, Nada, Kobe 657-0013 (Japan)] [Molecular Photoscience Research Center, Kobe University, Nada, Kobe 657-0013 (Japan); Hayashi, Michitoshi, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp; Wang, Houng-Wei [Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan (China)] [Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan (China); Kambara, Ohki; Sasaki, Tetsuo [Research Institute of Electronics, Shizuoka University, 3-5-1 Jyohoku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan)] [Research Institute of Electronics, Shizuoka University, 3-5-1 Jyohoku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Nishizawa, Jun-ichi, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp [Jun-ichi Nishizawa Memorial Research Center, Tohoku University, 519-1176 Aoba, Aramaki, Aoba-ku, Sendai 980-0845 (Japan)] [Jun-ichi Nishizawa Memorial Research Center, Tohoku University, 519-1176 Aoba, Aramaki, Aoba-ku, Sendai 980-0845 (Japan)

2014-05-07

368

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

369

Polarization Modulation Infrared Reflection Absorption Spectroscopy at Elevated Pressures: CO Adsorption on Pd(111) at Atmospheric Pressures  

E-print Network

Adsorption on Pd(111) at Atmospheric Pressures Emrah Ozensoy, Douglas C. Meier, and D. Wayne Goodman systems at or near the pressures of technical catalysts, that is, ambient (atmospheric) pressures. PMPolarization Modulation Infrared Reflection Absorption Spectroscopy at Elevated Pressures: CO

Goodman, Wayne

370

Terahertz spectroscopic investigation of four kinds of vitamins  

NASA Astrophysics Data System (ADS)

The terahertz spectra of four kinds of vitamins are presented. The refractive index and absorption spectra of these vitamins are obtained by the terahertz time-domain spectroscopy. The full-geometry optimizations and frequency calculations using the density functional theory are applied to obtain the structure and vibration frequencies of these vitamin molecules. The calculated vibration frequencies are compared with the experimental data. The results show that there are terahertz fingerprint absorptions for all of four kinds of vitamins. The terahertz absorbance spectra of vitamins result from not only the intramolecular vibration modes, but also the intermolecular interaction or phonon modes.

Zhao, Guozhong; Yu, Bin; Zhang, Cunlin

2009-11-01

371

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

372

Diffuse reflectance spectroscopy for monitoring diabetic foot ulcer - A pilot study  

NASA Astrophysics Data System (ADS)

Foot ulceration due to diabetes mellitus is a major problem affecting 12-25% of diabetic subjects in their lifetime. An untreated ulcer further gets infected which causes necrosis leading to amputation of lower extremities. Early identification of risk factors and treatment for these chronic wounds would reduce health care costs and improve the quality of life for people with diabetes. Recent clinical investigations have shown that a series of factors including reduced oxygen delivery and disturbed metabolism have been observed on patients with foot ulceration due to diabetes. Also, these factors can impair the wound healing process. Optical techniques based on diffuse reflectance spectroscopy provide characteristic spectral finger prints shed light on tissue oxygenation levels and morphological composition of a tissue. This study deals with the application of diffuse reflectance intensity ratios based on oxyhemoglobin bands (R542/R580), ratios of oxy- and deoxy-hemoglobin bands (R580/R555), total hemoglobin concentration and hemoglobin oxygen saturation between normal and diabetic foot ulcer sites. Preliminary results obtained are found to be promising indicating the application of reflectance spectroscopy in the assessment of foot ulcer healing.

Anand, Suresh; Sujatha, N.; Narayanamurthy, V. B.; Seshadri, V.; Poddar, Richa

2014-02-01

373

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

374

Phthalocyanine identification in paintings by reflectance spectroscopy. A laboratory and in situ study  

NASA Astrophysics Data System (ADS)

The importance of identifying pigments using non invasive (n.i.) analyses has gained increasing importance in the field of spectroscopy applied to art conservation and art studies. Among the large set of pigments synthesized and marketed during 20th century, surely phthalocyanine blue and green pigments occupy an important role in the field of painting (including restoration) and printing, thanks to their characteristics like brightness and fastness. This research focused on the most used phthalocyanine blue (PB15:1 and PB15:3) and green pigments (PG7), and on the possibility to identify these organic compounds using a methodology like reflectance spectroscopy in the UV, visible and near IR range (UV-vis-NIR RS), performed easily through portable instruments. Laboratory tests and three examples carried out on real paintings are discussed.

Poldi, G.; Caglio, S.

2013-06-01

375

An attenuated total reflectance mid infrared (ATR-MIR) spectroscopy study of gelatinization in barley.  

PubMed

The aim of this study was to evaluate the use of attenuated total reflectance and mid infrared (ATR-MIR) spectroscopy and to understand the gelatinization and retro-gradation of flour barley samples and the relationship with malting quality. Samples were sourced from two commercial barley varieties exhibiting high hot water extract (HWE) namely Navigator (n=8), and Admiral (n=8). Samples were analysed using the Rapid Visco Analyser (RVA) and ATR-MIR analysis. These results showed that ATR-MIR spectroscopy is capable of characterising gel samples derived from barley flour samples having different malting characteristics. Infrared spectra can effectively represent a 'fingerprint' of the sample being analysed and can be used to simplify and reduce analytical times in the routine methods currently used. PMID:24751273

Cozzolino, D; Roumeliotis, S; Eglinton, J

2014-08-01

376

Infrared Attenuated Total Reflectance Spectroscopy: An Innovative Strategy for Analyzing Mineral Components in Energy Relevant Systems  

PubMed Central

The direct qualitative and quantitative determination of mineral components in shale rocks is a problem that has not been satisfactorily resolved to date. Infrared spectroscopy (IR) is a non-destructive method frequently used in mineral identification, yet challenging due to the similarity of spectral features resulting from quartz, clay, and feldspar minerals. This study reports on a significant improvement of this methodology by combining infrared attenuated total reflection spectroscopy (IR-ATR) with partial least squares (PLS) regression techniques for classifying and quantifying various mineral components present in a number of different shale rocks. The developed multivariate classification model was calibrated using pure component mixtures of the most common shale minerals (i.e., kaolinite, illite, montmorillonite, calcite, and quartz). Using this model, the IR spectra of 11 real-world shale samples were analyzed and evaluated. Finally, the performance of the developed IR-ATR method was compared with results obtained via X-ray diffraction (XRD) analysis. PMID:25358261

Müller, Christian Menno; Pejcic, Bobby; Esteban, Lionel; Piane, Claudio Delle; Raven, Mark; Mizaikoff, Boris

2014-01-01

377

Infrared attenuated total reflection spectroscopy for the characterization of gold nanoparticles in solution.  

PubMed

In situ synthesis of bare gold nanoparticles mediated by stainless steel as reducing agent was monitored via infrared attenuated total reflection (IR-ATR) spectroscopy. Gold nanoparticles were directly synthesized within the liquid cell of the ATR unit taking immediate advantage of the stainless steel walls of the ATR cell. As nanoparticles were formed, a layer of particles was deposited at the SiO2 ATR waveguide surface. Incidentally, the absorption bands of water increased resulting from surface-enhanced infrared absorption (SEIRA) effects arising from the presence of the gold nanoparticles within the evanescent field. Next to the influence of the Au(III) precursor concentration and the temperature, the suitability of IR-ATR spectroscopy as an innovative tool for investigating changes of nanoparticles in solution, including their aggregation promoted by an increase of the ionic strength or via a pH decrease, and for detailing the sedimentation process of gold nanoparticles was confirmed. PMID:24313342

López-Lorente, Ángela Inmaculada; Sieger, Markus; Valcárcel, Miguel; Mizaikoff, Boris

2014-01-01

378

Enzymatic hydrolysis of monolayers: A polarization modulated-infrared reflection absorption spectroscopy study  

Microsoft Academic Search

Hydrolysis experiments have been performed on monolayers of l-dipalmitoylphosphatidylcholine (l-DPPC) and on monolayers of the ether-ester l-1-O-hexadecyl-2-stearoylphosphatidylcholine (l-HSPC). The investigation was carried out using phospholipase A2 (PLA2), derived from snake venom (Crotalos Atrox), which selectively hydrolyzes the sn-2 ester bond of l-phospholipids. Pressure-area isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS),\\u000a a versatile tool in the “in situ” investigation of

U. Dahmen-Levison; G. Brezesinski; H. Möhwald

379

Remote diffuse reflectance spectroscopy sensor for tissue engineering monitoring based on blind signal separation.  

PubMed

In this study the first results on evaluation and assessment of grafted bioengineered skin substitutes using an optical Diffuse Reflectance Spectroscopy (DRS) system with a remote optical probe are shown. The proposed system is able to detect early vascularization of skin substitutes expressing the Vascular Endothelial Growth Factor (VEGF) protein compared to normal grafts, even though devitalized skin is used to protect the grafts. Given the particularities of the biological problem, data analysis is performed using two Blind Signal Separation (BSS) methods: Principal Component Analysis (PCA) and Independent Component Analysis (ICA). These preliminary results are the first step towards point-of-care diagnostics for skin implants early assessment. PMID:25401034

Martín-Mateos, Pedro; Crespo-Garcia, Sergio; Ruiz-Llata, Marta; Lopez-Fernandez, José Ramón; Jorcano, José Luis; Del Rio, Marcela; Larcher, Fernando; Acedo, Pablo

2014-09-01

380

Fourier transform infrared reflection absorption spectrometry and electron spectroscopy for chemical analysis for surface analysis  

SciTech Connect

The combination of electron spectroscopy for chemical analysis (ESCA) and Fourier transform was tested for usefulness in surface analysis. The surface sensitivity of IR was increased by the use of IR reflection absorption spectrometry (IR-RAS) coupled with FT-IR. Examination of oxide layers of thickness of about 100 A formed on copper plates with both techniques together with ellipsometry is described in detail. Growth of oxide layers of different composition corresponding to different heating temperatures was manifested with the analysis. The result verifies effective combination of these two complementary techniques. 14 figures, 1 table.

