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Sample records for broadband thz spectroscopy

  1. Josephson broadband spectroscopy to 1 THz

    NASA Astrophysics Data System (ADS)

    Edstam, J.; Olsson, H. K.

    1994-05-01

    We demonstrate the operation of a ``Josephson Broadband Spectrometer'' (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.

  2. Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics.

    PubMed

    D'Angelo, Francesco; Mics, Zoltán; Bonn, Mischa; Turchinovich, Dmitry

    2014-05-19

    Terahertz-range dielectric properties of the common polymers low-density polyethylene (LDPE), cyclic olefin/ethylene copolymer (TOPAS®), polyamide-6 (PA6), and polytetrafluoroethylene (PTFE or Teflon®) are characterized in the ultra-broadband frequency window 2-15 THz, using a THz time-domain spectrometer employing air-photonics for the generation and detection of single-cycle sub-50 fs THz transients. The time domain measurements provide direct access to both the absorption and refractive index spectra. The polymers LDPE and TOPAS® demonstrate negligible absorption and spectrally-flat refractive index across the entire spectroscopy window, revealing the high potential of these polymers for applications in THz photonics such as ultra-broadband polymer-based dielectric mirrors, waveguides, and fibers. Resonant high-frequency polar vibrational modes are observed and assigned in polymers PA6 and PTFE, and their dielectric functions in the complete frequency window 2-15 THz are theoretically reproduced. Our results demonstrate the potential of ultra-broadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science.

  3. Broadband THz Spectroscopy of 2D Nanoscale Materials

    NASA Astrophysics Data System (ADS)

    Chen, Lu; Tripathi, Shivendra; Huang, Mengchen; Hsu, Jen-Feng; D'Urso, Brian; Lee, Hyungwoo; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    Two-dimensional (2D) materials such as graphene and transition-metal dichalcogenides (TMDC) have attracted intense research interest in the past decade. Their unique electronic and optical properties offer the promise of novel optoelectronic applications in the terahertz regime. Recently, generation and detection of broadband terahertz (10 THz bandwidth) emission from 10-nm-scale LaAlO3/SrTiO3 nanostructures created by conductive atomic force microscope (c-AFM) lithography has been demonstrated . This unprecedented control of THz emission at 10 nm length scales creates a pathway toward hybrid THz functionality in 2D-material/LaAlO3/SrTiO3 heterostructures. Here we report initial efforts in THz spectroscopy of 2D nanoscale materials with resolution comparable to the dimensions of the nanowire (10 nm). Systems under investigation include graphene, single-layer molybdenum disulfide (MoS2), and tungsten diselenide (WSe2) nanoflakes. 1. Y. Ma, et al., Nano Lett. 13, 2884 (2013). We gratefully acknowledge financial support from the following agencies and grants: AFOSR (FA9550-12-1-0268 (JL, PRI), FA9550-12-1-0342 (CBE)), ONR (N00014-13-1-0806 (JL, CBE), N00014-15-1-2847 (JL)), NSF DMR-1124131 (JL, CBE) and DMR-1234096 (CBE).

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  5. A Study of Electron and Phonon Dynamics by Broadband Two-Dimensional THz Time-Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fu, Zhengping

    Terahertz (THz) wave interacts with semiconductors in many ways, such as resonant excitation of lattice vibration, intraband transition and polaron formation. Different from the optical waves, THz wave has lower photon energy (1 THz = 4.14 meV) and is suitable for studying dynamics of low-energy excitations. Recently the studies of the interaction of THz wave and semiconductors have been extending from the linear regime to the nonlinear regime, owing to the advance of the high-intensity THz generation and detection methods. Two-dimensional (2D) spectroscopy, as a useful tool to unravel the nonlinearity of materials, has been well developed in nuclear magnetic resonance and infrared region. However, the counterpart in THz region has not been well developed and was only demonstrated at frequency around 20 THz due to the lack of intense broadband THz sources. Using laser-induced plasma as the THz source, we developed collinear broadband 2D THz time-domain spectroscopy covering from 0.5 THz to 20 THz. Broadband intense THz pulses emitted from laser-induced plasma provide access to a variety of nonlinear properties of materials. Ultrafast optical and THz pulses make it possible to resolve the transient change of the material properties with temporal resolution of tens of femtoseconds. This thesis focuses on the linear and nonlinear interaction of the THz wave with semiconductors. Since a great many physical processes, including vibrational motion of lattice and plasma oscillation, has resonant frequency in the THz range, rich physics can be studies in our experiment. The thesis starts from the linear interaction of the THz wave with semiconductors. In the narrow band gap semiconductor InSb, the plasma absorption edge, Restrahlen band and dispersion of polaritons are observed. The nonlinear response of InSb in high THz field is verified in the frequency-resolved THz Z-scan experiment. The third harmonic generations due to the anharmonicity of plasma oscillation and the

  6. Spatio-spectral characteristics of ultra-broadband THz emission from two-colour photoexcited gas plasmas and their impact for nonlinear spectroscopy

    NASA Astrophysics Data System (ADS)

    Blank, V.; Thomson, M. D.; Roskos, H. G.

    2013-07-01

    We present a characterization of the combined spatial and spectral properties of the terahertz (THz) and mid-infrared emission from gas plasmas generated and driven by two-colour femtosecond optical pulses. For its use in nonlinear spectroscopy, the impact of the relatively complex spatial profile for both broadband (∼ 10 THz) and ultra-broadband (> 100 THz) emission needs to be considered, in particular for experiments based on z-scan techniques. Here we apply spatially resolved measurements based on both field autocorrelation and sum-frequency (up-conversion) detection. Based on these results, we present simulations of the ultra-broadband profile during its passage through a focal region. In addition to the inherent features of the emission profile due to the generation mechanism in the plasma filament, we also analyse the role of the semconductor (silicon) wafer typically placed after the plasma to discard the optical pump beams, whose photoexcitation also can play a role in the resultant THz profile.

  7. High-power Broadband Organic THz Generator

    PubMed Central

    Jeong, Jae-Hyeok; Kang, Bong-Joo; Kim, Ji-Soo; Jazbinsek, Mojca; Lee, Seung-Heon; Lee, Seung-Chul; Baek, In-Hyung; Yun, Hoseop; Kim, Jongtaek; Lee, Yoon Sup; Lee, Jae-Hyeok; Kim, Jae-Ho; Rotermund, Fabian; Kwon, O-Pil

    2013-01-01

    The high-power broadband terahertz (THz) generator is an essential tool for a wide range of THz applications. Here, we present a novel highly efficient electro-optic quinolinium single crystal for THz wave generation. For obtaining intense and broadband THz waves by optical-to-THz frequency conversion, a quinolinium crystal was developed to fulfill all the requirements, which are in general extremely difficult to maintain simultaneously in a single medium, such as a large macroscopic electro-optic response and excellent crystal characteristics including a large crystal size with desired facets, good environmental stability, high optical quality, wide transparency range, and controllable crystal thickness. Compared to the benchmark inorganic and organic crystals, the new quinolinium crystal possesses excellent crystal properties and THz generation characteristics with broader THz spectral coverage and higher THz conversion efficiency at the technologically important pump wavelength of 800 nm. Therefore, the quinolinium crystal offers great potential for efficient and gap-free broadband THz wave generation. PMID:24220234

  8. Nanowires for THz Spectroscopy

    DTIC Science & Technology

    2013-10-01

    03-D-0009 Mansoor Sheik- Bahae Prepared by: OVPR/ University Strategic Partnership MSC02 1660 1 University of New Mexico Albuquerque, New...Z39.18 00-10-2013 Technical 07/21/2010 - 04/30/2012 Nanowires for THz Spectroscopy HDTRA1-03-D-0009 Mansoor Sheik- Bahae 3 26 OVPR/University Strategic...kilogram (C/kg) second (s) kilogram (kg) kilo pascal (kPa) 3 TABLE OF CONTENTS: I . Introduction ………....…………………………………………………… 01 II

  9. THz stark spectroscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Feurer, Thomas; Rohwer, Egmont; Akbarimoosavi, Maryam

    2016-09-01

    Stark spectroscopy has been pioneered many decades ago and is a unique tool to extract information on molecular constants such as changes of dipole moments or polarizabilities upon excitation. Here we introduce a new twist, i.e. THz Stark spectroscopy. In THz fields the electric field vector oscillates on time scales of picoseconds and thus much faster than in conventional Stark spectroscopy. It therefore may allow to distinguish between different electric field contributions by analyzing the dynamics of the THz response. We first demonstrate that conventional THz sources can be boosted by combination with field enhancement structures, reaching field strength of GV/m driving several different materials into the nonlinear response regime. Then we discuss THz fields influencing charge transfer in different molecules.

  10. THz Emission Spectroscopy for THz Spintronics

    NASA Astrophysics Data System (ADS)

    Jarik Huisman, Thomas; Rasing, Theo

    2017-01-01

    Spintronics is used as the standard for the readout of magnetically stored data and also has commercial applications for writing data. The generation, control and detection of spin-polarized currents, spin-dependent electric transport, and pure spin currents on the subpicosecond (10-12 s) timescale are the next challenges in spintronics. Terahertz (THz, 1012 Hz) emission spectroscopy has proven to be an excellent tool for investigating these challenges. In this short review, we outline the functioning of this spectroscopic technique and its recent applications to spintronics.

  11. 20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas.

    PubMed

    Hale, P J; Madeo, J; Chin, C; Dhillon, S S; Mangeney, J; Tignon, J; Dani, K M

    2014-10-20

    We demonstrate broadband (20 THz), high electric field, terahertz generation using large area interdigitated antennas fabricated on semi-insulating GaAs. The bandwidth is characterized as a function of incident pulse duration (15-35 fs) and pump energy (2-30 nJ). Broadband spectroscopy of PTFE is shown. Numerical Drude-Lorentz simulations of the generated THz pulses are performed as a function of the excitation pulse duration, showing good agreement with the experimental data.

  12. THz spectroscopy of polar liquids

    NASA Astrophysics Data System (ADS)

    Libon, Imke. H.; Hempel, M.; Seitz, S.; Hecker, Nancy E.; Feldmann, Jochen; Hayd, A.; Zundel, G.; Mittleman, Daniel; Koch, M.

    1999-04-01

    The mesoscopic structure of water has long been a subject of discussion. We postulate that, on the mesoscopic scale, liquid water forms nm-size ice-like crystals and that his structure is responsible for absorption in the THz-frequency range. However, until the recent development of Thz-time domain spectroscopy (THz-TDS), it was difficult to determine the optical constants in this frequency range with a good signal-to-noise ratio and hence to study the absorption properties of water. Here we report on the optical properties of water in the frequency range 0.05-1.4 THz and discuss the mesoscopic structure of water. We use THz-TDS based on photoconductive dipole antennas gated by a 150 femtosecond laser pulses to generate and detect the THz- frequency pulses. A new theoretical approach is also presented which were use to explain the absorption behavior in the measured THz frequency range. In this theory, molecular plasma oscillations of H3O2 complexes, that are distinctly separate from the H5O2+ complexes which form an underlying crystalline lattice, are assumed to be responsible for absorption in the THz- frequency range. This model provides good agreement to our data.

  13. THz spectroscopy of the atmosphere

    NASA Astrophysics Data System (ADS)

    Pickett, Herbert M.

    1999-04-01

    THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing.THe IR region near 3 micrometers requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH result from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the microwave limb sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on 24 May 1998. Results from this flight will be presented.

  14. THz Spectroscopy of the Atmosphere

    NASA Technical Reports Server (NTRS)

    Pickett, Herbert M.

    2000-01-01

    THz spectroscopy of the atmosphere has been driven by the need to make remote sensing measurements of OH. While the THz region can be used for sensitive detection on many atmospheric molecules, the THz region is the best region for measuring the diurnal behavior of stratospheric OH by remote sensing. The infrared region near 3 microns suffers from chemiluminescence and from spectral contamination due to water. The ultraviolet region near 300 nm requires solar illumination. The three techniques for OH emission measurements in the THz region include Fourier Transform interferometry, Fabry-Perot interferometry, and heterodyne radiometry. The first two use cryogenic direct detectors while the last technique uses a local oscillator and a mixer to down convert the THz signal to GHz frequencies. All techniques have been used to measure stratospheric OH from balloon platforms. OH results from the Fabry-Perot based FILOS instrument will be given. Heterodyne measurement of OH at 2.5 THz has been selected to be a component of the Microwave Limb Sounder on the Earth Observing System CHEM-1 polar satellite. The design of this instrument will be described. A balloon-based prototype heterodyne 2.5 THz radiometer had its first flight on, 24 May 1998. Results form this flight will be presented.

  15. Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pate, Brooks

    2014-06-01

    The past decade has seen several major technology advances in electronics operating at microwave frequencies making it possible to develop a new generation of spectrometers for molecular rotational spectroscopy. High-speed digital electronics, both arbitrary waveform generators and digitizers, continue on a Moore's Law-like development cycle that started around 1993 with device bandwidth doubling about every 36 months. These enabling technologies were the key to designing chirped-pulse Fourier transform microwave (CP-FTMW) spectrometers which offer significant sensitivity enhancements for broadband spectrum acquisition in molecular rotational spectroscopy. A special feature of the chirped-pulse spectrometer design is that it is easily implemented at low frequency (below 8 GHz) where Balle-Flygare type spectrometers with Fabry-Perot cavity designs become technologically challenging due to the mirror size requirements. The capabilities of CP-FTMW spectrometers for studies of molecular structure will be illustrated by the collaborative research effort we have been a part of to determine the structures of water clusters - a project which has identified clusters up to the pentadecamer. A second technology trend that impacts molecular rotational spectroscopy is the development of high power, solid state sources in the mm-wave/THz regions. Results from the field of mm-wave chirped-pulse Fourier transform spectroscopy will be described with an emphasis on new problems in chemical dynamics and analytical chemistry that these methods can tackle. The third (and potentially most important) technological trend is the reduction of microwave components to chip level using monolithic microwave integrated circuits (MMIC) - a technology driven by an enormous mass market in communications. Some recent advances in rotational spectrometer designs that incorporate low-cost components will be highlighted. The challenge to the high-resolution spectroscopy community - as posed by Frank De

  16. THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

    2016-06-01

    GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction.

  17. THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy

    PubMed Central

    Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

    2016-01-01

    GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction. PMID:27346494

  18. THz spectroscopy for THz spintronics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Huisman, Thomas

    2016-10-01

    Controlling currents using circularly polarized light and spin-orbit coupling could lead to the development of ultrafast spintronic devices driven by laser pulses and operating at the femtosecond timescale. Here we demonstrate that such a helicity dependent photocurrent can be generated in metallic heterostructures consisting of a single ferromagnetic layer and a non-magnetic one. In particular, using terahertz emission spectroscopy we show that the direction of the generated ultrafast photocurrent is controlled by the helicity of light, the magnetization of the ferromagnetic layer and the growth direction of the layers. We argue that the helicity and magnetization dependent photocurrent in metallic multilayers originates from a combination of the spin-orbit interaction and a lack of center of symmetry at the interface.

  19. Highly efficient broadband double-sided Fresnel lens for THz range.

    PubMed

    Sypek, Maciej; Makowski, Michał; Hérault, Emilie; Siemion, Agnieszka; Siemion, Andrzej; Suszek, Jarosław; Garet, Frédéric; Coutaz, Jean-Louis

    2012-06-15

    Modern passive THz setups require effective optical elements with a large numerical aperture. Here we propose a new type of the optical element for THz applications, which is a broadband double-sided Fresnel-like lens with an optimized thickness. The optimization is performed to obtain a very low attenuation, low material cost, and small weight in the element media. It also provides achromatic properties for the assumed wavelength range. The experimental evaluation of the proposed diffractive lens by means of time-domain spectroscopy is presented and discussed.

  20. Broadband Terahertz Computed Tomography Using a 5k-pixel Real-time THz Camera

    NASA Astrophysics Data System (ADS)

    Trichopoulos, Georgios C.; Sertel, Kubilay

    2015-07-01

    We present a novel THz computed tomography system that enables fast 3-dimensional imaging and spectroscopy in the 0.6-1.2 THz band. The system is based on a new real-time broadband THz camera that enables rapid acquisition of multiple cross-sectional images required in computed tomography. Tomographic reconstruction is achieved using digital images from the densely-packed large-format (80×64) focal plane array sensor located behind a hyper-hemispherical silicon lens. Each pixel of the sensor array consists of an 85 μm × 92 μm lithographically fabricated wideband dual-slot antenna, monolithically integrated with an ultra-fast diode tuned to operate in the 0.6-1.2 THz regime. Concurrently, optimum impedance matching was implemented for maximum pixel sensitivity, enabling 5 frames-per-second image acquisition speed. As such, the THz computed tomography system generates diffraction-limited resolution cross-section images as well as the three-dimensional models of various opaque and partially transparent objects. As an example, an over-the-counter vitamin supplement pill is imaged and its material composition is reconstructed. The new THz camera enables, for the first time, a practical application of THz computed tomography for non-destructive evaluation and biomedical imaging.

  1. Nonphasematched broadband THz amplification and reshaping in a dispersive chi(3) medium.

    PubMed

    Koys, Martin; Noskovicova, Eva; Velic, Dusan; Lorenc, Dusan

    2017-06-12

    We theoretically investigate non-phasematched broadband THz amplification in dispersive chi(3) media. A short 100 fs pump pulse is interacting with a temporally matched second harmonic pulse and a weak THz signal through the four wave mixing process and a significant broadband THz amplification and reshaping is observed. The pulse evolution dynamics is explored by numerically solving a set of generalized Nonlinear Schroedinger equations. The influence of incident pulse chirp, pulse duration and the role of wavelength, THz seed frequency and losses are evaluated separately. It is found that a careful choice of incident parameters can provide a broadband THz output and/or a significant increase of THz peak power.

  2. Computed tomography using broadband Bessel THz beams and phase contrast.

    PubMed

    Bitman, Assaf; Goldring, Sharone; Moshe, Inon; Zalevsky, Zeev

    2014-04-01

    We present new results demonstrating the capability of performing computed tomography (CT) using broadband Bessel terahertz (THz) beams. Nondiffractive beams such as these exhibit propagation-invariant lines of focus with an extended depth-of-field compared to conventional Gaussian beams. Using this property, we demonstrate a considerable improvement in the 3D reconstruction image of a synthetic sample through the backprojection algorithm. Only when THz Bessel beams are used, a full reconstruction of the object structure is made. Moreover, we use phase-contrast mechanism which improves the spatial resolution and reconstructed images. Our results highlight the potential in using nondiffractive Bessel beams to significantly improve 3D-image reconstruction of THz CT.

  3. Broadband Sources in the 1-3 THz Range

    NASA Technical Reports Server (NTRS)

    Mehdi, Imran; Ward, John; Maestrini, Alain; Chattopadhyay, Goutam; Schlecht, Erich; Thomas, Bertrand; Lin, Robert; Lee, Choonsup; Gill, John

    2009-01-01

    Broadband electronically tunable sources in the terahertz range are a critical technology for enabling space-borne as well as ground-based applications. By power-combining MMIC amplifier and frequency tripler chips, we have recently demonstrated >1 mW of output power at 900 GHz. This source provides a stepping stone to enable sources in the 2-3 THz range than can sufficiently pump multi-pixel imaging arrays.

  4. Thz Spectroscopy of D_2H^+

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Pearson, John; Amano, Takayoshi

    2015-06-01

    Pure rotational transitions of D_2H^+ observed by high-resolution spectroscopy have been limited so far to the J = 110-101 transition at 691.7 GHz, J=220-211 at 1.370 THz, and J=111-000 at 1.477 THz. As this ion is a light asymmetric-top molecule, spectroscopic characterization and prediction of other rotational transition frequencies are not straightforward. In this presentation, we extended the measurements up to 2 THz by using the JPL frequency multiplier chains, and observed three new THz lines and re-measured the three known transitions. D_2H^+ was generated in an extended negative glow discharge cell cooled to liquid nitrogen temperature. Six rotational transition frequencies together with the combination differences derived from three fundamental bands were subject to least square analysis to determine the molecular constants. New THz measurements are definitely useful for better characterization of spectroscopic properties. The improved molecular constants provide better predictions of other unobserved rotational transitions. T. Hirao and T. Amano, Ap. J.,597, L85 (2003) K. M. Evenson et al cited by O. L. Polyansky and A. R. W. McKellar, J. Chem. Phys., 92, 4039 (1990) O. Asvany et al, Phys. Rev. Lett., 100, 233004 (2008)

  5. Broadband transmission EPR spectroscopy.

    PubMed

    Hagen, Wilfred R

    2013-01-01

    EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field. The X-band spectrometer is the general standard with a frequency in the 9-10 GHz range. Most (bio)molecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin - nuclear spin interactions and electron spin - electron spin interactions, and unambiguous analysis requires data collection at different frequencies. Extant and long-standing practice is to use a different spectrometer for each frequency. We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8-2.7 GHz. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed.

  6. Broadband photophoretic spectroscopy.

    PubMed

    Arnold, S; Amani, Y

    1980-06-01

    A means for obtaining broadband photophoretic spectra is described. The sensitivity of the technique is found in accordance with radiometric theory to increase markedly with pressure reduction below 1 atm. Noise oscillation induced by radiometric torques is contained through the use of electronic damping. The first broadband spectrum on a single crystallite (approximtely 5 microm) of CdS is presented.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  8. Broadband mid-infrared and THz chemical detection with quantum cascade laser multi-heterodyne spectrometers (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Westberg, Jonas; Sterczewski, Lukasz A.; Patrick, Link; Wysocki, Gerard

    2017-05-01

    Majority of chemical species of interest in security and safety applications (e.g. explosives) have complex molecular structures that produce unresolved rotational-vibrational spectroscopic signatures in the mid-infrared. This requires spectroscopic techniques that can provide broadband coverage in the mid-IR region to target broadband absorbers and high resolution to address small molecules that exhibit well-resolved spectral lines. On the other hand, many broadband mid-IR absorbers exhibit well-resolved rotational components in the THz spectral region. Thus, development of spectroscopic sensing technologies that can address both spectral regions is of great importance. Here we demonstrate recent progress towards broadband high-resolution spectroscopic sensing applications with Fabry-Perot quantum cascade lasers (QCLs) and frequency combs using multi-heterodyne spectroscopy (MHS) techniques. In this paper, we will present spectroscopic sensing of large and small molecules in the mid-IR region using QCLs operating at 8.5µm. An example high-resolution, broadband MHS of ammonia (small molecule) and isobutane (broadband absorber) at atmospheric pressure in the 1165-1190 cm^-1 range will be discussed. We have developed a balanced MHS system for mitigation of the laser intensity fluctuations. Absorption spectroscopy as well as dispersion spectroscopy with minimum fractional absorption down to 10^-4/Hz1/2 and fast spectral acquisition capabilities down to 10 µs/spectrum range will be demonstrated. In order to mitigate the shortcomings of the limited chemical selectivity in the mid-IR, THz QCL based spectrometer is currently under development to provide spectral de-congestion and thus significantly improve chemical identification. Preliminary characterization of the performance of THZ QCL combs for the THz QCL-MHS will be presented.

  9. Broadband Transmission EPR Spectroscopy

    PubMed Central

    Hagen, Wilfred R.

    2013-01-01

    EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field. The X-band spectrometer is the general standard with a frequency in the 9–10 GHz range. Most (bio)molecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin – nuclear spin interactions and electron spin – electron spin interactions, and unambiguous analysis requires data collection at different frequencies. Extant and long-standing practice is to use a different spectrometer for each frequency. We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8–2.7 GHz. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed. PMID:23555819

  10. Progress Towards Chirped-Pulse Fourier Transform Thz Spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

    New opportunities are provided by the development of higher power THz frequency multiplier sources, the development of a broadband Chirped-Pulse FTMW spectroscopy technique at microwave and mm Wave frequencies, and recently demonstrated heterodyne hot electron bolometer detection technology in the THz frequency region with near quantum noise-limited performance and high spectral resolution. Combining these three technologies and extending the chirped-pulse technique to 0.85 THz enables a host of new applications. NIST is currently pursing applications as a point sensor for greenhouse gases, volatile organic compounds, and potentially human breath. The generation and detection of phase stable chirped pulses at 850 GHz will be demonstrated. A description of the experimental setup and preliminary data will be presented for nitrous oxide. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S. Shipman and B.H. Pate, Rev.Sci.Instrum. 79 (2008) 053103. E. Gerecht, D. Gu, L. You, K.S. Yngvesson, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES. 56, (2008) 1083.

  11. Improving depth-of field in broadband THz beams using nondiffractive Bessel beams.

    PubMed

    Bitman, Assaf; Moshe, Inon; Zalevsky, Zeev

    2012-10-01

    We report new results related to imaging using broadband Bessel-like beams at the terahertz (THz) domain that were generated by use of axicons and pulsed THz radiation emitting at a bandwidth 0.1 to 1 THz. Such Bessel-like beams exhibit an invariant line of focus with an extended length compared to Gaussian-beams Rayleigh range, which enables imaging through the extended length. We demonstrate this imaging property using a resolution target illuminated by broadband-THz beams and show an improvement by a factor of 3.5 in imaging depth while using Bessel-like beams over Gaussian beams. Our results highlight the potential in using broadband THz radiation together with nondiffractive Bessel beams to significantly improve spatial separation over deep view.

  12. 2D THz-THz-Raman Photon-Echo Spectroscopy of Molecular Vibrations in Liquid Bromoform.

    PubMed

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

    2017-09-13

    Fundamental properties of molecular liquids are governed by long-range interactions that most prominently manifest at terahertz (THz) frequencies. Here we report the detection of nonlinear THz photon-echo (rephasing) signals in liquid bromoform using THz-THz-Raman spectroscopy. Together, the many observed signatures span frequencies from 0.5 to 8.5 THz and result from couplings between thermally populated ladders of vibrational states. The strongest peaks in the spectrum are found to be multiquantum dipole and 1-quantum polarizability transitions and may arise from nonlinearities in the intramolecular dipole moment surface driven by intermolecular interactions.

  13. Superconducting Solenoid for Superfast THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bragin, A. V.; Khrushchev, S. V.; Kubarev, V. V.; Mezencev, N. A.; Tsukanov, V. M.; Sozinov, G. I.; Shkaruba, V. A.

    This project is related to new spectroscopy method in little-developed THz range. The method is founded on using of a free electron laser (NovoFEL) with high spectral power radiation which can be smoothly tuned in desirable range of spectrum. The objects of research of this method are fast processes in physics, chemical and biological reactions. Uniform magnetic field of 6 T value in the research area can considerably increase possibilities of this method. The magnetic field will modulate radiation of free molecules induction on characteristic frequencies of the Zeeman splitting that gives more possibilities of identification of molecules having even weak magnetic momentum. Moreover, the use of magnetic field allows essentially increase sensitivity of this method due to almost complete separation of weak measuring signals from powerful radiation of the laser. A superconducting solenoid was developed for this method. Its design and peculiarities are described in this paper.

  14. Broadband local dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Labardi, M.; Lucchesi, M.; Prevosto, D.; Capaccioli, S.

    2016-05-01

    A route to extend the measurement bandwidth of local dielectric spectroscopy up to the MHz range has been devised. The method is based on a slow amplitude modulation at a frequency Ω of the excitation field oscillating at a frequency ω and the coherent detection of the modulated average electric force or force gradient at Ω. The cantilever mechanical response does not affect the measurement if Ω is well below its resonant frequency; therefore, limitations on the excitation field frequency are strongly reduced. Demonstration on a thin poly(vinyl acetate) film is provided, showing its structural relaxation spectrum on the local scale up to 45 °C higher than glass temperature, and nanoscale resolution dielectric relaxation imaging near conductive nanowires embedded in the polymer matrix was obtained up to 5 MHz frequency, with no physical reason to hinder further bandwidth extension.

  15. Broadband and high modulation-depth THz modulator using low bias controlled VO2-integrated metasurface.

    PubMed

    Zhou, Gaochao; Dai, Penghui; Wu, Jingbo; Jin, Biaobing; Wen, Qiye; Zhu, Guanghao; Shen, Ze; Zhang, Caihong; Kang, Lin; Xu, Weiwei; Chen, Jian; Wu, Peiheng

    2017-07-24

    An active vanadium dioxide integrated metasurface offering broadband transmitted terahertz wave modulation with large modulation-depth under electrical control is demonstrated. The device consists of metal bias-lines arranged with grid-structure patterned vanadium dioxide (VO2) film on sapphire substrate. Amplitude transmission is continuously tuned from more than 78% to 28% or lower in the frequency range from 0.3 THz to 1.0 THz, by means of electrical bias at temperature of 68 °C. The physical mechanism underlying the device's electrical tunability is investigated and found to be attributed to the ohmic heating. The developed device possessing over 87% modulation depth with 0.7 THz frequency band is expected to have many potential applications in THz regime such as tunable THz attenuator.

  16. s-SNOM based IR and THz spectroscopy for nanoscale material characterization

    NASA Astrophysics Data System (ADS)

    Gokus, Tobias; Huber, Andreas; Cernescu, Adrian

    Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) allows to overcome the diffraction limit of conventional light microscopy enabling optical measurements at a spatial resolution of 10nm. s-SNOM employs an externally-illuminated sharp metallic AFM tip to create a nanoscale hot-spot at its apex. The optical tip-sample near-field interaction is determined by the local dielectric properties (refractive index) of the sample and detection of the elastically tip-scattered light yields nanoscale resolved near-field images simultaneous to topography. Development of a dedicated Fourier-transform detection module for analyzing light scattered from the tip which is illuminated by a broadband laser source enables IR spectroscopy of complex polymer nanostructures. Applications presented further demonstrate characterization of embedded structural phases in biominerals (bone), organic semiconductors or functional semiconductor nanostructures.Furthermore, by extending the concept of broadband-s-SNOM spectroscopy to the THz-spectral range, we demonstrate optical near-field imaging and spectroscopy at THz-frequencies (0.5-2.5 THz) by coupling the free space beam of a dedicated THz-TDS to the s-SNOM system.

  17. THz Spectroscopy and Spectroscopic Database for Astrophysics

    NASA Technical Reports Server (NTRS)

    Pearson, John C.; Drouin, Brian J.

    2006-01-01

    Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular database maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

  18. THz Spectroscopy and Spectroscopic Database for Astrophysics

    NASA Technical Reports Server (NTRS)

    Pearson, John C.; Drouin, Brian J.

    2006-01-01

    Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular data base maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

  19. THz time-domain spectroscopy imaging for mail inspection

    NASA Astrophysics Data System (ADS)

    Zhang, Liquan; Wang, Zhongdong; Ma, Yanmei; Hao, Erjuan

    2011-08-01

    Acquiring messages from the mail but not destroying the envelope is a big challenge in the war of intelligence. If one can read the message of the mail when the envelope is closed, he will benefit from the message asymmetry and be on a good wicket in the competition. In this paper, we presented a transmitted imaging system using THz time-domain spectroscopy technology. We applied the system to image the mail inside an envelope by step-scanning imaging technology. The experimental results show that the THz spectroscopy can image the mail in an envelope. The words in the paper can be identified easily from the background. We also present the THz image of a metal blade in the envelope, in which we can see the metal blade clearly. The results show that it is feasible of THz Time-Domain Spectroscopy Imaging for mail inspection applications.

  20. THz spectroscopy of D2H+

    NASA Astrophysics Data System (ADS)

    Yu, S.; Pearson, J. C.; Amano, T.; Matsushima, F.

    2017-01-01

    We extended the measurements of the rotational transitions of D2H+ up to 3 THz by using the JPL frequency multiplier chains and a TuFIR system at Toyama. D2H+ was generated in an extended negative glow discharge cell cooled to liquid nitrogen temperature. We observed five new THz lines. All the available rotational transition frequencies together with the combination differences derived from the three fundamental bands were subject to least square analysis to determine the molecular constants. New THz measurements are definitely useful for better characterization of spectroscopic properties. The improved molecular constants provide better predictions of other unobserved rotational transitions.

  1. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Wei, Q.; Ding, W. J.; Hafez, H. A.; Fareed, M. A.; Laramée, A.; Ropagnol, X.; Zhang, G.; Sun, S.; Sheng, Z. M.; Zhang, J.; Ozaki, T.

    2017-01-01

    We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

  2. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses.

    PubMed

    Mondal, S; Wei, Q; Ding, W J; Hafez, H A; Fareed, M A; Laramée, A; Ropagnol, X; Zhang, G; Sun, S; Sheng, Z M; Zhang, J; Ozaki, T

    2017-01-10

    We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20-200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

  3. Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

    PubMed Central

    Mondal, S.; Wei, Q.; Ding, W. J.; Hafez, H. A.; Fareed, M. A.; Laramée, A.; Ropagnol, X.; Zhang, G.; Sun, S.; Sheng, Z. M.; Zhang, J.; Ozaki, T.

    2017-01-01

    We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results. PMID:28071764

  4. Multifrequency high precise subTHz-THz-IR spectroscopy for exhaled breath research

    NASA Astrophysics Data System (ADS)

    Vaks, Vladimir L.; Domracheva, Elena G.; Pripolzin, Sergey I.; Chernyaeva, Mariya B.

    2016-09-01

    Nowadays the development of analytical spectroscopy with high performance, sensitivity and spectral resolution for exhaled breath research is attended. The method of two-frequency high precise THz spectroscopy and the method of high precise subTHz-THz-IR spectroscopy are presented. Development of a subTHz-THz-IR gas analyzer increases the number of gases that can be identified and the reliability of the detection by confirming the signature in both THz and MIR ranges. The testing measurements have testified this new direction of analytical spectroscopy to open widespread trends of its using for various problems of medicine and biology. First of all, there are laboratory investigations of the processes in exhaled breath and studying of their dynamics. Besides, the methods presented can be applied for detecting intermediate and short time living products of reactions in exhaled breath. The spectrometers have been employed for investigations of acetone, methanol and ethanol in the breath samples of healthy volunteers and diabetes patients. The results have demonstrated an increased concentration of acetone in breath of diabetes patients. The dynamic of changing the acetone concentration before and after taking the medicines is discovered. The potential markers of pre-cancer states and oncological diseases of gastrointestinal tract organs have been detected. The changes in the NO concentration in exhaled breath of cancer patients during radiotherapy as well as increase of the NH3 concentration at gastrointestinal diseases have been revealed. The preliminary investigations of biomarkers in three frequency ranges have demonstrated the advantages of the multifrequency high precise spectroscopy for noninvasive medical diagnostics.

  5. THz-Raman spectroscopy for explosives, chemical, and biological detection

    NASA Astrophysics Data System (ADS)

    Carriere, James T. A.; Havermeyer, Frank; Heyler, Randy A.

    2013-05-01

    Raman and Terahertz spectroscopy are both widely used for their ability to safely and remotely identify unknown materials. Each approach has its advantages and disadvantages. Traditional Raman spectroscopy typically measures molecular energy transitions in the 200-5000cm-1 region corresponding to sub-molecular stretching or bending transitions, while Terahertz spectroscopy measures molecular energy transitions in the 1-200cm-1 region (30GHz - 6THz) that correspond to low energy rotational modes or vibrational modes of the entire molecule. Many difficult to detect explosives and other hazardous chemicals are known to have multiple relatively strong transitions in this "Terahertz" (<200cm-1, <6THz) regime, suggesting this method as a powerful complementary approach for identification. However, THz signal generation is often expensive, many THz spectroscopy systems are limited to just a few THz range, and strong water absorption bands in this region can act to mask certain transitions if great care isn't taken during sample preparation. Alternatively, low-frequency or "THz-Raman" spectroscopy, which covers the ~5cm-1 to 200cm-1 (150GHz - 6 THz) regions and beyond, offers a powerful, compact and economical alternative to probe these low energy transitions. We present results from a new approach for extending the range of Raman spectroscopy into the Terahertz regime using an ultra-narrow-band volume holographic grating (VHG) based notch filter system. An integrated, compact Raman system is demonstrated utilizing a single stage spectrometer to show both Stokes and anti-Stokes measurements down to <10cm-1 on traditionally difficult to detect explosives, as well as other chemical and biological samples.

  6. Invited Article: Single-shot THz detection techniques optimized for multidimensional THz spectroscopy

    SciTech Connect

    Teo, Stephanie M.; Ofori-Okai, Benjamin K.; Werley, Christopher A.; Nelson, Keith A.

    2015-05-15

    Multidimensional spectroscopy at visible and infrared frequencies has opened a window into the transfer of energy and quantum coherences at ultrafast time scales. For these measurements to be performed in a manageable amount of time, one spectral axis is typically recorded in a single laser shot. An analogous rapid-scanning capability for THz measurements will unlock the multidimensional toolkit in this frequency range. Here, we first review the merits of existing single-shot THz schemes and discuss their potential in multidimensional THz spectroscopy. We then introduce improved experimental designs and noise suppression techniques for the two most promising methods: frequency-to-time encoding with linear spectral interferometry and angle-to-time encoding with dual echelons. Both methods, each using electro-optic detection in the linear regime, were able to reproduce the THz temporal waveform acquired with a traditional scanning delay line. Although spectral interferometry had mediocre performance in terms of signal-to-noise, the dual echelon method was easily implemented and achieved the same level of signal-to-noise as the scanning delay line in only 4.5% of the laser pulses otherwise required (or 22 times faster). This reduction in acquisition time will compress day-long scans to hours and hence provides a practical technique for multidimensional THz measurements.

  7. Broadband field enhancement of THz electromagnetic wave by surface-textured micron PVDF cylinders

    NASA Astrophysics Data System (ADS)

    Li, Xinxin; Liu, Xuan; Zhang, Luoning; Zhou, Jing; Liu, Dahe

    2015-07-01

    A cylindrical dimmer system is proposed to realize broadband field enhancement for terahertz (THz) electromagnetic wave. A surface-textured crescent-shaped cylinder is proposed to red-shift the absorption spectrum comparing to the traditional crescent-shaped cylinder based on the concept of spoof surface plasmons. Such cylinders made of ferroelectric polyvinylidene fluoride can realize the electromagnetic wave harvesting at terahertz frequencies with a broadband and huge absorption cross section. Two such cylinders in close proximity could achieve considerable electromagnetic field enhancement and field confinement in the gap, which could be applied in THz molecules detection, toxic chemical sensing, and safety screening and could break the detection binding that limits the molecules <100 nm.

  8. Perspective: Echoes in 2D-Raman-THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Hamm, Peter; Shalit, Andrey

    2017-04-01

    Recently, various spectroscopic techniques have been developed, which can measure the 2D response of the inter-molecular degrees of freedom of liquids in the THz regime. By employing hybrid Raman-THz pulse sequences, the inherent experimental problems of 2D-Raman spectroscopy are circumvented completely, culminating in the recent measurement of the 2D-Raman-THz responses of water and aqueous salt solutions. This review article focuses on the possibility to observe echoes in such experiments, which would directly reveal the inhomogeneity of the typically extremely blurred THz bands of liquids, and hence the heterogeneity of local structures that are transiently formed, in particular, in a hydrogen-bonding liquid such as water. The generation mechanisms of echoes in 2D-Raman-THz spectroscopy are explained, which differ from those in "conventional" 2D-IR spectroscopy in a subtle but important manner. Subsequently, the circumstances are discussed, under which echoes are expected, revealing a physical picture of the information content of an echo. That is, the echo decay reflects the lifetime of local structures in the liquid on a length scale that equals the delocalization length of the intermolecular modes. Finally, recent experimental results are reviewed from an echo perspective.

  9. Frequency-comb-assisted broadband precision spectroscopy with cascaded diode lasers.

    PubMed

    Liu, Junqiu; Brasch, Victor; Pfeiffer, Martin H P; Kordts, Arne; Kamel, Ayman N; Guo, Hairun; Geiselmann, Michael; Kippenberg, Tobias J

    2016-07-01

    Frequency-comb-assisted diode laser spectroscopy, employing both the accuracy of an optical frequency comb and the broad wavelength tuning range of a tunable diode laser, has been widely used in many applications. In this Letter, we present a novel method using cascaded frequency agile diode lasers, which allows us to extend the measurement bandwidth to 37.4 THz (1355-1630 nm) at megahertz resolution with scanning speeds above 1 THz/s. It is demonstrated as a useful tool to characterize a broadband spectrum for molecular spectroscopy, and in particular it enables us to characterize the dispersion of integrated microresonators up to the 4th-order.

  10. Frequency-comb-assisted broadband precision spectroscopy with cascaded diode lasers

    NASA Astrophysics Data System (ADS)

    Liu, Junqiu; Brasch, Victor; Pfeiffer, Martin H. P.; Kordts, Arne; Kamel, Ayman N.; Guo, Hairun; Geiselmann, Michael; Kippenberg, Tobias J.

    2016-07-01

    Frequency comb assisted diode laser spectroscopy, employing both the accuracy of an optical frequency comb and the broad wavelength tuning range of a tunable diode laser, has been widely used in many applications. In this letter we present a novel method using cascaded frequency agile diode lasers, which allows extending the measurement bandwidth to 37.4 THz (1355 to 1630 nm) at MHz resolution with scanning speeds above 1 THz/s. It is demonstrated as a useful tool to characterize a broadband spectrum for molecular spectroscopy and in particular it enables to characterize the dispersion of integrated microresonators up to the fourth order.

  11. Dielectric tube waveguides with absorptive cladding for broadband, low-dispersion and low loss THz guiding

    PubMed Central

    Bao, Hualong; Nielsen, Kristian; Bang, Ole; Jepsen, Peter Uhd

    2015-01-01

    Research on terahertz waveguides is experiencing a tremendous growth due to their importance for compact and robust THz systems. However, designing compact, broadband, mechanically stable and environmentally shielded THz waveguides is still a challenge due to high losses of both metals and dielectrics in this frequency range. Here we report on a novel twist on the classical tube waveguide where we deliberately introduce a thick and highly lossy cladding layer. By this we attenuate the field in the cladding and thus prevent interference with the core field. This mechanism breaks the well-known ARROW guiding mechanism, and as a result, extremely broad bandwidth and low dispersion can be achieved with a very simple design. Since the main part of the field propagates inside the air-core, the propagation loss is still kept at a very low level. Simulations, analytical modelling and experiments verify our findings. The proposed THz waveguide is robust, insensitive to external perturbation and easy to handle, and thus the design represents a significant advance of the field of THz dielectric waveguides suitable for the 0.3–1 THz band which in the future will be important for ultrafast wireless communication systems. PMID:25557284

  12. Broadband terahertz dielectric spectroscopy of alcohols

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    We have studied the complex dielectric properties of a series of alcohols in 0.5-10 THz frequency range using THz time-domain spectroscopy. The dielectric response observed has contribution from a Debye relaxation process and three damped harmonic oscillators. Combination of experimental observations, all-atom molecular dynamics simulations and ab initio quantum calculations reveals that the complex dielectric spectra of alcohols result from a complex dynamics involving vibrational motions of several atoms across multiple interacting alcohol molecules. The major contribution comes from the fast hydrogen-bond rupture and reformation dynamics, the motion of alkyl chains, and the motions of the H-bonded OH groups.

  13. A broadband THz receiver for low background space applications

    NASA Technical Reports Server (NTRS)

    Hagmann, C.; Benford, D. J.; Clapp, A. C.; Richards, P. L.; Timbie, P.

    1992-01-01

    We have developed a sensitive bolometric receiver for low background space applications. In a 10 percent bandwidth at 1 THz, this receiver is approximately 100 times more sensitive than a quantum limited heterodyne receiver with a 1 GHz IF bandwidth. This receiver is designed to be used for the long wavelength band (200-700 microns) in the MIPS instrument on NASA's SIRTF satellite. The bolometers are cooled to 100 mK by an adiabatic demagnetization refrigerator. Roughly 60 g of cesium chrome alum salt is partially demagnetized to 100 mK, followed by a slow regulated downramp to compensate for the heat leak. The hold time of the ADR system is about 18 hours with a temperature stability of delta T(sub rms) approx. equals 10 micro-K. The composite bolometers have electrical responsivities of 10(exp 9)V/W and electrical NEP's of about 3x10(exp -17) W/square root of Hz. The bolometer signals are read out by JFET preamplifiers located on the helium plate and operated at 120 K. We have addressed a number of space qualification issues, such as the development of an analog magnet controller, construction of a cryogenic shake-table for bolometers and selection of the paramagnetic salt CCA which can survive a bakeout at 50 C. The receiver is scheduled to be flown in the spring of 1992 on a balloon telescope. This flight has a dual purpose. One is to provide realistic test of the capabilities of the new receiver. The other is to search for anisotropies in the cosmic microwave background on scales of a few degrees.

  14. A broadband THz receiver for low background space applications

    NASA Astrophysics Data System (ADS)

    Hagmann, C.; Benford, D. J.; Clapp, A. C.; Richards, P. L.; Timbie, P.

    We have developed a sensitive bolometric receiver for low background space applications. In a 10 percent bandwidth at 1 THz, this receiver is approximately 100 times more sensitive than a quantum limited heterodyne receiver with a 1 GHz IF bandwidth. This receiver is designed to be used for the long wavelength band (200-700 microns) in the MIPS instrument on NASA's SIRTF satellite. The bolometers are cooled to 100 mK by an adiabatic demagnetization refrigerator. Roughly 60 g of cesium chrome alum salt is partially demagnetized to 100 mK, followed by a slow regulated downramp to compensate for the heat leak. The hold time of the ADR system is about 18 hours with a temperature stability of delta T(sub rms) approx. equals 10 micro-K. The composite bolometers have electrical responsivities of 10(exp 9)V/W and electrical NEP's of about 3x10(exp -17) W/square root of Hz. The bolometer signals are read out by JFET preamplifiers located on the helium plate and operated at 120 K. We have addressed a number of space qualification issues, such as the development of an analog magnet controller, construction of a cryogenic shake-table for bolometers and selection of the paramagnetic salt CCA which can survive a bakeout at 50 C. The receiver is scheduled to be flown in the spring of 1992 on a balloon telescope. This flight has a dual purpose. One is to provide realistic test of the capabilities of the new receiver. The other is to search for anisotropies in the cosmic microwave background on scales of a few degrees.

  15. Commercial perspective in THz spectroscopy, sensing and imaging (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Bouyé, Clémentine; Taoudi, Sarah; Cochard, Jacques; d'Humières, Benoît

    2017-02-01

    For their ability to be transmitted by materials opaque in the visible and IR ranges (clothes, plastic, …), for being non-ionizing, for providing sub-mm resolution imaging, for the specific signatures of numerous materials, Terahertz waves - ranging from 200 GHz to 10 THz - have been raising the interest of industrials for about fifteen years. This study focuses on the penetration of THz technologies into the industrial applications driving the THz market growth at short and long term: Non Destructive testing (NDT), Defense and Security, Biomedical. For 15 years, Terahertz technologies have been continuously tested on a wide variety of applications. Thanks to these ongoing feasibility studies, manufacturers and end-users gained a deeper knowledge about the abilities and the limitations of the different Terahertz systems (Time-Domain spectroscopy, Frequency-Domain spectroscopy, Time-Domain reflectometry, etc). The demand from end-users is more qualified and is segmented as follows: 1. Detection of objects and defects on large areas 2. Thickness measurement on large areas 3. Chemical and Structural characterization of small objects and defects on small areas (2D) or volumes (3D) Each of these 3 functions leads to a specific family of THz systems with distinct requirements in terms of performance and cost: 1. Detection: cheap and compact imaging systems. 2. Thickness measurement: cost-effective and high speed systems. 3. Characterization: high resolution, high reliability and real-time sensing systems. This article will present the existing and incoming THz systems and components addressing each function. Terahertz technologies are currently finding their place on the market, outside research and scientific applications. The objective of this article is to identify the industrial applications where THz techniques will be adopted and to provide market growth perspectives.

  16. High-resolution waveguide THz spectroscopy of biological molecules.

    PubMed

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

    2008-02-01

    Low-frequency vibrational modes of biological molecules consist of intramolecular modes, which are dependent on the molecule as a whole, as well as intermolecular modes, which arise from hydrogen-bonding interactions and van der Waals forces. Vibrational modes thus contain important information about conformation dynamics of biological molecules, and can also be used for identification purposes. However, conventional Fourier transform infrared spectroscopy and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recently developed, resulting in sharper features. For this technique, an ordered polycrystalline film of the molecule is formed on a metal sample plate. This plate is incorporated into a metal parallel-plate waveguide and probed via waveguide THz-TDS. The planar order of the film reduces the inhomogeneous broadening, and cooling of the samples to 77K reduces the homogenous broadening. This combination results in the line-narrowing of THz vibrational modes, in some cases to an unprecedented degree. Here, this technique has been demonstrated with seven small biological molecules, thymine, deoxycytidine, adenosine, D-glucose, tryptophan, glycine, and L-alanine. The successful demonstration of this technique shows the possibilities and promise for future studies of internal vibrational modes of large biological molecules.

  17. THz time-domain spectroscopy for tokamak plasma diagnostics

    SciTech Connect

    Causa, F.; Zerbini, M.; Buratti, P.; Gabellieri, L.; Pacella, D.; Romano, A.; Tuccillo, A. A.; Tudisco, O.; Johnston, M.; Doria, A.; Gallerano, G. P.; Giovenale, E.

    2014-08-21

    The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

  18. THz time-domain spectroscopy for tokamak plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Causa, F.; Zerbini, M.; Johnston, M.; Buratti, P.; Doria, A.; Gabellieri, L.; Gallerano, G. P.; Giovenale, E.; Pacella, D.; Romano, A.; Tuccillo, A. A.; Tudisco, O.

    2014-08-01

    The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

  19. Frequency-domain spectroscopy using high-power tunable THz-wave sources: towards THz sensing and detector sensitivity calibration

    NASA Astrophysics Data System (ADS)

    Takida, Yuma; Minamide, Hiroaki

    2017-05-01

    The development of reliable, high-power, frequency-tunable terahertz (THz)-wave sources is crucial for a wide variety of applications, such as spectroscopy, imaging, and sensing. In order to generate frequency-tunable THz waves at room temperature, one of the most promising methods is a wavelength conversion in nonlinear optical crystals. Here, we present our recent results on high-power, widely-tunable, frequency-agile THz-wave sources based on nonlinear parametric processes in MgO:LiNbO3 crystals. By changing the noncollinear phase-matching condition in MgO:LiNbO3, the tunability of sub-nanosecond-pumped injection-seeded THz-wave parametric generators (is-TPGs) covers the 3.65-octave frequency range from 0.37 THz up to 4.65 THz. The monochromatic THz-wave output from is-TPGs is greater than 10 kW peak power with the linewidth of approximately 3 GHz and the stability of 1%. These is-TPG systems are reliable and promising high-power tunable THz-wave sources for frequency-domain spectroscopic measurements towards THz sensing and detector sensitivity calibration.

  20. Highly nonlinear organic crystal OHQ-T for efficient ultra-broadband terahertz wave generation beyond 10 THz.

    PubMed

    Kang, Bong Joo; Baek, In Hyung; Lee, Seung-Heon; Kim, Won Tae; Lee, Seung-Jun; Jeong, Young Uk; Kwon, O-Pil; Rotermund, Fabian

    2016-05-16

    We report on efficient generation of ultra-broadband terahertz (THz) waves via optical rectification in a novel nonlinear organic crystal with acentric core structure, i.e. 2-(4-hydroxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate (OHQ-T), which possesses an ideal molecular structure leading to a maximized nonlinear optical response for near-infrared-pumped THz wave generation. By systematic studies on wavelength-dependent phase-matching conditions in OHQ-T crystals of different thicknesses we are able to generate coherent THz waves with a high peak-to-peak electric field amplitude of up to 650 kV/cm and an upper cut-off frequency beyond 10 THz. High optical-to-THz conversion efficiency of 0.31% is achieved by efficient index matching with a selective pumping at 1300 nm.

  1. Planar diode multiplier chains for THz spectroscopy

    NASA Technical Reports Server (NTRS)

    Maiwald, Frank W.; Drouin, Brian J.; Pearson, John C.; Mehdi, Imran; Lewena, Frank; Endres, Christian; Winnewisser, Gisbert

    2005-01-01

    High-resolution laboratory spectroscopy is utilized as a diagnostic tool to determine noise and harmonic content of balanced [9]-[11] and unbalanced [12]-[14] multiplier designs. Balanced multiplier designs suppress unintended harmonics more than -20dB. Much smaller values were measured on unbalanced multipliers.

  2. THz acoustic phonon spectroscopy and nanoscopy by using piezoelectric semiconductor heterostructures.

    PubMed

    Mante, Pierre-Adrien; Huang, Yu-Ru; Yang, Szu-Chi; Liu, Tzu-Ming; Maznev, Alexei A; Sheu, Jinn-Kong; Sun, Chi-Kuang

    2015-02-01

    Thanks to ultrafast acoustics, a better understanding of acoustic dynamics on a short time scale has been obtained and new characterization methods at the nanoscale have been developed. Among the materials that were studied during the development of ultrafast acoustics, nitride based heterostructures play a particular role due to their piezoelectric properties and the possibility to generate phonons with over-THz frequency and bandwidth. Here, we review some of the work performed using this type of structure, with a focus on THz phonon spectroscopy and nanoscopy. First, we present a brief description of the theory of coherent acoustic phonon generation by piezoelectric heterostructure. Then the first experimental observation of coherent acoustic phonon generated by the absorption of ultrashort light pulses in piezoelectric heterostructures is presented. From this starting point, we then present some methods developed to realize customizable phonon generation. Finally we review some more recent applications of these structures, including imaging with a nanometer resolution, broadband attenuation measurements with a frequency up to 1THz and phononic bandgap characterization. Copyright © 2014 Elsevier B.V. All rights reserved.

  3. Broadband single-molecule excitation spectroscopy

    PubMed Central

    Piatkowski, Lukasz; Gellings, Esther; van Hulst, Niek F.

    2016-01-01

    Over the past 25 years, single-molecule spectroscopy has developed into a widely used tool in multiple disciplines of science. The diversity of routinely recorded emission spectra does underpin the strength of the single-molecule approach in resolving the heterogeneity and dynamics, otherwise hidden in the ensemble. In early cryogenic studies single molecules were identified by their distinct excitation spectra, yet measuring excitation spectra at room temperature remains challenging. Here we present a broadband Fourier approach that allows rapid recording of excitation spectra of individual molecules under ambient conditions and that is robust against blinking and bleaching. Applying the method we show that the excitation spectra of individual molecules exhibit an extreme distribution of solvatochromic shifts and distinct spectral shapes. Importantly, we demonstrate that the sensitivity and speed of the broadband technique is comparable to that of emission spectroscopy putting both techniques side-by-side in single-molecule spectroscopy. PMID:26794035

  4. THz Time-Domain Spectroscopy of Complex Interstellar Ice Analogs

    NASA Astrophysics Data System (ADS)

    Ioppolo, Sergio; McGuire, Brett A.; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey

    2014-06-01

    It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 - 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, and CH4) compared to more complex molecules (e.g., HCOOH, CH3COOH, CH3CHO, (CH3)2CO, HCOOCH3, and HCOOC2H5). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.

  5. Dielectric response of pure and doped-GaSe crystals studied by an indigenously developed broadband THz-TDS system

    NASA Astrophysics Data System (ADS)

    Das, Amit C.; Bhattacharya, S.; Mandal, K. C.; Mondal, S.; Jewariya, M.; Ozaki, T.; Bhaktha, S. N. B.; Datta, P. K.

    2016-04-01

    Publisher's Note: This paper, originally published on 12 July 2016, was replaced with a corrected/revised version on 26 July 2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. We have developed a terahertz time domain spectroscopy system (THz TDS). For THz generation, optical rectification process and for detection, electro-optic sampling processes are used. Identical < 110 > cut ZnTe crystals are used for both generation and detection of THz radiation.This spectroscopy system can be used for the noninvasive and contactless electrical and optical characterizations of various samples. In this work spectroscopic measurements of pure, Chromium and Indium doped GaSe crystals within 0.4 THz to 3 THz range are taken by the developed set-up to study the dielectric response of the samples.

  6. Low THz spectroscopy of some widely used explosives

    NASA Astrophysics Data System (ADS)

    Globus, Tatiana; Gelmont, Boris; Khromova, Tatyana

    2010-04-01

    We investigated resonance spectroscopic features from several widely used explosives materials including RDX and PETN in the low THz range with the goal of understanding the mechanism of interaction between radiation and material in the form of solid films, gels and dilute solutions (suspensions). FTIR spectroscopy was used to measure spectra in transmission and reflection modes. We demonstrated that very small amount of material with a simple sample preparation technique can be used still providing very accurate results. Spectral features are specific not only for main ingredients but for modifications with different plasticizers. The consistency of results for different amount of material was observed. Computational modeling confirmed the lowest frequency modes.

  7. Broadband Phase Spectroscopy over Turbulent Air Paths

    NASA Astrophysics Data System (ADS)

    Giorgetta, Fabrizio R.; Rieker, Gregory B.; Baumann, Esther; Swann, William C.; Sinclair, Laura C.; Kofler, Jon; Coddington, Ian; Newbury, Nathan R.

    2015-09-01

    Broadband atmospheric phase spectra are acquired with a phase-sensitive dual-frequency-comb spectrometer by implementing adaptive compensation for the strong decoherence from atmospheric turbulence. The compensation is possible due to the pistonlike behavior of turbulence across a single spatial-mode path combined with the intrinsic frequency stability and high sampling speed associated with dual-comb spectroscopy. The atmospheric phase spectrum is measured across 2 km of air at each of the 70 000 comb teeth spanning 233 cm-1 across hundreds of near-infrared rovibrational resonances of CO2 , CH4 , and H2O with submilliradian uncertainty, corresponding to a 10-13 refractive index sensitivity. Trace gas concentrations extracted directly from the phase spectrum reach 0.7 ppm uncertainty, demonstrated here for CO2 . While conventional broadband spectroscopy only measures intensity absorption, this approach enables measurement of the full complex susceptibility even in practical open path sensing.

  8. THz time-domain spectroscopy on plant oils and animal fats

    NASA Astrophysics Data System (ADS)

    Hu, Ying; Guo, Lantao; Wang, Xiaohong; Zhang, Xi Cheng

    2005-01-01

    Terahertz (THz) radiation, generated by ultra short laser pulses, occupies a broad band on electromagnetic spectrum chart. This radiation band belongs to far-infrared. It is a new research field of studying THz radiation interacting with materials especially with biomaterials. The paper shows experimental results of five plant oil samples from different kind of plants and two kinds of animal fat samples by using THz-TDS (THz time-domain spectroscopy) technology. The refraction indices and the absorption coefficients of these samples are measured in the range from 0.2 to 2.0 THz. The results show that different oils have different refraction indices. For oil samples, refraction indices decrease slowly while their coefficients of absorption increase with the increases of THz frequency. For the animal fat samples, the refraction indices show almost no change while the absorption coefficients increase with the increasing THz frequency. The absorption coefficients increase with the increasing temperature.

  9. Terahetz spectroscopy of molten sulfur using a tunable THz source

    NASA Astrophysics Data System (ADS)

    Mross, M.; Lowell, T.; Guertin, C.; O'Donnell, A.; Vezzoli, G. C.

    2006-10-01

    We have studied the liquid-liquid allotropic transitions in molten sulfur using terahertz (THz) spectroscopy. Liquid sulfur is selected as an initial choice of materials because its structure and properties are well established from previous in-situ studies by one of the current investigators (and by other researchers) using a variety of physical and chemical methodologies. It is known that sulfur melts to an equilibrium mixture of octameric (S 8) rings and short chains, with a small concentration of hexameric rings (S 6). As temperature is increased, thermal energy initiates ring scission and the resulting diradically-terminated short chains undergo covalent bonding to induce polymerization at 159-166°C. Further increase in temperature causes an increase in chain length and an increase in chain species concentration until a temperature of 188°C is reached at which the long chains (~10 6 atoms in length) undergo chain scission, and although the chains start to break up, the polymer concentration of the mixed phases still increases. We have experimentally mapped THz absorption, transmission, and reflection/scattering effects with these known transitions in liquid sulfur, as a function of temperature and wavelength.

  10. Active metamaterial: Gain and stability, and microfluidic chip for THz cell spectroscopy

    NASA Astrophysics Data System (ADS)

    Tang, Qi

    Metamaterials are artificially designed composite materials which can exhibit unique and unusual properties such as the negative refractive index, negative phase velocity, etc. The concept of metamaterials becomes prevalent in the electromagnetic society since the first experimental implementation in the early 2000s. Many fascinated potential applications, e.g. super lens, invisibility cloaking, and novel antennas that are electrically small, have been proposed based on metamaterials. However, most of the applications still remain in theory and are not suitable for practical applications mainly due to the intrinsic loss and narrow bandwidth (large dispersion) determined by the fundamental physics of metamaterials. In this dissertation, we incorporate active gain devices into conventional passive metamaterials to overcome loss and even provide gain. Two types of active gain negative refractive index metamaterials are proposed, designed and experimentally demonstrated, including an active composite left-/right-handed transmission line and an active volumetric metamaterial. In addition, we investigate the non-Foster circuits for broadband matching of electrically small antennas. A rigorous way of analyzing the stability of non-Foster circuits by normalized determinant function is proposed. We study the practical factors that may affect the stability of non-Foster circuits, including the device parasitics, DC biasing, layouts and load impedance. A stable floating negative capacitor is designed, fabricated and tested. Moreover, it is important to resolve the sign of refractive index for active gain media which can be quite challenging. We investigate the analytical solution of a gain slab system, and apply the Nyquist criterion to analyze the stability of a causal gain medium. We then emphasize that the result of frequency domain simulation has to be treated with care. Lastly, this dissertation discusses another interesting topic about THz spectroscopy of live cells

  11. Continuous Monitoring of Photolysis Products by Thz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Omar, Abdelaziz; Cuisset, Arnaud; Mouret, Gaël; Hindle, Francis; Eliet, Sophie; Bocquet, Robin

    2015-06-01

    We demonstrate the potential of THz spectroscopy to monitor the real time evolution of the gas phase concentration of photolysis products and determine the kinetic reaction rate constant. In the primary work, we have chosen to examine the photolysis of formaldehyde (H_2CO). Exposure of H_2CO to a UVB light (250 to 360 nm) in a single pass of 135 cm length cell leads to decomposition via two mechanisms: the radical channel with production of HCO and the molecular channel with production of CO. A commercial THz source (frequency multiplication chain) operating in the range 600-900 GHz was used to detect and quantify the various chemical species as a function of time. Monitoring the concentrations of CO and H_2CO via rotational transitions, allowed the kinetic rate of H_2CO consummation to be obtained, and an estimation of the rate constants for both the molecular and radical photolysis mechanisms. We have modified our experimental setup to increase the sensitivity of the spectrometer and changed sample preparation protocol specifically to quantify the HCO concentration. Acetaldehyde was used as the precursor for photolysis by UVC resulting in the decompositon mechanism can be described by: CH_3CHO+hν→ CH_3 + HCO → CH_4 + CO Frequency modulation of the source and Zeeman modulation is used to achieve the high sensitivity required. Particular attention has been paid to the mercury photosensitization effect that allowed us to increase the HCO production enabling quantification of the monitored radical. We quantify the HCO radical and start a spectroscopic study of the line positions. H. M. Pickett and T. L. Boyd, Chem. Phys. Lett, Vol 58, 446-449, (1978) S. Eliet, A. Cuisset, M Guinet, F. Hindle, G. Mouret, R. Bocquet, and J. Demaison, Journal of Molecular Spectroscopy, Vol 279, 12-15 (2012). G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet and F. Hindle, Sensors Journal. IEEE, Vol 13, 133 - 138, (2013)

  12. Robust identification of concealed dangerous substances using THz imaging spectroscopy

    NASA Astrophysics Data System (ADS)

    Nystad, Helle E.; Haakestad, Magnus W.; van Rheenen, Arthur D.

    2015-05-01

    False alarm rates must be kept sufficiently low if a method to detect and identify objects or substances is to be implemented in real life applications. This is also true when trying to detect and identify dangerous substances such as explosives and drugs that are concealed in packaging materials. THz technology may be suited to detect these substances, especially when imaging and spectroscopy are combined. To achieve reasonable throughput, the detection and identification process must be automated and this implies reliance on algorithms to perform this task, rather than human beings. The identification part of the algorithm must compare spectral features of the unknown substance with those in a library of features and determining the distance, in some sense, between these features. If the distance is less than some defined threshold a match is declared. In this paper we consider two types of spectral characteristic that are derived from measured time-domain signals measured in the THz regime: the absorbance and its derivative. Also, we consider two schemes to measure the distance between the unknown and library characteristics: Spectral Angle Mapping (SAM) and Principal Component Analysis (PCA). Finally, the effect of windowing of the measured time-domain signal on the performance of the algorithms is studied, by varying the Blackman-Harris (B-H) window width. Algorithm performance is quantified by studying the receiver-operating characteristics (ROC). For the data considered in this study we conclude that the best performance is obtained when the derivative of the absorbance is used in combination with a narrow B-H window and SAM. SAM is a more straight-forward method and requires no large training data sets and tweaking.

