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1

Scattering effects in terahertz reflection spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2008-04-01

2

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

3

Terahertz time-domain attenuated total reflection spectroscopy in water and biological solution  

NASA Astrophysics Data System (ADS)

We demonstrate time-domain attenuated total reflection spectroscopy in terahertz frequency region. Geometry of the reflection measurement is well optimized to obtain accurate optical constants of water or aqueous biomolecular system. We determine the dielectric constants of distilled water and sucrose solutions with this technique. This technique will open new aspects in the research field of biological systems in water.

Nagai, Masaya; Yada, Hiroyuki; Arikawa, Takashi; Tanaka, Koichiro

2006-04-01

4

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

5

Design and performance of reflective terahertz air-biased-coherent-detection for time-domain spectroscopy.  

PubMed

When a sample being tested is optically opaque or has a high absorption coefficient, a reflective measurement is often more suitable than a transmission measurement. We report the design and evaluation of a reflective terahertz time-domain spectroscopy (R-THz-TDS), using air as THz wave emitter and sensor, together with air-biased-coherent-detection (ABCD) method for the first time. With an 85 fs pulse amplified laser, we demonstrate a usable bandwidth from 0.5 THz to 12 THz, together with a peak dynamic range (DR) better than 2000:1 and a peak THz electrical field greater than 30 kV/cm. With a 32 fs pulse amplified laser, the usable bandwidth is remarkably expanded to a continuous 35 THz. Several far-infrared optical properties in various samples are reported. Furthermore, the time-resolved optical pump-THz probe experiment is performed. Finally, the uniqueness and advantage of this spectrometer are comprehensively compared with traditional THz-TDS and Fourier transform infrared (FTIR) spectroscopy. PMID:20174116

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

2010-02-01

6

Spectroscopy by pulsed terahertz radiation  

NASA Astrophysics Data System (ADS)

Spectroscopies using terahertz (THz) radiation excited by ultrashort laser pulses have been rapidly developing recently. In this paper, the principles of various types of THz time domain spectroscopies (THz TDSs), i.e. transmission-, reflection-and ellipsometry-type THz TDSs, and their applications to the characterization of semiconductors are described. In addition to the THz TDS using a femtosecond laser, a sub-THz TDS system using a cheap and compact continuous multimode laser diode is also described.

Hangyo, M.; Nagashima, T.; Nashima, S.

2002-11-01

7

Terahertz Time-Domain Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy (THz-TDS) is one of the most successful fields of THz optoelectronics. Measurements of semiconductors, ferroelectric crystals of current industrial interest, photonic crystals and biomolecules by means of standard THz-TDS are shown first, then modified versions such as attenuated total reflection spectroscopy and ellipsometry are described. In addition to the THz-TDS, generation and detection of THz radiation with the use of multimode laser diodes and applications in spectroscopy are described, although the radiation is emitted in CW mode. This Chapter is composed of topical sections written by specialists of the respective topics.

Nishizawa, Seizi; Sakai, Kiyomi; Hangyo, Masanoi; Nagashima, Takeshi; Takeda, Mitsuo Wada; Tominaga, Keisuke; Oka, Asako; Tanaka, Koichiro; Morikawa, Osamu

8

Hybrid continuous wave terahertz spectroscopy.  

PubMed

We propose a hybrid architecture for continuous wave terahertz spectroscopy employing a conventional two color photomixing system combined with a quasi time domain spectrometer, driven by a multimode laser diode. This approach fuses high spectral intensity with broadband frequency information and overcomes the ambiguity of standard continuous wave thickness measurements. PMID:20720971

Scheller, Maik; Stecher, Matthias; Gerhard, Marina; Koch, Martin

2010-07-19

9

Medical diagnostics using terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

The paper contains recent results of studying the ability of human body disease diagnosis with terahertz time-domain spectroscopy. In vitro skin cancer samples (squamous cell carcinoma, epithelioid cell melanoma, infiltrating carcinoma) were studied experimentally with terahertz pulsed spectrometer. The parametrical in vitro images of skin cancers are presented. The ability to make early tooth cariosity diagnosis with terahertz time-domain spectroscopy was also shown experimentally. The results of studying the in vitro tooth samples are presented and discussed.

Zaytsev, Kirill I.; Kudrin, Konstantin G.; Koroleva, Svetlana A.; Fokina, Irina N.; Volodarskaya, Svetlana I.; Novitskaya, Ekaterina V.; Perov, Artem N.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

2014-03-01

10

Toward practical terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

Brigada, David J.

11

Terahertz quasi time domain spectroscopy.  

PubMed

It is shown theoretically and experimentally that for the specific case of an equidistant frequency spacing of semiconductor laser modes, signals similar to terahertz (THz) time domain spectroscopy (TDS) can be detected in a standard photomixer setup. This quasi TDS system approach enables for both, time and frequency domain data processing. Measurements with a THz system which is based on a low cost multimode laser diode are presented. The system exhibits a bandwidth of 600 GHz and can be applied to the classical THz TDS application scenarios. PMID:19907558

Scheller, Maik; Koch, Martin

2009-09-28

12

Pulsed Terahertz Spectroscopy of Biomolecules  

NASA Astrophysics Data System (ADS)

Measurements of the collective vibrational modes associated with the 3D tertiary structure of biomolecules were undertaken using pulse terahertz spectroscopy. Transmission measurements of calf thymus DNA (CT-DNA), bovine serum albumin (BSA), and collagen were made for 2 cm-1 to 45 cm-1. For all three biomolecules, low frequency absorption bands could be distinguished from a broadband absorption increasing with frequency. For lyophilized powder samples, features appear at 15 cm-1 and 22 cm-1 for CT-DNA, 10 cm-1 for BSA, and 8 cm-1 and 12 cm-1 for collagen. Measurements were performed as a function of hydration and conformation.

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

1998-03-01

13

Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures  

SciTech Connect

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

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

2009-01-01

14

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

15

Developments and advances in nonlinear terahertz spectroscopy  

E-print Network

Nonlinear terahertz (THz) spectroscopy is a rapidly developing field, which is concerned with driving and observing nonlinear material responses in the THz range of the electromagnetic spectrum. In this thesis, I present ...

Brandt, Nathaniel Curran

2014-01-01

16

Investigation of inflammable liquids by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2005-07-01

17

Terahertz spectroscopy techniques for explosives detection  

Microsoft Academic Search

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

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

2009-01-01

18

Microfluidic devices for terahertz spectroscopy of biomolecules  

E-print Network

modes of bovine serum albumin from 0.5 - 2.5 THz and find good agreement with previously reported data terahertz spectroscopy of DNA, bovine serum albumin and collagen between 0.1 and 2.0 THz," Chem. Phys. Lett serum albumin," J. Am. Chem. Soc. 98, 990­992 (1976). 3. W. Zhuang, Y. Feng, and E.W. Prohofsky, "Self

Afshari, Ehsan

19

Extending applicability of terahertz spectroscopy for biosensing  

NASA Astrophysics Data System (ADS)

Terahertz (THz) vibrational resonance spectroscopy has recently emerged as a promising technique for fingerprinting biological molecules. Absorption spectra in this frequency range (0.1-10 THz) reflect molecular internal vibrations involving the weakest hydrogen bonds and/or non-bonded interactions, which are species specific. Of prime importance is improving detection sensitivity of molecules with low absorption characteristics in the THz gap. Also of importance is the characterization of biological molecules in the THz gap (10-25 cm-1) by physical parameters (refractive index and absorption coefficient) rather than sample dependent parameters (transmission, reflection) and extending spectroscopy to the low THz range where remote sensing is most viable. To address the sensitivity issue, it is shown that periodic arrays of rectangular slots with subwavelength width provide for local electromagnetic field enhancements due to edge effects in the low frequency range of interest, 10-25 cm-1 (300-750 GHz). Periodic structures of Au, doped Si and InSb were studied. InSb is confirmed to offer the highest results with the local power enhancements on the order of 1100 at frequency 14 cm -1. InSb and Si have large skin depths in the frequency range of interest and so the analysis of their structures was done through the Fourier expansion method of field diffracted from gratings. Au however has small skin depths at these frequencies compared to the thickness. Surface impedance boundary conditions were employed to model the Au structure, for which the Fourier expansion method was unsuitable owing to the huge magnitude of Au permittivity. The applications possibly include development of novel bio-sensors, with the strongly enhanced local electromagnetic fields leading to increased detection sensitivity, and monitoring biophysical processes such as DNA denaturation. Transmission and reflection data from parallel, independent experiments are utilized in the Interference Spectroscopy Technique model based on thin film interference to calculate the fine structure of refractive index and absorption coefficient of biological molecules (DNA, proteins) in the THz gap. As to spectroscopy in the low THz range (3-10 cm-1), a noise source was used in free space configuration in the FT-IR set-up to obtain transmission and reflection data of biological molecules that act as fingerprints.

Parthasarathy, Ramakrishnan

20

High frequency resolution terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

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

Sangala, Bagvanth Reddy

21

Metamaterial radiation from attenuated total reflection at terahertz frequencies  

NASA Astrophysics Data System (ADS)

The focus of this research was to explore the behavior of two-dimensional planar metamaterials or metafilms and understand the various excitation schemes for application of metafilms to Terahertz-Attenuated Total Reflection spectroscopy (THz-ATR). A standard THz time domain spectroscopy system based on photoconductive switches was modified to implement the ATR technique. Finite metamaterial arrays with varying singly- split ring resonator sizes were excited in the Kretschmann ATR configuration using finite sized terahertz beams. Numerical approaches using commercial software were looked into to explain the experimental observations. Various theoretical models were used to explain the observed phenomena. The ATR measurements showed an unexpected strengthening of the resonance when the metafilm sample was illuminated near the edge. This phenomenon referred to in this study as "the anomalous edge enhancement" was observed strongly in metafilms with closely spaced rings. A re-radiation signal was observed across the total internal reflection barrier where no signal is expected. It consisted of two peaks one at the fundamental metamaterial resonance and the second peak was due to the periodicity of the metafilm array. The anomalous behavior seen in the ATR measurements is attributed to the edge currents at the boundary of the metafilm array giving rise to this re-radiation signal. Results from analytic treatments based on Floquet method and method of moments were able to qualitatively model the measurements. The observed re-radiation signal is a potential loss mechanism that could impact observations from commonly used transmission measurements on metamaterials.

Ramani, Suchitra

22

Investigation of inflammable liquids by terahertz spectroscopy  

Microsoft Academic Search

We have examined a nondestructive and contactless screening method for water and inflammable liquids stored in common beverage plastic bottles by the terahertz time-domain spectroscopy. No THz transmission has been observed between 10 and 60 cm-1 for 45-mm-thick water in plastic bottles. Part of the THz wave, on the other hand, has been transmitted through the commercially available inflammable liquids

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

2005-01-01

23

Terahertz spectroscopy for quantifying refined oil mixtures.  

PubMed

In this paper, the absorption coefficient spectra of samples prepared as mixtures of gasoline and diesel in different proportions are obtained by terahertz time-domain spectroscopy. To quantify the components of refined oil mixtures, a method is proposed to evaluate the best frequency band for regression analysis. With the data in this frequency band, dualistic linear regression fitting is used to determine the volume fraction of gasoline and diesel in the mixture based on the Beer-Lambert law. The minimum of regression fitting R-Square is 0.99967, and the mean error of fitted volume fraction of 97# gasoline is 4.3%. Results show that refined oil mixtures can be quantitatively analyzed through absorption coefficient spectra in terahertz frequency, which it has bright application prospects in the storage and transportation field for refined oil. PMID:22907017

Li, Yi-nan; Li, Jian; Zeng, Zhou-mo; Li, Jie; Tian, Zhen; Wang, Wei-kui

2012-08-20

24

[Frequency correction in terahertz absorption spectroscopy].  

PubMed

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

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

2013-09-01

25

Metallic phase transition investigated via terahertz time-domain spectroscopy  

E-print Network

of surface particle plasmons in- duced dipolar surface charge on the individual particles,9 the amplitudeMetallic phase transition investigated via terahertz time-domain spectroscopy K. J. Chau,a K. M; accepted 15 December 2006; published online 26 January 2007 Terahertz time-domain spectroscopy is applied

Chau, Kenneth

26

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

27

A Comparison of Terahertz Pulsed Spectroscopy and Backward-Wave Oscillator Spectroscopy  

NASA Astrophysics Data System (ADS)

This paper presents new experimental and theoretical results for the material parameter reconstruction utilizing the terahertz (THz) pulsed spectroscopy (TPS). The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. The algorithm takes into account multiple reflections of THz pulse within the flat sample during the transmission mode measurements. Therefore the samples with small thickness or low refractive index could be studied utilizing the proposed method. In order to estimate the reconstruction accuracy, test sample material parameters, obtained with the TPS, were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated.

Zaytsev, Kirill I.; Gavdush, Arseniy A.; Chernomyrdin, Nikita V.; Kruchkov, Nikita P.; Kudrin, Konstantin G.; Nosov, Pavel A.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

2014-09-01

28

Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials  

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

29

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

30

Resonant terahertz reflection of periodic arrays of subwavelength metallic rectangles  

E-print Network

-domain spectroscopy and is attributed to the contributions from the dipole localized surface plasmons of isolated to as plasmonic crystals, have demonstrated enhanced terahertz transmission, prima- rily due to resonant excitation of surface plasmons at the metal-dielectric interface.1­7 It shows promising applications

Oklahoma State University

31

Terahertz spectroscopy of ionized air and explosive vapor  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

32

Terahertz reflection response measurement using a phonon polariton wave  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

33

Terahertz spectroscopy: Its future role in medical diagnoses  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

34

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

35

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

36

[Identification of Chinese herbal medicines based on terahertz spectroscopy analysis].  

PubMed

In order to study the feasibility of the identification of Chinese herbal medicines based on terahertz spectroscopy, the optical characteristic of astragalus, angelica, eucommia and three kinds of astragalus samples with different impurities in the frequency range 0.2-2.2 THz were researched by terahertz time-domain spectroscopy (THz-TDS), and their time-domain spectra, the frequency spectra and the absorption spectra were obtained at room temperature. The results indicated that the time-domain spectra, frequency-domain spectra and absorption spectra of astragalus, angelica, and eucommia have large differences in such a frequency range, the frequency-domain spectra and absorption spectra of three kinds of astragalus samples with different impurities are similar but there exists distinct difference. These researches proved that it is feasible to use terahertz time-domain spectroscopy to identify Chinese herbal medicine and provided a new method for Chinese herbal medicine quality control. PMID:25269292

Zhou, Yong-Jun; Liu, Jin-Song; Wang, Ke-Jia; Yang, Zhen-Gang; Zhang, Hui

2014-07-01

37

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 optical phonon depopulation scheme is studied using terahertz time domain spectroscopy. At laser threshold

Boyer, Edmond

38

Metal-wire terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz (THz) pulses propagating on a metal-wire waveguide are used to perform terahertz time-domain spectroscopy of lactose powder dispersed on top of the wire. The THz pulses are generated by a photoconductive switch at one end of the metal wire and are detected at the other end by electro-optic sampling in a ZnTe crystal that can be moved parallel to the axis of the metal wire. A large enhancement in the peak amplitude of the THz signal is observed by contacting the metal wire to one of the electrodes of the photoconductive switch. The propagation characteristics of the THz pulse along the metal wire and near its end are studied. Potential applications of metal-wire terahertz time-domain spectroscopy are discussed.

Walther, Markus; Freeman, Mark R.; Hegmann, Frank A.

2005-12-01

39

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

40

Terahertz spectroscopy of quantum 2D electron systems  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy permits the coherent motion of charges to be examined in a diverse range of two-dimensional semiconductor heterostructures. Studies of the THz conductivity and magnetoconductivity of two-dimensional quantum systems are reviewed, including cyclotron resonance spectroscopy and the transverse conductivity in the Hall and quantum Hall regimes. Experiments are described that demonstrate quantum phenomena at THz frequencies, principally coherent control and enhanced light-matter coupling in electromagnetic cavities.

Lloyd-Hughes, James

2014-09-01

41

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

42

Terahertz spectroscopy on hole transport in pentacene thin films  

NASA Astrophysics Data System (ADS)

Charge transport in pentacene thin films is investigated using terahertz electromodulation spectroscopy. Although the material is highly polycrystalline, a hole mobility of about 20 cm2/Vs is found, which exceeds the mobility obtained in DC measurements by orders of magnitude. The high AC mobility results from a motion of charge carriers, which is not hindered by grain boundaries. An upper limit of mh*?0.8 me is deduced for the conductivity effective mass of holes in pentacene.

Engelbrecht, S. G.; Prinz, M.; Arend, T. R.; Kersting, R.

2014-07-01

43

Terahertz spectroscopy properties of the selected engine oils  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

44

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 of photonic research as well. #12;Overcoming Resolution Limits in Terahertz Spectroscopy C. Alfaro, H. Koga, S

Mellor-Crummey, John

45

Terahertz probe for spectroscopy of sub-wavelength objects.  

PubMed

A system of two probes is designed for terahertz (THz) time-domain spectroscopy of sub-wavelength size objects. A twin-needle probe confines broadband THz pulses spatially by means of surface plasmon waves to a sub-wavelength spot smaller than 10 microns. The confined pulses are detected within the near-field zone of the twin-needle probe by a sub-wavelength aperture probe. The system allows THz spectroscopy to be applied to single micrometer-size objects in the 1-2.5THz region. PMID:22418501

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

2012-03-12

46

Data Extraction from Terahertz Time Domain Spectroscopy Measurements  

NASA Astrophysics Data System (ADS)

The potential of terahertz (THz) time domain spectroscopy to simultaneously determine the complex dielectric parameters of materials and their geometrical thickness is of high interest for scientific spectroscopy and for general metrology. This paper provides an overview of the background of the data extraction from THz measurements and discusses the accuracy and ambiguity of this extraction process. It is shown that the signal to noise ratio of the measurement as well as the bandwidth of the accessible THz spectrum define the limitation of the achievable accuracy in the data extraction.

Scheller, Maik

2014-08-01

47

Spectral artifacts from non-uniform samples analyzed by terahertz time-domain spectroscopy.  

PubMed

We report the impact of the spatial coherence distortion on the measured absorption spectra and the identification of materials analyzed by terahertz time-domain spectroscopy. It is shown that the deformation of the terahertz beam wave front can result into the overestimation of the electromagnetic absorption, the generation of artificial absorption peaks and even to the disappearance of characteristic absorption peaks. Obtaining clear absorption spectra without artifacts is crucial for applications based on terahertz imaging and spectroscopy. PMID:19550484

Théberge, Francis; Châteauneuf, Marc; Dubois, Jacques; Désilets, Sylvain; Lussier, Louis-Simon

2009-06-22

48

TeraHertz Time-Domain Spectroscopy for Explosive Trace Detection  

Microsoft Academic Search

This paper presents Terahertz time-domain spectroscopy for stand-off detection of explosive traces. Despite several well-developed explosive detection techniques available, the detection of a small amount of explosive traces is still challenging. Terahertz spectroscopy demonstrates potential for explosive detection through unique absorption spectra pattern of various kinds of explosive materials. Terahertz waves show good penetration through many dielectric materials that are

Seong G. Kong; Dong H. Wu

2006-01-01

49

Gapless dual-comb spectroscopy in terahertz region  

E-print Network

We demonstrated combination of gapless terahertz (THz) comb with dual-comb spectroscopy, namely gapless dual-THz-comb spectroscopy, to achieve the spectral resolution equal to width of the THz comb tooth. The gapless THz comb was realized by interpolating frequency gaps between the comb teeth with sweeping of a laser mode-locked frequency. The demonstration of low-pressure gas spectroscopy with gapless dual-THz-comb spectroscopy clearly indicated that the spectral resolution was decreased down to 2.5-MHz width of the comb tooth and the spectral accuracy was enhanced to 10-6 within the spectral range of 1THz. The proposed method will be a powerful tool to simultaneously achieve high resolution, high accuracy, and broad spectral coverage in THz spectroscopy.

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

2014-01-01

50

Chirped-pulse terahertz spectroscopy for broadband trace gas sensing.  

PubMed

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

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

2011-04-25

51

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

Microsoft Academic Search

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

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

2002-01-01

52

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

E-print Network

, benzoic acid and salicylic acid, as well as the salicylic acid isomers 3- and 4-hydroxybenzoic acid spectroscopy; Terahertz Time-domain spectroscopy; Far infrared; Waveguide; Aspirin; Benzoic acid. INTRODUCTION

53

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

54

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

55

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

56

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

57

High Resolution Terahertz Spectroscopy with Quantum Cascade Lasers  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

58

Terahertz spectroscopy of intrinsic biomarkers for non-melanoma skin Cecil S. Joseph1*  

E-print Network

Terahertz spectroscopy of intrinsic biomarkers for non-melanoma skin cancer. Cecil S. Joseph1 of human cancers. The aim of this study was to identify intrinsic biomarkers for non-melanoma skin cancer wave terahertz imaging, skin cancer imaging 1. INTRODUCTION 1.1 Non-Melanoma Skin Cancer Non-melanoma

Massachusetts at Lowell, University of

59

Determination of tetracycline hydrochloride by terahertz spectroscopy with PLSR model.  

PubMed

Antibiotic residues in agricultural and food products are of great concern to legislatures and consumers. Reliable techniques for rapid and sensitive detection of these residues are necessary to ensure food safety. In this study, tetracycline hydrochloride (TC-HCl) in powder and solution form was detected and quantified using terahertz (THz) spectroscopy. Partial least-squares regression (PLSR) was used to build calibration models. The results obtained in this study indicated that the PLSR model for powder samples was excellent and could be used for quality control. However, the PLSR model for solution samples was not robust and needed to be improved. Overall, THz spectroscopy combined with PLSR model had its potential for the rapid and non-destructive prediction of TC-HCl residue without sophisticated methods, although the accuracy was not high for solution samples which should be improved in future study. PMID:25306365

Qin, Jianyuan; Xie, Lijuan; Ying, Yibin

2015-03-01

60

Detection and identification of explosives using terahertz pulsed spectroscopic imaging  

NASA Astrophysics Data System (ADS)

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

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

2005-06-01

61

Spectroscopy study of Yungang Grottoes weathered material in terahertz range  

NASA Astrophysics Data System (ADS)

In this paper, the terahertz time domain spectroscopy (THz-TDS) technology is used to study the terahertz (THz) spectral characteristics of the Yungang Grottoes weathered material samples winch collected from No. 4, 9 and 39 these three different caves dug in different periods, A.D.520, A.D.494 and A.D. 484 years. The available effective wave band is between 0.2-2.6 THz. It is found that the transmission coefficient is high in low frequency region but low in high frequency region for all of the three kinds of samples. Experimental results also indicate that all of the samples have weak absorption in low frequency region, but the absorption coefficient increase quickly by exponential function as the frequency increasing. This character is more obvious especially for the absorption spectrum of the samples from the cave of late period. The refraction coefficient for the three kinds of samples has obvious differences in the whole THz wave band. The mean refraction coefficient of them is 1.53, 1.57 and 1.51 separately. According the results above, different periods of caves weathered samples can be identified. In addition, we can also offer the various optic constant of Yungang Grottoes samples in THz wave band for other studies work.

Meng, Tian-hua; Yang, Cheng-quan; Lu, Yu-he; Zhao, Guo-zhong

2011-08-01

62

Characteristics of Gadolinium Oxide Nanoparticles Using Terahertz Spectroscopy  

SciTech Connect

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

Lee, Dongkyu; Maeng, Inhee; Son, Joo-Hiuk [Department of Physics, University of Seoul, Seoul (Korea, Republic of); Oh, Seung Jae [Brain Korea 21 Project for Medical Science, Yonsei University, Seoul (Korea, Republic of); Kim, Taekhoon; Cho, Byung Kyu; Lee, Kwangyeol [Department of Chemistry, Korea University, Seoul (Korea, Republic of)

2009-04-19

63

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

64

Terahertz absorption spectroscopy of protein-containing reverse micellar solution  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

65

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

66

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.

67

Modal characteristics of antiresonant reflecting pipe waveguides for terahertz waveguiding.  

PubMed

Modal characteristics of the THz pipe waveguide, which is a thin pipe consisting of a large air core and a thin dielectric layer with uniform but low index, are investigated. Modal indices and attenuation constants are calculated for various core diameters, cladding thicknesses, and cladding refractive indices. Numerical results reveal that the guiding mechanism of the leaky core modes, which transmit most of the power in the air-core region, is that of the antiresonant reflecting guiding. Moreover, modal patterns including modal intensity distributions and electric field vector distributions are shown for the fundamental and higher order modes. Experiments using time-domain spectroscopy with PMMA pipes also confirm the antiresonant reflecting guiding mechanism. PMID:20173851

Lai, Chih-Hsien; You, Borwen; Lu, Ja-Yu; Liu, Tze-An; Peng, Jin-Long; Sun, Chi-Kuang; Chang, Hung-Chun

2010-01-01

68

Terahertz spectroscopy of Ni-Ti alloy thin films  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

69

Terahertz spectroscopy applied to the analysis of artists' materials  

NASA Astrophysics Data System (ADS)

Terahertz (THz) spectroscopy and imaging have been actively studied in these decades. THz waves (0.1-10 THz) are non-invasive, can penetrate opaque materials, and can be used to obtain fingerprint spectra whose characteristics depend upon molecular and intermolecular behavior. Unlike the mid-infrared region, no commercial spectral library is available for the THz region. Consequently, a spectral database of artists’ materials was developed in order to include THz spectroscopy among conservation science techniques. Most pigments and some synthetic polymers have characteristic fingerprint spectra in the THz region. With this technique most of these materials used in paintings can be identified alone or as paint, a combination of pigments and binders. Although the meaning of the spectral features has so far not been fully explained, previous studies on optical materials suggest that phonon absorption and the behavior of hydrogen bonds contribute to their spectral features. Examples of THz spectra of various art materials are discussed on the basis of measurements obtained using a conventional Fourier transform system.