Ishitani, A.; Ishida, H.; Soeda, F.; Nagasawa, Y.

1982-04-01

381

Prediction of leaf chemistry by the use of visible and near infrared reflectance spectroscopy  

NASA Technical Reports Server (NTRS)

The chemical content of dry, ground leaf material sampled from deciduous and conifer tree species from sites in Alaska, Wisconsin, and California was estimated using visible and shortwave IR spectroscopy. Seven chemical components - sugar, starch, protein, cellulose, total chlorophyll, lignin, and total nitrogen - were analyzed by wet chemical methods and their concentrations regressed against log 1/rho and first and second differences of log 1/rho (where rho is measured reflectance) at wavelengths selected by stepwise regression. Predictions of chemical concentrations based on cross validation suggest that this technique may be useful for extracting vegetation canopy biochemical information by remote sensing.

Card, Don H.; Peterson, David L.; Matson, Pamela A.; Aber, John D.

1988-01-01

382

Remote diffuse reflectance spectroscopy sensor for tissue engineering monitoring based on blind signal separation  

PubMed Central

In this study the first results on evaluation and assessment of grafted bioengineered skin substitutes using an optical Diffuse Reflectance Spectroscopy (DRS) system with a remote optical probe are shown. The proposed system is able to detect early vascularization of skin substitutes expressing the Vascular Endothelial Growth Factor (VEGF) protein compared to normal grafts, even though devitalized skin is used to protect the grafts. Given the particularities of the biological problem, data analysis is performed using two Blind Signal Separation (BSS) methods: Principal Component Analysis (PCA) and Independent Component Analysis (ICA). These preliminary results are the first step towards point-of-care diagnostics for skin implants early assessment. PMID:25401034

Martín-Mateos, Pedro; Crespo-Garcia, Sergio; Ruiz-Llata, Marta; Lopez-Fernandez, José Ramón; Jorcano, José Luis; Del Rio, Marcela; Larcher, Fernando; Acedo, Pablo

2014-01-01

383

Dynamical characteristics of a coherent longitudinal optical phonon in a GaAs buffer layer optically covered with a GaSb top epitaxial layer investigated with use of terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate that, in a GaSb/GaAs epitaxial structure, a coherent longitudinal optical (LO) phonon in a GaAs buffer layer optically covered with a GaSb top layer is observed utilizing terahertz spectroscopy. It is confirmed from Raman scattering measurements that only the optical phonons in the GaSb layer is optically observable. In the terahertz-wave measurement, the Fourier power spectrum of a terahertz waveform exhibits both the coherent GaAs and GaSb LO phonon bands; namely, the coherent LO phonon in the optically covered GaAs buffer layer is observed in the terahertz-wave measurement. This fact demonstrates that the instantaneous surface potential modulation, which originates from the impulsive carrier excitation by the pump beam, reaches the GaAs buffer layer. Consequently, the above-mentioned surface potential modulation generates the coherent GaAs LO phonon that cannot be optically excited. In addition, we perform a time-partitioning Fourier transform analysis in order to investigate the decay dynamics of the coherent GaAs and GaSb LO phonons. The decay times of the coherent GaAs and GaSb LO phonons are estimated to be 2.0 and 3.3 ps, respectively. The longer decay time of the coherent GaSb LO phonon is attributed to the fact that the phonon density of state in a final state of the decay process of GaSb is relatively small in comparison with that of GaAs.

Takeuchi, Hideo; Tsuruta, Shuichi; Nakayama, Masaaki

2012-12-01

384

Sub-terahertz spectroscopy reveals that proteins influence the properties of water at greater distances than previously detected.  

PubMed

The initial purpose of the study is to systematically investigate the solvation properties of different proteins in water solution by terahertz (THz) radiation absorption. Transmission measurements of protein water solutions have been performed using a vector network analyser-driven quasi-optical bench covering the WR-3 waveguide band (0.220-0.325 THz). The following proteins, ranging from low to high molecular weight, were chosen for this study: lysozyme, myoglobin, and bovine serum albumin (BSA). Absorption properties of solutions were studied at different concentrations of proteins ranging from 2 to 100 mg/ml. The concentration-dependent absorption of protein molecules was determined by treating the solution as a two-component model first; then, based on protein absorptivity, the extent of the hydration shell is estimated. Protein molecules are shown to possess a concentration-dependent absorptivity in water solutions. Absorption curves of all three proteins sharply peak towards a dilution-limit that is attributed to the enhanced flexibility of protein and amino acid side chains. An alternative approach to the determination of hydration shell thickness is thereby suggested, based on protein absorptivity. The proposed approach is independent of the absorption of the hydration shell. The derived estimate of hydration shell thickness for each protein supports previous findings that protein-water interaction dynamics extends beyond 2-3 water solvation-layers as predicted by molecular dynamics simulations and other techniques such as NMR, X-ray scattering, and neutron scattering. According to our estimations, the radius of the dynamic hydration shell is 16, 19, and 25 Å, respectively, for lysozyme, myoglobin, and BSA proteins and correlates with the dipole moment of the protein. It is also seen that THz radiation can serve as an initial estimate of the protein hydrophobicity. PMID:25662667

Sushko, Oleksandr; Dubrovka, Rostyslav; Donnan, Robert S

2015-02-01

385

Mössbauer spectroscopy, magnetic characteristics, and reflection loss analysis of nickel-strontium substituted cobalt ferrite nanoparticles  

SciTech Connect

In current research work, Co{sub 1-x}Ni{sub x/2}Sr{sub x/2}Fe{sub 2}O{sub 4} (x?=?0–1 in a step of 0.2) ferrite nanoparticles were synthesized by a sol-gel method. According to the evolution in the subspectral areas obtained from Mössbauer spectroscopy, it was found that the relaxing iron belongs mostly to the site B, since the Mössbauer fraction of site A does not vary appreciably. With an increase in Ni-Sr substitution contents in cobalt ferrite, the coercivity and saturation of magnetization decrease. Variation of reflection loss versus frequency in microwave X-band demonstrates that the reflection peak shifts to lower frequency by adding substituted cations and the synthesized nanoparticles can be considered for application in electromagnetic wave absorber technology.

Ghasemi, Ali, E-mail: ali13912001@yahoo.com [Materials Engineering Department, Malek Ashtar University of Technology, Shahin Shahr (Iran, Islamic Republic of); Paesano, Andrea; Cerqueira Machado, Carla Fabiana [Departamento de Física, Centro de Ciências Exatas, Universidade Estadual de Maringá, Maringá (Brazil); Shirsath, Sagar E. [Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad (India); Spin Device Technology Center, Faculty of Engineering, Shinshu University, Nagano (Japan); Liu, Xiaoxi; Morisako, Akimitsu [Spin Device Technology Center, Faculty of Engineering, Shinshu University, Nagano (Japan)

2014-05-07

386

Flexible metamaterial absorbers for stealth applications at terahertz frequencies  

E-print Network

Flexible metamaterial absorbers for stealth applications at terahertz frequencies Krzysztof: We have wrapped metallic cylinders with strongly absorbing metamaterials. These resonant structures of the reflection spectrum of the metamaterial. ©2011 Optical Society of America OCIS codes: (110.6795) Terahertz

Zhang, Xin

387

Noninvasive blood glucose sensing on human body with near-infrared reflection spectroscopy  

NASA Astrophysics Data System (ADS)

The non-invasive blood glucose sensing method has shown its high impact on the clinic application. This can make the measurement on the clinically relevant concentrations of glucose be free from the pain of patient. The transmission spectrum study indicates that the dependence of glucose concentration on the absorbance is in linear manner for the glucose concentration in the region of 30mg/dL to 4.5×104mg/dL. By the near infrared reflection spectroscopy of fiber spectrometer, the reflection band between 1.2?m and 1.35?m can be used to correlated with the glucose concentration in the range of 30 to 300 mg/dL. This reflection band is finally used to measure the glucose concentration effect in non-invasive manner, which gives the statistical significance of P value 0.02. Our experiment result shows that it is possible to get the glucose concentration by the near infrared reflection spectrum measurement on the human forefinger. This non-invasive blood glucose sensing method may useful in clinic after more experiment for different people.

Huang, Zhen-hao; Hao, Chang-ning; Zhang, Lin-lin; Huang, Yan-chao; Shi, Yi-qin; Jiang, Geng-ru; Duan, Jun-li

2011-08-01

388

Optimally designed narrowband guided-mode resonance reflectance filters for mid-infrared spectroscopy.  