  13. Broad-band frequency references in the near-infrared: Accurate dual comb spectroscopy of methane and acetylene

    NASA Astrophysics Data System (ADS)

    Zolot, A. M.; Giorgetta, F. R.; Baumann, E.; Swann, W. C.; Coddington, I.; Newbury, N. R.

    2013-03-01

    The Doppler-limited spectra of methane between 176 THz and 184 THz (5870-6130 cm-1) and acetylene between 193 THz and 199 THz (6430-6630 cm-1) are acquired via comb-tooth resolved dual comb spectroscopy with frequency accuracy traceable to atomic standards. A least squares analysis of the measured absorbance and phase line shapes provides line center frequencies with absolute accuracy of 0.2 MHz, or less than one thousandth of the room temperature Doppler width. This accuracy is verified through comparison with previous saturated absorption spectroscopy of 37 strong isolated lines of acetylene. For the methane spectrum, the center frequencies of 46 well-isolated strong lines are determined with similar high accuracy, along with the center frequencies for 1107 non-isolated lines at lower accuracy. The measured methane line-center frequencies have an uncertainty comparable to the few available laser heterodyne measurements in this region but span a much larger optical bandwidth, marking the first broad-band measurements of the methane 2ν3 region directly referenced to atomic frequency standards. This study demonstrates the promise of dual comb spectroscopy to obtain high resolution broadband spectra that are comparable to state-of-the-art Fourier-transform spectrometer measurements but with much improved frequency accuracy.Work of the US government, not subject to US copyright.

  14. Ultrafast Laser-Based Spectroscopy and Sensing: Applications in LIBS, CARS, and THz Spectroscopy

    PubMed Central

    Leahy-Hoppa, Megan R.; Miragliotta, Joseph; Osiander, Robert; Burnett, Jennifer; Dikmelik, Yamac; McEnnis, Caroline; Spicer, James B.

    2010-01-01

    Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS), coherent Raman spectroscopy, and terahertz (THz) spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by the use of ultrafast pulses in the signal generation process. Depending on the energy of the pulses used, the essential laser interaction process can primarily involve lattice vibrations, molecular rotations, or a combination of excited states produced by laser heating. While some of these techniques are currently confined to sensing at close ranges, others can be implemented for remote spectroscopic sensing owing principally to the laser pulse duration. We present a review of ultrafast laser-based spectroscopy techniques and discuss the use of these techniques to current and potential chemical and environmental sensing applications. PMID:22399883

  15. High precision spectroscopy and imaging in THz frequency range

    NASA Astrophysics Data System (ADS)

    Vaks, Vladimir L.

    2014-03-01

    Application of microwave methods for development of the THz frequency range has resulted in elaboration of high precision THz spectrometers based on nonstationary effects. The spectrometers characteristics (spectral resolution and sensitivity) meet the requirements for high precision analysis. The gas analyzers, based on the high precision spectrometers, have been successfully applied for analytical investigations of gas impurities in high pure substances. These investigations can be carried out both in absorption cell and in reactor. The devices can be used for ecological monitoring, detecting the components of chemical weapons and explosive in the atmosphere. The great field of THz investigations is the medicine application. Using the THz spectrometers developed one can detect markers for some diseases in exhaled air.

  16. Rotational Spectroscopy for Astrophysical Applications: the Thz Frequency Region

    NASA Astrophysics Data System (ADS)

    Puzzarini, Cristina; Cazzoli, Gabriele

    2011-06-01

    Recent missions, such as the Herschel Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA), have pointed out the need for precise and accurate frequency measurements and spectroscopic parameters in the THz range. In the present contribution, the THz spectrometer working at the University of Bologna and its applications are presented. The focus is here on the accuracy of the retrieved transition frequencies of neutral as well as ionic species and on line-broadening investigations.

  17. A Broadband THz-TDS System Based on DSTMS Emitter and LTG InGaAs/InAlAs Photoconductive Antenna Detector

    PubMed Central

    Zhang, Ying; Zhang, Xiaoling; Li, Shaoxian; Gu, Jianqiang; Li, Yanfeng; Tian, Zhen; Ouyang, Chunmei; He, Mingxia; Han, Jiaguang; Zhang, Weili

    2016-01-01

    We demonstrate a 4-f terahertz time-domain spectroscopy (THz-TDS) system using an organic crystal DSTMS as the THz emitter and a low temperature grown (LTG) InGaAs/InAlAs photoconductive antenna as the receiver. The system covers a frequency range from 0.2 up to 8 THz. The influences of the pump laser power, the probe laser power and the azimuthal angle of the DSTMS crystal on the time-domain THz amplitude are experimentally analyzed. The frequency accuracy of the system is verified by measuring two metamaterial samples and a lactose film in this THz-TDS system. The proposed combination of DSTMS emission and PC antenna detection realizes a compact and low-cost THz-TDS scheme with an ultra-broad bandwidth, which may promote the development and the applications of THz-TDS techniques. PMID:27244689

  18. A Broadband THz-TDS System Based on DSTMS Emitter and LTG InGaAs/InAlAs Photoconductive Antenna Detector

    NASA Astrophysics Data System (ADS)

    Zhang, Ying; Zhang, Xiaoling; Li, Shaoxian; Gu, Jianqiang; Li, Yanfeng; Tian, Zhen; Ouyang, Chunmei; He, Mingxia; Han, Jiaguang; Zhang, Weili

    2016-05-01

    We demonstrate a 4-f terahertz time-domain spectroscopy (THz-TDS) system using an organic crystal DSTMS as the THz emitter and a low temperature grown (LTG) InGaAs/InAlAs photoconductive antenna as the receiver. The system covers a frequency range from 0.2 up to 8 THz. The influences of the pump laser power, the probe laser power and the azimuthal angle of the DSTMS crystal on the time-domain THz amplitude are experimentally analyzed. The frequency accuracy of the system is verified by measuring two metamaterial samples and a lactose film in this THz-TDS system. The proposed combination of DSTMS emission and PC antenna detection realizes a compact and low-cost THz-TDS scheme with an ultra-broad bandwidth, which may promote the development and the applications of THz-TDS techniques.

  19. Hollow plasmonic antennas for broadband SERS spectroscopy.

    PubMed

    Messina, Gabriele C; Malerba, Mario; Zilio, Pierfrancesco; Miele, Ermanno; Dipalo, Michele; Ferrara, Lorenzo; De Angelis, Francesco

    2015-01-01

    The chemical environment of cells is an extremely complex and multifaceted system that includes many types of proteins, lipids, nucleic acids and various other components. With the final aim of studying these components in detail, we have developed multiband plasmonic antennas, which are suitable for highly sensitive surface enhanced Raman spectroscopy (SERS) and are activated by a wide range of excitation wavelengths. The three-dimensional hollow nanoantennas were produced on an optical resist by a secondary electron lithography approach, generated by fast ion-beam milling on the polymer and then covered with silver in order to obtain plasmonic functionalities. The optical properties of these structures have been studied through finite element analysis simulations that demonstrated the presence of broadband absorption and multiband enhancement due to the unusual geometry of the antennas. The enhancement was confirmed by SERS measurements, which showed a large enhancement of the vibrational features both in the case of resonant excitation and out-of-resonance excitation. Such characteristics indicate that these structures are potential candidates for plasmonic enhancers in multifunctional opto-electronic biosensors.

  20. Electronic resonances in broadband stimulated Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Batignani, G.; Pontecorvo, E.; Giovannetti, G.; Ferrante, C.; Fumero, G.; Scopigno, T.

    2016-01-01

    Spontaneous Raman spectroscopy is a formidable tool to probe molecular vibrations. Under electronic resonance conditions, the cross section can be selectively enhanced enabling structural sensitivity to specific chromophores and reaction centers. The addition of an ultrashort, broadband femtosecond pulse to the excitation field allows for coherent stimulation of diverse molecular vibrations. Within such a scheme, vibrational spectra are engraved onto a highly directional field, and can be heterodyne detected overwhelming fluorescence and other incoherent signals. At variance with spontaneous resonance Raman, however, interpreting the spectral information is not straightforward, due to the manifold of field interactions concurring to the third order nonlinear response. Taking as an example vibrational spectra of heme proteins excited in the Soret band, we introduce a general approach to extract the stimulated Raman excitation profiles from complex spectral lineshapes. Specifically, by a quantum treatment of the matter through density matrix description of the third order nonlinear polarization, we identify the contributions which generate the Raman bands, by taking into account for the cross section of each process.

  1. Chiral Molecules Revisited by Broadband Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Schnell, Melanie

    2014-06-01

    Chiral molecules have fascinated chemists for more than 150 years. While their physical properties are to a very good approximation identical, the two enantiomers of a chiral molecule can have completely different (bio)chemical activities. For example, the right-handed enantiomer of carvone smells of spearmint while the left-handed one smells of caraway. In addition, the active components of many drugs are of one specific handedness, such as in the case of ibuprofen. However, in nature as well as in pharmaceutical applications, chiral molecules often exist in mixtures with other chiral molecules. The analysis of these complex mixtures to identify the molecular components, to determine which enantiomers are present, and to measure the enantiomeric excesses (ee) remains a challenging task for analytical chemistry, despite its importance for modern drug development. We present here a new method of differentiating enantiomers of chiral molecules in the gas phase based on broadband rotational spectroscopy. The phase of the acquired signal bares the signature of the enantiomer, as it depends upon the combined quantity, μ_a μ_b μ_c, which is of opposite sign between enantiomers. It thus also provides information on the absolute configuration of the particular enantiomer. Furthermore, the signal amplitude is proportional to the ee. A significant advantage of our technique is its inherent mixture compatibility due to the fingerprint-like character of rotational spectra. In this contribution, we will introduce the technique and present our latest results on chiral molecule spectroscopy and enantiomer differentiation. D. Patterson, M. Schnell, J.M. Doyle, Nature 497 (2013) 475-477 V.A. Shubert, D. Schmitz, D. Patterson, J.M. Doyle, M. Schnell, Angewandte Chemie International Edition 53 (2014) 1152-1155

  2. Characteristics and development of the coherent synchrotron radiation sources for THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Barros, J.; Evain, C.; Roussel, E.; Manceron, L.; Brubach, J.-B.; Tordeux, M.-A.; Couprie, M.-E.; Bielawski, S.; Szwaj, C.; Labat, M.; Roy, P.

    2015-09-01

    We report on the characteristics of coherent synchrotron radiation (CSR) as a source for spectroscopy. The optimization of the source and the resulting figures of merits in terms of flux, signal to noise, spatial distribution and spectral and temporal distribution are presented together with a spectroscopic application. The emission of THz during the slicing operation is also described. The conclusion opens up perspectives made possible by the availability of this intense and stable THz source.

  3. Pulsed THz spectroscopy of substance under disordered opaque cover

    NASA Astrophysics Data System (ADS)

    Trofimov, V. A.; Zagursky, D. Yu.; Zakharova, I. G.

    2016-02-01

    Remote sensing using the pulsed THz-TDS is of great interest because of its possible practical applications. Many ordinary materials (paper, for example) are transparent to THz radiation while the hazardous substances, which have to detect, possess fingerprints in this frequency range. However, cover of ordinary material can distort its spectrum in such a way that the spectrum of reflected THz pulse or transmitted THz pulse will contain absorption frequencies, which are inherent to dangerous substance (explosives, illistic drugs....), despite their absence in the material under consideration. This is a consequence of covering material influence due to its density fluctuation or its structure variation, for example. As rule, covering material structure fluctuation may be comparable with some wavelengths of the probing THz radiation. Thus, the cover can act as a disordered photonic structure with respect to incident THz pulse and its action results in additional absorption spectral lines appearance and in turn, the incorrect substance identification will take place. In this paper we discuss an influence of quasi-periodic structure with variable dielectric constant on the spectrum of a substance, which is placed behind or inside such structure. The investigation is conducted by means of computer simulation. We consider a single layer of optically active substance placed between two covers consisting of linear layers with random dielectric permittivity. Incident Gaussian pulse with a few-cycles falls on the substance covered by layers. Both transmitted pulse and reflected pulse are analyzed and their spectra are compared to those of the incident pulse. For description of a THz pulse interaction with an optically active substance covered by disordered structures we use the Maxwell's equations together with matrix-density formalism. The appearance of additional spectrum extremes due to the layered structure influence is illustrated. Computer simulation results were

  4. New developments in THz quartz enhanced photoacoustic spectroscopy

    NASA Astrophysics Data System (ADS)

    Spagnolo, Vincenzo; Patimisco, Pietro; Sampaolo, Angelo; Giglio, Marilena; Vitiello, Miriam S.; Scamarcio, Gaetano; Tittel, Frank K.

    2016-09-01

    We will report on new developments of quartz-enhanced photo-acoustic (QEPAS) sensor employing THz quantum cascade laser (QCLs). The extension of the QEPAS technique in the THz range was made possible by the realization of custom made QTFs. With the aim to improve the QTF acousto-electric transduction efficiency, we designed and realized new QTF designs. A detailed analysis of the quality factor, the resonance frequency and the electrical resistance of custom quartz tuning forks (QTFs) with different geometrical parameters is reported. The custom QTFs were employed in QEPAS sensors using THz QCLs as the laser excitation sources and targeting CH3OH and H2S. Minimum detection limits of a few tens of ppb and normalized noise equivalent absorption factors down to 3.75×10-11 cm-1W/Hz½ were achieved.

  5. Thin layered drawing media probed by THz time-domain spectroscopy.

    PubMed

    Tasseva, J; Taschin, A; Bartolini, P; Striova, J; Fontana, R; Torre, R

    2016-12-19

    Dry and wet drawing materials were investigated by THz time-domain spectroscopy in transmission mode. Carbon-based and iron-gall inks have been studied, some prepared following ancient recipes and others using current synthetic materials; a commercial ink was studied as well. We measured the THz signals on the thin films of liquid inks deposited on polyethylene pellicles, comparing the results with the thick pellets of dried inks blended with polyethylene powder. This study required the implementation of an accurate experimental method and data analysis procedure able to provide a reliable extraction of the material transmission parameters from a structured sample composed of thin layers, down to a thickness of a few tens of micrometers. THz measurements on thin ink layers enabled the determination of both the absorption and the refractive index in an absolute scale in the 0.1-3 THz range, as well as the layer thickness. THz spectroscopic features of a paper sheet dyed by using one of the iron-gall inks were also investigated. Our results showed that THz time-domain spectroscopy enables the discrimination of various inks on different supports, including the application on paper, together with the proper determination of the absorption coefficients and indices of refraction.

  6. Detection and identification of explosive RDX by THz diffuse reflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Hai-Bo; Chen, Yunqing; Bastiaans, Glenn J.; Zhang, X.-C.

    2006-01-01

    The reflection spectrum of the explosive RDX was acquired from a diffuse reflection measurement using a THz time-domain spectroscopy system in combination with a diffuse reflectance accessory. By applying the Kramers-Kronig transform to the reflection spectrum, the absorption spectrum (0.2-1.8 THz) was obtained. It agrees with the result from a transmission measurement and distinguishes RDX from other materials. The effect of the reference spectrum was examined by using both a Teflon pellet and a copper plate as references. The strong absorption of RDX at 0.82 THz allowed it to be identified by the diffuse reflection measurement even when the RDX sample was covered with certain optically opaque materials. Our investigation demonstrates that THz technique is capable of detecting and identifying hidden RDX-related explosives in a diffuse reflection mode, which is crucial for the standoff detection in the real world applications.

  7. Characterization of ofloxacin-oxalic acid complex by PXRD, NMR, and THz spectroscopy.

    PubMed

    Limwikrant, Waree; Higashi, Kenjirou; Yamamoto, Keiji; Moribe, Kunikazu

    2009-12-01

    A novel ofloxacin-oxalic acid complex was prepared by the cogrinding method. The obtained complex was characterized by powder X-ray diffraction (PXRD), infrared (IR), solid-state nuclear magnetic resonance (NMR), and terahertz (THz) spectroscopy. The PXRD measurement revealed that the ofloxacin-oxalic acid complex induced by cogrinding was formed at a molar ratio of 1:2. Weak interaction between two components, not a hydrogen bonding, was found by IR and solid-state NMR spectroscopy. The distinctive THz spectrum showed that the vibrational modes of the complex were different from those of the starting materials, suggesting that THz spectroscopy is an alternative tool to evaluate complex formation through weak interactions.

  8. IR/THz Double Resonance Spectroscopy Approach for Remote Chemical Detection at Atmospheric Pressure

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    A remote sensing methodology based on infrared/terahertz (IR/THz) double resonance (DR) spectroscopy is shown to overcome limitations traditionally associated with either IR or THz spectroscopic approaches for detecting trace gases in an atmosphere. The applicability of IR/THz DR spectroscopy is explored by estimating the IR and THz power requirements for detecting a 100 part-per-million-meter cloud of methyl fluoride, methyl chloride, or methyl bromide at ranges up to 1km in three atmospheric windows below 0.3 THz. These prototypical molecules are used to ascertain the dependence of the DR signal-to-noise ratio on IR and THz beam power. A line-tunable CO_2 laser with 100 ps pulse duration generates a DR signature in four rotational transitions on a time scale commensurate with collisional relaxations caused by atmospheric N_2 and O_2. A continuous wave THz beam is frequency tuned to probe one of these rotational transitions so that laser-induced absorption variations in the analyte cloud are detected as temporal power fluctuations synchronized with the laser pulses. A combination of molecule-specific physics and scenario-dependent atmospheric conditions are used to predict the signal-to-noise ratio (SNR) for detecting an analyte as a function of cloud column density. A methodology is presented by which the optimal IR/THz pump/probe frequencies are identified. These estimates show the potential for low concentration chemical detection in a challenging atmospheric scenario with currently available or near term hardware components.

  9. The flexibility of hydrated bovine serum albumin investigated by THz spectroscopy and molecular modeling

    NASA Astrophysics Data System (ADS)

    Mernea, Maria; Calborean, Octavian; Petrescu, Livia; Dinca, Mihai P.; Leca, Aurel; Apostol, Dan; Dascalu, Traian; Mihailescu, Dan

    2009-09-01

    The native cellular environment represents a crowded system comprising high concentrations of soluble molecules that interact mostly in a nonspecific manner. Some of the macromolecular crowding effects occurring in biological media are conformational changes and macromolecular associations. Most of our knowledge on protein folding and protein-protein interactions was acquired from experiments on proteins in dilute solutions or from theoretical models of isolated proteins in either explicit or implicit solvent. Here we present a 50% w/w bovine serum albumin (BSA) solution model that comprises two solute molecules included in a single water box. We determined the vibration spectrum of the 50% w/w BSA solution using THz spectroscopy and we calculated the theoretical THz spectrum. We observed a good correlation between the experimental and theoretical spectra for the frequency range of 0.3 - 1.5 THz. We also investigated the contribution of each BSA molecule to the solution THz spectrum by simulating THz spectra of the two BSA molecules from the solution model and water, each accounting for a 50% w/w BSA solution. The spectra appear to be similar. As the two molecules in our solution model have different conformations, we investigated the importance of the apparently insignificant differences between simulated THz spectra of the two proteins. We found that the differences should be considered significant, as they reflect differences between the flexibility of the two BSA molecules.

  10. The flexibility of hydrated bovine serum albumin investigated by THz spectroscopy and molecular modeling

    NASA Astrophysics Data System (ADS)

    Mernea, Maria; Calborean, Octavian; Petrescu, Livia; Dinca, Mihai P.; Leca, Aurel; Apostol, Dan; Dascalu, Traian; Mihailescu, Dan

    2010-05-01

    The native cellular environment represents a crowded system comprising high concentrations of soluble molecules that interact mostly in a nonspecific manner. Some of the macromolecular crowding effects occurring in biological media are conformational changes and macromolecular associations. Most of our knowledge on protein folding and protein-protein interactions was acquired from experiments on proteins in dilute solutions or from theoretical models of isolated proteins in either explicit or implicit solvent. Here we present a 50% w/w bovine serum albumin (BSA) solution model that comprises two solute molecules included in a single water box. We determined the vibration spectrum of the 50% w/w BSA solution using THz spectroscopy and we calculated the theoretical THz spectrum. We observed a good correlation between the experimental and theoretical spectra for the frequency range of 0.3 - 1.5 THz. We also investigated the contribution of each BSA molecule to the solution THz spectrum by simulating THz spectra of the two BSA molecules from the solution model and water, each accounting for a 50% w/w BSA solution. The spectra appear to be similar. As the two molecules in our solution model have different conformations, we investigated the importance of the apparently insignificant differences between simulated THz spectra of the two proteins. We found that the differences should be considered significant, as they reflect differences between the flexibility of the two BSA molecules.

  11. THz time-domain spectroscopy of mixed CO2-CH3OH interstellar ice analogs.

    PubMed

    McGuire, Brett A; Ioppolo, Sergio; Allodi, Marco A; Blake, Geoffrey A

    2016-07-27

    The icy mantles of interstellar dust grains are the birthplaces of the primordial prebiotic molecular inventory that may eventually seed nascent solar systems and the planets and planetesimals that form therein. Here, we present a study of two of the most abundant species in these ices after water: carbon dioxide (CO2) and methanol (CH3OH), using TeraHertz (THz) time-domain spectroscopy and mid-infrared spectroscopy. We study pure and mixed-ices of these species, and demonstrate the power of the THz region of the spectrum to elucidate the long-range structure (i.e. crystalline versus amorphous) of the ice, the degree of segregation of these species within the ice, and the thermal history of the species within the ice. Finally, we comment on the utility of the THz transitions arising from these ices for use in astronomical observations of interstellar ices.

  12. Dispersion of carbon nanotubes in melt compounded polypropylene based composites investigated by THz spectroscopy.

    PubMed

    Casini, R; Papari, G; Andreone, A; Marrazzo, D; Patti, A; Russo, P

    2015-07-13

    We investigate the use of Terahertz (THz) Time Domain Spectroscopy (TDS) as a tool for the measurement of the index dispersion of multi-walled carbon nanotubes (MWCNT) in polypropylene (PP) based composites. Samples containing 0.5% by volume concentration of non-functionalized and functionalized carbon nanotubes are prepared by melt compounding technology. Results indicate that the THz response of the investigated nanocomposites is strongly dependent on the kind of nanotube functionalization, which in turn impacts on the level of dispersion inside the polymer matrix. We show that specific dielectric parameters such as the refractive index and the absorption coefficient measured by THz spectroscopy can be both correlated to the index of dispersion as estimated using conventional optical microscopy.

  13. Sub-Thz Vibrational Spectroscopy for Analysis of Ovarian Cancer Cells

    NASA Astrophysics Data System (ADS)

    Ferrance, Jerome P.; Sizov, Igor; Jazaeri, Amir; Moyer, Aaron; Gelmont, Boris; Globus, Tatiana

    2016-06-01

    Sub-THz vibrational spectroscopy utilizes wavelengths in the submillimeter-wave range ( 1.5-30 wn), beyond those traditionally used for chemical and biomolecular analysis. This low energy radiation excites low-frequency internal molecular motions (vibrations) involving hydrogen bonds and other weak connections within these molecules. The ability of sub-THz spectroscopy to identify and quantify biological molecules is based on detection of signature resonance absorbance at specific frequencies between 0.05 and 1 THz, for each molecule. The long wavelengths of this radiation, mean that it can even pass through entire cells, detecting the combinations of proteins and nucleic acids that exist within the cell. This research introduces a novel sub-THz resonance spectroscopy instrument with spectral resolution sufficient to identify individual resonance absorption peaks, for the analysis of ovarian cancer cells. In vitro cell cultures of SK-OV-3 and ES-2 cells, two human ovarian cancer subtypes, were characterized and compared with a normal non-transformed human fallopian tube epithelial cell line (FT131). A dramatic difference was observed between the THz absorption spectra of the cancer and normal cell sample materials with much higher absorption intensity and a very strong absorption peak at a frequency of 13 wn dominating the cancer sample spectra. Comparison of experimental spectra with molecular dynamic simulated spectroscopic signatures suggests that the high intensity spectral peak could originate from overexpressed mi-RNA molecules specific for ovarian cancer. Ovarian cancer cells are utilized as a proof of concept, but the sub-THz spectroscopy method is very general and could also be applied to other types of cancer.

  14. A tunable, linac based, intense, broad-band THz source forpump-probe experiments

    SciTech Connect

    Schmerge, J.; Adolphsen, C.; Corbett, J.; Dolgashev, V.; Durr, H.; Fazio, M.; Fisher, A.; Frisch, J.; Gaffney, K.; Guehr, M.; Hastings, J.; Hettel, B.; Hoffmann, M.; Hogan, M.; Holtkamp, N.; Huang, X.; Huang, Z.; Kirchmann, P.; LaRue, J.; Limborg, C.; Lindenberg, A.; Loos, H.; Maxwell, T.; Nilsson, A.; Raubenheimer, T.; Reis, D.; Ross, M.; Shen, Z. -X.; Stupakov, G.; Tantawi, S.; Tian, K.; Wu, Z.; Xiang, D.; Yakimenko, V.

    2015-02-02

    We propose an intense THz source with tunable frequency and bandwidth that can directly interact with the degrees of freedom that determine the properties of materials and thus provides a new tool for controlling and directing these ultrafast processes as well as aiding synthesis of new materials with new functional properties. This THz source will broadly impact our understanding of dynamical processes in matter at the atomic-scale and in real time. Established optical pumping schemes using femtosecond visible frequency laser pulses for excitation are extended into the THz frequency regime thereby enabling resonant excitation of bonds in correlated solid state materials (phonon pumping), to drive low energy electronic excitations, to trigger surface chemistry reactions, and to all-optically bias a material with ultrashort electric fields or magnetic fields. A linac-based THz source can supply stand-alone experiments with peak intensities two orders of magnitude stronger than existing laser-based sources, but when coupled with atomic-scale sensitive femtosecond x-ray probes it opens a new frontier in ultrafast science with broad applications to correlated materials, interfacial and liquid phase chemistry, and materials in extreme conditions.

  15. 0.1-20 THz ultra-broadband perfect absorber via a flat multi-layer structure.

    PubMed

    Xu, Gongjie; Zhang, Jun; Zang, Xiaofei; Sugihara, Okihiro; Zhao, Hongwei; Cai, Bin

    2016-10-03

    An ultra-broadband perfect absorber based on graded-index mechanism is designed and fabricated. The perfect absorber is comprised of a heavily-doped silicon absorption substrate and a flat six-layer antireflective structure. The refractive index of each layer was widely tuned by hollow polystyrene microsphere and TiO2 nanoparticle dopants, which can offer a gradually changed refractive index profile from 1.3 to 2.9. The experimental results show that 98% absorption can be achieved within the range of 0.1-20 THz. Moreover, the high absorption efficiency as well as the ultra-broad range can maintain for incident angle from 0 to 75° by the theoretical simulation.

  16. Thz Spectroscopy of 12CH^+, 13CH^+, and 12CD^+

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Drouin, Brian; Pearson, John; Amano, Takayoshi

    2015-06-01

    In 1937, Dunham detected a couple of unidentified lines in near-UV, and later Douglas and Herzberg identified them based on their laboratory observations to be low-J electronic transitions of CH^+. The electronic spectra, in particular the A^1Π-X^1σ^+ band, have been investigated extensively. On the other hand, the pure rotational transitions have not been studied so extensively. Only the lowest rotational transition, J=1-0, was observed in the laboratory for the normal species, 13CH^+, and CD^+. Based on the laboratory frequency, CH^+ was detected in star forming regions with the Hershel space observatory. Cernicharo et al identified pure rotational transitions from J=2-1 to J=6-5 in the far-infrared region in the ISO spectrum of the planetary nebula NGC 7027. The ISO spectra, however, were of low-resolution, so high-resolution spectroscopic observation is highly desirable. In this presentation, we have extended the measurements to higher-J lines up to 2 THz. For production of CH^+, an extended negative glow discharge in a gas mixture of CH_4 (˜ 0.5 mTorr) diluted in He (˜ 60 mTorr) was used. The optimum discharge current was about 15 mA and the axial magnetic filed to 160 Gauss was applied up. The discharge cell was cooled down to liquid nitrogen temperature. Several frequency multiplier chains, developed at JPL and purchased from Virginia Diodes, were used as THz radiation sources. New THz measurements are not only useful for providing better characterization of spectroscopic properties but also will serve as starting point for astronomical observations. T. Dunham, Publ. Astron. Soc. Pac., 49,~26 (1937) A. E. Douglas and G. Herzberg, Ap. J. 94,~381 (1941) T. Amano, Ap.J.Lett., 716, L1 (2010) T. Amano, J. Chem. Phys., 133, 244305 (2010) J. Cernicharo et al., Ap. J. Lett., 483, L65 (1997)

  17. Earle K. Plyler Prize for Molecular Spectroscopy & Dynamics Lecture: Broadband Rotational Spectroscopy for Chemical Kinetics, Molecular Structure, and Analytical Chemistry

    NASA Astrophysics Data System (ADS)

    Pate, Brooks

    2013-03-01

    Advances in high-speed digital electronics have enabled a new generation of molecular rotational spectroscopy techniques that provide instantaneous broadband spectral coverage. These techniques use a chirped excitation pulse to coherently excite the molecular sample over a spectral bandwidth of 10 GHz or larger through rapid passage. The subsequent time-domain emission is recorded using high-speed digitizers (up to 100 Gigasample/s) and the frequency domain spectrum is produced by fast Fourier transformation. The chirped-pulse Fourier transform (CP-FT) method has been implemented in the microwave frequency range (2-40 GHz) for studies of cold samples in pulsed jet sources and in the mm-wave/terahertz (THz) frequency range for studies of samples at room-temperature. The method has opened new applications for molecular rotational spectroscopy in the area of chemical kinetics where dynamic rotational spectroscopy is used to measure the rates of unimolecular isomerization reactions in highly excited molecules prepared by pulsed infrared laser excitation. In these applications, the isomerization rate is obtained from an analysis of the overall line shapes which are modified by chemical exchange leading to coalescence behavior similar to the effect in NMR spectroscopy. The sensitivity of the method and the ability to extend it to low frequency (2-8 GHz) have significantly increased the size range of molecules and molecular clusters for structure determination using isotopic substitution to build up the 3D molecular structures atom-by-atom. Application to the structure of water clusters with up to 15 water molecules will be presented. When coupled with advances in solid-state mm-wave/THz devices, this method provides a direct digital technique for analytical chemistry of room-temperature gases based on molecular rotational spectroscopy. These high-throughput methods can analyze complex sample mixtures with unmatched chemical selectivity and short analysis times. Work

  18. A highly linear superconducting bolometer for quantitative THz Fourier transform spectroscopy.

    PubMed

    Kehrt, Mathias; Monte, Christian; Beyer, Jörn; Hollandt, Jörg

    2015-05-04

    A superconducting transition edge sensor (TES) bolometer operating in the spectral range from 0.1 THz to 3 THz was designed. It is especially intended for Fourier transform spectroscopy and features a higher dynamic range and a highly linear response at a similar response compared to commercially available silicon composite bolometers. The design is based on a thin film metal mesh absorber, a superconducting thermistor and Si3N4 membrane technology. A prototype was set up, characterized and successfully used in first applications.

  19. Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy

    PubMed Central

    Hindle, Francis; Yang, Chun; Mouret, Gael; Cuisset, Arnaud; Bocquet, Robin; Lampin, Jean-François; Blary, Karine; Peytavit, Emilien; Akalin, Tahsin; Ducournau, Guillaume

    2009-01-01

    A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements. PMID:22291552

  20. THz-Raman: accessing molecular structure with Raman spectroscopy for enhanced chemical identification, analysis, and monitoring

    NASA Astrophysics Data System (ADS)

    Heyler, Randy A.; Carriere, James T. A.; Havermeyer, Frank

    2013-05-01

    Structural analysis via spectroscopic measurement of rotational and vibrational modes is of increasing interest for many applications, since these spectra can reveal unique and important structural and behavioral information about a wide range of materials. However these modes correspond to very low frequency (~5cm-1 - 200cm-1, or 150 GHz-6 THz) emissions, which have been traditionally difficult and/or expensive to access through conventional Raman and Terahertz spectroscopy techniques. We report on a new, inexpensive, and highly efficient approach to gathering ultra-low-frequency Stokes and anti-Stokes Raman spectra (referred to as "THz-Raman") on a broad range of materials, opening potential new applications and analytical tools for chemical and trace detection, identification, and forensics analysis. Results are presented on explosives, pharmaceuticals, and common elements that show strong THz-Raman spectra, leading to clear discrimination of polymorphs, and improved sensitivity and reliability for chemical identification.

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

    PubMed

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

    2008-06-23

    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.

  2. Perspective: Watching low-frequency vibrations of water in biomolecular recognition by THz spectroscopy.

    PubMed

    Xu, Yao; Havenith, Martina

    2015-11-07

    Terahertz (THz) spectroscopy has turned out to be a powerful tool which is able to shed new light on the role of water in biomolecular processes. The low frequency spectrum of the solvated biomolecule in combination with MD simulations provides deep insights into the collective hydrogen bond dynamics on the sub-ps time scale. The absorption spectrum between 1 THz and 10 THz of solvated biomolecules is sensitive to changes in the fast fluctuations of the water network. Systematic studies on mutants of antifreeze proteins indicate a direct correlation between biological activity and a retardation of the (sub)-ps hydration dynamics at the protein binding site, i.e., a "hydration funnel." Kinetic THz absorption studies probe the temporal changes of THz absorption during a biological process, and give access to the kinetics of the coupled protein-hydration dynamics. When combined with simulations, the observed results can be explained in terms of a two-tier model involving a local binding and a long range influence on the hydration bond dynamics of the water around the binding site that highlights the significance of the changes in the hydration dynamics at recognition site for biomolecular recognition. Water is shown to assist molecular recognition processes.

  3. Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling

    PubMed Central

    Tomasino, A.; Parisi, A.; Stivala, S.; Livreri, P.; Cino, A. C.; Busacca, A. C.; Peccianti, M.; Morandotti, R.

    2013-01-01

    We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement. PMID:24173583

  4. Perspective: Watching low-frequency vibrations of water in biomolecular recognition by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Yao; Havenith, Martina

    2015-11-01

    Terahertz (THz) spectroscopy has turned out to be a powerful tool which is able to shed new light on the role of water in biomolecular processes. The low frequency spectrum of the solvated biomolecule in combination with MD simulations provides deep insights into the collective hydrogen bond dynamics on the sub-ps time scale. The absorption spectrum between 1 THz and 10 THz of solvated biomolecules is sensitive to changes in the fast fluctuations of the water network. Systematic studies on mutants of antifreeze proteins indicate a direct correlation between biological activity and a retardation of the (sub)-ps hydration dynamics at the protein binding site, i.e., a "hydration funnel." Kinetic THz absorption studies probe the temporal changes of THz absorption during a biological process, and give access to the kinetics of the coupled protein-hydration dynamics. When combined with simulations, the observed results can be explained in terms of a two-tier model involving a local binding and a long range influence on the hydration bond dynamics of the water around the binding site that highlights the significance of the changes in the hydration dynamics at recognition site for biomolecular recognition. Water is shown to assist molecular recognition processes.

  5. THz dynamics of nanoconfined water by ultrafast optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Taschin, A.; Bartolini, P.; Torre, R.

    2017-01-01

    We investigated the vibrational dynamics and structural relaxation of water nanoconfined in porous silica samples with a pore size of 4 nm at different levels of hydration and temperature. We used the time-resolved optical Kerr effect (OKE), a spectroscopic technique that enables investigation of ultrafast water dynamics in a wide time (0.1-10 ps) or frequency (10-0.1 THz) window. At low hydration levels corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all investigated temperatures. Meanwhile, at full hydration we witness a partial ice formation at about 248 K that coexists with the surface water remaining in the supercooled state. At low hydration, both structural and vibrational dynamics show significant modifications compared to bulk liquid water. This is due to the strong interaction of the water molecules with silica surfaces. Inner water, however, reveals relaxation dynamics very similar to bulk water.

  6. Fiber-coupled THz spectroscopy for monitoring polymeric compounding processes

    NASA Astrophysics Data System (ADS)

    Vieweg, N.; Krumbholz, N.; Hasek, T.; Wilk, R.; Bartels, V.; Keseberg, C.; Pethukhov, V.; Mikulics, M.; Wetenkamp, L.; Koch, M.

    2007-06-01

    We present a compact, robust, and transportable fiber-coupled THz system for inline monitoring of polymeric compounding processes in an industrial environment. The system is built on a 90cm x 90cm large shock absorbing optical bench. A sealed metal box protects the system against dust and mechanical disturbances. A closed loop controller unit is used to ensure optimum coupling of the laser beam into the fiber. In order to build efficient and stable fiber-coupled antennas we glue the fibers directly onto photoconductive switches. Thus, the antenna performance is very stable and it is secured from dust or misalignment by vibrations. We discuss fabrication details and antenna performance. First spectroscopic data obtained with this system is presented.

  7. [Research on detecting explosive content of 2, 4-dimitroanisole based on THz spectroscopy].

    PubMed

    Wang, Gao; Xu, De-Gang; Yao, Jian-Quan

    2013-04-01

    In order to detect the content of a new kind of insensitive melting-cast explosive (DNAN), the system detected the THz characteristics wavelength of DNAN, and solved the content of DNAN by the Bill-Lambert law. Time coherent THz spectroscopy detection system was designed, in which the master system controlled stepper motor to get the micro-scanning of the photoelectric detector. The system parameters were calculated and derived for solving the content of DNAN, and THz characteristic spectrum of DNAN was obtained. Experiment used three methods to detect explosives samples with different content of DNAN, and the results show that the accuracy of this system is close to that of MINI-Z terahertz spectrometer currently broadly applied in THz spectroscopy detection equipment at home and abroad. On this basis, the optimization algorithm of characteristic absorption peak was designed, and by the origin software simulation analysis, it shows that the algorithm can further improve accuracy and stability of the detection system.

  8. Sensitive, time-resolved, broadband spectroscopy of single transient processes

    NASA Astrophysics Data System (ADS)

    Fjodorow, Peter; Baev, Ivan; Hellmig, Ortwin; Sengstock, Klaus; Baev, Valery M.

    2015-09-01

    Intracavity absorption spectroscopy with a broadband Er3+-doped fiber laser is applied to time-resolved measurements of transient gain and absorption in electrically excited Xe and Kr plasmas. The achieved time resolution for broadband spectral recording of a single process is 25 µs. For pulsed-periodic processes, the time resolution is limited by the laser pulse duration, which is set here to 3 µs. This pulse duration also predefines the effective absorption path length, which amounts to 900 m. The presented technique can be applied to multicomponent analysis of single transient processes such as shock tube experiments, pulse detonation engines, or explosives.

  9. Studies on spectroscopy of glycerol in THz range using microfluidic chip-integrated micropump

    NASA Astrophysics Data System (ADS)

    Su, Bo; Han, Xue; Wu, Ying; Zhang, Cunlin

    2014-11-01

    Terahertz time-domain spectroscopy (THz-TDS) is a detection method of biological molecules with label-free, non-ionizing, non-intrusive, no pollution and real-time monitoring. But owing to the strong THz absorption by water, it is mainly used in the solid state detection of biological molecules. In this paper, we present a microfluidic chip technique for detecting biological liquid samples using the transmission type of THz-TDS system. The microfluidic channel of the microfluidic chip is fabricated in the quartz glass using Micro-Electro-Mechanical System (MEMS) technology and sealed with polydimethylsiloxane (PDMS) diaphragm. The length, width and depth of the microfluidic channel are 25mm, 100μm and 50μm, respectively. The diameter of THz detection zone in the microfluidic channel is 4mm. The thicknesses of quartz glass and PDMS diaphragm are 1mm and 250μm, individually. Another one of the same quartz glass is used to bond with the PDMS for the rigidity and air tightness of the microfluidic chip. In order to realize the automation of sampling and improve the control precise of fluid, a micropump, which comprises PDMS diaphragm, pump chamber, diffuser and nozzle and flat vibration motor, is integrated on the microfluidic chip. The diffuser and nozzle are fabricated on both sides of the pump chamber, which is covered with PDMS diaphragm. The flat vibration motor is stuck on the PDMS diaphragm as the actuator. We study the terahertz absorption spectroscopy characteristics of glycerol with the concentration of 98% in the microfluidic chip by the aid of the THz-TDS system, and the feasibility of the microfluidic chip for the detection of liquid samples is proved.

  10. Broadband MgB2 Hot-Electron Bolometer THz Mixers Operating up to 20 K

    NASA Astrophysics Data System (ADS)

    Novoselov, Evgenii; Cherednichenko, Sergey

    2017-01-01

    We discuss performance of submicron size hot-electron bolometer mixers made from thin MgB2 superconducting films. With a superconducting transition temperature of ∼30 K, such terahertz (THz) mixers can operate with high sensitivity at temperatures up to 20 K. Due to very small dimensions local oscillator power requirements are rather low. In the intermediate frequency band of 1-3 GHz, the double sideband receiver noise temperature is 1600 K at 10 K operation temperature, 2000 K at 15 K, 2500-3000 K at 20 K. The gain bandwidth of such devices is 6 GHz and the noise bandwidth is estimated to be 6-8 GHz.

  11. Holographic Spectroscopy for Rapid Electron Bunch Analysis: Development of an Instrument with THZ Resolved Optical Gating

    SciTech Connect

    Sievers, Albert

    2011-10-28

    The main thrust of our project was to apply the concepts of holographic spectroscopy, developed earlier in the visible and near IR spectral regions for satellite mapping, to the THz region in order to measure the spectral signature of the coherent radiation emanating from a relativistic electron bunch to obtain the bunch length itself. There were four major discoveries. (1) In the course of this ground-breaking work we developed and built the first static THz interferometer suitable for the realization of such a holographic Fourier transform spectrometer. Experimental tests and analysis of the observed results have provided the necessary foundation for future development of THz detector arrays optimized for spectroscopic applications. (2) Since such detectors do not exist at the present time our next effort was to find an alternative approach. We explored the electro-optic (EO) detection of the THz pulse using the short pulse of a visible diode laser synchronized to the bunch with the long-term goal aimed at single bunch measurement capability. The main hurdle was found to be the parasitic scattering of the diode radiation in the EO medium. By using the optical Fourier transform of the THz interference pattern the effects of this background were suppressed enough to obtain the spectrum using multiple shot acquisition. During our experiments at the FLASH facility at DESY we determined that for single bunch measurement capability the diode laser has to be able to produce sub 100 ps pulses with peak power of at least 1 W. Since these parameters are quite feasible at the current stage of diode laser science this combination of techniques can be used for single shot measurement of a short electron bunch. (3) In carrying out the above effort a simpler measurement possibility was uncovered involving the visible/nearIR pulse of incoherent radiation produced by the same bunch. This observation made possible the cross-correlation of the THz coherent and visible incoherent

  12. Rotational spectroscopy of methylamine up to 2.6 THz

    NASA Astrophysics Data System (ADS)

    Motiyenko, R. A.; Ilyushin, V. V.; Drouin, B. J.; Yu, S.; Margulès, L.

    2014-03-01

    Context. Methylamine (CH3NH2) is the simplest primary alkylamine that has been detected in the interstellar medium. The molecule is relatively light, with the 50 K Boltzmann peak appearing near 800 GHz. However, reliable predictions for its rotational spectrum are available only up to 500 GHz. Spectroscopic analyses have been complicated by the two large-amplitude motions: internal rotation of the methyl top and inversion of the amino group. Aims: To provide reliable predictions of the methylamine ground state rotational spectrum above 500 GHz, we studied its rotational spectrum in the frequency range from 500 to 2650 GHz. Methods: The spectra of methylamine were recorded using the spectrometers based on Schottky diode frequency multiplication chains in the Lille laboratory (500-945 GHz) and in JPL (1060-2660 GHz). The analysis of the rotational spectrum of methylamine in the ground vibrational state was performed on the basis of the group-theoretical high barrier tunneling Hamiltonian developed for methylamine by Ohashi and Hougen. Results: In the recorded spectra, we have assigned 1849 new rotational transitions of methylamine. They were fitted together with previously published data, to a Hamiltonian model that uses 76 parameters with an overall weighted rms deviation of 0.87. On the basis of the new spectroscopic results, predictions of transition frequencies in the frequency range up to 3 THz with J ≤ 50 and Ka ≤ 20 are presented. Full Tables 2 and 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.frftp://130.79.128.5 or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/563/A137

  13. High Resolution Thz and FIR Spectroscopy of SOCl_2

    NASA Astrophysics Data System (ADS)

    Martin-Drumel, M. A.; Cuisset, A.; Sadovskii, D. A.; Mouret, G.; Hindle, F.; Pirali, O.

    2013-06-01

    Thionyl chloride (SOCl_2) is an extremely powerful oxidant widely used in industrial processes and playing a role in the chemistry of the atmosphere. In addition, it has a molecular configuration similar to that of phosgene (COCl_2), and is therefore of particular interest for security and defense applications. Low resolution vibrational spectra of gas phase SOCl_2 as well as high resolution pure rotational transitions up to 25 GHz have previously been investigated. To date no high resolution data are reported at frequencies higher than 25 GHz. We have investigated the THz absorption spectrum of SOCl_2 in the spectral region 70-650 GHz using a frequency multiplier chain coupled to a 1 m long single path cell containing a pressure of about 15 μbar. At the time of the writing, about 8000 pure rotational transitions of SO^{35}Cl_2 with highest J and K_a values of 110 and 50 respectively have been assigned on the spectrum. We have also recorded the high resolution FIR spectra of SOCl_2 in the spectral range 50-700 wn using synchrotron radiation at the AILES beamline of SOLEIL facility. A White-type cell aligned with an absorption path length of 150 m has been used to record, at a resolution of 0.001 wn, two spectra at pressures of 5 and 56 μbar of SOCl_2. On these spectra all FIR modes of SOCl_2 are observed (ν_2 to ν_6) and present a resolved rotational structure. Their analysis is in progress. T. J. Johnson et al., J. Phys. Chem. A 107, 6183 (2003) D. E. Martz and R. T. Lagemann, J. Chem. Phys. 22,1193 (1954) H. S. P. Müller and M. C. L. Gerry, J. Chem. Soc. Faraday Trans. 90, 3473 (1994)

  14. Broadband infrared vibrational nano-spectroscopy using thermal blackbody radiation

    DOE PAGES

    O’Callahan, Brian T.; Lewis, William E.; Möbius, Silke; ...

    2015-12-03

    Infrared vibrational nano-spectroscopy based on scattering scanning near-field optical microscopy (s-SNOM) provides intrinsic chemical specificity with nanometer spatial resolution. Here we use incoherent infrared radiation from a 1400 K thermal blackbody emitter for broadband infrared (IR) nano-spectroscopy.With optimized interferometric heterodyne signal amplification we achieve few-monolayer sensitivity in phonon polariton spectroscopy and attomolar molecular vibrational spectroscopy. Near-field localization and nanoscale spatial resolution is demonstrated in imaging flakes of hexagonal boron nitride (hBN) and determination of its phonon polariton dispersion relation. The signal-to-noise ratio calculations and analysis for different samples and illumination sources provide a reference for irradiance requirements and the attainablemore » near-field signal levels in s-SNOM in general. As a result, the use of a thermal emitter as an IR source thus opens s-SNOM for routine chemical FTIR nano-spectroscopy.« less

  15. Broadband infrared vibrational nano-spectroscopy using thermal blackbody radiation

    SciTech Connect

    O’Callahan, Brian T.; Lewis, William E.; Möbius, Silke; Stanley, Jared C.; Muller, Eric A.; Raschke, Markus B.

    2015-12-03

    Infrared vibrational nano-spectroscopy based on scattering scanning near-field optical microscopy (s-SNOM) provides intrinsic chemical specificity with nanometer spatial resolution. Here we use incoherent infrared radiation from a 1400 K thermal blackbody emitter for broadband infrared (IR) nano-spectroscopy.With optimized interferometric heterodyne signal amplification we achieve few-monolayer sensitivity in phonon polariton spectroscopy and attomolar molecular vibrational spectroscopy. Near-field localization and nanoscale spatial resolution is demonstrated in imaging flakes of hexagonal boron nitride (hBN) and determination of its phonon polariton dispersion relation. The signal-to-noise ratio calculations and analysis for different samples and illumination sources provide a reference for irradiance requirements and the attainable near-field signal levels in s-SNOM in general. As a result, the use of a thermal emitter as an IR source thus opens s-SNOM for routine chemical FTIR nano-spectroscopy.

  16. Detection of Transgenic Cotton Using THz Spectroscopy and Weighted Discriminate Analysis

    NASA Astrophysics Data System (ADS)

    Liu, J.; Luo, J.; Li, P.; Xion, M.; Cao, H.; Yang, B.; Jiang, Y.; Hu, C.

    2017-05-01

    Terahertz spectroscopy combined with weighted discriminate analysis (WDA) is performed with different transgenic cottons (HD-1, HD-73, and Coker 312). The time-domain spectra of the samples are transformed into frequency-domain spectra by using fast Fourier transform. Then the absorbance curve of the samples is obtained. By applying the absorbance data in conjunction with the WDA model, the identification rates of the different transgenic cottons are 89.4, 89.7, and 92.5%, respectively. The experimental results demonstrate that THz spectroscopy combined with WDA is a novel and feasible way to detect transgenic cottons.

  17. Structure of fenchone by broadband rotational spectroscopy

    NASA Astrophysics Data System (ADS)

    Loru, Donatella; Bermúdez, Miguel A.; Sanz, M. Eugenia

    2016-08-01

    The bicyclic terpenoid fenchone (C10H16O, 1,3,3-trimethylbicyclo[2.2.1]heptan-2-one) has been investigated by chirped pulse Fourier transform microwave spectroscopy in the 2-8 GHz frequency region. The parent species and all heavy atom isotopologues have been observed in their natural abundance. The experimental rotational constants of all isotopic species observed have been determined and used to obtain the substitution (rs) and effective (r0) structures of fenchone. Calculations at the B3LYP, M06-2X, and MP2 levels of theory with different basis sets were carried out to check their performance against experimental results. The structure of fenchone has been compared with those of norbornane (bicyclo[2.2.1]heptane) and the norbornane derivatives camphor (1,7,7-trimethylbicyclo[2.2.1]heptan-2-one) and camphene (3,3-dimethyl-2-methylenebicyclo[2.2.1]heptane), both with substituents at C2. The structure of fenchone is remarkably similar to those of camphor and camphene. Comparison with camphor allows identification of changes in ∠CCC angles due to the different position of the methyl groups. All norbornane derivatives display similar structural changes with respect to norbornane. These changes mainly affect the bond lengths and angles of the six-membered rings, indicating that the substituent at C2 drives structural adjustments to minimise ring strain after its introduction.

  18. Ultrafast broadband spectroscopy of crystalline bismuth

    SciTech Connect

    Mel'nikov, A A; Misochko, Oleg V; Chekalin, Sergei V

    2013-04-30

    Femtosecond spectroscopy in the wavelength range 0.4 - 2.3 {mu}m has been used to probe ultrafast electronic and lattice processes in bismuth. The photoresponse of a bismuth crystal is shown to comprise components with relaxation times of 1 ps, 7 ps, and {approx}1 ns. The electron-hole and electron-phonon interaction strengths in bismuth are found to depend significantly on the wave vector in the {Gamma}-T direction of the Brillouin zone. Comparison of the spectral dependences of the amplitudes of coherent E{sub g} and A{sub 1g} phonons and the corresponding dependences of the Raman scattering cross sections indicates that these phonon modes differ in generation mechanism. The generation of coherent A{sub 1g} phonons is mainly due to displacement of the equilibrium position of atoms in the crystal lattice in a nonequilibrium state. This process differs fundamentally from resonance Raman scattering responsible for the coherent excitation of low-symmetry phonon modes. (extreme light fields and their applications)

  19. Single-shot spectroscopy of broadband Yb fiber laser

    NASA Astrophysics Data System (ADS)

    Suzuki, Masayuki; Yoneya, Shin; Kuroda, Hiroto

    2017-02-01

    We have experimentally reported on a real-time single-shot spectroscopy of a broadband Yb-doped fiber (YDF) laser which based on a nonlinear polarization evolution by using a time-stretched dispersive Fourier transformation technique. We have measured an 8000 consecutive single-shot spectra of mode locking and noise-like pulse (NLP), because our developed broadband YDF oscillator can individually operate the mode locking and NLP by controlling a pump LD power and angle of waveplates. A shot-to-shot spectral fluctuation was observed in NLP. For the investigation of pulse formation dynamics, we have measured the spectral evolution in an initial fluctuations of mode locked broadband YDF laser at an intracavity dispersion of 1500 and 6200 fs2 for the first time. In both case, a build-up time between cw and steady-state mode locking was estimated to be 50 us, the dynamics of spectral evolution between cw and mode locking, however, was completely different. A shot-to-shot strong spectral fluctuation, as can be seen in NLP spectra, was observed in the initial timescale of 20 us at the intracavity dispersion of 1500 fs2. These new findings would impact on understanding the birth of the broadband spectral formation in fiber laser oscillator.

  20. Performance of the AILES THz-Infrared beamline at SOLEIL for High resolution spectroscopy

    SciTech Connect

    Brubach, Jean-Blaise; Rouzieres, Mathieu; Roy, Pascale; Manceron, Laurent; Pirali, Olivier; Balcon, Didier; Tchana, Fridolin Kwabia; Boudon, Vincent; Tudorie, M.; Huet, Therese; Cuisset, Arnaud

    2010-02-03

    The new THz beamline (AILES) located at the third generation Synchrotron Radiation source SOLEIL is now operating for applications in a wide variety of research themes. In particular, this source with its adapted optics allows high resolution spectroscopic measurements of molecules in the entire infrared and THz range. This presentation focuses on the performances concerning flux, spectral range and stability for molecular spectroscopy. Thanks to these performances, the coupling of synchrotron radiation from a highly stable third generation source with high resolution FTIR spectrometer and with a long path cell (150 m or more) can be particularly advantageous. This fact is related to the optics of the beamline permitting the entire source to be used without aperture stop (entrance iris), even for measurements at highest-resolution of approx0.1 mueV (10{sup -3} cm{sup -1}).

  1. Gold nanoparticle mediated graphene plasmon for broadband enhanced infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Peng, Lilan; Zhang, Lei; Yuan, Jian; Chen, Chen; Bao, Qiaoliang; Qiu, Cheng-Wei; Peng, Zeping; Zhang, Kai

    2017-06-01

    Graphene plasmonics, with dynamic tunable resonance wavelength, has been successfully used in broadband plasmon-enhanced infrared spectroscopy. However, the requirement for external voltage loading makes the practical application sophisticated. In this work, the hybrid structure of graphene nanodot array (GNA) and gold nanoparticles (AuNPs) has been proposed as a passive platform for broadband infrared absorption enhancement. Numerical simulations show that the plasmon resonance peak of GNA becomes stiffer and broader when introducing AuNPs, and this is also proved by experimental results that the vibrational modes of polyethylene oxide molecule in a broad spectral range can be simultaneously enhanced. The metal-graphene hybrid plasmonic system has been proved to be a promising candidate for infrared sensing, which is significant for safety and healthy applications.

  2. All electrical propagating spin wave spectroscopy with broadband wavevector capability

    SciTech Connect

    Ciubotaru, F.; Devolder, T.; Manfrini, M.; Adelmann, C.; Radu, I. P.

    2016-07-04

    We developed an all electrical experiment to perform the broadband phase-resolved spectroscopy of propagating spin waves in micrometer sized thin magnetic stripes. The magnetostatic surface spin waves are excited and detected by scaled down to 125 nm wide inductive antennas, which award ultra broadband wavevector capability. The wavevector selection can be done by applying an excitation frequency above the ferromagnetic resonance. Wavevector demultiplexing is done at the spin wave detector thanks to the rotation of the spin wave phase upon propagation. A simple model accounts for the main features of the apparatus transfer functions. Our approach opens an avenue for the all electrical study of wavevector-dependent spin wave properties including dispersion spectra or non-reciprocal propagation.

  3. Combination of broadband diffuse optical spectroscopy with magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Merritt, Sean Isaiah

    Broadband diffuse optical spectroscopy (DOS) is an emerging optical technique used to measure absorption and scattering of bulk tissue non-invasively within the near-infrared (600--1050 nm). The ultimate aim of my advisors group is for broadband DOS to become an established medical diagnostic technique used clinically on various tissue types including breast, muscle and bone. The specific goal for my research is to use established magnetic resonance (MR) techniques for the purpose of continued development and validation of broadband DOS. The initial studies carried out were a validation of broadband DOS through a direct comparison with MRI. Both techniques are sensitive to signals produced by water and lipids in tissue. There is also sensitivity to blood flow, which MRI measures using exogenous contrast agents and broadband DOS is sensitive through measurement of total hemoglobin content (THC) and tissue oxygen saturation (StO2). These validation studies were compared initially in a rat tumor model in which both techniques were used simultaneously. A qualitative correlation was found between the MR images of water content and blood perfusion compared with the DOS water and THC values. A more quantitative comparison was made between measuring absolute water and lipid content in phantoms and in human tissue, which showed a strong correlation. The in vivo study also validated that broadband DOS was interrogating bone marrow in the tibia. The second half of this thesis is focused on developing new capabilities of broadband DOS and the MRI literature is used as a guide. When a water molecule hydrogen bonds to another molecule, the absorption spectrum in the near-infrared which is due to the vibrational overtone of the OH bond will change. The expected changes were observed in tissue and an algorithm was developed to fit for a tissue bound water parameter. Also, as tissue temperature changes, the fraction of water bound to other water molecules changes and can be used to

  4. Development of a high-throughput solution for crystallinity measurement using THz-Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Roy, Anjan; Fosse, Jean-Charles; Fernandes, Filipe; Ringwald, Alexandre; Ho, Lawrence

    2017-02-01

    Rapid identification and the quantitative analysis of crystalline content and the degree of crystallinity is important in pharmaceuticals and polymer manufacturing. Crystallinity affects the bioavailability of pharmaceutical molecules and there is a strong correlation between the performance of polymers and their degree of crystallinity. Low frequency/THz-Raman spectroscopy has enabled determination of crystalline content in materials as a complementary method to X-ray powder diffraction. By incorporating motion stages and microplates, we have extended the applicability of THz-Raman technology to high-throughput screening applications. We describe here a complete THz-Raman microplate reader, with integrated laser, optics, spectrograph and software that are necessary for detecting low-frequency Raman signals. In powder materials scattering is also affected by particle size and the presence of cavities, which lead to a lack of precision and repeatability in Raman intensity measurements. We address this problem by spatial averaging using specific stage motion patterns. This design facilitates rapid and precise measurement of low-frequency vibrational modes, differentiation of polymorphs and other structural characteristics for applications in pharmaceuticals, nano- and bio-materials and for the characterization of industrial polymers where XRPD is commonly used.

  5. Measurement of plasma densities by dual frequency multichannel boxcar THz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Meier, St. M.; Tsankov, Ts V.; Luggenhölscher, D.; Czarnetzki, U.

    2017-06-01

    In this paper we show the development and the application of the terahertz time domain spectroscopy (THz TDS) diagnostic technique for the determination of plasma densities in low-pressure discharges. A commercially available system was modified to reach a better signal-to-noise ratio. For that the THz emitter and the detection method were changed and a fast lock-in amplifier was used to reach 38 MHz lock-in frequency. These modifications in a combination with the novel method of dual frequency multichannel boxcar embedded as a feature in the lock-in amplifier allowed us to make also time-resolved measurements. The temporal resolution can potentially go down to 100 ps and is limited only by the spectral range that needs to be recovered for the measurement of low electron densities. Further, the cause of artefacts found in all THz TDS based systems, but not understood until now, is identified and explained. As an application the electron densities in inductively coupled plasmas sustained in a magnetic multi-cusp chamber are determined. Results from steady-state discharges in noble gases (He, Ne, Ar, Kr, Xe) and time-resolved measurements in pulsed discharges in Ar and Ne are presented. The technique is benchmarked against microwave interferometry with good agreement in the applicability range of both techniques. The THz TDS performs reliably also in much denser plasmas where standard microwave interferometry fails. The lower limit for the technique is at a line-integrated electron density of 1012 cm-2, corresponding to about 1011 cm-3 for typical plasma dimensions.

  6. THZ Phonon Spectroscopy of Bi-2223 and Bi-2212: Evidence for Phonon Pairing

    NASA Astrophysics Data System (ADS)

    Ponomarev, Ya. G.; Van, Hoang Hoai

    Facts are presented evidencing the strong electron-phonon interaction and the scaling of a superconducting gap and a critical temperature in doped Bi-2212 single crystals. A sharp extra structure in the current-voltage characteristics (CVC's) of Bi-2212 contacts is attributed to the presence of the extended van Hove singularity (EVHS) close to the Fermi level in slightly overdoped and slightly underdoped samples. THZ phonon spectroscopy studies of Bi-2223 and Bi-2212 are overviewed. An observed giant instability in I(V) - characteristics of Bi-2223 nanosteps is probably caused by a resonant emission of 2Δ - optical phonons in a process of recombination of nonequilibrium quasiparticles (Krasnov model).

  7. Femtosecond broadband fluorescence upconversion spectroscopy: Improved setup and photometric correction

    SciTech Connect

    Zhang, X.-X.; Wuerth, C.; Resch-Genger, U.; Zhao, L.; Ernsting, N. P.; Sajadi, M.

    2011-06-15

    A setup for fluorescence upconversion spectroscopy (FLUPS) is described which has 80 fs temporal response (fwhm) for emission in the spectral range 425-750 nm. Broadband phase matching is achieved with tilted gate pulses at 1340 nm. Background from harmonics of the gate pulse is removed and sensitivity increased compared to previous designs. Photometric calibration of the upconversion process is performed with a set of fluorescent dyes. For Coumarin 153 in methanol the peak position, bandwidth, and asymmetry depending on delay time are reported.

  8. Femtosecond broadband fluorescence upconversion spectroscopy: Improved setup and photometric correction

    NASA Astrophysics Data System (ADS)

    Zhang, X.-X.; Würth, C.; Zhao, L.; Resch-Genger, U.; Ernsting, N. P.; Sajadi, M.

    2011-06-01

    A setup for fluorescence upconversion spectroscopy (FLUPS) is described which has 80 fs temporal response (fwhm) for emission in the spectral range 425-750 nm. Broadband phase matching is achieved with tilted gate pulses at 1340 nm. Background from harmonics of the gate pulse is removed and sensitivity increased compared to previous designs. Photometric calibration of the upconversion process is performed with a set of fluorescent dyes. For Coumarin 153 in methanol the peak position, bandwidth, and asymmetry depending on delay time are reported.

  9. Broadband enhanced backscattering spectroscopy of strongly scattering media.

    PubMed

    Muskens, O L; Lagendijk, A

    2008-01-21

    We report on a new experimental method for enhanced backscattering spectroscopy (EBS) of strongly scattering media over a bandwidth from 530-1000 nm. The instrument consists of a supercontinuum light source and an angle-dependent detection system using a fiber-coupled grating spectrometer. Using a combination of two setups, the backscattered intensity is obtained over a large angular range and using circularly polarized light. We present broadband EBS of a TiO(2) powder and of a strongly scattering porous GaP layer. In combination with theoretical model fits, the EBS system yields the optical transport mean free path over the available spectral window.

  10. Application of THz Vibrational Spectroscopy to Molecular Characterization and the Theoretical Fundamentals: An Illustration Using Saccharide Molecules.

    PubMed

    Zhang, Feng; Wang, Houng-Wei; Tominaga, Keisuke; Hayashi, Michitoshi; Hasunuma, Tomohisa; Kondo, Akihiko

    2017-02-01

    This work illustrates several theoretical fundamentals for the application of THz vibrational spectroscopy to molecular characterization in the solid state using two different types of saccharide systems as examples. Four subjects have been specifically addressed: (1) the qualitative differences in the molecular vibrational signatures monitored by THz and mid-IR vibrational spectroscopy; (2) the selection rules for THz vibrational spectroscopy as applied to crystalline and amorphous systems; (3) a normal mode simulation, using α-l-xylose as an example; and (4) a rigorous mode analysis to quantify the percentage contributions of the intermolecular and intramolecular vibrations to the normal mode of interest. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Broadband nonlinear vibrational spectroscopy by shaping a coherent fiber supercontinuum

    PubMed Central

    Liu, Yuan; King, Matthew D.; Tu, Haohua; Zhao, Youbo; Boppart, Stephen A.