Fukunaga, Kaori; Picollo, Marcello

2010-09-01

70

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

71

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

72

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

73

Determination of cellulose crystallinity by terahertz-time domain spectroscopy.  

PubMed

Terahertz-time domain spectroscopy (THz-TDS) has the ability to probe the crystallinity of several materials, due to the interaction of THz radiation with optical phonons in crystal lattices. In this work, THz-TDS has been used to quantify the degree of crystallinity of microcrystalline cellulose (MCC) samples. The THz spectra of cellulose present absorption features which could be directly correlated with the crystallinity index (CI) obtained by means of the well-established powder X-ray diffraction (PXRD) technique. The effect of THz time-domain signal processing was investigated, and both univariate and multivariate, based on partial least-squares (PLS), regressions were carried out with the signal in the frequency domain to correlate the THz spectra with CI. Results show that the multivariate regression models based on spectral data, collected with the sample displaced from the focal plane of the THz optics to improve representativeness and measurement repeatability, present the best performance with external validation achieving an absolute root-mean-square error of prediction (RMSEP) of 4% for CI. This result compares well with the PXRD technique. PMID:24654843

Vieira, Francisco Senna; Pasquini, Celio

2014-04-15

74

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

75

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

76

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

77

Time-domain terahertz spectroscopy of artificial skin  

NASA Astrophysics Data System (ADS)

Time-domain Terahertz (THz) spectroscopy and imaging is currently evaluated as a novel tool for medical imaging and diagnostics. The application of THz-pulse imaging of human skin tissues and related cancers has been demonstrated recently in-vitro and in-vivo. With this in mind, we present a time-domain THz-transmission study of artificial skin. The skin samples consist of a monolayer of porous matrix of fibers of cross-linked bovine tendon collagen and a glycosaminoglycan (chondroitin-6-sulfate) that is manufactured with a controlled porosity and defined degradation rate. Another set of samples consists of the collagen monolayer covered with a silicone layer. We have measured the THz-transmission and determined the index of refraction and absorption of our samples between 0.1 and 3 THz for various states of hydration in distilled water and saline solutions. The transmission of the THz-radiation through the artificial skin samples is modeled by electromagnetic wave theory. Moreover, the THz-optical properties of the artificial skin layers are compared to the THz-optical properties of freshly excised human skin samples. Based on this comparison the potential use of artificial skin samples as photo-medical phantoms for human skin is discussed.

Corridon, Peter M.; Ascázubi, Ricardo; Krest, Courtney; Wilke, Ingrid

2006-02-01

78

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

NASA Astrophysics Data System (ADS)

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

Zimdars, David A.

2003-08-01

79

An anti-reflection coating for silicon optics at terahertz frequencies  

Microsoft Academic Search

A method for reducing the reflections from silicon optics at terahertz frequencies has been investigated. In this study, we used thin films of parylene as an anti-reflection (AR) layer for silicon optics and show low-loss behavior well above 1 THz. Transmittance spectra are acquired on double-sided-parylene-coated, high-resistivity, single-crystal silicon etalons between 0.45 THz and 2.8 THz. Modeling the optical behavior

A. J. Gatesman; J. Waldman; M. Ji; C. Musante; S. Yagvesson

2000-01-01

80

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

Microsoft Academic Search

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

Hideki Hirori; Masaya Nagai; Koichiro Tanaka

2005-01-01

81

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

82

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

PubMed

Goos-Hänchen (GH) shifts of terahertz wave reflected on the Cyclo-Olefin Copolymer (COC)-air interface was investigated in simulation and experiment. The relationship between the GH shifts with the incident angle and the frequency of incident wave were calculated to get a reference for the simulation and experiment. The reflected GH shift was measured on the COC-air interface when a terahertz wave with the frequency of 0.206 THz was incident to a COC double-prism. By changing the thickness of the air layer we find experimentally and simulatively that the GH shift and the energy of the reflected wave increases with the increase of the air layer thickness. The study of GH shift can provide useful information for applications of THz waves in sensor and power delivery systems. PMID:23482217

Li, Qingmei; Zhang, Bo; Shen, Jingling

2013-03-11

83

Terahertz time-domain and Fourier-transform infrared spectroscopy of traditional Korean pigments  

NASA Astrophysics Data System (ADS)

Representative traditional Korean pigments (oyster shell white [hobun], massicot [miltaseung], indigo [jjok], azurite [seokcheong], malachite [seokrok], and red lead [yeondan]) have been studied with terahertz time-domain spectroscopy (THz-TDS) and Fourier-transform infrared spectroscopy (FTIRS) over the spectral region of 0.1-7.5 THz. Both the refractive index n and the extinction coefficient k were simultaneously and independently determined in the terahertz region without a Kramers-Kronig analysis while the absoprtion coefficient spectra were acquired in the infrared region. All pigments studied in the present work exhibited a set of characteristic absorption peaks unique to the pigment species in addition to a background that increased with increasing frequency. Our study demonstrates that terahertz and infrared techniques can be useful identification and diagnostic tools for the traditional Korean pigments used in heritage buildings and artworks.

Hong, Taeyoon; Choi, Kyujin; Ha, Taewoo; Park, Byung Cheol; Sim, Kyung Ik; Kim, Jong Hyeon; Kim, Jae Hoon; Kwon, Jy Eun; Lee, Sanghyun; Kang, Dai Ill; Lee, Han Hyoung

2014-03-01

84

Low-temperature time-domain terahertz spectroscopy of terbium gallium garnet crystals  

NASA Astrophysics Data System (ADS)

We report an experimental observation of high frequency magnetic excitations in terbium gallium garnet crystals using terahertz time-domain spectroscopy. We show that precessional modes of terbium magnetic sublattices can be excited by a magnetic field of a terahertz broadband pulse. We study and discuss the dependence of the observed resonances upon the temperature and the strength and orientation of the bias magnetic field. The behavior of the observed magnetic modes is in agreement with the theory of paramagnetic resonance in the multisublattice system. We also show that the illumination of the crystal with intense optical pulses destroys the magnetic ordering. Our results demonstrate that the time-domain terahertz spectroscopy can be a powerful tool by which to study high frequency properties of dielectric magnetic materials, with perceived extensions to studies in femtomagnetism and magnonics.

Mikhaylovskiy, R. V.; Hendry, E.; Ogrin, F. Y.; Kruglyak, V. V.

2013-03-01

85

Direct MD Simulations of Terahertz Absorption and 2D Spectroscopy Applied to Explosive Crystals  

E-print Network

Direct MD Simulations of Terahertz Absorption and 2D Spectroscopy Applied to Explosive Crystals G for Molecular Dynamics, Hebrew University of Jerusalem, Jerusalem 91904, Israel Materials and ProcessFF force field. The proposed direct method avoids the linear response and harmonic approximations

Goddard III, William A.

86

Solid-state phase transition onset detection in estrogen-like chemical via terahertz transmission spectroscopy  

NASA Astrophysics Data System (ADS)

Solid-state phase transition onset in an endocrine-disrupting estrogen-like chemical (1,4-naphthol) is detected using terahertz transmission spectroscopy. Differential scanning microscopy and temperature-dependent X-ray diffraction analysis confirmed the occurrence of such phenomenon.

Quema, Alex; Goto, Masahiro; Sakai, Masahiro; Janairo, Gerardo; El Ouenzerfi, Riadh; Takahashi, Hiroshi; Ono, Shingo; Sarukura, Nobuhiko

87

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

88

Ultrafast terahertz generation and spectroscopy for accelerator diagnostics  

NASA Astrophysics Data System (ADS)

The generation of strong terahertz (THz) radiation has recently drawn considerable attention owing to the potential for intense THz excitation spectroscopy, nonlinear THz optics, as well as biomedical and security imaging. For these applications, THz field strength of MV/cm (or several microjoule under single-cycle, diffraction-limited focusing) is required. Such field strength can be obtained currently at electron accelerator facilities such as linacs, synchrotrons, and free electron lasers, as well as at laser-plasma accelerators, where all mediate highly relativistic electrons. Surprisingly, non-relativistic electrons can also generate intense coherent THz radiation. Recently, high-energy (>5 microjoule), super-broadband (>75 THz) THz radiation has been produced via ultrafast two-color photoionization [1]. In this scheme, a femtosecond laser's fundamental and its second harmonic pulses are mixed in a gas to generate a directional electron current on the time scale of sub-50 fs with simultaneous THz radiation in the far field. Another important THz application is diagnosing the temporal profiles of relativistic electron beams. As a noninvasive method, the longitudinal profile can be characterized from field-induced birefringence in an electro-optic crystal in the vicinity of the electron beam. To monitor the bunch profiles in real time, a chirped optical pulse can be used to map out the charge field onto the probe spectrum. Here, the temporal resolution, previously limited by the chirp, can be greatly improved with an in-line spectral interferometric algorithm [2]. The diagnostic can also provide 2D spatio-temporal imaging of ultrashort electron bunches in real time. Another single-shot diagnostic recently developed is an echelon-assisted spatial encoding method [3] which can provide a >10 ps time window with ˜25 fs temporal step sizes, with many advantages over other single-shot THz diagnostics. [4pt] [1] K. Y. Kim et al., Nature Photon. 2, 605 (2008)[0pt] [2] K. Y. Kim et al., Appl. Phys. Lett. 88, 041123 (2006)[0pt] [3] K. Y. Kim et al., Opt. Lett. 32, 1968 (2007).

Kim, Ki-Yong

2009-05-01

89

Identification of tooth decay using terahertz imaging and spectroscopy  

Microsoft Academic Search

Terahertz (THz) frequency spectroscopic imaging studies of teeth are reported. The aim is to establish the characteristic properties of the enamel and dentine at these high frequencies. Changes to the THz characteristics as a result of various types of tooth decay are reported showing the potential of this technique for dental diagnosis.

N. N. Zinov'ev; A. F. Fitzgerald; S. M. Strafford; D. J. Wood; F. A. Carmichael; R. E. Miles; M. A. Smith; J. M. Chamberlain

2002-01-01

90

Terahertz pump-probe spectroscopy in YBCO thin films  

Microsoft Academic Search

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

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

2004-01-01

91

Application of femtotechnologies and terahertz spectroscopy methods in cataract diagnostics  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

92

Application of terahertz spectroscopy and molecular modeling in isomers investigation: Glucose and fructose  

NASA Astrophysics Data System (ADS)

Terahertz spectra of glucose and fructose have been measured by terahertz time-domain spectroscopy (THz-TDS) at room temperature. Because they have the same molecular formula, the differences of the THz spectra can be attributed to their molecular structures and the arrangement of molecules in unit cell. In this paper, gaseous-state theory has been employed to simulate the isolated molecule of these two isomers. The results indicate that experimental THz spectral features (0.5 - 4.0 THz) of glucose and fructose arise from the mixture of intramolecular and intermolecular modes, involving hydrogen bonds and covalent bonds, and with the intermolecular modes dominating.

Zheng, Zhuan-Ping; Fan, Wen-Hui; Liang, Yu-Qing; Yan, Hui

2012-04-01

93

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

Microsoft Academic Search

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

Ryan M. Smith; Mark A. Arnold

2011-01-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

95

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

96

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

PubMed

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

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

2008-05-01

97

Diffuse reflection imaging at terahertz frequencies for security applications  

NASA Astrophysics Data System (ADS)

We report diffuse reflection imaging of concealed powdered samples in atmospheric air using a quantum cascade laser operating at 2.83 THz. The imaging system uses a helium-cooled silicon bolometer for mapping radiation diffusely reflected and scattered from samples, and a room-temperature pyroelectric sensor for simultaneously acquiring a specular image. A range of powders concealed within plastic packaging and standard FedEx envelopes was imaged with a resolution of better than 0.5 mm, and it was possible to detect powdered samples concealed within packaging from which there was a strong component of surface reflection. The feasibility of performing dual-wavelength diffuse reflection imaging for identification of illicit drugs and explosives is discussed.

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

2007-10-01

98

Terahertz time-domain spectroscopy of congruent LiNbO3 and LiTaO3 crystals  

NASA Astrophysics Data System (ADS)

The complex dielectric constants of congruent LiNbO3 and LiTaO3 single crystals in a THz frequency region have been determined directly by using broadband terahertz time-domain spectroscopy (THz-TDS) with reflection configuration. We have successfully extracted the accurate complex dielectric constants by using corrected phase information derived from the transmission measurement results. The lowest E(TO1) phonon modes of both crystals have been observed clearly. On the other hand, additional bands at approximately 2.5 THz below the lowest A1(TO1) mode frequency have been observed. These bands have also been reported by Raman and hyper-Raman spectroscopy and attributed to intrinsic defects in congruent crystals. According to the experimental results that these additional bands were observed at almost the same frequency on Raman, hyper-Raman, and THz-TDS, these bands are suggested to be assigned as a first-order scattering process.

Igawa, Hikaru; Mori, Tatsuya; Kojima, Seiji

2014-01-01

99

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

100

Continuous Wave Terahertz Reflection Imaging of Human Colorectal Tissue  

E-print Network

the microwave and infrared regions of the spectrum. The high sensitivity of THz radiation to water concentration the effects of formalin fixation while determining reflectance level of tissue response. The resulting co in the THz can penetrate several millimeters of tissue to enable detection of the differences in water

Massachusetts at Lowell, University of

101

Tuning photoinduced terahertz conductivity in monolayer graphene: Optical-pump terahertz-probe spectroscopy  

NASA Astrophysics Data System (ADS)

Optical-pump terahertz-probe differential transmission measurements of as-prepared single layer graphene (AG) (unintentionally hole doped with Fermi energy EF at ˜-180meV), nitrogen doping compensated graphene (NDG) with EF˜-10 meV, and thermally annealed doped graphene (TAG) are examined quantitatively to understand the opposite signs of photoinduced dynamic terahertz conductivity ??. It is negative for AG and TAG but positive for NDG. We show that the recently proposed mechanism of multiple generations of secondary hot carriers due to Coulomb interaction of photoexcited carriers with the existing carriers together with the intraband scattering can explain the change of photoinduced conductivity sign and its magnitude. We give a quantitative estimate of ?? in terms of controlling parameters—the Fermi energy EF and momentum relaxation time ?. Furthermore, the cooling of photoexcited carriers is analyzed using a supercollision model which involves a defect mediated collision of the hot carriers with the acoustic phonons, thus giving an estimate of the deformation potential.

Kar, Srabani; Mohapatra, Dipti R.; Freysz, Eric; Sood, A. K.

2014-10-01

102

Relativistic Doppler frequency upconversion of terahertz pulses reflecting from a photoinduced plasma front in silicon  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally the frequency upconversion of a terahertz (THz) pulse by the relativistic Doppler reflection from a counterpropagating charge-carrier plasma front in high-resistivity Si. The plasma front is generated via interband excitation with an ultrashort optical pump pulse. Spectral components extending to ˜28 THz are observed, using an input THz pulse with a bandwidth of ˜20 THz obtained from a two-color gas plasma emitter. We model the experiment using one-dimensional finite-difference time-domain simulations with realistic values of the Drude parameters for the plasma front, including effects due to excitation from a weak prepulse structure on the pump pulse.

Meng, Fanqi; Thomson, Mark D.; Roskos, Hartmut G.

2014-10-01

103

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

104

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

105

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

106

Qualitative and Quantitative Detection of Pesticides With Terahertz Time-Domain Spectroscopy  

Microsoft Academic Search

This paper used the newly developed terahertz time-domain spectroscopy (THz-TDS) to detect pesticides, especially imidacloprid, qualitatively and quantitatively in the frequency range of 0.5-1.6 THz. All together, four pesticides and three food powders, as well as polyethylene, were investigated. Different weight ratios of imidacloprid in polyethylene and in sticky rice powder were detected and analyzed with the partial least squares

Yuefang Hua; Hongjian Zhang

2010-01-01

107

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

108

Onset detection of solid-state phase transition in estrogen-like chemical via terahertz transmission spectroscopy  

NASA Astrophysics Data System (ADS)

Solid-state phase transition onset in an endocrine-disrupting estrogen-like chemical (1,4-naphthol) is detected using terahertz transmission spectroscopy. The appearance of two absorption peaks and the sudden upsurge of terahertz-radiation power at 210 K indicate the onset of the solid-state phase transition. Differential scanning microscopy reveals a first-order phase transition at around 240 K while temperature-dependent x-ray diffraction analysis shows the occurrence of such phenomenon also at around 240 K. This demonstrates the sensitivity of the terahertz spectroscopic technique to phase transition since it provides a signal before such phenomenon actually occurs.

Quema, Alex V.; Goto, Masahiro; Sakai, Masahiro; Ouenzerfi, Riadh El; Takahashi, Hiroshi; Murakami, Hidetoshi; Ono, Shingo; Sarukura, Nobuhiko; Janairo, Gerardo

2004-10-01

109

Terahertz surface plasmon polariton coupling on metallic gratings  

Microsoft Academic Search

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

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

2004-01-01

110

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

111

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

NASA Astrophysics Data System (ADS)

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

Li, Jiu-sheng; Zhao, Xiao-li; Li, Jian-rui

2009-07-01

112

Detection of tulobuterol crystal in transdermal patches using terahertz pulsed spectroscopy and imaging.  

PubMed

Applicability of a Terahertz Pulsed Spectroscopy (TPS) and a Terahertz Pulsed Imaging (TPI) for detection of tulobuterol (TBR) crystals in transdermal patches was investigated. Because TBR has high permeability in dermis, crystalline TBR in patch matrices contributes to controlling the release rate of TBR from a matrix. Therefore, crystalline TBR is one of the important factors for quality control of TBR transdermal tapes. A model tape that includes 5 w/w%, 10 w/w%, 20 w/w% or 30 w/w% of TBR was measured by TPS/TPI. TBR crystals in the matrices were successfully detected by TPI. Identification of TBR in an image of a crystal-like mass was done by comparison between the spectra of tapes and a TBR standard substance. These results indicate that TPS and TPI are applicable to identifying crystalline lumps of an active drug in tapes for quality control. PMID:19618670

Sakamoto, T; Portieri, A; Taday, P F; Takada, Y; Sasakura, D; Aida, K; Matsubara, T; Miura, T; Terahara, T; Arnone, D D; Kawanishi, T; Hiyama, Y

2009-06-01

113

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

NASA Astrophysics Data System (ADS)

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

Watanabe, Shinichi; Shimano, Ryo

2007-10-01

114

Terahertz Time-Domain Spectroscopy Study of Silica Aerogels and Adsorbed Molecular Jiangquan Zhang and D. Grischkowsky*  

E-print Network

Terahertz Time-Domain Spectroscopy Study of Silica Aerogels and Adsorbed Molecular Vapors Jiangquan time-domain spectroscopy (THz-TDS) study of hydrophobic and hydrophilic silica aerogels, and the adsorption of several molecular vapors in the hydrophilic silica aerogel. The hydrophobic and hydrophilic

115

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

116

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

PubMed

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

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

2014-01-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

118

Temperature-Dependent Terahertz Spectroscopy of Liquid n-alkanes  

E-print Network

, Rice University, MS-366 6100 Main St., Houston, TX 77005, USA e-mail: daniel@rice.edu #12;techniques such as x-ray scattering [2, 10], Raman scattering [6, 11], and infrared absorption spectroscopy [12

Mittleman, Daniel

119

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

120

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

121

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

122

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

123

Bacillus spores and their relevant chemicals studied by terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time domain spectroscopy has been used to investigate 0.2-2.2 THz transmission responses of Bacillus spores and their related chemical components. Whilst no THz signatures could be clearly associated with either sporulated cells or their chief chemical components, differing degrees of signal attenuation and frequency-dependent light scattering were observed depending on spore composition and culture media. The observed monotonic increase in absorption by spores over this THz spectral domain is mainly from Mie scattering and also from remnant water bound to the spores.

Tang, Jianhua; Yang, Bin; Llewellyn, Ian; Cutler, Ronald R.; Donnan, Robert S.

2014-01-01

124

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

125

Measurement of electron paramagnetic resonance using terahertz time-domain spectroscopy.  

PubMed

We present a frequency-domain electron spin resonance (ESR) measurement system using terahertz time-domain spectroscopy. A crossed polarizer technique is utilized to increase the sensitivity in detecting weak ESR signals of paramagnets caused by magnetic dipole transitions between magnetic sublevels. We demonstrate the measurements of ESR signal of paramagnetic copper(II) sulfate pentahydrate with uniaxial anisotropy of the g-factor under magnetic fields up to 10 T. The lineshape of the obtained ESR signals agrees well with the theoretical predictions for a powder sample with the uniaxial anisotropy. PMID:22273888

Kozuki, Kohei; Nagashima, Takeshi; Hangyo, Masanori

2011-12-01

126

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

SciTech Connect

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

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

2009-11-20

127

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

128

Terahertz surface plasmons for subwavelength sensing and spectroscopy  

Microsoft Academic Search

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

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

2008-01-01

129

Total internal reflection photoacoustic detection spectroscopy  

NASA Astrophysics Data System (ADS)

Total Internal Reflection Photoacoustic Spectroscopy (TIRPAS) is a method that exploits the evanescent field of a nanosecond duration laser pulse reflecting off a glass/water interface to generate photoacoustic responses. These photoacoustic events are generated in light absorbing analytes suspended in the fluid medium in contact with the glass that are within the penetration depth of the evanescent wave. This method has been employed in previous studies by Hinoue et al. Hinoue et al. used an optically chopped HeNe laser at 632.8 nm to detect Brilliant Blue FCF dye at different angles of incidence. In recent years, the advent of high power nanosecond pulsed tunable lasers has allowed for the re-visitation of the TIRPAS idea under stress confinement and orders of magnitude larger peak energy conditions. Compared to conventional detection methods, this approach has the potential to detect much smaller quantities of disease indicators, such as circulating tumor cells and hemazoin crystals in malaria, than other optical methods. The detection limit of the TIRPAS system was quantified using chlorazol black solution with an absorption coefficient of 55 cm-1 at 532 nm. Interaction with the evanescent field was verified by varying the angle of incidence of the probe laser beam that generated the photoacoustic waves, thereby changing the penetration depth of the evanescent field as well as the photoacoustic spectroscopy effect from angled excitation.

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

2011-03-01

130

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

131

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

132

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

133

Mid infrared upconversion spectroscopy using diffuse reflectance  

NASA Astrophysics Data System (ADS)

We present a novel approach for mid infrared (mid-IR) spectral analysis using upconversion technology applied in a diffuse reflectance setup. We demonstrate experimentally that mid-IR spectral features in the 2.6-4 ?m range using different test samples (e.g. zeolites) can be obtained. The results are in good agreement with published data. We believe that the benefit of low noise upconversion methods combined with spectral analysis will provide an alternative approach to e.g. mid-IR Fourier Transform microscopy. We discuss in detail the experimental aspects of the proposed method. The upconversion unit consists of a PP:LN crystal situated as an intracavity component in a Nd:YVO4 laser. Mixing incoming spectrally and spatially incoherent light from the test sample with the high power intracavity beam of the Nd:YVO4 laser results in enhanced conversion efficiency. The upconverted light is spectrally located in the near infrared (NIR) wavelength region easily accessible for low noise Silicon CCD camera technology. Thus the room temperature upconversion unit and the Silicon CCD camera replaces noisy mid infrared detectors used in existing Fourier Transform Infrared Spectroscopy. We demonstrate specifically that upconversion methods can be deployed using a diffuse reflectance setup where the test sample is irradiated by a thermal light source, i.e. a globar. The diffuse reflectance geometry is particularly well suited when a transmission setup cannot be used. This situation may happen for highly scattering or absorbing samples.

Sanders, Nicolai; Kehlet, Louis; Dam, Jeppe Seidelin; Tidemand-Lichtenberg, Peter; Beato, Pablo; Pedersen, Christian

2014-02-01

134

Plasmonic terahertz detectors for biodetection  

E-print Network

Plasmonic terahertz detectors for biodetection N. Pala and M.S. Shur A report is presented on the biodetection capabilities of plasmonic ter- ahertz detectors. Large changes in the terahertz response. Terahertz time domain spectroscopy (TDS) [1], terahertz dielectric spec- troscopy [2], surface

Pala, Nezih

135

Terahertz polariton propagation in patterned materials.  

