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Sample records for porous dielectric thz

  1. Square dielectric THz waveguides.

    PubMed

    Aflakian, N; Yang, N; LaFave, T; Henderson, R M; O, K K; MacFarlane, D L

    2016-06-27

    A holey cladding dielectric waveguide with square cross section is designed, simulated, fabricated and characterized. The TOPAS waveguide is designed to be single mode across the broad frequency range of 180 GHz to 360 GHz as shown by finite-difference time domain simulation and to robustly support simultaneous TE and TM mode propagation. The square fiber geometry is realized by pulling through a heat distribution made square by appropriate furnace design. The transmitted mode profile is imaged using a vector network analyzer with a pinhole at the receiver module. Good agreement between the measured mode distribution and the calculated mode distribution is demonstrated. PMID:27410645

  2. First-Principles Dielectric Spectra of Silicon: THz through UV

    NASA Astrophysics Data System (ADS)

    Lawler, H. M.; Dalosto, S.; Levine, Z. H.; Shirley, E. L.; Rehr, J. J.

    2007-03-01

    We present an implementation of the GW-Bethe-Salpeter-equation approach to first-principles calculations of dielectric response based in part on input from the plane-wave, pseudopotential code ABINIT. This work, together with lattice dynamical calculations, aims to develop versatile codes capable of calculating dielectric spectra in insulators for the full spectral range from THz to the UV. Below the bandgap, lattice vibrations absorb light in the THz range. These spectra are generally composed of sharp infrared-active features (absent by symmetry in silicon); weak, temperature dependent continuum effects from IR-active-multiphonon state hybridization; and contributions to the macroscopic polarization directly from multiphonon states. Above the bandgap, density-functional band structures are taken as a starting point for the inclusion of many-body interactions within the GW-BSE approximation. Emphasis will be on treating the excitionic effects and non-zero-momentum application of the modern theory of polarization with ABINIT.

  3. The source of THz radiation based on dielectric waveguide excited by sequence of electron bunches

    NASA Astrophysics Data System (ADS)

    Altmark, A. M.; Kanareykin, A. D.

    2016-07-01

    We present a new method for excitation of THz Cherenkov radiation in a dielectric waveguide by relativistic electron bunches. A sequence of bunches generates monochromatic radiation. The frequency of radiation is defined by the distance between the bunches. The studies were carried by using the newly updated BBU-3000 code which permits taking into account a number of additional options: an external quadrupole focusing system, group velocity of the wakefield, and the dielectric material loss factor. In this paper, we present our algorithm for optimizing the number and sequential positions of bunches for generation of narrow band high power THz radiation.

  4. Form birefringence in porous semiconductors and dielectrics: A review

    SciTech Connect

    Golovan', L. A. Kashkarov, P. K.; Timoshenko, V. Yu.

    2007-07-15

    The phenomenon of optical anisotropy in porous semiconductors and dielectrics (porous silicon, gallium phosphide, and alumina) and photonic crystal structures formed on their basis is reviewed. It is shown that anisotropic nanostructuring of initially isotropic media leads to the occurrence of strong birefringence. Applicability of the effective-medium model to description of the form birefringence in porous semiconductors and dielectrics is discussed.

  5. A THz Coaxial Two-Channel Dielectric Wakefield Structure for High Gradient Acceleration

    SciTech Connect

    Marshall, T. C.; Sotnikov, G. V.; Hirshfield, J. L.

    2010-11-04

    A coaxial two-channel dielectric wakefield structure is examined for use as a high gradient accelerator. A THz design, having radius {approx}1 mm, is shown to provide GeV/m--level acceleration gradient, high transformer ratio, and stable accelerated bunch motion when excited by a stable-moving 5-GeV 6-nC annular drive bunch.

  6. A THz Coaxial Two-Channel Dielectric Wakefield Structure for High Gradient Acceleration

    NASA Astrophysics Data System (ADS)

    Marshall, T. C.; Sotnikov, G. V.; Hirshfield, J. L.

    2010-11-01

    A coaxial two-channel dielectric wakefield structure is examined for use as a high gradient accelerator. A THz design, having radius ˜1 mm, is shown to provide GeV/m—level acceleration gradient, high transformer ratio, and stable accelerated bunch motion when excited by a stable-moving 5-GeV 6-nC annular drive bunch.

  7. THz Dielectric Properties of High Explosives Calculated by Density Functional Theory for the Design of Detectors

    NASA Astrophysics Data System (ADS)

    Shabaev, A.; Lambrakos, S. G.; Bernstein, N.; Jacobs, V.; Finkenstadt, D.

    2011-12-01

    The current need for better detection of explosive devices has imposed a new necessity for determining the dielectric response properties of energetic materials with respect to electromagnetic wave excitation. Among the range of different frequencies for electromagnetic excitation, the THz frequency range is of particular interest because of its nondestructive nature and ability to penetrate materials that are characteristic of clothing. Typically, the dielectric response properties for electromagnetic wave excitation at THz frequencies, as well as at other frequencies, are determined by means of experimental measurements. The present study, however, emphasizes that density functional theory (DFT), and associated software technology, is sufficiently mature for the determination of dielectric response functions, and actually provides complementary information to that obtained from experiment. In particular, these dielectric response functions provide quantitative initial estimates of spectral response features that can be adjusted with respect to additional information such as laboratory measurements and other types of theory-based calculations, as well as providing for the molecular level interpretation of response structure. This point is demonstrated in the present study by calculations of ground-state resonance structure associated with the high explosives RDX, TNT1, and TNT2 using DFT, which is for the construction of parameterized dielectric response functions for excitation by electromagnetic waves at frequencies within the THz range. The DFT software NRLMOL was used for the calculations of ground-state resonance structure presented here.

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Investigation of optical pump on dielectric tunability in PZT/PT thin film by THz spectroscopy.

    PubMed

    Ji, Jie; Luo, Chunya; Rao, Yunkun; Ling, Furi; Yao, Jianquan

    2016-07-11

    The dielectric spectra of single-layer PbTiO3 (PT), single-layer PbZrxTi1-xO3 (PZT) and multilayer PZT/PT thin films under an external optical field were investigated at room temperature by time-domain terahertz (THz) spectroscopy. Results showed that the real part of permittivity increased upon application of an external optical field, which could be interpreted as hardening of the soft mode and increasing of the damping coefficient and oscillator strength. Furthermore, the central mode was observed in the three films. Among the dielectric property of the three thin films studied, the tunability of the PZT/PT superlattice was the largest. PMID:27410799

  11. Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method.

    PubMed

    Dupuis, Alexandre; Allard, Jean-François; Morris, Denis; Stoeffler, Karen; Dubois, Charles; Skorobogatiy, Maksim

    2009-05-11

    We report several strategies for the fabrication of porous subwavelength fibers using low density Polyethylene plastic for low-loss terahertz light transmission applications. We also characterize transmission losses of the fabricated fibers in terahertz using a novel non-destructive directional coupler method. Within this method a second fiber is translated along the length of the test fiber to probe the power attenuation of a guided mode. The method is especially suitable for measuring transmission losses through short fiber segments, a situation in which standard cutback method is especially difficult to perform. We demonstrate experimentally that introduction of porosity into a subwavelength rod fiber, further reduces its transmission loss by as much as a factor of 10. The lowest fiber loss measured in this work is 0.01 cm(-1) and it is exhibited by the 40% porous subwavelength fiber of diameter 380 microm. For comparison, the loss of a rod-in-the-air subwavelength fiber of a similar diameter was measured to be approximately 0.1 cm(-1), while the bulk loss of a PE plastic used in the fabrication of such fibers is >or= 1 cm(-1). Finally, we present theoretical studies of the optical properties of individual subwavelength fibers and a directional coupler. From these studies we conclude that coupler setup studied in this paper also acts as a low pass filter with a cutoff frequency around 0.3 THz. Considering that the spectrum of a terahertz source used in this work falls off rapidly below 0.25 THz, the reported loss measurements are, thus, the bolometer averages over the approximately 0.25 THz-0.3 THz region. PMID:19434133

  12. Dielectric properties of KDP filled porous alumina nanocomposite thin films.

    PubMed

    Boni, O; Berger, S

    2001-12-01

    A new concept of a composite dielectric thin film fabrication is presented. The fabrication process consists of two stages. The first stage is anodizing a thin aluminum film to produce a porous alumina film that contains an array of nanometer sized parallel pores. The second stage is filling the pores with a saturated KDP (KH2PO4) liquid solution due to capillary forces. After drying KDP nanocrystals are formed inside the pores. This process results in a formation of a composite dielectric thin film composed of the alumina pores walls as one dielectric material and the KDP nanocrystals inside the pores as another dielectric material. The dielectric permittivity of this composite film is higher than that of the porous alumina film at all applied frequencies. The dielectric enhancement is more pronounced at low frequencies due to an interface polarization mechanism. This fabrication process enables controlling the size, composition, and microstructure of the composite dielectric film constituents and thus changing its dielectric properties over a wide range of values. PMID:12914085

  13. Wakefields in THz cylindrical dielectric lined waveguides driven by femtosecond electron bunches

    NASA Astrophysics Data System (ADS)

    Nie, Yuancun

    2015-01-01

    This paper reports the wakefield effects driven by a high-intensity relativistic electron bunch in a dielectric lined waveguide (DLW). A state-of-the-art electron bunch is employed to serve as the drive bunch, which has an rms length of 10 μm, i.e. 33 fs, and a charge of 200 pC. Such bunch parameters are comparable to those of DESY's FLASH and SLAC's LCLS and FACET facilities. It is demonstrated that coherent Cherenkov radiation (CCR) at the fundamental mode with frequency above 1 THz and accelerating gradient as high as 2 GV/m can be obtained in a single layer cylindrical diamond-DLW structure, as long as the geometrical parameters of the DLW are properly selected to match the drive bunch. Wakefield-induced energy modulations on the drive bunch itself are studied as well, which can be used to reduce its energy spread or to produce microbunches with much shorter length from it. The simulated results agree well with the theoretical predictions. Such wakefields can be used to accelerate or modulate electron bunches with ultra-high gradients, and produce high power THz radiations directly. These properties have potential applications in the fields of compact colliders and advanced radiation sources.

  14. The dielectric properties of porous zinc oxide ceramics

    SciTech Connect

    Calame, J.P.; Carmel, Y.; Gershon, D.; Birman, A.; Martin, L.P.; Dadon, D.; Rosen, M.

    1996-12-31

    Measurements of the complex dielectric constant of microwave sintered, porous ZnO at 2.45 GHz are presented. The dielectric properties as a function of porosity do not obey the standard Maxwell-Garnet dielectric mixing law with the ceramic material as the major phase, but instead behave as if the ceramic grains always remain in relatively poor electrical contact even at very high densities. Electromagnetic simulations, carried out for a variety of microstructure geometries, are performed to explore this observation. A model which treats the ceramic as an array of grains and pores, with the grains separated from each other by non- or slightly-percolating, fractal-geometry surfaces, provides a good description of the experimental results.

  15. Dielectric breakdown in nano-porous thin films

    NASA Astrophysics Data System (ADS)

    Borja, Juan Pablo

    Unknown to most computer users and mobile device enthusiasts, we have finally entered into a critical age of chip manufacturing. January of 2014 marks the official start of the quest by the semiconductor industry to successfully integrate sub 14nm process technology nodes in accordance to the International Technology Roadmap for Semiconductors (ITRS). The manufacturing of nano-scale features represents a major bottleneck of its own. However, a bigger challenge lies in reliably isolating the massive chip interconnect network. The present work is aimed at generating a theoretical and experimental framework to predict dielectric breakdown for thin films used in computer chip components. Here, a set of experimental techniques are presented to assess and study dielectric failure in novel thin films. A theory of dielectric breakdown in thin nano-porous films is proposed to describe combined intrinsic and metal ion catalyzed failure. This theory draws on experimental evidence as well as fundamental concepts from mass and electronic charge transport. The drift of metal species was found to accelerate intrinsic dielectric failure. The solubility of metals species such as Cu was found to range from 7.0x1025 ions/m3 to 1.86x1026 ions/m3 in 7% porous SiCOH films. The diffusion coefficient for Cu species was found to span from 4.2x10-19 m2/s to 1.86x10-21 m2/s. Ramped voltage stress experiments were used to identify intrinsic failure from metal catalyzed failure. Intrinsic breakdown is defined when time to failure against applied field ramp rate results in ∂(ln(TTF))/∂(ln(R)) ≈ -1. Intrinsic failure was studied using Au. Here, ∂(ln(TTF))/∂(ln(R)) ≈ -0.95, which is an experimental best case scenario for intrinsic failure. Au is commonly reluctant to ionize which means that failure occurs in the absence of ionic species. Metal catalyzed failure was investigated using reactive electrodes such as Cu, and Ag. Here, trends for ∂(ln(TTF))/∂(ln(R)) significantly

  16. 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.

  17. Towards low-loss, infrared and THz nanophotonics and metamaterials: surface phonon polariton modes in polar dielectric crystals (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Caldwell, Joshua D.; Lindsey, Lucas; Giannini, Vincenzo; Vurgaftman, Igor; Reinecke, Thomas L.; Maier, Stefan A.; Glembocki, Orest J.

    2015-09-01

    The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based surface plasmon materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. One highly promising alternative are polar dielectric crystals whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Both SiC and hexagonal BN are two exemplary SPhP systems, which along with a whole host of alternative materials promise to transform nanophotonics and metamaterials in the mid-IR to THz spectral range. In addition to the lower losses, these materials offer novel opportunities not available with traditional plasmonics, for instance hyperbolic optical behavior in natural materials such as hBN, enabling super-resolution imaging without the need for complex fabrication. This talk will provide an overview of the SPhP phenomenon, a discussion of what makes a `good' SPhP material and recent results from SiC and the naturally hyperbolic material, hBN from our research group.

  18. Experimental Plans to Explore Dielectric Wakefield Acceleration in the THZ Regime

    SciTech Connect

    Lemery, F.; Mihalcea, D.; Piot, P.; Behrens, C.; Elsen, E.; Flottmann, K.; Gerth, C.; Kube, G.; Schmidt, B.; Osterhoff, J.; Stoltz, P.

    2011-09-07

    Dielectric wakefield accelerators have shown great promise toward high-gradient acceleration. We investigate the performances of a possible experiment under consideration at the FLASH facility in DESY to explore wakefield acceleration with an enhanced transformer ratio. The experiment capitalizes on a unique pulse shaping capability recently demonstrated at this facility. In addition, the facility incorporates a superconducting linear accelerator that could generate bunch trains with closely spaced bunches thereby opening the exploration of potential dynamical effects in dielectric wakefield accelerators.

  19. Time-dependent dielectric breakdown measurements of porous organosilicate glass using mercury and solid metal probes

    SciTech Connect

    Pei, Dongfei; Nichols, Michael T.; Shohet, J. Leon; King, Sean W.; Clarke, James S.; Nishi, Yoshio

    2014-09-01

    Time-dependent dielectric breakdown (TDDB) is one of the major concerns for low-k dielectric materials. During plasma processing, low-k dielectrics are subjected to vacuum ultraviolet photon radiation and charged-particle bombardment. To examine the change of TDDB properties, time-to-breakdown measurements are made to porous SiCOH before and after plasma exposure. Significant discrepancies between mercury and solid-metal probes are observed and have been shown to be attributed to mercury diffusion into the dielectric porosities.

  20. Sub-THz complex dielectric constants of smectite clay thin samples with Na+/Ca++ ions

    NASA Astrophysics Data System (ADS)

    Rahman, Rezwanur; McCarty, Douglas K.; Prasad, Manika

    2015-09-01

    We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm-1 to 4.95 cm-1) of oriented smectite samples using an open cavity resonator connected to a submillimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na+ ion and Ca++ ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner (˜30 μm) than the glass substrate (˜2.18 mm). The real part of dielectric constant, ɛre, is essentially constant over this frequency range but is larger in Na+ ion than in Ca++ ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, ɛim) of both samples increases monotonically at lower frequencies (<110 GHz) but shows rapid increase for Na+ ions in the regime > 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., ζ potential in the Stern layers.

  1. Mechanical property changes in porous low-k dielectric thin films during processing

    SciTech Connect

    Stan, G. Gates, R. S.; Kavuri, P.; Torres, J.; Michalak, D.; Ege, C.; Bielefeld, J.; King, S. W.

    2014-10-13

    The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

  2. Mechanical property changes in porous low-k dielectric thin films during processing

    NASA Astrophysics Data System (ADS)

    Stan, G.; Gates, R. S.; Kavuri, P.; Torres, J.; Michalak, D.; Ege, C.; Bielefeld, J.; King, S. W.

    2014-10-01

    The design of future generations of Cu-low-k dielectric interconnects with reduced electronic crosstalk often requires engineering materials with an optimal trade off between their dielectric constant and elastic modulus. This is because the benefits associated with the reduction of the dielectric constant by increasing the porosity of materials, for example, can adversely affect their mechanical integrity during processing. By using load-dependent contact-resonance atomic force microscopy, the changes in the elastic modulus of low-k dielectric materials due to processing were accurately measured. These changes were linked to alterations sustained by the structure of low-k dielectric films during processing. A two-phase model was used for quantitative assessments of the elastic modulus changes undergone by the organosilicate skeleton of the structure of porous and pore-filled dielectrics.

  3. Non-porous low-k dielectric films based on a new structural amorphous fluoropolymer.

    PubMed

    Yuan, Chao; Jin, Kaikai; Li, Kai; Diao, Shen; Tong, Jiawei; Fang, Qiang

    2013-09-20

    A non-porous and amorphous fluoropolymer PFN with low dielectric constant of 2.33 and dielectric loss less than 1.2 × 10(-3) is reported here. PFN also exhibits good mechanical properties and high thermostability. This study is a new example of a fully dense material showing a low k value and having good thermo/mechanical properties. PMID:23857724

  4. Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

    SciTech Connect

    Im, Ji Sun; Bae, Tae-Sung; Lee, Sung Kyu; Lee, Sei-Hyun; Jeong, Euigyung; Kang, Phil Hyun; Lee, Young-Seak

    2010-11-15

    We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.

  5. Skeletal silica characterization in porous-silica low-dielectric-constant films by infrared spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Takada, Syozo; Hata, Nobuhiro; Seino, Yutaka; Fujii, Nobutoshi; Kikkawa, Takamaro

    2005-06-01

    Porous-silica low-dielectric-constant (low-k) films were prepared using a sol-gel method based on the self-assembly of surfactant templates. No change in the refractive index at 633 nm nor in the infrared-absorption intensities of C-H and O-H stretching vibrations at around 2900 and 3400cm-1 of porous-silica low-k films were observed after annealing at each temperature from 523 to 723 K. On the other hand, the Young's elastic modulus and hardness increased with the increase of annealing temperature. The structure in the complex dielectric function of porous-silica low-k films observed in between 1000 and 1400cm-1 is assigned as the asymmetric stretching vibration mode of the Si-O-Si bond. By applying the effective-medium theory by Bruggeman to the experimental results from infrared spectroscopic ellipsometry, we analyzed the skeletal silica structures. The peak positions of transverse (ωTO) and longitudinal (ωLO) vibration modes for Si-O-Si network in the silica skeleton of porous-silica films changed from 1061 to 1068cm-1 and from 1219 to 1232cm-1, respectively, with the annealing temperature. It is shown that the ωLO2/ωTO2 of skeletal silica correlates with Young's elastic modulus of porous-silica low-k films.

  6. Dielectric/metal sidewall diffusion barrier for Cu/porous ultralow-k interconnect technology

    NASA Astrophysics Data System (ADS)

    Chen, Zhe; Prasad, K.; Li, C. Y.; Lu, P. W.; Su, S. S.; Tang, L. J.; Gui, D.; Balakumar, S.; Shu, R.; Kumar, Rakesh

    2004-03-01

    With the acknowledged insufficiency of traditional Ta or TaN barriers, deposited by physical vapor deposition (PVD), in the Cu/porous ultralow-k intermetal dielectric integration, an amorphous hydrogenated SiC (a-SiC:H)/Ta bilayer sidewall diffusion barrier has been fabricated using 0.13 μm Cu/porous ultralow-k [Porous-SiLK (Proprietary product from Dow Chemical Corporation, USA), k˜2.2] single damascene process. The electrical tests show that the line-to-line leakage current and the electrical breakdown field (EBD) of samples with this a-SiC:H/Ta dielectric/metal bilayer structure are significantly improved compared to the conventional PVD multi-stacked Ta(N) sidewall barrier. This improvement is mostly due to surface roughness modification after the deposition of a-SiC:H film, which, in addition to being a good barrier to Cu diffusion, can effectively "seal" the weak points on the surface of porous low-k material that are responsible for the sidewall barrier failure.

  7. Preparation and structure of porous dielectrics by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Gates, S. M.; Neumayer, D. A.; Sherwood, M. H.; Grill, A.; Wang, X.; Sankarapandian, M.

    2007-05-01

    The preparation of ultralow dielectric constant porous silicon, carbon, oxygen, hydrogen alloy dielectrics, called "pSiCOH," using a production 200mm plasma enhanced chemical vapor deposition tool and a thermal treatment is reported here. The effect of deposition temperature on the pSiCOH film is examined using Fourier transform infrared (FTIR) spectroscopy, dielectric constant (k), and film shrinkage measurements. For all deposition temperatures, carbon in the final porous film is shown to be predominantly Si -CH3 species, and lower k is shown to correlate with increased concentration of Si -CH3. NMR and FTIR spectroscopies clearly detect the loss of a removable, unstable, hydrocarbon (CHx) phase during the thermal treatment. Also detected are increased cross-linking of the Si-O skeleton, and concentration changes for three distinct structures of carbon. In the as deposited films, deposition temperature also affects the hydrocarbon (CHx) content and the presence of C O and C C functional groups.

  8. Study of the dielectric function of aqueous solutions of glucose and albumin by THz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Nazarov, M. M.; Cherkasova, O. P.; Shkurinov, A. P.

    2016-06-01

    We report a study of aqueous solutions of glucose and bovine serum albumin using THz time-domain spectroscopy. To describe the permittivity of the solutions of these substances, we use a simplified model being applicable in the frequency range of 0.05 – 2.7 THz. On the assumption that most of the water molecules become bound at high concentrations of glucose and protein in the solution, the changes in water characteristics are investigated. To improve the reliability of the results, the measurements are performed by two independent methods: the method of attenuated total internal reflection and the transmission method. Combination of the results obtained by these two methods allows expanding the spectral range towards lower frequencies.

  9. Water and ion transport in ultra-adsorbing porous magnesium carbonate studied by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Pochard, Isabelle; Frykstrand, Sara; Ahlström, Olle; Forsgren, Johan; Strømme, Maria

    2014-01-01

    Porous materials are used in application areas ranging from drug and vaccine delivery, medical implants, molecular sieves and cosmetics to catalysis and humidity control. In the present work, we employed an alternative approach to gain in-depth understanding about water interaction properties in such materials by the use of dielectric spectroscopy and thereby show that it is possible to obtain information that is not accessible from the more commonly employed water interaction analysis techniques. Specifically, the complex dielectric response of Upsalite, a novel, super-hydroscopic, high-surface area, porous magnesium carbonate material was measured in isothermal frequency scans between 10-3 and 106 Hz at controlled relative humidity (RH). We found the dielectric constant of the dry material to be 1.82. The ratio of bound to free water present in Upsalite after adsorption at room temperature was found to be high irrespective of the surrounding humidity with values ranging from ˜67% to ˜90%. We further found that OH- ions are the charge carriers responsible for the electrode polarization observed in the dielectric response and that the amount of these ions that are free to move in the material corresponds to a concentration of the order of 1-10 μmol l-1 independent of RH. Finally, the OH- diffusion coefficient displayed a drastic decrease with decreasing RH, typical of transport in unsaturated conditions. The presented results provide detailed insight about water interactions in the novel water adsorbing material under study and it is foreseen that the employed analysis methods can be used to evaluate other types of moisture adsorbing materials as well as the movement of functional species in the pores of inorganic drug delivery materials and materials tailored for adsorption of harmful charged species.

  10. Porous Polyimide Membranes Prepared by Wet Phase Inversion for Use in Low Dielectric Applications

    PubMed Central

    Kim, Soohyun; Jang, Keon-Soo; Choi, Hee-Dok; Choi, Seung-Hoon; Kwon, Seong-Ji; Kim, Il-Doo; Lim, Jung Ah; Hong, Jae-Min

    2013-01-01

    A wet phase inversion process of polyamic acid (PAA) allowed fabrication of a porous membrane of polyimide (PI) with the combination of a low dielectric constant (1.7) and reasonable mechanical properties (Tensile strain: 8.04%, toughness: 3.4 MJ/m3, tensile stress: 39.17 MPa, and young modulus: 1.13 GPa), with further thermal imidization process of PAA. PAA was simply synthesized from purified pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in two different reaction solvents such as γ-butyrolactone (GBL) and N-methyl-2-pyrrolidinone (NMP), which produce Mw/PDI of 630,000/1.45 and 280,000/2.0, respectively. The porous PAA membrane was fabricated by the wet phase inversion process based on a solvent/non-solvent system via tailored composition between GBL and NMP. The porosity of PI, indicative of a low electric constant, decreased with increasing concentration of GBL, which was caused by sponge-like formation. However, due to interplay between the low electric constant (structural formation) and the mechanical properties, GBL was employed for further exploration, using toluene and acetone vs. DI-water as a coagulation media. Non-solvents influenced determination of the PAA membrane size and porosity. With this approach, insight into the interplay between dielectric properties and mechanical properties will inform a wide range of potential low-k material applications. PMID:23615465

  11. A Study Of Porous Cordierite As A Potential Candidate For VLSI Dielectric Substrates

    NASA Astrophysics Data System (ADS)

    Thompson, R. G.; Shyu, J.; Poret, J. C.; Buckhalt, C.; Shealy, D. L.; Tohver, H. T.

    1988-05-01

    Porous substrates of a low dielectric constant (K) ceramic such as cordierite offer the opportunity to produce substrates with very low composite K values. This is attractive in VLSI packages because a low K allows the package to operate at higher frequencies. However, the porosity causes problems with conduction line integrity and thermal conductivity. These problems could be relieved somewhat if the pores were filled with a second phase such as glass. Various mixing laws are available to predict the resultant K value in a two phase mixture and these have been applied with some success. The research reported here involves a quantitative analysis of the volume fraction of porosity and pore size distribution in several cordierite compositions processed in various ways. These data are correlated with measurements of density and dielectric constant. They are also compared to several mixing laws to evaluate the relative fit between quantitative volume fraction measurements and density measurements. Finally, the results of this research are analyzed with respect to other recent research on porous substrate ceramics to identify the direction for future work.

  12. Investigation of the dielectric relaxation and the transport properties of porous silicates containing humidity

    NASA Astrophysics Data System (ADS)

    Papathanassiou, A. N.

    2000-07-01

    The dielectric relaxation responses of pelite, which is a porous silicate sediment containing a low content of inherent humidity, were identified and characterized by employing the experimental scheme of the thermally stimulated depolarization current (TSDC) spectroscopy. Comparative experiments were performed on dry samples. The elementary responses that compose the dielectric spectrum were recorded by applying certain sampling techniques. The dielectric relaxation spectrum consists of two low-temperature mechanisms, which are related to different modes of relaxation of water molecules. A third one is probably produced by permanent dipoles consisting of point defects in the calcium participant. Three relaxation mechanisms were sampled within the intermediate temperature region and were strongly affected by the outgassing of the pore network. They correspond to polarization processes occurring in the multi-layer shell of humidity over the surface the solid aggregates. At higher temperatures, two mechanisms were traced: the first is related to the homogeneous polarization of the specimen as charge carriers migrate within conducting territories until they are trapped at internal boundaries and the latter is described as a long-distance conduction mechanism which is enhanced by the presence of humidity. The activation energy profiles of the above-mentioned relaxation mechanisms were obtained from the analysis of the experimental signals of the thermal sampling and the partial heating schemes.