    2013-01-01

    Vibrational spectroscopy has been widely applied in different fields due to its label-free chemical-sensing capability. Coherent anti-Stokes Raman scattering (CARS) provides stronger signal and faster acquisition than spontaneous Raman scattering, making it especially suitable for molecular imaging. Coherently-controlled single-beam CARS simplifies the conventional multi-beam setup, but the vibrational bandwidth and non-trivial spectrum retrieval have been limiting factors. In this work, a coherent supercontinuum generated in an all-normal-dispersion nonlinear fiber is phase-shaped within a narrow bandwidth for broadband vibrational spectroscopy. The Raman spectra can be directly retrieved from the CARS measurements, covering the fingerprint regime up to 1750 cm−1. The retrieved spectra of several chemical species agree with their spontaneous Raman data. The compact fiber supercontinuum source offers broad vibrational bandwidth with high stability and sufficient power, showing the potential for spectroscopic imaging in a wide range of applications. PMID:23571917

  12. Broadband transmission spectroscopy in tissue: application to radiofrequency tissue fusion

    NASA Astrophysics Data System (ADS)

    Floume, Timmy; Syms, Richard R. A.; Darzi, Ara W.; Hanna, George B.

    2009-05-01

    Radiofrequency tissue fusion consists in heating apposed tissue faces, which results in their sealing. Tissue transformations must be controlled to obtain reliable reproducible seal. In this paper we demonstrate how to extract information on the two main tissue transformations, thermal damage and dehydration, from continuous wave transmission spectra. A fibre based near infrared transmission spectroscopy system is presented and described theoretically. Show demonstrate that such system can be fully modeled using ray optics considerations for the coupling of the light into optical fibers, and MC simulations of light propagation in tissue. We then develop an algorithm based on the absolute measurement of attenuation and the modified Beer Lambert Law that enables the extraction of absolute tissue hydration and information on the degree of thermal damage, via scattering losses. We also discuss the basis and limit of absolute measurement during broadband submicronic tissue transmittance spectroscopy.

  13. Broadband Plasmon Waveguide Resonance Spectroscopy for Probing Biological Thin Films

    PubMed Central

    ZHANG, HAN; OROSZ, KRISTINA S.; TAKAHASHI, HIROMI; SAAVEDRA, S. SCOTT

    2010-01-01

    A commercially available spectrometer has been modified to perform plasmon waveguide resonance (PWR) spectroscopy over a broad spectral bandwidth. When compared to surface plasmon resonance (SPR), PWR has the advantage of allowing measurements in both s- and p-polarizations on a waveguide surface that is silica or glass rather than a noble metal. Here the waveguide is a BK7 glass slide coated with silver and silica layers. The resonance wavelength is sensitive to the optical thickness of the medium adjacent to the silica layer. The sensitivity of this technique is characterized and compared with broadband SPR both experimentally and theoretically. The sensitivity of spectral PWR is comparable to that of spectral SPR for samples with refractive indices close to that of water. The hydrophilic surface of the waveguide allows supported lipid bilayers to be formed spontaneously by vesicle fusion; in contrast, the surface of an SPR chip requires chemical modification to create a supported lipid membrane. Broadband PWR spectroscopy should be a useful technique to study biointerfaces, including ligand binding to transmembrane receptors and adsorption of peripheral proteins on ligand-bearing membranes. PMID:19796490

  14. Diffraction-limited ultrabroadband terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  15. Near-infrared broadband dual-frequency-comb spectroscopy with a resolution beyond the Fourier limit determined by the observation time window.

    PubMed

    Okubo, Sho; Hsieh, Yi-Da; Inaba, Hajime; Onae, Atsushi; Hashimoto, Mamoru; Yasui, Takeshi

    2015-12-28

    We performed broadband dual-frequency-comb spectroscopy in the near-infrared region with a much higher resolution than the Fourier limit by using discrete Fourier transforms and spectral interleaving. We observed the resonant spectrum of a Fabry-Perot cavity over a spectral range of 187 to 218 THz using this technique, and measured its free spectral ranges and finesses. The recorded spectrum includes cavity resonance lines with widths of about 2 MHz, which is much narrower than the resolution of 48 MHz determined by the observation time window.

  16. Principal limitation of standard THz time-domain spectroscopy method of the detection and identification of substance and way of its overcoming

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Varentsova, Svetlana A.; Zakharova, Irina G.; Zagursky, Dmitry Y.

    2015-10-01

    We demonstrate principal limitations of standard Time Domain Spectroscopy based on a broadband THz pulse for the detection and identification of substance using paper napkins as a sample. To avoid these limitations we propose a new high effective algorithm for this purpose. We demonstrate its applicability in realistic and simulated situation for various substances under consideration. The interaction of a THz pulse with a disordered layered structure was simulated in order to show the influence of the disordered layers on the spectral characteristics of the transmitted and reflected signals. Spectral characteristics of these signals were analyzed in a direct comparison with the spectrum of the incident pulse as well as by means of Spectral Dynamics Analysis method and integral correlation criteria. The efficiency of the detection and identification method, based on integral correlation and likeness criteria, is confirmed on the basis of computer simulation. To demonstrate the possibilities of the integral correlation criteria in real experiment, they were applied for the identification of explosive HMX in the reflection mode.

  17. Characterization of Large Water Clusters by Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Perez, Cristobal; Zaleski, Daniel P.; Seifert, Nathan A.; Pate, Brooks H.; Kisiel, Zbigniew; Temelso, Berhane; Shields, George C.; Shipman, Steven T.; Finnerman, Ian

    2013-06-01

    Most theoretical water models match with experimental result reasonably well up to n=10. For clusters larger than the decamer there is no clear consensus in the global minimum geometries, as the low-energy landscape for a given cluster size changes considerably depending on the model applied. However, there is agreement in considering the undecamer regime as one of the richer pure water cluster regimes, with a large number (>50) of isomers within 1 kcal/mol of the global minimum. Using broadband chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy operating in the 2-8 GHz frequency range, seven low-energy isomers of the water undecamer have been identified in a pulsed molecular beam. The observed water cluster structures have been identified as belonging to four families on basis to their rotational constants according to their different oxygen atom frameworks. These families can be explained by building up the structures from smaller water cluster subunits. Rotational spectra consistent with theoretical predictions for two isomers of (H_{2}O)_{13} and one of (H_{2}O)_{15} have also been identified. Due to the high density of lines observed in the broadband spectrum, the traditional method of pattern recognition using ab-initio calculations was replaced with a new approach combining high-level ab-initio calculations with automatic fitting tools. These autofitting routines were tested on these systems and are also briefly described.

  18. Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source.

    PubMed

    Pearson, John C; Drouin, Brian J; Maestrini, Alain; Mehdi, Imran; Ward, John; Lin, Robert H; Yu, Shanshan; Gill, John J; Thomas, Bertrand; Lee, Choonsup; Chattopadhyay, Goutam; Schlecht, Erich; Maiwald, Frank W; Goldsmith, Paul F; Siegel, Peter

    2011-09-01

    We report the first demonstration of a continuous wave coherent source covering 2.48-2.75 THz, with greater than 10% instantaneous tuning bandwidth and having 1-14 μW of output power at room temperature. This source is based on a 91.8-101.8 GHz synthesizer followed by a power amplifier and three cascaded frequency triplers. It demonstrates for the first time that purely electronic solid-state sources can generate a useful amount of power in a region of the electromagnetic spectrum where lasers (solid state or gas) were previously the only available coherent sources. The bandwidth, agility, and operability of this THz source have enabled wideband, high resolution spectroscopic measurements of water, methanol, and carbon monoxide with a resolution and signal-to-noise ratio unmatched by any other existing system, providing new insight in the physics of these molecules. Furthermore, the power and optical beam quality are high enough to observe the Lamb-dip effect in water. The source frequency has an absolute accuracy better than 1 part in 10(12) and the spectrometer achieves sub-Doppler frequency resolution better than 1 part in 10(8). The harmonic purity is better than 25 dB. This source can serve as a coherent signal for absorption spectroscopy, a local oscillator for a variety of heterodyne systems and can be used as a method for precision control of more powerful but much less frequency agile quantum mechanical terahertz sources.

  19. Thz Spectroscopy and DFT Modeling of Intermolecular Vibrations in Hydrophobic Amino Acids

    NASA Astrophysics Data System (ADS)

    Williams, michael R. C.; Aschaffenburg, Daniel J.; Schmuttenmaer, Charles A.

    2013-06-01

    Vibrations that involve intermolecular displacements occur in molecular crystals at frequencies in the 0.5-5 THz range (˜15-165 cm^{-1}), and these motions are direct indicators of the interaction potential between the molecules. The intermolecular potential energy surface of crystalline hydrophobic amino acids is inherently interesting simply because of the wide variety of forces (electrostatic, dipole-dipole, hydrogen-bonding, van der Waals) that are present. Furthermore, an understanding of these particular interactions is immediately relevant to important topics like protein conformation and pharmaceutical polymorphism. We measured the low-frequency absorption spectra of several polycrystalline hydrophobic amino acids using THz time-domain spectroscopy, and in addition we carried out DFT calculations using periodic boundary conditions and an exchange-correlation functional that accounts for van der Waals dispersion forces. We chose to investigate a series of similar amino acids with closely analogous unit cells (leucine, isoleucine, and allo-isoleucine, in racemic or pseudo-racemic mixtures). This allows us to consider trends in the vibrational spectra as a function of small changes in molecular arrangement and/or crystal geometry. In this way, we gain confidence that peak assignments are not based on serendipitous similarities between calculated and observed features.

  20. Spin injection into silicon detected by broadband ferromagnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Ohshima, Ryo; Klingler, Stefan; Dushenko, Sergey; Ando, Yuichiro; Weiler, Mathias; Huebl, Hans; Shinjo, Teruya; Goennenwein, Sebastian T. B.; Shiraishi, Masashi

    2017-05-01

    We studied the spin injection in a NiFe(Py)/Si system using broadband ferromagnetic resonance spectroscopy. The Gilbert damping parameter of the Py layer on top of the Si channel was determined as a function of the Si doping concentration and Py layer thickness. For a fixed Py thickness, we observed an increase in the Gilbert damping parameter with decreasing resistivity of the Si channel. For a fixed Si doping concentration, we measured an increasing Gilbert damping parameter for decreasing Py layer thickness. No increase in the Gilbert damping parameter was found for Py/Si samples with an insulating interlayer. We attribute our observations to an enhanced spin injection into the low-resistivity Si by spin pumping.

  1. Far-infrared spectroscopic characterization of explosives for security applications using broadband terahertz time-domain spectroscopy.

    PubMed

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

    2007-06-01

    Broadband terahertz time-domain spectroscopy (THz-TDS) has been used to measure the far-infrared (FIR) vibrational spectra of several commonly used pure explosives, including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3-dinitrato-2,2-bis(nitratomethyl)propane (PETN), and two types of plastic explosive, SEMTEX and SX2. A number of distinct absorption peaks, originating from FIR-active vibrational modes of these polycrystalline energetic materials, were observed in the frequency range 0.3-7.5 THz (10-250 cm(-1)). In addition, the temperature-dependent FIR vibrational spectra of PETN were measured between 4 K and 296 K with several well-resolved absorption peaks observed across this temperature range. We find that as the temperature is reduced, the observed absorption peaks resolve into narrower features and shift towards higher frequencies. The temperature dependence of the spectra is explained in terms of the anharmonicity of the vibrational potentials of crystalline compounds, and an empirical fit is given to describe the peak shift with temperature.

  2. Rotational Spectroscopy of Vibrationally Excited N_2H^+ and N_2D^+ up to 2 Thz

    NASA Astrophysics Data System (ADS)

    Yu, Shanshan; Pearson, John; Drouin, Brian; Crawford, Timothy J.; Daly, Adam M.; Elliott, Ben; Amano, Takayoshi

    2015-06-01

    Terahertz absorption spectroscopy was employed to extend the measurements on the pure rotational transitions of N_2H^+, N_2D^+ and their 15N-containing isotopologues in the ground state and first excited vibrational states for the three fundamental vibrational modes. In total 88 new pure rotational transitions were observed in the range of 0.7--2.0~THz. The observed transition frequencies were fit to experimental accuracy, and the improved molecular parameters were obtained. The new measurements and predictions will support the analysis of high-resolution astronomical observations made with facilities such as SOFIA and ALMA where laboratory rest frequencies with uncertainties of 1 MHz or smaller are required for proper analysis of velocity resolved astrophysical components.

  3. Note: Deep UV-pump THz-probe spectroscopy of the excess electron in water

    NASA Astrophysics Data System (ADS)

    Berger, Arian; Savolainen, Janne; Shalit, Andrey; Hamm, Peter

    2017-06-01

    In the work of Savolainen et al. [Nat. Chem. 6, 697 (2014)], we studied the excess (hydrated) electron in water with the help of transient THz spectroscopy, which is a sensitive probe of its delocalization length. In that work, we used laser pulses at 800 nm, 400 nm, and 267 nm for photoionization. While the detachment mechanism for 400 nm and 267 nm is complicated and requires a concerted nuclear rearrangement, we provided evidence that 800 nm pumping excites the excess electron directly and vertically into the conduction band, despite a highly nonlinear field-ionization process. In the present note, we extend that work to 200 nm pumping, which provides a much cleaner way to reach the conduction band. We show that the detachment pathways upon 200 nm and 800 nm pumping are in essence the same, as indicated by the same initial size of the electron wavefunction and the same time scales for the collapse of the wavefunction and geminate recombination.

  4. THz spectroscopy on graphene-like materials for bio-compatible devices

    NASA Astrophysics Data System (ADS)

    Papari, Gian Paolo; Gargiulo, Valentina; Alfè, Michela; Di Capua, Roberto; Pezzella, Alessandro; Andreone, Antonello

    2017-04-01

    Graphene-like (GL) layers and eumelanin-based graphene-like (EUGL) hybrids have been investigated through THz time domain spectroscopy. The interest in these materials lies on their peculiar chemical-physical properties: the former are conductive water stable materials, whereas the latter are biocompatible materials with good conductive and adhesive properties. Both exhibit promising optoelectronic and bioelectronic applications. We measured mixtures of GL layers or EUGL hybrids with KBr, shaped in pellets with uniform thickness, in order to circumvent problems related to sample inhomogeneity and roughness. A mean field theory was applied to extract direct information on permittivity and conductivity. Data have been carefully fitted through the Drude-Smith theory, confirming the conductive nature of the hybrid materials. The results show that EUGL hybrid-based devices can be promising for the next generation of printable bio-circuits.

  5. False Detection of Dangerous and Netural Substances in Commonly Used Materials by Means of the Standard THz Time Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Trofimov, V. A.; Varentsova, S. A.

    2016-04-01

    Essential limitations of the standard THz Time Domain Spectroscopy (TDS), which lead to false detection of dangerous and neutral substances in commonly used materials, are demonstrated using the physical experiment with chocolate under real conditions as well as with semiconductors under laboratory conditions. To overcome this disadvantage, we propose using the time-dependent spectrum of the THz pulse, transmitted through or reflected from a substance. For quality assessment of the standard substance absorption frequency presence in the signal under analysis, we use time-dependent integral correlation criteria. The influence of aperture placed in front of the sample on spectral properties of silicon wafers with different resistivity is demonstrated as well.

  6. A quantitative study for determination of sugar concentration using attenuated total reflectance terahertz (ATR-THz) spectroscopy

    NASA Astrophysics Data System (ADS)

    Suhandy, Diding; Suzuki, Tetsuhito; Ogawa, Yuichi; Kondo, Naoshi; Ishihara, Takeshi; Takemoto, Yuichiro

    2011-06-01

    The objective of our research was to use ATR-THz spectroscopy together with chemometric for quantitative study in food analysis. Glucose, fructose and sucrose are main component of sugar both in fresh and processed fruits. The use of spectroscopic-based method for sugar determination is well reported especially using visible, near infrared (NIR) and middle infrared (MIR) spectroscopy. However, the use of terahertz spectroscopy for sugar determination in fruits has not yet been reported. In this work, a quantitative study for sugars determination using attenuated total reflectance terahertz (ATR-THz) spectroscopy was conducted. Each samples of glucose, fructose and sucrose solution with different concentrations were prepared respectively and their absorbance spectra between wavenumber 20 and 450 cm-1 (between 0.6 THz and 13.5 THz) were acquired using a terahertz-based Fourier Transform spectrometer (FARIS-1S, JASCO Co., Japan). This spectrometer was equipped with a high pressure of mercury lamp as light source and a pyroelectric sensor made from deuterated L-alanine triglycine sulfate (DLTGS) as detector. Each spectrum was acquired using 16 cm-1 of resolution and 200 scans for averaging. The spectra of water and sugar solutions were compared and discussed. The results showed that increasing sugar concentration caused decreasing absorbance. The correlation between sugar concentration and its spectra was investigated using multivariate analysis. Calibration models for glucose, fructose and sucrose determination were developed using partial least squares (PLS) regression. The calibration model was evaluated using some parameters such as coefficient of determination (R2), standard error of calibration (SEC), standard error of prediction (SEP), bias between actual and predicted sugar concentration value and ratio prediction to deviation (RPD) parameter. The cross validation method was used to validate each calibration model. It is showed that the use of ATR-THz

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  8. Scanning, non-contact, hybrid broadband diffuse optical spectroscopy and diffuse correlation spectroscopy system

    PubMed Central

    Johansson, Johannes D.; Mireles, Miguel; Morales-Dalmau, Jordi; Farzam, Parisa; Martínez-Lozano, Mar; Casanovas, Oriol; Durduran, Turgut

    2016-01-01

    A scanning system for small animal imaging using non-contact, hybrid broadband diffuse optical spectroscopy (ncDOS) and diffuse correlation spectroscopy (ncDCS) is presented. The ncDOS uses a two-dimensional spectrophotometer retrieving broadband (610-900 nm) spectral information from up to fifty-seven source-detector distances between 2 and 5 mm. The ncDCS data is simultaneously acquired from four source-detector pairs. The sample is scanned in two dimensions while tracking variations in height. The system has been validated with liquid phantoms, demonstrated in vivo on a human fingertip during an arm cuff occlusion and on a group of mice with xenoimplanted renal cell carcinoma. PMID:26977357

  9. Large Molecule Structures by Broadband Fourier Transform Molecular Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Evangelisti, Luca; Seifert, Nathan A.; Spada, Lorenzo; Pate, Brooks

    2016-06-01

    Fourier transform molecular rotational resonance spectroscopy (FT-MRR) using pulsed jet molecular beam sources is a high-resolution spectroscopy technique that can be used for chiral analysis of molecules with multiple chiral centers. The sensitivity of the molecular rotational spectrum pattern to small changes in the three dimensional structure makes it possible to identify diastereomers without prior chemical separation. For larger molecules, there is the additional challenge that different conformations of each diastereomer may be present and these need to be differentiated from the diastereomers in the spectral analysis. Broadband rotational spectra of several larger molecules have been measured using a chirped-pulse FT-MRR spectrometer. Measurements of nootkatone (C15H22O), cedrol (C15H26O), ambroxide (C16H28O) and sclareolide (C16H26O2) are presented. These spectra are measured with high sensitivity (signal-to-noise ratio near 1,000:1) and permit structure determination of the most populated isomers using isotopic analysis of the 13C and 18O isotopologues in natural abundance. The accuracy of quantum chemistry calculations to identify diastereomers and conformers and to predict the dipole moment properties needed for three wave mixing measurements is examined.

  10. CW-THz vector spectroscopy and imaging system based on 1.55-µm fiber-optics.

    PubMed

    Kim, Jae-Young; Song, Ho-Jin; Yaita, Makoto; Hirata, Akihiko; Ajito, Katsuhiro

    2014-01-27

    We present a continuous-wave terahertz (THz) vector spectroscopy and imaging system based on a 1.5-µm fiber optic uni-traveling-carrier photodiode and InGaAs photo-conductive receiver. Using electro-optic (EO) phase modulators for THz phase control with shortened optical paths, the system achieves fast vector measurement with effective phase stabilization. Dynamic ranges of 100 dB · Hz and 75 dB · Hz at 300 GHz and 1 THz, and phase stability of 1.5° per minute are obtained. With the simultaneous measurement of absorbance and relative permittivity, we demonstrate non-destructive analyses of pharmaceutical cocrystals inside tablets within a few minutes.

  11. Broadband Mid-Infrared Comb-Resolved Fourier Transform Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Kevin; Mills, Andrew; Mohr, Christian; Jiang, Jie; Fermann, Martin; Maslowski, Piotr

    2014-06-01

    We report on a comb-resolved, broadband, direct-comb spectroscopy system in the mid-IR and its application to the detection of trace gases and molecular line shape analysis. By coupling an optical parametric oscillator (OPO), a 100 m multipass cell, and a high-resolution Fourier transform spectrometer (FTS), sensitive, comb-resolved broadband spectroscopy of dilute gases is possible. The OPO has radiation output at 3.1-3.7 and 4.5-5.5 μm. The laser repetition rate is scanned to arbitrary values with 1 Hz accuracy around 417 MHz. The comb-resolved spectrum is produced with an absolute frequency axis depending only on the RF reference (in this case a GPS disciplined oscillator), stable to 1 part in 10^9. The minimum detectable absorption is 1.6x10-6 wn Hz-1/2. The operating range of the experimental setup enables access to strong fundamental transitions of numerous molecular species for applications based on trace gas detection such as environmental monitoring, industrial gas calibration or medical application of human breath analysis. In addition to these capabilities, we show the application for careful line shape analysis of argon-broadened CO band spectra around 4.7 μm. Fits of the obtained spectra clearly illustrate the discrepancy between the measured spectra and the Voigt profile (VP), indicating the need to include effects such as Dicke narrowing and the speed-dependence of the collisional width and shift in the line shape model, as was shown in previous cw-laser studies. In contrast to cw-laser based experiments, in this case the entire spectrum (˜ 250 wn) covering the whole P and R branches can be measured in 16 s with 417 MHz resolution, decreasing the acquisition time by orders of magnitude. The parallel acquisition allows collection of multiple lines simultaneously, removing the correlation of possible temperature and pressure drifts. While cw-systems are capable of measuring spectra with higher precision, this demonstration opens the door for fast

  12. The design of circuit for THz time domain spectroscopy system based on asynchronous optical sampling

    NASA Astrophysics Data System (ADS)

    Wang, Ruike; Zhang, Mile; Li, Yihan; He, Jingsuo; Zhang, Cunlin; Cui, Hailin

    2016-11-01

    Terahertz time domain spectroscopy system (THz-TDS) is the most commonly means of measuring terahertz time-domain spectroscopy. The time delay between the pump and probe laser is an important technology to realize THz time domain spectrum measurement. The translation platform with two mirrors and the mechanical structure is the popular means to adjust the optical path difference between the pump and probe laser to get the time delay of femtosecond pulse. Because of the limit of the mechanical structure and the phase-locked amplifier, this technique can't scan spectrum fast. In order to obtain high quality signal, a long time will be taken to scan spectrum. So a more rapid and convenient time delay technology is required to Instead of the machine translation platform and accomplish the Rapid spectral measurement. Asynchronous optical sampling technique is a way to get the time delay by producing a very small frequency difference between the repetition frequency of two femtosecond lasers. The scanner time will be reduced, because of there is no waste of time, due to mechanical inertia, not only by using the asynchronous optical sampling method to replace the mechanical structure without the influence of vibration. It will greatly increase the degree of integration by using the fiber femtosecond laser and highly integrated circuit to realize optical asynchronous sampling. To solve the problem above, a terahertz time-domain spectroscopy system based on asynchronous sampling is designed in this thesis. The system is based of two femtosecond laser whose repetition frequency is 100MHz.In order to realize asynchronous sampling, the control circuit of the two lasers is the most important. This thesis focuses on the researching, designing and experiment of this circuit. Firstly, the circuit is designed overall. Then the selection of the key device and the designing of the circuit principle is done by myself. Secondly, the test of the circuit to phase locked the master and

  13. Tip-enhanced THz Raman spectroscopy for local temperature determination at the nanoscale.

    PubMed

    Balois, Maria Vanessa; Hayazawa, Norihiko; Catalan, Francesca Celine; Kawata, Satoshi; Yano, Taka-Aki; Hayashi, Tomohiro

    2015-11-01

    Local temperature of a nanoscale volume is precisely determined by tip-enhanced terahertz Raman spectroscopy in the low temperature range of several tens of degrees. Heat generated by the tip-enhanced electric field is directly transferred to single-walled carbon nanotubes by heat conduction and radiation at the nanoscale. This heating modulates the intensity ratio of anti-Stokes/Stokes Raman scattering of the radial breathing mode of the carbon nanotube based on the Boltzmann distribution at elevated temperatures. Owing to the low-energy feature of the radial breathing mode, the local temperature of the probing volume has been successfully extracted with high sensitivity. The dependence of the temperature rise underneath the tip apex on the incident power coincides with the analytical results calculated by finite element method based on the tip enhancement effect and the consequent steady-state temperature via Joule heat generation. The results show that the local temperature at the nanoscale can be controlled in the low temperature range simply by the incident laser power while exhibiting a sufficiently high tip enhancement effect as an analytical tool for thermally sensitive materials (e.g., proteins, DNA). Graphical Abstract Tip-enhanced THz Raman spectroscopy detects the low frequency Raman mode both in Stokes and anti-Stokes shifts, which precisely reflects the local temperature of the sample volume.

  14. Femtosecond broadband stimulated Raman spectroscopy: Apparatus and methods

    PubMed Central

    McCamant, David W.; Kukura, Philipp; Yoon, Sangwoon; Mathies, Richard A.

    2005-01-01

    The laser, detection system, and methods that enable femtosecond broadband stimulated Raman spectroscopy (FSRS) are presented in detail. FSRS is a unique tool for obtaining high time resolution (<100 fs) vibrational spectra with an instrument response limited frequency resolution of <10 cm–1. A titanium:Sapphire-based laser system produces the three different pulses needed for FSRS: (1) A femtosecond visible actinic pump that initiates the photochemistry, (2) a narrow bandwidth picosecond Raman pump that provides the energy reservoir for amplification of the probe, and (3) a femtosecond continuum probe that is amplified at Raman resonances shifted from the Raman pump. The dependence of the stimulated Raman signal on experimental parameters is explored, demonstrating the expected exponential increase in Raman intensity with concentration, pathlength, and Raman pump power. Raman spectra collected under different electronic resonance conditions using highly fluorescent samples highlight the fluorescence rejection capabilities of FSRS. Data are also presented illustrating our ability: (i) To obtain spectra when there is a large transient absorption change by using a shifted excitation difference technique and (ii) to obtain high time resolution vibrational spectra of transient electronic states. PMID:17183413

  15. Broadband dielectric spectroscopy of inhomogeneous and composite weak conductors

    NASA Astrophysics Data System (ADS)

    Petzelt, J.; Nuzhnyy, D.

    2016-08-01

    In this paper, we discuss broadband dielectric spectroscopy from mHz up to the infrared range mainly for materials with inhomogeneous weak conductivity, including conductor-dielectric nanocomposites. Our discussion is based on the effective medium approximation (EMA) and experiments modeled by this approach are reviewed. We discuss core-shell composites modeled by coated-spheres (Hashin-Shtrikman model) and normal composites with a possible percolation of the conductor component resulting in sharp or smeared percolation threshold of the DC conductivity and diverging static permittivity in the former case. The sharp percolation threshold is modeled by the Bruggeman EMA or by general EMA with arbitrary percolation threshold and arbitrary critical exponents of the DC conductivity and static permittivity. For the case of smeared percolation threshold in the case of complex topologies, we use the Lichtenecker model allowing for partial percolation of both the components. Finally, numerous papers reporting negative permittivity in weakly conducting materials are criticized and concluded to be due to spurious effects.

  16. The structure and dynamics of carbon dioxide and water containing ices investigated via THz and mid-IR spectroscopy.

    PubMed

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

    2014-02-28

    Icy dust grains play a key role in the chemistry of the interstellar medium. The cumulative outcome of recent observations, laboratory studies, and astrochemical models indicates that solid-phase reaction mechanisms may dominate the formation of complex organic molecules such as amino acids and sugars in space. Consequently, the composition and structure of the icy grain mantle may significantly influence solid-phase reaction pathways. In this work, we present a new experimental setup capable of studying astrochemical ice analogs in both the TeraHertz (THz), or far-Infrared (far-IR), region (0.3-7.5 THz; 10-250 cm(-1)) and the mid-IR (400-4000 cm(-1)). The instruments are capable of performing a variety of spectroscopic studies that can provide especially relevant laboratory data to support astronomical observations from telescopes such as Herschel, SOFIA, and ALMA. Experimental spectra of astrochemical ice analogs of water and carbon dioxide in pure, mixed, and layered ices were collected at different temperatures under high vacuum conditions with the goal of investigating the structure of the ice. We tentatively observe a new feature in both amorphous solid water and crystalline water at 33 cm(-1) (1 THz). In addition, our studies of mixed and layered ices show how it is possible to identify the location of carbon dioxide as it segregates within the ice by observing its effect on the THz spectrum of water ice. The THz spectra of mixed and layered ices are further analyzed by fitting their spectral features to those of pure amorphous solid water and crystalline water ice to quantify the effects of temperature changes on structure. From the results of this work, it appears that THz spectroscopy is potentially well suited to study thermal transformations within the ice.

  17. Programmatic perspectives with technical examples for THz materials characterization

    NASA Astrophysics Data System (ADS)

    Buchwald, Walter

    2011-06-01

    THz technology has a rich history of use in the field of interstellar molecule identification where a variety of molecule specific vibrational and rotational spectroscopic signatures exist and has been aggressively investigated for use in advanced radar applications because of the immediate improvement in object resolution obtained at higher frequencies. Traditionally, high power THz systems have relied upon millimeter wave sources and frequency multiplication techniques to achieve acceptable output power levels, while lower power, table top spectroscopic systems, have relied on broadband incoherent light sources. With the advent of high power lasers, advances in non-linear optics, and new material systems, a number of promising techniques for the generation, detection and manipulation of THz radiation are currently under development and are considered the enabling technologies behind a variety of advanced THz applications. This work presents a programmatic overview of current trends in THz technology of interest to a variety of government organizations. It focuses on those techniques currently under investigation for the generation and detection of THz fields motivated, for example, by such diverse applications as metamaterial spectroscopy, TH imaging, long standoff chem/bio detection and THz communications. Examples of these new techniques will be presented which in turn will motivate the need for the characterization of application specific active and passive THz components.

  18. Optimal multisine excitation design for broadband electrical impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Sanchez, B.; Vandersteen, G.; Bragos, R.; Schoukens, J.

    2011-11-01

    Electrical impedance spectroscopy (EIS) can be used to characterize biological materials in applications ranging from cell culture to body composition, including tissue and organ state. The emergence of cell therapy and tissue engineering opens up a new and promising field of application. While in most cases classical measurement techniques based on a frequency sweep can be used, EIS based on broadband excitations enables dynamic biological systems to be characterized when the measuring time and injected energy are a constraint. Myocardial regeneration, cell characterization in micro-fluidic systems and dynamic electrical impedance tomography are all examples of such applications. The weakness of such types of fast EIS measuring techniques resides in their intrinsic loss of accuracy. However, since most of the practical applications have no restriction over the excitation used, the input power spectrum can be appropriately designed to maximize the accuracy obtained from the measurements. This paper deals with the problem of designing the optimal multisine excitation for electrical bioimpedance measurements. The optimal multisine is obtained by the minimization of the Cramer-Rao lower bound, or what is the same, by maximizing the accuracy obtained from the measurements. Furthermore, because no analytical solution exists for global optimization involving time and frequency domains jointly, this paper presents the multisine optimization approach partially in both domains and then combines the results. As regards the frequency domain approach, a novel contribution is made for the multisine amplitude power spectrum. In the time domain, multisine is optimized by reducing its crest factor. Moreover, the impact on the information and accuracy of the impedance spectrum obtained from using different multisine amplitude power spectra is discussed, as well as the number of frequencies and frequency distributions. The theory is supported by a set of validation measurements when

  19. Characterization of Microsolvated Crown Ethers from Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Perez, Cristobal; Schnell, Melanie; Blanco, Susana; Lopez, Juan Carlos

    2016-06-01

    Since they were first synthetized, crown ethers have been extensively used in organometallic chemistry due to their unparalleled binding selectivity with alkali metal cations. From a structural point of view, crown ethers are heterocycles containing oxygen and/or other heteroatoms, although the most common ones are formed from ethylene oxide unit. Crown ethers are conventionally seen as being hydrophilic inside and hydrophobic outside when the structures found for the metal cation complexes are considered. However, crown ethers are extremely flexible and in isolation may present a variety of stable conformations so that their structure may be easily adapted in presence of a strong ligand as an alkali metal cation minimize the energy of the resulting complex. Water can be considered a soft ligand which interacts with crown ethers through moderate hydrogen bonds. It is thus interesting to investigate which conformers are selected by water to form complexes, the preferred interaction sites and the possible conformational changes due to the presence of one or more water molecules. Previous studies identified microsolvated crown ethers but in all cases with a chromophore group attached to the structure. Here we present a broadband rotational spectroscopy study of microsolvated crown ethers produced in a pulsed molecular jet expansion. Several 1:1 and 1:2 crown ether:water aggregates are presented for 12-crown-4, 15-crown-5 and 18-crown-6. Unambiguous identification of the structures has been achieved using isotopic substitution within the water unit. The subtle changes induced in the structures of the crown ether monomer upon complexation and the hydrogen-bonding network that hold them together will be also discussed. F. Gámez, B. Martínez-Haya, S. Blanco,J. C. López and J. L. Alonso, Phys. Chem. Chem. Phys. 2014, 14 12912-12918 V. A. Shubert, C.W. Müller and T. Zwier, J. Phys. Chem. A 2009, 113 8067-8079

  20. Enantiomer Identification in Chiral Mixtures with Broadband Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Shubert, V. Alvin; Schmitz, David; Medcraft, Chris; Patterson, David; Doyle, John M.; Schnell, Melanie

    2014-06-01

    In nature and as products of chemical syntheses, chiral molecules often exist in mixtures with other chiral molecules. The analysis of these complex mixtures to identify the components, determine which enantiomers are present, and to measure the enantiomeric excesses (ee) is still one of the challenging but very important tasks of analytical chemistry. These analyses are required at every step of modern drug development, from candidate searches to production and regulation. We present here a new method of identifying individual enantiomers in mixtures of chiral molecules in the gas phase. It is based on broadband rotational spectroscopy and employs a sum or difference frequency generation three-wave mixing process that involves a closed cycle of three rotational transitions. The phase of the acquired signal bares the signature of the enantiomer (see figure), as it depends upon the combined quantity, μaμbμc, which is of opposite sign between members of an enantiomeric pair. Furthermore, because the signal amplitude is proportional to the ee, this technique allows for both determining which enantiomer is in excess and by how much. The high resolution of our technique allows us to perform molecule specific measurements of mixtures of chiral molecules with μaμbμc ≠ 0, even when the molecules are very similar (e.g. conformational isomers). We introduce the technique and present results on the analysis of mixtures of the terpenes, carvone, menthone, and carvomenthenol. D. Patterson, M. Schnell, J. M. Doyle, Nature. 497, 475-477, 2013 V. A. Shubert, D. Schmitz, D. Patterson, J. M. Doyle, M. Schnell, Ang. Chem. Int. Ed. 53, 1152-1155,2014

  1. Broadband Near-Infrared Spectroscopy of X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Froning, Cynthia S.; Robinson, Edward L.; Bitner, Martin A.

    2008-05-01

    We present broadband NIR spectroscopy of the X-ray binaries A0620-00, Cen X-4, V404 Cyg, and GX 13+1. The NIR spectra consist of emission from the late-type donor star and the accretion disk. In A0620-00 and Cen X-4, the donor star is the dominant component but there are emission lines from the accretion disk as well as evidence of a continuum disk component. In V404 Cyg, there are no signatures of the accretion disk in the NIR spectrum, whereas in GX13+1, the accretion disk is the dominant emitter. Using spectra of field stars of known spectral type, we have examined the donor star absorption spectra in these systems. The apparent spectral types of the donor stars in A0620-00 and Cen X-4 are those of late-type dwarf stars (K7 or later). In A0620-00, the weakness of the 12CO bandhead features relative to the atomic lines indicates a depleted carbon abundance in the system, [C/H] = -1.5. The spectrum of Cen X-4 does not show this abundance anomaly. The donor stars in the V404 Cyg and GX13+1 are evolved, but while the donor star in V404 Cyg appears to the only NIR source, the donor in GX13+1 only accounted for about 1/4 of NIR flux at the time of our observations. For A0620-00, we have used scaled fits of spectral type template stars to determine the donor star contribution in the H-band, which is combined with previous work to determine the binary inclination and, in turn, the mass of the black hole: MBH = 9.7+/-0.6 Msolar.

  2. Thz Spectroscopy of Acetaldehyde and Search of 13C Species in Orion

    NASA Astrophysics Data System (ADS)

    Margulès, L.; Motiyenko, R. A.; Ilyushin, V. V.; Tercero, B.; Cernicharo, J.; Guillemin, J.-C.

    2012-06-01

    Acetaldehyde (CH_3CHO) is one of the high priority complex organic molecules for the astrophysical community. There is a lack of data concerning the 13C species since the measurements are limited to 40 GHz up to date. This molecule displays a large amplitude motion: the hindered rotation of the methyl group with respect to the rest of the molecule. The analysis is performed with RAM36 code which used the Rho Axis Method. Last year we presented the analysis of the millimeterwave spectra of the 13CH_3CHO species. We extended the analysis to the THz range of the vibrational ground state for both species. We are also analyzing the first torsional state (≈140 cm-1) for two reasons: first, this permits to remove correlation between parameters. Second, this state contribute to the partition function even at ISM temperature (100--150 K) since there is an influence on the column density determined in case of detection. The searches of these isotopomers are in progress in ORION. This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI. This work was also done under the ANR-08-BLAN-0054. Kilb, R.W.; Lin, C.C.; and Wilson, E.B. J. Chem. Phys. 26, (1957) 1695 Ilyushin, V.V. et al J. Mol. Spectrosc. 259, (2010) 26 Margules, L. et al. FA07, 66th International Symposium on Molecular Spectroscopy (2011)

  3. Single-shot time-resolved THz spectroscopy using non-collinear electro-optic imaging

    NASA Astrophysics Data System (ADS)

    Wang, Zhenyou; Su, Fuhai; Hegmann, Frank A.

    2010-03-01

    We demonstrate a technique for rapid substance identification via single-shot, coherent THz imaging using non-collinear electro-optic sampling. A THz probe pulse generated in ZnTe is transmitted through the sample then focused on a (110) ZnTe detection crystal. An 800nm, 100fs optical pulse employed as a sampling beam passes through the ZnTe detection crystal at an angle of 7^o relative to the THz beam.footnotetextT. Yasuda et al., Opt. Commun. 267, 128 (2006) The THz field induced birefringence is resolved as a variation of the intensity of the sampling pulse transmitted through a crossed polarizer. The modified sampling beam spot is imaged using a CCD camera. Because of the non-collinear geometry, the spatial overlap between the THz field and the optical pulse depends on the temporal position within the THz waveform. Consequently, we obtain high-resolution 2D images of the THz waveform without scanning the relative path length. The resolution of the absorption spectra extracted from wet paper and lactose using the single-shot imaging approach is comparable to the resolution obtained through conventional scanning lock-in measurements. Possible applications for substance detection are discussed.

  4. Direct and quantitative broadband absorptance spectroscopy with multilayer cantilever probes

    DOEpatents

    Hsu, Wei-Chun; Tong, Jonathan Kien-Kwok; Liao, Bolin; Chen, Gang

    2015-04-21

    A system for measuring the absorption spectrum of a sample is provided that includes a broadband light source that produces broadband light defined within a range of an absorptance spectrum. An interferometer modulates the intensity of the broadband light source for a range of modulation frequencies. A bi-layer cantilever probe arm is thermally connected to a sample arm having at most two layers of materials. The broadband light modulated by the interferometer is directed towards the sample and absorbed by the sample and converted into heat, which causes a temperature rise and bending of the bi-layer cantilever probe arm. A detector mechanism measures and records the deflection of the probe arm so as to obtain the absorptance spectrum of the sample.

  5. The spectrum of density fluctuations of noble gases probed by THz neutron and x-ray spectroscopy

    SciTech Connect

    Cunsolo, Alessandro

    2016-02-26

    Approximately 50 years of inelastic scattering studies of noble gases are reviewed to illustrate the main advances achieved in the understanding of the THz dynamics of simple systems. The gradual departure of the spectral shape from the hydrodynamic regime is discussed with an emphasis on the phenomenology of fast (sub-ps) relaxation processes. This review shows that relaxation phenomena in noble gases have an essentially collisional origin, which is also revealed by the parallelism between their characteristic timescale and the interatomic collision time. In addition, recent THz spectroscopy results on noble gases at extreme thermodynamic conditions are discussed to illustrate the need for a revision of our current understanding of the supercritical phase.

  6. The spectrum of density fluctuations of noble gases probed by THz neutron and x-ray spectroscopy

    DOE PAGES

    Cunsolo, Alessandro

    2016-02-26

    Approximately 50 years of inelastic scattering studies of noble gases are reviewed to illustrate the main advances achieved in the understanding of the THz dynamics of simple systems. The gradual departure of the spectral shape from the hydrodynamic regime is discussed with an emphasis on the phenomenology of fast (sub-ps) relaxation processes. This review shows that relaxation phenomena in noble gases have an essentially collisional origin, which is also revealed by the parallelism between their characteristic timescale and the interatomic collision time. In addition, recent THz spectroscopy results on noble gases at extreme thermodynamic conditions are discussed to illustrate themore » need for a revision of our current understanding of the supercritical phase.« less

  7. Broadband stimulated Raman spectroscopy in the deep ultraviolet region

    NASA Astrophysics Data System (ADS)

    Kuramochi, Hikaru; Fujisawa, Tomotsumi; Takeuchi, Satoshi; Tahara, Tahei

    2017-09-01

    We report broadband stimulated Raman measurements in the deep ultraviolet (DUV) region, which enables selective probing of the aromatic amino acid residues inside proteins through the resonance enhancement. We combine the narrowband DUV Raman pump pulse (<10 cm-1) at wavelengths as short as 240 nm and the broadband DUV probe pulse (>1000 cm-1) to realize stimulated Raman measurements covering a >1500 cm-1 spectral window. The stimulated Raman measurements for neat solvents, tryptophan, tyrosine, and glucose oxidase are performed using 240- and 290-nm Raman pump, highlighting the high potential of the DUV stimulated Raman probe for femtosecond time-resolved study of proteins.

  8. Hierarchical viscosity of aqueous solution of tilapia scale collagen investigated via dielectric spectroscopy between 500 MHz and 2.5 THz

    PubMed Central

    Kawamata, H.; Kuwaki, S.; Mishina, T.; Ikoma, T.; Tanaka, J.; Nozaki, R.

    2017-01-01

    Aqueous solutions of biomolecules such as proteins are very important model systems for understanding the functions of biomolecules in actual life processes because interactions between biomolecules and the surrounding water molecules are considered to be important determinants of biomolecules’ functions. Globule proteins have been extensively studied via dielectric spectroscopy; the results indicate three relaxation processes originating from fluctuations in the protein molecule, the bound water and the bulk water. However, the characteristics of aqueous solutions of collagens have rarely been investigated. In this work, based on broadband dielectric measurements between 500 MHz and 2.5 THz, we demonstrate that the high viscosity of a collagen aqueous solution is due to the network structure being constructed of rod-like collagen molecules surrounding free water molecules and that the water molecules are not responsible for the viscosity. We determine that the macroscopic viscosity is related to the mean lifetime of the collagen-collagen interactions supporting the networks and that the local viscosity of the water surrounded by the networks is governed by the viscosity of free water as in the bulk. This hierarchical structure in the dynamics of the aqueous solution of biomolecules has been revealed for the first time. PMID:28345664

  9. Hierarchical viscosity of aqueous solution of tilapia scale collagen investigated via dielectric spectroscopy between 500 MHz and 2.5 THz

    NASA Astrophysics Data System (ADS)

    Kawamata, H.; Kuwaki, S.; Mishina, T.; Ikoma, T.; Tanaka, J.; Nozaki, R.

    2017-03-01

    Aqueous solutions of biomolecules such as proteins are very important model systems for understanding the functions of biomolecules in actual life processes because interactions between biomolecules and the surrounding water molecules are considered to be important determinants of biomolecules’ functions. Globule proteins have been extensively studied via dielectric spectroscopy; the results indicate three relaxation processes originating from fluctuations in the protein molecule, the bound water and the bulk water. However, the characteristics of aqueous solutions of collagens have rarely been investigated. In this work, based on broadband dielectric measurements between 500 MHz and 2.5 THz, we demonstrate that the high viscosity of a collagen aqueous solution is due to the network structure being constructed of rod-like collagen molecules surrounding free water molecules and that the water molecules are not responsible for the viscosity. We determine that the macroscopic viscosity is related to the mean lifetime of the collagen-collagen interactions supporting the networks and that the local viscosity of the water surrounded by the networks is governed by the viscosity of free water as in the bulk. This hierarchical structure in the dynamics of the aqueous solution of biomolecules has been revealed for the first time.

  10. THz and mid-IR spectroscopy of interstellar ice analogs: methyl and carboxylic acid groups.

    PubMed

    Ioppolo, S; McGuire, B A; Allodi, M A; Blake, G A

    2014-01-01

    A fundamental problem in astrochemistry concerns the synthesis and survival of complex organic molecules (COMs) throughout the process of star and planet formation. While it is generally accepted that most complex molecules and prebiotic species form in the solid phase on icy grain particles, a complete understanding of the formation pathways is still largely lacking. To take full advantage of the enormous number of available THz observations (e.g., Herschel Space Observatory, SOFIA, and ALMA), laboratory analogs must be studied systematically. Here, we present the THz (0.3-7.5 THz; 10-250 cm(-1)) and mid-IR (400-4000 cm(-1)) spectra of astrophysically-relevant species that share the same functional groups, including formic acid (HCOOH) and acetic acid (CH3COOH), and acetaldehyde (CH3CHO) and acetone ((CH3)2CO), compared to more abundant interstellar molecules such as water (H2O), methanol (CH3OH), and carbon monoxide (CO). A suite of pure and mixed binary ices are discussed. The effects on the spectra due to the composition and the structure of the ice at different temperatures are shown. Our results demonstrate that THz spectra are sensitive to reversible and irreversible transformations within the ice caused by thermal processing, suggesting that THz spectra can be used to study the composition, structure, and thermal history of interstellar ices. Moreover, the THz spectrum of an individual species depends on the functional group(s) within that molecule. Thus, future THz studies of different functional groups will help in characterizing the chemistry and physics of the interstellar medium (ISM).

  11. THz Plasma Diagnostics: an evolution from FIR and Millimeter waves historical applications

    NASA Astrophysics Data System (ADS)

    Bombarda, F.; Doria, A.; Galatola Teka, G.; Giovenale, E.; Zerbini, M.

    2016-08-01

    Extremely broadband (100 GHz-30 THz) single cycle THz pulses are routinely generated with femtosecond laser for Time Domain Spectroscopy applications (TDS). The wide frequency range has an unquestionable diagnostic potential for Tokamak plasmas and not surprisingly THz TDS finds a natural field of application in this area, which is an evolution of the FIR and millimeter waves diagnostics, where ENEA Frascati holds historical expertise. By illuminating the plasma with a THz beam, phase, intensity and polarization of both reflected and transmitted beams can be detected, devising a single diagnostic instrument capable of measuring multiple plasma parameters. We will describe and discuss the laboratory work now in progress to realise a tailored THz-TDS spectrometer with design parameters optimised for the requirements of Tokamak plasmas and the tests of optical fibers and quasioptical couplers to optimise access to plasma. ENEA Frascati and the Photonics group of Physics Dept. of Oxford University are collaborating on this subject [1].

  12. In-situ THz spectroscopy on lead halide perovskite film for monitoring transient crystallization phase (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Park, SaeJune; Ahn, Yeong Hwan

    2017-02-01

    In the past few years, perovskite film has been considered as a promising materials for solar cell devices due to its outstanding performance. To maximize the perovskite solar cell performance, it is necessary to understand the crystallization mechanism of perovskite film. In this study, we monitored the crystallization and decrystallization of the lead halide perovskite (MAPbI3-xClx) film under thermal annealing and UV-laser exposure processes by using in-situ terahertz time-domain spectroscopy. The strength of vibrational resonances in THz frequency range is found to be a good indicator of perovskite crystallinity. We measured the THz spectra as we annealed the perovskite film at various temperatures in order to achieve the degree of crystallization, i.e., the transition of perovskite structure from the intermediate phase to the tetragonal phase. In addition, we investigated the UV-laser-induced phase transition of the perovskite film. Because it is widely known that UV light illumination on perovskite film tends degrade the perovskite cell efficiency, its influence on the crystallization is our primary concern. Surprisingly, the crystallization phase increases for 10 min, until it starts to degrade over a couple of hours. We also studied the transient transport properties of the films under UV illumination. The correlation between the degree of crystallization (obtained from THz transmission) and the transport parameters exhibited the electric percolation threshold behaviors in the perovskite films. These information are expected to be crucial for optimizing the fabrication method of perovskite solar cell.

  13. Broadband coherent Raman spectroscopy running at 24,000 spectra per second

    NASA Astrophysics Data System (ADS)

    Hashimoto, Kazuki; Takahashi, Megumi; Ideguchi, Takuro; Goda, Keisuke

    2016-02-01

    We present a Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) spectroscopy technique that achieves broadband CARS measurements at an ultrahigh scan rate of more than 20,000 spectra/s – more than 20 times higher than that of previous broadband coherent Raman scattering spectroscopy techniques. This is made possible by an integration of a FT-CARS system and a rapid-scanning retro-reflective optical path length scanner. To demonstrate the technique’s strength, we use it to perform broadband CARS spectroscopy of the transient mixing dynamics of toluene and benzene in the fingerprint region (200–1500 cm‑1) with spectral resolution of 10 cm‑1 at a record high scan rate of 24,000 spectra/s. Our rapid-scanning FT-CARS technique holds great promise for studying chemical dynamics and wide-field label-free biomedical imaging.

  14. Ultrafast broadband Fourier-transform CARS spectroscopy operating at 50,000 spectra/second

    NASA Astrophysics Data System (ADS)

    Tamamitsu, Miu; Sakaki, Yusuke; Nakamura, Tasuku; Podagatlapalli, G. Krishna; Ideguchi, Takuro; Goda, Keisuke

    2017-02-01

    We present a coherent Raman scattering (CRS) spectroscopy technique achieving a CRS spectral acquisition rate of 50,000 spectra/second over a Raman spectral region of 200 - 1430 cm-1 with a resolution of 4.2 cm-1. This ultrafast, broadband and high-resolution CRS spectroscopic performance is realized by a polygonal Fourier-domain delay line serving as an ultra-rapid optical-path-length scanner in a broadband Fourier-transform coherent anti-Stokes Raman scattering (CARS) spectroscopy platform. We present a theoretical description of the technique and demonstrate continuous, ultrafast, broadband, and high-resolution CARS spectroscopy on a liquid toluene sample using our proof-of-concept setup.

  15. Broadband coherent Raman spectroscopy running at 24,000 spectra per second

    PubMed Central

    Hashimoto, Kazuki; Takahashi, Megumi; Ideguchi, Takuro; Goda, Keisuke

    2016-01-01

    We present a Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) spectroscopy technique that achieves broadband CARS measurements at an ultrahigh scan rate of more than 20,000 spectra/s – more than 20 times higher than that of previous broadband coherent Raman scattering spectroscopy techniques. This is made possible by an integration of a FT-CARS system and a rapid-scanning retro-reflective optical path length scanner. To demonstrate the technique’s strength, we use it to perform broadband CARS spectroscopy of the transient mixing dynamics of toluene and benzene in the fingerprint region (200–1500 cm−1) with spectral resolution of 10 cm−1 at a record high scan rate of 24,000 spectra/s. Our rapid-scanning FT-CARS technique holds great promise for studying chemical dynamics and wide-field label-free biomedical imaging. PMID:26875786

  16. A novel THz spectroscopy recognition method for transgenic organisms based on APSO combined with SVM

    NASA Astrophysics Data System (ADS)

    Li, T. J.; Liu, J. J.; Shao, G. F.; Fan, L. L.

    2016-04-01

    Currently, the transgenic products detection methods are mostly based on visible/near-infrared light spectrum. In addition, it is hard to set up the parameters in the support vector machine (SVM) model and there is a large amount of calculation on spectrum data. To solve these problems, this paper proposed an algorithm based on terahertz (THz) spectrum and SVM using adaptive particle swarm optimize (APSO-SVM) for building up the classifications of transgenic cotton seed. To conduct the transgenic cotton seed classification, within the wavelength region 150 μm—3 mm, the THz spectrums are first sampled from 165 samples of three newest transgenic cotton seeds. Then, the 165 transgenic cotton seeds are recognized based on the APSO-SVM. Experiment results indicate that the total recognition rate is up to 97.3%, which prove that the THz spectrum combined with APSO-SVM can provide a reliable, rapid, simple and nondestructive detection method for transgenic cotton seed.

  17. Power-Stabilization of High Frequency Gyrotrons Using a Double PID Feedback Control for Applications to High Power THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Idehara, Toshitaka; Kuleshov, Alexei; Ueda, Keisuke; Khutoryan, Eduard

    2013-11-01

    High stabilization of the output power of high frequency gyrotrons for high power THz spectroscopy is an important issue in order to extend the applications of gyrotrons to wider subjects. For this objective, we tried a PID feedback control on a heater current of a triode magnetron injection gun (MIG) for stabilization of an electron beam current and an additional PID control of an anode voltage of the gun for direct stabilization of output power. This double PID control achieved effective responses for the stabilization of output power in both slow (from several tens seconds to several minutes) and fast (from milliseconds to seconds) time scales.

  18. Hot-Electron Gallium Nitride Two Dimensional Electron Gas Nano-bolometers For Advanced THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Rahul

    Two-dimensional electron gas (2DEG) in semiconductor heterostructures was identified as a promising medium for hot-electron bolometers (HEB) in the early 90s. Up until now all research based on 2DEG HEBs is done using high mobility AlGaAs/GaAs heterostructures. These systems have demonstrated very good performance, but only in the sub terahertz (THz) range. However, above ˜0.5 THz the performance of AlGaAs/GaAs detectors drastically deteriorates. It is currently understood, that detectors fabricated from standard AlGaAs/GaAs heterostructures do not allow for reasonable coupling to THz radiation while maintaining high conversion efficiency. In this work we have developed 2DEG HEBs based on disordered Gallium Nitride (GaN) semiconductor, that operate at frequencies beyond 1THz at room temperature. We observe strong free carrier absorption at THz frequencies in our disordered 2DEG film due to Drude absorption. We show the design and fabrication procedures of novel micro-bolometers having ultra-low heat capacities. In this work the mechanism of 2DEG response to THz radiation is clearly identified as bolometric effect through our direct detection measurements. With optimal doping and detector geometry, impedances of 10--100 O have been achieved, which allow integration of these devices with standard THz antennas. We also demonstrate performance of the antennas used in this work in effectively coupling THz radiation to the micro-bolometers through polarization dependence and far field measurements. Finally heterodyne mixing due to hot electrons in the 2DEG micro-bolometer has been performed at sub terahertz frequencies and a mixing bandwidth greater than 3GHz has been achieved. This indicates that the characteristic cooling time in our detectors is fast, less than 50ps. Due to the ultra-low heat capacity; these detectors can be used in a heterodyne system with a quantum cascade laser (QCL) as a local oscillator (LO) which typically provides output powers in the micro

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

    PubMed

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

    2012-03-12

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

  20. Simplified THz Instrumentation for High-Field DNP-NMR Spectroscopy

    PubMed Central

    Sirigiri, Jagadishwar R.

    2012-01-01

    We present an alternate simplified concept to irradiate a nuclear magnetic resonance sample with terahertz (THz) radiation for dynamic nuclear polarization (DNP) experiments using the TE01 circular waveguide mode for transmission of the THz power and the illumination of the DNP sample by either the TE01 or TE11 mode. Using finite element method and 3D electromagnetic simulations we demonstrate that the average value of the transverse magnetic field induced by the THz radiation and responsible for the DNP effect using the TE11 or the TE01 mode are comparable to that generated by the HE11 mode and a corrugated waveguide. The choice of the TE11/TE01 mode allows the use of a smooth-walled, oversized waveguide that is easier to fabricate and less expensive than a corrugated waveguide required for transmission of the HE11 mode. Also, the choice of the TE01 mode can lead to a simplification of gyrotron oscillators that operate in the TE0n mode, by employing an on-axis rippled-wall mode converter to convert the TE0n mode into the TE01 mode either inside or outside of the gyrotron tube. These novel concepts will lead to a significant simplification of the gyrotron, the transmission line and the THz coupler, which are the three main components of a DNP system. PMID:22977293

  1. Simplified THz Instrumentation for High-Field DNP-NMR Spectroscopy.

    PubMed

    Maly, Thorsten; Sirigiri, Jagadishwar R

    2012-07-01

    We present an alternate simplified concept to irradiate a nuclear magnetic resonance sample with terahertz (THz) radiation for dynamic nuclear polarization (DNP) experiments using the TE(01) circular waveguide mode for transmission of the THz power and the illumination of the DNP sample by either the TE(01) or TE(11) mode. Using finite element method and 3D electromagnetic simulations we demonstrate that the average value of the transverse magnetic field induced by the THz radiation and responsible for the DNP effect using the TE(11) or the TE(01) mode are comparable to that generated by the HE(11) mode and a corrugated waveguide. The choice of the TE(11)/TE(01) mode allows the use of a smooth-walled, oversized waveguide that is easier to fabricate and less expensive than a corrugated waveguide required for transmission of the HE(11) mode. Also, the choice of the TE(01) mode can lead to a simplification of gyrotron oscillators that operate in the TE(0n) mode, by employing an on-axis rippled-wall mode converter to convert the TE(0n) mode into the TE(01) mode either inside or outside of the gyrotron tube. These novel concepts will lead to a significant simplification of the gyrotron, the transmission line and the THz coupler, which are the three main components of a DNP system.

  2. 2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

    NASA Astrophysics Data System (ADS)

    Hamm, Peter

    2014-11-01

    In a recent paper, the experimental 2D-Raman-THz response of liquid water at ambient conditions has been presented [J. Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U. S. A. 110, 20402 (2013)]. Here, all-atom molecular dynamics simulations are performed with the goal to reproduce the experimental results. To that end, the molecular response functions are calculated in a first step, and are then convoluted with the laser pulses in order to enable a direct comparison with the experimental results. The molecular dynamics simulation are performed with several different water models: TIP4P/2005, SWM4-NDP, and TL4P. As polarizability is essential to describe the 2D-Raman-THz response, the TIP4P/2005 water molecules are amended with either an isotropic or a anisotropic polarizability a posteriori after the molecular dynamics simulation. In contrast, SWM4-NDP and TL4P are intrinsically polarizable, and hence the 2D-Raman-THz response can be calculated in a self-consistent way, using the same force field as during the molecular dynamics simulation. It is found that the 2D-Raman-THz response depends extremely sensitively on details of the water model, and in particular on details of the description of polarizability. Despite the limited time resolution of the experiment, it could easily distinguish between various water models. Albeit not perfect, the overall best agreement with the experimental data is obtained for the TL4P water model.

  3. 2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

    SciTech Connect

    Hamm, Peter

    2014-11-14

    In a recent paper, the experimental 2D-Raman-THz response of liquid water at ambient conditions has been presented [J. Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U. S. A. 110, 20402 (2013)]. Here, all-atom molecular dynamics simulations are performed with the goal to reproduce the experimental results. To that end, the molecular response functions are calculated in a first step, and are then convoluted with the laser pulses in order to enable a direct comparison with the experimental results. The molecular dynamics simulation are performed with several different water models: TIP4P/2005, SWM4-NDP, and TL4P. As polarizability is essential to describe the 2D-Raman-THz response, the TIP4P/2005 water molecules are amended with either an isotropic or a anisotropic polarizability a posteriori after the molecular dynamics simulation. In contrast, SWM4-NDP and TL4P are intrinsically polarizable, and hence the 2D-Raman-THz response can be calculated in a self-consistent way, using the same force field as during the molecular dynamics simulation. It is found that the 2D-Raman-THz response depends extremely sensitively on details of the water model, and in particular on details of the description of polarizability. Despite the limited time resolution of the experiment, it could easily distinguish between various water models. Albeit not perfect, the overall best agreement with the experimental data is obtained for the TL4P water model.

  4. High Resolution Spectroscopy Using a Tunable Thz Synthesizer Based on Photomixing

    NASA Astrophysics Data System (ADS)

    Cuisset, Arnaud; Hindle, Francis; Mouret, Gael; Eliet, Sophie; Guinet, Mickael; Bocquet, Robin

    2011-06-01

    Optical heterodyning, also know as photomixing is an attractive solution as a single device able to cover the entire frequency range from 300 GHz to 3 THz. As the THz frequency is extracted from the difference frequency of two lasers, the accuracy with which the generated frequency is known is directly determined by the frequency accuracy of the lasers. In order to fully characterize the spectral fingerprint of a given molecule an accuracy approximately one order of magnitude finer than the Doppler linewidth is required, around 100 kHz for smaller polar compounds. To generate accurate cw-THz the frequency spacing of the modes of a Frequency Comb (FC) has been employed to constrain the emission frequency of a photomixing source.footnote{G. Mouret, F. Hindle, A. Cuisset, C. Yang, R. Bocquet, M. Lours, D. Rovera, Opt. Express, 2009, 17: 22031.} Two phase locked loops are implemented coherently locking the two cw-lasers (CW1 and CW2) to different modes of the FC. Although this solution allows accurate generation of narrowband THz the continuous tuning of the frequency presents some obstacles. To overcome these difficulties a system architecture with a third cw-laser (CW3) phase locked to CW2 has been implemented. The beatnote between CW2 and CW3 is free from the FC modes therefore the PLL frequency can be freely scanned over its entire operating range, in our case around 200 MHz. The most of polar compounds may be studied at high resolution in the THz domain with this synthesizer. Three different examples of THz analysis with atmospherical and astrophysical interests will be presented: The ground and vibrationnally excited states of H_2CO revisited in the 0.5-2 THz frequency region The rotational dependences of the broadening coefficients of CH_3Cl studied at high J and K values The molecular discrimination of a complex mixture containing methanol and ethanol. F. Hindle, A. Cuisset, G. Mouret, R. Bocquet Comptes Rendus Physique, 2008, 9: 262-275.

  5. High power and spectral purity continuous-wave photonic THz source tunable from 1 to 4.5 THz for nonlinear molecular spectroscopy

    NASA Astrophysics Data System (ADS)

    Kiessling, J.; Breunig, I.; Schunemann, P. G.; Buse, K.; Vodopyanov, K. L.

    2013-10-01

    We report a diffraction-limited photonic terahertz (THz) source with linewidth <10 MHz that can be used for nonlinear THz studies in the continuous wave (CW) regime with uninterrupted tunability in a broad range of THz frequencies. THz output is produced in orientation-patterned (OP) gallium arsenide (GaAs) via intracavity frequency mixing between the two closely spaced resonating signal and idler waves of an optical parametric oscillator (OPO) operating near λ = 2 μm. The doubly resonant type II OPO is based on a periodically poled lithium niobate (PPLN) pumped by a single-frequency Yb:YAG disc laser at 1030 nm. We take advantage of the enhancement of both optical fields inside a high-finesse OPO cavity: with 10 W of 1030 nm pump, 100 W of intracavity power near 2 μm was attained with GaAs inside cavity. This allows dramatic improvement in terms of generated THz power, as compared to the state-of-the art CW methods. We achieved >25 μW of single-frequency tunable CW THz output power scalable to >1 mW with proper choice of pump laser wavelength.

  6. Broadband coherent anti-Stokes Raman scattering spectroscopy in supercontinuum optical trap

    NASA Astrophysics Data System (ADS)

    Shi, Kebin; Li, Peng; Liu, Zhiwen

    2007-04-01

    The authors report on a supercontinuum tweezer which combines tweezing with broadband (˜3000cm-1) coherent anti-Stokes Raman scattering (CARS) spectroscopy by taking advantage of the high spatial coherence and broad bandwidth of pulsed supercontinuum generated in a nonlinear photonic crystal fiber. Polarization-discriminated and time-resolved CARS is investigated to suppress the nonresonant four-wave-mixing background.