PubMed

An alternative to the well-established Fourier transform infrared (FT-IR) spectrometry, termed discrete frequency infrared (DFIR) spectrometry, has recently been proposed. This approach uses narrowband mid-infrared reflectance filters based on guided-mode resonance (GMR) in waveguide gratings, but filters designed and fabricated have not attained the spectral selectivity (? 32 cm(-1)) commonly employed for measurements of condensed matter using FT-IR spectroscopy. With the incorporation of dispersion and optical absorption of materials, we present here optimal design of double-layer surface-relief silicon nitride-based GMR filters in the mid-IR for various narrow bandwidths below 32 cm(-1). Both shift of the filter resonance wavelengths arising from the dispersion effect and reduction of peak reflection efficiency and electric field enhancement due to the absorption effect show that the optical characteristics of materials must be taken into consideration rigorously for accurate design of narrowband GMR filters. By incorporating considerations for background reflections, the optimally designed GMR filters can have bandwidth narrower than the designed filter by the antireflection equivalence method based on the same index modulation magnitude, without sacrificing low sideband reflections near resonance. The reported work will enable use of GMR filters-based instrumentation for common measurements of condensed matter, including tissues and polymer samples. PMID:22109445

Liu, Jui-Nung; Schulmerich, Matthew V; Bhargava, Rohit; Cunningham, Brian T

2011-11-21

389

C-axis Josephson plasma resonance observed in Tl_2Ba_2CaCu_2O_8 superconducting thin films by use of terahertz time-domain spectroscopy  

Microsoft Academic Search

We have unambiguously observed the c-axis Josephson Plasma Resonance (JPR) in\\u000ahigh-T$_{c}$ cuprate Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$ superconducting thin\\u000afilms employing terahertz time-domain spectroscopy in transmission as a\\u000afunction of temperature in zero magnetic field. These are the first\\u000ameasurements of the JPR temperature dependence of a high-$T_{c}$ material in\\u000atransmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K

V. K. Thorsmølle; R. D. Averitt; M. P. Maley; L. N. Bulaevskii; C. Helm; A. J. Taylor

2001-01-01

390

Single nanowire photoconductive terahertz detectors.  

PubMed

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

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

2015-01-14

391

Terahertz analysis of an East Asian historical mural painting  

NASA Astrophysics Data System (ADS)

Terahertz (THz) spectroscopy and THz and imaging techniques are expected to have great potential for the non-invasive analysis of artworks. We have applied THz imaging to analyse the historic mural painting of a Lamaism temple by using a transportable time-domain THz imaging system; such an attempt is the first in the world. The reflection image revealed that there are two orange colours in the painting, although they appear the same to the naked eye. THz imaging can also estimate the depth of cracks. The colours were examined by X-ray fluorescence and Raman spectroscopy, and the results were found to be in good agreement. This work proved that THz imaging can contribute to the non-invasive analysis of cultural heritage.

Fukunaga, K.; Hosako, I.; Kohdzuma, Y.; Koezuka, T.; Kim, M.-J.; Ikari, T.; Du, X.

2010-05-01

392

Simultaneous dual scanning Terahertz system  

Microsoft Academic Search

Terahertz time domain spectroscopy (THz-TDS) currently requires expensive components, in particular an ultra-fast Ti:Sapphire laser, and signal acquisition is not a real time process. In order to speed up the process for acquiring sample and reference data, we propose to approach dual scanning THz-TDS by using a single fast high precision translation stage and a single lock-in amplifier.

B. Ung; B. W.-H. Ng; D. Abbott

2008-01-01

393

Identification of mineral composition and weathering product of tuff using reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Tuff is intricately composed of various types of rock blocks and ash matrixes during volcanic formation processes. Qualitative identification and quantitative assessment of mineral composition of tuff usually have been done using manual inspection with naked-eyes and various chemical analyses. Those conventional methods are destructive to objects, time consuming and sometimes carry out biased results from subjective decision making. To overcome limits from conventional methods, assessment technique using reflectance spectroscopy was applied to tuff specimens. Reflectance spectroscopy measures electromagnetic reflectance on rock surface and can extract diagnostic absorption features originated from chemical composition and crystal structure of constituents in the reflectance curve so mineral species can be discriminated qualitatively. The intrinsic absorption feature from particular mineral can be converted to absorption depth representing relative coverage of the mineral in the measurement area by removing delineated convex hull from raw reflectance curve. The spectral measurements were performed with field spectrometer FieldSpec®3 of ASD Inc. and the wavelength range of measurement was form 350nm to 2500nm. Three types of tuff blocks, ash tuff, green lapilli tuff and red lapilli tuff, were sampled from Hwasun County in Korea and the types of tuffs. The differences between green tuff and red tuff are from the color of their matrixes. Ash tuff consists of feldspars and quartz and small amount of chalcedony, calcite, dolomite, epidote and basalt fragments. Green lapilli tuff consists of feldspar, quartz and muscovite and small amount of calcite, chalcedony, sericite, chlorite, quartzite and basalt fragments. Red lapilli tuff consists of feldspar, quartz and muscovite and small amount of calcite, chalcedony, limonite, zircon, chlorite, quartzite and basalt fragments. The tuff rocks were coarsely crushed and blocks and matrixes were separated to measure standard spectral reflectance of each constituent. Unmixing of mineral composition and their weathering products of blocks and matrixes in tuff were conducted and the ratio of mineral composition was calculated for each specimen. This study was supported by National Research Institute of Cultural Heritage (project title: Development on Evaluation Technology for Weathering Degree of Stone Cultural Properties, project no.: 09B011Y-00150-2009).

Hyun, C.; Park, H.

2009-12-01

394

Characterizing the Moisture Content of Tea with Diffuse Reflectance Spectroscopy Using Wavelet Transform and Multivariate Analysis  

PubMed Central

Effects of the moisture content (MC) of tea on diffuse reflectance spectroscopy were investigated by integrated wavelet transform and multivariate analysis. A total of 738 representative samples, including fresh tea leaves, manufactured tea and partially processed tea were collected for spectral measurement in the 325–1,075 nm range with a field portable spectroradiometer. Then wavelet transform (WT) and multivariate analysis were adopted for quantitative determination of the relationship between MC and spectral data. Three feature extraction methods including WT, principal component analysis (PCA) and kernel principal component analysis (KPCA) were used to explore the internal structure of spectral data. Comparison of those three methods indicated that the variables generated by WT could efficiently discover structural information of spectral data. Calibration involving seeking the relationship between MC and spectral data was executed by using regression analysis, including partial least squares regression, multiple linear regression and least square support vector machine. Results showed that there was a significant correlation between MC and spectral data (r = 0.991, RMSEP = 0.034). Moreover, the effective wavelengths for MC measurement were detected at range of 888–1,007 nm by wavelet transform. The results indicated that the diffuse reflectance spectroscopy of tea is highly correlated with MC. PMID:23012574

Li, Xiaoli; Xie, Chuanqi; He, Yong; Qiu, Zhengjun; Zhang, Yanchao

2012-01-01

395

Reversible immobilization of peptides: surface modification and in situ detection by attenuated total reflection FTIR spectroscopy.  

PubMed

A generic method is described for the reversible immobilization of polyhistidine-bearing polypeptides and proteins on attenuated total reflecting (ATR) sensor surfaces for the detection of biomolecular interactions by FTIR spectroscopy. Nitrilotriacetic acid (NTA) groups are covalently attached to self-assembled monolayers of either thioalkanes on gold films or mercaptosilanes on silicon dioxide films deposited on germanium internal reflection elements. Complex formation between Ni2+ ions and NTA groups activates the ATR sensor surface for the selective binding of polyhistidine sequences. This approach not only allows a stable and reversible immobilization of histidine-tagged peptides (His-peptides) but also simultaneously allows the direct in situ quantification of surface-adsorbed molecules from their specific FTIR spectral bands. The surface concentrations of both NTA and His-peptide on silanized surfaces were determined to be 1.1 and 0.4 molecules nm-2, respectively, which means that the surface is densely covered. A comparison of experimental FTIR spectra with simulated spectra reveals a surface-enhancement effect of one order of magnitude for the gold surfaces. With the presented sensor surfaces, new ways are opened up to investigate, in situ and with high sensitivity and reproducibility, protein-ligand, protein-protein, protein-DNA interactions, and DNA hybridization by ATR-FTIR spectroscopy. PMID:12674599

Rigler, Per; Ulrich, Wolf-Peter; Hoffmann, Patrik; Mayer, Michael; Vogel, Horst

2003-03-17

396

Conjugated polymer-based broadband terahertz wave modulator.  

PubMed

An optical broadband terahertz (THz) wave modulator, based on a polymer-inorganic interface, is investigated. The THz pulse transmission was efficiently modulated by an external continuous wave (CW) laser. The effects on the poly[2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV)/silicon interface were measured by THz time-domain spectroscopy. The modulation factor reached 99.6%, at an external laser beam intensity of 6.3??W/cm2. In the proposed THz-CW system, a significant fall (in both THz transmission and reflection) was also observed at the MEH-PPV/Si interface. This reduction in THz transmission and reflection has been induced by absorption at the MEH-PPV/Si interface. The results show that an optically controlled polymer/inorganic broadband THz modulator can be realized. PMID:25361291

Zhang, Bo; He, Ting; Shen, Jingling; Hou, Yanbing; Hu, Yufeng; Zang, Mengdi; Chen, Tianji; Feng, Shengfei; Teng, Feng; Qin, Liang

2014-11-01

397

EXPERIMENT #3 REFLECTANCE SPECTROSCOPY We will use the reflectance attachment and fiber optics OceanOptics spectrophotometer to  

E-print Network

OceanOptics spectrophotometer to measure the reflectance spectrum of several paint samples and a powdered solid. A. Calibration of Spectrophotometer in Reflectance mode. Turn on the computer and the power

Nazarenko, Alexander

398

The Use of UV-Visible Reflectance Spectroscopy as an Objective Tool to Evaluate Pearl Quality  

PubMed Central

Assessing the quality of pearls involves the use of various tools and methods, which are mainly visual and often quite subjective. Pearls are normally classified by origin and are then graded by luster, nacre thickness, surface quality, size, color and shape. The aim of this study was to investigate the capacity of Artificial Neural Networks (ANNs) to classify and estimate the quality of 27 different pearls from their UV-Visible spectra. Due to the opaque nature of pearls, spectroscopy measurements were performed using the Diffuse Reflectance UV-Visible spectroscopy technique. The spectra were acquired at two different locations on each pearl sample in order to assess surface homogeneity. The spectral data (inputs) were smoothed to reduce the noise, fed into ANNs and correlated to the pearl’s quality/grading criteria (outputs). The developed ANNs were successful in predicting pearl type, mollusk growing species, possible luster and color enhancing, donor condition/type, recipient/host color, donor color, pearl luster, pearl color, origin. The results of this study shows that the developed UV-Vis spectroscopy-ANN method could be used as a more objective method of assessing pearl quality (grading) and may become a valuable tool for the pearl grading industry. PMID:22851919

Agatonovic-Kustrin, Snezana; Morton, David W.