  13. Effect of vacuum ultraviolet and ultraviolet Irradiation on capacitance-voltage characteristics of low-k-porous organosilicate dielectrics

    SciTech Connect

    Sinha, H.; Lauer, J. L.; Nichols, M. T.; Shohet, J. L.; Antonelli, G. A.; Nishi, Y.

    2010-02-01

    High frequency capacitance-voltage (C-V) measurements are used to determine the effects of vacuum ultraviolet (VUV) and ultraviolet (UV) irradiation on defect states in porous low-k organosilicate (SiCOH) dielectrics. The characteristics show that VUV photons depopulate trapped electrons from defect states within the dielectric creating trapped positive charge. This is evidenced by a negative shift in the flat-band voltage of the C-V characteristic. UV irradiation reverses this effect by repopulating the defect states with electrons photoinjected from the silicon substrate. Thus, UV reduces the number of trapped positive charges in the dielectric and can effectively repair processing-induced damage.

  14. Mechanism of the typical relaxation process at low frequency based on dielectric measurements of water absorbed in porous titanium dioxide

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Wang, Qiang; Sun, Gang; Li, Chenxi; Hu, Lin

    2016-02-01

    Dielectric spectroscopy is a valuable tool in physics, chemistry, biophysics, and materials science. However, there is still an argument about the typical relaxation process at low frequency, which is always masked by electrode polarization. Low-frequency dielectric measurements of water absorbed in porous titanium dioxide have been performed. The experimental results show that typical polarization at low frequency is caused by space-charge polarization. A model is proposed to explain the experimental results, which indicates that the electric field in the sample is close to 0. An effective circuit is given, and the calculation gives similar dielectric spectra to those measured in experiments, which confirms the physical model.

  15. Gold Nanoparticle Synthesis by 3D Integrated Micro-solution Plasma in a 3D Printed Artificial Porous Dielectric Material

    NASA Astrophysics Data System (ADS)

    Sotoda, Naoya; Tanaka, Kenji; Shirafuji, Tatsuru

    2015-09-01

    Plasma in contact with HAuCl4 aqueous solution can promote the synthesis of gold nanoparticles. To scale up this process, we have developed 3D integrated micro-solution plasma (3D IMSP). It can generate a large number of argon microplasmas in contact with the aqueous solution flowing in a porous dielectric material. The porous dielectric material in our prototype 3D IMSP reactor, however, consists of non-regularly arranged random-sized pores. These pore parameters may be the parameters for controlling the size and dispersion of synthesized gold nanoparticles. We have hence fabricated a 3D IMSP reactor with an artificial porous dielectric material that has regularly arranged same-sized pores by using a 3D printer. We have applied the reactor to the gold- nanoparticle synthesis. We have confirmed the synthesis of gold nanoparticles through the observation of a plasmon resonance absorption peak at 550 nm in the HAuCl4 aqueous solution treated with 3D IMSP. The size and distribution of the synthesized gold nanoparticles are under investigation. We expect that these characteristics of the gold nanoparticles can be manipulated by changing pore size and their distribution in the porous dielectric material.

  16. Factors affecting an efficient sealing of porous low-k dielectrics by physical vapor deposition Ta(N) thin films

    NASA Astrophysics Data System (ADS)

    Iacopi, F.; Tokei, Zs.; Le, Q. T.; Shamiryan, D.; Conard, T.; Brijs, B.; Kreissig, U.; Van Hove, M.; Maex, K.

    2002-08-01

    The deposition of homogeneous thin films on porous substrates has been investigated. The thin film deposition of Ta(N) by physical vapor deposition on porous films with different average pore sizes and material compositions has been studied. The continuity of Ta(N) films on top of porous low-k dielectrics is evaluated by means of ellipsometric porosimetry combined with sheet resistance and atomic force microscopy measurements. Interface reactions are analyzed by x-ray photoelectron spectroscopy profiling. It has been observed that the minimal Ta(N) thickness required to obtain a continuous metal layer on top of the porous film depends, on the one hand, on the porosity and pore size and, on the other hand, on the chemical interaction of the thin film with the porous substrate. The sealing of pores is favored by the presence of carbon in the dielectric matrix. This is explained through a mechanism of local enhancement of the degree of crosslinking in the dielectric matrix, catalyzed by Ta.

  17. Optical second-harmonic generation measurements of porous low-k dielectric materials

    NASA Astrophysics Data System (ADS)

    Atkin, Joanna; Shaw, Thomas; Laibowitz, Robert; Heinz, Tony

    2009-03-01

    Low-k dielectric materials based on porous carbon-doped oxides, with relative dielectric constants as low as 2.1, are widely used as thin insulating films in the microelectronics industry. Knowledge of these materials' basic electronic properties, such as energy gaps, barrier heights, and trap states, is essential for modeling their electrical leakage and stability characteristics. We use femtosecond laser pulses to probe the dynamics of charge-carrier transfer processes across Si/LKD interfacial barriers by optical second harmonic generation (SHG). Larger electric fields from multiphoton injection can be developed in Si/LKD systems compared to Si/SiO2, indicating a significantly higher density of traps in the LKD. This is consistent with previously reported measurements of trap density by photoinjection techniques^*. We will also discuss results on the dynamics of discharging and on the dependence of charging phenomena on layer thickness. ^*J. M. Atkin, D. Song, T. M. Shaw, E. Cartier, R. B. Laibowitz, and T. F. Heinz, J. Appl. Phys. 103, 094104 (2008).

  18. Nanocrystal characterization by ellipsometry in porous silicon using model dielectric function

    NASA Astrophysics Data System (ADS)

    Petrik, Peter; Fried, Miklos; Vazsonyi, Eva; Basa, Peter; Lohner, Tivadar; Kozma, Peter; Makkai, Zsolt

    2009-01-01

    Porous silicon layers were prepared by electrochemical etching of p-type single-crystal Si (c-Si) of varying dopant concentration resulting in gradually changing morphology and nanocrystal (wall) sizes in the range of 2-25nm. We used the model dielectric function (MDF) of Adachi to characterize these porous silicon thin films of systematically changing nanocrystal size. In the optical model both the surface and interface roughnesses have to be taken into account, and the E0, E1, and E2 critical point (CP) features are all described by a combination of several lineshapes (two-dimensional CP, excitonic, damped harmonic oscillator). This results in using numerous parameters, so the number of fitted parameters were reduced by parameter coupling and neglecting insensitive parameters. Because of the large number of fitted parameters, cross correlations have to be investigated thoroughly. The broadening parameters of the interband transitions in the measured photon energy range correlate with the long-range order in the crystal. The advantage of this method over the robust and simple effective medium approximation (EMA) using a composition of voids and c-Si with a nanocrystalline Si reference [Petrik et al., Appl. Surf. Sci. 253, 200 (2006)] is that the combined EMA +MDF multilayer method of this work provides a more detailed description of the material and layer structure.

  19. Pool boiling of dielectric liquids on porous graphite and extended copper surfaces

    NASA Astrophysics Data System (ADS)

    Parker, Jack L.

    This work investigated pool boiling of the dielectric liquids HFE-7100 and FC-72 on plane copper and porous graphite and on copper surfaces with corner pins. The work investigated the effects of surface orientation and liquid subcooling and, for the copper surfaces with corner pins, the effect of surface roughness. In addition, investigations were made studying the heat transfer by natural convection and nucleate boiling, as well as the effects of liquid subcooling (up to 30 K) and surface inclination (0°--upward facing, to 180°--downward facing) on nucleate boiling heat transfer and Critical Heat Flux (CHF). The results are applicable to direct immersion cooling by nucleate boiling of high power computer chips dissipating 50 - 100 W/cm2 while maintaining the junction temperature for the chips below the recommended values (˜85 °C). Pool boiling experiments are performed with degassed HFE-7100 and FC-72 liquids using uniformly heated 10 x 10 mm porous graphite and copper surfaces with corner pins. The measured footprint temperatures and thermal power removed from the surfaces are used to construct the pool boiling curves and determine the critical heat flux and corresponding surface superheat. Results are compared with those obtained on plane copper of same heated footprint area. The obtained CHF values are also compared with those reported in the open literature for plane, micro-porous, and macro-structured surfaces. Digital photographs and video are obtained to help explain and interpret the results. For the first time, natural convection correlations for dielectric liquids on plane, porous, and copper with corner pins developed. These correlations are important to electronic cooling in the stand-by mode when the heat dissipation by the chips is only a few watts. Results show that the power removed by natural convection from surfaces with corner pins is 67% more than from plane Si and Cu surfaces at the same surface superheat. Using porous graphite and copper

  20. Porous AlN with a Low Dielectric Constant Synthesized Based on the Physical Vapor Transport Principle

    NASA Astrophysics Data System (ADS)

    Wang, Hua-Jie; Liu, Xue-Chao; Kong, Hai-Kuan; Xin, Jun; Gao, Pan; Shi, Er-Wei

    2016-07-01

    Porous AlN with low dielectric constant has been synthesized by the sacrificial template method based on the physical vapor transport principle. It is quite different from the traditional method that mixes the matrix with a pore-forming agent and utilizes liquid-phase sintering. The method consists of two parts. Firstly, AlN powder is placed in a graphite crucible. C/AlN composite can be formed by mixing decomposed AlN vapor and volatile carbon originated from a crucible at high temperature. Secondly, pores are formed after removing carbon from the C/AlN composite by an annealing process. The structure, morphology, porosity and properties of porous AlN are characterized. It is shown the obtained porous AlN has a thermal conductivity of 37.3 W/(m K) and a reduced dielectric constant of 5.5-6.1 (at 1 MHz). The porosity measured by a mercury porosimeter is 24.09%. It has been experimentally proved that porous AlN with a sufficiently porous structure and properties can be synthesized based on the vapor-phase principle.

  1. Porous AlN with a Low Dielectric Constant Synthesized Based on the Physical Vapor Transport Principle

    NASA Astrophysics Data System (ADS)

    Wang, Hua-Jie; Liu, Xue-Chao; Kong, Hai-Kuan; Xin, Jun; Gao, Pan; Shi, Er-Wei

    2016-05-01

    Porous AlN with low dielectric constant has been synthesized by the sacrificial template method based on the physical vapor transport principle. It is quite different from the traditional method that mixes the matrix with a pore-forming agent and utilizes liquid-phase sintering. The method consists of two parts. Firstly, AlN powder is placed in a graphite crucible. C/AlN composite can be formed by mixing decomposed AlN vapor and volatile carbon originated from a crucible at high temperature. Secondly, pores are formed after removing carbon from the C/AlN composite by an annealing process. The structure, morphology, porosity and properties of porous AlN are characterized. It is shown the obtained porous AlN has a thermal conductivity of 37.3 W/(m K) and a reduced dielectric constant of 5.5-6.1 (at 1 MHz). The porosity measured by a mercury porosimeter is 24.09%. It has been experimentally proved that porous AlN with a sufficiently porous structure and properties can be synthesized based on the vapor-phase principle.

  2. 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.

  3. Impact of reductive N2/H2 plasma on porous low-dielectric constant SiCOH thin films

    NASA Astrophysics Data System (ADS)

    Cui, Hao; Carter, Richard J.; Moore, Darren L.; Peng, Hua-Gen; Gidley, David W.; Burke, Peter A.

    2005-06-01

    Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2/H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2/H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film.

  4. The experimental dielectric function of porous anodic alumina in the infrared region; a comparison with the Maxwell-Garnett model

    NASA Astrophysics Data System (ADS)

    Wäckelgård, Ewa

    1996-06-01

    The infrared reflectance from thin alumina films on metal substrates has a deep minimum for p-polarized light at oblique incidence. This originates from absorption when light couples with a longitudinal optical (LO) phonon mode with k-vector zero. The absorption band is wide for amorphous alumina and is shifted to longer wavelengths for porous oxides compared to non-porous ones. Anodic alumina, prepared in phosphoric acid, with a pore volume fraction of 0.3, has been investigated. The s- and p-polarized reflectance has been measured for selected angles of incidence between 0953-8984/8/23/019/img1 and 0953-8984/8/23/019/img2, and the dielectric function has been determined from these measurements. The effective dielectric function has been calculated using Maxwell-Garnett effective-medium theory for a two-component anisotropic medium consisting of air-filled cylindrical pores perpendicular to the surface in an alumina matrix with optical constants of non-porous evaporated alumina. The theoretical and experimental results are in good agreement, which shows that the redshift of the LO mode absorption for p-polarized light can be explained by the presence of pores.

  5. Mechanical reliability of porous low-k dielectrics for advanced interconnect: Study of the instability mechanisms in porous low-k dielectrics and their mediation through inert plasma induced re-polymerization of the backbone structure

    NASA Astrophysics Data System (ADS)

    Sa, Yoonki

    Continuous scaling down of critical dimensions in interconnect structures requires the use of ultralow dielectric constant (k) films as interlayer dielectrics to reduce resistance-capacitance delays. Porous carbon-doped silicon oxide (p-SiCOH) dielectrics have been the leading approach to produce these ultralow-k materials. However, embedding of porosity into dielectric layer necessarily decreases the mechanical reliability and increases its susceptibility to adsorption of potentially deleterious chemical species during device fabrication process. Among those, exposure of porous-SiCOH low-k (PLK) dielectrics to oxidizing plasma environment causes the increase in dielectric constant and their vulnerability to mechanical instability of PLKs due to the loss of methyl species and increase in moisture uptake. These changes in PLK properties and physical stability have been persisting challenges for next-generation interconnects because they are the sources of failure in interconnect integration as well as functional and physical failures appearing later in IC device manufacturing. It is therefore essential to study the fundamentals of the interactions on p-SiCOH matrix induced by plasma exposure and find an effective and easy-to-implement way to reverse such changes by repairing damage in PLK structure. From these perspectives, the present dissertation proposes 1) a fundamental understanding of structural transformation occurring during oxidative plasma exposure in PLK matrix structure and 2) its restoration by using silylating treatment, soft x-ray and inert Ar-plasma radiation, respectively. Equally important, 3) as an alternative way of increasing the thermo-mechanical reliability, PLK dielectric film with an intrinsically robust structure by controlling pore morphology is fabricated and investigated. Based on the investigations, stability of PLK films studied by time-dependent ball indentation tester under the elevated temperature, variation in film thickness and

  6. Investigation on thermo-mechanical instability of porous low dielectric constant materials

    NASA Astrophysics Data System (ADS)

    Zin, Emil Hyunbae

    This study investigates the structural stability of porous low dielectric constant materials (PLK) under thermal and mechanical load and the influence of contributing factors including porosity as intrinsic factor and plasma damage and moisture absorption as extrinsic factors on thermo-mechanical instability of PLK in advanced Cu/PLK interconnects. For this purpose, a ball indentation creep test technique was developed to examine the thermal and mechanical instability of PLK at relevant load and temperature conditions in the interconnect structure. Our exploration with the ball indentation creep test found that PLK films plastically deforms with time, indicating that viscoplastic deformation does occur under relevant conditions of PLK processing. On the basis of the results that the increase of the indentation depth with time shows more noticeable difference in PLK films with higher porosity, plasma exposure, and moisture absorption, it is our belief that PLK stability is greatly affected by porosity, plasma damage and moisture. Viscous flow was found to be mechanism for the viscoplastic deformation at the temperature and load of real PLK integration processing. This finding was obtained from the facts that the kinetics of the indentation creep fit very well with the viscous flow model and the extracted stress exponent is close to unity. Based on the results of temperature dependence in all PLK films, the activation energy(~1.5eV) of the viscosity back calculated from the experimental value of the kinetics was found to be much small than that of a pure glass (> 4eV). This suggests that the viscous flow of PLK is controlled by chemical reaction happening in PLK matrix. The FT-IR measurement for the examination of chemical bond reconfiguration shows that the intensity of Si-OH bonds increases with the flow while that of Si-O-Si, -CHX and Si-CH 3 bonds decreases, indicating that chemical reactions are involved in the deformation process. From these findings, it is

  7. Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

    SciTech Connect

    Marneffe, J.-F. de Lukaszewicz, M.; Porter, S. B.; Vajda, F.; Rutigliani, V.; Verdonck, P.; Baklanov, M. R.; Zhang, L.; Heyne, M.; El Otell, Z.; Krishtab, M.; Goodyear, A.; Cooke, M.

    2015-10-07

    Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

  8. Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

    NASA Astrophysics Data System (ADS)

    de Marneffe, J.-F.; Zhang, L.; Heyne, M.; Lukaszewicz, M.; Porter, S. B.; Vajda, F.; Rutigliani, V.; el Otell, Z.; Krishtab, M.; Goodyear, A.; Cooke, M.; Verdonck, P.; Baklanov, M. R.

    2015-10-01

    Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

  9. Mechanical reliability of porous low-k dielectrics for advanced interconnect: Study of the instability mechanisms in porous low-k dielectrics and their mediation through inert plasma induced re-polymerization of the backbone structure

    NASA Astrophysics Data System (ADS)

    Sa, Yoonki

    Continuous scaling down of critical dimensions in interconnect structures requires the use of ultralow dielectric constant (k) films as interlayer dielectrics to reduce resistance-capacitance delays. Porous carbon-doped silicon oxide (p-SiCOH) dielectrics have been the leading approach to produce these ultralow-k materials. However, embedding of porosity into dielectric layer necessarily decreases the mechanical reliability and increases its susceptibility to adsorption of potentially deleterious chemical species during device fabrication process. Among those, exposure of porous-SiCOH low-k (PLK) dielectrics to oxidizing plasma environment causes the increase in dielectric constant and their vulnerability to mechanical instability of PLKs due to the loss of methyl species and increase in moisture uptake. These changes in PLK properties and physical stability have been persisting challenges for next-generation interconnects because they are the sources of failure in interconnect integration as well as functional and physical failures appearing later in IC device manufacturing. It is therefore essential to study the fundamentals of the interactions on p-SiCOH matrix induced by plasma exposure and find an effective and easy-to-implement way to reverse such changes by repairing damage in PLK structure. From these perspectives, the present dissertation proposes 1) a fundamental understanding of structural transformation occurring during oxidative plasma exposure in PLK matrix structure and 2) its restoration by using silylating treatment, soft x-ray and inert Ar-plasma radiation, respectively. Equally important, 3) as an alternative way of increasing the thermo-mechanical reliability, PLK dielectric film with an intrinsically robust structure by controlling pore morphology is fabricated and investigated. Based on the investigations, stability of PLK films studied by time-dependent ball indentation tester under the elevated temperature, variation in film thickness and

  10. Thin film deposition at atmospheric pressure using dielectric barrier discharges: Advances on three-dimensional porous substrates and functional coatings

    NASA Astrophysics Data System (ADS)

    Fanelli, Fiorenza; Bosso, Piera; Mastrangelo, Anna Maria; Fracassi, Francesco

    2016-07-01

    Surface processing of materials by atmospheric pressure dielectric barrier discharges (DBDs) has experienced significant growth in recent years. Considerable research efforts have been directed for instance to develop a large variety of processes which exploit different DBD electrode geometries for the direct and remote deposition of thin films from precursors in gas, vapor and aerosol form. This article briefly reviews our recent progress in thin film deposition by DBDs with particular focus on process optimization. The following examples are provided: (i) the plasma-enhanced chemical vapor deposition of thin films on an open-cell foam accomplished by igniting the DBD throughout the entire three-dimensional (3D) porous structure of the substrate, (ii) the preparation of hybrid organic/inorganic nanocomposite coatings using an aerosol-assisted process, (iii) the DBD jet deposition of coatings containing carboxylic acid groups and the improvement of their chemical and morphological stability upon immersion in water.

  11. 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. PMID:24921365

  12. Dependences of Young's modulus of porous silica low dielectric constant films on skeletal structure and porosity

    NASA Astrophysics Data System (ADS)

    Takada, Syozo; Hata, Nobuhiro; Seino, Yutaka; Fujii, Nobutoshi; Kikkawa, Takamaro

    2006-12-01

    Porous silica films were prepared by spin coating the mixtures of acidic silica sol and nonionic surfactant template. The (a) porosity and (b) skeletal structure of the films were varied by adjusting the (a) template concentration and the (b) annealing temperature, respectively. Fourier transform infrared spectroscopic ellipsometry was employed to evaluate the skeletal silica structure of the films. The analysis was focused on the midinfrared (1000-1300cm-1) spectral structure which is assigned as the asymmetric stretching vibration mode of Si-O-Si bonds [Kamitsos et al., Phys. Rev. B 48, 12499 (1993)]. The spectral structure depended on both porosity and chemical bonding structure. Bruggemann's effective medium theory was employed to obtain the spectrum of "skeletal" silica from that of "porous" silica. The skeletal silica structure was then discussed in terms of the peak positions of the transverse optical (ωTO) and longitudinal optical (ωLO) vibration modes of Si-O-Si network. It was shown that the Young's elastic modulus of skeletal silica correlates well with ωLO2/ωTO2. We have obtained good correlations between ωLO2/ωTO2 of skeletal silica and elastic modulus E for two series of porous silica films with around 55% and 40% porosity. The experimental results show that the structural change in silica skeleton strongly affects the mechanical properties of porous silica low-k films.

  13. Excitation of THz hybrid modes in an elliptical dielectric rod waveguide with a cold collisionless unmagnetized plasma column by an annular electron beam

    NASA Astrophysics Data System (ADS)

    Rahmani, Z.; Heidari-Semiromi, E.; Safari, S.

    2016-06-01

    The dispersion relation of electromagnetic waves propagating in an elliptical plasma waveguide with a cold collisionless unmagnetized plasma column and a dielectric rod is studied analytically. The frequency spectrum of the hybrid waves and the growth rate for excitation of the waves by a thin annular relativistic elliptical electron beam (TAREEB) is obtained. The effects of relative permittivity constant of dielectric rod, geometrical dimensions, plasma frequency, accelerating voltage, and current density of TAREEB on the growth rate and frequency spectra of the waveguide will be investigated.

  14. Modeling of the dielectric permittivity of porous soil media with water using statistical-physical models

    NASA Astrophysics Data System (ADS)

    Usowicz, Boguslaw; Marczewski, Wojciech; Usowicz, Jerzy B.; Łukowski, Mateusz; Lipiec, Jerzy; Stankiewicz, Krystyna

    2013-04-01

    Radiometric observations with SMOS rely on the Radiation Transfer Equations (RTE) determining the Brightness Temperature (BT) in two linear polarization components (H, V) satisfying Fresnel principle of propagation in horizontally layered target media on the ground. RTE involve variables which bound the equations expressed in Electro-Magnetic (EM) terms of the intensity BT to the physical reality expressed by non-EM variables (Soil Moisture (SM), vegetation indexes, fractional coverage with many different properties, and the boundary conditions like optical thickness, layer definitions, roughness, etc.) bridging the EM domain to other physical aspects by means of the so called tau-omega methods. This method enables joining variety of different valuable models, including specific empirical estimation of physical properties in relation to the volumetric water content. The equations of RTE are in fact expressed by propagation, reflection and losses or attenuation existing on a considered propagation path. The electromagnetic propagation is expressed in the propagation constant. For target media on the ground the dielectric constant is a decisive part for effects of propagation. Therefore, despite of many various physical parameters involved, one must effectively and dominantly rely on the dielectric constant meant as a complex variable. The real part of the dielectric constant represents effect of apparent shortening the propagation path and the refraction, while the imaginary part is responsible for the attenuation or losses. This work engages statistical-physical modeling of soil properties considering the media as a mixture of solid grains, and gas or liquid filling of pores and contact bridges between compounds treated statistically. The method of this modeling provides an opportunity of characterizing the porosity by general statistical means, and is applicable to various physical properties (thermal, electrical conductivity and dielectric properties) which

  15. Control of Ion Activation Energy to Surfaces in Atmospheric Pressure Plasmas Using Porous Dielectrics Films

    NASA Astrophysics Data System (ADS)

    Babaeva, Natalia Yu.; Kushner, Mark J.

    2011-10-01

    The electric field in the avalanche front of high pressure filamentary discharges such as dielectric barrier discharges (DBDs) can be many 100s kV/cm. When the streamer strikes a surface, this electric field is transferred to a transient sheath at the surface. With mean free paths of < 1 μm, ion energies to surfaces produced by the sheath can exceed 10s eV. These energies can be controlled by having a layered dielectric substrate as the applied voltage is divided between the sheath, and these layered capacitances. However, if the surface being treated is, for example, human tissue, one cannot change the properties of the surface to control the ion energies. In this talk, we use results from a computational study to propose a method to control the transient sheath formed at the surface of bulk materials by atmospheric pressure DBDs to in turn control ion energies to the surface. A thin dielectric film having small holes through which the streamers can partially penetrate is placed on the surface. We show that ion energies can be controlled by the capacitance of the film and the size of the holes. Results are discussed for streamer penetration into the hole, sheath formation and the delivery of activation energy by ions and photons to the surfaces of polymers and human tissue. Work supported by Dept. of Energy Office of Fusion Energy Science.

  16. Terahertz Artificial Dielectric Lens

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-03-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  17. Terahertz Artificial Dielectric Lens.

    PubMed

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M

    2016-01-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

  18. Terahertz Artificial Dielectric Lens

    PubMed Central

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-01-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

  19. Low-temperature dielectric measurements of confined water in porous granites

    NASA Astrophysics Data System (ADS)

    Gonçalves da Silva, Hugo; Prezas, Pedro; Vinagre, Ana; Graça, Manuel F.; Monteiro, Jorge H.; Tlemçani, Mouhaydine; Moita, Patrícia; Pinho, António; Bezzeghoud, Mourad; Mendiratta, Sushil K.; Rosa, Rui N.

    2014-05-01

    Three different granitic rocks extracted from Évora (in the south of Portugal) where used to perform dielectric measurements in the frequency range from 100 Hz to 1 MHz and temperatures 100 - 350 K. Thin cylindrical samples were prepared and circular electrodes were established using silver conductive paint. A clear anomaly appears, for T ~ 200 - 220 K, in the dielectric measurements of the samples studied. This anomaly occurs in different materials and coincides with a phase transition of supercooled water. Tightly bounded water confined in the pores of the rock do not crystallize at 273 K, but form a metastable liquid down to 200 - 220 K increasing water polarization. Below this temperature water molecules solidify and polarizability decreases. The rock presenting the most sizeable anomaly has a very low specific surface area, ~ 0.09 m2g-1, and connected porosity, ~ 1.10 %. In addition, geochemical analyses reveal almost inexistence of water molecules in its structure confirming the role of confined water in the anomaly. Comparison between saturated, oven dried, and vacuum dried samples is done. Finally, a logarithmic dependency of the critical temperature for the supercooled water phase transition with the measuring frequency is found. The authors acknowledge the support of FCT (Portuguese Science and Technology Foundation) through the project PTDC/GEO-FIQ/4178/2012.

  20. Mitigation of plasma-induced damage in porous low-k dielectrics by cryogenic precursor condensation

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; de Marneffe, Jean-François; Leroy, Floriane; Lefaucheux, Philippe; Tillocher, Thomas; Dussart, Remi; Maekawa, Kaoru; Yatsuda, Koichi; Dussarrat, Christian; Goodyear, Andy; Cooke, Mike; De Gendt, Stefan; Baklanov, Mikhail R.

    2016-05-01

    The present work describes the plasma etch properties of porous organo-silicate materials at cryogenic temperature. The mechanism of plasma damage is studied by means of in situ ellipsometry and post-etch material evaluation. Using conventional volatile reactants such as SF6, it is found that low plasma damage can be achieved below  ‑120 °C through two main channels: pore sidewall passivation by molecular SF6 and partial condensation of non-volatile etch by-products. The protection can be enhanced by means of gas phase precursors with low saturated vapor pressure. Using C4F8, complete pore filling is achieved at  ‑110 °C and negligible plasma-induced damage is demonstrated on both blanket and patterned low-k films. The characteristics of the precursor condensation process are described and discussed in detail, establishing an optimal process window. It is shown that the condensation temperature can be raised by using precursors with even lower vapor pressure. The reported in situ densification through precursor condensation could enable damage-free plasma processing of mesoporous media.