  7. Conformational Analysis of Ibuprofen Using Broadband Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zinn, Sabrina; Betz, Thomas; Schnell, Melanie

    2014-06-01

    The broadband rotational spectrum of ibuprofen ((RS)-2-(4-isobutylphenyl)-propanoic acid), a well-known drug, will be presented. As it is used to relieve pain, reduce fever, and inhibit inflammation, the knowledge of its biological activity is very interesting. Insights to the conformational flexibility of this drug might lead to a better understanding of the class of non-steroidal anti-inflammatory drugs that ibuprofen belongs to. The spectrum was recorded with our broadband chirped-pulse Fourier transform microwave spectrometer in the frequency range of 2.0 - 8.3 GHz. With the obtained results, we are able to identify several conformers of ibuprofen and to determine their rotational constants. Density functional theory calculations were performed and used to support the conformational assignments. Fragments of ibuprofen could be also identified in the spectrum, which can be explained by thermal decomposition during the heating process for vaporizing it. The analysis of this fragmentation process as a function of temperature might provide us with some interesting insights into its mechanism.

  8. Ultra-broadband plasmonic super absorbers for universal surface enhanced Raman spectroscopy substrate (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Zhang, Nan; Liu, Kai; Song, Haomin; Zeng, Xie; Ji, Dengxin; Gan, Qiaoqiang

    2015-08-01

    Although Raman spectroscopy has been commercialized, low-cost and large-area surface enhanced Raman spectroscopy (SERS) substrates with localized enhanced field are heavily required. However, currently dominant manufacturing techniques are expensive and complicated for large-area fabrication. Furthermore, most SERS substrates can only be used for individual excitation wavelengths. In this work, we will report an ultra-broadband super absorbing metasurface to enhance SERS signals in a broadband region (i.e. from 450 nm to 1000 nm). The design consisting of an Ag ground plate, a SiO2 spacer, and a layer of Ag nanoparticles was fabricated using simple film deposition and thermal annealing techniques. A broadband absorption over 80% from 414 nm to 956 nm was obtained, resulting in localized field enhancement between adjacent nanoparticles. We employed this metasurface to test its broadband SERS signal by adsorbing 1,2-Bis(4-pyridyl)-ethylene (BPE) molecules on top of it. We employed 5 laser lines (i.e., 514, 532, 633, 671 and 785 nm) to excite the sample and observed fingerprint signature of BPE molecules under all 5 excitation wavelengths with the average enhancement factor up to 5.3×107. Therefore, the designed SERS substrate can work for almost "all" available excitation wavelengths over a broadband, which is particularly useful for sensing a broad spectrum of chemicals on the same chip.

  9. Broadband mid-IR subharmonic OPOs for molecular spectroscopy

    NASA Astrophysics Data System (ADS)

    Leindecker, Nick; Marandi, Alireza; Vodopyanov, Konstantin L.; Byer, Robert L.

    2012-02-01

    We generate broadband mid-infrared frequency combs via degenerate optical parametric oscillation in a subharmonic OPO. This technique efficiently transfers the desirable properties of shorter wavelength mode-locked sources to the mid- IR. Our OPO resonator is a 3m or 4m ring cavity composed of one pair of concave mirrors with R=50mm and four flat mirrors, all but one of which are gold coated with > 99% reflection. A single dielectric mirror is used to introduce the pump (2.05 micron from IMRA America, 75 MHz, 80 fs, 600mW or 1.55 micron from Menlo Systems C-fiber, 100 MHz, 70 fs, 350 mW or 1.56 micron from Toptica Photonics FemtoFiber Pro, 80 MHz, 85 fs, 380 mW). The dielectric mirror is transmissive for the pump and reflective in a 2.5- 4 micron or 3- 6 micron (for 2 micron pump) range. Broadband parametric gain around the 3.1-micron subharmonic is provided by short (0.2-0.5mm) periodically poled lithium niobate (MgO:PPLN) at Brewster angle. Crystals were cut from Crystal Technology Inc. material having QPM period of 34.8 microns for type 0 (e=e+e) phase matching at t=32 deg. C. With the 2-micron pump, orientation patterned gallium arsenide from BAE systems is used as the non-linear material In both systems, the enormous acceptance bandwidth at degeneracy, typical for OPOs with type 0 (or type I) phase-matching, gives broad bandwidth and makes temperature tuning insignificant. Broadband oscillation is achieved when signal/idler are brought into degenerate resonance by fine-tuning the cavity length with a mirror on a piezo stage. Using an 8% reflective pellicle, we outcouple a frequency comb of more than 1000nm bandwidth, centered around 3.1 microns from the Er/PPLN system. A 1mm or 2.5mm thick ZnSe plate at Brewster angle provides 2nd-order group velocity dispersion compensation, improving the OPO bandwidth. The OPO threshold was measured to be < 30mW. When locked, the OPO outputs 60 mW of average power centered at 3.1 microns. With the Tm/OP-GaAs system we

  10. THz transmission spectroscopy and imaging: application to the energetic materials PBX 9501 and PBX 9502.

    PubMed

    Funk, David J; Calgaro, F; Averitt, R D; Asaki, M L T; Taylor, A J

    2004-04-01

    We report the measurement of the effective complex index of refraction near 1 THz for the Plastic-Bonded eXplosives PBX 9501 and PBX 9502. These plastic-bonded explosives consist of organic crystalline energetic materials, HMX and TATB, embedded in a binder matrix. We find that they are partially transparent at a few hundred GHz and we have applied a two-dimensional imaging technique for the detection of pre-fabricated defects in small samples.

  11. Non Destructive Thermal Analysis and In Situ Investigation of Creep Mechanism of Graphite and Ceramic Composites using Phase-sensitive THz Imaging & Nonlinear Resonant Ultrasonic Spectroscopy

    SciTech Connect

    Zhang, XI-Cheng; Hurley, David; Redo-Scanchez, Albert

    2012-11-26

    In this project, we conducted a comprehensive study on nuclear graphite properties with terahertz (THz) imaging. Graphite samples from Idaho National Laboratory were carefully imaged by continuous wave (CW) THz. The CW THz imaging of graphite shows that the samples from different billet with different fabricating conditions have different pore size and structure. Based on this result, we then used a phase sensitive THz system to study the graphite properties. In this exploration, various graphite were studied. By imaging nuclear graphite samples in reflection mode at nine different incident polarization angles using THz time-domain spectroscopy, we find that different domain distributions and levels of porosity will introduce polarization dependence in THz reflectivity. Sample with higher density is less porous and has a smaller average domain distribution. As a consequence, it is less polarization-dependent and the polarization-dependent frequency is higher. The results also show that samples oxidized at higher temperatures tend to be more polarization dependent. The graphite from the external billet is more polarization dependent compared to that from the center billet. In addition, we performed laser-based ultrasonic measurements on these graphite samples. The denser, unoxidized samples allow surface acoustic waves to propagate more rapidly than in the samples that had already undergone oxidation. Therefore, for the oxidized samples, the denser samples show less polarization-dependence, higher polarization-dependent frequency, and allow the surface acoustic waves propagate faster.

  12. Broadband sample holder for microwave spectroscopy of superconducting qubits

    SciTech Connect

    Averkin, A. S.; Karpov, A.; Glushkov, E.; Abramov, N.; Shulga, K.; Huebner, U.; Il'ichev, E.; Ustinov, A. V.

    2014-10-15

    We present a practical design and implementation of a broadband sample holder suitable for microwave experiments with superconducting integrated circuits at millikelvin temperatures. Proposed design can be easily integrated in standard dilution cryostats, has flat pass band response in a frequency range from 0 to 32 GHz, allowing the RF testing of the samples with substrate size up to 4 × 4 mm{sup 2}. The parasitic higher modes interference in the holder structure is analyzed and prevented via design considerations. The developed setup can be used for characterization of superconducting parametric amplifiers, bolometers, and qubits. We tested the designed sample holder by characterizing of a superconducting flux qubit at 20 mK temperature.

  13. Broadband sample holder for microwave spectroscopy of superconducting qubits.

    PubMed

    Averkin, A S; Karpov, A; Shulga, K; Glushkov, E; Abramov, N; Huebner, U; Il'ichev, E; Ustinov, A V

    2014-10-01

    We present a practical design and implementation of a broadband sample holder suitable for microwave experiments with superconducting integrated circuits at millikelvin temperatures. Proposed design can be easily integrated in standard dilution cryostats, has flat pass band response in a frequency range from 0 to 32 GHz, allowing the RF testing of the samples with substrate size up to 4 × 4 mm(2). The parasitic higher modes interference in the holder structure is analyzed and prevented via design considerations. The developed setup can be used for characterization of superconducting parametric amplifiers, bolometers, and qubits. We tested the designed sample holder by characterizing of a superconducting flux qubit at 20 mK temperature.

  14. Spectral and spatial nondestructive examination of dielectric materials with THz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Beckmann, J.; von Chrzanowski, L. S.; Fratzscher, D.; Ewert, U.

    2012-05-01

    A time domain spectrometer T-ray 2000® operating in the range of 0.2-2 THz was used for Time of Flight measurements. A series of ethanol water mixtures from 10% to 90% were produced subsequently filled in polystyrene cells and analyzed in the T-ray 2000 TDS system in the reflection mode. The reflectivity of the material liquid interface is strongly influenced by the ethanol concentration in water. The reciprocal reflection coefficient of the material liquid interface was found to be a useful discriminating feature for further Probably of Detection calculations which can be used for the performance evaluation of potential THz bottle scanners. THz pulse echo (PE) measurements were performed in comparison to the established ultra sound PE technique for flaw detection of plastics. Synthetic aperture reconstructions were applied for simulated data to reconstruct the flaw shape. The results were compared with B-scan images of a high density polyethylene (HDPE) test cylinder. Existing restrictions on the quality of the back projected images and limits of the existing model are discussed in detail.

  15. Broadband near-field mid-infrared spectroscopy and application to phonon resonances in quartz.

    PubMed

    Ishikawa, Michio; Katsura, Makoto; Nakashima, Satoru; Ikemoto, Yuka; Okamura, Hidekazu

    2012-05-07

    Infrared (IR) spectroscopy is a versatile analytical method and nano-scale spatial resolution could be achieved by scattering type near-field optical microscopy (s-SNOM). The spectral bandwidth was, however, limited to approximately 300 cm(-1) with a laser light source. In the present study, the development of a broadband mid-IR near-field spectroscopy with a ceramic light source is demonstrated. A much wider bandwidth (at least 3000 to 1000 cm(-1)) is achieved with a ceramic light source. The experimental data on quartz Si-O phonon resonance bands are well reproduced by theoretical simulations indicating the validity of the present broadband near-field IR spectroscopy.

  16. CH3D photomixing spectroscopy up to 2.5 THz: New set of rotational and dipole parameters, first THz self-broadening measurements

    NASA Astrophysics Data System (ADS)

    Bray, Cédric; Cuisset, Arnaud; Hindle, Francis; Bocquet, Robin; Mouret, Gaël; Drouin, Brian J.

    2017-03-01

    Several previously unmeasured transitions of 12CH3D have been recorded by a terahertz photomixing continuous-wave spectrometer up to QR(10) branch at 2.5 THz. An improved set of rotational constants has been obtained utilizing a THz frequency metrology based on a frequency comb that achieved an averaged frequency position better than 150 kHz on more than fifty ground-state transitions. A detailed analysis of the measured line intensities was undertaken using the multispectrum fitting program and has resulted in a determination of new dipole moment parameters. Measurements at different pressures of the QR(7) transitions provide the first determination of self-broadening coefficients from pure rotational CH3D lines. The THz rotational measurements are consistent with IR rovibrational data but no significant vibrational dependence of self-broadening coefficient may be observed by comparison.

  17. An All-Solid-State, Room-Temperature, Heterodyne Receiver for Atmospheric Spectroscopy at 1.2 THz

    NASA Technical Reports Server (NTRS)

    Siles, Jose V.; Mehdi, Imran; Schlecht, Erich T.; Gulkis, Samuel; Chattopadhyay, Goutam; Lin, Robert H.; Lee, Choonsup; Gill, John J.; Thomas, Bertrand; Maestrini, Alain E.

    2013-01-01

    been specifically optimized to maximize the mixer performance beyond 1 THz. The measured DSB noise temperatures and conversion losses of the receiver are 2,000 to 3,500 K and 12 to 14 dB, respectively, at 120 K, and 4,000 to 6,000 K and 13 to 15 dB, respectively, at 300 K. These results establish the state-of-the-art for all-solid-state, all-planar heterodyne receivers at 1.2 THz operating at either room temperature or using passive cooling only. Since no cryogenic cooling is needed, the receiver is eminently suited to atmospheric heterodyne spectroscopy of the outer planets and their moons.

  18. Broadband "Infinite-Speed" Magic-Angle Spinning NMR Spectroscopy

    SciTech Connect

    Hu, Yan-Yan; Levin, E.M; Schmidt-Rohr, Klaus

    2009-06-02

    High-resolution magic-angle spinning NMR of high-Z spin- 1/2 nuclei such as {sup 125}Te, {sup 207}Pb, {sup 119}Sn, {sup 113}Cd, and {sup 195}Pt is often hampered by large (>1000 ppm) chemical-shift anisotropies, which result in strong spinning sidebands that can obscure the centerbands of interest. In various tellurides with applications as thermoelectrics and as phase-change materials for data storage, even 22-kHz magic-angle spinning cannot resolve the center- and sidebands broadened by chemical-shift dispersion, which precludes peak identification or quantification. For sideband suppression over the necessary wide spectral range (up to 200 kHz), radio frequency pulse sequences with few, short pulses are required. We have identified Gan's two-dimensional magic-angle-turning (MAT) experiment with five 90{sup o} pulses as a promising broadband technique for obtaining spectra without sidebands. We have adapted it to broad spectra and fast magic-angle spinning by accounting for long pulses (comparable to the dwell time in t{sub 1}) and short rotation periods. Spectral distortions are small and residual sidebands negligible even for spectra with signals covering a range of 1.5 {gamma}B{sub 1}, due to a favorable disposition of the narrow ranges containing the signals of interest in the spectral plane. The method is demonstrated on various technologically interesting tellurides with spectra spanning up to 170 kHz, at 22 kHz MAS.

  19. Characterization of mechanical properties of materials using ultrasound broadband spectroscopy.

    PubMed

    Agrawal, Megha; Prasad, Abhinav; Bellare, Jayesh R; Seshia, Ashwin A

    2016-01-01

    This article explores the characterization of homogenous materials (metals, alloys, glass and polymers) by a simple broadband ultrasonic interrogation method. The novelty lies in the use of ultrasound in a continuous way with very low input power (0 dBm or less) and analysis of the transmitted acoustic wave spectrum for material property characterization like speed of sound, density and dimensions of a material. Measurements were conducted on various thicknesses of samples immersed in liquid where continuous-wave, frequency swept ultrasonic energy was incident normal to the sample surface. The electro-acoustic transmission response is analyzed in the frequency domain with respect to a specifically constructed multi-layered analytical model. From the acoustic signature of the sample materials, material properties such as speed of sound and acoustic impedance can be calculated with experimentally derived values found to be in general agreement with the literature and with pulse-echo technique establishing the basis for a non-contact and non-destructive technique for material characterization. Further, by looking at the frequency spacing of the peaks of water when the sample is immersed, the thickness of the sample can be calculated independently from the acoustic response. This technique can prove to be an effective non-contact, non-destructive and fast material characterization technique for a wide variety of materials. Copyright © 2015 Elsevier B.V. All rights reserved.

  20. THz Spectroscopy with a Holographic Fourier Transform Spectrometer Plus Array Detector Using Coherent Synchrotron Radiation (PREPRINT)

    DTIC Science & Technology

    2010-05-14

    burst of the spatial interferograms. When the maximum possible resolution was desired it was located at the 10th pixel, and when a better phase ...n +1( )4 1+ n −1( )4 n +1( )4 + 2 n −1( )2 n +1( )2 cos 4πσnd +ϕ( )         , (3) where the constant phase angle ϕ has been included to...refractive index and the phase at THz frequencies. This spectrum is represented by the dotted trace in Fig. (6). Clearly the modulation occurs at the

  1. THz spectroscopy based high sensitivity measurement of protein using a metal mesh device

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Ogawa, Y.; Kondo, T.; Kamba, S.; Kondo, N.

    2011-06-01

    A label-free bioaffinity sensor working in terahertz (THz) region with a nitrocellulose membrane filter was demonstrated, which is based on the resonant transmission phenomenon and the dip in the spectra of the metal mesh device. By using this sensor, we succeeded in the highly sensitive detection of small amounts of protein avidin-biotin complex. A distinct change of transmittance caused by shift of the transmission dip was observed for 8 ng/mm2 (74 fmol) of horseradish peroxidase (HRP) labeled avidin. The sensing method has broad utility for many reactions on the membrane filter as a simple and rapid sensor.

  2. Rotational spectroscopy of vibrationally excited N2H+ and N2D+ up to 2.7 THz

    NASA Astrophysics Data System (ADS)

    Yu, S.; Pearson, J. C.; Drouin, B. J.; Crawford, T.; Daly, A. M.; Elliott, B.; Amano, T.

    2015-08-01

    Terahertz absorption spectroscopy was employed to extend the measurements on the pure rotational transitions of N2H+, N2D+ and their 15N-containing isotopologues in the ground state and first excited vibrational states for the three fundamental vibrational modes. In total, 91 new pure rotational transitions were observed in the range of 0.7-2.7 THz. The observed transition frequencies were fit to experimental accuracy, and the improved molecular parameters were obtained. The new measurements and predictions reported here will support the analysis of high-resolution astronomical observations made with facilities such as SOFIA and ALMA where laboratory rest frequencies with uncertainties of 1 MHz or smaller are required for proper analysis of velocity resolved astrophysical components.

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

    SciTech Connect

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

    2015-08-31

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

  4. Using Thz Spectroscopy to Probe Intramolecular Electron Transfer and Solvent Dynamics

    NASA Astrophysics Data System (ADS)

    Schmuttenmaer, Charles

    2002-03-01

    We have measured the electromagnetic radiation emitted during intramolecular electron transfer using a method does not rely on secondary processes.^1 The motion of the electrons themselves generates the measured signal (as understood by Maxwell's equations). If the electron transfer occurs on a timescale of 0.1 to 10 picoseconds, the emitted radiation will fall in the THz or far-infrared region of the spectrum (1 THz = 33.33 wavenumbers). We photoexcite a sample of partially oriented molecules and measure the emitted waveform. The polarity of the emitted field determines the direction of charge transfer unambiguously, and the shape of the field encodes the dynamics of the charge transfer -- a slower transfer rate produces a broader temporal pulse. Solvent repolarization dynamics also contribute to the measured response, and will be discussed. Future work will extend this method to systems that are difficult to study by traditional means. 1. M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, J. Phys. Chem. A, In Press (2001).

  5. Broadband pump-probe imaging spectroscopy applicable to ultrafast single-shot events

    NASA Astrophysics Data System (ADS)

    Minami, Yasuo; Yamaki, Hiromoto; Katayama, Ikufumi; Takeda, Jun

    2014-02-01

    We propose a scheme for frequency-resolved single-shot spectroscopy with an echelon mirror. The echelon mirror is employed to generate spatially encoded time delays for the white-light continuum probe beam; it produces a temporal step of 66 fs and an overall time delay of 33 ps. We demonstrate broadband pump-probe imaging spectroscopy and present time-frequency two-dimensional images of the transient absorption of β-carotene between 420 and 630 nm with single-shot detection. The results show that this technique is a powerful tool for observing the ultrafast, broadband transient dynamics of materials that exhibit irreversible reactions or deterioration by laser pulse irradiation.

  6. Broadband light scattering spectroscopy utilizing an ultra-narrowband holographic notch filter

    NASA Astrophysics Data System (ADS)

    Fujii, Yasuhiro; Katayama, Daisuke; Koreeda, Akitoshi

    2016-10-01

    The broadband spectroscopic analysis over Brillouin, quasi-elastic, and Raman regions arising from the same position of the sample has been achieved by employing an ultra-narrowband holographic notch filter (HNF) and an optical isolator. Recently, HNFs are often employed to reject strong elastic scattering in low-frequency Raman experiments. Meanwhile, the rejected spectral component agrees with the frequency range that can be observed by a triple-pass tandem Fabry-Pérot interferometer. Thus the broadband spectroscopy can be accomplished by introducing the rejected light to the interferometer. This system, in combination with the local symmetry analysis by polarization-direction-resolved Raman spectroscopy, is particularly advantageous for the investigation of spatially inhomogeneous systems.

  7. Perspective: The first ten years of broadband chirped pulse Fourier transform microwave spectroscopy.

    PubMed

    Park, G Barratt; Field, Robert W

    2016-05-28

    Since its invention in 2006, the broadband chirped pulse Fourier transform spectrometer has transformed the field of microwave spectroscopy. The technique enables the collection of a ≥10 GHz bandwidth spectrum in a single shot of the spectrometer, which allows broadband, high-resolution microwave spectra to be acquired several orders of magnitude faster than what was previously possible. We discuss the advantages and challenges associated with the technique and look back on the first ten years of chirped pulse Fourier transform spectroscopy. In addition to enabling faster-than-ever structure determination of increasingly complex species, the technique has given rise to an assortment of entirely new classes of experiments, ranging from chiral sensing by three-wave mixing to microwave detection of multichannel reaction kinetics. However, this is only the beginning. Future generations of microwave experiments will make increasingly creative use of frequency-agile pulse sequences for the coherent manipulation and interrogation of molecular dynamics.

  8. Background-free broadband CARS spectroscopy from a 1-MHz ytterbium laser.

    PubMed

    Kumar, Vikas; Osellame, R; Ramponi, R; Cerullo, G; Marangoni, M

    2011-08-01

    We introduce a novel configuration for broadband, time-resolved CARS spectroscopy/microscopy in which pump, Stokes and probe pulses are all derived from a single femtosecond Yb:KYW laser. The 1-MHz repetition rate of the system allows very intense CARS signals to be obtained over short acquisition times, while a delayed probe pulse ensures an efficient non-resonant background suppression.

  9. Broadband terahertz ultrasonic transducer based on a laser-driven piezoelectric semiconductor superlattice.

    PubMed

    Maznev, A A; Manke, Kara J; Lin, Kung-Hsuan; Nelson, Keith A; Sun, Chi-Kuang; Chyi, Jen-Inn

    2012-01-01

    Spectral characteristics of laser-generated acoustic waves in an InGaN/GaN superlattice structure are studied at room temperature. Acoustic vibrations in the structure are excited with a femtosecond laser pulse and detected via transmission of a delayed probe pulse. Seven acoustic modes of the superlattice are detected, with frequencies spanning a range from 0.36 to 2.5THz. Acoustic waves up to ∼2THz in frequency are not significantly attenuated within the transducer which indicates excellent interface quality of the superlattice. The findings hold promise for broadband THz acoustic spectroscopy.

  10. Broadband Terahertz Ultrasonic Transducer Bbased on a Laser-driven Piezoelectric Semiconductor Superlattice

    SciTech Connect

    Maznev, A A; Manke, K; Lin, K.-H.; Nelson, Keith A; Sun, C.-K.; Chyi, J.-I.

    2011-01-01

    Spectral characteristics of laser-generated acoustic waves in an InGaN/GaN superlattice structure are studied at room temperature. Acoustic vibrations in the structure are excited with a femtosecond laser pulse and detected via transmission of a delayed probe pulse. Seven acoustic modes of the superlattice are detected, with frequencies spanning a range from 0.36 to 2.5 THz. Acoustic waves up to ~2 THz in frequency are not significantly attenuated within the transducer which indicates excellent interface quality of the superlattice. The findings hold promise for broadband THz acoustic spectroscopy.

  11. Ultrafast relaxation dynamics of nitric oxide synthase studied by visible broadband transient absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Hung, Chih-Chang; Yabushita, Atsushi; Kobayashi, Takayoshi; Chen, Pei-Feng; Liang, Keng S.

    2017-09-01

    Ultrafast dynamics of endothelial nitric oxide synthase (eNOS) oxygenase domain was studied by transient absorption spectroscopy pumping at Soret band. The broadband visible probe spectrum has visualized the relaxation dynamics from the Soret band to Q-band and charge transfer (CT) band. Supported by two-dimensional correlation spectroscopy, global fitting analysis has successfully concluded the relaxation dynamics from the Soret band to be (1) electronic transition to Q-band (0.16 ps), (2) ligand dissociation and CT (0.94 ps), (3) relaxation of the CT state (4.0 ps), and (4) ligand rebinding (59 ps).

  12. Probing the effect of dopants (donors) within InAs/InGaAs/InAlAs Asymmetric Heterostructure wafer by magneto-THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Pakmehr, Mehdi; Heyn, Christian; Hansen, Wolfgang

    Probing the effect of impurities within semiconductor structures have been the topic of interest both from applied and scientific point of views. We studied the effect of dopants (donors) within InAs/InGaAs/InAlAs asymmetric heterostructure wafer by means of THz magneto-transmission (TR) spectroscopy, in conjunction with THz magneto-photoresponse (PR) spectroscopy. The sample wafer has been immersed in pumped liquid Helium at 1.6 K, while being exposed to sweeping magnetic field up to 10 Tesla, with THz laser beam (1.4 THz) being focused on sample by off-axis parabolic mirror. The transmitted beam was detected by silicon composite bolometer. Two broad absorption features other than sharp Cyclotron resonance (CR) absorption dip within magneto-TR signal attributed to 1s -->2P transition within donors of doped layer (InAlAs) in heterostructure. We plan to discuss the analysis of magneto-TR signal, in conjunction with Magneto-PR signals from Hall bar samples made from same type of wafer at same frequency to clarify how dopants could possibly alter these signals.

  13. Metamaterial-based gradient index lens with strong focusing in the THz frequency range.

    PubMed

    Neu, J; Krolla, B; Paul, O; Reinhard, B; Beigang, R; Rahm, M

    2010-12-20

    The development of innovative terahertz (THz) imaging systems has recently moved in the focus of scientific efforts due to the ability to screen substances through textiles or plastics. The invention of THz imaging systems with high spatial resolution is of increasing interest for applications in the realms of quality control, spectroscopy in dusty environment and security inspections. To realize compact THz imaging systems with high spatial resolution it is necessary to develop lenses of minimized thickness that still allow one to focus THz radiation to small spot diameters with low optical aberrations. In addition, it would be desirable if the lenses offered adaptive control of their optical properties to optimize the performance of the imaging systems in the context of different applications. Here we present the design, fabrication and the measurement of the optical properties of spectrally broadband metamaterial-based gradient index (GRIN) lenses that allow one to focus THz radiation to a spot diameter of approximately one wavelength. Due to the subwavelength thickness and the high focusing strength the presented GRIN lenses are an important step towards compact THz imaging systems with high spatial resolution. Furthermore, the results open the path to a new class of adaptive THz optics by extension of the concept to tunable metamaterials.

  14. Broadband femtosecond transient absorption spectroscopy for a CVD Mo S2 monolayer

    NASA Astrophysics Data System (ADS)

    Aleithan, Shrouq H.; Livshits, Maksim Y.; Khadka, Sudiksha; Rack, Jeffrey J.; Kordesch, Martin E.; Stinaff, Eric

    2016-07-01

    Carrier dynamics in monolayer Mo S2 have been investigated using broadband femtosecond transient absorption spectroscopy (FTAS). A tunable pump pulse was used while a broadband probe pulse revealed ground and excited state carrier dynamics. Interestingly, for pump wavelengths both resonant and nonresonant with the A and B excitons, we observe a broad ground state bleach around 2.9 eV, with decay components similar to A and B. Associating this bleach with the band nesting region between K and Γ in the band structure indicates significant k-space delocalization and overlap among excitonic wave functions identified as A, B, C, and D. Comparison of time dynamics for all features in resonance and nonresonance excitation is consistent with this finding.

  15. Characterisation of high current density resonant tunneling diodes for THz emission using photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Jacobs, Kristof J. P.; Baba, Razvan; Stevens, Benjamin J.; Mukai, Toshikazu; Ohnishi, Dai; Hogg, Richard A.

    2016-03-01

    Resonant tunneling diodes (RTDs) provide high speed current oscillation which is applicable to THz generation when coupled to a suitably designed antenna. For this purpose, the InGaAs/AlAs/InP materials have been used, as this system offers high electron mobility, suitable band-offsets, and low resistance contacts. However for high current density operation (~MA/cm2) the epitaxial structure is challenging to characterize using conventional techniques as it consists of a single, very thin AlAs/InGaAs quantum well (QW). Here, we present a detailed low temperature photoluminescence spectroscopic study of high current density RTDs that allow the non-destructive mapping of a range of critical parameters for the device. We show how the doping level of the emitter/collector and contact layers in the RTD structure can be measured using the Moss-Burstein effect. For the full device structure, we show how emission from the QW may be identified, and detail how the emission changes with differing indium composition and well widths. We show that by studying nominally identical, un-doped structures, a type-II QW emission is observed, and explain the origin of the type-I emission in doped devices. This observation opens the way for a new characterization scheme where a "dummy" RTD active element is incorporated below the real RTD structure. This structure allows significantly greater control in the epitaxial process.

  16. a New Broadband Cavity Enhanced Frequency Comb Spectroscopy Technique Using GHz Vernier Filtering.

    NASA Astrophysics Data System (ADS)

    Morville, Jérôme; Rutkowski, Lucile; Dobrev, Georgi; Crozet, Patrick

    2015-06-01

    We present a new approach to Cavity Enhanced - Direct Frequency Comb Spectroscopy where the full emission bandwidth of a Titanium:Sapphire laser is exploited at GHz resolution. The technique is based on a low-resolution Vernier filtering obtained with an appreciable -actively stabilized- mismatch between the cavity Free Spectral Range and the laser repetition rate, using a diffraction grating and a split-photodiode. This particular approach provides an immunity to frequency-amplitude noise conversion, reaching an absorption baseline noise in the 10-9 cm-1 range with a cavity finesse of only 3000. Spectra covering 1800 cm-1 (˜ 55 THz) are acquired in recording times of about 1 second, providing an absorption figure of merit of a few 10-11 cm-1/√{Hz}. Initially tested with ambient air, we report progress in using the Vernier frequency comb method with a discharge source of small radicals. Rutkowski et al, Opt. Lett., 39(23)2014

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-06-02

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

  19. THz time domain sensing and imaging

    NASA Astrophysics Data System (ADS)

    Cheville, R. A.; Reiten, Matthew T.; O'Hara, John; Grischkowsky, Daniel R.

    2004-09-01

    Over the past decade the experimental technique of THz time domain spectroscopy (THz-TDS) has proved to be a versatile method for investigating a wide range of phenomena in the THz or far infrared spectral region from 100 GHz to 5 THz. THz-TDS has wide potential for sensing and imaging. The experimental technique is described along with recent results on THz beam propagation for long base-line THz measurements. THz imaging has been demonstrated using both quasi-optical and synthetic aperture approaches, results are presented including images of scatterers as well as non-destructive evaluation of ceramics. Two potential sensing applications of THz-TDS are discussed, thin film characterization and use of waveguides for sensing.

  20. Ultra-broadband terahertz spectroscopy of InP wafer using coherent heterodyne time domain spectrometer

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoyan; Zhang, Liangliang; Zhang, Cunlin

    2015-08-01

    Indium Phosphide (InP) has attracted great physical interest because of its unique characteristics and is indispensable to both optical and electronic devices. In this paper, we study the optical properties of undoped (100) InP wafer in the ultra-broad terahertz frequency range (0.5-18 THz) by using air-biased-coherent-detection (ABCD) system. It is observed that InP wafer is opaque at the frequencies spanning from 6.7 THz to 12.1 THz. In the frequency regions of 0.8-6.7 THz and 12.1-18 THz it has relatively low absorption coefficient. Meanwhile, the refractive index increases monotonously in the 0.8-6.7 THz region and 12.1-18 THz region. These findings will contribute to the design of InP based component for nonlinear terahertz devices.

  1. THz Spectroscopy of Excited Torsional States of Monodeuterated Methyl Formate (DCOOCH_3)

    NASA Astrophysics Data System (ADS)

    Carvajal, Miguel; Duan, Chuanxi; Yu, Shanshan; Pearson, John; Drouin, Brian; Kleiner, Isabelle

    2016-06-01

    Recently, a measurement of the rotational spectrum of DCOOCH_3 has been carried out in the frequency range from 0.85 to 1.5 THz at Jet Propulsion Laboratory (JPL) (Duan et al. 2015). These JPL data and the available spectroscopic millimeter- and submillimeter-wave data (Margulès et al. 2010 and references therein) of the ground state were analyzed using the Rho Axis Method (RAM) (Kleiner 2010). At present, a new analysis of JPL lines of DCOOCH_3 in the first excited vt=1 torsional states is undertaken. This analysis may help the future identification of vt=1 lines in the interstellar and circumstellar media as was carried out for the vt=0 lines in Orion KL (Margulès et al. 2010). In this communication, the progress of this study is presented as well as a short outline of the spectral analyses accomplished for other methyl formate isotopologues. C. Duan, M. Carvajal, S. Yu, J.C. Pearson, B.J. Drouin, I. Kleiner 2015, A&A, 576, A39 I. Kleiner 2010, J. Mol. Spectroc., 260, 1 L. Margulès, T.R. Huet, J. Demaison, M. Carvajal, I. Kleiner, H. Møllendal, B. Tercero, N. Marcelino, J. Cernicharo 2010, ApJ, 714, 1120 This research is supported by the FIS2014-53448-C2-2-P project (MINECO, Spain), the French PCMI (Programme National de Physique Chimie du Milieu Interstellaire), and the National Natural Science Foundation of China (Grant No. 11174098). Portions of this work is carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Government sponsorship is acknowledged.

  2. The separation of overlapping transitions in β-carotene with broadband 2D electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Calhoun, Tessa R.; Davis, Jeffrey A.; Graham, Matthew W.; Fleming, Graham R.

    2012-01-01

    Broadband 2D electronic spectroscopy is applied to β-carotene, revealing new insight into the excited state dynamics of carotenoids by exploring the full energetic range encompassing the S0→S2 and S1→S1n transitions at 77 K. Multiple signals are observed in the regime associated with the proposed S∗ state and isolated through separate analysis of rephasing and nonrephasing contributions. Peaks in rephasing pathways display dynamic lineshapes characteristic of coupling to high energy vibrational modes, and simulation with a simple model supports their assignment to impulsive stimulated Raman scattering. A signal persisting beyond 10 ps in the nonrephasing spectra is still under investigation.

  3. Broadband cavity enhanced spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde

    NASA Astrophysics Data System (ADS)

    Washenfelder, R. A.; Attwood, A. R.; Flores, J. M.; Rudich, Y.; Brown, S. S.

    2015-09-01

    Formaldehyde (CH2O) is the most abundant aldehyde in the atmosphere, and strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH2O and nitrogen dioxide (NO2) using broadband cavity enhanced spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99933 ± 0.00003 (670 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.49 km within the 1 m cell. We measure the cavity output over the 315-350 nm spectral region using a grating monochromator and charge-coupled device (CCD) array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH2O and NO2 concentrations. Independent measurements of NO2 standard additions by broadband cavity enhanced spectroscopy and cavity ringdown spectroscopy agree within 2 % (slope for linear fit = 0.98 ± 0.03 with r2 = 0.998). Standard additions of CH2O measured by broadband cavity enhanced spectroscopy and calculated based on flow dilution are also well-correlated, with r2 = 0.9998. During constant, mixed additions of NO2 and CH2O, the 30 s measurement precisions (1σ) of the current configuration were 140 and 210 pptv, respectively. The current 1-min detection limit for extinction measurements at 315-350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and ground-based field experiments. Additionally, the instrument provides highly accurate, spectroscopically-based trace gas detection that may complement higher precision techniques based on non-absolute detection methods. In addition to trace gases, this approach will be appropriate for

  4. Femtosecond broadband fluorescence spectroscopy by down- and up-conversion in β-barium borate crystals

    NASA Astrophysics Data System (ADS)

    Sajadi, M.; Quick, M.; Ernsting, N. P.

    2013-10-01

    Broadband transient fluorescence spectroscopy is performed by difference- and sum-frequency generation in β-barium borate crystals at a fixed geometry. Phase matching is spectrally broadened by using (i) 1340 nm gate pulses, (ii) a fluorescence angle of ˜4° extended at the crystal, and (iii) angular dispersion of the fluorescence in a calcite prism. The latter provides 1° angular separation between the two spectral wings of the fluorescence. By combining down- and up-conversion processes, a 26 000 cm-1 wide multiplex window is realized with ˜100 fs time resolution.

  5. Broadband infrared spectroscopy using optical parametric oscillation in a radially-poled whispering gallery resonator.

    PubMed

    Meisenheimer, Sarah-Katharina; Fürst, Josef Urban; Werner, Christoph; Beckmann, Tobias; Buse, Karsten; Breunig, Ingo

    2015-09-07

    We demonstrate optical parametric oscillation in a millimeter-sized whispering gallery resonator suitable for broadband infrared spectroscopy. This nonlinear-optical process is quasi-phase-matched using a radial domain pattern with 30 µm period length, inscribed by calligraphic poling. The output wavelengths are selected in a controlled way over hundreds of nanometers. We achieve this by increasing the temperature of the resonator in steps such that the azimuthal mode number of the pump wave rises by one. As a proof-of-principle experiment, we measure a characteristic resonance of polystyrene in the spectral range of 2.25 - 2.45 µm.

  6. Broadband 2D electronic spectroscopy reveals a carotenoid dark state in purple bacteria.

    PubMed

    Ostroumov, Evgeny E; Mulvaney, Rachel M; Cogdell, Richard J; Scholes, Gregory D

    2013-04-05

    Although the energy transfer processes in natural light-harvesting systems have been intensively studied for the past 60 years, certain details of the underlying mechanisms remain controversial. We performed broadband two-dimensional (2D) electronic spectroscopy measurements on light-harvesting proteins from purple bacteria and isolated carotenoids in order to characterize in more detail the excited-state manifold of carotenoids, which channel energy to bacteriochlorophyll molecules. The data revealed a well-resolved signal consistent with a previously postulated carotenoid dark state, the presence of which was confirmed by global kinetic analysis. The results point to this state's role in mediating energy flow from carotenoid to bacteriochlorophyll.

  7. Accurate optical parameter extraction procedure for broadband near-infrared spectroscopy of brain matter

    PubMed Central

    Najafizadeh, Laleh; Gandjbakhche, Amir H.; Pourrezaei, Kambiz; Daryoush, Afshin

    2013-01-01

    Abstract. Modeling behavior of broadband (30 to 1000 MHz) frequency modulated near-infrared (NIR) photons through a phantom is the basis for accurate extraction of optical absorption and scattering parameters of biological turbid media. Photon dynamics in a phantom are predicted using both analytical and numerical simulation and are related to the measured insertion loss (IL) and insertion phase (IP) for a given geometry based on phantom optical parameters. Accuracy of the extracted optical parameters using finite element method (FEM) simulation is compared to baseline analytical calculations from the diffusion equation (DE) for homogenous brain phantoms. NIR spectroscopy is performed using custom-designed, broadband, free-space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 780, and 820 nm. Differential detection between two optical Rx locations separated by 0.3 cm is employed to eliminate systemic artifacts associated with interfaces of the optical Tx and Rx with the phantoms. Optical parameter extraction is achieved for four solid phantom samples using the least-square-error method in MATLAB (for DE) and COMSOL (for FEM) simulation by fitting data to measured results over broadband and narrowband frequency modulation. Confidence in numerical modeling of the photonic behavior using FEM has been established here by comparing the transmission mode’s experimental results with the predictions made by DE and FEM for known commercial solid brain phantoms. PMID:23322361

  8. Wavelength dependent resonance Raman band intensity of broadband stimulated Raman spectroscopy of malachite green in ethanol

    NASA Astrophysics Data System (ADS)

    Cen, Qiongyan; He, Yuhan; Xu, Mei; Wang, Jingjing; Wang, Zhaohui

    2015-03-01

    Resonance broadband stimulated Raman spectroscopy of malachite green in ethanol has been performed. With a tuning picosecond visible laser source and a broadband Raman probe, the Raman gain and loss spectra have been measured simultaneously. By scanning the Raman pump across the first absorption band of the molecule, we found that the resonant Raman bands could be only seen when the pump laser tuned in the range of the red edge of the S1←S0 transition. Dispersive lineshapes of resonant Raman bands have been observed in the Raman loss spectra, while the line shape is normal (same as spontaneous Raman) in the Raman gain spectra. Although, the resonant bands in the loss spectrum are usually stronger than that in the gain spectrum, the band intensities of both loss and gain linearly increase with the pump energy. The relative magnitude of each corresponding resonant band in the Raman loss and gain varies with the pump wavelength. Mode specified Raman excitation profiles have been obtained through broadband stimulated Raman measurement.

  9. Submillimeter/THz Rotational Spectroscopy of SH+ (X3Σ-): The Complete N = 1 ← 0 Transition

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The N = 1 ← 0 transition of SH+ X3Σ-) in its complete fine structure multiplet (J = 0 ← 1, 2 ← 1, and 1 ← 1) has been measured using submillimeter/THz direct absorption spectroscopy in the frequency range near 346-683 GHz. This work is the first direct laboratory measurement of the J = 0 ← 1 and 1 ← 1 spin components. This molecular ion was created in the gas phase from a mixture of H2S and argon in an AC discharge. Hyperfine components, arising from the nuclear spin of H (I = 1/2), were resolved in every fine structure multiplet. The data have been analyzed using a Hund's case {b}β J Hamiltonian, resulting in further improvement in the accuracy of the rotational, spin-rotation, spin-spin, and magnetic hyperfine constants for SH+. From these new data, frequency predictions have been made for the N = 2 \\to 1 and 3 \\to 2 transitions, with an estimated uncertainty of less than 1 MHz. These data also confirm the recent detection of the two hyperfine components of the N = 1 \\to 0, J = 0 \\to 1 transition of SH+ in the Orion Bar, as well as the J = 1 \\to 1 component of this molecular ion near 683 GHz toward Sgr B2.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  11. Study of Application of Thz Time Domainspectroscopy in Food Safet

    NASA Astrophysics Data System (ADS)

    Lang, Liying; Cai, Na

    In this paper, a new spectroscopy technology named terahertz time-domain spectroscopy (THz-TDS) is introduced, which is used in food safety. We describe a coherent subpicosecond THz spectroscopy system based on nonresonant optical rectification for the generation of THz radiation. As an example, we measured absorption spectrum of water vapor by THz-TDS in frequency from 0.5 to 2.5 THz, The experiment demonstrated that the spectroscopy resolution of system was up to 0.0001THz, which can be measured vegetable pesticide residual, for it neither need sample pretreatment nor cause pollution.

  12. Actively coupled cavity ringdown spectroscopy with low-power broadband sources.

    PubMed

    Petermann, Christian; Fischer, Peer

    2011-05-23

    We demonstrate a coupling scheme for cavity enhanced absorption spectroscopy that makes use of an intracavity acousto-optical modulator to actively switch light into (and out of) a resonator. This allows cavity ringdown spectroscopy (CRDS) to be implemented with broadband nonlaser light sources with spectral power densities of less than 30μW/nm. Although the acousto-optical element reduces the ultimate detection limit by introducing additional losses, it permits absorptivities to be measured with a high dynamic range, especially in lossy environments. Absorption measurements for the forbidden transition of gaseous oxygen in air at ∼760nm are presented using a low-coherence cw-superluminescent diode. The same setup was electronically configured to cover absorption losses from 1.8×10-8cm-1 to 7.5% per roundtrip. This could be of interest in process analytical applications.

  13. Solvation and Deprotonation Dynamics in Reverse Micelles via Broadband Femtoseond Transient Absorption (BFTA) Spectroscopy

    NASA Astrophysics Data System (ADS)

    Cole, Richard

    2009-10-01

    Broadband femtosecond transient absorption (BFTA) spectroscopy is a useful tool in characterizing femtosecond and picosecond physical and chemical dynamics such as solvation, electron transfer, and deprotonation dynamics. This presentation will focus on our most recent results, which utilize BFTA spectroscopy in the ultraviolet-visible (UV-vis) spectral range to probe deprotonation and solvation dynamics in the nanoscopic confinement of reverse micelles. In these studies, pyranine, a `photo-acid', probes both solvation and deprotonation dynamics in reverse micelles formed from cationic (cetyl trimethylammonium bromide, CTAB), anionic (sodium dioctyl sulfosuccinate, AOT), and neutral (polyoxyethylene nonylphenylether, Igepal) surfactants. Dynamic behavior will be discussed in terms of the degree of nanoscopic confinement (micellar size) and the impact of varying interfacial environments.

  14. Segmented chirped-pulse Fourier transform submillimeter spectroscopy for broadband gas analysis.

    PubMed

    Neill, Justin L; Harris, Brent J; Steber, Amanda L; Douglass, Kevin O; Plusquellic, David F; Pate, Brooks H

    2013-08-26

    Chirped-pulse Fourier transform spectroscopy has recently been extended to millimeter wave spectroscopy as a technique for the characterization of room-temperature gas samples. Here we present a variation of this technique that significantly reduces the technical requirements on high-speed digital electronics and the data throughput, with no reduction in the broadband spectral coverage and no increase in the time required to reach a given sensitivity level. This method takes advantage of the frequency agility of arbitrary waveform generators by utilizing a series of low-bandwidth chirped excitation pulses paired in time with a series of offset single frequency local oscillators, which are used to detect the molecular free induction decay signals in a heterodyne receiver. A demonstration of this technique is presented in which a 67 GHz bandwidth spectrum of methanol (spanning from 792 to 859 GHz) is acquired in 58 μs.

  15. Windowing of THz time-domain spectroscopy signals: A study based on lactose

    NASA Astrophysics Data System (ADS)

    Vázquez-Cabo, José; Chamorro-Posada, Pedro; Fraile-Peláez, Francisco Javier; Rubiños-López, Óscar; López-Santos, José María; Martín-Ramos, Pablo

    2016-05-01

    Time-domain spectroscopy has established itself as a reference method for determining material parameters in the terahertz spectral range. This procedure requires the processing of the measured time-domain signals in order to estimate the spectral data. In this work, we present a thorough study of the properties of the signal windowing, a step previous to the parameter extraction algorithm, that permits to improve the accuracy of the results. Lactose has been used as sample material in the study.

  16. Broadband Microwave Spectroscopy as a Tool to Study Intermolecular Interactions in the Diphenyl Ether - Water System

    NASA Astrophysics Data System (ADS)

    Fatima, Mariyam; Perez, Cristobal; Schnell, Melanie

    2017-06-01

    Many biological processes, such as chemical recognition and protein folding, are mainly controlled by the interplay of hydrogen bonds and dispersive forces. This interplay also occurs between organic molecules and solvent water molecules. Broadband rotational spectroscopy studies of weakly bound complexes are able to accurately reveal the structures and internal dynamics of molecular clusters isolated in the gas phase. Amongst them, water clusters with organic molecules are of particular interest. In this work, we investigate the interplay between different types of weak intermolecular interactions and how it controls the preferred interaction sites of aromatic ethers, where dispersive interactions may play a significant role. We present our results on diphenyl ether (C_{12}H_{10}O, 1,1'-Oxydibenzene) complexed with up to three molecules of water. Diphenyl ether is a flexible molecule, and it offers two competing binding sites for water: the ether oxygen and the aromatic π system. In order to determine the structure of the diphenyl ether-water complexes, we targeted transitions in the 2-8 GHz range using broadband rotational spectroscopy. We identify two isomers with one water, one with two water, and one with three water molecules. Further analysis from isotopic substitution measurements provided accurate structural information. The preferred interactions, as well as the observed structural changes induced upon complexation, will be presented and discussed.

  17. Applications of broadband cavity enhanced spectroscopy for measurements of trace gases and aerosols

    NASA Astrophysics Data System (ADS)

    Washenfelder, R. A.; Attwood, A. R.; Brock, C. A.; Brown, S. S.; Dube, W. P.; Flores, J. M.; Langford, A. O.; Min, K. E.; Rudich, Y.; Stutz, J.; Wagner, N.; Young, C.; Zarzana, K. J.

    2015-12-01

    Broadband cavity enhanced spectroscopy (BBCES) uses a broadband light source, optical cavity, and multichannel detector to measure light extinction with high sensitivity. This method differs from cavity ringdown spectroscopy, because it uses an inexpensive, incoherent light source and allows optical extinction to be determined simultaneously across a broad wavelength region.Spectral fitting methods can be used to retrieve multiple absorbers across the observed wavelength region. We have successfully used this method to measure glyoxal (CHOCHO), nitrous acid (HONO), and nitrogen dioxide (NO2) from ground-based and aircraft-based sampling platforms. The detection limit (2-sigma) in 5 s for retrievals of CHOCHO, HONO and NO2 is 32, 250 and 80 parts per trillion (pptv).Alternatively, gas-phase absorbers can be chemically removed to allow the accurate determination of aerosol extinction. In the laboratory, we have used the aerosol extinction measurements to determine scattering and absorption as a function of wavelength. We have deployed a ground-based field instrument to measure aerosol extinction, with a detection limit of approximately 0.2 Mm-1 in 1 min.BBCES methods are most widely used in the near-ultraviolet and visible spectral region. Recently, we have demonstrated measurements at 315-350 nm for formaldehyde (CH2O) and NO2. Extending the technique further into the ultraviolet spectral region will allow important additional measurements of trace gas species and aerosol extinction.

  18. Time-Resolved Broadband Cavity-Enhanced Absorption Spectroscopy behind Shock Waves.

    PubMed

    Matsugi, Akira; Shiina, Hiroumi; Oguchi, Tatsuo; Takahashi, Kazuo

    2016-04-07

    A fast and sensitive broadband absorption technique for measurements of high-temperature chemical kinetics and spectroscopy has been developed by applying broadband cavity-enhanced absorption spectroscopy (BBCEAS) in a shock tube. The developed method has effective absorption path lengths of 60-200 cm, or cavity enhancement factors of 12-40, over a wavelength range of 280-420 nm, and is capable of simultaneously recording absorption time profiles over an ∼32 nm spectral bandpass in a single experiment with temporal and spectral resolutions of 5 μs and 2 nm, respectively. The accuracy of the kinetic and spectroscopic measurements was examined by investigating high-temperature reactions and absorption spectra of formaldehyde behind reflected shock waves using 1,3,5-trioxane as a precursor. The rate constants obtained for the thermal decomposition reactions of 1,3,5-trioxane (to three formaldehyde molecules) and formaldehyde (to HCO + H) agreed well with the literature data. High-temperature absorption cross sections of formaldehyde between 280 and 410 nm have been determined at the post-reflected-shock temperatures of 955, 1265, and 1708 K. The results demonstrate the applicability of the BBCEAS technique to time- and wavelength-resolved sensitive absorption measurements at high temperatures.

  19. Pulsed THz TDS of objects covered by disordered structure

    NASA Astrophysics Data System (ADS)

    Trofimov, V. A.; Zakharova, I. G.; Zagursky, D. Y.; Varentsova, Svetlana A.

    2016-05-01

    Using both computer simulation and physical experiment, we demonstrate principal limitations of standard Time Domain Spectroscopy based on a broadband THz pulse for the detection and identification of substance placed inside the disordered structure. The interaction of a THz pulse with a disordered layered structure was simulated in order to show the influence of the disordered layers on the spectral characteristics of the transmitted and reflected signals. Spectral characteristics of these signals were analyzed in a direct comparison with the incident pulse spectrum. We showed that a disordered structure disturbs the reflected pulse spectrum dramatically. To avoid this, we used the integral correlation criteria in real experiment. Computer simulation results were confirmed by physical experiment. We provided the experiments with paper bag, and ordinary sheets of paper, and napkins.

  20. Broad-band conductivity and dielectric spectroscopy of composites of multiwalled carbon nanotubes and poly(ethylene terephthalate) around their low percolation threshold.

    PubMed

    Nuzhnyy, D; Savinov, M; Bovtun, V; Kempa, M; Petzelt, J; Mayoral, B; McNally, T

    2013-02-08

    Composites of multiwalled carbon nanotubes with poly(ethylene terephthalate) (PET-MWCNT) with up to 3 vol% MWCNTs were prepared and characterized by broad-band AC conductivity and dielectric spectroscopy up to the infrared range using several techniques. A very low electrical percolation threshold of 0.07 vol% MWCNTs was revealed from the low-frequency conductivity plateau as well as from DC conductivity, whose values show the same critical power dependence on MWCNT concentration with the exponent t = 4.3. Above the plateau, the AC conductivity increases with frequency up to the THz range, where it becomes overlapped with the absorption of vibrational modes. The temperature dependence down to ~5 K has shown semiconductor behaviour with a concentration-independent but weakly temperature-dependent small activation energy of ~3 meV. The behaviour is compatible with the previously suggested fluctuation-induced tunnelling conductivity model through a thin (~1 nm) polymer contact layer among the adjacent MWCNTs within percolated clusters. At higher frequencies, deviations from the simple universal conductivity behaviour are observed, indicating some distribution of energy barriers for an electron hopping mechanism.

  1. Broadband spectroscopy with external cavity quantum cascade lasers beyond conventional absorption measurements.

    PubMed

    Lambrecht, Armin; Pfeifer, Marcel; Konz, Werner; Herbst, Johannes; Axtmann, Felix

    2014-05-07

    Laser spectroscopy is a powerful tool for analyzing small molecules, i.e. in the gas phase. In the mid-infrared spectral region quantum cascade lasers (QCLs) have been established as the most frequently used laser radiation source. Spectroscopy of larger molecules in the gas phase, of complex mixtures, and analysis in the liquid phase requires a broader tuning range and is thus still the domain of Fourier transform infrared (FTIR) spectroscopy. However, the development of tunable external cavity (EC) QCLs is starting to change this situation. The main advantage of QCLs is their high spectral emission power that is enhanced by a factor of 10(4) compared with thermal light sources. Obviously, transmission measurements with EC-QCLs in strongly absorbing samples are feasible, which can hardly be measured by FTIR due to detector noise limitations. We show that the high power of EC-QCLs facilitates spectroscopy beyond simple absorption measurements. Starting from QCL experiments with liquid samples, we show results of fiber evanescent field analysis (FEFA) to detect pesticides in drinking water. FEFA is a special case of attenuated total reflection spectroscopy. Furthermore, powerful CW EC-QCLs enable fast vibrational circular dichroism (VCD) spectroscopy of chiral molecules in the liquid phase - a technique which is very time consuming with standard FTIR equipment. We present results obtained for the chiral compound 1,1'-bi-2-naphthol (BINOL). Finally, powerful CW EC-QCLs enable the application of laser photothermal emission spectroscopy (LPTES). We demonstrate this for a narrowband and broadband absorber in the gas phase. All three techniques have great potential for MIR process analytical applications.

  2. A broadband x-ray imaging spectroscopy with high-angular resolution: the FORCE mission

    NASA Astrophysics Data System (ADS)

    Mori, Koji; Tsuru, Takeshi Go; Nakazawa, Kazuhiro; Ueda, Yoshihiro; Okajima, Takashi; Murakami, Hiroshi; Awaki, Hisamitsu; Matsumoto, Hironori; Fukazawa, Yasushi; Tsunemi, Hiroshi; Takahashi, Tadayuki; Zhang, William W.

    2016-07-01

    We are proposing FORCE (Focusing On Relativistic universe and Cosmic Evolution) as a future Japan-lead Xray observatory to be launched in the mid 2020s. Hitomi (ASTRO-H) possesses a suite of sensitive instruments enabling the highest energy-resolution spectroscopy in soft X-ray band, a broadband X-ray imaging spectroscopy in soft and hard X-ray bands, and further high energy coverage up to soft gamma-ray band. FORCE is the direct successor to the broadband X-ray imaging spectroscopy aspect of Hitomi (ASTRO-H) with significantly higher angular resolution. The current design of FORCE defines energy band pass of 1-80 keV with angular resolution of < 15 in half-power diameter, achieving a 10 times higher sensitivity above 10 keV compared to any previous missions with simultaneous soft X-ray coverage. Our primary scientific objective is to trace the cosmic formation history by searching for "missing black holes" in various mass-scales: "buried supermassive black holes (SMBHs)" (> 104 M⊙) residing in the center of galaxies in a cosmological distance, "intermediate-mass black holes" (102-104 M⊙) acting as the possible seeds from which SMBHs grow, and "orphan stellar-mass black holes" (< 102 M⊙) without companion in our Galaxy. In addition to these missing BHs, hunting for the nature of relativistic particles at various astrophysical shocks is also in our scope, utilizing the broadband X-ray coverage with high angular-resolution. FORCE are going to open a new era in these fields. The satellite is proposed to be launched with the Epsilon vehicle that is a Japanese current solid-fuel rocket. FORCE carries three identical pairs of Super-mirror and wide-band X-ray detector. The focal length is currently planned to be 10 m. The silicon mirror with multi-layer coating is our primary choice to achieve lightweight, good angular optics. The detector is a descendant of hard X-ray imager onboard Hitomi (ASTRO-H) replacing its silicon strip detector with SOI-CMOS silicon pixel

  3. A Broadband X-Ray Imaging Spectroscopy with High-Angular Resolution: the FORCE Mission

    NASA Technical Reports Server (NTRS)

    Mori, Koji; Tsuru, Takeshi Go; Nakazawac, Kazuhiro; Ueda, Yoshihiro; Okajima, Takashi; Murakami, Hiroshi; Awaki, Hisamitsu; Matsumoto, Hironori; Fukazawai, Yasushi; Tsunemi, Hiroshi; hide

    2016-01-01

    We are proposing FORCE (Focusing On Relativistic universe and Cosmic Evolution) as a future Japan-lead X-ray observatory to be launched in the mid 2020s. Hitomi (ASTRO-H) possesses a suite of sensitive instruments enabling the highest energy-resolution spectroscopy in soft X-ray band, a broadband X-ray imaging spectroscopy in soft and hard X-ray bands, and further high energy coverage up to soft gamma-ray band. FORCE is the direct successor to the broadband X-ray imaging spectroscopy aspect of Hitomi (ASTRO-H) with significantly higher angular resolution. The current design of FORCE defines energy band pass of 1-80 keV with angular resolution of <15" in half-power diameter, achieving a 10 times higher sensitivity above 10 keV compared to any previous missions with simultaneous soft X-ray coverage. Our primary scientific objective is to trace the cosmic formation history by searching for "missing black holes" in various mass-scales: "buried supermassive black holes (SMBHs)" (> 10(exp 4) Stellar Mass) residing in the center of galaxies in a cosmological distance, "intermediate-mass black holes" (10(exp 2)-(10(exp 4) Stellar Mass) acting as the possible seeds from which SMBHs grow, and "orphan stellar-mass black holes" (< 10(exp 2) Stellar Mass) without companion in our Galaxy. In addition to these missing BHs, hunting for the nature of relativistic particles at various astrophysical shocks is also in our scope, utilizing the broadband X-ray coverage with high angular-resolution. FORCE are going to open a new era in these fields. The satellite is proposed to be launched with the Epsilon vehicle that is a Japanese current solid-fuel rocket. FORCE carries three identical pairs of Super-mirror and wide-band X-ray detector. The focal length is currently planned to be 10 m. The silicon mirror with multi-layer coating is our primary choice to achieve lightweight, good angular optics. The detector is a descendant of hard X-ray imager onboard Hitomi (ASTRO-H) replacing its

  4. Coregistration of dynamic contrast enhanced MRI and broadband diffuse optical spectroscopy for characterizing breast cancer.

    PubMed

    Hsiang, David; Shah, Natasha; Yu, Hon; Su, Min-Ying; Cerussi, Albert; Butler, John; Baick, Choong; Mehta, Rita; Nalcioglu, Orhan; Tromberg, Bruce

    2005-10-01

    A hand-held scanning probe based on broadband Diffuse Optical Spectroscopy (DOS) was used in combination with dynamic contrast enhanced MRI (DCE-MRI) to quantitatively characterize locally-advanced breast cancers in six patients. Measurements were performed sequentially using external fiducial markers for co-registration. Tumor patterns were categorized according to MRI morphological data, and 3D DCE-MRI slices were converted into a volumetric matrix with isotropic voxels to generate views that coincided with the DOS scanning plane. Tumor volume and depth at each DOS measurement site were determined, and a tissue optical index (TOI) that reflects both angiogenic and stromal characteristics was derived from broadband DOS data. In all six cases, optical scans showed significant TOI contrast corresponding to MRI morphological information. Sharp TOI peaks were recovered for well-circumscribed masses. A reduction in TOI was found inside a tumor with a necrotic center. A broadened peak was observed for a diffuse tumor pattern, and an inflammatory septal case provided two TOI peaks that correlated qualitatively with MRI enhancement. These results provide qualitative confirmation of the common signal origin and complementary information content that can be achieved by combining optical and MR imaging for breast cancer detection and clinical management.

  5. Some Signal Processing Techniques for Use in Broadband Time Domain Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Cooke, S. A.

    2016-06-01

    At the present time, in the typical broadband, time domain microwave spectroscopy experiment each free induction decay (FID) collected is on the order of 10^6 data points in length with a sampling rate on the order of 10-12 seconds per point. Traditionally, the FID is processed using a fast Fourier transform algorithm (FFT) with the resulting power spectrum used in ensuing spectral analyses. For use with the FFT algorithm we have implemented some pre- and post-processing techniques to improve the signal quality. These techniques include the use of Lissajous plots to ensure phase stability in signal addition, novel windowing functions, and also automated broadband phase corrections which allow the absorption spectrum to be used as a more highly resolved version of the traditional power spectrum (see figure). We have also implemented alternatives to the FFT algorithm for time domain signal processing including Hankel singular valued decomposition, a maximum entropy method, and wavelet transformations. Although these techniques are unlikely to be used in place of a fast Fourier transform we will demonstrate how each of these techniques may be used to augment the traditional FFT algorithm in regards to spectral analysis.

  6. Devices and materials for THz spectroscopy: GHz CMOS circuits, periodic hole-arrays and high-frequency dielectric materials

    NASA Astrophysics Data System (ADS)

    Arenas, Daniel J.

    This dissertation is composed of three main projects, linked together by the THz region of the electromagnetic spectrum. In the first project, we detected the radiation from a silicon CMOS circuit, using a fourier transform interferometer. At the time of measurement, this 410 GHz circuit had the highest operating frequency for silicon integrated technology. The measured radiated power from the 410 GHz circuits was in the order of 0.01 muW. This circuit had radiated intensities comparable to those of commercially available black-body sources in the 400 GHz region. The high power and high emission per source area suggested possible spectroscopy applications. We also studied the optical properties of periodic hole-arrays with resonant frequencies in the THz region. Although the transmittance spectra of these structures have been extensively studied, here we present reflectance measurements that allow the analysis of the extinction/absorption spectra. The results were compared to predictions from the trapped-mode theory on the ohmic losses of these systems. Our results did not support the prediction of a suppression of the R + T spectra at the resonant frequency. Also, we studied the time-dependence of femtosecond pulses reflected from periodic hole arrays with resonant frequencies in the NIR region. Our results show that if the trapped modes theory is correct, then the lifetime of these modes are below 100 fs. Finally, in the third project, we studied the Raman active modes of various bismuth pyrochlores Bi3/2ZnNb3/2O7 (BZN), Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb 3/2O7 (BMN) and Bi3/2MgTa3/2O 7 (BMT), which have earned recent attention for high-frequency applications. The spectra of the four compositions are very similar, suggesting no major structural differences among these materials. The spectra were compared to those of other pyrochlores and specific discussions are offered for the assignment of each mode. Although there are clear differences between the spectra of

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

    NASA Astrophysics Data System (ADS)

    Tulsyan, Gaurav

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

  8. Broadband terahertz dynamics of propylene glycol monomer and oligomers

    NASA Astrophysics Data System (ADS)

    Koda, Shota; Mori, Tatsuya; Kojima, Seiji

    2016-12-01

    We investigated the broadband terahertz spectra (0.1-5.0 THz) of glass-forming liquids, propylene glycol (PG), its oligomers poly (propylene glycol)s (PPGs), and poly (propylene glycol) diglycidyl ether (PPG-de) using broadband terahertz time-domain spectroscopy and low-frequency Raman scattering. The numerical value of the dielectric loss at around 1.5 THz, which is the peak position of broad peaks in all samples, decreased as the molecular weight increased. Furthermore, the peak at around 1.5 THz is insensitive to the molecular weight. For PPGs, the side chain effect of the oligomer was observed in the terahertz region. Based on the experimental and calculation results for the PPGs and PPG-de, whose end groups are epoxy groups, the beginnings of the increases in the observed dielectric loss above 3.5 THz of the PPGs are assigned to the OH bending vibration. The higher value of the dielectric loss in the terahertz region for the PPG-de can be the tail of a broad peak located in the MHz region. The difference between the Raman susceptibility and dielectric loss reflects the difference in the observable molecular dynamics between the infrared and Raman spectroscopies.