2012-01-01

399

Oblique polarized reflectance spectroscopy for depth sensitive measurements in the epithelial tissue  

NASA Astrophysics Data System (ADS)

Optical spectroscopy has shown potential as a tool for precancer detection by discriminating alterations in the optical properties within epithelial tissues. Identifying depth-dependent alterations associated with the progression of epithelial cancerous lesions can be especially challenging in the oral cavity due to the variable thickness of the epithelium and the presence of keratinization. Optical spectroscopy of epithelial tissue with improved depth resolution would greatly assist in the isolation of optical properties associated with cancer progression. Here, we report a fiber optic probe for oblique polarized reflectance spectroscopy (OPRS) that is capable of depth sensitive detection by combining the following three approaches: multiple beveled fibers, oblique collection geometry, and polarization gating. We analyze how probe design parameters are related to improvements in collection efficiency of scattered photons from superficial tissue layers and to increased depth discrimination within epithelium. We have demonstrated that obliquely-oriented collection fibers increase both depth selectivity and collection efficiency of scattering signal. Currently, we evaluate this technology in a clinical trial of patients presenting lesions suspicious for dysplasia or carcinoma in the oral cavity. We use depth sensitive spectroscopic data to develop automated algorithms for analysis of morphological and architectural changes in the context of the multilayer oral epithelial tissue. Our initial results show that OPRS has the potential to improve the detection and monitoring of epithelial precancers in the oral cavity.

Jimenez, Maria K.; Fradkin, Leonid; Nieman, Linda T.; Lam, Sylvia; Poh, Catherine; Sokolov, Konstantin

2013-02-01

400

Probing ultrafast carrier dynamics in semiconductor nanostructures with terahertz pulses  

Microsoft Academic Search

We use time-resolved terahertz spectroscopy to probe ultrafast carrier dynamics in a variety of semiconductor nanostructures including InGaAs quantum dot chains and wires, GaAs nanowires, and Si nanoclusters embedded in glass.

D. G. Cooke; A. N. MacDonald; A. Hryciw; A. Meldrum; F. A. Hegmann; Yu. I. Mazur; H. Wen; W. Q. Ma; X. Wang; Z. M. Wang; G. J. Salamo; M. Xiao; T. D. Mishima; G. D. Lian; J. Keay; M. B. Johnson; J. Wang; Q. Li; Z. H. Wu; C. DeSouza; H. E. Ruda

2005-01-01

401

Terahertz spectroscopic investigations of leather in terahertz wave range  

NASA Astrophysics Data System (ADS)

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

Song, Mei-jing; Li, Jiu-sheng

2011-11-01

402

Terahertz spectroscopic investigations of leather in terahertz wave range  

NASA Astrophysics Data System (ADS)

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

Song, Mei-jing; Li, Jiu-sheng

2012-03-01

403

Monitoring the in-situ oxide growth on uranium by ultraviolet-visible reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate the in-situ monitoring of oxide growth on U-0.1 wt. % Cr by means of UV-visible reflectance spectroscopy in the thickness range of ˜20-150 nm. Two different approaches are presented: In the "modeling approach," we employ a model for a metallic substrate covered by a dielectric layer, while taking into account the buildup of oxygen gradient and surface roughness. Then, we fit the simulated spectra to the experimental one. In the "extrema analysis," we derive an approximated analytical expression, which relates the oxide thickness to the position of the extrema in the reflectance spectra based on the condition for optical interference of the reflected light. Good agreement is found between the values extracted by the two procedures. Activation energy of ˜21 kcal/mole was obtained by monitoring the oxide growth in the temperature range of 22-90 °C. The upper bound for the thickness determination is argued to be mostly dictated by cracking and detachment processes in the formed oxide.

Schweke, Danielle; Maimon, Chen; Chernia, Zelig; Livneh, Tsachi

2012-11-01

404

Probe pressure effects on human skin diffuse reflectance and fluorescence spectroscopy measurements.  

PubMed

Diffuse reflectance and fluorescence spectroscopy are popular research techniques for noninvasive disease diagnostics. Most systems include an optical fiber probe that transmits and collects optical spectra in contact with the suspected lesion. The purpose of this study is to investigate probe pressure effects on human skin spectroscopic measurements. We conduct an in-vivo experiment on human skin tissue to study the short-term (<2 s) and long-term (>30 s) effects of probe pressure on diffuse reflectance and fluorescence measurements. Short-term light probe pressure (P0<9 mN?mm2) effects are within 0?±?10% on all physiological properties extracted from diffuse reflectance and fluorescence measurements, and less than 0±5% for diagnostically significant physiological properties. Absorption decreases with site-specific variations due to blood being compressed out of the sampled volume. Reduced scattering coefficient variation is site specific. Intrinsic fluorescence shows a large standard error, although no specific pressure-related trend is observed. Differences in tissue structure and morphology contribute to site-specific probe pressure effects. Therefore, the effects of pressure can be minimized when the pressure is small and applied for a short amount of time; however, long-term and large pressures induce significant distortions in measured spectra. PMID:21280899

Lim, Liang; Nichols, Brandon; Rajaram, Narasimhan; Tunnell, James W

2011-01-01

405

Probe pressure effects on human skin diffuse reflectance and fluorescence spectroscopy measurements  

PubMed Central

Diffuse reflectance and fluorescence spectroscopy are popular research techniques for noninvasive disease diagnostics. Most systems include an optical fiber probe that transmits and collects optical spectra in contact with the suspected lesion. The purpose of this study is to investigate probe pressure effects on human skin spectroscopic measurements. We conduct an in-vivo experiment on human skin tissue to study the short-term (<2 s) and long-term (>30 s) effects of probe pressure on diffuse reflectance and fluorescence measurements. Short-term light probe pressure (P0 < 9 mN?mm2) effects are within 0?±?10% on all physiological properties extracted from diffuse reflectance and fluorescence measurements, and less than 0?±?5% for diagnostically significant physiological properties. Absorption decreases with site-specific variations due to blood being compressed out of the sampled volume. Reduced scattering coefficient variation is site specific. Intrinsic fluorescence shows a large standard error, although no specific pressure-related trend is observed. Differences in tissue structure and morphology contribute to site-specific probe pressure effects. Therefore, the effects of pressure can be minimized when the pressure is small and applied for a short amount of time; however, long-term and large pressures induce significant distortions in measured spectra. PMID:21280899

Lim, Liang; Nichols, Brandon; Rajaram, Narasimhan; Tunnell, James W.

2011-01-01

406

Feedstock and Web Analysis Using Mid-Infrared Diffuse Reflectance Spectroscopy and Imaging Spectroradiometry  

SciTech Connect

Potential applications of mid-infrared (MIR) spectroscopy in the forest products industry include on-line analysis of feedstock and web materials; these applications differ dramatically in purpose, speed, and overall chemical heterogeneity. Characterization of feedstock will enable sorting of the stock and/or wet chemistry adjustment prior to the web stage of paper production. Sorting will require imaging of the stock as well as classification of the wide variety of chemistry found in recycled stock. At the opposite end of the manufacturing process, on-line analysis of the web will enable adjustment of machine parameters to maximize product quality and minimize waste. Spectroscopic requirements for web analysis include high-speed capability and measurement precision. If successful, both applications could result in a reduction of resource waste, a reduction of plant pollution, and a reduction of energy use while simultaneously improving product quality. Here the progress towards feedstock and web analysis with MIR spectroscopy is presented. To date, work has progressed in three main areas: Diffuse Reflectance mid-Infrared Fourier Transform (DRIFT) spectroscopy of cellulose-based materials, chemometrics analysis, and research of MIR instrumentation for prototype development. The DRIFT spectroscopy data represents a database of the chemistries and spectroscopic signatures of interest to the applications discussed here. Over 50,000 spectra were obtained from cellulose-based materials infised with a wide variety of non-cellulose chemistry. Chemometrics analysis was performed on the DRIFT database to determine the quantitative and qualitative limits of the technique. Emphasis was placed on qualitative evaluation of spectroscopic signatures unique to the particular classes of cellulose-based material; thus, the degree to which classes could be sorted was determined. Finally, investigations of MIR instrumentation suitable for transfer of the technique from the lab-based instrument to a field ready prototype were made.