PubMed

Generation and control of pulsed terahertz-frequency radiation have received extensive attention, with applications in terahertz spectroscopy, imaging and ultrahigh-bandwidth electro-optic signal processing. Terahertz 'polaritonics', in which terahertz lattice waves called phonon-polaritons are generated, manipulated and visualized with femtosecond optical pulses, offers prospects for an integrated solid-state platform for terahertz signal generation and guidance. Here, we extend terahertz polaritonics methods to patterned structures. We demonstrate femtosecond laser fabrication of polaritonic waveguide structures in lithium tantalate and lithium niobate crystals, and illustrate polariton focusing into, and propagation within, the fabricated waveguide structures. We also demonstrate a 90 degrees turn within a structure consisting of two waveguides and a reflecting face, as well as a structure consisting of splitting and recombining elements that can be used as a terahertz Mach-Zehnder interferometer. The structures permit integrated terahertz signal generation, propagation through waveguide-based devices, and readout within a single solid-state platform. PMID:12618821

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

2002-10-01

136

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

137

Parylene anti-reflection coating of a quasi-optical hot-electron-bolometric mixer at terahertz frequencies  

Microsoft Academic Search

Parylene C was investigated as anti-reflection coating for silicon at terahertz frequencies. Measurements with a Fourier-transform spectrometer show that the transmittance of pure silicon can be improved by about 30% when applying a layer of Parylene C with a quarter wavelength optical thickness. The 10% bandwidth of this coating extends from 1.5 to 3 THz for a center frequency of

H.-W Hübers; J. Schubert; A. Krabbe; M. Birk; G. Wagner; A. Semenov; G Gol’tsman; B. Voronov; E. Gershenzon

2001-01-01

138

Optical Reflection Spectroscopy of GEO Objects  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

139

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

140

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

141

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

PubMed

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

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

2012-05-01

142

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

143

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

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

144

Longitudinally resolved measurement of plasma density along femtosecond laser filament via terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We report on a longitudinally resolved measurement of plasma density along femtosecond laser filament in air via terahertz (THz) spectroscopy. By applying a needlelike high-voltage direct current (DC) electric field on the laser filament and scanning it along filament, the longitudinal evolution of amplified THz emission has been demonstrated. The peak frequency of the DC electric field biased THz emission is proportional to the plasma density inside the laser filament. This latter phenomenon was used to characterize the plasma density. Longitudinal distribution of plasma density of ˜1015 cm-3 along laser filament has been experimentally recorded. The technique demonstrated is very simple and helpful for understanding the THz generation process through laser filamentation.

Wang, Tie-Jun; Ju, Jingjing; Wei, Yingxia; Li, Ruxin; Xu, Zhizhan; Chin, See Leang

2014-08-01

145

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

146

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

147

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

PubMed

The far-infrared dielectric function of a wide range of organic molecules is dominated by vibrations involving a substantial fraction of the atoms forming the molecule and motion associated with intermolecular hydrogen bond vibrations. Due to their collective nature such modes are highly sensitive to the intra- and intermolecular structure and thus provide a unique fingerprint of the conformational state of the molecule and effects of its environment. We demonstrate the use of terahertz time-domain spectroscopy (THz-TDS) for recording the far-infrared (0.5-4.0 THz) dielectric function of the four nucleobases and corresponding nucleosides forming the building blocks of deoxyribose nucleic acid (DNA). We observe numerous distinct spectral features with large differences between the molecules in both frequency-dependent absorption coefficient and index of refraction. Assisted by results from density-functional calculations we interpret the origin of the observed resonances as vibrations of hydrogen bonds between the molecules. PMID:12452571

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

2002-11-01

148

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

149

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

150

Distinguishing different parts of objects by terahertz imaging  

NASA Astrophysics Data System (ADS)

Since every matter has its distinctive absorption and transmission capacity of terahertz, Terahertz time domain spectroscopy provides a powerful means to distinguish the different parts of objects. The transmittance of terahertz under different frequency can reflect the absorption distribution of the different parts of the samples. The phase shift of the terahertz wave indicates the change of optical thickness of the sample. Tree leaves, plastic ring, plastic convex lens and plastic piece with a small hole have been imaged by terahertz. As widespread samples, leaves are proved to be well imaged by terahertz wave. For the moisture content at different parts of leaves, such as mesophyll and vein, is not the same, the absorption of terahertz at these parts are quite different. At 1.4THz, the leaf's image is of good quality and the vein grids are well shown. The hole and defects in the plastic ring are also clearly shown in the THz image because the phase shifts of terahertz in different parts, such as air, defects or plastic region are not the same. It is also shown that objects with large radius of curvature are suitable for THz imagining and the scattering of THz does not affect THz phase information too much. In short, Terahertz imaging is a powerful technique to distinguish the different parts of most objects as long as the absorption of THz is not very strong.

Ge, Jin; Wang, Reng; Hu, Shuhong; Dai, Ning; Li, Dong; Ma, Hong; Ma, Guohong

2010-10-01

151

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

PubMed

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

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

2011-01-01

152

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

153

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

154

Laliotis et al. Selective Reflection spectroscopy at the interface between a calcium fluoride window... SELECTIVE REFLECTION SPECTROSCOPY AT THE INTERFACE  

E-print Network

Laliotis et al. Selective Reflection spectroscopy at the interface between a calcium fluoride window... SELECTIVE REFLECTION SPECTROSCOPY AT THE INTERFACE BETWEEN A CALCIUM FLUORIDE WINDOW AND Cs and thermal fragility of fluoride windows make common designs of vapour cells unpractical, so that we have

Paris-Sud XI, Université de

155

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

156

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

157

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

158

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

159

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

160

Comparative dielectric study of pentanol isomers with terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Using terahertz (THz) time-domain spectroscopy, we have measured the complex permittivity of seven pentanol isomers (1-pentanol, 2-pentanol, 3-pentanol, 2-methly-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, and 3-methyl-2-butanol) in the frequency range of 0.2-2.5 THz at temperatures from 253 to 323 K. For all samples, the complex permittivity contains the following three components: (i) a high-frequency side of dielectric relaxation processes, (ii) a broad vibration mode around 1.5 THz, and (iii) a low-frequency side of an intermolecular stretching mode located above 2.5 THz. At low temperatures, the relaxation process moves to a low-frequency range and a peak of the broad vibration mode, which is independent of temperature, is clearly observed around 1.5 THz. Spectra in the THz region change sensitively according to the molecular structure of the pentanol isomers. We have also observed the complex permittivity in the microwave range of 1 MHz-20 GHz. The behavior of the dielectric relaxation processes below GHz region much depend on the isomers. Our experimental data demonstrate that the molecular structures of the pentanol isomers influence all the molecular dynamics ranging from dielectric relaxation phenomena, which are due to reorientational motion of the molecules, to vibration dynamics within the hydrogen-bonded network structure.

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

2010-04-01

161

Spectroscopy studies on the Tuha crude oil in the terahertz range  

NASA Astrophysics Data System (ADS)

In this paper, the optical characteristics of crude oil samples from selected territories in Tuha oil field have been investigated with THz-TDS at room temperature in nitrogen environment. The absorption coefficient and refraction index of crude oil are calculated in the frequency range of 0.20~2.5 THz. No distinct absorption peak has been found in the spectra, which may result from the complexity of the constitution of the samples and the water content. The absorption coefficients increase with the content of wax in the samples with different slopes, which means the intensity of absorption in THz wave band increases with enhanced density of the sample and unaltered thickness. The average refractive indices were 0.62070, 0.59767 and 0.59290 corresponding to TuLuFan, ShanShan and WenMi territories, respectively. The refractive values show the phenomenon of abnormal dispersion, which meant the samples had the characters of strong selective absorption in this wave band. In contrast, we have also utilized Fourier transform infrared spectroscopy (FTIR) in the 400-4000cm-1 to measure the mid-IR absorption spectra, and the results revealed that the crude oil is more active in the range of Terahertz than in the mid-IR band. The experiments demonstrated that THz-TDS is a powerful tool to complement the conventional analytical approaches and can be applied to detect and analyze the features of the constituent in crude oil.

Bao, Ri-ma; Tian, Lu; Zhao, Kun; Zhu, Shou-ming; Liu, Li-ming; Zhao, Guo-zhong

2011-08-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

163

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

164

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

165

Asteroids: surface composition from reflection spectroscopy.  

PubMed

Minerals partly composing the surfaces of 14 asteroids are determined by using asteroid reflectance spectra and optical properties of meteorites and other materials. Individual electronic absorption features are identified in the asteroids' spectra. The energies, relative strengths, and shapes of these features are interpreted by using laboratory and theoretical studies. Analysis of the initial 14 asteroid reflectance spectra indicates the presence of the following types of surface materials: six carbonaceous chondrite-like; two stony-iron-like (metal/silicate approximately 1); one iron meteorite-like; one basaltic achondrite-like; and four silicate-metal assemblages (metal/silicate approximately 0.25). These results support the conclusion that the asteroid belt is a source of at least some meteoritic material, and they show a relation between certain asteroids and certain classes of meteoritcs. PMID:17839866

McCord, T B; Gaffey, M J

1974-10-25

166

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

Microsoft Academic Search

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

K. J. Chau; A. Y. Elezzabi

2006-01-01

167

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

168

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

169

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

PubMed

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

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

2012-10-17

170

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

NASA Astrophysics Data System (ADS)

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 active. Transmission measurements at room temperature showed increasing FIR absorption with hydration and denaturing.

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

2000-03-01

171

Terahertz laser frequency combs  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

172

43—THE YIELD-TESTING OF WOOL BY REFLECTANCE SPECTROSCOPY  

Microsoft Academic Search

Results are presented of the measurement of diffuse reflectance in the near-infra-red and visible regions, and it is shown that a new method of yield-testing of wool by reflectance spectroscopy in the two regions is available. The method gives a measure of the concentration of the components in washed wool.It is demonstrated that measurements obtained from the InfraAIyzer and the

J. P. Connell; G. H. Brown

1978-01-01

173

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

PubMed

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

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

2013-01-14

174

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

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy holds great promise in the advancement of the field of astrochemistry. The sensitive observation of interstellar THz radiation is expected to lower detection limits and allow the study of larger and more complex species than is currently possible at millimeter wavelengths, which will place further constraints on chemical models and permit a direct comparison to the organic compounds seen in carbonaceous chondrites. With the successful recent launch of the Herschel Space Telescope, which will give high-fidelity access to interstellar THz radiation for the first time, and the completion of the Atacama Large Millimeter Array (ALMA) by 2013, the THz astronomy era is upon us. Unfortunately, laboratory THz spectroscopy presents significant challenges and will be soon be lagging behind the newly available observational platforms. Technologies to extend the capabilities of high-resolution spectroscopic systems into the THz domain are actively being pursued on many fronts, but affordable systems that are broadly tunable, sensitive and achieve the necessary resolution are not yet available. The work in this thesis should therefore be seen as part of the effort in the transition from centimeter-/millimeter-wave to THz spectroscopy that is currently taking place in the astrochemistry community. As part of this thesis, observational searches for the complex organics hydroxyacetone (CH3COCH2OH), 2-cyanoethanol (OHCH 2CH2CN) and methoxyacetonitrile (CH3OCH2 CN) were attempted at millimeter wavelengths. The unsuccessful nature of these searches highlight the current limits of studying interstellar chemistry using pure rotational spectroscopy. The characterization of the laboratory spectra of these molecules is nonetheless important as it will aid in the assignment and description of the rotational substructure and band shapes of their THz torsional spectra, features that may allow their interstellar detection; and this thesis presents methods by which such complex spectra may be rapidly and efficiently collected and fit using automated spectrometers and modern software tools. The description of the spectrum of hydroxyacetone is furthermore of interest due to the presence of the very low barrier to internal rotation in this molecule. Many interstellar compounds, both known and potential future targets, have functional groups capable of internal rotation in their structure; and so the effort in understanding the complex effects of the low barrier rotor in this case will benefit the general effort to further understand internal rotation. In searching for new interstellar molecules, both at millimeter wavelengths and at higher THz frequencies, characterization of the complete spectra of known interstellar molecules is of great importance to allow substraction of their contribution to observational spectra. In this thesis, the ground-state rotational spectrum of methanol, the most important "interstellar weed", is catalogued and described in detail through most of the THz region that will be accessible with Herschel and ALMA. Lastly, as part of the effort to increase the sensitivity of THz spectrometers, the use of Fabry-Perot cavities at these frequencies is explored. Such resonant cavities hold the potential to significantly increase the possible path lengths in spectroscopic system and to allow novel and sensitive detection techniques. Optimal configurations and the limits on achievable path lengths and Q-factors of such cavities are discussed, as are the possible extensions of Fourier Transform MicroWave (FT-MW) techniques to THz frequencies.

Braakman, Rogier

2010-11-01

175

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

176

Material parameter extraction for terahertz time-domain spectroscopy using fixed-point iteration  

NASA Astrophysics Data System (ADS)

A simple method to extract the far-infrared dielectric parameters of a homogeneous material from terahertz signals is explored in this paper. Provided with a reference, sample-probing terahertz signal and a known sample thickness, the method can determine the underlying complex refractive index of the sample within a few iterations based on the technique of fixed-point iteration. The iterative process is guaranteed to converge and gives the correct parameters when the material thickness exceeds 200 ?m at a frequency of 0.1 THz or 20 ?m at a frequency of 1.0 THz.

Withayachumnankul, W.; Ferguson, B.; Rainsford, T.; Mickan, S. P.; Abbott, D.

2005-07-01

177

Experimental demonstration of reflectarray antennas at terahertz frequencies.  

PubMed

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

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

2013-02-11

178

Abstract--Terahertz (THz) time domain spectroscopy is used to investigate the gain and losses of a THz quantum cascade laser  

E-print Network

1 Abstract--Terahertz (THz) time domain spectroscopy is used to investigate the gain and losses of a THz quantum cascade laser (QCL) operating at 2.86THz. This measurement technique allows access, gain measurement. I. INTRODUCTION ERAHERTZ (THz) quantum cascade lasers (QCL) have shown considerable

Paris-Sud XI, Université de

179

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

180

Apollo 17 Soil Characterization for Reflectance Spectroscopy  

NASA Technical Reports Server (NTRS)

It is the fine fractions that dominate the observed spectral signatures of bulk lunar soil, and the next to the smallest size fractions are the most similar to the overall properties of the bulk soil. Thus, our Lunar Soil Characterization Consortium has concentrated on understanding the inter-relations of compositional, mineralogical, and optical properties of the <45-micron size fraction and its component sizes (20-44 micron, 10-20 micron, and <10 micron size fractions). To be able to generalize our results beyond the particular sample set studied, it is necessary to quantitatively identify the observed effects of space weathering and evaluate the processes involved. For this, it is necessary to know the chemistry of each size fraction, modal abundances of each phase, average compositions of the minerals and glasses, I(sub s)/FeO values, reflectance spectra, and the physical makeup of the individual particles and their patinas. This characterization includes the important dissection of the pyroxene minerals into four separate populations, with data on both modes and average chemical compositions. Armed with such data, it should be possible to effectively isolate spectral effects of space weathering from spectral properties related to mineral and glass chemistry. Four mare soils from the Apollo 17 site were selected for characterization based upon similarities in bulk composition and their contrasting maturities, ranging from immature to submature to mature. The methodology of our characterization has been discussed previously. Results of the Apollo 17 mare soils, outlined herein, are being prepared for publication in MAPS. As shown, with decreasing grain size, the agglutinitic (impact) glass content profoundly increases. This is the most impressive change for the mare soils. In several soils we have examined, there is an over two-fold increase in the agglutinitic glass contents between the 90-150- micron and the 10-20-micron size fractions. Accompanying this increase in agglutinitic glass is a definite decrease in pyroxenes and to lesser extents, the oxides (ilmenite), volcanic glass, and olivine. Unexpectedly, however, the absolute plagioclase abundances stay relatively constant throughout the different grain sizes, although the abundance of plagioclase relative to the mafic minerals increases with decreasing particle size. These soils were chosen for study based upon their similarities in FeO and Ti02 content, allowing for direct comparisons between evolutions of chemistry between size fractions and among different maturities of soils. The bulk chemistry of these fractions was determined by EMP analyses of fused glass beads. In contrast to the systematic variations in bulk chemistry discussed below, the relatively uniform composition of agglutinitic glass with grain size and soil maturity is illustrated. The composition of the bulk fraction of each size fraction becomes more feldspathic with increasing maturity, with the effect being most pronounced for the finest fractions. The composition of the agglutinitic glass, however, is relatively invariant and more feldspathic (i.e., rich in Al2O3) than even the <10-micron fraction. This relation not only strengthens the "fusion of the finest fraction" (F(sup 3)) hypothesis, but also highlights the important role of plagioclase in the formation of agglutinitic glass. With decreasing grain size, FeO, MgO, and TiO2 contents decrease, whereas CaO, Na2O, and Al2O3 (plag components) increase for all soils. These chemical variations would appear to be coupled with the significant increase in agglutinitic glass and decrease in oxide (ilmenite),pyroxene, and volcanic glass. These changes in chemistry do not appear to be due to distinct changes in the compositions of individual phases but to their abundances. Values of I(sub s)/FeO increase with decreasing grain size, even though the bulk FeO contents decrease. That is, the percentage of the total Fe that is present as nanophase Fe(sup O) has increased substantially in the smaller size fraction. Note that the incre

Taylor, L. A.; Pieters, C.; Patchen, A.; Morris, R. V.; Keller, L. P.; Wentworth, S.; McKay, D. S.

1999-01-01

181

Terahertz-range free-electron laser electron spin resonance spectroscopy: techniques and applications in high magnetic fields.  

PubMed

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave terahertz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The combination of two linac-based FELs (covering the wavelength range of 4-250 microm) with pulsed magnetic fields up to 70 T allows for multifrequency ESR spectroscopy in a frequency range of 1.2-75 THz with a spectral resolution better than 1%. The performance of the spectrometer is illustrated with ESR spectra obtained in the 2,2-diphenyl-1-picrylhydrazyl and the low-dimensional organic material (C6H9N2)CuCl3. PMID:19655938

Zvyagin, S A; Ozerov, M; Cizmár, E; Kamenskyi, D; Zherlitsyn, S; Herrmannsdörfer, T; Wosnitza, J; Wünsch, R; Seidel, W

2009-07-01

182

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

183

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

NASA Technical Reports Server (NTRS)

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

Hapke, B.

1981-01-01

184

Analytical study of spacecraft deposition contamination by internal reflection spectroscopy  

NASA Technical Reports Server (NTRS)

Infrared absorption spectra of ten individual contaminant materials and four binary mixtures of these have been studied using the internal reflection spectroscopy technique. The effect of ultraviolet radiation on these contaminants has also been studied. It has been observed that all siloxanes, silanes, and esters are drastically affected by ultraviolet irradiation. In most cases polymerization and tar formation results.

Mookherji, T.

1972-01-01

185

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

186

Inferring sedimentary chlorophyll concentrations with reflectance spectroscopy: a novel approach  

E-print Network

Inferring sedimentary chlorophyll concentrations with reflectance spectroscopy: a novel approach it possible to rapidly and nondestructively assess the chlorophyll content of plants and natural waters. However, to date this approach has not been applied to chlorophyll and chlorophyll deriv- atives preserved

Wolfe, Alexander P.

187

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

PubMed

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

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

2013-04-01

188

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

E-print Network

Ultrafast conductivity in a low-band-gap polyphenylene and fullerene blend studied by terahertz-band-gap polyphenylene copolymer and fullerene derivative. The optical excitation pulse generates free holes delocalized in these systems. The pri- mary excitation in polymer/fullerene bulk heterojunctions is an exciton on the polymer

KuÂ?el, Petr

189

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

190

Far-Infrared Dielectric Properties of Polar Liquids Probed by Femtosecond Terahertz Pulse Spectroscopy  

E-print Network

to study gases,2 semiconductors,3 super- conductors,4 dielectrics,5 nonpolar liquids,6 and water.7 WeFar-Infrared Dielectric Properties of Polar Liquids Probed by Femtosecond Terahertz Pulse (), over the frequency range from 2 to 50 cm-1 for water, methanol, ethanol, 1-propanol, and liquid ammonia

191

Conductivity of ZnO Nanowires, Nanoparticles, and Thin Films Using Time-Resolved Terahertz Spectroscopy  

E-print Network

Conductivity of ZnO Nanowires, Nanoparticles, and Thin Films Using Time-Resolved Terahertz. ZnO properties were measured directly for thin films and were extracted from measurements of nanowire samples. Annealing significantly reduces the intrinsic carrier concentration in the ZnO films

192

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

National Technical Information Service (NTIS)

Continuous wave terahertz imaging has the potential to offer a safe, non-invasive medical imaging modality for detecting different types of human cancers. The aim of this study was to identify intrinsic biomarkers for non- melanoma skin cancer and their a...

A. N. Yaroslavsky, C. S. Joseph, J. C. Dickinson, M. Al-Arashi, T. M. Goyette

2009-01-01

193

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

E-print Network

electromagnetic wave. Owing to the non-ionizing, non-invasive, coherent quasi-optic, and phase-sensitive. As the sen- sitivity of terahertz radiation to polar molecules of water is very high, biological tissues). www.elsevier.com/locate/optcom Optics Communications 259 (2006) 389­392 #12;the transmission

194

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

SciTech Connect

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

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

2010-06-01

195

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

Microsoft Academic Search

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

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

2007-01-01

196

Polarization orientation dependence of the far infrared spectra of oriented single crystals of 1,3,5,-trinitro-s-triazine (RDX) using terahertz-time-domain spectroscopy  

SciTech Connect

The far infrared spectra of (100), (010), and (001)-oriented RDX single crystals were measured as the crystal was rotated about the axis perpendicular to the polarization plane of the incident radiation. Absorption measurements were taken at temperatures of both 20 K and 295 K for all rotations using terahertz time-domain spectroscopy. A number of discrete absorptions were found ranging from 10-100 cm(-1) (0.3-3 THz). The absorptions are highly dependent on the orientation of the terahertz polarization with respect to crystallographic axes.

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

2008-01-01

197

Terahertz direct-contact refractometer/spectrometer.  

PubMed

A method for terahertz (THz) reflection spectroscopy is presented that utilizes direct contact between the backside of the pulsed emitter and the sample. Changes in the complex reflectivity of the emitter-sample interface are used to measure the spectrum. This method is especially useful for spectroscopy of liquid samples and soft materials. It simplifies the optical apparatus, has good sensitivity, and has capability for use in the construction of miniaturized THz probes. The problem of nonplanar wave fronts inside the emitter is discussed. PMID:17632637

Hirsch, Ole; Alexander, Paul

2007-07-15

198

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

199

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

200

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

201

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

202

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

SciTech Connect

Spectral dependencies of terahertz radiation from the femtosecond laser-illuminated surfaces of Ga{sub x}In{sub 1-x}As (x=1, 0.8, and 0.47) have been investigated experimentally at high optical fluencies and laser wavelengths ranging from 600 to 800 nm. The terahertz pulse amplitude increased with the increasing laser photon energy due to larger excess energies of photoexcited electrons and more efficient spatial separation of electrons and holes at the illuminated surface. This increase was stopped with the onset of electron transitions to subsidiary conduction band valleys. Analysis of these experiments was used for evaluating the energy positions of the X and L conduction band valleys in Ga{sub x}In{sub 1-x}As alloys as a function of their composition.

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

2009-03-02

203

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

204

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

205

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

SciTech Connect

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

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

2005-09-08

206

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

207

Magnetic circular dichroism in reflection electron energy loss spectroscopy?  

SciTech Connect

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

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

1996-07-01

208

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

209

Terahertz gas-phase spectroscopy: chemometrics for security and medical applications.  

PubMed

We describe a spectrometer consisting of a vector network analyzer, a gas absorption cell, and a quasi-optical bench that acquires terahertz spectra of gaseous substances and mixtures. We tested volatile organic compounds that are medical biomarkers or chemicals which can be found on the US Environment Protection Agency list of harmful substances. Absorption spectra at gas pressures between 10 Pa and 5000 Pa were recorded. A subsequent multivariate data analysis demonstrated excellent qualitative and quantitative identification of pure substances and complex mixtures. The applied multivariate algorithms are principal components analysis, partial least square regression and soft independent modelling of class analogy. PMID:25406969

Neumaier, P F-X; Schmalz, K; Borngräber, J; Wylde, R; Hübers, H-W

2014-12-01

210

Using terahertz spectroscopy and solid-state density functional theory to characterize a new polymorph of 5-(4-pyridyl)tetrazole.  

PubMed

A new high-temperature polymorph of 5-(4-pyridyl)tetrazole has been discovered and characterized using X-ray crystallography and terahertz (THz) spectroscopy. The THz spectrum of the new polymorph was compared to the previously published form and was replicated by means of solid-state density functional theory. Terahertz spectroscopy was used to determine the influence of the different packing motifs on the molecular and low energy lattice vibrations displayed in the region from 10 to 100 cm(-1). It was found that there is only a ?2 cm(-1) difference in the primary peak location, caused by a whole molecule rotation along the principal a axis, between the two polymorphic forms. In addition, the energy of formation was determined, and it was found that the previously known polymorphic form is more stable by ?0.25 kJ/mol, compared to the newly discovered form. PMID:24354392

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

2014-01-16

211

High-speed terahertz reflection three-dimensional imaging for nondestructive  

E-print Network

is obtained, which is made of glass fiber reinforced polymer composite material and has defects) imaging based on electronically controlled optical sampling (ECOPS). ECOPS enables scanning of an axial such as delamination and inclusion, and is compared with an ultrasonic reflection 3D image of the sample. ©2012 Optical

212

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

213

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

214

A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons surface plasmons Jingbo Liu, Rajind Mendis and Daniel M Mittleman1 Department of Electrical and Computer. The patterned facet supports a spoof surface plasmon mode, which modifies the reflectivity at the waveguide

Mittleman, Daniel

215

Assessing human skin with diffuse reflectance spectroscopy and colorimetry  

NASA Astrophysics Data System (ADS)

Colorimetry has been used as an objective measure of perceived skin color by human eye to document and score physiological responses of the skin from external insults. CIE color space values (L*, a* and b*) are the most commonly used parameters to correlate visually perceived color attributes such as L* for pigment, a* for erythema, and b* for sallowness of the skin. In this study, we investigated the relation of Lab color scale to the amount of major skin chromophores (oxy-, deoxyhemoglobin and melanin) calculated from diffuse reflectance spectroscopy. Thirty two healthy human subjects with ages from 20 to 70 years old, skin types I-VI, were recruited for the study. DRS and colorimetry measurements were taken from the left and right cheeks, and on the right upper inner arm. The melanin content calculated from 630-700 nm range of DRS measurements was shown to correlate with the lightness of skin (L*) for most skin types. For subjects with medium-to-light complexion, melanin measured at the blue part spectrum and hemoglobin interfered on the relation of lightness of the skin color to the melanin content. The sallowness of the skin that is quantified by the melanin contribution at the blue part spectrum of DRS was found to be related to b* scale. This study demonstrates the importance of documenting skin color by assessing individual skin chromophores with diffuse reflectance spectroscopy, in comparison to colorimetry assessment.