  9. GaSe1-xSx and GaSe1-xTex thick crystals for broadband terahertz pulses generation

    NASA Astrophysics Data System (ADS)

    Nazarov, M. M.; Yu. Sarkisov, S.; Shkurinov, A. P.; Tolbanov, O. P.

    2011-08-01

    We demonstrate the possibility of broadband THz pulse generation in mixed GaSe1-xSx and GaSe1-xTex crystals. The ordinary and extraordinary refractive indices of the crystals have been measured by the terahertz time-domain spectroscopy method, those values strongly influence the efficiency of THz generation process. The high birefringence and transparency of pure GaSe and mixed crystals allow optical rectification of femtosecond laser pulses in the several millimeters thick crystal using the еее interaction process (with two pumping waves and generated THz wave all having extraordinary polarization in the crystal).

  10. Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy.

    PubMed

    Yeh, Tien-Tien; Shirai, Hideto; Tu, Chien-Ming; Fuji, Takao; Kobayashi, Takayoshi; Luo, Chih-Wei

    2017-01-11

    In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200-5000 cm(-1) region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm(-1) especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.

  11. Structures of cage, prism, and book isomers of water hexamer from broadband rotational spectroscopy.

    PubMed

    Pérez, Cristóbal; Muckle, Matt T; Zaleski, Daniel P; Seifert, Nathan A; Temelso, Berhane; Shields, George C; Kisiel, Zbigniew; Pate, Brooks H

    2012-05-18

    Theory predicts the water hexamer to be the smallest water cluster with a three-dimensional hydrogen-bonding network as its minimum energy structure. There are several possible low-energy isomers, and calculations with different methods and basis sets assign them different relative stabilities. Previous experimental work has provided evidence for the cage, book, and cyclic isomers, but no experiment has identified multiple coexisting structures. Here, we report that broadband rotational spectroscopy in a pulsed supersonic expansion unambiguously identifies all three isomers; we determined their oxygen framework structures by means of oxygen-18-substituted water (H(2)(18)O). Relative isomer populations at different expansion conditions establish that the cage isomer is the minimum energy structure. Rotational spectra consistent with predicted heptamer and nonamer structures have also been identified.

  12. Intermolecular and intramolecular reorientations in nonchiral smectic liquid-crystalline phases studied by broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Schacht, J.; Zugenmaier, P.; Buivydas, M.; Komitov, L.; Stebler, B.; Lagerwall, S. T.; Gouda, F.; Horii, F.

    2000-04-01

    Molecular dynamics has been studied by broadband dielectric relaxation spectroscopy in the Sm-A, Sm-B, and Sm-E phases (Sm denotes smectic) of a homologous series of nonchiral stilbenes. An assignment of modes is presented based on their dependence on temperature and molecular length, and, as far as they obey the Arrhenius law, their activation energy has been determined. In general, reorientations of entire molecules around their short axis are active, whereas reorientations of entire molecules around their long axis are locked out in the Sm-E phase of shorter homologs, yet intramolecular reorientations of polar sites have been established. Strong evidence is presented for an interdependence of reorientations of entire molecules around the short and long axes within the biaxial Sm-E phase of longer homologs.

  13. Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Yeh, Tien-Tien; Shirai, Hideto; Tu, Chien-Ming; Fuji, Takao; Kobayashi, Takayoshi; Luo, Chih-Wei

    2017-01-01

    In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200-5000 cm-1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm-1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.

  14. Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy

    PubMed Central

    Yeh, Tien-Tien; Shirai, Hideto; Tu, Chien-Ming; Fuji, Takao; Kobayashi, Takayoshi; Luo, Chih-Wei

    2017-01-01

    In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200–5000 cm−1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm−1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation. PMID:28074933

  15. Glassy dynamics and physical aging in fucose saccharides as studied by infrared- and broadband dielectric spectroscopy.

    PubMed

    Kossack, Wilhelm; Adrjanowicz, Karolina; Tarnacka, Magdalena; Kipnusu, Wycliffe Kiprop; Dulski, Mateusz; Mapesa, Emmanuel Urandu; Kaminski, Kamil; Pawlus, Sebastian; Paluch, Marian; Kremer, Friedrich

    2013-12-21

    Fourier Transform Infra Red (FTIR) and Broadband Dielectric Spectroscopy (BDS) are combined to study both the intra- and inter-molecular dynamics of two isomers of glass forming fucose, far below and above the calorimetric glass transition temperature, T(g). It is shown that the various IR-active vibrations exhibit in their spectral position and oscillator strength quite different temperature dependencies, proving their specific signature in the course of densification and glass formation. The coupling between intra- and inter molecular dynamics is exemplified by distinct changes in IR active ring vibrations far above the calorimetric glass transition temperature at about 1.16T(g), where the dynamic glass transition (α relaxation) and the secondary β relaxation merge. For physically annealed samples it is demonstrated that upon aging the different moieties show characteristic features as well, proving the necessity of atomistic descriptions beyond coarse-grained models.

  16. Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber.

    PubMed

    Hernández, M; Grande, A M; van der Zwaag, S; García, S J

    2016-04-27

    Broadband dielectric spectroscopy (BDS) is introduced as a new and powerful technique to monitor network and macroscale damage healing in an elastomer. For the proof of concept, a partially cured sulfur-cured natural rubber (NR) containing reversible disulfides as the healing moiety was employed. The forms of damage healed and monitored were an invisible damage in the rubber network due to multiple straining and an imposed macroscopic crack. The relaxation times of pristine, damaged, and healed samples were determined and fitted to the Havriliak-Negami equation to obtain the characteristic polymer parameters. It is shown that seemingly full mechanical healing occurred regardless the type of damage, while BDS demonstrates that the polymer architecture in the healed material differs from that in the original one. These results represent a step forward in the understanding of damage and healing processes in intrinsic self-healing polymer systems with prospective applications such as coatings, tires, seals, and gaskets.

  17. Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

    SciTech Connect

    Sheps, Leonid; Chandler, David W.

    2013-04-01

    Experimental measurements of elementary reaction rate coefficients and product branching ratios are essential to our understanding of many fundamentally important processes in Combustion Chemistry. However, such measurements are often impossible because of a lack of adequate detection techniques. Some of the largest gaps in our knowledge concern some of the most important radical species, because their short lifetimes and low steady-state concentrations make them particularly difficult to detect. To address this challenge, we propose a novel general detection method for gas-phase chemical kinetics: time-resolved broadband cavity-enhanced absorption spectroscopy (TR-BB-CEAS). This all-optical, non-intrusive, multiplexed method enables sensitive direct probing of transient reaction intermediates in a simple, inexpensive, and robust experimental package.

  18. A versatile setup for ultrafast broadband optical spectroscopy of coherent collective modes in strongly correlated quantum systems

    PubMed Central

    Baldini, Edoardo; Mann, Andreas; Borroni, Simone; Arrell, Christopher; van Mourik, Frank; Carbone, Fabrizio

    2016-01-01

    A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide temperature range. By combining high temporal resolution and a broad detection window, this apparatus can investigate the interplay between coherent collective modes and high-energy electronic excitations, which is a distinctive characteristic of correlated electron systems. Using a single-shot readout array detector at frame rates of 10 kHz allows resolving coherent oscillations with amplitudes <10−4. We demonstrate its operation on the charge-transfer insulator La2CuO4, revealing coherent phonons with frequencies up to 13 THz and providing access into their Raman matrix elements. PMID:27990455

  19. Detection of Bacillus subtilis spores in water by means of broadband coherent anti-Stokes Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Petrov, Georgi I.; Yakovlev, Vladislav V.; Sokolov, Alexei V.; Scully, Marlan O.

    2005-11-01

    Broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy is used for detection of bacterial spores in aqueous solution. Polarization CARS spectroscopy is employed to suppress the non-resonant background. CARS spectrum recorded in the spectral region from 700 to 1900 cm-1 exhibits all the characteristic features of spontaneous Raman spectrum taken for a solid powder and resembles that one of the dipicolinic acid, which is considered to be the major component of bacterial spores, including anthrax.

  20. Broadband terahertz time-domain spectroscopic study on form II polyvinylidene fluoride

    NASA Astrophysics Data System (ADS)

    Mori, Tatsuya; Igawa, Hikaru; Okada, Daichi; Yamamoto, Yohei; Iwamoto, Kei; Toyota, Naoki; Kojima, Seiji

    2015-06-01

    The complex dielectric constant of semicrystalline form II polyvinylidene fluoride (PVDF (II)) in the frequency range from 0.2 to 6.0 THz has been determined by broadband terahertz time-domain spectroscopy (THz-TDS). The obtained dielectric constant consists of superposition of four vibration modes at 1.60, 2.36, 3.04 and 5.31 THz of crystalline part and a broad relaxation mode with center frequency of 0.68 THz which will be attributed to boson peak of amorphous fraction. In addition, the temperature dependence of the dielectric constant has also been measured, and we have determined the glass transition temperature of amorphous fraction of PVDF (II) as about 192 K by analysis of the temperature variation of peak frequency of the lattice vibration mode.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  2. Efficiency of using the spectral dynamics analysis for pulsed THz spectroscopy of both explosive and other materials

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Varentsova, Svetlana A.

    2015-05-01

    One of the modern problems arising in the detection and identification of substances is a development of criteria for the assessment of a presence of explosive (or other dangerous substance) fingerprints in THz signals transmitted through or reflected from a sample. Obviously, criteria depend on the method used for the substance detection and identification. Taking into account our previous experience, we use for a solution of this problem the SDA method (method of the spectral dynamics analysis). Essential restrictions of usually used THz TDS method for the detection and identification under real conditions (at long distance about 3.5 m and at a high relative humidity more than 50%) are demonstrated using the physical experiment with paper napkins and thick paper bag. We show also that the THz TDS method detects spectral features of dangerous substances even in the THz signals measured in laboratory conditions (at distance 30-40 cm from the receiver and at a low relative humidity less than 2%) with semiconductors of different types used as samples. However, the integral correlation criteria, based on SDA method, allows us to detect the absence of dangerous substances in semiconductors. In order to demonstrate the possibilities of the integral criteria for finding additional substances in the mixture with semiconductors, we modeled several mixtures of n-doped Silicon with neutral substance Soap in different ratio. The discussed algorithms show high probability of the substance identification and a reliability of realization in practice, especially for non-destructive testing and security applications.

  3. Investigating molecular structures: Rapidly examining molecular fingerprints through fast passage broadband fourier transform microwave spectroscopy

    NASA Astrophysics Data System (ADS)

    Grubbs, Garry Smith Smitty, II

    Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ≤1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation off, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (≤10 mus) than the molecular relaxation (≈100 mus). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, and transient species may be studied with the spectrometer with high sensitivity, making it a viable option for many molecules wanting to be rotationally studied. The spectrometer has a relative correct intensity feature that, when coupled with theory, may ease the difficulty in transition assignment and facilitate dynamic chemical studies of the experiment. Molecules studied on this spectrometer have, in turn, been analyzed and assigned using common rotational spectroscopic analysis. Detailed theory on the analysis of these molecules has been provided. Structural parameters such as rotational constants and

  4. Terahertz (THz) Wireless Systems for Space Applications

    NASA Technical Reports Server (NTRS)

    Hwu, Shian U.; deSilva, Kanishka B.; Jih, Cindy T.

    2013-01-01

    NASA has been leading the Terahertz (THz) technology development for the sensors and instruments in astronomy in the past 20 years. THz technologies are expanding into much broader applications in recent years. Due to the vast available multiple gigahertz (GHz) broad bandwidths, THz radios offer the possibility for wireless transmission of high data rates. Multi-Gigabits per second (MGbps) broadband wireless access based on THz waves are closer to reality. The THz signal high atmosphere attenuation could significantly decrease the communication ranges and transmittable data rates for the ground systems. Contrary to the THz applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. The manufacturing technologies for the THz electronic components are advancing and maturing. There is great potential for the NASA future high data wireless applications in environments with difficult cabling and size/weight constraints. In this study, the THz wireless systems for potential space applications were investigated. The applicability of THz systems for space applications was analyzed. The link analysis indicates that MGbps data rates are achievable with compact sized high gain antennas.

  5. Enhancing the low frequency THz resonances (< 1 THz) of organic molecules via electronegative atom substitution

    NASA Astrophysics Data System (ADS)

    Dash, Jyotirmayee; Ray, Shaumik; Pesala, Bala

    2015-03-01

    Terahertz (THz) technology is an active area of research with various applications in non-intrusive imaging and spectroscopy. Very few organic molecules have significant resonances below 1 THz. Understanding the origin of low frequency THz modes in these molecules and their absence in other molecules could be extremely important in design and engineering molecules with low frequency THz resonances. These engineered molecules can be used as THz tags for anti-counterfeiting applications. Studies show that low frequency THz resonances are commonly observed in molecules having higher molecular mass and weak intermolecular hydrogen bonds. In this paper, we have explored the possibility of enhancing the strength of THz resonances below 1 THz through electronegative atom substitution. Adding an electronegative atom helps in achieving higher hydrogen bond strength to enhance the resonances below 1 THz. Here acetanilide has been used as a model system. THz-Time Domain Spectroscopy (THz-TDS) results show that acetanilide has a small peak observed below 1 THz. Acetanilide can be converted to 2-fluoroacetanilide by adding an electronegative atom, fluorine, which doesn't have any prominent peak below 1 THz. However, by optimally choosing the position of the electronegative atom as in 4-fluoroacetanilide, a significant THz resonance at 0.86 THz is observed. The origin of low frequency resonances can be understood by carrying out Density Functional Theory (DFT) simulations of full crystal structure. These studies show that adding an electronegative atom to the organic molecules at an optimized position can result in significantly enhanced resonances below 1 THz.

  6. Broadband Microwave Spectroscopy and Automated Analysis of 12 Conformers of 1-HEXANAL

    NASA Astrophysics Data System (ADS)

    Seifert, Nathan A.; Perez, Cristobal; Zaleski, Daniel P.; Neill, Justin; Steber, Amanda; Suenram, Richard D.; Pate, Brooks; Shipman, Steven; Finneran, Ian; Lesarri, Alberto

    2014-06-01

    The rotational spectrum of 1-hexanal is used as a test case for developing automated assignment algorithms in molecular rotational spectroscopy, for the purpose of lowering the barrier to new users of rotational spectroscopy. There are two ways that the automated fitting algorithm, implemented in the AUTOFIT program, is used: 1) Assignment of the rotational spectrum of a molecule expected to be in the sample mixture (in this case, a conformer of 1-hexanal), using quantum chemistry estimates of the spectroscopic parameters to efficiently guide the search for the experimental spectrum. 2) Once a new spectrum is assigned, the algorithm is used to automatically assign isotopologue spectra (sensitivity permitting) to provide verification of the molecular structure. Using a combination of quantum chemical calculations and automated spectral assignment, 12 conformations of 1-hexanal have been identified using chirped-pulse Fourier transform (CP-FTMW) spectroscopy in the 6.5-18, 18-26 and 26-40 GHz bands. Of these 12 conformers, the four lowest energy conformers were intense enough to resolve each of the six 13C isotopologues for each conformer, and sufficient intensity was achieved to assign the 18O isotopologues of the two lowest energy conformers. The full set of assignments were made using the AUTOFIT program, and a summary of results for all 38 observed species via automated assignment will be presented. Additionally, by using all 12 conformers of 1-hexanal as a benchmark set, a discussion of dispersion-corrected density functional theory for the purpose of automated broadband spectroscopic searches will be presented, with specific results regarding rotational constant prediction. Results will also be presented on the correlation between the predicted conformational energetics predicted by multiple levels of theory and the sensitivity limits of the 1-hexanal CP-FTMW spectrum.

  7. Industrial applications of THz systems

    NASA Astrophysics Data System (ADS)

    Wietzke, S.; Jansen, C.; Jördens, C.; Krumbholz, N.; Vieweg, N.; Scheller, M.; Shakfa, M. K.; Romeike, D.; Hochrein, T.; Mikulics, M.; Koch, M.

    2009-07-01

    Terahertz time-domain spectroscopy (THz TDS) holds high potential as a non-destructive, non-contact testing tool. We have identified a plethora of emerging industrial applications such as quality control of industrial processes and products in the plastics industry. Polymers are transparent to THz waves while additives show a significantly higher permittivity. This dielectric contrast allows for detecting the additive concentration and the degree of dispersion. We present a first inline configuration of a THz TDS spectrometer for monitoring polymeric compounding processes. To evaluate plastic components, non-destructive testing is strongly recommended. For instance, THz imaging is capable of inspecting plastic weld joints or revealing the orientation of fiber reinforcements. Water strongly absorbs THz radiation. However, this sensitivity to water can be employed in order to investigate the moisture absorption in plastics and the water content in plants. Furthermore, applications in food technology are discussed. Moreover, security scanning applications are addressed in terms of identifying liquid explosives. We present the vision and first components of a handheld security scanner. In addition, a new approach for parameter extraction of THz TDS data is presented. All in all, we give an overview how industry can benefit from THz TDS completing the tool box of non-destructive evaluation.

  8. Time-Domain Terahertz Spectroscopy (0.3 - 7.5 THz) of Molecular Ices of Simple Alcohols

    NASA Astrophysics Data System (ADS)

    McGuire, Brett A.; Ioppolo, Sergio; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey

    2014-06-01

    We have recently constructed a time-domain TeraHertz (THz) spectrometer for the study of molecular ices in the far-infrared. Here, we present the results of a study of amorphous and crystalline ices of simple alcohols from methanol (CH_3OH) through butanol (CH_3(CH_2)_3OH) in the region of 0.3 - 7.5 THz. We examine the effects of the length and degree of branching of the carbon chain on the observed spectra arising from the bulk, large-amplitude motions which are prominent in this spectral region. We also discuss these results in an astrochemical context: the application of these spectra to astronomical observations of interstellar ices with Herschel PACS/SPIRE and SOFIA.

  9. The Jefferson Lab High Power THz User Facility

    SciTech Connect

    John Klopf; Amelia Greer; Joseph Gubeli; George Neil; Michelle D. Shinn; Timothy Siggins; David W. Waldman; Gwyn Williams; Alan Todd; Vincent Christina; Oleg Chubar

    2007-04-27

    We describe here, a high power (100 Watt average, 10 MW peak) broadband THz facility based on emission from sub-picosecond bunches of relativistic electrons and the beam transport system that delivers this beam in to a user laboratory.

  10. Continuous Vernier filtering of an optical frequency comb for broadband cavity-enhanced molecular spectroscopy

    NASA Astrophysics Data System (ADS)

    Rutkowski, Lucile; Morville, Jérôme

    2017-01-01

    We have recently introduced the Vernier-based Direct Frequency Comb Cavity-Enhanced Spectroscopy technique which allows us to record broadband spectra at high sensitivity and GHz resolution (Rutkowski and Morville, 2014) [1]. We discuss here the effect of Vernier filtering on the observed lineshapes in the 3 ν + δ band of water vapor and the entire A-band of oxygen around 800 nm in ambient air. We derive expressions for the absorption profiles resulting from the continuous Vernier filtering method, testing them on spectra covering more than 2000 cm-1 around 12,500 cm-1. With 31,300 independent spectral elements acquired at the second time scale, an absorption baseline noise of 2 ×10-8cm-1 is obtained, providing a figure of merit of 1.1×10-10 cm-1/√{ Hz } per spectral element with a cavity finesse of 3000 and a cavity round-trip length around 3.3 m.

  11. Thermoplastic starch modified with microfibrillated cellulose and natural rubber latex: A broadband dielectric spectroscopy study.

    PubMed

    Drakopoulos, S X; Karger-Kocsis, J; Kmetty, Á; Lendvai, L; Psarras, G C

    2017-02-10

    Thermoplastic starch (TPS) biocomposites modified with cellulose microfibers and/or natural rubber were prepared via extrusion compounding. Glycerol and water served as plasticizers for starch. The dielectric properties of the TPS composites were examined via broadband dielectric spectroscopy in the temperature and frequency ranges of 30°C-65°C and 0.1Hz-10MHz, respectively. Each specimen was tested twice in order to study the effect of absorbed water. The hydrophobic/hydrophilic character of the modifiers governed the dielectric performance of the corresponding TPS biocomposites. Conducted analysis revealed two relaxation processes attributed to matrix-water-reinforcement interfacial polarization and glass to rubber transition of the TPS. Evaporation of water significantly affected the first process and only slightly the second one. Energy density, prior and after water evaporation, was also determined at constant field. By employing dielectric reinforcing function the contributions of water-assisted and constituents' originated interfacial phenomena could be separated. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Broadband coherent anti-Stokes Raman spectroscopy characterization of polymer thin films.

    PubMed

    Schultz, Zachary D; Gurau, Marc C; Richter, Lee J

    2006-10-01

    Broadband coherent anti-Stokes Raman spectroscopy (CARS) is demonstrated as an effective probe of polymer thin film materials. A simple modification to a 1 kHz broad bandwidth sum frequency generation (SFG) spectrometer permits acquisition of CARS spectra for polymer thin films less than 100 nm thick, a dimension relevant to organic electronic device applications. CARS spectra are compared to the conventional Raman spectra of polystyrene and the resonance-enhanced Raman spectra of poly(3-hexylthiophene). The CARS spectra obtained under these conditions consistently demonstrate enhanced signal-to-noise ratio compared to the spontaneous Raman scattering. The sensitivity of the CARS measurement is limited by the damage threshold of the samples. The dielectic properties of the substrate have a dramatic effect on the detected signal intensity. For ultrathin films, the strongest signals are obtained from fused silica surfaces. Similar to surface-enhanced Raman scattering (SERS), Au also gives a large signal, but contrary to SERS, no surface roughening is necessary.

  13. Broadband stripline ferromagnetic resonance spectroscopy of ferromagnetic films, multilayers and nanostructures

    NASA Astrophysics Data System (ADS)

    Maksymov, Ivan S.; Kostylev, Mikhail

    2015-05-01

    This paper presents a comprehensive critical overview of fundamental and practical aspects of the modern stripline broadband ferromagnetic resonance (BFMR) spectroscopy largely employed for the characterisation of magnetic low-dimensional systems, such as thin ferro- and ferromagnetic, multiferroic and half-metallic films, multi-layers and nanostructures. These planar materials form the platform of the nascent fields of magnonics and spintronics. Experimental and theoretical results of research on these materials are summarised, along with systematic description of various phenomena associated with the peculiarities of the stripline BFMR, such as the geometry of stripline transducers, the orientation of the static magnetic field, the presence of microwave eddy currents, and the impacts of non-magnetic layers, interfaces and surfaces in the samples. Results from 240 articles, textbooks and technical reports are presented and many practical examples are discussed in detail. This review will be of interest to both general physical audience and specialists conducting research on various aspects of magnetisation dynamics and nanomagnetism.

  14. Vibrational dynamics of aqueous hydroxide solutions probed using broadband 2DIR spectroscopy

    NASA Astrophysics Data System (ADS)

    Mandal, Aritra; Tokmakoff, Andrei

    2015-11-01

    We employed ultrafast transient absorption and broadband 2DIR spectroscopy to study the vibrational dynamics of aqueous hydroxide solutions by exciting the O-H stretch vibrations of the strongly hydrogen-bonded hydroxide solvation shell water and probing the continuum absorption of the solvated ion between 1500 and 3800 cm-1. We observe rapid vibrational relaxation processes on 150-250 fs time scales across the entire probed spectral region as well as slower vibrational dynamics on 1-2 ps time scales. Furthermore, the O-H stretch excitation loses its frequency memory in 180 fs, and vibrational energy exchange between bulk-like water vibrations and hydroxide-associated water vibrations occurs in ˜200 fs. The fast dynamics in this system originate in strong nonlinear coupling between intra- and intermolecular vibrations and are explained in terms of non-adiabatic vibrational relaxation. These measurements indicate that the vibrational dynamics of the aqueous hydroxide complex are faster than the time scales reported for long-range transport of protons in aqueous hydroxide solutions.

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

  16. Vibrational dynamics of aqueous hydroxide solutions probed using broadband 2DIR spectroscopy

    SciTech Connect

    Mandal, Aritra; Tokmakoff, Andrei

    2015-11-21

    We employed ultrafast transient absorption and broadband 2DIR spectroscopy to study the vibrational dynamics of aqueous hydroxide solutions by exciting the O–H stretch vibrations of the strongly hydrogen-bonded hydroxide solvation shell water and probing the continuum absorption of the solvated ion between 1500 and 3800 cm{sup −1}. We observe rapid vibrational relaxation processes on 150–250 fs time scales across the entire probed spectral region as well as slower vibrational dynamics on 1–2 ps time scales. Furthermore, the O–H stretch excitation loses its frequency memory in 180 fs, and vibrational energy exchange between bulk-like water vibrations and hydroxide-associated water vibrations occurs in ∼200 fs. The fast dynamics in this system originate in strong nonlinear coupling between intra- and intermolecular vibrations and are explained in terms of non-adiabatic vibrational relaxation. These measurements indicate that the vibrational dynamics of the aqueous hydroxide complex are faster than the time scales reported for long-range transport of protons in aqueous hydroxide solutions.

  17. Interplay of phenol and isopropyl isomerism in propofol from broadband chirped-pulse microwave spectroscopy.

    PubMed

    Lesarri, Alberto; Shipman, Steven T; Neill, Justin L; Brown, Gordon G; Suenram, Richard D; Kang, Lu; Caminati, Walther; Pate, Brooks H

    2010-09-29

    The conformational equilibrium of the general anesthetic propofol (2,6-diisopropylphenol) has been studied in a supersonic expansion using broadband chirped-pulse microwave spectroscopy. Three conformers originated by the combined internal rotation of the hydroxyl and the two isopropyl groups have been detected in the jet-cooled rotational spectrum. The most stable conformer exhibits tunneling splittings associated with the internal rotation of the hydroxyl group, from which we determined the torsional potential and barrier heights (905-940 cm(-1)). The carbon backbone structure was derived from the spectral assignments of all 12 (13)C monosubtituted isotopologues in natural abundance and confirmed a plane-symmetric gauche orientation of the two isopropyl groups (Gg) for this conformer. In the other two detected conformers (EG and GE) one of the isopropyl groups is eclipsed with respect to the ring plane while the other is gauche, differing in a ∼180° rotation of the hydroxyl group. Supporting ab initio calculations provided information on the potential energy surface and molecular properties of the title compound.

  18. Monitoring angiogenesis using a human compatible calibration for broadband near-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Runze; Zhang, Qiong; Wu, Ying; Dunn, Jeff F.

    2013-01-01

    Angiogenesis is a hallmark of many conditions, including cancer, stroke, vascular disease, diabetes, and high-altitude exposure. We have previously shown that one can study angiogenesis in animal models by using total hemoglobin (tHb) as a marker of cerebral blood volume (CBV), measured using broadband near-infrared spectroscopy (bNIRS). However, the method was not suitable for patients as global anoxia was used for the calibration. Here we determine if angiogenesis could be detected using a calibration method that could be applied to patients. CBV, as a marker of angiogenesis, is quantified in a rat cortex before and after hypoxia acclimation. Rats are acclimated at 370-mmHg pressure for three weeks, while rats in the control group are housed under the same conditions, but under normal pressure. CBV increased in each animal in the acclimation group. The mean CBV (%volume/volume) is 3.49%±0.43% (mean±SD) before acclimation for the experimental group, and 4.76%±0.29% after acclimation. The CBV for the control group is 3.28%±0.75%, and 3.09%±0.48% for the two measurements. This demonstrates that angiogenesis can be monitored noninvasively over time using a bNIRS system with a calibration method that is compatible with human use and less stressful for studies using animals.

  19. Rapid profiling of enteric coated drug delivery spheres via broadband acoustic resonance dissolution spectroscopy (BARDS).

    PubMed

    Fitzpatrick, D; Evans-Hurson, R; Fu, Y; Burke, T; Krüse, J; Vos, B; McSweeney, S G; Casaubieilh, P; Keating, J J

    2014-03-07

    There is an increased trend towards the use of drug and enteric coated sugar spheres for controlled oral delivery of active pharmaceutical ingredients (API). This trend is driven by increased efficacy and ease of formulation of different dosage levels. However, difficulties exist in determining the thickness of drug and enteric coatings in a time efficient manner during manufacture, quality assurance and stability testing. The thickness of the coating determines the dosage of the API and the thickness of the enteric coating determines the release rate of the drug in the gastro-intestinal tract. Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) offers a rapid new approach to characterising the enteric coating thickness and the raw materials used in their manufacture. BARDS applications are based on reproducible changes in the compressibility of a solvent during dissolution which is monitored acoustically due to associated changes in the speed of sound in solution. It is demonstrated how core delivery sugar spheres have unique acoustic spectra attributable to the mean size distribution of the spheres. A steady state acoustic lag time is associated with the disintegration of the enteric coating, in basic solution. This lag time can be manipulated by varying the concentration of the base which affects the rate at which the coating dissolves. It is anticipated that the thickness/loading of the spheres can be estimated from the lag time.

  20. Evidence for a Complex Between Thf and Acetic Acid from Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zaleski, Daniel P.; Bittner, Dror M.; Mullaney, John Connor; Stephens, Susanna L.; King, Adrian; Habgood, Matthew; Walker, Nick

    2015-06-01

    Evidence for a complex between tetrahydrofuran (THF) and acetic acid from broadband rotational spectroscopy will be presented. Transitions believed to belong to the complex were first identified in a gas mixture containing small amounts of THF, triethyl borane, and acetic acid balanced in argon. Ab initio calculations suggest a complex between THF and acetic acid is more likely to form compared to the analogous acetic acid complex with triethyl borane, the initial target. The observed rotational constants are also more similar to those predicted for a complex formed between THF and acetic acid, than for those of a complex formed between triethyl borane and acetic acid. Subsequently, multiple isotopologues of acetic acid have been measured, confirming its presence in the structure. No information has yet been obtained through isotopic substitution within the THF sub-unit. Ab initio calculations predict the most likely structure is one where the acetic acid subunit coordinates over the ring creating a "bridge" between the THF oxygen, the carboxylic O-H, and the carbonyl oxygen to a hydrogen atom on the back of the ring.

  1. Broadband Infrared Spectroscopy for Non-Contact Measurement of Neurological Disease Biomarkers in Cerebrospinal Fluid.

    PubMed

    Horosh, Michael; Feldman, Haim; Yablonovich, Avi; Firer, Michael A; Abookasis, David

    2017-03-01

    Cerebrospinal fluid (CSF) is a clear and colorless biological fluid which circulates within brain ventricles (cavities), the spinal cord's central canal, the space between the brain and the spinal cord, as well as their protective coverings, the meninges. Cerebrospinal fluid contains different constituents, such as albumin and lactate, whose levels are used clinically as biomarkers of neurodegenerative disorders. In current clinical practice, analysis of CSF content for the diagnosis of central nervous system disorders requires an invasive procedure known as lumbar puncture or spinal tap. With the aim of developing a noninvasive alternative, we report here the spectral behavior of albumin and lactate over a broad wavelength range of 600-2000 nm, after each was added separately at varying normal and abnormal concentration levels to artificial CSF ( aCSF). Spectral measurements were conducted simultaneously by two different spectrometers working at different spectral ranges in transmittance mode. Spectral analysis revealed that albumin and lactate each possesses its own first and second derivative absorbance spectra fingerprint between 1660 and 1810 nm. Distinguishing albumin from lactate by their spectral data enabled the differentiation between aCSF conditions modeling different neurological disorders. Spectral changes of each compound strongly correlated ( R(2 )> 0.9) with absorbance derivative spectra peaks at specific wavelengths, when analyzed by linear regression with variations in their concentration. These findings suggest the feasibility of CSF biomarker assessment by broadband infrared spectroscopy.

  2. Incoherent broadband cavity-enhanced total internal reflection spectroscopy of surface-adsorbed metallo-porphyrins.

    PubMed

    Ruth, Albert A; Lynch, Kieran T

    2008-12-21

    An improvement of conventional attenuated total reflection (ATR) spectroscopy is demonstrated by applying an incoherent broadband light source (short-arc Xe-lamp) in a cavity-enhanced evanescent-wave absorption method. With this novel approach the absorption spectra of several metallo-octaethyl porphyrins (palladium (PdOEP), platinum (PtOEP) and zinc (ZnOEP)) in thin acetone solution layers and on a fused silica (FS) surface are studied between approximately 390 and 625 nm. The time dependence of the evaporation process of the solution on the FS surface is described. The maximum sensitivity of the setup is estimated at approximately 2 x 10(-5) per pass, which translates into a minimal detectable surface density of less than 2 x 10(-3) monolayers for the porphyrins studied (based on the strong absorption in the Soret bands). Changes of surface and solution spectra are characterised and discussed on the basis of observed band broadenings and spectral shifts. For Pd- and PtOEP the changes of spectral feature can be interpreted with respect to J-aggregate formation supported by polarization dependent measurements. The reason for an observed blue-shift of ca. 10 nm for the Soret band in ZnOEP in combination with a large red-shift of the Q-bands (11 nm for Q1 and 18 nm for Q2) is discussed.

  3. Incoherent broadband cavity-enhanced total internal reflection spectroscopy of surface-adsorbed metallo-porphyrins

    NASA Astrophysics Data System (ADS)

    Ruth, A. A.; Glaczynski, G.; Lynch, K. T.

    2009-04-01

    An improvement of conventional attenuated total reflection (ATR) spectroscopy is demonstrated by applying an incoherent broadband light source (short-arc Xe-lamp) in a cavity-enhanced evanescent-wave absorption method. With this novel approach the absorption spectra of several metallo-octaethyl porphyrins (Palladium (PdOEP), Platinum (PtOEP) and Zinc- (ZnOEP)) in thin acetone solution layers and on a fused silica (FS) surface were studied between 390 and 625 nm. The time dependence of the evaporation process of the solution on the FS surface is described. The maximum sensitivity of the setup is estimated at approximately 2 Ã- 10-5 per pass, which translates into a minimal detectable surface density of less than 2 Ã- 10-3 monolayers for the porphyrins studied (based on absorption in the strong Soret bands). Changes of surface and solution spectra are characterised and discussed on basis of observed band broadenings and spectral shifts. This new approach is of relevance for investigations in atmopsheric and planetary sciences involving absorbers on surfaces and heterogeneous chemistry.

  4. Infrared Phonon Fingerprinting of Nanocrystals through Broadband Near-Field Spectroscopy

    NASA Astrophysics Data System (ADS)

    McLeod, Alexander S.; Dominguez, Gerardo; Kelly, Priscilla; Thiemens, Mark; Zhang, Lingfeng M.; Rodin, Alex; Fogler, Michael M.; Keilmann, Fritz; Basov, D. N.

    2012-02-01

    Near-field infrared spectroscopy has recently been demonstrated with the capability to resolve optical properties of sub-wavelength sample areas across a broad range of infrared frequencies. This method holds promise for the direct identification of sub-wavelength chemical composition in nanostructured and heterogeneous samples. We apply this technique to the study of phonon-resonant silicon carbide nanocrystals tens of nanometers in size using an apertureless scanning near-field optical microscope (SNOM) coupled to a pulsed broadband infrared laser source and FTIR spectrometer. We present measurements of nanocrystal near-field spectra in the range of 700-1200 cm-1 evaluated in comparison with the near-field spectra of bulk silicon carbide, calibrated using ellipsometry. A detailed analytic model of the probe-sample near-field interaction is applied for the identification of nanoscale resonant size effects. These techniques provide a powerful method for identifying and characterizing sub-wavelength nanocrystals in heterogeneous samples via near-field infrared ``phonon fingerprinting.''

  5. Concentration measurements of complex mixtures of broadband absorbers by widely tunable optical parametric oscillator laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Ruxton, K.; Macleod, N. A.; Weidmann, D.; Malcolm, G. P. A.; Maker, G. T.

    2012-11-01

    The ability to obtain accurate vapour parameter information from a compound's absorption spectrum is an essential data processing application in order to quantify the presence of an absorber. Concentration measurements can be required for a variety of applications including environmental monitoring, pipeline leak detection, surface contamination and breath analysis. This work demonstrates sensitive concentration measurements of complex mixtures of volatile organic compounds (VOCs) using broadly tunable mid wave infrared (MWIR) laser spectroscopy. Due to the high absorption cross-sections, the MWIR spectral region is ideal to carry out sensitive concentration measurements of VOCs by tunable laser absorption spectroscopy (TLAS) methods. Absorption spectra of mixtures of VOCs were recorded using a MWIR optical parametric oscillator (OPO), with a tuning range covering 2.5 μm to 3.7 μm. The output of the MWIR OPO was coupled to a multi-pass astigmatic Herriott gas cell, maintained at atmospheric pressure that can provide up to 210 m of absorption path length, with the transmission output from the cell being monitored by a detector. The resulting spectra were processed by a concentration retrieval algorithm derived from the optimum estimation method, taking into account both multiple broadband absorbers and interfering molecules that exhibit narrow multi-line absorption features. In order to demonstrate the feasibility of the concentration measurements and assess the capability of the spectral processor, experiments were conducted on calibrated VOCs vapour mixtures flowing through the spectroscopic cell with concentrations ranging from parts per billion (ppb) to parts per million (ppm). This work represents as a first step in an effort to develop and apply a similar concentration fitting algorithm to hyperspectral images in order to provide concentration maps of the spatial distribution of multi-species vapours. The reported functionality of the novel fitting algorithm

  6. Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy.

    PubMed

    Brás, Ana R; Noronha, João P; Antunes, Alexandra M M; Cardoso, Maria M; Schönhals, Andreas; Affouard, Frédéric; Dionísio, Madalena; Correia, Natália T

    2008-09-04

    The molecular mobility of amorphous ibuprofen has been investigated by broadband dielectric relaxation spectroscopy (DRS) covering a temperature range of more than 200 K. Four different relaxation processes, labeled as alpha, beta, gamma, and D, were detected and characterized, and a complete relaxation map was given for the first time. The gamma-process has activation energy E a = 31 kJ.mol (-1), typical for local mobility. The weak beta-relaxation, observed in the glassy state as well as in the supercooled state was identified as the genuine Johari-Goldstein process. The temperature dependence of the relaxation time of the alpha-process (dynamic glass transition) does not obey a single VFTH law. Instead two VFTH regimes are observed separated by a crossover temperature, T B = 265 K. From the low temperature VFTH regime, a T g (diel) (tau =100 s) = 226 K was estimated, and a fragility or steepness index m = 93, was calculated showing that ibuprofen is a fragile glass former. The D-process has a Debye-like relaxation function but the temperature dependence of relaxation time also follows the VFTH behavior, with a Vogel temperature and a pre-exponential factor which seem to indicate that its dynamics is governed by the alpha-process. It has similar features as the Debye-type process observed in a variety of associating liquids, related to hydrogen bonding dynamics. The strong tendency of ibuprofen to form hydrogen bonded aggregates such as dimers and trimers either cyclic or linear which seems to control in particular the molecular mobility of ibuprofen was confirmed by IR spectroscopy, electrospray ionization mass spectrometry, and MD simulations.

  7. Ultra-Broadband Two-Dimensional Electronic Spectroscopy and Pump-Probe Microscopy of Molecular Systems

    NASA Astrophysics Data System (ADS)

    Spokoyny, Boris M.

    Ultrafast spectroscopy offers an unprecedented view on the dynamic nature of chemical reactions. From charge transfer in semiconductors to folding and isomerization of proteins, these all important processes can now be monitored and in some instances even controlled on real, physical timescales. One of the biggest challenges of ultrafast science is the incredible energetic complexity of most systems. It is not uncommon to encounter macromolecules or materials with absorption spectra spanning significant portions of the visible spectrum. Monitoring a multitude of electronic and vibrational transitions, all dynamically interacting with each other on femtosecond timescales poses a truly daunting experimental task. The first part of this thesis deals with the development of a novel Two-Dimensional Electronic Spectroscopy (2DES) and its associated, advanced detection methodologies. Owing to its ultra-broadband implementation, this technique enables us to monitor femtosecond chemical dynamics that span the energetic landscape of the entire visible spectrum. In order to demonstrate the utility of our method, we apply it to two laser dye molecules, IR-144 and Cresyl Violet. Variation of photophysical properties on a microscopic scale in either man-made or naturally occurring systems can have profound implications on how we understand their macroscopic properties. Recently, inorganic hybrid perovskites have been tapped as the next generation solar energy harvesting materials. Their remarkable properties include low exciton binding energy, low exciton recombination rates and long carrier diffusion lengths. Nevertheless, considerable variability in device properties made with nearly identical preparation methods has puzzled the community. In the second part of this thesis we use non-linear pump probe microscopy to study the heterogeneous nature of femtosecond carrier dynamics in thin film perovskites. We show that the local morphology of the perovskite thin films has a

  8. An ultra-broadband frequency-domain terahertz measurement system based on frequency conversion via DAST crystal with an optimized phase-matching condition

    NASA Astrophysics Data System (ADS)

    Qi, Feng; Fan, Shuzhen; Notake, Takashi; Nawata, Kouji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

    2014-08-01

    By applying the frequency conversion technique to 4-dimethylamino-N-methyl-4-stilbazolium tosylate crystal, a monochromatic terahertz (THz) measurement system, including both generation and detection, has been developed over quite a broad frequency band, from 1.85 to 30 THz. In the case of frequency upconversion detection of THz waves, for the first time, we used gratings instead of filters to tackle the tough phase-matching conditions for broadband operations. By synchronizing the rotation of two gratings to extract the frequency upconverted signal, the infrared (IR) pumping beam can be tuned freely over 300 nm with decent diffraction efficiency and sufficient isolation between the weak frequency upconversion signal and the strong IR pumping beam to be realized. Such a large tuning range has overcome the limit of commercial filters with a fixed passband, while such a high optical density value has been beyond the limit of commercial tunable filters. Consequently, the proposed frequency domain system gives the largest THz frequency band. Unlike THz time-domain spectroscopy systems in which a fs laser is applied and broadband THz pulses are applied, our system works based on a ns laser and it can function at a single THz frequency with random frequency access ability from pulse to pulse.

  9. Study on the THz spectrum of methamphetamine

    NASA Astrophysics Data System (ADS)

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

    2005-09-01

    The spectral absorption features of methamphetamine (MA), one of the most widely consumed illicit drugs in the world, are studied experimentally by Terahertz (THz) time-domain spectroscopy (THz-TDS), and the characteristic absorption spectra are obtained in the range of 0.2 to 2.6 THz. The vibrational frequencies are calculated using the density functional theory (DFT). Theoretical results show significant agreement with experimental results, and identification of vibrational modes are given. The calculated results further confirm that the characteristic frequencies come from the collective vibrational modes. The results suggest that use of the THz-TDS technique can be an effective way to inspect for illicit drugs.

  10. Revealing plasma oscillation in THz spectrum from laser plasma of molecular jet.

    PubMed

    Li, Na; Bai, Ya; Miao, Tianshi; Liu, Peng; Li, Ruxin; Xu, Zhizhan

    2016-10-03

    Contribution of plasma oscillation to the broadband terahertz (THz) emission is revealed by interacting two-color (ω/2ω) laser pulses with a supersonic jet of nitrogen molecules. Temporal and spectral shifts of THz waves are observed as the plasma density varies. The former owes to the changing refractive index of the THz waves, and the latter correlates to the varying plasma frequency. Simulation of considering photocurrents, plasma oscillation and decaying plasma density explains the broadband THz spectrum and the varying THz spectrum. Plasma oscillation only contributes to THz waves at low plasma density owing to negligible plasma absorption. At the longer medium or higher density, the combining effects of plasma oscillation and absorption results in the observed low-frequency broadband THz spectra.

  11. A THz Tomography System for Arbitrarily Shaped Samples

    NASA Astrophysics Data System (ADS)

    Stübling, E.; Bauckhage, Y.; Jelli, E.; Fischer, B.; Globisch, B.; Schell, M.; Heinrich, A.; Balzer, J. C.; Koch, M.

    2017-06-01

    We combine a THz time-domain spectroscopy system with a robotic arm. With this scheme, the THz emitter and receiver can be positioned perpendicular and at defined distance to the sample surface. Our system allows the acquisition of reflection THz tomographic images of samples with an arbitrarily shaped surface.

  12. A THz Tomography System for Arbitrarily Shaped Samples

    NASA Astrophysics Data System (ADS)

    Stübling, E.; Bauckhage, Y.; Jelli, E.; Fischer, B.; Globisch, B.; Schell, M.; Heinrich, A.; Balzer, J. C.; Koch, M.

    2017-10-01

    We combine a THz time-domain spectroscopy system with a robotic arm. With this scheme, the THz emitter and receiver can be positioned perpendicular and at defined distance to the sample surface. Our system allows the acquisition of reflection THz tomographic images of samples with an arbitrarily shaped surface.

  13. Metallic wave-impedance matching layers for broadband terahertz optical systems.

    PubMed

    Kröll, Josef; Darmo, Juraj; Unterrainer, Karl

    2007-05-28

    We examine the potential of ultra-thin metallic layers for broadband wave-impedance matching in the terahertz frequency range. The metallic layer is modeled using Fresnel formulae for stratified optical medium. Experimental data for chromium and indium-tin-oxide layers, measured using time-domain terahertz spectroscopy over the frequency range 0.4 - 4.5 THz, are compared with theoretical results.

  14. Using THz time-scale infrared spectroscopy to examine the role of collective, thermal fluctuations in the formation of myoglobin allosteric communication pathways and ligand specificity.

    PubMed

    Woods, K N

    2014-06-28

    In this investigation we use THz time-scale spectroscopy to conduct an initial set of studies on myoglobin with the aim of providing further insight into the global, collective thermal fluctuations in the protein that have been hypothesized to play a prominent role in the dynamic formation of transient ligand channels as well as in shaping the molecular level basis for ligand discrimination. Using the two ligands O2 and CO, we have determined that the perturbation from the heme-ligand complex has a strong influence on the characteristics of the myoglobin collective dynamics that are excited upon binding. Further, the differences detected in the collective protein motions in Mb-O2 compared with those in Mb-CO appear to be intimately tied with the pathways of long-range allosteric communication in the protein, which ultimately determine the trajectories selected by the respective ligands on the path to and from the heme-binding cavity.

  15. Broadband multi-layer terahertz metamaterials fabrication and characterization on flexible substrates.

    PubMed

    Han, N R; Chen, Z C; Lim, C S; Ng, B; Hong, M H

    2011-04-11

    Microscopic split-ring-resonator (SRR) arrays are fabricated on 100 μm thick polyethylene naphthalate (PEN) films by femtosecond laser micro-lens array (MLA) lithography. The transmission properties of these metamaterials are characterized by THz Time Domain Spectroscopy (THz-TDS). Tunable resonance responses can be achieved by changing SRR structural design parameters. By stacking 2D PEN metamaterial films with different frequency responses together, a broadband THz filter with full width at half maximum (FWHM) of 0.38 THz is constructed. The bandwidth of the resonance response increases up to 4.2 times as compared to the bandwidths of single layer metamaterials. Numerical simulation reveals that SRR layers inside the multi-layer metamaterials are selectively excited towards specific frequencies within the broadband response. Meanwhile, more than one SRR layers respond to the chosen frequencies, resulting in the enhancement of the resonance properties. The multi-layer metamaterials provide a promising way to extend SRR based metamaterial operating region from narrowband to broadband with a tunable feature.

  16. 3D Non-destructive Imaging of Punctures in Polyethylene Composite Armor by THz Time Domain Spectroscopy

    NASA Astrophysics Data System (ADS)

    Palka, N.; Panowicz, R.; Ospald, F.; Beigang, R.

    2015-08-01

    An ultra-high molecular weight polyethylene composite sample totally punctured by a projectile was examined by THz TDS raster scanning method in reflection configuration. The scanning results correctly match the distribution of delaminations inside the sample, which was proven with cross-sectional and frontal views after waterjet cutting. For further analysis, a signal-processing algorithm based on the deconvolution method was developed and the modified reference signal was used to reduce disturbances. The complex refractive index of the sample was determined by transmission TDS technique and was later used for the simulation of pulse propagation by the finite difference time domain method. These simulations verified the correctness of the proposed method and showed its constraints. Using the proposed algorithm, the ambiguous raw THz image was converted into a binary 3D image of the sample, which consists only of two areas: sample—polyethylene and delamination—air. As a result, a clear image of the distribution of delaminations with their spatial extent was obtained which can be used for further comparative analysis. The limitation of the proposed method is that parts of the central area of the puncture cannot be analyzed because tilted layers deflect the incident signal.

  17. Broadband dielectric spectroscopy of glucose aqueous solution: Analysis of the hydration state and the hydrogen bond network

    NASA Astrophysics Data System (ADS)

    Shiraga, Keiichiro; Suzuki, Tetsuhito; Kondo, Naoshi; Tajima, Takuro; Nakamura, Masahito; Togo, Hiroyoshi; Hirata, Akihiko; Ajito, Katsuhiro; Ogawa, Yuichi

    2015-06-01

    Recent studies of saccharides' peculiar anti-freezing and anti-dehydration properties point to a close association with their strong hydration capability and destructuring effect on the hydrogen bond (HB) network of bulk water. The underlying mechanisms are, however, not well understood. In this respect, examination of the complex dielectric constants of saccharide aqueous solutions, especially over a broadband frequency region, should provide interesting insights into these properties, since the dielectric responses reflect corresponding dynamics over the time scales measured. In order to do this, the complex dielectric constants of glucose solutions between 0.5 GHz and 12 THz (from the microwave to the far-infrared region) were measured. We then performed analysis procedures on this broadband spectrum by decomposing it into four Debye and two Lorentz functions, with particular attention being paid to the β relaxation (glucose tumbling), δ relaxation (rotational polarization of the hydrated water), slow relaxation (reorientation of the HB network water), fast relaxation (rotation of the non-HB water), and intermolecular stretching vibration (hindered translation of water). On the basis of this analysis, we revealed that the hydrated water surrounding the glucose molecules exhibits a mono-modal relaxational dispersion with 2-3 times slower relaxation times than unperturbed bulk water and with a hydration number of around 20. Furthermore, other species of water with distorted tetrahedral HB water structures, as well as increases in the relative proportion of non-HB water molecules which have a faster relaxation time and are not a part of the surrounding bulk water HB network, was found in the vicinity of the glucose molecules. These clearly point to the HB destructuring effect of saccharide solutes in aqueous solution. The results, as a whole, provide a detailed picture of glucose-water and water-water interactions in the vicinity of the glucose molecules at

  18. Broadband dielectric spectroscopy of glucose aqueous solution: Analysis of the hydration state and the hydrogen bond network.

    PubMed

    Shiraga, Keiichiro; Suzuki, Tetsuhito; Kondo, Naoshi; Tajima, Takuro; Nakamura, Masahito; Togo, Hiroyoshi; Hirata, Akihiko; Ajito, Katsuhiro; Ogawa, Yuichi

    2015-06-21

    Recent studies of saccharides' peculiar anti-freezing and anti-dehydration properties point to a close association with their strong hydration capability and destructuring effect on the hydrogen bond (HB) network of bulk water. The underlying mechanisms are, however, not well understood. In this respect, examination of the complex dielectric constants of saccharide aqueous solutions, especially over a broadband frequency region, should provide interesting insights into these properties, since the dielectric responses reflect corresponding dynamics over the time scales measured. In order to do this, the complex dielectric constants of glucose solutions between 0.5 GHz and 12 THz (from the microwave to the far-infrared region) were measured. We then performed analysis procedures on this broadband spectrum by decomposing it into four Debye and two Lorentz functions, with particular attention being paid to the β relaxation (glucose tumbling), δ relaxation (rotational polarization of the hydrated water), slow relaxation (reorientation of the HB network water), fast relaxation (rotation of the non-HB water), and intermolecular stretching vibration (hindered translation of water). On the basis of this analysis, we revealed that the hydrated water surrounding the glucose molecules exhibits a mono-modal relaxational dispersion with 2-3 times slower relaxation times than unperturbed bulk water and with a hydration number of around 20. Furthermore, other species of water with distorted tetrahedral HB water structures, as well as increases in the relative proportion of non-HB water molecules which have a faster relaxation time and are not a part of the surrounding bulk water HB network, was found in the vicinity of the glucose molecules. These clearly point to the HB destructuring effect of saccharide solutes in aqueous solution. The results, as a whole, provide a detailed picture of glucose-water and water-water interactions in the vicinity of the glucose molecules at

  19. Broadband diffuse optical spectroscopy assessment of hemorrhage- and hemoglobin-based blood substitute resuscitation

    NASA Astrophysics Data System (ADS)

    Lee, Jangwoen; Kim, Jae G.; Mahon, Sari; Tromberg, Bruce J.; Mukai, David; Kreuter, Kelly; Saltzman, Darin; Patino, Renee; Goldberg, Robert; Brenner, Matthew

    2009-07-01

    Hemoglobin-based oxygen carriers (HBOCs) are solutions of cell-free hemoglobin (Hb) that have been developed for replacement or augmentation of blood transfusion. It is important to monitor in vivo tissue hemoglobin content, total tissue hemoglobin [THb], oxy- and deoxy-hemoglobin concentrations ([OHb], [RHb]), and tissue oxygen saturation (StO2=[OHb]/[THb]×100%) to evaluate effectiveness of HBOC transfusion. We designed and constructed a broadband diffuse optical spectroscopy (DOS) prototype system to measure bulk tissue absorption and scattering spectra between 650 and 1000 nm capable of accurately determining these tissue hemoglobin component concentrations in vivo. Our purpose was to assess the feasibility of using DOS to optically monitor tissue [OHb], [RHb], StO2, and total tissue hemoglobin concentration ([THb]=[OHb]+[RHb]) during HBOC infusion using a rabbit hypovolemic shock model. The DOS prototype probe was placed on the shaved inner thigh muscle of the hind leg to assess concentrations of [OHb], [RHb], [THb], as well as StO2. Hemorrhagic shock was induced in intubated New Zealand white rabbits (N=6) by withdrawing blood via a femoral arterial line to 20% blood loss (10-15 cc/kg). Hemoglobin glutamer-200 (Hb-200) 1:1 volume resuscitation was administered following the hemorrhage. These values were compared against traditional invasive measurements, serum hemoglobin concentration (sHGB), systemic blood pressure, heart rate, and blood gases. DOS revealed increases of [THb], [OHb], and tissue hemoglobin oxygen saturation after Hb-200 infusion, while blood total hemoglobin values continued did not increase; we speculate, due to hyperosmolality induced hemodilution. DOS enables noninvasive in vivo monitoring of tissue hemoglobin and oxygenation parameters during shock and volume expansion with HBOC and potentially enables the assessment of efficacy of resuscitation efforts using artificial blood substitutes.

  20. Broadband Microwave Spectroscopy as a Tool to Study Dispersion Interactions in Camphor-Alcohol Systems

    NASA Astrophysics Data System (ADS)

    Fatima, Mariyam; Perez, Cristobal; Schnell, Melanie

    2016-06-01

    Many biological processes such as chemical recognition and protein folding are mainly controlled by the interplay between hydrogen bonds and dispersive forces. Broadband rotational spectroscopy studies of weakly bound complexes are able to accurately reveal the structures and internal dynamics of molecular clusters isolated in the gas phase. To investigate the influence of the interplay between different types of weak intermolecular interactions and how it controls the preferred active sites of an amphiphilic molecule, we are using camphor (C10H16O, 1,7,7-trimethylbicyclo[2.2.1]hepta-2-one) with different aliphatic alcohol systems. Camphor is a conformationally rigid bicyclic molecule endowed with considerable steric hindrance and has a single polar group (-C=O). The rotational spectrum of camphor and its structure has been previously reported [1] as well as multiple clusters with water [2]. In order to determine the structure of the camphor-alcohol complexes, we targeted low energy rotational transitions in the 2-8 GHz range under the isolated conditions of a molecular jet in the gas phase. The data obtained suggests that camphor forms one complex with methanol and two with ethanol, with differences in the intermolecular interaction in both complexes. With these results, we aim to study the shift in intermolecular interaction from hydrogen bonding to dispersion with the increase in the size of the aliphatic alcohol. [1] Z. Kisiel, et al., Phys. Chem. Chem. Phys., 5 (2003), 820-826. [2] C. Pérez, et al, J. Phys. Chem. Lett., 7 (2016), 154-160.

  1. Glass transition of partially crystallized gelatin-water mixtures studied by broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Sasaki, Kaito; Kita, Rio; Shinyashiki, Naoki; Yagihara, Shin

    2014-03-01

    The glass transition of partially crystallized gelatin-water mixtures was investigated for gelatin concentrations of 40 and 20 wt. % by broadband dielectric spectroscopy (BDS) in wide frequency (10 mHz-50 GHz) and temperature (113-298 K) ranges. Three dielectric relaxation processes were clearly observed. The origin of each relaxation process was the same as that observed for partially crystallized bovine serum albumin (BSA)-water mixtures [N. Shinyashiki et al., J. Phys. Chem. B 113, 14448 (2009)]. The relaxation process at the highest frequency is originated from uncrystallized water (UCW) in the hydration shell of gelatin. Its relaxation time is almost the same as that of water in uncrystallized system; water in various binary aqueous mixtures and confined water in nanoscale region. The relaxation process at the intermediate frequency is originated from ice, and its relaxation time and strength were similar to those for the relaxation of pure ice, particularly above 240 K. The glass transition temperature Tg, is defined by BDS measurement as the temperature at which dielectric relaxation time τ, is 100-1000 s. The relaxation process at the lowest frequency, Tg is approximately 200 K, is originated from the cooperative motion of water and gelatin. This relaxation is strong and has a similar relaxation strength to that of hydrated BSA. At Tg for the relaxation process involving the cooperative motion of gelatin and water, the temperature dependence of the relaxation process of UCW crosses over from Vogel-Fulcher behavior to Arrhenius behavior with decreasing temperature. A characteristic property of the gelatin-water mixture is a change in the temperature dependence of the relaxation time of the relaxation processes of hydrated gelatin at approximately 260 K.

  2. Broadband diffuse optical spectroscopy assessment of hemorrhage- and hemoglobin-based blood substitute resuscitation.

    PubMed

    Lee, Jangwoen; Kim, Jae G; Mahon, Sari; Tromberg, Bruce J; Mukai, David; Kreuter, Kelly; Saltzman, Darin; Patino, Renee; Goldberg, Robert; Brenner, Matthew

    2009-01-01

    Hemoglobin-based oxygen carriers (HBOCs) are solutions of cell-free hemoglobin (Hb) that have been developed for replacement or augmentation of blood transfusion. It is important to monitor in vivo tissue hemoglobin content, total tissue hemoglobin [THb], oxy- and deoxy-hemoglobin concentrations ([OHb], [RHb]), and tissue oxygen saturation (S(t)O(2)=[OHb][THb]x100%) to evaluate effectiveness of HBOC transfusion. We designed and constructed a broadband diffuse optical spectroscopy (DOS) prototype system to measure bulk tissue absorption and scattering spectra between 650 and 1000 nm capable of accurately determining these tissue hemoglobin component concentrations in vivo. Our purpose was to assess the feasibility of using DOS to optically monitor tissue [OHb], [RHb], S(t)O(2), and total tissue hemoglobin concentration ([THb]=[OHb]+[RHb]) during HBOC infusion using a rabbit hypovolemic shock model. The DOS prototype probe was placed on the shaved inner thigh muscle of the hind leg to assess concentrations of [OHb], [RHb], [THb], as well as S(t)O(2). Hemorrhagic shock was induced in intubated New Zealand white rabbits (N=6) by withdrawing blood via a femoral arterial line to 20% blood loss (10-15 cckg). Hemoglobin glutamer-200 (Hb-200) 1:1 volume resuscitation was administered following the hemorrhage. These values were compared against traditional invasive measurements, serum hemoglobin concentration (sHGB), systemic blood pressure, heart rate, and blood gases. DOS revealed increases of [THb], [OHb], and tissue hemoglobin oxygen saturation after Hb-200 infusion, while blood total hemoglobin values continued did not increase; we speculate, due to hyperosmolality induced hemodilution. DOS enables noninvasive in vivo monitoring of tissue hemoglobin and oxygenation parameters during shock and volume expansion with HBOC and potentially enables the assessment of efficacy of resuscitation efforts using artificial blood substitutes.

  3. Very High Power THz Radiation Sources.

    PubMed

    Carr, G L; Martin, M C; McKinney, W R; Jordan, K; Neil, G R; Williams, G P

    2003-06-01

    We report the production of high power (20watts average, ∼ 1 Megawatt peak) broadbandTHz light based on coherent emission fromrelativistic electrons. Such sources areideal for imaging, for high power damagestudies and for studies of non-linearphenomena in this spectral range. Wedescribe the source, presenting theoreticalcalculations and their experimentalverification. For clarity we compare thissource with one based on ultrafast lasertechniques.

  4. InGaAs Schottky barrier diode array detectors integrated with broadband antenna (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Park, Dong Woo; Lee, Eui Su; Park, Jeong-Woo; Kim, Hyun-Soo; Lee, Il-Min; Park, Kyung Hyun

    2017-02-01

    Terahertz (THz) waves have been actively studied for the applications of astronomy, communications, analytical science and bio-technologies due to their low energy and high frequency. For example, THz systems can carry more information with faster rates than GHz systems. Besides, THz waves can be applied to imaging, sensing, and spectroscopy. Furthermore, THz waves can be used for non-destructive and non-harmful tomography of living objects. In this reasons, Schottky barrier diodes (SBD) have been widely used as a THz detector for their ultrafast carrier transport, high responsivity, high sensitivity, and excellent noise equivalent power. Furthermore, SBD detectors envisage developing THz applications at low cost, excellent capability, and high yield. Since the major concerns in the THz detectors for THz imaging systems are the realizations of the real-time image acquisitions via a reduced acquisition time, rather than the conventional raster scans that obtains an image by pixel-by-pixel acquisitions, a line-scan based systems utilizes an array detector with an 1 × n SBD array is preferable. In this study, we fabricated the InGaAs based SBD array detectors with broadband antennas of log-spiral and square-spiral patterns. To optimize leakage current and ideality factor, the dependence to the doping levels of ohmic and Schottky layers have been investigated. In addition, the dependence to the capacitance and resistance to anode size are also examined as well. As a consequence, the real-time THz imaging with our InGaAs SBD array detector have been successfully obtained.

  5. Broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde

    NASA Astrophysics Data System (ADS)

    Washenfelder, R. A.; Attwood, A. R.; Flores, J. M.; Zarzana, K. J.; Rudich, Y.; Brown, S. S.

    2016-01-01

    Formaldehyde (CH2O) is the most abundant aldehyde in the atmosphere, and it strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH2O and nitrogen dioxide (NO2) using broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99930 ± 0.00003 (1- reflectivity = 700 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.43 km within the 1 m cell. We measure the cavity output over the 315-350 nm spectral region using a grating monochromator and charge-coupled device array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH2O and NO2 concentrations. Independent measurements of NO2 standard additions by broadband cavity-enhanced absorption spectroscopy and cavity ring-down spectroscopy agree within 2 % (slope for linear fit = 1.02 ± 0.03 with r2 = 0.998). Standard additions of CH2O measured by broadband cavity-enhanced absorption spectroscopy and calculated based on flow dilution are also well correlated, with r2 = 0.9998. During constant mixed additions of NO2 and CH2O, the 30 s measurement precisions (1σ) of the current configuration were 140 and 210 pptv, respectively. The current 1 min detection limit for extinction measurements at 315-350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and ground-based field experiments. Additionally, the instrument provides highly accurate, spectroscopically based trace gas detection that may complement higher precision techniques based on non

  6. Broadband femtosecond transient infrared spectroscopy using a 256 x 256 element indium antimonide focal-plane detector.

    PubMed

    Arrivo, S M; Kleiman, V D; Dougherty, T P; Heilweil, E J

    1997-10-01

    Application and characterization of large-format IR focal-plane arrays as detectors for ultrafast, high-resolution IR spectroscopy are discussed. We also present generation of broadband IR probe-reference pulses by use of collinear non-phase-matched geometry and shot-to-shot dual-track normalization to obtain transient spectra from broadly absorbing hydrogen-bonded systems. As much as 400-cm(-1)-wide coverage with 15-cm(-1) FWHM spectral resolution and +/-6.4 x 10(-4)(DOD = 3 x 10(-4)) baseline standard deviation (+/-1sigmas) is demonstrated near 2.9 microm.