G.L. Powell; J.E. Parks II

1997-09-15

407

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

SciTech Connect

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{sup ?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 [LISA, Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris-Est Créteil (UPEC) et Université Paris-Diderot (UPD), 61 Avenue du Général de Gaulle, 94010 Créteil Cedex (France)] [LISA, Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris-Est Créteil (UPEC) et Université Paris-Diderot (UPD), 61 Avenue du Général de Gaulle, 94010 Créteil Cedex (France); Lago, Leatitia; Chapuis, Mylène; Herbeaux, Christian; Roy, Pascale; Manceron, Laurent [High Vacuum Group and Beamline AILES, Synchrotron SOLEIL, L’Orme des Merisiers, F-91192 Gif-sur-Yvette (France)] [High Vacuum Group and Beamline AILES, Synchrotron SOLEIL, L’Orme des Merisiers, F-91192 Gif-sur-Yvette (France)

2013-09-15

408

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

PubMed

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 Cre?teil, 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. PMID:24089810

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

2013-09-01

409

Time-Domain TeraHertz Spectroscopy and Observational Probes of Prebiotic Interstellar Gas and Ice Chemistry  

NASA Astrophysics Data System (ADS)

Understanding the origin of life on Earth has long fascinated the minds of the global community, and has been a driving factor in interdisciplinary research for centuries. Beyond the pioneering work of Darwin, perhaps the most widely known study in the last century is that of Miller & Urey, who examined the possibility of the formation of prebiotic chemical precursors on the primordial Earth. More recent studies have shown that amino acids, the chemical building blocks of the biopolymers that comprise life as we know it on Earth, are present in meteoritic samples, and that the molecules extracted from the meteorites display isotopic signatures indicative of an extraterrestrial origin. The most recent major discovery in this area has been the detection of glycine (NH2CH2COOH), the simplest amino acid, in pristine cometary samples returned by the NASA STARDUST mission. Indeed, the open questions left by these discoveries, both in the public and scientific communities, hold such fascination that NASA has designated the understanding of our "Cosmic Origins" as a key mission priority. Despite these exciting discoveries, our understanding of the chemical and physical pathways to the formation of prebiotic molecules is woefully incomplete. This is largely because we do not yet fully understand how the interplay between grain-surface and sub-surface ice reactions and the gasphase affects astrophysical chemical evolution, and our knowledge of chemical inventories in these regions is incomplete. The research presented here aims to directly address both these issues, so that future work to understand the formation of prebiotic molecules has a solid foundation from which to work. From an observational standpoint, a dedicated campaign to identify hydroxylamine (NH2OH), potentially a direct precursor to glycine, in the gas-phase was undertaken. No trace of NH2OH was found. These observations motivated a refinement of the chemical models of glycine formation, and have largely ruled out a gas-phase route to the synthesis of the simplest amino acid in the ISM. A molecular mystery in the case of the carrier of a series of transitions was resolved using observational data toward a large number of sources, confirming the identity of this important carbon-chemistry intermediate B11244 as l-C3H+ and identifying it in at least two new environments. Finally, the doubly-nitrogenated molecule carbodiimide HNCNH was identified in the ISM for the first time through maser emission features in the centimeter-wavelength regime. In the laboratory, a TeraHertz Time-Domain Spectrometer was constructed to obtain the experimental spectra necessary to search for solid-phase species in the ISM in the THz region of the spectrum. These investigations have shown a striking dependence on large-scale, long-range (i.e. lattice) structure of the ices on the spectra they present in the THz. A database of molecular spectra has been started, and both the simplest and most abundant ice species, which have already been identified, as well as a number of more complex species, have been studied. The exquisite sensitivity of the THz spectra to both the structure and thermal history of these ices may lead to better probes of complex chemical and dynamical evolution in interstellar environments.

McGuire, Brett Andrew

410

Terahertz Kerr effect  

E-print Network

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

Hoffmann, Matthias C.

411

Comparison of single-reflection near-infrared and attenuated total reflection mid-infrared spectroscopies to identify and monitor hydrocarbons spilled in the marine environment.  

PubMed

The capability of single-reflection near-IR (NIR) spectroscopy to differentiate, characterize and monitor the fate of a set of hydrocarbons spilled in the marine environment was compared with that of multiple-reflection horizontal attenuated total reflection mid-IR (ATR-MIR) spectroscopy. Multivariate pattern recognition techniques [principal component analysis (PCA), multivariate polynomial regression, cluster analysis and potential curves] were applied to unravel the major trends of the weathering processes of four generic types of crude oils and two heavy fuel oils spilled under controlled conditions for almost 4 months. A chemical interpretation of the NIR spectra related the weathering processes and the PCA loadings, which had not already been done in the literature. Weathering for both light and heavy products was characterized by a contrast among the linear aliphatic structures (more volatile and easy to degrade) and the branched and aromatic structures (more recalcitrant). Potential curves were applied to model each product and determine objectively whether unknown samples could be classified correctly. Polynomial regression on the PCA scores was employed to evaluate the time elapsed from the oil spillage to its sampling; this represents a new approach to assess the age of a hydrocarbon lump. In general, NIR spectroscopy yielded good results when light crude oils were studied, whereas ATR-MIR spectroscopy led to satisfactory results for both light and heavy products. PMID:19787339

Pérez-Caballero, G; Andrade, J M; Muniategui, S; Prada, D

2009-12-01

412

Diagnostic power of diffuse reflectance spectroscopy for targeted detection of breast lesions with microcalcifications  

PubMed Central

Microcalcifications geographically target the location of abnormalities within the breast and are of critical importance in breast cancer diagnosis. However, despite stereotactic guidance, core needle biopsy fails to retrieve microcalcifications in up to 15% of patients. Here, we introduce an approach based on diffuse reflectance spectroscopy for detection of microcalcifications that focuses on variations in optical absorption stemming from the calcified clusters and the associated cross-linking molecules. In this study, diffuse reflectance spectra are acquired ex vivo from 203 sites in fresh biopsy tissue cores from 23 patients undergoing stereotactic breast needle biopsies. By correlating the spectra with the corresponding radiographic and histologic assessment, we have developed a support vector machine-derived decision algorithm, which shows high diagnostic power (positive predictive value and negative predictive value of 97% and 88%, respectively) for diagnosis of lesions with microcalcifications. We further show that these results are robust and not due to any spurious correlations. We attribute our findings to the presence of proteins (such as elastin), and desmosine and isodesmosine cross-linkers in the microcalcifications. It is important to note that the performance of the diffuse reflectance decision algorithm is comparable to one derived from the corresponding Raman spectra, and the considerably higher intensity of the reflectance signal enables the detection of the targeted lesions in a fraction of the spectral acquisition time. Our findings create a unique landscape for spectroscopic validation of breast core needle biopsy for detection of microcalcifications that can substantially improve the likelihood of an adequate, diagnostic biopsy in the first attempt. PMID:23267090

Soares, Jaqueline S.; Barman, Ishan; Dingari, Narahara Chari; Volynskaya, Zoya; Liu, Wendy; Klein, Nina; Plecha, Donna; Dasari, Ramachandra R.; Fitzmaurice, Maryann

2013-01-01

413

Diagnostic power of diffuse reflectance spectroscopy for targeted detection of breast lesions with microcalcifications.  

PubMed

Microcalcifications geographically target the location of abnormalities within the breast and are of critical importance in breast cancer diagnosis. However, despite stereotactic guidance, core needle biopsy fails to retrieve microcalcifications in up to 15% of patients. Here, we introduce an approach based on diffuse reflectance spectroscopy for detection of microcalcifications that focuses on variations in optical absorption stemming from the calcified clusters and the associated cross-linking molecules. In this study, diffuse reflectance spectra are acquired ex vivo from 203 sites in fresh biopsy tissue cores from 23 patients undergoing stereotactic breast needle biopsies. By correlating the spectra with the corresponding radiographic and histologic assessment, we have developed a support vector machine-derived decision algorithm, which shows high diagnostic power (positive predictive value and negative predictive value of 97% and 88%, respectively) for diagnosis of lesions with microcalcifications. We further show that these results are robust and not due to any spurious correlations. We attribute our findings to the presence of proteins (such as elastin), and desmosine and isodesmosine cross-linkers in the microcalcifications. It is important to note that the performance of the diffuse reflectance decision algorithm is comparable to one derived from the corresponding Raman spectra, and the considerably higher intensity of the reflectance signal enables the detection of the targeted lesions in a fraction of the spectral acquisition time. Our findings create a unique landscape for spectroscopic validation of breast core needle biopsy for detection of microcalcifications that can substantially improve the likelihood of an adequate, diagnostic biopsy in the first attempt. PMID:23267090

Soares, Jaqueline S; Barman, Ishan; Dingari, Narahara Chari; Volynskaya, Zoya; Liu, Wendy; Klein, Nina; Plecha, Donna; Dasari, Ramachandra R; Fitzmaurice, Maryann

2013-01-01

414

Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materials  

NASA Technical Reports Server (NTRS)

Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mossbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mossbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mossbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.

Bishop, J. L.; Pieters, C. M.; Burns, R. G.; Edwards, J. O.; Mancinelli, R. L.; Froschl, H.