  1. THz wave emission microscope

    NASA Astrophysics Data System (ADS)

    Yuan, Tao

    Sensing and imaging using Terahertz (THz) radiation has attracted more and more interest in the last two decades thanks to the abundant material 'finger prints' in the THz frequency range. The low photon energy also makes THz radiation an attractive tool for nondestructive evaluation of materials and devices, biomedical applications, security checks and explosive screening. Due to the long wavelength, the far-field THz wave optical systems have relatively low spatial resolution. This physical limitation confines THz wave sensing and imaging to mostly macro-size samples. To investigate local material properties or micro-size structures and devices, near-field technology has to be employed. In this dissertation, the Electro-Optical THz wave emission microscope is investigated. The basic principle is to focus the femtosecond laser to a tight spot on a thin THz emitter layer to produce a THz wave source with a similar size as the focus spot. The apparatus provides a method for placing a THz source with sub-wavelength dimension in the near-field range of the investigated sample. Spatial resolution to the order of one tenth of the THz wavelength is demonstrated by this method. The properties of some widely used THz wave emission materials under tight focused pump light are studied. As an important branch of THz time domain spectroscopy (THz-TDS), THz wave emission spectroscopy has been widely used as a tool to investigate the material physics, such as energy band structure, carrier dynamics, material nonlinear properties and dynamics. As the main work of this dissertation, we propose to combine the THz wave emission spectroscopy with scanning probe microscopy (SPM) to build a tip-assisted THz wave emission microscope (TATEM), which is a valuable extension to current SPM science and technology. Illuminated by a femtosecond laser, the biased SPM tip forms a THz wave source inside the sample beneath the tip. The source size is proportional to the apex size of the tip so

  2. Improving interpretation of geoelectrical signatures arising from biomineralization process in porous media: Low-frequency dielectric spectroscopy measurements on Desulfovibrio vulgaris cell suspensions

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Prodan, C.; Slater, L. D.; Bot, C.; Ntarlagiannis, D.

    2009-12-01

    Previous geophysical studies have demonstrated the sensitivity of complex conductivity measurements to microbial growth, biofilm formation, and microbial-mineral alternations, indicating that complex conductivity has the potential to serve as non-invasive tool for bioremediation monitoring. However, the inherent dielectric properties of microbes and how they might directly contribute to the geophysical responses observed during microbial-mineral transformations are not well understood. As a first step towards improving the understanding of electrical signals from microbial-mineral transformations in porous media, we studied the low frequency dielectric properties of sulfate-reducing bacteria (Desulfovibrio vulgaris) cell suspensions, a common soil borne microorganism involved in remediation of toxic metals in solution. We utilized a two-electrode dielectric spectroscopy measurement, common in biophysics applications,to acquire high quality dielectric dispersion curves of Desulfovibrio vulgaris cell suspensions over the frequency range 0.1 Hz to 1M Hz. Desulfovibrio vulgaris cell suspensions were placed between two parallel steel electrodes that are enclosed in a cylindrical glass tube, and the complex impedance of sample was measured relative to a known resistor. The measured impedance includes an electrode polarization impedance arising at the interface between electrodes and ionic solutions at low frequencies. This electrode impedance has traditionally precluded the reliable interpretation of two electrode techniques at low frequencies (< 1000 Hz). In order to obtain the true dielectric dispersion curve of sample, we adopt a simple and robust strategy to measure, analyze and remove the polarization impedance. The feasibility of this polarization removal technique was tested on water saturated glass beads. We show that the broadband dielectric response of Desulfovibrio vulgaris can be reliably determined with this approach. The measurements are modeled based on a

  3. Damage by radicals and photons during plasma cleaning of porous low-k SiOCH. II. Water uptake and change in dielectric constant

    SciTech Connect

    Shoeb, Juline; Kushner, Mark J.

    2012-07-15

    Porous dielectric materials provide lower capacitances that reduce RC time delays in integrated circuits. Typical low-k materials include porous SiOCH-silicon dioxide with carbon groups, principally CH{sub 3}, lining the pores. With a high porosity, internally connected pores provide pathways for reactive species to enter into the material. Fluorocarbon plasmas are often used to etch SiOCH, a process that leaves a fluorocarbon polymer on the surface that must later be removed. During cleaning using Ar/O{sub 2} or He/H{sub 2} plasmas, reactions of radicals that diffuse into the SiOCH and photons that penetrate into the SiOCH can remove -CH{sub 3} groups. Due to its higher reactivity, cleaning with Ar/O{sub 2} plasmas removes more -CH{sub 3} groups than He/H{sub 2} plasmas, and so produce more free radical sites, such as -SiO{sub 2} Bullet (a -SiO{sub 2}-CH{sub 3} site with the -CH{sub 3} group removed).Upon exposure to humid air, these free radical sites can chemisorb H{sub 2}O to form hydrophilic Si-OH which can further physisorb H{sub 2}O through hydrogen bonding to form Si-OH(H{sub 2}O). With the high dielectric constant of water, even a small percentage of water uptake can significantly increase the effective dielectric constant of SiOCH. In this paper, we report on results from a computational investigation of the cleaning of SiOCH using Ar/O{sub 2} or He/H{sub 2} plasmas and subsequent exposure to humid air. The authors found that plasma cleaning with He/H{sub 2} mixtures produce less demethylation than cleaning with Ar/O{sub 2} plasmas, as so results in less water uptake, and a smaller increase in dielectric constant. The water that produces the increase in dielectric constant is roughly half chemisorbed and half physisorbed, the latter of which can be removed with mild heating. Sealing the pores with NH{sub 3} plasma treatment reduces water uptake and helps prevent the increase in dielectric constant.

  4. 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.

  5. Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials

    SciTech Connect

    Wu, C. De Wolf, I.; Li, Y.; Leśniewska, A.; Varela Pedreira, O.; Marneffe, J.-F. de; Ciofi, I.; Verdonck, P.; Baklanov, M. R.; Bömmels, J.; Tőkei, Zs.; Croes, K.

    2015-10-28

    Stress-Induced Leakage Current (SILC) behavior during the dielectric degradation of ultra-porous SiOCH low-k materials was investigated. Under high voltage stress, SILC increases to a critical value before final hard breakdown. This SILC increase rate is mainly driven by the injected charges and is negligibly influenced by temperature and voltage. SILC is found to be transient and shows a t{sup −1} relaxation behavior, where t is the storage time at low voltages. This t{sup −1} transient behavior, described by the tunneling front model, is caused by both electron charging of neutral defects in the dielectric close to the cathode interface and discharging of donor defects close to the anode interface. These defects have a uniform density distribution within the probed depth range, which is confirmed by the observed flat band voltage shift results collected during the low voltage storage. By applying an additional discharging step after the low voltage storage, the trap energies and spatial distributions are derived. In a highly degraded low-k dielectric, the majority of defects have a trap depth between 3.4 eV and 3.6 eV and a density level of 1 × 10{sup 18 }eV{sup −1 }cm{sup −3}. The relation between the defect density N and the total amount of the injected charges Q is measured to be sub-linear, N ∼ Q{sup 0.45±0.07}. The physical nature of these stress-induced defects is suggested to be caused by the degradation of the Si-O based skeleton in the low-k dielectric.

  6. Enhanced THz guiding properties of curved two-wire lines.

    PubMed

    Zha, Jingshu; Kim, Geun Ju; Jeon, Tae-In

    2016-03-21

    We present experimental and simulation studies of enhanced terahertz (THz) guiding properties of curved two-wire lines for several surface conditions. When a THz-wave propagates through curved two-wire lines, a rough wire surface with dielectric coating contributes to a lower bending loss compared to a smooth or rough wire surface without coating. Dielectric coating and rough surface confine the THz field to the wire surface making the bending loss low. The guiding property at a curve depth of 30 mm of a rough wire surface with 25-μm-thick coating is improved by 34% compared to that of a smooth wire without coating. Furthermore, computer simulation technology (CST) software visually shows the bending loss as same as the experimental studies. PMID:27136807

  7. Metallic and 3D-printed dielectric helical terahertz waveguides.

    PubMed

    Vogt, Dominik Walter; Anthony, Jessienta; Leonhardt, Rainer

    2015-12-28

    We investigate guidance of Terahertz (THz) radiation in metallic and 3D-printed dielectric helical waveguides in the frequency range from 0.2 to 1 THz. Our experimental results obtained from THz time-domain spectroscopy (THz-TDS) measurements are in very good agreement with finite-difference time-domain (FDTD) simulations. We observe single-mode, low loss and low dispersive propagation of THz radiation in metallic helical waveguides over a broad bandwidth. The 3D-printed dielectric helical waveguides have substantially extended the bandwidth of a low loss dielectric tube waveguide as observed from the experimental and simulation results. The high flexibility of the helical design allows an easy incorporation into bench top THz devices. PMID:26832000

  8. Dielectric properties of porous aluminum and silicon oxides with inclusions of triglycine sulfate and its modified analogs

    NASA Astrophysics Data System (ADS)

    Golitsyna, O. M.; Drozhdin, S. N.; Nechaev, V. N.; Viskovatykh, A. V.; Kashkarov, V. M.; Gridnev, A. E.; Chernyshev, V. V.

    2013-03-01

    This paper reports on an investigation of the temperature dependences of the capacitance and conductance of composite materials prepared by incorporating the ferroelectric TGS and its analogs—TGS with addition of L,α-alanine and chromium—into porous Al2O3 and SiO2 matrices. It has been established that conduction of the structures under study involves charge transport predominantly through the ferroelectric embedded in the porous matrix. A mechanism is proposed to account for the displacement of the phase transition temperature of the ferroelectric inclusion under "restricted geometry" conditions, which is driven by the difference between the thermal expansion coefficients of the porous matrix and the embedded ferroelectric.

  9. Spin-coated and PECVD low dielectric constant porous organosilicate films studied by 1D and 2D solid-state NMR.

    PubMed

    Gerbaud, Guillaume; Hediger, Sabine; Bardet, Michel; Favennec, Laurent; Zenasni, Aziz; Beynet, Julien; Gourhant, Olivier; Jousseaume, Vincent

    2009-11-14

    In the research field of the sub-65 nm semiconductor industry, organosilicate SiOCH films with low dielectric constant (k < 2.4) need to be developed in order to improve the performance of integrated circuits [International Roadmap for Semiconductors (ITRS), San Jose, CA, 2004]. One way to produce SiOCH films of low dielectric constant is to introduce pores into the film. This is usually obtained in two steps. Firstly, co-deposition of a matrix precursor, with a sacrificial organic porogen, either by plasma enhanced chemical vapor deposition (PECVD) or spin-coating. Secondly, application of a specific thermal treatment to remove the porogen and create the porosity. This last step can be improved by adding to the thermal process a super-critical CO(2) treatment, an UV irradiation or an electronic bombardment (e-beam). In this study, the two deposition processes as well as the various treatments applied to eliminate the porogens were evaluated and compared using high-resolution solid-state NMR. For this purpose, hybrid (containing porogens) and porous films were extensively characterized on the basis of their (1)H, (13)C and (29)Si high-resolution NMR spectra. Information was obtained concerning the crosslinking of the Si skeleton. Spectral features could be correlated to the processes used. Isotropic chemical shift analyses and 2D correlation NMR experiments were used to show the existence and nature of the interactions between the matrix precursor and the organic porogen. PMID:19851550

  10. Three-dimensional THz lumped-circuit resonators.

    PubMed

    Todorov, Yanko; Desfond, Pascal; Belacel, Cherif; Becerra, Loïc; Sirtori, Carlo

    2015-06-29

    Our work describes a novel three dimensional meta-material resonator design for optoelectronic applications in the THz spectral range. In our resonant circuits, the capacitors are formed by double-metal regions cladding a dielectric core. Unlike conventional planar metamaterials, the electric field is perpendicular to the surface and totally confined in the dielectric core. Furthermore, the magnetic field, confined in the inductive part, is parallel to the electric field, ruling out coupling through propagation effects. Our geometry thus combines the benefit of double-metal structures that provide parallel plate capacitors, while maintaining the ability of meta-material resonators to adjust independently the capacitive and inductive parts. Furthermore, in our geometry, a constant bias can be applied across the dielectric, making these resonators very suitable for applications such as ultra-low dark current THz quantum detectors and amplifiers based on quantum cascade gain medium. PMID:26191695

  11. Microwave and THz sensing using slab-pair-based metamaterials

    SciTech Connect

    Kenanakis, G.; Shen, Nianhai; Mavidis, Ch.; Katsarakis, N.; Kafesaki, M.; Soukoulis, Costas M.; Economou, E.N.

    2012-10-15

    In this work the sensing capability of an artificial magnetic metamaterial based on pairs of metal slabs is demonstrated, both theoretically and experimentally, in the microwave regime. The demonstration is based on transmission measurements and simulations monitoring the shift of the magnetic resonance frequency as one changes a thin dielectric layer placed between the slabs of the pairs. Strong dependence of the magnetic resonance frequency on both the permittivity and the thickness of the dielectric layer under detection was observed. The sensitivity to the dielectrics′ permittivity (ε) is larger for dielectrics of low ε values, which makes the approach suitable for sensing organic materials also in the THz regime. The capability of our approach for THz sensing is also demonstrated through simulations.

  12. Dielectric properties of porous silicon for use as a substrate for the on-chip integration of millimeter-wave devices in the frequency range 140 to 210 GHz

    PubMed Central

    2014-01-01

    In this work, the dielectric properties of porous Si for its use as a local substrate material for the integration on the Si wafer of millimeter-wave devices were investigated in the frequency range 140 to 210 GHz. Broadband electrical characterization of coplanar waveguide transmission lines (CPW TLines), formed on the porous Si layer, was used in this respect. It was shown that the dielectric parameters of porous Si (dielectric permittivity and loss tangent) in the above frequency range have values similar to those obtained at lower frequencies (1 to 40 GHz). More specifically, for the samples used, the obtained values were approximately 3.12 ± 0.05 and 0.023 ± 0.005, respectively. Finally, a comparison was made between the performance of the CPW TLines on a 150-μm-thick porous Si layer and on three other radiofrequency (RF) substrates, namely, on trap-rich high-resistivity Si (trap-rich HR Si), on a standard complementary metal-oxide-semiconductor (CMOS) Si wafer (p-type, resistivity 1 to 10 Ω.cm) and on quartz. PACS 84.40.-x; 77.22.Ch; 81.05.Rm PMID:25206316

  13. Dielectric properties of porous silicon for use as a substrate for the on-chip integration of millimeter-wave devices in the frequency range 140 to 210 GHz

    NASA Astrophysics Data System (ADS)

    Sarafis, Panagiotis; Nassiopoulou, Androula Galiouna

    2014-08-01

    In this work, the dielectric properties of porous Si for its use as a local substrate material for the integration on the Si wafer of millimeter-wave devices were investigated in the frequency range 140 to 210 GHz. Broadband electrical characterization of coplanar waveguide transmission lines (CPW TLines), formed on the porous Si layer, was used in this respect. It was shown that the dielectric parameters of porous Si (dielectric permittivity and loss tangent) in the above frequency range have values similar to those obtained at lower frequencies (1 to 40 GHz). More specifically, for the samples used, the obtained values were approximately 3.12 ± 0.05 and 0.023 ± 0.005, respectively. Finally, a comparison was made between the performance of the CPW TLines on a 150-μm-thick porous Si layer and on three other radiofrequency (RF) substrates, namely, on trap-rich high-resistivity Si (trap-rich HR Si), on a standard complementary metal-oxide-semiconductor (CMOS) Si wafer (p-type, resistivity 1 to 10 Ω.cm) and on quartz.

  14. Generation of THz-radiation in the Cherenkov decelerating structure with planar geometry at frequency ∼ 0.675 THz

    NASA Astrophysics Data System (ADS)

    Ashanin, I. A.; Polozov, S. M.

    2016-07-01

    One of the ways to generate THz-radiation is by the relativistic electron bunches travelling through Cherenkov decelerating dielectric filled capillary channel. Sapphire or other dielectric materials can be used for the internal surface coating of the capillary. Relativistic electron bunches of ∼100 µm in diameter and pulse durations of 1 ps or shorter are capable to produce substantial power of THz-radiation. The aperture of Cherenkov decelerating structure should be comparable with the sub-mm wavelength (0.05-3 mm). Such type of decelerating system allows providing of the wide range of operating parameters at the various geometrical sizes. But it is necessary to consider that such capillaries are difficult in production as there is a requirement to drill a small aperture in a long crystal of high hardness but brittle. In this regard it would be desirable to offer transition option from the axial to the planar geometry. Furthermore the ribbon beam has some advantages as focusing at low energies and possessing smaller expansion in the drift space. The authors present design and results of electrodynamics study of the decelerating planar dielectric filling Cherenkov channel at frequency 0.675 THz in this article. It is also delivered characteristic comparison with axial geometry channel. A horn antenna attached to such channel at 0.675 THz resonant frequency is considered.

  15. 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

  16. Ultrasensitive Speciation Analysis of Mercury in Rice by Headspace Solid Phase Microextraction Using Porous Carbons and Gas Chromatography-Dielectric Barrier Discharge Optical Emission Spectrometry.

    PubMed

    Lin, Yao; Yang, Yuan; Li, Yuxuan; Yang, Lu; Hou, Xiandeng; Feng, Xinbin; Zheng, Chengbin

    2016-03-01

    Rice consumption is a primary pathway for human methylmercury (MeHg) exposure in inland mercury mining areas of Asia. In addition, the use of iodomethane, a common fumigant that significantly accelerates the methylation of mercury in soil under sunlight, could increase the MeHg exposure from rice. Conventional hyphenated techniques used for mercury speciation analysis are usually too costly for most developing countries. Consequently, there is an increased interest in the development of sensitive and inexpensive methods for the speciation of mercury in rice. In this work, gas chromatography (GC) coupled to dielectric barrier discharge optical emission spectrometry (DBD-OES) was developed for the speciation analysis of mercury in rice. Prior to GC-DBD-OES analysis, mercury species were derivatized to their volatile species with NaBPh4 and preconcentrated by headspace solid phase microextraction using porous carbons. Limits of detection of 0.5 μg kg(-1) (0.16 ng), 0.75 μg kg(-1) (0.24 ng), and 1.0 μg kg(-1) (0.34 ng) were obtained for Hg(2+), CH3Hg(+), and CH3CH2Hg(+), respectively, with relative standard deviations (RSDs) better than 5.2% and 6.8% for one fiber or fiber-to-fiber mode, respectively. Recoveries of 90-105% were obtained for the rice samples, demonstrating the applicability of the proposed technique. Owing to the small size, low power, and low gas consumption of DBD-OES as well as efficient extraction of mercury species by porous carbons headspace solid phase micro-extraction, the proposed technique provides several advantages including compactness, cost-effectiveness, and potential to couple with miniature GC to accomplish the field speciation of mercury in rice compared to conventional hyphenated techniques. PMID:26828416

  17. Coherent Cherenkov radiation as an intense THz source

    NASA Astrophysics Data System (ADS)

    Bleko, V.; Karataev, P.; Konkov, A.; Kruchinin, K.; Naumenko, G.; Potylitsyn, A.; Vaughan, T.

    2016-07-01

    Diffraction and Cherenkov radiation of relativistic electrons from a dielectric target has been proposed as mechanism for production of intense terahertz (THz) radiation. The use of an extremely short high-energy electron beam of a 4th generation light source (X-ray free electron laser) appears to be very promising. A moderate power from the electron beam can be extracted and converted into THz radiation with nearly zero absorption losses. The initial experiment on THz observation will be performed at CLARA/VELA FEL test facility in the UK to demonstrate the principle to a wider community and to develop the radiator prototype. In this paper, we present our theoretical predictions (based on the approach of polarization currents), which provides the basis for interpreting the future experimental measurements. We will also present our hardware design and discuss a plan of the future experiment.

  18. A photoconductive model for superior GaAs THz photomixers

    NASA Astrophysics Data System (ADS)

    Brown, E. R.

    1999-08-01

    Theoretical methods are used to evaluate the THz output from photomixer structures consisting of interdigitated electrodes and planar antennas on top of a low-temperature-grown GaAs layer. Consistent with experiment, the THz power from a standard photomixer is found to be limited by low external quantum efficiency (˜1%). This arises primarily from low photoconductive gain, which is attributed to a long transit time (between electrodes) for the majority of photocarriers generated in the structure. The modeling is then applied to an improved structure containing a thinner absorbing layer (≈0.34 μm for λ=0.85 μm pump) with a dielectric mirror below it to induce resonant-cavity absorption near the surface where the gain is higher. Through increased gain and absorptivity, the model predicts ≈7× greater THz output for the same optical pump power.

  19. Characteristics of nanocomposites and semiconductor heterostructure wafers using THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Altan, Hakan

    All optical, THz-Time Domain Spectroscopic (THz-TDS) methods were employed towards determining the electrical characteristics of Single Walled Carbon Nanotubes, Ion Implanted Si nanoclusters and Si1-xGe x, HFO2, SiO2 on p-type Si wafers. For the nanoscale composite materials, Visible Pump/THz Probe spectroscopy measurements were performed after observing that the samples were not sensitive to the THz radiation alone. The results suggest that the photoexcited nanotubes exhibit localized transport due to Lorentz-type photo-induced localized states from 0.2 to 0.7THz. The THz transmission is modeled through the photoexcited layer with an effective dielectric constant described by a Drude + Lorentz model and given by Maxwell-Garnett theory. Comparisons are made with other prevalent theories that describe electronic transport. Similar experiments were repeated for ion-implanted, 3-4nm Si nanoclusters in fused silica for which a similar behavior was observed. In addition, a change in reflection from Si1-xGex on Si, 200mm diameter semiconductor heterostructure wafers with 10% or 15% Ge content, was measured using THz-TDS methods. Drude model is utilized for the transmission/reflection measurements and from the reflection data the mobility of each wafer is estimated. Furthermore, the effect of high-kappa dielectric material (HfO2) on the electrical properties of p-type silicon wafers was characterized by utilizing non-contact, differential (pump-pump off) spectroscopic methods to differ between HfO2 and SiO 2 on Si wafers. The measurements are analyzed in two distinct transmission models, where one is an exact representation of the layered structure for each wafer and the other assumed that the response observed from the differential THz transmission was solely due to effects from interfacial traps between the dielectric layer and the substrate. The latter gave a more accurate picture of the carrier dynamics. From these measurements the effect of interfacial defects on

  20. Review of THz wave air photonics

    NASA Astrophysics Data System (ADS)

    Sun, X.; Buccheri, F.; Dai, J.; Zhang, X.-C.

    2012-12-01

    THz wave air photonics involves the interaction of intense femtosecond laser pulses with air or selected gases. The very air that we breath is capable of generating and detecting THz waves with field strength greater than 1 MV/cm and useful spectral coverage from 0.1 THz to 60 THz. Broadband THz wave remote sensing is feasible.

  1. Polarization Sensitive THz TDS and Fabrication of Alignment Cells for Solution Phase THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    George, Deepu Koshy

    The overall goal of this thesis is to explore polarization sensitive THz time domain spectroscopy techniques and elucidate the need for aligned sample studies in protein solution. To that end, I have chosen PYP as a model system to show the limitations of traditional, non-aligned sample THz TDS and progressed towards the fabrication of a Dynamical Alignment THz Spectroscopy sample cell for alignment based spectroscopy. Measurements on Photoactive Yellow Proteins address aspects of two previous studies with conflicting results. PYP was chosen as a model system because of its small size and ease of switching between functional states. My measurements in a more controlled environment eliminating the sources of errors and uncertainties in the previous studies have proved that THz dielectric response is invariant between the ground and excited states of PYP which vastly differ in their structure. This `negative' result proves that structural vibrational modes in protein solution are often masked by the background due to relaxational response from solvent and side chains. Low temperature measurements on Cytochrome C and Salmon testes DNA have shown contrast in THz measurements as a result of denaturing. At below freezing temperature the contribution from bulk water is minimized but any water which is unfrozen due to confinement will give rise to the background signal. Even though specific vibrational modes could still not be observed, low temperature measurements provided insights into the nature of interaction between protein surface and water. The section on Polarization Modulation Orientation Terahertz Spectroscopy deviates from the rest of this thesis in the sense that it was a technique developed to study solid state samples like 2DEG in GaAs as well as topological insulators, which give rise to a change in the polarization of the incident THz radiation as it is transmitted through them. Nevertheless this also falls into the general discussion in this thesis in the

  2. In Situ Synthesis of Porous Carbons by Using Room-Temperature, Atmospheric-Pressure Dielectric Barrier Discharge Plasma as High-Performance Adsorbents for Solid-Phase Microextraction.

    PubMed

    Lin, Yao; Wu, Li; Xu, Kailai; Tian, Yunfei; Hou, Xiandeng; Zheng, Chengbin

    2015-09-21

    A one-step, template-free method is described to synthesize porous carbons (PCs) in situ on a metal surface by using a room-temperature, atmospheric-pressure dielectric barrier discharge (DBD) plasma. This method not only features high efficiency, environmentally friendliness, and low cost and simple equipment, but also can conveniently realize large-area synthesis of PCs by only changing the design of the DBD reactor. The synthesized PCs have a regulated nestlike morphology, and thus, provide a high specific surface area and high pore volume, which result in excellent adsorption properties. Its applicability was demonstrated by using a PC-coated stainless-steel fiber as a solid-phase microextraction (SPME) fiber to preconcentrate polycyclic aromatic hydrocarbons (PAHs) prior to analysis by gas chromatography with flame ionization detection (GC-FID). The results showed that the fiber exhibited excellent enrichment factors (4.1×10(4) to 3.1×10(5)) toward all tested PAHs. Thus, the PC-based SPME-GC-FID provides low limits of detection (2 to 20 ng L(-1)), good precision (<7.8%), and good recoveries (80-115%) for ultra-sensitive determination of PAHs in real water samples. In addition, the PC-coated fiber could be stable enough for more than 500 replicate extraction cycles. PMID:26267394

  3. Preparation and Characterization of Ultralow-Dielectric-Constant Porous SiCOH Thin Films Using 1,2-Bis(triethoxysilyl)ethane, Triethoxymethylsilane, and a Copolymer Template

    NASA Astrophysics Data System (ADS)

    Fu, Shuang; Qian, Ke-Jia; Ding, Shi-Jin; Zhang, David Wei

    2011-10-01

    Ultralow-dielectric-constant ( k) porous SiCOH films have been prepared using 1,2-bis(triethoxysilyl)ethane, triethoxymethylsilane, and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer template by means of spin-coating. The resulting films were characterized by cross-section scanning electron microscopy, small-angle x-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, nanomechanical testing, and electrical measurements. Thermal treatment at 350°C for 2 h resulted in the formation of ultralow- k films with k of ˜2.0, leakage current density of 3 × 10-8 A/cm2 at 1 MV/cm, reduced modulus ( E r) of ˜4.05 GPa, and hardness ( H) of ˜0.32 GPa. After annealing between 400°C and 500°C for 30 min, the resulting films showed fluctuant k values of 1.85 to 2.22 and leakage current densities of 3.7 × 10-7 A/cm2 to 3 × 10-8 A/cm2 at 0.8 MV/cm, likely due to the change of the film microstructure. Compared with 350°C annealing, higher-temperature annealing can improve the mechanical strength of the ultralow- k film, i.e., E r ≈ 5 GPa and H ≈ 0.56 GPa after 500°C annealing.

  4. Quantitative study of rectangular waveguide behavior in the THz.

    SciTech Connect

    Rowen, Adam M.; Nordquist, Christopher Daniel; Wanke, Michael Clement

    2009-10-01

    This report describes our efforts to quantify the behavior of micro-fabricated THz rectangular waveguides on a configurable, robust semiconductor-based platform. These waveguides are an enabling technology for coupling THz radiation directly from or to lasers, mixers, detectors, antennas, and other devices. Traditional waveguides fabricated on semiconductor platforms such as dielectric guides in the infrared or co-planar waveguides in the microwave regions, suffer high absorption and radiative losses in the THz. The former leads to very short propagation lengths, while the latter will lead to unwanted radiation modes and/or crosstalk in integrated devices. This project exploited the initial developments of THz micro-machined rectangular waveguides developed under the THz Grand Challenge Program, but instead of focusing on THz transceiver integration, this project focused on exploring the propagation loss and far-field radiation patterns of the waveguides. During the 9 month duration of this project we were able to reproduce the waveguide loss per unit of length in the waveguides and started to explore how the loss depended on wavelength. We also explored the far-field beam patterns emitted by H-plane horn antennas attached to the waveguides. In the process we learned that the method of measuring the beam patterns has a significant impact on what is actually measured, and this may have an effect on most of the beam patterns of THz that have been reported to date. The beam pattern measurements improved significantly throughout the project, but more refinements of the measurement are required before a definitive determination of the beam-pattern can be made.