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

2012-02-01

216

Autofluorescence and diffuse reflectance patterns in cervical spectroscopy  

NASA Astrophysics Data System (ADS)

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

Marin, Nena Maribel

217

Terahertz Scattering  

NASA Astrophysics Data System (ADS)

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

Zurk, L. M.; Schecklman, S.

218

Birefringence of wood at terahertz frequencies  

NASA Astrophysics Data System (ADS)

Fibre content of solid wood plays an important role in the wood products industry in terms of value. Additionally, fibre structure in composite wood products such as Oriented Strand Board (OSB) and paper products plays an important role in terms of strength properties. The effect of moisture content on wood properties is important in the manufacturing process and final product performance, and therefore its effect on the birefringence is of considerable interest. Since solid wood exhibits strong birefringence at terahertz frequencies, there may be potential applications of terahertz spectroscopy to fibre content and structure sensing. There are two potential sources for this strong birefringence: (i) form birefringence resulting from the porous structure of solid wood and (ii) intrinsic birefringence resulting from the dielectric properties of the material itself. In this report, the variability of birefringence within and between species, the dependence of the birefringence on moisture content and the relative contributions from form and intrinsic birefringence are examined. In order to clarify the role of these contributions to the measured birefringence, polarized terahertz reflection spectroscopy is examined and compared to the results obtained in a transmission geometry. Comparison of the birefringence measured in transmission and reflection geometries suggests that form birefringence may dominate.

Todoruk, Tara M.; Schneider, Jon; Hartley, Ian D.; Reid, Matthew

2008-06-01

219

Terahertz wave spectrum analysis of microstrip structure  

NASA Astrophysics Data System (ADS)

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

Song, Mei-jing; Li, Jiu-sheng

2012-03-01

220

Terahertz wave spectrum analysis of microstrip structure  

NASA Astrophysics Data System (ADS)

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

Song, Mei-jing; Li, Jiu-sheng

2011-11-01

221

Terahertz time-domain spectroscopy combined with fuzzy rule-building expert system and fuzzy optimal associative memory applied to diagnosis of cervical carcinoma.  

PubMed

Combined with terahertz time-domain spectroscopy, the feasibility of fast and reliable diagnosis of cervical carcinoma by a fuzzy rule-building expert system (FuRES) and a fuzzy optimal associative memory (FOAM) had been studied. The terahertz spectra of 52 specimens of cervix were collected in the work. The original data of samples were preprocessed by Savitzky-Golay first derivative (?derivative), principal component orthogonal signal correction (PC-OSC) and emphatic orthogonal signal correction to improve the performance of FuRES and FOAM models. The effect of the different pretreating methods to improve prediction accuracy was evaluated. The FuRES and FOAM models were validated using bootstrapped Latin-partition method. The obtained results showed that the FuRES and FOAM model optimized with the combination S-G first derivative and PC-OSC method had the better predictive ability with classification rates of 92.9 ± 0.4 and 92.5 ± 0.4 %, respectively. The proposed procedure proved that terahertz spectroscopy combined with fuzzy classifiers could supply a technology which has potential for diagnosis of cancerous tissue. PMID:25433946

Qi, Na; Zhang, Zhuoyong; Xiang, Yuhong; Yang, Yuping; Harrington, Peter de B

2015-01-01

222

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

223

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

224

[Diffusion reflectance spectroscopy of ZrO2 phase structure].  

PubMed

Diffusion Reflectance Spectroscopy (DRS) was employed to study the surface phase structure of ZrO2-based catalysts. The effect of calcining temperature, and the addition of Al2O3 and platinum on the surface and bulk phase structures of zirconia was studied by DRS combined with XRD, DTA and XPS. The same trend was observed that heating to higher temperatures results in the conversion to monoclinic zirconia in undoped samples, while incorporation of an appropriate amount of Al2O3 would stabilize the tetragonal phase zirconia. And the reduction processing of Pt/ZrO2 affects crystallization and phase transitions, resulting in certain fraction of tetragonal ZrO2 transferred to monoclinic ZrO2. The DRS shows an appreciable difference in the corresponding XRD spectra that more monoclinic zirconia formed on the surface of catalyst during the reduction processing of Pt/ZrO2, compared to the bulk of catalyst. PMID:15766106

Zhan, Ying-Ying; Cai, Guo-Hui; Xiao, Yi-Hong; Wei, Ke-Mei; Chen, Tian-Ming; Zhang, Han-Hui; Zheng, Qi

2004-08-01

225

Reflectance difference spectroscopy microscope for nanometer step height detection  

SciTech Connect

A reflectance difference spectroscopy (RDS) microscope with 3-nm step height resolution and subwavelength lateral resolution for exposed surfaces and 5-nm step height resolution for interfaces 45 nm beneath a transparent layer with smooth surface, is demonstrated. It has extremely high tolerance to optical path drift (up to 3.7 {mu}m at wavelength of 512 nm), high tolerance to power fluctuation ({approx}5%), and a long working distance (8 mm). Better height resolution can be achieved with higher laser power. The RDS signal that reveals the presence of the edges is due to the depolarization of light caused by scattering by the edges, so edges of any orientation can be detected with equal sensitivity without the need to rotate the sample.

Zhang Weifeng; Qin Zongyi; Yang, Z. [Department of Physics, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong Special Administrative Region (China)

2005-04-01

226

Carrier dynamics of composite and nanolayered films of zinc phthalocyanine and C60 measured by time-resolved terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We present a study of charge transfer and carrier dynamics in films of zinc phthalocyanine (ZnPc) and buckmisnsterfullerene (C60) investigated by time-resolved terahertz spectroscopy (TRTS). These films are model structures for charge generation layers in organic photovoltaics and their intrinsic properties are therefore of interest. We compare two classes of films: composite films of ZnPc and C60 prepared by co-evaporation and layered ZnPc/C60 films prepared by alternating deposition. We find evidence for a short-lived charge transfer state of C60 that decays within several picoseconds of excitation. In contrast, both composite and multi-layered films have a long-lived THz absorption that depends on the composition and structure of the fims. The optimum composition for charge transfer within composite films is a 1:1 blend of ZnPc and C60. Amongst the layered films, there is an increase in charge photogeneration with decreasing layer thickness with a sample having ultrathin (2 nm) exhibiting the strongest THz absorption. A much stronger THz absorption signal was obtained from the layered structure than for the best composite film, even both structures contain similar fractions of ZnPc and C60 .

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

2009-08-01

227

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

228

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

229

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

E-print Network

relationship between the spectrum of near-infrared light reflected by a sample and a set of standard laboratoryNear-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

Marsh, Helene

230

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

231

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

232

Terahertz plasmonic high pass filter  

NASA Astrophysics Data System (ADS)

Metamaterials, which contain engineered subwavelength microstructures, can be designed to have positive or negative ? and ? at desired frequencies. In this letter, we demonstrate a metamaterial which has a "plasmonic" response to electromagnetic waves in the terahertz (THz) range. The sharp change of reflection and transmission at this plasma frequency makes the structure a high pass filter. The reflection response is characterized by Fourier transform infrared spectroscopy, and a plasma frequency at 0.7 THz is observed, which agrees with the theoretical calculation. The metamaterial is a two-dimensional cubic lattice consisting of thin metal wires, having wire diameter of 30 ?m, lattice constant of 120 ?m, and wire length of 1 mm. The microstereolithography technique is employed to fabricate the high-aspect-ratio lattice.

Wu, Dongmin; Fang, Nicholas; Sun, Cheng; Zhang, Xiang; Padilla, Willie J.; Basov, Dimitri N.; Smith, David R.; Schultz, Sheldon

2003-07-01

233

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

234

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

E-print Network

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

Gan, Choon How

2013-01-01

235

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 candidate for a real-time drug or explosive detection instrument that would be benign to human subjects

Ryan, Michael D.

236

VIS-NIR reflectance spectroscopy of eucrites: the MILLBILLILLIE case.  

NASA Astrophysics Data System (ADS)

In this work we report the main experimental results obtained with VIS-NIR reflectance spectroscopy techniques applied to a sample extracted from Millbillillie eucrite meteorite This activity was done to support the scientific interpretation of the hyperspectral data produced by VIR-MS imaging spectrometer aboard Dawn mission to minor planets 1 Ceres and 4 Vesta In particular we want to investigate the possibility that 4 Vesta could be the source of eucrite howardite and diogenite meteorites HEDs meteorites For this reason we have developed in our laboratory an experimental setup to reproduce several possible illumination geometries of the sample in order to simulate the observation of the target by VIR-MS This system is based on a spectrogoniometer consisting in 2 arms rotating around a common axis perpendicular to the horizontal plane on which the sample is located Each of the two arms carries an optical fiber joined to a microcollimator to focus the beams the first fiber interfaced with a radiometric source is used to illuminate the sample while the second fiber collects the reflected light and transmits it to the spectrometer FieldSpec Pro covering the 350-2500 nm spectral range The two arms can rotate thanks to computer-controlled step motors that allow to move the light source at different angles looking always the same region of the sample Data of inclusions and matrices of the Millbillillie sample have been acquired with the spectrogoniometer at different illumination angles During the on-ground calibration campaign of VIR-MS

Coradini, A.; Ammannito, E.; Capaccioni, F.; Capria, M. T.; de Sanctis, M. C.; Filacchione, G.; Piccioni, G.; Boccaccini, A.

237

Terahertz metamaterials  

SciTech Connect

In this paper we present our recent developments in terahertz (THz) metamaterials and devices. Planar THz metamaterials and their complementary structures fabricated on suitable substrates have shown electric resonant response, which causes the band-pass or band-stop property in THz transmission and reflection. The operational frequency can be further tuned up to 20% upon photoexcitation of an integrated semiconductor region in the splitring resonators as the metamaterial elements. On the other hand, the use of semiconductors as metamaterial substrates enables dynamical control of metamaterial resonances through photoexcitation, and reducing the substrate carrier lifetime further enables an ultrafast switching recovery. The metamaterial resonances can also be actively controlled by application of a voltage bias when they are fabricated on semiconductor substrates with appropriate doping concentration and thickness. Using this electrically driven approach, THz modulation depth up to 80% and modulation speed of 2 MHz at room temperature have been demonstrated, which suggests practical THz applications.

Chen, Hou-tong [Los Alamos National Laboratory; Taylor, Antoineete J [Los Alamos National Laboratory; Azad, Abul K [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory

2009-01-01

238

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

239

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

240

Characteristics of THz carrier dynamics in GaN thin film and ZnO nanowires by temperature dependent terahertz time domain spectroscopy measurement  

NASA Astrophysics Data System (ADS)

We present a comprehensive study of the characteristics of carrier dynamics using temperature dependent terahertz time domain spectroscopy. By utilizing this technique in combination with numerical calculations, the complex refractive index, dielectric function, and conductivity of n-GaN, undoped ZnO NWs, and Al-doped ZnO NWs were obtained. The unique temperature dependent behaviors of major material parameters were studied at THz frequencies, including plasma frequency, relaxation time, carrier concentration and mobility. Frequency and temperature dependent carrier dynamics were subsequently analyzed in these materials through the use of the Drude and the Drude-Smith models.

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

2012-12-01

241

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

242

Intramyocardial oxygen transport by quantitative diffuse reflectance spectroscopy in calves  

NASA Astrophysics Data System (ADS)

Intramyocardial oxygen transport was assessed during open-chest surgery in calves by diffuse reflectance spectroscopy using a small intramuscular fiber-optic probe. The sum of hemo- and myoglobin tissue fraction and oxygen saturation, the tissue fraction and oxidation of cytochrome aa3, and the tissue fraction of methemoglobin were estimated using a calibrated empirical light transport model. Increasing the oxygen content in the inhaled gas, 21%-50%-100%, in five calves (group A) gave an increasing oxygen saturation of 19+/-4%, 24+/-5%, and 28+/-8% (p<0.001, ANOVA repeated measures design) and mean tissue fractions of 1.6% (cytochrome aa3) and 1.1% (hemo- and myoglobin). Cardiac arrest in two calves gave an oxygen saturation lower than 5%. In two calves (group B), a left ventricular assistive device (LVAD pump) was implanted. Oxygen saturation in group B animals increased with LVAD pump speed (p<0.001, ANOVA) and with oxygen content in inhaled gas (p<0.001, ANOVA). The cytochrome aa3 oxidation level was above 96% in both group A and group B calves, including the two cases involving cardiac arrest. In conclusion, the estimated tissue fractions and oxygenation/oxidation levels of the myocardial chromophores during respiratory and hemodynamic provocations were in agreement with previously presented results, demonstrating the potential of the method.

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

2010-03-01

243

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.

244

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

245

Asymmetric planar terahertz metamaterials  

SciTech Connect

Using terahertz time-domain spectroscopy, we report an experimental observation of three distinct resonances in split ring resonators (SRRs) for both vertical and horizontal electric field polarizations at normal incidence. Breaking the symmetry in SRRs by gradually displacing the capacitive gap from the centre towards the comer of the ring allows for an 85% modulation of the fundamental inductive-capacitive (LC) resonance. Increasing asymmetry leads to the evolution of an otherwise inaccessible high quality factor electric quadrupole resonance that can be exploited for bio-sensing applications in the terahertz region.

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

2010-01-01

246

Selective reflection spectroscopy of a vapour at a calcium fluoride interface  

E-print Network

Selective reflection spectroscopy of a vapour at a calcium fluoride interface T. Passerat de Silans) Institute for Physical Research, Armenian Academy of Sciences, Ashtarak 2, Armenia Abstract. Fluoride interest for selective reflection spectroscopy (SR) of a vapour at fluoride interface : (i) fluoride

Paris-Sud XI, Université de

247

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

PubMed

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

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

2011-10-01

248

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

249

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; Brathen, Kari Anne

2014-01-01

250

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

251

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

E-print Network

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

252

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

253

Reflectance Spectroscopy: Quantitative Analysis Techniques for Remote Sensing Applications  

Microsoft Academic Search

Several methods for the analysis of remotely sensed reflectance data are compared, including empirical methods and scattering theories, both of which are important for solving remote sensing problems. The concept of the photon mean optical path length and the implications for use in modeling reflectance spectra are presented. It is shown that the mean optical path length in a particulate

Roger N. Clark; Ted L. Roush

1984-01-01

254

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

255

Electronic control of extraordinary terahertz transmission through  

E-print Network

; (240.6680) Surface plasmons; (250.6715) Switching (260.5740) Resonance; (300.6495) SpectroscopyElectronic control of extraordinary terahertz transmission through subwavelength metal hole arrays 02215, USA chenht@lanl.gov Abstract: We describe the electronic control of extraordinary terahertz

256

Polarization modulation infrared reflection absorption spectroscopy for heterogeneous catalytic applications at elevated pressures  

E-print Network

and temperatures higher than room temperature). Thus, some of the few detailed examples of the polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) as an in situ vibrational spectroscopic tool for the elevated-pressure investigation of gas...

Ozensoy, Emrah

2005-08-29

257

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

258

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

259

Assessment of chemical weathering of granite stone monuments using reflectance spectroscopy  

Microsoft Academic Search

Reflectance spectroscopy was applied to assess the degree of weathering of the granite sculpture of Buddha in Gyeongju, South\\u000a Korea, using diagnostic absorption features of representative weathering products (iron oxides and clay minerals). The relative\\u000a weathering degree map obtained using reflectance spectroscopy corresponds closely with the visual interpretation of exfoliations\\u000a and cracks. Eight chemical weathering indices (Vogt ratio, weathering potential

C. U. HyunH; H. D. Park

2011-01-01

260

Using Visible and Near Infrared Diffuse Reflectance Spectroscopy to Characterize and Classify Soil Profiles  

E-print Network

USING VISIBLE AND NEAR INFRARED DIFFUSE REFLECTANCE SPECTROSCOPY TO CHARACTERIZE AND CLASSIFY SOIL PROFILES A Thesis by KATRINA MARGARETTE WILKE Submitted to the Office of Graduate Studies of Texas A&M University in partial... fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2010 Major Subject: Soil Science USING VISIBLE AND NEAR INFRARED DIFFUSE REFLECTANCE SPECTROSCOPY TO CHARACTERIZE AND CLASSIFY SOIL PROFILES A Thesis...

Wilke, Katrina Margarette

2011-10-21

261

Quantitative Orientation Measurements in Thin Lipid Films by Attenuated Total Reflection Infrared Spectroscopy  

E-print Network

, namely polarized transmission spectroscopy (Rothschild and Clark, 1979; Chollet and Messier, 1982; Vogel (Golden et al., 1981; Buf- feteau et al., 1991; Blaudez et al., 1993), and polarized attenuated total reflection (ATR) spectroscopy (Harrick, 1967; Fringeli and Gu¨nthard, 1981; Kimura et al., 1986; Ahn

Pezolet, Michel

262

Determination of refractive index and thickness of a multilayer structure with a single terahertz time domain spectroscopy measurement.  

PubMed

A processing technique for the determination of the average refractive index and thickness of a two-layer system is presented. It is based on a single measurement with a standard terahertz time-domain spectrometer and the multilayer system thickness. The technique relies on the interference caused by the main pulse with the echoes produced in each material. This approach allows noninvasive inspection of double-layer compound products. PMID:25090321

Sanjuan, Federico; Bockelt, Alexander; Vidal, Borja

2014-08-01

263

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

264

Working Process Development For Weathering Degree Mapping Of Stone Monument Using Reflectance Spectroscopy  

Microsoft Academic Search

Most stone monuments have been weathered on the field with exposure of rain and wind during hundreds or thousands years. Reflectance spectroscopy can be applied to assess weathering degree of those stone monuments composed of granite which is the most general material of stone monument in Korea. Weathering degree was analyzed by using reflected and transmitted electromagnetic energy based on

C. Hyun

2008-01-01

265

Monitoring bruise age using visible diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

The ability to determine the age of a bruise of unknown age mechanism is important in matters of domestic and child abuse and forensics. While physicians are asked to make clinical judgment on the age of a bruise using color and tenderness, studies have shown that a physicians estimate is highly inaccurate and in cases no better than chance alone. We present here the temporal progression of reflection spectrum collected from accidentally inflicted contusions in adult and child study participants with a synopsis of the observed phenomena. Reflection spectra collected using a portable fiber optic reflection spectrometer can track the increase in extravasated hemoglobin from trauma caused blood vessel rupture and subsequent removal of this hemoglobin occurring concurrent with an increase in the absorption attributed to the breakdown product bilirubin. We hypothesize that this time dependent pattern can be used to determine the age of an unknown bruise in an individual provided rate constant information for the patient can be determined in a controlled calibration bruise. Using reflection spectra to estimate bruise age can provide a rapid and noninvasive method to improve the ability of physicians in dating the age of a contusion.

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

2007-02-01

266

Three-dimensional invisibility cloaks functioning at terahertz frequencies  

NASA Astrophysics Data System (ADS)

Quasi-three-dimensional invisibility cloaks, comprised of either homogeneous or inhomogeneous media, are experimentally demonstrated in the terahertz regime. The inhomogeneous cloak was lithographically fabricated using a scalable Projection Microstereolithography process. The triangular cloaking structure has a total thickness of 4.4 mm, comprised of 220 layers of 20 ?m thickness. The cloak operates at a broad frequency range between 0.3 and 0.6 THz, and is placed over an ?-lactose monohydrate absorber with rectangular shape. Characterized using angular-resolved reflection terahertz time-domain spectroscopy, the results indicate that the terahertz invisibility cloak has successfully concealed both the geometrical and spectroscopic signatures of the absorber, making it undetectable to the observer. The homogeneous cloaking device made from birefringent crystalline sapphire features a large concealed volume, low loss, and broad bandwidth. It is capable of hiding objects with a dimension nearly an order of magnitude larger than that of its lithographic counterpart, but without involving complex and time-consuming cleanroom processing. The cloak device was made from two 20-mm-thick high-purity sapphire prisms. The cloaking region has a maximum height 1.75 mm with a volume of approximately 5% of the whole sample. The reflected TM beam from the cloak shows nearly the same profile as that reflected by a flat mirror.

Cao, Wei; Zhou, Fan; Liang, Dachuan; Gu, Jianqiang; Han, Jiaguang; Sun, Cheng; Zhang, Weili

2014-05-01

267

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

268

Core-level reflectance spectroscopy of black phosphorus single crystals  

Microsoft Academic Search

The 2p core reflectance spectra have shown strong anisotropy for E-->||a and E-->||c. A remarkably sharp doublet structure observed at the 2p core threshold for E-->||a (at 130.33 and 131.20 eV) is assigned to the spin-orbit partner of the 2p core excitons with finite binding energy. The difference between the spectra for E-->||a and E-->||c is explained on the basis

M. Taniguchi; M. Seki; S. Suga; A. Mikuni; H. Kanzaki; Y. Akahama; S. Endo; S. Narita

1983-01-01

269

Measuring Black Hole Spin Using X-Ray Reflection Spectroscopy  

NASA Astrophysics Data System (ADS)

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

Reynolds, Christopher S.

2014-09-01

270

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

271

Identification of mineral components in tropical soils using reflectance spectroscopy and advanced spaceborne thermal emission and reflection radiometer (ASTER) data  

Microsoft Academic Search

Soil characteristics provide important support for understanding transformations that occur in environmental systems. Physical characteristics and chemical compositions of soils controlled by pedogenetic processes, climatic changes and land use imply different types of environmental transformations. Reflectance spectroscopy is an alternative soil mapping technique that uses spectral absorption features between visible (VIS) and short-wave infrared (SWIR) wavelengths (0.3–2.5?m) for determining soil

Luiz Eduardo Vicente; Carlos Roberto de Souza Filho

2011-01-01

272

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

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

273

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

274

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

275

Thermal infrared reflectance and emission spectroscopy of quartzofeldspathic glasses  

USGS Publications Warehouse

This investigation seeks to better understand the thermal infrared (TIR) spectral characteristics of naturally-occurring amorphous materials through laboratory synthesis and analysis of glasses. Because spectra of glass phases differ markedly from their mineral counterparts, examination of glasses is important to accurately determine the composition of amorphous surface materials using remote sensing datasets. Quantitatively characterizing TIR (5-25 ??m) spectral changes that accompany structural changes between glasses and mineral crystals provides the means to understand natural glasses on Earth and Mars. A suite of glasses with compositions analogous to common terrestrial volcanic glasses was created and analyzed using TIR reflectance and emission techniques. Documented spectral characteristics provide a basis for comparison with TIR spectra of other amorphous materials (glasses, clays, etc.). Our results provide the means to better detect and characterize glasses associated with terrestrial volcanoes, as well as contribute toward understanding the nature of amorphous silicates detected on Mars. Copyright 2007 by the American Geophysical Union.

Byrnes, J. M.; Ramsey, M. S.; King, P. L.; Lee, R. J.

2007-01-01

276

Near-Earth asteroids: possible sources from reflectance spectroscopy.  

PubMed

Spectra of near-Earth asteroids were compared to spectra of selected asteroids, planets, and satellites to determine possible source regions. The diversity of reflectance spectra of the near-Earth asteroids implies different mineralogical compositions and hence more than one source region. The presence of near-Earth asteroid spectral signatures similar to those of certain main-belt asteroids supports models that derive some of these asteroids from the 5:2 Kirkwood gap and the Flora family by gravitational perturbations. Planetary and satellite surfaces are different in composition than the near-Earth asteroids, which is in agreement with theoretical arguments that such bodies should not be sources. Some near-Earth asteroids supply portions of Earth's meteorite flux, but other sources must also contribute. PMID:17746289

McFadden, L A; Gaffey, M J; McCord, T B

1985-07-12

277

Measurements of Terahertz Electrical Conductivity of Intense Laser-Heated Dense Aluminum Plasmas  

Microsoft Academic Search

We report the electrical conductivity of laser-produced warm dense aluminum plasmas measured using single-shot ultrafast terahertz (THz) frequency spectroscopy. In contrast with experiments performed at optical frequencies, measurements based upon THz probe reflectivity directly determine a quasi-dc electrical conductivity, and therefore the analysis does not require a free-electron Drude model based extrapolation to recover the near zero frequency conductivity. In

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

2008-01-01

278

Terahertz radiation study on FRP composite solid laminates  

NASA Astrophysics Data System (ADS)

Investigation of terahertz time domain spectroscopy (THz TDS) was made and reflection and transmission configurations were studied as a nondestructive evaluation technique. Here carbon fiber-reinforced plastics (CFRP) derived their excellent mechanical strength, stiffness and electrical conductivity from carbon fibers. Especially, the electrical conductivity of CFRP composites depends on the direction of unidirectional fibers since carbon fibers are electrically conducting while the epoxy matrix is not. The THz TDS can be considered as a useful tool using general non-conducting materials; however it is quite limited to conducting materials. In order to solve various material properties, the index of refraction (n) is derived by using the terahertz time domain spectroscopy. Also, for a 48-ply thermoplastic PPS(poly-phenylene sulfide)-based CFRP solid laminate, the terahertz scanning images were made at the angles ranged from 0° to 180° with respect to the nominal fiber axis. So, the images were mapped out based on the electrical field (E-field) direction in the CFRP solid laminates.