  7. Broadband Spectroscopy of CO_2 Bands Near 2 μm Using a Femtosecond Mode-Locked Laser

    NASA Astrophysics Data System (ADS)

    Klose, Andrew; Maser, Daniel L.; Ycas, Gabriel; Diddams, Scott; Newbury, Nathan R.; Coddington, Ian

    2014-06-01

    The optical frequency comb provided in the output of a femtosecond, mode-locked laser has been employed for many applications, including broadband spectroscopic measurements of trace gases using a variety of detection techniques. One environmentally significant trace gas is CO_2, which has characteristic absorption bands near 1.6 μm and 2.0 μm. Continuous wave (cw) lasers have typically been used to measure CO_2 at atmospheric-level concentrations. However, a broadband frequency comb source can provide rapid, simultaneous and accurate measurements of multiple transitions without the need for mechanical scanning or frequency tuning. Previously, precision broadband spectroscopy was performed on CO_2 bands near 1.6 μm. However, the CO_2 absorption bands near 2 μm have nearly a ten-fold increase in line strength compared to the bands near 1.6 μm, making the 2 μm bands attractive candidates for precision measurements of CO_2 with improved signal-to-noise and reduced uncertainty. Here, broadband quantitative spectroscopy of CO_2 bands near 2 μm is pursued. The source that was developed consists of an Er:fiber oscillator, Er:doped fiber amplifier, and highly nonlinear optical fiber, which generates a broadband spectrum spanning from 1 to 2.2 μm with an average power of 270 mW. Over 70 mW of the optical power is contained in the 1.8-2.2 μm region relevant to the CO_2 measurement. After generation, the laser light is passed through laboratory gas cells or open air where the absorption features from the sample gas are imprinted onto the laser light. Initial detection efforts involve a virtually imaged phased array- (VIPA-)based spectrometer whose output is subsequently imaged on a InSb array detector. The bandwidth of the measured spectrum is 50 nm, limited by the size of the detector array. The characteristics of the spectrometer, including the detection limits and temporal resolution, will be presented. In addition, the progress towards the use of the present

  8. THz Dynamic Nuclear Polarization NMR

    PubMed Central

    Nanni, Emilio A.; Barnes, Alexander B.; Griffin, Robert G.; Temkin, Richard J.

    2013-01-01

    Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140–600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology. PMID:24639915

  9. THz Dynamic Nuclear Polarization NMR.

    PubMed

    Nanni, Emilio A; Barnes, Alexander B; Griffin, Robert G; Temkin, Richard J

    2011-08-29

    Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140-600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology.

  10. Development of a hybrid broadband NIRS/diffusion correlation spectroscopy system to monitor preterm brain injury (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Rajaram, Ajay; St. Lawrence, Keith; Diop, Mamadou

    2017-02-01

    In Canada, 8% of births occur prematurely. Preterm infants weighing less than 1500g are at a high risk of neurodevelopmental impairment: 5-10% develop major disabilities such as cerebral palsy and 40-50% show other cognitive and behavioural deficits. The brain is vulnerable to periods of low cerebral blood flow (CBF) that can impair energy metabolism and cause tissue damage. There is, therefore, a need for an efficient neuromonitoring system to alert the neonatal intensive care team to clinically significant changes in CBF and metabolism, before injury occurs. Optical technologies offer safe, non-invasive, and cost-effective methods for neuromonitoring. Cerebral oxygen saturation (ScO2) can be measured by exploiting the absorption properties of hemoglobin though Near-Infrared Spectroscopy (NIRS), and Diffuse Correlation Spectroscopy (DCS) can monitor CBF by tracking red blood cells. These measures can be combined to describe metabolism, a key indicator of tissue viability. In this study we present the development and testing of a hybrid broadband NIRS/DCS neuromonitor. This system is novel in its ability to simultaneously acquire broadband NIRS and DCS signals, providing a truly real-time measure of metabolism. Narrow bandpass and notch filters have been incorporated to diminish light contamination between the two modalities, preferentially filtering out each source from the opposing detector, allowing for an accurate measure of ScO2, CBF, and metabolism. With a broadband NIRS/DCS system, a real-time measure of CBF and metabolism within the developing brain can aid clinicians in monitoring events that precede brain injury, ultimately leading to better clinical outcomes.

  11. Observation of broadband terahertz wave generation from liquid water

    NASA Astrophysics Data System (ADS)

    Jin, Qi; E, Yiwen; Williams, Kaia; Dai, Jianming; Zhang, X.-C.

    2017-08-01

    Bulk liquid water is a strong absorber in the terahertz (THz) frequency range, due to which liquid water has historically been sworn off as a source for THz radiation. Here, we experimentally demonstrate the generation of broadband THz waves from liquid water excited by femtosecond laser pulses. Our measurements reveal the critical dependence of the THz field upon the relative position between the water film and the focal point of the laser beam. The THz radiation from liquid water shows distinct characteristics when compared with the THz radiation from air plasmas with single color optical excitation. First, the THz field is maximized with the laser beam of longer pulse durations. In addition, the p-polarized component of the emitted THz waves will be influenced by the polarization of the optical excitation beam. It is also shown that the energy of the THz radiation is linearly dependent on the excitation pulse energy.

  12. Image reconstruction of oxidized cerebral cytochrome C oxidase changes from broadband near-infrared spectroscopy data.

    PubMed

    Brigadoi, Sabrina; Phan, Phong; Highton, David; Powell, Samuel; Cooper, Robert J; Hebden, Jeremy; Smith, Martin; Tachtsidis, Ilias; Elwell, Clare E; Gibson, Adam P

    2017-04-01

    In diffuse optical tomography (DOT), overlapping and multidistance measurements are required to reconstruct depth-resolved images of oxy- ([Formula: see text]) and deoxy- (HHb) hemoglobin concentration changes occurring in the brain. These can be considered an indirect measure of brain activity, under the assumption of intact neurovascular coupling. Broadband systems also allow changes in the redox state of cytochrome c oxidase (oxCCO) to be measured, which can be an important biomarker when neurovascular coupling is impaired. We used DOT to reconstruct images of [Formula: see text], [Formula: see text], and [Formula: see text] from data acquired with a broadband system. Four healthy volunteers were measured while performing a visual stimulation task (4-Hz inverting checkerboard). The broadband system was configured to allow multidistance and overlapping measurements of the participants' visual cortex with 32 channels. A multispectral approach was employed to reconstruct changes in concentration of the three chromophores during the visual stimulation. A clear and focused activation was reconstructed in the left occipital cortex of all participants. The difference between the residuals of the three-chromophore model and of the two-chromophore model (recovering only [Formula: see text] and [Formula: see text]) exhibits a spectrum similar to that of oxCCO. These results form a basis for further studies aimed to further optimize image reconstruction of [Formula: see text].

  13. High-resolution broadband N2 coherent anti-Stokes Raman spectroscopy: comparison of measurements for conventional and modeless broadband dye lasers.

    PubMed

    Kuehner, Joel P; Woodmansee, Mark A; Lucht, Robert P; Dutton, J Craig

    2003-11-20

    We have performed high-resolution N2 coherent anti-Stokes Raman spectroscopy (CARS) measurements using a modeless dye laser (MDL) as the Stokes beam source to determine the effects of a reduction in mode noise on the accuracy and precision of the method. These results are compared with previous research that employed a conventional broadband dye laser (CBDL) as the Stokes beam source. A new spectral-fitting procedure was developed to avoid starting-point bias in the least-squares fitting results, which possibly had altered the previous measurements. Single-shot measurements of pressure were performed in a static-pressure vessel over the range of 0.1-4.0 atm to examine the pressure sensitivity of the technique. The precision of these measurements is a measure of the baseline noise level of the system, which sets the detection limit for flow-field pressure fluctuations. Centerline measurements of pressure and temperature in an underexpanded jet (Mj = 1.85) were also used to determine the performance of the technique in a compressible flow field. Our study represents the first known application, to our knowledge, of a MDL CARS system in a low-temperature, low-pressure supersonic environment. Improvements in accuracy for mean single-shot measurements and increased precision were found for pressure vessel conditions above 1.0 atm. For subatmospheric pressure vessel conditions (0.1-1.0 atm) and the underexpanded jet measurements, there was a decrease in accuracy and precision compared with the CBDL results. A comparison with the CBDL study is included, along with a discussion of the MDL system behavior.

  14. The time-dependent emission of molecular iodine from Laminaria Digitata measured with incoherent broadband cavity-enhanced absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Dixneuf, S.

    2009-04-01

    The release of molecular iodine (I2) from the oceans into the atmosphere has been recognized to correlate strongly with ozone depletion events and aerosol formation in the Marine Boundary Layer (MBL), which affects in turn global radiative forcing. The detailed mechanisms and dominant sources leading to the observed concentrations of I2 in the marine troposphere are still under intense investigation. In a recent campaign on the Irish west coast at Mace Head Atmospheric Research Station [1], it was found that significant levels of molecular iodine correlated with times of low tide, suggesting that the emission of air-exposed macro-algae may be a prime source of molecular iodine in coastal areas [2]. To further investigate this hypothesis we tried to detect the I2 emission of the brown seaweed Laminaria digitata, one of the most efficient iodine accumulators among living systems, directly by means of highly sensitive incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) [3]. IBBCEAS combines a good temporal and spatial resolution with high molecule-specific detection limits [4] comparable to that of typical LP-DOAS. IBBCEAS thus complements LP-DOAS in the search for sources of tropospheric trace gases. In this presentation the first direct observation of the time dependence of molecular iodine emission from Laminaria digitata will be shown. Plants were studied under naturally occurring stress for quasi in situ conditions for many hours. Surprisingly, the release of I2 occurs in short, strong bursts with quasi-oscillatory behaviour, bearing similarities to well known "iodine clock reactions". References [1] Saiz-Lopez A. & Plane, J. M. C. Novel iodine chemistry in the marine boundary layer. Geophys. Res. Lett. 31, L04112 (2004) doi:10.1029/2003GL019215. [2] McFiggans, G., Coe, H., Burgess, R., Allan, J., Cubison, M., Alfarra, M. R., Saunders, R., Saiz-Lopez, A., Plane, J. M. C., Wevill, D. J., Carpenter, L. J., Rickard, A. R. & Monks, P. S. Direct

  15. Broadband Mid-Infrared Stand-Off Reflection-Absorption Spectroscopy Using a Pulsed External Cavity Quantum Cascade Laser.

    PubMed

    Liu, Xunchen; Chae, Inseok; Miriyala, Naresh; Lee, Dongkyu; Thundat, Thomas; Kim, Seonghwan

    2017-07-01

    Broadband mid-infrared molecular spectroscopy is essential for detection and identification of many chemicals and materials. In this report, we present stand-off mid-infrared spectra of 1,3,5-trinitro-1,3,5-triazine or cyclotrimethylene trinitramine (RDX) residues on a stainless-steel surface measured by a broadband external cavity quantum cascade laser (QCL) system. The pulsed QCL is continuously scanned over 800 cm(-1) in the molecular fingerprint region and the amplitude of the reflection signal is measured by either a boxcar-averager-based scheme or a lock-in-amplifier-based scheme with 1 MHz and 100 kHz quartz crystal oscillators. The main background noise is due to the laser source instability and is around 0.1% of normalized intensity. The direct absorption spectra have linewidth resolution around 0.1 cm(-1) and peak height sensitivity around 10(-2) due to baseline interference fringes. Stand-off detection of 5-50 µg/cm(2) of RDX trace adsorbed on a stainless steel surface at the distance of 5 m is presented.

  16. Broadband UV spectroscopy system used for monitoring of SO 2 and NO emissions from thermal power plants

    NASA Astrophysics Data System (ADS)

    Zhang, Y. G.; Wang, H. S.; Somesfalean, G.; Wang, Z. Y.; Lou, X. T.; Wu, S. H.; Zhang, Z. G.; Qin, Y. K.

    2010-11-01

    A gas monitoring system based on broadband absorption spectroscopic techniques in the ultraviolet region is described and tested. The system was employed in real-time continuous concentration measurements of sulfur dioxide (SO 2) and nitric oxide (NO) from a 220-ton h -1 circulating fluidized bed (CFB) boiler in Shandong province, China. The emission coefficients (per kg of coal and per kWh of electricity) and the total emission of the two pollutant gases were evaluated. The measurement results showed that the emission concentrations of SO 2 and NO from the CFB boiler fluctuated in the range of 750-1300 mg m -3 and 100-220 mg m -3, respectively. Compared with the specified emission standards of air pollutants from thermal power plants in China, the values were generally higher for SO 2 and lower for NO. The relatively high emission concentrations of SO 2 were found to mainly depend on the sulfur content of the fuel and the poor desulfurization efficiency. This study indicates that the broadband UV spectroscopy system is suitable for industrial emission monitoring and pollution control.

  17. Applying Broadband Dielectric Spectroscopy (BDS) for the Biophysical Characterization of Mammalian Tissues under a Variety of Cellular Stresses

    PubMed Central

    Souli, Maria P.; Klonos, Panagiotis; Fragopoulou, Adamantia F.; Mavragani, Ifigeneia V.; Pateras, Ioannis S.; Kostomitsopoulos, Nikolaos; Margaritis, Lukas H.; Zoumpoulis, Pavlos; Kaklamanis, Loukas; Kletsas, Dimitris; Gorgoulis, Vassilis G.; Kyritsis, Apostolos; Pissis, Polycarpos; Georgakilas, Alexandros G.

    2017-01-01

    The dielectric properties of biological tissues can contribute non-invasively to a better characterization and understanding of the structural properties and physiology of living organisms. The question we asked, is whether these induced changes are effected by an endogenous or exogenous cellular stress, and can they be detected non-invasively in the form of a dielectric response, e.g., an AC conductivity switch in the broadband frequency spectrum. This study constitutes the first methodological approach for the detection of environmental stress-induced damage in mammalian tissues by the means of broadband dielectric spectroscopy (BDS) at the frequencies of 1–106 Hz. Firstly, we used non-ionizing (NIR) and ionizing radiation (IR) as a typical environmental stress. Specifically, rats were exposed to either digital enhanced cordless telecommunication (DECT) radio frequency electromagnetic radiation or to γ-radiation, respectively. The other type of stress, characterized usually by high genomic instability, was the pathophysiological state of human cancer (lung and prostate). Analyzing the results of isothermal dielectric measurements provided information on the tissues’ water fraction. In most cases, our methodology proved sufficient in detecting structural changes, especially in the case of IR and malignancy. Useful specific dielectric response patterns are detected and correlated with each type of stress. Our results point towards the development of a dielectric-based methodology for better understanding and, in a relatively invasive way, the biological and structural changes effected by radiation and developing lung or prostate cancer often associated with genomic instability. PMID:28420124

  18. Set-up for broadband Fourier-transform multidimensional electronic spectroscopy.

    PubMed

    Al Haddad, A; Chauvet, A; Ojeda, J; Arrell, C; van Mourik, F; Auböck, G; Chergui, M

    2015-02-01

    We present a compact passively phase-stabilized ultra-broadband 2D Fourier transform setup. A gas (argon)-filled hollow core fiber pumped by an amplified Ti:Al2O3 laser is used as a light source providing spectral range spanning from 420 to 900 nm. Sub-10-fs pulses were obtained using a deformable mirror-based pulse shaper. We probe the nonlinear response of Rhodamine 101 using 90 nm bandwidth and resolve vibrational coherences of 150 fs period in the ground state.

  19. Broadband 308 nm vibrational Raman spectroscopy of gaseous species using a potassium hydrogen phthalate liquid filter and polarization fluorescence suppression.

    PubMed

    Saunders, J E A; Davy, M H

    2010-01-01

    Broadband XeCl excimer lasers operating at 308 nm are not currently used in the field of gas phase vibrational Raman spectroscopy (VRS). An explanation as to why alternative wavelengths, and in particular tuneable, narrowband lasers are currently preferred for gas phase VRS is presented in addition to demonstrating a setup which makes the XeCl laser a viable alternative when considering excitation sources for VRS. A solution of potassium hydrogen phthalate is shown to be a practical low-pass liquid filter and to reduce substantially the effects of Rayleigh scattering on collected Raman spectra. The use of a commercial beam polarizer is also shown to be effective in suppressing background fluorescence that otherwise necessitates the use of expensive tuneable, narrowband lasers when performing VRS with sources of background fluorescence. Finally, an unconventional excitation beam arrangement is shown to produce viable Raman spectra from which species concentrations and distributions can be determined.

  20. Influence of the cavity parameters on the output intensity in incoherent broadband cavity-enhanced absorption spectroscopy.

    PubMed

    Fiedler, Sven E; Hese, Achim; Heitmann, Uwe

    2007-07-01

    The incoherent broadband cavity-enhanced absorption spectroscopy is a technique in measuring small absorptions over a broad wavelength range. The setup consists of a conventional absorption spectrometer using an incoherent lamp and a charge coupled device detector, as well as a linear optical cavity placed around the absorbing sample, which enhances the effective path length through the sample. In this work the consequences of cavity length, mirror curvature, reflectivity, different light injection geometries, and spot size of the light source on the output intensity are studied and the implications to the signal-to-noise ratio of the absorption measurement are discussed. The symmetric confocal resonator configuration is identified as a special case with optimum imaging characteristics but with higher requirements for mechanical stability. Larger spot sizes of the light source were found to be favorable in order to reduce the negative effects of aberrations on the intensity.

  1. 3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure

    NASA Astrophysics Data System (ADS)

    Vogt, Dominik Walter; Leonhardt, Rainer

    2016-11-01

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

  2. Non-destructive Analysis of Material Detachments from Polychromatically Glazed Terracotta Artwork by THz Time-of-Flight Spectroscopy

    NASA Astrophysics Data System (ADS)

    Krügener, Kirsti; Busch, Stefan F.; Soltani, Amin; Castro-Camus, Enrique; Koch, Martin; Viöl, Wolfgang

    2016-11-01

    The damage caused by the environment to exposed glazed terracotta objects is usually not externally visible. For instance, the detachment of the glaze owing to subsurface crack formation or whole cavities in the area of the terracotta cannot be located visually. In this article, we demonstrate that terahertz time-of-flight spectroscopy is suitable to locate and measure the air gaps under the glaze detachments which could only be done by X-ray axial tomography before. This tool will be very useful to guide the restoration process, particularly for pieces that are still attached to buildings or other structures that cannot be transported to a tomography facility.

  3. Non-destructive Analysis of Material Detachments from Polychromatically Glazed Terracotta Artwork by THz Time-of-Flight Spectroscopy

    NASA Astrophysics Data System (ADS)

    Krügener, Kirsti; Busch, Stefan F.; Soltani, Amin; Castro-Camus, Enrique; Koch, Martin; Viöl, Wolfgang

    2017-04-01

    The damage caused by the environment to exposed glazed terracotta objects is usually not externally visible. For instance, the detachment of the glaze owing to subsurface crack formation or whole cavities in the area of the terracotta cannot be located visually. In this article, we demonstrate that terahertz time-of-flight spectroscopy is suitable to locate and measure the air gaps under the glaze detachments which could only be done by X-ray axial tomography before. This tool will be very useful to guide the restoration process, particularly for pieces that are still attached to buildings or other structures that cannot be transported to a tomography facility.

  4. Singular Value Decomposition-Based Modeling of Time Domain Signals in Broadband Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Minei, A. J.; Cooke, S. A.

    2013-06-01

    A singular value decomposition (SVD) signal processing method is newly applied to molecular free induction decays (FIDs) obtained using a time domain, broadband rotational spectrometer. It is demonstrated that for the strongest spectral transitions the SVD method can determine transition frequencies with a precision matching that of the fast Fourier transform method. Furthermore, the SVD-based analysis produces information concerning transition phase, amplitude, damping, and frequency for the strongest molecular signals. These parameters are shown as useful in regards to time-domain signal filtering. The computational expense of the SVD method is high and therefore this approach has the disadvantage that with our present computers the full molecular FID must be considerably truncated. The effects of FID truncation on the determined transition frequencies have been examined. Conversely, this truncation method illustrates that broadband spectra may be recovered from fragments as small as 1 % of the complete FID. The success of the SVD-based method is further examined in regards to weak signal detection, and frequency dependent detection. The pure rotational spectrum of 1H,1H,2H-perfluorocyclobutane is used for illustrative purposes in this study.

  5. High-resolution broadband spectroscopy with a resonator-based phase modulator.

    PubMed

    Berger, Naum K

    2013-07-01

    A method for significant enhancement of the spectral resolution of a Fabry-Perot resonator in transmission and absorption measurements is proposed. In the method, a laser with ultrashort pulses is used as the optical source. A dispersive element is placed in front of the Fabry-Perot resonator and a phase modulator is incorporated into the resonator. The spectrum of the laser pulse transmitted through the system is approximately periodic with ultranarrow peaks. The sample transmission spectrum is measured by scanning the output pulse spectrum. It is demonstrated, in numerical simulations, that for realistic parameters of the phase modulator, the finesse of the Fabry-Perot resonator is increased from 72 to 1900 and a resolution of 1 MHz is achieved. A method for increasing the spectral range of measurements with scanning the periodic spectra is also proposed. The method is based on the use of a waveguide array of Mach-Zehnder interferometers or a single discretely tunable interferometer. The measurement of the sample transmission spectrum within 33 free spectral ranges of the resonator is numerically demonstrated. The spectral range of the measurement can be increased up to 10 THz resulting in the equivalent finesse of the system of 10(7) for a 100 fs laser pulse.

  6. Very high power THz radiation sources

    SciTech Connect

    Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

    2002-10-31

    We report the production of high power (20 watts average, {approx} 1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source to one based on ultrafast laser techniques.

  7. Very High Power THz Radiation Sources

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-10-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity, we compare this sources with one based on ultrafast laser techniques.

  8. High-speed multi-THz-range mode-hop-free tunable mid-IR laser spectrometer.

    PubMed

    Courtois, Jérémie; Bouchendira, Rym; Cadoret, Malo; Ricciardi, Iolanda; Mosca, Simona; De Rosa, Maurizio; De Natale, Paolo; Zondy, Jean-Jacques

    2013-06-01

    We report on a widely (2.25 THz or 75 cm(-1)) and rapidly (4.5 THz/s) mode-hop-free (MHF) tunable mid-IR laser source at ~3.3 μm, consisting of a 5%-MgO:LiNbO(3) singly resonant optical parametric oscillator (SRO) pumped by an automated broadly MHF tunable extended-cavity diode laser (ECDL). The broad and rapid MHF tuning capability of the ECDL is readily transferred to the SRO idler wave owing to the quasi-noncritical pump spectral acceptance bandwidth of the quasi-phase-matching. Fast and broadband high-resolution Doppler spectroscopy measurements of the ν(3) band of CH(4) are presented to illustrate the performance of the mid-IR optical parametric oscillator spectrometer.

  9. Optical properties of human nails in THz frequency range

    NASA Astrophysics Data System (ADS)

    Guseva, Victoria A.; Gusev, Sviatoslav I.; Demchenko, Petr S.; Sedykh, Egor A.; Khodzitsky, Mikhail K.

    2017-03-01

    This work is devoted to investigation of optical properties (dispersion of refractive index, permittivity and absorption coefficient) of human nails in THz frequency range. These data were obtained by THz time-domain spectroscopy (TDS) technique in transmission mode. These results may be used to develop non-invasive technique of human pathologies control using nail as reference sample in reflection mode of THz TDS.

  10. Broadband absorption spectroscopy by combining frequency-domain and steady-state techniques

    NASA Astrophysics Data System (ADS)

    Berger, Andrew J.; Bevilacqua, Frederic; Jakubowski, Dorota B.; Cerussi, Albert E.; Butler, John A.; Hsiang, D.; Tromberg, Bruce J.

    2001-06-01

    A technique for measuring broadband near-infrared absorption spectra of turbid media is presented using a combination of frequency-domain (FD) and steady-state (SS) reflectance methods. Most of the wavelength coverage is provided by a white-light SS measurement, while the FD data are acquired at a few selected wavelengths. Coefficients of absorption ((mu) a) and reduced scattering ((mu) s') derived from the FD data are used to intensity-calibrate the SS measurements and to estimate (mu) s' at all wavelengths in the spectral window of interest. After these steps are performed, (mu) a can be determined by comparing the SS reflectance values to the predictions of diffusion theory, wavelength by wavelength. We present an application of this method to breast tumor characterization. A case study of a fibroadenoma is shown, where different absorption spectra were found between the normal and the tumor sides.

  11. Near-infrared broad-band cavity enhanced absorption spectroscopy using a superluminescent light emitting diode.

    PubMed

    Denzer, W; Hamilton, M L; Hancock, G; Islam, M; Langley, C E; Peverall, R; Ritchie, G A D

    2009-11-01

    A fibre coupled near-infrared superluminescent light emitting diode that emits approximately 10 mW of radiation between 1.62 and 1.7 microm is employed in combination with a broad-band cavity enhanced spectrometer consisting of a linear optical cavity with mirrors of reflectivity approximately 99.98% and either a dispersive near-infrared spectrometer or a Fourier transform interferometer. Results are presented on the absorption of 1,3-butadiene, and sensitivities are achieved of 6.1 x 10(-8) cm(-1) using the dispersive spectrometer in combination with phase-sensitive detection, and 1.5 x 10(-8) cm(-1) using the Fourier transform interferometer (expressed as a minimum detectable absorption coefficient) over several minutes of acquisition time.

  12. Broad-Band X-Ray Telescope spectroscopy of Xi Puppis

    NASA Technical Reports Server (NTRS)

    Corcoran, M. F.; Swank, J. H.; Serlemitsos, P. J.; Boldt, E.; Petre, R.; Marshall, F. E.; Jahoda, K.; Mushotzky, R.; Szymkowiak, A.; Arnaud, K.

    1993-01-01

    The Broad-Band X-Ray Telescope obtained moderate-resolution (about 90 eV) X-ray spectra of the O4 f star Xi Pup during the STS 35/Astro 1 mission in 1990 December. Despite the shortness of the observation (600 s), the data show a surprising amount of detail. We report the detection of an O absorption edge produced by ionized overlying wind material and K-shell line emission from Mg produced by a thermal plasma of temperature near 6 x 10 exp 6 K. The data are used to place constraints on the location, temperature, and amount of the X-ray-emitting gas, as well as the abundance and ionization of the wind material.

  13. Broadband spectroscopy of magnetic response in a nano-scale magnetic wire

    NASA Astrophysics Data System (ADS)

    Yamaguchi, A.; Motoi, K.; Miyajima, H.; Utsumi, Y.

    2014-09-01

    We measure the broadband spectra of magnetic response in a single layered ferromagnetic nano-scale wire in order to investigate the size effect on the ferromagnetic resonance. We found that the resonance frequency difference between 300-nm- and 5-μm-wide wires was varied by about 5 GHz due to the shape anisotropy. Furthermore, we experimentally detected the magnetization precession induced by the thermal fluctuation via the rectification of a radio-frequency (rf) current by incorporating an additional direct current (dc) by using Wheatstone bridge circuit. Our investigation renders that the shape anisotropy is of great importance to control the resonance frequency and to provide thermal stability of the microwave devices.

  14. A Dark-field Scanning In Situ Spectroscopy Platform for Broadband Imaging of Resected Tissue

    PubMed Central

    Krishnaswamy, Venkataramanan; Laughney, Ashley M.; Paulsen, Keith D.; Pogue, Brian W.

    2012-01-01

    A dark-field geometry spectral imaging system is presented to raster-scan thick tissue samples in situ in 1.5cm square sections, recovering full spectra from each 100 microns diameter pixel. This spot size provides adequate resolution for wide field scanning, while also facilitating scatter imaging without requiring sophisticated light-tissue transport modeling. The system is demonstrated showing accurate estimation of localized scatter parameters and the potential to recover absorption-based contrast from broadband reflectance data measured from 480nm up to 750nm in tissue phantoms. Results obtained from xenograft pancreas tumors show the ability to quantitatively image changes in localized scatter response in this fast imaging geometry. The polychromatic raster scan design allows the rapid scanning necessary for use in surgical/clinical applications where timely decisions are required about tissue pathology. PMID:21593932

  15. Compact, high-repetition-rate source for broadband sum-frequency generation spectroscopy

    NASA Astrophysics Data System (ADS)

    Heiner, Zsuzsanna; Petrov, Valentin; Mero, Mark

    2017-06-01

    We present a high-efficiency optical parametric source for broadband vibrational sum-frequency generation (BB-VSFG) for the chemically important mid-infrared spectral range at 2800-3600 cm-1 to study hydrogen bonding interactions affecting the structural organization of biomolecules at water interfaces. The source consists of a supercontinuum-seeded, dual-beam optical parametric amplifier with two broadband infrared output beams and a chirped sum-frequency mixing stage providing narrowband visible pulses with adjustable bandwidth. Utilizing a pulse energy of only 60 μJ from a turn-key, 1.03-μm pump laser operating at a repetition rate of 100 kHz, the source delivers 6-cycle infrared pulses at 1.5 and 3.2 μm with pulse energies of 4.6 and 1.8 μJ, respectively, and narrowband pulses at 0.515 μm with a pulse energy of 5.0 μJ. The 3.2-μm pulses are passively carrier envelope phase stabilized with fluctuations at the 180-mrad level over a 10-s time period. The 1.5-μm beamline can be exploited to deliver pump pulses for time-resolved studies after suitable frequency up-conversion. The high efficiency, stability, and two orders of magnitude higher repetition rate of the source compared to typically employed systems offer great potential for providing a boost in sensitivity in BB-VSFG experiments at a reduced cost.

  16. BROADBAND X-RAY IMAGING AND SPECTROSCOPY OF THE CRAB NEBULA AND PULSAR WITH NuSTAR

    SciTech Connect

    Madsen, Kristin K.; Harrison, Fiona; Grefenstette, Brian W.; Reynolds, Stephen; An, Hongjun; Boggs, Steven; Craig, William W.; Zoglauer, Andreas; Christensen, Finn E.; Fryer, Chris L.; Hailey, Charles J.; Nynka, Melania; Markwardt, Craig; Zhang, William; Stern, Daniel

    2015-03-01

    We present broadband (3-78 keV) NuSTAR X-ray imaging and spectroscopy of the Crab nebula and pulsar. We show that while the phase-averaged and spatially integrated nebula + pulsar spectrum is a power law in this energy band, spatially resolved spectroscopy of the nebula finds a break at ∼9 keV in the spectral photon index of the torus structure with a steepening characterized by ΔΓ ∼ 0.25. We also confirm a previously reported steepening in the pulsed spectrum, and quantify it with a broken power law with break energy at ∼12 keV and ΔΓ ∼ 0.27. We present spectral maps of the inner 100'' of the remnant and measure the size of the nebula as a function of energy in seven bands. These results find that the rate of shrinkage with energy of the torus size can be fitted by a power law with an index of γ = 0.094 ± 0.018, consistent with the predictions of Kennel and Coroniti. The change in size is more rapid in the NW direction, coinciding with the counter-jet where we find the index to be a factor of two larger. NuSTAR observed the Crab during the latter part of a γ-ray flare, but found no increase in flux in the 3-78 keV energy band.

  17. Reaction Product Identification in Extreme Chemical Environments by Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pate, Brooks

    Molecular rotational spectroscopy has several advantages for detection of reaction intermediates and products under extreme laboratory conditions. Rotational spectroscopy has high sensitivity to the molecular structure and provides high spectral resolution in low pressure environments. Furthermore, quantum chemistry provides accurate estimates of the spectroscopic parameters. As a result, rotational spectroscopy can identify molecular species in complex reaction mixtures without the need for chromatographic separation and without the need for a previously recorded ``library spectrum'' of the molecule. The application of chirped pulse Fourier transform rotational spectroscopy methods for the identification of molecules of astrochemical interest formed in pulsed discharge sources will be described including recent advances for high-throughput mm-wave spectroscopy. The set of reaction products created in the experiment can provide insight into the reaction mechanism. Reactions involving the CN radical will be discussed. These reactions can be barrierless making them candidates for interstellar gas reactions. The possibility that interstellar cyanomethanimine is produced by gas phase radical-neutral reactions instead of surface chemistry on grain-supported ices will be discussed using recent spatially resolved chemical images in Sagittarius B2 observed with the Jansky Very Large Array. This work supported by NSF CHE 1213200.

  18. High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers

    PubMed Central

    Khanal, Sudeep; Gao, Liang; Zhao, Le; Reno, John L.; Kumar, Sushil

    2016-01-01

    Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, terahertz QCLs with bidirectional operation are developed to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport in the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Broadband lasing in the frequency range of 3.1–3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. These are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays. PMID:27615416

  19. High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers

    NASA Astrophysics Data System (ADS)

    Khanal, Sudeep; Gao, Liang; Zhao, Le; Reno, John L.; Kumar, Sushil

    2016-09-01

    Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, terahertz QCLs with bidirectional operation are developed to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport in the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Broadband lasing in the frequency range of 3.1-3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. These are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays.

  20. High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers.

    PubMed

    Khanal, Sudeep; Gao, Liang; Zhao, Le; Reno, John L; Kumar, Sushil

    2016-09-12

    Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, terahertz QCLs with bidirectional operation are developed to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport in the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Broadband lasing in the frequency range of 3.1-3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. These are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays.

  1. High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers

    SciTech Connect

    Khanal, Sudeep; Gao, Liang; Zhao, Le; Reno, John L.; Kumar, Sushil

    2016-09-12

    Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, we develop terahertz QCLs with bidirectional operation to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport in the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Furthermore, broadband lasing in the frequency range of 3.1–3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. Finally, these are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays.

  2. High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers

    SciTech Connect

    Khanal, Sudeep; Gao, Liang; Zhao, Le; Reno, John L.; Kumar, Sushil

    2016-09-12

    Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, we develop terahertz QCLs with bidirectional operation to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport in the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Furthermore, broadband lasing in the frequency range of 3.1–3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. Finally, these are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays.

  3. High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers

    DOE PAGES

    Khanal, Sudeep; Gao, Liang; Zhao, Le; ...

    2016-09-12

    Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, we develop terahertz QCLs with bidirectional operation to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport inmore » the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Furthermore, broadband lasing in the frequency range of 3.1–3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. Finally, these are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays.« less

  4. Analysis of propagation properties of terahertz hollow-optical fiber by using time-domain spectroscopy and application for THz wave remote spectroscopy

    NASA Astrophysics Data System (ADS)

    Ito, K.; Katagiri, T.; Matsuura, Y.

    2017-02-01

    Terahertz pulse propagation in hollow optical fibers is investigated by using terahertz time-domain spectroscopy. From evaluation of transmission loss spectra of hollow optical fiber, it is found that TM11 mode propagates as well as TE11 mode that is the lowest order mode in terahertz metal-hollow fiber. Short-time Fourier transform is also applied for investigation of mode properties and as a result, it is confirmed that the interference peaks in the loss spectra are due to mode mixing in hollow optical fibers. Finally we performed a terahertz wave remote spectroscopy using the hollow optical fiber and acquired a clear transmission spectrum of the theophylline.

  5. Sample cells for probing solid/liquid interfaces with broadband sum-frequency-generation spectroscopy

    NASA Astrophysics Data System (ADS)

    Verreault, Dominique; Kurz, Volker; Howell, Caitlin; Koelsch, Patrick

    2010-06-01

    Two sample cells designed specifically for sum-frequency-generation (SFG) measurements at the solid/liquid interface were developed: one thin-layer analysis cell allowing measurement of films on reflective metallic surfaces through a micrometer layer of solution and one spectroelectrochemical cell allowing investigation of processes at the indium tin oxide/solution interface. Both sample cells are described in detail and data illustrating the capabilities of each are shown. To further improve measurements at solid/liquid interfaces, the broadband SFG system was modified to include a reference beam which can be measured simultaneously with the sample signal, permitting background correction of SFG spectra in real time. Sensitivity tests of this system yielded a signal-to-noise ratio of 100 at a surface coverage of 0.2 molecules/nm2. Details on data analysis routines, pulse shaping methods of the visible beam, as well as the design of a purging chamber and sample stage setup are presented. These descriptions will be useful to those planning to set up a SFG spectrometer or seeking to optimize their own SFG systems for measurements of solid/liquid interfaces.

  6. Rapid, broadband spectroscopic temperature measurement of hbox {CO}_2 using VIPA spectroscopy

    NASA Astrophysics Data System (ADS)

    Klose, Andrew; Ycas, Gabriel; Cruz, Flavio C.; Maser, Daniel L.; Diddams, Scott A.

    2016-04-01

    Time-resolved spectroscopic temperature measurements of a sealed carbon dioxide sample cell were realized with an optical frequency comb combined with a two-dimensional dispersive spectrometer. A supercontinuum laser source based on an erbium fiber mode-locked laser was employed to generate coherent light around 2000 nm (5000hbox { cm}^{-1}). The laser was passed through a 12-cm-long cell containing hbox {CO}_2, and the transmitted light was analyzed in a virtually imaged phased array-based spectrometer. Broadband spectra spanning more than 100hbox { cm}^{-1 } with a spectral resolution of roughly 0.075hbox { cm}^{-1} (2.2 GHz) were acquired with an integration period of 2 ms. The temperature of the hbox {CO}_2 sample was deduced from fitting a modeled spectrum to the line intensities of the experimentally acquired spectrum. Temperature dynamics on the timescale of milliseconds were observed with a temperature resolution of 2.6 K. The spectroscopically deduced temperatures agreed with temperatures of the sample cell measured with a thermistor. Potential applications of this technique include quantitative measurement of carbon dioxide concentration and temperature dynamics in gas-phase chemical reactions (e.g., combustion) and plasma diagnostics.

  7. Online tissue discrimination for transcutaneous needle guidance applications using broadband impedance spectroscopy.

    PubMed

    Trebbels, Dennis; Fellhauer, Felix; Jugl, Michael; Haimerl, Gerd; Min, Mart; Zengerle, Roland

    2012-02-01

    This paper reports on a novel system architecture for measuring impedance spectra of a biological tissue close to the tip of a hollow needle. The measurement is performed online using fast broadband chirp signals. The time domain measurement raw data are transformed into the transfer function of the tissue in frequency domain. Correlation technique is used to analyze the characteristic shape of the derived tissue transfer function with respect to known "library functions" for different types of tissue derived in earlier experiments. Based on the resulting correlation coefficients the exact type of tissue is determined. A bipolar coaxial needle is constructed, simulated by finite element method and tested during various in vitro and in vivo experiments. The results show a good spatial resolution of approximately 1.0 mm for a needle with a diameter of 2.0 mm. The correlation coefficients for the three tested tissue types muscle, fat, and blood allow for a clear tissue classification. Best results have been obtained using the characteristic phase diagrams for each tissue. Correlated to the corresponding library transfer function the coefficients are in the range of +0.96 to +0.99 for the matching tissue. In return, the resulting coefficients for correlation with nonmatching tissues are in the range of -0.93 to +0.81. © 2011 IEEE

  8. Hydrogen Bond Network Isomers of the Water Nonamer and Decamer Observed by Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Perez, Cristobal; Zaleski, Daniel P.; Seifert, Nathan A.; Pate, Brooks H.; Kisiel, Zbigniew; Temelso, Berhane; Shields, George C.

    2013-06-01

    After our previous study of the rotational spectrum of water clusters in the 6-18 GHz region, in order to study clusters of larger size (>8 water molecules), a chirped-pulse Fourier transform microwave spectrometer in the 2-8 GHz frequency range has been used to obtain the broadband rotational spectra of five water nonamer isomers and four water decamer isomers in a pulsed molecular beam. The oxygen atom framework geometries for three nonamers and two decamers have also been unambiguously identified from isotopic labeling measurements using an H_{2}^{18}O enriched sample. Three of the four observed water decamer show tunneling effect associated with the internal dynamics of hydrogen-bond network in a similar fashion as the prism water hexamer. These tunneling paths are quenched upon a single incorporation of a H_{2}^{18}O molecule in the cluster. Due the large amount of closely-spaced rotational transitions in the H_{2}^{18}O spectrum, automated fitting tools were employed to extract the corresponding rotational spectra, which will be also briefly described. C. Perez, M. T. Muckle, D. P. Zaleski, N. A. Seifert, B. Temelso, G. C. Shields, Z. Kisiel, and B. H. Pate, Science 336, 897 (2012).

  9. Terahertz Frequency-Domain Spectroscopy of Low-Pressure Acetonitrile Gas by a Photomixing Terahertz Synthesizer Referenced to Dual Optical Frequency Combs

    NASA Astrophysics Data System (ADS)

    Hsieh, Yi-Da; Kimura, Hiroto; Hayashi, Kenta; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Yasui, Takeshi

    2016-09-01

    A terahertz (THz) frequency synthesizer based on photomixing of two near-infrared lasers with a sub-THz to THz frequency offset is a powerful tool for spectroscopy of polar gas molecules due to its broad spectral coverage; however, its frequency accuracy and resolution are relatively low. To tune the output frequency continuously and widely while maintaining its traceability to a frequency standard, we developed a photomixing THz synthesizer phase-locked to dual optical frequency combs (OFCs). While the phase-locking to dual OFCs ensured continuous tuning within a spectral range of 120 GHz, in addition to the traceability to the frequency standard, use of a broadband uni-traveling carrier photodiode for photomixing enabled the generation of CW-THz radiation within a frequency range from 0.2 to 1.5 THz. We demonstrated THz frequency-domain spectroscopy of gas-phase acetonitrile CH3CN and its isotope CH3 13CN in the frequency range of 0.600-0.720 THz using this THz synthesizer. Their rotational transitions were assigned with a frequency accuracy of 8.42 × 10-8 and a frequency resolution of 520 kHz. Furthermore, the concentration of the CH3CN gas at 20 Pa was determined to be (5.41 ± 0.05) × 1014 molecules/cm3 by curve fitting analysis of the measured absorbance spectrum, and the mixture ratio of the mixed CH3CN/CH3 13CN gas was determined to be 1:2.26 with a gas concentration of 1014-1015 molecules/cm3. The developed THz synthesizer is highly promising for high-precision THz-FDS of low-pressure molecular gases and will enable the qualitative and quantitative analyses of multiple gases.

  10. Broadband Sum-Frequency Generation Spectroscopy of High-Frequency Vibrations of Water Molecules at Silica Surfaces

    NASA Astrophysics Data System (ADS)

    Isaienko, Oleksandr; Nihonyanagi, Satoshi; Sil, Devika; Borguet, Eric

    2012-06-01

    Building on our discovery of a method to extend noncollinear optical parametric amplification to a broad class of materials, we developed one of the first sources generating ultrabroadband infrared pulses with bandwidths Δν > 2500 cm-1 in the near-IR (λ = 1.1-1.6 μm) and Δν > 1000 cm-1 in the mid-IR (λ = 1.7-3.5 μm; ν = 2800-6000 cm-1). The ultra-broadband IR source enabled surface-sensitive sum-frequency generation (SFG) vibrational spectroscopy of mineral-water interfaces crucial in many natural and man-made processes such as ion exchange in geochemical environments and oil extraction from tar sands. This novel ultrabroadband IR source allowed the acquisition of SFG spectra of water OH stretch (spanning 3000-3800 cm-1) from mineral surfaces without tuning the IR frequency, in 60 sec or less. The high signal-to-noise ratio of the broadband-IR SFG setup allowed the extension of SFG spectroscopy of interfacial hydroxyls at mineral/water surfaces to the low cross-section vibrational modes found in the high frequency range (4000-7000 cm-1). We performed, what we believe to be, the first surface-specific vibrational SFG spectroscopic measurements of the stretch+bend combination band, νcomb = νOH+δHOH of liquid water at silica surfaces near 5200 cm-1. SFG of the νcomb mode allows in-situ probing of surface-bound, e.g., SiOH, and H-OH hydroxyls separately. This provides access to the interfacial water bending mode δ (near 1600 cm-1), which has not been observed directly in SFG. O. Isaienko and E. Borguet Opt. Express 16(6), 3949-3954 March 2008. O. Isaienko and E. Borguet Opt. Express 20(1), 547-561 January 2012. O. Isaienko, S. Nihonyanagi, D. Sil and E. Borguet (in preparation).}.

  11. Multidimensional resonant nonlinear spectroscopy with coherent broadband x-ray pulses

    NASA Astrophysics Data System (ADS)

    Bennett, Kochise; Zhang, Yu; Kowalewski, Markus; Hua, Weijie; Mukamel, Shaul

    2016-12-01

    New x-ray free electron laser (XFEL) and high harmonic generation (HHG) light sources are capable of generating short and intense pulses that make x-ray nonlinear spectroscopy possible. Multidimensional spectroscopic techniques, which have long been used in the nuclear magnetic resonance, infrared, and optical regimes to probe the electronic structure and nuclear dynamics of molecules by sequences of short pulses with variable delays, can thus be extended to the attosecond x-ray regime. This opens up the possibility of probing core-electronic structure and couplings, the real-time tracking of impulsively created valence-electronic wavepackets and electronic coherences, and monitoring ultrafast processes such as nonadiabatic electron-nuclear dynamics near conical-intersection crossings. We survey various possible types of multidimensional x-ray spectroscopy techniques and demonstrate the novel information they can provide about molecules.

  12. Broadband Velocity Modulation Spectroscopy of Molecular Ions for Use in the Jila Electron Edm Experiment

    NASA Astrophysics Data System (ADS)

    Gresh, Daniel N.; Cossel, Kevin C.; Cornell, Eric A.; Ye, Jun

    2013-06-01

    The JILA electron electric dipole moment (eEDM) experiment will use a low-lying, metastable ^3Δ_1 state in trapped molecular ions of HfF^+ or ThF^+. Prior to this work, the low-lying states of these molecules had been investigated by PFI-ZEKE spectroscopy. However, there were no detailed studies of the electronic structure. The recently developed technique of frequency comb velocity modulation spectroscopy (VMS) provides broad-bandwidth, high-resolution, ion-sensitive spectroscopy, allowing the acquisition of 150 cm^{-1} of continuous spectra in 30 minutes over 1500 simultaneous channels. By supplementing this technique with cw-laser VMS, we have investigated the electronic structure of HfF^+ in the frequency range of 9950 to 14600 cm^{-1}, accurately fitting and assigning 16 rovibronic transitions involving 8 different electronic states including the X^1Σ^+ and a^3Δ_1 states. In addition, an observed ^3Π_{0+} state with coupling to both the X and a states has been used in the actual eEDM experiment to coherently transfer population from the rovibronic ground state of HfF^+ to the eEDM science state. Furthermore, we report on current efforts of applying frequency comb VMS at 700 - 900 nm to the study of ThF^+, which has a lower energy ^3Δ_1 state and a greater effective electric field, and will provide increased sensitivity for a measurement of the eEDM. A. E. Leanhardt et. al., Journal of Molecular Spectroscopy 270, 1-25 (2011). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, Journal of Chemical Physics 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, Physical Review Letters 107, 093002 (2011). K.C. Cossel et. al., Chemical Physics Letters 546, 1-11 (2012).

  13. High-performance broad-band spectroscopy for breast cancer risk assessment

    NASA Astrophysics Data System (ADS)

    Pawluczyk, Olga; Blackmore, Kristina; Dick, Samantha; Lilge, Lothar

    2005-09-01

    Medical diagnostics and screening are becoming increasingly demanding applications for spectroscopy. Although for many years the demand was satisfied with traditional spectrometers, analysis of complex biological samples has created a need for instruments capable of detecting small differences between samples. One such application is the measurement of absorbance of broad spectrum illumination by breast tissue, in order to quantify the breast tissue density. Studies have shown that breast cancer risk is closely associated with the measurement of radiographic breast density measurement. Using signal attenuation in transillumination spectroscopy in the 550-1100nm spectral range to measure breast density, has the potential to reduce the frequency of ionizing radiation, or making the test accessible to younger women; lower the cost and make the procedure more comfortable for the patient. In order to determine breast density, small spectral variances over a total attenuation of up to 8 OD have to be detected with the spectrophotometer. For this, a high performance system has been developed. The system uses Volume Phase Holographic (VPH) transmission grating, a 2D detector array for simultaneous registration of the whole spectrum with high signal to noise ratio, dedicated optical system specifically optimized for spectroscopic applications and many other improvements. The signal to noise ratio exceeding 50,000 for a single data acquisition eliminates the need for nitrogen cooled detectors and provides sufficient information to predict breast tissue density. Current studies employing transillumination breast spectroscopy (TIBS) relating to breast cancer risk assessment and monitoring are described.

  14. Probing Spin and Spin-Orbit Coupling effects in Narrow-gap Semiconductor Nano-structures by THz Magneto-photoresponse Spectroscopy and Magneto-transport Measurements

    NASA Astrophysics Data System (ADS)

    Pakmehr, Mehdi

    Using the spin degree of freedom in a emergent field Known as Spintronics has motivated scientist in different disciplines including physicist within last 10 years. Due to different interaction mechanisms which affects the physical behavior of spin (eg its state and transport properties) within solid medium (Semiconductors in our case), one needs to distinguish these mechanisms and their importance for making any practical spin based devices. For example the idea of making spin based transistors with electrons being transported within InGaAs and their spin state is being controlled by Rashba type field has been around for around 25 years but injection of spin polarized currents from a source into the channel has not been solved yet. Spin orbit coupling (SOC) is one of the mechanisms which changes the spin state of electrons and avoid the existence of pure spin state as a favorable one from device point of view. SOC could have a different origin depending on material type or structure of device. One method of measuring and quantifying this mechanisms within semiconductor nanostructures is through measuring the parameters known as Lande g-factor. This parameters turns out to be a promising one to probe different effects on electronic band structure including quantum confinement, strain, electric filed, etc. We probe a combination of these effects (SOC, Strain, band mixing, etc) by measuring different g-factor tensor components of narrow gap Zinc blend semiconductor nanostructures which we hope finally serve to the purpose of making reliable spin based devices* (Spintronics). To reach this goal we have developed and implemented THz magneto-Photoresponse spectroscopy in conjunction with magneto-transport measurements at cryogenic temperatures. The samples include InAs and HgTe based Quantum wells as well as InAs based quantum point contact. Our findings clarify the situation where the combination of SOC, Strain, quantum confinements as well as many body electron effect

  15. Identifying the distinct phases of THz waves from K-valley electrons in graphite

    SciTech Connect

    Irfan, Muhammad; Yim, Jong-Hyuk Jho, Young-Dahl; Kim, Changyoung

    2013-12-04

    The polarity change of THz electromagnetic waves radiated from single-crystalline graphite and polycrystalline graphite films has been studied to identify the main generation mechanism in conventional reflective THz time-domain spectroscopy scheme. The excitation wavelength variation around the K-valley produces no significant changes in THz field strength. We further found that THz waves become fully dispersed without polarity change in lateral detection geometry.

  16. Novel materials, fabrication techniques and algorithms for microwave and THz components, systems and applications

    NASA Astrophysics Data System (ADS)

    Liang, Min

    This dissertation presents the investigation of several additive manufactured components in RF and THz frequency, as well as the applications of gradient index lens based direction of arrival (DOA) estimation system and broadband electronically beam scanning system. Also, a polymer matrix composite method to achieve artificially controlled effective dielectric properties for 3D printing material is studied. Moreover, the characterization of carbon based nano-materials at microwave and THz frequency, photoconductive antenna array based Terahertz time-domain spectroscopy (THz-TDS) near field imaging system, and a compressive sensing based microwave imaging system is discussed in this dissertation. First, the design, fabrication and characterization of several 3D printed components in microwave and THz frequency are presented. These components include 3D printed broadband Luneburg lens, 3D printed patch antenna, 3D printed multilayer microstrip line structure with vertical transition, THz all-dielectric EMXT waveguide to planar microstrip transition structure and 3D printed dielectric reflectarrays. Second, the additive manufactured 3D Luneburg Lens is employed for DOA estimation application. Using the special property of a Luneburg lens that every point on the surface of the Lens is the focal point of a plane wave incident from the opposite side, 36 detectors are mounted around the surface of the lens to estimate the direction of arrival (DOA) of a microwave signal. The direction finding results using a correlation algorithm show that the averaged error is smaller than 1º for all 360 degree incident angles. Third, a novel broadband electronic scanning system based on Luneburg lens phased array structure is reported. The radiation elements of the phased array are mounted around the surface of a Luneburg lens. By controlling the phase and amplitude of only a few adjacent elements, electronic beam scanning with various radiation patterns can be easily achieved

  17. Two-dimensional stimulated resonance Raman spectroscopy of molecules with broadband x-ray pulses

    PubMed Central

    Biggs, Jason D.; Zhang, Yu; Healion, Daniel; Mukamel, Shaul

    2012-01-01

    Expressions for the two-dimensional stimulated x-ray Raman spectroscopy (2D-SXRS) signal obtained using attosecond x-ray pulses are derived. The 1D- and 2D-SXRS signals are calculated for trans-N-methyl acetamide (NMA) with broad bandwidth (181 as, 14.2 eV FWHM) pulses tuned to the oxygen and nitrogen K-edges. Crosspeaks in 2D signals reveal electronic Franck-Condon overlaps between valence orbitals and relaxed orbitals in the presence of the core-hole. PMID:22583220

  18. Broadband Ftmw Spectroscopy of the Urea-Argon and Thiourea-Argon Complexes

    NASA Astrophysics Data System (ADS)

    Medcraft, Chris; Bittner, Dror M.; Cooper, Graham A.; Mullaney, John C.; Walker, Nick

    2017-06-01

    The rotational spectra complexes of argon-urea, argon-thiourea and water-thiourea have been measured by chirped-pulse Fourier transform microwave spectroscopy from 2-18.5 GHz. The sample was produced via laser vaporisation of a rod containing copper and the organic sample as a stream of argon was passed over the surface and subsequently expanded into the vacuum chamber cooling the sample. Argon was found to bind to π system of the carbonyl bond for both the urea and thiourea complexes.

  19. Laser absorption spectroscopy based on a broadband external cavity quantum cascade laser

    NASA Astrophysics Data System (ADS)

    Sun, Juan; Liu, Ningwu; Deng, Hao; Ding, Junya; Sun, Jiancha; Zhang, Lei; Li, Jingsong

    2017-02-01

    A tunable diode laser absorption spectroscopy (TDLAS) system based on a broad band external cavity quantum cascade laser (ECQCL) near 7.78 μm was used to study volatile organic compounds (VOCs) measurements. Instead of using a standard infrared mercury cadmium telluride (MCT) detector, a quartz crystal tuning fork (QCTF) as a light detector was successfully used for laser signal detection. Fast Fourier transform (FFT) was used to extract vibration intensity information of QCTF. Primary results indicate that the new developed system has a good reproducibility, and a good agreement was obtained by comparing with data taken from standard spectroscopic database.

  20. Coupling between amino acid and water dynamics by broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Saiz, Luciana; Cerveny, Silvina

    2014-05-01

    The dynamics of proline aqueous solution was investigated for water concentrations from 40 to 60 wt% by dielectric spectroscopy (106 - 109 Hz) in the temperature range from 230 to 300 K, where the solutions remain amorphous. We found two relaxation processes, related with the reorientation of proline and water as previously observed in a higher frequency range at room temperature [1]. We found that both dynamics are strongly coupled, as previously observed in hydrated proteins powders, in spite of the fact that a single amino acid is a molecule much simpler than a protein.

  1. Impact of heat on metabolic and hemodynamic changes in transcranial infrared laser stimulation measured by broadband near-infrared spectroscopy.

    PubMed

    Wang, Xinlong; Reddy, Divya D; Nalawade, Sahil S; Pal, Suvra; Gonzalez-Lima, F; Liu, Hanli

    2018-01-01

    Transcranial infrared laser stimulation (TILS) has shown effectiveness in improving human cognition and was investigated using broadband near-infrared spectroscopy (bb-NIRS) in our previous study, but the effect of laser heating on the actual bb-NIRS measurements was not investigated. To address this potential confounding factor, 11 human participants were studied. First, we measured time-dependent temperature increases on forehead skin using clinical-grade thermometers following the TILS experimental protocol used in our previous study. Second, a subject-averaged, time-dependent temperature alteration curve was obtained, based on which a heat generator was controlled to induce the same temperature increase at the same forehead location that TILS was delivered on each participant. Third, the same bb-NIRS system was employed to monitor hemodynamic and metabolic changes of forehead tissue near the thermal stimulation site before, during, and after the heat stimulation. The results showed that cytochrome-c-oxidase of forehead tissue was not significantly modified by this heat stimulation. Significant differences in oxyhemoglobin, total hemoglobin, and differential hemoglobin concentrations were observed during the heat stimulation period versus the laser stimulation. The study demonstrated a transient hemodynamic effect of heat-based stimulation distinct to that of TILS. We concluded that the observed effects of TILS on cerebral hemodynamics and metabolism are not induced by heating the skin.

  2. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 1, data analysis and results

    SciTech Connect

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward H.; Sirk, Martin; Muirhead, Philip S.; Muterspaugh, Matthew W.; Lloyd, James P.; Ishikawa, Yuzo; McDonald, Eliza A.; Shourt, William V.; Vanderburg, Andrew M.

    2016-05-27

    High-resolution broadband spectroscopy at near-infrared wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar. Observations of stars were performed with the “TEDI” interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec near-infrared echelle spectrograph. These are the first multidelay EDI demonstrations on starlight, as earlier measurements used a single delay or laboratory sources. We demonstrate very high (10×) resolution boost, from original 2700 to 27,000 with current set of delays (up to 3 cm), well beyond the classical limits enforced by the slit width and detector pixel Nyquist limit. Significantly, the EDI used with multiple delays rather than a single delay as used previously yields an order of magnitude or more improvement in the stability against native spectrograph point spread function (PSF) drifts along the dispersion direction. We observe a dramatic (20×) reduction in sensitivity to PSF shift using our standard processing. A recently realized method of further reducing the PSF shift sensitivity to zero is described theoretically and demonstrated in a simple simulation which produces a 350× times reduction. We demonstrate superb rejection of fixed pattern noise due to bad detector pixels—EDI only responds to changes in pixel intensity synchronous to applied dithering. This part 1 describes data analysis, results, and instrument noise. Lastly, a section on theoretical photon limited sensitivity is in a companion paper, part 2.

  3. Vibrational spectral signatures of crystalline cellulose using high resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS)

    DOE PAGES

    Zhang, Libing; Lu, Zhou; Velarde, Luis; ...

    2015-03-03

    Both the C–H and O–H region spectra of crystalline cellulose were studied using the sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) for the first time. The resolution of HR-BB-SFG-VS is about 10-times better than conventional scanning SFG-VS and has the capability of measuring the intrinsic spectral lineshape and revealing many more spectral details. With HR-BB-SFG-VS, we found that in cellulose samples from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the O–H region were unique for the two allomorphs, i.e. Iα and Iβ, while the spectral signaturesmore » in the C–H regions varied in all samples examined. Even though the origin of the different spectral signatures of the crystalline cellulose in the O–H and C–H vibrational frequency regions are yet to be correlated to the structure of cellulose, these results lead to new spectroscopic methods and opportunities to classify and to understand the basic crystalline structures, as well as variations in polymorphism of the crystalline cellulose.« less

  4. Vibrational spectral signatures of crystalline cellulose using high resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS)

    SciTech Connect

    Zhang, Libing; Lu, Zhou; Velarde, Luis; Fu, Li; Pu, Yunqiao; Ding, Shi-You; Ragauskas, Arthur; Wang, Hong-Fei; Yang, Bin

    2015-03-03

    Both the C–H and O–H region spectra of crystalline cellulose were studied using the sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) for the first time. The resolution of HR-BB-SFG-VS is about 10-times better than conventional scanning SFG-VS and has the capability of measuring the intrinsic spectral lineshape and revealing many more spectral details. With HR-BB-SFG-VS, we found that in cellulose samples from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the O–H region were unique for the two allomorphs, i.e. Iα and Iβ, while the spectral signatures in the C–H regions varied in all samples examined. Even though the origin of the different spectral signatures of the crystalline cellulose in the O–H and C–H vibrational frequency regions are yet to be correlated to the structure of cellulose, these results lead to new spectroscopic methods and opportunities to classify and to understand the basic crystalline structures, as well as variations in polymorphism of the crystalline cellulose.

  5. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 1, data analysis and results

    SciTech Connect

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward H.; Sirk, Martin; Muirhead, Philip S.; Muterspaugh, Matthew W.; Lloyd, James P.; Ishikawa, Yuzo; McDonald, Eliza A.; Shourt, William V.; Vanderburg, Andrew M.

    2016-05-27

    High-resolution broadband spectroscopy at near-infrared wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar. Observations of stars were performed with the “TEDI” interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec near-infrared echelle spectrograph. These are the first multidelay EDI demonstrations on starlight, as earlier measurements used a single delay or laboratory sources. We demonstrate very high (10×) resolution boost, from original 2700 to 27,000 with current set of delays (up to 3 cm), well beyond the classical limits enforced by the slit width and detector pixel Nyquist limit. Significantly, the EDI used with multiple delays rather than a single delay as used previously yields an order of magnitude or more improvement in the stability against native spectrograph point spread function (PSF) drifts along the dispersion direction. We observe a dramatic (20×) reduction in sensitivity to PSF shift using our standard processing. A recently realized method of further reducing the PSF shift sensitivity to zero is described theoretically and demonstrated in a simple simulation which produces a 350× times reduction. We demonstrate superb rejection of fixed pattern noise due to bad detector pixels—EDI only responds to changes in pixel intensity synchronous to applied dithering. This part 1 describes data analysis, results, and instrument noise. Lastly, a section on theoretical photon limited sensitivity is in a companion paper, part 2.

  6. Dynamics of water-alcohol mixtures: Insights from nuclear magnetic resonance, broadband dielectric spectroscopy, and triplet solvation dynamics

    SciTech Connect

    Sauer, D.; Schuster, B.; Rosenstihl, M.; Schneider, S.; Blochowicz, T.; Stühn, B.; Vogel, M.; Talluto, V.; Walther, T.

    2014-03-21

    We combine {sup 2}H nuclear magnetic resonance (NMR), broadband dielectric spectroscopy (BDS), and triplet solvation dynamics (TSD) to investigate molecular dynamics in glass-forming mixtures of water and propylene glycol in very broad time and temperature ranges. All methods yield consistent results for the α process of the studied mixtures, which hardly depends on the composition and shows Vogel-Fulcher temperature dependence as well as Cole-Davidson spectral shape. The good agreement between BDS and TDS data reveals that preferential solvation of dye molecules in microheterogeneous mixtures does not play an important role. Below the glass transition temperature T{sub g}, NMR and BDS studies reveal that the β process of the mixtures shows correlation times, which depend on the water concentration, but exhibit a common temperature dependence, obeying an Arrhenius law with an activation energy of E{sub a} = 0.54  eV, as previously reported for mixtures of water with various molecular species. Detailed comparison of NMR and BDS correlation functions for the β process unravels that the former decay faster and more stretched than the latter. Moreover, the present NMR data imply that propylene glycol participates in the β process and, hence, it is not a pure water process, and that the mechanism for molecular dynamics underlying the β process differs in mixtures of water with small and large molecules.

  7. Vibrational Spectral Signatures of Crystalline Cellulose Using High Resolution Broadband Sum Frequency Generation Vibrational Spectroscopy (HR-BB-SFG-VS)

    SciTech Connect

    Zhang, Libing; Lu, Zhou; Velarde Ruiz Esparza, Luis A.; Fu, Li; Pu, Yunqiao; Ding, Shi-You; Ragauskas, Art J.; Wang, Hongfei; Yang, Bin

    2015-03-03

    Here we reported the first sub-wavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) study on both the C-H and O-H region spectra of crystalline cellulose. HR-BB-SFG-VS has about 10 times better resolution than the conventional scanning SFG-VS and is known to be able to measure the intrinsic spectral lineshape and to resolve much more spectral details. With HR-BB-SFG-VS, we found that in cellulose from different sources, including Avicel and cellulose crystals isolated from algae Valonia (Iα) and tunicates (Iβ), the spectral signatures in the OH regions were unique for different allomorphs, i.e. Iα and Iβ, while the spectral signatures in the C-H regions varied in all samples examined. Even though the origin of the different behaviors of the crystalline cellulose in the O-H and C-H vibrational frequency regions is yet to be correlated to the structure of cellulose, these results provided new spectroscopic methods and opportunities to classify and understand the basic crystalline structure, as well as variations, in polymorphism of the crystalline cellulose structure.