  5. Corrugated capillary as THz Cherenkov Smith-Purcell radiator

    NASA Astrophysics Data System (ADS)

    Lekomtsev, K. V.; Aryshev, A. S.; Tishchenko, A. A.; Ponomarenko, A. A.; Sukharev, V. M.; Terunuma, N.; Urakawa, J.; Strikhanov, M. N.

    2016-07-01

    In this article we discussed Particle In Cell electromagnetic simulations and mechanical design of dielectric capillaries that produce THz Cherenkov Smith-Purcell radiation (ChSPR), arising when a femtosecond electron multi-bunch beam propagates through corrugated and non-corrugated dielectric capillaries with metallic radiation reflectors. We investigated the influence of the four-bunch beam on the SPR field spectrum and on the ChSPR power spectrum, and the influence of the non-central beam propagation on the ChSPR power spectrum. We also discussed the design and assembly of the capillaries, constructed as sets of cylindrical rings.

  6. 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.

  7. THz Imaging of Skin Burn: Seeing the Unseen—An Overview

    PubMed Central

    Dutta, Moumita; Bhalla, Amar S.; Guo, Ruyan

    2016-01-01

    Significance: This review article puts together all the studies performed so far in realizing terahertz (THz) spectra as a probing mechanism for burn evaluation, summarizing their experimental conditions, observations, outcomes, merits, and demerits, along with a comparative discussion of other currently used technologies to present the state of art in a condensed manner. The key features of this noncontact investigation technique like its precise burn depth analysis and the approaches it follows to convert the probed data into a quantitative measure have also been discussed in this article. Recent Advances: The current research developments in THz regime observed in device design technologies (like THz time domain spectrometer, quantum cascade THz lasers, THz single-photon detectors, etc.) and in understanding its unique properties (like nonionizing nature, penetrability through dry dielectrics, etc.) have motivated the research world to realize THz window as a potential candidate for burn detection. Critical Issues: Application of appropriate medical measure for burn injury is primarily subjective to proper estimation of burn depth. Tool modality distinguishing between partial and full-thickness burn contributing toward correct medical care is indeed awaited. Future Directions: The overview of THz imaging as a burn assessment tool as provided in this article will certainly help in further nurturing of this emerging diagnostic technique particularly in improving its detection and accompanied image processing methods so that the minute nuances captured by the THz beam can be correlated with the physiological–anatomical changes in skin structures, caused by burn, for better sensitivity, resolution, and quantitative analysis. PMID:27602253

  8. Exploration of the effects of burn parameters on THz wound imaging

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Sung, Shijun; Fishbein, Michael; Grundfest, Warren S.; Taylor, Zachary D.

    2015-08-01

    The high contrast resolution afforded by terahertz (1 THz = 1012 Hz) imaging of physiologic tissue continues to drive explorations into the utility of THz technology for burn wound detection. Although we have previously reported the use of a novel, reflective THz imaging technology to sense spatiotemporal differences in reflectivity between partial and full thickness burn wounds, no evidence exists of a one-to-one correlation between structural damage observed in histological assessments of burn severity and THz signal. For example, varying burn induction methods may all result in a common burn wound severity, however, burn features observed in parallel THz imagery may not be identical. Successful clinical translation of THz technology as a comprehensive burn guidance tool, therefore, necessitates an understanding of THz signal and its relation to wound pathophysiology. In this work, longitudinal THz imagery was acquired with a quartz (n = 2.1, 500 μm) window of cutaneous wounds induced with the same brand geometry and contact pressure but varying contact times (5, 7, and 10 seconds) in in vivo, pre-clinical rat models (n=3) over a period of 3 days. Though all burn wounds were evaluated to be deep partial thickness with histology, THz contrasts observed for each burn contact time were intrinsically unique. This is the first preliminary in vivo evidence of a many-to-one relationship between changes in THz contrast and burn severity as ascertained by histology. Future large-scale studies are required to assess whether these observed changes in THz contrast may be interpreted as physiological changes occurring over time, morphometric changes related to anatomical change, or electromagnetic changes between dielectric substrate windows and the underlying tissue.

  9. Optically-electrically pumped THz source

    NASA Astrophysics Data System (ADS)

    Haji-Saeed, Bahareh; Khoury, Jed; Buchwald, Walter; Woods, Charles; Wentzell, Sandra; Krejca, Brian; Kierstead, John

    2010-08-01

    In this paper, we propose a design for a widely tunable solid-state optically and electrically pumped THz source based on the Smith-Purcell free-electron laser. Our design consists of a thin dielectric layer sandwiched between an upper corrugated structure and a lower layer of thin metal, semiconductor, or high electron mobility material. The lower layer is for current streaming, which replaces the electron beam in the Smith-Purcell free-electron laser design. The upper layer consists of two micro-gratings for optical pumping, and a nano-grating to couple with electrical pumping in the lower layer. The optically generated surface plasmon waves from the upper layer and the electrically induced surface plasmon waves from the lower layer are then coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

  10. 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.

  11. Sapphire decelerating capillary channel integrated with antenna at frequency 0.675 THz

    NASA Astrophysics Data System (ADS)

    Ashanin, I. A.; Polozov, S. M.

    2016-07-01

    In recent years, there has been an increasing interest in THz-radiation for application in medicine (THz tomographs), in pharmaceutics (composition analysis for medicines), in introscopy of large-scale objects (ships, trains, containers) and others. THz-radiation can be generated by relativistic electron bunches passing through the Cherenkov decelerating capillary channel (circular waveguide with dielectric filling) with horn extraction. Relativistic electron beams having ∼100 µm in diameter and pulse durations of 1 ps or less (as in photoinjectors) are capable of producing substantial power of THz-radiation. High-peak power coherent Cherenkov radiation can be produced by a properly modulated high-brightness electron beam or by a single, high-density bunch having sub-wavelength dimension. The aperture of a Cherenkov decelerating structure should be comparable with the mm or sub-mm wavelength (0.1-3 mm). Different dielectric materials for the internal surface coating of the capillary channel of mm-sub-mm cross-section can be used. As is known, a frequency of 0.675 THz corresponds to the atmospheric window with high transparency. This report presents the results of electrodynamics study of the metallized sapphire decelerating Cherenkov capillary. A horn antenna attached to the metallized sapphire capillary channel at the 0.675 THz resonant frequency will be considered.

  12. THz pump-THz probe study of electrostatically gated graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Jingdi; Liu, Mengkun; Wagner, Martin; Basov, D. N.; Averitt, Richard D.

    2015-03-01

    We investigate ultrafast carrier dynamics in graphene using THz-pump THz-probe spectroscopy. In contrast to recent studies using optical excitation, THz excitation exclusively initiates intra-band transitions, resulting in an increase in the carrier scattering rate. The corresponding transient peak of the transmitted probe signal scales linearly with the E-field of the incident THz pump pulse. Further, the decay time of the excited carriers is independent of the gating voltage. As the Fermi level is tuned toward the charge neutral point (CNP) by varying the electrostatic gate voltage, the induced increase in transmission is strongly suppressed. We believe that the low density of states near the CNP is responsible for this suppression. Work supported by DOE-BES. RDA and JZ also with Boston University. ML also with Stony Brook University.

  13. Compact broadband slow wave system based on spoof plasmonic THz waveguide with meander grooves

    NASA Astrophysics Data System (ADS)

    Yang, Bao Jia; Zhou, Yong Jin

    2015-12-01

    Conformal surface plasmons (CSPs) on ultrathin corrugated metallic strips have been proposed to develop versatile spoof plasmonic subwavelength integrated devices at lower frequencies bands, especially at terahertz (THz) frequencies. However, the effects of the groove shapes have not been fully investigated. Here we have proposed the CSPs waveguide constructed by meander grooves on an ultrathin dielectric substrate. The dispersions and propagation characteristics of the CSPs on the proposed waveguide have been investigated in the THz frequencies. A very compact broadband slow wave system based on such waveguide has been demonstrated, whose lateral dimension decreases about 43.2% than that based on the conventional CSPs waveguide. To verify the performance of the THz plasmonic device, we implemented experimental validation in the microwave frequencies by scaling up its geometry structure. It is believed that the CSPs waveguide and device can find more applications in the surface plasmonic THz platform such as signal processing and optical communication system.

  14. Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy

    SciTech Connect

    Minami, Yasuo; Horiuchi, Kohei; Masuda, Kaisei; Takeda, Jun; Katayama, Ikufumi

    2015-10-26

    We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si plate was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.

  15. 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.

  16. Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe₃O₄ nano-fillers: an interface-mediated superior dielectric and EMI shielding performance.

    PubMed

    Rao, B V Bhaskara; Yadav, Prasad; Aepuru, Radhamanohar; Panda, H S; Ogale, Satishchandra; Kale, S N

    2015-07-28

    In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm(-3) is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA-SLGAPC-Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz-10 MHz, enhanced by a factor of 4 as compared to that of the PVA-SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell-Wagner-Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2-12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm(-3))(-1), indicating the promising character of this material for flexible EMI shielding applications. PMID:26105548

  17. Bulk size crystal growth, spectroscopic, dielectric and surface studies of 4-N,N-dimethylamino-4-N'-methylstilbazolium m-nitrobenzenesulfonate (DSMNS): A potential THz crystal of stilbazolium family.

    PubMed

    Antony Raj, A; John Sundaram, S; Gunaseelan, R; Sagayaraj, P

    2015-10-01

    The synthesis and growth of a potentially useful and efficient nonlinear optical organic single crystal of 4-N,N-dimethylamino-4-N'-methylstilbazolium m-nitrobenzenesulfonate (DSMNS) is reported. The growth experiment involved the slope nucleation method coupled with slow cooling as well as slow solvent evaporation techniques. Single crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR), FT-Raman and nuclear magnetic resonance (NMR) techniques have been employed to ascertain the structure and composition of the crystal. Second harmonic generation (SHG) efficiency of the sample has been examined by Kurtz and Perry powder test. Thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) techniques are employed to investigate the thermal behavior of the grown crystal. The frequency/temperature dependent dielectric properties of the organic crystal of DSMNS are studied. The surface features of the grown crystal are investigated by chemical etching study and atomic force microscopy (AFM). PMID:26010563

  18. THz Local Oscillator Sources

    NASA Astrophysics Data System (ADS)

    Mehdi, Imran; Schlecht, Erich; Chattopadhyay, Goutam; Siegel, Peter H.

    Most operational Submillimeter-wave radio telescopes, both space borne and ground based, employ local oscillator sources based on Gunn diodes followed by whisker contacted Schottky multipliers. Enough progress, however, has been made on a number of fronts to conclude that next generation of radio telescopes that become operational in the new Millennium will have a different local oscillator (LO) generation architecture. MMIC power amplifiers with impressive gain in the Ka- to-W band have enabled the use of microwave synthesizers which can then be actively multiplied to provide a frequency agile power source beyond 100 GHz. This medium power millimeter source can then be amplified to enable efficient pumping of follow-on balanced multiplier stages. Input power to the multipliers can be further enhanced by power combining to achieve close to half a Watt at W-band. An 800 GHz three-stage multiplier chain, implemented this way has demonstrated a peak output power of 1 mW. A second advance in LO generation lies in the Schottky diode varactor technology. Planar Schottky diode multipliers have now been demonstrated up to 1500 GHz and it can be assumed that most of the future multiplier chains will be based on these robust devices rather than the whisker contacted diode of the past. The ability to produce planar GaAs diode chips deep into the THz range, with submicron dimensions, has opened up a wide range of circuit design space which can be taken advantage of to improve efficiency, bandwidth, and power handling capability of the multipliers. A third breakthrough has been the demonstration of photonic based LO sources utilizing GaAs photomixers. These sources, though not yet implemented in robust space borne missions, offer a number of advantages over their electronic counterparts, including extremely broad tuning, fiber coupled components, and solid-state implementation. Another development, which holds some promise, is the use of micro-machining technology to implement

  19. Compact electron acceleration and bunch compression in THz waveguides.

    PubMed

    Wong, Liang Jie; Fallahi, Arya; Kärtner, Franz X

    2013-04-22

    We numerically investigate the acceleration and bunch compression capabilities of 20 mJ, 0.6 THz-centered coherent terahertz pulses in optimized metallic dielectric-loaded cylindrical waveguides. In particular, we theoretically demonstrate the acceleration of 1.6 pC and 16 pC electron bunches from 1 MeV to 10 MeV over an interaction distance of 20mm, the compression of a 1.6 pC 1 MeV bunch from 100 fs to 2 fs (50 times compression) over an interaction distance of about 18mm, and the compression of a 1.6 pC 10 MeV bunch from 100 fs to 1.61 fs (62 times) over an interaction distance of 42 cm. The obtained results show the promise of coherent THz pulses in realizing compact electron acceleration and bunch compression schemes. PMID:23609686

  20. Monolithic THz Frequency Multipliers

    NASA Technical Reports Server (NTRS)

    Erickson, N. R.; Narayanan, G.; Grosslein, R. M.; Martin, S.; Mehdi, I.; Smith, P.; Coulomb, M.; DeMartinez, G.

    2001-01-01

    Frequency multipliers are required as local oscillator sources for frequencies up to 2.7 THz for FIRST and airborne applications. Multipliers at these frequencies have not previously been demonstrated, and the object of this work was to show whether such circuits are really practical. A practical circuit is one which not only performs as well as is required, but also can be replicated in a time that is feasible. As the frequency of circuits is increased, the difficulties in fabrication and assembly increase rapidly. Building all of the circuit on GaAs as a monolithic circuit is highly desirable to minimize the complexity of assembly, but at the highest frequencies, even a complete monolithic circuit is extremely small, and presents serious handling difficulty. This is compounded by the requirement for a very thin substrate. Assembly can become very difficult because of handling problems and critical placement. It is very desirable to make the chip big enough to that it can be seen without magnification, and strong enough that it may be picked up with tweezers. Machined blocks to house the chips present an additional challenge. Blocks with complex features are very expensive, and these also imply very critical assembly of the parts. It would be much better if the features in the block were as simple as possible and non-critical to the function of the chip. In particular, grounding and other electrical interfaces should be done in a manner that is highly reproducible.

  1. Electrodynamic model of the field effect transistor application for THz/subTHz radiation detection: Subthreshold and above threshold operation

    SciTech Connect

    Dobrovolsky, V.

    2014-10-21

    Developed in this work is an electrodynamic model of field effect transistor (FET) application for THz/subTHz radiation detection. It is based on solution of the Maxwell equations in the gate dielectric, expression for current in the channel, which takes into account both the drift and diffusion current components, and the equation of current continuity. For the regimes under and above threshold at the strong inversion the response voltage, responsivity, wave impedance, power of ohmic loss in the gate and channel have been found, and the electrical noise equivalent power (ENEP) has been estimated. The responsivity is orders of magnitude higher and ENEP under threshold is orders of magnitude less than these values above threshold. Under the threshold, the electromagnetic field in the gate oxide is identical to field of the plane waves in free-space. At the same time, for strong inversion the charging of the gate capacitance through the resistance of channel determines the electric field in oxide.

  2. CVD Diamond Dielectric Accelerating Structures

    SciTech Connect

    Schoessow, P.; Kanareykin, A.; Gat, R.

    2009-01-22

    The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

  3. 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

  4. 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. PMID:24639915

  5. Silver-Coated Teflon Tubes for Waveguiding at 1-2 THz

    NASA Astrophysics Data System (ADS)

    Navarro-Cía, Miguel; Melzer, Jeffrey E.; Harrington, James A.; Mitrofanov, Oleg

    2015-06-01

    Realization of single-mode low-loss waveguides for 1.0-2.0 THz remains a challenging problem due to large absorption in most dielectrics and ohmic losses in metals. To address this problem, we investigate dielectric-lined hollow metallic waveguides fabricated by coating 1-mm diameter 38-μm-thick polytetrafluoroethylene tubes with silver. These waveguides support a hybrid HE11 mode, which exhibits low attenuation and low dispersion. Quasi-single-mode propagation is achieved in the band of 1.0-1.6 THz, in which the hybrid HE11 mode is supported by the waveguide. In this band, the experimentally measured loss is ~20 dB/m (~0.046 cm-1), whereas the numerically computed loss is ~7 dB/m (~0.016 cm-1). The difference is attributed to additional losses in the dielectric layer, which can be reduced by using alternative polymers.

  6. Dielectric response of the human tooth dentine

    NASA Astrophysics Data System (ADS)

    Leskovec, J.; Filipič, C.; Levstik, A.

    2005-07-01

    Dielectric properties of tooth dentine can be well described by the model which was developed for the dielectric response to hydrating porous cement paste. It is shown that the normalized dielectric constant and the normalized specific conductivity are proportional to the model parameters ɛ and σv, indicating the deposition of AgCl in the dentine tubules during the duration of the precipitation. The fractal dimension of the tooth dentine was determined by dielectric spectroscopy.

  7. Tribological Effects of Brush Scrubbing in Post Chemical Mechanical Planarization Cleaning on Electrical Characteristics in Novel Non-porous Low-k Dielectric Fluorocarbon on Cu Interconnects

    NASA Astrophysics Data System (ADS)

    Gu, Xun; Nemoto, Takenao; Tomita, Yugo; Teramoto, Akinobu; Sugawa, Shigetoshi; Ohmi, Tadahiro

    2011-05-01

    Damage reduction during planarization is strongly required to avoid scratch generation and the variation in the electrical properties of low-k dielectrics leading to yield loss in an integrated circuit after the implementation of an ultralow-k dielectric in Cu damascene interconnects. An optimum process condition to reduce damage on brush scrubbing in post-chemical-mechanical-planarization (post-CMP) cleaning was proposed for advanced nonporous organic ultralow-k dielectric fluorocarbon/Cu interconnects. Increasing brush rotation rate by decreasing down pressures results in the improvement in both electric properties and particle removal efficiency. The tribological effects of brush scrubbing in post-CMP cleaning on the electrical characteristics were explored. The brush scrubbing condition of a high brush rotation rate at low down pressures contributes to the suppression of damage generation.

  8. Enhancing THz Absorption using Thin-Film Multilayer Stacks

    NASA Astrophysics Data System (ADS)

    Grbovic, Dragoslav; Bolakis, Christos; Karunasiri, Gamani

    2010-03-01

    Terahertz imaging has seen significant proliferation in recent years. This band of electromagnetic spectrum has been underutilized for a long time due to the lack of sufficiently powerful sources and sensitive detectors. Because of virtually harmless effects on living tissue, terahertz (THz) radiation is attractive for various applications, ranging from non-invasive medical diagnostics to detection of concealed weapons. Our work focuses on identifying materials, or more specifically a stack of thin-films with increased absorption in the band of interest. In this work, we demonstrate a method that combines finite element modeling, thin-film deposition and experimental characterization to create highly-absorptive multi-layer stacks. Finite element modeling is used to simulate the absorption of a combination of thin dielectric and metallic films. Metals are deposited using e-beam evaporation and dielectric films using plasma enhanced chemical vapor deposition (PECVD). The simulated and measured THz absorption characteristics of the composite thin-film multilayer stacts will be presented.

  9. 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. PMID:26191876

  10. Evaluation of SiO2@CoFe2O4 nano-hollow spheres through THz pulses

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Pal, Monalisa; Serita, Kazunori; Chaudhuri, Arka; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-05-01

    We have synthesized cobalt ferrite (CFO) nanoparticles (NPs) of diameter 100 nm and nano-hollow spheres (NHSs) of diameter 100, 160, 250, and 350 nm by a facile one step template free solvothermal technique and carried out SiO2 coating on their surface following Stöber method. The phase and morphology of the nanostructures were confirmed by X-ray diffraction and transmission electron microscope. The magnetic measurements were carried out by vibrating sample magnetometer in order to study the influence of SiO2 coating on the magnetic properties of bare CFO nanostructures. Furthermore, we have applied THz time domain spectroscopy to investigate the THz absorption property of these nanostructures in the frequency range 1.0-2.5 THz. Detailed morphology and size dependent THz absorption study unfolds that the absorption property of these nanostructures sensitively carries the unique signature of its dielectric property.

  11. A high sensitivity THz detector

    NASA Astrophysics Data System (ADS)

    Su, Bo; Duan, Guoteng

    2011-08-01

    We have developed a novel THz detector which uses the cantilever technology and surface plasmon resonance (SPR) technology to achieve a high sensitivity. The Micro Electro Mechanical System (MEMS) technology is adopted to fabricate the detector, which comprise thermo-sensitive bi-material micro-cantilever, prism and optical readout system. The bi-material of Si3N4 and Al is used to fabricate the micro-cantilever because of the good absorption characteristic for THz of Si3N4 and the great difference in thermal expansion coefficient of the bi-material for the deformation of the micro-cantilever. In order to increase the deformation of micro-cantilever, the method of computer simulation is used to obtain the optimal structure of micro-cantilever and the thickness of Si3N4 and Al. The function of the glass prism is to make the incident light generate total reflection under certain conditions. The gold film is sputtering on the top of glass slide using the method of magnetron sputtering and it is necessary for the generation of SPR performance. The optical readout system can make the change of cantilever bending convert to the change of reflection luminous intensity proportionally. The heat on the micro-cantilever coming from the THz radiation can lose easily in the air, so the detector is placed vertically in a cylindrical vacuum chamber which is sealed with quartz glasses and polyethylene lamina at the two end surfaces respectively. The quartz glass is used for the incidence of visible polarized light and the polyethylene lamina for the THz radiation. In order to maintain the vacuum performance of the chamber, the mechanical pump and molecular pump are adopted. In static mode, THz radiation absorption raises the temperature of micro-cantilever, so it bends proportionally. The micro-cantilever bending changes the thicknesses of the gap between the micro-cantilever and the metallic thin film on the micro-prism. It will result in a shift of the SPR angle. Therefore, the

  12. Acoustic vibration induced high electromagnetic responses of Fe3O4 nano-hollow spheres in the THz regime

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Sarkar, Debasish; Pal, Monalisa; Serite, Kazunori; Tonouchi, Masayoshi; Mandal, Kalyan

    2015-06-01

    Herein, we investigate the origin of enhanced absorption and complex conductivity of magnetite (Fe3O4) nano-hollow spheres (NHSs) in contrast to its nanoparticles (NPs) configuration in the frequency range 0.4-2.0 THz. The maximum absorption for NHSs and NPs of the same average diameter (~100 nm) are found to be 246.27 and 48.35 cm-1 at 1.8 THz, respectively. A detailed study suggests that the multiple resonance peaks in the absorption spectra are due to low frequency acoustic vibrational phonon modes of Fe3O4 nanostructures. Moreover, we demonstrate that the magnitude of total absorption can be tailored by varying the shell thickness of NHSs. It is found to increase with increasing shell thickness, and attain a maximum value of 498.5 cm-1 for the NHSs of average diameter 350 nm at 1.8 THz. The invariance of frequency dependent magnetic permeability points out that the absorption is basically due to dielectric loss instead of magnetic loss. The enhanced THz conductivity of Fe3O4 NHSs, as compared to NPs is described in light of thermally activated polaronic hopping which is found to increase with increasing THz absorption. Finally, the size dependent THz conductivity of NHSs confirms its sole dependence on the magnitude of THz absorptivity.

  13. Improvement of passive THz camera images

    NASA Astrophysics Data System (ADS)

    Kowalski, Marcin; Piszczek, Marek; Palka, Norbert; Szustakowski, Mieczyslaw

    2012-10-01

    Terahertz technology is one of emerging technologies that has a potential to change our life. There are a lot of attractive applications in fields like security, astronomy, biology and medicine. Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. The reasons of this fact were difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. The THz waves can penetrate through various materials. However, automated processing of THz images can be challenging. The THz frequency band is specially suited for clothes penetration because this radiation does not point any harmful ionizing effects thus it is safe for human beings. Strong technology development in this band have sparked with few interesting devices. Even if the development of THz cameras is an emerging topic, commercially available passive cameras still offer images of poor quality mainly because of its low resolution and low detectors sensitivity. Therefore, THz image processing is very challenging and urgent topic. Digital THz image processing is a really promising and cost-effective way for demanding security and defense applications. In the article we demonstrate the results of image quality enhancement and image fusion of images captured by a commercially available passive THz camera by means of various combined methods. Our research is focused on dangerous objects detection - guns, knives and bombs hidden under some popular types of clothing.

  14. Photo-generated THz antennas

    PubMed Central

    Georgiou, G.; Tyagi, H. K.; Mulder, P.; Bauhuis, G. J.; Schermer, J. J.; Rivas, J. Gómez

    2014-01-01

    Electromagnetic resonances in conducting structures give rise to the enhancement of local fields and extinction efficiencies. Conducting structures are conventionally fabricated with a fixed geometry that determines their resonant response. Here, we challenge this conventional approach by demonstrating the photo-generation of THz linear antennas on a flat semiconductor layer by the structured optical illumination through a spatial light modulator. Free charge carriers are photo-excited only on selected areas, which enables the realization of different conducting antennas on the same sample by simply changing the illumination pattern, thus without the need of physically structuring the sample. These results open a wide range of possibilities for the all-optical spatial control of resonances on surfaces and the concomitant control of THz extinction and local fields. PMID:24394920

  15. 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.

  16. Technological customization of uncooled amorphous silicon microbolometer for THz real time imaging

    NASA Astrophysics Data System (ADS)

    Pocas, S.; Deronzier, E.; Brianceau, P.; Imperinetti, P.; Dumont, G.; Roule, A.; Rabaud, W.; Meilhan, J.; Simoens, F.; Goudon, V.; Vialle, Claire; Arnaud, A.

    2013-03-01

    Terahertz uncooled antenna-coupled microbolometer focal plane arrays are being developed at CEA Leti for real time THz imaging and sensing. This detector relies on LETI amorphous silicon uncooled infrared bolometer technology that has been deeply modified to optimize sensitivity in the THz range. The main technological key lock of the pixel structure is the quarter wavelength cavity that consists in a thick dielectric layer deposited over the metalized CMOS wafer; such cavity improves significantly the optical coupling efficiency. Copper plugs connect the microbolometer level down to the CMOS readout circuit (ROIC) upper metal pads through this thick dielectric cavity. This paper explains how we have improved the copper vias technology and the challenges we have faced to customize the microbolometer while keeping a monolithically above IC technology fully compatible with standard silicon processes. The results show a very good operability and reproducibility of the contact through this thick oxide cavity. Due to these good results, we have been able to characterize a very efficient THz absorption that enables real time imaging with high sensitivity in the 1-3 THz range.

  17. 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.

  18. A multiband THz bandpass filter based on multiple-resonance excitation of a composite metamaterial

    NASA Astrophysics Data System (ADS)

    Chen, Xu; Fan, Wen-Hui

    2015-05-01

    We present a systematic numerical study on a metal-dielectric-metal (MDM) sandwich structure for multiple resonance transmission in terahertz (THz) region. The designed structure consists of periodic square close ring array on both side of a flexible dielectric substrate, exhibits a multiband transmission, with low average insertion loss, steep skirts and high out-of-band rejection. In addition, due to its rotationally symmetric structure, this filter is polarization-insensitive for normal incidence of the electromagnetic waves, keeping highly transmission at a wide range of incident angles for transverse electric waves and transverse magnetic waves. The metamaterial structure can be utilized as a desirable multiband filter with many practical applications, especially for THz communication, spectroscopic detection and phase imaging.