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

2012-05-01

279

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

280

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

281

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

PubMed

With the rapid development of the GMO, more and more GMO food has been pouring into the market. Much attention has been paid to GMO labeling under the controversy of GMO safety. Transgenic corns and their parents were scanned by continuous wave of near infrared diffuse reflectance spectroscopy range of 12000-4000 cm(-1); the resolution was 4 cm(-1); scanning was carried out for 64 times; BP algorithm was applied for data processing. The GMO food was easily resolved. Near-infrared diffuse reflectance spectroscopy is unpolluted and inexpensive compared with PCR and ELISA, so it is a very promising detection method for GMO food. PMID:16395887

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

2005-10-01

282

Effect of data pretreatment on the noninvasive blood glucose measurement by diffuse reflectance NIR spectroscopy  

NASA Astrophysics Data System (ADS)

Recent progress in spectroscopy and chemometrics have brought in-vitro blood glucose analysis into clinical reach. Parallel to these efforts noninvasive experiments by NIR- spectroscopy have also been proposed and carried out. A specially designed and optimized accessory for diffuse reflectance measurements in the spectral range of 9000 - 5000 cm-1 was used. The spectral data and reference concentration values were obtained using oral glucose tolerance tests. Calibration results are provided for log(1/R) and single beam spectra. In addition, the effects of smoothing and the use of derivative filtering were evaluated. The best results were achieved by multivariate PLS-modeling with raw data from single beam reflectance spectra.

Heise, Herbert M.; Marbach, Ralf

1994-01-01

283

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

284

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

285

In vivo soft tissue differentiation by diffuse reflectance spectroscopy: preliminary results  

NASA Astrophysics Data System (ADS)

Remote laser surgery does not provide haptic feedback to operate layer by layer and preserve vulnerable anatomical structures like nerve tissue or blood vessels. The aim of this study is identification of soft tissue in vivo by diffuse reflectance spectroscopy to set the base for a feedback control system to enhance nerve preservation in oral and maxillofacial laser surgery. Various soft tissues can be identified by diffuse reflectance spectroscopy in vivo. The results may set the base for a feedback system to prevent nerve damage during oral and maxillofacial laser surgery.

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

286

Visible and infrared reflectance imaging spectroscopy of paintings: pigment mapping and improved infrared reflectography  

NASA Astrophysics Data System (ADS)

Reflectance imaging spectroscopy, the collection of images in narrow spectral bands, has been developed for remote sensing of the Earth. In this paper we present findings on the use of imaging spectroscopy to identify and map artist pigments as well as to improve the visualization of preparatory sketches. Two novel hyperspectral cameras, one operating from the visible to near-infrared (VNIR) and the other in the shortwave infrared (SWIR), have been used to collect diffuse reflectance spectral image cubes on a variety of paintings. The resulting image cubes (VNIR 417 to 973 nm, 240 bands, and SWIR 970 to 1650 nm, 85 bands) were calibrated to reflectance and the resulting spectra compared with results from a fiber optics reflectance spectrometer (350 to 2500 nm). The results show good agreement between the spectra acquired with the hyperspectral cameras and those from the fiber reflectance spectrometer. For example, the primary blue pigments and their distribution in Picasso's Harlequin Musician (1924) are identified from the reflectance spectra and agree with results from X-ray fluorescence data and dispersed sample analysis. False color infrared reflectograms, obtained from the SWIR hyperspectral images, of extensively reworked paintings such as Picasso's The Tragedy (1903) are found to give improved visualization of changes made by the artist. These results show that including the NIR and SWIR spectral regions along with the visible provides for a more robust identification and mapping of artist pigments than using visible imaging spectroscopy alone.

Delaney, John K.; Zeibel, Jason G.; Thoury, Mathieu; Littleton, Roy; Morales, Kathryn M.; Palmer, Michael; de la Rie, E. René

2009-07-01

287

Terahertz characterization of multi-walled carbon nanotube films  

NASA Astrophysics Data System (ADS)

Multi-walled carbon nanotube films are characterized using terahertz time-domain spectroscopy. Both transmission and reflection experiments are performed in order to measure both the complex refractive index and the wave impedance. This method allows simultaneous extraction of both the permittivity (? =?'-i??) and permeability (? =?'-i??) without any assumptions. Experimental results are obtained from 50 to 370 GHz and compared well with the microwave data (8-50 GHz) of the same sample measured using a vector network analyzer. The measured complex permittivity can be fitted with a Drude-Lorentz model in the 8-370 GHz frequency range.

Wu, Ziran; Wang, Lu; Peng, Yitian; Young, Abram; Seraphin, Supapan; Xin, Hao

2008-05-01

288

Terahertz superconducting plasmonic hole array  

E-print Network

We demonstrate thermally tunable superconductor hole array with active control over their resonant transmission induced by surface plasmon polaritons . The array was lithographically fabricated on high temperature YBCO superconductor and characterized by terahertz-time domain spectroscopy. We observe a clear transition from the virtual excitation of the surface plasmon mode to the real surface plasmon mode. The highly tunable superconducting plasmonic hole arrays may have promising applications in the design of low-loss, large dynamic range amplitude modulation, and surface plasmon based terahertz devices.

Tian, Zhen; Han, Jiaguang; Gu, Jianqiang; Xing, Qirong; Zhang, Weili

2010-01-01

289

Diffuse Reflectance Spectroscopy of Human Skin Using a Commercial Fiber Optic Spectrometer  

SciTech Connect

Diffuse reflectance spectroscopy is a reliable and easy to implement technique in human tissue characterization. In this work we evaluate the performance of the commercial USB4000 miniature fiber optic spectrometer in the in-vivo measurement of the diffuse reflectance spectra of different healthy skin sites and lesions in a population of 54 volunteers. Results show, that this spectrometer reproduces well the typical signatures of skin spectra over the 400-1000 nm region. Remarkable spectral differences exist between lesions and normal surrounding skin. A diffusion-based model was used to simulate reflectance spectra collected by the optical probe of the system.

Atencio, J. A. Delgado; Rodriguez, M. Cunill [Department of Optics, Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), 72000 (Mexico); Centre for Technological Applications and Nuclear Development, CEADEN.P.O. Box 6122 (Cuba); Montiel, S. Vazquez y; Castro, Jorge; Rodriguez, A. Cornejo [Department of Optics, Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), 72000 (Mexico); Gutierrez, J. L.; Martinez, F.; Gutierrez, B. [Oncology Deparment, Universitary Hospital of Puebla, Puebla (Mexico); Orozco, E. [Department of Optics, Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), 72000 (Mexico); Departamento de Fisica, Universidad de Carabobo, Facultad Experimental de Ciencia y Tecnologia (Venezuela)

2008-08-11

290

Sorting of polypropylene resins by color in MSW using visible reflectance spectroscopy  

Microsoft Academic Search

In this paper, an automated sorter is proposed for distinguishing polypropylene (PP) plastics based on their color. This sorting system uses visible (VIS) reflectance spectroscopy to separate PP resins according to their colors. A “Three-Filter” identification algorithm was developed to recognize the PP color (blue, red, green, white or yellow), and accordingly, give the command for throwing or not throwing

S. M. Safavi; H. Masoumi; S. S. Mirian; M. Tabrizchi

2010-01-01

291

Estimating the amino acid composition in milled rice by near-infrared reflectance spectroscopy  

Microsoft Academic Search

This study was conducted to develop near-infrared reflectance spectroscopy (NIRS) equations to predict the amino acid and nitrogen content of milled rice powder. The samples were scanned by NIRS and analyzed for amino acid composition and total nitrogen by HCl hydrolysis–HPLC methodology and Kjeldahl method, respectively. The NIRS equations of 15 different amino acids, except for cystine, methionine and histidine,

Jianguo G. Wu; Chunhai Shi; Xiaoming Zhang

2002-01-01

292

Nondestructive Depth Profiling of Polymer Thin Films Using Variable Angle Internal Reflection Raman Spectroscopy  

Microsoft Academic Search

We have developed variable angle internal reflection Raman spectroscopy (VAIRRS) into a practical tool for the nondestructive depth profiling of molecular concentrations, molecular orientations, and bond polarizabilities in thin polymer films. The technique relies on the analysis of Raman spectra obtained during precise control of the electromagnetic field distribution. The approach is closely related to Raman scattering by means of

T. E. Furtak; N. H. Fontaine

1996-01-01

293

Real time, in-situ temperature monitoring using diffuse reflectance spectroscopy  

SciTech Connect

Real time temperature measurements have been performed on both GaAs and silicon substrates during wafer processing using a technique based upon diffuse reflectance spectroscopy (DRS). Good temperature resolution ({+-}O.4 {degrees}C) and rapid updates have enabled the process control potential of the device to be demonstrated.

Booth, J.L.; Beard, B.T. [Thermionics Northwest, Inc., Port Townsend, WA (United States); Pearsall, T.P.; Wang, Z.Z. [Washington Univ., Seattle, WA (United States). Dept. of Electrical Engineering; Stevens, J.E.; Blain, M.G.; Meisenheimer, T.L. [Sandia National Labs., Albuquerque, NM (United States)

1996-11-01

294

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

295

Single-component reflecting objective for low-temperature spectroscopy in the entire visible region  

E-print Network

consists of two concentric concave and convex mirrors. To maintain a rigid alignment of the mirrors at low-component reflecting objective was constructed for low-temperature spectroscopy with optimal imaging and transmission at a temperature of 1.5 K was tested by comparing dark-field images of uncolored polymer beads taken at wavelengths

296

RAPID COMMUNICATION: Stress-induced optical anisotropy in polycrystalline copper studied by reflection anisotropy spectroscopy  

Microsoft Academic Search

The optical properties of polycrystalline copper subjected to tensile stress are monitored in situ and in real time using reflection anisotropy spectroscopy (RAS). It is shown that RAS allows investigation of the plastic regime. Here, in contrast to the Hooke's law regime, the stress-induced RAS lineshape is found to be dependent on the applied stress. The optical anisotropy in the

R. J. Cole; S. Kheradmand; D. D. Higgins; F. Madani; B. F. Macdonald; V. Koutsos; J. R. Blackford

2003-01-01

297

Fecal near-infrared reflectance spectroscopy calibrations for predicting diet quality and intake of donkeys  

E-print Network

The objective of these studies was to develop near-infrared reflectance spectroscopy calibration equations from diet-fecal pair datasets to predict the diet quality and intake of donkeys. One hundred-forty diet-fecal pair samples were generated from...

Kidane, Negusse Fessehaye

2006-08-16

298

Terahertz antireflection coatings using metamaterials  

SciTech Connect

We demonstrate terahertz metamaterial antireflection coatings (ARCs) that significantly reduce the reflection and enhance the transmission at an interface of dielectric media. They are able to operate over a wide range of incidence angles for both TM and TE polarizations. Experiments and finite-element simulations will be presented and discussed.

Chen, Hou-tong [Los Alamos National Laboratory; Zhou, Jiangfeng [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Azad, Abul K [Los Alamos National Laboratory; Chen, Frank [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

2010-01-01

299

In vivo detection of epileptic brain tissue using static fluorescence and diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Diffuse reflectance and fluorescence spectroscopy are used to detect histopathological abnormalities of an epileptic brain in a human subject study. Static diffuse reflectance and fluorescence spectra are acquired from normal and epileptic brain areas, defined by electrocorticography (ECoG), from pediatric patients undergoing epilepsy surgery. Biopsy specimens are taken from the investigated sites within an abnormal brain. Spectral analysis reveals significant differences in diffuse reflectance spectra and the ratio of fluorescence and diffuse reflectance spectra from normal and epileptic brain areas defined by ECoG and histology. Using these spectral differences, tissue classification models with accuracy above 80% are developed based on linear discriminant analysis. The differences between the diffuse reflectance spectra from the normal and epileptic brain areas observed in this study are attributed to alterations in the static hemodynamic characteristics of an epileptic brain, suggesting a unique association between the histopathological and the hemodynamic abnormalities in an epileptic brain.

Yadav, Nitin; Bhatia, Sanjiv; Ragheb, John; Mehta, Rupal; Jayakar, Prasanna; Yong, William; Lin, Wei-Chiang

2013-02-01

300

Investigation of the mineralization process of biosystems by IR diffuse reflection spectroscopy methods  

NASA Astrophysics Data System (ADS)

Particular features of the application of Fourier-transform IR diffuse reflection spectroscopy methods to the in situ investigation of spectra of porous rough objects have been considered. The reciprocal influence of the scattering and absorption of porous objects on the formation of the impurity-band contour in the diffuse reflection spectrum when the impurity center is in the vicinity of the fundamental IR absorption band has been analyzed. Using methods of Fourier-transform IR diffuse reflection spectroscopy, processes of mineralization of fragments of mammoth tusks from a multilayer paleolithic site at Yudinovo (Bryansk oblast, Russia) and fragments of mammoth tusks from Yakutia (Russia) have been investigated. Particular features of mineralization processes (carbonate formation and silicification) on the surface and in the volume of objects at different conditions of their burial (humidity, temperature, soil acidity) have been studied.

Zolotarev, V. M.

2014-04-01

301

Cryogenic temperatures as a path toward high-Q terahertz metamaterials Ranjan Singh,1,2  

E-print Network

Cryogenic temperatures as a path toward high-Q terahertz metamaterials Ranjan Singh,1,2 Zhen Tian,1 terahertz time-domain spectroscopy. The operation of metamaterials at cryogenic temperatures is anticipated we investigate the behavior of terahertz planar MM at cryogenic temperatures. It is shown that thin

Oklahoma State University

302

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

Microsoft Academic Search

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

Michael Kemp

2005-01-01

303

Conducting dielectric polymer properties at Terahertz wavelength  

Microsoft Academic Search

The dielectric function of polyaniline (Pani) doped by couple drug\\/solvent sulphonic camphoracid\\/dichloroacetic CSA\\/DCAA is studied in the terahertz range. Numerous films of this polymer with different doping level are measured by Terahertz Time-Domain Spectroscopy (THz-TDS). The Fourier transmission spectrum, the permittivity and conductivity are then precisely obtained between 0.1 and 4 THz. The behavior of the dielectric function does not

E. Nguema; J. D. Delagnes; A. Elfatimy; P Mounaix

304

Discrimination between immature and mature green coffees by attenuated total reflectance and diffuse reflectance Fourier transform infrared spectroscopy.  

PubMed

The objective of this work was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) in the characterization and discrimination between immature and mature or ripe coffee beans. Arabica coffee beans were submitted to FTIR analysis by reflectance readings employing attenuated total reflectance (ATR) and diffuse reflectance (DR) accessories. The obtained spectra were similar, but in general higher absorbance values were observed for nondefective beans in comparison to immature ones. Multivariate statistical analysis (principal component analysis, PCA, and agglomerative hierarchical clustering, AHC) was performed in order to verify the possibility of discrimination between immature and mature coffee samples. A clear separation between immature and mature coffees was observed based on AHC and PCA analyses of the normalized spectra obtained by employing both ATR and DR accessories. Linear discriminant analysis was employed for developing classification models, with recognition and prediction abilities of 100%. Such results showed that FTIR analysis presents potential for the development of a simple routine methodology for separation of immature and mature coffee beans. Practical Application: The ultimate goal of this research is to be able to propose improvements in the way immature coffee beans are separated from graded mature beans in coffee facilities (cooperatives and other coffee producer's associations). The results obtained herein point toward FTIR as a potential tool for the aimed improvements. PMID:22417580

Craig, Ana Paula; Franca, Adriana S; Oliveira, Leandro S

2011-10-01

305

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

306

Time-dependent diffuse reflectance spectroscopy for in vivo characterization of pediatric epileptogenic brain lesions  

NASA Astrophysics Data System (ADS)

Optical spectroscopy for in vivo tissue diagnosis is performed traditionally in a static manner; a snap shot of the tissue biochemical and morphological characteristics is captured through the interaction between light and the tissue. This approach does not capture the dynamic nature of a living organ, which is critical to the studies of brain disorders such as epilepsy. Therefore, a time-dependent diffuse reflectance spectroscopy system with a fiber-optic probe was designed and developed. The system was designed to acquire broadband diffuse reflectance spectra (240 ~ 932 nm) at an acquisition rate of 33 Hz. The broadband spectral acquisition feature allows simultaneous monitoring of various physiological characteristics of tissues. The utility of such a system in guiding pediatric epilepsy surgery was tested in a pilot clinical study including 13 epilepsy patients and seven brain tumor patients. The control patients were children undergoing suregery for brain tumors in which measurements were taken from normal brain exposed during the surgery. Diffuse reflectance spectra were acquired for 12 seconds from various parts of the brain of the patients during surgery. Recorded spectra were processed and analyzed in both spectral and time domains to gain insights into the dynamic changes in, for example, hemodynamics of the investigated brain tissue. One finding from this pilot study is that unsynchronized alterations in local blood oxygenation and local blood volume were observed in epileptogenic cortex. These study results suggest the advantage of using a time-dependent diffuse reflectance spectroscopy system to study epileptogenic brain in vivo.

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

2008-02-01

307

[Estimations of chlorophyll and water contents in live leaf of winter wheat with reflectance spectroscopy].  

PubMed

For estimating the yield of wheat, and for crop growth monitoring by using hyperspectral remote sensing, it is very important to quantitatively determine the chlorophyll and water contents in live leaf of winter wheat. In the range of 350-1650 nm, the reflectance spectrum of winter wheat's leaf in different growth periods were scanned by ASD FieldSpec Pro FR portable spectrometer and LI-COR 1800 integrating spheres. Partial least squares method was used to develop the quantitative analysis models for chlorophyll and water contents with reflectance spectroscopy. The model of chlorophyll content with reflectance spectroscopy was built in the range of 400-750 nm, and the results show that the correlation coefficient between the estimated values and the real values is 0.898, and relative standard deviation is 13.6%. The model of water content with reflectance spectroscopy was built in the range of 1400-1600 nm, and the results indicate that the correlation coefficient between the estimated values and the real values is 0.999, and relative standard deviation is 0.3%. These results are satisfying in agricultural production. PMID:17554911

Ji, Hai-yan; Wang, Peng-xin; Yan, Tai-lai

2007-03-01

308

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

NASA Astrophysics Data System (ADS)

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

Zhang, Feng; Hayashi, Michitoshi; Wang, Houng-Wei; Tominaga, Keisuke; Kambara, Ohki; Nishizawa, Jun-ichi; Sasaki, Tetsuo

2014-05-01

309

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

PubMed

The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D(*) have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D(*) simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D(*) data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D(*) produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D(*). PMID:24811648

Zhang, Feng; Hayashi, Michitoshi; Wang, Houng-Wei; Tominaga, Keisuke; Kambara, Ohki; Nishizawa, Jun-ichi; Sasaki, Tetsuo

2014-05-01

310

Tunable terahertz fishnet metamaterial  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

311

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

312

Development of techniques for advanced optical contamination measurement with internal reflection spectroscopy, phase 1, volume 1  

NASA Technical Reports Server (NTRS)

The feasibility of monitoring volatile contaminants in a large space simulation chamber using techniques of internal reflection spectroscopy was demonstrated analytically and experimentally. The infrared spectral region was selected as the operational spectral range in order to provide unique identification of the contaminants along with sufficient sensitivity to detect trace contaminant concentrations. It was determined theoretically that a monolayer of the contaminants could be detected and identified using optimized experimental procedures. This ability was verified experimentally. Procedures were developed to correct the attenuated total reflectance spectra for thick sample distortion. However, by using two different element designs the need for such correction can be avoided.

Hayes, J. D.

1972-01-01

313

In Situ Diffuse Reflectance IR Spectroscopy and X-ray Absorption Spectroscopy for Fast Catalytic Processes  

SciTech Connect

A new instrument for synchronous in situ investigations of catalytic materials by IR and X-ray absorption spectroscopies was designed and built at the X18A beamline of the National Synchrotron Light Source of Brookhaven National Laboratory. It provides analytical tools for solving structural, electronic and kinetic problems in catalysis science by two complementary methods. Among the features attractive for catalysis research are the broad range of catalytically active elements that can be investigated (starting with Ni and beyond), the wide range of reaction conditions (temperatures up to 873 K, various reactive gases) and time scales (starting from tens of seconds). The results of several representative experiments that illustrate the attractive capabilities of the new set-up are discussed.

N Marinkovic; Q Wang; A Frenkel

2011-12-31

314

Infrared and terahertz studies of polar phonons and magnetodielectric effect in multiferroic BiFeO3 ceramics  

Microsoft Academic Search

BiFeO3 ceramics were investigated by means of infrared reflectivity and time domain terahertz transmission spectroscopy at temperatures 20-950K , and the magnetodielectric effect was studied at 10-300K with the magnetic field up to 9T . Below 175K , the sum of polar phonon contributions to the permittivity corresponds to the value of measured permittivity below 1MHz . At higher temperatures,

S. Kamba; D. Nuzhnyy; M. Savinov; J. Sebek; J. Petzelt; J. Prokleska; R. Haumont; J. Kreisel

2007-01-01

315

Application of transcutaneous diffuse reflectance spectroscopy in the measurement of blood glucose concentration  

NASA Astrophysics Data System (ADS)

In this paper, the propagation characteristics of near-infrared (NIR) light in the palm tissue are analyzed, and the principle and feasibility of using transcutaneous diffuse reflectance spectroscopy for non-invasive blood glucose detection are presented. An optical probe suitable for measuring the diffuse reflectance spectrum of human palm and a non-invasive blood glucose detection system using NIR spectroscopy are designed. Based on this system, oral glucose tolerance tests are performed to measure the blood glucose concentrations of two young healthy volunteers. The partial least square calibration model is then constructed by all individual experimental data. The final result shows that correlation coefficients of the two experiments between the predicted blood glucose concentrations and the reference blood glucose concentrations are 0.9870 and 0.9854, respectively. The root mean square errors of prediction of full cross validation are 0.54 and 0.52 mmol/l, respectively.

Chen, Wenliang; Liu, Rong; Cui, Houxin; Xu, Kexin; Lv, Lina

2004-07-01

316

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

SciTech Connect

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

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

2006-12-31

317

Monitoring of landfill leachate dispersion using reflectance spectroscopy and ground-penetrating radar.  

PubMed

The utility of ground-penetrating radar and reflectance spectroscopy in the monitoring of landfill sites has been investigated. Strong correlations between red edge inflection position and chlorophyll and heavy metal concentrations have been demonstrated from grassland species affected by leachate contamination of the soil adjacent to the landfill test site. This study demonstrated that reflectance spectroscopy can identify vegetation affected by leachate-contaminated soil at a range of spatial resolutions. To identify the vegetation affected by leachate contamination, the spectroradiometer must have contiguous bands at sufficient spectral resolution over the critical wave range that measures chlorophyll absorption and the red edge (between 650 and 750 nm). The utility of ground-penetrating radar data to identify leachate escaping from breakout points in the contaminant wall has also been demonstrated. An integrated approach using these techniques, combined with field and borehole sampling and contaminant migration modeling, offers a possible cost-effective monitoring approach for landfill sites. PMID:14524467

Splajt, T; Ferrier, G; Frostick, L E

2003-09-15

318

Characterization of edible oils, butters and margarines by Fourier transform infrared spectroscopy with attenuated total reflectance  

Microsoft Academic Search

The combination of attenuated total reflectance (ATR) and mid-infrared spectroscopy (MIRS) with statistical multidimensional\\u000a techniques made it possible to extract relevant information from MIR spectra of lipid-rich food products. Wavenumber assignments\\u000a for typical functional groups in fatty acids were made for standard fatty acids: Absorption bands around 1745 cm?1, 2853 cm?1, 2954 cm?1, 3005 cm?1, 966 cm?1, 3450 cm?1 and

M. Safar; D. Bertrand; P. Roberta; M. F. Devaux; C. Genot

1994-01-01

319

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

Microsoft Academic Search

Mid-IR fiber-optic reflectance spectroscopy (FORS) is a totally noninvasive infrared analytical technique allowing the investigation\\u000a of artworks without the need for any sampling. The development and optimization of this analytical methodology can provide\\u000a a tool that is capable of supporting conservators during the first steps of their interventions, yielding fast results and\\u000a dramatically reducing the number of samples needed to

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

2011-01-01

320

Rapid Identification of Oil-Contaminated Soils Using Visible Near-Infrared Diffuse Reflectance Spectroscopy  

Microsoft Academic Search

In the United States, petroleum extraction, refinement, and transportation present countless opportunities for spillage mishaps. A method for rapid field appraisal and mapping of petroleum hydrocarbon-contaminated soils for environmental cleanup purposes would be useful. Visible near-infrared (VisNIR, 350-2500 nm) diffuse reflectance spectroscopy (DRS) is a rapid, nondestructive, proximal-sensing technique that has proven adept at quantifying soil properties in situ. The

Somsubhra Chakraborty; David C. Weindorf; Cristine L. S. Morgan; Yufeng Ge; John M. Galbraith; Bin Li; Charanjit S. Kahlon

2010-01-01

321

Strategies for Detecting Organic Liquids on Soils Using Mid-Infrared Reflection Spectroscopy  

Microsoft Academic Search

Stand-off monitoring for chemical spills can provide timely information for clean-up efforts and mid-infrared reflection-absorption spectroscopy is one approach being investigated. Anomaly and target detection strategies were examined for detection of four different low-volatility organic liquids on two different soil types. Several preprocessing and signal weighting strategies were studied. Anomaly detection for CH bands was very good using second derivative

Neal B. Gallagher; Paul L. Gassman; Thomas A. Blake

2008-01-01

322

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

323

Evaluation of density and strength of Norway spruce wood by near infrared reflectance spectroscopy  

Microsoft Academic Search

The non-destructive evaluation of wood properties by Near Infrared Reflectance Spectroscopy (NIR) has been assessed. The surfaces\\u000a of specimens of clear wood (Picea abies) were NIR-scanned, and the results compared to such properties as moisture content, density, compression strength and chemical\\u000a and biological degradation. In addition, the NIR-scans of clear wood specimens were compared to the bending strength of the

P. Hoffmeyer; J. G. Pedersen

1995-01-01

324

Measurements of the Carrier Dynamics and Terahertz Response of Oriented  

E-print Network

and the resulting magnitudes of the surface plasmon frequencies. In recent years, semiconductor nanowires haveMeasurements of the Carrier Dynamics and Terahertz Response of Oriented Germanium Nanowires using Optical-Pump Terahertz-Probe Spectroscopy Jared H. Strait,*, Paul A. George, Mark Levendorf, Martin Blood

Afshari, Ehsan

325

[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

326

Plasmonic photoconductive detectors for enhanced terahertz detection sensitivity.  