1995-01-01

415

Femtosecond demodulation in low-temperature-grown gallium arsenide: A high-spectral-purity submillimeter and terahertz source for spectroscopy  

NASA Astrophysics Data System (ADS)

The development of a submm source capable of producing high spectral purity THz radiation for high resolution Doppler limited spectroscopy is technologically difficult. However, the potential usefulness of such a source for spectroscopy has driven our development of a technique whereby pulses from an 800 MHz, 200 femtosecond mode-locked Ti:sapphire laser are demodulated with a Low Temperature Grown GaAs Photo-Conductive Switch (LTG GaAs PCS) and the resulting submm radiation used for molecular spectroscopy. Current technology incorporates a sputtered gold antenna on the surface of the LTG GaAs substrate and the pulse train from the mode-locked laser is focused onto the 5 ?m gap at the center of the biased antenna structure. The antenna radiates all the spectral components produced by the demodulation process into free space. A single component from this ``comb'' of frequencies may then be employed for molecular spectroscopy. Scanning through the molecular transition is achieved by changing the length of the laser cavity, and, therefore, the spacing of the spectral components. The spectral purity of the source is dependent upon fluctuations in the timing of the optical pulses. In this thesis, the noise on passively mode-locked Ti:sapphire lasers is developed completely from the frequency domain using simple Frequency Modulation (FM) theory. It will be shown that the primary source of ``noise'' on these systems is a result of AM noise on the Argon Ion pump laser. It will also be shown that the inclusion of low frequency amplitude fluctuations and white noise from the Argon Ion pump laser as sources of FM results in power spectrum ``skirts'' which match those commonly found on higher order spectral components. While understanding the spectral purity and laser characteristics is a major portion of this research, the primary goal of this thesis work was to produce a spectrometer capable of measuring molecular rotational transitions at frequencies above 1 THz. Towards this goal, initial studies involving rotational transitions in the molecules carbonyl sulfide and carbon monoxide were used to characterize and calibrate the system at frequencies around 1 THz. Novel studies of hydrogen peroxide at frequencies around 1.3 THz were also successfully performed.

Demers, Joseph Raymond

416

Tunable terahertz quantum cascade lasers with external gratings  

E-print Network

We demonstrate a frequency tunable external cavity terahertz quantum cascade laser using an abutted antireflection-coated silicon lens to reduce facet reflection and as a beam-forming element, with an external grating ...

Lee, Alan Wei Min

417

[Applications of near infrared reflectance spectroscopy technique to determination of forage mycotoxins].  

PubMed

The near infrared reflectance spectroscopy technique (NIRS) has been explored at many fields such as agriculture, food, chemical, medicine, and so on, due to its rapid, effective, non-destructive, and on-line characteristics. Fungi invasion in forage materials during processing and storage would generate mycotoxins, which were harmful for people and animal through food chains. The determination of mycotoxins included the overelaborated pretreatments such as milling, extracting, chromatography and subsequent process such as enzyme linked immunosorbent assay, high performance liquid chromatography, and thin layer chromatography. The authors hope that high precision and low detection limit spectrum instrument, and software technology and calibration model of mycotoxins determination, will fast measure accurately the quality and quantity of mycotoxins, which will provide basis for reasonable process and utilization of forage and promote the application of NIRS in the safety livestock product. PMID:20672610

Xu, Qing-Fang; Han, Jian-Guo; Yu, Zhu; Yue, Wen-Bin

2010-05-01

418

Dipalmitoyl-phosphatidylcholine/phospholipase D interactions investigated with polarization-modulated infrared reflection absorption spectroscopy.  

PubMed Central

The hydrolysis of 1,2-dipalmitoylphosphatidylcholine (DPPC) catalyzed by Streptomyces chromofuscus phospholipase D (PLD) has been investigated using monolayer techniques and polarization-modulated infrared absorption reflection spectroscopy. The spectroscopic analysis of the phosphate groups provides a quantitative estimation of the hydrolysis yield. The hydrolysis kinetics was investigated in dependence on the phase state of the lipid monolayer. It was found that PLD exhibits maximum activity in the liquid-expanded phase, whereas PLA2 has its activity maximum in the two-phase region. A lag phase was observed in all experiments indicating that small amounts of the hydrolysis product 1,2-dipalmitoylphosphatidic acid (DPPA) are needed for initiating the fast hydrolysis reaction. Higher concentrations of DPPA inhibit the hydrolysis. The critical inhibition concentration of DPPA is a function of the monolayer pressure. PMID:11159442

Estrela-Lopis, I; Brezesinski, G; Möhwald, H

2001-01-01

419

Understanding the collapse mechanism in Langmuir monolayers through polarization modulation-infrared reflection absorption spectroscopy.  

PubMed

The collapse of films at the air-water interface is related to a type of 2D-to-3D transition that occurs when a Langmuir monolayer is compressed beyond its stability limit. Studies on this issue are extremely important because defects in ultrathin solid films can be better understood if the molecular mechanisms related to collapse processes are elucidated. This paper explores how the changes of vibration of specific groups of lipid molecules, as revealed by polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS), are affected by the monolayer collapse. Different mechanisms of collapse were studied, for those lipids that undergo constant-area collapse (such as stearic acid) and for those that undergo constant-pressure collapse (such as DPPC, DPPG, and DODAB). Lipid charges also affect the mechanism of collapse, as demonstrated for two oppositely charged lipids. PMID:23806167

Goto, Thiago Eichi; Caseli, Luciano

2013-07-23

420

Layer-dependent optical conductivity in atomic thin WS? by reflection contrast spectroscopy.  

PubMed

Optical conductivity, which originates from the interband transition due to electron-phonon interaction, is one of the powerful tools used for studying the electronic states in layered transition metal dichalcogenides (TMDCs). Here, we report for the first time the optical conductivity of WS2, one of the emerging classes of TMDCs, prepared directly on SiO2/Si substrate using reflection contrast spectroscopy. The measured optical conductivity at direct excitonic transition point K of the Brillouin zone for monolayer WS2 shows a value of 0.37 e(2)/?? in the visible range of the energy spectrum. Our results reveal that the optical conductivity of WS2 layers is frequency-dependent and show additional features in the conductivity spectra for bilayer to bulk counterparts, signifying a transition from direct band gap to indirect band gap with the evolution of layer numbers as predicted by our calculations. PMID:25153193

Nayak, Pramoda K; Yeh, Chao-Hui; Chen, Yu-Chen; Chiu, Po-Wen

2014-09-24

421

[Use of visible and near infrared reflectance spectroscopy to identify the cashmere and wool].  

PubMed

The wool and cashmere samples (n = 130) from different areas of Gansu province were identified by visible and near-infrared reflectance spectroscopy (Vis/NIRs). The result shows that principal component-mahalanobis distance pattern can identify the wool and cashmere, and the boundary between two categories was clear; The calibration set samples were used to establish calibration qualitative model using PCR combined with the best pretreatment of the spectra and math, including multivariate scattering correction (MSC), first derivative, eight for the best principal component factor, one for uncertainty factor, this calibration model of the predicted was the best, and the result of the external validation was correct completely. Results from this experiment indicate that Vis/NIRs can be utilized to identify the wool and cashmere. PMID:24159853

Liu, Xin-Ru; Zhang, Li-Ping; Wang, Jian-Fu; Wu, Jian-Ping; Wang, Xin-Rong

2013-08-01

422

Fast determination of total ginsenosides content in ginseng powder by near infrared reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Near infrared (NIR) reflectance spectroscopy was used to develop a fast determination method for total ginsenosides in Ginseng (Panax Ginseng) powder. The spectra were analyzed with multiplicative signal correction (MSC) correlation method. The best correlative spectra region with the total ginsenosides content was 1660 nm~1880 nm and 2230nm~2380 nm. The NIR calibration models of ginsenosides were built with multiple linear regression (MLR), principle component regression (PCR) and partial least squares (PLS) regression respectively. The results showed that the calibration model built with PLS combined with MSC and the optimal spectrum region was the best one. The correlation coefficient and the root mean square error of correction validation (RMSEC) of the best calibration model were 0.98 and 0.15% respectively. The optimal spectrum region for calibration was 1204nm~2014nm. The result suggested that using NIR to rapidly determinate the total ginsenosides content in ginseng powder were feasible.

Chen, Hua-cai; Chen, Xing-dan; Lu, Yong-jun; Cao, Zhi-qiang

2006-01-01

423

Attenuated total reflectance Fourier transform infrared spectroscopy analysis of red seal inks on questioned document.  

PubMed

Seals are traditionally used in the Far East Asia to stamp an impression on a document in place of a signature. In this study, an accuser claimed that a personal contract regarding mining development rights acquired by a defendant was devolved to the accuser because the defendant stamped the devolvement contract in the presence of the accuser and a witness. The accuser further stated that the seal ink stamped on the devolvement contract was the same as that stamped on the development rights application document. To verify this, the seals used in two documents were analyzed using micro-attenuated total reflectance Fourier transform infrared spectroscopy and infrared spectra. The findings revealed that the seals originated from different manufacturers. Thus, the accuser's claim on the existence of a devolvement contract was proved to be false. PMID:24844350

Nam, Yun Sik; Park, Jin Sook; Kim, Nak-Kyoon; Lee, Yeonhee; Lee, Kang-Bong

2014-07-01

424

Inexpensive diffuse reflectance spectroscopy system for measuring changes in tissue optical properties  

NASA Astrophysics Data System (ADS)

The measurement of changes in blood volume in tissue is important for monitoring the effects of a wide range of therapeutic interventions, from radiation therapy to skin-flap transplants. Many systems available for purchase are either expensive or difficult to use, limiting their utility in the clinical setting. A low-cost system, capable of measuring changes in tissue blood volume via diffuse reflectance spectroscopy is presented. The system consists of an integrating sphere coupled via optical fibers to a broadband light source and a spectrometer. Validation data are presented to illustrate the accuracy and reproducibility of the system. The validity and utility of this in vivo system were demonstrated in a skin blanching/reddening experiment using epinephrine and lidocaine, and in a study measuring the severity of radiation-induced erythema during radiation therapy.

Glennie, Diana L.; Hayward, Joseph E.; McKee, Daniel E.; Farrell, Thomas J.

2014-10-01

425

Combining total internal reflection sum frequency spectroscopy spectral imaging and confocal fluorescence microscopy.  