  19. Surface roughness limited contrast to clutter ratios THz medical imaging (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Bajwa, Neha; Goell, Jacob; Taylor, Zachary

    2016-03-01

    The THz electromagnetic properties of rough surface are explored and their effect on the observed contrast in THz images is quantified. Rough surface scatter is a major source of clutter in THz imaging as the rough features of skin and other tissues result in non-trivial reflection signal modulation. Traditional approaches to data collection utilize dielectric windows to flatten surfaces for THz imaging. However, there is substantial interest surrounding window free imaging as contact measurements are not ideal for a range of candidate diseases and injuries. In this work we investigate the variation in reflected signal in the specular direction from rough surfaces targets with known roughness parameters. Signal to clutter ratios are computed and compared with that predicted by Rayleigh Rough surface scattering theory. It is shown that Rayleigh rough surface scattering theory, developed for rough features larger than the interacting wavelength, holds acceptable at THz frequencies with rough features much smaller than the wavelength. Additionally, we present some biological tissue imaging examples to illustrate the impact of rough surface scattering in image quality.

  20. Gigavolt-per-Meter Wakefields in Annular Dielectric Structures

    NASA Astrophysics Data System (ADS)

    O'Shea, Brendan Donald

    A wakefield accelerator uses a medium capable of sustaining appropriate electric fields to transfer energy from a drive beam to a witness beam. Examples of such systems include electron beam driven plasma wakefields, laser driven plasma wakefields and electron beam driven dielectric wakefield structures. Dielectrics and plasmas are of particular interest because they are capable of maintaining electric fields on the order of GV/m and in the case of plasmas upwards of TV/m. These systems provide a significant step beyond current radiofrequency accelerating structures capable of peak electric fields on the order of 100 MV/m and average effective electric fields of 20 MV/m. Furthermore, beam driven dielectric structures produce a wakefield which is phase synchronous with the beam, these structures do not suffer from transit time or dephasing effects. In the case of dielectric wakefield accelerators, the structures under study in this publication, the modes generated by the driving beam are in the terahertz (THz) regime. Thus development of dielectric wakefield accelerators is seen as a path to smaller, more compact accelerating systems and as a means to generate THz radiation. Here we demonstrate a beam-driven dielectric wakefield accelerating structure that produces sustained fields of 1.35 GV/m for many hundreds of thousands of drive beam pulses. In addition we show beam-driven dielectric structures have the potential to produce single mode, high spectral purity THZ radiation of unprecedented energy scale.

  1. Fabrication of THz Sensor with Metamaterial Absorber

    NASA Astrophysics Data System (ADS)

    Gonzalez, Hugo; Alves, Fabio; Karunasiri, Gamani

    The terahertz (THz) portion of the electromagnetic spectrum (0.1-10 THz) has not been fully utilized due to the lack of sensitive detectors. Real-time imaging in this spectral range has been demonstrated using uncooled infrared microbolometer cameras and external illumination provided by quantum cascade laser (QCL) based THz sources. However, the microbolometer pixels in the cameras have not been optimized to achieve high sensitivity in THz frequencies. Recently, we have developed a highly sensitive micromechanical THz sensor employing bi-material effect with an integrated metamaterial absorber tuned to the THz frequency of interest. The use of bi-material structures causes deflection on the sensor to as the absorbed THz radiation increases its temperature, which can be monitored optically by reflecting a light beam. This approach eliminates the integration of readout electronics needed in microbolometers. The absorption of THz by metamaterial can be tailored by controlling geometrical parameters. The sensors can be fabricated using conventional microelectronic materials and incorporated into pixels to form focal plane arrays (FPAs). In this presentation, characterization and readout of a THz sensor with integrated metamaterial structure will be described. Supported by DoD.

  2. 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.

  3. 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.

  4. Curvature Control of Silicon Microlens for THz Dielectric Antenna

    NASA Technical Reports Server (NTRS)

    Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran

    2012-01-01

    We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.

  5. Integrated diode circuits for greater than 1 THz

    NASA Astrophysics Data System (ADS)

    Schoenthal, Gerhard Siegbert

    The terahertz frequency band, spanning from roughly 100 GHz to 10 THz, forms the transition from electronics to photonics. This band is often referred to as the "terahertz technology gap" because it lacks typical microwave and optical components. The deficit of terahertz devices makes it difficult to conduct important scientific measurements that are exclusive to this band in fields such as radio astronomy and chemical spectroscopy. In addition, a number of scientific, military and commercial applications will become more practical when a suitable terahertz technology is developed. UVa's Applied Electrophysics Laboratory has extended non-linear microwave diode technology into the terahertz region. Initial success was achieved with whisker-contacted diodes and then discrete planar Schottky diodes soldered onto quartz circuits. Work at UVa and the Jet Propulsion Laboratory succeeded in integrating this diode technology onto low dielectric substrates, thereby producing more practical components with greater yield and improved performance. However, the development of circuit integration technologies for greater than 1 THz and the development of broadly tunable sources of terahertz power remain as major research goals. Meeting these critical needs is the primary motivation for this research. To achieve this goal and demonstrate a useful prototype for one of our sponsors, this research project has focused on the development of a Sideband Generator at 1.6 THz. This component allows use of a fixed narrow band source as a tunable power source for terahertz spectroscopy and compact range radar. To prove the new fabrication and circuit technologies, initial devices were fabricated and tested at 200 and 600 GHz. These circuits included non-ohmic cathodes, air-bridged fingers, oxideless anode formation, and improved quartz integration processes. The excellent performance of these components validated these new concepts. The prototype process was then further optimized to

  6. THz pulse shaping and improved optical-to-THz conversion efficiency using a binary phase mask.

    PubMed

    Ropagnol, Xavier; Morandotti, Roberto; Ozaki, Tsuneyuki; Reid, Matt

    2011-07-15

    We demonstrate improved optical-to-terahertz (THz) conversion efficiency and THz pulse shaping from an interdigitated GaAs large area photoconductive antenna by using a binary phase mask. The binary phase mask results in a time-delayed excitation of the adjacent antennas, which allows subsequent antennas to produce an additive field, thus resulting in a quasi-single-cycle THz pulse. We demonstrate control over the temporal profile of the THz waveform to maximize optical-to-THz conversion efficiency. PMID:21765501

  7. Surface sealing using self-assembled monolayers and its effect on metal diffusion in porous low-k dielectrics studied using monoenergetic positron beams

    NASA Astrophysics Data System (ADS)

    Uedono, Akira; Armini, Silvia; Zhang, Yu; Kakizaki, Takeaki; Krause-Rehberg, Reinhard; Anwand, Wolfgang; Wagner, Andreas

    2016-04-01

    Surface sealing effects on the diffusion of metal atoms in porous organosilicate glass (OSG) films were studied by monoenergetic positron beams. For a Cu(5 nm)/MnN(3 nm)/OSG(130 nm) sample fabricated with pore stuffing, C4F8 plasma etch, unstuffing, and a self-assembled monolayer (SAM) sealing process, it was found that pores with cubic pore side lengths of 1.1 and 3.1 nm coexisted in the OSG film. For the sample without the SAM sealing process, metal (Cu and Mn) atoms diffused from the top Cu/MnN layer into the OSG film and were trapped by the pores. As a result, almost all pore interiors were covered with those metals. For the sample damaged by an Ar/C4F8 plasma etch treatment before the SAM sealing process, SAMs diffused into the OSG film, and they were preferentially trapped by larger pores. The cubic pore side length in these pores containing self-assembled molecules was estimated to be 0.7 nm. Through this work, we have demonstrated that monoenergetic positron beams are a powerful tool for characterizing capped porous films and the trapping of atoms and molecules by pores.

  8. THz detection in graphene nanotransistors

    NASA Astrophysics Data System (ADS)

    Tredicucci, Alessandro; Vitiello, Miriam S.; Polini, Marco; Pellegrini, Vittorio

    2014-03-01

    Nanotransistors offer great prospect for the development of innovative THz detectors based on the non-linearity of transport characteristics. Semiconductor nanowires are appealing for their one-dimensional nature and intrinsically low capacitance of the devices, while graphene, with its record-high room-temperature mobility, has the potential to exploit plasma wave resonances in the transistor channel to achieve high-responsivity and tuneable detection. First graphene detectors have been recently demonstrated in both monolayer and bilayer field effect devices performances already suitable for first imaging application. Here will discuss the physics and technology of these devices, their operation, as well as first examples of imaging applications.

  9. High power THz sources for nonlinear imaging

    SciTech Connect

    Tekavec, Patrick F.; Kozlov, Vladimir G.

    2014-02-18

    Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source delivers 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.

  10. Tactical systems applications for THz devices

    SciTech Connect

    McGee, R.A.

    1994-12-31

    Currently several weapons systems use millimeter wave, infrared or both for sensing. THz technology is spectrally located so as to be able to exploit the best features of MMW and infrared technology. The items for discussion are Army needs that could be addressed by THz technology. The emphasis is on active and passive sensing parameters for ``Smart`` munitions and combat vehicles.

  11. Laser Micromachining Fabrication of THz Components

    NASA Technical Reports Server (NTRS)

    DrouetdAubigny, C.; Walker, C.; Jones, B.; Groppi, C.; Papapolymerou, J.; Tavenier, C.

    2001-01-01

    Laser micromachining techniques can be used to fabricate high-quality waveguide structures and quasi-optical components to micrometer accuracies. Successful GHz designs can be directly scaled to THz frequencies. We expect this promising technology to allow the construction of the first fully integrated THz heterodyne imaging arrays. At the University of Arizona, construction of the first laser micromachining system designed for THz waveguide components fabrication has been completed. Once tested and characterized our system will be used to construct prototype THz lx4 focal plane mixer arrays, magic tees, AR coated silicon lenses, local oscillator source phase gratings, filters and more. Our system can micro-machine structures down to a few microns accuracy and up to 6 inches across in a short time. This paper discusses the design and performance of our micromachining system, and illustrates the type, range and performance of components this exciting new technology will make accessible to the THz community.

  12. Majolica imaging with THz waves: preliminary results

    NASA Astrophysics Data System (ADS)

    Catapano, Ilaria; Affinito, Antonio; Guerriero, Luigi; Bisceglia, Bruno; Soldovieri, Francesco

    2016-05-01

    Recent advancements performed in the development of stable and flexible devices working at TeraHertz (THz) frequencies have opened the way at considering this technology as a very interesting noninvasive diagnostic tool in cultural heritage. In this frame, the paper aims at assessing the ability of THz imaging to gather information about preservation state and constructive modalities of majolica artworks. In particular, THz surveys have been carried out on two majolica tiles dated back to the nineteenth century and realized as building cladding at Naples (Italy). The analysis has been performed by means of the Zomega fiber-coupled THz time-domain system. This analysis corroborates the ability of THz to reconstruct irregularities of majolica tile topography, to characterize pigment and glaze losses, and to detect and localize glaze and pigment layer as well as the glaze-clay body interface.

  13. Monitoring leaf water content with THz and sub-THz waves.

    PubMed

    Gente, Ralf; Koch, Martin

    2015-01-01

    Terahertz technology is still an evolving research field that attracts scientists with very different backgrounds working on a wide range of subjects. In the past two decades, it has been demonstrated that terahertz technology can provide a non-invasive tool for measuring and monitoring the water content of leaves and plants. In this paper we intend to review the different possibilities to perform in-vivo water status measurements on plants with the help of THz and sub-THz waves. The common basis of the different methods is the strong absorption of THz and sub-THz waves by liquid water. In contrast to simpler, yet destructive, methods THz and sub-THz waves allow for the continuous monitoring of plant water status over several days on the same sample. The technologies, which we take into focus, are THz time domain spectroscopy, THz continuous wave setups, THz quasi time domain spectroscopy and sub-THz continuous wave setups. These methods differ with respect to the generation and detection schemes, the covered frequency range, the processing and evaluation of the experimental data, and the mechanical handling of the measurements. Consequently, we explain which method fits best in which situation. Finally, we discuss recent and future technological developments towards more compact and budget-priced measurement systems for use in the field. PMID:25767560

  14. Characterization of cylindrical terahertz metallic hollow waveguide with multiple dielectric layers.

    PubMed

    Sun, Bang-Shan; Tang, Xiao-Li; Zeng, Xuan; Shi, Yi-Wei

    2012-10-20

    Dielectric-coated metallic hollow waveguides (DMHW) are drawing considerable attention for their application in terahertz (THz) waveguiding. This paper theoretically analyzes the multilayer structure to reduce the transmission and bending loss of DMHW. The efficiency of THz multilayer DMHW depends on a proper selection of dielectric materials and geometrical parameters. The low-loss properties are demonstrated by studying the multilayer gold waveguides with a stack of polypropylene (PP) and Si-doped polypropylene (PP(Si)). Comparisons are made with single-layer Au/PP and Au-only waveguides. The effect of dielectric absorption is discussed in detail. It is found that low index dielectric causes more additional loss than that of high index dielectric layers. Several design considerations for the THz multilayer DMHW are pointed out by studying the effects of multilayer structure parameters with a stack of polyethylene (PE) and TiO(2)-doped polyethylene (PE(TiO2)). We conclude that the inner radius of the waveguide and the refractive indices of the dielectrics tend to be larger in order to reduce the influence of material absorption. An optimal value exists for the total number of layers when the dielectrics are absorptive. The absorption tolerances are pointed out to guarantee a smaller loss for multilayer DMHW than that of metal-only waveguide. Finally, a fabrication method for THz multilayer DMHW Ag/PE/PE(TiO2) is proposed based on co-rolling technique. PMID:23089782

  15. The Thz Spectrum of Glycolaldehyde

    NASA Astrophysics Data System (ADS)

    Goubet, Manuel; Huet, Therese R.; Haykal, Imane; Margules, Laurent; Pirali, Olivier; Roy, Pascale

    2011-06-01

    The vibration-rotation spectrum of the ν_1-0, ν_2-0 and ν_3-0 bands of glycolaldehyde was recorded up to 12 THz, using the far-infrared beamline AILES at the synchrotron SOLEIL and a Fourier transform spectrometer coupled to a multipass cell. More than eight thousands lines were assigned, revealing the rotation structure up to J=80, K_a=38 for the ground state. The THz data were fitted simultaneously with pure rotational transitions of better accuracy observed in the microwave (1), in the millimeter-wave (2) and in the sub-millimeter-wave (3) range. In addition new data were recorded at Lille in the 150-300 GHz and 750-950 GHz range. The THz lines and the microwave - (sub)-millimeterwave lines are reproduced with a standard deviation of 2 10-4 Cm-1 and 40 KHz, respectively. Glycolaldehyde has been identified toward the galactic center (4). The vibrational state partition function can be re-evaluated according to the bands origins associated with ν_1, ν_2, and ν_3, which are observed experimentally for the first time. This work is supported by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS) and by the contract ANR-08-BLAN-0054. 1. M. Rey, J.-R. Aviles-Moreno and T. R. Huet, Chem. Phys. Lett. 430(2006) 121 ; K.-M. Marstokk and H. Mollendal, J. Mol. Struct. 5 (1970) 205. 2. R. A. H. Butler, F. C. De Lucia, D. T. Petkie, H. Mollendal, A. Horn, and E. Herbst, ApJS 134 (2001) 319. ; S. L. Widicus-Weaver, R. A. H. Butler, B. J. Drouin, D. T. Petkie, K. A. Dyl, F. C. De Lucia, and G. A. Blake, ApJ 158(2005)188. 3. P. B. Carroll, B. J. Drouin, and S. L. Widicus-Weaver, ApJ 723 (2010) 845. 4. J. M. Hollis, S. N. Vogel, L. E. Snyder, P. R. Jewell, and F. J. Lovas, ApJ 554 (2001) L81. ; M.T. Beltran, C. Codella, S. Viti, R. Niri, R. Cesaroni, ApJ 690 (2009) L93.

  16. Resonant-tunnelling diodes for THz applications

    NASA Astrophysics Data System (ADS)

    Feiginov, Michael; Sydlo, Cezary; Cojocari, Oleg; Meissner, Peter

    2012-10-01

    We investigate experimentally resonant-tunnelling-diode (RTD) oscillators, which are based on RTDs with heavily doped collector. We demonstrate that such RTD oscillators can work at frequencies, which are far beyond the limitations imposed by resonant-state lifetime and relaxation time. Exploiting further such RTDs, we have achieved the record operating frequency of 1.1 THz and show that substantially higher frequencies should be also achievable with RTD oscillators. RTD oscillators are extremely compact (less than a square millimeter) room-temperature sources of coherent cw THz radiation. Such sources should enable plenty of real-world THz applications.

  17. DNA detection by THz pumping

    SciTech Connect

    Chernev, A. L.; Bagraev, N. T.; Klyachkin, L. E.; Emelyanov, A. K.; Dubina, M. V.

    2015-07-15

    DNA semiconductor detection and sequencing is considered to be the most promising approach for future discoveries in genome and proteome research which is dramatically dependent on the challenges faced by semiconductor nanotechnologies. DNA pH-sensing with ion-sensitive field effect transistor (ISFET) is well-known to be a successfully applied electronic platform for genetic research. However this method lacks fundamentally in chemical specificity. Here we develop the first ever silicon nanosandwich pump device, which provides both the excitation of DNA fragments’ self-resonant modes and the feedback for current-voltage measurements at room temperature. This device allows direct detection of singlestranded label-free oligonucleotides by measuring their THz frequency response in aqueous solution. These results provide a new insight into the nanobioelectronics for the future real-time technologies of direct gene observations.

  18. 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.

  19. Morphological study of human sweat ducts for the investigation of THz-wave interaction (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo; Tripathi, Saroj R.

    2016-03-01

    Recently, some studies reported that the sweat ducts act as a low-Q-factor helical antenna due to their helical structure, and resonate in the terahertz frequency range according to their structural parameters. According to the antenna theory, when the duct works as a helical antenna, the dimension of the helix plays a key role to determine the frequency of resonance. Therefore, the accurate determination of structural parameters of sweat duct is crucially important to obtain the reliable frequency of resonance and modes of operations. Therefore, here we performed the optical coherence tomography (OCT) of human subjects on their palm and foot to investigate the density, distribution and morphological features of sweat ducts. Moreover, we measured the dielectric properties of stratum corneum using terahertz time domain spectroscopy and based upon this information, we determined the frequency of resonance. We recruited 32 subjects for the measurement and the average duct diameter was 95±11μm. Based upon this information on diameter of duct and THz dielectric properties of stratum corneum (ɛ=5.1±1.3), we have calculated the frequency of resonance of sweat duct. Finally, we determined that the center frequency of resonance was 442±76 GHz. We believe that these findings will facilitate further investigation of the THz-skin interaction and provide guidelines for safety levels with respect to human exposure. We will also report on the EEG measurement while being shined by micro watt order THz waves.

  20. Spectral characterization of dielectric materials using terahertz measurement systems

    NASA Astrophysics Data System (ADS)

    Seligman, Jeffrey M.

    The performance of modern high frequency components and electronic systems are often limited by the properties of the materials from which they are made. Over the past decade, there has been an increased emphasis on the development of new, high performance dielectrics for use in high frequency systems. The development of these materials requires novel broadband characterization, instrumentation, and extraction techniques, from which models can be formulated. For this project several types of dielectric sheets were characterized at terahertz (THz) frequencies using quasi-optical (free-space) techniques. These measurement systems included a Fourier Transform Spectrometer (FTS, scalar), a Time Domain Spectrometer (TDS, vector), a Scalar Network Analyzer (SNA), and a THz Vector Network Analyzer (VNA). Using these instruments the THz spectral characteristics of dielectric samples were obtained. Polarization based anisotropy was observed in many of the materials measured using vector systems. The TDS was the most informative and flexible instrument for dielectric characterization at THz frequencies. To our knowledge, this is the first such comprehensive study to be performed. Anisotropy effects within materials that do not come into play at microwave frequencies (e.g. ~10 GHz) were found, in many cases, to increase measured losses at THz frequencies by up to an order of magnitude. The frequency dependent properties obtained during the course of this study included loss tangent, permittivity (index of refraction), and dielectric constant. The results were largely consistent between all the different systems and correlated closely to manufacturer specifications over a wide frequency range (325 GHz-1.5 THz). Anisotropic behavior was observed for some of the materials. Non-destructive evaluation and testing (NDE/NDT) techniques were used throughout. A precision test fixture was developed to accomplish these measurements. Time delay, insertion loss, and S-parameters were

  1. Experiment of THz transmission through plasma

    NASA Astrophysics Data System (ADS)

    Sun, Jinhai; Gallacher, Jordan; Issac, Riju; Huang, Zhixun; Jaroszynski, Dino

    2014-12-01

    Research on terahertz wave transmission through plasma is significant for researches on plasma itself and transmission discipline of terahertz wave through plasma. It is possible for plasma with suitable density to be an available stealth outerwear for plane or missile in THz waveband. In this paper, plasma is gotten by ionizing inert gases such as argon and helium gases with pulsed high alternating voltage. With electro-optic pump-probe measurement, THz transmission phenomena through plasma have been studied. The experiments show that some parts of THz frequency components have been cut off by plasma, and with the density of plasma rising, the starting frequency of THz prohibited by plasma is going higher. Experiments also provide an assistant scheme for plasma diagnose with terahertz technique.

  2. New THz opportunities based on graphene

    SciTech Connect

    Hartnagel, Hans

    2015-04-24

    Graphene is a new material of a single or multiple layer carbon structure with impressive properties. A brief introduction is initially presented. Graphene does not have a bandwidth and is a semimetal with charge carriers of zero mass. A bandgap can be formed by confining the graphene width in nanoribbon or nanoconstricition structures. For example, the induced bandgap by a 20 nm wide nanoribbon is about 50 meV. The charge carrier mass then increases, but is still very small. This material can especially be employed for various Terahertz applications. Here several examples are to be described, namely a) a THz transistor, b) the opportunities of ballistic electron resonances for THz signal generation, c) the simultaneous optical transmission and electrical conduction up to THz frequencies and d) Cascaded THz emitters. The optical advantages of multilayer graphene can be compared to ITO (Indium Tin Oxide)

  3. THz Medical Imaging: in vivo Hydration Sensing

    PubMed Central

    Taylor, Zachary D.; Singh, Rahul S.; Bennett, David B.; Tewari, Priyamvada; Kealey, Colin P.; Bajwa, Neha; Culjat, Martin O.; Stojadinovic, Alexander; Lee, Hua; Hubschman, Jean-Pierre; Brown, Elliott R.; Grundfest, Warren S.

    2015-01-01

    The application of THz to medical imaging is experiencing a surge in both interest and federal funding. A brief overview of the field is provided along with promising and emerging applications and ongoing research. THz imaging phenomenology is discussed and tradeoffs are identified. A THz medical imaging system, operating at ~525 GHz center frequency with ~125 GHz of response normalized bandwidth is introduced and details regarding principles of operation are provided. Two promising medical applications of THz imaging are presented: skin burns and cornea. For burns, images of second degree, partial thickness burns were obtained in rat models in vivo over an 8 hour period. These images clearly show the formation and progression of edema in and around the burn wound area. For cornea, experimental data measuring the hydration of ex vivo porcine cornea under drying is presented demonstrating utility in ophthalmologic applications. PMID:26085958

  4. A continuous-wave THz imaging system

    NASA Astrophysics Data System (ADS)

    Pei, Ting-Hang; Huang, Yang-Tung; Wang, Yu-Jiu; Chen, Wei-Zen; Kuo, Chien-Nan; Cheng, Yu-Ting

    2013-08-01

    We develop a continuous wave terehertz (THz) imaging system operating at 288 GHz. This imaging system simply consitutes three parts including the source, two optical lenses, and the detector. The entire size is smaller than the tranditional pulsed THz imaging system. In this developed system, the THz wave is generated by a horn attenna which concentrates the wave in an azimuth angle of 3° ~ 5°. The source originates from a singnal generator, and then the frequency increases to 288 GHz after passing through an 8X multiplier. Next, THz wave is focused by a THz lens on the test sample. By controling the sample position in the x-z plane, we can scan it pixel-by-pixel in which each step along the x- or z- axes is 0.1 mm. After penetrating the test sample, another lens collects the transmitted THz wave and focuses them into the thermal detector. This detector can disply the collected THz power. Finally, by drawing the detected power of each pixel, a transmitted-intensity figure for all pixels is obtained. The resolution of this THz imaging system is about 1~2 mm at present. We have measured human molar tooth and obtained its transmitted figures. Besides, we also develop a technology to adjust the positions of the source and detector by a system containing one laser, one beamsplitter, and two mirrors. The relative positions between the source and detector is very important. The input of the source and the output of the detector are small so that they have to aim at each other very accurately in order to collect maximum transmitted power in the detector.

  5. THz Detection and Imaging using Rydberg Atoms

    NASA Astrophysics Data System (ADS)

    Wade, Christopher; Sibalic, Nikola; Kondo, Jorge; de Melo, Natalia; Adams, Charles; Weatherill, Kevin

    2016-05-01

    Atoms make excellent electromagnetic field sensors because each atom of the same isotope is identical and has well-studied, permanent properties allowing calibration to SI units. Thus far, atoms have not generally been exploited for terahertz detection because transitions from the atomic ground state are constrained to a limited selection of microwave and optical frequencies. In contrast, highly excited `Rydberg' states allow us access to many strong, electric dipole transitions from the RF to THz regimes. Recent advances in the coherent optical detection of Rydberg atoms have been exploited by a number of groups for precision microwave electrometry Here we report the demonstration of a room-temperature, cesium Rydberg gas as a THz to optical interface. We present two configurations: First, THz-induced fluorescence offers non-destructive and direct imaging of the THz field, providing real-time, single shot images. Second, we convert narrowband terahertz photons to infrared photons with 6% quantum efficiency allowing us to use nano-Watts of THz power to control micro-Watts of laser power on microsecond timescales. Exploiting hysteresis and a room-temperature phase transition in the response of the medium, we demonstrate a latching optical memory for sub pico-Joule THz pulses.

  6. Frequency tuning of THz quantum cascade lasers

    NASA Astrophysics Data System (ADS)

    Qian, Xifeng; Danylov, Andriy A.; Light, Alexander R.; Waldman, Jerry; Erickson, Neal

    2015-03-01

    This paper introduces the continuously tunable THz radiation through sideband generation of a free running and solidnitrogen- cooled THz quantum cascade laser. The 2.324 THz QCL operating in a single longitudinal mode (SLM) in continuous-wave (cw) was mixed with a swept synthesized microwave signal by a THz Schottky-diode-balanced mixer. Through sideband generation, two frequency branches were observed at low and high frequency, characterized with a Fourier-transform spectrometer. At low frequency, the sideband generates frequencies from -50 GHz to +50 GHz. At high frequency, it generates sideband frequencies from 70 GHz to 115 GHz. The total +/-100 GHz tuning range can be further expanded with higher frequency millimeter wave amplifier/multiplier source. The sideband generates total 1 μW of output power at both upper and lower frequency with 200 μW of driven power from the THz QCL, showing a power conversion efficiency of 5 × 10-3. The demonstration of this SM, continuously tunable THz source enables its applications where SM, spatially coherent beam is required.

  7. Modelling of sub-wavelength THz sources as Gaussian apertures.

    PubMed

    Lin, Hungyen; Fumeaux, Christophe; Fischer, Bernd Michael; Abbott, Derek

    2010-08-16

    The THz emission point on a nonlinear electro-optical crystal for generating broadband THz radiation is modeled as a radiating Gaussian aperture. With the wavelengths of the infrared pump beam being much smaller than the wavelength components of the generated THz pulse, a THz sub-wavelength radiating aperture with Gaussian profile is effectively created. This paper comprehensively investigates Gaussian apertures in focused THz radiation generation in electro-optical crystals and illustrates the breakdown of the paraxial approximation at low THz frequencies. The findings show that the shape of the radiation pattern causes a reduction in detectable THz radiation and hence contributes significantly to low signal-to-noise ratio in THz radiation generation. Whilst we have demonstrated the findings on optical rectification in this paper, the model may apply without a loss of generality to other types of apertures sources in THz radiation generation. PMID:20721154

  8. Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

    SciTech Connect

    Askari, Nasim; Eslami, Esmaeil; Mirzaie, Reza

    2015-11-15

    The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

  9. Method of casting patterned dielectric structures

    DOEpatents

    Poco, John F.; Hrubesh, Lawrence W.