PubMed

A photoconductive terahertz detector based on plasmonic contact electrodes is presented. The use of plasmonic electrodes mitigates the inherent tradeoff between high quantum efficiency and ultrafast operation of the employed photoconductor, enabling significantly higher detection sensitivities compared to conventional photoconductive terahertz detectors. Prototypes of comparable photoconductive detectors with and without plasmonic contact electrode gratings were fabricated and characterized in a time-domain terahertz spectroscopy setup under the same operation conditions. The experimental results show that the plasmonic photoconductive detector offers more than 30 times higher terahertz detection sensitivities compared to the comparable conventional photoconductive detector without plasmonic contact electrodes over 0.1-1.5 THz frequency band. PMID:23938568

Wang, Ning; Hashemi, Mohammad R; Jarrahi, Mona

2013-07-15

327

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

328

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

329

Highly Sensitive Terahertz Sensing of Glycerol-Water Mixtures with Metamaterials  

NASA Astrophysics Data System (ADS)

We demonstrate the highly sensitive terahertz (THz) sensing of a water-glycerol mixture poured on a metamaterial surface using reflection-based THz time domain spectroscopy. The reflectance at the resonant dip frequency changes significantly with glycerol concentration. The detection sensitivity is about 8 times higher than that compared to the case without a metamaterial structure. We also investigate how sensitivity depends on the Q factor of the metamaterial resonance for highly absorptive media, such as a water solution in the THz region.

Miyamaru, F.; Hattori, K.; Shiraga, K.; Kawashima, S.; Suga, S.; Nishida, T.; Takeda, M. W.; Ogawa, Y.

2013-11-01

330

Terahertz standoff identification: influence of environment and sample properties  

NASA Astrophysics Data System (ADS)

Terahertz (THz) spectroscopy is a promising technique for the stand-off identification of hidden objects. The THz band is particularly well suited firstly because THz radiation penetrates many dielectrics like clothing and secondly because many potentially hazardous substances have characteristic signatures in the THz spectral region. In order to demonstrate the full potential of THz radiation for identifying possible hazards using characteristic signatures, different disturbing influences must be taken into account. We have performed experiments and simulations in order to investigate the possibilities and the challenges of terahertz stand-off identification. A special emphasis is paid on humidity in ambient air and properties of the sample like surface roughness and orientation with respect to the incident THz beam. Water vapor absorption strongly affects the THz spectra. Since the absorption lines are strong and narrow, the calculation must be precise. We have checked models well-known in meteorology covering the infrared and the microwave regions of the electromagnetic spectrum and achieved an accurate description of the measured THz spectral absorption using the program LINEFIT. The surface roughness of the sample strongly affects the bandwidth of the reflected spectra. Specular and diffuse reflection measurements using samples with different roughnesses have been used for determining the influences of different properties on the reflection spectra.

Herrmann, Michael; Wohnsiedler, Sabine; Wiegand, Christian; Theuer, Michael; Jonuscheit, Joachim; Beigang, René

2009-05-01

331

Terahertz Science and Technology Trends  

Microsoft Academic Search

The recent progress in terahertz science and technology (THz-S&T) opens up a range of potential research opportunities. Historically, THz technologies were mainly used by the astronomy community for searching far-infrared radiation (cosmic background), and by the laser fusion community for the diagnostics of plasmas. Since the first demonstration of THz wave time-domain spectroscopy in the late 1980s, there has been

Albert Redo-Sanchez; Xi-Cheng Zhang

2008-01-01

332

High-speed time domain terahertz security imaging  

Microsoft Academic Search

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Time domain terahertz imaging can be employed in reflection mode to image with sub millimeter resolution. Previously, single pixel acquisition times for THz waveforms

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

2005-01-01

333

Dual-band bandpass terahertz wave filter based on microstrip resonant structure  

NASA Astrophysics Data System (ADS)

The terahertz (THz) band, which refers to the spectral region between 0.1 and 10THz, covers the fingerprints of many chemical and biological materials. Within the past few years, there are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology, nanotechnology, space science, security, chemical and biological sensing, terahertz wave communications, and medical diagnostics. For potential applications, the functional devices, such as beam polarizers, switchs and filters, are crucial components for a terahertz system. Terahertz wave filter based on two kinds of microstrip resonant structures, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. The experimental results for the frequency dependence of the transmittance of the terahertz wave filter show that the terahertz wave transmittance peak is of 79.5% at 0.5THz and 82.5% at 0.81THz.

Liu, Yu-hang; Li, Jiu-sheng

2011-11-01

334

Dual-band bandpass terahertz wave filter based on microstrip resonant structure  

NASA Astrophysics Data System (ADS)

The terahertz (THz) band, which refers to the spectral region between 0.1 and 10THz, covers the fingerprints of many chemical and biological materials. Within the past few years, there are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology, nanotechnology, space science, security, chemical and biological sensing, terahertz wave communications, and medical diagnostics. For potential applications, the functional devices, such as beam polarizers, switchs and filters, are crucial components for a terahertz system. Terahertz wave filter based on two kinds of microstrip resonant structures, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. The experimental results for the frequency dependence of the transmittance of the terahertz wave filter show that the terahertz wave transmittance peak is of 79.5% at 0.5THz and 82.5% at 0.81THz.

Liu, Yu-hang; Li, Jiu-sheng

2012-03-01

335

Method for rapid multidiameter single-fiber reflectance and fluorescence spectroscopy through a fiber bundle  

NASA Astrophysics Data System (ADS)

We have recently demonstrated a means for quantifying the absorption and scattering properties of biological tissue through multidiameter single-fiber reflectance (MDSFR) spectroscopy. These measurements can be used to correct single-fiber fluorescence (SFF) spectra for the influence of optical properties, enabling quantification of intrinsic fluorescence. In our previous work, we have used a series of pinholes to show that selective illumination and light collection using a coherent fiber bundle can simulate a single solid-core optical fiber with variable diameter for the purposes of MDSFR spectroscopy. Here, we describe the construction and validation of a clinical MDSFR/SFF spectroscopy system that avoids the limitations encountered with pinholes and free-space optics. During one measurement, the new system acquires reflectance spectra at the effective diameters of 200, 600, and 1000 ?m, and a fluorescence spectrum at an effective diameter of 1000 ?m. From these spectra, we measure the absolute absorption coefficient, ?a, reduced scattering coefficient, ?'s, phase function parameter, ?, and intrinsic fluorescence, Q?fa, across the measured spectrum. We validate the system using Intralipid- and polystyrene sphere-based scattering phantoms, with and without the addition of the absorber Evans Blue. Finally, we demonstrate the combined MDSFR/SFF of phantoms with varying concentrations of Intralipid and fluorescein, wherein the scattering properties are measured by MDSFR and used to correct the SFF spectrum for accurate quantification of Q?fa.

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

2014-03-01

336

Working Process Development For Weathering Degree Mapping Of Stone Monument Using Reflectance Spectroscopy  

NASA Astrophysics Data System (ADS)

Most stone monuments have been weathered on the field with exposure of rain and wind during hundreds or thousands years. Reflectance spectroscopy can be applied to assess weathering degree of those stone monuments composed of granite which is the most general material of stone monument in Korea. Weathering degree was analyzed by using reflected and transmitted electromagnetic energy based on the theory of reflectance spectroscopy on the surface of rock to identify rock forming minerals using their diagnostic spectral absorption features. This method could be used as an improved nondestructive assessment method compared with conventional subjective and qualitative assessment methods. We tested feasibility of this technique for actual granite stone monuments. Granite is generally composed of quartz, feldspars and micas. Feldspars are changed to clay minerals such as kaolinite and illite after weathering process. Biotite of mica produce iron oxides which induce color changes on surface of rocks. The experiments were conducted using field spectrometer FieldSpec®3 of ASD Inc. and the range of measurement was form 350µm to 2500µm wavelength. Spectral reflectance of weathering products at each measuring point was processed by removing delineated convex hull from raw reflectance curves to exclude background effects and to extract quantitative absorption depths which indicate relative distribution degree of weathering products. We produced deterioration map on the surface of the monument by interpolating absorption depth values of each point with consideration of spatial distribution of measurements. For facilitation of practical uses a chain of working process of this method was designed using whole experimental processes.

Hyun, C.; Park, H.

2008-12-01

337

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

338

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

339

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

340

Portable, Fiber-Based, Diffuse Reflection Spectroscopy (DRS) Systems for Estimating Tissue Optical Properties  

PubMed Central

Steady-state diffuse reflection spectroscopy is a well-studied optical technique that can provide a noninvasive and quantitative method for characterizing the absorption and scattering properties of biological tissues. Here, we compare three fiber-based diffuse reflection spectroscopy systems that were assembled to create a light-weight, portable, and robust optical spectrometer that could be easily translated for repeated and reliable use in mobile settings. The three systems were built using a broadband light source and a compact, commercially available spectrograph. We tested two different light sources and two spectrographs (manufactured by two different vendors). The assembled systems were characterized by their signal-to-noise ratios, the source-intensity drifts, and detector linearity. We quantified the performance of these instruments in extracting optical properties from diffuse reflectance spectra in tissue-mimicking liquid phantoms with well-controlled optical absorption and scattering coefficients. We show that all assembled systems were able to extract the optical absorption and scattering properties with errors less than 10%, while providing greater than ten-fold decrease in footprint and cost (relative to a previously well-characterized and widely used commercial system). Finally, we demonstrate the use of these small systems to measure optical biomarkers in vivo in a small-animal model cancer therapy study. We show that optical measurements from the simple portable system provide estimates of tumor oxygen saturation similar to those detected using the commercial system in murine tumor models of head and neck cancer. PMID:21499501

Vishwanath, Karthik; Chang, Kevin; Klein, Daniel; Deng, Yu Feng; Chang, Vivide; Phelps, Janelle E.; Ramanujam, Nimmi

2010-01-01

341

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

342

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

343

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

344

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

345

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

346

Infrared attenuated total reflectance spectroscopy: an innovative strategy for analyzing mineral components in energy relevant systems.  

PubMed

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

347

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

348

Sediment mineralogy based on visible and near-infrared reflectance spectroscopy  

USGS Publications Warehouse

Visible and near-infrared spectroscopy (VNIS) can be used to measure reflectance spectra (wavelength 350-2500 nm) for sediment cores and samples. A local ground-truth calibration of spectral features to mineral percentages is calculated by measuring reflectance spectra for a suite of samples of known mineralogy. This approach has been tested on powders, core plugs and split cores, and we conclude that it works well on all three, unless pore water is present. Initial VNIS studies have concentrated on determination of relative proportions of carbonate, opal, smectite and illite in equatorial Pacific sediments. Shipboard VNIS-based determination of these four components was demonstrated on Ocean Drilling Program Leg 199. ?? The Geological Society of London 2006.

Jarrard, R. D.; Vanden, Berg, M. D.

2006-01-01

349

Characterization of aqueous alcohol solutions in bottles with THz reflection spectroscopy.  

PubMed

We demonstrate a method based on self-referenced THz time-domain spectroscopy for inspection of aqueous liquids, and in particular alcohol solutions, inside closed containers. We demonstrate that it is possible to determine the alcohol content of an aqueous solution, and that liquids can be classified as either harmless or inflammable. The method operates in reflection mode with the result that liquids opaque to THz radiation can be characterized with little influence of the bottle shape. The method works with plastic bottles as well as glass bottles, with absorption of THz radiation by the plastic or the glass being the limiting factor. The reflection mode allows for automatic control of the validity of the measurement. The method will be useful in liquid scanning systems at security checkpoints. PMID:18575495

Jepsen, Peter U; Jensen, Jens K; Møller, Uffe

2008-06-23

350

Application of reflectance anisotropy spectroscopy to laser diode growth in MOVPE  

NASA Astrophysics Data System (ADS)

The growth of layer structures for visible and near-infrared laser diodes is investigated in metal-organic vapour phase epitaxy (MOVPE) under production-like conditions using reflectance anisotropy spectroscopy (RAS). For this purpose the dependence of the reflectance anisotropy (RA) signal on doping type and level is studied for AlGaAs and AlGaInP. The growth of complete layer structures can then be fingerprinted by the significant features of the RA spectra. The reproducibility of the growth process is controlled using the RA transients taken with a high time resolution at a fixed photon energy. Additionally, the emission wavelength of a GaAsP quantum well (QW) can be correlated to the RA level during QW growth. Information about buried interfaces can also be gained from the RA transients as demonstrated for AlGaInP laser structures.

Zorn, M.; Weyers, M.

2005-03-01

351

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

352

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

353

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

PubMed Central

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.

2011-01-01

354

Photonic band structures of colloidal crystals measured with angle-resolved reflection spectroscopy.  

PubMed

We acquired angle- and polarization-resolved reflection spectra from a colloidal crystal made of polystyrene spheres along the two perpendicular directions corresponding to the LU and LW directions in the first Brillouin zone of an fcc lattice. Dispersion relations between the reflection peak positions and the wave vectors of the incident light were obtained from the measured spectra and compared with calculated photonic band structures. For the first stop band region in the spectra, the behavior of the reflection peak due to Bragg diffraction agreed with the calculated band structure and revealed some differences induced by the polarization and crystalline orientations. The spectral features observed in the higher energy regions also revealed these differences. In addition, dispersion relationships between the peak positions and the wave vectors were obtained from the results of fitting each spectrum with several Gaussian curves, compared with the calculated photonic band structures. The relationships obtained for the LU direction almost matched the calculated band structure, while the relationships obtained for the LW direction revealed the features of the mixed band structure calculated for the two perpendicular directions. These results indicate that angle- and polarization-resolved reflection spectroscopy has the potential to experimentally analyze the photonic band structures of actual photonic crystals. PMID:17258899

Ishii, Masahiko; Harada, Masashi; Tsukigase, Azusa; Nakamura, Hiroshi

2007-04-15

355

Metal wires for terahertz wave guiding.  

PubMed

Sources and systems for far-infrared or terahertz (1 THz = 10(12) Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal waveguides for microwave radiation, nor dielectric fibres for visible and near-infrared radiation can be used to guide terahertz waves over a long distance, owing to the high loss from the finite conductivity of metals or the high absorption coefficient of dielectric materials in this spectral range. Furthermore, the extensive use of broadband pulses in the terahertz regime imposes an additional constraint of low dispersion, which is necessary for compatibility with spectroscopic applications. Here we show how a simple waveguide, namely a bare metal wire, can be used to transport terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity. As an example of this new waveguiding structure, we demonstrate an endoscope for terahertz pulses. PMID:15549101

Wang, Kanglin; Mittleman, Daniel M

2004-11-18

356

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

357

Reflections  

NSDL National Science Digital Library

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

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

1997-01-01

358

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

PubMed

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

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

2009-12-01

359

Reflectance-difference spectroscopy of mixed arsenic-rich phases of gallium arsenide ,,001... M. J. Begarney,1  

E-print Network

Reflectance-difference spectroscopy of mixed arsenic-rich phases of gallium arsenide ,,001... M. J on the reflectance difference spec- tra of a series of gallium arsenide 001 reconstructions at arsenic coverages. At the same time, gallium atoms are liberated to the surface, disrupting the c(4 4) ordering. At about 1.4 ML

Li, Lian

360

Spatially resolved scattering correlation spectroscopy using a total internal reflection configuration.  

PubMed

In the paper, we present a novel single particle method, named spatially resolved scattering correlation spectroscopy (SRSCS), based on a total internal reflection (TIR) configuration and strong resonance light scattering (RLS) of silver nanoparticles (AgNPs). The principle of SRSCS is similar to fluorescence correlation spectroscopy (FCS), and it is based on measuring the RLS fluctuations in a small volume due to Brownian motion of single nanoparticles. We first established a highly sensitive SRSCS system. In the SRSCS system, a millimeter-scale hole is employed to efficiently separate nanoparticle scattering light from the background reflected beam, and an electron multiplying charge-coupled device (EMCCD) is used as an array detector. The SRSCS system was successfully used for detection and imaging of single AgNPs in solution. Furthermore, we developed the model of SRSCS according to the FCS method and systematically investigated the effects of certain factors such as particle concentration, viscosity of the solution, hardware and software binning and accumulation time on SRSCS measurements using AgNPs as a model sample. A series of calibration experiments were conducted, and the experimental data obtained were in good agreement with the SRSCS model. This new method is multiplexing, spatially resolved, and free of photobleaching and may become a useful method for study on heterogeneous systems, such as the motion of proteins on the cell membrane. PMID:22443085

Liu, Heng; Dong, Chaoqing; Huang, Xiangyi; Ren, Jicun

2012-04-17

361

[Application of near-infrared reflectance spectroscopy to the discrimination of salt tolerance of alfalfa cultivars].  

PubMed

Near infrared reflectance spectroscopy is a new developed method able to analyse the content of specific compound in the detected sample quickly and efficiently, and has been wildly used in many fields such as evaluation of nutrition value of forage, cultivar discrimination and so on. In the present paper a new method was developed for the discrimination of salt tolerance of alfalfa cultivars by Fourier transform near infrared reflectance spectroscopy. Firstly absorbance spectrum generated by Fourier transform near infrared spectrometry was used to classify twenty alfalfa cultivars. These cultivars were obviously clustered into two groups: salt tolerant and salt sensitive, similar to the result, screened by the traditional methods. Based on these results, a discrimination model was built for identification of salt tolerant cultivars. And then, six other cultivars were used to verify the function of the discriminating model. Result showed that the distinguishing rate of 100% was achieved with the performance index of 85.7%. It is concluded that Fourier transform near infrared spectrum is useful for classification and discrimination of salt tolerance of alfalfa cultivars. The method can be applied to estimate salt tolerance of alfalfa cultivars, and works more quickly and efficiently than the traditional screening methods. Application of Fourier transform near infrared spectrum to discriminating salt tolerance of alfalfa cultivars is significant in both academic and technical areas. PMID:19445209

Ren, Wei-Bo; Han, Jian-Guo; Zhang, Yun-Wei; Guo, Hui-Qin

2009-02-01

362

Hybrid bilayer membranes in air and water: infrared spectroscopy and neutron reflectivity studies.  

PubMed Central

In this report we describe the fabrication and characterization of a phospholipid/alkanethiol hybrid bilayer membrane in air. The bilayer is formed by the interaction of phospholipid with the hydrophobic surface of a self-assembled alkanethiol monolayer on gold. We have characterized the resulting hybrid bilayer membrane in air using atomic force microscopy, spectroscopic ellipsometry, and reflection-absorption infrared spectroscopy. These analyses indicate that the phospholipid added is one monolayer thick, is continuous, and exhibits molecular order which is similar to that observed for phospholipid/phospholipid model membranes. The hybrid bilayer prepared in air has also been re-introduced to water and characterized using neutron reflectivity and impedance spectroscopy. Impedance data indicate that when moved from air to water, hybrid bilayers exhibit a dielectric constant and thickness that is essentially equivalent to hybrid bilayers prepared in situ by adding phospholipid vesicles to alkanethiol monolayers in water. Neutron scattering from these samples was collected out to a wave vector transfer of 0.25 A(-1), and provided a sensitivity to changes in total layer thickness on the order of 1-2 A. The data confirm that the acyl chain region of the phospholipid layer is consistent with that observed for phospholipid-phospholipid bilayers, but suggest greater hydration of the phospholipid headgroups of HBMs than has been reported in studies of lipid multilayers. PMID:9512035

Meuse, C W; Krueger, S; Majkrzak, C F; Dura, J A; Fu, J; Connor, J T; Plant, A L

1998-01-01

363

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

364

Nonlinear terahertz superconducting plasmonics  

NASA Astrophysics Data System (ADS)

Nonlinear terahertz (THz) transmission through subwavelength hole array in superconducting niobium nitride (NbN) film is experimentally investigated using intense THz pulses. The good agreement between the measurement and numerical simulations indicates that the field strength dependent transmission mainly arises from the nonlinear properties of the superconducting film. Under weak THz pulses, the transmission peak can be tuned over a frequency range of 145 GHz which is attributed to the high kinetic inductance of 50 nm-thick NbN film. Utilizing the THz pump-THz probe spectroscopy, we study the dynamic process of transmission spectra and demonstrate that the transition time of such superconducting plasmonic device is within 5 ps.

Wu, Jingbo; Zhang, Caihong; Liang, Lanju; Jin, Biaobing; Kawayama, Iwao; Murakami, Hironaru; Kang, Lin; Xu, Weiwei; Wang, Huabing; Chen, Jian; Tonouchi, Masayoshi; Wu, Peiheng

2014-10-01

365

High pressure sample cell for total internal reflection fluorescence spectroscopy at pressures up to 2500 bar  

NASA Astrophysics Data System (ADS)

Total internal reflection fluorescence (TIRF) spectroscopy is a surface sensitive technique that is widely used to characterize the structure and dynamics of molecules at planar liquid-solid interfaces. In particular, biomolecular systems, such as protein adsorbates and lipid membranes can easily be studied by TIRF spectroscopy. Applying pressure to molecular systems offers access to all kinds of volume changes occurring during assembly of molecules, phase transitions, and chemical reactions. So far, most of these volume changes have been characterized in bulk solution, only. Here, we describe the design and performance of a high pressure sample cell that allows for TIRF spectroscopy under high pressures up to 2500 bar (2.5 × 108 Pa), in order to expand the understanding of volume effects from the bulk phase to liquid-solid interfaces. The new sample cell is based on a cylindrical body made of Nimonic 90 alloy and incorporates a pressure transmitting sample cuvette. This cuvette is composed of a fused silica prism and a flexible rubber gasket. It contains the sample solution and ensures a complete separation of the sample from the liquid pressure medium. The sample solution is in contact with the inner wall of the prism forming the interface under study, where fluorescent molecules are immobilized. In this way, the new high pressure TIRF sample cell is very useful for studying any biomolecular layer that can be deposited at a planar water-silica interface. As examples, high pressure TIRF data of adsorbed lysozyme and two phospholipid membranes are presented.

Koo, Juny; Czeslik, Claus

2012-08-01

366

The use of UV-visible reflectance spectroscopy as an objective tool to evaluate pearl quality.  

PubMed

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

2012-07-01

367

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

368

Evaluation of vitamin C content in kiwifruit by diffuse reflectance FT-NIR spectroscopy  

NASA Astrophysics Data System (ADS)

Vitamin C is considered an important nutrition component of fruits, especially of kiwifruit. Traditional destructive method for vitamin C measurement is very complex and fussy. Near Infrared (NIR)spectroscopy is a promising technique for nondestructive measurement of fruit internal qualities, such as soluble solid content (SSC), valid acidity (VA). The objective of this research was to study the potential of NIR diffuse reflectance spectroscopy as a way for nondestructive measurement of vitamin C content in "Qinmei" kiwifruit. NIR spectral data were collected in the spectral range of 800-2500 nm with different combinations of resolution (4 cm-1, 16 cm-1 and 32 cm-1) and scan number (32, 64 and 128). Statistical models were developed using partial least square (PLS) method. The combination with resolution of 4 cm-1 and scan number of 64 gave the best result when all samples were used in calibration sample set. Then two spectral pretreatments multiplicative signal correction (MSC) and standard normal variate (SNV), and three kinds of mathematical treatment of original spectra, first derivative spectra and second derivative spectra were discussed. The PLS model of second derivative spectra using SNV pretreatment turned out better prediction results: correlation coefficient (r) of 0. 93, root mean square error of calibration (RMSEC) of 9.24 mg/100g and root mean square error of prediction (RMSEP) of 10.3 mg/100g. The results of this study showed that NIR diffuse reflectance spectroscopy could be used for kiwifruit vitamin C prediction. The higher the resolution, the better the results, but longer time will be taken, which may not be suitable for on-line use. Therefore, further research still needs to be done.