PubMed

Understanding surface and interfacial lateral organization in material and biological systems is critical in nearly every field of science. The continued development of tools and techniques viable for elucidation of interfacial and surface information is therefore necessary to address new questions and further current investigations. Sum frequency spectroscopy (SFS) is a label-free, nonlinear optical technique with inherent surface specificity that can yield critical organizational information on interfacial species. Unfortunately, SFS provides no spatial information on a surface; small scale heterogeneities that may exist are averaged over the large areas typically probed. Over the past decade, this has begun to be addressed with the advent of SFS microscopy. Here we detail the construction and function of a total internal reflection (TIR) SFS spectral and confocal fluorescence imaging microscope directly amenable to surface investigations. This instrument combines, for the first time, sample scanning TIR-SFS imaging with confocal fluorescence microscopy. PMID:25506739

Allgeyer, Edward S; Sterling, Sarah M; Gunewardene, Mudalige S; Hess, Samuel T; Neivandt, David J; Mason, Michael D

2015-01-27

426

Reflection-Absorption Infrared Spectroscopy of Thin Films Using an External Cavity Quantum Cascade Laser  

SciTech Connect

We present experimental demonstrations using a broadly tunable external cavity quantum cascade laser (ECQCL) to perform Reflection-Absorption InfraRed Spectroscopy (RAIRS) of thin layers and residues on surfaces. The ECQCL compliance voltage was used to measure fluctuations in the ECQCL output power and improve the performance of the RAIRS measurements. Absorption spectra from self-assembled monolayers of a fluorinated alkane thiol and a thiol carboxylic acid were measured and compared with FTIR measurements. RAIRS spectra of the explosive compounds PETN, RDX, and tetryl deposited on gold substrates were also measured. Rapid measurement times and low noise were demonstrated, with < 1E-3 absorbance noise for a 10 second measurement time.

Phillips, Mark C.; Craig, Ian M.; Blake, Thomas A.

2013-02-04

427

The use of UV-VIS-NIR reflectance spectroscopy to identify iron minerals  

NASA Astrophysics Data System (ADS)

Iron minerals - which behave as indicators in earthly and Martian environments - can be identified by UV-VIS-NIR reflectance spectroscopy. The aim of this study was to compare the spectra of various soils and sediments all of which contain iron minerals but developed under different environmental conditions. To identify the mineral of the sediments we used the first and second derivatives of the Kubelka-Munk transformed spectra. According to their iron mineral composition, the analysed samples can be divided into three distinct groups. Goethite refers to the hydromorphic conditions, hematite suffers from the long and intense weathering in leaching environment. In the case of steppe climatic conditions the weathering is so weak that the appearance of pedogenic iron minerals is improbable in these soils.

Szalai , Z.; Kiss, K.; Jakab, G.; Sipos, P.; Belucz, B.; Németh, T.

2013-11-01

428

Cryomagnetic Point-Contact Andreev Reflection Spectroscopy on Single Crystal Iron-Chalcogenide Superconductors  

NASA Astrophysics Data System (ADS)

We report on cryomagnetic point-contact Andreev reflection spectroscopy performed on single crystals of superconducting FeTe1-xSx and FeTe1-xSex. The samples are cleaved in-situ and the measurements are carried out at temperatures down to 4.2K and in a field up to 9T. At base temperature and zero field, we observe a cone-shaped hump at lower voltages in the conductance spectra with no dips at zero bias and a linear background at higher voltages. The spectral evolution of gap size, zero-bias conductance, and excess spectral area are analyzed as a function of temperature and field. Further spectral analysis is carried out using theoretical models of conductance spectra in multiband superconductors [1,2] and of gap symmetry in Fe-based superconductors [3]. The role of interstitial iron is also considered, by comparison with atomically-resolved scanning tunneling spectroscopy data.[4pt] [1] V. Lukic and E.J. Nicol, PRB 76, 144508 (2007) [2] A. Golubov et al., PRL 103, 077003 (2009) [3] P.J. Hirschfeld et al., RPP 74, 124508 (2011)

Yen, Y. T.; Hu, Rongwei; Petrovic, C.; Yeh, K. W.; Wu, M. K.; Wei, J. Y. T.

2012-02-01

429

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

SciTech Connect

The U.S. Department of Energy (DOE) has millions of gallons of radioactive liquid and sludge wastes that must be retrieved from underground storage tanks. This waste, in the form of slurries, must be transferred and processed to a final form, such as glass logs. On-line instrumentation to measure the properties of these slurries in real-time during transport is needed in order to prevent plugging and reduce excessive dilution. The results, describes a collaborative effort between Pacific Northwest National Laboratory (PNNL) and the University of Washington to develop a completely new method for using ultrasonics to measure the particle size and viscosity of a slurry. The concepts are based on work in optics on grating-light-reflection spectroscopy (GLRS) at the University of Washington and work on ultrasonic diffraction grating spectroscopy (UDGS) carried out at PNNL. The objective of the research was to extend the GLRS theory for optics to ultrasonics, and to demonstrate its capabilities of UDGS. The proposed ultrasonic method could result in an instrument that would be simple, rugged, and very compact, allowing it to be implemented as part of a pipeline wall at facilities across the DOE complex

Burgess, L.W.; Brodsky, A.M.

2005-12-15

430

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

PubMed

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 microm from the ATR sampling unit surface (a 7 cm(2) hydrophobic ZnSe crystal). Applying a 0.2-0.3 microm thick film on the ATR unit surface, any chemical changes within this film as well as at the interface can be continuously monitored, even having an aqueous phase on top of the film. Infrared film analysis is considered especially useful for studying detergent enzymes, which act on surface bound films consisting of food component like vegetable oils (triacylglycerols) and carbohydrates (e.g. starch). Experimental data are presented for hydrolysis of a triacylglycerol film (triolein) by use of a triacylglycerol lipase (cutinase), and starch film degradation by use of an alpha-amylase. PMID:11911924

Snabe, Torben; Petersen, Steffen Bjørn

2002-05-01

431

Infrared attenuated total reflection spectroscopy of 6H-SiC(0001) and (0001¯) surfaces  

NASA Astrophysics Data System (ADS)

Fourier-transformed infrared attenuated total reflection (FTIR-ATR) spectroscopy was used to study the adsorbates on 6H-SiC(0001) and (0001¯) surfaces after chemical treatments and after heat treatments in hydrogen. We obtained clear absorption bands attributable to hydrides and oxides on the SiC surfaces. The ATR spectroscopy revealed polarity dependencies of Si-H and C-H stretch modes between the 6H-SiC(0001) and (0001¯). The surface Si-H bonds on 6H-SiC(0001) formed by the heat treatment in hydrogen were found to have a quite long life time against air exposure, and the heat treatment in hydrogen also produced a flat (0001¯) surface with ordered surface C-H bonds. The oxidation characteristics of 6H-SiC(0001) and (0001¯) surfaces were also studied, and we discussed the roles of surface treatments using H2O2 solution and H2SO4 solution at elevated temperature.

Tsuchida, H.; Kamata, I.; Izumi, K.

1999-04-01

432

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

PubMed

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 of NIR to predict chemical composition (crude protein, intramuscular fat, moisture/dry matter, ash, gross energy, myoglobin and collagen), technological parameters (pH value; L*, a*, b* colour values; water holding capacity; Warner-Bratzler and slice shear force) and sensory attributes (colour, shape, marbling, odour, flavour, juiciness, tenderness or firmness) are reviewed. Secondly, the usefulness of NIR for classification into meat quality grades is presented and thirdly its potential application in the industry is shown. The review indicates that NIR showed high potential to predict chemical meat properties and to categorize meat into quality classes. In contrast, NIR showed limited ability for estimating technological and sensory attributes, which may be mainly due to the heterogeneity of the meat samples and their preparation, the low precision of the reference methods and the subjectivity of assessors in taste panels. Hence, future work to standardize sample preparation and increase the accuracy of reference methods is recommended to improve NIR ability to predict those technological and sensory characteristics. In conclusion, the review shows that NIR has a considerable potential to predict simultaneously numerous meat quality criteria. PMID:20416766

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

2009-10-01

433

Estimate of heavy metal contamination in soils after a mining accident using reflectance spectroscopy.  

PubMed

The possibility to adapt chemometrics approaches for the quantitative estimation of heavy metals in soils polluted by a mining accident was explored. In April 1998, the dam of a mine tailings pond in Aznalcóllar (Spain) collapsed and flooded an area of more than 4000 ha with pyritic sludge contaminated with high concentrations of heavy metals. Six months after the end of the first remediation campaign, soil samples were collected for chemical analysis and measurement of visible to near-infrared reflectance (0.35-2.4 microm). Concentrations for As, Cd, Cu, Fe, Hg, Pb, S, Sb, and Zn were well above background values. Prediction of heavy metals was achieved by stepwise multiple linear regression analysis (MLR) and an artificial neural network (ANN) approach. It was possible to predict six out of nine elements with high accuracy. Best R2 between predicted and chemically analyzed concentrations were As, 0.84; Fe, 0.72; Hg, 0.96; Pb, 0.95; S, 0.87; and Sb, 0.93. Results for Cd (0.51), Cu (0.43), and Zn (0.24) were not significant. MLR and ANN both achieved similar results. Correlation analysis revealed that most wavelengths important for prediction could be attributed to absorptions features of iron and iron oxides. These results indicate that it is feasible to predict heavy metals in soils contaminated by mining residuals using the rapid and cost-effective reflectance spectroscopy. PMID:12099473

Kemper, Thomas; Sommer, Stefan

2002-06-15

434

Near IR Scanning Angle Total Internal Reflection Raman Spectroscopy at Smooth Gold Films  

SciTech Connect

Total internal reflection (TIR) Raman and reflectivity spectra were collected for nonresonant analytes as a function of incident angle at sapphire or sapphire/smooth 50 nm gold interfaces using 785 nm excitation. For both interfaces, the Raman signal as a function of incident angle is well-modeled by the calculated interfacial mean square electric field (MSEF) relative to the incident field times the thickness of the layer being probed in the Raman measurement (D{sub RS}). The Raman scatter was reproducibly enhanced at the interface containing a gold film relative to the sapphire interface by a factor of 4.3–4.6 for aqueous pyridine or 2.2–3.7 for neat nitrobenzene, depending on the analyzed vibrational mode. The mechanism for the increased Raman signal is the enhanced MSEF at incident angles where propagating surface plasmons are excited in the metal film. The background from the TIR prism was reduced by 89–95% with the addition of the gold film, and the percent relative uncertainty in peak area was reduced from 15 to 1.7% for the 1347 cm–1 mode of nitrobenzene. Single monolayers of benzenethiol (S/N = 6.8) and 4-mercaptopyridine (S/N = 16.5) on gold films were measured by TIR Raman spectroscopy with 785 nm excitation (210 mW) without resonant enhancement in 1 min.