  8. Determination of 3D molecular orientation by concurrent polarization analysis of multiple Raman modes in broadband CARS spectroscopy

    PubMed Central

    2016-01-01

    A theoretical description is presented about a new analysis method to determine three-dimensional (3D) molecular orientation by concurrently analyzing multiple Raman polarization profiles. Conventional approaches to polarization Raman spectroscopy are based on single peaks, and their 2D-projected polarization profiles are limited in providing 3D orientational information. Our new method analyzes multiple Raman profiles acquired by a single polarization scanning measurement of broadband coherent anti-Stokes Raman scattering (BCARS). Because the analysis uses only dimensionless quantities, such as intensity ratios and phase difference between multiple profiles, the results are not affected by sample concentration and the system response function. We describe how to determine the 3D molecular orientation with the dimensionless observables by using two simplified model cases. In addition, we discuss the effect of orientational broadening on the polarization profiles in the two model cases. We find that in the presence of broadening we can still determine the mean 3D orientation angles and, furthermore, the degree of orientational broadening. PMID:26561197

  9. Broadband ultrafast photoluminescence spectroscopy resolves charge photogeneration via delocalized hot excitons in polymer:fullerene photovoltaic blends.

    PubMed

    Chen, Kai; Barker, Alex J; Reish, Matthew E; Gordon, Keith C; Hodgkiss, Justin M

    2013-12-11

    Conventional descriptions of excitons in semiconducting polymers do not account for several important observations in polymer:fullerene photovoltaic blends, including the ultrafast time scale of charge photogeneration in phase separated blends and the intermediate role of delocalized charge transfer states. We investigate the nature of excitons in thin films of polymers and polymer:fullerene blends by using broadband ultrafast photoluminescence spectroscopy. Our technique enables us to resolve energetic relaxation, as well as the volume of excitons and population dynamics on ultrafast time scales. We resolve substantial high-energy emission from hot excitons prior to energetic relaxation, which occurs predominantly on a subpicosecond time scale. Consistent with quantum chemical calculations, ultrafast annihilation measurements show that excitons initially extend along a substantial chain length prior to localization induced by structural relaxation. Moreover, we see that hot excitons are initially highly mobile and the subsequent rapid decay in mobility is correlated with energetic relaxation. The relevance of these measurements to charge photogeneration is confirmed by our measurements in blends. We find that charge photogeneration occurs predominately via these delocalized hot exciton states in competition with relaxation and independently of temperature. As well as accounting for the ultrafast time scale of charge generation across large polymer phases, delocalized hot excitons may also account for the crucial requirement that primary charge pairs are well separated in efficient organic photovoltaic blends.

  10. Broadband Ultrahigh-Resolution Spectroscopy of Particle-Induced X Rays: Extending the Limits of Nondestructive Analysis

    NASA Astrophysics Data System (ADS)

    Palosaari, M. R. J.; Käyhkö, M.; Kinnunen, K. M.; Laitinen, M.; Julin, J.; Malm, J.; Sajavaara, T.; Doriese, W. B.; Fowler, J.; Reintsema, C.; Swetz, D.; Schmidt, D.; Ullom, J. N.; Maasilta, I. J.

    2016-08-01

    Nondestructive analysis (NDA) based on x-ray emission is widely used, for example, in the semiconductor and concrete industries. Here, we demonstrate significant quantitative and qualitative improvements in broadband x-ray NDA by combining particle-induced emission with detection based on superconducting microcalorimeter arrays. We show that the technique offers great promise in the elemental analysis of thin-film and bulk samples, especially in the difficult cases where tens of different elements with nearly overlapping emission lines have to be identified down to trace concentrations. We demonstrate the efficiency and resolving capabilities by spectroscopy of several complex multielement samples in the energy range 1-10 keV, some of which have a trace amount of impurities not detectable with standard silicon drift detectors. The ability to distinguish the chemical environment of an element is also demonstrated by measuring the intensity differences and chemical shifts of the characteristics x-ray peaks of titanium compounds. In particular, we report measurements of the K α /K β intensity ratio of thin films of TiN and measurements of Ti K α satellite peak intensities in various Ti thin-film compounds. We also assess the detection limits of the technique, comment on detection limits possible in the future, and discuss possible applications.

  11. Incoherent broad-band cavity-enhanced absorption spectroscopy of the marine boundary layer species I2, IO and OIO.

    PubMed

    Vaughan, Stewart; Gherman, Titus; Ruth, Albert A; Orphal, Johannes

    2008-08-14

    The novel combination of incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) and a discharge-flow tube for the study of three key atmospheric trace species, I(2), IO and OIO, is reported. Absorption measurements of I(2) and OIO at lambda=525-555 nm and IO at lambda=420-460 nm were made using a compact cavity-enhanced spectrometer employing a 150 W short-arc Xenon lamp. The use of a flow system allowed the monitoring of the chemically short-lived radical species IO and OIO to be conducted over timescales of several seconds. We report detection limits of approximately 26 pmol mol(-1) for I(2) (L=81 cm, acquisition time 60 s), approximately 45 pmol mol(-1) for OIO (L=42.5 cm, acquisition time 5 s) and approximately 210 pmol mol(-1) for IO (L=70 cm, acquisition time 60 s), demonstrating the usefulness of this approach for monitoring these important species in both laboratory studies and field campaigns.

  12. Real-time monitoring of reactive species in downstream etch reactor by VUV broad-band absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Soriano, R.; Vallier, L.; Cunge, G.; Sadeghi, N.

    2016-09-01

    Plasma etching of nanometric size, high aspect-ratio structures is more challenging at each new technological node. Remote plasmas are beginning to find use when damages on nanostructures by ion bombardment become critical or when etching with high selectivity on different materials present on the wafer is necessary (i . e . tungsten oxide etching with fluorine and hydrogen containing plasmas in remote reactor from AMAT). Furthermore, it is expected that downstream plasma will replace many wet chemical etching processes to alleviate the issue of pattern collapses caused by capillary forces when nanometer size high aspect ratio structures are immersed in liquids. In these downstream plasmas, radicals are the main active species and a control of their density is of prime importance. Most of gases used and radicals produced in etching plasmas (HBr, BrCl, Br2, NF3, CH2F2,...) have strong absorption bands in the vacuum UV spectral region and we have shown that very low concentration of these species can be detected by VUV absorption. We have recently improved the technique by using a VUV CCD camera, instead of the PMT, which render possible the Broad-Band absorption spectroscopy in the 120-200 nm range, with a deuterium lamp, or a laser produced xenon arc lamp as light source. The multi-spectral detection ability of the CCD reduces the acquisition time to less than 1 second and can permit the real time control of the process control.

  13. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 1, data analysis and results

    NASA Astrophysics Data System (ADS)

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward H.; Sirk, Martin; Muirhead, Philip S.; Muterspaugh, Matthew W.; Lloyd, James P.; Ishikawa, Yuzo; McDonald, Eliza A.; Shourt, William V.; Vanderburg, Andrew M.

    2016-04-01

    High-resolution broadband spectroscopy at near-infrared wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar. Observations of stars were performed with the "TEDI" interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec near-infrared echelle spectrograph. These are the first multidelay EDI demonstrations on starlight, as earlier measurements used a single delay or laboratory sources. We demonstrate very high (10×) resolution boost, from original 2700 to 27,000 with current set of delays (up to 3 cm), well beyond the classical limits enforced by the slit width and detector pixel Nyquist limit. Significantly, the EDI used with multiple delays rather than a single delay as used previously yields an order of magnitude or more improvement in the stability against native spectrograph point spread function (PSF) drifts along the dispersion direction. We observe a dramatic (20×) reduction in sensitivity to PSF shift using our standard processing. A recently realized method of further reducing the PSF shift sensitivity to zero is described theoretically and demonstrated in a simple simulation which produces a 350× times reduction. We demonstrate superb rejection of fixed pattern noise due to bad detector pixels-EDI only responds to changes in pixel intensity synchronous to applied dithering. This part 1 describes data analysis, results, and instrument noise. A section on theoretical photon limited sensitivity is in a companion paper, part 2.

  14. High resolution broad-band spectroscopy in the NIR using the Triplespec externally dispersed interferometer at the Hale telescope

    NASA Astrophysics Data System (ADS)

    Erskine, David J.; Edelstein, J.; Sirk, M.; Wishnow, E.; Ishikawa, Y.; McDonald, E.; Shourt, W. V.

    2014-07-01

    High resolution broad-band spectroscopy at near-infrared wavelengths has been performed using externally dis- persed interferometry (EDI) at the Hale telescope at Mt. Palomar. The EDI technique uses a field-widened Michelson interferometer in series with a dispersive spectrograph, and is able to recover a spectrum with a resolution 4 to 10 times higher than the existing grating spectrograph. This method increases the resolution well beyond the classical limits enforced by the slit width and the detector pixel Nyquist limit and, in principle, decreases the effect of pupil variation on the instrument line-shape function. The EDI technique permits arbi- trarily higher resolution measurements using the higher throughput, lower weight, size, and expense of a lower resolution spectrograph. Observations of many stars were performed with the TEDI interferometer mounted within the central hole of the 200 inch primary mirror. Light from the interferometer was then dispersed by the TripleSpec near-infrared echelle spectrograph. Continuous spectra between 950 and 2450 nm with a resolution as high as ~27,000 were recovered from data taken with TripleSpec at a native resolution of ˜2,700. Aspects of data analysis for interferometric spectral reconstruction are described. This technique has applications in im- proving measurements of high-resolution stellar template spectra, critical for precision Doppler velocimetry using conventional spectroscopic methods. A new interferometer to be applied for this purpose at visible wavelengths is under construction.

  15. Hydration dependence of myoglobin dynamics studied with elastic neutron scattering, differential scanning calorimetry and broadband dielectric spectroscopy.

    PubMed

    Fomina, Margarita; Schirò, Giorgio; Cupane, Antonio

    2014-01-01

    In this work we present a thorough investigation of the hydration dependence of myoglobin dynamics. The study is performed on D2O-hydrated protein powders in the hydration range 0Broadband Dielectric Spectroscopy; finally, Differential Scanning Calorimetry is used to obtain a thermodynamic description of the system. The effect of increasing hydration is to speed up the relaxations of the myoglobin+hydration water system and, thermodynamically, to decrease the glass transition temperature; these effects tend to saturate at h values greater than ~0.3. Moreover, the calorimetric scans put in evidence the occurrence of an endothermic peak whose onset temperature is located at ~230K independent of hydration. From the point of view of the protein equilibrium fluctuations, while the amplitude of anharmonic mean square displacements is found to increase with hydration, their onset temperature (i.e. the onset temperature of the well known "protein dynamical transition") is hydration independent. On the basis of the above results, the relevance of protein+hydration water relaxations and of the thermodynamic state of hydration water to the onset of the protein dynamical transition is discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

  16. Broadband ultraviolet-visible transient absorption spectroscopy in the nanosecond to microsecond time domain with sub-nanosecond time resolution.

    PubMed

    Lang, Bernhard; Mosquera-Vázquez, Sandra; Lovy, Dominique; Sherin, Peter; Markovic, Vesna; Vauthey, Eric

    2013-07-01

    A combination of sub-nanosecond photoexcitation and femtosecond supercontinuum probing is used to extend femtosecond transient absorption spectroscopy into the nanosecond to microsecond time domain. Employing a passively Q-switched frequency tripled Nd:YAG laser and determining the jitter of the time delay between excitation and probe pulses with a high resolution time delay counter on a single-shot basis leads to a time resolution of 350 ps in picosecond excitation mode. The time overlap of almost an order of magnitude between fs and sub-ns excitation mode permits to extend ultrafast transient absorption (TA) experiments seamlessly into time ranges traditionally covered by laser flash photolysis. The broadband detection scheme eases the identification of intermediate reaction products which may remain undetected in single-wavelength detection flash photolysis arrangements. Single-shot referencing of the supercontinuum probe with two identical spectrometer/CCD arrangements yields an excellent signal-to-noise ratio for the so far investigated chromophores in short to moderate accumulation times.

  17. Evidence from Broadband Rotational Spectroscopy for a Complex Between AgCCH and C6H6

    NASA Astrophysics Data System (ADS)

    Zaleski, Daniel P.; Stephens, Susanna Louise; Walker, Nick; Legon, Anthony

    2014-06-01

    Last year, at the 68th International Symposium of Molecular Spectroscopy, the rotational spectrum of a complex formed between C2H2 and AgCCH was presented. The geometry was found to be T-shaped with the silver atom coordinated to the center of the CC bond in acetylene. Evidence for a new complex formed between AgCCH and C6H6 is now presented in the form of deep-averaged broadband rotational spectra. The spectra are observed only when both C2H2 and C6H6 are present in the gas sample. The relative intensities of the observed spectra are consistent with the naturally-occurring abundance ratio of the isotopes of silver. The shift on substitution of 107Ag for 109Ag implies a silver atom positioned close to the center of mass. The isotopic shifts observed when C2D2 is used as a precursor instead of C2H2 are also consistent with assignment to a complex formed between C6H6 and AgCCH/D. The geometry of the complex is yet to be precisely established.

  18. Dynamics of water-alcohol mixtures: Insights from nuclear magnetic resonance, broadband dielectric spectroscopy, and triplet solvation dynamics

    NASA Astrophysics Data System (ADS)

    Sauer, D.; Schuster, B.; Rosenstihl, M.; Schneider, S.; Talluto, V.; Walther, T.; Blochowicz, T.; Stühn, B.; Vogel, M.

    2014-03-01

    We combine 2H nuclear magnetic resonance (NMR), broadband dielectric spectroscopy (BDS), and triplet solvation dynamics (TSD) to investigate molecular dynamics in glass-forming mixtures of water and propylene glycol in very broad time and temperature ranges. All methods yield consistent results for the α process of the studied mixtures, which hardly depends on the composition and shows Vogel-Fulcher temperature dependence as well as Cole-Davidson spectral shape. The good agreement between BDS and TDS data reveals that preferential solvation of dye molecules in microheterogeneous mixtures does not play an important role. Below the glass transition temperature Tg, NMR and BDS studies reveal that the β process of the mixtures shows correlation times, which depend on the water concentration, but exhibit a common temperature dependence, obeying an Arrhenius law with an activation energy of Ea = 0.54 eV, as previously reported for mixtures of water with various molecular species. Detailed comparison of NMR and BDS correlation functions for the β process unravels that the former decay faster and more stretched than the latter. Moreover, the present NMR data imply that propylene glycol participates in the β process and, hence, it is not a pure water process, and that the mechanism for molecular dynamics underlying the β process differs in mixtures of water with small and large molecules.

  19. Very high Power THz radiation from Relativistic Electrons

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-08-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques.

  20. Femtosecond Broadband Stimulated Raman: A New Approach for High-Performance Vibrational Spectroscopy

    PubMed Central

    McCAMANT, DAVID W.; KUKURA, PHILIPP; MATHIES, RICHARD A.

    2005-01-01

    Femtosecond stimulated Raman spectroscopy (FSRS) is a new technique that produces high-quality vibrational spectra free from background fluorescence. FSRS combines a narrow-bandwidth picosecond Raman pump pulse with an ∼80 fs continuum probe pulse to produce stimulated Raman spectra from the pump-induced gain in the probe spectrum. The high intensity of the Raman pump combined with the broad bandwidth of the probe produces high signal-to-noise vibrational spectra with very short data acquisition times. FSRS spectra of standard solutions and solvents such as aqueous Na2SO4, aqueous KNO3, methanol, isopropanol, and cyclohexane are collected in seconds. Furthermore, stimulated Raman spectra can be obtained using just a single pump–probe pulse pair that illuminates the sample for only ∼1 ps. Fluorescence rejection is demonstrated by collecting FSRS spectra of dyes (rhodamine 6G, chlorophyll a, and DTTCI) with varying degrees of fluorescence background and resonance enhancement. The high signal-to-noise, short data acquisition time, fluorescence rejection, and high spectral and temporal resolution of femtosecond stimulated Raman spectroscopy make it a valuable new vibrational spectroscopic technique. PMID:14658143

  1. Concerted Breaking of Two Hydrogen Bonds in Water Hexamer Prism Revealed from Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Richardson, Jeremy O.; Perez, Cristobal; Lobsiger, Simon; Reid, Adam A.; Temelso, Berhane; Shields, George C.; Kisiel, Zbigniew; Wales, David J.; Pate, Brooks; Althorpe, Stuart C.

    2016-06-01

    Over the past few years, we have used H218O water substitution to determine the structures of water clusters by molecular rotational spectroscopy. In the case of the water hexamer, the energy difference between the cage and prism structures is calculated to be about 0.1 kcal/mol and this energy difference is of the order of the zero-point energy variation between the isomers. Using rotational spectroscopy we provided experimental evidence for three isomers, i.e, cage, prism and book and established their relative energy ordering. In the special case of the prism hexamer, cluster dynamics causes measurable splitting in rotational transitions resulting from tunneling between discernible equivalent minima. Multiple isotopic substitution measurements involving all 64 possible isotopologues of the water hexamer prism (H218O)n(H216O)6-n were performed in order to identify the water molecules involved in the tunneling motion. The analysis of these tunneling-rotation spectra suggests that there are two distinct tunneling paths that involve concerted motion of two water molecules, implying a prototype scenario involving the breaking of two hydrogen bonds. C. Pérez, et al, Science. 2012, 336 897-901 J. O. Richardson et al, Science. 2016, in press

  2. A compact THz imaging system

    NASA Astrophysics Data System (ADS)

    Sešek, Aleksander; Å vigelj, Andrej; Trontelj, Janez

    2015-03-01

    The objective of this paper is the development of a compact low cost imaging THz system, usable for observation of the objects near to the system and also for stand-off detection. The performance of the system remains at the high standard of more expensive and bulkiest system on the market. It is easy to operate as it is not dependent on any fine mechanical adjustments. As it is compact and it consumes low power, also a portable system was developed for stand-off detection of concealed objects under textile or inside packages. These requirements rule out all optical systems like Time Domain Spectroscopy systems which need fine optical component positioning and requires a large amount of time to perform a scan and the image capture pixel-by-pixel. They are also almost not suitable for stand-off detection due to low output power. In the paper the antenna - bolometer sensor microstructure is presented and the THz system described. Analysis and design guidelines for the bolometer itself are discussed. The measurement results for both near and stand-off THz imaging are also presented.

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  4. RDX Detection with THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Michalopoulou, Zoi-Heleni; Mukherjee, Suman; Hor, Yew Li; Su, Ke; Liu, Zhiwei; Barat, Robert B.; Gary, Dale E.; Federici, John F.

    2010-10-01

    Spectroscopic analysis in the Terahertz frequency range, providing characteristic “signatures” for explosive and non-explosive materials, is proposed as an efficient and powerful tool for explosive identification. It is demonstrated that spectral responses of materials can be used as fingerprints that distinguish cyclotrimethylenetrinitramine (RDX) from other materials even with simple detectors and a limited number of available frequencies. Detection is performed using a modified least squares approach and multilayer perceptrons that operate on smoothed reflectance spectra. The performance of the detectors is evaluated through application to spectra of RDX and several common materials. A Receiver Operating Characteristic curve analysis demonstrates that our detectors exhibit the desirable properties of high probability of detection and low probability of false alarm.

  5. Spectral modification of the laser emission of a terahertz quantum cascade laser induced by broad-band double pulse injection seeding

    SciTech Connect

    Markmann, Sergej Nong, Hanond Hekmat, Negar; Jukam, Nathan; Pal, Shovon; Scholz, Sven; Kukharchyk, Nadezhda; Ludwig, Arne; Wieck, Andreas D.; Dhillon, Sukhdeep; Tignon, Jérôme; Marcadet, Xavier; Bock, Claudia; Kunze, Ulrich

    2015-09-14

    We demonstrate by injection seeding that the spectral emission of a terahertz (THz) quantum cascade laser (QCL) can be modified with broad-band THz pulses whose bandwidths are greater than the QCL bandwidth. Two broad-band THz pulses delayed in time imprint a modulation on the single THz pulse spectrum. The resulting spectrum is used to injection seed the THz QCL. By varying the time delay between the THz pulses, the amplitude distribution of the QCL longitudinal modes is modified. By applying this approach, the QCL emission is reversibly switched from multi-mode to single mode emission.

  6. Broadband Ftmw Spectroscopy of 2-METHYLIMIDAZOLE and Complexes with Water and Argon

    NASA Astrophysics Data System (ADS)

    Medcraft, Chris; Heitkämper, Juliane; Mullaney, John C.; Walker, Nick

    2017-06-01

    The rotational spectrum of 2-methylimidazole has been measured using laser ablation chirped-pulse Fourier transform microwave spectroscopy from 2-18.5 GHz. 2-methylimidazole was laser vaporised then entrained within an argon buffer gas undergoing supersonic expansion allowing for efficient rotational cooling. Carbon-13 and nitrogen-15 isotopologues were measured in natural abundance and substitution coordinates have been determined. The barrier to internal rotation of the methyl group was found to be 122.697(20) cm^{-1}. Nuclear quadropole coupling constants for the two nitrogen nuclei were determined via a rigid rotor fit of the A internal rotor state. Complexes with water and argon were also observed and fit in a similar way.

  7. Muscle oxygenation during exercise under hypoxic conditions assessed by spatially resolved broadband NIR spectroscopy

    NASA Astrophysics Data System (ADS)

    Geraskin, Dmitri; Platen, Petra; Franke, Julia; Andre, Christiane; Bloch, Wilhelm; Kohl-Bareis, Matthias

    2005-08-01

    Near-infrared spectroscopy (NIRS) is used for the non-invasive measurement of muscle oxygenation during an incremental cycle test in healthy volunteers. A broad band spatially resolved system is used that allows the reliability of current algorithms to be inspected with the main emphasis on tissue oxygen saturation (SO2) and oxygenated and deoxygenated haemoglobin concentrations. Physiological conditions were modulated by changing oxygen supply from normal (21 % O2 in inspired air) to conditions corresponding to 2000 and 4000 m altitude above sea level (15.4 and 11.9 % O2). Under these hypoxic conditions the decrease in SO2 with increased exercise power is highly correlated with the oxygen content of the inspired air. There is a clear correlation with physiological parameters (heart rate, pulse oxymetry, blood gas, lactate, spirometric data). Skin oxygenation parameters are compared to those of muscle.

  8. A superconfiguration model for broadband spectroscopy of non-LTE plasmas

    NASA Astrophysics Data System (ADS)

    Peyrusse, O.

    2000-10-01

    We present an atomic physics package called AVERROÈS/TRANSPEC for studying plasma spectroscopy of complex L-, M-shell emitters or even core-excited multielectron K-shell emitters. The model, which is also intended to give some insights on ionization properties of M-shell ionized plasmas, is divided into two parts. The first part (AVERROÈS) is based on the superconfiguration concept and on the supertransition array method. It generates superconfiguration average-energies, collisional and radiative rates needed for a calculation of population kinetics. It also calculates the statistical shift and width associated with each possible radiative electron jump between selected superconfigurations. All the previously mentioned quantities are stored on files readable by a multicell time-dependent collisional-radiative model (TRANSPEC) that calculates population kinetics and synthetic emission spectra. This last code can be employed with a hydrodynamics code to provide simulated x-ray ouputs of non-steady-state inhomogeneous plasmas.

  9. Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas

    NASA Astrophysics Data System (ADS)

    Liu, Kaipeng; Guo, Yinghui; Pu, Mingbo; Ma, Xiaoliang; Li, Xiong; Luo, Xiangang

    2017-01-01

    Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanning ±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8 THz to 1.2 THz.

  10. Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas.

    PubMed

    Liu, Kaipeng; Guo, Yinghui; Pu, Mingbo; Ma, Xiaoliang; Li, Xiong; Luo, Xiangang

    2017-01-30

    Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanning ±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8 THz to 1.2 THz.

  11. Algorithm-Independent Pattern Classification Techniques for Improved Broadband Chemometrics for Laser-Induced Breakdown Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dunsin, Kehinde Samuel

    Laser-induced breakdown spectroscopy (LIBS) has seen significant attention in recent years, in part because of several unique characteristics that distinguish it from other techniques for atomic emission spectroscopy. As a technology capable of fielded, portable deployment, it is possible to take analytical chemistry to the field, which may serve in a variety of applications such as industrial monitoring, geological surveys and hazard detection. The use of LIBS in a variety of material applications has been on the rise in recent years, however, in order for LIBS to successfully transition into the field, the sensor must be paired with appropriate algorithm for accurate and robust processing. In this research dissertation, the result of testing two classification algorithms on eight LIBS datasets is reported. The results suggest that the standard cross validation techniques may not accurately estimate generalization performance and a proposed "Leave-One-Sample-Out (LOSO)" approach to experimental design for LIBS classifier validation may provide a more robust measure of performance. In another study focused on building a robust multi class classifier for LIBS, three modifications of the partial least square discriminant analysis (PLSDA) classifier were used to test six distinct LIBS datasets with different number of classes. The results show that the pairwise PLSDA classification scheme performed better than the traditional M-ary PLSDA classification scheme and the One-against-all PLSDA classification scheme especially on datasets with large number of classes. The presence of contaminants in a LIBS spectral measurement can significantly degrade the generalization performance of classifier for LIBS. A proposed technique known as "Localized In-Sample Tunable Extreme-value Remover (LISTER)" is capable of removing these contaminants in a multivariate data, specifically LIBS spectral measurement. Removing the contaminated observations from the "contaminated" LIBS

  12. High Resolution GHZ and Thz (ftir) Spectroscopy and Theory of Parity Violation and Tunneling for 1,2-DITHIINE (C4H4S2) as a Candidate for Measuring the Parity Violating Energy Difference Between Enantiomers of Chiral Molecules

    NASA Astrophysics Data System (ADS)

    Albert, Sieghard; Bolotova, Irina; Chen, Ziqiu; Fábri, Csaba; Horny, Lubos; Quack, Martin; Seyfang, Georg; Zindel, Daniel

    2016-06-01

    We report high resolution spectroscopic results for 1,2-dithiine-(1,2-dithia-3,5-cyclohexadiene,C4H4S2) in the Gigahertz and Terahertz spectroscopic ranges and exploratory theoretical calculations of parity violation and tunneling processes in view of a possible experimental determination of the parity violating energy difference ΔpvE in this chiral molecule. Theory predicts that the parity violating energy difference in the ground state (ΔpvE≃11x10-11(hc) wn)is in principle measurable as it is much larger than the calculated tunneling splitting for the symmetrical potential Δ±E≃10-24(hc) wn. With a planar transition state for stereomutation at about 2500 wn tunneling splittings become appreciable above 2300 wn. This makes levels of well defined parity accessible to parity selection by available powerful infrared lasers and thus useful for one of the existing experimental approaches towards molecular parity violation. The new GHz spectra lead to greatly improved ground state rotational parameters for 1,2-dithiine. These are used as starting point for the first successful analyses of high resolution interferometric Fourier Transform Infrared (FTIR, THz) spectra for the fundamentals ν17 (1308.873 wn or 39.23903 THz), ν22 (623.094 wn or 18.67989 THz) and ν3 (1544.900 wn or 46.314937 THz) for which highly accurate spectroscopic parameters are reported. The results are discussed in relation to current efforts to measure ΔpvE.a-. M. Quack , Fundamental Symmetries and Symmetry Violations from High-resolution Spectroscopy, Handbook of High Resolution Spectroscopy, M. Quack and F. Merkt eds.,John Wiley & Sons Ltd, Chichester, New York, 2001, vol. 1, ch. 18, pp. 659-722 S. Albert, I. Bolotova, Z. Chen, C. Fábri, L. Horny, M. Quack, G. Seyfang and D. Zindel,Proceedings of the 20th Symposium on Atomic, Cluster and Surface Physics (SASP 2016), Innsbruck University Press, 2016, pp. 127-130, ISBN:978-3-903122-04-8. and to be published P. Dietiker, E. Miloglyadov, M

  13. Ethanol Dimer: Observation of Three New Conformers by Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Loru, Donatella; Peña, Isabel; Sanz, M. Eugenia

    2017-06-01

    The conformational behaviour of the hydrogen-bonded cluster ethanol dimer has been reinvestigated by chirped pulse Fourier transform microwave spectroscopy in the 2-8 GHz frequency region. Three new conformers ({tt}, {tg}+, and {g}-{g}+) have been identified together with the three ({g}+{g}+, {g}-{t}, and {g}+{t}) previously observed by Hearn et al. (J. Chem. Phys. 123, 134324, 2005) and their rotational and centrifugal distortion constants have been determined. By using different carrier gases in the supersonic expansion, the relative abundances of the observed conformers have been estimated. The monosubstituted ^{13}C species and some of the ^{18}O species of the most abundant conformers {g}+{g}+, {g}-{t}, and {tt} have been observed in their natural abundance, which led to the partial determination of their r_{s} structures, and the r_{0} structure for the {tt} conformer. The six observed conformers are stabilized by the delicate interplay of primary O-H...O and secondary C-H...O hydrogen bonds, and dispersion interactions between the methyl groups. Density functional and ab initio methods with different basis sets are benchmarked against the experimental data.

  14. Ethanol dimer: Observation of three new conformers by broadband rotational spectroscopy

    NASA Astrophysics Data System (ADS)

    Loru, D.; Peña, I.; Sanz, M. E.

    2017-05-01

    The conformational behavior of the hydrogen-bonded cluster ethanol dimer has been reinvestigated by chirped pulse Fourier transform microwave spectroscopy in the 2-8 GHz frequency region. Three new conformers (tt, tg+, and g-g+) have been identified together with the three (g+g+, g-t, and g+t) previously observed by Hearn et al. (2005) and their rotational and centrifugal distortion constants have been determined. By using different carrier gases in the supersonic expansion, the relative abundances of the observed conformers have been estimated. The monosubstituted 13C species and some of the 18O species of the most abundant conformers g+g+, g-t, and tt have been observed in their natural abundance, which led to the partial determination of their rs structures, and the r0 structure for the tt conformer. The six observed conformers are stabilized by the delicate interplay of primary Osbnd H···O and secondary Csbnd H···O hydrogen bonds, and dispersion interactions between the methyl groups. Density functional and ab initio methods with different basis sets are benchmarked against the experimental data.

  15. Terahertz wave reference-free transmission spectroscopy of aminophenol

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  16. Terahertz vibration-rotation-tunneling spectroscopy of the water tetramer-d8: combined analysis of vibrational bands at 4.1 and 2.0 THz.

    PubMed

    Lin, Wei; Han, Jia-Xiang; Takahashi, Lynelle K; Harker, Heather A; Keutsch, Frank N; Saykally, Richard J

    2008-03-07

    We report the measurement of terahertz vibration-rotation-tunneling spectra of (D(2)O)(4) in the spectral region near 4.13 THz. The characterization of this perpendicular band extends a previously reported study [J. Chem. Phys. 111, 7801 (1999)]. We observed 239 new transitions, each being split into a doublet of constant (approximately 192 MHz) spacing. These are included in a combined fit with the 113 previously measured transitions of the 2.03 THz parallel band using an effective Hamiltonian similar to that used in the global fit of the water trimer. The detailed understanding of the water tetramer evolving from this work underlies our efforts to quantify the contribution of many-body forces to the hydrogen bonding interactions in condensed phase water.

  17. Broadband Frequency Comb and Cw-Laser Velocity Modulation Spectroscopy of ThF+

    NASA Astrophysics Data System (ADS)

    Gresh, Dan; Cossel, Kevin; Ye, Jun; Cornell, Eric

    2015-06-01

    An experimental search for the permanent electric dipole moment of the electron (eEDM) is currently being performed using the metastable ^3Δ_1 state in trapped HfF^+ ^(^). The use of ThF^+ could significantly increase the sensitivity due to the larger effective electric field and longer ^3Δ_1 state lifetime. Previous work by the Heaven group has identified several low-lying ThF^+ electronic states; however, the ground state could not be conclusively assigned. In addition, transitions to intermediate electronic states have not been identified, but they are necessary for state detection, manipulation, and readout in an eEDM experiment. To date we have acquired 3700 wn of densely-sampled ThF^+ spectra in the 695 - 1020 nm region with frequency comb and cw-laser velocity modulation spectroscopy. With high resolution, we have accurately fit more than 20 ThF^+ vibronic transitions, including electronic states spaced by the known X-a energy separation^b. We will report on the ThF^+ ground state assignment and its implications for an eEDM experiment. H. Loh, K. C. Cossel, M. C. Grau, K.-K. Ni, E. R. Meyer, J. L. Bohn, J. Ye, E. A. Cornell, Science 342, 1220 (2013). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, J. Chem. Phys. 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, PRL 107, 093002 (2011). K.C. Cossel et. al., Chem. Phys. Lett. 546, 1 (2012).

  18. Development of a THz spectroscopic imaging system.

    PubMed

    Usami, M; Iwamoto, T; Fukasawa, R; Tani, M; Watanabe, M; Sakai, K

    2002-11-07

    We have developed a real-time THz imaging system based on the two-dimensional (2D) electro-optic (EO) sampling technique. Employing the 2D EO-sampling technique, we can obtain THz images using a CCD camera at a video rate of up to 30 frames per second. A spatial resolution of 1.4 mm was achieved. This resolution was reasonably close to the theoretical limit determined by diffraction. We observed not only static objects but also moving ones. To acquire spectroscopic information, time-domain images were collected. By processing these images on a computer, we can obtain spectroscopic images. Spectroscopy for silicon wafers was demonstrated.

  19. High-power THz to IR emission by femtosecond laser irradiation of random 2D metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Zhang, Liangliang; Mu, Kaijun; Zhou, Yunsong; Wang, Hai; Zhang, Cunlin; Zhang, X.-C.

    2015-07-01

    Terahertz (THz) spectroscopic sensing and imaging has identified its potentials in a number of areas such as standoff security screening at portals, explosive detection at battle fields, bio-medical research, and so on. With these needs, the development of an intense and broadband THz source has been a focus of THz research. In this work, we report an intense (~10 mW) and ultra-broadband (~150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

  20. High-power THz to IR emission by femtosecond laser irradiation of random 2D metallic nanostructures.

    PubMed

    Zhang, Liangliang; Mu, Kaijun; Zhou, Yunsong; Wang, Hai; Zhang, Cunlin; Zhang, X-C

    2015-07-24

    Terahertz (THz) spectroscopic sensing and imaging has identified its potentials in a number of areas such as standoff security screening at portals, explosive detection at battle fields, bio-medical research, and so on. With these needs, the development of an intense and broadband THz source has been a focus of THz research. In this work, we report an intense (~10 mW) and ultra-broadband (~150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

  1. Atmospheric propagation of THz radiation.

    SciTech Connect

    Wanke, Michael Clement; Mangan, Michael A.; Foltynowicz, Robert J.

    2005-11-01

    In this investigation, we conduct a literature study of the best experimental and theoretical data available for thin and thick atmospheres on THz radiation propagation from 0.1 to 10 THz. We determined that for thick atmospheres no data exists beyond 450 GHz. For thin atmospheres data exists from 0.35 to 1.2 THz. We were successful in using FASE code with the HITRAN database to simulate the THz transmission spectrum for Mauna Kea from 0.1 to 2 THz. Lastly, we successfully measured the THz transmission spectra of laboratory atmospheres at relative humidities of 18 and 27%. In general, we found that an increase in the water content of the atmosphere led to a decrease in the THz transmission. We identified two potential windows in an Albuquerque atmosphere for THz propagation which were the regions from 1.2 to 1.4 THz and 1.4 to 1.6 THz.

  2. THz Pulse Detection by Multilayered GeTe/Sb2Te3.

    PubMed

    Makino, Kotaro; Kuromiya, Shota; Takano, Keisuke; Kato, Kosaku; Nakajima, Makoto; Saito, Yuta; Tominaga, Junji; Iida, Hitoshi; Kinoshita, Moto; Nakano, Takashi

    2016-11-30

    We proposed and demonstrated terahertz (THz) pulse detection by means of multilayered GeTe/Sb2Te3 phase-change memory materials that are also known as a multilayer topological insulator-normal insulator (MTN) system. THz time-domain spectroscopy measurement was performed for MTN films with different multilayer repetitions as well as a conventional as-grown Ge-Te-Sb (GST) alloy film. It was found that MTNs absorb THz waves and that the absorption coefficient depends on the number of layers, while the as-grown GST alloy film was almost transparent for THz waves. Simple MTN-based THz detection devices were fabricated, and the THz-induced change in the current signal was measured when a DC bias voltage was applied between the electrodes. We confirmed that irradiation of THz pulse causes a decrease in the resistance of the MTNs. This result indicates that our devices are capable of THz detection.

  3. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 1, data analysis and results

    DOE PAGES

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward H.; ...

    2016-05-27

    High-resolution broadband spectroscopy at near-infrared wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar. Observations of stars were performed with the “TEDI” interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec near-infrared echelle spectrograph. These are the first multidelay EDI demonstrations on starlight, as earlier measurements used a single delay or laboratory sources. We demonstrate very high (10×) resolution boost, from original 2700 to 27,000 with current set of delays (up to 3 cm), well beyond the classical limits enforced bymore » the slit width and detector pixel Nyquist limit. Significantly, the EDI used with multiple delays rather than a single delay as used previously yields an order of magnitude or more improvement in the stability against native spectrograph point spread function (PSF) drifts along the dispersion direction. We observe a dramatic (20×) reduction in sensitivity to PSF shift using our standard processing. A recently realized method of further reducing the PSF shift sensitivity to zero is described theoretically and demonstrated in a simple simulation which produces a 350× times reduction. We demonstrate superb rejection of fixed pattern noise due to bad detector pixels—EDI only responds to changes in pixel intensity synchronous to applied dithering. This part 1 describes data analysis, results, and instrument noise. Lastly, a section on theoretical photon limited sensitivity is in a companion paper, part 2.« less

  4. Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) - A novel approach to investigate the wettability of pharmaceutical powder blends.

    PubMed

    Peddapatla, Raghu V G; Ahmed, M Rizwan; Blackshields, Caroline A; Sousa-Gallagher, M J; McSweeney, Sean; Krüse, J; Crean, Abina M; Fitzpatrick, Dara

    2017-09-19

    The ability of Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) to assess the wettability of powder blends is investigated. BARDS is a novel analytical technology developed based on the change in acoustic phenomenon observed when material is added into a solvent under resonance. Addition of solid material to the solvent results in the introduction of gas (air) into the solvent, changing the compressibility of the solvent system and reducing the velocity of sound in the solvent. As a material is wetted and dissolved, the gas is released from the solvent and resonance frequency is altered. The main purpose of this work is to demonstrate the ability of BARDS to assess differences in the wetting behaviour of tablet excipients (microcrystalline cellulose (MCC) and magnesium stearate (MgSt)) and a model drug (metoclopramide hydrochloride) as single component powders and multi-component powder blends. BARDS acoustic responses showed a prolonged release of gas for the powdered blends with lubricant compared to un-lubricated blends. As the elimination of gas from the solvent was assumed to follow first order elimination kinetics, a compressible gas elimination rate constant was calculated from the log plots of the gas volume profiles. The gas elimination rate constant was used as a parameter to compare the release of gas from the powder introduced to the solvent and hence the powder wetting behavior. A lower gas elimination rate constant was measured for lubricated blends compared to non-lubricated blends, suggesting the prolonged hydration of lubricated blends. Standard wetting techniques such as contact angle measurements and wetting time analysis were also used to analyze the blends and confirmed differences in wetting behavior determined by BARDS. The study results demonstrate the capability of BARDS as a rapid, analytical tool to determine the wetting behavior of the pharmaceutical powder blends and the potential of BARDS as a process analytical technology

  5. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization

    SciTech Connect

    Sidabras, Jason W.; Anderson, James R.; Mainali, Laxman; Hyde, James S.; Strangeway, Robert A.; Mett, Richard R.

    2016-03-15

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE{sub 10} mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  6. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization.

    PubMed

    Sidabras, Jason W; Strangeway, Robert A; Mett, Richard R; Anderson, James R; Mainali, Laxman; Hyde, James S

    2016-03-01

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  7. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization

    PubMed Central

    Strangeway, Robert A.; Mett, Richard R.; Anderson, James R.; Mainali, Laxman; Hyde, James S.

    2016-01-01

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  8. THz optics and metamaterials: Design, fabrication and characterization

    NASA Astrophysics Data System (ADS)

    Turaga, Shuvan Prashant

    In the past decade, terahertz(THz) based optics and metamaterials have been extensively researched to create components and devices in the frequency range of 0.1 to 5 THz also known as 'THz gap'. Metamaterials, in particular, have realized concepts such as negative refraction, slow light and superlensing through artificially engineered media. The naturally available materials have very weak interaction of terahertz light. Therefore, the design of THz metamaterials to manipulate THz radiation is an important task towards furthering the usage of terahertz light for practical applications. The thesis involved the development of two lab facilities for fabrication and characterization. A state-of-the-art two photon lithography( TPL) system was developed which enables us to manufacture 3D structures with sub-diffraction limit resolution(280nm at 800 nm wavelength). The software was written to enable easy fabrication of multiple structures with different algorithms. For characterizing our metamaterial structures in the terahertz regime, a THz time-domain spectroscopy(THz-TDS) and imaging system was built. This transmission based spectrometer has a dynamic range of 50 dB at 0.5 THz and a bandwidth of about 2.5 THz. To demonstrate the application of these home-built facilities, the metamaterials in the THz regime were fabricated using TPL and UV lithography. To investigate conductive coupling effects in meta-atoms, a new design was proposed, fabricated and characterized. As an application of TPL, free standing polymer helices were fabricated and coated with silver electroless plating. These silver helical metamaterials have potential application as circular polarizers in the MIR and THz regimes. The aspect ratio effects of these helical metamaterials were also studied in order to improve their polarizing performance.

  9. Millimetre and FIR Broadband Quasi Optical Devices

    NASA Astrophysics Data System (ADS)

    Haynes, V.; Maffei, B.; Melhuish, S. J.; Piccirillo, L.; Pisano, G.; Shakeshaft, D.

    2009-12-01

    We present a set of techniques and materials we are currently developing which enable very broadband and highly effective optical devices in the spectral region from 20 GHz to 20 THz. Many of these devices have already been employed in terrestrial, airborne and space based telescope systems.

  10. Very high power THz radiation at Jefferson Lab

    SciTech Connect

    Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, K.; Neil, George R.; Williams, G.P.

    2002-03-31

    We report the production of high power (20 watts average, {approx};1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  11. Very high Power THz radiation at Jefferson Lab

    SciTech Connect

    G.L. Carr; Michael C. Martin; Wayne R. McKinney; Kevin Jordan; George R. Neil; Gwyn P. Williams

    2002-03-01

    We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with one based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to that produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  12. Very high power THz radiation at Jefferson Lab.

    PubMed

    Carr, G L; Martin, Michael C; McKinney, Wayne R; Jordan, K; Neil, George R; Williams, G P

    2002-11-07

    We report the production of high power (20 W average, approximately 1 MW peak) broadband THz light based on coherent emission from relativistic electrons. We describe the source, presenting theoretical calculations and their experimental verification. For clarity we compare this source with that based on ultrafast laser techniques, and in fact the radiation has qualities closely analogous to those produced by such sources, namely that it is spatially coherent, and comprises short duration pulses with transform-limited spectral content. In contrast to conventional THz radiation, however, the intensity is many orders of magnitude greater due to the relativistic enhancement.

  13. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 2, photon noise theory

    SciTech Connect

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward; Sirk, Martin; Muirhead, Philip S.; Muterspaugh, Matthew W.; Lloyd, James P.

    2016-10-01

    High-resolution broadband spectroscopy at near-infrared (NIR) wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar, with the TEDI interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec NIR echelle spectrograph. These are the first multidelay EDI demonstrations on starlight. We demonstrated very high (10×) resolution boost and dramatic (20× or more) robustness to point spread function wavelength drifts in the native spectrograph. Data analysis, results, and instrument noise are described in a companion paper (part 1). This part 2 describes theoretical photon limited and readout noise limited behaviors, using simulated spectra and instrument model with noise added at the detector. We show that a single interferometer delay can be used to reduce the high frequency noise at the original resolution (1× boost case), and that except for delays much smaller than the native response peak half width, the fringing and nonfringing noises act uncorrelated and add in quadrature. This is due to the frequency shifting of the noise due to the heterodyning effect. We find a sum rule for the noise variance for multiple delays. The multiple delay EDI using a Gaussian distribution of exposure times has noise-to-signal ratio for photon-limited noise similar to a classical spectrograph with reduced slitwidth and reduced flux, proportional to the square root of resolution boost achieved, but without the focal spot limitation and pixel spacing Nyquist limitations. At low boost (~1×) EDI has ~1.4× smaller noise than conventional, and at >10× boost, EDI has ~1.4× larger noise than conventional. Readout noise is minimized by the use of three or four steps instead of 10 of TEDI. Net noise grows as step phases change from symmetrical arrangement with wavenumber across the band. As a result, for three (or four) steps, we calculate a multiplicative

  14. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 2, photon noise theory

    DOE PAGES

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward; ...

    2016-10-01

    High-resolution broadband spectroscopy at near-infrared (NIR) wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar, with the TEDI interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec NIR echelle spectrograph. These are the first multidelay EDI demonstrations on starlight. We demonstrated very high (10×) resolution boost and dramatic (20× or more) robustness to point spread function wavelength drifts in the native spectrograph. Data analysis, results, and instrument noise are described in a companion paper (part 1). This part 2 describes theoreticalmore » photon limited and readout noise limited behaviors, using simulated spectra and instrument model with noise added at the detector. We show that a single interferometer delay can be used to reduce the high frequency noise at the original resolution (1× boost case), and that except for delays much smaller than the native response peak half width, the fringing and nonfringing noises act uncorrelated and add in quadrature. This is due to the frequency shifting of the noise due to the heterodyning effect. We find a sum rule for the noise variance for multiple delays. The multiple delay EDI using a Gaussian distribution of exposure times has noise-to-signal ratio for photon-limited noise similar to a classical spectrograph with reduced slitwidth and reduced flux, proportional to the square root of resolution boost achieved, but without the focal spot limitation and pixel spacing Nyquist limitations. At low boost (~1×) EDI has ~1.4× smaller noise than conventional, and at >10× boost, EDI has ~1.4× larger noise than conventional. Readout noise is minimized by the use of three or four steps instead of 10 of TEDI. Net noise grows as step phases change from symmetrical arrangement with wavenumber across the band. As a result, for three (or four) steps, we calculate a

  15. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: Part 2, photon noise theory

    SciTech Connect

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward; Sirk, Martin; Muirhead, Philip S.; Muterspaugh, Matthew W.; Lloyd, James P.

    2016-10-01

    High-resolution broadband spectroscopy at near-infrared (NIR) wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar, with the TEDI interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec NIR echelle spectrograph. These are the first multidelay EDI demonstrations on starlight. We demonstrated very high (10×) resolution boost and dramatic (20× or more) robustness to point spread function wavelength drifts in the native spectrograph. Data analysis, results, and instrument noise are described in a companion paper (part 1). This part 2 describes theoretical photon limited and readout noise limited behaviors, using simulated spectra and instrument model with noise added at the detector. We show that a single interferometer delay can be used to reduce the high frequency noise at the original resolution (1× boost case), and that except for delays much smaller than the native response peak half width, the fringing and nonfringing noises act uncorrelated and add in quadrature. This is due to the frequency shifting of the noise due to the heterodyning effect. We find a sum rule for the noise variance for multiple delays. The multiple delay EDI using a Gaussian distribution of exposure times has noise-to-signal ratio for photon-limited noise similar to a classical spectrograph with reduced slitwidth and reduced flux, proportional to the square root of resolution boost achieved, but without the focal spot limitation and pixel spacing Nyquist limitations. At low boost (~1×) EDI has ~1.4× smaller noise than conventional, and at >10× boost, EDI has ~1.4× larger noise than conventional. Readout noise is minimized by the use of three or four steps instead of 10 of TEDI. Net noise grows as step phases change from symmetrical arrangement with wavenumber across the band. As a result, for three (or four) steps, we calculate a multiplicative

  16. High-resolution broadband spectroscopy using externally dispersed interferometry at the Hale telescope: part 2, photon noise theory

    NASA Astrophysics Data System (ADS)

    Erskine, David J.; Edelstein, Jerry; Wishnow, Edward; Sirk, Martin; Muirhead, Philip S.; Muterspaugh, Matthew W.; Lloyd, James P.

    2016-10-01

    High-resolution broadband spectroscopy at near-infrared (NIR) wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar, with the TEDI interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec NIR echelle spectrograph. These are the first multidelay EDI demonstrations on starlight. We demonstrated very high (10×) resolution boost and dramatic (20× or more) robustness to point spread function wavelength drifts in the native spectrograph. Data analysis, results, and instrument noise are described in a companion paper (part 1). This part 2 describes theoretical photon limited and readout noise limited behaviors, using simulated spectra and instrument model with noise added at the detector. We show that a single interferometer delay can be used to reduce the high frequency noise at the original resolution (1× boost case), and that except for delays much smaller than the native response peak half width, the fringing and nonfringing noises act uncorrelated and add in quadrature. This is due to the frequency shifting of the noise due to the heterodyning effect. We find a sum rule for the noise variance for multiple delays. The multiple delay EDI using a Gaussian distribution of exposure times has noise-to-signal ratio for photon-limited noise similar to a classical spectrograph with reduced slitwidth and reduced flux, proportional to the square root of resolution boost achieved, but without the focal spot limitation and pixel spacing Nyquist limitations. At low boost (˜1×) EDI has ˜1.4× smaller noise than conventional, and at >10× boost, EDI has ˜1.4× larger noise than conventional. Readout noise is minimized by the use of three or four steps instead of 10 of TEDI. Net noise grows as step phases change from symmetrical arrangement with wavenumber across the band. For three (or four) steps, we calculate a multiplicative bandwidth

  17. Spectroscopy of the ground, first and second excited torsional states of acetaldehyde from 0.05 to 1.6 THz

    NASA Astrophysics Data System (ADS)

    Smirnov, I. A.; Alekseev, E. A.; Ilyushin, V. V.; Margulés, L.; Motiyenko, R. A.; Drouin, B. J.

    2014-01-01

    We present a new global study of the millimeter wave, submillimeter wave and THz spectra of the lowest three torsional states of acetaldehyde (CH3CHO). New measurements have been carried out between 0.05 and 1.62 THz using three different spectrometers in IRA NASU (Ukraine), PhLAM Lille (France), and JPL (USA). The new data involving torsion-rotation transitions with J up to 66 and Ka up to 22 were combined with previously published measurements and fitted using the rho-axis-method torsion-rotation Hamiltonian. The final fit used 109 parameters to give an overall weighted root-mean-square deviation of 0.69 for the dataset consisting of 8748, 6959, and 4524 transitions belonging, respectively, to the ground, first, and second excited torsional states and 1481 Δvt ≠ 0 FIR transitions belonging to the torsional vt = 0 → 1 and 1 → 2 bands of the molecule. This investigation presents more than a twofold expansion in the J quantum number and almost fourfold expansion in the frequency range coverage for the acetaldehyde rotational spectrum.

  18. Ultra-broadband terahertz absorption by exciting the orthogonal diffraction in dumbbell-shaped gratings.

    PubMed

    Zang, XiaoFei; Shi, Cheng; Chen, Lin; Cai, Bin; Zhu, YiMing; Zhuang, SongLin

    2015-03-10

    Metamaterials, artificial electromagnetic media consisting of periodical subwavelength metal-based micro-structures, were widely suggested for the absorption of terahertz (THz) waves. However, they have been suffered from the absorption of THz waves just in the single-frequency owing to its resonance features. Here, in this paper, we propose a simple periodical structure, composed of two 90 degree crossed dumbbell-shaped doped-silicon grating arrays, to demonstrate broadband THz wave absorption. Our theoretical and experimental results illustrate that THz waves can be efficiently absorbed more than 95% ranging from 0.92 THz to 2.4 THz. Such an ultra-wideband polarization-independent THz absorber is realized mainly based on the mechanisms of the anti-reflection effect together with the [±1, 0]-order and [0, ±1]-order grating diffractions. The application of our investigation can be extend to THz couplers, filters, imaging, and so on.

  19. Photoconductive ultrafast low gap materials: pulsed THz emitters and detectors

    NASA Astrophysics Data System (ADS)

    Petrov, Branko; Fekecs, Andre; Chicoine, Martin; Schiettekatte, Francois; Ares, Richard; Morris, Denis

    2014-03-01

    Commonly photoconductive (PC) switches used for pulsed THz generation and detection are made on GaAs which works at 800 nm. However, there is a need for PC materials compatible with laser sources emitting at 1550 nm since they are of high interest for fiber-coupled devices to be integrated in THz imaging and spectroscopy systems. We have developed such materials based on low bandgap III-V semiconductors. With our novel approach, based on cold-implantation of heavy ions followed by a rapid thermal annealing (RTA) treatment, it was possible to obtain high resistivity (up to 2500 Ω . cm) and short lifetime (<1ps) materials. THz PC antennas were made on these materials and their characteristics were studied by using a THz time-domain spectroscopy (TDS) setup. The impact of the RTA process and different electrode designs were investigated in order to compare the characteristics of PC antennas in terms of amplitude, bandwidth, and signal to noise ratio. For the emitters, bias-voltage and pump-power dependences are shown. Remarkably high electric field (>50 kV/cm) could be applied for increased emission of pulsed THz radiation due to the high resistivity of our materials. Our THz-TDS setup offers measurement capabilities from 0.1 to 3 THz.

  20. Dispersion in a broadband terahertz quantum cascade laser

    NASA Astrophysics Data System (ADS)

    Bachmann, Dominic; Rösch, Markus; Scalari, Giacomo; Beck, Mattias; Faist, Jérôme; Unterrainer, Karl; Darmo, Juraj

    2016-11-01

    We present dispersion data of a broadband terahertz quantum cascade laser with a heterogeneous active region. The experimental method to extract the group velocity dispersion of the entire laser cavity, including the contributions of the active region, the semiconductor material, and the waveguide relies on a time-domain spectroscopy system. The obtained group velocity dispersion curves exhibit oscillations with amplitudes up to 1 × 105 fs2/mm between 2.0 and 3.0 THz and strongly depend on the driving conditions of the laser. This indicates that the group velocity dispersion is mainly determined by the intersubband gain in the active region. The obtained dispersion data are compared to a dispersion model based on multiple Drude-Lorentz gain media yielding a significant correlation.

  1. Heat Induced Damage Detection by Terahertz (THz) Radiation

    NASA Astrophysics Data System (ADS)

    Rahani, Ehsan Kabiri; Kundu, Tribikram; Wu, Ziran; Xin, Hao

    2011-06-01

    Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic waves. Capability of THz electromagnetic waves in detecting heat induced damage in porous materials is investigated in this paper. Porous pumice stone blocks are subjected to long time heat exposures to produce heat induced damage in the block. The dielectric properties extracted from THz TDS (Time Domain Spectroscopy) measurements are compared for different levels of heat exposure. Experimental results show noticeable and consistent change in dielectric properties with increasing levels of heat exposure, well before its melting point.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  3. Pore-size dependent THz absorption of nano-confined water.

    PubMed

    Sun, Chi-Kuang; You, Borwen; Huang, Yu-Ru; Liu, Kao-Hsiang; Sato, Shusaku; Irisawa, Akiyoshi; Imamura, Motoki; Mou, Chung-Yuan

    2015-06-15

    We performed a THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21, of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk-water-like THz absorption behavior in the core water region and a solid-like THz absorption behavior in the interfacial water region.

  4. THz Local Oscillator Technology

    NASA Technical Reports Server (NTRS)

    Mehdi, Imran

    2004-01-01

    The last decade has seen a number of technological advancements that have now made it possible to implement fully solid state local oscillator chains up to 2 THz. These chains are composed of cascaded planar multiplier stages that are pumped with W-band high power sources. The high power W-band sources are achieved by power combining MMIC amplifiers and can provide in access of 150 mW with about 10% bandwidth. Planar diode technology has also enabled novel circuit topologies that can take advantage of the high input power and demonstrate significant efficiencies well into the THz range. Cascaded chains to 1.9 THz have now been demonstrated with enough output power to successfully pump hot-electron bolometer mixers in this frequency range. An overview of the current State-of-the-Art of the local oscillator technology will be presented along with highlighting future trends and challenges.

  5. Spectroscopy of the Ground, First and Second Excited Torsional States of Acetaldehyde from 0.05 to 1.6 THz.

    NASA Astrophysics Data System (ADS)

    Ilyushin, Vadim V.; Smirnov, Ivan; Alekseev, Eugene A.; Margules, Laurent; Motiyenko, Roman A.; Drouin, Brian

    2013-06-01

    A new global study of the acetaldehyde (CH{_3}CHO) spectrum is reported. The new measurements cover the frequency range from 49 GHz to 1.6 THz and have been carried out using three different spectrometers in IRA NASU (Ukraine), PhLAM Lille (France), and JPL (USA). The rotational transitions belonging to the three lowest torsional states, as well as previously published data on the FIR torsional bands, of the molecule have been analyzed using the rho-axis-method. The dataset consisting of more than 19700 line frequencies and including rotational transitions with J up to 66 and K{_a} up to 22 was fit using a model consisting of 117 parameters and weighted root-mean-square deviation of 0.71 has been achieved. Details of this new study and problems encountered in analysis of the second torsional state will be discussed.

  6. Terahertz (THZ) Imaging

    DTIC Science & Technology

    2006-03-01

    beam or by moving the sample around. THz TDS is by no means confined to transmission data. It is possible to get reflective data from samples by slight...Wallace, V.P.; Fitzgerald, A.J.; Cole, B.C.; Pye , R.J.; Arnone, D.D., “Biomedical applications of THz imaging” Microwave Symposium Digest, 2004 IEEE MTT-S...2002. A perspective on state of art. 13. Wallace, V.P.; Arnone, D.A.; Woodward, R.M.; Pye RJ; “Biomedical applications of terahertz pulse

  7. Insights into the nature of radar attenuation through impure ice from broadband dielectric spectroscopy of polar ice cores

    NASA Astrophysics Data System (ADS)

    Stillman, D.; MacGregor, J. A.; Grimm, R. E.

    2011-12-01

    Water ice is ubiquitous in our solar system and is a key target for planetary radar sounders. A primary unknown in many radar surveys is the energy loss due to conduction (attenuation) within the medium being studied. Electrical conduction through ice is controlled by the mobility, concentration and charge of lattice- and water-soluble impurities. Despite extensive study of the physical and chemical characteristics of lab-frozen and naturally forming ices, several questions have remained as to which impurities can increase conduction and the mechanisms by which this conduction occurs. Here we investigate the role of impurities in electrical conduction using broadband dielectric spectroscopy of terrestrial polar ice cores and report several findings of interest to present and future radar investigations of extraterrestrial ice masses. 1. The dielectric strength of meteoric ice-core samples we studied was often much less than that of pure lab-frozen ice, which suggests that the balance of minority and majority charge carriers in naturally forming ice is much closer to being "crossed-over" than previously realized. 2. Samples with high acid concentrations also have high HF conductivities due to an increase in L-defects caused by chloride, i.e., the ionic defects induced by acid in the lattice partition more chloride into the lattice for charge balance. This behavior explains the larger HF conductivity of acids per unit concentration versus that of chloride and their similar activation energies. 3. The DC conductivity of polar ice is much lower than reported previously from in situ Antarctic field surveys, and is best explained if conduction from acids arises from ionic defects in the ice lattice, rather than through liquid networks. Its conductivity is much less than that of single crystal ice because of the low conductivity of grain boundaries through which charges must migrate. 4. In nearly all the meteoric ice-core samples that we studied, we observed two

  8. High Power THz Generation from Sub-ps Bunches of Relativistic Electrons

    SciTech Connect

    S. Benson; D.R. Douglas; H.F. Dylla; J. Gubeli; K. Jordan; G.R. Neil; Michelle D. Shinn; S. Zhang; G.P. Williams

    2004-11-01

    We describe a > 100 Watt broadband THz source that takes advantage of the relativistic enhancement of the radiation from accelerating electrons according to the formula assigned the name of Sir Joseph Larmor [1,2]. This is in contrast to the typical 1 milliwatt sources available in a laboratory. Specifically, for relativistic electrons the emission is enhanced by the fourth power of the increase in mass. Thus for 100 MeV electrons, for which the mass increases by a factor of {approx} 200, the enhancement is > 109. The experiments use a new generation of light source called an energy recovery linac (ERL) [3], in which bunches of electrons circulate once, but in which their energy is recovered. In such a machine the electron bunches can be very much shorter than those, say, in storage rings or synchrotrons. The Jefferson Lab facility operates in new limits of emission from relativistic particles involving both multiparticle coherence and near-field emission in which the velocity (Coulomb) term in the classical electrodynamical theory becomes as important as the acceleration term (synchrotron radiation). The sub-picosecond pulses of light offer unique capabilities in 2 specific areas, namely time resolved dynamics, and imaging. High resolution THz spectroscopy has recently revealed sharp vibrational modes for many materials including malignant tissue, proteins, DNA, pharmaceuticals and explosive materials. Energetically the THz range embraces superconducting bandgaps, and regions of intense interest in the understanding of systems in which correlated motions of electrons are important, such as colossal magneto-resistive and high-Tc materials. The very high power levels of the new source will allow non-linear effects to be observed as well as the creation of novel states of materials, including electric-field driven localization [4]. We will give examples of existing work in these areas and present opportunities afforded by the new source.

  9. Model of THz Magnetization Dynamics

    PubMed Central

    Bocklage, Lars

    2016-01-01

    Magnetization dynamics can be coherently controlled by THz laser excitation, which can be applied in ultrafast magnetization control and switching. Here, transient magnetization dynamics are calculated for excitation with THz magnetic field pulses. We use the ansatz of Smit and Beljers, to formulate dynamic properties of the magnetization via partial derivatives of the samples free energy density, and extend it to solve the Landau-Lifshitz-equation to obtain the THz transients of the magnetization. The model is used to determine the magnetization response to ultrafast multi- and single-cycle THz pulses. Control of the magnetization trajectory by utilizing the THz pulse shape and polarization is demonstrated. PMID:26956997

  10. Evolution of the high power THz source program at Jefferson Lab

    SciTech Connect

    George Neil; Gwyn Williams

    2004-10-01

    We report the evolution of the high power THz source program at Jefferson Lab. The source is based on coherent synchrotron radiation in which short bunches of relativistic electrons radiate when traversing a dipolar magnetic field. In our first accelerator we produced 20 W of broadband THz light. Our upgraded accelerator with higher current and improved THz extraction optics will considerably enhance the output power to >100 W. In this paper we describe the source in some detail and present theoretical calculations for the upgrade.

  11. THz identification and Bayes modeling

    NASA Astrophysics Data System (ADS)

    Sokolnikov, Andre

    2017-05-01

    THz Identification is a developing technology. Sensing in the THz range potentially gives opportunity for short range radar sensing because THz waves can better penetrate through obscured atmosphere, such as fog, than visible light. The lower scattering of THz as opposed to the visible light results also in significantly better imaging than in IR spectrum. A much higher contrast can be achieved in medical trans-illumination applications than with X-rays or visible light. The same THz radiation qualities produce better tomographical images from hard surfaces, e.g. ceramics. This effect comes from the delay in time of reflected THz pulses detection. For special or commercial applications alike, the industrial quality control of defects is facilitated with a lower cost. The effectiveness of THz wave measurements is increased with computational methods. One of them is Bayes modeling. Examples of this kind of mathematical modeling are considered.

  12. The study of gas species on THz generation from laser-induced air plasma

    NASA Astrophysics Data System (ADS)

    Zhao, Ji; Zhang, LiangLiang; Wu, YiJian; Wu, Tong; Yuan, Hui; Zhang, CunLin; Zhao, YueJin

    2015-08-01

    Intense Terahertz waves generated from air-induced plasma and serving as broadband THz source provide a promising broadband source for innovative technology. Terahertz generation in selected gases has attracted more and more researchers' interests in recent years. In this research, the THz emission from different atoms is described, such as nitrogen, argon and helium in Michelson. The THz radiation is detected by a Golay Cell equipped with a 6-mm-diameter diamond-inputting window. It can be seen in the first time that when the pump power lies at a stable level, the THz generation created by the femtosecond laser focusing on the nitrogen is higher than which focusing on the helium, and lower than that produced in the argon gas environment. We believe that the THz intensity is Ar > N > Ne because of its atomic mass, which is Ar > N > Ne as well. It is clear that the Gas molecular decides the release of free electrons ionized from ultra short femtosecond laser through the electronic dynamic analysis. The higher the gas mass is, the stronger the terahertz emission will be. We further explore the THz emission at the different laser power levels, and the experimental results can be commendably quadratic fitted. It can be inferred that THz emission under different gas medium environment still complies with the law of four-wave mixing (FWM) process and has nothing to do with the gas environment: the radiation energy is proportional to the quadratic of incident laser power.