Fu, Xiaping; Ying, Yibin; Lu, Huishan; Yu, Haiyan; Liu, Yande

2005-11-01

369

Development of transient attenuated total reflectance spectroscopy and investigation of photoinduced kinetics in thin films  

NASA Astrophysics Data System (ADS)

The efficiency of photoconversion systems such as organic photovoltaic cells and photocatalytic water-splitting cells is largely governed by the interfacial charge transfer processes. Understanding the structure-function relationship, specifically at the molecular thin film/transparent conducting oxide interface will allow for engineering these interfaces to promote charge transfer and reduce the rate of charge recombination. Important factors that are hypothesized to influence charge transfer are morphology, chemical characteristics, electronic properties and molecular orientation. As molecules are bound to a transparent conducting oxide or incorporated into a thin film, the local solid-state molecular environment greatly influences the excited state properties of the molecule. Pathways for quenching, radiative and nonradiative decay drastically limit the excited state lifetimes. In order to investigate the photoinduced kinetics of thin films and at interfaces a instrument was developed coupling transient absorbance spectroscopy to attenuated total reflectance spectroscopy. The photoinduced kinetics of a thin film of bacteriorhodopsin was used to evaluate the instrument performance, and it was determined that 1% of a close-packed monolayer could be detected with this geometry. The properties of a molecular thin film/transparent conducting oxide were investigated by tethering zinc porphyrin to ITO. The electrochemical properties were influenced by the functional group of the binding moiety. To improve our understanding of how the solid state molecular environment affects excited states lifetimes, zinc porphyrins were incorporated into mono- and multilayer thin films and measured with transient ATR spectroscopy. Finally, multilayer films related to photocatalytic water-splitting were investigated with the incorporation of inorganic nanosheets. The nanosheets helped to create a stratified assembly for multilayer films, spatially segregating electron donor (palladium porphyrin) and electron acceptor (poly(viologen)) molecules. The role of the nanosheets in the electron transfer between the donor and acceptor was studied by monitoring the triplet state lifetimes of a palladium porphyrin with transient ATR spectroscopy.

Simon, Anne M.

370

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

371

Measuring joint cartilage thickness using reflectance spectroscopy non-invasively and in real-time  

NASA Astrophysics Data System (ADS)

Joint cartilage thickness has been estimated using spatially resolved steady-state reflectance spectroscopy noninvasively and in-real time. The system consists of a miniature UV-VIS spectrometer, a halogen tungsten light source, and an optical fiber probe with six 400 um diameter fibers. The first fiber was used to deliver the light to the cartilage and the other five were used to detect back-reflected diffused light. Distances from the detector fibers to the source fiber were 0.8 mm, 1.6 mm, 2.4 mm, 3.2 mm and 4 mm. Spectra of back-reflected diffused light were taken on 40 bovine patella cartilages. The samples were grouped into four; the first group was the control group with undamaged cartilages, in the 2nd, 3rd and 4th groups cartilage thickness was reduced approximately 25%, 50% and 100%, respectively. A correlation between cartilage thicknesses and hemoglobin absorption of light in the wavelength range of 500 nm- 600 nm for source-detector pairs was found. The proposed system with an optical fiber probe less than 4 mm in diameter has the potential for cartilage thickness assessment through an arthroscopy channel in real-time without damaging the cartilage.

Canpolat, Murat; Denkceken, Tuba; Karagol, Cosar; Aydin, Ahmet T.

2011-03-01

372

Quantitative characterisation of pigment mixtures used in art by fibre-optics diffuse-reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Fibre-optics diffuse reflectance spectroscopy (FORS) was used to characterise pigment mixtures in paints used in art. Measurements are non invasive, without any contact with the sample. The experimental device is portable, therefore measurements can be performed in situ, without moving the work of art under investigation from its conservation place. The protocol was validated thanks to modern gouache paints: 10 pure gouaches were used as references and 27 binary mixtures of these pure gouaches were studied. Reflectance spectra are processed using the Kubelka-Munk theory in order to get scattering and absorption coefficients of the references. Assuming a linear dependance of these optical properties with the pigment volume concentration (PVC) of the components of paint layers, the protocol enables qualitative as well as quantitative interpretation of the reflectance spectra measured on binary mixtures of references. Indeed, for most cases, numerical processing of FORS-measurements performed on a mixture leads to the identification of its components. Besides, once the components are identified, it is possible to compute their respective proportions with an accuracy of 5%.

Dupuis, G.; Menu, M.

2006-06-01

373

Terahertz phase contrast imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging is presently in its exploratory stage. Although plots of time versus terahertz amplitude, and frequency versus terahertz magnitude are some of the most common ways of analyzing terahertz data, no standard rendering technique has been established. While existing methods are indispensable, improvements to how terahertz data is rendered and analyzed should be explored so that new techniques can complement existing ones and/or provide a means of displaying new information that existing methods cannot. This paper reports on one solution to terahertz imaging: an implementation of a new form of phase contrast imaging, which is based on a well-established technique for optical microscopy. This will provide us with a further way of interpreting information from terahertz imaging systems.

Png, Gretel M.; Mickan, Samuel P.; Rainsford, Tamath J.; Abbott, Derek

2005-02-01

374

Multiband terahertz metamaterial absorber  

NASA Astrophysics Data System (ADS)

This paper reports the design of a multiband metamaterial (MM) absorber in the terahertz region. Theoretical and simulated results show that the absorber has four distinct and strong absorption points at 1.69, 2.76, 3.41 and 5.06 THz, which are consistent with ‘fingerprints’ of some explosive materials. The retrieved material parameters show that the impedance of MM could be tuned to match approximately the impedance of the free space to minimise the reflectance at absorption frequencies and large power loss exists at absorption frequencies. The distribution of the power loss indicates that the absorber is an excellent electromagnetic wave collector: the wave is first trapped and reinforced in certain specific locations and then consumed. This multiband absorber has applications in the detection of explosives and materials characterisation.

Gu, Chao; Qu, Shao-Bo; Pei, Zhi-Bin; Xu, Zhuo; Liu, Jia; Gu, Wei

2011-01-01

375

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

376

Broadband graphene terahertz modulators enabled by intraband transitions.  

PubMed

Terahertz technology promises myriad applications including imaging, spectroscopy and communications. However, one major bottleneck at present for advancing this field is the lack of efficient devices to manipulate the terahertz electromagnetic waves. Here we demonstrate that exceptionally efficient broadband modulation of terahertz waves at room temperature can be realized using graphene with extremely low intrinsic signal attenuation. We experimentally achieved more than 2.5 times superior modulation than prior broadband intensity modulators, which is also the first demonstrated graphene-based device enabled solely by intraband transitions. The unique advantages of graphene in comparison to conventional semiconductors are the ease of integration and the extraordinary transport properties of holes, which are as good as those of electrons owing to the symmetric conical band structure of graphene. Given recent progress in graphene-based terahertz emitters and detectors, graphene may offer some interesting solutions for terahertz technologies. PMID:22510685

Sensale-Rodriguez, Berardi; Yan, Rusen; Kelly, Michelle M; Fang, Tian; Tahy, Kristof; Hwang, Wan Sik; Jena, Debdeep; Liu, Lei; Xing, Huili Grace

2012-01-01

377

Quantitative assessment of hydrocarbon contamination in soil using reflectance spectroscopy: a "multipath" approach.  

PubMed

Petroleum hydrocarbons are contaminants of great significance. The commonly used analytic method for assessing total petroleum hydrocarbons (TPH) in soil samples is based on extraction with 1,1,2-Trichlorotrifluoroethane (Freon 113), a substance prohibited to use by the Environmental Protection Agency. During the past 20 years, a new quantitative methodology that uses the reflected radiation of solids has been widely adopted. By using this approach, the reflectance radiation across the visible, near infrared-shortwave infrared region (400-2500 nm) is modeled against constituents determined using traditional analytic chemistry methods and then used to predict unknown samples. This technology is environmentally friendly and permits rapid and cost-effective measurements of large numbers of samples. Thus, this method dramatically reduces chemical analytical costs and secondary pollution, enabling a new dimension of environmental monitoring. In this study we adapted this approach and developed effective steps in which hydrocarbon contamination in soils can be determined rapidly, accurately, and cost effectively solely from reflectance spectroscopy. Artificial contaminated samples were analyzed chemically and spectrally to form a database of five soils contaminated with three types of petroleum hydrocarbons (PHCs), creating 15 datasets of 48 samples each at contamination levels of 50-5000 wt% ppm (parts per million). A brute force preprocessing approach was used by combining eight different preprocessing techniques with all possible datasets, resulting in 120 different mutations for each dataset. The brute force was done based on an innovative computing system developed for this study. A new parameter for evaluating model performance scoring (MPS) is proposed based on a combination of several common statistical parameters. The effect of dividing the data into training validation and test sets on modeling accuracy is also discussed. The results of this study clearly show that predicting TPH levels at low concentrations in selected soils at high precision levels is viable. Dividing a dataset into training, validation, and test groups affects the modeling process, and different preprocessing methods, alone or in combination, need to be selected based on soil type and PHC type. MPS was found to be a better parameter for selecting the best performing model than ratio of prediction to deviation, yielding models with the same performance but less complicated and more stable. The use of the "all possibilities" system proved to be mandatory for efficient optimal modeling of reflectance spectroscopy data. PMID:24160885

Schwartz, Guy; Ben-Dor, Eyal; Eshel, Gil

2013-11-01

378

Terahertz surface plasmon polariton generation with metallic gratings and silicon prisms  

Microsoft Academic Search

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

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

2005-01-01

379

Reflection-Image-Spectroscopy (RIS) of the South American subduction zone  

NASA Astrophysics Data System (ADS)

A new method for extracting additional information from deep seismic reflection images will be presented in this paper. In complicated evironments it is not always possible to deliver one uniquely valid seismic image. Instead, the image will differ significantly when focusing over different frequency ranges. For example enhanced concentrations of scatterers may be masked in one frequency band and become visible in another frequency band. We therefore apply 3D prestack Kirchhoff depth migration to data containing the full frequency range on one hand and different narrow frequency ranges on the other hand. We call this approach "Reflection Image Spectroscopy" (RIS). It provides frequency dependent images which enable for instance the characterization of the medium in terms of scatterer concentration and length scale. Furthermore, the analysis of these images allows to differentiate between small-scale structures in the high-frequency band and large-scale structures in the low-frequency band. This technique was applied to an onshore deep seismic reflection line (ANCORP96) across the Chilean subduction one. The dominant features in the full-frequency image are the mid-crustal Quebrada Blanca Bright Spot (QBBS) and the subducted oceanic crust (Nazca reflector). The latter appears as a thick reflector with no further interpretable internal structure. However, the narrow-frequency images yield more information (see figure below). At a depth of 70 km the Nazca reflector changes its appearance. The clearly separated double reflection zone continues downward but a wedge-shaped body attached to its top can be resolved. We interpret this body as a possible fluid trap above the slab. Serpentinization within this part of the mantle wedge may lead to the increased reflectivity. Further up towards the QBBS a strongly heterogeneous zone can be observed. This zone coincides with a tomographic low-velocity anomaly and can be explained as the location of possible fluid ascend paths, eventually along pre-existing faults. The QBBS therefore seems to be directly linked to the downgoing plate. Another seismic reflection line (PRECORP95) in that area shows similar features and supports our interpretations.

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

2004-12-01

380

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

381

[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

382

Point-contact Andreev-reflection spectroscopy in anisotropic superconductors: The importance of directionality (Review Article)  

NASA Astrophysics Data System (ADS)

Point-contact Andreev-reflection spectroscopy (PCARS) has demonstrated to be one of the most effective experimental tools for the investigation of fundamental properties of superconductors such as the superconducting gap and the electron-phonon (or, more generally, electron-boson) coupling. By reviewing relevant examples reported in literature and presenting new results, in this paper we show that when the direction of the interface with respect to the crystallographic axes can be controlled (as in single crystals and epitaxial films) PCARS can provide invaluable information about the anisotropy of the pairing wavefunction or—in the case of multiband superconductors—on the number, amplitude and symmetry of the energy gaps. Moreover, the analysis of PCARS results within a suitable 3D generalization of the BTK model allows obtaining qualitative information about the topology of the Fermi surface.

Daghero, D.; Tortello, M.; Pecchio, P.; Stepanov, V. A.; Gonnelli, R. S.

2013-03-01

383

Reflection electron energy loss spectroscopy of keV bombarded polystyrene at high ion fluences  

NASA Astrophysics Data System (ADS)

Reflection Electron Energy Loss Spectroscopy (REELS) is used to characterize the surface of thin films of polystyrene bombarded with keV ion beams in the fluence range 1 × 10 14-1 × 10 16 ions/cm 2. The characteristic features of REELS spectra of irradiated samples are in agreement with the formation of a hydrogenated amorphous carbon phase. The bulk plasmon shift and the inelastic scattering increase in the low-energy range of REELS spectra showed that the final structure is correlated to the total ion energy loss ( St) and to the predominant elastic or inelastic stopping regime. In particular, samples irradiated at a high St an predominant elastic regime show a higher film density and a higher valence electron density with respect to those irradiated at a low St and a predominant inelastic regime.

Marletta, Giovanni; Licciardello, Antonino; Calcagno, Lucia; Foti, Gaetano

1989-02-01

384

Strategies for Detecting Organic Liquids on Soils Using Mid-Infrared Reflection Spectroscopy  

SciTech Connect

Stand-off monitoring for chemical spills can provide timely information for clean-up efforts and mid-infrared reflection-absorption spectroscopy is one approach being investigated. Anomaly and target detection strategies were examined for detection of four different low-volatility organic liquids on two different soil types. Several preprocessing and signal weighting strategies were studied. Anomaly detection for C?H bands was very good using second derivative preprocessing and provided similar performance to target detection approaches such as generalized least squares (GLS) and partial least squares (PLS) with detections at soil loads of approximately 0.6 to 1.5 mg/cm2. Good performance was also found for detection of P=O, O–H and C=O bands but the optimal strategy varied. The simplicity and generality of anomaly detection is attractive, however target detection provides more capability for classification.

Gallagher, Neal B.; Gassman, Paul L.; Blake, Thomas A.

2008-08-01

385

Strategies for detecting organic liquids on soils using mid-infrared reflection spectroscopy.  

PubMed

Stand-off monitoring for chemical spills can provide timely information for cleanup efforts, and mid-infrared reflection spectroscopy is one approach being investigated for spill detection. Using laboratory data, anomaly and target detection strategies were examined for the detection of four different low-volatility organic liquids on two different soil types. Several preprocessing and signal-weighting strategies were studied. Anomaly detection for C-H bands was good using second-derivative preprocessing and provided similar performance to that of target detection approaches such as generalized least-squares and partial least-squares, with detections at soil loads of approximately 3-6 microg/cm2 a real dosage. Good performance was also found for the detection of P=O, O-H, and C=O stretching vibrational modes, but the optimal strategy varied. The simplicity and generality of anomaly detection is attractive; however, target detection provides more capability for classification. PMID:18754496

Gallagher, Neal B; Gassman, Paul L; Blake, Thomas A

2008-08-01

386

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

387

Influence of plasmons on terahertz conductivity measurements  

NASA Astrophysics Data System (ADS)

Time-domain terahertz spectroscopy allows measuring the complex conductivity spectrum of materials at frequencies on the order of 1 THz. Typically, terahertz (THz) studies produce conductivity spectra that are different from those predicted by the classical Drude model, especially in nanostructured materials. We claim that plasmon resonances in particles that are small compared to the THz wavelength cause these deviations. This is supported by measurements on photoexcited silicon, in bulk as well as in micron-sized particles. In the latter, the behavior is vastly different and strongly dependent on charge carrier concentration.

Nienhuys, Han-Kwang; Sundström, Villy

2005-07-01

388

¹³C magnetic resonance spectroscopy detection of changes in serine isotopomers reflects changes in mitochondrial redox status.  

PubMed

The glycine cleavage system (GCS), the major pathway of glycine catabolism in liver, is found only in the mitochondria matrix and is regulated by the oxidized nicotinamide adenine dinucleotide (NAD(+) )/reduced nicotinamide adenine dinucleotide (NADH) ratio. In conjunction with serine hydroxymethyltransferase, glycine forms the 1 and 2 positions of serine, while the 3 position is formed exclusively by GCS. Therefore, we sought to exploit this pathway to show that quantitative measurements of serine isotopomers in liver can be used to monitor the NAD(+) /NADH ratio using (13) C NMR spectroscopy. Rat hepatocytes were treated with modulators of GCS activity followed by addition of 2-(13) C-glycine, and the changes in the proportions of newly synthesized serine isotopomers were compared to controls. Cysteamine, a competitive inhibitor of GCS, prevented formation of mitochondrial 3-(13) C-serine and 2,3-(13) C-serine isotopomers while reducing 2-(13) C-serine by 55%, demonstrating that ca. 20% of glycine-derived serine is produced in the cytosol. Glucagon, which activates GCS activity, and the mitochondrial uncoupler carbonyl cyanide-3-chlorophenylhydrazone both increased serine isotopomers, whereas rotenone, an inhibitor of complex I, had the opposite effect. These results demonstrate that (13) C magnetic resonance spectroscopy monitoring of the formation of serine isotopomers in isolated rat hepatocytes given 2-(13) C-glycine reflects the changes of mitochondrial redox status. PMID:22190282

Johnson, C Bryce; Tikunov, Andrey P; Lee, Haakil; Wolak, Justyna E; Pediaditakis, Peter; Romney, Doug A; Holmuhamedov, Ekhson; Gamcsik, Michael P; Macdonald, Jeffrey M

2012-09-01

389

Near infrared reflectance spectroscopy for the fast identification of PVC-based films  

E-print Network

First published as an Advance Article on the web 19th June 2001 Near infrared (NIR) reflectance spectroscopy was used to develop a non-destructive and rapid qualitative method for the analysis of plastic films used by the pharmaceutical industry for blistering. Three types of films were investigated: 250 mm PVC [poly(vinyl chloride)] films, 250 mm PVC films coated with 40 g m 22 of PVDC [poly(vinylidene dichloride)] and 250 mm PVC films coated with 5 g m 22 of TE (Thermoelast) and 90 g m 22 of PVDC. Three analyses were carried out using different pre-treatment options and a PLS (partial least squares) algorithm. Each analysis was aimed at identifying one type of film and rejecting all types of false sample (different thickness, colour or layer). True and false samples from four plastics manufacturers were included in the calibration sets in order to obtain robust methods that were suitable regardless of the supplier. Specificity was demonstrated by testing validation sets against the methods. The tests showed 0 % of type I (false negative identification) and 1 % of type II errors (false positive identification) for the PVC method, 13 and 3%, respectively, for the PVC–PVDC method and no error for the PVC–TE–PVDC method. Type II errors, mostly due to the slight sensitivity of the methods to film thickness, are easily corrected by simple thickness measurements. This study demonstrates that NIR spectroscopy is an excellent tool for the identification of PVC-based films. The

Magali Laasonen; A Jukka Rantanen; B Tuulikki Harmia-pulkkinen; C Erik Michiels

2001-01-01

390

In-situ FTIR reflection spectroscopy for the semiconductor electrolyte interfaces  

NASA Astrophysics Data System (ADS)

Polarization modulation fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS) and subtractively normalized interfacial fourier transform infrared spectroscopy (SNIF-TIRS) have been applied to the studies of adsorption of ions and neutral molecules on p-silicon and p-gallium phosphide electrodes in aqueous as well as non-aqueous solutions. The potential and concentration dependence of adsorption were observed. Thiourea is adsorbed on silicon through the sulfur atom and adsorption increases in the anodic direction. Thiourea adsorption on silicon follows a Temkin type isotherm and the free energy adsorption was calculated to be - 5.63 kJ/mole. Acetate in aqueous medium is adsorbed as neutral acetic acid molecule on silicon. The potential dependence of adsorption passes through a maximum which lies close to the potential of zero charge. The tetraethylammonium ion in acetonitrile is adsorbed according to a Langmuir isotherm. Acetonitrile is adsorbed strongly on gallium phosphide when used as a solvent for sodium acetate at cathodic potentials. At anodic potentials adsorbed acetonitrile is replaced by acetate ions. Adsorption of acetate ion starts at potentials cathodic to the potential of zero charge, due to specific adsorption. Ammonium ion adsorption on gallium phosphide occurs through two hydrogen atoms and the other two hydrogen atoms project towards the solution. Two peaks corresponding to different N-H deformation vibrations are observed at 1560 and 1700 cm -1. At sufficiently cathodic potentials, adsorbed ammonium ions are reduced.

Chandrasekaran, K.; Bockris, J. O'M.

1986-10-01

391

Early detection of cell activation events by means of attenuated total reflection Fourier transform infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Activation of Jurkat T-cells in culture following treatment with anti-CD3 (Cluster of Differentiation 3) antibody is detectable by interrogating the treated T-cells using the Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy technique. Cell activation was detected within 75 min after the cells encountered specific immunoglobulin molecules. Spectral markers noted following ligation of the CD3 receptor with anti CD3 antibody provides proof-of-concept that ATR-FTIR spectroscopy is a sensitive measure of molecular events subsequent to cells interacting with anti-CD3 Immunoglobulin G. The resultant ligation of the CD3 receptor results in the initiation of well defined, specific signaling pathways that parallel the measurable molecular events detected using ATR-FTIR. Paired t-test with post-hoc Bonferroni corrections for multiple comparisons has resulted in the identification of statistically significant spectral markers (p < 0.02) at 1367 and 1358 cm-1. Together, these data demonstrate that early treatment-specific cellular events can be measured by ATR-FTIR and that this technique can be used to identify specific agents via the responses of the cell biosensor at different time points postexposure.

Titus, Jitto; Filfili, Chadi; Hilliard, Julia K.; Ward, John A.; Unil Perera, A. G.

2014-06-01

392

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

393

Soil discrimination using diffuse reflectance Vis-NIR spectroscopy in a local toposequence  

NASA Astrophysics Data System (ADS)

Vis-NIR spectroscopy is nowadays presented as a possible routine method for soil sample analysis. However, there is still no consensus on which is the best multivariate statistical method to use. We propose to use principal component analysis to complete the spectral data treatment. The soil samples came from a pedological cover made up of red-yellow Latosols: 88 samples of 11 soil profiles on four toposequences were collected; clay, organic matter, silica, iron, aluminum and titanium total contents were determined; the contents of goethite, hematite, gibbsite, and kaolinite were calculated. Diffuse reflectance Vis-NIR spectroscopy at wavelengths from 400 to 2400 nm combined with principal component analysis (PCA) was sufficiently sensitive to discriminate different Latosols. Wavelengths of 700 nm and 2200 to 2300 nm were influenced by content ratios of organic matter and iron oxides (700 nm), and kaolinite and gibbsite absorption (2200 and 2300 nm). The spectral responses were affected not only by the content of these constituents, but also by the composition of the minerals, so that the same class of Latosol may have different or similar spectral responses. The role of microaggregation is discussed.

Oliveira, José Francirlei; Brossard, Michel; Vendrame, Pedro Rodolfo Siqueira; Mayi, Stanislas, III; Corazza, Edemar Joaquim; Marchão, Robélio Leandro; Guimarães, Maria de Fátima

2013-11-01

394

High pressure sample cell for total internal reflection fluorescence spectroscopy at pressures up to 2500 bar.  

PubMed

Total internal reflection fluorescence (TIRF) spectroscopy is a surface sensitive technique that is widely used to characterize the structure and dynamics of molecules at planar liquid-solid interfaces. In particular, biomolecular systems, such as protein adsorbates and lipid membranes can easily be studied by TIRF spectroscopy. Applying pressure to molecular systems offers access to all kinds of volume changes occurring during assembly of molecules, phase transitions, and chemical reactions. So far, most of these volume changes have been characterized in bulk solution, only. Here, we describe the design and performance of a high pressure sample cell that allows for TIRF spectroscopy under high pressures up to 2500 bar (2.5 × 10(8) Pa), in order to expand the understanding of volume effects from the bulk phase to liquid-solid interfaces. The new sample cell is based on a cylindrical body made of Nimonic 90 alloy and incorporates a pressure transmitting sample cuvette. This cuvette is composed of a fused silica prism and a flexible rubber gasket. It contains the sample solution and ensures a complete separation of the sample from the liquid pressure medium. The sample solution is in contact with the inner wall of the prism forming the interface under study, where fluorescent molecules are immobilized. In this way, the new high pressure TIRF sample cell is very useful for studying any biomolecular layer that can be deposited at a planar water-silica interface. As examples, high pressure TIRF data of adsorbed lysozyme and two phospholipid membranes are presented. PMID:22938334

Koo, Juny; Czeslik, Claus

2012-08-01

395

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

396

[Rapid quantitative analysis of hydrocarbon composition of furfural extract oils using attenuated total reflection infrared spectroscopy].  