    2001-01-01

    A pattern of dielectric structures are formed directly on a substrate in a single step using sol-gel chemistry and molding procedures. The resulting dielectric structures are useful in vacuum applications for electronic devices. Porous, lightweight structures having a high aspect ratio that are suitable for use as spacers between the faceplate and baseplate of a field emission display can be manufactured using this method.

  10. Novel detectors for traceable THz power measurements

    NASA Astrophysics Data System (ADS)

    Müller, Ralf; Bohmeyer, Werner; Kehrt, Mathias; Lange, Karsten; Monte, Christian; Steiger, Andreas

    2014-08-01

    Several novel types of detectors for the measurement of electromagnetic radiation in the THz spectral range are described. Firstly, detectors based on pyroelectric foil coated with different absorbers have been developed focusing on the following features: high accuracy due to well-characterized absorption, high sensitivity, large area absorbers and frequency and polarization independence. A three-dimensional design with five absorptions gave an overall absorption of more than 98 %. Secondly, detectors based on pyroelectric foils with thin metal layers were realized. An absorption of 50 % can be obtained if the thickness of the layers is carefully adjusted. According to electromagnetic theory this degree of absorption is independent of the polarization and frequency of the radiation in a wide range from at least 20 GHz to 5 THz. The third type of detector is based on a new type of volume absorber with a polished front surface and a gold-coated back side. It is the absorber of choice of the standard power detector for disseminating the spectral power responsivity scale. This standard detector allows the application of a physical model to calculate its spectral responsivity in the range from 1 THz to 5 THz if the detector has been calibrated at one single frequency. Finally, a THz detector calibration facility was set up and is now in operation at PTB to calibrate detectors from customers with an uncertainty as low as 1.7 %.

  11. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

    PubMed Central

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

    2015-01-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5–10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields. PMID:25800287

  12. Tunable Room Temperature THz Sources Based on Nonlinear Mixing in a Hybrid Optical and THz Micro-Ring Resonator

    NASA Astrophysics Data System (ADS)

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K.; Güney, Durdu Ö.; Pala, Nezih

    2015-03-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5-10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields.

  13. Tunable room temperature THz sources based on nonlinear mixing in a hybrid optical and THz micro-ring resonator.

    PubMed

    Sinha, Raju; Karabiyik, Mustafa; Al-Amin, Chowdhury; Vabbina, Phani K; Güney, Durdu Ö; Pala, Nezih

    2015-01-01

    We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5-10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ((2))) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields. PMID:25800287

  14. Reflective THz and MR imaging of burn wounds: a potential clinical validation of THz contrast mechanisms

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Nowroozi, Bryan; Sung, Shijun; Garritano, James; Maccabi, Ashkan; Tewari, Priyamvada; Culjat, Martin; Singh, Rahul; Alger, Jeffry; Grundfest, Warren; Taylor, Zachary

    2012-10-01

    Terahertz (THz) imaging is an expanding area of research in the field of medical imaging due to its high sensitivity to changes in tissue water content. Previously reported in vivo rat studies demonstrate that spatially resolved hydration mapping with THz illumination can be used to rapidly and accurately detect fluid shifts following induction of burns and provide highly resolved spatial and temporal characterization of edematous tissue. THz imagery of partial and full thickness burn wounds acquired by our group correlate well with burn severity and suggest that hydration gradients are responsible for the observed contrast. This research aims to confirm the dominant contrast mechanism of THz burn imaging using a clinically accepted diagnostic method that relies on tissue water content for contrast generation to support the translation of this technology to clinical application. The hydration contrast sensing capabilities of magnetic resonance imaging (MRI), specifically T2 relaxation times and proton density values N(H), are well established and provide measures of mobile water content, lending MRI as a suitable method to validate hydration states of skin burns. This paper presents correlational studies performed with MR imaging of ex vivo porcine skin that confirm tissue hydration as the principal sensing mechanism in THz burn imaging. Insights from this preliminary research will be used to lay the groundwork for future, parallel MRI and THz imaging of in vivo rat models to further substantiate the clinical efficacy of reflective THz imaging in burn wound care.

  15. Different roles of electron beam in two stream instability in an elliptical waveguide for generation and amplification of THz electromagnetic waves

    NASA Astrophysics Data System (ADS)

    Safari, S.; Jazi, B.; Jahanbakht, S.

    2016-08-01

    In this work, two stream instability in a metallic waveguide with elliptical cross-section and with a hollow annular dielectric layer is studied for generation and amplification of THz electromagnetic waves. Dispersion relation of waves and their dependents to geometric dimensions and characteristics of the electron beam are analyzed. In continuation, the diagrams of growth rate for some operating frequencies are presented, so that effective factors on the growth rates, such as geometrical dimensions, dielectric constant of dielectric layer, accelerating voltage, and applied current intensity are analyzed. It is shown that while an electron beam is responsible for instability, another electron beam plays a stabilizing role.

  16. Millimeter wave and terahertz dielectric properties of biological materials

    NASA Astrophysics Data System (ADS)

    Khan, Usman Ansar

    Broadband dielectric properties of materials can be employed to identify, detect, and characterize materials through their unique spectral signatures. In this study, millimeter wave, submillimeter wave, and terahertz dielectric properties of biological substances inclusive of liquids, solids, and powders were obtained using Dispersive Fourier Transform Spectroscopy (DFTS). Two broadband polarizing interferometers were constructed to test materials from 60 GHz to 1.2 THz. This is an extremely difficult portion of the frequency spectrum to obtain a material's dielectric properties since neither optical nor microwave-based techniques provide accurate data. The dielectric characteristics of liquids such as cyclohexane, chlorobenzene, benzene, ethanol, methanol, 1,4 dioxane, and 10% formalin were obtained using the liquid interferometer. Subsequently the solid interferometer was utilized to determine the dielectric properties of human breast tissues, which are fixed and preserved in 10% formalin. This joint collaboration with the Tufts New England Medical Center demonstrated a significant difference between the dielectric response of tumorous and non-tumorous breast tissues across the spectrum. Powders such as anthrax, flour, talc, corn starch, dry milk, and baking soda have been involved in a number of security threats and false alarms around the globe in the last decade. To be able to differentiate hoax attacks and serious security threats, the dielectric properties of common household powders were also examined using the solid interferometer to identify the powders' unique resonance peaks. A new sample preparation kit was designed to test the powder specimens. It was anticipated that millimeter wave and terahertz dielectric characterization will enable one to clearly distinguish one powder from the other; however most of the powders had relatively close dielectric responses and only Talc had a resonance signature recorded at 1.135 THz. Furthermore, due to

  17. THz spectra of cortisone and the related medicine

    NASA Astrophysics Data System (ADS)

    Ma, Shihua; Ge, Min; Liu, Guifeng; Song, Xiyu; Zhang, Peng; Wang, Wenfeng

    2009-07-01

    THz-TDS are used to study four kinds of drug: cortisone, hydrocortisone, prednisone and prednisolone. The THz spectra of them are obtained and analyzed from 0.2 - 1.6 THz. The experimental results shows the four samples have the different THz spectra. Cortisone has a peak at 1.5 THz and a broad absorption peak at 0.96 THz, while hydrocortisone has a weak absorption peak that lies at 1.27 THz. At the same time the prednisone has the stronger absorption peaks than the others, and its two peaks shows at 1.24 THz and 1.5 THz. Prednisolone has a weak broad peak at 1.43 THz. The results of the theoretical calculation were performed using Gaussian 03 software with Density Functional Theory at the basis set of 6-31+G (d, p). The theoretical vibrational frequencies are compared with the experimental results, and the deviations are discussed. The THz spectra of the medicine show THz technique may be help to distinguish some different chemical bond and functional group.

  18. Silicon Based Millimeter Wave and THz ICs

    NASA Astrophysics Data System (ADS)

    Chen, Jixin; Hong, Wei; Tang, Hongjun; Yan, Pinpin; Zhang, Li; Yang, Guangqi; Hou, Debin; Wu, Ke

    In this paper, the research advances in silicon based millimeter wave and THz ICs in the State Key Laboratory of Millimeter Waves is reviewed, which consists of millimeter wave amplifiers, mixers, oscillators at Q, V and W and D band based on CMOS technology, and several research approaches of THz passive ICs including cavity and filter structures using SIW-like (Substrate Integrated Waveguide-like) guided wave structures based on CMOS and MEMs process. The design and performance of these components and devices are presented.

  19. A Dedicated THz Beamline At BESSY

    NASA Astrophysics Data System (ADS)

    Holldack, K.; Ponwitz, D.

    2007-01-01

    A special beamline dedicated to the Far Infrared (THz) region was successfully commissioned at BESSY for the spectral range between 50 GHz and 4.5 THz. The beamline accepts synchrotron radiation from a bend magnet source close to the interaction region of a femtosecond laser with the electron bunch. Either edge radiation as well as the regular bend magnet fan can be accepted. The beamline was tailored for diagnostics and experiments employing coherent synchrotron radiation (CSR) from regular and compressed bunches as well as from a laser-induced fs density modulation on the electron bunch. Besides a technical description of the beamlinethe the sources are compared using Fourier Transform Spectroscopy (FTIR).

  20. THz spectroscopy and polarization of jade

    NASA Astrophysics Data System (ADS)

    Guo, Xuejiao; Xiong, Wei; Shen, Jingling

    2010-11-01

    A terahertz time-domain spectrometer is employed to study various properties of jade, including the kind identification and polarization analysis. The characteristic absorption spectra and refractive index of jade are obtained in the range of 0.2 to 2.6 THz. Studying the absorption spectra and the transmission temporal THz waveform with two peaks, which were confirmed to be coming from ordinary and extraordinary beams, respectively, and result in fake absorption features. A practical ways are suggested to remove the fake absorption features and therefore the real absorption spectra of jade which accurately indicate the information of the samples can be obtained.

  1. THz techniques for human skin measurement

    NASA Astrophysics Data System (ADS)

    Guan, Yu; Mizukoshi, Koji; Suizu, Koji; Kawase, Kodo

    2011-03-01

    Metal meshes work as band-pass filters in the terahertz (THz) region, with their transmission spectra acutely affected by the refractive index of the material inside and above the metal mesh openings. We used a metal mesh for high-sensitivity observations by focusing on the "dip", that is, a sudden change in transmittance that only appeared when the THz wave was obliquely incident onto the metal mesh. Here we report a measurement of stratum corneum to inspect the feasibility of applying the metal mesh sensor to observations of human skin.

  2. Complex dielectric properties of anhydrous polycrystalline glucose in the terahertz region

    NASA Astrophysics Data System (ADS)

    Sun, P.; Liu, W.; Zou, Y.; Jia, Qiong Z.; Li, Jia Y.

    2015-03-01

    We utilized terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric properties of solid polycrystalline material of anhydrous glucose (D-(+)-glucose with purity >99.9%). THz transmission spectra of samples were measured from 0.2 to 2.2 THz. The samples were prepared into tablets with thicknesses of 0.362, 0.447, 0.504, 0.522 and 0.626 mm, respectively. The imaginary part of the complex dielectric function of polycrystalline glucose showed that there were multiple characteristic absorption peaks at 1.232, 1.445, 1.522, 1.608, 1.811 and 1.987 THz, respectively. Moreover, for a given characteristic absorption peak, the real part of the complex dielectric function showed anomalous dispersion within the full width half maximum (FWHM) of the absorption peak. Both finite difference time-domain (FDTD) numerical simulations and experimental results showed that the complex dielectric function of anhydrous polycrystalline glucose fits well with the Lorentz dielectric mode. The plasma oscillation frequency was below the frequency of the light waves suggesting that the light waves passed through the polycrystalline glucose tablets. Calculations based on density functional theory (DFT) showed that the characteristic absorption peaks of polycrystalline glucose originated mainly from collective intermolecular vibrations such as hydrogen bonds and crystal phonon modes. The THz radiation can excite the vibrational or rotational energy levels of the biological macromolecules. This leads to changes in their spatial configuration or interactions. This study showed that THz-TDS has potential applications in biological and pharmaceutical research and food industry.

  3. 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.

  4. Broadband Dielectric Spectroscopy on Lysozyme in the Sub-Gigahertz to Terahertz Frequency Regions: Effects of Hydration and Thermal Excitation.

    PubMed

    Yamamoto, Naoki; Ohta, Kaoru; Tamura, Atsuo; Tominaga, Keisuke

    2016-06-01

    We have performed dielectric spectral measurements of lysozyme in a solid state to understand the effects of hydration and thermal excitation on the low-frequency dynamics of protein. Dielectric measurements were performed under changing hydration conditions at room temperature in the frequency region of 0.5 GHz to 1.8 THz. We also studied the temperature dependence (83 to 293 K) of the complex dielectric spectra in the THz frequency region (0.3 THz to 1.8 THz). Spectral analyses were performed using model functions for the complex dielectric constant. To reproduce the spectra, we found that two relaxational modes and two underdamped modes are necessary together with an ionic conductivity term in the model function. At room temperature, the two relaxational modes have relaxation times of ∼20 ps and ∼100 ps. The faster component has a major spectral intensity and is suggested to be due to coupled water-protein motion. The two underdamped modes are necessary to reproduce the temperature dependence of the spectra in the THz region satisfactorily. The protein dynamical transition is a well-known behavior in the neutron-scattering experiment for proteins, where the atomic mean-square displacement shows a sudden change in the temperature dependence at approximately 200 K, when the samples are hydrated. A similar behavior has also been observed in the temperature dependence of the absorption spectra of protein in the THz frequency region. From our broadband dielectric spectroscopic measurements, we conclude that the increase in the spectral intensities in the THz region at approximately 200 K is due to a spectral blue-shift of the fast relaxational mode. PMID:27158918

  5. Subwavelength silicon through-hole arrays as an all-dielectric broadband terahertz gradient index metamaterial

    SciTech Connect

    Park, Sang-Gil; Jeong, Ki-Hun; Lee, Kanghee; Han, Daehoon; Ahn, Jaewook

    2014-09-01

    Structuring at subwavelength scales brings out artificial media with anomalous optical features called metamaterials. All-dielectric metamaterials have high potential for practical applications over the whole electromagnetic spectrum owing to low loss and optical isotropy. Here, we report subwavelength silicon through-hole arrays as an all-dielectric gradient index metamaterial with broadband THz operation. The unit cell consists of a single subwavelength through-hole on highly resistive monocrystalline silicon. Depending on the fill-factor and period, the effective index was linearly modulated at 0.3–1.6 THz. The experimental results also demonstrate silicon gradient refractive index (Si-GRIN) lenses with parabolic index profiles through the spatial modification of a single unit cell along the radial direction. Si-GRIN lenses either focus 0.4–1.6 THz beam to the diffraction-limit or serve as a flat and thin solid immersion lens on the backside of THz photoconductive antenna for highly efficient pulse extraction. This all-dielectric gradient index metamaterial opens up opportunities for integrated THz GRIN optics.

  6. Growth dependent optical properties of ZnMgO at THz frequencies

    NASA Astrophysics Data System (ADS)

    Rivera, Abdiel; Mazady, Anas; Ahi, Kiarash; Anwar, Mehdi

    2015-05-01

    A relatively high Mg mole fraction of 7% is achieved using the cavitation effect under sonication to overcome the low solubility of ZnO-MgO at low temperature. The Mg mole fraction is confirmed by shift in the near band emission of free exciton under photoluminescence spectroscopy at room temperature. The x-ray diffraction pattern has a large peak associated to ZnO (002) from which the c-lattice constant is calculated to be 5.1967Ǻ. The nanorods (NRs) grown via sonochemical are compared to nanowires (NWs) grown using metal organic chemical vapor deposition (MOCVD) and hydrothermal synthesis. Also, the effect of the ZnO film used as seed layer is described and compare to a simple spin coated layer. Terahertz (THz) index of refraction and dielectric constant of wurtzite Zn1-xMgxO NWs with Mg mole fraction of 7% via sonochemical are determined using THz time domain spectroscopy (THz-TDS). The results are compared with ZnO and ZnMgO NWs with 10% Mg mole fraction grown using MOCVD. The successful growth of Zn1-xMgxO with wurtzite structure at low temperature permits realization of the growth of heterostructures, quantum well, nanowires and nanorods on flexible substrates providing lower cost, optical and carrier confinement necessary in advanced light emitting diodes (LEDs), laser diodes (LDs) and high efficiency solar cells.

  7. [Characterization of the organic crystal DAST as a THz emitter].

    PubMed

    Li, Kun; Li, Chun; Hu, Zhang-gui; Wang, Li; Zhang, Jie

    2006-10-01

    Using THz time-domain spectroscopy, the home-grown organic crystal DAST and widely used high-efficient ZnTe were characterized as THz emitters. Bolometer was also used to measure the absolute energy of THz radiation from DAST and ZnTe. The refractive index and absorption coefficient of DAST were measured too. It is concluded that the home-grown DAST is a kind of high-efficiency THz material, and could become a good THz emitter and detector after the improvement in growing process. PMID:17205718

  8. 17 THz continuous-wave optical modulator

    NASA Astrophysics Data System (ADS)

    Weber, J. J.; Green, J. T.; Yavuz, D. D.

    2012-01-01

    We use coherently rotating hydrogen molecules and demonstrate a continuous-wave optical modulator at a frequency of 17.6 THz that can modulate any laser within the optical region of the spectrum. The molecules are coherently excited using two intense laser beams spaced by the Raman transition frequency inside a high-finesse cavity.

  9. Nanotechnology-supported THz medical imaging

    PubMed Central

    Stylianou, Andreas; Talias, Michael A

    2013-01-01

    Over the last few decades, the achievements and progress in the field of medical imaging have dramatically enhanced the early detection and treatment of many pathological conditions. The development of new imaging modalities, especially non-ionising ones, which will improve prognosis, is of crucial importance. A number of novel imaging modalities have been developed but they are still in the initial stages of development and serious drawbacks obstruct them from offering their benefits to the medical field. In the 21 st century, it is believed that nanotechnology will highly influence our everyday life and dramatically change the world of medicine, including medical imaging. Here we discuss how nanotechnology, which is still in its infancy, can improve Terahertz (THz) imaging, an emerging imaging modality, and how it may find its way into real clinical applications. THz imaging is characterised by the use of non-ionising radiation and although it has the potential to be used in many biomedical fields, it remains in the field of basic research. An extensive review of the recent available literature shows how the current state of this emerging imaging modality can be transformed by nanotechnology. Innovative scientific concepts that use nanotechnology-based techniques to overcome some of the limitations of the use of THz imaging are discussed. We review a number of drawbacks, such as a low contrast mechanism, poor source performance and bulky THz systems, which characterise present THz medical imaging and suggest how they can be overcome through nanotechnology. Better resolution and higher detection sensitivity can also be achieved using nanotechnology techniques. PMID:24555052

  10. Substrate independence of THz vibrational modes of polycrystalline thin films of molecular solids in waveguide THz-TDS

    NASA Astrophysics Data System (ADS)

    Harsha, S. Sree; Melinger, Joseph. S.; Qadri, S. B.; Grischkowsky, D.

    2012-01-01

    The influence of the metal substrate on the measurement of high resolution THz vibrational modes of molecular solids with the waveguide THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two-surface passivated substrates. The independence of the observed THz vibrational modes to the metal substrate is demonstrated. Independently, surface passivation is presented as a viable experimental addition to the waveguide THz-TDS technique to aid the characterization of samples with known reactivity to metal surfaces.

  11. Design and characterization of terahertz-absorbing nano-laminates of dielectric and metal thin films

    SciTech Connect

    Bolakis, Christos; Grbovic, Dragoslav; Lavrik, Nickolay V; Karunasiri, Gamani

    2010-01-01

    A terahertz-absorbing thin-film stack, containing a dielectric Bragg reflector and a thin chromium metal film, was fabricated on a silicon substrate for applications in bi-material terahertz (THz) sensors. The Bragg reflector is to be used for optical readout of sensor deformation under THz illumination. The THz absorption characteristics of the thin-film composite were measured using Fourier transform infrared spectroscopy. The absorption of the structure was calculated both analytically and by finite element modeling and the two approaches agreed well. Finite element modeling provides a convenient way to extract the amount of power dissipation in each layer and is used to quantify the THz absorption in the multi-layer stack. The calculation and the model were verified by experimentally characterizing the multi-layer stack in the 3-5 THz range. The measured and simulated absorption characteristics show a reasonably good agreement. It was found that the composite film absorbed about 20% of the incident THz power. The model was used to optimize the thickness of the chromium film for achieving high THz absorption and found that about 50% absorption can be achieved when film thickness is around 9 nm.

  12. Design and characterization of terahertz-absorbing nano-laminates of dielectric and metal thin films.

    PubMed

    Bolakis, C; Grbovic, D; Lavrik, N V; Karunasiri, G

    2010-07-01

    A terahertz-absorbing thin-film stack, containing a dielectric Bragg reflector and a thin chromium metal film, was fabricated on a silicon substrate for applications in bi-material terahertz (THz) sensors. The Bragg reflector is to be used for optical readout of sensor deformation under THz illumination. The THz absorption characteristics of the thin-film composite were measured using Fourier transform infrared spectroscopy. The absorption of the structure was calculated both analytically and by finite element modeling and the two approaches agreed well. Finite element modeling provides a convenient way to extract the amount of power dissipation in each layer and is used to quantify the THz absorption in the multi-layer stack. The calculation and the model were verified by experimentally characterizing the multi-layer stack in the 3-5 THz range. The measured and simulated absorption characteristics show a reasonably good agreement. It was found that the composite film absorbed about 20% of the incident THz power. The model was used to optimize the thickness of the chromium film for achieving high THz absorption and found that about 50% absorption can be achieved when film thickness is around 9 nm. PMID:20639934

  13. 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

  14. Coherent electro-optical detection of THz-wave generated from synchronously pumped picosecond THz parametric oscillator

    NASA Astrophysics Data System (ADS)

    Takida, Yuma; Ohira, Tatsuya; Tadokoro, Yuzuru; Kumagai, Hiroshi; Nashima, Shigeki

    2012-02-01

    Terahertz (THz) radiation via parametric down-conversion of optical pulses in a nonlinear optical crystal is an attractive way to develop frequency tunable THz-wave sources. Therefore, we have focused on developing low-laser-powerpumped THz-wave parametric sources and then successfully demonstrated a synchronously-pumped picosecond THz parametric oscillator (TPO) in pump-enhanced idler-resonant cavity with a bulk 5 mol% MgO-doped lithium niobate (MgO:LN) crystal. In this paper, toward coherent electro-optical (EO) detection of THz waves generated from our synchronously pumped picosecond TPO, we reported time-domain measurements of the THz electric fields using a bowtie- shaped low-temperature grown gallium arsenide (LT-GaAs) photoconductive (PC) antenna as a THz detector. As a result, we obtained temporal waveforms of the THz electric pulses, for the different number of Si-prism couplers, and then found that the radiated THz waves separated multiple unanticipated pulses by use of the arrayed-prism coupling technique. Also, we compared the time-domain system with a Fourier transform Michelson interferometer using a highresistance silicon (Si) beam splitter, from the some viewpoints. The present results reveal great prospects for the realization of THz spectroscopy and imaging applications using our THz-wave source.

  15. Quantum well intersubband THz lasers and detectors

    NASA Astrophysics Data System (ADS)

    Soref, Richard A.; Friedman, Lionel R.; Sun, Gregory; Noble, Michael J.; Ram-Mohan, L. R.

    1999-11-01

    This paper presents modeling and simulation results on Si- based quantum-well intersubband THz detectors and THz lasers (tasers) in the 3 to 10 THz range where the intersubband transition energy is 12 to 41 meV. The incoherent cryogenically cooled (4 K to 20 K) quantum well terahertz detector (QWTD) consists of p-type Si0.9Ge0.1 QWs with Si barriers on an Si substrate, or of p-Si0.85Ge0.15/Si on a relaxed Si0.97Ge0.03 buffer on Si. The QWTD senses THz radiation at normal incidence (the XY polarization on the HH1 to LH1 transition) or at edge- illumination (the Z polarization on the HH1 to HH2 transition). Resonant-cavity enhancement, coupling to Si THz waveguides, and integration with SiGe transistor preamplifiers appear feasible for QWTDs. The quantum staircase taser is a simplified far-infrared version of the quantum cascade laser in which each superlattice transfer region is replaced by a thin tunnel-barrier layer. We have adapted to group IV the III-V idea of Sun, Lu, and Khurgin; the `inverted mass taser'. On a Si0.81Ge0.19 substrate, we find that an inverted effective mass exists in LH1 at kg equals 0.013 angstroms-1 in 9-nm single- wells of Si0.7Ge0.3 with 5-nm Si barriers. Selective electrical injection of holes into LH1 at T equals 77 K is postulated. This offers local-in-k-space LH1-HH1 population inversion and tasing at 7.2 THz. Since the taser emission is XY-polarized, the active MQW staircase (a set of identical square QWs) is suitable for insertion into a vertical cavity surface-emitting taser. The VCSET would have resonator thickness of (lambda) /2n equals 6 micrometers , and Bragg mirrors constructed from SiO2/Si multilayers.

  16. MEASUREMENTS OF HIGH-FIELD THZ INDUCED PHOTOCURRENTS IN SEMICONDUCTORS

    SciTech Connect

    Wiczer, M.; Lindenberg, A.

    2008-01-01

    THz pulses have provided a useful tool for probing the time-resolved dynamics of free carriers in a system. However, the development of methods to produce intense THz radiation has been slow. We have developed a method for producing intense ultra-short THz pulses, which have a full width at half maximum of 300 fs — approximately a half cycle of THz radiation. These intense half cycle pulses (HCPs) allowed us to use THz radiation as a source of excitation. By exposing the semiconductor indium antimonide (InSb) to intense THz HCP radiation, we have observed non-linear optical effects which suggest the generation of new free carriers by below band-gap THz photons. This generation of free carriers appears to be due to an avalanche multiplication process which then induces a current in the time-scale of our THz pulse. This amplifi cation on such a short timescale suggests the possibility of an ultrafast detector of weak above band-gap radiation. We constructed a device which detects these currents by painting an electrode structure on the surface of the semiconductor. The currents induced across the electrodes by this avalanche multiplication process were measured and compared with other measurements of this non-linear optical process. We successfully measured THz induced currents in InSb, suggesting promise towards the development of an ultra-fast detector. Further, we have gained insight into a possible physical explanation of the THz induced free carriers we observe in InSb.

  17. Dielectric wakefield acceleration of a relativistic electron beam in a slab-symmetric dielectric lined waveguide.

    PubMed

    Andonian, G; Stratakis, D; Babzien, M; Barber, S; Fedurin, M; Hemsing, E; Kusche, K; Muggli, P; O'Shea, B; Wei, X; Williams, O; Yakimenko, V; Rosenzweig, J B

    2012-06-15

    We report first evidence of wakefield acceleration of a relativistic electron beam in a dielectric-lined slab-symmetric structure. The high energy tail of a ∼60  MeV electron beam was accelerated by ∼150  keV in a 2 cm-long, slab-symmetric SiO2 waveguide, with the acceleration or deceleration clearly visible due to the use of a beam with a bifurcated longitudinal distribution that serves to approximate a driver-witness beam pair. This split-bunch distribution is verified by longitudinal reconstruction analysis of the emitted coherent transition radiation. The dielectric waveguide structure is further characterized by spectral analysis of the emitted coherent Cherenkov radiation at THz frequencies, from a single electron bunch, and from a relativistic bunch train with spacing selectively tuned to the second longitudinal mode (TM02). Start-to-end simulation results reproduce aspects of the electron beam bifurcation dynamics, emitted THz radiation properties, and the observation of acceleration in the dielectric-lined, slab-symmetric waveguide. PMID:23004279

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

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

    PubMed

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

    2015-05-01

    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. PMID:26026507

  20. 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.

  1. 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.

  2. THz Emission Based On Intersubband Plasmon Resonances

    SciTech Connect

    Coquelin, M.; Zobl, R.; Strasser, G.; Gornik, E.; Bakshi, P.; Umansky, V.; Heiblum, M.

    2010-01-04

    The radiative decay of collective plasma oscillations as a new mechanism for THz emission is studied. This phenomenon is based on the attractive interaction of two intersubband plasmons. This interaction can be viewed as a collective e-e scattering phenomenon. The emission results fit very well to the results of the current voltage measurements indicating that the conditions for a plasma instability are reached.