  13. Analysis of high voltage dielectric insulation materials of XLPE by THz-TDS system

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Yan, Zhijin; Yang, Lei; Dai, Yang; Zhang, Like; Bian, Kangkang; Hou, Lei

    2015-11-01

    In this paper, cross-linked polyethylene (XLPE) was analyzed by THz time domain spectroscopy (TDS) system at room temperature. By recording time domain signal of terahertz radiation field, frequency spectrum can be obtained by Fourier transform. Then the refractive index and dielectric constant in THz band are calculated. This proves that the THz-TDS system has a potential application for detecting the aging characteristic of XLPE.

  14. Co-integrated microfluidic and THz functions for biochip devices

    NASA Astrophysics Data System (ADS)

    Laurette, S.; Treizebre, A.; Bocquet, B.

    2011-06-01

    TeraHertz (THz) spectroscopy is becoming an alternative way to probe biological interactions in real-time conditions. However, accurate and reproducible THz measurements of aqueous solutions, largely represented in life sciences, remain difficult. A THz microsystem which couples both electromagnetic and microfluidic integrated functions is presented here. Its technological process is accurately detailed and enables easy designs of advanced THz and microfluidic functions. It is composed of the deposition of gold wires on a glass wafer to guide the THz waves. Then, a whole silicon wafer is bonded by using a thermosensitive-polymer thermo-compression. Silicon is deep-etched to create the microchannels which are finally covered with a second glass wafer. This bonding-etching process enables huge freedom and independence for electromagnetic and microfluidic designs. The technological process characterization has shown that the manufactured biochip is compatible with pressures up to 37 bar. First measurements with empty and water-filled channels have been carried out and have shown the ability to perform THz spectroscopy inside the chip. Then, first measurements on proteins have been performed and shown the system ability to probe protein concentration. This kind of microfluidic microsystem, allowing complex design for integrated electronic and microfluidic circuits, defines a true new instrumental way for life science investigations.

  15. Tunable THz metamaterials based on phase-changed materials (VO2) triggered by thermal and electrical stimuli

    NASA Astrophysics Data System (ADS)

    Crunteanu, Aurelian; Humbert, Georges; Leroy, Jonathan; Huitema, Laure; Orlianges, Jean-Christophe; Bessaudou, Annie

    2017-02-01

    One of the most peculiar characteristics of the insulator-to-metal transition (MIT) in vanadium dioxide (VO2) material is its broadband response, manifested by drastic electrical and dielectric properties changes between the insulator and metallic states on a very large frequency spectrum. We are presenting the characterization of the MIT in VO2 films over a wide range of the electromagnetic spectrum (75-110GHz, 0.1-1.4THz) and illustrate the materials' capabilities for manipulating the electromagnetic radiation in the millimeter-waves and THz domains. We demonstrate the possibility of realizing tunable THz devices by introducing this phase transition material as localized patterns in the structure of THz planar metamaterials. We designed, simulated and fabricated tunable VO2-based THz metamaterials devices which show significant variations in their THz transmission under the effect of thermal stimuli but also by applying an electrical voltage across the devices.

  16. First tests of THz transmission through a Diamond Anvil Cell

    SciTech Connect

    John Klopf

    2011-01-24

    The THz source generated by the accelerator driver for the Jefferson Lab Free Electron Laser is unique in the world in its ability to deliver a high average power beam of ultrashort (<500 fs FWHM) broadband THz pulses. The spectrum of this source presents an ideal probe for many low energy phenomena, and the time structure enables measurement of dynamic processes with sub-ps resolution. An outline of the range of potential applications for this THz source as a probe of sub-ps dynamics in materials under extreme conditions will be presented. To demonstrate the capabilities of this source for just such experiments, the first set of tests to characterize the transmission of the THz beam through a diamond anvil cell (DAC) have been performed. These preliminary results will be presented along with a description of the optical design used to deliver the THz beam into and out of the DAC. The current design will be compared with other possible techniques and the plans for the next set of measurements will also be given.

  17. THz near-field imaging of biological tissues employing synchrotronradiation

    SciTech Connect

    Schade, Ulrich; Holldack, Karsten; Martin, Michael C.; Fried,Daniel

    2004-12-23

    Terahertz scanning near-field infrared microscopy (SNIM) below 1 THz is demonstrated. The near-field technique benefits from the broadband and highly brilliant coherent synchrotron radiation (CSR) from an electron storage ring and from a detection method based on locking onto the intrinsic time structure of the synchrotron radiation. The scanning microscope utilizes conical wave guides as near-field probes with apertures smaller than the wavelength. Different cone approaches have been investigated to obtain maximum transmittance. Together with a Martin-Puplett spectrometer the set-up enables spectroscopic mapping of the transmittance of samples well below the diffraction limit. Spatial resolution down to about lambda/40 at 2 wavenumbers (0.06 THz) is derived from the transmittance spectra of the near-field probes. The potential of the technique is exemplified by imaging biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 mu-m at about 12 wave numbers (0.36 THz). The THz near-field images reveal distinct structural differences of leaves from different plants investigated. The technique presented also allows spectral imaging of bulky organic tissues. Human teeth samples of various thicknesses have been imaged between 2 and 20 wavenumbers (between 0.06and 0.6 THz). Regions of enamel and dentin within tooth samples are spatially and spectrally resolved, and buried caries lesions are imaged through both the outer enamel and into the underlying dentin.

  18. THz Magneto-Photoresponse Spectroscopy of Two-Dimensional Electrons in an InAs/InGaAs/InAlAs Inserted-Channel

    NASA Astrophysics Data System (ADS)

    Pakmehr, Mehdi; Khaetskii, A.; McCombe, B. D.; Chiatti, O.; Fischer, S. F.; Heyn, Ch.; Hansen, W.

    2015-03-01

    We have used THz magneto-photoresponse/transmission to measure various electronic parameters of a two-dimensional electron gas (2DEG) located primarily within an InAs inserted-channel and the surrounding InGaAs well in an asymmetric InAs/InGaAs/InAlAs inserted-well heterostructure in magnetic fields up to 10 T. We have developed an analytical approach to the photoresponse based on resonant heating of the 2DEG by cyclotron resonance (CR) absorption. The analysis incorporates a resonant T-profile mimicking the CR absorption, combined with the theoretical expression for quantized resistance oscillations of a 2DEG. Fitting of an individual set of PR data vs. magnetic field can in principle, provide g-factor, cyclotron effective mass, SdH scattering time, CR scattering time and carrier density of the 2DEs. This is a temperature differential technique, which leads to enhanced sensitivity to harmonic content of the Shubnikov-deHaas (S-dH) oscillations and thus to clearer spin-splitting of the Landau levels at lower fields than is possible in direct S-dH measurements at the same bath temperature. Results show an enhanced g-factor for electrons and large g-factor anisotropy.

  19. A broadband terahertz ultrathin multi-focus lens

    PubMed Central

    He, Jingwen; Ye, Jiasheng; Wang, Xinke; Kan, Qiang; Zhang, Yan

    2016-01-01

    Ultrathin transmission metasurface devices are designed on the basis of the Yang-Gu amplitude-phase retrieval algorithm for focusing the terahertz (THz) radiation into four or nine spots with focal spacing of 2 or 3 mm at a frequency of 0.8 THz. The focal properties are experimentally investigated in detail, and the results agree well with the theoretical expectations. The designed THz multi-focus lens (TMFL) demonstrates a good focusing function over a broad frequency range from 0.3 to 1.1 THz. As a transmission-type device based on metasurface, the diffraction efficiency of the TMFL can be as high as 33.92% at the designed frequency. The imaging function of the TMFL is also demonstrated experimentally and clear images are obtained. The proposed method produces an ultrathin, low-cost, and broadband multi-focus lens for THz-band application PMID:27346430

  20. Ultrafast broadband laser spectroscopy reveals energy and charge transfer in novel donor-acceptor triads for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Roland, T.; Hernandez Ramirez, G.; Léonard, J.; Méry, S.; Haacke, S.

    2011-02-01

    Triggered by the quest for new organic materials and micro-structures for photovoltaic applications, a novel class of donor-acceptor-donor (DAD) triads extended with siloxane chains has been synthesized in our labs. Because of the siloxane chains, the molecules self-organize into a smectic liquid crystal phase, resulting in a stacking of the DAD cores.We report here a preliminary study of the ultrafast dynamics of energy and charge transfer studied by femtosecond broadband transient absorption experiments on isolated triads in chloroform.

  1. Broadband terahertz pulse emission from ZnGeP_2

    NASA Astrophysics Data System (ADS)

    Rowley, J. D.; Pierce, J. K.; Brant, A. T.; Halliburton, L. E.; Giles, N. C.; Schunemann, P. G.; Bristow, A. D.

    2012-03-01

    Optical rectification is demonstrated in (110)-cut ZnGeP_2 (ZGP) providing broadband terahertz (THz) generation. The source is compared to both GaP and GaAs over a wavelength range of 1150 nm to 1600 nm and peak intensity range of 0.5 GW/cm^2 to 40 GW/cm^2. ZGP peak-to-peak field amplitude is larger than in the other materials due to either lower nonlinear absorption or larger second order nonlinearity. This material is well suited for broadband THz generation across a wide range of infrared excitation wavelengths.

  2. Electromagnetic THz Radiation Modeling by DPSM

    NASA Astrophysics Data System (ADS)

    Rahani, Ehsan Kabiri; Kundu, Tribikram

    2012-03-01

    THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated.

  3. THz Sources for Space

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Ward, John; Maiwald, Frank; Mehdi, Imran

    2007-01-01

    Terahertz is the primary frequency for line and continuum radiation from cool (5-100K) gas (atoms and molecules) and dust. This viewgraph presentation reviews the reasons for the interest in Terahertz Space Applications; the Terahertz Space Missions: in the past, present and planned for the future, Terahertz source requirements and examples of some JPL instruments; and a case study for a flight deliverable: THz Local Oscillators for ESA s Herschel Space Telescope

  4. Broadband homonuclear correlation spectroscopy driven by combined R2(n)(v) sequences under fast magic angle spinning for NMR structural analysis of organic and biological solids.

    PubMed

    Hou, Guangjin; Yan, Si; Trébosc, Julien; Amoureux, Jean-Paul; Polenova, Tatyana

    2013-07-01

    We recently described a family of experiments for R2n(v) Driven Spin Diffusion (RDSD) spectroscopy suitable for homonuclear correlation experiments under fast MAS conditions [G. Hou, S. Yan, S.J. Sun, Y. Han, I.J. Byeon, J. Ahn, J. Concel, A. Samoson, A.M. Gronenborn, T. Polenova, Spin diffusion drive by R-symmetry sequencs: applications to homonuclear correlation spectroscopy in MAS NMR of biological and organic solids, J. Am. Chem. Soc. 133 (2011) 3943-3953]. In these RDSD experiments, since the broadened second-order rotational resonance conditions are dominated by the radio frequency field strength and the phase shifts, as well as the size of reintroduced dipolar couplings, the different R2n(v) sequences display unique polarization transfer behaviors and different recoupling frequency bandwidths. Herein, we present a series of modified R2n(v) sequences, dubbed COmbined R2n(v)-Driven (CORD), that yield broadband homonuclear dipolar recoupling and give rise to uniform distribution of cross peak intensities across the entire correlation spectrum. We report NMR experiments and numerical simulations demonstrating that these CORD spin diffusion sequences are suitable for broadband recoupling at a wide range of magnetic fields and MAS frequencies, including fast-MAS conditions (νr=40 kHz and above). Since these CORD sequences are largely insensitive to dipolar truncation, they are well suited for the determination of long-range distance constraints, which are indispensable for the structural characterization of a broad range of systems. Using U-(13)C,(15)N-alanine and U-(13)C,(15)N-histidine, we show that under fast-MAS conditions, the CORD sequences display polarization transfer efficiencies within broadband frequency regions that are generally higher than those offered by other existing spin diffusion pulse schemes. A 89-residue U-(13)C,(15)N-dynein light chain (LC8) protein has also been used to demonstrate that the CORD sequences exhibit uniformly high cross peak

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  6. Tunable near- to mid-infrared pump terahertz probe spectroscopy in reflection geometry

    NASA Astrophysics Data System (ADS)

    Zhang, S. J.; Wang, Z. X.; Dong, T.; Wang, N. L.

    2017-10-01

    Strong-field mid-infrared pump-terahertz (THz) probe spectroscopy has been proven as a powerful tool for light control of different orders in strongly correlated materials. We report the construction of an ultrafast broadband infrared pump-THz probe system in reflection geometry. A two-output optical parametric amplifier is used for generating mid-infrared pulses with GaSe as the nonlinear crystal. The setup is capable of pumping bulk materials at wavelengths ranging from 1.2 μm to 15 μm and beyond, and detecting the subtle, transient photoinduced changes in the reflected electric field of the THz probe at different temperatures. As a demonstration, we present 15 μm pump-THz probe measurements of a bulk EuSbTe3 single crystal. A 0:5% transient change in the reflected THz electric field can be clearly resolved. The widely tuned pumping energy could be used in mode-selective excitation experiments and applied to many strongly correlated electron systems.

  7. Oxidation kinetics of nanoscale copper films studied by terahertz transmission spectroscopy

    NASA Astrophysics Data System (ADS)

    Ramanandan, Gopika K. P.; Ramakrishnan, Gopakumar; Planken, Paul C. M.

    2012-06-01

    Terahertz (THz) transmission spectroscopy is used to measure the oxidation kinetics of copper thin films evaporated on silicon substrates. The transmission of broadband THz pulses from 1 to 7 THz through the copper film is measured while it gets oxidized at an elevated temperature in ambient air. The change in the transmitted THz electric field is correlated with the growth of the cuprous oxide layer and the decrease in thickness of the copper layer. Oxidation curves were obtained for heating temperatures of 120-150 °C and were found to follow a parabolic rate law. Using the Arrhenius equation, we calculate an activation energy for diffusion of 0.55 eV. By measuring the THz transmission through unoxidized copper layers of several thicknesses, we also measured the optical properties of thin copper films around the percolation threshold thickness of 7 nm. Around the percolation transition, the optical properties of freshly deposited copper thin films are very different from that of copper layers of the same thickness remaining after partial oxidation of thick copper films.

  8. Quantitative broadband absorption and scattering spectroscopy in turbid media by combined frequency-domain and steady state methodologies

    DOEpatents

    Tromberg, Bruce J.; Berger, Andrew J.; Cerussi, Albert E.; Bevilacqua, Frederic; Jakubowski, Dorota

    2008-09-23

    A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain and steady-state reflectance methods. Most of the wavelength coverage is provided by a white-light steady-state measurement, whereas the frequency-domain data are acquired at a few selected wavelengths. Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest. The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values.

  9. Primary α and secondary β relaxation dynamics of meta-toluidine in the liquid state investigated by broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Švajdlenková, H.; Ruff, A.; Lunkenheimer, P.; Loidl, A.; Bartoš, J.

    2017-08-01

    We report a broadband dielectric spectroscopic (BDS) study on the clustering fragile glass-former meta-toluidine (m-TOL) from 187 K up to 289 K over a wide frequency range of 10-3-109 Hz with focus on the primary α relaxation and the secondary β relaxation above the glass temperature Tg. The broadband dielectric spectra were fitted by using the Havriliak-Negami (HN) and Cole-Cole (CC) models. The β process disappearing at Tβ,disap = 1.12Tg exhibits non-Arrhenius dependence fitted by the Vogel-Fulcher-Tamman-Hesse equation with T0βVFTH in accord with the characteristic differential scanning calorimetry (DSC) limiting temperature of the glassy state. The essential feature of the α process consists in the distinct changes of its spectral shape parameter βHN marked by the characteristic BDS temperatures TB1βHN and TB2βHN. The primary α relaxation times were fitted over the entire temperature and frequency range by several current three-parameter up to six-parameter dynamic models. This analysis reveals that the crossover temperatures of the idealized mode coupling theory model (TcMCT), the extended free volume model (T0EFV), and the two-order parameter (TOP) model (Tmc) are close to TB1βHN, which provides a consistent physical rationalization for the first change of the shape parameter. In addition, the other two characteristic TOP temperatures T0TOP and TA are coinciding with the thermodynamic Kauzmann temperature TK and the second change of the shape parameter at around TB2βHN, respectively. These can be related to the onset of the liquid-like domains in the glassy state or the disappearance of the solid-like domains in the normal liquid state.

  10. A review on the sub-THz/THz gyrotrons

    NASA Astrophysics Data System (ADS)

    Kumar, Nitin; Singh, Udaybir; Bera, Anirban; Sinha, A. K.

    2016-05-01

    A review on the sub-THz/THz gyrotrons is performed in this manuscript. The present development status of gyrotrons can be divided into three streams for the sake of better understanding: 1. low frequency (<35 GHz), medium power (<100 kW), small size and easy to handle gyrotrons for industrial applications, 2. very high power (1 MW or more), medium frequency (100-200 GHz) gyrotrons for plasma fusion applications, 3. low power (few tens of watt to kW), high frequency (>200 GHz) gyrotrons for various innovative applications. In this manuscript, the third stream of gyrotron development is reviewed. In last few decades several innovative applications are searched in sub-THz/THz band where the gyrotrons could be used as an efficient source of RF radiation. The applications of sub-THz/THz gyrotrons including the futuristic scope of the device are also discussed in this article. Further, several criticalities arise in the design and development when the gyrotron operation shifts toward the high frequency band. Various such design and technological challenges are also discussed here. Finally the development status of sub-THz/THz gyrotrons as per the use in various scientific and technological applications is also discussed.

  11. Polarization-sensitive electro-optic detection of terahertz wave using three different types of crystal symmetry: Toward broadband polarization spectroscopy

    SciTech Connect

    Oguchi, Kenichi; Iwasaki, Hotsumi; Okano, Makoto; Watanabe, Shinichi

    2016-01-04

    We investigated polarization-sensitive electro-optic (EO) detection of terahertz (THz) waves by using two uniaxial crystals: a c-cut gallium selenide and a c-cut lithium niobate crystals. We formulated a general frequency-domain description of EO detection by in-plane isotropic EO crystals, which holds regardless of the frequency. Based on this description, the polarization of THz waves can be derived by analyzing EO sampling signals measured with two orthogonal configurations of the in-plane isotropic EO crystals as well as typical (111) zinc-blende EO crystals. In addition, we experimentally demonstrated that the frequency-dependent polarization of THz waves can be reproducibly retrieved using three EO crystals with different crystal symmetries and with different phase matching conditions. Our description provides essential information for practical polarization sensing in the THz frequency range as well as in the mid-infrared range.

  12. A polarization-independent broadband terahertz absorber

    SciTech Connect

    Shi, Cheng; Zang, XiaoFei E-mail: ymzhu@usst.edu.cn; Wang, YiQiao; Chen, Lin; Cai, Bin; Zhu, YiMing E-mail: ymzhu@usst.edu.cn

    2014-07-21

    A highly efficient broadband terahertz absorber is designed, fabricated, and experimentally as well as theoretically evaluated. The absorber comprises a heavily doped silicon substrate and a well-designed two-dimensional grating. Due to the destructive interference of waves and diffraction, the absorber can achieve over 95% absorption in a broad frequency range from 1 to 2 THz and for angles of incidence from 0° to 60°. Such a terahertz absorber is also polarization-independent due to its symmetrical structure. This omnidirectional and broadband absorber have potential applications in anti-reflection coatings, imaging systems, and so on.

  13. Ultra-broadband room-temperature terahertz quantum cascade laser sources based on difference frequency generation.

    PubMed

    Fujita, Kazuue; Hitaka, Masahiro; Ito, Akio; Yamanishi, Masamichi; Dougakiuchi, Tatsuo; Edamura, Tadataka

    2016-07-25

    We present ultra-broadband room temperature monolithic terahertz quantum cascade laser (QCL) sources based on intra-cavity difference frequency generation, emitting continuously more than one octave in frequency between 1.6 and 3.8 THz, with a peak output power of ~200 μW. Broadband terahertz emission is realized by nonlinear mixing between single-mode and multi-mode spectra due to distributed feedback grating and Fabry-Perot cavity, respectively, in a mid-infrared QCL with dual-upper-state active region design. Besides, at low temperature of 150 K, the device produces a peak power of ~1.0 mW with a broadband THz emission centered at 2.5 THz, ranging from 1.5 to 3.7 THz.

  14. Dielectric THz waveguides

    NASA Astrophysics Data System (ADS)

    Dupuis, Alexandre

    In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (˜25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber

  15. In Vivo, Non-Invasive Characterization of Human Bone by Hybrid Broadband (600-1200 nm) Diffuse Optical and Correlation Spectroscopies

    PubMed Central

    Pagliazzi, Marco; Negredo, Eugènia; Martelli, Fabrizio; Farina, Andrea; Dalla Mora, Alberto; Lindner, Claus; Farzam, Parisa; Pérez-Álvarez, Núria; Puig, Jordi; Taroni, Paola; Pifferi, Antonio; Durduran, Turgut

    2016-01-01

    Non-invasive in vivo diffuse optical characterization of human bone opens a new possibility of diagnosing bone related pathologies. We present an in vivo characterization performed on seventeen healthy subjects at six different superficial bone locations: radius distal, radius proximal, ulna distal, ulna proximal, trochanter and calcaneus. A tailored diffuse optical protocol for high penetration depth combined with the rather superficial nature of considered tissues ensured the effective probing of the bone tissue. Measurements were performed using a broadband system for Time-Resolved Diffuse Optical Spectroscopy (TRS) to assess mean absorption and reduced scattering spectra in the 600–1200 nm range and Diffuse Correlation Spectroscopy (DCS) to monitor microvascular blood flow. Significant variations among tissue constituents were found between different locations; with radius distal rich of collagen, suggesting it as a prominent location for bone related measurements, and calcaneus bone having highest blood flow among the body locations being considered. By using TRS and DCS together, we are able to probe the perfusion and oxygen consumption of the tissue without any contrast agents. Therefore, we predict that these methods will be able to evaluate the impairment of the oxygen metabolism of the bone at the point-of-care. PMID:27997565

  16. In Vivo, Non-Invasive Characterization of Human Bone by Hybrid Broadband (600-1200 nm) Diffuse Optical and Correlation Spectroscopies.

    PubMed

    Konugolu Venkata Sekar, Sanathana; Pagliazzi, Marco; Negredo, Eugènia; Martelli, Fabrizio; Farina, Andrea; Dalla Mora, Alberto; Lindner, Claus; Farzam, Parisa; Pérez-Álvarez, Núria; Puig, Jordi; Taroni, Paola; Pifferi, Antonio; Durduran, Turgut

    2016-01-01

    Non-invasive in vivo diffuse optical characterization of human bone opens a new possibility of diagnosing bone related pathologies. We present an in vivo characterization performed on seventeen healthy subjects at six different superficial bone locations: radius distal, radius proximal, ulna distal, ulna proximal, trochanter and calcaneus. A tailored diffuse optical protocol for high penetration depth combined with the rather superficial nature of considered tissues ensured the effective probing of the bone tissue. Measurements were performed using a broadband system for Time-Resolved Diffuse Optical Spectroscopy (TRS) to assess mean absorption and reduced scattering spectra in the 600-1200 nm range and Diffuse Correlation Spectroscopy (DCS) to monitor microvascular blood flow. Significant variations among tissue constituents were found between different locations; with radius distal rich of collagen, suggesting it as a prominent location for bone related measurements, and calcaneus bone having highest blood flow among the body locations being considered. By using TRS and DCS together, we are able to probe the perfusion and oxygen consumption of the tissue without any contrast agents. Therefore, we predict that these methods will be able to evaluate the impairment of the oxygen metabolism of the bone at the point-of-care.

  17. On-chip visible-to-infrared supercontinuum generation with more than 495 THz spectral bandwidth.

    PubMed

    Epping, Jörn P; Hellwig, Tim; Hoekman, Marcel; Mateman, Richard; Leinse, Arne; Heideman, René G; van Rees, Albert; van der Slot, Peter J M; Lee, Chris J; Fallnich, Carsten; Boller, Klaus-J

    2015-07-27

    We report ultra-broadband supercontinuum generation in high-confinement Si3N4 integrated optical waveguides. The spectrum extends through the visible (from 470 nm) to the infrared spectral range (2130 nm) comprising a spectral bandwidth wider than 495 THz, which is the widest supercontinuum spectrum generated on a chip.

  18. Excitation of coherent oscillations in underdoped cuprate superconductors by intense THz pulses

    NASA Astrophysics Data System (ADS)

    Hoffmann, Matthias C.; Lee, Wei-Sheng; Dakovski, Georgi L.; Turner, Joshua J.; Gerber, Simon M.; Bonn, Doug; Hardy, Walter; Liang, Ruixing; Salluzzo, Marco

    2016-05-01

    We use intense broadband THz pulses to excite the cuprate superconductors YBCO and NBCO in their underdoped phase, where superconducting and charge density wave ground states compete. We observe pronounced coherent oscillations at attributed to renormalized low-energy phonon modes. These oscillation features are much more prominent than those observed in all-optical pump-probe measurements, suggesting a different excitation mechanism.

  19. Investigation of the Brill transition in nylon 6,6 by Raman, THz-Raman, and two-dimensional correlation spectroscopy.

    PubMed

    Bertoldo Menezes, D; Reyer, A; Musso, M

    2017-09-21

    The Brill transition is a phase transition process in polyamides related with structural changes between the hydrogen bonds of the lateral functional groups (CO) and (NH). In this study, we have used the potential of Raman spectroscopy for exploring this phase transition in polyamide 6,6 (nylon 6,6), due to the sensitivity of this spectroscopic technique to small intermolecular changes affecting vibrational properties of relevant functional groups. During a step by step heating and cooling process of the sample we collected Raman spectra allowing us from two-dimensional Raman correlation spectroscopy to identify which spectral regions suffered the largest influence during the Brill transition, and from Terahertz Stokes and anti-Stokes Raman spectroscopy to obtain complementary information, e.g. on the temperature of the sample. This allowed us to grasp signatures of the Brill transition from peak parameters of vibrational modes associated with (CC) skeletal stretches and (CNH) bending, and to verify the Brill transition temperature at around 160°C, as well as the reversibility of this phase transition. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. Kinetic inductance driven nanoscale 2D and 3D THz transmission lines

    PubMed Central

    Mousavi, S. Hossein; Williamson, Ian A. D.; Wang, Zheng

    2016-01-01

    We examine the unusual dispersion and attenuation of transverse electromagnetic waves in the few-THz regime on nanoscale graphene and copper transmission lines. Conventionally, such propagation has been considered to be highly dispersive, due to the RC time constant-driven voltage diffusion below 1 THz and plasmonic effects at higher optical frequencies. Our numerical modeling across the microwave, THz, and optical frequency ranges reveals that the conductor kinetic inductance creates an ultra-broadband linear-dispersion and constant-attenuation region in the THz regime. This so-called LC region is an ideal characteristic that is known to be absent in macro-scale transmission lines. The kinetic-LC frequency range is dictated by the structural dimensionality and the free-carrier scattering rate of the conductor material. Moreover, up to 40x wavelength reduction is observed in graphene transmission lines. PMID:27137628

  1. Freely-tunable broadband polarization rotator for terahertz waves

    NASA Astrophysics Data System (ADS)

    Peng, Ru-Wen; Fan, Ren-Hao; Zhou, Yu; Jiang, Shang-Chi; Xiong, Xiang; Huang, Xian-Rong; Wang, Mu

    It is known that commercially-available terahertz (THz) emitters usually generate linearly polarized waves only along certain directions, but in practice, a polarization rotator that is capable of rotating the polarization of THz waves to any direction is particularly desirable and it will have various important applications. In this work, we demonstrate a freely tunable polarization rotator for broadband THz waves using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized THz wave to any desired direction with nearly perfect conversion efficiency. The device performance has been experimentally demonstrated by both THz transmission spectra and direct imaging. The polarization rotation originates from multi wave interference in the three-layer grating structure based on the scattering-matrix analysis. We can expect that this active broadband polarization rotator has wide applications in analytical chemistry, biology, communication technology, imaging, etc.. Reference: R. H. Fan, Y. Zhou, X. P. Ren, R. W. Peng, S. C. Jiang, D. H. Xu, X. Xiong, X. R. Huang, and Mu Wang, Advanced Materials 27,1201(2015). Freely-tunable broadband polarization rotator for terahertz waves.

  2. Combined zero-quantum and spin-diffusion mixing for efficient homonuclear correlation spectroscopy under fast MAS: broadband recoupling and detection of long-range correlations.

    PubMed

    Lu, Xingyu; Guo, Changmiao; Hou, Guangjin; Polenova, Tatyana

    2015-01-01

    Fast magic angle spinning (MAS) NMR spectroscopy is emerging as an essential analytical and structural biology technique. Large resolution and sensitivity enhancements observed under fast MAS conditions enable structural and dynamics analysis of challenging systems, such as large macromolecular assemblies and isotopically dilute samples, using only a fraction of material required for conventional experiments. Homonuclear dipolar-based correlation spectroscopy constitutes a centerpiece in the MAS NMR methodological toolbox, and is used essentially in every biological and organic system for deriving resonance assignments and distance restraints information necessary for structural analysis. Under fast MAS conditions (rotation frequencies above 35-40 kHz), dipolar-based techniques that yield multi-bond correlations and non-trivial distance information are ineffective and suffer from low polarization transfer efficiency. To overcome this limitation, we have developed a family of experiments, CORD-RFDR. These experiments exploit the advantages of both zero-quantum RFDR and spin-diffusion based CORD methods, and exhibit highly efficient and broadband dipolar recoupling across the entire spectrum, for both short-range and long-range correlations. We have verified the performance of the CORD-RFDR sequences experimentally on a U-(13)C,(15)N-MLF tripeptide and by numerical simulations. We demonstrate applications of 2D CORD-RFDR correlation spectroscopy in dynein light chain LC8 and HIV-1 CA tubular assemblies. In the CORD-RFDR spectra of LC8 acquired at the MAS frequency of 40 kHz, many new intra- and inter-residue correlations are detected, which were not observed with conventional dipolar recoupling sequences. At a moderate MAS frequency of 14 kHz, the CORD-RFDR experiment exhibits excellent performance as well, as demonstrated in the HIV-1 CA tubular assemblies. Taken together, the results indicate that CORD-RFDR experiment is beneficial in a broad range of conditions

  3. Broad-band spectroscopy of the eclipsing high-mass X-ray binary 4U 1700-37 with Suzaku

    NASA Astrophysics Data System (ADS)

    Jaisawal, Gaurava K.; Naik, Sachindra

    2015-03-01

    We present the results obtained from broad-band spectroscopy of the high-mass X-ray binary 4U 1700-37 using data from a Suzaku observation in 2006 September 13-14 covering 0.29-0.72 orbital phase range. The light curves showed significant and rapid variation in source flux during entire observation. We did not find any signature of pulsations in the light curves. However, a quasi-periodic oscillation at ˜20 mHz was detected in the power density spectrum of the source. The 1-70 keV spectrum was fitted with various continuum models. However, we found that the partially absorbed high-energy cut-off power law and Negative and Positive power law with Exponential cut-off (NPEX) models described the source spectrum well. Iron emission lines at 6.4 and 7.1 keV were detected in the source spectrum. An absorption-like feature at ˜39 keV was detected in the residuals while fitting the data with NPEX model. Considering the feature as cyclotron absorption line, the surface magnetic field of the neutron star was estimated to be ˜3.4 × 1012 G. To understand the cause of rapid variation in the source flux, time-resolved spectroscopy was carried out by dividing the observation into 20 narrow segments. The results obtained from the time-resolved spectroscopy are interpreted as the accretion of inhomogeneously distributed matter in the stellar wind of the supergiant companion star as the cause of observed flux variation in 4U 1700-37. A sharp increase in column density after ˜0.63 orbital phase indicates the presence of an accretion wake that blocks the continuum and produces the eclipse like low-flux segment.

  4. Properties of aqueous solutions in THz frequency range

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    Terahertz time-domain spectroscopy has been used for measuring of bovine serum albumin and glucose solutions response. The transmission and the attenuated total internal reflection geometries have been combined for analyzing the dielectric properties of aqueous solutions spectra at 0.07-3.2 THz.

  5. THz characterization of lysozyme at different conformations

    NASA Astrophysics Data System (ADS)

    Globus, Tatiana; Khromova, Tatyana; Lobo, Rebecca; Woolard, Dwight; Swami, Nathan; Fernandez, Erik

    2005-05-01

    This work demonstrates application of Fourier Transform Infrared Spectroscopy (FTIR) technique in the low terahertz frequency range of 10-25 cm-1 to discriminate between different protein conformations and evaluate possible application of THz spectroscopy for monitoring of protein folding-unfolding process. A specific procedure developed earlier for unfolding lysozyme by salt (KSCN) precipitation and refolding the lysozyme molecules by removing of KSCN and dissolving in sodium acetate was used to prepare three different forms of lysozyme. In addition, two standard procedures were used to prepare samples in unfolded conformation: denaturation at high temperature ~95° C followed by fast freezing, and dissolution in 6 M guanidine. Thin, air dried protein films were characterized as well as material in the form of gel. Spectra reveal resonance features in transmission which represent vibrational modes in the protein samples. A great variability of spectral features for the different conformational states showed the sensitivity of vibrational frequencies to the three dimensional structure of proteins. The results obtained on liquid (gel) samples indicate that THz transmission spectroscopy can be used for monitoring folding-unfolding process in a realistic, aqueous environment.

  6. THz generation by two-color femtosecond filaments with complex polarization states: four-wave mixing versus photocurrent contributions

    NASA Astrophysics Data System (ADS)

    Fedorov, V. Yu; Koulouklidis, A. D.; Tzortzakis, S.

    2017-01-01

    Two-color filamenation in gases is known to produce intense and broadband THz radiation. There are two physical mechanisms responsible for the THz generation in this scheme: four-wave mixing and emission from the induced plasma currents. The case when the main and second harmonic are linearly polarized is well studied including the impact from each of the above mechanisms. However, for the cases when the two-color fields have complex polarization states the role of the four-wave mixing and plasma mechanisms in the formation of the THz polarization is still under-explored. Here we use both the four-wave mixing and photocurrent models in order to consider the THz generation by two-color fields with arbitrary polarizations. We show that under specific polarizations of the two-color field components it is possible to determine which of the mechanisms is responsible for the THz polarization formation.

  7. The Kassel Laboratory Astrophysics Thz Spectrometrs

    NASA Astrophysics Data System (ADS)

    Chantzos, Johanna; Herberth, Doris; Kutzer, Pia; Muster, Christoph; Fuchs, Guido W.; Giesen, Thomas

    2016-06-01

    We present a brief overview of the recently established laboratory astrophysics group in Kassel/Germany with a focus on our THz technology. After an outline of our laboratory equipment and recent projects the talk will focus on our new fast spectral scan technique for molecular jet experiments. Here, a new test setup for broadband fast sweep spectrometry in the MW to submm wavelength region has been realized and can be applied to identify transient molecules in a supersonic jet. An arbitrary waveform generator (AWG) is used to generate chirped pulses with a linear frequency sweep in the MHz regime. Pulse durations are of a few microseconds. These pulses are up-converted in frequency, e.g. into the 50 GHz microwave frequency range utilizing a synthesizer, or using a synthesizer plus standard amplifier multiplier chain (AMC) to reach the 100-300 GHz region. As test, NH_3 has been measured between 18-26 GHz in a supersonic jet of 500 μ s duration. Acetonitrile (CH_3CN) was tested in the (90-110) GHz range. The spectrometer is capable of providing fast, broadband and low-noise measurements. Experiments with non-stabel molecular production conditions can greatly benefit from these advantages. The setup enables the study of Van-der-Waals-clusters, as well as carbon chain molecules and small metal-containing refractory molecules when combined with appropriate molecule sources.

  8. Transmission enhancement of THz pulse through Ag2O-Ag layer detected by THz-TDS

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Li, Wang

    2008-12-01

    We used terahertz time-domain spectroscopy (THz-TDS) to probe the enhancement transmission of Ag2O-Ag compound. Using a 500μm- GaAs substrate attaching to the sample, the evanescent wave is coupled to the far field. And the transmitted amplitude is enhanced, corresponding to the frequent shift and spectra broadening.

  9. Continuously Frequency Tunable High Power Sub-THz Radiation Source—Gyrotron FU CW VI for 600 MHz DNP-NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Idehara, Toshitaka; Kosuga, Kosuke; Agusu, La; Ikeda, Ryosuke; Ogawa, Isamu; Saito, Teruo; Matsuki, Yoh; Ueda, Keisuke; Fujiwara, Toshimichi

    2010-07-01

    A high frequency gyrotron with a 15 T superconducting magnet named Gyrotron FU CW VI has achieved continuous frequency tuning through the relatively wide range of 1.5 GHz near 400 GHz. The operation is at the fundamental cyclotron resonance of the TE06 cavity mode with many higher order axial modes. The output power measured at the end of the circular waveguide system ranges from 10 to 50 watts at the low acceleration voltage of 12 kV for beam electrons. The beam current is also low. It is around 250 mA. This gyrotron is designed as a demountable radiation source for the 600 MHz DNP-NMR spectroscopy. The design and operation results of the gyrotron FU CW VI are presented.

  10. Nondestructive evaluation of crystallized-particle size in lactose-powder by terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamauchi, Satoshi; Hatakeyama, Sakura; Imai, Yoh; Tonouchi, Masayoshi

    2014-03-01

    Transmission-type terahertz time-domain spectroscopy is applied to evaluate crystallized lactose particle of size below 30 μm, which is far too small compared to the wavelength of incident terahertz (THz)-wave. The THz-absorption spectrum of lactose is successfully deconvoluted by Lorentzian to two spectra with peaks at 17.1 cm-1 (0.53 THz) and 45.6 cm-1 (1.37 THz) derived from α-lactose monohydrate, and a spectrum at 39.7 cm-1 (1.19 THz) from anhydrous β-lactose after removal of the broad-band spectrum by polynomial cubic function. Lactose is mainly crystallized into α-lactose monohydrate from the supersaturated solution at room temperature with a small amount of anhydrous β-lactose below 4%. The absorption feature is dependent on the crystallized particle size and the integrated intensity ratio of the two absorptions due to α-lactose monohydrate is correlated in linear for the size.

  11. Optical and THz reflectance investigations of organic solar cells

    NASA Astrophysics Data System (ADS)

    Sporea, Dan; Mihai, Laura; Sporea, Adelina; Galagan, Yulia

    2016-04-01

    Two Organic Photovoltaic devices having a photoactive layer containing Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, 99%), and the layer sequences - glass/ITO/ZnO/PAL/PEDOT:PSS/Ag/encapsulation were non-destructively investigated by diffuse optical spectral reflectance, THz spectroscopy and THz imaging. The proposed methods proved to be powerful tools to support quality assurance in organic solar cells development, facilitating both the localization of manufacturing defects and the device degradation, as they are combined with "classical" evaluation means.

  12. Functional multi-band THz meta-foils

    PubMed Central

    Wu, Jianfeng; Moser, Herbert O.; Xu, Su; Jian, Linke; Banas, Agnieszka; Banas, Krzysztof; Chen, Hongsheng; Bettiol, Andrew A.; Breese, Mark B. H.

    2013-01-01

    In this paper, we present the first experimental demonstration of double- and triple-band negative refraction index meta-foils in the terahertz (THz) region. Multi-band meta-foils constructed by multi-cell S-string resonators in a single structure exhibit simultaneously negative permittivity and negative permeability responses at multiple frequencies. The phenomena are confirmed by numerical simulations and Fourier transform infrared spectroscopy measurements. The flexible, freestanding multi-band meta-foils provide a promising candidate for the development of multi-frequency THz materials and devices. PMID:24346309

  13. Experimental and Theoretical Study of Carnosine in THz Range

    NASA Astrophysics Data System (ADS)

    Yan, Hai-Tao; Wang, Wei-Ning

    2005-12-01

    The characteristic fingerprints of carnosine from 0.2 to 2.6 THz are first measured by terahertz time-domain spectroscopy at room temperature. For the pure carnosine, the refractive index varies between 1.79 and 1.85 with the average value 1.84, while for the carnosine-polyethylene mixture, four absorption peaks centred at 1.37, 1.56, 1.85 and 2.49 THz are detected. A comparison of the theoretical predictions using the density functional theory with the experimental results shows satisfactory agreement except somewhat blue shift.

  14. Independent component analysis applications on THz sensing and imaging

    NASA Astrophysics Data System (ADS)

    Balci, Soner; Maleski, Alexander; Nascimento, Matheus Mello; Philip, Elizabath; Kim, Ju-Hyung; Kung, Patrick; Kim, Seongsin M.

    2016-05-01

    We report Independent Component Analysis (ICA) technique applied to THz spectroscopy and imaging to achieve a blind source separation. A reference water vapor absorption spectrum was extracted via ICA, then ICA was utilized on a THz spectroscopic image in order to clean the absorption of water molecules from each pixel. For this purpose, silica gel was chosen as the material of interest for its strong water absorption. The resulting image clearly showed that ICA effectively removed the water content in the detected signal allowing us to image the silica gel beads distinctively even though it was totally embedded in water before ICA was applied.

  15. A Broadband Terahertz Waveguide T-Junction Variable Power Splitter

    PubMed Central

    Reichel, Kimberly S.; Mendis, Rajind; Mittleman, Daniel M.

    2016-01-01

    In order for the promise of terahertz (THz) wireless communications to become a reality, many new devices need to be developed, such as those for routing THz waves. We demonstrate a power splitting router based on a parallel-plate waveguide (PPWG) T-junction excited by the TE1 waveguide mode. By integrating a small triangular septum into the waveguide plate, we are able to direct the THz light down either one of the two output channels with precise control over the ratio between waveguide outputs. We find good agreement between experiment and simulation in both amplitude and phase. We show that the ratio between waveguide outputs varies exponentially with septum translation offset and that nearly 100% transmission can be achieved. The splitter operates over almost the entire range in which the waveguide is single mode, providing a sensitive and broadband method for THz power splitting. PMID:27352772

  16. A Broadband Terahertz Waveguide T-Junction Variable Power Splitter

    NASA Astrophysics Data System (ADS)

    Reichel, Kimberly S.; Mendis, Rajind; Mittleman, Daniel M.

    2016-06-01

    In order for the promise of terahertz (THz) wireless communications to become a reality, many new devices need to be developed, such as those for routing THz waves. We demonstrate a power splitting router based on a parallel-plate waveguide (PPWG) T-junction excited by the TE1 waveguide mode. By integrating a small triangular septum into the waveguide plate, we are able to direct the THz light down either one of the two output channels with precise control over the ratio between waveguide outputs. We find good agreement between experiment and simulation in both amplitude and phase. We show that the ratio between waveguide outputs varies exponentially with septum translation offset and that nearly 100% transmission can be achieved. The splitter operates over almost the entire range in which the waveguide is single mode, providing a sensitive and broadband method for THz power splitting.

  17. A Broadband Terahertz Waveguide T-Junction Variable Power Splitter.

    PubMed

    Reichel, Kimberly S; Mendis, Rajind; Mittleman, Daniel M

    2016-06-29

    In order for the promise of terahertz (THz) wireless communications to become a reality, many new devices need to be developed, such as those for routing THz waves. We demonstrate a power splitting router based on a parallel-plate waveguide (PPWG) T-junction excited by the TE1 waveguide mode. By integrating a small triangular septum into the waveguide plate, we are able to direct the THz light down either one of the two output channels with precise control over the ratio between waveguide outputs. We find good agreement between experiment and simulation in both amplitude and phase. We show that the ratio between waveguide outputs varies exponentially with septum translation offset and that nearly 100% transmission can be achieved. The splitter operates over almost the entire range in which the waveguide is single mode, providing a sensitive and broadband method for THz power splitting.

  18. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation

    SciTech Connect

    Conradson, Steven D.; Gilbertson, Steven M.; Daifuku, Stephanie L.; Kehl, Jeffrey A.; Durakiewicz, Tomasz; Andersson, David A.; Bishop, Alan R.; Byler, Darrin D.; Maldonado, Pablo; Oppeneer, Peter M.; Valdez, James A.; Neidig, Michael L.; Rodriguez, George

    2015-10-16

    Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. Furthermore, that some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. Interestingly, a macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.

  19. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation

    DOE PAGES

    Conradson, Steven D.; Gilbertson, Steven M.; Daifuku, Stephanie L.; ...

    2015-10-16

    Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. Furthermore, that some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novelmore » mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. Interestingly, a macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.« less

  20. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation

    PubMed Central

    Conradson, Steven D.; Gilbertson, Steven M.; Daifuku, Stephanie L.; Kehl, Jeffrey A.; Durakiewicz, Tomasz; Andersson, David A.; Bishop, Alan R.; Byler, Darrin D.; Maldonado, Pablo; Oppeneer, Peter M.; Valdez, James A.; Neidig, Michael L.; Rodriguez, George

    2015-01-01

    Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields. PMID:26472071

  1. THz spectroscopy of AlH (X {sup 1}Σ{sup +}): Direct measurement of the J = 2 ← 1 transition

    SciTech Connect

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

    2014-08-10

    The J = 2 ← 1 rotational transition of AlH (X {sup 1}Σ{sup +}) near 755 GHz and the J = 4 ← 3 line of AlD (X {sup 1}Σ{sup +}) near 787 GHz have been measured using terahertz direct absorption spectroscopy. Both species were created in an AC discharge of Al(CH{sub 3}){sub 3} and H{sub 2} or D{sub 2} in the presence of argon. This work is the first direct measurement of both transitions. These data were combined with previous submillimeter transition frequencies for both molecules recorded by Halfen and Ziurys in global analyses to refine their spectroscopic parameters. The constants B and D for AlH were determined for the first time based on pure rotational data only, improving their accuracy, while those for AlD were slightly refined. Predictions for higher-lying transitions of AlH must consequently be revised by at least 50 MHz, a significant difference. AlH has been observed via its A {sup 1}Π-X {sup 1}Σ{sup +} electronic transition in stellar photospheres, suggesting that this species may be present in circumstellar gas surrounding late-type stars, where five aluminum-bearing molecules have already been detected.

  2. THz-metamaterial absorbers

    NASA Astrophysics Data System (ADS)

    Tuong Pham, Van; Park, J. W.; Vu, Dinh Lam; Zheng, H. Y.; Rhee, J. Y.; Kim, K. W.; Lee, Y. P.

    2013-03-01

    An ultrabroad-band metamaterial absorber was investigated in mid-IR regime based on a similar model in previous work. The high absorption of metamaterial was obtained in a band of 8-11.7 THz with energy loss distributed in SiO2, which is appropriate potentially for solar-cell applications. A perfect absorption peak was provided by using a sandwich structure with periodical anti-dot pattern in the IR region, getting closed to visible-band metamaterials. The dimensional parameters were examined for the corresponding fabrication. Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology, 30 October-2 November, 2012, Ha Long, Vietnam.

  3. Effect of contact force on breast tissue optical property measurements using a broadband diffuse optical spectroscopy handheld probe

    PubMed Central

    Cerussi, Albert; Siavoshi, Sarah; Durkin, Amanda; Chen, Cynthia; Tanamai, Wendy; Hsiang, David; Tromberg, Bruce J.

    2010-01-01

    We investigated the effects of operator-applied force on diffuse optical spectroscopy (DOS) by integrating a force transducer into the handheld probe. Over the typical range of contact forces measured in the breasts of eight patients, absorption and reduced scattering coefficients (650 to 1000 nm) variance was 3.1 ± 1.0% and 1.0 ± 0.4%. For trained operators, we observed <5% variation in hemoglobin and <2% variation in water and lipids. Contact force is not a significant source of variation, most likely because of a relatively wide probe surface area and the stability of the DOS method for calculating tissue optical properties. PMID:19623242

  4. Determination of nitrous acid emission factors from a gasoline vehicle using a chassis dynamometer combined with incoherent broadband cavity-enhanced absorption spectroscopy.

    PubMed

    Nakashima, Yoshihiro; Kajii, Yoshizumi

    2017-01-01

    Nitrous acid (HONO) is a well-known source of hydroxyl radicals in the troposphere. Vehicle exhaust is considered to be one of the primary emission sources of HONO. In this study, measurements of HONO in gasoline vehicle exhaust were carried out using a chassis dynamometer combined with incoherent broadband cavity-enhanced absorption spectroscopy. When catalysts were warm, concentrations of HONO were higher than those prior to catalysts warming. Other species, such as CO, and total hydrocarbons (THCs), showed the opposite pattern. There were no correlations evident between HONO and other trace species concentrations immediately after emission. The HONO/NOx ratio, a good proxy for the formation of HONO in atmosphere, ranged from 1.1 to 6.8×10(-3), which was consistent with previous studies. HONO emission factors (EFs) were calculated to be 0.01-3.6mgkg(-1) fuel, which was different from the vehicle's specifications and those reported under different driving cycles. Annual HONO emissions in Japan were estimated using the calculated EFs and other statistical data.

  5. Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

    SciTech Connect

    Maiuri, Margherita; Réhault, Julien; Polli, Dario; Cerullo, Giulio; Carey, Anne-Marie; Hacking, Kirsty; Cogdell, Richard J.; Garavelli, Marco; Lüer, Larry

    2015-06-07

    We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Q{sub x} and Q{sub y} transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S{sub 2} of the Spx towards the Q{sub x} state of the B890, and (iii) the internal conversion from Q{sub x} to Q{sub y} within the B890.

  6. Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

    NASA Astrophysics Data System (ADS)

    Maiuri, Margherita; Réhault, Julien; Carey, Anne-Marie; Hacking, Kirsty; Garavelli, Marco; Lüer, Larry; Polli, Dario; Cogdell, Richard J.; Cerullo, Giulio

    2015-06-01

    We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Qx and Qy transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S2 of the Spx towards the Qx state of the B890, and (iii) the internal conversion from Qx to Qy within the B890.

  7. Study of the dielectric properties of weathered granite, basalt and quartzite by means of broadband dielectric spectroscopy over a wide range of frequency and temperature.

    NASA Astrophysics Data System (ADS)

    Araujo, Steven; Delbreilh, Laurent; Antoine, Raphael; Dargent, Eric; Fauchard, Cyrille

    2016-04-01

    Broadband Dielectric Spectroscopy (BDS) allows the measurement of the complex impedance of various materials over a wide range of frequency (0.1 Hz to 2 MHz) and temperature (-150 to 400°C). Other properties can be assessed from this measurement such as permittivity and conductivity. In this study, the BDS is presented to figure out the complex behaviour of several rock parameters as a function of the temperature and frequency. Indeed, multiple processes might occur such as interfacial polarization, AC and DC conductivity. The measurements of a weathered granite, basalt and quartzite were performed. The activation energy associated to each process involved during the measurement can be calculated by following the relaxation time as a function of the temperature, taking into account the Havriliak-Négami model. The principle of the technique and the whole study is presented here and several hypothesis are advanced to explain the dielectric behaviour of rocks. Finally, as the range of frequency and temperature of the BDS method is common to several electromagnetic and electrical techniques applied in subsurface geophysics, some perspectives are proposed to better understand geophysical measurements in hydrothermal systems.

  8. Determination of spin pumping as a source of linewidth in sputtered Co90Fe10/Pd multilayers by use of broadband ferromagnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Shaw, Justin M.; Nembach, Hans T.; Silva, T. J.

    2012-02-01

    We performed a systematic study of damping in Co90Fe10/Pd multilayers by use of broadband (1-60 GHz) ferromagnetic resonance (FMR) spectroscopy in the perpendicular geometry. The data were fitted with the conventional Landau-Lifshitz equation in conjunction with an inhomogeneous contribution to linewidth ΔH0. Samples were prepared with net perpendicular anisotropy field values ranging from -0.5 to +1.2 T. ΔH0 shows a dependence on the perpendicular anisotropy, though the Landau-Lifshitz damping parameter α, which ranged from 0.016 to 0.04, exhibits no trend as a function of anisotropy. We explain the wide variation of α as a result of spin pumping from Co90Fe10 into adjacent nonmagnetic layers. We use a quantitative model for spin pumping that includes the intrinsic spin-mixing conductance at the Co90Fe10/Pd interface and the spin-diffusion length of Pd, which were experimentally measured at room temperature to be (1.07 ± 0.13) × 1019 m-2 and 8.6 ± 1.0 nm, respectively. We quantitatively show how α is enhanced by spin pumping through an FMR investigation of individual Pd/CoFe/Pd, and Pd/CoFe/Pd/CoFe/Pd layer structures.

  9. A new broadband near-infrared spectroscopy system for in-vivo measurements of cerebral cytochrome-c-oxidase changes in neonatal brain injury.

    PubMed

    Bale, Gemma; Mitra, Subhabrata; Meek, Judith; Robertson, Nicola; Tachtsidis, Ilias

    2014-10-01

    We present a novel lens-based broadband near-infrared spectroscopy system to simultaneously measure cerebral changes in tissue oxygenation and haemodynamics via estimation of the changes in haemoglobin concentration; in addition to oxygen utilization via the measurement of the oxidation state of cytochrome-c-oxidase (CCO). We demonstrate the use of the system in a cohort of 6 newborn infants with neonatal encephalopathy in the Neonatal Intensive Care Unit for continuous measurement periods of up to 5 days. NIRS data was collected from above the frontal lobe on the left and right hemispheres simultaneously with systemic data to allow multimodal data analysis. This allowed us to study the NIRS variables in response to global pathophysiological events and we focused our analysis to spontaneous oxygen desaturations. We identified changes from the NIRS variables during 236 oxygen desaturations from over 212 hours of data with a change from the baseline to nadir of -12 ± 3%. There was a consistent negative change in the Δ[HbD] (= oxygenated - deoxygenated haemoglobin) and Δ[oxCCO] measurements, mean decreases were 3.0 ± 1.7μM and 0.22 ± 0.11μM, and a positive change in the Δ[HbT] (= oxygenated + deoxygenated haemoglobin) measurements across all subjects, mean increase was 0.85 ± 0.58μM. We have shown with a feasibility study that the relationship between haemoglobin oxygenation changes and CCO oxidation changes during these desaturation events was significantly associated with a magnetic resonance spectroscopy (MRS)-measured biomarker of injury severity (r = 0.91, p<0.01).

  10. Optical Spectroscopy of Serendipitous Chandra Sources from the ChaMP and a Thousand Broad-band SEDs

    NASA Astrophysics Data System (ADS)

    Trichas, Markos; Green, P. J.; Aldcroft, T. L.; Constantin, A.; Silverman, J. D.; Ruiz, A.; Haggard, D.; Barkhouse, W. A.; Kim, D.; Wik, D. R.; Wolfgang, A.; Covey, K. R.; Romero-Colmenero, E.; Smith, M. G.; Wilkes, B. J.; Schechter, P. L.; Marschall, H. L.

    2011-09-01

    From optical spectroscopy of X-ray sources observed as part of the Chandra Multiwavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-ups using the FLWO 1.5m, WIYN 3.5m, CTIO 4m, Magellan 6.5m, MMT 6.5m and Gemini 8m telescopes, and from archival SDSS spectroscopy. We classify the optical counterparts as 50% broad line AGN, 16% emission line galaxies, 14%s absorption line galaxies, and 20% stars. We detect QSOs out to z 5.5 and galaxies out to z 3. We have compiled extensive photometry, including X-ray (ChaMP), UV (GALEX), Optical (SDSS), NIR (UKIDSS, 2MASS), MIR (WISE) and Radio (FIRST, NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for all our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGN and starburst components where both present. The latter in combination to the derived X-ray spectral fits for all our sources will provide us with a large sample to be able to study in detail the AGN/Star-formation coevolution and the relationship between nuclear obscuration and star-formation.

  11. Temperature-dependent THz vibrational spectra of clenbuterol hydrochloride

    NASA Astrophysics Data System (ADS)

    Yang, YuPing; Lei, XiangYun; Yue, Ai; Zhang, Zhenwei

    2013-04-01

    Using the high-resolution Terahertz Time-domain spectroscopy (THz-TDS) and the standard sample pellet technique, the far-infrared vibrational spectra of clenbuterol hydrochloride (CH), a β 2-adrenergic agonist for decreasing fat deposition and enhancing protein accretion, were measured in temperature range of 77-295 K. Between 0.2 and 3.6 THz (6.6-120.0 cm-1), seven highly resolved spectral features, strong line-narrowing and a frequency blue-shift were observed with cooling. However, ractopamine hydrochloride, with some structural and pharmacological similarities to clenbuterol hydrochloride, showed no spectral features, indicating high sensitivity and strong specificity of THz-TDS. These results could be used for the rapid and nondestructive CH residual detection in food safety control.

  12. Relative Infrared (IR) and Terahertz (THz) Signatures of Common Explosives

    SciTech Connect

    Sharpe, Steven W.; Johnson, Timothy J.; Sheen, David M.; Atkinson, David A.

    2006-11-13

    Pacific Northwest National Laboratory (PNNL) has recently recorded the infrared (IR) and far-infrared (sometimes called the terahertz, THz) spectral signatures of four common explosives, in the condensed phase. The signatures of RDX, PETN, TNT and Tetryl were recorded both in the infrared and the THz domains, using Fourier transform infrared (FTIR) spectroscopy. Samples consisted of thin films and were made by depositing and subsequent evaporation of an acetone-explosive mixture. The complete spectrum spanned the range from 4,000 to 8 cm-1 at 2.0 cm-1 spectral resolution. Preliminary results in the infrared agree with those of previous workers, while the THz signatures are one order of magnitude weaker than the strongest IR bands.

  13. Broadband radiometer

    DOEpatents

    Cannon, T.W.

    1994-07-26

    A broadband radiometer is disclosed including (a) an optical integrating sphere having generally spherical integrating chamber and an entry port for receiving light (e.g., having visible and ultraviolet fractions), (b) a first optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to broadband radiation, (c) a second optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to a predetermined wavelength fraction of the broadband radiation, and (d) an output for producing an electrical signal which is proportional to the difference between the two electrical output signals. The radiometer is very useful, for example, in measuring the absolute amount of ultraviolet light present in a given light sample. 8 figs.

  14. Broadband radiometer

    DOEpatents

    Cannon, Theodore W.

    1994-01-01

    A broadband radiometer including (a) an optical integrating sphere having a enerally spherical integrating chamber and an entry port for receiving light (e.g., having visible and ultraviolet fractions), (b) a first optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to broadband radiation, (c) a second optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to a predetermined wavelength fraction of the broadband radiation, and (d) an output for producing an electrical signal which is proportional to the difference between the two electrical output signals. The radiometer is very useful, for example, in measuring the absolute amount of ultraviolet light present in a given light sample.

  15. Terahertz broadband modulation in a biased BiFeO3/Si heterojunction.

    PubMed

    Liu, Xiankuan; Zhang, Zeyu; Lin, Xian; Zhang, Kailin; Jin, Zuanming; Cheng, Zhenxiang; Ma, Guohong

    2016-11-14

    A new terahertz (THz) modulator based on bias-driven carrier conductivity change in a heterojunction was proposed. BiFeO3 film and silicon were selected as building blocks for fabricating the THz modulator. THz nonlinear transmission as a function of bias voltage was studied systematically. THz peak transmission as a function of bias shows a similar tendency as the current-voltage response of the heterojunction: the forward bias leads to the exponential enhancement of THz transmission, and in contrast, the reverse bias shows no observable changes in THz transmission. The modulation depth and modulation bandwidth of THz pulse can reach up to 42% and 1.0 THz with forward bias of 4.8 V, respectively. The observed bias dependent THz transmission in the BFO/Si heterojunction is well-interpreted by the proposed model: the diffused carriers across the heterojunction are localized in BFO thin film with applied forward bias. Our finding provides great potential for applications in designing all electrical broadband THz modulators.

  16. Monitoring long-range electron transfer pathways in proteins by stimulated attosecond broadband X-ray Raman spectroscopy

    DOE PAGES

    Zhang, Yu; Biggs, Jason D.; Govind, Niranjan; ...

    2014-10-09

    In this study, long-range electron transfer (ET) plays a key role in many biological energy conversion and synthesis processes. We show that nonlinear spectroscopy with attosecond X-ray pulses provides a real time movie of the evolving oxidation states and electron densities around atoms, and can probe these processes with high spatial and temporal resolution. This is demonstrated in a simulation study of the stimulated X-ray Raman (SXRS) signals in Re-modified azurin, which had long served as a benchmark for long-range ET in proteins. Nonlinear SXRS signals are sensitive to the local electronic structure and should offer a novel window formore » long-range ET.« less

  17. Compact High Power THz Source

    SciTech Connect

    Geoffrey Krafft

    2003-08-01

    In this paper a new type of THz radiation source, based on recirculating an electron beam through a high gradient superconducting radio frequency cavity, and using this beam to drive a standard electromagnetic undulator, is discussed. Because the beam is recirculated, short bunches may be produced that radiate coherently in the undulator, yielding high average THz power for relatively low average beam power. Deceleration from the coherent emission, and the detuning it causes is discussed.

  18. Investigation of fingerprints for small polar molecules by using a tunable monochromatic THz source

    NASA Astrophysics Data System (ADS)

    Sun, Hongqian

    Over the past 20 years, considerable efforts have been dedicated to the generation and the application of electromagnetic waves in the Terahertz (THz) regime. Among all of the proposed applications, the THz spectroscopy is probably the most mature and promising one. According to the previous reports, the THz spectroscopy has been extensively applied into many analysis fields, including the investigation of vibrational modes for the crystalline solids, the characterization of electron transport in the condense matters and the identification of explosive materials at a standoff distance. More interestingly, since most gas phase chemicals exhibit unique transition peaks in the THz spectra, one could in principle achieve highly accurate molecular fingerprinting and chemical sensing as well. However, all of the practical THz spectroscopy applications were still greatly hampered by the lack of suitable sources and detectors. In this thesis, a unique approach to measure the THz spectrum is developed based on a novel tunable narrowband source. Unlike the previous THz systems, high power THz pulses were generated by the difference frequency generation processes between two collinearly propagated near infrared laser beams. To tune the output THz signal frequency, one can simply adjust one of the incident beam frequencies. Therefore, based on a convenient wavelength tuning scheme, the transmission spectra can be measured for a series of polar gases with either similar or distinct molecular structures. According to the measured spectra, it is found that the obtained transition frequencies, absorption intensities and molecular constants are all in good agreement with the theoretical results tabulated in the molecular spectroscopic databases, such as the HITRAN database. By further analyzing the transition frequencies, it is also discovered that one can confidently identify each polar molecule and differentiate between various isotopic variants based on their characteristic

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  20. On Ultrafast Time-Domain TeraHertz Spectroscopy in the Condensed Phase: Linear Spectroscopic Measurements of Hydrogen-Bond Dynamics of Astrochemical Ice Analogs and Nonlinear TeraHertz Kerr Effect Measurements of Vibrational Quantum Beats

    NASA Astrophysics Data System (ADS)

    Allodi, Marco A.

    . We tentatively observe a new feature in both amorphous solid water and crystalline water at 33 wavenumbers (1 THz). In addition, our studies of mixed and layered ices show how it is possible to identify the location of carbon dioxide as it segregates within the ice by observing its effect on the THz spectrum of water ice. The THz spectra of mixed and layered ices are further analyzed by fitting their spectra features to those of pure amorphous solid water and crystalline water ice to quantify the effects of temperature changes on structure. From the results of this work, it appears that THz spectroscopy is potentially well suited to study thermal transformations within the ice. To advance the study of liquids with THz spectroscopy, we developed a new ultrafast nonlinear THz spectroscopic technique: heterodyne-detected, ultrafast THz Kerr effect (TKE) spectroscopy. We implemented a heterodyne-detection scheme into a TKE spectrometer that uses a stilbazoium-based THz emitter, 4-N,N-dimethylamino-4-N-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS), and high numerical aperture optics which generates THz electric field in excess of 300 kV/cm, in the sample. This allows us to report the first measurement of quantum beats at terahertz (THz) frequencies that result from vibrational coherences initiated by the nonlinear, dipolar interaction of a broadband, high-energy, (sub)picosecond THz pulse with the sample. Our instrument improves on both the frequency coverage, and sensitivity previously reported; it also ensures a backgroundless measurement of the THz Kerr effect in pure liquids. For liquid diiodomethane, we observe a quantum beat at 3.66 THz (122 wavenumbers), in exact agreement with the fundamental transition frequency of the lowest energy vibration of the molecule. This result provides new insight into dipolar vs. Raman selection rules at terahertz frequencies. To conclude we discuss future directions for the nonlinear THz spectroscopy in the Blake lab