PubMed

A set of rapid analysis system for hydrocarbon composition of heavy oils was designed using attenuated total reflection FTIR spectrometer and chemometrics to determine the hydrocarbon composition of furfural extract oils. Sixty two extract oil samples were collected and their saturates and aromatics content data were determined according to the standard NB/SH/T0509-2010, then the total contents of resins plus asphaltenes were calculated by the subtraction method in the percentage of weight. Based on the partial least squares (PLS), calibration models for saturates, aromatics, and resin+asphaltene contents were established using attenuated total reflection FTIR spectroscopy, with their SEC, 1.43%, 0.91% and 1.61%, SEP, 1.56%, 1.24% and 1.81%, respectively, meeting the accuracy and repeatability required for the standard. Compared to the present standard method, the efficiency of hydrocarbon composition analysis for furfural extract oils is significantly improved by the new method which is rapid and simple. The system could also be used for other heavy oil analysis, with excellent extension and application foreground. PMID:25269288

Li, Na; Yuan, Hong-Fu; Hu, Ai-Qin; Liu, Wei; Song, Chun-Feng; Li, Xiao-Yu; Song, Yi-Chang; He, Qi-Jun; Liu, Sha; Xu, Xiao-Xuan

2014-07-01

397

Perfect terahertz absorber using fishnet based metafilm  

Microsoft Academic Search

We present a perfect terahertz (THz) absorber working for a broad-angle of incidence. The two fold symmetry of rectangular fishnet structure allows either complete absorption or mirror like reflection depending on the polarization of incident the THz beam. Metamaterials enable the ability to control the electromagnetic wave in a unique fashion by designing the permittivity or permeability of composite materials

Abul Kalam Azad; Dmitry Yu Shchegolkov; Houtong Chen; Antoinette Taylor; E I Smirnova; John F O Hara

2009-01-01

398

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

Microsoft Academic Search

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

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

399

Terahertz wave filter based on photonic crystal  

NASA Astrophysics Data System (ADS)

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

Liu, Yu-hang; Li, Jiu-sheng

2011-11-01

400

Terahertz wave filter based on photonic crystal  

NASA Astrophysics Data System (ADS)

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

Liu, Yu-hang; Li, Jiu-sheng

2012-03-01

401

Influence of the Electron-Cation Interaction on Electron Mobility in Dye-Sensitized ZnO and TiO2 Nanocrystals: A Study Using Ultrafast Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

Charge transport and recombination in nanostructured semiconductors are poorly understood key processes in dye-sensitized solar cells. We have employed time-resolved spectroscopies in the terahertz and visible spectral regions supplemented with Monte Carlo simulations to obtain unique information on these processes. Our results show that charge transport in the active solar cell material can be very different from that in nonsensitized semiconductors, due to strong electrostatic interaction between injected electrons and dye cations at the surface of the semiconductor nanoparticle. For ZnO, this leads to formation of an electron-cation complex which causes fast charge recombination and dramatically decreases the electron mobility even after the dissociation of the complex. Sensitized TiO2 does not suffer from this problem due to its high permittivity efficiently screening the charges.

N?mec, H.; Rochford, J.; Taratula, O.; Galoppini, E.; Kužel, P.; Polívka, T.; Yartsev, A.; Sundström, V.

2010-05-01

402

Terahertz Physics  

NASA Astrophysics Data System (ADS)

1. Introduction; Part I. Basics: 2. Oscillations; 3. Combining oscillations; 4. Light; 5. Matter; 6. Interaction of light and matter; Part II. Components: 7. Sources; 8. Optics; 9. Detectors; Part III. Applications: 10. Spectroscopy; 11. Imaging; Glossary; Appendices; Index.

Lewis, R. A.

2013-01-01

403

Terahertz conductivity in nanoscaled systems: effective medium theory aspects  

NASA Astrophysics Data System (ADS)

Ultrafast photoconductivity and charge carrier transport in nanostructured semiconductors is poorly understood on the microscopic level in many systems. The terahertz spectroscopy constitutes a suitable method to probe the nanoscopic motion of charges with a sub-picosecond time resolution and without the need to deposit electrical contacts. However, straightforward fitting of the raw terahertz conductivity spectra by the Drude-Smith model, which is abundantly used in the literature, has not lead to a significant advance in an in-depth understanding of these phenomena. This is mainly because of the depolarization fields which build up in any inhomogeneous system. On the one hand, these fields reflect the sample morphology and our understanding of each particular system may provide new information about e.g. the nanostructure connectivity; on the other hand, the effect of unknown depolarization fields can hide or distort fingerprints of the nanoscopic transport. In this paper we provide a general analytical description of the photoconductivity and transient transmission spectra, where the effects of depolarization fields are systematically disentangled from the local carrier response function for both percolated and non-percolated samples. Application of our formula to the retrieval of the carrier response function may help significantly in uncovering the nature of charge carrier transport at the nanoscale level in quite arbitrary nanostructured systems.

Kužel, P.; N?mec, H.

2014-09-01

404

Simulation and experiment of terahertz stand-off detection  

NASA Astrophysics Data System (ADS)

Terahertz (THz) spectroscopy is a promising technique for the stand-off detection and characterization of hidden objects. The THz band is particularly well suited firstly because THz radiation penetrates many dielectrics like clothes and secondly because many potentially hazardous substances have characteristic signatures in the THz spectral region. In order to utilize the full potential of THz radiation for detecting possible hazards and recognizing characteristic signatures, disturbing influences must be accounted for. We have performed experiments and simulations in order to investigate the limits of terahertz stand-off detection. A special emphasis is paid on humidity in ambient air and properties of the sample like surface roughness, alignment and interfaces. Water vapor absorption strongly affects the THz spectra. Since the absorption lines are strong and narrow, the calculation must be precise. We have checked various models well-known in meteorology covering the infrared and the microwave region of the electromagnetic spectrum. By extending the models into the THz region, an accurate description of the measured spectral absorption is achieved. In our studies transmission spectra for different substances were tested. In a reflection scheme metallized sandpaper of various grit sizes was used to determine the influences of different surface properties. Further measurements were performed for different tilt angles to analyze the influence of the surface roughness. We are currently creating a look-up table to show which parts of the THz spectrum can be used for THz stand-off detection.

Wohnsiedler, Sabine; Theuer, Michael; Herrmann, Michael; Islam, Shany; Jonuscheit, Joachim; Beigang, René; Hase, Frank

2009-02-01

405

Integrated heterodyne terahertz transceiver  

DOEpatents

A heterodyne terahertz transceiver comprises a quantum cascade laser that is integrated on-chip with a Schottky diode mixer. An antenna connected to the Schottky diode receives a terahertz signal. The quantum cascade laser couples terahertz local oscillator power to the Schottky diode to mix with the received terahertz signal to provide an intermediate frequency output signal. The fully integrated transceiver optimizes power efficiency, sensitivity, compactness, and reliability. The transceiver can be used in compact, fieldable systems covering a wide variety of deployable applications not possible with existing technology.

Lee, Mark (Albuquerque, NM); Wanke, Michael C. (Albuquerque, NM)

2009-06-23

406

Integrated heterodyne terahertz transceiver  

DOEpatents

A heterodyne terahertz transceiver comprises a quantum cascade laser that is integrated on-chip with a Schottky diode mixer. A terahertz signal can be received by an antenna connected to the mixer, an end facet or sidewall of the laser, or through a separate active section that can amplify the incident signal. The quantum cascade laser couples terahertz local oscillator power to the Schottky diode to mix with the received terahertz signal to provide an intermediate frequency output signal. The fully integrated transceiver optimizes power efficiency, sensitivity, compactness, and reliability. The transceiver can be used in compact, fieldable systems covering a wide variety of deployable applications not possible with existing technology.

Wanke, Michael C. (Albuquerque, NM); Lee, Mark (Albuquerque, NM); Nordquist, Christopher D. (Albuquerque, NM); Cich, Michael J. (Albuquerque, NM)

2012-09-25

407

Quasi-DC Terahertz Electrical Conductivity Measurements of Dense Aluminum Plasma  

Microsoft Academic Search

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

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

2007-01-01

408

influences of real-world conditions on terahertz stand-off detection: Simulation and experiment  

Microsoft Academic Search

Terahertz spectroscopy has become a well-established tool under laboratory conditions but terahertz stand-off detection in the real world is hampered by a number of influences related to the environment and the sample properties such as air humidity, surface roughness and angle of detection. A terahertz stand-off system must be calibrated in order to account for these influences. We have performed

S. Wohnsiedler; M. Theuer; M. Herrmann; S. Islam; J. Jonuscheit; R. Beigang; F. Hase

2008-01-01

409

Terahertz spectroscopy of hydrogen sulfide  

NASA Astrophysics Data System (ADS)

Pure rotational transitions of hydrogen sulfide (H2S) in its ground and first excited vibrational states have been recorded at room temperature. The spectrum comprises an average of 1020 scans at 0.005 cm-1 resolution recorded in the region 45-360 cm-1 (1.4 to 10.5 THz) with a globar continuum source using a Fourier transform spectrometer located at the AILES beamline of the SOLEIL synchrotron. Over 2400 rotational lines have been detected belonging to ground vibrational state transitions of the four isotopologues H232S, H233S, H234S, and H236S observed in natural abundance. 65% of these lines are recorded and assigned for the first time, sampling levels as high as J=26 and Ka=17 for H232S. 320 pure rotational transitions of H232S in its first excited bending vibrational state are recorded and analysed for the first time and 86 transitions for H234S, where some of these transitions belong to new experimental energy levels. Rotational constants have been fitted for all the isotopologues in both vibrational states using a standard effective Hamiltonian approach. Comprehensive comparisons are made with previously available data as well as the data available in HITRAN, CDMS, and JPL databases. The 91 transitions assigned to H236S give the first proper characterization of its pure rotational spectrum.

Azzam, Ala'a. A. A.; Yurchenko, Sergei N.; Tennyson, Jonathan; Martin-Drumel, Marie-Aline; Pirali, Olivier

2013-11-01

410

Terahertz spectroscopy of isotopic acrylonitrile  

NASA Astrophysics Data System (ADS)

Rotational spectra of four isotopically enriched, singly substituted species of acrylonitrile have been studied up to 1.2 THz. Extensive analysis of the spectra recorded for H 213C dbnd CHCN, H 2C dbnd CH 13CN, H 2C dbnd CHC 15N, and H 2C dbnd CDCN, revealed the presence of the same characteristic perturbations between the ground state and the v11 = 1 excited vibrational state, that have recently been identified in the parent molecule. For this reason transitions in v11 = 1 have also been assigned in each of the four isotopic species and a coupled state analysis of g.s. and v11 = 1 was performed on a total of around 3000 lines for each species. The derived precise values of E( v11 = 1) are found to be consistent with estimates from anharmonic force field calculations. In addition, transitions for six new doubly substituted isotopic species of acrylonitrile, H 213C dbnd 13CHCN, H 213C dbnd CH 13CN, H 2C dbnd 13CH 13CN, H 213C dbnd CHC 15N, H 2C dbnd 13CHC 15N, and H 2C dbnd CH 13C 15N, have been assigned, and their ground state spectroscopic constants have been determined. Rotational constants for all known isotopic species of acrylonitrile have been combined with ab initio calculation of vibration-rotation constants in the first evaluation of the reSE geometry of this molecule.

Kra?nicki, Adam; Kisiel, Zbigniew; Drouin, Brian J.; Pearson, John C.

2011-12-01

411

Photoinduced phase transition in tetrathiafulvalene- p -chloranil observed in femtosecond reflection spectroscopy  

NASA Astrophysics Data System (ADS)

Photoinduced transitions from ionic (I) to neutral (N) and neutral (N) to ionic (I) phases in an organic charge transfer (CT) complex, tetrathiafulvalene- p -chloranil (TTF-CA), were investigated by femtosecond pump-probe reflection spectroscopy. Transient reflectivity changes of the intramolecular transition band of TTF sensitive to the degree of CT between a donor molecule of TTF and an acceptor molecule of CA are measured as a function of excitation energy, excitation density, and temperature. By adopting the multilayer model for the analysis of the obtained transient reflectivity spectra, we have derived the time characteristics of amounts and spatial distributions of photoinduced N(I) states in the I(N) phase. The results reveal that the I to N(IN) transition induced by the resonant excitation of the CT band at 4K is composed of three processes; (1) formation of a confined one-dimensional (1D) N domain, that is, a sequence of D0A0 pairs, just after the photoexcitation, (2) multiplication of the 1D N domains to the semimacroscopic N states up to 20ps within the absorption depth of the excitation light, and (3) proceeding of the IN transition along the direction normal to the sample surface. At 77K near the NI transition temperature (Tc=81K) , the size of the 1D N domain initially produced is enlarged and its multiplication process is strongly enhanced. When the excitation energy is increased, the initial photoproduct is changed from the confined 1D N domain to the positively and negatively charged N states. The spatial size of the latter is considerably larger than that of the former, indicating that the introduction of charge carriers makes the neighboring I state strongly unstable. The dynamics of the photoinduced N to I(NI) transition has also been investigated. The 1D I domains are initially produced by lights, however, they decay within 20ps even if the density of the I domains is increased. The results demonstrate that there is a clear difference of the dynamics between the photoinduced IN and NI transitions. In these photoinduced transitions, three kinds of coherent oscillations with the period of ˜0.6 , ˜50 , and ˜85ps have been detected on the photoinduced reflectivity changes, which are reasonably assigned to the dynamical dimeric displacements of molecules associated with the spin-Peierls instability, the shock wave driven by the sudden volume change due to the photoinduced transitions, and the oscillation of the NI domain boundary. On the basis of the results, dynamical aspects of the photoinduced IN and NI transitions have been discussed in detail.

Okamoto, H.; Ishige, Y.; Tanaka, S.; Kishida, H.; Iwai, S.; Tokura, Y.

2004-10-01

412

Some aspects of far-infrared spectroscopy of explosive materials  

NASA Astrophysics Data System (ADS)

This paper presents some potentially interesting aspects of spectroscopic transmission measurements of explosive materials in Far-Infrared (Terahertz) range: preparation of the samples, influence of covering by clothes and influence of phlegmatization of explosives (addition an agent to an explosive material to stabilize or desensitize it). Moreover, two commonly used techniques - Far Infrared Fourier Spectroscopy and Time Domain Spectroscopy are presented and compared. We also shown and compared spectra of materials obtained in two Time Domain Spectroscopy reflection configurations: specular (45° incident angle) and stand-off with distance 30 and 40 cm to a sample.

Palka, Norbert; Trzcinski, Tomasz

2011-02-01

413

The clinical effectiveness of reflectance optical spectroscopy for the in vivo diagnosis of oral lesions  

PubMed Central

Optical spectroscopy devices are being developed and tested for the screening and diagnosis of oral precancer and cancer lesions. This study reports a device that uses white light for detection of suspicious lesions and green–amber light at 545?nm that detect tissue vascularity on patients with several suspicious oral lesions. The clinical grading of vascularity was compared to the histological grading of the biopsied lesions using specific biomarkers. Such a device, in the hands of dentists and other health professionals, could greatly increase the number of oral cancerous lesions detected in early phase. The purpose of this study is to correlate the clinical grading of tissue vascularity in several oral suspicious lesions using the Identafi® system with the histological grading of the biopsied lesions using specific vascular markers. Twenty-one patients with various oral lesions were enrolled in the study. The lesions were visualized using Identafi® device with white light illumination, followed by visualization of tissue autofluorescence and tissue reflectance. Tissue biopsied was obtained from the all lesions and both histopathological and immunohistochemical studies using a vascular endothelial biomarker (CD34) were performed on these tissue samples. The clinical vascular grading using the green–amber light at 545?nm and the expression pattern and intensity of staining for CD34 in the different biopsies varied depending on lesions, grading ranged from 1 to 3. The increase in vascularity was observed in abnormal tissues when compared to normal mucosa, but this increase was not limited to carcinoma only as hyperkeratosis and other oral diseases, such as lichen planus, also showed increase in vascularity. Optical spectroscopy is a promising technology for the detection of oral mucosal abnormalities; however, further investigations with a larger population group is required to evaluate the usefulness of these devices in differentiating benign lesions from potentially malignant lesions. PMID:25059250

Messadi, Diana V; Younai, Fariba S; Liu, Hong-Hu; Guo, Gao; Wang, Cun-Yu

2014-01-01

414

The clinical effectiveness of reflectance optical spectroscopy for the in vivo diagnosis of oral lesions.  

PubMed

Optical spectroscopy devices are being developed and tested for the screening and diagnosis of oral precancer and cancer lesions. This study reports a device that uses white light for detection of suspicious lesions and green-amber light at 545?nm that detect tissue vascularity on patients with several suspicious oral lesions. The clinical grading of vascularity was compared to the histological grading of the biopsied lesions using specific biomarkers. Such a device, in the hands of dentists and other health professionals, could greatly increase the number of oral cancerous lesions detected in early phase. The purpose of this study is to correlate the clinical grading of tissue vascularity in several oral suspicious lesions using the Identafi(®) system with the histological grading of the biopsied lesions using specific vascular markers. Twenty-one patients with various oral lesions were enrolled in the study. The lesions were visualized using Identafi(®) device with white light illumination, followed by visualization of tissue autofluorescence and tissue reflectance. Tissue biopsied was obtained from the all lesions and both histopathological and immunohistochemical studies using a vascular endothelial biomarker (CD34) were performed on these tissue samples. The clinical vascular grading using the green-amber light at 545?nm and the expression pattern and intensity of staining for CD34 in the different biopsies varied depending on lesions, grading ranged from 1 to 3. The increase in vascularity was observed in abnormal tissues when compared to normal mucosa, but this increase was not limited to carcinoma only as hyperkeratosis and other oral diseases, such as lichen planus, also showed increase in vascularity. Optical spectroscopy is a promising technology for the detection of oral mucosal abnormalities; however, further investigations with a larger population group is required to evaluate the usefulness of these devices in differentiating benign lesions from potentially malignant lesions. PMID:25059250

Messadi, Diana V; Younai, Fariba S; Liu, Hong-Hu; Guo, Gao; Wang, Cun-Yu

2014-09-01

415

Perfect terahertz absorber using fishnet based metafilm  

SciTech Connect

We present a perfect terahertz (THz) absorber working for a broad-angle of incidence. The two fold symmetry of rectangular fishnet structure allows either complete absorption or mirror like reflection depending on the polarization of incident the THz beam. Metamaterials enable the ability to control the electromagnetic wave in a unique fashion by designing the permittivity or permeability of composite materials with desired values. Although the initial idea of metamaterials was to obtain a negative index medium, however, the evolution of metamaterials (MMs) offers a variety of practically applicable devices for controlling electromagnetic wave such as tunable filters, modulators, phase shifters, compact antenna, absorbers, etc. Terahertz regime, a crucial domain of the electromagnetic wave, is suffering from the scarcity of the efficient devices and might take the advantage of metamaterials. Here, we demonstrate design, fabrication, and characterization of a terahertz absorber based on a simple fishnet metallic film separated from a ground mirror plane by a dielectric spacer. Such absorbers are in particular important for bolometric terahertz detectors, high sensitivity imaging, and terahertz anechoic chambers. Recently, split-ring-resonators (SRR) have been employed for metamaterial-based absorbers at microwave and THz frequencies. The experimental demonstration reveals that such absorbers have absorptivity close to unity at resonance frequencies. However, the downside of these designs is that they all employ resonators of rather complicated shape with many fine parts and so they are not easy to fabricate and are sensitive to distortions.

Azad, Abul Kalam [Los Alamos National Laboratory; Shchegolkov, Dmitry Yu [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; Smirnova, E I [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory

2009-01-01

416

In-situ measurement of epithelial tissue optical properties: Development and implementation of diffuse reflectance spectroscopy techniques  

NASA Astrophysics Data System (ADS)

Cancer is a severe threat to human health. Early detection is considered the best way to increase the chance for survival. While the traditional cancer detection method, biopsy, is invasive, noninvasive optical diagnostic techniques are revolutionizing the way that cancer is diagnosed. Reflectance spectroscopy is one of these optical spectroscopy techniques showing promise as a diagnostic tool for pre-cancer detection. When a neoplasia occurs in tissue, morphologic and biochemical changes happen in the tissue, which in turn results in the change of optical properties and reflectance spectroscopy. Therefore, a pre-cancer can be detected by extracting optical properties from reflectance spectroscopy. This dissertation described the construction of a fiberoptic based reflectance system and the development of a series of modeling studies. This research is aimed at establishing an improved understanding of the optical properties of mucosal tissues by analyzing reflectance signals at different wavelengths. The ultimate goal is to reveal the potential of reflectance-based optical diagnosis of pre-cancer. The research is detailed in Chapter 3 through Chapter 5. Although related with each other, each chapter was designed to become a journal paper ultimately. In Chapter 3, a multi-wavelength, fiberoptic system was constructed, evaluated and implemented to determine internal tissue optical properties at ultraviolet A and visible wavelengths. A condensed Monte Carlo model was deployed to simulate light-tissue interaction and generate spatially distributed reflectance data. These data were used to train an inverse neural network model to extract tissue optical properties from reflectance. Optical properties of porcine mucosal and liver tissues were finally measured. In Chapter 4, the condensed Monte Carlo method was extended so that it can rapidly simulate reflectance from a single illumination-detection fiber thus enabling the calculation of large data sets. The model was implemented to study spectral reflectance changes due to breast cancer. The effect of adding an illumination-detection fiber to a linear array fiber for optical property determination was also evaluated. In Chapter 5, an investigation of extracting the optical properties from two-layer tissues was performed. The relationship between spatially-resolved reflectance distributions and optical properties in two-layer tissue was investigated. Based on all the aforementioned studies, spatially resolved reflectance system coupled with condensed Monte Carlo and neural network models was found to be objective and appear to be sensitive and accurate in quantitatively assessing optical property change of mucosal tissues.

Wang, Quanzeng

417

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

PubMed Central

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

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

2012-01-01

418

Reflection  

NSDL National Science Digital Library

In this activity, students learn that infrared light is reflected in the same manner as visible light. Students align a series of mirrors so that they can turn on a TV with a remote control when the remote is not in a direct line with the TV. As a result of their experiment with reflection, students deduce that infrared light is another form of light and is a part of the electromagnetic spectrum. Section 1 of the activity guide includes teacher notes, information on materials and preparation, student misconceptions and a student pre-test. Each activity section also includes teacher notes, student activity sheets, and answer keys. This activity requires a TV and remote control. It is the third of four activities in Active Astronomy, which are designed to complement instruction on the electromagnetic spectrum, focusing on infrared light.

419

Application of Internal Reflectance Spectroscopy to the Study of Solid Propellants: I. Composite and Double Base Propellants  

Microsoft Academic Search

It is shown that by using Internal Reflectance Spectroscopy the infrared spectra of solid propellants can be obtained with the expenditure of a minimum effort in sample preparation. Applications of this technique as a quality control technique and a method of studying surface charring are discussed.

G. E. SALSER; L. DAUERMAN

1972-01-01

420

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

421

Assessment of condensation of aromatic aldehydes with polyurethane foam for their determination in waters by diffuse reflectance spectroscopy and colorimetry  

Microsoft Academic Search

The new reaction of polyurethane foam (PUF) with different aromatic aldehydes has been investigated. It proceeds with participation of terminal toluidine groups of PUF and yields coloured polymeric Shiff bases which can be used as convenient analytical forms for the determination of aromatic aldehydes by diffuse reflectance spectroscopy. The spectral characteristics of the products have been discussed. The optimal conditions

Vladimir V. Apyari; Stanislava G. Dmitrienko; Yuri A. Zolotov

2009-01-01

422

/II sifu reflection electron energy loss spectroscopy measurements of low temperature surface cleaning for Si molecular beam epitaxy  

E-print Network

/II sifu reflection electron energy loss spectroscopy measurements of low temperature surface temperatures be kept as low as possible. Such exacting requirements also have a significant impact on surface analysis of hydrocarbon desorption from hydrogen terminated Si( 100) surfaces was performed in a silicon

Atwater, Harry

423

Controversy in linearity assumption for reflectivity of metals upon non-equilibrium electron heating revisited with ultrafast broadband spectroscopy  

NASA Astrophysics Data System (ADS)

We discuss the capacity of ultrafast broadband spectroscopy to become a test bed for investigating dynamics of metals driven far from equilibrium by a femtosecond laser pulse. A controversy in conventional description of the reflectivity of metals is looked upon by means of pump-probe white light set-up.

Kaszub, Wawrzyniec; Kubicki, Jacek; Arnaud, Brice; Naskr?cki, Ryszard; Servol, Marina; Cailleau, Hervé; Lorenc, Maciej

2014-08-01

424

Total reflection infrared spectroscopy of water-ice and frozen aqueous NaCl solutions  

SciTech Connect

Liquid-like and liquid water at and near the surface of water-ice and frozen aqueous sodium chloride films were observed using attenuated total reflection infrared spectroscopy (ATR-IR). The concentration of NaCl ranged from 0.0001 to 0.01 M and the temperature varied from the melting point of water down to 256 K. The amount of liquid brine at the interface of the frozen films with the germanium ATR crystal increased with salt concentration and temperature. Experimental spectra are compared to reflection spectra calculated for a simplified morphology of a uniform liquid layer between the germanium crystal and the frozen film. This morphology allows for the amount of liquid observed in an experimental spectrum to be converted to the thickness of a homogenous layer with an equivalent amount of liquid. These equivalent thickness ranges from a nanometer for water-ice at 260 K to 170 nm for 0.01 M NaCl close to the melting point. The amounts of brine observed are over an order of magnitude less than the total liquid predicted by equilibrium thermodynamic models, implying that the vast majority of the liquid fraction of frozen solutions may be found in internal inclusions, grain boundaries, and the like. Thus, the amount