  3. Time-resolved THz studies of carrier dynamics in semiconductors, superconductors, and strongly-correlated electron materials

    SciTech Connect

    Kaindl, Robert A.; Averitt, Richard D.

    2006-11-14

    materials occur at lower energies. The terahertz (THz) regime is particularly rich in such fundamental resonances. This includes ubiquitous lattice vibrations and low-energy collective oscillations of conduction charges. In nanoscale materials, band structure quantization also yields novel infrared and THz transitions, including intersubband absorption in quantum wells. The formation of excitons in turn leads to low-energy excitations analogous to inter-level transitions in atoms. In transition-metal oxides, fundamental excitation gaps arise from charge pairing into superconducting condensates and other correlated states. This motivates the use of ultrafast THz spectroscopy as a powerful tool to study light-matter interactions and microscopic processes in nanoscale and correlated-electron materials.A distinct advantage of coherent THz pulses is that the amplitude and phase of the electric field can be measured directly, as the THz fields are coherent with the fs pulses from which they are generated. Using THz time-domain spectroscopy (THz-TDS), both the real and imaginary parts of the response functions (such as the dielectric function) are obtained directly without the need for Kramers?Kronig transforms. The THz response can also be expressed in terms of absorption and refractive index, or as the optical conductivity. The optical conductivity describes the current response of a many-body system to an electric field, an ideal tool to study conducting systems. A second important advantage is the ultrafast time resolution that results from the short temporal duration of the THz time-domain sources. In particular, optical-pump THz-probe spectroscopy enables a delicate probe of the transient THz conductivity after optical photoexcitation. These experiments can provide insight into quasiparticle interactions, phase transitions, or nonequilibrium dynamics. In this chapter we will provide many such examples. Since THz spectroscopy of solids is a quickly expanding field

  4. Identification of wheat quality using THz spectrum.

    PubMed

    Ge, Hongyi; Jiang, Yuying; Xu, Zhaohui; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong

    2014-05-19

    The terahertz (THz) spectra in the range of 0.2-1.6 THz (6.6-52.8 cm-1) of wheat grains with various degrees of deterioration (normal, worm-eaten, moldy, and sprouting wheat grains) were investigated by terahertz time domain spectroscopy. Principal component analysis (PCA) was employed to extract feature data according to the cumulative contribution rates; the top four principal components were selected, and then a support vector machine (SVM) method was applied. Several selection kernels (linear, polynomial, and radial basis functions) were applied to identify the four types of wheat grain. The results showed that the materials were identified with an accuracy of nearly 95%. Furthermore, this approach was compared with others (principal component regression, partial least squares regression, and back-propagation neural networks). The comparisons showed that PCA-SVM outperformed the others and also indicated that the proposed method of THz technology combined with PCA-SVM is efficient and feasible for identifying wheat of different qualities. PMID:24921371

  5. THz polarization difference imaging of aqueous targets

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Bajwa, Neha; Ramirez, Lucia; Grundfest, Warren; Taylor, Zachary

    2015-08-01

    This paper describes the basic design, implementation, and testing of a polarization difference imaging system for use on aqueous targets. The ultimate performance limitation of THz imaging in many active areas of research is clutter from surface geometry. While the signal to nose ratio (SNR) of standard THz imaging systems is quite large, the signal to clutter ratio (SCR) often faced in an imaging application is orders of magnitude lower and, in many cases, lower than the contrast to noise (CNR) resulting in imagery where the contrast mechanism of interest does not significantly contribute to the overall observed contrast. To overcome these limitations we develop a system that uses a circularly polarized source and linearly polarized detectors to acquire images of transverse electric (TE) and transverse magnetic (TM) reflectivities of the target over the same field of view. Geletin based tissue mimicking phantoms are fabricated with spatially varying water content and modified with a range of surface topologies and surface roughness. TE and TM images are combined to yield self-calibrated clutter-suppressed images. The resulting image indicates that the imaging field clutter affected both polarization channels nearly equally allowing the system to resolve differences in phantom water content. This design is a step toward windowless THz imaging capability critical for clinical translation where patient imaging is dominated by clutter.

  6. THz imaging system with the IJJ emitter

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Manabu; Minami, Hidetoshi; Sawamura, Masashi; Delfanazari, Kaveh; Yamamoto, Takashi; Kashiwagi, Takanari; Kadowaki, Kazuo

    2011-03-01

    The intrinsic Josephson junction (IJJ) emitter consisted of thousands of IJJs uniformly stacked in single crystalline high-Tc superconductor Bi 2 Sr 2 CaCu 2 O8 + δ (Bi-2212) [L. Ozyuzer et al., Science 318, (2007) 1291.] is expected to be a novel source of the continuous terahertz electromagnetic waves (THz-waves). The maximum emission power of tens of microwatts recently obtained with the mesa structure of IJJs seems to be sufficient to make use of the IJJ emitter for some practical applications such as THz imaging. According to the cavity resonance condition, we can control the radiation frequency by changing the geometrical size of the mesa. In this study, we develop the THz imaging system with IJJ emitter. In the presentation, we will show some transparent images of standard specimens obtained by the raster scanning method. Also, we will mention some problems to be solved for the future applications of the IJJ emitter. CREST-JST, WPI-MANA, Strategic Initiative A (University of Tsukuba).

  7. New application of terahertz time-domain spectrometry (THz-TDS) to the phonon-polariton observation on ferroelectric crystals.

    PubMed

    Nishizawa, Seizi; Tsumura, Naoki; Kitahara, Hideaki; Wada Takeda, Mitsuo; Kojima, Seiji

    2002-11-01

    A new instrument for terahertz time-domain spectroscopy (THz-TDS) has been developed. It consists of a composite THz-TDS system and a high throughput (Martin-Puplett) interferometer. The instrument is for use in the qualitative study of optoelectronic constants of materials. The spectral transmission intensity and phase shift related to phonon-polariton dispersion have been measured between 100 cm(-1) and 3 cm(-1) on ferroelectric crystals of industrial interest. These include bismuth titanate Bi4Ti3O12 (a key material for FeRAM), lithium niobate LiNbO3 (a typical nonlinear crystal for parametric oscillator applications) and lithium heptagermanate Li2Ge7O15 for surface elastic wave filter applications. The complex dielectric constants are well reproduced by the phonon-polariton dispersion relation based on the Kurosawa formula. The instrument details and phonon-polariton dispersion results are described. PMID:12452567

  8. Experimental and theoretical study on THz spectrum artesunate

    NASA Astrophysics Data System (ADS)

    Zhang, Ai-Bing; Kong, Ling-Gao; Wang, Shi-Jin; Li, Lei; Zheng, Xiang-Zhi

    2008-10-01

    Artesunate is a very effective drug to treat malaria. They 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 that 0.71, 1.94 and 2.46 THz are significant agreement with the experimental results in 0.87, 1.82 and 2.46THz, 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 the use of the THz-TDS technique can be an effective way to inspect for Chinese medicine.

  9. Nonlinear THz absorption and cyclotron resonance in InSb

    NASA Astrophysics Data System (ADS)

    Heffernan, Kate; Yu, Shukai; Talbayev, Diyar

    The emergence of coherent high-field terahertz (THz) sources in the past decade has allowed the exploration of nonlinear light-matter interaction at THz frequencies. Nonlinear THz response of free electrons in semiconductors has received a great deal of attention. Such nonlinear phenomena as saturable absorption and self-phase modulation have been reported. InSb is a narrow-gap (bandgap 0.17 eV) semiconductor with a very low electron effective mass and high electron mobility. Previous high-field THz work on InSb reported the observation of ultrafast electron cascades via impact ionization. We study the transmission of an intense THz electric field pulse by an InSb wafer at different incident THz amplitudes and 10 K temperature. Contrary to previous reports, we observe an increased transmission at higher THz field. Our observation appears similar to the saturable THz absorption reported in other semiconductors. Along with the increased absorption, we observe a strong modulation of the THz phase at high incident fields, most likely due to the self-phase modulation of the THz pulse. We also study the dependence of the cyclotron resonance on the incident THz field amplitude. The cyclotron resonance exhibits a lower strength and frequency at the higher incident THz field. The work at Tulane was supported by the Louisiana Board of Regents through the Board of Regents Support Fund Contract No. LEQSF(2012-15)-RD-A-23 and through the Pilot Funding for New Research (PFund) Contract No. LEQSF-EPS(2014)-PFUND-378.

  10. THz sources using indium phosphide high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Deal, W. R.

    2013-09-01

    In the last few years, InP HEMT maximum frequency of oscillation (fMAX) has pushed well beyond 1 THz (1000 GHz). This implies that solid state amplification is possible to frequencies approaching 1 THz. In this paper, we provide an overview of power amplifier and power generation work which has been done using InP HEMT technology. In particular, power generation has been demonstrated to 0.67 THz

  11. Extremely low-loss, dispersion flattened porous-core photonic crystal fiber for terahertz regime

    NASA Astrophysics Data System (ADS)

    Islam, Saiful; Islam, Mohammad Rakibul; Faisal, Mohammad; Arefin, Abu Sayeed Muhammad Shamsul; Rahman, Hasan; Sultana, Jakeya; Rana, Sohel

    2016-07-01

    A porous-core octagonal photonic crystal fiber (PC-OPCF) with ultralow effective material loss (EML), high core power fraction, and ultra flattened dispersion is proposed for terahertz (THz) wave propagation. At an operating frequency of 1 THz and core diameter of 345 μm, simulation results display an extremely low EML of 0.047 cm-1, 49.1% power transmission through core air holes, decreased confinement loss with the increase of frequency, and dispersion variation of 0.15 ps/THz/cm. In addition, the proposed PCF can successfully operate in single-mode condition. All the simulations are performed with finite-element modeling package, COMSOL v4.2. The design can be fabricated using a stacking and drilling method. Thus, the proposed fiber has the potential of being an effective transmission medium of broadband THz waves.

  12. THz quantum cascade lasers for standoff molecule detection.

    SciTech Connect

    Chow, Weng Wah; Wanke, Michael Clement; Lerttamrab, Maytee; Waldmueller, Ines

    2007-10-01

    Remote optical detection of molecules, agents, and energetic materials has many applications to national security interests. Currently there is significant interest in determining under what circumstances THz frequency coverage will aid in a complete sensing package. Sources of coherent THz frequency (i.e. 0.1 to 10 THz) electromagnetic radiation with requisite power levels, frequency agility, compactness and reliability represent the single greatest obstacle in establishing a THz technology base, but recent advances in semiconductor-based quantum cascade lasers (QCLs) offer huge improvements towards the ultimate THz source goals. This project advanced the development of narrow-linewidth THz quantum cascade lasers. We developed theoretical tools to guide the improvement of standard THz quantum cascade lasers, the investigation of nonlinear optics employing infrared QCLs, and the exploration of quantum coherence to improve QCL performance. The latter was aimed especially towards achieving high temperature operation. In addition we developed a computer algorithm capable of shifting the frequencies of an existing THz QCL to a different frequency and invented a new type of laser that may enable room temperature THz generation in a electrically driven solid-state source.

  13. Dielectric property of MoS(2) crystal in terahertz and visible regions.

    PubMed

    Yan, Xianding; Zhu, Lipeng; Zhou, Yixuan; E, Yiwen; Wang, Li; Xu, Xinlong

    2015-08-01

    Two-dimensional materials such as MoS2 have attracted much attention in recent years due to their fascinating optoelectronic properties. The dielectric response of MoS2 crystal in both the terahertz (THz) and visible regions is studied in this work. Time-domain THz spectroscopy is employed for the THz property investigation. The real and imaginary parts of the complex dielectric constant of MoS2 crystal are found to follow a Drude model, which is due to the intrinsic carrier absorption. In the visible region, ellipsometry is used to investigate the dielectric response. The general trend of the complex dielectric constant is found to be described with a Lorentz model, while two remarkable dielectric response peaks are observed to be located at 1.85 and 2.03 eV, which has been attributed to the splitting arising from the combined effect of interlayer coupling and spin-orbit coupling. This work can be the research foundation for future optoelectronic applications with MoS2. PMID:26368087

  14. Dielectric property of MoS_2 crystal in terahertz and visible regions

    NASA Astrophysics Data System (ADS)

    Yan, Xianding; Zhu, Lipeng; Zhou, Yixuan; E, Yiwen; Wang, Li; Xu, Xinlong

    2015-08-01

    Two-dimensional materials such as MoS2 have attracted much attention in recent years due to their fascinating optoelectronic properties. Dielectric property of MoS2 is desired for the optoelectronic application. In this paper, terahertz (THz) time-domain spectroscopy and ellipsometry technology are employed to investigate the dielectric response of MoS2 crystal in THz and visible region. The real and imaginary parts of the complex dielectric constant of MoS2 crystal are found to follow a Drude model in THz region, which is due to the intrinsic carrier absorption. In visible region, the general trend of the complex dielectric constant is found to be described with a Lorentz model, while two remarkable peaks are observed at 1.85 and 2.03 eV, which have been attributed to the splitting arising from the combined effect of interlayer coupling and spin-orbit coupling. This work affords the fundamental dielectric data for the future optoelectronic applications with MoS2.

  15. 3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure

    NASA Astrophysics Data System (ADS)

    Vogt, Dominik Walter; Leonhardt, Rainer

    2016-07-01

    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.

  16. THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions.

    PubMed

    Dietz, Roman J B; Gerhard, Marina; Stanze, Dennis; Koch, Martin; Sartorius, Bernd; Schell, Martin

    2011-12-19

    We present first results on photoconductive THz emitters for 1.55µm excitation. The emitters are based on MBE grown In0.53Ga0.47As/In0.52Al0.48As multilayer heterostructures (MLHS) with high carrier mobility. The high mobility is achieved by spatial separation of photoconductive and trapping regions. Photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer (THz TDS). The high carrier mobility and effective absorption significantly increases the optical-to-THz conversion efficiency with THz bandwidth in excess of 3 THz. PMID:22274179

  17. Single-mode porous fiber for low-loss polarization maintaining terahertz transmission

    NASA Astrophysics Data System (ADS)

    Rana, Sohel; Saiful Islam, Md.; Faisal, Mohammad; Roy, Krishna Chandra; Islam, Raonaqul; Kaijage, Shubi F.

    2016-07-01

    We report on a polymer-based porous-core photonic crystal fiber for simultaneous high-birefringent and low-loss propagation of narrowband terahertz (THz) electromagnetic waves. The high birefringence is induced by using rotated elliptical air holes inside the porous-core. The fiber is numerically analyzed with an efficient finite-element method. The simulation results exhibit an extremely high birefringence of ˜0.042 and a very low effective material loss of ˜0.07 cm-1 at an operating frequency of 1 THz. Moreover, we have found an optimal rotation angle (θ)=n30 deg (n is an odd integer). Other modal features of the fiber, such as confinement loss, power fraction, effective area, bending loss, and dispersion, also have been analyzed. We anticipate that the proposed fiber would be suitable in polarization maintaining THz wave guidance applications.

  18. Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide.

    PubMed

    Chu, Zheng; Liu, Jinsong; Wang, Kejia

    2012-05-01

    A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100  kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60  kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed. PMID:22555695

  19. 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.

  20. Measurements of High-Field THz Induced Photocurrents in Semiconductors

    SciTech Connect

    Wiczer, Michael; /Illinois U., Urbana

    2007-11-07

    THz pulses have provided a useful tool for probing, with time resolution, the free carriers in a system. The development of methods to produce intense THz radiation has been slow since spectroscopists and condensed matter physicists first began probing materials with THz pulses. We have developed a method for producing intense ultra-short THz pulses, which have full width half maximum of 300 fs - approximately a half cycle of THz radiation. These intense half cycle pulses (HCPs) allow us to use THz radiation not only as a probe of the free carriers in a system but also as a source of excitation to alter a system in some way. In particular, HPCs perturb free carriers considerably in short time scales but show minimal effect to individual free carriers over long time. By exposing the semiconductor indium antimonide (InSb) to our intense THz HCP radiation, we have observed non-linear optical effects which suggest the generation of new free carriers by below band-gap THz photons. This generation of free carriers appears to be caused by an avalanche multiplication process, which should amplify the number of free carriers already in the system and then induce a current in the timescale of our THz pulse. This amplification on such a short timescale suggests the possibility of an ultra-fast detector of weak above band-gap radiation. We constructed a device which detects these currents by painting an electrode structure on the surface of the semiconductor. The currents induced across the electrodes by this avalanche multiplication process were measured and compared with other measurements of this non-linear optical process. We successfully measured THz induced currents in InSb, which indicate promise towards the development of an ultra-fast detector, and we gain insight into a possible physical explanation of the THz induced free carriers we observe in InSb.

  1. Method for producing high dielectric strength microvalves

    SciTech Connect

    Kirby, Brian J.; Reichmuth, David S.; Shepodd, Timothy J.

    2006-04-04

    A microvalve having a cast-in-place and lithographically shaped mobile, polymer monolith for fluid flow control in microfluidic devices and method of manufacture. The microvalve contains a porous fluorinated polymer monolithic element whose pores are filled with an electrically insulating, high dielectric strength fluid, typically a perfluorinated liquid. This combination provides a microvalve that combines high dielectric strength with extremely low electrical conductivity. These microvalves have been shown to have resistivities of at least 100 G.OMEGA. and are compatible with solvents such as water at a pH between 2.7 and 9.0, 1-1 propanol, acetonitrile, and acetone.

  2. Terahertz dielectric response dependence on protein melting and hydration

    NASA Astrophysics Data System (ADS)

    He, Yunfen; Knab, J. R.; Shah, B.; Markelz, A. G.

    2006-03-01

    Hydration is critical for protein structure stability and flexibility. The hydration dynamics of denatured proteins necessarily plays a significant role in protein folding/unfolding and aggregation. We previously reported the observation of a transition in the THz dielectric response for native state hen egg white lysozyme (HEWL) with hydration. As hydration increases the response slowly increases until at 0.25h (gm water/gm protein) the absorbance and index sharply increase. The frequency range is associated with structural vibrational modes and the hydration level coincides with the filling of the first solvation shell. We present recent THz hydration dependence results as a function of denaturing. The THz absorption coefficient is nearly independent of denaturation while the index of refraction significantly decreases compared to native state and has a stronger frequency dependence with a peak appearing near 0.5 THz. Most significantly the hydration transition at 0.25h is still present for the denatured samples, suggesting the net bound water content is nearly identical to the native state.

  3. Silicon Micromachined Microlens Array for THz Antennas

    NASA Technical Reports Server (NTRS)

    Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, IImran; Gill, John J.; Jung-Kubiak, Cecile D.; Llombart, Nuria

    2013-01-01

    5 5 silicon microlens array was developed using a silicon micromachining technique for a silicon-based THz antenna array. The feature of the silicon micromachining technique enables one to microfabricate an unlimited number of microlens arrays at one time with good uniformity on a silicon wafer. This technique will resolve one of the key issues in building a THz camera, which is to integrate antennas in a detector array. The conventional approach of building single-pixel receivers and stacking them to form a multi-pixel receiver is not suited at THz because a single-pixel receiver already has difficulty fitting into mass, volume, and power budgets, especially in space applications. In this proposed technique, one has controllability on both diameter and curvature of a silicon microlens. First of all, the diameter of microlens depends on how thick photoresist one could coat and pattern. So far, the diameter of a 6- mm photoresist microlens with 400 m in height has been successfully microfabricated. Based on current researchers experiences, a diameter larger than 1-cm photoresist microlens array would be feasible. In order to control the curvature of the microlens, the following process variables could be used: 1. Amount of photoresist: It determines the curvature of the photoresist microlens. Since the photoresist lens is transferred onto the silicon substrate, it will directly control the curvature of the silicon microlens. 2. Etching selectivity between photoresist and silicon: The photoresist microlens is formed by thermal reflow. In order to transfer the exact photoresist curvature onto silicon, there needs to be etching selectivity of 1:1 between silicon and photoresist. However, by varying the etching selectivity, one could control the curvature of the silicon microlens. The figure shows the microfabricated silicon microlens 5 x5 array. The diameter of the microlens located in the center is about 2.5 mm. The measured 3-D profile of the microlens surface has a

  4. Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

    PubMed Central

    Grant, James P.; McCrindle, Iain J.H.; Cumming, David R.S.

    2012-01-01

    Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ λ/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems. PMID:23299442

  5. Direct Visualization of a Polariton Resonator in the THz Regime.

    PubMed

    Stoyanov, Nikolay; Feurer, T; Ward, David; Statz, Eric; Nelson, Keith

    2004-05-31

    We report fabrication of a THz phonon-polariton resonator in a single crystal of LiNbO3 using femtosecond laser machining with high energy pulses. Fundamental and overtone resonator modes are excited selectively and monitored through spatiotemporal imaging. The resonator is integrated into a single solid-state platform that can include THz generation, manipulation, readout and other functionalities. PMID:19475075

  6. Broadband antireflective surface-relief structure for THz optics.

    PubMed

    Brückner, Claudia; Pradarutti, Boris; Stenzel, Olaf; Steinkopf, Ralf; Riehemann, Stefan; Notni, Gunther; Tünnermann, Andreas

    2007-02-01

    The requirements for a broadband antireflective structure in the THz spectral region are derived. Optimized structural parameters for a surface-relief grating adapted to the spectrum of an intended THz pulse are deduced. The effect of a structure fabricated into Topas((R)) by a single-point diamond-turning process is demonstrated. PMID:19532301

  7. Investigation of bovine serum albumin glycation by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Cherkasova, Olga P.; Nazarov, Maxim M.; Shkurinov, Alexander P.

    2016-04-01

    Protein glycation is accelerated under hyperglycemic conditions resulting to loss in the structure and biological functions of proteins. The transmission THz spectroscopy has been used for measuring of bovine serum albumin glycation dynamics. It was found that amplitude of albumin THz absorption depends on type of sugars and incubation time.

  8. A scanned beam THz imaging system for medical applications

    NASA Astrophysics Data System (ADS)

    Taylor, Zachary D.; Li, Wenzao; Suen, Jon; Tewari, Priyamvada; Bennett, David; Bajwa, Neha; Brown, Elliott; Culjat, Martin; Grundfest, Warren; Singh, Rahul

    2011-10-01

    THz medical imaging has been a topic of increased interest recently due largely to improvements in source and detector technology and the identification of suitable applications. One aspect of THz medical imaging research not often adequately addressed is pixel acquisition rate and phenomenology. The majority of active THz imaging systems use translation stages to raster scan a sample beneath a fixed THz beam. While these techniques have produced high resolution images of characterization targets and animal models they do not scale well to human imaging where clinicians are unwilling to place patients on large translation stages. This paper presents a scanned beam THz imaging system that can acquire a 1 cm2 area with 1 mm2 pixels and a per-pixel SNR of 40 dB in less than 5 seconds. The system translates a focused THz beam across a stationary target using a spinning polygonal mirror and HDPE objective lens. The illumination is centered at 525 GHz with ~ 125 GHz of response normalized bandwidth and the component layout is designed to optically co-locate the stationary source and detector ensuring normal incidence across a 50 mm × 50 mm field of view at standoff of 190 mm. Component characterization and images of a test target are presented. These results are some of the first ever reported for a short standoff, high resolution, scanned beam THz imaging system and represent an important step forward for practical integration of THz medical imaging where fast image acquisition times and stationary targets (patients) are requisite.

  9. Recent progress of room temperature THz sources based on nonlinear frequency mixing in quantum cascade lasers

    NASA Astrophysics Data System (ADS)

    Razeghi, M.; Lu, Q. Y.; Bandyopadhyay, N.; Slivken, S.; Bai, Y.

    2014-05-01

    We present the recent development of high performance compact THz sources based on intracavity nonlinear frequency mixing in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the spectral purity, frequency coverage as well as THz power are achieved by systematic optimizing the device's active region, waveguide, phase matching scheme, and chip bonding strategy. Room temperature single-mode operation in a wide THz spectral range of 1-4.6 THz is demonstrated from our Čerenkov phase-matched THz sources with dual-period DFB gratings. High THz power up to 215 μW at 3.5 THz is demonstrated via epi-down mounting of our THz device. The THz power is later scaled up to mW level by increased the mid-IR power and conversion efficiency. The rapid development renders this type of THz sources promising local oscillators for many astronomical and medical applications.

  10. Comparative Study of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2016-04-01

    We analyze a large set of 17 solar radio bursts observed at sub-THz (0.2 and 0.4 THz) in 2012-2014 together with the new solar patrol radio telescopes (45 and 90 GHz), operated at El Leoncito, in the Argentinean Andes, allowing the derivation of complete burst spectra in this unexplored range of frequencies. We discuss the uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission. The burst spectra were completed with microwave bursts data obtained by the Radio Solar Telescope Network - RSTN. The events selection was based on GOES soft X-rays burst reported for classes stronger then C. Nearly 50 percent of the bursts exhibited a frequency increasing sub-THz spectral component. The results suggest that the THz component might be always present, with the minimum turn-over frequencies shifting to higher frequencies for larger energies of the electrons producing the emissions.

  11. Diagnose human tumors by THz near-field imaging

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Wang, Xiaozhou; Zhao, Tian; Yang, Jinwen

    2014-09-01

    Based on a THz pipe-based near-field imaging system, we demonstrated the capability of THz imaging to diagnose human breast and liver cancers. Through THz near-field mapping of the absorption constants of cancer tissues, the acquired images can not only clearly distinguish cancer from normal tissues fast, automatically, and correctly without pathological H&E staining, but also identify the distribution region of cancer, which matches well with the identification with pathological examination. Due to its capability to perform quantitative analysis, our study indicates the potential of the THz pipe-based near-field imaging for future automation on human tumor pathological examinations and for quick definition of the tumor margins during the surgical procedure such as breast-conserving surgery. With the help of THz imaging, we can expect to economize the use of hospital and human resources.

  12. THz transceiver characterization : LDRD project 139363 final report.

    SciTech Connect

    Nordquist, Christopher Daniel; Wanke, Michael Clement; Cich, Michael Joseph; Reno, John Louis; Fuller, Charles T.; Wendt, Joel Robert; Lee, Mark; Grine, Albert D.

    2009-09-01

    LDRD Project 139363 supported experiments to quantify the performance characteristics of monolithically integrated Schottky diode + quantum cascade laser (QCL) heterodyne mixers at terahertz (THz) frequencies. These integrated mixers are the first all-semiconductor THz devices to successfully incorporate a rectifying diode directly into the optical waveguide of a QCL, obviating the conventional optical coupling between a THz local oscillator and rectifier in a heterodyne mixer system. This integrated mixer was shown to function as a true heterodyne receiver of an externally received THz signal, a breakthrough which may lead to more widespread acceptance of this new THz technology paradigm. In addition, questions about QCL mode shifting in response to temperature, bias, and external feedback, and to what extent internal frequency locking can improve stability have been answered under this project.

  13. The mechanism of the dielectric relaxation in water.

    PubMed

    Popov, Ivan; Ishai, Paul Ben; Khamzin, Airat; Feldman, Yuri

    2016-05-18

    Although relating to the same system, the interpretations of the water spectra from Raman and Dielectric spectroscopy present independent pictures of the nature of water. We show that in the overlap region of the two methods it is possible to combine these views into a coherent concept of what drives the dynamic features of water. In this work, we develop the idea that the dielectric relaxation in water is driven by the migration of defects through the H-bond network, leading to a Debye-like peak in the lower frequencies. The deviation from the Debye law in the higher sub-THz frequencies is traced to a global fluctuation of the same H-bond network, clearly evident in the Raman Spectra. By incorporating these two views, a mathematical formalism is presented that can aptly explicate the dielectric spectra of liquid water. PMID:27148837

  14. THz Hot-Electron Photon Counter

    NASA Technical Reports Server (NTRS)

    Karasik, Boris S.; Sergeev, Andrei V.