McKee, Kristopher; Meyer, Matthew; Smith, Emily

2012-04-13

435

Terahertz reflectarray as a polarizing beam splitter.  

PubMed

A reflectarray is designed and demonstrated experimentally for polarization-dependent beam splitting at 1 THz. This reflective component is composed of two sets of orthogonal strip dipoles arranged into interlaced triangular lattices over a ground plane. By varying the length and width of the dipoles a polarization-dependent localized phase change is achieved on reflection, allowing periodic subarrays with a desired progressive phase distribution. Both the simulated field distributions and the measurement results from a fabricated sample verify the validity of the proposed concept. The designed terahertz reflectarray can efficiently separate the two polarization components of a normally incident wave towards different predesigned directions of ±30°. Furthermore, the measured radiation patterns show excellent polarization purity, with a cross-polarization level below -27 dB. The designed reflectarray could be applied as a polarizing beam splitter for polarization-sensitive terahertz imaging or for emerging terahertz communications. PMID:24977867

Niu, Tiaoming; Withayachumnankul, Withawat; Upadhyay, Aditi; Gutruf, Philipp; Abbott, Derek; Bhaskaran, Madhu; Sriram, Sharath; Fumeaux, Christophe

2014-06-30

436

Applications of microstructured silicon wafers as internal reflection elements in attenuated total reflection Fourier transform infrared spectroscopy.  

PubMed

A novel internal reflection element (IRE) for attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectral acquisition is introduced and applied for several surface-sensitive measurements. It is based on microstructured double-side-polished (100) silicon wafers with v-shaped grooves of {111} facets on their backside. These facets of the so-called "microstructured single-reflection elements" (mSRE) are formed by a crystal-oriented anisotropic wet etching process within a conventional wafer structuring process. They are used to couple infrared radiation into and out of the IRE. In contrast to the application of the commonly used silicon multiple-reflection elements (MRE), the new elements provide single-reflection ATR measurements at the opposite wafer side by using simple reflection accessories without any special collimation. Due to the short light path, the spectral range covers the entire mid-infrared region with a high optical throughput, including the range of silicon lattice vibrations from 300 to 1500 cm(-1). In addition to typical ATR applications, i.e., the measurement of bulk liquids and soft materials, the new reflection elements can be effectively used and customer-specifically designed for in situ and ex situ investigations of aqueous solutions, thin films, and monolayers on Si. Examples presented in this article are in situ etching of native as well as thermal SiO(2) and characterization of polydimethylsiloxane (PDMS) films on Si under various measuring conditions. PMID:20828439

Schumacher, Henrik; Künzelmann, Ulrich; Vasilev, Boris; Eichhorn, Klaus-Jochen; Bartha, Johann W

2010-09-01

437

Nondestructive inspection of organic films on sandblasted metals using diffuse reflectance infrared spectroscopy  

SciTech Connect

Diffuse reflectance infrared spectroscopy is a very useful tool for the determination of surface contamination and characterization of films in manufacturing applications. Spectral data from the surfaces of a host of practical materials may be obtained with sufficient insensitivity to characterize relatively thick films, such as paint, and the potential exists to detect very thin films, such as trace oil contamination on metals. The SOC 400 Surface Inspection Machine/InfraRed (SIMIR) has been developed as a nondestructive inspection tool to exploit this potential in practical situations. This SIMIR is a complete and ruggidized Fourier transform infrared spectrometer with a very efficient and robust barrel ellipse diffuse reflectance optical collection system and operating software system. The SIMIR weighs less than 8 Kg, occupies less than 14 L volume, and may be manipulated into any orientation during operation. The surface to be inspected is placed at the focal point of the SIMIR by manipulating the SIMIR or the surface. The SIMIR may or may not contact the surface being inspected. For flat or convex items, there are no size limits to items being inspected. For concave surfaces, the SIMIR geometry limits the surface to those having a radius of curvature greater than 0.2 m. For highly reflective metal surfaces, the SIMIR has a noise level approaching 1 {times} 10{sup {minus}4} absorbance units, which is sufficient for detecting nanometer thick organic film residues on metals. The use of this nondestructive inspection tool is demonstrated by the spatial mapping of organic stains on sand blasted metals in which organic stains such as silicone oils, mineral oils, and triglycerides are identified both qualitatively and quantitatively over the surface of the metal specimen.

Powell, G.L. [Oak Ridge Y-12 Plant, TN (United States); Cox, R.L. [Oak Ridge National Lab., TN (United States); Barber, T.E. [Sam Houston State Univ., Huntsville, TX (United States); Neu, J.T. [Surface Optics Corp., San Diego, CA (United States)

1996-07-08

438

Measurements of the Carrier Dynamics and Terahertz Response of Oriented  

E-print Network

ultrafast optical-pump terahertz-probe spectroscopy. We present results on the time, frequency optical-pump THz-probe spectroscopy. Ultrafast carrier dynamics in group III-V, II-VI, and group IV semiconductor nanowires have been studied with optical-pump optical-probe spectroscopy measurements7

Afshari, Ehsan

439

Comparing local vs. global visible and near-infrared (VisNIR) diffuse reflectance spectroscopy (DRS) calibrations for the prediction of soil clay, organic C  

E-print Network

Comparing local vs. global visible and near-infrared (VisNIR) diffuse reflectance spectroscopy (DRS Elsevier B.V. All rights reserved. 1. Introduction Visible and near-infrared (VisNIR) diffuse reflectance

Lawrence, Rick L.

440

Laser terahertz emission microscopy  

NASA Astrophysics Data System (ADS)

Laser terahertz (THz) emission microscopy (LTEM) is reviewed. Femtosecond lasers can excite THz waves in various electronic materials due to ultrafast current modulation. The current modulation is realized by the acceleration or deceleration of photo-excited carriers, and thus LTEM visualizes the dynamic photo-response of substances. We construct a free-space type and scanning probe type with transmission or reflection modes. The developed systems have a minimum spatial resolution better than 2 ?m, which is defined by the laser beam diameter. We present some examples of LTEM applications, such as ferroelectric domain imaging, quantitative supercurrent distribution in high- T superconductors, defect detection of MOS devices as well as the visualization of the photo-responses in materials and devices. To cite this article: H. Murakami, M. Tonouchi, C. R. Physique 9 (2008).

Murakami, Hironaru; Tonouchi, Masayoshi

2008-03-01

441

Secondary cell wall development in cotton fibers as examined with attenuated total reflection Fourier transform infrared spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

Cotton fibers harvested at 18, 20, 24, 28, 32, 36 and 40 days after flowering were examined using attenuated total reflection Fourier transform-infrared (ATR FT-IR) spectroscopy. The selected harvesting points coincide with secondary cell wall (SCW) development in the fibers. Progressive but moderat...

442

PREDICTION OF COLOR, TENDERNESS, AND SENSORY CHARACTERISTICS OF BEEF STEAKS BY VISIBLE AND NEAR INFRARED REFLECTANCE SPECTROSCOPY. A FEASIBILITY STUDY  

Technology Transfer Automated Retrieval System (TEKTRAN)

Color, texture and sensory attributes of 24 beef carcasses at 2, 4, 8, 14, and 21 days post mortem were predicted by visible/near infrared (visible/NIR) reflectance spectroscopy in 400-1080 nm region. Predicting the Hunter a*, b*, and E* values yielded the coefficient of determination (R**2) in cal...

443

Comparison and detection of total and available soil carbon fractions using visible/near infrared diffuse reflectance spectroscopy  

E-print Network

Comparison and detection of total and available soil carbon fractions using visible/near infrared. With the advent of visible/near-infrared-diffuse reflectance spectroscopy (VNIR-DRS) to infer on soil C fractions 2500 Pg C, which is nearly four times higher than the global biotic pool and three times higher than

Grunwald, Sabine

444

SEARCHING FOR THE PARENT BODIES OF METEORITES THROUGH REFLECTANCE SPECTROSCOPY: CURRENT STATE. T. Hiroi, Dept. of Geological  

E-print Network

SEARCHING FOR THE PARENT BODIES OF METEORITES THROUGH REFLECTANCE SPECTROSCOPY: CURRENT STATE. T_hiroi@brown.edu) Introduction: Some meteoriticists may falsely assume that the parent bodies of meteorites they are studying do is not important. I understand the difficulty of using two very different methods: Analyzing meteorites

Hiroi, Takahiro