    2004-01-01

    We present a concept for the hot-electron transition-edge sensor capable of counting THz photons. The main need for such a sensor is a spectroscopy on future space telescopes where a background limited NEP approx. 10(exp -20) W/H(exp 1/2) is expected at around 1 THz. Under these conditions, the rate of photon arrival is very low and any currently imaginable detector with sufficient sensitivity will operate in the photon counting mode. The Hot-Electron Photon Counter based on a submicron-size Ti bridge has a very low heat capacity which provides a high enough energy resolution (approx.140 GHz) at 0.3 K. With the sensor time constant of a few microseconds, the dynamic range would be approx. 30 dB. The sensor couples to radiation via a planar antenna and is read by a SQUID amplifier or by a 1-bit RSFQ ADC. A compact array of the antenna-coupled counters can be fabricated on a silicon wafer without membranes.

  15. Accelerator Sources for THz science: A Review

    SciTech Connect

    Neil, George R.

    2013-07-10

    Free Electron Lasers have been around since 1977 providing not only a test bed for the physics of FELs and electron/photon interactions but as a workhorse of scientific research. More than 30 FELs are presently operating around the world spanning a wavelength range from the millimeter region to the hard x-ray using direct current and rf linear accelerators or storage rings as electron sources. The characteristics that have driven the development of these sources are the desire for high peak and average power, high micropulse energies, wavelength tunability, timing flexibility, and wavelengths that are unavailable from more conventional laser sources. Operation of FELs in the far infrared to terahertz regime poses special challenges which have been and are being addressed at a number of facilities around the world. This paper will review a number of former and existing FELs operating in this regime and discuss future efforts. Broadband collective radiation from relativistic electrons also plays a significant role in the production of FIR/THz radiation and several groups are taking advantage of this source for users. Applications for use of the radiation have evolved from simple imaging to complex pump probe tests of insulator/metal transitions and energy flow in organic molecules. We will discuss the technologies for generating the IR/FIR/THz radiation and cover some of the unique applications of such sources.

  16. 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.

  17. Micromachined TWTs for THz Radiation Sources

    NASA Technical Reports Server (NTRS)

    Booske, John H.; vanderWeide, Daniel W.; Kory, Carol L.; Limbach, S.; Downey, Alan (Technical Monitor)

    2001-01-01

    The Terahertz (THz) region of the electromagnetic spectrum (about 300 - 3000 GHz in frequency or about 0.1 - 1 mm free space wavelength) has enormous potential for high-data-rate communications, spectroscopy, astronomy, space research, medicine, biology, surveillance, remote sensing, industrial process control, etc. It has been characterized as the most scientifically rich, yet under-utilized, region of the electromagnetic spectrum. The most critical roadblock to full exploitation of the THz band is lack of coherent radiation sources that are powerful (0.001 - 1.0 W continuous wave), efficient (> 1%), frequency agile (instantaneously tunable over 1% bandwidths or more), reliable, and comparatively inexpensive. To develop vacuum electron device (VED) radiation sources satisfying these requirements, fabrication and packaging approaches must be heavily considered to minimize costs, in addition to the basic interaction physics and circuit design. To minimize size of the prime power supply, beam voltage must be minimized, preferably 10 kV. Solid state sources satisfy the low voltage requirement, but are many orders of magnitude below power, efficiency, and bandwidth requirements. On the other hand, typical fast-wave VED sources in this regime (e.g., gyrotrons, FELs) tend to be large, expensive, high voltage and very high power devices unsuitable for most of the applications cited above. VEDs based on grating or inter-digital (ID) circuits have been researched and developed. However, achieving forward-wave amplifier operation with instantaneous fractional bandwidths > 1% is problematic for these devices with low-energy (< 15 kV) electron beams. Moreover, the interaction impedance is quite low unless the beam-circuit spacing is kept particularly narrow, often leading to significant beam interception. One solution to satisfy the THz source requirements mentioned above is to develop micromachined VEDs, or "micro-VEDs". Among other benefits, micro-machining technologies

  18. Complex extraordinary dielectric function of Mg-doped lithium niobate crystals at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Kuznetsov, K. A.; Kitaeva, G. Kh.; Kovalev, S. P.; Germansky, S. A.; Buryakov, A. M.; Tuchak, A. N.; Penin, A. N.

    2016-08-01

    We study the dispersion of the extraordinary dielectric function real and imaginary parts in the wide terahertz-frequency range of the lowest polariton branch for bulk LiNbO3 and Mg:LiNbO3 crystals. At frequencies 0.1-2.5 THz, both dispersion parts are measured by means of standard time-domain terahertz spectroscopy, and at higher frequencies up to 5.5 THz, the dielectric function real part is determined using a common scheme of spontaneous parametric down-conversion under near-forward Raman scattering by phonon polaritons. A special approach is applied for measuring of the dielectric function imaginary part at frequencies 1-3 THz, based on the analysis of visibility of three-wave second-order interference under spontaneous parametric down-conversion. The generalized approximate expressions are obtained for complex dielectric function dispersion within the lower polariton branches of LiNbO3 and Mg:LiNbO3. It is shown that the well-known decrease in terahertz-wave absorption of lithium niobate crystals under Mg-doping is caused by changes in the defect structure and reduction of coupling of the terahertz-frequency polaritons with Debye relaxational mode.

  19. Temperature-dependent time-domain THz spectroscopic study of spinel NiCo2O4 thin films

    NASA Astrophysics Data System (ADS)

    Silwal, Punam; Shan, Tianqi; Kim, Daeho; Talbayev, Diyar

    2013-03-01

    The unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order makes the spinel NiCo2O4 an attractive material for various technological applications. Our previous study showed that high quality epitaxial spinel NiCo2O4 films on MgAl2O4 (001) substrate exhibit metallic behavior accompanied by ferrimagnetic order. The electrical properties of these films can be tuned from metallic to insulating by changing the growth temperature. The comprehensive understanding of the microscopic details of carrier transport in these films requires the study of frequency-dependent optical properties. Terahertz time-domain spectroscopy (THz TDS) can determine the frequency dependent complex dielectric constant, refractive index, and optical conductivity. We used THz TDS to measure the optical properties of NiCo2O4 in the 0.2 - 2.7 THz spectral region. The complex conductivities display a Drude-type frequency response. The extrapolated DC conductivity is consistent with our previous work. The temperature- and growth-condition dependent Drude parameters provide further insight in the metal-insulator transition in these materials.

  20. High-birefringence, low-loss porous fiber for single-mode terahertz-wave guidance.

    PubMed

    Chen, Na-na; Liang, Jian; Ren, Li-yong

    2013-07-20

    A new kind of polymer porous fiber with elliptical air-holes is designed for obtaining high birefringence in the terahertz (THz) frequency range in this paper. Using the finite element method, the properties of this kind of fiber are simulated in detail including the single-mode propagation condition, the birefringence, and the loss. Theoretical results indicate that the single-mode THz wave in the frequency range from 0.73 to 1.22 THz can be guided in the fiber; the birefringence can be enhanced by rotating the major axis of the elliptical air-hole and there exists an optimal rotating angle at 30°. At this optimal angle a birefringence as high as 0.0445 can be obtained in a wide frequency range. Low-loss THz guidance can be achieved owing to the effective reduction of the material absorption in such a porous fiber. This research is useful for polarization-maintaining THz-wave guidance. PMID:23872779

  1. Fabrication of MEMS Bimaterial Sensors for Uncooled THz Imaging.

    NASA Astrophysics Data System (ADS)

    Grbovic, Dragoslav; Karunasiri, Gamani

    2009-03-01

    Recently, there has been a significant interest in Terahertz (THz) technology, primarily its applications in concealed object detection and medical imaging. THz region of the spectrum has been underutilized due to lack of compact and efficient sources and detectors. THz imaging has recently been achieved using uncooled, microbolometer infrared (IR) camera and quantum cascade laser (QCL) operating as a THz illuminator. However, bolometer IR cameras are not optimized for the THz band and fabrication of their focal plane arrays (FPAs) is complex due to requred monolithic integration of detectors and readout electronics. Recent developments in bi-material based IR FPAs with optical readout, substantially simplify the fabrication process by decoupling readout from sensing. This presentation describes the design and fabrication of THz-optimized bi-material FPAs, as well as integration of the real-time imaging system. The detection scheme involves detector deformation to minute temperature changes due to absorption of THz radiation. Individual detector deformations are simultaneously probed by shining visible light on entire FPA and reflecting it into a CCD camera. Optical readout eliminates the self-heating effects, enabling longer integration times and, better signal-to-noise ratio.

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

    NASA Astrophysics Data System (ADS)

    Glancy, Paul Michael

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  4. Two dimensional spectroscopy of Liquids in THz-domain: THz analogue of 2D Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Okumura, K.; Tanimura, Y.

    1998-03-01

    After the initial proposal(Y. Tanimura and S. Mukamel, J. Chem. Phys. 99, 9496 (1993)), the two dimensional Raman spectroscopy in the liquid phase has been received a considerable attention. Both experimental and theoretical activity of this field has been quite high. Since we have two controllable delay times, we can obtain more information than the lower-order experiments such as OKE. The new information includes that on heterogeneous distribution in liquids. Recently, it is found that the coupling between the modes in liquids can be investigated by the technique, both experimentally and theoretically(A. Tokmakoff, M.J. Lang, D.S. Larsen, G.R. Fleming, V. Chernyak, and S. Mukamel, Phys. Rev. Lett. (in press))^,(K. Okumura and Y. Tanimura, Chem. Phys. Lett. 278, 175 (1997)) In this talk, we will emphasize that we can perform the THz analogue of the 2D Raman spectroscopy if the THz short-pulse laser becomes available, which may not be in the far future. Theoretically, we can formulate this novel THz spectroscopy on the same footing as the 2D Raman spectroscopy. We will clarify new aspects of this technique comparing with the 2D Raman spectroscopy--- the reason it worth trying the tough experiment. See

  5. Sensitivity increase for coating thickness determination using THz waveguides.

    PubMed

    Theuer, M; Beigang, R; Grischkowsky, D

    2010-05-24

    We report on layer thickness determination down to a thickness of 2.5 microns using terahertz waveguide spectroscopy. Compared to typical single-pass transmission measurements in the time domain, the effective THz pulse delay is considerably increased for a given layer thickness by using the high filling factor of the THz waveguide. This corresponds to a sensitivity increase up to a factor of 50 for the measured delay, allowing the direct measurement of layer thicknesses down to below hundredths of a THz wavelength. PMID:20589006

  6. Residual absorption of high temperature superconductors at THz frequencies

    SciTech Connect

    Keller, P.; Barowski, H.S.; Prenninger, M.; Pechen, E.V.; Renk, K.F.

    1996-12-31

    The authors report on a study of the residual absorption of high temperature superconductors (HTS) at THz frequencies. Using transmission Fabry-Perot interferometry, they determined both, real and imaginary part of the conductivity. They especially studied YBCO thin films. They found that the dynamical conductivity varied strongly from sample to sample. As a main result, they find that the absorptivity increases at frequencies above 1 THz much weaker than quadratically, i.e., the {omega}{sup 2} behavior of the absorptivity at microwave frequencies is not continued in the THz frequency range.

  7. THz-Pulse-Induced Selective Catalytic CO Oxidation on Ru.

    PubMed

    LaRue, Jerry L; Katayama, Tetsuo; Lindenberg, Aaron; Fisher, Alan S; Öström, Henrik; Nilsson, Anders; Ogasawara, Hirohito

    2015-07-17

    We demonstrate the use of intense, quasi-half-cycle THz pulses, with an associated electric field component comparable to intramolecular electric fields, to direct the reaction coordinate of a chemical reaction by stimulating the nuclear motions of the reactants. Using a strong electric field from a THz pulse generated via coherent transition radiation from an ultrashort electron bunch, we present evidence that CO oxidation on Ru(0001) is selectively induced, while not promoting the thermally induced CO desorption process. The reaction is initiated by the motion of the O atoms on the surface driven by the electric field component of the THz pulse, rather than thermal heating of the surface. PMID:26230806

  8. THz-Spectroscopy on High Density Polyethylene with Different Crystallinity

    NASA Astrophysics Data System (ADS)

    Sommer, Stefan; Raidt, Thomas; Fischer, Bernd M.; Katzenberg, Frank; Tiller, Jörg C.; Koch, Martin

    2016-02-01

    The different crystallinity states of high density polyethylene (PE-HD) are investigated using THz time-domain spectroscopy by exploiting the complex permittivity at a frequency range from 0.5 up to 3.5 THz. We found that samples with different crystallinity can be distinguished by comparing the material specific refractive index ( n) or rather the linked complex part of the permittivity (∈ ' '). Correlating the calorimetrically determined degrees of crystallinity with the absolute values of the refractive index and the specific absorption peak at 2.18 THz, respectively, suggests in both cases a linear correlation.

  9. 0.3THz wireless communication systems for space applications

    NASA Astrophysics Data System (ADS)

    Yuan, Weiwen; Wang, Hanqing; Li, Huiyuan; Zhang, Zhuo; Yang, Xiaojie; Shi, Weixun

    2015-11-01

    Contrary to the terahertz (THz) applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. In this study, a 0.3 THz wireless communication systems designed for potential space applications has been set up. It consists of transmitter and detector units based on Schottky diode mixers technology. The system performance is shown including the received signal levels and Eb/N0. For demonstration of THz communications, HD video signals have been transmitted over a distance of 14 m at the data rate of 1.5Gbps.

  10. Development of SIS Mixers for 1 THz

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, J.; Kooi, J.; Chattopadhyay, G.; Bumble, B.; LeDuc, H. G.; Stern, J. A.

    1998-01-01

    SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4 Delta/h). However, the performance degrades rapidly above the gap frequency of niobium (2 Delta/h approx. 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.

  11. Coupleurs fibres - metasurfaces aux frequences THz

    NASA Astrophysics Data System (ADS)

    Girard, Martin

    Metamaterials are a class of arficial materials where the electromagnetic properties can be tailored during the design process. Currently demonstrated properties are varied, ranging from frequency filters to enhancement of quentum effects such as photon spin Hall effect. While these materials are mastered from a theoretical point of view, their fabrication is much more complicated. It is generally accepted that metamaterial elements must be under the effective medium limit (Lambda < lambda/10). Moreover, assembly of a 3D periodical system becomes much more complicated for small elements. For this reason, metamaterials are usually printed in 2D, on a surface, which are called metasurfaces. Generally, these are produced for the THz frequencies (˜ 1012 Hz) or lower to have a large wavelength and thus easy fabrication. Working at THz frequencies also carries additional problems. Absorption in traditional optical mediums is typically large (for exemple, BK7 glass has losses of 20 dB / cm) and powers supplied by THz sources are generally weak ( 100 muW for a THz-TDS standard source). Metasurfaces can thus play an important role by replacing traditional mediums. Moreover, we can use the resonant properties of metamaterials to produce sensors and other devices. Currently, the metasurfaces are used in conjuction with a free-space beam instead of a typical waveguide, which may be problematic when implementing devices. A simple solution to this problem is to use the metamaterial as a standard coupler by placing a waveguide above the metasurface. As stated before, we generally consider metasurfaces as effective mediums, where the permittivity is insensitive to the angle of the incident beam. However, a large amount of publications on this subject shows that this is not respected. This can have a huge impact on properties of a coupler based on such a material. First, modelisation is not a simple 2D mode calculation with a simple expression for permittivity. Second, contra

  12. A Periodic Dielectric Resonator Structure for Terahertz Wave Amplification

    NASA Astrophysics Data System (ADS)

    Fawole, Olutosin; Tabib-Azar, Massood

    2014-03-01

    We present a periodic Slow Wave Structure (SWS) that consists of an arrangement of closely spaced cylindrical resonators with low dielectric constant. In this compact arrangement, coupling between resonators was via evanescent field coupling. This arrangement contrasts earlier infinite high dielectric constant SWSs with widely spaced resonators coupled via magnetic dipole moments. The presented periodic structure is an alternative to the metallic slow wave structures that have been proposed for TWT THz amplifiers. The fabricated low frequency (8 GHz) prototype of our structure consists of an array of cylindrical resonators with dielectric constant 9.2, diameter 12 mm, and height 6.35 mm. Slow waves, which setup a TE01δ-like electric field mode in each resonator, propagate in the structure when then the structure was excited with a microstrip line. We will present detailed simulation and experimental results of this prototype at the conference. Furthermore, efforts to scale the SWS to THz frequency and to interact the SWS with high-energy particle beams will be presented.

  13. Room temperature strong light-matter coupling in 3D THz meta-atoms (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Paulillo, Bruno; Manceau, Jean-Michel; Li, Lianhe; Linfield, Edmund; Colombelli, Raffaele

    2016-04-01

    We demonstrate strong light-matter coupling at room temperature in the terahertz (THz) spectral region using 3D meta-atoms with extremely sub-wavelength volumes. Using an air-bridge fabrication scheme, we have implemented sub-wavelength 3D THz micro-resonators that rely on suspended loop antennas connected to semiconductor-filled patch cavities. We have experimentally shown that they possess the functionalities of lumped LC resonators: their frequency response can be adjusted by independently tuning the inductance associated the antenna element or the capacitance provided by the metal-semiconductor-metal cavity. Moreover, the radiation coupling and efficiency can be engineered acting on the design of the loop antenna, similarly to conventional RF antennas. Here we take advantage of this rich playground in the context of cavity electrodynamics/intersubband polaritonics. In the strong light-matter coupling regime, a cavity and a two-level system exchange energy coherently at a characteristic rate called the vacuum Rabi frequency ΩR which is dominant with respect to all other loss mechanisms involved. The signature, in the frequency domain, is the appearance of a splitting between the bare cavity and material system resonances: the new states are called upper and a lower polariton branches. So far, most experimental demonstrations of strong light-matter interaction between an intersubband transition and a deeply sub-wavelength mode in the THz or mid-infrared ranges rely on wavelength-scale or larger resonators such as photonic crystals, diffractive gratings, dielectric micro-cavities or patch cavities. Lately, planar metamaterials have been used to enhance the light-matter interaction and strongly reduce the interaction volume by engineering the electric and magnetic resonances of the individual subwavelength constituents. In this contribution we provide evidence of strong coupling between a THz intersubband transition and an extremely sub-wavelength mode (≈λ/10

  14. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging.

    PubMed

    Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P; Zolliker, Peter

    2016-01-01

    In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8-14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. PMID:26861341

  15. Comparison of Thermal Detector Arrays for Off-Axis THz Holography and Real-Time THz Imaging

    PubMed Central

    Hack, Erwin; Valzania, Lorenzo; Gäumann, Gregory; Shalaby, Mostafa; Hauri, Christoph P.; Zolliker, Peter

    2016-01-01

    In terahertz (THz) materials science, imaging by scanning prevails when low power THz sources are used. However, the application of array detectors operating with high power THz sources is increasingly reported. We compare the imaging properties of four different array detectors that are able to record THz radiation directly. Two micro-bolometer arrays are designed for infrared imaging in the 8–14 μm wavelength range, but are based on different absorber materials (i) vanadium oxide; (ii) amorphous silicon; (iii) a micro-bolometer array optimized for recording THz radiation based on silicon nitride; and (iv) a pyroelectric array detector for THz beam profile measurements. THz wavelengths of 96.5 μm, 118.8 μm, and 393.6 μm from a powerful far infrared laser were used to assess the technical performance in terms of signal to noise ratio, detector response and detectivity. The usefulness of the detectors for beam profiling and digital holography is assessed. Finally, the potential and limitation for real-time digital holography are discussed. PMID:26861341

  16. Controlling the transverse localization of THz waves in an InSb based disordered waveguide array using temperature.

    PubMed

    Ardakani, Abbas Ghasempour

    2013-06-20

    We propose that the transverse localization in a semiconductor-based disordered waveguide array can be made controllable in the terahertz (THz) regime by changing the ambient temperature. The standard scalar Helmholtz equation is used to describe THz wave propagation through the waveguide array. It is assumed that the waveguides are fabricated from the indium-antimonide (InSb) semiconductor, while the spacing between them is a dielectric. Disorder is introduced in the system by the random refractive index of the spacing medium. Our results demonstrate that the transverse width of the output intensity increases when increasing the temperature. This effect is attributed to the temperature-dependent electric permittivity of the used semiconductor. Then, the waveguides are composed of a dielectric and the spacing between them is filled with the InSb semiconductor. For this case, to introduce disorder, we assumed that the refractive indices of the waveguides are randomized. It is found that the output intensity becomes more localized with increasing temperature. However, further increasing the temperature leads to the delocalization of output intensity. The effect of spacing between adjacent waveguides on the threshold degree of disorder has also been investigated. PMID:23842164

  17. 2D THz and GHz signature for identification of explosive on reflected THz signal

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Varentsova, Svetlana A.; Chen, Jian

    2010-11-01

    The method of THz spectrum dynamics analysis (SDA - Spectral dynamics analysis - method) is applied for the detection and identification of substances by using the signal reflected from sample. It allows to obtain the spectrogram - composite Fourier spectrum dynamics - of the signal and to analyze the dynamics of many spectral lines simultaneously, even if the measurements are made on short time interval (less than 50 ps). The efficiency of the SDA method used for longer time intervals (more than 100 ps) is discussed also. The Fourier-Gabor sliding window method is used for obtaining the spectrogram. We consider the examples of finding the pure RDX and harmless materials (L-Tartaric Acid, Sucrose, PTFE) or their mixture in pellets by using a THz pulse reflected from them. A THz pulse with a few cycles falls on the sample and reflects from it. The receiver makes the discrete measurements of electric field strength of signal reflected from the sample. To restore the signal to the required accuracy the SVD - Single Value Decomposition - technique is used. Our investigations show that the spectrograms and dynamics of several spectral lines of the THz pulse reflected differ from the corresponding spectrograms and dynamics of spectral lines for the reference pulse under certain conditions and hence it is possible to detect the presence of the material in the sample of interest. The comparison of the Fourier spectrum of the substance with the corresponding spectrum calculated on the base of using an autocorrelation function for obtaining the spectrum shows that the AC-spectrum gives us essential less information about substance. From our consideration follows that in some cases the analysis of reflected signal on the short time interval (less than 50 ps) is insufficient for the reliable identification. It is necessary to analyze the response on the long time interval (about 300 - 400 ps). The analysis of spectrogram and spectral lines dynamics on the long time intervals

  18. FLUTE: A versatile linac-based THz source

    NASA Astrophysics Data System (ADS)

    Nasse, M. J.; Schuh, M.; Naknaimueang, S.; Schwarz, M.; Plech, A.; Mathis, Y.-L.; Rossmanith, R.; Wesolowski, P.; Huttel, E.; Schmelling, M.; Müller, A.-S.

    2013-02-01

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (˜1 ps) THz pulses (up to ˜4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (˜100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

  19. Top Gated Graphene PN junctions for THz detection

    NASA Astrophysics Data System (ADS)

    Boyd, Anthony; Nath, Anindya; Jadidi, Mehdi; Suess, Ryan; Sushkov, Andrei; Jenkins, Gregory; Drew, H. Dennis; Murphy, Thomas; Myers-Ward, Rachael; Daniels, Kevin; Gaskill, D. Kurt

    2015-03-01

    The search for terahertz (THz) detectors based on graphene is encouraged by the fact that the ballistic regime in graphene occurs at room temperature over a distance of few hundred nanometers. The naturally occurring 2-DEG carriers have extremely high intrinsic mobility at room temperature. Despite being only one atomic layer thick, graphene still adsorbs several percent of incoming THz radiation well. THz detectors are fabricated on epitaxial graphene using an improved lithography process using lift off resist to achieve low contact resistance. The devices are field effect transistors constructed with a thin asymmetric nichrome (NiCr) top gate that facilitates tuning the photovoltaic response. The thin NiCr gate possesses a sheet resistance of 390 ohms which enables better matching of free space and does not block the incoming Thz radiation. This work was sponsored by the U.S. Office of Naval Research (Award Number N000141310865)

  20. THz-wave parametric sources and imaging applications

    NASA Astrophysics Data System (ADS)

    Kawase, Kodo

    2004-12-01

    We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We have also developed a novel basic technology for THz imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral trasillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

  1. Emission of coherent THz-radiation from superconductors.

    SciTech Connect

    Ozyuzer, L.; Koshelev, A. E.; Kurter, C.; Gopalsami, N.; Li, Q.; Tachiki, M.; Kadowaki, K.; Yamamoto, T.; Minami, H.; Yamaguchi, H.; Tachiki, T.; Gray, K. E.; Kwok, W.- K.; Welp, U.; Izmir Inst. Tech.; Illinois Inst. Tech.; Univ. Tokyo; Univ. Tsukuba; Nat. Defence Academy

    2007-11-23

    Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to 50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

  2. SUB-THz RADIATION MECHANISMS IN SOLAR FLARES

    SciTech Connect

    Fleishman, Gregory D.; Kontar, Eduard P.

    2010-02-01

    Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

  3. 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.

  4. FLUTE: A versatile linac-based THz source

    SciTech Connect

    Nasse, M. J.; Schuh, M.; Schwarz, M.; Naknaimueang, S.; Mathis, Y.-L.; Rossmanith, R.; Wesolowski, P.; Huttel, E.; Plech, A.; Schmelling, M.; Mueller, A.-S.

    2013-02-15

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short ({approx}1 ps) THz pulses (up to {approx}4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range ({approx}100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

  5. FLUTE: a versatile linac-based THz source.

    PubMed

    Nasse, M J; Schuh, M; Naknaimueang, S; Schwarz, M; Plech, A; Mathis, Y-L; Rossmanith, R; Wesolowski, P; Huttel, E; Schmelling, M; Müller, A-S

    2013-02-01

    A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (~1 ps) THz pulses (up to ~4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (~100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments. PMID:23464187

  6. Calculations for Tera-Hertz (THZ) Radiation Sources

    SciTech Connect

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    We explore possibilities for THz sources from 0.3-30 THz. While still inaccessible, this broad gap is even wider for advanced acceleration schemes extending from X or, at most, W band RF at the low end up to CO{sub 2} lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that lower frequency, superconducting RF is currently preferred. Similarly, the validity of modeling techniques varies greatly over this range of frequencies but generally mandates coupling Maxwell's equations to the appropriate device transport physics for which there are many options. Here we study radiation from undulatory-shaped transmission lines using finite-difference, time-domain (FDTD) simulations. Also, we present Monte-Carlo techniques for pulse generation. Examples of THz sources demonstrating coherence are shown with the goal of optimizing on-chip THz radiators for applications that may lead to accelerators.

  7. In vitro osteosarcoma biosensing using THz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Ferguson, Bradley S.; Liu, Haibo; Hay, Shelley; Findlay, David; Zhang, Xi-Cheng; Abbott, Derek

    2004-03-01

    Terahertz time domain spectroscopy (THz-TDS) has a wide range of applications from semiconductor diagnostics to biosensing. Recent attention has focused on bio-applications and several groups have noted the ability of THz-TDS to differentiate basal cell carcinoma tissue from healthy dermal tissue ex vivo. The contrast mechanism is unclear but has been attributed to increased interstitial water in cancerous tissue. In this work we investigate the THz response of human osteosarcoma cells and normal human bone cells grown in culture to isolate the cells' responses from other effects. A classification algorithms based on a frequency selection by genetic algorithm is used to attempt to differentiate between the cell types based on the THz spectra. Encouraging preliminary results have been obtained.

  8. 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.

  9. Multiple THz pulse generation with variable energy ratio and delay

    NASA Astrophysics Data System (ADS)

    Ungureanu, R. G.; Grigore, O. V.; Dinca, M. P.; Cojocaru, G. V.; Ursescu, D.; Dascalu, T.

    2015-04-01

    Two methods for multiple high energetic THz pulse generation by two-color filamentation in air with controllable energy ratio and delay ranging from one to hundreds of ps were investigated. In the first method the laser pulse is split into two inside the optical stretcher of a CPA laser system, the resulting consecutive filaments occur in the same region and allows the study of the influence of the first plasma filament on the THz emission of the delayed filament. Based on a polarization sensitive thin film beam splitter placed in front of a 45° mirror, the second method produces multiple parallel consecutive filaments. Above a certain total pump level the THz energy delivered by multiple pulses exceeds the value given by a single filament for the same pump energy, thereby overcoming the THz emission saturation of the single filament.

  10. 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.